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SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au Vol.8, No.5; May 1995 Contents FEATURES 4 CMOS Memory Settings – What To Do When The Battery Goes Flat Check your hard disc parameters & CMOS settings & be prepared – by Greg Swain 8 Electronics In The New EF Falcon, Pt.3 Avoiding electromagnetic interference to vital electronic systems– by Julian Edgar 16 Introduction To Satellite TV INTRODUCTION TO SATELLITE TV – PAGE 16 All about satellites, dishes & block converters plus a sneak preview of our do-it-yourself satellite receiver – by Garry Cratt PROJECTS TO BUILD 32 Build A Mains Music Transmitter & Receiver Listen to music from your stereo system anywhere there is a power point – by Jeff Monegal 41 Guitar Headphone Amplifier For Practice Sessions Practice to your heart’s content without disturbing the rest of the neighbourhood – by John Clarke 58 Build An FM Radio Trainer; Pt.2 The full construction & alignment details – by John Clarke 68 Low-Cost Transistor & Mosfet Tester For DMMs Checks small signal, power & Darlington transistors plus Mosfets as well – by John Clarke SPECIAL COLUMNS 53 Remote Control TRANSISTOR & MOSFET TESTER FOR DMMs – PAGE 42 A 16-channel decoder for radio remote control – by Bob Young 76 Serviceman’s Log All it needs is a new fuse plus the set that fell – by the TV Serviceman 82 Vintage Radio A console receiver from junk – by John Hill DEPARTMENTS 2 Publisher’s Letter 24 Circuit Notebook 31 Order Form 86 Back Issues 88 Product Showcase 91 Ask Silicon Chip 94 Market Centre 96 Advertising Index BUILD THIS GUITAR HEADPHONE AMPLIFIER – PAGE 41 May 1995  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Reader Services Ann Jenkinson Advertising Enquiries Leo Simpson Phone (02) 979 5644 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Jim Lawler, MTETIA Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER Australia can do better with greenhouse gases As I write this editorial, Australia is getting heaps of criticism for its stand on greenhouse gases at the 1995 climate convention in Berlin. And rightly so. Australia, or rather the Australian Government, has wimped out on the issue. Because there was so much opposition from industry groups to a carbon tax, the Government has basically thrown its hands up in the air and given up. Well, that’s not good enough and now Australia is copping criticism. Sure, Australia’s contribution to total greenhouse emissions is small but there is no reason we can’t do a lot better. The Government took the right tack in not adopting a carbon tax. It could have hurt the economy right at the time when it was emerging from a recession. The Government also correctly judged that any new tax would be heavily opposed, especially as there is considerable pressure for it to balance the budget by cutting expenditure rather than by increasing revenue. But this general pressure to cut expenditure also points the way in which Austra­lia could move towards meeting the aim of the last climate con­ference in Rio De Janiero in which we undertook to reduce our carbon emissions to 1990 levels by the year 2000. Cutting energy use is dead easy and virtually everyone can do it. I’ll go further and state that everyone and every organi­sation can probably cut their yearly energy consumption by at least 10% right now, with very little effort. It only requires sensible actions like not using lights unnecessarily, turning down the thermostats on water heaters to 60°C, turning off stoves and ovens earlier so that food finishes cooking with stored heat and so on. How about using your car less often? Industry can also do much better in its use of motor vehicles, lighting, air-condi­tioning and process heating. The Government should adopt a positive policy of encourag­ing energy conservation. This approach has worked quite well with water conservation over the last year in New South Wales and there is no reason why it should not work for energy consumption throughout Australia. But the Government can also do a lot more in encouraging the development of solar technology in this country. It is where we have lots of natural advantages and could be an area of great export potential in the future. Instead, we have all this silly posturing by politicians and industry leaders about the “Informa­tion Superhighway”, something they obviously know very little about. Let’s face it: the “Information Superhighway” is little more than a catchy phrase thought up by Al Gore in the last US Presidential campaign. And like most political slogans, it is practically meaningless. On the other hand, climate change is real and while we may not know or understand all the causes, we should do our bit to conserve energy and reduce our emissions of greenhouse gases. Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip HEWLETT PACKARD 334A Distortion Analyser HEWLETT PACKARD 200CD Audio Oscillator • measures distortion 5Hz600kHz • harmonics up to 3MHz • auto nulling mode • high pass filter • high impedance AM detector HEWLETT PACKARD HEWLETT PACKARD 3400A RMS Voltmeter 5328A Universal Counter • voltage range 1mV to 300V full scale 12 ranges • dB range -72dBm to +52dBm • frequency range 10Hz to 10MHz • responds to rms value of input signal • 5Hz to 600kHz • 5 ranges • 10V out • balanced output HEWLETT PACKARD 5340A Microwave Counter • allows frequency measurements to 500MHz • HPIB interface • 100ns time interval • T.I. averaging to 10 ps resolution • channel C <at> 50ohms • single input 10Hz - 18GHz • automatic amplitude discrimination • high sensitivity -35dBm • high AM & FM tolerance • exceptional reliability $1050 $79 $475 $695 $1950 BALLANTINE 6310A Test Oscillator BALLANTINE 3440A Millivoltmeter AWA F240 Distortion & Noise Meter ...................... $425 AWA G231 Low Distortion Oscillator ...................... $595 EATON 2075 Noise Gain Analyser ...................$6500(ex) EUROCARD 6 Slot Frames ........................................ $40 GR 1381 Random Noise Generator ........................ $295 HP 180/HP1810 Sampl CRO to 1GHz ................... $1350 HP 400EL AC Voltmeter .......................................... $195 HP 432A Power Meter C/W Head & Cable .............. $825 HP 652A Test Oscillator .......................................... $375 HP 1222A Oscilloscope DC-15MHz ........................ $410 HP 3406A Broadband Sampling Voltmeter ................................................................ $575 HP 5245L/5253/5255 Elect Counter ....................... $550 HP 5300/5302A Univ Counter to 50MHz ................ $195 HP 5326B Universal Timer/Counter/DVM ............... $295 HP 8005A Pulse Generator 20MHz 3 Channel ........ $350 HP 8405A Vector Voltmeter (with cal. cert.) ......... $1100 HP 8690B/8698/8699 400KHz-4GHz Sweep Osc ............................................................ $2450 MARCONI TF2300A FM/AM Mod Meter 500kHz-1000MHz ................................................... $450 MARCONI TF2500 AF Power/Volt Meter ................. $180 SD 6054B Microwave Freq Counter 20Hz-18GHz ......................................................... $2500 SD 6054C Microwave Freq Counter 1-18GHz ............................................................... $2000 TEKTRONIX 465 Scope DC-100MHz .................... $1190 TEKTRONIX 475 Scope DC-200MHz .................... $1550 TEKTRONIX 7904 Scope DC-500MHz .................. $2800 WAVETEK 143 Function Gen 20MHz ...................... $475 FLUKE 8840A Multimeter RACAL DANA 9500 Universal Timer/Counter • true RMS response to 30mV • frequency coverage 10kHz1.2GHz • measurement from 100µV to 300V • stable measurement • accuracy ±1% full scale to 150MHz • list price elsewhere over $5500 • 2Hz-1MHz frequency range • digital counter with 5 digit LED display • output impedance switch selectable • output terminals fuse protected $350 $795 HEWLETT PACKARD 1740A Oscilloscope RADIO COMMUNICATIONS TEST SETS: IFR500A ............................................................... $8250 IFR1500 .............................................................. $12000 MARCONI 2955A .................................................. $8500 SCHLUMBERGER 4040 ........................................ $7500 TEKTRONIX 475A Oscilloscope TEKTRONIX 7603 Oscilloscope (military) • frequency range to 100MHz • auto trigger • A & B input controls • resolution 0.1Hz to 1MHz • 9-digit LED display • IEEE • high stability timebase • C channel at 50 ohms • fully programmable 5½ digit multimeter • 0 to 1000V DC voltage • 0.005% basic accuracy • high reliability/self test • vacuum fluoro display • current list $1780 $695 $350 TEKTRONIX FG504/TM503 40MHz Function Generator TEKTRONIX CF/CD SERIES CFC250 Frequency Counter: $270 • DC-100MHz bandwidth • 2-channel display mode • trigger - main/delay sweep • coupling AC, DC, LF rej, HF rej $990 • 250MHz bandwidth • 2-channel display mode • trigger - main/delay sweep • coupling AC, DC, LF rej, HF rej • mil spec AN/USM 281-C • triggers to 100MHz • dual trace • dual timebase • large screen $1690 $650 The name that means quality CFG250 2MHz Function Generator $375 • 0.001Hz-40MHz • 3 basic waveforms • built-in attenuator • phase lock mode $1290 CDC250 Universal Counter: $405 NEW EQUIPMENT Affordable Laboratory Instruments PS305 Single Output Supply SSI-2360 60MHz Dual Trace Dual Timebase CRO • 60MHz dual trace, dual trigger • Vertical sens. 1mV/div. • Maximum sweep rate 5ns/div. • Built-in component tester • With delay sweep, single sweep • Two high quality probes $1110 + Tax Frequency Counter 1000MHz High Resolution Microprocessor Design CN3165 • 8 digit LED display • Gate time cont. variable • At least 7 digits/ second readout • Uses reciprocal techniques for low frequency resolution $330 + Tax Function Generator 2/5MHz High Stability FG1617 & FG 1627 • • • • • • Multiple waveforms 1Hz to 10MHz Counter Output 20V open VCF input Var sweep lin/log Pulse output TTL/CMOS FG1617 $340 + Tax FG1627 $390 + Tax PS303D Dual Output Supply • 0-30V & 0-3A • Four output meters • Independent or Tracking modes • Low ripple output $420 + Tax • PS305D Dual Output Supply 0-30V and 0-5A $470 + Tax PS303 Single Output Supply • 0-30V & 0-3A • Two output meters • Constant I/V $265 + Tax Audio Generator AG2601A • 10Hz-1MHz 5 bands • High frequency stability • Sine/Square output $245 + Tax • 0-30V & 0-5A $300 + Tax PS8112 Single Output Supply • 0-60V & 0-5A $490 + Tax Pattern Generator CPG1367A • Colour pattern to test PAL system TV circuit • Dot, cross hatch, vertical, horizontal, raster, colour $275 + Tax MACSERVICE PTY LTD Australia’s Largest Remarketer of Test & Measurement Equipment 20 Fulton Street, Oakleigh Sth, Vic., 3167   Tel: (03) 9562 9500 Fax: (03) 9562 9590 **Illustrations are representative only CMOS memory settings – what to do if the battery goes flat So you’ve just bought a new computer? Would you know what to do if the backup battery on the motherboard went flat & the computer lost its vital settings? Here’s how to get things going again. By GREG SWAIN They used to say that there were two certainties in life: death and taxes. To that, you can now add a third. Yep, you’ve guessed it – computer failure. If the floppy drives don’t get you first, then eventually the hard drive will. Or perhaps the monitor will croak (a common fault), or the hard disc controller card will go haywire and scramble your files. Or maybe the contacts on the video con­troller card will get dirty and the machine will spit out confus­ing RAM parity error messages. And then there’s a flat battery on the motherboard. This one’s virtually guaranteed to happen at some stage, often after just 2-3 years from new. When that happens, your machine loses vital setup information that’s stored in a CMOS memory on the motherboard and refuses to boot up. The type of backup battery used varies but generally a lithium battery or a rechargeable nicad battery is used. In theory, a nicad battery is “topped up” while the computer is switched on but, regardless of the type used, they don’t last for ever. Indeed, a rechargeable battery can soon go flat if the computer is not used very much or has not been used for some time. If the existence of this backup battery comes as a surprise to you, then you’re not alone. Very few retailers (if any) point this out when the machine is purchased. Not that there’s any deliberate conspiracy involved. After all, there are far more important things to talk about in the store – things like software, printers, CD-ROMs, hard disc size, how much RAM, what size monitor and, of course, how much it’s all going to cost. The backup battery on the mother­ board is a mere detail! And so you take your new computer home. And you plug it in and everything is fine for a few years. And then, one day, the machine refuses to boot up after performing its memory check routine. What gets lost? The CMOS setup program is usually accessed by hitting the <DEL> key after the system has completed its RAM-checking routine during boot-up. The CMOS setting can then be inspected by selecting “Standard CMOS Setup” from the menu & pressing the <ENTER> key. 4  Silicon Chip What is this vital information that the computer loses? Well, when you turn your computer on, the system needs to be told certain things in order to boot up successfully. This information mainly concerns the amount of RAM, the disc drives and the type of video controller used. For example, the system needs to know what type of floppy disc drives are installed, along with the hard disc type and its physical parameters. These parameters include the number of cylinders, heads and sectors on the hard disc. When the computer is initially set up, this information is entered into a setup program and stored in the CMOS memory. Unfortunately, CMOS memory is screen similar to that shown in Fig.2. As indicated by the legend at the bottom of the screen, you can select any of the entries using the arrow keys and you can modify these entries using the Page Up and Page Down keys. Do not alter any of the entries since they will be correct for your computer. Instead, make a note of all the settings on a piece of paper, with particular emphasis of the hard disc drive parameters, and store this in a safe place. Alternatively, you can obtain a printed copy by pressing the <Print Screen> key. Note, however, that only the standard ASCII characters will print correctly using this method. Any graphics will either be omitted or will print as special characters. When you have made your copy, hit <ESC> to exit this screen, then select “Do Fig.2: this is the Standard CMOS Setup screen. Make a record of all the settings for your Not Write To CMOS & Exit”. computer (they will generally be quite different from those shown here), with particular Setup will then ask you if emphasis on the hard disc drive parameters. Alternatively, you can hit the <Print Screen> you want to quit without key to obtain a printed record. saving. Type <Y> to answer yes, then press <enter> to volatile which means that it loses will be self-evident (eg, the date, the exit the setup program. Your comdata if power is removed. Normally, types of floppy disc drives used and puter will now continue to boot up the backup battery maintains the the primary display), the hard disc as normal. CMOS settings when the computer type and the number of cylinders, Another (even easier) way of obis switch­ed off but when the battery heads and sectors on the disc will be taining the hard disc drive parameters fails, these settings are lost. And when a mystery. is to use the Microsoft Diagnostics that happens, the computer no longer If you have a manual on the hard program (MSD.EXE) that comes with knows how to access the drives or the disc, then it’s a simple matter of look- MS-DOS 6.0 and above. First, quit video card. ing the data