GERNSBACK SPECIALTY SERIES - americanradiohistory.com · Farmingdale, NY 11735 1-516-293-3000 Fax:...

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CIRCLE 126 ON FREE INFORMATION CARD

bpular ELECTRONICSFlanks

8 HOBBYISTSHANDBOOK,.

A GERNSBACK

PUBLICATION

Fall 1995

CONTENTS19 The "g" Machine -A portable, digital readout,acceleration measurement gadget that measures the powerimpulse your car can deliver!

24 25 -MHz Frequency Counter - An inexpensive wayto place a valuable testing tool on your workbench.

30 FM Transmitter -As large as the law allows, thishome-brew transmitter is ideal for budding disc jockeys.

35 Novel Nightlight - The glow of a vacuum tubeagainst a mirrored corner reflector brings nostalgia to thehome.

37 WWV Receiver - Pull in the government time stationand get bonuses like weather, standard frequencies, andother scientific information.

41 Add a Switch to Your Serial Port - Enable ordisable serial ports with a flip of a switch.

42 Headphone Amplifier for Your Guitar - Prepare fora rock -n -roll career or just practice without disturbing anyone.

46 Build a Solar -Powered Model Airplane -A toy togaze at that moves and never needs batteries.

49 Vacuum -Tube Audio Amplifier - Hear thedifference tubes make in sound without putting a dent in yourwallet.

52 Build the PK Tester - Discover and develop yourlatent mind -over -matter abilities.

(Continued on next page)

As a service to readers, Popular Electronics Electronics Hobbyists Handbook publishes available plans or information re-lating to newsworthy products, techniques and scientific and technological developments. Because of possible variances in thequality and condition of materials and workmanship used by readers, we disclaim any responsibility for the sale and proper func-tioning of reader -built projects based upon or from plans or information published in this magazine.

Since some of the equipment and circuitry described in Popular Electronics Fall 1995 Electronics Hobbyists Handbook mayrelate to or be covered by U.S. patents, we disclaim any liability for the infringement of such patents by the making, using, orselling of any such equipment or circuitry, and suggest that anyone interested in such projects consult a patent attorney.

Popular Electronics Electronics Hobbyists Handbook is published semi-annually by Gernsback Publications Inc. All rightsreserved. Printed in U.S.A. Single copy price $3.95. Canadian G.S.T. Registration No. 125166280. Canada $4.50©Gernsback Publications Inc., 1994, 1995.

Surface -Mount Technology(See page 86)

,,kz,JILIgiotato

Auto Stethoscope(See page 63)

WWV Receiver(See page 37)

0

Sprinkler Guardian(See page 55)

I

CONTENTS1111081111111SVS'

INIANIDBOOKLarry Steckler

ENE. CET

Editor -in -Chief and Publisher

Julian S. MartinEditor

POPULAR ELECTRONICSEDITORIAL DEPARTMENT

Carl LaronEditor

Dan KaragiannisA "Oriare Editor

Teri ScadutoAssociate Editor

Evelyn RoseEditorial Assistant

Marc SpiwakEditorial Associate

PRODUCTION DEPARTMENTRuby M. Yee

Production Director

Karen S. Brownpmd,,tion Moorage,'

Kathy CampbellPieduction Assistant

ART DEPARTMENTAndre Duzant

Art Director

Russell C. TruelsonIllustrator

Jacqueline P. CheeseboroCirculation Director

Michele TorrilloP E Bookstore

BUSINESS AND EDITORIAL OFFICESGernsback Publications, Inc.

500-B Bi-County Blvd.Farmingdale, NY 11735

1-516-293-3000Fax: 1-516-293-3115

President: Larry Steckler

Advertising Sales Offices listed on page 112.

Cover byLoewy DesignOak Ridge, TN

Cover Illustration byJonathan Baron

Composition byMates Graphics

Clifton, NJ

(Continued)

55 Sprinkler Guardian - Automatically shut off yourprogrammed garden sprinklers at the first drop of rain andsave money.

58 Security in the Information Age - All about codesin straight talk.

63 Auto Stethoscope - Go high-tech to discover thosetroublesome squeaks in the family chariot.

66 The "LED-Tric" Christmas Tree - Light up yourholidays with this unusual and festive conversation piece.

69 Telephone Line Simulator - You can set up yourown mini telephone system, or test telephone equipment.

78 Frequency Response Tester - You'll never againhave to guess about the frequency response of an audiodevice.

84 Variometer Radio -A new version of a classicdesign.

86 Getting Started in Surface Mount Technology -Develop the skills required to make surface -mountcomponents while building two useful projects.

90 8 -Channel A/D Converter - Let your computerinterface with the physical world.

97 Making Square Waves at Home -A cookbook ofcircuits that'll knock you off your block!

And Other Things To Read and Do

4 New Products

12 Electronics Library

16 Free Information Card

111 Classified Advertising

111 Advertising Index

112 Advertising Sales Office

2

TECHNOLOGY UPDATE

How to stay coolwithout turning downthe air conditioning...New device redirects air conditioning to roomsthat need it most so you can be more comfortablewithout inflating your electric bill.

by Charles Anton

Are you constantly adjusting the ther-mostat every time you're uncomfort-able? Turning it down in the summer,

up in the winter? Do you manually open orclose vents just so air will be redirected torooms that are too hot or too cold? Mosthomeowners who have central air condition-ing and heating systems have the same re-curring problem. Highutility bills are the unfor-tunate result of manuallyadjusting your home'svents and thermostat.Forced air problem. Ifyou have rooms that nev-er seem cool enough in thesummer no matter howthe thermostat is set, theproblem isn't your air con-ditioner, it's your registersand ducts.

Some rooms have poorairflow because of bends inthe ductwork or their dis-tance from the blower.So if your home has cen-tral cooling and heating,you'll probably have atleast one room that is al-ways too hot or too cold.The better solution.Now there's the EqualizerEQ2 by Suncourt. Its built-in fan is designed to pullextra air out of poor -per-forming registers, helpingequalize the temperature

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in your home. Every time your cooling or heat-ing system operates, it will pull twice as muchair through the duct in half the time. This gives80% more of the air you have already paidfor-air that usually gets lost in the ductwork.

Air doesn't warm up because it spends lesstime getting to the vent. The Equalizer EQ2even continues to run after your system shuts

off, making sure all theconditioned air is out ofthe air duct.

Air from the EqualizerEQ2 is not diverted fromother vents in your home.It is made up of air fromthe air conditioner instead.The effect on the other reg-isters of your home is neg-ligible. It installs in justseconds-simply place iton top of your existingfloor or wall vent and plugit into a standard outlet.Intelligent thermostat.This sophisticated elec-tronic thermostat consistsof dual solid-state sensors.When your cooling systemstarts, it measures the tem-perature of the register airand the room air and thencalculates the temperaturedifferential. It allows youto adjust the thermostat forthe automatic on/off func-tion best suited for theregister air temperature.

The perfectproblem cooli

solution forng and heating

Uneven temperatures. You

have rooms that are always toohot or too cold.

Saving money. You want tokeep the thermostat turned upwithout sacrificing comfort.

Apartment. You live in anapartment and want to increasefuel efficiency without making apermanent investment.

II Convenience. You don't wantto bother with opening or closingoff vents in the problem rooms.

Your ventsare wastingyour money.The EqualizerEQ2 can cutyour fuel billdown to size

HOW DOES THE EQUALIZER EQ' SAVE MONEY?When a room is uncom-fortable, you adjust

the thermostat. But for everydegree you turn it up or downyou increase your fuel billby at least 3%.Raising the ther-mostat just 4°

can add as much as $1.25 toyour daily energy costs.Turning the thermostat downis even more costly since airconditioners are notoriouslyinefficient. Even then, yourhome may not be comfortable.

A thermostat in a draftyhallway may stop

running even though an up-stairs room is still boiling.The Equalizer EQ2 maximizesyour system by pulling

80% more air from yourduct into the problem

room-in halfof the time.

When set on continuous running, it ventilatesstuffy rooms. The fan is designed to increaseairflow in several directions at once.Costs next to nothing. The Equalizer EQ2has no cooling or heating elements, and it turnson and off automatically with your central sys-tem. It cost less than two cents a day to run.Compare this to the $1.25-$1.75 a day it coststo constantly adjust the thermostat by four de-grees to make your rooms comfortable.Try it risk -free. At Comtrad, we back all ourproducts with a risk -free hometrial. If you're not com-pletely satisfied, returnthe Suncourt EqualizerEQ2 within 30 days fora full "No QuestionsAsked" refund. Italso comes with a fullone-year manufacturer''.limited warranty. Mostorders are processed

The Equalizer Ea'swithin 72 hours and microprocessorshipped UPS.

Money -saving offer. For a limited time,we're offering this breakthrough directly toyou. For greatest efficiency, place severalEqualizer EQ2s throughout your home. Toenable you to do this, we're offering youthis special offer. The first two EqualizerEQ2s you order are $49 each, but when youorder a third Equalizer EQ2 or more, theprice is reduced to just $24.50 each!

Your third Equalizer EQ2 is just $24.50 $4 S&H

Suncourt Equalizer EQ2 $49 $4 S&H

Please mention promotional code 265 -PL -6527.

For fastest service call toll -free 24 hours a day

800-992-2966= MOTo order by mail, send check or money order for the totalamount including S&H (VA residents add 4.5% sales tax.)Or charge it to your credit card by enclosing your accountnumber and expiration date.

INDUSTRIES2820 Waterford Lake Drive, Suite 106

Midlothian, Virginia 23113

3

Full -SpectrumDesktopScanner

4

NEW PRODUCTSACIs Trident TR4500 pulls inbroadcast frequencies from theshortwave bands through themicrowave -range public-servicebands-from below AM broad-cast to 1.300 GHz-and can becontrolled via a personal com-puter. Users can tune in topractically every type of voicebroadcast from around theworld, including the broadcast,world -band, and civil and mili-tary aviation frequencies foundin AM mode; police, fire, andemergency services in NarrowFM; radio and TV -audio broad-casts in Wide FM; and evensingle sideband for transo-ceanic aircraft and shipcommunications.

Desired frequencies can beselected directly using the key-pad, or the unit can be set tosearch through all active chan-nels. The user can store anyinteresting frequencies in any of2016 permanent memory loca-tions. Up to 16 different searchranges can be set into memory.Tuning increments can be se-lected in steps as low as 5000cycles. The TR4500 will scanthrough memorized frequenciesat up to 36 channels per sec-ond, and will lock on active callsto receive the broadcast. Theuser can listen through the built-in speaker or use the suppliedheadphone.

With the TR4500 connectedto a PC's serial interface, thecomputer can be used to setthe search ranges. The comput-er allows various frequencies to

be loaded and saved, and ac-tive frequencies to be stored.And, when used with a comput-er, the TR4500 effectivelybecomes a storage spectrumanalyzer. An MS-DOS "comm"program is included.

The desktop scanner mea-sures just 21/4 x 5% x 61/2 inches.It comes with a 12 -volt DC cord,an AC adaptor, an earphone, aflexible antenna, software, andoperating instructions that in-clude a listing of allocated usesfor all frequencies covered bythe unit.

The TR4500 desktop scannerwith computer interface has asuggested retail price of $849;the street price is expected tobe under $500. For more infor-mation, contact ACI;Tel. 1-800-445-7717 or317-849-2570;Fax: 1-800-448-1084 or317-849-8794.

CIRCLE 37 ON FREEINFORMATION CARD

MULTIMEDIASPEAKERS

Although many of today's per-sonal computers are equippedwith a CD-ROM drive andsound card, the built-in speak-ers are usually inadequate. TheMedia 3 and Media 4 speakersfrom JBL Consumer Productsaddress the needs of PC usersseeking to enhance their multi-media experiences in learning,entertainment, and game -play-ing.

The Media 3 powered speak-er incorporates a 4 -inch wooferand a 1.5 -inch tweeter with aseven -watt -per -channel hi-fi am-plifier. Subwoofer output allowsthe system to be further up-graded, dual inputsaccommodate a second audiosource, and a headphone jackprovides private listening. TheMedia 3 speakers also featureseparate bass and treble con-trols and automatic poweron/off.

The Media 4 incorporates afive -inch woofer, a one -inchtweeter, and a 10 -watt -per -chan-

nel hi-fi amplifier. Key featuresinclude switchable subwooferoutput or headphone output,polyolefin cabinet material todampen internal resonances,automatic turn onioff, and anacoustically efficient design forloud sound levels.

The Media 3 (pictured here)and Media 4 multimedia speak-ers have suggested retail pricesof 5199/pair and $299 pair, re-spectively. For more information,contact JBL Consumer Prod-ucts, Multimedia Division, 80Crossways Park West,Woodbury, NY 11797;Tel. 516-496-3400.


FIELDPACK WITH"STICK" DMMThe HS24K11 Fieldpack fromFieldpiece Instruments consistsof a leather holster that holds aheavy-duty HS24 "stick" digitalmultimeter along with a 300 -amp current clamp head, deluxetest leads, two short and twolong probe tips, and one al-ligator ground clip. All theaccessories are modular, usingstandard banana plugs andjacks for connections.

Specifically designed for field -service use, the leather holsterholds the meter and test leads

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Line TrackerMV -963

$52.95(Infra -red Sensor)The robot follows

a black lineon white paper

Preassembled PCB

Dual -Display,--LCR Meter-LED.

w/ Stet Functions4...,!!..... '''' B+K Model 878,....

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_,,,..... $239.95f Auto/manual range

Many features!I') with Q factor'fir High Accuracy

Electronic Tool Kit Model TK-1000A professional organizer tool kit at affordable prices. Nostudent should be without this unique tool kit that holds allthe tools you need.Including: $39.95Diagonal CutterLong Nose Pliers6" Wire StripperSolder 60/406" Screwdriver6" Phillips Driver

Robotic ArmY-01

Stereo Cassefte PlayerKit

Safety Goggles 'IC Puller

- ' 3pc Nut Drivers$49.95(Wired Control)

Movement grabs& releases,

lifts & lowers,from to

tt ModelTR-18K

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Included

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DigitalMultimeter

EDM-83B$175.00

Almost everyfeature available

Bargain ofthe decade

Function GeneratorGF-8026

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Int/ExtOperation

Sine, Square, Triangle, PulseamP.1 to 2MHz, Freq Ctr

ElencoLCR + DMM

LCM-1960

$7912 Functions

Freq to 4MHzInductance

DigitalCapacitance

MeterCM -1555

$49.95Measures capacitors

DigitalLCR Meter

4.- 0 LCR-680$79.953-1/2 Digit

LCD DisplayInductance

Capacitance Ifrom .1pf to 20,000µf ®

luH to 20MQ

3-3/4 Digit Multimeter Digital'Multimeter Kit

Frequency CounterF-1225

-Fluke Multimeters

(All Models Available Call)ScoDemeters 70 Series

.:, BK-390$139.00 w/ Training Course

M -2665K

$49.95:Ade Full function 34 ranges

Ideal school projectM-2661 Assembled) $55.00

=,,-___

Input impedance10:1 input

$225.008 Digit LED display

Wide mess rangeHigh sensitivity

Data hold function'IMO or 500

attenuation function

0.1% DCV accyAnalog bar graph

Auto/manual rangingCapacitance meas

Temperature probe

Model 97 Model 7011 $89.9510 Series Model 7311597.50Model 10 $62.95 Model 77118149Model 12 $84.95 Model 7911 $17520 Series 80 SeriesModel 2911 $175 Model 87 $289

Triple PowerSupplyXP -620

By ElencoWM" $75.003 fully regulated supplies, 1.5-15V l(

1A, -1.5 to -15V @ 1A or 3-30V © 1A& 5V @ 3A Kit XP -620K $49.95

Quad PowerSupply

.., XP -581By Elenco

$79.95Four supplies in one unit, 2-20V © 2.5A,5V © 3A, -5V © .5A and 12V © 1A. All

regulated and short protected

High Current DCPower Supply

as rea BK-1686 $169.953 to 14 VDC Output

12A @ 13.8VFor servicing high

power car stereos,camcorders, ham radios, etc.Connect 2 or more in parallel

Wide Band-'1,---

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SignalGenerators

SG -9000

$124.95RF Frequency 100K-450MHz

AM modulation of 1KHz VariableSG -9500 150MHz $239.00

Telephone KitPT -223K N

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AvailableAssembledPT -223$15.95

Function GeneratorBlox

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Learn to Build & ProgramComputers with this Kit

Digital/Analog TrainerComplete Mini -Lab For Building,

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XK-525$159.95

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Kit $28.95Sine, Triangle,angle, Square Wave . f -- i,

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AM/FM TransistorRadio Kit

with Training CourseModel AM/FM 108

S29.9514 Transistor, 5 DiodesEasy to build because

schematic is printed on the PCBMakes a great school project

Model AM -660 AM Only $17.95

TelephoneAnalyzer

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..si...m. MM -8000MOOD By Elenco

$129.00From scratch you build a complete system.Our Micro -Master trainer teaches you towrite into RAMs, ROMs and run a 8085microprocessor, which uses similarmachine language as IBM PC.

Designed for school projects, with 5 built-inpower supplies. Includes a function generatorwith continuously variable, sine, triangular,square wave forms. All power supplies areregulated and protected against shorts.

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6

NEW PRODUCTS

on the inside and has loops forthe current clamp head andlong probe tips on the outside.A belt loop on the back allowseasy carrying.

The HS24 meter offers the 12most popular ranges for fieldservice and will withstandsteady-state voltages up to1000 -volts DC and 750 -voltsAC. It measures volts, ohms,continuity, capacitance, and ACcurrent (with the included cur-rent clamp). A HOLD buttonfreezes the display to makeone -handed testing easy. ItsValox plastic case withstandsdrops up to 10 feet, "0" -ringseals protect against con-taminants, and metal -oxidevaristors (MOVs) protect againstvoltage transients. An audiblebeeper and a blinking red LEDwarn of voltages over 28 volts,even if the meter is set to thewrong range or function.

The heavy-duty HS24K11Fieldpack costs $159. For moreinformation, contact FieldpieceInstruments, 231 East ImperialHighway, Suite 250, Fullerton,CA 92635; Tel. 714-992-1239;Fax: 714-992-6541.


PCMCIA MODEM

The MT2834LT PCMCIAmodem features a patent -pend-ing "CoolJax" duplex phoneconnector, eliminating the needfor messy cables. The modemis compliant with the recentlyadopted ITU standard for 28.8 -kilobyte per second, V.34 mod-ems, and also supports all lower

speed standards. It is designedfor use in standard Type IIPCMCIA slots, and comes withMultiExpress fax and data com-munications software forWindows. The MT2834LT usesindustry -standard "AT" com-mands for modem configurationand dialing, and includes a re-

mote configuration feature thatallows the user to remotelychange parameters and run di-agnostics for troubleshooting,technical support, and systemadministration purposes.

The MT283LT PCMCIAmodem costs $399. For addi-tional information, contact Multi -Tech Systems, Inc., Tel.800-328-9717 or 612-785-3500.


PERSONAL POCKETDIGITAL MULTIMETERS

The Model 380933 3200 -count,autoranging, digital multimeterfrom Extech Instruments offershigh -resolution, bar -graph dis-play, function indicators, datahold, diode test, and an audiblecontinuity checker. It measuresDC voltage from 300 mV to 450volts, AC voltage from 3 to 450volts, and resistance from 300ohms to 30 megohms. The dig-ital multimeter weighs just 3.4ounces and measures4.8 x 3 x 0.8 inches.

The Model 380933 pocket -sized digital multimeter, com-plete with a wallet -style carryingcase, test leads, 1.5 -volt bat-teries, and a user's manual,costs $39. A 2000 -count, man-ual -ranging version (Model380929), which features alarger display, 200-mA range,continuity indication, data hold,and diode test, costs $25. Forfurther information, contact Ex -tech Instruments, 335 Bear HillRoad, Waltham, MA02154-1020; Tel. 617-7440;Fax: 617-890-7864.


DIGITAL STILL CAMERA

Casios QV -10 handheld digitalstill camera allows you to viewimages as they are shot, thanksto a high -resolution, active -ma.trix, 1.8 -inch color LCD screen.

The images can then be trans-ferred to a personal computerby using an optional transferpackage, or to a TV or VCRusing a video cable.

The camera's semiconductormemory can hold up to 96 colorstill images that can be addedor deleted at any time. Thefixed -focal -length lens with mac-ro positioning allows point -and -shoot picture taking. The cam-era also features a high-speed(1 8 to 1.4000 -second) shutter,1/5 -inch CCD element, and ap-erture -priority automaticexposure system.

The OV-10 LCD digital cam-era has a suggested retail priceof $700. For further information,contact Casio, Inc., 570 Mt.Pleasant Avenue, Dover, NJ07801; Tel. 201-361-5400.


EXTERNAL FAX/MODEM

The Bullet 100E 28.8 -kilobyte -per -second (Kbps) externalmodem with integrP1,x1 fax from

E -Tech complies with all thespecifications of the recentlyadopted ITU V.34 standard. It isalso V.23 -compatible for Euro-pean and other videotext users.A 16 -bit CPU, along with anenhanced controller code, max-imizes data throughput. Themodem can operate at all con-ventional line speeds from 28.8Kbps to 300 bps. The integratedfax operates at 14.4 Kbps andcan communicate with Group 3send and receive fax machines.Free fax software for DOS and

Windows is included; Mac soft-ware is available as an option.

The Bullet's sleek, attractivedesign resembles a CD-ROMplayer. Its LCD panel displaysline conditions and throughputspeeds so that the connectioncan be easily checked. TheLCD and Smartkeys make iteasy for users to set andchange their modem configura-tions. Other high -end featuresinclude lease -lined operationwith auto -dial backup, caller ID,distinctive ring, built-in Flash -ROM for easy upgrades, localand remote configuration, andpassword and callback security.

The Bullet 100E external fax/modem costs $499. For addi-tional information, contact E -Tech Research Inc., 1800 WyattDrive, Suite 2, Santa Clara, CA95054; Tel. 1-800-EBULLET;Fax: 408-988-8109.


KEYBOARD -ENHANCEDPERSONAL DIGITALASSISTANT

Sharp's Zaurus ZR-5000 key-board -enhanced personaldigital assistant (K-PDA) is ahandheld personal communica-tions tool that offers speedyaccess to information, powerfulintegrated software, and monthsof battery life. Unlike PDA's thatrely primarily on handwritingrecognition for inputting infor-mation, Zaurus offers both theconvenience of the pen for note -taking, drawing, and accessinginformation, and the productivityof a keyboard for text -intensiveapplications. The K-PDA hasone megabyte of internal mem-ory, 750K of which is availablefor user data and add-on soft-ware programs.

Aimed primarily at mobile pro-fessionals, Zaurus can sendand receive e-mail, send faxes,

AMAZING Electronic andScientific Products

MysteryLevitatingDevice!Remember War of the World? Objects float in air and move tothe touch. Defies gravity, amazing gift, conversation piece, magic

trick or great science project.ANTI K Easy to Assemble Kit I Plans ____-_. $19.50

Laser Ray Gun

DANGERIMRE LASER RADIATION

AVOID EYE OR SPUN EXPOSURE

TO DIRECT OR SCATTER RADIATORCUSS HLA9ERPPCOUCT

Advanced project produces a burst of light energy capable ofburning holes in most matenals. Hand-held device uses

rechargeable batteries. 500 joules of hash energy excite either a

neodynium glass, yag or other suitable 3' laser rod. This is adangerous CLASS IV project (individual partsrassembliesavailable). LAGUN1 Plans $20.00LAGUNIK Kit / Plans Price on Request

ExtendedPlayTelephone Recording-S-ystemREADY TO USE! Automatically controls and records on our X-4extended play recorder, taping both sides of a telephoneconversation. Intended for order entry verification. Check yourlocal laws as some states may require an alerting beeper.TAP2OX Ready to Use System $129.50

Shocker Force Field/A ! Vehicle Electrifier

Neat Gthe device allows you to make hand and shock balls, shockwands and electrify object, charge capacitors. Great paybackfor those wise guys who have wronged you!

SHK1KM Easy to Assemble Electronic Kit $24.50

ElectricCharge

Gun

All NewTechnology!

Stunslimmobilizes attackers up to 15 feet away''Legal in most state (not in NY. NJ, MA, WI) More knock -down

power than most handguns No permanent injury ID coded Free 80KV stun gun with every purchase.

ECGI Data Packet, Creditable toward purcase ....... $10.00ECOIO Charge Gun, Ready to Use, w/Free 80KV Gun $249.50

Homing / Tracking TransmitterBeeper device, 3 mile range.HODI Plans ............410.00 HOD1K Klt / Plans $49.50

Listen Through Walls, FloorsHighly sensitive stethoscope mike.STETHI Plans 48.00 STETH1K KIVPIans $44.50

Infinity Transmitter ++

Telephone Line Grabber/Room Monitor / ControllerAil New - The Ultimate in Home /Office Security & Safety!

Simple to use! Call your home or office, push a secret tone

on your telephone keypad to access: On premises soundsand voices Ongoing phone conversation wibreak-in capability

Up to 10 external electrical functions, lights, TV, alarms, coffee

pots, heater, etc. CAUTION! Check legality with your state'sattorney general's office before use for monitoring of voices.

TELECOM2 Kit, Includes PC Board $149.50

TELECOM2 Ready to Use .....$199.50

Visible Beam LaserEasy to build, RED Beam, visible for miles. Use for lightshows, window bounce holography. cloud illumination and much

more' LAS1KM Kit w/1mw Laser Tube, Class It......... .$69.50LAS3KM Kit w/2.5mw Laser Tube, Class IIIA $99.50

Life is Precious -Protect It!Hard hitting 200.000 volts of

crackling, sizzling plasma. Shuns and immobilizes most attackersSTUN40 Ready

STUNIO Smaller Unit ..... $39.00

Ion Ray GunProjects charged ions that induce shocks in people and objects

without any connection! Great science project as well as a hightech party prank. 10G3 Plans $8.00

Invisible PainField Generator a)))Shirt pocket size electronicdevice produces time variant

complex shock waves of intense directional acoustic energy,

capable of warding off aggressive animals, etc.IPG7 Plans ....-..S8.00 IPG7K Kit/Plans ...$49.50IPG70 Assembled _ $74.50

1000 Ft++otato Cannon

NOT A TOY. Uses electronic or piezoIgnition CAUTION REQUIRED!POT1 Plans

(Dangerous Product) $10.00

FireBall GunShoots naming ball - two shot capacityGreat for special effects and remotefire starting CAUTION REQUIRED'FIREBALL Plans (Dangerous Product) $10.00 4111.

TV & FM Joker / JammerShirt pocket device allows you to totally control and remotely

disrupt TV or radio reception. Great gag to play on family orfriends. Discretion required.

EJKIKM Easy to Assemble Electronic Kit------. $24.50

ATTENTION:High Voltage Fans!4,000 volts in the palm of your hand! Experiment

with and -gravity, hovercraft, ion guns, force fields,

plasma guns, shock devices, wireless energy and

electrical pyrotechnics. Input 9-14VDC.MINIMAX4 Ready to Use.__._.__...._._......_.._.4 19.50

AP,

"Laser Bounce" Listener SystemNEW Latest Technology! Allows you to hear sounds from apremises without gaining access. Aim at room window and listen

to sounds from within via reflected laser light. Not for illegal use.Requires video tripods.

LWB3K 5mw Laser and Receiver Kit . $149.50

LWB30 Ready to Use, includes Laser Gun Sight ___. $199.50

5mw Visible Red Pocket LaserUtilizes our touch power control'VRLSKM Kit / Plans -4 74.50

Electronic- Hypnotism

Puts subjects under control using highly effective electronicstimuli. Intended for parties and entertainment but must be usedwith caution Includes valuable text book reference and plans.EH2 Plans and Ted Book . $.19.50

Automotive

NEON!Easy -to -Install

4 -Tube Kit/

for Cars, Trucks, VanslAvailable in Pink, Purple, Blue or Green

;:ease specify color when ordering.RG4K (Specify Color) ..........4 129.50

Flash-To-Muslc Option for abovekit FMU1. $ 29.50

3 Mi FMWirelessMicrophoneSubminiature! Crystal clear, ultra sensitive pickup transmitsvoices and sounds to FM radio. Excellent for security, monitoringof children or invalids. Become the neighborhood disk jockey!FAIV1 Plans --$7.00 FMVIK Kit and Plans .-... $39.50

Telephone Transmitter -3 MIAutomatically transmits both sides of a telephone conversation toan FM radio. Tunable Frequency Undetectable on Phone Easy to Build and Use Up to 3 Mile Range Only transmits

VWPM7K Kit/Plans$7.00$during phone use. VIVPM7 Plans

39.50

T1ON Dept PEM18, Box 716, Amherst, NH 03031

Phone: 603-673-4730 FAX 603-672-5406NLIMITEDMC, VISA, COD, Checks accepted Please add 55.00 Shipping & Handling

CATALOGWith many

more itemsiFree with Orderor send S1 PSH

License Frame Kit(Specify Color)UC1K $ 24.50

Order by Mailor by 24 Hour

Orders -Only Phone

800-221-1705

7

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NEW PRODUCTS

access on-line services, ex-change information with localand remote PC's, take notes onan electronic note pad, createmaps and drawings, generatedocuments with an intelligentword processor, and managetheir time and information any-time, anywhere. Adding to itscommunications capabilities,Sharp's optional Zaurus Mailsystem allows small workgroups to exchange messagesand data using a single Win-dows -based PC as anelectronic post office. Em-ployees of small companies, orindividual departments withinlarger corporations, can keep incontact with each other and withthe home office.

A PCMCIA Type II slot allowsusers to expand both the mem-ory and the communicationscapabilities of the Zaurus. Userscan add additional memoryusing uc to 2 -megabyte SRAMcards ur 16 -megabyte FLASHcards. The K-PDA also supportsmany PCMCIA Type II devices,including cellular -capable faxmodems and pager cards. Toleave the PCMCIA slot open forother devices, Sharp's ultra -compact, low -power CE-FM49600 2400 -bps fax modem canbe attached directly to the serialport of the Zaurus.

The Zaurus uses Sharp's pro-prietary 16 -bit processor toprovide both fast performanceand low power consumption,with up to two months of batterylife. The Synergy operating sys-tem is hidden from the user,freeing him or her from mun-dane system -managementtasks. Synergy is "data -centric,"with the ability to relate to dif-ferent types of information. Agraphical user interface pro-vides elements that Windowsand Macintosh users will findfamiliar, such as check boxes,radio buttons, scroll bars, andpop-up menus. In addition, pen -enabled features, such as textselection and drag -and -drop,provide fast and intuitive opera-tion.

The Zaurus ZR-5000 has asuggested retail price of $749.The ZR-5000FX, which includesthe CE-FM4 fax modem, has asuggested retail price of $849.

For more information, contactSharp Electronics Corporation,Sharp Plaza, Mahwah, NJ07430-2135; Tel. 1 -800 -BE -SHARP.


POCKET DMM WITHBARGRAPH

B + K Precision's first pocketdigital multimeter, Model 2700,measures AC and DC volts andresistance, and offers data hold,range hold, audible continuitytest, diode test, a bar -graphdisplay, and a 3200 -count LCDreadout. Data hold freezes thedisplay to hold a reading, whilerange hold allows users to de-feat autoranging and select onespecific voltage or resistancerange for all their measure-ments.

The Model 2700 is aimed atelectronic technicians, electri-cians, home handymen, collegestudents, and hobbyists. Thepocket DMM measures up to450 DC volts in five ranges with1.3% accuracy (0.7% on the 3 -volt range). It measures ACvolts to 450 volts in four ranges,and resistance to 30 megohmsin six ranges.

The Model 2700 pocket dig-ital multimeter, complete withtest leads that store conve-niently in its carrying case, aninstruction manual, and two 2.5 -volt button cells, has a sug-gested retail price of $33. Foradditional information, contactB + K Precision, 6470 WestCortland Street, Chicago, IL60635; Tel. 312-889-1448.


AMPLIFIED TV/FMANTENNA

Recoton recommends itsBullseye amplified TV/FM an-

tenna for general use as well asin homes equipped with thenew Digital Satellite System(DSS), which does not deliverlocal broadcast channels 2through 13. Bullseye can pro-vide DSS subscribers who live aconsiderable distance from TV

transmitters with a cost-efficientway of receiving those pro-grams.

The antenna's built-in, ultra -low -noise amplification circuitryimproves reception of TV pro-grams broadcast from up to 125miles away, as well as enhanc-ing AM and FM broadcasts.Using the antenna results inVHF signal gains of up to 24decibels, UHF signal gains ofup to 29 decibels, and up to 12 -dB FM -signal gains.

Bullseye also features circuit-ry to reduce RFI, which causessignal interruptions fromsources such as CB radio trans-missions. The antenna'somnidirectional reception pat-tern, achieved through the useof a sophisticated quad-yagi cir-cuit, eliminates the need to aimthe antenna toward stationtransmitters.

With its circuitry enclosed in asealed copolymer housing thatis resistant to ultraviolet raysand hostile weather, the Bulls -eye is suited for outdoormounting on rooftops or chim-neys. It can also be tucked outof the way indoors in attics,closets, lofts, or garages.

The Bullseye omnidirectionalTV FM antenna has a sug-gested retail price of $139.95.For further information, contactRecoton, 46-23 Crane Street,Long Island City, NY 11101; Tel.800-742-3438 or 718-392-6442;Fax: 718-784-1080.


CARBON MONOXIDEDETECTOR

A malfunctioning furnace orhousehold appliance can fill a

poorly ventilated room with car-bon monoxide, an odorless,colorless, and tasteless gas thatcan poison the air in a homewithout warning. The RadioShack Carbon Monoxide Detec-tor can warn your family of thepotentially deadly fumes.

The detector continuouslymonitors the air in your home towarn of dangerously high con-centrations of carbon monoxide,sounding an 85 -dB alarm whenhigh levels are reached. Meet-ing UL -approved safetystandards. the device automat-ically compensates fortemperature changes for max-imum sensitivity and reliability.

The Carbon Monoxide Detec-tor installs by simply plugginginto an AC wall outlet. An op-tional DC adaptor allows it to beused in recreational vehicles,travel trailers, and boats. Detec-tors should be placed nearappliances or equipment thatuse combustible fuel, includingclothes dryers, stoves, fire-places, and furnaces. TheFederal Consumer ProductSafety Commission recom-mends that multilevel homesshould be equipped with a UL -listed detector on each level.

The Carbon Monoxide Detec-tor is available for $79.99 atRadio Shack stores nationwide.For more information, contactRadio Shack, 700 One TandyCenter, Fort Worth, TX 76102;Tel. 817-390-3300.


"NEXT -GENERATION"HF TRANSCEIVER

DX'ers can work all the HFbands and receive 300 kHz to29.995 MHz with /com's "next -generation" IC -738 transceiver.SSB, CW. AM, and FM are builtin for a full 100 -watts output (40watts in FM). A heatsink withtwo large cooling fans ensuresstable 100% duty -cycle opera-tion even during DX'ingmarathons. The IC -738 offersan analog feeling to the tuning,faster PLL lockup times, im-proved phase -noise blocking,and high dynamic range. Bring-ing the IC -738 into the "next -generation" are an automaticantenna tuner, frequency -man-agement features, and CW-contest features.

Be a high -paid computerservice technician

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You'll also appreciate the brilliantdisplay of your Super VGA color monitor,the drama of your CD-ROM drive and16 -bit sound card, as well as thecutting -edge technology of Windows 95.

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NEW PRODUCTS

The built-in antenna tunerhas preset memories for eachband (in 100 -kHz steps), provid-ing high-speed tuning on the HF

and six -meter bands. The trans-ceiver's two antenna connectorsare directed by an automaticantenna selector that switchesto antenna one or antenna twowhen you change the operatingband.

Frequency management isaccomplished with the unit'squick -split function, which al-lows the offset frequency to beprogrammed in advance. Press-ing the SPLIT button thenautomatically selects all thenecessary settings for split -fre-quency operation. A split -lockfunction prevents users from ac-cidentally changing the receivefrequency while changing thetransmit frequency, and a dial -lock function electronically locksthe main dial.

CW contest features of theunit include a built-in electronickeyer with separate key jack,full break-in (QSK) operation,and separate jacks for an ex-tended CW key or memorykeyer. The CW enthusiast canuse a memory keyer (or TNCwith CW capability) to easilymake contacts, then use thepaddle for normal operation.

The IC -738 also features adouble -band stacking register,which memorizes two frequen-cies and the mode in eachband, allowing it to be used liketwo VFO's in one band. Forcontesting or DX'ing, up to 10electronic memo pads are avail-able to temporarily store thefrequency and mode by pushingthe memo-pad/write switch.Three scanning functions pro-vide operating versatility:Programmed scan searches forsignals over a specified range,memory scan searches allmemories, and memory selectscan searches only those mem-ories specified by the user.Other features include pass -

band tuning, a notch filter, a setmode for adjusting infrequentlychanged values or conditions, aVOX function for convenientphone operation, fast/slow se-lectable AGC time constant,multiple metering, a keypad fordirect frequency input, and com-patibility with Icom's CI -Vsystem for control from a per-sonal computer.

The IC -738, including a hand-held microphone, has asuggested retail price of $1935.For more information on theunit, contact Icom America, Inc.,2380 116th Avenue N.E., Bell-evue, WA 98004;Tel. 206-454-8155.


20 -INCH MONITORS

Two high -resolution, colormonitors from ViewSonic fea-ture 20 -inch screens and arecompatible with PC, Mac, andPower Mac computer systems.Capable of displaying twopages of text and graphics, andoffering a maximum resolutionof 1600 x1280, 0.28mm dotpitch, and a refresh rate of 77Hz at 1280 x 1024, the monitorsare ideal for CAD/CAM/CAE

and desktop -publishing applica-tions. Both offer the ViewMatchcolor -control system, which al-lows the user to adjust thescreen image to match printeror plotter output. The monitorscomply with the EPA's EnergyStar program by powering downto under 8 watts in off mode,and are MPR-11 certified for lowradiation.

The ViewSonic 20 PS, part ofthe high -end professional se-ries, offers an on -screen controlsystem that permits the user tocustomize screen images,choosing from and adjustingmore than 20 different functions,including trapezoid, paral-lelogram, moire, pincushioning,and ViewMatch color control. It

also includes a tilt -managementsystem to counteract the effectof the earth's magnetic field,thereby ensuring precise screenalignment to the bezel. A spe-cial coating virtually eliminatesscreen glare and reflection, anda super -dark screen providesgreater contrast and brilliance tocolors.

The ViewSonic 20G, part ofthe midrange Graphics Series,features an Inver Shadow maskfor sharply defined screen im-ages and a digital controlsystem for adjusting screensize, position, and geometry. Italso offers tilt management.

The ViewSonic 20PS and20G have suggested list pricesof $1695 and $1495, respec-tively. For further information,contact ViewSonic Corporation,20480 Business Parkway, Wal-nut, CA 91789; Tel.909-869-7976 or 800-888-8583;Fax: 909-869-7958.


FOUR -PORT SERIALBOARD

B&B Electronics' Model3PXCC4A serial card featuresfour serial ports in a single slot,saving valuable space for otherapplications. Each of the portscan be independently config-ured for any I/O address andany IRQ, as well as RS -232,422, or 485 data protocols, al-lowing it to fit any serialapplication.

TD, RD, RTS, CTS, DSR,DCD, and DTR port lines aresupported by the RS -232 mode,with each port using a buffered,high-speed UART. In addition,the 3PXCC4A has interrupt -sharing capabilities and an in-terrupt -status register toincrease throughput in shared

IRQ applications, and to in-crease the number of availableinterrupts in the system.

The 3PXCC4A uses eight -conductor RJ45 connectors.

Optional pre -wired adaptor kitsallow the user to convert toDB-9 or DB-25 connectors, andvarious adaptors to configurethe pinouts to fit any customapplication are available.

The 3PXCC4A four -port serialcard costs $209.95. The op-tional adaptor kits, includingseven feet of RJ45 cable, eachcost $10.95. For additional infor-mation, contact B&B ElectronicsManufacturing Company, 707Dayton Road, P. 0. Box 1040,Ottawa, IL 61350;Tel. 818-434-0846;Fax: 815-434-7094;BBS: 815-434-2927.


THERMOMETER -TIMERALARM

Extech's Model 401362 ther-mometer -timer alarm providesinstant, simultaneous readout oftemperature, countdown time,and setpoints on a large (1.4 -inch) LCD. When the tempera-ture setting or countdown timeis reached, an alarm sounds. Aremote temperature probe mea-sures from 32 to 392°F (0 to

200°C) with an accuracy of 2°Cand a 1° resolution. The ther-mometer -timer alarm featuresan adjustable desktop stand aswell as a magnetic wall -mount-ing device. It comes completewith a heat -resistant, six-inchstainless -steel probe and an"AAA" battery.

The Model 401362 ther-mometer -timer alarm costs $29.For additional information, con-tact Extech Instruments, 335Bear Hill Road, Waltham, MA02154-1020; Tel. 617-890-7440;Fax: 617-890-7864.


Breakthrough device repels pests..without chemicals or trapsThe new Transonic ESP generates ultrasonic and sonic noisesto drive away annoying pests electronically.

by Paige Clements Yasnowsky

Fleas that torment your pet. Rats thatspread dangerous diseases. Squirrelsthat nest in your attic. Spiders that spin

webs endlessly. Are you waging a constant bat-tle to get these pests out of your home?

If you're like me,you don't like the ideaof using poisons ortraps, especially if youhave small children.Up until now, therewasn't another choice.But not anymore.

Drive them away.Now, thanks to mod-em technology, there'sa better way to get ridof household pests-the Transonic ESP.

This remarkable newelectronic device useshigh -frequency soundwaves to repel com-mon household pests.

Best of all, theTransonic ESP doesn'ttrap or kill pests, itsimply drives themaway. Pests are forcedto flee the area to getaway from the annoy-ing and confusingsound waves. Thereare no dead bodies ormesses to clean up.

Ultrasonic/sonic repellent. The key tothe Transonic ESP is a patented electronicsound generator which broadcasts powerfulultrasonic and sonic noises in the five to 50 KHzrange. These frequencies and pulse sequences

are extremely uncom-fortable to insects andsmall rodents. Pestsare forced to leave orthey will die.

Why It works. Mostwild creatures dependon their acute hearingabilities for survival.They rely on hearingmechanisms for com-municating with eachother, for establishingterritorial boundariesand for locating avail-able food sources.

When critical hear-ing frequencies aredisrupted by high -fre-quency pulses, insectsand small rodents feelthreatened and con-fused. They are forcedto leave. Remaining inthe area causes apathyand immobility.

Just plug it in. TheTransonic ESP comeswith its own trans-former which plugs

Tired of battling pests?Fleas and ticks. Famous for caus-ing skin discomfort, these pestsalso spread disease and parasites.

I1114

Spiders. Eliminate webs drapedacross your furniture and in thecorners of your living room.

Bats. Dark places invite bats toroost. They can make a mess ofyour attic or storage building.

Squirrels. Gnawing squirrels inyour walls or attic can causestructural and electrical damage.

Mice and rats. Well-known car-riers of disease, rodents can behard to get rid of once they haveinfested your home or office.

The Transonic ESP covers an area ofup to 5,000 square feet

Are poisons and traps endangeringmore than just household pests?

Traps. In addition to the trouble of setting upa trap and the danger of accidentally

stepping into it, you also face theunpleasant task of disposing

of the animal once itis caught

Foggers. Using a fogger is both time-consuming and inconvenient You mustcover up all of your belongings in orderto shield them from the chemicals. Youalso must wait several hours for the

fumes to disperse before re-_entering the area.

Pest sprays. Exposing your carpet andfurniture to chemicals can be potentiallydangerous, especially if you have youngchildren who are still crawling. Plus,chemical sprays are difficult to apply ina way that eliminates all the pests, espe-cially the hidden ones.

into any standard outlet. To operate, simplypress the appropriate button on the front pan-el. You can repel fleas, ticks, spiders, bats, mice,rats or squirrels, depending upon the soundfrequency you select. (For optimum perfor-mance, follow proper pest control practices.)

Factory-dlrectoffer. The Tran-sonic ESP is an ex-tremely cost-effec-tive way to controlpests. And throughthis special factory -direct offer, it's evenmore affordable. Inorder to introducethis product to thepublic, we're offer-ing a $25 discountoff the retail price.You can purchasethe new TransonicESP for only $99.

Try it risk -free. The Transonic ESP is backedby Comtrad's exclusive risk -free home trial.Try it and if you're not completely satisfied, re-turn it for a full "No Questions Asked" refund.The Transonic ESP is also backed by a two-yearmanufacturer's warranty. Most orders are pro-cessed within 72 hours and shipped UPS.

Transonic ESP ..$11/4" $12 S&H

With special factory -direct offer $99



The versatile TransonicESP Is perfect for home,barn or storage shed.

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INDUSTRIES2820 Waterford Lake Drive, Suite 106

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12

Old -TimeTelephones!Technology,Restoration,

and Repairby Ralph 0. Meyer

ELECTRONICSLIBRARv

Serious collectors of antiquetelephones, as well as casualhobbyists and museum cura-tors, will be intrigued with thehistorical information on thepast 120 years of telephonescontained in this book. Much ofthe material, obtained from theauthor's painstaking research ofpatents and journal articles andhis precise electrical measure-ments, has never been widelypublished before.

The book is divided into foursections covering the develop-ment of the telephone, types oftelephones used in commercialservice, electrical circuits usedthroughout the telephone's his-tory, and a comprehensive

CI IL D TIMET hones!

TECHNOLOGYRESTORATION

AND REPAIR

guide to the restoration andrepair of antique telephones.The fourth section covers me-chanical and electrical repairs,testing, modifications to put an-

tique phones to use today, andFCC regulations on the restora-tion of antique instruments.

The book contains many pho-tographs and drawings ofantique phones, as well asunique schematic drawings.There is also an appendix ofelectronics fundamentals, con-ventions, and related physicsprinciples.

Old -Time Telephones! Tech-nology, Restoration, and Repaircosts $19.95 and is publishedby Tab Books Inc., Blue RidgeSummit, PA 17294-0850; Tel.1-800-233-1128.


INTRODUCTION TORADIO FREQUENCYDESIGNby Wes Hayward, W7ZO1

Aimed at engineers and ad-vanced radio amateurs who arecomfortable with digital hard-ware methods and basic analogdesign, this book -and -diskpackage presents basic RF-de-sign concepts usingmathematics as needed. Wher-ever possible, simple circuitmodels are used to preparereaders to actually design HF,VHF, and UHF equipment.

The book emphasizes theuse of models and their applica-tion to both linear and nonlinearcircuits. Traditional materials arereviewed from the viewpoint ofthe RF designer. The book pre-sents system design using thecommunications receiver as anexample, and further illustratessubject matter with numericalexamples. A discussion of os-cillator design covers oscillatornoise, starting conditions, andlimiting mechanisms. Two -portnetwork methods are applied tothe design of amplifiers andoscillators, including the use ofS -parameters.

The 31/2 -inch disk (for IBM PCand compatible computers) in-

cludes programs that will designand analyze LC bandpass, low-pass, and high-pass filters;crystal ladder filters; feedbackamplifiers; RF system dynamicrange; phase -locked loops; andmore. A user manual is includedon the disk.

Introduction to Radio Fre-quency Design costs $30 and ispublished by The American Ra-dio Relay League, 225 MainStreet, Newington, CT 06111:Tel. 203-666-1541;Fax: 203-665-7531.


