THE INTERNATIONAL ELECTRONICS MAGAZINEJANUARY 1992 UK £1.90

Build a compacitEdi k playerWindspeed and direction meter"PWM temperature controllerLow -frequency counterDirect conversion radioMini Z-80 system

Please mention ELEKTOR ELECTRONICS when comac tin.t! advertisers

IILTr3Five successful years

Twenty five man years developmentOver three thousand five hundred users

To celebrate the continued success of ULTIboard we have a very special:

JUBILEE OFFERdal CDC M ULITI(DOS-versions)COMPUTER AIDED PCB DESIGN SCHEMATIC CAPTURE

£295;excluding V.A.T

This is not a stripped down or old version of our software. Updates with new features added,are released every six months.

This is not a low cost package without a growth path. Upgrades are available to our highercapacity, 32 bit, Advanced and Professional systems.u This version includes our high -quality interactive autorouter (not an external batch router) whichallows you to selectively route components/nets/windows as well as the whole board.

ULTImate's Jubilee offer is the only true low cost system available today which gives you leadingedge software with a future.Ask for your demo disk and see for yourself how easy it is to take the ULTImate route.

I F Lomputer Aided PCB Design

Real lime (Direct) Reconnect, ForcevectoHistograms guarantee optimal placementReal lime Design Rule Check prevents illegalconnections and/or clearances during traceeditingTrace Shove & Reroute -while- Move reduceediting time.Automatic power & ground plane generation.

LUMPhermitic Capture

Red lime Electrical Check prevents errors duringediting

Auto wiring easily makes connections Wire Move and Shove reduce editing time

.. Perfect Intergration with ULTIboarcl, even tracewidths may be entered during schematic captureNetlist-toolkit allows interfacing to any CAD/CAEsystemUnlimited attributes on parts, pins & nets

International headquarters

LT i r1)cu Salespa&r uallk,iF:rerrtmOofsftioc B e2r Bs a cRcGh7u s4:0-ioNAuls e

Tel. 02159-44424 Fax. 02159 43345 TECHNOLOGY Tel.: 0734-812030 Fax: 0734-815323Energistrciat 36 1411 AT Naarden

Front coverBuilding a record player,cassette or tape recorder,or compact -disk player, isoften hampered by themechanical constructionand the availabity of certainparts, particularly the deck.In the past, manufacturershave generally tended to bereluctant to make tape orCD decks available to theretail trade, but Philips hasrecently decided to breakaway from this policy. A kit,containing its CDM-4 deckand associated motherboard, can now be obtainedfrom certainretailers at an affordableprice.

We regret that owing tocircumstances beyondour control, the article`PWM temperaturecontroller' has had to beheld over till theFebruary issue.

In next month's issue:

Among others: Improving portable radio

performance l2C interface for PCs Mini square -wave

generator RAM extension for mini

Z80 system Audio/video switching

unit PWM temperature

controller Why lithium cells?

Direct digital synthesis -DDS

Copyright ; 1992 Elektuur BV

ABCtra9ER CF ,LOT

CF anna.4..ATK7uS

CONTENTSAUDIO &

36 PROJECT: Build a compact disk playerby T. Giffard

COMPUTERS & MICROPROCESSORS

14 PROJECT: Mini Z80 systemby A. Rigby

56 PROJECT: Prototyping board for IBM PCsby A. Rigby

DESIGN IDEAS

54 Exploring negative resistance: the lambda diodeby Samuel Dick

GENERAL INTEREST

26 PROJECT: Computer -controlled weather stationPart 3 - windspeed and direction meterby J. Ruffell

RADIO. TELEVISION & COMMUNICATIONS

20 NE602 primerby Joseph J. Carr

48 PROJECT: A direct conversion radioby David J. Silvester, G4TJG

60 PROJECT: Universal RC5-code infra -red receiverby A. Rigby

SCIENCE & TECHNOLOGY

46 Cochlear implantsby Douglas Clarkson

TEST & MEASUREMENT

31 PROJECT: Fast, precise thermometerby J. Ruffell

42 PROJECT: Low frequency counterby F. Hueber

MISCELLANEOUS INFORMATION

Electronics scene 11-13; Events 13; Readers services 65:Switchboard 66: Terms of business 66; Readers corner 67;Corrections 67: Index of advertisers 74

January 1992Volume 18Number 196

Computer -controlled weatherstation - Part 3 - windspeed and

direction meter - p. 26

Fast. precise thermometer, p. 31

Prototyping board for IBM PCs.p 56

Mini Z80 system - p. 14

ELEKTOR ELECTRONICS JANUARY 1992

U Please mention ELEKTOR ELECTRONICS when contacting advertisers

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ELEKTOR ELECTRONICS JANUARY 1992

ELECTRONICS SCENEm

MODERN MUSIC IS A 'DUET'THE computer revolution in digital audio

has created new possibilities for musicalcomposition and research scarcely imagineda decade ago. The consequent demandingand rapidly developing field of modern elec-trophonic (electrosonic or electroacoustic)music calls for harmony between composerand sound engineer.

At York University in northern England,researchers have been involved in the devel-opment of a variety of systems geared to therequirements of modern composers. Under-standing the fast pace of change in this field,the university has set up courses in 'musictechnology' that are designed to train musi-cians in new technological advances and totrain electronic engineers in current musicalthinking. The students are integratedthroughout most of the course and form a

new middle ground between the two maindisciplines. Graduates are able to use theirknowledge and skills in the recording indus-try, in sound production in radio and televi-sion, musical instrument technology and incomposition of music. They may also be-come designers of studio and contemporarymusic systems.

Research by the university's music de-partment has included 'the composer's desk-top project', which originated in York but isnow an international co-operative venture. Itis a compact system that brings togethersound -file, score generation and processing,graphical interfaces, in short, everything thatis essential to today's composers.

Ambisonics, a British -designed methodof coding and decoding spatial informationconcerning sound, is a major interest_ Boththe technology and compositional use ofthree-dimensional sound diffusion based onambisonics are being studied. A program-mable decoder, devised at the university, thatcan drive up to 16 loudspeakers in a three-dimensional array, has been used and appre-ciated in a variety of concerts, as well as forresearch into improved diffusion techniques.University of York, Music Department, Hes-lington, York YO1 5DD, England.

SAFER LANDINGS WITHMICROWAVES

TN 1995, the Siemens Plessey Radar (SPR)IP-SCAN 2000 microwave landing sys-tem (MLS) will come into use at London'sHeathrow airport. This will represent a sig-nificant stage in the development of MLS,which is designed to meet the growing de-mand for precision landing guidance into thenext century.

For many years. the instrument landing

system (ILS) has been the standard approachand landing aid and bas undergone develop-ment and refinement to enhance reliabilityand improve accuracy. Development hasbeen such as to permit automatic landings toCategory Bib since the early 1970s. Theseconditions are defined as a precision instru-ment approach and landing with a decisionheight lower than 15 m, or no decisionheight; and a runway visual range less than200 in, but not less than 50 m. Decisionheight in this context means a specifiedheight in the precision approach at which amissed landing procedure must be initiatedif the required visual reference to continuethe approach has not been established.

The azimuth equipment installed at Lon-don's Heathrow airport for the evaluationof the Siemens -Plessey microwave land-ing system.

Despite the considerable progressachieved with ILS, it has become evidentthatit will not meet the operational needs in thefuture, and a search has, therefore, been pro-ceeding for a better system. After lengthyconsideration of various proposals world-wide, international agreement has been ob-

Produced and published by ELEKTORELECTRONICS (Publishing)

Editor/publisher. Len SeymourTechnical Editor 1. BuitingEditorial Offices:Dona HouseBreomhflt RoodLONDON SW18 4IQEnglandTelephone: 0814177 1688 (National )or +44 81877 1688 (in:emotional 1Min: 917003 (LPC G)Fax: 0814174 9153 (Nationalor -144 81874 9153 (International )

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European (Wets:P.O. Box 756190 AB BEEKThe NetherlandsTelephone: +31 46 38 9444Telex: 56617 (elekt n11Fax: +31 46 37 01 61Managing Director: WWI andmin

Distribution:SEYMOUR1270 London RoadLONDON SW16 .4131-1

Printed in the Netherlands by NOB.Zoeterwaude

Overseas editions:FRANCEFlaw sariLes Trois TilleulsB.F. 59: 59850 NIEPPEEditors: D.R.S. Meyer,G.C.P. RaedersdorfGERMANYElektor 'eriag GmbH

Strafe 255100 AACHENEditor: F_J.A. KrempoisauerGREECEElekior EPEKariAaki 1416673 Voula - ATHENAEditor: E. XanthoulisHUNGARYFlektor Elektronikai folyorat1015 BudapestBanhydny u. 13Editor: Laken:6 AndrasINDIAElektor Electronics PVT LtdChhotani Building52C. Proctor Road, Grant Road (EtBOMBAY 400007Editor. C.R. ChandaranaISRAELF1.4nonal

P 0 Box 41096TEL AVIV 61410Publisher: Si. As rah=NETHERLANDSDelmar BVPeter Tro-epnelstraat 2-46191 VK BEEKEditor. P.EJ_KerserrsdrersPORTUGALFerreira & Remo Lda_R.D. EsteCirri. 32 -ice

LLSBOAEditor: Jemmies SequeiraSPAINResistor Electmnice AplicadaCalle Nlandes 15 Eralo C.28003 MADRIDEditor: Agustin Gonzales BueltaSWEDENElectronic Press ABBox 550514105 HUDDINGEEditor: Bill CedrumUSA & CANADAElector Electronics USAP O Bos 876PETERBOROUGH NH 03458-0876Publisher. Edward T. Dell

ELEKTOR ELECTRONICS JANUARY 1992

11E1 ELECTRONICS SCENE

tamed to adopt the time reference scanningbeam MLS and implement a transition planto enable timely conversion of all ground andairborne installations from ILS to MLS.

