THE MAGAZINE FOR THE RADIO & ELECTRONICS EXPERIMENTALIST

July/August 1990 £2.95

36 -PAGE St PPLEMENT OFFERING A VARIETYOF SMALL CONSTRUCTION PROJECTS

Battery testerSound demodulator bar SAT TV receiversSquare -wave generatorTTL-level 100 MHz quartz oscillatorSCART-plug FM mini senderVersatile NiCd battery charger

or as e !very e ep oneyour order on 081-205 9558using VISA/Access Card

art TECHNOMATICAll prices ex VAT.Prices are subject tochange without notice.

Orders welcome fromgovernment depts &educational establishments

Techno House 468 Church Lane. London NW9 8UF.Tel: 081-205 9558 Fax: 081-205 0190

MonFri: 9.15-5.30. Sat: 10.30-4.00

rchirriedes COMPUTERS

A3000 (no monitor)A3000 Acorn ColourA410/1 (no monitor)A410/1 Acorn ColourA410/1 Taxan 775'Acorn 420/1 systems420/1 (no monitor)420/1 Acorn Colour

Acorn 440/1 systems440/1 Acorn Colour440/1 Taxan 775'Techno 410 1 systemsupgraded to 420 1 spec.Acorn Colour systemTaxan 770- system

vouchers do nor apply to Taxan systems

Carriage £8/computer E12/s3 stem

£599£799

£1099£1299£1385

£1499£1699

£2299£2284

£1459£1699

SPECIAL FINANCIAL DEALComputers alone or complete systems can bepurchased over 9 months. The deposit will bepayable with the order followed by 9 monthlypayments. Please phone or write for full detailsand a personal quotation. Subject to status. weshould be able to despatch your order within 7days of receivina your order

100o VOUCHER ON CASH &CREDIT CARD SALES

Cash and credit card purchasers of Archimedescomputers and complete systems will receive avoucher to the value of 10clb of the purchaseprice when purchased at the prices shownabove. Vouchers will be valid for 90 days fromthe date of issue. Vouchers are not available onTechno bundled packages.

Please add carriage(a) £8.00 (Courier, 2 days)(b) £3.50 (c) £2.00 (d) £1.50Next day delivery atextra charge

What we offer in addition to efficientsales service and professional backup!We not only offer professional advice when you are purchasing your systembut we will also provide friendly assistance afterwards. All our products carrya 12 month full ...,arranty for parts and labour.

TECHNO 410/1 SPECIALOffer extended due to popular demand.Archimedes 410 1 upgraded to full440 1 specification with 4 MB RAM

and 50 MB Hard Disc (Acorn)plus

Taxan 770- Multisync Monitorand including Pipedream 3 and

Atelier as well asRISC OS Extras & SID Utilities

discs, a packet of discs, a printerlead and a mouse mat.

for only £1999 carr £12

TECHNO 410/40 UPGRADESA410/1 upgraded to 4 MB RAM and 40 MBHard Drive complete with Mouse Mat. 1box of 3.5" discs, printer lead and FirstWord Plus Release 2.Now with the Atelier art package & RISC OSExtras & SID Utilities discsOur 40 MB Hard Drive is a high spec. AutoPark.25ms. quality drive with a reliable Toshibamechanism.

techno 410/40 with Acorn Colour Monitor£1699

techno 410/40 with Taxan 770- £1899Finance available on chargeable bas s

technoTabletThe latest model of the Genius GT1212A PC tablet adapted for use with Archimedescomputers offers a resolution of 1000 lines/in over a 12" x 12" working area and connectsthrough the serial port of the computer.The Tablet is operated by moving a four button puck controller over the special surfaceand a two button stylus with switched tip is also available.The software to drive the tablet is supplied as a module to operate within the RISC OSdesktop environment. Once loaded. several commands are available to control the tablet:

turn the tablet on or offselect relative or absolute coordinates etc.change puck movement sensitivity

Three of the puck buttons act as standard mouse buttons and the fourth allows specialoperations such as changing the size of the tablet work area.

The tablet can virtually take over all the functions of a mouse making the use of graphicspackages much simpler. The puck has a set of cross -wires which allow simple andaccurate transfer of technical drawings. The optional stylus will make tracings. linedrawings etc much easier and more accurate.

The standard Archimedes mouse or a Tracker Ball can be left connecfed and can evenbe used as alternatives for some operations.The package includes the tablet. puck. software and mains power supply.

GT1212A Tablet £259(a) PC mouse drivers andOptional Stylus £35(d) and Art package £12(c)

TECHNO DTP PACKAGEArchimedes 410 1 Colour System

upgraded to full 420 1spec with 2 Mb RAM and 20 Mb

Hard disc featuring ourtechnoSCAN package and

RISC OS Extras & SID Utilitiesdiscs and the Atelier art package

and either

Acorn DTP PackageFirst Word Plus Rel 2,

Logistixor

Impression and Pipedream 3and a free mouse mat

for only £1 777 carr £12Finance available on chargeable basis.Special Educational Subsidy on

the Techno DTP package.

R140 UNIX SYSTEMLimited Period Offer

R140 Base Systemwith

Taxan 770- and PC Emulatoror

Viking IIplus

Ethernet Card andAdministrators Guide

for only

£3000and it also includes on -site

maintenance contract.

A3000 LEARNINGCURVE PACKAGE

with 1MB ACORN A3000Tutorial Video

GENESIS DatabasePC Emulator

FIRST WORD PLUSWordprocessor

the parents guide to the nationalcurriculum

A3000 LEARNING CURVE

£999Suitable monitor available

separately

TEL: 081-205 9558

tt CONTENTS

July/August 1990Volume 16Number 180

In our next issue:

S -VHS RGB converter

36 -PAGE SUPPLEMENT OF CONSTRUCTION PROJECTSbetween pages 38 and 39

- i ill""High -current Hfetester LEADER rILight -dimming robot 11 Computers take over in the car

I

Mixer -amplifierIsolation amplifier COMPUTERS & MICROPROCESSORS

_ -, I

Inter IC communications r, The 8031/8731 microcontroller ILF-HF test probe by Dr David K yteAC motor control 37 PROJECT: Daylight -resistant opto-isolator

Science & technology

Front cover52 DESIGN NOTES p. 49

Information about 'The 'Times

Atlas of the World' is among

more than one million authorita-

ELECTROPHONICSi PROJECT: MIDI master keyboard -Part2 ..0.).,,L6,ti

tive records now stored on CD- by D. DoepferROM for use by professional

librarians all over the world. GENERAL INTEREST \\A \ \ \ \ \The British Library's National 16 PROJECT: Glow plug switch for 4 -stroke modelBibliographic Service has placed

comprehensive details of fiction

and non-fiction books published

rnin Britain since 1950 on the co-

pact disc system.

As the British National Bibliogra-

1S

enginesby A. PeperkampDecoupling power rails

4' 8 PROJECT: Door chime/alarm sirenby T. Giffard

i or -r 1-

phy (BNB) on CD-ROM is 56 In quest of a pangram Compact 10-A power supplyexpected to be of interest to the by Lee C.F. Sallows p. 19:-._:, c. academic and industrial

oraries of many countries, the

user interface can be switched

between English, Frenc- Ger-

man or Italian.

The system employs the same

INTERMEDUTE PROJECTS43 Versatile NiCd battery charger45 Reversing car alarm46 Electronic siren ... -

easy -to -use software as the 47 Simple square -wave generatorws#

-,,,, . -

British Library General Cate- 47 Simple effective car theft deterrent.. ,,.

1

a,.

loge of Printed Books to 1975,databases of the Biblitheque

Nationale of France, the

POWER SUPPLIES & BATTERY CHARGERS

14 PROJECT: Battery tester - an ELV design

44 '.,... ,--.,,.

...

Deutsche Bibliothek of West 19 PROJECT: Compact 10 A power supplyGermany and the Library of by G. Boddington 100 MHz TTL-compatibleCongress, USA. oscillator - p. 18!ri the background of the photo-

graph is the beautiful and his-RADIO & TELEVISION

:oric Reading Room at the

British Library in London, which

s the site for research by peoplefrom all over the world.

18 PROJECT: 100by J. Bareforct

24 INMARSAT's Standardby B. Higgins

MHz TTL-compatible

C

oscillator

33 PROJECT: Mini FM transmitter - !..P' PvThe British Library by J. BarefordBibliographic Services

2 Sheraton Street39 PROJECT: Sound demodulator for satellite TV

receiversLONDON W1V 4BH by R.G. Krijgsman '.t 1-i-1Telephone 081 323 7255 --Facsimile:081 323 7039 49 SCIENCE & TECHNOLOGY -..f.--rif

4

MISCELLANEOUS INFORMATION____Iila 4aili

---,.z.-4-,---- i,, : 41 41...

. -Electronics scene 12; New books 32; Events 61:Letters 62; Switchboard 62; Readers services 63: Terms 64:Buyers guide 74: Index of advertisers 74

The 8031 8731 microcontrollerp. 36

ELEKTOR ELECTRONICS KU /at; GUST 1990

4Please mention ELEKTOR ELECTRONICS when contacting advertisers

CLASS A AUDIO POWER AMPLIFIERS.3 COMPLETE SUPERMOS KITS NOW AVAILABLE (complete down to the very last nut & bolt)

Move up to a better class of HiFi. build your ownultra high fidelity audio power amplifier with ourFULL kits. Based on tried and tested Supermostechnology. we now offer a choice of 3 FULL kitsranging from 90Wichannel pure class A stereoamp to an earth shattering 500W ch Supermos2based system.

The Supermosli2 modules are now recognisedworldwide for their unequalled technicalexcellence combined with the very bestaudiophile quality components. Our completekits cost around 1 8 that of commercial esotericand very overpriced HIFI's such as Krell,Threshold. Musical Fidelity. Naim etc. whilstoffering substantially better performance. Thuswe now bring esoteric classA amplification withinthe budaet of the average HiFi enthusiast.

Our new kits are simple to assembledue to the use of a ready built and testedmodular approach eliminating thevariable performance otherwiseassociated with homemade kit HiFi's.

What Do You Get- ?Compared to commercial amplifiers costing manytimes more. there are few amplifiers that canoffer ANY of these features at any price! TheSAGE SUPERMOS2 kits offer ALL thesefeatures. and much much more.

Pure Class A operation into any speaker load withoutspurious switching to class B. Industries lowest everdistortion 0 1ppm. Industries highest ever slewrateof 685t1Us essential for digital audio. extremely lowfeedback factor. superb damping factor.unconditionally stable. total independence of PSUripple. DC restoration. stabilised supplies.