ELECTRONIC TESTACCESSORIESCATALOGfrom ITT Pomona Electronics

Although test accessories are amajor market in their own right,many test -equipment directoriesand buyer's guide fail to includea separate test -accessory cate-gory. This catalog is intended to

ISST ACCEEVOI,

fill that gap by providing aneasy -to -use source of accesso-ries. Its 172 pages contain morethan 3800 specialized productslogically arranged and accom-panied by helpful selectionguides. All of the accessoriesare designed to optimize theperformance of electronic testequipment and to guaranteeconsistently reliable test results.The catalog also includes shorttutorial sections, such as "Se-lecting the Right Scope Probe"and "Extending Your DMM's Ca-pability."

The Electronic Test Accesso-ries Catalog is free uponrequest from ITT Pomona, Cus-tomer Service, 1500 East NinthStreet, Pomona, CA91766-3835; Tel. 909-469-2900;Fax: 909-629-3317.


MACINTOSHREVELATIONS:Customizing, Upgrading& Troubleshooting UsingSystem 7.5by Ken Maki

Macintosh computers are par-ticularly easy to use. With asimple click of the mouse, Macusers can play games, writeletters, enter a spreadsheet, ordo almost anything else. Butthey are also powerful ma-chines, and this book showsusers how to unleash thatpower.

With an emphasis on the un-documented features of theMac's latest operating platform,the book and its included CD-ROM provide practical adviceand valuable hints that canmake a System 7.5 run like a10. It teaches readers how tocustomize their Macs, guidesthem through the upgrade pro-cess, and providestroubleshooting help for bothsoftware and hardware. Thebook also offers chapters onnetworking and system enhan-cements.

The CD-ROM contains morethan 600 -MB of System -7.5 -compatible software. It containssoftware for games and enter-tainment; telecommunications;fonts, graphics, and sounds; ed-ucational programs;programming utilities; PowerPCutilities; and BMUG information.

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ELECTRONICS LIBRARY

emens was instrumental increating the conditions for theadvancement of electrical tech-nology, helping to bring it fromthe experimental stage into themodern electrical industry.

Werner Von Siemens: Inven-tor and InternationalEntrepreneur is available for$19.95 in hard cover and $12.50in paperback from Ohio StateUniversity Press, 180 PresseyHall, 1070 Carmack Road, Co-lumbus, OH 43210-1002;Tel. 614-292-6930;Fax: 614-292-2065.


PACKET: SPEED, MORESPEED, ANDAPPLICATIONScompiled by Bob Schetgen,KU7G

There have been a lot of excit-ing developments in packetradio recently, if you lookbeyond the local BBS and pack-et cluster. Hams are increasing

their speed, building high-speedLANs that span whole towns,using packet to report weatherconditions automatically, map-ping positions using GlobalPositioning receivers orLORAN -C, tracing the flow ofmessages through the packetnetwprk, and exchanging pack-et information via meteor scatterpropagation. This book-actu-ally a collection of articles fromsuch publications as QST andQEX, and ARRL ConferenceProceedings-shows you howto find the areas that interestyou.

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Packet: Speed, More Speed,and Applications costs $15 andis published by The AmericanRadio Relay League, 225 MainStreet, Newington, CT 06111;Tel, 203-666-1541;Fax: 203-665-7531.


1995 GENERALCATALOG OFPRODUCTS FORTESTING, REPAIRING &ASSEMBLINGELECTRONICEQUIPMENTfrom Contact East

The 144 pages of this full -linecatalog are filled with hundredsof new test instruments andtools for engineers, technicians,hobbyists, and managers. Qual-ity. brand -name products for

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THE WHOLE SPYCATALOGby Lee Lapin

This 440 -page, hands-on ency-clopedia of "secret sources"provides a wealth of profession-al secrets, tricks of the trade,"insider" phone numbers, andcutting -edge techniques fortracing, tracking, surveillance,and investigating anyone oranything.

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SIMPLIFIED DESIGN OFSWITCHING POWERSUPPLIESby John D. Lenk

This all-inclusive, one -stopguide to switching power -supplydesign describes the operationof each circuit in detail. Aimedat students and experimentersas well as design professionals,no previous design experienceis required to use the tech-

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Simplified Design of Switch-ing Power Supplies costs$39.95 and is published byButterworth -Heinemann, 225Wildwood Avenue, Woburn, MA01801; Tel. 1-800-366-2665.


VOODOO UNIX: MasteryTips & Masterful Tricksby Charlie Russel & SharonCrawford

Filled with timesaving tricks andinsider tips, and purposely de-void of unnecessary detail andtechnical jargon, this book isdesigned to help ordinary UNIXusers become faster and moreefficient at their work. It offerspractical advice and solutionsfor a variety of challengingUNIX tasks. Beginning with thebasics, it explains how to getgoing and get help, coveringshells, security, and keepingtrack of your files. It goes on tocover moving around and mov-

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Just ask any of the150,000 -plus graduates ofthe Cleveland Institute ofElectronics who are workingin high -paying positions withaerospace, computer,medical, automotive andcommunications firmsthroughout the world.They'll tell you successdidn't come easy...but itdid come...thanks to theirCIE training. And today, acareer in electronics offersmore rewards than everbefore.

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For pricing and ordering infor-mation on the "How it Works"books, contact Jensen ToolsInc., 7815 South 46th Street,Phoenix. AZ 85044:Tel. 800-426-1194.


One tree can make3,000,000 matches.

One match can burn3,k_XXVXX) trees.

V,11.11

BY ANTHONY J. CARISTI

MACHINEDetermine the "g" forces generated by your car with this

portable, digital acceleration- measurement system.

If you would like a high-tech way tomeasure the gravitational or "g"forces generated by your car,

then this unusual project might beright for you. It's called the "g" Ma-chine, and if you build it, you'll proba-bly be the first one in your circle offriends to have a car equipped with asophisticated g meter!

The "g" Machine measures accel-eration and deceleration levels en-countered in any moving vehicle, anddisplays those levels on an LCD. Youcan use it to compare the perfor-mance of your car's engine and brak-ing system with that of other vehicles.The unit can also be used as a sophis-ticated electronic level by taking ad-vantage of its sensitivity to the Earth'sgravitational force.

Velocity and Acceleration. Beforewe get into how the "g" Machineworks, let's quickly review how velocityand acceleration are measured. Ve-locity is the change in distance withrespect to time, and can be specifiedas ft/s (feet per second). Accelerationis the change in velocity with respectto time and is specified as ft/s2. Some-times, acceleration is referred to interms of "g's," where 1 g is equal to theacceleration caused by Earth's grav-itational field, or 32 ft/s2. Let's now lookat an example:

An automobile traveling at a con-stant speed of 60 mi/hr (miles perhour) has an acceleration of zero, be-cause there is no change in its ve-locity with respect to time. Thevelocity, 60 mi/hr, can also be spec-

ified in the unit of ff/s by using a simplealgebraic equation that convertsmiles to feet and hours to seconds:

(60 mi/hr x 5280 ft/mi x 1 hr) / 3600 s= 88 ff/s

Note that miles (mi) and hours (hr) arecanceled out in the above equationto arrive at the desired units of ff/s.

Acceleration can easily be calcu-lated using the equation

acceleration = velocity/time

Let's say that the automobile fromthe preceding example starts out at 0ft/s and accelerates to 88 ff/s (60 mi/hr) in 8 seconds. That car has an aver-age acceleration of

(88 ff/s) / 8 s

or 11 ft/s2. Because 1 g = 32 ft/s2, theautomobile has an average acceler-ation of 11/32 or about 0.34 g's.

If the automobile was driven at aconstant rate of acceleration as itsspeed increased from zero to 60 mi/hr,the "g" Machine would measure anddisplay that automobile's perfor-mance with a display of about 0.34g's. However, if the braking systemcould similarly stop the vehicle in 8seconds, the deceleration would bedisplayed as -0.34 g's.

The Accelerometer. The "g" Ma-chine uses the ADXL50 acceler-ometer, which is a monolithic inte-grated circuit designed by AnalogDevices (the IC is available from thesource in the Parts List or from an Ana-log Devices distributor). An acceler-

ELECTRONICSHOBBYISTSHANDBOOK.FALL 1995

ometer is a device that generates anelectrical output signal that is propor-tional to any acceleration forces(changes in velocity) affecting it. TheADXL50 is used by at least one auto-mobile manufacturer in airbag -de-ployment systems, and by othercompanies for different applications.

How does the accelerometerwork? The ADXL50 IC is a completelyself-contained measurement systemthat uses a change in capacitance todetermine acceleration. Figures 1Aand 1B are simplified diagrams of thesensor at rest and when subjected tothe force of acceleration, respec-tively. The actual structure of the sen-sor consists of 42 unit cells, only one ofwhich is shown in the figures. Its con-struction is such that each cell com-prises a differential capacitor shownas Ca and Cb.

When the sensor is at rest, the valuesof Ca and Cb in each unit cell areidentical. However, when the sensorexperiences a change in velocity (ac-celeration), the center beam struc-ture of the IC is deflected (as shown inFig. 1B). That causes the capacitancevalue of Ca to decrease while that ofCb increases.

The fixed capacitor plates of thesensor are each driven by a 1 -MHzsquare wave, and are 180 degreesout -of -phase with each other. With noacceleration force present, the volt-ages fed through the capacitors tothe center plate cancel each otherout, resulting in a voltage output at thecenter plate of zero.

When the force of acceleration is 19

present, the change in the capaci-tance of C, and Cb causes an unbal-ance in the system, and a 1 -MHzoutput signal is produced at the cen-ter plate. That signal is passed througha synchronous demodulator to pro-duce a DC output voltage that is pro-portional to acceleration. Circuitrywithin the IC, if connected to the cor-rect external components, providesan output voltage of 2.5 volts whenthe sensor is at rest. That voltage willincrease or decrease in magnitude inaccordance with the level of acceler-ation or deceleration affecting thesensor.

Circuit Description. Power for the"g" Machine (shown in Fig. 2) Is takenfrom a 9 -volt battery, B1. That battery'soutput voltage is regulated by U1,which supplies a constant 5 volts todrive the remainder of the circuit. Ofcourse, the circuit can also run off of acar battery.

The heart of the circuit is U2, theADXL50 accelerometer. The sensitivityof that chip is set to ± 20 g's in order toaccommodate the full scale ca-pability of LCD module DISP1 (19.99).Circuit gain Is determined by the val-ues of R4, R5, and R6, which controlthe gain of the internal buffer ampli-fier of the accelerometer. The seriesstring composed of R1, potentiometerR2, and R3 provides a way to man-ually set the zero -g voltage -outputlevel at pin 9 of U2 to half the supplyvoltage -2.5 volts. That output volt-age will vary linearly by 01-voltper-gof acceleration. Therefore, when sub -

SEMICONDUCTORSU1-7XL05 5 -volt regulator,

integrated circuitU2-ADXL50 accelerometer,

integrated circuit (Analog Devices)li3-1CL7106 AiD converter,

integrated circuitDISPI-31/2-digit LCD module (Digi-

Key LCD002VT-ND or similar)QI-BS170 N -channel enhancement

MOSFET

RESISTORS(All fixed resistors are 1/4 -watt,

metal -film units unless otherwisenoted.)

RI. R3 -20,000 -ohmR2 -10,000 -ohm potentiometer,

panel -mount

Ject to the maximum value of 20 g's,the output voltage will swing 2 voltsfrom its zero -g level of 2.5 volts.

In order to achieve good circuitperformance at low g levels, thebandwidth of the amplifier is limitedto about 30 Hz by C6. That capacitor isexternally connected across thefeedback resistor of the internal op -amp of the accelerometer.

The digital -display section of the cir-cuit is composed of DISP1 and U3. Thelatter is an analog -to -digital convert-er chip that contains all the necessaryactive components to drive DISP1, the31/2 -digit LCD module. Included in U3are the ND converter, clock oscillator,storage registers and latches, 31/2 -dig-it seven -segment decoders, andbackplane generator.

The differential analog input of U3 isapplied between pins 30 and 31. Thepositive input, pin 31, is driven by out-put -pin 9 of U2 through R8, a bufferresistor, and the negative Input, pin 30,is biased at a fixed voltage of 2.5 voltsby a voltage -divider string composedof R9 and R10. That provides the desir-ed display of 0.00 when the acceler-ometer is at rest.

A reference voltage is required byU3. That is applied between pins 35and 36 to set the full-scale displayrange of the ND converter. Full-scaledisplay, 19.99, occurs when the dif-ferential, analog input voltage ap-plied between pins 31 and 30 is equalto twice the reference voltage. Be-cause the scale factor of U2 has beenset to 2.0 volts for 20 g's, the referencevoltage must be 1.0 volts. The voltage -

PARTS LIST FOR THE "g" MACHINE

R4 -23.700 -ohmR5 -5000 -ohm, cermet

potentiometer, PC -mountR6 -137,000 -ohmR7, R9, RIO, RII, R13 -100.000 -

ohmR8-1-megohm, 5(4, carbonR12 -49,900 -ohmRI4, RI6--100,000-ohm, 5%, carbonRI5-470,000-ohm, 5%, carbon

CAPACITORS25-WVDC. electrolytic

C2. C3, C7, C9 0.1-iLE metallized -film

C4, C5 -0.022-µF, metallized -filmC6, CIO -0.047-1J', metallized -filmC8-100-pF, ceramic -discC11 -0.22-11E, metallized -film

CENTERPLATE

Ca

A

Cb

ANCHOR

Ce

B

Fig. I. When the accelerometer sensor isat rest (A), the capacitance of C. isequal to that of C,,. However, when thesensor is accelerated to the left 113i, thecenter plate shifts to the right, causingthe capacitance of C, to increase, andthat of Ca to decrease.

ADDITIONAL PARTS ANDMATERIALS

S1--SPST toggle or slide ~witchBI---9-volt batteryPrinted -circuit materials. project

enclosure. 90 -degree header (seetext). 411 -pin I(' socket. batterssnap with leads, spacers, machinescrews and nuts. %Aire, solder,hardware, etc.

Note: The following parts arcavailable from A. Caristi 164 WhitePond Road, Waldwick, NJ (17413).Set of 3 PC boards: S24.95; vt.$2.00; U2: S66.50:1.3: 514.45;QI: S2.00. set of 10 resistors:s5.00. Please add 55.00 postagehandling. New Jersey residentsplease add appropriate sales tax.

20

S1

POWER

B1

9V

47

U1

78L05O

C2.1 ^

C4 C5 C3.022 .022 .1

12 1-4-1 (-4--41-1119

U2ADX1130

8

R1

20K

R4 10R6

23.7K 137K

R210K

ZERO ADJUST

R320K

R55K

CALIBRATION

R7100K

C6047

'SEE TEXT

R81MEGA./48

C7.1

WI

31

R9100K

R10100K

'4%.#*

R11

100K

R1249.9K

DISP1*nn10 .nn

2 3 30 29 11 10 9 31 32 25 24 15 14 13 26 27 21 20 19 18 17 22

20 19 23 16 24 15 18 17 22 12 11 10 9 14 13 25 5 4 3 2 8 6

U3ICL7106

7

R18100K

12

37

Q1BS170

35 126

R13100K -

40

R14100K

1 C8100pF

33 29 127

C10 R15 C11.047 - 470K .22 T

Fig. 2. As this schematic shows, the ADXL50 accelerometer, U2, interfaces with an AiD converter, U3, to drive a 31/2 -digit LCDmodule, DISPI. Because that module displays any number from - 19.99 to +19.99, the circuit is designed to measure g's within thatrange.

r - --1

H1-1/4 INCHES

Fig. 3 Here is the template for theaccelerometer printed -circuit board.

divider string composed of R11, R12,and R13 provides that voltage.

The decimal point of the LCD has tobe illuminated to display readingsfrom 0.00 to 19.99. That is done byinverting the backplane square -wavedrive signal appearing at pin 21 of U3,through MOSFET Ql, and applying the180 -degree out -of -phase signal topin 12 of DISP1.

Construction. The author's pro-totype for the "g" Machine was as-sembled using three single -sidedprinted -circuit boards that aremounted within a small enclosure.Those are the accelerometer board(Fig, 3), the A/D-converter board (Fig.

2 INCHES

Fig. 4. This is the AID -converterprinted -circuit board.

4), and the display -module board(Fig. 5). The printed -circuit boards canbe obtained from the source given inthe Parts List, or you can etch and drillyour own. Alternatively, the circuit canbe hard -wired on one or more perf-boards providing that proper orienta-tion of the accelerometer is main-tained, as explained later.

If you choose to build the project onPC boards, use Figs. 6, 7, and 8 asguides to ensure that you properly ori-ent all polarized components. Installthose parts first, then install the othercapacitors and resistors. Next, installU3 using a 40 -pin socket.

The accelerometer, U2, can be sol-dered directly onto the acceler-ometer board. Note the position ofU2's tab shown in Fig. 6, and make surethat the orientation of the partmatches. Then, gently bend the leadsto fit into the ten holes on the board.

[4-- 1-3/4 INCHES

Fig. 5. The display board template isshown here. 21

22

TOA/D-

CONVERTERBOARD

+5V

GND0--

o m.

-R6- R3

-R7- H R2

CR5 111

C4 C5

Fig. 6. Use this parts -placementdiagram as a guide when assembling theaccelerometer board. Check the positionof the tab on U2 to make sure theaccelerometer is oriented correctly.Also, note the connections to the A,D-converter board that can be made with a3 -pin header.

Be careful with that operation; theleads are fragile and you don't wantto inadvertently break any of themwith repeated bending.

The accuracy of the circuit relies onthe stability of the accelerometer andND -converter voltage -reference -re-sistor values. For that reason, youshould use only metal -film resistors forthe resistors specified in the Parts Listas 1% units. Ordinary carbon resistorsare not temperature stable andshould only be used where specified.

When you have completed assem-bly of the circuit boards, examinethem very carefully for bad solderJoints and/or incorrect orientation ofparts. It is much easier to correct prob-lems at this stage rather than after theboards are connected.

Connecting the Boards. Before youcan connect the printed -circuitboards to the front panel of the en-closure, the ND -converter board anddisplay board must be wired togetherusing light gauge (#22 to #26), insu-lated stranded wire (do not use solidwire-it has a tendency to break).Those connections include three setsof seven wires, each labeled athrough g, for the seven -segment dis-play digits, the half digit (1), the minussign, and the backplane drive.

Use Figs. 2, 7, and 8 as guides whenmaking the connections. Be sure toallow sufficient wire length to accom-modate the final position of theboards. Check the wiring betweenthe two boards carefully; an errorthere will result in garbled display dig-its, or no display at all.

A rectangular cutout measuring 2by 7/8 inches should be made at thedesired location in the front panel of

your enclosure. The two operatingcontrols, S1 and R2, can be placed atany convenient location; they will beconnected to the circuit boards later.

For the "g" Machine to provide apositive acceleration reading when itis facing the user, the accelerometerPC board must be oriented perpen-dicular to the front panel of the en-closure. The tab of U2 has to pointtowards the front panel of the instru-ment, as indicated in Fig. 9 (a sideview of the assembly from the bottomedge of the front panel). Precise ori-entation of U2 is important to ensure a

balance between positive- andnegative -acceleration forces.

One way to accomplish proper ori-entation of U2 is to mount the acceler-ometer board to the ND -converterboard using a 3 -pin, 90 -degreeheader with 0.1 -inch spacing (Digi-Key S1112 -3 -ND or similar), as wasdone in the author's prototype. Theassembly can then be stacked withthe display board and mounted tothe front panel of the enclosure withspacers, machine screws, and nuts (asshown in Fig. 9). If you are not planningon using the supplied PC -board tern -

TO ACCELEROMETER BOARD

+5V? GND ?SIG.

I

c2Ri4

I Ictl 0---cl 0-bl

1R11C8 R12

I I I

---R9-al 0flo--

TO U3

C91 -R10-C7

-R8-C10

91 o ---el 0--c12 0

c2 o ---b20--

DISPLAY R13a20f2BOARD -R15-

TODISPLAYBOARD

e2 0 ---dl

C11

Oggo

bl 0---f10--- c3

0 a30g3el o

1C0 BP0 --- (:I -R16 --

DP 0

B1 10Fig. 7. On -board component placement on this A,D-converter board is pretty simple.Just be careful when making the off -board connections to the display board. Also, notethe placement of the 3 -pin header.

TOA/D-

CONVERTERBOARD

al 0-fl o--gl o-b2 o-a2 0-f2 0--1;2 0--b3 0-a3 O

C

DISP1

S1

-o bl-0 cl-0 dl-o el-0 c2-0 d2-O e2-0 DP-0 c3-0 d3-0 03

-0 1- BP

TOAID -

CONVERTERBOARD

Fig. 8. The only component that mounts on this board is DISPI. However, watch thoseconnections to the AD converter board!

ACCELEROMETER

ND -CONVERTERBOARD

TAB

FRONTPANEL

ACCELEROMETER BOARD

DISPLAY BOARD

Fig. 9. This is a top -side view of the "g" Machine. Make sure U2 is placed so that itstab points towards the front panel, as shown. The boards are mounted with spacersand machine screws and nuts.

plates, and will use a different partslayout, make sure that the acceler-ometer is still aligned properly (withthe tab pointing to the front panel).

Attach a battery clip, switch S1, andpotentiometer R2 to the circuit usingFigs. 6 and 7 as guides. Be sure tocheck polarity when wiring the clip tothe circuit. The battery should be se-cured within the cabinet to keep itfrom moving around,

Checkout. The checkout procedurerequires the use of a digital voltmeteror VOM, Set R2 and R5 to mid -positionand connect a fresh 9 -volt battery tothe circuit. Turn the power on andmeasure the voltage at the output ofU1 with respect to the circuit common(negative battery terminal). If all is

well, it should measure between 4.75to 5.25 volts.

Do not proceed with the checkoutprocedure if you do not obtain thecorrect voltage reading. Instead,check the orientation of C1 and U1.The next step in the procedure is tocheck the positive battery -terminalvoltage and polarity under load to besure it is delivering at least + 7 volts tothe circuit. If it's not, turn off the powerand check the resistance betweenthe 5 -volt bus and circuit common tobe sure that there is no short circuit.Locate and repair the fault beforeproceeding.

With the 5 -volt regulator operatingproperly, apply power to the circuitand measure the voltage at pin 9 ofU2 while adjusting potentiometer R2over its range. A normal indication isabout + 2.3 to + 2.7 volts. If necessary,a different -valued resistor can beused for R1 and/or R3 to obtain aswing that is centered about 2.5 volts.

If you do not obtain the correct volt-age at pin 9 of U2, disconnect powerand check the orientation of U2 on itsboard to be sure it is correct as shownin Fig. 6. Check the wiring to R2, and allthe components on the acceler-ometer board. Check the voltage be-tween pins land 5 of U2 to be sure it isbeing powered by the + 5 -volt regu-lated supply.

With U2 operating properly, checkthe display as R2, the ZERO ADJUSTcontrol, is rotated over its range. Youshould obtain readings that cover therange of at least -1.00 to + 1.00, ormore. Of course, adjustment of R2should allow the display to be set to0.00.

If the display is blank, check the ori-entation of U3 and DISP1, and verifythat all component values associatedwith U3 are correct. Check pin 21 of U3with an oscilloscope to verify the pres-ence of the 5 -volt, peak -to -peak, 55 -Hz, backplane square -wave signal.

If some of the digits are not properlyformed, then there is either a wiringerror, a short, or an open in one ormore of the connections between theA/D-converter and display boards.Check the boards for solder bridgesor poor connections. If the decimalpoint is not illuminated, check Q1 andits associated wiring, and if that is cor-rect, try a new transistor.

Calibration. You will have to cali-brate the "g" Machine against theforce of gravity, which averages 1 g. Todo that, set R5 to approximately mid -position first. Then, hold the enclosureso that the front panel is exactly ver-tical, and apply power. Carefully ad-just R2, the ZERO ADJUST front -panelpotentiometer, for a display of 0.00.

Now place the panel in a horizontalposition with the display facing up-ward. The reading should be a nega-tive number. Position the panel in ahorizontal position so that the displayfaces down. The reading should be apositive number. Proper calibration isattained by adjusting R5 so that thereadings in the last two positions areas close to -1.00 and + 1.00 as possi-ble. That will take several adjustmentsof R5. Before each adjustment, alwayshold the panel in an exact verticalposition and re -zero the display to0.00 with the front -panel potentiome-ter, R2.

Note: If there seems to be an im-balance in the positive and negativereadings with the panel placed ineach horizontal direction, the orienta-tion of U2 is not exact. !twill be possibleto balance the readings by slightlyadjusting the position of U2 on itsboard, rotating it either clockwise orcounterclockwise as required. Withcareful calibration it should be possi-ble to obtain positive and negativereadings that are reasonably close toeach other, within OA g's or less.

Using the "g" Machine. The bestway to check the operation of the "g"Machine is to take it for a test run in avehicle. Be sure to have someonedrive while you operate the instru-ment. Always hold the front panel in avertical direction and zero the displaywhile stopped, before taking a mea-surement.

Remember: acceleration is the rateof change of velocity or speed, somaximum acceleration readings oc-cur when the vehicle is starting out.When a final speed is attained, theacceleration should become zero.For example, if the vehicle is driven sothat its speed increases from zero to55 MPH in as short a time as is prac-tical, the g force will be about 0.3 to0.5 when beginning the test and it willdecrease to zero when speed be-comes constant.

It should be noted that it is possibleto attain much -higher g forces whenbraking. When that is done, the instru-ment will display a negative number,indicating deceleration.

The display will start to become er-ratic, and will eventually go blank,when the battery needs to be re-placed. To extend battery life, shut offthe unit when it's not in use. 23

41'

Unbuffered

Off

Buffered

25 MHzFrequencyCounter

Freeze

.. .

......

RectdiedInput

AmplifiedInput

41/44:'

UnbufremdInput

fh. 25 -MHzFrequencyCounter

Here's an inexpensive way to gain a valuable test -gearaddition to any hobbyist's workbench.

With the way that the elec-tronics world has changedin the last twenty years, a

frequency counter is no longer a luxu-ry; it is a necessity. Unfortunately, likemost of us, I walk a delicate line be-tween what my test bench needs andwhat my budget can afford. A fewyears back, I spent nearly $200 on afancy signal-generator/frequency-counter unit; but, unfortunately, it onlygoes to 2 MHz. As even the simplestcircuits these days have clock speedsthat exceed that many, many timesover, I constantly found myself perus-ing the catalogs, looking for some-thing I could afford.

Then I came up with the 25 -MHzFrequency Counter described in thisarticle. It accurately counts frequen-cies to 25 MHz, is so small that it could

, fit in a coat pocket, and can be builtfor less than forty dollars.

z1" The complete schematic for the fre-<i quency counter Is shown in Fig. 1. Any(4.) frequency counter, including this one,to

CD>- can be broken down into five basic

iCD

O sections: counting, input conditioning,

(..)u, ranging, timing, and display. Let's lookE at each of those functions separately.0cr

ai Counting. When building a frequen-d cy counter, ifs hard to ignore the chips

made by Intersil/Harris Semiconduc-1/14

,q2 tor. Some of them are really completefrequency counters on a single chip;

u_ you just hook them up to a display,add some conditioning circuitry,throw it into a box, and voila, you have

24 a frequency counter.

BY MARK EMERY BOLLES

That said, I didn't use one of thosechips for a variety of reasons. To startwith, they generally only count to 10MHz; that isn't high enough for manyapplications. Secondly, the chips arequite pricey; some of them cost morethan this whole project. And finally, itjust feels like cheating to throw a sin-gle chip in a box and say: "Hey! Lookwhat I made!" Part of the joy of elec-tronics, whether as a hobby or a pro-fession, is the chance to exercise yourgray matter a little and come up withsomething innovative. The single -chipsolution is lacking in challenge.

Having discarded the one -chip so-lution, there are still some extremelygood Intersil chips that we can use.For the heart of the frequency coun-ter, I chose the Intersil ICM7224IPL. It isa higher performance version of theCMOS family 74C946 counter/latch/display driver, but where the lattertops out at around 3 MHz, the former isguaranteed to count to 15 MHz, andtypically counts to 25 MHz or better.Best of all, the ICM7224IPL costs lessthan $10.

The ICM7224 directly drives a fourdigit LCD display; it has reset, clock,and enable inputs. The reset input setsall counters to zero. The enable inputessentially disables the clock input.That means that we can connect theoutput of the counter's input -con-ditioning circuitry directly to the chip'sclock line, and control when countingoccurs with the enable input.

Input Conditioning. Input con-

ditioning is the area where mosthome-brew frequency counters falldown. The reason is simple enough:Designing a good input -conditioningcircuit is usually difficult, expensive, orboth. For this design, I wanted to beable to count frequencies from 0 to 25MHz, using input signals from 0 to 50volts, allowing both AC and DC signalsof any wave shape. For use with theselected counter chip, the input -con-ditioning circuit must be able tochange sine, triangle, or any otherwave shape to a clean square waveof 0 to 5 volts, with fast rise and falltimes. And, of course, the input -con-ditioning circuit had to be simple andcheap.

I am not above stooping to theft(although I prefer to call it "research"),so the first thing I did was to pull out allthe old books and magazines and trya few front-end circuits from other fre-quency counters. Amazingly, I foundthat very few worked as claimed, andnone would work for my design. All ofthe circuits I checked used op -ampsfor signal conditioning. I bread-boarded the designs, but found thatthe chips required were either too ex-pensive, required a dual power sup-ply, or weren't fast enough. I needed anew approach.

Most of you are probably familiarwith the CMOS 4049 chip. That chiphouses six inverters in a 16 -pin DIP Itwas designed for use in digital circuitsfor logic purposes, as well as for inter-facing between TTL and CMOS. Whatmany people don't know is that it can

be used in a linear fashion, too, muchlike an op -amp.

The 74HC family has a version of the4049, the 74HC4049, that is excep-

CC0

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U77805

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spond to frequencies well above the25 MHz we need. If we use the chip ina linear fashion with sufficient gain,even a small input signal will saturate

16

12

LCD15 30LCD16 29

LCD17LCD18LCD19LCD20

LCD21

11

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LCD23LCD24LCD25LCD26

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LCD1 7

LCD2LCD3

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LCD8 6

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LCD10 8

LCD11 9

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1/674HCO4

34

RESET

IA1B

1C U3

1 O ICM7224

I E

1F

102A2B2C

ENABLECARRY

STORE

CLOCKBACKPLNE

3A3B

3C

3D

3E3F

304A

484C

4D

4E

4F40LZI

5

13 LCD1514 LCD16,15 LCD17,16 LCD18,17 LCD19,19 LCD20,18 LCD21

20 LCD22A21 LCD23/I22 LCD24,23 LCD2524 LCD26.26 LCD27.25 LCD28

29

35

R9 Vcc

U5t 08 33434,440 t

1/674HCO4 LED2P,a( KHz

R1010KAN*

012N3904

R11

10K

Fig. I. Here's the complete schematic for the 25 -MHz Frequency Counter. The heart ofthe circuit is an Intersil ICM7224IPL counterilatchldisplay-driver IC.

R1210K

4AN

022N3904

1/674HCO4

65-c

QAC:11)2N3904

25

26

the chip, and we can convert slow riseand fall times into fast ones. Lastly, as istypical with the HC family, high leveloutputs go all the way to Vcc

By choosing input and feedback re-sistors that give a gain of 100, we canbe assured that any significant inputsignal will drive the chip's output fromrail to rail, ensuring a nice cleansquare wave for us to feed to theICM7224IPL.

The one thing that the 74HC4049does not like is a negative input volt-age. The databooks say the minimuminput voltage is 0 volts, but in reality, itwill handle up to around -1 volt with-out complaint. Also, although the chipis designed to handle up to 15 volts, itruns cooler if the maximum input doesnot exceed Vcc (5 volts in our design).Therefore, as part of our input con-ditioning, we need to be able to takesignals that can range as far as - 50to + 50 volts, and convert them sothat they fit into a -1 to + 5 volt range.

The obvious choice for that job is aZener diode. The circuit uses a 1N7515.1 -volt Zener, along with a 47K resistorand capacitive coupling, so that aminimum load is put on the circuit un-der test.

When price is a factor, any circuit isa compromise. The one used herehas two problems: The first is that theZener diode has a relatively slow re-covery time and starts to performpoorly at speeds above 8 MHz. Thesecond problem is that the 74HC4049uses a lot of supply current. So I choseto provide three different inputs to thefrequency counter

Input -jack J1 is used when the signalneeds to be amplified and con-ditioned for the ICM7224 chip. TheZener rejects all signals that fall out-side the range of - 0.7 to + 5.1 volts.Therefore, that input is used for sinewaves and AC signals up to about 50volts; it works well to about 8 MHz ormore, depending on signal symmetry.

Input -jack J2 is used when the inputsignal needs conditioning, but notrectification; a 0- to 15 -volt DC tri-angular wave, for example. The inputworks up to the full 25 -MHz limit of thefrequency counter.

Input -jack J3 is used for an uncondi-tioned signal; it goes directly to theICM7224's clock input. If you arecounting the frequency in a typicaldigital circuit, where you generallyfind only 0- to 5 -volt square waves,

4 Os INCHES

Fig 2. The counter is built on a compact double -sided PC -board. The artwork for thefoil side of the board is shown here.

input conditioning is not required.When that input is used, switch S1should be placed in position 3, theunbuffered position. Besides con-necting the input directly to the coun-ter chip's clock input, that removessupply power from the 74HC4049,which is not used in the unbufferedconfiguration. Since the input -con-ditioning circuitry consumes about100 mA, that setting can extend bat-tery life considerably.

Ranging. Since our design can dis-play only 4 digits, some type of rang-ing is essential. The frequency counterhas three ranges: 0000-9999 Hz;000.0-999.9 kHz; and 00.00-99.99MHz.

There are two different ways wecould achieve the required rangingscheme: The first is to divide the in-coming signal with counters so thatthe ICM7224 counts fewer pulses. Thesecond method is to change the timeperiod within which the input signal'spulses are counted. For the frequen-cies we will be dealing with, the sec-ond method is easier, cheaper, usesfewer chips, and is more accurate. Allwe need is a way of accurately con-trolling the timing period.

Timing. Actually, the term "frequencycounter" is a misnomer; a frequencycounter really doesn't count frequen-cies, it counts pulses. So when we de-sign a frequency counter, we arereally designing a piece of test equip-ment that shapes incoming pulsesinto a form it likes, counts them, and

displays the count. Of course, thatsounds like the definition of an eventscounter; in order for it to be a frequen-cy counter, it must count the pulsesthat occur within a specific timeperiod. Therefore, we can think of afrequency counter as an events coun-ter that contains accurate timing cir-cuitry; that circuitry determines whenthe pulses (events) are counted.

It then becomes obvious that theaccuracy of the frequency countercompletely depends on the ac-curacy of the sampling period. If it iseven a fraction of a second off, theICM7224 will miss counts, or countmore pulses than it should, giving aninaccurate readout.

As you can then see, next to thecounter chip itself, the timing circuitryis the most critical part of an accuratefrequency counter. For our design, weneed a chip that will accurately de-fine the three timing periods we re-quire for the three different ranges.

The Statek PXO-1000 is a 16 -pin DIPthat contains a 1 -MHz laser -trimmedcrystal, along with internal logic anddividers that allow you to get 57 dif-ferent frequencies from 1 MHz downto 0.008? Hz, depending on the logiclevels :1,:sent at the chip's programpins. Ala , the chip has good temper-ature stability (0.015% over its operat-ing range), doesn't have start-upproblems like crystal oscillators occa-sionally do, and runs on about 700 µAof current. Epson America also makesa compatible chip, the SE3102 (avail-able from Digi-Key, and elsewhere).

We can get the three frequencies

00

0

S.O o o 0 0e e

e e.

4Y2 INCHES

Fig. 3. Here is the component side of the project's PC -board. Like the foil side shownin Fig. 2, it appears full sized.

we need by changing the logic levelson just two of the chip's program pins.We can then take the frequenciesthat are output from the PXO-1000and convertthem into the timing peri-ods that we need for the enable line.

Let's see how all of that works. Thefrequency from the PXO-1000 is fed tothe clock input of the 74HC4017. Asthe clock counts, each of the74HC4017's Q outputs goes high insuccession. Two of the outputs are fedinto an RS latch, the output of which isfed to the 74HC7224's enable input.

CA3to ---48e

LED1

LED2

LED3

There are a couple of advantagesto using that method. One is that theenable period becomes dependentonly on the PXO-1000's output fre-quency, which in this case is easilycontrolled with just two logic pins. Sec-ondly, we can use other outputs fromthe 74HC4017 to control the reset andlatching inputs of the ICM7224. Lastly,and probably most important, is thatthe circuit, using the RS latch, is com-pletely immune to propagation de-lays. Since the rise and fall propaga-tion delays for the 74HCO2 are exactly

C7

a

11,- C14 ti -C241,-C34 0-R1-4 Asa-{4--

the same, the delay in turning on theRS latch is exactly the same as thedelay in turning off the latch; there-fore, the enable period suffers no vari-ations, and we can be confident thatthe ICM7224 is giving us an accuratecount.

Display. Our frequency counter usesa 4 -digit LCD display that is directlydriven by the ICM7224. What theICM7224 does not do is control thedecimal points, nor does it directlycontrol an overflow indicator; we musttake care of that ourselves.

The ICM7224 generates a 150 -Hzsquare wave for the display; that sig-nal is called the backplane. When asegment of the LCD should be off, thatsegment is fed a square wave that isidentical to, and in -phase with, thebackplane. When a segment is to beon, the segment is fed a square wavethat is 180° out -of -phase with thebackplane, causing the segment tobecome visible.

Therefore, the easiest way to displaythe decimal points is to take the back -plane signal, invert it, and gate it tothe appropriate decimal point seg-ments on the LCD with transistors. Instrict theory, that isn't quite ideal. In ourimplementation we cause the deci-mal point segments to be on with asquare wave 180° out -of -phase with

U2 2(

Fig. 4. Mount the components using this parts -placement diagram as a guide. Notethat the LCD (DISPJ) and the LED's mount on the foil side of the board. Be sure tosolder all components on both sides of the board wherever pads are provided.

4.112.-AN

B1

27

PARTS LIST FOR THE25 MHz FREQUENCY

COUNTER

SEMICONDUCTORSUl-74HC4049 high-speed CMOS

hex inverter. integrated circuitU2-PX0-1000 or SE3102

programmable frequency source.integrated circuit (see text)

U3-1CM72241PL counter/latch;display -driver. integrated circuit

U4-74HC4017 high-speed CMOSdecade counter, integrated circuit

U5-74HC04 high-speed CMOS hexinverter, integrated circuit

U6-74HCO2 high-speed CMOSquad 2 -input NOR gate. integratedcircuit

U7-LM7805 5 -volt regulator.integrated circuit

DISPI-LCD003 4 -digit liquid -crystal display. see text

QI-Q3-2N3904 NPN transistorD1 -1N750 5.1 -volt Zener diodeLED1-LED3--20-mA light -emitting

diode. %s -inch diameter

RESISTORS(All resistors are %x -watt, 5% units.)R I -47.000 -ohmR2 -100,000 -ohmR3-10-megohmR4, R5. R7 -2200 -ohmR6, RS. R9 -330 -ohmR 10-R 12 -10,000 -ohm

CAPACITORSCI-C3-0.022-µF, MylarC4 -1-µF, tantalumC5-C8--0.01-)LE ceramic -disc


SI-3PDT, mini toggle. center offS2-SPDT, mini toggle, center offS3-SPST momentary push-button,

normally offJI-J3-BNC connector, female.

panel mountB1 -9 -volt battery. transistor -radio

typePC -hoard and materials, enclosure

(Radio Shack 270-222 or similar),9 -volt battery clip, hardware,solder, wire, etc.

the backplane, but cause the seg-ment to be off by providing it with nosignal at all. Strict theory would de-mand that we turn the decimal pointsoff by feeding them the backplanesignal, rather than no signal. However,that would increase the parts count ofthe circuit, and whatever "points" welose by not adhering to strict theory,we gain back through our "admirable

28 down-to-earth pragmatism!"

Some Final Touches. We have nowdescribed most of the major points ofthe circuit shown in Fig. 1. However,there are still a few points we need totouch upon.

The range switch, S2, is a center -offSPDT toggle switch. In position 1, wefeed Vcc to a HZ LED Indicator, and pullPXO-1000 program pin 4 high. Thatresults in a PXO-1000 output of 5 Hz,and a 1 -second timing period on theICM7224's enable line.

In switch position 3, we feed the MHZLED, and pull no program pins low.That results in a PXO-1000 output of 50kHz, which corresponds to a 0.1 mstiming period.

For the "kHz" range, the center -offposition (position 2) of the rangeswitch causes a NOR gate (U6 -d) togenerate an output; that output pullsPXO-1000 pin 5 high, and feeds the ki-izLED through an inverter.

We also need an over -range in-dication to tell us when the input fre-quency exceeds the range we haveselected. The ICM7224 has a carryline, intended for cascading counters;it goes high whenever the count ex-ceeds 9999, and remains high until areset. While we don't need that line forits intended purpose, it is ideal for im-plementing an over -range indication.

The LCD display I used was originallyintended for a variety of purposes,one of which was a digital -clock dis-play. It has a "I:.M." indicator in the up-per left display corner, in the form of atriangle; we will use that for our "over -range" indicator, and control it withthe ICM7224's carry line in the sameway we turn on the decimal points.

The 74HC4017 is used for more thanJust gating the enable line through theRS latch. Every timing cycle, just priorto the sampling period, we use the74HC4017 to reset the counters in theICM7224, and then after the timingperiod, we latch the count into thedisplay.

Finally, we need to deal with one ofthose problems that you generallydon't think about until you build andtest a design like this. When we areusing the MHz range, for example, thefrequency counter is testing and dis-playing the frequency 5000 timesevery second. If the input frequency is,say, half way between 10.15 MHz and10.16 MHz, then sometimes the lastdigit will be a "5", and sometimes it is a"6." The relatively slow recovery time

of the LCD, coupled with an effectcalled "persistence of vision" (the slowrecovery time of the human eye) cancause that last digit to look like a 5 anda 6 combined, showing a weirdcharacter that looks like an 8 with onesegment missing, It would be nice tobe able to freeze the display for situa-tions like this, as well as for those timeswhen you are measuring a rapidlychanging frequency, and want totake a "snapshot" of the frequency ata particular instant.

Therefore, you will notice in theschematic that there is a "freeze"switch (S3) hooked up to the74HC4017's enable line. When closed,that normally open pushbutton dis-ables the 745HC4017's clock inputand stops the chip from cycling; theLCD display therefore becomesfrozen.

That is not a perfect solution,though; although the display is frozen,if you press the freeze button duringthe sample period (statistically, thechances of that are 50%), then thecounters will keep counting, eventhough that count will not be latchedand displayed. What will be displayedis the over -range indicator So, al-though the count displayed is accu-rate, you cannot expect an accurateover -range indication when thefreeze button is pressed.

Construction. One of the designparameters for the frequency counterwas portability; consequently, thewhole circuit fits on a small double -sided board that measures just 41/2 x2% inches. The artwork for the solder(foil) side of the board is shown in Fig.2, while the component side is shownin Fig. 3. The board fits into a RadioShack 270-222 project box, or a sim-ilar enclosure.

Start the construction by etchingand drilling the board; check alltraces for shorts and opens. Note thecut-out area; that area is necessary toallow room for the BNC connectorsand can be made using a jeweler'ssaw or another suitable tool. Drill outthe four areas indicated by squarepads near the board's four corners toaccommodate the project box'smounting screws; take care to notbreak any of the traces near the pads.

A parts -placement diagram isshown in Fig. 4. Note that DISP1 andthe three LED's mount on the foil side

of the board. Begin assembly bymounting the IC's on the componentside of the board. Note that most ICpins must be soldered on both the foiland component sides. To do that, be-gin by tacking the IC's in place bysoldering a couple of pins on theboard's foil side. Because of the smallboard size and relatively high circuitdensity, use the smallest soldering irontip you have.

When all the IC's are in place, finishsoldering all of the pins that need sol-dering on the board's foil side, andthen turn the board over. You will seethat all of the power and ground pins,as well as certain other pins, must besoldered on the component side. TheIC pins that need to be soldered onthe component side all have largepads to make the soldering go easier,and to identify which pins on the com-ponent side require soldering.

When all of the IC's are soldered,check each of the connections with acontinuity tester, particularly the con-nections for the ICM7224 (U3); oncethe display is in place, you will not beable to correct any mistakes on theU3's foil -side connections.

Once you are sure that all the IC'sare installed correctly, it is time tomount the display on the foil side ofthe board as indicated in Fig. 4. Firstsolder all of the foil -side connectionsto the LCD, then turn the board overand solder all of the component -sideconnections.

The next step is to mount and solderall of the discrete components. All ofthose mount on the component side,with the exception of the three LED's,which, like the LCD, are mounted onthe foil side. Be sure to note the orien-tation for all of the polarized cornpo-nents and the Zener. Note that to aidin assembly, the LED cathodes and thetransistor emitters were given squarepads. When installing the LED's, mountthem so that they stick up about 3A3 ofan inch, measured from the boardsurface to the LED's extreme top. Besure to solder all parts on both sides ofthe board anywhere that pads areprovided.

Once all parts are mounted, dou-ble check all soldered connections toensure you have not only good elec-trical connections, but also that thereare no shorts or solder bridges. Theboard is very compact, and mistakesare easy to make.

While the enclosure for the projectis not critical, the one mentioned ear-lier is nearly ideal and was used by theauthor in his prototype; it does, how-ever, require some minor modifica-tions. Using a hand grinder (like aDremel) and a miniature circular -sawblade, trim each of the mountingposts in the project box down byabout 1/8 -inch. Also, take a notch outof the upper left mounting post tomake room for U4.

Regardless of the enclosure you se-lect, you will need to drill holes formounting the three switches andthree BNC connectors. You will alsoneed to drill openings for the displayand the three LED's. Once that is done,mount the switches and connectorssecurely to the case and wire them tothe appropriate points on the boardusing 5 -inch lengths of stranded wire.Connect a 9V battery clip to the B1terminals; be sure to observe properpolarity. Attach a battery to the bat-tery clip, lay the board on the mount-ing posts, and put the face plate inplace and screw it down. Label theswitches, LED's, and connectors, andyou are done. Now is the time to per-form the final wiring inspection.Check it out carefully before you blowit out.

Using the Frequency Counter. Thefrequency counter is a cinch to use;the only thing you need to be carefulof is which input you use. If you haveany doubts about what kind of signalyou are going to be testing, then usethe rectifying input. The only time thatyou should use the unbuffered input iswhen you know you are working withTTL or 5 -volt CMOS circuits. TheICM7224 has a certain degree of in-put -protection circuitry, but you canfry it if you try hard enough.

If you are using too low a range,then the over -range indicator willflash at you. Switch to a higher range.

Notice that although the display isonly four digits, the ranging feature ofthe counter can give you up to eightdigits of precision. Say, for example,the frequency you are measuring is10.018763 MHz. In the "MHz" range,you will read "10.01" on the display;then switch to the "Hz" range, and youwill read "8763", with an overflow in-dication. That way, you can achievethe same degree of precision as youwould with an 8 -digit display.

rYou can Build Gadgets!Here are 3 reasons why!

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n BP349-I-1 PRACTICAL OPTO-

ELECTRONIC

PROJECTS $5.95If you shun opto-elec-tronic projects for lack ofknowledge, this is thebook for you. A bit of in-troductory theory comesfirst and then a numberof practical projectswhich utilize a range of opto devices, from a fil-ament bulb to modern infrared sensors and emit-ters-all are easy to build.