Unlike ILS. MLS provides accurateguidance information over a wide azimuthsector up to -±40° from runway centre -lineto a range of 18 km from threshold. Accu-rate elevation guidance is provided between+1° and +15', which enables the use ofsteeper glidepaths. An additional back az-imuth facility is also available for missedapproach and departure guidance.

Two hundred channels are currently avail-able in the 5030 MHz to 5090 MHz band,which overcomes LS problems with fre-quency allocation. MLS operates on the timereference scanning beam principle, in whicheach radiating antenna (azimuth, elevation,back azimuth) forms a very narrow beam,which is scanned electronically, to and fro,at very high speed across the coverage sector.

The aircraft receiver detects the passingbeams and measures the elapsed time be-tween the 'to' and 'fro' beams, which givesa precise measurement of the angle of the air-craft relative to the zero degree runway -cen-treline reference, in the case of the azimuthantenna. In the same manner. the elevationsystem scans a beam up or down, and theback azimuth operates in a similar way to theforward or approach azimuth.

The complete system operates with timedivision multiplex, which means that each ofthe MLS functions (azimuth, elevation andback azimuth) is synchronized and takes itsturn to radiate signals while the other trans-mitters remain silent.

The MLS antennas are very much smallerthan their ILS counterparts as a result of thehigh frequency used. The antenna system isalso independent of any ground effects andis highly immune to multipath effects be-cause of the very narrow beamwidths that areused for microwave frequencies. MLS alsooffers considerable flexibility in the choiceof approach path.

As part of the United Kingdom and inter-national programme for MLS developmentand transition planning, a Plessey uncatego-rized system was installed at Heathrow in late1986, following trials at Royal AerospaceEstablishments. A second Plessey systemwas installed at Manchester in 1988. co -lo-cated with a newly installed ILS.Siemens Plessey Radar Ltd, Oakcroft Road.Chessington KT9 I QZ, England.

ANALYSER HI SPEEDS ACCURATELINEAR CIRCUIT DESCRIPTION

Number One Systems' new software pro-mum, Analyser III, allows circuit de-

signs to be tested and proved before a singlecomponent is soldered, thereby saving timeand money as well as providing greater testaccuracy. In many cases, the breadboardingstage can be eliminated completely. allowingprototypes to be built directly on the PCB.

Analyser III is claimed to be ideal for theanalysis of filters, amplifiers, cross -over net-works, wideband amplifiers, aerial matching

networks, radio and TV IF amplifiers.crhoma filters, linear integrated circuit, andmore.

Analyser III, which is not copy protected,costs £195, excl. VAT, complete with com-prehensive manual, example circuit files andunlimited free telephone support.Number One Systems Ltd, Harding Way,Somersham Road, St Ives. HuntingdonPE17 4WR. England. See also p.10.

SAFETY WITH MAPLINNrfrom Maplin are three safety prod-

s.The 'Street Alert' is a compact per-sonal alarm with an extremely tough blackplastic case. Because of its slim size, it canbe carried easily by hand or be attached to abelt with the very rigid clip moulded into itshousing.

A large pink button, recessed to preventaccidental operation, is pressed to operate anextreme]) powerful 130 dB siren guaranteedto draw attention to passers-by. The alarm isdeactuated by simply pressing the buttonagain. The alarm is powered by a 9 V PP3(6F22) battery. (Our engineers have testedthis unit and can vouch for the claims madeby Maplin). At £19.95, incl. VAT, this is amost worthwhile protection unit for womenon their own. school children, elderly citi-zens, and many more.

The 'Keypad Door Alarm is versatile andeasily fitted on the inside of a door. It com-prises an attractive and robust main unit. fit-ted on the door itself, and a magnet assemblythat is mounted on the frame.

When the door is closed, the magnet is de-tected by the proximity sensor within thealarm. When the door is opened. and the mag-net moved away from the unit, the sensor de-tects the change and actuates a loud, piercingalarm. The alarm can be turned off only byentering a 3 -digit code on the keypad foundon the main unit.

There are four main modes of operation:visitors' chime; instant alarm; delay alarm;off (cannot be turned by simply selecting thisswitch). In addition. there is a red 'panic' but-ton on the main unit that sets off the alarminstantly. Its price is £19.95, incl. VAT.

The "PhotoNideo Flight' case is a high-quality ABS plastic instrument case de-signed for the safe and easy transport of cam-eras and portable video equipment. Solidfoam provides protection from damage,while convoluted foam is fitted to the top lidto provide a wide surface for securing itemsof a complex shape.

The GL32K case is 380 mm long,465 mmwide and 165 mm deep; it weighs 2.1 kg. Itcosts £34.95, incl. VAT.Maplin Electronics PLC. P.O. Box 3,Rayleigh SS6 8LR, England. Telephone0702 552 911; fax 0702 553 935

HENRY'S NEW 1991-92 CATALOGUErrifIE NEW Henry's 300 -page plus. colour1 catalogue is available by post (send C4

size with £2.65 stamps affixed for dispatchin Britain) or at £2.00 to callers at Henry'sstore in London. The catalogue comes witha retail/mail order price list, £90.00 worth ofpurchase voucers, and £2.00 off first pur-chase. There are also further supplements ontest equipment, components and security.

A quantity price list is also available freeto Trade and Industry, and Education/train-ing Establishment. Supplements are issuedregularly for new products.

As main distributors for a wide range ofelectronics products, Henry's can quote com-petitively for supplies in Britain and for ex-port. Enquirers can telephone 071-258-1831or fax 071-724-0322.Henry's Audio Electronics, 404 EdgwareRoad, London W2 1ED. England.

HIGHLAND FOR BERNSTEIN CASES-LT IGHLAND Electromech has become a1 'franchised distributor for the German -made Bernstein ranges of aluminium andplastic enclosures for electronic and indus-trial applications.Highland Electronics Ltd, Albert Drive,Burgess Hill RH15 9TN. Telephone 0.111236 000; fax 0411 236 641.

NEW HQ FOR OKI EUROPETO COPE with its current and planned ex-

pansion in Europe. OKI Europe Ltd hascentralized the management of its three busi-ness departments: Data, Telecommunica-tions and Finance and Information Systemsat a new headquarters. The new address isOKI Europe Ltd. Central House, BalfourRoad, Hounslow TW3 1HY. Telephone 0344779 000; fax 0344 779 555.

ADVANCED DIGITAL LOGIC GUIDETEXAS Instrument haspublished a pocket

booklet detailing its broad range of dig-ital logic functions. It is intended as a toolthat can assist engineers to keep pace withthe rapid evolvement of new solutions invarious applications.Texas Instruments Ltd. Manton Lane, Bed-ford MK4I 7PA, England.

ELEKTOR ELECTRONICS JANUARY 1992

IIIELECTRONICS SCENE

AN INTEGRATED SERVICEAN integrated service for the whole

specturm of electrical engineers will beprovided by The Institution of ElectricalEngineers (IEE) and The Institution ofElectronic, and Electrical Incorporated En-gineers (IEEE), following the signing of aMemorandum of Understanding by theirpresidents.

The IEE, with 110 000 members, willcontinue to be responsible for the needs ofits chartered engineers and the IEEIE, with28 000 members, for the needs of its incor-porated engineers and technicians. The twoinstitutions will collaborate in a number ofactivities, including accrediting academicand training courses, promoting careers inelectrical and electronic engineering toyoung people, promoting joint technicalmeeting and providing a united voice to theGovernment and the the European Com-mission.

The IEE has already merged with the In-stitution of Electronic and Radio Engineersand is about to merge with the Institution ofManufacturing Engineers, while the LEETF.has already merged with the Society ofElectronics and Radio Technicians. Bothinstitutions are now the largest bodies intheir respective fields who are nominatedbodies of The Engineering Council.

The Memorandum of Understanding isa further drawing together of the institu-tions concerned with electrical and elec-tronic engineering, computing, informationtechnology and manufacturing engineer-ing. It will strenghten the existing partner-ship for the benefit of members and the pro-fession they serve.11-'1-. Savoy Place, London WC2R OBL.IFF1F Savoy Hill House, Savoy Hill, Lon-don WC2R OBL.

