Fullscreen HTML5Med Res (??MB)HTML4

SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au Vol.8, No.4; April 1995 Contents FEATURES 4 Electronics In The New EF Falcon, Pt.2 Electronic fan control & variable intake manifold control – by Julian Edgar 8 VW Releases An Electric Car It runs off maintenance-free lead-gel batteries & has a range of 80km– by Julian Edgar PROJECTS TO BUILD ELECTRONICS IN THE NEW EF FORD FALCON & FAIRMONT CARS – PAGE 4 14 Build An FM Radio Trainer, Pt.1 Easy-to-build unit offers excellent performance – by John Clarke 25 A Photographic Timer For Darkrooms Gives timed periods from 1-450 seconds – by John Clarke 38 Balanced Microphone Preamplifier & Line Mixer Has two auxiliary inputs & low noise & distortion – by Leo Simpson 42 50W/Channel Stereo Amplifier, Pt.2 The full construction details – by Leo Simpson & Bob Flynn 52 Wide Range Electrostatic Loudspeakers, Pt.3 BUILD THIS FM RADIO TRAINER & LEARN ALL ABOUT FM RADIO – PAGE 14 Final wiring plus some tips on obtaining optimum sound quality – by Rob McKinlay SPECIAL COLUMNS 56 Serviceman’s Log Sets aren’t made of rubber, but . . . – by the TV Serviceman 65 Computer Bits Prune & tune your hard disc for best performance – by Greg Swain PHOTOGRAPHIC TIMER FOR DARKROOMS – PAGE 25 70 Remote Control An 8-channel decoder for radio control – by Bob Young 86 Vintage Radio Fault finding: there’s always something different – by John Hill DEPARTMENTS 2 Publisher’s Letter 7 Mailbag 37 Order Form 68 Circuit Notebook 81 Product Showcase 92 Ask Silicon Chip 94 Market Centre 96 Advertising Index BUILD THIS 50W/CHANNEL STEREO AMPLIFIER – PAGE 42 April 1995  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Reader Services Ann Jenkinson Advertising Enquiries Leo Simpson Phone (02) 979 5644 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Jim Lawler, MTETIA Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER The Gordon Dam must not be emptied It could only happen in a rich democracy: this recent proposal that the Gordon Dam in Tasmania should be emptied so that the original Lake Pedder can be restored. To put it bluntly, this is environmentalism gone crazy. I well remember writing an editorial in the June 1982 issue of “Electronics Australia” opposing the then proposed Gordon River dam scheme. This seemed to be a completely unnecessary scheme and one which was eventual­ly stopped by the Federal Government in 1984. However, the Gordon Dam which flooded the original Lake Pedder is a much larger scheme which was completed in 1976. It was described in detail in the February 1991 issue of SILICON CHIP, as part of the popular series entitled “The Story of Electrical Energy” by Bryan Maher. At present, it has an installed generating capacity of 432 mega­watts and is the major component of Tasmania’s electricity sup­ply. Now I don’t really think that the dam will be emptied but, in today’s topsy turvy world, you never know what crazy scheme might succeed. So let’s look at the proposal objectively. Sure, the original Lake Pedder was a pleasant enough lake although the only aspect that made it unusual was the salmon pink sand beach which showed when the water level was down – when the water level was high, the beach was not visible. Offsetting the subtle colour of the sand was the dirty brown colour of the water, a result of tannin leached from the nut grass which is prevalent in the catchment region. Actually, the water looks like a cola drink. Very few people ever saw the original lake since it was accessi­ble only to trekkers or by plane (which had to land on the beach). Today, we have a much larger body of (still brown) water which is visited by tens of thousands of tourists a year. If it were to be emptied, it would be a financial and environmental disaster. Not only would Tasmania lose a substantial portion of its electricity generating capacity but all the tourist dollars produced by this major attraction would vanish. And how would all the vegetation in the area now covered by water (260,000 square kilometres) be restored? Would the dam wall with its 280,000 tonnes of steel and concrete be demolished and disposed off? What about the two other dams in the scheme which also raise the water level? And what about the very expensive generating plant? Would that be scrapped? And how would Australia then stand in its attempts to reduce carbon dioxide emissions in the years to come, if hydroelectricity has to be replaced by fossil fuels? How would Tasmania cope for water and electricity in the next drought? These questions and many others have very unsatisfactory answers. Or very expensive answers. Really, the whole proposal is crazy and should be dismissed out of hand. Australia may be a rich democracy but we aren’t that rich and nor, I hope, are we that silly! Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip HEWLETT PACKARD 334A Distortion Analyser HEWLETT PACKARD 200CD Audio Oscillator • measures distortion 5Hz600kHz • harmonics up to 3MHz • auto nulling mode • high pass filter • high impedance AM detector HEWLETT PACKARD HEWLETT PACKARD 3400A RMS Voltmeter 5328A Universal Counter • voltage range 1mV to 300V full scale 12 ranges • dB range -72dBm to +52dBm • frequency range 10Hz to 10MHz • responds to rms value of input signal • 5Hz to 600kHz • 5 ranges • 10V out • balanced output HEWLETT PACKARD 5340A Microwave Counter • allows frequency measurements to 500MHz • HPIB interface • 100ns time interval • T.I. averaging to 10 ps resolution • channel C <at> 50ohms • single input 10Hz - 18GHz • automatic amplitude discrimination • high sensitivity -35dBm • high AM & FM tolerance • exceptional reliability $1050 $79 $475 $695 $1950 BALLANTINE 6310A Test Oscillator BALLANTINE 3440A Millivoltmeter AWA F240 Distortion & Noise Meter ...................... $425 AWA G231 Low Distortion Oscillator ...................... $595 EATON 2075 Noise Gain Analyser ...................$6500(ex) EUROCARD 6 Slot Frames ........................................ $40 GR 1381 Random Noise Generator ........................ $295 HP 180/HP1810 Sampl CRO to 1GHz ................... $1350 HP 400EL AC Voltmeter .......................................... $195 HP 432A Power Meter C/W Head & Cable .............. $825 HP 652A Test Oscillator .......................................... $375 HP 1222A Oscilloscope DC-15MHz ........................ $410 HP 3406A Broadband Sampling Voltmeter ................................................................ $575 HP 5245L/5253/5255 Elect Counter ....................... $550 HP 5300/5302A Univ Counter to 50MHz ................ $195 HP 5326B Universal Timer/Counter/DVM ............... $295 HP 8005A Pulse Generator 20MHz 3 Channel ........ $350 HP 8405A Vector Voltmeter (with cal. cert.) ......... $1100 HP 8690B/8698/8699 400KHz-4GHz Sweep Osc ............................................................ $2450 MARCONI TF2300A FM/AM Mod Meter 500kHz-1000MHz ................................................... $450 MARCONI TF2500 AF Power/Volt Meter ................. $180 SD 6054B Microwave Freq Counter 20Hz-18GHz ......................................................... $2500 SD 6054C Microwave Freq Counter 1-18GHz ............................................................... $2000 TEKTRONIX 465 Scope DC-100MHz .................... $1190 TEKTRONIX 475 Scope DC-200MHz .................... $1550 TEKTRONIX 7904 Scope DC-500MHz .................. $2800 WAVETEK 143 Function Gen 20MHz ...................... $475 FLUKE 8840A Multimeter RACAL DANA 9500 Universal Timer/Counter • true RMS response to 30mV • frequency coverage 10kHz1.2GHz • measurement from 100µV to 300V • stable measurement • accuracy ±1% full scale to 150MHz • list price elsewhere over $5500 • 2Hz-1MHz frequency range • digital counter with 5 digit LED display • output impedance switch selectable • output terminals fuse protected $350 $795 HEWLETT PACKARD 1740A Oscilloscope RADIO COMMUNICATIONS TEST SETS: IFR500A ............................................................... $8250 IFR1500 .............................................................. $12000 MARCONI 2955A .................................................. $8500 SCHLUMBERGER 4040 ........................................ $7500 TEKTRONIX 475A Oscilloscope TEKTRONIX 7603 Oscilloscope (military) • frequency range to 100MHz • auto trigger • A & B input controls • resolution 0.1Hz to 1MHz • 9-digit LED display • IEEE • high stability timebase • C channel at 50 ohms • fully programmable 5½ digit multimeter • 0 to 1000V DC voltage • 0.005% basic accuracy • high reliability/self test • vacuum fluoro display • current list $1780 $695 $350 TEKTRONIX FG504/TM503 40MHz Function Generator TEKTRONIX CF/CD SERIES CFC250 Frequency Counter: $270 • DC-100MHz bandwidth • 2-channel display mode • trigger - main/delay sweep • coupling AC, DC, LF rej, HF rej $990 • 250MHz bandwidth • 2-channel display mode • trigger - main/delay sweep • coupling AC, DC, LF rej, HF rej • mil spec AN/USM 281-C • triggers to 100MHz • dual trace • dual timebase • large screen $1690 $650 The name that means quality CFG250 2MHz Function Generator $375 • 0.001Hz-40MHz • 3 basic waveforms • built-in attenuator • phase lock mode $1290 CDC250 Universal Counter: $405 NEW EQUIPMENT Affordable Laboratory Instruments PS305 Single Output Supply SSI-2360 60MHz Dual Trace Dual Timebase CRO • 60MHz dual trace, dual trigger • Vertical sens. 1mV/div. • Maximum sweep rate 5ns/div. • Built-in component tester • With delay sweep, single sweep • Two high quality probes $1110 + Tax Frequency Counter 1000MHz High Resolution Microprocessor Design CN3165 • 8 digit LED display • Gate time cont. variable • At least 7 digits/ second readout • Uses reciprocal techniques for low frequency resolution $330 + Tax Function Generator 2/5MHz High Stability FG1617 & FG 1627 • • • • • • Multiple waveforms 1Hz to 10MHz Counter Output 20V open VCF input Var sweep lin/log Pulse output TTL/CMOS FG1617 $340 + Tax FG1627 $390 + Tax PS303D Dual Output Supply • 0-30V & 0-3A • Four output meters • Independent or Tracking modes • Low ripple output $420 + Tax • PS305D Dual Output Supply 0-30V and 0-5A $470 + Tax PS303 Single Output Supply • 0-30V & 0-3A • Two output meters • Constant I/V $265 + Tax Audio Generator AG2601A • 10Hz-1MHz 5 bands • High frequency stability • Sine/Square output $245 + Tax • 0-30V & 0-5A $300 + Tax PS8112 Single Output Supply • 0-60V & 0-5A $490 + Tax Pattern Generator CPG1367A • Colour pattern to test PAL system TV circuit • Dot, cross hatch, vertical, horizontal, raster, colour $275 + Tax MACSERVICE PTY LTD Australia’s Largest Remarketer of Test & Measurement Equipment 20 Fulton Street, Oakleigh Sth, Vic., 3167   Tel: (03) 9562 9500 Fax: (03) 9562 9590 **Illustrations are representative only Electronics in the Electronically controlled fuel injection & ignition timing is now common but the engine management system can also be used to control other functions. The latest Falcon range also uses electronic control for the radiator cooling fans & the variable intake manifold. To meet styling and aerodynamic criteria, the new EF Falcon was designed to draw all of its engine cooling air from an open­ing positioned under the front bumper. This required the design of a new intake duct, with the opportunity also taken to develop dual electronically controlled electric fans. The design of the new intake duct was undertaken using CAD techniques, with numerical modelling of the airflow being used to plot streamlines. In particular, the shape of the duct was tuned so that only attached (ie, laminar) airflow was present for the majority of the duct system. This design was then tested at the Ford Lara Proving Ground and in an environmental testing room. The results indicated a 32.7% improvement over the cooling system intake used in the previous model. In addition, cooling test comparisons between a convention­ al engine-driven fan and electric fans showed that the latter configuration gave better cooling performance. This showed up in two ways: (1) increased headroom between the coolant temperature and its boiling point; and (2) a reduction in the airconditioning refrigerant pressure (due to more efficient condensation). However, the new duct’s 32.7% improvement in heat rejection over the previous design was reduced to only 19.8% with the electric fans fitted and operating in their “off” mode. This reduction in free-flow 80 km/h heat rejection was due to the obstruction posed by the fans and Pt.2: engine management secondary control 4  Silicon Chip e new EF Falcon By JULIAN EDGAR their shroud. Even so, it still represented a significant improvement over the EA Falcon’s non-ducted radiator and engine-driven fan design. As can be seen from the photos, the Fairmont model has slightly different front-end styling to that of the Falcon. The “grille” located between the headlights is actually a fake and has no bearing on engine cooling airflow. However, the “styling bar” placed across the lower intake was found to have a poten­ tially adverse effect on cooling air intake – if it was angled at four degrees from the horizontal, it degraded engine cooling by 8%! For this reason, production line assembly of this component must be very accurate. Supplementing the improved intake duct is the twin electric fan package. This was also designed to give greater air flow through the radiator. One fan is a single speed unit, while the other has two speeds. These fans are controlled by four relays linked to the EEC-V engine management computer. These relays operate the fans by means of series and parallel circuits – see Fig.1. Although seven fan-speed combinations are possible, only four are used in prac­tice. Potential problems with NVH (noise, vibration & harshness), caused by fan beats and a whirling noise, precluded the use of all speed combinations and, in any event, proved unnecessary. The fans may be operated by the engine management system at idle, depending on engine coolant and airconditioning refrigerant temperature. In fact, in hot environments, the airflow provided by low-speed driving and during city driving is insufficient to cool the airconditioning condenser. The EEC-V module controls the fan speeds using the follow­ ing inputs: (1) engine coolant temperature; (2) RELAY 1 N/O RELAY 3 N/C RELAY 2 N/O M2 M1 M1 SINGLE SPEED FAN RELAY 4 N/C M2 TWO SPEED FAN Fig.1: the dual electric fans are controlled by the EEC-V engine management system via relays. Four different fan speeds can be selected, depending on engine coolant temperature; aircondition­ing head evaporative temperature; engine speed; transmission temperature; & heater fan speed. air­ c onditioning head evaporative temperature; (3) engine speed; (4) transmission temperature; and (5) heater fan speed. Relay operation of the fans was Dual electric fans have replaced the enginedriven fan of the previous model. These are controlled by the EEC-V engine management computer on the basis of five inputs. April 1995  5 SECONDAY RUNNER PRIMARY RUNNER CROSSOVER VALVE Fig.2: this sectional diagram shows the dual-resonance intake system used in the EF Falcon. The crossover butterfly valves are controlled by the EEC-V engine management system. The cutaway view of the variable length intake manifold at right clearly shows one of the crossover butterfly valves. The valve operation is dependent on engine rpm. decided on after evaluating a pulse width modulation (PWM) system. The PWM system had the advantage of allowing stepless variable fan speed control but it was not selected because it was not sufficiently proven to meet Ford in-service durability criteria. Intake manifold control The new EF Falcon features a clever and compact dual intake runner system for the manifold. Depending on the movement of six internal crossover butterfly valves, the intake air is either forced to flow through a short primary runner only or to take a longer path through a secondary runner. Fig.2 shows a cross sec­tion of the intake system. The different resonance characteristics of the dual length runners means that the volumetric efficiency of the engine is boosted at two different rpm points, rather than at a single point as for a single fixed length runner. By using dual-length runners, the resonant behaviour of the intake system can be tuned to provide maximum torque at low engine speeds and maximum power at high engine rpm, without one compromising the other. Engine dynamometer testing by Ford indicated that a transi­ t ion between short and long runners at 3800rpm gave the best results for the Falcon’s engine. In particular, the new engine has worthwhile improvements in both power and torque compared to the previous single length manifold ED design. Engine rpm is the single control criteria used to activate the manifold changeover. This is achieved by using the EEC-V module to control a solenoid which, in turn, directs an engine vacuum source to actuate the SC butterflies. Acknowledgement The bar across the under-bumper air intake on Fairmont models (left) needs to be precisely angled during manufacture so that it does­n’t degrade cooling performance. The above-bumper grille is a dummy & is there for styling only! 6  Silicon Chip Thanks to Ford Australia and the Society of Automotive Engineers for permission to use material from the “SAE Australa­sia” journal of October/November 1994. MAILBAG Making PC boards from photocopies I have had good results in making PC boards from photocop­ies or laser prints. Here’s the formulae and method for your readers: (1) Make a reversed original full size with any method you like then photocopy it. (2) Clean the PC board copper surface. Any method will do provided you have a shiny surface when you finish. Wipe it over with a cloth soaked in some methylated spirits. If it is physi­cally and chemically clean, the surface will wet evenly when water is run over the surface. (3) Make up a solution of 50% Dupont thinners and white spirit by volume. This is a solvent for toner as used on photo­copies. (4) Place the toner side of the photocopy against the copper side of a blank PC board and lightly apply the solvent to the rear of the photocopy with light pressure. Ensure that the paper is wet. With a little practice you will get the toner to come off cleanly onto the copper (now the right way around). (5) Let it dry for a few hours to ensure all of the solvent has evaporated Keeping faulty parts – a form of theft? I wish to comment on some moral and possibly legal aspects of the article “Serviceman’s Log” in the February 1995 issue of SILICON CHIP. In this article the author tells how he was unable to repair a faulty remote control and eventually sold its owner a new one. In the Serviceman’s words, “the old one finished up in the scrap box as a possible source of spare bits” (p.64). This raises some interesting questions. Did the Serviceman believe that he was entitled to keep the faulty device? If so, on what grounds, since it was clearly the customer’s property? Alternatively, if the customer had given it to the Service­man, surely and to let the toner re-harden. Then etch and drill in the normal way. Graham Dicker, Kensington, SA. SILICON CHIP, PO Box 139, Collaroy, NSW 2097. Just a few thoughts on Darren Yates’ article on adding a CD-ROM to your computer, as featured in the February 1995 issue of SILICON CHIP. (1) When installing any peripheral to a computer it is preferable to leave the computer plugged into a mains (240V) supply (with the power turned off). Otherwise there is no refer­ence to ground and the mere act of innocently plugging in a card may in fact cause considerable damage to the computer, due to ESD that your body (and hand) will be wielding. Also for the above reasons, you should perform any “surgery” on a table or bench – not the carpet! (2) A CD-ROM at present is limited to 660 megabytes. This is the same whether the drive is double-sped or not as the mere act of swapping a CDROM into a double speed drive does not double the capacity of the disc. It merely doubles the drive’s motor speed which provides double the data transfer rate and hopefully half the access time. The reason we are “stuck” with 660Mb capacity is to keep compatibility with audio CDs. There is progress in developing a new standard which will allow much higher storage capacity. I. Strawbridge, Canley Heights, NSW. Comment: We cannot agree with your suggestion to leave the com­ puter connected to the mains while work is carried out on its insides. In fact, one of our own staff recently received a severe electric shock while installing an extra hard disc in one of our machines. He had accidentally come into contact with a bare terminal on the mains switch – such things can happen very easi­ly. The reference to a double-speed CD-ROM having a 1.2Gb capacity is quite wrong – a silly mistake that was noted before going to print but by then it was too late. Philips and Sony have recently suggested a new standard for CD-video discs which will provide 3.7Gb on one layer and 7.4Gb on two. This could ultimate­ly be quadrupled if there is a move to blue laser LEDs. this should be mentioned. Later in the article, the Serviceman describes how he found and fixed the fault, con­cluding “so I now have a spare unit, which will come in handy for testing”. Did he tell the customer about this, and if not, why not? It would seem that the practice by servicemen of keeping faulty appliances or parts of such appliances is somewhat wide­ spread, since another article (in another magazine) refers to “a working set that was junked because of a bad tube”. But if in each of these cases the owner’s permission had not been given (and there is nothing in the articles to suggest that it had), then isn’t this a form of theft? B. Smith, Glen Iris, Victoria. Comment: of course a serviceman needs a customer’s permission to keep any faulty parts or equipment that can not be economically repaired. No serviceman would simply assume that he is entitled to “confiscate” someone else’s property – if he did, that would indeed amount to theft. In fact, our Serviceman writer has alluded to this on a number of occasions in the past, when he has described how a customer has retrieved a faulty board etc, and prevented him from later following up on the exact cause of the fault, to satisfy his curiosity. As for a set with a crook tube, why would you want it back? Unless you have an identical set and intend keeping it for spares, it’s nothing more than junk. CD-ROMs have only 660 megabytes April 1995  7 The battery powered VW Golf CityStromer uses main­tenance-free lead-gel batteries for a top speed of 100km/h & a range of about 80km. Refuelling takes on a new meaning with this car – just plug it into a handy power point. VW releases electric car 8  Silicon Chip s an The batteries (above) carry a 3-year warranty. They power a 17.5kW synchronous electric motor & this drives through a conventional clutch & gearbox. Now available in Germany, the battery-powered VW Golf is claimed to be the first production electric car to go on sale anywhere in the world. Its performance is poor relative to its petrol-powered brethren, though. By JULIAN EDGAR Manufacturers continue to trumpet their progress with elec­tric vehicles; a technology largely stalled for the last 20 years because of a lack of progress in battery design. However, unlike many manufacturers, Volkswagen is actually selling its design to the public; a welcome change from numerous electric ‘concept’ cars which have remained unavailable to the mass market. The VW Golf CityStromer uses maintenance-free lead-gel batteries which power a synchronous motor with an output of 17.5kW. This drives through a conventional manual gearbox and clutch. The CityStromer has a range of up to 80km, a top speed of 100km/h and can accelerate to 60km/h in 13 seconds. By compari­son, the 2-litre petrol-engined Golf can accelerate to 100km/h in the same time the battery-powered unit takes to get to 60. It also has a range of at least 560km and a top speed of nearly 200km/h. The batteries of the Stromer are split between the front and rear of the vehicle – a strategy designed to minimise the han­dling changes which would otherwise be associated with locating a heavy mass of batteries at one end of the car. Prototype vehicles covered around 1.4 million kilometres during testing and this provided VW with the confidence to offer a 3-year unlimited kilometre warranty on the batteries. Volkswagen also plans to release an electro-diesel hybrid at some stage in the future. In the meantime, the electric vehicle is on sale in Germany for the equivalent of $33,000. There are no plans to sell the vehicle in Austra­lia SC at this stage. April 1995  9 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au BUILD AN FM RADIO TRAINER; PT.1 This FM Radio Trainer is ideal for learning the basics of FM circuitry. By building it, you will not only gain a very good understanding of FM receiver principles but will also ac­quire an FM radio which has very good performance. By JOHN CLARKE The AM Radio Trainer described in SILICON CHIP in June 1993 was very popular with schools and TAFE colleges as a project to demonstrate receiver principles. However, since then, many popu­lar AM stations have moved across to the FM band, so many people would now prefer to build an FM radio. The SILICON CHIP FM Radio Trainer is designed as a learning aid for people studying electronics. Most mono FM receivers use one or two integrated 14  Silicon Chip circuits (ICs), with a few external compon­ents. However, for this design, we have opted for a more discrete approach, so that the major circuit blocks are all clearly sepa­rated. To simplify construction, we have produced a PC board which has a screen printed overlay. This shows the position of each component plus its circuit interconnections. In addition, the layout on the PC board closely follows the circuit layout, so that the novice can easily come to grips with the functions of the various components. Although some ICs have been used in the circuit, each only performs a single task. The circuit is therefore discrete in the sense that each functional block is separate and this makes it easy to understand what it does. The tuner is also easy to build and align, despite the fact that some coil winding is involved (full details will be published next month). The alignment is carried out with the aid of a simple 10.7MHz oscillator, which we will describe next month. Apart from that, the only other items required for alignment are a multimet­er and a plastic trimming tool. Performance The performance of the FM Radio Trainer is shown by the accompanying Main F eatures • Ideal for le arn • Mono outp ing FM receiver circuit ry ut • On-board amplifier & loudspe • Battery p aker owered fo r safety • Circuit & PC • Excellent board overlay have sam sig e layout • Low disto nal-to-noise performan ce rtion • Receives local & s trong dis antenna tant stati ons with • Automati on-board c frequen extend­ c y able control (A • Calibrate FC) keep d tuning d s ra d io ia l o n -station • Reductio n drive fo r ease of • Easy alig tuning nment us ing a sim ple IF osc illator & a multimete r graphs and the specifications panel. As shown, the usable RF signal level is around 30µV, at which point the audio signal level is about 6dB down (half level). At 100µV, the signal-to-noise ratio is better than 70dB which is quite a good figure. The ultimate signal-tonoise ratio is 82dB and there are very few commercial tuners which would approach this figure. So although the radio is not super sensitive, it provides excellent performance on all local stations, with good reception for signals up to 70kms away. In fact, this receiver will better many commercial receivers when it comes to performance. What is FM anyway? Before getting involved in how the circuit works, let’s first take a look at the basic principles of FM transmission. FM or frequency modulation is a method of applying informa­ tion to a radio frequency (RF) carrier. If the RF carrier is fixed at one particular frequency and level, then the only way that information can be conveyed is by switching the RF signal on and off. This is the technique used for Morse Code. By suitably modulating the carrier with another signal, however, we can transmit speech or music. One meth- od is to vary the level of the carrier as shown by the bottom waveform of Fig.1. This technique is called amplitude modulation (or AM) and we can detect these changes in amplitude using a suitable AM receiver that’s tuned to the carrier frequency. Frequency modulation (or FM), on the other hand, conveys information by varying the frequency of the carrier. Fig.1 shows a typical FM waveform. Note that the amplitude of this waveform is kept constant. At the other end, the variations in carrier frequency are detected (or demodulated) in the receiver to recover the original audio. Any variations in amplitude that may occur in the received signal are effectively ignored, which means that FM receivers are far less prone to electrical interference than their AM counter­parts. Broadcast band FM transmitters FM SIGNAL AM SIGNAL Fig.1: an FM signal (top) conveys information by varying the frequency of the carrier. In an AM signal, it is the carrier amplitude that is varied. modulate the RF carrier by a maximum of 75kHz above and below the carrier frequency. They also include pre-emphasis, whereby signals above 3.183kHz (a 50µs time constant) are boosted. These signals are subsequently re­ stored to normal in the receiver using a complementary de-empha­sis circuit. The idea here is to reduce high-frequency noise in the output of the tuner. Block diagram The circuit for the FM Radio Trainer is based on the super­heterodyne principle. Fig.4 shows the general configuration. The antenna at left feeds into a bandpass filter, which is a parallel resonant circuit comprising inductor L1 and two capacitors. These tune the filter to the centre of the FM band (ie, to around 100MHz). Following the bandpass filter is an RF amplifier stage. This stage has a parallel resonant circuit which is tuned by L2 and variable capacitor VC1. The latter is one section of a tuning gang capacitor and can tune the RF amplifier to any nominal frequency from 88-108MHz. The bandwidth of the tuned circuit is about 200kHz. By this means, the wanted (or tuned) signal is amplified, while other signals are rejected. Following the RF amplifier, the signal is fed to the mixer (Q2 & T1) where it is mixed with the local oscillator signal. VC3, the second section April 1995  15 AUDIO OUTPUT 0 4 TP2-TP3 VOLTAGE -10 -20 -40 2 -50 -60 TP2-TP3 SIGNAL LEVEL (V) OUTPUT (dB) 3 -30 1 -70 HUM + NOISE -80 20 NOISE 100 1k RF INPUT (uV) Fig.2: these curves plot the hum & noise performance of the prototype. They also show the audio output level & the filtered detector output (TP2-TP3) voltage. Full limiting does not occur until the RF input reaches about 600µV but this is not important in this circuit due to