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Vol.7, No.7; July 1994 FEATURES FEATURES   6 More TV Satellites To Cover Australia by Garry Cratt A smorgasbord of new programs for enthusiasts   9 Silicon Chip/Tektronix Reader Survey Winners by Leo Simpson The winners of the Tektronix test gear DUBBED THE SMALLTALK, this tiny digitiser lets you record voice signals in RAM or on your PC’s hard disc. It uses just one common op amp & the software can be easily added to other programs – see page 17. 22 Electronic Engine Management, Pt.10 by Julian Edgar A look at ignition systems 77 Review: Yokogawa’s 7544 01 5-Digit Multimeter by Leo Simpson Has true RMS measurement & .05% accuracy 80 TV Coder: The Sequel to Video Blaster by Darren Yates Outputs VGA graphics to your TV or VCR PROJECTS PROJECTS TO TO BUILD BUILD 17 SmallTalk: A Tiny Voice Digitiser For The PC by Darren Yates Uses one common op amp & interfaces to the games port 32 Build A 4-Bay Bow-Tie UHF Antenna by Leo Simpson & Bob Flynn High gain design covers both UHF bands IV & V 43 The PreChamp 2-Transistor Preamplifier by Darren Yates Has 40dB of gain & provision for an electret microphone 54 Steam Train Whistle & Diesel Horn Simulator by John Clarke Adds realism to your model railroad layout 62 Build A Portable 6V SLA Battery Charger by Darren Yates This simple passive circuit does the job SPECIAL SPECIAL COLUMNS COLUMNS THINKING ABOUT building an antenna to pick up UHF TV in your area. This 4-bay bow-tie design has high gain & covers both UHF bands IV & V – details page 32. 66 Serviceman’s Log by the TV Serviceman A screw loose somewhere? 72 Computer Bits by Darren Yates BIOS interrupts: speeding up the keys 84 Vintage Radio by John Hill Crackles & what might cause them DEPARTMENTS DEPARTMENTS   2   4 14 53 77 Publisher’s Letter Mailbag Circuit Notebook Order Form Product Showcase 88 90 92 94 96 Back Issues Ask Silicon Chip Notes & Errata Market Centre Advertising Index ADD REALISM TO YOUR model railroad layout with this steam whistle simulator. It produces a very realistic steam whistle & can be easily modified to provide a diesel horn sound – turn to page 54. Cover concept: Marque Crozman July 1994  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates, B.Sc. Reader Services Ann Jenkinson Sharon Macdonald Advertising Enquiries Leo Simpson Phone (02) 979 5644 Mobile phone (018) 28 5532 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ John Hill Jim Lawler, MTETIA Bryan Maher, M.E., B.Sc. 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 Valve amplifiers are dead & buried Every month we receive suggestions and requests from read­ers for a whole range of projects. Some of these are practical, some are too specialised for us to consider and then there are the occasional letters asking about valve amplifiers. Because people see glowing references to valve amplifiers in hifi maga­zines, they ask if SILICON CHIP has done or will be doing an article on a buildit-yourself hifi valve amplifier. Now when I read or hear about some of the things said about valve amplifiers in hifi magazines, mostly those from overseas I might add, my comments tend to become derogatory in the extreme. This is because I feel that articles promoting valve amplifiers are just plain dishonest. Let’s face it, valve amplifiers were once the “state of the art” and many people, myself included, built valve amplifiers and gained immense pleasure from them. But that was then. I can state right now that SILICON CHIP will never publish a design for a hifi valve amplifier unless it is for academic interest only. In fact, let’s be even more absolute and just say NEVER. There are three reasons for this stance. First, valve amplifiers of “reasonable” power output and quality are extraor­dinarily expensive. Typically, we could be talking about a kit cost of $1000 or more for a valve power amplifier capable of producing only 30 watts per channel. Second, such a “reasonable” valve amplifier would be no match at all for even run of the mill solid state amplifier modules. Take the 25W module published in the December 1993 issue for example. Using the cheap LM1875 module, it has a signal to noise ratio of 110dB and a distortion of around .025%, figures that blow virtually any valve amplifier ever designed out of the water. And remember, there’s nothing really special about the LM1875. Apart from that, valve amplifiers have several other big disadvantages. They run very hot, their valves are often micro­phonic and, the biggest disadvantage of all, they wear out. While a solid state amplifier can easily run for 20 years or more without anything wearing out, valves need to be replaced quite frequently if they are to give the best performance and this applies particularly to the output devices. And that brings me to the final disadvantage – availability. Good valves with a perfor­mance equal to the original published specifications are now virtually unobtainable, at any price. So unless you are an eccentric millionaire with a taste for esoteric hifi gadgetry, you can forget all about valve amplifi­ers. And don’t take any notice of comments about “special valve sound quality” or “gentle overload”, or other such rubbish. All these are just ways of describing valve distortion. So by all means enjoy reading about and perhaps even re­storing valve equipment. That’s nostalgia. But valve amplifiers have no place in today’s technology. 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 High Purchase Costs Taking a “Bite” Out of Your Budget? NOT AT MACSERVICE. WE HELP YOU STRIKE BACK BY OFFERING THE LOWEST PRICES AND GOOD OLD FASHIONED SERVICE - Just look at these SPECIALS BALL EFRATOM M100 Rubidium Frequency • Factory cal. certs. • Perfect for ISO    accreditation • GPS applications • Ruggedised military    design TEKTRONIX 5440 Oscilloscope • DC to 60MHz • 1mV - 100V/div (x 10) • Dual Trace • Dual Timebase • Large Screen TEKTRONIX 7603 Oscilloscope • Mil spec AN/USM 281-C • Triggers to 100MHz • Dual Trace • Dual Timebase • Large Screen SUPER SALE $850 GREAT VALUE $2950 (new) Video Dist Amp & Cable Equaliser   $100 ADVANCE PP7 30V3A DC Power Supply   $150 AVO MK.IV Avometer With Cal.   $275 BPL CB154/4 Electrolytic Cap Bridge   $450 B&K 1466A 10MHz Oscilloscope   $275 EH 129 Pulse Generator   $90 ELGENCO 603A White Noise Gen 5MHz   $200 ENI 503L RF Power Amp 40dB 510MHz $1025 FLUKE 102 VAW Cal Meter    $75 FLUKE 9010A Logic System Troubleshooter $1000 GR 1608 LCR Meter – Lab Standard $1500 HP 211B 10MHz Square Wave Generator   $275 HP 302A Audio Selective Level Meter   $145 HP 400L True RMS Voltmeter   $170 HP 410B Vacuum Tube Voltmeter   $130 HP 432A 10GHz Power Meter (c/w sensor)   $875 SUPER DEAL $950 HP HP HP HP HP HP HP HP I/S Elect. MARCONI MARCONI MARCONI MARCONI MARCONI MARCONI MARCONI HEWLETT PACKARD HEWLETT PACKARD 200CD Audio Oscillator 410C Multimeter • 5Hz to 600kHz • 100Hz to 700MHz • 5 Ranges • AC/DC Volts • 10V Out • DC Amps • Balanced Output • 10 ohms to 10M ohms • Complete with probes BARGAIN $265 RIDICULOUS $79 467A Power Amp   $175 536A Frequency Meter   $75 721A 30V 0.3A Power Supply    $60 1610B Logic Analyser   $450 1980 100MHz Storage Oscilloscope $1650 3400A True rms voltmeter   $425 6226A Power Supply 40V 1.5A   $200 54111D Ultimate Digital Storage Scope $19000 845 Prog Function Generator   $800 TF893A Power Meter   $150 TF1020A RF Power Meter 75Ω 100W    $75 TF1020A-1 RF Power Meter 50Ω 100W   $150 TF1245/46/47 Q Meter 40KHz-300MHz   $600 TF2167 RF Amplifier 47dB gain   $600 TF2300 FM/AM Mod Meter   $300 TF2300A FM/AM Mod Meter   $495 MARCONI TF2300B MARCONI TF2303 MARCONI TF2700 MARCONI TF2701 MARCONI TF2914 PACIFIC PM1017 RACAL 9500 SHALLTRONIX 10K SIEMENS G2212 SIEMENS P2005 SOLA Series 200 Spectral Dyn. SD112-1 Systron Don. 1037 Telequipment CT71 TRIMAX G1B VARIAC Mod Meter 1200MHz $1100 AM/FM Mod Meter   $550 LCR Bridge   $325 Universal Bridge in circuit   $700 Insertion Signal Analyser   $150 Log Freq-Voltage Converter   $150 100MHz GPIB Counter   $350 Decade Box   $150 1.6/18.6MHz Generator   $250 Controllable Phase Meter   $200 750VA Line Stabiliser   $180 Voltmeter Freq-Log Conv 2ch   $150 500MHz Counter   $350 Curve Tracer   $900 Ionisation Tester 10kV   $260 0/280V <at> 15A   $260 NEW METROLOGY INSTRUMENTS AT FANTASTIC PRICES!!! M36 $55 VCE 150 $120 CM 25 $45 SEPTEMBER SPECIAL TEKTRONIX 465M 100MHz Oscilloscope VCE-150 VCE-200 VCD-150 DI-10 DI-1 TDI-0.8 CM-25 CM-50 150mm/6" Electronic Digital Vernier in box $120 200mm/8" Electronic Digital Vernier in box $180 150mm x 0.02 Dial Vernier Caliper   $75 10 x 0.01mm Dial Indicator   $45 1" x 0.001" Dial Indicator   $45 0-0.8 x 0.01mm Test Dial Indicator   $95 0-25mm x 0.01mm Outside Micrometer   $45 25-50mm x 0.01mm Outside Micrometer   $55 The Name That Means Quality CM-75 50-75mm x 0.01mm Outside Micrometer   $65 CM-01 0-1" x0.001" Outside Micrometer   $45 MB-6 CZ-6C Magnetic Base Stand   $55 VC-150 Dual Scale Vernier Caliper 150 x 0.02mm/6" x 0.001"   $35 VC-200* Dual Scale Vernier Caloper 200 x 0.02mm/8" x 0.001"   $45 VC-600* Dual Scale Vernier Caliper 600 x 0.02mm/24" x 0.001" $250 HI-600 600mm/24" x 0.02mm Height Gauge $550 *WITH FINE ADJUSTMENT Affordable Laboratory Instruments SSI-2360 60MHz Dual Trace Dual Timebase Oscilloscope BRA BRAN D EQUIP NEW MENT ND EQUIP NEW MENT Bandwidth DC to 100MHz; Rise time <=3.5ns; Deflection factor 5mV/div to 5V/ div in 10 steps; DC accuracy ±2%; 2-channel display mode; Horizontal deflection - main & delayed timebases; A - 0.5s/div to 0.05µs/div in 22 steps; B - 50ms/div to 0.05µs/div in 19 steps; Trigger - main/delay sweep; Coupling AC, DC, LF Rejection, HF Rejection TOP VALUE $1150 • • • • • • 60MHz dual trace, dual trigger Vertical sensitivity 1mV/div. Maximum sweep rate 5ns/div. Built-in component tester With delay sweep, single sweep Two high quality probes $1050 + Tax PS303D Dual Output Supply • 0 to 30V and 0 to 3 amps • Four output meters • Independent or Tracking modes • Low ripple output $385 + Tax PS303 Single Output Supply PS305D Dual Output Supply PS305 Single Output Supply • 0 to 30V and 0 to 5 amps $430 + Tax • 0 to 30V and 0 to 3 amps • Two output meters • Constant current/voltage • Low ripple output $225 + Tax • 0 to 30V and 0 to 5 amps $260 + Tax IF IT’S NOT HERE WE CAN GET IT... CALL US FIRST OR CALL US LAST... BUT DON’T FORGET TO CALL US! MACSERVICE Australia’s Largest Remarketer of Test & Measurement Equipment 26 Fulton Street, Oakleigh Sth, Vic., 3167   Tel: (03) 562 9500 Fax: (03) 562 9615 **Illustrations are representative only MAILBAG Manufacturers should not hide behind voltage barriers Regarding the proposed change of nominal voltage from 240V to 230V, I certainly agree with your scorn at the reported advan­tage that “it is going to improve the opportunities for the electrical equipment we produce, opening up the world to our industry”. Some years ago, I was responsible for the design of slide projectors which were exported all over the world. There was certainly no problem in designing and manufacturing for different voltages (different frequencies were a bit more of a problem). However, I believe the main reason for the proposal is that with England converting to 230 volts we will be very much on our own, with possibly only South Africa and New Zealand still on 240 volts. The inevitable result of this will be that our imported equipment will be designed for 230 volts and will be over-run here. I have already had this happen to me with a special light globe made in Germany. The last time I bought replacements I was told that 240 volt versions were no longer available, so I am forced to use 230 volt globes. With a tungsten filament globe, this order of overvoltage will result in a reduction of life of about 50%. Looking at what will happen to existing appliances with a reduced voltage, I feel you have overstated the problems. The switching controllers on stove hotplates will automatically compensate because the lower voltage/current will increase the “on” time except, of course, on maximum. Thermostatically con­trolled appliances will maintain correct temperature but will take at least 8% longer to reach that temperature, and thereafter recovery times (from open oven doors, etc) would be longer. I do not believe that replacing all house lamps is a major problem but there is a problem with low voltage halogen lamps and fluorescent lamps. Halogen lamps will burn at a significantly lower colour temperature and this problem would apply to slide projectors as well. New transformers 4  Silicon Chip would be required and new ballasts would be required for fluorescent lamps to achieve full light output. I believe the above problems are relatively minor but the area which would concern me more is that of all motor operated appliances, including all industrial motors, single phase and three phase. There is no doubt that both starting torque and full load torque will be reduced and, in marginal cases, this will result in stalling and (if not properly protected) motor burn outs. Having said that though, all competently designed equipment should be quite capable of running satisfactorily at 10% under or over-voltage. Problems would only occur if the equipment was fully loaded and happened to be at the end of the distribution line. In spite of the above problems, I believe we should accept the inevitable and fall into line with the rest of the (50Hz) world. I have no sympathy with your argument that we should stick to 240 volts to assist local manufacturers. I worked for Austra­ lian- owned manufacturers all my professional life and we are quite capable of competing both in Australia and overseas without hiding behind artificial barriers. P. Badham, Frenchs Forest, NSW. Circuits need better description The recent proposal to lower the mains voltage to 230 volts has obviously come from the same sheltered workshop for the intellectually challenged in Canberra that foisted the metric system on us; what a dog’s breakfast that has turned out to be. The insurance industry should be very concerned about this proposal as just about every household policy includes cover for fusion of electric motors. One of the most vulnerable to continu­ous undervoltage is the sealed unit motor in every refrigerator. On an entirely different subject, I would like to take you to task over what I have come to consider as totally SILICON CHIP, PO Box 139, Collaroy, NSW 2097. inadequate discussion of the theory behind many of your projects. To name one, in the Metal Locator in the May 1993 issue under the heading “operating principle” is an interesting collec­ tion of irrelevancies on BFO devices but virtually nothing on the device being described. Induction balance is only mentioned and the device does not appear to be of the gated Transmit/Receive variety. Why 80kHz, why the limited transmit power, were the test results obtained in air, under sand, etc? As I see it, there are two low Q resonant circuits very loosely coupled, tuned to slightly different frequencies. Both the transmit and receive inductors are in the search head so that ground capacitance affects them equally. Mutual coupling and correct phasing are adjusted to achieve some nominal output. The effect of metal in the transmit loop is to pull its frequency closer to the receive coil resonance, with a consequent increase in output. I appreciate that the above may be a load of nonsense. If so, the operation of “Variable Mutual Reluctance” may be worthy of some explanation to your readers. There is some point to all this; I can see a use for a miniaturised hand held version of this for finding that elusive bolt, nut, screw, etc that just fell into the grass while repair­ ing the lawn mower or whatever. Bill Jolly, Hahndorf, SA. Comment: as far as the metal locator description was con­cerned, the BFO type was mentioned only as a matter of back­ground, since it is by far the most common system used for lowcost metal locators. Having said that, we take your point that we could have covered the theory of the induction balance system in greater detail. The induction balance operation can be also called trans­mit/receive. It is not a gated transmit/receive circuit which switches the transmission on and off at an audible rate, say at 1kHz. In this system, the resulting received signal is amplified and heard through a loudspeaker so that the louder the sound, the closer the search head is to metal. Our circuit uses continuous transmission and the received signal is rectified and filtered and applied to a VCO. The VCO changes its pitch (or frequency) when the search head approaches metal. Since the ear is more sensitive to changes in pitch than volume, our circuit is effec­tively more sensitive than the gated type. 80kHz was chosen as a transmit frequency since it provides good ground penetration and pinpoint accuracy. Of course, the frequency needs to be matched with the search head size. The larger the head, the greater the ground penetration but pinpoint accuracy suffers. Similarly, the lower the frequency, the greater the ground depth. We can understand that you might find the term “induction balance” confusing but that is not a name we thought up. It has been applied to this type of circuit in the past. It might have been more helpful to think of it as a “Variable Mutual Reluc­tance” circuit with the mutual coupling between the coils being varied by the presence or absence of metal near the search head. We tested the metal locator in air and over wet sand, dry sand and soil. Passive re-broadcasting is a viable process This letter is in response to a feature entitled “Passive Re-Broadcasting For TV Signals” published in your May 1994 edi­tion. I read the article with interest, as I have had over 10 years in the field conducting propagation and path loss measure­ments for the Australian Government for designing point to point links. I have to point out that the article goes a very long way around to arrive at its destination and, in fact, arrives at the wrong conclusion. A reason for this is that the process has been made unduly complicated, with a great deal of mathematics which are not required. If one is going to wax mathematical, you have to plug the correct figures into the formulas. A normal approach would be to convert the path into gains and losses in dB. Firstly, we have a 100 watt transmitter feeding a 10dBd antenna – no mention is made of feeder losses, so we will keep it that way. The receive antenna is quoted as 6dBi, which is 3.8dBd. To convert 100 watts to dBm: dB = 10 logP1/P2 = 10 log 100/(1 x 10-3) = +50dBm Now we add our antenna gains of 10dBd + 3.85dBd = 13.85dBd. Add this to our transmit level and we get +63.85dBm ERP. Now we need to calculate the path loss which is obviously a true line of sight situation. So, Path loss in dB = 32.5 + 20log F + 20log D Where F is in Megahertz and D is in kilometres. This gives: 32.5 + 20log 640 + 20log 30 = 118.1dBm Now we have a level of +63.85 118.1 = -54.25dBm. This level is present at the antenna terminals of the receiver end and is simply a level of 54.25dB below a milliwatt. This corresponds to 3.7 nanowatts and this is equivalent to 531 microvolts for a 75Ω termination. Note that it not 679 micro­volts, as stated in the previous article. This difference amounts to 2.15dB. This then reveals that the figures in the previous article were out by the amount of dBd/dBi. There is an easy way to check these results. This stems from the fact that two dipoles separated by a distance of one wavelength will have a path loss of 22dB. Using the parameters of the previous article gives: dB = 32.5 + 20log 0.000468 + 20log 640 = 22dB OK, so lets return to the original article and calculate the received level using the corrected formula. The receive antenna has 3.85dB gain or 2.42 in arithmetical terms. P = 100 x 10 x 2.42 x 0.468 x 0.468/ (4π 30,000)2 = 531.5/1.42 x 1011 = 3.7 nanowatts As this agrees within 0.1dB with the other method we can assume that it is correct and in fact I know it to be, as I had come across the same value in a BBC publication some time ago, in its correct form. Mathematicians do not formulate equations using dBd at one end of the path and dBi at the other and from my experience, I keep away from isotropic radiators altogether. The thing that really made me reach for my calculator was the path loss quoted in the path from the hill to the house. To save space I will not give examples, but using the formula alrea­dy supplied and putting reverse figures into it, it can be calcu­lated that the distance is 37 metres, not exactly worth a passive link, as lowly RG6 would only have a loss of 7dB over this dis­tance and the coax would be cheaper than another two antennas. I also take note of several references to microvolts/metre which is a field intensity, instead of Vrx/rms. Having shot a few holes in the article, I would have to agree with the author that passive antenna systems have very limited use but the amplified or boosted system is another mat­ter. There are several systems supplying small towns in both Australia and in New Zealand. Gundagai in NSW is one which comes to mind. There are, of course, problems with this type of setup, mainly the power supply. If no mains are available on top of your remote hill, it is then a matter of supplying your needs from solar or wind generation. If this is not a problem however, systems with as little as 0.5 watt ERP make a real improvement in reception – up to several kilometres, depending on the receive end equipment. Anyone wishing to set up a communal system will get a great deal of assistance from the Spectrum Management Authority in Canberra, ACT, Station Planning Branch. Peter Mallon, Maitland, NSW. Video effects generator wanted I recently built the “Colour Video Fader” which appeared in the August 1993 issue of SILICON CHIP. It is a most useful pro­ ject and has enabled my students to add in simple effects while producing video tapes. The article outlining the project refers to an additional circuit which will allow the wipes to be varied. Are you able to let me know if this circuit has appeared in the magazine? Bruce Sandford, Lecturer in Technology Education, Auckland College of Education, NZ. Comment: this circuit is still under development but we hope to publish it some time later this year. July 1994  5 More TV satellites to cover Australia Advances in satellite technology & an increasing availability of launch vehicles looks set to bring a smorgasbord of programs to those willing to equip themselves for satellite reception during the late 1990s. By GARRY CRATT Until now, electronics enthusiasts have had few “birds” from which to draw those elusive and fortuitous satellite sign­ als. For those suitably equipp­ ed, the sources have to date been limited. The list comprises Australia’s own Optus B1 and A3 satellites, the ageing Pacific cluster of Intelsat satellites, and the higher powered Russian “Gorizont” series of domestic spacecraft. 6  Silicon Chip Designed to be utilised by wellequipped commercial tele­ v ision networks, the signals emanating from such satellites are often weak, requiring specialised narrow bandwidth receiving techniques and often complex dish tracking mechanisms to have any degree of success. For those enthusiasts patient enough to toler­ate these drawbacks, the results can often be rewarding, provid­ing an uncensored look at the world through this high technology medium. But thanks to a new breed of higher powered spacecraft, satellite reception will soon become much easier. The latest generation of spacecraft, soon to be launched to fill the growing Asian “transponder gap”, operate at much higher power levels, reducing the necessity for large aperture dishes and eliminating the need for dish tracking. Apart from television distribution, these satellites will play a vital role in the distribution of data and telephony in regions previously isolated by geographic location. This great advantage of satellite communications has been seized upon by some countries seeking to register as many orbital “slots” as possible with the world regulating body, the ITU, for consequent “sale” or “lease”. Slot profiteering The main target of accusations about orbital slot prof­iteering is the tiny kingdom of Tonga which, through a corp­ ora­ tion named Tongasat in 1989, applied for and was granted 31 orbital slots. After due debate, this was finally reduced to six. Rights to use all six orbital locations have now been granted to two satellite operators, Unicom USA) and another US firm, Rimsat. Rimsat now operates Gorizont spacecraft at 130, 134 and 142.5 degrees east longitude. Rimsat 1 is located at 134 degrees and has the ability to cover Australia – see Fig.1. In May this year, Rimsat was granted another two slots, at 70 degrees and 170.75 degrees east longitude, allowing coverage of most of Africa, Europe and the western United States. Until recently, the primary player in providing interna­ tional satellite communications was Intelsat, who launched their second satellite in 1966 over the Pacific ocean and their third satellite over the Indian ocean in 1969. In our area of interest, there are presently four Intelsat satellites over the Pacific and all are visible from the east coast of Australia using dishes of 3 metres or more but plenty of competition is on the way. Several private international operators now threaten the monopoly held by Intelsat. 60ø 30ø 0ø 30ø 60ø 60ø 90ø 120ø 150ø 150ø 180ø Fig.1: the footprint provided by Rimsat 1 (located at 134° East). Indonesia’s Palapa system Perhaps the first challenge to the Intelsat stronghold was Indonesia’s Palapa satellite system, launched in 1976. Originally designed to provide Indonesia with a basic telephone and tele­vision service, the original Palapa B1 satellite was purchased at the end of its predicted service life by a privately owned Indo­nesian company. The satellite was placed into an inclined orbit to conserve station keeping fuel and is now co-located with Rimsat 1. Palapa B1 is used to pro-vide lowcost communication links through­out Indonesia. At present there are three Palapa satellites in operation (B2P, B2R, & B4), serving Thailand, the Philippines, Papua New Guinea, Indonesia, UN forces in Cambodia, and Vietnam. The Aus­ tralian ABC has a transponder on the Palapa B2P satellite, carry­ing Fig.2: Palapa 1 covers most of South East Asia & also has extensive footprints over Australia & New Zealand. Other spacecraft in the series will also cover Australia. the Australian ATVI service, and will shortly add US CNBC programming to this schedule. The first of the new series C Palapa satellites is sched­uled for launch in 1995 and this will have a significant foot­print over Australia – see Fig.2. The present B series satellites require a 4 metre dish for reasonable reception on the south eastern coast of Australia. Another Intelsat competitor, Panam­sat, already has a fully loaded satellite, PAS-1, located over the July 1994  7 Fig.3: PAS-2 is configured with K & C band transponders. Signal levels covering Australia & New Zealand will allow the use of dishes 1.8-2.4 metres in diameter Atlantic ocean and will launch their second satellite PAS-2 as this article goes to press. PAS-2 is an HS-601 spacecraft, configured with K and C band downlink transponders. Signal levels covering Australia and New Zealand will allow the use of small dishes (1.8 metres to 2.4 metres in diameter) – see Fig.3. Asiasat 3.4m 3.7m (a) 1.2m 0.9m O.75m 0.75m 1.2m 0.9m (b) 39dBW EQUATOR 37dBW 34dBW 33dBW Asiasat 2, to be launched later this year, will provide strong signal levels in Australia. Good reception should be possible using dishes in the 1.8-metre diameter range. 8  Silicon Chip Another high profile operator, Asiasat, launched its first satellite in April 1990. Asiasat 1 is the refurbished Westar 4 US domestic satellite, originally launched in 1984 and subse­ quently retrieved by the Space Shuttle. This satellite is fully loaded with many premium services. Covering over 30 countries and an audience of 3 billion people (although not receivable in Australia), this is the satellite that started the Asian trans­ponder boom. Asiasat 2 will be launched late this year or early in 1995 and will be located at 100.5 degrees east longitude. The foot­print covering Australia indicates that small dishes in the 1.8 metre diameter range will provide good results from this satel­lite – see Fig.4. One of Asiasat’s fiercest competitors is the APT satellite company, a Beijing commercial company located in Hong Kong. Apstar 1, scheduled for launch later this year and to be located at 131 degrees east longitude, will provide signals covering most of Asia and the northern parts of Australia. The satellite is fully booked by the Chinese Ministries of Posts and regional TV broad­casters. The second satellite, Apstar 2, presently filed for a slot at 134 degrees east, is scheduled for launch in early 1995 and will cover all of Australia. The Australian ABC has reserved space on Apstar 1 and will transfer to Apstar 2 by mid 1995. Japan Satellite Systems Inc (JSAT) also has plans to launch a satellite in August 1995. This satellite will be a Hughes HS-601 with multiple beam coverage. Called JCSAT3, this bird will cover an area from India and Russia, to Australia, New Zealand and Hawaii. A special K band spot beam will be used to cover Australia and new Zealand. Apart from the four satellites operated by Intelsat in both the Pacific Ocean Region (POR) and the Indian Ocean region (IOR), a separate satel- lite, Intelsat 501, is located at 91.5 degrees east longitude, specifically to service the Asia Pacific region. This satellite, launched in 1981, is nearing the end of its life and will be replaced by Intelsat 805, to be launched by the China Great Wall Industry during 1995. It will be located at 87.5 degrees east longitude. Existing Gorizont series C band satellites continue to operate at 140 degrees east (Gorizont 18) and 96.8 degrees east (Gorizont 19). Gorizont 19 covers most of Australia and can be received along the east coast with a 1.8 metre dish. Winners of the Silicon Chip/Tektronix 1994 Reader Survey Optus B2 replacement The replacement for the Optus satellite B2 lost last year is likely to be launched using a Long March launch­er around September this year. It will replace the existing A2 satellite located at 164 degrees east longitude. A2 is presently in an inclined orbit, due to its low level of station keeping propel­lant, and serves as a backup for the Optus fibre optic network. This will ease the congestion on the B1 satellite and allow the release of transponders 10 and 11 on that unit for future pay TV operations. Optus is also reported to have filed an applica­ tion with the ITU for a fourth orbital slot at 151.5 degrees east longitude. This slot is proposed to be used for a digital audio broadcasting service, downlinking on L band (1452-1492MHz). Video compression One result of the increased demand for transponder space has been the acceleration of the finalisation of the MPEG 2 digital video compression standard. This new technique allows up to 10 digitally compressed TV signals to be downlinked using only one satellite transponder (at one tenth of the normal cost). Australian satellite delivered pay TV will use this transmission method, requiring a special “decompressor” to be used in conjunc­ tion with existing reception hardware. Many of the new satellites we have mentioned will no doubt migrate to this higher efficiency, lower operating cost transmis­sion system. Even if you disregard the new digital compression tech­niques though, the next few years will see an explosion of satel­ lite services aimed at SC Australia. Our second reader survey, carried in the January, February & March 1994 issues, had an unprecedented response. We are delighted that so many readers took the time to fill in all the questions and, in many cases, also wrote letters expressing their views. Winner of the first prize, a Tektronix TDS 310 2-channel digital storage oscilloscope with GPIB, RS-232 and Centronics interfaces, was Mr Kerry Power, 93 Beryl St, Coffs Harbour, NSW 2450. The second prize was a suite of Tektronix test equipment comprising a CPS250 triple output power supply, a CDM250 bench digital multimeter, a CFG250 2MHz function generator and a CFC250 100MHz frequency count­er. This was won by Mr Colin Mooney, 4 Anchorage St, Sea­ ford, SA 5169. The third prize was a Tektronix DM254 digital multimeter which      SILICON was won by Mr K. Eldridge, 1 Craigholm St, Sylvania, NSW 2224. Our thanks to all readers who participated in the survey and to Tektronix Australia Pty Ltd for sponsoring the competition. The response was unprecedented, with over 4000 surveys being returned by the due date. Full processing of the completed surveys is expected to take several months. Above: pictured is Mr Kerry Power with his son Daniel, receiving the Tektronix TDS310 digital oscilloscope from Alan Richards, senior sales engineer. CHIP BINDERS These beautifully-made binders will protect your copies of SILICON CHIP. To order, just fill in & mail the order form in this issue, or phone or fax your order to:     Silicon Chip Publications,      PO Box 139, Collaroy Beach, 2097.      