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Electronics for the enthusiast PLAY ,.._ ia, 0. al z 0 z C :8 "' .!:! :a:::, 0. Getting the most out of nicad batteries B5601 Dual Trace 20MHz/1 mV 93 ~ only ex-stock at this prices. Probes extra. Quantity discounts available. $740* ex tax $890* inc tax Talk to your local Elmeasco distributor about Aaron M.L John Pope Electrical (062) 80 6576 • J Blackwood & Sons (062) 80 5235 21 ELMEASCO Instruments Ply.Ltd. Incorporated in N .S.W . NEW SOUTH WALES 18 Hilly Street, MORTLAKE P.O.Box 30, CONCORD NSW 2137 Tel: (02) 736 2888 Fax: (02) 736 3005 VICTORIA 12 Maroondah Highway, RINGWOOD P.O.Box 623, RINGWOOD VIC 3134 Tel: (03) 879 2322 Fax : (03) 879 4310 QUEENSLAND 192 Evans Rd, SALISBURY P.O.Box 274 SALISBURY QLD 4107 Tel : (07) 875 1444 Fax: (07) 277 3753 S.AUSTRALIA 241 Churchill Rd,PROSPECT P.O.Box 154 PROSPECT SA 5082 Tel: (08) 344 9000 Fax: (08) 269 6411 W. AUSTRALIA 32 Teddi ngton Road, Victoria Park, W.A. 6100 Tel: (09) 470 1855 Fax: (09) 470 3173 • George Brown (062) 80 4355 li..S..Yi. Ames Agency 699 4524 • J Blackwood & Sons• George Brown 519 5855 Newcastle 69 6399 • Auto-Catt Industries 526 2222 • D.G.E. Systems (049) 69 1625 • W.F.Dixon (049) 69 5177 • Ebsen 707 2111 • Macelec (042) 29 1455 • Novacastrian Electronic Supply (049) 62 1358 • Obiat Pty Ltd 698 4776 • Petro-Ject 569 9655 • David Reid 267 1385 • Digital 709 6511 • Geoff Wood 427 1676 N.TERRITORY J Blackwood & Son (089) 84 4255, 52 1788 • Thew & Mccann (089) 84 4999 QUEENSLAND Auslec (07) 854 1661 • G. Brown Group (07) 252 3876 • Petro-Ject (075) 91 4199 • St Lucia Electronics 52 7466 • Cliff Electronics 341 4655 • L.E.Boughen 369 1277 • The Electronics Shop (075) 32 3632 • Thompson Instruments (Cairns) (070)51 2404 • Nortek (Townsville)(077) 79 8600 S AUSTRALIA Protronics 212 3111 • Trio Electrix 212 6235 • J Blackwood & Sons 46 0391 • Petro-Ject 363 1353 TASMANIA George Harvey (003) 31 6533 (002) 34 2233 ~ Radio Parts 329 7888 • George Brown Electronics Group 878 8111 • G.B. Telespares 328 4301 • A.W.M. Electrical Wholesalers• Petro-Ject 419 9377 • J Blackwood & Sons 542 4321 • Factory Controls (052) 78 822 • Mektronics Co 690 4593 • Truscott Electronics 723 3094 W AUSTRALIA Atkins Carlyle 481 1233 • Debbie Instruments 276 8888 • Protronics 362 1044 AUGUST 1988 FEATURES FANCY A PLASMA DISPLAY just like the one shown on the front cover? This easy-to-build EHT supply goes with a commerdal plasma bottle to give you a fascinating project. Details page B. 54 A Look at Insulated Tab Trlacs by Leo Simpson A safer way of switching mains voltages 63 Digital Fundamentals, Pt.9 by Louis Frenzel Input/output operations 76 The Evolution of Electric Railways by Bryon Moher Pt.10: Electrification in Central Europe PROJECTS TO BUILD 8 Bulld a Plasma Display by Leo Simpson Lightning bolts in a bottle 18 High Performance AC Millivoltmeter by Bob Flynn Measures signals down into the microvolt region 38 Universal Power Supply Board by Leo Simpson Use it with op amp circuits 42 Building the Discollght, Pt.2 by Greg Swain Construction plus troubleshooting 56 Remote Controlled Chimes Unit by John Clarke Use it as a patient sick call or wireless doorbell SPECIAL COLUMNS IF YOU'RE CROOK in bed with a bad back, there's no need to shout for a cup of tea. Just press the button on our new remote controlled chimes unit to gain attention. It also makes a beaut wireless doorbell. See page 56. -' 4 Vintage Radio by John Hill Capacitors cause lots of problems 14 The Way I See It by Neville Williams Some things are enough to make a grown man cry 28 Serviceman's Log by the original TV serviceman Sound reasons for confusion 84 Amateur Radio by Garry Crott How to get the most out of nicad batteries DEPARTMENTS 2 Publisher's Letter 34 Circuit Notebook 49 Back Issues 89 Subscriptions 91 94 95 96 Product Showcase Ask SIiicon Chip Notes & Errata Market Centre THIS HIGH-PERFORMANCE AC millivoltmeter is the latest in the SIUCON CIJIP line-up of test equipment. ·It con measure audio signals down into the microvolt region. Construction starts on page 18. NEGATIVE FEEDBACK SERIES: due to severe demands on space in this issue, we have had to hold the Negative Feedback article over until next month. AUGUST 1988 1 SILICON CHIP Publisher & Editor-In-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Advertising Manager Paul Buchtmann Regular Contributors Neville Williams, FIREE, VK2XV Bryan Maher, M.E. B.Sc. Jim Yalden, VK2YGY Garry Cratt, VK2YBX Jim Lawler, MTETIA John Hill David Whitby Photography Bob Donaldson Edltorlal Advisory Panel Philip Watson, VK2ZPW Norman Marks Steve Payor, B.Sc., B.E. SILICON CHIP is published 1 2 times a year by Silicon Chip Publications Pty Ltd. All material copyright (c). No part of the contents of this publication may be reproduced without prior written consent of the publisher. Kitset suppliers may not photostat articles without written permission of the publisher. Typesetting/makeup: Magazine Printers Pty Ltd, Waterloo, NSW 2017. Printing: Masterprint Pty Ltd, Dubbo, NSW 2830. Distribution: Network Distribution Company. · Subscription rates are currently $42 per year (12 issues). Outside Australia the cost is $62 per year surface mail or $1 20 per year air mail. Liability: 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. Address all mail to: Silicon Chip Publications Pty Ltd, PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 982 3935. ISSN 1030-2662 * Recommended and maximum Australian price only. 2 SILICON CHIP PUBUSHER'S LE'l-l'E.R The importance of chemistry in electronics This month's issue of SILICON CHIP features an unusual do-ityourself project, the Plasma Display. In essence, it seems simple enough: just an evacuated glass jar containing minute quantities of inert gases and powered by a high voltage source, the EHT generator. Even the latter is superficially simple, being a transformer-coupled push-pull inverter powered by a DC source. Superfically simple it may be, but understanding the workings of such an inverter is not simple at all. And the workings of the Plasma Display are not easy to understand either, although we have tried to explain them as well as possible, without being too long-winded. Even so, while the Plasma Display is a fascinating project, some people may tend to dismiss it as just an exercise in technical trivia with no real purpose other than to be a visual attraction. But it is much more than that. It embodies principles which are employed in all the vapour discharge lamps in use today as well as the exotic and expensive plasma discharge displays used for some computers. For us, the Plasma Display highlights the importance of chemistry in electronics. The industrial chemist is the unsung hero of today's electronic componentry. Why? Just consider the process of evacuating the glass jar, introducing the small amounts of inert gas and the subsequent sealing of the container against leakage and contamination. While efficient vacuum pumps are nowadays easily obtainable, achieving and maintaining a very high vacuum in a container is not an easy matter. The internal surfaces of the glass can easily be contaminated with substances which later "outgas" and degrade the vacuum. Any sealant used must not itself "outgas" and thereby contaminate the inert gases. Similarly, the purity, mixture and pressure of the inert gases are extremely important if the best display is to be obtained. This is a demonstration of the importance of chemistry. In the manufacture of every electronic component, chemistry assumes an over-riding importance. Without efficient epoxy encapsulating compounds, we could not have today's integrated circuits the ingress of water and other contaminants would quickly destroy them. Similarly, we could not have today's high performance capacitors and resistors without enormous research on the part of industrial chemists. Low leakage aluminium and tantalum electrolytics would just not be possible without the work of chemists. So the Plasma Display is as much a demonstration of chemistry as it is of electronics. It is indeed a fascinating project. Leo Simpson MO D EM S foi dfu~tiafia Don't buy imported • unsupported The Avtek advantage • Australian designed Australian manufactured Australian supported MEGAMODEMS 12/123 The Avtek Megamodems provide Australia's best value communications products. with a range of fully automatic, autodialling modems. Megamodems are suitable for data transfer from personal computers. terminals, mainframes and mini host computers and for all videotex services such as Viatel. The use of the latest technology has enabled us to make the Megamodem more compact and reliable than any other modem. Price is very competitive and reflects efficiencies incorporated in the design. The Megamodems are locally designed and built. SeNice. support and specialist R&D for the Megamodem range is all based in Australia. Available either as a standalone RS232 model or as a plug in 1/2 card for IBM PCs and compatibles. The · Megamodem range of modems are Telecom authorised. Specifications Data Standards Data Rates MAIL ORDER WELCOME VISA Automatic Dial, Answer, and Disconnect: The Megamodems will automatically answer an incoming call and connect the computer to the line. When originating a call it will then dial out the required number and auto-connect to the computer at the other end. It will then ''hang-up" at the end of a communications session. Both pulse and tone dialling are supported. The modem is compatible with new Telecom exchanges and modern PABXs and can handle high speed tone dialling. Fully Hayes AT Smartmodem Compatible: The Megamodems are industry standard "HAYESSMARTMODEM "compatible which means they can take advantage of all the communications facilities of packages such as Crosstalk. Open Access. Symphony and Multicom. All communications parameters such as baud rate, parity and number of stop bits are set up automatically by the software and the Megamodem. Using appropriate software data can be sent and received while the Megamodem is unattended. CCITTV2l. Bell 103, CCITT V22 Bell 212. (123 model only CCITT V23) 300/300.1200/1200 (123 model only 1200/75, 75/ 1200) BUY DIRECT FROM THE MANUFACTURER Model 12 & PC12 $375iw:tax Model 123 & PC123 $449 iw:tax / (~ · =-~ 1yT'r1( ~~~;~-· . ~ I ~~ 7 PO Box 284 Pymble 2073 Telephone (02) 888 5333 Facsimile (02) 887 2839 VINTAGE RADIO By JOHN HILL Capacitors cause lots of problems Vintage radios, like all radios, have a considerable number of capacitors in their circuitry. Many of these capacitors are a potential source of trouble, especially the paper and electrolytic types. Here's what to look for. The first type of capacitor (referred to back then as a condenser) was the Leyden jar. These early capacitors consisted of a glass jar (being the insulating dielectric) with a layer of foil on the inside and the outside of the jar. In principle, they were like any other capacitor: two metal plates separated by a dielectric, their prime function being to store an electrical charge. Although it worked, the Leyden jar had several disadvantages. It was big and bulky which meant that a much more convenient form of capacitor was necessary to meet the demands of radio. This was done by rearranging the shape of the plates and by using a thinner dielectric. Early radio capacitors were constructed out of layers of either brass or copper shim which were separated by thin slivers of mica. Mica capacitors were quite enduring and many of those that have survived from the 1920s are still quite useable today. Mica capacitors are frequently encountered in valve radios of all ages and they rarely give trouble. Only once have I found it necessary to replace a mica capacitor. However, mica capacitors are only good for relatively small capacitance values. As valve radio developed from battery-operated reaction type receivers to ACpowered superhets, there was an increasing need for capacitors of greater capacity than the mica type could conveniently accommodate. The paper capacitor was the next stage in the development of this common radio component. Paper capacitors A paper capacitor is made by rolling up two strips of foil which are separated by wax impregnated paper. Each foil has a wire connected to it and the unit is either housed in a cardboard tube, a plastic casing or a metal can. While a wax impregnated paper dielectric may sound a bit primitive in the high-tech world of the 1980s, it was about the only practical and reasonably economical material available in the early 1930s when paper capacitors were first put to good use. Incidentally, paper capacitors were still being manufactured for radio and TV use in the 1960s. Today's capacitors have shrunk in size, the reason being that the old wax impregnated paper has now been replaced with a thinner plastic dielectric. Plastic dielectrics such as polyester allow the plates of the capacitor to be much closer and, therefore, smaller capacitors can be made. Modern capacitors are about one tenth the size of their old paper counterparts. Paper capacitor faults A selection of old mica capacitors. These capacitors are very reliable and seldom require replacement with more modern types. 4 SILICON CHIP As far as a valve radio is concerned, paper capacitors are Many early mica capacitors featured mounting lugs and thumbscrew terminals. This particular unit is rated at .0002JLF. A couple of typical paper capacitors - cracked, troublesome and quite unreliable. troublesome and seem to develop lots of faults as time goes on. The older they get, the more unreliable they become. The reason for this decline in performance is simple: the capacitor absorbs moisture over the years, thus allowing electrical leakage between the two plates. Paper capacitors are one of the most suspect components one can find in an old valve radio, with some brands being more suspect than others. If a modern capacitor of say 0.1µ,F is tested with a multimeter set on the x1k0 scale, the needle will rise a little as the capacitor is charged, then drop back to zero when full charge is reached. A similar test with an old paper capacitor will also show the meter needle rise and fall but in many instances it will not fall back to zero. Often a reading of 2-10MO is common, indicating that the dielectric allows a certain amount of leakage. Of course, the voltage applied by the multimeter to the capacitor is quite low. If this causes leakage, think how much worse the situation will be when the capacitor is placed into a circuit where hundreds of volts are across it. Many paper capacitors simply can no longer take this high voltage strain. Those old black AW A paper capacitors, in particular, are most troublesome and frequently split open at the ends. On odd occasions, they may even blow themselves apart. It has been my experience that defective paper capacitors are the cause of many problems in valve radios and are highly suspect at the best of times. To combat this problem I replace all the paper capacitors in the radio sets that I restore. This simple step often cures a multitude of ills and a set that was acting up a bit beforehand will often behave as it should after the capacitors have been replaced. There are probably a good many readers who agree with my total replacement strategy but there would be others who may object to this procedure, particularly as I use modern replacements. Some restorers have very definite views when it comes to originality and replacing components with modern equivalents just simply isn't done. I'll go along with originality to a certain extent, but only as far as is reasonably practical. So long as things look original from the back view, I'm happy. Not many people are going to insist on the chassis being removed so as to check for nonstandard components underneath. Now if this originality bit worries you, perhaps there are ways of implanting a modern capacitor inside an old casing. Those paper capacitors that are housed inside a cardboard tube could respond to this treatment quite well, although one would have to be keen to bother. Replacing capacitors Although it seems a relatively simple task to replace a dozen or so capacitors in an old radio, one can run into considerable trouble when doing so. The best advice I can offer is not to unsolder any capacitor that is beAUGUST 1988 5 Old electrolytic capacitors are a common source of serious trouble in vintage radios. The replacement of all electrolytics during restoration can save a lot of hassles later on. ing replaced. It is so easy to lose track of where it came from, it just isn't funny. One interruption is all that is needed and the mental picture of where that capacitor was connected has gone forever. By far the best method is to cut the component out using a pair of sidecutters, leaving the original leads in place to indicate where the new part should be fitted. Of course, you should remove and replace only one capacitor at a time. Paper capacitors were usually rated at 200, 400 and 600 volts. Modern replacements will usually either be rated at 100, 160 or 630 volts, although other voltage ratings are available. Even low voltage capacitors can be used quite extensively in a vintage radio. While a valve radio is basically a high voltage instrument, not all the capacitors are subject to high voltages. This means that 100 volt greencaps are quite suitable for use in many circuit locations. Generally speaking, most 200 volt paper capacitors can be replaced with a greencap. It has been my observation that This old 4µF paper capacitor has seen better days, with internal problems forcing the end off the can. 6 SILICON CHIP the 100 volt rating on a greencap can be exceeded by 50% without any trouble. They seem very tolerant of voltages above their nominal rating, although it may not be wise to exceed the rating. If a set is in going order, it is a simple matter to check out the voltage on each capacitor and mark those that really do need a high voltage replacement. 630 volt capacitors are considerably more expensive than 100 volt ones, so they should only be used where needed. A final word on paper capacitors. Not all paper capacitors are faulty and I dare say I have thrown out a good many of them that were perfectly OK. I also know that I have saved myself quite a few problems by replacing these highly suspect components. Electrolytic capacitors Another type of capacitor found in valve radios is the electrolytic type. They are mostly fitted to the high tension DC supply to filter out the 50Hz mains hum. Considerable variations are found in these electrolytics and they vary in capacity from 8-32µF and can be rated anywhere from 350-600 volts. High voltage electrolytics are often difficult to come by. Very few manufacturers appear to be making them and even fewer retailers sell them. Like radio valves, they can be found if you shop in the right places but for how much longer remains to be seen. Electrolytics are also troublesome components in old valve radios and their replacement is frequently required. Electrolytics usually contain a liquid or paste which often leaks away, leaving the capacitor dry and useless. Leaking electrolytics are a sure sign of trouble and should always be replaced. There seems to be no rule that applies to electrolytics. Odd ones seem to last forever while others are relatively short-lived. While some continue to work after 40 years of service, such a life span is the exception rather than the rule. If old electrolytics are to be used again, they should first be tested using an ohmmeter for short circuits and excessive electrical leakage. In Many tuning capacitors have the outside plates bent outwards (though not usually as much as shown here) to compensate for capacitance discrepancies between the gangs. Don't bend them back otherwise you won't get accurate tracking across the dial. Many of the capacitors used in valve radios are high voltage types. Always make sure that replacement capacitors have an adequate voltage rating. addition, a capacitance test is needed to determine whether the capacity is somewhere near the marked value. When checked with an ohmmeter, most old electrolytics show a considerable amount of leakage. However, this situation often improves when the capacitor is put back into service. Applying a potential across an old electrolytic capacitor helps to "reform" the oxide dielectric. Faulty electrolytics can cause a pronounced 100Hz mains hum in the loudspeaker. And if an electrolytic develops an internal short circuit, it will result in the rectifier anodes glowing red hot. Capacitors with these ailments must be replaced. Now I will probably get wrapped over the knuckles for this statement but the capacitance of an electrolytic replacement is not all that critical. As far as I can see, BµF, 16µF and 24µF electrolytic capacitors all work pretty much the same no matter what type of radio they go into. About the only effect they might have is to cause a slight change in the high tension voltage. If someone wants to take me to task about this, just keep in mind that the only high voltage electrolytics I can buy at the time of writing are 22µF 450VW types and these are the ones I use when needed. What's more, they seem to work very nicely. Some radios also have low voltage electrolytics which are used for biasing. As these capacitors are usually rated at 25µF 40VW they offer few problems regarding a suitable replacement and a modern 22µF 63VW electrolytic is a suitable substitute. Tuning gangs Perhaps the only other capacitor worth mentioning at this stage is the variable capacitor or tuning gang. While this particular unit does not usually need replacing, it can require a bit of routine maintenance in addition to a good clean. Tuning capacitors have bearings that sometimes work loose. These can be given a drop of oil or a dab of grease and readjusted if necessary. A good many old tuning gangs have a lock nut on the rear bearing which allows the play to be taken up if the bearings have worn to any extent. Adjustment is only required on odd occasions; usually a lube job on the bearings is sufficient maintenance. Another point regarding the tuning capacitor: don't straighten the outside moveable plates if they appear to have been bent away in different places. This has been deliberately done so that the two (or three) gangs will track accurately over the full range of the dial - so don't interfere with them. In summary, the vintage radio restorer needs to pay particular attention to the capacitors in the sets he restores. Electrolytics and paper capacitors, in particular, can be very troublesome and in most cases, total replacement is the only sure method of obtaining reliable and lasting results. •~ AUGUST 1988 7 BUILD A PLASMA DIS Imagine a pulsating high voltage discharge which continually changes its shape and colours. It's a Plasma Display which you can control directly with your finger-tips, providing endless fascination as it sizzles and arcs. One of the most striking attractions of the new Sydney Powerhouse Museum is a large plasma discharge sphere which is over 550mm in diameter. It capitalises on the endless fascination that everyone has with lightning or with any high voltage display. It has the inexorable element of danger but paradoxically, it is completely safe as its great fluorescing arcs continually dance over the inside surface of the sphere. The Powerhouse's Plasma Display is truly spectacular but few people could afford to pay the $15,000 or would have the space needed to own one. But now you can have your very own Plasma Display. It is capable of the same PARTS LIST 1 plasma display bottle 1 circular disc of particle board 1 aluminium heatsink, 7 5 x 75mm (see text) 1 TV horizontal output transformer (not a tripler type) 2 2N3055 silicon power transistors 1 1N4002 silicon diode 1 1N5407 silicon diode 1 1 000 5W wirewound resistor 1 270 1 W resistor 2 16U or 1 50 5W resistors 1 in-line 3AG fuseholder and 3A fuse 8 SILICON CHIP 6 solder lugs 1 cordgrip grommet 1 one-way insulated terminal block Power supply 1 1 2V battery charger or 12-15VDC power supply rated at 2 amps or more (see also Fig.2). Miscellaneous Mica washers and insulating washers to suit T0-3 power transistors, rainbow hook-up wire, screws, nuts, lockwashers, solder. spectacular visual effects which you and your friends can enjoy to your heart's content. In essence the Plasma Display we're talking about is a large glass container containing an inert gas or a mixture of inert gases at a very low pressure - almost a vacuum in fact. High voltage AC feeds a specially shaped electrode inside the glass container and this produces a continually varying electrical discharge. You can put your hands or finger-tips directly over the glass and the high voltage discharge will pass right through the glass into your body- it's spooky, mysterious and hair-raising but completely safe. After you have seen and experienced this Plasma Display it is hard to comprehend that it is not dangerous. After all, in air a spark 10cm long not only looks and sounds dangerous but can be a painful experience if it jumps to you. It requires about 12,000 volts to generate a 10cm arc in dry air. But here in the Plasma Display you can have continuous electrical ·discharges more than 20cm long jumping all over the inside surface of the container and they can't possibly hurt you! There are several reasons why the Plasma Display is so spectacular yet completely safe, even though you can put your hands directly on the glass container. First, the gas inside the container is at an extremely low pressure and By LEO SIMPSON + __-C,...._.0-_ ___,_ _ _ _ _ _ ___, 3A 1000 5W PLAY this means that an electrical discharge can jump over much larger distances than are possible in air at normal atmospheric pressures. But since the container is glass this means it is an excellent insulator. So how can any current flow at all? How can the electrical discharge take place at all? And ·where is the discharge path since there is only one high voltage electrode, inside the glass, with no visible return path? High voltage DC Well, if the Plasma Display was fed with a very high voltage DC supply it would not work. No current could pass and no visible discharge could exist. Instead, the Plasma Display is powered with a high voltage high frequency AC (alternating current) supply. This means 'that minute' alternating currents can flow, firstly via the low pressure ionised gas inside the glass container, then via the very small capacitance of the glass container to earth. How can there be capacitance in the glass container when there are no apparent metal electrodes either on the inside or outside of the glass container? One electrode is the atmosphere on the outside of the evacuated glass container. Air is not a perfect insulator - its water content and very low ion content prevent it from being so. So it is possible for very minute alternating currents to flow from the outside of the glass container to earth. The low pressure ionised gas inside the container actually provides the internal electrode and therefore what is. an apparently invisible path is quite able to sustain the visible electrical discharge. Q1 2N3055 C 12-15VDC 01 1N5407 160 5W 270 1W Q2 2N3055.,___ __ oz 1N41J07 C ~ VIEWED FROM PLASMA DISPLAY EHT GENERATOR eaow SC0B-2-0888 Fig.1: the circuit for the EHT generator uses two 2N3055 power transistors connected as a transformer coupled multivibrator. This produces about 20,000 volts AC at a frequency somewhere between 20kHz and 30kHz. The EHT generator uses a horizontal output transformer intended for a blaclc and white TV set. Before mounting the transformer, you have to remove the existing low voltage winding and wind on two new windings (see text). Even so, the currents involved are extremely small and that is the other reason they are harmless when they pass through your person. OK, so what is plasma? The very name is a mystery to most people and something they may have heard of in the attempts to produce nuclear fusion - an extremely hot plasma is thought to be the requirement for fusion to take place. AUGUST 1988 9 enough. Take one large glass container, evacuate it, introduce a small amount of gas and seal it. You don't have to worry about that side of it though because the plasma container is supplied ready to go. What you have to do is assemble the EHT generator and the stand for the display bottle and provide a suitable 12V DC power supply. EHT Generator The EHT lead from the coil is connected to a one-way terminal block and then to the lead from the lid of the plasma container. Be sure to isolate the transistors from the heatsink correctly (see Fig.3). Actually, plasma is the term used to describe a highly ionised gas. Because it contains roughly equal numbers of positive ions and electrons it is electrically neutral but highly conductive. In fact, plasmas occur in all fluorescent lamps, mercury discharge tubes and so on. They are designed to be efficient sources of light. But with the right mixture of gases at the right pressure, plasmas can be quite different, as the display shown on our front cover illustrates. Actually, photos can hardly do justice to the Plasma Display we are talking about. The display is so dynamically variable it is just not possible to capture its essence in a still picture. In the case of the Plasma Display under discussion the particular mixture and pressure of inert gases inside the glass container is a trade secret. We don't know it. It has been arrived at after much trial and error. So has the shape of the fancy wire electrode inside the glass container. In principle though, the process for producing the display is simple EHT stands for "extra high tension" and is the term used to describe high voltages of several thousand volts or more, whether DC or AC. The EHT generator for the Plasma Display produces about 20,000 volts [20kV) AC at a frequency somewhere between 20kHz and 30kHz. In essence, the EHT generator is a DC to AC converter which takes low voltage DC and steps it up to very high voltage AC at a high frequency. It uses two 2N3055 power transistors connected as a transformer coupled multivibrator. The transformer is a horizontal output transformer intended for a black and white television .set. Normally a transfornmer of this type would be driven by the horizontal output transistor at 15,625Hz. For our circuit, the transformer is modified by adding two centretapped windings and these are driven by the two power transistors, as shown in the circuit of Fig.1. Each transistor's base is driven by a one-turn feedback winding 6A BRIDGE RECTIRER (P04) AO-O 240VAC N· EO---;;;,,--. Fig.2: if you don't have a 12V battery charger, this circuit can be used to make up a suitable DC power supply. No filter capacitors are required. Fig.3: the 2N3055 power transistors must be insulated from the heatsink using mica washers and insulating bushes. This diagram shows the mounting details. 10 SILICON CHIP 0 0 HEATSINK ~ -INSULATING BUSH <§:::i>- SOLDER LUG <at>-WASHER ~-SPRING WASHER ~---NUT Fig.4: wire up the EHT generator as shown here. The text gives full details on adding the two low voltage windings. ~ EHT TO PLASMA TUBE 16!l 5W E 02 8 ~ EHT COIL • .--1-6!l_5_W_~ ~ mounted upside down with the lid a push-fit into the plastic stand. The stand is made from two plastic mouldings which are standard sewer pipe fittings. These, in turn, fit onto a disc of timber which provides a stable base. The whole stand assembly is sprayed matte black so as to be as unobtrusive as possible. The EHT generator fits inside the plastic stand and is connected to the external power supply (battery charger or whatever) via a length of figure-8 power flex. Assembling the EHT supply HEATSINK 3A IN-LINE FUSE while each collector drives half the main low voltage winding. When the circuit is oscillating, each transistor alternately turns hard on, which applies the full DC voltage across the associated winding while the other transistor is biased off. So the transistors apply a square wave voltage to this low voltage winding and this is stepped up by more than a thousand times in the high voltage secondary winding. The 160 1W resistors in series with the bases of transistors Ql and Q2 are there to limit the amount of feedback current. They therefore have the effect of reducing the amount of damping on the transformer and thus improve efficiency. Initial bias to start the circuit oscillating is provided by the 1000 5W and 270 lW resistors. Protection against reverse biasing is provided by diodes Dl and D2, in conjunction with the 3A fuse. DC power supply Any DC power power supply capable of delivering 12 to 15 volts at more than two amps is adequate for the EHT generator. In fact, virtually any 12V battery charger will do the job, provided it can deliver 2A or more. (Note: some chargers with internal monitoring circuits are not suitable for this job). If you don't have an adequate DC supply or battery charger, the circuit of Fig.2 will do the job. It uses a 15V 2A transformer driving a bridge rectifier. No filter capacitors are necessary. Construction Kits for the Plasma Display will be available from Jaycar stores at $299. This will include the plasma bottle which is evacuated, charged with inert gas and sealed. At the time of writing, two different plasma displays were being considered. One, which we suspect contains mainly helium, gives a striking lightning-like display, leaping in three jagged tonges from the specially shaped discharge electrode. The other, which the staff at SILICON CHIP preferred, is probably a mixture of mainly helium and neon and gives a wavy aurora-like display which dances over the entire inside of the container in flares or pink, reds, violets and blues. Really, though words (or still photos) can't do justice to the displays. You have to see them in the glass! As supplied, the plasma container is a large glass jar with a sealed lid having a short length of wire attached to it. The jar is This is wired and assembled onto the circular piece of timber which serves as the base for the plasma display stand. In our prototype we used a circular piece of particle board 210mm in diameter and 15mm thick, although the exact dimensions are not important. The two transistors are mounted on a small heatsink fashioned from a piece of aluminium scrap about 75mm wide by 75mm high, with a foot section 10mm wide which mounts on the timber with a couple of small self-tapping screws. The details can be seen in the photos. The TV horizontal output transformer comes complete with a mounting bracket which makes it easy to mount on the timber with a couple of screws. Before you do that, remove the existing low voltage winding (on the opposite leg The EHT generator is mounted on a circular disc of timber and fits neatly inside the plastic stand. It is connected to the power supply via a length of figure-8 power flex. AUGUST 1988 11 When the EHT lead has been connected, the lid of the plasma bottle can be pushed into the top of the stand. Note the fancy shape of the wire electrode. to the large circular EHT encapsulated winding). Now wind on the two new low voltage windings. We used ribbon cable for this purpose as it makes bifilar winding easy. Wind on the two 4-turn windings together and do the same with the two one-turn windings. Secure the windings in place by running some hot wax from a candle over them. Four solder lugs should be secured to the timber base, adjacent to the transistor heatsink. 12 SILICON CHIP These take the 1000 and 270 resistors and the two diodes. The diagram of Fig.3 shows how the transistors are mounted on the heatsink using mica washers and insulating bushes. The transistor mounting surfaces and the heatsink should be lightly smeared with heatsink compound before they are assembled together. Fig.4 shows how the wiring of the EHT generator goes together. The two 160 resistors stand off the bases of the transistors while the other ends go to the relevant transformer connections in ''midair" . Nothing fancy, but it works. Make sure you connect the diodes the correct way around. An in-line fuseholder is used for the 3-amp fuse and the power flex is secured to a hole in the plastic base using a cordgrip grommet. When you have finished the wiring check your work carefully to see that it agrees with the circuit and wiring diagrams. Now use an insulated terminal connector to connect a short length of stiff wire from the EHT output wire over to the earth end of the EHT coil. Arrange the two ends so that there is a gap of about 7mm or so. Apply power from your 12V battery charger or power supply to the EHT generator and note that a continuous arc occurs across the spark gap. OK, so it works. Let it run for 15 seconds or so and then turn the power off. Feel the transistor cases to make sure that they are not running hot. After running for quite some time they will become pretty warm but not so hot that you can't touch them. Now it is merely a matter of connecting the short wire from the lid of the plasma bottle to the EHT output from the transformer. Carefully place the plasma bottle into the stand and apply power. A colourful discharge should immediately appear in the container. It is best viewed in darkness or dim light. You can put your hands all over the container to "control" the plasma display but keep your hands and fingers away from the lid of the container. If your hands stray too close you may get a nasty shock directly from the lid. We advise that the Plasma Display be placed in the centre of a suitable table, not near the edge. You should avoid any chance of the glass container being knocked to the floor. Replacement would be expensive if it was broken. [!II;! Where to get the parts: a .complete kit of parts for the Plasma Display is available from Jaycar Electronics Pty Ltd for $299.00. This will not include the 1 2V DC power supply. z DAVID REID ELECTRONICS • 4 sectors plus "panic" or emergency sector • Optional keypad (KPI) and key switch (CPI) inputs • Phone dialler input NOW 12 volt 6 .5 amp ttery to suit $ 249 Escort Diode check Continuity test Logic text Frequency up to 200kHz Capacitance HFE test 20 AMP AC/DC Large 20mm display High impact plastic housing • 1 year warranty AC/DC Volts Resistance Continuity buzzer Diode check s99.oo Control keyswitch • Optional remote keyswitch suit control alarms AUTO RANGING DIGITAL MULTIMETER MODEL - BC7790 • • • • • • • 3½ digit LCD display HFE test Diode test Continuity test Data hold 10 AMP AC/DC Includes case and test leads VALUE INCL TAX Vol 1. - VOLT AGE REGULATORS OPERATIONAL LAMPS BUFFERS VOLTAGE COMPARATORS INSTRUMENTATION AMPS SURFACE MOUNT ACTIVE FILTEAS ANALOG SWITCHES/MULTIPLEXERS A to D CONVERTORS D to A CONVERTORS SAMPLE AND HOLD DAVID REID ELECTRONICS • • • • ONLY AT ONLY NSD LINEAR DATABOOKS - 3½ DIGIT "PEN" MULTIMETER . • Control your alarm from this keypad - turning the system on or off, isolating sectors etc. "CPI" - S69.95 s185 • • • • • • • • • Vol 2. - . ~4f~ • 3 sector plus 2X24hr sectors WAS $235.00 • Optional keypad (KOi) and key switch NOW (CPI) inputs • Complete with power supply and backup battery ~. . , I "KPI" CONTROL KEYPAD . ~ 3 ½ DIGIT MULTI METER - ALL ONE PRICE .. 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FOX - CONTROL 4 ALARM • 6 sectors plus two(2) 24 hour monitored inputs • Alarm memory • Optional keypad (KPI) and keyswitch (CPI) inputs • Phone dialler input • Power supply included For the electronics enthusiast ONLY s79.oo s110.9s - TEMPERATURE SENSORS - VOLT AGE REFERENCES - SURFACE MOUNT Vol 3. - AUDIO CIRCUITS - RADIO CIRCUITS - VIDEO CIRCUITS - MOTION CONTROL - SPECIAL FUNCTIONS - SURFACE MOUNT BUY ALL 3 VOLUMES FOR ONLY s45.oo PER SET (SOLD ONLY IN SETS) 127 York St, Sydney 2000 Ph (02) 267 1385 Fax: (02) 261 8905 BUSINESS HOURS Mon-Fri 8.30-5.30 Thurs 8.30-7.00 Sat 9.00-12.30 MAIL ORDERS WELCOME P.O. Box 0103 Sydney 2000 $1 - $25: $3.00 P&P $26 & over: $6.00 P&P 6 VOLT LANTERN RECHARGEABLE BATTERY • 6 volt <at> 5000MAH • Complete with charger ONLY s59.9s 6 VOLT LANTERN BATTERY AVAILABLE SEPARATELY - $29.95 VISA B THE WAY I SEE IT By NEVILLE WILLIAMS Some things are enough to make a grown man cry! An anecdote in a recent historical Bicentennial Review paper by Dr E. G. Bowen struck a familiar chord in the writer's memory and suggested the theme for this present article. Whether in the past or present electronic scene, certain situations stand out as sufficiently incredible and frustrating to make a grown man cry. In order to set the scene for the quote from Dr Bowen's paper, it is necessary to recall the situation in which radio engineers, amateurs and hobbyists found themselves in the immediate postwar period. During the war, production and supply of civilian radio equipment and components had been severely curtailed, amateur stations had been shut down and the size and circulation of technical magazines pegged, along with other publications, to conserve paper. But quite suddenly, after years of personal and national trauma, the conflict ended and all concerned had to about-face and begin to rebuild their lives around former or newly acquired interests. For radio enthusiasts, it meant getting involved afresh in practical audio-hifi, receivers, DX or amateur radio, test equipment and other allied activities. New parts were scarce and expensive but before long, all sorts of bits and pieces began to appear in newly established disposals stores, ranging from "junk" and oddments, through ever-useful valves, meters and crystals, to much coveted lab equipment and multi-band HF communications receivers. 