THE PRACTICAL MAGAZINE WITH THE PROFESSIONAL APPROACHSeptember 1988

glektor001000

9 770268 451012

PCB design on the BBC andPC1512/1640 computers64 K RAM for MSXDBS Conference 1988Fast NiCd chargerSelf-inductance meter

UK £1.50 IR £2.20 (incl. VAT)

EE

September 1988

""MIN!IIP"

BBC Micro Computer SystemBBC MASTER SERIES:AM815 BBC MASTER 128K £356ADC06 Turbo (65C1021 Card £95ADCO8 512 Processor E185AOF14 Rom Cartridge £13ADF10 Econet Card £40ADJ22 Ref. Manual I £14ADJ23 Ref. Manual Part II E14ADJ24 Adv Ref Manual £18

(al(dl(5)(d)(dl(e)lel(c)

88C ARCHIMEDESPlease enquire about 300 & 400 serieshardware and software.

UPGRADE KITS:1.2 OS ROM £15DNFS ROM E19BASIC II ROM (BBC 81 .... E22.50ADFS ROM £261770 DES Kit £43.50Econet Kit (B&B+) £55

(dl(dl

(dl(dl(dl(dl

ACORN ADD-ON PRODUCTS:Torch ZEP 100 E229 la)512 2nd Processor E249 (b)SEE Interface E265 (5)

Teletext Adapt& £95 (5)32016 Co Prot £949 (a)X25 Gateway 12.175 fa)Ask for full details on our full range of software

WORD PROCESSOR ROMs:VIEW 2.1 . £35 (d) VIEW 3.0 .. E48 (c1Speamaster £49 (d) VIEW INDEX E12 (diWORDW1SE £24 (dl WORDW1SE+ £38 (dl

SPELLCHECK IIIWYSIWIG- E21 d E31 (dlINTERWORD £46 a EDWORD II £43 (alLANGUAGE ROMSMicro Prolog E62 z ,..,efotext E52 felISO PASCAL £51 LOGOTRON . £55 (c)LOGO £46 (el MACROM £33 (dlLISP £39 Id) COMAL £43 (dl

Oxford Pascal £36 (c)COMMUNICATIONS ROMS:TERMULATORMASTER TERMULATORCOMMSTAR IIMODEM MASTERCOMMAND

£25 (dl£34.75 (dl

£28 Id)E11 (d)£34 (dl

UTILITY ROMs:DOTPFIINT PLUS for FX/RX compatiblesDOTPRINT DUAL for MX rangeAcorn Graphics Extension Rom ... £28 (dlMerlin with 57 disc utility commands100 page manual E37.50 (Cl

MULTIFORM Z80 2nd Processor for the BBCThis unique Z80 2nd Processor running OSM wA allow use of almost any standard CPIM soft-ware on the BBC (rem. It is supplied with a number of different CP,M1 formats and includes auti':,ty to configure it to read other formats. This is particularly useful in environments where com-puters with different CP4.1 formats are used and the data cannot be easily exchanged betweenthem. Mains powered (includes Pocket Wordstar & MSIDOS RiW utirtyl £249 (3)MSDOS ReadWrite Ut £49 (c)

META Version 3 ASSEMBLERAsse,b,, 17 of the popular processors. Over 70K long program on two reins and a disc and

rco. ::-fete Editing and Assembly facknies. It uses appropriate mnemonics for differenty nestable macros, nestable conditional assembly (IFiELSErENDIF), modular

. code. true !GCBl and global (abets. 32 bit labels and arithmetic. 30 ways to send obit -et_ and 50 directives.' a a..ierhd editor with many features. Send for detailed leaflet. £145 UM

BBC DISC DRIVES5.25- Single Drive:1 a 400K 40380T 05: TS400 _ _ E90 (b) PS400 with psu £104 lb)5.25" Dual Drive:2 a 400K 403801 DS: TDBOO .... £170 (a) P0800 with psu £190 (al2 a 40011 4011301 DS with psu and built in monitor stand PD800P £209 (a)3.5" Drives:1 a 400K SOT DS TS35 1 E67 (b) PS35 1 with psu £85 Ill

1 x 400K SOT DS with psu TD35 2 E126151 P035 2 with psu £149 lb)Combo drives (5.25" & 3.5"l:

PD853 with integral PSU £165 ,a, PD853P .r,e-gral PSU £179 (al

3M FLOPPY DISCSIndustry standard floppy discs with a life time guarantee. Discs in packs of 10:

5% DISCS 3% DISCS40T SS DD £8.00 Id) 40T DS DD. £9.75 (d) 801 SS DD £13.50 (dl80T SS DDE12.00 (d) 80T DS DD. £12.75 (d) 80T DS DD £15.00 (d)

EPSONLX800FX800FX1000EX800EX1000GO 3500 Resell10500L0850 180 col)L01050 1136 col)

PRINTERS£179 (a) TAXAN KP815 (80 col) E179£309 (a) KP915 1156 col) £350 ia,E419 (al BROTHER HR20 £349 (al£395 (a) STAR LC10 E185 fa)£539 (a) JUKI 6100 (Daisy Wheel) . E295

£1,290 (a) INTEGREX (Colour) E519£299 (a) NAT PANASONIC KX P 1081 E149 la)£419 la) NAT PANASONIC KX P 3131 E249 (a)E529 (a) NAT PANASONIC KX P1082 E175 la)

(Ye hold in stock a large variety of printer attachments. interfaces and consumabteaPlease write or phone for details.

DISC ACCESSORIESSingle Disc Cable E6 Id) Dual Dist Cs.:. - E8.50 (d)10 Disc Library Case 1E1.80 (c) 30 Disc S -a,_ Box E6 lc)40 Disc Lockable Box E8.50 (c) 100 D:: __likable Box 113 (c)Floppicler.e Ornehead C=s -]nn Kit with 20 cr-som-at'i a -e.,- - -7 its 56" £14.50 Id); 314" E16 (dl

ACCESSORIESBUFFALO 32K Buffer for Epson printers E75 (dl: FX80 plus sheet feeder £129 (b):EPSON Serial Interface: 8143 E30 (51: 8148 with 2K buffer £65 lb).EPSON Paper Roe Holder E17 lb); FX80S0+,85 Tractor Attach E37 15); RXJFX8ODust Cover £4.50 (di: LX80 Tractor Unit £20 (c): L0800 Tractor Feed £47 Ibl.EPSON Ribbons: MX,RX,FX80 £5: MX.41X,FX100 £10 (dl: LX80 £4.50 (d):JUKI: Serial Interface E65 Id): Tractor Attach. E149 (al: Sheet Feeder £219 (a)Ribbon 12.50 la): Spare Daisy Wheel £14 (d).

.BROTHER HR20: Sheet Feed E22111: Ribbons - Carbon or Nylon £3; Tractor Fee:E116 (a): 2000 Sheets Fanfold with extra fine perf. 9.5" E13.50; 15" E17.50 (b).BBC Pare& Lead £6: Serial Lead 1E6 IBM Parallel Lead (2m) E12 (d).

BT APPROVED MODEMSMIRACLE TECHNOLOGY WS Range

WS4000 V21123. WS3000 V22 Na Professional(Hayes Compatible. Intelligent. Auto Diet' As V22 arid 2400 baud full duplex E509 (alAuto Answer) £129 (b) WS3000/1111C Data Lead £10 Id)W53000 V21123 Professional WS2000 V21N23As WS4000 and with BELL standards and Manual Modem E92 Illbattery back up for inernury E244 lb) WS 2000 Auto Dial Card E27 (dlWS3000 V22 Professional WS 2000 Auto Answer E27 (diAs WS3000 V21123 but with 1200 baud full WS 2000 SKI Kit E5 (dlduplex E395 (a) WS 2000 Uses Port Lead £5 (d)

(Offer knifed to current stocks)

SPECIAL OFFEREPROMs/RANIS

2764-2527256275126264LP-1527128-25 (12.5 Vpp)27128-25 (21.0 Vpp)

Priceson

appli-cation

LANGUAGES:6502 Asst' Lang Prog (19.958086 Book E23.95Acorn BCPL User Guide £15.00Acorn FORTH £7.50Acorn LISP (7.50Acorn ISO Pascal Ref Manual ..110.00Intro to COMAL E10.00Intro to LOGO E7.50Micro Prolog Ref Manual £10.00Introduction to Turbo Pascal__ _114.95Prog the Micro with Pascal ....18.50The UNIX BookUnix User GirsdeUnderstanding Unix

BBC MICRO GUIDE BOOKSBBC User Guide Acorn88C Rim User GuideDrawing your Own BBC ProgranisE6.95Inside Information E8.95Math Prog in BBC Basic E7.95Toolbox 2 £10.95VIA 6522 Book 4 50

PROGRAMMING(UTUJTYAdvanced Sideways Ram UserGuide (9.95Advanced User Guide (USC) £12.50Applied AssJLang on the BBC 19.95BBC Micro Sideways ROM's RAM'sE9.95Guide to the BBC ROM E9.95Beginners Guide to VI.P (7.95

17.50£19.95£18.45

E15.00£15.00

MONITORSMICROVITEC 14" RGB1431 Standard Resolution. £179 la)1451 Medium Resolution E225 la)1441 I-fi Res E359 (a)MICROVITEC 14" RGB/PAL & Aullo1431 AP Standard Resolution E199 (al1451 AP Medium Resolution £255 la)MICROVITEC 20" RGIIIPAL/Aucio2030 CS std Res E3802040 CS 15 Res E675 la)Mitsubishi 14" RGB Med Res 188C118M)

E219 la)

TAXAN Supervision 620 E269TAXAN Supervision 625 E319 fa)TAXAN Supervision 770+

lwnh swivel stand) £499 Is

12" MONOCHROME MONITORS:PHIUPS:

7502 Green Screen E 69 to7522 Amber Screen E 75 (a7552 £ 851a)

AB Philips Monitors supplied withswivel stand

BOOKSNo VAT on books; Carriage (c)

View ao User GuideViewstoreViewsheetWordvitse Plus

E9.00E9.00E9.00E9.95

SOUND & GRAPHICS:Mastering Music (6.95

DISC DRIVE SYSTEMS:Advanced Disc User Guide ....E14.95Disc Book E3.50Disc Programrning Techniques . £7.95Disc Systems E6.95

Handing on the BBC E6.95

APPLICATIONS:Interfacing Prot' for BBC E6.9588C and Small Business E5.75

PROFESSIONAL SOFTWAREWordstar made easy E16.95Introduction to Wordstar E17.95Wordstar Handbook £11.95dBase-II for the first time user E16.95Understanding dBase-Ill E22.95Muitiplan Made Easy E18.95Multimate Complete Guide .. (16.95ABC of LOTUS 123 E17.451-2-3 for Business £16.95Ark Tech in dBase 11111 122.95Mastering CPIM (17.95CPIM Bible 116.50Introducing CP.M on BBC & 280 £9.95MSPC DOS Prompt £10.95

PROJECTS:Junior Computer Kit £86 lb)Housekeeper kit £58 Ib)Elekterminal Kit (1980) £50 lb)ASCII Keyboard kit £75 (b)J C Books 1, 2, 3, & 4E6.90 (c) eaUniversal Terminal (6502) Kit £75 (b)Elekterminal Kit (1983) .. . £70 (b)

PROGRAMMED ROMS FOR ELEKTORPROJECTS

503-N Jrv. Computer Monitor2708E 4.80

504 Disco fights 2708 E 4.80505 Chess Inteiekt . 2 x 2715 (14.60506 .1 C Tape Monitor . 2716E 7.30507-N J C Printer Mon & PME

2716E 7.30508 .1 C Bus Control 82523- £ 4.80510 150 MHz Fret) Meter 2 x82523

E 9.60514 Dark Room Computer 2716 E 7.30

516 Ta'. -a Dice 2716 E 7.30521 C-a3an & Video Routine forDOS J - 2732 + 2716 E16.40522 Cr & video: Routine for ex-tender -- - 2732 + 2.2716(24.00523 "]'-a-ator .. 2732E 9.005240_s s .... 2732 E 9.00525 L- .r Term.... 2732 E 9.00526 - - - -a 2716E 7.30527 E -.- -tn 2716E 7.30

ALL PRICESEXCLUDE VAT.Please add carriage 50p unless

indicated as follows:

falf8 fb).£2.50 (0E1.501 id/£1.00

111.00 TECHNOLINEVIEWDATA SYSTEM

Tel 01-450 9764Using 'PresteF type protocols.