Phone (02) 979 5644. Fax: (02) 979 6503. July 1994  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 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. Positive to negative DC inverter This circuit generates a regulated negative voltage in the range of -8V to -15V from an unregulated input voltage of about 9-24V DC. The output current capability is 30mA or more. A possible design approach is to use one of the many available switch­ mode inverter ICs in a flyback circuit. However, I wanted to avoid the use of inductors if at all possible, be­cause they significantly add to the cost and complexity of this type of circuit. An alternative approach is to use the well-known 7660 chip which can generate a negative voltage from a positive input voltage without the use of an inductor. However, this IC has a few drawbacks which precludes its use in this application. The circuit shown here was developed to satisfy the criter­ia mentioned above. It is based on the cheap and readily avail­able LM494 PWM Control Circuit (IC1). It uses comparatively few parts and gives good output voltage regulation. The circuit works in basically the same way as a typical circuit using the 7660, in that on-chip transistors chop the DC input voltage to generate a pulse width modulated output. Floating constant current limit This circuit was inspired by the need to charge a capacitor at constant current from a high voltage source (1000µF from 340V at 250mA). The circuit is based on power Mosfet transistor Q2, with current limiting provided by Q1 (BC549) and R2. In operation, resistor R1 provides forward bias to Q2 so that it turns on and allows current to flow through R2. When this current reaches 250mA, Q1 begins to turn on and this limits drive to Q2. This 14  Silicon Chip C4 100 INPUT 9-12V C1 470 12 10 11 8 4x1N5819 C5 100 R2 390k 2 15 14 13 C2 .001 5 R1 33k 6 1 VOUT -8V TO -15V D3 D2 C3 100 D1 IC1 LM394 D4 4 7 9 A diode-capacitor multiplier circuit (D1-D4) then converts this chopped waveform to a DC voltage (Vout). A sample of the output voltage is fed back to pin 2 of the LM494 to give output voltage regulation. The output voltage is adjustable by means of VR1, while the chopping frequency is set by R1 and C2 (the exact value is not critical). Optimum efficiency is achieved using 1A Schottky diodes in the voltage multiplier circuit. If lower efficiency is tolerable, fast recovery or general purpose signal diodes would probably be adequate. Ordinary (slow) diodes (eg, the in turn limits the current through Q2 to the 250mA level. Other constant current limits can be set simply by changing R2. The formula to calculate its value is: R2 = 0.6/Imax, where Imax is the constant current, Zener diode ZD1 protects Q2’s gate from excessive voltages, while fuse F1 and diode D1 provide reverse supply polarity and device failure protection. Provided it is safely heatsinked, the circuit is capable of working from approximately 5V to 400V. Be sure to observe the usual precautions when working at high vol­tages. ADJ VOUT VR1 10k 16 C6 100 R3 120k 1N4002) are not recommended. The prototype was tested with input voltages from 9-24V DC but there would seem to be no reason why it will not work with voltages outside this range. The circuit was found to inherently limit the output current to about 50mA so that extra current-limiting protection was not needed. The efficiency is not as good as might be obtained from a 7660, being about 60% at 40mA/8V output. However, this order of efficiency was quite adequate for the application at hand. H. Nacinovich, Gulgong, NSW. ($25) V+ F1 1.5A MAX Q2 IRF740 R1 270k G ZD1 15V 1W Q1 BC549 D S D1 1N4007 R2 R2 = 0.6/IMAX V- E. Kochnieff, Lutwyche, Qld. ($20) Tester for IR remote controls REG1 78L05 OUT This circuit can be used to test infrared remote control transmitters that use a 40kHz carrier. It will sound a piezo buzzer and light a LED whenever the transmitter is sending a transmission code. The circuit is based on a GPIU52X IR receiver/demodulator, which is available from Tandy. This incorporates an infrared diode, an amplifier, a limiter, a 40kHz bandpass filter, a demod­ulator and a wave-shaping circuit. The output is a series of high and low signals which mimic the 40kHz modulation signal from the infrared transmitter. Transistor Q1 is connected in an emitter follower to buffer the Analog to digital interface circuit GND 220  Q1 BC547 LED2 SENSOR1 GP1U52X IN 9V  BNC SOCKET 220  LED1 PIEZO BUZZER  output from sensor 1. This drives LED 1 (via a 220Ω resistor) and a piezo transducer to indicate the presence of a demodulated signal. In addition, Q1’s emitter output is AC-coupled via a 0.1µF capacitor to a BNC socket, so that the signal can be fed to a CRO or frequency counter. Power for the circuit is derived from a 9V battery and regulated using a 78L05 low-power 5V regulator. LED 2 provides power on/ off indication, while S1 acts as an on/off switch. The current drain is about 18mA. A kit of parts for this circuit, including a PC board and a case with a battery compartment, is available from the author (address below) for $49.95 (includes postage). Alternatively, the kit can be supplied with a small zippy case (ie, no battery compartment) for $36.95. G. Turner, 34 Butler Street, Gladstone Qld 4680. ($20) +5V +8V LK5a LK4a 220k 220k LK3a 220k 220k 3 8 D1 1N914 10k IC1a 1 A/D INPUT This circuit has been LM358 220k 220k 220k 220k 2 designed to allow A/D .01 4 converters running from VR2 LK5b LK4b LK3b 22k 150k 10k a single ended supply to sample voltages that swing 150k +8V SWITCHED .01 to or below their 0V rail. CAPACITOR Many transducers deliver a A/D CONVERTER 2.7k 22k signal that ranges from 0V 10k +5V +3V VREF HIGH LK2 to 5V or 10V. This interface 5 has selectable input voltage 8.2k LK1 LM336-5 ranges and will accept an 7 IC1b 6 input voltage down to -20V VR1 3.3k without a split rail supply. +1V IC1a is a differential amplifier with VREF LOW selectable input resistors for 5V, 10V 10k 10k and 20V ranges with the resulting gain set to limit the output swing to 4V. IC1b provides an input voltage offset Link 3 Link 4 Link 5 for IC1a so that its output, pin 1, will Input Voltage Link 1 Link 2 swing between 1V and 5V. The offset a b a b a b from IC1b is selectable with link LK1 0 to 5V Closed Open Closed Closed Open Open Open Open or LK2 (see table). 0 to 10V Closed Open Open Open Closed Closed Open Open An LM336 5V voltage reference is used to set the Vref-high and Vref-low 0 to 20V Closed Open Open Open Open Open Closed Closed inputs on the A/D converter and the -2.5 to +2.5V Open Closed Closed Closed Open Open Open Open offset for IC1b. The LM336-5’s 5V (1%) -5V to +5V Open Closed Open Open Closed Closed Open Open reference will be accurate enough for 8-bit A/D converters but for 12-bit -10V to +10V Open Closed Open Open Open Open Closed Closed and 16-bit ADCs, a higher precision reference should be used. The output of IC1a feeds a low pass matched 220kΩ resistors for the inA voltage divider from the LM336 filter to reduce hash and diode D1 put string will improve performance. provides 3V and 1V taps for IC1b. provides overdrive protection for the Ten-turn trimpots should be used for Trimpot VR1 zeros the ADC for either A/D converter. VR1 and VR2. range and VR2 adjusts the amplifier Note: even through 1% resistors Marque Crozman, gain for a full-scale reading. should be used throughout, using SILICON CHIP. July 1994  15 16  Silicon Chip By GARY YATES Computers & programs that just go “beep” are old hat. This tiny digitiser records voice input through the games port & replays it on the PC’s speaker. What’s more, it can record to your hard disc for long recording & playback times. SmallTALK A tiny voice digitiser for the PC PCs are moving into the world of sound – there’s no denying it. Manufacturers are moving away from the days when the computer just beeped at you and are launching themselves into voice recog­nition and voice-annotated software packages. So much so that Compaq computers now come with a sound board as standard and there are other manufacturers about to follow suit. However, sound cards are still quite expensive and if you’re a programmer, writing programs that July 1994  17 GAMES PORT PIN 1 33  100 16VW 1k 4.7k A 100k LED1 ON 1 3 IC1a 2 LM358 4 100k MIC  K 8 1 5 47k 1k A K PIN 2 PIN 4 100k 33k 1 7 IC1b 6 .001 .0022 SMALLTALK FOR PCS Fig.1: the circuit is based on IC1, an LM358 dual op amp. IC1a functions as a microphone preamplifier stage & its output modulates a 40kHz carrier signal produced by IC1b. 18  Silicon Chip • • Sound playback is independent of PC clock speed; Uses only one IC. How it works This design uses a novel method of interfacing with the PC via the games port. Not only does this port have its own 5V supply rail, removing the need for an external power source, but it leaves the serial and parallel printer ports for their more traditional roles. Over the years, the printer and serial ports have been used for externally interfaced projects which meant you could be without the use of either your printer or mouse. By using the games port, these problems are avoided. It also has the benefit of a small con100uF 33  1k K 1uF 1 1k 100k 33k IC1 LM358 MIC .001 100k A DB-15 SOCKET 100k 4.7k LED1 47k use any sound other than a “beep” means that you’re relying on the end-user to have a compatible sound card in their machine. However, as popular as sound cards are becoming, the days when you can count on every machine having a sound card installed are still a fair way off. Those of you who built the PC Voice Recorder back in the August 1991 issue of SILICON CHIP will have been aware of its limitations – it required hardware for both recording and play­ back. GWBASIC was required to run the software and only 16Kb of storage was available which gave a maximum recording time of just 20 seconds. The SmallTALK digitiser presented here overcomes all of these problems and has to be one of the world’s smallest voice digitiser systems. It has the following features: • No additional hardware required for playback; • Either 3-minute RAM version or optional hard disc recording (an 85Mb HDD would give 13 hours recording time); • No external power supply required; • Fully self-executable software; • QuickBASIC .QLB and .LIB libraries available;. • Easily added to other programs; • Voice files can be stored on disc for replay; • Requires less than 2Kb per second storage; .0022 1uF Fig.2: install the parts on the PC board as shown in this diagram. Note that the mic insert will need a link connected to the shielding can tab so that it can be earthed via the cir­cuit. nector which results in a smaller PC board as well. Looking at the circuit diagram in Fig.1, you can see that there aren’t a great number of components involved. The circuit uses only one IC, a LM358 dual op amp. In fact there are so few components used in the circuit that it is difficult to see how it works. The first half of IC1 is connected as a non-inverting AC amplifier with a gain of 48. This is used to amplify the signal coming from the electret microphone which is biased via the 4.7kΩ resistor. That’s the straightforward part. Now comes the tricky bit. The output signal from pin 1 of IC1a is connected to pin 5 of IC1b. This second op amp has two RC filter networks providing the feedback from pin 7 to pin 6. These components have been selected so that with no signal present at the input, the output is effec­tively muted and the DC voltage at pin 2 sits at half supply; ie, around +2.5 volts DC. However, when a signal is present, IC1b rings severely at around 40kHz or so and this damped oscillation is superimposed on the amplified signal from the electret micro­phone. In effect, the audio signal from the electret modulates a 40kHz carrier and this is presented to one of the switch inputs of the game port. From here on, the signal present at the games port is sam­pled by the computer at a rate of 15kHz or, to be precise, 15 thousand samples per second. The resulting samples are stored directly as one-bit information either in RAM or on the hard disc. All of these functions are controlled by the software program which has been written to accompany this circuit. Because it’s only one bit per sample, the SmallTALK is memory efficient – it uses about 1.8Kb per second or less than 25% that required by conventional 8-bit analog-to-digital conver­sion. This method of conversion is similar to Delta-Sigma Modula­ tion and is briefly described in the accompanying panel. Storing to HDD While saving the sound data directly to RAM is relatively straight­ forward, saving the information to disc is a less simple process. What happens is that a 128Kb block of memory is allocated to storage of the sound data and this block is divided into two 64Kb regions. PARTS LIST 1 PC board, 52 x 40mm 1 DB15 PC-mount female socket 1 electret mic insert 2 male DB15 sockets 2 DB15 backshells 1 SmallTALK software disc 1 1-metre length of twin shielded audio cable (supplied with kit) Semiconductors 1 LM358 dual op amp IC 1 5mm red LED The board is connected to the games card inside the computer via a DB15-DB15 cable. Because there are only three connections, you can easily make up your own cable using two male DB15 sockets & some twin shielded audio cable. When sound recording begins, data is stored in the first region, which for ease of understanding we’ll call the “lower” region. Once the data fills the lower region, the computer switches over and begins to fill the “upper” region. While it is recording to this upper region, it stores the contents of the lower region to the hard drive. When the upper region has been filled, the program loops the data address counter back down to the beginning of the lower region and begins to fill this region up again, over-writing the data in the RAM which has been saved to the hard drive. Similarly, while it’s recording in the lower region, the contents of the upper region are stored to disc and this cycle continues until the user ends the recording by pressing a key. In effect, what happens is that while recording is continu­ing into one memory region, the other memory region is being saved to disc. This way, we can store huge amounts of sound data whilst only using 128Kb of memory, which is great for systems that only have 640Kb of RAM. Creative Lab’s Sound Blaster and other sound cards use a similar process to achieve the same result. Capacitors 1 100µF 16VW electrolytic 2 1µF 63VW electrolytics 1 0.0022µF 63VW MKT polyester 1 0.001µF 63VW MKT polyester Resistors (0.25W, 5%) 3 100kΩ 1 4.7kΩ 1 47kΩ 2 1kΩ 1 33kΩ 1 33Ω System requirements In order for SmallTALK to work, your system must have the following: • One floppy drive; • One hard disc drive (with at least 500Kb free); • One joystick port; • DOS 3.0 or later (DOS 5 or later preferred); • 512Kb of RAM minimum; • 80286 processor or higher. Sound recording on a PC is by its nature a very CPU-hungry process and unfortunately the 8086/8088 processor just isn’t fast enough to do the job. However, any sound file recorded on a 286 can be replayed at exactly the same pitch on any other ma­chine and you don’t need to set any special parameters. This is made possible by the program’s use of what can be termed “interrupt-driven sampling” or IDS. This relies on reprogramming the computer’s internal clock circuitry to take approximately 14,900 samples per second, re­gardless of the machine architecture. It also does this in the “background”, which means that provided you have the Quick­BASIC libraries (which we’ll get onto shortly), it’s possible to do other things such as print to the screen or get keyboard input while all this is happening. Software The software is available in two versions – RECORD and PLAY.EXE for the 3-minute version and HDRECORD and HDPLAY.EXE for the HDD option. In both cases, to record a file, you simply plug in the SmallTALK board, type in the program name and then a filename on the same line; eg, RECORD SOUND.VOC would start a 3-minute maximum RESISTOR COLOUR CODES ❏ No. ❏   3 ❏   1 ❏   1 ❏   1 ❏   2 ❏   1 Value 100kΩ 47kΩ 33kΩ 4.7kΩ 1kΩ 33Ω 4-Band Code (1%) brown black yellow brown yellow violet orange brown orange orange orange brown yellow violet red brown brown black red brown orange orange black brown 5-Band Code (1%) brown black black orange brown yellow violet black red brown orange orange black red brown yellow violet black brown brown brown black black brown brown orange orange black gold brown July 1994  19 Delta-Sigma Modulation (DSM) Delta-Sigma ModulaHIGH FREQUENCY tion (DSM) is a form of OSCILLATOR analog-digital converter (ADC) which transforms COMPARATOR ANALOG analog signals into a series CLK DIGITAL IN D Q of high and low digital OUT FLIP voltage levels. Fig.3 shows FLOP the basic elements of a DSM ADC. R The analog input signal is connected to the C LOW-PASS non-inverting input of a FILTER/ INTEGRATOR comparator. The output of this comparator is then Fig.3: the basic elements of a DSM ADC. fed to the D-input of a D flipflop, which is clocked at a very is higher that the returning signal, high frequency by an oscillator. the comparator produces a high The digital output of the D output; otherwise it is low. flipflop then passes through a The D flipflop and the associatlow-pass filter which is then routed ed clock circuit ensure that the back to the inverting input of the samples produced by the circuit comparator. The low-pass filter are at equal intervals. reconstructs the original signal so The D flipflop and oscillator that the comparator can com- circuitry is not necessary for the pare the slope of the incoming SmallTALK as the sample rate signal against that of the recon- produced by the op amp itself structed signal. If the input signal is sufficient for our application. recording with the data stored in the file SOUND.VOC in the current drive and directory. The sound files are compatible on both systems provided that files recorded on the HDD system are less than 320Kb. Longer files can only be replayed using the HDD system. The 3-minute version must load the complete file into memory before playback begins whereas the HDD system needs to only load in 64Kb before playback will begin, regardless of the size of the file. In both cases, only 128Kb of memory are used for data storage. If you are conscious about using up too much disc space for your sound files, a byte counter displays the current number of kilobytes used on screen and the exact number of bytes used when recording is completed. If you find that a sound file is too long, you can simply re-record the file and check it against the byte counter. Uses The PLAY.EXE program has also been designed to be incorpo­rated into your own programs – it plays the file 20  Silicon Chip without writing any information to the screen. You can simply use the SHELL command in either Quick­ BASIC or DOS’s QBasic to play sound files within your own programs. For example, you may wish to have the computer say “Press a key to continue”. You could record this into a file called, say, PRESS.SND and use the shell command at the appropriate time to replay the file: SHELL “PLAY PRESS.SND” The only condition is that both PLAY.EXE and the sound file, PRESS. SND, must be in the same directory that is currently in use. If your program is in a different directory or even a different drive, you can type: SHELL “E:\JUNK\PLAY D:\SOUND\ PRESS.SND” The only concern that this method raises is that you can’t do anything else while the SHELLed program is running. You can add this PLAY program to games, process control programs, word processors, database management programs, file utilities – just about anything where the computer needs to warn or indicate to the user that some process is occurring or needs the user’s attention. You could even use it as a message recorder, talking clock, talking voltmeter etc – the list is basically as long as your arm. QuickBASIC libraries Now if you’re sitting down and thinking “Wait a minute! BASIC’s not fast enough to do that!” then you’re quite right. The crucial routines which sample and play back the audio have been written in assembler and linked into QuickBASIC libraries, SMAL­ TALK.LIB/QLB and HDTALK.LIB/QLB which are also being made avail­able. The beauty of these libraries is twofold. Firstly, you can create your own programs using only QuickBASIC and not have to know anything about assembler. Secondly, you can combine all of the routines into one program name and do away with the SHELL command. These libraries contain easily-accessible routines which carry out the initialisation and the setting up of the record and replay clock reprogramming parameters, and a status routine which returns the total number of bytes either played or recorded so far. This feature is handy for when you need to keep an eye on file size or wish to stop at a certain point in the file. The libraries allow you to access any part of the sound file and initiate playback from one point to another. One example of where this idea would be useful is in speech pathology where speech analysis of a particular word spoken is necessary. Construction This is quite simple and can be done in about an hour or so – less if you’re more experienced. Before you begin any solder­ing, check the board thoroughly for any shorts or breaks in the copper tracks. These should be repaired with a small artwork knife or a touch of the soldering iron where appropriate. When you’re sure that the board is OK, you can start con­struction by installing the resistors, capacitors, the LED and the IC. These last two components and the two electrolytic capacitors are polarised so make sure that you follow the overlay wiring diagram and install them correctly. The final two components are the electret mic insert and the DB15 female connector. In both cases, each component should just drop into place. The mic insert will need a link connected to the shielding can tab so that it can be earthed via the cir­cuit. Simply use one of the clipped off leads from a resistor to do this. Wiring the cable Rather than buy a complete DB15 male-male cable which costs about $32, you can make your own (all of the required parts will be included in the kit). Twin shielded microphone cable is used to make the connections. Use the two inner conductors to make the pin 1 and pin 2 connections to each socket and the shield to make the pin 4 connections. Testing To test the unit, connect the cable and the PC board to your computer and measure the voltage drop across the 33Ω resistor. This should be around 120mV (0.12V). Any more than 200mV and you should disconnect the board and check for errors. If this measures correctly, you should also see the LED light up. Other voltages to check are the +5V rail Where to get the kit SmallTALK is available in two versions: the 3-minute ver­sion including software and kit for $34.95; and the HDD version including software and kit for $39.95. Additional QuickBASIC .QLB and .LIB libraries of the record and playback routines for either versions are available for $7 each. Please add $3.05 to all orders for postage and packaging and allow two weeks for delivery. You can send your cheque or money order to: R.A.T. Elec­tronics, PO Box 641, Penrith, NSW 2750. Note: Copyright © 1994. All software, circuits and PC art remain the property of R.A.T. Electronics. from pin 1 which should also appear at pin 8 of IC1 (it should be around 4.9V). Pins 3, 5 and 7 of IC1 should be 2.45V as well. Now depending upon the software you request, run the in­stall program to load it onto your hard drive. Once in the direc­tory SMALTALK type: RECORD TEST.VOC and press enter. You’ll be asked to press enter again to initiate recording. At this point, say a few words and then press the space bar. You should get a file byte count of around 8-10Kb depending on how long you speak. Now type in the same directory: PLAY TEST.VOC and you should hear the file being replayed through your PC’s speaker. If you purchased the HDD system, then you would substi­tute the names HDRECORD and HDPLAY for these tests. If all goes well, you can now include the PLAY program and your own sound files into your own programs whether they are written in PASCAL, C or “plain SC old” BASIC. July 1994  21 Electronic Engine Management Pt.10: Ignition Systems – by Julian Edgar The conventional automotive ignition system comprising points, a combination of centrifugal and vacuum advance mechan­isms, a coil and spark plugs has been largely replaced in modern engine managed cars. Multiple coils and electronic timing control are often matched with platinum plugs which may require changing only once every 50,000km. Ignition timing While it is obvious that an engine working at full throttle requires more fuel than at idle, the changes needed in the timing of the spark plug firing are not as easy to understand. On average, it takes about two milliseconds from the time of ignition until the end of the fuel burn. The optimum time for this process to occur is slightly after the piston has reached Top Dead Centre (TDC) – ie, when it has started on its way down again. If the spark occurs too early – ie, when the piston is moving upwards - then the combustion process will slow the piston and detonation (an uncontrolled burning) may occur. Conversely, if ignition occurs too late, then the pressure developed in the combustion chamber will be lessened as the piston will already have descended too far down the cylinder. Fig.1 shows the different cylinder pressures experienced with different ignition timing. The timing of the ignition is described in degrees of crankshaft rotation before or after TDC; ie, BTDC or ATDC. If the spark plug is fired late in the crankshaft’s rotation (ie, ATDC), the spark is said to be retarded. If it’s fired early (BTDC), then the spark is said to be advanced. Combustion time This photo shows a typical small moulded coil from a current ignition system utilising a distributor. 22  Silicon Chip Because the combustion time varies little over the rev range, a fixed ignition timing ATDC would mean that combustion would extend further and further into the power stroke as the engine rpm increased. Thus, in order to maintain maximum combus­ tion pressure, the ignition point must be advanced as rpm in­creases. If it were this simple, then that would be the end of the story – but it’s not! The optimal ignition timing is also in­fluenced by engine design factors, such as spark plug position and combustion chamber shape, and transient factors like mixture richness, engine load and engine temperature. In practice, the correct ignition advance is a compromise based on the criteria of: • • • • maximum engine power; economical fuel consumption; no engine knock; and clean exhaust emissions. Traditional systems The conventional system of ignition timing advances the spark by means of centrifugal weights mounted within the dis­tributor. This produces an advance curve which is solely depend­ent on rpm and so a vacuum canister connected to the intake manifold is used to additionally advance the ignition point as a function of load. The typical resulting ignition advance curves are shown in Fig.2. The high voltage (25-30kV) required to generate the spark for ignition is obtained from the ignition coil. During the dwell period (when the points are closed), current flows through the primary side of the ignition coil which stores energy. When the points open, a high-voltage pulse is generated in the secondary side of the coil and this is applied to one of the spark plugs. The “correct” plug is selected by the rotor arm inside the dis­tributor. Fig.1 (left): the ignition timing must be correct for the combustion pressure to be at its peak immediately after the piston passes top dead centre (ATDC). However, if the timing is over-advanced, knocking may result. (Bosch). Engine managed systems With input sensors in place to control the fuel injection, extending the influence of these to control the ignition timing was a logical next step. Fig.4 shows a typical electronic ignition system as used in some Fig.2: a conventional weights-and-vacuum ignition advance system can produce only a relatively simple advance map. (Bosch). Fig.3: by using the input data from various sensors, an electron­ically-managed ignition system can provide a far more comprehen­sive advance map than the old weights and vacuum system. This ensures optimal spark timing over a much wider range of load and rpm conditions. (Bosch). July 1994  23 Fig.5: unlike a conventional ignition system, an ECM system can have a special softwarecontrolled ignition advance map for very cold staring. Note the complex shape of the ignition advance curve when this engine’s coolant is below 0°C. Fig.4: this diagram shows the ignition timing inputs to the ECM in a recent Nissan system. Nissan engines. It comprises the ECM, an ignitor (or power transistor) ignition module, and the traditional distributor, coil and plugs. The ignition timing is provided by “maps” (such as shown in Fig.3) built into the ECM software, with ignition angles selected on the basis of inputs from the crankshaft posi­tion sensor, airflow meter, coolant temperature sensor and knock sensor. Nissan timing system The Nissan electronic ignition timing control can be clas­sified into three different phases: ordinary operation, engine starting, and idling and decelerating. During ordinary operation (sensed when the throttle position sensor or TPS is in its off-idle position), the ignition timing advance is selected from the maps stored within the ECM. During starting, the coolant Fig.6: the Subaru Liberty Turbo ignition system uses a coil mounted on each spark-plug. The ‘ignitor’ module is external to the ECM. (Subaru). Fig.7: this Daihatsu Mira system uses a power transistor within the ECM to control a single ignition coil which then feeds a distributor. (Daihatsu). 