14 SILICON CHIP Most of us soon collected plenty of the smaller items but the really desirable equipment proved very elusive or disconcertingly expensive. Nor did it help to be told that job lots had been "cornered" and "gone for a song" at the disposals auction or that a lot of it never even went under the hammer. There were also stories about huge quantities of surplus military stores being dumped into worked-out clay pits and buried by bulldozers. The stories may have grown more colourful in the telling but they were rendered credible by the fact that some disposals dealers simply ran out of space to store any further purchases, either indoors or out in the open. To hear such stories and to walk through such places really was enough to make a grown man cry; all that potentially useful equipment just sitting there in the rain! At a professional level That brings me to the paper "From Wartime Radar to Postwar Radio Astronomy in Australia" by Dr E. G. Bowen, CBE, FRS, Honorary Fellow, CSIRO Division of Radiophysics (published in the Jour- nal of Electrical and Electronics Engineering, Australia, Vol.8, No.1, March 1988). It describes how the team that kept Australia abreast of radar developments during the war (Division of Radiophysics/CSIR) was re-allocated in 1946 to peacetime research by the then chairman of the CSIR, Sir David Rivett. Not surprisingly, interest turned to further study of the electrical noise that had been observed by radar teams in England and Australia, coming from the Sun and from outer space generally. Such research was to become the starting point for present-day radio astronomy. Although it initially lacked specialist expertise in astronomy, the CSIR team was highly skilled in electronic and radio research and engineering. It had laboratory facilities and a large inventory of state-of-the-art equipment and components accumulated during the wartime years magnetrons, klystrons, pulse-forming networks, pulse counting circuits and so on. But no research and engineering team seems ever to have enough reserve resources and this is where the agony began, which paralleled on a grand scale that of individual amateurs and enthusiasts, described above. Looking back on the period immediately following the Japanese surrender, Dr Bowen recalls: "A Jorge segment of the Pacific f1eet had assembled in Sydney Harbour prior to its returning to the USA; already in Sydney were gigantic stores of radar and communications equipment assembled for the Reach For The Tissues Taxpayers: last month, in these columns, reference was made to the exasperation of a taxpayer who was apparently the victim of a major computer crash in the Taxation Department. Instead of a receipt, he received a final demand for payment and notification that the supposedly overdue debt was now incrementing at so many dollars per week. But that was nothing compared to the dismay of a taxpayer in Beecroft, NSW, as noted in Column-8 of the Sydney Morning Herald, May 4: "A Beecroft reader was expecting a $70 tax refund this year but instead, received a debt notice for $231,142.60 with an additional charge of $889.01 a week for late payment. The taxable income on which the demand was calculated was nearly 10 times the reader's actual salary." Hifi promoters: according to the same newspaper on May 19, a billboard on the railway station at Bondi Junction, NSW, was currently carrying an advertisement final stages of the Pacific war. It was impractical to return much of this to the United States and orders were given to destroy the surplus. So, huge quantities of technical equipment, including whole aircraft, were loaded on the decks of aircraft carriers, taken a few miles outside Sydney heads and bulldosed into the Pacific". No mention is made of anyone shedding visible tears . but Dr Bowen does admit that "our friends in both the US and Australian services were disturbed by all this destruction". Presumably the aforesaid friends were still in sufficiently high places to be useful because they were able to quietly encourage the CSIR research team to salvage all they could lay our hands on. So, and again I quote: "After a frantic few weeks loading our own trucks at the dockside, we ended up with a cornucopia of invaluable equipment, often brand new and in the original crates. I seem to remember two large for Miranda Hifi which read: "Talking to us about hifi and video is like talking to Captain Cook about the first fleet". That's not very reassuring: by the time the first fleet set sail, Captain Cook was dead! Servicemen: for decades, radio and TV servicemen have been routinely checking sets with intermittent faults by letting them run for long periods at the far end of the test bench, hoping to catch them out in the act of "intermitting". As often as not, the sets don't cooperate. Checking through recent publicity material, I came across information about a couple of new Philips digital oscilloscopes, the PM 3320 and PM 3340 which, among other high-tech facilities, offer the so-called "Stop/save" feature. Both CROs can store a waveform for future reference and continue thereafter to monitor it for as long as required. If the signal varies from the stored reference by more than a specified amount, the aber- warehouses full of these things near Botany Bay, which we were to draw on for many years to come". Laws and regulations In relating the above, I am reminded of another set of circumstances which obtained about this same period. One arm of the Australian Government, the military, was busily off-loading its own mountain of surplus equipment, including HF and VHF transceivers; dealers were buying them cheaply and advertising them for sale; and enthusiasts were purchasing them in large numbers at what was still an attractive price. To that point it was perfectly legal and above board but ironically, it then became the responsibility of another arm of government, the Radio Branch of the PMG's Department, to ensure that the transmitter sections were not used by those who had purchased them unless they were: • Licensed amateur operators, in ration is digitally recorded for subsequent playback on demand. Some earlier Philips analog CROs included a similar "baby sit" feature but few servicemen could afford them. Sadly, at around $20,000 to $30,000 apiece, the new digital CROs are even further out of their reach! Maybe, as the cost of the technology reduces, they will become more affordable. TV viewers: speaking of Philips: don't get upset if and when you discover that the latest series of TV receivers from that illustrious company do not provide 3D viewing - despite the logo "STEREO VISION" prominently displayed on the front of a 4-page brochure recently to hand. The sets may offer "brilliant 4-speaker stereo sound", an FSQ (flat square screen) image, teletext, integrated remote control and provision for peripheral audio, video and computer equipment but the simple fact is that there is no earthly way that a 3D (stereo?) image can be successfully simulated from 2D photographic information. conformity with the technical requirements applicable to amateur stations, or; • Other individuals or groups, licensed for a particular class of service and conditional on the equipment ·conforming to the relevant technical specifications. While departmental officers accepted the task with an official stiff upper lip, more .than one of them confided to me that they resented having to police an unprecedented "pirate" situation that had been created by the government in the first place. It added to the resentment they already felt at having to resolve interference problems affecting radio (and later TV) reception without firm legal support. Any authority that they had rested on an insecure tangle of regulations, which were wide open to challenge by anyone not inclined to accept their intervention. I still remember the dismay of one departmental official who had AUGUST 1988 15 Many of these departmental edicts made very definite interference with personal liberty .. been told to "go jump" by a manufacturer whose high-powered RF industrial heating equipment was interfering with the department's own radio communications facilities. Since it wasn't a wireless transmitter within the meaning of the Act, the RF heating equipment in question was outside the officer's jurisdiction. If that's not enough to make a grown public servant cry, I don't know what is! Problems evident in 1933 ding act in 1920 adding the words 'and telephonic' after the word 'telegraphic' in the original act. Big deal! "Small though the addition was", continued Dr Louat, "it was all that officialdam needed. With the arrival of public broadcasting as a new public institution, batch after batch of regulations was issued. "These had the effect of limiting rights and imposing duties in a widening field, which thenceforth was to become a matter of personal moment to every citizen of the Commonwealth. Many of these departmental edicts made very definite interference with personal liberty .... "An Act was passed last year (1932) controlling stations and their programs. Except in this one respect, the regulations have been left as the only law on the matter". The ironic aspect of the above is that I have in my files a copy of an article from Wireless Weekly, July 24, 1933, page 11. It summarises an address at Mosman, NSW, by a young Frank Louat, who had just previously received his doctorate of law for a thesis dealing with the growth of bureaucracy in Australia. With the Postmaster-General, Mr After 80 long years Archdale Parkhill, in the audience, Despite these protestations and Dr Louat cited the field of radio . many more since, the original broadcasting as providing: "a Wireless Telegraphy Act was still remarkable instance of the way in being used as a basis for prosecuwhich the laws of the country are tions up to the end of 1985, when it being made for us by public depart- was finally superseded by the ments instead of Parliament". By Radiocommunications Act, 1983. way of explanation, he pointed out Retired radio inspectors must have felt forlorn indeed, to be greeted by that: "The present broadcasting law headlines like: "New Act gives Rl's almost entirely consists of regula- greater clout!" But while the new Radiocomtions made by ministers on the advice of officials. It imposes on the munications Act may have racitizens stringent obligations which tionalised some of the routine adthe people's elected represen- ministrative matters, there's still a tatives never even considered, let way to go in the overall management of the air waves, with Federal alone discussed.'' The statuary authority under Parliament in a bind over broadcast which all this had been done, accor- television. In a recent address to the ding to Dr Louat, was the Wireless Telegraphy Act, passed by the Com- Australian Telecommunications monwealth Parliament way back in Users' Group (ATUG) 1988 Con1905. Enacted at a time when ference in Melbourne, Senator wireless broadcasting was un- Evans (Minister for Transport and dreamed of, it consisted of ten sec- Communications) indicated the tions only and dealt mainly with possible need, after a series of policy reviews, for a new Act to wireless installations on ships. Belatedly, and "dimly aware that replace seven existing Acts and new doors were being opened by their associated regulations which the unresting hand of science", have a bearing on Australia's elecParliament passed a small amen- tronic communications. 16 SILICON CHIP Efforts to make the existing regulatory framework more rational, effective and cost efficient, he said, have made it apparent that "some (such) simplification will be necessary to ensure effective administration''. Networks or nondescripts? I may stand accused of oversimplification but as I see it, certain propositions in relation to television broadcasting are reasonably logical and supportable: (1). With present technology, the number of TV stations which can be accommodated in the available band space is limited. It is therefore a waste of time to rave on about "freeing up" the system to accommodate all-comers. (2). Experience seems to indicate that in the Australian context, five channels (ABC, SBS and three commercial), as in the major capitals, offer a reasonable choice of broadcast programs while at the same time being technically and commercially viable. (3). A smaller number of channels, as in provincial centres, provides an unacceptably limited choice of TV fare. There is little chance of any improvement in this situation other than by the introduction of networking, with local overheads reduced to a minimum. (4). The 7, 9 and 10 networks are already in a highly competitive situation by reason of their involvement in the major capital cities. What provincial viewers need is for that sort of competition to be extended into their particular area, hopefully with the injection of some local news and advertising. (5). Concern about networks controlling media other than their local TV outlet could readily be covered by the multi-media legislation currently under consideration. That's the way I see it. But thenI'm not obliged to look at the situation through polarised spectacles, as issued from time to time by the various political parties. ~ WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS .. WOOD FOR CHIPS ... WOOD FOR CHIPS .. WOOD FOR C Instrument Cases ~ ti Cl:: a lJ.. Cl a ~ Geoff Is now stocking the most comprehens~ve range available! Diecast 90x38x30mm $7.80 120x95x24mm $11 .50 120x95xx60mm $16.30 186x118x55mm $19.50 Horwood Black Marviplata steal wit h aluminium front and rear panels. Complete with Handles 21Ox155x100 84/6/v $24.50 230x205x75mm 93/8/v $24.50 21Ox255x100mm 84/ 10/v $28.95 230x305x75mm 93/12/v $29.75 Plastic Two Piece 83x54x28mm $2.20 130x68x41mm $2.95 150x90x50mm $3.95 ABS Plastic with Aluminium Lid 83x54x28mm $2.25 130x68x41mm $2.95 150x90x50mm $3.60 195x113x60mm $5.50 ABS Plastic Four Piece 155x200x65mm (ivory with black panels or all black) $14.95 190x255x80mm (all black) $19.95 ABS Plastic/Aluminium Four Piece 150x80x38m m $6.50 150x80x58mm $9.50 Professional Quality RE TEX Boxes Computer Service Kits Geoff has an excellent range -of tool kits intended for computer servicing but ideal for any electronics professional. The selections of tools are based on those commonly used by service technicians. All tools are demagnetised. They come in a quality vinyl zipper case so you should never lose 'em! CSK-4 contains • IC extractor for 8-1 Spin DIPs • IC locating tool e 3 claw holder (pearl catch) • 3. 17 and 4. 76mm slotted screwdrivers• 2 Phillips head screwdrivers• 4.76 and 6.4mm nutdrivers • Reversible torque screwdriver • Spare parts tube• All in a vinyl zipper case 230x150x40mm $46.95 CSK-8 contains • IC inserter and pin straightener for 14-16pin IC's • IC extractor and pin straightener for 14-40 pin IC's • Pearl catch • Tweezers • 2 Phillips head and two slotted screwdrivers (3.17mm and 4. 76mm) • Two nutdrivers (4.76mm and 6.4mm) • Reversible torque screwdriver • All in a vinyl zipper case 230x150x40mm $52.95 Sick of changing blown fUSeS? Then here's the answer - ~ ~ Cl:: M;'u ded wit two a Sloping Panel 375x1 20mm Upright Panel 375x 60mm Sloping panel 248x100mm Upright panel 248x48mm $72.95 $49.95 Moulded ABS with aluminium face and two position legs $41 .95 H igh Quality Potter & Brumfield Circuit Breakers . Single Pola, thermal operation . About the same size as a fusaholder (39mm x 16mm dia approx). Needs 20mm square panel space. Snap in panel clip mounting. Reset button cannot be used as on-off switch . Visual indication of trip. Cannot be overridden . Approved by Energy Authority of N.S.W. , UL etc. Available in 3Aor 5A rating for only $7.80each. a lJ.. Cl a ~ Crimper for Modular Telephone Plugs Handy tool for installing the new miniature telephone oonnectors. Not the usual plastic junk, this one is made of steel, for professional installers. Has built-in stripper blades to remove insulation with guide to give correct length . Insert prepared cable into the plug and the jobs done in seoondsl Spring loaded handle but has closing lock to protect blades. $31 .50 Parallel Printer Cables Back in stock again in both lengths - 1.8 and 4metres - so w hy make your own? It'll cost you more! 1.8m $14.95, 4m $29.95 CSK-12 (see pie) contains • IC inserter for8-16pinlC's • ICextractorfor8-16pinlC's • 30W soldering iron • Solder • Cutters • Tweezers • Pearl Catch • Wire cutter/ strippers • Spare Parts Tube • 3 slotted screwdrivers (3.2, 4.0 and 6.4mm) • 3 Phillips head screwdrivers • 2 Nutdrivers • Reversible torque screwdriver • All in a vinyl case 290x190x40mm $119.95 CSK-16 contains• 2 IC inserters with pin straighteners for 14-16 and 24-28pin IC's • an extractor with pin straightener for 14 to 40 pin IC's • Anti-static wrist strap • Desoldering tool • Soldering iron • Solder • Soldering tools (knife/brush, scraper/hook, fork/spike, heat sink)• Nippers • Cutters •Allin a vinyl case 290x190x40mm $122.95 CSK-32 contains • Antistatic wrist strap • IC inserter with pin straightener for 8-20pin IC's • Extractor with pin straightener for 1440pin IC's • A square IC (pin grid) extractor for 44-84 pin IC's • Multiple extension screwdriver set with 3 Phillips and 3 slotted screwdrivers and two nutdrivers • Two torque screwdrivers All in a vinyl case 240x 155x40mm $127 .95 CSK-64oontains • Antistaticwriststrape A square IC (pin grid) extractor for 44-84 pin IC's • Multiple 'extension screwdriver set with 3 Phillips and 3 slotted screwdrivers and two nutdrivers • Two torque screwdrivers • Logic Probe and Pulser • 2 IC inserters with pin straighteners (8-20pin and 36-40pin) • An IC extractor with pin straightener for 14 to 40pin !Cs • 3pairs of tweezers • All in a vinyl zipper case 290x190x40mm $289.95 ~ a a -r, a :0 () :i: 'o (/J ~ a a -r, a :0 () :i: j Linear Data Books We have a quantity of the vary latest edition of the 3 volume set of Linear Data from National Semiconductor Volume 1 covers Voltage Regulators, Op Amps, Buffers, Voltage Comparators, Instrument Amps, Surface Mount . Volume 2 covers Active Filters, Analog Switches/Mux, AID and DIA converters, Sample/Holds, Temp Sensors, Voltage ref's and Surface Mount Volume 3 covers Audio Circuits, Radio and Video Circuits, Motion Control, Spacial Functions and Surface Mount Volume 1 is $22.50, Volumes 2 and 3 are $1 5.00 each P&P is $5.00 per volume (They're pretty massive books!) But Geoff's in a generous mood so you can have the complete set for $45 (P&P $10) a -r, a :0 () :i: ~ ~ a a -r, a () Quality Australian made 2 metres long 229 Burns Bay Road , (Corner Beatrice St.) INC IN Nsw Lane Cove West, N.S.W. P.O. Bo x 671 , Lane Cove N.S.W. 2066 Telephone: (02) 4271 676, Fax: (02) 428 5198. 8.30am to 5.00pm Monday to Friday, 8.30am to 12 noon Saturday. PENAOSE Mail Orders add $5.00 to cover postal charges. Next day delivery in Sydney add $5.00. All prices INCLUDE sales tax. Tax exemption certificates accepted if line value exceeds $10.00. BANKCARD, MASTERCARD, VISA , CHEQUES OR CASH CHEERFULLY ACCEPTED a :0 IEC Cordsets GEOFF WOOD ELECTRONICS PTY LTD ~ $7.50 :i: 'o (/J ~ a a -r, a :0 () :i: 'o (/J State of the art AC MILLIVOLTME Just how do you measure the extremely low noise output voltages of modern audio equipment, particularly power amplifiers and compact disc players? Our AC millivoltmeter has been designed for those specialist tasks and can measure audio signals down into the microvolt region. By LEO SIMPSON & BOB FLYNN Today's topline high fidelity equipment really does stretch the measuring limits of even the best audio test equipment. The run-ofthe-mill AC millivoltmeter with a bottom range of 1 or 3 millivolts full scale is nowhere in the race. Just consider a typical CD player today. It will have a signal to noise ratio of - 96dB as a minimum and it might be as low as - 106dB. Take the - 96dB figure for a moment, which is with respect to the maximum 2 volts RMS output. To confirm that noise figure, the AC millivoltmeter must be able to measure accurately down to below 30 microvolts. To confirm a noise figure of -106dB below 2V, it must be able to measure accurately to below lOµV. Modern stereo preamplifiers and power amplifiers present a similar challenge. Consider the Sony TA-N77ES stereo power amplifier reviewed in the February 1988 issue of SILICON CHIP. It has a signal to noise ratio of - 120dB 'A' weighted with respect to its rated power output (200 watts into 80). To be able to confirm that, the millivoltmeter must be able to be accurately measure below 40µV. · Or consider the Studio 200 Stereo Control Unit presented in our June and July issues. It has a signal-to-noise ratio of - 107dB 'A' weighted with respect to its rated output of 1.25V. To confirm that, you need an instrument capable of measuring signals down to less than 5µ V! In fact, if the measuring instrument's own internal 'noise floor' is not to intrude on the measurement, it must be able to measure down to around 1µ V. Now you see why conventional millivoltmeters are just not in the race. In addition, modern hifi equipment may be measured with wide frequency bandwidth, say to lOOkHz or beyond, band-limited (20Hz to 20kHz) or, as already mentioned, with 'A' weighting. As far as we know, there is no commercial Most of the parts, with the exception of the resistors on the main attenuator switch, are mounted on this PCB. TER Designed specially for audio measurements, this instrument has a noise floor of less than one microvolt. equipment available today which is up to the task. OK, so we've demonstrated the problem. Now we present the solution, our new state-of-the-art AC millivoltmeter. Its performance is summarised in the accompanying panel. Incidentally, our use of the term "state of the art" may lead some people to jump to conclusions. They may associate SOA equipment with programmable microprocessorcontrolled digital measuring equipment costing tens of thousands of dollars. But while such equipment is available, their absolute measuring limits are often pretty ordinary. As you can see from the specification panel, the new AC millivoltmeter is designed especially for measuring modern high performance audio equipment. It does not have the very high input impedance of 10 megohms, typical of digital voltmeters and some older designs of AC millivoltmeters. Such high input impedances are not required, for two reasons. First, most audio measurements are made at the output of equipment which has very low impedance. For example, most CD players, tuners, cassette decks and preamplifiers have output impedances considerably less than 1k0. For measurements on power amplifiers we are looking at outputs with source impedances of a few milliohms! Second, even where measurements are being made between stages of audio equipment, they still involve low impedances. Accordingly, we have adopted the standard input impedance used by commercial noise and distortion meters; ie, lOOkO unbalanced. The frequency response of the instrument is - 3dB at 5Hz and 160kHz, on the 3V range. We quote the specific range because the ultimate bandwidth does vary slightly, depending on the input range selected. Mind you, some power amplifiers have a small signal bandwidth far in excess of 160kHz, sometimes to as high as 1MHz or more. Where such figures have to be confirmed, the only practical way is to use an oscilloscope. For the vast majority of audio measurements though, the 160kHz bandwidth of the AC millivoltmeter will be more than adequate. More typically, where noise measurements are to be made, bandwidth limiting is required. For unweighted noise measurements (ie, with a flat frequency response), it is usual to measure with a frequency response of 20Hz to 20kHz, at the - 3dB points. The alternative is to make an 'A' weighted measurement, with a frequency response specified by the IHF-A-202 (or EIA RS-490 ) specification, and defined in ANSI S1.4 (specification for a sound level meter) as shown in Fig .1. This filter characteristic is designed to more Specifications Input impedance 1 00k0 (unbalanced) Frequency response 5Hz-160kHz at - 3d8 points (on 3V range) 5Hz-130kHz at -3d8 points (on -30dB range) Measuring ranges 1mV to 1 00V RMS f.s.d. in 11 ranges Noise (ratio) ranges 0dB to -60d8 f.s.d. in six ranges Noise floor -64d8 below 1mV (630nV) with 20Hz to 20kHz filter; -68 .5d8 below 1mV (375nV) with 'A' weighting . AUGUST 1988 19 ~ /,r .... "'"'" ~r-,....._ " -10 / V -2 I) II' II 0 I/ / -4 0 I -50 I j -6 0 -7 0 The circuitry / I I 100 10 HERTZ 1k 10k 20 Fig.1: this is the A-weighting characteristic used for measuring most audio equipment today. It tends to approximate the response of the human ear to very low noise but neglects the more audible effects of mains ripple in power amplifiers. or less approximate the sensitivity of the human ear to low level sounds. Therefore, both the high frequency response and low frequency response are rolled off, as illustrated. No provision has been made for DC measurements. The average digital multimeter is more than adequate for this task, even where voltage measurements down to a fraction of a millivolt have to be made (as for example, when measuring the DC offset voltage at the output of an op amp). Features Our prototype is housed in a folded metal case with aluminium base and blue Marviplate (steel) cover. It measures 235mm wide, 210mm deep and 120mm high (including rubber feet). It is mains powered and is switched on at the rear of the unit. On the front panel it has a large meter movement (nominally 100mm wide) with scales 0-lV, 0-3.16V, and decibels, with 0dB referenced to 0.775 on the 0-lV scale. There are four rotary switches and one potentiometer: the Input range switch, Noise range switch, Mode switch and Filter selector. The input selector has 11 ranges measuring from lmV fsd (full scale deflection on the meter) to 100 volts 20 SILICON CHIP the instrument and when very low noise measurements are being made; eg, lower than - 60dB with respect to lmV. Just to show how good this instrument is, it can measure signal noise ratios of better than - 120dB with respect to 1V RMS (or - 126dB below 2V). Alternatively, for an input reference of 30V RMS (typical for a 100W amplifier), it can measure SIN ratios better than -150dB. In other words, our new AC millivoltmeter is several orders of magnitude better than even the best audio equipment. fsd. The input divider runs with the standard 3.16 ratio between ranges. This odd figure is used because it is equivalent to lOdB steps when switching ranges. The Noise range switch has six positions, giving settings of 0dB to - 60dB. It is used in conjunction with the Set Level potentiometer which sets the meter's pointer to the 0dB mark on the scale before taking a signal-to-noise ratio measurement. The Mode switch has three positions: Volts, Set Level and Noise. These will be explained later in this article. Finally, the Filter switch has three positions: Flat (giving the widest freqency response), 20Hz 20kHz, and A Wt ('A' weighted) which has already been mentioned above. There are two insulated BNC sockets on the front panel, one for the input signal and one for the output signal to an oscilloscope or a frequency meter. The output level from this socket is around 140mV RMS, for a full scale deflection of the meter. There are two more switches to be mentioned. One is a toggle switch which is used to connect the CRO signal earth to the case of the instrument or to the mains earth. The other is a pushbutton switch used to check the "noise floor " of The circuitry relies for its performance on a number of carefully selected op amps. The most important op amp is the input device. Contrary to what a number of readers have expected, we have not used the low noise LM833 in this application. Instead, we have used a quieter and more tightly specced device, the ultra-low noise OP27. This was first produced by Precision Monolithics, Inc, USA and has since been second-sourced by Harris Corporation and Motorola Inc. Not only is the OP27 one of the quietest op amps currently available, it also has the advantage of a relatively high input resistance which is a minimum of 700k0. Also specified are three LM318 op amps. These have been selected for their wide bandwidth. The LM833 dual op amp is featured too, in the precision rectifier and meter driver. Apart from those, there are two LF351 Fet-input op amps and one LF353 dual Fet-input op amp. Let's now have a look at how the circuit works. The easiest way to understand it is to look at it in the "Volts" mode first and then look at the other functions. In the "Volts" mode, the Mode selector (S3) is set to Volts, the Noise (ratio) switch (S4) is set to its 0dB setting and the Filter selector switch (S5) is set to Flat. This is depicted on the complete circuit Fig.2 (right): of the eight op amps ► specified in the circuit, IC1 (OP27) is the key to the high performance of the unit. It has very low noise and high input resistance. I N ... I (0 0:) 0:) .... ~ en c::: ~ > c::: E 240VAC - L--S&. (Ut//30k) . ALL RUISTOIIS 1% 111111() 5.54k -10d8 PRESS FOR Mlt NOISE +15V +15V 1-~ 6 F'' f NOISE All'l.flER NOISE .,. 6 f NOIS S-4' 6 f +15V 10tlf GND II -~~~M .,. S5a SC04-1-11888-1 AC MILUVOLTMETER -15V +15V ______·_·:~~! VOLTS 1 100k: FlA 3.3k 3.3k 20k .002 (.0011/.001) +1_5V +1JV 20Hz IIGH•PASS FI.TER +15V 25.5k * SELECT FOR MIIIIUII OFFSET 18k 'A' WElll1111116 FI.TER 2k CAL VR2 50 . • MAINS EAIITN rJ~, ~~ steps (ie, 3.16 times) by switch sections S4a and S4b. S4a switches the feedback resistors for IC3 while S4b switches the feedback resistors for IC4. For the OdB setting, both op amps have a gain of unity. For the - lOdB setting, IC3 has a gain of + lOdB. For the - 30 to - 60dB settings, IC3 has a gain of + 30dB (set by the 12k0 and 3900 resistors). The gain of IC4 varies from unity at the - 30dB setting to + 30dB at the - 60dB setting. The output from IC4 is then fed via S3b to IC2 and then passes through to IC7 as before. We'll explain just how noise and ratio measurements are made in practice, later in the article. In the Set Level mode, the gain of IC2 is varied by the Set Level control, VRL The gain can be varied between 6 and 2L6 times. Filter stages Here's what the completed unit looks like inside the chassis. Note that the power supply is mounted near fhe rear panel, to keep mains hum away from the meter circuitry. Full constructional details will be published next month. diagram, Fig.2. The signal to be measured is fed in via the BNC socket to the stepped input attenuator SL The total resistance of the attenuator is very close to l lOkO and the resistor values are arranged to give the 1 to 3.16 ratio between ranges mentioned above. If set to its highest setting (ie, lOOV) and with an input signal of lOOV, the signal at the wiper of Sl will be lmV. In fact, for each range, when the maximum input signal is fed in, the signal at the wiper will be lmV. For example, on the 300mV range, if you feed in 300mV, you will get lmV at the wiper of SL This lmV signal is then fed via the 4.7k0 resistor to the non-inverting (+)input of !Cl, the OP27. This is arranged to have a voltage gain of 34, as set by the 3.3k0 and 1000 feedback resistors. So for an input of lmV from Sl, the output at pin 6 of !Cl will be 34mV. From there the signal is fed via switch S3a and S3b to IC2. In the Volts mode, as set by S3c, the gain of IC2 is 6, as set by the 6.Bkn 22 SILICON CHIP and 3300 resistors, and the lkn pot, VRL For the same lmV input to Sl, the output from IC2 will now be 204mV (6 x 34). This signal is fed via switch S5a, trimpot VR2 and S5b and then via a 50µF capacitor to the stages consisting of IC7a and IC7b. IC7a and IC7b form a precision full wave rectifier and filter circuit to drive the meter. The lµF capacitor across the 160k0 resistor, in the feedback loop of IC7b, provides a DC-averaged output to drive the meter movement. VR4 is provided for calibration. ICB provides a buffered version of the signal from S5 for viewing on an oscilloscope. After calibration has been performed on the instrument, a lmV RMS sinewave fed into the input of ICl will be displayed on the oscilloscope with an amplitude of about 400mV peak-to-peak. Noise & ratio measurements In the Noise mode, the output signal from ICl is fed via S3a to variable gain amplifiers IC3 and IC4 which are LM318s. The gain of these op amps is varied in lOdB Now let's have a look at the filter stages, as selected by S5. As mentioned before, there are two filters, for 'A' weighting and for the 20Hz to 20kHz bandpass. The 'A' weighted characteristic (shown in Fig.l) is provided by a 4-stage passive filter, consisting of four capacitors and four resistors. This is buffered by IC6 which is connected as a unity gain voltage follower. The 20Hz to 20kHz filter is provided by IC5a, connected as a 20kHz low pass filter, followed by IC5b which is connected as a 20Hz high pass filter. In other words, IC5a effectively passes all frequencies below 20kHz and IC5b passes frequencies above 20Hz. Between the two of them, they provide the 20Hz to 20kHz bandpass. The 'A' weighting filter has a loss of about - 3dB and to ensure that there is no jump in gain when the 20 to 20kHz bandpass or Flat filter conditions are selected, trimpots VR2 and VR3 are provided to equalise the signal levels, at lkHz, for all three settings of switch S5. Power supply The millivoltmeter is powered from a 30V centre-tapped transformer feeding a full-wave rectifier, two lO00µF capacitors and PARTS LIST 1 aluminium case with Marviplate lid, 235 x 21 0 x 117mm (W x D x H) 1 Scotchcal front panel label, 228 x 113mm 1 30V 1 50mA centre-tapped transformer (Altronics Cat. No. M-2855) 1 meter PCB, code 04108881, 193 x 98mm 1 power supply PCB, code 04106881, 71 x 52mm 1 MU65 1 OOµA panel meter, 100mm x 82mm (Altronics Cat. No. Q-0550 or equivalent) 1 set of metal shields (see metalwork diagrams, Part 2) 2 insulated panel-mount BNC sockets (Belling Lee LX04-0503-ZZOO5N or equivalent) 2 miniature SPST toggle switches 1 single pole 12-position switch (make before break contacts) 1 2-pole 3-position switch (make before break contacts) 1 2-pole ?-position switch (2 wafers, make before break contacts) 1 3-pole 3-position switch (3 wafers, make before break contacts) 1 momentary contact, miniature pushbutton switch 4 23mm fluted plastic pointer knobs (Altronics Cat. No. H-6050 or equivalent) 1 15mm knob 8 6mm PC standoffs 28 PC pins two 3-terminal regulators to provide balanced outputs of ± 15 volts DC. The regulator outputs are further filtered by 100µF and 220µF capacitors. There are also 16 0.lµF capacitors dotted around the circuit to provide extra power supply rail bypassing. Three switches remain to be mentioned. S2 is the momentary contact pushbutton switch. It shorts out the 4. 7k0 resistor in series with the input to IC1. It is used when making extremely low noise measurements or when confirming the "noise floor" of the instrument. 1 3-core mains flex with moulded 3-pin plug 1 cord-grip grommet 1 2-way insulated terminal block 1 3-way tagstrip 2 solder lugs 4 rubber feet Semiconductors 1 OP2 7 ultra low noise op amp 3 LM318 op amps 2 LF351, TL071 FET-input op amps 1 LF353, TL072 dual FETinput op amp 1 LM833 dual low noise op amp 1 7815 3-terminal +15V regulator 1 7915 3-terminal -15V regulator 4 1N4002 1A silicon diodes 2 1N4148, 1N914 small signal diodes Capacitors 2 1OOOµF 25VW PC electrolytics 2 220µF 16VW PC electrolytics 2 100µF 16VW PC electrolytics 3 4 7 µF 50VW bipolar electrolytics 1 1µF 200VW metallised polyester (greencap) 1 1µF tantalum or low leakage electrolytic 2 0.22µF 63VW miniature metallised polyester 2 0.15µF 63VW miniature metallised polyester S6 is a toggle switch which connects the CRO signal earth to the case of the instrument. This is used if the equipment being measured gives an erroneous display on the CRO, which is likely to occur with double-insulated audio gear. S7 is the power switch and is mounted on the rear panel so that mains wiring is kept as remote as possible from the sensitive front panel circuitry. Using the millivoltmeter As a further help to understanding how the circuit works, let's consider a typical signal-to-noise 16 0 .1µF miniature ceramics or greencaps 1 .047µF 63VW miniature metallised polyester 1 .0022µF metallised polyester (greencap) 3 .001 µF metallised polyester (greencap) 1 39pF ceramic 1 22pF ceramic 1 12pF ceramic 1 1OpF ceramic Potentiometers 1 1 kO linear pot, 16mm diameter, PC mount 1 1OkO trimpot, horizontal mount 2 2k0 trimpots, horizontal mount Resistors (0.25W, 1 %) 1 X 910k0, 1 X 160k0, 3 X 100k0, 1 x 91 kO, 1 x 75k0, 1 x 68k0, 1 x 56k0, 3 x 51 kO, 1 X 30k0, 2 X 22k0, 2 x 20k0, 2 x 12k0, 3 x 1 OkO, 1 x 7 .5k0, 3 x 6.8k0, 1 X 6 .2k0, 2 X 5.6k0, 1 X 4.7k0, 2 X 3.9k0, 4 X 3.3k0, 1 X 2. 7k0, 1 X 2.2k0, 2 X 2k0, 1 x 1.8k0, 1 X 1.5k0, 1 X 7500, 1 X 3900, 1 X 3300, 1 X 2200, 1 X 1800, 4 X 1000, 1 X 750, 1 X 220, 1 X 200, 1 X 180, 1 X 7.50, 1 X 2.70, 1 X 1.80, 1 X 1.10 Miscellaneous Insulated hook-up wire, tinned copper wire, shielded cable, heatshrink tubing, copper or brass shim, screws, nuts, lockwashers, solder, Presspahn insulating material ( 1 50 x 75mm). ratio measurement. Say we're measuring a run-of-the-mill 60 watt power amplifier. For 60 watts into an 80 load, it will deliver 21. 9 volts RMS. This would be confirmed on the 30V range. Note that the Filter switch must be in the 'Flat' position for voltage measurements. Then the mode switch would be moved to the 'Set Level' position and the Set Level control adjusted to bring the meter's pointer to 0dB. The input signal would then be removed from the power amplifier and its inputs loaded with a 4. 7k0 continued on page 71 AUGUST 1988 23 ~ ~-::====================----------------~~~== ====::::::: : : :-. ~ WIRE WRAP IC SOCKET UNIDIRECTIONAL WIRELESS AT LAST! TRAVEL ADAPTORS AT GIVEAWAY PRICES Save a fortune over the machine pin wire wrap style which we now stock. We have sorre old style standard wire wrap left. ... , Cat Special Pl-6510 8 pin 50t ea Pl-6513 18pin $1.25 ea Pl-6515 22pin $1.25 ea Australian to Overseas Pack 6:) A must If you are travelling overseas. A pack of 3 adaptor plugs which will enable you to use an Australian appliance anywhere In the world • The British Plug 8 © 3 square pins for Great Britain, Ireland, Singapore, partts of the Middle East, Hong Kong & Asia The European Plug • I • 2 round pins for Europe, Noumea, Tahiti, pans of Middle East, Asia and South America The USA Plug Pack of three • I I 2 flat pins and round earth for North America and Canada e .· . WIRE WRAP WIRENow available In 2 sizes In 5 metre lengths. High quality US made made wire wrap wire in 24 & 28 gauge. Both green In colour. Cat. WW-4350 24g/5m $2.95 Cat. WW-4365 28g/5m $2.95 , •'•'\ ; .,,.,,.. . , SAVE $12 $19.95 Cat. PP-4022 Adcola Soldering Station •Note. These adaptors will not change the voltage. You will need to switch the voltage on your appliance Australian Adaptor For use In Australia by visitors from Europe, USA and Japan. •Note. will not change voltage Cat. PP-4020 l~~~~.-, (·,:: i~:) AUGUSTONL $24.50 .. . • MICROPHONE This Incredibly small microphone just clips on your tie or collar and transmits on FM. High quality, Australian made, 240 volt soldering station. See catalogue for full details. Base station only Cat. TS-1475 $7.95 $159.50 SOLDERING IRONS TO SUIT 40 watt 80watt High voltage capacitor bargain. sr.;;~12:soeach ~ Desolderlng Tool to Sult ~ TRANSFORMER BARGAINS Yet another SCOOP PURCHASE TRANSFORMER No.1 1s a 2oovA unit measuring $5 TRANSFORMER No.2 This 1oovA unit measuring 100(H) x 90(W)n x 75(D)mm features a mounting bracket that enables you to mount It vertical or on Its side. Primary winding Is tapped from 200-240 volts. Secondarles are 1 x 16V, 1 x 12V. Bolh would be minium 2 amps. Another bargain transformer this time only $14 Cat. MM-1812 $79.95 Cat. TS-1476 Cat. RC-5378 115(H) x 95(W) x 105(D)mm. It has a 6 volt 'heater winding and two other secondaries one 22V and the other 47V. Each secondary would pass several amps. We don, know what to do with them so Hyou do you will pay only $5 - that's right five dollars for onel (Personal shoppers only) . Cat. MM-1810 $49.95 $55.00 Cal. TS-1478 Cal. TS-1480 WAL.KMAN ,,.:.:=================~ Temperature Probe Adaptor for Digital Multimeters This device simply plµgs into the banana sockets of your digital multimeter. It will give an output of 1mV for f!Nery degree increase in temperature. Switch form C to F. High quality probe with semiconductor sensor In tip. Requires 9V battery. Cat. QM-1590 SPEAKERS Pair of micro mini stereo speakers. Ideal for Walkman type radios, players. Cat. AA-2050 $15.95 pair SAVE $10 ONLY $49.95 ~ $14 Discolite Kit Ref: Silicon Chip July 1988 Build your own light show. More features than the Muslcolor. New design. The Jaycar kit includes punched and screened front panel, punched and anodised rear panel and all specHied parts . Cat. KC-5032 $159.50 STROBOSCOPIC TUNER KIT Ref : EA July 1988 This simple circuit provides crystal-locked accuracy fortuning virtually any musical instrument. It also doubles as a stable frequency reference Hyou prefer to tun up by ear. Kit Includes box and all parts. Cat. KA-1705 ' ,, Ref: Silicon Chip Jun91'July 1988 The new Studio 200 Preamp offers excellent specifications and features for a very moderate price. Main Features • Very low noise on Inputs - less than many CD players • • Very low harmonic and intermodulation distortion • Up to 7 stereo program sources can be connected • Tape monitor loop • Separate high quality headphone amp • Headphone socket disables output signal to power amp • Tone and balance controls Cat. KC-5033 ·' $229 00 240 VOLT LINE FILTER KIT Cat. KA-1703 $39.95 KIii those clicks and pops from next doors vacuum cleaner or lawn edger etc. Kit Includes 240V socket and plug, PCB, all components and hardware. Call into any one of our showrooms for an audition (not Concord) SA•100 Upgraded AEM6102 speaker kit. Uses new design crossover, and they do sound better. Complete kit with cabinets: SA•50 UnbeliBYable sound from such small speakers. Measures only 26(H) x 17(W) x 195(D)cm. Incorporates a 5' woofer and D19 dome tweeter. See AEM magazine for a full review, May edition. Complete kit with cabinets only: $799 $399 SA•70 Upgraded EA60/60 speaker kit incorporating 8" woofer and D19 tweeter. Complete kit with cabinets only: $499 SA-130 Upgraded AEM6103 speaker kit. New design crossovers, new slimmer cabinets, upgraded dome tweeter. Complete kit and new designed crossovers are excellent value at: $1199 See our catalogue for full details. • ••••••••••••••••• • •••• • : Rover Negative Ion : Generator • Yes, we've made another scoop purchase. The importer contacted us with his dilemma and we purchased a quantity of these fully imported fully guaranteed air purniers. These units are 240 volt operated, draw about 1/2 watt, deliver about 250 billion ions per second, and cover about 25 square metres. It's even supplied with a Taster PC board and spare needles. tt you've ever wondered about negative ion generators, this MUST be the time to buy one. These were selling for about $80. Jaycar has a llmlted quantity available for: Cat. YX-2905 $29.95 REMOTE CONTROL ACCESSORIES FOR OPERATION OF CAR ALARMS, LOCKING , ETC. This range consists of a key-fob type transmitter (Australian standard 304MHz, remote receiver and door lock actuators e Key Fob Transmitter This unit measures 60(L) x 34(W) x 14(D)mm. It is supplied with a vinyl slip wallet (which is pretty useless). it is powered by a 12V cigarette lighter type battery. You can custom code It with from 1024 combinations. Instructions supplied. Works the LR-8810 Remote Control Receiver. Cat. LR-8814 $27.95 Remote Control Receiver The hand controller LR-8814 will latch this unit on and off with alternate depressions of the button. A relay (SPOT) with 5A contacts is actuated. This relay can be used to control solenoid door locks as wall as no-entry delay burglar alarms, etc. Dimensions 122(W) x 90(0) x 30(H)mm. Cat. LR-8810 $54.95 12 Volt Door Lock Actuator (Master) • ••••••••••••••••••••••• , - - - - - - - - - - - - - -- This soenold device is especially designed for alter-market installation. it is made of durable materials (fibreglass reinforced body, acetal resin gears) with an operational ltte of 30,000 times. Requires SA <at> 12V. Will give 2.8kg thrust (max) over 23mm. Fitted with a SA microswltch which can be used to power slave • actuators. Supplied with comprehensive kit of hardware fittings to connect to door lock hardware. Dimensions • 145(L) extended body x 28(W) x 62(D)mm - -- - - --.. Cat. LR-8816 PHILIPS GENERAL CATALOGUE $29.55 12 Volt Door Lock Actuator (Slave) 1988 Edition NOW AVAILABLE - Brand newl Just released! Line data Is provided on the full range of preferred Philips products Similar to above but with no microswitch. Including: Logic, memory, analogue, radio, audio, video, semiconductors, tubes, capacitors, resistors and other materials Including speakers, etc. Cat. LR-8817 1.25 Inches thick. Dimensions 210 x 145mm. Cat. BP-4402 $24.95 'TECHNICAL BOOK CLEARANCE - 25.00 CHEMISTRY Ferric Chlorlde Two sizes, conveniently packed In a plastic jar for easy storage with a childproof cap. Use only as your require, and simply store the rest until needed. 200g makes 1 lltre Cat. NC-4251 $4.95 400g Makes 2 litres Cat. NC-4252 $7.95 AMMONIUM PERSULPHATE The alternative to Ferric Chloride. Mix contents (400 grams) with 1.5 lltres of hot water to etch copper board approximately 500sq/crn. Supplied In child proof bottle. Cat. NC-4254 $6.95 QUALITY TIE CLASP MICROPHONE Low Impedance, omni directional electret microphone. lmpedancez: 1k ohm. Freq. Aesp. 40-1 BkHz With 3.5mm plug on 3 metre lead. Cat. AM-4067 NORMALLY $29.95 AUGUST ONLY $21.95 SA VE $8 - National Linear Data Books Vol. 1, 2 & 3 We have managed to obtain a small quantity of the definitive National Linear Data Books. These have not been avallable for many years. Sat of three books. We don, expect these to last very long - so be quick. SET OF THREE BOOKS Cat. BN-4002 _'$~9).~5 IFor full details see our 1988 catalogue. Fibre optics experiments projects IBS-0720 BS-0730 How to read schematic diagrams Computer connections solved IBS-0422 BS-0406 Soul of CP/M BS-0456 Understanding microprocessors IBS-0416 programming techniques IBS-0404 Macintosh Intro automotive solid state Understanding digital electronics IBS-0458 BS-0590 8080/8085 software design BS-0420 C prog. techniques for Macintosh IBS-0453 Basic electricity 6 cassettes Complete guide - car audio IBS-0732 BS-0703 Crash course dlgltal technology I I & - Was $26.95 $27.50 $37.95 $39.95 $27.95 $44.50 $19.95 $27.95 $24.95 $37 .95 $26.50 $19.95 $34.95 - ' Now $19.95 $19.95 $27.95 $27.95 $1 9.95 $29.95 $14.95 $19.95 $14.95 $25.95 $16.50 $14.95 $24.95 Jaycar have available two transistors which will replace a multltude of common hard to get devices. PN100 Is NPN general purpose medium power amp and switch with continuous collector current up to 500rnA. PN200 Is PNP general purpose amplifier at collector currents to 1A. Both are T0-82 plastic package. PN100 replaces PN2221 , PN2222, PN2222A, PN3565, PN3568, PN3569, PN3643, PN5133, 2N2219A, 2N2222A, 2N3414, 2N3415, 2N3416, 2N3417, 2N3700, 2N3704, 2N3904, 2N4123, 2N4124, 2N4401, 2N5088 and 2N5210. Cat.ZT-2283 2.5mm Black WH-5531 3.5mm Black WH-5532 5mm Black WH-5533 7mm Black WH-5534 10mm Black WH-5535 16mm Black WH-5537 ELCHEAPO ~ DESOLDERING BRAID MIDRANGE Quality s• sealed back midrange with large magnet. Power Handling System 100 watts nms Freq. Response 350 - 7.5kHz Resonant Freq. 400Hz Sensltlvlty90dB/1W-1 metre Impedance 8 ohm $19.95 5" WOOFER/MIDRANG E Cat CM-2078 High quality NZ made speaker with large magnet. Power Handling 20 watts rms Freq. Response 80 - 15kHz Resonant Freq. BOHz Senslvlty 90dB Cat. CW-2104 PN200 replaces PN2907, PN2907A, PN3638, PN3638A, PN3640, PN3644, PN4121, PN4143, PN4248, PN4249, PN4250, PN4355, PN4916, PN4917, PN5910, 2N2905A, 2N3467, 2N3702, 2N3906, 2N4125, 2N4126, 2N4291, 2N4402, 2N4403, 2N5086, 2N5087, 2N5447 Cat. ZT-2284 Our usual desolderwick Is sold in a plastic spool and contains 5 feel for $2.50. That~ ~roxlmately $1.50 per metre. El cheapo braid is 2mm wide and will take solder off a PCB reasonably well although the braid gets a bit hot because there is no plastic spool to hold. You could easily put some In your old spool. Supplied in a 5 metre length for $2.50. That 'S 50e metre - or 113rd the price of normal desolderwlck. Cat NS-3025 5 metre pack Please note: braid is not loaded with flux and wlll not work quite as well as normal desolder braid. 