For information and ordersavailable 24 hours, 7 days

a week.

SEE OUR PAGE 5 ADVERTISEMENT FOR COMPONENT PRICES

TECHNOMATIC LTDMAIL ORDERS TO: 17 BURNLEY ROAD, LONDON NW10 1ED

SHOPS AT: 17 BURNLEY ROAD, LONDON NW10(Tel: 01 208 1177, Telex 922800)

305 EDGWARE ROAD, LONDON W2, Tel: 01 723 0233

PLEASE ADD CARRIAGE AS PER CODE & 15% VAT

(Export: no VAT. pap al Cost)Orders from Government Depts. et Colleges etc. welcome.- Minimum telephone order £5.

Detailed Price list on request.Prices subject to change without notice

Please mention ELEKTOR ELECTRONICS when contacting advertisers

CONTENTSSeptember 1988Volume 14Number 159

64 Kbyte static RAM extension forMSX computersp. 14

Editorial

13 Open systems at crossroads?

Audio & Hi-fi29 PROJECT: Microphone preamplifier with

active filterby S.G. Dimitriou

111,Components

42 A high-speed depletion -mode DMOS FETfor small -signal applicationsby Alan Pritchard

Computers

14 PROJECT: 64 Kbyte static RAM extensionfor MSX computers

45 PCB design on the BBC and PC1512 1640computers

54 Shielding computers with metal -coatedglassby Bill Pressdee

57 Data Protection Act keeping the recordsstraightby Nigel Waters

General Interest

37 PROJECT: Fast NiCd charger

56 The British Libraryby Ann Abbott

59 PROJECT: Microcontroller-driven powersupply - 3

Radio & Television

32 DBS Conference 1988by our Technical Editor

48 PROJECT: Microprocessor -controlled radiosynthesizer - 2

69 Computer -generated colour test chart

Science & Technology Brief

19 Where industry leans on the shoulders ofscienceby Dr John Geake

Fast NiCd chargerp. 37

Self-inductance meterp. 24

Test & Measurement

22 REVIEW: Part 9 - Function generators (3)by Julian Nolan

24 PROJECT: Self-inductance meter

InformationNewsbriefs: 18, 21, 28, 35, 53, 55; Events 36;New literature 40; New products 44; Corrections58; Readers' services 67

Guide lines

Switchboard 67; Buyers' guideads 74; Index of advertisers 74

70; Classified

In next month'sissue: mAcRovisiorq

decoder Programming

PALs Distance meter Preamplifier for

purists Transistor -curve

tracer Peripherals for

BASIC computer Application

notes: prescalerSDA 4212

Front coverA scientist at BristolPolytechnic's TransputerCentre illustrates thetransputer'scapabilities in solvingthe Mandelbrot Set.sometimes describedas the most com-plicated object inmathematics.Bristol Polytechnic'sTransputer Centre hasbeen set up to carryout research and de-velopment on uses ofthe transputer in in-dustry, help companiesto exploit the parallelprocessing potential ofthe transputer, and totrain students and per-sonnel in its use.One of the new super-computers, Supernode,developed under theEC's ESPRIT programmeby Britain's Thorn EMIand France's Telemat.incorporates 350transputers and is ex-pected to be on themarket shortly atabout one tenth thecost of existing super-computers.

4 EESeptember 1988

AMPLIFIERS FROM

The UK Distributor for thecomplete I LP Audio Range

BIPOLAR AND MOSFET MODULESThe unique range of encapsulated amplifier moduleswith integral heatsink.

30 15ii amp L11.30 n'T 245 12oe, B po.v amp 12.:nm £24.1511Y63 3ON Bipolar amp £11.30 HY364 18311,1 Bipolar amp 14ohm) £36.00-Y61160301Y Stereo Bipolar amp £23.63 HY368 180W Bipolar amp 18ohm) £37.55- . 124 6Q. Bipolar amp lrlohml £18.50 MOS' 28 613111 Mostet amp £40.70" '128 EON Bipolar amp leohml £18.50 4t0S248 1205 Mosfet amp E4635

Y244 120Vi Bipolar amp (4ohm) E24.15 M05364 1801V fitos-fet amp £75.75

POWER SUPPLIESComprising toroidal transformer and DC boardpower the ILP amplifier modules.

to

Application PS1/532 1.105128 (21 £25.40r-stao PreamplMer E 9.75 PSU542 HY248 £25.40P5U212 1 or 2 HY30 E17.70 PSU552 1.!05248 E27.45PSU412 HY6060.14Y124.1or2 HY60E19.95 PSU712 HY244 121 £2920P511422 HY128 £22.00 P51.1722 HY248 121 f30.20PSU432 4105128 £23.00 PSU732 HY364 £30.20PSU512 HY244 -0'128121 £24.40 PSU742 HY368 £32.20P5U522 HY17z £24.40 PSU752 MO5364.1105248 121 E32.20

PRE -AMP and MIXER MODULESThese encapsulated modules are supplied within -line connectors but require potentiometers,'witches etc. Individual data sheets on request.

0 ort-3-p A:1, ni;3 £ 9.25i-iY 7 Mont) newer 8 channel E 8.75HY8 Stereo maw 5 channel E 8.75HY9 Stereo pre -amp 9.30HY11 Mono mixer 5 channel with bass & trz: . £ 9.75HY12 Mono pre -amp 4 charm! with bass. £ 9.30HY13 Mono VU meter driver E 835HY66 Stereo pre -amp with bass & treble £15.00HY67 Stereo headphone driver £16.60H YU Sit/e0 r31:Iff 10 channel £1 1.30HY69 Mono pre -amp 2 channel with ban & treble £15.40HY71 Duel pre -amp £14.95HY 73 Guitar pre -amp with bass & treble E15.00HY74 Stereo mix., 5 channel with bass & treble £15.95HY75 Stereo pee -amp with bass. mid & treble 05.40HY76 Stereo twitch matrix £19.50HY77 Stereo VU meter driver £14.35HY78 Stereo pre -amp £14.70HY83 th special effects £18.9586 1.1- -:9 6,- E 1.158E6 £ 1.75

LOUDSPEAKERS£78.8512 _ _!speaker

312W 5 200N 12" W 7 7 -d bass lowlife - £78.65

POWER SLAVESThese cased amplifiers are supplied assembled andtested in 60 and 120 watt Bipolar or Mosfet versions.US12 60 Ali: t4-nnmi £7500 1_331 _US22 120 watt Bipolar (4ohml £83.75 US42' 1'

ric.ies include VAT and earflap. 57SA

Quantity prices available on requestWrite or phone for free Data Pack

Jaytee Electronic Services143 Reculver Road, Belt inge, Herne Bay, Kent CT6 6PL

Telephone:(0227)375254 Fax: 0227 365104

SUMMER SALEMassive reductions on old Bargain List items -mostly half price! Reductions on many CatalogueLines-inc. 10% off all Antex and Vero products.

.Ring or write for our special Free Sale List whichgives full details. (You'll need our 1988 Catalogue,Price £1, and our Spring Supplement and SpringSale List, both Free.)

Some of the goods on offer:Z993 65W switch mode

"L'2495 £14.95Z660 8-24V in 5V 2A out

£2.50Z975 1 600mAE6T--;a4 £3.25AMPLIFIER PANELSZ914 1W amp -217456-75p2915 Stereo 1W amp

C3.:0 £1.75Z974 Mixer amp £1.25Z469 AL30A panele2-.-5e- £1.25

CPUIMEMORY PANELSZ494 Newbrain Motherboard

e575(4 2.75Z672 Reject Motherboards

-E9754 £1.75

'Jimmy'football game-e5784 £2.50

'Simon' panel -E-1-3 for £1Fibre Optics 20m coil twin

£2

LE PRICES IS E20-£2 POST

J135 Headphones-±-87944-£2.00

J136 Walkman headphonesplus speakers -t5t95 £2.00COMPONENT PACKSK544 Mullard polyester

£1.50K540 500 Resistors

±2755. £1.00K503 100 Wirewound Resistors

f2799 £1.00f4'5 £2.00

K547 100 ZenersSPEAKERSZ945 5 x 3in. 8OR 1W

-81- 2 for £1Z575 70 .: 45mm 45R 0.5W

-..Hrrr 4 for £1Z578 30 30mm 16R 0.4V.,

-63* 3 for £1POWER SUPPLIESM4''.!88 vvas f now 3 for £3

MIN ORDER TO OBTAIN SA

NEW THIS MONTH28837 DUAL SHEET FEEDER. Brand new:ea...dov.n unit_ Costars 3 1 2V step-: er motors (48 step) plus driver panel with

TIP115. 4 x 111.110, U.13302, 2 x7407; 2 solenoids, buzzer, microswit-CneS, control panel. 2 oplocouplers plus:Ts of gears and mechanical bits.

£24.95-E3 carr_Full details plus pie on 811.40. All partsavailable separately e.g.:

Z4089 Stepper Motors E6.00

REMOTE CONTROL for Toshiba VCR_ 16555 x 25mm case has 7 push buttons.

slider pot and edge pot. 6mm long 8 corelead. PCB had 4001 and 4582 plus fewother bits. E1.99

Back in stock Z8833 Tatung casedkeyboard VT4100. 85 keys inc sep.numeric keypad. 450 a 255 . 65:25.

£14.95

24081 CB Aerial eliminator. Black steelcase 77. 70.30 for using car radio aerialwith CB. Has 2. 500pF trimmers,switches, coil etc -- 2 leads approx. 2mlong. Originally £7.95 Our price E2.00

Z4080 AMiC8 converter. Enables all CBchannels to be picked up on MW.85.70 x 50mm £4.50SOLAR CELLS''.ega size - 300a 300mm. These incor-t:Drate a glass screen and backing panel

wires attached. 12V 200mA output.:Leal for charging Meads. E24.00

Z4069 STEREO HEADPHONES -compact, fold -up. Amazing value. £1.95

Z4071 MAP LIGHT - In car use withmagnet and magnifier, curly lead and plug.