the type of detector employed. of the tuning gang capacitor, tunes the local oscillator by resonating with inductor L3. In operation, the local oscillator runs at 10.7MHz less than the tuned RF signal (ie, it runs from 77.3-97.3MHz, depending on the setting of VC3). It is in the mixer that the superheterodyne process takes place. The word “heterodyne” refers to a difference in frequency or beating effect, while the “super” prefix refers to the fact that the beat frequency is supersonic (ie, well beyond the range of human hearing). Four signals are produced as a result of the mixing pro­cess: the two original signals plus the sum and difference fre­quencies. These are then passed to an IF (intermediate frequency) amplifier and bandpass filter stage based on IC1-IC3, XF1 and Q4. This stage is tuned to ensure that only the 10.7MHz difference frequency (now known as the IF) is allowed to pass. In reality, the IF amplifier consists of four separate amplifier stages (IC1, IC2, IC3 & Q4) which, when losses in the bandpass filter are taken into account, have an overall gain of about 1000. This figure is low by comparison 16  Silicon Chip with typical FM tuners which generally have an IF gain of 10,000 or more to ensure that the IF signal is driven into limiting. Limiting Limiting simply refers to the fact that the signal is driven well into overload in the IF amplifier stages. This is done to eliminate any amplitude variations in the tuned signal before it is fed into the demodulator. This is one of the factors that enables FM tuners to reject atmospheric and man-made noise. Note that no distortion is introduced by the limiting pro­cess because the final stage is tuned to 10.7MHz. This filters out any harmonics which would normally result when an amplifier is driven into overload. In this circuit, however, the gain is too low for limiting to occur at low signal levels (ie, less than about 600µV). This doesn’t really matter though, because the type of detector used here has a high degree of AM rejection. As alluded to earlier, the local oscillator frequency always “tracks” the tuned frequency of the RF amplifier so that the difference between their 10k 0 100k output frequencies is 10.7MHz. So if the radio is tuned to 88MHz, the local oscillator will be set to 88 - 10.7 = 77.3MHz. Similarly, if the radio is tuned to the upper limit of the FM band at 108MHz, the local oscillator oper­ates at 97.3MHz. All this happens automatically by virtue of the 2-section tuning gang – one section controlling the RF amplifier and the other the local oscillator. The 10.7MHz difference frequency is standard for broadcast band FM receivers. The big advantage of producing an IF signal is that we now only need to provide gain at one frequency rather than for the whole 88108MHz range which would require complicat­ed filters and a multi-gang capacitor to track with the local oscillator. The output from the IF stage is now fed to a demodulator (T4, D1 & D2) to recover the audio signal. This stage also in­ cludes the necessary de-emphasis to compensate for the pre-emphasis in the treble of the transmitted signal. From there, the demodulated audio is fed to an audio amplifier (IC4) and this then drives the loudspeaker. Automatic frequency control There’s one important feature that we haven’t yet mentioned and that’s the AFC line. AFC stands for automatic fre­quency control and it works to keep the local oscillator in lock with the tuned signal, so that the radio does not drift off station. It also produces a “snap-in” effect, whereby the station suddenly locks in as the tuning approaches the station frequency. As shown on Fig.4, the AFC line is derived from the demodu­ lator. The resulting control voltage is then fed back to the local oscillator. We’ll examine the control action in some detail when we come to the circuit description. AUDIO PRECISION 5 THD+N(%) vs FREQ(Hz) 07 DEC 94 01:28:46 1 Circuit details Refer now to Fig.5 for the circuit of the FM Radio Trainer. It’s main components are dual-gate Mosfets Q1, Q2 & Q4, high frequency transistor Q3, three HF (high frequency) gain blocks (IC1-IC3), and audio amplifier stage IC4. The function of each stage is shown on Fig.5 and, in addition, each stage can be directly related back to the block diagram (Fig.4). Starting at the antenna, the incoming RF signal is coupled to the junction of two capacitors (39pF & 47pF) which, together with parallel inductor L1, form the input bandpass filter. A 1kΩ resistor is included in parallel with L1 and this damps out the Q of the filter so that it covers the entire FM band without ad­justment. This input filter prevents signals with frequencies outside the FM band from entering the circuit and possibly overloading the following stages. Following the input filter, the RF 0.1 20 100 1k 10k 20k Fig.3: the tuner has excellent distortion characteristics, as revealed by these plots at 60kHz deviation & 75kHz deviation (measured at the demodulator output). Note that the THD is 0.32% at 1kHz & 75kHz deviation & less than 0.2% at 1kHz & 60kHz deviation. signal is fed via RF1 to Q1. This is a BFR84 dual-gate Mosfet amplifier which operates in common source configuration. Its quiescent current is set by the 330Ω source resistor and this is bypassed by a .01µF capacitor to ensure maximum AC gain. The gain is set to a high value by bias­ing G2 to around 6.5V, as set by the 10kΩ and 27kΩ bias resis­tors. The amplified signal appears at Q1’s drain and is tuned mainly by variable capacitor VC1 and inductor L2. Note that the junction of L2 and the 47Ω decoupling resistor is bypassed by a .01µF capacitor. As a result, L2 is effectively grounded at this point as far as RF signals are concerned. The same technique is used to provide an RF ground for one side of L3 in the local oscillator. The 56pF capacitor in series with VC1 effectively reduces the tuning capacitance range from 2-160pF to 1.9-41pF. This is done to restrict the bottom end of the tuning range to the ANTENNA 10.7MHz 88-108MHz BAND-PASS FILTER L1 RF AMPLIFIER Q1, L2 VC1 MIXER Q2, T1 IF AMPLIFIER AND 10.7MHz BAND-PASS FILTER IC1, IC2, IC3, XF1, Q4 DEMODULATOR T4, D1, D2 AUDIO AMPLIFIER IC4, VR1 SPEAKER 77.3-97.3MHz LOCAL OSCILLATOR Q3, L3, VC5 VC3 AFC(VC5) Fig.4: the incoming RF signal passes through a bandpass filter & is then fed to a tuned RF amplifier stage. The tuned signal is then mixed with the local oscillator signal to produce a 10.7MHz IF which is then further amplified & fed to the demodulator. April 1995  17 18  Silicon Chip X 39pF 47pF ANTENNA 1k .01 .01 2 100  8 .01 G1 75  .01 100k 560  G1 G2 E S D 4TH IF AMPLIFIER 330  Q4 BFR84 .01 VC2 1.822pF 47  .01 L3 .01 56pF VC6 328pF LOCAL OSCILLATOR TP1 330  3.9pF VC1 2160pF .01 470k 220pF .01 47  VC3 267pF 82pF TUNED RF AMPLIFIER 56pF D L2 47W S Q1 BFR84 G2 .01 Q3 BF199 C B RF1 7 3,4,5,6 IC3 1 270k .01 NE5205AN 3RD IF AMPLIFIER 18k 10k BAND-PASS FILTER L1 27k 10k 68 2 1 VC4 1.822pF 4.7pF 4 5 S D AFC D2 1N4148 390pF 390pF 47k .01 68pF D1 1N4148 1 18k 100k 47k MIXER 330  Q2 BFR84 DEMODULATOR 100pF 6 A K .01 G1 G2 .01 VC5 BB119 10pF 330pF 10k RF2 +9V T4 10k SHIELD 1k T1 1 .01 .01 8 6 TP3 TP2 AUDIO AMPLIFIER IC4 2 LM386 4 10  NE5205AN 1ST IF AMPLIFIER 3 7 3,4,5,6 IC1 1 .01 FM RADIO TRAINER 5.6k 5.6k 2 100 .01 VOLUME VR1 50k LOG 4 5 DE-EMPHASIS 10 1k 3 1 .0068 8.2k .01 47  100  .047 10  5 470 .01 XF1 SFE10.7ML D G1 T3 2:1 S1 POWER .01 VR1 VIEWED FROM ABOVE 4 56 3 21 E B S VIEWED FROM BELOW G2 8 +9V 10.7MHz BAND-PASS FILTER 470 +9V T2 1:2 2 IC2 1 C A B 9V 7 3,4,5,6 8 .01 NE5205AN 2ND IF AMPLIFIER C 100  +9V X ▲ Fig.5 (left): each stage in the circuit is labelled & can be directly related back to the block diagram (Fig.4). Dualgate Mosfet Q1 forms the heart of the tuned RF amplifier, while Q2 is the mixer. IC1, IC2, IC3 & Q4 form the IF amplifier stages, & T4, D1, D2 & their associated resistors & capacitors form a ratio detector. Varicap diode VC5 provides AFC for the local oscillator. broadcast band. In addition, trimmer capacitor VC2 is included in parallel with these two components and is used to set the minimum tuning capacitance. It is adjusted during alignment so that the maximum tuning frequency is 108MHz. Specifications Tuning range �������������������������������������� 88-108MHz (FM broadcast band) 50dB quieting sensitivity ������������������ 18µV Signal-to-noise ratio ������������������������� 82dB with respect to 150mV (see Fig.2) Hum & noise �������������������������������������� -75dB with respect to 150mV Distortion ������������������������������������������� 0.32% THD at 1kHz & 75kHz deviation; <0.2% at 1kHz & 60kHz deviation (measured at demodulator output) Frequency response ������������������������� -3dB at 3Hz & 30kHz at demodulator output; -3dB at 40Hz & 30kHz at power amplifier output Demodulator output �������������������������� 150mV RMS for 75kHz deviation at 1kHz Local oscillator De-emphasis �������������������������������������� 50µs Q3 and its associated components make up the local oscilla­tor. This transistor is biased by the 10kΩ and 18kΩ resistors connected to its base, and by a 560Ω emitter resistor. It oscil­lates by virtue of its tuned collector load and the 3.9pF feed­back capacitor between its emitter and collector. The collector load is tuned using VC3, while the series 82pF capacitor effectively reduces VC3’s range to 2-37pF (down from 2-67pF) to limit the bottom end of the frequency range to the required value. VC4 sets the minimum capacitance across L3 and is adjusted during alignment to set the upper frequency limit of the local oscillator. For this reason, a test point (labelled TP1) has been pro­vided at Q3’s emitter to allow a frequency meter to be connected. AM rejection for 30% modulation ���� 30dB for 100µV input; 53dB for 1mV input Mixer stage The output from the local oscillator (LO) appears at Q3’s collector and is lightly coupled into the G2 input of Q2 via a 4.7pF capacitor. Note also that a 330pF capacitor is used to shunt some of the LO signal to ground, to reduce the level in­jected into the mixer. This is necessary because too much oscil­lator signal can reduce receiver sensitivity. Q2 functions as the mixer stage – it mixes the LO signal with the tuned RF signal which is fed (via a 220pF capacitor and RF2) to its G1 input. The bias for G2 is set to about 5.1V by two 10kΩ resistors, while G1 is biased to ground by a 470kΩ resistor. Current drain ������������������������������������� 110mA <at> 9V & minimum volume Minimum operating voltage �������������� 5.5VDC Maximum operating voltage ������������� 10.5VDC Note: although a 9V battery can be used to power the FM Radio Trainer, it will have a relatively short life. For prolonged usage, we recommend powering it from a 9V 300mA DC plugpack. Be sure to remove battery first. RF2 is included to prevent parasitic oscillation in Q2. Q2’s drain load is tuned to 10.7MHz using a 68pF capacitor and an adjustable ferrite-cored inductor (the primary winding) in IF transformer T1 (between pins 1 & 3). Note that the pin 3 end of the primary is grounded at RF via a .01µF capacitor, which means that the inductor is effectively in parallel with the 68pF capacitor. As a result of this tuning, Q2 operates as a very efficient amplifier over a narrow band centred on 10.7MHz, while frequen­cies outside the wanted band are strongly rejected. These fre­quencies include the original RF signal, the LO signal and the sum of these two signals. Only the 10.7MHz difference signal is allowed to pass. Note that Q2’s drain current is fed via the primary winding in T1. Similarly, the drain current for Q1 is fed via inductor L2, while Q3’s collector current is fed via L3. Gain stage The secondary winding of T1 (pins 5 & 4) now couples the IF signal from the mixer to gain stage IC1 via a .01µF capacitor. IC1 is an NE5205AN wide­ band high-frequency amplifier which oper­ ates with a fixed gain of 20dB (x10). Its supply rail is derived from the 9V rail via a 100Ω resistor and is decoupled using a .01µF capacitor to ensure stability. Note that input and output coupling capacitors, in this case .01µF, must be used here to prevent shunting of the internal bias vol­tages. Note also that the input and output impedances of the NE5205AN are a nominal 75Ω. Ceramic filter Following IC1, the IF signal is coupled to ceramic filter XF1 via transformer T2. It is then fed via transformer T3 to a second identical 20dB gain stage based on IC2. This stage func­ tions as the second IF amplifier. The ceramic filter (XF1) is there to provide further rejec­tion of unwanted signals. This is a bandpass filter with a 10.7MHz centre frequency and a 280kHz bandwidth. However, April 1995  19 PARTS LIST 1 PC board, code 06303951, 363 x 115mm, with screen print­ed component overlay 3 pieces of blank PC board, 19mm x 70mm 2 pieces of blank PC board, 25 x 90mm 1 piece of blank PC board, 19 x 90mm 1 35mm diameter self-adhesive tuning dial 1 57mm diameter 8-ohm loudspeaker 1 9V PC-mount battery holder plus mounting screws 1 9V 216 battery 1 SPDT toggle switch (S1) 6 25mm tapped spacers plus 6-screws 2 15mm diameter knobs 1 50kΩ log pot (16mm) (VR1) 1 panel mount PAL socket 1 PAL line plug with plastic outer case 1 715mm telescopic antenna (eg, Tandy 270-1406) plus 2 x 20mm screw & nut 1 miniature dual tuning gang, 2-160pF & 2-67pF, with dial & mounting screws (VC1,VC3) 1 Murata SFE10.7ML 10.7MHz ceramic filter (XF1) 1 16mm pot shaft assembly (see text) 1 13mm round screw-on rubber foot 20 PC stakes 1 330pF ceramic 1 220pF ceramic 1 100pF NP0 ceramic 1 82pF NP0 ceramic 1 68pF NP0 ceramic 2 56pF NP0 ceramic 1 47pF NP0 ceramic 1 39pF NP0 ceramic 1 10pF NP0 ceramic 1 4.7pF NP0 ceramic 1 3.9pF NP0 ceramic Semiconductors 3 NE5205AN wideband amplifiers (IC1-IC3) 1 LM386 power amplifier (IC4) 3 BFR84 dual gate VHF Mosfets (Q1,Q2,Q4) 1 BF199 NPN VHF transistor (Q3) 1 BB119 varicap diode (VC5) 2 1N4148 signal diodes (D1,D2) Wire 1 300mm length of 0.8mm ENCW 1 1-metre length of 0.25mm ENCW 1 1-metre length of 0.125mm ENCW 1 300mm length of 0.8mm tinned copper wire 1 40mm length of 3-way rainbow cable 1 40mm length of twin loudspeaker lead Capacitors 2 470µF 16VW PC electrolytic 1 100µF 16VW PC electrolytic 1 10µF 16VW PC electrolytic 2 1µF 16VW PC electrolytic 1 .047µF MKT polyester 22 .01µF ceramic 1 .0068µF MKT polyester 2 390pF ceramic 20  Silicon Chip Trimmer capacitors 2 1.8-22pF trimmers (VC2,VC4) 1 3-28pF trimmer (VC6) Resistors (0.25W, 1%) 1 470kΩ 3 1kΩ 1 270kΩ 1 560Ω 2 100kΩ 3 330Ω 2 47kΩ 3 100Ω 1 27kΩ 1 75Ω 2 18kΩ 1 68Ω 4 10kΩ 4 47Ω 1 8.2kΩ 2 10Ω 2 5.6kΩ Coils & ferrites 2 Neosid type A adjustable inductance assemblies; 99007-96 base, former, can & F29 screw core (T1,T4) 2 balun formers, 6 x 13 x 8mm; Philips 4313 020 4003 1 (T2,T3) 2 RFI suppression beads, Philips 4330 030 3218 2 (RF1,RF2) Miscellaneous Plastic alignment tool, four rubber feet for mounting PC board, 10.7MHz alignment oscillator (to be de­scribed) it does require nominal 300Ω source and output loads to obtain the cor­ rect amplitude and frequency characteristics. This requirement has been provided by including T2 and T3. These two transformers provide the correct 75Ω:300Ω and 300Ω:75Ω impedance matching between IC1 and XF1 and between XF1 and IC2. If you are wondering why these transformers only have a 2:1 turns ratio, just remember that the impedance ratio is multiplied by the square of the turns ratio. So a 2:1 winding ratio produces the 4:1 impedance ratio required. The output from IC2 appears at pin 7 and is fed to a third IF amplifier stage based on IC3. From there, the signal is cou­pled to G1 of dual-gate Mosfet Q4 which functions as a fourth IF amplifier stage. Its drain load is tuned to 10.7MHz by a 56pF capacitor, trimmer VC6 and the primary of T4. The 75Ω resistor on G1 provides the correct loading for IC3. Taken together, the four IF amplifier stages and the band­pass filter provide a gain of about 1000 at 10.7MHz, with a bandwidth (or selectivity) of 280kHz. This means that signals at 10.7MHz ±280kHz are amplified and fed through to the demodula­tor, while higher and lower frequencies are excluded. Demodulator To demodulate an FM signal, the demodulator (or detector) must produce a change in audio level as the signal deviates from the 10.7MHz centre frequency. The greater the deviation, the greater the output level that must be produced. The frequency of the recovered audio depends on the rate of the deviation. Fig.6 shows the response curve of the demodulator. This is often called an “s-curve” but the important thing is that it is linear over the -75kHz to +75kHz deviation range. As the frequency is shifted above 10.7MHz, the demodulator voltage goes increasingly positive. Conversely, as the frequency shifts below 10.7MHz, the demod­ulator voltage goes increasingly negative. The demodulator is based on the windings in T4 plus diodes D1 and D2 and their associated capacitors. The secondary winding (pins 6 & 5), along with its parallel 100pF capacitor, resonates at a nominal 10.7MHz and AUDIO LEVEL -75kHz +75kHz this is set during alignment by adjust­ ing a ferrite slug in the coil. In addition, there is a third winding (sometimes called a tertiary winding) which connects to the centre-tap of the second­ary. The other end of this winding connects to the output of the demodulator (ie, the junction of the two 390pF capacitors) via a 68Ω resistor. The tertiary winding is wound directly over the primary to ensure close coupling, so that the signal phases in both windings are the same. At the 10.7MHz resonance frequency, both ends of the secondary are 90° out of phase with respect to the primary and 180° out of phase with each other. In addi­tion, the voltage across the secondary is 90° out of phase with the tertiary winding. As a result, two equal voltages of opposite polarity are applied to D1 and D2 and so equal but opposite voltages are applied across the two 390pF capacitors. Since the voltages across the two 390pF capacitors are equal, their centre-point voltage is zero (and there is no output). Any frequency deviations from 10.7MHz, however, produce a corresponding phase shift in the secondary. The centre-tapped secondary winding then becomes unbalanced, so that the voltage at one end (with respect to the centre tap) is greater than the voltage at the other. Hence, when the FM signal is above Fig.6: the response curve of the demodulator. Note that it is linear over the -75kHz to +75kHz deviation range. As the frequency is shifted above 10.7MHz, the demodulator voltage goes increasingly DEVIATION positive. Conversely, FROM 10.7MHz as the frequency shifts below 10.7MHz, the demodulator voltage goes increasingly negative. 10.7MHz, the output from D1 is greater than the output from D2. Thus, the junction of the two 390pF capacitors goes positive. Conversely, when the FM signal is below 10.7MHz, the output from D2 is greater than the output from D1 and the junction of the 390pF capacitors goes negative. Hence, as the FM signal deviates above and below 10.7MHz, the result is an audio signal at the junction of the 390pF ca­pacitors. AM rejection In order to make the FM detector less sensitive to changes in the IF level, the total voltage across the two 390pF capaci­tors is stabilised so that it cannot vary at an audible rate. This is achieved using a filter network consisting of two 1kΩ resistors and a 10µF capacitor. The effect of the 10µF capacitor is to keep the sum of the voltages across the two 390pF capacitors constant. This means that variations in the level of the FM signal will not produce variations in the output of the demod­ulator. The two 5.6kΩ resistors and their parallel .01µF capacitors provide con­venient test points which are used during the align­ment procedure. This type of FM demodulator is called a ratio detector. It differs from other FM detectors such as the Foster-Seeley detector because, as we have just seen, it incorporates AM rejection. This is important in the circuit because, as discussed earlier, limiting does not occur on low-level signals. De-emphasis The output from the demodulator is de-emphasised using an 8.2kΩ resistor and a .0068µF capacitor, and then fed to audio amplifier stage IC4. IC4 operates with a gain of 20; its output appears at pin 5 and drives an 8-ohm loudspeaker via a 470µF ca­pacitor. VR1 functions as the volume control, while a Zobel network consisting of a 10Ω resistor and a series .047µF capaci­tor is connected across the output to ensure stability. Power for the audio amplifier is derived from the 9V rail via a 10Ω resistor and a 470µF decoupling capacitor. This ar­rangement ensures a low impedance supply for IC4 over the life of the battery. Automatic frequency control As well as being fed to IC4, the demodulated signal is also filtered using a 47kΩ resistor and a 1µF capacitor and applied to the anode of varicap diode VC5. At the other end, VC5’s cathode is connected via a 47kΩ isolating resistor to a 1.37V bias vol­tage, as set by a voltage divider consisting of 100kΩ and 18kΩ resistors. Because it is a varicap diode, VC5 varies its capacitance according to the voltage across it. Its anode is at RF ground due to the .01µF capacitor, which means that VC5 and its series 10pF capacitor are effectively in parallel with the tuned circuit incorporating L3. We can now see how VC5 provides automatic frequency control. When the radio is correctly tuned, the filtered output from the demodulator (ie, the AFC control line) is at 0V DC. However, if the local oscillator drifts off frequency, or if the tuning is slightly off frequency, then the AFC control line will apply a DC bias to VC5’s anode. As a result, VC5 changes its capacitance and this shifts the local oscillator back to its correct frequency. The 1µF capacitor across the AFC line provides a long time constant so that the low frequency audio response is maintained down to below 20Hz. That describes the circuit description. Next month, we will continue with the full details on construction SC and alignment. April 1995  21 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au If you’re looking for an accurate way to control film developing times, then take a look at this Photographic Timer. It will switch on mainspowered fluorescent ultraviolet tubes or incandescent lamps rated at up to 1200W for a preset time ranging from 1-450 seconds. D eveloping photos or making PC boards and front panels re quires a controlled light source. Depending on the process, this could be based on special incandescent globes or ultraviolet tubes. In either case, the developing time needs to be accurately set so that the exposure is correct. Now this is all well and good if you have a light box or enlarger which incorporates a timer but these are usually very expensive. What’s more, controlling the mains power requires specialised circuitry, so we’ve come up with this low-cost Photo­graphic Timer which should fit the bill. It uses only a handful of components, including an optocou­ p led Triac driver to isolate the mains from the low-voltage control circuitry. We’ve also used an isolated-tab Triac to eliminate the need for an isolating kit. By the same token, any project that requires 240V wiring must be done with extreme caution. We recommend that if you haven’t worked with 240VAC wiring before, then it would probably be a good idea to give this project a miss or find an experienced constructor to build it for you. Main features Let’s now discuss the main features of the unit. As can be seen from the photos, the Photographic Timer is housed in a metal case and uses a small mains transformer to power the control circuitry. All the controls are located on the front panel and these are as follows: (1) a Power switch with neon indication; (2) a Focus switch; (3) a Range switch (x1 or x10); (4) a Start switch; and (5) a 12-position rotary switch which selects between the 12 timer settings on each range (ie, 1-45 seconds and 10-450 seconds). A photographic timer for darkrooms By JOHN CLARKE The prototype was built into a compact metal case which is earthed. It provides timed periods ranging from 1-450 seconds over two ranges. April 1995  25 39k 10k 1s 16k 24k 33k 43k 62k 91k 120k 200k 270k 360k 510k 10k 10k 1.4s 8 10 START S3 PERIOD 2.8s S1 5.6s 8s 3.3k 470  x10 TIMER A K 1 2 45s A1 A2 G G 4 F1 5A A A1 22  1W E A POWER S5 E T1 2851 GPO CASE BR1 WO4 N REG1 IN 7812 OUT 12.6V 470 25VW N I GO 0.1 TR1 250VAC MAC320 A2 A8FP .033 250V AC IC2 MOC3021 23s 32s 6  C 330  1W 10k B E C VIEWED FROM BELOW Q1 MODE BC338 S4 4.7k B VR1 5k 0.1 220 16VW LL  680  FOCUS IC1 7555 3 6 OUT T'HOLD MOD 1 5 11s 16s 0.1 R 7 DISCH RANGE S2 x1 22 35VW LL 4 2 TRIGGER 2s 4s ON LED1 +12V 330  1W 680  GND +12V 10 16VW E CASE PHOTOGRAPHIC TIMER Fig.1: the circuit uses 7555 timer IC1 to provide the timing period. When the start switch (S3) is pressed, its pin 3 output goes high & turns on Q1. Q1 then drives optocoupler IC2 which in turn switches on Triac TR1. The Focus switch is typically used to switch a photographic enlarger lamp on so that an image can be focused prior to print­ing. The lamp is then switched off and the Start button pressed to initiate the exposure period. A red LED adjacent to the Start switch lights while ever power is applied to the 240V GPO socket mounted on the rear panel. The 12 timing values are arranged in a geometric progres­sion, with the square root of 2 (ie, 1.414) as the multiplier. This gives nominal values of 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 23, 32 and 45 seconds on the x1 range. This type of geometric progression is ideal for photographic work, since doubling the exposure time represents one stop. What this means is that the selector switch effectively steps in half-stop increments. This order of resolution should be quite sufficient for photographic purposes and other general exposure work involving light boxes. Circuit details Let’s now take a look at the circuit details – see Fig.1. The circuit is based on a CMOS 7555 timer (IC1) which is connected in monostable mode. Switch S1 se26  Silicon Chip lects one of 12 outputs provided by a resistive divider network to set the basic timing interval, while S2 selects between two timing capacitors to provide the x1 or x10 range. The resulting RC time constant is connected to pin 6 (threshold) of IC1 and thus sets the overall timing interval. Note that the two main timing capacitors selected by the Range switch (S2) are both specified as low leakage (LL) types. This is necessary because at high settings of S1, the charging Main Features • • • • • • • Controls loads up to 1200W Timer operates from 1-45s in 12 steps for x1 range; & from 10s-450s (7.5min) in 12 steps for x 10 range Timing steps arranged in 1.41:1 increments (equivalent to half a stop) Focus switch Red “safe light” indicators Compact case Isolated control circuitry & isolated tab Triac current is very low. As a result, standard electrolytic capaci­tors with their higher leakage currents would never charge up to a level sufficient to end the timing cycle (ie, the lamps would never switch off). The circuit works like this: at power on, the reset pin (pin 4) of IC1 is momentarily pulled low via a 0.1µF capacitor. This prevents the pin 3 output of IC1 from initially going high. After a short period, the reset input is then pulled high via a 10kΩ pullup resistor and the timer can function normally. The timing sequence is initiated by pressing the Start switch (S3). This momentarily pulls the pin 2 trigger input of IC1 low via a 10µF capacitor and this, in turn, causes the pin 3 output to go high. The 10µF trigger capacitor then quickly charg­es via an associated 10kΩ resistor to end the trigger pulse. This ensures that the timing period cannot be influenced by holding S3 switch down. When S3 is released, the 10µF timing capacitor discharges via a second 10kΩ resistor connected between the switch and the positive supply rail (Vcc). The circuit is then ready for the next trigger input. Once triggering has occurred, the pin 3 output stays high while the timing capacitor charges via the resistive HIGH VOLTAGE WITHIN DOTTED LINES TERMINAL BLOCK .033 250VAC 22  1W 0.1 250VAC TR1 330  1W 330  1W BR1 REG1 3.3k POWER TRANSFORMER T1 470uF IC2 MOC3021 10uF 4.7k 680  16k 24k 62k 43k Q1 VR1 10k 39k LK1 680  33k 1 0.1 470  IC1 7555 0.1 220uF 1 10k 91k 120k 200k 270k 510k 360k 10k 10k 10uF 22uF Fig.2: install the parts on the PC board as shown here & note that the parts enclosed by the dotted lines operate at mains potential when power is applied. network selected by S1. When the capacitor voltage subsequently reach­es a preset threshold, pin 3 goes low again and the timing period ends. The timing capacitor on pin 6 then discharges via the 470Ω resistor connected to pin 7. This resistor limits the capacitor discharge current to prevent damage to the IC. The pin 6 threshold voltage is nominally 2/3Vcc but, in this circuit, can be shifted about this value by adjusting the voltage applied to the modulation input at pin 5. This is achieved using VR1 which forms part of a resistive divider con­nected across the supply rails. Basically, VR1 functions as a calibration control and is necessary because the timing capaci­tors have a very wide tolerance range (±20%). In practice, it’s simply a matter of calibrating the unit on the x1 range for one setting. The x10 range should Fig.3: this is the full-size etching pattern for the PC board. It is a good idea to check carefully for etching defects before mounting any of the parts. then be within 5%, provided that the 22µF and 220µF capacitors are sup­ plied matched – see parts list. Power control Assuming S4 selects the TIMER position, IC1’s pin 3 output drives transistor Q1 via a 4.7kΩ base current limiting resistor. Q1 thus turns on whenever pin 3 is high (ie, for the duration of the monostable period). Alternatively, when S4 selects the FOCUS position, Q1’s base is pulled to the positive supply rail and so the transistor is permanently held on. Q1 in turn drives IC2 which is a MOC3021 optocoupled Triac driver. Its job is to provide very high voltage isolation between the low voltage control circuitry and the switched mains voltage. When Q1 turns on, an internal LED between pins 1 and 2 of IC2 also turns on and this triggers an internal Triac between pins 6 and 4. Finally, Warning! Potentially lethal mains voltages are present on some components on the PC board when power is applied to this unit (see Fig.2). Do not attempt to build this unit unless you are experienced at working with mains voltages. Also, do not attempt to work on any high voltage circuitry while the unit is plugged into the mains. IC2 triggers TR1, an MAC­ 320A8FP isolated tab Triac, which turns on and connects the Active mains line to the Active pin on the GPO. The 22Ω 1W resistor and the 0.1µF capacitor provide a snub­ber network for TR1, while the two 330Ω resistors April 1995  27 power the low voltage circuitry. The Triac circuitry is fed by an Active AC supply lead which goes from the switched side of S5 directly to the