25ft ea 10+ 22"- ea $18.95 "Plastl•Dlp" Heavy Duty Flexlble Liquid Coating NEW TRANSISTOR IGNITION Ref: SIiicon Chip May/June 1988 A high energy Ignition system which uses the cars existing ignition coil and points. Unit has extended dwell and Is compatible with both our Hall Effect and Opto Sensors. In fact, all CO"l)Onents to Interface both these are now Included free In the TAI kit. Complete kit with dlecast box and all components and Interface co"l)Onent&. Cat. KC-5030 se count or under $100. Features: • Coverage 12 metre x 12 metre • DeteClion angle 110° • Detection beamss - 38 • Adjustable angle • Tamper proof protected • N/C and N/O output Cat. LA-5017 $49.95 OPTION l BREAl( ERLESS (HALL EFF-EC ) ~;~~:I:.~J:STEM A professionally engineered eleclronlc (breakerfesa") contact breaker system. Yes, only Jaycar has a complete Hall Effect ~\r~~ I · ,', ___,.', J :~ : extensive nurrber of cars. Each kit contains the "'-~ , following: ' ; /~ • Hall Effect Trlggerhead • Magnetic rotors for both 4 & 6 cylinder cars • Over 6 cam-lobe adaptors "-=-""'= • • Over 12 different adaptor plates for your palllcular distributor • Olher hardware (l.e screws, etc) • You can remove this system and re-equip your car with the original breaker points when you sell. the earl • As easy to install as a set of point& • lnS1ructlon (simple to follow) Included This set Is designed 10 flt most European and Japanese cars. In fact, It wlll also flt many AuS1rallan cars fitted with Lucas, Bosch, Motorcraft, AC Delco, or Autollte eleclrlcs. Hyou wish you can check first by sending a SAE for a car/distributor 11st. Cat. KJ-6655 ·=,,~- - > ONLY S99.95 , ,.,., MM $49.95 OPTION 2 SIEMENS HALL EFFECT CONVFRSION Ref: Silicon Chip June 1988 Hyou have a car that will not take the very comprehensive KJ-6655 Hall type breaker point set, then this device Is for you. German made Siemens HKZ-101 Hall Effect switch. Interface CO"l)Onents Included in TAI kit. Cat. ZD-1980 $34.95 Plastic Dip is an &lr dry liquid plaS1Ic coating that produces a tough, thick pliable finish. It Is Ideal for making a pliable coating for the handles of tools,etc. Supplied lna470ml dipping can. =c: Will do ~......... ~.dozens of tools. Cat, NP-1100 Red colour N/C and N/O on one assembly. Saves buying one or the other. Powerful magnets, self adhesive or screw mount. Selectable normally open or normally closed. Cat. LA-5070 $4.7510+ $4.50 ea $24.95 i'-' J ~ ', IV ((!I ~ ~r.~o:o,,rll• . ~, _ ~ ~ --~~~ 500mW <at> 6V Audio Amplifier ;;~ ----------- A six transistor 1/2 watt amp for the cost of two hamburgers! It has two transistor tape preamp which Is NAB equallsed and a four transistor power amp, It has facilltles 10 take line level Inputs. The (irregularly shaped) board measures roughly 110(L) x 48(W)mm. Each amp comes complete with schematicand connection diagram. (2 required for stereo). cat. AA-0290 10 up $3.50 each DRYT Quallty lettering sets, available In 4 different styles. Can be used on most smooth surfaces Including metal, glass, plastic, wood, cardboard and paper. Ideal for lettering on rack cabinets, control panels, etc. Simply position the letter and rub with the cap of a ball point pen or soft pencil. Made In Holland. STYLE 1 Black lettering 4mm high, Capital letters, lower case letters, numbers. Cat. NL-4100 STYLE 2 Black lettering 6.5mm high. Capitals, lower case, numbers. Cat. NL-4102 STYLE 3 Silver letters with black shadow 7mm high. Capital letters and numbers. Cat. NL-4104 STYLE 4 Flourescent yellow on black background. Capitals and numbers. Cat. NL-4106 ALL ONE PRl(.E TYPE 1 vom11 TYPE 2 .99 et h Dix2! TYPE 3 TYP 4 RS6! JAYCAR No.l FOR EX-STOCK KITS Electronic Australia Kits KA-1010Musicolor 4 $125.00 KA-1109 Electric Fence $23.50 KA-1115300W amp module $119.95 KA-1116 300W power supply $105.00 KA-1117 300W speaker protector $23.50 KA-1119Transistor tester $21.50 KA-1-220 Signal tracer $27 .95 KA-1225Transistor & PUT tester $26.50 KA-1230 Zener diode tester $16.95 KA-1390Frequency counter 50MHz $169.50 KA-1392 Prescaler 500MHz $46.50 KA-1428 Function generator $129.50 KA-1430Vocal canceller $24.95 KA-1505TAI Hall effect $44.95 KA-1506Transistor assisted ignition $42.50 KA-1508Touch light dimmer $29.95 KA-1522Guitar effects BBD $115.00 KA-1535Ignition killer $23.50 KA-1550Deluxe car alarm $89.50 KA-1555CQUAM stereo decoder $26.50 KA-1556 Ultra sonic movement det. $34.95 KA-1500Railmaster controller $109.95 KA-1559 Railmaster walkaround $13.95 KA-1561 Railmaster diesel sound $22.50 KA-1562 Railmaster steam sound $22.50 KA-1563 Rail master light control $21 .95 KA-157430V 1A power supply $89.50 KA-1582House alarm $169.00 KA-1595Digital capacitance meter $85.00 KA-159840W inverter 121230V $99.95 KA-1610300W inverter 121230V $249.00 KA-1626 Video fader $24.95 KA-163012V lamp flasher $12.95 KA-1635AIWFM stereo tuner $599.00 KA-1636AIWFM remote control $99.50 KA-1650 Playmaster 60160 $329.00 KA-1652Blueprint 60/60 $369.00 KA-1660Electric fence $59.50 KA-1670 light saver $15.99 KA-1674Digital photo timer $89.95 KA-1675Screecher car alarm $34.95 KA-16n Audio oscillator (metered) $165.00 KA-1679Turbo timer $29.95 KA-16813 band short wave radio $79.50 KA-1682Dual tracking power supply$129.95 KA-1683Battery monitor $14.95 KA-16848 channel VR transmitter $45.00 KA-1685IR receiver (std) $127.95 KA-1686 IR receiver (add-on) $55.00 KA-1687Electronic rain gauge $49.95 KA-1688 Electronic stroboscope $13.95 KA-1689Exp. power supply $26.95 KA-1690DI box $39.95 KA-1691 TV colour bar/pattern gen $169.00 KA-1692Voice operated relay $24.95 KA-1693Metronome $19.95 KA-1694 Volt/continuity test $29.95 KA-1695AC/DC Millivoltmeter $46.50 KA-1696Econ. Temp probe DMM $19.95 KA-1697 Utility timer $21 .95 KA-1698Transistor, FET, Zener test KA-16998ench amp- signal trace KA-1700 Power transistor tester KA-1701 RF detector probe KA-170250MHz Dig Freq meter KA-1703Line Filter KA-1704 FM Receiver KA-1705 Stroboscopic Tuner $55.00 $39.95 $22.95 $13.50 $99.00 $39.95 $55.00 $47.50 Australian Electronics Monthly Kits KM-301 O60W Mosfet amp KM-3012 120W Mosfet amp KM-3015 Listening post KM-3016 RTTY encoder KM-3030 Ultrafidelity preamp KM-3040 Dual speed modem KM-3042 Speech synthesiser KM-3050 Workhorse amp KM-3054 Audio clipping meter KM-3056100W module less MFets KM-3058 64 packet radio KM-3060 Balanced line driver KM-3061 Microphone preamp KM-3062 RS true 232 interface KM-3063 Uo satellite decoder KM-3064 Octave EQ mod KM-3065 RS true 232 interface KM-3066 VHF rec for weather sat KM-3067 NiCad charger KM-3068 FM minder bug $59.50 $79.50 $39.95 $32.50 $359.00 $169.00 $43.50 $35.00 $14.50 $79.50 $59.96 $99.50 $36.95 $24.95 $55.00 $59.95 $27.95 $99.00 $24.95 $11.95 Electronics Today International Kits KE-4013Microwave leak detector KE-4014 Mixer preamp KE-4023Signal Spkr protector KE-4029 NiCad battery charger KE-4033 Temperature probe KE-4050 ETl480 SOW amp module KE-4052ETl480 100W amp module KE-4048ETl480 power supply KE-42005000 power amp KE-4204 5000 1/3 octave equaliser KE-4220 ETl499 150W Mosfet amp KE-4405ETl581±1-15V power supply KE-4666 RS232 Centronics interface KE-4578ETt340 car alarm KE-4690ETl342 CDI KE-4698 4 sector house alarm KE-4706DI box KE-4711 Mini FM transmitter KE-4720Digital sampler KE-4722 RS232 Commodore KE-4724 Parametric equaliser KE-4725 Solder iron temp control KE-4728 Ring tone customiser KE-4729 Guitar preamp $17.95 $39.50 $22.50 $14.95 $32.95 $27.50 $34.50 $29.50 $499.00 $219.00 $109.50 $27.50 $32.50 $79.50 $79.50 $29.95 $42.50 $9.95 $119.00 $16.95 $23.50 $39.50 $29.95 $45.00 KE-4730 Solar gen p/supply KE-4731 Telephone intercom KE-4732 Baby minder KE-4733Active Crossover $12.95 $59.95 $34.95 $39.95 Silicon Chip Kits KC-501 0 Capacitance meter KC-5011 Off-hook indicator KC-5012Car radio power supply KC-50131GHz Digi Freq meter KC-5014 Subcarrier adaptor KC-5015Telephone ringer KC-5016Speed control/dimmer KC-5017 24 to 12V converter KC-501850W amp mdule KC-5019100W amp module KC-5020 Door minder KC-5021 Protector car alarm KC-5022 Dual track power supply KC-5023Low ohms adapt DMM KC-5024 Mode end file ind KC-5025 Line grabber - phone KC-5027 Ph meter KC-5028 Train controller KC-5029CD Htphone amp KC-5031 Optical tacho KC-5032Disco Light KC-5033 Studio 200 Preamp KC-5034 Remote Control for Car Alarm $27.95 $12.95 $28.95 $299.00 $22.95 $19.95 $18.95 $59.00 $32.95 $38.95 $37.50 $79.50 $99.95 $29.95 $9.95 $19.95 $49.95 $89.00 $24.95 $49.95 $159.50 $229.00 $79.50 Jaycar Kits KJ-6502 Syntom drum synth KJ-6504 8 channel mixer KJ-6505 Console Psupply for above KJ-6531 2801 1/3 octave Eq. KJ-6535 2010 10 band stereo Eq. KJ-6655 Hall Effect Trigger kit KJ-7000 Red light flasher $42.50 $595.00 $119.00 $239.00 $169.00 $49.95 $19.95 POST & PACKING $5 $9.99 $ 2.00 $10 $25 $24.99 $ 3.75 $49.99 $ 4.50 $99.99 $ 6.50 OVER $100 $10.00 $50 IN AUSTRALIA $13.50 ■ V/S4 SYDNEY - CITY 111vor1<St. (02)2671614• Mon-Fri 8.30 • 5.30 Thurs 8.30 pm• Sat 9 -12 Cnr. Cartingtord & Pennant Hills Rd (02) 872 4444 • Mon-Fri 9 • 5.30 Thurs 8.30 pm • Sat 9 • 2pm GORE HILL 188 Pacific Hwy cnr Bellevue Ave (02) 439 4799 • Mon-Fri 9. 5.30 Sat 9 • 4pm BURANDAQLD 144 Lo9an Ad (07) 393 0777 • Mon-Fn 9. 5.30 fhurs 8.30- Sat 9. 12 CONCORD 115ParramattaAd(02)74530nMon-Fri 8.30 • 5.30 • Sat 8.30 -12 MELBOURNE-CITY Shop 2, 45 A'Beckett St City (03) 663 2030 Mon-Fri 9 • 5.30 Fri 8.30- Sat 9 -12 HURSTVILLE 121 Forest Rd (02) 570 7000Mon-Fri 9- 5.30 fhurs 8.30 pm • Sat 9 • 12 SPRINGVALE VIC 887-889 Springvale Road Mulgrave (03) 5471022 NrCnr. Dandenong Road Mon-Fri 9- 5.30 Fri 8.30 • Sat 9-12 CARLINGFORD EE ~ = =;;;;....!) Sound reasons for confusion Last month I commented on the rarity of sound faults in TV equipment, and compared them with the old fashioned radio sound faults. Well, hardly was the ink dry on the papyrus - and before I'd had time to cut myself a new quill pen - than another one landed on the bench. And it was as tricky as they come. The device involved was a General colour TV set, model GC187 and the complaint was simple enough; no sound of any kind. I thought the solution would be equally simple; which just goes to show how naive one can be. The set belonged to a local motel for which I have the contract for the whole TV installation. This particular set was one of several devices which had failed after a particularly violent thunderstorm. During the storm there was a lightning strike which probably hit the antenna directly. Anyway, it knocked out the distribution amplifier, put several other TV sets out of action, and cooked a microwave oven. All in all, quite a mess. Most of the repairs were quite straightforward, though somewhat ,s rr .... SAt>? WEL-l-, "flie:. FLOAAL- AR~ANGEME.tJ1""'S HAD 1-r. .. expensive and not particularly newsworthy. As things worked out, the GC187 was last on the list. Knowing the capriciousness of lightning strikes I was quite prepared to find the fault in almost any part involved with the sound channel; ie, it could be anywhere between the antenna and the speaker. At a practical level I started at the input to the audio amplifier. This uses three transistors; QB0l, Q802 and Q803. Q802 and 803 form a complementary symmetry output pair, driven by QB0l; a perfectly conventional set-up. Feeding a suitable level of audio signal into the base of Q801 produced a healthy output from the speaker; nothing wrong there. Back-tracking from this point brings us to pin 2 of IC2 (uPC1382C), the sound IF and audio detector system. This amplifies and demodulates the 5.5MHz sound carrier applied to pin 14. This signal comes from pin 12 of ICl (T A7607 AP); the video IF amplifier and detector. And signal into this is via pin 1 from the first IF amplifier, Ql and the SAW filter, FLl. Considering that the set was producing a first class picture, I felt that the fault was most likely to be closer to IC2 than the front end. Colour bar signal ''"--t nus PA~1"1CUl-AR S6,,.. w~s ONE. ~•c.~ HAO FAll..EO APfER A PA~i,cu1..~Rl.'t V\Ot..EWr' 'O'\UN~S1'"01'M ••• 28 SILICON CHIP I fed a colour bar signal into the set and checked the output at pin 12 of ICl. As far as I could determine all was well at this point, so I moved on to IC2 and gave it a full voltage check. Again I found nothing suspicious, all values being acceptably within tolerances. Next I used the CRO in an effort to check the 5.5MHz level at pin 14 of IC2. Results were inconclusive except that the level seemed to be well down on what I expected. So what could cause this? ICl was obviously delivering adequate video I UNtK .,. VHF/UHF CA-335S TP15 IF A [IBJ JJK TA 760 VR1 SK(B l VB UI vsw E TU + 15Y ... ,,.. :HAN NEL ;ELECTOR !OARD R672 100K ED C673 o.o,, l CUI 2200P I IC670 uPC574J ca10 1200P .. 05 y IF SOUND .,- - BOARD ~ •uo10 OUT - + ~AIN BOARD - ISV CEC:ill 0670 EQAOI -15Rl ~ 'f '" C661 _ 0.01 - C672 -1 J,. ,oisev1F rl,- R667 1a1< ( 1/2) Relevant portion of the GC187 circuit. The audio stage is at bottom left, fed from IC2 to its right, which in turn is fed from IC1 at top right. The video line goes off to the right from pin 12 of IC1. and chrominance (colour) signal to the rest of the set. Only the 5.5MHz component seeming to be missing. So was something in ICl, or even earlier, upsetting the response curve to the point where the sound plateau had been lost? I didn't think this was very likely since the chrominance carrier was obviously intact. Still it had to be considered. I had a spare IC2 on hand, and it was an easy job to fit it, so I went ahead. Well, as Thomas Edison would have said, I now knew one more thing that wasn't wrong, because it made no difference. So where to now? Still thinking in terms of front-end distortion of the response curve, my thoughts turned to the SAW (surface acoustic wave) filter. It would not be the first time I had encountered a SAW filter which upset the response curve, though the effect is usually less subtle than this. Still, there is always a first time. Again it wasn't a difficult point to prove. I had a spare filter on hand and it took only a few moments to fit it. And that was another victory for the Edison philosophy; I now knew of two things that weren't wrong. More importantly, it now seemed obvious that the fault was not at the front end or in ICl, but somewhere from pin 12 of this IC onwards. I made some attempt to observe the 5.5MHz level at pin 12, in order to compare it with that at pin 14 of IC2, but results were inconclusive. There was some loss between the two but this could have been normal, considering that there were several components in the signal path. On the other hand, one of these could be faulty. Fortunately, most were easy enough to test and a lk0 resistor, a 39pF capacitor and an 18µH choke all proved to be OK. That left only the 5.5MHz filter, CF2. This presented a problem, in that I had no spare on hand to substitute. I could have ordered one but that would mean a few days' delay, and I was anxious to get on with the job. This prompted a rather wild idea. There was another filter, CF3, in this part of the circuit (pins 9 and 10) and by all that I could determine the two were identical. What would happen if I swapped them over? Granted, I could hardly expect it to solve the problem. If CF2 was faulty I would be simply shifting the fault from one place to another. But I reasoned that it would at least change the symptoms and help confirm whether or not CF2 was faulty. It was a simple operation and in a few minutes I was ready for the big test. But I was hardly ready for the result. The set came on with a perfect picture as before but also with full sound; not a thing wrong with it. But what did it mean? Frankly, I wasn't sure. The most likely possibility seemed to be that (a) CF2 was faulty and (b) the filter in the CF3 position was more of a technical nicety than a necessity, such that a faulty filter in this position wasn't all that serious. But even as I formed the theory I had AUGUST 1988 29 SERVICEMAN'S LOG doubts. I couldn't shake off the feeling that it was just too glib an explanation. Dead silence I left the set running while I pondered over all this, and tried to decide whether I should order up a new filter anyway. This went on for about half an hour, while I pottered around tidying up the bench and attending to routine matters, then suddenly there was dead silence; the fault was back just as it was before. So what did this mean? In one sense I was almost relieved. It meant that the rather nebulous and unsatisfactory situation I had been trying to resolve was a furphy. There was now a chance that the fault could be nailed more positively, and with less chance of a rebound. But I still had to nail it; and that meant starting all over again. Considering what had already been done, I felt that about all that was left was a more or less brute force approach; to check every component around IC2, for I was convinc- ed that it was in this area that the trouble lay. In fact, there weren't all that many components involved, so it wasn't such a big deal. The few resistors were easily checked, in situ, and all were within specs. Then there were the capacitors. Prime suspects were three low-value electrolytics; C23, C24 and C27. These were lifted at one end and measured for capacitance and leakage but again, all appeared well. That left only a few ceramic types and statistically, these seemed unlikely suspects; ceramic capacitors in Japanese sets are extremely reliable. I started by removing each capacitor and checking it on the capacitance meter. But then, since the fault was obviously inter- r SPURIOUS IY\A&NE-,l'SIV\ ~ SHAD0WMA59 30 SILICON CHIP · mittent, I decided to replace each one anyway, regardless of how it tested, just to make sure. This achieved nothing initially, the set remaining dead as each one was replaced. Finally, there was only one left - C30, a .OlµF from pin 13 to chassis. It tested OK along with all the rest but when I fitted a new one in this position, the sound came forth at full voloume. Had I really found it? I re-fitted the original capacitor and again I had full sound, so I simply let the set run. This time I was lucky. After about 15 minutes the set went dead again. I had hoped for such situation and was ready for it. I bridged C30 with the other .OlµF whereupon the sound came good. More importantly, when I took it away the sound vanished. So that was it. I don't think there is anything more satisfying than pinning down a fault in circumstances like this. If any more proof was needed it emerged when I pulled the capacitor out and put it on the checker again; this time it showed zero capacitance. Which was the end of the story from a practical point of view; the set went back to the customer and a recent check confirmed that it had not missed a beat since. But a couple of questions remained unanswered. For one thing, I'm not clear as to the role of C30, or why it is so critical, except that it is associated with the limiter circuit. Which only emphasises how difficult it is to keep pace with all the circuit design theory these days. There is also the question as to why the set failed in the first place. Was it really the result of the lightning strike, or was the timing purely coincidental? We will never know but I'm inclined to support the lightning strike theory, with the rider that the capacitor was probably a bit dodgy in the first place. Lightning strikes I suppose this raises the old query as to just why lightning strikes behave the way they do. Why do they destroy one component in the middle of a circuit, often far removed from the antenna and front-end circuitry, while leaving the rest of the equipment intact? While there is no simple answer to this question, we do know a lot more about the effects of lightning strikes than we used to. There are really two major mechanisms by which lightning causes damage. The first is the obvious one where the lightning actually strikes some object, such as an antenna, and causes quite catastrophic damage, often melting the antenna elements and associated cables, coils and other components. The second effect is more subtle and is due to the intense magnetic field created by the massive current flow which accompanies such a strike. This magnetic field can induce damaging currents in electronic components, solid state devices being particularly susceptible. f was actually reminded of this phenomenon, and just how intense the magnetic fields can be, by another case which came up shortly after the aforementioned lightning strike. The customer lives about TETIA TV TIPS Philips CA826 (Toshiba chassis) Symptom: Raster narrowed unevenly but more so at top of screen. Picture hiccups and set occasionally cuts out. 11 2V rail down to only 90 volts. Cure: 0801 (2SC1195) open circuit between base and emitter. This transistor is the power series regulator, in parallel with 25W resistors R81 0/R811 . When it fails, the resistors will pass sufficient current to keep the set going, though obviously not very well. 50 metres from the motel and he called me a couple of days after the storm with a complaint about his AWA Mitsubishi TV set. As he described it, the colour had "gone funny". It was a large set (63cm) so I made it a house call. And when the owner ushered me into the lounge room where the set was running, I needed only one glance to know what was wrong. It was one of the worst cases of purity error I had seen for a long time. Turning the colour off left the screen displaying all the colours of the rainbow in a psychedelic pattern. But before I had time to ask the obvious question the owner volunteered the information that this fault had appeared immediately after the lightning strike. Since several days had passed since the strike, and the set had been in constant use, I was a little surprised that the normal degaussing system had not corrected the condition, and even considered the possibility that this had been knocked out by the strike. But a quick check confirmed that it was still intact, meaning that the spurious magnetism in the shadowmask was far too strong for it to correct. Fortunately, a couple of passes with the old faithful degaussing wand wiped out this latest example of modern art, and made the set suitable for the more mundane art form for which it had been designed. But the real point of the story is to emphasise the strength of the magnetic field which must have ac- companied the strike, remembering that there was a good 50 metres between the point of strike and this TV set. So don't be surprised at anything that happens when lightning strikes. One day at a time And here's another contribution from my colleague, J.L., in Tasmania. He calls it "One Day at a Time" and, as this implies, it describes a typical day in the life of a serviceman - or as near to typical as one can get. This is how he tells it. Began the day by collecting an old Akai video recorder from a customer's home, then made some money disappear into my bank account. I hate those state and federal bank taxes. Sales and income tax I have learned to live with - well, more less - but not FID, SDT and BAD! Then it was across the river and up a steep hill to a house with the best view in Australia. I was hoping for a lengthy repair so I could spend some time admiring the scene. Unfortunately, I had only to put a new fuse in an old Rank colour TV set. Ten minutes and I was on my way, back across the river to the workshop. On the bench was a G.E. colour TV set awaiting attention. It was a fairly common problem - R731 burnt up. This is a fusible resistor in the 120V line to the horizontal driver stage. A new resistor lasted 10 minutes, so I assumed it was probably a protection circuit fault. This protection circuit, TR56 and its drivers TR57 and TR58, cause more trouble than enough by going over-sensitive. They tend to trip for no reason. The easy solution is to remove TR56, which is the crowbar switch. This invariably cures the problem and R731 never fails again. Nor does anything else that I have ever encountered. But first it is necessary to check that the 120V rail and the EHT are not running high. They never are but they must be checked before it is safe to remove the protection. (Some Rank Arena sets also have one of these "protector" circuits that often fail for no reason at all. AUGUST 1988 31 SERVICEMAN'S LOG Whether they are ever called on to actually protect something is a moot point)! The next job was an old National colour TV set and a new National VCR, both from the same customer. The TV set was supposed to spit and splutter whenever a commercial came on the air. It was reported to be OK on ordinary program material, and ABC and SBS programs. All of which only goes to demonstrate its good taste. I know a lot of viewers who behave in much the same way - including spitting and spluttering at some of the tasteless commercials they try to bash our ears with. The VCR was brand new and had never been tuned to the local channels. Nor could the owner find any combination of buttons that would allow the machine to play a prerecorded tape. I have often complained about incomprehensible service manuals and now I will add user manuals. This National manual was written in tolerable English but omitted 50% of the info needed to enable the user to set up the tuner and timer. I was able to get things working because I have done it before but a non-technical owner might have fiddled for years and got nowhere. The number of buttons and the permutations of them is staggering. (In recent months I have had dozens of calls from people prepared to pay me to come to their homes to teach them how to use their new "'what's it". Often I have nearly as much trouble as they do, sorting out the user manual). In this case the TV set was badly off tune on all channels and this was easily fixed. The VCR was not so easy to tune but eventually responded to some gentle prodding and twiddling. After this·, the picture was perfect on all channels and also off tape. I let the set run all day but it showed no signs of any other fault, so the owner can collect it tomorrow. Thorn 3500 The next set in line was an old Thorn 3500 series. It had no blue in the picture, due to total lack of voltage on G2 in the blue gun. This can be caused by an open circuit or high resistance feed resistor, a faulty adjustment pot, or a faulty beam switch. The last is the least common, but also the hardest to find as the switch tests perfect in or out of circuit. In this set it was switch trouble. It seems that the switch develops a leakage path at the high voltages at which it normally operates but tests OK at the modest voltages normally used for measuring. Replacement switches are now unobtainable and, as the switch is only needed for occasional purity adjustments, I prefer to remove it entirely and fit a jumper in its place. Philips K11 The next problem concerned a Philips Kl 1 with intermittent pincushion distortion. The problem came and went at odd times; from seconds to minutes to nearly an hour. When the fault was present no amount of thumping or bumping would alter it, so there seemed to be little chance that it was a dry joint. I tried freezing the E-W correction transistor, TS421, when the problem showed and again when it vanished, but results were inconclusive. The spray did seem to have some effect on what little .°c,~ "o/. "f' ,,. ~ o"• C) --f" I' tt q p ~~": : r..: . .. -y~~~~-·:·-...__, :,.,.. , ___,, - -- -- . . ----- ' · ~ -------~-~-~ffw: -· So l>Orv'-r a£ SUR?R\SEJ:> A"T' AN"<-r\-\\tvG ~ ~ . ~-,, 'THAT HA'PP&NS WHE.N l-\GHTtJIN6 ST'R\~~4S. 32 SILICON CHIP ------------ ' I wasted some time on the Akai VCR because it was unfamiliar gear. The time I lost on this one will be made up the next time I see one of these machines - it will go straight to my colleague and no messing about. Bread and dripping --o~ L t(f._ ·--.. 1\-l&: TV S£.T WAS SOPf>OS~D iO SPI, IN 'DISGUST WHENE.VE.R A COMMERCIAL.CAME. -ro A\R ..... behaviour pattern there was, so I changed the transistor just to see what would happen. In a sense nothing happened, because there was no distortion when I switched back on, and there has been no sign of it since. After several hours the set was still working perfectly, so I felt it was safe to consider the fault cured. So, another one down and one to go. Akai video recorder The Akai video recorder mentioned at the beginning was an old toploading machine. All I had been told was that it didn't work. It was left to me to find out in what way it didn't work. I fired it up and was rewarded with all the expected lights on the front panel. I pressed the eject lever and received an unenthusiastic response from the cassette carrier. It came up about one centimetre and then stopped. It took some gentle pressure to release it from whatever was holding it. I put in my test cassette and closed the machine, whereupon the drum motor started and nothing would stop it. Normally the drum does not start until the play lever is pressed, so this looked like some sort of clue. Unfortunately, this was of little value because the cassette carrier was locked down (or jammed) and I could find no way to get the cover off to release it. Without a manual and little detailed knowledge of this particular model, I was out of my depth. It will go into a specialist colleague in the morning. By this time it was too late to start another job so I spent what was left of the day doing the books, trying to make the income bigger than the outgo. This has been an easy day; Apart from the VCR, each job was done fairly quickly because past experience has taught me where to look for these faults. Well, that's J.L.'s story of a typical day, and it emphasises a point that I have made in these notes many times; elusive intermittent faults and similar nasties may make interesting reading, and even boost one's ego - at least in retrospect - but they don't put the bread and dripping on the table (Oh dear, how sad, never mind. Ed.). That comes from the routine, day to day faults , which one takes in one's stride on the basis of previous experience. And there is another point in J.L.'s story worthy of comment; his complaint about the inadequacy of user manuals. I couldn't agree more. At one time customers were advised: "If in doubt, read the instructions." Now, the more appropriate advice would be: "Find someone to show you how to operate it, then read the instructions to see if they make sense". That may sound cynical, but it's true. It's not that the manuals are inaccurate but simply that they are inadequate. They are apparently usually written by people who are very familiar with the device and its workings - people who simply cannot understand the confusion it is likely to cause the consumer the first time he encounters it. I have no doubt that their defence - if ever one should be fortunate enough to confront them concerning any inadequately explained point - would be, "Oh everyone knows that". Carried to its logical conclusion, that means that we don't need a user manual at all; which is close to what is happening, in effect. So it is not until the user has found someone who has already been through the exercise the hard way, and is able to instruct him, that the manual begins to make sense. Which makes it all a bit pointless, really. See you next month. 1§::l AUGUST 1988 33 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. 82k 40106 89 IC1a 14 K IC2 4017 EN RESET 13 5 1 5..,_-f-l~---4 8 Telephone ring simulator Designed for use in a child's toy intercom system, this telephone ring simulator uses only a few low cost parts. It provides the typical 0.4 second on, 0.2 second off, 0.4 second on, 1.0 second off ring sequence of a standard Telecom phone. ICla is a Schmitt trigger oscillator operating at about 5Hz. It drives the clock input of IC2, which is a divide-by-10 counter with 10 decoded outputs. Each output goes DC stereo volume. control Using the National Semiconductor LM13600 dual transconductance amplifier, a close tracking stereo DC volume control can be made at low cost and using few parts. The transconductance amplifiers provide a high degree of linearity with good signal-to-noise performance. The amount of current into the bias inputs at pins 1 and 16 sets the gain for both channels. The output of each transconductance amplifier is buffered with internal Darlington transistors to procontinued on page 95 34 SILICON CHIP 2x1N914 high in turn from the '0' output to the '9' output. The '5 ', '6' , '8' and '9' outputs are used to pull the pin 3 input of ICl b high when any of these outputs go high. The unused '0' to '4' outputs provide the one second gap in the ring sequence. The '5' and 6' outputs provide the 0.4 second ring, the unused '7' output, the 0.2 second gap and finally the '8' and '9' outputs, the final 0.4 second ring. Dl to D4 form an OR gate which is buffered by IClb and IClc. D5 and D6 form another OR gate which enables the "ring" oscillator. When the outputs of IClc and IClf are high, D5 and D6 are both reverse-biased and so ICld can oscillate. When either IClc or IClf go low, D5 or D6 conducts and stops ICld from oscillating. This allows IC2 to provide the ring cycle, while IClf modulates the ring oscillator for a realistic sound. The output of ICld is buffered by ICle which then drives Ql via a 0. lµF capacitor C4. Ql drives the loudspeaker via a current-limiting resistor. $25 to R. J. Martindale, Mill Park, Vic. LM13600 ----------------+15V 0.22 .---,t---111--0 V01 0.22 -----1---0vo2 -15V The circuit for this DC stereo volume control is based on a single IC. +5V o.1I 1k .,. 16 24 15 17 16 14 1315' 7 EN lO TEil OA 14 23 A 08 13 22 B 12 14 11 1 QC 1 21 C OD 11 20 D 10 11 10 9 89 A 4 IC2 74161/163 5 60 1 CLR 9 LOAD1 1489 IC1a IC4 74154 2 CK .,. 78 6 7 56 8 -:- 4 5 +5V 16 PEN lD TEN 3A 48 5 C 741~ft163 34 0.1 23 1.,. 1 2 01 18 G1 19 G2 12 -:- 6D 1 CLR IC1b INPUT B 9 DAD 2 CK The circuit uses four ICs which drive 16 LEDs arranged in a circle for the rotating display. Digital Lissajous frequency comparator At first glance this circuit looks similar to the frequency comparator on page 39 of the March 1988 issue but there is one important difference; this circuit is capable of displaying frequency ratios other than 1:1. The March 1988 design only displays a frequency ratio of one when the LEDs are stationary. The input signals are first buffered and squared-up by a 1489 quad line receiver. This IC is normally only used in RS232C interfaces but it also makes a good general purpose signal conditioner for TTL circuitry. The Schmitt trigger input has typical switching thresholds of + 1V and + 1.25V, a 4k0 input impedance, and can handle signals up to ± 30V maximum.. (Note: the 1489A has wider switching thresholds, typically + 0.8V and + 1.95V). The signal from input A clocks a 4-bit synchronous counter which has its output decoded by IC4 to drive a circle of 16 LEDs. If the decoder is enabled continuously (by grounding its strobe inputs G1 and G2) and a slow clock signal fed into input A, the display would show one bright dot revolving clockwise at 1/16 of the clock frequency. But the counter is not enabled all of the time. IC3 is another 4-bit counter and its carry output enables the counter for one clock period out of 16 from input B. This strobes the rotating display, and if frequencies A and B are equal, the display will be stationary. If input A is slightly faster, the dot will drift clockwise and vice versa. Now suppose input Bis about five times the frequency of input A. The display will now be turned on five times per revolution, and a rotating five-dot star pattern will be displayed. On the other hand, if input B is one-fifth the frequency, the display will be on for five clock periods of A, and so a contiguous group of five dots will be displayed. (Actually, 6 dots will be lit most of the time, with the brightness of the first and last dots effectively adding up to one full dot). Other ratios such as 3:2 and 4:5 also provide recognisable patterns. The circuit does have one disadvantage though. For frequencies less than a few hundred Hertz the pulsation of the display becomes annoying, chiefly because of the initial division by 16 of the counters. The circuit in the March 1988 issue is better for comparing low frequency signals, since it will work right down to DC. Wiring hint: if you're wiring this circuit up on perf board, wire up the LED anodes with a circle of tinned copper wire on the top side of the board. Then you can run the cathode connections straight across from the decoder pins on the underside. The starting point and direction are quite arbitrary, as long as the LEDs are in sequence. $30 to Steve Payor, Kogarah Bay, NSW. AUGUST 1988 35 The best value, range and advice on communications equipment - we're as close as the phone! CB Antenna Accessories Lightweight ~ Spring Designed to suit standard loaded 1/4 wave mobile whiP,S. Gives the sort of flexibility that's required getting in and out of today's low car parks. Gal D-4500 sgss Quick Disconnect Allows quick and easy removal of your antenna from its mount! Just press and twist. Save the antenna being stolen! ' I'"~~· 5995 Folding Snap Down Allows CB and similar tennas to be folded down in car park parks, garages, etc. Simply lift and fold over. Male and female 5/16" threads. Electrically becomes part of antenna (SWR antenna after fitting). Cat D-4506 sgss Folding Angle Adjuster · · r to the folding nap down daptor only his one allows adjust and antenna at The Big Daddy Bearcal BOOXLT This has to be THE benchtop scanner of all time! Program 40 frequencies from virtually infinite combinations. 12- band coverage includes Low, High, UHF and UHF - 'T', air band, 2/6/10 metre and 70cm, mobile, military and 800MHz. With automatic or manual step search, track tuning, weather search, two channel banks...the list goes on. Superbly finished, it's a dream to use! Cat D-2811 ... !tf!99 U Performance Is Tops! The IIBarcat Hand Held Scanner. The Bearcat 1OOXL is hard to beat when you consider the power, performance, reliability, versatility ... it doesn't really matter what you consider, it's just outstanding value! 16 channels, 9 band coverage, auto/manual search, lockout, track tuning. Comes with 6 NiCads, protective case, belt clip and covers 66-88MHz, 118-135, 136-174MHz and 406-512MHz. What more can we say? Cat D-2813 s399 Folded J 2M Vertical It's amazing how times change. Once, just about every amateur would tackle the problem of making his own 'Slim Jim' - these days it's just not worth the effort. They're so inexpensive! Covers full 2m band with VSWR <1.2:1, power rating 500W. Cat D-4211 VHF/UHF Universal Antenna Kit: Whip, coax and bass • Quality stainless steel 520mm whip, complete with cutting chart, suitable for mid VHF band (about 120MHz) up. • 5/6", 26TPI coaxially fed antenna base (intended for UHF work - even better at VHF!) which fits gutter gripper base perfectly. • 2 metres UHF quality RG58C/U coaxial cable. • PL-259 UHF converter (as used on most transceivers). All this makes the perfect solution to your mobile antenna problems, whether they're amateur, UHF CB or commercial radio. Complete kit. Cat D-4025 Was $29.95 200/oOFF! Now s24es UHF Base Station Now's the time to set up your antenna base and save yourself $10! Colinear base station antenna with omnidirectional characteristics. Ground independent construction, terminated in S0-239 socket. 2.4 metres high. All it needs is a saddle ~a;p to mount it to your mast. Cat D-4011 Reduced to s3995 • N8W • Albury 21 8399 • lankltown Square 707 4888 • Blacktown 671 7722 • Bondi Junction 387 1444 • Brookvalll (W1ntngahM1II) 930-141 • CompboHtown/046)272199• Cha-oodCh-4111955• Chullo,16428922• QoroHlll439 5311 • Qoatord260235• Hornaby4776633• Llverpoo1600 9888• Maltland33 7866• Mlr■ nda5252722• Newcntle61 1896 • North Rydo 883855 • Porromotta 889 2188 • Pennlll/047)32 3400• Rlllwoy 8:l::1,.2113777• Sydney City 267 ~~1.:11T~:=~6c~~ • :8~=,!~=..:,A~~~~t~n:~:i~;}: •=~i;:=~,,:::; 889 2055. FrM!uton 78311 «. ONtong 43 88/U. Mllboumo City 326 6088. Rlctwnond 428 1614. Ringwood 879 5338 • 8prtngYllo 547 0522 •OLD• ■ rtobono City 229 9377 • ■ wondo 3916233 • Colma 311515 • C""'-'do 359 8255 • Aedb1nk 288 5599 • Aockhlmpton 27 9644 • Southport 32 9863 • Toowoomb1 38 4300 • Townsvlle 72 5722 • Underwood 341 0844 • 8A • Adolold• City 232 1200 • - - y 347 1900 • St. Morya 277 8977 • Ellzobolll 255 8099 • Enflold2608088• WA• CM!nlngton4518686• Fromontto3359733• North Pwlll32869.f4• PwlllClt,4813281 •TAB • Hobart 31 0800 •NT• Stuart Plrtl 81 19n ORDER BY PHONE TOLL FREE (008) 22 6610 fOR DSXpress 24 HOUR DESPATCH YOU'LL READ THE BOOK ... AND GET THE PICTURE! Quick! Nicad Barga!n is Barlains Trannies Electronic Laser UHF/VHF Log Band V UHF Wh1 le They ~h~ Projects for Technology Periodic Last Photographers ~~~y~;~1 ~~:r~~s":~~ ~~~~ =~~ ~~~~!~~~~~t ~~~~O Normally $7 .95 ~ c,,al I'~•• fl] ';,~•••... $1995 · ' THIQ~es V_- _ _ s3195 ·/ Learning 95 Get into brainfood at your nearest Dic:k Smith store: there"s books for every aspect of hobby elec:tronic:sl 1 1·. Dic:k Smith Elec:tronic:s the one place for all yourTV reception needs - from the antenna to the TV plug and everything in between, • Combines two great hobbies m 243 pages of great ideas to make photography easier and better.Cat B-1740 .;--.,_ R.1.P1J c 11 :.c ~ Bugging and ·its Prevent·ion _ ~ Magazme-style book ~~~~~~ w~~hd1~~0 on 9 misunderstood This one w111 tell you what you need to knowl 8 1861 Cat · bulld for fun Good reference bOok , too Cat B-3008 , job (probably better!) r'"' \ S139 ,f Don't forget your binder! Band IV and V amateur licence_ or Cat B-4002 -1-f!: ••,, I~ 11'_ • etc. Now work out what s3995 . · True 9V (beware of other "216" size which are often 7 .2V!) Great for strobes and other lighting effects. 5W maximum input, needs around 200-400V DC with 4kV trigger Woops! We ordered too many so you save. Standard 40 channel coded rotary switch, as used in CB's made by Cybernet (eg Midland, OS, GE & many others). Great tor experimentation. Cat S-6300 Was $3.25 Now $2&5 4kV Trigger Tranny $150 Designed for above tube. 300V input pulse, 4kV out. Cat M-0104 Blacklight Globe Standard 240V BC type globe which emits mostly UV light: great for parties, displays, & experiments. Cat S-3900 $595 NowS14 LES Globes Digital Save $50 Sensational value. "4000" count means twice the resolution of standard 2000 count dlgitats. And this one has a bargraph display TOO. Up to 40 meg resistance, 10A AC & DC, & 10 megs input Impedance on DC AND AC - it's a superb meter. And look at the price! Cat 0-1666 WAS$249N0W Bargraph Di.9ital: ! ! ~ ~ ! 1 ! e ~ 7.2V Racing Packs Suit Tamiya dipole (300 ohm) antennas to 75 ohms impedance so you can ru~ coax instead of twrnlead (less ghosting ). Cat L-4465 11 95 CD __ $ .. - socIm ..... Cat__;;_ W-2082 // 75 OHM F1·11·1ng ... li~~~i~:~I:::::E~s Both: s1 ao Somewhere To Put It All: Check out these parts drawers: they're great for resistors., c:apac:ltors, semis, fish hooks (eh?) etc etc. 2 Drawer Modular They're stackable: just keep on adding as many modules as you require. And if you add them this month, you'll save! 2 drawers Single Tilt Drawer Similar to leh, but this has one drawer on an axle which allows tilting forward. Cat H-2581 per u n i t H-2580 .~Ca . t SAME SAVING! . 54,15 Was "'-~\'~\'j $4.75 c;::::::-:;;;· WAS$99 NOW ONLYs79 L) ~ Now 95 95 NOW s3 ea s3 ea And The Big Guns (With Big Savings!): Hard leather-like case holds meter, leads etc. Q5 Cat Q-1667 A big 290X220 X 45mm case with internal High density cradle protects divider containing multiple sections. meter from shocks and abuse. Was $47 .95 Cat H-2596 This month S29 95 s2495 Now available at 60 stores: 2 4 ;.~~~; ~~~~'!J!!