Kit I Complete stereo 90W chincludes the following- 2xSupermoslmodules. total 40.000uF capacitors.2x35amp bridges rectifiers. 2xDC protectionmodules. 1xtransformer softstart unit.1x400VA toroid. 1xblack textured finishedcase 280xx190x90mm. 1x hardware packcontaining all input output plugs sockets.

clips. fuses, cable ties. assemblyinstructions etc. Total component price £328full kit price just £299 p&p £6 (UK).

Kit 2 As above but monoblockconstruction yielding over 100W ch. twoKIT 2's are required for stereo price of totalcomponents is £201. FULL kit price £180p&p £6 each.

Kit 3 Top of the range. Supermos2based stereo kit complete as kit 1 exceptwithout toroids and includes a total88.000uF capacitance. Power output user

defined by transformer rating power outputsfrom 100W to 500W. total component costis £483 kit price just £430 p&p £9

In addition. all kits come with a £30discount voucher off the purchase of aDigitrap2 compact disc digital noisefilter, normal price £62.

To order direct please send a cheque payable to SAGE AUDIO and send to the address below.To obtain more information on these and all our products please send a large SAE together with

£2 coins (Overseas pIease send 6 International reply coupons) to SAGE AUDIO,

Construction House, Bingley, W' Yorks BD16 4JH England.

EPROM ERASERWIPEOUT!

Just DCP oriis P&P & VATPerfect condition erasers hold up to 40 EPROMS.Ideal for home use and in development labs.

We must sell 100 of these to makeway for a new model.

Send Cheque with order or telephone with credit carddetails. 1st come 1st served.

We also have available: -A wide range of components. Cross Assemblers.EPROM Programmers and Microprocessor basedcontrol cards.

Call us today for more details and your freecopy of our catalogue on v,di(035 388) 325 or 455 LAIVIA

Ai&J. P. istribution.

The Old School. Prickwillow. Ely. Cambs. CB7 4UN

ft Happy Memories4116 150ns only pulls £1.00 2716 450ns 5 Volt £3.204164 100ns 64K x 1 £1.25 2532 450ns Only pulls £3.5041256 100ns 256K x 1 £2.25 2732 450ns £2.1541464 100ns 64K x 4 £2.75 2764 250ns £2.1544256 100ns 256K x 4 £7.50 27128 250ns £2.2541000 100ns 1024K x 1 £6.95 27256 250ns £2.456116 150ns Low power £1.45 27C256250ns £2.456264 100ns Low power £2.45 27512 250ns £4.7562256 100ns Low power £5.95 27C512250ns £4.75SIMMS 100ns 1 Meg x 9 £75.00 and 8Ons £79.00

Please call for prices of other chips. Same chips but different speecs.quantity discounts etc. Second (pulled) chips available for many of theabove devices at substantially lower cost. Call for availability and price

of these and other items.

Low profile IC sockets: Pins 8 14 16 18 20 24 28 40Pence 5 9 10 11 12 15 17 24

We always have a large quantity of surplus computer equipmentfor sale; printers. disk -drives, add-on boards, monitors etc:Please ask for our surplus equipment list or call with your

requirements as new items are added so frequentlythe list is never up to date !

'ease add 50p post & packing to orders under £15. VAT to be addedtotal. Access orders by 'phone or mail welcome. PLC. government &Educational orders welcome for minimum invoice value of £15 net.

HAPPY MEMORIES (EL), FREEPOST,Kington, Herefordshire. HR5 3BR.Tel: (054 422) 618 Sales, 628 fax MEM

VISA(no stamp needed unless first-class required) 111.

LLEKTOR ELECTRONICS JULY AUGLST 1990

Produced and published by ELEKTORELECTRONICS (Publishing)

COMPUTERS TAKE OVER IN THE CAREditor/publisher: Len SeymourTechnical Editor: J. SuitingEditorial Offices:Down HouseBroomhill RoadLONDON SW18 4J0EnglandTelephone: 081-877 1688 (National)or -44 81877 1688 (International)Telex: 917003 (LPC 0)Fax: 051-874 9153 (National)or -44 81874 9153 (International)Advertising: PRB Limited3 Wolseley TerraceCHELTENHAM GL50 1THTelephone: (0242) 510760Fax: (0242) 226626European Offices:Postbus 756190 AB BEEKThe NetherlandsTelephone: +31 4490 89444Telex: 56617 (elekt nI)Fax: +31 4490 70161Managing Director: M.M.J. Landman

Overseas editions:FEDERAL GERMANYElektor Verlag GmoHaisterfeld &ratite 255100 AachenEditor: E.J.A. KrempelsauerFRANCEElektor sariRoute Nationale: Le SeauB.P. 53; 59270 BailleulEditors: D.R.S. MeyerG.C.P. RaedersdorfGREECEElektor EPEKariskaki 1416673 Voula - AthenaEditor: E. XanthoulisINDIAElektor Electronics PVT LtdChhotani Building52C, Proctor Road. Grant Road (E)Bombay 400 007Editor: Surendra lyerNETHERLANDSElektuur ByPeter Treckpoelstraat 2-46191 VK BeekEditor: P.E.L. KersemakersPAKISTANElectro-shop35 Naseem PlazaLasbella ChavricKarachi 5Editor: Zain AhmedPORTUGALFerreira & Sento Lda.R.D. Esterani, 32-V1000 LisboaEditor: Jeremias SequeiraSWEDENElectronic Press ABBox 550514105 HuddingeEditor: Bill Cedrum

Distribution:SEYMOUR1270 London RoadLONDON SW16 4DH

Printed in the Netherlands by NOB.Zoetenvoude

Copyright i; 1990 Elektuur BV

ABC

Motorists may not normally be thought ofas computer operators. yet the inescapablefact is that the electronics and micorchipsof the computer age are now becoming in-volved in virtually every aspect of moderncars, from engine control to braking.

There are even suspension systems inwhich a computer takes the place ofsprings, while electronics are increasinglypart of in -car entertainment and mobilecommunication systems.

In Britain, road and traffic experts arealready well on the way to developing apractical computer -based system that willserve as both an aid to car navigation anda means of avoiding traffic congestion.

The latest Jaguar XJ6, for instance, hasno fewer than seven computers that lookafter the engine, suspension and brakes,cruise control and the vehicle's sophisti-cated air-conditioning system.

Many of the latest car engines haveelectronic management systems that bringhigher levels of efficiency and economy.Typical of recent advances is the ModularEngine Nlanagemat System-MEMS-de-signed and developed by the RoverGroup. This controls functions such asfuel injection, emissions and spark timingfrom a single microchip unit.

Totally interlinked systems

NlEMS has its own 8 kbyte memory andalso helps in servicing the engine, as themicroprocessor can signal any developingfaults.

Paul Ryder. head of engine manage-ment at Lucas Components, one ofBritain's leading electronic car systemmakers, recently predicted cars in die nearfuture with interlinked electronic systemsin which chassis, engine and brake con-trollers would share the information fromtheir various sensors to manage the car asa whole.

A new £10 million research centre setup by Ford in Britain houses Europe'smost modern test equipment for automa-tive electronic systems. including themost advanced spark plug laboratory andthe largest anechoic chamber for researchinto in -car audio entertainment systems.

Sensors and electronic engine manage-ment systems such as Ford's EEC IV aretested there, while the anechoic facil-ity-a chamber designed to be free fromall echoes and sound reflections-is usedto perfect audio equipment.

The centre is also working v. ith inter-national broadcasting authorities on radio

data systems that avoid the need to retunemanually to the strongest signal in differ-ent areas. These systems also allowdrivers to be given traffic information au-tomatically for their location.

Used by the champion

Sports car manufacturer Lotus is perhapsthe best-known developer of active, orcomputerized. suspension systems. NigelMansell drove a Lotus 92 racing car fittedwith this type of suspension in GrandsPrix as long ago as 1983.

Lotus systems use microprocessor -con-trolled hydraulic rams powered by the en-gine to control the wheels' path overbumps. as well as chassis braking, corner-ing and pitching of the car body.

So far no mass production car has yetbeen made with this type of sophisticatedcomputerized suspension. However.Rolls-Royce, traditionally among themost conservative of designers, recentlyintroduced a microchip -controlled auto-matic ride control system said to be un-equalled.

In this, the stiffness of the suspensionadapts in only 1/100th of a second tochanges in road conditions and selects theappropriate 'comfort', 'normal' or 'hard'setting automatically. To do so, it uses amicroprocessor and sensors that continu-ously monitor acceleration, road surfacecondition, braking and steering changes.

A new era of computer -aided vehiclenavigation seems to be just around thecorner. Drivers in London, for instance,will by 1993 have access to a an advancedguidance system that promises to cutdown both journey times and driver fa-tigue.

The GEC Autoguide system has beenchosen for a government -sponsored pilotscheme that will be operational in centralareas of the city next year. It will providethe driver with up -to -the minute direc-tions for the best route to a chosen desti-nation by a dashboard -mounted displayand audible instructions.

The heart of this system is a centralcomputer that notes current journey timeson each route. continuously updates cal-culation of preferred routes, and broad-casts instructions to drivers from roadsidebeacons using an infra -red beam.

Later, it may even be able to adviseabout the availability of parking space ina chosen area. Urban motoring will justnot be the same again.

ELEKTOR ELECTRONICS JULY/AUGUST 1990

RADIOCOMMUNICATIONSEXECUTIVE AGENCY

The Radio Communications Division ofthe Department of Trade and Industry hasbecome the Radiocommunications Agencyas one of the government's 'Next Steps'Executive Agencies.

The creation of Next Step ExecutiveAgencies within Government is part of theNext Steps Initiative launched by theprime minister in February 1988. They aredesigned to bring about lasting improve-ments in the quality and efficiency of gov-ernment services to the benefit of cus-tomers and texpayers.

There will not be a lot of immediatedifference between the old Radiocommu-nications Division and the new Radiocom-munications Agency, but over time thechange will be substantial. According tothe chief executive of the new agency, "wewill be working hard to face the chal-lenges of the 1990s and to build on theprogress achieved by the Radiocommuni-cations Division in recent years. In partic-ular, Agency status will give us an addi-tional incentive to provide an improved,effective, quality service to radio usersthroughout the country."

TEST SET FOR DIGITALTELEPHONE NETWORKS

A low-cost, easy -to -use error -performancetester for digital telephone networks oper-ating between 2 and 140 Mbit/s has beenintroduced by Uplec Industries.

Designed to comply with the specifica-tion for British Telecom's 414A tester, theType 4301 Test Set will be useful to allerrs using ccirr telecom standards andother providers of telecommunicationsnetworks. It has been officially approvedby British Telecom.