(1.95Z345 OPTICAL SHAFT ENCODER. Similar:c RS631-632. but 80% cheaper! £8.50

TELETEXT PANEL2037 265. 145mm by GEC. Uses8085A. 8155. 8255A, 8251. 8212 all byIntel. 2 x 2114. 2 x TC5501 custom:hips - 10 others. Nicad back up. Nev.

£9.90

* STAR BUY *GREEN SCREEN HIRES 12" MONITORCHASSISBrand new and complete except for case.the supitr high definition (1000 lines atcentre) makes this monitor ideal for com-puter applications. Operates from 12V DCat 1.1A. Supplied complete with circuitdiagram and 2 pots for braliance:conuast.plus connecting instructions. Standard in-put from IBM machines, slight mod(details includedl for other computers.

Only E24.95 E3 carr

COMMODORE INTERFACEZ030 Plugs into user port on C64 andgives serial output to 5 pin plug. Uses27256, 6502 plus LS & CMOS £5.95

SPEECH SYNTHESIZER KITZ315 All parts inc. PCB to make a speechsynth for the BBC micro E4.99

Z316 De -luxe version -also includes215V case. 1m 20W cable plus connector

£7.99

MAINS LEAD24057 Mains Lead. 2m long grey 3 core6A lead with 13A plug fitted with 5Afuse. 713p: 10 55p: 100+ 40p

SOLDER SPECIAL!!* 15w 240V ac soldering iron* High power desolder pump* Large tube solder

ALL FOR

£7.95

LM358's for 5p!2347 4 a LM358 op amps surfacemounted on ceramic substrate. easilyremoved. 5 panels for £1.00

JOYSTICK

Z004 Skeleton Joystick, switch type.Good quality. made by AB. Brassspindle has 44mm long black plastichandle attached. Body has 4 mountingholes. These really are a fantasticbargain!! ONLY £1.00

GREENWELDELECTRONICCOMPONENTS

ircksle VAT: Osst acid 1.00 P&P- lE51E2 sate items! No min. CWO or Access.Ofh.W ceders from schools etc. yiercorre

invoice charge £10. Our s)cs, has e,iuniiuus ssf °wear -ems end is open 9-5.30 Von -Sat. Come s-:

Ls!443E Millbrook Road SouthamptonSO1 OHX Tel 10703) 772501 783740FAX 107031 787555: EMail 72: MAG36026: TELEX 265871 MONREF Gquoting 72: MAG 36026

Please mention ELEKTOR ELECTRONICS when contacting advertisers

EE 111September 1988

A V.'oft:irs Kluwer CompanyManaging Editor: Len SeymourPersonal Assistant: L. VousdenTechnical Editor. J BuitingAdvertisement executive:Pauline O'Rourke

Editorial offices:1 Harlequin AvenueBRENTFORD TW8 SEWEnglandTelephone: 01-847 2618 (National!or +44 1847 2618 (International)Advertising: 01-847 2619Telex: 917490 (elektr g)Fax: 01.847 2610European offices:Postbus 756190 AB BEEK IllThe NetherlandsTelephone: +31 4490 89444Telex: 56617 (elekt nilFax: +31 4490 70161Overseas editions:Publitron Publicacoes Tecnicas LtdaAv 1piranga 1100, 9° andarCEP 01040 Sao Paulo - BrazilEditor: Juliano BarsaliElektor sariRoute Nationale; Le Seau; B.P. 5359270 Bailieu! - FranceEditors: D R S Meyer:G C P Raedersdorf

Elektor Verlag GmbHSiisterfeld-Stralle 255100 Aachen - West GermanyEditor: E J A KrempelsauerElektor EPEKaraiskaki 1416673 Voula - Athens - GreeceEditor: E Xanthoulis

Elektor Electronics PVT Ltd.Chhotani Building52 C, Proctor Road, Grant Road (E)Bombay 400 007 - IndiaEditor: Surendra lyer

Elektuur B.V.Peter Treckpoelstraat 2-46191 VK Beek - the NetherlandsEditor: P E L Kersemakers

Ferreira & Bento Lda.R.D. Estefania, 32-1°1000 Lisboa - PortugalEditor: Jorge Gonsalves

Ingelek S.A.Plaza Reptlblice Ecuador2-28016 Madrid - SpainEditor: A M Ferrer

Electronic Press ABBox 63182 11 Danderyd - SwedenEditor: Bill Cedrum

International co-ordinating& technical manager:K S M Wa!ravenInternational editorial secretariat:G W P v Linden; M PardoDistribution:SEYMOUR334 Brixton RoadLONDON SW9 7AG.

Typeset & composed in theNetherlands by GBS, Beek U.Printed in the Netherlands byNDB, Zoeterwoude.

Copyright = 1988 Elektuur B.V.

ABC

OPEN SYSTEMS ATCROSSROADS?When early last year it was announced that a group of major European andAmerican computer manufacturers, the X/Open Group, had agreed to adoptAT&T's UNIX operating system as an industry standard, it seemed that we wereat last moving towards an open standard of sorts. But, alas, these intentionsare in danger of going the same way as those of the makers of MSXmachines: to Never Never Land.

A number of the XIOpen Group participants, among them IBM, DEC, Siemens,and Honeywell Bull, have accused AT&T of attempting to influencedevelopments in computer hardware by using UNIX as a lever. They alsoclaim that certain computer companies in which AT&T has a stake, particu-larly Sun Microsystems, are given advance notice and the opportunity of in-fluencing future versions of UNIX.

AT&T, backed by Unisys, the world's second largest computer manufacturer,ICL, and Xerox, says that all it is trying to do is to unify the many differentvariants of UNIX into one consistent system that will allow all computers run-ning it to be fully interoperational.

While AT&T maintains that it is fully committed to keeping UNIX open and giv-ing all computer manufacturers unbiased access to future versions of UNIX,the dissenting companies claim that they have been refused to lend a handin the development of UNIX, although Sun is doing so.

This whole rumpus is, of course, about money - lots of money. Dataquest, theUS market research organization, estimates that the world computer marketwill amount to some $ 11 billion by 1992 and to perhaps more than $ 20billion by the mid -1990s. Already, UNIX has more than five per cent of thismarket, and this share is likely to grow to over ten per cent by 1992. Thatwould put AT&T in a very strong position to influence hardware development.

Since AT&T has apparently not agreed to grant the dissenting companies thesame facilities as Sun, these manufacturers, led by Hewlettt Packard and IBM,have set up Open Software Foundation. They claim that this non-profit makingorganization, in which they have invested hundreds of millions of dollars, is in-tended to develop a new version of UNIX that will not be under the control ofAT&T, but will be truly open.

Although this would seem to indicate (encouragingly for users the world over)that the major manufacturers are converging on an open system that theircustomers have been clamouring for since the early 1980s, are we right in be-ing optimistic? After all, the XIOpen Group is not dead. In fact, IBM has onlyjust joined the 15 manufacturers, including AT&T and Unisys, that participate inthis group. So, there are now two powerful groups of major computermanufacturers (seven of whom belong to both groups) whose aim it is to pro-mote UNIX as a common standard. But which UNIX?

Users the world over can only hope that the two groups will be able to burythe hatchet soon and together produce a universal operating system.

14 EESeptember 1988

64 KBY1E STATIC RAMEXTENSION FOR MSX COMPUTERS

Although the concept of MSX allows the addressing of up to1 Mbyte of memory, the number of computers that use more than

128 Kbyte is surprisingly low, and ready-made RAM extensionmodules thin on the ground. We decided to do something aboutthis, and developed a plug-in RAM extension that enables MSXusers to increase the total available memory of the computer in

steps of 32 or 64 Kbyte.

With a mere 64 Kbyte installed as a stan-dard, and 128 Kbyte available on newermodels only, MSX computers do notfollow the trend towards the use of vastamounts of system memory. Thediagram of Fig. 1 shows the theoreticalmemory structure of the MSX concept,which was originally designed for1 Mbyte of addressable memory. Inpractice, however, there is not a singleMSX computer that actually uses all ofthe available system memory.In principle, any MSX computer canhave up to four so-called primary slots,which are, in turn, subdivided into fourblocks of 16 Kbyte. The BASIC and sys-tem ROM are located in the addressrange of the first slot (number 0). Thetwo ROMs use up half the memory inthis, occupying address range 0000H to7FFFH, i.e., two blocks of 32 Kbyte.Random access memory is usuallylocated in another slot, and in addressrange 8000H to FFFFH. After a reset,the control system runs a test routine toexamine which slots hold RAM.A slot can be expanded with the aid ofadditional hardware. Slot expansionmakes it possible to use four equal banksper slot. Like the slot itself, these banksare in principle composed of four blocksof 16 Kbyte. In practice, a slot expandercircuit enables extending the memory ca-pacity of a primary slot from 64 to256 Kbyte.

Table 1 lists the slot structure of a num-ber of MSX computers, and also showswhich slots are expanded internally. Thefunction of the so-called memory map-per in MSX-2 machines can be disregard-ed as far as the present RAM extensioncard is concerned. Most MSX computershave one or two non -expanded slots, sothat 64 or 128 Kbyte of RAM can beadded without problems.

More memory, moreworkspace?When running in BASIC, MSX corn-

puters have relatively little free memory- in practice, this hardly ever amountsto more than 23 Kbyte. It may come asa surprise that adding 128 Kbyte ofRAM does not resolve this limitation,since BASIC can not address this ad-ditional memory. Does this make anyRAM extension useless? Fortunately, theanswer is no. Evidently, the present cir-cuit would not have been developed ifthe computer could not benefit from it.There are programs capable of using theextra memory by bypassing the memoryhandling routines in MSX BASIC. Stillother programs can only work when ad-ditional memory is installed, and theabove limitations of BASIC are, ofcourse, unknown when machine code isused.In a number of cases, the RAM exten-sion card described makes it possible torun older programs on more recently in-troduced computers. This is because thefirst releases of some programs did not

assume that the 64 Kbyte of memorywas divided over several slots. This, how-ever, is not strictly required according tothe MSX standard. In the case of thepresent RAM extension, this rule is, ofcourse, observed.In BASIC, the extension card offers aninteresting feature by allowing memoryto be made 'read-only' for testingwhether a machine code or BASICprogram can run from EPROM. Pro-grams developed by the user and in-tended for storing in EPROM can,therefore, be tested in RAM, obviatingthe need to clear and load EPROMs forevery minor change in the program (anEPROM programmer for MSX com-puters was described in 0)).Because the internal memory is nearlyalways in a 'high' slot number, the con-trol system does not encounter it until allother slots have been examined for thepresence of RAM. The control systemuses the first RAM bank found. Testingis done in blocks of 16 Kbyte, i.e., in theareas C000H through FFFFH, and 8000Hthrough BFFFH. This means that the32 Kbyte RAM may be divided over twoslots.When a lower slot is selected, the controlsystem will find the extension cardbefore it finds the internal one, and useit as workspace. When, for example, theinternal memory is located in slot 3, theRAM extension can be used in slots 0, 1and 2. The slot allocation of the internalmemory is given in Table 1 for a numberof commonly used MSX micros. For acomputer not listed, consult the techni-cal reference manual supplied with it.The internal RAM is always selectedwhen it is in slot #0 or #1.