A2 termi­nal of TR1. The A1 terminal of the Triac is then connected to the Active terminal on the GPO, while the Neutral terminal is con­nected directly to mains Neutral. The Earth terminal is connected to mains Earth via the metal case. Note that the 5A fuse limits the maximum power handling capability to 1200W. Don’t increase the rating of this fuse in an effort to power greater loads though. The 5A rating has been selected to ensure that the Triac (TR1) is operated well within its ratings. Construction A right-angle bracket is fitted between the rear panel & the lid to prevent flexing of the aluminium rear panel in the vicinity of the GPO. This bracket can be deleted if a metal diecast case is used. and the 0.033µF capacitor do the same for the Triac in IC2. Note that because we are only switching the mains on and off at widely spaced intervals, we haven’t worried about sup­ pressing any RF noise radiated by the switching action of TR1. However, if this is a problem, you can substitute a MOC3041 for IC2. This device has zero voltage crossing detection circuitry to ensure that the Triac switches on at the zero voltage crossing points. It costs slightly Most of the parts, including the mains transformer, are mounted on a PC board coded 10304951 and measuring 127 x 76mm. This was installed in a metal case measuring 100 x 60 x 150mm but you can use a larger metal case if you wish. Do not substi­tute a plastic case, as this could compromise electrical safety. Before starting construction, carefully check the PC board for any breaks or shorts between tracks by comparing it with the published pattern. Repair any faults that you do find (in most cases, there will be none), then start the assembly by installing PC stakes more and is harder to obtain than the MOC3021 though. Power supply Power for the low-voltage timing circuitry is derived from the mains via fuse F1, power switch S5 and a small 12.6V transformer. This trans­former drives bridge rectifier BR1 and the resulting DC is filtered using a 470µF capacitor and applied to 3-terminal regulator REG1. The regulated +12V output from REG1 is then used to TABLE 1: RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 1 1 1 1 1 1 1 1 4 1 1 2 1 2 1 28  Silicon Chip Value 510kΩ 360kΩ 270kΩ 200kΩ 120kΩ 91kΩ 62kΩ 43kΩ 39kΩ 33kΩ 24kΩ 16kΩ 10kΩ 4.7kΩ 3.3kΩ 680Ω 470Ω 330Ω 22Ω 4-Band Code (1%) green brown yellow brown orange blue yellow brown red violet yellow brown red black yellow brown brown red yellow brown white brown orange brown blue red orange brown yellow orange orange brown orange white orange brown orange orange orange brown red yellow orange brown brown blue orange brown brown black orange brown yellow violet red brown orange orange red brown blue grey brown brown yellow violet brown brown orange orange brown brown red red black brown 5-Band Code (1%) green brown black orange brown orange blue black orange brown red violet black orange brown red black black orange brown brown red black orange brown white brown black red brown blue red black red brown yellow orange black red brown orange white black red brown orange orange black red brown red yellow black red brown brown blue black red brown brown black black red brown yellow violet black brown brown orange orange black brown brown blue grey black black brown yellow violet black black brown orange orange black black brown red red black gold brown at all external wiring points –see Fig.2 and Fig.3. This done, install the wire link, resistors, capacitors and trimpot VR1. Table 1 shows the resistor colour codes but it is a good idea to also check them using a digital multimeter. Make sure that the electrolytic capacitors are correctly oriented. The semiconductors can now all be installed. These include the transistor (Q1), the regulator (REG1), the two ICs, the bridge rectifier (BR1) and the Triac (TR1). The latter should be mounted at full lead length, so that it can later be bolted to the back of the rear panel. Once again, take care to ensure that all these parts are correctly oriented. The power transformer is secured to the board using 3mm screws, nuts and washers. It should be oriented as shown in Fig.3, with its primary leads (brown and blue) adjacent to the edge of the PC board. Secure it firmly in position, then secure the mains terminal block to the board using a 3mm machine screw and nut. By this stage, the board assembly should be complete. It can now be used as a template for marking out the positions of its corner mounting holes on the base of the case. Drill these holes to 3mm, then mark out and drill holes for the mains cord grip grommet, the panel mount fuse holder, the GPO socket, the earth lug and the Triac (TR1). Fig.4 shows how these parts are arranged on the rear panel. The position of the Triac mounting hole can be determined by temporarily positioning the board in the case on 9mm spacers. At the same time, be sure to position the hole for the cord grip grommet so that it will clear the PC board. Drill a small pilot hole initially, then carefully ream and file the hole to the correct shape so that the grommet is a snug fit. This is neces­sary to ensure that the mains cord will be firmly anchored. The hole positions for the GPO can be marked out by using it as a template. It should be oriented as shown on Fig.4 (ie, with the Earth terminal towards the bottom). The entry holes for the Active, Neutral and Earth leads must be fitted with small rubber grommets to protect the lead insulation. Right angle bracket As can be seen from the photographs, a right angle bracket was fitted PARTS LIST 1 PC board, code 10304951, 76 x 127mm 1 front panel label, 100 x 52mm 1 metal cabinet, 100 x 60 x 150mm or similar 1 10A panel mount mains socket (HPM Cat. N0 35 or equivalent) 1 12-position single pole rotary switch (S1) 2 SPDT toggle switches (S2,S4) 1 momentary pushbutton normally open switch (S3) 1 SPST mains rocker switch with integral Neon (S5) 1 2851 12.6V 150mA mains transformer (T1) 1 M205 panel-mount fuse holder 1 M205 5A 250VAC fuse 1 10A 250VAC 2-way terminal block 1 14mm diameter knob 1 cord grip grommet for 10A mains flex 1 10A mains cord & plug 3 5.5mm ID grommets 1 right angle bracket plus screws & nuts (see text) 1 5mm LED bezel 1 solder lug 4 9mm tapped spacers 5 12mm x 3mm dia. screws & nuts 4 9mm x 3mm dia. screws & nuts 1 3mm dia. star washer 1 30mm length of 6-way rainbow cable 2 30mm lengths of 6-way rainbow cable 1 120mm length of blue hookup wire 1 120mm length of red hookup wire 1 120mm length of yellow hookup wire 1 200mm length of brown 10A mains wire 1 100mm length of blue 10A mains wire 1 50mm length of 0.8mm tinned copper wire to the rear panel of the prototype, just above the GPO. This bracket is secured to the rear panel by the top GPO mounting screw and to the lid using a screw and a captured nut. 5 100 x 2.4mm cable ties 1 70mm length of 19.1mm diameter heatshrink tubing 25 PC stakes 1 5kΩ miniature horizontal trimpot (VR1) Semiconductors 1 TLC555CP, LMC555CN, 7555 or equivalent CMOS timer (IC1) 1 MOC3021 opto-isolated Triac driver (IC2) 1 WO4 1.2A 400V DIP bridge rectifier (BR1) 1 7812, 12V 3-terminal regulator (REG1) 1 MAC320A8PF 8A isolated tab Triac (TR1) 1 BC338 NPN transistor (Q1) 1 5mm diameter red LED (LED1) Capacitors 1 470µF 25VW PC electrolytic 1 220µF 16VW RBLL electrolytic 1 22µF 35VW RBLL electrolytic 2 10µF 16VW PC electrolytic 2 0.1µF MKT polyester 1 0.1µF 250VAC plastic film 1 0.033µF 250VAC plastic film Note: the 220µF capacitor should be selected so that its measured value is 9.5 -10.5 times larger than the measured value of the 22µF capacitor. Resistors (0.25W, 1%) 1 510kΩ 1 24kΩ 1 360kΩ 1 16kΩ 1 270kΩ 4 10kΩ 1 200kΩ 1 4.7kΩ 1 120kΩ 1 3.3kΩ 1 91kΩ 2 680Ω 1 62kΩ 1 470Ω 1 43kΩ 2 330Ω 1W 1 39kΩ 1 22Ω 1W 1 33kΩ Miscellaneous Heatsink compound (for Triac), solder, heatshrink tubing. This was done to add rigidity to the aluminium rear panel on the prototype, to prevent flexing as the plug is pushed in and out. If a metal diecast case or a steel case April 1995  29 GPO NEUTRAL F1 SOLDER LUG EARTHED TO CASE GREEN/YELLOW ACTIVE TR1 A (BROWN Fig.4 (left): follow this diagram carefully when wiring up the Photographic Timer & be sure to use mains-rated cable for all 240V wiring. The Triac (TR1) should be smeared with heatsink compound before it is bolted to the rear panel. Make sure that the earth lug is firmly secured. A (BROWN) CORD GRIP GROMMET BLUE E GREEN/ YELLOW BROWN EARTH 22  1W 0.1 250VAC N (BLUE) 330  1W E BLU BR1 330  1W N OW BR POWER TRANSFORMER T1 470uF YELLOW REG1 3.3k YELLOW IC2 MOC3021 10uF 9 8 0.1 220uF 1 10k 7 9 8 10k 91k 120k 200k 270k 510k 10 360k 10k 7 12 5 Wiring K LED1 6 1 14 10uF 22uF A 11 START S3 14 POWER S5 13 2 3 PERIOD S1 4 30  Silicon Chip 15 15 RANGE S2 ACTIVE (BROWN) 10 13 IC1 7555 ACTIVE (BROWN) 11 4.7k 6 680  3 5 16k 2 0.1 470  NEUTRAL (BLUE) 12 1 24k 62k 43k Q1 4 VR1 680  39k 33k LK1 10k 1 is used, this bracket can be left out. However, it must be included where the rear panel is made from light-gauge aluminium. The front panel label can now be affixed to the case and used as a template for drilling out the switch mounting holes. A hole will also have to be drilled to accept the LED bezel. The hole for the mains switch can be made by drilling a series of small holes around the inside perimeter of the cutout area, then knocking out the centre piece and carefully filing the hole to shape. This done, mount the PC board in the case on 9mm spacers and install all front and rear panel components except for the rotary switch (S1). When mounting the earth solder lug, be sure to scrape away any paint from around the hole to ensure a good contact. The solder lug should be firmly secured using a star washer under the nut to prevent it from coming loose. The Triac can be directly bolted to the case since its tab is isolated. Smear a small amount of heatsink compound between the mating surfaces before bolting it to the case to aid heat transfer. Warning: do not substitute a Triac with a non-insulated tab, as this will create a short between mains active and the case. The shaft of the rotary switch can now be trimmed to suit the knob. In addition, its locking tab washer must be removed to allow the switch to select all 12 positions. This locking tab can be accessed by first removing the mounting nut and washer. Do not mount the switch yet, as it is easier to wire outside the case. MODE S4 The construction can now be completed by installing the wiring as shown in Fig.4. Rainbow cable is used for the connec­tions to S1. Use a 6-way cable for pins 7-12 and two 3-way cables for pins 4-6 and 1-3. When all the connections have been made, install the switch with the Use cable ties to keep the mains wiring neat & tidy & be sure to sleeve the fuseholder & power switch with heatshrink tubing to prevent accidental electric shock. Note that some components on the PC board operate at high voltage – see Fig.2. x1 SECONDS 5.6 8 11 16 4 + 2.8 23 2 32 1.4 1 45 contact with other PC stakes. LED 1 has its leads connected directly to the PC stakes (note: the anode lead is the longer of the two). The remainder of the wiring (ie, to the terminal block, fuseholder, power switch S5 and earth lug) must be run using mains-rated cable. Use brown cable for the Active connections, blue for Neutral and green/yellow for Earth. Strip back about 130mm of the outer sheath of the mains cord before + + x10 FOCUS RANGE + + ON START + POWER Photographic Timer WARNING! HIGH VOLTAGES INSIDE 6-way cable at the bottom and tighten the nut. Adjust the switch so that the marker on the knob aligns with the “1” on the front panel when the switch is fully anticlockwise. Don’t forget the connection from S1’s wiper to S2. The connections to S2 and S4 are run using light duty hookup wire, while S3 only requires very short lengths of tinned copper wire to connect it to the board. Note that its terminals are bent sideways to prevent Fig.5: this full-size artwork can be used as a drilling template for the front panel. The warning label at right should be stuck to the lid of the case. pushing it through the entry hole on the back of the case. This done, clamp the mains cord using the cord grip grommet and terminate the Earth lead to the solder lug. A second Earth lead must then be run from the solder lug to the Earth terminal on the GPO. The wiring to the fuseholder and power switch can now be run. Before making these connections, slip some heatshrink tubing over the leads. After the connections have been made, push the heatshrink tubing over the switch and fuseholder bodies and shrink it down with a hot air gun (see photo). This will insulate the connections to these devices to guard against accidental contact. Finally, complete the wiring to the terminal block and to the GPO, then secure the mains wiring with cable ties as shown in the photograph. The transformer secondary leads and the low-voltage wiring to S2 and S4 should also be secured using cable ties. This will prevent any accidental contact between the low-voltage and high-voltage sections of the circuit if a lead comes adrift. Testing Exercise extreme caution when testing the Photographic Timer. As April 1995  31 Fig.2 indicates, one section of the PC board operates at high voltage (240V AC), so you must not touch any parts inside the area enclosed by the dotted lines when the unit is plugged into the mains. This includes the two connections on either side of TR1. The same goes for the fuseholder and power switch termi­nals which, in any case, should be insulated using heatshrink tubing (see above). So the area inside the dotted lines on Fig.2 must be treat­ed as dangerous. At no time should the circuit be worked on while the unit is connected to the mains. VR1 can, however, be adjusted safely, provided that the live component area is avoided. To test the unit, connect a multimeter between the tab of REG1 and link LK1 and set the meter to DC volts. This done, apply power and check that the meter reads about 12VDC. If it is sub­stantially below this, switch off, unplug the mains cord and check for assembly errors. SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. ORDER FORM PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 Calibration POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏ 3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ MasterCard Card No. Signature­­­­­­­­­­­­_______________________________ Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). 32  Silicon Chip ✂ Street ___________________________________________________________ Assuming that all is well, set the Focus switch to off, select the 16-second range (using S1 & S2), and press the Start button. Check that the LED immediately comes on and stays on for a short period of time. If it does, adjust calibration control VR1 on a trial and error basis until the period is exactly 16 seconds. Note: wind VR1 clockwise to increase the period and anticlockwise to decrease it. If the LED fails to come on, switch the Focus on. If the LED now comes on, check the circuitry around IC1. Conversely, if the LED stays out, check transistor Q1 and the LED polarity. Calibration on the x10 range position can now be checked. Provided that the timing capacitors have been properly selected, it should be within 5% of the expected value. If the period is too low and accuracy is critical, simply pad the 220µF capacitor until the correct period is obtained. This can be done by con­necting a low-value (eg, 10µF) capacitor in parallel with the 220µF capacitor on the underside of the board (be sure to use a low-leakage type and don’t forget to pull that mains plug from the wall). Finally, attach the lid, plug a lamp into the output socket and check that it lights for the preset time when the Start button is pressed. The Photographic SC Timer is now finished. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) TOTAL Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS ❏ New subscription – month to start­­___________________________ ❏ Renewal – Sub. No._______________   ❏ Gift subscription ☞ RATES (please tick one) Australia Australia with binder(s)* NZ & PNG (airmail) Overseas surface mail 2 years (24 issues) 1 year (12 issues) ❏ $A90 ❏ $A49 ❏ $A114 ❏ $A61 ❏ $A135 ❏ $A72 ❏ $A135 ❏ $A72 ❏ $A240 Overseas airmail ❏ $A120 *1 binder with 1-year subscription; 2 binders with 2-year subscription GIFT SUBSCRIPTION DETAILS Month to start__________________ Message_____________________ _____________________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) YOUR DETAILS Your Name_________________________________________________ (PLEASE PRINT) Address___________________________________________________ Address______________________ _____________________________ State__________Postcode_______ ______________________________________Postcode___________ Daytime Phone No.____________________Total Price $A __________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ Master Card 9am-5pm Mon-Fri. Please have your credit card details ready ______________________________ Card expiry date________/________ Card No. Phone (02) 9979 5644 Signature OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail coupon to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia April 1995  37 This multipurpose circuit is a balanced microphone preamplifier & line input mixer. It can operate from a variety of AC & DC supply voltages & has low noise & distortion. By LEO SIMPSON Balanced microphone preamplifier & line mixer All professional public address systems use balanced micro­phone lines. These have the advantage of considerable immunity from hum and noise even when long lines are necessary. The disad­vantage is that the preamplifier requires either an expensive balanced-to-unbalanced transformer or a fairly complex circuit involving two or three low noise op amp ICs. This project gets around that problem by using the SSM2017 IC from Analog Devices. This chip has been specially designed as a balanced microphone preamplifier. The resulting circuit has high gain, low noise and very low distortion. As presented here, the preamplifier Performance of Prototype Microphone Input Gain ��������������������������������������� 59.5dB Signal-to-noise ratio ��������������� -74dB A-weighted with respect to 0.75mV input and 1V output; -71.5dB unweighted (22Hz to 22kHz); both measurements taken with a 50Ω balanced source. Frequency Response ������������� 180Hz to 20kHz, +0dB & -3dB Auxiliary Inputs Gain ��������������������������������������� 13.5dB Signal-to-noise ratio ��������������� -98.7dB A-weighted with respect to 0.24V input and 1V output; -96.7dB unweighted (22Hz to 22kHz); both measurements taken with a 600Ω unbalanced source. Frequency response �������������� 30Hz to 20kHz, +0dB & -3dB 38  Silicon Chip is a small PC board measuring 90 x 56mm. It has two ICs, two 3-terminal regulators and a number of trimpots for level setting. As well as providing a pair of balanced inputs for a low impedance microphone, it also has provi­ sion for two line-level inputs. Fig.1 shows the complete circuit. Circuit operation IC1, the SSM2017 balanced microphone preamplifier, requires very few external components for its basic operation and its gain is set to 200 (+46dB) by the 33Ω resistor (R3) between pins 1 & 8. The balanced input is AC-coupled via 10µF capacitors C1 & C2 which are there to block any DC signals and also to prevent any DC being applied to the microphone if the circuit is operated in single-supply mode. We’ll explain that point in a moment. The input impedance is set to about 1.3kΩ by two 680Ω resistors (R1 & R2), while C3 & C4 attenuate unwanted signals above the audio passband. The output of IC1 is AC-coupled by a 1µF capacitor to trimpot VR1 which acts as the microphone level control. PIN4 AUX 1 C10 1 VR2 10k C11 1 R9 10k C12 1 R10 10k Fig.1: the heart of this circuit is the SSM2017 balanced micro­ phone preamplifier (IC1). Its output is fed into a mixer stage using IC2a, half of an LM833 dual low noise op amp. IC2b, provides a rail splitting facility if the circuit is to be pow­ered from a single supply rail. PIN5 PIN6 AUX 2 PIN7 C13 1 VR3 10k MICROPHONE + PIN2 R11 10k GND PIN1 R12 10k PIN3 C8 180pF R3 33 C1 10 C3 .001 R1 680  C4 .001 R2 680  3 +12V 1 8 IC1 2 SSM2017 7 6 4 VR1 10k 5 R5 10k 5 C6 10 R7 47k C7 0.1 R6 10k -12V C2 10 +12V R4 10k C5 1 6 PIN10 12VAC 8 IC2b LM833 7 SINGLE SPLIT JP1 PIN11 CT 4 PIN12 12VAC -12V 7812 7912 2 3 1 IC2a C9 10 R8 10k PIN8 OUTPUT PIN9 D1-D4 4x1N4004 IN C14 470 35VW C17 470 35VW REG1 7812 OUT GND C15 10 GND C16 10 OUT IN +12V -12V REG2 7912 I GO GIO BALANCED MICROPHONE PREAMPLIFIER Line level signals are AC-coupled to trimpots VR2 & VR3 and these act as mixing controls for these signals. All three signals are fed to op amp IC2a which is a conventional mixer stage with its gain set to 4.7, the ratio of the 47kΩ feedback resistor (R7) to the 10kΩ mixing resistors. The total gain of the preamplifier is therefore close to 940 (+59.5dB) which is more than sufficient for most microphone applications. The bass response of the preamplifier is curtailed below 300Hz and is -3dB down at about 180Hz, mainly due to the interac­tion of C7 with R6. This rolloff is desirable for most microphone applications to prevent pick-up of building rumble and also to prevent serious overload by users who tend to blow into micro­phones. This rolloff can be seen in the frequency response plot of Fig.2. By contrast, the high level inputs have a more of less normal bass response, with the -3dB point at just Fig.2: this graph shows the frequency response of the microphone preamplifier input, taken with VR1 set for maximum sensitivity. As shown, the response is 3dB down at 180Hz & 20kHz. April 1995  39 Fig.3: frequency response plot for the auxiliary 1 input, taken with VR2 set for maximum sensitivity. the bridge rectifier (diodes D1-D4). The input supply can be ±12V to ±30V DC, or AC (24V centre-tapped up to 40V centre-tapped). Alternatively, it can be run from a single rail DC supply ranging from 15-30V or from an AC supply ranging from 12-20V. If the unit is powered from a centretapped supply, the resulting supply rails from the 3-terminal regulators are ±12V DC and the link at JP1 is set for split supply opera­tion. In this case, IC2b does nothing. On the other hand, if a single rail supply is used, the negative 3-terminal regulator is not used. Instead, C17 & C16 are omitted and links wired in their place. The result is a single rail supply of 12V DC from REG1. This is then split by IC2b and so the circuit effectively has its reference, pin 5 of IC1 and pin 3 of IC2a, set to +6V. Alternatively, IC1 and IC2 effectively run from a supply of ±6V. For this condition, the link at JP1 is set to the “single” setting. Ideally, for maximum signal hand­ ling and lowest distortion, the circuit should be run with dual supply rails. The distortion curves of Fig.3 and Fig.4 were measured with the prototype pow­ered from spilt supplies (ie, ±12V DC). Fig.4 shows the harmo­nic distortion of the preamplifier for the microphone input (10mV in and with trimpot VR1 set for 1V out). Both VR2 & VR3 were set to maximum attenuation. Fig.5 shows the harmonic distortion of the preamplifier for one of the line inputs. In this case, VR1 was set to zero, while the line input in question was 0.24V in and 1V out. Construction Fig.4: total harmonic distortion & noise versus frequency plot for the microphone preamplifier input (10mV in & 1V out). below 40Hz, as can be seen in the frequency response plot of Fig.3. Both these frequency response plots exhibit a high frequency rolloff above 10kHz and this is due mainly to the 180pF capacitor C8 shunting 47kΩ feedback resistor R7. Again, this rolloff is desirable for public address work, to keep noise to a minimum and also to minimise 40  Silicon Chip breakthrough of radio interference. Well, the function of IC1 and IC2a (half of an LM833 dual low noise op amp) is fairly straightforward but what is the function of the remaining op amp (IC2b). This acts as a supply rail splitter in case the unit is powered from a single DC source. The power supply section can accept an AC or DC input by virtue of Assembly of the PC board is quite straightforward. We sug­gest installing the 12 PC pins and the 3-pin header first, fol­lowed by the links, resistors and diodes. This done, install the trim­ pots, the capacitors, ICs and regulators. Make sure that all polarised parts such as the electrolytic capacitors, diodes and other semiconductors are installed the right way around. If you don’t make sure of this point, the circuit could be damaged when power is applied for the first time. Before applying power to the finished board, check your work carefully to make sure that all components are correctly in­stalled and that there are no solder bridges or missed solder joints PARTS LIST 1 PC board, code PED5531, 90 x 56mm 12 PC pins 1 3-pin header (JP1) 1 mini jumper 3 10kΩ horizontal trimpots (VR1-VR3) Semiconductors 1 SSM2017 balanced microphone preamplifier (IC1) 1 LM833 dual low noise op amp (IC2) 1 7812 +12V regulator (REG1) 1 7912 -12V regulator (REG2) 4 1N4004 silicon diodes (D1-D4) Fig.5: total harmonic distortion & noise versus frequency plot for the auxiliary 1 input at maximum sensitivity. 10k AUX1 PIN4 INPUT PIN5 PIN6 AUX2 INPUT PIN7 .001 VR2 10uF 470uF 680  VR1 10k Where to buy the kit 470uF JP1 1 10k 47k 1uF 10k 10uF 10k 10uF PIN8 PIN9 OUTPUT 10k Fig.6: the component overlay diagram for the PC board. Make sure that the jumper is correctly installed for dual supply or single supply operation. VR1 sets the level for the microphone input, while VR2 & VR3 set the levels for the two auxiliary inputs. on the underside. If the unit is to be powered from a single supply, the 7912 regulator can be omitted and links installed in place of electrolytic capacitors C16 & C17. Make sure that the jumper has been set correctly as well. Testing Connect a microphone to the microphone input, making sure that the correct pins are used: Pin 1 = Ground/Shield Pin 2 = Signal Hot (In Phase) Resistors (0.25W 5%) 1 47kΩ (yellow violet orange gold) 8 10kΩ (brown black orange gold) 2 680Ω (blue grey brown gold) 1 33Ω (orange orange black gold) PIN12 CT D4 10uF 1uF VR3 PIN11 12VAC D3 1uF 0.1 PIN10 12VAC D2 REG2 680  1uF 1uF D1 IC2 LM833 MIC +PIN2 INPUT GND PIN1 .001 1 180pF 10uF REG1 33W IC1 2017 -PIN3 10k 10uF Capacitors 2 470µF 35VW electrolytic 6 10µF 35VW electrolytic 5 1µF 63VW electrolytic 1 0.1µF 100VW metallised polyester (greencap) 2 .001µF disc ceramic 1 180pF disc ceramic Pin 3 = Signal Cold (Out Phase) If you are using an unbalanced microphone make sure you have connected pins 1 and 3 together. Now turn all gain trimpots fully anticlockwise for minimum gain and connect the output to an amplifier. If the amplifier has a gain control, you should set this to about midway. If you now apply power, all should be quiet. If any undue noises appear from the loudspeakers, switch off immediately and check your work carefully. All seems OK? Whilst talk- This preamplifier has been de­ signed and produced by Al­tronics. The kit is priced at $27.50 (Cat. K-5531) and is avail­ able from Altron­ics in Perth or from any of their resellers. Note: copyright© of the PC pattern associated with this design is retained by Altronics. ing into the microphone, you can then increase the gain adjusting trimpot VR1, until a suitable level is obtained. The auxiliary inputs are tested in a similar way. The signal source for these inputs could be a CD player, tuner or cassette deck. If your application requires it, the trimpots can be re­ placed with standard pots. If this is done, we recommend the use of shielded cable for the wiring of the pots to minimise hum and noise. Naturally, the preamplifier should be situated away from any power transformers to minimise SC hum pick-up. April 1995  41 Build a 50W/channel stereo amplifier; Pt.2 Last month, we introduced our new high performance 50W/channel stereo amplifier & described the circuit operation. This month, we conclude with the presentation of the construction details. By LEO SIMPSON & BOB FLYNN Most of the construction of the new amplifier is quite straightforward. The work mainly involves mounting components on the five printed circuit board assemblies. These are the power amplifier board, the input selector board, the selector switch board, the tone control board and the optional RIAA preamp board. The first job is to assemble the input selector board which is shown in Fig.7(a). This board is coded 01103951 and carries the RCA input and output sockets. Before mounting any of the parts, it is a good idea to carefully check the copper pattern on the underside of the board. You should especially check for shorts between the long parallel tracks to the selector switch. 