COMPACT LASER MODULESriOMPACT visible laser diode modules in

the Imatronic range now have an addedmodulation option. Modulated versions offer1-100 Idle modulation with a 1µs rise timeand can be driven from any TTL compatiblesource. These small modules make an ideal

TEE & IEEIE PROGRAMME8 Jan-Sub-micron VLSI reliability.9 Jan -27th Appleton lecture.10 Jan-Developments in terrestrial broad-

casting for the UHF band.13 Jan-Enhanced and widescreen PAL

television systems.13 Jan-Electronics in traffic controL13 Jan-Teacher training for engineering

awareness.14 Jan-Automating formal methods for

computer assisted prototyping.14 Jan-Digital signal processing in instru-

mentation.15 Jan-Computer graphic systems.

replacement forHe:NeLisers, offering the ad-ditional advantages of ruggedness and size.

Also, an infra -red (IR) version, operatingat 820 nm and packaged in the same compact49x16 min housing, has been added to therange.

Units in both ranges include all the focus-ing optics and require 4-5.25 V to drive them.Lambda Photometrics Ltd, Lambda House,Batford Mill, Harpended AL5 5BZ. England.

AVANTEK PRODUCT SELECTIONGUIDE

AVANTEK's 48 -page Product SelectionGuide is designed to provide the engi-

neer with a quick overview of the company'sstandard products. For a free copy, contactyour nearest Avantek regional office: inBritain, phone 0276 685 753.

A NEW ERA - AFTER SIX DECADESAT THE TOP

GARDNERS (formerly Gardners Trans-formers), long a stalwart of the British

electronics industry, is gearing up fora growthin the nineties that will match its rise to promi-nence through the past six decades. The com-pany's extensive design and manufacturingexpertise is based on a 'total capability' phi-losophy. This capability includes a wide rangeof PSUs. SMPs. d.c.--d.c. converters. andleading -edge telecommunication and ITequipment. A particularly comprehensivewound component capability is offered with

EVEN S15 Jan-Professional development seminar.17 Jan-Quality assurance in electrical in-

stallation.21 Jan-Growing a telecommunications

business21 Jan-MBAs for engineers.22 Jan-Practical applications of field com-

putation in design and development atlow frequency.

23 Jan-Conformance testing of instrumen-tation to international standards.

27 Jan-Advanced modulation and codingtechniques for satellite communications.

29 Jan-Education in radar and sonar.Further information on these events may be

specialist product development and manufac-ture for virtually any application.Gardners. Somerford Road. ChristchurchBH23 3PN, England. Phone 0202 482 284.

LEVELL ELECTRONICSALIVE AND WELL

ALTER joining the AET Group 15 monthsLevell Electronics are now operat-

iII2 from their new site in Hertford. If you havelost track of them, you can keep up to datewith their new and existing products by re-questing their updated 6 -page shortformbrochure. The new brochure shows theirrange of test and measurement equipment fora wide range of markets, including avionics,audio and hi-fi, electronics, and research andeducational establishments.Levell Electronics Ltd, Technology House.Mead Lane, Hertford SG13 7AW. Telephone0992 501 231: fax 0992 500 028.

ALPHA SOFTWARE OPENS OFFICEIN UNITED KINGDOM

ALPHA Software Corporation, theurlington, Massachuchetts-based de-

veloper and publisher of PC software for busi-ness users, has opened an office in Plymouth.The new office will provide a full range ofsales and support services to its British dis-tributors, resellers, corporate clients and endusers.Alpha Software Corp.. Suite 113. The Com-puter Complex, City Business Park, Stoke,Plymouth PL3 4BB. Phone 0752 606 881.

PRINTED -CIRCUIT SERVICEGraham Slee, who works at Audiotronics,

provides what may well be a unique ser-vice in the electrical/electronics industry-hedesigns and builds bespoke boards and man-ufactures short runs only. He is geared up toto manufacture 10-1000 PCBs per produc-tion run. His average run is 200 and he can,if required. produce one -offs. He works froma client's drawings or will produce a circuitdiagram on their behalf.Phone Graham Slee on 0742 422 333.

obtained from the IEE. Savoy Place, LondonWC2R OBL. Telephone 071 240 1871, orfrom the IEEIE, Savoy Hill House, SavoyHill. London WC2R OBS, Telephone 071836 3357.

ALL FORMATS COMPUTER FAIRSwill be held this month in the Midlands, theNorth. London, the West and Scotland. Fordates and venues, contact Bruce Everiss.P.O. Box 71, Bishops ftrhington. Leaming-ton Spa CV33 OXS. Telephone 0926613 047.

ELEKTOR ELECTRONICS JANUARY 1992

14

MINI Z80 SYSTEM

Call it what you like: an all-time favourite, an evergreen in computerland, or just a die-hard electronic component: the Z80 8 -bit

microprocessor enjoys tremendous popularity because it isinexpensive, widely available and easy to program. Furthermore, a

massive amount of software and paperware is available for thispowerful CPU. Here, we present a no -frills miniature computersystem based on the Z80 CPU, with I/O and ROM. No RAM, no,

because that is not strictly necessary for small applications if yourprogramming is up to scratch (but we have a RAM extension up our

sleeve).

PROBABLY the most remarkable featureof the present computer board is the ab-

sence of RAM (random access memory).This is unusual, but in many cases the inter-nal registers of the Z80 can function as RAMequally well. Omitting a RAM IC then allowsus to cut down on components (cost), andsave board space.

The block diagram of the Z80 system isshown in Fig. 1. Remarkably, the arrange-ment of the functions corresponds closely tothat of the associated ICs on the circuitboard. In fact, Fig. 1 shows the classic setupof a microprocessor system. The Z80 CPU(central processing unit) uses I/O -mappedinput-output operations, which means thatthe CPU works with different addresses forthe memory and the I/O blocks. The presentsystem has four I/O addresses, althoughtwo further blocks of four addresses may heselected via the two I/O ports.

The I/O ports available in the system arecompatible with the universal I/O interfacefor IBM PCs (Ref. 1), which allows the exten-sions originally developed for this to be con-nected without problems (for instance, the

by A. Rigby

relay card discussed in Ref. 2).From the block diagram it may appear

that the memory address decoder is a super-fluous luxury: there is only one EPROM, and

that could have been connected direct to theCPU without a decoder. The decoder, how-ever, divides the memory range into fourblocks of 16 Kbyte each, and so allows RAM

0a

I/o

I 0

1/0addressdecoder

MEM -1;0/.

de.:tiEr X.

data busaddress bus /

..0"/

EPROM Z 60

output

910060 - 11

output I

Fig. 1. Block diagram of the Z80 microprocessor system. Note the absence of RAM.

ELEKTOR EI.ECTRONICS JANUARY 1992

MINI Z80 SYSTEM

to be added (more about this next month), ormore EPROMs. Moreover, the memory ad-dress decoder is formed by the remainingtwo 1 -of -4 decoders contained in the IC usedfor the I/O address decoder. This means thatalthough it may not be used in many cases,the memory decoder does not require addi-tional hardware anyway.

Circuit descriptionThe circuit diagram shown in Fig. 2 closelyresembles the block diagram. Only two ICs

have been added: a voltage regulator and ahex inverter. Three inverters in the latter IC(ICs), are used to implement the 2 -MHzdock oscillator. The unused controlinputs ofthe Z80 (ICI) are held at +5 V via a pull-upresistor array. The reset input of the CPU isconnected to an R -C network and a switch toground (SI) that allows the system to bereset. The control, address and data lines ofthe Z80 are connected to the I/O and mem-ory sections in the usual way.

Address decoder IC7a divides the 64-KByte memory range into four sections of

MAIN SPECIFICATIONS

CPU: Z80Clock: 2 MHzMemory: 8 K ROM (EPROM 2764)

or16 K ROM (EPROM 27128)

I/O: 2x8 bit input/output;2x8 bit output

Option: 8 K RAM extension

5V

IC7 = 74HCT139

IC3 74HCT04

5Vla

It20

22

21

IC1

FEMT

WAIT

MALT

ITrO Z80IHT

444 CLX

I"

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AlA2

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Is takAa3-1151..5 5AGceAE a

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32 A5 AI 2523 AS WAS 2410 A10 A10 21

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Fig. 2. Circuit diagram of the mini Z80 system.

ELEKTOR ELECTRONICS JANUARY 1992

16COMPUTERS AND MICROPROCESSORS

20190000000000,00000000002 1

K3K4

20 19000000000000000000002 1

OOOOOOOOO

0

0 0 00 8 8 8 0 e

0 0 0 0 0

1 200000000009 10

1 200000000009 10

OOOOOOO0

Fig. 3. Track layouts (mirror images) and component mounting plan of the PCB for the mini Z80 system.

ELEKTOR ELECTRONICS JANUARY 1992

MINI Z80 SYSTEM ElCOMPONENTS LIST

Resistors:1 7 -way SIL array 100ki11 330k.O.