24  Silicon Chip tempera­ture has a major input into timing, especially if the temperature is below 0°C – see Fig.5. If the battery is nearly flat during starting, combustion might occur before the piston reached TDC – with reverse rotation a possibility. To prevent this, the ignition is further delayed when the cranking speed is below 100 rpm. Finally, when the TPS indicates that the car is decelerating, the ignition angle se­lected is retarded at engine speeds over about 2000 rpm, probably to benefit exhaust emissions. The external ignition module – containing the power tran­sistor to switch the primary side of the coil – may also contain its own inbuilt timing. Usually, this is bypassed and the ECM controls ignition timing, but should a problem develop in the ECM the ignition module will run the engine with the small amount of ignition advance built into it. This limp-home advance is rpm dependent. Multiple coil systems While the Nissan system discussed above uses full electron­ic timing control, it is slightly old-fashioned in that a single coil and a distributor are used. More sophisticated systems use multiple coils and power transistors, and avoid the use of a distributor totally. One such system is used by Subaru on their Liberty Turbo, with some Saab, Nissan and BMW engines using similar systems. Other manufacturers (like Holden on their V6) use multiple coils and a waste-spark system. Subaru mount four coils directly on top of The Subaru Liberty Turbo uses four individual coils, each mount­ed on top of its corresponding plug. The platinum spark plugs only need changing at 50,000km intervals. the spark plugs, meaning that no high tension leads are used at all. The ECM switches four power transistors (which are exter­nally mounted in an ignitor module) and determines the correct spark timing based on the inputs from seven sensors. Fig.6 shows the layout of the Subaru system. Fully programmable aftermarket ECMs like this Autronic unit, shown here installed on a 260kW turbocharged rotary engine, can have full ignition maps programmed into them. These maps give the appropriate ignition timing for a variety of engine conditions. July 1994  25 Fig.8: the Mazda RX-7 Turbo ignition system uses two coils for the rotary engine. Turbocharged engines require very good knock-sensing if advanced timing is to be run without engine damage being caused through detonation. (Mazda). Knock sensing is used, with a self-learning algorithm incorporated into the ECM. Knock sensing is particularly import­ant in turbocharged engines like the Subaru, because best power will be gained by advancing the ignition timing almost to the point of detonation. Detonation (knocking) can severely damage a high-performance engine within a few seconds, 26  Silicon Chip however. In some cars, the knock sensor input is used to immediately retard the timing by up to 7°, with the timing then progressively advanced back to stan­dard. In Saab’s Automatic Performance Control (APC) system, the turbo­ charged cars will run on fuels varying in octane from 91 to 98. (Note: the octane rating of a fuel is an indica- tion of its anti-knock properties. The higher the octane number, the lower its propensity to detonate). The APC system uses the input from a knock sensor to regulate turbo boost pressure, meaning that the engine can extract more power from the fuel than an engine with conventional ignition timing (which must always have a SC large safety margin). 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 BUILD A 4-BAY BOW-TIE UHF ANTENNA This photo shows how the antenna is oriented to receive horizontal TV transmissions while the photo on the facing page shows the orientation for receiving vertical TV transmissions. 32  Silicon Chip BILL OF MATERIALS Thinking about building an antenna to pick up UHF TV in your area? This 4-bay bow-tie array has high gain & covers both UHF bands IV & V. It can be used for horizontal or vertical polarised TV transmissions. By LEO SIMPSON & BOB FLYNN If you can do basic metalwork, you can build this antenna. Your bill of materials will be around $45 and the finished anten­na should give better performance than commercial UHF Yagi anten­nas costing up to a hundred dollars and more. We presented a very similar 4-bay bow-tie design in January 1988. That design used 6mm aluminium tubing, 3mm aluminium rod and 19mm square aluminium tubing. The 6mm tubing proved difficult to obtain at the time (many people used 1/4-inch rod instead) and the 3mm rod was virtually unobtainable as well. This new design uses 4.74mm aluminium tubing for all ele­ ments and the harness, dispensing with the need for a blowtorch to make the harness connectors. As well, the balun box is simpli­fied and the over- all construction is lighter and more straight­forward. The 4.74mm diameter tubing has a wall thickness of 0.9mm. Its diameter is close to the Imperial dimension of 3/16-inch (4.7625mm) and is a neat fit into 3/16-inch holes. Background to bow-tie arrays In Australia, on the UHF (ultra high frequency) TV bands, the Yagi antenna is king. UHF Yagis are now very familiar on Australian roof-tops. They have a long boom, up to 1.8 metres or more, with many short elements arranged along it. The Yagi design for UHF has many advantages. It is easy to mass produce, uses a modest amount of material, has relatively low windage (ie, force due to wind acting on it), good direction­al characteristics and Antenna 1.5 metres of 12.7mm square aluminium tubing with 1.6mm wall thickness 14.5 metres of 4.74mm diameter aluminium tubing with 0.9mm wall thickness 330mm x 125mm x 1.6mm thick aluminium sheet 330mm x 40mm x 3mm thick acrylic sheet 26 stainless steel self-tapping screws No.4 gauge x 10mm long 16 stainless steel self-tapping screws No.4 gauge x 6mm long 4 3mm diameter x 20mm long stainless steel metric screws 12 3mm diameter x 16mm long stainless steel metric screws 16 3mm stainless steel metric nuts 18 3mm stainless steel shakeproof washers 2 U-bolts and clamps to suit mast Balun Box 1 83mm x 54mm x 30mm black plastic jiffy box, Jaycar Cat. No. HB-6015 or equivalent 1 printed circuit board, 37 x 39mm, code 02108941 250mm of 0.67mm diameter enamelled copper wire 2 3mm diameter x 16mm long stainless steel screws 3 3mm diameter x 10mm long stainless steel screws 12 3mm stainless steel nuts 4 3mm stainless steel shakeproof washers 6 3mm stainless steel plain washers Miscellaneous 75-ohm semi air-spaced coaxial cable, Delrin plugs for square tubing. good gain, depending on the number of elements. The Yagi does have a number of drawbacks though. It must be made with considerable precision if it is to perform well, so it is not so easy for the enthusiast with basic metalworking facili­ties to build. It is also a July 1994  33 600 46 370 A 46 B 46 E H 46 184 46 F 230 D E H 46 46 46 46 184 46 46 46 46 C 46 46 G 46 46 D 18 REFLECTOR ELEMENTS REQUIRED 600mm LONG AND 16 DIPOLE ELEMENTS 183mm LONG MATERIAL : 4.74mm DIA ALUMINIUM TUBING Fig.1: front & side elevation of the new UHF antenna. The letters A-H indicate the special hardware items that you have to make. These are: (A) the dipole carriers, four required; (B) the dipole mounting clips, eight required; (C) the boom clamp plate; (D) the dipole boom; (E) the reflector boom; (F) the bent harness connec­tors, four required; (G) the straight harness connectors, two re­quired; & (H) the boom tie plates, four required. Also shown on Fig.1 but not labelled as such are the re­flector elements, of which 18 (600mm long) are required, & the dipole elements, of which 16 are required (each 183mm long). Not shown on Fig.1 is the balun box assembly which is mounted at the centrefront of the antenna. The assembly details for each item are shown in a separate diagram. 34  Silicon Chip no-compromise design in that it is not practical to design a Yagi which will cover both UHF bands, particularly if you want a reasonable amount of gain. You can have band IV or band V but not both. In Australia, by the way, UHF Band IV covers channels 28 to 35 (526-582MHz). UHF Band V covers 46 28 46 46 648 434 202 46 46 28 46 46 46 802 46 46 28 46 46 156 26 46 10 26 81 46 26 46 156 10 26 46 11 28 D E 46 12 FRONT HOLES 2mm DIA 12 SIDE HOLES THROUGH BOTH SIDES 2mm DIA 5 channels 39 to 69 (603-820MHz). Each channel occupies a 7MHz slot. In Europe and other parts of the world, there are common alternatives to the Yagi design. One is a Yagi with a corner reflector, another is a bow-tie with corner reflector, while a third is the most common, the bow-tie array. This is essentially a dipole (shaped like a bow-tie) with a plane reflector close behind it. Higher gain is obtained by stacking bow-ties, in either two-bay or four-bay arrays. The latter is the design we are presenting. The four-bay UHF bow-tie array antenna has a number of advantages over typical Yagis. First, it can cover both bands IV and V without modification. Second, it has better gain than all except the highest gain UHF Yagis which may measure up to three metres long. Third, it has good frontto-back ratio and a much narrower acceptance angle, in both the vertical and horizontal planes. (Note: the 18-element TC-18 from Hills is a combination of a long Yagi with a small corner reflector. The corner reflector gives it slightly higher gain and a narrower acceptance angle. For those who do not wish to build their own antenna, it is a good choice in fringe areas. It is available in Band IV and Band V versions). The narrow acceptance angle of a four-bay bow-tie array is important, particularly if your location does not have a good line-of-sight to the transmitter and if you are often over-flown by aeroplanes. This combination of circumstances can lead to a phenomenon known as “aircraft flutter”. When this occurs, the signal reflected from the aircraft to your antenna can be stronger than the more direct signal received from the transmitter. This causes very strong ghost­ing on the screen and a slowly fluctuating vertical bar on the screen which is the ghost of the horizontal sync pulse. The picture flutters because the plane is moving at high velocity relative to your antenna and so the path of the strong reflected signal is changing rapidly. In severe cases, aircraft flutter can cause the picture to lose horizontal synchronisation. Where the bow-tie array has a considerable advantage over the Yagi is that it has a much narrower vertical (and horizontal) acceptance. This is about half that for a Yagi of equivalent 3.5 12 SIDE HOLES THROUGH BOTH SIDES 4.76mm DIA HOLES ON 26mm CENTRES ARE 2mm DIA 12 REAR HOLES 2mmDIA DIPOLE BOOM MATL: 12.7mm SQUARE x 1.6mm WALL THICKNESS ALUMINIUM TUBE DIMENSIONS IN MILLIMETRES REFLECTOR BOOM MATL: 12.7mm SQUARE x 1.6mm WALL THICKNESS ALUMINIUM TUBE Fig.2: cut & drill the reflector (left) & dipole booms exactly as shown here. July 1994  35 gain; ie, about 27° versus about 40°. This means that the bow-tie array will pick up much less reflected signal from high flying aeroplanes and therefore interference is much less. Well, what about the disadvantages of the bow-tie array versus the Yagi. Yes, it does have some. First, because it is a vertical rather than horizontal array, it has more windage. Second, there is probably more work in fabricating a do-it-yourself design such as this. 34 25 9 18 N DOW BEND BEND DOW N 7.5 15 30 B DIPOLE MOUNTING CLIPS 8 REQUIRED MATL: 1.6mm ALUMINIUM HOLES 3.2mm DIA 38 6 26 Performance 6 80 92 BOOM TIE PLATES 4 REQUIRED MATL: 1.6mm ALUMINIUM HOLES 3.2mm DIA 14 40 14 H 15 15 15 15 80 A DIPOLE CARRIERS 4 REQUIRED MATL: 3.2mm ACRYLIC HOLES 3.2mm DIA Fig.3: this diagram shows the fabrication & drilling details for the dipole mounting clips (top), the boom tie plates (centre) & the dipole carriers (bottom). The dipole carriers are made from 3.2mm-thick acrylic sheet (eg, Lexan or Perspex), while the dipole mounting clips & boom tie plates are made from 1.6mm-thick aluminium sheet. Be sure to keep to the exact dimensions shown here & drill all holes to 3.2mm-dia. 36  Silicon Chip While we did not have equipment for measuring the absolute performance of the bow-tie array featured here, we have been able to make a lot of direct comparisons with commercial UHF Band IV and Band V Yagi designs. These were essential to optimise the performance for both Band IV and Band V. After a lot of trial and error, we are pleased to present a design which is very competitive with present commercially avail­able Yagis and as noted above, it is notably less susceptible to “aircraft flutter”. As well, this new design is easier to make than the design presented in January 1988. Inevitably, we must draw a comparison with the Corner Re­flector design we presented in the June 1991 issue. This new bow-tie array appears to have higher gain than the June 1991 design and it also is less cumbersome to handle. Against that, the corner reflector is probably easier to make. Having said that, our overall preference is for the bow-tie array. Design features Our bow-tie array is similar in appearance to a number of commercial designs which are available overseas. It is construct­ed mainly of 4.74mm aluminium tubing with the two vertical struc­tural members (booms) being 12.7mm square tubing with 1.6mm wall thickness. The four dipoles are effectively vestigial bow-ties, being Vees made of tubing rather than triangular pieces of flat sheet. This cuts down on the windage while keeping the bandwidth essentially the same. The reflector is essentially a large grille 60cm wide and 80cm high. The four dipoles are mounted on a common boom (the dipole boom) which is spaced away from the reflector boom of the grille by 67mm. The two dipole bays near the centre of the antenna are connected as shown in this photograph. The ends of the harness connectors are flattened using a vyce. A B 46 B Z A 100 After a few years’ exposure to the elements, many antennas are in a poor state. Because aluminium is such an active metal, the right fasteners must be used otherwise corrosion will be very rapid, especially in seaside areas. We recommend three types of fastener for this project: (1) Aluminium pop rivets with aluminium mandrels. Those with steel mandrels are not recommended. Eventually, their mandrels will rust and while this may not harm the antenna it will cause un­sightly discoloration. (2) Though often hard to get, aluminium screws are recommended although they are not available in self-tapping types and so all screw holes would have to be tapped. (3) Stainless steel self-tapping screws. These are strong, readily available and corrosion resistant. We strongly recommend the use of stainless steel for all screws used in this project. We do not recommend galvanised, bright zinc or cadmium plated steel screws as these do not stand the test of time. Often they will start to rust within a few days’ exposure in seaside areas or in areas subject to industrial fallout. They may be OK for roofing work but in combination with aluminium they rust. If you live away from the sea and decide to use these types of screw anyway, we recommend that you paint the antenna. We’ll talk about that later. Do not, on any account, use brass or mild steel screws. If you use these, Z Fasteners This view shows one of the dipole bays at one end of the antenna. Note how the ends of the harness connectors are crossed over to provide correct phasing. B B 46 The antenna is shown in front elevation and side elevation in Fig.1. The diagram of Fig.1 labels each special hardware item you will have to make. These are: (A) the dipole carriers, four required; (B) the dipole mounting clips, eight required; (C) the boom clamp plate; (D) the dipole boom; (E) the reflector boom; (F) the bent harness connec­tors, four required; (G) the straight harness connectors, two re­quired; and (H) the boom tie plates, four required. Not shown on Fig.1 is the balun box assembly. Also shown on Fig.1 but not labelled as such are the re­flector elements, of which 18 (600mm long) are required; and the dipole elements, of which 16 are required (each 183mm long). A Fig.4: the boom clamp plate is attached to the back of the rear boom using self-tapping screws which are also used to secure three of the reflectors. Drill the holes labelled ‘B’ to suit the U-bolts. Z Z 100 C BOOM CLAMP PLATE MATL: 1.6mm ALUMINIUM HOLES A: 3.2mm DIA B: TO SUIT U-BOLTS DIMENSION Z TO SUIT U-BOLTS July 1994  37 you are wasting your time and you will spoil the job. 5 Making your antenna WIRING HARNESS 4 REQUIRED MATL: 4.76mm DIA ALUMINIUM TUBE HOLES 3.2mm DIA F 184 194 WIRING HARNESS 2 REQUIRED MATL: 4.76mm DIA ALUMINIUM TUBE HOLES 3.2mm DIA 115 G 240 30 115 30 5 30 Fig.5 (left): the inner & outer harness connectors are made from 4.76mm-dia. aluminium tube. Use a vise to flatten the end & centre sections as shown & drill all holes to 3.2mm. The text describes how the outer harness connectors are bent. 38  Silicon Chip Most enthusiasts will have the tools needed for this pro­ject. You will need a hacksaw, electric drill, vyce and pop-rivet gun. Apart from a pair of antenna clamps (U-bolts), no special hardware or fittings are needed as we will detail how every part is made. Making and assembling this antenna is a fairly straightfor­ward process although some steps are a little tedious. You must first obtain all the aluminium and hardware listed in the Bill of Materials, and make sure you have access to all the tools we have listed above. Having assembled together all the raw materials, you can start work by cutting all the aluminium elements with a hacksaw. Cut the two booms first, which are made of 12.7mm square aluminium tubing. The details are shown in Fig.2. The reflector boom is 802mm, while the dipole boom is 648mm long. Once cut, centre-punch and drill all the holes in both booms. Make sure that all the holes for the reflector elements in the rear boom are precisely in line and that their centres are 3.5mm from the front surface as shown on Fig.2. Do not forget the holes for the tie plates or the holes in the back of the rear boom, for the boom clamp plate. Trying to drill these after the antenna has been partially assembled would be a tricky task. Next, cut all 18 reflector elements and the 16 dipole ele­ments. These are made from 4.74mm aluminium tubing with a 0.9mm wall thickness. The reflector and dipole element dimensions are shown in Fig.1. Assemble each reflector element into the rear boom, one at a time. The method we used was to thread one element through the boom, centre it precisely and then drive in a 4-gauge stainless steel screw from the rear of the boom so that the element is held firmly in place. Do this for all 18 reflector elements. Note that three of these screws are also used to secure the boom clamp plate. Dipole plate & clips Next, make the four dipole carrier plates, as shown in Fig.3. We used TO RECEIVER TO PRI ANTENNA SEC BALUN PRIMARY: 12T, 0.67mm DIA ENAMELLED COPPER WIRE CLOSE-WOUND ON A 3.2mm DIA MANDREL SECONDARY: 6T, 0.67mm DIA ENAMELLED COPPER WIRE CLOSE WOUND ON A 4.76mm DIA MANDREL Fig.6 (above): this diagram shows the winding & termination details for the air-cored balun. Fig.8: here is the full-size pattern for the balun board. Ready-etched boards can be purchased from RCS Radio Pty Ltd (see page 96). Fig.7 (right): the balun coils are mounted on the copper side of the PC board. Note that the secondary coil is simply slid over the primary & has both ends soldered to earth (ie, the track that runs to the cable clamp & the braid of the coax). 3.2mm thick white Perspex but you can use clear Lexan or Perspex as they stand the weather equally well. When drilling, do not use too high a speed otherwise the Perspex will tend to melt and congeal on the drill. Now, make the eight dipole mounting clips. We cut and bent these from a strip of 1.6mm-thick aluminium, 30mm wide. Again, Fig.3 shows the details. Each clip can be cut with tin snips, flattened with a hammer and then each side bent up in a vyce. That done, you can make up the four dipole assemblies, each requiring a Perspex dipole carrier plate, two dipole clips, four dipole elements plus four stainless steel 3mm machine screws, nuts and lock washers. Next, make the four boom tie plates (Fig.3) which tie the front (dipole) and rear (reflector) booms together. You can also make the boom clamp mounting plate (see Fig.4) at this stage, since it uses the same material (1.6mm thick aluminium sheet). Now assemble the front and rear booms together, using the four tie plates. You can use pop rivets or stainless steel self-tapping screws for this job. Next, fix the boom clamp plate (and three of the reflectors) to the rear boom using stainless steel self-tappers, then mount the four dipole assemblies onto the dipole boom. Harness connectors Your antenna now looks the part and only lacks the harness and balun box assembly. Make the straight and bent harness Above: the completed balun box assembly. The coaxial cable enters through a grommeted hole in the bottom of the box & is secured using a large cable tie & the earth clamp. When the assembly has been tested, use silicone sealant to seal the case against the weather. July 1994  39 PLASTIC BOX WIRING HARNESS 3mm SHAKEPROOF WASHERS PCB 3mm SCREW 16mm LONG 3mm FLAT WASHERS This close-up view of one end of the reflector boom shows how the reflector elements are held in place using stainless steel self-tapping screws. Make sure that each element is correctly centred on the boom. BOX CENTRE LINE 3mm SCREWS 10mm LONG EARTH CLAMP GROMMET COAXIAL CABLE 7.5 BALUN BOX DETAIL TWO MOUNTING HOLES FOR PCB REQUIRED IN BASE OF BOX 3.2mm DIA. ON 30mm CENTRES 10mm ABOVE BOX CENTRE LINE 7 12.7 20 EARTH CLAMP HOLES 3.2mm DIA. MATL: 0.75mm BRASS Fig.9: this diagram shows how the balun box assembly is attached to the harness connectors using 16mm long screws & shows how the earth clamp is made. 40  Silicon Chip connectors, as shown in Fig.5. Again, these are made from 4.76mm diameter aluminium tubing. This is the trickiest stage in the whole process. The straight connectors are the easiest to make, so we’ll talk about those first. Cut two lengths 240mm long, then squeeze the ends and centre section flat, as shown in the diagram of Fig.5. That done, centre-punch each end and the centre section and drill 3mm holes, as shown. The bent connector requires a few extra steps. First, cut four lengths of 4.76mm aluminium tube 210mm long. Next, drill two 4.76mm (3/16-inch) diameter holes in a block of wood; one hole 72mm deep and one 30mm deep. Clamp the drilled block of wood in your vyce. Put one end of the tube fully into the 72mm deep hole and bend it over at 45°, then place the bent length of tubing into the 30mm deep hole and bend it back 45° so that the short section is parallel to the long section, as shown in Fig.5. Do this for all four 210mm lengths of tube. This done, squeeze the ends in a vyce, centre-punch each end and drill 3.2mm holes, as shown in Fig.5. The six connectors are then ready to be attached to the four dipoles but before you can do that you need to prepare the balun box assembly. Balun box assembly The balun box provides a correct termination for the anten­na harness and terminals for 75-ohm coax cable, all sealed away from the elements for protection. It takes the form of a black plastic box with a small printed circuit board inside. This mounts the air-cored balun and the terminations. The printed circuit board measures 37 x 39mm (code 02108941) and has a very simple pattern. The balun is made of two coils of enamelled copper wire, as shown in Fig.7. Use wire with self-fluxing enamel for this job. Self-fluxing enamel melts easily in a solder pot or with a soldering iron and is much easier to work with than high temperature wire enamels which must be thoroughly scraped off before the wire can be tinned with solder. Incidentally, do not think that the connection of the outer coil of the balun is a mistake, as shown in Fig.7. It is correct, with both ends soldered together. The balun printed circuit board and its accompanying box is tricky to mount. We used a standard black plastic Jiffy box measuring 83 x 54 x 30mm (Jaycar Cat. HB-6015). We suggest the following method for mounting the balun box which is depicted in Fig.9. First, drill the two 3.2mm holes in the rear of the balun box and a 9.5mm hole for the cable grommet which is fitted to one end. Attach the two straight harness connectors to the balun box using two 3mm diameter x 16mm long stainless steel screws, nuts and lock washers. This done, fit three 3mm diameter x 10mm long The front & rear booms are fastened together using four boom tie plates (see Fig.3 for dimensions). You can use either pop rivets or stainless steel self-tapping screws to secure these tie plates. stain­less steel screws and nuts to the balun board for the cable clamp and cable inner conductor terminal. We tinned the copper lands on the board where the nuts bedded down, to make good contact. You can use brass or copper plated steel for the coax cable clamp and it is attached using an additional two nuts on the board screws. Fit a grommet for the 6mm coax cable to the end of the balun box. Now attach the balun box assembly and the four bent harness connectors to the dipole assemblies and the antenna is virtually finished. You will need to bend each pair of bent harness connectors slightly so that there is about 2mm clearance between them. Do not overtighten the dipole assembly screws otherwise the Pers­ pex will distort and possibly crack. Mounting the antenna You will need a pair of antenna clamps or U-bolts to mount the antenna to the mast or J-pole (for barge-board mounting). We prefer the use of galvanised U-bolts and V-clamps for this job rather than the cadmium-plated and passivated types used for some antenna hardware. The latter have a gold finish and often start to rust prematurely. 42  Silicon Chip This view, taken from the rear of the antenna, shows how the balun box is attached to the harness connectors at the centre of the dipole boom. The coax cable (not shown here) exits through a hole in the bottom of the box. U-bolts and clamps for automotive exhaust systems are generally quite suitable and have good corrosion resistance. Or, if you want to be really fancy, go to a ship’s chandlers and buy stainless steel U-bolts and clamps. They’re costly but good. We suggest that the ends of all the reflector and dipole elements be stopped up with silicone sealant. This will stop them from whistling in the wind. You can do the same with the booms although, for a neater result, you can buy square Delrin plugs from aluminium centres. Installing the antenna Take a lot of care when installing your antenna. There’s no point doing a fine job of assembly and saving all that money if you end up in hospital because you fell off the ladder. Climbing ladders with antennas is dangerous work. The first step is to decide where to mount the antenna. For best results, mount it as high as possible and well clear of other antennas. It is not really practical to mount this bow-tie array on the same mast as a VHF antenna unless it is vertically separated from it by at least one metre. Having mounted your mast, take the antenna up and secure it with the U-bolts, then terminate the coax cable. For minimum signal attenuation and good cable life, we recommend Hills semi-airspaced cable (the dielectric has a cellular cross-section), type SSC32 or equivalent. At the TV set end of the cable, you will probably need a diplexer to enable you to terminate the cables from your VHF and UHF antennas. A single cable then goes from the diplexer to the TV set. Alternatively, the diplexer output may be fed to a splitter and then to various TV wall plates around your home. Tune your TV to the local UHF station(s) and then orient the antenna for best reception. Finally, secure the cable to the mast with plastic cable ties to prevent the cable from flapping in the wind and seal the balun box with silicone sealant to weatherproof it. Painting Depending on where you live, painting the antenna can be worthwhile, particularly in seaside areas or near industrial areas where there may be a lot of fallout. In these cases, we suggest painting the antenna with an etch primer and then finish­ing with an aluminium loaded paint such as SC British Paints “Silvar”. Build the PreChamp – a tiny, versatile preamplifier to mate with the CHAMP! If you’ve built the Champ amplifier from the February 1994 issue then you will probably have a use for this tiny pream­plifier. It uses two common transistors, provides up to 40dB of gain, runs from a 6-12V supply & has provision for an electret microphone. By DARREN YATES The CHAMP amplifier has been a great success with kits available from most of the kit retailers, with lots of interest coming from schools and colleges. However, as versatile as the CHAMP is, unless you have a signal of sufficient amplitude, it will not provide its maximum power output. And if you need to use the CHAMP’s maximum gain of 200 (46dB), the sound quality is not as good as it would be when the circuit has less gain. So we thought, “Why not produce a simple preamp to go with it?” The PreChamp is the answer. It’s not much bigger than a 9V battery yet it has a gain in excess of 40dB, which is more than enough for most applications. You can also vary the gain by changing a single resistor. Furthermore, we have made provision on the circuit board for an electret mic insert. The circuit Let’s take a look at the circuit diagram – see Fig.1. As you can see, the circuit consists of just two transistors – a BC548 NPN type and a BC558 PNP type. These make up a DC feedback pair, with the negative feedback coupled from the collector of Q2 to the emitter of Q1. The input signal is applied via a 0.1µF capacitor to the base of transistor Q1. The bias voltage for this transistor is set up by the 2.2kΩ, 100kΩ and 150kΩ resistors. A lowpass filter consisting of the 2.2kΩ resistor and a 10µF capacitor removes This tiny preamplifier board was specifically built to match the CHAMP power amplifier featured in the February 1994 issue of SILICON CHIP. However, it can be used anywhere you need a preamp with a gain of up to 100 times. unwanted hum and noise from the DC bias voltage. This is known as “supply decoupling” and is usually necessary in preamp circuits to ensure that the output signal is free from hum and unnecessary noise. The output from the first stage is taken from the collector of Q1 and its 22kΩ load resistor. Although this 22kΩ resistor is not strictly necessary, it helps to linearise the output and significantly reduces distortion. Q1’s output is fed to the base of Q2 (the BC558 PNP transistor) and the final output signal appears at its collector. Negative feedback is applied by the 2.2kΩ resistor between the collector of Q2 and the emitter of Q1. The 1500pF capacitor across this resistor ensures that the circuit’s response to radio frequency (RF) is greatly reduced by rolling off frequencies above 48kHz. The overall gain is set by the ratio of the 2.2kΩ resistor and the 100Ω resistor also connected to the emitter of Q1. The full gain equation is: Gain = 1 + (2200/100) = 23 which is equivalent to 27dB. The 22µF electrolytic capacitor in series with the 100Ω resistor sets the lower frequency response to 72Hz. The output is taken from across the 2.2kΩ collector load resistor of Q2 via a 10µF electrolytic capacitor. Power is supplied from any DC source of 6-12V. At 12V the current drain of the preamp is 3mA, dropping to 2mA at 9V. Optional electret microphone We mentioned at the start that the preamp has provision for an electret microphone. This is simply the 10kΩ resistor connect­ing the input side of the 0.1µF capacitor to the decoupled supply rail. This resistor provides bias current to the electret micro­phone’s internal FET. To use the electret all July 1994  43 2.2k 10 16VW 10k Q1 BC548 B 0.1 INPUT Q2 100 BC558 E 16VW B 22k 100k C GND 0V C E 2.2k 150k Fig.1: this is the circuit of the PreChamp. Just two transistors are employed & it can run from a 6-12V supply. Current drain at 12V is 3mA. The 10kΩ resistor at the input makes provision for an electret mic capsule. If the electret is not used, the 10kΩ resistor should be omitted. +6-12V 10 16VW .0015 OUTPUT 100k GND B 100  E C VIEWED FROM BELOW 22 16VW 2.2k Construction All of the components for the PreChamp are installed on a PC board which measures 46 x 36mm and is coded 01107941. Before you begin any soldering, check the board carefully for any shorts or breaks in the copper tracks. These should be repaired with a small artwork knife or a touch of the soldering iron where appropriate. That done, you can start by installing the resistors, fol­lowed by the capacitors. Make sure that you install the electro­ lytic capacitors correctly otherwise reverse polarity will damage them – use the overlay wiring diagram to be sure. Next, install the two transistors and finally the six PC stakes. As noted above, if you are not using the electret mic capsule, then don’t install the 10kΩ resistor at the input. Testing You can test the circuit by just connecting it up to the CHAMP amplifier Q2 GND Q1 .0015 100 2.2k 100k INPUT OUTPUT 2.2k 150k 100uF +6-12V 10uF 10uF 0.1 you need do is to connect it between the INPUT and GND. If you are not going to use the preamplifier with an electret microphone, the 10kΩ resistor must be omitted from the circuit. 