Operating at 2.048, 8.448, 34.368 and139.264 Mbit/s over 75-0 lines and2.048 Mbit/s over 120-f/ balanced lines,the 4301 generates a pseudo -random bit

sequence to ccrrr Standard 0.151 and a16 -bit programmable word pattern to mon-itor the error performance of digital tele-com networks.

Intended for field operation, the 4301weighs under 10 kg and can operate from200-250 V 50-60 Hz supplies. An internalNiCd battery maintains settings and datafor up to 30 days.

Uplec Industries Ltd, Oakhurst Hall,Oakhurst Road, OSWESTRY SY10 7BZ.Telephone (0691) 650422; Fax (0691)658553.

ABERDEEN ENGINEERINGSTUDENTS WIN PLACE ON

NASA SHUTTLEEngineering students from Robert Gor-don's Institute of Technology in Aberdeenwere given a boost recently when theylearned that their project to test thestrength of gravitational fields at altitudewould be sent into orbit on board a NASAspace shuttle next year.

The group had competed against twoother teams from Nottingham and HatfieldPolytechnics in the national final of theSpace Shuttle Competition organized bythe Institution of Electrical Engineers andBritish Sugar.

The nationwide competition waslaunched in 1988 to give engineering stu-dents the opportunity to design and build asmall self-contained payload to be carriedon NASA'S Space Shuttle 4060. Space onthe shuttle (a 'Getaway Special') wasbought from NASA by British Sugar anddonated to the Institution.

The winning team now have one yearto build their project ready for launchlate next year. Financial and practicalsupport will be given by British Sugarand local industry.

BBC's TIME SIGNALEarlier this year, the BBC assumed re-sponsibility for the generation of the 'sixpips' time signal. The pips had since 5February 1924 been generated at 15 -minute intervals by the Royal Green-wich Observatory.

The new Time and Frequency systemhas been designed to provide accuratetime and frequency signals to users inthe BBC Network Radio and other BBCareas as required.

The Time Standard uses three off -airradio receivers in a triple redundancyformat. Two of these derive time/dateinformation from Global PositioningSystem-cPs-satellites, while the thirdis a low -frequency receiver capable ofreceiving MSF at Rugby or DCF at Mann-flingen in Germany. Time and date in-formation from all three receivers is pro-cessed via a specially designed 'TimeVoting Switch' which ensures that therest of the system receives accuratetime/date information, even if off -air re-ception is lost for a period.

The Frequency Standard has two ru-bidium atomic oscillators in dual redun-dancy configuration. Each oscillator ismounted in a GPS receiver and any driftis automatically compensated by off -airGPS signals, thus avoiding the need ofregular calibration of these units. The re-sulting accuracy and stability of the fre-quency standard is half -way between aconventional rubidium system and acaesium system, and as such this systemcan act as the primary timing level in adigital transmission system.

BBC Engineering Information,Broadcasting House, LONDON W1A1AA. Telephone 081 927 5432.

01-5.5 GHZ PLASTIC -PACKAGEDSILICON MMIC

9

Avantek has now available a plastic -packaged version of its highest -fre-quency monAmPTm silicon monolithic lcamplifier. Designated MSA-0986, themmrc amplifier provides 7.2 dB gainwith ±0.5 dB gain flatness from 01 GHzto 3.0 GHz, and a 3 dB bandwidth oftypically 0.1 GHz to 5.5 GHz. At 2 GHzthe unit provides +10.5 dBm outputpower, a noise figure of 6.2 dB, typi-cally 1.6:1 input and 1.8:1 output vswit(0.1-3.0 GHz) and is unconditionallystable.

Avantek Inc., 481 Cottonwood Drive,IvilLPTI'AS, Ca 95035-7492, or, in UK:Wave Devices, Laser House, 132-140Goswell Road, LONDON EC1V 7LE.

ELEKTOR ELECTRONICSK1N/AUGUST 1990

UNIVERSAL COMPUTER/PRINTERBUFFER

Micro Control Systems has developed acomputer memory unit that provides aprinter buffer with two inputs and two out-puts. The advantages of the `X Buffer' in-clude the ability to connect any computerwith a serial or parallel output to anyprinter with a serial or parallel input-equipment that would otherwise be in-compatible. The buffer memory starts at64 kbytes and can be expanded with plug-in modules up to 4096 kbytes, big enoughto store a very long document or even awhole book (over half a million words).

Micro Control Systems Ltd, ElectronHouse, Bridge Street, SANDIACRENGIO 5BA.

DUXFORD RADIO SOCIETYThe Duxford Radio Society was formed in1986. It saw its beginnings during the pre-vious two years when former members ofthe Special Forces Signal Section operateda radio station from Duxford to celebratethe 40th anniversaries of D Day and VEDay in 1984 and 1985 respectively.

LONDON

The association between the societyand the Imperial War Museum was put ona firm footing when in September 1986the society's call sign GB2IWM was regis-tered at the Home Ofice. Since then, regu-lar exhibitions of communications equip-ment relating to particular themes havebeen held at Duxford on special eventdays. The radios and associated items ondisplay are from both the Imperial WarMuseum's communications collection andmembers of the Radio Society.

The society is not an Amateur RadioClub, but aims to combine amateur radiowith interest in radio history and to offer

OA] r;',11

some expertise in the documentation,restoration and operation of historic mili-tary and clandestine radio gear.

Duxford Radio Society, Duxford Air-field, CAMBRIDGE CB2 4QR. Tele-phone (0223) 833963.

NEW DEVELOPMENTS INTRANSFORMER TECHNOLOGY

At present, the majority of condition mon-itoring techniques for transformers rely onthe detection of a fault. Provided the faultevolves relatively slowly, the consequen-tial effects can be minimized.

Progressing a stage further, ERA Tech-nology is developing Frequency DomainMeasuring-Fiat-techniques capable ofdetecting a weakness, rather than a fault,within the transformer. The types of weak-ness that the techniques will uncover, forinstance, winding displacement or slack-ness, often remain undetected and can leadto catastrophic failure and unplanned out-age if they ate not treated. Winding slack-ness in particular can be removed and fur-ther damage prevented.

The techniques being developed workby identifying and tracking resonantmodes exhibited by any electrical wind-ing. It is generally recognized that the res-onant behaviour of a winding is stronglyinfluenced by changes in the relative posi-tion of winding conductors or, indeed, therelative position of the windings. The pre-sent development makes use of a swept si-nusoidal source to excite winding reso-nances.

Experimental work at ERA has alreadyproved that FDM techniques can identifycertain specific forms of winding distor-tion. These include extreme winding col-lapse, axial displacement between concen-tric windings and winding slackness.

Two forms of Film test instrumentationare also being developed b y ERA. Thefirst of these, static FDM testing, involvesan assessment of the windings in their`rest' or static positions. Developmentwork to date allows a number of windingfaults and displacement disorders to be de-termined from typical test data.

Work is also being carried out on dy-namic FDM testing-that is, the process oftracking dynamically the movement ofconductors. ERA's objective is to developinstrumentation that will provide a mea-surement of winding slackness. A tech-nique capable of dynamically tracking

winding vibration is currently being evalu-ated and ERA hopes ultimately to apply itto on-line monitoring.

ERA Technology Ltd, Cleeve Road,LEATHERHEAD KT22 7SA. Telephone(0372) 374151.

UL RECOGNITION FOR SILICONIXPOWER TRANSISTOR MODULES

Siliconix's Type SPMB50A500 and TypeSPMF50A500, a range of 500 V, 50 A ISO -POWER transistor modules, have UL statusas recognized components under SectionQQQX2-Component Power SwitchingSemiconductors.

UL recognition means that the modu-lates have been 100% tested to ensure thatthey conform to UL safety standards for2500 V insulation and flammability intough industrial applications.

The modules allow the construction ofmotor controls and power supplies withoutthe need to parallel discrete transistors.They will operate directly from 240 Vpower lines, thus reducing parts count,size and weight of power conversionequipment.

Siliconix Ltd, Weir House, OverbridgeSquare, Hambridge Lane, NEWBURYRG14 5UX. Telephone (0635) 30905.

ADD-ON MODULE FORSATELLITE TV RECEPTION

An add-on unit is claimed to save TVviewers about £200 on the cost of satelliteTV. The unit, about 100x75x25 mm, con-verts existing TV receivers and videorecorders so that they can be used to watchand record the new satellite channels aswell as the terrestrial broadcasts. Viewersstill need a dish, but will no longer have tobuy or rent a separate set -top converter.

The unit, developed by Zeta Services,allows viewers to do what most convertersdo not: watch one satellite channel whilerecording another-most current set -topconverters can pick up only one channel ata time.

The Zeta module uses the spare tuningcapacity built into most modern TV setsand VCRS. Many of these can be set to tuneinto up to 99 channels. The unit leavesplenty of space for the current and plannedterrestrial channels, but mere the remainderof the tuning capacity for existing and fu-ture satellite channels.Zeta Services Ltd, Harden Park, ALDER -LEY EDGE SK9 7QN. Telephone (0625)583850; Fax (0625) 585282.

ELEKTOR ELECTRONICS JULY. AUGUST 1990

BATTERY TESTER

This compact tester,designed and marketedas a kit by ELV, has three

LEDs that indicate thecondition of

alkali -manganese,carbon -zinc, and

alkali -zinc primarybatteries of the mignon,

mono, baby orpower -block type.

The growing mass of battery -poweredequipment brings with it the need of quickbattery condition testing. The battery tes-ter described here helps you to preventgetting stuck, at crucial moments, with aflat battery or battery pack in, for instance,a cassette recorder, a torch, a remote con-trol unit or a personal radio.

The tester is simple to use: the primarybattery to be tested is connected by twotest clips and flexible wires. Three LEDswith different colours immediately indi-cate whether the battery is as good as new('full'; green LED), usable (yellow LED),or exhausted ('empty'; red LED).

The tester is automatically actuatedwhen a battery is connected to the testleads. This does not work, however, whenthe battery is completely exhausted.When this is suspected, the TEST button

lAger, Bab, Yana V b.%OM O aswR 4GF ZA

all Battery Tester

must be pressed to prove to the user thatthe battery is really exhausted, or that theinternal 9-V battery of the tester itself isflat. When the red LED lights in this con-dition, the battery under test is completelyempty.

Circuit descriptionThe circuit diagram of the battery tester isgiven in Fig. 1. The circuit is powered bya 9-\' (PP3) battery. of which the _termi-nal is connected to PCB terminal ST3, andthe -terminal to PCB terminal ST4. Thetest circuit is powered only when transis-tor Ti conducts. Normally, TI is held offby R25 so that the circuit does not receivea supply voltage.