up in there. If you don’t Windows and go to the C:\> prompt; At this stage, most users simply have a manual, you can quite easily ie, type cd \ <enter>. Now type MSD assume that their computer has de- check the current CMOS settings. <enter>. A screen similar to that veloped a fault and pay to have it ser- The following procedure is typical of shown in Fig.3 will now appear. If viced. But what if you need to get the most computers, although you may you now select the “Disc Drives” computer going immediately, or you’re encounter some variations along the button, the program will check your poor and cannot afford the service fee? way. Be sure to consult the manual system and display a screen similar Well, there’s good news and there’s for your motherboard, to obtain the to that of Fig.4. good news. You can get the computer exact procedure. As before, make a note of all the disc going immediately and a permanent First, switch the computer on and parameters (or hit <Print Screen>) and fix will cost you no more than half an wait until it has com­pleted the RAM store it in a safe place. This done, click hour of your time and a new battery. checking procedure. The setup pro- OK to go back to the main menu, then Let’s see how we go about restoring gram, which is contained in ROM press <F3> to exit MSD. the system. (read-only memory), is then (usually) entered by pressing the <Del> key. Restoring the settings Be prepared Most systems then display a warning Armed with all this information, it’s The fix really starts back when you screen, after which you press any key now easy to restore the CMOS settings first purchased your computer. One (other than <Esc>) to obtain a screen when the power fails. All you have to of the first things that you should do similar to that shown in Fig.1. do is enter the Standard CMOS Setup Selecting “Standard CMOS Setup” Program (just hit <DEL> after the is make a record of the existing CMOS setup. While most of the data re­quired and pressing <enter> now gives a computer completes its memory check May 1995  5 “yes” to the question “Save CMOS Settings & Exit?” and the job is done. Your computer will now complete its boot-up procedure. Lost records Fig.3: the Microsoft Diagnostics (MSD) program is accessed by first quitting Windows, then going to the C:\> prompt & typing MSD. This is what the opening screen looks like. By clicking on the buttons, you can check out the various operating parameters of your system. What if you didn’t make a record of your CMOS settings or you’ve lost the bit of paper with all the disc drive parameters? There’s a way around that as well, since all the relevant parame­ ters are usually printed on a label that’s attached to the drive unit. The problem here is that the hard disc drive is usually buried in the drive bay beneath one or more floppy disc drives and perhaps a CD-ROM drive as well, which means that the label is obscured. The answer is to temporarily remove the hard disc drive so that the label can be seen. In some cases, this will be an easy job while in others it will be complicated by the need to remove the floppy disc drives first. Do not attempt this unless you know exactly what you are doing and always double-check that you have disconnected the power first (pull the plug from the wall). So the procedure for restoring the CMOS settings can be difficult or straightforward. It just depends on whether or not you made a proper record of the settings (and stored it in a safe place) when you first bought the computer. Replacing the battery Fig.4: to check the disc drive parameters, simply click the “Disk Drives . . .” button of the opening menu to obtain the screen shown above. This information can be printed out & stored for future reference (select “File”, “Print”). routine during boot-up) and re-enter the values. As explained above, the various entries are selected using the arrow keys, while the <Page Up> and <Page Down> keys are used to modify existing data. Hard disc types Be sure to select the correct type number for the hard disc drive before attempting to enter any of its other parameters. If the disc is a fixed type (ie, it has a type number between 01 and 46), then all you have to do is enter the type number. The re­maining parameters will then automatically appear. A type 47 disc, on the other hand, is a “User Defined” type. This means 6  Silicon Chip that you have to enter the various disc parameters (the number of cylinders, heads and sectors, etc) yourself. You do this by selecting the appropriate parameter and then entering its value directly via the keyboard. After entering the date and hard disc drive information, select the appropriate floppy disc drive, primary display and keyboard parameters. However, you don’t have to worry about the base memory and extended memory values, since the system checks these at switch-on and automatically displays the correct values. When all the entries are correct, press <Esc> to exit and select “Write To CMOS & Exit” from the menu – see Fig.1. Finally, press <Y> to answer While you can quickly get the computer going again, the re-entered CMOS values will be lost again when the computer is switched off. To affect a permanent cure, you must replace the battery before going through the CMOS setup routine. Once again, the exact procedure will depend on the mother­board. On some motherboards, the battery can be easily discon­nected and you can substitute an identical type obtained from a dealer. Be sure to disconnect the mains before opening up the case. The common practice these days is to use a 3.6V nicad bat­tery which is soldered directly to the motherboard. If you know exactly what you are doing, you can remove the motherboard from the case, de-solder the battery and substitute a new one. As well as the on-board battery, many motherboards also carry a 4-pin battery connector. This connector normally has a shorting jumper in- How To Create An Emergency System/Backup Disc Another thing that you should do when you first buy a com­puter (even before you inspect the CMOS settings) is create an emergency boot (or system) disc. This will enable you to boot the computer from one of the floppy disc drives if something goes wrong. A boot disc can be very useful under certain circumstances. For example, COMMAND.COM or the file allocation table (FAT) on the hard disc might become corrupted and the machine will refuse to boot. If this happens, you can boot the machine from your emergency system disc so that you can start troubleshooting. A clean boot disc is also handy if your machine “catches” a virus. By booting from a clean backup disc, you can prevent further damage from the virus and keep the virus out of memory while you run anti-virus software. A boot disc is created during floppy disc formatting by adding the “/s” switch to the format command. To do this, insert a floppy disc into drive A and type the following command at the c:\> prompt: format a: /s/u This will format the disc unconditionally and copy across three system files – IO.SYS, MSDOS.SYS and COMMAND.COM. Note that IO.SYS and MSDOS.SYS are hidden files, so you won’t see them in directory listings unless you include the “/a” switch with the “dir” command or instruct File Manager to show stalled between its two centre pins. If your motherboard has this connector (check the manual), an easy option is to purchase an external lithium battery that comes fitted with a matching 4-pin socket. This then plugs directly into the moth­erboard connector (remove the jumper first). It is also a good idea to remove the on-board battery, otherwise it may eventually leak and cause corrosion. You don’t have to remove the mother­ board to do this – just cut the leads to hidden/system files (click View, By File Type). Having created your system disc, it is also a good idea to back up two very important files in case you ever accidentally delete (or corrupt) them. These