Circuit descriptionThe circuit diagram of the RAM exten-sion card is given in Fig. 2. Composed ofonly two 32 Kbyte static RAM chips,one CMOS IC, two resistors, threecapacitors and one FET, the memory ex-tension could hardly be simpler.Connector Ki is formed by the (pretiun-

=0

C

=1 =1 =3

Slot =0 expanded 101 Slot =1 expanded 1 k Slot =2 expanded id k Slot =3 expanded

Total: 024K bytes (16 64K bytes) 87311-10

Fig. 1. Theoretical memory structure of MSX computer.

Table 1

Slot assignment of MSX computers

MSX1

AVT Daewoo DPC-200Canon V20Goldstrar FC 200JVC HC-7-gbMitsubishi MFL-FX 1Mitsubishi MFL-48Mitsubishi MFL-80Panasonic CF2700Philips VG8020Philips VG8010V68020:20Sanyo MPC-100Sony HB201pSony HB75pSony HB55p

Sony HB1OpSony HB501pSpectravideo 738Spectravideo 728Toshiba HX-10Yamaha CX5MYashica YC-64

MSX2

AVT Daewoo CPC -300

Sony H8-F500PSony HB-F700P

Sony HB-F900P

Sony HB-F9P

Philips VG8220

Philips VG8230Philips VG823518245

Philips VG825018255

Philips VG8280

RAM- REMARKSSLOT1

3223-2 Slot 3 expanded, 64 Kb RAMO 32 Kb RAM1

1

3O 32 Kb RAM, slot 2 not usable3-233 16 Kb ROM firmware in slot 02 16 Kb ROM firmware in slot 0O 16 Kb RAM. 16 Kb ROM

firmware in slot 0331 Slot 3 expanded, RS232; Iskrom

2O 32Kb RAM3 Slot 1 not usable

RAM -SLOT0-2

REMARKS

Slot 0 expanded.128 Kb Memory mapper

0-0 0-2 Slot 0 expanded.3-3 Slot 3 expanded.

256 Kb Memory mapper0-0 0 -2 Slot 0 expanded.

Video digitizer3-2 Slot 3 expanded.

128 Kb Memory mapper16 Kb ROM firmware

3-2 Slot 3 expanded.16 Kb ROM firmware

3-2 Slot 3 expanded.3-2 Slot 3 expanded.

128 Kb Memory mapper3-2 Slot 3 expanded.

128 Kb Memory mapper3-2 Slot 3 expanded.

128 Kb Memory mapperVideo -digitizer

EE

September 1988

ed) contact fingers of the double -sided,through -plated, printed circuit board.Gate NI combines SLTSL and MERQto enable addressing the memory chips.Since these have a capacity of 32 Kbyteeach, and SLTSL is intended for a rangeof 64 KByte, the selected address blockneeds to be divided in two 32 Kbyteblocks. This is accomplished by N3 andN4 combining true and inverted signalA15 and A15 with the output of NI.Write protect switch St blocks the WRsignal for both memory chips via gateN2.RAMs ICI and IC2 work independently,and one of them may be omitted whenonly 32 Kbyte of extra RAM is required.

A compact moduleThe construction of the RAM extensionmodule on PCB Type 87311 is straight-forward because the board is through -plated and available ready-made. Beforemounting the parts, use a jig -saw to cutoff the two corners beside the slot con-nector along the lines printed on theoverlay. Do the same with the areabehind St.It is recommended to use good -qualityIC sockets for the RAM chips, ICI andIC2. Although the solder resist mask onthe ready-made PCB affords protectionagainst excess solder short-circuitingpins or closely running tracks, unex-perienced constructors are well advisedto work carefully here, and use a low -power soldering iron with a small tip.Switch St is preferably a miniature slidetype that can be fitted securely in theclearance at the rear of the PCB.A problem may arise ith MOSFET Ti.The Type BS170 may be supplied in adifferent enclosure under the type indi-cation BSI70P. The P version also has adifferent pin -out - see the circuitdiagram. The component overlay of thePCB for the RAM extension is correctfor the standard BS170.

TestingThe RAM extension should be testedbefore it is fitted in an enclosure. Figure4 shows the listing of a test programtyped in under MSX BASIC. The actualtest program is machine code loaded asDATA with the aid of a POKE instruc-tion in a FOR/NEXT loop.Before switching the computer on, closeSt to turn the extension card into aROM block. After the computer hasfinished its initialisation, open St, typein or load the test program, and makesure that it addresses the right primaryslot, which corresponds to the valuePOKEd in line 130. It should be notedthat the program tests the entire64 Kbyte space. When the RAM exten-sion functions correctly, the programshows the message MEMORY OK in thetop left-hand corner of the screen. When

16 EESeptember 1988

2K1 28 AO

27 Al30 A229 A3

32 A4

31 A5

22 A6

21 A7

24 A8

17 A9

2019

23

2625

A10AllAl 2A13A14

18 A15

5V

N M V0 C11 r1Ul<

CO< < <

EE 111September 1988

4 10 ' 64k nexory check2030 This pr.7,gran fist writes SHOO to each address fr,n AH0000 to40 AFIFFFF It then cheeks each addr,-ss, starting at AH0000, and if50 the byte returned reads SHOO. &HEE is written to that address.60 Next. each address is checked again. now starting at AliFFFF.70 and SHOO is written when the address reads ABETBO The current nenory address is displayed in the top line of the90 ' screen_ The progran halts when a faulty address is found_100 ' The nachine code progran can be halted by pressing110 ' keys (CTRL!. (EHIEFI. (GRAPH' and ICOOKI sisultanebuSIE.

120130 CLEAR 200.M/8000, POKE AH9170.1 ' onleet prinary slot nunber11.0 EOKE AFE990 ' enable stop by pressing ctrl -shift -graph -codeISO CUE: LOCATE 7.0: PRINT -Busy -160 WEBS 200170 LOCATE 5.11E0 END200 PESTCRE 330210 FZF 1=0 TO 11116220230 :.3 7.3 TO AHF240 .E.: A1,9.VALI-AH".A512E0260 - _ -

27n SEX. _FE.7 ;s 'F 1=2ALC-AH--ASI755E31 300

-2ATA 'ERROR IN LINE -,320.I.1.0 END

-F19000, A=USR(0I320 FE32C, :, .85. F5.DE.21.0 .0 .11.0 .0 . 4203-: :A -7E:..7:: 2 21.20,E1,24.7C.FE.CO. 786

:5..E.FE. E6.3F.47.3A.70,81.C9.E 803257 IA 77 F1.03,A8,E8,2C,20.E2. 942370 0.A. .14.70.51.CD.31.81.CD. 652390 ..70.BI.CD.14.0 .2C. 4D1390 CA7A _ 0:.:E.1D.31.21.D9.AS. 973400 ['AT; 50.F3.03.A2.7E. SIC410 2525 - 7E4

:A7A 868:,.A FE 'i 7E. 90C

445 257: FF 84C450 ZA.7;, FE 976460 :A7A FE 641a"' 2,7, FF E 695

EL A7A :2 T; -F _ EE2

E- ' 3.1.2E.81.11. .0 .35.7 . EC5.7E. A .38.2 .15.7 ,C6.30.E8. 647.26. EE.ED.67.23.5 .1 .D .28. 5DC

A7A. El.DI.C1.C9.0 .0 0 .0 .0 .0 .0 .0 .0 .0 . SIO

61111.11

Fig. 4. This program can he used to test the RAM extension card.

Parts list

Resistors (±5%):111;112=1K0

Capacitors:CI;C2= 100nC3= 100i4; 16 V; axial

Semiconductors:Ti =BS170 or BS170P (see text)IC1;1C2=43256 or 62256 32K x8 static RAM

(C-1 Electonics, Happy Memories)1C3 = 74HCT32

Miscellaneous:St = miniature slide switch.PCB Type 87311 !see Readers Services page).

Fig. 5. Component mounting plan of thedouble -sided, through -plated, printed circuitboard for building the RAM extension.

18 EESeptember 1988

Sony HitBit MSX micro upgraded with 64 Kbyte of random -acre's memor).

a fault is encountered, it displays MEM-ORY ERROR in the same location.

FinishingThe completed printed circuit board canbe made into a compact and sturdy plug-in module by fitting it in a music cassettebox - see the introductory photographand the drawing of Fig. 3. After remov-ing the lower panel of the box, the PCBis fitted by means of four screws andspacers. After spraying the box withpaint, the extension module is ready foruse.

Reference:

(1)MSX extensions - 5: EPROM pro-grammer. Part I: Elektor ElectronicsMarch 1987; Part 2: Elektor ElectronicsApril 1987.

COMPUTER NEWS

Micro -imaging products inEuropeThe cross -breeding of computers, laserdisks, and microfilm is revolutionizingthe storage and retrieval of images, andin Europe alone this will create a S 243million annual equipment market in lessthan five years' time, according toAnalogue and digital micro -imaging inEurope (#E1009), a look at the emergingtechnology and issues by Frost &Sullivan.The national markets of FederalGermany, France, and the UK will eachgrow to around S 43 million by 1992.At present, according to the study, thedominant sectors of the market areWORMs (write once write many timesoptical disks) at 33% and COM (com-puter output on microfilm) at 24%. Themarket will shift dramatically, however,and by 1992 it is forecast that 65% of allexpenditure will be on WORMs, and lessthan 5% on COM.Frost & Sullivan Sullivan House 4Grosvenor Gardens LONDONSW1W ODH Telex 261671 FAX+44 1730 3343.

IBM quality award for SaloraOne of the few companies that recentlyreceived the IBM Supplier Award for1987 was the Finnish company Salora, apart of the Nokia consumer electronicsindustry. Salora supplies monitors toIBM's manufacturing plant atGreenock.The award is given to suppliers inrecognition of a highly distinguishedlevel of quality in the materials or servicesupplied to IBM Greenock. It is part of

the company's dynamic quality pro-gramme, which is aimed at ensuring 100per cent customer satisfaction.Salora Oy Salorankatu 5-7 SF -24240 SALO Finland Telephone+358 24 3011 FAX +358 24 18661.

Testing of 80386 -based PCBsReal-time emulation testing of 80386 -based PCBs is now available on AQL'sStation 20 ATE system. The new supportpackage, called micro MIMIC/386, of-fers users the ability to test any boardbased on an Intel 80386 processor, orany PCB that might be processor -dependent such as a PC expansion card,at full real-time speeds. The product'smaximum operating rate of 32 MHz ismore than adequate to deal with all cur-rent speed selections of this populardevice. AQL also provides the supportpackage for other members of this pro-cessor family, such as the 80286.Full details from AQL 16 CobhamRoad Ferndown Industrial Estate WIMBORNE BH21 7PG Telephone+44 202 861175 FAX +44 202861176.