When the TEST button, Tat, is pressed,Ti receives base current via R24 and con-sequently starts to conduct. The test cir-cuit then receives its supply voltage. Thecircuit is actuated in a similar mannerwhen a voltage greater than about 0.65 Vexists at the input terminals, ST1 and 5T2.In that case, resistor R22 feeds a base cur-rent into transistor T2. The resultant basecurrent of Ti causes the tester to beswitched on automatically.

The load resistance of the batteryunder test is determined by a four -posi-tion slide switch, Si, and one of fourpotential dividers:

'Mignon (IEC R6) batteries:R1-R7'Baby' (IEC R14) batteries:R2-Rs'Mono' (IEC R20) batteries:Rs-R9

kT

mon M449-11 S14

Fig. 1. Circuit diagram of the battery tester. The batery type is selected with a four -position slide switch. S1.

LLEKTOR ELECTRONICS JULY/AUGUST 1990

BATTERY TESTER

O 00 00O 00 00

of 10 .01 ,._ lo o.04 = 10

el -100000

0 0 0 0[5.=10

a. loo{===107W -0- -0 0

-41 -

ziS111 a

-411111-

--041!1-

NI. -emir_

-4118*. _

11111-

-

'94/ power -pack' (IEC 6F22) batteries:Rs-Ro-R it

The voltage at the junction of the potentialdivider (R1 -R11) selected with St is fed tothe -inputs (pins 2 and 6) of comparators10A and 10 B. The +inputs of these corn-parators are held at a reference level cre-ated by zener diode Di and potentialdivider 1213 -Rio. Resistor R12 limits thecurrent through this stabilizer, whoseinput voltage is decoupled and bufferedby electrolytic capacitor Ct. Feedback re-sistors RI7 and Ris provide a certain hys-teresis to ensure flicker -free operation ofthe LEDs.

When the battery voltage exceeds theminimum value of 1 V, both comparatoroutputs, pins 1 and 7 of IC IA and 10s, areat a high potential, so that the red LED, D4,lights. When the batten' voltage is be-tween 1.0 V and 1.3 V, the output of 'CIAremains high, but that of IC113 goes low.Consequently, the red LED goes out, andthe yellow LED, D3, lights. When the bat-tery voltage exceeds about 1.3 V, [CIA tog-gles, so that only the green LED, D2, lightsto indicate that the battery is full.

The above comparator switching thre-sholds apply to the three types of 1.5-V

COMPONENTS LIST

content of kit supplied by ELV France

Resistors:2 1115 R3;R92 3123 R2:R82 5126 Rt;R72 150 R6;R111 15052 R5

1 68011 R12

4 1k0 1315;1319:F120:R21

1 3k3 R163 10k R22;R24;R251 15k R14

1 100k R23

2 WO R17;R181 5k preset H R13

Capacitors:2 10oF 25V radial C1 ;C2

Semiconductors:1 11.1358 let1 ZPD3V3 Di1 BC548 T21 8C558 T11 LED 3mm red D41 LED 3mm yellow D31 LED 3mm are en 02

Miscellaneous:1 PCB -mount push button Tat1 4 -way 1 -pole slide switch Si2 test lead with crocodile clip1 battery clip6 solder pin-15rnm silver-plated wire1 printed circuit board1 enclosure

A complete kit of parts for the batterytester is available from the designers'exclusive worldwide distributors (re-grettably not in the USA and Canada):

ELV FranceB.P. 40F-57480 Sierck-les-BainsFRANCETelephone: +33 82837213Fax: +33 82838180

battery that can be tested. For 9-V PP3batteries, they lie at about 6.0 V and 7.8 V.

Preset R13 is adjusted to give a refer-ence voltage of 0.65 V at pin 3 of ICI. Thisadjustment is made with a full batteryconnected to ST1-ST2, i.e., the input volt-age must be 1.4 V or greater.

ConstructionThe construction of this small circuit isrelatively simple. Start by fitting thesingle wire link on the board, followed bythe resistors and the zener diode. This parthas a coloured ring to mark the cathode.

Next, fit the three LEDs so that theirtops are about 15 mm above the boardsurface. The cathode of a LED is usuallymarked by the flat side of the plastic body.When the device is held against the light,the cathode is identified as the larger met-al surface. The LEDs in this circuit are notnormally damaged when fitted the wrongway around.

The last components to be fitted on theboard are the capacitors, the transistors,the integrated circuit, the slide switch andthe TEST button. Finally, connect the redwire of the battery clip to PCB terminalST3, and the black wire to PCB terminalST4.

Two flexible test leads with crocodileclips are supplied with the kit. The redlead (for the positive battery terminal) isconnected to PCB terminal ST1, and theblack lead (for the negative battery termi-nal) to PCB terminal ST2. The test leadspass through 2 -mm dia. holes drilled inthe short side of the top half of the enclo-sure. Make a knot in each wire, at about20 mm from the free end, to provide somestrain relief.

Fit the completed printed -circuit boardinto the top half of the enclosure, aligningits central hole over the moulded boss andmaking sure that the LEDs go into therespective holes. Then connect the 9-Vbattery and fit the other half of the enclo-sure with the self -tapping screw supplied.

ELEKTOR ELECTRONICS JULY/AL:GUST 1990

16

GLOW PLUG SWITCH FOR4 -STROKE MODEL ENGINES

A. Peperkamp

A notorious problem with four-stroke model engines is theirtendency to stutter or even stall at low speeds with all the obviousrisks of carefully wrought model aeroplanes fluttering helplessly

about before crashing to the ground. This circuit gives ease of mindto aeroplane modellers by automatically switching on the glow -plugwhen required at low engine speeds to keep the combustion going.

Among the conditions for a reliably run-ning model engine are a correctly ad-justed carburettor, the use of the rightfuel, and a suitably rated glow plug. Thelatter is fitted to ensure a sufficiently hightemperature in the combustion chanber ofthe engine to enable this to be started. Aglow plug is normally powered by a start-ing battery, which may be disconnectedonce the engine is running.

Most engines in model aeroplanes are2 -stroke types with glow ignition. Recent-ly, however, 4 -stroke types have becomeavailable with two main advantages: first,they produce less noise, and, second, theirsound is more like that of a real aeroplane_Unfortunately, 4 -stroke engines also havedisadvantages with respect to 2 -stroketypes: their fuel/performance ratio isworse, their construction is more com-plex, they weigh more, and, importantly,their combustion is optimum at relativelyhigh speeds only. When a 4 -stroke engineruns at low speed for some time, its oper-ating temperature drops to a level wherecombustion strokes fail, or the enginestalls altogether. Clearly, the additionalheat of the glow -plug may help to preventthis happening. The present circuit con-nects the glow plug to a battery on boardthe plane. This connection is made auto-matically when the engine speed dropsbelow a certain value.

Not the mechanical way...A simple form of mechanical control is alever switch coupled to the acceleratorservo. In practical terms, this can take theform of a cam or notch in the servo discoperating a switch when a certain position(corresponding to a given engine speed) isreached. The switch, in turn, connects orbreaks the supply voltage to the glowplug. The main problem of this approachis finding the right switching point by ex-perimenting with a running engine. Also,taking into account that space is always ata premium in a model, a mechanical con-struction with a lever and a switch, how-ever small, can become very complexindeed and take a lot of time to install andadjust.

...but with electronics!The first 'electronics' idea that comes tomind is, of course, replacing the leverswitch by a relay or a power transistor.The choice in favour of the latter will beobvious in view of reliability in a fairlyhostile environment (vibration and shockcaused by the model). The next step is toeliminate the mechanical coupling to theaccelerator servo disc. Instead, the rele-vant pulses received from the remote con-trol transmitter are accepted andprocessed in parallel by a special circuit

0

50

12

-7 a

ICI.at

C3

74

ICI

X11 TICUS

IN1143i

TO

1141143

ICI=4Ma B$170 o

Mat t

3B5170

0

0 SG

20:03 - I.

Fig. 1. Circuit diagram of the glow plug control.

i.e., the glow plug switch is controlled bythe accelerator servo pulses supplied bythe receiver on board the model. When thepulse -width of the accelerator control sig-nal reaches a certain (predefined) levelcorresponding to a relatively low enginespeed, the glow -plug is automaticallypowered, and switched off when the en-gine is revved up again.

Powering the glow plugGlow plugs fitted in model engines gener-ally operate from a 1.5-V supply. Depend-ing on the type, the current consumptionis usually between 2 A and 4 A. Providedthe switch is virtually loss -free, a NiCd(nickel -cadmium) battery with a capacityof 1.2 Ah or 1.8 Ah mar be used as apower source. Since the glow plug isswitched on at low engine speeds only(e.g., while the model idles on the ground,or while descending or landing), this sortof battery capacity is sufficient for a num-ber of flights.

The author has fitted one of his modelswith a 9 -way sub -D plug for outboardcurrent supply and charging of the re-ceiver battery as well as the glow plugbattery. A switch is added to enable theglow plug to be powered by an external(outboard) battery or power supply dur-ing starting on the ground. At the sametime, this external power source chargesthe on -board battery. When the switch isset to the 'fly' position, the glow -plug bat-tery is connected to the control board.

Circuit descriptionThe circuit diagram of the glow plugswitch is given in Fig. 1. The power FET,T4, used to switch the current to the plug,has a typical on -resistance of 0.04 n. Thisextremely low value is only achieved,however, at a sufficiently high gate volt-age. Since the battery voltage is usually4.8 V in models, voltage doubling is usedto ensure that T4 can be driven into satu-ration.

The voltage doubler consists of T2, Di,D2, C4 and R4. The circuit supplies an out-

ELEKTOR ELECTRONICS JULY 'AUGUST 1990

GLOW PLUG SWITCH FOR 4 -STROKE MODEL ENGINES

Fig. 2. Printed -circuit board for the glowplug switch.

COMPONENTS LIST

Resistors:1 10k1 68k1 33001 82002 100k1 50k preset H

Capacitors:1 101iF 25V1 47nF1 2112 25V radial2 471.1F 25V radial

RI.

R2

R3R4

R5:R6Pi

C1

C2C3C4:C5

Semiconductors:2 1N4148 01:021 LED D3

1 39V 0.4W zener diode D43 BS170 ;T2:T3

1 11211 T41 4538 ICI

put voltage of about 9 V across C5. Thiscapacitor is discharged by R5 after the re-ceiver is switched off to ensure that T4 isoff no longer than 3 seconds afterwards.The value of Rs is a compromise betweenrapid turning off of 14 after the receiver isswitched off, and a small load for the volt-age doubler. The PWM (pulse -widthmodulated) signal taken from the acceler-ator servo terminals provides the clock forthe voltage doubler, obviating a separateoscillator.