=,:~rJ::J~ ~,~:~~ ~~ :~~~~~~~ 1~1:r~ ;h~ri::! ~~~c8~~~ !BJ;:e ~1;1 ~;f5ic;;~~ 4 & most other radio control cars, etc. With socket. Cat S-3326 495 Were$59.95 You need low loss cable, especially at UHF. Our air dielectric 75 ohm cable Is what you need! at;:w prices: C~ $20 OFF! NOW SS95 ~ Mini 9 Voller When space is tight, this one usually ms. 9 volts AC centretapped at 150mA - great for battery replacement supplies. Cat M-2840 Normally $5.95 THIS MONTH s495 ~ - ~~ And A Bench Supply: So many " things" need 13.8 volts at an amp or so. CB's & small amateur gear, car audio & other car products ... the Super Panther 13.8V regulated DC Supply gives 1.5A continuous, up to 2A peak.Ideal for the service bench too. Cat M-9545 S(;995 ....,._-,...._ Coax Cable 0 s199 ,L.IM~;:ggK Carry Case s3 4 Bench Protection Cat 0-1668 ~~~TIV~r~~~ave only :~=~ Be quick for this one; bargraph digital combines all the "best" features of analog meters in a digital format. Hurry - if you miss out on this one you·11 kick yourself! Cat 0-1777 Were $6.50 one antenna socket - and you want to watch UHF & VHF from two antennas - this'll tixit! Low loss. Cat L-4470 Prefer ribbon? We have that too: quality 300 ohm twin 50c ea or 10 for $2.00 fast charging. Cat S-3324 300 to 75 ohm 300 Ohm Ribbon Here's value. Mixed 6 and 12 volt LES globes with big savings for bulk buyers. Normally 50c each - but buy 10 and you can have them for two dollars!! Grab some tor the junk box - at this price you can't miss! Cat S-3843 Sub "C" High capacity cells as used in racing packs, Can stand UHF/VHF $ Was $19.95 95 BARGAIN CORNER 4000 Count \-~ :;;95 These are just a tiny selection from our great range. Call in and choose what you need! 40 Channel CB Switch: $5 OFF Was $11.95 NOW $9.95 G Hard-To- et- Types , lioo•• s 119 ~ Accessories, too ... Xenon Flashtube $3.95 Was $4. 75 NOW " D" Size (1200mAh)Cat S-3353 g:~nL~~o~:tro channels. ~· Don't miss these specials! pulse. Cat S-3882 If you don't have UHF, this is $3.75 NOW "AA" Size (500mAh) Cat S-3351 gg!:r:~~i~;:~1~ ~:~~~ts, ~,,,,,, ~ VHF Only Ghostbuster "AAA" Size (180mAh) Cat S- 3350 Was $4.95 for you! Superb anti-ghosting antenna, designed 1or maximum gold anodised finish for long long Ufe.CatL-4084 j / s7 95 .-- those mags are! Cat B-4045 1 amp. You won't beat that - or the price! Cat M-2155 What a performer! Covers all UHF channels, so it you've got tt pays to keep them m tip-top 9 be a great -reference ..., s59 •• \ \ ' " " \ \ \ \ \ • · .O , 1 _ ,• EA, SC, AEM, ETI, AA. ARA, YC, APC, CA , etc ~ r\ L-405 i ~ ~ ~f_ Radm Theory Handbook for With mags costing $4 and more, Amateurs..~~:~:; ~~fd~~~:a~ o~zln© New AUSSIE book which will get you your ~ ■ You'll be better off with rechargeable Nicads! And you'll be even better off this month while we clear excess stock. Brand .new, prime spec Toshiba NiCads and throwaway prices! , ._,.,. g~;~_;:: •a" s3 antennas when one'II do the . . 1495 ' : .- • prevention. At this low st Wide bandwidth, top performing antenna, even 1or fringe areas. Why put up two Electromcs Theory 2s great pro1ects to v!~!t!!~!ng from 1 to 15 volts AC is yours at A great performer for band V stations (which include most '::.1::J;~ 0235 • HomabJ 4178833 • Llverpool 600 9888 • Maitland 33 7866 • Miranda 525 2722 • Newc■ 1tle 611696 • North Ayde88 3855 •Parramatta 689 2188 •Penrith (047)32 3400 •Railway Square 211 3777 •Sydney City 267 9111 •Tamworth 66 1711 • Wollongong 28 3800 • ACT• Fythwlck 80 4944 • VIC • Ballarat 31 5433 • Bendigo 43 0388 • Box Hiil 890 0699 • Coburg 383 4455 • Dandenonu 794 9377• Eat Brighton 592 2366 • EHendon 379 7444 • Footscray689 2055 • Franklton 783 9144 • Geelong 43 8804 • Melbourne City 326 6088 • Richmond 4281614 • Ringwood 879 5338 • 8pringvale 547 0522 •OLD• BNb ■ne City 229 9377 • Buranda 391 6233 • Calm• 311 515 • Chermaide 359 6255 • Redbank 288 5599 • Rockh■ mpton 27 9644 • Southport 32 9863• Toowoomba384300• Townavllle 72 5722• Underwoocf 3410844 •SA• Adelaide City 232 1200• 8evertey3471900 • SL Marya 277 8977• Elizabeth 255 6099 • Enfield 260 6088 •WA• Cannington 451 8666 • Fremantte 335 9733 • North Perth 328 _6944 • Perth City 481 3261 •TAB• Hobart 31 0800 •NT• Stuart Park 811977 Nows5495 Gell Cells, Too! OK, so they're not Nicads. But they're non-spill rechargeables so they're just as good (better in many applications!) As used in burglar alarms, back up supplies, models, robots, etc. 12V 1.2Ah Cat S-3315 Save $1 .00 $35.95 $34.95 NOW 12V 1.9Ah Cat S-3316 Save $2.00 $37.95 NOW $35.95 12V 2.6Ah Cat S-3320 Save $3.00 $38.95 $35.95 NOW 12V 6.5Ah Cat S-3322 Save $4.00 $55.95 NOW $51.95 NEED TO CHARGE NICADS? Here's the answer: our Nicad Charging Cabinet accepts up to 8 AAA, AA, C or D or 3 9V Nicads & charges them at their correct current. Simply plug it in to the 240V mains. ltsa Bewdy! Cat M-9505 It's Incredible! You 'll agree as soon as you wrap your fingers around this one: a mains voltage "sniffer" that doesn't need to contact the mains. ln fact, it works through insulation, even plasterboard walls! Talk about safe - every hobbyist, every technician, every electrician should own onet Strictly limited stock in first shipment. Cat Q-1530 ONLY s12 95 ~~ The Penultimate Cable Everyone knows Heliax is pretty much the ultimate 50 Ohm cable. Here's the penultimate: almost as good, but$$$$ less, especially when you're buying enough for a run. Belden 9913 cable is as thick as RG-8, but has only 2.6dB/ 100ft at 7 ~Y 400MHz] Now that's low! CatW-2097 Save 10% 11 you buy it by the , OOm roll!) ,. - MAJOR DICK SMITH ELECTRONICS AUTHORISED STOCKISTS: • NSW • _ , Sound Components, 724981 •Illa: Ballina Electronics, 867022•11Nnf: F.R.H. Electrical, 611861 •-111:Hobbies & Electronics, 88 4098 • tarttllDwl: Newtronics, 43 9600 • Ceffl ltnllr: C:Offs Harbour Electronics. 52 5684 • - . . , Deni Electronics, 81 3672 • _ , Cluis's Hi-FI, 8711 • 6rtffl: Miatronks, 62 4534 •_,Lyn Willing Electronics, 221821 • _ , Moree Electronics, 52 3458 • l'lrbs: Strad Mu~c Centre, 62 3366 • f'lt1 . _ . , Hall 33 ~m:~r:,~k;~.·L~i'i :~~';5==:~!5nr5!.i:~~;i~•~;1 ,"m~~--~~ -=r:b Elkin Electronics, 72 1785 • _ , , , Electro-Mart, 9t 8533 • _ , Splitec, 94 7349 • - , , Steveos Electronics, 511723 • ~fllllll; Keller Electronics. 21 4559 • JI Gl■Mtr: Hutchessons Communications c:entre, ~~~c:AHed~::;g~~fJe:3o;~~~=~l=~,~~:~~chs~~~[Jf!t'~=:~J~1~ & Hobb~s. 24 8322 Low-cost circuit gives +15V, -15V or -+15V Universal power supply There is more than one way to skin a cat they ·reckon, and the same applies to designing a power supply. This small board enables you to obtain + 15V, - 15V or ± 15V DC from a number of different transformer and rectifier combinations. By LEO SIMPSON It's a problem that has confronted us on a number of occasions over the years; many circuits require ± 15V DC rails or one or the other and, in each case, a suitable printed circuit board has to be designed. So we decided to· solve this problem for a number of different transformer combinations. One common situation is when you are powering a circuit from a 12VAC plugpack transformer but you want ± 15V rails, using 3-terminal regulators. Sounds difficult? Nope, piece of cake. Just use two half wave rectifiers to obtain the positive and negative rails and then follow with the regulators. Or maybe you have a more conventional situation with a 12VAC transformer such as the Ferguson PF2851 (or equivalent). To obtain ± 15V DC the circuit is the same. But if you have a 30VAC centretapped transformer such as the one from Altronics (Cat. No. M-2855), you then use a bridge rectifier, followed by the filter capacitors and 3-terminal regulators. Anyway, you get the general idea. We are presenting one PCB pattern and showing how to use it in four different ways, depending on what your requirements are and This version of the universal power supply board uses half-wave rectifiers and two 3-terminal regulators to give ± 15 rails (see Fig.1). Note that the LED indicator circuit was added after this photo was taken. 38 SILICON CHIP what transformer you are using. Actually, there are other options and we'll mention those later. The board measures 71 x 52mm (code 04106881) and was used for the first time in the Studio 200 Stereo Control Unit, part two of which was featured in the July issue. We are using it again in the AC Millivoltmeter described elsewhere in this issue. The circuit variations Fig.1 shows the first circuit situation presented above and could be used with 1 a 12VAC plugpack or with any chassis mounting transformer with an output voltage or 12 to 15 volts AC. You can regard the circuit in two ways. First, as two half-wave rectifiers, Dl and D2, . producing filtered but unregulated DC supply rails of ± 18-22V, depending on the transformer secondary voltage. The other way of regarding the circuit of Fig.1 is as a conventional half-wave voltage doubler circuit which has been "centre-tapped" at the junction of the two 1000µF capacitors. Either way, the result is the same. Because Dl and D2 function as half-wave rectifiers, the ripple voltage superimposed on the DC supplies will be 50Hz. This may or may not be a problem but, for a given current drain from the supplies, the ripple voltage will be slightly more than twice the 100Hz ripple obtained if the bridge rectifier circuit of Fig.2 is used. Fig.2 may be used with the 30V centre-tap M-2855 transformer supplied by Altronics or the 24V centre-tap model from Tandy (Cat. No 273-7013). Following the bridge rectifier diodes, the unregulated DC voltage will be again be ± 18-22V, depending on the transformer. The 3-terminal regulators to be used will normally be 7815 or LM340T-15 (or other variants) for supply rails board for op amp circuits POSmVE REGULATOR 01 A OUT PARTS LIST +V + 02 100 0.1 LED OV N 0.1 -V OUT NEGATIVE REGULATOR SINGLE WINDING HALF-WAVE RECTIAER DUAL POLARITY Fig.1: this dual polarity version uses a 12-15V transformer to drive half-wave rectifiers (D1 and D2) and two 3-terminal regulators. A ± 15V Supply (See Fig.1) 1 PCB, code 04106881, 71 x 52mm 1 2851 power transformer with 12.6V secondary 2 1 N4002 silicon diodes 1 7815 3-terminal regulator 1 7915 3-terminal regulator 2 1 000µF 25VW PC-mount electrolytic capacitors 2 1 00µF 25VW PC-moun_t electrolytic capacitors 2 0.1 µF metallised polyester capacitors (greencaps) 1 red LED 1 1.5k0 0.25W resistor +v 100 N + 0.1 LED ov .,. 0.1 1000 -V OUT NEGATIVE REGULATOR CENTRE TAPPED, FULL WAVE DUAL POLARITY Fig.2: in this circuit, a centre tapped transformer and bridge rectifier are used to drive the 3-terminal regulators. 01 :J IN POSmVE REGULATOR OUT +v GND + + 1000 100 Alternative ± 15V Supply (See Fig.2) 1 PCB, code 04 106881 , 71 x 52mm 1 M-2855 power transformer (Altronics) 4 1N4002 silicon diodes 1 7815 3-terminal regulator 1 7915 3-terminal regulator 2 1 000µF 25VW PC-mount electrolytic capacitors 2 100µF 25VW PC-mount electrolytic capacitors 2 0. 1µF metallised polyester capacitors (greencaps) 1 red LED 1 1.5k0 0.25W resistor 0.1 LED . ov POSmVE REGULATOR CENTRE TAPPED, FULL WAVE Fig.3: this single supply circuit uses D1 and D2 to provide full wave rectification from a centre-tapped transformer. the + 15V supply. For the negative rail, the equivalent types are 7915 or LM320T-15 (or other variants). The output side of the regulators have lOOµF and 0. lµF capacitors connected to ensure good transient response and stability. We also made provision for a LED (light emitting diode) power indicator fed via a resistor from the positive supply. "~oo, GND NEGATIVE REGULATOR ~~M IN Fig.5: here are the pinouts for the 3-terminal regulators and the LED. Single supply versions Fig.3 is a single supply version of the board using a 30V centre-tap (CT) or 24V CT transformer. Here, Ill and D2 provide full wave rectification and the resulting ripple is 100Hz. The unregulated DC voltage will be between + 18-22V. Fig.4 is a single supply circuit using a 12 or 15V transformer feeding a bridge rectifier. Again, the AUGUST 1988 39 can be 1.5k0 for + 12 or + 15V outputs, reduced to 6800 for 8V outputs and to 4700 for 5V outputs. The LED can be omitted, of course, in which case the limiting resistor can be left out too. A + 100 N 0.1 LED Other variants .,. SINGLE WINDING BRIDGE RECTIFIER Fig.4: single supply version using a 12-15V transformer and a bridge rectifier. The unregulated DC voltage will be between 18-22V. unregulated DC voltage will be between + 18-22V with ripple at instead of the 1000µF units shown on the circuits. 100Hz. Less than 15V supplies All the circuits presented here are good for several hundred milliamps but those which use full wave rectification will naturally be able to extract more current from the given transformer. If you want more current, a bigger transformer will be required and the regulator(s) will have to be fitted with heatsink(s). It is also a good idea to go for bigger filter capacitors; ie, 2200µF or 2500µF , Want less than 15V? No problem, you can install 12V regulators instead although for a given current drain their dissipation will be slightly higher. You can also go for 5V or 8V regulators if you wish although then it would be wise to reduce the transformer secondary voltage from 30V CT to 15V CT for Fig.2 and to around 6-7V for Fig.1. The LED current limiting resistor NEGATIVE REGULATOR -- TRANSFORMER SECONDARY ••• i ·i!:5 ....... ~ 02 C)~--V I =~ijr:: 100uF I TRANSFORMER SECONDARY You can also produce a single (positive) supply version of Fig.1 if you wish, by leaving out D2 , the negative 3-terminal regulator and the three associated capacitors. Or,. if you want a negative supply version, leave out Dl, the positive 3-terminal regulator and its three associated capacitors. Wiring them up We have shown four wirmg diagrams for the circuits depicted in Figs.1 to 4. There are only two particular wrinkles to watch out for when wiring up these boards. First, watch out for the polarity of diodes and capacitors. Second, note that the pinouts for the positive and negative regulators are not the same. ~ ...... ....... -__L ..... ....... I 01-04 er- J-rCD ••• ~ ~-+v o~ lE°lli 5 POSITIVE •••REGULATOR iEllia POSITIVE •••REGULATOR I ··~~,-· -'ov NEGATIVe REGULATOR I LEO Fig.6: parts layout diagram for the circuit shown in Fig, 1. The value of R depends on the supply rail (see text). -+ ........... TRANSFORMER SECONDARY I CT-- 01 1o~F =~ - lov :®--+v iEllia POSITIVE •• •REGULATOR Fig.7: this parts layout diagram corresponds to the circuit shown in Fig.2. Take care with component polarity. ...... lI ....... ....... - -g TRANSFORMER SECONDARY 01 -04 -~Ilov C) Cl- ~ ~-+v iEllia POSITIVE • • • REGULATOR 1 Fig.8: parts layout the single supply version shown in Fig.3. A centre-tapped transformer must be used. 40 SILICON CHIP Fig.9: parts layout for the circuit shown in Fig.4. Don't forget to install the wire link. 5¼" DISK STORAGE E_fficient ant~PaJt2~~~lotect your disks from bei ng damaged or lost! Features ... • 100 x 5 1/4 " disk capacity • Smoked plastic hinged lid • L<:>ckable (2 keys supplied) • High impact ABS plastic base. • Contemporary design only $15.95 C16020 ... ... .. .. ... .. ECONOMY TRANSFORMERS 1-9 2155 240V6-15V 1A Cat. M12155 S9.95 2156 240V 6-1 SV 2A Cat. M12 156 $14.95 2840 240V 9V CT Cat. M1 2840 $5.95 10+ $8.95 $13.95 $4.95 2851 240V 12-6V CT 150mA Cal . M12851 $5.95 $5.50 2860 240V 15V CT 250mA Cat. M12860 $5.95 $4.95 6672 240V 15-30V 1A tapped Cat . M16672 $14.95 $13.95 5 PIN DIN WALL PLATE • Fitted with 5 pin DI N socket • Anodised aluminium plate. • Includes mounting hardware. P10940 $9.95 RS232 WIRING •Male ~'?.~~JOR BOX • 25 Detachable plug on leads • 2 mini jumpers • Ideal for experimenting or temporary connections Cal. X15665 . .. Normally $49 .95 Only $44.95 r1e .'Ulla, . . . . Rod Irving Electronics MELBOURNE : 48 A "Beckett St. Phone (03) 663 6151 NORTHCOTE : 425 High St. Phone (03) 489 8866 CLAYTON : 56 Aenver Ad . Phone (03) 543 7877 SOUTH AUSTR ALIA : Electronic Discounters P/L, 305 Morphett St. ADELAIDE 2 1~s~~~i?i~ls re1ghtcosl5-1 !~/v~7;mte1stale dueto EXTERNAL SIREN & FLASHING LIGHT MAIL ORDER : Local Orders : (03) 543 7877 Interstate Orders : (008) 33 5757 All Inquiries : (03) 543 7877 CORRESPONDENCE : P.O. Box 620, CLA YTON 3168 Telex : AA 151938 Fa x : (03) 543 2648 Housed in a waterproof, m etal case, with tamper switch . SPECIFICATIONS , Siren: DC 12V. 450 mA k~~(d~~trr~ Dimensions: 135 x 150mm Flashing Light : - DC12V 100 flashes per minute Dimensions: 82 x 100mm ... ............ $89.50 METEX M-3650 MULTIMETER K&WMETAL Us~~1~M~~~J,~A~~a~es have hammertone finish and are both versatile and ecconomical. H 10478 125 x 40 x 65mm $ 5.95 H 10479 150 x 55 x 95mm $ 6.95 H1 0480100x92x130mm ... $ 8.95 H10481150x55x 100mm ... S 7.95 H1 0482200x80x130mm ... $ 9.95 H10485 255 x 92 x 155mm .. . $14.95 H1 0487255x 165x 155mm . $16.95 H 10489305x 105x200mm . $16.95 Save a fort~~G,~5Jx~ nslve throw away batteries with these quality Nicads and Rechargers! Size Oesc . 1-9 10+ 100+ AA 450 mA. H. $2.95 $2.75 $2.50 C D 1.2 A. H . 1.2 A. H. $9.95 $9.50 $8.95 $9.95 $9.50 $8.95 ~ SUPER DELUXE • c~~Tsr;,~.!,'l~oG~~~l¾. N. and up to 3 x 9V batteries at the same time . • Dual colour LED in first three compartments to designate 1-5V or9V. • 240V AC/50Hz. • Approval No. N10637 Cat.M23525 20A, 3½ digit f requency counter multimeter with capacitance meter and transistor tester. This spectacular, rugged and compact DMM has a bright yellow ~irr~~~~~g~ ~~~~~~,t~e2ici~~~~es d iode and transistor test. continuity (with buzzer). capacitance meter, up to 20 amp current measurement and comprehensive AC/DC voltage . cu rrent and resistance ranges. CHEC K THESE FEATURES .... • Push-button ON/OFF switch. • Audible continuity test • ~~i~~:~~~~7tci0,~t0ti{,6~0 • • • • • • • • • and RANGE selection Transistor test Diode test Quality probes 112-- High contrast LCD. Full overload protection 20 Amp Built in tilting bail Capacitance meter In struction manual 0 91550 . Normally $165 Special, only $129 I MAIL ORDER HOTLINE 008 335757 /TOLL FREEi /STRICTLY O RDERS O NLY) LOCAL ORDERS &INQUIRIES (03J 543 7877 POSTAGE RATES : S1 $9.99 S10 $25 S24.99 $49.99 $50 $99.99 S2.00 $3.00 $4.00 S5.00 $7 .50 $100 $199 $200 $499 $ 10.00 S500 plus .$12.50 The above postage rates are for basic postage only . Road Freight. bulk y and fragile items will be charged at different rates. All sates tax exempt orders and wholesale inquiries to : AITRONICS WHOLESALE, 56 Renver Rd. Clayton . Ph . (03) 543 2166 (3 lines) Errors and omissions excepted. Pnces and specilica!ions sub1ect to change :~a~~!a~~s~T;~~;~a~~en~~~~~~~s Machines · Apple 1s a registered lrademark ·oeno!es reg1s1e1 ed t1 admark s ot !heir respective owne, s Building the Discolight, Pt.2 Despite the circuit complexity, the Discolight is easy to build. This month, we give you the full construction and troubleshooting details. By GREG SWAIN Last month, we introduced our new Discolight light show and described its various features and the circuit operation. We're very proud of the circuit. It's an extremely versatile unit that should ser the standard for years to come. By now, you've probably taken a close look at the circuit and concluded that such a complicated looking beast must also be complicated to build and get going. But it's not. Many of the circuit elements are hidden inside multielement ICs and these, together with most of the other parts, are mounted on a single large printed circuit board (PCB). If you can follow the wiring 42 SILICON CHIP & JOHN CLARKE diagram shown in Fig.4, you should have little difficulty building this project. Even so, this is not a project that we recommend for beginners. As noted last month, part of the circuit is powered directly from the 240V AC mains supply and is therefore potentially hazardous (see warning panel). So take great care with the Discolight. If the circuit is not built and tested correctly, you could receive quite a nasty shock (or worse). Buying the parts By far the easiest way to collect the parts for this project is to buy the complete kit. At least three ma- jor retailers will be stocking kits and these will be supplied complete with pre-punched chassis and silkscreened front panel labels. If you do elect to go it alone, you should have little difficulty in buying the parts separately. The only parts that may initially cause problems are the isolated tab Triacs so be sure to check their availability before going in too deep. We expect that retailers will offer the Triacs separately once the initial demand for kits has been satisfied. Everything else, including the surface-mount mains sockets and the ICs, are standard items. The PCB will be available separately from the usual sources (see address panel on page 96). Starting construction It is a good idea to carefully inspect the copper side of the PCB before mounting any of the parts. While most boards will be quite OK, you might just be unlucky enough to get a board that has not been cleanly etched. In particular, look for small breaks in the copper tracks or very fine bridges between tracks. A little detective work at this stage can save a lot of trauma later on. Fig.4 shows where all the parts go on the PCB (code SC101688, 218 x 172mm). No particular order need be followed here although it's best to mount the small components first. These include the wire links, resistors, ICs and diodes. Be sure to use the correct part at each location and check that the ICs and diodes are correctly oriented before soldering the leads. It's quite easy to identify pin 1 of an IC. This pin is always adjacent to a small notch (or sometimes a dot) in one end of the plastic body (see Fig.4). You can use tinned copper wire for most of the wire links but note that the three links along the rear of the board must be run using insulated 240VAC cable. These three leads interconnect the A2 terminals of the Triacs (Q1-Q4) and are run in parallel with copper tracks on the PCB to ensure adequate current capacity. Once the low-profile parts have been installed, you can install PC stakes at the external wiring points shown numbered on the PCB (but not at location 7). PC stakes are also used to support the electret microphone and to terminate the transformer secondary leads. Do not use PC stakes to terminate the active (A) leads from the mains sockets - these leads must be soldered to the PCB. Similarly, the active lead from the mains fuse must be soldered to location 7 on the PCB. We'll say more about this later. The capacitors, trimpots and 3-terminal regulators can be installed next. Be careful with the orientation of the electrolytic capacitors and make sure that you don't confuse the two regulators. If you put the 7812 in where the 7912 should go (and vice versa), you'll have trouble for sure. The pin-outs for the regulators are shown on the circuit diagram (Fig.3 on page 60 of the July issue). The four toroid coils (11-14) in the interference suppression circuit are wound using 29 turns of 0.63mm enamelled copper wire. This close-up view shows how the insulated tab Triac Ql (at end of pen) is mounted on the PCB and bolted to the rear panel. Ql-Q3 are all mounted in similar fashion. Interference suppression coil L1 is in the foreground and is secured to the PCB by a loop of tinned copper wire (near bottom of photo). Space the windings evenly around the circumference of the toroid and clean and tin the ends of the leads before soldering them to the PCB. The toroid can then be anchored to the PCB using a U-shaped loop of 1mm tinned copper wire which is soldered to the two adjacent pads. Triac mounting You are now ready to mount the Triacs. When the PCB is finally installed in the case, the Triacs are bolted to the rear panel for heatsinking. This means that the Triac leads must be cranked so that the rear mounting surface of the Triac is vertical and parallel with the edge of the PCB (see photo). The PCB assembly can now completed by installing the power transformer. This should be oriented with the secondary winding leads towards the centre of the board. Terminate the secondary leads on the two adjacent PC stakes as shown. Mounting the PCB Before mounting the PCB in the case, it is first necessary to connect all the leads for the mains active wiring. There are five leads in all: four 80mm-long leads at the rear of the board which later connect to the mains sockets; and one 160mmlong lead at location 7 which goes to the fuse. All these leads must be run using 240VAC cable and must be soldered directly to the PCB. You can now position the PCB in the case and secure it to the inAUGUST 1988 43 Most of the parts are mounted on a single large printed circuit board. Lace up the low-voltage and 240V AC mains wiring using cable ties as shown and sleeve all mains connections to the switch and fuseholder with heatshrink tubing. tegral plastic standoffs using selftapping screws. When this has been done, the various items of hardware can be mounted oil the front and rear panels. If you've purchased a complete kit, the front and rear panels will probably be supplied pre-punched. For those starting from scratch, the front panel artwork can be used as a drilling guide while Fig.5 shows the rear panel drilling details. Note that it is necessary to bolt the Triacs to the rear panel before mounting the mains sockets. This is because two of the mounting screws are actually covered by the socket bodies. Smear the mating surfaces of the Triac tabs with heatsink compound before securing them to the rear panel. 44 SILICON CHIP The rear panel slides into the second set of slots in the case rather than into the rear-most slot. This brings the rear panel nearer to the edge of the PCB and also reduces the overall depth of the completed instrument. As seen on Fig.4, two earth lugs are bolted to the rear panel at top left. In most instances, it will be necessary to scrape away the anodising around the mounting hole to ensure proper electrical contact. Internal wiring Take great care with the mains wiring as your personal safety depends on it. Fig.4 shows the mains wiring details. The mains cord enters through a hole in the rear panel and should be fed into the case until it reaches the front panel. Remove about 120mm of the outer sheath, then clamp the cord to the rear panel using a cord-grip grommet. The mains wiring to the fuseholder, switch and rear-panel sockets can now be completed. Be sure to use 240VAC cable for all this wiring - brown for active, blue for neutral and green/yellow for the earth wiring. Fig.4 (right): mount all the parts on the PCB as shown on this diagram. You can use ribbon cable for all the low voltage wiring but be sure to use 240VAC cable for the wiring to the mains switch, fuseholder, transformer and to the mains outlet sockets. Note that the circuitry at the back of the chassis operates at mains potential. 0 0 0 A Q MAINS SOCKET Q _ CHANNEL 2 MAINS SOCKET E si~~E\ I'I \., E 0 CHANN~L 1 Q E 0 0 MAINS CORO NE TRAL (BLUE) ACTIVE (BROWN) POWER TRANSFORMER RATE VR6 SENSmVITY VR5 VrrlJJ ~;;- p/27 25 ~26 S1 ,(\; d;,s g '-!.:; ✓ ,,119 S3 AUGUST 1988 45 I ~ ::1. 41 41 - I . 15 ~4.51 . 41 , , 14.5t 41 ~ -$-8--$-8 $!I ~ I ♦B 1 ¥ ~ ♦A "' -¥ .., ,...._ I I• 53 I I• I 52 N I 52 22 I HOLES: A : TRIAC MOUNTING B: HPM CAT35 MAINS SOCKETS (HOLES FOR WIRING NOT SHOWN) C : EARTH LUG D : CORD GRIP GROMMET Fig.5: this drilling diagram for the rear panel shows the mounting holes for the mains sockets, the Triacs, the earth lugs and the cordgrip grommet. Not shown are the holes for the speaker socket panel and the holes for the Active, Neutral and Earth leads to the mains sockets. Sleeve all exposed connections to the fuse and switch with heatshrink tubing to prevent accidental contact. This step is absolutely imperative. If you leave them exposed, it is highly likely that you will get an electric shock later on. Although not shown on the prototype, all the leads to the rear panel sockets should pass through small rubber grommets. Don't leave these out - the insulation on the leads must be protected from the metal edge around each hole. Once the mains wiring has been completed, it must be laced together with cable ties as shown in the photographs. This will prevent any of the wires operating at mains potential from coming into contact with low voltage circuitry, if a wire happens to come adrift. The remainder of the wiring to the pots, miniature toggle switches, LEDs and speaker terminals can be run using rainbow cable or light duty hookup wire. This wiring must also be laced to prevent accidental contact with mains wiring if a wire breaks. Testing Before switching on, go over your wiring carefully and check for possible errors. Note that the circuitry on the output side of the MOC3021 optocouplers operates at mains potential, so don't go poking around here indiscriminately. These components include the 46 SILICON CHIP Triacs (Ql-Q4), coils Ll-14, the associated 6800 resistors and O.lµF capacitors, the MOC3021 optocouplers, and the mains sockets. The rest of the circuit operates at low voltage potential ( ± 12V) and is safe to work on provided the mains wiring to the switch and power transformer has been correctly installed and insulated. Once you are satisfied that the wiring is correct, apply power and check for + 12V at the output of the 7812 3-terminal regulator and - 12V at the output of the 7912 3-terminal regulator. If these Warning! Part of the circuitry in the Discolight is directly powered from the 240VAC mains so take care when working on this project. Those components on the PCB which operate at mains potential are as follows: the MOC3021 optocouplers, the Triacs (01 -04), coils L1-L4, the associated 6800 resistors and 0.1 µF capacitors, and the mains sockets. Before working on the lowvoltage circuitry, it is a good idea to disconnect the mains supply to these components. To do this, disconnect the Active lead (lead 7) at the fuseholder and the Neutral lead (lead 5) at the mains switch. voltages are incorrect, switch off immediately and check for power supply wiring errors. Assuming that the voltages are correct, you should also check the voltages on the supply pins of the ICs. Once again, switch off and check for wiring errors should anything be amiss here. If everything checks out OK, then the chances are your Discolight is working perfectly. Here's how to test the unit: e Set the BEAT switch to Oscillator, the DISPLAY switch to Unmodulated and the RATE control to mid-position. The four frontpanel LEDs should now operate according to the pattern selected by the PATTERN switch (ie, Chaser, Strobe or Alternate). • Set the PATTERN switch to Chaser mode and check that the DIRECTION switch provides Forward, Reverse and Automatic operation. Note that when the DIRECTION switch is set to Automatic, the display should automatically reverse direction every minute or so. • Set the BEAT switch to Music, the SOURCE switch to Microphone and the SENSITIVITY control to maximum. This now sets the pattern rate to the beat of the music and this can be simulated by tapping on the top of the case. e Set the DISPLAY switch to 4-Band Modulated. You should now ro .7 0 0 0 a0 0 /; 0 0 - I D~ - ~ o o :,: L!:2::= ~ ~~=:::::::.____.K.~ Fig.6: you can use this full-size pattern to etch your own printed circuit board. Alternatively, you can buy a ready made PCB as part of a kit or from one of the suppliers listed on page 96 of this issue. Carefully inspect the board for defects before installing any of the components. AUGUST 1988 47 r CHANNEL 4 CHANNEL 3 0 0 MICROPHONE MUSIC 4 BAND MODULATED 0 0 SPEAKER OSCILLATOR UNMODULATED J SOURCE BEAT DISPLAY DISCOLIGHT • POWER • RATE SENSITIVITY I\ I\ [MOD- LFUSE10A Fig.7: this full-size artwork can be used as a drilling template for the front panel. get a variable brightness display, according to volume and frequency. Note that you will either have to whistle or play music to get the midtreble and upper-treble bands to operate. • Set the DISPLAY switch to Modulated mode and the BEAT switch to Oscillator. The display brightness of the pattern, as selected by the PATTERN switch, should now vary according to the music volume. • Set the DISPLAY switch to 4-Band Modulated, set trimpots VR1-VR4 to maximum (ie, fully clockwise as seen from the front of each trimpot), and connect 240V coloured lamps to the mains outlets. Now play some music and adjust the SENSITIVITY control so that the dimmest lamp is driven to mid brightness. The trimpots for the other three channels should now be wound back to give equal brightness on all four channels. Troubleshooting Provided that you've followed the wiring diagrams carefully, your Discolight should work first time. If you do run into problems, the most likely causes are broken PC tracks, missed solder joints or solder bridges between IC pins. Wiring errors and incorrect component orientation are other common problems with projects that don't work. Before working on the circuit 48 SILICON CHIP though, it is a good idea to disconnect the mains wiring to the Triacs and mains outlets sockets. To do this, disconnect the active lead (lead 7) at the fuseholder and disconnect the neutral lead (lead 5) at the mains switch. This will make the circuit safer to work on when you are troubleshooting the low voltage circuitry. Despite the circuit complexity, the Discolight is quite easy to troubleshoot if you do run into problems. The block diagram (Fig.1) published on page 57 of the July issue should be particularly useful here. Let's look at some typical situations: Symptom: front panel LEDs all work OK but one of the 240V lamps fails to operate. Check: the Triac and associated circuitry between the MOC3021 and the mains socket in that channel (make sure that the lamp itself is OK). Symptom: one channel fails to operate when the DISPLAY switch is set to 4-Band Modulated. Check: filter circuit, rectifier and comparator for that channel (ie, IC2, D1-D4 and IC3). Note that the output of each op amp filter stage (IC2a-lC2d) should be very close to 0V DC. Under no-signal conditions, the outputs of the comparator stages (IC3a-lC3d) should all be low. Symptom: unit works when the SOURCE switch is in Speaker posi- tion but not in Microphone position. Check: the electret microphone and the circuitry associated with op amp IC1 b. There should be 6-BV across the electret microphone. Symptom: unit works only when the DISPLAY switch is set to Unmodulated mode and the BEAT switch is set to Oscillator. No channels light for other settings of the DISPLAy switch. Check: wiring to SOURCE switch S1, SENSITIVITY control VR5 and the circuitry associated with ICla. Symptom: lights do not chase or strobe when BEAT switch set to Oscillator. Check: circuit associated with ICld. Note that the output of ICld should oscillate between + 12V and -12V at a frequency determined by the setting of the RATE control. You can check for correct operation by monitoring the output of ICld with an analog multimeter. If everything is OK at this point, use your multimeter to check that outputs Ql and Q2 (pins 6 and 11) of IC6 are also oscillating (between 0V and + 12V). If there is no signal here, the fault is in the vicinity of IC5 and IC6. Symptom: the pattern fails to automatically reverse after every minute or so when the DIRECTION switch is set to Automatic. Check: the wiring to the DIRECTION switch and the circuitry associated with IC4a. Use your multimeter to check that the output of IC4a swit- I STRI CHANNEL 2 0 0 -CHASER DBE- Back Issues CHANNE777 FORWARD REVERSE-0 I ~ALTERNATE AUTOMATIC PATTERN Issue Highlights ches high and low at about one minute intervals as the 100µF capacitor charges and discharges. Symptom: lamps stay on in both 4-Band Modulated and Modulated mode. Check: that the ramp voltage from IC4d does not remain low all the time. If you check the output of IC4d (pin 14) with a multimeter, you should get a reading of about 2.8V. If the voltage is close to 0V, check the ramp signal circuitry associated with IC4b, IC4c and IC4d. The ramp signal circuit is best checked using a CRO to verify the waveforms shown on the circuit diagram (Fig.3). If you don't have a CRO, then the best procedure is to measure the average DC voltage on the op amp and Schmitt trigger outputs. You should find + 5.3V on the output of IC4b, + 6V on pins 2 and 4 of IC9a and IC9b respectively, + 0.9V on pin 1 of IC4c and on pin 6 of IC9c, and 2.8V on pin 12 of IC4d. That's a fairly comprehensive list of possible faults. The trick is to isolate the fault to a particular part of the circuit and then critically examine that circuit section. Footnote: 10 small plastic cable ties and 12 small rubber grommets should be added to the parts list published last month. Also, the four 10kn pullup resistors at the outputs of the IC3 op amps, as shown on the circuit diagram (Fig.3), are not necessary and have been omitted from the PCB. ~ November 1987: Car Stereo in Your Home; 1GHz Frequency Meter; Capacitance Adapter for DMMs. December 1987: 100W Power Amplifier Module; Passive lnfrared Sensor for Burglar Alarms; Universal Speed Control and Lamp Dimmer; 24 V to 1 2V DC Converter February 1988: 200 Watt Stereo Power Amplifier; Deluxe Car Burglar Alarm; End of File Indicator for Modems; Simple Door Minder; Low Ohms Adapter for Multimeters. March 1988: Remote Switch for Car Alarms; Telephone Line Grabber; Low Cost Function Generator. April 1988: Walkaround Throttle for Model Railroads; pH Meter for Swimming Pools; Slave Flash Trigger; Mobile Antennas for the VHF and UHF Bands. May 1988: Optical Tachometer for Aeromodellers; High Energy Ignition for Cars; Ultrasonic Car Burglar Alarm; Restoring Vintage Radio Receivers. June 1988: Stereo Control Preamplifier; Breakerless Ignition For Cars; Automatic Light Controller; Mega-Fast Nicad Battery Charger. July 1988: Fitting a Fuel Cut-Off Solenoid; Booster for TV & FM Signals; The Discolight Light Show; Tone Burst Source for Amplifier Testing. Price: $5.00 each (incl. p&p). Fill out the coupon below (or a photostat copy or letter) and send it to: SILICON CHIP, PO Box 139, Collaroy Beach, NSW 2097. Please send me a back issue for □ November 1987 □ December 1987 tJ dtt11t10F'f 1 QiS. (Sold Out) □ February 1 988 □ March 1 988 D April 1 988 D May 1 988 □ June 1 988 □ July 1 988 Enclosed is my cheque or money order for $ ..... ... or please debit my □ Bankcard □ Visa Card Name .. .......... .... ....................... .. .... .. ............................ .......... ...... . Address .. ....................... ... ...... ..... .... ............... .... ........... ........ ...... . I Suburb/town .................. ............. .... ..... .. .......... Postcode .. ... ......... . . ; Card No .... .. ..... .. ... ..................... ... ........ ...... ... .. ...... .... .......... ....... .. . ____________ . --------------~ I,..... Signature ... ..... ..... ..... ...... .. ... ... ..... .... Card expiry date .. .... ./ .... .. ./ ...... . ' AUGUST 1988 49 1•n1:1m11=::1111:::::::a11m11:1,11::::i;ijij~::::::111i;;::iiii_:;_;;_ii_!\_;:_:_\:_;;_::_::_;:_ ;_:_ •__ ;:__ ;: : : : : : : :=:=': :i:i:i;i\i: : ,:\ : \: : :-::::\!}!:! it\:·•:• , - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - , ft) :;/g//} Why Waste Your time With Other Suppliers I Altronics Can Deliver Any Of The Quality Products To You Tomorrow - Just Phone Your Order Toll Free 1 1 I Jack O'Donnell On 008 999 007 1 I M/Director Country Clients Please Allow Additional 48-72 Hours I I I I ~-------------------------------..1 Mlcroproceaaor Controlled Detector Cllpa On To Sunvlaor lnvl1lble from out1lde your vehicle • thll lIntHtlC high ,pee RIdIr Detector Detect, X 1nd K Bind RId1r up to an Amazing 13KM This super compact "Sunvisor clip on" Microeye Detector is virtually invisible from the outside of most vehicles at normal eye tieioht hence its very unlikely yours would attract the attention a thief (or the Gendarmes for that matter) However, please remember that use of Radar Detectors is not permitted in some states. MICRO EYE VECTOR Th• Flrat Detector With GaAa Diode• DC Bru1hle11 Fan 120MMx120MMx38MM Brushless, Electronically Commuted DC Motor Voltage 24V DC Current 330mA Speed 3100 RPM Air Flow 23 C.F.M. No1.. Level 32 dbA Until now, GaAs diodes have only been used in sophisticated military radar equipment. The Microeye Vector is the first consumer electronics product equipped with this new technology. Why GaA, Diode, Make The Difference • Lower threshold allows for a better signal to noise ratio• Lower signal conversion loss • Higher barrier reduces noise. Quite simply GaAs diodes increase the sensitivity of the Microeye Vector.•Using the latest digital processing technology the unit will filter out and ignore emissions from 80% of poorly designed Radar Detectors that emit microwaves. • Simply plugs into your cigarette lighter socket. • Clips onto sunvisor • Detects Mobile Radar Equipment. • Highway/City Modes switch allows monitoring oi City or Highway conditions. Normally $ 29.98 This Month f 1040 $24 ■O0 6 or More $20 ea Ultra High Power Capacity Polypropylene •••• Driver• Save 25% Thi• Month 12" (300mm) Model 100 Watts continuous input 150 Watts intermittent input Impedance 8 Ohm Sen1ltlvlty 93db s499 i Welgh~ 3: ; ;Q s9 9 Normally S139 Acce11orlH Included:- Visor bracket • Velcro • Cigarette lighter plug. 21 Day Money Back Guarantee. High Performance ALC Wlrele11 Microphone Our incredible ALC _Mic is • Cardiod-Uni Directional Pick-up pattern• Freq.Res.: 30Hz-15KHz • Carrier Frequency.Adjust Range: one of the most exc1trng products for '88. Wireless Mics suffer from overmodulation distortion with too higher input sound level making them unsuitable for high grade vocal entertainment use of ALC (Automatic Level compressor) fixes all this. With in +1MHz, 88-108MHz. Built-in Antenna C 0328 99 Super Bargain Save $50 Fantastic Negative ,on Generator There have been volumes written about the benefits of negative ions combating air pollution, cigarette smoke etc. can be very beneficial to Asthma sufferers. Our great little Rover generates billions of ions per second! Includes tester. Why a Toroid? • Smaller size and weight to meet modern "Slimline" requirements . • Low electrically induced noise demanded by compact equipment. • High efficiency enabling conservative rating whilst maintaining size advantages. • Lower operating temperature. • Simple, quick single bolt mounting . Dlmen1lon1 and Weight 180 VA Model• 110 Diam . 45mm H. 1.8Kgs Leads 200mm 300 VA Model• 125 Diam. 45mm H. 25Kgs Leads 200mm 1 80 Watt Models $65 10 up $62 cat.No. M 3050 M 3055 s29 M M M M 3060 3065 3070 3075 SEC.V 12 18 25 30 35 + 12 + 18 + 25 • 30 • 35 40 + 40 ea Cat.No. M M M M M M 3085 3086 3088 3090 3092 3100 SEC.V 12 18 25 30 35 • 12 + 18 + 25 + 30 + 35 40 • 40 ,- -.: 1111111■1: llll llli llllliltlli111111111 .:.:.:.:.:.: .... ·,•-•.•.·.·-•,·,•.•,•,• ,•.•. •.•::,:.:.:._._.,.. •.·.·.·.·-·,·.•-·-·,·-:.·.·.·_:_:_:_:_:,:_:_:,:_:_;_:,:,:_:,:,:.:.:,:,:_:_:_:_:_:,.;.".'_"_"_'_:_:-:.:.:.:.:.:.:_:_:_:_:_:.:.:.:.:_:_:_:_:;::-:,:-:-:-:-:-:-:-:-:-:-:-:.:-:-:-:-:-:-:-:.:•:❖:-:. ❖ • Great Value At $139 - This Month Only $119 Micron Electronic Temperature Controlled Temperature Selectable t }I : ~~~:~;t~: :,I -------~~1 y,.e\\ 8 9t\C Professional Serles j Items Marked • are 1/ 2 Price or Less Y · Solder~ ax: < <W<:< !: { Exhilarating Sound Pe rforman ce :m o >' Brilliant Digital Headphones .•,•.,1 .l_•. ~ E.v,E. ,-tO~ Incredibly Comfortable d~~~e ~ ~g~g ~:~eafe~ir;,i n ~:~: v1Ms aoi~u~ts;tta:Etgr{s~0P:~I~~~~{i~h~ ; ~g~g~~~:~ilibl !:~~ P 3040 Male PCB mnt. 2.95 0 ;r~;~~~~;R~!Pu~n~~ 2~~t:20KHz. ~ ~g~g ~;;:;:e~~o~;; t:~ f'J. :iir~~~~~~;;~; i:~e!fi~1n'.~~ 0 ) The MICRON T 2440 soldering station offers tile ultimate in contro 11ea temperature hand soldering 320 deg.C 350 deg . C 380 deg .C, 410 deg. C. (608 deg . F. 662 deg .F, 716 deg .F, 770 deg. Fa nd824 deg .F) Fixed temperatures are selectab le by rotating the detained rotary switch freely without changing heater or tip. Temperature Readout via lead baragraph instantly visab le. Patented Heating Element. The specially insu lated NICHROME wire heating element is compressed between two layers of stainless steel for ruggednes and is located at the end of the barrel to insure instant heat < ) / / / \ / Tempera ture Readout via lead bargraph instantly visab le. Patented Heating Element. Heat Capacity. Full 48 watts of het energy available for heavy duty work. Zero Voltage Switching The revolutio nary electronic " Zero Voltage" switchi ng, protects voltage and current sensitive devices such as CMOS against transient voltage spikes caused in stations . Grounded Tip. The solderi ng tip is grou nded thro ugh the power unit to ensure the tip leakage is less than 0.4 mil livolt or 0.03 microampere. Low Voltage Element.24V. Chrome Plated Iron Plated Tip. i 0 c 0010 s19.so High Quality UHF 14 Element YAGI LeH Than 1/ 2 Price! These high grade Yagi Antennas are from DX Antenna Co of Japan and original ly sold for over $70! We bought up an entire import shipment at distress stock rates & hence the fantastic sav ings to y.:,u. ··w· I I 08 15 P 3100 Male 15 Pin P3110Fm ale15Pin P 3120 Male PCB RVL P 3130 Fmale PCB RVL P 3140 Male PCB mn t. P 3150 Fm ale PCB P 3190 Ba ckshell cover 3.25 3.85 4.35 5.50 3 .85 4 .85 2.20 f.~!R I 0 825 P 3200 P 3210 P 3220 P 3230 P 3240 P 3250 P 3290 Male 25 Pin Fma le 25 Pin Male PCB RVL Fm ale PCB RVL Male PCB mnt. Fmale PCB mnt. Backsh el I cover I/ 4.95 2.47• . 5.50 2.74• : 4.95 3.50 . 6.90 3.90 . 