Supercontroller for CADOne problem of old -machine -tool usersis that of feeding data straight from theCAD station to the machine's controlsystem. Normally, unless a serial inter-face exists, this is done by producingpaper tapes, installing a memory in themachine tool or installing a paper tapeemulator.Each of these solutions presents well-known problems of its own, so Tangramhave developed an IBM PC based toolthat can act as a `supercontroller'. Itoperates by taking NC programs fromthe main CAE processing system and

passing them, at appropriate speeds, toNC machine tools' control panel. Up to64 machines can be controlled in thisway.For further information, contactTangram Computer Aided EngineeringLtd Greyfriars 2 Eaton Road COVENTRY CV1 2SB Telex 31529 FAX +44 203 552182.

New breed of process controlcomputers.A new miniature control computer, theScorpion, with on -board processor,memory, and interfacing, and costingunder £ 300, has been announced byMicro -Robotics Ltd.This general-purpose controller is beingused in applications as diverse as marineinstrumentation, humidity control in teadrying, and specialist controls in labora-tories.The computer has many different built-in interface ports, including analogue in-puts, digital outputs, keyboard and serialinterfaces plus LCD, pulse counting in-puts, and an PC expansion port. In ad-dition, it has 24 K of RAM, a built-inclock/calendar and very low currentconsumption of 80 mA at 12 V.A range of expansion modules, pricedbetween 15 and 50, can be added tothe Scorpion to meet exactly a client's re-quirement.For further information, contact Micro -Robotics Ltd 264 Newmarket Road CAMBRIDGE CB5 8JR Telephone+44 223 323100.

EE

September 1988

SCIENCE & TECHNOLOGY BRIEF19

Where industry leans on the shoulders of science

by Dr John Geake, Department of Pure and Applied Physics, University of Manchester Institute of Scienceand Technology

Science parks mushrooming alongside universities reflect thedependence of industry on pure and applied academic work.

They have proved the value of often unforseen contributions fromscientists working on the frontiers of knowledge. One industrialscience group at UMIST (University of Manchester Institute of

Science and Technology) has taken this concept into a broaderfield to provide a consultancy for firms around the world, with aninvestigative and design service that requires no investment innew buildings and attendant infrastructure. It can call upon the

services of more than 100 locally based scientists and reach outto a nationwide pool of expertise.

Modern technology -based industrialcompanies depend on scientific researchfor their progress and competitive edge.The big ones have their own research anddevelopment departments, of course,and a great deal more work in the UK iscarried out in laboratories operated orsupported by Government. But it isprobably true to say that the bulk ofpure research originates in universities.Many firms, especially smaller enter-prises that cannot yet afford to supportlaboratories of their own, may have noscientific staff at all. It is these that needall the help they can get from universitysources.Here there is a problem: universities haveother commitments and, -although theirengineering and technological depart-ments are naturally orientated towardsindustrial requirements, a large part ofthe research done in pure science depart-ments may have no obvious direct in-dustrial application. Yet it is from thepure sciences that most fundamentalknowledge springs, so industry may havea lot to gain by improving its links withuniversity laboratories. At UMIST weare busy developing a new way of bring-ing this about.Science departments of most Britishuniversities already undertake industrialwork. Some have long and distinguishedhistories of industrial involvement, whileothers have only recently found it econ-omically advantageous. Their activitiesrange from individual staff consultancyto running separate, university -owned

companies. UMIST, one of Britain'smajor scientific and technological uni-versity institutions, is also the Faculty ofTechnology of Manchester University, inan important industrial area. It has along tradition of industrial research, es-pecially into engineering and technologi-cal topics, and is now in the forefront ofexciting developments in collaborationwith industry.The story began over twelve years ago inUMIST's Physics Department, whichpioneered a new type of industrialliaison by forming its Applied PhysicsUnit (APU). This was an experiment inenlisting pure scientists in the service ofindustry, by involving the whole of a uni-versity science department in industrialconsultancy work - probably the firsttime that this had been attempted otherthan in wartime. Nearly all of theacademic staff of the department agreedto spend a small part of their time onjobs that call for expertise in their ownlines of research. I served as the co-ordinator, providing a single entry pointfor enquiries. I knew the research topicsin which my colleagues were involvedand was usually able to find someonewilling to tackle the job. When the APUdid not have the relevant expertise, it wasusually possible to find someone else-where in UMIST, or even outside, whowas able to solve the problem; this wasdone as a service, so as not to disappointthe client.Since it started, late in 1974, the APUhas carried out more than 180 jobs for

over 100 clients and has established astrong reputation, especially in the fieldof optical and electronic instrumentdesign. We are listed by the UK DesignCouncil as consultants under theGovernment's Department of Trade andIndustry Support for Design Scheme,and have been undertaking design proj-ects under its provisions.Tne concept pioneered by the physics -based APU has now been greatly ex-tended to include other disciplines byour forming a new organisation calledthe Industrial Science Group (ISG). Ex-perience with the APU showed clearlythat expertise in pure physics could oftenprovide the solutions to practical in-dustrial problems. It therefore seemedlikely that the same would apply to theother pure sciences and that it would bevery useful to be able to bring together,on certain problems, scientists from dif-ferent disciplines. This new idea is nowgathering momentum. Initially, a groupof about 80 academic staff was as-sembled, with expertise in physics,chemistry, mathematics and electricalscience. These were all people who hadagreed to be approached when problemscame in that seemed to require their par-ticular scientific expertise, and who werewilling to form part of a multidisciplin-ary team. However, when the first jobswere undertaken it became necessary toinvolve other specialists from the techno-logical and engineering departments,and the group now numbers over 100academic staff in 13 departments. It

20 EESeptember 1988

soon became obvious that it was essen-tial to be able to call upon engineeringand technological expertise, even whenthe jobs were mainly based on purescience, to bring about an industriallypracticable solution as efficiently aspossible.Including as it now does 15 Professorsand 34 Readers and Senior Lecturers, theISG consultancy team represents apowerful concentration of scientific ex-pertise covering a remarkably wide rangeof subjects. It is probably the first timethat such a group has been placed at thedisposal of industry. In spite of its highlyacademic nature, it is alreadydemonstrating to clients that it can solvedown-to-earth industrial problems in apractical way.Jobs undertaken so far range from one -day consultancies to major programmes,one of which already involves seven con-sultants from three departments. It hasbeen necessary to learn certain ad-ministrative lessons: the ISG was startedwith a few preliminary ideas as to thetypes of job we would get, but most ofthe jobs that have come to us so far havehad unexpected features, so ad-ministrative flexibility is essential; thismeans that the structure and operatingsystem of the ISG are continually evolv-ing. Practical operation and analysis areperformed on a microcomputer, withspecially written software based on aspread -sheet. There is a novel self -checking accounts system and we have afinancial future -projection program. Allmoney is handled by the UMIST Bursar,who has approved a scale of fees and in-come distribution: staff consultants timeis reckoned by the day, while overheadsare paid to UMIST and to the consult-ants' departments. The ISG is guided bya management comittee of UMIST staff,with a senior industrialist as chairman.When an enquiry is received from aclient the first step is usually to arrangea meeting, perhaps at UMIST, betweenthe client and the potential consultants.At this meeting, which is free of chargeand in complete confidence, we aim tofind out whether we can help and, if so,to define the problem and decide whichconsultants can provide the necessary ex-pertise. Next, a simple standard agree-ment is completed, setting out the workto be done, and a firm quotation for theconsultancy fees is given. A charge forhardware and expenses is assessed whenthe job has been completed, at cost plusa handling charge; a rough estimate ofthese factors accompanies the quo-tation. The job gets under way with theminimum of formality.After only 18 months in operation theISG now has 34 jobs completed or inprogress, involving 28 consultants fromeleven departments. This rapid take -offillustrates industry's need for the type ofservice we offer and the willingness ofacademic staff to devote part of their

I NOW MOMThe UK Civil Aviation Authority's radome on Great Dun Fell in northwestern England.Manchester's ISG was commissioned to investigate ways of preventing ice forming on its sur-face in one of the world's worst combinations of high -humidity, strong winds and sub -zerotemperatures.

time to such work. But let us look atsome examples of the type of job under-taken.Our biggest job so far is for the BritishCivil Aviation Authority. The new radarinstallation on Great Dun Fell in north-western England has a potential problemwith ice formation on its radome. Theice can absorb radio waves and changetheir phase, and lumps of it can fall offand cause damage. The ISG was calledin to study ways of preventing ice for-mation and our consultants investigatedvarious forms of heating, as well asother techniques to stop ice sticking tothe structure.The CAA installation is on the samehilltop as the research station run by ourPhysics Department's AtmosphericPhysics Group, who chose the site ashaving about the worst weather in theNorth of England. It is in cloud formore than 250 days a year, which is justwhat the research station wants for itsstudy of cloud properties. The CAAchose the same hilltop for quite differentreasons, but it is in what is probably oneof the world's worst places for ice for-mation because high humidity, sub -zerotemperatures and strong winds combineto produce grotesque pinnacles of ice.Radomes in Arctic regions, where it ismuch colder and the winds are evenworse, do not have this problem becausethe humidity is lower.The first part of the project involvedconsultants in the Department ofPhysics, Electrical Engineering andMechanical Engineering, who mademeasurements on the radome itself andperformed laboratory tests and ex-periments. Some of the tests made use ofa large cold room in the Physics Depart-ment which allowed conditions of tem-perature, humidity and wind at theradome surface to be reproduced, so thatpreventive measures could be tried outunder controlled conditions.The second part is now under way andinvolves statistical analysis of data from

the UK Meteorological Office to predictthe probable frequency of serious icingat the radome. This calls on the expertiseof our Mathematics Department.

Automatic chemical analyserAnother job in progress is for anAmerican company based in Cambridge,Massachusetts, that makes automaticchemical analysers. Our work on it in-volves physics, electronics andchemistry, and is being carried out inseveral stages. The first was a feasibilitystudy of ways of improving an existinginstrument. One of our consultantsvisited the company's factory and werecommended certain modifications,which we have now completed. Testshave shown a great improvement in itsperformance. The final stage is to designa totally new unit forming part of the in-strument and then to construct a work-ing prototype of it.Yet another job is to make prototypes forindustrial evaluation of a new type oflinear critical -angle refractometer in-vented by an ISG consultant.Other problems tackled by the ISG haveincluded testing circuit board construc-tion, diagnosing moulding faults, advis-ing on distillation techniques, testing asteriliser and diagnosing faults in print-ing on water-repellent fabrics. A majorproject now under way is to develop asystem for monitoring the performanceof an injection moulding plant. It in-volves specifying and selecting a range oftransducers and a microcomputer, andwriting all the necessary software fordata acquisition and processing.So far, work undertaken has called forexpertise in fluid flow and vapourproperties, surface adhesion, thermalproperties of materials, the physics ofice, electronics and software design,chemical analysis, and biochemistry. Be-tween them, the ISG consultants cover acomprehensive range of measurement,analysis and important mathematical

techniques, including statistical analysisof production faults. Mathematicalmodelling is also of growing importance,enabling the designs of potentially haz-ardous equipment to be tested todestruction on a computer in completesafety.During the previous twelve years theAPU, which now forms the physics com-ponent of the ISG, had worked on manyjobs in the general area of instrumen-tation, including optics, electronics,electrostatics, thermal measurement andX-ray analysis. About half of the jobs in-volved making measurements with exist-ing instruments, on site or at UMIST,and about a quarter were the type of jobwe like best, where we have to design andbuild working prototypes of new instru-ments. It is interesting that about half ofthe instruments were invented within theUnit, some of them before the industrialproblems to which they provided ready-

made solutions were brought w ournotice.