Practical ElectronicMusic Projects

PracticalOpto-Electronlc

Projects

BP363-I-I PRACTICAL

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MUSIC PROJECTS$5.95

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Mail to:

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30

FMSTEREO

TRANSMITTERBuild this inexpensive gadget and becomea local disc jockey, or just do away with

excessive wiring around the house.

Would you like to be able tosend good -audio -qualityFM transmissions? Here is a

device that will let you do Just that. It iscalled the FM Stereo Transmitter, andit is definitely not a toy. With the properchoice of antenna, the Transmittercan broadcast up to a quarter of amile, or more, with left and right chan-nel separation.

You can use the unit to transmit yourtape -deck or CD -player outputthroughout your house or yard, oreven to a nearby car. The transmissioncan then be received on any broad-cast -band FM radio.

Because the Transmitter broadcastsin stereo, it can be used for two -chan-nel experiments and demonstrations.It uses from 3- to 15 -volts DC power,has a crystal -controlled subcarrier forfrequency stability, and can be built totransmit anywhere in the standard88- 108 MHz, FM -broadcast band.

However, there is one caution youmust observe: You cannot interferewith anyone else's broadcast FM re-ception. See the "Frequency RangeSelection" box for more on that restric-tion.

Circuit Description. Figure 1 showsthe schematic of the FM Stereo Trans-mitter. The heart of the unit is L11, a

BA -1404 FM stereo -transmitter IC. Ablock diagram of the BA -1404 IC isshown in Fig. 2, Internally, the chip ac-cepts separate left and right audio -

POWERratik

input signals, and contains all the cir-cuitry needed to create and transmita multiplexed FM -Stereo signal on theFM -broadcast band.

The aforementioned FM signal con-sists of a main audio channel, whichcontains the combined left- andright -channel (L + R) audio informa-tion; a 19 -kHz pilot subcarrier; and thedifference -signal (L R) sidebands,which are centered around a sup-pressed 38 -kHz stereo subcarrier. Thatcomplete signal can be processedand demodulated by any FM -broad-cast receiver. Monaural FM receiversreproduce left- and right -audio sig-nals together through a single speak-er (no stereo). Stereo FM receiversseparate left and right audio to indi-vidual speakers for the stereo effect,or to provide two 'channels" on thesame FM carrier.

Now, back to the Fig. 1 schematic.The left and right audio signals are fed

WARNING!!

The publisher makes no representa-tions as to the legality of constructingandor using the FM Stereo Transmitterreferred to in this article_ The con-struction and.or use of the transmitterdescribed in this article may violatefederal and:or state law Readers areadvised to obtain independent adviceas to the propriety of its constructionand the use thereof based upon theirindividual circumstances and jurisdic-tion

BY

FRED BLECHMAN

RAMSEY ELECTRONICS

STEREO TRANSMITTER

Into jacks J1 and J2. Those signal levelscan range from the type that feedsmall speakers or earphones, to theline -level outputs normally fed to am-plifiers. If you wish to use a micro-phone, however, you'll need to boostits output voltage with a pre -amplifier.

Because the input voltages cancover a broad range, potentiometersR1 and R4, together with resistors R3and R6, and capacitors C1, C2, C4,and C5, are used to control the volt-ages at pin 18 and pin 1 of U1. Thatprevents overloading. The pre -em-phasis characteristic (U.S. or Euro-pean) is set by the values of R3 and R6,as described later.

The 3 to 15 volts of required powercan be provided by either a battery(B1 shown in Fig. 1 Is a 9 -volt battery) ora well -filtered power supply. Silicon di-odes D1-D3 are forward -biased in se-ries, with a voltage drop of about 0.7volts each, to provide a stable voltageof about 2.1 volts to power U1.

Potentiometer R7 permits the ad-justment of the stereo balance. Crys-tal XTAL1, together with 07, C10, andU1's internal components, provide the38 -kHz subcarrier oscillator needed tocarry the (L - R) sideband signals.Tunable inductor L1 and capacitorC16 form a resonant circuit to deter-mine the operating frequency of Ul'soscillator section. The value of 016 de-termines the frequency adjustmentrange within the FM -broadcast band,as specified later.

15

-018%.001 C20

001iC6

11

.001L1C16'

33pF.11µH4

10

U1

BA -1404

C1510pF

C1410pF

=Z.

5C7 1.

10pF

D3 D2 D11N914 1N914 1N914

611 I/ 14

INPUT 1

,-... .-..

C47109".

ti) .1.R7

LEFT ,._,, RIGHT 100KJ2 kiI) 1.!!, J1 BALA19.L.,

R3'75K

C210

1816 17

1+

C1

001 C310

2

C810pF

)(TALI38 kHz

G9

220pr

13 14

R114.7K

R12150K

1.-- C11

12

4ANR8

4700

C10.001

R13A 2700

C12.001

'SEE TEXT

-2-0 0

C17.001

2700R9

R1010K91.0

C21.001

IC

B1

9V

ANTI

C13.001

J3(TO

EXTERNALANTENNA)

Fig. 1. At the heart of the schematic for the FM Stereo Transmitter is the BA -I404 FM stereo -transmitter IC. Note that there is no R2or R5 in the circuit.

RIGHTCHANNEL L/R

INPUT BALANCE

18 117

RIGHTCHANNEL

AMPLIFIER

+DC

116

BALANCE

LEFTCHANNEL

AMPLIFIER

OUTPUTBUFFER

STEREOMULTIPLEX

GND0

13 12

BA -1404

DIVIDEBY

BUFFER

38 kHz OSCILLATOR

BIAS

11 10

N/C

OSCILLATORAND

MODULATOR

RFAMPLIFIER

GND

1

LEFTCHANNEL

INPUT

7

RFOUTPUT

Fig. 2. The overall simplicity of the FM Stereo Transmitter is made possible by themany internal functions performed by the BA -1404 IC, which are shown in this blockdiagram.

VHF transistor Q1 and its associatedcomponents amplify the RF output atpin 7 of U1, feeding either telescopingantenna ANTI, or an external antennajack at J3. That RF signal is modulatedby three signals from Ut the stereo -

multiplex signal at pin 14, the 19 -kHzpilot tone at pin 13, and the oscillatorand modulator signal at pin 12.

Construction. Portions of the Trans-mitter circuit operate at a relatively

high frequency. Therefore, if youhand -wire the circuit, you could runinto trouble with stray inductance andcapacitance. To avoid that, use theprinted -circuit template shown in Fig.3 to etch your own board.

If you don't feel like making yourown printed -circuit board, you couldorder an etched, drilled, and silk-screened PC -board from the sourcegiven in the Parts List. Other parts kitsavailable for the Transmitter are alsoavailable from the same source, asdetailed in the parts list.

The parts layout is shown in Fig. 4. Becareful to orient the diodes, transistor,and electrolytic capacitors as shown.The use of a socket for U1 is recom-mended.

You must make two choices alongthe way regarding certain capacitorsand resistors. First, you must decidewhat portion of the FM -broadcastband you wish to use; that's becausethe Transmitter is only tunable overabout one-third of the entire band.See the "Frequency Range Selection"box for help in making the proper se-lection.

Capacitor C16 sets the frequencyrange of the FM Stereo Transmitter. Totransmit at approximately 88-95 MHz, 31

use a 33-pF capacitor for C16; for95 -102 -MHz transmission, use a 27-pF capacitor; and for 102-108 MHz,use a 22-pF capacitor. If you are notsure in which part of the FM band totransmit, solder a "trial" C16 with somelead length to spare. That way youcan desolder the capacitor and re-place it with one of another appropri-ate value.

The second choice you need tomake is to decide what pre -emphasisvalue you want. Pre -emphasis is atechnique used in FM transmitters toincrease the high -frequency signal-to-noise ratio. If you want the pre -em-phasis to be 75 microseconds (asused in North America and Japan),use 75K resistors for R3 and R6. If youwant the pre -emphasis to be 50 mi-croseconds (as used in Europe, Russia,and in some other countries), use 47Kresistors for R3 and R6.

Some Options. Because the Trans-mitter consumes power and emits RFwhenever it is on, a visual "on the air"indicator is a useful addition. Simplyconnect an LED in series with a 1K re-sistor between one of the positive DCterminals of the switch and a groundpoint in the circuit; the cathode of theLED should be connected to the latter.When power switch S1 is on, the LEDshould light. If it doesn't, you either

0

fl

RAMSEY ELECTRONICS

© 1993 FM -10A Rev D

4 -INCHES

Fig. 3. The foil pattern for the Transmitter's PC -board is shown here.

PARTS LIST FOR THE FM STEREO TRANSMITTER

SEMICONDUCTORSU1 -BA -1404 FM stereo transmitter.

integrated circuit*Q1-2SC2498, 2SC2570, or 2N5179

low -noise VHF/UHF NPNtransistor*

Dl, D2, D3 -1N914 or IN4148silicon diode

RESISTORS(All fixed resistors are 1/4 -watt. 5%

units.)RI. R4 -1000 -ohm trimmer

potentiometer*R2. R5 -not usedR3, R6 -75,000 -ohm or 47,000 -ohm

(see text)R7 -100,000 -ohm trimmer

potentiometer*R8 -470 -ohmR9, R13 -270 -ohmR10 -10,000 -ohmRII-4700-ohmR12 -150,000 -ohm

CAPACITORSCI, C4. C6, C10, C12, C13, C17,

32

C18, C20, C21 -0.001 -p -F,ceramic -disc

C2, C3, C5, C11 -10-g, I6-WVDC,electrolytic

C7. C8, C14, C15-10-pF, ceramic -disc

C9-220-pF, ceramic -discCI6-22-, 27-, or 33-pF. ceramic -

disc (see text)C19-470-p.F. 16-WVDC,

electrolytic


ANTI -4- to 19 -inch telescopingantenna

L1-0.11-p.H, shielded adjustableinductor*

XTALI-38-kHz crystal, watchcrystal package*

ii, J2, J3 -RCA -type PC -mountedjacks*

BI -9 -volt alkaline battery (or other3--I5-volt DC power source)

SI-SPST pushbutton switch,normally open, PC -mounted*

Printed -circuit materials, enclosure.

18 -pin socket for UP. solder.hardware, etc.

Note: The following items areavailable from Ramsey Electronics,Inc. (793 Canning Parkway, Victor,NY 14564, Order Tel.800-446-2295, Information Tel.716-924-4560. Fax: 716-924-4555):A complete kit for the FM StereoTransmitter (FM-I0ABP).including the printed -circuit board(but not the custom case orantenna) -$34.95; an etched anddrilled, silk-screened printed -circuit board (FM-10APCBP)-$10.00: a "Special Parts Kit"(FM-IOASPKBP) containing allparts marked * above -524.95; acustom case complete with knoband antenna (CFM-BP)--$14.95; a110VAC power adapter (FMAC-BP)--$9.95. Postage/handling/insurance per order is $4.95.Please add an additional $3 fororders under $20. New Yorkresidents please add 7% sales tax.

ANTENNA CONSIDERATIONS

0211

I R3

11

C1 1

C19+C19

B11

Ti

C11I -C9-C1

1

0

D1-4-

132-14- R7

D3 -44-

C5

I ca1 R6

CI1

1

R11

I

R1I 2I

C161

111

J1 = J2

1 1

C6 C81

C7

L1XTAL1

L1

C15

I C18C14 R13 1

C121

S1

-R8-

C20

ANTI

C17 I

1 R3

C21

-R10-a1

CI13

Fig. 4. Use this parts -placement diagram as a guide when mounting components onthe board. Before soldering the polarized components, check to make sure theirorientations match the ones shown here.

The assembled circuit board is shown here. Note the addition of an LED and a 1Kresistor in series, which act as a power indicator (see text).

FCC Part -15 Rules specify a max-imum field strength for an unlicensed.FM -broadcast device -- 250 microvoltsat a one -meter -long receiving antennalocated 3 meters (9.94 feet) from thetransmitter. That field strength is inver-sely proportional to distance (at twicethe distance, the field strength ishalved) Therefore. at 384 meters (1260feet --almost a quarter of a mile). theallowable signa! is 1 95 microvolts.which is still strong enough to be pickedup by an average stereo FM receiver Asensitive' receiver responds to a sl gnat

as small as 0 5 microvolts!Note that the FCC Rules do not spec-

ify the power output of the transmitter ---only the field strength at the receivingantenna Because it is possibie to cou-ple an amplifier and high -gain antennato your FM Stereo Transmitter. you couldinadvertentiy exceed FCC limitations

Unless you have a means of measur-ing field strength at those low levels. thebest way to stay within the FCC -allowedfield strength is to use the 19 -inch tele-scoping antenna provided with thecustom cabinet kit. or one like it. Thatantenna will give you a horizontally non -directional signal.

For a more directional signal. use ahorizontally mounted dipole antenna(each half of the antenna should beabout 30 inches). plugged into J3, in-stead of using a telescoping antenna.When mounted horizontally. the max-imum radiated signal of a dipole is per-pendicular to the direction of the wire. anorth -south antenna will have maximumradiation to the east and west

have the LED connected backwards,or to the wrong points in the circuit.

A custom, two-part plastic case,with front and back panels and aknob for the switch, is available fromthe source in the Parts List. Use of thecustom cabinet enhances the ap-pearance of your Transmitter, whileprotecting its circuitry.

The custom cabinet also comeswith a telescoping "whip" antennathat opens to a length of 19 inches.Except for the antenna hole (and LEDhole, if you use one), all other holes inthe cabinet are drilled, and silk-screened with the appropriate leg-ends. If you do not use the customcabinet, you will still need to get somekind of antenna. See the "AntennaConsiderations" box for suggestions.

Audio Sources. The FM Stereo Trans-mitter can accommodate a fairlybroad range of audio sources at its J1(right) and J2 (left) inputs, but the in - 33

34

put -voltage levels must fall within rea-sonable limits. For example, amicrophone by itself does not put outenough voltage, so a pre -amplifier oran amplified mike mixer is necessary.The same applies to many recordplayers.

The recommended inputs for theTransmitter are the line -level outputsof a stereo device, but many don'thave those outputs. So instead, youcan use the earphone or speaker out-put of a small radio, tape player, or CDplayer. However, be careful not to usethe speaker output of a powerful Hi-Fisystem as direct input to the Transmit-ter jacks. Using that output, or anyother audio level that is too high, willresult in a terribly distorted sound. Ifyou suspect an audio source is toopowerful, you can use an attenuatingdubbing cord, an attenuating con-nector, or a similar device to drop theoutput to an appropriate level.

Shielded audio cables should beused for the interconnections. De -

THE COLLECTED WORKS OFMOHAMMED ULLYSES FIPS

#166-By Hugo Gernsback.Here is a collection of 21 April 9941Fools Articles, reprinted from oft" 1 "rt.the pages of the magazinesthey appeared in, as a 74 -page, 84 x 11 -inch book.The stories were written be- rn9,4tween 1933 and 1964. Some jMof the devices actually existtoday. Others are just around the corner. Allare fun and almost possible. Stories include theCordless Radio Iron, The Visi-Talkie, Electron-ic Razor, 30 -Day LP Record, Teleyeglasses andeven Electronic Brain Servicing. Get your copytoday. Ask for book #166 and include $16.00(Includes shipping and handling) in the USand Canada, and order from CLAGGK Inc.,P.O. Box 4099, Farmingdale, NY 11735-0793.Payment in US funds by US bank check or In-ternational Money Order. Allow 6-8 weeks fordelivery. MA05

THE TRANSDUCERPROJECT BOOK

1992T-From TAB Books. Aunique collection of practicaltransducer devices that youcan put together simply andinexpensively. You can builda seismic sensor, a tempera-ture survey meter, an open-door annunciator, a moisturedetector, an automatic night

light, and more. To order-ask for book 1992T,and include your check for $11.95 (includess&h) in the US and Canada, and order from -Electronic Technology Today Inc., P.O. Box240, Massapequa Park, NY 11762-0240. USfunds only: use US bank check or Internationalmoney order. Allow 6-8 weeks for delivery.

MA06

FREQUENCY RANGE SELECTION

When deciding what frequency totransmit on, choose one that is notbeing used by an FM -broadcast stationthat can be received in your location. Inorder to comply with Federal Communi-cations Commission (FCC) Part 15 reg-ulations. it is your responsibility todetermine fully that your operation willnot cause interference to broadcast re-ception.

It is not sufficient to search for anapparently open frequency using a sim-ple FM portable radio. Many mediumpower. National Public Radio stationsmight be received by a neighbor with agood receiver and an outdoor antenna.Interfering with such reception is a di-rect violation of Federal law'

The most reliable way of finding atruly open frequency on the FM band isto check that band with a very good FMreceiving system that uses an externalantenna If you don't have access tosuch a radio. most modern. FM car radi-os are also very sensitive.

When choosing an operating fre-quency. remember that most digital -tuned FM receivers. --regardless ofwhether they are portable. mobile, or hi-fi --are designed to tune in 200 -kHz in-crements. Therefore. they might notproperly receive a signal operating be-tween those pre -tuned. standardbroadcasting frequencies.

Unlicensed operation of small trans-mitting devices is discussed in Part 15of the FCC Rules Licensed. FM -broad-cast stations have the right to inter-ference -free broadcasting. and theirlisteners have the right to interference -free reception. Make sure you are notinterfering with those rights when youuse your Transmitter.

pending on the cable terminations,you might need adapters for themany types of plugs and jacks incommon use. Those are readily avail-able at Radio Shack and elsewhere.

Note that you can use two entirelydifferent audio sources-such as theoutputs of a tape player and a CDplayer-as inputs to the FM StereoTransmitter. Remember, the Transmit-ter has both a left and right channel,and an FM receiver will receive themboth. On a stereo FM receiver, oneinput is heard on the right speakerand the other on the left speaker. Thestereo's balance control can be usedto mix or separate them.

Checkout and Use. You'll need anearby stereo FM radio to adjust yourtransmitting frequency and balance.Tune the radio to a suitable "open"

frequency that will not interfere withany broadcast stations (see the "Fre-quency Range Selection" box). Witheither the telescoping or external an-tenna connected, turn on the FM Ster-eo Transmitter. Then use a plastic (notmetal) alignment tool to adjust induc-tor L1 while listening for a quieting inthe FM radio's normal backgroundnoise. Maximum quieting indicatesyou are transmitting on the receiver'sfrequency.

Adjust audio -level potentiometersR1 and R4 to their minimum level (fullycounterclockwise) and set balancecontrol R7 to the center position. Con-nect your audio sources to jacks J1(right) and J2 (left). Advance R1 andR4 and you should begin to hear theaudio on your stereo FM receiver. Youmight also have to increase the vol-ume setting on your receiver.

When you have sufficient volumeon each "channel" (left and right), ad-just R7 all the way clockwise. Youshould only be able to receive onechannel. Turning R7 all the way coun-terclockwise should enable you to re-ceive only the other channel. Tobalance the audio, set R7 so that bothchannels can be received equally.

Troubleshooting. When operatingwith a fresh 9 -volt alkaline battery,and without audio input, your Trans-mitter should draw about 32 milliam-peres (about 37 milliamperes if you'veadded an LED power indicator). Youcan measure that with a milliammeterin series with the battery. If your Trans-mitter deviates more than 20% fromthat figure, you might have made anerror in assembly.

If you think you have made an error,use Fig. 4 to double-check the place-ment and orientation of all compo-nents. Also, check all solder joints andcable connections.

If you can not get your Transmitter totransmit, check first to see if your audiosources are operating. If they are,then make sure you're tuning the cor-rect portion of the broadcast band,based on the value you used for C16.That could be the problem, and youmight end up unintentionally interfer-ing with broadcast transmissions inanother portion of the FM band. Fre-quency drift (caused by a weak bat-tery or temperature extremes) canalso cause you to broadcast out of theanticipated broadcast band.

Glowing gas -discharge tubeswere among the first elec-tronic wonders. In the pas-,

they were used as voltage regulatorsin tube circuits. However, even thoughgas -discharge tubes are still one ofthe easiest ways to regulate voltageshigher than 75 volts, they are rarelyapplied to that task anymore.

What's a good use for a glowingtube? Well, because it is a source offaint light, a voltage -regulating gas -discharge tube makes a great night -light. With just one of the tubes (whichyou can pick up on the antique -tubemarket for a buck or two), a couple ofmirrors, and a few other components,you can build the Novel Nightlight, atruly unique project for the elec-tronics -oriented household.

Voltage -Regulator Tubes. Voltage -regulator (VR) tubes are diodes; theyhave a plate and a cold cathode (i.e.one without a filament). During themanufacture of a VR tube, air is re-moved from the tube and the glassenvelope is filled with small quantitiesof helium, neon, argon, or other gasesat very low pressure. When enoughvoltage is placed between the plate

BY LARRY LISLE, K9KZT

Build this unusual nightlightin an evening or two, usingan old, gas filled voltage -

regulator tube.

and the cathode, the tube glows.Let's take a look at how the tubes

work. A typical circuit using a VR tubes shown in Fig. 1. As long as the currentthrough the tube is kept within themanufacturer's ratings (typically 5 to40 mA), the voltage at E2 will changevery little, despite variations in supply -voltage E., or in the load current.

The above circuit only as one re-sistor, R1 To find the value of that re-sistor in ohms, use:

R1 = (E1 - E2)/In

where Imax is the maximum tube cur-rent.

AS you can see, the operation of aVR tube s simple. However, for this

NovelNightlight

project we won't be using it to regu-late voltages. We just want to makethe tube glow!

The Circuit. Figure 2 shows the cir-cuit of the Novel Nightlight. It'sbasically a transformerless, half -wavepower supply that puts out enoughvoltcge to keep V1, the 0A3NR75 VRtube, glowing. Because the circuit hasno transformer, Vs absolutely neces-sary for safety that all conductors beenclosed in insulated material!

In the event o' component failure,fuse Fl will blow and interrupt the cur-rent flow. Resisto! R1 limits the currentthrough diode, D1, which rectifies theAC; capacitor C1 smoothes out thepulsctions. The function of resistor R2isn't immediately obvious but it is im-portant. If R2 wasn't ir the circuit, un-plugging the nightlight would causethe voltage ir C1 to dischargethrough R3 anc V1. However, whenthe voltage dropped below 75 volts,V1would go out and the 75 volts in thetube would just st there waiting to zapsomeone. Even with a "bleeder" re-sisto' like R2, it's always a good idea toshort power -supply capacitors withan insulated screwdriver after unplug -

35

Fig. I. This is the basic circuit for usinga gas -discharge tube as a voltageregulator. In the nightlight project,however, we just want to make the tubeglow!

Fl

vl0A3NR75

Fig. 2. The circuit for the NovelNightlight is basically a transformerless,half -wave power supply that providesenough DC to light up VI, the voltage -regulator tube.

PARTS LIST FOR THENOVEL NIGHTLIGHT

Dl -1N5408 silicon rectifier diodeR1 -100 -ohm. 1 -watt resistorR2 -47,000 -ohm, 2 -watt resistorR3 -2000 -ohm, 5 -watt resistorC1 -20 -p -F, 250-WVDC, electrolytic

capacitorV1-0A3/VR75 voltage -regulator

tubeF1 -1/4 -amp, fast -acting fuse73/4 -inch square baseboard, 7 -inch

square pieces of glass (2), 7 -inchsquare pieces of mirror (2). 71/4 -inch square piece of glass. rubbermounting feet (4), molding strips(8), power cord and plug, octalrelay socket for tube (Potter &Brumfield 27E122 or equiv.),Fahnestock clips, fuse holder,epoxy glue. wire, solder, etc.

0zging the circuit and before touching

V2 anything.

8 Construction. The method of wiringN used to build the nightlight isn't crit-

ical. For the prototype, Fahnestock2 clips and some of the unused tube -hi socket terminals were used to makeWI connections. If you do the same, beut) aware that pins 7 and 3 of the 0A3/cr)cn VR75 are connected internally.

The circuit should be mounted on au- wood baseboard. In the prototype,

that measures 73/4 x 73/4 inches. Drill ahole in one corner of the board for the

36 power cord to go through, but make

Fig. 3. Here is an exploded view of the nightlight-case assembly. The molding stripshold the pieces of glass and the mirrors together once they are glued. Note the 45°angles on the top molding which allow for a tight fit.

sure to tie a knot in the cord beforeinserting it, as that prevents strain onthe wiring. To keep the unit from wob-bling, attach four rubber feet on thebottom of the baseboard.

There are a few ways to adjust thebrightness of the Novel Nightlight. Firstof all, you can change the value of R3.However, keep in mind that the cur-rent shouldn't exceed 40 mA (with thevalues shown in Fig. 2, it's about 31 mA).Also, other voltage -regulator tubescan be used instead, even though the0A3NR75 was the brightest of the sev-eral that I tried. For a little variety, youcould also add flashing neon bulbswith a capacitor and resistor for each,or an old mercury-vapor rectifier suchas an 866.

Because of the high voltages pres-ent in the nightlight and the fact thatthe tube will get hot, once you havethe circuit working, you should place itin some kind of enclosure or cover. Aninverted food -preserving jar, an oldaquarium, or a Plexiglas enclosurecan be used. In the author's pro-totype, the enclosure was built as a 7 -inch -on -a -side glass and mirror box(see Fig. 3). Two of the sides weremade of mirror squares, so that whenthe unit is assembled and viewed atan angle, it looks as if there are fourglowing tubes.

To duplicate the enclosure shown inFig. 3, you will need two glass squaresand two mirror squares, measuring 7

(Continued on page 104)

WWV RECEIVER

Next to the crystal detector andsuper -regenerative receivers,the direct -conversion receiver

is the simplest radio that any experi-menter can build. Despite its beingimmune to spurious IF signals, whichplague super -heterodyne receivers,the direct -conversion receiver hasbeen shunned in the past because ofcomponent limitations that make first -try receivers sensitive to 60 -Hz hum,mIcrophonics, and low -frequencynoise generated by active compo-nents. But ever -evolving electronicstechnology has produced low -noise/low -power amplifiers and mechan-ically stable components that prom-ise to revive the direct -conversionreceiver. Low -power active elementsalloW battery operation, significantlyimproving 60 -Hz suppression.

The WWV Receiver described in thisarticle (which contains only onetuned circuit) is comprised of readilyavailable parts and its operating fre-quency can be easily modified, al-lowing you to monitor other signals.

WWV/WWVH Broadcasts. Radiostations WWV (Fort Collins, CO) andWWVH (Kauai, HI), operated by theNational Institute of Standards andTechnology (NIST), broadcast vastamounts of information 24 hours aday. The most obvious are the fre-quency standards of the carrier (2.5,5, 10, 15, and 20 MHz), the 1 -secondtime interval, and the standard audiotones (440, 500, and 600 Hz), whichmodulate the carrier at regular inter-vals.

Voice announcements, broadcastat one -minute intervals, give the timeof day based on a cesium clock andexpressed in "Coordinated UniversalTime" (UTC). The radio stations areidentified by voice on the half hour

WWVReceiver

Get time, weather, frequency, and otherinformation with this easy -to -build receiver.

BY BRIAN MCKEAN

and the hour, and continuouslyvia au-dio tones, WWV transmits 500 Hz oneven minutes while WWVH transmits600 Hz on even minutes. The 5-, 10-,and 15 -MHz carriers operate at 10 kWmaking them easily audible through-out the continental US.

Special voice announcements,providing Global Positioning Satellitestatus, Geophysical data, OMEGAnavigation system status, and Pacificand Atlantic storm warnings, arebroadcast in regular time slots.

Those stations also broadcast thetime of day, day of year, year, daylightsaving's time status, leap second sta-tus, and UTC to UT1 conversion in adigital format. The digital code istransmitted at a rate of 1 -bit -per -sec-ond on a 100 -Hz subcarrier that ispulsed on and off, with the duration ofthe pulse representing the bit value"1" or "0" at the beginning of eachsecond. The 100 -Hz subcarrier is typ-ically below the bandwidth providedby commercial shortwave receivers,so the pulses are not audible.

The direct conversion receiver doesnot have a high cutoff frequency onthe HPF so the 100 -Hz pulses will beclearly audible on the direct -con-version receiver described in this arti-cle. Although intended for digitaldecoding, the low bit rate allows theBCD code to be decoded by ear witha little practice and a strong signal.

The most useful data transmitted bythe NIST stations are the frequencystandards. Those carriers allow world-wide frequency calibration to an ac-curacy of 1 ppm. The directconversion receiver can serve in asecondary capacity as a 10 -MHz, lo-cal -frequency standard since the lo-cal oscillator must be zero beat for

best reception. The voltage -stabilizedcrystal oscillator will allow the receiverto maintain its calibration under vary-ing conditions.

Shortwave listeners will find thegeophysical alert messages useful incorrelating radio propagation condi-tions with solar activity and geomag-netic field disturbances. The NISTsignals themselves provide direct in-formation on band conditions. Poorreception in an otherwise good local -reception time period is usually in-dicative of some geophysical distur-bance, which will be noted in the alertmessage. The geophysical bulletins(18 minutes after the hour for WWVand 45 minutes after the hour forWWVH) provide a daily summary ofpast 24 -hour's solar and geomag-netic -field activity with 3 -hour up-dates of current geomagnetic fieldconditions.

The solar -flux measurement is ameasure of the solar emission at 2800MHz, and is related to the solar con-stant, which is a measure of the totalsolar flux at the Earth. Solar flux is re-sponsible for ionizing the upper atmo-sphere and, as such, affects long-distance high -frequency communi-cations, which rely on ionospherepropagation modes.

The "A" and "K" indices in the mes-sage provide information on geo-magnetic -field activity. The "K" index ismeasured at 3 -hour intervals, and the"A" index is derived by taking theweighted average of the K index for a24 hour period. From 0 UT to 2100 UT,the "A" index represents the previousday's measure. Between 2100 and2400 UT, the "A" index is estimatedfrom the 7 "K" indices for that day. The"A" index is finally produced at 2400 UTand remains unchanged until 2100the following day. 37

ANTI

E RF AMPLIFIER+9V

20-100pF

C10.01

EARTH//7777 CHASSIS

GROUND

T1* 032N2222

R8C.0113 I 100K

R747012

C1401

LOCALOSCILLATOR

XTAL110MHz C3

360pF C533pF

R24.7K

C601

+9V

R1 01 = R4100K 100K2N2222

C215pF

C1 C47-` 20-100pF 56pF

L*SEE TEXT

R31.5K

T2*

C16

MIXER 100 C17.1

D1

1N34

101

AUDIO AMPLIFIER

+9VSOURCE

C18.001

D21N34

R910K

METALSHIELD

2U1 -a

cYo--1-11819V

C 9.47

1/2 CA3240

44.M.R11

270K

I( 1/2 CA3240

11-b 7

R15180KAM

C20680pF

R0K

10K

10 C24R14(001

C21 -+

R1622K

47

C22 D3 R13.1 '..... ,.... 1N4729 4700

A 3.6VZENER

LM386

3

Fig. I. The single balanced -diode mixer used in the WWV Receiver comprises T2, DIand D2. The LO amplitude must be sufficient to forward bias the diodes.

5 INCHES

- C23T .1

+9V

7 C9100

C2547

Fig. 2. The (loth m's prototype wris as.sembled on a small printed -circuit board.measuring abou 5 hr 21/2 inches, and /.s shown here on a I:I .scale.

Geomagnetic -field activity is de- are selected based on the current "K" surements of peak X-ray emissionsscribed in broad terms such as "quiet," and "A" indices. Solar activity de- from a flare event.

38 "unsettled," "minor storm," etc., which scribes the solar -flare activity by mea- Note: Further information regarding

ANTINIST broadcasts can be obtained bywriting to: National Institute of Stan-dards and Technology, Radio StationVVWV, 2000 East County Road, FortCollins, CO 80524. Ask for NIST pub-lication SP 432.

Circuit Detail. Figure 1 shows a sche-matic diagram of the WWV Receiver.Incoming RF is picked by the antenna(ANTI) and is coupled via an auto -transformer to a grounded -base am-plifier (Q3). before being applied to adiode -mixer network that is com-prised of T2, D1, and, D2. Best mixerperformance is obtained when bothsecondary windings of T2 are identi-cal, and D1 and D2 are matched.

The output of the local oscillator(L0) --a grounded -collector Colpittsoscillator (built around Q1) --is ap-plied to emitter-follower/buffer Q2,which provides a low impedancedrive signal for the mixer.

The demodulated signal is coupledto a pair of high gain op -amp stages(U1 -a and U1 -b). The op -amps providea 50 -dB gain and incorporate low-pass filter capacitors in the feedbackpath. Amplifier U2 provides a 20 -dBgain, thereby producing sufficientoutput drive for an 8 -ohm speaker, or32 -ohm headphones.

Note that our receiver lacks a vol-ume control and AGC circuitry. Thatsimplifies the circuit without introduc-ing operational problems. The vol-ume is controlled merely by adjustingthe length of the whip antenna.

When driving 32 -ohm headphones,the circuit consumes less than 25 mA;however, the current drain increasesto 40 mA when driving an 8 -ohmspeaker. That current drain is close tothe limit of 9 -volt alkaline batteries, soheadphone operation is preferred,especially under weak -signal condi-tions.

Assembly. The WWV Receiver wasassembled on a printed -circuitboard, measuring about 5 by 21/2inches. A template of the author'sprinted -circuit layout is shown in Fig. 2.The parts -placement diagram for theauthors layout is shown in Fig. 3. All theparts except power switch S1, battery81, speaker SPKR1, and antenna ANTIare located on the board.

The crystal can be any of a numberof physical sizes (note that the boardlayout is designed to accommodate

-C19-

C24

R15 R12R14

C23

D2

-C18- D1

R11--HI--

R1

I

0 19C17

C20 IU1

JL

1.2*

-R13- + C21

C5 U2

R16 -C9-+11.

J1

1=T

C22

C16

SHIELDED 1-11--1 4E -C'CABLE 9V S1

SPKR1

Fig. 3. All the parts that comprise the WWVswitch, the antenna, and the headphone jack)board. A metal shield (see text for details) isto isolate the RF input section from the local

EARTH/CHASSISGROUND

_R7_ _R8 _ C13 C10

-C14- CI

C8

IR5 R2

di7

D(;)

cl3XTAL1

ip -M-64

-C11-C12

SHIELD

'SEE TEXT

Receiver (except the battery, the powerare mounted directly to the circuit

added to the board at the position shownoscillator.

PARTS LIST FOR THE

SEMICONDUCTORS1i-C,A3240, 11A3-5152,

11A7-5222, or similar, dual op -amp. integrated circuit

U2--l.M386 low -voltage, audio -power amplifier, integrated circuit

QI-Q3-2N2222. 2N3904, orsimilar general-purpose NPNsilicon transistor

DI, 1)2-IN34 germanium orNTEII2 Schottky. small -signaldiode

D3--IN4729, or similar 3.6 -volt, 1 -

watt lener diode

RESISTORS(All resistors are Vi -watt. 5( units,

unless when.% ise noted.)RI. R4. R8 -100,000 -ohmR2 -4700 -ohmR3. R5, R6 -1500 -ohmR7, R13 -470 -ohmR1). RIO. R12. R14 -10,0(X) -ohmRI 1 -270.000 -ohmRI5-180,000-ohmR16--22,000-ohm

CAPACITORSCI, C11-20- to 100-pF ceramic or

mica trimmer ( Mouser242-3610-1(X) or equivalent)

C2-15-pE mica or ceramic -discC3-360-pF mica or ceramic -discC4--56-pE mica or ceramic -disc

WWV RECEIVER

C5-33-pF mica or ceramic -discC6, C7. CIO, C13, C14 0.01-µF,

ceramic -discC8. C18. C24 -0.001-µF. ceramic -

discC9, C16 -100-µ,F. 16-WVDC,

electrolyticC12-47-pF mica or ceramic -discC15-Not usedC19-0.47-p.F, polystyrene,

mylar, or multilayer ceramicC17. C22, C23 -0.1-1.1.F. ceramic

discC20-680-pF mica or ceramic discC21. C25 -47-µF. 10-Vv'VDC,

electrolyticADDITIONAL PARTS AND

MATERIALSANTI -50- to 100 -cm telescoping

antenna11-Closed circuit 1/4 -inch headphone

jackSPKR1-8- to 32 -ohm, 0.5 -watt or

less, speakerSI-SPST power switchB1 -9 -volt alkaline, transistor -radio

batteryT1, T2-See textXTAL1-10-MI-li, 30-pF crystalPrinted -circuit materials, metal

enclosure, metal shield material(see text), headphone (32 ohm),battery holder and connector, wire,solder, hardware, etc.

39

ANTGND Q3

Component Notes. The crystal is

used in its parallel (anti -resonant)mode in the Colpitts oscillator. Paral-lel -mode crystals are specified for aparticular circuit load-capaci-tance-usually 20 to 40 pF-for the

101/2T crystal to oscillate on frequency. Ca-pacitors C1 and C2 provide seriescoupling to reduce the relativelylarge load capacitance of 01 and

271/2T

} 21/2T

0.5cm

Fig. 4. Transformer TI is a home-made unit comprised of 40 closely wound turnsof #26 AWG enameled wire on a 1/4 -inch diameter air -core form, with taps at 21/2and 101/2 turns from each end; after each tap, the winding continues in the same direction.

the most common crystal -packagesizes; the HC -49 and HC -33). To mini-mize microphonics-the generationof an electrical noise signal by me-chanical motion (vibration) of partswithin a device-after soldering XTAL1in place, secure it to the board withR1V or similar silicone cement.

Tuning capacitors C1 and C11should be installed with the tuningscrew connected to ground to allowuse of a metal tuning tool. The holesfor T1 are arranged for use with a 1/4 -inch diameter, plastic coil form with amolded base of the type commonlyfound in older 1V sets. The holes for T2are sized for a common subminiatureIF can. The leads of T2 should be cut asshort as possible and secured to mini-mize vibration.

Install a solderable-foil metal shield(approximately 1 -inch high) betweenthe local oscillator (01 and Q2) and RF

40 amplifier (Q3), as shown in Fig. 3. Sol-

der the shield to the ground traceusing short segments of stiff wire assupports. Once all of the board -mounted components have been in-stalled, connect the off -board com-ponents to the printed -circuit boardthough short lengths of hook-up wire.

Mount the whip antenna on theproposed case for the unit; if the an-tenna that you choose for your unithas a pivoting base, the unit can bemounted in just about any convenientlocation on the enclosure using a lowcapacitance mounting method; oryou can connect the antenna (ver-tically mounted) directly to the board.Many whip antennas are equippedwith a threaded base that can be se-cured directly to the appropriateprinted -circuit pads using a screw. Ifthat arrangement is used, use a largegrommet tc isolate the whip from themetal case where the antenna pass-es through.

A

B

A A'

0

0

B B'C c'

B'

Fig. 5. Construction details for T2 (themixer transformer) are shown here. Thediagram in A is a schematicrepresentation of the unit oncecompleted; B illustrates how the threelengths of wire are wound as a set on thebobbin; and C shows how the bobbin isconnected to the pinned base.

allow tuning the crystal frequency. Thetrimmer range specified for C1 shouldsatisfy most crystals. If you have noinformation about your crystal, try itanyway. The oscillator's operation canbe checked by any number of meth-ods, but the easiest way is to listen tothe receiver itself.

The mixer diodes should be small -(Continued on page 112)

Add a Switch to your Serial PortEnable or disable serial ports with a simple

flip of a switch!

Sometimes a simple solution to an annoying problem is staring youright in the face, although you don't even know it. You see, athome, I have a pretty loaded 486 PC that's used not only as a day-

to-day workhorse, but also as a test bed for various peripherals andaccessories for review in this magazine and other purposes. While settingup the software for a computer -controlled construction set I was review-ing, I had a tough time getting the COM2 serial port to work peacefullywith the set's interface. Using COM1 was out of the question, since it wasused by my serial mouse. So here I was with this presumably easy -to -useinterface unit that would not respond to COM2. What was going on?Could it be "the dreaded IRQ conflict?"

Now, I consider myself pretty goodat setting up computers; I'm just notvery good at remembering howthings are set up (or at rememberingwhere I put the piece of paper onwhich I jotted down the settings).Sometimes diagnostic software canbe used to find a conflict, or a pe-ripheral's setup program (if you arefortunate enough to have peripheralswhose IRQ's are set via software) cangive you the information you need.More often, however, you are left withone unpleasant task; opening thecase. Of course, if you are like me, it'snot that simple. First, all the junk piledon top of the case has to be moved.Then the case has to be opened.Then lots of cables have to be discon-nected so that lots of cards can beremoved so that lots of jumper set-tings can be noted.

After doing all of that, I found theproblem. My internal modem was seton COM2, and so my machine's multi -I/O card was set to disable its ownCOM2- -the one I was trying to use forthe construction set's serial -interfaceunit. The first solution was to simply en-able COM2 on the multi -I/O card; butthe situation got worse. Now, not onlywouldn't the serial interface respond,but the modem would no longer con-nect with any other modem-di-though it would dial out. Trying to getthe modem and mouse to share aninterrupt led to even more flakinesswith both the modem and the mouse.

So I set the moaem back to its origi-nal settings where it worked per-fectly. "Try another interrupt' you say.Let's see: IRQO is reserved for the sys-tem timer, IRQ1 is for the keyboard,IRQ2 is a DOS system area, the

MULTI -1/0JUMPER BLOCK

0

O

0

0

0

DISAB. ? ENAB. 0

0 O

o ooloo0 0 0 0 0 9 0 0

MODEMJUMPER BLOCK

3 4 5 7 1 2 3 4

IRO COM

DPDTSWITCH

Fig. I. This switching scheme allowedan internal modem and COM2 on amulti I/O card to share the sameinterrupt (1RQ). While it won't work asshown for every set-up, it can bemodified to handle similar problems.

MATERIALS LISTFOR THE

PC SWITCHDPDT switchWire -crimp single -pin header socketsWire, heat -shrink tubing. unused

expansion slot cover, solder,hardware, etc.

BY MARC SPIWAK

modem (COM2) uses IRQ3, themouse (COM1) uses IRQ4, my soundcard uses IRQ5, diskette drives useIRQ6, and the printer (LPT1) uses IRQ7.These settings are pretty much stan-dard-- -depending on your hardwareand software, it is unlikely you'd beable to configure any of these de-vices to more obscure settings. Ohhow I just love the flexibility of PC ar-chitecture!

That sort of problem has plaguedPC users starting with the first IBM PC'sright up to the present-day 486's. Evenon the newer local -bus systems,where the COM ports are often set inCMOS, a modem's settings still have tobe checked visually, or at leastthrough hard -to -find setup menus-

and changing settings usually re-quires that jumpers be moved man-ually. The odds are, in a loadedsystem, a game of musical jumpersusually forces you to return a card to itsoriginal settings because it workedproperty that way in the first place.Another solution, although often not avery good one, is disabling the least -significant device that's conflictingwith the most -significant device. That'swhat led me to having a disabledCOM2 on the multi -I/O card.

A Partial Solution. As it seemed,after many hours of experimenting,the only way to get the serial interfaceto work was to enable COM2 on themulti -I/O card and to either removethe modem from the computer or todisable it-which meant removing itfrom the machine anyway! At least Icould now work with the construction

(Continued on page 102) 41

42

BY RODRICK SEELY

With this headphoneguitar amplifier you canpractice your guitarplaying and prepare for arock n' roll career, allwithout waking up theneighbors.

HEADPHONE AMPLIFIERFOR YOUR GUITAR

Any electric -guitar playerknows about the high cost ofmusical equipment. To pur-

chase a small practice amp, one orIwo effects pedals, associated patchcords, and batteries and otherpower -supplies can cost at least afew hundred dollars. Not only is thatequipment bulky and expensive, butto make things worse for the buddingmusician, there's always someonewho doesn't appreciate a killer over-drive sound rattling the windows!

It's not easy becoming a rock 'n' rollsuperstar. However, with the Jam Pakheadphone guitar amplifier de-scribed in this article, you will find iteasier to practice. Simply plug in your"ax," put on the headphones, andcrank it up as loud as you like. You canjam anytime, anywhere, without dis-turbing your family or neighbors. Sim-ilar headphone amplifiers availablethrough music stores typically costaround a hundred dollars, but youcan build the Jam Pak for under $50!

The Jam Pak is a personal -head-phone guitar amplifier featuring aunique stereo -imaging effect, andadjustable distortion, overdrive, andtone controls. It also has an auxiliaryinput that allows you to plug in anywalkman-style tape- or CD -playerand play along with your favorite

songs. That input can also be usedwith a keyboard or drum machine.The Jam Pak works with any stereoheadphones and will operate forhours from a single 9 -volt battery.

Circuit Description. Figure 1 is aschematic diagram of the Jam Pak.The main components in the circuitare two LM324 quad op -amp IC's (U1and U2) and two LM386 power -ampIC's (U3 and U4). The inputs to U1 andU2 are biased to a little less than halfthe power -supply voltage by resistorsR10 and R11. Capacitors C1 and C2filter the power -supply and bias volt-ages.

There is no power switch in the cir-cuit. Input -jack J1 turns on the Jam Pakwhen the input plug is inserted. Whenan audio signal from an instrument isinput through J1, the signal is fedthrough coupling -capacitor C3 to thetone -control circuit composed of U1 -c, R2, R4, and C4. Frequencies above1 kHz are amplified or attenuated de-pending on the position of potenti-ometer R4, which is the tone control.Resistor R2 and capacitor C4 filter un-wanted high frequencies.

Audio level and overdrive are con-trolled by potentiometer R9; with thatlevel -control adjusted to full volume,the circuit's final amplifiers are over-

driven to produce a soft distortioneffect. To prevent any unwanted DC"swishing" noise, a coupling capaci-tor, C8, is used.

Switch S1 toggles between theclean and distorted signals. When S1 ison the CRUNCH setting, diodes D1 andD2, and U1 -d produce a distortioneffect by clipping the amplified signalat 0.7 volts. Frequencies below 160 Hzare attenuated by R5 and C6. Theamount of gain or "fuzz" is controlledby R7 and potentiometer R6, and re-sistor R8 adjusts the distortion level tomatch the tone -control level.

One of the reasons that the JamPak sounds great through a pair ofheadphones is its unique stereo -imaging effect. That is produced by aphase -shift circuit, composed of U2 -athrough U2 -d, R20-R23, and C9-C12.Each stage shifts 90 degrees at thesame frequency. The frequency of theshift at U2 -a is:

f = 1/(2nRC)

where f is the frequency in hertz, IT isequal to 3.14159, R is the value of R20,and C is the value of C9. For the fre-quency of the shift at U2-b-U2-d, usethe values of R21-R23 and C10-C12,respectively (as Fig. 1 shows, those val-ues are all equal). The four stages pro-vide 360 degrees of phase -shift at 330

J1

GUITARINPUT

+V

R10 R1

100K 1MEG

II+ 0 +VB1

9V +J. C1T100

R4 7A_A A

,7100K R3

TONE 1K

AM,

C4R2

.00147K

C5.01

K

C6 R5-1 4.7K

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D21N4148

CLEAN o S1

04''°CRUNCH

1/4LM324

C

1% '

R6 C7

500K .001FUZZ

D11N4148

C8

R910K

LEVELR12 R1322K 22K

R14 R1522K 22K

R16 R17 R18 R1922K 22K 22K 22K

R11

82K

11

J2AUXILIARY

INPUT

C2100

C13 R26.1 47K

R24330

wC14 R27

.1 47K

R2533"

A

C9.022 . 3

R2022K .1

1/4LM324

U2 -a

C11

10

.022

R2122K

R2232K 7'

13

C12.022 12

R2322K

VVR2810K R29

10KVV

R31

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R3010K

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R3510K

1/4LM324 C17-1 °-

R3410K

C20.01

K

J3(TO STEREO

HEADPHONES)

+VC18220

U4

LM386N-1 - C19T .01

Fig. I. From the hard distortion provided by U1 -d and DI and D2 to the stereo imaging accomplished by U2, the Jam Pak isaguitarist's dream come true. Note that there is no power switch in the circuit, as JI turns on the unit whenever an instrument cable isplugged in.