4.95 3.00 . 6.25 3.95 . 2.20 1.10• • (A Dollar Or So Morel) There are some quite valid reasons of course. Such as fully punched chassis and hardware. Beautifully screened faceplates and panels. Prototypes built, tested and proven in our lab. Easy to follow instructions and free helpful! advice is just a phone call away if you should ever need it. (EA May'88) Fantastic 50MHz Frequency Meter For The Work Bench & Tool Box · For LeH Than $1001 Inexpensive 4 digit 50MHz frequency counter offering high sensitivity and input impedance. Simple single PC board construction . *K2510$99.00 (EA Aprll'88) Test Ampllfler For All Occasions High_ input impedance. 4 different input sensitivities suits virtually all requirements and delivers 5 watts of power. Complete with own in built speaker. Br/11/ant Performance Stereo Pre Amp (SIiicon Chip June/July'88) Out-Performs Commercial Units Costing $600 Plus ,-~ :.:;: ;i)~~j~ l ne ::,1uaI0 .!UU ::,1ereo <.;ontrol Unit is companion to the studio 200stereo pov,:er amplifier (or other power amps) . It features slim 1u rackmount profile, treble, bass. balance. input selector. tape monitor switch, stereo/ mono switch and volume control. Inputs include phone, tu ner. CD. VCR and tape loop. t (EA May'88) Gain Matched, Power Transistors for Ampllfler Output Stages K5015 ii =\ -It : 0 ..: Super simple circuit, enables evaluation of current gain and Vbe of power transistors & Darlingtons. K 2532 r (ETI Dec'87) Charge Your Batteries Free From The Sun Controls the charge of 12V lead acid batteries hooked to a solar cell Ideal for use on boats & caravans. K 1680 (ETI March'88) This incredible "Voice" generator will store 127 messages or statements each an amazing 128 bytes long. (A sentence such as "You've left the lights on" uses only 31 bytes) Simply programmed with an eprom s24 .95 Sola Cha $13 99 ■ I s229 Calling All Audio Purists This Great New Amp From Silicon Chip Is For You K 5010 s399 Featurea: • In-Built speaker protection • Toroidal Transformer (l ow hum)• Black Satin Finish• Low leakage power supply capacitors • Housed in Rugged Custom Chassis. Speclllcatlon1: • Output Power 100W into 8 Ohms Freq. Raa.(at 1W) ~::.:;~:KH.:z) g;o/o 1:i~~~r~~ ~•c:::~•~!?,!~~~:b ~~r:;~~~ ~::::~::~ i~!t~~;~!~~~ ·~ Fantastic for installing at home. behind your car dash or for interfacing with alarm systems. control systems etc. Requires enternal 12V DC supply. Kit ❖❖ K9500\\\\/i} , : ,:: 85 $ .00 ,..·:. · :·. ·..:· includes 27128 eprom. SA fuses plus RDE245A Polyswitch Damping Factor (without Polyswitches) 100 (with Polyswitches) 100. StabUlty Unconditional. ·=: :. ·.:._. :/.' :~~ ':::'.: :l!RI.IIElllll:': '. ': !1111_= .=f:_:_:l,_1_ :_._<>:=1: 1 =_ :' lll_;._.-.:■1.·: ?;.;._ _~_.:::11 _❖ .:_ ._· ·::.;:Fll _. ,_ :._ :>•'JIE' :'.:':'.:': : : :=:·= =: ·: ' .' ' ' \!;, :,: :::::=::::::?::=:·:·:·:·:-::.:.;.:.;.::❖:• •:.:,:-:• ..:.:':::::::,:-:-:-:,:: ::::::::: - - - -- - - ~- Check Appllance1 And Electrical Wiring The Protector Megohm Meter (SIiicon Chip Feb'88) Save Over $100 On An Equivalent Commercial System ( 1985 Successor to the " Megger") It uses a transistor inverter to produce a regulated 1000V DC supply which is applied to the insulation under test. Insulation resistances between 2M Ohm and more than 2000 Ohm can be measured . K 2550 (See EA July '85) s65.oo s•~e ''\ ., \~e C \9\ ol\ 11\efC FeaturH: Internal & E xternal Sirens Super Low Price on Famous ~e"'• EA 8 Sector Alarm System Kit o e~\l,~• • Dash lamp flasher • Battery back up • Delayed & Non delayed inputs • Ignition killer • Easy to build & install. , co11' (See EA Mag.Jan '85) K 1900 FHturea: • Alarm has 8 separate input circuits - 8 sectors can be monitored independently. • Each input circuit is provided with an . indicator LED and a sector On/ Off switch . • Individual sector isolation allows the user to have some areas of the premises habited while others remain protected e.g. Inside Off/ Outside On . • Inputs accept both normally closed and normally open sensors. • Two inputs provided with an entry delay between 10-75 seconds) . Internal t rip warning buuer-alerts owner occupant of pending alarm operationgreat for th e " forgetful " amoungst us . This buzzer ls pre-settable between 5 and 55 seconds prior to Alar.m. • Unique circuit detects automatically when an y N/ O or N/ C loops are either open circuit or dead short. e.g. oomeone trying to bridge rHd ■witch - ■ etc. • Switched output can be used to send a silent alarm through an auto-dialler circuit or similar. (w ithout Bac k Up Battery) (12V 1.2AH Backup Battery) S5065 24V To 12V DC 14310 s129.oo T.V. Colour Bar and Pattern Generator (See EA Oct'87) Service Your Own TV & Save Dollars Housed in rugged "ABS" instrument case. 12100 s179.oo Ideally suit ed to T.V. repairs and amateu r televis ion production . Features: 8 patterns to choose f rom • PAL o r N TSC compatible • Operates on Channel 1 • Horizontal sy nc output • Vertical sync output • RF Output. S149.50 S24.95 (Slllcon Chip Dec'87) Laboratory Power Supply Enables 12V appliances li k e stereos, 2 way radios, CB' s etc . to operate from a 24 V battery. • Operates f rom 18V-30V. Output is 13.6V a t 5 amps. 1 3255 K 3300 3.5 Voltl at up to 5 Amp, s195 Designed by Electronics Australia , this suppl y has been one of our most popular kits. Our version incorporates ref inements and is now housed in an attractive, tough " ABS" instrument case. This all new compact version has been made possible by the use of a highefficiency Toroid Power Transformer. So you win four ways - less heat, less weight - Greatly enhanced appearance and easier to build Remember the Altronlc ■ Kit 11 fully drilled and punched. s59 .oo Manufacturers, Contracto rs and Bul k Users Please Contact Our Wholesale Sales Dept. Sydney (NSW Only) Colin Fobister 436 042 2 Perth 09 328 2199 174 Roe St. Pert h W.A. 6000 PHONE TOLL FREE 008 999 007 Perth Metro & After Hours (09) 328 1599 ALL MAIL ORDERS P.O. Box 8350 Perth Mail Exchange W.A.6000 AL TRONICS RESELLERS Chances are there is an A ltronics Reseller right near you - check this list or phone us for details of the nearest dealer. PleHe Note: Resellers have to pay the cost of freight and insurance and therefore the prices charg ed by individual Dealers may vary slightly from this Catalogue - in many cases, however, Dealer prices will still represent a significant cost saving from prices charged by A ltronics Competitors. Don't forget our Expre11 Mall and Phone Order Service - for the coat of • local call, Bankcard, V118 or Ma■ tercard holder ■ can phone order for ■ame day d e ■pat ch. STANDARD DELIVERY I PACKING CHARGE $4.00 to 1Kg $7 over 1Kg AUSTRALIA WIDE - We process your order the day recei ved and despatch via . Australia Post. Allow approx 7 days from day you post order to when you receive goods $7.00 OVERNIGHT JETSERVICE - We process your order the day received and despatch via . Ov.,nlght Jet■■ rv lce Courter fo r delivery next day Country areas please allow additional 24-48 hours. Weight limit 3Kgs (3Kgs covers 95% of Orders) . $10.00 HEAVY HEAVY SERVICE - All orders of 10Kgs or more must travel Express Road - Please allow 7 days for delivery. INSURANCE - As with virtually every other Australian supplier, we send goods at consignees risk . Should you requ ire comprehensive insurance cover against loss or damage please add 1% to order value (minimum ch arg e $1) . When phone ordering please request " Insurance" . TOLL FREE PHONE ORDER - Bankcard .Visa, Mastercard Holders can phone order toll free up to 6pm Eastern Standard Time. Remember with our Overnight Jet ■■ rvlce we deliver next day. WA COUNTRY ALBANY BP Elec t ronic s ■ 4 12681 ESP ERAN C E Esp er ance Communic at ion s 7 133 44 GERALDTON K. B.Elec t ronlc s & Marine 212176 KALGOORLIE Tod a ys Electronic s ■ 2127 77 KARRATHA Dave s O s citronic 8 5 4 83 8 MANDURAH L a nc e Roc k Retrav ision 3512 46 WYALKATCHEM D & J Pease 81 1132 NT ALICE SPR I N G S Ascom El ectronic s 521713 Farm e r Elec t ron ics 522987 ACT CANBERRA Bennett Commercial Electronics 805359 Scientron ics 548334 VICTORIA CITY All Electronic Components 6623506 SOUTH MELBOURNE Winsco tt Trading 69957 40 SUBURBAN CHELTENHAM Talking Electronic s 58 42386 CROYDEN T r usco tt El ectronics ■ 7233860 PRESTON Pres ton Elec t ronic s 4 8 4 0191 COUNTRY BEND IG O KC John son ■ 4 11 411 MORWELL Mor we ll El ect ronic s 346133 QUEENSLAND CITY Delsound P/ L 8396155 SUBURBAN FORTITUDE VALLEY Economic Electronics 2523762 WOODRIDGE David Hall Electronics 8082777 COUNTRY CAIRNS Electronic World ■ 518555 BUNDABERG Bob Elkins Electronics 721785 GLADSTONE Supertron ics 724321 MACKAY Phillronics ■ 578855 ROCKHAMPTON Access Electronics (East St.) 221058 Electron World 278988 TOOWOOMBA Hu nts Elect ronic s ■ 329677 TOWNSVILLE Solex ■ 722015 SA CITY Electronic Comp & Equip. 2125999 Force Electronic ■ 2125505 SUBURBAN BRIGHTON Force Electronics ■ 3770512 CHR ISTIE& BEACH Force Electronic s ■ 3823366 EN FI ELD Force Elect ronic s ■ 34963 40 FI NDON Force Elect ronics ■ 3471188 COUNTRY MT.GAMBIER South East Electronics 250034 WHYALLA Eyre Electronics ■ 454784 TASMANIA HOBART George Harvey ■ 342233 LAUNCESTON George Harvey ■ 316533 Nichols Radio TV 316171 NSW CITY David Reid Electronics ■ 2671385 CARINGHAH Hicom Unltronics 52 47878 LEWISHAM PrePak Electronic s 5699770 SMITHF IELD Chantronics 609721 8 COUNTRY COFFS HARBOUR Coifs Habour . Electronics 525684 GOSFORD Tomorrows Electronics ■ 247246 NELSON BAY Nelson Bay Electronics 813885 NEWCASTLE Novocastrian Elect.Supplies ■ 621358 NOWRA Ew ing Electronic s ■ 218 4 12 RAYMOND TERRAC E Alback Electronic s 873 4 19 WINDSOR M & E El e c tr onic s 775935 WOLLONGONG Newtek Electronics ■ 271620 Blue Ribbon DHle'8 are highlighted with a ■. These Dealers generally carry a comprehensive range of Altronic products and kits o r will o rder any required Item for you. Insulated tab Triacs: a safer method of mounting Mounting Triacs and SCRs to heatsinks has always been something of a hassle. You need a special mica washer, an insulating bush, plus a normal screw, nut, lockwasher and so on. With insulated tab Triacs and SCRs, the mica washer and insulating bush can be eliminated. By LEO SIMPSON These days the vast majority of power transistors, Triacs and SCRs (silicon controlled rectifiers) are available in plastic encapsulations, commonly TO-220 or TO-218 (or SOT-93 as made by Philips). While these are single-hole mounting and therefore easier to mount than metal case semis such as TO-3 (eg, 2N3055s), they are still a pain to mount. The mica washers and insulated bushes can be hard to get too, which merely emphasises the problem. More importantly, the metal tab of the plastic encapsulation is internally connected and therefore may operate at a high voltage. This is particularly hazardous in Triacs and SCRs where the tab is normally at mains potential; ie, 240V AC. Now there is a better way; fully encapsulated packages. These have no exposed metal tab and can be mounted directly on an earthed heatsink without the need for mica washers or insulating bushes. These encapsulations have been available to OEMs (original equipment manufacturers) for several years but until publication of the Discolight in SILICON CHIP (July and August, 1988), they have not been specified in an electronics project for enthusiasts. Two companies are leading the way with the new encapsulations: Philips and Motorola. They call the new packages the "full pack", meaning fully insulated; F-pack or FP for short. Philips' substitute for the TO-220 package is the SOT-186 pack. For the SOT-93, Philips' "full pack" equivalent is the SOT-199. For Motorola, the "full pack" version of the TO-220 is the case 221C-01. It is specified by adding the suffix FP to the device part number. Construction So what is the difference in construction between the old and new packages? Unlike the TO-220 and TO-218 (SOT-93) encapsulations where the nickel-plated copper mounting base and tab is visible, in the new F-pack it is hidden under an extremely thin layer of epoxy. This is selected for its excellent thermal and insulating properties. For consistent performance, the thickness of the epoxy coating is closely controlled, within ± 25µm. For Philips SOT-186 (ie, the TO-220 F-pack) the epoxy insulating layer is 400µm thick while for the SOT-199 it is 500µm thick. Breakdown voltage of the insulating layer is quoted as in excess of 2000 volts. In practice though, because the lead spacing to the heatsink mounting for the F-pack is slightly smaller than for the uninsulated versions, slightly lower voltage ratings apply. So for the SOT-186 package the maximum device rating is 1000V while for the larger SOT-199 it is 1500V. Power dissipation Fig.1: the MAC-218A8FP insulated tab Triac from Motorola is rated at 600 volts. Because the tab is insulated, it can be bolted directly to an earthed heatsink without a mica washer or insulating bush. 54 SILICON CHIP Thermal conductivity of the epoxy insulating layer is comparable to that of a standard 50µm mica washer. When used without a heatsink, the F-packs can dissipate slightly more power in free air. Typically, the increase is about 30%. So for most purposes, the new Fpacks are a direct drop-in replacement for the older TO-220 and TO-218 packs. For Triacs and SCRs which operate at mains voltage, they are a much safer alternative. We recommend that parts stockists change over to the new F- plain washer lock washer insulating bush Fig.2: compared to the TO-220 style device, the SOT-186 insulated tab device (left) is far easier to mount. Both the mica washer and the insulating bush are eliminated. Also, because the mounting screw does not contact a metal tab, it no longer sits at mains potential as occurs with the TO-220 device. plain washer less an industry standard for mains operated circuitry in Australia. However, there is no particular reason why insulated tab devices rated at 400V or 500V could not be used. Finally, we would be remiss if we did not mention that General Electric have had isolated tab TO-220 packages available for many years. For example, the isolated tab version of the popular SC141D 6A 400V Triac is the SC142D. Acknowledgement Fig.3: the Philips SOT-199 package uses an epoxy insulating layer some 500µm thick and has a breakdown voltage rating of 1500V. packs for Triacs and SCRs. There is little difference in price and they do away with the need to stock mica washers and insulating bushes. In the Discolight , we have specified a number of F-pack Triacs. From Philips, the suggested device is the BT137F-600 while from Motorola there are two choices, the MAC-218A8FP or the T-2500MFP (note: the latter device was not listed in the Discolight parts list). These devices are all rated at 600 volts which is more or Our thanks to Philips Elcoma for permission to publish photos and diagrams from their literature. For further information about Philips Fpacks, contact Elcoma, 11 Waltham St, Artarmon, NSW 2064. Phone (02) 439 3322. For further information about Motorola F-packs, contact VSI Electronics (Australia) Pty Ltd, 16 Dickson Avenue, Artarmon, NSW 2064. Phone (02) 439 8622. ~ AUGUST 1988 55 By JOHN CLARKE & GREG SWAIN Crook in bed with a bad back, mate? Want someone to bring you a nice hot cup of tea? Don't shout - just press the button on a small keyring transmitter to attract attention. The traditional way for someone confined to bed to attract attention is to shout at the top of his (or her) lungs. But when one of our staff members (who had best remain nameless) tried that recently, there was no response. His pathetic whimperings were muffled by two sets of closed doors and by a TV set going full-bore in the family room. That started him thinking (and not before time). What was needed was a unit that would sound a bell or a chime in the family room in response to the press of a button on a small transmitter in the bedroom. Aha! Why not base the circuit on 56 SILICON CHIP the UHF Remote Alarm Switch described in the March issue for switching car burglar alarms on and off? And that's exactly what we've done. We simply stripped the Remote Alarm Switch receiver of any unnecessary circuitry and married it to a two-tone chime IC, the SAB0602. So, whenever you press the button on a small keyring transmitter, the receiver picks up the signal and sounds a pleasant two-tone chime. For want of a better name, we've called the finished project the Remote Alert. It works like a charm. And it eliminates enraged yells, fist banging on walls, and the aforesaid pathetic, self-pitying whimperings. Another ideal use for this project is as a wireless doorbell. In this version, the transmitter PCB can be housed in a small plastic project box, together with a 9V battery and a pushbutton switch. Depending on circumstances, the completed unit should have a range of 12 metres or more. By the way, you could have as many "bell pushes" as you wanted. Just build as many transmitters as necessary (one for each door?) and code them all exactly the same. To keep costs low and simplify construction, we've designed a new printed circuit board for the receiver. This PCB leaves out any unnecessary circuitry from before and includes the two-tone chime IC. No changes are necessary for the transmitter circuit so we have simply reused the original PCB. Transmitter Fig.1 shows the transmitter circuit. It consists of a digital encoder integrated circuit (IC1) and a UHF oscillator operating at 304MHz. ICl is a Motorola MC145026 9-bit trinary encoder. Trinary code is like binary code except that it uses three logic states instead of two (ie; high, low or open-circuit). Only one transmitter code word (one 9-bit word) is possible, as selected by connections to the IC's nine address inputs, Al fo A9. In keeping with the trinary states just mentioned, each of the nine address inputs can be connected to the + 12V rail, to ground or left open circuit. In our application, because of the particular decoder used in the receiver, the A9 input must either be connected to the + 12V rail or to ground. The 9-bit code word appears as a series of pulses on pin 15 of ICl. The frequency of these pulses is set by the two resistors and the capacitor connected to pins 11, 12 and 13. For our circuit, the frequency is about 2kHz. Pushing the Transmit button (St) causes the IC to deliver the coded word from pin 15. This is used to key the UHF oscillator Qt on and off at a rate of 2kHz. When pin 15 is high ( + 12V), Qt oscillates. Qt is a BFR91A which is a surface mounting transistor intended for use in UHF and microwave amplifiers. Inductor 11 and the 2-6pF capacitor form a tuned circuit load for the collector while the base is grounded (to AC signals) by a 470pF capacitor. Stray capacitance between the emitter and collector of Qt provides positive feedback which causes it to oscillate at 304MHz. To increase the oscillator's output, the emitter deger ,: rntion resistor is bypassed with J 1.5pF capacitor, which is critical in value. The value of this capacitor cannot be too large because this would reduce the positive feedback and stop oscillation. The transmitter is powered from a 12V lighter battery (VR22, EL12, GP23 or equivalent), but will work from voltages down to as low as 4.5V (a 9V battery is used in the doorbell transmitter version). The When you press the button on the small keyring transmitter, the receiver picks up the signal and sounds a pleasant two-tone chime. You can also build the transmitter into a larger case for use as a doorbell. + LOW 14 IC1 MC145026 13 12 TE11 ... 100k .0022 + 220k E TYPE MARKING 8 ... L1 : 32mm OF 0.71mm TINNED COPPER WIRE FOR SMALL VERSION. LARGER VERSION USES PCB TRACKS. toN LARGE VERSION ONLY UHF REMOTE TRANSMITTER SC03-1-288 Fig.1: the transmitter uses an MC145026 trinary encoder IC to key UHF oscillator Qt on and off. A1-A9 are connected to give the address code (see text). battery is bypassed by a 0.1µ:F capacitor located near IC1 and by a 0.047µF capacitor near the tuned circuit for Ql. When S1 is closed the current drawn by the circuit is a few milliamps, the exact figure depending on the code word selected at Al to A9. The current through LED 1 is abou ~ 7mA. When St is open, AUGUST 1988 57 4,70 r - - - -.....- ......--~-'Wl,,,.....--------~~----.----.....---+sv ANTENNA L4 L1 .,.. .,. 12VDC + PLUG-PACK 47 + 100 + 16VW+ 16 -_i 16VWL ,. . 1 INPUT A1 2 A2 3 220 A3 OUTPU 4 5 A4 11 IC2 MC145028 A5 4 39k 7 10 12 A9 .,. DECODING OPTIONS ~SPEAKER L1 : 15T OF 0.63mm ENAMELLED COPPER WIRE ON 3.2mm DIA. FORMER L2 : 1.5T OF 0. 71 mm TINNED COPPER WIRE ON 5mm DIA. F29 FERRITE CORE L4 : BT OF 0.63mm ENAMELLED COPPER WIRE ON 3.2mm DIA. FORMER 13 AB SC03-1-DBBB-1 8 1sv~ so .0068t .022+ REMOTE ALERT l 0 33 · 6 15 A6 14 IC3 SAB0602 ,. ,. 0.1+ Fig.2: the receiver circuit can be divided into four sections: an RF input amplifier and detector (Ql, Q2), a tuned 2kHz amplifier (ICl), trinary decoder IC2, and a chime generator circuit (IC3). Power comes from a 12V DC plugpack transformer. the current drain is less than 0.2µA. The transmitter can be built into one of two cases, one of which is small enough to be attached to a key ring. We'll talk about these later in the section on construction. Receiver The receiver circuit is shown in Fig.2 and is identical to the circuit used for the Remote Alarm Switch as far as the output (pin 11) of ICZ. It consists of four sections: an RF input amplifier and detector (Qt and QZ), a tuned ZkHz amplifier (IC1), trinary decoder IC2 , and the chime generator circuit (IC3). The transmitted signal is picked up by the antenna which is loaded 58 SILICON CHIP by inductor 11. The signal is then coupled via a .001µF capacitor to the base of Qt , which is an RF amplifier with a tuned collector load. Signal from the collector of Qt is fed via a voltage divider consisting of a 2.7pF and a 22pF capacitor to self-oscillating detector stage QZ . Whenever signal is received, this stage oscillates at 304MHz. When no signal is received, the circuit is quiescent. The detected signal from QZ appears across the .001µF capacitor connected to its base. This capacitor bypasses the 304MHz signal but not the ZkHz pulse modulation which is superimposed on the signal fed to the antenna. This ZkHz pulse signal is coupled via 14 and a 2.ZµF capacitor to ICla, an inverting op amp with a gain of about 470. L4 is there to keep RF energy out of this op amp stage. ICtb is a Schmitt trigger. It squares up the amplified signal from ICla before feeding it to ICZ, the trinary decoder. ICZ is an MC145028 decoder which is compatible with the MC145026 used in the transmitter circuit. It is set up to respond only to the unique code word sent by the transmitter. This is done by connecting the address inputs Al to A9 in exactly the same way as for IC1 . in the transmitter. When IC2 detects a correct code 1=' -~,:~®:~~ T ~/0., { ~ .0470 1Al-H1G_"- -~ ~--Lo_w A7• • •A6 A9 AS• •A4 A3• eA2 <<at>)t2·6pF ~ctlOOk Al• ~i220k + Fig.3: parts layout for transmitter PCB. Substitute a battery snap connector for the battery clips and leave out the LED and PC-mounting switch if you are building the doorbell version. Fig.4: to code the transmitter each A1-A8 input is connected to the high rail, the low rail, or left open circuit. A9 must he connected high or low; it cannot be left open circuit. The transmitter PCB fits neatly into the small keyring case which is available from Dick Smith Electronics. Power comes from a 12V lighter battery. Fig.5: mount the parts on the transmitter PCB as shown here. The RF transistors (Qt & Q2) are installed from the copper side of the PCB, with the part number visible from the component side. Winding details for the coils are shown on Figs.2 & 6. from the transmitter, the output at pin 11 goes high. This triggers the two-tone chime IC (SAB0602) which produces a rich, heavily modulated chime sound. Note that the chime IC only sounds once and will not retrigger if the transmitter button is held down (ie, if pin 11 of IC2 stays high). IC3 drives an 80 loudspeaker via a 330µF capacitor. The O.lµF capacitor and 33k0 resistor on pins 6, 7 & 8 set the chime tone frequency, while the 0.33µF capacitor on pin 3 provides a degree of high frequency filtering. Power for the circuit is derived from a 12V DC plugpack transformer . This feeds a 7808 3-terminal regulator and several filter capacitors to produce a regulated + 8V supply. This supply regulation is necessary to prevent false triggering. Transmitter construction Construction of the transmitter mainly involves the assembly of a small printed circuit board. This board measures 46 x 33m and is coded SC0312882. Fig.3 shows where all the parts go. The keyring transmitter case r L2 FORMATION DIMENSIONS IN MILLIMETRES Fig.6: L2 is made by winding 0.71mm tinned copper wire. on a 5mm plastic former. The former is fitted with an F29 ferrite core for tuning. from DSE is supplied complete with PC-mounting battery clips. If you intend installing the PCB in the larger case for use as a doorbell, delete the battery clips and wire in a battery snap connector instead. You must install the IC with pin 1 towards the battery clip side of the PCB as shown. The RF transistor (Ql) is mounted on the copper side of the PCB (see Fig.1 for pinouts). The body of the transistor fits into a hole in the PCB with the type marking uppermost and the leads then soldered to the copper tracks (which should be pre-tinned). Note that some of the resistors are mounted flat on the PCB while others are mounted end on as shown in Fig.3. All the capacitors are mounted flush against the PCB except the .0022µF greencap which is bent to lie flat over the top of the IC (see photo). Pay particular attention when installing the switch (S1). It must be installed so that the flat side of the switch body is towards the battery terminal end of the PCB. The LED must be mounted so that the top of its body is about 13mm above the PCB surface. Delete both the LED and the PCmounting switch for the doorbell version in the zippy case. In this AUGUST 1988 59 r: 0 1-- a: 0 w 0 ...J <( 0 0 w 0 1-- 0 0 0 ~ w 0 L..: .:J o] 0 SC03 -1-288-2 The front panel and printed circuit board artworks are shown here for the convenience of those who prefer to make their own. Alternatively, you can buy ready made boards and panels from the usual suppliers (see page 96). version, the PCB is soldered to a panel-mounting pushbutton switch via two short lengths of tinned copper wire. It will be necessary to angle the board as shown in one of the photographs so that there will be enough .room to mount the battery. Receiver construction The UHF receiver and chime cir60 SILICON CHIP cuits are combined on a single PCB coded 03107881 and measuring 87 x 8 7mm. This is designed to clip into a plastic utility case measuring 159 x 96 x 51mm. Fig.5 shows the parts layout on the receiver PCB. Begin construction by installing all the low profile components such as the resistors, ICs and the wire link adjacent to IC2. When these have been install- ed, you can mount the capacitors and the 3-terminal regulator. The BFR91 transistors (Ql and Q2) are mounted on the underside of the PCB. As in the transmitter, the bodies of these RF transistors fit into holes, with the part number visible from the component side of the board. You will find it easier to solder the leads if you tin the copper tracks first. Transmitter 1 transmitter case (DSE Cat. H-2497, 31 x 58 x 17mm) 1 PCB, code SC0312882, 46 x 33mm 1 PC-mounting pushbutton switch, DSE Cat. S-1200 1 3mm LED 1 12V lighter battery (VR22, EL 12, GP23 or equivalent) Semiconductors 1 BFR91 NPN UHF transistor 1 MC145026,SC41342 trinary encoder Capacitors 1 1 1 1 1 1 0.1 µF miniature polyester .04 7 µF ceramic .0022µF metallised polyester 4 70pF ceramic 1.5pF ceramic 2-6pF ceramic trimmer Resistors (0.25W, 5%) 1 X 220k0, 1 X 100k0, 1 X 4 7k0, 1 x 1 OkO, 1 x 1 .5k0, 1 x 1 kO PARTS LIST Receiver 1 plastic utility case, 158 x 96 x 54mm 1 PCB, code SC03107881, 87 x 87mm 1 mini 80 loudspeaker 1 1 2V DC plugpack supply Semiconductors 1 MC145028,SC41344 trinary decoder 1 SAB0602 dual-tone chime 1 LF353, TL072 dual FET input op amp 1 7808 8V 3-terminal regulator 2 BFR91 NPN UHF transistors Capacitors 1 1 1 2 1 1 3 1 1 220µF 16VW PC electrolytic 1 OOµF 16VW PC electrolytic 4 7 µF 1 6VW PC electrolytic 1 OµF 1 6VW PC electrolytic 2.2µF 16VW PC electrolytic 0 .33µF metallised polyester 0. 1µF metallised polyester .022µF metallised polyester .01 µF ceramic 1 4 1 1 1 1 .0068µF metallised polyester .001 µF ceramic 22pF ceramic 3.3pF ceramic 2. 7pF ceramic 2.2pF ceramic Inductors and wires L 1 190mm 0.62mm enamelled copper wire L2 65mm 0.71mm tinned copper wire, 5mm former DSE Cat. L 1010, F29 ferrite screw core L3 3.3µH RF choke L4 100mm 0.62mm enamelled copper wire 1 300mm-length of 1mm solid core insulated wire (for antenna) Resistors (0.25W, 5%) 2 X 4.7MQ, 1 X 470k0, 1 X 180k0, 1 x 150k0, 1 x 1 OOkO, 2 X 47k0, 1 X 39k0, 1 X 33k0, 1 X 22k0, 1 x 18k0, 5 x 10k0, 1 x 1 kO, 1 X 4 700, 1 X 2700, 1 X 4.70 11 is made by winding a 190mm length of 0.63mm enamelled copper wire around a 3.2mm (1/8-inch) drill bit. Wind on 15 turns and strip the insulation from the ends with a sharp knife before soldering the coil to the PCB. 14 is wound in exactly the same fashion as 11 but requires only 8 turns. 12 is wound on a 5mm plastic former, the base of which is pushfitted into a hole in the PCB. The winding details are shown in Fig.6. Don't forget to screw in the F29 ferrite core. 13 is a standard 3.3µH inductor that can be purchased ready wound (eg, DSE Cat. 1-1765). The antenna is simply a 300mm length of single-core hookup wire soldered to the antenna input pad on the board (see Fig.5). Testing and alignment Both the transmitter and receiver must be coded before they can be tested. Initially, to allow testing, we recommend that only the A9 input on both the transmitter and receiver be coded. This input must be connected to either the high or The receiver PCB clips into slots in the side of the standard plastic case. For best range, you should make the antenna about 300mm long. low rails (ie, it must not be left open circuit). The Al-A8 inputs can all be left open circuit for the time being. The transmitter frequency can now be set to 304MHz by using a frequency meter. Temporarily connect pin 15 of IC1 to the positive AUGUST 1988 61 111r . . . ·. · . · ·~- - -[ir For the doorbell version, the transmitter PCB is soldered to the pushbutton switch on the case lid via two short lengths of tinned copper wire. Angle the PCB as shown to allow room for the battery. (ie, for maximum reading on the DMM). You may need to move the transmitter away from the receiver to obtain the setting for maximum sensitivity. If everything is working correctly, the chimes should now sound whenever the transmitter button is pressed. In fact, you may wish to disconnect one of the speaker leads during the adjustment procedure to prevent the chimes from continually sounding. When the correct setting has been found, drip some molten candle wax into the screw core of 12. This will prevent it from moving and thereby detuning the receiver. rail. This will set the oscillator in operation. Now hold the transmitter near the input of the frequency meter and adjust the trimmer capacitor for a reading of 304MHz. In some cases it may be necessary to connect a coil of wire between the input and ground of the frequency meter to obtain a satisfactory reading. Once the frequency has been set, remove the temporary connection to pin 15. Now connect the receiver to a 12V power supply and check that the output of the regulator is at + BV. If everything is OK, switch off and connect a multimeter set to read DC volts between pin 7 of IC1 and ground. Apply power and wait 10 seconds for the 2.2µF capacitor on the base of Q2 to charge. Adjust the slug in 12 for maximum signal when the transmitter switch is pressed Coding Because this project is not being used in a security application, there's really no need to worry too much about working out an ·elaborate security code. The main eA1 eA2 eA3 eA4 A&• A7• AB• A9• With this doorbell, you don't have to run connecting wires between the bell push and the chimes unit. Because the current drain is so low, the battery should last for its normal shelf-life. I eA5 LOW Fig.7: connect the Al-A9 receiver inputs to exactly match the transmitter code. Al·A8 can be high, low or open circuit; A9 must be tied high or low. 62 SILICON CHIP thing to watch out for here is that both the transmitter and receiver codes are made identical. For example, you may wish to code only the Al, A2, A3, A4 and A9 inputs (A9 must be tied high or low as mentioned above). The remaining A5-A8 inputs could all be left open circuit. Coding is achieved simply by connecting each A1-A8 input to the high rail or to the low rail, or by leaving it open circuit. For example, you could bridge Al to the high rail, A2 to the low rail, leave A3 open circuit, bridge A4 high and so on. Figs.4 and 7 show the Al to A9 code inputs on the copper side of the PCB for the transmitter and receiver respectively. It's a good idea to write your selected code down on a piece of paper before actually making the necessary connections. Once coding has been completed, the receiver PCB an be clipped into the plastic case and the wiring to the speaker and plugpack transformer installed as shown in Fig.5. You will have to drill holes in the side of the case to allow access for the supply leads and for the antenna wire. The loudspeaker is affixed to the lid of the case using an epoxy adhesive (eg, Araldite). Before mounting the speaker, attach the adhesive label to the lid and drill a 4mm hole at each marked location to let the sound out. Deburr the holes using an oversize drill. ~ .... '""i" ' ' DIGITAL FUNDAMENT~ LS There are several ways of getting data into and out of a microprocessor. This lesson covers input/output (1/0) operations and microprocessor interfacing. • LESSON 9: INPUT/OUTPUT OPERATIONS By Louis E. Frenzel IN THE PREVIOUS LESSON WE DISCUSSED the operation of microprocessors. We showed how the microprocessor, which is a miniature digital computer on a chip, can perform virtually any digital function that can be duplicated with discrete logic devices, such as gates and flipflops. The microprocessor can be programmed to perform arithmetic functions as well as logical operations such as AND and OR. It can also do storage operations in registers or memory chips, and other functions such as exclusive OR comparing, counting, shifting, and all those functions you ordinarily associate with SSI and MSI logic chips. The microprocessor is so versatile, in fact, that it has virtually replaced individual logic circuits in many digital designs. A microprocessor, which is an integrated-circuit central processing unit (CPU), is referred to as a processor because its primary function is to process digital data. By process we mean manipulate the binary numbers supplied to it in such a way as to create new binary numbers as required by the application. In other words, the microprocessor accepts inputs from some source, processes them according to the application, and generates new signals which are then sent as outputs to some destination. Our main focus in the previous lesson was on the processing power of the microprocessor. In this lesson we want to focus on the input and output functions. That is, how do we get the data into and out of the microprocessor? Input/output (1/0) operations are essential to any microprocessor-based equipment. The microprocessor can usually perform the desired processing, but there must be some formal means of getting the data into and out of the processor. That is done with a circuit called the interface. Our emphasis in this lesson will be on how the microprocessor communicates with the external circuits and equipment via the interface. Types of 1/0 There are three basic types of input/output processes used with microcomputers. They are programmed 1/0, interrupt 1/0, and direct memory access (DMA). Let's take a look at each of those key methods, as well as a ._ .1riation of the programmed 1/0 method called "memory-mapped 1/0". Programmed 1/0 The simplest and most widely used way of getting data into and out of a microprocessor is to simply pass it through the accumulator or one of the general purpose registers in the microprocessor (see Fig .1 ). Special input and output instructions cause the data transfers to occur when executed. For example, to perform an output function, a desired binary number, word or bit pattern is loaded into the accumulator register. Then an output instruction is issued. That causes the data in the accumulator to be placed on the data bus where it is picked up by the interface and passed on to some external circuit or equipment connected to it. The number in the accumulator is not erased or destroyed. An input operation is performed in a similar manner. An external circuit or device sends its data to the interface which, in turn, places it on the data bus. An input instruction is then executed. That causes the input data to be transferred via the data bus to the accumulator register. Additional instructions in the program will then cause the word to be stored in memory or otherwise operated upon. AUGUST 1988 63 A A ACCUMULATOR REGISTER v--,, MICROPROCESSOR (CPU) . A CONTROL SIGNALS DATA BUS y r CONTROL SIGNALS ,I UD INTERFACE L -- • ADDRESS BUS 1-- I> • RAM -• - r ' SILICON CHIP r ' ~ EXTERNAL CIRCUIT, ::::ER~RL EQUIPMENT INTERRUPT INTERRUPT Fig.1: the most commonly used way to get data into and out of a microprocessor is to simply pass it through the accumulator or one of the general purpose registers. • ' ' ROM In order for a programmed 1/0 transfer to occur, two conditions must be met. First, the external circuit or peripheral device must be addressed or identified. Second, that circuit or device must indicate to the microprocessor that it is ready to send or receive data. To identify or enable an external circuit or device, the microprocessor usually issues an address word when an 1/0 instruction is executed. That address appears on the standard address bus of the microprocessor. In some CPUs, the entire address word (usually 16 bits) is used for the 1/0 device address. In other CPUs, only the eight least significant bits are used. Even with only eight bits, up to 256 external devices and circuits can be identified. That is far more than ever needed. The interface contains an AND gate decoder that is set up to recognise a particular address word. Should the address of that device be placed on the address bus, it will be identified and the interface will be enabled. Second, once the external device has been selected with the address, it must be ready to send or receive data. To illustrate this, assume that the microprocessor is sending ASCII characters to an external printer. Printers are slow mechanical devices and they cannot operate as quickly as electronic circuits. If the microprocessor sends the information to be printed at its maximum rate, the printer will not be able to keep up. Data will be lost. For that reason, some circuitry must generally be incorporated to permit the remote printer to tell the computer when it has received a character and printed it, and that the printer is ready for the next one. The same is true on input. An input instruction may be executed, but the external device may not have data re_ady to put on the bus. The external device must signal the interface, which can then inform the microprocessor of its readiness. The readiness indication is usually handled by a short segment of instructions that poll the external devices, waiting for a signal that indicates they are ready. A single logic signal generated within the external circuit or device and passed along by the interface can be placed on the data bus and the microprocessor can read it repeatedly, looking for a particular condition. If the pulse is a binary 0, then the external device is 64 . . not ready. If that pulse becomes a binary 1, then the readiness condition is signalled. The microcomputer inputs that pulse, checks its value with a short sequence of instructions, and determines that data may now be sent or received. The actual transfer of data takes place when one or more control signals are sent from the CPU through the interface to the external device. Those control signals are either generated directly by the microprocessor or can be derived from selected signals on the microprocessor control bus using simple logic gates. Interrupt 1/0 A modified form of programmed 1/0 is called "interrupt 1/0". Every microprocessor has an input signal called an interrupt. It does not have to be used; but if it is used, it greatly facilitates input/output operations. An interrupt is a signal from an external circuit or device which indicates to the CPU that some input or output operation is called for or desired (refer to Fig.1). That is similar to the input signal described previously, which must be periodically checked with an input operation to ascertain if the external device is ready. The interrupt provides a way to signal the microprocessor and causes it to interrupt any program in progress and perform the desired 1/0 operation. Using the polling technique described in programmed 1/0 is a wasteful and time consuming process. It means that the microprocessor must continually look for an input signal from the external device. It simply waits until that external device is ready. That is an inefficient use of the processor because ordinarily other computing operations could go on while you are waiting. Interrupt 1/0 makes that possible. The microprocessor may go about executing other programs until an input or output operation is desired. When an interrupt occurs, the microprocessor finishes executing any instruction currently in progress. Then, it stores the content of the program counter in the stack. (Recall that the stack is an area of RAM set aside for temporarily holding addresses and data words). By storing the program counter, the microprocessor thereby remembers its place in th0 current program. Remember that the program counter always points to the next instruction to be executed. Once an instruction is complete, the program . MICROPROCESSOR (CPU) . DATA BUS DATA PATH - \r- A r INTERRUPT ill !J RAM . ADDRESS PATH ADDRESS BUS ~ 1/D INTERFACE ... F INTERRUPT EXTERNAL DEVICE (le HARO DISC) F I ADDRESS COUNTER CONTROL LOGIC I INCREtNT OMA CONTROLLER CHIP Fig.2: in direct memory addressing, a DMA controller is connected as if it were an output device. It can therefore be set up by the microprocessor prior to a given operation. counter is incremented so that it points to the next instruction in sequence in the program. By storing that address, the processor can pick up where it left off once the called-for input or output operation is complete. In addition to storing the program counter, other information may also· be saved. The contents of the accumulator, which usually contains the intermediate results of a calculation, are also stored on the stack. The contents of other registers may also be saved in the stack if necessary. The saving of all that information may take place automatically in some processors but, in others, special instructions associated with the stack must be used. For example, a PUSH instruction causes register data to be put on the stack. A POP or PULL instruction causes information to be retrieved from the stack and put back into the appropriate register. Once the status of the microprocessor has been saved, the interrupt signal causes the program counter to be automatically loaded with a predetermined address. In some microprocessors, that address is zero (0000 hex); in others it is the maximum address value (FFFF). With that number loaded into the program counter, the microprocessor then looks for an instruction at that location and fetches the instruction word stored there. That is usually a jump or branch instruction that loads the program counter with another address that points to a subroutine stored in RAM that will carry out the desired I/O operation. A subroutine is a short sequence of instructions designed to perform some specific operation. It may be a calculation or some other process. In this case, it is an input or output routine using the standard input and output instructions described under programmed I/0. That subroutine sends data to the device requesting service or accepts input from it. The input or output subroutine passes the data through the accumulator and usually stores it away in memory for later use. Once the I/O operation is complete, a RETURN instruction at the end of the subroutine is executed. That causes the microprocessor to go back to where it left off. It automatically retrieves all the data stored in the stack and the address for the program counter. The microprocessor then continues with the program it was executing prior to the interrupt. Interupt I/O is an extremly efficient and productive way to handle input or output data transfers. It allows the computer to continue computing as long as no input or output operation is desired. Most microprocessor I/O is interrupt driven. Where more than one I/O device exists, multiple interrupts must be dealt with. That is usually handled by an external interrupt chip, which accepts inputs from several sources and generates a single interrupt to the CPU. The chip also helps the microprocessor identify which external device generated the interrupt, so that the proper address can be put on the address bus for enabling that device interface prior to executing the I/O subroutine associated with it. Memory Mapped 1/0 Some microprocessors use a special form of I/O known as memory-mapped I/0. Special input and output instructions are not used. Instead, the existing LOAD and STORE instructions are used. In this method of input/output, a peripheral device is treated as if it were simply another memory location in RAM. In many microprocessor applications, the full amount of RAM isn't used. Those unused locations may be used for input/output operations. The external circuits or devices that are to send or receive data are still connected to the data bus and receive an enabling address from the address bus. To perform an input operation, a STORE instruction is executed. Recall that a STORE instruction simply takes the contents of the accumulator or some other register and sends it to a location in RAM designated by the address portion of the instruction. That address word identifies the external device to receive data. An input operation is performed with a LOAD instruction. The LOAD instruction finds a word at the address given in memory and transfers it to the accumulator or some other designated register. The external sending device simply appears to be a memory location where the desired word is. Other than that, the input/output operations are carried out in the same way. Either programmed or interrupt data transfers may take place. AUGUST 1988 65 +v r-----------------, I ' ACCIJMULAtOR DATA BUS (8 BITS) REGISTER I I MICROPROCESSOR (CPU} AD~~iss I 1 ________ ...J ---1---01 I LED INfflCATOR ~--,-+--O-l-1 _ \_ AND GATE __/ ......._ _1_1- - - - L--,...,,,,...... - -_,.