The drive signal for the power FETgenerated by two monostable multivibra-tors, ICI: and ICis. The former suppliesan output pulse at the leading edge of thePWM input signal. The pulse width of thisoutput signal (available at pin 6) may beset to a value between 0.5 ms and 3.0 msby adjusting preset Pi.

Monostable !CIF; is wired to trigger atthe trailing edge of the pulse supplied byICI A, i.e., when the receiver output signalis at '0'. The control signal for T4 is takenfrom the Q output of ICis and applied tothe gate via a small -signal FET, T3.

0

CP.hartext witherria

battery

2charge on -board

.,'" battery

CP batterycharge receirer

servo controlof carburettor

S2 a

0er

battery

charge flyre- -en

0

S ow plugcwitcr. control

engine ground connection

R-CRX

Jon 900028-12

Fig. 3. Interconnections in a model aeroplane.

LED D3 forms the glow plug on/offindicator. Where appropriate, it may bereplaced by an actuator such as a low -power piezo buzzer. The engine speed atwhich the glow plug is switched on maybe adjusted with PI.

Construction and wiringThe printed -circuit board for this circuit issmall (Fig. 2) in view of the restrictedspace in the model. Jumpers A and B allowthe control to be geared to the polarity ofthe servo control signal supplied by the

remote -control receiver.The wiring between the control circuit,

the two batteries, the glow plug, the'charge/fly' switch and the 9 -way sub -Dconnector is connected as shown in Fig. 3.Be sure to use heavy-duty wire for theconnections that carry the glow plug cur-rent.

The current consumption of the circuitis negligible relative to that of the glowplug. In the off state, about 1 mA is drawn,in the on state, about 12 mA, mainly onaccount of the LED. - -

ELEKTOR ELECTRONICS JULY/AUGUST 1990

18

100 MHz TEL- OMPATIBLECRYSTAL OSCILLATOR

J. Bareford

2

Al

XI 152 C2

ItoOMHz 22P

T2

L2

ICI

C4

6-133p R3

8F982 Dll

T1N4148;:r

caw = ICI = 74F00 893176 .

*see text5V

The use these days of clock frequencies ofup to 100 MHz is not uncommon in digitalsignal processing (DSP) equipment, RFsynthesizers, video storage circuits andlogic analysers. The circuit described hereis based on a quartz crystal, and suppliesan output signal of 100 MHz with suffi-cient drive capacity for TTL circuits.

The circuit consists of three sections: aquartz -crystal controlled oscillatoraround XI and Tt; an impedance conver-ter, T2, and an output buffer, ICI.

Tuned circuit L1 -C2 is designed tomake the quartz crystal, Xi, operate at itsfifth overtone (i.e., its fundamental, paral-lel -resonant, frequency is 20 MHz). Posi-tive feedback in the oscillator is providedby C5 between the emitter and the base ofTi.

Since the oscillator must be loaded aslightly as possible to prevent startingproblems and instability, the output sig-nal is applied direct to a dual -gate MOS-FET, T2, of which gate 1 forms a very highimpedance. The high transconductance ofthe N1OSFET enables the oscillator signalto be taken from the drain at a relativelylow impedance. Network R3 -Di raises thetop level of the 100 -MHz to above the TTLthreshold for a logic 1 (approx. +2.42 V).

Four parallel -connected NAND gatesin a 74F00 or 74AS00 package are used todigitize and boost the oscillator signal.The 5-Vpp logic swing of the output signalenables it to be applied direct to TTL-com-patible clock inputs.

ConstructionThe oscillator is best constructed on thesmall, double -sided printed -circuit boardshown here. The component side of this

board has a ground plane of unetchedcopper to assist in decoupling the high -frequency signal.

Start the construction with windingthe two inductors. Li consists of 10 turnsof 0.5 mm diameter enamelled copperwire (e.c.w.), and has an internal diameterof 3 mm. L2 consists of 25 turns of 0.3 mme.c.w., and also has an internal diameterof 3 mm. Use the shaft of a 3 -mm drill asa former to make these inductors, whichare fitted just (

MPACT 10-A POWG. Boddington

SJPPLY

It has been some time since we published a 200+ Watt powersupply like the one described here. Capable of supplying up to 10 A(and more if so configured) at an output voltage range of 4 to 20 V,

this ultra -reliable PSU uses a minimum of components and issimple to build.

If there is one instrument in the electronicsworkshop or laboratory you must be ableto rely on at all times, it is the powersupply. These days, a d.c. power supplywith excellent regulation, low noise out-put and high output current can be builtwith relatively few components. The pres-ent design is based on the well-knownType L\t317 integrated regulator. Sincethe LN1317 is capable of supplying an out-put current of 'only' 1.5 A, a number ofthese devices is connected in parallel,under the control of a single voltage set-ting circuit. The result is a surprisinglysimple PSU, which, in its basic version, iscapable of providing an output current ofup to 10 A.

The present PSU is ideal for chargingbatteries, for experiments with a widerange of electronic circuits, and for usewith high -power transistorized RF ampli-fiers.

Design backgroundBefore discussing the circuit in detail, it is

worth while looking at the basic operationof the LNI317.

The LN(1317 is a three -pin integratedhigh -power voltage regulator which maybe used in a 'floating' circuit. As shown inFig. 1, a voltage of 1.25 \ e\i'zts betweenthe output and the ADJLsr input. Providedthe output current is 5 mA or greater, andthere exists a sufficiently high voltage dif-ference between the input and the output,the internal control circuit will maintainthe 1.25 V voltage difference between theoutput and the adjust input. Evidently,this voltage disappears when the chipswitches off owing to a thermal overload.condition.

Since the regulator may be used in a'floating' circuit, it is possible to set theoutput voltage by raising the potential atthe ADJUST input with the aid of a voltagedivider between the output and ground asshown in Fig. 1. The constant voltage of1.25 V across R1 causes a constant currentthrough RI and R2 (disregarding, for themoment, the small current supplied by theADJUST terminal). In this configuration,

MAIN SPECIFICATIONS

Output voltage:

Output current:

4-20 V

10A(basic version)

Current limiting:

Thermal protection:

Ripple rejection:

Operating temperature:

internal

internal

>80 dB

0-50 CSimple to extend for higher outputcurrents

Separate voltage and current indica-tors

the output voltage, U, is determined bythe ratio of Rt and R2. The output voltagerises when R2 is increased. When R2 ismade 0 S2, the output voltage equals thereference voltage of 1.25 V. In the form ofan equation:

Or

1.25 = (R1/ (RI + R2))

= 1.25 (RI + R2)/ R1)

It will be clear that when a number ofregulators are connected in parallel, theoutput current must be distributedequally. This may be achieved as shownin Fig. 2 by fitting a small resistance, Rs,

0SL,n45 12

0

Fig. 1. Lt.1317 in basic regulator circuitwith adjustable output voltage.

ELEKTOR ELECTRONICS .R tX AL GUST 1990

20 GENERAL. INTEREST

Fig. 2. Principle of parallel -connectedU.1317s with series output resistors to en-sure equal current distribution.

in series with each regulator output. As-suming that Rs«R 1, the operation of thetop voltage regulator in Fig. 2 is expressedby:

L25 = Uo (Rt /(R1 +R2)) + 10 R.

and that of the one below by

L25 = Llo (RI / (Ri +R2)) + 11 R,

Since the equations are identical with theexception of the terms I. and II, these cur-rents must be equal. The equations alsosuggest the use of more than two regula-tors in parallel, since the output currentdistribution is, in principle, determinedby two tolerance factors only: first, thereference voltage of the LM317s used, andsecond, the values of resistors R,_

Unfortunately, connecting LM3I 7s inparallel is not so simple in practice,mainly for two reasons. First, the voltagedrop across resistors R., is dependent onthe output current, so that the regulatorscan not keep the output voltage constant.This is so because they will attempt tokeep the voltage across the series combi-nation of RI and Rs at a constant level ofL23 V. The upshot is that the voltage atthe supply output (i.e., behind resistorsR,1 will drop when the output current

Fig. 3. LM317-based series regulator withactive, external, voltage setting.

rises, since this means that the drop acrossresistors Rs. rises. Second, small differen-ces between the reference voltages of theregulators will result in unequal currentdistribution.

External voltage regulationFigure 3 shows the basic circuit of an ex-tended voltage control circuit connectedto the LM317. For simplicity's sake, it isassumed that the power supply containsonly one L\.1317.

The -input of the opamp (a Type 741)is held at half the supply output voltage,LI., with the aid of R4 -R5, while the +inputis held at a reference potential. This refer-ence is obtained from a constant currentthrough resistor R3 and preset Pt. Thisconstant current is obtained from a resis-tor connected between the output and theADJUST input of the regulator. Since the

From theory to practiceAfter the above description of the basicoperation of the power supply, little re-mains to be said about the circuit diagramin Fig. 5.

The mains transformer, Tri, is a toroidtype with two secondary windings of15 V/7.5 A each. The current specificationis not obligatory, however, and may begeared to the anticipated loads. In anycase, the transformer output current mustbe greater than or equal to 1.4 times themaximum anticipated load current of thepower supply.

Although most high -power toroidtransformers have two secondary wind-ings which may be connected in parallelto boost the output current, it is better inpractice to fit each secondary windingwith its own bridge rectifier and associ-ated reservoir capacitor.

Fig. 4. Completed 10-A regulator board with heat -sink. and voltage control board.

regulator maintains a constant voltage(1.25 V) between these terminals, R3 andPt draw a constant current via a transistor,Ti.

Because the opamp is a difference am-plifier, it will attempt to regulate its out-put voltage until its inputs are at equallevels. Transistor Ti is, therefore, drivensuch that the voltage across R3 and Ptequals half the supply output voltage.This means that the changing resistanceformed by the transistor causes the volt-age at the ADJUST input to rise, and with itthe output voltage of the supply. Thiscloses the control loop. In the circuitshown in Fig. 3, preset Pt forms the out-put voltage control because it determinesthe voltage at the +input of the opamp.

The high currents that may have to besupplied by the bridge rectifiers force theuse of adequately sized heat -sinks forthese devices. As a rule of thumb, thereservoir capacitors must be 10,000 1.1Feach per 10 A of output current. When thesize of your enclosure allows it, this is bestincreased to 20,000 !IF per 10 A.