42  Silicon Chip Don’t just rely on a visual check here – switch your multi­meter to a high Ohms range and use it to confirm that the tracks are isolated from each other. This test will quickly locate faults on any board that has not been correctly etched. You will need to go through a similar checking procedure with each of the other boards when you come to them. Now install the parts as shown in Fig.7(a). The first job is to install the 25 PC pins. Fourteen of these support the selector switch assembly and these should be in­stalled from the copper side of the PC board; ie, so that the shoulder of each pin sits against its respective copper pad. The remaining pins are located at the left and right channel outputs, the tape inputs and the optional RIAA preamp inputs. If you’re not building this latter board, you can forget the pins for the preamp inputs but install a couple of links instead. These links are shown dotted on the diagram. This board is completed by soldering in the three 3 x 2-way RCA socket panels. One of these, at the end adjacent to the selector switch, is cut down to a 2 x 2-way, so that a total of 16 RCA sockets is provided. Fig.8(a) shows the selector switch board (code 01103952). Position the switch with the locating spigot towards the top and push the body of the switch all the way down onto the board before soldering the terminals. The pads along the bottom edge of the switch board can now be soldered to the 14 PC pins on the input selector board. Tone control board Fig.9(a) shows the parts layout on the tone control PC board (code 0110­ 3953). Commence assembly by installing PC pins at the external wiring points, then fit the wire links, resistors, capacitors and semiconductors. Check the orientation of polarised Fig.7(a): the input selector board. Note that if the optional RIAA preamp is not included in the amplifier, the two links shown dotted should be included & the associated PC pins omitted. TAPE IN TAPE OUT AUX2 AUX 1 VCR TUNER CD PHONO GND IF RIAA PREAMPLIFIER IS FITTED: REMOVE LINKS SHOWN DOTTED. R AND L CONNECT TO INPUTS AND RR AND LL CONNECT TO OUTPUTS OF PREAMP BOARD LL R L RR 1k 1k PCB PINS SOLDERED TO TRACKS OF SWITCH BOARD LEFT GND RIGHT TO TAPE INPUT OF CONTROL BOARD LEFT GND RIGHT TO SOURCE INPUT OF CONTROL BOARD Fig.7(b): this is the fullsize etching pattern for the input selector board. parts carefully when installing them on the board. These include the ICs, diodes, transistors and electrolytic capacitors. The 6.8µF and 22µF capacitors are bipolar types and can be installed either way around. The headphone socket, pots and pushbutton switches should be left till last. Be sure to push them all the way down onto the board but don’t solder all the leads at this stage. Instead, tack solder diagonally opposite pins at either end of each component. The tone control assembly can now be tested in the chassis to ensure that everything aligns properly. Adjust the alignment of the pots and switches as necessary before soldering the remaining pins. Balance control Fig.10 shows the wiring of the switch for the balance con­trol. The resistors are wired around the switch pins together with three short lengths of hook-up wire. These are soldered to the tone control board which can now be mounted in the chassis. It is mounted to the front panel using the pot nuts and lockwash­ers. The rear of the tone control board is secured using two 12mm tapped spacers and screws. Don’t fit the dress panel to the chassis at this stage. It should be left in its protective wrapping for as long as possi­ble, to protect it from scratches. When all the pot nuts are secured, use your multimeter to check that all the pot cases are electrically connected together, via the chassis. If not, it might be necessary to remove the board from S1 Fig.8(a): the selector switch board. This mates up to the 14 pins on the input selector board & is soldered at right angles to it. Fig.8(b): the etching pattern for the selector switch board. Check that it has been trimmed correctly along the bottom, so that there are no shorts. April 1995  43 MONITOR S2 3 2 BALANCE S4 1 1k 1k MODE S3 1k SOURCE INPUT L GND R TAPE INPUT L GND R 1k 1uF 1 22uF 22uF 100uF 100pF VOLUME VR1 100pF 100uF 1uF 15k 4.7k 1k 100k IC1 LM833 15k 4.7k 1k 100k 4.7k 4.7k TREBLE VR3 .0047 33pF 22k 22k .0047 100uF 4.7k 100uF 1 33pF IC2 LM833 .0047 .0047 4.7k -15V LED K 22k GND .01 0.1 3.9k .01 +15V LED A BASS VR2 22k 0.1 22k 82  82  Q2 5.6k Q1 6.8uF HEADPHONES D2 5.6k Q2 6.8uF 1 D1 5.6k 47k 33pF 15  15  100  100  Q1 22k 10k 10k 15  15  OUTPUT TO POWER AMPLIFIERS R GND L 22k D1 5.6k D2 47k 33pF 10k 10k IC3 TLO72 TONE DEFEAT S5 100uA 100uF 22k 44  Silicon Chip Fig.9(a) (left): the tone control board. Note that while the balance con­trol (S4) looks like a single potentiometer, it is actually a rotary switch, as shown in Fig.10 on the facing page. Fig.9(b) (above) shows the PC pattern for this board. This is shown 70% of actual size & may be reproduced full size by enlarging it by a factor of 1.41 on a photostat machine. RIAA preamp board As noted previously, this preamp board is optional and we assume that many readers will not need it. The parts layout is shown in Fig.11(a). It’s best to start with the smaller parts (resistors and wire links) first. Take care with the orientation of the LM833 IC and the electrolytic capacitors. The two input inductors (L1) are each made by winding four turns of 0.4mm enamelled copper wire on a ferrite bead (Philips type 4330 030 3218). Power amplifier board This board is identical to that presented in the February 1995 issue but we are repeating the assembly instructions here for the sake of completeness. The component layout is shown in Fig.13(a). To begin, first install the PC pins and links, followed 91k 7 6 7k 4. 4. 7k 91k 5 1.6k 4 9 1.6k 8 3 S4 82 0  A 10 2 11 6k 1. 12 82 0  the chassis and then take a round file to lightly clean off any paint or anodising from around the pot mounting holes. The reason for making sure that the pots are properly earthed is to keep hum and noise to a minimum. Don’t forget to strip the enamel off the ends of the lead wires before the inductors are soldered into the PC board. 1 1. 6k This photo gives a good general view of the tone control board and the power amplifier board. 1 3 2 CONNECT TO PINS 1, 2 AND 3 ON CONTROL BOARD The balance control is an 11-position rotary switch with resistors wired around its terminals. This arrangement gives much better separation between channels than a potentiometer. Fig.10: here’s how the rotary switch is wired with the resistors to provide the balance control. April 1995  45 10uF 22uF 1M RIGHT OUTPUT GND 150  RIGHT INPUT .015 390W 100pF 100k 100  100k GND 200k 16k .0047 1 L1 100k LEFT OUTPUT 100pF 1M 10uF 390  GND 100  100k 0V -15V 16k 150  GND 0.1 47uF .0047 0.1 IC1 LM833 LEFT INPUT +15V 47uF L1 200k .015 22uF Fig.11(a): the optional RIAA preamplifier board. The large electrolytic capacitors are bipolar types & can be installed either way around. by the resistors and capacitors. Make sure that you install the electrolytic capacitors with correct polarity. This done, install the fuse clips and note that there is a trick to this task. The clips have little lugs at one end which stop the fuse from moving longitudinally. If you install the clips the wrong way around, you won’t be able to fit the fuses. HEATSINK 3mm SCREW DEVICE MICA WASHER INSULATING BUSH Fig.11(b): the full-size etching pattern for the optional RIAA preamplifier board. In most cases, this board will not be needed. 3mm WASHER 3mm NUT Fig.12: each LM3886 is insulated from its heatsink using a mica washer & insulating bush. Smear the mating surfaces lightly with heatsink compound before bolting the assembly together. The mains switch should have its lugs sleeved with heatshrink tubing to avoid the possibility of electric shock. 46  Silicon Chip L1, the loudspeaker filter inductor, consists of 15 turns of 0.5mm enamelled copper wire wound onto a 10Ω 1W resistor and soldered at both ends. To wind it, first scrape the enamel off the start of the copper wire and solder it to one end of the resis­tor. Now neatly wind 15 turns onto the resistor body, then scrape the enamel off the end of the wire and solder it to the other end of the resistor. Finally, install and solder the assembly into the PC board. The positive and negative power supply connections to the right channel should be made with heavy duty hook-up wire (32 x 0.2mm or better) which should be twisted as shown on Fig.13(a). The 0V connections should be made via the same sort of hook-up wire but underneath the board. Finally, you can install the power ICs. Make sure that the tabs of the devices line up precisely with the back edge of the PC board so that they can be properly secured to the heatsinks. Next, fit 15mm metal standoffs to the board and line up the heat­sinks against the ICs so that the positions of the mounting screws can be marked. After drilling these holes, use standard TO-3P mounting kits to secure the ICs to the heatsinks – see Fig.12. Use your multimeter (switched to a high “Ohms” range) to make sure that the IC mounting tabs are isolated from the heat­sinks. The heatsinks we used are supplied by Altronics (Cat H-0522). To mount them into the chassis, you could use small L-shaped brackets or, April 1995  47 -15V 100uF 47uF 0V 4700uF 0V +35V -35V F3 32 x 0.2 INSULATED WIRE ON COPPER SIDE OF BOARD +15V 100uF REG1 330  1W 47uF 4700uF SPEAKER GND 1 10 / L1 0.1 SPEAKER 47uF 1k 1uF GND INPUT (NC) 1k 22uF 22k 5.6 1W F2 Fig.13(b): this is the full-size artwork for the power amplifier PC board. Check all PC boards carefully for possible etching defects (compare them with the published patterns) before installing any of the parts. -35V F3 +35V 0.1 100uF SPEAKER GND 1 47uF GND INPUT (NC) 1k 22uF 22k IC1 3886 SPEAKER 0.1 5.6 1W 0.1 100uF 39k 100uF 10 / L1 IC1 3886 220pF 22k Fig.13(a): this is the parts layout on the power amplifier board. Use PC stakes to terminate external connections & note the twisted supply con­nections for the righthand channel. The leads shown dotted are underneath the board. The two LM3886 audio amplifier ICs must be insulated from the heatsinks, as shown in Fig.12. REG2 25VAC BR1 330  1W 100uF 39k CT 330  1W 330  1W 0.1 220pF 22k 25VAC 0.1 1k 1uF F2 LEFT F1 1A RIGHT SPEAKER OUTPUTS CORD GRIP GROMMET EARTH A (BROWN) POWER TRANSFORMER EARTH  LUE) N (B TRANSFORMER SECONDARIES GREY BLACK, BLUE AND GROUND CONNECTION ACTIVE RED POWER AMPLIFIER BOARD -35V WHITE +15V 0V G (NC) L -15V WHITE GND (0V) -35V LEFT OUTPUT DO NOT EARTH SIGNAL BRAIDS AT POWER AMPLIFIER +35V +35V R G L OUTPUT TO POWER AMPLIFIER EARTHED TO CASE A LED1 K -15V  TWO SOLDER LUGS +15V 0V .01 250VAC MAINS TERMINAL STRIP CONTROL BOARD TONE DEFEAT S5 HEADPHONES BASS VR2 POWER S7 K LED1 48  Silicon Chip A TREBLE VR3 VOLUME VR1 as we did, blind-tap holes into the edge to secure them directly. EXTERNAL EQUIPMENT GROUND PHONO CD TUNER VCR AUX 1 AUX 2 TAPE IN TAPE OUT Chassis wiring GND R L L INPUT BOARD R SELECTOR S1 G (NC) R RIAA-IEC PREAMPLIFIER BOARD BALANCE S4 GND RIGHT OUTPUT +15V 0V MONITOR S2 -15V MODE S3 GND RIGHT INPUT LEFT INPUT L G R SOURCE INPUT GND GND L G R TAPE INPUT LEFT OUTPUT RIGHT OUTPUT Fig.14 shows the chassis wiring details. The mains cord enters through a hole in the rear panel and is securely clamped using a cord-grip grommet. Strip back the outer sheath of the mains cord by about 80mm. The Active (brown) lead goes to the fuseholder while the Neutral (blue) lead goes to the mains terminal block. The other side of the fuseholder goes to the mains termi­nal block and then to the mains switch. The Earth lead (green/yellow) is soldered to one of the adjacent solder lugs. The second solder lug terminates the earth lead which is run along the rear panel from the binding post terminal adjacent to the RCA input sockets. Don’t alter the earth wiring – you may get a hum loop if you do. The primary leads of the transformer are connected to the mains terminal block, as shown, while the 25V secondary leads are connected to the screw terminal block on the power amplifier board. Be careful to use the correct phasing of the secondary leads, otherwise you will not get any DC output from the bridge rectifier. Be sure to use mains-rated 250VAC cable for the connections to the power switch. We used heatshrink tubing to cover the switch lugs after the wires had been soldered on. We also sleeved the connections to the fuseholder. This avoids the possibility of an electric shock from the switch terminals. Note that the .01µF 250VAC “anti-thump” capacitor con­nected at the mains terminal block must be rated at 250VAC. Do not install the shielded signal cables at this stage. The next step is to power up each board in turn and check that it is operating correctly. We start with the power amplifier board, since it the most involved. But first, Fig.14 (left): the chassis wiring details. Take care when installing the mains wiring & sleeve all exposed terminals on the fuseholder & mains switch with heatshrink tubing to avoid accidental contact. Make sure also that the mains cord is securely clamped by the cord grip grommet. April 1995  49 RESISTOR COLOUR CODES ❏ No. ❏   2 ❏   2 ❏   2 ❏   2 ❏ 12 ❏   2 ❏   4 ❏   4 ❏   8 ❏   1 ❏   4 ❏ 12 ❏   2 ❏   4 ❏   2 ❏   2 ❏   4 ❏   2 ❏   2 Value 100kΩ 91kΩ 47kΩ 39kΩ 22kΩ 15kΩ 10kΩ 5.6kΩ 4.7kΩ 3.9kΩ 1.6kΩ 1kΩ 820Ω 330Ω 100Ω 82Ω 15Ω 10Ω 5.6Ω 4-Band Code (1%) brown black yellow brown white brown orange brown yellow violet orange brown orange white orange brown red red orange brown brown green orange brown brown black orange brown green blue red brown yellow violet red brown orange white red brown brown blue red brown brown black red brown grey red brown brown orange orange brown brown brown black brown brown grey red black brown brown green black brown brown black black brown green blue gold brown 5-Band Code (1%) brown black black orange brown white brown black red brown yellow violet black red brown orange white black red brown red red black red brown brown green black red brown brown black black red brown green blue black brown brown yellow violet black brown brown orange white black brown brown brown blue black brown brown brown black black brown brown grey red black black brown orange orange black black brown brown black black black brown grey red black gold brown brown green black gold brown brown black black gold brown green blue black silver brown OPTIONAL RIAA PREAMP ❏ No. ❏   2 ❏   2 ❏   4 ❏   2 ❏   2 ❏   2 ❏   2 Value 1MΩ 200kΩ 100kΩ 16kΩ 390Ω 150Ω 100Ω check all your work carefully against the associated wiring diagrams of Fig.13(a) and Fig.14. Power amplifier testing Before checking the power amplifier board, connect a 1kΩ 0.5W resistor between the +15V and 0V rails at the 3-way terminal block (adjacent to the 3-terminal regulators). This 1kΩ resistor will draw a 15mA current from the +15V supply rail and thus ensure that the input voltage to the 7815 regulator does not exceed the ratings (ie, 35V). Now apply power and check the supply rails. They will nor­ m ally be around ±37V, depending on the value of the AC mains voltage. Now check the quiescent current in each channel. This can be done in one of two ways. The first is to remove 50  Silicon Chip 4-Band Code (1%) brown black green brown red black yellow brown brown black yellow brown brown blue orange brown orange white brown brown brown green brown brown brown black brown brown one fuse (while the power is off) and connect your multimeter, switched to an “Amps” range, across the fuse clips. With no input signal and no load, the quiescent current should typically be around 30mA but may range up to 70mA. Alternatively, you can connect a 100Ω 1W resistor across the positive rail fuse clips and measure the voltage across it. For a current of 30mA, the voltage across the 100Ω resistor should be 3V DC. The DC voltage at the output of each channel should be within ±15mV of 0V DC. Next connect suitably rated loudspeakers and check that you can get an output. With no signal, both channels should be very quiet. If you touch the input PC pins on the PC board you should get an audible “blurt” from the relevant loudspeaker. 5-Band Code (1%) brown black black yellow brown red black black orange brown brown black black orange brown brown blue black red brown orange white black black brown brown green black black brown brown black black black brown If the circuit isn’t working, check all the audio paths from the input through to the output for continuity. You should also check that the PC pins are well soldered into position, as is link LK1. If LK1 is open circuit, the amplifier will be muted. If all is well, switch off, connect the ±15V supply wires to the tone control board and check the voltages on it. This done, connect the supply wires to the RIAA preamp (if fit­ ted) and check the voltages on it. If all these checks are OK, you can complete the wiring of the amplifier by running all the shielded cable, as shown in Fig.14. You will also need to fit the extension shaft to the selector switch. Troubleshooting If the above measurements are not OK, the most likely causes are broken Compare this photo of the amplifier with the chassis wiring diagram of Fig.14. Note that the RIAA preamp in the righthand front corner is optional & if left out, it leaves an extra pair of high level inputs. tracks or solder bridges between IC pins. For example, if you have the correct supply voltages on an IC but its output is close to +15V or -15V, it is most likely that there is a break in the feedback network or to the inputs to that IC. You can follow this up by measuring the voltage at the input pins of the ICs. Again, these should all be very close to 0V. If not, check for breaks in the copper track, poor solder joints, and that the IC is not in the wrong way around. Note: if you’ve put the IC in the right way around, it is most unlikely that any malfunction will be due to a faulty IC. So don’t immediately rush out and buy new ICs if you strike problems. What happens if one of the power amplifiers is not working? If the other channel is working correctly, then you have an ideal crosscheck. Check the voltages in the good channel and then in the bad channel and you can usually get a fair idea of what the problem is. It is unlikely that you will get the same fault in both channels, unless you have made the same assembly mistake in both! Listening tests No, we’re not going to listen to music – yet. The idea of the next few checks is to make sure that everything is really working as it should. You’ll need a pair of headphones. Plug them into the headphone socket, turn on the power and listen. With the Volume at minimum you shouldn’t be able to hear anything. If you now select the phono input and wind up the Volume to max­imum, you will hear some hiss and a small amount of hum. That is normal. If you now switch to the other inputs (CD, Tuner, etc), the noise should drop to extremely low levels (we doubt you’ll be able to hear anything, even in a very quiet room). Now wind the Volume control back, switch to the CD inputs and try poking a small screwdriver into the left channel input socket. You should hear a “blurt” in the left channel. Now try the test for the right channel. If you repeat this test for extreme CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value 1µF .01µF .0047µF 220pF 100pF 33pF IEC 1u0 10n 4n7 220p 100p 33p EIA 105 103 472 221 101 33 OPTIONAL RIAA PREAMP ❏ ❏ ❏ ❏ ❏ Value 1µF .015µF .0047µF 100pF IEC 1u0 15n 4n7 100p EIA 105 153 472 101 settings of the tone controls (eg, full bass boost, full bass cut, etc) you can confirm that they are working as well. Similarly, you can check the operation of the Mono/Stereo switch and the Balance control. If all is well, the front panel can now be mounted but be careful – one scratch and you’ll ruin the appearance of the whole project. Fit the lid to the SC case and the job is finished. April 1995  51 In this third & final article, we conclude the assembly procedure for these wide range electrostatic speakers & give some hints & tips on obtaining the optimum sound quality. By ROB McKINLAY Wide range electrostatic loudspeakers; Pt.3 Last month, we finished assembly of the half panels of which there are 12. One of each pair of half panels was fitted with the diaphragm which was tensioned and painted with a conductive coating. The next task is to assemble the pairs of half panels together. The result will be four complete bass panels and the two central treble panels. Before assembly takes place, wires should be attached to the panels for the audio drive signal. The half panels which have the diaphragm attached should have a red wire connected to the metal grid. The matching half pan+9-15VDC FROM PLUG-PACK IN 1500 16VW 0.22 7805 GND GND els should have a black wire attached to their metal grids. The panels which have red wires attached are mounted at the front of the finished speaker system. This procedure ensures that all panels are in phase when they are connected together. The two matching half panels are placed face to face with the diaphragm in the middle. Using the channel section supplied, clip the two halves together. A small cutout will need to be made in one long channel section to allow for exit of the EHT wire. Mark the channel section where the cutout is to be made. Drill a 10mm OUT hole through the flange close to the channel web, then use side cutters to cut the flange out to make a ‘U’ shaped cutout. Clip the channel over the two half panels starting at the EHT terminal end and push it firmly towards the centre. Ensure that the two panel halves line up with each other. The front panel wire (the red one) is passed under the panel before the bottom channel is clipped on. It will be neces­sary to break out some small pieces of plastic matrix to allow easy exit. Solder the red wire to an eye terminal. Screw a brass nut onto the ter- +5V 10 16VW GND I GO Fig.1: this circuit provides 5V DC to the EHT inverter in both electrostatic loudspeakers. 52  Silicon Chip The 5V regulator is supplied pre-assembled on a piece of Veroboard but the wiring must be completed before it can be used. 2.2k D1 1N914 220  +5V C1 10 ZD1 Q1 2N2219A C 33V B D5 E C2 22 680pF 3kV C2 220pF 1k T1 3 GND B E C 2 D4 10M EHT OUTPUT 680pF 3kV D3 3kV 4 D2 680pF 3kV VIEWED FROM BELOW 1 GND It produces an output of close to 3kV with a 5V DC input. The circuit is wired onto a small PC board, using the component layout shown in Fig.3. One of these boards is required for each complete electrostatic loudspeaker. Each board is mounted in its own plastic box which is itself mounted in the base of the speaker cabinet. Final wiring The photo of Fig.5 shows the details of the wiring. At left is the audio transformer which is driven from one channel of a stereo amplifier. The transformer has two primary windings and these are connected in parallel but with a 1.2Ω 10- watt wire­wound resistor in series with each winding. The high voltage side of the transformer has three connections. The centre tap is connect­ed to the 0V connection of the EHT board. The two other terminals are connected to the paralleled red and black wires from the three electrostatic panels. Finally, the EHT output from the inverter board is connected to the paralleled EHT wires from the three panels. All of this high voltage wiring should be terminated in an insulated terminal block, as shown in the photo of Fig.6. When all the wiring is complete, the back panels should be installed so that listening tests can begin. Fig.2: the EHT inverter is a 1-transistor blocking oscillator feeding a 2-stage CockroftWalton voltage multiplier. It generates about 3kV to provide the polarising voltage for the three electrostatic panels in each speaker. minal screw. Do not overtighten. Place a brass washer on the connection. Break out sufficient matrix toward the bottom of the panel, to allow the eye terminal to sit flush on the connection allowing the wire to pass underneath the completed panel. Now clip on the bottom channel section. The black audio wire should be soldered to an eye terminal which is then bent through 90° to allow connection to the rear grid through the plastic matrix segment. Fit a 3mm brass nut onto the connec­tion screw and tighten it but do not overtighten it. Place a 3mm brass washer on the connection followed by the eye terminal, another washer and a brass nut. Tighten carefully. It may be necessary to break out some small pieces of matrix to provide sufficient clearance for the terminal. This procedure is carried out on all panels. The three panels are installed in the speaker frame with the treble panel in the centre. There are two pairs of bass panels with left hand connections and two with right. One of each is used per finished loudspeaker. The three panels are connected in parallel; ie, all three red audio wires connected together, all three black audio wires connected together and all three EHT wires connected together. Electronic assembly Three electronic modules need to be put together to provide the EHT supply for the speakers. Briefly, a 9V DC plugpack feeds a 5V regulator module which is mounted in its own small plastic case. The 5V DC from the module then supplies a DC-toEHT invert­ er in each loudspeaker cabinet. Fig.1 shows the 5V regulator circuit which is quite standard. This is supplied in the kit pre-assembled on a small piece of Veroboard. It needs to be soldered and assembled into its plastic box. The two sets of output leads are wired to 3.5mm jack plugs. These plug into 3.5mm sockets on the rear of the loudspeaker cabinets. The DC-to-EHT inverter circuit is shown in Fig.2. This is essentially a 1-transistor blocking oscillator driving a 2-stage Cockroft-Walton multiplier. WARNING! The voltages generated by the EHT supply and the step-up audio transformer are very high. Never touch the output cables or terminals from the audio transformer with the amplifier run­ning. The high voltage output from the transformer, depending on the amplifier used, could reach 5kV AC. This is a lethal voltage. The EHT supply operates at about 3kV with very low current. The high voltage capacitors used will retain a charge for some time after switch off. Always discharge the EHT cable to ground before making any connections or doing any work on the speakers. Operating the electrostatics The loudspeakers will take two or more hours to reach their optimum state of charge. When reached it will be maintained by the internal electronics. The plugpack power supply should be permanently connected and switched on. Its power connection is quite small (less than five watts). Optimum loudspeaker placement is dependent on room size and shape. The following suggestions are guidelines to achieve the best perfor­mance from the ESL III’s. Start with the loudspeak­ers about one metre from the rear wall and, in a 3.5-5 metre wide room, about half a metre from the side walls. Toe the speak­ers in towards the listening position. April 1995  53 C1 220 2.2k +5V C2 D1 T1 2 680pF 4xHV DIODES 10M C 1 Q1 B ZD1 E EHT 2x680pF GND MOUNT ZD1 ON COPPER SIDE OF BOARD EHT OUT 1k GND 4 3 220pF Fig.3: this is the component overlay for the EHT inverter. Note that it generates a very high voltage which is retained after switch-off (see warning panel). Play some familiar music with a centre stage vocalist. Adjust the toein on one or both of the loudspeakers to make the vocalist appear centrally located. Room inter­ ference effects may cause one loudspeaker to be toed in more or less than the other. It may be necessary to toe-in the speakers until they are pointing directly at the listening position. The speakers may now be moved either closer to or away from the rear and side walls to achieve the best bass response. The loudspeaker panel is designed as a symmetrical vertical array. This produces the best sound quality at ear level when seated. To reduce tonal variation when standing, tilting back the loudspeaker may be desirable in some rooms. The spikes supplied will provide the necessary adjustment. It is advisable to fit the spikes after the best position has been found for the speakers. This will avoid damage to floors and toes! Use some packing to determine the best angle of lean, then fit the spikes and carry out fine adjustments. Make small adjust­ments to toe-in and lean; they can make big differences to the sound quality. These loudspeakers radiate sound from the rear as well as the front. To avoid adverse effects on the imaging, it may be necessary to have some sound absorbent material such as heavy curtains on the rear wall or in the rear wall corners. You can expect to devote a few hours of “tweaking” to achieve the best results. Like most high quality loudspeakers, the ESL III’s will need running in. It will take two to three weeks of normal use before the diaphragms reach maximum compliance. You will notice better bass and improved treble after this period. Troubleshooting Some common problems causing poor performance are listed below. The first of these is leakage of diaphragm bias voltage to rear (black wire) grid. Just one panel with this problem will cause the three panels in one loudspeaker to perform poorly. This is due to the faulty panel causing a drain on the EHT power supply. The sound will be distorted and at a lower level than normal. There are several checks that can be made to locate the problem. Disconnect the panel wires from the terminal blocks. Connect a multimeter on a high Ohms range (200 megohms or more) between the EHT wire from the diaphragm and the rear grid audio wire (the black one). The reading should be “open circuit”. If a finite reading is obtained, there is a conductive path between the dia­ phragm and its connections to the grid. To check this, split the panel into its halves and use your multimeter to check both half panels. If a finite reading is again obtained, the problem lies on the relevant half panel. The cause is likely to be some conduc­tive material which has been caught between the foil tape or the connection point and the grid. If no reading is obtained when the panel is disassembled, the problem will be between the diaphragm and the grid. Look for conductive material between the grid and diaphragm: hair, lint, fine wire and insects can all cause problems. Absolute cleanli­ness during construction pays off. During each stage of construc­tion, vacuum any dirt or grit from the panels. Flakes of dry conductive coating can cause problems if they get in the wrong places. Always remove your gloves away from the construction area. If the conductive coating is being applied in more than one session, wear new gloves. Other causes can be: the centre tap of the audio transformer not connected to 0V on the EHT supply or one grid wire not making a good connection; EHT supply not working properly; the conductive coating on the diaphragm applied incorrectly (ie, patchy, too light or not making contact with the EHT foil tape); and finally, the diaphragm tension may be too low. Care of your speakers Fig.4: the finished 5V regulator is installed in a plastic box. It has two separate leads to supply the EHT inverter in each electro­static loudspeaker. 