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BONUS 148-PAGE JAYCAR CATALDO Build this LED Message Board High Performance In Your Shirt Pocketl "S:!{~'.~w 3 l /2 digit LCD Display Ranges Max Res Accuracy Vdc Vac Ade 100µV 1mV 1001-tA 10mA 100µA 10mA 0.1Q 200mV-1 kV 2V-750V 200mA 10A Aac 200mA 10A Ohms 200Q-2MQ Display also has Low Battery & Over-Range Indication 0.5% + 1dig 0.75%+5dig 0.75%+ 1dig 1.5%+5dig 1%+5dig 2%+ ?dig 0.75%+1dig Built In Diode Check, Lo-Power Ohms & Continuity Test Beeper 4c •QOc/ /Lori .,, Autoranging ~ .{;;.. I Ft~ Memory Function for Relative Readings (DM6235 & DM6335) Manual Ranging Over-Ride (DM6235 & DM6335) At~ ii One Year Warranty Hold Reading Function (DM6335) l0A Range Automatic Current Limiting Overload Protected to 1000Vdc/750Vac $69.00* $79.00* Look At The Low Pricesl DM6135 Autoranging 3 1/2 digit 10A ac/dc DM6235 As above with Memory function and Range Hold Prices include 9V Battery and High Quality Silicon Rubber Test Leads with Screw-On Alligator Clips DM6335 As above with Data Hold l0MQ Input Impedance Got ta • G (! t ta • G 0 IdSta ,- $89 00* • You 've Gotta Getta Goldstar from : Supported & Serviced Australia-wide by Elmeasco Instruments Pty Ltd Dealer enquiries welcome. Call (02)736 2243 Recommended prices only including Sales Tax A.C.T. John Pope Electrical 80 6576 • J Blackwood & Sons 80 5235 • George Brown 80 4355 N.S. W. George Brown 519 5855 Newcastle 69 6399 • Ames Agency 699 4524 • J Blackwood & Sons Auto-Catt Industries 545 1322 • D:G.E. Systems (049) 691625 • WF.Dixon (049) 69 5177 • Macelec (042) 29 1455 • Newtek (042) 27 1620 • Novacastnan Electronic Supply (049) 62 1358 • Obiat Pty Ltd 698 4776 • David Reid 267 1385 • Dig1tel 709 65 11 • Geoff Wood 427 1676 N.TERRITORY J Blackwood & Son (089) 84 4255, 52 1788 • Thew & McCann (089) 84 4999 QUEENSLAND Auslec 85_41661 • George Brown 252 3876 • St Lucia Electronics 52 7466 • L.E.Boughen 3691 277 BAS. Au d1otrorncs 844 7566 • Colourview Wholesale 275 3188 • E.C.Q. Electronics 376 5677 The Electronics Shop (075) 32 3632 • Thompson Instruments (Cairns) (070)51 2404 • Solex (Townsville)(077) 72 4466 • Xanthos Electrical (079) 27 8952 $.AUSTRAL IA George Brown 212 311 1 • J Blackwood & Sons 46 0391 TASMANIA George Harvey (003) 31 6533 (002) 34 2233 VICTORIA • G.B. Telespares 328 4301 • J Blackwood & Sons 542 4321 • The Electronic Components Shop 670 6471, • Factory Controls (052) 78 8222 • Mektronics _Co 587 3888 • Truscott Electronics 723 3094 • AW.M. Electrical Wholesalers W AUSTRALIA Atkins Carlyle 481 1233 • Dobb1e Instruments 478 1366 • George Brown 3621044 PAPUA NEW GUINEA T E (PN G.) Pt Moresby 25 6322 Lae 42 6246 MARCH 1989 FEATURES HERE'S A MOVING MESSAGE display board that you can build yourself. It can be controlled from a personal computer or directly from an IBM PCcompatible keyboard. Details page 34. 4 Electronics For Everyone by Leo Simpson Ptl: what you need to know about resistors 42 The NE572 Compandor Chip by Malcolm Young Abridged data & specifications 84 The Technology Letters by Richard Kopf Fun & games in the security industry 88 The Evolution of Electric Railways by Bryan Maher Pt.17: NSW XPT express passenger trains PROJECTS TO BUILD WANT TO RECORD compact discs for use in your car's tape player? You'll need this CD Compressor to record the music without distortion. See page 26. 26 Stereo Compressor For CD Players by Greg Swain Lets you tape compact discs without distortion 34 Build a LED Message Board by Don McKenzie Works from an IBM-compatible keyboard or computer 44 Studio Series 32-Band Equaliser by John Clarke Uses special slider pots for improved boost & cut action 64 Map Reader For Trip Calculations by M. Young Simple circuit uses a LED & phototransistor SPECIAL COLUMNS 16 Vintage Radio by John Hill Timber cabinets are a lot of work 56 Serviceman's Log by the original TV serviceman The line of most resistance 68 Amateur Radio by Garry Cratt Build a simple VHF FM monitor receiver, Pt.2 74 The Way I See It by Neville Williams "Spycatcher": do Wright's electronics bear scrutiny? OUR TV SERVICEMAN suffered a few jibes this month and struck problems with substitute transistors. His story starts on page 56. DEPARTMENTS 2 Publisher's Letter 3 32 41 51 Mailbag Circuit Notebook Subscription Page Bookshelf Product Showcase Ask Silicon Chip Notes & Errata Market Centre IBC Back Issues 79 93 95 96 THIS SIMPLE VHF FM monitor receiver use just two ICs and a handful of other parts. We show you how to build it for the 2-metre amateur band. See page 68. MARCH 1989 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 Editorial Advisory Panel Philip Watson, MIREE, 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 rate: currently $42 per year (12 issues) inside Australia. For overseas rates, refer to the subscription page in this issue. 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 PUBLISHER'S LE'l-l'ER Deceiving the eye of the beholder This month we have a number of interesting constructional projects in the magazine but the one which is most appealing to us is the LED Message Board. We feel that this will be very popular among computer users because it is one of the few build-it-yourself computer peripherals that is really useful. Apart from its ability to be controlled by a personal computer, the LED Message Board is intriguing because of its wide variety of visual displays: scrolling up and down, wiping up and down and from side to side, flashing words and so on. It is all made possible by clever programming of the Message Board's ZBOA microprocessor but there is another interesting aspect - the use of multiplexed drive to the LEDs, all 672 of them. Multiplexed displays make use of the well-known persistence of vision of the human eye. If it were not for this persistence, movie films, TV screens and fluorescent lamps would flicker badly and virtually every digital display would be unreadable as the digits flashed individually on and off. Multiplexing digital displays achieves two economies. First, it reduces the power needed to produce a perceived brightness level in the display and secondly, it greatly reduces the number of connecting wires. In a typical 4-digit 7-segment display, a minimum of 11 drive wires is required if multiplexing is used, compared with 32 if each digit is driven separately. That is a big reduction but consider the Message Board: with 672 LEDs it would need a phenomenal number of drive wires and it would be difficult to get the variety of visual effects. With multiplexing and a clever serial to parallel data conversion it only needs a minimum of 8 signal drive wires. But perhaps the most intriguing aspect of the Message Board is not all the clever driving circuitry but the way in which the observer must "cooperate" with it in order to see the moving messages. Your eyes must follow the words as they move from right to left or from left to right. If you stare fixedly at one of these displays, you will only see a jumble of lights. So as well as exploiting the persistence of vision, message boards also exploit the natural tendency of our eyes to constantly scan our field of vision and to follow moving objects. Not only are our eyes being deceived but they are cooperating in the process. Leo Simpson MAILBAG Success with train controller You may be pleased to hear that I built the Railpower controller [SILICON CHIP, April 1988) and that it has been thoroughly "thrashed" by all the local model railway enthusiasts. It has been rated the best controller·so far! Some locos however have resisted all attempts to reduce the "sing" and the writer/assembler has almost been done over for suggesting to owners of these locos to try again [to improve the mechanism). To change the subject, the Mains Muzzler described in the January issue is a good project but may I humbly suggest the following: (1). Use a PCB-mounted 3-bay terminal strip to terminate the incoming power cord; ie, with screw-down terminals [rather than soldered) as the electricity authorities take a dim view of soldered joints, especially on flex leads. (2). The electricity authorities are down on homebrew multiple power boards - especially as the multiple is not switched individually, requiring plugs to be pulled out of the line sockets. Of course they frown on switches on cord/multiples anyway. Where I worked for many years we confiscated all made up multiples as soon as they were discovered - the faults in some were alarming! A simpler version with one wall type socket and switch combination in a box with PCB and anchored cord may be a useful variation. S. Dogger Stokers Siding, NSW Pleased with high energy ignition circuit Excellent, that's the only way to describe the High Energy Ignition [SILICON CHIP, May 1988). It took a while to obtain the kit but it's fitted now and what a difference. I drive a 350 Chev-powered Monaro and this kit has transformed the engine. It has noticeably more power, dead smooth idle, easier starting and 1-2mpg more economy. I've had the car eight years and usually tune it myself. In the past, points were deterioriating in two months so I hope they'll go a lot longer now. Also I used to get an ignition buzz when playing a tape but not on FM; this has now gone. I guess if the Kettering system was pressed with 4 or 6 cylinders, 8 is even worse. VB owners should be made aware of this kit: $39.95 versus an expensive twin-points distributor set up. Tom Lloyd SILICON CHIP, PO Box 139, Collaroy Beach 2097. now very little wasted audio and I get good listening volume at a control setting only about one third on. This was the first of your projects that I have built and it worked first off. I'm impressed and very pleased with the result. More in the same vein please. Jim Lawler Hobart, Tasmania Reynella, SA Comment: Yes, the points will last a great deal longer but don't forget to regap them every 10,000km or so. If you forget this task, wear on the rubbing block will degrade your timing and, if let go too far, will stop the engine altogether as the points eventually won't open at all. Alternatively, you could go the whole hog and convert to a Hall Effect system, as described in the June 1988 issue. The best project ever The Speakerphone project in the September edition of SILICON CHIP is a winner - I think it's the best and most useful project any magazine has ever offered. The ability to use both hands while still carrying on a phone conversation is the most useful thing ever to happen to my workshop. I don't have to ask my customers to "hold on while I look up the file". Everything in the workshop is accessible without having to interupt the call. Goodonya SILICON CHIP! There's only one suggestion I would make. It seems a pity to waste three quarters of the audio power in the 220 resistor in series with the speaker. In fact, the kit I built up came with an 80 speaker and a 220 resistor, further limiting the audio output so that comfortable listening could only be had by turning the volume control almost flat out. In my junk box I have some 150 Rola speakers taken from old Astor b&w TVs. The 3-inch (7.5cm) round versions are too low-fi for music but are very efficient on speech which is exactly what is needed in the Speakerphone. I fitted the 150 speaker and reduced the series resistor to 100. There is Battery chargers for standby generators I have just a few minor comments on a couple of articles that appeared in the December 1988 issue of SILICON CHIP. First, regarding the "anti-tinkle" module mentioned on page 87, you might have pointed out that your own "line grabber" [March 1988) does the same job if fitted to a tinkling phone. I fitted it originally for this purpose, not as a line grabber. Second, regarding the circuit on page 59 entitled, "Charger for 12V Gel Batteries", this circuit is almost identical to one I designed about 18 months ago to prevent over-charging of starting batteries on standby generators. Many of these are charged by elcheapo chargers with a nominal rating of about 4 amps or so. These have a full wave rectified output with about 20 volts peak on the "high" charge setting and a half wave rectified output on the "low" setting. The normal life of an unattended truck battery under these conditions [low setting) is only a few months and at approximately $120 each (for the battery), the cost of charger modifications is recouped immediately. The circuit as shown, minus the transformer and rectifier, is simply added between the charger and battery and can be built into the charger. If the standby generator has an alternator on it as well, a diode in series with the output of the charger is required to protect the LM317. The circuit could also be useful in marine applications to keep a boat's battery topped up when not in use. Keep up the good work with the magazine. John Whittingham The Gap, Qld MARCH 1989 3 ' . . · . . - ·. . . . . - · " _ · 1 ·· ·. . . - - . · • ·• ······._.. -- - - . . . ··· .. . - o· .., .. - . - -veryon - ii. . ' -- , .. . Pt.1: What you need to · know about resistors 11111, . -, ❖,• ,. ,,. ~ 111, ·: •:❖:;}·'. • • ''""" Virtually every electronic circuit has resistors in it. They are.the most basic of electronic components and the easiest to understand. One of the big problems for beginners is how to read the labelling. On wirewounds, the labelling is printed while on film resistors it is in the form of colour code bands. By LEO SIMPSON Well, what is a resistor anyway? A resistor is a component which "resists" or impedes the flow of electrical current. If the resistor has a high resistance, not much current will flow, for a given voltage. Perhaps the most familiar resistors are those used in domestic electrical appliances. For example, the heating element in your electrical radiator is nothing more than a large wirewound resistor. It has a relatively low resistance and is designed to run red hot. So are the heating elements in your electric stove. They draw a relatively high current of several amps from the 240V AC mains and so they dissipate quite a lot of power - up to several kilowatts. Other resistors which are widely found in people's houses are the heating elements in toasters, electric irons and kettles, hair dryers and incandescent lamps. All the examples just cited are designed to run from the high voltage of the mains supply - 240 volts AC. They are specially designed to dissipate (ie, give off) a lot of power (heat) and they may run extremely hot; eg, the white hot filament in an incandescent lamp. Another point about the resistors just mentioned is that they are all designed for a particular purpose and they can't be adapted to other tasks. In the world of electronics though, we deal with resistors that are general purpose - they are designed for a wide variety of tasks. Resistors fall into two broad types, wirewounds and film types. The latter type use a carbon or metal film as the resistive medium. Most resistors used in electronic applications do not have to dissipate a lot of heat. Carbon and metal film resistors commonly dissipate only small fractions of a I I i I ,, 11 »w, ,,,,..... ,.Jtl ~ ' I '\ ' , Fig.1: an array of general purpose resistors as used in electronic equipment. The values are directly printed on the two wirewound types while the carbon film types have colour bands. watt while wirewound resistors commonly come in ratings of 5 and 10 watts, although they can be made in ratings up to several hundred watts. Even so, they are puny compared to the high power heating elements in electric heaters, stoves and toasters. The photo of Fig.1 shows an array of general purpose resistors, widely used in electronic equipment. The unit of resistance The unit of resistance is the Ohm (named after George Simon Ohm). A resistor has a value of one ohm when it is necessary to apply a voltage of one volt across it in order to drive a current of one amp through it. On circuits and in texts about electronics, it is not usual to spell out the word "Ohm" every time a resistance value is measured. Instead, we use the Greek letter Omega - 0. So when we write about or specify a 12 ohm resistor, it is written as 120. Resistance multipliers The range of resistor values used in practical electronic devices is extremely wide, from fractional values below 10 to ten million ohms or more. Since the use of large numerical values is unwieldy, it is standard practice to use multipliers in front of the O symbol to specify thousands or millions of ohms. So to specify thousands of ohms, we use the multiplier " kilo" - hence "kff'. So to specify a resistor value of ten thousand ohms we write 10k0. Similarly, to specify millions of ohms, we use the multiplier "mega" - hence MO. To specify a resistor of 1.5 million ohms we write 1.5MO. In normal conversation, you would refer to a 10k0 resistor as ''ten kilohms'' (pronounced killomes) or more usually as a " ten kay resistor". For a resistor value of lOMO you would say it has a value This article is the beginning of a new series for people who have little or no knowledge of electronics but would like to gain some practical experience without delving into a lot of theory. Hence, the emphasis will be on practical matters rather than on theory. MARCH 1989 5 --------+12V I- OUTPUT --------ov I- OUTPUT 10k!l --------ov Fig.2: resistors are most commonly represented on circuits as zigzag symbols. Alternatively, they can be represented as rectangular boxes as shown in Fig.3 at right. of "ten megohms" or you might refer to it as a "ten meg resistor". For low values, you use the value direct. When referring to a 1500 resistor, you say exactly that, a "150 ohm" resistor. Recognising resistors on circuits There are two recognised ways of drawing resistors on circuits. The older and more easily recognised way, as used in SILICON CHIP, most other electronics magazines and on most commercial electronic circuits, is to show the resistor as a zigzag symbol. This is shown in Fig.2. This shows a number of components in a small circuit. The zigzag symbols are resistors and their values are shown close to them. The zigzag symbol was adopted originally because it suggests the construction of many wirewound resistors. These are usually a coil of wire on a ceramic former but they can take on a zig zag format. Have a look at the element in your toaster, hair-dryer or in incandescent lamps. Often, in order to make the circuit easier to describe, or when there are very large numbers of resistors (as in TV and VCR circuits), it is common to number the resistors - hence R1, R2 and so on. On some circuits, the resistors may be numbered but their values in ohms will not be shown. You might have to look up a parts list to find the values. In SILICON CHIP we always use the zigzag symbol but we don't often use R numbers. And when we show resistors in circuit we usually leave out the "O" symbol where the k or M multiplier is used. Hence, a 6.8k0 resistor will be shown on SILICON CHIP circuits as 6.8k. This practice is commonly used elsewhere. Circuits of European origin (and some drawn to the Australian Standard ASl 102 which is not widely used) show resistors as rectangular boxes. Fig.3 shows the same circuit as Fig.2 but is redrawn to show the resistors as boxes. You will recognise the boxes as resistors because they will have R numbers (eg, R3) near them or the actual values. Decimal points On some circuits, often of European origin, you won't see values such as 0.330, 1.50, 4.7k0, 6.8MO and so on. Instead of showing decimal points, these same component values are shown on circuits as R33, 1R5, 4k7 and 6MB, respectively. Instead of using the decimal point, the multiplier (k or M) is used in its place. And for small res~stance values, R is used in place of the decimal point. This "non-decimal" method of labelling resistors is set out in an IEC standard, publication 62. IEC stands for "International Electrotechnical Commission". So when you see a resistor marked 5R6, you will recognise it as having a value of 5.60. Similarly, a resistor marked 3k9 is 3.9k0 and one marked 2M7 is 2.7MO. Odd labels such as lRO, lkO and 1Mo simply mean rn, lkO and lMO, respectively. Resistor types Fig.4: a selection of 5-watt and 10-watt wirewound resistors. In each case, the resistor's value and its rating is printed on the resistor body. 6 SILICON CHIP As mentioned before, resistors for electronic circuits fall into two broad types: wirewound and carbon or metal film. In Australia, the most commonly available wirewound resistors have power ratings of 5 watts, 10 watts or 15 watts. Larger values are available but are seldom used in most circuits. Where wirewound resistors are specified on circuits their power ratings are usually also shown, hence 5W, 10W or 15W. Often, there may be the designation To give you an idea of how hot these resistors become, if you run one of these 5 watt "bathtub" resistors at 5 watts, its surface temperature is likely to be at least 120°C above ambient (ie, the surrounding air temperature). For a 10 watt resistor, run at full power, the surface temperature will be at least 200°C above ambient. This may not be enough to set anything on fire but it can be enough to char a printed circuit board or other components, if the resistor is too close. Derating Fig.5: this heating element (from an electric heater) is simply a large wirewound resistor. This unit is rated at several hundred watts. '.I Fig.6: a selection of carbon-film resistors. These resistors are too small to have values printed on them, so colour bands are used to indicate the values instead. The six resistors on the left are 4-band 5% tolerance types, while the six on the right are 5-band 2% types. "WW" to show that the resistor is wirewound. If you go into an electronics parts dealer and ask for a 5 or 10 watt resistor, you will most likely be sold cine like those shown in Fig.4. Externally, they don't look like wirewound resistors, but they are. These are a fireproof resistor housed in a ceramic "bathtub". If you broke one of these resistors open, you would find the resistance element inside, wound with very fine wire (usually Nichrome) on a round ceramic former about 2mm in diameter. Incidentally, the fact that these resistors are listed as being fireproof should not suggest that they don't get hot - they get very hot. But if they are badly overloaded, with excess current through them, they don't catch fire and their casing does not become red hot. Instead the internal resistor element fuses and goes open-circuit. It is normal practice to "derate" resistors in normal operation. This gives a margin of safety, minimises long-term drift in the value of the resistor and makes the component much less likely to break down. Typically, resistors are derated to 60% or 70% of rating. For a 5 watt resistor, this means it is normal to run it at 3 to 3.5 watts. Incidentally, sometimes when reading about resistors, you might see the term "fixed" resistors. The resistors we're talking about right now are "fixed" because their value is (more or less) constant, regardless of the applied voltage, operating temperature or whatever. Examples of resistors which are not "fixed" include potentiometers which can be manually varied or thermistors, which vary their resistance markedly according to their operating temperature. Wirewound resistors are normally made in values which span the range from o.rn to about lOOkO or so. For values above lOOkO you normally need to go to carbon or metal film resistors. Carbon and metal film resistors Much more common than wirewound resistors in typical electronic circuits are carbon and metal film resistors with a power rating of less than one watt. In fact, the most common resistors today, which are used in quantities of hundreds of millions every year throughout the world, are resistors with a rating of a quarter watt or less. MARCH 1989 7 wm ~ ~ DAVID REID W For the electronics enthusiast ELECTRONICS PTY. LTD. ~===========================~==:::::::::::::::::::::::::::::::::::::::::::::~. . . RS-232 BREAKOUT BOX FLUKE 80 SERIES MUL TIMETERS ~ r ... "The first multimeters that are truly multi" FLUKE 87 TRUE RMS *. 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UNIT PRICE SUB TOTAL P+P TOTAL TOTAL PRICE SUPPLIED P + P RATES $5-$2 5 . . $4 $26-$50 ...... $7 $51 over . . ... $9 Table 1: 4-Band Resistor Colour Code A B C D i:::::::====1( I 11 11 11 I )~= ~ ~ Band A B C D Colour Tens Units Multiplier Tolerance Black Brown Red Orange Yellow Green Blue Violet Grey White Gold Silver 0 1 2 3 4 5 6 7 8 9 0 1 1 2 10 100 1k (= 1000) 1 Ok (= 10,000) 1 00k (= 100,000) 1 M (= 1,000,000) None 1% 2% 3 4 5 6 7 8 9 0.1 (divide by 10) 0.01 (divide by 100) These are the "workhorse" resistors of the electronics industry. They set bias values for transistors and op amps, and are used in feedback networks, filter time constants and a hundred and one other circuit tasks which would not be practical with wirewound resistors. These resistors are so small that it is not practical to print their values on them so a series of colour bands is used to show the value. The most common colour code system used these days has four bands but as close tolerance resistors (2 % or 1 % ) become cheaper and more readily available, the five band colour code is becoming more common. In a few years, these may completely displace resistors with only four colour bands. The resistor colour code For many newcomers to electronics, the resistor colour code is probably the biggest stumbling block. While you are becoming familiar with the colour codes, working out resistor values does require some mental gymnastics but you can get around the need for these. Bear with us for a few paragraphs or so while we tell you about it and then we'll show you how you 10 11 SILICON CHIP = 20% these, the last two bands will be gold and silver or combinations thereof. For example, consider a 4. 70 resistor with a tolerance of 5 % . The first two bands are easy enough: yellow and violet for 47. To get 4. 7, the multiplier needs to be 0.1 which is gold. Since it has a 5 % tolerance, the last band will be gold too, so the code will be yellow, violet, gold, gold. If the value is 0.470 with 5% tolerance, the bands will run yellow, violet, silver, gold. Reading the codes 5% 10% can get by without knowing the colour code at all. Table 1 shows the four band colour code system. The first two bands give the first two numbers of the value while the third band gives the multiplier. Take a look at the table now to familiarise yourself with it. The easiest way to become familiar with the colour code is to · cite a few examples. Let's pick an easy one: a 22k0 5% resistor. The first two bands will be red followed by orange for the multiplier. That gives 22k0 while the fourth band being gold gives a tolerance of ±5%. As another example, consider a resistor with four bands reading yellow, violet, green, gold. Yellow and violet give the first two numbers as 47 multiplied by lOOk (green) to give a value of 4. 7MO. Gold gives the tolerance of ± 5 % . One more example: consider a resistor with four bands reading blue, grey, brown, silver. Blue and grey give the first two numbers as 68 with the multiplier as 10 [brown) to give a value of 6800 with a tolerance of ± 10 % . Low resistance values It can be tricky to latch on to the colour codes for low value resistors; ie, those below 100. On This brings us to the question: in which direction do you read the colour codes. If you pick up a resistor with gold or silver bands, it's easy - just put the gold or silver bands to the right and then read off the code from left to right, as shown in the diagram associated with Table 1. It gets tricky though when the fourth band is red, for a 2 % tolerance, or brown, for a 1 % tolerance. How do you go then? It would be possible to read the value off in either direction. In most cases though, you will realise that, if you read off the code in the wrong direction, you will get a value which is invalid. For example, consider a 680k0 resistor with a tolerance of 2 % . If you consult Table 1, you will come up with bands [from left to right) of blue, grey, yellow, red. If you read it the other way, ie red, yellow, grey, blue, you would have a resistor of 24,000MO with a tolerance of 0.25%. Now there just isn't any such animal. Well, we might have picked an easy example there. It is possible to get some values which read the same way, no matter which direction you read the bands. An example is a resistor with four red bands. That would be a 2.2k0 resistor with a tolerance of 2 % . Or you could have a resistor with four brown bands. That would be a 1100 1 % resistor. But once you get away from those examples, it is possible to get resistors with four bands which give valid values in either direction. Take a 1000 1 % resistor for exam- Table 2: Resistor Colour Codes: E12 Series with 5 % Tolerance o.rn 0 .12n 0.15Q 0.18Q 0.22n 0.2m 0.33Q 0.39Q 0.47Q 0 .56Q 0.68Q 0.82Q brown brown brown brown red red orange orange yellow green blue grey black red green grey red violet orange white violet blue grey red silver silver silver silver silver silver silver silver silver silver silver silver gold gold gold gold gold gold gold gold gold gold gold gold R1 R12 R15 R18 R22 R27 R33 R39 R47 R56 R68 R82 1kQ 1.2kQ 1.5kQ 1 .8kQ 2.2kQ 2.7kQ 3 .3kQ 3.9kQ 4.7kQ 5 .6kQ 6.8kQ 8.2kQ brown brown brown brown red red orange orange yellow green blue grey black red green grey red violet orange white violet blue grey red red red red red red red red red red red red red gold gold gold gold gold gold gold gold gold gold gold gold 1 kO 1 k2 1 k5 1 k8 2k2 2k7 3k3 3k9 4k7 5k6 6k8 8k2 1.0Q 1.2n 1.5Q 1.8Q 2.2n 2 .rn 3 .3Q 3 .9Q 4 .rn 5.6Q 6.8Q 8 .2Q brown brown brown brown red red orange orange yellow green blue grey black red green grey red violet orange white violet blue grey red gold gold gold gold gold gold gold gold gold gold gold gold gold gold gold gold gold gold gold gold gold gold gold gold 1RO 1R2 1R5 1 R8 2R2 2R7 3R3 3R9 4R7 5R6 6R8 8R2 10kQ 12kQ 15kfl 18kQ 22kQ 27kQ 33kQ 39kQ 47kQ 56kQ 68kQ 82kQ brown brown brown brown red red orange orange yellow green blue grey black red green grey red violet orange white violet blue grey red orange orange orange orange orange orange orange orange orange orange orange orange gold gold gold gold gold gold gold gold gold gold gold gold 1 Ok 12k 15k 18k 22k 27k 33k 39k 47k 56k 68k 82k 10n 12n 15Q 18Q 22Q 27Q 33Q 39Q 47Q 56Q 68Q 82Q brown brown brown brown red red orange orange yellow green blue grey black red green grey red violet orange white violet blue grey red black black black black black black black black black black black black gold gold gold gold gold gold gold gold gold gold gold gold 10R 12R 15R 18R 22R 27R 33R 39R 47R 56R 68R 82R 100kQ 120kQ 150kQ 180kQ 220kQ 270kQ 330kQ 390kQ 470kQ 560kQ 680kQ 820kQ brown brown brown brown red red orange orange yellow green blue grey black red green grey red violet orange white violet blue grey red yellow yellow yellow yellow yellow yellow yellow yellow yellow yellow yellow yellow gold gold gold gold gold gold gold gold gold gold gold gold 100k 120k 150k 180k 220k 270k 330k 390k 470k 560k 680k 820k 100n 120n 150Q 180Q 220n 270Q 330Q 390Q 470Q 560Q 680Q 820Q brown brown brown brown red red orange orange yellow green blue grey black red green grey red violet orange white violet blue grey red brown brown brown brown brown brown brown brown brown brown brown brown gold gold gold gold gold gold gold gold gold gold gold gold 100R 120R 150R 180R 220R 270R 330R 390R 470R 560R 680R 820R 1 MQ 1.2MQ 1.5MQ 1.8MQ 2.2MQ 2.7MQ 3.3MQ 3 .9MQ 4.7MQ 5 .6MQ 6 .8MQ 8.2MQ 10MQ brown brown brown brown red red orange orange yellow green blue grey brown black red green grey red violet orange white violet blue grey red black green green green green green green green green green green green green blue gold gold gold gold gold gold gold gold gold gold gold gold gold 1MO 1M2 1M5 1M8 2M2 2M7 3M3 3M9 4M7 5M6 6M8 8M2 10M ple. It will have a colour code (from left to right) of brown, black, brown, brown. Read it back the other way, and you get a value of 110 1 %. In this case, both values are valid. Sometimes there is a bigger gap between the third and fourth band, which gives you a clue as to which direction is right but that is not often the case. So which is right? The only way to be sure is to use your multimeter, switched to the Ohms range. We'll come back to this point later. To help make it easier for you to recognise resistors with four colour bands, we have listed out all the available resistors in Table 2, for the E12 series. We'll explain what E12 means in a moment. These are the values that you will find readily available from most electronic parts suppliers. MARCH 1989 11 Table 3: 5-Band Resistor Colour Code A B C D E ( 111 II II II ~I 111 ) Band A B C D E Colour Hundreds Tens Units Multiplier Tolerance Black Brown Red Orange Yellow Green Blue Violet Grey White Gold Silver 0 1 2 3 0 1 2 3 0 1 10 100 1k (= 1000) 1 Ok (= 10,000) 1 00k (= 100,000) 1 M (= 1,000,000) 1 OM(= 10,000,000) 2 3 4 4 4 5 6 5 6 5 7 8 9 7 8 9 6 7 8 9 Table 2 gives the colour codes for 97 different resistor values, from o.rn to 10MO. Note that we've listed the values in the conventional way down the lefthand side of the table and have used the nondecimal (IEC 62) method down the righthand side. So if look on the lefthand side of the table for a value such as 5.6k0, you'll see it listed as 5k6 on the righthand side. This will help you to identify colour codes no matter how the resistors are specified on a circuit diagram. Having boggled on the 4-band colour code, consider the 5-band code, as shown in Table 3. The first three bands give the three most significant figures in the value, followed by the fourth band as the multiplier and then the fifth band being the tolerance. A couple of examples will suffice to show that the 5-band system is merely an extension of the 4-band system. Consider a 10k0 1 % resistor. In the 4-band code, it would have a code of brown, black, orange, brown. In the 5-band code, it goes brown, black, black, red, brown. A 33k0 1 % resistor will have a code orange, orange, black, red, brown. Even those who are fully familiar with the four band code will sometimes stumble with the five band code so if you're having trou12 SILICON CHIP 1% 2% 0.5% 0.25% 0 .1% 0 . 1 (divide by 1 0) 0.01 (divide by 100) ble grasping resistor codes, don't worry - you're not the only one. E-series Before you go too far in the fascinating pursuit of electronics, you're going to come up against the E-series. For many years, there was only one series of resistor values and it used to cater for most design needs. Now called the E12 series, it progresses as follows: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68 and 82. From there the series repeats but with a multiplier of ten, for the next decade. Hence: 100, 120, 150, 180, 220 and so on up to 820. In a given decade of resistance, say from 1000 to lkO, the E12 series gives 12 values, as just described. Let's just explain that point about decades of resistance further. A decade of resistance is a series of values which increases by a factor of ten. The range of resistance values commonly used in modern electronics circuits ranges over more than eight decades from o. rn to over 10MO. For the E12 series, the eight decades are as follows: o.rn to 0.820 rn to 8.20 100 to 820 1000 to 8200 lkn to 8.2k0 10k0 to 82k0 1ooko to 82oko lMO to 8.2MO. Every one of the E12 series values is shown in Table 2. Now this series does meet a wide variety of design needs but what about when the design calls for a value just about half way between one of the values in the E12 series? Say the designer needs a value of 200, which is half way between 180 and 220. For this requirement, the designer picks a resistor from the E24 range. Instead of 12 possible values per decade, the E24 range gives 24 values: 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27,30, 33,36,39,43,47,51, 56, 62, 68, 75, 82 and 91. From there, the series repeats with a multiplier of 10. Hence, 100, 110, 120, 130, 150, 160 and so on. We've shown only a portion of two decades here, from 100 to 1600 but the E24 series spans the same range of resistance values as the E12; ie, from o.rn to above lOMO. Notice that every value in the E12 series is included in the E24 series. Sometimes though, the range of values available from the E24 series is not enough. Designers want more. For these occasions there are the E48 and E96 series. As you might expect, the E48 series gives 48 possible values in a decade of resistance while the E96 range gives 96 values per decade. We've set out the E48 and E96 series in Table 4. Notice that each value has three significant figures plus the multiplier - this is why resistors with five colour bands are necessary. Again, if you look through the values in Table 4 you will notice that not all the values in the E24 series are included in the E48 and E96 series. This isn't normally a problem for two reasons. First, you can always get a value in the E96 range which is pretty close to the wanted value in the E24 (or E12} series. Second, most manufacturers of precision resistors make both the E24 and E96 series in any given type. This does not always apply but it usually does. There is a problem with the E24 and E96 series though and that is that very few parts stockists will keep the whole Table 4: E48 and E96 Series (One Decade Shown) E48 E48 E96 E96 E48 E96 100 105 110 115 121 127 133 140 147 154 162 169 178 187 196 205 100 102 105 107 110 113 115 118 121 124 127 130 133 137 140 143 147 150 154 158 162 165 169 174 178 182 187 191 196 200 205 210 215 226 237 249 261 274 287 301 316 332 348 365 383 402 422 442 range. So if the circuit you are building specifies values from the E24 or E96 range you may have to search out a supplier who has them in stock. Just as a matter of interest, there is also an E192 series. This has 192 different values per decade. It includes all the values from the E12, E24, E48 and E96 series but it is used only for very high precision resistors. These are normally only available by special order from electronics manufacturers. Tolerance We've already mep.tioned tolerance on resistors but it needs some explanation. Resistors are commonly made these days in the following tolerances: 10%, 5%, 2% and 1 %. Much higher precision resistors are made to tolerances of 0.5 % , 0.25% and 0.1 % and are used, for example, for the range multiplier 215 221 226 232 237 243 249 255 261 267 274 280 287 294 301 309 316 324 332 340 348 357 365 374 383 392 402 412 422 432 442 453 464 487 511 536 562 590 619 649 681 715 750 787 825 866 909 953 464 475 487 499 511 523 536 549 562 576 590 604 619 634 649 665 681 698 715 732 750 768 787 806 825 845 866 887 909 931 953 976 resistors in digital multimeters. However these precision resistors are not normally available "off the shelf" and have to be specially ordered from the manufacturers. On resistors with colour code bands, the tolerance is indicated with the fourth or fifth band; eg, gold for 5 % , red for 2 % and brown for 1 % . If you come across carbon resistors with only three bands, they are not only very old but they were made with a tolerance of 20%. On wirewound resistors where the values are normally printed on the bodies, the tolerance may be printed (eg, 10%) or, these days, may be indicated with a letter code. The letter tolerance codes are set out by a United States EIA standard (EIA stands for Electrical Industries Association). The letter code is as follows: M ..................... 