--rr-1-1I - - - LOGIC c~~ml .f1_ L- - - - - - - - - - - - - INTERFACE _ _J Fig.3: inverters are often required ahead of some address lines, which feed an output interface, in order to provide the right combination of Os and 1s for decoding. The 6800 and 6502 microprocessors discussed previously in this series use memory-mapped 1/0 exclusively. Direct-Memory Access The third basic type of input/output operation is known as "direct-memory access" or DMA. As its name implies, input/output operations take place directly between the microcomputer RAM and the external circuit or device through an interface. The microprocessor or CPU is completely bypassed. Input/output operations using microcomputer instructions and causing data to be passed through the accumulator or a general purpose register and an interface are usually slow processes. While more than adequate for peripheral devices and circuits, there are applications where the processor cannot act fast enough. In those cases, DMA can be used. In DMA, the speed of the input/output operation is limited only by the RAM's read/write times. These are typically very fast, of the order of several hundred nanoseconds or less. For this reason, extremely high data rates can be achieved. This is necessary when dealing with high-speed peripheral devices such as floppy and hard discs. In data acquisition applications where high speed analog-to-digital and digital-toanalog converters are used, DMA is invaluable. To use DMA, some external circuitry is required. That is usually contained in a single-chip LSI circuit known as a DMA controller. It contains all the necessary logic and addressing circuits needed to perform the operation. As shown in Fig.2, the DMA is connected to the microprocessor as if it were an output device. In that way, the microprocessor can be used to set up the DMA controller prior to a given operation. For example, before the data transfer can occur, 66 SILICON CHIP the controller must know the starting address in RAM where the data to be transferred are stored. Alternatively, that address may point to the beginning of a sequence of memory locations where input data is to be stored. Using a special subroutine, the microprocessor sends the information to the DMA controller. The address is stored in a special address counter and placed on the microprocessor address bus. The DMA controller seizes control of the address bus and causes the RAM to recognise its address rather than the one directly from the microprocessor itself. The DMA controller also takes control of the data bus. As the data transfers occur, the DMA address counter is incremented. That causes data to be output from sequential memory locations to the external device or causes input data from the external device to be stored in sequential memory locations. Data to or from the external device or circuit are put on the data bus where the RAM circuitry accepts it and stores it. Alternatively, memory may put the desired data on the data bus which will be received by the external device or circuit. Finally, interrupts can be used with the DMA. The external circuit or device will still generate an interrupt to signal the CPU to initialise the DMA controller and begin a necessary data transfer. Microcomputer Interfaces An interface is the collection of logic circuits that connect an external device to the microcomputer. The purpose of the interface is to make the input or output circuit or equipment compatible with the microcomputer. That means taking care of such things as timing, intermediate storage, interrupt generation, voltage-level matching, and logic signal generation. ,---------------7 I 3-:~~JMus 5 51 · JE\Tffe\6E t------ I cout~iRs I --~ I I I I I I I I DATA BUS I I I I MICROPROCESSOR (CPU) I I CLOCK (COUNT INPUTI 3-STATE CONTROL LINE L _____ - - - - , LOGIC CONTROL PULSE fl I I IL I LOAO INTERRUPT FLIP-FLOP s:i -------- ~8Ei1 R,t----i,-CLEAR .n.. _______________ _ Fig.4: in this simplified input interface, a 3-state buffer can also represent a high impedance which effectively isolates the buffers from the line to which they are wired. The interface is generally unique to a specific external device. The logic circuits are assembled to specifically connect that device to the microcomputer and nothing else. Also called a device controller, the interface is sometimes included as part of the input/output device. In other instances, the interface is on a separate printed circuit board and often may be plugged into the bus of a microcomputer. You will also hear the interface called an 1/0 port. The interface performs one of the types of I/O operations that were described previously. Let's take a look at some of the circuit details of a typical interface. Output Interface Suppose that we wish to monitor the binary state of the accumulator in a microcomputer with LED indicator lights. That could be done with a simple output interface that accepts a data transfer from the accumulator register. Such an interface is illustrated in Fig.3. The heart of the interface is an 8-bit storage register where the accumulator contents will be stored. That register uses simple D-type flipflops and their data (D) inputs are connected to the eight lines of the microcomputer data bus. The load. strobe or clock input to the D-type flipflops (labelled T) is controlled by an AND gate, which performs two functions. First, it decodes the address from the address bus and accepts a logic-control pulse from the microcomputer, which causes the data to be strob- ed or loaded into the flipflops . Note here that only eight bits of the address are decoded. The number of bits that must be used in the address to identify an output port depends on how the address lines and memory are allocated. In some microcomputers, the entire 16-bit address will have to be decoded. In other cases, 1/0 ports are designated by only the lower eight bits of the address. In other situations, where not all of the memory is allocated, an unused memory address bit may be used to provide a simple single-line address decoding. As shown in Fig.3, inverters must be used ahead of some address lines in order to provide the right combination of ls and 0s for decoding. Inverters are needed on those input lines that will be binary 0, so that all inputs to the AND gate are binary 1 when the device is selected. In the example shown, the address being decoded is 10110011. To display the contents of the accumulator then requires that an output instruction be executed. For memory-mapped 1/0 microprocessors, a store accumulator instruction would be executed. That would cause the data to be loaded into the register and displayed on the LED indicators monitoring the flipflop outputs. Input Interface Now let's look at a simple input interface circuit. Suppose that you wished to monitor the content of a 2-digit BCD counter. The interface for such a circuit is AUGUST 1988 67 Fig.5: the programmable peripheral interface (PPI) is bidirectional. An 8-bit word sent on the data bus enables one or more ports and configures them for the desired mode. TO MICROPROCESSOR DATA BUS '-"--✓ shown in Fig.4. Clock pulses are stepping the counter for some application. The microcomputer needs this data to perform a computation. At a specific instant of time, the BCD numbers stored in the two counters are transferred to an 8-bit storage register. That is done by a logic pulse developed somewhere in the interface according to the application. This pulse does two things: it loads the storage register and also sets the interrupt flipflop. The output of this flipflop goes to the interrupt-request input line on the microprocessor, signalling the microprocessor that input data is ready. The interrupt causes the current instruction to finish executing; then the status of the processor is stored in the stack. An interrupt service routine is then executed. This is an input instruction that will cause the input data to be read in. When the input instruction is executed, the contents of the interface register will be transferred into the accumulator register. This is done by first activating the interface. The input in!;)truction or, in the case of memory mapped 1/0 microprocessors, the load accumulator instruction, causes an address to be placed on the bus, which is decoded by the interface. This enables the input interface. The decoding AND gate turns on the 3-state logic buffers connected between the interface storage register and the microcomputer data bus. Recall that 3-state logic circuits can assume the normal binary 0 and binary 1 output states but also have a high impedance state, which effectively disconnects them from the line they are physically wired to. Such buffers are required in bus-oriented systems where many systems and devices share a common bus. The 3-state buffers allow the different circuits to be connected to the bus when they are requested to send information. The bus may be continuously applied to any circuit input, but output circuits driving the bus must only be connected to the bus when data is being transmitted. In the interface circuit shown here, the address decoder will turn on the bus buffers, thereby allowing the data stored in the interface register to be placed on the bus and then read into the accumulator by the input instruction. Note that a control pulse from the microprocessor is also a part of the decoder AND gate input. That pulse will occur while the address is applied and will cause the register data to be strobed onto the bus as the bus buffers are activated. 1/0 Integrated Circuits While simple interfaces like those described above can be implemented with various MSI and SSI logic 68 SILICON CHIP DATA BUS BUFFERS iiii--wii-----1 A1- ----I 8 BITS PORT A 8 BITS 4 BITS PORTC VO 8 BITS 4 BITS PORT D VO 8 BITS VO CONTROL CIRCUITS A0- - - - - 1 8 BITS CS- - - < l l l (FROM ADDRESS --DECODER) BBITS VO INTERNAL CHIP BUS gates, in practice, most parallel data interfaces are implemented with special input/output integrated circuits. Those devices are designed specifically to connect microprocessors to external circuits and devices. Virtually all of the circuitry required in an interface is contained within these interface chips. Some examples of the most widely used interface chips are the Intel 8255, Motorola 6820/6821, MOS Technology 6522 and Zilog PIO. Those chips typically feature two or three complete parallel interface circuits that may be configured under program control for either input or output operations. Fig.5 shows a simplified block diagram of the Intel 8255 programmable peripheral interface (PPI). It consists of three input/output ports. These may be used independently for either input or output. Each port con. tains a storage register for holding data and also provides the necessary 3-state bus buffers. The configuration of the 8255 is determined by a special control word sent by the microprocessor as part of a program-initialisation sequence. That 8-bit word specifies which of the ports will be used, whether input or output operation is desired, and the desired mode of operation. That 8-bit word is sent over the data bus to the 8255 and stored in the control logic. There it is decoded and various logic circuits enable one or more of the external ports and configure them to the desired operation. The 8255 can operate in three basic modes. In the first mode, the three ports are simply configured for either input or output operation. One or more of them may be used. Note that port C is divided into two independent 4-bit sections. Those may be used separately or together as an 8-bit input or output port. The second mode allows only the use of 8-bit ports A and B. Port C, either onff or both sections, is used to accept "handshaking" signals from or to the peripheral .circuits. These handshaking or strobe signals allow the interface and microcomputer to communicate with one another. That permits the timing and control of the data transfers. The third mode is where only port A is used for both input and output operations. Again, port C is used for handshaking operations. TO MICROPROCESSOR DATA BUS DATA REGISTER A Fig.6: the peripheral interface adapter (PIA) has registers that store control words which designate the operation of the device. Each port has its own pair of registers. 8-BIT INPUT/OUTPUT REGISTERS j COIITROL REGISTER A DATA . . . - - - - - - - --., 1 REGISTER B 8 BITS 8 DATA DIRECTION REGISTER 8 Finally, note the control signals that come into the 8255. The CS line means chip select. Usually the output of a NAND gate address decoder is connected to this line. That enables the chip when the proper address is received. Input bits AO and Al are the two lower order address bits from the address bus. Those are used to select which of the three ports or the control word register is to be selected by the CPU to send or receive data. The RD and WR control signals are strobes from the microprocessor that cause data transfers to take place. CONTROL REGISTER 8 INTERRUPT ADDRESS LINES 1/0 PORT CONTROL LOGIC INTERRUPTS Programmable Interface CHIP SELECT "I•- - -- _J t Another example of an LSI interface chip is the Motorola 6820 or 6821 programmable interface adapter (PIA). That device contains two fully configurable 8-bit data ports, A and B. A simplified drawing of the chip is shown in Fig.6. It contains two data registers used for storing data temporarily in either an input or output operation. Associated with each of the data registers is a datadirection register (DDR) and a control register (CR). The registers are loaded with control words from the microprocessor and these words designate the operation of the PIA. The DDR word configures the 1/0 registers for either input or output operations on a bit-by-bit basis. The control register sets up various control lines for use as interrupts or handshaking lines with the peripherals. The control logic processes the interrupts, helps select the chip, and determines which internal register receives data from the microprocessor bus by interpreting the input address lines. -DATA WORD-------1 L I 1I , J STOP BIT$ PARITY AXED BIT INTERVAL DETERMINES TRANSMISSION SPl:ED IN BAUD BIT Fig.7: in an asynchronous serial-data transmission, bits representing data are flanked by start and stop bits that tell the receiving equipment when to expect data and when the data is complete. The parity is a form of self-test or it can be part of the data. 0 ~ 1 :i. •25 ----+15V - - - - +12/ - - - - + 3 V _ __,__ _ ----ov ---+--- tv -----12V-----L...\--- -- - - - 1 5 V ---+-- VALID LEVELS ON-SPACING BINARY 0 TRANSITION REGION INVALID LEVELS VALID LEVELS OFF-MARKING BINARY 1 TYPICAL SIGNAL SWITCHING BETWEEN -12V(1) AND +12V(O) • ••• •• •• •• • • •• •• •• •• PIN FUNCTION 2 3 TRANSMITTED DATA RECBVED DATA REQUEST TD SEND CLEAR TO SEND DATA SET READY SIGNAL GROUND RECBVED LINl: SIGNAL DETECTOR DATA TERMINAL READY 4 5 6 7 8 20 •14 0 REAR VIEW 25-PIN II-SHELL CONNECTOR Fig.8: RS-232 signals operate between ± 12 volts. Special circuits convert these signals to 5-volt TTL levels and back again. AUGUST 1988 69 Overall, both the 8255 and 6820 are extremely flexible 1/0 circuits that can be configured to deal with almost any type of external circuit or peripheral device. Serial Interfacing So far, all we have talked about are parallel interfaces, those that move data in parallel 8-bit chunks. The data path into and out of a microprocessor is the parallel-data bus, so it makes sense to move data in that format. It is fast and convenient. However, there are occasions when serial data must be used. One example is where data is to be transmitted to and received from a floppy or hard disk. Another example is where data is to be exchanged with a video terminal or some data communications device such as a modem. In those cases, data is sent in 7 or 8-bit segments, one bit at a time. Most data transmitted serially in this way are ASCII characters. Recall that the ASCII code represents letters (both upper and lower case), numbers, punctuation marks, and other special symbols as a 7 or 8-bit code. The format of a serial data word is shown in Fig.7. To the data bits is added a start bit to indicate the beginning of the word, a parity bit which is used for er ror-detecting purposes, and one or two stop bits to designate the end of the word. Each bit occurs for a specific duration. The shorter the duration, the higher the transmission rate. The transmission rate is normally expressed in terms of baud, where one baud is approximately one bit per second. Typical standard baud rates are 300, 600, 1200, 2400, 4800, 9600 and 19.2K. To send and receive such serial data, a specific interface is required. The major elements of such a serial port include bus buffering, address decoding, parallel/serial conversions, logic control, and logiclevel matching. The main purpose of that interface is to provide parallel-to-serial conversion for output data and serial-to-parallel conversion for input data. The interface should also add, extract, and respond to the stop, start, and parity bits. Further, it should control the transmission/reception baud rate. Finally, the interface must make the external serial device compatible with the interface. That generally means using the proper connector and signal connections as well as logic-voltage levels. Most serial devices conform to the popular RS-232 interface. That is an Electronics Industries Association standard that SHORT QUIZ ON DIGITAL FUNDAMENTALS 1 . List the basic types of 1/0 methods used in microcomputers. a. LESSON 9 6. The program used to service a request for an 1/0 operation is called a(n) _ _ _ _ _ _ _ __ 7. In OMA 1/0, data transfers take place between the _ _ _ _ _ _ _ and the _ _ _ _ _ __ b. c. 2. What register in the CPU is usually used for 1/0 operations? a. instruction register b. program counter c. accumulator d. address register 3. An external signal that signals the CPU for an 1/0 operation is called a(n) _ _ _ _ _ _ __ 4. The stack is a(n) : a. set of registers b. read-only memory c. first-in first-out memory d. area in RAM for temporary storage 5. Which type of 1/0 makes the most efficient use of CPU time? a. interrupt b. programmed c. memory-mapped d. OMA 8 . Treating a memory location like an 1/0 port is called _________________ 9. The circuit that connects the computer to the external device is called a(n) _ _ _ _ _ _ __ 10 . What circuit acts as inputs from a peripheral a. register b. 3-state drivers a buffer between the device and the CPU? c. decoder d. multiplexer 11 . The most commonly used serial interface is the __________________ 1 2 . What is the name of performs serial-to-parallel conversions? a. PIA b. OMA the LSI circuit that and parallel-to-serial c . PPI d . UART 1 3 . Serial data transfer speed is expressed in either ________ or _ _ _ _ _ _ __ ANSWERS (puooas Jad si1q) sdq JO pneq '£ ~ ll::IVn ·p ·c: ~ C:£C:·Sl::I Vl3 . ~ ~ sJa11pp aiei s-£ ·q ·o ~ a0BJJatU! '6 70 SILICON CHIP O/1 paddew-AJowaw ·g ao111ap O/1 pue AJowaw · L au1in0Jqns ·9 tdOJJ8lU! ·e .9 a6eJots AJeJodwai J0J pasn I/\IVl::I LI! eam ·p ·v tdOJJatU! '£ Jote1nwnooe ·o ssaooe AJowaw ioaJ!P ·o 0/1 tdnJJ8lU! ·q O/1 pawweJ60Jd ·e . ~ ·c: ,------------------~I I STOP PARITY START I I m -~- m __ I TO DATA BUS MICROPROCESSOR DATA BUS ..,.__ _,,. BUFFERS I I ...,__.__...__ _._~ SHIFT REGISTER I I I SERIAL 1----,,-DATA OUTPUT TRANSMIT CIRCUITS RS-232 INTERFACE ClRCUITRY I PARITY CHECK I _____________ UART_j CLOCK (SETS BAUD RATE) ADDRESS DECODE - . . , _ _ . J Fig.9: block diagram of a UART. It is capable of full duplex operation. specifies all of those characteristics. They are summarised briefly in Fig.8. The UART The main logic functions of the serial interface are usually taken care of by a special LSI serial interface chip called a UART, or universal asynchronous receiver transmitter. A simplified block diagram of a UART integrated-circuit chip is shown in Fig.9. Bi-directional data-buffers connect the CPU data bus to the UART. Inside the UART, there are two separate sections: one for transmitting, the other for receiving. The heart of each section is a shift register that performs the parallel-to-serial or serial-toparallel conversion as required. Other logic circuits add the stop, start and parity bits in the transmit mode, or extract and respond to them in the receive mode. Most UARTs can operate full duplex, meaning AC millivoltmeter - SERIAL --DATA INPUT RECEIVE CIRCUITS cs L_ _ _ - SHIFT REGISTER CONTROL --..;..._- CONTROL LINES LOGIC send and receive operations can take place simultaneously. The UART chip is set up and controlled by the host microprocessor. Special data words transmitted to the UART specify things like baud rate; 1 or 2 stop bits; odd, even or no parity; and data word length from 5 to 8-bits. A short initialising subroutine in the main program sets up the UART prior to its use. Another way to create a serial interface is to do it with software. A short program can be written to do the parallel/serial or serial/parallel conversions, deal with the start, stop and parity bits, and provide the timing for the desired baud rate. We will show you how that is done in the next and final instalment of this series devoted to microprocessor programming. lltl Reproduced from Hands-On Electronics by arrangement. (c) Gernsback Publications, USA. ctd from page 23 resistor (or shorted, according to the manufacturer's specs). The amplifier's output voltage will then drop to a very low value. The next step is to move the Mode switch to the Noise setting. The Noise range switch should be at the 0dB setting. Now we switch down the input attenuator until a reading above 1/3 of meter deflection is obtained. If the amplifier is any good (ie, reasonably quiet), very little pointer deflection will be obtained even on the lmV range. At this point, we are measuring a signal which is better than - 90dB with respect to the amplifier's rated output voltage of 21.9 volts. (Remember each change of range on the input attenuator corresponds to todB). To increase the gain of the measurement, we start rotating the Noise range switch until the meter's pointer moves up the scale. That may be obtained with the Noise switch on the - 20dB range. If the pointer is indicating - 4dB, the overall signal-to-noise ratio of the amplifier is - 90 + - 20 + - 4dB = -114dB. This is a measurement of the wideband residual noise. For most hifi equipment this measurement would be taken with the 20Hz to 20kHz filter selected which will normally improve the measurement slightly, to say, - 116dB. If an 'A' weighted measurement is taken instead, the reading may improve slightly again, particularly if there is hum in the residual noise. The procedure is similar when measuring separation between channels of a stereo amplifier, except that the Flat filter condition would be selected. Next month, we will conclude the description with the info on construction and calibration. lltl AUGUST 1988 71 JAYCAR No.I FOR BARGAINS rn;®IT<at>Jj)<at>®IB Evir®<at>l<at> BAR.GAIN Electros Cassette Microphone Bargain Evir®fi<at>~ Wfil1\1<at>IT We are hopelessly overstocked and need to move some electros. Brand new, 1st grade quality RT style 4 70uF 50V RT Normally $1.90 ea YID filrr{! ®fi<at> AUGUST PRICE 10 for $2 Famous Sanyo brand hand held small microphone fitted with cable and 3.5mm plug. Normally worth about $10. Limited quantity. Cal. AM-4095 Another scoop purchase. This ti me a quality, high pertormance 4 amp 240V PCB mount mains fi lter. The schematic and pinout of the filter is printed on the top of the 45(L)x28(W)x 16.5(H)mm potted plastic case. The unit has all of the major electricity authority approvals (German, US, Canadian, elc) marked on It as well. It has twin series chokes (2 x 1mH) MKT and MKP quality mains caps as shunts. As a filter It is very effective. This product sells to OEM's in OOO's for about $19. Due to the enormous loss that the distressed manufacturer made when selling the goods to us you will pay almost hatt this one offll The quantity is limited and it is a once only offer. OEM's. We can supply this to you at a great price! Call nowl Cat. MS-4008 $9.95 10 up $8.95 ea I !"_RA~~!!;~~o~!/:E (BC557 equivalent) Cat. ZT-2295 Normally 15e each • · THIS MONTH 20 for $1 2. 2N5400 : PNP TO 92 120V 600mA ~ Cat. ZT-2370 Normally 30e each ~ THIS MONTH 20 for $1 TIT, 31/fll,81 Infra Red LED & Photo transistor Originally, these were used in the EA Opto Ignition kit back in about 1983. ; T IL31 Infra Red LED T0 18 NORMALLY $1.50 Cal. ZD- 1952 TIL81 NPN Phototransistor T0t 8 NORMALLY $2.00 Cal. ZD-1 953 AUGUST SPECIAL $1.50 per pair SA VE $2.00 lUlL TIP?.A § (0) NII <C JFIE § 'J[' A IP?.IEJFIE lL lLIE IP?.§ IP?.IE JI)) 1'J <CIE 0 Pestrepeller is effective in controlling mice, rats, roaches ants, fleas , crickets, silverfish, wale rbugs , moths and most other common pests. Laboratory research has shown ultrasonic sound waves attack the auditory system and nervous system of most common pests causing them pain and discomfort. 130dB's of sound waves are out of the range of hearing of humans and most household pets such as dogs, cats, fish and farm animals. Supplied with 240V adaptors. NEW MODEL NOW AVAILABLE with DUAL TRANSDUCERS Special Introductory Price ONLY $39.95 ONLY $2.95 Cat. RE-5905 1OOuF 25V RT Normally 55e ea AUGUST PRICE 10 for 60ft Cat. RE-5880 KIT SPECIALS FOR AUGUST • Baby Minder (ref: ETI April 1988) Cat. KE-4732 WAS $34.95 NOW $22.95 SAVE $12 • Telephone Intercom (Ref: ETI Feb 1988) Cat. KE-4731 WAS $59.95 NOW $39.95 SAVE $20 • Line Grabber (Ref: SC Mar 1988) Cat. KC-5025 WAS $19.95 NOW $12.95 SAVE $7 • Modem End File (Ref: SC Feb 1988) cat. KC-5024 WAS $9.95 NOW $5.95 SAVE $4 • ETl340 Car Alarm (Ref: ETI April 1984) Cat. KE-4678 WAS $79.50 NOW $59.50 SAVE $20 IGHQUALITY ULTIMETER EADS • Supplied complete with heavy duty cable • Right angle banana plugs with plastic sleeve • Finger protection built into the probes Cat. WT-5318 NORMALLY $8.95 pair AUGUST ONLY $5.95 SAVE$3.00 12V CAR ANALOGUE CLOCK MOVEMENT MASSIVE SCOOP PURCHASE! Grab a quartz crystal car clock with a set of automotive style hands at a price that wi ll astonish youl Once again our suppliers huge loss is your gain I Convert that broken unreliable or inaccurate mechanical clock in your car to space age precision! Made in West Germany by VDO, the module measures roughly 45 x 38 x 40 deep. The compact size virtually ensures that It will flt in any space! Quantity strictly limltedl ONLY $9."c- 5 Cat. XC-0108 8" White Cone Woofer ~~[Rl<at>~ □ [N] D D D D D a D a D D D Best looking and sounding 8' woofer we've ever seen for the price. White cone, large magnet 10oz, roll surround Power Handling : 30 watts rms Resonant Freq. : 45Hz Freq. Response: 45 • 5000Hz l"1)8dance: 8 ohm Sensitivity: 96dB Cat.CW-2111 NORMALLY $26.95 AUGUST SPECIAL ~ $19.95 each ' .,,, _ I 1 SAVE $10 ON LOGIC TESTER ~ Now direct imported, we can pass on the savings to you. Will test all logic famllle~ (ffi, LS, CMOS , etc) / SPECIFICATIONS Working Voltage: Current Consurf'4)tion: Frequency Reponse: Response Puise Width : ; ,, ,, . / DC 4 • 16V Max 32mA at 5V Max 20MHz Longer than 25nsec ~i :~ !f~1' ~>i NOW ONLY $29.95 ,, ~·,. ) / " Cat. YS-5512 Single Unit still available SAVE $10 on catalogue price Only $29.95 Cat. YS-5510 ..."" ,~"'- C "b--\- ! ~a~e~~I! s: c~~~!2s~~=~ of R used in kits. Size : 200 x 24 x 20mm ~ r : es. These are constant~ . obe c~ ---===::J _ ---m1illffllllllll-l AND MORE BARGAINS SENSATIONAL SCOOP PURCHASE! ONLY $99.95 Enjoy a "SOUNDTRACKER 1" Video Processing centre for less than 1/3 the cost of recent retai l. The Soundtracker 1 Is a U.S. made video graphic equaliser. mono to stereo digltal synthesiser and noise reduction unit. It goes between your VCR and audio arrp to enable you to apporach that cinema sound of the movie theatre! If you have, for example, a mono (fixed head) VCR - the most common type by far - you probably only play the audio back thru the TV set speaker. If you were to play the one chan nel sound thru a HI Fi you would notice 3 things, tape hiss similar to cassette hiss, poor frequency response .and poor dynamic range apan from the fact that Its still MONOI The Soundtracker 1 can help most of these things, but only to a degree. It has a 5 band graphic to improve Bass, treble, muddy mids, etc. It has a noise gate to help reduce annoying tape hiss and It will synthesise a STEREO signal as welll It also works with stereo VCR's . They were on the market for around $379 and at that price were a FLOP. For that money, plus a little more you could trade in the old VCR and buy a 6 head Hi Fi stereo VCR. But not everyone has $1500 odd to spend on a fancy VCR, nor $379 for a gadget no matter how useful! So Jaycar bought the imponers stock at a way below cost end-of-financial year price. The result Is that you (once again) get a fantastic BELOW COST bargain. But hurry, stocks are genuinely limited on this quality made U.S. product. You can grab one ex these at a never-to-be-repeated prcie of $99.95, that's right! less than 1/3 of the price that sold thousands. • , Sorry, no room for specs - just buy one I Cat. AV-6500 HIGH VOLTAGE CAPACITOR PACK This Is rare. Attention servicemen. We can offer you a bag d over 175 pcs of both high quality Polycarbonates and ceramic capacitors. Many of these are from current colour TV manufacturers surplus. Limited quantity, and probably will never be repealed . (We rarely see high quality high voltage caps anymore). Here's what you get : Polycarbonate We have many different values in small quantities so most bags will be different. Higher quantities include: 0.0056, 0.047, 0.068, 0,056, 0.1, 0.18, 0.22, 0.27, 0.33, 0.56, In voltages 200V, 400V, 630V, 1.5kV, 1.6kV, 2kV Ceramic: Include a good range of values. 100pF, 220,270,330, 470, 500,680, 1000, 2200, 4700pF in voltages 400V, 500V, 1kV, 2kV and 3kV. DON'T MISS OUT!! LIMITED QUANTITY!! WON'T LAST OVER 175 CAPS FOR $10.00 ~ C a ~ ?~ ~ Clock Movement Accessory ~ ~ [LJ,©Ml WAS $14.95 NOW $6.95 SAVE $8 Another Jaycar scoop purchasell Installers please notell Quality AIR SPACED coax at 1/2 our usual price. Available in 4 different roll lengths. Normally sells for $1.20 per metre. Special price only applies to purchases of full rolls as listed below. 50 metre roll Cat. WB-2020 • MD-202 12 Songs Plus Chime Cat. XC-0122 ONLY $30 SAVE $30 WAS $14-95 NOW $6.95 SAVE $8 60 metre roll Cat. WB-2021 • Pendulum Driver Cat. XC-0110 ONLY $36 SAVE$36 WAS $14.95 NOW $4.95 SAVE $10 65 metre roll Cat. WB-2022 • Quanz Movement with Switch Contacts - to suit all the above Cat. XC-0105 ONLY $39 SAVE$39 See our 1988 catalogue for full specifications • MD-01 Melody Module - 12 songs Cat. XC-0115 WAS $12.95 NOW $4-95 SAVE $8 • MD-02 Westminster Chimes Cat. XC-0120 WAS $16.95 Cat. RZ-6695 $12.50 SAVE OVER 60% 1J~gJ<II~RF CHOKE PACK Over 50 pieces supplied I A pack d 30 brand new RF chokes with at least 14 different values I Popular values include: 1.5, 4. 7, 12, 15, 18, 22, 68,100 & 1000uH. Each choke is resin dipped and colour coded ~hey look like bead tantalums). A colour coding chart Is supplied so that you can decipher the value. BONUS I Not only do you get 30 useful chokes we will give you at no extra charge at least another 30 more RF chokes I These are genuine chokes but are commonly called 'peaking coils'! They look like a 1/2 watt resistor. (Read the choke value in uH as you would a resistor value). WAS $3.95 NOW $1.95 SAVE $2 Digital Alarm Thermometer/Clock This great new product has a built-in temperature sensor, so displays the terrperature in both Celcius and Farenheit. It also tells the time. An alarm will sound when the temperature falls below or above a preset temperature. Handy pocket size, measures 53 x 82 x 22mm. Temperature measuring range -20"C to 70°C O"F to 160°F. Use one AAA battery. Cat. XW-0390 ONLY $10.00 WAS $27.95 SAVE $8 NOW ONLY $19.95 UHF TV TUNER Sanyo Model T1087 RA II!"!"~~ Yet another fabulous scoop purchase. A compact high quality tuner that operates from 526814MHz (corresponding to channels 28 thru 63). This tuner Is designed for Australian standard reception (AS1053 1973), and Is offered at a very low price. You can grab one now for the silly price of $29.951 This price includes circuit diagrams and connection drawing. You can have a photocopy of the complete manual for $4 but a lot of the Info Is in Japanese! This is a very cheap way to conven a VHF only TV to UHFI (Some skill may be required) . Spees: Power+ 12V DC nominal<at> 14mA. Case neg. Bandwidth 526-814MHz (28-63 eh). AFT +6.SV. Dimensions 150 x 65 x 28mm. Tuning multi rotation of 1/4" shaft. Knob not supplied. $29.95 Cat. DM -1 000 LCD Thermometer Travel Alarm Clock Credit card size 85 x 55 x 8mm thick and is supplied in handy wallet. Loud alarm and snooze function. Easy to use. Degrass in C or F. Uses one LR-44 battery. Has quanz accuracy. Cat. XW-0392 $29.95 NORMALLY SAVE $8 ONLY $21 .95 " ~ t} I i'i I ' ;I \ , \ ~:::::::;;.:,;;;.;_______.====~ 4 Cat. RC-5600 SAVE $42 • "Twinkle, Twinkle little star" module Cat. XC-0130 Capacitor Pack Tantalums are getting more expensive all the time. Due to a very large bulk purchase, we can offer you a mixed pack of over 50 Tantalums. Over 40 of these are tag type, and the rest high quallty rrilltary spec RT style which are wonh up to $5 each. A typical pack will include: TAG STYLE 2 x 0.33135V, 10 x 2.2/16V, 5 X 6.8/6.3V, 1 X 0.15150V, 20 X 4.7/16V, 1 X 4.7/25V, 3 x 68110V, 1 x 100/ 16V. RT STYLE 1 x 0.1/ 35V, 1 X 0.22135V, 1 X 0.33135V, 1 X 0.68135V, 6 X 15{ 20V, 1 x 32/35V, 1 x 47/20V. We reserve the right to make changes Wstock shonages occur. This is a once only offer. Doni miss out. OVER 50 TANTALUMS FOR ONLY $12.50 Over $35 wonh of Tag Tantalums alone, without taking into account the expensive Milspec style also supplied. Cat. WB-2023 NOW $14.95 SAVE $2 ~""'···-- \ AND MORE BARGAINS HALF PRICE POT PACKS Slider Pots A pack of at least 35 potentiometers which Includes slider pots - single and dual, an assortment of pots and lab style pots with assorted shafts and a slection of quality 5mm vertical sealed trimpots and open 5mm horizontal styles . This represents excellent value at $10 Cat. RP-3902 NORMALLY$10 You don't see this very often. A pack of 20 sliders in assorte values between 5k and 500k. 20 for $1 0. That's only 50t each I The majority In the pack are dual gang which have been selling for $5.50 each. A typical pack includes values such as 51<, 50k, 1OOk, 250k, and 500k in 45 and 60mm lengths in single and dual styles GET A PACK WHILST THEY LAST Cat. RP-3903 NORMALLY$10 SAVE 50% $5 per SAVE 50% $5 per Mixed Pots . i Utility Box ◊ Ideal system for the serviceman , or mobile workshop, or just to keep all those resistors and capacitors tidy. Also ideal for fishing tackle boxes and many other uses. Six of these utillty boxes will fit snugly into the carry case pictured. Size of utility box 188 x 115 x 36mm. Colour opaque white. Cat. HB-6310 $2.29 ~ffi\[ffi<at>ffi\000 ~ -- without the cable grommet. NORMALLY $3.95 Limited quantity Cat. PP-1400 10 up $1.75 each TELEPHONE DOUBLE ADAPTOR SENSATION t, <;:J ~~(W<at> ONLY $1.95 ea .,, ~~ '\\ 't ,t · +f ,,,,, pack ~ .. ~ • -'" ~ ---- - - -.:,ii ~ ~~~~~~©00~ - .1 ~----------------------- , ~<at>ll©l<at>IT IB.<at><at>ll = WAS $7.95 SAVE47% ll<at>\W<at>!l' JJ)!l'fi©<at> 200 gram reel. 1mm universal gauge. Sultable for all types of electronic soldering. / ... · Resin cored and including bit saving additive.( ·.'~ ' ·· .·. Cat. NB-3010NEW LOWER PRICE I $6.95 (f:'~_d'. 10 up $6.50 \ ~ ,/ Cat. XT-6020 $3.95 ea ' _., · 'BICENTENNIAL" LIGHTS IN YOUR OWN HOME! 10 up $2.10 ea Utility Carry Case Spec~ically designed to hold 6 utility boxes snugly to give a 30 compartment totally portable parts storage system. Size 365 x 210 x 80mm. Colour white. Cat. HB-6312 $17.95 SPECIAL INTRODUCTORY OFFER 6 • UTILITY BOXES AND A CARRY CASE FOR ONLY $ 28.95 • SAVE $ 2.74. I Now Illuminate your garden, trees or windows with this low volatge lighting systeml can have the same beautiful 'firefly' lighting that is all over the civic squares around Australia. I Until you now weatherproof outdoor low wattage festoon lighting simply has not been available. That is behind us, because Jaycar has an exclusive outdoor/indoor lighting kit to enable you to beautify your home or garden. Each festoon set I comprises a 6 metre cord with 20 lamp bases moulded in parallel onto the cord at 300mm intervals. (At the end of the is a clear 700mm of cord.) Each lamp base is fitted with a 12V 50mA globe and clear polycarbonate weatherI festoon proof cap. The entire festoon draws, of course, 1 amp AC or DC, only. THE RATED LAMP LIFE IS 20,000 HOURS I Each lamp Is in parallel and In the likely event of an Individual bulb failure THE REST STAY ON (unlike cheap series I type festoons). The 'Pixiel1te· festoon is moulded in water clear plastic. At one amp per festoon a cheap 2155 type (Cat. MM-2002 $10.95) is all you need for power. The festoon, however, is NOT CHEAP. It is a quality made I transformer in Australia product designed to last a l~etime. A 6.7 metre 20 lamp festoon will cost you $49.95. You can buy a mixed I bag of coloured caps (red, amber, green, blue, 5 of each) to convert the festoon for Christmas use - it will last MANY II I I I I I I ~:is~~-;:;~ I $49.95 Festoon Set I Cat. SL-2805 I g $9.95 Bag of 20 coloured caps., Q - 1 - ·. ~ ~~ {i::.:_J ~ ~ \1 - I ~ ....-::;,,,,-· - . ~ - - - - - - - - - - - - ~ · - ______ __ J 6" x 2" SPEAKER!!!! Yes, a 6" x 2" speaker, that's 157 x 57mm. The size may be strange, but the quality certainly Isn't. They are Japanese made, with a large magnet. It even has a foam roll surround. These were used in colour TV's, so the quallty is excellent. Sanyo brand a ohm 5 wan. Limited quantity. These would probably cost $30 as a spare partll Cat. AS-3030 $4.95 ea This cord has a moulded 2-pin (i.e. no earth) approved plug with a very generous 3 metres of flex stripped and tinned at the end. Ideal as a replacement lamp cord or any long cord that need not have an earth. Worth $3.95 Cat.PS-4 112 ATTENTION PA INSTALLERS Jaycar can offer GREAT prices on 8'' twin cones eakers and plastic grills. 8 Ohm 10 watt Speaker $13.95 10 up $13.50 Cat. CE-2325 4 Ohm 1Owan Speaker $8.95 10 up $8.00 Cat. CE-232 8" grill to suit both speakers $3.95 10 up $3.75 Cat. AX. .. -.~---~ .,t ·•· ...,..._,_ ,· DUTY SPEAKER FLEX Cat. WB-1712 $1.50 metre BREADBOARD JUMPER KIT?? $120 per 100m roll ~ =· We supply a pack with 5 metres of ideal size for breadboards. All yoo n requireandstrlpthe end 'Practical MIDI Handbook' 2-Wire AC Mains 7.5 Amp Flex .. HEAVY Doni pay through the nose for heavy duty speaker flex. High quality figure 8 speaker cable 2 x 7910.2mm strands in a white covering with black trace. , ::--: Low Cost Direct Imports for the U.K. 10+ $4.50 ea THIS MONTH $2.00 NEW R.A Penfold. 215 x 140 (soft) 150 pages The Musical Instrument Digital Interface (MIDI) is a subject that many people have heard of but know little about. Many electronics magazines produce MIOI type electronic projects and these are proving to be reasonably popular - especially in the U.K. This book is primarily aimed at the musician who has some technical knowledge of electronics. It explains what MIDI is, what MIDl's vast capabillties are, how to interconnect, etc. Special emphasis is placed on MIDI and computers and operating a MIDI connected system. An excellent book. Cat. BP-1202 $17.95 'Practical Digital Electronics Handbook' By Mike Tooley 215 x 140 (soft) 198 pages The vast majority of modern electronic systems rely heavily on the application of digital electronics. This book aims to provide readers with a practical introduction to the subject. Anyone involved with the design, manufacture or servicing of digital equipment should find the book invaluable. Anyone just interested in the subject will find it rewarding. The book Introduces basic digital concepts and covers such areas as Logic gates, bistables, timers, etc. It quickly moves on to microprocessors, support devices and lnpuVOutput (VO) devices. The popular RS232C interface is discussed in detail as well as the general purpose instrument bus IEEE-488 and finally the IEEE-1000 based microprocessor bus. Test gear projects are also shown for the reader to contruct. An excellent book on this subject. Cat. BP-1204 $19.95 I LOW COST CAPACITANCE METER GUITAR PRACTICE AMP Ref: EA August 1988 Turn your analogue or digital multimeter into a direct reading capacitance meter. Will read a capacitor in the range from 3.3pF to 2000uF Cat. KA-1700 Ref: AEM August 1988 Short form kit, includes PC board and components . Uses a single chip 8 watt audio power amp. Suggested speaker is our NZ made 8" 4 ohm twin cone 10 watt Cat. CE-2322 $8.95 $16.95 1----------------t UNIVERSAL POWER SUPPLY · RECEIVER KIT Cat. KC-5037 $12.95 • ~, ~ TURN YOUR SURPLUS STOCK INTOCASHII Jaycar will purchase your surplus stocks of components and equipment. We are continually on the lookout for sources of prime quality merchandise. CALL GARY JOHNSTON OR BRUCE ROUTLEY NOW ON 02 747 2022 Ref: Silicon Chip August 1988 Change your voice to sound like Darth Vader from Star Wars. Full kit including box, mic insert and speaker Cat. KC-5039 $19.95 MAIL ORDERS POST & PACKING 115 Parramatta Road Concord 2137 P.O. Box 185 Concord 2137 HOTLINE (02) 7471888 $25 FOR ORDERS ONLY $50 Telephone (02) 747 2022 Telex 72293 FACSIMILE (02) 744 0767 MAIL ORDER VIA YOUR ~~ ';' VISA $16.95 $42.50 VADER VOICE HEAD OFFICE · t .._..,.___....._.._.._.._.......,._....._. I ■ $19.95 Ref: Silicon Chip August 1988 What a great idea. A wireless doorbell with the option to have as many sounders as your house requires. Transmitter is mounted in a UBS Jiffy box with a pushbutton switch which mounts outside your front door. Powered by a 9V battery. Receiver mounts in plastic box and requires a 12V DC plugpack. our MP-3006will do $14.95. Use as many receivers as you require. TRANSMITTER KIT Cat. KC-5036 Ref: Silicon Chip August 1988 This small kit enables you to obtain +15V, -15Vor±15V DC from two different transformers. Kit includes PCB and all components for either supply, less transformer. Transformers to suit: 2851 Cat. MM2006 $5.95. 2855 Cat. MM2007 $6.95 Cat. KC-5038 1 Cat. KM-3069 WIRELESS DOORBELL TOLLFREE (008) 022 888 ff fi 0 ~~;n ~ ~.