Benefits from industrial work

Apart from its obvious benefit to thecompanies whose problems have beensolved, our kind of industrial activity isbeneficial to the University in severalways: it has an invigorating effect on thestaff, who are introduced to intriguingproblems to which someone really needsan answer; it must enliven our teaching,for real applications of basic scientificprinciples hold the interest of thestudents and illustrate the relevance ofwhat they are being taught. The extrafunds that such activity brings in lead tothe upgrading of equipment and facili-ties. Furthermore it is quite possible thata project which starts out as a small in-dustrial job will develop in the long runinto a major collaborative research con-tract, which may in turn be seen to have

EE

September 1988

wider consequences and to be worth es-tablishing as a new line of research in thedepartment concerned. This is all part ofthe evolutionary process that continuallyadapts the universities to serve simul-taneously the pursuit of knowledge andthe needs of the community.The UMIST experiment is demonstrat-ing the practicability and the advantagesof a new type of industrial involvementfor a university, in which a large numberof the staff spend a small part of theirtime on industrial work. This is quitedifferent from either specialist units orseparate university companies, and it hasthe big advantage that the range of ex-pertise available is very wide. Moreoverthe overheads are low, because there areno separate premises and there need beno separate staff, at least initially. Sothis idea can be tried out, withouthaving to commit financial resources, byany university where there is someoneprepared to organise it.

GEN. INTEREST NEWS

Prototyping serviceProfessional Cable Systems providesprototyping of electronic circuitry inshort turn -round times, enabling de-signers to get on with their designingrather than constructing prototypes. Thecompany uses the BICC-VERO speed -wire system for fast and efficient com-pletion of prototypes direct from a cir-cuit diagram.Typical prices for populated boards are:single Eurocard (100x160 mm) £72.26;IBM board (with interface - 333 x97 mm) £125.46.Unpopulated boards may also be pro-vided: single Eurocard £12.23; 5100board (254x135 mm) £33.34.Full price lists and further informationfrom Professional Cable SystemsUnit 4B Chamber Mill HeronStreet OLDHAM OL8 4LX Tele-phone 061-627 1185.

Third shop for Marco TradingMarco Trading, the mail order, retail andwholesale suppliers of electronic equip-ment and components, have openedtheir third retail shop: SUPERTRONICSat 65 Hurst Street, BIRMINGHAM,Telephone 021-666 6504.SUPERTRONICS is five minutes' walkfrom New Street Station and Birm-ingham's main shopping area, and isjust across the road from a large carpark.The new shop has over 1000 sq.ft. ofsales area. On display are a wide selec-tion of active and passive components,loudspeaker drive units (4 W to 200 W),test equipment, both new and secondhand, alarm equipment, videosurveillance cameras, and cable. Alsoavailable is an on -site audio and video

repair service from Marco's residentengineer.Also on sale in the shop is Marco's latestmail order catalogue, priced at £1.00(but containing £6.50 worth of creditvouchers).The shop is open Monday to Saturdayfrom 9 a.m. to 6 p.m., but closed all dayWednesday.

Radio Amateurs ExaminationCourseThe annual RAE course at PaddingtonCollege commences at 6.30 p.m. on 13September. Enrolments take place dur-ing the week commencing 5 Septemberbetween 1 and 4 p.m. and between 6 and8 p.m. on the 3rd Floor at PaddingtonCollege.Owing to recent ILEA economies, it islikely that this course will be the onlyILEA -sponsored RAE course to be heldin the whole of the ILEA area during theacademic year 1988-89.The RAE course at Paddington isperhaps rather different from the normalrun of RAE courses: not only does itcover the syllabus for the City & GuildsRAE examination, but also makesavailable college facilities to allowstudents to carry out practical ex-periments in the electronic theorycovered. The aim of the course is,therefore, to provide not only anAmateur Radio Licence, but also anelementary grounding in electronics. Thecourse is intended for students with noprevious experience of radio or elec-tronics. None the less, Paddington Col-lege has over the past few years main-tained a very creditable RAE pass rateclose to 90% of the candidates enteredfor the examination.The course tutors are David Peace(G41CKM) and David Hunt (G6MFR).Further information from Paddington

College Paddington Green LON-DON W2 1NB Telephone 01-402 6221or from David Peace on 01-892 7585.

ITU Film LibraryThe ITU has published the 9th edition ofthe Catalogue of Films on Telecommuni-cations and Electronics 1988-89, whichgives information on the 230 films/videocassettes kept by the Film Library.The films are arranged in numericalorder and each one has a synopsis inEnglish, French, and Spanish.The films/videocassettes are lent free ofcharge for non-profit, non-commercialshowings to Administrations, univer-sities, professional and training in-stitutes, and other interested bodiesanywhere in the world.Copies of the catalogue and conditionsfor borrowing the films/videocassettesare available on request from Inter-national Telecommunication Union The Film Library Place des Nations CH -1211 GENEVE 20 Switzerland

Telex 421 000 FAX +41 22 33 72 56.

PCB test and repair serviceA comprehensive test and repair servicefor PCBs has been developed by Swap-tronics. A computerized system, using a`bed of nails' fixture, tests for open -circuit and short-circuit tracks; checksthe function, orientation and toleranceof every analogue component; checksthe function of all ICs at very high oper-ational frequencies; and tests the oper-ation of the entire board.Details from Swaptronics Universityof Warwick Sciences Park COVEN-TRY CV4 7EZ Telex 312401 FAX+44 203 410156.

E

ESntember 1988

TEST & MEASURING EQUIPMENTPart Function Genera ors (3)

Topward Type TFG-8114Topward of Taiwan manufacture a widerange of test instruments, ranging fromAC Millivoltmeters to a 4 1/2 -digitDMM. The whole range is characterizedby its cost effective design and com-petitive pricing. The TFG-8114 retails at£327, excl. VAT, and includes a digitalfrequency counter and a sweep gener-ator: it provides a maximum output fre-quency of 5 MHz. Its facilities includetrigger, gate, linear and logarithmicsweeping. Accessories include a probeand a mains lead.Compared with most other similarlyspecified instruments, the TFG-8114 isrelatively small: 233 x 80 x 300 mm(Wx Hx D). It weighs a mere 2 kg.The operating voltage may be selectedinternally between 115 V and 240 V a.c.±10%. Power consumption is 18 VA.Connection to the mains is via an IECplug.An 18 -position plastic swivel enables theinstrument to be operated at an angle orstacked; the stand can rotate through360°.The frequency range is selected - un-conventionally by two up -down switchesrather than the more usual group ofpush-button switches. This arrangementwas, no doubt, dictated by the crampedfront panel, which also resulted in theTTL OUT and VCF IN sockets beingmounted inconveniently on the rearpanel. The up -down switches, althoughnot inconvenient in themselves, cause aslight delay in the time taken in selectinga frequency range as compared with themore usual approach.The MAIN and FINE controls enableaccurate setting of the output frequency.In conjunction with a built-in frequencycounter, these uncalibrated controls pro-vide an improvement over the moreusual single -course variable control. Theoutput frequency may be variedlogarithmically or linearly: in either caseits value is displayed by the counter.The frequency range may be varied frombelow 0.05 Hz to 5.3 MHz (logarithmicsweep). Some instability is noticeable inthis mode at lower frequencies, but thisis not the case in the linear sweep mode.A reasonably effective symmetry controlis provided, which enables the duty fac-tor to be increased or decreased by up to80% and 20% respectively. This also ap-pears to suffer from slight instability atlower frequencies.None the less, overall frequency stability

by Julian Nolan

is generally good over all ranges.Two output modes are available: con-tinuous and gated. A manual override isavailable in the gated mode. Notably, asingle -shot facility is not provided.Risetime on the rn. output is of theorder of 10 ns, and on the main output,45 ns.In addition to the usual triangular,square and sinusoidal outputs, pulse,ramp and haverwave functions are pro-vided, enabling the generator to providea really versatile performance. Any er-rors on most of the waveforms are onlyvisible at the extreme ends of the fre-quency range.In the gated mode, the start and stopphase are not variable, which may provea limiting factor in some operations.Distortion is fair at

EE

September 1988

Table 11

Table 12

Unsatis-factory

Satis-factory

GoodVerygood

Excellent

Dial accuracyDial resolutionExternal sweep rangeDistortionFrequency rangeOutput level rangeInternal constructionExternal constructionOverall specificationEase of useManual

xx

x

NANA

x

x

x

x

xx

The TFG-8114 was supplied by TelonicInstruments Ltd, Boyn Valley Road,MAIDENHEAD SL6 4EG, telephone(0628) 73933.

Other function generatorsavailable in the Topward range

TFG-8101 - sine, square, and trianeularfunctions as well as ramp and pulse. Fre-quency range 0.1-2 MHz. Peak open -circuit output 5 mVpp-2 V. Distortion< 1%. TTL output. VCF input. Retailprice £115, excl. VAT.

TM -8104 - same as TFG-8101, butwith AM (0-100%) and FM (0-±10%). Retail price £129, excl. VAT.

TFG-8111 - based on TFG-8114, butwithout sweep, trigeer, gate or burstfacilities. Frequency range 0-2 MHz.Instead of the TFG-8114's 5 -digit fre-quency counter, the TFG-8111 is pro-vided with a 6 -digit unit. Retail price£189, excl. VAT.

TFG-4613 - frequency range 0.1 Hz to13 MHz. FM and AM. Triggered, gated,sweep, and burst modes. Sweep rates0.01 Hz to 10 kHz. Variable start/stopphase. Retail price £549, excl. VAT.

TAG -4005 - audio signal generator.Frequency range 5 Hz to 500 kHz. Dis-tortion 0.005%. Comprehensive variableattenuation facilities. Retail price £222,excl. VAT.

OPERATING RANGE

Frequency range: 1000.1(linear) or >10,000:1 (logarithmic) by0-5 V d.c. Sweep rate 10 ms to 1 s.

Frequency accuracy - same as counteraccuracy.

OPERATING MODES

Sine wave: distortion

24 EESeptember 1988

SELF-INDUCTANCE METERMeasuring self-inductance reliably is notoriously difficult and

inductance meters are, therefore, few and far between and alsoquite expensive. The instrument described here offers reasonablyaccurate (within 1%) measuring of low -frequency inductors from

10 f/H to 2 H.

One of the reasons that the measurementof inductance is so tricky is that thevalue of inductance varies considerablywith the conditions of measurement.The principal reason for the variation ininductance is the variation of per-meability, which changes with the levelof the test signal and the d.c. bias.

Principle of meterWhen a non -constant current is passedthrough an inductance, an e.m.f., u, isinduced whose magnitude depends onthe rate of change of current, di, in aunit of time, dt, i.e.

u =L (di /dt).

If di/dt is kept constant (=k) by increas-ing or decreasing the current uniformly,

u =Lk

that is, the e.m.f. is directly proportionalto the inductance (see Fig. 1).

Fig. 1. A uniformly increasing or decreasingcurrent through an inductor causes a con-stant voltage to be induced across the induc-tor.