20% K ...................... 10% J ......................... 5% G ........................ 2% F ......................... 1% D ..................... 0.5% C ................... 0.25% B ..................... 0.1% If you have a look at the photo of Fig.4 you will see that the wirewound resistors have a J or K printed on them to indicate a 5% or 10% tolerance. It is important to realise that the tolerance is a plus and minus limit on the nominal value of the resistor. So if you have lkO 5 % resistor it really means lkO ± 5%. This means that the true value of the resistor may be anywhere between 9500 and 10500. In practice, depending on how closely the manufacturer controls quality, the true values of 5% lkO resistors will tend to cluster quite closely to lkO. This can be handy to know in some situations. For example, if a circuit specifies a lkO 1 % resistor and you only have lkO 5 % resistors in your kitty, you may well be able to get by, provided you check the value on your digital multimeter. Using your multimeter OK, if you've stuck with us up till this point, you deserve a medal for perseverance. But what if you still feel that you will have great pro- 1 I Fig.7: this photo shows the resistance element of a wirewound resistor (right). This is encased in a fireproof ceramic "bathtub" at shown at left. MARCH 1989 13 blems making any sense of colour codes and therefore lack the confidence to put any electronic circuits together? And what if you are partially or totally colour blind? Well, don't let that stop you. This is where the digital multimeter really comes into its own. Instead of trying to fathom out the code just switch your digital multimeter to the appropriate "Ohms" range and whack the prods across the resistor. As quick as a wink the meter will display the value. No worries at all. And if you feel guilty about using a multimeter instead of being intimately aware of the resistor colour codes, consider these points. First, as we noted above, there, is the problem of reading resistor bands the right way, where the tolerance band is not gold or silver (which is the usual tip-off). Second, as resistors continue to get smaller for a given rating, it is becoming much harder to discern what the colours actually are, even if you are reasonably keen sighted. And with some brands of resistor it ca,n be very hard to distinguish between red and orange, or between green and grey. This particularly applies if the lighting is poor or if you are using fluorescent lights which give a different colour rendering. In these situations, it can be pretty well impossible to determine what the colour code is. In those situations, even the most experienced electronics practitioners have no qualms about resorting to their digital multimeters. We certainly don't have any such qualms and neither should you! Incidentally, you really do need a digital multimeter to check resistor values accurately. Analog multimeters are just not accurate enough. There is one trap to watch out for when you are measuring resistors, particularly those with high values. The tendency is to grasp one end of the resistor in each hand and hold it against the probe tips. In this situation the reading will not be accurate because the digital multimeter will be measuring your skin resistance as well as the resistor 14 SILICON CHIP Fig.8: this photo shows the correct way of measuring a resistor on a digital multimeter. Don't touch the resistor's leads with your hands, otherwise your skin resistance will upset the reading. the result will be lower than it should be. The way to avoid this trap is to make up a pair of very short leads for your multimeter. Fit a banana plug to one end of each lead and a crocodile clip to the other end. This will enable you to connect the resistor to the meter without having to hold the prods in contact. Our photo (Fig.8) shows the method. Before making the measurement, set the meter to the appropriate resistance range. This should be higher than the resistor to be measured otherwise you'll get an overrange or blank indication on the meter. Short the meter leads together and check that the meter reads zero. If it doesn't, jiggle the banana plugs in their sockets to make sure they are making good contact. Now connect the resistor and measure its value. ~ WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD F OR CHIPS .. . 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The gun can also be used as a hot blow tool. $399.00 ex tax ($479.50 inc tax) Optional Stand $18.00 RF Chokes 3.3uH RF Chokes pack of 25 were $12.50 now $6.25 • l' L LSI design e Big 0.56" Red/Orange LEDs • Balanced Diff Input/Floating e 1ooov CMV This 5V operated DPM was in our catalogue at $49.95, but to clear the remaining few , out they go. Uses AD2020 chip, Bournes trii:n pots etc. You will never see quality cheaper at only$ 25.00 Teflon Coated Wi We were astounded at the response to Teflon insulated wire in our recent catalogue . It obviously fills a need and we have located further supplies. Teflon Insulated 1 x 0,50mm (24AWGJ Blue Brown Green Grey Orange Violet White Yellow Per Metre $0.30 Per 30 Metre Roll $7.50 We still have available a replacement for that old favourite FND500 still used in magazine projects and what's more we are still discounting them. LTS543R FND500 Replacement 0.5in 10 for $8.00 ~ a a .,, a :i:, 2 ~ 240V to 24 V at 250mA was $10.00 reduced to $5.00 Teflon Insulated 19 x 0. 10mm (26AWG) Black, Blue, Brown,Green,Grey, Orange, Red, Violet, White, Yellow Per Metre $0.50 Per 30 Metre Roll $12.50 Teflon Insula ted 7 x 0.079mm (32A WG) Black Red Per Metre $0.30 Per 30 Metre Roll $7.50 Teflon 250V Insulated 7 x 0.010mm Black Green Per Metre $0.40 Per 30 Metre Roll $9.50 .:iEOFF WOOD ELECTRONICS PTV LTD 229 Burns Bay Road, (Corner Beatrice St.) INC IN Nsw Lane Cove West, N .S.W. P.O. Box 671 , Lane Cove N .S.W. 2066 Telephone: (02) 4271676, Fax: (02) 428 5198. 8.30am to 5.00pm Monday to Friday, 8.30am to 12 noon Saturday. 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 a .,, a :i:, r, :i: ~ ~ a a .,, a :i:, r, :i: ;; (/) ~ a a .,, a :i:, r, :i: ;; (/) VINTAGE RADIO By JOHN HILL Timber cabinets are a lot of work Last month, I divided radio cabinets into two categories - synthetic materials (plastic and Bakelite) and natural materials such as timber. This month's topic is the restoration of timber cabinets. The restoration of a timber cabinet is a far more daunting task than the restoration of a Bakelite (or plastic) cabinet and would be at least 10 times more time consuming. To do a tradesman-like job of a large console type cabinet can easily consume 20 or more hours of time. If one was to charge at plumber's rates for that amount of time, the real value of such a restoration soon becomes apparent. In time alone, a well-restored radio with a timber cabinet must be valued at hundreds of dollars. Whether anyone would actually pay that amount is entirely another matter. Enough of this hypothetical speculation. Let's get on with the restoration of a timber cabinet. Strip down A complete strip-down of unnecessary bits and pieces is a good starting point. Everything must be stripped from the cabinet, leaving it a completely bare shell and nothing else. A thorough clean-up is next and the cabinet should be brushed down, both inside and out, to remove cobwebs, dust, fluff and other rubbish that has attached An old flat file makes a handy varnish scraper but care must be taken not to dig the corners into the timber. If the lacquer is difficult to scrape off, you may have to resort to using paint stripper. 16 SILICON CHIP itself to the woodwork. A good blast of compressed air helps to finish off this operation. Many old radio cabinets were made back in the days when animal glues were in common use. These natural glues were quite effective but they weren't waterproof and 40-50 years or more is a long time for any glue to hold things together. As a result, many of the glued joints may have come unstuck and will require re-gluing. Some cabinets are better than others as far as loose joints are concerned. In odd cases the cabinet frame is strong and rigid and, if it has always been indoors, it may not require much attention at all. On the other hand, if a relatively weak cabinet has spent the past 15-20 years under the leaky iron roof of a backyard shed, then there is a good chance of it being in fairly poor condition. Such a cabinet will require extensive re-gluing and the odd nail or two to tighten up the frame. The first major task (and undoubtedly the worst aspect of restoring a timber cabinet) is to remove all the old varnish and strip the outside surface back to bare wood. On a large console type cabinet this can amount to anything from five to eight hours work with every minute of that time being totally boring to say the least. With really ancient radio cabinets, removing the old lacquer is not that difficult because it becomes crazed and loses its grip on the surface of the wood. When this is the case, the old varnish scrapes off with ease. Although there are many commercial paint scrapers available, it A nicely restored timber radio cabinet is a joy to behold. This old HMV has a pleasant blend of several different timbers. At least 8-hours of work was required to restore this console cabinet. The old lacquer had to be scraped back to bare wood. sitting on the cabinet and working on it in every imaginable position which could spring a joint open. Cabinet repairs Paint stripper, woodstop putty and wood stain are all part of the act when preparing a timber cabinet for respraying. is perhaps better to make one from an old flat file. If the end is ground off at a 90° cutting angle, the homemade scraper works quite well. What's more, it is easily resharpened and will just about last forever. Not all exterior surfaces are easily removed. Some of the timber cabinets from the late 1940s and early 1950s still have their lacquer well attached and it can be extremely difficult to scrape off. These cabinets require a more drastic means of attack and paint stripper is usually quite effective. Even then, removing the old varnish can be a long and tedious job. It can also be a bit messy. Anyway, like it or not, if one is to restore a timber radio cabinet, then all the original surface treatment must be removed by some means or other. And no matter how it is done, it will involve a good many hours of work. Once all the lacquer has been removed, it's a good idea to recheck for loose joints again. The scraping operation often involves One disadvantage with wood is that it dents easily and these dents are the next problem to overcome. Applying steam (either by a boiling kettle or a hot iron placed on a damp cloth) will help to lessen the dents. Steaming makes the wood fibres swell, thus reducing the depth of the depression. However, this operation is not always successful due to the size of some of the dents. The majority of timber cabinets, with the exception of very early radios, are of the wood veneer type. In other words, the cabinet construction is basically of cheap plywood which has a thin veneer of attractive wood on the outside. Occasionally, the veneer develops blisters and these must be properly treated before sanding the cabinet down. Blisters and other raised portions of the veneer are repaired by first cutting a slit into the trouble spot in order to get some glue inside the blister. Once this has been done, the blister must be clamped flat and held that way for 24 hours untii the MARCH 1989 17 When sanding, the aim is to remove all imperfections without going through the thin skin of the veneer. There are times when this cannot be done and it is better to "bog up" a deep groove or depression with filler rather than risk ruining the cabinet with too much sanding. Sanding should be done in the direction of the grain with a relatively fine grade of paper. Interior finish Open joints and split timbers must be re-glued before the cabinet is sanded down. You will also have to repair any blisters that have developed, while cracks and chips can be repaired using woodstop putty. glue has thoroughly dried. A webbing clamp is a very useful gadget when doing those tedious repairs. Any separation of the plywood will also require re-gluing and clamping. Ply separations are usually caused by moisture which softens the glue and allows the layers of ply to part company. Another problem with timber cabinets is chipping of the veneer at the edges. These hollows can be repaired by replacing them with a suitable patch of similar veneer or by filling in the gaps with a woodstop putty of the appropriate shade to match the timber. When all these little jobs have been done, it's time to start sanding down the cabinet with sandpaper. Sanding must be done carefully because the thickness of the veneer is considerably less than 1mm, which leaves only a small margin for error. A coarse grade of sandpaper is not advisable as it can rip through the veneer in a couple of heavy rubs. An air compressor is a very useful accessory for the vintage radio enthusiast. A blast of compressed air is often useful when cleaning up the cabinet and it can also be used drive a spray gun. 18 SILICON CHIP The insides of timber radio cabinets are usually quite roughly finished and they are either painted black or given a quick coat of whatever went on the outside. Personally, I prefer to touch up the inside of a cabinet before finishing the outside, although there is no reason why the reverse procedure cannot be adopted. If the cabinet is black inside (as a good many are), a suitable treatment is a full gloss black enamel paint diluted about 50:50 with mineral turps. The thinned down paint can be applied with a brush and will soak into the wood so readily that it leaves a matt finish. Cabinets that are lacquered inside can be given a one coat touchup with low gloss varnish. Outside finish At this stage, some cabinets will be ready for a final finish but many others will require further preparation. For example, some cabinet frames are made of very lightcoloured timbers which require staining to a darker shade so as to match the veneer of the plywood. This must be done before the lacquer is applied otherwise the contrast between the near white pine frame and the dark walnut veneer is just too great. Other cabinets will require some external painting of trim areas before the clear lacquer is administered. It seems logical to complete these trim areas first and then cover the paintwork with the clear lacquer. The paintwork may require several coats and will need 24 hours drying time before the final top coating. Those highlighted trim spots are usually either black or dark brown and can give the cabinet quite a lift Vintage Radio Kits & Parts ORPHEUS *RADIO* A small spray gun is the only way to go when restoring timber radio cabinets. This touch up spray gun cost around $75. A fully restored console cabinet. A lot of work was involved in this restoration hut the results made the effort well worthwhile. as far as appearance goes. The paintwork invariably matches the colour of the knobs and the dial escutcheon. It takes time and a great deal of care to neatly cover these painted areas and a sloppy job will spoil the overall effect of the restoration. When applying the clear lacquer (three or four coats if a really good deep finish is required), a small spray painting outfit is the only way to go. The job can be done with a brush but generally speaking, brushes produce a second rate job. To my knowledge, radio cabinets were never French polished. Clear lacquers such as "Estapol" seem to be as good as any to use and one must choose between gloss and satin (semi-gloss) or mix a bit of each for a surface lustre somewhere in-between. This bit-ofeach treatment is particularly good as a full gloss finish on an antique radio often looks out of place. Antiques should have a subdued appearance and a brilliant high-gloss finish seems inappropriate to me. Speaker fabrics, as mentioned last month, also play a big part in the restoration of a timber radio cabinet. Rather than repeat myself, I will refer readers to last month's column for details on this aspect of cabinet restoration. To sum up, restoring a timber radio cabinet is a major job that will test the skill and enthusiasm of any vintage collector. If he can come at this task time and time again, he is either truly insane or really keen on his hobby. Perhaps a bit of both? ~ Suppliers of • • • • • VALVES RADIO KITS CAPACllORS RESISlORS BOOKS, ETC. Please send for our free catalogue ORPHEUS RADIO RSD 898 BALLARAT VICTORIA 3352 Ph. (053) 34 2513. Fax (053) 31 3412 DESIGN MANUFACTURE REPAIR of Electronic Equipment No Job too Small or too Large Industrial and commercial control and testing systems, designed and manufactured to your requirements. Audio Amplifier Modules: from 60 Watt rms 0.01 % THD to 500 Watt rms 0 .0001 % THD (Only 5 connections to be made) . Temperature Meters: from -200 deg. C. to 1300 deg. C. Remote Sensing up to 1 km HYCAL INSTRUMENTS Design, Manufacture, Repair of Electronic Equipment (02) 633 5897 (02) 92 6309 Fax (02) 925 0840 MARCH 1989 19 YOUR 1988 DICK SMITH ELECTRONICS CATALOGUE Many In-Store Specials As All Hobbyist and Enthusiast Well. Products About The Sale 10-300/o OFF We're tearing pages out of our 1988 catalogue All price reductions are off current prices. and reducing everything! It's THE BIGGEST Store stocks only. Some discontinued lines HOBBYIST SALE WE'VE HAD IN YEARS. We may not be available at all stores. Some items have to make room for all the new and on '88 Catalogue pages may already have sold exciting products in our bigger, more out, however hundreds of items not shown are colourful, more informative 1989 catalogue. at reduced prices. STORES: DISTRIBUTORS: • NSW • Albury 21 8399 • Bankstown Square 707 4888 • Blacktown 671 7722 • Bondi Junction 387 1444 • Campbelltown (046)27 2199 • Chatswood Chase 411 1955 • Chullora 642 8922 • Gore Hill 439 5311 • Gosford 25 0235 • Hornsby 477 6633 • Liverpool 600 9888 • Maitland 33 7866 • Miranda 525 2722 • Newcastle 61 1896 • North Ryde 88 3855 • Parramatta 689 2188 • Penrith (047)32 3400 • Railway Square 211 3777 • Sydney City 267 9111 •Tamworth 66 1711 • Warrlngah Mall 905 0441 • Wollongong 28 3800 •ACT• Fyshwick 80 4944 • VIC • Ballarat 31 5433 • Bendigo 43 0388 • Box Hill 890 0699 • Dandenong 794 9377 • East Brighton 592 2366 • Essendon 379 7444 • Footscray 689 2055 • Frankston 783 9144 • Geelong 43 8804 • Melbourne City 326 6088 • Richmond 428 1614 • Ringwood 879 5338 • Sprlngvale 547 0522 • QLD • Brisbane City 229 9377 • Calms 311 515 • Chermside 359 6255 • Redbank 288 5599 • Rockhampton 27 9644 • Southport 32 9863 • Toowoomba 38 4300 • Townsville 72 5722 • Underwood 341 0844 • SA • Adelaide City 223 4122 • Beverley 347 1900 • St. Marys 277 8977 • Elizabeth 255 6099 • Enfield 260 6088 • WA • Cannington 4518666• Fremantle335 9733• NorthPerth328 6944 • PerthCity4813261 • TAS • Hobart 31 0800 •NT• Stuart Park 811977 N.S.W.: BALLINA: Ballina Electronlcs86 7022 BOWRAL: F.R.H. Electrical 611861 BROKEN HILL: Hobbies & Electronics 88 4098 CHARLESTOWN: Newtronics 43 9600 COFFS HARBOUR: Coffs Harbour Electronics 52 5684 DU BBO: Chris's Hi Fi 82 8711 FORSTER: Forster Village Electronics 54 5006 GLEN INNES: John Sommerlad Electronics 32 3661 GRAFTON: Repairs and Spares 42 1911 GRIFFITH: Mlatronics 62 4534 INVERELL: Lyn Willing Electronics 22 1821 LISMORE: Decro Electronic Services 214137MOREE: Moree Electronics52 3458 MUDGEE: Headware 72 3895 NOWRA: Nowra Electronics 21 0722 WAGGA WAGGA: Phillips Electronics 21 6558 VIC: MORWELL: Morwell Electronics 34 6133 SHEPPARTON: Phillips Electronics Ply Ltd 21 9497 WARRNAMBOOL: Marrtronics 62 9870 QLD: BUNDABERG: Bob Elkin Electronics 72 1785 KINGAROY: Holmes Today Electronics 621658 MACKAY: Stevens Electronics 51 1723 MARYBOROUGH: Keller Electronics 21 4559 TAS: DEVONPORT: A.I.Electronics 24 8322 SA: LOXTON: G & S Electrical 84 7495 MT GAMBIER: Hutchesson's Communication Centre 250400 WA:ALBANY: Micro Electronics 41 2077 BUNBURY: Micro Electronics 21 6222 GERALDTON: Batavia Lighting & Electrical 21 1966 KARRATHA: Daves Oscitronic 85 4836 ORDER BY PHONE,TOLL FREE (008) 22 6610 FOR 24 HOUR DESPATCH .----------, • S,-... " ooM•O<"'·~''°'" ""~ '° m · aeco, ~ ;t!i,1"E."i.""~ t1,Jpp"'1l-.rt,cnov I IMppl"9•iu: 110 , 1to, 40mm s91s 2IKl , 115,l40m m IOupH .l! ~tHOOt.voly StylOdbloci< ABS <ow co,nploto w:1nnand,._ O ~~::~~ g-;'~~= P:~~'~:; •· ~~~: ~::; c,! ~~0n~:!, --=~= l'Ot ': ''P" ' "'·COOll"',1. ..C c.. ,s,,. no,.. 1, g-Sl " I_ • l h,ppi<19H'9hl; 0 09 Sl>IPP"'OC OLI0: 220 , 70> 140mm s179s 200,u,,aomm 10up l1 1.1! A oupo,0 <1M !o, , :i .,,1 , . u1ypop, 01tc10, ond"1 ony C oH 1pl,1ttPo<1!o r " Ho1 ,. orkmv c<;>mo~e<> rcp:~1• m(I'" ::~=~::,,;'~:.::;':i ~~~;~~;~::.,~•,:;;-.,;r,,.•,~o~~~ :;;:;~c~:o~•:t.:=;2:~:;,~:;"'" ~ ,..,u,,odl S,u 1ppro, lhipp if111woi\Jhl: lt$,;J With Both Aluminium And Plastic lids... The New Zippy Box Tho bo, mo.,.,.o1.,, od~lhomo;o<olo<tr on,c, m"fjo11 nH Oo<OuHol ,10Qu • "'• • " a • 0<0 1111,ty' '°""" · ...,,h .....,,., OSE Z< pP)' DO• yo,, got on o,on ~ ~or '"" °""''" • ''G" ' lmong pint« oca ,..:ou, a olum,,..vm hd - Yes two •a• '"'" H eh bo• ' 210 ,551 175m m Do0<gn.a ! 0< uH • ""' OutU H< Tr 1noct..., K111K,63001, l>IJ I 1uporb !or 1 ,o, ger011g1ol ,n., rumen.o, com"1umco~on ::••::::::•,0;17~••:~~=•~:,'~•,::m o>0hlolront ond '"' ~1.~95 ~l~~~t:-g,~ ~ 2 Sizes ~ff~~\~i~li~~!i}~;f~: ~ 1 •,•,•,•.•,•,•, E~~:~,;~,~~~;i,:~::::"i:~,~~~~~:: ,; ::::::::::::;: ;~~~•.-~~~•de~: ii~•,o ,a..1!o, , mo>I 0, 0.-.:1, ;:;:;::::::::: I/ii mH " l lhot notc ,...,1 oro ,0Qu 'IOd W11h ,,o,, 10M bt<\ S•• • 9~ :'u~~~~~~}?.~,~~atd io, s9:s o« •t1 o, '-• >• lng tnn1m1ne, o lnl,•••• d, utt,u c ,-c, Ulif <tlcfor ~':V~;J: :~:,7i~~;l~~-~~~;:/;~,~~~: :•' ~~~;=.:~~- If!~~'~ ' :::::l::l:l:l:::::::::::ttIJt:::::::::::1::::::::::1::::t:::::11:::: : : : : : :JJII1::::::::::::1::::::=:11:::::::::::JJ)JJJI: Plastic and Metal Zippy Boxes D/o <at>ID~2l2J:Bl s ·" " " " "'" --"""'~----·,w ~-.-us•~"••~ •- -•o,q,,.......... ..,,un.c,on,....... ..,,,_o<l b, .. 01"1peot, ........ 1•0 ....,., 5,mp1y,.......... Mm. 1w I rn .. ,·, 1oo c1IIIOIJ<JO num.,.. ol ~our <H1m1r• <a•IH>• ,,,., .., VALUI IN \",W IOUI , ~,., Ol!M$ ·~:::· '~"': · '~t-m:· 1< ..,. ¼W V,W 1W C0tlH>• f dm co, bon f il m C otl>c• fdm s. ..,n •• •••• ,,. ,... WHO Wound '"" " "" ~ALI.I I IN OHM S 'i'O:'.'.::' •~,;:';;:~· .., A• l<Q:I R.1<1),1 u A· 1'0II R.1.,2 R-1'16 R.\ .. I A- 1111 A-10;Q R-,.22 A- 1~22 ,..u "u u u A-1<:t A• " )() R.1031 A-1434 A·1<36 Duol Roto,yPoh $2.95eo (10 up $2 75 ea) M!TAICLINEAA 10 , 1\-11 3• MUI\I C LOG A ' 603 ,oo ,:, ::mi A•IUO A-IUI 50o. IMPllllAL UtlEAII A-l<OI ,.... 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A,132:I A- IJ20 A, 15:1:1 A-152• 100 ZOO SOO A-1956 A-19'7 11- 1¥.,9 1!11< 1\.1960 !>, 1$$ , A-111112 20011 R- 111&• 11. 1;,i;s R,1 9" •• 11. , .,,., ,oo,. 2< A1 W J 5000 A-1M7 ~ SOO too• 1M 2M2 H- 19~ R-1()69 Hofl1ontol Tl1mpots soe eo (10 up ,s, ea) :::ili :::ii! !1 ,.. :::ill :::m H ,,.... ::;: ::::: :1r §: ~ ~ ;i A- 13311 A- l s:18 j!!= IM:1<6 A•I™ Ii .!:! ~::E =::::i }H :::;: ::~~ 1¥1 •• """ ::m ::::: ,,, ::: : :~ iiili 1:~ m:= ~~l':,,~,s1.,o,,1. .,, ~--., ......,,. ~~~~~ :. l~/i\1imI1~iiiiiiiii;ii~ifiliiimt1tm!llllliI:mmim11111it11lllmi:· Resistors and Capacitors What the buyer thinks ... "Some of the most popular capacitors and resistors in packs, individually or in bulk at a huge 25% reduction ... lt's about time we gave the hobbyists something extra for all their 21 years of support." D/o 1,tc,...,.,.._,.,.,..,...,,0_.,,.,.,. 11>ey COfl\Jlle!OIJ ...!e7Vou.. co:.il<ll>elll" "'' ~~-=.,:;;,::.:~=~==., c., . _, * =111-:r,::~:,.- $1295 Negative Ion Gen Ma,,1"90Po--u .. ion, ore g0<,0 1o, rou1 we·•• ,.,..,.... - ,1 co!M oe • pi.,__ ..i.t!' .....,0,,1ol-•"" -t,,jl 'fW"'Og• ~· · t,-.,...,o11n1p,oce 01""""""'"'.. ""'" - Du' :-.:.•~c:~=• """'d"'$,r,eompcn,e.t ="!.':~~:-... 2495 lnfrared 240 vott Controller t>m'" Fluoro Starter Oo - • · lluOrH Ce<l! hgl," 1JOD""~- l>l!fl, , l>M"fll' ~=~:~=:--1.:.:.:: _ ...,..,,ou ..,.1,:n"'•"' ""' Tlu1-..1><1n~11 o!Kl•on ........,.....,.,...,p,oo,......,, _,, :s:-~':"'.. 1,,o.i!Q>11 co,,..:'rl>ortll>1ot1.,,., .,o1u P,OIO-gtvh Me "°' ""'"' r.::=r::.s:.u,,,... How ma ny tomes hl ve you .,,a nted 10 sw,1cn a powt1, po,M "ON '0 , ·0 FF ,. hen ,t s acro,s 1ne ::::::::,::;,:,::;::::',:':;.:,•i~;·,::: tan1a .ioc 1n1,a ,&(l Rem01~ Conu ct sw,1ch. rou c"" swdch on the TC. lamp, , ~a,o or many .....,,M appl,1nces w011>01>1 n:o.,n5 !ro,r,11,. cor:,looolrou• bedorcn.. 11,,e 1,..,,u,,·1te• t5~sed ,n5pe,;Oll:!y on.g,:>edca$8abaul the si, a olama tChbo• -SO •l'l ~rtocau r ,n s5995 , 0urpoc: ket o,chp lOJOUf l h,,i 0,c.en11 n Operale upto 12 m,u es !r omth esw,tch a nO ~-••i a,lly Ou ,gn<1 0!0 ,m« MfflUffl $695 Speed Controller Spore Transmitter for above: • SC)95 It's here . . . The Discolight! ~i~:i'·;'~~~:~~o~~~ ~·.~~J.i~~ ~ ~!_r·~&l~~:~Why? B- ~~t:~:1:1:::~:.w:u~: Yaelh1 Dl1co1igt,1do11 a l/ o !the so -1namo,11 H.,1'1 wha1,1w,"do !o, ,ou,,,., tp,a rty· • Conftft -iodir.ci .,_.,. M'l:Plifi«'• _..,., lfffflinala (lnpa,ahl lriW, . . . ..,), "'dncl ltom lta own lrlMfflal ffllcrOph- to drinr lour ~ ot bancll ofcolourwcl liehh (11plolOOW1~cti1nMI). • l'orw•cl, rew.,.. or aut•re..,."111 e h - pattarn, • SIIIIUII•- atrobt, Ol'I a!Wwr cha11M11 •A.ll•11atir,gpalnolchlln,,.._IINhi"9 anne Remote Controller ;..:...~=~onorln1,,n,1oecHl.. ortw1i11bleonchaff1', 1!r- • . 1nO so much mo r1llnshort ~ s 1n, compk,llllgllM11 con1tolcentre!o,an111141 v1,iety<>luH,1_!,om ll>e!'.Offll o• ~. 1n, 0111111ema 1eu, and oroien,onal 51.ag,e wo,k, ::orw:.•~:~~t~!~~:'.~':':,~::uons, meetre1. 1Mc - t1gl'II up 10 (end includ1n11• 1 ~~:,~~ - ·,. ,.v,ng 8b0ul 0':8 new OIM:Dligl'II .. yau',e l!lsOlutlMr "Iii"'' 165 1 The latest and the bes1 in electronics Hobbyist's Kits Here's what the buyer says! "We've over 50 kits to clear, to make way for our new 1989 projects, and over 100 on-going kits - so we've reduced them all. 15% off everything from beginner to expert. All are high quality kits and all come with comprehensive instruction manuals." D/o Soldering Accessories Som,gk>adod, pl1er g r,pei1ps lo rnu 1 se1,our,o compor1<n1S P1otoe1your>00Job,o < . nonll "'"'••""'• .,.,..v-ano m,U S01d...-,o,nto tn11<ut - w,tt>11'1.oio,, .co,:u1 Desoldering Wick :;'!,~•: : .~:;,;;.~~":~'::'o~~-"~~~t:.!',:~".~'.'~~~ S~lppl!>1Jwfi9111;i0s, Cartvoai<•:H0,1G,o.,,nm Top Quality Solder Aid Set DSE - the World-Wide company that .~nows you r needs Soldering Accessories From the buyer... "Give them 15% Off, right across the board! That's everything, solder, braid, soldering accessories ... the lot! It doesn't matter if they're our best selling items or not... I need the room." D/o T0-220 Heatsink High Efficiency Packs Power Heafsink f>o o>; Ol l<vOClP•Otl hHlllnk O!OfT0 -220 lypoH m.. 1olaol<lop .. blo !OOth0< !yp. .1 ...,...,,1,11,ie,1»-H I Mtt<l,olt n<IUg n =.-..~:~~;==~":' .......,,a,N,_ . :. f~zg:~::~=~ .._..._ ..........,_....,,n, l'>100Utslnk11oblo lOO> .. lj>&IOhYgo ,.,,.u.. ,oi ....1n111>16C• 1"°°'""io, ...,,g,..1orr.t~Tn.,.ma1,..,.,,oc, m<>U<>11ngau....,,io,m1>:- -1•c,...n 1ot ~ """""" ' IN: 101• IIO • - Versatile Power Heatslnk !I ffi] Round T0 -5 .... ..,,..,....... !0.,..,..,,o1..,,..,.. ,., ""'"'"I.,,~ ,~ a nd bU I pon; b:o hu t lranlPl!Otll0-5c1 -. M• H " O t>o<ly ~,r~~{ Powerfln for T0-3 ~~~==~ : , ~ •ln: 1..:i ,110,».nm t,t.so ==~10,u- 10up",Cl5 ,.._..., ..... ,, =I ~.___ ---' iv More and more people are becoming salislied DSE customers every day eatsinks ~ ge 43 ....:. . :S!I Stereo compressor for CD players Ever tried to record a compact disc for use in your car's tape player? We'll bet that you struck problems. This simple compressor circuit reduces the dynamic range from CDs so that you can make good recordings. By MALCOLM YOUNG & GREG SWAIN If there has ever been an ideal music medium then the compact disc (or CD) must come pretty close. But while CDs give great music reproduction, recording the contents of a CD onto tape usually gives a disappointing result, particularly if the tape is to be used in your car. The major problem when interfacing these two pieces of equipment is that the humble cassette tape cannot handle the wide dynamic output range of the CD. As a result, high level signals will be severely clipped while low level 26 SILICON CHIP signals will be lost forever down in the noise of the recording system. If you do try to play such a recording on your car's tape player, the soft passages will be drowned out by vehicle noise while the loud passages will sound distorted because of signal overload. In short, the tape will sound dreadful. Dynamic range Some readers will not be familiar with the term "dynamic range" so let's explain what this means. In simple terms, it is the difference in level between the softest and the loudest passages on the recording. Compact disc players can handle a very wide dynamic range, up to 96dB, while tape players only have a dynamic range of about 50dB. From those figures, you can see that a tape player simply cannot handle the wide variation in signal level that a CD player can deliver. But even if it could, we don't want a wide dynamic range in cars anyway. There's no point having a tape with a wide dynamic range if the soft passages are drowned out by vehicle noise and the loud passages almost deafen the driver. To overcome the above problems, you need the CD Compressor described here. It makes soft passages louder and loud passages softer. By compressing the dynamic range, it makes music much easier to hear in noisy environments like a car. LEFT SPEAKER CD PLAYER LEFT COMPRESSOR RIGHT LEFT RIGHT SPEAKER PARTS LIST RECORD LEFT RIGHT AMPLIFIER TAPE DECK RIGHT RIGHT PLAYBACK LEFT TAPE MONITOR LOOP Fig.1: the CD Compressor is simply installed in the line between the CD player and the inputs of your stereo amplifier. Alternatively, for a direct connection, it can be installed between the CD player and the cassette deck. 3V 3V 2V 2V 1 Printed circuit board , code SC01203891, 112 x 7 4mm 4 screw mount RCA phono plugs 1 DPDT miniature toggle switch 1 SPST miniature toggle switch 1 plastic box, 160 x 95 x 55mm 1 1 2VAC plugpack 1 O PC stakes 1 aluminium ground plane , 148 x 85mm 4 5mm PC standoffs 4 1 0mm x 2mm-dia. bolts plus nuts & washers 1V Semiconductors 1V 1 1 1 1 2 - 1V - 2V -2V -3V Fig.2a: a lkHz 5V peak-topeak waveform and a 3kHz 1V peak-to-peak waveform. In use, the CD Compressor is simply installed in the line between the CD player and the inputs of your stereo amplifier (see Fig .1 ). In practice, you connect the leads from your CD player to the RCA input sockets of the CD compressor. You then take a pair of leads with RCA plugs on both ends and connect the CD Compressor outputs to the CD inputs on your amplifier. To make recordings from CDs, you use the Tape Monitor function in the usual way. Alternatively, for a direct connection, the CD Compressor can be connected between the CD player and the tape deck. When you are not recording from the CD player, you simply switch the Compressor to the bypass mode to eliminate compression. Signal degradation in the bypass mode is negligible. We measured a signalto-noise ratio in this mode of - 116dB. The CD Compressor can also be very useful when you want background music at a dinner party. In this situation, if you turn the volume right down to allow comfortable conversation, the soft passages of the music will be lost completely. By switching in the CD Compressor and keeping the volume low, you can comforta bly hear all -3V MAX DYNAMIC RANGE 6V pk-pk Fig.2b: if the two waveforms are simply fed to an amplifier, the system can be overloaded and the lkHz signal clipped. 3V --- ---- - - -- 2V LM4136 quad op amp (IC1) NE572 compander (IC2) 7812 3-terminal regulator 7912 3-terminal regulator 1 N4001 rectifier diodes (D1, D2) 4 3 .3V zener diodes (ZD1, ZD2, ZD3, ZD4) 5mm red LED Capacitors 2 4 2 4 1V 4 2 4 2 -1V -2V -3V - ------ -- - 1 OOOµF 25VW electrolytic 1 OµF 16VW electrolytic 2.2µF 25VW electrolytic 2.2µF 50VW bipolar electrolytic 1µF 50VW electrolytic 0 .1 8µF metallised polyester 0.1 µF metallised polyester 1 OOpF disc ceramic - - Fig,2C: a compressor solves the problem by attenuating the high-level signal and amplifying the low-level signal. the music while keeping it at an unobtrusive level. What it does To get a better idea of what the CD Compressor does, take a look at the diagrams shown in Fig.2. In Fig.2a , we see two separate signal waveforms: a lkHz waveform with an amplitude of 5V peak-to-peak and a 3kHz waveform with an amplitude of 1V peak to peak. Fig.2b shows what happens if these signals are simply fed to an amplifier and applied to a system with a maximum dynamic range of 6V peak-to-peak. The 3kHz signal can still be handled OK but the Resistors 4 1 OOkO 6 47k0 2 18kQ 2 3.3k0 3 1k0 peaks of the lkHz signal exceed 6V peak-to-peak and so a re clipped, thus causing distortion. Fig.2c shows what happens to the · same signals after they have been fed through a compressor. As can be seen, the original lkHz signal has been slightly attenuated to make it softer while the low-level 3kHz signal has been amplified to make it louder. In effect, the CD Compressor is basically a variable gain amplifier which is controlled by the average signal input level. At low input levels , the circuit has a high gain to boost the signal well above the noise floor. Conversely, at high inM ARCH 1989 27 47k 47k 100pF 100k +12V RIGHT INPUT RIGHT 0~ Cf100k .,. 2.2 + 25VWI .,. 1k +12V 6 16 2.2 BP NE572 IC2a 2.2 BP 3.3k 4 10 + 16VWI 1 + .,. 50VW+ 100pF 100k LEFT BYPASS OUTPUT S1b 10 .,. + 2.2 25VWI ... COMPRESS -12V 1k -12V 10 2.2 BP 11 IC2b 13 12 + 1 50VWJ ~ 2.2 BP 3.3k + 7912 7812 14 10 16VWr ~ ~K .,. .,. 