files are “autoexec.bat” and “config.sys” and they reside in the root directory of the hard disc. These two files are best copied to a sub-directory on your emergency system disc. To create a sub-directory, go to the C:\> prompt, insert the system disc into drive A, and log onto this drive by typing A: <enter>. Now, at the A:\> prompt, type md backup. This will create a subdirectory called “backup” on the floppy disc. Now type C: <enter> to go back the root directory on the hard disc. The two files can then be copied across by typing copy autoexec.bat a:\ backup <enter> and copy config. sys a:\backup <enter>. Alternatively, you can create a system disc and copy the autoexec.bat and config.sys files to a subdirectory on this disc using the Windows File Manager. To do this, first launch File Manager and choose Format Disk from the Disk menu. Choose the appropriate disc parameters (ie, the drive and disc capacity), then check the “Make System Disk” box and click OK. You can then create a sub­directory on the resulting system disc and copy the autoexec.bat and config.sys files into it by dragging them across from the C: drive. the battery using a pair of sidecutters. If necessary, remove some of the plugin cards on the mother­board to gain access to the battery. Finally, don’t be fooled by an onboard battery that meas­ures close to its rated voltage – ie, about 3.6V. A healthy battery will usually charge to about 4.2V. If the computer’s clock suddenly starts to lose by large amounts (eg, up to 20 minutes a day), then it’s a sure sign that the battery is on the SC way out. SATELLITE SUPPLIES Aussat systems from under $850 SATELLITE RECEIVERS FROM .$280 LNB’s Ku FROM ..............................$229 LNB’s C FROM .................................$330 FEEDHORNS Ku BAND FROM ......$45 FEEDHORNS C.BAND FROM .........$95 DISHES 60m to 3.7m FROM ...........$130 LOTS OF OTHER ITEMS FROM COAXIAL CABLE, DECODERS, ANGLE METERS, IN-LINE COAX AMPS, PAY-TV DECODER FOR JAPANESE, NTSC TO PAL TRANSCODERS, E-PAL DECODERS, PLUS MANY MORE For a free catalogue, fill in & mail or fax this coupon. ✍     Please send me a free catalog on your satellite systems. Name:____________________________ Street:____________________________ Suburb:_________________________ P/code________Phone_____________ L&M Satellite Supplies 33-35 Wickham Rd, Moorabin 3189 Ph (03) 553 1763; Fax (03) 532 2957 May 1995  7 Electronics in the The complexity of the electronic systems used in a modern car means that extensive testing is required to ensure that these systems do not suffer from electromagnetic interfer­ence. Here’s how Ford tested the systems used in its EF Falcon. One major criterion that a vehicle’s electronics systems must satisfy is electromagnetic compatibility. The last thing a driver needs is to have an airbag trigger unexpectedly or to have the engine stall because of interference with the engine manage­ment module from a nearby transmitter. For this reason, all electronic systems must be thoroughly tested to ensure that they can not be disrupted by electromagnet­ic interference (EMI). Nor should the systems themselves generate EMI to a degree which is either illegal or which interferes with 8  Silicon Chip the operation of other systems. Furthermore, the car’s electronics should be able to with­stand a diversity of abuses, ranging from a suddenly disconnected battery to electrostatic discharges generated by people sliding in and out of the seats. Electromagnetic interference A car presents a very hostile environment for electronic circuitry. Not only are there physical factors involved, such as vibration and heat, but there may also be high-level EMI from 50Hz to over 1GHz in areas where the vehicle operates. Strong emitters typically include power lines; radio navigation systems; AM, FM and TV transmitters; amateur and mobile radios; cellular phones and radar. The potential effect of this EMI on a vehicle can vary from a flashing clock display to engine stalls during the use of a mobile phone. The possible effects of EMI on vehicle electronic systems can have legal and safety implications. An airbag trigger or anti-lock braking system adversely affected by EMI has serious ramifications, while the digital odo­m­ eter incorporated in all EF Falcons is required by Australian Design Rules (ADRs) to operate without data corruption. In-car EMI EMI generated by electronic and electrical components within the car is not produced at the same high levels as by radio transmitters or power e new EF Falcon By JULIAN EDGAR Pt.3: Avoiding Electromagnetic Interference lines. However, because of its close proximity and the use of common wiring harnesses, it can still cause significant problems. The EMI generated by a car can be divided into two types: narrowband and broadband. Narrowband EMI is generated mainly by microprocessor modules and consists of discrete inLeft: the development of a new car now involves extensive elec­ tromagnetic compatibility testing to ensure that the numerous electronic systems will operate reliably in all environments. Testing of the EF Falcon was carried out in a special facility located in the United States. terference harmonics related to the microprocessor clock frequency. Two main problems are associated with this type of EMI. First, fringe area reception of FM radio can be degraded when one of the interference harmonics falls within the broadcast band­width of the station frequency. And second, there can be a prob­lem with mobile radios where continuous scanning of a number of frequencies is carried out. If the interference harmonic falls on or close to a scanned frequency, the radio can lock onto the interference signal and be effectively disabled. Broadband EMI, on the other hand, is generated by switching transients Fig.1: the Ford electromagnetic compatibility test facility, Michigan, USA. May 1995  9 wiring located on the front and the sides of the car are directly exposed to the field. The transverse electromagnetic cell is also calibrated to produce free space fields but, because the field distribution is more uniform, a turntable is not used. Remote control Fig.2: the transverse electromagnetic (TEM) cell is used for testing at frequencies below 20MHz. The dynamometer allows the vehicle to be ‘driven’ while being tested. Fig.3: the anechoic chamber is used for vehicle testing with frequencies from 20MHz to 1GHz. Note the turntable which allows the car to be rotated during testing. from ignition coils, motor commutators, solenoids and relays. This can cause radio interference and corruption of engine management sensor inputs. EMI compatibility testing Testing of the EF Falcon for electromagnetic compatibility (EMC) was carried out at Ford’s state-of-the-art facility at Michigan, USA. Fig.1 shows the layout of this facility. High-level narrowband EMI testing is carried out in two specially constructed test cells. These comprise a transverse electromagnetic cell designed for testing below 20MHz (Fig.2) and a shielded anechoic chamber for testing above 20MHz (Fig.3). Note that both test cells have chassis dyna­mom­ eters installed, allow­ ing the test­ ed vehicle to be run under load while remaining stationary. 