10k 100k 2.2k 22k LOW-COST PREAMP FOR THE "CHAMP" 22uF GND 0V Fig.2: the PreChamp board is easy to assemble. If you want to use an electret mic, install the 10kΩ resistor shown dotted & connect the mic between the INPUT and GND terminals. PARTS LIST 1 PC board, 01107941, 46 x 36mm 4 PC stakes Semiconductors 1 BC548 NPN transistor 1 BC558 PNP transistor Capacitors 1 100µF 16VW electrolytic capacitor 1 22µF 16VW electrolytic capacitor 2 10µF 16VW electrolytic capacitors 1 0.1µF MKT polyester 1 1500pF MKT polyester Resistors (0.25W, 5%) 1 150kΩ 1 10kΩ 2 100kΩ 3 2.2kΩ 1 22kΩ 1 100Ω Miscellaneous Solder, shielded audio cable etc. anti-clockwise. When you do this, you should hear a “blurt” from the speaker. If you don’t, check that all the connections between the two PC boards are correct and compare the PreChamp board with the overlay wiring diagram (Fig.2) to double-check for any possible mistakes. You should also inspect the back of the PC board for missed solder joints. Bench amplifier Fig.3: here is the full size PC artwork for the PreChamp board. and doing the “blurt” test. This consists of simply touching the two input PC stakes with your finger with the input pot of the CHAMP wound fully Because of their size, you could quite easily mount the two PC boards and the battery inside a small zippy box and use the completed unit as a bench amplifier for other projects. Be sure to use shielded audio cable for the input signal wiring and for the signal wiring between the PreChamp SC and CHAMP. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 2 1 1 3 1 44  Silicon Chip Value 150kΩ 100kΩ 22kΩ 10kΩ 2.2kΩ 100Ω 4-Band Code (1%) brown green yellow brown brown black yellow brown red red orange brown brown black orange brown red red red brown brown black brown brown 5-Band Code (1%) brown green black orange brown brown black black orange brown red red black red brown brown black black red brown red red black brown brown brown black black black brown 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 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 July 1994  53 Steam Train Whistle & Diesel Horn Simulator There’s nothing like a steam whistle to add realism to your model railroad layout. This unit sounds just like the real thing & can be easily modified to provide a diesel horn sound. By JOHN CLARKE Mention steam trains to those who are old enough and it brings back memories of “the good old days”, the steam engine and, of course, the steam whistle. Many would wish that the days of steam were still here. However, it is perhaps fortunate that they are not. While it is now a novelty to ride in a restored steam train, it does not take long to realise that they are extremely noisy and dirty. In their favour though, steam trains do have a character which is distinctive and exciting. Part of the unique character of 54  Silicon Chip the steam engine is the whistle. The sounds from a steam whistle are unmistakable. Its well-know trademarks include the rise and fall in pitch as the train approaches and then passes the observer; the dying sound of the whistle as the train blasts into a tunnel; the warning whistle as the train is about to leave the station; and the variations in intensity heard when the train is traversing hilly country. In Australia, steam train whistles are more sonorous than their British counterparts and this is because they actually consist of several whistles, each producing a different note. The result is a distinctive sound that remains embedded in the memory of those who love steam. Although the steam whistle does create much nostalgia, its origins are rather prosaic. Because there is steam in the boiler, some of it can drive the whistle and this is done by pulling a cord which opens a steam valve. Initially, as the steam pressure builds up, the sound level rises until it reaches its maximum intensity. When the steam valve is subsequently closed, the sound level drops off abruptly. Note that, because the whistle is driven by steam, there is a significant amount of white noise evident in the steam whistle sound. The SILICON CHIP Steam Whistle/ Diesel Horn simulates all the requisite notes, noise and level changes to produce a very re­alistic effect. It uses just two ICs and the circuitry all fits on a small PC board. This PC board carries two pushbutton switches, labelled FAST and SLOW, to produce two different steam train whistle sounds. Pressing the SLOW switch simulates the effect of the engineer opening the valve slowly, while the FAST switch simulates the sound when the cord is pulled quickly. Alternatively, the whistle sound can be triggered using remote switches or by using the Level Crossing Detector described in the March 1994 issue. In this way, the whistle can be made to sound automatically as the train goes through a level crossing. Fig.1: block diagram of the Steam Train Whistle. The sound is produced by mixing the outputs of three oscillators & a white noise source together. OSCILLATOR 1 740Hz IC1a OSCILLATOR 2 525Hz IC1b ENVELOPE SHAPER MIXER OSCILLATOR 3 420Hz SLOW S1 IC1c Block diagram AMPLIFIER Q2 VOLUME VR1 IC2 FAST S2 8 WHITE NOISE GENERATOR Fig.1 shows the block diagram of the steam whistle. As shown, the whistle sound is made up by mixing the outputs from three oscillators and a white noise source. The re­sulting output from the mixer is then fed to an envelope shaper and finally to an audio amplifier via volume control VR1. The three oscillators, IC1a-IC1c, operate at 740Hz, 525Hz and 420Hz respectively. These frequency values were obtained from the NSW State Rail Archives and match those used in real steam locomotives. Note that the oscillators do not produce pure sine waves but include second harmonics extending up to 1480Hz. Q1,IC1d Typical Australian locomotives use a 5-chime whistle but we have elected to use only three oscillators. The reason we can get away with this is that some of the chime frequencies are very closely related (ie, second harmonic) and the oscillators we use are already rich in second harmonics. The envelope shaper is triggered using either S1 or S2 to provide the slow or fast rise time respectively. S1 gradually increases the volume of the mixer output over about 200ms, while S2 provides a virtually instantaneous response. For diesel horn sounds, the oscillator frequencies are altered and the Fig.2 (below): the final circuit uses op amps IC1a-IC1c as the oscillator stages, while Q1 forms the white noise source. The outputs from these stages are mixed together & fed via envelope shaper Q2 to audio output stage IC2. +12V 1.8k 100k 1.8k 100k 100k Q1 120k BC548 C 1.8k 100k 100k 100k 10k 12 100k 10 14 IC1a LM324 13 100k IC1b 9 22k .039 100k +12V 0V .056 100k 100k 6 7 IC1c +6V 27k .056 525Hz OSCILLATOR 100k 100k .033 3 10k 2 420Hz OSCILLATOR 1 IC1d 11 10 16VW 10k 4 2.2M NOISE GENERATOR 47k 10  +12V 33k D1 1N4148 1000 16VW 100k 15k 390  FAST S2 C VOLUME VR1 50k E B 22 16VW 3 2 6 IC2 LM386 4 2.2 16VW B .047 Q2 BC548 SLOW S1 14 22k 740Hz OSCILLATOR B 5 0.1 0.1 1k 5 10 16VW E C VIEWED FROM BELOW 22  10  8 .047 STEAM WHISTLE/DIESEL HORN SIMULATOR July 1994  55 EXT SWITCH C3 .056 10uF 0.1 100k 1 .047 47k IC1 LM324 10uF D1 VR1 IC2 LM386 .047 1000uF 100k 0V C1 .039 10  S2 10  1k Q2 2.2uF 390  +12V 1.8k R1 22k 100k 100k 100k 100k 100k 100k R2 22k 1.8k C2 .056 TO SPEAKER 100k 1 100k 22  S1 33k Q1 15k 120k 10k 10k 10k 2.2M 100k 100k 100k 100k R3 27k 1.8k .033 22uF EXT SWITCH Fig.3: the two pushbutton switches are shown here mounted on the board but may be mounted at some remote location if desired (eg, on the control panel of your layout). Alternatively, the circuit can be triggered using the Level Crossing Detector described in the March 1994 issue, or triggered using the optional reed switch/ monostable circuit shown in Fig.6. Fig.4: check your etched board against this full-size artwork before installing any of the parts. noise generator output is disconnected from the mixer. Again, typical Australian diesel horns have five chimes but only three are used here for the reasons discussed above. Circuit details Refer now to Fig.2 for the full circuit details. The three oscillators are Schmitt trigger types which use three of the four op amps in a quad LM324 package. The remaining op amp (IC1d) is used to amplify the white noise generated by transistor Q1. Transistor Q2 and its associated components make up the envelope shaper, while IC2 forms the audio amplifier. Since the Schmitt trigger oscillators all operate in iden­tical fashion, we’ll just consider IC1a. As shown, its non-inverting input (pin 12) is biased by two 100kΩ resistors across the 12V supply, while a 100kΩ feedback resistor is connected between pin 12 and TABLE 1 C1 C2 C3 IC1a IC1b IC1c Steam .039uF .056uF .056uF 740Hz 525Hz 420Hz 2-Car Diesel .047uF .056uF .056uF 600Hz 520Hz 420Hz 40-43, 4401-4440 Diesel 0.1uF 0.12uF .056uF 277Hz 329Hz 440Hz 422, 442, 47, 73 48126 Diesel .056uF 0.12uF .056uF 548Hz 322Hz 429Hz 56  Silicon Chip the output at pin 14. A 1.8kΩ pull-up resistor is also connected to the output and this ensures that pin 14 goes fully high (to produce a more symmetrical waveform). The oscillator action is as follows. At switch on, capaci­ tor C1 at the inverting input (pin 13) of IC1a is discharged and so the pin 14 output is high and pin 12 is at +8V. The capacitor now begins to charge via resistor R1 (22kΩ) until the voltage on pin 13 reaches 8V (the upper threshold of pin 12). At this point, pin 14 goes low and the 100kΩ feedback resistor pulls pin 12 to +4V. C1 now discharges via R1 and pin 14 until it reaches the lower threshold voltage (+4V). When this voltage is reached, pin 14 switches high again and so the process is repeated indefinite­ly while ever power is applied. The frequency of oscillation (740Hz) is determined by the values of R1 & C1. Oscillators IC1b & IC1c operate in exactly the same manner except that the frequencies are different because of the differ­ing RC values at their inverting inputs. The resulting triangle wave capacitor voltages from the three oscillator stages are mixed together via 100kΩ resistors and fed to the collector of transistor Q2. This waveshape is used instead of the square wave from the op amp output since it has a high second harmonic content, which is what we want for the whistle. The noise source is obtained by reverse connecting tran­sistor Q1, so that its base-emitter junction breaks down. This breakdown occurs at about 5V and the 120kΩ resistor limits the current into Q1 to prevent damage to the transistor. The resulting output at the collector is rich in noise and is AC-coupled into pin 3 of non-inverting amplifier stage IC1d. IC1d operates with a gain of 221, as set by the 2.2MΩ feed­back resistor and the 10kΩ resistor at pin 2. The amplifier is DC biased to 1/2Vcc via the two 10kΩ resistors across the supply and the 100kΩ resistor to pin 3. A 10µF capacitor decouples the half-supply rail. The amplified noise output appears at pin 1 of IC1d and is mixed with the oscillator signals at the collector of Q2 via a 47kΩ resistor. Envelope shaper As previously mentioned, Q2 forms the envelope shaper. Normally, Q2 is biased on via D1 which taps a voltage divider consisting of 33kΩ and 15kΩ resistors. The 1kΩ emitter resistor stabilises the bias, while the 2.2µF capacitor shunts signal to ground. Since Q2 is normally turned on, all of the signal at the collector is shunted to ground and no sound is heard from the loudspeaker. However, if switch S1 is pressed, the 22µF capacitor on Q2’s base slowly discharges via the associated 100kΩ resistor and so Q2 gradually turns off. As a result, the signal on Q2’s collector gradually increases to a maximum to produce a steam whistle sound with a slow attack time (about 200ms). When S1 is subsequently released, the 22µF capacitor quick­ ly charges via the 33kΩ/15kΩ voltage divider and diode D1. Q2 now turns on again and shunts the signal to ground, thus shutting off the steam whistle sound. The FAST switch (S2) works in virtually identical fashion to S1 except the it shunts Q2’s base voltage to ground almost immediately via the associated 390Ω resistor. This produces a whistle with a fast attack time (ie, the whistle rises to maximum volume almost immediately when the switch is pressed). The signal at Q2’s collector is AC-coupled to volume con­trol VR1 and then fed into pin 3 of IC2, an LM386 audio amplifi­er. This IC has an output power capability of about 325mW and a gain of 20 when connected as shown in Fig.2. Its output appears at pin 5 and drives an 8-ohm loudspeaker via a 10µF capacitor and a 22Ω current limiting resistor. In addition, a Zobel network comprising a series 10Ω resistor and .047µF capacitor is connect­ed PARTS LIST 1 PC board, code 09305941, 142 x 61mm 2 2-way PC-mount screw terminal blocks 2 PC-mount pushbutton click action switches (S1,S2) 4 PC stakes 1 20mm length of 0.8mm tinned copper wire (for link) 1 50kΩ horizontal trimpot (VR1) Semiconductors 1 LM324 quad op amp (IC1) 1 LM386 audio amplifier (IC2) 2 BC548 transistors (Q1,Q2) 1 1N4148, 1N914 diode (D1) Capacitors 1 1000µF 16VW PC electrolytic 1 22µF 16VW PC electrolytic 2 10µF 16VW PC electrolytic 1 2.2µF 16VW PC electrolytic 1 0.1µF MKT polyester 2 .056µF 5% MKT polyester 2 .047µF MKT polyester 1 .039µF 5% MKT polyester 1 .033µF MKT polyester Resistors (0.25W, 1%) 1 2.2MΩ 1 15kΩ 1 120kΩ 3 10kΩ 14 100kΩ 3 1.8kΩ 1 47kΩ 1 390Ω 1 33kΩ 1 22Ω 1 27kΩ 2 10Ω 2 22kΩ Diesel horn parts Note: add 1 x 0.47µF, 1 x 0.1µF & 1 x 0.12µF 5% MKT polyester capacitors to include the diesel horn sounds listed in Table 1. RESISTOR COLOUR CODES ❏ No. ❏   1 ❏   1 ❏ 14 ❏  1 ❏   1 ❏   1 ❏   2 ❏   1 ❏   3 ❏   3 ❏   1 ❏   1 ❏   2 Value 2.2MΩ 120kΩ 100kΩ 47kΩ 33kΩ 27kΩ 22kΩ 15kΩ 10kΩ 1.8kΩ 390Ω 22Ω 10Ω 4-Band Code (1%) red red green brown brown red yellow brown brown black yellow brown yellow violet orange brown orange orange orange brown red violet orange brown red red orange brown brown green orange brown brown black orange brown brown grey red brown orange white brown brown red red black brown brown black black brown 5-Band Code (1%) red red black yellow brown brown red black orange brown brown black black orange brown yellow violet black red brown orange orange black red brown red violet black red brown red red black red brown brown green black red brown brown black black red brown brown grey black brown brown orange white black black brown red red black gold brown brown black black gold brown July 1994  57 Make sure that all polarised parts are correctly oriented when installing them on the PC board & don’t forget the wire link. A small 8-ohm loudspeaker hidden underneath the layout can be used to provide the sound. This should be mounted near a level crossing or some other appropriate place. across the output to maintain high frequency stability. Power for the circuit can be derived from a 12V DC plugpack supply or from the train controller itself. A 10Ω resistor and a 1000µF capacitor provide supply decoupling and filtering. followed by the diode and the capacitors. Note that the values shown for C1, C2 & C3 are for the steam whistle simulation. If you want a diesel horn sound, these capacitors will have to be selected from Table 1. There are three different diesel horn sounds to Construction choose from, to suit your locomotive. The Steam Train Whistle circuit is In addition, the noise generator must built on a PC board coded 09305941 be disabled by omitting the 47k# mixand measuring 142 x 61mm. Fig.3 ing resistor at pin 1 of IC1 Fig.3 shows switches S1 and S2 shows the parts layout on the board. Begin construction by inserting the mounted on the board and you can PC stakes (for the external switches) do the same if you wish. In most apand the wire link. This done, install plications, however, the switches will the ICs, making sure that they are ori- be mounted separately from the board (eg, on the control panel) or some other ented correctly. The resistors are installed next, triggering device will be used. The main point to watch here +12V is that the switches are cor­rectly D1 oriented (ie, the flat section on 33k 1N4148 each switch body goes towards the adjacent transistor). If you orient 5 6 the switches incorrectly, the whis100k Q1 IC4c tle will sound permanently when BC548 C 10k B 4 power is applied. 390  15k Finally, install the transistors E (Q1 & Q2), VR1 and the PC-mount FAST S2 screw terminals. The unit should LEVEL CROSSING STEAM now be carefully checked to DETECTOR WHISTLE ensure that all parts are in their Fig.5: this diagram shows how the Level correct locations and that all poCrossing Detector can be used to trigger larised parts are correctly oriented. the Steam Whistle circuit. The output The circuit is designed to be from the Level Crossing Detector simply powered from a regulated +12V takes the place of switch S1 (or switch S2 supply. Our Railpower Walk­ if you want a fast attack time). 58  Silicon Chip around Throttle for Model Railroads (April 1988 and May 1988) and the Infrared Remote Control for Model Railroads (April, May and June 1992) have suit­able supply rails or, as previously mentioned, you can use a 12V DC plugpack supply. To test the unit, set VR1 to mid-position, connect the loudspeaker and apply power. The steam whistle (or diesel horn) should now sound when either S1 or S2 is pressed. Adjust VR1 so that the unit produces the desired volume. A basic installation would simply involve mounting the switches in a convenient position on the main control panel of your layout. Leads could then be run back to the PC board, which could be hidden under the layout along with the loudspeaker. The best place to mount the loudspeaker would probably be near a level crossing or near a station or tunnel. If you do elect to use this approach, make sure that the switch wiring is correct (see previous warning). A more complex arrangement would involve using the Level Crossing Detector (SILICON CHIP, March 1994) to trigger the unit. All you have to do is connect the output from the Level Crossing Detec­ tor across one set of switch terminals – see Fig.5. That way, the steam whistle will automatically sound each time the train goes through the level crossing. The whistle will sound for as long as it takes the train to pass through the section between the detec­tion magnets. A third option is to trigger the steam A Simple Timer Circuit For The Steam Train Whistle +12V This simple interface 10 circuit will enable you to 16VW 10k Q1 10k BC548 trigger the Steam Train 4 8 C OUTPUT TO 7 3 10k B D1 Whistle from either the D1 STEAMWHISTLE TIME 10k 10k 10k 10k 1N4148 1N4148 SWITCH ADJUST IC1 Level Crossing Detector TO E VR1 7555 100  LEVEL CROSSING 5 6 or from a separate reed 100k DETECTOR OR .01 REED SWITCH switch, and have it sound 2 1 0.1 for a preset time (adjustable 47 from 0.5 to 5.5 seconds). N B INPUT The circuit is simply a E C S mono­stable which, when VIEWED FROM REED triggered, provides a low BELOW SWITCH STEAM WHISTLE TIMER output signal of between 0.5 seconds and 5.5 secFig.6: the circuit for the Steam Whistle Timer uses monostable IC1 to drive onds, depending on the switching transistor Q1. VR1 adjusts the period. setting of trimpot VR1. This low output can be used to capacitor decouples the supply so that the magnet will close the simulate the closing of a switch. for IC1, while the 0.1µF capacitor contacts. Fig.6 shows the circuit details. at pin 5 decouples the internal IC1 is a 7555 timer which is con66% resistive divider across the PARTS LIST nected as a monostable. Initially, its supply. 1 PC board, code 05207941, pin 2 input is high, the pin 3 outConstruction of the circuit in62 x 39mm put is low and transistor Q1 is off. volves assembling the parts onto 1 7555, LMC555CN, TLC555 When a low going signal is applied a PC board coded 05207941 (62 x CMOS timer (IC1) to the input, pin 2 is pulled low via 39mm) – see Fig.7. Follow the over1 BC548 NPN transistor (Q1) a .01µF capacitor. As a result, pin lay diagram when installing the 1 1N4148, 1N914 diode (D1) 3 now goes high and turns on Q1 parts on the board and make sure 1 100kΩ horizontal trimpot which in turn triggers the Steam that D1, IC1 and the electrolytic 4 10kΩ 0.25W 1% resistors Train Whistle. capacitors are oriented correctly. 1 100Ω 0.25W 1% resistor The pin 3 output remains high The circuit can be tested by ap6 PC stakes or 1 x 4-way & 1 until the 47µF capacitor at pins 6 plying power and shorting the inx 2-way PC-mount screw and 7 charges to 66% of the supply put terminals to trigger IC1. When terminals voltage. This period is set by the this is done, the steam whistle value of VR1 and its series 10kΩ should sound. Capacitors resistor. In practice, VR1 is adjustThe reed switch can be laid 1 47µF 16VW PC electrolytic ed to set the required duration of inside the track and triggered by 1 10µF 16VW PC electrolytic the whistle. a permanent magnet in a similar 1 0.1µF MKT polyester Power for the circuit is derived manner to the Level Crossing De1 .01µF MKT polyester from the +12V rail used to power tector. Note that the reed switch the Steam Train Whistle. A 10µF will need to be oriented correctly Fig.7: the parts layout for the timer circuit. whistle using the monostable circuit shown in Fig.6. This option allows you to set the duration of the whistle to between 0.5 and 5.5 seconds and Fig.8: the full-size PC board pattern. will give a more realistic effect. Naturally, the loudspeaker should be mounted near to where the train will be when the whistle blows, to ensure maximum realism. If you want the whistle to sound at different locations on the track, just add additional SC circuits. July 1994  59 MISCELLANEOUS ITEMS COMPONENTS AND KITS WE HAVE LARGE QUANTITIES OF MANY OF THE FOLLOWING AND CAN OFFER HIGHER QUANTITY DISCOUNTS. 3CD! 5mm LED ................................................................................................$1.50 Blue LED ..........................................................................................................$2 IEC EXTENSION LEADS: with moulded IEC plug & socket, 2 metres long .....$5 HIGH INTENSITY LED’s: 550-1000mCD output at 20 mA, 5mm dia. 10 for ....$4 IR DIODES: 16mW O/P <at> 100mA, 880 or 940nM, 10 for ...............................$5 IR DETECTOR: Very fast rectangular PIN diode 10 for ....................................$10 TRIACS: 60A - 600V stud mounted THOMPSON type TGAL606 ....................$8 PIR DETECTOR: Dual element detector plus fresnel lens only, typical movement detector cct. supplied ......................................................................$10 ULTRASONIC TRANSDUCERS: Murata (Japanese), 40kHz Tx - Rx pair .......$3 MICROPHONE INSERTS: Standard Electret Omnidirectional insert ..........................................................$1 Miniature Electret Omnidirectional insert ..........................................................$1.80 Unidirectional electret insert .............................................................................$6 Unidirectional Dynamic insert ...........................................................................$7 HIGH VOLTAGE DIODES: 8kV 3mA ...........................................................................................................$1.20 10kV 20mA .......................................................................................................$1.80 HIGH VOLTAGE DISC CERAMICS: 0.01uF 3kV .......................................................................................................$1.20 0.01uF 5kV .......................................................................................................$1.80 1000pF 15KV ...................................................................................................$5 470uF 380V electro’s as used in TVs (rectified mains) ....................................$3.50 ELECTRIC FENCE KIT: PCB and comonents .................................................$40 GARAGE - DOOR - GATE REMOTE CONTROL KIT: Tx $18; Rx ...................$79 LASER BEAM COMMUNICATOR KIT: Tx, Rx, plus IR Laser ..........................$55 PLASMA BALL KIT: PCB and comonents kit, needs any bulb .........................$25 ENCODER - DECODER ICs: AX527’s, AX528’s, AX526’s. All one price .........$4Ea. OP27: Super operational amplifier IC at below 1/2 price ..................................$4Ea. LENSES A pair of lens assemblies that were removed from brand new laser printers. They contain a total of 4 lenses which by differ­ent combinations/placement in a laser beam can diverge, collimate, make a small line, make an elipse, etc. $8 for the two assemblies. ITEM No. 0236 POLYGON SCANNERS Precision motor with 8-sided mirror, plus a matching PCB driver assembly. Brand new matching components, out of laser printers. Will deflect a laser beam and generate a line. Needs a clock pulse and DC supply to operate: Simple information sup­plied. ITEM No. 0237 $25 HIGH POWER LED IR ILLUMINATOR Available late July 94. This kit includes two PCBs, all on-board components, plus casing. Switched mode power supply plus 60 high intensity 880nm IR (invisible) LEDs. Variable output power, 6-20VDC input, suitable for illuminating IR responsive CCD cam­eras, IR night 60  Silicon Chip viewers, etc. Professional perfomance at a frac­tion of the price of the commercial product. COMPLETE KIT PRICE: $49 SPECIALS BY FAX IF YOU HAVE A “POLLING” FUNCTION ON YOUR FAX MACHINE, DIAL OUR FAX NUMBER AND PRESS THE “POLLING” BUTTON. THE PAGES OF INFORMATION THAT YOU WILL OBTAIN WILL BE PRECEDED BY THE CURRENT SPECIALS AND NEW ADDITIONS, FOLLOWED BY THE REGULAR ITEM KIT LISTING. THE PRECEDING PAGES WILL BE UPDATED BY AT LEAST THE 20th. DAY OF EACH MONTH. USED LCD DISPLAYS Backlit Hitachi LM565 dot matrix displays (display area 125 x 65mm). Supplied with part of a PCB assembly that contains the backlighting inverter and a complete PCB assembly that amongst other things contains the HD61830B controller IC. We only supply information on getting the inverter functional. Used but func­tional units out of equipment that is about 2-3 years old. ALL THE MENTIONED ITEMS FOR A TOTAL PRICE OF: $28 ITEM No. 0238 ITEMS OUT OF LATE MODEL MEDICAL EQUIPMENT Small precision (ball bearing) WST GERMAN made gas/air pumps (3-12V) $12. Small electrically operated 12V gas solenoids $8. Isolated +/-15V 500mA output switched mode regulator blocks (75 x 65 x 20mm) with 9-18V unregulated input $10. Small electrically operated 12V gas solenoids $8. 