In practice, however, it is impossible tocreate a uniformly increasing or de-creasing current, but a good alternativeis a current whose waveform istriangular (see Fig. 2). If such a currentis passed through an inductance, the in-duced e.m.f. will have a rectangularwaveform as shown in Fig. 2. If thate.m.f. is rectified, the resulting directvoltage is a measure of the inductance.Unfortunately, no inductance is pure: it

always has some internal 'resistance, R,in series with it. Thus,

U=Uti-UR.

Fig. 2. A triangular current through an in-ductor causes a rectangular voltage acrossthe inductor.

The three voltages are shown in Fig. 3.Rectification produces a direct voltagewith a small sawtooth-shaped ripple,which is caused by uR. The averagevalue of the direct voltage (showndashed in Fig. 3d), remains a true indi-cation of the inductance, however.This shows that in this method ofmeasurement the internal resistance ofthe inductor (unless it becomes large)does not affect the measurement.

Block schematicThe block diagram of the proposedmeter is given in Fig. 4.The function generator, consisting of acombination of an integrator and aSchmitt trigger, generates a triangularand a rectangular voltage.The triangular voltage is converted intoa triangular current superimposed on adirect current. The composite current,which is thus always greater than 0, ispassed through the inductor on test, Lx.Range switching is effected by reducingthe current by a factor 10 for each highermeasuring range.The a.c. component of the voltage acrossL is amplified and then applied to thefirst of three electronic switches, ESi toES3.

The electronic switches are controlled bythe rectangular voltage from the func-tion generator and provide half -wavesynchronous rectification of the alter-nating voltage.Since this type of rectification halves theaverage value of the input voltage, thepreceding amplifier raises the magnitudeof the a.c. component across 1, by afactor 2.The rectified voltage is applied to adigital voltmeter, DVM, which displaysthe value of L., in henrys.

Triangular currentIf the DVM has a full-scale deflection,f.s.d., of, say, 200 mV, the input to it

0

UL

0

RIR

u

Fig. 3. In a practical inductor, its internal re-sistance causes a deviation from the rec-tangular shape of the induced e.m.f. Theaverage value of this e.m.f. does not change,however.

EE

September 1988

4FunctionGenerator

A2, RI -t, A3

a5V

2s

S2

Integralor

C3

DVM

1:7830134-13

Fig. 4. The block diagram of the self-inductance meter.

when an inductance of 2 mH is beingmeasured on the lowest range, must be200 mV.In the following, it will be assumed thatthe maximum current, im, through theinductor is 20 mA (a reasonable valuefor inductors of 2 mH or smaller).Starting at one edge of the triangularcurrent,

di/dt =uL/L =200x 10-3/2 x10-3=100.

Since the current increases linearly,

imite=di/dt =100

so that,

to= 20x10-3/100=2 x10-4=200 ps,

where to is the duration of the edge. Thefrequency of the triangular current istherefore

f =1/2to=1/2x 2 x10-4=2500 Hz.

Circuit descriptionThe function generator consists of in-tegrator Al and Schmitt trigger IC1. Thefrequency of the generated signal is, ascalculated above, 2500 Hz.The Schmitt trigger provides a square -wave voltage that is used to control elec-tronic switches ES1 to ES3.Resistor R3 provides a DC offset to en-sure that the triangular voltage does notdrop below 0 V. This is necessary forgood control of the voltage -to -currentconverter.Circuit ICI is a Type 3130 opamp, whichis one of the few devices whose outputvoltage can really be driven positive andnegative. That output serves as referencevoltage for the following integrator.The output of Al is a triangular voltage,which varies between 4.9 V and 2 V. Thevoltage -to -current converter around A2and T1 transforms this voltage into acurrent that is passed through the induc-tor on test, L.

The value of the current, and thus themeasuring range, is determined by re-sistors R5 to R8. When the 2 H range isselected, the current is 20/10' =0.02 mA.Resistors R9 to R11 in parallel with Lxprovide some damping. This isnecessary, because the inductor is alsoshunted by various parasitic capaci-tances (connecting wires, internal ca-pacitance of the inductor, etc.) whichresults in an LC circuit. The high -impedance drive of this circuit (by apractically ideal current source) wouldcertainly give rise to oscillations in theabsence of some damping. The value ofthese resistors is chosen to ensure thatthey have a negligible effect on themeasurement. Note that when the 2 Hrange is selected, R14 serves as dampingelement.If an attempt is made to measure a smallinductance with a high range selected,e.g., a coil of 1.5 mH in the 2 H range,it may be that the value of the dampingresistor is too high, with the result thatoscillations may occur. It is, therefore,advisable always to start in the lowestrange and then switch to a higher rangeas required (shown by the absence of anoverflow indication on the DVM). This

Specification

Measuringraces 0.2-2 mH (resolution I pH)

2-20 mH (resolution 10 pH)20-200 mH (resolution 0.1 mH)

0.2-2 H (resolution 1 mH)

Internal resistance of coil for a measuring errorsmaller than 1% of full-scale deflectionRange 0.2-2 mH: 608

2-20 mH: 600R20-200 mH: 6 k

0.2-2 H: 60 k

Measuring frequency 2500 Hz

Accuracy Better than 2% off.s.d.

Current drawn About 20 mA

Fig. 5. The various waveforms in Fig. 4: L isthe voltage applied to the voltage -to -currentconverter, a falling edge indicates an increas-ing current.

method also ensures the highest possibleresolution.The overflow indication is provided bycomparator A4, which connects the in-put of the voltmeter to +5 V via ES4when too low a range has been selected.Opamp A3 raises the magnitude of themeasured alternating voltage by a factor2. Note that C2 at its non -inverting inputblocks any direct voltages. The offset ofthis opamp is compensated with the aidof Pl.The half -wave rectifier is formed by ES1and ES2, while ES3 serves to invert therectangular control pulses. During thepositive part of the measured alternatingvoltage, ES1 is closed and ES2 is open;during the negative part, ES1 is openand ES2 is closed. The resulting steadyvoltage is smoothed with the aid of RI9and C3 and converted into a readablequantity by IC7.The digital voltmeter consists of thewell-known Type 7106 IC and a 3digit LCD. The 7106 contains all that isnecessary for converting a steady voltageinto a digital quantity and displayingthis on the LCD. The decimal points ofthe display are provided by XORs NI toN3. Which decimal point is visibledepends on the position of switch S2c.LEDs D8 and D9 indicate whether thedisplay must be read in henrys ormillihenrys.The voltmeter is powered by two 9 -voltPP3 batteries and two voltage regu-lators. Note that the 7805 and 7905regulators provide better interferencesuppression than the smaller L types.

ConstructionThe meter, constructed on the PCBshown in Fig. 7, fits in a small, hand-held case.All resistors and diodes are mountedupright, except R1, R3, and R24. Elec-trolytic capacitors should be PCB types.Sockets should be used for the ICs.The display is best mounted on somestacked terminal boards so that it islocated just under the window in the en-closure.

SI

9V;

9V OIC

S

7805

C6

C7

220n

229

16V

9V

Ion

R3 0

R2 EE

O

IC1 7

CA

3130

5

4 100n

C8

C9

22p

10V

229

10V

IC6

7905

0

SV

5V

5V

5V9V

saa

00

RI EM

I17

.

R4 I. 1

%

3

C1 3

n3 Al

13

23

Rb

861

R7

HO E

1%11

%11

%

O SV

A2

T1

7

BC

5571

3

Al,

A2

= IC

2 =

TLC

272

A3,

A4

= IC

3 =

TLC

272

ES

1...E

54 =

1C4

= 4

066

N1.

..N4

= IC

8 =

407

0

R20

S2

1: 2

.000

mH

2: 2

0.00

mH

3: 2

00.0

mH

4; 2

.000

mll

1%

813 2

R12

FIO

RIO

811

0 S2b

5V

4

C14

A4

R21 SVC

5V *

PI

R17

2 0

10k R16

II=

1110

p1'

C2

10n

RI4

0 0

R15

A3 4

4

810

ES

1

3

5V

IC4

5V 5V

ES

41

13

Si

R19

ES

2

12

500k

2

31

SV

5V

IC8

R22

(arr

ay)

4.10

0k

04

15S

2c12

DS

rD

O

MIN

7x1N

4148

8T

95

181

LCD

10

LCD

3.0

DIG

IT

212

113

413

121

16

DP

3D

P2

DP

I

040

<IP

-a OF

37 0--

AC OP

39X 0

=cF

,ro

pap,

,a0o

,,0DPI

2P

3231

910

11

37 2

122

17

18 1

5 24

ID

C3

MK

T 1

0n30

O 5vE

S3

g

SV

29 3

027

18 2

3 25

26 1

3

13 1

4IL

rIX

(NI

In0.

ID I

LII

IrI0

I.)

al 4

Z O

IO

SC

23

1415

2425

23 2

217

1019

20 2

1

9 10

11

127

0 8

2 3

4 5

i;W

21)

l717

. W E

1;

IC7

7106

C R

EF

A/Z

DU

FF

INT

28

ffot

iLE

D

ffno

SLE

DR

27 CM

C

19 2

0

<+

RE

F H

I

RE

F L

O

CO

MM V

R26 P2

38 3 3

R25

4031

1

R23

O

3034

3329

2827

C10

C12

R24

,r,

C13

CD

.1t ri

min

7cio

o47

0722

0nM

KT

1%M

KT

100n

MK

T

* m

ulllt

urn

a

1%

5V 5

2500

1% C)s

v

vl

m m

co 3 0 so op

EE

September 1988

Parts list

Resistors:

F11;1115:R16=10 k 1%R2=33k2 1%R3;R7= 15 k 1%R4=100 k 1%R5=150R 1%R6=1k5 1%R8=150 k 1%R9;R21=2k2R10=22 kR11=220 kR12= 5k6R13;R17=10 MR14 = 2M2R18=3k3R19=560 kR20=10 kR22=array of 4-x100 k or four discrete 100 k

resistorsR23=100 kR24=47k5 1%R25=681R 1%R26= 22k1 1%R27= 1k5P1=10 k multiturn preset (e.g. Bourns Type3266)

P2 = 250R multiturn preset le.g. Bourns Type3266)

Capacitors:

C1 =3n3'C2;C3= 10 n*C4;C5= 100 nC6=220 nC7;C8;C9= 22 p; 16 V (radial)C10=100 pC11=100 nC12=470 n`C13=220 n'C14= 10 p

metallized polyester or metallizedpolycarbonate

Semiconductors:

D1 to D7= 1N4148D8;09 =LED 3 mm redT1 =BC557BIC1=CA31301C2;IC3=TLC272IC4=4066IC5=7805IC6=7905IC7=7106IC8=4070

Miscellaneous:

LCD = 3 YI-digit liquid crystal displayS1 =double -pole on -off switchS2=rotary switch, 4 -position, 3 -pole2 batteries, PP3 (9 V)2 spring action terminalsenclosure 155 x 92 x 33 aim (e.g. OWNA9409111)

PCB Type 880134

Fig. 7. The PCB for the self-inductance meter.