2x 1N4002 01 ---0 12VAC FROM PLUG PACK CD COMPRESSOR ,~oo, GNO OUT +12V 0.1 0.1 - 12V Fig.3: the compressor circuit consists of an NE572 compandor chip (IC2) connected into the feedback path of inverting op amp stages ICla and IClc. IClh and ICld function as inverting op amp stages with gains of 2. put levels, the circuit attenuates the signal so that it doesn't exceed the maximum allowable limit to a tape recorder. Specifications The specifications panel clearly 28 SILICON CHIP shows how the CD Compressor varies its gain in response to different input signal levels. The maximum gain is about 21dB (11.5 times) for a 2.6mV input and decreases to - 7.1dB for a ZV input. This means that the circuit pro- vides about 28dB of compression over its useful range. The remaining figures for noise, distortion and frequency response . are all quite good, although not quite up to CD player standards. However, we can safely say that the CD Compressor will outperform all cassette decks and players. Circuit operation Fig.3 shows the circuit details of our CD Compressor. Note that both the left and right channels are identical, so we will look at how the left channel operates only. The design is based on a Signetics NE572 stereo compandor chip (ICZ). This chip is called a compandor because it can be used either as a compressor or an expandor. It is essentially a variable transconductance cell. What this means is that the NE572 is basically a resistance which varies in proportion to a control voltage. Let's see how this is done. To produce a very effective compressor circuit, we simply connected the NE572 (ie, the variable resistance) into the feedback path of an inverting op amp stage (IC1a). Thus, depending on the control voltage, the NE572 controls the gain of IC1a to provide signal compression. IC1a is actually part of an LM3146 quad op amp package. This device was chosen not only for its low noise performance but also because of its low cost and ready availability . The action starts on the left hand side of the circuit. Signals from the CD player are applied to the inverting input of IC1a via a 1µF capacitor and series 18k0 resistor. Together, these roll off the response below 10Hz while the 18k0 resistor sets the input impedance. The 100k0 resistor at the input ties the input to signal ground when no signal is applied. DC biasing for IC1a is provided by the two 4 7k0 resistors connected between the output and the input of the op amp (pins 3 and 1). Because the NE572 biases the non-inverting input to + 2.5V, this means that the output of IC1a also sits at + 2.5V. The 10µF capacitor at the junction RIGHT LEFT Fig.4: install the parts on the PCB as shown in this diagram. Make sure that all parts are correctly oriented and be sure to use shielded audio cable where shown. of the two 47k0 resistors prevents AC feedback via this loop by shunting any AC signals to ground. The two zener diodes, ZDl and ZD2, provide hard clipping for any signals that exceed 3.9V peak (3.3V + 0.6V). This is necessary to prevent overloading a full-wave averaging rectifier stage in the NE572 compandor. To control the gain of ICla, the output signal is fed to the rectifier (pin 3) in IC2 via a 2.2µF capacitor and series 3.3k0 resistor. The output of the rectifier then drives a voltage to current converter stage which, in turn, controls a variable resistance circuit (or variable gain cell) between pins 7 and 5. This variable resistance circuit is connected in the feedback loop of ICla and thus controls the instantaneous gain of the amplifier. Thus, the gain of ICla varies in response to the signal level on its output. A feature of the NE572 compandor IC is that the attack and release times can be varied. We simply used the values recommended in the Signetics applications literature. The lµF capacitor on pin 4 sets the attack time while the lOµF capacitor on pin 2 sets the recovery time. Following ICla, the signal feeds into ICl b which is wired as an inverting amplifier with a gain of 2. A lOOpF capacitor in parallel with the lOOkO feedback resistor rolls off the response above 16kHz. This stops high frequency noise from being fed into the recording system. Power for the circuit is derived from a 12VAC plugpack transformer. This feeds positive and negative half-wave rectifiers D1 and D2 and two lOOOµF filter capacitors. The resulting ± 17V DC rails are then fed to positive and negative 12V 3-terminal regulators. Specifications Frequency Response: 20Hz-1 6kHz (-3d8) Total Harmonic Distortion: 0 .30% at 1 OOHz; 0.25% at 1 kHz; 0.20% at 1 OkHz; 0 .12% at 20kHz Signal to Noise Ratio: -60d8 (20-20kHz); -80d8 ('A' weighted) Input Impedance: 18k0 Output Impedance: 0.30 Typical Gain: +21 .2d8 at 2 .6mV (RMS) input; +18 .5d8 at 5 .0mV; + 15.6d8 at 1 OmV; +5.1 dB at 1 OOmV; +2.6d8 at 200mV; -1.1dBat500mV; -4.1dBat1V; -7 .1d8at2V The PCB is earthed to the ground plane using a solder lug which is secured to one of the PCB mounting screws. Construction This project should be built up on the PC board pattern provided as circuit layout is critical for best performance. By using the PC pattern, you will avoid problems such as ground loops which can cause hum. Before installing any parts on the board, you should carefully inspect the copper pattern for defects. In particular, look for breaks in the pattern and shorts between tracks. It is easier to locate and repair any faults at this stage before the parts are soldered in. Begin the board assembly by installing PC pins at all external wiring points. Fig.4 shows the details. Once this has been done, the power supply components should all be installed. This involves installing D5 and D6, the two lOOOµF capacitors, MARCH 1989 29 This photo shows how the PCB is mounted on the lid of the plastic case, along with the aluminium ground plane. Don't forget to connect the earth track on the PCB to the ground plane via a solder lug as shown in Fig.4. Solder the leads to the tags of the RCA sockets quickly, otherwise they wdl melt the plastic case. Once the wiring has been completed, the leads should be bound using plastic cable ties to prevent fraying. the two 3-termmal regulators and the two 0. lµF capacitors across the regulator outputs. Be careful not to swap the two 3-terminal regulators over and make sure that the diodes and electrolytic capacitors are correctly oriented. The two regulators are installed with their metal tabs closest 30 SILICON CHIP to the edge of the board. The power supply can now be checked for correct operation. To do this, you will have to temporarily connect the leads from the 12VAC plugpack transformer. Switch on and check for + 12V on the output of the 7812 regulator and - 12V on the output of the 7912 regulator. There's a good reason for checking the power supply at this stage. A faulty supply can quickly damage an IC and a replacement NE572 compandor will set you back $6.00 or more. By the way, the AC plugpack will probably be fitted with a 3.5mm plug. We decided not to use the plug as it involves buying an extra socket which is sometimes prone to shorting out. Instead, we simply cut off the plug and soldered the two leads directly to the PC pins. If everything checks out, disconnect the plugpack supply and install the rest of the parts on the board as shown in Fig.4. It's best to install the low profile components first (ie, the resistors and diodes) and then move on to the capacitors. Push each component down onto the PCB as far as it will gD before soldering the leads. The two ICs can be left till last. Take care to ensure that each IC is installed in the correct location and is correctly oriented. Pin 1 of an· IC is always adjacent to a notch (or dot) in one end of the body moulding. With the PCB assembly now completed, attention can be turned to the plastic case. You will have to drill holes in the front of the case to accept the RCA sockets, LED and toggle switch as shown in the photograph. Another hole in the rear panel [actually one end of the plastic case) carries the ON/OFF switch. Note that the specified plastic case is actually used upside down so that the lid forms the base of the CD Compressor. The front panel label has been designed so that the large block letters "CD COMPRESSOR" sit on the top surface of the case as shown in the photo. The "ON/OFF" label is affixed to the top right hand corner of the rear panel. The best way to prepare the case is to first affix the front and rear panel labels and then drill pilot holes at each of the locations indicated. Each hole can then be carefully enlarged to its correct size, preferably by using a tapered reamer to ensure a neat finish. Clean out the holes using an oversize drill before mounting the various iterns of hardware. You will have to drill an additional hole beneath the ON/OFF switch on the rear panel to allow cord entry from the plugpack transformer. The PCB assembly is mounted on the lid of the case with an aluminium ground plane (see photo) to minimise noise. You can make your own ground plane by cutting out a 148 x 85mm piece of aluminium sheet. Trim the corners of the ground plane to provide clearance for the corner holes in the lid, then mark out four mounting holes using the PCB as a template. • Fig.5: here is an actual-size reproduction of the PC artwork. CD COMPRESSOR - The ON/OFF switch is mounted on the rear panel, with the 12VAC power cable entry directly below it. The PCB and ground plane can now be mounted on the lid of the case and secured using machine screws, nuts and washers. Note that a solder lug is fitted to one of the mounting screws so that a lead can be run back to the earth pattern on the PCB. Check to ensure that there is adequate clearance between the bottom of the PCB and the ground plane (the PCB should be stood off the ground plane by about 5mm). All that remains now is to complete the internal wiring as shown in Fig.4. There are a couple of things to watch out for here, though. First, be sure to use shielded audio cable between the input RCA sockets and the PCB and between the PCB and the BYPASS switch. Second, solder the leads to the tags of the RCA sockets as quickly as possible, otherwise they will melt the plastic and loosen the fitting. The leads from the AC plugpack POWER BYPASS + ♦ COMPRESS INPUT .,. + LEFT RIGHT ~ t_;_J OUTPUT LEFT RIGHT Fig.6: the front panel artwork has been designed so that the words CD COMPRESSOR sit on the top surface of the case (see photo). enter through the hole in the rear panel, beneath the ON/OFF switch. Bring about 100mm of cord into the case and then tie a knot to prevent it from being pulled out. The two leads can then be separated and wired to the switch and PCB as shown. Testing Before switching on, go over your work carefully and check for possible wiring errors. You should also check the PCB assembly carefully, particularly the component orientations. Now plug in the plugpack transformer and switch on. There should be + 12V at pin 11 of ICl and - 12V at pin 7 with respect to ground. Check also that pin 16 of ICZ is connected to the + 12V rail. If everything checks out OK, screw down the lid and fit four rubber feet to the bottom of the case. To check the circuit operation, connect the CD Compressor between the CD player and amplifier as shown in Fig.1. Select BYPASS and check that the signal from the CD player is unaffected. Finally, switch S1 to COMPRESS and check that signal compression takes place. Notice that the CD Compressor makes the soft passages considerably louder and the loud passages a little softer. That's it! You can now enjoy your CDs via your car's tape player. !c MARCH 1989 31 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. R 330 rl 5W Photo-interrupter for digital counter This photo-interrupter circuit was designed to allow a frequency counter to be used as a digital tachometer. It uses a readily available photo-interrupter (such as the ZD-1901 from Jaycar) together with a disc having 60 slots to be attached to the shaft to be measured. By having a disc or vane with 60 slots, a frequency meter with a 1-second counting period will give a direct reading in revolutions per minute. As an example, consider a shaft rotating at 60rpm or 1 revolution per second. Because it has a 60 slots, it will generate 60 pulses per second which will be read by the frequency counter as 60Hz. Thus the counter gives the correct reading in rpm. The interface circuit provides power for the interrupter and squaring up of the pulse signal. Power input to the circuit is via a 3300 5W resistor feeding a 12V 1W +20-30V 32 SILICON CHIP 16VWr 10k .,. OUTPUT TO COUNTER GREEN 680pF IRLED 10k 390k .,. zener diode and 220µF 16VW capacitor. ·This makes the circuit compatible with DC supplies from 17 to 30 volts DC. The infrared LED in the interrupter to fed via an 8200 resistor while the phototransistor's collector drives a lOkO resistor. The signal developed across this Schmitt trigger uses discrete transistors If you want a Schmitt trigger function in a circuit it is not necessary to employ a hex Schmitt trigger IC (eg, 74C14). In those cases where you only want one Schmitt trigger, you end up wasting most of the IC. If you have a couple of small transistors on hand, you can use those instead. Another advantage of the discrete transistor Schmitt trigger presented here is that you don't have to put up with the hysteresis (the difference between upper and lower threshold levels for triggering) of the IC package - you can design in 220 0.1i 10k + ov resistor is then fed to one op amp of an LM324 package, connected as a Schmitt trigger to square up the pulse signal. The LM324 then drives a BC338 to make the output signal compatible with TTL circuitry. John Whittingham, The Gap, Qld. ($25) The circuit of the discrete transistor Schmitt trigger. You can select your own trigger levels by changing the feedback components. your own selected trigger levels. You can adjust the hysteresis by changing the feedback components. Assuming a 9V supply and that the input is held low, Ql will be turned off. The base of Q2 will then be around 5V as determined by the voltage divider formed by the two lkO and 3.3k0 resistors. Because the base-emitter voltage drop is about 0.6V the voltage across the 2.7k0 emitter resistor is 4.4V. Since the collector current of Q2 is l.6mA (4.4V 2.7k0 = l.6mA), the voltage at the collector of QZ will be continued on page 71 1pF ISET (OUT) 1 14 VOUT B VOUT A 2 13 COMP B COMP A 3 12 v+ 11 GND B GND A 4 eoul 10 ININ(-) B NC 5 IN(-) A 6 9 IIN(+) B 8 ISET (IN) Wide bandwidth video amplifier If you have a need for a wide bandwidth video amplifier for driving a 750 line, this could be an ideal choice. The circuit presented here uses one op amp of an LM359 dual Norton op amp. This can be regarded as a very high speed version of the familiar LM3900 quad Norton amplifier. At unity gain, the gain band- High impedance 1-watt amplifier If you need an amplifier with a modest power output but a very high impedance input, this is one that can be built from parts you'll probably have in your junk box. The input stage is a bootstrapped Darlington emitter follower . By using positive feedback (with almost unity gain so it doesn't oscillate) from the emitter of the second transistor to the junction of the two 100k0 bias resistors, virtually no current flows in the lMO input resistor. This means that the input impedance becomes extremely high. In effect, the input impedance is determined by the product of the combined gains of the two transistors (500 x 500 = 250,000} and the parallel combination of the lkO emitter resistor and the lOkO input resistor for the following op amp. This gives a resultant input impedance of more than 22MO. The 741 op amp is used in an inverting configuration with a maximum gain of 50. The inverting con- width product of the LM359 is 30MHz and for gains between 10 and 100, the gain bandwidth product is over 400MHz. For this video application, one LM359 op amp is used in inverting configuration. A 750 resistor provides correct loading for the input while the input resi~tor to the op amp is set at 7500. This causes negligible additional loading of the input but is still low enough so that parasitic capacitance does not limit the circuit bandwidth. As presented the circuit has a gain of 20dB and a bandwidth of 20MHz. If the other op amp in the package is not used its inputs should be tied high via a 22k0 resistor. (Reproduced from National Semiconductor applications literature. The LM359 is available as a stock item from Geoff Wood Electronics. Phone (02} 427 1676}. 100k 470 + - The input stage is a bootstrapped Darlington emitter follower with positive feedback from the emitter of the second transistor to the junction of the two 100kfl bias resistors. This gives an input impedance of 22Mfl. figuration has the advantage of a constant 10k0 input impedance, regardless of the gain setting via the 500k0 potentiometer. The op amp drives a complementary pair of emitter followers which act as a class-B output stage [ie, with no quiescent current). To minimise crossover distortion, the output stage is incorporated in the overall feedback loop. Output coupling to the loudspeaker is via a 470µF 16VW electrolytic capacitor. The amplifier will deliver almost one watt into an 80 loudspeaker. (Editor's note: one drawback of this amplifier is that it will not have a good signal to noise ratio. Partly this will be because the bootstrapped emitter follower input is inherently a fairly noisy stage. Secondly, it is followed by a 741 in the inverting configuration, which again is not the most noisefree combination. Still, if high input impedance is required, and low noise is not a requirement, the circuit should work well). Darren Yates, Frenchs Forest, NSW. ($25) MARCH 1989 33 By DON McKENZIE "Have your name up in lights". That is the ambition of every budding actor and actress. Well, we can't help you with any breakthroughs in the acting business but we can show you how to put your name up in lights. Your own lights, that is, with your own moving message display board. If you live in or around any city you can't fail to have seen these moving message displays. They are used by all sorts of commercial establishments to highlight their goods and services. Apart from television, they must be one of the most effective advertising devices 34 SILICON CHIP available. Wherever they are placed, they really do catch the eye. Watch them for any more than a few seconds or so and they can have a mesmerising effect. They can be programmed to move the words from left to right, up and down, to flash or pause - in fact, you name it, these new computer-driven message boards can do it. The message board presented in this article has all the features of expensive commercial moving message displays but at much lower cost. The main reason for the saving, of course, is that you have to do the work in putting it together. Many uses come to mind for this message board. If you are in business then you already have an application. If you are a member of a club or charitable organisation, a moving message board provides an admirable method of advertising, particularly at fetes, flea markets, conventions and so on. We should place a qualification here: LEDbased displays of any sort are up against it in bright sunlight. Under any other lighting conditions, this display works well. Features The message board itself is 740mm long and 100mm high and is mounted in a dark Perspex housing which effectively hides the individual light emitting diodes (LEDs) when they are not illuminated. In this shot, the Message Board has a static display but the real visual interest comes from the variety of moving displays possible: shot on, scrolling up and down, wiping up and down and sideways, flashing letters, or words and extra large letters. Messages can be either entered via a computer or direct from any IBM PC-compatible keyboard. I <, .. i .· [ ,,. Build .your own LED ··Message Board If yoµr computer has been languishing for several years for want of some exciting peripheral to drive, this is the one. It is a large and enticing moving message display board. It can be driven from the Centronics port on your computer or from any IBM PC compatible keyboard. The LED characters are 50mm high and up to 16 characters can be displayed simultaneously. With bright characters this high, the display can be read from a distance of 20 metres or more, the upper limit depending more on your keenness of eyesight. For even greater visual impact, the message board has a "large letter" mode which produces extra wide letters. The full ASCII character set is available - ie, every character available on an IBM PC keyboard or computer. This includes all upper and lower case characters. Each ASCII character is presented in a 5-wide by 7-high LED matrix with a column of LEDs bet- ween each character. This allows all upper case characters to be presented correctly but lower case characters with descenders (ie, g, j, p, q and y) are squashed with respect to others. This is not really a problem as most message board displays tend to use all upper case letters for greater impact. Interestingly, the considerable visual impact of a moving message display depends on the unwitting cooperation of the viewer. You can only comprehend a moving message written in moving LEDs because your eyes follow the moving characters. If you stare fixedly at the display, to stop any eye movement, you will only see a jumble of rapidly LEDs. The total number of characters that can be displayed at any one time is 16. Since each character is a matrix of 7 x 5 LEDs, each having the additional column of 7 LEDs just mentioned, the total number of LEDs employed is 672. No computer required As noted above, the message board can be controlled from the Centronics port of a computer or from an IBM PC XT type keyboard. In the latter mode, no computer is necessary. So if you presently don't have a computer but have a yen for a message board, then it will only be necessary to purchase an IBM XT type keyboard. These are widely available at modest cost. For example, you can purchase an 84-key model from Electronic Solutions at around $125. (Phone (02) 427 4422). Large and varied messages can be entered and stored in the message board (or actually in its control unit). The unit has 10 message buffers, the first two of 2K bytes and the remaining 8 of 256 bytes each. So the facility is there to store or display a wealth of information MARCH 1989 35 The LED display panel is covered and protected by a dark Perspex channel which makes it look smart and professional. on the message board. This could include a whole catalog of prices, news and coming events and so on. Display modes Most message boards used in shops just have the words running across from right to left, so you can read them in the normal way, from left to right. But there is much more to this message board than that. It has quite a few display modes. Some examples are as follows. The Flash mode enables single letters, words or sentences to be flashed on and off as they pass across the display. The display can also be paused for as long as you want and the flash mode can be operating at this time. A message can be built up on the display by individually shooting the letters from right to left. The display can then be pushed off to the left (exit left) or to the right (exit right). The display can also be scrolled down to reveal the next line of text, overwriting the previous line (wipe down). Alternatively, the new line of text can be scrolled down, pushing the previous line out of sight (roll down). The same two modes can also be made to scroll up rather than down 36 SILICON CHIP (wipe up and roll up). Then there are two more "wipe" modes, whereby a new line of text is displayed from left to right, or from right to left, wiping over the old line of text (wipe-forward and wipe-back). Finally, there is the large letter mode mentioned previously, which can be combined with the modes listed above. In fact, when all the combinations of display are used, the message board can give a very interesting and intriguing display. Mesmerising, did we say? Writing and editing Writing a message onto the display is easy. Having done it both ways, we are inclined to the view that it is easier to use the keyboard to enter messages directly rather than use a computer to create the message and then dump it to the printer port (ie, the Centronics port). Perhaps using a computer is easier if very long messages are to be composed. Writing the message entails no special software although there are single or two-key control codes (entered using the Ctrl key) which are necessary to engage the display modes described above. Messages can be stored for as long as you want, even if the unit is turned off, provided the optional RAM battery backup feature is included. We'll talk more about writing and editing the messages in a future episode of this article. System description In addition to the keyboard and the Perspex LED display already briefly mentioned, the message board also includes a Controller. This is housed in a standard plastic instrument case and has a number of sockets on the back. One is a 5-pin DIN socket for the keyboard while another is a 25-pin (male DB25) socket for the multiway cable to the display unit. The third socket is for the Centronics cable from a computer. On the front panel of the case are two LEDs, a toggle switch and a pushbutton. The two LEDs are: one Fig.1: this is the heart of the Message ► Board and is essentially a Z80A microprocessor controller with a 2764 EPROM, 6264 8K x 8 static RAM and 8255 programmable peripheral interface (PPI). The Z80A runs at the relatively high speed of 4.9MHz. ..:i ~ .... ::r:: co 0:) co n ::0 > ~ 10k~ R3: +5V ! 8 m} 8 r8 19 i ELJc VIEWED FROM BELOW " " ~ RN7f +5V 16VW RESE T ~TANT 4.7k 1 3 R6 4.7k ~"" E15 +5V ,,,. J C7.• .,. Cl 220pF "T" .o,T RB lk R7 285k 4.91MHI x1i:;'° INT ~9 1-7' NMI , RrnET I 26 16 ElD ZBOA 19 IORQ 20 22 jijj 21 wii Ml 27 MREQ A A Al Al Al Al ., -- +5V N/C N/C : DO 01 02 D3 D4 D5 D6 D7 A2 A3 A4 A5 A6 A7 AB A9 AlD All A15 C A14 DATA BUS 20 CS 18 19 17 11 12 13 15 16 9 8 7 6' 5: 4 3 25 24 21 23 22 " A RN2 RN3 RN4 RN5 RN6 RN7 N/C l. 2o 3o 4o 5o 6o 7o 8o Huuncoo ouo AnnDCC'(' D11<' .,.14 Ell EPROM A1021 A924 _U 12 11 " f """I J Q4 __j§_ D5 17 D6 181 !!1 19 WE 27 E14 6264 I GND OUT ~ IN 5 t t -¥4 22 oe 201cs1 26 CS2 fil_JJi ,DO !!1 D2 :A14 A15 A122 1\1123 I C5 5 3 A825 A7 ~A....! '7ii'a1 "A37 J AO 3 9V AC OR DC INPUT Al ~ CSRESETPC3, 5 7 E12 8255 [ RN5 4.7k f -- 't +5V 2fii10.J: 16VW"'f!_ .,. GNO .1.t 16VW"'f!_ TANT f3 2 J4 +12V 1oA .!osre D7 D6 D5 D4 D3 D2 • 40 +5V r.lo+5V 5~ -r-- PAUSE (CUT HERE) BC1-BC111 llx.Olr R5 lk • RN2 4.7k .,__.,_...1N"'-I 7805 1ouT • +5V RN4 4.7k ================~~• =-------=:.:J~ PAl!l PA2::f11,:4 PAD PC41i1I3 rt 6 . WR ...-3liiii ifa---!!j A1 ~ - t 7GND Jl fil E D6 D4 D1 iii 03 DO \' PC5t:1jj2 ◄--------~___j:i,, 8SY PA71_37 PA6 38 D7 PAS 39 D6 PA4 4D D5 1 PA 2 Rl ~ ~ - = - r ~ ~ ~ - - + 5 LEDl eV DATA }. 100k RN6 J2 RN3 _ 128 127 126 ,, 24 26 11 25 4.7k ll 4.7k R4 INPUT BSRO WT Hi 3300 260+5V AD 10 25 ~ PC7 2 S2 l'ii,"'g 23 0GND ACK COM/KBD RB 2.211 10W JJ CENTRONICS 36 PtN FEMALE INPUT . - - - -6 a.N.DU16, 19-30,33 J2 26 +5V 25 GND I JA 12V INO--'IIM-~P-0""-0-➔-----, r-------------o+9V 9VINo---- 32 J1 13 12 25 + BC1-BC5I 5x.01 24~11 COM MONO--+-----➔---__. 23~10 22~9 POWER TO PBUFF 21~8 +5V 2 ~ 7 16 19~6 IBM PC/XT KEYBOARD CONNECTIONS 5-PtN DIN SOCKET 2 18~5 17~4 16 ~ 3 0 15~2 3 14~1 PINS 14,15,17,18, 31,34,35,36 N/C +5V013 I GND 012 BSY·-11 6 - 1 CLOCK 2 DATA KEYBOARD 4 GNO 5 +5V 74LS02 4 E4b 5 ACK 010 D7 -9 11, 8 17 14 D4= e I 6 13 B D3.,. 5 4 02::; 3 01::; El 74LS373 ENABLE 13 5 S1 14 2 so 15 I oo;:; 2 ,,. +5V 47011 E2 7445 7 4 4 MMB STB 3 1 ROW 1 2 ROW 2 3 ROW 3 4 ROW 4 5 ROW 5 6 ROW 6 7 ROW 7 1k BI/ : \..._~c Q1-Q7 7x8D646 +5V J5 D825 MAL J4 OUTPUT + 5 V ~ 1 3,26 _ -12,25 ROW 1 2,25 - 11 10 07 12 06 13 D5 14 D4 15 03 1 ROW 3 ~ 1 0,23 ROW 4 ~ 9,22 47011 Q7 1k ROW5~ 2 D1 3 DO 4 - -~ 2_:r E4a 3 R1 100k 7 ':' 8 4 E3 74LS151 1 5 +5V ·< : ES 555 ~ 12 * LEDf€ RUN R7 150f! ~ fii::- ; 8D646 .8r== 16VW ,,. -- DATA_ - _4,17 - CLOCK- -3 16 -- - 4,17 R3 1k ;- 8 K>-'-~ ~ 1 5,18 74LS04 .........,2 R2 100k - +5V t!L--+5v 7 +5V ~ 8,21 ROW 6 ~ 7,20 _6,19 ROW 7 6,19 BI/; 9 • D2 -, - ROW 2 ~ 11,24 .I! ,,. ..J,!O 15 OPTIONAL COMP/KBD DECODE CIRCUIT ~c -1:! STBol- .,. J2/14 +5V 12 6 S2 2 TO RN6 SIDE OF COMP/KBO SWITCH - J2/22 74LS157 KBO CLK DIN/1 l,6 9 COM STB J3/1 J2/14 STB J2/22 D7 J2/25 GNO MMBCNT J2/26 +5V 120 7 MMB D7 KBO DATA DIN/2 1 18 05- 7 D6= e COMP 07 JJ/9 BCE 7805 •;oo, - 3,16 R4 1k .,. +sv---o--oLlL-o-:- 2,15 ~ 1,14 GNO Fig.2: this is the interface board circuitry. It takes data lines from the PPI (programmable peripheral interface) and decodes it to obtain the 7 row driver lines. It also produces the serial data to drive the 8-bit shift registers in the LED display panel. to monnor Data input from the keyboard or computer while the other is a Run indicator when a message is being displayed. The toggle switch is used to select input 38 SILICON CHIP from the keyboard or computer while the pushbutton switch is a system reset in case you goof and latch it up. We used this button quite a lot while we learnt to program the message board. Inside the case of the controller is a power transformer and two printed circuit boards. One is a Jl + 5 V ~ 1 3,26 ROW 1- 12,25 ROW 2- 11,24 ROW 3 10,23 ROW 49,22 ROW 5_ 8,21 HOWL _ 7,20 ROW 7- 6,19 J2 13,260-0---+5V 12,25 - -ROW 1 11,24 10,23 9,22 --- 5,18 ·, -- I' ROW 4 ' , -ROW 5 --- -ROW 6 ROW 7 ~ +5V Lu -v 4,17 _ 9 7 6 2 1 9 13 + ~ 11 10 8 5 3 114 - 2 5 12 11 10 6 5 4 3 +~ E6 74LS164 -¥- -- 6 1 L 13 +5V 9 7 6 1 2 13 11 E3 75492 3 14 12 11 12-F 5,18 Li 7 9 6 8 5 3 6 5 4 3 14 12 -r 1 13 El 75492 4 10 2 10 8 5 3 14 12 10 6 5 4 3 "~' -DATA -CLOCK .,F¥ 24x33i! 0.5W +5V E5 75492 2 - 7 E7 75492 13 3,16 ---- ----- --- ROW 2 ROW 3 8,21 7,20 6,19 7x24 LED DISPLAY r 10 13 lJ 12 11 .l- E4 74LS164 9 +5V____r; -¥ r 2 QATA 13 2 li.J E2 74LS164 9 +5V_r:; -¥ r - -- 4,17 CLOCK- - - 3,16 +5V---o--<)2,15 2,150-0---+5V +5V 1,1 4 + + 1 ,14 + BCHC61 6x.01 COLUMN COLUMN Fig.3: the circuit of a 7 x 24 LED panel. Four of these multiplexed panels are employed in the Message Board. The 74LS164s are 8-bit shift registers which take the incoming serial data line and convert it to parallel data, to drive the columns of the display. Note that the data is shown coming in on the righthand side of the circuit and passing across to the left. The 75492s are hex inverting buffers. To turn on a particular LED, the row driver line goes high while the column line goes low. complete microprocessor controller which is the basis of the designer's (Don McKenzie) printer buffer. It employs a Z80A microprocessor, a 2764 EPROM, a 6264 BK x 8 static RAM and an 8255 I/O (input/output) driver, also known as a " programmable peripheral interface" (PPI). The PPI takes care of communications with an external computer via the Centronics 8-bit parallel port or with the keyboard (if connected). The PPI also distributes the data to the LED display panel. The second printed board inside the case functions as the moving message board controller and is actually a parallel and serial interface board. It decodes 4 lines of parallel data from the 8255 PPI (programmable peripheral inter- face) to produce 7 row drivers (for the 7 rows in the LED display). It also converts 8-bit data from the PPI into serial data which is later used to drive the 96 columns of the LED display panel. In addition, this board carries the 36-pin connector for the Centronics parallel port. This latter board drives a 25-way cable (from the DB25 connector on the rear panel) to the LED display panel. The ea ble carries the 7 row driver lines, doubled up to occupy 14 of the cable lines. It also carries the serial data line for column signals. This serial data is also doubled up and is carried on lines 4 and 17 from the DB25 connector. As well, there is a clock signal (lines 3 and 16), + 5V supply (lines 2 and 15) and GND return (OV, on lines 1, 5, 14 and 18). LED display panel The LED display panel is made up of four panels, each having 7 rows and 24 columns of LEDs (168 in all). It is actually possible to build up the display with 1, 2, 3 or 4 of these 24 column panels but our description will concentrate on the 4-panel version. Each panel incorporates 8-bit shift registers to convert the serial data line mentioned earlier to column drive signals. Naturally, the display is fully multiplexed. We'll describe how it works in more detail later in this article. Hardware operation Since the software which drives this moving message display is proprietary and subject to copyright, it is not possible to give an exact MARCH 1989 39 A rear view of the Message Board controller, showing the three sockets: 5-pin DIN for the IBM PC keyboard, 36-pin for Centronics cable and 25-pin for the display drive lines. description of how the microprocessor circuitry [the hardware) functions to produce the moving characters. The description which follows can only be generalised. With that proviso, let us describe how the circuit works. The microprocessor controller, containing the Z80 processor, 2764 EPROM and 8325 PPI, is depicted in Fig.1. The interface board, containing the 7 row drivers and Centronics parallel port, is shown in Fig.2. And the 7 x 24 LED display panel (4 required) is shown in Fig.3 . When power is first applied, the Z80 microprocessor gets its operating instructions from the 2764 EPROM. It gathers, processes and stores data from the 6264 static RAM and picks up and sends data to the 8255 PPL The PPI handles 8 lines of parallel data and distributes (outputs) or picks up (inputs) data to and from 24 data lines which are arranged as three 8-bit parallel ports - port A, port B and port C. In this design, all 8 lines from ports A and B are used but not all lines from port C. You can tell which lines are from which ports from the labelling on the circuit. For example, data line DO on the J2 header socket (righthand side of Fig .1) is the O line from port A [PAO). 40 SILICON CHIP Whether or not the line from PC7 on the PPI is connected to OV determines whether data is accepted from an external computer via the Centronics port or from the keyboard on line PA7. This line goes to pin 2 of the 5-pin DIN socket for the keyboard. 21 lines from the PPI go via the J2 header socket on the controller board (righthand side of Fig.1) to the Jl header socket on the interface board [lefthand side of Fig.2). 13 of those lines go to J3, the 36-pin Centronics connector. The 8 data lines from port B [PBO to PB7) are used to drive the LED display panel. The 8 data lines feed a 74LS373 octal latch. At the appropriate timing, 8 bits are latched [ie, stored) in the 74LS373 by a positive-to-negative transition of the enable line, pin 11. Only four of the output lines of the 74LS373 are used and, of these, only three are used as data lines [pins 2, 5 and 6). These drive a 7445 which is a BCD decoder. It produces the 7 row driver lines: Each of these row driver lines is buffered by a BD646 PNP switching transistor which handles the heavy currents to the LEDs. The fourth line to the 7445, acts as the enable line for this chip. The three data lines from the 74LS373 also feed a 74LS151 which is an 8-to-1 multiplexer. Effectively, what it does is convert the 8 data lines to a single 8-bit serial data line, from pin 5. This line is buffered by a 74LS04 before being fed to pins 4 and 17 on the DB25 plug. Now refer to Fig.3. At the top of the diagram can be seen the seven row driver lines to the LEDs. Each of the 96 columns (only 24 shown on this diagram) is driven by one output of a 75492. This is simply a high current inverting buffer device so the real players on this circuit are the 74LS164 8-bit shift registers. Three are shown on this circuit but 12 are employed in total, to give the 96 column lines. Now consider the action as the display works. Each row is turned on in sequence and when each row is turned on, the appropriate columns are turned on so that the LEDs connected to the energised rows and columns are alight. For example, if we want the character " I" to be lit in the leftmost position, the column line 6 from E7 must be low when each row line goes high. Row lines are 'active high' while column lines are 'active low'. So what must happen is that each time a row driver goes high, the data in the 8-bit shift registers must be changed. In effect, all 12 8-bit shift registers are in series, making a 96-bit register. So before each row driver goes high, all 96 bits of data in the shift registers must be changed. The sequence goes something like this. First, 96 bits of data are latched into the registers and row 1 goes high. Row 1 then goes low, 96 new bits of data are shuffled through the registers and latched, and then row 2 goes high to turn on its LEDs. Then row 2 goes off (low), another 96 bits of data are shuffled in and latched, and then row 3 goes high and so on. It becomes a bit mind boggling when you think about moving characters, but data is all the same to the circuitry, whether the displayed characters are moving or static. Next month we will continue the description of the moving message display. ~ Don't miss a single issue ' i Electronic ! house number I! Convert a CB radio IF YOU'RE THE KIND OF READER that can't wait to get the next copy of SILICON CHIP, then why not have the magazine delivered direct to your door? 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Just ring us on (02) 982 3935 and quote your Bankcard or Visa Card number and the expiry date . Enclosed is my cheque/money order for $ _ _ _ or please debit my Detach and mail to: FREEPOST 25 SILICON CHIP PUBLICATIONS PO BOX 139 COLLAROY BEACH D Bankcard NSW 2097 Card No. I D Visa Card I I I I I i D MasterCard I I I I I I I I I I Signature _ _ _ _ _ _ _ _ Card expiry date_/_/__ •No post~ge stamp. reqmred m Austraha . W dftJ I ~-------------------------- - ----------~41 MARCH 1989 Abridged data for the NE572 programmable analog compandor Elsewhere in this issue we have published the complete circuit of a CD Compressor, based on the Signetics NE572 IC. This dual channel gain control circuit can be used as a compressor or expandor and in noise reduction systems. ~ - - -- ----------<-(5,11) (8.10) In use, the two channels may be used independently for dynamic range compression or expansion. As shown in the block diagram of Fig.1, each channel has a full wave rectifier to detect the average value of the input signal, a variable gain cell and a signal buffer. The buffer stage permits independent control of dynamic attack and recovery time with a minimum of external components. This leads to improved distortion compared with previous compandors. (1.15) r---+---+-+- Main features (18) (8) (4,12) (:Z,14) Fig.1: each channel of the NE572 has a full wave rectifier to detect the average value of the input signal, a variable gain cell and a signal buffer. v+ + ,, 140µA The gain cell IQ 02 ., 6 .8K IG I Vin Fig. 2: the gain cell circuitry. Qt, Q2, Q3 & Q4 form two differential pairs with bases connected to the inputs and output of op amp Al. 42 The main features of the NE572 compandor chip are as follows: • Independent control of attack and recovery time. • Improved low frequency gain control ripple. • Complementary gain compression and expansion with external op amp; suitable for noise reduction systems. • Wide dynamic range () 1 lOdB). • Temperature-compensated gain control. • Low distortion gain cell. • Low noise - 6µ V typical. • Wide supply voltage range 6-22V. • System level adjustable with external components. SILICON CHIP Fig.2 shows the circuit of the gain cell. Ql, QZ, Q3 and Q4 are two differential pairs with the bases connected to the inputs and output of op amp Al. The negative feedback through Ql holds the VEE of Q3 and Q4 equal. There is an offset voltage at the output due to mismatching of the transistors and this leads to even harmonic distortion. The offset voltage can be trimmed out by R,4 R3 17.3t< (5 , 11~ ~G CIN1 YIN o----j ,_____.. 2.2µF VREF (4.12) CIN3 2.2µF JJ R2 3.3K CA ....i-- (3.13) CR 1µF 10µF (18) (8) -=- +vcc Fig.3: the basic expandor circuit. The NE572 acts as a variable resistance in the input signal path to op amp A2. At acts as an input buffer. feeding a current source within ± 25µ,A into the THD (total harmonic distortion) trim pin. Effectively, the gain cell works by varying the current through the second differential pair, Q3 and Q4. The gain current is controlled by VREF· The output current 10 must feed the virtual ground input of an operational amplifier in noninverting mode. The non-inverting input of the op amp has to be biased at VREF if the output current 10 is to be DC coupled. The buffer amplifier In audio systems it is desirable to have fast attack time and slow 9,11( recovery time for a tone burst input. The fast attack time reduces transient channel overload but also causes low frequency ripple distortion. The low frequency ripple distortion is cured by a slow recovery period. The buffer amplifier makes it easy to have independent attack and recovery times. Basic expandor The basic expandor circuit shown in Fig.3 can be viewed as an inverting amplifier circuit based around op amp A2. The NE572 acts as a variable input resistance that changes according to the average input signal level detected by the ½coc Basic compressor 10µF C2 , 1µF c .. , ... e>------j 1--,vv,,......