10  Silicon Chip Although test procedures in the anechoic chamber vary de­pending on standards, the process essentially involves irradiat­ing the vehicle with RF signals at a set field strength. Because the field within the chamber varies with frequency and position, the Ford method initially establishes the free space values of the electric fields; ie, the calibrated field strengths are first measured in the empty chamber without the vehicle distorting the field. In addition, to improve field distribution around the car, the antennas are set as far back as possible and so very high powers are used for testing. During susceptibility testing of the vehicle, the amplifier can be set to produce the test field strength at varying frequen­cies. Because the antenna is fixed, a turntable is used to rotate the car after each frequency sweep. This ensures that all compon­ents and It’s worth noting here that dangerously high field levels are present in the EMI chambers during testing. As a result, all vehicle functions are activated and monitored remotely. Two video cameras are used to view the instrument cluster and the centre console, while an intake manifold vacuum gauge (installed within view of one of the cameras) monitors engine performance. To prevent RF from leaking into the control room, all video, audio and other test signals are routed using optical fibres. In addition, all actuators and switches on the car are pneumatically controlled to eliminate a potential source of unwanted RF which would affect the accuracy of the test proce­ dure. The switches controlled in this manner are used to inter­rupt fuse lines to enable emergency shutdown. They are also used to reset electronic modules, so that start-up routines can be monitored, and for the extraction of fault codes. Actuators are also installed to activate switches for cruise control operation and to depress the brake pedal to test ABS operation. Test procedure The actual testing is performed both when the car is at idle and also at 70km/h. The test starts by sweeping each fre­quency band at the highest test field strength and during this process the frequencies where susceptibility affects appear are noted. At the conclusion of the sweep test, the frequencies where potential problems existed are pinpointed, with the RF level increased until failure is observed. The field strength at which this occurs is noted and then checks are made against standards criteria. The specific fault criteria for which each system is exam­ined are listed in Table 1. Internally-generated EMI The production of EMI by the car is regulated in the US by Federal TABLE 1: EMC TEST FUNCTIONS System Functions Monitored Engine management Vacuum gauge monitoring for engine stumbles or stalls; production of fault codes Anti-lock braking Brake fluid pressure reduction as appropriate at each wheel Automatic transmission Shift of transmission to limp-home constant third gear mode; production of fault codes Cruise control Constant speed cruising ability measured by dynamometer roller speed; sudden throttle opening as indicated by the vacuum gauge Airbag Warning of light illumination, indicating the presence of fault codes Body electronics module Timing of intermittent wiper period; production of fault codes Instrument cluster Errata gauge, LCD, odometer or warning light operation Communications Commission (FCC) standards and these have been adopted by Ford as the corporate standard for EMI generation. In Australia, a voluntary Australian Standard applies and both radi­ated EMI tests are performed. Narrowband EMI testing is performed in the transverse elec­ tromagnetic cell, with special emphasis placed on any interactive problems caused by vehicle wiring and components. Ignition test­ing is carried out in the open air with the engine running, with a field plot of the EMI carried out around the car. These values are then checked against the AS 2557 standard, which is designed to control vehicle EMI on TV and radio broadcasts and on communi­cations services. Other testing Other tests involve electrostatic discharges, load dumping and the effects of low battery voltage. Electrostatic discharges (ESD) occur when a charged body comes in contact with parts of the car. It can cause damage in two ways: (1) by direct charge injection into sensitive semicon­ductors via the housing or wiring; and (2) by indirect RF radia­tion generated by the discharge. The test for ESD susceptibility is conducted with a commer­ cially produced simulator. A high voltage power supply is used to charge a capacitor to the required voltage, with the simulator then brought close to the instrument panel to cause the dis­ charge. The test voltage starts at 4kV and is increased to 15kV. At locations where it is conceivable that a person standing outside the vehicle could contact the interior, the test voltage is increased to no less than 25kV. All components are checked for damage after each discharge. Load dump testing is necessary to evaluate the effect of a heavy current being switched off in a car in which the battery is disconnected. Such a situation could occur if the battery termi­nals are corroded or loose and can result in a surge of up to 150V being generated on the 12V supply line. The test procedure involves running the engine at 2000 rpm with the battery disconnected. A resistive load drawing 80% of the alternator’s rating is then suddenly disconnected, after which all accessory items are checked to ensure that they have not been destroyed by the load dump. The effect of low battery voltage (eg, due to a broken alterna­tor belt) is also explored. In this case, testing is carried out with the battery and alternator disconnected, and the car run from a high-current voltage source. The supply voltage is then gradually reduced while various functions in the car are monitored. Typically, the alternator, ABS and airbag warning lights glow first to warn of abnormal operating conditions. At lower volt­ ages, the cruise control, instrument cluster and other components shut down until, finally, SC the engine stalls at about 6V. Acknowledgement Thanks to Ford Australia and the Society of Automotive Engineers for permission to use material from the “SAE Australa­sia” journal of October/November 1994. May 1995  11 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Introduction To Almost every day, in some way, satellite communications affect all Australians. Direct television links across the world are now commonplace and satellite TV usage in the Pacific area is set to expand at an astounding rate. All of this is good news for the electronics enthusiast. Many of the satellite signals covering our country are receivable using inexpensive equipment including our new satellite receiver kit, as this series of articles will explain. Satellite TV has grown enormously since the 1970s, linking millions of people around the world. In 1957, the world’s first satellite (Sputnik 1) 16  Silicon Chip was launched in a low Earth orbit, several hundred miles above the Earth. Sputnik orbited the Earth at a faster velocity than the Earth’s rotation and consequently had to be tracked by ground stations – quite a cumbersome operation. By 1965, the scientific community had realised that three satel­ lites placed strategically around the Earth in geostationary orbit could be used to relay TV and telephone signals. Geostationary orbit A geostationary orbit places a satellite above the equator at an altitude of 37,000km, at a rotational velocity the same as that of the Earth’s. The two main advantages are that the path between satellite and Earth remains constant and there is no need to track the satellite. As the theoretical minimum spacing between satellites is 2 degrees (based on achievable dish beam­width), the maximum number of satellites that can be placed around the equator in geostationary orbit is 180. In practice this is not the case and already there are several orbital locations where more than one satellite is locat­ed. At longitude 19.2 degrees west (over the UK), there are four satellites co-located and operating on a non-interference basis. In the Pacific, there are two satellites co-located at Using a pre-aligned module, you can build a satellite TV receiver to pick up signals from around the world. There are a great many satellite signals to receive & with a dish antenna & an LNB, you can take your pick from a plethora of programs. By GARRY CRATT* *Av-Comm Pty Ltd o Satellite TV May 1995  17 INTELSAT 507 (708 95) INTELSAT 604 INTELSAT 602 INTELSAT 704 (803 1996) RIMSAT (RESERVED) PANAMSAT PAS-4 GORIZONT 16 APSTAR 2 (1995) INTELSAT 501 GORIZONT 19 (STATSIONAR 14) ASIASAT 11 (1995) STATSIONAR 21 PALAPA C2 (1995) ASIASAT 1 PALAPA B2R PALAPA C1 (1995) PALAPA B2P PALAPA B4 JSAT 3 (1995) RIMSAT 2 RIMSAT 1 APSTAR 1 GORIZONT 18 (STATSIONAR 7) RIMSAT 3 G2 STATSIONAR 16 OPTUS A3 (BS 1995) OPTUS B1 OPTUS A2 (A3 1995) PANAMSAT PAS-2 RIMSAT (RESERVED) INTELSAT 701 (801 1996) INTELSAT 703 (802 1996) INTELSAT 511 INTELSAT 503 = C (3.6-4.2GHz) = K (12.5-12.75GHz) = K (11.2-11.5GHz) 57ø 60ø 63ø 66ø 70øE 72ø 80ø 87.5ø 91.5ø 96.5ø 100.5ø 103ø 104ø 105.5ø 108ø Fig.1: this diagram shows the large range of C and K-band satellites which can be received in Australia. 