2 2k112

2 8 -way SIL array 100kI2

Capacitors:1 1pF 16V radial2 68pF1 1uF solid MKT1 100µF 25V radial6 100nF

Semiconductors:1 Z80 CPU1 2764 or 271282 74HCT5742 74HCT2451 74HCT139

1 74HCT041 7805

Miscellaneous:2 10 -way box header2 20 -way box header2 6 -way box header1 push-button1 quartz crystal 2.00MHz1 Enclosure 150x80x55mm,

e.g. Bopla E440VL1 printed circuit board

R1

R2

R3:1:14

R5:R6

C1

C2:C3C4

C5C6 -C11

IC1

IC2IC3:1C4

IC5:1C6

IC7

IC8IC9

K1;K2K3:1(4K5:1

18 COMPUTERS AND MICROPROCESSORS

Table 1. I/O address overview

Port1C3

IC4

IC5

IC6

I/O address0

1

2+4n3+4n

(n = 0 - 3)

ConnectorK1

K3

K3

K4

on the level supplied by the circuit connectedto connector 1:3 or K4 whether or not a dan-gerous situation can arise from readingfrom, or writing to, ICs or ICs. In addition tothe eight datalines, connectors K3 and K4therefore also carry the RD and WR signals,which indicate read and write operations re-spectively, and so enable an external circuitto disable its inputs or outputs accordingly.There are more signals on 1C3 and K4: one en-able signal, and two address lines, A2 andA3. These allow the Z80 card to work withextensions originally developed for theuniversal I/O interface for PCs.

The enable signal on the extension con-nectors indicates that the I/O lines are ad-dressed, so that the circuit connected canstart reading or writing data. Address linesA2 and A3 give us access to a total of eightexternal addresses: four each via each exten-sion connector, as shown in Table 1.

To prevent the output ports being left inan undesired state after switching on the sys-tem, the outputs of JO and IC4 are brieflyswitched to high impedance with the aid ofnetwork R2 -C4, whose R -C constant is aboutthree times greater than that of the CPU resetnetwork_ Provided the relevant instructionsare placed right at the start of the program(i.e., from 0000 onwards), network R2 -C4 af-fords sufficient time for the CPU to initializethe outputs properly and prevent output -to-output conflicts.

The system is completed by a voltageregulator, IO. This allows a mains adaptorwith an output rating of 9 V to 15 V d.c. at300 mA to be used, which is a safe as well asinexpensive way of powering the computer.

ConstructionThe design of the double -sided through-plated board used for building the Z80 sys-tem is shown in Fig. 3. This board is availableready-made through our Readers Services.

Construction is straightforward work,and merits no further discussion. Applica-tion circuits can be connected to the Z80board either via short lengths of flatcable, ordirect via the connectors. In the latter case,the ZSO card is best fitted on top of the appli-cation circuit. This ensures that the EPROMsocket remains accessible for a new EPROM,an EPROM emulator, or a RAM extension.As shown in one of the photographs, such anassembly is obtained by fitting sockets to theunderside of the Z80 card (see Fig. 8).

The fixing holes in the PCB are locatedsuch that the completed board is easily fitted

ma a 1011Tip Ut :lila SET

a a:Coo.,..,::. . FLAG Haan* a at.C.,,,marOm r t,,..:-. :Ea S.F.

a liEttitlat ...11.01E C. G EttLtaL PiA0CLE a =MULL ittouCi1E C Ctfillika1 a,MaCtiE

a CANEttal P.rasati E 01.1030: 0..A105F a a A.01 P.AIVIL r GEttelnat. auzatatE

N GINERAL itss MEE t 0051 C' yr CILNEA.lt. PuazattiE L. GEMMEL PIAIKKI

IS maga WASTE"

rf apps WE...WU

Sa 01000 11130111

aC aliatattaY COtatrEit

t 01111.0.90T TEMA IR YEW*. Illastiet

La = e. Tr...Arra C.SEILL2. ot-E.S,WIE LI.A.2410

par./..Tar fits non STATuS

tiorEAus.r ImardE BO flan

airy

0

CrafrE sr,Wo.

SEtroU

tarrE51,571030E :1001,1EO` 511150 F5 to0,:l

to.z910060-14

Fig. 6. Z80 register overview.

SIMPLE TEST PROGRAM FOR MINIZ80 BOARDUSING MACRO'S

1111-**-111*.1141

IC5 and IC6 jumpers set for input only111,01111N11 -11 -

outputl: equ 0 ;address for KIoutput2: equ 1 ;address for K2inputl: equ 2 ;address for K3input2: equ 3 ;address for K4

MACRO DEFINITION

init_to_zero:.MACROId a,0out (output1),aout (output2),a.MACEND

A_to_output:.MACRO outputcplout (output).a.MACEND

input_to_A:.MACRO inputin a,(input).MACEND

MAIN PROGRAM

-111,11-11

;load initial value;set output to zero;set output to zero

;define variable: output;invert each bit;output contents of A

;define variable: input;read input into A

org Oh

begin: init_to_zero

loop: input_to_A inputlA_to_output outputlinput_to_A input2A_to_output output2jr loop

;program start address

;initialize outputs

;loop to check inputs

910060-15

Fig. 7. Because of the absence of RAM, subroutines are best replaced by macros duringthe assembly phase.

ELEKTOR ELECTRONICS JANUARY 1992

tNi Z80 SYSTEM 111

Table 2. Non -executableinstructions (without RAM)

CALL cc.nn ;conditional subroutine:call

CALL nn

Itvl 1

IM 2

POP IX

POP IY

POP qq

PUSH IXPUSH IYPUSH qqRET

RETI

RETN

:direct subroutine call:interrupt mode:interrupt mode:get data from stack:get data from stack:get data from stack:put data onto stack:put data onto stack:put data onto stack:return from subroutine;return from interrupt:return from non-:maskable interrupt

qq = AF. BC. DE or HLcc = condition to execute instructionnn = address

into the enclosure mentioned in the parts list.Where the board is used as a controller forone application only (as discussed above),the sections with the fixing holes in themmay be cut off to reduce the board size evenfurther.

Writing programsAs already mentioned, a massive amount ofliterature exists on programming the Z80. Inaddition, assemblers and cross -assemblersfor the ZSO are widely available. Lackingthese, you may still program the Z80 purely

Fig. 8. Z80 board fitted 'piggy back on to adescribed elsewhere in this issue.

by hand, i.e., by writing a machine code pro-gram, looking up the opcodes, and loadingthem into an EPROM. A far more flexibleway of developing software is afforded byan EPROM emulator (fig. 4), which goesround the problem of having to erase and re-program an EPROM every time a change isrequired (and debugging, as you probablyknow, almost invariably involves a lot ofchanges).

For now, you probably want to know ifthe card works. Well, that can be found outquite easily with the aid of the test programlisted in Fig. 5. Set the two jumpers on theboard to input before running the program(from EPROM). The program turns the Z80card essentially into an input data operator.As you can see, this can be achieved withoutRAM, since the (many) registers of the Z80can be used for the 'scratch' functions. Fig-ure 6 shows a register overview of the Z80.

The absence of RAM means that a num-

prototype of the RC5-code infra -red receiver

her ot 1130 instructions can not be used.These instructions, listed in Table 2, are es-sentially those related to stack operations. Asyou can see, it is not possible to callinterruptand subroutines if you do not have RAM.Fortunately, this need not result in 'spaghettisoftware', because most assemblers supportthe use of macros. Macros are small pieces ofmachine code that are used frequently in aprogram, and which need to be written insource code only once. In most cases, it ispossible to use variables in macros, for in-stance, to indicate the register or address themacro is to make use of. An example of apiece of source code containing macros isgiven in Fig. 7.

References:1. "Universal I/O interface for IBM PCs".Elektor Electronics May 1991.2. "Relay card for universal I/O interface".Elektor Electronics November 1991.

32-MByte Solid-state FLASHDISK module from DES

DES Innovative Electronics have developeda memory modulebased on flash -type mem-ory ICs, to take over the function of a harddisk in PC XTs and ATs. The module sup-ports various memory sizes up to 32 MByte,and can be expanded in steps of 1 .1v1Byte. Of-fering a read access time of 250 ns (typ.), thesolid-state hard disk is about 100 times fasterthan a conventional drive unit. Hence, thedata transfer rate that can be achieved dur-ing read operations is limited by the systembus or driver software only.

Unlike a conventional hard disk, a solid-state memory module will not wear out, andis far less sensitive to environmental factorssuch as dust, vibrations, etc. This makes thesolid-state disk particularly suitable for usein industrial environments. Another majorapplication area of this new product is in net-works, where workstations can operate in an'off-line' mode, having the most frequentlyused programs stored on a solid-state disk.

The FLASH solid-state disk is PC XT and

NEW PRODUCTS

AT bus compatible (ISA and EISA). A total of16 S1MM sockets are available on the card toinstall up to 16 Mbyte using 1 MByte SIMMmodules, or 32 MByte using 2 MbyteSIMMs. An autoboot version is also avail-able. The disk cards can be taken out of the

system without losing data or programs.Battery backup is not required for this func-tion. The FLASH disk can be erased and re-programmed in the PC under DOS, andfunctions like a hard disk.

des innovative electronics b.v., Accustraat25, 3903 Veenendaal, Holland. Telephone:+31 8385 4130L Fax: +31 8385 26751.