+--2,2,uF ,:;K 2 .2,uF C..3 2.2µF l1 * CR 10µF 3 ,31( R2 CA 1µF t---+------vv\r(3,13) vcc (1e1 rectifier. The rectifier alters the output current of the gain cell which in turn controls the overall gain of the amplifier. The amplifier stage is preceded by op amp A1 which acts as an input buffer. The resulting output signal range is greater than that present at the input. The expansion is centred about input levels of lO0mV so there is no change to a signal of this magnitude. Signals above lO0mV can be boosted by up to 14dB and those below this level can be attenuated down by as much as 40dB. In Fig.3 resistors Rl and R2 are tied to internal summing nodes. Rl is an internal 6.8kfl resistor. The maximum input current into the gain cell can be as large as 140µ,A. This corresponds to a voltage level of 952mV peak (6.8kn x 140µ,A). The input peak current into the rectifier is limited to 300µ,A. Note that the addition of external resistances in series with Rl will accommodate a higher input level. R2 and R3 are external resistors and the ratio of R3/R2 is set to obtain desirable system voltage and current levels. A small R2 results in higher gain control current and smaller static and dynamic tracking error. In high performance applications, A2 has to be low noise, high speed and wide band so that the high performance output of the gain cell will not be degraded. The capacitor CA connected to the NE572 sets the attack time and CR sets the recovery time constant. Fig.4: the compressor circuit. This uses an NE572 in the feedback loop of inverting op amp stage At. The resistance of the gain cell varies according to the signal level on the output of At. The arrangement of the NE572 in a compressor circuit is shown in Fig.4. The NE572 is placed in the feedback loop of op amp Al. This circuit has the opposite effect of an expandor on input signals. The operation is essentially the same as that of our CD Compressor. Compandor systems involve the combined use of both a compressor and an expandor to process a signal. These systems are usually applied to tape/disc noise reduction, digital audio, and bucket brigade delay lines. More elaborate compandor systems have features such as band limiting, band splitting, pre-emphasis, de-emphasis and equalisation incorporated. ~ MARCH 1989 43 Studio series 32-band 1/3-octave equaliser If you 're running a disco, doing your own recordings, or involved in a rock group or PA work, you will be interested in this new design for a 1/3-octave equaliser. It has 32 separate frequency bands and excellent audio performance. By LEO SIMPSON & JOHN CLARKE Most people are probably familiar with the stereo graphic equalisers used in home hifi systems. Generally these have 10 frequency bands or less but this results in too coarse a control over the audio bands for more serious applications, particularly for PA work. If there are nasty peaks or troughs in a a system's overall response, due to room acoustics or whatever, you really need a 1/3-octave equaliser to cure the problem. It can provide a boost or cut to a very narrow band of frequencies and thereby provide fine 44 SILICON CHIP acoustic tuning which is just not possible with a 10-band equaliser. Since the equaliser to be described here is intended for semiprofessional use, it is a mono instrument only. For use in stereo systems, two equalisers will be required. Note that while the Studio series 1/3-octave equaliser is specifically intended for semi-professional use there is no reason why it cannot be used in domestic stereo systems. If you want 1/3-octave control, it is the only way to go. In most stereo systems the easiest way to connect two of these equalisers [one for each channel) would be via the Tape Monitor loop or between the preamplifer and power amplifier. 32 bands are used to cover the audible frequency range. The centre frequencies of the bands are as follows: 16Hz, 20Hz, 25Hz, 32Hz, 40Hz, 50Hz, 63Hz, 80Hz, l00Hz, 125Hz, 160Hz, 200Hz, 250Hz, 320Hz, 400Hz, 500Hz, 630Hz, 800Hz, lkHz, 1.25kHz, 1.6kHz, 2kHz, 2.5kHz, 3.2kHz, 4kHz, 5kHz, 6.3kHz, 8kHz, lOkHz, 12.5kHz, 16kHz and 20kHz. For a strict relationship of 1/3 of an octave between each band, the centre frequencies should increase in the relationship 1:1.26 [actually 1:1.259921 to be precise). However, the centre frequencies we have chosen are suitably precise and easily recognised. They are also the same as used in commercial equalisers. The equaliser is housed in a standard 2-unit high rack mounting case [ie, the front panel is 435mm wide by 88mm high). In all, there are 33 sliders on the front panel, 32 for the individual 1/3 octave bands and one as a master level control. Apart from the sliders, there are only two switches. One is a bypass control which passes the signal through completely unmodified while the other is the push-on pushoff mains switch. The back panel is completely bare except for two RCA sockets, one for the input signal and one for the output. Inside, virtually all the wiring is taken care of by three printed circuit boards. There is one long board to accommodate the 33 slider controls and another large board to accommodate the active equaliser circuitry. Finally, a smaller board takes care of the power supply circuitry. The slider board and the main board are linked together by five short multiway cables with plugs and sockets at each end for easy removal. To ensure that no problems are likely to occur with earth loops, the entire circuit of the equaliser is completely isolated from chassis although the chassis itself is connected to mains earth. tion performance and with plenty of signal overload margin, even if full boost is applied. Full details of the performance are noted in the specifications panel. In one very important respect though, the performance of the equaliser is not apparent from the spec panel and this involves the slider pots. In the past, graphic equalisers have been designed with linear pots and this has led to a problem whereby the boost and cut for each slider is concentrated at the extremes of travel. In other words, to obtain an audi- ble effect from .a particular slider, you had to push it a fair way from the centre detent setting (which gave a flat response) before an audible effect was heard. This characteristic is inevitable with linear pots. To solve it, the potentiometer manufacturers in Asia have come up with a new design of resistance element for sliders intended for graphic equaliser use. Called the 4BM taper, it is effectively a centre tapped element with a log/antilog resistance taper; log in one direction, antilog ~n the other. The new element concentrates more of the boost and cut action in the slider travel immediately either side of the centre detent setting and thereby gives a better control action. As far as we know, this is the first design using these pots to be published in a magazine. They are already being used in the best commercial 1/3-octave equalisers. They really do give a much better apparent response from the equaliser controls. In fact , we regard these pots as being one of the key features of this new design. (We are indebted to Jaycar Electronics for their efforts in sourcing these pots from Asia). Circuit principles The circuit principle used in virtually all of today's graphic equaliser designs is the same. Each Specifications Frequency Response Equaliser out Equalis8r in Boost and cut Flat 5Hz-20kHz ± 1dB ; - 3dB at 45kHz ±12dB Signal Handling Gain Maximum input and output Unity (see text) 1 O volts RMS (all controls flat) Harmonic Distortion <.05% for frequency range 1 OHz to 2GkHz Signal to Noise Ratio With respect to 1 V RMS 95dB unweighted (20Hz-20kHz) 97dB A-weighted Special slider pots Input Impedance 33k0 The entire circuit has been designed for low noise, low distor- Output impedance 1 kO MARCH 1989 45 R2 1k l Vout Fig.1: this circuit demonstrates the basic principle of a graphic equaliser with only one slider control. The tuned LC circuit shunts signal to ground to give either boost or cut. In practical circuits, inductor L is a gyrator. frequency band requires its own resonant circuit, as shown in Fig.1. This resonant circuit is connected into the negative feedback circuit of an operational amplifier connected in the inverting mode. Fig.1 shows the op amp with just one resonant circuit. A real circuit has a resonant circuit for each frequency band but we show just one to keep things simple. Now consider how it works. With the 50k0 slider control in the centre setting, the op amp provides unity gain and the tuned LC circuit has virtually no effect on the frequency response. When the slider pot is set to the le:::::::--..,_ ~ _,,,,.---- loul~"--- Fig.3: this diagram shows the voltage and current relationships around the gyrator circuit of Fig.2. 46 SILICON CHIP Fig.2: the circuit configuration of a gyrator. The op amp effectively transforms capacitor C into an inductor which is proportional to Rt, R2 and C. boost end, the negative feedback tends to be shunted to ground by the tuned circuit. Since it is a series tuned circuit it will have a low impedance at its resonant frequency. Hence, the feedback will be reduced at the resonant frequency (and for the narrow band of frequencies on either side of resonance) and so an increase in the gain will result. Thus, the signal will be boosted over a narrow frequency range. When the slider is set to the cut end, the negative feedback is at a maximum and the tuned LC circuit actually tends to shunt the input signal to ground. This results in a reduction in gain at the resonant frequency. Naturally, the amount of boost and cut is proportional to the slider setting and reduced settings give reduced amounts of boost and cut. Gyrators instead of inductors Tuned LC circuits mean inductors should be used throughout the circuit; 32 in fact, one for each frequency band. But if you look at the complete circuit or at a photo of the inside of the chassis, you will see no evidence of inductors. Indeed there are none and nor will you find any in current commercial equalisers (as far as we know). Instead, we use an op amp circuit which simulates the performance of an inductor. This is known as a gyrator. Inductors are not used these days because they are bulky and expensive components to make (compared with resistors and capacitors) and they are also prone to hum pickup and mutual interaction. In short, they are bad news compared to gyrators. Fig.2 shows the circuit of a gyrator using an op amp. It effectively transforms a capacitor into an inductor. It does this by altering the phase of the current through the capacitor for a given applied signal voltage. In an inductor, the current lags the voltage (ie, the current is delayed in phase by go 0 ) while in a capacitor, the voltage lags the current [by go 0 ). Consider an AC signal source, Vin, connected to the input of Fig.2. This causes a current to flow through the capacitor and through the associated resistor Rl. The voltage impressed across Rl, as a result of the capacitor current le, is fed to the non-inverting input of the op amp which is connected as a voltage follower [with inverting input connected directly to the output). Because it is a voltage follower, the op amp reproduces its input voltage exactly at its output. Vout then causes a current to flow through resistor R2. This current, lout, then adds vectorially with the input current le and the resultant current which flows from the source lags the input voltage. As far as the signal source is concerned then, the gyrator looks like an inductor, not like an op amp with PARTS LIST 1 rack mounting case, 483 x 88 x 200mm (from Jaycar) 1 30V 1 50mA centre-tapped transformer (Altronics Cat. M-2855) 1 DPDT 250VAC toggle switch 33 50k0 45mm slider pots with 4BM taper, Jaycar Cat. RP-3914 1 2-pole push on/push off switch with mounting bracket 1 cord-grip grommet 1 0 18mm PC board spacers 1 0 3mm x 25mm screws 22 3mm nuts 10 3mm x 12mm screws 2 3mm x 6mm screws (to mount transformer) 2 insulated panel mount RCA sockets 4 stick on rubber feet 1 solder lug 9 8-way pin headers (Jaycar Cat. HM-321 0) 9 8-way connector socket (Jaycar Cat. HM-3220) 1 5 1 mm PC pins Cable 1 3-core mains cord and moulded 3-pin plug 1 800mm length of 8-way rainbow cable 1 metre shielded audio cable 1 metre of 250VAC rated insulated hookup wire two resistors and -a capacitor connected to it. The inductance is given by the formula: L = Rl x R2 x C where L is in Henries, R is in ohms and C is in Farads. With the use of quad op amp ICs (four op amps in a package), gyrator circuitry can be made much more compact than equivalent tuned LC filters. Which is a good thing otherwise this 1/3-octave band equaliser would use much larger circuit boards. To make the tuned LC circuit shown in Fig.1, all we need do is to connect a capacitor in series with the input to Fig.2. Now refer to the main circuit diagram. We quite understand if you have just opened the two pages of the full circuit diagram, shuddered and Printed Circuit Boards 1 main equaliser PCB, code SC01103891 1 power supply PCB, code SC01103892 1 equalizer control PCB, code SC01103893 Semiconductors 8 LF347N quad op amps 1 LM833 low noise op amp 1 7 81 5 3-terminal regulator 1 7915 3-terminal regulator 4 1 N4004 rectifier diodes 1 5mm red LED Capacitors 2 2200µF 25VW PC electrolytic 4 220µF 25VW PC electrolytic 2 1 00µF 25VW PC electrolytic 5 1 0µF 16VW PC electrolytic 2 1µF metallised polyester (greencap) 1 0 .68µF metallised polyester 1 0.56µF metallised polyester 3 0. 4 7 µF metallised polyester 1 0.39µF metallised polyester 2 0.33µF metallised polyester 2 0. 2 7 µF metallised polyester 2 0.22µF metallised polyester 1 0.18µF metallised polyester 3 0.15µF metallised polyester 1 0.12µF metallised polyester 14 0.1 µF metallised polyester 1 . 082µF metallised polyester then closed -it again. However, it really isn't all that complicated. It basically is just one gyrator circuit repeated 32 times, albeit with different values for Rl, R2 and C. The key op anip in the circuit is IClb and it performs the same function as the one in Fig.1. 32 50k0 slider pots are connected in parallel in the feedback network of IClb and each has an associated gyrator and additional series capacitor. For example, the gyrator for the 20Hz 1/3-octave band is IC2d and this is connected to the wiper of the slider via a lµF capacitor. Similarly, for the 2kHz band, the gyrator is IC7a and it is connected to the wiper of its slider via a .OlµF capacitor. Apart from the 32 gyrators and their common unity gain feedback 2 1 2 1 2 2 2 1 3 1 2 1 2 1 2 1 3 2 2 1 3 1 2 1 1 1 1 1 2 .068µF metallised polyester .056µF metallised polyester .04 7 µF metallised polyester .039µF metallised polyester .033µF metallised polyester .027 µF metallised polyester .022µF metallised polyester .018µF metallised polyester .015µF metallised polyester .012µF metallised polyester .01 µF metallised polyester .0082µF metallised polyester .0068µF metallised polyester .0056µF metallised polyester .004 7 µF metallised polyester .0039µF metallised polyester .0033µF metallised polyester .0027 µF metallised polyester .0022µF metallised polyester .0018µF metallised polyester .0015µF metallised polyester .0012µF metallised polyester .001 µF metallised polyester 680pF polystyrene 560pF polystyrene 4 70pF polystyrene 330pF polystyrene 270pF polystyrene 33pF disc ceramic Resistors (0.25W, 1 %) 1 x 1 Mn, 32 x 22okn, 1 X 1 00k0, 2 x 1 0k0, 1 x 3.3k0 0.5W (5%). 1 x 1.2k!1 (see text), 4 x 1 .1 kn, 1 7 x 1 kn, 13 x 91 on . amplifier, IClb, there is only one other op amp, ICla, which functions as an input buffer stage. It can be configured for a gain of unity or 2.2, as we shall see later. ICl is an LM833 low noise dual op amp made by National Semiconductor. Its excellent characteristics (previously featured in the Studio 200 Stereo Control Unit published in the June and July 1988 issues of SILICON CHIP) are largely responsible for the high performance of the circuit. It not only has very low noise and distortion, but can also drive 6000 lines which is an advantage in this circuit. Fig.4 (next page): the circuit has 32 ► gyrator circuits connected in parallel into the negative feedback loop of IClb. ICla functions as an input buffer stage. MARCH 1989 47 +15V INPUT~ BYPASS 10 16VW S1 ,--0 1.,.~1~-r;r- ~OUTPUT >,:+-~+Ul1..-M .... 1 .0033! 10k 33pF 50k 50k 50k 50k 50k 1.1k +15V 1k 910!l 1k 0.22 0.27 0.391- 0.47 0.68 910!l +15V 0.18 0.12 220k .,. 20Hz 16Hz 32Hz 25Hz 40Hz JC2·1C9 : LF347 ONLY 50k 50k 50k .082 0.1 910!l 1k +15V .027 ... .047 .068 1.1k 320Hz 50k 1.1k 50k .0047 910!l .0022 500Hz 50k .0068 1k +15V 400Hz 50k .0082 .01 +15V .015 250Hz 50k 1k 1k .018 200Hz 50k 50k .0039 .0015 .0018 1k 1k .0012 .00331-.001 220k .,.. 2kHz 2.SkHz 3.2kHz 4kHz STUDIO SERIES THIRD OCTAVE EQUALISER 5kHz POWER 01-04 4x1N4002 .,oa:U.;.T...._ _ _ _.,__ _ _-+---t----+---t----+-----+15V + E tm7 2200 25VW CASE 10 16VW _ "o"'u=r....____________.....,....._ _...._ _.....,....._ _..........__ 15v -~"' . ill"' GND IN 0.27 910!:l 1k f+· 0.22 fi""' 0.15 910\l 1k .056 .068 f+· 0.15 i3""' 910(] 1k .033 .047 220k 160Hz 63Hz 50Hz .033 r+· .027 fi""' .022 1k 910!:l 125Hz 100Hz 80Hz ft·· .015 910!:l fi""' .015 f+· 910!:l 1k .0068 1.6kHz 800Hz p. . 630Hz 50k ,.,; p. . '"" 1k 910!:l 680pF 1kHz +15V 910\l 560pF ·'"'" FI·. 1k 470pF 1.25kHz ·'"'" Ff""' .001 910\l 330pF ff""' 1.1k 270pF +15V 20kHz 6.3kHz 8kHz 10kHz 12.5kHz 16kHz The new equaliser is easy to build with virtually all the circuitry accommodated on three printed circuit boards. Plug in wiring connectors take care of most of the wiring between the two main boards. The gyrators are all based on LF347 quad FET-input op amps, made by National Semiconductor. It is important that these are used and not the ostensibly equivalent TL074s made by Texas Instruments. The reason for this is that op amp gyrato-r circuits have a tendency to misbehave when the power is turned off. As the supply rails to the gyrators drop to very low values, they can burst into high frequency oscillation which then dies away as the supply rails drop further. The effect of this misbehaviour is that the equaliser emits a loud chirp, about a second or so after the power is turned off. Since this sort of behaviour is undesirable, it is essential that LF347s be used instead of TL074s. While these op amps are functionally equivalent they are quite different in their internal circuitry and so behave differently as their supply rails are reduced to very low values. Power supply Power for the circuit is provided 50 SILICON CHIP The power supply PCB is mounted on the rear panel and delivers regulated ± 15V rails to power the equaliser circuitry. by a 30V centre-tapped mains transformer feeding a bridge rectifier and two 2200µF capacitors. This produces unregulated supplies of about ± 21 volts which are then fed to 3-terminal regulators to produce balanced supply rails of ± 15 volts. The outputs of the regulators are bypassed on the power supply board with lOµF capacitors and on the main circuit board with 220µF, 100µF and O. lµF capacitors. A light emitting diode in series with a 3.3k0 0.5W resistor across the ± 15V supply rails functions as the power indicator on the front panel. That's all we have space for this month. Next month we'll present the full details of construction. ~ BOOKSHELF Computer software for amateur radio Some of the topics covered by the programs include the following: Morse code (send and receive), radioteletype (RTTY) and data, antennas and propagation, distances and bearings, satellite orbits, Sun and Moon positions, circuit design (mainly filters) and network analysis. For the amateur starved of computer software, this book will be a bargain. As a bonus, it is in hard cover form at the very reasonable price of $25. Our copy came from the NSW Division of the Wireless Institute of Australia, PO Box 1066, Parramatta, NSW 2150. Phone (02) 689 2417. Compendium of circuits Amateur Radio Software, compiled by John Morris GM4ANB. Published 1985 by the Radio Society of Great Britain. Hard covers, 170 x 252, 328 pages. ISBN 0 9006 12 71 1. These days a large number of amateur radio operators are already using computers in their hobby and quite a few more have a computer even though they may not yet be using it for amateur radio. For both these groups and for those who have yet to embrace a personal computer, this book will provide considerable inspiration. It has a large number of program listings, mostly in Basic although a few are in assembler language. They will be particularly useful to amateurs. First, the programs can be used in their entirety for their original purpose and second, we have no doubt that readers will lift many useful subroutines out of these programs and apply them to other purposes. We have not had the opportunity to try any of the programs although, with the text coming from the RSGB, we have no doubt that they will work. Master Handbook of 1001 Practical Electronic Circuits. Solid State Edition. Edited by Kendall Webster Sessions. Published 1988 by TAB Books Inc, Blue Ridge Summit, PA, USA. Soft Covers, 131 x 211 mm, 391 pages. ISBN 0 8306 2980 7. Price $29.95. This book is exactly what it says it is - a collection of 1001 circuits grouped in 18 categories. As it is intended primarily as a source book MASTER HANDBOOK OF c'"··· /' .: < .: ·, ; : i • PRACTICAL ELECTRONIC CIRCUITS of circuits for experimenters and designers, details on each circuit have been kept to a minimum. The captions accompanying most diagrams will tell you the key function of the circuit, perhaps one or two details and that it is it. Many of the components used have American part numbers so to make best use of the book you will need a comprehensive cross reference available for transistors and maybe even !Cs. An appendix for IC substitution has been included but these once again refer to unfamiliar part numbers. You could easily work out what is required because internal diagrams are given for most of the !Cs. The circuits in this book have been designed to work as stand alone building blocks or more usefully they can be used with other compatible circuits. This approach allows you to build, test and modify each stage of your circuit before you interconnect them together. Most of the circuits in this book will find valid applications though some are pretty trivial. There were a couple of aspects we didn't like. Some of the circuits are drawn in the American practice with the negative supply rail at the top. This can make the circuit very hard to follow as it is effectively turned upside down. And we noticed a couple of errors which would stop circuits working. For example, on page 39, in a rudimentary complementary symmetry amplifier, the output transistors are swapped over - NPN where PNP should be and vice versa . So for the slightly more advanced enthusiast who has some circuit experience, and is familiar with prototyping on Veroboard or breadboarding, this book has the potential of becoming a useful circuit source. The Master Handbook is available from your nearest Dick Smith Electronics store at $29.95. M ARCH 1989 51 SOLDERING SPECIALS IN '89 Superb West German made 19mm Dame Tweeter with polymer diaphragm. Very smooth clean response to 20KHz. High power handling and excellent damping. U sc wwi th spcak<:r systems to 7 0 atts. $29 50ea C30lO : De-Solder Iron SPECIAL $49.95 II ,. Ideal for the service technician and hobbyist alike. Allows components to be I quickly and cleanly removed with . one hand. Comes with a cleaning wand. • 240V AC 50Hz 30WISEC Approval W/22281Easy single handed actianlSimple cleaning action. ~h?se~~!·:~.~~ 19 9 lnour s Cat. 1 I NEW FOR '89 T 1250 Normally $59.95 I Temperature AdJ"ustable 250°C to 450°C YOU CAN _ _ _ SAV~$14.50e~ antastic New Pure, compressed inert gas for cleaning very delicate or inaccessible areas of delicate equipment. Toe direct jet of air ensures dust ·is ttansfcred away from the equipment 400g. TOP VALUE AT$14.50 T3095 Excellent new iron, ,crewdrivcr temperature adjustable between 250oC and 450oC enabling very delicate soldering on low settings with surprising heat energy reserve on maximum setting. Relati..: temperature is indicated by LED lamp brighlllcss. Much lower cost than a soldering station. T2445 Great Value at $37.95 Fantastic Value at only $29.95 Cuts any shape cut out in steel, aluminium or plastic. Very easy to use. Capacity stoel bmn aluminium 1.6mm Audio Purists This is For You! VIFA2 Way 100 Watt Weatherproof Speaker T 2355 Normally $19.95 ONLY $14.95 SAVE $5 .00 Extra Heavy Duty PC 8 Re Ia y s / ,.i--------------,I Sec through acrylic parts drawer. Slide-in !dent card fronted drawers. !dent. cards supplied. Sturdy steel construction. Value Plus! H0240 WAS$29.95 NOW $20 SA VE $9.95 Look for product review feature in Electronics Australia Magazine April/May '89 Utility Parts Case ,k" \ r-- j . The heart of the system is the now famous 5" VIFA Woofer/Midrange, computer optimised for u,c in a 5 litrc Bass n:flex cabinet. The classic VIFA 19mm fcno fluid Dame Tweeter is incorporated with the crossover network. as employed with the SA-50 bookshelf system. Has unique overdrive protection enabling amplifier input of up to 100 Watt, without damage. Overall performance and appearance is superior to any competitive weatherproof speaker on the Australian market. Each spcak<:r is supplied complete with mounting brackets. s 4085 were $5.95ea $399 00 pr C 0970 Black, C 0972 White, ONLY 10 up $5.SOea NOW ONLY $5.00ea OR $199.50ea Low profile 25mmH 12V DC coil. HUGE SA contact rating at240V AC.DFDT. ONLY ■ • • ;::L Featuring a clear plastic lid so you can tell contents at• glance. Simple slide lock. 48 partition combinations. Very sturdy ABS plastic. H0249WAS $23.95 NOW ONLY $20.00 SPECIAL 10 up $4.00ea ;;:===.: Stere Phone With Dynamic Mic Simply brilliant Mylar Stcn:o bcad,cts &dynamic mic combination. Headphone: 20Hz - 20,000Hz, 320hm, 3.5mm stereo jack, 6.35mm 1111:reo jack, adapt<r. Microphone: Dynamic type, 3000hm, lOOHz15,000Hz, 3.5mm mono jack. $29.95 VALUE! Use of ALC (Automatic Level CompressorJ u-..a all overmodulation distortion problems. Spectncallons: • Cardioid-Uni Dlrecllonal Pick-Up patl,rn • Frequency Response: S0llz-1SKHz • Carrier Frequency: 88-108Mllz adjustable. • Capsule: Eleclret condenser microphone • Battery Compliment: 4 x AA • Weight: 235g Fantastic New Model Has Built-In Antenna C0328 NORMALLY $129.50 C 0304 NOW $19 C 0385 $119.95 SPECIAL $99.00 SAVE OVER $20.00 NOW ONL V .,.$:..:::9:..;:9::.:•:.::0:.::0=---_ _c•_n_non_con_ne_ct_or_&_&_M_1e_ac1_1n_c1u_ded __ Nicad Rechargeable Batteries C 9055 Pn:mium Gtade - Good f<r up to 1000 n:-cbarges. Charge Rate 45-SOmA f<r AA, 20mA for AAA, 10.15mA for 9V 120mA Cat.No. · S 5020 AA 1.2V 500mAh / NORMALLY 1-9 $ 3.99 THIS MONTH'S SPECIALS $ 3.50 S 5021 AAA 1.2V 180mAH $ 4.50 THIS MONTH'S SPECIALS $ 4.00 10.99 $ 3.25 $ 2-50 $ 3.95 $ 3.00 · $29.80 Will, uut1UU11•dM,t,,/V11c11""' EvopONll•d FilM diaplsn,gm Simply superb entertainers' microphone. Inbuilt wind filter eliminated "Pops". Balanced line circuit enables long mic cable runs. Cardioid, 250 Ohm, 70.15.00Hz (uscable 1D 18KHz) Senaitivity -7 + 3db On-Off Switch with built-in lock Sturdy carry ca,c included For Professiooal 2 way Radios on All'CI'aft, Boats, Vehicles & also Industrial PA Systems. Fantastic voice clarity, absence of feedback and baclcground noise. Frequency Response 400SKHz. hnpedance 160 Ohms. Sensitivity -65db A 2570 240V Mai. ,s Operated Normally ~499 This Month $399 You Sav•f $100.00 Increase YOUR SECURITY! ~ -----------------7 Infra Red Movement Detector I Pulse CountModel Type !RD now includes pulse oount circuitry with a specific I Our 1989 delay between sensing. 11uec pulses of lR radiation are th:: I I Featurn: •Lens simply 'snaps' to either wide angle (range 40ft) for normal use Narrow angle (and 80ft plus) for corridor applications. I or*Snazzy Integral mounting bracket allows corner 90o mounting. •12v DC Powered I •Built-In test lamp. output SPST la max. I •Relay •9-18V DC I s 5301 Excellent value · 30V at$79.00 I I L-----------------~ Passive Infra-Red Lite Guard Floodlight Control J . ,.. 7 lAlarm time pulse required to trigger detector. Providing the detectors arc sensibly positioned false triggering is completely eliminated. 1 . ' Multi Sector Burglar II ······· ·· Protect your Home or Business from Intrude rs with this 11State of the Art" Burglar Alarm System Over the last few years, House Break-Ins have increased dramatically. The recovery rate of stolen goods is very low. Now more than ever before, it makes extremely good sense to build and install this ingenioWI Multi-Sector System. This unique Alann System incorporates the features of the mare expensive commercial models - at a fraction of the pric.c. }..eatures: • 8 sectors can be monitored Independently • F.ach Input circuit Is prov ided with an Indicator LED and a sector On/Off switch • Indiv idual sector Isolation • Inputs accept both normally closed and normally open sen90rs • Two Inputs provided with an entry de lay • Alarm Is disabled by frontpanel key switch • Internal trip warning buzzer • Unique circuit detects tampering• Automatic muting of the siren driver when under test • Fully variable exit delay • Will drive external horn speaker• Alarm output variable between 1 & 15 minutes• When triggered, gives a connection to external devices e.g. Bells, TV Camera etc • Switched output can be used to send a silent alarm • Full battery back up • Alamt wlll operate for approx. 2 days with mains disconnected • Supplied In an attractive functional security case. (See EA Jan/Feb'85) Kit (Less Battery Back Up) K 1900 ~ckUpBattery~~2AH~06~ $149 .50 24.9~ ----~ More TOP VALUE SECURITY KITS on our 2nd OPS How onen have you thought there could be a prowler outside your door? Install a Lite Guard & (once armed) any "guest" will be floodlit wbcn detected by this highly scmitivc Infra.Red Detector. Toe Litc Guard detects a moving person or vehicle by comparing the background temperature with a rapid change of temperature across the detection beams. So when Litc Guard detects movement across the coverage area it will tum on the floocilight(s) for 1-20 minutes as prcadjusted. Security: Prowlers are startled by an unexpected blast of light. Convcnicna:: Litc Guard will detect your arrival and twn light on to welco~ you home. Energy Saving: Built-in photo cell deactivates unit in daylight. s 53so was $135.00 SPECIAL ONLY $99.00 Please note: Floodlamp, & holders not supplied 2 Amp Regulated Power Supply Input Voltage: 240V AC -50Hz Output Voltage: 12V DC +/-0.5V Output Current: 2A DC Dimensions: 84 x 68 x 200mm Weight: 1.2kg, M 9050 Normally $69.95 Now only $50.00 Solar Cell Module Great experiments Solar Module. Connect in parallel or series as you wish. Tenninal strap enables easy interconnection to other cells. Flat Key Cam Lock ...... -~ 11:~- ~!if, Zinc alloy die.cast bOUBmg wilh stainleu ltCcl cap. Key removable in cilbc:r politioo. 2 1olid brau kcy1 ~lied. S 2550 WERE $4.95 NOW ONLY $4.00ea S 2552 Spare Key Blmt1 $120 CL Telephone or Security Keyboard Switch Matrix Type Speclflcatlons: Contact Conductive rubber. Rating DC 24V 5mA. Contact Resistance 200 Ohms. Max. Withstand Voltage 250V AC. Bounce Sm sec. max. S 5380 WERE $9.90ea 10 up $8.90ea ISolar Charger Charges up to 4AA Nicads by simply placing in sun light. Will charge from dead flat to fully charged in 8-10 houn average sunlight. Take care if charging inside - ensure car is well ntilated. 230 was $14.95 NO Hz Frequency Counter This Is just a sample of our HUGE RANGE make sure you have a copy of our NEW 1989 Catalogue to check out our full range of meters and thousands of GREAT PRODUCTS. te I A frequency counter Is Invaluable for the accurate alignment and testing of many modern electronic circuits. Specifications: Frequency Range 1Olli • 150MHz Gate Time 1 sec, 6 sec. Accurscy +/· 1 count Max. Input 'UJV P-P Scnsitivity:110Hz • 30MHz 25mV ·lOOmV 110MHz • 150MHz lOOmV • 300mV I Power requirement 9V DC <at> lOOmA Use our 9V Plug Pack M 9004 Value .00 Special $149.00 YOU SAVE $50 01520 With Built-In Capacitance Meter 11\ --------7 IAU di O F e U enc I Ge ne r:\ t I I from the Labtcch range.: • Continuity Test • Buzzer S0W1d: Less 200 ohm I I anywhere near the • Capacitance: S Ranges 2000pP. 204P • Transistor Tester DC Voltage .2, 2, 20,200, 1000V I doorway as it dctecta DC Current 200uA, 2mA, 20mA, 200mA, 2A, l0A pressure change. Ideal AC Voltage .2, 2, 20, 200, 750V I for use in shops, office, AC Current 200uA,2mA, 20mA, 200mA, 2A, lOA doctors surgeries, Resistance 200, 2K, 20K, 200K, 2M, 20M I Cb::mists etc. General: Display: 3 1/2 digit LCD, 05" height, with K1915 was $45.00 polarity and LO-BAT indication• Ovcrrange Indication I Maximum Common Mode Voltage: SOOY peak IIn testing au~ic., ~ircu.itty it is necessary to have an I $NQW Power: 9V alkaline or carbon-zinc battery. Dimensions, Weight: 170mm x 'iflmm x 42mm, 350 grams Iaccurate audio signal source. It even allows you I 39 .OO Specifications: Input Impedance: !OM on all ranges to test 455KHz IF stages! Normal Mode Noise Rejection: 46db at 601-lz (lK unbalanced) , specifications: I SAVE $6.00 Common Mode Noise Rejecticm: l0Odb at 601-lz Frequency Range 101-lz 1MHz O Overload Protecticn: 1000V de or peak on all ranges IAccuracy +/· 3% +2Hz 5 I i===============:;r,,½ Response Time: less than 1 Second. Output Waveforms: Sine: 8V RMS ne Grabber Q 1085USUALLY $139.00 r~,,tJ-IOutput Square: lOVP-P I (Sec Silicon c:::/41 ... Atlenuator: -20db, -40db fine adjust. S f ilP~E;!C ~I ____1:.,_____J-~~•!!-~•!!•~-~!.._________J~~was $249.~ow $ ~ _ _ _j Chip Mar'88J ➔1,~ ➔1,~ LIGHT UP YOUR LIFE! ➔11 ~ .:-1~ .:-~ .:-1~ Wehavelotsofspecialswe . couldn't fit. Come in and look All the normal ranges of current, resistance and voltage plus. convenient and simple to USC capacitance meter in five ranges, plus transistor tester, Check the features of this top quality digital multimcler than ~ 1.. -·-"- and ' 1' ' 1' ,,, / ,J--------------.,---~-:-:::--::----r-e- d-:----, Up To Now Similar Lamps Sold For $1,000 And More NEW FOR '89 around and make sure you have ourNEW1989Catalogue The telephone Line Grabber preveuta interruption from one extension to another. When one extension is being used it automatically mutes the other extcnsion(s). Line Filter A Conditioner (SecEAJuly'88) Pl::isr LRmp Gives you comple11C security. Also great for use with modems. One unit required far each extension. K 1415 Disp a Le I I OP vALUE $19.95 ht: The House b (Sec Silicon Chip Oct'88) endless fascination as it siulcs and arcs. Supplied complete with AC Mains Adaptor. Price Breakthrough for '89 A 0120 $199.00 NOW PRICE Add More Li!, To Your Next Party F1ashcs in time to your music, or as normal strobe. Exclusively customised by Altronics into our H 0480 Instrument Case. Includes silk sa,:cned panel. • LED fuse tripped NORMALLY NOW P 0530 8 Pin P053214Pin P 0534 16 Pin P 0536 18 Pin P 0538 'Ul Pin P054024Pin P 0542 28 Pin P 054440 Pin $1.10 $1.45 $1.65 $1.80 $1.99 $2.45 $2.80 $3.25 $ .79 $1.00 $1.15 $1.25 $1.39 $1.70 $1.9S $2.25 Identify your House indicator. • Operates off 1 single 9V batlery (not supplied) • Two current Settings easily adjustable via a pot and calibrated scale. • HoUICd in a rugged Jiffy Box. A must fer prototyping and service worlc. No Electronic workshop should be without one. K2535 GREAT VALUE AT $39 50 LED light makes your house easily recognisable at night by illuminating your house number. Great for people visiting, easy for taxis and emergency services to locate you at night. Operates off low voltage plug pack* Automatic operation* Works only at night* Automatic switch off after 4-5" hrs. Altronic Kit comes complete. 64 LEDs supplied. The Smooth power for stereo, TV & computers. Altronics customised version housed in strong Jiffy Box. Nickel sprayed for E.\il shielding. K 5790 $79.95 NOW $75.0 For Increased Power Two Tube Option K 5795 $16.50 NOW $15.00 (Sec EA Nov'87) Simply clips across the DC Fuse holder, Offer, protection adjustable from 0-lOA in 2 ranges. Features: • Fast blow - slow blow setting. • Manual reset button. L [iT 14 K6040 was $39.50 f 500 r:--------7 et e r ctl Je tion , was $59.95 NOW $55 00 1 1 I I I I I I I(Sec EA Oct '87) high impedance unbalanced inputs to IConverts low impedance balanced outputs, Do,:cns of studiq/PA uses. IFeatures: I• Sturdy dlecast box Black lo11&h powder coat finish I•• Professionally screen printed. lndusL 1• Earth Isolate switch. • +5db pad. K1960 1• Plumtorn powering plus Internal 9V bat. K 5550 $45.00 0 $39 00 Protect your valuable loudspeaker system. This easy to construct kit, provides both DC and ovctpowcr protection for your valuable Hi-Fi speakers. Self-powered unit disconnects the speakers within 1/lOtb of a second of a fault occuring yet in no way effect, the sound quality. I unit raclc box includes quality silk scz,:cncd froutponc!. K 5050 WAS $125.00 NOW $99.00 S VE$26.00 . C (SeeE.A. March'88) Time your SID calls and Save Money. Tinting is adjustable from 10 seconds to 15 (See SC Dec'87 or our '89 Cat for full spes.) Utility T imer (:- 4 " t:>• '!, • . t: "' ' <at> ~ Mf ~ t, ~ ~ ,,.-J:_ ,.,,, .•tr ·•· \, (See EA May '88) Fantastic for Work Bench & Tool Box For Less Than $ 100 Easy to build. Over 50MHz in 5 ranges. 