Hz, which is about the center of thefrequency range for guitars. At fre-quencies above and below 330 Hz,various degrees of phase shift occur.That phase -shifted signal is summedwith the original signal for one chan-nel (U1 -a), and subtracted from theoriginal signal for the other channel(U1 -b). The result of all that is an inter-esting panning effect that is frequen-cy dependent.

To play along with prerecordedmusic, or a keyboard or drum ma-chine, you can feed the stereo signalsfrom those sources into auxiliary -jackJ2. Those signals are attenuated byR24- and R25, AC -coupled throughC13 and C14, and mixed into the sum

and difference amplifiers through R26and R27. Capacitors C15 and C17provide AC -coupling of the sum anddifference signals to U3 and U4, thefinal amplifiers.

Both U3 and U4 have a fixed gain of20. With a supply voltage of 9 volts,they produce a power output ofabout 1/2 a watt into 8 -ohm head-phones. Capacitors C16 and C18high-pass filter and couple the outputto headphone -jack J3. Now, let's turnto building the amplifier.

Construction. The Jam Pak pro-totype was built on a double -sidedprinted -circuit board, which can beetched from the templates provided

in Figs. 2 and 3.or purchased from thesource listed in the Parts List. There area couple of good reasons why a PC -board is recommended for the proj-ect. One reason is to prevent the noiseand self -oscillation problems that canoccur in audio projects using otherconstruction techniques. Also, using aPC -board simplifies construction andmakes the finished product look neatand compact.

Most of the components listed inthe Parts List are inexpensive andreadily available from hobbyistsources and catalog distributors. Anyenclosure of a suitable size can beused for housing the circuit board,jacks, and panel components. A pre - 43

117\48 es

Fig. 2. Use this template to etch the component side of the printed -circuit board. Thepattern is shown here in its full size of 21/4 x 3 inches.

147111EfiljEro moan so

NOM

IS

o

CO

a

13

CI CS 1:3 II

Ilea SOO

as

Sao

SO

N

Fig. 3. This is the template for the solder side of the PC board. Like Fig. 2, it is alsoshown full size.

drilled enclosure with battery com-partment, belt clip, and two-color silk-screening is available from the kit sup-plier.

Use the parts -placement diagramin Fig. 4 as a guide when building theJam Pak, but keep the following inmind: To keep the circuit board small,most of the resistors are installed closetogether and standing up. To preventa short, make sure that those partleads are not touching. Double-check your placement of integrated -circuits U1. U4 and the six electrolyticcapacitors (C1, C2, and C15- C18) tomake sure their polarities are correct.Also check to see if diodes D1 and D2are installed with their banded endsfacing in the directions indicated bythe parts -placement diagram.

Install the IC's, jacks, capacitors,and fixed resistors on the componentside of the PC board. The switch andthe potentiometers should bemounted on the solder side of the cir-cuit board (using PC -mount potenti-ometers eliminates the need formessy wiring, but panel -mountedunits could be substituted if absolutelynecessary). Make sure to solder onboth sides of the circuit board wher-ever necessary. After you have in-stalled all the circuit -board compo-nents, solder the 9 -volt -battery snapin place, making sure that the polarityof the snap's ":ads is correct.

PARTS LIST FOR THE JAM PAK HEADPHONE GUITAR AMPLIFIER

SEMICONDUCTORSUl. U2-LM324A quad operational

amplifier, integrated circuitU3, U4-LM386N-1 low -power

amplifier, integrated circuitDI, D2 -1N4148, small -signal diode

RESISTORS(All fixed resistors are Vi -watt. 5%

units)RI-1-megohmR2, R8, R26, R27 -47,000 -ohmR3 -1000 -ohmR4 -100,000 -ohm, linear -taper

potentiometerR5 -4700 -ohmR6 -5(X),000 -ohm. linear -taper

potentiometerR7-470.000 -ohmR9-I0.000-ohm, linear -taper

potentiometerR10 -100,000 -ohmR11 -82,000 -ohmRI2-R23-22.000-ohmR24. R25 -33 -ohm

R28-R35-10,000-ohm

CAPACITORSCl, C2 -100-µF, 10-WVDC,

electrolyticC3, C6, C8, C13, C14 -0.1-µF,

ceramic -discC4, C7-0.001-p,F. ceramic -discC5, C19, C20 0.01-µF, ceramic -

discC9-C12-0.022-p.F, ceramic -discC15, C17-1-p.F, 35-WVDC.

electrolyticC16, C18-220-p.F, 10-WVDC,

miniature electrolytic


.11 -1/4 -inch stereo phone jack,circuit -board mount

J2, J3-3.5 mm stereo phone jack,circuit -board mount

SI-SPDT, micro -miniature toggleswitch

B1 -9 -volt alkaline battery

Printed -circuit materials. enclosure.knobs, stereo headphones, 9 -volt -battery snap with leads, wire,solder, hardware. etc.

Note: The following items areavailable from Lvnn-ErenElectronics (17093 S.W. LynnlyWay, Sherwood, OR 97140: Tel.503-625-2205): a complete kit ofparts including an etched, drilledand plated -through PC -hoard withsolder mask, and a pre -drilledenclosure with belt clip and two-color silk-screening. 549; a fullyassembled and tested unit. 559. thePC -board only. 515; stereoheadphones only. SIO: a 72 -inchauxiliary -input cable 13.5 mmstereo plug to 3.5 mm stereo plug).55. Please add 5% shipping andhandling. Check or money order.VISA and MasterCard areaccepted.

44

R1 1

C5 R3L J

-C6-

D-001-1 IR

D25

44- 1

S7

1 iR3I R28

rR7

L J

B1 +

-C14- R25

R8

R27

R26

R29

R32

1133

R19 C12

R24 -r 1 C16I I I

I I +I R9 I

1

I C20I I

L J IC18

Si

R16 R111 1 c

Fig. 4. Be sure to double-check the placement and polarity of your components withthis diagram to avoid damaging any of them. Note that switch ,S7 and potentiometersR4, R6, and R9 mount on the solder side of the board.

AEA compact amplifier lei., guitar playerA brush up on their skills without annoyingothers.

Checkout and Use. When theplacement of all components hasbeen thoroughly checked, you areready to try out the Jam Pak. Plug aguitar, bass, or other unamplified mu-sical instrument into input -jack J1, andplug stereo headphones into head-phone -jack J3. Note, however, thatthe sound heard through the head-phones might be surprisingly loud, soit is a good idea notto put them on justyet.

Connect a fresh, 9 -volt alkaline bat-tery to the unit. With switch S1 in the"clean" position and level -control R9set at low to moderate volume, theamplifier should sound undistorted.Adjusting potentiometer R9 to a highvolume setting should overdrive theamplifier and produce a soft distor-tion effect. Level controls on the guitaror other instrument might need to beturned up to achieve the overdriveeffect.

With switch S1 in the "crunch" posi-tion, the amplifier should produce ahard distortion or fuzz sound, whichcan be adjusted using the "fuzz" con-trol, R6. The tone control, R4, shouldadjust the treble of both the "clean"and "crunch" sounds.

Playing scales is a good way to hearhow the Jam Pak amplifier's stereoeffect works. As the frequencychanges, the position or panning ofthe stereo channels also changes.The stereo effect will sound the fullestwhen playing chords or fast riffs with awide frequency range.

To use the auxiliary input, connectany stereo walkman-type cassette- orCD -player, drum machine, or otheramplified audio equipment to jockJ2. That input has a low impedance,which is appropriate only for devicesintended to drive headphones orspeakers. Other high -impedancesources might be damaged if con-nected to J2.

The unit will operate for severalhours on a good alkaline battery. Be-cause the power switch is part of J1, itis a good idea to disconnect the plugfrom the input when the amplifier isnot in use.

Once you get the Jam Pak working,you'll be able to practice any time ofday or night you please, without irritat-ing those around you. And who knows,with a bit of practice and some luck,rock n' roll stardom could be justaround the corner! 45

co

§

ci)cr)

u_

46

Most readers of this magazineprobably tinkered with allkinds of unusual hardware-

both electrical and mechanical-when they were kids. I'm assumingthat because I certainly did, andwe're all birds of the same feather-orat least we are all similarly feathered.

I've made robots out of clocks;strobe lights out of record-playermotors and coffee cans; go-karts outof wood, wheels, and vacuum -clean-er motors; very dangerous "powersaws" out of X-Acto blades and a DCmotor; and a "wired" remote -controlcar out of various motors, gears, andother hardware. A motor-anymotor-was always a good find, Anybroken item that contained a motorwas immediately ripped apart for itsmotor and anything else that wasuseful-switches, lights, and gearbox-es were all pretty valuable (to me, atleast).

Even though I'm over 30 years oldnow, I still find sometimes that I can'tresist slapping together various itemsto make something unusual, or justplain fun. I can't help it-if I see someparts that beg to be assembled intoone unit, I do just that. And believe me,since I startedworking for thismagazine, moun-tains of assortedelectronic partshave piled up.

One day I wasstaring at somesolar panels won-dering if theycould power amotor I had. To find out, I connectedthe panels to the motor and took theassembly out into bright sunlight. It

worked well, and I soon after thoughtup the concept of the Solar -PoweredAirplane-a toy that could per-petually fly in circles as long as brightlight is available.

The Airplane Concept. Out of allthe applications that a solar -poweredmotor could have, why did I decide tobuild a toy airplane? Well, for starters,the two solar panels I had looked likethey would make perfect wings. Also,my low -voltage DC motor ran per-fectly well from the low power pro-duced by the solar panels (at least

well enough for an attached pro-peller to produce a little force). Let'sjust say that the two solar wing panelsand the low -voltage motor screamedout to be assembled as an airplane.And so, to my workbench I went.

The only design problems I couldthink of were how to make a pivotingstand assembly and how to properlybalance the plane. I realized that lowfriction on the pivoting stand wouldbe essential for the plane to be ableto move with the little force producedby the propeller. I decided that a ballbearing would be necessary to mini-mize friction as much as possible-nothing fancy, just any old ball bear-ing I could find. As for my other prob-lem, balancing the plane could onlybe accomplished with the finishedplane and stand assembly in hand, sothat was left for later.

Building the Plane. Figure 1 showsthe "schematic" of the airplane cir-cuit, If you want to call it that. Do twosolar panels plus one DC motor makea circuit?-technically I guess theydo, albeit a very simple one!

Getting the solar panels is the easypart. The rest of the airplane and the

stand, however, have to be fabricatedout of some kind of material, andwood is the best alternative. Wood iseasy to come by-anyone can get itfrom a nearby source-and is proba-bly the easiest material to work with. Ialso like the irony of a solar -powered,electric airplane that's made out ofwood.

I had thought about using an actualairplane model-either a plastic or atissue -paper -covered, balsa -woodtype-and adding the solar panelsand motor to it, but that would requireextra work, extra money, and extratime to complete the project.

Figure 2 shows how the airplane isput together. To fasten everything inplace, you will need hot -melt glue,double -sided tape, and a few screws.Due to the differences in weight be-tween woods of various type andthickness, I will provide only approxi-mate dimensions to follow in buildingyour airplane. Also included are theprocedures necessary to arrive at awell-balanced airplane, since an air-plane that is poorly balanced will flyslow, wobble, or even topple over.

The solar panels specified in theParts and Materials List come with a

Build a Solar -PoweredModel Airplane

BYMARC SPIWAK

Build this inexpensive toy airplanethat flies nonstop and never needs

batteries.

Fig. I. As this "schematic" shows, two solar panels and one DC motor are the only components that make up the airplane's circuit.

metal strap, probably intended forconnecting multiple panels together.On each panel, the positive andnegative terminals on the bottom arethreaded and come with a nut andlockwasher. Simply connect the Iwopanels together-from the positiveterminal of one to the negative of theother-with the metal strap and somehot -melt glue.

Next, cut a length of wood about51/2 -inches long for the airplane fuse-lage. Also cut three pieces of wood forthe tail, each approximately 2 -incheslong by 11/2 -inches wide, and securethem to the fuselage with hot -meltglue. Attach a small "shelf" for themotor, of the same width as the fuse-lage (probably about 2 -inches long,and Y8 of an inch thick), to the under-side of the fuselage at the front of theplane using hot -melt glue. Stick themotor to the top of the shelf with apiece of double -sided tape. The tapewill hold because the weight of themotor presses down on it.

Make the pivot arm from anotherpiece of wood about 13 -inches long.Drill a hole vertically in the approxi-mate center of the pivot arm to ac-cept the bearing you will use. Makesure the hole provides a snug fitaround the outside diameter of thebearing.

PARTS AND MATERIALSLIST FOR THE

SOLAR -POWERED AIRPLANE

Solar panels (2), 0.45 -volt, 1000-milliamp (Kelvin Electronics No.260099 or equivalent)

DC motor, low -voltage (KelvinElectronics No. 852211 or equivalent)

Plastic propeller, 3 -blade (KelvinElectronics No. 850590 or equivalent)

Ball hearing, H -inch outside -diameter,or similar unit

Wood. screws, spacer, hot -melt glue.double -sided tape, paint, and assortedhardware.

Note: The solar panels ($5.95 each), lowvoltage motor (60 cents), andpropeller ($1.20) are available fromKelvin Electronics, 10 Huh Drive,Melville, NY 11747. Tel.516-756-1750 or 800-645-9212.

Use another piece of wood, about9 -inches long, to form a support col-umn. Then attach the base, a 7 -inchsquare piece of plywood, to the col-umn with a screw through the under-side of the base and into the column.Countersink the hole in the plywoodso that the head of the screw does notinterfere with the base.

Mount the bearing on top of thecolumn with a screw and a spacer.Make sure that the bearing rests on itsinner race and that its outer race canspin freely (see Fig. 2). If you can't finda suitable spacer, one can be madefrom a piece of a ball-point pen'scase.

At this point, the plane must be tem-porarily assembled so that it can bebalanced. Everything must be inplace to balance the plane-themotor, the propeller, the wings, andany hardware.

Place the pivot arm so that when it isconnected the plane is balancedfront -to -back (see Fig. 3). Then, attachthe solar wings to the fuselage and tothe pivot arm with double -sided tape,and fasten the plane in place with ascrew going through the side of thefuselage and into the pivot arm. Thepivot arm looks best if it's hidden underthe wing of the plane. If you find thatyou can't balance your plane thatway, simply add weight (or remove it ifpossible) to the front or back of theplane to balance the load.

Next, add a counterweight to theother end of the pivot arm to balancethe entire assembly for rotational mo-tion. Use something that closelymatches the weight of your finishedplane. I used a large bolt and two 47

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48

SCREW

BALLBEARING

SPACER

SUPPORTCOLUMN

1Fig. 2. This is the general assembly of the airplane and its stand. Hot -melt glue, double -sided tape, and a few screws hold everythingtogether.

BALANCETHISWAY

0

48......

Fig. 3. The pivot arm must be connected so that the plane is balanced front -to -back.

gigantic washers. All together, thathardware was slightly heavier thanthe plane, so I mounted it about 1/4 ofan inch from the end of the arm. Ex-

periment to find the perfect balancebetween the weight of your counter-balance, and its distance from theend of the arm.

Using a bolt and washers makes iteasy to balance the arm. Temporarilytighten them on the edge of the armto find the spot of balance, and drill ahole for the bolt. You might find it easi-er to balance the plane by drilling ahole for the bolt in a position wherethe counterweight is a little lighterthan the plane. Then, you can fine -balance the arm by adding lighterwashers to the counterweight.

After everything is balanced, youcan disassemble the plane and paintit, or you can skip the paint and con-nect the power leads from the motorto the solar panels. Before you perma-nently attach the power leads, how-ever, go outdoors and test for thepolarity that will drive the propeller inthe proper direction for forwardmovement.

Vacuum -TubeAudio Amplifier

Build this audio amplifier and hear the difference tubes make in sound,without making a big difference in your wallet.

Vacuum tubes seem to have aglowing future in expensive,high -end audio equipment.

How come? What makes people shellout good money for amplifiers usingdevices that most thought were ob-solete years ago?

Those who like them say that tubessound better. They use words like"mellow" and "warm" to describe thetube sound. On the other hand, thereare also those who don't like tube au-dio, or say that there's no difference inthe sound at all.

How do you tell if you like the soundof tubes without making a big invest-ment? Build the super -simple ampli-fier described below and hear whattube sound is like at a reasonablecost. That way, you can get some ex-perience working with tubes whilebuilding a nice little amp you'll beproud to own.

Circuit Description. The circuitshown in Fig. 1 is the classic push-pull

BY LARRY LISLE

tube amplifier used for generations.That amplifier is flat within ± 1 dB from20 to 20,000 Hz into a resistive load,and is deceptively uncomplicatedconsidering its performance. As ex-plained below, the amplifier's designprevents hum and unwanted feed-back-two of the toughest problemsin the home construction of tube -au-dio systems.

Hum is minimized by balancing thetwo sides of the circuit via R1, locatedin the cathode circuit.

Unwanted feedback is avoided be-cause the circuit is designed as a sin-gle -stage amplifier. The sensitivity ofthe 60FX5 vacuum tubes, V1 and V2,makes that possible.

The amplifier can be driven to fulloutput with less than 3 volts of audioinput on the grids, making it ideal foruse with a battery -operated radio ortape player. At about 3 watts, the out-put of the amp is adequate for quietlistening on a 15 -inch speaker, and isgreat for earphones. Of course, the

tubes can be pushed slightly beyondthe linear portion of their operatingcurve (overdriven) to give a kind ofdistortion that some "tube-philes" like;more on that later.

The amplifier operates on a 120 -volt power supply. That is low for tubesand was selected for safety reasons.The "60" in the designation of the60FX5's indicates the filament voltage.Connecting the filaments of the twotubes in series permits them to bewired directly across the 120 -volt DCoutput of the power supply. The fila-ments of audio tubes should be oper-ated with DC whenever possible.

The 60FX5 is a sensitive, inexpensivetube (currently selling for under $3)that works well in the circuit, but othertubes could also be used withoutchanging the socket connections. Ifyou want to substitute tubes with 50 -volt filaments, the 50FK5, the 50EH5,and the very common 5005 aregood choices. However, a resistor willbe needed in series with the filaments, 49

and the values of cathode resistors R2and R3 might have to be changed.

Transformer T2 is a good quality 10 -watt tube -type audio -output unit thatis also available from Antique Elec-tronic Supply (as model PT -1608). Itsprimary has an impedance of about8000 ohms, center tapped, and thesecondary has taps for 4, 8, and 16ohms. The 220 -ohm screen resistor, R4,is used to drop the screen voltage to alittle below the plate voltage. Bypasscapacitors were not found necessaryin either the cathode or screen cir-cuits.

The power supply, shown in Fig. 2,uses two low -voltage transformers, T1

T1'

INPUT

?,F

2 OR 5

and T2, connected back-to-back al-though a conventional isolation trans-former could be used instead. Bridgerectifier BR1 rectifies the input AC, andcapacitor C1 filters the resultant DC.The filament voltage is taken from that120 -volt point. Resistor R1 then dropsthat voltage, and capacitor C2 filtersit further. The plate and screen volt-ages are then taken from the resulting92 -volt output. For safety and for hum -control reasons, ground the circuit asshown.

Construction. The amplifier pro-totype was built on a 24- by 10 -inchlaminated board that is sold at home

'SEE TEXT

2 OR 5

V1 V2/\ /\4 3

7

*82470R4

220C2Rt

7/. 250

R3

T2'

OUTPUT

+120VDC +92VDCFILAMENT PLATE/SCREEN

Fig. I. Here is the schematic for the tube amplifier. Its single -stage design, whicheliminates unwanted feedback, was made possible by the sensitive 60FX5 vacuumtubes.

BR1

T1' T2' 4A 400 PIV

*SEE TEXT

+120VDCFILAMENT

R1

+: 3300 +92VDC

PLATE/SCREEN

Fig. 2. The power supply for the amplifier uses two low -voltage transformersconnected back-to-back. The full -wave bridge rectifier, BRI, provides DC for the

50 filaments, plates, and screens.

improvement centers for shelving. Asmaller board could be used, but thelarge one provides room for experi-menting and for the input radio ortape player.

To wire the circuit, use insulated wireand make connections withfahnestock or similar clips; fasten theclips to the board with wood screws.Mount R1 on a corner bracket so it israised above the surface of theboard. That prevents you from cominginto contact with the exposed con-nections when making adjustments.

When connecting the tube sockets,it is easiest to wire them, screw them tothe board, and then trim the wires toan appropriate length. As for theleads of T1 and T2, don't trim them tooshort-you might want to use thetransformers in other projects. The au-dio output from T2 can either be wiredto fahnestock clips, or connected toan audio jack, depending on thenature of your speaker's leads.

The power -supply prototype wasbuilt on a separate 9- by 4 -inch pineboard so it could be physically sepa-rated from the amplifier. That is agood practice in audio work becausehum might be radiated by the mag-netic fields of the transformers and

PARTS LIST FOR THETUBE AMPLIFIER

RESISTORS(All fixed resistors are 50% units.)RI -25 -ohm. 2 -watt, potentiometerR2, R3 -47 -ohm, 1/2 -wattR4 -220 -ohm, 1 -watt


TI-Tube interstage transformer, 1:1to 1:3 turn ratio, AntiqueElectronic Supply PT -I57 orequivalent

T2-Tube-type audio -outputtransformer. Antique ElectronicSupply PT -I608 or equivalent(Available from Antique ElectronicSupply, 6221 S. Maple Avenue,Tempe, AZ 85283. Telephone:602-820-5411 or Fax:602-820-4643.1

VI, V2-60FX5 vacuum tube24- by 10 -inch baseboard, corner

bracket, knob for variable resistor,two 7 -pin miniature tube sockets,fahnestock clips, audio -output jack(optional), speaker or headphones,alligator clips, screws, insulatedwire, solder, hardware, etc.

hash (RF noise) might be given off bythe rectifier.

Like the amplifier, you can wire thepower supply using insulated wire andfahnestock clips. A small terminal stripcan be used to mount BR1. To preventstrain on T1 and T2, use a couple ofcable clamps on the power cord.

If you're new to tube voltages, becareful! Do not touch any part of theamplifier except the knob of RIwhile the power supply Is pluggedin. After unplugging the amplifier,short the two positive -outputfahnestock clips on the power supplyto the negative clip to make sure thecapacitors have discharged. If theamplifier and power supply are to beplaced in regular service whereothers might come in contact withthem, they should be enclosed. Ex-posed high voltages are not the onlydanger present-tubes get hot!

Checkout and Use. Double-checkall wiring to make sure it is correct.Then, make the following connectionsbetween the amplifier and power -supply using insulated wires that haveinsulated alligator clips on both ends.

Begin with the power supplyunplugged. Temporarily connect theplate/screen lead clip from the ampli-fier to the filament clip on the powersupply. Properly connect the negativeground lead to the power supply.Then, short the input of the amplifierwith a piece of wire, and connect aspeaker to the output of T2.

Plug in the power supply and wait aminute or so for the tubes to warm up,then balance the circuit by adjustingR1 for minimum hum.

After the circuit is balanced, unplugthe power supply. Connect the ampli-fier plate/screen lead clip to the prop-er clip on the power supply. Then, plugin the power supply and wait for thetubes to warm up again. When theydo, the hum should be inaudible ornearly so. If it isn't, try moving thepower supply away from the amplifieror change the physical orientation ofthe two circuits.

Unplug the power supply and re-move the short from the input of theamplifier. Connect a battery -powered radio or tape player with anaudio cable from its earphone jack tothe amplifier input. Then, connect thefilament -lead clip on the amplifier tothe proper clip on the power supply.

This power -supply prototype was built on a separate board from the amplifier. It'susually wise to build audio power supplies as separate units to prevent unwantednoise.

PARTS LIST FOR THEPOWER SUPPLY

BRI-4-amp, 400 -Ply, full -wavebridge rectifier

R1 -330 -ohm. 5 -watt, 10% resistorCl, C2 -100-µF, 250-WVDC,

electrolytic capacitorTi, T2 -1I7 volt to 12.6 volt, 3 -amp,

power transformerPLI-3-conductor power cord and

plug9- by 4 -inch pine board, terminal

strip, fahnestock clips, screws,cable clamps, insulated wire,solder, hardware, etc.

would like to hear the difference, tryPlug in the power supply, adjust thevolume control on the radio, and en-joy the music.

Any distortion in the radio or tapeplayer will, of course, be passed on tothe amplifier (though "tube-philes"say tubes make it sound better!). Also,you'll find some music played over -the -air has built-in distortion-- es-pecially on "oldies" stations. Soundquality is also affected by sources thatuse bass boost, as they will sound"bossier" through the amplifier. Soconsider the above when makingevaluations in the experiments thatfollow.

Some Experiments. There's longbeen a debate in tube -audio circlesabout pentodes vs. triodes. If you

reconfiguring the amplifier for triodeoperation. To do that, disconnect thescreen of each tube from R4. Then,connect the screen of each tube to itsown plate at the appropriatefahnestock clip. The output and distor-tion should be less in the triode mode.Try both modes to see which you likebetter.

The idea of pushing a tube slightlybeyond the linear portion of its oper-ating curve was mentioned earlier.Some authorities say that tubes soundbest when slightly over -driven thatway. That is easy enough to try, just turnup the volume!

The push-pull arrangement of thetubes tends to cancel the even har-monics. You can put the harmonicsback in by disconnecting the plateand screen of one tube; however,. hum might increase.

There is no "tone" control on theamplifier, but you can cut the highsand thereby boost the bass by con-necting a 0.1-pf capacitor across thesecondary of the input transformer. Avariable resistor can be placed in se-ries with the capacitor to make theeffect adjustable.

You can sometimes cause subtlevariations in amp and speaker perfor-mance by connecting a small resistorbetween the output transformer andthe speaker system. Also, resistors canbe used to experiment with the vari-ous forms of negative feedback. Theopen construction of the amplifiermakes it easy to try them all. 51

Discover and develop your latentmind -over -matter abilities.

Build thePK Tester

BY LARRY A. DUARTE

sychokinesis (PK) is the sup-posed ability of being able tomove objects or influence

events with one's mind. Over the years,many scientific investigations havegathered surprising evidence to sup-port a belief in PK, but there is a con-tinued skepticism among the generalpopulation. If you would like to settlethat issue for yourself and your friends,build the PK Tester described in thisarticle.

The project duplicates a devicecreated by the German physicistHelmut Schmidt. In 1969, Schmidt wasworking for the Boeing Company,which allowed him time and re-sources to do PK and ESP research.With his traditional physics training, hebelieved psychic powers could notexist. However, being open minded,Schmidt decided to design an experi-ment that would scientifically attemptto resolve the mind -over -matter ques-tion.

Schmidt's Experiment. The heartof Schmidt's device was a random -number generator (RNG). To makethat RNG, Schmidt used a radioactivesubstance called Strontium -90, whichcreated a random strobe due to itserratic decay. That would cause asample to be taken of a 50% -duty -cycle square wave at random inter-vals (see Fig. 1). The result was a totallyrandom series of lows and highs (0'sand l's) that would cancel out overtime.

Schmidt linked the output of hisRNG to a box with 10 lights on it, ar-ranged in a circle. Only one lightwould be lit at a time. Therefore, the

52 light would give the appearance of

Ps Yr,/ se,iRcy

a.11470$11ftr

moving counterclockwise or clock-wise depending on the RNG state.When the device was not being "influ-enced" by PK, it would drift in one di-rection or the other, but over time, itsmovement should be statistically neu-tral,

The person whose PK abilities werebeing tested was asked to "think" thelights in either a clockwise or coun-terclockwise direction. It is interestingto note that the people tested werenot aware of the underlying methodor electronics used to create the light'smovement. Schmidt's results werestartling: some people influenced themotion of the light by odds of over10,000 to 1.

A Modern Approach. In his day,Schmidt used some very advancedequipment to carry out his experi-ments. However, Strontium -90 is a ra-dioactive isotope that many scientistsbelieve to be dangerous. For that rea-son, a different method is used tocreate the random strobe in this proj-ect (that is discussed later). However,developing an RNG is only part of the

50% -DUTY -CYCLESQUARE WAVE

STRONTIUM -90RANDOM STROBE

STATISTICALLY EVENRANDOM OUTPUT

RE.31;

process of recreating Schmidt's ex-periment. A method is also neededfor translating the random output intodirectional movement, and for keep-ing track of the direction of that move-ment.

The solution to those problems is aMicrochip Technology PIC16C55 mi-crocontroller. The PlC's RISC -like archi-tecture combined with its top clock of20 -MHz allows it to process 5 -million -

instructions -per -second (MIPS), mak-ing it one of the fastest micro -controllers around. The PIC used in thePK Tester is available preprogrammedfrom the source given in the Parts List.However, if you have the ability andequipment to program your own PIC,the firmware fisting is available on theGernsback BBS (516-293-2283).

Circuit Description. The schematicfor the PK Tester is shown in Fig. 2.Power is provided by a 12 -volt -DC walladapter, which plugs into power -jackJ1. That is used instead of batteriesbecause, to guarantee the PK Tester'srandomness, the circuit should betested for many hours or even days at

1 0 00

Fig. I. Here's a sample of the statistically even output produced by Schmidt's random -number generator. A similar output is generated by the PK Tester using a non-radioactive method.

a stretch. A regulated 10 volts isneeded by the noise circuit; that isprovided by U4, an LM317 adjustablevoltage regulator. High ripple rejec-tion is accomplished by R11 and C10.The rest of the circuit runs off a regu-lated 5 volts produced by U5, a 7805.

2N4404

C2

+10V

R7R8 100K1M

A

R64 1M

02-2N4404

Resistor R2 and capacitor C1 pro-vide the RC timing for the PIC (U1),giving it a 78-0 clock. The cathodesof LED1- .LED16 are directly connectedto the PIC. The anodes of the LED's areconnected in common through R1, a220 -ohm resistor, to + 5 volts. During

3R10

100K 7.t

C3M.0047

R910011

S2RESET

-

+5V R1210K

R4 R3

10K 7' 10K

S1

STATUS/TEST

*---0 0-*LED1

C5220pF

K

D1

1N4148

D21N4148 I

R1547.5K

R1642.2K 7'

C11.001 M

R510K

+5V

8 4

5

C12.01 M

10

LED2 CA -Ay 11

LED5 rb-"A-'V

14

LED3

LED4

12

13

LED6 15

LED7 16

LED8 17

LED16 18

LED15 19O

U1

PIC16C55

+5V

.01

R21OK

27

pg, C1

220pF

LED9

R1

non?.

24 LED10

LED11

LED12

21 LED13

LED14

S1

POWERJ1

(TO 12VDC) yr

U57805

0 +5V

KC7 = C810 100

U4LM317

G

LiC9 R13.1 1.5K

VNR1422on

R11

10K W 0+10V

+7 -woo

Fig. 2. This circuit generates a random output that is translated into LED"movement" by a preprogrammed PICI6C55 microcontroller, Ul . That PIC alsosenses and records the bias of the LED's movement.

normal use, only one LED is on at atime, so that bypasses the need forseparate current -limiting resistors oneach LED. Two push-button switches,S1 and S2, are used to initiate the STATUS/

TEST and RESET functions described later.

The random strobe is produced thisway. Transistor Q1's emitter -to -basejunction is reverse -biased over thebreakdown point. That type of config-uration produces random noise that isthen amplified by Q2. The resultingoutput is fed into U2, an LM311 com-parator, and comes out as a clean,TTL-logic-level high or low signal.

The other signal that is needed toreproduce Schmidt's experiment is asquare wave with a 50% duty cycle.That is created by U3, a 555 timer.Diodes D1 and D2 are used to gener-ate the separate timing paths neces-sary for a precision 50% duty cycle.Also, to ensure that the square wavehas a perfect 50% duty cycle, potenti-ometer R5 should be properly ad-justed (more on that later). Thecombination of that square wave plusthe random strobe equals a randombut statistically neutral series of highsand lows.

The output of highs and lows is fedto pins 6 and 7 of U1. A section of thefirmware then translates the signalsinto LED "movement." Each individualmovement is also recorded by the PICand the total number of movementsare tabulated for display once thesrArusqEsr button is pressed.

Construction. The constructiontechnique used is not critical, but Ifyou would like to build the circuit on aPC board, a full-size pattern is shownin Fig. 3. An etched and drilledprinted -circuit board (as well as a pre-programmed PIC) is available fromthe source given in the Parts List. Theother parts for the PK Tester can bereadily acquired from hobbyistsources like Radio Shack or Digi-Key.

If you decide to build the project ona PC board, use the parts -placementdiagram in Fig. 4 as a guide. Mount allthe resistors, capacitors, and IC sock-ets first; then insert the IC's n their sock-ets. Last, mount the LED's so that theystand on 3/4 -inch leads. That will en-sure that there is enough room for theother components when the circuit isplaced in the case.

Wire the ground connection frompower -jack J1 to the board as shown 53

0

-JLu

cnul)

cn

LL

54

PARTS LIST FOR THEPK TESTER

SEMICONDUCTORSUI----PICI0055 microcontroller,

integrated circuitU2---LM3I1 comparator, integrated

circuitU3-555 timer. integrated circuitU4---LN1317 adjustable voltage

regulator. inteerated circuitU5---7805 5 -volt regulator. integrated

circuitQl. Q2 ---2N4404 general-purpose

NPN transistorDl. D2 ---1N4148 small -signal diodeLEDELED16--Red light -emitting

diode

RESISTORS(All fixed resistors are 1/4 -watt. 5%

units. unless otherwise noted.)RI, R14--220-ohm, wattR2. R3. R4. RII, R12 -10,000 -ohmR5 -10.000 -ohm. 15 -turn

potentiometerR6. R8---1-megohmR7. RIO- I 00 .000 -ohmR'1-I(10-ohmR13 -1.50(1 -ohmR15---47,500-ohm, 1,4R16---42,200-ohm, 1%

CAPACITORSCl, C5-220-pF, ceramic -discC2, C4. C9 -0.1-µE, polyesterC3 -0.004711E, polyesterCO. C12----0.01-1.11, polyester

25-WVDC, electrolyticC8 -10011E, 16-WVDC, electrolyticC10--1000-iiE 16-WVDC,

electrolyticC11 -0.001-µE polyester


J1 ----Mono phone jackSI, 82-Normally open SPST,

momentary pushbutton switchS3-SPST switchPrinted -circuit materials, enclosure,

IC sockets, lens caps for LED's,12 -volt AC adapter (with plug tomatch ill. wire, solder, hardware,etc.

Note: The following are availablefrom Larry Duarte (P.O. Box 1232,Englewood, CO 8015W: a pre-programmed P1C16C55: 512.00: anetched and drilled PC board:$12.00: add $4.50 S&H to allorders. Colorado residents mustadd appropriate sales tax.

Fig. 3. Use this full-size template to etch your own PC board.

R11C10R131

C9 --

R14I

U4

/1°LED2

z.N,41

140Ft

LED1

WA? R101

LED3 --c2- R7

11 C--) 1R8

LED4 ® -C3 --R9

II

C61

C51

R12LED5 R31 I

R4

'ZIOF

LED6

111410

LED7

LED16

U2

-04-J -

U1

R2

C1

LED8 LED9

IWOLED15

se-O-CrAPO--S3J1

C8 I

RI

LED14

Cl

116VLED13

N\\ LED12

ORS

LED11

LED10

-C11-

U3

D1

D2

1

0315R16

C12

Fig. 4. When assembling the PK Tester, use this parts -placement diagram as a guide.

In Fig. 4, and then make the other off -board connections shown in that di-agram. Mount the switches and thejack to the case.

Before you can mount the PCboard in the case, you will have toadjust potentiometer R5 so that U3produces a 50% -duty -cycle square

wave. The best way to accomplishthat is by using a scope. However, ifyou do not have a scope handy, youcould adjust R5 to an approximately"halfway" setting, and then use trialand error to determine if the output ofthe PK Tester is statistically neutral.

(Continued on page 108)

Build theSprinkler

Guardian

0 0

Here is a rain shut-off for your automatic sprinkler -systemthat overcomes common problems, and can save dollars on your water bill.

Ever drive by a yard during theheight of a rain storm and won-der why the sprinkler system

was working? The answer is simple:sprinkler systems are on timers, anddon't know that it's raining. If youwould like to keep your system fromrunning in the rain, you can do one oftwo things: you can either turn off yoursprinklers every time it looks like rain, orbuild the Sprinkler Guardian de-scribed in this article.

The Sprinkler Guardian is an add-onunit that works with your sprinkler con-troller and turns off your system whenthe ground is damp. Using it can sig-nificantly cut the watering bill for yourlawn. The Guardian also solves someof the shortcomings with a few com-mercially available sensing units.

Some commercial units that detectlawn moisture have this problem tocontend with: when the sprinklers turnon, the probes get wet, causing theunit to shut off the sprinklers (becausethe unit "thinks" it is raining). That prob-lem is usually solved by telling the in-staller to bury the probes 4 to 6 inchesbelow the ground. Doing so allowstime for the water to soak down fromthe surface before it indicates that theground is wet and the sprinklersshould be off. There are a couple ofdrawbacks to that: For one thing, itsolves the control problem by addingmore work to the installation. In addi-tion, that type of sensing does not de-tect dry soil at the surface where grassroots are, but waits for soil to dry clear

down to the depth of the sensors be-fore calling for watering.

The above method also presents aproblem with systems that have multi-ple branches. If the sensor probes arelocated in the first branch being wa-tered, the probes might get wet andthe second and remaining branchesmight never turn on. To avoid that, theprobes must always be placed wherethey are in the last area watered.

Another type of sensing unit detectsthe resistance of water trapped in asmall cup during a rain storm, andwaits for that water to evaporate be-fore it turns on the sprinklers. The ob-vious drawback to that type of sensoroperation is that it has nothing to dowith the amount of moisture in theground.

How It Works. The Sprinkler Guard-ian can be used in conjunction withany sprinkler controller that uses stan-dard, 24 -volt AC valves. The add-onunit senses the moisture content at theground surface, and if the ground isdry, the unit allows the controller toexecute all the on -times preset by thecontroller clock. If there is enoughmoisture in the ground already, how-ever, the Guardian will prevent thevalves from opening.

The schematic for the SprinklerGuardian is shown in Fig. 1. The unitobtains its power from the 24 -volt ACpower supply of the controller it is

used with. That power is supplied toterminals 1 and 2 of terminal block TB1,

O

and the AC is then rectified by thebridge composed of diodes D1through D4. Capacitors Cl and C2act as supply filters, while C5 and C8are bypass capacitors. The 10 -watt re-sistor, R1, drops the supplied 24 voltsdown to about 14 volts, which is inputto Ul, the 12 -volt regulator. The outputof U1 supplies a regulated 12 volts tothe rest of the circuit.

The ground probes are connectedto terminals 1 and 2 of TB2. Resistor R2is used to balance the resistance ofthe earth between the two probes sothat op -amp U2, which is configuredas a comparator, outputs a high whenthe ground is dry. When that happens,PNP transistor Q1 is turned off, K1 is notenergized, and terminals 1 and 2 ofTB3 are shorted. Under those condi-tions, if the controller calls for wateringthe lawn, watering will commence.

Now, let's assume that it rains, andthat the ground is wet. The resistancebetween the probes drops, causingthe output of U2 to go low, which turnson Ql. That energizes Kl, causing itscontacts to open. Under those condi-tions, even when the controller is pro-grammed to water, the valves will notopen. That covers the wet and dryconditions normally encountered.

Now let's assume the soil is dry. RelayK1 is off and all is ready for the neededwatering -cycle. When the pro-grammed watering time arrives, thewater valve is opened, starting thetimed watering -cycle. The probes arewetted immediately and U2 goes low. 55

12V

TB1(TO

24VAC)

102 0-

TB2(TO

PROBES)

2010

TB3(TO

COMMONLEG)

D3D21 N4001 1 N4001

U1

MC7812CT1D1

1N4001D4

1N4001

144R1

5052R3

10052

C1 CS

2201 50K

R5700 10K

R61K

R410K 7"

7=7

R71K

K1 8,

LED1

OLED2

R83.3MEG

6

7

C71000

U3LA4555

15

C3100

R10100K

012N3905

73..21 -b

0= MANUAL AUTOMATIC

R111K

C6 LED3.1

Fig. 1. The Sprinkler Guardian uses probes to sense the change in the ground'sresistance when moist. If the moisture is caused by the sprinkler system, U3, a 555tinier, allows the sprinkler to run for about an hour with the values shown for R8 andC7.

4 INCHES

Fig. 2. The Sprinkler Guardian prototype was assembled on a printed -circuit board. Afull-size template of it is shown here.

As the voltage output of U2 drops, a through C4 to pin 2 of U3, a 555 timer,56 negative -going pulse is delivered which triggers the timer into opera-

V R9

4700

R1247K

C5.1

022N3905

tion. The timer output from pin 3 turnsQ2 off, which keeps K1 from closingduring the time cycle determined byR8 and C7. That allows time for thesprinkler system to complete the wa-tering cycle.

By the end of the U3 time period,the controller has most likely com-pleted its on -time and has shut off.With the component values shown,the time period set on the SprinklerGuardian is about one hour, afterwhich the sensor becomes activeagain. If an hour is not long enough,the U3 period can be adjusted usingthe formula:

T=RxCx 1.1where T is the time in seconds, R is theresistance of R8 in ohms, C is the ca-pacitance of C7 in farads, and 1.1 is aconstant.

A DPDT switch, S1, is used to placethe circuit in either the "automatic" or"manual" modes. In the "automatic"mode, the circuit operates as pre-viously described. In the "manual"

PARTS LIST FOR THESPRINKLER GUARDIAN

SEMICONDUCTORSU 1-MC7812CI 12 -volt regulator,

integrated circuit1.12-U0741 op -amp, integrated

circuitLI3--LM555 timer, integrated circuitQI, Q2 -2N3905, general-purpose

PNP transistorDl-D4-1N4001, 1 -amp, 50-PIV

rectifier diodeLEDI-Red light -emitting diodeLED2-Green light -emitting diodeLED3-Yellow light -emitting diode

RESISTORS(All fixed resistors are 1/4 -watt. 5c4

units, unless otherwise indicated.)RI -50 -ohm, 10 -watt. 10'4R2 -50,000 -ohm, potentiometer, PC -

mount (Digi-Key K4A54 orsimilar)

R3 -100 -ohmR4, R5 -10.000 -ohmR6, R7. R11 -1000 -ohmR8-3.3-megohmR9 -470 -ohmR10 -100,000 -ohmR12-47 .000 -ohm

CAPACITORSCI, C2 -220-µE 50-WVDC,

electrolyticC3 -100-µF, 16.-WVDC. electrolyticC4, C.5. C6, C8 -0.1-µE metallized -

filmC7 -1000-µf, 25-WVDC,

electrolytic


KI-12-volt DC relay, AROMAT#HB2-DC12V (Jameco 18577 orequivalent)

TBI-TB3-2-terminal, terminalblock, PC -mount

SI-DPDT slide switchPrinted -circuit materials, two 201)

nails, insulated wire, solder,hardware, etc.

mode, the terminals of TB3 are short-ed, effectively removing the Guard-ian from the system, and U3 isremoved from the Guardian circuit,allowing R2 to be adjusted withoutworrying about the action of the timer.Note that R2 should always be ad-justed with S1 in the "manual" position.

Two LED's are used to indicate thecondition of the relay. When greenLEDI is on, it indicates that the relay isoff and that all watering cycles will becompleted, When the relay is ener-

TB3 TB2

0 0 0 00 0 0 0

-C7- +

K1

C6

11

18

S1

U3

-R12 ....,s0 _R9_-J -R11-

/.7.N. LED2

LED3Ufi

R10 c4

U2

R1

TB1

0 00 0

+ -c2-

j -C 5 -

D2 D1

+ -C1-

Fig. 3. Assemble your unit using this parts -placement diagram as a guide. Be sure toleave a 1/4 -inch space between the PC board and RI for ventilation.

24VAC SOURCE'

O

SPRINKLER GUARDIAN

EXISTING CONTROLLER

0 0 0 0,,COMMON LEG

t

SOL

02TB3

10 02TB2

10 02TB1

CUT HERE'

SOL

Z

SOL

tg'SEE TEXT

GROUND PROBES

Fig. 4. This illustration shows how to properly connect the Sprinkler Guardian to yoursprinkler -system controller and to the buried ground probes.

gized, red LED2 is on, indicating thatthe sensor is wet and that the demandfor water by the controller will not beaccommodated. Because the timerkeeps the relay from being energizedeven if the probe is moist, it is essentialto know if the timer is in its timing cycleor if it is off. Yellow LED3 is on when thetimer is in its timing cycle.

Construction. The unit can be builton either perforated constructionboard or on a printed -circuit board.For those who want to use a PC board,a template is shown in Fig. 2, and theparts -placement diagram is shown inFig. 3. Using the PC -board layout elimi-

nates wiring mistakes, but might limitparts substitutions, because of phys-ical differences in part sizes.

All the components are mountedflush on the board except for R1.Leave about a 1/4 -inch space be-tween that high -wattage resistor andthe surface of the PC board to allowbetter air -flow cooling. When install-ing capacitors C1, C2, C3, and C7, besure to check that their polaritymatches that shown in Fig. 3. Also, besure to install the two jumper connec-tions at the correct places.

The probes can be two 20D nails,with the needed length of insulated


Securityin the

Information Agetop-UCI?

How information is protected from falling into the wrong hands.

Cryptology, the science ofcodes and ciphers, has untilfairly recently only been used

by kings and generals. Because fewpeople could read, illiteracy was theultimate file protection. However, withthe advent of universal literacy, thepersonal computer, and a govern-ment that can eavesdrop on a world-wide scale, cryptology has moved outfrom the back chambers and into thepublic domain. We can now protectinformation at the push of a computerRETURN key.

But how is that done? Well, beforewe can take a look at achieving truesecurity in the information age, per-haps a little background material oncodes and ciphers is in order.

Codes and Ciphers. Codes andciphers are completely different en-tities, even though the two terms areoften incorrectly used interchangea-bly. The first type, codes, changes thevalue of entire words, phrases, or sen-tences. For instance, the code phrase"CLIMB MOUNT NIITAKA" was used bythe Japanese Navy to mean "ATTACKPEARL HARBOR." '

Ciphers change the position or val-ue of each individual character in themessage. Ciphers are much easier touse than codes, which require largecode books listing every word or

58 group of words that will be used. A

BY CRAIG HOWARD

cipher, on the other hand, requiresonly a mathematical formula, calledan algorithm, that can often be easilymemorized. The message to be en-crypted is called plaintext the mes-sage after it is encrypted is calledciphertext.

Ciphers can be divided into eithertransposition or substitution groups. Atransposition cipher shuffles the plain -text message until it is unreadable. Forexample, the plaintext message "RE-TREAT AT ONCE" becomes "ETRNECTORA TE." Break the ciphertext intosequential blocks of five characters, inorder to hide the placement of ob-vious words like "AT"

A substitution cipher changes thevalue of each character in the plain -text. Most substitution ciphers use akey, which can be a word that's easyto remember, a passage from a book,or even a piece of music. To use a key,convert the plaintext into numbers-"A" becomes 00, "B" becomes 01, andsoon. Do the same with your key. Thenadd each plaintext number to its cor-responding key number and you getthe ciphertext.