Provided the reservoir capacitors aresufficiently large, a secondary voltage of15 VAC will provide an output voltage ofup to 12 VDC. Similarly, a transformervoltage of 18 VAC allows the circuit tosupply up to 15 VDC. A maximum outputvoltage slightly lower than 28 V may beobtained by using a transformer with two24-V secondary windings and reservoircapacitors rated at 63 V. Note that a 33-Vtransformer must not be used since it

ELEKTOR ELECTRONICS JULY AUGUST 1990

COMPACT 10-A POWER SUPPLY

U4317

K1

Trl

healsink

printed circuit board 1

- B1

7A 5

, re: Ao IC8 01

LM317

R13

I Id

0++-f3++

IC7LM317

all.

/ I

111

1

3W

R52

106LM317

adi.

3W

an

105LM317

3W

I

CIC=I

00014 25Y

++

0

C2CI100005 255

51. 52 = B80C10 000

printed circuit board 2

IC4LM317

./I

/I111

1

3W

R9

0 1C3 R8

LM317 I

J

0

R2

TI

3W

_

C C141P2 R6`III MN

Ik

H

BC161

25V

R3

6

1N4148

INiatt

R4

IC1

7 2

LM741

H

PI14

R?

CtO471, 25Y

P3 ,474

1.4

- - - -Si.,Z075.11

Fig. 5. Circuit diagram of the power supply (basic version with one regulator board for an output current of 10 A).

would cause the maximum input voltageof the circuit to be exceeded.

Two moving -coil meters are includedin the circuit, one for voltage measure-ment and one for current measurement.These meters may be replaced by digital(LCD) read-outs, which are available asready-made modules. Two such modulesare used in the prototype of the powersupply. Their one disadvantage is thatthey require a floating power supply. Thesimplest way to avoid problems with thissupply is to power the modules from twoseparate 9-V batteries. To save batterypower, an optocoupler circuit may beused to enable the power supply to switch

the modules on and off. The basic circuitto realize this type of control is shown inFig. 8. Alternatively, construct a small,separate, power supply for the LCD mo-dules.

Most LCD modules are 200 -mV volt-meters. Fortunately, they are easily con-verted into 100-uA ammeters as requiredhere by shunting the input with a 1-k0resistor.

ConstructionFigure 6 shows the two printed -circuitboards You need to build the power sup-ply: one holds the seven regulators and

their associated power resistors, the other,a much smaller type, the voltage controlcircuit.

All components, with the exception ofthe mains transformer, the bridge recti-fiers and the reservoir capacitors, are ac-commodated on the two PCBs. The sevenregulators are fitted on the heat -sink in amanner that allows them to be soldereddirect to the printed -circuit board asshown in the photographs. Each regulatormust be electrically insulated from theheat -sink. In the prototype, 1.5 -mm thickceramic insulators are used instead of themore common mica washers for reasonsof safety and mechanical stability.

FLEKTOR ELECTRONICS JULY/AUGUST 1990

GENERAL INTEREST

PNociireurahfro.:\m-jiAir.\0

000A

ICE 000 IC7 0 0 0 ICE

r

6

Its .0cc0c0

o -61 IC5

P3

000

a

0 -{E16 -K)

01:

C3-40

IC4 0-00-

0 A 0000

103

0

O 0ccCO

Fig. 6. Track layouts (mirror images) and component mounting plans of the two boards that go into the making of the 10-A power supply.

COMPONENTS LIST

Resistors: Semiconductors: 1 toroid mains transformer Tn7 01222 3W RI:RS-813 1 1N4148 2x15 V'7.5 A e.g. ILP1 10052 R2 1 8C161 Type 63013 (240V mains)1 15012 R3 1 741 ICI or 61013 (220V mains)

2 4k7 R4;135 7 11.4317 (S0-220 enclosure) IC2-ICS 7 Insulating washer for LM317

1 1k5 R6 1 Heat -sink 1 KW: e.g..

1 82k2 1k0 preset H

R7

Pi:P2Miscellaneous:2 100pA f.s.d. moving -coil M I ,M2 1

Fischer SK120SA100printed -circuit board 900045-1

1 47k preset H P3 meter, or two 200 -mV LCD 1 printed -circuit board 900045-2

voltmeter modules 1 enclosure e.g.. Tetet

Capacitors: 2 B80C10000 B1;132 Type LC1050

2 10,000pF 25V1 10µF 25V1 47µF 25V

C1;C2C3

C4

1 Mains appliance socketwith built-in switch andfuseholder

KI

1 100n CS 1 Fuse 3.15 A slow Fl

ELEKTOR ELECTRONICS JULY AUGUST 1990

COMPACT 10-A POWER SUPPLY

Fig. 7. Wiring diagram of the power supply. Use heavy-duty insulated wire as indicatedby the heavy lines.

Fig. 8. Power supply and automatic on'offcontrol for the LCD -based V,l read-outs.

The.population of the two single -sidedprinted circuit boards is not expected tocause problems. Mount the power resis-tors on the regulator board at a height ofabout 3 mm above the PCB surface.

The completed boards are fitted in asturdy metal enclosure as shown in thephotographs of the prototype. A clearanceis cut in the rear panel to enable the heat -sink with the attached regulators to befitted.

The mains on/off switch is purposelynot fitted on the front panel to avoid wiresinside the enclosure that carry the mainsvoltage. Figure 9 illustrates the use of amains socket with integral fuseholder andon/off switch fitted in the rear panel of theenclosure. The supply output terminalson the front panel are heavy-duty wandersockets.

Fig. 9. Close-up of the rear panel assembly. Note the mains socket and the clearance cufor the heat -sink.

The thick lines in the wiring diagramin Fig. 7 show the connections that mustbe made in heavy-duty insulated wire. Allother connections are made in medium -duty insulated wire. Do not forget to con-nect the output terminal to the '0'terminals on the two boards. The heavy-duty wires are best connected to the PCBsvia spade terminals and mating sockets asused in cars. When this is done, the outputvoltage of the supply will remain constanteven at heavy loads. Our prototype wastested in this respect and found to degradeby only 60 mV when the load was in-creased from 0 to 10 A.

Need more than 10 A?The power supply may, in principle, beextended with as many regulator boardsType 900045-1 as required for a particularmaximum output current. Each addi-tional regulator board increases the cur-rent by 10 A. If that is too much, simply fitone regulator per 1.4 A of additional cur-rent. The construction of the additionalregulator boards is identical to that of thebasic version described above. They aresimply connected in parallel by intercon-necting corresponding terminals, exceptterminal 'B', which is connected from oneboard 900045-1 only to the correspondingterminal on board 900043-2.

AdjustmentSwitch the supply and on adjust Pi untilthe output voltage is 10 V. Next, connecta load (e.g., a 12-V car lamp). Use a digitalmultimeter to calibrate the current meterby adjusting P:, and the voltage meter byadjusting P3.

Note that when the supply is notloaded, the LM317 with the lowest refer-ence voltage will supply the output volt-age. In this condition, it may happen thatcurrent flows into the outputs of the otherLM317s, causing the current meter to in-dicate a negative value. This is normal.however, and no cause for concern.

ELEKTOR ELECTRONICS JULY AUGUST 1990

24

INMARSAT'S STANDARD -CB. Higgins

International Maritime Satellite organisation (Inmarsat) are nowmarketing a package of satellite -based communications services to

the business community generally. This article provides anintroduction into the technical aspects of these services.

Inmarsat uses geostationary satellites inthe three geographical regions of the At-lantic (AOR). Pacific (POR) and IndianOcean (IOR) regions. For each region aworking pair (known as a dual) and onespare satellite are employed. An over-view of the currently used nine satellitesis given in Table I. It should be notedthat Inmarsat plans to widen the AtlanticOcean coverage towards the West. mov-ing the \tarecs B2 satellite from 26° \Vto 55.:;\V.

What is Standard -C?Standard -C is a satellite -based data com-

munications system that operates at aspeed of 600 bit per second. Data. in theform of computer output. or the outputof various telemetry systems on boardcraft and vehicles, can be sent to a basestation from almost any location onearth.

Standard -C is a message -based sys-tem. i.e.. the sending equipment must'pack' its data for each individual trans-mission. Once formatted. the data pack-age ('packet') is stored in a messagebuffer until a suitable time slot is ob-tained on the satellite. The message buff-er has a single packet .capacity of32 KBytes.

Standard -C \ stems on board craftand vehicles are made with connectionsvia an RS -232 port to allow for easyinterfacing with data equipment such aspersonal computers. terminals. data log-ging systems. etc. functioning as DCE(data circuit terminating equipment)and/or DTE (data terminal equipment).

Two main categories of service arepossible in the Standard -C stem:

store -and -forward message transferend -to -end services

Store -and -forward message transfer in-volves the formatting of complete mess -

COAST EARTH STATIONStore and Forward

Message Switch

TELECOMMUNICATIONS NETWORK

TelexVoice Band DataLeased LinesTeletexElectronic Moil

Packet SwitchedData NetworksLettergrom ServiceX.25X.400

PUBLIC NETWORK

per

0 0 CLOSEDUSERGROUPS

ma Weiwigs

oft II NagOMR'

11.

111114

thesimai

Fig. 1. Coast earth station (CES) acts as a store -and -forward message switch on to the satellite link (illustration courtesy of Inmarsat).

ITLEKTOR ELECTRONICS JULY/AUGUST 1990

ages at the coast earth station or the shipearth station before transmission overthe satellite channel. The (telex) mess-ages are then transmitted to ship or toshore on a simplex basis when capacityis available.

End -to -end services require a perma-nent or semi -permanent circuit to be es-tablished from the coast earth station tothe appropriate terrestrial facilities forthe duration of the (telex) connection.

All other services provided by Stand-ard -C are optional. These services in-clude ship -to -shore half -duplex circuits.full -duplex circuits, polling, individ-ually -directed. group -directed and area -directed calls, and automatic datareporting.

Standard -C uses radio frequencies inthe L band and C band sections of thespectrum as shown in Table 2. Incre-ments of 5 kHz are used throughout thebands.

ManufacturersAround the world, interest is beingshown by manufacturers of electronicequipment to produce Standard -C com-patible communications sets for use atcoast -earth stations and on board ships.vehicles and, recently. aircraft.

STC International Marine based atMitchem in the UK produce equipmentcalled Mascot C that is designed for allsizes of shipping vessels. Denmark -based Thrane & Thrane make systemsfor use in and on land -mobile vehicles.Table 3 shows the major equipment ma-kers and the names of their products.

The SES: antennas and RFconsiderations

All manufacturers of ship earth stations(SES) use omnidirectional antennas intheir systems. as this eliminates the needfor the user to re -adjust for ever\ trans-mission or reception.

INMARSAT'S STANDARD -C

Fig. 2. Intelsat -V -F1 satellite undergoing tests in an anachoic chamber.