54  Silicon Chip The timber cabinets should be oiled occasionally. Grille cloths should be lightly vacuumed from time to time Fig.5: the compartment at the base of the speaker houses the audio step-up transformer and the EHT inverter. Note the wire­wound resistors connected in series with the transformer primary windings. The inverter is normally housed in the plastic box at the rear, for safety’s sake. Fig.6: this close-up view shows the wiring connections to the three panels. to remove dust. Care must be taken with the front grille as the speaker diaphragm is only a few millimetres from the grille cloth. Always use the “partial suction” position on the vacuum cleaner. Avoid exposure to direct sunlight, moisture or temperature extremes. Avoid overdriving the loudspeakers too. Power limits will be apparent by a “snap” (high voltage flashover) followed by a temporary loss of volume. Continued use under these conditions SC may cause damage. Kit Availability The ESL III electrostatic loudspeakers are available in kit form at $1199 a pair plus an extra $499 for the two ready-built timber enclosures. Freight, packaging and insurance will vary from state to state. For further information, contact Rob McKinlay, E. R. Audio, 119 Brookton Highway, Roley­ stone, WA 6111. Phone (09) 397 6212 or fax (09) 496 1546. April 1995  55 SERVICEMAN'S LOG Sets aren’t made of rubber, but... Nobody likes to have a set bounce. But let’s face it; it’s an occupational hazard. It happens to all of us sooner or later but it’s still a blow to our professional pride &, poten­tially, to our reputation. Occasionally, a set bounces by reason of our own careless­ ness or lack of experience with a particular brand. But most of the time, it is just plain bad luck. A second fault occurs short­ly after the set is returned to the customer, probably producing similar symptoms, and the customer expects an explanation. To be fair, most customers are reasonable but once in while one will go off his brain. And it sometimes takes fair bit of diplomacy to quieten them down. But they are not the worst. The worst ones are the ones you don’t hear about, except much later on the grapevine, when the damage to your reputation has been done. Naturally, all those thoughts were prompted by a recent experience. In fact, none of these nasty things happened but they could have, and it served as a reminder that this threat is always there. The story is about an AWA model C3423 colour TV set, a 34cm model which is actually made in Korea by Daewoo. It belongs to one of my long-standing customers. His complaint was straightforward enough – distorted sound on all channels – and I imagined the cure would be quite simple. And initially, this appeared to be the case. When checked on the bench there was no doubt about the validity of the complaint; the distortion was really severe. And, as I had expected, the cause was simple enough; fai­lure of one of the two transistors in the audio output stage. These are designated on the circuit as Q601 and Q602 and both carry the type number KTC2230Y. In this case it was Q601. Fortu­nately, I had a replacement in stock but it appears that a 2SC2230 is, as far as I can determine, the same device, the KT prefix and Y suffix being a Korean version. Anyway, I had the specified type number, so I simply fitted it. And that cured the fault. I finished the job late in the afternoon, and left the set running on the bench for an hour or so until I closed the shop for the night. When I switched it on again the next morning, it performed quite normally and so I rang the customer with the good news. I subsequently unplugged the set and pushed it aside when I needed the bench space but later turned it back on again to demonstrate it to the customer when he called in. It’s back again Fig.1: the audio output stage in the AWA C3423 colour TV set. The audio drive comes from pin 3 of IC101 (top) & is applied to the base of Q602 which apparently operates as a single-ended class-A stage, with Q601 as a cascode. The output appears at the junction of Q601 & Q602 & is fed to the loudspeaker via a trans­former. 56  Silicon Chip So that was another job finished – or so I thought until it bounced. A couple of days later, the owner was on the phone with the bad news that the sound was still distorting. He was quite reason­able about it though, because he realised that it wasn’t exactly the same fault as before. While the original fault was obvious the moment the set was switched on, the set would now run normally for an hour or so and then would gradually begin to distort. At the end of about two hours, it was really bad. And I gathered that the owner had prob­ ably been trapped in the same way I had been, by initially using the set for relatively short periods. So the set finished up back on the bench. Initially, I let it run for about two hours, by which time it was quite intoler­able. I then decided to check the audio feeding the output stage, on pin 3 of IC101. This was easy enough to do using a small audio signal tracer and it confirmed that the signal was perfectly clean at this point. My next thought was to make some voltage checks but I didn’t have much to go on. The circuit is one of those that a colleague calls “a street directory with no street names”; or, in this case, no voltages. Well, there was one, the supply rail to this stage, at 103V. Assuming this figure was correct I reckoned there would be about 50V across each transistor. It also seemed reasonable to expect that there would be around 0.5V or 0.6V between the base and emitter of each transistor. So in spite of the circuit limitations, I was able to build up a fair picture of the likely voltages. After allowing the set to cool down, I switched it on again and confirmed that these voltages were correct. The supply rail measured the indicated 103V rail, there was roughly 50V across each transistor, and there was about 0.5V between the base and emitter of each transistor. Having confirmed this, I let the set run until the distortion reappeared, then made another voltage check. It was a different story this time. While the other voltag­ es remained as before, the base-emitter voltage of Q601 had dropped significantly. I left the meter connected and let the set run. The voltage continued to drop as the distortion increased until, after about two hours, it had dropped to a mere 0.05V. Well, that was a clue but that was all it was; I still had to find the cause. Fortunately, there is only a handful of components in this section: six resistors, six capacitors, and the two transistors. I was inclined to ignore the transistors. After all, Q601 had just been re- placed and the chances of two failures in a row seemed remote. But statistics can let one down. I had more spares on hand and it was only a few minutes work to change both. And that promptly ruled out that possibility; it made no difference. The resistors did not seem to be a high risk but were easy to check anyway. And again I drew a blank. That seemed to leave only the capacitors – two low value plastic types and four electrolytics. Of the latter, C608 (22µF) served as a decoupler for the 103V rail. However, I couldn’t relate a fault here with the observed symptoms. All things considered, including the change in Q601’s base-emitter voltage, the most likely suspect was C610, a 3.3µF cou­pling capacitor to the loudspeaker. It was an electrolytic, of low value, and in what appeared to be the fault area. It was simple matter to pull it out and test it. Its ca­pacitance measured 3.3µF as marked and there was no significant leakage. But it was just as easy to fit a new one anyway, whereupon the set produced good clean sound. More importantly, it April 1995  57 continued to do so for the rest of the day, after which I consid­ ered the point proved. So I’m not sure what was wrong with the capacitor. Normal­ly, there are three likely faults in a capacitor: loss of ca­pacitance, leakage and internal series resistance. Since it appeared to have correct capacitance and no leakage, that left only internal resistance, which is not quite so easy to measure. On the other hand, there seems little doubt that it was a temper­ature sensitive fault and it is sometimes difficult to duplicate the exact temperature conditions when making measurements. So, all things considered, I’d put my money on leakage. After all, one side of it connects via the output transformer (T601) to the 103V rail and the other side to Q601’s emitter. So, if it was leaky, the effect would be pretty drastic. So it all ended happily. But it was a nasty trap and I’m not sure whether there were two quite separate faults or whether the faulty capacitor was the cause of Q601’s failure in the first place. In any case, I fell into the trap. With the benefit of hindsight I should have given the set a longer soak test. But this is not always convenient and 58  Silicon Chip there were no symptoms to suggest that it would be advisable. How does it work anyway? Finally, having solved the problem, I couldn’t help but wonder about that output stage configuration. It is not an uncom­mon arrangement and I must have looked at it many times in vari­ous makes and models of sets. And despite having replaced faulty components in these circuits, I have never bothered to think much about the arrangement. Until now, that is. It must have been the need to service it twice in quick succession, and the need to work out voltages, which prompted me to start wondering about how it operates. The first point to note is that the two output devices are of the same type number and, therefore, of the same polarity. Compared with the popular complementary symmetry pair configurations, I find this arrangement puzzling. And the more I look at it the more confused I become. I simply cannot grasp how the circuit works. And those colleagues I have consulted appear to be equally as confused. Some made suggestions based on other circuits with which they were familiar but nothing seemed to add up. As already noted, the two transistors are effectively in series in the DC sense and operate from the 103V rail. The audio drive is from pin 3 of IC101 and the output is taken from the junction of the two transistors and capacitively coupled to the speaker transformer, the other side of which connects to the 103V rail. It also appears that the output is at relatively high im­pedance, hence the speaker transformer. There is also a feedback network into pin 2 of IC101. Beyond that, it is not clear how the circuit works. It would appear that Q602 operates as a single-ended class-A stage, with Q601 as a cascode. But the biasing arrangements for Q601 are something of a mystery since the base of this transistor is tied one diode drop below its emitter. So there it is; an ultimately successful job but one which left a frustrat­-ing circuit puzzle. If anyone can throw any light on this circuit, I would be happy to pass it on to readers. In the beginning My next story takes us back a few years; some 20 years in fact, to the beginning of colour TV in Australia in 1975. More particularly, it involves Fig.2: the power supply for the Kriesler 59-1. The two mains fuses (F101 & F102) are at left, while fuse F120 is to the right of the bridge rectifier. TR120 is the chopper transistor. one of the first colour sets of that era. I refer to the model 59-1 made by Kriesler which, in vari­ous modified forms, was popular for many years. And while this particular set may not necessarily be 20 years old, it would be pretty long in the tooth. It belongs to a lady customer who moved into my district a couple of years ago She first sought my assistance about a year ago. On that occasion, the main problem was due to some dry joints, of which this set had its share. In addition, I made a routine modifica­tion to permit the set’s use with a video recorder. It had been a long time since I had done this and I had to dig out the appro­priate modification note to refresh my memory. The modification involves the horizontal oscillator cir­cuit. In greater detail, it involves modifying the time constant of the automatic frequency control (or flywheel sync system). In these early Kriesler sets and in some Philips sets of the same era, before the advent of the domestic VCR, this time constant was relatively long. This was perfectly satisfactory for the highly stable off-air TV signals but was too severe for some video recorders. The modification is relatively simple. It involves the Line Control Unit (CU701) and pins 3, 10 & 11. Pins 3 and 10 must be connected together, while pin 11 is connected to chassis. With that done, and the dry joints repaired, the set was returned to the customer. When it came in this time round it was completely dead and I had a gut feeling that it was power supply failure. There was no life of any kind; not even a hiccup to suggest an overload shutting down the power supply. My first check was at the fuses. The two mains fuses (F101 and F102) were intact, but fuse F120, a 2A type between the bridge rectifier and the chopper transistor (TR120), was blown. So it looked like a fault on the board itself, most likely TR120. Fortunately, I still have a fair stock of boards for this model, salvaged from sets scrapped for other reasons. So it was a relatively simple job to pull out the power supply board and substitute a known good one. This would at least confirm my suspicion and clear the rest of the set. And it did; the set came to life immediately and put up quite a creditable performance, considering its age. Even the picture tube looked as though it was good for a few more years. OK, so the fault was on the power supply board. If it was as simple as I suspected, it would be well worthwhile repairing. Naturally, I went straight to the chopper transistor pins, on the underside of the board. And a quick check with the meter con­firmed my suspicion – it was shot, base to emitter. I unscrewed the mounting nuts, then turned the board over to pull the transistor clear. And this was the first hint of something unusual. One glance was enough to indicate that there had been “a certain amount of mucking about going on”, as one of my colleagues often puts it. Sticking out from under the transis­tor were some pieces of black insulating tape as used by electri­cians. It was now clear that TR120 had been replaced on a previous occasion. This was no surprise – faults of this kind are common enough in all sets. But the nature of the repair was. The insu­lating tape had been used in place of the isolate mica washer that’s used to separate the transistor from its heatsink. In fact, two strips of tape had been used, with one overlapping the other to provide the necessary width. A real shocker Such a bodgie repair was a real shocker. At that stage, I had no idea when, or by whom, the repair had been done. I could only assume that someone had been caught out in the field without a washer and had taken this way out to do a quick repair and avoid a return visit. Well, that would be an explanation, if not an excuse. But it is a pretty rough approach. For one thing, as we all know, insulation tape degenerates with time, particularly in a heated situation such as this. And, in any case, it would provide very poor thermal con­duction compared to a standard mica washer. The standard washer is made as thin as possible, consistent with adequate electrical insulation, in order to provide maximum thermal conductivity, usually aided by a heatsink compound. Insulation tape is thicker and, in this case, there was a double thickness of tape where the two strips overlapped in the middle of the transistor between the two pins. In fact, I took a few minutes off to check these thicknesses with a micrometer. A typical washer is of the order of .005in, while a single thick­ ness of this tape was .008in, making a double thickness of .016in (pardon the imperial measurements; my micrometer goes way back.) So the poor old transistor must have been running much hotter April 1995  59 SERVICEMAN’S LOG – CTD Fig.3: a previous “serviceman” had isolated the chopper transistor using two pieces of electrical tape instead of a proper mica washer. It’s a wonder it lasted as long as it did. than it should have been since the repair was made. Naturally, I fitted a new TR120, complete with the correct washer, whereupon the set came back to life. There had been no other side effects from the failure. But the bodgie repair raises the question as to why this transistor failed. Maybe it was due to fail anyway but there are two far more likely possibilities. One was that there had been an electrical breakdown between the transistor case and the heat­sink, as the tape did not fit too snugly around the mounting bolts. Alternatively, the lack of adequate heatsinking may have finally taken its toll. Who did it? But regardless of the reason, that is no way to repair a TV set. I was curious as to how it had happened so, when I rang the lady to advise her that the job was finished, I raised the matter of the previous service – after all, it did involve the same component. In fact, she was most helpful. It transpired that, before moving into my area, the set had been covered by a service con­tract with a large service organisation. And when she came in to collect the set, she brought all the relevant documents with her, including the job sheet for the service in question. And this produced another surprise. There was no suggestion of an emergency repair in the house, as I had envisaged. Accord­ing to the dockets, it had been taken to the company’s workshop and the job done there. So 60  Silicon Chip how on earth could such a bodgie job be justified? The documents also pinpointed when the job had been done, which was about six years previously. So it had lasted rather longer than I would have expected. But that’s no excuse. What firm was it? No, I’m not saying. I’ve seen and heard only one side of the story. There could be an explanation which completely absolves them, so we’ll let it rest there. But it was a nasty act on somebody’s part. The intermittent VCR And finally, here is a story from a reader, J. S. of Portarlington, Victoria. Here’s how he tells it: After reading the Serviceman’s Log in the August issue of SILICON CHIP about the NV-370 and NV-600 VCRs, it rekindled my memory of an NV-470 I had fixed two months earlier. This was one of those intermittent faults. Don’t you just love those? This particular problem seemed to involve the power switch. At times, one could keep pressing it and get no response whatsoever. Even shaking the whole unit, or prodding the board around the power section, would not revive it. And then, for no apparent reason, it would come good and remain so. Once again I repeated the shake and prod tests, with no result. I waited for it to reappear of its own volition. When it did, I took the covers off and removed and replaced a couple of the 3-pin wire connectors (PJ1003 & P1002 ) on the power section of the board. And bingo, the problem vanished. A dirty connector? I subjected the unit to another shaking and prodding test and, as it did not fail again, I more or less accepted that this could have been the cause of the problem. At that time, I did not have a circuit diagram with which to check the layout. But not being 100% satisfied that the problem was solved, I kept it for further observation. Sure enough, some eight days later it happened again. It was time to get serious and get a copy of the circuit. Thus equipped, I realised that at least one of the connectors I had changed, PJ1003, had little to do with the power supply circuit. On closer examination of the copper side of the board, in the power supply region, I noticed some discoloration, apparent­ly due to overheating, around transistor Q1001 (2SD­1275), the voltage regulator for the 12.7V rail. At the same time, I had my finger on Q1001’s heatsink and as I applied pressure, it sank towards the board. My interest aroused, I wiggled it and watched it from the solder side. The unit was plugged in at the time, and I noticed arcs being emitted from Q1001’s collector and its copper track. Sure enough, the fault could be induced and corrected by wriggling Q1001’s heatsink. Closer examination of the copper tracks around Q1001 revealed that the collector track had broken due to the size of the heatsink. This was attached directly to the transistor body, without any anchoring pins into the board. Q1001’s base and emitter pads were also beginning to lift off the board. I soldered a substantial piece of tinned copper wire to each lead of Q1001 and along their corresponding copper tracks, which gave the transistor and its hefty heatsink a solid base. Hopefully, this will solve the problem for the life of the unit. This fault clearly illustrates that one should always start any diagnosis with a thorough visual inspection. The telltale signs could be very time saving, as in this case, especially as I was looking around and at the fault right from the start. Thank you J. S. for an interesting story. Your point about a thorough visual inspection is well taken. I’ve been telling myself that for years but SC I still get caught. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au COMPUTER BITS BY GREG SWAIN Prune & tune your hard disc for optimum performance Is your hard disc bulging at the seams? A good clean out might be all that’s need to restore performance & free up lots of valuable space. It wasn’t too long ago that a 20Mb hard disc was considered more than adequate. Why would you need anything bigger? We all know the answer to that, of course. With the advent of Windows, programs grew in size, with some now requiring up to 30Mb of disc space just to install them. Now, you would be foolish to contemplate purchasing a com­puter with a hard disc capacity of less than 240Mb. And if you intend running a lot of graphics-intensive programs, then a 540Mb or larger hard disc is the minimum requirement (along with a high-end processor and lots of RAM). Even so, it’s all too easy to fill up a large hard disc. But before going out and investing in another drive, take a good hard look at your files. It’s just possible that, with some simple housekeeping, you can free up great chunks of hard disc space and save those hard earned dollars. Here then are five simple steps to freeing up hard disc space and tuning it for best performance. Some of them are obvious but you would be surprised just how many people ignore the obvious. Step 1: Delete Old Files Work files that are no longer wanted simply tie up valuable disc space. Delete them using the Windows File Manager. This job can often be made Watch Out For Computer Viruses The six basic steps listed in this article are all essential for good hard disc maintenance. But there’s one more thing that you should do to keep your hard disc healthy – scan it regularly for viruses. In fact, you can virtually eliminate the risk of a virus by scanning every floppy disc that goes into the machine. Be par­ ticularly diligent with those obtained from an outside source. A virus checker comes with MSDOS 6.0 and above but unfor­tunately it’s not cheap to update on a regular basis. The one used at SILICON CHIP is McAfee’s ViruScan. It is updated on a regular basis and has detected viruses on incoming floppy discs on quite a few occasions. The Stoned virus is the most common but it has also saved us from other nasties, including the dreaded Michelangelo virus. McAfee’s authorised agent in Australia in Doctor Disk. You can contact them in Sydney on (02) 281 2099 and they also have offices in Melbourne, Canberra, Perth, Brisbane and Adelaide. easier if you first sort your files by type or by date. To do this, click on View in File Manager, then select the wanted option from the drop-down menu box. If you are in doubt about deleting a file, create a “gar­bage” directory (ie, C:\GARBAGE) and drag the file into it. If you haven’t used the file after several months, then it’s prob­ably safe to delete it. By the way, avoid mixing work files with program files. Store your work files in a separate directory (or subdirectory) instead. This will make it easier to keep track of your work files and prevent accidental deletions of wanted program files. Finally, if you no longer use a program, then why leave it sitting on the hard disc? It can always be reinstalled at a later date if need be. Step 2: Run Chkdsk Regularly When a program crashes, it can create lost allocation units (file segments) which, over time, will eventually occupy lots of hard disc space. To retrieve this space, first quit all appli­ cations, including Windows and MSDOS Shell, and go the root directory of the drive you want to check. Now type chkdsk /f. If lost allocation units are found, a screen prompt appears asking if you want to convert the lost chains to files. If you press N, the lost chains are deleted and your disc space is freed. Conversely, if you press Y, Chkdsk converts the lost allo­cations units to files (eg, FILE0000.CHK, FILE­0001. CHK, etc) and stores them in your root directory. You can then examine the April 1995  65 K ALEX The UV People ETCH TANKS ● Bubble Etch ● Circulating LIGHT BOXES ● Portuvee 4 ● Portuvee 6 ● Dual Level TRIMMER ● Ideal PCB DRILL ● Toyo HiSpeed MATERIALS Fig.1: temporary (.tmp) files can soon clog up a hard disc if not cleaned off regularly. These files can be left on the hard disc if Windows crashes or a Windows application stops running unexpectedly. Be sure to exit Windows before deleting .tmp files – see text. ✸ AUSTRALIA’S NO.1 STOCKIST ✸ contents of these files and retrieve any data that you might want to keep. The .CHK files should then be deleted using the del command. More information on chkdsk can be found in your MS-DOS manual. By the way, it’s always a good idea to run Chkdsk before running Defrag or DoubleSpace (see below). ● PC Board: Riston, Dynachem ● 3M Label/Panel Stock ● Dynamark: Metal, Plastic K ALEX 40 Wallis Ave, East Ivanhoe 3079. Phone (03) 9497 3422, Fax (03) 9499 2381 TRANSFORMERS • TOROIDAL • CONVENTIONAL • POWER • OUTPUT • CURRENT • INVERTER • PLUGPACKS • CHOKES STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1990 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 66  Silicon Chip Step 3: Delete Temporary Files Windows applications create temporary files on the hard disc while they are running. These files always have a .TMP extension and they should all be automatically deleted when you exit Windows. However, if Windows or a Windows application crash­es, or you switch off the computer without leaving Windows, these temporary files can be left scattered on the disk. Eventually, temporary files can occupy a huge amount of hard disc space, so it pays to delete them regularly. How do you know where these files are? Just take a peek at your auto­exec.bat file. To view it, go to the root directory (eg, C:\) and enter “type autoexec. bat”. Temporary files will be written to the directory specified by the line SET TEMP=C:\directory. All you have to do is go to that directory and erase all the .TMP files. Don’t do this from inside Windows, though – you must exit Windows first, otherwise you will erase valid .tmp files that are in use. Actually, its a good idea to create a separate “temp” directory and edit the line in your autoexec.bat file to read “SET TEMP=C:\TEMP”. That way, the .TMP files will be written to the temp directory and will not get mixed up with wanted files. This will make it easier to delete them (you could even write a batch file to do this). Alternatively, you can place the temp directory on a RAM disc (if you have one). By doing this, any .tmp files will be automatically erased when the computer is turned off. Step 4: Zip Up Little-Used Files Lots of valuable disc space can be retrieved by zipping up little-used files. Two very popular file compression programs are LHArc and PKZIP and these can either be downloaded as shareware from bulletin boards or obtained from software vendors. Many graphics files will zip up to 20% or less of their original size, so file compression can be very worthwhile. There’s just one thing to watch out for here – be sure to delete the original file after zipping it up. Another approach is to use “compression on the fly”. This involves creating a compressed drive on the hard disc using DoubleSpace or some other disc compression program. The advantage of DoubleSpace is that it comes “free” with MS-DOS 6.0 and above. To use it, just follow the instructions in the manual. Compression on the fly is trans- parent to the user. Your files are automatically compressed when they a saved to a com­pressed drive and can be opened in the normal fashion. You don’t have to manually zip files up or unzip them when you want to use them, as with LHArc and PKZIP. On the other hand, your files will not be zipped up as tightly (typically, 2:1) and they will take slightly longer to open and save than files that are not com­pressed. Creating A Permanent Swapfile Step 5: Defrag The Disc Having run Chkdsk and deleted all those unwanted files, it’s time for a disc tune-up. You can do that by “defragging” the remaining files so that they are written in contiguous (consecu­tive) blocks on the hard disc. In normal use, files on the disk can become fragmented. This occurs because there is often not enough contiguous space to store a file and so it is broken into fragments and stored in different locations on the disc. These locations are then stored in a “file allocation table”, so that DOS knows where to find the various fragments. Unfortunately, fragmentation slows the computer down be­cause the disc heads have to move over larger areas of the disc in order to read and write files. The way around this is to run the Defrag utility that’s supplied with MS-DOS 6.0 and above and with other software (eg, Norton’s Utilities). On a badly defrag­mented disc, this can give a worthwhile performance boost. To run the Defrag utility, quit all programs including Windows, go to the DOS prompt, type “defrag” and press <enter>. After that, select the hard disc drive you wish to defrag and choose “OK”. The utility will then analyse that drive and recom­ mend a defragmentation option. Choose “Optimise” to begin, then sit back and watch the show as files are shuffled about the disc. Don’t interrupt or switch off while Defrag is running, otherwise you could loose data. Step 6: Create A Permanent Swap File When you start Windows in Enhanced mode, it frees up memory by temporarily swapping information to a “swap file” on your hard disc. If you Fig.2: to create a permanent swapfile, double-click 386 Enhanced in the Control Panel, then choose Virtual Memory & Change. The recommended swapfile size is usually the best option but you can change it if you wish. don’t have a permanent swap file, then Windows creates a temporary swap file each time it is started. This can shrink and grow in size as required, which means that it can fragment. A permanent swap file on the other hand is contiguous and will therefore boost performance. To create a permanent swap file, first exit Windows and run Chkdsk and Defrag to optimise the drive and create a large block of contiguous disc space. This done, restart Windows and double-click the Control panel icon in the Main group. Now double-click the 386 Enhanced icon and choose the Virtual Memory button. Click Change, then choose Permanent from the Type list. You can now either accept the size recommended by Windows or type in a new figure if you wish to alter this. Finally, click OK and click Restart. Windows will now restart so that your changes take effect. A large contiguous swapfile will now be present on the hard disc. In fact, if you run Defrag again, this file can be seen as a large string of Xs (indicating that they are unmoveable). Note that this area cannot be written to by other files, which means that the remaining disc space is shrunk by the size of the swap­file. If hard disc space is at a premium, try using a smaller permanent swapfile or, if you have lots of RAM, try deleting the permanent SC swapfile altogether. April 1995  67 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. 