ELEKTOR ELECTRONICS JANUARY 1992

20

NE602 PRIMER

THE Signetics (Philips Components)NE602 /SA602 is a monolithic integrated

circuit containing a double balanced mixer(DBM), an oscillator, and an internal voltageregulator in a single eight -pin package(Fig. 1). The DBM operates to 500 MHz,while the internal oscillator works to200 MHz. The primary uses of theNE602/SA602 are in FIF and VHF receivers,frequency converters and frequency transla-tors. The device can also be used as a signalgenerator in many popular inductor -capaci-tor (L -C) based variable frequency oscillator(VFO), piezoelectric crystal (XTAL), orswept -frequency, configurations. In this ar-tide we will explore the various configura-tions for the d.c. power supply, the RF input,the local oscillator and the output circuits.We will also examine certain applications ofthe device.

VersionsThe NE602 version of the device operatesover a temperature range of 0 to +70 °C,while the SA602 operates over the extendedtemperature range of -40 to +85 Themost common form of the device is probablythe NE602N, which is an eight -pin mini -DIPpackage. Eight -lead SO Surface mount (D -suffix) packages are also available. In this ar-ticle the NE602N is featured, although thecircuits also work with the other packagesand configurations, including the improvedfollow-up types NE602AN and NE602ADwhich are now available.

Because the NE602 contains both a mixerand a local oscillator, it can operate as a radioreceiver 'front-end' circuit. It provides verygood noise and third -order intermodulationperformance. The noise figure is typically5 dB at a frequency of 45 MHz. The NE602has a third -order intercept point of about -15 dBm referenced to a matched input, al-though it is recommended that a maximumsignal level of -25 dBm (approx. 3.16 mW)be observed. This signal level corresponds toabout 126 mV into a 5042 load, or 68 mVinto the 1,50041 input impedance of theNE602. The NE602 is capable of providing0.2-µV sensitivity in receiver circuits withoutexternal RF amplification. One criticism ofthe NE602 is that it appears to sacrifice somedynamic range for high sensitivity -a prob-lem said to be solved in the A -series (e.g.,NE602AN).

Frequencyconversion/translation

by Joseph J. Carr

LNG UT

A

IRPUT

GROUND

OUTPUTA

REGUATORVOLTAGE Fe!_}DC

SUFFER

U

O

-0 hE ECI

V+

050ER ;TER

cooSATE

OUTPUT

410155.11

Fig. 1. Block diagram of the NE602 show-ing pinouts.

called heterodyning. When two signals atdifferent frequencies (fi and f,) are mixed ina non-linear circuit, a collection of differentfrequencies will appear at the output of thecircuit. These are characterized as ft, f2 and

where ii and in are integers. Inmostpractical situations, and in are 1, so the totaloutput spectrum will consist at least of ft, f2,

andfi-f2. Of course, if the two input cir-

cuits contain harmonics, additional productsare found in the output In superheterodyneradio receivers, either the sum or differencefrequency is selected as the intermediate fre-quency (IF). In order to make the frequencyconversion possible, a circuit needs a localoscillator (LO) and a mixer circuit (both ofwhich are provided in the NE602).

The local oscillator consists of a VHF n -p -n transistor with the base connected to pin 6of the NE602, and the emitter to pin 7; thecollector of the oscillator transistor is notavailable on an external pin. There is also aninternal buffer amplifier which connects theoscillator transistor to the DBM circuit. Anyof the standard oscillator circuit configura-tions can be used with the internal oscillator,provided that access to the collector terminalis not required. Thus, Colpitts, Clapp, Har-tley, Butler and other oscillator circuits canbe used with the NE602 device, while thePierce and Miller oscillator circuits can not.

The double balanced mixer (DBM) circuitis shown in Fig. 2; it consists of a pair ofcross -connected differential amplifiers (Ti -T2 with Ts as a current source; similarlyT3/ T4 with To working as a current source).

The process of frequency conversion is Fig. 2. Partial internal schematic showing the Gilbert Transconductance Cell.

ELEKTOR ELECTRONICS JANUARY 1992

IINE602 PRIMER

O , 4.5 TO+ 8 'id:.

NE602

3

0

+ 9 Vdc

11'. TO

k5

4n7

NE602 NE602

amm 0.1p LM 340 - XX78XX or

2 IC1

NE602

O

+9 To+2a Vdc

1000 if 5,5XX*8 Volts10000 if XX= 9 Volts

..C1E-."-: 13

Fig. 3. DC power supply configurations for the NE602: a) for supplies +4.5--V

111 RADIO AND TELEVISION

LI

ct

180

mV

P -P

mim14n7

mi=

=MI

MainTuning

NE602

4n7

0

ct

7:n7

CS

4n7

NE602

NE602

910155-14

Fig. 4. NE602 input circuit configurations:a) direct. untuned input (Vin 180 mVpp); b)broadbanded RF transformer couples signaland transform aerial impedance to 1500 U: c)tuned input uses a tap on the inductor forimpedance matching; d) tuned input uses atapped capacitor voltage divider for imped-ance matching: e) tuned transformer inputthat uses a grounded frame variable capaci-tor.

winding (L2) to the number of turns in thesecondary winding (Lt). The situationshown schematically in Fig. 4e is for the casewhere the source impedance is smaller thanthe input impedance of the NE602.

The secondary of the RF transformer (Lt)

resonates with a capacitance made up of CI(main tuning), C2 (trimmer tuning or band -spread), and a fixed capacitor, C3. An ad-vantage of this circuit is that the frame of themain tuning capacitor is grounded. This fea-ture is an advantage because most tuning ca-pacitors are designed for grounded frameoperation, so construction is easier. In addi-tion, most of the variable frequency oscilla-tor circuits (discussed shortly) used with theNE602 also have a grounded frame capaci-tor. The input circuit of Fig. 4e can thereforeuse a single dual -section capacitor for singleknob tuning of both RF input and local oscil-lator.

Figure 5 shows a tuned input circuit thatrelies, at least in part, on a voltage variablecapacitance (varactor or varicap) diode forthe tuning function. The total tuning capacit-ance that resonates transformer secondaryL2 is the parallel combination of Co (trim-mer), C2 (a fixed capacitor), and the junctioncapacitance of varactor diode Di. The valueof capacitor 0 is normally chosen large com-pared with the diode capacitance so that itwill have little effect on the total capacitanceof the series combination C.3/CD1. In othercases, however, the capacitance of C3 ischosen dose to the capacitance of the diodeso it becomes part of the resonant circuit ca-pacitance_

A varactor diode is tuned by varying thereverse bias voltage applied to it. Tuningvoltage Vt is set by a voltage divider consist-ing of Ri, R2 and R3. The main tuning poten-tiometer (Rt) can be a single -turn model, butfor best resolution of the tuning control use amultiturn potentiometer. The fine tuningpotentiometer can be a panel mountedmodel for use as a bandspread control, or atrimmer model for use as a fine adjustmentof the tuning circuit (a function also sharedby trimmer capacitor CI).

The voltage used for the tuning circuit( VA) must be well regulated, or the tuningwill shift with variations of the voltage.Some designers use a separate three -termi-nal IC regulator for VA, but that is not strictlynecessary. A more common solution is to usea single low -power 9-V three -terminal ICvoltage regulator for both the NE602 and thetuning network. However, it will only workwhen the diode needs no more than +9 V forcorrect tuning of the desired frequencyrange. Unfortunately, many varactor diodesrequire a voltage range of about +1 V to+37 V to cover the entire range of availablecapacitance.

When oscillator circuits are discussed, wewill also see a version of the Fig. 5 circuit thatis tuned by a sawtooth waveform (for swept -frequency operation) or a digital -to -anal-ogue converter (for computer -controlledfrequency selection).

NE602 output circuitsThe NE602 output circuit consists of thecross -coupled collectors of the two halves ofthe Gilbert transconductance cell (Fig. 2),and are available on pins 4 and 5. In general,it makes no difference which of these pins is

Fig. 5. Voltage -tuned RF input circuit.

used for the output - in single -ended out-put configurations only one terminal is used,and the other one is ignored. Each output ter-minal is connected internally to the NE602 toV+ through separate 1.5-kil resistors.

Figure 6a shows the wideband, high im-pedance (1.5-kt1) output configuration.Either pin 4 or 5 (or both) can be used. A ca-pacitor is used to provide d.c. blocking. Thiscapacitor should have a low reactance at thefrequency of operation, so values between1 nF and 100 nF are generally selected.