5V 4A output switched mode regula­tor blocks( 85 x 65 x 20mm) with 9-18V unregulated input $10. WEST GERMAN made OXYGEN SENSOR cartridge with four connections (no information) $10. US made gas analyzer assembly with IR source, spinning filters driven by a precision SWISS made motor etc (no information) $40. ITEM NO’s 0239 + DESCRIPTION. PCB WITH AD7581LN IC This PCB was removed from used but working late model equip­ment. Amongst many other components, the PCB contains a MAXIM AD7581LN IC: 8-bit, 8-channel memory buffered data acquisition system designed to interface with microprocessors. This high perfomance CMOS IC contains an 8-bit successive approximation A-D converter, 8-channel multiplexer, 8 x 8 dual port RAM, address latches and microprocessor compatible control logic. The complete PCB assembly is priced at a small fraction of the price of the AD7581LN IC: $29 ITEM No. 0240 30-second exit delay, 7-second entry delay, flashing LED - intrusion indicator provided, flashes vehicle indicators when alarm is sounding, extra negative output to power second siren or pager, colour coded wiring siren provid­ed, powerful 40 watt 125dB siren which employs a dynamic speaker. A sound that makes most car alarm sirens sound like toys! Priced at about 1/3 of their original price. ITEM No. 0229 $40 The entry and exit times are easy to change and the unit is easy to modify for UHF remote or hidden magnetic reed switch ON/OFF control, as the main control IC has a toggle input. Some information included. EHT POWER SUPPLY These EHT power supplies were designed to deliver -600V, -7.5kV and +7kV in a laser printer, whilst powered from a 24V 800mA DC supply. They were removed from brand new equipment and are contained in a plastic case with overall dimensions of 100 x 85 x 80mm. The electronics inside these supplies actually con­tains three separate supplies on two seperate PCB’s. The output connections are easy to access and a prewired input power connec­tor is also provided. Connecting up information is provided. Great for experienced experimenters. BARGAIN PRICED. ITEM No. 0222NS. $16 1.5V-9V CONVERTER Use inexpensive 1.5V batteries and this simple (three com­ponents) swiched mode inverter to power equipment that normally employs 9V batteries. We supply a set of the essential components only: TL496 IC/socket, prewound inductor, a capacitor, and the instructions. The PCB is not supplied but a simple PCB design is included. The components can be easily wired without the PCB. Cat No. GK 112A. $5 for the set or 3 sets for $12 SINGLE CHANNEL UHF REMOTE SPECIAL S.C. Dec. 1992. Use it to switch your car alarm, central locking, activate a door opener, etc. * Up to 100 metre range * Range can be reduced if desired * Low power consumption * Has separate switch and indicator relays * More than 1/2 million code combinations * The transmitter (Tx) is SAW resonator locked and the receiver (Rx) features a preassembled and tuned front end. SPECIAL reduced July - Sept. prices! Cat No. GK 141. $45 for one transmitter & one receiver. Extra transmitters $15Ea. CAR ALARM We have purchsed a good but limited quantity of this well-known brand Australian made car alarm. It has been made obsolete because it doesn’t feature UHF remote control. But look at the features! Voltage drop detection (wired directly or internal), pin switch detection for bonnet/ boot, piezoelectric vibration detector, optional passive arming via ignition switch, ignition disable via master switch if passive arming is not used, may be wired to existing door pin switches to act as a switch – sensing last door arming alarm, SWITCHED MODE POWER SUPPLIES WITH ISOLATION TRANSFORMER Modern low profile 240V - 30V AC transformer (125 x 80 x 40mm, 1.8kg), plus a totally self-contained matching switched mode regulated power supply (165 x 55 x 90mm, 0.4kg). Intercon­necting leads and plugs/sockets and information is provided. Regulated DC outputs: +24V/2A, +12V/0.5A, +5V/0.5A, and -12V/50mA. We do not have the full specifications on these two matching units that were removed from BRAND NEW laser print- ers, but have tested the transformer with a 100W load. We have a LIMITED stock and the price is below the value of the transformer itself: $28 For the 240V - 30V transformer, the matching switched mode supply, the interconnecting leads with matching plugs and sockets and information. ITEM No. 0215NS. STEPPER MOTOR DRIVER KIT SPECIAL This kit will drive two stepper motors: 4, 5, 6 or 8-wire stepper motors from an IBM computer parallel port. A separate power supply is required to run the motors. A detailed manual on the COMPUTER CONTROL OF MOTORS plus circuit diagrams/descriptions are provided. Note that no stepper motors are provided with this kit. We also provide the necessary software on a 5.25" disc. Great “low cost” educational kit: $35 THE SPECIAL??: We will include one of our $14 (5V, 6-wire, 7.5 degree) stepper motors “FREE” with this kit! MASTHEAD AMPLIFIER KIT Based on an IC with 20dB of gain, a bandwidth of 2GHz, and a noise figure of 2.8dB, this amplifier kit outperforms most other similar ICs and is priced at a fraction of their cost. The cost of the complete kit of parts for the masthead amplifier PCB and components and the power and signal combiner PCB and components is AN INCREDIBLE: $18 Cat. No. GK136 For more information, see a novel and extremely popular antenna design which employs this amplifier: MIRACLE TV ANTENNA - E.A. May 1992. Box, balun and wire for this antenna: $5 extra. DC FANS These IC controlled 24V 110mA 3" ball bearing Japanese made DC fans work well from 5-24V. They also move a good amount of air whilst drawing 60mA from a 12V battery. ITEM No. 0217NS. $8 button. Up to 125V AC or DC operation, mounting screws and spade connectors provided. Approved Hosiden brand (JAPANESE), removed from new equipment. Inexpensive additional protection on all your supplies. ITEM No. 0220NS. $2 MAINS FILTERS 240V 8A made by Tokin in Japan. Removed from new equipment, are in a cylindrical metal case, mounting screw/ nut and spade connectors provided. Diameter 44mm, 40mm long. Internal circuit includes 2 x 1.5mH inductors, 2 x 0.47uF capacitors, 2 x 4700pF capacitors and 1 x 470k resistor. Surge suppressing varistor provided with each filter. Good, but LIMITED STOCK.ITEM No. 0221NS. $9 IR LASER DIODE SURPLUS SPECIAL BRAND NEW 780nm LASER DIODES (barely visible), mounted in a professional adjustable collimator-heatsink assembly. Each of these assemblies is supplied with a CONSTANT CURRENT DRIVER kit and a suitable PIN DIODE that can serve as a detector, plus some INSTRUCTIONS. Suitable for medical use, perimeter protection, data transmission, IR illumination, etc. Exerimenters’ delight at a SPECIAL PRICE. ITEM No. 0223NS. $28 3mW VISIBLE LASER DIODE SPECIAL We have bought a surplus quantity of some BRAND NEW Toshiba TOLD9200 3mW-670nm visible laser diodes and are offering a kit that includes one of these diodes, plus an APC driver kit, plus a collimating lens - heatsink assembly. That’s a complete 3mW collimated laser diode kit for a RIDICULOUS TOTAL PRICE OF: $45 ITEM No. 0164B MAINS CONTACTOR RELAY Approved mains contactor that has a 24V 250-ohm relay coil and four seperate SPST switch outputs. Two of the output contacts are rated at 20A and the other two at 10A. Removed from new equipment, Omron brand, connection is by spade connectors (pro­vided), mounting bracket provided, relay body dimensions: 60 x 60 x 35mm. ITEM No. 0219NS. $8 BIGGER LASER We have a good but LIMITED QUANTITY of some brand new red 3mW+ tubes and some “as new” red 6mW+ laser heads that were removed from new equipment. Tube dimensions (3mW+): 35mm diameter by 190mm long, Head dimensions: 45mm diameter by 380mm long. With each of the lasers we will include our 12V Universal Laser Power Supply. BARGAIN AT: $110 - 3mW + tube/supply. ITEM No. 0225A. $170 - 6mW + head/supply. ITEM No. 0225B. CIRCUIT BREAKERS Small chassis mount 3.15A circuit breakers (30 x 18 x 10mm) with reset push 12V 2.5-WATT SOLAR PANELS These US-made amorphous glass solar panels only need termi­nating and weath- er 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. BARGAIN PRICED: $25 Ea. or 4 for $80. ITEM No. 0226. Each panel is provided with a sheet of backing glass, termi­natig clips, an isolating diode, and the instructions. Higher quantity discounts apply on this item: Ring. A very professional and efficient switching solar regulator to suit 12-24V Panels/Batteries (16A capacity) will be available in late July: $27 FOR THE COMPLETE KIT! BUDGET LASER A very economical laser tube/12V laser supply combination. The 12V swiched mode power supply kit provides the tube with a constant current and will work from 10-15V. Draws 0.5A at 12V - very efficient! The tube supplied is used, tested and guaranteed, 632.8nm (red), power output 0.5-1mW. The tube/power supply kit combination for a total price of only: $49 ITEM No. 0233 CCD CAMERA 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 0.1 Lux and it is IR responsive. Can be used in total darkness with infrared illumination. Overall dimensions of camera are 24 x 46 x 70mm and it weighs less than 40 grams! Can be connected to any standard monitor or the video input on a video cassette recorder. $239. ITEM NO. 0227 FIBRE OPTIC TUBES These US made tubes are used but in excellent condition. Have 25/40mm diameter fibre optically couled input and output windows. The 25mm tube has an overall diameter of 57mm and and is 60mm long; the 40mm tube has an overall diameter of 80mm and is 92mm long. The gain of these is such that they would produce a good image in aproximately 1/2 moon illumination, when used with a suitable “fast” lens, but they can also be IR assisted to see in total darkness. The superior resolution of these tubes would make them suitable for low light video preamplifiers, wild life observation and astronomical use. Each of the tubes is suplied with a 9V EHT power supply kit. INCREDIBLE PRICES: $120 for 25mm tube plus supply. ITEM No. 0230A. $190 for 40mm tube plus supply. ITEM No. 0230B. Three of these tubes can be cascaded to make a very high gain image intensifier! We should have a kit and instructions available to make these. Approximately $280 for 25mm kit and $380 the three stage kit. SIMPLE KITS for these sub-starlight resposive tubes are available now! Ring. IR “TANK SET” ON SPECIAL is a set of components that can be used to make a a very responsive infrared night viewer. The match­ing lens tube and eyepiece sets were removed from working military quality tank viewers. We also supply a very small EHT power supply kit that enables the tube to be operated from a small 9V battery. The tube employed is probably the most sensitive IR responsive tube we have ever supplied. The resultant viewer requires low level IR il­lumination. Basic instructions provided. ITEM No. 0228UTS. $120 for the tube, lens, eyepiece and the power supply kit. When ordering specify preference for a wide angle or a telescopic objective lens. 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 12V 4.5A Peltier effect semiconductor, two thermal cut-out switches, and a 12V DC fan for a total price of: $45 ITEM No. 0231 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. OATLEY ELECTRONICS PO Box 89, Oatley, NSW 2223 Phone (02) 579 4985. Fax (02) 570 7910 Major cards accepted with phone & fax orders. P & P for most mixed orders: Aust. $6; NZ (airmail) $10. July 1994  61 Build this portable 6V SLA battery charger If you own one of the new 6V SLA batteries from Jaycar, this simple charger will keep them in top condition. It uses only a single IC and charges the battery to a fixed voltage of 6.9V at currents up to 500mA. By BRIAN DOVE Keeping batteries in top condition is not as easy as you may think. Many of the more popular battery chargers simply thump the battery with a rough DC current and hope for the best. Anoth­er problem is that very few chargers cater for the 6V variety. Whether you’re operating a video camera, a security torch or other equipment requiring a 6V supply, a 6V SLA battery has many advantages over the more traditional nicads. These include less critical charging parameters and 62  Silicon Chip much greater power capaci­ty. This Portable 6V SLA battery charger is specifically designed to mate with Jaycar’s range of 6V SLA batteries. What’s more, it uses only a handful of components and can be powered from your car battery or any 12V DC source. In operation, the charger will initially supply over 300mA to the battery, with this current gradually decreasing as the battery voltage reaches 6.9V. This makes it suitable for use with batteries with a rating of 2A.h or more. Note that because the output of the charger is fixed at 6.9V, no damage to the battery will occur if the unit is left on for an indefinite period of time. The circuit is based on the MC­ 34063A DC-DC convert­er IC. In this circuit, it’s connected as a “buck” or step-down converter which switches a 12V DC input down to 6.9V. The beauty of this circuit is that it is very efficient. Whereas a linear regulator would need to waste about half the input power, this circuit is about 80% efficient. Block diagram Fig.1 shows the internals of the MC34063A IC. It contains all the necessary circuitry to produce either a step-up, step-down or inverting DC converter for any voltage from 3-40V. Its principal sections are a 1.25V ref- PARTS LIST 88 1 S Q Q2 Q1 R 2 77 IPK CT OSC RSC 66 VIN D1 VCC 3 COMP 100 100 1 PC board, code 6VSLA, 61 x 41mm 1 plastic case, 83 x 54 x 28mm 1 toriodal core (Jaycar Cat. LF1240) 1 1.5-metre length x 0.5mm dia. enamelled copper wire 2 red alligator clips 2 black alligator clips 1 2-metre length medium-duty figure-8 cable (for input & output connections) 2 M205 PCB mounting fuse clips 1 2A M205 fuse 1 SPST or SPDT toggle switch 6 PC pins CT 1.25V REF 55 L 4 R2 Semiconductors 1 MC34063A DC-DC converter (IC1) 1 FR104 1A fast recovery diode (D1) 1 5mm red LED (LED 1) VOUT R1 CO Fig.1: this diagram shows the major internal elements of the MC34063 controller IC & shows how it is wired to function as a step-down converter. erence, a comparator, an oscil­lator, an RS flipflop and a Darlington transistor pair (Q1 & Q2). The frequency of the oscillator is set by timing capacitor CT, connected between pin 3 and ground. A value of .001µF gives a frequency somewhere between 24kHz and 42kHz (the exact frequency is not important). As shown in Fig.1, the oscillator drives the RS flipflop via a gate and this flipflop in turn drives Darlington pair Q1 & Q2. Each time Q1 & Q2 turn on, L1 is effectively placed across the supply voltage. These transistors stay on just long enough for the current through the inductor to build up to saturation, at which point they both Fig.2: the final circuit for the 6V SLA battery charger. The output of the internal Darlington pair appears at pin 2 and drives diode D1, inductor L1 and a 470µF capacitor which together form a standard step-down circuit. The 6.9V output is set by the 47kΩ and 10kΩ resistive divider across the output. turn off. The energy in the inductor is then dumped into reservoir capacitor CO via a diode (D1). The IPK sense line at pin 7 is used to monitor the peak current through the RSC sensing resistor – ie, it monitors the voltage across RSC and thereby limits the peak current through the inductor to a value of I = 0.3V/RSC. Voltage regulation is provided by the internal comparator. This compares the internal 1.25V reference with the output from a voltage divider consisting of resistors R1 & R2. These two resis­tors set the output voltage (VOUT) as follows: VOUT = 1.25 x (1 + R2/R1). The comparator works as follows. POWER S1 TO CAR BATTERY Capacitors 1 470µF 16VW electrolytic 1 .001µF MKT polyester Resistors (0.25W, 1%) 1 47kΩ 1 470Ω 1 10kΩ 1 0.33Ω 5W Where to buy parts A kit of parts for this project will be available from Jaycar Electronics Pty Ltd for $29.95 plus $4.50 p&p (Cat. KC-5164). Note: copy­ right of the PC board for this project is owned by Jaycar Electronics. If the output voltage goes too high, the inverting input of the comparator will be higher than 1.25V and so the output of the comparator will be low. 0.33  5W F1 2A ZD1 15V 1W 6 7 IC1 MC34063A 3 4 L1 : 2 LAYERS 0.5mm DIA ENCU WIRE ON NEOSID 17-732-22 TOROIDAL CORE 8 1 2 L1 A 5 D1 FR104 470 16VW 47k .001 .001 A  LED1 TO 6V SLA BATTERY K 470 K 10k 10k PORTABLE 6V SLA BATTERY CHARGER July 1994  63 LED1 TO 6V SLA BATTERY A K D1 470 .001 1 L1 IC1 TO CAR BATTERY 470uF 0. 33 5W 47k 10k ZD1 POWER S1 F1 Fig.3: the parts layout on the PC board. Inductor L1 consists of two layers of 0.5mm-dia. enamelled copper wire wound on a small toroidal core. As a result, the oscillator is effectively gated off and so Q2 & Q1 will both be off. Conversely, if the output goes too low, the inverting input of the comparator will be below 1.25V. The output of the compara­tor will thus be high and so the Darlington pair can now be toggled by the RS flipflop to switch current through the inductor. The result is a form of pulse width modulation which effec­tively reduc- es the amount of inductor current when only light loads are connected to the output and thus dramatically increases the efficiency. More importantly, it regulates the output voltage so that, under most loads, the output remains as set. Circuit diagram Fig.2 shows the final circuit diagram of the unit. The PC board sits in the bottom of the case, while the LED protrudes through a hole in the front panel. Tie knots in the power & output leads before they exit the case to prevent them from coming adrift. 64  Silicon Chip Power is applied to the circuit from a car battery (either directly from the battery terminals or from the cigarette lighter socket), or from some other suitable 12V DC source. This passes via switch S1 and is fed to pin 6 of IC1 and to a 0.33Ω resistor (RSC) via a 2A fuse (F1). Zener diode ZD1 protects the circuit against high voltage spikes (eg, from an automotive electrical system). It will also conduct heavily and blow the fuse if the input voltage rises above 15V. In addition, the 2A fuse protects the circuit if the output is inadvertently short circuited. The 0.33Ω 5W resistor between pins 6 & 7 sets the current limiting, in this case to about 900mA (ie, 0.3V/0.33Ω = 900mA). Pins 8 and 1 are the collectors of the two transistors inside IC1 and these are connected to the output side of the 0.33Ω resistor. This internal Darlington transistor pair is capable of switching a maximum of 1.5A, so it is more than capable of han­dling the job. The output of the Darlington pair appears at pin 2 of IC1 and drives diode D1, inductor L1 and a 470µF capacitor which together form a standard stepdown circuit. When pin 2 of IC1 goes high (ie, when the internal Darlington transistor turns on), current flows through the inductor to the load – in this case, the battery being charged. During this time, D1 is reverse biased and the inductor stores energy. When the internal Darlington transistor turns off, the collapsing magnetic field around the inductor tends to maintain the current flow through it in the same direction. D1, an FR104 fast recovery type, acts as a flywheel diode. It now provides the return current path from the load and prevents the IC side of the inductor from going below -0.7V. The 470µF capacitor is used to store the energy from the inductor and also acts as a filter to smooth out the ringing waveform. The 6.9V output is set by a voltage divider consisting of 47kΩ and 10kΩ resistors which are strung across the output. These provide a feedback voltage to pin 5 of IC1. The resistor values are chosen so that when the output reaches 6.9V, the feedback voltage equals 1.25V. LED 1 provides a visual indication that the circuit is working correctly. In operation, the circuit has a quiescent current of about 20mA and will consume about 250-300mA when charging a battery. It will typically provide 400-500mA of charging current, this cur­rent gradually tapering off as the battery voltage approaches 6.9V. Construction Most of the parts for the Portable 6V SLA battery Charger are installed on a small PC board coded 6VSLA and measur­ing 61 x 41mm (see Fig.3). Before installing any of the parts, make sure that there are no errors such as breaks or shorts in the copper tracks. If you find any, use a small artwork knife or your soldering iron to fix the problem. Once you are sure that the board is OK, you can start by installing PC pins at the external wiring points. The resistors, diodes and capacitors can then be installed, followed by the IC and the fuse clips. Note that each M205 fuseclip has a small retainer at one end and this should go towards the outside position. If the fuseclips don’t fit into the board, use a 1.2mm drill bit to enlarge the holes. Make sure that the semiconductors and the electrolytic capacitor are oriented correctly. The next task is to wind the inductor (L1). This is a fairly simple job, since all you have to do is wind two layers of 0.5mm-diameter enamelled copper wire onto a small toroidal core. Begin with a 1.5-metre length of wire and just keep winding on the turns, nice and close together, until you have made two complete layers. Make sure that each turn is tightly wound, as loose turns will reduce the circuit’s efficiency. When all the turns are wound, clean and tin the wire ends, then mount the coil on the board. The completed PC board sits in the bottom of a small plastic case. Drill a hole in one end of the case to accept the power switch and another in the lid for the LED. You will also have to drill holes in either end of the case for the input and output leads. Once these holes have been drilled, complete the wiring as shown in Fig.3. Use red and black alligator clips to terminate the input and output leads (red for positive; black for negative). Alternatively, the input leads can be attached to a cigarette lighter plug. You can use either a bezel to mount the LED on the top of the case or you can use a dab of superglue. INDUSTRIAL STRENGTH COMPUTER ELECTRONICS Introducing everything you will ever need for your comput­ing needs from industrial automation control to product develop­ment. Communications Products ❏ Data/FAX/Voice modem cards and modems ❏ Intelligent RS232 and RS422 serial cards ❏ LAN-COM cards for Novell networks ❏ Multiport serial cards (4 and 8 port) ❏ RS232 and RS422 serial cards ❏ RS232 to RS485 interface converters Computer and Peripheral Repair Services ❏ Australia wide on-site and workshop service ❏ Maintenance agreements Device Programmers and Testers ❏ EPROM programmers (up to 8Mb) ❏ IC testers ❏ Programmable device components ❏ RAM/ROM Emulators ❏ RAM Sip/Simm testers ❏ Universal Device Programmer and Tester Diagnostic Equipment ❏ Break-out boxes for serial and parallel ❏ Computer Debugging cards ❏ Datascope for serial data diagnostics ❏ Extender cards Driver Controllers ❏ MFM 1:1 HDD controllers (gives 3 times speed) ❏ Other controllers ❏ RLL 1:1 HDD controllers (give 50% more capacity) ❏ 2.88Mb high speed floppy/ tape controllers Industrial Control Data Acquisition System ❏ AD/DA (from 12 to 16-bit res) Cards ❏ CPU Cards with plug-in I/O ❏ Digital I/O (TTL and Isolated) Cards ❏ IEEE 488 Cards ❏ Prototype Cards ❏ Silicon disk ROM and SRAM hardcards Laboratory Development Equipment ❏ Circuit trainers ❏ In-Circuit emulators ❏ PC based logic analysers Multi Media Equipment ❏ Audible message systems for industrial control ❏ Sound cards ❏ Video conversion cards from VGA to PAL to VGA ❏ Other____________________________________________ Company Name: ____________________________________ Testing Contact Name: _____________________________________ To test the unit, you will need a 12V DC supply and a multimeter. Don’t use a 12V DC plugpack supply, however. Its output voltage under no-load conditions will be generally be about 17V DC, which is much too high. A 9V DC plugpack supply should be OK but check its no-load output voltage first. Connect the supply, switch on and measure the voltage across the output. It should be about 6.9V but this may vary by 100mV or so. If you don’t get the correct reading, switch off immediately. If everything is OK, set your multimeter to the 1A range, connect it in series with the battery to be charged and reapply power. Assuming that the battery is discharged, you should get a reading of about 300-500mA but this will taper off as the battery charges. Once everything is working, you can fasten the lid to SC the case and get to work on those flat batteries! Phone No: _________________Fax No:_________________ Title: _____________________________________________ Your Address:_______________________________________ State: ________________________P/Code: _____________ Nature of Business ❏ Computer Service ❏ Computer Systems Retailer ❏ Distributor of our Products ❏ End User ❏ Industrial Control and Data Acquisition ❏ Manu­facturer ❏ Product Development ❏ Other For detailed information tick the boxes provided and Fax or Mail this form back NOW! NUCLEUS COMPUTER SERVICES Pty Ltd 9 Morton Avenue, Carnegie, Vic 3163 Ph: (03) 569 1388 Fax: (03) 569 1540 July 1994  65 SERVICEMAN'S LOG A screw loose somewhere? It was a screw tight actually. My first story this month is relatively simple but there are still enough puzzling aspects to make it worth the telling. And from down south comes a story which must be close to the ultimate in servicing by remote control. This story concerns a Sharp model CX1020; basically a port­able colour TV set but which also incorporates an AM/FM radio and a cassette tape recorder. Although a portable unit, it is de­signed for mains operation only. It measures about 45cm wide, 30cm high and 23cm deep. The picture tube is around 22cm. The owner is a retired man who had travelled around Austra­lia a lot during his retirement and had bought the set specifi­cally with these travels in mind. The set is around 10 years old now and had given him good service during that time. But now a fault had developed which brought the set onto my bench. But not directly. The fault was a failure in the cassette recorder section and the owner, who is something of a handyman type, decided to open the set and look for anything obvious. At least, that was the idea until he took the back off the cabinet. He progressed as far as sliding the TV chassis out – which is quite easy – then took one look, recoiled in horror, and decided that access to the cassette section was far too compli­cated for him to tackle (he’s right; it really is a nightmare). In fact, he decided that the recorder wasn’t that important after all; he didn’t use it a great deal and he had a separate unit available anyway. So he slid the chassis back into place, refitted the back on the cabinet, and wrote off the recorder. The trouble was, having done that, the TV set wouldn’t work any more. And that was how he turned up at the workshop with it, along with the above history. Exploded view In order that the reader can better understand what fol­ lows, I am including some exploded views of the unit, taken from the manual. The main one (Fig.1) shows the cabinet, with the picture tube opening on the left. Above the picture tube is a straight line dial, calibrated in VHF and UHF TV channels. Tuning is by means of the knob on the left which, via a dial cord assem­bly, operates a pot which sets the voltage fed to a varicap diode; a popular arrangement with portable TV sets. The bright­ness, contrast and colour controls are on the top of the cabinet. Immediately to the right of the picture tube is the speaker grill and to the right of that the cassette recorder. Above this is the radio tuning dial, with the tuning knob on the righthand end of the cabinet. Other radio controls and the cassette con­trols are on the top of the cabinet. The smaller drawing (Fig.2) is of the TV chassis, which I will deal with in due course. When the customer related his story, I immediately plugged the set in and turned it on. And it was just as he said; quite dead and so he left it with me. Later, I pulled the back off. It is held by four screws and it is also necessary to remove two screws holding the AM/ FM telescopic antenna assembly. An unexpected cure Fig.1: this exploded diagram shows the general layout of the cabinet used in the Sharp CX1020. Note the chassis supports which are visible through the lower righthand corner of the picture tube opening. 66  Silicon Chip I had a good look and prod around inside and could see nothing obvious. So the next step was to turn it on again – whereupon it immediately leapt into 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 ● PC Board: Riston, Dynachem ● 3M Label/Panel Stock ● Dynamark: Metal, Plastic ✸ AUSTRALIA’S NO.1 STOCKIST ✸ K ALEX 40 Wallis Ave, East Ivanhoe 3079. Phone (03) 9497 3422, Fax (03) 9499 2381 life and turned in a first class picture. The only fault I could find was that the tuning was very touchy, which turned out to be due to the tuning pot feeding the varicap. A dose of cleaning fluid sprayed into this soon put that to rights and we had a nice smooth tuning action. But why was the set dead when I first tried it? I had another look and prod, without actually moving the chassis, but could not recreate the fault. I decided to refit the back and see what happened. In fact the set was running while I fitted the back. I had it face down on a felt pad on the bench, with the bottom of the cabinet to­wards my body and, initially, I simply pressed the back into place. The set continued to chortle away so I fitted the top lefthand screw, the bottom left one, then the top right one. There was nothing planned about this sequence; it was just convenient, and it had no effect on the set. Finally, I fitted the bottom right screw. And this had no effect either – initially. It was only as I gave it a final tighten that the set suddenly stopped. I slackened off the screw but the set did not respond. It was only when I switched it off, and then on again, that it came good. What’s more, I was able to repeat this sequence quite reliably. So what was I to make of that? I took the back off again and went straight to the offend­ing screw position, thinking it might be touching something. But no, I had to rule that out. Or was there a lead being pinched somewhere? No, that was out too. The next theory was that the back was pressing against the chassis, distorting it, and aggra­vating a dry joint or hairline crack in a board. Fig.2: the chassis layout for the Sharp CX1020. The two side runners mate with the chassis supports inside the cabinet. RETAIL OPPORTUNITIES NEW ZEALAND Jaycar Electronics (Australia) is looking to expand its service to NZ customers by appointing key resellers in that country. If you have a business which you think would benefit by reselling Jaycar products, please contact us. We are particularly interested in retail establishments which are already in the electronic hobby area. This is not to exclude TV/ video service, camera stores or other businesses which are related to the sale of technical products. For more information, contact: Bruce Routley, PO Box 185, Concord, NSW 2137, Australia. Fax 612 743 2066. July 1994  67 SERVICEMAN’S LOG – CTD plastic supports in the front of the cabinet, one of which can be seen through the bottom righthand corner of the picture tube opening. There is a similar assembly in the bottom left corner, part of which is just visible. Now, somehow or other, the owner had misaligned the chassis on this support system. Don’t ask me how – as I said before, I lost this evidence when I pulled the chassis out. I refitted the chassis and made some attempt to recreate the fault by twisting, prodding and pounding it. It was all to no avail; nothing I could do had any effect. So I screwed the antenna back in place – the holes for which now lined up exactly – and refitted the back. And this time all four screws were tightened without any ill effects. And that really was the answer. The set hasn’t missed a beat since. Unanswered questions In order to investigate these theories I needed to pull the chassis out of the cabinet; the first time I had moved it. But in preparing to do this I suddenly realised that there was something amiss with the chassis position. It was not sitting exactly level in the cabinet; one side was slightly lower than the other. The error was not very great and was easily overlooked with casual observation. But it wasn’t right and I then realised that this probably explained something else I had noticed. When I had replaced the two screws holding the antenna, I found that the holes did not line up exactly. I did not pay a 68  Silicon Chip great deal of attention to it at the time. Errors like this are not unusual, it was very small, and I was able to juggle the screws into position quite easily. Suddenly everything started to make sense. When the owner had pulled the chassis out to investigate the cassette recorder, he had not replaced it correctly. I’m not exactly sure what he had done, because I destroyed the evidence when I pulled the chassis out, but the drawings of the cabinet and chassis give some idea of the setup. The chassis drawing (Fig.2) shows that it is fitted with two side runners. And these are designed to mate with But it does leave some questions up in the air. I don’t know exactly how the chassis was misaligned and I don’t know how this misalignment caused the set to fail when the back was fitted. I can only assume that, somehow, it was triggering a protective circuit which shut the set down and could only be reset by turn­ing off the power. Anyway, the owner was quite happy to have the TV set back in operation. By mutual consent, we did not investigate the tape cassette problem as it would have been an expensive job to get at. But it was not a totally wasted effort. I had cleaned up the touchy tuning system and I also repaired the supports for the ferrite rod (AM) band antenna, which had broken away. The owner was fully appreciative of both repairs and so it all ended