48V charger for SLA batteries 12V CAR This circuit is essentially a BATTERY rejig of the 12V SLA battery charger published in the July 1992 issue of SILICON CHIP. It uses a Motorola MC34063 DC-DC converter (IC1). This operates as a boost converter to switch current through inductor L1. Each time Q1 switches off, the energy stored in L1 is transferred to the output via high speed diode D1. This mechanism steps up the input voltage of 12V to 55.2V, as set by the feedback network resistors connected to pin 5 of IC1. Current limiting is provided by the 0.1Ω resistor between pins 6 and 7. Transistor Q1 is switched off when the voltage across the resistor becomes more than 300mV and this prevents damage to Q1 if L1 should saturate. The current limit feature also indirectly controls the charge current which we have set to around 1A. The frequency of operation is around 25kHz and consequently a fast recovery diode must be used for D1. L1 is wound on a Neosid 17-742-22 Tachometer pick-up for diesel engines This add-on circuit allows the Digital Tachometer described in the August 1991 issue of SILICON CHIP to be used with a diesel engine. A pick-up coil is used to detect two magnets which are installed with equal spacing on the harmonic balancer. The origi­nal points detecting circuit connected to the base of transistor Q1 is modified to suit the coil output signal. Normally, transistor Q1 is held off because its base cur­rent from the 10kΩ resistor is shunted away by diode D1 and coil L1. When 68  Silicon Chip 0.1  5W S1 2A 10 16VW 180W 6 7 L1 8 1 IC1 MC34063 3 ECB K A 4 A Q1 BD679 B 2 5 4.7k .001 L1 : 45T OF 0.5mm ENCW ON 17-742-22 NEOSID CORE D1 BY229 C K 0.22 63V MKT 91k TO 48V SLA BATTERY E 3.9k 2.2k iron powdered toroid which is larger than the one used for the 12V version to avoid core saturation. It is made by neatly winding 45 turns of 0.5mm enamelled copper wire on the toroid (Altronics Cat L-5120). Transistor Q1 should be mounted on a heatsink with at least 12°C per watt dissipation. A diecast case which is large enough to hold the circuit should be adequate. Note that the transistor must be electrically isolated from the case with a mica washer, etc. SILICON CHIP Psstt! Wanna Make Some Money? That neat little circuit you’ve nutted out to serve in your latest project could make you some money. Why not send it to us for publication in these pages? Depending on the circuit merit and complexity, we will pay up to $50. Send your circuit, along with a brief description of how it works, to SILICON CHIP, PO Box 139, Collaroy Beach, NSW 2097. Or fax it to us at (02) 979 6503. a magnet spins past the coil, the generated voltage reverse biases D1 and transistor Q1 is then able to turn on. The .01µF capacitor prevents multiple triggering of Q1 by slowing down the switching rate. The magnets are placed so that the north pole is facing outwards, with the south pole against the harmonic balancer. Alternatively, the south pole could be facing outwards provided that both magnets are arranged with the same polarity. The coil is made by winding 300 turns of 0.25mm enamelled copper wire onto a 6mm steel bolt. Apply insulation tape to the bolt thread first and secure the coil with in- sulating tape or heatshrink tubing. The bolt is attached with nuts onto a mounting bracket and positioned so that the head has a 2-3mm gap between it and the magnet faces. Note that the polarity of the coil is important for correct operation of the circuit. Swap the coil lead connections if it does not operate correctly. The Digital Tachometer circuit should be calibrated as for a 4-cylinder engine; ie, RX should be 82kΩ and VR1 should be adjusted for a reading of 1500 RPM during the suggested calibration procedure with a 50Hz frequency reference. Note: back issues of August 1991 E A1 22 16VW 470 63VW 2  RED LED2 13 IC4 MOC3021 1 470  100k 22k 4 IC1b 100 16VW 10k 2 3 RTH 120k are still available at $7.00 including postage. John Clarke, SILICON CHIP 1.2k L1 : 300T, 0.25mm ENCW WOUND ON BOLT (INSULATE BOLT BENEATH WINDING) 120k 6mm STEEL BOLT MOUNTING BRACKET VR1 120k 5mm +12V MAGNETS ON HARMONIC BALANCER 1 .01 D2 1N4148 Q1 BC337 E DIGITAL TACHOMETER CIRCUITRY 180k N C IC1a TL072 B L1 N 18k 10k D1 1N4002 5 +9V 6 8 7 R1 22k 22k +5.3V 7 2.2M 1 5 6 IC2b R2 2.2M 2 IC2a LM339 +6.4V 4 103.3k 22 11 IC2d +12V 10 9 C1 22 10k IC2c 12  +12V 2 10k 8 3 IC3 MOC3021 LED1 GREEN 14   4 6 32VAC TR2 SC151 G A2 HEATER 4 120  .033 250VAC D1 ZD1 1N4004 10V 1W L1 A GND CASE N GPO 0.1 250VAC IN 78M12 OUT +12V N 0.1 A1 250VAC A2 22  1W TR1 BTA100600B G 470  390  6 1 +12V 470  +12V To make a good beer it’s important to keep the temperature of the brew constant at 26°C. Since the ambient tempera­ture can be well above that, an effective temperature controller needs to cool as well as heat. This one uses an old refrigerator to provide the cooling and a heater element run from 32VAC. The heating element is installed in the bottom of the fridge while the brew container is installed on a shelf above. If the temperature goes below 25°C, the heater ele­ment is turned on and if the temperature goes above 27°C, the fridge is turned on. The resulting temperature control is quite effective. The temperature of the brew is monitored by a thermistor, Rth, in a bridge circuit consisting of two 120kΩ resistors and trimpot VR1 which is set to about 95kΩ at 26°C. The output of the bridge is then amplified by op amp IC1a which feeds a low pass filter consisting of a 10kΩ resistor and a 100µF capaci­tor. This filter is buffered by op amp IC1b which then drives a set of comparators based on IC2. Comparators IC2a & IC2b provide high temperature sensing (ie, above 27°C) and drive IC3, an MOC3021 optocoupler, which turns on the Triac. This turns on the refrigerator, which runs from 240VAC. Similarly, comparators IC2b & IC2d provide low temperature sensing (below 25 degrees C) and drive IC4, another MOC3021 which turns on Triac TR2 and the heater element which runs from 32VAC. A small heatsink is required for each Triac. A suitable heater element can be made by connecting a number of jug elements in parallel. Paul Chen, Dundas, NSW $45. 10A A 240VAC Temperature controller for home brewers April 1995  69 REMOTE CONTROL BY BOB YOUNG An 8-channel decoder for radio control This decoder is designed to mate with the AM receiver described in the previous four months. The PC board is exactly the same size as for the receiver & the two plug into each other so that no interconnecting wires are required. The development of this decoder has been a classic example of the problems thrown up by component manufacturers constantly changing their components. There should have been no difficulty whatsoever in changing my original two-IC design to a surface mount unit, or at least so I thought. I expected to produce two prototypes in the development schedule. What an optimist! To begin with, 74C series ICs are not readily available in surface mount although we did manage to locate some in the USA at about US$3.50 per IC. So I blithely proceeded to substitute 74HC series ICs which are available over the counter at several large component stores. All hell broke loose. When switched on, the circuit which has been in more or less continuous production from 1974 did not work at all. It needed a lot of work to sort it out. For many years and particularly since the introduction of the very large quarter scale models, there have been mutterings about noise or interference problems related to the long servo leads in these models. The talk was always vague and no one appeared to have any definite idea as to what was the nature of the noise or where it came from. The implication seemed to be that RF was being picked up on these long leads from other transmitters and was then finding its way back into the receiver – much the same as CB transmitters break into older stereo sets. As a result, we were often asked to fit ferrite beads and all sorts of suppressors to long servo leads. I might add here that I spent hours examining my sets and never located any definite signs of this problem. When I finally managed to trick the first prototype decoder into working, the very first thing I noticed when I plugged in a servo was a very strong noise spike at the receiver detector, associated with any channel which had a servo lead attached. Removing This photo shows how the 8-channel decoder sits in the bottom of the case & the receiver plugs into and sits on top of it. Note the slot in the decoder board to give access to the crystal on the receiver board. 70  Silicon Chip April 1995  71 B E VIEWED FROM ABOVE C E Q1 BC848 C C11 B .01 R12 10k C9 .001 R11 47k R16 1M 1 7 14 C12 xx 2 IC2a 40106 3 D2 BA516 IC2b 4 SILVERTONE MK22 8-CHANNEL DECODER R15 100k R18 1M C15 1.5 C16 0.1 5 6 C13 1.5 C10 .033 R9 1k IC2c R10 100k Fig.1: the decoder takes the serial data stream from the receiver & produces up to eight pulse outputs to drive the servos. IC2 is essentially a pulse shaper, while IC1 is the shift register where the decoding actually takes place. RX IN TB10 R14 100  C14 47 +4.8V R13 220k D1 BA516 O2 O1 O0 5 4 3 EXPANSION TB9 7 R1 1k 6 O3 10 IC1 O4 1 74HC164 11 O5 A 12 2 B O6 13 O7 9 MR 8 CLK 14 R2 1k R3 1k R4 1k R5 1k R6 1k C1 .001 C2 .001 C3 .001 C4 .001 C5 .001 C6 .001 C7 .001 R7 1k C8 .001 R8 1k R17 56  CHANNEL 8 TB1 CHANNEL 7 TB2 CHANNEL 6 TB3 CHANNEL 5 TB4 CHANNEL 4 TB5 CHANNEL 3 TB6 CHANNEL 2 TB7 CHANNEL 1 TB8 Fig.2: this is a typical data stream from the receiver, as meas­ured at the collector of Q6. Fig.3: this is the same data stream as in Fig.2 after it has been squared up by IC2a. Fig.4: this is output waveform from IC2b, showing the synchronisation pulse. Fig.5: this is typical of the pulse output that will be found on any of the servo lines from IC1. the servo lead caused the spike to disappear. It was fairly obvious that the high speed switching (about 15MHz) was radiating from the servo lead. Is this the problem that modellers were concerned about? From memory it was about the time of the introduction of high speed CMOS that the noise was first mentioned. The problem was however, what was I going to do about it? CMOS surface mount was not available and I had already gone into print and promised 8, 16 and 24-channel decoders. (4000-series CMOS is readily available in surface mount but there is not a suitable 8-bit shift register in this series). So here I was with a decoder that did not work reliably and when it did, it radiated like a transmitter. It was while discussing these prob72  Silicon Chip lems with a colleague that the answer to the entire dilemma popped up. My friend showed me an article in an electronics magazine which stated that HCMOS chips ring like bells in the output stage and that an anti-ringing filter was most helpful, especially on clock lines. This article went on to say that a 1kΩ resistor followed by a 1000pF capacitor was all that was required to cure the problem. The circuit diagram of Fig.1 shows the arrangement. The addition of the filter in the servo leads eliminated the radiation completely and the decoder began working reliably when the filter was placed in the clock line between IC2 and IC1. However, I am really annoyed about this whole affair. In the case of the 24-channel decoder, I am now stuck with adding 51 components on PC boards that are too small to accom­modate this many components – all this to get rid of switching speed I do not need. In the end, the 8-channel decoder called for a compromise and I used a 40106 in place of the 74HC04 (unfortunately, I could not change the 74HC164). This at least got rid of the filter on the clock line and I managed to complete the PC board layout without jumpers and with all components in place except for C1 which ended up on the bottom layer. I was not so lucky with the 16-channel expansion PC board, unfortunately. Here I ended up with about six jumpers. This module will be presented next month and features a double sided surface mount board. Still, the completed 24-channel receiver is a very professional looking piece of TB1 TB2 TB3 TB4 TB5 TB6 TB7 TB8 TB9 C10 R14 R18 C15 R15 C11 C9 R11 R9 R10 R12 C12 R13 C14 R2 C2 R3 C3 C4 R4 C5 R5 C6 R6 C7 R7 C8 R8 R16 R17 IC2 40106 R1 (IC2) is used as a pulse shaper and driver for the 74HC164 shift register (IC1). Inverter IC2a provides the clock data C1 (as shown in the scope photo of Fig.3) and also drives IC2b. D1 D2 1 IC2b’s output supplies the IC1 synchronisation pulse (shown 74HC106 in the scope photo of Fig.4) in Q1 association with D2, R10 and 1 C10. During the long pause TB10 C14 TB10 between pulse frames (6ms C16 minimum), C10 charges via R10 and lets pins 1 and 2 on IC1 go Fig.6: here are the component overlays for the top & bottom of the 8-channel decoder high, ready for the first pulse on board. Only a single capacitor (C1) & the 3-way header are mounted on the underside (see text). the next frame. R9 is included to introduce a small delay in work. All of the PC boards simply supply decoupling network for the the switching, to stop mistriggering. plug together. receiver and decoder. The signal pin IC2b also drives IC2c which develFinally, I have just a few words on on TB10 goes to the audio slicer which ops a chip enable voltage at pin 9 on the servo leads them­ selves. One of consists of Q1, C15, R18, R15 and IC1. This acts as a fail-safe in the abthe problems faced by modellers with R12. The input floats on the receiver sence of the incoming pulse train and older equip­ment is the need for re- noise floor and rejects the bottom 1V thus helps to stop servo gears being placement receivers. The transmitters of hash. Thus only clean high level damaged. C13 and R13 smooth out never seem to wear out and servos are audio pulses are fed to the audio the pulses and provide approx­imately fairly robust but receivers often die and amplifier. The scope photo of Fig.2 +4.5V DC on pin 9, thus enabling the the agents often discontinue service on shows the signal from the receiver (at chip. Loss of signal sends pin 9 low, the collector of Q6). older models. shutting down IC1 and completely C11, R11 and C9 form a filter to re- eliminating spurious outputs on the This leaves the modeller with an unuseable system. Added to this is the move any remaining hash. The 40106 servo lines. confusion brought about by non-standardisation of the servo plugs. Most servos these days plug into header pins Receiver & Decoder Kit Availability mounted directly onto the PC board but the arrangement of these header Receiver PC board (double-sided with plated-through holes) ..........$11.50 pins can vary from manufacturer to Basic receiver kit: all parts except crystal .........................................$45.00 manufacturer. Built & tested AM receiver less crystal .............................................$59.00 This new receiver/decoder package is designed to replace as wide a Decoder PC board (double-sided with plated-through holes) ..........$11.50 variety of receivers as possible and a 8-channel decoder kit: all parts less servo pins or connec­tors .........$32.00 considerable amount of thought has Built & tested 8-channel decoder but less servo plugs ....................$45.00 gone into making this possible. To Expansion kit: all components to build the 16-channel decoder ......$42.00 begin with, the polarity of the power pins may be reversed by simply Built & tested 16-channel decoder less servo connectors ...............$55.00 cutting two tracks and jumpering. 8-channel receiver case (includes labels) ........................................$11.50 In addition, the header pins may be 16-channel receiver (includes labels) ...............................................$19.50 replaced with fly leads for even more Machine wound RF coils ....................................................................$2.95 versatility. Machine wound IF coils ......................................................................$2.95 Circuit operation Crystals (AM) per pair ......................................................................$17.95 The decoder is contained on a sepServo header pins (each) ...................................................................$0.12 arate PC board and con­nects to the receiver through a 4-pin header plug Futabe EXT lead .................................................................................$3.40 (TB10). Power to the receiver is deJ.R. EXT lead ......................................................................................$3.40 rived from the power rails associated Sanwa EXT lead .................................................................................$3.40 with the servo plugs. Depending upon the number of channels in use, you can either use a spare servo output as the power input or if all eight channels are in use, a “Y” or splitter lead can be inserted between one servo and header pins. R17, R14, C14 and C16 form a Notes: (1). When ordering crystals, do not forget to specify frequency. (2). All orders should add $3.00 for postage and packing. Payments may be made by cheque, money order, Bankcard, Visa Card or Mas­tercard. Send all orders to Silvertone Electronics, PO Box 580, Riverwood, NSW 2210. Phone (02) 533 3517. April 1995  73 Provided the conditions are all correct on pins 1, 2, 8 and 9, the pulses will clock through the shift register and servo outputs will appear at pins 3, 4, 5, 6, 10, 11, 12 and 13, as shown in the scope photo of Fig.4 (ie, if all eight pulses in a frame are transmitted). If only two pulses per frame are trans­ mitted, then output 3 will be the sync pause and output 4 will be channel 1 again and output 5 will be channel 2; output 6 will be the sync pause and so on. Thus, in a 24-channel receiver channel 1 will appear three times if only eight pulses are transmitted. This is a useful feature during testing if only transmitters with a lesser number of channels are available or it can be very useful as a splitter/driver for parallel servo operation. In this case, each output only drives one servo as against two in the case of a “Y” lead. The three unused inputs on IC2 (pins 9, 11 & 13) are tied to ground. Finally, TB9 is the expansion port for the 16-channel add-on PC board. This port carries clock, data and enable infor­mation, as well as the two power rails. Construction The PC board provided with the kit is a double sided plated-through board with solder resist over all but the component pads. For those not familiar with surface mount assembly, read the article on this subject in the January 1995 issue of SILICON CHIP. The component overlays for the top and bottom of the boards are shown in the diagrams of Fig.6. First, the polarisation of the power rails must be decided and set accordingly. As delivered, the PC board is set up for centre rail positive (JR, Futaba, Hi Tech). To reverse this order (KO, Sanwa), simply cut the thin tracks connecting the power rails with the decoder supply rails (along the top edge of the board as shown in Fig.6) and reconnect them to the appropriate rails. There are pads located alongside the power rails for this purpose. Note that one track is located on the top layer and the other on the bottom layer. Use 10amp fuse wire or a component lead for the jumper. No reverse voltage protection Be very careful here for there is insufficient voltage for a reverse voltage protection diode when using a 4.8V 74  Silicon Chip Fig.7: this exploded diagram shows how the decoder & receiver sit in the case. The various slots in the case give access to the crystal & provide exit holes for the antenna & servo lines. battery. Whilst on this subject, the receiver is set up for 4.8V and will not operate satisfactorily from a 6V battery. If you need to operate from 6V then insert two diodes in series with the +6V lead, to reduce the voltage by 1.2V. Be certain to mark your finished unit clearly because if you end up with two receivers, one positive and one negative, you could land yourself in bother at some later date. Begin assembly by mounting the SM devices and solder one pad on each component first. Order is not important here, just suit yourself. Once all of the SM components are mount­ed, mount the two capacitors. C14, the 47µF tantalum, is polarised so be careful to follow the markings. Next, mount the 3-pin socket (TB10), making sure that it is on the correct side of the PC board. This is on the opposite side to the components. If the thought of having a plug in the systems worries you in regard to vibration, then this connector pair may be deleted and replaced with wire connections. At this point, it needs to be clearly understood how many channels will be required and whether fly leads or pins are to be used for the servo connectors. Presumably you have ordered a kit and specified the number and type of servo connectors required. If you are using fly leads, just solder the leads into the appro­priate holes in the servo connector pads in the order they lay on the servo lead. If the leads are centre-negative, do not forget to reverse the PC board connections if you have not already done so. If you do decide to use fly-leads for the servo outputs, you will need to file one or two slots in the case end for the lead exits. Do not forget to thread the servo leads through the grommets before soldering them to the PC board (see the exploded case diagram of Fig.7 for details). If you intend to use the pins, then just simply push the 3-pin plug through the PC board with the plastic base on the component side and with the long pins going through the holes. Solder the pins from the reverse side. Snip off the excess pins on the reverse side and remove the plastic from the pins on the component side. This now leaves pins the correct length for a servo socket on the component side of the PC board. If you intend using more than eight channels, you must now install the expansion port. Follow the same routine as for the servo pins. You now have a finished decoder. Testing Plug the decoder into a pre-tuned receiver and leave both units out of the case. It is wise to insert a piece of insu- lating card between the two boards, as otherwise they can touch if bumped. Once they are snapped into the slots in the case, this is not necessary. Testing can now proceed as all components are accessible from the servo pin side of the PC board. Alternative­ly, an extension lead can be made up to keep the two PC boards well separated during servicing and testing. Turn on the associated transmitter and, using an oscillo­scope, check the input to the slicer and compare the waveshape with Fig.2. Next proceed to check pins 1-6 on IC2. These should compare with Fig.3 on the odd-numbered pins and should be inverted on the even-numbered pins. Now test IC1 pins 1 and 2 and compare the waveshape here with Fig.4. Pin 8 on IC1 compares with Fig.3 and pin 9 should be a DC voltage with a low level of ripple on top floating at about +4.5V above ground. Whilst monitoring pin 9, switch off the transmitter and note that it goes low no more than one second after switch off. If all of the foregoing is in order, the output at pins 3, 4, 5, 6, 10, 11, 12 & 13 will look like Fig.5. Plug in one or more servos and check the operation from the transmitter. Be careful not to reverse the servo plug as the polarising key is in the case. Case assembly If you are using the header pin layout, complete the assembly by simply snapping the decoder PC board into the case, with the pins pointing towards the punched holes in the case bottom. Next, plug the receiver board into the 3-pin socket, leaving the fourth pin (closest to the edge of the PC board) outside the socket. This now provides a useful test point to attach an oscilloscope or meter. The receiver simply rests in the notch in the case sides. Slip on the case lid, attach the labels and open the servo slots in the bottom label that you wish to use. Leave any of the unused slots covered to prevent ingress of dust. Secure the lid with a wrap of clear tape. Now go and have some fun. Troubleshooting Now for the sad cases, it is back to the test bench. First­, check the assembly for missing components, soldering faults, etc. Check the decoder power rails to see if they are compatible with the servo leads you are using. Be sure that these have not been accidentally reversed and do not suit the servo leads you are using. Now grab your multimeter and start testing voltages. The input voltage at the power rails will be the battery voltage unless dropping diodes are installed. Next, check the power rails in the decoder. With a nicad battery reading 5.0V, pin 14 on both chips should be approximately 4.9V. Pin 7 on both chips is the ground pin. The base of Q1 should be +0.35V and the collector +4.9V, with no signal from the transmitter. The rest is routine servicing. If all of the DC and input voltages are correct, then you may suspect a faulty IC, but let me tell you, it is rarely ever the IC. I have found from experience that 99 times out of 100, it is an associated fault. If all your best efforts are to no avail, then send it back to Silvertone and we will sort it out for you. Next month, we will describe the 16-channel decoder board. This will be a double-side board with surface mount components on both sides. SC 20MHz Dual Trace Scope $795 100MHz Kikusui 5-Channel, 12-Trace 50MHz Dual trace Scope $1300 COS6100M Oscilloscope $990 These excellent units are the best value “near brand new” scopes we have ever offered. In fact, we are so confident that you’ll be happy, we will give you a 7-day right of refusal. Only Macservice can offer such a great deal on this oscilloscope . . . and you are the winners! 1. Power switch 2. LED 3. Graticule illumination switch 4. Trace rotation 5. Trace focus 6. Trace intensity for B sweep mode 7. Brightness control for spot/trace 8. Trace position 9/10/11. Select input coupling & sensitivity of CH3 12. Vertical input terminal for CH3 13. AC-GND-DC switch for selecting connection mode 14. Vertical input terminal for CH2 15/22. Fine adjustment of sensitivity 16/23. Select vertical axis sensitivity 17/24. Vertical positioning control 18/25/38. Uncal lamp 19. Internal trigger source CH1,CH2,CH3,ALT 20. AC-GND-DC switch for selecting connection mode 21. Vertical input terminal for CH1 26. Select vertical axis operation 27. Bezel 28. Blue filter 29. Display selects A & B sweep mode 30. Selects auto/norm/single sweep modes 31. Holdoff time adjustment 32/51. Trigger level adjustment 33/50. Triggering slope 34/49. Select coupling mode AC/HF REJ/LF REJ/DC 35. Select trigger signal source Int/Line/Ext/Ext÷10 MACSERVICE PTY LTD 36. Vertical input terminal for CH4 37. Trigger level LED 39. A time/div & delay time knob 40. B time/div knob 41. Variable adj of A sweep rate & x10 mag 42. Ready lamp Australia’s Largest Remarketer of Test & Measurement Equipment 20 Fulton Street, Oakleigh Sth, Vic., 3167. Tel: (03) 562 9500; Fax: (03) 562 9590 43. Calibration voltage terminals 44. Horizontal positioning of trace 45. Fine adjustment 46. Vertical input terminal for CH5 47. Delay time MULT switch 48. Selects between continuous & triggered delay 52. Trace separation adjustment 53. Ground terminal April 1995  75 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd PRODUCT SHOWCASE Portable DSO & test instrument The Palmscope 320, designed and manufactured by Escort Instruments, is unlike other portable, integrated test instrument packages. The four auto-ranging instruments integrated into Escort's Palmscope 320 are: a 2-channel 20MHz digital storage scope; a 3-3/4 digit true-RMS digital multimeter (with AC/DC amps); a 7-digit, 20MHz frequency/period counter and an 8-channel, 20MHz logic analyser. The unit has specifications normally only found on dedicated bench top instruments. The unit has specifications normally only found on dedicated bench top instruments. Some of these specifications include: 2K (1920 point) deep DSO memory; accuracy of 10ppm on the frequency counter and an 8 channel logic analyser with both timing and state signal displays. The Palmscope 320 is supplied complete with oscilloscope and multimeter probes, protective rub- VF-100 true-RMS mains monitor For country people who generate their own electricity, whether by wind, solar or water power, Callignee Electronics has released the VF-100 mains monitor. The device is intended to prevent damage to sensitive equipment by verifying that generators are running at the correct speed and that battery inverters are adjusted correctly. The unit measured "true RMS voltage" and cycles per second" of the mains supply and displays the results on a LED bar-graph display. The VF-100 is also widely used by electricians and generator mechanics who service and install alternative power systems. The price is $170 plus tax where applicable. Write for a pamphlet to Callignee Electronics, PO Box 483, Traralgon, Vic 3844 or phone (051) 955 503. ber holster, AC power pack, NiCad rechargeable battery pack and slim brief-case style carrying case. Options include an RS-232 interface cable, PC data transfer software and logic analyser probes. For further information contact Emona Instruments, 86 Parramatta Road, Camperdown, NSW 2050. Phone (02) 519 3933. Fax (02) 550 1378. New A/D converter board from Procon Procon Technology has released an externally mounted analog input board that extends its range of input/ output boards manufactured in Australia. The ADC-808 provides eight analog inputs with 8-bit resolution and is available with 0 to 10V or 0 to 20mA input ranges. Other configurations are available on request. An industrial version, the ADC-808/I, is also available with 500 volt isolation between each analog input, detachable screw terminals for easy installation and extended supply voltage range. The board measures 240mm by 100mm and is capable of being DIN rail mounted. A single IBM-PC interface card (PB-BD-IO) is available that plugs into an 8-bit card slot and connects to 15 ADC-808 boards. This offers up to 120 analog inputs. Alternatively, the boards may be connected to any standard bi-directional parallel printer port (available on most notebook and industrial computers) to provide up to 56 analog inputs. Different configurations of analog and digital input/ output cards are possible with this interface. Typical applications include process April 1995  81 monitoring and control, energy management, home automation, security systems and industrial control. Other boards are available in the range, including opto-isolated digital input and relay output boards. All are available with the industrial option. All boards come with example IBMPC software for programming from most languages and are compatible with the Programmable Logic Control (PLC) language, developed by Procon Technology. For further details contact Peter King, Procon Technology, PO Box 655, Mount Waverley, Vic 3149. Phone (03) 807 5660. Fax (03) 807 8220. CCTV observation systems The OLS-100 with 10" screen and OLS-120 with 12" screen, are complete packaged plug-in ready to use observation systems. They are Intel microprocessor controlled and feature automatic, period adjustable sequential camera switching, 2 way monitor/ camera audio communication, sensor inputs & VCR output. Each package includes a combination monitor/intercom and automatic 4-channel switcher, a 400-line 0.2 Lux CCD camera with 12mm lens, a camera stand and a 20 metre camera cable. To use, simply mount the camera, connect the monitor and switch on. Camera cable length may be extended using a plug-in coupler. The single lightweight multi-core 5mm diameter camera cable is installed with the aid of adhesive cable holders. Each unit supports up to four cam- eras and four sensors. Three styles of intercom camera units are available, conventional C mount, eyeball and flat, with wide angle lenses. In addition, tiny pinhole modules, which can see through a 2mm hole, are available for concealed applications. Sensor inputs on each camera allow monitoring of camera locations using PIR or other devices. If a sensor is tripped, an alarm sounds and the image from the camera in the violated area is automatically displayed on screen. PowerPCB Cad package PADS Software Inc has announced PowerPCB for PC board design, intended for users who work with UNIX or Windows. This has a number of advanced features including a shape-based PCB editor which allows freedom from grid restraint during placement, routing and editing, a dynamic route editor which has semi-automatic 45* routing to avoid obstacles or move them out of the way, plus conditional rules and design rules hierarchy. At the same time as the release, special offers are being made to users of protel and P-CAD to enable them to buy PADS software. For further information, contact the Australian distributors, GEC Electronics Division, Unit 1, 38 South St, Rydalmere, NSW 2116. Phone (02) 638 1888. 