Transformer output coupling is shown inFig. 6b. In this circuit, the primary of a trans-former is connected between pins 4 and 5 ofthe NE602. For frequency converter or trans-lator applications, the transformer could be abroadband RF transformer wound on eithera conventional slug -tuned form or a toroidform. For direct conversion autodyne re-ceivers the transformer would be an audiotransformer. The standard 1:1 transformersused for audio coupling can be used. Thesetransformers are sometimes marked withimpedance ratio rather than turns ratio (e.g.600 D:600 Q, or 1.5k111.5k0).

Frequency converters and translators arethe same thing, except that the 'converter'terminology generally refers to a stage in asuperhet receiver, while 'translator' is moregeneric For these circuits, the broadbandtransformer will work, but it is probably bet-ter to use a tuned RF/IF transformer for theoutput of the NE602. The resonant circuitwill reject all but the desired frequency pro-duct; e.g., the sum or difference (IF) fre-quency. Figure 6c shows a common form ofresonant output circuit for the NE602. Thetuned primary of the transformer is con-nected across pins 4 and 5 of the NE602,while a secondary winding (which could betuned or untuned) is used to couple the sig-nal to the following stages.

A single -ended RF tuned transformeroutput network for the NE602 is shown inFig. 6d. In this coupling scheme, the outputterminal of the IC is coupled to the V+ sup-ply rail through a tuned transformer. Per-haps a better solution to the single -endedproblem is the circuit of Fig. 6e. In this cir-

ELEKTOR ELECTRONICS JANUARY 1992

NE602 PRIMER ED

NE602

1:

11-0 )n7 k use

either

5 11-04n7

O

NE602

NE602

=V

cry4

LPF

4 c: 5

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NE602

Ti

4 cr 51

4n7

NE602

O

NE602

NE602

CI n14 c: 5

47C IF

OUT4n7(optional)

R2

FL

150, C2

70p120p El=

910155- 16

Fig. 6. Output circuit configurations: a) direct capacitor coupled output (untuned); b) broadband transformer coupled output; c) tunedtransformer output; d) tuned transformer to V+; e) grounded tuned transformer output; f) tapped capacitor tuned output (VHF circuits); g)low-pass filter output; h) filter output.

cuit, the transformer primary is tapped for alow impedance, and the tap is connected tothe NE602 output terminal through a d.c.blocking capacitor. These transformers areeasily available as either 455 KHz or10.7 MHz versions, and may also be maderelatively easily.

Still another single -ended tuned outputcircuit is shown in Fig. 6f. In this circuit, oneof the outputs is grounded for RF frequen-cies through a capacitor. Tuning is a functionof the inductance of Li and the combinedseries capacitance of 0, C2 and C3. By tap-ping the capacitance of the resonant circuit,at the junction of C2-Ci, it is possible tomatch a lower impedance (e.g., 50 LI) to the1.5-ki2 output impedance of the NE602.

The single -ended output network ofFig. 6g uses a low-pass filter as the frequencyselective element. This type of circuit can beused for applications such as a heterodynesignal generator in which the local oscillatorfrequency of the NE602 is heterodyned withthe signal from another source applied to theRF input pins of the IC. The difference fre-qUency is selected at the output when thelow-pass filter is designed such that its cut-off frequency is between the sum and dif-ference frequencies.

In Fig. 6h an IF filter is used to select the

desired output frequency. These filters areavailable in a variety of different frequenciesand configurations, including the Collinsmechanical filters that were once used exten-sively in high-grade communications re-ceivers (260 kHz, 455 kHz and 500 kHzcentre frequencies). Current high-gradecommunications receivers typically use crys-tal IF filters centred on 8.83 MHz, 9 MHz,10.7 MHz or 455 KHz (with bandwidths of100 Hz to 30 kHz). Even broadcast radio re-ceivers can be found using IF filters. Such fil-ters are made of piezoceramic material, andare usually centred on either 260 or267 5 kHz (AM auto radios), 455 or 460 kHz(other AM radios) or 10.7 MHz (FM radios).The lower frequency versions are typicallymade with 4-, 6- or 12 -kHz bandwidths,while the 10.7 -MHz versions have band-widths of 150 to 300 kHz (200 kHz beingmost common).

In the circuit of Fig. 6h it is assumed thatthe low-cost (typically US$ 3) ceramic AM orFM filters are used (for other types, com-patible resistances or capacitances areneeded to make the filter work properly).The input side of the filter (FLO in Fig. 6h isconnected to the NE602 through a 47042 re-sistor and an optional d.c. blocking capacitor(Cr). The output of the filter is terminated

into a 3.9-ka resistor. The difference IF fre-quency resulting from the conversion pro-cess appears at this point.

One of the delights of the NE602 chip isthat it contains an internal oscillator circuitthat is already coupled to the internal doublebalanced mixer. The base and emitter con-nections to the oscillator transistor inside theNE602 are available through pins 6 and 7, re-spectively. The internal oscillator can beoperated at frequencies up to 200 MHz. Theinternal mixer works to 500 MHz. If higheroscillator frequencies are needed, use an ex-ternal local oscillator. An external signal canbe coupled to the NE602 through pin 6, butmust be limited to no more than about -13.8dBm, or 250 mV across 1,500 SI

NE602 local oscillatorcircuits

There are two general methods for control-ling the frequency of a local oscillator circuit:inductor -capacitor (LC) resonant circuits orpiezoelectric crystal resonators. We will con-sider both forms, but first the crystal oscilla-tors.

Figure 7a shows the basic Colpitts crystaloscillator. It will operate with fundamental

ELEKTOR ELECTRONICS JANUARY 1992

24RADIO AND TELEVISION

mode crystals on frequencies up to about20 MHz. The feedback network consists of acapacitor voltage divider (C1 -C2). The valuesof these capacitors are critical, and may becaluculated front

= loo/NTCa = 100 0/ F

[21

131

Where the capacitor values are in pF and thefrequency in MHz. The values resultingfrom these equations are approximate, butwork well under circumstances where exter-nal stray capacitance does not dominate thetotal. However, the practical truth is that ca-pacitors come in standard values and thesemay not be exactly the values required byEqs. [2] and [31.

When the capacitor values are correct, theoscillation will be consistent. If you pull thecrystal out, and then reinsert it, the oscilla-tion will restart immediately. Also, if thepower is turned off and then back on again,the oscillator will always restart. If the capa-citor values are incorrect, the occillator willeither fail to run at all, or will operate inter-mittently. Generally, an increase in the capa-citances will suffice to make operationconsistent.

A problem with the circuit of Fig. 7a isthat the crystal frequency is not controllable.The actual operating frequency of any crys-tal depends, in part, on the circuit capacit-ance seen by the crystal. The calibratedfrequency is typically valid when the loadcapacitance is 20 pF or 32 pF, but this can bespecified to the crystal manufacturer at thetime of ordering. In Fig. 7b a variable capaci-tor is placed in series with the crystal in orderto set the frequency. This trimmer can be ad-justed to set the oscillation frequency to thedesired frequency.

The two previous crystal oscillators oper-ate in the fundamental mode. The resonantfrequency in the fundamental mode is set bythe dimensions of the slab (wafer) of quartzused for the crystal-the thinner the slab, thehigher the frequency. Fundamental modecrystals work reliably up to about 20 MHz,but above 20 MHz the slabs become too thinfor safe operation. Above about 20 MHz, thethinness of the slabs of fundamental modecrystal causes them to fracture easily. An al-ternative is to use overtone crystals. Theovertone frequency of a crystal is not necess-arily an exact harmonic of the fundamentalfrequency, but is close to it. The overtonestend to be dose to odd integer multiples of

the fundamental (3rd, 5th, 7th). Overtonecrystals are marked with the appropriateovertone frequency, rather than the fun-damental.

Figures 7c and 7d are overtone modecrystal oscillator circuits. The circuit inFig. 7c is the Butler oscillator. The overtonecrystal is connected between the oscillatoremitter of the NE602 (pin 7) and a capacitivevoltage divider that is connected betweenthe oscillator base (pin 6) and ground. Thereis also an inductor in the circuit (A), and thismust resonate with Ct to the overtone fre-quency of crystal XI. Figure 7c can use either3rd or 5th overtone crystals up to about80 MHz. The circuit in Fig. 7d is a third -over-tone crystal oscillator that works from25 MHz to about 50 MHz, and is simplerthan Fig. 7c

A pair of variable frequency oscillator(VFO) circuits are shown in Figs. 7e and 7f.The circuit in Fig. 7e is the Colpitts oscillator,while Fig. 7f is the Hartley oscillator. In bothoscillators, the resonating element is an LCtuned resonant circuit. In Fig. 7e, however,the feedback network is a tapped capacitivevoltage divider, while in Fig. 7f it is a tap onthe resonating inductor. In both cases, a d.c.blocking capacitor to pin 6 is needed to pre-

NE602 NE602 NE602

6

7

O

Cl

NE602

7

22

6

5p6

Ixl

25 to 50IMHz 3rdOvertoneCrystal

O

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30p

C2

77p

rolm

NE602

LI Cl resonateto overtoneFrequency of X1

C2

1407

C3

11407

L

Cl

910155 - 17

Fig. 7. Local oscillator circuits for the NE602: a) simple Colpitts crystal oscillator: b) Colpitts crystal oscillator with adjustable frequencycontrol: c) Butler overtone oscillator for low -hand VHF: d) additional overtone oscillator: e) Colpitts VFO; 1) Hartley VFO.