For example, if you wanted to con-vert the plaintext word "ATTACK" intonumbers, it would become: 00 19 1900 02 10. To encrypt that word youwould need a key; let's say that the keyused was "BUSBUS." That key would be-come 01 20 18 01 20 18 when convert-

ed. To create the final ciphertext youwould have to add those series ofnumbers, one series on top of theother, like this:

00 19 19 00 02 10+01 20 18 01 20 18

01 39 27 01 22 28

Notice that noncarry addition wasused; that reduces the number of er-rors. Because the key provides threedifferent numbers, a plaintext numbercan be converted into three possibleciphertext numbers. For example, thefirst "T" in plaintext (19) is added to a"U" (20) in the key, and is turned into aciphertext 39, but the second "T" is

added to an "S" (18) in the key, whichresults in a ciphertext 27. That variationmakes the cipher harder to crack.

One -Time Pads. Instead of using akey "word" that repeats, what if thekey was a random string of numbersthe length of the message? It wouldbe unbreakable. Period. That un-breakable cipher is called a one-timepad, and is the favorite of spies every-where. It requires only a pad of paperfilled with random numbers on eachpage. That pad is the key.

Here is how to use the method. Firstof all, come up with a one-time padof random numbers, and use them toencrypt your message, just like a sub-stitution cipher. Then, tear off the

pages that were used and burn them.because they could never be usedagain. Your friend who receives themessage can use a one-time pad,which is an exact duplicate of yours, todecrypt the message.

If that cipher is so secure, why don'tbanks and governments use it for all oftheir message traffic? Because thecipher requires that each sender andreceiver have exactly the same one-time pads. Banks transmit and receiveso many messages that they'd needmillions of pads per day, all of whichwould have to be distributed in com-plete security to everyone commu-nicating with the bank. Hence, theinfallible one-time pad is used only bythose who must communicate withbomb -proof security, such as a spy.

Numbers Stations. Occasionally,shortwave listeners will hear an an-nouncer on an unlicensed stationreading off a seemingly randomstring of numbers. The announcer issending a message to a spy who'sequipped with nothing more than ashortwave receiver and a one-timepad the size of a postage stamp.Shortwaves con reach halfwayaround the world, so the transmittercan be located on friendly soil.

Although most "numbers stations"transmit their messages in four- or five -digit blocks, occasionally you canhear a three/two station. On those sta-tions, each block consists of three dig-its, a pause, then two digits. Thosemessages are using a dictionary -keysystem. The first three digits of eachblock are the page number of abook. The last two digits are the loca-tion of the word on the page. By look-ing up each word, the message isreconstructed. The dictionary -key sys-tem is safer than the one-time padbecause being caught with a pad ofrandom numbers is bad news, where-as being caught with a paperbacknovel is not.

Numbers stations can be foundacross the short-wave spectrum, butare especially active on 6840 kHz and7415 kHz in the evening to morninghours. Brush up on your Spanish; it

seems to be the language of choicefor those types of stations in the west-ern hemisphere. For more informa-tion, read The Shortwave ListeningGuidebook, listed in the "FurtherReading" box.

MODULAR MATH CIPHERS

Modular math is easy. we use it everyday If the time is 10.00, what will it be in6 hours? Well. 10 plus 6 equals 16 but aregular clock only goes up to 12 (It is amod 12 system). Therefore. we have toaiso figure out that 16 mod 12 equals 4(o'clock). To do that simp'y divide thenumber by the modulus, keeping onlythe remainder Subtraction could alsowork in that case. but not always Forexample. if it's 10.00, and you want toknow what time it will be in 34 hours,then you'd use 44 mod 12. which equals8 (44'12 = 3 remainder 8).

Modular math is good for locking upsecrets in code. Even though finding 14mod 12 is easy (the answer is 2) doingthe reverse is difficult, even 7 you knowthe modulus. If the remainder is 2. thenthe original number can be 2. 14. 26.etc

To use modular math for an RSAcipher, start by picking two prime num-bers. p and a For this example '.tie r.

use 3 and 5. out in practice. the twonumbers should he 100 digits longeach We'll also need a public key (r)but first we have to come up with itsmodifier (n). using

n - oqIn this case n.equais 15. Next. you haveto figure out the value of e. a numberthat determines the range of the pubickey (r) To find e. use

(p -1)(q-1)

which equals 8 So, in this case, thepublic key (r) is any number between 1and 8. which isn't a factor of 8 (thateliminates 2 and 4). Let's have r equal 3

Then find a number that when multi-plied by r and divided by e leaves aremainder of 1 We li use 11, which wiHbe s. the private key. Now you're readyto give your friends the numbers n (15)and r (3).

If a friend wants to send you a mes-sage, say the number 12, he or she canuse the public key to encrypt the mes-sage. 12r mod n. or simplified 1728mod 15, which equals 3 The ciphertextmessage 3 can then be transmitted

To decrypt to get the plaintext mes-sage, use 3s mod n, or 177147 mod 15,which equals 12. With a little practiceit's not as complicated as it seems atfirst.

Electronic One -Time Pads. As wesaw earlier, a one -time -pad cipheruses a random key that is the length ofthe plaintext message. The key is dif-ferent for every message, and is add-ed to the plaintext using noncarryaddition. To make an electronic one-time pad, you can use the exclusive -OR gate (XOR) to perform the addi-tion. That can be done either with

hardware-an XOR-gate chip (Fig.1A), or with software the XOR instruc-tion in BASIC.

Looking at the truth table in Fig. 1B,we can see that the XOR gate is abinary adding machine. Input A isadded to input B, and the sum isshown in the output column. Now, lookat the last line. If A -- land B 1 then 1

- 1 - 10. Because the XOR uses non -carry addition, the 1 is dropped, leav-ing the output to equal 0.

The best source of random bits forthe key is not the RND instruction inBASIC. That instruction doesn't grab arandom number out of the air; in-

stead, it generates a pseudo -randomsequence that repeats after a longtime. The sequence could be brokengiven enough ciphertext messages.

Instead, use random noise in theform of radio static. Fill a CD ROM withstatic, and make a copy for the otherone-time pad (see Fig. 2). Use a CDROM drive that has its laser powerboosted. As the laser reads a bit, thebit is burned away. That makes it im-possible to crack previous messages ifthe CD ROM is captured.

Encryption in Banking. Every daythe Clearinghouse Interbank Pay-ment System electronically movesmore than 1 -trillion dollars. That data isencrypted with the Data EncryptionStandard (DES), which is based onIBM's Lucifer algorithm. The original Lu-cifer used a 128 -bit key, but the USgovernment thought that a key thatlong would make the cipher too hardto break by their people at the NSA. SoDES was given a 56 -bit key, making thecipher too difficult to break by anyoneexcept the government.

How weak is DES with a 56 -bit key? A56 -bit binary key has 7,6 possible keys,which is equal to 7.2 X 1016 or72,000,000,000,000.000 possible keys.A 128 -bit key has 2,28 or 3.4 X 1038possibilities (that's written as 34 fol-lowed by 37 zeros!). Double the size ofthe key, and you square the numberof possible keys and the amount ofwork a codebreaker must put in.

DES encrypts a chunk of data byusing o three -step cycle of substitu-tion, transposition, and exclusive-OR'ing, which is repeated for a total ofsixteen cycles. It has three modes:Electronic Codebook (ECB), CipherFeedback (CFB) Cipher Block Chain-ing (CBC). 59

INPUT A

INPUT BX -ORGATE

OUTPUT

A

X -OR TRUTH TABLE

A B OUTPUT

0 0 0

0

0

0

B

Fig. I. This is the block diagram of aXOR-gate chip (A). The truth table (B)shows that the XOR gate is really abinary adding machine.

The Electronic Codebook mode isso weak that even the governmentrecommends not using it. Ironically, anumber of commercial encryptionprograms use it anyway. For a com-plete description of DES, read Securityin Computing, listed in the "FurtherReading" box.

Can DES be broken? MichaelWiener of Bell Northern Research inOttawa wrote a paper on how to dojust that. He designed a chip thatbreaks DES keys by trying every com-bination until it finds the right one, thebrute -force attack. The chip costs$10.50 to manufacture. For $1 million,you could build a machine that uses57,000 of those chips to try every keyin 7 hours, with the average time tosolution being 3.5 hours. For $10 mil-lion, you can get a solution in an aver-age time of 21 minutes. Finally, for $100million, you can have a solution in 2minutes! Wiener hasn't built the chipyet, but it is feasible.

DES will retire soon. Among its otherflaws it uses a single key for encryption

a and decryption, just like the basicciphers we looked at earlier. A single -

J2 key system, also called a conven-

COtional system, allows anyone who

,T) sends you an encrypted message toalso decrypt your other messages.

02 The solution: either use a separate keycc for each person with whom you corn-,Lc:A municate, or use the latest rage, the

public -key cipher.

))

01 Public -Key Ciphers. Let's dust offsome basic math terminology. Re -

LL<

member prime numbers? They'renumbers that can be divided only bythemselves and one. Three is a prime

60 number; so is five. Take two prime

numbers, say 100 digits each, andmultiply them together to get a 200 -digit number, X. If a computer is givenX, it will take years to find the originalprime numbers again. Public -keyciphers use prime numbers for thatvery reason.

A public -key cipher is perfect forcomputers and E-mail. It uses twokeys: a public key that can be given toanyone, and a private key that is keptsecret. If someone wishes to send youa message, he or she would encrypt itwith your public key. Once It has beenturned into ciphertext, the public keycannot decrypt it: only the private keycan do that. So you can distribute your

PLAINTEXT IN

KEY

CD ROMFILLED WITH

NOISE

X -ORGATE

Pretty Good Privacy. In 1978, threeresearchers at the Massachusetts In-stitute of Technology introduced apublic -key algorithm. They called itRSA after their names-Rivest, Shamir,and Adleman. The researchers pub-lished their algorithm before filing apatent, out of fear that the U.S. gov-ernment would classify the patent anational secret, disallowing them towrite about it. Because the rest of theworld requires patenting before pub-lication, RSA is patented only in theUnited States.

Enter Philip Zimmermann, a com-puter consultant in Boulder, Colorado.He wrote an encryption program that

CIPHERTEXT

KEYX -OR

GATE

PLAINTEXT OUT

DUPLICATECD ROM

Fig. 2. To use an electronic one-time pad, fill a CD ROM with static, and make a copyfor the other one-time pad. Use a CD ROM drive that has its laser power boosted. Asit reads each bit, the laser burns the bit away, making it impossible to crack previousmessages if the CD ROM is captured.

public key to the four winds, but noone can use it to decrypt any mes-sages sent to you.

Digital Signatures. You get a callfrom Icepick: he wants the money youowe him. Now. The bank closes in afew minutes, and it's too far to drive. Ifyou send a message to the bank totransfer money to Icepick's account,how will the bank know that it's you?

We know that a public key encrypts;a private key decrypts. However apublic -key system is commutative-that is, it can also encrypt with theprivate key and decrypt with the pub-lic one. Of course! You fire up the com-puter, and write a quick note to thebank. You encrypt the note with yourprivate key and send it. The bank thenlooks up your public key and uses it todecrypt the message. Icepick gets hismoney, and your kneecaps feel great.

Using a private key to encrypt amessage is called a digital signature,because it is unique, like your ownhandwriting. To make sure that no onebut the bank can read your note, sim-ply encrypt the note with your privatekey, then encrypt the ciphertext usingthe bank's public key,

uses the RSA algorithm and called itPGP for Pretty Good Privacy. Heposted it on a local computer bulletinboard, Someone else downloadedPGP from the bulletin board, andposted it on the Internet. Copies ofPGP multiplied exponentially, withthousands of people around theworld downloading the program fromone bulletin board, and posting it onanother.

PGP is simple and free for the tak-ing. It can encrypt personal files thatyou keep on disk, E-mail messages, orfiles to be sent to someone else. Thebest source for a clean, bug -freecopy of the program is the bulletinboard "The Catacombs,"303-772-1062. Grab the PGP Shell too,which has screen menus to make PGPeasier to use.

When PGP first came out, the RSApatent holders claimed infringement.That is odd considering that RSA wascreated with public funds, and waspublished in widely read academicjournals. Today, the infringement bat-tle is over: the 2.6 version of PGP usesencryption algorithms that have nolicense fees for personal, non-com-mercial use.

The Clipper Chip. PGP has a distantcousin, the Clipper chip, which is theU.S. Government's replacement forDES. The chip is based on the Skipjackalgorithm, which is classified.

But why look any further than RSAand PGP for use as our national en-cryption standard? If RSA is goodenough for protecting our nation's nu-clear weapons (and according toRon Rivest, it is used for precisely that),why can't banks and phone compa-nies use it? Because if everyone usedan unbreakable encryption method,court -ordered wiretapping would beuseless, The NSA, whose mission is tobreak codes and to eavesdrop on allforms of communication, would bedefunct. Thus the Clipper was born. Itallows the government to break anymessages sent or received by thatchip.

During the chip -manufacturingprocess, each chip is loaded with aserial number, a family key, and a unitkey. The family key is the same for allClipper chips; the serial number andunit key are unique to each chip. Tworandom, 80 -bit binary numbers arefactored (multiplied) together to formthe unit key. A copy of the unit key ismade, then split in half, each halfbeing tagged with the chip's serialnumber One half of the key is kept atthe US Treasury Department, the otherhalf at the National Institute of Stan-dards and Technology (NISI).

If a law enforcement agency wish-es to decrypt the messages of a spe-cific Clipper -equipped phone, faxmachine, or modem, it will need acourt order for permission to place awiretap. Every time a Clipper transmitsa ciphertext message, it also sends itsserial number in the clear, in a formatcalled a LEAF-Law Enforcement Ac-cess Field. The police write down theserial number and fax it, along withthe court order, to NIST and the Trea-sury Department, The two halves ofthe unit key are faxed to the wiretap-pers, who can then decrypt any mes-sages sent by that Clipper.

If you design and manufacture se-cure phones or modems, must youuse the Clipper? Only if you want todo business with the government, orplan on exporting your product.Though it's doubtful whether a world-wide market exists for encryption de-vices that can be broken by the USgovernment.

Whenever two Clippers attempt tocommunicate with each other, a ses-sion key is created, which is used foronly that communications session. Acopy of the session key is encryptedwith the Clipper's unit key, and is trans-mitted in the LEAF. The two Clippersexchange LEAF'S, checking to see ifthey are valid. Thus if you possess theunit key, you can get the session keyevery time the chip communicates.The LEAF is 128 bits total, and containsthe 80 -bit session key, 32 -bit serialnumber, and 16 -bit checksum. The en -

32 -B TSERIAL

NUMBER

80 -BITSESSION

KEY

16 -BITCHECKSUM

ENCRYPTED WITHUNIT KEY

-0-ENCRYPTED WITH FAMILY KEY -0 -

Fig. 3. The Clipper chip's LEAF (LawEnforcement Access Field) is shownhere. It is 128 bits total, and containsthe 80 -bit session key, 32 -bit serialnumber, and 16 -bit checksum. The entireLEAF is encrypted with the family key.

tire LEAF is encrypted with the familykey (see Fig. 3).

The Clipper is manufactured by My-kotronix in Torrance, California. It is

also called an EES chip, for EscrowedEncryption Standard. There will be twoEES chips: the Clipper or MYK-78,which will be used mainly in securetelephones, and the Capstone orMYK-80, which is a jazzed -up Clipperthat can use public -key ciphers to en-crypt computer files and E-mail. It willalso have digital signature capability.

The Clipper chip itself is tamper-proof anyone who tries to crackopen the chip to examine its "guts" iswasting their time. However, the infor-mation entering and exiting the Clip-per is not tamper -proof, as we shallsee.

The Clipper's Flaw. When DES, RSA,and PGP were first devised, their

creators published full details of thesystems and challenged the world'stop math and code experts to "breakit." That approach made it easy to findany flaws in the ciphers. Not so withthe Clipper chip; the NSA allowedonly five outside cryptologists to ex-amine it, which was a big mistake.

The June 3, 1994 Wall Street Journalmentions an AT&T Bell Labs scientistwho experimented with a prototypeClipper. Matthew Blaze found a wayto make the chip generate a "bogus"LEAF making it impossible for a wire-tapper to get the right escrow key.

Simply removing the LEAF will notwork; the receiving Clipper will not de-crypt data unless the LEAF is presentand its checksum appears to be valid.Generating the fake checksum isdone by the brute -force attack. Thattakes a computer about 42 minutes,and it must be done each time theClipper chip wants to connect withanother, making that techniqueuseless for a phone. It is quite useful fora fax machine or E-mail system, how-ever.

You could speed up the process byusing parallel-processing-a ma-chine using 60 Clippers wired to-gether could find a valid -looking LEAFin under 45 seconds. Also, the ma-chine could precompute a list of ses-sion keys and fake LEAF's (if thenumber of possible recipients is small),but that will work only with fax and E-mail, not phones.

The government could counter thatmethod by doubling the size of thechecksum, which would square thenumber of possible checksums, mak-ing a brute -force attack too time-consuming, For that to work, however,the Clipper would have to be re-designed extensively.

Do Citizens Need Encryption? Inthe past, if the government wanted toread someone's paper mail, it re-quired alot of time and effort: open-ing, reading, copying, and resealingthe letters. Today many letters are inthe form of E-mail, which is nothingmore than a stream of digits flowingfrom one computer to another.

It is possible to listen in on thosemessages and run them through acomputer, which is programmed tocopy any messages that contain trig-ger words such as "bomb," "assassi-nate," or "protest." That can be done 61

VCRCross Reference

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CR055 REFERENCEThis 119 -page reference containsboth model and part -number cross-references updated to include 1994units.

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quickly, automatically, and withoutdetection. The listeners don't evenhave to put a tap on your phone, be-cause most long-distance calls aretransmitted via microwaves. An NSAlistening post located in the micro-wave flow can intercept thousands ofcalls an hour.

Storm on the Horizon. Computermonitors are low -powered, radio -fre-quency (RF) transmitters. For about$300, a receiver can be built to readthe information displayed on a com-puter monitor from several -hundredfeet away. In fact, the U.S. governmenttakes that problem seriously enoughto have devised a set of standards forlow -emission computers called TEM-PEST, for Transient ElectroMagneticPulse Emanation STandard. A comput-er product meets TEMPEST standardsby using two methods: modifying theRF emissions by adding dummy sig-nals, or by capturing the emissions.The first method is classified, but thesecond can be done by anyone.

To capture the RF emissions, amonitor should be completely en-closed with copper that is grounded,with a fine copper mesh on themonitor screen itself. The monitor ca-ble and its junctions should beshielded also. The entire computer

FURTHER READING

The Puzzle Palace. by James Bam-ford, 1982. Houghton Mifflin Company,Boston This is the story of the NSA

Protocol Failure in the Escrowed En-cryption Standard, by Matthew Blaze.June 1994. A paper on how to defeat theClipper chip.

Cryptologia. Rose-Hulman Instituteof Technology. Terre Haute. IN 47803.Tel. 812-877-1511 The quarterly journalon cryptology. Heavy math, but worththe struggle. $34 per year

Shortwave Listening Guidebook, byHarry Helms. 1993, High Text Publica-tions, Solana Beach, CA

Kahn On Codes. by David Kahn,1983, Macmillan. NY The history ofcryptoiogy.

Security In Computing. by Charles PPlleeger. 1989. Prentice Hall. En-glewood Cliffs, NJ. An excellent text-book on encryption, computer andnetwork security. copy protection, vir-uses. and more.

room can be shielded with copper,but water pipes and heating ductsleading out of the shielded room canact like antennae, so that approachmust be used carefully.

Using a laptop computer with alow -powered, LCD screen isn'tfoolproof. The computer processor,disk drive, and modem also generateRF signals. Even the phone cable run-ning from the modem to the wall Jackacts like an antenna. Other sources ofRF leakage are: the printed -circuitboard, internal wires, the power ca-ble, switching transistors, and high -power amplifiers.

If the computer's wall outlet has abad earth ground, it can also in-crease the amount of RE emissions. Infact, if even part of the earth groundhas bad conduction, as from paint ona water pipe, it will increase the RFsignal.

What about a roomful of comput-ers, all using the same type ofmonitor? Wouldn't they emit RF signalsall on the same frequency, making itimpossible to sort through the signals?Not really. Even if two monitors are ex-actly the same model, they mighthave been manufactured at differenttimes, using different componentsdue to a change in the design. If so,they will not have the same RF sig-nature. As a general rule, digitalequipment emits RF signals in the formof pulses, which is easier to recon-struct than the non -pulse RF signalsgenerated by analog equipment.

So, as you can see, there are waysto protect your private informationfrom becoming a little too public.However, advances in computertechnology will probably continue tomake the ciphers of today obsoletetomorrow, which means cryptologywill have to constantly strive to keepup. That should make the scienceworth watching .in the future.

"Oh, I cornered the market in8 -track tapes

Hunting down car noises is noteasy because of the highbackground -noise level of the

automobile. The cheapest method in-volves using a length of tubing or hoseheld up to one's ear to focus the noise,but that has a number of disadvan-tages. First of all, the tube acts as anaudio filter that tends to resonate in anarrow frequency range determinedby its length. Also, the limited bendradius of the tube restricts motion, andmight not allow you to focus on thenoise. Another option is to use an inex-pensive mechanic's stethoscope,which is a metal probe connected toa metal or plastic diaphragm. How-ever, that requires that you be in phys-

headphone amplifier, which is builtaround the other half of the dual op -amp. That audio output can be heardon any "Walkman -style" 32 -ohmheadphones.

Figure 1 is the schematic for theElectronic Auto Stethoscope. That cir-cuit is powered by a 9 -volt battery, 81,and power -supply filtered by capaci-tor C1. The NE5532 audio op -amp U1,directly drives low impedances andcan therefore drive the headphoneswithout the need for a dedicatedpower -amplifier IC such as the LM386.A bipolar power supply has to be usedwith U1. So, to replace the bipolar -supply ground connection, two re-sistors, R1 and R2, are used to split the

through C6, to the tone -control circuitconsisting of C7, C8, R7, R8, and R9.Tone -control potentiometer R8 allowsthe user to peak the amplifier re-sponse to the frequency of the noisebeing investigated. When R8 is cen-tered, the frequency response is flatfrom 20 Hz to 15 kHz. When R8 ismoved toward the bass or treble posi-tion, response in the rejected fre-quency range (i.e. bass is rejected inthe treble position) is cut by as muchas 12 dB.

The output of R8 is connected tovolume -control potentiometer R10,and U1 -b amplifies the signal at thewiper of R10. Gain is determined byR11 and R12. The output of U1 -b is bi-

AutoStethoscope

1

HEADPHONE

Find the sourceof those annoying car noises

with this high-tech ear.

BY CHARLES HANSEN

ical contact with the noise source.The Electronic Auto Stethoscope

presented in this article has a numberof advantages over the previouslymentioned mechanical ones. It has abuilt-in amplifier that amplifies low-level sounds, earphones to help blockout other background noises, and atone control that allows you to focuson the frequency range of the noisebeing investigated, whether it is low -frequency road noise or a high-pitched wind whistle or rattle.

How it Works. The Stethoscope usesan electretmicrophone element,MIC1, which is amplified by 1/2 of U1, anNE5532, dual audio op -amp. The out-put of the op -amp is connected tothe tone -control section and the vol-ume control, where it is sent to the

9 -volt, DC power supply and providea "virtual ground." To provide bal-anced headroom for the audio sig-nals, R1 and R2 are of an equalresistance. Capacitor C2 provides abypass for audio signals and improvesload regulation.

The 4.5 -volt DC bias for the electretmicrophone, MIC1, is obtained fromB1 through resistor R3. Capacitor C3couples the audio output from MIC1to U1 -a, resistor R4 provides the virtual -ground connection, and resistors R5and R6 determine the audio gain ofU1 -a. High -frequency roll -off above 15kHz is provided by capacitor C4, andcapacitor C5 rolls off the low -frequen-cy response below 20 Hz. CapacitorC11 provides decoupling for thepower -supply pins of U1.

The output of U1 -a is coupled,

ased to the virtual -ground voltage of4.5 volts by R1 and R2. If that outputwere fed directly to the headphones,there would be a DC voltage continu-ously applied to them, which couldlimit battery life. For that reason, it wasdecided to isolate the headphonesfrom the DC voltage.

To couple only the audio signal tothe headphones, capacitor 010 isconnected in series with the output.Large capacitive loads have a tend-ency to cause instability, peaking, andringing in the output of a closed -loopop -amp circuit. To prevent that, R13 isconnected in series to decouple theoutput of U1 -b from 010. Feedback -capacitor C9 then provides a high -frequency feedback bypass, restoringstability to the amplifier.

The stereo headphones are con- 63

Oz

cn

Fig. 2. If you would like to build the project on a PC board, use this full-size templateto etch your own.

cr)cr)

S1

B1 C1 +9V 47

it R12.7K

R3'18K

R2 + C2 R42.7K 10 18K ?

C34.7

R610K

A

3

2

8

a1/2NE5532

AAA

R5C4233pF 220K

%I

C61

4.1E

C7 1 R7 1!.1

033

10K

C8 _.033

R910K

R850K

TONE

..R12

680K C9 R1310pF loon

R11 15K

- WS,RIO50K 9

VOLUME

+ C10

1.

Fig. I. The heart of the Stethoscope is the NE5532 audio op -amp, Ul . That componentdirectly drives low impedances and allows the use of headphones without addinganother amplifier.

3 INCHES

nected in series to make it easier forthe op -amp to drive them to a usefulvolume. Because the microphone sig-nal is monophonic, there is no needfor stereo output.

IL Construction. The prototype Elec-tronic Auto Stethoscope was built on aperforated board. Because of the

64 high gain used, wire lengths were kept

short to prevent noise pickup and os-cillation. For your convenience, aprinted -circuit board template is pro-vided in Fig. 2 if you prefer to etch anddrill one. If that is the case, use theparts -placement diagram shown inFig. 3 to make building the projecteasier. Select a project enclosure thathas sufficient room for the perforatedboard or PC board and all chassis -

PARTS LIST FOR THEELECTRONIC AUTO

STETHOSCOPE

RESISTORS(All fixed resistors are 1/4 -watt, 5%

units, unless otherwise noted.)RI, R2 -2700 -ohmR3, R4 -18,000 -ohmR5 -220,000 -ohmR6, R7, R9 -10,000 -ohmR8 -50,000 -ohm, linear

potentiometerR10 -50,000 -ohm, audio -taper

potentiometerR11 -15,000 -ohmR12 -680,000 -ohmR13 -1.00 -ohm

CAPACITORSCI -47-11F, 35-WVDC, electrolyticC2 -10-µF, 35-WVDC, electrolyticC3 -4.7-µF, 35-WVDC, electrolyticC4-33-pF, mica or metallized -filmC5, C6 -1-11F, 35-WVDC, tantalumC7, C8 0.033-µF, metallized -filmC9-10-pF, mica or metallized -filmC10 -220-µF, 35-WVDC,

electrolyticC11-0. l -µF, ceramic -disc


U I-NE5532N, low -noise dual op -amp, integrated circuit

MICI-electret microphone (RadioShack #270-092 or equivalent/

J1 -3.5 -mm phone jackSl-SPST toggle switchB1 -9 -volt alkaline batteryPrinted -circuit materials, project

enclosure, 9 -volt -battery snap withleads, 1/4 -inch ID tubing (see text),two -conductor shieldedmicrophone cable, control knobs,32 -ohm stereo headphones,standoffs, wire, solder, hardware,etc.

mounted components.In keeping with good assembly

practice, install the least -sensitiveparts first, followed by the more -sen-sitive parts. Start by installing the bat-tery connector and an IC socket atthe position for U1. Next, connect thewiring to potentiometers R8 and R10,switch S1, and jack J1. Solder in thepassive parts (resistors, then capaci-tors) and double check the orienta-tion of the polarized components.

Before installing the last on -boardcomponent, U1, into its socket, andbefore attaching MIC1, test the powersupply. Turn on S1 and measure the

B1

C1

S1

0MIC1

+

GND

R3CR54

C7R1

C3 R6

+I R9

+ R2C5

I

C2

J1

II

C10

R7

-C11-

U1

R4

C8

C9R13

R11R12

R8

-Nah-A

R10

Fig. 3. Use this parts -placement diagram is a guide when assembling theStethoscope. Be sure to double check the c lignment of the polarized components.

MICROPHONE ELEMENTPROBE TUBE 2 -CONDUCTOR

SHIELDED MICROPHONE CABLE

SPLICES (3)

Fig. 4. The electret microphone element, MICI, needs to be mounted in a tubeassembly. Before doing that, extend the reach of MICI's short leads by attaching themto a two -conductor, shielded microphone cable.

battery voltage across C1. Thencheck the virtual -ground voltageacross C2; it should read half the bat-tery voltage. If that is the case, turn offS1 and prepare the microphone as-sembly for attachment. If the voltageseems too high, check for wiring mis-takes.

Microphone MICI can be mountedin a number of ways. The prototypehas the microphone installed inside asix -inch -long, 3/8 -inch diameter, plastictube "wand," with the end of MICI justbelow flush with the open end of thetube. Because the leads on MICI areonly a couple of inches long (as sup-plied by the vendor), they need to beextended (as shown in Fig. 4) beforethe microphone is mounted in thetube.

To extend the leads of MIC1, usetwo -conductor, shielded microphonecable; splice the red (+) microphonewire to the red wire in the cable, andthen splice the white microphone -sig-nal wire to the black wire in the cable.

Finally, splice the ground wire of themicrophone to the shield of the ca-ble. Use shrink sleeving over each ofthe splices, and then cover them allwith one larger piece of shrink sleevefor ruggedness. You can then eitherdirectly connect the other end of thecable to the circuit board (as indicat-ed in Fig. 1) or you can add anotherjack and plug to make the micro-phone detachable.

If you do mount the microphoneprobe directly to the case of the am-plifier module, the tone and volumecontrols of the Stethoscope will beeasier to use because the entire casecan be aimed at the noise source.That is why a six -inch -long probe wasrecommended.

Once the microphone assembly isprepared and the leads are con-nected to the circuit board, turn on S1again and measure the voltageacross the red microphone lead tothe shield. It should be 3.5- to 6 -voltsDC (4.5 -volts DC nominal). If that is so,

turn off S1. You can then safely insert U1into its socket.

If you want to use the Stethoscopein physical contact with engine noisesources (similar to a mechanicalprobe -diaphragm unit), mount MICIin a metal tube. That will provide thenecessary rigidity to transmit me-chanical sounds to the microphone.Be sure to electrically insulate thecase of the microphone elementfrom the metal tube. It is also a goodidea to cover the metal tube with anon-conductive material such asshrink sleeving to prevent the tubefrom causing any electrical shorts un-der the hood.

Checkout and Use. Plug in theheadphones and turn on theStethoscope. Place the TONE control,R8, in the center of rotation and turnthe VOLUME control, R10, all the waydown (to the left). There should be nosound in the headphones. If you donot get any noise, proceed as follows.

Aim the microphone at a knownlow -volume audio source such as aradio speaker, and turn the VOLUME upuntil you can hear the audio sourcethrough the headphones. You shouldthen be able to turn up the VOLUME highenough so that the sound in theheadphones drowns out the source.Also, you should be able to greatlyaffect the tone of the audio sourcewith the TONE control. That completesthe check-out procedure.

When selecting headphones to usewith the Stethoscope, keep in mindthat the differences in sensitivity andfrequency response between variousWalkman -style headphones is surpris-ing. Of course, the more expensiveheadphones have higher volume andfidelity; however, the Stethoscopecan drive even the cheapest head-phones to adequate volume. Watchout for small headphones, though. Athigh volume, acoustic feedback canoccur between them and the micro-phone. Closed earpiece head-phones are less prone to feedbackthan the smaller, open type.

The author originally built theStethoscope to track down a rattle inthe console of his car (which turnedout to be a lost jeweler's screwdriver).Without the Stethoscope, thatwouldn't have been possible, evenwith someone else driving. You shouldfind it to be just as useful. 65

If you are looking for an unusualway to add some electronics funto your Christmas, here's a project

that you are sure to love. Called theLED-Tric Christmas Tree, it is a three-dimensional flashing Christmas -treedisplay that can help brighten up theholidays. To achieve its 3-D look, thetree Is built using three identicalboards connected together at thespine and spaced at 120 degreesapart. Each board sports six LED's,which are mounted to straddle theboard edges so their light is directedoutward. To complete the look, a sin-gle flashing LED is mounted at thetree's top

How it Works. The Tree consists ofthree essentially identical circuits. Thebasic schematic is shown in Fig. 1. Asyou can see, each circuit consists ofan LM3909 LED flasher IC (U1), six LED's,

and some support circuitry. However,note that the six LED's of each circuitare distributed equally over the threeboards. That is done using intercon-nection pads located at the boards'spines. The pads on the compo-nent side are designated CPwhile thepads on the foil side are desig-nated SP For the purposes of ourdiscussion, the first of the threeboards is identified as A, thesecond as B, and the thirdboard as C.

Let's see how all of thatworks. The drive signal istaken from pin 8 of U1 onboard A. It leaves thatboard via pad SP1 onboard A and is fed to padCP1 on board B, where itdrives LED1 and LED4 onthat board. That same drive

2 signal then leaves board Bat SP2 and goes on to con-nect with CP2 on board C,where it drives LED3 and

o LED6. Finally, the signal

00, leaves board C via pad6 SP3 and is fed back to

board A via CP3, where itdrives LED2 and LED5. Theresult of all of that is to al-ways move the drive signal

°2 one level higher as the sig-nal rotates around the tree.

LL To create a more randomlook, however, the value ofthe timing resistor, R8, is dif-

66 ferent on each board.

Light up your holidayswith this unusual and

festive conversation piece

BY RICHARD PANOSH

The"LED -Trio"Christmas

Tree

One independent blinking LED isplaced at the very top of the Tree onboard A. Power for that LED, LED7, issupplied by installing jumpers JU1 andJU2 on that board only. The powerswitch and battery also appear onlyon board A.

Construction. Building the Tree is rel-atively straightforward. The pattern forthe foil side of the PC board is shownin Fig. 2; the component side's patternis shown in Fig. 3. Remember, the com-plete tree requires three of theseboards, and aside from S1, B1, andLED7, three sets of parts. If you prefer,boards, kits, and assembled units arealso available from the source givenin the Parts List.

The parts -placement diagram isshown in Fig. 4. Care should be exer-cised when soldering the LED's to theedge of the board. Cut both LEDleads to about a quarter of an inch,but remember to leave the negative,cathode, lead a little shorter for easyidentification. Make sure the positive,

anode, lead is soldered to the com-ponent side of the board, and the

cathode lead is soldered to the foilside so that the LED straddles the

edge of the board.Similarly, care should be exer-

cised when mounting LED7.Again, its anode lead is sol-

dered to the componentside of board A while thecathode is soldered to thefoil side of that board. Becareful when selecting theunit used for LED7. Someblinking units require 5 voltsor more of power for prop-er operation. The specifiedunit is rated to operate at2.5 volts, and is ex-tinguished at 2 volts.

Mounting the LED's onthe board edge can get alittle tricky. Fortunately, atechnique used in assem-bling surface -mount com-ponents can be used hereto good advantage. Thetechnique involves the useof an epoxy such as DuroDepend II, available frommost hardware stores. Adrop of the part A epoxy isapplied to the first surfaceto be joined, and a drop ofpart B epoxy is applied to

LED6 LED5 ILED4 ILED3

R53952 7'

R63952

ACP2 SP3

SEE TEXT

R4

390

CT.P3

R3390

R2

LED2 ILED1

R1

390

CP1*

C21000

>SP2*

SP1<

8

8

5

ci22 "m`

R7

2200

2

VCC OUT

SLOWLM3909

GND

14

LED7

SP+* CP+*

I JU2*xx)

CP4*

SP4

)./

Jul'

OS1

3V B1

ACP- SP -

Fig. I. The LED-Tric Christmas Tree consists of three essentially identical circuits. Theschematic for the basic circuit is shown here.

4oc a

0

0

2 3/4 INCHES

Cr)

0r-0m

cip

the second surface. Then, when theIwo pieces are brought together, abond is established in a few minutes.

To mount the LED's, place a smallamount of the part A epoxy on thebottom surface of the LED and a smallamount of the part B epoxy at theappropriate spot on the board edge.Once the bond has been formed, justsolder the leads to the pads. Be sure touse as little epoxy as possible to avoidgetting any on the leads or the pads.

The same technique can also beused to join the three boards at theirspines. You may find it helpful to drawa template showing the proper an-gles (120°) and use it as a guide.Again, be careful to not get any epoxyon the interconnecting solder pads.Once the epoxy has set, bridge alladjoining interconnection pads on allboards with a healthy amount of sol-der. In addition to providing electrical

2 3/4 INCHES

Fig. 2. Here's the foil side of the Tree's PC Pattern. It is shown Fig. 3 Here's the component side of the board. Remember thatyou will need three boards to build the Tree.here full size. 67

68

connections, these pads are used togive mechanical strength to the as-sembly.

The power switch (S1) should bemounted on PC board A at the ap-propriate location. On boards B andC, a feedthrough should be installedat the rightmost pad at the S1 locationas indicated in Fig. 4. A secondfeedthrough, near C2, should be in-stalled on all boards.

Two jumpers are also installed onboard A. The first, JU1, installs on the foil

PARTS LIST FOR THELED-TRIC CHRISTMAS TREE

SEMICONDUCTORSU l-LM3909 LED flasher, integrated

circuitLEDI-LED6--T-I-1/4 superbright

LED, assorted colorsLED7-Flashing LED, Radio Shack

276-036C or equivalent

RESISTORS(All resistors are 1/4 -watt, 5% units)R1-R6-39-ohmsR7-220 ohmsR8 -a -1000 -ohms, see textR8 -b -1200 -ohms, see textR8 -c -1500 -ohms, see text


C1 -22µF, 16 WVDC, electrolyticcapacitor

C2 -1000g, 16 WVDC, electrolyticcapacitor

Bt -3 volts, 2 alkaline C -cellbatteries

SI-SPST slide switch, PC mountPrinted -circuit board, battery holder

(twin C -cell size, see text), 6-32x 1/4 screw, nylon spacer, 6-32brass nut, wire, solder, etc.

Note: The following items areavailable from Vista, PO Box 1425.Bolingbrook, IL. 60440. (708)378-5534. A set of three printedcircuit boards is available asXMASBRD at $18.00. A kit of allparts including etched, drilled, andplated -through silk-screened PCboards and 2 alkaline batteries areavailable as XMASKIT at $35.50.A fully assembled tree is availableas XMASASSEM at $45.50.Please add $5.00 for shipping andhandling in the U.S. and Canada.Illinois residents please add 7.5%sales tax. Check, money order, andcredit cards are accepted. For fastcheck verification, please providestreet address (no P.O. box),telephone number, and driverslicense number and state of issue.

lrLED7*

CP4/SP4

.1111* 1U2*

til-R6-4i";7;

CP3/SP3

13-415-0

CP2/SP2

CP1/SP1

CP-/SP-

CP+/SP+

LEM***

LED5***

B1'

LED4***

/%°

LED3

BOARD A ONLY (SEE TEXT)

**FEEDTHROUGH (SEE TEXT)

***SEE TEXT

LED2***

LED1

Fig. 4. Use this parts -placement diagram when building your unit. Note that some of thecomponents mount on only one of the boards.

side of the board, while the second,JU2, installs on the component side.Those jumpers are used to get powerto the blinking LED at the top of thetree.

The battery leads are connected tothe appropriate positions on board A(BAT + and BAT-). Incidentally, if youwish to omit the switch, the batteryleads can be connected to the CP + /SP + and CP - /SP - pads on board AIf you do that, however, the Tree willrun continuously. On the positive side,the current draw of this project is soslight that a pair of alkaline C -cellscan power it for about a month.

Speaking of the batteries, they andtheir holder make up the base of theTree. The battery holder should be atwin plastic C -cell type with a mount-

ing hole located at the center; if yoursdoes not have a hole, it will have to bedrilled. The battery holder is mountedto the tree by means of that hole anda 3/4 -inch long, 6-32 machine screw. Ahalf -inch long, unthreaded, nylonspacer is installed over the screw andthe screw is fastened to the tree baseby means of a large 6-32 brass nutthat is soldered in the notch at thebottom of the tree spine. The length ofthe screw can be trimmed to fit, or,alternately, one or Iwo washers canbe installed as spacers.

That's all there is to it. The circuit Issimple enough that it should work thefirst time power is applied. Once it iscompleted, your LED-Tric ChristmasTree is sure to brighten up your holi-days.

Telephone -Line SimulatorMr. Watson, comehere; I want you.Ever since those

famous words were spokenover the first telephone in-strument by Alexander Bell,we've discovered unlimiteduses for the telephone. Nowwe can communicate notonly with our trusty tele-phone, but we can also usePC modems, Fax machines,answering machines, andthe like.

But those gadgets havebecome complicated, andthey occasionally breakdown. Testing them can be areal chore, unless you haveaccess to multiple phonelines so that you can conve-niently place test calls. Ofcourse, there are commer-cial phone -line simulatorsthat can be used instead ofa phone line, but they cancost several hundred dollars.

Well, with Ring -Ill you cannow have a complete tele-phone system in a box. Forget abouttying up your telephone line; simplyplug in the telephone device that youwant to check, and do your tests.

All of the standard telephone -sys-tem features that you need are sup-ported. You can ring -up telephones,Fax machines, modems, and answer-ing machines. Just about anythingthat you can connect to a standardphone line can be activated withRing It!.

Because the standard telephone -call progress sounds are generated(dial tone, busy signal, ringing, etc.),you can even use Ring -It! to demon-strate telephone equipment. Don'tever tie up your home or businessphone again while you show off yourtelephone products. In fact, with Ring -It!, it's almost impossible to tell that youaren't using a real phone line.

You can even connect a pair ofstandard phones and create a simplephone system. In that configuration,

BY THOMAS E. BLACK

Use it to test or demonstratetelephone equipment, to setup your own mini telephone

system, and more.

the phone on line 2 automaticallyrings when the phone on line 1 is

picked up. The lines are connectedwhen both phones are in use, and theconversation ends by hanging up.

The flexibility of Ring -It! is providedby a single -chip microprocessor,which allows us to keep the compo-nent count to a minimum. An on-board ring generator provides theprecise voltages required to activatethe phone equipment, and a call -progress tone -generator IC createsthe normal telephone -related sounds(busy signal, ring signal, etc.).

Features. Ring -It! has five differentoperational modes that can be invok-ed through one of the front -panel -mounted push switches. There is evenan LED readout that displays the cur-rent mode that is in use.

The LED display is used to indicatemode, cycle time, and dialed -digit in-formation. Its decimal point is illumi-

nated only when the modeor cycle time is shown; a de-coded DTMF (Dual -ToneMulti -Frequency) digit isshown as a value without thedecimal point.

The five modes can be in-voked by pressing the Modeswitch; the active mode isshown in the LED display. Themodes are summarized asfollows (the bracketed valueindicates the correspondingLED display):

[n.] Normal Ring Mode [A.] Automatic Ring Mode [b.] Beep Tone Mode [c.] Cycle Ring Test Mode [d.] Dumb Mode

The normal ring mode isused when you want stan-dard telephoneulation. When you take theline -1 (main) phone off -hook, a dial tone is heard. Ifyou do nothing for twentyseconds, a "reorder" sound isheard. If you tone dial any

seven -digit phone number, the line -2(test) phone will start to ring. When line2 answers, the front -panel connectLED will light up.

While you press the DTMF keys ofyour phone, the corresponding digitwill appear in the LED display for up totwo seconds. Because of limitations inour display, the * tone is shown as "A"and the # key is shown as

If you attempt to ring the test lineand it is off -hook, then a busy signalwill be heard. Please note that be-cause it is a one-way device, line 2can not be used to ring line 1.

There are some shortcuts in the nor-mal mode that can be used to ringthe test line. For example, pressing themain phone's DTMF * key will imme-diately start the ring request. The front -panel Ring switch will also start thering cycle, which can be used if themain line's phone is not DTMF com-patible.

The normal mode is perfect for 69

70

demonstrating telephone equipmentsuch as answering machines, Fax sys-tems, voice mail, modems, and more.Becuuse the standard call -progressaudio tones are heard, your demon-stration will appear more natural toyour audience and equipment.

The automatic ring mode is similarto the normal ring mode, except thatin the automatic mode, ringing be-gins immediately after the line -1phone is picked up. That operation issometimes called a "Ring -Down line"by phone -system manufacturers. If ei-ther line is off -hook when the other ispicked up, the two lines will be auto-matically connected together.

The automatic mode, besidesbeing used to test phone equipment,is also perfect for use as a front -entryintercom for home or office use. Placea phone near you and one near yourentry. Be sure to post a note near theentry phone that instructs your visitorsto "lift the receiver for assistance."

The beep tone mode is speciallydesigned for cycle testing answeringmachines and other types of tele-phone equipment. That mode doesnot start until the Ring button or theDTMF * key is pressed.

It is not necessary to have the line -1phone off -hook during the beepmode. Whenever line 2 is taken off -hook the two lines will be automat-ically connected together and a se-ries of repeating test tones will begenerated.

During the beep mode, the test lineautomatically rings after a short ad-justable delay (the delay is skipped onthe first cycle). If the test line is an-swered, staggered beep tones areplayed. Those tones have been de-signed to keep a voice -controlled an-swering machine from hanging up.The ring -up cycle repeats (after therequested delay) until the mode iscanceled by pressing the Modeswitch.

For example, if the delay is set forthirty seconds, the device being test-ed will be rung -up thirty seconds afterthe last answer/disconnect cycle. Thetest tones will be played as long as thetest line is off -hook. If the test line goeson -hook, the delay cycle starts upagain.

The cycle ring -test mode providesmost of the features of the beepmode, except that in the former, thebeep tones are not played and a

TABLE 1-DTMF TONE PAIRS

Low Group

Column 01209 Hz

High Group

Column 11336 Hz

Column 21477 Hz

Row 0, 697 Hz 1 2 3

Row 1, 770 Hz 4 5 6

Row 2, 852 Hz 7 8 9

Row 3, 941 Hz 0

Note. In 16 -digit DTMF, there is an eighth tone (1633 Hz. Column 3)

phone must be plugged into themain line. To start the cycle you mustpick up the phone attached to line 1.Again, if either line is off -hook whenthe other is picked up, the two lines willbe automatically connected to-gether.

When line 2 answers, your con-versation may begin. If line 2 hangs upand the main phone remains off -hook, the test line is automaticallyrung up after the delay time. That cy-cle repeats until the main phone ishung up.

The dumb mode provides a silenttalk path and allows a manual ring.You will not hear any call progresstones; however, you can conversenormally.

Line -2 ringing is controlled by usingthe Ring switch or the main phone'skey. The ring signal will follow the keypresses. Unlike the other modes, theydo not continue to ring when the keysare released.

The dumb mode is perfect for test-ing the basic operation of equip-ment. And because you can controlthe duty cycle (cadence) of the ringsignal, non-standard equipment canbe tested for ring operation.

How it Works. A schematic diagramof the Ring-Itl telephone -line simulatoris shown in Fig. 1. The circuit's intel-ligence is provided by U9, aPIC16C57-XT/P microcontroller IC.That chip is a member of MicrochipTechnology's family of high -perfor-m a nce, low-cost 8 -bit micro -controllers.