82  Silicon Chip Packaged sets from $699 including tax, are available from Allthings Sales & Services, PO Box 25, Northlands, WA 6021. Phone (09) 349 9413. High capacity tape backup system Hewlett-Packard has announced the release of its Jumbo 1400 tape backup system which provides 680 megabytes of storage on a single mini-cartridge or 1.36Gb using data compresion. The Jumbo 1400 is an internal drive that installs in normal 3.5-inch or 5.25-inch half-height bay. It can inerface to a PC's floppy disc controller but the system also includes a separate high speed controller that takes advantage of the drive's maximum transfer rate of 2Mb/s and provides backup rates of up to 15Mb/ minute. The system includes one pre-formatted mini cartridge and backup programs for Windows and DOS. Australian pricing is expected to be under $700. For further information, contact Hewlett-Packard by phoning 131 347. New Yokogawa digital scope Wi t h u n i q u e 1 0 - b i t , 100Ms/s A/D converters in each channel and a 100K word length, the new DL4100 digital oscilloscope from Yokogawa gives four times better vertical resolution and 100 times better horizontal resolution than scopes with conventional 8-bit A/D converters and 1K word memories. This allows highly accurate measurements to be made on the most complicated waveforms. The DL4100, 4 channel 150MHz digital storage oscilloscope is designed specifically for use where accurate and reliable measurements are to be made on complicated waveforms, such as TV signals, AM signals and noise signals. Greater measurement accuracy is also achieved in multi-channel measurements by virtue of the DL4100's split display mode. This allows a full scale to be applied to each signal in a separate screen area, rather than the amplitude of the trace having to be reduced to view each input signal, and thus incurring an increase in errors. Also ensuring high accuracy measurements at all times, the DL4100 automatic self-calibration feature initiates every 30 seconds or when settings such as time/div are changed. When the DL4100 is to be used for advanced analysis or as part of a larger measurement system, or if hard copy plots are to be obtained, connection can be made via a built-in GPIB interface. For further information, contact Yokogawa Australia Pty Ltd, 25-27 Paul Street North, North Ryde, NSW SC 2113. Phone (02) 805 0699. April 1995  83 NICS O R T 2223 LEC 7910 y, NSW EY E OATLBox 89, Oa8t5leFax (02) 5s7a0 C a rd KITS & BITS i 9 PO 579 4 r C a rd , V e & fax ) 2 0 ( n e e Phon rd , M a s t with pho orders: a d c ed B a n k x accepte most mix 0. Orders $3; 50 x 72 x 3mm: $3. LINE GENERATING e r 1 OPTIC: makes a line out of a laser beam: & Am . P & P fo (airmail) $ s $5. LASER DIODE COLLIMATING LENS: order 4-$10; NZ world.net $4. PORRO 90 deg. PRISM: makes a $ <at> . y t e s l t u rainbow from white light: $10. PRECISION ROTATING a A AIL: o MIRROR ASSEMBLY: as used in levelling equipment, by EM needs small motor/belt, plus a laser beam, will draw a HIGH INTENSITY RED LEDs 550-1000mCd <at> 20mA, 100mA max, 5mm housing: 10 for $4, or 100 for $30. LOW COST IR ILLUMINATOR Employs 42 high output 880nM IR LEDs (30mW <at> 100mA ea.) & a seven transistor adjustable constant current driver circuit. Designed to be powered from 10-14V DC, current depends on power level setting: 5 - 600mA. The compact PCB is designed to replace the lid on a standard small 82 x 53 x 28mm plastic box. Good for illuminating IR responsive CCD cameras, IR & passive night viewers & medical use. The complete kit even includes the plastic box & is priced at a low: $40 MINIATURE FM TRANSMITTER Not a kit, but a very small ready made self contained FM transmitter enclosed in a small black metal case. It is powered by a single small 1.5V silver oxide battery, and has an inbuilt electret microphone. SPECIFICATIONS: tuning range: 88-108MHz, antenna: wire antenna - attached, microphone: electret condenser, battery: one 1.5V silver oxide LR44/G13, battery life: 60 hours, weight: 15g, dimensions: 1.3" x 0.9" x 0.4". $32. COLOUR MONITORS Used but guaranteed 12" colour computer monitors: $40 REEL TO REEL TAPES New studio quality 13cm-5" “Agfa” (German) 1/4" reel to reel tapes in original box, 180m-600ft: $8 ea. ARGON HEADS These low voltage air cooled Argon Ion Laser Heads are priced according to their hours of operation. They produce a bright BLUE BEAM (488nM) and a power output in the 10-100mW range - depending on the tube current. The head includes power meter circuitry, and starting circuitry. We provide a simple circuit for the supply. Limited supplies at a fraction of their real cost: $300 - $500. AC MOTOR Small but very powerful GEARED AC motor. 1 RPM/60Hz/24V/5watt. We supply a circuit diagram that shows how to power this motor from 12V DC: Variable speed/full power (bridge output). Bargain priced: $9 PCB and all on-board components kit for the 12V driver kit will be available late in May: $8 OPTICS BEAM SPLITTER for 633nM: $45. PRECISION FRONT SURFACE ALUMINIUM MIRRORS 200 x 15 x 3mm: 84  Silicon Chip line right around a room (360 deg.) with a laser beam: $45. LARGE LENS: out of a night viewer, can easily be pulled apart: $18. ARGON MIRRORS: high reflector and output coupler used to make an Argon tube: $50. POWER SUPPLIES Used but very clean non standard computer power supplies, enclosed in metal casing with perforated ends for air circulation, built in fan, IEC input connector and OFF-ON switch, “flying” DC output leads, overall dimensions: 87 x 130 x 328mm, 110-220V input, +5V/8A, +12V/3A, and -12V/0.25A DC outputs. BARGAIN PRICED: $18 ea. or 4 for $60. Used IEC lead with Australian plug $2.50 extra. TWO STEPPER MOTORS PLUS A DRIVER KIT This kit will drive two stepper motors: 4, 5, 6 or 8-wire stepper motors from an IBM computer parallel port. Motors require separate power supply. A detailed manual on the COMPUTER CONTROL OF MOTORS plus circuit diagrams/descriptions are provided. We also provide the necessary software on a 5.25" disc. Great “low cost” educational kit. We provide the kit, manual, disc, plus TWO 5V/6 WIRE/7.5 Deg. STEPPER MOTORS FOR A SPECIAL PRICE OF: $42. MAINS LASER SPECIAL Includes a compact potted US made power supply which can be powered from 110/220-240V AC, a 2-3mW He-Ne tube, a ballast resistor and instructions. The power supply requires 4-6V <at> 2mA DC enable to run. Brand new components. Giveaway price: $65 27MHz TRANSMITTERS These new Australian made transmitters are assembled (PCB and components) and tested. They are Xtal locked on 26.995 MHz and were originally intended for transmitting digital information. Their discrete component design employs many components, including 5 transistors and 8 inductors: circuit provided. A heatsink is provided for the output device. Power output depends on supply voltage and varies from 100mW to a few watts, when operated from 3-12V DC. These are sold for parts/experimentation/educational purposes, and should not be connected to an antenna as licensing may be required: $7 ea. or 4 for $20. 12V FANS Brand new 80mm 12V-1.6W DC fans. These are IC controlled and have four different approval stamps: $10 ea. or 5 for $40 CD MECHANISMS Used compact disc player mechanisms. Include IR laser diode, optics, small conventional DC motor, gears, stepping motor, magnets etc. Great for model railway hobbyists: The motor/gear assembly produces a linear movement of approx. 60mm. The whole assembly is priced at less than the value of the collimating lens, which is easy to remove: $6. We also have some similar CD assemblies that have linear motors. Used CD mechanisms with linear motors: $4. IMAGE INTENSIFIER TUBES Used but in excellent condition second generation image intensifier tubes. Can be used to make a small and very sensitive scope that can produce high resolution pictures in very low illumination. US made tubes that produce superior results! $650 We should have a complete kit of parts for a small scope available at the time of the publication of this advertisement: “Ring”. VIDEO TRANSMITTERS Low power PAL standard UHF TV transmitters. Have audio and video inputs with adjustable levels, a power switch, and a power input socket: 10-14V DC/10mA operation. Enclosed in a small metal box with an attached telescopic antenna. Range is up to 10M with the telescopic antenna supplied, but can be increased to approximately 30M by the use of a small directional UHF antenna. INCREDIBLE PRICING: $25. IR REMOTE SWITCH KIT Consists of a PCB and all on board components kit for an IR receiver with a toggle output, and a brand new commercial ready made slimline IR remote control transmitter, which was designed for a CD player. Simply press any button on the IR transmitter to toggle the output on the receiver. The system has up to 20M range and will also work from most other IR remote controls! Receiver uses an IC “front end”, has a toggle output, operates from 8-15V DC, and will drive a relay. Transmitter operates from two “AAA” batteries (not supplied). Unbelievable pricing: $18 For the slimline IR remote control transmitter and a kit for the IR receiver. Suitable 12V/8A relay with 4kV isolation: $3, 12V DC plugpack: $10. PRINTER MECHANISMS Brand new Epson dot matrix printer mechanisms: overall dimensions are 150 x 105 x 70mm. These are complete units and contain many useful parts: 12V DC motor (50mm long - 30mm diam.) with built in tachometer, gears, solenoid, magnet, reed switch, dot matrix print head etc.: $12. VISIBLE LASER DIODE MODULES Industrial quality 5mW/670nM laser diode modules. Overall dimensions: 11mm diameter by 40mm long. Have APC driver built in and need approximately 50mA from 3-6V supply. $60. SOLID STATE “PELTIER EFFECT” COOLER-HEATER These are the major parts needed to make a solid state thermoelectric cooler-heater. We can provide a large 3.4A Peltier effect semiconductor, two thermal cutout switches, and a 12V DC fan for a total price of: $35. We include a basic diagram/circuit showing how to make a small refrigerator-heater. The major additional items required will be an insulated container such as an old “Esky”, two heatsinks, and a small block of aluminium. 12V-4.5A Peltier device only: $25. DOT MATRIX LCDs Brand new Hitachi LM215 400 x 128 dot matrix Liquid Crystal Displays in an attractive housing. These have driver ICs fitted but require an external controller. Effective display size is 65 x 235mm. Available at less than 10% of their real value: $25 ea. or 3 for $60 VISIBLE LASER DIODE KIT A 5mW/670nM visible laser diode plus a collimating lens, plus a housing, plus an APC driver kit (Sept. 94 EA) UNBELIEVABLE PRICE: $35. The same kit is also available with a 3mW/650nM laser diode: $60. WELLER SOLDERING IRON TIPS New soldering iron for low voltage Weller soldering stations and mains operated Weller irons. Mixed popular sizes and temperatures. Specify mains or soldering station type: 5 for $10. $215 CCD VIDEO SECURITY SYSTEM Monochrome CCD Camera which is totally assembled on a small PCB and includes an auto iris lens. It can work with illumination of as little as 0.1Lux and it is IR responsive. This new model camera is about half the size of the unit we previously supplied. It is slightly bigger than a box of matches! Can be used in total darkness with Infra Red illumination. NEW LOW PRICE: $180 With every camera purchased we can supply an used but tested and guaranteed 12V DC operated Green computer monitor. We can also supply a simple kit to convert these monitors to accept the signal from the CCD camera: monitor $25, conversion kit $10. A COMPLETE 12V CCD VIDEO SECURITY SYSTEM FOR $215!! LOW COST 1-2 CHANNEL UHF REMOTE CONTROL A single channel 304MHz UHF remote control with over half a million code combinations which also makes provision for a second channel expansion. The low cost design includes a complete compact keyring transmitter kit, which includes a case and battery, and a PCB and components kit for the receiver that has 2A relay contact output!. Tx kit $10, Rx kit $20 additional components to convert the receiver to 2 channel operation (extra decoder IC and relay) $6. is available: suits 12-24V batteries, 0.1-16A panels, $27. Also available is a simple and efficient shunt regulator kit, $5. BLEMISHED 3 STAGE TUBES We have accumulated a good number of 40mm three stage fibre optically coupled 3 stage image intensifiers that have minor blemishes: similar to above but three tubes are supplied already bonded together: extremely high gain!! Each of these tubes will be supplied with the power supply components only. See SC Sept. 94. $200 For the 3 stage 40mm tube, supply kit. We can also supply the full SC Sept. 94 Magazine: $5 TDA ICs/TRANSFORMERS We have a limited stock of some 20 Watt TDA1520 HI-FI quality monolythic power amplifier ICs: less than 0.01% THD and TIM distortion, at 10W RMS output! With the transformer we supply we guarantee an output of greater than 20W RMS per channel into an 8ohm load, with both channels driven. We supply a far overrated 240V-28V/80W transformer, two TDA1520 ICs, and two suitable PCBs which also include an optional preamplifier section (only one additional IC), and a circuit and layout diagram. The combination can be used as a high quality HI-FI Stereo/Guitar/P.A., amplifier. Only a handful of additional components are required to complete this excellent stereo/twin amplifier! Incredible pricing: $25. For one 240V-28V (80W!) transformer, two TDA1520 monolythic HI-FI amplifier ICs, two PCBs to suit, circuit diagram/layout. Some additional components and a heatsink are required. RUBY LASER HEADS These complete and functional heads include a flash tube, mirrors, and 4" ruby rod! Produce a high intensity visible red beam! We should have suitable circuits - components to drive these available. Dangerous units with restricted sales. Limited quantity. $695 BIGGER LASER We have a good, but LIMITED QUANTITY of some “as new” red 6mW+ laser heads that were removed from new equipment. Head dimensions: 45mm diameter by 380mm long. With each of the heads we will include our 12V Universal Laser power supply. BARGAIN AT: $170 6mW+ head/supply ITEM No. 0225B INCREDIBLE PRICES: COMPLETE 1 CHANNEL TX-RX KIT: $30 COMPLETE 2 CHANNEL TX-RX KIT: $36 ADDITIONAL TRANSMITTERS: $10 We can also supply a 240V-12V/4A-5V/4A switched mode power supply to suit for $30. FIBRE OPTIC TUBES Originally designed for bicycles, but these suit any moving vehicle that has a rotating wheel! A nine function computer with speed, average speed, maximum speed, distance, odometer, timer, scan, freeze frame memory, and a clock. Its microprocessor based circuitry can be adapted to work with almost any wheel diameter. Simply divide the wheel diameter in millimetres by 6.8232, and program the resultant figure into the computer. We have a good supply of some tubes that may have a blemish which is not in the central viewing area! These produce a very high resolution image but would require IR illumination: !!ON SPECIAL!! $50 for a blemished 25 or 40mm (specify preference) image intensifier tube and supply kit. Matching good quality eyepiece lens only, $2 extra! That’s almost a complete night viewer kit for: $52. 12V-2.5 WATT SOLAR PANEL KITS These US made amophorous glass solar panels only need terminating and weather proofing. We provide terminating clips and a slightly larger sheet of glass. The terminated panel is glued to the backing glass, around the edges only. To make the final weatherproof panel look very attractive some inexpensive plastic “L” angle could also be glued to the edges with some silicone. Very easy to make. Dimensions: 305 x 228mm, Vo-c: 18-20V, Is-c: 250mA. SPECIAL REDUCED PRICE: $20 ea. or 4 for $60 Each panel is provided with a sheet of backing glass, terminating clips, an isolating diode, and the instructions. A very efficient switching regulator kit VEHICLE COMPUTERS $29.90 $70. SWITCHED MODE POWER SUPPLIES: mains in (240V), new assembled units with 12V-4A and 5V-4A DC outputs: $32. ELECTRIC FENCE KIT: PCB and components, includes prewound transformer: $40. PLASMA BALL KIT: PCB and components kit, needs any bulb: $25. MASTHEAD AMPLIFIER KIT: two PCBs plus all on board components, low noise (uses MAR-6 IC), covers VHF-UHF: $18. INDUCTIVE PROXIMITY SWITCHES: detect ferrous and nonferrous metals at close proximity, AC or DC powered types, three wire connection for connecting into circuitry: two for the supply, and one for switching the load, these also make excellent sensors for rotating shafts etc.: $22 ea. or 6 for $100. BRAKE LIGHT INDICATOR KIT: 60 LEDs, two PCBs and ten Rs, makes for a very bright 600mm long high intensity red display: $30. IEC EXTENSION LEADS: 2M long, IEC plug at one end, IEC socket at other end: $5. MOTOR SPECIAL: these permanent magnet motors can also double up as generators, type M9: 12V, I No load = 0.52A-15,800 RPM at 12V, 36mm diam.-67mm long: $5, type M14: made for slot cars, 4-8V, I No load = 0.84A at 6V, at max efficiency I = 5.7A-7500 RPM, 30mm diam.-57mm long: $5. EPROMS: 27C512, 512K (64k x 8), 150nS access CMOS EPROMS, removed from new equipment, need to be erased, guaranteed: $4. 40 x 2 LCD DISPLAY: brand new 40 character by 2 line LCD displays with built in driver circuitry that uses Hitachi ICs, easy to drive “standard” displays, brief information provided: $30 ea. or 4 for $100. MODULAR TELEPHONE CABLES: 4 way modular curled cable with plugs fitted at each end, also an 4M long 8way modular flat cable with plugs fitted at each end, one of each for: $2. POLYGON SCANNERS: precision motor with 8 sided mirror, plus a matching PCB driver assembly. Will deflect a laser beam and generate a line. Needs a clock pulse and DC supply to operate, information supplied: ON SPECIAL $15. PCB WITH AD7581LN IC: PCB assembly that amongst many other components contains a MAXIM AD7581LN IC: 8 bit, 8 channel memory buffered data acquisition system designed to interface with microprocessors: $20. EHT POWER SUPPLY: out of new laser printers, deliver -600V, -7.5kV and +7kV when powered from a 24V-800mA DC supply, enclosed in a plastic case: $16. MAINS CONTACTOR RELAY: has a 24V-250ohm relay coil, and four separate SPST switch outputs, 2 x 10A and 2 x 20A, new Omron brand, mounting bracket and spade connectors provided: $8. FM TRANSMITTER KIT - Mk.2: high quality - high stability, suit radiomicrophones and instruments, 9V operation, the kit includes a PCB and all the on-board components, an electret microphone, and a 9V battery clip: $11. FM TRANSMITTER KIT - Mk.1: this complete transmitter kit (miniature microphone included) is the size of a “AA” battery, and it is powered by a single “AA” battery. We use a two “AA” battery holder (provided) for the case and a battery clip (shorted) for the switch. Estimated battery life is over 500 hours!!: $11. BATTERY CHARGER S2: accessory set for Telecom Walkabout “Phones”. Includes cigarette lighter cable, fast rate charger, and desktop stand. Actually charges 6 series connected AA Nicad batteries: $27. LITHIUM BATTERIES: button shaped with pins, 20mm diameter, 3mm thick. A red LED connected across one of these will produce light output for over 72 hours (3 days): 4 for $2. SUPERCAPS: 0.047F/5.5V capacitors: 5 for $2. PCB MOUNTED SWITCHES: 90 deg. 3A-250V, SPDT: 4 for $2. 3-INCH CONE TWEETERS: sealed back dynamic 8-ohm tweeters: $5 ea. CASED TRANSFORMERS: 230V-11.7V 300mA AC-AC transformers in small plastic case with separate input and leads, each is over 2 metres long: $6. MORE KITS-ITEMS SINGLE CHANNEL UHF REMOTE CONTROL: SC Dec. 92, 1 x Tx plus 1 x Rx: $45, extra Tx $15. 4 CHANNEL UHF REMOTE CONTROL KIT: Two transmitters and one receiver: $96. GARAGE-DOOR-GATE REMOTE CONTROL KIT: SC DEC 93: Tx $18, Rx $79. 1.5-9V CONVERTER KIT: $6 ea. or 3 for $15. LASER BEAM COMMUNICATOR KIT: Tx, Rx, plus IR Laser: $60. MAGNETIC CARD READER: Professional assembled and cased unit that will read information from plastic cards, needs low current 12V DC supply-plugpack: MORE ITEMS AND KITS Poll our (02) 579 3955 or (02) 579 3983 fax numbers for instructions on how to obtain our Item and Kit lists. MANY MORE ITEMS AND KITS THAN ARE LISTED HERE!! You can also ask for a copy of these to be sent out with your next order. April 1995  85 VINTAGE RADIO By JOHN HILL Fault finding – there’s always something different Vintage radio receivers can develop some very unusual faults. Here’s what it took to bring two old receivers back to life again. Having done numerous vintage radio repairs during the past 10 years, I have encountered a wide range of faults and problems. After a while, repairs become fairly routine and it usually does­n’t take long to diagnose a fault and repair it. However, this is not always the case and whenever I come across anything unusual, I like to pass the details on so that others can benefit from my experiences. Not all the repairs I do are for myself and I frequently become involved in the problems of other collectors. This often means having to solve some nasty problem or doing a full restora­tion for someone who has no idea of what is involved. They wrong­ly believe that I can fix anything, have all the necessary spare parts and that the whole job takes about 20 minutes. In the following stories, one receiver had some hard to find faults, while the other is interesting because of the extent of damage the set had sustained. The HMV table model The first headache was an early post-war dual-wave 5-valve HMV ta- The HMV receiver was an early post-war 5-valve table model in a timber cabinet. Some misplaced wiring, a short circuit in some shielded wire & a missing capacitor caused quite a few headaches. 86  Silicon Chip ble model with a timber cabinet. On removing the chassis, it was evident that someone had already replaced most of the capacitors, including the electrolytics, but a couple of the old original paper capacitors still remained. These were replaced before any serious attempt was made to see why the set was not working. The usual routine continuity checks were also made on the aerial and oscillator coils, intermediate frequency (IF) trans­formers, the resistors, output transformer and the field coil. All passed OK. In addition, a valve tester revealed that all the valves were in excellent condition. But despite all these favourable indications, the receiver was quite mute. Now I have a handy little gadget called an “astable mul­tivibrator”. This is a simple 2-transistor signal generator that outputs a 2kHz tone. The signal generator can be used to inject an audible signal into either the radio or audio frequency circuits of a receiver so as to test whether or not a particular stage is working (see SILICON CHIP, August 1992). Placing the signal generator’s probe onto the control grid of the output valve produced a beep from the loudspeaker. That immediately cleared the output stage. Similarly, connecting the probe to the grid of the output driver (or first audio valve) produced a much louder beep, indicating that this stage was also alive and well. By contrast, moving the probe back to the control grid of the IF amplifier valve resulted in no sound whatsoever through the speaker. So the fault lay somewhere between this stage and the next. But although a signal generator can An ohmmeter was used to track down the fault in the shielded cable. As can be seen, it indicates a short between the inner lead & the shielded cable. It’s no wonder that the receiver was mute. This photo shows the troublesome shielded wire in the old HMV radio. The short circuit was at the solder joint where the heat of the soldering iron had damaged the rubber insulation of the inner lead. This problem has been encountered before in other old receivers, so it was not an isolated incident. help locate which sec­tion is at fault, it only narrows the field down a little. There were a lot of components to check out between the grid of the IF valve and the grid of the first audio valve in order to find out which one is faulty, disconnected, shorted, or whatever. By using a pair of high-impedance headphones in conjunction with a small mica capacitor (to block high DC voltages) and a signal diode (for detection), it was noted that a local radio station could be heard when this simple test equipment was connected to the plate of the IF amplifier valve. (Warning: a valve plate operates at This HMV receiver has two shielded leads that bring audio signals from the detector and the pick-up socket to the volume control, after which they are fed to the control grid of the first audio valve. It occurred to me that I had a similar problem once before, which turned out to be a short circuit in a shielded cable. A quick investigation revealed a similar fault in this unit – the inner wire from the pick-up socket was found to be shorting where a wire had been soldered to the shielding to make an earth connection. Apparently, the heat of the soldering iron had dam­ aged the rubber insulation between high voltage. Do not try this unless you know exactly what you are doing). So where the signal injector implied that this valve may not have been working, in actual fact it was and the trouble spot was further on down the line. The problem was obviously between the IF valve output and the control grid of the first audio valve. As the second IF transformer had checked out OK, then perhaps there was something wrong with the detector circuit or the volume control. The volume control was removed, checked and found to be perfectly OK. It was therefore reinstalled in the chassis. This home-made 2-transistor signal generator is powered by two AA cells. It produces a 2kHz signal that can be injected into the RF & audio stages in a receiver. The signal generator circuit was housed in an old Tandy burglar alarm case. It is a very handy device when it comes to trou­bleshooting old radio receivers. April 1995  87 Taking on an unfinished repair that someone else has aban­doned is not always easy! The AWA Radiola This little AWA Radiola receiver required a major restoration job, due to the failure of the set’s high tension supply. In fact, the costs exceeded the value of the old receiver but the owner insisted that the job be done. the inner wire and the shield, which eventually shorted and muted the receiver. The shielded lead probably gave no trouble until it was disturbed and that most likely happened when the capacitors were replaced. After replacing the shielded cable, one would expect everything to work OK but there were still problems! Who ever had previously replaced the capacitors had not reconnected two of them correctly to the volume control. Although the receiver was partly working, there were audio problems and the shortwave section was only just functioning. Not having a circuit diagram, I did the next best thing. I borrowed a similar model HMV from a friend and used it to trace the muddled connections. A bit of a swap around at the volume control and all was well in that department. The shortwave recep­ tion was restored by adding a capacitor that had been previously removed and not replaced. After realignment, the receiver then worked normally. The Radiola’s field coil suffered permanent damage due to the flow of excessive high tension current. Note that the enamel insulation has been burnt off the wire. The paper wrapping on the outside was charred to a crisp. 