9

4-40

2,11

20_

2 0 C.H

2H

NOIJCTANCEMETER

Fig. 8. Prototype of the self-inductance Fig. 9. Design of a possible front panel formeter before it is fitted in the enclosure. the self-inductance meter.

R22 is an array of four 100 k resistors;this may be replaced by four discrete100 k resistors that are mounted uprightwith their upper terminals interconnec-ted.The LEDs are mounted at such a heightthat they are seated just under the frontpanel once the PCB has been installed inthe case.The rotary switch is soldered direct tothe PCB to make the best possible use ofthe available space and also to preventnoise and interference from connectingwires.The centre pin of IC5 and IC6 should bebent forward so that the pins form atriangle (just as with a standard transis-

tor). The ICs are mounted on the PCBwith their case just clear of the board:this means that the wider part of thepins also goes into the relevant hole,which allows for this. Where a very flatenclosure is used (possible), it may benecessary to carefully cut off the metaltops of IC5 an IC6.To secure the PCB, three holes must bedrilled in the case: the non -populatedboard may be used as a template.Switch Si is best mourned at one of thesides of the case, while the two batteriesmay be located at the underside of theenclosure (after the small mouldingshave been removed).Note that the mouldings on the lid

28 EESeptember 1988

should also be removed before the dis-play is mounted.The spring action terminals for connect-ing the inductor on test should be fittedat one of the sides of the enclosure asclose as possible to the relevant pins onthe PCB.

CalibrationAn inductor of between 1 and 1.8 mH.whose value is accurately known, is re-quired for the calibration. A cross -overfilter coil with an accuracy of better than3% may suffice, but some retailers canprovide an air -cored inductor of 1.5 mHwith an accuracy better than 1%.It is also possible to determine theinductance of an air coil of about1-1.5 mH accurately as follows. Con-nect it in parallel with a capacitor of47 nF or 100 nF (accuracy 1% or 2%)and connect this circuit via a series re-sistor of about 3.3 k to a frequency gen-erator. The resonance frequency of thecircuit is then determined with the aid ofan oscilloscope and a frequency meter.The self-inductance of the air coil is thencalculated from

Fig. 10. This small circuit may be added toensure automatic switch -off of the batteries.

L =1/(270=C [H].

Short-circuit the measuring terminalsand select the 20 mH range.Adjust P1 till the display read 0.000.Connect the reference coil to the measur-ing terminals and select the 2 mH range.Adjust P2 till the display reads the exactvalue of the reference coil.Since the accuracy and precision of theother ranges are determined by the toler-ance of resistors R5 to R8, this com-pletes the calibration.

Automatic switch -offThe meter draws about ±20 mA. A pairof batteries will have a fairly long life, aslong as they are always switched offwhen the meter is not in use.Forgetful users may find the circuit inFig. 10 ideal: this automatically switchesthe batteries off after about half a mi-nute. The meter is switched on again bypressing the reset button. This circuitmay be connected behind Sl or simplyreplace it altogether. The meter is thenalways switched on by pressing the resetbutton.

AUDIO & HI -Fl NEWS

Music -making control deviceSynthesizers, samplers, and similar elec-tronic sound sources can be controlled ina simple movement with a device devel-oped by Electronic Music Studios.Called 'EMS Soundbeam', the deviceuses an ultrasonic echo sounder to detectthe presence and range of any object thatenters the beam, and converts the infor-mation into musical instrument digitalinterface (MIDI) data to control the elec-tronic sound source.Full information from Electronic MusicStudios Trendeal Vean BarnLadock TRURO TR2 4NW Tele-phone +44 726 883265.

MOSFET amplifier kit fromMaplinA new 1 kW MOSFET Audio AmplifierKit, the equivalent of products selling at£800 to £900, is available from Maplin at

Lamm= 14/LIAJILILLIAILIA,Digisound SynthesizersAll the kits of the Digisound 80 ModularSynthesizer are available from TimHigham. The Digisound range will beexpanded in the near future with a new

polyphonic keyboard and a soundsampler.For a free copy of the relevant cataloguewrite to Tim Higham 16 LauristonRoad LONDON SW19 4TQ.

£193.00, excl. VAT.The amplifier is intended for use inhalls, auditoriums, or wherever the situ-ation demandslarge-scale audio amplifi-cation. Loudspeakers can be driven bythe amplifier at full power before protec-tion circuits come into effect. A built-inmonitor prevents the amplifier fromdelivering power continuously into ashort-circuit. This may occur, for in-stance, when the loudspeaker cables areinadvertently shorted, rendering themliable to overheat very quickly - andoften disastrously.Write or phone for your nearest Maplinshop or to:Maplin ElectronicsPO Box 3RAYLEIGH SS6 8LRTelephone (0702) 552911

Four times more music on aCDA new recording technique capable ofquadrupling the digital music datastored on a compact disc has beendeveloped at Queen's University, Belfast.The technique will make it possible, forinstance, to transmit high -quality musicsignals over the telephone network (sincethe signal bandwidth is reduced to 25%of that of current techniques). Anotherpossible application is the transmissionof high -quality music worldwide via sat-ellite (because the transmission rate is re-duced by a factor four compared withcurrent systems).

EE

S pt a be °88

MICROPHONE PREAMPLIFIERWITH ACTIVE FILTER

by S.G. Dir:nitriou

When a microphone is used a good distance away from anamplifier, its relatively small output signal is inevitably affected by

noise and attenuation caused by the cable.The simple, yet versatile, preamplifier/line driver described herecan be used with a variety of microphones, has a user -defined

frequency response, and prevents signal degradation because itsability to load long cables enables it to be installed near the

signal source.

Many types of modern audio equipmenthave a built-in microphone, or allow anexternal microphone to be attachedsemi -permanently. This is the generalcase with portable tape or cassetterecorders, video and movie cameras. Inspite of the apparent benefits of havinga built-in microphone, this will almostalways pick up mechanical noise fromthe to. Also, it is oflittle or no use when sounds from remotesources are to be recorded, as the level ofambient noise is bound to exceed that ofthe wanted sound.Obviously, reasonable signal-to-noiseratios and, therefore, good -quality recor-dings, can only be achieved when themicrophone - or microphones - is in-stalled relatively close to the source ofthe sound, but this arrangementnecessitates the use of a long coaxialcable between microphone and associ-ated equipment. With cable capacitancetypically of the order of 200 pF/m, up to100 m of coaxial cable with Z=600 Qmay be used without running into con-siderable attenuation of the upper partof the audio spectrum. In this case, thecut-off frequency, fe, becomes:

fc=1/(2nRC) [Hz]fc=1/(2/tx 600 x 20 x 10-9) [Hz]/1=13.263 kHz

In practice, however, the microphone im-pedance often rises with frequency, sothat the cable must be kept shorter toprevent bandwidth reduction. In anycase, it is not a very good idea to havethe small microphone signal travelthrough any appreciable length of cable,as this will cause degradation of thesignal-to-noise ratio.A better method is to amplify the signallocally, i.e., as close as possible to the

-

microphone, and drive the coaxial lineby means of an amplifier with low out-put impedance. In this way, the wantedsignal on the line is too strong to be af-fected by noise or capacitive loading.The signal amplitude can be reducedfairly easily at the receiver end with theaid of a two -resistor voltage divider(Fig. 1), in which

R2.-- 0.9A RI

Fig. 1. A line driver with attenuator to over-come microphone signal degradation in along coaxial cable.

29

where A is the amplification of the linedriver, and Ri=100 Q (typical value).

Bandwidth and filteringThe line driver is readily modified to op-erate as an active filter that can help toimprove the signal-to-noise ratio of thesound picked up by the microphone.This is particularly useful in applicationsinvolving the recording of speechsignals. From acoustic engineering it isknown that the frequency spectrum ofspeech has relatively large redundantparts. The dynamic and spectrum -related characteristics of speech havebeen widely studied, but a further dis-cussion of this interesting field is, unfor-tunately, beyond the scope of this article.Here, it is sufficient to say that a simpleWien -type bandpass filter can aid inshaping the spectrum such that speechbecomes more intelligible due to theelimination of redundant signals and agood deal of ambient noise. In this way,the signal-to-noise ratio of the soundpicked up by the microphone issignificantly improved.The response of the standard, passive,Wien filter is fairly smooth (Fig. 2),making it suitable for use with musicsignals without unduly affecting theoriginal sound.

Practical circuitThe preamplifier/active filter proprosedhere is mainly intended for use with low -impedance dynamic or electretmicrophones. Electret microphones of-fer a wide frequency response, supply arelatively large output signal, and are ofsmall size. They do have the disadvan-tage of requiring a biasing voltage, butthis is no problem here as a supply is re-

30 EESeptember 1988

quired anyway for the line driver.With reference to the circuit diagram ofFig. 3, the line driver is built aroundlow -noise operational amplifier ICI,which is configured to work as an invert-ing active Wien filter. With the valuesshown for RI, R2, CI and C2, the centrefrequency of the filter will be 3.3 kHznominally:

fo=159,155/(R ICI)

with RI in kilo -ohms and CI in nano -farads. Related to the acoustic behaviourof the human ear, and with reference tothe audible threshold curves set up byFletcher and Munson "), 3.3 kHz cor-responds to the point of maximum sensi-tivity. The filter suppresses both low fre-quencies (whose reverberant nature tendsto impair intelligibility of speech) andfrequencies above 10 kHz, which can beconsidered as noise in the context of thespectral redundancy of speech.The voltage amplification, 4 , of the linedriver is about 10 at the passband centrefrequency, and the value of the gain- andfrequency- determining components iscalculated from

RI=2A R2 and C2=24C1

Components Cs and R5 ensure DCblocking at the output and phasestabilization respectively. The latterfunction is required to isolate thedistributed capacitance of the coaxialcable from the feedback network ofICI, thus preventing parasitic high -frequency oscillation. Evidently, thevalue of R3 should be kept as low aspossible, because otherwise the benefitof the low output impedance of ICI (asseen from the line) is lost. The resistormay be omitted if the LF356 is replacedwith a (less expensive) 741, but this, un-fortunately, increases the output noiselevel.Potential divider R3 -R4 biases the non -inverting input of ICI at half the supplyvoltage. LED Di is the power indicator.It is connected in series with the rest ofthe circuit to minimize the total currentdrain from the 9 V (PP3) battery. In thisway, the preamplifier draws only4.5 mA, which is still sufficient to lighta LED with good efficiency. Owing tothe drop across Di, the preamplifierworks from a supply voltage of 7 to7.5 V.

Microphone and supplyoptionsThe basic circuit diagram of Fig. 3shows a 3 -terminal electret microphone.This will typically have an output im-pedance of 500 4 or less, which is lowwith respect to the value of R2, so thatthe microphone has very little effect onthe centre frequency of the active filter.Where a 2 -terminal electret microphone

2. I IIIF3 I I I WIEN FLTER=t FREQUENCY RESPONSE CURVE4 I I I l I le1 Qd8 relative frequency points

04=F1.9 LOW : 0.3 fo HIGH : 3.3333 to

Iic' IH, L=11.11O

%0

aop 1. =0.32967 ,

90

so 2I

70 -3

-460

-sSO 6If -7

a,40 /9i

-1030 / ,1 -12

Bandpass fines I t20-16

1111-la