ELEKTOR ELECTRONICS JANUARY 1992

vent the oscillator from being d.c.-groundedthrough the resistance of the inductor.

NE602 PRIMER Ea

Voltage -tuned NE602oscillator circuitsFigure ti shows a pair of VFO circuits inwhich the capacitor element of the tuned cir-cuit is a variable capacitance diode, or varac-tor (DI in Figs. 8a and 8b). These diodesexhibit a junction capacitance that is a func-tion of the reverse bias potential appliedacross the diode. Thus, the oscillating fre-quency of these circuits is a function of tun-ing voltage Vt. The version shown in Fig.is the parallel -resonant Colpitts oscillator,while that in Fig. 8b is the series -tuned Clapposcillator.

Figure 9 shows an application of the volt-age -tuned oscillator (in this example, theClapp oscillator). Two tuning modes areprovided in Fig. 9. When switch Si is in posi-tion 'A', the tuning voltage is manually setwith a potentiometer, R2. If a d.c. level is ap-plied to the top end of the potentiometer, theoscillator will operate on a discrete fre-quency that is a function of VTA. If a sinusoi-dal waveform is applied to thepotentiometer, however, the oscillator fre-quency will deviate back and forth in fre-quency modulation (FM). Or, if a sawtoothwaveform is applied, the circuit becomes asweep oscillator: the frequency will increaseas the applied voltage increases, and thensnap back to the lowest frequency in its

Fig. 8. Voltage -tuned (varactor) VFO cir-cuits: a) Colpitts; b) Clapp.

C4

2

T

cs

ra

VIA

e=1

V. v.,

Sawtoothor

DC Level

"E VA

DAC -OSDigital to AnalogueConverter

8 -8ilDaleBus

i10155- ID

Fig. 9. LO frequency control by either manual or digital means. according to the setting ofswitch S1. This circuit can be swept for FM or sweep generator use. or computer controlledby applying a binary word to the DAC input corresponding to the desired drive voltage for aspecified frequency.

range when the sawtooth drops back to zero.When switch Si is in position `13', the fre-

que_ncy is controlled by a digital -to -analogueconverter (DAC). In this case, a current out-put device (DAC-08 or its relatives) isshown. The output of the DAC is a currentbetween 0 and 2 mA, which is converted intoa voltage by operational amplifier At. Thetuning voltage VTB is the product loRi. A d.c.offset, for trimming the actual frequency, isprovided by potentiometer Rs and a nega-tive reference d.c. source, VA).

There are several advantages to the DAC-driven version of this circuit. One is to digi-tally control the sweep in a manner similar tothe analogue sawtooth waveform. If the digi-tal inputs of the DAC are cycled through thebinary numbers 00 to FF hex (i.e., 255 deci-mal) in sequence, the analogue output risesas a sawtooth.

Another application is to let the computerset the frequency of the oscillator. When thecircuit is calibrated, you can set one of 256discrete frequencies by sending the correctbinary number to the DAC (which, of course,corresponds to a discrete voltage).

Finally, the digitally driven voltage -con-trolled oscillator can be programmed for amore linear frequency characteristic. Varac-tor diodes have a non-linear voltage vs. fre-quency characteristic, and therefore anon-linear frequency characteristic in a res-onant circuit. A linearized look -up tablestored in the computer can be used to gener-ate the voltage that produces a series of equaldiscrete frequency steps for each 1-LSBchange of the applied binary word.

NE602 as an oscillatorThe NE602 is usually thought to be a receiveror frequency converter, but it can also beused as an oscillator or signal generator.Normally, the LO signal and the RF signalare suppressed in the output. Figure 10shows a generic circuit that will allow the LOsignal to appear at the output (no RF or Wsignal appears). In this circuit, one RF input(pin 2) is bypassed to ground for RF, while

El

riEE2

1

C .71sins=INN

°l C _I: _ I

FrequencyConedNetwork

Fig. 10. Method for using the NE602 as asignal generator.

the other input (pin 1) is grounded for d.c.through a 10-1T2 resistance.

ConclusionThe NE602 is a well-behaved RF chip thatwill function in a variety of applicationsfrom receivers, to converters, to oscillators,to signal generators. Good luck.

ELEKTOR ELECTRONICS JANUARY 1992

26

COMPUTER -CONTROLLEDWEATHER STATIONPART 3: WINDSPEED AND DIRECTIONMETER

Having dealt with sensor interfaces that measuretemperature and relative humidity, we now tackle two otherimportant meteorological parameters: the speed anddirection of that eternal friend or foe of ours, the wind.

by J. Ruffell

OF all factors that determine the weather,wind and precipitation are the ones

that matter most to us. Since the wind bringsus cold or warm air, it contributes greatly toour feeling comfortable or not, out of doors.Particularly on a cold winter's day, the windforce and wind directionhave a considerableeffect on the perceived temperature: whenthe air temperature is, say, a few degreesbelow zero, a stiff breeze can make it feel ascold as minus 20 degrees. This is the so-called chill factor. OE all living creatures,only mammals have this impression becausetheir blood circulation, skin and body liquidevaporation system work in such a way thatthe body temperature is held constant.

Apart from having an effect on the per-ceived temperature, the wind can also causeproblems and become a tremendous dangerwhen its force increases from a breeze to astorm (wind force 10 or greater on the Beau-fort scale).

The wind direction is measured becauseitis often an indication of the type of weatherand related temperature we can expect. Inareas close to, or surrounded by, the sea,wind from the sea has a cooling effect, whilewind from the inland usually brings rela-tively warm air. This situation exists in thesummer months, when the sea water is'colder' than the land. In the winter months,the sea works as a thermal buffer because itforms a large source of residual heat, built upduring the summer. Hence, coastal regionsare often warmer in the winter. Also notethat air carried over land is much drier thanair carried over sea. In condusion, windspeed and wind direction are important par-ameters to meteorologists, and play a signi-ficant role in weather forecasting.

The sensorsBecause repeatable, accurate measurementsof the wind speed and wind direction re-quire standardized sensors, we propose the

use of a ready-made unit for this. The com-bined sensor is shown in Fig. 1. Its outputsignals are fed to the PC measurement card(Ref. 1) at the heart of our weather station.The PC runs a program that converts the sen-sor signals into information that is meaning-ful to us.

The wind direction meter consist of avane secured to a spindle. The spindle is at-tached to a transparent disk with a Graycode on it. The advantage of the Gray code isthat one bit changes between two successivepositions of the vane, which allows us to im-plement a basic error checking procedure.The sensor proper consists of four slottedopto-couplers that 'read' the code on thedisk This means that the wind direction isfed to the PC in the form of a 4 -bit code.Hence, the sensor is capable of indicating16 wind directions. This is sufficient for mostpurposes, and meteorologists never seem touse a more accurate scale anyway.

The connection of the wind direction sen-sor output to the PC measurement card in-volves more precautions than one wouldexpect, and this matter is taken up in detailfurther on.

The wind speed, which is later convertedinto a corresponding value that indicates thewind force, is measured with the aid of ananemometer. As you can see from Fig. 1, thisconsists of three small arms secured at anglesof 120° to a vertical spindle. Each full spindlerevolution results in 12 output pulses.Hence, the computer need only measure thefrequency of the output signal of the windspeed sensor, and convert this into a nor-malized value (see Table 1).

Lightning protectionSince the wind speed and direction sensorassembly is usually fitted on the roof or inanother elevated location, fairly long cablesmay be required to bring the output signalsto the computer. As far as the digital signalsare concerned that travel along this cable,there are no difficulties. A problem, though,is formed by the voltages induced in the

Fig. 1. This ready-made unit contains allthe mechanical parts needed to measurewind speed and wind direction.

MAIN SPECIFICATIONS

Wind speedValues:

Range;Resolution:Sampling rate:Recording:

Wind directionValues:Wind dial:Angle:Resolution:Sampling rate:Recording:

peak: current;average0-30 m/s0.1 m/s2 per minutecontinuous (interval:10 minutes)

16 wind directionsN; NNE. NE. E,0-360 degrees22.5 degrees18.2 Hzcontinuous (interval:10 minutes)

SoftwareMemory -resident (TSR) data loggerplus full -colour graph display pro-gram

cable by lightning. Without suitable precau-tions, lighting that strikes close to your homecan turn your costly PC into scrap metal andelectronics. It is for this reason that we haveto make sure that induced voltages areshunted off in the safest possible manner.

ELEKTOR ELECTRONICS JANUARY 1992

WINDSPEED AND DIRECTION METER Ea

DWI

DIR3

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A2 1W

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1E1= 1=1

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$

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4

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14

141

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Fig. 2. Circuit diagram of the sensor interface.