Antennas used in the Standard -C sys-tem must be installed at least 5 m awayfrom C -band radar equipment. For X -

Region Longitude

AOR 26=1N

AOR 18.5=IN

AOR 15°W

IOR 63=E

IOR 60'EIOR 73=E

POR 180°E

POR 177.5'E

Satellite Use

Memos 82 operationalIntelsat -V (MCS) dual

Marisat Fl spare

Intelsat -V (MCS) operationalIntelsat -V (MCS) dual

Marisat F2 spare

Intelsat -V (MCS) operational!.larecs A dual

Table 1. Satellite positions and earth coverage.

band radar. the minimum distance ismuch smaller.

Antenna designs vary from manufac-turer to manufacturer. Special designshave been adopted for use on differenttypes, of sea vessel and on land basedvehicles. One innovative design stili tobe tested is a flat circular antenna thatcan withstand an automatic car wash.

Power levels in the standard -C sys-tem are low compared to. say. satellite -TV. This is mainly because of the muchsmaller bandwidth requirement (typi-cally. about 1 MHz instead of 27 MHzon a satellite -TV transponder). Circularpolarisation is used to reduce the effectsof Faraday rotation in the uplink anddownlink paths to and from the satellite.Althoueh the antenna gain pattern is not

ELEKTOR ELECTRoNICS JULY" AUGUST 1990

26 CONIMUNICATIONS

ACTUATOR

DCP

DATA TERMALECUPMENIT

(DTE)

N I -AFACE 4AND CONTROL

INT

LEVEL

FLOWMETERTEMPERATURE

GASESCONDUCTIVITY

PRESSLP.E

Fig. 3. Schematic diagram of Standard -C interfaces for remote data collection and control

Use Up Down link Frequency Radio band

Coast earth station up 6 GHz CCoast earth station down 4 GHz CShip earth station up 1.6 GHz LShip earth station down 1.5 GHz L

Table 2. Band frequency assignment for Inmarsat Standard -C communication links.

Country Manufacturer Equipmentname

Denmark Thrane & Thrane TT -3020AFrance SNEC STC 01Japan Japan Radio Co. JUE 65AUK STC International Mascot C

Marine

Table 3. Standard -C equipment manufacturers.

directly specified. provision must bemade. e.g.. 1t ith a gyroscope. to ensurethat the minimum EIRP and GfT figuresare met down to -15' to cope with shipmotion. Table 4 shows some typical RFequipment parameters.

Out at sea...s Inmarsat is mainly concerned with

maritime aspects of communication.equipment designed for the system hasto conform to the rigours of operating atsea. Therefore. specifications alwayshave a strong leaning to environmentalconditions such as temperature. hu-midity and vibration-see Table 5.

Coast earth station

The link between the Inmarsat systemand communications companies of vari-

220 220 3:: 320 34: 20 £3 50 100 120 143 150 180 2c,0 220 240

-....- Alimr-_Ary;11 .... ...,-...___._ in"..,... 11111111111111.____-....___ __ --

GOONHILL . '4, \, SARYDESSA ' 1%., 1

80JING id:N , e -

I OUTHBURY8 ITR 0

ATA0 #10PYLAE RAH

!BARAK!FUCA YAMAGU H SANTA P

I 1.11AA4D 1.

1.14U- KARACHI

r

FDA ARV I -tN

SINGASOR

TANGUA

2ALCARCE

U

583

trie 873

11414

4.582fir 872

28: 220 34: 0 20 43 :0 '20 '40 750 .20 2:: 220 240-AL OCEAN REGION CODE (TELEX) ear OCEAN REGION CODE (TELEPHONE)

SATELLITE LOCATION, ACRE 18.5°W, IOR 636E. POR 180°E, AORW 55°W COAST EARTH STATIONS AIN OPERATION OPLANNED

0

Fig. 4. Overview of frequencies used for Standard -C communications between vessels, satellites and coast earth stations.

ELEKIOR ELECTRONICS JULY AUGUST 1990

INNIARSAT'S STANDARD -C

Parameter TT -3020A

Antenna polarisation RHCEIRP (at 5' elevation) 12 dBW (min.)Figure of merit GiT -23 dB,K(at 5- elevation)

TX frequency band 1.6265 - 1.6465 GHzRX frequency band 1.530 - 1.545 GHz

JUE65A

RHC

14 -z2 dBW

-23 dBiK

1.6265 - 1.6465 GHz1.530 - 1.545 GHz

Table 4. Some antenna unit specifications.

ous countries is all-important for the im-plementation of the complete Standard -C system.

Figure 3 illustrates how the coastearth station fits into the total system. It

acts as a store -and -for ard messageswitch to the satellite. Operating. on C -band (i.e., 4/6 GHz). the link to the sat-ellite is less susceptible to atmosphericinterference as a result of problematic

weather conditions.Developments are continuously tak-

ing place in coast earth station technol-ogy. For example. Thrane and Thranehave recently been ax% arded contracts bySingapore Telecom and Telecom Den-mark for the supply of equipment forcoast earth stations in the respectivecountries.

Further information on the Standard-C communications system may be ob-tained fromInternational Maritime Satellite Or-ganisation (Inmarsat) 40 MeltonStreet Euston Square LONDONNW1 2E0.

Parameter

Temperature (electronics)

Temperature (antenna unit)

Humidity

Ice

PrecipitationWind

Vibration (electronics unit)

Vibration (antenna unit)

TT -3020A

O'C to 45:C (operating)-20:C to 70 C (storaae)-35: to 55'C (operating)-40:C to 70=C (storage)95% non -condensing

up to 2.5 cmup to 10 cm,hrup to 100 knots2-15.8 Hz at 1 mm peak'15.8-100 Hz at 1.0 g peak acceleration2-10 Hz at 2.54 mm peak10-100 Hz at 1.0 g peak acceleration

JUE-65A

0=C to 45'C

-35:C to 55'C

up to 95% at 40:C

2 to 15.8 Hz at 2.54 mm peak15.8 to 100 Hz at 1.0 g peak acceleration2-10 Hz at 2.54 mm peak10-100 Hz at 1.0 g peak acceleration

Table 5. Environmental specifications of two types of Inmarsat Standard -C SES (ship earth) stations.

NATIONAL ANDINTERNATIONAL NETWORKS

Fig. 5. Inmarsat satellite coverage at 0 and 5 degrees elevation above the horizon. The illustration shows the three ocean regions, AOR,POR and 10R, ocean codes and locations of coast earth stations (illustration courtesy of Inmarsat).

ELEKTOR ELECTRONICS JULY AUGUST 1990

28

HAND-HELD 8 -CHANNEL LOGICANALYSER

The new TA -100 from Thurlby-Thandar is alow-cost logic analyser that replacesmultiple logic probes or logic checkers. andcan be substituted for more complex logicanalysers in many applications.

The TA- 100 has eight data inputs. an exter-nal clock input, a trigger input and a triggerchaining capability. Maximum clock fre-quency is 25 MHz. and data pulses less than10 ns wide can be captured and displayed.The trigger circuits of up to four pods can

be linked together to expand the trigger rec-ognition to up to 32 channels. Each channelof the trigger word can be set to 0. 1 or X(don't care). The logic status of each channelis continuously shown on a LED display. andpulse -stretching enables short pulses andhigh frequencies to be clearly displayed.

The TA -100 is priced at £89 (plus VAT).

Thurlby-Thandar Ltd. Glebe Road HUNTINGDON PE18 7DX. Telephone:10480) 412451. Fax: (0480) 450409.

NEW PHOTODETECTOR RANGEFROM CENTRONIC

Centronic have launched a new ranee ofphotodetectors. the 0S135 series. The newrange of devices has a photodiode mountedtogether with an amplifier in a hermeticallysealed TO8 package. and incorporates a low -profile cap.

The new photodetectors are claimed to sim-

i\ EW PRODUCTS

design by eliminating the needfor a head amplifier. Applications includeoptical instrumentation. colour coding. am-bient brightness control. alarm systems andflow meters.The detectors are available in four ver-

sions. tailored to operate within the follow-ing wavelength bands: ultra -violet(250-400 nm), visible (400-900 mu). infra-red (600-1100 nm) and for eye -response de-tection.

Centronic Ltd. Centronic House KingHenry's Drive New Addington CROY-DON CR9 08G. Telephone: (0689) 47021.Fax: (0689) 45117.

LOW-COST 31/, -DIGIT LED PANELMETER

Autona's low-cost DVM module has anoverall depth of only 11 mm. which allowsit to be built into the most compact of equip-ments.

Introduced as the DVM 456. the unit fea-tures 0.56 -inch high -efficiency displayswhich, [(nether with the red filter in themoulded bezel (supplied with the unit). pro-vides a display which is readable under highambient light conditions.

An on -board supply stabiliser simplifiesinstallation into a wide ranee of equipment,since the module operates from an unregu-lated supply of 7-12 V. whilst protectionagainst input overload and reverse polaritysupplies ensure safe operation in hostile en-vironments.

Available in a standard form with a basicsensitivity of ±L999 V. the unit may be sup-plied with alternative f.s.d. specificationswhere quantity requirements exist.

Supplied with a comprehensive, data sheet.the unit is priced at £19.95 (plus VAT) forsingle quantities.

Autona Ltd 51 Poppy Road PRINCESRISBOROUGH HP17 9DB. Telephone:(084 44) 5740. Fax: (084 44) 7102.

TR_t\SPARENTSATELLITE DISHGETS GREEN VOTE

Zeta Services have recently introduced atransparent glass satellite dish designed toovercome environmental objections to un-sightly metal and fibreglass alternatives.

The patented 60 -cm see-through dish,CrystalVision. is made from Armourplatemetal -impregnated glass that has the samereflective qualities to microwaves as stand-ard metal dishes.

The electronics for the CrystalVision dishare supplied by Marconi. and the whole unit.which is the same size as the smallest Astradish. is mounted on a clear polycarbonatebase plate for unobtrusive installation. Pro-duction of the glass dish is expected to startlate summer for autumn delivery at a priceclaimed as slightly higher than opaque metalor fibreglass options.

Zeta Services Ltd. Harden Park Alder -ley Edge CHESHIRE SK9 7QN. Tele-phone: (0625) 583850. Fax: (0625) 585282.

NEW SERIES COMPACT 15-75W DC -DC CONVERTERS

A new series of DC -DC converters, desig-nated 700 Series, has been introduced byIntrOnics Inc.. U.S.A.

There are six models in the ranee offering5 V. 12 V and 15 VDC single outputs at 3 Ato 5 A (remote sense and remote control arcstandard on the 5-A models). The voltageinput range varies from 8-40 VDC to 18-40 VDC depending on the specified outputs_All models operate at 40 kHz (typ.) arid from-25'C to 70°C with derating. The storagetemperature is specified at -40°C to 105°C.