183ø 180ø 177ø 174ø 170.75øE 169ø 113ø 118ø 128ø 130ø 134ø 138ø 164ø 140ø 160ø 142.5ø 156ø 145ø (801) 130 de­grees east longitude. By careful adjustment of the satellite transmit dish “footprint”, power levels and down­link signal polarity, it is possible to operate in this way without causing interference In some cases, extended frequency coverage is also used, requiring wide­ band LNBs and feedhorns at the Earth station. Fig.1 shows the satellites visible in Australia. Since 1966 when Intelsat 1 (carrying 240 telephone circuits or one TV channel) was launched into a geostationary orbit over the Atlantic ocean, there has been a tremendous amount of devel­ opment in launch vehicles. There are presently four countries offering sat- ellite launch facilities and all of these operators have a significant backlog. The 1994 World Satellite Yearbook lists 108 operational satellites distributing television and radio around the world. In addition to this figure, there are scientific, military, weather and navigation satellites. The capacity of satellites has also increased dramatically. The latest Hughes HS-601 spacecraft operated by Optus has the capacity for 30 half transponders of analog television and up to 120 channels of digitally compressed television signals. The satellite is 3-axis stabilised, weighs 3000kg, has 6kW of battery capacity, 50 watt transmit power capacity, steerable antennas covering Australia and New Zealand, and a design lifetime of 13 years, a far cry from the late 1970s when the maximum capacity of any Intelsat spacecraft was two television channels. History of TVRO Small dishes, such as this 1.6-metre prime focus K band dish are usually made of pressed metal or spun aluminium, while larger dishes (eg, the 3.7-metre dish on page 17) are usually of mesh construction to cut down on wind resistance. 18  Silicon Chip Electronics enthusiasts and amateur radio operators have long played an important role in the development of home satel­lite TV equipment or TVRO (television receive only) equipment as it is sometimes known. In 1975 a British experimenter, Steve Birkill, pio- ITU 1 ITU 2 ITU 3 Fig.2: Australia is located in ITU region 3, while the frequency range band in use for K-band satellites in this region is 12.25-12.75GHz. neered the construction of home-made dishes, mi­ crowave amplifiers and receivers for satellite TV reception. In the USA, enthusiasts Bob Cooper and Taylor Howard were busy developing techniques and modifications to allow surplus military equipment to be pressed into service, and subsequently a group of 30 or so radio amateurs began the “Home Satellite TV” industry in the UK and USA. Australia had its pioneers too, like Victor Barker VK2BTV who pioneered reception of Intelsat 3 in the mid 1970s using low-threshold receiving techniques which the experts thought impossi­ble. In fact, it wasn’t until 1980 that satellite distribution was used in Australia to relay ABC programming from Sydney to outback locations in Western Australia. These signals were transmitted by Intelsat 4 and received initially using large spherical anten­ nas, for re-transmission terrestrially to local communities. By 1981, a handful of satellite enthusiasts had developed techniques for receiving these signals. Not only were the ABC transmissions available but so were signals from Japan and the American AFRTS (Armed Forces Radio and Television Service). As technology improved, receiving equipment became more affordable. A microwave amplifier purchased in 1980 cost 10 times the current price and was only 10% as efficient as those available today. After a feasibility study using a Canadian “Anik” satel­lite, specially moved above Australia for various experiments in 1982, the Australian government formed AUSSAT, the body responsi­ble for design, purchase and operation of Australia’s domestic satellite system. The “A” series satellites (Hughes type HS 376) were launched in 1984, 1985 and 1987. The first of the “A” series satellites was re­placed in August 1992 with the B1 satellite, a Hughes HS 600, A1 having exceeded its mission life. The B2 satellite was destroyed at launch in December 1992, while the final satellite in the B series (B3) was successfully launched in August 1994. Fig.3: this diagram shows the coverage of the Optus B1 satellite. Optus is the only operator using K band in our part of the world. For good reception of K band signals, dishes up to 2-metres are required in fringe areas, whilst a 1.6-metre dish will perform adequately along the east coast of Australia. May 1995  19 SOUTH POLAR AXIS ALIGNED WITH EARTH'S NORTH/SOUTH AXIS NORTH DECLINATION OFFSET ELEVATION ANGLE POLAR AXIS ANGLE Fig.4: the geometry of a polar mount. Polar mounts are used where a number of geostationary satellites must be tracked in the azimuth axis. Polar mounts are equivalent to the “equatorial” mounts used by astronomers to make a telescope track the motion of the stars. To date, the B3 satellite remains as an in-orbit spare, the B1 satellite carries most domestic TV traffic, the A3 satellite carries most itinerant traffic, and the ageing A2 “bird” is now in an inclined orbit to save precious station-keeping propellant. The latter satellite is used as a backup to the 0.5 0.4 0.3 0.25 f/D RATIO DIAMETER (D) f f f Frequency bands There are two frequency bands used for satellite television delivery. The oldest system operates in the 3.7GHz4.2GHz range and is known as C band. This band is used internationally and, depending on the satellite power, may require a dish from 3m-5m for good reception. The other band used is known as K band and the frequency allocation depends on the ITU region. Australia is located in ITU region 3 and the frequency band in use is 12.25-12.75GHz. Fig.2 shows the ITU boundaries. FOCAL POINT The only operator using K band (f) in our part of the world is Optus Communications. For good reception of K band signals, dishes up to 2m are required in fringe areas, whilst a 1.6m dish will be adequate along the east coast of Australia. Fig.3 shows the Optus B1 satellite national beam. Fig.5: deep dishes have a shorter focal length than shallow dishes. This allows the feedhorn to be shielded by the dish itself, providing some rejection for terrestrial interference or “TI”. This diagram shows the difference between a shallow & a deep dish. Note the location of the focal point. 