happily. Remote control servicing And now to the story I mentioned earlier: the problem of servicing by remote control – and an old colour TV set no less. We’ve all encountered this situation – at least potential­ly. It is nothing new for a customer to present the bald state­ment and question, “My TV set (or something) doesn’t work; what’s wrong with it?” And it often takes a good deal of diplomacy to explain that no such simple diagnosis is possible. And even then, one is not always believed. Fig.3: the horizontal & vertical drive circuitry in the Rank C2205. Transistor TR412 is the righthand one of a group of three at the left of the drawing. Its class B mate, TR409, is above it & to the right, & is connected into circuit via a plug & socket. The auxiliary board, PWC470, is at the top righthand corner. A serviceman I once worked for, back in the old valve radio days, had a simple approach. He would nominate the first compon­ent that came to mind, usually one of the more expensive ones, like the power transformer or the speaker. He reasoned it was bad policy to admit that one didn’t know and that an answer didn’t have to make sense to satisfy the customer. Mind you, he often had to do a lot of faking when making out the bill. But assuming that an attempt at remote diagnosis is justi­fied for some reason, it calls for maximum co-operation and observation on the part of the owner, to provide intelligent answers to the questions the serviceman will have to ask. And when the only link between serviceman and owner is by mail ... well, that really makes it hard. But that is gist of the story from my colleague, J. L., from the Apple Isle. This is how he tells it. Regular readers of The Serviceman’s Log might remember that until recently I conducted a feature called “TETIA TV Tip”. One result of having my name and address listed each month was that I received a lot of correspondence from readers, most asking for help in solving their TV set or VCR problems. In most cases, I had to ignore these pleas: I was too busy on my own bench and I could afford neither the time nor the postage needed to reply. Those correspondents who included a stamped addressed envelope always received an answer, even if it wasn’t exactly the one they hoped for. July 1994  69 SERVICEMAN’S LOG – CTD However, there has been one correspondent who has received much better service, since he usually enclosed a $5 note and a stamped envelope with his letter. (Not that $5 would buy much time from a busy serviceman but it was the principle that counted – he appreciated that time was money!) The following story comes from this correspondent, whom I shall henceforth identify by his initials N. B., and it provides an opportunity to discuss a common fault in a very old but still-popular colour TV set. On one occasion, N. B. wrote asking my help in (1) identi­fying a particular early model Rank Arena colour TV set, (2) sup­plying a circuit diagram for same, and (3) suggesting any likely causes for vertical non-linearity and bright retrace lines. One of the difficulties in tracking down information on these old TV sets is identifying the model number. The only model identification on the old Ranks was on a small slip of paper, pasted on the outside of the cabinet back. Most have long since fallen off and identification is a process of comparing chassis details with those from all the likely manuals. In this case, N. B. helped considerably. He described the old set in considerable detail and from this information I was able to identify it as one of the “14 70  Silicon Chip pcb” (printed circuit boards) models. In the very early days, Rank did not assign chassis numbers to particular models. Only the indi­ vidual printed boards were numbered and these could change unpre­ dictably in the various models. But I needed further details so I wrote back asking for the numbers of some of the boards; in particular, the horizontal output board number, since this was where most of the circuit changes occurred during the life of these models. N. B. replied with the numbers of most of the boards. Using a cross reference published by Rank many years ago, I was able to identify the set as most probably a C2205. One or two of the boards had different numbers but that was par for the Rank course in those days. The main identifying feature was the horizontal output board, in this case a PWC433 (one of the later boards in this series). I made a copy of the circuit for the 2205 and marked on it some of the components that I have found to give trouble in the vertical stage. Most are electrolytic capacitors, as might be expected. There are several electros in the vertical oscillator, drive and output stages, and failure of any of these will cause bad linearity. The degree of non-linearity varies with the particular capacitor but the most dramatic and common problem lies with two small tantalum capacitors, C451 and C452. These are in series with the vertical linearity control, so it’s not surprising that changes in them cause odd faults. On that subject, tantalum capacitors were introduced as much for their low leakage as for their tiny size. Unfortunately, they have not proved to be stable and many 10µF tantalums measure as low as 1µF. This doesn’t matter in some circuits but it’s fatal in linearity networks. My final advice to N. B. was to check the voltages around the circuit. Wrong or missing voltages usually point to some kind of total failure, not partial failures. Since N. B. has no oscilloscope, a careful check of volt­ages and capacitor values was about his only course of action. All of that went off to N. B. in one of his prepaid envel­opes and I heard nothing more for several months. Then I received a letter saying “Thanks a million! It’s going again, thanks to your suggestions”. He didn’t say which suggestions were helpful but from further discussions it would seem that the voltage analysis did the trick. N. B. advised that all the electros had been replaced and produced no improvement. He then found that TR412, one of the vertical output transistors was completely open circuit. Replac­ing this restored normal linearity but did nothing to improve the retrace lines. This part of the story puzzles me, since TR412 is one of a class-B output pair and open circuiting one of these should collapse the picture to little more than a line across the centre screen. Yet N. B.’s description of “non-linearity” implies a far less dramatic symptom. I shall have to experiment with that next time one of these sets comes into my workshop. (Serviceman’s comment: yes, you’ve raised an interesting point about that class-B output stage, J. L. And note that it is not a symmetrical arrangement. TR412 is a small power transistor (2SA653) which is mounted directly on the board, whereas its mate is a much larger unit (2SC1104) which is mounted remotely on its own heatsink. And while I can’t be sure, the implication is that it contributes the major portion of the vertical scan. So, if the failure of TR412 only partially reduced the scan, and someone tried to correct this by simply winding up the height control, the result might well be poor linearity – to the extent that the trick worked at all. Just a thought, J. L. – carry on). Retrace lines The rest of N.B’s story centres around the retrace lines. He solved the problem almost by accident but doesn’t really know what he did! He found a small printed board, PWC470, mounted on the top of the horizontal output board. It held only two transistors and a few other components, but oddly enough, it was not connected into the circuit. A 3-pin plug had been disconnected and left hanging loose near the board. When he reconnected the small board, the retrace lines va­nished but he was greeted with an array of broad black lines moving up the screen and a degree of vertical rolling. Removing the plug immediately stopped the black lines but restored the white (retrace) ones! N. B. removed the small board for a closer examination and found that it had been worked on extensively at some time or another in the past. In particular, the two 2SC945 transistors had been replaced with two BC547s. So he decided to restore the proper types, if for no other reason than that substitutes can often introduce faults of their own. And that was all that it took. When he replaced the board, the retrace lines had disappeared and there was no sign of the black lines. In fact, he claims that the set is giving as good a picture as any set of its age that he’s ever seen. So what did he do? What connection does PWC470 have with vertical linearity? Well, none that I know of. I believe that N. B. had two different faults and the retrace lines are a fault that is quite common and easily explained. On the various early Rank horizontal output boards, vertical blanking pulses were picked off the vertical output and fed into one of the low level video amplifier stages. This system relied on the DC stability of the video amplifiers since any drift altered the black level of the picture and in some circumstances allowed the appearance of retrace lines. In the C2205 model, vertical blanking was applied much later, at the video output stage. Because the blanking was now added to whatever DC level had already been established, variations in DC level made no difference. However, a much more substantial blanking pulse was required compared to earlier systems. This was the purpose of PWC470. It was a simple 2-stage amplifier which was used to boost the vertical blanking pulse amplitude. Unfortunately, it was also very critical as to circuit values and in some circumstances it could turn itself into a very effective multivibrator. In this condition, it would produce blanking pulses at three or four times the correct rate, hence the black lines on the screen – they were synthetic blanking pulses manufactured by a faulty PWC470. An easy cure A cure was ridiculously easy – just replace any component on the board! I usually replaced one of the transistors but I have also solved the problem by replacing one of the resistors or capacitors. All that was needed to create the fault was to upset the critical balance of component values – and as far as I could tell any component could do this. In N. B.’s case, someone had found that pulling the plug was an easy way to stop the black lines. Apparently the retrace lines were less annoying. I dunno; it takes all kinds! Nice going J. L. – a most interesting story and it makes a very important technical point. But you won’t become a millionaire serviceman that SC way! Subscribe now to the largest faults & remedies library in Australia ✱ ✱ 1994 manuals are now available. Our database is regularly updated with information supplied by technicians such as yourself. ✱ Exclusive backup service by qualified technicians. ✱ ✱ Over 10,000 faults and remedies on file with flow charts and diagrams. Covers Colour TVs and VCRs of all brands sold in Australia EFIL Phone or fax now for your FREE information package ELECTRONIC FAULT INFORMATION Reply Paid 4 P.O. Box 969 AIRLIE BEACH 4802 Ph 079 465690 Fax 079 467038 July 1994  71 COMPUTER BITS BY DARREN YATES BIOS interrupts: speeding up the keys This month, we continue our discussion of BIOS inter­rupts. We’ll look at how Windows speeds up the key repeat & delay rates & describe how you can do likewise with DOS pro­grams. If you’ve ever sat down and written an essay or letter on a word processor, then you’ve probably found it much easier to move the around the screen page by using the cursor keys on the key­ board rather than having to go searching with the mouse. And of course, many older word processor programs do not have mouse control. One of the problems with most DOS word processors though, is the speed at which the key repeat setting allows you to move around the screen. Just briefly, the key repeat rate is the rate at which the computer enters in the same character while you hold that particular key down. Another parameter which affects the keyboard speed is the key delay rate. This sets the time delay between the first character being entered to the beginning of the character repeated sequence. Most word processors, particular- ly older DOS programs, don’t touch these parameters nor do they provide access to them. In­stead, they rely on the DOS default settings or values left by a previous program. Try this for a test. If you have DOS 5 or 6, boot up the DOS Editor and when in document mode, hold the right cursor key down. Note the speed at which the cursor moves across the screen. Now boot up Windows until you get to the desktop and then exit back out. Boot up the DOS editor again and hold the right cursor key down. You should see a significant increase in the speed at which the cursor whizzes across the screen. Nothing magical has happened in Windows but what it has done is to reset the key repeat and delay parameters to a faster setting. You can do this yourself by opening up the keyboard option in the Windows Control Panel. This might be great for Table 1: Adjust Repeat Rate (Extended Keyboard Services) Registers on entry AH 03h AL 00h = restore default values (PCjr only) AL 01h = increase initial delay (PCjr only) AL 02h = cut repeat rate in half (PCjr only) AL 03h = do both 01 and 02 (PCjr only) AL 04h = turn off keyboard repeat (PCjr only) AL 05h = set repeat rate and delay (AT and PS/2) BH repeat delay (0-3 x 250ms; AT and PS/2) BL repeat rate (0-31; lower values are faster, AT and PS/2) 72  Silicon Chip speeding up Windows but it’s a pain in the neck if you want to speed up a DOS program. As it turns out, you can do the same thing Windows is doing with the small utility we’re presenting this month called KEYREP.EXE. This program allows you to reprogram the key repeat and delay settings via BIOS interrupt 16H service 03H. This interrupt is specifically designed to control these keyboard parameters and we can easily access them through DOS either via QBasic or QuickBASIC. Interrupt parameters In order for the interrupt to know what you’re talking about, we need to set the parameters in the general purpose 16-bit registers AX and BX. Table 1 shows how it works. Register AX must have the value 0305h which signifies that we want service 03h (ie, AH = 03h) and that we want sub section 05h (ie, AL = 05h). Register BX is also split into its two 8-bit halves, BH and BL, with BH setting the number of 250ms intervals before the keyboard repeat action takes place and BL setting how fast that repeat rate is. Once these values are set, we simply call the interrupt and the job is done. Again, to give the maximum number of readers the chance to get this program up and running, we’ve used the CALL ABSOLUTE() routine which allows both QuickBASIC and DOS QBasic to run small assembler-like programs. I say “assembler-like” because the CALL ABSOLUTE() routine only gives you a subset of 8086 assembler instructions. Although this allows you to run the program on any machine, it does prevent you from accessing the extended reg­ isters and much higher Basic Listing For Keyboard Repeat Rate Utility ‘ Keyboard Repeat Rate Adjust Utility ‘ Copyright 1994 Silicon Chip Publications Pty Ltd DEFINT A-Z DIM asmprogram(1 TO 20) DATA &h55 DATA &h89,&he5 DATA &hb8,&h05,&h03 DATA &hbb,&h00,&h00 DATA &hcd,&h16 DATA &h5d DATA &hca,&h00,&h00 : ‘ PUSH BP : ‘ MOV BP,SP : ‘ MOV AX,0305h : ‘ MOV BX,0000h : ‘ INT 16h : ‘ POP BP : ‘ RET 0 start = VARPTR(asmprogram(1)) DEF SEG = VARSEG(asmprogram(1)) FOR byte = 0 TO 15 - 1   READ newbyte    POKE start + byte, newbyte NEXT byte CLS PRINT “Keyboard Repeat Rate Changer Utility” PRINT “Copyright 1994 Silicon Chip Publications.” PRINT : PRINT “Enter in repeat delay time [0-3]:”; : INPUT “”, delay PRINT “Enter in repeat speed [0-31 0-fast 31-slow]:”; : INPUT “”, rate POKE start + 7, rate POKE start + 8, delay CALL absolute(VARPTR(asmprogram(1))) DEF SEG PRINT “Changes made.” END processor-level instructions supported by the 386 and 486 machines. If you’ve been following the series so far, you should be able to see fairly easily how the program works. The program, Keyrep.bas, is really in two parts: the QuickBASIC main program and the assembler routine which does the bulk of the work. The first section we shall take a look at is the DATA statements. These lines contain the hexadecimal code for our small assembler program. When we run the assembler routine, we are really passing control from the QuickBASIC main program to the assembler rou­tine. This not only involves loading and running the code in the DATA statements but it also involves saving the run-time reg­isters inside the processor. The reason for this is that if we change some of these registers during the execution of our assembler routine and we don’t restore them back to the way they were, QuickBASIC is then going to use these new values in the run-time registers and the result could be a complete crash. Looking at the data statements, the first line saves the base pointer. You can think of this as the address of the stack as it stands when it enters the assembler program. This is im­portant so that when we go back to our QuickBASIC program, the base pointer can be restored to its present address and QuickBA­SIC remembers where all of the data it wants is located. The second line moves the current stack pointer into the base pointer register. This is really computer-speak for moving the address of the stack pointer to the beginning of our assem­ bler routine. The next two lines set up our AX and BX register parame­ ters. At the moment, register AX is loaded with the required 0305h hexadecimal number, but we’re loading BX with 0000h – more about this in a moment. After that, we run the interrupt, restore the old base pointer and then return to the QuickBASIC or QBasic program. The following two lines set the segment and offset pointers to point at the first address of our assembler array, called ASMPROG. The program then POKEs each of the DATA statements into the memory at the SEG­M ENT:OFFSET address we’ve specified. The program proper begins with the CLS and following PRINT statements. Remember how we left the BX register value as 0000h? Well, we’re about to get that information from the two INPUT lines in the BASIC program. These two lines asks the user for the delay rate and the repeat rate in the numbers that we require; ie, 0-3 for the delay rate and 0-31 for the repeat rate. Now before we actually run the assembler routine, we now POKE these two numbers into the position currently taken up by the 0000h. The computer is clever enough to be able to easily translate our decimal numbers into the hexadecimal numbers re­quired by the assembler routine. We now CALL the routine, change the segment back to the current one used by the BASIC program with the DEF SEG statement and finally indicate to the user that the changes have been made. You can automatically call up the executable version of the program in your AUTOEXEC.BAT so that the settings can be made as soon as you boot up. If none of your DOS programs alter these settings then they will remain constant while your machine is on. If they modify them, then you’ll need to run KEYREP to change them back again. To change your AUTOEXEC.BAT, simply enter your DOS 5 or DOS 6 directory and enter the following line: EDIT C:\AUTOEXEC.BAT Once it’s up one the screen, go to the line before the MENU command and type: KEYREP <enter> Note that you will have to include the directory path so that DOS can find the program. After that, save the file, exit and reboot your computer. References: (1). “Using Assembly Language”, Wyatt, Allen L. Que Pub­lishing 1990. (2). “The Programmer’s PC Source­ book”, Hogan, Thom, Micro­soft Press, SC 1991, 2nd Edition. Where to buy the software A copy of Keyrep.bas plus the executable version, Keyrep.exe, is available from SILICON CHIP. The software order form on page 56 has the details. July 1994  73 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 PRODUCT SHOWCASE Yokogawa's 5-digit DMMs have true RMS measurement These new meters from Yokogawa have a 5-digit readout and very high accuracy for handheld instruments. They also provide true RMS measurements for AC voltage & current, and they have a new safety feature in the form of a shutter which prevents connection of probes into the terminal sockets unless the current ranges are selected. Superficially, the new Yokogawa 7544 01 multimeter does not look a great deal different from most other meters on the market. It is not until you turn it on that you realise that it is substantially different because it has a 5-digit liquid crystal display with a maximum display count of 49,999. This new high resolution display together with a basic accuracy of ±.05% +2 counts ( on the 500mV range) means that handheld digital multimeters have been shifted to a new level of precision - at least for those made by Yokogawa. True RMS measurements As well, the two top models in the Yokogawa range have true RMS measurement for AC voltage and current. By contrast, the vast majority of multimeters have "average value" indica­ t ion for AC measurements. This means that their measurements are accurate only when the voltage or current wave­form is a sine wave. For other wave­forms such as square, sawtooth or rec­tified sinewave, their readings will be inaccurate. Yokogawa's true RMS measurement applies for AC waveforms with a crest factor of less than three or less than six for readings of less than half full scale for any AC voltage or current range. (Crest or peak factor is the ratio of the peak to the RMS value of a waveform). In addition, it will read the true RMS values of AC voltages and currents up to 30kHz (100kHz for the model 7544 02). although the accuracy is degraded for the higher frequencies. Safety lock shutter These days with all the measurements engineers and technicians have to make when designing and repairing equipment, it's so easy to plug the probes into the wrong sockets, select the current range and then either blow the fuse or damage the multimeter and even the gear you're work­ing on. Some multimeters give you an audible warn­ing that you have selected the wrong range for the terminals in use but it is still possible to do the wrong thing and cause damage if you are not paying attention. To combat this problem, Yokogawa have come up with a "safety shutter" for the current terminals. This slides over the terminal openings, thereby preventing you from inserting a banana socket probe. To open the shut­ter, you must first select a current range with the range switch and then you can push the slider upwards. Once the shutter is open, you can only select different current ranges; if you want to select one of the other ranges you must first remove the probes and close the terminal shutter. Both current terminals are fused, with the 10A range having a 15A 600V fast acting cartridge fuse. Incidentally, the back the multimeter is removable after you undo the four screws and importantly, these screws run into integral pillars with threaded brass inserts. Some quite expensive multimeters do not have threaded metal inserts and conse­quently it is quite easy to strip the threads after the screws have been removed several times. And after all, over the life of the meter you will have to remove the back quite a few times to replace the batteries, unless of course, they are in their own com­partment. July 1994  77 Universal device programmer The Power-100 has been designed to meet the demand for a universal programmer with a built­ in power supply and PC printer port connection. It is intended for development and volume production and ISO 9000 requirements for customer calibration and test­ ing have been met. Since a programmer must cope with many new devices, the ability to upgrade is important for most customers. The software can cope with "self definition" which is ideal for ASIC devices and there is pro­vision for chips with up to 256 pins. Some of the features are as follows: 48 pin Textool socket as standard – each of the pins are programmable, including GND, VCC, VHH, VOP, clock oscillator, quick pull up and protection driver etc; a full range of adaptors to And this brings us the next feature. Instead of the usual 9V alkaline battery, this meter uses two 1.5V AA cells which have the advantage of being cheaper. Battery life is quoted as 120 hours with alkaline cells being used. Naturally, the unit has auto­matic switch off to conserve the bat­teries. This operates 30 minutes after the last switch operation but gives an audible beep warning 30 seconds be­ fore it signs off. Interestingly, although the battery voltage is 3V, the DMM apparently has an internal step-up converter. This cover a wide range of packages; up to 8- gang programming for production use; rapid programming – 27C256 in 6 seconds; over 1500 devices supported – manufacturer ap­ proved algorithms; FlashE/ EPROM, PLD, PAL, PEEL, GAL, MAPL, MAX, MACH, bipolar & serial PROM, MPU/MCU; test and allows it to develop an open circuit voltage of more than 5.5V for diode and continuity tests. This means that it will readily test light emitting diodes and other semiconductors with a high forward bias voltage. However, Yokogawa have gone one step further to cater for in-circuit resistance measurements. In this instance, a high open circuit voltage is a problem because semiconductor junctions will conduct and falsify the reading. To overcome this situation, you select the "LP#" mode which has an open circuit voltage of just 0.2V, CALLING ALL HOBBYISTS We provide the challenge and money for you to design and build as many simple, useful, economical and original kit sets as possible. We will only consider kits using lots of ICs and transistors. If you need assistance in getting samples and technical specifications while building your kits, let us know. YUGA ENTERPRISE 705 SIMS DRIVE #03-09 SHUN LI INDUSTRIAL COMPLEX SINGAPORE 1438 TEL: 65 741 0300    Fax: 65 749 1048 78  Silicon Chip identify TTL & CMOS LOG IC, SR AM, DRAM, SIMM/SIP & logic vector; and cus­tomer calibration and self-diagnosis to meet ISO 9000. For further information, contact Nucleus Computer Services Pty Ltd, 9B Morton Ave, Carnegie, Vic 3163. Phone (03) 569 1388 or fax (03)569 1540. low enough not to be a problem with semiconductors. Other features As can be seen from the photo, the Yokogawa meter has a large rotary function switch which selects the parameter to be measured, eg, current. You then use the Select button to se­lect AC or DC measurement. For AC and DC voltage measurements, the unit has auto ranging and auto polar­ity indication but you can also manu­ally select ranges using the Range but­ton. We should point out that normal operation of the DMM is a full 50000 (actually 49,999) but you if you don't want your measurements to have this order of resolution you can suppress the least significant digit by pressing the "5000" button to give a 4-digit mode. The Data-H key will store and hold the present reading on the display while the Min/Max key, as you might expect, will store and display minimum and maximum values but will also calculate and display an average (AVG) value. Finally, the REL key ze­ros the existing reading on the display and then shows relative measurements. Inter- estingly, it also provides the facility to cancel out test lead resistance on the low resistance ranges thus giving better accuracy. Frequency & decibels Apart from its 5-digit display and high accuracy, the Yokogawa 7544 01 is the first handheld multimeter that we know of to feature measurements in decibels for AC voltage. Actually, you can measure in dB or dBm (deci­bels relative to 775mV or 1mW into a 600W load). When you select the AC voltage function, you can measure volts or millivolts depending on amplitude, dBm or the frequency, by pressing the Select button. You can also have a display which alternates between frequency and volt­ age at 6-second intervals. To measure in dB as opposed to dBm, the REL key must be pressed. The frequency range of the multimeter is from 10Hz to 999.9kHz. Accuracy As already noted, the model 7544 01 has an accuracy of ±.05% + 2 counts for the 500m V DC range, while for the other DC voltage ranges (5V - 1000V) it is ±.07% + 2 counts. For AC voltage, the accuracy for all ranges (500mV 750V) is ±1 % for frequencies be­tween 40Hz and 50Hz; ±0. 