Important features of the new supplies in-clude ultra -wide input voltage range. effi-ciency of up to 90g. thermal overloadprotection, low thermal gradient and reversepolarity protection.

Measuring just 3x2.5x0.81 inch. theDC700 series are all copper encased for six -sided shielding and are pin -compatible forPC board mounting. They are suitable forapplications in telecommunications. processcontrol systems and battery -operated sys-tems.

Pascal! Electronics Ltd. Saxon House Downside SUNBURY-ON-THAMESTw 16 6RY. Telephone: (01 979) 0123.Fax: (0932) 782402.

ELEKTOR ELECTRONICS JULYiAtGUST 1990

all ICs on the controls board. Switch onand check that the LEDs light in a certainpattern (depending on the software ver-sion). When the processor works, the LEDdisplays indicate a start-up code. Possiblesources of failure: incorrect connection be-tween main board and controls board;empty EPROM; LEDs fitted the wrongway around, short-circuited PCB tracks;bad IC socket(s); faulty component.

Switch off. Insert the remaining ICs intheir sockets, then connect the keyboardvia the 40 -way cable- Switch on. The start-up code (software version number)should appear on the display. Connect aMIDI expander (set to ON INI mode) to theMIDI output. If everything is all right sofar, it should produce notes when youplay on the MIDI keyboard. If not, reversethe 40 -way keyboard connector. Possiblesources of failure: incorrect keyboard con-nection; short-circuited PCB tracks; faultyMIDI cable; wrong MIDI channel on ex-pander; faulty component_

MIDI MASTER KEYBOARD

PART 2: TESTING AND PROGRAMMING

D. Doepfer

In this second and last instalment we check the operation of the twoprinted -circuit boards, help you on your way in faultfinding (if

necessary) and last but not least discuss the various programmingand menu options offered by the microprocessor -controlled

operating system running on the keyboard.

Even experienced electronics constructorsshould not fit the completed printed -cir-cuit boards in the keyboard enclosurewithout a thorough functional check_First, inspect the boards visually, lookingfor short-circuits and bad solder joints.Once again refer to the component over-lay and the parts list to make sure that allcomponents have the right value andorientation. Test all flatcables by checkingthe continuity of every individual wire.

Connect the two boards via the 16 -wayflatcable, observing the polarity of the1DC sockets. If applicable, remove all in-tegrated circuits from the boards. Applypower, and check the presence of +5 V atall relevant points (consult the circuit di-agram). Possible sources of failure at thisstage are the mains adapter, the 7805 or itsassociated smoothing capacitors, a defec-tive tantalum decoupling capacitor, or ashort-circuit between PCB tracks.

Switch off the power, and insert ICI,IC2 and IC3 into their sockets, followed by

MIDS-MASTERKEYBOARD

Lint11\72IMete-

0r r I

When the previous tests check out, thehardware is likely to function correctly_Note, however, that errors like a stuck keymay not come to light until later.

Testing the modulationwheelAs already noted in the description of themodulation wheel function, the mechan-ical end stops of the potentiometer do notallow this to cover the full turning rangeof 270°. Although this is taken into ac-count by the control software, the periodof the VCO signal (IC4) should be made tolie in the range between 4.2 ms and 8 ms_The actual limits are 4096 us and 8192 is.Values outside this range produce erro-neous control values.

The range limits are simple to adjustwith the aid of a period meter or a fre-quency meter: alternately adjust Pt (span)and operate the modulation wheel (peri-od) until the above range is achieved.

In case such test equipment is notavailable, the modulation wheel may alsobe adjusted with the aid of routine 1 orroutine 2 provided by the keyboard con-trol software. These routines enable themicroprocessor to send the MIDI controldata obtained from the modulation wheelto the LED displays in two different ways.

Routine 2 is invoked by keeping the sec-ond key to the left in the upper rowpressed while the keyboard is switchedon. The displays indicate the measuredcontrol data in hexadecimal (00-FF). Thecorrect range is achieved by alternatelyadjusting PI (parameter span) and opera-ting the modulation wheel (actual par-ameter value). Set a sufficiently largerange to allow for wear and tear, compo-nent tolerance, and drift owing to mech-anical strain. Remember that the softwarecaters for the reduction of the full range(00-FF) to OF -FO to cover the requiredMIDI range of 00-7F. This means thatMIDI parameter value 00 is sent when themodulation wheel supplies a value smal-ler than OF. Similarly, 7F is sent when the

ELEKtOR ELECIRuNICS t_(tsT 1990

30 ELECTROPHON1CS

,--! N CI F? :4 C9.07")' 1:3 7- C'i In CO CO ° .'j C-.3 L'" N - CO 0C,4 Cs.ICN: 7,,N ir)N t!'N CPCsj 001 CqCOBank Nr.

930339 -II- I

Fig. 7. A number of keys on the musical keyboard are used in conjunction with the control software to enter menu options and settings.

value exceeds FO. Hence, a range settingof, say, 0A -F2 is perfectly adequate.

Routine 1 is invoked by keeping the ex-treme leftmost key in the upper rowpressed while the keyboard is switchedon. It enables the processor to indicate thetransmitted MIDI parameter value, i.e.,the control data sent to the MIDI instru-ment after averaging and proportioningvia a look -up table in the control program.Obviously, the range of this indication is00-7F, corresponding to the permissiblerange of MIDI parameter values. When aself-adjusting modulation wheel is used,its rest position should produce a displayreading of 40 (64 decimal), irrespective ofthe side from which it arrives at the restposition. If necessary ensure this centrevalue by carefully re -adjusting Pi andchecking the range limits with the aid ofroutine 2.

In the pitch -bend mode, the softwareprovides an automatic correction functionthat subtracts or adds a certain value togive a range where only 40 is produced atthe centre position of the modulationwheel. In case a steady value can not beachieved, fit a 2.2 tiF tantalum capacitor(Cu)) between the control voltage sup-plied by the potentiometer and ground.An instability of ±-1 digit is allowed be-cause it is compensated by averaging andthreshold detection routines in the controlprogram.

After the above adjustment, carefullytighten the nut on the modulation poten-tiometer, making sure its setting is notchanged. Switch on the keyboard (with-out invoking either of the test routines)and check the correct range and functionof the MIDI control parameters.

Programming functionsMost of the functions provided by theMIDI master keyboard are selected withthe aid of the programming keys on thefront panel. These keys work in conjunc-tion with a menu, the control of whichrests with the microprocessor and the soft-ware.

Connect either one of the MIDI outputsof the keyboard to the MIDI input of anexpander synthesizer, sequencer or sam-pler. Connect the foot switch to the key-board via the jack socket. When soprogrammed and actuated in a particularkeyboard zone, thiS foot switch forms aSUSTAIN pedal. Do not connect or dis-connect the foot switch with the keyboardswitched on.

Apply power. The LED displays indi-cate the software version number (e.g.,100), and the LEDs should light up briefly.Next, the display indicates 'PLA' for PLAYmode. At this stage, PRESET 1 is used.

The menu has the following eight options:presetprogram change/real timesplitchanneltransposedynamiccontrollerspanic

which are selected by the eight associatedkeys. The current option is indicated by aLED. In the PLAY mode, no LED lights. Insome menus, the keyboard keys are usedin addition to the control keys to set cer-tain parameters. Also note that somemenus return automatically to the PLAYmode after the parameter has been set.Most menus, however, can be left only bypressing another menu key.

In all menus, except PRESET and PANIC,the next keyboard zone is selected bypressing the same menu key once more(note: the boundaries of a zone are markedby splits). Therefore, press the menu keyas many times as required to arrive at acertain zone. The selection is cyclic: i.e.,zone 1 follows zone 4.

With some functions, the displaysbriefly shows a letter- or number -se-quence before returning to `PLA'. Duringthese sequences, however, the play modeis active. The indication period before thedisplay switches to 'PLA' allows set par-ameter values to be read off easily.

Figure 6 shows which keyboard keys

are used in conjunction with the menukeys to set certain parameters. As shownin Fig. 7, the white keyboard keys in thelowest octave are assigned the followingfunctions:

Bank 1-4 (C; D; E; F)Start (G)Stop (A)Continue (B)

The number keys start at the next higheroctave, i.e., C=1; C#=2, D=3, D#=4; etc. forall number entries required (programnumber, channel, dynamic response table,control code, etc.)

PRESETThe EPROM contains 16 presets, any oneof which may be selected by the user as thebasic keyboard setting. Each preset con-tains data on each of the four zones, theMIDI channel, transposition, assignmentand actuation of control data, and the vel-ocity table. The currently selected presetis indicated on the LED displays for acouple of seconds- before the keyboardgoes to PLAY mode as indicated by theletters `PLA'.

PROGRAM CHANGE/REAL TIMEThis menu allows the programs runningon the connected MIDI equipment to bechanged. It is used together with key-board keys to send PROGRAM CHANGE com-mands and, with certain keys only,real-time .MIDI commands START, STOPand CONTINUE.

The selected zone is shown to the lefton the read-out, while the current bankappears to the right. The zone indicationis important for the MIDI channel onwhich the PROGRAM CHANGE command issent.

The programs are organized in theform of 4 banks of 32 numbers each.Bank 1 contains program numbers 1-32,bank 2 program numbers 33-64, bank 3program numbers 65-96, and bank 4 pro-gram numbers 97-128. The banks are se-lected by the first four keys on thekeyboard (see Fig. 7). When a bank num-ber is changed, the new number is shown

ELEKTOR ELECTRONICS JULY/AUGUST 1990

MIDI MASTER KEYBOARD PART 2

Fig. 8. Software -selected dynamic response curves. A linear response (curve 'a') oftengives the impression that the dynamic characteristic can not be set with sufficient accuracyin the low -volume ranges. This may be compensated in three steps by response charac-teristics 'b', 'c' and 'd'. Curve 'e' provides the inverse effect, giving greater resolution in thehigh -volume ranges. Curve 'f' is exponential with a certain low -volume off -set. The inversecurve, 'g', gives a smaller dynamic range at greater key velocities. This response isparticularly suited to velocity -controlled mixing effects: one zone is assigned a normalresponse (e.g., 'c'), and another zone, of equal size, the inverse response. These two zonesare used to control two MIDI channels simultaneously, e.g., on two expanders, or on oneexpander capable of generating two sounds on two different Channels. The key velocity thenallows you to switch between these channels as you play. Curve 'h', finally, producesvelocity parameter '64' irrespective of the key strike force. This response is particularlysuited to non -dynamic sounds, e.g., those