A microcontroller is a small, gener-al-purpose computer chip that con-tains a microprocessor -type, CentralProcessing Unit (CPU), similar to theone found in your personal computer.However, it also incorporates Ran-dom -Access Memory (RAM), Read -

Only Memory (ROM), and digital In-put/Output (I/O) lines. In other words,it's a complete computer system thatis housed in one IC.

Because the PIC16C57-XT/P is acomputer, it needs software to oper-ate. The internal ROM holds the soft-ware program, which is calledfirmware. The firmware is permanentlyprogrammed and is non-volatile,which means that it isn't lost whenpower is turned off. The RAM is used bythe program for storing temporarydata variables and state conditions.Although there are only 72 bytes ofRAM, it's more than enough fcr ourapplication.

The firmware -controlled functions,such as ring generation, tone detec-tion, LED and relay control, etc., areevent -driven, so all features workseamlessly together. Unlike simpleloop -controlled programs, our soft-ware design uses a time -based taskscheduler to control the hardwareoperations.

Installing the firmware into ROM in-volves a process called prom burning,and special equipment is used to per-form that task. For those without therequired equipment or expertise, apreprogrammed microcontroller isavailable from the source given in theParts List. On the other hand, for thoseof you who want to "roll -your -own," wehave made the compiled object -code file, in Intel 8 -bit merged(INHX8M) format, available on thismagazine's BBS (516-293-2283, 8N1).Although the software is copyrightprotected, you are free to dowr loada copy for your personal use. For otheruses, consult the source given in theParts List.

Getting back to the circuit, U9'sRTCC input is used to emulate an ad-justable -time -delay timer. The fre-quency of the oscillator formed by

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U11 -d, U11 -e, R41, and C24 can bevaried using potentiometer R35. Its re-petition cycle is sampled by the mi-crocontroller and then translated bythe software into a 10- to 90 -secondend -of -cycle timer. The delay featureis used in the beep and cycle modes.

InpuVOutput Control. The micro -controller's input/output control linesare used to monitor the mode, ring,and hook -switch switches. They alsocontrol the LED display, line relay, andcall -progress tone generator.

Those twenty I/O lines are labeledon the microcontroller as RAO-RA3,RBO-RB7, and RCO-RC7. Under soft-ware control, RA2-RA3 and RC3-RC7are configured as outputs, RAO-RA1as well as RB4-RB7 are configured asinputs, and RBO-RB3 are used as bothinputs and outputs; RCO-RC2 are un-used.

Microcontroller-input RAO monitorsS2 (ring) and input RA1 is used to readS1 (mode). Software is used to de -bounce those momentary switches,which ensures that contact bouncedoes not cause multiple operations.

Under microcontroller control,RBO-RB3 can be configured to read(input) the decoded DTMF codes fromU7. They can also output call -progresstone codes to U8 or LED codes to U10.We will discuss the DTMF decoder,call -progress generator, and LED in-terface in just a moment.

The direction of those four I/O databits is also accompanied by micro -controller outputs RA2 and RA3. Nor-mally low bit RA2 is set high to read theDTMF values. Normally high bit RA3 isset low to write the current call -pro-gress tone code into U8.

The RB4 input is normally low, butgoes to a logic high when a valid

DTMF is detected. The microcontrolleruses that signal to determine when todecode a new DTMF digit.

The RB5-RB6 inputs are used tomonitor the line 1 and line 2 optoiso-lated, loop -current hook switches (U2and U1 respectively). Those act as nor-mally open switches and detectwhen the attached telephones havebeen taken off -hook. For example, ifline 2 is off -hook, current will flowthrough optoisolator U1's input, whichwill force its output at pin 4 low. Themicrocontroller can read the outputof U1 and U2 and act appropriately.

The input at RB7 is used to read thecircuit -board mounted, power -upconfiguration jumper, JU1. If thejumper is not installed, Ring -111 will de-fault to the normal (n) mode upon ACpower up. If the jumper is installed, theautomatic (A) mode will be used asthe power -up default.

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RINS-ITIDI 6 I TOL PRODUCTS CO-

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6 INCHES

Fig. 3. Here is the foil -pattern for the main board's component side.

The RCO-RC2 port bits are unused.The RC3-RC7 bits are configured asoutputs and are used to control theline relay, ring -voltage generator, andCPC pulse. When used in conjunctionwith the RB0-RB3 output bits, they cansend new LED display values to U10, a74HC259 8 -bit addressable latch.

LED Display. Microcontroller outputbits RB0-RB2 and RC3-RC4 are usedto control the single -character, seven -segment LED display, DISP1. (Note thatthe display actually has eight seg-ments if you count the decimal point.)Like most LED readouts, it was origi-nally designed for displaying numbers0-9. But by using a combination ofupper and lowercase, and a littleimagination, it is possible for us to geta limited number of alphabeticcharacters.

We use the alpha characters to dis-

play the current test mode and someof the DTMF tone values (* and #). Asmentioned earlier, the * and # DTMFcharacters are not displayable, so weshow them as "A" and "Fr

The LED segments are enabled bythe addressable latch, U10. The micro -controller uses RB0-RB2 to addresswhich of eight LED segments are to bemodified. The RC3 output selects howthe LED segment will be illuminated(on/off) and RC4 latches the ad-dressed value.

To update the display, the micro -controller must step through all eightbits of U10 and set or clear them asrequired. Of course, that is done sofast that it appears to happen as asingle action. Eight 330 -ohm series re-sistors are used to safely limit the cur-rent into each segment of the display.

Ring Generator. Microcontroller

output -bit RC5 is used to provide the20 -Hz frequency used by the step-upring -voltage transformer, T2. BecauseAmerican and many foreign phonecompanies use 20 -Hz ring frequen-cies, we have provided the same inthe Ring -It! design. Note that somelow -end commercial telephone sim-ulators use 60 -Hz ring frequencies be-cause they are easily derived from theAC power line. However, some phoneequipment will not operate correctlywith them. To maintain compatibilitywith all standard telephone equip-ment, a software -controlled, standard90 -volt AC, 20 -Hz ring generator isused.

The 20 -Hz generator provides relia-ble ring activation for at least twostandard telephones. The high volt-age (approximately 90 volts AC) isgenerated by T2, a step-up ring -volt-age transformer, which is driven by 73

ICI 1994 016111L MODS CO 1910E IN 181

REV

RINS-ITIAC POWER BOARD

M1 3/4 INCHES

Fig. 4. For better performance, thepower -supply circuitry is located on aseparate board. The foil side of thatpower board is shown here.

push-pull power transistors Q3 andQ4. Because square -wave -derivedring voltages are used, some spe-cialized telephone equipment maynot respond correctly. However, allstandard telephone equipment willwork with the unit.

Please note that T2 is used "back-wards" in this circuit. That is, the lowvoltage input is at its secondary andthe output is taken from the trans-former's primary.

Calling -Party Control. To help dis-connect some telephone equip-ment, Ring-Itl uses a method calledCPC (calling -party control). On mostphone lines, the phone voltage is in -

DANGER -H I GH VOLTAGE!

Per1 3/4 INCHES

Fig. 5. The component side of the power74 board is shown here full size.

terrupted for a few hundred millise-conds after the phone call ends. Thatcauses a current -interruption pulsethat is sensed by some devices suchas answering machines, whichcauses them to disconnect imme-diately.

Microcontroller port bit RC7 is usedto control the CPC pulse. Normallylow, that bit will be set high for about500 ms to turn on optoisolator U12,which shuts down voltage regulatorU3. Because U3 supplies the talk volt-age to the phones, when it tem-porarily shuts down, the attachedphone equipment senses a CPC in-terruption. The CPC feature can bedisabled by removing the JU2, theCPC -configuration jumper.

Line -Connect Relay. While thephone lines are idle or during line -2ringup, microcontroller port pin RC6 isa logic low and relay K1 is de -ener-gized. That places T2, the high -volt-age ring transformer, in series with line2. That allows power for the talk pathand/or microcontroller-controlledring voltage.

Energizing relay K1 connects thetwo phone lines together and dis-ables the ring -voltage signal path.The relay is switched whenever portpin RC6 is a logic high.

You can monitor pin 12 of U11 if youhave an application that needs toknow when the two lines are con-nected. That signal is available at theexternal -control output (labeled EXTCTRL on the schematic) and is a logiclow when the relay is energized. Itcould be used to turn on an externalaudio source, relay, or whatever. It is aTTL-compatible signal and can sink orsource about 10 mA.

DTMF Decoder. Decoding the di-aled phone -number digits is a simpleexercise because of the use of theindustry -standard M-8870 DTMF tone -receiver for U7. That popular IC ismade by the Teltone Corporation,Mitel Semiconductor, and others.

The receiver decodes only DTMF-type telephone digits; rotary -pulse -di-aled digits are ignored. The DTMF fea-ture allows you to conveniently testthe tone dialing feature of your phoneequipment.

As long as a DTMF tone is presentthe display will show its value; speeddialers may operate too quickly to al -

TABLE 2-FOUR-BIT CODE

DIGIT D3 02 D1 DO

1 0 0 0 1

2 0 0 1 0

3 0 0 1 1

4 0 1 0 0

5 0 1 0 1

6 0 1 1 0

7 0 1 1 1

8 1 0 0 0

9 1 0 0 1

0 1 0 1 0

1 0 1 1

1 1 0 0

low adequate viewing. To help seesome very short DTMF digits, the mi-crocontroller extends the viewinglime of the last digit for about twoseconds.

The DTMF encoding standard de-fines up to 16 dual -tone combina-tions, but standard phones onlygenerate 12 of them. In a telephone,those 12 keys are arranged in fourrows and three columns, and those ina given row or column have one tonein common.

For example, if you press the 3 digit,a 697 -Hz tone and a 1477 -Hz tone arecombined. Sevenvolved in standard DTMF generationand they are separated into twogroups. The row information is calledthe low group and has the frequen-cies that range from 697 Hz to 941 Hz.The column information is called thehigh group and it covers frequenciesfrom 1209 Hz to 1477 Hz. Table 1 showsthe layout of the DTMF tone pairs.

DTMF Decoder U7 incorporatesswitch capacitor filtering to separatethe low- and high -frequency tonegroups. Qualified DTMF digits are de-coded into a four bit code as shown inTable 2.

Call -Progress Tone Generator.Phone -company generated soundsthat are heard on the phone, such asdial tone, busy signals, telephoneringing, etc., are considered comforttones. They are present only to con-firm the progress of the telephonecall. Although foreign countries usesimilar tones, they are slightly differentthan those heard in the U.S. In Ring It!,the comfort tones are largely pro-duced using U8, a Teltone Corpora-tion M-991 call -progress tone -gener-ator chip.

Actually, Ring -It uses both software

PARTS LIST

SEMICONDUCTORSUl. U2, 1112--PS2501-1 optoisolator

(NEC). integrated circuitU3-LN1317T 1.2 -37 -volt adjustable

regulator. integrated circuitU4-LM7812 12 -volt regulator,

integrated circuitU5-LM7805 5 -volt regulator.

integrated circuitU6-LM358N km -power dual op -

amp, integrated circuitU7-M-8870, CMOS DTMF

receiver (Te'tone Corporation),integrated circuit

U8-M-991, CMOS call -progresstone -generator (Teltone), integratedcircuit

U9-PIC16C57-XT/P CMOS 8 -hitmicrocontroller (;MicrochipTechnology), integrated circuit

U10-74HC259 or 7411CT259CMOS addressable latch.integrated circuit

U11-74HCT14 CMOS hex inverter.integrated circuit

QI, Q2-PN2222 NPN transistorQ3-TIP110 NPN Darlington

transistorQ4-TIP115 PNP Darlington

transistorBR1-1 amp. 50 PIV, bridge rectifierDI. D9 -1N914 or 1N4148 general-

purpose silicon diodeD2-D8-IN4001 silicon rectifier

diodeDISPI-7-segment LED. 0.56 -inch.

common anode, RH decimal pointLEDI-Green LED. TI Y, size

RESISTORS(All fixed resistors are VI -watt,units unless otherwise specified.)Rl,R9 ,R17-R20, R26 -100,000 -

ohmR2, RIO -150 -ohmR3. R13, R23. R29--1000-ohmR4, R6 -220 -ohm, 2 -watt. metal

oxideR5 -300 -ohm, 2 -watt, metal oxideR7, R25, R31-R33, R36-R40-330-

ohmR8 -7,500 -ohm

FOR THE TELEPHONE -LINE SIMULATOR

R11. R22 -100 -ohmR12-not usedR14 -100.000 -ohm, trimmer

potentiometer. PC mountR15, R16, R24, R27, R28. R34,

R4I-10,000-ohmR21 -300,000 -ohmR30 -2.2 -ohmR35 -10.000 -ohm. potentiometer.

panel -mount. linear -taper

CAPACITORSCl. C4, C5-0.47-p,F, 50-

WVDC.radial-lead, electrolyticC2, C3. CO. C23-10-1J,F, 16-

WVDC, radial -lead, electrolyticC7, CS 170-µ,E 35-WVDC. radial -

lead, electrolyticC9--470-p_E 50-WVDC.

electrolyticCIO-C13. C16, C18-C21--0.1-µ,F.

50-WVDC, radial lead.monolithic -ceramic

C14, C15, C17-27-pF, ceramic -disc,see text

C22 -2200-µF, 16-WVDC. axial -lead, electrolytic

C21 0.01-µF, radial -lead. polyester


KI-DPDT relay. l2-VDC coil. DIPPackage, P&B T83S11 D212-12,Aromat DS2YE-S-DCI2V. orsimilar

SI. S2-SPST switch, normallyopen. momentary -contactpushbutton, panel mount

TI-Telephone-coupling transfOrmer,600-ohm:600-ohm, PREMMagnetics SPT130 or equivalent

T2 --Ring transformer, split bobbin,dual 115 -VAC primary to dual 6.3 -VAC secondary, Magnetek/TriadFS12-200 or equivalent

T3-AC power transformer, splitbobbin, dual I l5 -VAC priamary todual I4 -VAC secondary., Magnetek:.Triad FS28-200 or equivalent

XTALI-4.00-MHz crystal, HCIS orHC49 package, or 4.00-N1Hzceramic resonator, see text

XTAL2-3.5795-MHz crystal, HC18or HC49 package JI, .12-RJ11 6/2or 6/4 modular telephone jacks

H -0.5 -amp fuse, 5 x 20 mmPrinted -circuit boards. IC sockets,

right-angle socket, fuse clips(Keystone 3521 or similar), ACline cord and plug. enclosure, heatsinks, wire, solder, etc.

The following parts are availablefrom: Digital Products Company.134 Windstar Circle, Folsom, CA95630; Tel. 916-985-7219; FAX916-985-8460. Complete Ring -It!kit, including pre-programmedinicrocontroller, PC -board set,relay, transformers, IC's, resistors,capacitors, seven -segment LEDsocket, documentation, etc. (casenot included); $145.00. BasicRing -It! kit, including PC -boardset, programmed microcontroller,complete documentation; $53.95.Transformerirelay kit, includingK1, T1, T2, and T3; $38.95. Hard -to -get IC kit, including UI, U2,U7. U8. U10, Ull, U12; $24.50.Printed -circuit board set; $34.95.Programmed P1C16C57-XT/Pmicrocontroller (licensed copy);$20.00. Seven -segment LEDsocket; $3.75. Completedocumentation package withschematic; $6.00. Software disk,RI.OBJ object code, INHX8Mliirmat (disk provides single -uselicense; specify 3.5- or 5.25 -inchsize); $8.00. Please add $6.50($14.00 Canada) to all kit ordersand $5.00 ($9.50 Canada) to allcomponent/documentation/softwareorders for shipping and handling.Other countries, please write/Faxfor shipping information.California residents must add localsales tax. Checks, money orders,Visa. Master Card, and Discoveraccepted; checks must clear beforeshipping. Payment in U.S. fundsonly.

and hardware to create the call -pro-gress tones. Under microcontrollercontrol, L18 can simulate a number ofthe audio tones that are normallyheard while using a phone. Some ofthe sounds are composed of Iwo fre-quencies mixed together; others aresimple single tones. Table 3 lists a fewof the four bit codes that are sent to U8to create the call progress sounds.

Because the tones may need to be

gated on and off, such as in a busy -signal pattern, the microcontrollermust occasionally get involved. Tocreate the cadence heard in the ringand busy tones, the microcontrollermust set pin 13 of 08 to a logic high tomute the audio during the silent peri-ods Our task -based software pro-gram is used to schedule those timesensitive operations.

The progress tones are generated

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whenever pin 13 of 08 is at a logic low. gBecause the four -bit code is latchedat the falling edge of waveform pre- S'<'

sented to pin 13 of U8, the RBO- 4283bits can be immediately freed for use T.

by the DTMF receiver or the LED dis- 6play latch.

Power Supplies. There are three dif-ferent low -voltage, DC power sup-plies in the design. Common three - 75

TABLE 3-CALL-PROGRESS-SOUND CODES

Tone Frequency D3 D2 D1 DO

Dial 350/440 0 0 0 0

Special 400/off 0 0 0

Alert 440/off 0 0 0

Ring 440/480 0 0

Busy 480/6200

terminal IC regulators are used to de-rive the required digital, analog, andtalk -path power.

The digital logic and analog circuit-ry is powered by LM7805 (U5) andLM7812 (U4) fixed voltage regulators.Those popular devices provide excel-lent voltage regulation and have in-ternal over -current and over -temper-ature protection.

The power supply uses a center-

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tapped, full -wave rectifier design thatbegins with diodes D3 and D4. Ca-pacitor C8 is used as a bulk filter to theraw DC (about 16-20 volts DC) beforebeing applied to the IC regulators.Regulator U5 provides 5 volts DC forthe digital logic and U4 provides 12volts DC for the relay and analog cir-cuitry.

We only need a few hundred milli -amps of current to operate the circuit -

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ry, so either the 0.5 -amp (78Mxx) or l-amp (78>o<) type regulators can beused. Because they are series -pass -type regulators, they can run verywarm while in operation. You must usea heatsink on U5 to maintain a com-fortable operating temperature.

The simulated phone -line talk -pathpower ("battery' voltage) is providedby an LM317 IC (U3), another popularthree -terminal regulator. Unlike the78xx-series regulators, that devicecan provide an adjustable range ofvoltages as selected by resistors R7and R8. The chosen resistor values setthe output to about 29 volts DC. Al-though most phone lines use a 48 -voltDC talk voltage, our 29 -volt DC supplywill work correctly with all standardtelephone equipment.

The talk supply begins with rectifierTO

POWERBOARD

-.9 CT

R41

EXT CTRL'Fig. 6. Use this parts -placement diagram when mounting components on the unit's

76 main board.

96

BR1

T2

03

0

04

0

BR1, the full -wave bridge, which con-verts the incoming low -voltage AC tounregulated DC (about 36 -volts DC).Capacitor C9 is used to bulk filter theraw DC voltage before it is applied tothe regulator.

You may also notice that the reg-ulator's ADJ terminal is connected tooptoisolator U12. That optically iso-lated switch is used to shut off the volt-age regulator during the CPC(calling -party control) pulse. Whenenabled by the microcontroller, U12reduces the talk voltage to about 1.2-

volts DC, which is low enough to simu-late the CPC condition.

Construction. Although Ring -It! is afun project to assemble, it certainly isnotfor beginning electronics -kit build-ers. If you don't have experience withCMOS IC's and PC -board assembly,please obtain help before starting.

We have provided PC foil patternsfor the main board (Figs. 2 and 3) andthe power board (Figs. 4 and 5) so thatyou can etch your own boards if youwish. You may find it more convenientto purchase a commercial -quality PCboard from the source listed in theParts List. If you do purchase theboard, do not clean it before solder-ing; the boards available from thesupplier have a special tin plate coat-ing that prevents oxidation.

The parts -placement diagrams forthe two boards are shown in Fig. 6(main board) and Fig. 7 (powerboard). The AC transformer (T3) andfuse (F1) are installed on the powerboard; the bulk of the remaining com-ponents, including all of the digital cir-cuitry, are installed on the mainboard. Among other things, the twoboard approach was used to pro-mote safety. Always exercise cautionwhen working near the power board'shigh voltages.

Use a 25 -47 -watt soldering -iron;temperature -controlled irons set to700°-800° work best. Do not use a sol-dering gun! Use only rosin -core solderwith a 60/40 tin/lead content.

Part substitutions are not recom-mended. Use the components shownin the Parts List and only substitutethose that you know are exact re-placements. For correct cycle -delayoperation, do not substitute U11 with anon-HCT type IC.

Use care in handling the IC's; theyare CMOS devices and are sensitive

TO117 VAC

*SEE TEXTcT4.

TOMAIN

BOARD

Fig. 7. The power board is set up for117 -volt operation, but can be modifiedfor 220 -volt use by cutting traces andadding jumpers as described in text.

to static. They can be damagedthrough mis-handling!

Component XTAL1 can be either aquartz -type crystal as specified, or aceramic resonator. Delete capacitorsC14 and C15 if using a ceramic reso-nator with built-in capacitors.

Use a socket to mount the micro -controller (U9). A special right-angleIC socket (made by Vertisocket andavailable from Digi-Key Electronics,701 Brooks Ave. South, PO Box 677,Thief River Falls, MN 56701-0677; Tel.800-344-4539) is used at DISP1 to ver-tically mount the seven segment LEDfor proper viewing. Sockets should beused for the other IC's, but are notabsolutely required. Install two -pinheaders with shorting blocks at theJU1 and JU2 positions.

Transistors Q3 and Q4 as well as thethree voltage -regulators (U3-U5)should be anchored to the PCB with4-40 x 1/4 -inch machine screws andnuts. Use a heatsink and thermalgrease (heatsink compound) on U5the 7805 regulator. Please note that it'snormal for that regulator to feel warmduring operation.

Install and label LED1 as CONNECT onyour enclosure's front panel. Wire it tothe PC board using 5 -inch -longpieces of 22-24 AWG stranded wire.Be sure to observe proper polarity.

Install and label Sias MODE and S2 asRING on your enclosure's front panel.Again, connect them to the PC boardusing 5 -inch -long pieces of 22-24AWG stranded wire.

Install modular jacks at the J1 andJ2 positions. Each jack's green wire isconnected to the square pad on theboard and the red wire is connectedto the other pad. Cut off any extrawires that may be on the connector.

Install potentiometer R35 on therear panel of your enclosure and la-bel it as DELAY. Connect the potentiom-eter to the appropriate points on thePC board using stranded wire.

If after testing your finished projectyou find that the delay control worksbackwards, merely reverse the con-nection to the potentiometer's wiper.If installed correctly, the delay timeshould increase as the control ismoved clockwise.

If you find that you can not achievea 10-90 second delay range, thenC24 or R35 are out of tolerance(check them). Although the softwarehas been designed to allow correctoperation over a wide range of com-ponent tolerances, it may be neces-sary to try different components atU11, C24, or R35 to get the desiredrange,

The power transformers, T2 and T3,are split bobbin types with dual50/60Hz primaries and secondaries.Using standard power transformers isnot recommended, especially at theT2 location. Such transformers areavailable from sources such as Micro-tran, Magnetek/Triad, Signal Trans-former, PREM Magnetics Inc., andothers.

Be sure to observe the orientation ofthe transformers. On T1, match the "P"and "S" references on the parts -placement diagram. It may be nec-essary to cut off the frame's mountingtabs on some transformer designs. In-stall T2 and T3 so that the transformer'spin 1 is in the square pad.

The power board layout is alreadyset for 117 -VAC operation. However, itcan be converted to 230 -VAC opera-tion for use outside the U.S. For 230 -VAC operation perform the followingcuts and jumps: Cut the trace be-tween the pads designated A and B inFig. 7, cut the trace between the padsdesignated c and D, and add ajumper between pads B and c.


FREQUENCY

RESPONSE

TESTER

BY RANDY CONSTAN

SweepRate

ON

ManualFrequency

Powr

ludio Response

Audio Level

SWEEP

CAL

ester

AudioOut

With it, you'll never again have to guess about thefrequency response of an audio device.

Many off -the -shelf audio pro-cessors, such as equalizers,enhancers, and pre -ampli-

fiers, alter audio signals even when intheir so-called "pass -through" modes.The resulting frequency -spectrumlosses often cause unwanted distor-tion, which can be very difficult to iso-late if there are several componentsin an audio system. Therefore, a de-vice that measures the frequency re-sponse of audio components shouldbe a welcome addition to the toolboxof any audio -electronics enthusiast.

With the Frequency -Response Test-er described in this article, you candirectly view the frequency responseof almost any audio gadget right onyour oscilloscope screen, with a mini-mum of fuss. If any lumps and bumpsappear in the signal of a device un-der test (DUT), the mystery of yoursound troubles will be solved. Further-more, the Tester will allow you to takecorrective action, and quickly viewthe results.

The Tester works by generating twosignals. The first is a linear-sawtoothsweep waveform that drives the hori-zontal input of your scope. Internally,that signal is transformed into a log-arithmic waveform that spans threedecades of voltage differential. Thatsignal is applied to a function -gener-ator IC to produce the second output,a sine -wave signal. The sine wave has

78 a frequency that follows the log-

arithmic waveform, and has an am-plitude that remains constant.

By connecting the DUT between thesine -wave sweep output and yourscope's vertical input, the DUT's re-sponse to the entire frequency spec-trum can be easily viewed. Thelogarithmic nature of the frequencysweep assures that the entire audiorange appears as an ordered display,in which each 1/3 of your scope's hori-zontal range depicts one decade offrequency span. In other words, theranges are: 20 to 200 Hz, 200 to 2,000Hz, and finally 2,000 to 20,000 Hz, fromleft to right. Because the unit also gen-erates your scope's horizontal sweep,the scaling remains stable and re-peatable no matter how you vary thesweep rate.

Frequency -sweep generators arenot a new or unique idea, but unfor-tunately their cost can be somewhatprohibitive for the average hobbyist.However, you can build the Frequen-cy -Response Tester for under $50, de-pending on your junk -box supplies.Even though this project will save yousome money, keep the following inmind: The circuit requires an initial set-up and occasional calibration; also,accuracy beyond two digits is im-practical unless your scope uses so-phisticated on -screen digital read-outs for frequency and voltage levels.

A plain, vanilla scope will work finewith the Tester, as long as its time base

and vertical amplifiers provide rea-sonable accuracy. A frequency coun-ter is also recommended, at least forthe initial setup.

Circuit Description. The schematicfor the Frequency -Response Tester isshown in Fig. 1. The two quad op -ampsections, U3 -c and U3 -d, are config-ured as a linear -ramp generator. Withswitch S2 in the SWEEP position asshown, the output of U3 -d is low. Zenerdiodes D2 and D3 limit that output toabout -7 volts, which is the 6.2 -voltreverse drop across D3, plus the for-ward drop of D2. The internal short-circuit protection of the op -amp limitsthe Zener current to several milliam-peres.

Because the output of U3 -d is nega-tive, integrator U3 -c generates a lin-ear ramp in a positive direction, at arate determined by the resistance ofR4 and R29, and the capacitance ofC5. A portion of that output is fed backto the noninverting input of U3 -d viathe voltage -divider network consist-ing of R2 and R3. Because U3 -d isbasically operating as a comparatorwith its inverting input grounded, itsoutput will switch positive as soon as itsnoninverting input crosses zero volts.That will occur when the positive -go-ing ramp reaches about + 5.8 volts.

Once U3 -d switches to a high -out-put state, the operation is repeatedwith the opposite polarity except that

PL1

120VAC

R1

100K

S2 -b

D21N4735

D31N4735

J2AUDIO

OUTPUT0

R212K

S1-8O

I 0

S1 -b

R310Kss

.-C.W.

R295MEG

SWEEPRATE

T

R4470KV V

R51KA1

D1

1N914

R6 R274.7K 100K

MANUALFREQUENCY

-15V +15V

L

+15V

R21-15V.r" 100K

R19200KW

BR11.5A

1100PIV

C2330

J1

HORIZONTALOUTPUT

'a*

SWEEP R2210K

S2 -a

R2310K

R810K

4441-1 - R9 01

4700

WR2010K

.1 100KAUDIO LEVEL -44AA

R18100K

R74.7K

R1110K

2N2907

-15V

R102.2K

-15V

R1210K R13

1MEG

Q22N2907

R2510K 2 11 0

+15V

R1510K

R241K

R163K

-15V

+15V

-15V

1/2LF353R14

1MEG

U5ICL8038

46

TP1

0-C6

.0047

8

R1710K

10K6

Fig. I. As this schematic for the Frequency -Response Tester shows, there are five trimmer potentiometers, R22 -R26, that are used forcalibration. But don't worry, the process is not as hard as it might seem.

diode D1, now forward biased, allowsan additional current path to U3 -c viaR5. Because the resistance of R5 ismuch less than the combined valuesof R4 and R29, the negative -goingramp time is almost negligible com-pared to the positive ramp, and theoverall effect is to produce asawtooth waveform with an ampli-tude of over 10 -volts peak -to -peak.That is more than sufficient for justabout any scope's horizontal input.

Next, the linear ramp undergoes aseries of level and offset adjustmentsvia resistors R7, R8, R9, R22, and R23,and is then applied to the base of Q1.The emitter -coupled transistors, Q1and Q2, in combination with U3 -b,produce an anti -log transfer function.

That means that when properly ad-justed, the output at the collector ofQ2 will be logarithmic with respect tothe input, yielding a one -decade volt-age differential for every few volts ofinput. To be more specific, if you di-vide the peak -to -peak voltage of theinitial linear sweep by 3, the anti -log -generator output increases by a mul-tiple of 10 each time the input voltagecrosses another 1/3 milestone. That willall become much clearer when yousee the logarithmic curve on yourscope during the calibration phasediscussed later in this article.

Next, U4 -a inverts the polarity of thesignal, so that it starts high and endslow. That is necessary because theoutput frequency of the 8038 function

generator, U5, is inversely propor-tional to its input voltage. In addition,U3-d's offset voltage is nominally set atabout - 7.5 volts by the combinationof resistors R15 and R16, and can betrimmed precisely by the 15 -turn trim-mer potentiometer, R24. That shifts thelogarithmic -sweep waveform to suitU5, which in our circuit receives its sup-ply voltage from the ground and- 15 -volt source. Recall that our log-arithmic sweep must span three de-cades of voltage differential, whichmeans that if its final voltage were -5volts, its initial voltage would be 1/4000 ofthat, or - .005 volts. Tiny voltages likethat have to be carefully controlled,which is why R24 is used for that criticaladjustment. 79

Finally, we come to the heart of thecircuit, U5. That relatively inexpensiveICL8038 function generator producesconstant -amplitude sine waves, aswell as triangle- and square -waveoutputs, from 20 Hz through 20 KHz.Also, its output frequency is nearly aperfect inverse proportional to its in-put voltage, so driving its input with ourcustom logarithmic -sweep circuit willproduce the balanced, three -de-cade frequency sweep we desire.

The sine -wave output from U5 is fedto the voltage divider made up of R18and R19, which restores the DC offsetto zero. That eliminates the need forany coupling capacitors in the outputstage, which makes it possible for out-put level to remain independent offrequency. The voltage -divider outputis then applied to potentiometer R28for output -level control, and is subse-quently routed to U4 -b for a boost inboth amplitude- and current -drivecapability. Output can range from 0 -to over 10 -volts peak to peak, which isenough for testing almost any audiodevice.

The DPDT switch, S2, has anotherposition called "ca.." In that position,potentiometer R27 controls the fre-quency of the sine -wave output forsetup and calibration purposes. How-ever, because the output of R27 isbuffered by U3 -a and routed throughthe anti -log circuit, the Tester can alsoserve as a simple stand-alone signalgenerator. Potentiometer R27 is alsoindispensable for "homing in" on atroublesome frequency during actualresponse testing.

Construction. The method chosento build the Frequency -Response Test-er is not critical; however, the easiestmethod is to use the single -sided PC -board layout provided in Fig. 2. If

you're looking for a good PC -boardproject to try, the Tester PCB is an ex-cellent choice because it is both sin-gle -sided and reasonably low incomponent density. When cut to thesize shown, the board fits comfortablywithin the widely available metal en-closure noted in the Parts List.

If you choose to use a PC board, aparts -placement diagram is pro-vided in Fig. 3. If you choose not to usea PC board, a pert -board approachwith point-to-point wiring will workfine. Just remember that an oversized

go zero -volt ground bus, or the use of a

single -point grounding scheme is al-ways recommended in circuits involv-ing op -amps. In any case, a metalenclosure is recommended to re-duce noise and provide stable sup-port for output connectors. Oneimportant layout consideration is toplace R24 near the edge of theboard, so that an access hole drilledin the enclosure will allow occasionalcalibration.

Most of the components in the Test-er are of easy -to -obtain values, with afew exceptions; for that reason somereasonable parts substitutions can bemade. For example, power -trans-former T1 does not have to be a single36 -volt, 300mA center -tapped typeas shown. Two smaller single -outputtransformers may be wired with theiroutputs in series to yield the same re-sult, as long as each output is at least18 volts at 200 mA.

On the more critical side, Q1 andQ2 must be a reasonably matchedpair in order for the anti -log circuit towork properly. The 2N2907's specifiedare cheap, widely available, andhave a lot of uses, so buy a few extraso you can look for a reasonablematch. Using a DVM in diode -testmode, check the nominal voltagedrop across the transistor's emitter -base junction. Two transistors thatmatch up within or close to 3 -digitaccuracy are more than sufficient forthe project. If your DVM does not havea diode -test function, make a tempo-rary test jig with a 9 -volt battery, a 10Kresistor, and the base -emitter junctionof the transistor. When the junction isforward biased (positive at the emitterfor PNP devices), you can comparethe voltage drops across the junctionsof several transistors with an ordinaryDVM set on its 0- to 1 -volt range.

4 INCHES

e

Fig. 2. The PC -board template for the Tester is shown here in its full size of 4 x 5inches.

R28

R30

R25

Cs

U5

-R19- -R18-

LED1 + C3 C4

U2

S2-b

PL1

R6

C1 C2

S1 -a T1

D2*

D4

R26

-R20--R21-

-R17- twR16

R15

R24

-R14- -R13-

0 vJ2

J1

R3 R4

R22

IR5CI5

-R1-4421

R23

-R8-

-R9- S2 -a

U3

R29

-R11-

-R10-

-R12-

S1-b-1

Fig. 3. Use this parts -placement diagram as a guide ivhen making the various on- andoff -board connections. Note that there is an off -board ground between a few of thecomponents; connect those points and ground them to the metal chassis.

08.8

8

Fig. 4. Once calibrated, your Test( -

should display a three -decadelogarithmic waveform that resembles thisillustration.

Another critical item is R24, whichmust be a 15- or 20- turn trimmer po-tentiometer. It should also be obviousthat even though normal componenttolerances are not a problem, arbi-trary substitution of seemingly "close"resistor values is unwise in the Testercircuit.

Here are a few things to watch forwhen using the parts -placement di-

agram in Fig. 3: Be careful when inser-ting Q1 and Q2, because the physicalpinout of the transistors you obtainmight not match the case style shownin Fig. 3. There, the emitter pad is clos-est to the edge of the board, and thebase is the center pad. Also note thatall pads that connect to off -boardcomponents such as potentiometers,switches, and outputs are slightly over-sized for easy connection and identifi-cation. Some pads might not seem tobe logically placed, which is a neces-sary sacrifice in maintaining a single -sided layout. Extra pads are providedfor the center position of all trim potsexcept R24, to accommodate awider physical variety of those parts.Socketing of all but the voltage -reg-ulator IC's is recommended.

Potentiometers R27, R28, and R29mount on the faceplate of the projectcase. Use insulated wires to connectthem to the PC -board, as shown in Fig.

3. For best results, you might want touse coaxial cable for the connectionto R28; if you do so, ground the cableand the off -board ground pointsshown in Fig. 3 to the metal chassis toprovide shielding. Jacks J1 and J2,switches SI and S2, resistor R20, LED1,and power -transformer T1 all mountoff -board as well. Within the con-straints of the enclosure, mount T1 asfar from the board as possible.

Solder a small piece of stiff wire tothe board at test point TP1. Make thewire just long enough to access laterwith your scope probe. Finally, whenattaching the power cord to S1, usesome kind of strain relief or grommetwhere the cord enters the case.

Check and re -check your connec-tions before testing the project. Theboard itself can be mounted withsome insulated stand-offs, but youmight want to save that final mount-ing step until after initial checkout. Inany case, plan to mount the board insuch a way that a hole can be drilledto access R24 without opening thecase. That is the only trim adjustmentthat you will occasionally need totouch up after initial calibration.

Calibration and Set-up. With all thetrimmer potentiometers on the Tester'scircuit board you might think that cal-ibration is going to be a real nuisance,but that's not the case. The process isgreatly simplified because you canuse an oscilloscope to make almostall the adjustments visually. A separatefrequency counter is also useful, but isnot absolutely necessary. Anothersuggested tool to have on hand is apair of walkman-type headphones.Hearing the frequency of the audiooutput is a good way of roughly gaug-ing whether or not you're covering theentire audio range.

Start by centering all the trim pots,including R24. Before connecting anyexternal equipment, power up theunit by itself to check that correctpower -supply voltages are present inall the right places. Once you're con-fident that the circuit powers up cor-rectly, you can proceed. Note that it isnormal for the TL084 (U3) to run a littlewarm, and for both positive andnegative regulators to become ratherhot to the touch. If overheating be-comes a concern, small heatsinks canbe mounted on the regulators.

For your initial setup, connect the 81

horizontal output to the horizontal in-put on your scope, and the audio out-put to your headphones. If theheadphones are stereo, it is possibleto hear through both right and leftwith an appropriate adapter. In theabsence of headphones, a stereo -system auxiliary input will do, but becareful to keep the volume leveldown to avoid speaker damage.

Connect a probe to your scope'svertical input. Power up the scope, setthe horizontal time base for external,and set both the vertical and horizon-tal amplifiers for DC measurement.With S2 in the SWEEP position and bothR28 and R29 set to minimum resis-tance, power up the Frequency -Re-sponse Tester. The scope shoulddisplay a horizontal sweep, the speedof which you can adjust using R29. Forcalibration purposes, use the horizon-tal -gain and horizontal -position con-trols to produce a nine -division sweepdeflection that is lined up with the left-most, vertical graticule line. Becausenine divisions can easily be divided bythree, setting up the three -decadelogarithmic response we discussedearlier will be easy.

The next step is a bit tricky because itinvolves several coinciding adjust-ments. Connect the vertical input ofyour scope to the short wire you at-tached to TP1 earlier. If you turn up theAUDIO LEVEL control, R28, slightly, youshould hear some kind of audiosweep that appears to follow the rateof the horizontal sweep (don't panic ifthat is not the case; the trim pots mightjust be too far out of adjustment). FlipS2 to the CAL position; the horizontaldisplay will revert to a dot. Becausethe horizontal position of the dot is

8 related to the audio -output frequen-t cy, refer to the screen display while

using MANUAL FREQUENCY control R27 for

calibration. Set R27 so that the dotonce again lines up with the left -most,

co vertical graticule line on your scope.Then, adjust R24 to bring the audio -

2 output frequency as low as possible.0 You will have to calibrate that more

exactly later, but, for now, the lowest"bass note" you can hear without the

j, audio dropping out is close enough.rn Once the tone is established and

set to the lowest frequency you candetect, re -adjust R27 so that the dotmoves exactly nine divisions to theright on your scope screen. The fre-

82 quency should audibly rise. Adjust R22

20Hz 50 0.1KHz .3 5 7 1 2 3

FR EC) ENCYFig. 5. By copying this scale to transparent film, you can create a custom referencegraticule for 'our scope and greatly improve the visual accuracy of the display.

at this time to a point just past thehighest frequency you can hear. Re-peat the process of "low" and "high"adjustment of R24 and R22 at leastone more time, and then flip S2 backinto the SWEEP position.

With the SWEEP RATE control, R29, set to

maximum speed, you should be ableto adjust your scope's vertical sen-sitivity and position until you can see acurve starting high on the left, andsloping downward on the right. Con-tinue to adjust the position and ver-tical sensitivity, abandoning the "cali-brated" setting on your scope asneeded, so that the vertical deflec-tion exactly fills the screen, from thehighest vertical division available, tothe lowest. That resulting curve is alogarithmic progression.

The next step is to contour the curveso that every three horizontal divisionscorrespond to a 1/10 difference in ver-tical deflection. That is accomplishedmainly with R23, which serves as a"decades/volt" adjustment for theanti -log network. Unfortunately, ad-justing R23 is likely to affect the totalvertical amplitude, so you might haveto "see -saw" between R22 and R23until the desired curve is obtained.Trim pot R24, which mainly affects the"top" portion of the vertical deflec-tion, will probably not make much of adifference. In the end, your curveshould resemble the one shown in Fig.

5 7 10 20K

4 as much as possible.The curve in Fig. 4 assumes that your

scope graticule has eight major ver-tical divisions. Using the top line as areference, note that the total deflec-tion is eight divisions down at the rightedge of the trace. Because the widthof the trace has been set at nine divi-sions, you can easily divide the displayinto three sections. If you start at theright and move left, you'll see that thedeflection from the top line is 3/4o lesseach time we cross 1/3 of the totalwidth. So, the total deflection is 8, .8,and .08 vertical divisions at 9, 6, and 3horizontal divisions respectively. Ob-viously, - .08 divisions is not really visi-ble, and in fact, the start point of thecurve should really be - .008 divisions,which is certainly not visible. Becausethe anti -log network defines thecurve, we can assume that once onedecade is correctly "tuned," theothers will all fall into place. By con-tinuing to adjust the decades -per -volttrim pot, R23, along with the high log -level trim pot, R22, you should be ableto approximate that curve.

The two remaining trim pots, R25and R26, adjust the purity of the sine -wave output, and should be set asnecessary before final calibration. Po-tentiometer R25 adjusts the duty cycleso that the top portions of the sinewave equal the bottom half, whileR26 is used to trim out distortion. Those

controls do not treat all frequenciesequally, so waveform purity must beoptimized at a specific frequency. Theauthor recommends a mid frequencyof about 1000 Hz. Using your scope inits normal internal -sweep mode, setthe tester to CAL, and observe the au-dio -output waveform while makingthe above adjustments. In the end,both controls should be somewherenear their initial center position. or thefrequency span might suffer.

The final step in calibration is simplyto repeat the setups of R24, R23, andR22, this time with a frequency coun-ter added to the audio output. In-stead of using your ears for the low -and high -frequency adjustments, usethe frequency counter to obtain val-ues of 20 Hz and 20,000 Hz. For thatfinal calibration, make sure the unithas been on for a few minutes to al-low it to stabilize.

If no frequency counter is available,

you can use the scope as a frequencycounter by switching it back to inter-nal sweep, connecting the audio out-put to the vertical input, and makingcalculations based on time/division.That is a bit of a hassle because itmeans doing a lot of switching, andyou must remember to restore thehorizontal gain to the original nine -division setup in between each mea-surement. If you have a dual -tracescope, you can set up one channel torepresent the nine -division span ofthe Tester's horizontal output, and theother to monitor the audio output. Youwill still have to go back to the originalsetup at least once more to touch upthe log curve with R23. Remember,you've already set up the unit to spanfrom the lowest to the highest fre-quency you can hear, which is all thatreally matters. The good news is thatonce the Tester is set up, only the lowadjustment, R24, will need an occa-

PARTS LIST FOR THE FREQUENCY -RESPONSE TESTER

SEMICONDUCTORSUl-MC7815CT 15 -volt, positive -

voltage regulator, integrated circuitU2-MC7915CT 15 -volt, negative -

voltage regulator, integrated circuitU3-TL084 quad op -amp, integrated

circuitU4-LF353 dual op -amp, integrated

circuitU5-ICL8038 function generator.

integrated circuitQ1, Q2 -2N2907, PNP transistorBRI-1.5-amp. 100 -Ply, full -wave

bridge rectifierDl -1N914 general-purpose silicon

diodeD2, D3 -1N4735, 6.2 -volt, Zeiler

diodeLEDI-Red light -emitting diode

RESISTORS(All fixed resistors are 1/4 -watt. 5"

units, unless otherwise indicated.)RI, RI8, R21 -100,000 -ohmR2 -12,000 -ohmR3. R8, RII, R12, RI5, R17. R20----

10,000-ohmR4 -470,000 -ohmR5 -1000 -ohmR6, R7 -4700 -ohmR9-470 ohmR10 -2200 -ohmRI3, R14-1-megohmR16 -3000 -ohmR19 -200,000 -ohmR22, R23, R25. R26 -I0,000 -ohm,

trimmer potentiometer. PC mountR24 -1000 -ohm, 15 -turn. trimmer

potentiometer, PC mount

R27 -100.000 -ohm, linearpotentiometer

R28 -100,000 -ohm. logarithmicpotentiometer

R29-5-megohm, linearpotentiometer (see text)

R30 -3300 -ohm, V2 -watt

CAPACITORSCI, C2 -330-µF. 50-WVDC, radial -

lead electrolyticC3, C4 -1-µF, 25-WVDC, radial -

lead electrolyticC5 -0.22-µF, polyesterC6 -0.0047-µE ceramic -disc


SI. S2-DPDT toggle switchTI -AC power transformer, I15 -VAC

primary to 36 -VAC secondary,300-mA center -tapped (StancorP-8612 or equivalent, see text)

JI---BNC jackJ2 -Phone jackPLI-2-conductor power cord and

plugPrinted -circuit materials, metal

chassis (Radio Shack 270-253 orequivalent), insulated wire, solder,hardware. etc.

Note: A drilled and etched PC hoardis available postpaid from theauthor for 520. Contact him onGEnie at the E-mail address:R.CONSTAN for orderinginformation.

As this internal view shows, thetransformer in the Frequency -ResponseTester should he mounted as far from theboard as the project case allows.

sional touch up.If you wish, use a photocopier that

has a scaling capability to make acopy of the log scale in Fig. 5. By mak-ing the copy on a transparent sheet,such as the ones used for overheadprojectors, you can make a customreference graticule for your scopeand greatly aid the visual accuracy ofthe display.

Using the Tester. For accuracy atthe low -frequency range, always al-low the Frequency -Response Tester toremain powered -up for a few minutesprior to running response tests. Aswe've seen, the Tester's entire first de-cade from 20 to 200 Hz depends onthe stability of a very small control volt-age, which usually takes a little time tosettle. To test the response of an audiodevice, simply connect the Tester's au-dio output to the DUT's input, and theDUT's output to the vertical input ofyour scope.

(A note of caution is in order here:Some power amplifiers have outputsthat cannot be ground referenced. Insuch cases, a dual -channel scopeused in differential mode via both in-puts is the only safe way to monitor theamplifier. Also note that power ampli-fiers usually require output loading forproper operation.)

When your test set-up is complete,switch S2 to CAL mode, and select amiddle frequency using the MANUAL FRE-

QUENCY control, R27. Then, adjust the(Continued on page 102) 83

IVe always wanted to make a ra-dio using a variometer. In the oldradio books that I read as a kid,

variometers were pictured as two coilsconnected in series, one inside theother. The inner coil could be rotatedand would either cancel or add to theinductance of the outer coil, depend-ing on how it was oriented. Vari-ometers were used to tune radiosbefore variable capacitors becamecommon. Unfortunately, I couldn't fig-ure out an easy way to build one.