Table 1. Wind force measures

Beaufort m/s km/h mph knots Description0 0-0.4 1.6 1 1 calm

0.4-1.4 1.6 6 1-3 1-3 light air1.4-3 6-11 4-7 4-6 slight breeze3-5 12-19 8-12 7-10 gentle breeze5-8 20-29 13-18 11-16 moderate breeze

5 8-11 30-39 19-24 17-21 fresh breeze6 11-14 40-50 25-31 22-27 strong breeze7 14-17 51-61 32-38 38-33 high wind8 17-20 62-74 39-46 34-40 gale9 20-24 75-87 47-54 41-47 strong gale10 24-28 88-101 55-63 48-55 whole gale11 28-32 102-115 64-72 56-63 storm12 32-36 116-131 73-82 64-71 hurricane13 37-41 133-147 83-92 72-8014 42-46 148-165 93-103 91-8915 47-50 165-182 104-114 90-9916 51-56 183-200 115-125 100-10817 57-60 201-217 126-136 109-118 -

Note, however, that the measures taken hereto achieve this do not afford protectionagainst direct 'hits' on the sensor, the cable orthe PC itself, or even the mains wiring viawhich the system is powered. Remember,the proposed protection is effective and ade-quate for induced voltages only. Electricalsystems arc very difficult to protect againstdirect lightning hits, and you may want toconsider having a lightning conductor fittedto your home to deal with this problem.

The interfaceThe main function of the circuit shown inFig. 2 is to feed the sensor output signals tothe computer whilst affording protectionagainst voltages induced on the (long)downlead cable. Eve' sensor input is con-nected to ground via a surge arrester (At-Ao) with a spark -over voltage of 90 V. Thesurge arrester is a glass tube filled with anoble gas, and is capable of suppressing volt-age peaks within 1µs at peak currents up to10 kA, or continuous currents of 20 A. Al-though these arresters are pretty fast -acting

ELEKTOR ELECTRONICS JANUARY 1992

28 GENERAL INTEREST

Fig. 3. Track layout (mirror image) and component mounting plan of the PCB designed for the interface.

devices, they are not sufficient to protect thesensitive electronics in the circuit. Therefore,each input has additional protection in theform of a very fast 12-V zener diode (th-D6).The response time of these devices is 1 ps(typically), which is fast enough for adequ-

ate protection against overvoltages. As soonas the zener diode starts to conduct, the over -voltage is turned into heat by the associatedseries resistor (Rt-R5).

The buffers used here are Types 4050which are capable of handling signals levels

up to 20 V at a supply voltage of 8 V. Thismeans that the zener voltage is low enoughfor the buffers to operate safely at all times.Resistors Ro-Rto protect the buffers againstnegative input voltages. The buffer outputsare capable of sinking relatively high cur-

ELEKTOR ELECTRONICS JANUARY 1992

WINDSPEED AND DIRECTION METER 29

2

6

1

1

1

1

1

1

1

COMPONENTS LIST

Resistors:5 101.1 1W

5 2200.5 82052

5 1kil2 101(12

1 11(1.22

1 100kil

Capacitors:1 1011F 16V radial

1 470uF 25V radial3 100nF

1 47uF 16V radial

R1 -R5

R6 -R10

R11 -R16

R17 -R21

R22;R23R24R25

C1

C2

C3:C5:C7C4

Semiconductors:BZTO3C12 (12V/800W; Philips)or 1N5634 (8V9/1500W; GeneralSemiconductor Industries) Dl -D6

D7IC1

IC2IC3

1 LED red dia. 3mm1 CD40501 7808

1 74HC3683 It dual optocoupler

(Siemens)

1 680C1500

Miscellaneous:1 14 -way male box header

1 3 -way PCB terminal block;pitch 7.5mmPCB -mount straight spadeterminalA81-C9OX surge arrester(90V: Siemens)9V/166mA (e.g. MonacorlMonarch VTR1109)Printed circuit board

1501:1S02:IS03B1

K1

K2

K3:K4

A1 -A6

Tr1

900124-5Control software on disk ESS16418 -way DIN socket; 180'+2x41c (B81S)Mains appliance socket with earthconnectionMetal enclosure 185x119x51mm(Hammond 1590D)Miniature wind speed and wind directionsensor assembly. Type 455, with bracketand mounting hardware. Supplied via:Mierij Meteo, Tuinstraat 1-3, 3732 VJDe Bilt, Holland.Telephone: +31 30 200064.

rents, which is useful for the driving of opto-couplers L501, 1S02 and 1503.

Although the above safety measuresshould be adequate for most situations, afurther protection has been added: the entiresensor interface is electrically insulated fromthe computer with the aid of opto-couplers.The outputs of these devices (150t, ISO! and1503) supply the digital signals the computerneeds to interpret the data related to thewind speed and direction. The first par-ameter is supplied by 1S03, the second byMt and 1502.

Since the ILD74 used here is a dual opto-coupler, and the wind speed sensor requiresone output only, the remaining output isused to indicate that the circuit is powered.

Hence, output C2 of 1503 is used to enable1C3, a 74HC368. This HCMOS line driversquares up the signal edges, and so increasesthe noise margin with respect to ground.Note that 10 is powered by the PC-thispart of the circuit is, therefore, completely in-sulated from the rest of the interface.

The interface is connected to the PCmeasurement card via connector Ks. Thewind direction code is sent via datelinesWDO-WD3, while frequency meter input,F3, is used for the wind speed signal.

When the power supply of the interface isswitched off, the outputs of the line driversare automatically switched to a high -imped-ance state. This condition is signalled to thePC by the POWER GOOD line, PB1, goinghigh. Resistor RD prevents the 1/0 port onthe PC measurement card being damagedwhen it is set to output.

The remainder of the circuit is formed bythe power supply and the associated de -coupling capacitors. I Fr) D7 is the on/off in-dicator. The circuit diagram shows dearlythat the protective earth at the mains socketis connected to the ground of the electronicsahead of the op tocouplers. This connectionisabsolutely necessary for the surge arrestersto get rid of the induced currents. An evenbetter solution is to connect K3 town earthingpin-this enables the energy to bypass therest of the electrical system.

ConstructionThe construction of the interface should norpose problems because the circuit is com-pact, and a PCB design is available. Figure 3shows the component mounting plan andthe track layout (mirror image) of the PCBdesigned for the interface. To reduce strayinductance to a minimum, the surge arrestermust be mounted as dose as possible to thePCB. The same goes for diodes Di -Do.

On completion of the solder work, thePCB is fitted into a water -proof metal enclo-sure, which is earthed via connector K4. Thecopper track between the earth terminal onthe PCB and connectors 1(3 and K-1, and theearth tracks of the surge arresters, must bestrengthened by soldering pieces of 2.5 -mm(cross-sectional area) solid copper wire onthem.

The sensor is connected to the sensor in-terface via a short flexible cable terminatedinto an 8 -way DIN plug. The pinout of thisplug is given in Fig. 4.

The softwareOnce again this part of the computer -con-trolled weather station requires a powerfulpiece of software, which you can obtainthrough our Readers Services. As with theprevious two publications on the weatherstation, an IBM PC or compatible is used tocollect the measured data, and convert theseinto easily interpreted graphics images.

Procedures have been added to the latestversion of Xlogger (1.2) that enable the windspeed and wind direction to be measuredand recorded. A new graphics program,

1 OV2 Dir 23 Dir 34 --, 8V

5 Dir 06 Da 17 SPD

Seen item

Fig. 4. Pinout of the 8 -way DIN socket.seen from the solder side.

WIND.EXE, has been developed, and is in-duded on the disk. In the left-hand bottomcorner of the screen three coloured bars aredisplayed that indicate the current, the aver-age and the peak wind speed. The scale is inm/s with a range of 0 to 30, and has a nu-merical readout at the extreme right.

As usual in meteorology, the averagewind speed is computed progressively overthe last ten minutes. The peak indicator al -

Table 2a. Wind speed as a functionof sensor output frequency

Speed (m/s) Frequency (Hz)30 46527 415

24 365

21 315

18 265

15 215

12 170

9 120

6 75

3 30

Table 2b. Sensor codes as afunction of wind direction

Direction CodeN 0000

NNE 0001

NE 0011

ENE 0010

E 0110

ESE 0111

SE 0101

SSE 0100

S 1100

SSW 1101

SW 1111

WSW 1110

W 1010

WNW 1011

NW 1001

NNW 1000

ELEKTOR ELECTRONICS JANUARY 1992

30 GENERAL INTEREST

> Ok4

FlF2

F5F3/4r6F9F10

Load tileSwitch plotSelect hourSuitch gridAuto scaleHardcopgQuit

Direction

WC )E

SN SES

247.5

Date 1991-09-25Tine 13:16

Peak..........

=liarCurrentMENNEmma

Speed20.111.615.5

0 3 10 15 20 25 305

m/s

12

10

8

6

*** Elektor Electronics WA -14.

*** Copwright (C) -> 1991 ****** ESS: 164 (1, 2, 3, 4) ***

overage windspeed plot

1 2 3 4 5 6 7 8 9 1011121314151617181920212223-> Hours

Curren