1 Features high input impedance overflow LED indicator. KHz & MHz LED Indicators. All components mount onto a single PCB. Complete with prepunched & silk screened front panel. Ideal for use in testing CB radios, 1V's & AM Radios etc. .00 SAV cita, aotor (See SC N ov '87) Great for hand selecting exact values e.g. exact values for timer circuits into your meter via inbu.ilt banana plugs. Kit includes prepunched silk screened front panel. Suits Labrech Q 1075 K 2520 was $24.99 K2510 High power rugged reliable design featw-ing low distortion and inbuilt speaker protection. All components, including output tranistors mount on a single PCB. Suitable for rugh quality guitar amp. public address or in a high fidelity srerco amplifier. Kit includes angled heatsink bracket, main hcatsink and unlike other kit suppliers, the ln-Bu.ilt Polyswitch for loudspeaker prorection. Output Power: lOOW into 4 Ohms 150W into 4 Ohms 100WVersion NOW$65.00 150WVersion 99 0 VALUE K 5150 $99.00 NOW$95.00 r - - ffi H~ igitalFrequenciMeter - 1 - · · ··· ... .. " .,.,_, (See SC Nov'87 Jan'88) TI!is superb lGHzFrcquency Merer will out I I I I I perform many other instruments twice its price. Features: • Professional machined and screen printed red perspex front panel. • Easy to assemble . • Bright Hewlett Packard 8 digit display, • Electronic switch latching. • High performance IC's. • High Qual ity Components. SpeclflCJ1llons Operational Modes: Period Freq. to 100MHz Freq to 1GHz Freq. Ra nge: !OOlu-lGHz (1.7GHz typ.) in frequency mode; 10Hz-2.5MHz(5MHz typ.) in period mode . Gating times: 0.01 ,0.1,1 and 10 seconds (10MHz & 100MHz ranges); 0.128,1.28,12.8 & 128 sec. (IGHzrani;e), ~2~ ' : : $299.o~ ~~$~ /J=======~---==~ct=-==-== (See Sil icon Chip Jan'89) Ever reversed into a parking spot and hit~ car behind you? Well this proximity detector is the answer. A buzzer starts beeping and just before you hit the object the buzzing becomes continuous. Connects to your reversing light circuit, so it comes on automatically every time you reverse. Effective range of about 1 metre. Complete with all parts, boxes and cable. K4310 K 5140 $69.00 ',s..... T $~. 50 NEW FOR '89 9.o~ SA VE_$50.00 si W or lechn.icia,u work I _) TELEPHONE DOUBLE ADAPTOR S range megohm meter , Ideally suited for checking breakdown in electrical wiring, appliances transfonncrs, automtive generators and alternators etc. Breakdown can be measured at either ing on 1h: required Converts single relephone socket into a double socket into a double socket to allow you to P!!zf in two,.P.hones. P 0995 :i,4.50 NuW LESS THAN HALF PRICE AT ONLY $2.00ea Man ufact urers, Contractors and Bulk Users Please Contact Our Who lesale Sales Dept. Sydney (NSW Only) Colin Fobister 437 4077 Perth 09 328 2199 174 Roe St. Perth WA 6000 PHONE TOLL FREE 008 999 007 Perth Metro & After Hour■ (09) 328 1599 ALL MAIL ORDERS P.O. Box 8350 Perth Mail Exchange W.A.6000 AL TRONICS RESELLERS Ch ances are there is an Altron ics Reseller r ight near yo u- check thi s list or phone us for details of the nearest dealer. PleaH Note: Rese llers have to pay th e cost of freight and insurance and therefore the prices charged by individual Dealers may vary sl ightly from this Catalogue - in many cases, however, Dealer prices will still represent a sig nificant cost saving from prices charged by Altronics Competitors. Don't forget our Expre11 Mall and Phone Order Service • for the coat of a local call, BInkcIrd, VIN or Maatercard holder• can phone order tor Hmt day deapatch. !1~~~~ ~~;~::sR:o~r'!r~!/~ie, ~~:~e~:i:;i°~~~ ~~~::t~~e:i~K1!~!J:~~!: Allow approx 7 days from day you post order to when you rece ive goods $7.00 OVERNIGHT JETSERVICE - We process your order the day received and despatch via. Overnight Jeturvlce Courier for delivery next day Country areas please al low additional 24-48 hours. We ight limit 3Kgs (3Kgs covers 95% of Orders). $10.00 HEAVY HEAVY SERVICE - Al l orders of 10Kgs or more must t ravel Express Road - Please all ow 7 days for delivery. INSURANCE - As with virtua lly every other Australian supplier, we send goods at consignees risk. Should you require comprehensive insurance cover against loss or damage please add 1% to order val ue (minim um charge $1) . When phone ordering please request " Insurance" . TOLL FREE PHONE ORDER - Bankcard,Yisa, Mastercard Holders can phone order tol l free up to 6pm Eastern Standard Time. Re member with our Overnight JetNrvlce we deliver next day. ALBANY B P E lec t ro ni cs ■ 41 2681 ESPERANCE Espera n ce Commun ications 7 13344 GERALDTON K .B.Elect r o n ics II Mar in e 212176 KALGOORLIE Todays E lectro n ics ■ 212777 KARRATHA Daves Oscitron i c 854836 MANOURAH Lance Rock Retravision 351246 WYALKATCHEM O & J Pease 811132 NT ALICE SPRINGS Ascom Electronics 521713 Farmer Electronics 522967 CANBERRA Bennett Commercial Electronics 805359 Scientronics 548334 VICTORIA CITY All Electronic Components 6623506 SOUTH MELBOURNE Winscott Trading 6995740 SUBURBAN CHELTENHAM Talking Electronics 5842386 CROYDEN Truscott Electronics ■ 7233860 PRESTON Preston Electronics 484019 1 COUNTRY BENDIGO KC Johnson ■ 411411 MORWELL Morwell Electronics 346133 CITY Delsound P/L 8396155 SUBURBAN CAPALABA David Hall Electronics 3902399 FORTITUDE VALLEY Economic El ect ronics 25237 62 WOODRIDGE David Hall Elect roni cs 8082777 COUNTRY CAIRNS Electro nic Wo r ld ■ 518555 BUNDABERG Bob El kins El ect r on i cs 72 17 85 GLADSTONE S u pertro ni cs 72432 1 MACKAY Philt r onics ■ 578855 ROCKHAMPTONAccess E l ectron i cs ( Eas t St .) 221058 Electron World 278988 TOOWOOMBA Hunts Electronics ■ 329677 TOWNSVILLE Solex ■ 722015 SA CITY Electronic Comp & Equip. 2125999 Force Electronic ■ 2125505 SUBURBAN BR I GHTON Force Electronics ■ 377 0512 CHRISTIES BEACH Force Electron i cs ■ 3823366 ENFIELD Force E lectronics ■ 3496340 FINDON Force E l ectron i cs ■ 3471188 LONSDALE Forc e Electronics ■ 3260901 COUNTRY MT.GAMBIER South East Electronics 250034 WHYALLA Eyre Electronics ■ 454764 TASMANIA HOBART George Ha rvey ■ 342233 LAUNCESTON George Harvey ■ 316533 Nichols Radio TY 316171 NSW CITY David Reid Electronics ■ 2671385 CARINGHAH Hicom U nitronics 5247878 LEWISHAM PrePak Electro ni cs 5699770 SMITHF I ELD Chantro n ics 6097218 COUNTRY COFFS HARBOUR Coifs Habour El ect r on ics 525684 NELSON BAY Nelso n Bay Elec t ron ics 813685 NEWCAST L E Novocast r ian Elect.Supp l i es ■ 62 1358 NOWRA Ew in g El ectronics ■ 218412 RAYMOND TERRACE Alback Electronics 8734 19 WINDSOR M & E Electronics 775935 WOLLONGONG Newtek E l ectronics ■ 271620 Blue Ribbon Dealert are highlighted with a ■. These Dealers generally carry a comprehensi ve range of Altronic products and kits o r wil l order any required item tor you .~ The line of most resistance My main story this month comes from my Tasma~an colleague, J. L. As he freely admits, it is a comedy of errors - though I doubt whether there was much to laugh about at the time. But out of his trauma comes some good advice regarding the selection of substitute transistors. Customers are the strangest people. Often they will tolerate the most objectionable faults in their TV or radio sets and do nothing about it until some other relatively minor fault prompts them to seek help. I was reminded of this when a customer brought in a small Sony colour TV set, a KV1300-AS. The complaint was "a white line across the middle of the screen". When I fired it up, I saw the white line all right but I also saw the reason for it - the top quarter of the picture was folded over itself and Teletext lines were flickering across the newsreader's face. Not only that but the bottom of the picture was up about 25mm from the bottom of the screen. It seemed to be undistorted but was probably squashed a bit more than it should have been. When I pointed out these extra faults, the customer exclaimed: "They don't worry me at all. It's the line across the centre that is such a nuisance". All he wanted me to do was cure the white line, though I couldn't imagine how I could do that without curing the other faults at the same time. I began by looking at all the electrolytic capacitors in the vertical oscillator, drive and output stages. Dried out electros are far and away the most common cause of linearity troubles in vertical stages. Unfortunately, replacing all these made not the slightest difference. Voltage checks Next, I fired up the set with the vertical board exposed and set about measuring the various voltages for comparison with those given in the manual. The vertical 05082SC926A V. OR1VE 23 46.sw· 12 I ~I 200v 1 Fig.1: vertical deflection circuitry of the Sony KV-1300-AS. The fault was tracked down by carefully measuring the voltages around Q901, Q509 and Q508 and comparing them with those marked on the circuit. 56 SILICON CHIP output stage in this set is rather unusual. It uses dissimilar output transistors, Q901 and Q509, in a kind of asymmetrical push-pull circuit. One of the transistors is mounted on a heatsink on the vertical board and the other on a small tab attached to the main chassis. The collector of Q901 is fed from a 110V rail and the yoke drive is taken from its emitter. The circuit shows the emitter at 47V and the base at 46.5V. The collector of Q509 is shown as 47V, the same value as the emitter of Q901 to which it is directly connected. This level, in turn, is set by the bias on Q509, which is shown as 0.75V, while the emitter should be at 0.6V None of the measured voltages agreed with the circuit values and in one case the difference was quite marked; the emitter of Q901 was at 53V and the base at 42V, suggesting that there was a whopping 11 V reverse bias on this stage. But this meant very little, because the vertical oscillator was still driving these stages and the voltages I was observing were almost certainly being generated by rectification in the base-emitter diode junctions of the transistors. All they indicated was that something was very wrong with this part of the circuit - but I knew that already! I would have enjoyed the chance to sit down and work out just what was going on from the voltage readings but hard economics demanded a faster solution to the problem. In fact , the voltage measurements had yielded one important clue; the emitter of Q509 was at 0.4V relative to chassis instead of the 0.6V shown on the circuit. Since this voltage was being generated across a bypassed emitter resistor, it suggested that the transistor was not drawing as much current as it ooo-"fHex J:)ON'"'\ W~'< ME:1 ,,-....., ,, 'S 11-1-e:.. L-1 N ~ AC.ROSS -n-u~: c~e: -'l1;ig ,,,..____ _ _ _ _ _~('~•89-should and thus it did not have sufficient bias on its base. The bias for this transistor is derived from the divider chain R556, VR508, R560 and R559/ TH502. VR508 is labelled vertical bias and is used with the linearity control to optimise the vertical scan. When I went to measure the voltages down this chain, it turned out that R556 was dropping 109.4V and the rest of the chain only 0.6V. I guessed that R556 was open circuit. Having made that guess, I should have turned the set off and removed R556 before checking its resistance. But I tried to be smart and bypass all that rigmarole. Using my decade resistance box, I attempted to dab a 270kQ resistor across the suspect one. The only trouble was that I miscued and shorted the 110V rail to chassis. There was a small "pop" from the power supply board and the set stopped. The chopper transistor was circuit. short Transistor substitutes This transistor, Q903, is a 2SC1454 - a type which I didn't have in stock. But I do have many other power trnnsistors so I began a search for a suitable replacement. Although there are many thousands of transistor type numbers, there are only a thousand or so transistor types. So it stands to reason that many transistors are the same as, or very similar to, others with different type numbers. As a result, one of the most useful books in any service workshop is a transistor substitution manual. Or it would be if (1) it contained all type numbers and (2) it could be relied on for accuracy. Over the years,,I have collected a dozen different substitution manuals but only one has proved to be both comprehensive and accurate. Unfortunately, in the electronics field, every book ever published has been out of date before it leaves the press. As a result, we are forever buying new books and hoping that the latest one will be more accurate than the last. So it was that I turned to my 6-week-old copy of "Up-to-Date World's Transistor Comparison Table". This has 784 close printed pages and comes close to listing all transistor types ever made. The entry for 2SC1454 showed it to be a 300V 4A 50W NPN silicon transistor, intended for use as a power switch. The recommended alternatives were BU109, BUl 10, BU210, BUY21, BUY77 and 2N6306. As bad luck would have it, there were none of these in stock so I had to look further, to find substitutes for the substitutes. Those for the BU109 and 110 were not very helpful but when I came to the BU210 things looked better. The BU526 and BU626 were listed and these are higher voltage versions of the BU326 which I did have in stock. These are all listed as TV switches and this is the characteristic required for a chopper transistor. I have used the BU326 as a replacement chopper in many sets so I felt it would be satisfactory in this one. But you live and learn. The BU326 fired up all right and worked perfectly - for about two hours. During this time I went back to the vertical problem and found that R556 was indeed open circuit. Replacing this cured the vertical problems and it looked as though the set could go home next day. As a final check on the vertical scan, I switched the set over to SBS which I knew to be broadcasting their test pattern at that time. Just as the switch clicked over, so did the power supply and everything went dead. The BU326 was shorted. What gives? At first, I thought that the VHF/UHF switch-over had blown the chopper because both events happened simultaneously. Later, I came to the conclusion that the chopper must have been about to fail. The momentary loss of line sync as the bands changed might MARCH 1989 57 have created enough extra load to finish it off. But why did the BU326 fail? Rather than replace the chopper and risk another loss, I fired up the set using an external 110V supply. This showed that the set was running OK on VHF channels but that the UHF channel was showing only a white screen with a slight hiss from the speaker. This was turning into one of those jobs that goes from bad to worse. I began to wonder if I would ever get it finished. I could find nothing wrong with either the power supply or the line output stage. Apart from the UHF channel, everything seemed to be working properly. The only conclusion was that I should have used a BU426 (or better) and that the 326 just didn't have enough grunt for this set. Faced with the problem of finding yet another substitute for a substitute, I turned to "Towers International Transistor Selector". And against 2SC1454 I found two other recommended substitutes BDY94 and 2N5157. Looking further, I found that there were no substitutes for the BDY94 but a BU105 would substitute for a 2N5157. There was one significant difference between the characteristics given in the two books. While the "Up-to-Date World's Transistor Comparison Table" shows the 2SC1454 as merely a power switch, Towers rates the transistor as a "television line output extra high voltage". In fact, all the substitutes shown in Towers were labelled "extra high voltage". Clearly, this characteristic was one which the publishers considered to be particularly important. In the light of my experience, they were probably justified. What I wanted was a transistor of sufficient power handling capability, together with an extra-high voltage rating. At first I thought of using a 2SD350 line output transistor, which at 1500 volts can be considered to be extra high voltage, at least as far as a 1 lOV chopper supply is concerned. However, its power rating is only 22W and I needed something nearer 50W. otl)plf'q e<ti<; "be i • . ff l\ -. ou\N E:L-e:c-..-rRON\~ ~VE.R'-( :l3(:X)K E.VE:1<.. 'PlJe>L.\GM~P IS OU\ OF ~ ~~e: 1--r"' L-E.A\JES 11-\E'- ~SSooo 58 SILICON CHIP Fortunately, there is one common line transistor with these ratings, the 2SD380A, and I had several of these in stock. It took little time to fit one and soon the Sony was going like a charm - except that the UHF section still wasn't working. The possibilities My first thought was that the chopper failure had spiked the UHF tuner and knocked out the RF transistor. But a replacement tuner proved to be just as inactive as the first one. So if the tuner was OK and was receiving the proper rail voltage, what else could stop it from working? The only possibilities were the AFC and AGC voltages. Unfortunately, neither of these voltages is shown at the tuner on the schematic diagram. I had to work them out from figures given on other parts of the drawing. The AFC voltage was the lesser suspect because the same line goes to both the VHF and UHF tuners and the VHF tuner was working normally. This left the AGC line. In this set, there are no less than four amplifiers in the UHF AGC line. There are two, AGC amp 1 & 2 (Q781 & 782), on the UV board and two more, UIF AGC 1 & 2 (Q211 & Q212), on the S board. Also Q751, on the UIF board, is an AGC amp/buffer so there were plenty of locations for trouble. I injected an IF signal from a test tuner into the input of the UIF board and obtained a perfect picture. However, when the output of the Sony tuner was patched across to another TV set, there was no trace of any signal. not even snow. The tuner was completely inactive. Tracking back along the AGC line, I came to the moving arm of pot (VR201), designated UIF AGC, between the 18V rail and a tapping in the third video IF transformer, T208. From here the line goes to Q211, the first AGC amplifier. The base and emitter voltages of this transistor were correct but the collector voltage was way off. Q211 is directly coupled to Q212, the second AGC amp, and here I hit the jackpot. All three pins on Q212 were at the same voltage - give or take a few millivolts. It also allowed me to complete one of the most frustrating jobs I've had in a long while. The main point to emerge from the foregoing comedy of errors is the need to buy, keep and use every transistor comparison manual you can lay hands on. Although this story mentions only two volumes, I have in fact about a dozen books, all of which get occasional use. "Towers International Transistor Selector" has proved to be the most useful over a long period and it certainly gave the right information for this story. However, the new " Up-to-Date World's Transistor Comparison Table" is very comprehensive and if its overall accuracy proves to be better than it was in this story, then it too will become a reference in constant use in my workshop. And in future, I will check more than one reference before selecting a chopper or line output transistor. YOU NEED THIS T TEST I ENT SHORTED TURNS TESTER Including meter for checking EHT trans, yoke windings, drive trans. + $3.00 P&P HI-VOLTAGE PROBE $78.00 Including meter Reads positive or negative 0-50kV For TVs, microwave ovens and high voltage equipment $84.00 & $5.00 P&P TV TUNERS (PHILIPS) ECL 2060 Repair or exchange UV461 Repair only $17 .00 ea + $2.00 P&P CHEQUE, MONEY ORDER, BANKCARD OR MASTERCARD TO TUNERS 216 Canterbury Road Revesby 2212, Sydney, Australia Phone: (02) 77 4 1154 Back at the ranch l Fig.3: relevant section of the S board showing the two AGC amplifiers, Q211 and Q212. AGC voltage from T208 (not shown) is applied to the base of Q211 and taken off the emitter of Q212. Yet when I checked this transistor with a multimeter, all the junctions appeared to be perfect. They each had the normal forward voltage drop and no sign of leakage when reverse biased. So I pulled it out for a more accurate check. On my transistor tester, the thing showed its true colours. Although there was still no sign of leakage, when tested for gain the meter slammed against the right hand stop, as though the transistor had an extremely high beta . It was just as though it was short circuited. In fact, it was behaving more like an SCR, going short circuit as soon as any bias appeared on the base. And being in a DC circuit, once shorted it stayed shorted. A new 2SC1364 restored the correct AGC level to the UHF tuner and the whole set to normal operation. Well, having digested J. L.'s trauma, I think something a little lighter is called for. This story really started with one of my own sets; a General Electric model GE482 which I acquired several years ago and which serves as a very useful second set. The GE482 is about 7 years old and apart from the fault I am about to relate has been virtually trouble free. But before delving into the story, I should point out that this chassis has appeared under at least three brands: the GE482 as above, the Rank model C2020 and the General model GC205. So the fault and its cure could apply to any one of these. The fault showed up some time ago but it was intermittent and occurred only rarely. It took the form of loss of blue or, at other times, an excess of blue. Like the cobbler whose children were the last to wear shoes, I did nothing about it for a long while. There were a number of reasons for the duck-shoving. For one thing, it seemed like a potential nasty and it's bad enough having to solve nasties when one is being paid for it let alone doing it for nothing. Then there was the intermittent nature of D.DAUNER ELECTRONIC COMP ENTS WE STOCK A WIDE RANGE OF ELECTRONIC PARTS for • Development • Repair • Radio Amateur • Industrial Electronic • Analog and Digital WHILE STOCKS LAST CFE 455 RESONATOR $2.80 ea • 7552 COAXIAL CABLE (4 SHIELDS) CG7 $0.90/MTR • 50 ONLY MET AL PROJECT INSTRUMENT CASES 370mm(L) x 90mm(H) x 180mm (D) $4.50 ea • Come and see. Showroom: 51 Georges Crescent, Georges Hall, NSW 2198 (Behind Caltex Service Station In Blrdwood Read) Phone 724 982 TRADING HOURS: Monday to Friday 9.00 a.m. to 4.00 p.m. Saturday from 9.00 a.m. to 12.00 noon. MARCH 1989 59 SERVICEMAN'S LOG the fault plus its rare appearances. Of course, Mrs Serviceman made jibes from time to time but I could always find a good excuse. In fact, I did pull the back off the set on a couple of occasions and prodded around the red, green and blue drives, looking for possible dry joints or intermittent components but without success. So I more or less gave up. Then several months ago, one of my customers brought in the Rank version of this set and complained about exactly the same fault. I ran that set for about three weeks and it displayed the fault only once during that time and then so briefly that I had no chance to get to grips with it. Finally, I was forced to return it to him with the advice to keep it until the fault developed to a more predictable condition. And did Murphy have a field day on that one. The customer was back in a couple of days with the news· that the set had "gone blue" almost as soon as he took it home and had been like that almost continuously ever since. Yet when I set it up in the workshop it worked perfectly for several more weeks - not even a hint of trouble. So once again, all I could do was return the set with suitable explanations and advice. Having heard nothing since I assumed that the fault had not returned or if it had, only briefly. I know the customer well enough to know that he would be back immediately if he felt that the set's behaviour justified it (more about this later). Another Rank C2020 And so the problem lay dormant until a few weeks ago when a different customer fronted up with a Rank C2020 having the same fault. (/ " .-v~ ~~­ ,i\_~il~ -----------=-~.~ /2-- ~ 60 SILICON CHIP (;;# Once again, it showed a marked disinclination to misbehave when the customer tried to demonstrate the fault. By now, with three examples of the same fault hanging over my head, I realised that I had to make a real effort to come to grips with it. The best I could hope for was that this latest chassis might respond more readily to prodding, tapping, freezing, etc than had its predecessors and thus provide a clue. Neck board checks In this set the red, green and blue drive transistors are on the neck board (PWC677). I went over this board with a fine tooth comb and tried every trick I knew to bring on the fault. It was all a wasted effort; the set never missed a beat. Well, perhaps it wasn't wasted. Something, probably the sheer frustration of the problem, triggered a long dormant memory concerning a problem with this chassis when it first appeared. At that time the problem was more drastic; intermittent loss of all chroma. This problem was eventually traced to the chroma processing IC, IC701, a uPC1365C . More precisely, it was the socket used to mount the IC that caused all the trouble. The first time I struck the fault I assumed it was faulty contacts and went through the ritual of spraying both the IC and the socket contacts with a contact cleaner pressure pack. This worked for a while, then the set bounced. This time I changed the IC and that worked too, for a while. Then it bounced again. By this time I'd heard rumours of the same fault in other sets and a recommendation - I think by the manufacturer - to remove the socket and solder the IC directly to the board. And that fixed it. So was this a variation of that old gremlin'? It seemed that there was a good chance that it was but in any case, there was nothing to lose and everything to gain by dispensing with the potentially troublesome socket. It is a 28-pin device, so I used up a few centimetres of solder braid getting it out. I then I fitted the IC directly on the board. That was sim- ple enough but I realised I had made a minor goof. Mounted on the copper side of the board was a small capacitor with one end connected to the earthy copper pattern and the other end to one of the IC pins. But which one? In my haste to remove the socket I had neglected to note this vital point and the situation was not helped by the fact that the markings on the capacitor were no longer readable. I probably could have worked it out from the circuit but the situation was enough to prompt me to bring my own set into the workshop the next morning. Not only would it clarify this point beyond doubt but it would be a good opportunity to modify my own set at the same time. Well, it all worked out fine. The capacitor turned out to be a .OlµF unit which connects to pin 10 and modifying my own set presented no problems. Both sets fired up at switch-on but significantly, both were in obvious need of grey scaling. My own set, in particular, was now excessively blue. So that was attended to after which I had two very nice sets running on the bench. But had I cured the fault? Only time would answer that question. I ran the customer's set for several days with no sign of trouble, which was encouraging but not conclusive. And of course, I gave my own set a thorough workout both on the bench and then at home. It performed perfectly also and thus encouraged, I gave the customer back his set with strict instructions to contact me if there was any sign of trouble. That was several weeks ago as I write and all is well so far. So here's hoping. What about the first customer? And what about that first Rank set that Murphy had had so much fun with? Quite frankly, I was puzzled that I had not heard from the customer. I felt sure he would have contacted me in the event of trouble but at the same time, I found it hard to imagine that the set had run for nearly six months without trouble. So I rang him. And would you believe it - the set had not missed t -RE:AL.\5£.D t At> MAt>E. A MINOR GOOF9.... TETIA TV TIPS AW A-Thorn N Chassis Symptom: Small picture. 118V rail down to about 90V . R907 (2200 9 watt) spring resistor may open, cutting off the set altogether. Cure: L901, a 1 OµH miniature inductor, goes open circuit. This inductor feeds drive to the series regulator and, when it goes open circuit, the regulator is cut off. The set may still operate on current fed through R907 but this will get very hot and may spring open as a result. GEC 2213-A Symptom: Loud squealing from power supply. Squeal changes pitch or loudness as the load on the supply changes but even disconnecting the set entirely doesn't stop the noise. Cure: C510 (1 µF). C512 (1 OµF) a beat since he took it home all those months ago. Among other things, it just shows how easily one can get caught. Had I made any attempt to cure the fault, I would have blissfully imagined that I had fixed it. In fact, I know that it is still there waiting to happen. and/or C521 (4 .7µF) gone low in value. The first two capacitors modify the drive waveform to the chopper transistor while the third one is in the feedback network to the line oscillator in IC501. (All three were found faulty in one set and the noise from the chopper was deafening although the set would still work). Sanyo CTP5601, 6602 etc. Symptom: Very weak sound but no apparent distortion. A signal tracer will show sound to be normal at test point 1 G, the output of the sound IF chip , but not at the volume control. Cure: C178, a 1µF 1 OV electro open circuit. This capacitor and C 1 7 7 serve only to keep DC out of the volume control but failure of either will cause loss of sound. So I have suggested that he bring the set in immediately it gives trouble - or sooner if he likes - and I will modify it. But I doubt whether he will do anything until it does misbehave; I'm sure he's convinced that I've fixed it. Some people are funny like that. ~ MARCH 1989 61 NEW KIT! KIT'S COLUMN 1/3 Octave Graphic Equaliser Totally NEW design. Stunning audio performance. Toe 28 band Jaycar Graphic Equalisers have been unbelievably popular over the last 8 years. Jaycar, along with Silicon Chip have taken the best featun:s of the 28 band graphics and incarporatl:s them into this totally new electronic design, which featun:s vastly superior audio performance to our old graphics. apart from the 4 extra bands (which now cxtl:nd frcm 16Hz to 20KHz), the new 'Studio Series' graphic fcatun:s radically new slide pot> especially made foc the project. They have a much different resiltAD.ce taper than the old linear pots of previous designs and arc almost univcnally used in professional graphics that cost over one thousand ddlan!! In keeping with the profe11icnal natun: of the product they arc mountl:d in a staDdard 19", 2 unit configuration and powered directly fran mams. Naturally the Jaycar Hi Guysl Well, ~·s catalogue time again. The guys in the art department have been working around the clock for the last two months to get it together, It's the best one yet (they tell me) and the biggest. ( l\le heard that before I) kit ill :ruppli:,d with all metalwork, including the statl:-of-the-art LM833 low noise op -amp, specially made slide controls etc. You will find a copy of the catalogue in the centre of this magazine - that Is unless someone has stolen It. If it's not there call in to any one of our stores and $1.00 will get you one. SPECIF1CATI ONS Frequency Response Equaliser out Equaliser in Boost and out Harmonic Distortion <.05% for frequency range) Plat 5Hz-20kHz + !dB -3dB at 45kHz -12'18 Signal Handling Gain Maximum input and output Unity (sec text) IOV RMS (all controls flat) Signal to Noise Ratio with respect to IV RMS ONLY $229.oo n------------------, NEW KIT! ''Beat Me'' Ref; EA March '89 This unusual project is actually a metronome that has its rhythm set by simply tapping the unit at the desired rate. You can tap it with a drum stick, pencil - even your fingernail 4 times, and the "Beat Me" mimic the rate at which it was tapped indefinitely - so simple! The Jaycar kit includes case, speaker and all electronic components. It runs on a battery (not supplied) . Size 130 x 68 x 41mm Cat KA TOP VALUE! A new branch? The boss has been spending a lot of time In Melbourne lately. He tells me that we will be opening a new store in Melbourne soon. when I asked him where in Melbourne he said, "Corne down and I will show you." The problem Is that I'm not sure whether he actually wanted me to go or notl Aw. ~OUr? 1 $29.95 New Kit Dept. A new kit which tickled my fancy is out In EA this month. It's called "Beat Me"I (Now wt,y did I like that name?) It Is basically a metronome, which has something to do with music. You set the beat by tapping It. Stuffed HI know why anyone would want one, but I love the namel 95dB unwcightl:d (20Hz to 20kHZ) 97dB A-wcigblcd 33k01nn lkO!un Input Impedance Output Impedance Ref: Silicon Chip March '89 Cat KC-5050 I OHz to 20kHz I I I I I I I gyl Well, I went anyway. We arrived down there first thing in the morning. That way the boss saved the over-night accommodation - pretty short-sighted of him I thoughtl The 1989, 148 page Jaycar catalogue was inserted in this magazine this month. If the catalogue was taken and you want one, send a large (280 x 210 min) stamped (90cents ), addressed envelope to: We went straight to the A'Beckett Street store. Eyup (the manager - call him Ian) and the guys, had the place looking really splc'n'span. I really liked that shop and some of our guys there seemed to Ii ke me ... After that we went out to our big store at Springvale to see Sam and the guys. It's a fair way out of town but convenient I guess to the customers who live out that way. Jaycar Pty Ltd PO Box 185 CONCORD NSW 2137 I I I I The boss then took me to lunch and fil led me up on Mo'et - the rascal. I doni remember too much else about the rest of the time in Melbourne, but once again, I think I had a good time. and we'll send you one right back! OR call into any Jaycar store and collect one for ONLY $1.00 L------------------~ The boss never did show me the new Melbourne site but judging by the Cheshire cat grin on his face he (we?) may be back down real soon. OUR MOST POPULAR KIT IN 1988! SeeYal FM Stereo Transmitter "MINI MITTER" Ref: Silicon Chip October 1988 This fantastic project enables you to transmit a signal IN STEREO over the FM band. The range Is limited to about 20 metres or so, so irs not a nuisance to anyone else. It uses a single 1.5V M (penlight) cell which lasts for ages. Just imagine! You can listen to your CD player on your FM headphone receiver while washing your earl You can play your Walkman CD player over your car stereo - no wiresl The possibilities are endless! Set up your own mere FM Radio Station! The Jaycar kit of this projecl Includes the hard to get Rohm BA 1404 chip and the CORRECT 38kHz crystal - even harder to getl All other specified parts are included as well. ONLY TURN YOUR SURPLUS STOCK INTO CASH!! r--------7 SPECIAL AND 1 I ~ IC CRYSTAL FOR MINIMITTER KIT AVAILABLE SEPARATELY BA-1404 Trans IC 38MHz Mini Crystal Cat. Zl-3995 $6.75 Cat. R0-5298 $8.75 -------- I _J Jaycar will purchase your surplus stocks of components and equipment CALL GARY JOHNSTON OR BRUCE ROUTLEY (02) 747 2022 FANTASTIC NEW KITS FOR '89 MINSTREL 2/30 SPEAKER KIT Refer Silicon Chip Feb 89 Jaycar and Silicon Chip proudly present the first in a series of quality, economical speaker kits. These popular bookshelf type speakers will handle 60W RMS! AND They perform extremely well, showing a good overall balance between speakers and a very flat response through the tonal range. Just look at these features: ,. high efficiency- 96db - 1Wattl1meter * pre-built crossovers with aircore chokes * small size - 490(H) x 303(W) x 290(D)mm * Recessed push terminals on rear ,. quality black cabinets with removable grills If purchased together cat. CS-2540 Speakers cat. cS-2542 Cabinets $1 49 ■ 00 $1 29 ■ 00 only$269.00 complete PCB SHORTS LOCATOR Refer EA Feb 89 This kit will allow you to use anu analog RGB colour video monitor as a CGA colour monitor for your IBM PC or corrpatible. Kit includes PCB, box, panel, D sockets and plug and all specffied components. Cat. KA-1711 ' $49.95 Cat. KA-1712 MAINS MUZZLER Refer Silicon Chip Jan 89 A line filter kit for your computer which incorporates an effective filter for mains borne interference and a varistor to clip dangerous spike voltages. Kit includes PCB, box (HB5446) 4 mains sockets and all specffied components. Cat. KC-5046 $55.00 Refer EA Feb 89 This simple kit will help you locate shorted tracks on printed circuit boards by means of a varying audio tone. It's easily built and much cheaper than commercial units. r----------, 1 BETA TESTER 1 I I I I I Refer Silicon Chip Feb 89 Great NEW kit. Will measure the gain of a transistor, test NPN, PNP and power transistors, PLUS, by trial-and-error, you can identify BCE on an unmarked device. Kit includes PCB, box and all specHied components. L $18 95 - --- ---- -- Cat.KC-5047 • I I I I $22.95 BEEPO CONTINUITY TESTER Refer EA Feb 89 This ail-singing, all-dancing continuity tester kit features three audio tones, operation over six decades of resistance, auto-polarity reversal, and an ambient current so low, it needs no ON/OFF switch. Kit Includes PCB, box and all specHled components. Batteries extra (Cat. SB-2369 $4.35 for 2 Alkaline) I Cat. KA-1710 $19 95 .J ~ - - - - - - - - - - - - - - - - - - - - - - ~ ■ gr_#) lif____________________________________ MAIL ORDERS HEAD OFFICE POST & PACKING 137 7 2 ""~--iiiliii~iloiiiilii~iiAl,.,..n._._...,.l..~lli.o6,._~ 8 rL_::_i_i_i_\~_{;_~:_(~_(:_~a-~-:c_:4_~c_:_~:_:__ _ _ _ _~_t_R:_{_:~-~-~-~-~c_1l_l_::_;o_:_:ri_!8_8___1l_t_$_1o_o_l_!i_9J_i_i_1_l_l__.., MAIL ORDER VIA YOUR ff ROAD FREIGHT ANYWHERE IN AUSTRALIA $13 .50 .., SYDNEY-CITY 117YorkSt. (02) 2671614- GORE HILL 188 Pacific Hwy (Cnr. Bellevue Ave) (02) 439 4799 Mon-fri 9 • 5.30 Sat 9 - 4pm 144 Logan Rd (07) 393 om Mon-fri 9 • 5.30 Thurs 8.30 - Sat 9 · 12 Mon-Fri 8.30 • 5.30 Thurs 8.30 pm· Sat 9 · 12 PARRAMATTA 355 Church St (Cnr. Victoria Rd) (02) 683 3377 BURANDA QLD CONCORD 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 HURSTVILLE t 21 forest Rd (02) 570 7000 · Mon-fri 9 - 5.30 Thurs 8.30 pm · Sat 9 12 SPRINGVALE VIC Mon-fri 9 . 5.30 Thurs 8.30 pm · Sat 9 · 2pm -:-7 , Id Mon-fri 9 · 5.30 fri 8.30 · Sat 9 · 12 887-889 Springvale Road Mulgrave (03) 5471022 Nr Cnr. 0andenong Road Mon-fri 9 · 5.30 fri 8.30 - Sat 9 · 2 Map reader Have you ever had to work out the distance between two points on a map? Using a pair of dividers or a ruler is doing it the hard way. All you need do is run the wheel of our Map Reader over your route and the answer comes up on your calculator. By MALCOLM YOUNG & LEO SIMPSON There are times when you need to plan a particular route you wish to take, especially if you take part in activities such as orienteering in the bush. Part of that planning is working out which route is the shortest. But how do you do that if you only have a straight edged ruler? Unfortunately; roads and tracks tend to have a few bends as they meander about. Fun hermore, if you are tracing your rnute on a street directory, distances lose all perspective after you turn a few pages. 