7% between 50Hz and lO0Hz; ±0.5 between 100Hz and 2kHz; ±1 % between 2kHz and 10kHz; and ±2% between 10kHz and 30kHz. AC current accuracy is ±1%for frequencies between 40Hz and 1kHz. Well, how to conclude? This re­view really can't do full justice to a product with so many features but it should indicate that the Yokogawa 7544 series really has set a new stand­ard for accuracy, resolution and oper­ ating features. We are impressed. Recommended retail price for the model 7544 01 is $679 plus sales tax, while the higher accuracy model 7544 02 is $998 plus sale tax. For further information, contact Yokogawa Australia Pty Ltd, 25 Paul St, North Ryde NSW 2113. Phone (02) 805 0699. Frequency synthesiser for PCs Capable of ultra-wide frequency synthesis, the FSC-30 and 50 are half length cards for any PC-XT/AT/386 and provide up to two independent TTL level programmable square wave generators at low cost. Both models come with one or two synthesisers per card, with each channel being independent from the other, and crystal controlled for excellent stability. An optional external reference input is also available, with the reference source being jumper selectable between external or on-board frequency source. Software supplied with the cards provides either command line or popup menu selection of output frequency. Driver software is also sup­plied, with source code, for writing custom programs and an example pro­gram is included. The FSC-30 has a range of 0.024Hz to 30MHz while the FSC-50 has a range of 2.98Hz to 50MHz, with reso­lution for both being 27,000 steps per decade. The cards have three switch­able addresses for multiple card use and are connected via 50W coax with BNC connectors. For further information, contact Boston Technology Pty Ltd, PO Box 1750, North Sydney, NSW 2060. Phone SC (02) 955 4756. Power saving 486 processors from Texas Instruments Texas Instruments has announced a range of 486 chips designed for the PC manufacturing market. Designated the TI486DLC and TI486SLC, the new devices offer many advanced features. The TI486SLC is designed as a notebook device and offers 5V or 3V operation, saving up to 60% in power consumption for the CPU alone. When a portable based on the 486SLC has not been in use for some time, the CPU enters a special standby mode where power consumption is virtually zero. The TI486DLC version has a full 32-bit external data bus offering all the power and facilities de­manded by "Desktop" systems. As well, they offer the same circuit board footprint as existing 386 chips, allowing a manufacturer to upgrade older designs with only minimal changes. Both devices utilise a pipelined architecture to optimise instruction execution and thus improve perlormance. In addition, an on-chip data cache cuts data reads from main memory by up to four clock cycles. The TI devices also feature a built-in hardware multiplier that speeds up maths intensive applications such as CAD. For further information, contact Texas Instruments Australia Ltd, 17 Khartoum Rd, North Ryde, NSW 2113. Phone (02) 910 3100 or fax (02) 878 2489. July 1994  79 TVCoder: the sequel to Video Blaster! As good as the Video Blaster is, it does not have the ability to deliver output from your PC to your VCR or TV monitor. Now there is the TVCoder. It will output VGA graphics to NTSC & PAL video monitors & VCRs, & will also perform as a stand-alone unit. Review by DARREN YATES W HEN WE REVIEWED the Video Blaster from Creative Labs earlier in the year, our impressions were that it was a great product with one important feature missing – you could bring video into your PC but you couldn’t take it back out again. Creative Labs obviously thought the same and have completed the package with the TVCoder which will export video in either NTSC or PAL format to your TV or VCR. It supports both composite video and S-video compatible TVs and VCRs in any one of the following video standards: • NTSC (4.43) 50Hz; • NTSC (4.43) 60Hz; • NTSC-M 60Hz; • PAL (B/G) 50Hz; • PAL-M 60Hz; and • PAL-N 50Hz. It will also run both your TV monitor and your VGA display at the same time, which is something that most of the current generation PC-TV converters can’t do. System requirements In order for TVCoder to work on your PC, it must have at least the following: 80  Silicon Chip • • • • • • • 286 processor or higher; 1Mb of RAM minimum; 1Mb of hard disc space; VGA monitor and card; One 8-bit slot; DOS 3.3 or later; Microsoft Windows 3.1 or later. Obviously, if you only have 16-bit slots in your PC, then one of these will do equally as well. Note that you don’t have to have the Video Blaster package for the TVCoder to work. The package The TVCoder package is more hardware than software. There’s only a thin manual and one floppy disc. The rest of the box is taken up with external cables and the card itself. I don’t know about you but whenever I look at or buy one of these packages, I always like to have a squiz at the board and see what makes it tick. In the case of the TVCoder, there’s one monster 84-pin Philips SAA 7199B chip which I would hazard to guess does most of the TV standards conversion. However, it would seem that there is a combined effort in this card with devices also coming from NEC and Sony. A couple of Creative Lab’s own proprietary chips are also thrown in for good measure. The only components which are not surface-mounted devices (SMDs) are a few electroly­tic capacitors, the crystal and a couple of 7805 regulators. The card mounting bracket has two VGA DB-15H female sock­ets, one RCA socket and one S-video output socket. One thing which is great to see is that the card mounting bracket has labels for each connector stamped into it. How many times have you come across a card with three or four connectors and then had to go searching for the manuals to find out which connector plugs into which socket! As noted above, the card is only an 8-bit type which is great if you’re running a 386 with a Sound Blaster ASP16, Video Blaster and a memory card and you’ve only got an 8-bit expansion slot left. The only thing you need to be careful of is that the cable which connects the VGA card to the TVCoder card is quite short but this shouldn’t cause any problems. Software Before running the installation program and setting up the software you need to first install the card, otherwise when the installation program goes looking for it, you’ll be forced to quit out and start again later. The manual that comes with the TVCoder is quite good in this respect and shows that you can run the TVCoder card with or without the Video Blaster option. More importantly, it shows how to connect up the TVCoder, your VGA card and the TV set using the external cables. As mentioned before, the TVCoder comes with only one disc which suggests that most of the hard work is done by the card with the PC only acting like a “traffic controller”. With the software running under Windows, this reinforces the theory. As with all Creative Lab’s products, the installation of the software is basically automatic as it unzips the program files from the archive by itself. While it was running through this, one point worthy of interest was the fact that the package was written using Visual BASIC Version 2 which was evident by the appearance of the VBRUN 200. DLL run-time dynamic-linked library. Once the installation is completed, you’re then asked to reboot your machine so that the settings can be put into place. If you live in the US or anywhere where NTSC is the television standard, then setting up the package is easy. However, there’s a bit of work for us “poor” PAL users to do! The initial TV standard upon start up is one of the NTSC standards. Now although you will still get a picture on your PAL TV (I used a Samsung 34cm with external video input for the test), you won’t see any colour. Unfortunately, this NTSC default is not explained anywhere in the manual. To make the change you need to go to the TVCODER directory and run a little utility called TVSET. To select the correct PAL standard, you need to run the following command: TVSET VIDEO PAL-BG This will switch the card into our PAL mode and you should see colour appear on your screen if you’re running with a co­loured DOS prompt but you should definitely see it when you go back to the DOS shell. If you don’t, then you may have to switch the colour on, on the card. You also do this with TVSET by entering the following command: TVSET COLOR ON If you need to get at the settings of the TVCoder in a hurry, then you A spare 8-bit slot in your computer is all that’s need to mount the TVCoder card. The large 84-pin Philips chip at top centre apparently does most of the TV standards conversion. might as well run the TVAdjust terminate-and-stay-resident (TSR) program in the background. By holding the CRTL key down and pressing “5” on the numeric key­board, a panel with all of the controls appears on the screen. Here you can change the video standard, turn the colour on or off, and adjust the alignment, etc. If you’re not likely to want to change things in a hurry then you should stick with the TVSet program and save your memory space. TVTEST utility Once you have the TVCoder up and running, you can run the TVTEST utility. This will carry out the following: check the the port address for the card; perform a register check on the card to ensure that they are functioning correctly; and perform a colour output test which will produce colour bars on the screen and go through the video standards test. Initially, when I ran this, the video standards test only went through the NTSC standards which made me twig to the fact that the software is initially set up for NTSC standard. Finally, a fairly coarse graphic picture file is displayed on the screen. At this time, you should be seeing the display on both your VGA screen and the TV set. And this is where you’ll notice something else. Your VGA picture won’t look quite as good as it did before. As I write this, I’m looking at a Philips 14-inch SVGA monitor and the colours do appear to be a little washed out, the image is not as sharp and the screen seems to be suffering from a little “colour-run”. I have seen a few of This is the screen that appears as soon as you load the TVCoder Control Panel from within Windows. It allows you to select any one of three PAL or NTSC input signals, to switch colour on or off, & to position the display on both the VGA monitor & TV screen via the vertical & horizontal alignment bars. July 1994  81 got caught out) and have Windows running in Super-VGA (800 x 600) mode, then you’ll have to switch it back down. If you don’t, the result is a scrambled VGA display and a mess of flickering from your TV screen. Windows TVPanel This Colour Lookup Table shows the default settings of the software. As it stands, the TVCoder will process VGA colours & display them as they are on the TV screen. The input colour luminance is displayed on the horizontal axis and the output luminance is on the vertical. There are three graphs, one each for red, green & blue, each of which is selectable for on-screen display. Editing of the Colour Lookup Table is possible using a unique point & click method. By selecting one of the 14 grab points, the Lookup Table can be reprogrammed so that various shades of a given VGA colour appear on the TV screen as any colour you desire. Although all three colours are displayed on the same graph, you can only edit one at a time. these PC-TV encoders but this would still be the best out of all of them with regards to the lack of degradation to the VGA screen. So what does the TV picture look like? Well, it doesn’t look too bad at all. There is no obvious screen flicker which a number of other converters suffer from and the picture stability is quite good. The image isn’t as sharp as you would get on your VGA screen but if you choose 12-point Arial type from Windows Write and write a few 82  Silicon Chip lines you can easily read it on the TV screen. This reminds me of another possible trap. Don’t forget to switch your Windows video standard back to 640 x 480 VGA mode before you next run Windows. You can do this quite easily by going into your WINDOWS directory and running the DOS version of SETUP. You simply select to change the display adaptor and switch it to standard VGA. If you’re like most people (including yours truly, who The Windows software consists of only one program – TVCoder Control Panel – but it is an extremely versatile little tool. Firstly, when you run it, you’re given the option of set­ting the video standard to any one of the six listed above. When you make the changes, the results are instantly translated to the screen so you can quickly work out which standard suits the TV you’re using. If you’re already running Windows in standard VGA mode then you can come straight into Windows and select the correct video standard from here rather than using the DOS utili­ty if you prefer. Other parameters which you can change include the horizontal and vertical positions of the picture on both your TV and VGA displays. The “Vertical Align­ment” control is used to stop screen rolling if it is occurring. Horizontal alignment does likewise in the X direction. The Horizontal and Vertical pan allow you to shift the image around on the VGA display without affecting the TV screen. One of the reasons I would hazard to say this feature was includ­ed is that the VGA display shifts quite a bit when you toggle the TV screen output off and on. This option allows you to shift it back into place again. You can also switch the colour off if you wish to record black and white images on your VCR. Colour lookup table Instead of just feeding the same colours used by your programs straight out to the TV screen, the TVCoder uses a Colour Lookup Table. The great thing about this is that they’ve made it such that you can reprogram the three primary video colours – red, green and blue – and produce your own colour display. One of the screen shots of the Windows control panel shows what fun you can have with this tool. The way the Lookup Table works is as follows. Each of the three video colours has an 8-bit register which can have a count anywhere between 0 and 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 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 Street ___________________________________________________________ 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). ✂ 255; 0 for no luminance and 255 for full luminance. In the default mode, the TVCoder maps the lumi­ nance values used by your VGA card from these registers, through the video chip and out to your TV. If you look at the default graph, the output luminance values are on the vertical axis and the input values on the horizontal axis. You can see here that an input value of 0 corresponds with an output value of 0, 128 corresponds with 128 and 255 with 255. So white on your VGA screen appears as white on the TV screen, red as red and so on. If we load in one of the other colour bar options, say GAMMA_1.2, the graph then matches the pre-programmed table but as you can see from the next screen shot, there are a number of pick-up points along the plot. You can reprogram the colour Lookup Table by picking one of these points and dragging it around the graph with your mouse. By doing this, we could program out the colour red, for example. To do this, we just select the red line option from the panel and then pull all of the pick up points down to the hori­zontal axis. What this tells the TVCoder is that for any red input luminance value, we want each corresponding output level to be zero, so no matter what the input luminance for red is, the output for red will always be zero and hence there will be no red on the TV display. Make sure you remember to click on the enable button to see these changes on the screen. You can save any lookup tables you create to disc as well, so that you can easily set up the options you want just by load­ing in the correct file name. Also available is reverse colour. Not only does this turn blacks into whites and whites into blacks but it also turns blues to yellows, greens to red, etc. Using this reverse video mode, text is much easier to read on the TV screen as well. There’s also a comprehensive help manual within Windows so that if you get stuck, there should be a solution. Overall, the TVCoder is the best PCTV converter we have seen but there is still some room for improvement in the overall picture quality. The ability to change the Colour Lookup Table is a great feature which gives the TVCoder a lot of ver­satility. And the price? – $379 from all Dick Smith SC Electronics stores. July 1994  83 VINTAGE RADIO By JOHN HILL Crackles & what might cause them Crackles are common problem in old radio receivers & fixing them can be a real challenge. Here are a few tips to get you started. On many occasions in the past, I have emphasised in this column the importance of replacing old and highly suspect paper capacitors when restoring valve radios. Retaining the paper capacitors is an open invitation to trouble. I have also stated that mica capacitors give very few problems and rarely need replacing. I would now like to withdraw that statement! Of late, I have had a number of repairs where the major fault was not due to faulty paper capacitors (although they were replaced as a matter of routine), but due to mica capacitors – mica capacitors of the silvered mica variety to be precise. It is strange when something like this happens because there is usually a run of similar problems and that is exactly what happened in this instance: two identical model 5-valve Astors, each with a troublesome mica capacitor. What’s more, it was a fault that eluded me for quite some time. Since the Astor experience, however, several other sets have had mica capacitor faults and it would appear that these inconspicuous little components are not as troublefree as I had previously thought. I have had almost no problems with mica capacitors until the two Astors came along. Both receivers worked quite well except for an irritating intermittent crackle. The odd characteristic of this particular crackle was that it could be faintly heard through the loud­ speak­er for well over half a minute after the set had been switched off. Now that’s what I call a persistent crackle! Crackles can emanate from many places: a loose connection such as an ill-fitting valve pin socket, a dry solder joint, a wire that is on the verge of corroding through, a faulty valve, a failing capacitor, a faulty resistor, or just about any component that is about to break down. And the defective component or connection causing the crackle, wherever it is, must be found and replaced. However, some of these faults can be incredibly difficult to track down. If the troublesome component would actually break down completely instead of just malfunctioning, then it would be much easier to find. It is pleasing to know that some of these faults can elude even the experts at times. I know because they have told me so! Knowing that gives some comfort when confronted with a hard to find phantom fault. There is a lot more to vintage radio repairs than replacing a defective valve! Removing the valves This photo shows one of the troublesome Astors men­tioned in the text. One faulty mica capacitor caused no end of trouble with these receivers. Note the replacement control knobs – the originals disintegrated on removal. 84  Silicon Chip Anyway, let’s get back to those troublesome Astors. Pulling the valves, one at a time, indicated that the crackle was in the output stage of the receiver. The crackle could still be heard after the frequency changer, the interme­diate frequency and the first audio valves had been removed. A crackle in these circumstances could perhaps be a failing output transformer or a faulty output valve, but neither of these were the source of the fault. Replacing every component This new & unused mica capacitor shows an ominous bulge in its moulded casing. It may be OK but it certainly looks a bit suspect & should be discarded. associat­ed with the output stage failed to cure the crackle. I might add at this stage that the high voltage electrolyt­ics had already been replaced and the rectifier valve replaced with a known good one. The problem was not in the high tension supply. Now this particular model Astor is similar in construction to many other 5-valve receivers in that it has a small mica capacitor connected from the plate of the driver or first audio valve to chassis (in this case 220pF – see Fig.1). Its purpose is to bypass any unwanted radio frequency components in the audio signal. It also top clips the higher audio frequencies and makes the audio a little more pleasant to listen to. After much searching, this small mica capacitor was found to be faulty and was the source of the elusive crackle. Spasmodic high tension leakage across the capacitor was feeding through to the control grid of the output valve via the .02µF coupling capacitor. The crackle still fed through even when the driver valve was removed – which really threw me off the scent. When one lacks proper training in radio servicing, some of these more obscure faults can be devilishly hard to locate. If problems, such as the one just described, had been pointed out to me as an apprentice learning the trade, then life today would be much easier regarding fault finding. As I never served an appren­ticeship (well, not at radio servicing), I have had to work by trial and error with nearly every fault I have encountered. And although I am getting better as time goes by, there is always something new to test the grey matter. Actually, I’m glad that I did not serve Small styro & ceramic disc capacitors are suitable replace­ments for mica capacitors, provided they have an adequate voltage rating. Defective paper capacitors can cause many problems in an old valve receiver & that includes the odd crackle. Their replacement with modern counterparts is highly recommended. an apprenticeship in radio servicing because it would have spoilt my interest in vintage radio. The troubleshooting aspect of the hobby is a big plus as far as I’m concerned. Learning repair techniques by perseverance and shear cussedness makes the restoration of old receivers intensely inter­esting. The rewarding feeling when a new and baffling fault is found and rectified is very stimulating indeed. Collectors who do not do their own repairs are missing out on most of what vintage radio has to offer. Returning to the problems of mica capacitors, it’s now apparent that they too can contribute to odd and often 6BD7 6M5 100pF C1 200pF C2 100k SPEAKER .02 200k HT Fig.1: the output stage in the troublesome 5-valve Astor receivers. The fault was traced to capacitor C1. July 1994  85 Testing a suspect valve is usually of little use when looking for faults such as crackles. A valve test provides only an indication that the valve should work OK. Crackles don’t usually show up on test. be aware of this. One cannot assume that mica capacitors do not breakdown. They can and they do! As mica capacitors are no longer made, the options regard­ing their replacement are perhaps limited. One can use new old-stock mica capacitors if a supplier can be found. Failing that, secondhand ones may have to do. Unfor­tunately, used mica capacitors may be as troublesome as those being replaced. I have accumulated heaps of secondhand mica capacitors but now view them with considerable suspicion? If it’s good enough to replace old paper capacitors with modern equivalents, then it should be good enough to do the same thing with suspect mica capacitors. They can be replaced with ceramic discs or small styro types, providing that they have a suitable voltage rating. Even small polyester capacitors are OK in some instances. As soon as I can lay my hands on a megger, I will be better equipped to check out suspect capacitors. Capacitors new or used can then be given a real high voltage test. Testing the dielectric strength at 400-500V should soon sort out any weak or faulty ones. Other causes All these valves test OK but produce crackles & splutters when in service. It is a shame that they have to be discarded because of internal faults. difficult to locate faults. Perhaps they should be treated in a similar manner to paper capacitors? With paper capacitors, not all of them are troublesome nor do all of them need replacing, although to do so always removes doubt. Similarly, not all mica capacitors need replacing but some are perhaps more suspect than others. If a radio crackles or has other faulty capacitor symptoms after replacing the paper capacitors, then check the voltage across the mica capacitors and replace those that operate under high 86  Silicon Chip potentials. This could well solve some of those hard to locate problems. Silvered mica capacitors Of the mica capacitors found in valve receivers, it appears as though the silvered mica type is the one most likely to cause trouble. The problem may be due to ageing or perhaps a manufac­turing flaw that takes years before it causes a breakdown. I’m not in a position to state categorically what the reason is. However, silvered mica capacitors do cause the odd problem and vintage radio enthusiasts should Earlier in this story, mention was made of a failing output transformer as being a possible source of a crackle. This cause was listed because I have had first hand experience with such a fault. The set was working quite well before it developed a crack­le which steadily increased in intensity. Then, quite suddenly – silence! Within a few seconds of the receiver stopping, a red glow from the output valve’s screen grid immediately suggested that the output transformer primary had failed. Checking with an ohmmeter soon confirmed this theory and a replacement transformer was installed. The result – a clean, crackle-free sound reproduc­tion! No doubt there was a well corroded copper wire involved somewhere in the primary winding and it was on the point of total breakdown. Once the transformer had completely failed, the defec­tive component was much easier to locate. On another occasion, a hard-to-find intermittent crackle was traced to the set’s volume control. In this instance, RESURRECTION RADIO Valve Equipment Specialists Repairs – Restoration – Sales Crackles can have mechanical origins. Poor contacts in moving parts can lead to noise problems which can often be easily cured with a dash of solder. VALVES – 1200 types in stock    EL34/BCA7 matched $30 ea.    6L6GC matched $28 ea. Parts are available for the enthusiast, including over 900 valve types, high voltage cap­a citors, transformers, dial glasses, knobs, grille cloth etc. Circuit diagrams for most Australian makes and models. Send SAE for our catalog. WANTED: Valves, Radios, etc. Purchased for CASH Call in to our NEW showroom at: 242 Chapel Street (PO Box 2029), Prahran, Vic 3181. Phone: (03) 510 4486; Fax (03) 529 5639 Corroded solder joints in base pins & top caps can cause crackles in some cases. Resoldering the base pin connections has brought many a troublesome valve back into service. the wiper arm inside the potentio­meter was loose and often caused a poor contact. A replacement pot soon fixed that problem. Intermittent faults Old Doug is a friend of mine who has spent the best part of his working life involved in radio and TV repairs, including a 20-year stint at Astor. Although now retired, he still does a bit of vintage radio repair work at home to occupy his spare time. But even a man of Doug’s vast experience can have trouble finding an intermittent crackle. Doug had a crackle that eluded him for days, mainly because it was of an intermittent nature and only raised its ugly head on odd occasions. Then it would disappear completely for a while, only to come back again. The problem was eventually traced to the high tension filter resistor which needed replacing. While I have not come across this one myself, it is a location that I would expect to find the source of a crackle. Any faulty high tension component is likely to cause this sort of problem. Valve problems Valves are a common trouble spot for crackles and the cause can be both external and internal. External valve faults often originate where the solder connects the leadout wires to the base pins. In very old valves, it is advisable to clean and resolder these connections. Poorly soldered top caps can also cause trouble and a resolder job is sometimes necessary to establish a reliable connection. I can recall one instance where a resoldered top cap cured a persistent crackle. Most valve crackles originate inside the valve itself and there is little that can be done to overcome these faults other than to replace the valve. Cracked cathode material, faulty spot welds and loose components can all contribute to noisy, crackly valves. Valves with loose or defective internal components can often be detected by lightly tapping the glass envelope. On other occasions, the fault may not show up so easily but it can still be a valve that is at fault. Unfortunately, valve faults such as crackles do not usually show up on a valve tester so testing is of little use in this regard. Crackles in radio receivers can be of a mechanical nature as well as electrical, and can be frustrating things to locate. But a systematic approach will eventually find the problem. It’s just another of the many things that makes vintage radio such an interesting and SC challenging hobby. July 1994  87 Silicon Chip Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; 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 Radio Receivers From The 1920s. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data; What Is Negative Feedback, Pt.4. November 1988: 120W PA Amplifier Module (Uses Mosfets); Poor Man’s Plasma Display; Automotive Night Safety Light; Adding A Headset To The Speakerphone. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Design Factors For Model Aircraft; Fitting A Fax Card To A Computer. 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. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; Telephone Bell Monitor/ Transmitter; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. 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. May 1989: Electronic Pools/Lotto Selector; 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. 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. 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. 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. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; NSW 86 Class Electric Locomotives. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; Alarm-Triggered Telephone Dialler; High Or Low 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 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; Weather Fax Frequencies. 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 1990: Music On Hold For Your Tele­ phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. 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. 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. ORDER FORM Please send me a back issue for: ❏ May 1989 ❏ June 1989 ❏ November 1989 ❏ December 1989 ❏ April 1990 ❏ June 1990 ❏ October 1990 ❏ November 1990 ❏ March 1991 ❏ April 1991 ❏ August 1991 ❏ September 1991 ❏ January 1992 ❏ February 1992 ❏ June 1992 ❏ July 1992 ❏ January 1993 ❏ February 1993 ❏ June 1993 ❏ July 1993 ❏ November 1993 ❏ December 1993 ❏ April 1994 ❏ May 1994 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 July 1989 January 1990 July 1990 December 1990 May 1991 October 1991 March 1992 August 1992 March 1993 August 1993 January 1994 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ November 1988 September 1989 February 1990 August 1990 January 1991 June 1991 November 1991 April 1992 September 1992 April 1993 September 1993 February 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 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 88  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. ✂ Card No. 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. April 1992: Infrared 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. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; LowCost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages; Tasmania's Hydroelectric Power System. May 1992: Build A Telephone Intercom; LowCost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateurs & TV. 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; What’s New In Oscilloscopes?; A Look At Hard Disc Drives. 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. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Off-Hook Timer For Tele­phones; Multi-Station Headset Intercom, 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. 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. 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; Electric Vehicle Transmission Options; Tuning In To Satellite TV, Pt.1. 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. 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. 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. 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; Build A Fax/Modem For Your Computer; 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 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; Windows 3 & The Dreaded Un­ recov­erable Application Error; 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 Direct­ ories; Valve Substitution In Vintage Radios. 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. 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 Sine­wave Inverter, Pt.5; Making File Backups With LHA & PKZIP. March 1993: Build A Solar Charger For 12V Batteries; An Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders; Test Yourself On The Reaction Trainer; A 24-Hour Sidereal Clock For Astronomers. 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; A Look At The Digital Compact Cassette. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; Low-Cost Mini Gas Laser; 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; A Digital Voltmeter For Your Car; 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 1993: Low-Cost Colour Video Fader; 60LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits; Unmanned Aircraft – Israel Leads The Way; Ghost Busting For TV Sets. 