~ 9 $4999 $ 4.50 $99.99 $ 6.50 OVER $100 $10.oo ROAD FREIGHT ANYWHERE IN AUSTRALIA $13.50 SYDNEY - CITY 117 York St. (02) 2671614 - GORE HILL 188 Pacific Hwy cnr Bellevue Ave (02) 439 4799. Mon-Fri 9 - 5.30 Sat 9 - 4pm CARLINGFORD Cnr. Carlingford & Pennant Hills Rd (02) 872 4444 - BURANDAQLD 144 Logan Rd (07) 393 0777 Mon-Fn 9 - 5.30 Thurs 8.30 - Sat 9 - 12 Mon-Fri 8.30 - 5.30 Thurs 8.30 pm- Sat 9 -1 2 Mon-Fri 9 - 5.30 Thurs 8.30 pm - Sat 9 - 2pm 115 Parramatta Rd (02) 745 3077 Mon-Fri 8.30 - 5.30 - Sat 8. 30 - 12 MELBOURNE-CITY Shop 2, 45 A'Beckett St City (03) 663 2030 121 Forest Rd (02) 570 7000 Mon-Fri 9 - 5.30 Thurs 8.30 pm - Sat 9 - 12 SPRINGVALE VIC Mon-Fri 9 · 5.30 Fri 8.30 · Sat 9 · 12 887-889 Springvale Road Mulgrave (03) 547 1022 Nr Cnr. Dandenong Road Mon-Fri 9 - 5.30 Fri 8.30 - Sat 9. 12 PT.10: ELECTRIFICATION IN CENTRAL EUROPE THE EVOLUTION OF ELECTRIC RAILWAYS In this chapter we look at the electrification of Central European railways, ponder on some interesting synchronization problems and discuss the Germon development of cycloconverters. By BRYAN MAHER Switzerland, lacking indigenous coal supplies, had experienced great difficulty supplying her steam locomotives during the 1914-1918 war. Consequently, as soon as peace reigned again in Europe, the Swiss Federal Railways (SBB) set about electrifying all their main lines. Taking the highly successful example of the Bern-LotschbergSimplon railway system and the current work then developing on the Lappland Railway (see previous chapters), the Swiss Federal Railways also opted for a 15kV, 16.6Hz AC system, using series AC motors. Even though such motors do have a commutator and brushes, necessitating regular maintenance, the very high starting torque and variable speed characteristics were predominant advantages. Beginning, as was the custom of the time, with rod-drive locomotives, the Swiss Federal Railways built particularly powerful locos. This was by necessity, as the main line around their country has only two choices: go over every mountain in its path or go through them, steep gradients of 1 in 40 or more being common. Because one of their most successful steam locomotives in the pre-electric era was the 1913 type 2-10-0 design, the Swiss elected to build electric locomotives which also had large numbers of driving wheels. Their first example was an articulated electric locomotive having a two-piece hinged mainframe with one cab riding over all, the wheel arrangement being equivalent to 2-6-6-2; ie, twelve driving wheels. In electric locomotives this arrangement is called a "1-C-C-1" type, the translation being that "C" stands for three driving axles, the "1" meaning one non-driving axle as used in leading or trailing bogies having smaller diameter wheels. Smaller diameter leading bogie wheels help locomotives to follow curved track at high speed, as the smaller diameter wheels do not tend to ride up over the outside rail on curves. Being long and articulated, the 1-C-C-1 types earned the nickname "crocodile". Swiss loco classification A problem with electrifying existing tunnels for high voltages is the clearance needed by high-voltage insulators above the train. In some cases, this has required modification to the tunnel roof. (Photo SJ). 76 SILICON CHIP The Swiss invented their own classification of locomotive wheel arrangements. They give the 1-CC-1 type the classification "Ce6/8". The first upper-case letter is a maximum speed rating, the small "e" following means "electric" and "6/8" means six driving axles out of a total of eight axles. The speed rating letters originally chosen Concrete sleepers are now used by the Swiss Federal Railways in place of the older wooden sleepers. The overhead wires carry 15kV 16.6Hz AC. (Photo SJ). were "A" for highest speed, with successive letters meaning lower speed ratings, the slowest being "E". Thus the Ee3/3 class built in 1928 was limited to a top speed of 40km/h and was used for shunting service. The 3/3 means that three axles out of a total of three were driven. The "C" classification usually meant a speed rating of around 65km/h, "B" meant 70 to 80 km/h and "A" was applied to locos rated between 90 and 12 5 km/h. The Ae4/7 of 1927 was therefore an example of one of their top speed locomotives of the day, being rated at 100km/h. It also had a maximum starting tractive effort of 196 kilonewtons supplied by a traction motor-to-driving wheel gear ratio of 1:2.57. Their classification system presented a small problem in 1964 when a locomotive rated at 149km/h was built, as there is no earlier letter than "A" in the alphabet. This problem was overcome by using the letter "R" to denote high-speed locomotives. High speed locomotives Since 1946 the Swiss have built bogie type electric locomotives of both eight wheel and twelve wheel types. The former we would call a "Bo-Bo" type; that is two bogies each with four independent driving wheels. The Swiss call the eight wheel loco an "Re4/4" meaning high speed electric and four driving axles out of a total of four. The modern Re4/4 locos built in 1982 are rated for a maximum speed of 160km/h and have a maximum starting drawbar pull of 300 kilonewtons. Their total power is 4.960MW (6650hp) and their high speed traction motors are geared 1:2.77 to their bogie driving wheels. For all this power they weigh only 80 tonnes - wonderful engineering design! In later years the Swiss were the first in the world to produce locomotives with more than 1000HP per axle, a remarkable achievement. Larger still are the Swiss 12-wheel bogie Re6/6 locomotives built from 1972 to 1980. These are powered by six traction motors which are each rated at 1.308MW (1753hp), giving a total of 7.850MW (10523hp) - all this in a locomotive only 19.31 metres long and weighing 120 tonnes. This enormous power per axle in such a small locomotive was made possible by the latest technology in traction motor design and wheel slip control which we will investigate in a later chapter. For the moment we must say that the Swiss railway engineers, together with the research and manufacturing companies Brown Boveri, Swiss Locomotive Manufacturing Co, Verkehrshaus der Schweiz, and the Swedish company ASEA have been in the forefront of new developments. Now that ASEA and Brown Boveri have merged, we may expect to see still more startling advances in European locomotive design. Synchronous motoralternators An interesting point arises (in any country) with the starting up and placing on-line of the synchronous motor-alternator frequency conversion sets. Commonly, such sets are started by an auxiliary induction "pony" motor having two poles ·less than the main motor. Once running and on load all sets are synchronised with all other alternators and synchronous motors, both on the 50Hz side and on the 16.6Hz side as Fig.1 shows. You would expect that the procedure would be to start the 50Hz synchronous motor and, when it reached full speed, synchronise it with the 50Hz mains. The low frequency alternator would then surely be generating 15kV 16.6Hz. However there is only a 33 % probability that it is in synchronism AUGUST 1988 77 Series AC traction motors require regular maintenance. In this photo, the slots in the motor's armature are being cleaned, ready to accept a new winding. (Photo SJ). SYNCHROSCOPE 6kV 50Hz THREE-PHASE BUSBARS "' THREE-PHASE 50Hz SYNCHRONOUS MOTORS SINGLE PHASE 15kV 16.6Hz ✓BARS SINGLE PHASE 16.6Hz ALTERNATORS Synchronising two substations 'INCOMING MACHINE CLOSED r INCOMING 6kV 50Hz THREE-PHASE SUPPLY FEEDERS I CLOSED CLOSED THREE-PHASE CIRCUIT BREAKERS ALL CLOSED SINGLE PHASE CIRCUIT BREAKERS No. 4 t RUNNING MACHINES ON LINE / 15kV 16.6Hz ELECTRIC RAILW AY OVERHEAD CONTACT WIRE Fig.1: sketch of an electrical system with four synchronous motoralternators. Machines 2, 3 & 4 are running and on-line , supplying train lines. Machine No.1 is running at full speed but needs to be synchronised before it can be connected to the other machines. with the 16.6Hz supply being generated by the other motoralternator sets. Therefore, it cannot simply be placed on line without further thought. The reason for this problem is that the 50Hz motor has three times as many poles as the 16.6Hz alternator, so the 50Hz motor could have 78 SILICON CHIP started up and synchronised from the 16.6Hz side, it follows that the 50Hz synchronous motor (now acting as a generator) must also be in synchronism with the 50Hz supply. (2). If started and synchronised on the 50Hz side and the 16.6Hz side turns out to be not in synchronism, a procedure called " pole-slipping" can be adopted. The operator simply retards the rotor one or two thirds of a rotating electrical circle to find the synchronised position. Pole-slipping consists simply of removing the DC field supply for a very short time, during which time the rotor " slips back" a little in rotating angle. The DC field supply is then restored and chances are that the rotor has slipped back exactly one pole pitch and the correct rotating angular position has been found. Synchronisation would then be possible. If the first attempt at pole-slipping is not successful, the procedure must be repeated. However, another large problem arises in a complete electric railway system operated at 16.6Hz derived from the national 50Hz grid' system. its rotor in any of three angular positions and still be in synchronism with the 50Hz supply. But only one of these three angular positions will give synchronism for both the 50Hz and 16.6Hz supplies. Two methods are available to fix this vital problem: (1). If the motor-alternator set is Consider two motor alternator substations A and B situated 30km apart, each substation supplied by the same 50Hz power grid system and each supplying 15kV 16.6Hz power to its own section of the overhead contact wire system. Normally each section is kept separate from neighbouring sections so that faults will not affect all trains in all sections. The motor side of all motor-alternator sets in both substations are automatically in phase ; ie, in synchronism (because they are on a common 50Hz system). Also we have seen how the 16.6Hz sides of all motoralternators in any one substation are brought into synchronism. Say some fault , perhaps a heavy short circuit, causes all machines in substation B to trip off, following which they are immediately restarted and synchronised again on their 50Hz sides and all their 16.6Hz alternators brought into synchronism with each other. We now have a problem: there is no guarantee that the 16.6Hz supp- THREE-PHASE 50Hz COMMON SUPPLY TO ALL SUBSTATIONS SUBSTATION o· SUBSTATION C SUBSTATION SECTION 2 SECTION 3 B SUBSTATION A EMERGENCY CIRCUIT BREAKERS NORMALLY KEPT OPEN SECTION 1 RAIL RAIL Fig.2: sketch showing four sections of overhead contact wire. The sections are normally kept isolated so that a fault in one section will have no affect on other sections. Note that a locomotive with two pantographs will bridge two sections. If section 2 is not in phase with section 3, the locomotove will cause a short circuit. ly generated by substation B is in phase (ie, in synchronism) with that generated by substation A. In fact, there is only a 33% chance that both substations will be in synchronism. Of course different trains running in each separated contact-wire section would never know the difference. At the meeting of two sections, the overhead contact wires are usually kept separated by an insulator and trains running across the join may simply jump the gap with a momentary but unnoticed power interruption. Multiple unit passenger trains in which each power car has its own pantograph in contact with the overhead wire, or electric locomotives using one pantograph, have no problems in this situation. Even if substation A and substation B ,were out of phase, the motors in trains running over the join feel no ill since they are not synchronous motors, but series motors with commutators which run the same direction no matter what polarity or phase current is applied to them. So where is the problem? It becomes very apparent when the first large electric locomotive comes along with both pantographs up. Common practice is for very highpowered locomotives to raise both pantographs (connected in parallel) to share the current when heavy train loads and mountain line star- ting conditions cause the loco traction motor currents to be high. When twin pantographs, electrically connected directly in parallel, mounted atop one European 15kV AC locomotive, approach a junction of two overhead contact wire sections which happen to be out-ofphase, watch out! For you are about to see fireworks. This would cause huge short circuit currents to flow from substation A, via the overhead contact wire section A, through both parallel pantographs, through over head contact wire section B, through substation B and back to substation A via the running rails and return conductors. Such a short circuit would cause a violent explosion at the front pantograph of the locomotive at the moment of contact. Probably circuit breakers in both substations would trip on over-current and such a fault might even stop some of the machines. It is imperative that such a short circuit situation is never allowed to happen between two remote substations. The remedy is that a feedwire is run from substation A to substation B so that they can be synchonised (using the pole-slipping method) before they are connected together. German electrification Germany can lay claim to having the first electric railway carrying fare-paying passengers: the 1879 demonstration DC electric railway built by the Siemens brothers in Berlin. This was soon followed by a 2.5km electric line in 1881 from which a suburban electric system grew. Mainline German electrification from 1922 has used the 15kV 16.6Hz AC system as pioneered by the Swiss BLS. Today much of West Germany is electrified , allowing international travel by electric train. For example one can travel behind electric locomotives from Italy, through Switzerland and West Germany to Holland in through coaches. Static AC-DC rectifiers The Siemens company of Germany has been active in the development of static frequency conversion methods since the 1930s and are credited with the invention of a static 50Hz-to-16.6Hz frequency converter using mercury-arc rectifiers. These were used in a ' 'cyclo-converter' ' configuration which simply divides the frequency by a factor of three. Long before the invention of semiconductor diodes, thyristors and GTOs (gate turn-off thyristors), the mercury-arc rectifier had been used as a high power rectifier. For example, in Sydney's outer suburban railway DC substations, 6-phase steel-case water cooled mercury-arc rectifiers supplied AUGUST 1988 79 SIX PHASE 50Hz SUPPLY, STAR POINT GROUNDED STAR SIX PHASE TRANSFORMER FEED-THROUGH INSULATORS Static frequency conversion STAR POINT i---,,---ANODES FLASH-OVER SHIELDS CIRCULAR STEEL TANK, EVACUATED AND CONTAINING MERCURY MERCURY -VAPOUR ARC FROM MOST POSITIVE ELECTRODE DC NEGATIVE Fig.3: basic sketch for a 6-phase mercury-arc rectifier. An ionised mercury vapour arc is struck between the most positive AC anode and the common mercury cathode pool on the bottom of the tank. 1.5kV DC for trains. A 6-phase rectifier is effectively six separate mercury-arc anodes in one evacuated steel tank having a pool of liquid mercury at the bottom. The tank and the pool of mercury becomes the common cathode of the multiple diode. Our sketch (Fig.3) shows the essence of the system which operates by an arc of dense ionized mercury vapour being struck between the most positive AC anode and the common mercury cathode pool at the bottom. The mercury liquid is boiled to a vapour and ionized by the electric field into heavy positive mercury ions and much lighter negative electrons. When the anode is on the positive half of the AC cycle, the light-weight negative electrons are attracted to the positive anode, constituting a heavy current flow, experiencing an almost-constant voltage drop across the arc of about 15 volts. High current capability Many thousands of amps may 80 SILICON CHIP Typically, a mercury arc rectifier could cope with a 500% overload for about five or 10 seconds, and lesser overloads for longer times. Many mercury arc rectifiers are still in service throughout the world (there are still a few left in the Sydney electric railway system) but all will eventually be replaced by banks of silicon diodes. easily pass in this direction. When the same anode is on the negative half cycle of the AC supply the negative electrons are rejected but the heavy positive mercury ions are now attracted by the electric field. The comparatively much greater mass of those heavy positive mercury ions prevents any great acceleration towards the negative anode but a few do travel that path, thus giving a small "reverse leakage current", As the forward electron current is thousands of times more than the reverse leakage, the mercury-arc system is an efficient diode of quite low output impedance. They were used extensively for high-current rectification before silicon diodes took over the task. The advantage of the mercury arc rectifier has always been its very large short-duration overload capability, an excellent characteristic for supplying the large currents demanded when, say, five electric trains happen to start up simultaneously, For cyclo-converter (ie, frequency conversion) applications, the mercury-arc rectifier was constructed in single diode format, with many diode units in a ring formation, Cyclo-converter diodes must be switchable; ie, it must be possible to have them in the non-conducting state at times even though the anode is at positive potential. Then on command the diode can be made to conduct. This controlled rectifier action was accomplished by means of a cylindrical control-grid structure mounted between the mercury pool and the anode electrode. If this control grid is held sufficiently negative it strongly rejects the negative mercury ions, so the mercury arc diode cannot conduct even though the anode may be positive. If the negative potential is then removed from the control grid while the anode is still on the positive half cycle, the mercury arc immediately forms from cathode pool to main anode, and the diode conducts. Once the mercury arc is formed and the diode fully conducting, the control cylinder-grid loses control. Applying a negative potential to the grid cylinder now cannot stop the dense arc of negative ions unless the anode is made negative for a short time. "Bouncing" the line voltage This can be accomplished by using a pulse transformer in the anode circuit to produce a negative pulse superimposed on the AC supply to the anode. Such a pulse had to be of long enough duration for the flow of negative mercury ions to come to a halt. After that, a negative grid cylinder could prevent re-ignition of the arc even neither of these methods but applied a small positive potential to the grid to induce ionization, whereupon the main arc would strike as soon as the main anode became positive. If AC phase control is used, a small leading angle of control grid voltage was needed for full output. In this mode, these machines were analogous to the single pole mercury diodes called "Ignitrons", once used to switch large currents, and to the much smaller gridcontrolled gas-filled rectifier tubes known as "thyratrons", valves such as the EN32 series of the 1940s and 1950s. THREE PHASE 50H1 INPUT NOT GROUNDED SUPPLY DELTA CONNECTED TWELVE SINGLE PHASE CONTROLLED MERCURY ARC RECTIAERS IN SIX PULSE THREE PHASE CYCLOCONVERTER CONAGURATION Constructional details SINGLE PHASE 16.6Hz OUTPUT Fig. 4: basic scheme for a cycloconverter using 12 single phase mercury arc rectifier known as lgnitrons. though the anode may be positive, as the circuit of Fig.3 illustrates. The large currents demanded by electric railway service produced considerable heating in the mercury and tank, such heating being approximately equal to the 15V forward voltage drop in the arc multiplied by the thousands of amps of current flowing. This heat was easily removed by circulating water through a jacket outside the steel tank. The steel tanks admitted the anode AC circuit via porcelain insulator bushings, the conducting rod down the centre of the bushing being kept air-tight using liquid mercury as a sealant. The vacuum within the tank kept the mercury in position and if any did spill into the tank no harm was done as it just mixed with the pool at the bottom. Striking the arc At each cycle the mercury arc had to be initially struck. This could be achieved in one of three ways: (1). A heater placed under the surface of the mercury pool, in a large 6-phase or 12-phase rectifier, could vaporize sufficient mercury for the most positive anode to strike an arc. The resultant heating due to the main arc would keep the arc alive when the next anode became more positive and took over conduction. (2). In single anode mercury arc rectifiers, an auxiliary small anode could maintain sufficient arc continuously, such that as soon as the main anode became positive there was enough ionization present for the main arc to immediately strike. (3). Some grid-controlled singleanode mercury arc rectifiers used OA:::!, 0 ,,~ ~a ,:c u~ ~ c Wf' - r oa .~ RCS Radio Pty Ltd is the only company which manufa.ctures and sells .every PCB & front panel published in SILICON CHIP, ETl and EA. 651 Forest Road, Bexley, NSW 2207 Phone (02) 587 3491 for instant prices 4-HOUR TURNAROUND SERVICE Some steel tank mercury-arc rectifiers with many large electrical bushings entering the tank could not maintain vacuum for long periods. Therefore, these were fitted with a vacuum pump running continuously or when needed. The Hewitic Company of England was one organization which developed "pumpless mercury arc rectifiers" in which the seal was sufficiently good so as to not require continuous pumping. The German invention of the mercury arc cycloconverter in the 1930s gave the 16.6Hz AC supply needed by the railways without any need for rotating machinery. This giant step forward was a precursor of similar techniques which would be used in the future, once silicon controlled rectifiers (SCRs) were invented. The steel tank of a mercury-arc rectifier is alive at full DC output potential, so the tank is mounted on porcelain insulators. A limitation on all mercury-arc rectifiers is that they must be used in stationary position with the mercury liquid pool at the bottom. Transport while switched on is prohibited because of the dire consequences of "sloshing" of the mercury pool at the bottom. Short-circuits could easily occur. This prevents any such rectifier being installed in a locomotive. Such schemes had to wait until silicon diodes rated at thousands of volts and many thousands of amps were developed. :It AUGUST 1988 81 NEW KITS THIS MONTH! ELECTRONICS AUSTRALIA SILICON CHIP Low Cost Capacitance TV Field Strength Meter (August EA) Meter (August EA) What a great idea! This amazing little unit turns your digital or analogue multimeter into a direct-reading capacitance meter. It's a cinch to get going and uses $ 9S only a handful of parts. Cat K-3410 19 Sylon Voice Synthesiser (August SC) Just the kit for anyone dealing with FM/TV antenna installations or adjustments. Indicates the best antenna position. Can even be used to convert a video monitor into a TV set! Cat K-6329 As seen in August Silicon Chip! Just hold it up and talk through it and your voice will sound like Darth Vader, etc. Small hand held, simple to build! s199 '2995 Cat K-3510 AUSTRALIAN ELECTRONICS MONTHLY Guitar Practice Amp (August AEM) An easy to build low cost amp that uses a single chip and delivers 8 watts. It's ideal for musical instruments and can run from batteries. A low cost off-the-shelf speaker can be used with better than average performance. A great little amp! Cat K-3548 s1995 Remote Doorbell/ Pager (August SC) Mains Powered Lab Supply (August AEM) Used in conjunction with remote switch K-3256. Can be activated as a doorbell, pager, alert alarm, etc. Great for the sick room or as a safety alarm when you're in the workshop, etc. Cat K-2730 $ SO A fully metered 35V /2A mains powered lab supply at a surprisingly low cost. It's extremely easy to build and offers outstanding versatility. Cat K-3461 72 S109 Universal Power Supply Board (August SC) Batterv Power Supply Mini Mixer (June AEM) (July AEMJ Ideal as an inexpensive supply for kids, beginners servicemen etc. It can be carried in the toolbox, car, etc and delivers a hefty 2A/35V or more and can be powered by a couple of dry 6V batteries. Simple yet amazingly effective! Cat K-3460 SO Sfj Budget Beater Car Alarm! 2 Providing performance that's more than adequate for home or amateur use this four input mini mixer is a great alternative to high cost professional units and it's simple to build and use. Can be mounted in a case of its own or inside your present amplifier. Cat K-3039 Designed for OP Amp circuits. This tiny circuit enables you to obtain +15V, -15V or +I- 15V DC from a number of different transformer and rectifier combinations. s2995 Fluoro Starters Save 25%! Incredible value car alarm but It's really 'bare bones· stuff. Very effective at detecting voltage drop. Even has visual warning to deter thieves! Cat K-3250 Huge Reduction! Soldering Station Bench Amp & Signal Tracer One soldering Iron can now do all your work! It can even be your existing Iron with this fully regulated, adJustable ternperature control soldering station 240V operated, selectable 20-70 watts. Easy to build and now it's sensational value! Cat K-3479 ~ Finally, a means of audibly tracing through a cIrcuIt - and It takes up less space than your conventional amplifier and speaker. Offers high Input Impedance a wide range of input sens1tlvltles and up to 5 watts of output power. Cat K-3471 Savs $10 s3995 _-=~% · Stereo Simulator Was $49.95 A Simple Tester For Power Transistors Sensational value general purpose amp as used in TV, tape players, musical instruments. etc. Supply Voltage/power output - 35V/ 19W, 30V/12W, 20V/6.6W. Cat K-3445 $50FF! 95 ONLY S14 Superb Sound! They look and sound like speakers that cost $$$$ more! Easy as pie to build they use Magnavox 6MV 15cm drivers and 3AC tweeters with a second-order crossover network. You'll get superb performance. They're rated at nominal 40 watts but will · comfortably handle full power 100W on normal program material. Cat K-4000 s249 Now RF Detector Probe ~~,; .I/ Can be built from a handful of the most . common parts and it becomes a sensitive AM signal tracer when coupled with the bench amp (above) or an audio amplifier. Costs almost nothing to build yet it's invaluable in service and repair work. Cat K-3470 Appliances Off A Car Battery! ~ s249 sg95 DIC 0Th1s Is a fantastic Idea for tradespeople, farmers, campers, etc. 12-230V Inverter lets you power mains appliances directly off the car battery. With auto-start feature to he~p eliminate wasted power. $30 OFF! ". This value plus, super special. wh iz bang gadget turns almost any mono signal l~to synthf:ltic stereo! Imagine the fun you II have with those old mov1es! Cat K - 3 4 ~!I1 / ,._ aV8 ..,.. S s4595 Power Ma •,ns Cat K-3478 , Build and fit this high energy ignition system and forget about adjusting dwell, cleaning points and checking timing. More power. better fuel economy, smoother idle, longer time between tune ups.... better fit one now! Cat K-3302 j ;: s1995 2995 s FOrget The 1iUne Up,I Deceptively simple, yet it can evaluate the current gain and Vbe of all popular power transistors and even power Darlingtons. Simple to build, it's a must for hobbyist, technician, serviceperson. .. ,~~ anyone in the • • electronics field. nC-,.'· ~ Cat K-3053 ,,( -:) $395 Cat K-3435 $2195 _ Sound Bender Great for special effects! Can make voices sound like just about anY1hlng of the robot Ilk, eg. Darth vader, a Cylon ...etc. Ideal for electric guitars and other musical instruments. Cat K-3509 $100FF! 0LJNO!i~NO~ N;:s2795 ,=,,;'. - - -.,. .,.-.J ,,, ,,_ , $3 ~~--~~~■"."i! "".'."'P'~"T~P'::'.""P'~ SAVE ON LETTERS We're clearing out our stocks of Amical Panel Lettering. Here's your chance to save nearly one third off normal prices. Each pack contains hundreds of words, letters, numbers and symbols. 2.3mm high. Hurry - stocks won't last long at these prices! White letters: Cat N-1806 Was$9.50 NOW 1 &5" Remember the pen we used _____________________,. 1?;;~~ ::f~ti~g~~tsf~~ng AUGUST IS SOLDERING SPECIAL MONTH! Adjustable Temp Solder Station Pro quality at hobbyist price! Dial the temperature you want to protect sensitive cam• ponents. Cat T-2000 Mini Iron resist was a deadly poison (others still sell it!). The DATAK etch resist pen is a non-nasty, highly effective way to make one-off pcb's. Cat N-51B0 1495 Super slim 6W 12 volt iron, ideal for delicate work on pcb's etc. Even use it on the car wiring! Cat T-1920 Datak Burnishing Tool: Save $3 Was $19.95, now 1 1495 ~~~~~ga~~1B~:~~~tsJ~~~\ s s10.95 NOW A great little general purpose iron - ideal for the hobbyist and the technician. Even has soldering hints! Cat T-1310 30 Watt Iron Look at the price: it's crazy! You'd be crazy to miss this one: 12V, 30W iron for general work. Cat T-1910 Usually $9.95 WasS22.50 NOW 1 1995 w1595 Don't Forget Your Portasol! ~ Solder On! Hobby packs of solder are so convenient. Why buy a roll when you don't need a roll? 60/40 Electronic grade solder in two sizes. 0.71mm (22g) - contains approx 9 metres solder. Cat N-1636 1.25mm (1Bg) - contains approx 4 metres solder Cat N-163B ~:-6 Botti one low Especially if you're out of reach of a power point or bat• tery! Butane powered iron goes where you go, equivalent to 10-60W iron. Handy! Cat T-1370 Last Year Sold For Near $60 Now Only 139 95 And The Stand? NEW! "Savbit" Stop your iron becoming a dangerous weapon on the bench. Heavy cast base and spiral spring hold the iron in place. Suitable for mains irons to about SOW. Cat T-1302 cor.Iper Loaded Soder ONLY 7 A little copper in the solder is a highly effective way to lengthen soldering iron tip life. The new SAVBIT solder contains just thatl 0.71mm (22g) solder in 200 gram roll - lasts for ages! Cat N-1621 1 95 IHDNllAIU(02Ji;,t,l.l.Ml2IOII) NOW Shop 1, 399 Elizabeth St. Ph: (03) 326 6088 Datak Contact 7 St. Marys WAS AT DARLINGTON Main South & Flagstaff Rd's Yep, you'tl need one of these too. If you're serious, that is. Beats the old sheet'o glass and two books routine anytime. Cat N-5710 $13 NOW 1267 Main South Rd, Ph: (08) 277 8977 Eventually, you'll get a PCB that's RS. Fix it with Circuit Fix Kit. Pure Copper traces & donuts with adhesive backing, ready to repair a pcb or modify a new one. Great for developers too. Cat N·5900 w:- Bondi Junction WAS Oxford & Adelaide St's ~4195 Resist These Bargains? Unlikely! NOW 2 Denison St, Ph: (02) 387 1444 Datak quality resist products to make your PCB making a breeze. They're also refills for the Datak PCB kit. Developer Resist Fitter N-5711 N-5905 N-5907 Was $10.95 Was $11.95 Was$1B.95 Penrith Penrith Now$9.95 Now $15.95 Now $6.95 I- CJ -. Film ProcessPos/Neg Film ing Chemical Refills Pack Photo-sensitive polyester film Wei WAS High & Henry Si's NOW Cnr High & Film developer and fixer pos/ suitable for laying out pcb pat• neg film, or for replacement terns in pos or neg format. 6 pack for PCB kit. sheets 125 x 150mm. CatN-5909 Cat N-5705 Q wasS18.95 NOW 1 1595 was s11.oo Now'9 95 -1 ~ i- ,, - HEADPHONES FOR ALL TASTES. BARGAIN: QUALITY: Our $9.95 bargain If you're looking for outstand1 9 a~$3.~i, iuit1':;a":i~~;ei~~°o~~o able for walkie stereos, radios, Sennheiser HD-40's. Your ear~ etc. ~ will say "th anks!'Q ' t 4130 4120 ca cCatc- ~::~PE~~~~~a~l~e ~~~h:; ';r. ~99 -.., .-T,' 14295 Ionize It! NOW AVAILABLE AT ALL STORES - OR CALL TOLL FREE: (008) 22 6610 FOR HOME DELIVERY! I We were here moved Ill twwe enry Riley St's Ph: (047) 32 3400 u au,o - · '""" "'"-" ,.,.,.F,fi,f/i§. (008) 22 6610 Melbourne City WAS 291-293 Elizabeth St) Frame: Save $6 7 roll ' ~ Was $7.95 NOW s495 1 95 STD FREE ....-.---..........--..... NOW 1 1695 Fix It Kit: Save 15W Mains Iron Don't panic! It's closer than you think! Many Dick Smith Electronics stores are being up-graded at the moment - we think y~u'lt like the changes. Some are even moving to larger pre. mIses close by. These stores have recently, are in the process of, or will shortly be moved, moving or moving. Targets: PCB targets & crosshair registration marks. Cat N-5820 1 95 Datak Circuit / DATAK make some great transfers. To whet your appetite (no, Lucretia, you don't eat them) here are two. And we've reduced to price to make you even hungrier! Assortment: Con• tains one sheet from 17 different types. Very handy. Cat N-5766 WasS19.95 You'll need one of these if ~ Normally $129 NOW ONLY 199" WOT? THEY'VE STOLEN THE STORE? Black letters: Cat N-1B04 Was$9.50 NOW Sfj50 MALL Why Put Up With Fuses? Fuses are passe. Why muck around in the cold and dark look ing for fuse wire • just press a button and power is restored! Our circuit breakers fil most modern switchboards (Federal type)• and look at the range! BA P-590B 10A P-5910 15A P-5915 16A P-5916 20A P-5920 JOA P-5930 WERE $12.95 NOW ONLY s9 95 ea. Expect to pay near $14 elsewhere for equivalents! SOUNDS GOOD TO YOU • Quality Magnavox Speakers for' rep\acement in existing enclosures or building new designs. Compare the value, cam• pare the prices, compare the sa.vings! 10IN WOOFER Cat C-2052 , Normally $39.95 NOW $29.95 BIN WOOFER Cat C-2054 Normally $29.95 NOW BIN TWIN CONE Cat C-20B2 Normally$29.95Now$19.95 $19.95 '. 0fJ ~ / ~ \..: -------------------Don't Get Cross - Cross Over AMATEUR RADIO By GARRY CHATT, VK2YBX Getting the most out of nicads Proper charging techniques can extend the life of nicad batteries and 'repair' some common malfunctions. Here's how to get the most out of your nicads. High energy density and tolerance to abuse have made nickel cadmium [nicad) batteries popular for powering hand-held portable transceivers. They are arguably the most economical portable power supply available. While the nicad battery pack has the ability to stand up to all kinds of abuses, there are limits to the level of performance that the nicad can sustain. With some knowledge of these limits and knowing how to deal with some everyday difficulties, you can maintain peak performance levels and maximise operational life. The metal case is made from nickel plated steel, welded internally to the negative plate, and becomes the negative terminal. A sealing plate, located at the top of the cell, is welded to the positive plate and forms the positive terminal. A safety vent is also fitted to allow the escape of gas or electrolyte in the event of an abnormal increase in internal pressure. This vent is made from a special alkaline and oxidation resistant rubber which is self sealing and which maintains the normal internal operating pressure for the life of the battery. Construction Electrochemical processes A basic explanation of the operation of a typical nicad battery will show why maintenance and correct charging are so important. Fig.1 shows the internal details of a nicad cell. (A nicad battery pack is made up of a number of cells connected in series). Most nicads are cylindrical. The positive plate is normally made fFom porous sintered nickel which is filled with nickel hydroxide, while the negative plate is made from thin steel coated with a cadmium active material. The separator is made of polyamide fibre. These parts are all wound into a coil and inserted into a metal casing. An electrolyte is also included and this is a water-based alkaline solution which is totally absorbed into the plates and the separator. During the discharge process, oxy-nickel hydroxide combines with cadmium and water to form nickel hydroxide and cadmium hydroxide. The reverse occurs during the 84 SILICON CHIP Insulation gasket Current conector Nevattve plate Sepantor charging process. However, in the final stages of charging, oxygen is generated at the positive plate. This oxygen passes through the separator to the negative plate where it is absorbed to form hydroxide ions. This is why it is important not to overcharge nicads, as the oxygen liberated may not all be absorbed. If this is allowed to happen, the pressure inside the case increases and may even rupture the safety vent. When this occurs, electrolyte is lost and cell capacity is reduced. The information needed to correctly maintain a nicad battery should be clearly printed on its label. This information should include the nominal voltage rating, capacity and the recommended charge rate. Two charge rates should be indicated: a standard or slow rate, and a fast rate. The load voltage of a fully charged battery will vary between 1.2 and 1.3 volts per cell, depending on the cell design. A fully charged nicad battery will provide 1.2V per cell under load (see Fig.2). As the battery discharges its terminal voltage will be fairly constant until it is nearly depleted. A voltage of 1V or less per cell under load conditions indicates a fully discharged battery. Cell capacity The capacity (C) of a nicad battery is the amount of energy a cell or battery can provide. This is simply the time taken to discharge a cell to 1V multiplied by the current at Insulation plate which this discharge takes place. Nicad batteries are rated for Fig.1: internal details of a nicad cell. capacity based on a one hour The positive and negative plates and the separator are wound into a cylinder discharge rate at a temperature of 25°C. The unit of measure is the and inserted into a metal casing. Posttlve plate 1.3 1.2 110 - r-- §: ............... / l:i er ... "i\ \ 1.1 100 ► ~ w -' ./.,, 90 "' er = er \ ;. ~ 80 V / \ \ 0.9 70 -5 DISCHARGE TIME Temperature effects Nickel cadmium cells will operate over a wide temperature range although their performance will vary significantly when the operating temperature is far removed from room temperature (25°C). As temperature rises, useable capacity increases. This increase is due to the higher chemical activity at elevated temperatures but this is not considered when cells are rated for capacity. At 46°C, a cell will have approximately 106% of its room temperature capacity. Conversely, at - 6°C, the capacity will be 80% of room temperature capacity. Fig.3 shows the effect of temperature on nicad battery capacity. The standard charge rate for nicad batteries is the 10-hour rate or C/10. But higher charging rates are possible and practical for many modern cell designs. Five, three and one-hour chargers are common in communications equipment, and cells that can be fully charged in 15 minutes are available. 10 15 20 25 30 35 40 45 50 BATTERY TEMPERATURE (°C) Fig.2: the output voltage of a nicad cell is fairly constant at about 1.2V as the battery discharges. When the cell is depleted, its output voltage drops rapidly. milliampere-hour (mAh) or amperehour (Ah) for larger cells. For example, a cell that can provide a current of 450mA for one hour is rated at 450mAh or 0.45Ah. Capacity ratings at other than the one hour rate are not uncommon but the one hour rate is the most frequent reference. Some slight increase in capacity is available at the 10 hour rate but the improvement is usually not much greater than about 8%. 5 Fig.3: this graph shows how nicad battery capacity increases with temperature. Nicads should be allowed to reach room temperature (25°C) before recharging. Common nicad problems The most frequent complaint associated with nickel cadmium batteries relates to capacity loss and the consequent reduced operating time. There are a number of common causes for this: (1) incorrect battery for a given duty cycle; (2) effects of long term storage; (3) long term overcharge; (4) shallow discharge/full charge cycles; (5) cell depletion as a result of normal use; (6) insufficient charging time; and (7) charging at high temperature. Let's look at each of these common problems in turn. Duty cycle Poor discharge time or endurance may be due to excessive current drain under normal operation. For example, to estimate the energy required to operate a transceiver for a given period, we must know how much current is drawn from the battery pack during receive, transmit and standby modes. By then using a standard duty cycle (typically 5%, 5% and 90% for receive, transmit and standby respectively), the discharge time for the battery can be predicted. Fig.4 shows how this is done for a transceiver with the following current drains: receive, 45mA; transmit, 245mA; and standby, 1ZmA. The resulting figure of 236mAh represents the minimum capacity required for an 8-hour operating period. More active operations may require a 10%, 10%, 80% duty cycle or higher. A calculation of required capacity under more demanding service is shown in Fig.5 . A 450mAh battery, typical for many transceivers, will provide more than adequate service in both cases and still have reserve capacity for extended duty tours, or even heavier duty cycles. Long term storage Batteries that have been stored for long periods of time will not have full capacity when first placed in service. This is the result of two effects of long term storage. The first is called passivation. During storage, a crystal-like film grows on the positive plates (the anode) of nicad batteries. This passivation layer acts as an insulator and must be removed before the cells can provide full service. At the same time, the passivation layer prevents deterioration of the anode and, in that sense, is beneficial to the shelf life of the battery. The second effect of long term storage is pooling of the electrolyte. Electrolyte, as a result of gravity, will no longer be evenly distributed within the cell, leaving some portions of the cell dry while other areas are saturated. Both storage problems are easily corrected. After batteries are removed from storage, it will be necessary to "wake up" the cells with two or three charge/discharge cycles. This will "burn off" the passivation layer, and redistribute electrolyte evenly throughout the cells. Usually, about 40% of battery AUGUST 1988 85 STATUS STANDBY RECEIVE TRANSMIT CAPACITY CONSUMED IN 1 HOUR CURRENT X % 15 X .90 45 X .05 245 X .05 = 13.5 2 .25 12.75 STATUS STANDBY RECEIVE TRANSMIT CURRENT X % 15 X .80 45 X .1 0 245 X .10 X8 X8 328.0 mAh per 8 hr shift 236 .0 mAh per 8 hr shift Fig.4: this energy requirement calculation is for a portable transceiver with a 5-5-90% duty cycle. A typical 450mAh battery will provide capacity to spare. Long term overcharge Modern nickel cadmium cells have been designed to withstand the deteriorating effects of long term overcharge at the to-hour rate. Gassing, venting and leakage are rare, even when a cell has been left on charge for days or weeks at a time. The capacity of such a cell or battery will often appear to diminish after extended overcharge but this is not a permanent fault. Even batteries that appear to have lost as much as 35 % of total capacity can be resurrected by a single charge/discharge cycle. After this treatment, such batteries will typically exhibit 85-90% or more of their original capacity (Fig.6). Shallow discharge/full recharge of nicad cells is perhaps the most well-known effect, yet is probably the least frequent of nicad problems. Often called memory effect, it is the most misidentified problem associated with nicads. To explain, early nicad cells, 86 SILICON CHIP 12.00 4.50 24 .50 41.0 mAh per hour 29.5 mAh per hour capacity will be available after the first charging cycle, 70-80% after two cycles and more than 95 % after the third cycle. So it pays to cycle the batteries through several charge/discharge cycles before putting them into service. Apart from this, charged or discharged cells may be stored for indefinite periods of time with no significant degradation in performance. Where possible though, batteries should be charged before storage. Note that batteries which are stored in the charged condition will loose about 1 % of capacity per day due to self discharge. CAPACITY CONSUMED IN 1 HOUR Fig.5: the energy requirement calculation for a more demanding 10-10-80% duty cycle. Note that the energy requirement is still within the capacity of a 450mAh battery. when discharged to only a small portion of the total available capacity, would "memorise" that level of discharge. Such cells would then provide only the "memorised" capacity level and no more. Today's modern cell design has all but eliminated the memory effect. Special plate processing techniques have reduced the problem to the point where only repeated and identical discharges will cause a battery to exhibit memory. Even in cases where identical shallow discharge/full recharge cycles do produce a real memory effect, the condition may be corrected by several deep charge/discharge cycles (Fig.7). Cell depletion The electrochemical processes that occur when cells are charged and discharged are, in theory, fully reversible. In practice, the reformation of the chemical agents within the cell limits the life of the cell to a finite number of cycles. As time passes, less and less capacity is available and at some point, when available capacity is less than necessary for a given duty cycle, the battery should be replaced. Standard charge nicad batteries can take as many as 1000 full charge/discharge cycles before their capacity falls below 80%. Fast charge batteries should provide 600-700 cycles. Insufficient charge time Nickel cadmium batteries and cells are normally charged from a constant current source at some convenient rate. This rate is frequently chosen to provide fully charged batteries within a given time period. As stated previously, the "standard" rate is the 10 hour rate or C/10. If charge/discharge efficiencies were 100% perfect, then a cell charged at the 10 hour rate would be recharged in 10 hours. Unfortunately, this is not the case because charge efficiency is less than perfect. To recharge a fully depleted battery, it is necessary to provide 140% of the energy that the charged battery can deliver. This means that, when charging at the 10 hour rate, charge time must be increased by 40% to 14 hours for full recovery. This requirement also applies to " fast" chargers. These often use the temperature of a battery to trip a charge indication lamp. This usually means that the charge rate has been changed from fast to standard. The switch is often set to trip when the battery temperature reaches 45°C. It does not indicate end of charge. At this point the battery may be charged to only about 75-85% of full charge, so additional time should be spent in the charger to "top up" the charge. Charging at high temperatures Charging a battery when ambient temperature is high may reduce full charge capacity. When a battery or its environment is warmer than 25°C, full recharging will not occur and the battery will appear to have lost capacity (Fig.BJ. What ' s more , high ambient temperatures may cause premature tripping of fast chargers which are controlled by thermal sensors. 