The problem must have stuck In mysubconscious, because forty yearslater I realized that the coils didn'thave to rotate; one coil could be slidover another. When I realized that, I

put together the Variometer Radiodescribed in this article in a couple ofhours, and it works great! Even thoughit doesn't use a variable capacitor, itcan still be tuned "on the nose" tostations in the broadcast band.

The Variometer Principle. In theoriginal variometer design, when theinner coil is rotated to a 90 -degreeposition with respect to the outer coil,the mutual inductance of the coils isat its minimum. For the mutual induc-tance of the coils to be at its max-imum, the coils have to be aligned.

Figure 1 is a schematic diagram ofhow the variometer principle wasadapted to a linear design in the proj-ect. Three coils, L1-L3, are connectedin series; L1 and L3 are fixed, while L2can be slid over them. Unlike in the

Li*(FIXED)

L2.(MOVABLE)

(FIXED)

'SEE TEXT

Fig. I. This is the principle at work inthe modern variometer. The middle coil.L2. can be slid over either of the othertwo. Because LI and L3 are connected inopposite directions, the inductance of L2will either add or cancel when it is

84 moved over the other coils..

I:

VariometerRadio

A new version of a classic design.BY LARRY LISLE

original variometer, it is the outer coilthat moves over the inner coils. As L2 ismoved over L1, their mutual induc-tance is increased to the maximum.But when L2 is moved over L3, theirinductances cancel out because L3 isconnected backwards (with respectto L2).

The Circuit. The schematic of thecomplete Variometer Radio is shownin Fig. 2. An antenna can be con-nected to the Radio through either oftwo points labeled ANT: either directlyto the circuit or through a 100-pF ca-pacitor. The ground connection canbe made at any of the points markedGND. There is a reason for the preced-ing options: By varying the antennacapacitance, the ground connec-tion, and the position of the slidingcoil, the entire AM broadcast bandcan be tuned.

Depending on the antenna andground connections, it might be nec-essary to add a small capacitor, C3, at

the point indicated in the schematic.If so, experiment with values between25 and 200 pF (separately or in paral-lel) to find which gives the best result. Ifyou build the Variometer usingFahnestock clips (as explained later),adding the capacitor(s) after the Ra-dio is built should be easy, if the needarises.

When a signal is selected by adjust-ing the antenna, ground connection,and position of L2, the signal is passedon to the diode -detector part of thecircuit, composed of D1, which de-modulates the signal. That signal thengoes through bypass capacitor C2 tothe earphones. Only high -imped-ance earphones should be used withthe Variometer.

Construction. The two fixed coils ofthe Variometer, L1 and L3, are woundon an 81/2 -inch -long piece of 1 -inch -diameter plastic pipe (its outer diam-eter is about 11/4 inches). Each coil is21/4 -inches long. The number of turns is

not critical, but in the author's pro-totype, 86 tightly wound turns ofnumber -22 enameled wire wereused. When winding the coils, makesure you start at a point that will allowthem to be placed 2 inches apart onthe pipe. Drill holes in the pipe and runthe leads of the coils out the end ofthe pipe that is closest to each.

The movable coil, L2, is wound on apiece of 11/2 -inch plastic pipe (its outerdiameter is about V/8 inches). Thewinding is 2 inches long. Like L1 andL3, the actual number of windings ofthis coil are not critical, as long as thewinding is approximately the rightlength. However, in the author's pro-totype, 74 tightly wound turns ofnumber -22 enameled wire wereused.

One final note on winding the coils:Plastic pipe was used in the author'sprototype for durability. An alternativeto that is to use cardboard tubes, es-pecially if you only plan on experi-menting with the Variometer Radio.

To support the smaller plastic pipethat contains L1 and L3, get an 81/2 -inch -long piece of 1 -inch dowel rod.Using sandpaper or a knife, slightlyflatten one side of the dowel. Then,insert the dowel rod into the pipe, andorient the flattened side of the rod sothat the wires can run along it withsome clearance. Mount the assembly

(TOHIGH -IMPEDANCE

EARPHONES)

Fig. 2. Here is the modern variometerprinciple at use in a completeVariometer Radio. Even if you've neverbuilt a radio before, you can build thiscrystal set; the parts count is low, andthe coil windings are not critical.

Here's the acthor's completed radio. For simplicity, it is laid out much like theschematic shown in Fig. 2.

on a wooden basebocyd (approxi-mately 9- nches square) using a cou-p e of corner brackets.

To ma<e it easier to change groundand antenna connections, the pro-totype was built using Fahnestockclips, When laying out the placementof the parts on the baseboard, makesure to include adequate connectionpoints for the possible use of capaci-tor C3 in the circuit. 11 you can't getFahnestock clips, don t worn"; an al -

PARTS LIST FOR THEVARIOMETER RADIO

DI-IN34 germanium diodeC.1-100-pE ceramic -discC2-0.001-wF, ceramic -discC3-Optional, see textLI, L3-.See textL2-See ter tBaseboard (about 9 -inches square), 1 -

inch -diameter dowel rod, 2 piecesof plastic pipe (see text),Fahnestock clips, cornet brackets,screws wire, hardware, etc.

ternative way to build the Radio is touse brass wood screws for the com-mon points and simply wrap the wirearound them.

Other Uses. Just by assembling yourVariometer Radio and experimentingwith tuning different stations, youmight not realize that the variometerprinciple can be used in other ap-plications as well. Some of those in-clude uses in antenna loading coils,couplers, or matching aevices,

Also, taps on one coil could givecoarse adjustment, while a sliding coilcan be used for fine tuning. With vari-able capacitors suitable for medium -or high -power ham transmitters be-coming expensive and hard to find,the variometer principle might alsofind a use in the final output stage onthe low -frequency banes.

The Variometer Radio is a modernversion of an idea from radio pastthat's fun to play with in radio present.However, as you can see, the vari-ometer principle might also becomeimportant in radio future.

85

86

GettingStarted

inSurface Mount Technology

Two projects that will get you started in building with surface -mount components.

For most electronics hobbyists,the idea of hand -assemblingsurface -mount components

(SMC's) into a working project seemsludicrous. After all, as most of us knowsurface -mount technology (SMT) wasdeveloped with automatic assemblyin mind. Finding, grasping, arranging,and somehow soldering those tiny,leadless SMT components by hand isridiculous. Right? Wrong-delightfullywrong! Not only is it possible, but it canbe accomplished easily, quickly, and,for the most part, with tools and mate-rials you now have on your work-bench.

As mentioned in the article "A Hob-byist's Guide to Surface -Mount Tech-nology" (Popular Electronics, Janu-ary 1995), SMT is a packagingrevolution that attaches tiny, essen-tially "leadless" components to padson the surface of a printed -circuitboard (hence the name, "surface -mount technology"). That contrastswith traditional "insertion -mount tech-nology" (IMT), which uses compo-nents with leads that are insertedthrough the PC board.

As you are about to discover, proj-ect -building with SMT is fascinating,fun, and, increasingly, inevitable. Eventhough today, for the most part, youstill have a choice between tradi-tional IMC's (insertion -mount compo-nents) and SMC's, tomorrow you mightnot; already, 50% of all the compo-nents in commercial electronic as -

BY RONALD A. REIS

semblies are SMC's. So, if you don'twant to let a whole component -packaging revolution pass you by,learn to build the electronic projectsof the near future, now.

SMT Project Building. To get youstarted in building tomorrow's elec-tronic projects today, here are two fun,attention -getting, and, most impor-tant, easy -to -build SMT projects: the555 Dual -LED Flasher and the ToneBurst. Furthermore, to give you prac-tice in fabricating SMT PC boards andsoldering SMC's in place, a printed -circuit template for an SMT PracticeBoard is also included.

Both of the SMT projects presentedhere were chosen to give the begin -

Fig. I. Here is the schematic for the 555Dual -LED Flasher. The circuitalternately flashes LED1 and LED2, twosurface -mount LED's, at a rate ofapproximately 1 Hz.

ner the widest possible SMT project -building experience, using readilyavailable, low-cost surface -mountcomponents. Each project is built on a1- x 13/4 -inch PC board that is intend-ed to be taped to the side of a 9 -voltbattery, its power source. The 9 -volt -battery snap found in both projects,and the 8 -ohm speaker in the ToneBurst are the only non-SMT compo-nents used.

Circuit Descriptions. The first proj-ect, the 555 Dual -LED Flasher, alter-nately flashes a pair of tiny, surface -mount LED's at a rate of approximately1 Hz. Figure 1 contains the schematicfor that project.

The 555 timer, U1, is configured asan astable multivibrator (oscillator),the frequency of which is determinedby the values of resistors R1 and R2and capacitor C1. As C1 charges from1/3 to 2/3 the supply voltage through R1and R2, U1's output, pin 3, is high. As aresult, LED2 is on (its anode is positive,its cathode, negative) while LED1 is off(both its anode and cathode arepositive). When C1 discharges from 2/3to 73 the supply voltage through R2,pin 3 goes low. As a result, LED1 turnson (now its cathode is negative and itsanode is positive) and LED2 turns off(both its anode and cathode arenegative). The duty cycle for the cir-cuit is nearly 50 percent; therefore,each LED is on for close to an equalduration.

R1

2.2K

R2100K

C1

3.3

R61000

B1

9V

Fig. 2. The Tone Burst circuit puts out a500 -Hz tone, at a rate of I Hz, throughan 8 -ohm speaker, SPKRI. Besides the9 -volt battery and its connecting snap,SPKRI is the only non -surface -mountcomponent in the circuit.

The Tone Burst puts out a 500 -Hztone at a rate of 1 Hz. At the heart ofthe circuit is U1, a 556 IC, which is justIwo 555 IC's in one 14 -pin package(see Fig. 2). Both "555's" are configuredas astable multivibrators, The first, orlow -frequency, oscillator, using re-sistors R1 and R2 and capacitor C1,turns on the second, or high -frequen-cy, oscillator at a 1 -Hz rate. The latter isalternately on and off for half a sec-ond. When it is on, it generates a 500 -Hz signal, that value being deter-mined by resistors R3 and R4 and ca-pacitor C2. That signal is amplified byNPN transistor Q1, which drives the 8 -ohm speaker.

SMT PC -Board Fabrication. Thesteps in fabricating an SMT printed -circuit board are identical to thoseused in etching a traditional, single -sided, IMT PC board. There are, how-ever, two additional steps, or cautions,that should be observed when SMTboards are etched. We'll look at bothin a moment, but first, here are the tensteps required to produce either anIMT or SMT PC board:1. Clean the blank board with finesteel wool to get rid of contaminantsand oily residue.2, Spray a liquid photoresist onto thecopper -clad board.3. Dry the photoresist with a hair dryer.4. Expose the sensitized board, with

the artwork negative on top, to ultra-violet light.5. Let the image develop.6. Rinse and drip-dry the board.7. Immerse the board in acid (ferricchloride is often used).8. When etching is complete, thor-oughly wash the board and then dry itwith a paper towel.9. Remove the remaining photoresistlayer by lightly rubbing the board withsteel wool.10. Drill all necessary holes in the PCboard. In an SMT PC board, onlymounting holes might be required.

The PC -board template for the 555Dual -LED Flasher is shown in Fig. 3 andthe one for the Tone Burst is shown inFig. 4. Note the small componentpads and the extremely thin traces-in some cases, a mere 0.015 -incheswide, When fabricating those andother SMT boards, two cautions areworth observing:

First, because you are dealing with

z

Fig. 3. This template for the 555 Dual -LED Flasher's PC board is shown in itsactual size of only 1 x J3/4 inches! Notethe small pads and extremely thin traces.

wz0

CO

Fig. 4. The printed -circuit template forthe Tone Burst is also shown here fullsize.

traces not much thicker than a linedrawn with a pencil, it is a good ideato check the etching process fre-quently. Pull the board out of the acidbath often and examine it closely foracid undercuts. The narrow traces ofan SMT board are delicate-leavingyour board in the acid any longerthan necessary to etch away un-wanted copper might damage thetraces.

Second, once the board is com-plete, check the PC -board pattern

with a magnifying glass. However, thatmight not be enough to locate anypossible trace breaks, so you shouldcheck each trace (and pad) with acontinuity checker (ohmmeter). Thatway you can be sure that the board isready for the installation of surface -mount components.

Figure 5 is the template for an SMTpractice board. By fabricating thatboard, you can gain experience inetching SMT PC boards with smallpads and thin traces. Also, you canuse the practice board to rehearsethe SMC assembly techniques dis-cussed later. For those reasons, etch-ing the practice board beforetackling either of the two SMT projectboards is recommended.

Tools and Materials. In building ei-ther of the two projects presentedhere, you will need the right tools andmaterials. A full explanation of theitems required was presented in "AHobbyists Guide to Surface -MountTechnology" in the January 1995 issueof Popular Electronics. If you have acopy of that article, you might want tolook it over.

Briefly, here are some tools you'llneed: a soldering iron, a tweezers, avise, and a magnifying glass. The sol-dering iron needs to be from 25 to 40watts and should have a tinned tipwith a conical shape, 3/46 of an inch orless in diameter. The tweezers shouldhave forceps -style tips. A small vise isideal for securing the PC board whilecomponents are being attached. Be-cause SMC's are so tiny, no matter

O P =MISO

MM. OMB1.

MO11 10- /IRO

=MI 1111

IN III IIII

ZLI148--- 1-5/8 INCH --ad

Fig. 5. Fabricating this SMT practiceboard will give you practice in etchingan SMT PC Board, and in mountingSMC's. It is shown here full size. 87

88

Fig. 6. To tag solder a two -terminalSMC in place, create a pool of solder ona pad, place the component above it,and reheat the solder so the SMC can"sink" close to the board surface.

how good your eyesight is, you'll wanta magnifying glass close by. A desk-top illuminated magnifier, the kindthat sells for around $80, is ideal. At thevery least, get yourself an inexpensivehand-held lens.

The materials you'll require are sol-der, liquid flux, a drop dispenser, a de-fluxer, and solder wick. The soldershould have a 63/37 tin -lead mixture,and should be no greater than 0.020inches in diameter. If you can find it, a0.015 -inch -diameter solder is evenbetter. When purchasing a bottle ofliquid flux, be sure it is of the noncor-rosive type. To directly apply the fluxwhere it is needed, you will want adrop dispenser. Also purchase a light -duty defluxer, in a spray can, which willbe used to clean your assembled PCboard of all contaminants. Finally,when choosing solder wick, select awidth of 0.030 inches.

Attaching SMC's to PCB's. In build-ing an SMT project, we suggest thatyou use the tag solder method dis-cussed in the aforementioned article.Here is a review of the procedures fortag soldering various SMC's to a sur-face mount PC board:

To tag solder a two -terminal SMC tothe surface of your PC board, first,using your drop dispenser, apply adab of liquid flux to one PC -boardpad. Then, using your soldering ironand solder, create a small pool of sol-der on that pad. Allow the solder tosolidify.

Next, with the SMC held in yourtweezers, rest the component on itsPC -board pads and hold it in place.Then, using a soldering iron held inyour other hand, reflow the solder sothat the component "sinks" close to

the board surface (see Fig. 6). Removethe iron, allow the solder to coolagain, and release the tweezers. Withthe component "held" in place,you're ready to solder the other termi-nal in a traditional manner.

To solder gull -wing leads on three -and four -lead components, proceedas above. Tag solder one lead andthen solder the remaining leads in theconventional way (see Fig. 7).

When soldering DIP gull -wing sur-face -mount IC's (SOIC's), first create apool of solder on a corner pad inpreparation for tag soldering. Thenpick up the IC with a tweezers and

SOLDERING IRON TIP

Fig. 7. To solder gull -wing leads to aPC board, use a 63137 tin -lead solderthat is 0.015 inches in diameter, and aconical soldering -iron tip that is '46 ofan inch or less in diameter.

place it onto the copper pads, mak-ing sure to center the IC right -to -left aswell as top -to -bottom. While holdingthe chip in place, apply the solderingiron tip to the pre -tinned pad. Keepthe iron in place just long enough toflow the solder. If necessary, pivot theIC about the soldered pin to againalign all pins with their respectivepads.

To ensure the IC doesn't pivot, sol-der a second pin "kitty-corner" to thefirst. When doing so, don't forget toapply a small amount of liquid flux.When the chip is secure, "bathe" oneline of pins with liquid flux and soldereach pin, moving quickly to avoidoverheating the IC. Then repeat theabove step with the opposite row ofpins. Finally, inspect your work underthe magnifying glass, looking in par-ticular for solder bridges.

At this point, you could continue di-rectly to the assembly of your chosenproject. However, if the procedures

just outlined seem a bit intimidating,you might want to practice a littleSMC-placement first. That's where theSMT practice board, mentioned ear-lier, comes in. If you have etched theboard, as suggested, you can nowproceed to "stuff it" with surplus SMC's.As you will notice, pads to accommo-date various sized two- and three -ter-minal SMC's, as well as thin- and wide-bodied DIP SOIC's, are provided.

Before actual component -place-ment and assembly begins, cleanyour PC -board traces and pads withsteel wool. Next, mount the PC boardsecurely in a vise. If you don't have avise, you can try holding the PC boarddown by taping its corners to a flatsurface with masking tape.

If you are using a desk -top magni-fier, swing it into place and turn on thelight. Place the rest of your tools, mate-rials, and components nearby, withineasy reach, and get comfortable.Pretend you're a surgeon about toperform a delicate operation. Then,just pick out a component location onthe PC board, take a deep breath,exhale, and give it a go. You'll be a proat SMT hand assembly in no time. Now,let's build our projects!

Construction. The parts -placementdiagram for the 555 Dual -LED Flasheris shown in Fig. 8, and the parts -place-ment for the Tone Burst is given in Fig.9. Whichever project you build, beginby attaching the integrated circuit.Note that in both projects the IC isplaced so that pin 1 is on the top -leftpad. Next, install any polarized ca-pacitors (the positive terminal is indi-cated by either a colored bar or a

LED2

R4

B1

U1

R3

R1

LED1

Fig. 8. Use this diagram as a guidewhen building the 555 Dual -LEDFlasher. Because their markings are sosmall, polarized SMC's can be hard towork with, so be careful when aligningthem.

FR21Ell I

I+C1

SPKR1

-R1- -R3-

U1

-C2--R5 -

Re ()

Fig. 9. This Tone Burst parts -placementdiagram should make building theproject a lot easier. Double check yourbattery- and speaker -wire connections tomake sure they are correct.

PARTS LIST FOR THE555 DUAL -LED FLASHER

---555 timer, surface -mountintegrated

LLD I, Lt.D2 -Green LH), surfacemount

RI--I000-ohm resistor, surfacemount

R2 -100,000 -ohm resistor, surtacemount

R3, R4- 470 -ohm resistor, surtacemount

CI-I0-p.F. 10 -volt, electrolyticcapacitor. surtace mount

BI--9-volt alkaline hattersPrinted -circuit materials, 9 -volt -

battery snap with leads. wire.solder, hardware, etc.

PARTS LIST FOR THETONE BURST

LI --- 556 dual timer, surface -mountintegrated circuit

Q1 ---2N2221 transistor or equivalent,surtace mount

RI- 2200 -ohm resistor, surfacemount

R2-- 100,000 -ohm resistor. surfacemount

R3, R4 4700 -ohm resistor, surfacemount

R5 1000 -ohm resistor, surfacemount

Rb I00 -ohm resistor, surface mountCI ---3.3-u,E 10 -volt, electrolytic

capacitor, surface mountchip capacitor, surface

mountBI--9-volt alkaline batterySPKR -----K-ohm speakerPrinted -circuit materials. 9 -volt -

battery snap with leads, wire,solder, hardware, etc.

small marking). Proceed to install anynon -polarized capacitors.

You can then place all the resistors.Because those components have nopolarity, they can be installed in eitherdirection. Do, however, solder themplace so that their resistance value isvisible (for an explanation of how thevalues are read, once again refer tothe previously mentioned article).

The 555 Dual -LED Flasher uses twoLED's that are, of course, polarized. Thecathode end is usually marked with adot of green or red paint. If you'rebuilding the project, attach the LED'sat this time.

The Tone Burst Project includes athree -terminal transistor. Because thattiny component can be placed on

Surface -mount components are muchsmaller and lighter than their insertion -mount -component cousins.

the PC board in only one correct di-rection, you can't get its placementwrong. If you are building the ToneBurst, install the transistor now.

Tag solder the battery -snap wiresdirectly to the appropriate PC board -pads, Be sure to observe correct po-larity. Finally, if you are building theTone Burst, attach speaker wires, ap-proximately 2 -inches long, to the cor-rect pads on the PC board (see Fig. 9).Solder the other ends to SPKR1. For thesake of proportion, and to make aninteresting assembly (more on thatlater), select a miniature unit for thatspeaker.

Checkout and Use. Before testingyour project, spray it with the light -dutydefluxer. Then take a nail brush andscrub vigorously to remove con-taminants. Don't be afraid that you'llscrape off an SMC or two. If the com-ponents can't stand the rubbing

"abuse," this is the time to find out. Ifyour assembly techniques were good,the SMC's will hold.

Finally, attach a 9 -volt battery. Yourproject should blink or beep, depend-ing on which one you built. If the proj-ect fails to function correctly, makesure that you are using a fresh 9 -voltbattery. Then, check componentplacement and solder -joint integrity,and examine the project under yourmagnifier.

When your project is working, at-tach it to the battery with double -sided tape. For the Tone Burst, if youused a small enough speaker, youcan affix the unit by taping it to theopposite side of the battery.

How to Get SMC's. You can pur-chase surface -mount components insingle -lot (or "near -single -lot") quan-tities from a growing number of elec-tronics distributors and retail outlets.First, check with your local electronicsstore. Second, look at the list of dis-tributors presented in the aforemen-tioned SMT article.

One of those sources, the Elec-tronics Goldmine (PO. Box 5408, Scot-tsdale, AZ 85261; Tel. 602-451-7454),has exactly what you need for eitherof the above two projects. In somecases you will have to purchase com-ponents in lots of anywhere from 5 to20. That's practical, however, becauseyou'll probably want to use the extrasfor solder practice or for buildingmore projects.

Conclusion. Having built one or bothof the SMT projects presented In thisarticle, you have entered an entirelynew realm of project building. Indoing so, you have taken a leap notunlike that experienced by earlierelectronics hobbyists when goingfrom vacuum -tube-, to transistor-, toIC -based projects. You, too, are anelectronics pioneer. But don't stopnow.

SMT project kits are beginning toappear from a variety of sources. Pur-chase some of those kits and buildthem. Also, in the months to come, asyou page through new issues of Pop-ular Electronics, zero -in on the sim-pler IMT-based projects and trycreating your own SMT versions ofthem. In no time at all, you will be-come an experienced pro at SMTproject building. 89

90

BY JAMES J. BARBARELLO

Every now and then, you comeacross an electronic compo-nent that is easy to use in an

application. Such a device is NationalSemiconductors ADC0831-a single -input, 8 -Bit, Serial Input/Output (I/O),Analog -to -Digital (ND) Converter. Forstandard 0- to 5 -volt -input applica-tions, all you need is the ADC0831 anda 5 -volt power supply; no additionalcomponents are required! TheADC0831 output can connect directlyto any of your PC's available parallelports.

Many applications, however, usemultiple inputs that don't span thecomplete 0- to 5 -volt range. For in-stance, temperature sensors span-ning the - 40 to + 125°F range willtypically vary their input by only onevolt or so. With the addition of twopotentiometers, the ADC0831 can beadjusted to provide the full 255 stepsinherent in an 8 -Bit ND converter overa smaller input -voltage range, with-out the need for op -amps or otheranalog scaling devices. That rangecan also be adjusted to begin at avoltage other than zero volts. Then, byadding a single,.common multiplexerIC, up to eight input devices can beconnected.

The result of those preceding addi-tions is the ND Converter described inthis article. It is a circuit that has a non-critical layout, so it can be built on alow-cost prototyping board. Also,what's great about the project is that itcan be built for under $25. Even if youadd eight temperature probes (as isdone in an application that will bedealt with later), the cost can stay un-der $50! Don't think that the low pricemeans low performance, however.Depending on the speed of your PC,the circuit can capture 1000 or moresamples per second.

The ADC0831. One useful featureof the ADC0831 is that its analog, zero -input -voltage value can be offset; thevoltage -reference input can be ad-justed to allow encoding any smaller,analog voltage span to the full 8 bitsof resolution (with a ± 1 least -signifi-cant -bit error). As a result, it can oper-ate ratiometrically or with a 5 -volt -DCvoltage reference; no zero or full-scale adjust is required. The ADC0831

Wight-ChannelA/D Converter

Let 'our computer interface with the physical world.

is TTL/MOS-1/0 compatible. It operatesfrom a single 5 -volt power supply overa 0°C to 70°C temperature range,consuming only 15 milliwatts. The con-version time of the chip is 32 microse-conds.

As shown in Fig. 1, the ADC0831 is an8 -pin IC. Operation is enabled byplacing a logic low on pin 1, the chipselect (CS). Data is sent out of pin 6(1),,,), and the IC requires a clockingsignal at pin 7 (CLK). Power is appliedto pins 8 (Vc) and 4 (GND). The inputsignal is provided to V +, which is pin2. The zero -conversion reference volt-age is provided to V - (pin 3). Finally,the voltage representing the range ofthe 8 -bit conversion is provided to Vref(pin 5).

Figure 2 shows the timing diagramfor the ADC0831. In our application,the CLK (clock) signal will be derivedfrom the PC's parallel port, and theData Out will be sent to the parallelport. To begin, a conversion is initiatedby first pulling the CS line low. That linemust be held low for the entire con-version. The ADC0831 then waits for astart bit. Next, the clock is provided tothe CLK input. On the falling edge of

the first clock pulse, the Data Out(D00) line comes out of its high -im-pedance state and provides a lead-ing zero for one clock period. Each bitof the converted voltage level (be-ginning with the most significant bit,and proceeding through the least sig-nificant bit) is made available on theD0, line, beginning with the fallingedge of each succeeding clockperiod. After eight clock periods, theconversion is completed. The Dou, linegoes into the high -impedance stateagain when the CS line returns to thehigh state.

While the ADC0831 can be used inthe standard 0- to 5 -volt input mode,

CS VC C

2CLK

ADC0831

Dow 6

GND Vrat

Fig. 1. This is the pinout of theADC0831, which is the heart of the AIDConverter.

CLK

c7.9

DATAOUT

1 2 3 4 5

f --

6 7 8 9 10

1--

D7 D6 D5 D4 D3 , D2 D1 DO

Fig. 2. Here's the timing diagram of the ADC0831. In the application discussed in thearticle, the CLK signal is derived from a PC's parallel port, and the Data Out is sentto the same parallel port.

both its minimum analog input -volt-age and full-scale voltage values canbe adjusted. When the V, pin is bi-ased to other than ground, the con-verter will output a 0000 0000 digitalcode for that minimum input -voltagevalue. The voltage value applied to

determines the analog input -volt-age value that will produce the full-scale digital code (1111 1111). The sumof V and Vrf, must be less than orequal to 5 volts. For instance, by ap-plying 2.3 volts to V , and 1,28 voltsto \ire, an analog input voltage of 2.3volts will produce a digital code of 0,and an input of 3.58 (2.3 + 1.28) willproduce a digital code of 255. Thatprovides an effective resolution of1280 mV/256 counts, or 5 mV/count.That is four times the standard resolu-tion of 19.53 mV/count (5000 mV/256counts) that an 8 -bit A/D converterwould provide without the ratiometriccapability.

The 4051. As mentioned earlier, forour application of the ADC0831, wewill need to use an 8 -channel multi-plexer, the 4051. Figure 3A shows thepinout of that IC. Power is normallyapplied to Vdd (pin 16), and ground toV.. (pin 8); however, in our application,we'll connect Vee (pin 7) to groundalso.

Three inputs- -A B, and C form abinary counting scheme (as indicat-ed in the truth table in Fig. 3B). Thebinary number input to the A -B -C in-puts selects the same -numberedchannel in the chip. That selectedchannel is connected to the COMMterminal (pin 3) through the 4051's in-ternal circuitry, which adds a few -hun-dred ohms of resistance in seriesbetween the selected channel and

'4" vo, 16

2 15"6' "2"

3 14COMM 1

13'7" "0"

5 124051'5" '3'

11INH

7 10vo. B8

C

A

INN C B A 'ON'

0 0 0 0 0

0 0 0 1 1

0 0 1 0 2

0 0 1 1 3

0 1 0 0 4

0 1 0 1 5

0 1 1 0 6

0 1 1 1 7

1 X X X NONE

B

Fig. 3. The pinout of the 4051 8 -channelmultiplexer (At shows all of its inputsand output channels. As the truth table(313) shows, three inputs A. B, and C --form a binary counting scheme. Thebinary number input to the A -B -C inputsselects the same -numbered channel inthe chip.

pin 3. !f the INH (inhibit) line (pin 6) isbrought high, pin 3 is disconnectedfrom all inputs, regardless of the A -B -Cinput.

Temperature Sensors. The A/DConverter described in this article willbe put to use as a temperature mea-surer and data -logger. Let's take alook at the sensor that will make thatpossible: It is the LM335-a precision,easily calibrated, temperature -sensor

integrated -circuit. Shown in Fig. 4, thatthree -terminal device comes in aplastic TO -92 package. Operating asa 2 -terminal Zener, the LM335 has abreakdown voltage directly propor-tional to absolute temperature at+ 10 mV/°K, with the extrapolated out-put of the sensor going to a zero -voltoutput at 0°K ( - 273.15°C).

Fig. 4. This is a bottom view of theLM335 temperature sensor, showing thepinout configuration of its internalcircuitry.

With less than a 1 -ohm dynamic im-pedance, the device operates over acurrent range of 400 1.1A to 5 mA, withvirtually no change in performance.When calibrated at 25°C the LM335typically has less than a 1°C error overa 100°C temperature range. Unlikeother sensors, the LM335 has a linearoutput. The sensor operates over arange of - 40°C to + 125°C.

Errors in output voltage versus tem-perature are only slope or scale -fac-tor errors, so a slope calibration at onetemperature corrects all tempera-tures. The output voltage of the device(calibrated or uncalibrated) can beexpressed as:

V(t) = V(to) x t/to

where V(t) is the output -voltage read-ing at an unknown temperature, V(to)is the output voltage at the referencetemperature, t Is an unknown temper-ature in 'K, and to is the referencetemperature in 'K. By knowing three ofthe preceding variables, the otherone can be easily solved for.

Knowing that 'X = °C - 273.15, and°C = (°F - 32)/1.8, it is possible to figureout the output voltage of an LM335 forany given Fahrenheit temperature.That voltage would be equal to:

((x°F - 32)/1.8 + 273.15) x .01

where x is the Fahrenheit tempera-ture. The first term ((x°F - 32)/1.8) con-verts the Fahrenheit temperature tocentigrade. The addition of 273.15converts the centigrade temperatureto Kelvin. Finally, the 0.01 multiplier (10mV/°K) converts the temperature to 91

REM** ADC0831 with Up To 8 LM335 Temperature ProbesREM" V940126, c 1994 JJ BarbarelloREtvlREM" INITIALIZATION "REM1 ON ERROR GOTO errortest2 CLS : DEFINT A -S DIM a(7), tempcorr(8)3 FOR i = 0 TO 7: a(i) = 2 i: NEXT4 channel = 15 temp$ = " ###" + CHR$(248) + "F".4 -++++t+4 -4-4-1-41-4-4-++++++++++++++++4-414414++++4-44.444.4-

+4++

'GET SETUP DATA FROM FILE (If no file, error occurs. +' Then execution jumps to errortest subroutine). +

44,-4

6 OPEN "ADC831.DAT" FOR INPUT AS #17 LINE INPUT #1, vinminus$: xsupplyl =

VAL(vinminus$)8 LINE INPUT #1, vinplus$: xsupply2 = VAL(vinplus$)9 LINE INPUT #1, add$: add = VAL(add$)10 LINE INPUT #1, numberchannels$: channels =

VAL(numberchannels$)LINE INPUT #1, delay$: delay! = VAL(delay$) IchannelsFOR i = 1 TO channels

LINE INPUT #1, v$: tempcorr(i) = VAL(v$) - 2.732NEXT idatasource$ = "FILE ADC831.DAT"jump.trom.errortestroutine:

11

12

1314

1516REMREM" SCREEN SETUPREM

LISTING 1

4647

484950

51

52

17 COLOR 15, 6: CLS : LOCATE 2, 1518 PRINT "ADC -831 TEMPERATURE PROBE

PROGRAM. Press ESC key to End.";19 COLOR 14, 6: LOCATE 3, 26: PRINT "Data Source:

"; datasource$20 VIEW PRINT 5 TO 24: COLOR 15, 1: CLS21 LOCATE 6, 1922 PRINT USING "Vin Range is #.### to #.###v";

xsupplyl; xsupplyl + xsupply223 LOCATE 6, 48: PRINT USING "(##.##mViStep)";

xsupply2 / .25624 LOCATE 7, 10: PRINT USING "# Active Channels";

channels25 LOCATE 7, 28: PRINT USING "Using Parallel Port at

#### Decimal"; add26 LOCATE 7, 64: PRINT "("; HEX$(add); "H)"27 LOCATE 8, 2428 PRINT USING "Channel Scan Time is ####.#

seconds"; delay! ' channels29 COLOR 3, 130 FOR i = 1 TO channels31 LOCATE 10, i ' 8 + 232 PRINT USING "#.###v"; ternpcorr(i)33 NEXT i34 LOCATE 9, 23: PRINT "TEMPERATURE PROBE

CORRECTION FACTORS"35 COLOR 7, 0

-4,i++++++++++++++++++++++++++++++++++++++++++++4+++4

'DRAW BOXES ON BLACK BACKGROUND FOR VOLTAGE &TEMP DATA

36 LOCATE 11, 8: PRINT CHR$(201); 9437 FOR j = 1 TO 8: PRINT STRING$(7, 205); 95

CHR$(209), : NEXT j 9638 LOCATE 11, 72: PRINT CHR$(187) 9739 FOR i = 12 TO 16: LOCATE i, 8: PRINT CHR$(186); 9840 FOR j = 1 TO 8: PRINT SPACE$(7); CHR$(179); : 99

NEXT j 10041 LOCATE i, 72: PRINT CHR$(186) 101

42 NEXT i 102

43 LOCATE 13, 8: PRINT CHR$(204); 10344 FOR j = 1 TO 8: PRINT STRING$(7, 205); 104

CHR$(216); : NEXT )45 LOCATE 13, 72: PRINT CHR$(185) 105

REM

LOCATE 15, 8: PRINT CHR$(199);FOR j = 1 TO 8: PRINT STRING$(7, 196);CHR$(197); : NEXT jLOCATE 15, 72: PRINT CHR$(182)LOCATE 17, 8: PRINT CHR$(200);FOR j = 1 TO 8: PRINT STRING$(7, 205);CHR$(207); : NEXT jLOCATE 17, 72: PRINT CHR$(188)FOR i = 1 TO 8: LOCATE 12. i 8 + 2: PRINT USING"CH #": : NEXT

REM" SAMPLING CODEREM53 start:54 begin! = TIMER55 WHILE (TIMER - begin!) < delay! * .95: WEND56 LOCATE 12, channel 8 + 2: COLOR 0, 757 PRINT USING "CH #"; channel; : COLOR 7, 058 WHILE (TIMER - begin!) < delay!: WEND59 activech = (channel - 1) ' 460 OUT add, activech + 2: REM: Select 4051 channel

(1-8) which is input 0-761 FOR i = 1 TO 100: NEXT i62 OUT add. activech 0: REM: Set CS' low. CLK low.63 OUT add. activech + 1 OUT add. activech + 0: REM:

Pulse Clk Hilow. keep CS' low64 OUT add, activech + 1: REM: Pulse Clk High65666768

= 7WHILE j > -1OUT add, activech + 0: OUT add, activech 1

jsum = jsurn + (INP(add + 1) AND 64) ' a(j): REM:Get Bit J. Result is 64 or O.

69 i=l- 170 WEND71 jsum = jsum / 64: REM: Divide by 64 once, not each

time in jsum calc.72 LOCATE 14, channel 8 + 273 voltreading = xsupplyl + jsum ' (xsupply2) / 25574 PRINT USING "#.###v"; voltreading75 LOCATE 16, channel ' 8 + 176 tempreading = (voltreading + tempcorr(channel) -

2.332) / (.01 / 1.8) - 40'voltreading-tempcorr(channel)-2.332 is voltage diff. from -40F' .01/1.8 is C to F conversion of 10mV/degC77 IF tempreading < -40 THEN78 PRINT CHR$(32); STRING$(5, 25);79 ELSEIF tempreading > 125 THEN80 PRINT CHR$(32); STRING$(5, 24);81 ELSE82 PRINT USING temp$; INT(tempreading + .9)83 END IF84 COLOR 7, 185 LOCATE 18, channel ' 8 4 3: PRINT USING "###";

jsum86 COLOR 7, 087 jsurn = 0: REM: Clear Jsum88 LOCATE 12, channel ' 8 2

89 PRINT USING "CH #"; channel;90 channel = channel + 1: IF channel = channels + 1

THEN channel = 1a$ =1NKEY$: IF a$ = THEN GOTO startIF ASC(a$) <> 27 THEN BEEP: GOTO startVIEW PRINT: CLS : LOCATE 18, 1: END

919293REMREM** ERROR HANDLER "REM

errortest:IF ERR = 53 THENxsupplyl = 2.332xsupply2 = 3.248add = 888channels = 8FOR i = 1 TO 8: tempcorr(i) = 0: NEXT idatasource$ = "DEFAULT VALUES"RESUME jumpirorn.errodest.routine

END IFLOCATE 12, 20: PRINT "UNDEFINED ERROR.Unable to continue"LOCATE 18, 1: END

92

an output voltage. So, if we want tomeasure temperature between- 40°F and + 125°F we would have tofigure out the associated output -volt-age range, The voltage associatedwith - 40°F is:

(( - 40 - 32)/1.8 + 273.15) x .01

which equals 2.332 volts. The voltageassociated with the upper end of therange, + 125°E Is:

((125 - 32)/1.8 + 273.15) x .01

which equals 3.248 volts.If we set the ADC0831's V,n - to

2.332 volts, and its Vre, to 0.916 volts(the difference between 3.248 voltsand 2.332 volts), the ADC0831 will beable to sense a voltage difference assmall as 3.58 mV (because 0.916V/256 steps = 3.58 mV/step). That willallow the chip to resolve between

40°F and + 125°F (a 165°F tempera-ture span) with at least a 1°F resolution,because a 1°F change will produce avoltage difference of 0.916 V/165°F or5.5 mV/1

+ PL5U70LM335 - ^ r -o

+ PL6U8 0

LM335

+ PL7U9

LM335

+ PU10

L51335 -

1-0

R32.2K

13

J1 +5VO R4

2.2K14v o

+5V

Further, if we limit the temperaturespan to a smaller range, the resolutionwill increase. For instance, if we limitthe range to 25°E the output -voltagerange will be 0.139 volts. That willcreate an ADC0831 resolution of0.543 mV/step (0.139 mV/256 steps),which is more than ten times smallerthan the 5.5 mV/°F response of theLM335. Therefore, the ADC0831 will beable to resolve 0.1°F over that smallerrange. As you can see, the ratiometriccapability of the ADC0831 allows us totrade off range for greater resolution.

Circuit Description. The schematicof the A/D Converter is shown in Fig. 5.It is powered from a 9 -volt battery, B1,the output of which is regulated by a78L05, U1, to 5 volts. If a 5 -volt source ofregulated DC is available, U1, C1, andC2 can be eliminated.

The functions of the ADC0831 (U2)and 4051 (U3) IC's, were looked at ear-lier. Potentiometer R1 allows the userto set the minimum input voltage. Thesetting of potentiometer R2 deter -

v 0LI

2.2K15

J3 +5VR6

2.2K1

+5V

R72.2K

J5 +5V-0- R82.2K

v 0J7 +5VI R10

v 0J8 0

+5V

R92.2K

2

2.2K4

U34051

11 4

10 5

9 6

3

16

10

19

+5VO

o

7

2

PL1

Ut78L05

G

U2ADC0831

3

B1

9V

/%210K

N PUT -

VOLTAGERANGE

V+5R1 A

10KMINIMUM

INPUTVOLTAGE t

Fig. 5. The actual processing circu try of this A,D Converter consists of only fourparts: U2. U3, RI, and R2. As you can see, eight temperature probes are used withthe circuit; however, they can be replaced with other types of sensors, as long asresistors R3-RIO are removed.

PARTS LIST FOR THEA/D CONVERTER

SEMICONDUCTORSUI-78L05 5 -volt regulator,

integrated circuitU2-ADC0831 8 -bit serial 110 A/D

converter, integrated circuitU3-4051 analog multiplexer.

integrated circuit


RI, R2 -10.000 -ohm, 1/4 -watt, 10- or15 -turn PC -mount potentiometer

R3-R10-2200-ohm, 1/4 -watt, 5%resistor

Cl. C2 -1-µF, 15-WVDC (orgreater). electrolytic capacitor

PLI-DB25 male connector andhood

JI-J8-phone jack (see text)B1 -9 -volt batteryPerk)rated-board materials, project

enclosure or wooden base. ICsockets. 22 -gauge wire. 7 -conductor wire, screws and nuts,solder, hardware. etc.

Note: The following arc availablefrom James J. Barbarello (817Tennent Road, Manalapan, NJ.07726). Daytime Fax is908-532-0702. The A/D ConverterKit (ADC0831). consisting of allparts listed above less jacks withone temperature probe-S25.00.Enhanced software (ADC0831S).containing source and executablecode for temperature -sensing (andother) analog -input devices, andproviding data logging, datastorage, and data plotting-$12.00

mines the desired voltage span(which effectively sets the maximuminput voltage).

The AID Converter interfaces with aPC through a DB25 plug, PL1. Note thatthe numbers shown in PL1 relate to thepin numbers of the DB25 plug, and ofcourse, the parallel port of the com-puter, The Converter circuit containseight phone jacks, J1 -J8, to interfacewith eight temperature probes. Thoseprobes each contain one LM335(U4 --U11) and a phone plug (PL2--PL9).Of course, in other applications, andwith the appropriate external circuitry,J1-.16 can be used to interface withvirtually any other type of analog sen-sor or signal.

Construction. The author's pro-totype was built on a perforated pro-totyping board. Any other appropri- 93

PARTS LIST FOR THETEMPERATURE PROBES (8)

U4-Ull-LM335AZ temperaturesensor, integrated circuit

PL2-PL9-phone plug (see text)Twisted -pair wire (22 -gauge), heat -

shrink tubing (Via-, 1/8-, and 4/1h -

inch diameter), solder, etc.

Note: The following are availablefrom James J. Barbarello (817Tennent Road, Manalapan, NJ,07726). A kit of parts for a singletemperature probe (TP831)-$5.00. A four -probe kit(4TP831)-S17.50; and eight -probe kit (8TP831)--$32.50; arealso available.

ate construction technique can, ofcourse, be used. Regardless of thetechnique used, when installing thecomponents In the circuit, be sure tocheck their orientation (except for R3through R10, of course).

If you have difficulty finding eitherthe ADC0831 or the 4051 locally, theyare both available from Digi-Key (PO.Box 677, Thief River Falls, MN56701-0677; Tel. 800-344-4539). Use ICsockets for those IC's, and install themlast.

As shown in the photo at the begin-ning of this article, the author's com-pleted prototype board was at-tached to a block of wood usingscrews and nuts (as spacers). Any proj-ect enclosure can be used, however.Phone jacks J1 -J8 can be of any size;Just make sure you use matchingplugs for the temperature probes. Thejacks were mounted through holes inthe wood base in the prototype, but ifyou use a project enclosure, the jackscan be mounted on its cover. Con -

it neat the jacks to the circuit with indi-vidual pieces of 22 -gauge wire, andattach the ground points of the Jacks

cc,

8 together and to the common groundon the circuit.

O Use a 7 -conductor cable to makethe connections between the circuit

2 board and pins 2, 3, 4, 5, 6,10, and 190 of the DB25 plug, PL1. To attach the

battery to the circuit, use a batterych connector with leads,

The next step is to build a tempera-"- Lure probe, or probes. Remember, the

ND Converter can accommodate upto eight probes. To begin, hold an

94 LM335 with its flat side facing up and

CLIP OFF THIS LEAD

SOLDER HERE

ADJ

HEAT -SHRINK A(1/8 -INCH DIAMETER)

A

HEAT -SHRINK B(3/16 -INCH DIAMETER)

B

HEAT -SHRINK C(1/4 -INCH DIAMETER)

C

Fig. 6. To protect the temperature probeconnections, three pieces of heat -shrinktubing must be used. Heat -shrink Aprevents the negative lead from cominginto contact with the positive one (A),heat -shrink B protects both leads (B),and heat -shrink C covers the entireprobe (C).

the leads facing you (see Fig. 6A). Clipoff the left (ADJ) lead and bend thecenter (+) lead to the left, as shown.

Next, strip about 1/4 -inch of insulationfrom the ends of both wires in a twist-ed pair. That twisted -pair wire, whichwill connect the probe to the Con-verter, can be as long as 50 feet with-out affecting the probe's accuracy.Insert a 1/2 -inch length of 1/8 -inch -di-ameter heat -shrink sleeving over oneof the stripped wires (heat -shrink A inFig. 6A). Solder that wire to the right(-) lead of the LM335. Then, solderthe other wire to the center (+) leadof the LM335.

As an initial checkout, strip about 1/4 -inch of insulation from each of thewire's free ends. Connect the wirefrom the center lead of the LM335

through a 2200 -ohm resistor to a 5 -volt -DC source, Then, connect thewire from the right lead of the LM335to the power source's ground. Using adigital multimeter, measure the volt-age across the signal and groundleads. In a normal environment(around 70°F), the DMM should readaround 2.95 volts. Place an ice cubein contact with the LM335. The volt-age reading on the DMM should be-gin to decrease. If you don't obtainthose results, check the probe's wiringand solder joints.

If the probe works, remove thepower source and resistor. Push heat -shrink A over the solder joint andLM335 lead (see Fig. 6A). Using a por-table hair dryer, or a match (be care-ful not to actually touch the tubing),heat the tubing until it shrinks aroundthe joint and lead. Push the two LM335leads together, making sure heat -shrink A keeps them from making con-tact.

Push a 1 -inch -long piece of 3/16 -inch -diameter heat -shrink tubing,heat -shrink B, up the free end of thetwisted pair wire, and push it as closeto the body of the LM335 as possible(see Fig. 6B). Apply heat as before toheat -shrink B until it shrinks around thetwo leads.

Push a 11/2 -inch -long piece of 1/4 -inch -diameter heat -shrink tubing(heat -shrink C) over the LM335 anddown past the previously installedtubing on the LM335 leads. Leaveabout1/16-inch of the LM335 body pro-truding (see Fig. 6C). Apply heat toheat -shrink C. The last step in thepreparation is to connect the wires tothe plug. Make sure that the polaritymatches that shown in the schematic.

The Program. Listing 1 presents aQBasic program that performsADC0831 control, data -capture,data -display, and data -conversionoperations. It also uses a text setup filethat lets you customize operationwithout having to change the actualprogram. An enhanced version of theprogram, which makes it easier to usethe Converter with other analog -in-put devices, is available on disk fromthe source given in the ND ConverterParts List. To better understand how touse the Converter, let's examine thelines of the program.