64 SILICON CHIP With this Map Reader you simply run the guide wheel over the map scale to get a scale factor. Then it is a simple task to run the guide wheel over your proposed route to obtain the distance to be travelled. The electronics involved in the Map Reader is pretty complicated but it won't cost a bundle because it is all based on a cheap and readily available pocket calculator. All you have to to do is make up the guide wheel assembly and then wire it into the calculator. When complete you will not only have a handy Map Reader (or distance calculator) but the pocket calculator will still perform all its functions as normal. Digital display Small projects requiring a digital display can have a price that can make them impractical. For example, a 4-digit multiplexed display could cost over $30 and an LCD version even more. For this project we need at least three digits and preferably more. Ideally too, the readout should be a liquid crystal display (LCD) to keep battery drain to an absolute minimum. That requirement adds up to quite a lot of dollars if the display has to be made specially for the job. Fortunately, we don't have to use a special display. We can use an ordinary 4-function pocket calculator with LCD readout. You can buy these for around $10 to $12 or you might be able to use one you - r 3V_L S1 .---OOUTPUT TO+ SIOE OF EQUALS KEY IN CALCULATOR Fig.1: the circuit of the Map Reader is really simple - just a LED running from two AA cells and a phototransistor connected to the calculator. The guide wheel acts as a photo interrupter. B EOC VIEWEO FROM BELOW MAP READER interrupts light from a light emitting diode (LED) to a phototransistor. As the light hits the phototransistor it conducts and acts as a switch. This is connected across the " = " button on the calculator. So only two wires need be connected to the calculator. For our Map Reader we used a Tandy solar-powered 4-function calculator with LCD display (Cat. 65-563). This is listed in the current catalog at $24.95 but we purchased it on special for only $11.95. If you wish to buy another model or use one that you already have on hand, you should check that it has the constant function described above. Construction When we talk about 4-function calculators we mean the most basic models which provide addition, subtraction, multiplication and division. On many (but not all) 4-function calculators though, there is a fifth "hidden" feature; the "constant" function. The constant function allows you to enter a given number on the display and then repeatedly add, subtract, multiply or divide by that number. For example, if you enter the number 3, press the + button and then repeatedly press the "=" button, the number on the display will increase by 3 each time the " = " button is pushed. If you have not tried this on your calculator give it a try now. Many of the more deluxe multifunction calculators do not have the constant function - it tends to be confined to just the 4-function models and those that add a few more features such as percentage and square root. However, that is not a problem since we only require a cheap model. The basic principle of the Map Reader is to make use of the constant function. We enter the scale factor of the map concerned and then run the guide wheel over the map. As the guide wheel rotates it Construction of the Map Reader is in two phases. First, the Map Reader unit must be made and then the connections made inside the calculator . The Map Reader unit consists of a small printed circuit board (PCB) which carries the LED, phototransistor, interrupter wheel, pushbutton switch and double AA cell holder. The PCB measures 107 x 30mm and is coded SC 08103891. The first step is to make the interrupter assembly. The guide wheel we used was actually a 25mm diameter " servo horn" which can be obtained from most radio control hobby shops. Eight equally spaced 1.6mm holes (1116th inch) were drilled into this wheel at a radius of 7.5mm from the centre. Once all eight holes are drilled they should be deburred with a This is the guide wheel after it has been drilled. We used a 25mm diameter "servo horn" which is normally used in radio controlled models. It can be obtained from any hobby store. This view of the board shows the LED and phototransistor before the guide wheel is installed. We had to cut away the plastic bezel surround for the phototransistor to allow the guide wheel to rotate freely. This edge-wise view of the board shows how the guide wheel is installed. Make sure that the LED is accurately positioned over the holes in the guide wheel. Fig.2: wiring layout for the printed board. The dual AA cell holder is glued onto the board. already have on hand. The only requirement is that it must have a "constant" function. The constant function MARCH 1989 65 This photo shows the Map Reader before the board and battery holder is wrapped in electrical insulation tape. The insulation tape prevents your skin resistance from degrading the operation of the phototransistor. large drill, to clean them up. The next step is to mount and solder the phototransistor on the board. It should be pushed down on the board as far as it will go. That done, a plastic ring from a standard 5mm LED bezel should be fitted over the phototransistor and cemented into place with 5-minute epoxy or superglue. The plastic ring acts as a light shield for the phototransistor, to minimise the effect of ambient light. The guide wheel must now be fitted as close to the top of the bezel ring as possible while still allowing the wheel to rotate freely. We mounted the wheel using a 12mm long screw, two nuts and a lockwasher. With the wheel in place, the LED is mounted so that it shines directly on the phototransistor. The photos show how the assembly goes together. The double AA cell holder was glued to the printed board using superglue. We then connected it by soldering the two connectors to two PC pins on the board. With hindsight, this method can be improved upon. Instead of using PC pins, we suggest using a standard battery snap connector. The leads from the connector can then be shortened back and soldered directly to the appropriate pads on the PC board. 66 SILICON CHIP A 2700 resistor is required for current limiting to the LED and a momentary contact pushbutton closes the circuit when using the Map Reader. When the assembly is complete, you can check it with your multimeter, switched to a low Ohms range. Connect your multimeter across the relevant two pins on the Two connections need to be made to the calculator's printed circuit board. These are the connections for the " = " key on the particular Tandy calculator we used. PC board and rotate the interrupter wheel slowly. The multimeter should alternately show high and low resistance (close to zero ohns} as the phototransistor turns on and off. Connecting the calculator Some skill is required to connect up the wires from the Map Reader to the calculator. Remove the back of the calculator after noting the location of the "=" button. The back may need to be carefully prised off with a small flat blade screwdriver as there are usually a couple of plastic 'clips' holding it in position. This operation is best done with the calculator face down to prevent all the buttons from falling out if they happen to be loose on the inside. Once you have the back off the calculator, you will be faced with a myriad of razor thin tracks and pads all terminating at a square LSI chip in the centre. The pads will usually be covered with a protective coating to prevent the copper track underneath from corroding. Locating the two pads for the "=" button can be a tricky affair. If it is not obvious you may have to lift up the PC board retaining the keys in place and trace the tracks under the rubber mat. This may mean carefully cutting away plastic rivets from the top surface of the PC board. You will see tracks intermeshed together where they can be bridged by the conductive rubber mat. You should follow the two tracks corresponding to the " = " button to a pad, and if there is a corresponding pad on the opposite side of the PC board it usually means that they are plated through at that point. Mark this pad and do the same for the other track before carefully sandwiching everything back together again. Scrape away the protective coating from the two selected pads until the exposed copper is shiny. Now carefully tin these pads with a small amount of solder. You can test this pick off point by performing a calculation and shorting these pads together in place of the " = " keystroke. Solder two wires about 40cm in length to these pads. A length of miniature ribbon cable will be ideal for the purpose. Now check that you can perform the function of the " = " button by shorting the free ends of the wires together. You also need to check which wire from the calculator is positive. You can do this by switching your multimeter to a low DC voltage range and measuring across the two leads while the calculator is turned on. The voltage reading will typically be about 0.5V. Actually the voltage across the key contacts is a constant series of narrow pulses. This corresponds to the process whereby each key is "strobed" by the calculator chip to see if any button has been pressed. The frequency of this pulse train and the response time of the liquid crystal display limits the rate at which the buttons can be pressed and still register. With most calculators we have found that a practical limit is about four or five closures per second. This is quite adequate for this project. Before closing the calculator up again you should cut a small slot into the side of the case to give clearance for the two wires. You can then solder the leads from the calculator to the two pins on the PCB. Make sure that you have the positive wire connected to the collector of the phototransistor. Test that all is well by turning the calculator on and setting up the constant function as described before. Make sure this is working by pressing the "equals" button a few times, then switch on the LED and slowly rotate the guide wheel. You should see the readout value increment as each hole passes under the LED. Finally, we suggest you wrap the whole board and battery assembly with electrical insulation tape. Make sure you cover all the PC copper pattern with tape. The tape will not only hold the batteries securely in place but will stop any leakage from skin contact on the board from degrading the operation of the phototransistor. Reading maps Now that the Map Reader is functioning you'll want to go places. To use the device yo_u 'll first have to set up a scale factor on your calculator. Do this by pressing "1" followed by " + " and " = " then press the LED button and run the guide wheel over the scale. Subtract 1 from the readout and take note of the value. The scale on your map may read from O to 10km. If this is the case 0 0 08103891 Fig.3: this is the full size artwork for the printed board. PARTS LIST 1 PCB board, code SC08103891, 107 x 30mm 1 dual AA cell holder (Tandy Cat. 270-382, Jaycar Cat. PH-9202) 1 battery snap connector 2 AA-size 1 . 5V cells 1 25mm diameter servo horn (available from hobby stores) 1 SPST pushbutton switch (DSE Cat. S-1201) 2 PC board pins 1 1 2mm x 3mm machine screw 2 3mm spring washers 2 3mm nuts 1 pocket calculator (Tandy Cat. 65-563 or similar) Semiconductors 1 MEL 1 2 photodarlington transistor high efficiency red LED 2700 0 .25W carbon resistor Miscellaneous Superglue or 5-minute epoxy, electrical insulation tape , 40cm of light duty figure-8 (rainbow) cable, sleeving (for LED leads). then you must divide 10 by the scale factor just noted. Likewise if the scale is from O to 5km then divide 5 by the scale factor. To make things easy, consider the result if your map scale was 10km long and when you ran the Map Reader over the scale you get a scale factor of 10. Now let's suppose that you run the Map Reader guide wheel along a route on your map and get a result of 47 [after subtracting the initial value of 1 loaded into the calculator). To obtain the length of the route you then multiply the value of 47 by the length of the scale (10) and divide it by the scale factor (also 10). This then gives a result of 4 7km. Naturally, each time you read a different map you will have to work out the scale factor as described above . And you must always remember to subtract the initial '1' loaded into the calculator to obtain the "constant addition" function. For best results, do not use the Map Reader in bright sunlight as high ambient lighting can stop the phototransistor from working properly. :lb MARCH 1989 67 AMATEUR RADIO By GARRY CRATT, VK2YBX Build a simple VHF FM • monitor receiver, Pt.2 Last month we described the operation of our simple VHF FM monitor receiver. This month we cover construction and alignment of the unit. The basic configuration of the MC3362 was covered in last month's article, so we will discuss the additional circuitry here. We found that the receiver produced reasonable sensitivity without the suggested external BFR91 broadband amplifier shown last month, so this has been deleted as an unnecessary complication. As it stands, the receiver gives quite reasonable sensitivity (in the order of several microvolts). An LM386 audio amplifier was used to produce adequate volume levels for normal listening conditions. The squelch is configured so that the DC output from pin 11 of the MC3362 is used to bias the audio amplifier off when no signal is being received. This also minimises the current drawn by the receiver when no signal is being received, an important point to con- sider if the receiver is to be run from batteries in a portable, application. Construction The first prototype receiver was built on a single sided circuit board but we subsequently designed a double-sided PCB (using a groundplane on the component side) for additional stability. The board measures 108 x 55mm and is coded SC 06103891. Normal RF contruction techniques apply. Basically the most important thing is to keep component leads as short as possible. This The parts are all mounted on a small double-side printed circuit board. Note that where the ground plane comes right up to the edge of a hole, the component lead must be soldered on both sides of the board. 68 SILICON CHIP ANTENNA J C2 100pF lOOpF 23 C3 120pF VC1 2-20pF TUNING VR3 50k C9 ClO .01~.1 ~ .,.. C23 + 10 25VW+ C21 CfJ + 01 - 116VW+ C20I 0.1 R3 47k 22 Fll C24 27pF 455kHz FILTER L3 21 19 ICl MC3362 FL2 10.7MHz FILTER 18 17 SQUELCH VRl 200k 10 A0JUST~NJv-......--WfH,----"'t C11I 0.1 C12 .047+ R9 100 C7 0.1 11 455kHz QUADRATURE COIL 13 12 24 CB .01:t 16 .,.. SQUELCH R5 2.2k C16 + 100 25VWJ R6 22k C19 220 16VW +) VOLUME VR2 10k LOG ':' L1 : 4T, 25B&S ECW ON 4mm FORMER L3 : 21, 258&S ECW ON 6mm FORMER C18 .047 1 BO SPEAKER RlO 10[! - NARROW BAND FM RECEIVER Fig.1: the circuit is based on the Motorola MC3362 (IC1) which is virtually a complete narrowband FM receiver on a single chip. L3 and C24 set the frequency band while the output (at pin 13) drives an LM386 audio amplifier (IC2). means that all capacitors, resistors and transistors should be pushed down close to the board before soldering the leads. Fig.2 shows the parts layout on the PCB. Begin construction by installing all the resistors, working down the parts list from Rl to Rll. Bend the component leads against the copper side of the circuit board so that the components don't fall out of the PCB when it is turned upside down for soldering. Solder the resistor leads, then trim the excess lead lengths with a pair of side cutters. After soldering the resistors, proceed to the capacitors, working through the parts list from Cl to C23. It is a good idea to cross the components off the parts list as they are installed, so that nothing is missed during construction. Make sure that you install all the electrolytic capacitors with correct polarity. If you don't do this correctly, circuit damage can result. For example, on one of the prototype receivers the 220µ,F capacitor was installed incorrectly. When powered up, the reverse voltage across the capacitor caused it to go short circuit. This caused pin 5 of IC2 to deliver about 6 volts DC (about half the available supply voltage) to the speaker and consequently the IC blew its top. Learn by our mistake - put the capacitors in the right way around. At this stage the trimpots for squelch (VRl) and volume (VR2) can be installed, as can the two IF filters (10.7MHz and 455kHz) and the 10.245MHz crystal. Be careful not to use excessive heat when soldering the crystal, as the body of the crystal will be close to the tip of the soldering iron when soldering the leads. The next step is to install the semiconductors. Ensure that the ICs are oriented correctly before you start soldering the pins. We do not recommend the use of IC sockets in the receiver as they can be unreliable. They also add stray capacitance and inductance to every IC pin and this can prejudice operation at very high frequencies (VHF). So be careful to install the ICs correctly the first time - desoldering all those IC pins can be a pain and can render the ICs unusable. Note that where component leads are connected to earth, they should be soldered on both sides of the PCB. This applies to the GND terminal of the 3-terminal regulator, pin 16 of ICl, pin 2 of IC2 and to quite a few of the resistors and capacitors. The only components requiring any degree of preparation prior to installation on the PCB are the input coil Ll and the tank coil 13. 11 is made by winding four turns of 25 B&S tinned copper wire (TCW) or enamelled copper wire (ECW) on a 3.5mm former. After winding, stretch the coil as shown MARCH 1989 69 VR3 PARTS LIST X1 - 10.245MHz crystal FL 1 - 455kHz ceramic filter (Murata SFB-455) FL2 - 10. 7MHz ceramic filter or crystal Semiconductors IC1 - MC3362 narrowband FM receiver IC2 - LM386 audio amplifier IC3 - 7805 +5V 3-terminal regulator Inductors L 1 - 4 turns 25B&S tinned copper wire x 3.5mm dia. L2 - 455kHz coil (from DSE L-2060 coil pack) L3 - 2 turns 25B&S tinned copper wire x 6mm dia. Capacitors C1 ,C2 - 1 00pF ceramic C3 - 120pF ceramic C4 - 56pF ceramic C5,C6,C7 ,C11,C20,C21 0 .1 µF monolithic C8,C9 - .01 µF ceramic C10 - 0 .1µF ceramic or metallised polyester C12,C 14 ,C18 - .047µF ceramic C13 - .01 µF ceramic or metallised polyester C15 - 2.2µF 16VW electro C16 - 1 00µF 25VW electro C17 - 1 0µF tantalum C22,C23 - 1 0µF 16VW electro C19 - 220µF 16VW electro C24 - 27pF (depends on frequency band) VC1 - 2-20pF trimmer Resistors R1 - 1kn R2 - 68kn R3 - 47kn R4 - 18kn R5 - 2 .2kn R6 - 22kn R7 - 1 0kn R8 - 56kn R9,R1 o - 1 on R11 - 3 .3kn Potentiometers VR1 - 200kn miniature trimpot, horizontal mount (squelch) VR2 - 1 0k0 miniature trimpot, horizontal mount (volume) VR3 - 50k0 multiturn potentiometer (tuning) Miscellaneous 1 x PCB (code SC06103891, 108 x 53mm) , 1 x 8-ohm loudspeaker , 1 x 9V DC plugpack supply, 1 x case to suit. 70 SILICON CHIP J~ ~L1 ~ C2 VC1~ec::>41 Fig.2: wire up the PCB as shown in this parts layout diagram. Keep all component leads as short as possible and don't forget to solder to both sides of the PCB where appropriate (note: ground plane not shown). in the photograph so that there is a 3mm gap between windings. The l00pF input capacitor (Cl) is connected 1-1/2 turns from the C2 end of Ll. If using enamelled copper wire it will be necessary to scrape the enamel from both ends of the coil and pre-tin the leads prior to insertion into the circuit board. 13 is made by winding two turns of wire on a 6mm former. Once again, 25 B&S wire should be used although the gauge is not critical as we will be stretching the coil mechanically to set up the frequen- cy coverage required. The tuning control is a multi-turn 5okn potentiometer which is specified for ease of tuning. Because the tank circuit operates directly at VHF, the varicap tuning voltage is quite sensitive to adjust. Note that any drift of the tank frequency with temperature will cause a change in operating fr equency. This can only be compensated for by changing the tuning voltage, via the tuning control. In fact , to tune over the entire 2-metre amateur band requires a change of only 2V (from 2V to 4V) Where to buy the parts The 10.245 MHz crystal can be obtained from HY-Q Crystals, 1 Rosella St, Frankston, 3199 . Phone (03) 783 9611 . It is also used in many Dick Smith Electronics kits and may be available through their stores. The SFB-455 455kHz ceramic filter is available from Dauner Electronics, 51 Georges Crescent, Georges Hall , NSW 2198. Phone (02) 724 6982. It is listed in the current Murata catalog (Murata components are handled by IRH Components, phone 02 648 5455). Other types can be used if the pin configuration is modified . The 10.7MHz filter can be either a crystal type (available from HY-Q Crystals or DSE) or a ceramic type which could even be salvaged from a surplus cordless telephone or other communications equipment. They are also available from Murata distributors. The MC3362 is available from VSI Electronics in Sydney phone (02) 439 8622. The 50k0 1 0-turn potentiometer is available from Geoff Wood Electronics (phone 02 427 1676) or David Reid Electronics (phone 02 267 1385). The 455kHz quadrature coil came from a DSE " IF coil pack" , Cat. L 0260. Circuit Notebook continued from page 33 L3 is made by winding two turns of tinned copper wire on a 6mm former. The band of operation is set by squeezing or expanding L3. The input coil L1 is made by winding four turns of tinned copper wire on a 3.5mm former. Note the location of the 100pF input capacitor (Cl). on pin 23 of IC1. And to change the tuning by 600kHz (the difference between input and output of a repeater) requires very little change in tuning volts. For this reason a standard single-turn pot is not practical - you must use a multi-turn control. The tuning control itself should be located away from the circuit board, so that the capacitance of the user's hand when tuning the receiver does not affect the tank frequency. Because the tuning control carries only DC, ribbon cable can be used to connect it to the circuit board. An alternative would be to crystal lock the receiver by using an external overtone oscillator fed to pins 21 & 22. Motorola mention in their data sheet that a level of around 100mV is required for this style of operation. Power up Because the unit has its own 5V regulator, the receiver can be run from virtually any DC source over 7 volts or so. Normally this would be either a 9V or 12V battery, or a 9-12V power supply. If you have a power supply with current limiting, it is wise to set the limit as low as possible to ensure that there are no unexpected fireworks when power is first applied. A correctly assembled receiver will draw less than 20mA from a 12V source. + 3.6V and hence by Ohm's law the current through this resistor and Q2 is about 1.6 mA. The output voltage at the collector of Q2 will then be a little above the emitter voltage. Now if we increase the input voltage above 5V, Ql will begin to conduct. This lowers the voltage at the base of Q2, thus decreasing the current flowing through this transistor. However, the current through Ql increases so that the total current flowing through the emitter resistor is almost constant. Increasing the input voltage further will cause Ql to switch on harder and this in turn will switch Q2 off as the voltage at the collector of Ql rapidly diminishes. Further increase in the input voltage will cause the emitter voltage to rise, cutting off Q2 even further. The output voltage will now be around the supply voltage. If we now decrease the input voltage, we find that Ql does not begin to turn off until the input voltage is around 4.5V. When Ql begins to switch off, it's collector voltage rises and this in turn switches Q2 on. The loop gain of the circuit can be altered by varying the emitter resistance. Decreasing this to around 6800 from 2.7k0 will make the loop gain equal to unity. This eliminates the hysteresis (and defeats the purpose of this circuit), so the circuit behaves like a normal buffer. Increasing this resistance will have an opposite effect. The addition of a O. lµF capacitor between the collector of Ql and the base of QZ will allow enhanced operation at higher frequencies. If the input of the circuit is to be direct coupled to a stage which also operates from a 9V supply, the two 22kn input bias resistors may be omitted. Malcolm Young, SILICON CHIP. MARCH 1989 71 Assuming that you have checked the component placement and found no errors, power may be applied. Check initially that the current drawn is not excessive and that the receiver generates white noise or "hash". You should also check that the squelch control (VRl) operates correctly; turning it anticlockwise should mute the receiver. Check the volume control trimpot (VR2) too; rotating it clockwise should cause an increase in audio level. If a signal generator is available, it should be set to the desired frequency of operation and at a reasonable output level [say 100µ V) to make identification of the signal reasonably easy. If no signal generator is available, connect a suitable VHF antenna to the receiver, so that the local VHF repeater or beacon can be utilised. Once a suitable signal is available the receiver can be tuned by squeezing or expanding the tank coil to shorten or lengthen it. This varies the inductance and hence the tank resonant frequency. If you have access to a spectrum analyser, it is simple to check the actual tank frequency, which will be 10.7MHz above the desired input frequency. This could also be checked by using a sniffer probe hooked up to a frequency meter. It may also be helpful at this stage to replace C24 with a 2-20pF trimmer to allow greater flexibility in setting the correct tuning range. Once a signal has been located, peak 12 [the 455kHz quadrature coil) for maximum audio output. In fact, this can be done without any input signal - you simply adjust 12 for maximum receiver noise. The only other adjustment is to peak the VCl input trimmer for maximum quieting using a suitable off-air signal. Fig.3: here are the actual size patterns for the printed circuit board. The ground plane (bottom) ensures receiver stability. Alternatively, a simple discone antenna will provide good results on a far wider range of frequencies. The frequency coverage of the receiver is not limited to the 2-metre amateur band and it can be successfully used on the VHF marine band, paging frequencies and VHF commercial frequencies. Footnote The purpose of presenting this project is to stimulate active experimentation on the amateur bands. Obviously, a receiver of this simplicity will not perform as well as a $1000 2-metre transceiver. However , it does show that reasonable performance is available at very modest cost. No doubt amateurs will develop improvements to this circuit that will make it easier for others to build. We welcome comments on these projects and will endeavour to incorporate suggestions in future articles. Now who will be first to produce the 6-metre version? ~ Antennas You will find that the receiver performs quite well with just a single piece of hookup wire connected to the input capacitor. 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Normally $165 Special, only $129 - THE WAY I SEE IT By NEVILLE WILLIAMS "Spycatcher": do Wright's electronics bear scrutiny? As a former Assistant Director of Ml5, Peter Wright had a story to tell which the British Government tried desperately to suppress. But according to one informed critic, official concern may well have been misplaced, because the main effect of one section of the book, dealing with electronic surveillance, is to undermine the author's own credibility. In the normal course of events, I might not have given much thought to a book about the devious goingson in Britain's Ml5 and M16 intelligence organisations. Controversial though the matter may be, it is not one on which the average reader can bring informed judgment to bear. So why get involved? As it happens, however, the book was the subject of comment by British technical writer, Barry Fox, in "New Scientist" for October 22 last. Under the title "The Wright Stuff?", Barry Fox professed to be bewildered by the science of "Spycatcher". He pointed out that, far from being a mere administrator, Peter Wright professes a high level of expertise in wireless/radio technology, mainly as applied to the theory and practice of electronic surveillance and bugging. But despite this, various terms and expressions in the text were said by Barry Fox to be totally uncharacteristic of a writer with a technical background. Moreover, some of the explanations were so garbled that they conveyed little, even to an informed reader. 74 SILICON CHIP As a technical writer and editor from way back, I am certainly well aware of the sort of thing that Barry Fox is complaining about. Like most other specialist skills, electronics has its own vocabulary, expressions and conventions which become as much a part of those involved as their own mother tongue. In any technical text, inappropriate terminology, disregard for conventions and glib but inaccurate explanations are all indicators that the writer is out of his/her technical depth. As examples of Wright's alleged lapses in this general area, Fox mentions: • The author's use of "MH" and ''megacycles' ' when he presumably means "MHz". • In the context of bugging, using small parabolic objects irradiated by microwaves, "he muddles together the behaviour of sound and microwave radio signals" to the point where the explanation is "extraordinarily confusing". • When M16 interrogated double agent Kim Philby, they borrowed a high quality microphone from the BBC, hid it under a floorboard, fed the signal down a phone line and recorded the interview on dicta phone cylinders and acetate discs. Why the complex and rather odd procedures when Philby would have been well aware that such an interrogation would be recorded? • Wright apparently spent years working on a system called "MOP" which allowed DC to be fed down an audio pair to power a remote device. He seemed totally unaware that "phantom powering" is about as old as the telephone! • To make more sense of a covert (presumably mono) recording containing a babble of voices, Wright resorted to listening to the tape on a machine having two staggered heads. Wright does not explain how the echo effect so produced made "even the worst tapes much easier to understand", nor could Barry Fox find any support for this claim. • Wright claims to have developed techniques for identifying the frequencies being monitored by consulates by detecting signals being radiated by the receiver oscillators. He appears to be unaware that, in the 1930s, the British Post Office was using vans equipped with special receivers and directional aerials to track down unlicensed radio sets, by monitoring oscillator radiation. Based on these and other such observations, Barry Fox is led to speculate whether Peter Wright was over-estimating his own abilities or fantasising over his past career; or whether, in the context of prevailing secrecy, he was able to out-talk his technically uninformed superiors. Still further questions Although Barry Fox did not labour the point, the inference was clear enough: if, for whatever reason, the author's account of his technical activities is open to question, might it not be that other aspects of the text would need to be discounted? But then again, if the text was so transparently flawed, why all the costly and futile effort on the part of the British Government to have the book banned? Somewhat intrigued by all this, I sought out a copy of "Spycatcher" a few weeks later when I was on holiday on the north coast, with time to spare. I didn't need to read far to encounter the sort of thing Barry Fox had been complaining about and to register that, at the very least, the services of a good technical subeditor would have helped. On page 8, for example, Peter Wright credits his father with being joint developer of a "vacuum" receiver - a term that would appear to fall awkwardly between "valve" (British) and "vacuum tube'' (American) terminology. On page 10, Wright tells how his father spent hours explaining crystals and valves and showing him how to "delicately turn the dials of a set so that the random static suddenly became a clear signal". To my mind, both pars bear the stamp of a non-technical writer possibly Peter Wright's co-author Paul Greengrass. But why weren't they tidied up at the proof stage? I'm not sure who wrote the story on " the thing" on pages 18-20 relating to a listening device secreted in the Great Seal behind the Ambassador's chair in the US embassy in Moscow. Wright says that the Americans finally submitted the device to him to determine how it worked - which he managed to do some weeks later. But his explanation leaves much to be desired and I'm quite certain that in the past, if someone had submitted it to me for publication, it would have been returned to the author for clarification. In this instance, the authors would not have been inhibited by security, because it happened in 1951 and involved a device designed and installed by the Russians, who both Ml5 and Ml6 obviously saw as their ever-present threat. Glaqcing back over my notes, scribbled as I read, I was reminded 9f other questions that could reasonably be put to the authors: • Page 63: how a new "thin" cable, to be buried in masonary, "gave off far less electromagnetic emission". I would have thought that electromagnetic emission was a function of the current flow rather than of conductor dimensions. • Page 91: how the local oscillator in a superhet "always radiates sound waves as it operates". In fact, the oscillator of a traditional superhet radiates an RF signal, which may be rendered audible by a heterodyne process in a surveillance receiver. • Page 92: "Nothing happened. The static hummed". I'm willing to bet that that wasn't written by someone with a technical background. • Page 105: "We were careful to use straight receivers for the RAFTER operation, each operating on a single megacycle frequency, so there were no local oscillators on our side" . That has to be the clumsiest reference yet to a TRF receiver. • Page 105: "The Russians used large radio frequency amplifiers with the HF receivers". "Large" or high-gain? "RAFTER" , by the way, was the code name for a surveillance technique said to have been devised by Wright. While monitoring an oscillator in an embassy receiver, a powerful carrier was swept across the band on which the receiver was presumed to be operating. If the carrier passed through the frequency to which the receiver was actually tuned, it would hopefully produce an overload condition or otherwise disturb or modulate the oscillator being monitored, sufficiently for the effect to be apparent. A different perspective Discussion of surveillance is confined largely to the first third of the Problems? ... and you don't have our .120page catalogue . .. At last . .. a TRADE catalogue for the consumer ARISTA ... your one-stop problem solver. Video plugs and sockets ... Video extension speakers . . . Video flyleads ... Video RF interference filters ... Video splitters . .. Indoor antennas .. . Video switching units . . . Down converters . .. Video speaker controllers ... Video camera lights .. . Video tape rewinders ... Video cine adaptors ... Video head cleaners . . . 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The remainder of the book is taken up with a discourse on (precomputer} data filing and cryptography and with the relentless pursuit of undercover agentf such as Philby, Burgess, Maclean, Blunt and - according to Wright Hollis. Some may find this interesting; others will not. But, to get back to my earlier question, why all the expensive effort to prevent publication? It certainly could have had little to do with the technical content, which is "ancient history" from the pre-digital era. Even at that time, much of it would have been as accessible to the Russians as to the British. More likely, the legal action was a knee-jerk response to a principle - heightened by the fact that Wright was a self-educated oddman-out who would predictably present the British secret service in an unflattering light: dominated by "old-boy" and public service attitudes, inefficient and often grubby. Enough said! Jump-starting cars While there may be little in common between stopping Russian spies and starting Australian cars, that does happen to be the next subject on the list. Scarcely had my last article been fed down the line into the SILICON CHIP modem than I was confronted by a television advert that most readers will probably have seen by now - several times! Worried about his very pregnant wife, a husband pulls into the driveway of his home and hurries inside - leaving the car headlights on. Around 3 G' clock the next morning she needs transport to hospital but by now the battery is dead flat. With commendable presence of mind, the very pregnant wife lifts the car bonnet, slides the switch on the new Exide "Switch" battery and tells her husband to start the car. The engine responds immediately, she returns the switch to its original position, closes the bonnet and off they go. Pardon my bewilderment. Here was a major manufacturer ostensibly providing an on-board standby battery, using it to start the engine, TO STARTER CIRCUIT JUMPER CABLE DONOR BATTERY TO VEHICLE EARTH DISCHARGED BATTERY 4 -2~~=ENGINE BLOCK OR CHASSIS MAKE CERTAIN VEHICLES DO NOT TOUCH From the Automotive Division of Pacific Dunlop Batteries, this diagram summarises the four steps when jump-starting a stalled vehicle. It applies for negative earth vehicles only, which must not be in physical contact (see text). 