20  Silicon Chip Optus fibre optic network across the country. Equipment The most obvious piece of equipment needed is a dish. For C band operations a polar mount dish is desirable, so that geosta­ tionary satellites can easily be located using a single motor drive unit or actuator operating in a single axis. When used on telescopes, this is known as an equatorial mount. It was original­ly devised last century by astronomers who realised it would be much easier to keep a telescope aimed at a particular planet if it could be swivelled around a single axis to exactly counteract the Earth’s rotational motion. The polar axis of the Earth lies parallel with a line drawn through the North and South geographic poles. To achieve this orientation, the axis of the dish is set to an angle which is a function of the site latitude and the difference between the satellite and site longitude. For example, for an Earth station at the equator, where the latitude is zero, the polar axis angle equals zero because the arc of satel­lites can be tracked by moving the dish along a circle directly overhead. Fig.4 shows the geometry of a polar mount. Polar mounts are used where a number of geostationary satellites must be tracked in the azimuth axis. Inclined orbit Some ageing satellites, kept in orbit due to the backlog of launch bookings for new satellites, have been deliberately put into an “inclined” orbit, to prolong their useful life. In this situation, a certain amount of station keeping tolerance is acceptable to ground stations. By accepting the resultant effects of the gravitational pull of the Sun and the Moon, the radiation force of sunlight and the pull of the Earth’s gravitational field, and allowing the satellite to drift within a target “box” in space, a significant amount of propellant can be conserved. However, this does mean that ground stations must track the satel­lite in both azimuth and elevation. To track these satellites, a modified polar mount must be used, having bearings or bushes in both axes, and a declination angle set to zero. As the inclination of these satellites can reach 4 degrees, compared with the geostationary inclination of 0.1 degrees, significant movement of the dish is necessary to maintain the downlink. There exists a patented manoeuvre, called the Comsat Manoeuvre, which cleverly conserves satellite station-keeping fuel. Part of an excerpt from the patent reads “a conventional satel­lite uses an average of 37 pounds of station-keeping fuel for each year of design life . . . approximately 34 This is the view inside the completed Satellite TV Receiver to be described next month. It’s based on a pre-aligned module which makes it easy to assemble & get going. pounds of fuel is used for north/south correction, whilst only 2 pounds is used for east/west correction, and 1 pound for attitude control.” So it is obvious that any kind of manoeuvre that can minimise the amount of fuel used in north/south station keeping can prolong the life of the satellite. On the ground, an Earth station must be equipped with both a mechanical dish mount capable of moving in both axes and a satellite tracker capable of reading the incoming signal level and controlling two motors to pivot the dish. This is necessary in order to track the satellite. Dish construction Dishes can be made from fibreglass, steel, aluminium, and perforated sheet or mesh (where wind resistance is likely to be a problem). The larger dishes are used on the weaker satellites and these generally operate on the C band. Compared to K band, the requirement for surface accuracy is considerably relaxed and a C band dish can tolerate up to 10mm in surface inaccuracies without noticeable performance degrada­tion. On the other hand, K-band dishes must be very accurate and so are normally fabricated from either spun aluminium or hot pressed steel. Using either of these fabrication techniques, surface accuracy of a few millimetres is achievable. The size of the dish required is determined by the satel­lite “footprint” and signal level on Earth. From the centre of the “footprint”, called the “boresight”, where the signal is at the highest level, signal contours radiate outward at decreasing levels. The lowest signal contour is known as the “beam edge”. Mathematical formulas are used to calculate what is known as the “link budget”, and these formulas take into account path loss, satellite EIRP, available dish gain, dish noise temperature and signal bandwidth. Several computer programs are commercially available to perform these link calculations. In practice, the size of a dish required to receive a par­ticular satellite could be determined on a subjective basis. Whilst this technique will provide some results, there is normal­ly no margin allowed for rain fade or a drop off in satellite power as the spacecraft ages. In addition, broadcasters can change the direction of the satellite footprint and power level. For this reason, it’s always wise to use a dish larger than the calculated minimum. The shape of the dish is also important. There are two basic types of dish: (1) prime focus; and (2) offset. A prime focus dish is perhaps the most recognisable, May 1995  21 SECTION OF PARABOLA USED FOR OFFSET ANTENNA OFFSET ANTENNA SECTION FOCAL POINT FOCAL POINT Fig.6: the compact size of offset dishes has made them popular with enthusiasts, despite their mechanical instability for sizes over 90cm. Offset dishes have very good sidelobe performance & no aperture blockage, unlike the prime focus dish. This diagram shows the relationship between prime focus & offset dishes. as it is used almost exclusively on C band and more often than not for larger K band installations. Prime focus dishes Prime focus dishes can be made to various degrees of “deep­ness”. Deep dishes have a shorter focal length than shallow dishes. This allows the feed­ horn to be shielded by the dish itself, providing some rejection of terrestrial interference or “TI”. Fig.5 shows the difference between a shallow and a deep dish. Note the location of the focal point. and ice pooling on the dish degrades the incoming signal. Because the offset dish is actually only a section of a larger prime focus antenna, the offset angle means that the actual angle of the reflector with respect to the horizontal plane is much higher than that of a prime focus dish, ensuring that rain, ice and snow easily fall off the reflector. In Australia, we generally avoid such problems, due to our climate. However, the compact size of offset dishes has made them popular with enthusiasts, despite their mechanical instability for sizes over 90cm. Offset dishes have very good sidelobe per­ formance and no aperture blockage, unlike the prime focus dish. Nevertheless, the prime focus dish is much easier to align and point. Fig.6 shows the relationship between prime focus and offset dishes. For reception of a single satellite in geostationary orbit, a simple ground mount can be used. If the mounting location demands a pole supported mount, such as a wall bracket, an “Az/El” mount can be used. This type of mount allows adjustment of both elevation and azimuth, normally using a piece of threaded steel rod and lock nuts, for each axis, but has no facility for tracking through the polar arc, in order to view other geostation­ ary satellites. This is the main difference between a polar and an Az/El mount. Satellite receiver We have presented several articles in the past dealing with the equipment necessary for satellite television reception. Most readers would find Offset dishes Offset dishes were developed primarily for use in high latitude countries, where the effect of water, snow These photographs show some of the many foreign satellite TV programs which are available at any given time. Some of these are broadcast in NTSC format & you will need an NTSC VCR or standards converter to watch them in colour. Alternatively, they can be displayed in black & white on a standard PAL TV receiver. 