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 Electronic Cockroach; Restoring An Old Valve Tester; Servicing An R/C Transmitter, Pt.1. October 1993: Courtesy Light Switch-Off Timer For Cars; FM Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Mini Disc Is Here; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 2; Servicing An R/C Transmitter, Pt.2. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier, Pt.3; Build A Siren Sound Generator; Electronic Engine Management, Pt.2; More Experiments For Your Games Card; Preventing Damage To R/C Transmitters & Receivers. 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; Even More Experiments For Your Games Card. 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: More Than Just Bags Of Wind; Building A Simple 1-Valve Radio Receiver. 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; Switching Regulators Made Simple (Software Offer). 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; Spectrum Analysis Using An Icom R7000 Communications Receiver. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Muilti-Channel Infrared Remote Control; Dual Electronic Dice; Two simple servo Driver Circuits; Electrronic Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. 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; Electrronic Engine Management, Pt.9 PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, December 1988, January, February, March & 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 soldout issues, we can supply photostat copies (or tear­sheets) at $7.00 per article (incl. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. July 1994  89 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. Amateur swimming club timing system I am enquiring about the feasibility of a portable elec­tronic timing kit for use by amateur swimming clubs; a system that would be a basic, low-tech version of Olympic timing sys­tems. In its most trimmed down form, for single length 50-metre races, the system would need to have the following features: (1) Foolproof, unaffected by wet conditions and very simple to set up and dismantle each club night; (2) low voltage or battery operated; (3) timing started by the sound of the starter’s gun; (4) touch pads hanging in the water at the finishing end. The touch pads would need to be around 1200 x 600mm, possibly bigger if that is not a problem. There are usually eight lanes in a pool; (5) small LEDs or LCDs at the finishing end, from which the times are recorded for club records. Elapsed time displayed in minutes, seconds and hundredths of seconds; (6) starter and/or times recorder resets the system for the next race. Accurate stopwatch timing is generally said to be ±0.1 second of true Switch confusion in train controller Recently, I purchased a copy of your publication 14 Model Railway Pro­jects. I was very interested in the Walkaround throt­tle and as it is such a long time since I attempted to build an electronic project I decided to thoroughly study the details of this project. As a result, there are two points which I feel could be incorrect and wonder if you could clarify them before I at­ tempt this project. On page 22, the diagram of the local/remote switch S4 has its top row reading from left to right as 6’, 5’ & 3’. The middle row then reads 6, 3, 5. Should this row not read 90  Silicon Chip time, so that a portable electronic system would need to be no worse than that. Most races take less than a minute and the distance swims, of which there are few, take no more than 10 minutes. The main thoughts behind the portable electronic system are to save manpower on club nights and to improve general accuracy. The average club needs eight timekeepers; some are regulars with consistent timing skills, some are perhaps not quite as consist­ent. Possible embellishments for the system, providing the basic system is not too expensive, are: additional LEDs on or near each touch pad so the kids can see straight away what their time was; 150mm to 200mm high LED displays so the parents as well as the swimmers can see instantly what the times were; and touch pads at both ends of the pool for 100 metre and longer races. It is hard to know what the market is for an amateur swim­ming club timing system, but just about every school and munici­ pal swimming pool, of which there must be several hundred in Australia, has a swimming club the same as the top row; ie, 6, 5, 3? The circuit diagram on page 13 shows pin 1 of IC3 connected to pin 6 on the 6-way PC connector and pin 5 of IC3 connected to pin 5 on the 6-way connector. However, Fig.10 on page 22 shows these connections reversed. My thoughts are that problem one needs to be changed but problem two would work either way. I would like to clear up this confusion before I attempt to start this project. (J. P., Paralowie, SA). • Both your interpretations of the wiring are correct. The forward/reverse switch will still work correctly since the labelling is arbitrary but the local/remote switch must be wired as you suggest. attached to it. Most of these would absolutely love an electronic timing system, although they do tend not to have much money either. (R. W., Yeronga, Qld). • That’s a big ask. The requirements for a reliable timing system in a swimming pool would place this project outside the realms of what could be reasonably described in a magazine. The need for everything to be waterproof, to have large touch pads hanging in the water, multiple LED displays and hundredth of a second accuracy, would mean that the circuitry itself would probably run into $500 or more. The finished timing system could easily be worth several thousand dollars. We’ll have to pass on this one. More information on the 68705 processors Following the digital tank gauge project by Jeff Monegal which was published in your April 1994 issue, I was wondering where I could get any information on the 68705P3 microprocessor or similar relating to how the chip works, how it is programmed, how to adapt it to the outside world, and any projects I could make which would teach me how to design and program my own microcomputer. I have a good knowledge of electronics and digital systems but wish to learn more of microcomputers and mainly how to design working pro­ jects. (J. G., Mandurah, WA). • We have published a number of articles related to program­ ming the 68705 and the 68HC705C8 which have the same command set. The articles in question are as follows: A Look At The 68705 Microcontroller (September 1992); MAL-4.03 Microcontroller Board (November & December 1992 & February 1993); and Programming the Motorola 68HC705C8 (July, October & December 1993). In addition, we have published the following projects based on the 68705 or 68HC705: 8-Station Automatic Sprinkler Controller (July 1992); Multi-Sector Burglar Alarm (September & October 1992); Remote Volume Control for Hifi Systems (May & June 1993); and Stereo Preamplifier with Remote Control (September, October & November 1993). Champ fails the “blurt” test Last weekend, I put together a kit of the Champ amplifier, as described in the February 1994 issue of SILICON CHIP. I meas­ured the quiescent current at 4.5mA but the unit fails the “blurt” test. I have checked all components except the IC. Do you have any suggestions? (T. G., Elizabeth Bay, NSW). • We checked the text on this article and realised that the instruction to turn the trimpot clockwise is wrong – that would turn the amplifier gain to zero and no blurt would result. We suggest you wind the trimpot halfway and repeat the blurt test. If the amplifier still fails this test, you should try substitut­ing for the output coupling capacitor. You can do this by simply soldering another 220µF capacitor in parallel with the existing one on the board. The project is showing exactly the right quiescent current so there is no reason to suspect that there is anything wrong with the LM386 IC. Information on Nixie tubes In the September 1993 issue, someone “Asked Silicon Chip” about Nixie tubes. They are great devices but data is tough to find now. So I suggest following procedure. (1). Draw a diagram of the tube, assigning arbitrary pinouts. (2). Next, check for interconnections between the pins. Nixies are basically large neon lamps which only conduct via the ionised gas when voltages in excess of 50 volts are applied. (3). Sometimes you can see a grid like structure at the front or back of the tube and which pin it is connected to; this is the common electrode. The other electrodes will be in the shape of a digit or charac­ter. The next step should be done with caution. You will need an isolated source of between 120 and 200 volts DC. Connect this through a current limiting resistor of 100kΩ to 1MΩ (start Controller for antenna rotator My antenna rotator motor (a 12V wiper motor) is speed controlled by series resistors but lacks the grunt at the more desirable slower speed. Your January 1994 issue was a dream come true with Darren Yates’ project, the Mini Drill Speed Controller. I bought the kit straight away. The trouble is, my motor draws around 2A. I’m thinking of driving a bigger transistor, say a 2N3055, from the BD679. Can you suggest a modified circuit to do the job? Thanks in anticipation. (G. A., Cairns, Qld). • The main factor limiting the Mini Drill Speed Controller to a current of 1A is the rating of readily available DC plugpacks. The BD679 itself is capable of handling a peak current of 6A and so it should handle a 2A load without problems with the highest value as too much current will destroy the Nixie). Start experimenting between the pinouts from steps 1 & 2 above, being careful of pins which showed interconnection. You will soon find the right connections and polarity. Nixies typically draw 0.1 to 10mA per tube digit (never switch on more than one digit per tube at a time). Gradually increase the current until it reaches a plateau of brightness and settle on a current half of this value. Switching Nixies in a practical circuit will be the chal­lenge. There used to be suitable 74xx series ICs but you might have to use high voltage transistors or GTO thyristors now. My next comment concerns the item on a Cockroft-Walton voltage multiplier on pages 92 and 93 of the March 1994 issue. I don’t think you emphasised the safety aspect enough of operating capacitors directly from the mains. Several years ago I built up a circuit to drive a LED via a capacitor from the 240VAC mains and connected it to monitor a booster element on my solar hot water heater. The circuit used was published in the data sections of electronics catalogs. I had used all the proper components, good construction techniques, and insulated it with fibreglass although you may have to take the transistor off the board and fit it to a bigger heatsink. If you want to substitute a higher rated Darlington tran­sistor, then the BD649, which has a peak rating of 12A, would be the one to go for. Again, it would need a bigger heatsink. Apart from that, no modifications would be needed to the PC board. If you want to substitute a 2N3055 for the BD679, you will need to increase its base current drive since it is not a Dar­lington transistor. Its typical gain is less than 100 compared with over 2000 for the BD679. To increase the base current drive, change IC1 to a non-CMOS 555, change the 1kΩ resistor from pin 3 of IC1 to 100Ω, and change the 220Ω supply resistor to 47Ω. Naturally, the 2N3055 will need a large heatsink. electrical tape (designed for high temperature). After eight years, without any warning I heard a “pooff” when I was watching TV one night. No more than ten seconds later I discovered flames running up the wall under the house and the floor boards starting to catch fire. I was lucky! I managed to get the fire out without significant damage. What if I lost my house? My concern is that in the request­ed application of a bug zapper, that it is an application where it could likely be left on unattended for long periods of time. (D. H., Annandale, NSW). Southern Cross computer crashes I have built the Southern Cross computer and have had great success learning from it until I bought the relay board. The problem is “noise” crashing the computer or interfering with the chip on the relay board. I am switching lighting (400W metal halide) and other loads totalling no more than 200W. I removed the “GND” link and 10µF capacitor on the relay board as I have found it to behave better without them and added a 330µH choke to the input “GND” of the relay board. I also added 0.47µF 250V July 1994  91 Woofer Stopper has stopped I have assembled the Woofer Stopper kit and it worked fine for one day but it was accidentally left on overnight and hasn’t worked since. I have replaced every component except the ICs and I was hoping you could shed some light on what is wrong with it. I am getting 12V out of the tweeter terminal but it still doesn’t work. (D. F., Bradbury, NSW). • If you don’t have test equipment to verify that each stage is working then you will need to test the unit audibly. To do that, you must connect pin 1 of IC2 to pin 7 of IC1 (instead of pin 9) as described on page 29 of the article in the May 1993 issue. This makes the circuit capacitors to the Active and Neutral as filters plus tried different relays. Is my answer an opto-coupler plus Triac combination? I usually have no problems in assembly or trou­bleshooting kits but have no idea about inductive loads or RF noise on mains or DC. (D. D., Morley, WA). • The problem about switching any sort of incandescent lamp is that there are very large surge currents involved. These currents can be as much as 15 times the normal rated currents of the lamps and must be completely isolated from the relay board and the circuitry of the Southern Cross computer. It is also likely that the surge currents are causing momentary dips in the supply voltage to your computer and causing it to crash. The cure is to use a much better regulated power supply which will not be af­ fected by momentary drops in the mains voltage. We would not recommend connecting capacitors of the size you mention to the Active and Neutral lines. The Champ goes mobile I have built the “CHAMP” amplifier (SILICON CHIP, February 1994) and find it works exceptionally well with my mobile phone, driving a small 8Ω extension speaker. This set up has only been used as a bench test and I 92  Silicon Chip work at a frequency of 2kHz. You should not have 12V DC across the tweeter terminals. There should be 0V DC and about 10VAC (at 2kHz) present across the tweeter. You should also be able to measure about 6V DC between both sides of the tweeter and the 0V line. If the circuit fails these tests, check that +5V is present at the output of the 78L05 regulator and at pins 14 or 16 of the ICs. The output of each respective IC in the frequency divider should sit at somewhere between 0 and 5V DC. For example, pin 2 of IC5a should be at about +2.5V. Naturally, you should also carefully check the back of the PC board for bad or broken solder connections. would like your comments regarding the suitability of this idea for an in-car installation and hence a way of providing a clean regulated 12V supply. I also have a question for the Serviceman. I have been trying to locate a number of ICs for a Commander 48cm colour TV, model CHT-9102, for quite some time without success. I hope you can help. Without a circuit diagram I cannot be sure what these ICs do, however they are both located on the circuit board for chan­nel programming and frequency lock control. Any help would be appreciated. (B. G., Deception Bay, Qld). • There is no need to run your CHAMP from a regulated 12V supply as it will quite happily run up to +16V with an 8Ω load – see Fig.3 on page 47 of the February 1994 article. However, it would be a good idea to protect it from spikes and transients by connecting a 16V 1W zener diode across the supply rail, fed by a 10Ω 0.5W resistor from the 12V battery. We are unable to help you with circuit information for your TV set. You will need to approach the distributor direct. Using the voice recorder in loop mode I wish to use the ISD2590P voice recorder in continuous loop mode. Your data article in the February 1994 issue adequate­ly describes how this may be done. Is it possible to connect a higher quality microphone to the device? What additional circui­ try would be required if the device were to be connected to the line out level connection of, say, a CD or tape deck? I assume that the ISD2545 with its higher sampling rate would produce better output sound quality. Who supplies this range of devices in Australia? Your assistance in these matters would be much appreciated. Congratulations on a magazine of consistently high quality. (A. C., Woodford, NSW). • Since this device produces voice quality only, it is not really worth using a better microphone and this comment would still apply to the ISD2545. If you did want to use a dynamic microphone, you would omit the 2.2kΩ and 10kΩ resistors and the 10µF capacitor associated with the electret bias network. The microphone signal would then be fed in via the existing 0.22µF input capacitor to pin 17. If you want to connect a CD player or other line out source, you will need an attenuator to bring the signal down to a few millivolts. We suggest a 50:1 attenuator consisting of 47kΩ and 1kΩ resistors. The ISD range is distributed by R&D Electron­ics. Their phone number is (02) 638 0077. Notes & Errata 12-240VAC 200W Inverter; February 1994: Transistor Q16 on the circuit diagram (Fig.4) is incorrectly labelled as a BC338; it should be a BC328. In addition, the transistor marked Q12 near Q13 (Fig.4) should be designated Q14. On the overlay diagram (Fig.5), transistors Q13 and Q14 are transposed, while the .047µF capacitor near T2 should be a .0047µF capacitor to agree with the circuit. The parts list should also show a .0047µF MKT capacitor instead of a .047µF capacitor. Fast Charger for Nicad Batteries; May 1994: The circuit (Fig.2) shows a 680Ω current limiting resistor for LED 1. This should be changed to 470Ω to agree with the parts layout diagram (Fig.3). The parts list should also be SC altered. SILICON CHIP BOOK SHOP Newnes Guide to Satellite TV 336 pages, in paperback at $49.95. Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Servicing Personal Computers By Michael Tooley. First pub­ lished 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. Optoelectronics: An Introduction By J. C. A. Chaimowicz. First published 1989, reprinted 1992. This particular field is about to explode and it is most important for engineers and technicians to bring themselves up to date. The subject is comprehensively covered, starting with optics and then moving into all aspects of fibre optic communications. 361 pages, in paperback at $55.95. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. Power Electronics Handbook Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Surface Mount Technology By Rudolph Strauss. First pub­ lish-ed 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First pub­ lished 1989. 6th edition 1994. This just has to be the best reference book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. semicustom electronics & data communications. 63 chapters, in paperback at $140.00. Radio Frequency Transistors Principles & Practical Appli­ cations. By Norm Dye & Helge Granberg. Published 1993. This timely book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering techniques, impedance matching & CAD. 235 pages, in hard cover at $85.00. Newnes Guide to TV & Video Technology By Eugene Trundle. First pub­ lish-ed 1988, reprinted 1990, 1992. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 432 pages, in paperback, at $39.95.  Title Price  Newnes Guide to Satellite TV  Servicing Personal Computers  The Art Of Linear Electronics  Optoelectronics: An Introduction  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Surface Mount Technology  Electronic Engineer’s Reference Book  Radio Frequency Transistors  Newnes Guide to TV & Video Technology $55.95 $59.95 $49.95 $55.95 $55.95 $59.95 $99.00 $140.00 $85.00 $39.95 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A July 1994  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES VINTAGE RADIO 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. VINTAGE RADIO SWAP meet/fair. Inc. military, amateur radio and antique sound. Sunday 23rd October, 1994 10am to 5pm. Glenroy Technical School Hall, Melbourne. Bookings: R. Howarth, PO Box 9, Junortoun 3551. Phone (054) 49 3207. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ FOR SALE THE HOMEBUILT DYNAMO: (plans) brushless, 1000 DC watt at 740 revs. $A85 postpaid airmail from Al Forbes, PO Box 3919 - SC, Auckland, NZ. Phone Auckland (09) 818 8967 any time. Rotor magnets (3700 gauss) kit now available. FLUORESCENT INVERTER KIT (SC Feb 91) 12V or 24V/5W-21W.48V ver­ sion on request. Secondary wind, board plus components $30.00 plus P&P $4.00. Solar battery charging regulator short form kit 12V or 24V (series) (SC Jan 94) employs Mosfet to switch solar array max current 10A $54.00 plus p&p $4.00. Additional Mosfet $8.00 and Schottky diode $5.00 to make 20A regulator. Cheques and postal money orders accepted with mail orders. Send orders to Otakar Priboj, PO Box 362, Villawood, NSW 2163, Austra­lia. Phone (02) 724 3801. WEATHER FAX programs for IBM XT/ ATs *** “RADFAX2” $35 is a high res- 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 • • • • • • • BUSINESS FOR SALE TV, video & hifi repair – TV rental – electronic spare parts & accessories – authorised service centre for all major brands. Booming Sunshine Coast – Queensland –idyllic lifestyle. Well established with strong local reputation, consistent turno­ver with good sustained profits, centrally located ensuring “owner­-ship” of a large slice of the service and retail trade. Suit owner operator; minimal staff requirements. Turnover approx $185,000 – gross profit $100,000. Priced to sell: $120,000 WIWO. Phone Leonard Pey (074) 48 1633 or (074) 46 2732 A/H. MEMORY PRICES Building Your Speakers? Need Help? PRICES AT MAY 19TH, 1994 SIMM 1Mb x 3 1Mb x 9 4Mb x 9 4Mb (72-pin) 8Mb (72-pin) 16Mb (72-pin) 70ns 70ns 70ns 70ns 70ns 70ns $61 $63 $245 $242 $485 $960 DRAM DIP 1 x 1Mb 256 x 4 70ns 70ns $7.50 $8.00 IBM PS.2 55/65SXVP L40/N33 90/95 PS1 4Mb 4Mb 4Mb $240 $280 $250 MAC 4Mb 4Mb x 80 80ns 6Mb P’BOOK $215 $350 CO-PROCESSORS 387S/DX to 40 LASER PRINTER HP with 2Mb COMPAQ PROLINEA 8Mb TOSHIBA 2000SX 8Mb 46/1900 3.3 4Mb SUN SPARC 10/20 16Mb PCMCIA 1Mb V2 BAT SRAM 2Mb V2 BAT SRAM 2Mb FLASH RAM 20Mb SUN FLASH RAM $90 $198 $485 $680 $295 $1110 $205 $330 $345 $1500 Ring for Latest Prices 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. TRANSFORMER REWINDS PELHAM ALL TYPES OF TRANSFORMER REWINDS Speaker parameters measured Boxes designed & manufactured Crossovers designed Systems for lounge, car or PA For more details contact: Australian Audio Consultants Box 1031, Aldinga Beach, SA 5173. Phone or fax on (085) 56 6370 CTOAN ELECTRONICS Sales tax 21%. Overnight delivery. Credit cards welcome. 5-Year Warranty Tel: (02) 980 6988 Fax: (02) 980 6991 • • • • Got a great idea for a new device? Don’t leave it as just an idea. Call us; we can help make is work. You describe it – we’ll design it. PO Box 211, Jimboomba 4280. Phone (07) 297 5421. TRANSFORMER REWINDS Reply Paid No.7, PO Box 1058, St Marys, NSW 2760. Ph: (02) 833 1146. Fax: (02) 623 5559. • olution, shortwave weather fax, Morse & Rtty receiving program. Suitable for CGA, EGA, VGA and Hercules cards. Needs SSB HF radio & Radfax decoder. *** “SATFAX” $45 is a NOAA, Meteor & GMS weather satellite picture receiving program. Needs EGA or VGA plus “WEATHER FAX” PC card. *** “MAXISAT” $75 is similar to SATFAX but needs 2Mb expanded memory (EMS 3.6 or 4.0) and 1024 x 768 SVGA card. All programs are on 5.25-inch or 3.5-inch disks (state which) & include documentation. Add $3 postage. Only from M. Delahunty, 42 Villiers St, New Farm, Qld 4005. Phone (07) 358 2785. NETWORK YOUR PCs with “Little Big LAN”. Share disk drives and files (multi-user record locking), CD-ROMs and printers (with spooling). Connect PCs via serial or parallel ports, Arcnet and/or Ethernet cards. Supports up to 250 computers per network for only $95 ($100 for 3.5") for a whole network. Add $4 for postage in Australia. Works with MS-DOS, DR-DOS and Windows. For more information, write to GRAN­ TRONICS, PO Box 275, Wentworth­ville 2145. Phone A/H (02) 631 1236. REPAIRS TO: Commodore 64’s and accessories; all Atari’s; Spectra Video, Spectrum and Amstrad Computers. Phone: Adelaide (08) 377 2175. VALVE AMPLIFIERS: Australian made. Mono, stereo, guitar using 2A3, 211, 6L6 or 807 valves. williamson reproductions. Parts available for DIY constructors. Circuit diagrams and construction details for many types of valve amplifiers. Valve equipment repairs. Lancroft Pty Ltd, PO Box 439, Bexley 2207. Phone (02) 567 5390. BINARY CLOCK - OCTOBER 1993: complete documentation supplied, includes introduction to binary, how it works, PLD source list­ings, conversion tables. Kit with PCB and all components $75 + $5 p&p. Optional Z frame stand (includes spacers and chassis DC connector) $25 + $5 p&p. Prototype Electronics, 1/29 Stewart St, Parra­ matta, NSW 2124. Phone (02) 683 3510; Fax (02) 630 3148. Pay by cheque, money order, credit card. SUBSTITUTE FOR A HANDFUL OF ICs: Parallax “BASIC STAMP”. A gen­er­al purpose small circuit module, it is really a 25 x 50mm board with a computer chip (4MHz PIC 16C56), EEPROM, 8 I/O pins, board space includes prototyping area. Program it on a PC (only 33 instructions) with development kit which includes one “BASIC STAMP” ($249 plus S/T & post), extra modules ($66 plus S/T & post). Send 45c stamp for more information. Parallax distribu- • • • 350 Watt Power MOSFET Amplifier Module As published in the June 1994 issue of Silicon Chip. Kit price $159.00. Postage and handling $8.00. Payment by M/C, B/C, Visa, Cheque or Money Order. 3kg O/N Air Bag $10.00 Computer & Electronic Services Pty Ltd 27 Osborne Avenue, Trevallyn Launceston, Tasmania 7250 Phone 003-34 4218; Fax 003-31 4328 tor and techni­cal support in Australia: MicroZed Computers, PO Box 634, Armi­dale, NSW 2350. Facsimile (067) 72 8987. SATELLITE TV DX SUPER RX receiver. Threshold 2.5dB. Also digital picture, sound, synchron, resolution processors. Mobile DX re­ceivers, pay TV decoders. TV, radio, picture, sound mod­ulators. Digital, analog signal meters. Send $5 for info and catalog/refundable to John Papp, PO Box 472, Sanderson, NT 0812. Fax/Ph:(089) 27 4985. BURGLAR ALARM KIT: multi-sector, microprocessor controlled (refer SILICON CHIP, Sept. 1992). Main control panel $170.00 (no case); Remote keypads $47.00 (up to 4 can be used on each panel); Rockonet 3001 PIRD (passive infrared detector) $65.00; Rockonet 6000 PIRD $72.00. P&P $9.00. M. Zenere, 82 Headingley Rd, Mt. Waver­ley, Vic. 3149. Phone: (03) 803 3535. July 1994  95 INTERNATIONAL SATELLITE SYSTEM A fully complete commer­cial auto tracking system 1 OPAC 4.5 metre, 12-segment dish. Bearing configuration, styled on a commercial unit (18 months old). Includes two heavy duty actuators, 3-platform base, 1.2 metre raisers – heavy duty. Purchased <at> $6,600.00. 1 C-band (30K) LNB & ADL RHC feedhorn with 30 metres of RG11 cable. Purchased <at> $500.00. 1 Professional commercial (microprocessor) tracking system. Onboard internal clock, internal data base, fully automated updating, etc, etc. Purchased <at> $2,500.00. 1 WINNERSAT C/Ku band 920 computer synthesized satellite receiver (on screen graphics) with positioner built in system. All adjust­able bandwidths with IR remote. Purchased <at> $750.00. 1 WINNERSAT C/Ku programmable satellite receiver with IR remote, adjustable bandwidths. Purchased <at> $700.00. 1 WINNERSAT WR-370 stero manual satellite receiver. Adjustable bandwidths (Panda). Purchased <at> $450.00. 1 Custom built receiver unit. Includes 1 Nexus commercial receiv­er, 1 adjustable bandpass filter, 1 digital videplexer and switchmode power supply. Purchased <at> $2100.00. 1 portable satellite signal strength meter. Purchased <at> $180.00. 1 vertical/horizontal detail processor (commercial grade unit). Purchased <at> $1100.00 1 JVC 9 system plus 3 video/audio inputs 52cm colour monitor/television receiver with IR remote. Purchased <at> $1500.00. 1 JVC 10-inch video/RGB monitor (selectable inputs x 2). Pur­chased <at> $1400.00. 2 9-inch Pro B/W monitors. One has audio amp. Purchased <at> $900.00. 1 Video/audio signal unit (custom built) with amps, 8 inputs V/A x 10 outputs V/A, selectable audio and video output (known as a router). Purchased <at> $2000.00 To build this advanced system cost $20,680.00. Will sell for $6,950.00 ONO (genuine reason for selling) Phone Rod on 08 387 0372. Advertising Index Altronics ................................ 74-76 Aust. Audio Consultants...............95 Av-Comm.....................................41 Computer & Elect. Services.........95 Ctoan Electronics........................95 David Reid Electronics ..............21 Dick Smith Electronics........... 10-13 Electronic Fault Info.....................71 Harbuch Electronics....................79 Instant PCBs................................95 Jaycar .............................. 45-52,67 Kalex............................................67 Macservice....................................3 McLean Automation.....................21 Nucleus Computer Services........65 Oatley Electronics.................. 60-61 PC Computers.............................16 Pelham........................................95 RCS Radio ..................................94 Resurrection Radio......................87 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. 38 Garnet Street, Niddrie 3042. Phone (03) 337 1917 (a/h), (03) 575 3349 (b/h). Fax (03) 575 3369. MICASOFT Electronics and Computing tutor program, written in UK, ideal for TAFE, schools, or individual use. Now available in Australia. Send $1.80 in stamps for demo disk (tell us what size). MicroZed Computers, PO Box 634, Armidale 2350. COMPLETE Z-80 microprocessor package plus additional experimenter boards. As new. cost $500, sell $200. Joe (03) 742 3125. CONTROL RELAYS, Robots, Radios or Railways from LPT1: of your XT to 486 PC. 64 bits. Fully expandable. Demo programs, flow charts, circuits, drivers in M.L. & Basic. Bare PCB and software $38, or demo/promo disk $2. Don McKenzie, 29 Ellesmere Crescent, Tulla­marine, Vic 3043. Phone (03) 338 6286. REAL TIME ICE!!! The only way to go. MOTOROLA 6805 EMULATOR and programmers. Prices and data from Graham Blowes, Mantis Micro Products, 96  Silicon Chip PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. Microprocessor For Stereo Preamplifier Now back in stock: the 68HC705-C8P pre-programmed micro­pro­cessor for the Infrared Remote Controlled Stereo Preamplifier (SILICON CHIP, Sept.Oct. 1993). Also suits the Remote Volume Control (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. Rod Irving Electronics .......... 27-31 Silicon Chip Back Issues....... 88-89 Silicon Chip Binders..................IBC Silicon Chip Bookshop.................93 Silicon Chip Projects Book......OBC Silicon Chip Software..................83 Tektronix....................................IFC Transformer Rewinds...................95 Yuga Enterprise...........................78 _________________________________ 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.