1.3 1·3 r--,-::TE::::ST::-:S::':'HA::-:-L:-:LO:::,W-r--r---r-r---.--r--,-...---,----, DISCHARGE I 1NmAL /DISCHARGE ....... 1.2 " - r-- r-. -..... N ~['..., r-,...._ ........ ARST DISCHAR~ AFTER EXTENDED OVERCHARGE I" '\ 1' 1---1---1-.--+--+--+----l--l---l---l---l--l---" \ \\ I'. ' J SECOND DISCHARr& AFTER EXTENDED OVERCHARGE 0.9 ,_ \ \ DISCHARGE TIME DISCHARGE TIME Fig.6: an extended overcharge does not render nicad batteries unusable. Recycling can typically restore capacity to 85% or more of new battery specification. 90 ~ z et I... l;l! ..,~ ls 4.21·c v- 100 80 J 70 'I' I 50 40 / ... i..---- /" J 60 / -- 45•c s1·c v I V Fig.7: the 'memory effect' is rarely a problem with modern nicads. Even if repeated identical charge/discharge cycles produce some memory effect, recycling restores full capacity. i..-- ..... r--..1, r--.... V e ao II 'I/ / 10 I r-.... -L WEAK,~ ~ t'-... I I '// 'I NORMAL DISCHARGE '\ e:.11y CELL SHORTE60R DEAD CELL ~ 20 ...... J ' "\ ~ "\ "' \ ~ '1 \ I DISCHARGE TIME CHARGE TIME Fig.8: a nicad battery accepts a reduced charge at high temperatures, lowering apparent capacity. In addition, thermal sensors may switch the charging rate to 'trickle' prematurely. Fig.9: weak or shorted cells result in abnormal discharge voltage curves. Recycling may restore weak cells but batteries with shorted cells should be replaced. Charging methods Testing batteries A simple, economical nicad charging circuit is shown in Fig.10. This circuit consists of a transformer, a bridge rectifier and a current limiting resistor in series with the cell to be charged. For best results, component values should be selected for a C/10 charge rate. Let's say that we want the circuit to charge a 6V nicad pack rated at 500mAh. Here's how to calculate the circuit values: • The transformer secondary voltage should be two or three times the battery terminal voltage; eg, 6V x 3 = 18V. • We must now calculate the value of the limiting resistor so that the battery pack charges at about the C/10 rate; ie, about 50mA or 0.05A. The equation is as follows: Rs = (18V - 6V}/0.05A = 2400. Before batteries are replaced it is a good idea to check the available capacity. This is quite easy to do and requires only a suitable load resistor and a voltmeter. The battery should be tested fully charged. All you have to do is to choose the load resistor so that the battery discharges at its "C" rate and then measure the time taken for it to discharge to 1V per cell. For example, a 15V 450mAh battery containing 12 cells would be checked using a load resistance of 320. At a discharge rate of 450mAh, the battery should last for 60 minutes or more before the voltage under load falls to 12V (ie, 1V per cell). A discharge time of only 48 minutes corresponds to 80% capacity while 36 minutes equates to 60% capacity, a level at which the battery should be replaced. To determine the test conditions for any battery, the terminal voltage of the battery is divided by the cell voltage (1.2, 1.25 or 1.3V the correct value depends on the battery manufacturer). The answer is the number of cells in the battery. The terminal voltage is divided by the rated capacity to find the test load resistance, ie: Load resistance = (number of cells x 1.2V) -;- capacity. Other common problems When a nicad battery discharges to less than 1V per cell under load, cell reversal may result. This happens because, when the weakest cell in a series string reaches its end point, the remaining cells may still have enough capacity to drive current through this cell. This effectively "charges" the cell in reverse. AUGUST 1988 87 AMATEUR RADIO - CTD FUSE + NICAD T BATTERY : PACK ..L. Fig.10: an economical nicad charging circuit. For best results, Rs should be selected for a C/10 charge rate. The text shows you how to calculate the correct Rs value. Dirty contacts on the charger or battery can cause a runaway charger. So can high AC mains voltage or current transients, surges and dips. Many batteries have fuses or thermal cutouts to protect them from damage due to high currents or temperatures. However, open fuses will result in a dead battery that must be replaced. Thermal cutouts, on the other hand, will reset themselves after cooling which means that the battery can be reused. Nicad do's and don'ts If this occurs, the cell volt-a.ge actually reverses; the positive terminal becomes negative and the negative terminal become positive. If the battery has not been badly reversed, it may be possible to correct this situation by subjecting it to a full charge cycle. In the long term, however, the effect can lead to excessive gassing within the cell and possible venting, resulting in electrolyte loss and premature failure. A battery with a weak cell in a series string of cells will exhibit a lower than normal terminal voltage under load after it has been discharged for a short time (see Fig.9). Batteries with this difficulty should be replaced if cycling does not restore the weak cell. Batteries with shorted cells exhibit lower than normal voltages under load, usually by multiples of 1.2V. Batteries that have shorted cells should also be replaced. Vented or leaking batteries It is most unusual to see leaking electrolyte as a result of can or seal failure in modern nicad batteries. The steel can construction and crimp seals used have virtually eliminated leakage as a source of concern. Cells which have vented are another matter. Cell venting, with consequential spillage of electrolyte, is always the result of some other. problem. Long term overcharge, forced discharge, runaway charging systems, cell reversal and cold battery charging are common reasons for electrolyte spillage. 88 SILICON CHIP Spillage leads to a loss of capacity and to cell failure. If it is suspected that venting has caused a battery to lose electrolyte, the loss may be verified by measuring the voltage of the battery after charging is complete. Batteries suffering from vented cells typically have an abnormally high terminal voltage at the end of the charge cycle. For example, a battery having a rated voltage of 15V could show a terminal voltage of 17 to 18V at the end of the charging cycle. Such batteries should be replaced if they fail to provide adequate service capacity. Cracked or broken cases Plastic battery case design takes into consideration the effects of rough treatment, accidental mishandling and just plain abuse. ABS, Lexan and other polycarbonate materials are used to reduce the probability of case breakage. Cases do break though. Batteries with cracks and splits can be used but with discretion. Any battery with pieces missing or with internal parts showing should be replaced, because the cells may accidentally short-circuit. A melted or swollen case can occur with fast charge batteries when the fast charge cycle has failed to terminate properly. If this happens, the battery should be removed from service (distortion of the case will likely prevent it from fitting in the transceiver), and the charger should be checked thoroughly for correct ~peration. In general, nicad cells should not be charged continuously at rates greater than 2C. Doing so can overheat internal cell components and cause premature failure. Short term high discharge rates are permissable, but caution should be observed whenever discharge rates exceed the 2C rate. Short circuiting nickel cadmium cells and batteries should be avoided. Because nicad cells have extremely low internal impedance very high currents can flow in a dead short, causing very rapid heating. Tools, jumper leads, wires and other shorting devices will get hot, leading to the possibility of burns or even a fire. Cold batteries can rupture if charging is begun before they are allowed to reach moderate temperature. Fast charge batteries should reach 15°C before charging while standard charge batteries should be at 10°C or warmer. Such temperatures can be achieved by allowing cold batteries to stand at room temperature for a few hours. Wet batteries should be allowed to dry thoroughly before being placed in a charger. Moisture can act as a conduction path that can lead to permanent charger or battery malfunction. Finally, nicads should not be discharged to less than 1V per cell, since this can easily lead to cell reversal. Footnote: The author wishes to thank Mr Walter Ullrich, President of Multiplier Industries, USA for his permission to use material from his publication How to Get the Most From a Nicad Battery. ~ THE ELECTRONICS MAGAZINE FOR THE ENTHUSIAST WE INvITE BECOME You To A SUPPORTER We believe that electronics is a fascinating pursuit, and the most useful hobby that anyone can have, particularly for a young person in school. Anyone with a good grounding in electronics is better prepared to meet the challenge of today's and tomorrow's technology. Because we believed that many more people should come to know about and enjoy electronics, we decided to start a new magazine expressly for electronics enthusiasts, whether they be nervous beginners or seasoned veterans. We called it SILICON CHIP, a name which focuses on the very basis of today's electronics technology. We started SILICON CHIP as an independent magazine completely free from the influence of any existing publishing company, because we wanted to establish the highest possible standards for accurac_y and attention to detail. Our team is very small: founders Leo Simpson and Greg Swain, plus full time staff members John Clarke and Bob Flynn. SILICON CHIP has now been on sale for ten months and has been very well received. Even at this early stage, you, the readers, have clearly indicated that SILICON CHIP is the most entertaining and best produced electronics magazine in Australia. Considering the hard work in getting started, it has been a very gratifying response. But we want to make SILICON CHIP even better. To do this, we need the resources to employ more people; we need the services of technical illustrators, writers, designers and other creative people. This is the only way that we can be sure of attaining the highest possible editorial standard. We know this is what you want. Your letters tell us. But we can only do this with your enthusiastic support. Already, many hundreds of readers have taken out subscriptions to give SILICON CHIP a solid start but we would like to have thousands more. If you haven't already done so, please give us your vote by becoming a subscriber. By doing so, you will be ensuring the future of an entertaining, informative and independent SILICON CHIP magazine. Regular Features * * * * * Constructional Projects For The Enthusiast HiFi Review Digital Electronics Course Circuit Notebook Vintage Radio Junk Mail The Serviceman's Log * Amateur Radio, by Garry * Cratt, VK2YBX The Way I See It, by Neville * Willams * Book Reviews Most magazines sell their subscriber list to mail order companies, to earn extra income. We will not do this. We will lose some money by adopting this policy but we believe that your privacy is paramount. BECOME A SUPPORTER BY FILLING OUT THE POSTAGE FREE SUBSCRIPTION COUPON OVERLEAF ► AUGUST 1988 89 FREEPOST SUBSCRIPTION COUPON To: Freepost 25, Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097, Australia. BACK ISSUES NO POST AGE ST AMP REQUIRED IN AUSTRALIA PLEASE ST ART my subscription in .............. .. ................................ ..... ..... . NAME (Mr/Mrs/Ms) ..... ..................... ......... ............. ................ .... ............... . 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SUBURB/TOWN ........... .. ...... ......... ..... ......... ....... ..... .... POSTCODE ..... ....... . Subscription to commence in ..... ......... ........... .. ........ .. ............ .... .... .......... ... Subscription cost: Within Australia Overseas surface mail Overseas air mail 1 year (12 issues) $42 $62 $120 □ □ □ 2 years (24 issues) □ $84 □ $124 □ $240 Enclosed is my cheque or money order for$ ........... or please debit my □ Bankcard □ Visa Card Card No ........... ......... ... .......... ..... .. .... ................ ....... ............................... ... .. Signature .... .. ....... ....... .... .... ... ........ ... ....... . Card expiry date ...... ./ ... ... ./ ..... . . NEW ZEALAND & PNG SUBSCRIPTION COUPON Issue Highlights April 1988: Walkaround. Throttle for Model Railroads; pH Meter for Swimming Pools; Slave Flash Trigger; Mobile Antennas for the VHF and UHF Bands. May 1988: Optical Tachometer for Aeromodellers; High Energy Ignition for Cars; Ultrasonic Car Burglar Alarm; Restoring Vintage Radio Receivers. June 1988: Stereo Control Preamplifier; Breakerless Ignition For Cars; Automatic Light Controller; Mega-Fast Nicad Battery Charger. STREET ... .... .. .. ..................... ...... ...................................... .. ..... ................ ... . July 1988: Fitting a Fuel Cut-Off Solenoid; Booster for TV & FM Signals; The Discolight Light Show; Tone Burst Source for Amplifier Testing. SUBURB/TOWN ... .... ...... .... .................................... ..... POSTCODE ... ..... .. ... 1 year (12 issues) 2 years (24 issues) Subscription cost: Price: $5.00 each (incl. p&p). Fill out the coupon on page 49 PLEASE ST ART my subscription in .......... .. ........................ ................... ... .. NAME (Mr/Mrs/Ms)...... .. ....... ... .. .. ... ..... ..... ................................. .... ....... ... .. Air mail □ $65 □ $130 Enclosed is my cheque or money order for $ .......... . or please debit my □ Bankcard □ Visa Card Card No ....... .. ... ..... ...... ... .......... ..... .... .............. .............................. ......... ... .. Signature ...... ..... ........ ..... .... .... ........... .. ..... Card expiry date ...... ./ ...... ./ ...... . Note: photocopy this coupon if you don't wish to cut the magazine, or include the relevant details in a letter. 90 SILICON CHIP (or a photostat copy or letter) ana send it to: Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097. LIMITED NUMBERS OF BACK ISSUES ARE AVAILABLE SO DON'T DELAY l PRODUCT SHOWCASE I AT computers from Anabelle Bits Crimping tool for modular phone plugs AT-style computers are becoming cheaper all the time and this latest example made in Taiwan continues the trend. The system is built along conventional lines with a large motherboard in the main processor cabinet and eight expansion slots. It uses the 80236 processor and has four selectable clock speeds: 6MHz, 8MHz, 10MHz and 12MHz. The standard system line-up includes a 20 megabyte hard disc drive, a 1.2MB 5-1/4in drive, a 200 watt power supply and a RAM complement of 1 megabyte. Also standard is a monochrome monitor interface card and parallel printer interface. The keyboard has 101 keys, with LED indicators, numeric keyboard and ten function keys (ie, a standard AT-style keyboard). The price for the above system, including a monochome monitor, is just $2995. Optioning up with an If you are using US modular plugs in telephone equipment, this crimping tool is a beauty. The crimping process is done in several steps. First you cut the cable to the desired length and then use the stripper blades to remove the outer insulation sheath. You then arrange the conductors carefully and place them into the plug. The crimping tool is then used to squeeze the whole assembly together. Priced at $31, the telephone crimping tool is available from Geoff Wood Electronics, 229 Burns Bay Road, Lane Cove West, NSW 2066. Phone (02) 427 1676. UHF tuner modules from Jaycar If your TV set has provision for a UHF tuner it may be possible for you to do the conversion with a Sanyo UHF tuner module. These are powered from 12V, have provision for AFC connection and their output signal is at the Australian Extruded aluminium cases from Betacom These two extruded aluminium cases have internal slots to mount printed circuit boards (100mm wide) and have a folded aluminium lid. Both lid and extrusion are finished in an attractive but hard-wearing epoxy powder coat finish. The cases in question could be used as modules in a Eurocard rack system or can be used in a free-standing appplication such EGA card and colour monitor adds an extra $750.00. We understand that a new variant will be available soon with a 16MHz motherboard and a maximum RAM capacity of 8Mb. For further information and the name of your nearest dealer, contact the Australian distributors for ASI, Anabelle Bits Pty Ltd, 233 Bulwarra Road, Ultimo, NSW 2007. Phone (02) 552 1855. standard video intermediate frequency of 36.875MHz. The tuner covers the full frequency range for Australian UHF bands 4 and 5 and is continuously tuned via a 1/4-inch shaft. (No knob is available). It is supplied with a circuit diagram and connection details, and is priced at $29.95 from all Jaycar stores. as for a modem. Dimensions for the flat case are 110mm wide, 30mm high and 230mm long; for the larger case dimensions are 110mm wide, 90mm high and 170mm long. We understand that custom cases using either extrusion can be made in any length required. For further information, contact the Australian distributor of Betacom cases, Temple-Smith Australia Pty Ltd, 2-12 Harp St, Campsie NSW 2194. Phone (02) 78 3436. AUGUST 1988 91 Contact Belnew Pty Ltd, Shop 1, 140 Macquarie Street (PO Box 1110), Parramatta, NSW 2150. Phone (02) 689 3327. Belts, belts and even more belts Rechargeable 6V lantern battery & chargers from Arlec Can't get a spare belt for your VCR or audio cassette recorder? It's not a problem any longer. This company stocks belts for virtually every VCR ever made and most cassette decks too, including car cassette players. You can buy a kit of belts for most VCRs at $21.95 - if one belt goes it's a good idea to replace them all. Single belts are available though, if you want them. They have belts for turntables too, from $8.00, which is handy to know. Anyone who uses an Eveready Dolphin torch or any equipment taking the Eveready 509, 529 or 1209 6-volt lantern batteries will be interested in the new Arlec rechargeable 6-volt lantern battery and chargers. The Arlec RLB605 battery is the same size as the Eveready 509 although it is considerably heavier at almost 1kg versus 600g. The RLB605 is a nickel cadmium type and when fully charged it puts out 7.2 volts. If used in the Dolphin or other torches, it must be used with a 7.2 volt lamp instead of the 4.8V type normally specified. Fully charged, it has a capacity of 5000 milliamp-hours and is claimed to last longer than the SPECTACULAR ELEASE primary (ie, non rechargeable) batteries it replaces. Two chargers are available, a 240VAC mains plugpack and a 12V cigarette lighter type. Both are fitted with a standard 4.5mm female socket which plugs into a mating socket at the side of the battery. Charging time is 14 hours for both types. We were a little concerned that a Dolphin torch might not float with the heavier battery but when we tried a dunk test it was not a problem. You can buy the Arlec rechargeable kit, containing battery, the two chargers and a 7.2V lamp, for $59.95. The battery by itself is $29.95. We picked up our sample unit from David Reid Electronics, 127 York Street, Sydney. Mini mic/line mixer from Arista vifa NEWSA-100 SPEAKER KIT Since the introduction of VIFA speaker kits in Australia in 1985, thousands of speakers have been built with superb results. VIFA is now proud to release four new speaker kits ranging from a mere $399 to $1199 per pair including cabinets. Never before have speaker kits been so popular in Australia than after the heavy devaluation of the dollar. Similar fully imported quality loudspeakers are today · typically 2-2½ times more expensive. And these speakers may very well be using Danish VIFA drivers anyway, as VIFA supply more than 50 of the world's most respected loudspeaker manufacturers with drivers. ,. But why the big savings? Because fully imported speakers suffer from 25% import duty, 20-30% freight, 30% sales tax and 28% handling charges (typically). So if you would rather put your money into better quality than in other people's pockets, VIFA speaker kits are the only way to go. Are they difficult to build? No, the kits 92 SILICON CHIP are supplied with all parts needed includins fully built crossovers and pre-cut flatpack cabinets ready to assemble. No soldering or carpentry skills are needed, just a Phillips head screwdriver, some simple hand tools and a few hours of your leisure time. Are they as good as people say? Reac the reviews, listen and compare with any other speakers twice the price or more. Need we say anymore? VIFA for the quality conscious audiophile. For full details please contact Sole Australian Distributor: SCAN AUDIO Ply. Ltd. P.O. Box 242, Hawthorn 3122. Fax (03) 429 9309 Phone: 10! 4292199 (Melbourne) 02 5225697 (Sydney) 0 3577433 (Brisbane) 09 3224409 (Perth) Stocked by leading stores throughout Austral The Arista SM400 is a cute little mixer which handles two microphone inputs and a stereo line source. It provides both level control and echo for the two mic inputs and has a small stereo amplifier for driving a pair of loudspeakers. Power requirement is 12 volts at 1 amp maximum from a 240VAC plugpack. Dimensions of the sloping front case are teensy: just 165mm wide, 95mm deep and 50mm high at the rear. For further information, see your local Arista outlet. Variable temperature soldering iron According to Tandy, their latest Archer professional variable temperature controlled soldering iron has really "hit the spot" by outselling all other irons in their range. Rated at 240V, 16-25W, the temperature can be preset between a standby figure of 250°C up to a maximum of 450°C - this by means of a small, slotted shaft recessed into the handle. The iron uses iron-clad, chrome plated, pre-tinned tips which are said to far outlast conventional plated tips - provided they are wiped clean with a Problems? damped solder sponge when hot and are not attacked with a file! The tips are readily interchangeable and optional replacement tips include "micro chisel", "mini chisel" and "standard chisel" for various classes of soldering work. Tandy state that the iron is suitable for use i.p. all ordinary solid state environments. The iron is available through all Tandy stores for $37.95. Plastic coat your tools for a comfortable grip These days most small hand tools come with comfortable plastic handles but many of us have older tools such as pliers with steel handles which tend to rust. Now you can dress them up with Plasti Dip. Plasti Dip is a thick red plastic coating which is applied by dipping the tool handle in the can and then withdrawing it slowly to form a smooth coating. Several coats can be applied to produce a thick pliable finish. You could also use the dip to coat small printed boards or components to seal and preserve them from the elements. It is good stuff but expen- Check the light with a Lux meter If you're a keen video or film producer, a cricket umpire or anyone interested in measuring the available light intensity in a particular situation, you need a Lux meter. This digital unit win measure from 0 to 50,000 lux in three ranges: xl, x10 and x100. It is available from all Dick Smith Electronics stores at $149.00. ... and you don't have our 112 page catalogue ... you've got real problems! ARISTA ... your one-stop problem solver. Audio leads sive at $24.95 for a 470ml can. It is available at Jaycar stores. ... Batteries ... Chargers ... Battery holders ... Cables ... Car accessories ... CD accessories ... Converters ... "Cutec" ... Earphones ... Fuses ... Headphones ... Intercoms ... Knobs ... Microphones and accessories ... Mixers ... Multimeters ... Plugs/Sockets, etc ... Plug adaptors ... Power packs and leads ... PA ... Disc and Tape care ... Security equipment ... Signal modifiers ... Solderless terminals ... Storage boxes ... Switches ... Telephone and TV accessories ... Tools and Technical aids .. . Video accessories ... Wiring accessories ... You name it and we're bound to have It ...Try us ... NOW! Get your catalogue ... it'II solve a whole lot of your problems! Just send $2 + 50c p&h and your return address to: ARISTI\. ELECTRONICS PTY LTD PO BOX 191, LIDCOMBE, NSW 2141 AUGUST 1988 93 ASK SIUCON CHIP Got a technical problem? Can't understand a piece of jargon or some electronic principle? Drop us a line and we'll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Power supply zapped by mains I recently completed the Dual Tracking Power Supply described in the January 1988 issue of SILICON CHIP. Everything worked perfectly at switch-on and would have continued to do so had I not fiddled about with it. In the process of tidying up the wiring I broke one of the leads of the power LED and then decided to replace it. The problem was that I forgot to turn off the power and while soldering the new LED into place, I accidentally touched the Active wire to the power switch. Naturally, I received an electric shock but at the same time I've blown one or more components in the supply. I can't get the DC panel meter to read anything less than 10 volts and and LED dropout indicator is on all the time. I have replaced the two op amps but it is still not working as it should. Also, the lkn resistor from the output of !Cl, the TL071, gets quite hot to the touch and the voltages on the input and output of the LM337 negative regulator are the same. The + 15V and -14V rails are OK. Can you suggest what is wrong Auto level controls cause problems Over the past few years I have collected hundreds of popular songs onto tape from various sources. Occasionally I like to record some of these tracks onto a blank tape so that I can play them in my car. For this purpose I use a tape-to-tape machine which unfortunately has an automatic level control fo r recording. This causes problems when you are recording from different cassettes; some songs will be soft 94 SILICON CHIP with it? (D. D. , Marrickville, NSW). • We hate to preach but we do advise that power switches should be sleeved to avoid accidental contact. It is not all that easy to diagnose a fault like this but assuming that the positive output can be varied over the range from + 1.2V to + 18.5V or so, the fault would appear to be only in the LM337. Less likely is the possibility that D8, the reverse-biased diode across the LM337 is shorted instead. You can check this by clipping one end of D8 with your side-cutters. There are several clues pointing to a defunct LM337 and a normally operating LM317 positive regulator. First, the voltage across the LM337 is zero and second, you can't get the panel meter to read less than 10V. This is because the panel meter is connected across the positive and negative rails and so reads half the total voltage. So even when the positive regulator is set for minimum output, the panel meter will read half the total voltage and obtain a value of 10V as a minimum. Another clue is the LED dropout indicator. It is seeing the high ripple voltage on the unregulated negative supply rail and is registering that as a "drop-out" condition. Finally, the lkO resistor at the output of ICl is getting hot because IGl is trying to pull the ADJ terminal of the LM337 as high as it can, in a vain attempt to inake it track with the negative regulator. So with a bit of luck you should only have to replace the LM337. I wish to comment on the Headphone Amplifier described in your April 1988 issue. The NE5534 is a little unusual in terms of its performance. Apart from its low noise, wide bandwidth and high output current capabilities, it also has reasonably low input offset voltage and, unfortunately, rather high input bias current (500nA typical, 2µ,A max). What this means is that your Headphone Amplifier for CD players has a DC offset at the output. According to spec, if should be about - 0.4V ( - 1.6V, worst case, on a bad day). I lashed one up on a breadboard and it gave me - 0.27V. This is with no load of course, and what DC voltage appears across the phones and then further on they will be loud, making you grab for the volume control. I scouted around a number of electrical stores and found that not one had a tape-to-tape machine with an inbuilt record level control. They did not know why this was the case or if ever there was such a machine made. It must be possible to do this or to build a circuit to be linked to a system. What do you think? (R. P., Latrobe, Tas). • As far as we know, most larger dual tape decks do have manual level controls which allow the recording level to be modified when recording from one tape to another. In the "dubbing" mode though, no signal modification is possible, because dubbing produces an exact tape copy, without the need for Dolby decoding and re-encoding. We are not familiar with portable dual tape machines but we assume that since they generally have simpler facilities no manual level controls are fitted. If that is the case, there would be no easy way of making this provision. The only solution would appear to be to be the purchase of a more expensive dual hifi dual tape deck. Offset problem in headphone amplifier will depend on their resistance but I feel this is undesirable. You could easily cure this by putting a 100µF capacitor in the output, equalising the resistance seen by both inputs, putting a capacitor in series with the 8.2k0 resistor, reducing the 220k0 resistor or a combination of the above. Apart from that, you could substitute an OP27 which has better specs in nearly all departments except price and availability. (P. D., Sydney, NSW). • It is true there will be a DC offset voltage (0.4V typical) and yes, we could have eliminated it by equalising the bias resistances seen by both inputs or a combination of your solutions but there are problems with these approaches. Equalising the input bias resistors, while leaving the 220k0 resistor at pin 3, would have led to more circuit noise. Second, we're not keen on having capacitors in the output or feedback network if they're not strictly necessary. In a typical case, using 80 or 320 phones, less than 2mA will flow through the headphones as a result of the offset; that's nothing to worry about. Sure, high impedance phones will have an offset of several hundred millivolts applied to them but again, that isn't the end of the world. Perhaps the biggest reason for trying to avoid the offset would be to ensure symmetrical clipping of the output signal. In practice though,- do op amps always clip symmetrically when everything else is as it should be? And what about when they're heavily loaded? For the record though, you is right and we is wrong. Wants data on National three-in-one I would be most grateful if you would allow me to ask fellow readers for any service data or a circuit diagram for a National SG-990A three-in-one stereo. (N. Smith, PO Box 402, Stanthorpe, Qld. 4380). • Anyone possess this data? Hang on to your old stereograms out there. They will be vintage models soon. Low ohms adaptor has suspect op amp I built the Low Ohms Adaptor and it operated correctly on the two low ranges, xl and x10, but the two higher ranges were not correct. A thorough check (solder bridges, copper tracks, voltages, component orientation, etc) failed to reveal the cause of the problem. As the op amp is used for the x100 and x1000 ranges, it suggests that it could be faulty. On checking with the supplier, I ask- Notes & Errata 24V to 12V Converter for Trucks, December 1987: the 4.7k0 load resistor connected to the output side of 11 is incorrectly shown as 47k0 on the wiring diagram on page 31. The circuit diagram on page 30 is correct. Protector Car Burglar Alarm, February 1988: in some projects, the 4027 (IC2) has been damaged by voltage transients from the ignition cutout relay. To solve this problem, delete the link connecting the emitters of Q7, Q8 and Q9 to the earth track [ie, delete the link immediately to the left of Relay 1 - see Fig.2, p.22). A length of insulated hookup wire should then be run from the now vacant pad adjacent to Q8 directly to the Ground input on the PCB terminal block on the left hand side of the board. Optical Tachometer, May 1988: the 10µF electrolytic capacitor con- Circuit Notebook ctd from page 34 vide low impedance outputs at pins 8 and 9. These are coupled via 0.22µF capacitors to drive load impedances down to 47k0. Adjusting the Ve supply between 15mV and 15V DC will result in a signal level change of 60dB. Maximum volume is obtained with Ve at 15V. Expected distortion is less than 0.1 % at full output with a 60mV input signal. Signal to noise ratio should approach 80dB. Adapted from National Semiconductor literature ~ ed them if the IC should have been supplied in conductive foam and was told that it was not necessary. I would like your comments. (G. L., East Kew, Vic). • We doubt whether the op amp would have been damaged because of not being packed in conductive foam; it is not a fragile device. Have you checked for the presence of + 5V at pin 7 of the op amp? That is the first test to be done in troubleshooting the unit. Then follow the set up procedure as described in the article. nected to the cathode of photodiode ID1 is shown reversed connected on the wiring diagram on page 20. The circuit on page 19 is correct. Studio 200 Stereo Control Unit, June 1988: the following parts should be added to the parts list 2 x 100µF 16VW PC electrolytics, 2 x 0.1µF metallised polyester, 1 x .01µF 250VAC (Wima MP3 or Philips MKT-P 2222 330 40103). 4P Electronics - Technical Support CAREER OPPORTUNITY IN SALES Texas Instruments is a world leader in the electronics field and Australia's largest supplier of semiconductor components. We are seeking a young per-. son to begin a career with our Semiconductor Division. The role entails technical phone support, sales, and marketing support on our range of high-tech semiconductors. Ideally you'll be around 18-20 years with a keen interest and a good basic knowledge of electronics and computers. Any private studies you are undertaking in electronics will be highly regarded. Opportunity for future promotion is excellent. Interested applicants should phone Helen Wong on 887 1122 for further information. Texas Instruments Australia Ltd. 6-10 TALAVERA ROAD, NORTH RYDE 2113. AUGUST 1988 95 CEN'l Cash in your surplus gear. Advertise it here in Silicon Chip. Surplus Test Equipment Singer 6201 Signal Generators: cover 61 kHz to 512MHz with 6-digit LED display. Calibrated output +20dBm to -146dBm, continuously tunable, 1ppm stability, metered AM and FM modulation circuits, low leakage . Several to choose from. $3200 each. HP1 SOAR Oscilloscopes: solid state 100MHz mainframe, accepts 1800 series plug-ins, CRT 8 x 1 0 div., horiz9ntal b/w DC-5MHz. Supplied with HP1801 A dual trace 50MHz vertical amplifier and HP1820A timebase. Rack mount version. $1600. Spectrum Analysers: Systron Donner 762-2A, 10MHz to 40GHz, 7 overlapping bands, C/W wave-guide mixers, pads, cable. IF resolution FOR SALE NEARLY 1500 PRINTER buffer kits now sold. Prices start at $39 for a 256K short form kit. All items advertised are in stock. Dealer enquiries welcome. Bulk discounts. Schools, Govt. Depts. orders accepted. Oh yes!! IBM compatible. Australian designed and manufactured. Ideal project for user groups and students. For a free catalog send a 37c stamp to: Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. PROJECT REPAIRS - Having trouble getting your EA/ETI/SC kit to work? Phone (03) 7 49 3480 for estimate or send kit to K. Hunter, 5 Yatama Crescent, Werribee 3030. OATLEY ELECTRONICS - here we present some "short-form" kits at very special prices. All these kits include the PCB, instructions and those bits which are generally hard to obtain. Back-up Siren/Satellite Siren (EA, Sept. 87) : a totally self-contained second alarm that comes into action when your main - alarm in interfered with or when the vehicle battery is disconnected. Uses just four penlite nicads to 96 SILICON CHIP 300Hz, on-screen dynamic range 70dB, 51 dB stepped IF attenuation. $5500. Tektronix 491, 10MHz to 40GHz, 1 kHz IF resolution, C/W wave-guide mixers and attenuators. $5200. All equipment offered as is, operational and normally with technical manuals. Calibration service available. Phone or fax your requirements to: Av-Comm Pty Ltd, Telephone (02) 489 1439, Fax (02) 489 6493. No order too small. We have a large inventory in our US warehouse and regular monthly airshipments. We can supply most HP, General Microwave, Singer, Systron Donner etc. power a 12V " piezo screamer" via an on-board DC-DC converter. Could even be powered by inexpensive dry cells if you disable the charging circuit. Just leave out diode D3. The short-form kit includes the PCB, instructions, AD161 and AD162 transistors, battery holder and two 1 00µF bipolar capacitors. All this for only $10.95 plus $1.50 p&p. The Microphone (EA, Nov. 1986): this professional quality microphone will drive any amplifier, since it includes an on-board amplifier. You could even plug it into any line socket on your hifi amplifier to make an inexpensive PA system. Touch control on/off switch and battery check. Automatically switches off when not used. Extremely low battery consumption when on and negligible battery consumption when off. The short-form kit includes the PCB, instructions, aluminium tube and the threaded rod and nuts assembly. A very good start for only $9.95 plus $1.50 p&p. Stereo VU Meter (EA, June 1987): any audio signal will drive this unit since its sensitivity is adjustable from volts right down to millivolts. Even a microphone will drive it directly. Doubles up as a preamplifier and has backlighting lamps. The short form kit includes the PCB, instructions, dual meter movement, Advertisers Index Altronics . . . . . . . . . . . 50-53 Anabelle Bits . . . . . . . . . . OBC Arista Electronics . . . . . . . . 93 Av-Comm Pty Ltd . . . . . . . . 96 Avtek . .. . .. ... . . . . .. . . 3 David Reid . . . . . . . . . . . . . 13 Dick Smith Electronics . . 36,37 82,83 Elmeasco . . . . . . . . . . . . . IFC Geoff Wood Electronics . . . . 1 7 Jaycar Electronics . . ... 24-27 72-75 Kenwood Australia . . . . . . . IBC Oatley Electronics . . . . . . . 96 RCS Radio . . . . . . . . . . . . . 81 Rod Irving Electronics . . . . . 4 1 Scan Audio .. . . . .. . ... . 92 Texas Instruments . . . . . . 95 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. • Jemal Products, 5 Forge St, Welshpool, WA 6106 . Phone (09) 350 5555 . • Marday Services, 2139 Great North Rd , Avondale, Auckland, NZ. Phone 88 5730 . CA3401 IC and the backlighting lamps. A steal at only $6.95 plus $1.50 p&p. Mini Mixer (EA, May 1987): connects up with your existing stereo amplifier to give you total control of two additional microphones and any source you desire, in any proportion you desire. A simple way to make a PA system or a disco system. The short form kit includes the PCB, instructions, two special switches, front and rear panel adhesive artworks and eight RCA plugs. All this at the giveaway price of only $12.95 plus $1.50 p&p. For multiple orders of any of the above kits, include $2.00 p&p. Oatley Electronics, 5 Lansdowne Pde, Oatley West, NSW 2223. Mail orders: PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985. When ordering above quote: "short form kit". The above prices apply until the end of 1 988 or until stocks run out. NEW RZ-1 WIDEBAND RECEIVER "THE SCANNERS DELIGHT" COVERS 500 KHz TO 905MHz RANGE The new KENWOOD Wideband Receiver is a multipurpose receiver that covers the 500KHz-905MHz range. Its advanced features are made possible through the use of advanced microprocessor technology. Features Wideband Fre qu ency C overage (500KH z - 905 MHz ), in cl ud i ng FM Stereo B ro ad cast and M u lti-Channe l Te levi sion So und . 100 Easy -To-Op erat e Multi-Funct ion Memory Channels w ith M essage Capabi lit y. 10-Ban d Pro grammable Capabil ity. K ey boa rd Frequency Se lec t ion. Au to-Mode and Auto-Step Op erati o ns. Mult i-Scan Function . Easy-T o- Read La rge LCD Displa y. Compact and Lightweight . Auto-Sel ectabl e Dual Antenna Terminal s. Built-in speaker. Front-mounting phones jack . Easy- to-operate , illuminated ke ys. Accessory terminal s are Line Ou t/Video Ou t/ External Speaker Terminal. Squelch circuit for FM (narro w ) mode . UP / DOWN Keys forVFO and m emory channel . Specifications Frequ ency Range : 500KHz - 905MHz M o de : A3(A3E] (A M), F3[ F3E ] (FM ) Circuitry : AM , FM (N ) =Triple con ve rsion sy st em FM (W) =Doubl e co nvers ion system Sensit ivity: AM (S+N/ N =10dB ) = L ess than 5 uV (BC band 10uV). FM (N ) = 12dB SINAD less t han 6uV (500KHz - 60MHz ) less than 3uV (60 - 905MHz ). Operat ing T em pe rat ure -10° - +60°C . Au dio O utput Pow er: 2W (at 8 ohms load 10% distortion ). Cur rent D rain : L ess than 1A (audi o po we r ou t put 1W). Antenna Impedance : 50- 300 ohms . Power Requirement: 13 .8VDC ± 15%. Dimensions : 180 (W ) x 50 (H ) x 158(0 ) mm. Weight: 1.5kg. KENWOOD ELECTRONICS AUSTRALIA PTY. LTD. 4E WOODCOCK PLACE, LANE COVE, SYDNEY, N.S.W. 2066. Ph. (02) 4281455. YOUR DEALER BELOW WILL GUARANTEE SATISFACTION Further, beware of dealers nor listed in this advertisement who ore selling Kenwood communications equipment. All Kenwood products offered by them ore not supplied by Kenwood Electronics Australia Ply. Lid . and have no guarantee applicable. N.S.W.: VIC.: TAS.: EMTRONICS - 94 'MNlWORTHAVENU( SYDNEY (02) 211 0988 R£G STOCKM#J COMMUNICATIONS - CNR BANOCKllJRN RONJ & SHIRLEY STREET, INVERB.L (067) 22 1303 WORMALO COMMUNICATIONS - 51 DENNISON STREET, HPMILTON, NEWC'Sllf (049) 69 1999 QID.: ROBERTSON ELECTRONICS - 62 DESMOND STIHT, CESSNOO< (049) 90 7908 M!'CELEC PTY. LTD. - 99 KENNY STR!fT, WOLLONGONG (042) 29 1455 S.A.&N.T.: ALEX JOHNSON - 19 BANKSIASTREET. O'CONNOR, A.C.T. (062) 47 9125 WA : OX ENGINEERING - 158 GRANITE STREl'T, PORT MACQUARIE (065) 84 9922 FRANK BOUNDY - USMORE(066) 86 2145 INTERSTATE PA.RA.MffiRS PlY LTD. - 1064 CENTRE ROAD, SOUTIH OA.KLBGH (0 3) 575 0222 EMTRONICS - SHOP 5 TO 7. 288-294 OUEl:N STREET. MELl'OURNE (03) 670 0330 BRIAN STARES - 11 MA.UMSBURY STIHI. BALLA.RAT (053) 39 2808 SUMNER ELECTRONICS - 78 KING STREET. BENDIGO (054) 43 1977 WATSONS WIRELESS - 72 BRISBANE STREET. HOBART (002) 34 4303 MARINE & COMMUNICATION - 19 CHARLES STREET, L'IJNCESTON (003) 31 2711 VK ELECTRONICS - 214 MOUNT STREET, BURNIE (004) 31 7733 MITCHELL RNJIO CO. - 59 ALEION ROAD, ALEION (07) 357 6830 EMTRONICS - 416 LOGAN RONJ, STONES CORNER, BRISBANE (07) 394 2555 INTffiNATIONAL COMMUNICATIONS SYSITMS PTY. LID - 8 Nil£ STREET. PORT ADELAIDE(08) 47 3688 WILLIS ELECTRONICS - 165ALBA.NY HIGHWAY, VICTORIA PARK(09) 470 11 18 BAY RNJIO - 22 GRACE STREET. FERNOA.LE(09) 451 3561 FORD ELECTRONICS - UNIT 19, 70 ROBERTS STREET, OSBORNEPARK(09) 242 1766