Line 1 activates the error -trappingroutine. That is used to define default

LISTING 2

LINE CONTENTS: EXAMPLE:

[yin- 2.345[Vref 3.567[Parallel Port Address 888[Number of Active Channels 4[Total Scan Time (The time it takes to begin

at channel 1, sample all active channels,and then come back to channel 1) 0.8

[Temp Correction for Channel 1 0.014[Temp Correction for Channel 2 0

-0.005[Temp Correction for highest active channel 0.03

values in case the setup data file is notpresent. Line 2 dimensions the A array,and the TEMPCORR array, which will holdthe temperature -probe correctionfactors. In line 3, the A array is filled withthe powers of 2 (which we'll use later).Lines 4 and 5 initialize variables.

Line 6 accesses the setup file andlines 7 through 14 retrieve the data.The variable XSUPPLYI corresponds to

- , the zero offset, and XSUPPLY2corresponds to Vref, the voltage span.The variable ADD is the address of theparallel port being used. CHANNELS isthe number of channels to be used(between 1 and 8), DELAY1 is the delay -time -per -channel, and TEMPCORR(I) is

the temperature -probe correctionfactor for the different probes. Thatvalue is used to correct for any smallvariations in the responses of individu-al LM335's. Lines 17 through 52 simplydo housekeeping on the screen.

If the setup file is not available (we'lldeal with that file later), an error in line53 will result, and execution will pro-ceed to line 94, In that instance, thevariables needed for the program toexecute are defined in lines 96through 100, and execution returns tothe main program from line 102. If anundefined error occurs, lines 104 and105 identify that fact and end the pro-gram.

The heart of the program is be-tween lines 53 and 93. Lines 54 and 55create a delay loop that suspends ex-ecution until most of the time identi-fied by DELAY' has elapsed. Line 57displays the active channel, and line58 completes the delay processing.

The active channel is used to set amask that will control U3, the 4051 mul-tiplexer. For instance, if channel 4 isactive, we want to access U3's "3" in-

put, because the channels are 1 to 8,and U3's inputs are 0 to 7 (channels 1to 8 correspond to jacks J1 -J8). Thus,the variable ACTIVECH is set to 12, or00001100 binary (shown as bit 7through bit 0). That value can then beused to send a Ito pin 4 of PL1 (bit 2 toU3 "A"), a 1 to pin 5 of PL1 (bit 3 to U3"B''), and a 0 to pin 6 of PL1 (bit 4 to U3"C"). Referring back to Fig. 4, that bitpattern (or multiplex mask) selects U3's"3" input.

Line 60 uses the multiplex selectionmask and adds 2 (binary 10) whichalso keeps pin 3 of PL1 (CS) high. Line61 provides some settling time, andthen line 62 brings the CS line low. Line63 keeps CS low, and pulses the CLKline (pin 2 of PL1) high and then lowagain by bringing bit 0 high and thenlow. Line 64 brings the CLK line highagain.

At that point in the program, we'veselected the input channel, con-nected it through U3 to the input of U2,activated U2 by bringing its CS linelow, and pulsed the CLK line one -and -a -half times. Referring back to Fig. 2,the next time the CLK line goes low,data bit D7 will be available at thepout pin.

A counter is set to 7 in line 65. Line 66and 70 form a WHILE/WEND loop that willcount back from 7 to 0, performingthe commands in lines 67 through 69each time through the loop (retriev-ing data bits D7 through DO in theprocess). Line 67 pulses the CLK linelow and then high again. Even thoughwe could read the data when the CLKis brought low, pulsing it high again(the middle of the clock cycle) en-sures the data has settled before weread it. Line 68 gets bit j and deter-mines if it is high (returning a 64) or low

(returning a 0). The results of the eightdata reads are stored in JSUM. Becausethe actual value should be a 1 or 0(not 64 or 0), line 71 divides the sum by64 to arrive at a final value between 0and 255. Line 72 positions the cursorat the correct area on the screen todisplay the data for the selectedchannel.

Line 73 converts the 0-255 valueinto the appropriate voltage using theVin - (xsupPiyi) and Vref (XSUPPLY2) zero

reference and voltage span. Line 76converts the voltage reading to theappropriate temperature reading,using the temperature -correctionfactor for the selected temperatureprobe. Lines 77 through 83 format thetemperature reading, printing up ar-rows if the reading is above the max-imum allowed, and printing downarrows If the reading is below the mini-mum allowed, or printing the actualreading.

Line 90 increments the channeland resets it to 1 if the highest channelhas just been read. Line 91 allows theoperator to press any key to end theprogram (if so, line 93 ends the pro-gram), If no key is pressed, line 92loops execution back to line 53.

The Setup File. Creating the setupfile can be done with a word pro-cessor, from DOS, or better yet, fromQBasic (which you'll use to RUN the pro-gram in Listing 1). The file contains anumber of text lines, each ending witha line feed and carriage return. Thecontents of the lines are given in List-ing 2.

Note that if you have more thanone parallel port available in your PC(LPT2, LPT3, or LPT4), you can specify itsaddress. That way you can still use yourprimary parallel port (LPT1) for regularprinting.

Calibration. To calibrate the temper-ature probe, you have to comparethe probe's output to a known tem-perature. If you have an existing, cali-brated temperature -sensing device,place the probe next to that device'stemperature -sensing element andrecord the probe's output voltage.Then, to determine the theoreticaloutput voltage based on the ternper-ature-sensing device's temperaturereading, use the formula that wasgiven earlier:

((x°F - 32)/1.8 + 273.15) x .01 95

96

bands and frequencies adjacent tothem:

The Bilal Isotrons are very small am-ateur -band HF antennas designed forportable and restricted -space ap-plications where larger antennas areimpractical. Some users mount themout in the open, such as on a chimney,since they are smaller than a TV an-tenna and really don't look like anantenna at all. Most of the Bilal anten-nas are small enough to fit in an attic.

Despite their small size, the anten-nas have reasonably large areas andare made electrically resonant using

large coils in series with the antennas'capacitive plates. Six single -band ver-sions cover the 160-, 80-, 40-, 20-, 15-,and 10 -meter amateur bands. Othermodels cover various ranges in theregions from 1.8-7.3 MHz and 14.0-30,0MHz. Prices range from $32.95 to$149.95.

The Spider antennas, from Multi -Band Antennas, are loaded amateur -mobile antennas that automatically

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change bands without changing res-onators; they don't need an antennatuner. The four -band Spiders are goodcandidates for installation on vans,campers, motor homes, and fresh-water boats. The antennas offer goodoperating bandwidth and low SWR.Three additional resonators can beinstalled for seven bands.

The Spiders also are suitable for usein mobile home parks, apartments,and condominiums; balcony -railingand vent -pipe mounting is popular. Aspecial dipole version also is avail-able, as are models tuned to com-mercial HF marine bands. A selectionof resonators, mounts, and accesso-ries is available. A complete Spidersystem typically costs $150 or more,plus mount; dipoles are $170 and up,depending on the number of bandscovered.

Antenna Tuners and Couplers.Strictly speaking, you really don't usean antenna tuner to "tune" an anten-na. Instead, tuners (sometimes knownas couplers or transmatches) allowyou to get the most from certain an-tennas by adjusting the impedancematch between your receiver andantenna system.

While in amateur work tuners usu-ally are adjusted using an SWR bridge,you can adjust them very simply bymerely adjusting their controls for thestrongest received signal. Another,more "high tech" way is to use an in-strument such as an antenna bridge,dip meter, resistance analyzer, anten-na noise bridge (ANB), or similar de-vice that has a built-in signal source.

Those instruments letyou determineantenna resistance, standing -waveratio (SWR), resonant frequency, andother parameters without a transmit-ter, You can monitor changes as youtweak your antenna, lengthening orshortening it or adjusting its tuner tosee the effect, without transmitting.

Antenna tuners also perform a sec-ond useful function by rejecting un-wanted, out -of -band signals andpreventing them from gettingthrough to your radio. Many firms, in-cluding MFJ, Grove Enterprises, Pal-omar Engineers, and others, offer SWLtuners.

Some Final Thoughts. Just the factthat your antenna is physically smallerthan usual does not exempt it from

any of the usual concerns that sur-round antennas, That is especially trueof safety concerns.

If your antenna is outdoors, protectit from lightning. If it normally requiresa parallel -conductor transmissionline, consider placing a BALUN at theantenna to allow coax feeder to beused instead. The BALUN also con-nects both sides of the antenna to thecable shield (at DC and low AC fre-quencies). That reduces static -chargebuildup on the antenna; charges flowto ground, not through your radio.

Also protect your vertical ground -plane antenna, even if it's at DCground potential. When that type ofantenna is elevated above ground,run a direct ground wire to its radialsystem. Don't rely on the coaxfeedline shield alone for grounding.

Get a good ground. The best way todo that is to have a good, short con-nection between your antenna sys-tem and ground, both for lightningprotection and for good antennaperformance. If you can, install out-door ground rods, preferably severalsix-foot or longer rods connected to-gether with heavy wire. Don't use hot-water pipes, gas lines, electrical con-duit, or insulated plastic pipes.

You might have to settle for a wirerun to a cold water pipe. Sometimes,even that's hard to find in homes andapartments built with plastic piping.Inside steel -frame buildings, a groundconnection to the building's framecan be effective.

During an electrical storm, the onlysafe conductor is a grounded one, soground or disconnect all antennaswhen a storm threatens. Use an an-tenna switch that automaticallygrounds all antennas except the onein use and that has enough positionsso you can turn the antenna selectorto an unused position when not usingthe equipment. Your best bet mightbe to remove all of your equipmentfrom power and transmission linesduring storms, or disconnect themwhenever you're not using them.

We won't dwell further on antennasafety in this article. More informationcan be found in my article "AntennaSafety for Hams and SWL's," which ap-peared in the May 1995 issue of Popu-lar Electronics. Also, there is aninformative, four -page "AntennaSafety Advisory" pamphlet availablefree from Universal Radio.

sO BY JOSEPH J. CARR

Square waves are among themost useful waveforms around.

, They are used to makequalitative tests of amplifier and pas-sive -network circuits, and for radiotroubleshooting. Square waves areeven used as clocks in digital circuits.

Fortunately, square waves that arestable in both amplitude and fre-quency are relatively easy to gener-ate using the following circuits. Let'stake a look.

Types of Square Waves. Figure 1shows five different types of squarewaves. For all five, the signal is inher-ently binary-it quickly jumps be-tween two values ("high" and "low').Because the square wave never per-manently remains at just one level, it issaid to be astable. For that reason,most square -wave generators arecalled "astable multivibrators."

A positive, monopolar square waveis shown in Fig. 1A. For that type ofsquare wave, the two ideal voltagelevels are zero volts and some positivevoltage (V + ). In transistor -transistorlogic (TTL), the low level is anythingbelow 0.8 volts and the high level isanything from 2.4 to 5 volts. Non-TTL-based square waves of that typemight use different voltage levels. Forexample, while CMOS chips can gen-erate TTL-compatible voltage levels,they are often used in circuits withmuch larger high-level voltages.

Figure 1A also shows the time rela-tionships of a positive, monopolarsquare wave. A total cycle consists of

Generating square waves is easy whenyou follow the simple "recipes"

in this cookbook.

one high and one low, each of equallength. The total period required forthe square wave cycle is:

T = t1 + t2

while the frequency (t is:

f = 1/T

A negative, monopolar squarewave is shown in Fig, 1B. The negativesquare wave is similar to the positiveone shown in Fig. 1A, but in the nega-tive square wave, a high is defined as0 volts, while a low is some negativepotential ( - V).

Another square wave is the sym-metrical, bipolar square wave of Fig.1C. In that type of square wave, thehigh and low voltages are equal po-tentials above and below the voltageaxis. A variation on that is the offset,bipolar square wave of Fig. 1D. Thatwave has a DC offset voltage thatprevents it from being symmetricalaround the voltage axis. The squarewave shown has a positive DC com-ponent added to it, but that offsetvoltage could be negative instead.

Figure lE shows another asym-metrical square wave. In that case,however, the lack of symmetry is notacross the voltage axis but in the rela-tionship between t1 and t2-t1 doesnot equal t2. The percentage of thetime the wave is high, or:

100% x t1/(t1 + t2)

is called the "duty cycle" of the squarewave.

One of the things that make square

waves so useful for testing purposes isthat they contain a large number ofharmonics, or integer multiples of thefundamental frequency. Because thesymmetrical, bipolar square wave hasboth baseline and time symmetry, itproduces only even -order harmon-ics-harmonics with frequencies thatare even multiples of the fundamen-tal-as shown in Fig. 2. Theoretically,those harmonics extend to infinity, butin reality, a good, sharp, clean squarewave has even -order harmonics outto about 1000f

Square waves can be generatedby digital TTL and CMOS IC's, 555 -timer -based circuits, and operationalamplifier ("op -amp") circuits. Let's lookat each in turn.

TTL Generators. TTL integrated cir-cuits have a 74 or a 54 as the first twodigits of their part numberi. They arepowered by a 5 -volt DC supply. Be-cause a high level in UL IC's is any-thing from 2.4 to 5 volts, a TTL signal issaid to change state when it crosses a2.4 -volt threshold.

Normal TTL chips operate at speedsof up to 18 MHz, with some cookingalong at 25 MHz. Special types go upto 80 MHz or more.

The inverter is a basic element inTTL-based sauare-wave generators. 97

V+

0

V+

0

HIGH

.*t1 ---t2

A

LOW

HIGH

V-

C

LOW

v+

v -

t2

t

E

0

V-

V+

0

D

HIGH

LOW

DC

COMPONENT

Fig. I. Here are the five main types of square waves: positive monopolar (A), negativemonopolar (B) , symmetrical bipolar (C), asymmetrical bipolar (D), and timeasymmetrical (E).

Those components can be either dis-crete inverters (such as the 7405), orNAND gates (like the 7400) or NOR gates(for example, the 7402) with their in-puts tied together to form an inverter.Figure 3 shows a typical TTL ring os-cillator that will produce squarewaves in the 500 -kHz to 10 -MHz range.In that form, it is made from three sec-tions of a 7405 hex inverter chip.

The circuit's frequency is set by thevalues of C1 and R2. The value of C1should be in the range of 390 pF to0.005 i.LE while R2 can vary from 1 to3.9k ohms. It is common to use a cir-cuit like the one in Fig. 3 to generate afrequency that is higher than the oneneeded, and to then divide the fre-quency with a series of TTL countercircuits cascaded together,

CMOS Generator Circuits. TheCMOS family of digital integrated cir-cuits operates at lower frequenciesthan the TTL family, but in return, CMOSIC's consume less power. While a typ-ical TTL device might dissipate milli -watts of power, an equivalent CMOSdevice dissipates microwatts. Like TTLIC's, CMOS devices can also bepowered from a 5 -volt supply, and de -

98 pending on the situation, might be TTL

tt

f 2f 4f 61 131 10f 121 992f 1000fFREQUENCY

Fig. 2. The frequency spectrum ofsymmetrical square waves consists of thefundamental frequency and a largenumber of even harmonics.

I Il

OUTPUT

Fig. 3. A 771,ring-oscillator circuit usesan odd number of inverters in an astableconfiguration.

compatible. However, many CMOSdevices can be powered at highervoltages.

For a typical CMOS chip, a signal issaid to change state when it crossesthe voltage half -way between thesupply voltages. For example, when a+ mi12-volt supply is used, the thresh-old is 0 volts, and when a single 12 -voltsupply is used, the threshold is 6 volts.The first digits in a CMOS-chip numberare generally 4 or 45.

A Schmitt trigger is a special circuitthat obeys slightly different rules thando other forms of digital gates. Forexample, when the 4584 hex invertingSchmitt -trigger IC is operated from a5 -volt power supply, the output statewill change on positive -going inputsignals at 2.9 volts, and on negative -going input signals at 2.3 volts. Thedifference between the 2.9- and 2.3 -volt signals is called the "hysteresisband."

Figure 4 shows a 4584 inverter (Vo ofthe total 4584) used in a very simplesquare -wave oscillator circuit. Be-cause the 4584 is an inverter, a low atinput pin 1 produces a high at outputpin 2, and consequently, a high inputproduces a low output. When power isinitially applied, capacitor C1 is dis-charged so the input sees zero volts (itis low); the output is therefore high,allowing C1 to charge from the outputvoltage at a rate limited by the timeconstant R1C1. When the voltage atthe input reaches the Schmitt trigger'spositive -going trip point, the 4584's in-put sees a high. That results in a lowoutput, which causes C1 to dischargethrough R1 until the voltage drops be-low the negative -going threshold. Thecapacitor will continue to charge anddischarge between those two levelsat a frequency of approximately0.72R1C1.

Figure 5 shows a CMOS square -wave oscillator based on inverters (orNAND or NOR gates wired to act like in-verters), which is similar to the ring os-cillator shown previously. Unlike someCMOS inverter -based circuits, the onein Fig. 5 will produce a square wave

Vo

Fig. 4. A CMOS, inverting, Schmitt -trigger square -wave oscillator requiresvery few components to function.

OUTPUT

*SEE TEXT

Fig. 5. This CMOS, inverting square-

wave oscillator can be varied over awide range. Note that R2 should be tentimes the value of RI, as shown.

f/2

1/2

Fig. 6. This square -leave oscillator,based on the 4047 CMOS device, hascomplementary half -frequency outputs.

that has a 50% duty cycle. There areIwo resistors used in that circuit; R1 isused to set the operating frequencyand R2 is approximately 1081. Typicalvalues for R1 and R2 are 100,000 ohmsand 1 megohm, respectively. The val-ue of C1 is less than 1000 pF The oper-ating frequency can be from OA Hz to1 MHz, depending on the values of R1and C1, and is determined from:

fo = 1/(2.2R1C1)

where fo is in hertz, R1 is in ohms, andC1 is in farads.

Another CMOS square -wave gen-erator is shown in Fig. 6. That circuit isbased on the 4047 multivibrator cir-cuit, which can be used for eithermonostable ("one-shot") or astableapplications. In the configurationshown in Fig. 6, the 4047 is an astablemultivibrator. There are three outputsfrom the 4047. The first is the oscillator(OSC) output, which is connected di-rectly to the internal oscillator circuit,The other two outputs, Q and Q, arecomplementary to each other andoperate at one-half the frequency ofthe internal oscillator.

The output frequency is set by tim-ing components R1 and C1, as in thelast equation, but the Q and Q outputsobey:

fo = 1/(4.4R1C1)

The value of R1 should be between

10,000 ohms and 1 megohm, whilethe value of C1 should be 100 pF ormore (the maximum capacitance isnot limited theoretically, but a prac-tical limit exists when the leakage re-sistance of C1 is of the same order ofmagnitude as R1).

555 -Timer Oscillators. The 555timer, with the possible exception ofeither the 741 operational amplifier orsome microprocessors, is probablythe most popular IC. That is becausethe 555 is versatile, low-cost, and be-haves itself (which means that design-ing 555 projects is relatively easy).

The 555 is used to make monopolarsquare waves that can be either TTLcompatible (V+ must be 5 volts DC),or CMOS compatible. Any power -supply voltage from 4.5- to 18 -volts DCcan be used, as the voltage sets thevalue of the high state.

V+

C3.1

OUTPUT

Fig. 7. Of course, the old 555 timer canbe used as an astable multivibrator togenerate square waves. However, for thecircuit shown, then will not besymmetrical.

Fig. 8. An operafonal trunsconductanceamplifier, square -wave generator circuitlooks much simpler than it sounds.

The 555 can be connected in eithermonostable or astable configura-tions, but for continuous squarewaves, the astable version is used (seeFig. 7). The square -wave signal ap-pears at pin 3 of the 555, while timingsignals are processed at pins 2, 6, and7. The output frequency of the 555astable multivibrator is found from:

f. = 1.44/((R1 + 2R2)C1)

The duty cycle of the 555's square -wave output is determined by the re-lationship between R1 and R2, and isgiven by:

Duty Cycle = (R1 + R2)/R2

Linear IC Generators. Severaltypes of linear integrated circuits canbe used to make square waves. Thesimplest of those is the operationaltransconductance amplifier (OTA).The only components in the simplecircuit shown in Fig. 8 are a CA3048OTA, a feedback resistor (R1), and atiming capacitor (C1). The output fre-quency is approximately given by:

fo ---- 1/(2aR1C1)

Timing resistor R1 should be from 1megohm to 3.9 megohms. When R1 isof a greater value, the circuit some-times stops oscillating, dependingupon the specific CA3048 used.

Operational -Amplifier Gener-ators. The operational amplifier is

one of the most useful linear IC'smade. When introduced in the late1940's (in vacuum -tube form), the op -amp was intended for performingmathematical operations in analogcomputers. Very rapidly, however, de-signers realized that the op -ampcould be used for a wide variety ofapplications other than computing.The transistor soon introduced morepeople to the op -amp, but it wasn'tuntil the advent of the integrated cir-cuit that the complexity of the op -amp became an internal affair. Theresult was a simple amplifier in whichthe transfer function was set by ma-nipulating the feedback.

Figure 9A shows a common op -amp square -wave generator circuit. Ituses Iwo feedback paths: one sets theDC level at the noninverting input ( + ),while the other is the RC timing net-work (R1C1). In general, if the feed-back constant 43) is:

= R3/(R2 + R3)

the output frequency is set by:

fa = 2R1C1Lna1 + (3)/(1 - (3))

But, as with many circuits, a simpleassumption can simplify the equationquite a bit. If we assume R2 = R3, thenthe equation reduces to: 99

v-

-v

A

Fig. 9. This operational -amplifiersquare -wave generator (A) produces a50 -percent duty -cycle signal. That isbecause both the charge and dischargecurrent for Cl flow through RI. Theresulting charging and output waves areshown in B.

fo = 1/(2.2R1C1)

Figure 9B shows the annotated tim-ing waveform for the above circuit,with the capacitor charge/dischargecurves superimposed on the outputwaveform. Because the op -amp ispowered from a bipolar supply, out-put voltage Vo jumps between +Vsotand -Vsot. The noninverting input isbiased to voltage V1, which is a frac-tion of output voltage Vo accordingto:

= Vof3 = VoR3/(R2 + R3)

Since R2 = R3:

= V0/2

The rules for the operational ampli-fiers used in the above nonlinear cir-cuits are simple: If the inverting input is

100 less positive than the noninverting in-

put, then the output is high; if the inver-ting input is more positive than thenoninverting input, then the output islow; if the two inputs see the samepotential, then the output is zero.

Assume on initial turn -on that thecapacitor is discharged, so capacitorvoltage Vo is zero. According to therules for operational amplifiers, thatforces a high output. Capacitor C1can now charge under the influenceof +V5ot and the R1C1 time constant.After time to expires, the capacitorvoltage Vo reaches +V1, so the out-put snaps low to - Vs°, At that time,the low segment of the output wave-form begins, and C1 begins to dis-charge under the influence of -V50,.It then recharges under the opposite

Vo

*CHOOSE YOUR OWN OP -AMP

Fig. 10. Here is an op -amp -basedsquare -wave generator that uses diodeswitching to produce a fixed duty cycleother than 50 percent.

12

R4560K

v-

v+

R510K

DUTY -CYCLECONTROL

R22.7K

R32.7K

Vo

*SEE TEXT**CHOOSE YOUR OWN OP -AMP

Fig. 11. Use R5 to adjust this variable -duty -cycle square -wave generator. Thatpotentiometer controls 12 to vary thetiming.

polarity. The process then repeats it-self. The high time is to and the lowtime is to, while the total period is:

T=to+tband the output frequency is 1/T.

The circuit shown in Fig. 9A pro-duces a time- and voltage -sym-metrical square wave. We can alterthat time symmetry by making eitherof the following two modifications tothe circuit.

The first modification is shown in Fig.10. That circuit uses two resistors in thetiming network, and a pair of PN-junc-tion diode switches to select whichresistor is used at any given instant.Diodes D1 and D2 are backwards withrespect to each other, so they con-duct on alternate polarities of outputvoltage Vo. When the output is high,D1 is forward biased and D2 is reversebiased. As a result, R1 is used with CI totime the circuit. When the output statechanges to low, D1 is reverse biasedand D2 is forward biased. In that case,R2 times the circuit. Because R1 andR2 are not equal to each other, theirtiming is different, so the output wave.form's highs and lows are not equal.

A limitation on the circuit in Fig. 10 isthat the duty cycle of the outputsquare wave is fixed. The secondmodification to the circuit in Fig. 9A isthe variable -duty -cycle square -wavegenerator shown in Fig. 11. That modi-fication uses a DC -offset circuit (com-posed of R4 and R5) to inject asecond current (12). Because of thatbias, the half cycle when 1, and 12have the same polarity is shorter.When R5 is set to the mid -point, thevalue of V2 is zero, and the outputwaveform has the usual 50% duty cy-cle of the unmodified circuit.

The circuit shown in Fig. 11 can bemodified to perform pulse -widthmodulation. For that, one end of R5 isgrounded and the other end is con-nected to a source of triangle,sawtooth, or sinewaves that modu-lates the duty cycle of the square -wave signal. The modulating signalshould vary over a substantial portionof the V+ to V- voltage range (butnot more than those values) in orderto produce maximum duty -cycle vari-ation.

Square -wave generator circuits areeasy to design, easy to build, and areextremely useful for a wide variety ofapplications in electronics.

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101

ADD A SWITCH(Continued from page 41)

set, although after a day of jumperhunting I was somewhat less than en-thusiastic.

The worst part in all this was that thePC could not be closed up until I wasthrough playing with the constructionset. As we all know, a PC with its coverremoved is an accident just waiting tohappen. If only there was a way to getboth the construction set and themodem to work properly, at leastusing only one of them at a time, with-out having to reconfigure jumpers-and of course shutting down thecomputer-every time I switched be-tween the Iwo.

A Total Solution. Staring at my PCstrewn across the floor, a total solutioncame to me: If a double -pole, dou-ble -throw switch could be connectedto both the enable/disable-COM2jumper on the I/O card and theCOM2-enable jumper on themodem, all it would take to switch be-tween the two would be a flip of theswitch. The switch could easily bemounted on a spare expansion -slotcover or on a blank connector plateon the back of the computer case.

To avoid soldering to your computerperipherals, wire -crimp single -pinheader sockets can be used to connectthe switch to the cards.

0The only problem I could foresee

was how to connect switch leads tothe male jumper -block pins on the

otwo cards in question without solder-

= ing directly to them. The solution wasto use five wire -crimp single -pinheader sockets. Leads were crimpedto each header socket and the metalbody of each socket was coveredwith heat -shrink tubing. Figure 1 showshow the switch was connected to thejumper block on each card. With this

LL addition to my PC, the modem workswith the switch in one position and theserial port-along with the con -

1 0 2struction set-works in the other.

SPRINKLER GUARDIAN(Continued from page 57)

wire soldered to the nail heads. Theprobes should be buried horizontally,about 1 to 2 inches below the surfaceand about two feet apart.

Installation. Before you can use theGuardian, you have to know the resis-tance of the ground when it is dry. Tofind the resistance, bury your twoprobes as described before and waita few days. Then, measure the resis-tance across the probes when theground is dry and needs watering. Theresistance value between the probesmust fall within the range of R2 and R4,or between 10K and 40K ohms. If it fallsout of that range, the distance be-tween the probes might have to beadjusted.

The connections between thesprinkler controller and your Guardianare shown in Fig. 4. Three solenoidsare shown in that system to show howthe common leg connects to each; ofcourse, there are probably more sole-noids in your own system.

To install the Sprinkler Guardian, cutthe common leg from the valves, andconnect the leads to terminals land 2of TB3. Then, connect the buriedprobes to the terminals of TB2. Finallypirate power from the supply of thecontroller using insulated wires, andconnect the wires to terminals 1 and 2of TB1.

Checkout and Use. Place S1 in the"manual" position; then turn R2 fullycounter -clockwise. Relay K1 should beoff and LED1 should be on. Slowly ad-vance R2 clockwise until LED1 goes offand LED2 comes on indicating that K1has closed. Now, slowly turn R2 coun-ter -clockwise again until LED1 comesback on. Place S1 in the "automatic"position, and the unit is ready to use.

If adjusting R2 turns on LED1 but notLED2, the probe resistance is too high.On the other hand, if adjusting R2turns on LED2 but not LED1, the proberesistance is too low. Decrease or in-crease the distance between theprobes as needed to get the resis-tance in the proper range.

Once you get the Sprinkler Guard-ian up and running, you'll never haveto worry about the costs of wateringyour lawn in the rain again.

FREQUENCY-RESPONSETESTER(Continued from page 83)

AUDIO LEVEL control using your scope asa waveform monitor with internalsweep, to make sure no clipping oc-curs. Switch S2 into SWEEP mode, andset your scope to external sweep asyou did during calibration. If youmade your own log scale using Fig. 5,set your horizontal gain to match itswidth. By adjusting the vertical gain,you should be able to see the DUT'sresponse over the entire frequencyspectrum.

Here are a few hints: Although theresponse display seems most easilyviewed with SWEEP RATE control R29 set to

maximum, the low -frequency portionof the display (the left side) will not bevery accurate with that setting. TheTester's lowest output frequency isabout 20 Hz. Because that frequencyis constantly being modulated, if thefrequency increases significantly be-fore a single 20 Hz -cycle is com-pleted, then your test at 20 Hz isinvalid. For that reason, the slowestsweep rate should be selected whenseriously examining low -end re-sponse. A storage scope is of courseideal for that.

Note thatthe vertical display of yourscope simply reads peak -to -peakvoltage, which is very different fromthe decibel scale normally used foraudio. To put things in perspective, a50 percent dip in vertical deflectioncorresponds to a -3 -dB drop whenmonitoring power amplifiers, and a-6 -dB drop when testing almost anyother audio device.

Finally, you might wish to occasion-ally touch up the low -frequency cal-ibration via the access hole youdrilled for R24. As before, leave theTester powered -up for a few minutesbefore proceeding, and then per-form the calibration procedure aspreviously described.

"That explains the microchips."

1G r9e a9t Yearawr afso ar Popular Electronicsrr he twelve 1990 issues

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TOPICS FROM THE PASTSelected Projects

Audio Ambiance Ditherizer, April

Bit Grabber for Parallel I/O Testing, December

Car -Radio Silencer, October

Cordless Test Probes, January

CW and SSB, Add to a SW Receiver, May

Digital Entry Switch, November

Economy Portable SW Receiver, August

Exhaust Monitor for Car, June

Experimental AC Hum Sniffer, September

Game Reaction Timer, April

Headphone Output for Your CD Player, July

Hot -Wire Glass Bottle Cutter, December

Indoor Burglar Alarm, December

IR-Triggered Sound -Effects Generator, October

Lie Detector, Simple, January

Microphone Preamp, Simplest, March

Mobile Battery Charger, March

NiCd Battery Tester, August

Plasma Display, Custom, February

Receiver Circuits You Can Build, March

Remote -Control FAX Switch, August

Serial Cable Tester, January

Telephone Toll Totalizer, August

Tesla's Lightning Generators, September

The Lepton Candle, October

Ultrasonic Morse -Code Transceivers, July

Universal 3 -Terminal Power Supply, November

Video Titler, Super Simple, September

Vision System for Robotic Toys, March

VLF Receiver and Transmitter, July

Water Leak Alarm, January

Special FeaturesAntenna Installation, September

Capacitors, Choosing and Using, June

Classic Amateur Receivers, November

Drying Out Flood -Damaged Equipment, January

Early Radio Transmitters, May

External Drive for Laptop, June

First Electric Motor Project, October

Ground Fault Technology, November

Keeping Up with Pacemakers, July

Living with Lightning, October

Make Your Own Iron -on PC Patterns, July

Old-time Radio Circuits, March

Oliver Lodge: Radio's Forgotten Pioneer, July

Restoring a Classic SW Receiver, April

Solar Power, Experimenting with, June.

St. Elmo's Fire, September

Surface Mount Technology, November

Television Night, a Look Back, July

Tune -in to Satellite Radio, May

Using Appliances Overseas, January

Theory for Everyone3 -Terminal Voltage Regulators, May

200,000 -volt van de Graaff Generator, October

All About Batteries, August

All About Thermistors, December

CCTV Installation Guide, November

Connect Anything to Your Computer, August

Designing Power -supply Circuits, February

Digital Electronics Introduction, April

Experiments in Electrophotography, March

Fiber -Optic Communications, April

Galvanometer, Build and Learn, September

Lasers, All About, SeptemberPrinter Technology, October

Signal Generator Circuits Cookbook, November

Stepping Motors Introduction, March

Troubleshooting Computer Disk Drives, May

Troubleshooting Your Printer, December

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104

NOVEL NIGHTLIGHT(Continued from page 36)

x 7 inches each, for the sides of thenightlight. The top is a 71/4 -inch squareof glass. You will also need to cut fourpieces of top molding and fourpieces of corner molding, using thedimensions given in Fig. 3.

To assemble the nightlight cover,apply epoxy glue to the inside edgesof each piece of molding that you areready to attach. Carefully fit togetherthe pieces of glass and the mirrorsthat make up the sides of the boot (themirrors should be adjacent), and holdthem firmly in place to allow the glueample time to dry. When the sides areassembled, glue the top square ofglass to the pieces of top molding.After that has fully dried, glue the as-sembly to the top of the glass box.

The glass cover should be securedto the baseboard, especially if theNovel Nightlight will be used by youngchildren. That can be accomplishedin a number of ways. On the pro-totype, a piece of wire is connectedbetween two small screws on op-posite corner moldings. Sliding thewire under the baseboard preventsthe cover from being lifted. If you pre-fer, you can attach small latches onopposite sides of the project, instead.

With the case assembled, you cansafely plug in and use the Novel Night -light. So, put an antique VR tube togood use, and brighten up your eve-nings while you're at it.

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PK TESTER(Continued from page 54)

With 'R5 adjusted, you can com-plete the assembly of the unit. Drill 16holes on the top panel of the projectcase to match the pattern of the LED's.Insert an LED lens cap into each of theholes, then lift the board and press theLED's into their respective caps. Whenthat is done, the PC board will be heldfirmly under the panel.

Using the Tester. The finished unithas two pushbutton switches (S1 andS2). If the STATUS/TEST button (Si) is de-pressed when power -switch S3 is on,the Tester will go into a self -test mode.It will take 480 samples and see if theRNG is operating correctly. If it is, allthe LED's will flash and the unitwill thenproceed into its normal -operationmode. If there is a problem with thecircuit, all the LED's will continue flash-ing, indicating an error, until the unit ispowered down. Check the calibra-tion of R5 if that occurs.

Once in the normal -operationmode, the PIC keeps track of LED"movements" to the left or right. To findout if one direction has been comingup more frequently, hold down theSTATUS/TEST button. If the top two LED's

light up, then there is no excess move-ment. If one or more light to the left orright, then that means the unit is bi-ased in the indicated direction. To de-termine the maximum number ofmoves that the unit is biased in thatdirection, use:

n x 16

where n is the number of LED's lit. Thesystem of LED's used in the PK Testercan only indicate the left or right bias

in increments of 16 moves. For thatreason, the minimum number ofmoves is 15 less than the maximumnumber. For example, if three LED's arelit to the right, then movement to theright exceeds normal by 33 to 48moves. As a guide, a reading of sevenLED's to the left or right indicates anextreme bias in that direction. Whenyou have finished taking a reading,

you can either let go of the srmusfrEsTbutton and resume testing, or clearthe "movement" counters and restartthe PK Tester by pressing S2.

An Experiment. Leave the box onfor 24 hours and verify its randomnessby pressing srArusirEsT. Then, have a testsubject concentrate on the PK Tester.Have him or her "will" the movementof the LED either clockwise or coun-terclockwise. After about ten minutes,verify whether the LED movementsare neutral by again pressing theSTATUS/TEST button. Should the LED move-

ment be biased in one direction,have the subject continue his or her"willing" so that you can see if the biasis coincidental. After another ten min-utes the status response should showan even greater bias if the RNG actu-ally is being influenced. Next, press theRESET button and ask the subject toconcentrate in the reverse direction. Ifthe bias follows the desired directionafter several reversals, your subjectmost likely has a notable level of PKability.

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TELEPHONE -LINE SIMULATOR(Continued from page 77)

A power switch was not used in theprototype. Although a power controlis not necessary, you can add an SPSTtype toggle switch in series with theprimary of T1.

Connect the main board to thepower -supply board using shortlengths of insulated wire. Wire thesquare pad to the square pad, thecenter -tap (al pad to the center -tappad, and the remaining pad to theremaining pad.

Be sure to trim any long componentleads. After assembly, clean the solderflux off the circuit boards. Commercialsolvents are available that do a terrificjob of removing the flux residue.

Mount the two circuit boards onshort standoffs in an enclosure of yourchoice. Be careful when mountingthe power board; do not allow it tocome in contact with the conductivesurfaces of your cabinet! Position thepower board in your enclosure so thatT3 is a minimum of two inches from T1and T2. If they are placed too closetogether you may hear power -line AChum on the telephone audio.

Test and Check -Out. Disconnectany telephone equipment pluggedinto the line -1 and line -2 phone jacks.Remove the JU1 power -up -modeconfiguration jumper. Install the JU2CPC -configuration jumper. Adjust R14(which sets the audio level) to aboutthe middle of its range.

Turn on AC power and verify that theLED display shows "r." for a momentthen shows "n." (normal mode). Pressthe mode switch and verify that it canbe cycled through the five differentmodes (n, A, b, c, and d).

Remove power and install the JU1configuration jumper. Turn on ACpower and verify that the LED displayshows "r." for a moment then shows"A." (automatic mode).

Set the unit to the normal mode("n."). Connect a standard telephoneto the line 1 (main) modular phonejack. Pick up line 1 and verify that adial tone can be heard. If you areusing a DTMF phone, dial a digit andverify that the dial tone stops and thedigit is shown on the LED display.

Hang up the phone; then lift thehandset again. Verify that you can

hear a dial tone again. Press the ringswitch once and verify that a ringingsound can be heard in the telephonehandset (it should sound like an au-thentic ring signal). Pressing the Ringswitch again or hanging the phoneup will terminate the ring sound andreturn the dial tone.

Plug a second telephone into theline 2 (test) jack. Pick up the line -1phone and again press the ringswitch. Verify that the line -2 phone'sbell is activated. It should ring with acadence similar to a standard ringpattern.

Try the remaining operationalmodes. For example, set the mode to"A" to have line 2 ring whenever line 1is lifted off -hook.

Beep- and Cycle -Mode Operation.To use the beep or cycle modes withthe delay feature, connect an an-swering machine or telephone to line2. If you are using the cycle mode, besure to also install a phone in the line -1jack. Start line -2 ringing by lifting theline -1 phone off -hook (cycle mode) orpressing the ring switch (beep mode).

While the test line is ringing, you canadjust the delay potentiometer from10-90 seconds by viewing the LED dis-play; the display will show a readoutof 1 to 9. If the delay cycle has alreadystarted (as seen by the chasing LEDpattern), you can press and hold thering switch to review the delay -countsetting.

When line 2 is answered, a series ofbeeps will be generated that willmake most voice -operated (VOX) an-swering systems stay on the line (if theyare operating correctly). If you want toforce the answering system toperiodically hang up, just use thatunits VOX time limit switch.

Keep line 1 off -hook if using the cy-cle mode. After the answering ma-chine (or telephone) hangs up, it willbe cycled on again every 10-90 sec-onds, depending on the R35's setting.At any time you can cancel the beepor cycle modes by pressing the Modeswitch.

Conclusion. Using Ring -It! couldn'tbe easier. Plug the equipment to testor demonstrate into line 2 and use theline 1 telephone to place calls to it.Now that you're ready to use yourRing -It! project, reach out and touchsomeone.

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111

WWV RECEIVER(Continued from page 40)

signal germanium or Schottky units.Selecting two diodes with matchedforward -bias characteristics is not ab-solutely necessary; however, don't mixcompletely different types of diodesin the mixer!

The CA3240 op -amp was specifiedbecause of its low cost and moder-ately low, input -noise characteristic;the alternative HA series units listed inthe Parts List are preferred for theirlower noise figures. The MC1458 andother "741" derivatives should beavoided. With a single RF-amplifierstage, the receiver is noise limited bythe op -amp, so lowest -noise units arebeneficial to the overall operation ofthe receiver.

As for component replacementand substitution, most passive com-ponents are not critical and can bereplaced with close values. If youcan't find the Zener diode, it can besimulated by connecting five 1N914'sin series.

Transformer Winding. TransformerT1 is a home-made unit, consisting of40 closely wound turns of #26 AWGenameled wire on a 1/4 -inch diameterair -core form, as shown in Fig. 4, withtaps at 21/2 and 101/2 turns from eachend; after each tap, the windings pro-ceed in the same direction. Hot -meltglue can be used to secure the wind-ings to the form. The coil does notrequire a screw -type tuning slug in thecore.

Fig. 5 shows the assembly details forT2 (the mixer transformer). Shown

8 electrically in Fig. 5A, T2 is wound on aO ferrite bobbin taken from a sub-

miniature 10.7 -MHz IF transformer orV-) detector coil universally used in older

pocket, auto, and console FM radios.8 IF transformers are typically color -co-

ded brown, green, or blue, and the02 detector coils are typically black orcc white. The 10.7 -MHz detector coils are

easily confused with 455 -kHz transfor-mers, which also use black and white

o)as identifying codes. The internal ar-rangement of the detector coil differs

=I from that of a 455 -kHz transformer inthat it has a single winding, while the455 -kHz unit has two.

Disassemble the transformer or coil,112 remove the tuning sleeve, the wind-

ings, and any tuning capacitor in thebase. The bobbin is a dumb -bellshaped piece of ferrite materialglued to the base. Lay out three 13 cmlengths of #32 to #38 AWG enam-eled wire in parallel. Wind the threewires 10 times around the bobbin as aset, as shown in Fig. 5B. Solder the wireends to the base pins as shown in Fig.5C.

The core permeability and thewinding inductance are not critical aslong as the winding acts as a trans-former at 10 MHz with low inter -wind-ing capacitance. The windings shouldnot be glued within the bobbin.

Test. After completing the assembly,apply power to the circuit and checkthe voltage across Zener diode D3;the voltage across it should be be-tween 3.0 and 3.6 volts. Connect agood earth ground to the receiver.Static should be heard through thespeaker. Adjust trimmer capacitor C11until a WWV signal is audible; thenpeak C11 for the best reception. Thelocal -oscillator frequency will initiallybe offset from \AA,W, so you'll probablyhear the beat note. Adjust trimmer ca-pacitor C1 for zero beat.

If a WWV signal is not heard, verifythat the audio circuit is functioning;check the input of U1 pin 3 to U2 pin 3with an audio signal injector, while lis-tening to the receiver output. Checkthe local oscillator's operation usingan oscilloscope, dip meter/monitor, orother frequency -test device, or listenfor the 10 -MHz, local -oscillator signalon another 10 -MHz receiver.

If the audio amplifiers are function-ing, but no signal is heard, verify thewinding polarity of T2 and the windingorder on T1. If you have a dip meter,use it to verify and set the resonantfrequency of C11/T1 to 10 MHz. Checkthe receiver with a marker generatorcalibrated for 25-, 50-, or 100 -kHz in-crements. If a signal is still not heard,wait a few hours and try again. Verifyyour ground connection at bothends-the ground is essential for theshort antenna.

After the initial circuit test, it may benecessary to re -trim capacitor C11 foroptimum reception. If C11 does needre -trimming, re-examine your anten-na attachment to the case and see ifyou can't reduce the stray capaci-tance by increasing insulation widthor separation.

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TECHNOLOGY UPDATE

New microprocessor puts the brainof a $50,000 car under your hood...Breakthrough remote control lets you start your car, turn on itsheadlights, sound a panic alarm and unlock the doors andtrunk...from up to 400 feet away.

by Charles Anton

How many times haveyou had to sit in asticky, hot car and

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A better way. The newAutoCommand key chaintransmitter gives you thepower to start your car fromthe comfort of your home oroffice. Simply press a buttonto start cooling off or warming up your car from up to 400 feet away. Youcan turn on the air conditioner, heater or de-froster without leaving your seat.

The powerful microprocessor brain learnsyour car's starting pattern. It adjusts the start-ing routine based on the outside temperature,

Why AutoCommand is better...

Range. Most remotes only workup to 100 feet away. AutoCommandgives you a range of up to 400 feet.

Self -diagnostics. The uniquefeedback lights on AutoCommandconfirm proper wire connections dur-ing and after installation, just like acar's on -board computer.

IIII Total security and convenience.AutoCommand gives your car thecapability of remote car starting, key-less entry, panic alarm and car security.It also has built-in low temperatureand low battery voltage start options.

battery voltage and theamount of time since yourcar was last run to guar-antee starting every time.Give your car a brain.AutoCommand gives yourcar the same features asluxury cars, and even somethey don't have, by addingthis microprocessor brain.In addition to remote carstarting, your car will havefeatures such as keyless en-try and built-in car security.

You can call for help orscare someone away withthe panic alarm; locate yourcar with car finder; andhave your car automatical-

ly turn on its headrghts when it gets dark or turnthem off 20 seconds after leaving your car. Youcan even leave your car running with the doorslocked and no key in the ignition. If you forgetyour car is running, it will automatically shut off

after 10 or 15 minutes, you choose.

AUTOCOMMAND FEATURES

Built -In self -diagnostic Key requiredsystem, cold start to drive oarand "no tech" featuressimplify Installation

Keyless entry allowsyou to look and unlockdoors and trunk

Transmission check toverify car Is In park

Security switch preventsunauthorized usa

Works on diesel orcarburetor cars

Automatic shut-off after 10 or15 minutes (you choose)

Built-in car security system

Pln switch disables unitIf hood la opened

Monitore temperatureand voltage to pre-vent dead batteries

Penis Alarm, head-lights andior horn

can be activatedby remote control

Intelligent benefits. With AutoCommand,your car can't be driven until a key is put intothe ignition. AutoCommand immediately cutsoff the engine if your vehicle's hood is raised,brake pedal is pressed or the vehicle is

shifted out of gearwithout the key in theignition, preventingtheft or tampering.

AutoCommandalso monitors your carwhile you are away.The built-in VacationOption will automati-cally start and runyour car for 10 min-utes every four to sixhours when the tem-perature drops belowzero. On hot summerdays, AutoCommandwill also start your carwhen the interiorreaches 140 degrees. Ifyour battery drops be-low 11 volts, Auto -Command will startyour car to recharge it.

Try it risk -free. AtComtrad, we back allour products with arisk -free home trial.Try AutoCommandin your car and ifyou're not completelysatisfied with its valueand performance, re-turn it within 90 daysfor a full refund, "NoQuestions Asked."AutoCommand is also backed by a two-yearmanufacturer's limited warranty. Most ordersare processed within 72 hours and shipped UPS.

UPGRADE OPTIONS.

You can replace your

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Garage Door Remote

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extra key chain

remotes! You can also

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option to the built-in

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It detects any impact

on your car, giving you

added protection.

e key thetatransrahter

weftswith

allthe

avail-..---" able

Natural.

Exclusive $50 installation discount

AutoCommand comes with an installationvideo and has patented self -diagnostic feed-back lights which confirm wire connectionsstep-by-step during installation. But for thosewho prefer to have AutoCommand profes-sionally installed, we offer a $50 installationdiscount. Use the money for professionalinstallation, or install it yourself and keepthe money. Either way, AutoCommandmakes it easy and affordable to add luxurycar features to your automobile.

AutoCommand' .$241 $14 S&H

with installation discount .. 4299 $14 S&H

AutoCommand Upgrade FeaturesGarage Door Opener $79 $8 S&H

add -Shock Sensor to alarm $49 $4 S&H



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GERNSBACK SPECIALTY SERIES - americanradiohistory.com · Farmingdale, NY 11735 1-516-293-3000 Fax:...

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