88  Silicon Chip The other problem receiver was, once again, an early post war model and it had more faults than you could possibly imagine. The main problems were: a broken dial glass, an open field coil, a burnt out rectifier valve, defective capacitors and a couple of well-cooked resistors. As it was an old AWA receiver with its original black moulded paper capacitors, it was not unreasonable to assume that they were the cause of the trouble. This set had suffered a major breakdown and it would require a lot of time and spare parts to get it working again. The most likely scenario regarding the set’s demise is as follows. A shorted high tension component (possibly a paper capacitor or an electrolytic) caused a considerable increase in high tension current. As the receiver used an electrodynamic loudspeaker, the increased high tension current had no option but to flow through the field coil, which caused considerable over­heating. In fact, the field coil became so hot it burnt the enamel insulation off the wire and charred the paper wrapping around the coil to a crisp. Only a few fragments of blackened paper re­mained. A short circuit of this nature also usually results in the rectifier plates glowing red hot because of the high current demands and that no doubt happened in this case. This overheating caused the electrodes to distort and they shorted internally when the cathode and plates touched. But this was no ordinary short circuit between valve ele­ments. It would appear as though an arc was struck (as in arc welding) and this arc continued until part of the cathode sleeve of the 6X5 rectifier had been completely zapped away – see photo. While all this was happening, the two 100Ω half watt resis­tors between the rectifier plates and the high tension winding on the power transformer were severely overloaded. It was only when these resistors became open that the fireworks display came to an end. Naturally such abnormal demands on the power transformer caused it to overheat too. There were several dobs of black pitch stuck to the bottom of the cabinet to verify that the transformer had indeed become very hot at some time in the past. Readers may be able to think up other possible reasons for the high tension failure. While the scenario I have presented is possible and makes interesting speculation, it may have happened some other way! No doubt the receiver was unattended at the time of fai­lure. One assumes that such a performance would not have gone unnoticed and if someone had been nearby, they would have switched the set off. Generally speaking, a little plastic-cased late 1940s re­ ceiver is not a valuable item but the owner was insistent that it be fixed. He liked the set and wanted it going again. A quick check in my spare parts locker revealed that there was a spare dial glass; so work began. The electrodynamic loudspeaker was replaced with a permag type from a later model Radiola. Fortunately, that meant being able to use the same mounting screws and all the holes in the speaker baffle were in the right places. When restoring one of these AWA receivers, it is a good idea to glue the replacement speaker cloth to the cabinet rather than in its original position on the front of the loudspeaker baffle. By doing this, it makes the speaker much easier to work on next time and it can be readily removed without having to first remove the speaker cloth. The overcooked field coil was replaced with a 20W resistor of similar resistance. This substitution produced a little hum in the speaker but it was not objectionable by any means. While a resistor and choke would have given better results, there is little room to mount such things underneath the chassis. Naturally, all the defective paper capacitors were re­placed, as were the electrolytics and a couple of valves, includ­ing the burnt-out rectifier. As luck would have it, the power transformer appeared to have been unaffected by the mishap. It had lost a little pitch but the windings were intact and voltages normal. Prolonged use over several hours revealed no signs of overheating and it seemed that no real damage had been done. The fact that the power transformer These two burnt-out half-watt resistors were in series with the plates of the 6X5 rectifier & the high-tension winding on the power transformer. They have been totally destroyed, leaving only the ends and a powdery white centre piece. Their eventual failure probably saved the power transformer from destruction. This close-up view shows the effects of the overload within the rectifier valve. Arcing within the valve has completely removed the cathode sleeve, leaving the heater element clearly visible between the two plates. had survived so well can probably be attributed to the 100Ω half-watt resistors in the plate leads of the rectifier valve. While not fitted for this reason – their job is to limit the peak current through the rectifier on each conduction cycle – they did act like slow blow fuses (very slow blow fuses!) and eventually cut the circuit. Had they blown earlier, they may have prevented other damage. However, resistors are not fuses and, even when severely overloaded, they will still pass current for quite a while until they finally breakdown. Unfortunately, other components were being damaged or destroyed in the meantime. In fact, some restor­ers fit fuses into the high tension circuits for this very rea­son. In the end, the amount of time involved to fix the little Radiola was considerable and the repair costs exceeded the value of the radio. But that wasn’t my concern; the owner wanted it fixed and that’s all there was to it. To summarise, repairing old valve radios can be both inter­ esting and frustrating – depending on the nature of the problem. No matter how many repairs you may have done, there is always the possibility of finding something new and different. Sometimes fault finding can be a baffling experience but with a little perseverance, SC most problems can be solved. April 1995  89 Silicon Chip Power Supplies; A Speed Alarm For Your Car; Fitting A Fax Card To A Computer. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station. BACK ISSUES August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Wave Generator, Pt.2. September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. September 1990: Music On Hold For Your Tele­phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. December 1989: Digital Voice Board (Records Up To Four Separate Messages); UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; Installing A Clock Card In Your Computer; Index to Volume 2. October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; Using The NE602 In Home-Brew Converter Circuits. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3; All About Electrolytic Cap­acitors. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Rad­ios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.4. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Simple DTMF Encoder; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. March 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Receivers From The 1920s. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; Versatile 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages; Tasmania's Hydroelectric Power System. March 1991: Remote Controller For Garage Doors, Pt.1; ORDER FORM Please send me a back issue for: ❏ June 1989 ❏ July 1989 ❏ December 1989 ❏ January 1990 ❏ June 1990 ❏ July 1990 ❏ November 1990 ❏ December 1990 ❏ April 1991 ❏ May 1991 ❏ September 1991 ❏ October 1991 ❏ February 1992 ❏ March 1992 ❏ July 1992 ❏ August 1992 ❏ February 1993 ❏ March 1993 ❏ July 1993 ❏ August 1993 ❏ December 1993 ❏ January 1994 ❏ May 1994 ❏ June 1994 ❏ October 1994 ❏ November 1994 ❏ March 1995 ❏ April 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 September 1989 February 1990 August 1990 January 1991 June 1991 November 1991 April 1992 September 1992 April 1993 September 1993 February 1994 July 1994 December 1994 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ April 1989 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 May 1992 October 1992 May 1993 October 1993 March 1994 August 1994 January 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ May 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 June 1992 January 1993 June 1993 November 1993 April 1994 September 1994 February 1995 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Card No. Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 90  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ v Transistor Beta Tester Mk.2; Build A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Tuning In To Satellite TV, Pt.1. July 1991: Battery Discharge Pacer For Electric Vehicles; Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Step-By-Step Vintage Radio Repairs. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator For Model Railways Mk.II; Magnetic Field Strength Meter; Digital Alti­meter For Gliders & Ultralights, Pt.2; Getting To Know The Windows PIF Editor. November 1991: Colour TV Pattern Generator, Pt.1; Battery Charger For Solar Panels; Flashing Alarm Light For Cars; Digital Altimeter For Gliders & Ultralights, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Modifying The Windows INI Files. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Index To Volume 4. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Automatic Controller For Car Headlights; Experiments For Your Games Card; Restoring An AWA Radiolette Receiver. February 1992: Compact Digital Voice Recorder; 50-Watt/ Channel Stereo Power Amplifier; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; Designing A Speed Controller For Electric Models. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Direct­ories; Valve Substitution In Vintage Radios. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo Amplifier, Pt.2; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; Low-Cost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Multi-Station Headset Intercom, Pt.2; Electronics Workbench For Home Or Laboratory. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Electronically Regulated Lead-Acid Battery Charger. March 1994: Intelligent IR Remote Controller; Build A 50W Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Electronic Engine Management, Pt.6. April 1994: Remote Control Extender For VCRs; Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Low-Noise Universal Stereo Preamplifier; Build A Digital Water Tank Gauge; Electronic Engine Management, Pt.7. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Two Simple Servo Driver Circuits; Electronic Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. February 1993: Three Simple Projects For Model Railroads; A Low Fuel Indicator For Cars; Audio Level/VU Meter With LED Readout; Build An Electronic Cockroach; MAL-4 Microcontroller Board, Pt.3; 2kW 24VDC To 240VAC Sine­ wave Inverter, Pt.5. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; An 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; A PC-Based Nicad Battery Monitor; Electronic Engine Management, Pt.9 March 1993: Build A Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders;A 24-Hour Sidereal Clock For Astronomers. July 1994: SmallTalk – a Tiny Voice Digitiser For The PC; Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. April 1993: Solar-Powered Electric Fence; Build An Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Step-Up Voltage Converter; Digital Clock With Battery Back-Up. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; The Micro­soft Windows Sound System. June 1993: Windows-Based Digital Logic Analyser, Pt.1; Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; Remote Volume Control For Hifi Systems, Pt.2 July 1993: Build a Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Windows Based Digital Logic Analyser; Pt.2; Quiz Game Adjudicator; Programming The Motorola 68HC705C8 Micro­controller – Lesson 1; Antenna Tuners – Why They Are Useful. August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Build a Nicad Zapper; Simple Crystal Checker; Electronic Engine Management, Pt.11. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Aircraft Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Electronic Engine Management, Pt.12. October 1994: Dolby Surround Sound – How It Works; Dual Rail Variable Power Supply (±1.25V to ±15V); Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Temperature Controlled Soldering Station; Electronic Engine Management, Pt.13. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits. November 1994: Dry Cell Battery Rejuv­enator; A Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems: How They Work; How To Plot Patterns Direct To PC Boards. September 1993: Automatic Nicad Battery Charger/ Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach; Servicing An R/C Transmitter, Pt.1. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford – A Pesky Electronic Cricket; Cruise Control – How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 2; Servicing An R/C Transmitter, Pt.2. January 1995: Build A Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Preamplifier; The Latest Trends In Car Sound; Pt1. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Electronic Engine Management, Pt.2; More Experiments For Your Games Card. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers , Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt2; Remote Control System For Models, Pt.2. December 1993: Remote Controller For Garage Doors; Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier Module; Peripherals For The Southern Cross Computer; Build A 1-Chip Melody Generator; Electronic Engine Management, Pt.3; Index To Volume 6. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design For Beginners; Electronic Engine Management, Pt.4. February 1994: 90-Second Message Recorder; Compact & Efficient 12-240VAC 200W Inverter; Single Chip 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Electronic Engine Management, Pt.5; Airbags – How They Work. March 1995: 50W/Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras & Night Viewers; Remote Control System For Models, Pt.3; Simple CW Filter. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, November 1988, December 1988, January, February, March and Aug­ust 1989, May 1990, and November and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear­sheets) at $7.00 per article (includes. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. April 1995  91 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Electronic ignition for motorbikes I would like to update the ignition system on one of my motorbikes. Would it be possible for SILICON CHIP to arrange such a project? A modern compact unit with electronic advance/ retard and rev limiter based around an IC (MC3340?) would, I’m sure, be of interest to many car/motorbike racing enthusiasts. My existing unit is now 10 years old. It uses a Hall Effect switch and works well down to 4.5V but relies on mechanical advance/retard and, by modern standards, is fairly bulky, about 120 x 80 x 35mm. An adjustable ignition curve would be an asset, I’m sure. (S. A., Alice Springs, NT) • While the idea of an ignition system with electronic ad­vance/retard is attractive, it would require a microprocessor or at the very least an EEPROM to store the advance/retard values. This would need to be programmed for each brand and model of bike – a job that is far beyond the IR focussing for underwater photos I do a bit of underwater photography and, as I get older, I have difficulty in focusing, particularly in low light. Most shots are taken with electronic flash, so if I can focus, the shot can be taken. My latest camera is a Nikon 801s AF with auto-focus macro lens in a housing but it has the same problem. Nikon has an infrared system to focus in the dark on their above- water elec­ tronic flashes. Could you please tell me how this works? Would the IR LEDs flash and, if so, at what frequency? I have an old underwater torch which operates with four “D” cells that could be modified to house the IR diodes and a small amount 92  Silicon Chip capabilities of a small organisa­tion like ours. The alternative to a microprocessor is to use an analog system which varies the timing in response to engine revs but even this approach is not simple and would not really be satis­factory. Rev limiting would be much easier and it could be incorpo­rated into a circuit using the MC3334P ignition chip but we feel that it would be no real advantage over the system you already have. Problems with voice operated relay I am currently having problems with the above project from the September 1994 issue. The unit just won’t function at all, the relay being totally silent and not being activated. I have checked for wiring errors and everything is OK. I have checked out the microphone insert and the relay and both are operative. I have also changed the sensitivity resistor to a of circuitry. A normal UW torch helps with focusing but it scares the fish away when you point the rig at them. I was also wondering if you had any circuits for camera housing leakage detectors in your files. (G. J., Bundall, Qld). • We do not know how Nikon’s IR focusing system works but assume that it would be some sort of rangefinder system where­by a narrow IR beam is bounc­­ ed off the object to be photo­graphed and reflected back to the camera. The beam would be swept through a fairly wide angle until the camera receives a reflec­tion and that would give it the focus distance; at least that’s how we think it would be done. We do not have any circuits to detect camera leakage. variable 250kΩ type and tried many different resistors but still no joy. My other investigations seem to indicate that the op amp is not triggering transistor Q1 to turn it on. Is this the most likely scenario (meaning the IC is cactus?) or is there something else I should do before buying another LM358 chip? (N. P., Er­mington, NSW). • There are a number of tests you can do to diagnose the problem with your project. First, measure the voltage at pin 3 of IC1. It should be about 3-4V, or thereabouts. Pin 1 should have the same value. Pin 6 should be at +2.4V, depending on the input from the plugpack supply. Second, speak into the microphone while measuring the vol­tage at pin 5. With no sound, pin 5 will be close to 0V. With speech, it should rise to +3V or more and this should cause pin 7 to go high and switch on Q1. The most likely faults include cold solder joints, solder shorts between tracks, a faulty or wrongly connected electret microphone and reverse connected diodes. Queries on the solar tracker I have waited for some time for a construction article on a sun tracker. Now you have published one (January 1995) which is very good but I am puzzled by a couple of things about the circuit. Why is pin 4 of the 555 not connected to pin 8 as recommended in the National Semiconductor application notes for this device? Why is there no bypass capacitor on pin 5 for the above reason? I believe it would be normal practice to provide separate gate resistors for the FET switches. Finally, why are there no power supply filter capacitors across the 12V supply? Other than this I intend to build the unit as soon as I can get my hands on a PC board. (C. W., Leumeah, NSW). • While National Semiconductor do recommend that pin 4 be tied high, it is not mandatory for it to be so. Nor Preamplifier for digital speedo I would greatly appreciate your help with a digital speedo circuit I am working on. I am using a magnet/inductive pick-up sensor and the Pre-Champ preamplifier (July 1994) to amplify the signals. The Pre-Champ I used is contained in a box connected to the Champ amplifier and the signal tapped off after the Pre-Champ stage and then connected to the counter circuit. When using this setup, the unit works fine but if another PreChamp built into the speedo black box is used, all you get is a random display of flickering numbers with no useable (or intelligible) counting taking place. What can be done to this setup is a capacitor at pin 5 mandatory. Individual gate resistors for the Mosfets would normally be used in a switching circuit but since the voltages in this circuit are so static, they are not required. Bypass capaci­tors for the supply are also not mandatory since the circuit is powered directly from a lead-acid battery. Having said that, there is no reason why you should not change the circuit to tie pin 4 high, add a capacitor to pin 5 and so on. In fact, RCS Radio Pty Ltd has produced an improved version of the published board which includes the modifications discussed here. Noise & distortion in the graphic equalisers Recently, I have become interested in building a pair of the 32-band graphic equalisers, as published in the March & April 1989 issues. When compared with the 20-band graphic equaliser published in August & September of the same year, I am somewhat confused as to why such similar circuits have quite different specifications. By this, I am referring particularly to the harmonic distortion and the signal-to-noise ratio figures. There are several possibilities which may be contributors to the differing performance of the 32-band graphic equaliser: (1) the inclusion of 12 extra to make it work? (N. P., Ermington, NSW). • There are two possible problems with using the Pre-Champ preamplifier. The first is that its low frequency response is 3dB at 72Hz and would be rapidly attenuated below that frequency. Since 600RPM corresponds to 10Hz, the bass re­sponse should extend down to at least this frequency. To achieve this, increase the 22µF capacitor to 220µF and the 0.1µF input coupling capacitor to 0.33µF or larger. The second reason why your preamplifier may be playing up is that it is picking up hash from the ignition wiring of your car or from the digital speedo circuit. It may need to be mounted by itself in a shielded metal box and may need more supply decou­pling. gyrators in each channel; (2) the use of metallised polyester capacitors, as opposed to the metal­lised polycarbon­ ate capacitors specified in the 20-band graphic equaliser; (3) the master level control being placed in the signal path prior to the buffering action of IC1a, resulting in the input impedance and signal-to-noise ratio being affected by the position of the slider; (4) the PC board layout; and (5) the positioning of the power supply. Could you please advise me if any of the above factors (or perhaps others) are contributors to the differences in harmonic distortion and signal-tonoise ratio between the two published equalisers, as I am keen to alter the circuit of the 32-band graphic equaliser in any way to obtain performance enhancement. (T. T., Newtown, Vic). • The main reason why the 32-band equaliser has inferior performance to the 20-band unit is that it has 12 extra gyrators. The 32-band unit also had some gain following the buffer and if IC1a was changed to a voltage follower, as in the later design, a small improvement would probably occur. The MK series capacitors were used in the later design because of the their consistent (smaller) size and lead pitch and also because they reputedly give slightly lower distortion. There is little that can be done to improve the 32-band circuit, given that it is much SC more complicated. April 1995  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES FOR SALE Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly in the space below or on a separate sheet of paper, fill out the form & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 979 6503. TINY VIDEO CAMERAS from $199. MATCHBOX SIZE PCB MODULES 25 Types. Optional: Lenses, C Lens Mounts, Cases & Technical Manuals. See p.90 SC Feb 1995. ALSO C.C.T.V. Std & Mini Cameras, Quad Splitters, Auto Switchers, Audio/Visual Intercoms, Observation Systems, Camera-TV/VCR Antenna Patch Links, Cordless Portable Camera-TV/ VCR Links, Colour Modules/Cameras. TINY PINHOLE MODULES 32 x 32 x 15mm SEE through a 2mm hole from $239. Competitive Prices, Qty, Indent & Manufacturer Discounts. ALLTHINGS SALES & SERVICES Ph/Fax (09) 349 9413. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ DOS PROGRAMS: auto substitution databases, transistor $25, rectifier $25, zener $25, signal $25, PCBCAD $25, SCHCAD $35, VGA Test $25. Order by M.O. payable to G. A. Georgopoulos, 34 Scouller St, Marrickville 2204. 8051 SINGLE BOARD COMPUTER: use it to control stepper motors, robotics, build an electronic door lock or automate your house! Essential building block for any project. Simply download program into RAM and execute. Mac and PC assembler provided. NO EPROM PROGRAMMER REQUIRED! Features: RS232 Serial, 24 I/O lines, 128Kb Memory or I/O expansion bus, 64Kb UV ROM (128Kb max), 32Kb battery backed RAM Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Card No. ✂ ❏ Bankcard   ❏ Visa Card   ❏ Master Card Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip RCS Radio Pty Ltd is the only company that manufactures and sells every PC board and front panel published in SILICON CHIP, ETI and EA. RCS Radio Pty Ltd, 651 Forest Rd, Bexley 2207. Phone (02) 587 3491 YUGA ENTERPRISE BA, LA, LB, LC, UPA, UPB, UPC, TA, Buy TBA, TDA, TEA, & 2SA, 2SB, 2SC, Sell ese 2SJ, 2SK, SAA, Japan STA, STK, STR, s IC & tors HA, AC, KA, KIA, Transis IX, LM, MN, PA TEL: (65) 741 0300 FAX: (65) 749 1048 705 Sims Drive #03-09 Shun Li Industrial Complex Singapore 1438 CTOAN ELECTRONICS PO Box 211, Jimboomba 4280. (07) 297 5421 New Kits Coming – Send For Details (1) Digital Speedo & Fuel Gauge (2) Digital Engine Temperature Gauge (3) Digital Battery Voltage Monitor (4) Automatic Pool Pump Controller (5) Main Connected Remote Control System (6) Bar Of Light Tachometer (128Kb max), audio speaker output, watchdog timer, two external interrupts, two timers and real time clock option. Single qty tax inc: $120. SYCON TECHNOLOGIES. Phone (03) 738 0315. Fax (03) 859 2309. SATELLITE EQUIPMENT: dishes 65cm from $140. LNBs from $150 for 1.3dB voltage switching Ku or 25 deg C band. We also sell receivers, eg Pace PSR919 for $500. We carry many brands: Gardiner, Chaparrel, Pace, Drake, Swedish Microwave, ComStar, KTI, etc. Prices you can afford. Phone or fax Satellite Professionals (03) 803 0215. 68705 DEVELOPMENT SYSTEM: In Circuit Simulator/Emulator and programmer board. Supports 68705 and 68HC705 series of Motorola micro controllers. Oztechnics, PO Box 38, Illawong, NSW 2234. Phone (02) 541 0310. Fax (02) 541 0734. Email oztec<at> ozemail.com.au. "SATFACTS" Satellite Newsletter: monthly report on launches, satellite positioning, transmission formats, equipment, etc. Of interest to retailers, installers, system planners and all dish users in the Pacific Ocean region. The best $75 you'll ever spend (plus postage). Send for your free copy. Av-Comm Pty Ltd, 198 Condamine St, Balgowlah 2093. PO Box 225, Balgowlah 2093. MEMORY & DRIVES PRICES AT APRIL, 1995 SIMM (all 70ns) Parity/No Parity 1Mb 30-pin $64/58 4Mb 30-pin $200/200 2Mb 72-pin $148/135 4Mb 72-pin $258/228 8Mb 72-pin $515/470 16Mb 72-pin $780/690 32Mb 72-pin $1560/1380 Parallax “BASIC STAMP”: 8 I/O pins and proto­ typing area. Program it with a PC, 33 simple instructions. Development kit includes one “BASIC STAMP” ($270). Extra modules ($79.85). Chipset and Resonator to make your own $30.25. STAMP Stretch­ er 16 I/O 1 A/D $91.96. Serial input LCD display $102.85. Scarce com­ponents need­ed for Application notes now in stock. Small items XPress post $5, kit $8. Send four 45c stamps for details. Parallax Distributor and technical support in Australia. MicroZed Computers PO Box 634 (296 Cook’s Rd), ARMIDALE 2350 V (067) 722 777 F (067) 728 987 Credit cards accepted. MAC 8Mb P’BOOK CO-PROCESSORS 387S/DX to 40 $405 $90 LASER PRINTER HP with 2Mb $200 DRAM DIP 1Mb x 1 70ns DIP $7.80 256 x 4 70ns DIP $7.80 256 x 16 70ns SOJ $48.00 IBM PS.2 THINKPAD L40/N33 8Mb 4Mb $655 $275 TOSHIBA 3100SX 2100/50 4Mb 8Mb $255 $585 SUN SPARC 5 32Mb SPARC 10/20 64Mb $1780 $3696 DRIVES – SEAGATE 545Mb 14ms 3yr wty $335 1052Mb 9ms 5yr wty $550 COMPAQ 2148Mb 9ms 5yr wty $1470 CONTURA 8Mb $550 Sales tax 21%. Overnight delivery. Credit cards welcome. Ring for latest prices. We buy & trade RAM. 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Tel: (02) 980 6988 Fax: (02) 980 6991 • PELHAM ELECTROSTATIC LOUDSPEAKERS • 3-Panel Full Range Design. Available in kit form or fully assembled. Locally designed & manufactured. • For information brochure, Phone (09) 397 6212 Fax (09) 496 1546 Or write to: E. R. AUDIO, 119 BROOKTON HWY, ROLEYSTONE, WESTERN AUSTRALIA 6111. N.S.W. Ph. (02) 804 6859 S.A. Ph. (08) 332 6513 TAS. Ph. (002) 31 2403 ACN 002 174 478. Phone (02) 949 7417 or 948 2667; or fax 949 7095. Cheque or credit cards welcome. UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar Invisibility, Surveillance, Self-Protection, Unusual Chem­ istry and more. For a complete catalog, send 95 cents in stamps to Vector Press, Dept S, PO Box 434, Brighton, SA 5048. NEW SPRINKLER CONTROLLER KITS: RAIN BRAIN version uses 'C8 and switch mode supply. Features galore!! Contact Mantis Micro Products, 38 Garnet St, Niddrie 3042. Phone/fax (03) 337 1917. INFRARED AUDIO CONTROL KIT: based on the Intelligent Infrared Receiver kit (ref. Silicon Chip, March 94) to control volume, treble, bass, balance, mute and select between two inputs (CD, VCR, etc). Also available Intelligent Infrared Receiver kits and infrared transmitters, preprogrammed and learning models. For details call BENETRON P/L, phone (02) 963 3868 or (018) 200 108. C COMPILERS: everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC16, 8051/52, 8080/85, 8086 or 8096: $150.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $150 for the set. Debug monitors: $75 for 6 CPUs. All compilers, XASMs and monitors: $550. 8051/52 or 80C320 simulator (fast): $75. Demo disk: $5. Network Software: use serial, parallel, Arcnet or Ethernet to share files and printers on your PCs. DOS and Windows compatible. $105 per net­work. All prices + postage. GRANTRONICS, PO Box 275, Wentworth­ville 2145. Ph/Fax (02) 631 1236. April 1995  95 Microprocessor For Digital Effects Unit Microprocessor For Stereo Preamplifier Advertising Index Now available from SILICON CHIP: the 68HC705-C8P pre-programmed micro­pro­cessor IC for the Digital Effects Unit described in the Feb­ruary 1995 issue. Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Pub­lica­ tions, PO Box 139, Collaroy, NSW 2097. Phone (02) 979 5644; Fax (02) 979 6503. Now back in stock: the 68HC705-C8P pre-programmed micro­pro­cessor for the Infrared Remote Controlled Stereo Preamplifier (SILICON CHIP, Sept.Oct. 1993). This device also suits the Remote Volume Control published in May & June, 1993. Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. Phone (02) 9795644; Fax (02) 979 6503. Altronics ................................ 22-24 TECHNOLOGY BREAKTHROUGH: a $20 Programmer Kit for one of the newest, fastest, low power, single chip EEPROM micros available. The $15 PIC16C84 can be it’s own downloader development system as it will re-program 1Meg times, each time in 10 seconds. Send a $2 coin for my PROMO disk. Don McKenzie, 29 Ellesmere Crescent, Tullamar­ine 3043. Phone (03) 338 6286. VALVES: all types for radio, audio and industrial use. For sale and wanted to buy. SSAE for list. Electronic Valve and Tube Company, PO Box 381, Chad­ stone, Vic 3148. Fax (03) 571 1160. Ph (018) 557 380. LEARN MICROCONTROLLER programming with our Motorola 68HC­ 705K1 & P9 Kits. All code fully commented, provided on floppy disk. Intro- Av-Comm.....................................55 Avico Electronics.........................95 Dick Smith Electronics........... 10-13 Emona Instruments.....................83 E.R. Audio....................................95 Harbuch.......................................82 Instant PCBs................................95 duction to the K1 (reviewed in Everyday Electronics, 2/94), Reaction Timer (Electronics Australia, 3/94), Number Crunch­er (EA, 9/94), & Codepad (uses P9). DIY Electronics, phone/fax: (058) 62 1915. PELTIER EFFECT solid state modules 3cm x 3cm, 8V/5.4A. One side heats, the other cools. Up to 59 deg. C differential. Also 2.5mw, 635nm LASER DIODE modules, 10 times brighter than 670nm modules. HeNe replacement, 3V to 6V. 3-element glass collimating lens adjustable. DIY Electronics, tel/fax: (058) 62 1915. PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. Jaycar ......................... 33-36,61-64 Kalex............................................66 Macservice...............................3,75 MicroZed Computers...................95 Oatley Electronics.................. 84-85 Pelham.........................................95 RCS Radio ..................................94 Rod Irving Electronics .......... 76-80 SC Railway Projects Book.......OBC Silicon Chip Back Issues....... 90-91 Silicon Chip Software..................32 SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Silicon Chip Wallchart................IBC Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Yuga Enterprise...........................95 _________________________________ Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. Price $7.00 each + $3 p&p. Send your order to: Silicon Chip Publications, PO Box 139, Collaroy 2097; or phone (02) 979 5644 & quote your credit card number; or fax the details to (02) 979 6503. Please specify 3.5-inch or 5.25-inch disc. 96  Silicon Chip Tortech.........................................66 PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. • H. T. Electronics, 35 Valley View Crescent, Hackham West, SA 5163. Phone (08) 326 5590. Order by phone or fax from SILICON CHIP - or use the handy order form inside