76 SILICON CHIP then apparently disconnecting it and exposing the electronics to a flat-battery situation, without a second thought. As soon as practical, I got in touch with Exide batteries and in due course, found myself in conversation with Alan Hyde, National Sales Manager for the parent company, Pacific Dunlop Batteries in Sandringham, Victoria. I explained about the article I had just written and the possible problems of jump-starting vehicles. Based on my account of what the article contained, Alan Hyde endorsed all that had been said and indicated that his company was about to release a brochure on the subject entitled: "Jump Starting Procedure". He subsequently posted me a draft of the text, which makes a number of points additional to those mentioned last month: • Cars manufactured since 1971 normally have the negative battery terminal grounded to chassis. In earlier models, or where there is any doubt, check to ensure that neither of the vehicles has a positive earth system. • Where the discharged battery has removeable filler tops, make sure that they are firmly in place before using the jumper leads. A damp cloth draped over each battery will help confine explosive gases; but keep the cloth clear of moving parts! • Switch off the ignition of both vehicles, together with all electrical equipment, before making the jumper connections. Close all doors and the boot lid to disconnect courtesy lights. • Many modern cars have electronic components which remain active, even when the ignition switch is off. It is essential in such cases to use jumper leads which incorporate anti-surge circuitry. If in doubt, take the precaution of checking with the vehicle manufacturer. The diagram, as shown, indicates the connection procedure recommended by Pacific Dunlop for routine situations. The vital thing is that connection (4), which closes the jump circuit, should be made to a part of the engine block remote from the battery and fuel system. The "Switch" battery So what's the story behind the Exide "Switch" battery? Fortunately, there is more to it than the simple "jump" start implied by the TV advertisement. The "Switch" is actually two batteries in one assembly, the main unit being developed from the standard Exide PS500 - a design that the manufacturer claims to have half the warranty returns experienced by competitive Australian batteries. The second or "reserve" section has about one-quarter the capacity of the main unit, but sufficient in normal situations to ensure at least 24 routine starts. With the switch in the "off" position, the main section functions as an ordinary battery, maintained by the normal charging circuit and liable to being "flattened" if the driver carelessly leaves the headlights on, as per the TV advert. The reserve section ls connected internally to the main section by a semiconductor diode such that, while current can flow into the reserve section from the charging circuit, it cannot flow in the opposite direction into a load. The reserve section is therefore maintained automatically at near full charge during normal operation of the vehicle. In an emergency situation, sliding the switch to "on" puts the two batteries in parallel, making the still charged reserve section available for engine starting, etc. Immediately after starting, the switch can be returned to "off". Because the diode is still in circuit, it will conduct automatically if the charging voltage rises significantly above that of the reserve battery, effectively clamping any surges or transients to a safe level. Within about 30 minutes, the main section should have been substantially reactivated. Alan Hyde stressed that company engineers had gone to great lengths to get the design right and to ensure that the switching system can cope both with the rigours of the engine compartment and the proximity of battery acid. In "The Exide Switch Technical Brochure" the battery is described as "sealed and maintenance-free". It carries a 2-year warranty, provided it is used under the specified conditions: notably that it has not been tampered with and has never been exposed to a charge voltage in excess of 15V. Exide warns that overcharging will "boil off" the electrolyte which cannot thereafter be topped up. Something for the sceptics In the January and February issues, I referred to the fact that people have argued for decades about the alleged therapeutic qualities of electricity, wireless waves, magnets, &c. By way of example, I mentioned a couple of dubious American practitioners who, in the early 1920s, CONTACT INTERNATIONAL PO BOX 390 COW ANDILLA, SA 5033. 2/283 BURBRIDGE ROAD, BROOKLYN PARK, SA. 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W0064 LEAD GOLD BNC MALE TO RCA MALE W0029 LEAD GOLD RCA MALE TO 3,5mm MALE W0042 LEAD GOLD RCA MALE TO RCA MALE . W0207 LEAD GOLD RCA MALE TO 2 RCA MALES 5.95 5.50 3.00 3.50 3.95 COMPUTER POWER SUPPLIES D0057 D0061 D0060 D0058 D0358 150 150 200 200 220 WATT FOR XT .. 89.95 WATT FOR XT SQUARE . 89.95 WATT COMPACT FOR AT .. 145.00 WATT STANDARD FOR AT .. 119.95 WATT FOR TOWER COMPUTER . 169.95 CONTACT US FOR HARO TO GET ITEMS. MANY OTHER PRODUCTS AVAILABLE. SENO FOR FREE PRICE LIST. BROCHURES ANO FULL SPECIFICATIONS FOR " AT" COMPUTER AVAILABLE UPON REQUEST. ALL PRICES INCLUDE SALES TAX PRICES VALID WHILST STOCKS LAST Mall Order Postage Less than $50 ............................... $3.50 O ..... ················································································. BANKCARD O MASTERCARD O VISA Card No ............................................... . EXPIRY DATE $50 - $99 ...................................... $4.50 $1oo • $250 ... ............................... $7·00 Above $250 .. .............................. $10.00 s·ignaI ure: .. ...................................................................... WHOLESALE ENQUIRIES WELCOME Address: ....................................................................... .. Heavy Items adds extra (Note: unsigned credk card mail orders cannot be accepted) N ame: ........ •................................................................. .. • IBM is reg. trade mark of International Business Machines ... .............................. .... ............... Postoode: .................. . • XT, AT and Atari are registered trade names .. (Please_allow 14 DAYS for !'Ormal mall and bank clearance delays) were making outrageous claims for equally · dubious pieces of "wireless" medical equipment. One could possibly equate such excesses to the sheer novelty of wireless technology at the time but I did not have that option in respect to a certain middle-aged American gentleman who appeared on a local TV talk show a few weeks back. Identified as Malcolm Vogels, his self-appointed mission, apparently, was to publicise the amazing properties of crystals. As it happened, I had just previously seen mention of a resurgence of the crystal cult in America in the context of the "New Age" mentality - described in the particular article as '' a hodgepodge of mysticism and pseudoscience" that can all too readily become a substitute for more rigorous thinking. Presumably to establish his credentials in real science, Malcolm Vogels said that he had been employed by IBM for some 27 years and had invented the coating that was still being used by the aforesaid company for their computer discs. But wait a minute! Even without re-checking the literature, I knew that oxide-coated magnetic tapes dated back to around 1927 and that, in the early 1930s, the technology had been under intense investigation by major German companies such as AEG, I. G. Farben and BASF. Allowing for years of research work by other European interests, by American and Japanese ~ompanies, and the subsequent extension from audio into video recording, a great many individuals must surely have contributed to the technology behind the coating on IBM's computer discs. For me, I'm afraid, the claim raised more questions than it answered. Nor did I find his statements or demonstrations on television in any way convincing. By gripping a crystal firmly and concentrating his thoughts (as evidenced by the pained expression on his face), Malcolm Vo gels was purportedly able to transfer information to the crystal. Then by pointing it at the audience, the information could supposedly be projected towards them. It seemed to work for a couple of people; at least they came up with what he said were the right answers. The remainder looked amused and bemused by it all. A crystal filter? In another demonstration, passing Sydney_t_ap water through a simple 3-turn glass helix, surrounding a crystal, transformed it into what a teenager said tasted like "pure" water. A similar procedure transformed bottled orange juice into "freshly squeezed". We were assured that the idea worked just as well with apple juice. What a clever little crystal. Not only was it able to change the chemical content of Sydney tap water, bottled orange juice or canned apple juice, but it knew what chemicals to remove and what chemicals to leave in! But that's not all. I gather that, in a non-televised demonstration, it or a similar crystal proved to have therapeutic qualities as well - at least to the satisfaction of a couple of those present. What kind of a crystal? At the very least, I think it's fair to ask what kind of crystal exhibits these wonderful qualities? According to my dictionary, a real crystal is: "a solid body having a characteristic internal structure and enclosed by symmetrically arranged plane surfaces, intersecting at definite and characteristic angles''. That leaves open quite a range of elements from which to choose. Do they all have subtle, mysterious properties, or only some? The most interesting crystal I can recall personally was a newly grown chunk of germanium shown to me by the late Graham Hall. It was due to be sliced into thousands of tiny wafers for an early production run of the ill-fated Australian Ducon germanium transistors. Having in mind the therapeutic properties attributed to germanium by Dr Asia (see January issue], one might expect quite phenomenal results from a large germanium crystal! But I gather that the "New Age" cult is concerned with crystalline quartz, which exhibits such vitally important piezoelectric properties. Does it not, these days, control the frequency of just about every transmitter and professional receiver one can think of? And is it not responsible for the uncanny accuracy of countless quartz clocks and watches? If a tiny wafer of quartz can be so important electrically, it is surely not unreasonable to accept that a complete crystal should exhibit certain remarkable properties! Mind you, Malcolm Vogels didn't seem to be keen to define or explain those properties: how liquids could possibly be upgraded by dribbling them past a crystal; how a crystal could absorb and store and disseminate information; how it could heal human ills. Maybe that's not so surprising. According to those who like to question the improbable, it is characteristic of the "New Age" philosophy: maintain that certain things are so but don't get caught up on the specifics of how and why. Say the sceptics: if they don't define the property they are talking about, it makes it that much more difficult for us either to measure or disprove it! ~ The "New Age" philosophy: maintain that certain things are so but don't get caught up on the specifics of how and why. 78 SILICON CHIP I PRODUCT SHOWCASE I TV colour pattern generator This portable unit is a comprehensive unit intended for use in servicing TV receivers and video monitors for computers and VCRs. For convergence and picture linearity adjustments, it generates a full set of geometric patterns comprising vertical and horizontal lines, dots and a crosshatch grating. There is also a blank raster, useful for checking colour purity, and a function called "focus" which is a vertical pattern which uses a 1MHz sinewave as the video modulation (similar to the picture definition testing lines in broadcast TV patterns such as the Philips PM5534 used by SBS). In colour mode it produces a bar pattern 95% colour saturated. With the colour turned off, this pattern is produced as a repeating grey scale. It is also possible to selectively turn off the red, green or blue signals which <;:an be a help when chasing colour faults. The various patterns and modes of operation are selected by two banks of pushbuttons on the front panel. On the top row, which selects the patterns, the buttons are interlocked (pressing one cancels another) while on the bottom row the buttons are independent. A modulated UHF signal is available from a front panel 750 Belling Lee socket while the composite video signal comes from a BNC socket. Two other BNC sockets allow for connection of an external video input signal and provide an output trigger signal (line or frame) for synchronisation of video signals on an oscilloscope. On the back panel there are five BNC sockets. Three are for the separate RGB signals while a fourth gives the Intensity signal (for RGB video monitors). The two remaining BNC sockets give separate line and frame sync signals. All five BNC sockets can be switched to give 1V video, TTL or complementary TTL signals. As well, the I (intensity) and RGB signals are available from a 9-pin D socket for direct connection to a computer colour monitor (CGA standard). NTSC colour TV receivers can be checked by turning off the PAL colour burst signal (with the "killer" pushbutton). Different PAL standard receivers can be checked too because the sound intercarrier frequency can be switched to 5.5MHz, 6MHz or 6.5MHz. The generator has an internal lkHz oscillator for sound modulation or an external sound source may be connected, via the 5-pin DIN socket on the rear panel. We found the Orion pattern generator to be a good performer, producing sharp and stable patterns from both the direct video and modulated UHF outputs. We did note one quibble and that is that the unit will not produce a recognisable pattern on the screen unless one of the colour buttons (ie, I, R, G or B) is pressed. Once that little hurdle had been overcome though, we had no problems. It will be ideal for servicing applications. The Orion PAL TV/Video colour pattern generator is available at the recommended retail price of $808 plus 20% sales tax. A protective carry case is also available for an extra $47 plus 20% sales tax. The Australian distributor is Bell Test & Measurement, PO Box 14, Lidcombe, NSW 2141. Phone (02) 648 5455. The unit may also be purchased direct from David Reid Electronics Pty Ltd, 47 York Street, Sydney, NSW 2000. Phone (02) 267 1385. New technical writing service by Ross Tester After more than a decade of putting the words to advertisements, manuals, brochures, commercials and the annual catalog for Dick Smith Electronics, copywriter Ross Tester has started his own business, Writech Pty Ltd. Writech will specialise in all areas of writing where technical' accuracy is a must. Ross Tester sees the company as providing a much needed service to companies who wish to produce brochures, manuals and press releases. Writech's other services will include catalog and mailer design and production, print broking, print control and public relations. For further information, contact Writech Pty Ltd, 78 Mactier Street, Narrabeen, NSW 2101. Phone (02) 982 9624. MARCH 1989 79 Low cost portable gas soldering iron \ Handheld digital storage oscilloscope Tektronix has released what must be the most upmarket technician's accessory, a complete dual channel digital storage oscilloscope weighing only 2kg. Designated the Tek 222, it has a 10MHz bandwidth and fancy features such as automatic setup and digital save/recall of both front panel settings and stored waveforms. The cathode rav tube also features direct readoU:-t of timebase and attenuator settings. Measuring only 90 x 150 x 250mm the Tek 222 can be comfortably held in the hand and will fit easily into a service technician's kit. It is powered with rechargeable batteries as well as 240V AC mains. For measurements in tricky applications such as process control, avionics and medical equipment, the Tek 222 has the handy capability of signal grounds which may be floated at up to 400V above or below earth potential. For further information, contact Tektronix Australia Pty Ltd, 80 Waterloo Road, North Ryde, NSW 2113. Phone (02) 888 7066. Home burglar alarm from DSE To cater for the need for an easily installed home burglar alarm, Dick Smith Electronics have released their L-5140 Security Centre. Housed in a lockable steel case, the unit is a 4-sector alarm with mains power and optional battery backup. The circuitry has been designed to minimise false alarms and to fully comply with the latest noise pollution requirements for alarm duration and resetting. Included in the L-5140 Security Centre is a siren oscillator to suit a standard horn speaker and a constant 12V DC output to power passive infrared sensors (PIRs) and other accessories . If the alarm is 80 SILICON CHIP triggered there is a 12V switched output to operate a telephone dialler, alarm bells or a strobe light. Priced at $199, the L-5140 Security Centre is available from all Dick Smith Electronics stores. Gas-powered soldering irons have been around for quite a while now and they work very well. Powered by butane lighter fluid which is readily available in convenient refills (for cigarette lighters) they can be used anywhere and are often more convenient to use, even if mains power is available for a conventional soldering iron. This Gassol model has two extra attractions. The first is the optional blowtorch tip which is handy for silver soldering, bending metal pipe or using heatshrink tubing. The second attraction is the price of $29.95. It is available from all Jaycar stores. Courses for amateur radio For those interested in becoming an amateur radio operator, the Gladesville Amateur Radio Club conducts a series of theory courses for the Department of Transport and Communications licence examinations. The next available course commences in early March and will last till December. The theory lectures are each of 3 hours duration on Thursdays in Lane Cove (Sydney). The course starts from basic elementary theory (no prior knowledge required) and will enable the student to sit for the Novice Amateur Operator's Certificate of Proficiency (NAOCP) exam during the year and later on, the AOCP exam. These courses have been running for 8 years now, conducted by instructor Ron Bertrand, VK2DQ. Several hundred amateurs have received their licences as a result of doing the course. For those who can't attend in person, the courses are available on video tape in Beta and VHS format. For further information contact the Gladesville Amateur Radio Club, PO Box 48, Gladesville, NSW 2111. Phone (02) 427 0530, after 5.30pm. Dall 15 3-way loudspeaker system Buy direct from Australia's leading manufacturer and save on quality AVTEK Modems. A range of 16 internal &external modems from low priced manual to fully automatic 2400 bps models complete with power supply, instructions and telephone connections. Designed and built in Australia, all Avtek Modems are guaranteed, with service and technical support available direct from Avtek CALL TODAY ON 008 25 2754 or (02) 888 5333 TOLL FREE Danish loudspeaker manufacturer Dali has released an interesting new 3-way speaker system, the Dali 15. A variety of advanced measuring techniques have been used in its development, including a patented vibration analysis system for detecting and minimising panel resonances. As a result, the Dali 15 employs a number of measures to reduce panel resonance, including a 40mm thick front baffle made of high density fibre board. The 200mm woof er is a long throw (25mm) unit with a 1mm thick polypropylene cone. As well as using conventional bass reflex tuning, the system is designed to be used with any NAD preamplifier having the "Bass Eq" feature whereby bass extension down 33Hz can be achieved. A large 75mm dome unit (the largest dome driver we've seen) is used for the midrange while the tweeter is a 20mm dome with ferrofluid cooling for the voice coil. Sensitivity of the Dali 15 is 90dB/1 Wilm and maximum recommended amplifier power is 200 watts per channel. Recommended SYDNEY RESIDENTS For further information and to see how much you can save on the best modem for your needs. 'fTEK ATA COMMUNICATIONS (A Member of the NetComm Group of Companies) retail price is just under $2000 per pair. For further information see your hifi dealer or contact the Australian distributors for Dali, Scan Audio Pty Ltd, 52 Crown Street, Richmond, Victoria 3121. Phone (03) 429 2199. Stereo headphone & microphone headset The KHM-7602 stereo headphone and microphone unit from David Reid Electronics is a lightweight headset which has applications in stage production, sound engineering and intercom sets. They could also be adapted to the Hands-Free Telephone project published in the September and November 1988 issues of SILICON CHIP. The 40mm diameter dynamic headphones have a hifi performance with a claimed frequency response from 20 to 20kHz and a MARCH 1989 81 Low cost DMMs from Jaycar Impressive computer range from CompuHelp Just when you thought you had seen all the IBM compatible machines you'd want to, a new computer distributor has set up business. Called CompuHelp Australia, they have an impressive range of personal computers ranging from a PC/XT sensitivity of 102dB/mW. Their impedance is 320. The microphone is a dynamic pressure gradient type with an impedance of 3000 and a sensitivity of - 80dB at lkHz. The frequency response of the microphone ranges from 100Hz to 10kHz which is more than adequate for most voice applications. This headset is priced at only $29.95 from David Reid Electronics, 127 York Street, Sydney, NSW 2000. Phone (02) 267 1385. Experimenter's card for IBM PC XT/AT/386 For engineers and experimenters developing peripherals there is new universal wirewrap card for the 82 SILICON CHIP compatible machine right up to a large 80386 tower style machine with everything that opens and shuts. All machines are beautifully made and the units are backed up with Honeywell Bull's Totalcare warranty service. For further information and a system demo, contact CompuHelp Australia at 35-37 Higginbotham Road, Gladesville, NSW 2111. Phone (02) 809 6966. IBM PC XT/AT386 or compatible computers. The card provides data and address buses and an 1/0 line buffer. It includes a universal address decoding chip and a DB25 female connector. A large area (4000 holes) is provided on the card for experimental circuits and all holes are plated through. For further information, contact Electronic Solutions, PO Box 426, Gladesville, NSW 2111. Phone (02) 427 4422. Jaycar has released two new lowcost digital multimeters. Both have a 3-1/2 digit display and come in a high impact yellow case. The lower-priced model measures both AC and DC voltage and current and resistance up to 20MO. A third socket provides a 10A DC current range. There are six resistance ranges and five DC voltage ranges. The test probes connect to the meter via banana sockets and they can also physically clip to the side of the meter so that one-handed measurements can be made. Ideally, an alligator clip arrangement would have to be made for the common lead for this to be possible though. The unit is priced at only $59.95 (Jaycar Cat. QM-1410) and comes with a 3-month warranty. The more deluxe model incorporates all the features of the cheaper model and adds ranges for capacitance, frequency measurement and a logic probe function. The current and voltage ranges have also been extended for both AC and DC measurements. The frequency meter is capable of very accurate measurements from a few hertz up to 200kHz as checked by our own test equipment. The capacitance meter has 5 ranges of measurement f ram 2000pF up to 201,tF which makes life easy when reading those tricky capacitor values. The logic function tests TTL logic levels and gives a visual display and an audible beep whenever a logic O is detected. The claimed minimum pulse width which it can detect is 25ns and the maximum input frequency is 20MHz. The QM-1400 represents good value for money at the price of $109. Both meters are available from all Jaycar stores. Thermocouple adaptor for DMMs Polystyrene capacitors YES Made here in Australia? YES Made Special to Type? YES Where From? Allied Capacitors Australia Allied Capacitors Australia specialises in custom made good quality, high stability polystyrene capacitors. Why design circuitry which requires additional components to achieve a specific capacitance; we can wind exactly the capacitance you need to match your design criteria within the ranges of 1 OpF to 1J.tF and up to 10,000VDC. Capacitors are manufactured to 0.25%, 0.5%, 1.0%, 2 .0%, 2 .5%, 5%, 10% and 20% and are priced according to tolerance. All capacitors are tested to 2.5 times the rated voltage. Interested? Call us now on: (02) 938 4690 OR Cut out and post this coupon to Post Office Box 740 Brookvale, N.S.W. 2100 r----~--.... - . . _..., I Yes, I am interested in your capacitors. I I Please post me details of the following values: I I ... /... voc .. ./ ... VDC .. . / .. . voc ... / ... VDC I Name (Please print) . . : I Address . . . . . . . . . . . . . . I -------------L~~~ ~~-~-~~~~J This thermocouple adaptor will allow most digital multimeters to measure temperature in degress Celsius or Fahrenheit. Powered with a 9V battery, its outputs are simply plugged into the common and "Volts" input on the multimeter. The unit is supplied with a 1.2-metre long K-type thermocouple ( w ilh Chromel and Alumel wires) and will measure the range from - 50°C to 1300°C. Resolution is 0.1 °Con the 200mV range and 1 °C . on the 2V range. The module measures just 90 x 70 x 40mm and is priced at $59.95 from all Dick Smith Electronics and AT style keyboards, it also stores. eliminates the need for a separate mouse. Instead it has a trackball on Intelligent keyboard a comfortably raised section on the righthand side of the keyboard. The includes trackball mouse operating buttons are just If you desire a better keyboard below the spacebar where they are for your IBM or compatible com- convenient to the left hand. puter this "intelligent" unit from The trackball is compatible with Contact International is worth con- Microsoft Mouse and Mouse sidering because not only does it System mouse(!) and plugs in via a provide all the features of the XT D9P or D25P connector. The keyboard itself has the usual 5-pin DIN plug. In spite of the space devoted to the trackball, the keyboard is no larger than standard models offering 100 + keys. Dimensions are 487mm wide by 195mm deep. Priced at $199.95, the intelligent keyboard is available from Contact International, PO Box 390, Cowandilla, SA 5033. Phone (08) 231 2202. 231 2202. MARCH 1989 83 3rd March 197Australia Howdy Colin, Just received your saga of life in works at the flagship as a US television. Reading your letter copywriter and tells me at lunch made me reminisce. Before I relate sometimes the things that go on my most recent adventures, I'll tell there. you about my first television job. The subsidiary has been going From my diary, May 196-: started for 11 years. Suddenly, on one day, a new career, with some misgiv- a supervisor and four of his men ings. I tell myself Rod Serling (the resigned. They were going to build creator of Twilight Zone) began a UHF station in the area. But it's with this group, as a copywriter, my opportunity to get into teleOnce e ad .. e.hig tim0- · ll e-vision. could recall about his Midwest job June - now I know why those was a lady yodeller, who could fellows left en masse. break a beer mug at 20 paces, and a At my interview, I explain I was fundamentalist radio preacher for as green as they come - a first whom he wrote the sermons. class ticket and 10 years' exSerling worked for the flagship perience as an electronics technistation; I am beginning with the cian but I've never worked in satellite 50 miles (80km) away - a television. lot of driving. "That's all right, son", the chief Two things make me uneasy. Jen- engineer said to me. "We've got a nifer from my college days now comprehensive training program By RICHARD KOPF ers 84 SILICON CHIP here. Sort of a buddy system". In reality, the training is 'sink-orswim'. But when you sink you pull the station down too. Not that it matters for the old blokes. There's a strong union here to protect them. I found out after I started that it's closed shop. I am compelled to join but get no protection until my 3-month probationary period is up. 'Ilhey're taking my money for nothing! The first two weeks, they didn't ow what to do with me. The s pervisor found that the remote iUCk needed cleaning; also the orkshop and the storeroom. I rted transistors and other bits usywork any school dropout could do for a minimum wage. E Transmitter work Next I went to the transmitter for sign-on shift for three weeks, since no-one else wanted to do it. I expected to be an onlooker for at least a couple of days, learning from the senior man. When that worthy arrived, carrying a briefcase bulging with house plans, contracts and lists of materials, he didn't even say hello. He just unlocked the door and waved my self-introduction aside. The first thing he did was spread out his "real work" in the office, then pom himself a cup of coffee from a thermos, muttering all the while about lazy carpenters. I had a look around, inspected the program log and glanced at the clock with an anxious eye. I realised the senior man had no intention of getting the station on air. "Even if I were fully experienced", I told him, "as a new boy, I have no idea of your procedures here". Moaning and griping, he reluctantly came out, pointed out the hidden breakers and fired the rig up. "Sit down at the console - I'll tell you what to do". He led me through the first two hours of programming, then I was on my own. "What if I goof?", I asked. "At this time of the morning, who cares?" Later, I learned that he had been reprimanded for tying up the only telephone line while taking care of his business. The transmitter got sick - he never noticed. The studio supervisor had to come nine miles (14km) to fix the problem. w _-, Yo\ ~ o~~ \\,,-'~Q,o ,------.;;. ' ./ ~ 4, , 6e~ 0 :'.'t-41!11'\ G v•~J•- "~•1\--\~ 1'1RA\N\NG \S ''StNKOR ~W\lV\ 11 Studio work Back at the studio, I learned that most of the old-timers had their own outside interests; the TV station was really their second job. I watched one fellow at the master control blow every prime time break until the 11 o'clock news. He had a small installation business - intercoms, TV antennas and so forth. He too spent much time on the telephone. The network would go to black, he'd say, "Wait, Jack ... Oh, hell, I'm lost again". Then he'd fumble through the copy book and the program log, arbitrarily roll a film but forget to switch it to air at once, chop the end - and still get back to network late. A few nights later, I wasn't much better. At the console the first time, I was as nervous as a long-tailed cat in a room full of rocking chairs. At least, I didn't have the bad example to guide me. The evening supervisor actually intended to train me! He talked me through two breaks, showed me how to strip the projectors and load the next films and slides needed, and told me about log entries. At that point, I noticed no more films were out, so started to look for them. "Jeez, don't do that", he yelled. "It's the announcer's duty. Shop rules. Don't you know anything?" I went to find the announcer, discovered him hustling a young lady from Traffic. "Don't worry about it", he said. So I went back to MC, sat down by the supervisor and listened to him commenting on the good old days. Suddenly, Net was black, Supe nearly fell off his chair; the announcer came flying in, threw some reels at us. I felt really depressed but the supervisor said, "Don't worry about it". July - three weeks after my debut to switching, I came to work and met the chief engineer in the hallway. First time I'd seen him since I started ... "Explain about June 13th", he thundered. "Good day to you, too", I said. "June 13th? Follows the 12th and precedes the 14th". "Don't get smart with me, sonny", he snapped, waving a piece of paper. "You lost two commercials in one break. Cost the company money". I tried to explain that it was my first night on the desk. That didn't cut any ice, so I told him I didn't think much of his buddy system training. "Training can't overcome carelessness'', he said and showed me the discrepancy report: "engineer failed to load films". (Why did it take three weeks to address the problem?) Who writes the discrepancy report? The announcer ... When I told him my side of the story he left with this comment: "I take a dim view of scapegoating". I surely know what you're going through. Sturgeon's Law Trouble is, my lot hasn't improved since I left television. Maybe it's Sturgeon's Law: "90% of everything is garbage". MARCH 1989 85 THE TECHNOLOGY LETTERS - CTD Anyway, I travelled interstate to take a job in the security industry. I now work for a multi-national. I don't know how they got so big, if this state office is typical. We do the full gamut of security: fire, intruder, patrols, etc. But I'm sure the local crims smile when they see one of our warning signs. It's an odds-on chance that the system is either not working properly or the police have attended so many false alarms they no longer bother. If the electronics is suspect, the watching service is little better. Our contracts specify four random checks a night but the patrol shift is 8pm-4am. You can bet a whole lot of burglars start their workday at 4.15am. And random checks are hardly that when a set route is specified, from which the patrolman should not deviate. A couple of "high-tech" crims with CB radios would have no problems. Every patrolman applicant is supposed to receive a full background check. Sometimes, this is as simple as the supervisor calling one of his CID mates and saying: "Ever heard of so and so?" Therefore, occasionally the patrolman is the bloke ripping you off. Don't get me wrong though. Most of them are honest, hardworking souls. While electronic systems are not subject to temptation, they can be corrupted from incompetent salesmen quoting the wrong equipment to faulty installation, inadequate checkout and customer error. Basically, we have two systems: the local alarm and the silent (or monitored) alarm. Both have flaws. The electronic approach is useful against the amateur (ie, young and experienced) burglar - when it works. A 120dB siren shattering a quiet night is an unnerving experience for anyone. But more often than not, it is the owner who goes back in for some paperwork he left in his desk who sets off the system. Consider this scenario: you've had a local alarm installed, with switches on the front and back doors. There's a pressure pad under the carpet in the hallway and Silent alarms .n~T ~,~.,-~ =-1,~,0 '\\,' ,' ' ~- ~4<J-lR%"~--- ! WAS AS N'-'RVOUS AS A t..ONG "iAll-E.'D CAT \N f:>.. 'ROOM FUL.l... OF -ROC.K\NG C.HA\'RS.,, 86 SILICON CHIP a motion detector in the loungeroom where the expensive video and hifi gear lives; a siren is under the front eaves. You go to the theatre one evening. A professional crim enters via a bedroom window. He takes your wife's jewellery and some money from your dresser and heads for the front door. The alarm goes off. A quick look in the loungeroom reveals a handy VCR. In moments, it's under his arm and he's out the door. Your house has foliage obscuring it from the street. Your neighbour hears the siren. Either he grumbles about another damned false alarm, calls the police, or decides to investigate. The time lag between a call to the cop shop and the arrival of a patrol car will be sufficient for the pro to make his escape. If, however, your neighbour walks up the driveway, he is likely to be confronted by a masked man with a torch to smash over his head. It's odds-on though that you yourself have forgotten about the system when returning in the small hours. There's nothing like the blast of a siren in your ear to spoil a good evening out. The monitored or silent alarm is even worse for the inattentive customer. The first clue he has is a knock at the door. Apprehensively opening it, he confronts an irritated policeman and realises he has chalked up his nth false alarm. How well I remember my first experience along these lines. One of the stations I worked at had a silent alarm. One sign-on, I came up the stairs and met a second bloke who'd just stepped off the lift. We each headed for our areas, assuming that the other had secured the system. The next thing I know, two blues with pistols drawn are hassling me. Within four or five minutes, five patrolmen had arrived and two detectives. Embarrassing! An alternative silent alarm is a telephone dialler. The true monitored system uses a leased Telecom line. The dialler uses the existing telephone circuit and will auto-dial and alert the monitoring on the way to the office that I twigged. No heat at night! I SA\0,,~,NCH''! ,.,,& 1\·U~"THING" Central station ,s~e. a~~•'RV! ~~ I T\-IE: WE:NC.1-\ SL.l'P~E. 0, SHOR1lr.'D SA~'R'-f, AN t> 1'-\~ 1'HI N& E:X9\...0D6.D "™e:. station - assuming the line hasn't been cut. All manner of detectors can be used; they all have their drawbacks. Ultrasonic types can be triggered by swinging signs in supermarkets or the sudden movement of air as a fan heater or airconditioner switches on. I've even seen one installation in a government building that was repeatedly set off by the wind whistling through a poorly-fitted double door. The early photoelectric beams were cheap and nasty and visible - only a challenge to a blind burglar. The later ones are infrared. I found one warehouse having repeated false alarms - the transmitter had been knocked out of alignment. The receiver was reacting to a reflection. When the Sun went down, so did the system. Other bugs exist, literally. I've ·found transmitters out of action due to a spider spinning a web. Passive IR units monitor the ambient energy in an area and f automatically adjust to slow changes. An intruder is sensed as a quick transient variation. But these too can react to sunlight. I remember a system going off every Sunday morning at about the same time. My boss found that one by going there and watching. A milk truck turning the corner relected the morning sun into a second-story window. I've seen microwave detectors react to metal chaff in a machine shop. Almost anything and everything can be mistaken for the so-called "man-sized" target. One of the things few of the designers have cottoned onto is the temperature range of the usual commercial-grade ICs (0-70°C). A pharmaceutical war.ehouse system I helped install worked fine for a few weeks. Then just about everything in the place falsealarmed night after night. Repeated daily visits proved everything checked out OK. It was only when I stopped there one winter's morning Things aren't much better at the central station. A lot of old systems are direct-current types . The operators speak casually about "flick" alarms which are glitches attributed to Telecom exchange work but could equally be a hightech crim about his work. We had a widespread power failure one night. The on-line battery backup maintained the central station all of 12 minutes. No-one had checked the lead-acid batteries up in an unlighted loft for months. When I was told to sort out the problem, I could see why. Getting replacement batteries took two STD calls to the head office and the signature of the state manager. Then, working in this dark pigsty, I found no isolation switch, a 40year-old heavy-duty charging cabinet and a snarl of cables. In detaching the clamps from the second battery, I learned that a virtually dry battery can still present an appreciable voltage . The wrench slipped, shorted the battery and the thing exploded! The top lifted clean off, in little-bitty bits. It took a couple of glasses of Jack Daniels before I stopped shaking. Most alarm systems have battery backup too. But I went to one tobacco warehouse and found, though the system had grown, only the original single nicad pack for the load. And my boss learned that the late shift cut part of the building power at about 3am. Thus, excessive load over two or three hours on an old battery provided many false alarms. By now, you will have reached an inescapable conclusion: there is no such thing as a perfect security system. I call your attention to a humorous essay by Mark Twain, where he wrote, '' a burglar alarm combines in its person all that is objectionable about a fire, a riot and a harem, and at the same time has none of the compensating advantages ... that belong with that combination" . On that note, I will bid you adieu. Regards, Dick. ~ MARCH 1989 87 / Eight years after their introduction in 1981, the high-speed XPTs have become the mainstay of passenger services in NSW. The design is essentially a copy of the British Rail HST (High Speed Train). THE EVOLUTION OF ELECTRIC RAILWAYS Rail enthusiasts may be aware that the NSW State Rail Authority's XPT is very similar in appearance to the British Rail HST which inspired it. However, the British trains are longer, more powerful and sometimes reach 200km/h which is much higher than the XPT's running speed. By BRYAN MAHER The year 1972 ushered in something of a minor railway revolution in Europe. It was the year when Britain first ran the HST or High Speed Trains. These are high speed diesel electric trainsets. At the same time, France was on the way to very fast electric traction which would even- tually culminate in the TGV. In Japan, since 1964, the ShinKansen railway had been providing five trains per hour (day time) on what was then the world's fastest timetable. Their through trains were averaging nearly 200km per hour. The Japanese achieved such high speeds by building dedicated tracks with very gentle curves having a minimum radius of 4 kilometres. In fact, "Shin-Kansen" literally means " new lines" because they are separate from the original tracks and system. PT.17: NSW XPT EXPRESS PASSENGER TRAINS 88 SILICON CHIP British Rail took another approach to the design of very high speed trains. Instead of going for separate tracks with gentle curves, they aimed to use existing tracks which had fairly easy curves anyhow (by Australian standards, at least]. To get very high speed capability, British Rail designed special trains capable of tilting the car body in towards the centre of each curve. The idea is akin to a motorcycle banking in a turn. Trains have been doing this for a long time, of course, with super elevated tracks, whereby the outer track on a curve is higher than the inner track. This shifts the weight of the train to compensate for centrifugal forces when going around curves. By tilting the car body in proportion to the train speed, the train would effectively provide its own super elevation. Engineering problems in the hydraulically-powered tilt-body design proved very stubborn though, which held back the development of the APT or Advanced Passenger Train. In the meantime, British Rail continued with the HST. British Rail HST 42 HST train sets were initially ordered but, due to economic constraints in Britain at the time, this was subsequently cut to 32. The HST consists of a dieselelectric locomotive at each end and eight passenger cars in between. These trains endeared themselves to the travelling public, their high speed and frequent operation providing excellent service between London and Newcastle, Edinburgh, Hull and York. With 18 trains each way daily between Newcastle~ upon-Tyne and London alone, who would want to use their car? Each HST locomotive is powered by a Paxman-Vaienta 1.678MW (2250hp] diesel engine directcoupled to an AC alternator. The output of the alternator is rectified by silicon diodes to provide the DC supply for the four series traction motors. In the first 32 trainsets, the traction motors were supplied by Brush and some sets were extended to 10 cars. GEC Traction supplied the DC The XPT is a departure from normal Australian rail practice in using 4-wheel bogies and a high-speed diesel engine. The engine is a 12-cylinder turbocharged 4-stroke design rated at 1.48MW and has a maximum speed of 1500rpm. motors for a later order of a further 14 trains. In each train, control of the front and rear locomotives is from the driver's cabin at either end, so these trains need never be turned around. On the Newcastle run, the HST trains regularly achieved average speeds of 133km/h, with peak speeds of 170km/h. For this reason the HST trains in England are labelled "Inter City 125" trains, alluding to their 125mph design capability. The high travelling speed and the fast turnaround time at terminal stations enable these British HSTs to move an incredible number of people. British Rail claim that some trains often travel 1700km per day. Considering that 600-700km of this distance is covered at a speed of 170km/h (or more), tJ:\e diesel engines and traction motors certainly earn their keep! The NSW XPT With all these high performance goings-on in other parts of the world, how could Australia not join in? 1981 was a good year for Australian rail. Not only were two major improvements to Melbourne's city and suburban rail systems opened, but in New South Wales the SRA (State Rail Authority] put the first trial XPT or Express Passenger Train on the rails on 24th August. By 6th September, 1981 the trial XPT was running around New South Wales and had set an Australian rail record speed of 183km/h. By 1982, XPTs were in regular service on most NSW main lines. Today they are the backbone of NSW express passenger services, running between Sydney and Armidale, Tamworth, Grafton, Dubbo, Canberra and Albury. Connecting trains and air conditioned coaches feed all branch lines. XPT performance The NSW-SRA XPT trains are modelled on the British Rail HST design but are slightly lower powered. However, as the train set in NSW is usually only five passenger cars plus two locomotives, high speeds are still possible in some areas. The trains, manufactured by Comeng of Granville, Sydney, are available in two versions: the standard version rated at 160km/h maximum and a high-speed version rated at 200km/h maximum. However, in New South Wales MARCH 1989 89 In standard form, the XPT has a locomotive at both ends and five passenger cars. Speeds up to 160km/h are regularly achieved. The XPT presently holds the Australian rail speed record of 183km/h. the considerable number of sharp curves places a limit on the maximum usable speed. For example, on the Blue Mountains, the Hawkesbury Bank between the Hawkesbury River and Cowan, or between Murrurundi and Quirindi, the steep terrain has resulted in sharp curves with the track radius being as tight as 161 metres. Often there are consecutive reverse curves too, which slows things up even further. The 579km run from Sydney to Armidale includes two of the aforementioned sections, so that the 73.9km/h overall average speed with 22 stops is very creditable. Loco specifications Like the British HST, the New South Wales XPT has two diesel electric locomotives, one at each end. Each loco is powered by a Paxman Valenta turbocharged 4-stroke diesel engine. This is rated at 1.480MW (1984hp) at ambient temperatures up to 40°C and any 90 SILICON CHIP elevation up to 1000 metres. The 12 cylinders have a 19.7cm bore and 21.6cm stroke. The engine runs at a relatively high speed compared to other Australian diesels. It idles at 750rpm and has a maximum speed of 1500rpm. Two alternators The diesel engine is direct coupled to two alternators, one for traction and one for auxiliaries. The main alternator and associated silicon rectifiers provide the DC supply for the four Brush traction motors, each a 4-pole DC series type. The traction motors are not mounted within the bogies (as in many other locomotives). Instead, the traction motors are each mounted on the mainframe, with drive to the wheels being via flexible couplings and gear boxes with a 20:65 ratio. Wheel slip and slide detectors are fitted. Each locomotive can provide 84 kilonewtons tractive effort at a 1-hour rating or 77kN continuously. Two locomotives working a 5-car train can provide 240kN starting tractive effort, making for good acceleration. The weight of each locomotive in working trim is 74 tonnes which is really quite light for a diesel of this power. It is built for speed rather than lugging ability. Diesel fuel capacity is 4500 litres. The whole locomotive (except for the driver's cab) is of welded carbon steel, the hody sides being of stressed steel skin. The normal train of five passenger cars with two locomotives weighs a total of 354 tonnes. Bogies The bogies for the locos and cars are designed for high speed running (up to 2ookm/h) with safety and comfort. The suspension system has each axle box attached to a horizontal swing-arm link and maintained in position by a coil spring suspension in parallel with dampers (shock absorbers). The bogie frames carry the car body on a flexicoil pneumatic secondary suspension. The locomotive bogies run on heat-treated rolled-steel monobloc wheels. These are fitted with castiron brake discs in the form of cheek plates and each wheel is fitted with a disc brake caliper. The axles are made of solid forged steel and run iri tapered roller bearings. Brakes The braking system is the Westcode type EP, backed up by the "shadow" emergency brake system. Maximum retardation rate is 0.90 metres per second per second. The disc-brake calipers are air-driven and are fitted with composition brake blocks. Readers may ask why conventional brake blocks are not applied to the running wheels rather than using disc brakes. After all, cast iron brake blocks have been used for a century and are still used today by most freight trains as this method keeps the wheel surfaces clean and in good order. Two disadvantages accrue from the use of cast iron brake blocks. First, repeated stopping results in fast brake block wear and second, cast iron dust flowing from the brake blocks during braking permeates the atmosphere below the train. If this fine conducting dust gets into the traction motors, contactors or control resistances it can lead to electrical breakdowns. For this, reason, non-conducting composition brake blocks are now used on most high-performance trains. But composition brake blocks have the nasty habit of polishing the running surfaces of the wheeltyres. This leads to locomotive wheel slip during acceleration and during braking for both locomotive and carrige wheels. The complete solution invoked by modern train designers is to use composition brake blocks applied via air calipers to cast iron brake discs attached either to the side faces of the running wheels (as per photo) or to inboard discs on the axles. This picture shows the new-high speed hogies used on the XPT. Notice the polished steel cheek plates on both sides of the. running wheels. These function as the train disc brakes. Auxiliaries The auxiliary alternator is direct-driven by the loco's diesel engine and provides a 3-phase AC supply, regulated to 415 volts at any engine speed in the working range. This power is used for all train electrical equipment, such as squirrel-cage induction motors for air conditioning and ventilation, fluorescent lighting and cooking in the buffet car. In addition, the engine compartments and traction motors are force-ventilated with filtered air, while the driver's compartments at each end of the train are airconditioned. To allow for the sometimes very dusty atmosphere of western and southern NSW, the induced air supply for the diesel engine cylinders needs to be doubly filtered otherwise engine wear would be a real problem. British HSTs don't have to contend with either the dust or the high temperatures experienced by the Australian XPT. The manufacturers have provided for easy maintenance and replacement of components by building the driver's cab, electrical This picture shows the driver's winds_creen after testing with a large projectile at 240km/h. The heavy laminated glass is fractured hut no penetration has occurred. MARCH 1989 91 View inside the driver's cabin, showing all the major controls for the XPT. The cabin is air-conditioned to ensure comfortable conditions for long-distance high-speed operation. control cabinet, diesel engine/alternators, engine cooling radiator and the brake/air compressor gear as separate modules. These can all be easily removed and replaced so the loco need not be out of service for long periods. For fire safety, the electrical control and equipment ea binet and the diesel engine/alternator section are provided with automatic fire extinguishing equipment. Coach interiors The lightweight cars perform beautifully and are very well accepted by the travelling public. Normally fitted with groups of four fixed seats on each side of the centre aisle, the wide windows and air conditioning give a pleasant and enjoyable travelling experience. Alternative seating offered by the manufacturer includes groups of three seats, or recliners and/or rotating comfort seats, with or without tables. Individual reading lights complement the car fluorescent lighting. Toilets are provided at each end of each car with hot and cold water at the wash basins. 92 SILICON CHIP The buffet occupies half a car and is fully fitted with electric equipment for preparing meals. A guard's compartment is provided at each end of the train. Driver's cab The driver's cab is a resiliently mounted, glass-reinforced plastic module, resulting in effective isolation of the driver from the noise, heat and vibration of the diesel engine. The nose cone contains two large anti-collision buttresses to protect the driver in the event of frontal impact. To allow safe operation at 160 or 200km/h it is essential that the front end of the driver's cab be proof against accidental strike at speed by a bird or any object. (Occasionally rocks, bottles and other rubbish may fall or be thrown onto a train from overhead bridges and tunnel entrances). To ensure driver confidence and safety, the train manufacturer, Comeng, constructed a full-size timber mock-up of the driver's cab and tested the driver's window with missiles projected at 240km/h. The driver's cab is fitted with central controls plus meters for air pressure, motor current and train speed. To ensure a clear view, the front window is fitted with a heater-demister, windscreen wiper and washer. Comparing the XPT and HST Fundamentally, the XPT and British HST are quite similar although the former runs on radically different bogies to cope with the much rougher Australian tracks. The British, with their much larger population, can afford to provide more money for track straightening as each line carries many more trains. Furthermore, nowhere in the British system are mountains encountered as in Australia. These facts prevent the NSW XPTs from ever matching the high average speeds achieved in Britain. ~ Acknowledgement: thanks to Comeng of Granville, Sydney and the NSW-SRA for their assistance and photos. ASK SIUCON CHIP Got a technical problem? Can't understand a piece of jargon or s ome electronic principle? Drop us a line and we'll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Railpower model train controller I was interested to see the criticism of the Railpower model train controller in the December issue. I required a controller for use in the shunting yards of my model railway so I used just the "core" of the SILICON CHIP design, omitting the H-pack output and the IC3 & IC4 logic. I used a DPDT switch for reversing and just a single BD650 as the output transistor. Functionally the circuit was fine, except for the very noticeable and harsh buzz which the locos produced at around zero speed. I therefore decided to try other pulse frequencies, finally settling on 45Hz. This was chosen not because the noise was less significant but because the motor growl roughly approximated An idiosyncrasy of the Minimitter I have built the FM stereo transmitter described in the October 1988 issue and find it very useful up to a point. That point is when I connect it up to an FM stereo receiver, as a program source. This produces a rather interesting effect. When my second receiver (Walkman) is in stereo mode, the sound oscillates up and down to the tune of around 20dB. The frequency of oscillation is about 0.5-1Hz. Switching the first tuner to mono mode reduces the effect but then I lose the advantage of stereo. Also if the first receiver is a quartz PLL type tuner, the effect is more pronounced than if a standard analog type tuner is used. The effect only occurs when I use an FM tuner as the program source. It is not present when I use a CD player or cassette deck. the exhaust of the shunting locos I use. (What a bonus - a train controller and sound system in one package)! One other change effected a marked reduction in both the volume and harshness of the sound. I put a 33µF capacitor across the output to soften the sharp leading edges of the pulse waveform. This may seem crude but it is effective. In general, pulse power is fine for the cheaper models but its advantages diminish and disadvantages increase in those models with better designed motors. Some models perform superbly on pure DC at very low voltages but perform quite roughly on pulse power at low speed, despite being fitted with flywheels. Your statement in the article that pulse power is the "proper way" needs, I am afraid, I have also noticed that, in general, the signal received from the transmitter is cleaner when received on an analog type tuner than on a digital unit. Have you any ideas why this might be so? (M. D., Bilgola Plateau, NSW). • We assume that the oscillation effect is due to a beat between the 38kHz multiplex subcarrier in the original FM transmission and the 38kHz subcarrier in the FM transmitter. We are not sure what the mechanism is but the fact that it only occurs when you use an FM tuner is a vital clue. Perhaps it is because of direct radiation from the stereo transmitter into the first tuner. Perhaps other readers can throw more light on the subject. Having said that, we cannot see why you would wish to rebroadcast a received FM program. If you have a Walkman, why not listen to the program direct? some heavy justification. (D. I., Meadows, SA). • Your comments on the use of pulse power are interesting, particularly your choice of 45Hz to simulate the exhaust of a shunting loco. However, we are not keen on the use of a 33µF capacitor to quieten the buzz. This may well trigger the overload protection circuitry or cause an increase in the power dissipation of the output transistor. For another view of the Railpower controller see the Mailbag page in this issue. Availability of Siemens HKZ101 I noted the problem of L. B. of Netley (SA) who is trying to obtain the Siemens HKZ101 device in South Australia. This device is available from the local Siemens branch office at 297 Pirie Street, Adelaide. Phone (08) 236 0110. Keep up the good work, guys. Love the magazine. (C. H., Redwood Park, SA). • Thanks for the tip, C.H. Where to buy components Every month I buy your magazine as you often have projects I would like to make. But living in Brisbane is as good a place to buy electronic parts as the Black Stump would be. The major kit sellers aren't much good their catalogs haven't changed much since 1984. I want to buy the LM358 dual op amp for the House Number project described in the October 1988 issue, the 7808 8-volt regulator for the Car Proximity Detector in the January 1989 issue, and the MC145026 encoder plus MC145028 decoder for the UHF remote alarm switch described in March 1988. I don't want to buy kits for these MARCH 1989 93 High power controller for 5-inch gauge loco Thank you for the article on the Diesel Sound Generator described in the December 1988 issue of SILICON CHIP. It is just what I wanted. I propose to use it in a 5-inch gauge electric powered "diesel" locomotive, so I will be using just one amplifier and none of the switching circuitry. I am also interested in building the optical tachometer described in the May 1988 issue of SILICON CHIP but there is one feature that is awkward - the use of a very sensitive (50µA) meter for the readout. Can it be adapted to a more rugged and cheaper lmA meter or, alternatively, to an LCD readout using a cheap digital panel meter? The final thing I want to ask is whether you might consider doing an electric traction motor controller for the typical locos I projects as I already have most of the parts. Can you tell me where in Brisbane I might buy these semis? (W. V., Mt. Gravatt Central, Qld.) • Jaycar have the 7808 regulator as a standard catalog item (ZV-1508} at $1.20. The MC15026 (EE-4546 $8.50) and 15028 (EE-4547 $10.50) are available on special order from your local Jaycar store. They do not sell the LM358. However, you should be able to buy all these components over the counter at the Brisbane branch of George Brown & Co Pty Ltd. Amplifier for electrostatic headphones Is the Headphone Amplifier for CD players, as described in the April 1988 issue of SILICON CHIP, suitable for driving electrostatic headphones such as the Stax SRXIII? The owner's instructions say that amplifiers with power greater than 10 watts into 80 are required 94 SILICON CHIP mentioned above. The power requirements are similar to those of golf buggies or electric wheel chairs. These give 24VDC and 30 amps; 24VDC because two goodsized car batteries will give about a half day of running pulling two cars loaded with ten children plus the driver. This gives a gross power of 720 watts which is not required all the time, fortunately. The unit should have a full range of speed control and there must be provision for reversing. Dynamic or regenerative braking (possible with series motors) would also be desirable. (P. D., Orange, NSW). • Thanks for your comment on the Diesel Sound Generator. It should really go well in a 5-inch gauge loco because you will be able to use a decent sized loudspeaker. It should be possible to modify the tacho circuit to take a lmA movement although we have not tried it. We suggest that VR2 be changed to 5k0 and the associated 100µF capacitor to 470µF. but elsewhere say that continuous maximum input is 5 watts RMS. These headphones are powered entirely from the audio output of the supply amplifier. (B. W., Bulleen, Vic). • The headphone amplifier described in April 1988 is suitable only for driving conventional headphones. Since it only uses a 5534 op amp for each channel it puts out very low power. Electrostatic headphones are unusual in that they not only require high voltage drive but also require a high DC polarising voltage. The latter is provided by rectifying the high drive signal voltage from the output of the transformers. This means that no mains power supply is required but it does mean that the transformers do require a driving amplifier of quite a reasonable power output. The manufacturers quote 10 watts as a minimum figure but this would only be barely adequate. There would be a strong tendency to overload such a small amplifier As far as the controller for a 5-inch gauge loco is concerned we are not in a position to design a circuit but have you considered the Railpower controller published in the April and May issues? As it stands, this switchmode circuit has a rated output current of 4 to 5 amps and could easily handle an input from a 24V battery. It could easily be adapted to much higher rated Darlington transistors such as the Motorola 90 volt 50-amp MJl 1030 (NPN) and MJl 1031 (PNP). Alternatively, the circuit could be adapted to a high power Mosfet such as the 50 volt 45-amp BUZ15 from Siemens or the 50 volt 60-amp MTM60N06 from Motorola. If you did use Mosfets you would need a changeover relay for reversing the motors. Dynamic or regenerative braking would require quite a lot of extra switching but would probably be quite practical if the track had hills and dales, making long braking runs necessary. It sounds like a fascinating project. as you turn up the wick to make it loud enough. Preferably, the amplifier should put out 15 or 20 watts at least. Bigger amplifiers do carry a risk though because then you can overload the phones themselves. Unfortunately, we cannot suggest a suitable circuit for this application. Tri-wing screwdriver bits for appliances I found the article on "Screws & Screwdrivers" in the November issue most interesting and I agree with many of your comments about tamperproof screws. However, my specific question involves Tri-wing screws. I have a number of appliances which use these screws and when I attempted to order a Tri-wing bit from a specialist supplier they said that Tri-wings come in five point sizes. The question is, which point size do I go for? I have a number of ap- Insensitive optical tachometer After completing the optical tachometer described in the May 1988 issue of SILICON CHIP, the circuit functioned correctly but was not quite sensitive enough. I obtained a range of less than 50mm on aluminium surfaces. I took a number of steps to try and rectify this, including resoldering suspect joints, cleaning the surfaces of the photodiode and infrared LED and increasing the 68kn resistor at the gate of Q2. None of these produced the desired result. What can be done to bring the sensitivity of the tacho up to that of commercial models which have a range of about 100mm. pliances made by Black & Decker and Hotpoint but I can't get the screws out so I can't even send the suppliers a sample screw to help select the right bit. Please help. (I. F., Kempsey, NSW). • In our experience, one size of Tri-wing screw is widely used in electrical appliances. You should use point size 3 to fit them. Alternator whine from equaliser I have three questions to ask you. First, my car stereo emits an annoying oscillation. It is very noticeable when idling and the frequency increases when the engine is revved. The car is a 1982 VH Commodore. Of course, this is the ignition spikes coming through. However, when the equaliser is turned off, leaving only the radio, the noise is gone. Could it be that the equaliser is faulty or is there a need for more spike suppression as there is already a suppressor between the distributor and coil? Second, I have recently obtained a dynamic strain gauge (single channel amplifier) recording unit, made by Kelvin & Hughes, of Britain. Would you be able to tell me what it would be used for and if it can be used in general electronic On another subject, could you design a simple circuit to enable me to connect an antenna to my W alkman via the headphone socket. I believe the headphone cord acts as an antenna, although not always with satisfactory results. (K. B., Hawthorn, SA). • As far as we know there is no defect in the circuit design of the optical tacho; it has proved quite popular and trouble-free. However, we did see one version which was plagued by low sensitivity but which otherwise was working normally. The constructor had carefully housed the photodiode and IR LED in an aluminium knob and he'd done a very neat job of it too. The only problem was that reflections from the rim of the knob, from the LED to the photodiode, effectively de-sensitised the unit. So that is the clue. Is there any way whereby light can go directly from the IR LED to the photodiode, without being reflected from the rotating object being measured? If so, block that light path and the unit should work properly. As far as W alkman and similar portable receivers are concerned, the headphone leads do provide the antenna. This works OK in strong signal areas but the performance drops off badly in weaker signal areas. We could design a circuit to replace the headphone antenna function but we doubt whether it would work better. experimenting? It's an old valve unit but is in excellent condition. If you know of somewhere I can get instructions for it I would be grateful. Finally, could you tell me what a CMOS 4501 IC does? (S. S., Smithfield, NSW). • We will answer your questions in turn. First, the "oscillation" from your car stereo may not be from the ignition. If it is ignition noise it will sound like a buzz which rises in sound with the engine speed. At idle, it will sound like rapid clicking. We are more inclined to the view that you are hearing alternator whine. Either way, it is annoying and is probably due to the fact that the equaliser does not have good power supply suppression. If it is like most auto equalisers it will be very tightly packed inside and the chance of adding power supply components is slight. So there probably isn't a lot you can do about it. However, it is worthwhile checking to see if a suppression capacitor is fitted to the alternator. We have no knowledge of your dynamic strain recording unit but one of our readers may be able to answer your question. The 4501 IC is not a widely used device but is available readily enough. It is a dual 4-input NAND gate with 2-input NOR/OR gate in a r: i~ - 13 4 ~ r----' ;; _ _ ~_[)oXl-•~---14AND L L..{>o-15NAND l ~is ' " Vss 16-pin package. It can also be used as an 8-input NAND gate. The accompanying diagram shows the pin numbering while the dotted lines show how it can be used as an 8-pin NAND gate. Notes & Errata Hands-Free Speakerphone, September 1988: the lµF capacitor shown connected to pin 17 on the circuit diagram of page 17 is the wrong way around. The wiring diagram on page 19 is correct. Simple Ultrasonic Proximity Detector (Car Reversing Alarm) January 1989: D1, as shown on the wiring diagram of page 28, is reverse connected. The circuit diagram on page 27 is correct. MARCH 1989 95 CEli'l Cash in your suf'plus gear. Advertise it here in Silicon Chip. Advertising rates for this page: Classified ads - $7 .00 for up to 15 words plus 40 cents for each additional word ; Display ads (casual rate) - $20 per column centimetre (max. 10cm). Closing date: five weeks prior to month of sale. If you use a PO Box number, you must include your permanent address and phone number for our files. We cannot accept ads submitted without this information. To run your own classified ad, put one word on each of the lines below and send this form with your payment to: Silicon Chip Classifieds, PO Box 139, Collaroy Beach, NSW 2097. PLEASE PRINT EACH WORD SEPARATELY, IN BLOCK LETTERS 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ($7.00) Name ........... .. .... .. .. Address ................. . ........ .. ... .. .. .. .. . Suburb/Town .. .. ........ . Postcode Enclosed is my cneque or money order for$ .......... D Bankcard D Visa Card D MasterCard Card No FOR SALE SURPLUS TEST EQUIPMENT. We have the following test equipment surplus to requirements and available for purchase as is: Tektronix Type 453 50MHz oscilloscope, $750; Tektronix Type 454A 150MHz oscilloscope (rack-mount version), $950; Tektronix 491 spectrum analyser, 1 0MHz40GHz, $4200; Systron Donner 762-2A spectrum analyser, 1 0MHz40GHz, $4400; Hewlett-Packard 431 C power meter with thermistor mount, $800; Singer 6201 synthesised signal generator (to 520MHz), $1600; 5kW 240V stabilac, $120; Metrix brand HF signal generator, AM/CW 200kHz-20MHz, $200. We also have available a quantity of pre-loved 25W Alinco dual-band UPGRADES FOR THE TANDY 1000 20Mb hard disk plus controller card $899.00. 40Mb hard disc plus controller card $1099.00. RS232 plus real time clock card $89.00. Phone David on (047) 31 2559 for more details. 96 . or please debit my l'--~I~~~~~'--~~~~~~~~~~ Signature ........ .. . SILICON CHIP Advertising Index Allied Capacitors ................ .. 83 Altronics ............ ....... ..... 52-55 Arista Electronics ......... 75,OBC Avtek .. ..... .... .. .. .. .. .. ............ 81 Ballarat Electronic Supplies ... 1 9 Contact International ........... . 77 Dauner Electronics .. .. .. ........ 45 David Reid Electronics ......... 8,9 Dick Smith Electronics ..... 20-25 Geoff Wood Electronics ........ 1 5 Goldstar ............................ IFC Hycal Instruments .... ............ 1 9 Jaycar Electronics .... ...... 62,63 J.V. Tuners .... .. ...... .. .......... . 59 RCS Radio ............... ..... .. .... 72 Rod Irving Electronics ........... 73 ........... Card expiry date ....... ./ ........ / ........ transceivers, type ALD-24T, covering 144-148MHz and 430-440MHz with inbuilt duplexer. Complete with manuals and circuit diagrams. $500 each. Our US warehouse holds inventory too large to list. We regularly airship from the West Coast. Fax or mail your requirements to Av-Comm Pty Ltd, PO Box 175, Gordon, NSW 2072 . Fax (02) 489 6493. HI-TECH STEREO AMPLIFIERS built. Reasonable prices. For full details send SAE to 36 Palmer St, Nambucca Heads, 2448. RADFAX 2: HI-RES RADIO facsimilie, Morse and RTTY program for IBM PC/XT on 360K 5.25-inch floppy plus full documentation. Need CGA. SSB HF FSK/tone decoder. Has re-align, autostart, view, save, print. Also "RF2HERC" same as above but suitable for Hercules card and "RF2EGA" for EGA card (640 x 350 mode). Programs are $30 each plus $3 postage. Only from Michael Delahunty, 42 Villiers Street, New Farm, Qld 4005. Phone (07) 358 2785. NEW 64K-256K PRINTER BUFFER design release. VER 4.0 and REV G boards now available. Double-sided 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, PO Box 19-189, Avondale, Auckland , NZ. Phone 88 5730. PCB, EPROM and instructions: $39.00. Optional additions include 2 x ?-segment LED front panel display of percentage full, 1 to 99 copies ·select, 3 polled computer inputs , printer switches, computer switches and serial converter boards. For a free catalog send a 39c stamp to: Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. BOOKS & PLANS LOW SPEED GENERATORS for windmills,. water turbines, steam engines. The definitive book: "The Homebuilt Dynamo" (1987), 182 pages, 8.5" x 12", hardback. Generator design and construction with ceramic magnets. Complete plans, 268 photographs, step-by-step construction details . $A85.00 postpaid airmail (brochure $A5. 00 refundable). Todd-Forbes Publishing, 627 West Coast Road, Oratia, Auckland. Silicon Chip Back Issues November 1987: Car Stereo in Your Home ; 1 GHz Frequency Meter; Capacitance Adapter for DMMs . December 1987: 1 00W Power Ampl ifier Module ; Passive lnfrared Sensor for Burglar Alarms ; Universal Speed Control and Lamp Dimm er; 24V to 12V DC Converter. January 1988: __1.;.SaOowtie UHF Antenna; ~ cio\J)"i'ower Supply ; Custom a_lC!)~~ Subcarrier Adapter fo~ ers. February 1988: 200 Watt Stereo Power Amplifier ; Deluxe Car Burglar Alarm; End of File Indicator for Modems. March 1988: Remote Switch for Car Alarms ; Telephone Line Grabber; Low Cost Function Generator ; Endless Loop Tape Player. April 1988: Walkaround Throttle for Model Railroads ; pH Meter for Swimming Pools; Slave Flash Trigger ; Headphone Amplifier for CD Players. May 1988: Optical Tachometer for Aeromodellers ; High Energy Ignition for Cars; Ultrasonic Car Burglar Alarm . June 1988: Stereo Control Preamplifier; Breake rless Ignition For Cars ; Automatic Li ght Controller; Mega-Fast Nicad Battery Charger. Ju!y 1988: Fitting a Fuel Cut-Off Solenoid ; Booster for TV & FM Signals; The Discolight Light Show. August 1988: Plasma Display ; Remote Chime/Doorbell ; High Performance AC Millivoltmeter ; Getting the Most Out of Nicad Batteries . September 1988: Hands-Free Speakerphone ; Electronic Fish Bite Detector; Switchmode Charger for 1 2V Gel Batteries ; Vader Voice. October 1988: Stereo FM Transmitter; High Performance FM Antenna ; LedLight House Number; Matchbox Crystal Set. November 1988: 120W PA Amplifier Module ; Poor Man 's Plasma Display ; Car Safety Light ; How to Quieten the Fan in Your Computer. December 1988: 1 20W PA Amplifier; Diesel Sound Generator; Car Antenna/Demister Adaptor; SSB Adaptor for Shortwave Receivers. January 1989: Line Filter for Computers ; Proximity Detector for Cars; Computer Sound Repeater ; How to Service Car Cassette Players. February 1989:Transistor Beta Tester; Build th e Minstrel 2-30 Loudspeaker System ; LED Flasher for Model Railways; Lightning & Electronic Appliances. BACK ISSUES ORDER FORM Please send me a back issue for: □ March 1988 □ August 1988 □ April 1988 □ September 1 988 □ November 1 98 7 □ May 1988 □ December 1987 □ June 1988 □ February 1 988 □ July 1988 □ October 1 988 □ November 1 988 □ December 1 988 □ January 1 989 □ February 1 989 Enclosed is my cheque/money order for $ ______ or please debit my □ Bankcard □ Visa Card □ MasterCard Price: $A5 .00 each (includes postage) . Overseas orders add $A 1 .00 per issue for postage. Signature _ _ _ _ _ _ _ _ ___ Card expiry date _ _ / __ / _ _ NZ & PNG orders are sent by air mail. Name ___________________________ (PLEASE PRINT) Detach and mail to: SILICON CHIP PUBLICATIONS Street_________________________ PO BOX 139 COLLAROY BEACH Suburb/town _ _ _ _ _ _ _ _ _ _ _ _ _ Postcode____ NSW 2097 ~-------------------------------------~