22  Silicon Chip difficulty in “home-brewing” a dish or the microwave components required for satellite reception but few will have difficulty with the re­ceiver to be described. A typical satellite television receiving system comprises a dish antenna, microwave feedhorn, low noise block down-converter, cable and a receiver. Each of these components performs a vital function, and the interconnections are shown in Fig.7. A commercial satellite designed to carry television pro­gramming can operate on either (or both) of the two internation­ally agreed satellite bands: (1) C band (3.7-4.2GHz); and (2) K band (12.25-12.75GHz in our part of the world). A parabolic dish antenna is commonly used to provide a significant degree of gain, normally in the region of at least 40dB. Depending on the band used, this equates to an approximate dish diameter of 3m for C band or 1.2m for K band. LOW NOISE BLOCK DOWNCONVERTER (LNB) Home construction of a 3m C band dish is quite an undertak­ing considering the physical size. Similarly, the con­struction of a 1.2m dish for K band is also quite difficult, considering the surface accuracy required (3-4mm over the entire dish). Equally daunting is the prospect of constructing a mi­cro­wave feedhorn, polariser and low noise amplifier and, consid­ering the price concessions to be offered on these items to SILICON TELEVISION RECEIVER DISH VHF CH3 OR 4 950-1450MHz SATELLITE RECEIVER Fig.7: a typical satellite television receiving system comprises a dish antenna, microwave feedhorn, low noise block down-converter, cable & a receiver which feeds the TV set. CHIP readers in conjunction with the receiver kit, the incentive to build these items is minimal! A satellite receiver is the one component of a system that can easily be constructed, saving around 50% over the price of commercial units. As noted above, the incoming satellite signal “block” has a frequency of either 4GHz or 12GHz, depending on the band used. This signal is collected by the dish antenna and directed through a piece of waveguide called the feedhorn to a quarter-wave dipole antenna, an integral part of the LNB (low noise block converter). The LNB performs two vital functions: (1) it amplifies the incoming signal whilst maintaining a very low noise figure (typically around 50°K for K band and 20°K for C band); and (2) it converts the incoming 500MHz wide block of signals to a much more manageable range, normally 9501450MHz. This allows the use of inexpensive RG-6/U 75Ω coaxial cable to connect the LNB to the receiver. There is sufficient output from a typical LNB, and sufficient AGC range on our receiver, to allow cable runs of up to 100 metres without additional line amplifiers. Next month, we will present the circuit and assembly details of a complete satellite receiver, along with some special offers on dishes and LNBs for readers of SILICON CHIP. The off-screen photos included with this article are just a sample of what can SC be received. May 1995  23 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. +8V 10 10k OFFSET NULL VR1 10k 2.2k 2 3 10 38 7 IC1 OP27G 6 100pF 4 100  22k +8V 1k 0.47 0.1 3.3k +8V 2 IC2 3 OP27G 4 10k +8V 7 6 22k 7 2 IC3 3 OP27G 4 R 6 1M 10k +12V 10 16VW IN REG1 LM317T ADJ 10 16VW OUT 120  D1 0.1 34 36 31 0.1 B1 C1 33 CAL VR2 200  5 4 3 2 8 E1 6 IC4 F1 ICL7106 7 G1 BUFF 12 A2 11 B2 INT 10 C2 CREF 9 D2 14 E2 13 F2 CREF 25 G2 REFHI 23 A3 INHI 32 COM 35 REFLO 30 INLO +8V 10 16VW 680  A1 OSC2 27 +8V OSC3 40 OSC1 29 A/Z 47k 28 0.22 22k 22k 2x12uV/kg STRAIN GAUGES 1k 10k 39 10 +12V +8V 1 26 16 29 24 C3 15 D3 18 E3 F3 17 22 G3 19 K Y 20 BP 21 11 B3 30 27 26 13 14 15 24 25 23 22 17 18 19 20 21 3.5 DIGIT LCD 10 9 31 32 3 2 A Y K F K E D DP3 3 DP3 8 G B C DP2 DP2 12 2 DP1 DP1 16 1 1 38 39 40 AO I Digital readout for a weighbridge This circuit allows strain gauges in a cattle weighbridge to be interfaced with the 3-digit LCD panel meter featured in the September 1992 issue of SILICON CHIP. This project used an Intersil ICL7106 A/D converter and a 3½ -digit LCD. The strain gauge is connected in a Wheatstone bridge with the value of R equal to the no-load resistance of the strain gauge. If two strain gauges are used, due to the weighbridge configuration, they can be connected in series. The 12µV/kg output from the bridge is conditioned by op amps IC1, IC2 and IC3 to provide a nominal 100µV/kg output suitable for the A/D input of IC4. IC2 and IC3 together form a differential amplifier with a gain of 8.67 as set by the 22kΩ feedback resistors at the invert­ing inputs plus the 3.3kΩ resistor. The high impedance non-in24  Silicon Chip verting inputs of IC2 and IC3 monitor the negative and positive outputs of the bridge. IC1 is connected as a unity gain buffer which provides an offset adjustment for the differential amplifier output at pin 6 of IC3. VR1 allows variation of the DC voltage applied via IC1 to the inverting input of IC2 via a 22kΩ resistor. The offset adjustment allows the weighbridge reading on the LCD to be set to zero when there is no load. This compensates for the weight of the weighbridge platform itself. Signal to the A/D converter (IC4) is applied to the INHI input via an RC filter consisting of 1MΩ resistor and 0.1µF capacitor. The common (COM), REFLO and INLO inputs are all tied together while REFHI is set at about 100mV above the COM input using VR2. This gives the required 1000 reading for a 100mV input. Note that the COM input is held at close to half-supply by the 10kΩ resistors connected in series with VR2. The entire circuit is ratiometric, meaning that the reading on the LCD will be the same regardless of the supply voltage (within reason). This is because as the voltage drops, the output of the strain gauge will reduce at the same rate that the REFHI input varies. Consequently, no supply regulation is necessary and it can vary between 15V, the maximum for IC4, and about 7V, the minimum supply to drive the LCD with normal contrast. No decimal points are required since the readings are in kg. This means that the 4070 quad XOR gate driver for the decimal points in the original design can be omitted. Calibration is initially done with VR2 set at half position and with no load on the weighbridge. VR1 is adjusted for a 000 reading on the display. Now add a known weight on the weighbridge (best accuracy is achieved with 1000kg or more) and adjust VR2 for the correct reading. SILICON CHIP R10 100k C8 47 63VW R9 6.81k +48V R8 6.81k -IN Cin1 47 Rp1 63VW 49. 9W +IN Cin2 47 Rg2 63VW 49. 9W R2 20k +V Rg1 10k COMMON C5 33pF 2x1N752 ZD1 ZD2 7 3 CN 47 FILM Rg2 10k CRF2 100pF 2 IC1 SSM2107P 8 CRF1 100pF ZD3 6 1 5 +V R1 10k 2 8 IC2a OP275 3 GP 4 4 -V 2200 10VW GAIN (G) = 2 x ((10k/RG) + 1) +21V 0V -21V Balanced microphone preamplifier The circuit featured here is the subject of Application Note AN242 from Analog Devices. It uses the SSM2017 low noise microphone preamplifier IC which was featured in the balanced micro- 6 C4 100 25VW C7 0.1 7 OUT IC2b R5 221k 5 C2 1 FILM -V phone preamplifier on p.38 of the April 1995 issue of SILICON CHIP. As presented, this circuit is not greatly different from the April 1995 circuit but it incorporates “phan­tom power” for a capacitor microphone. This eliminates the need for batteries in the microphone itself. The 48V polarising Automatic charger/ discharger Quite a few nicad discharging circuits have been published but few incorporate automatic charging after discharging. The circuit shown here adds the charging function to a discharger based on an LM311, allowing you to upgrade an existing battery charger to an automatic dis­ charger and charger. This circuit shown is for two AAtype packs but by adjust­ing VR1 and changing the value of R1 (to set the correct discharge rate) it can be used for one to six cells, from AAA type to D types. If you want to discharge the cell before charging, press switch S1. This momentarily energises the relay which then con­nects the discharger. While ever the battery voltage at pin 2 is above the reference voltage at pin C6 0.1 D2 FILM +V C3 100 25VW 2x1N458 D1 C1 1 2200 10VW RG OUTPUT R4 221k -V 2x1N752 ZD4 R3 49. 4  1 CHARGER vol­tage is fed to the microphone capsule via the balanced signal wires, hence the term “phantom”. The gain of the circuit is set by varying RG whereby gain is equal to 10kΩ/RG. The SSM-2107 IC is available from Altronic Distributors in Perth, WA. IN +12V D1 1N4001 6V RELAY R2 270  +12V 2 NICAD CELLS R1 22  ZD1 7.5V VR1 20k +2.2V 0.1 3, the comparator’s output will be low and thus the relay will remain energised. When the voltage at pin 2 drops below that of pin 3, the comparator’s internal open-collector transistor will turn off and the relay will be de-energised. The relay contacts will then disconnect the discharger and connect 3 8 R3 220  LED1 IC1 LM311 7 4 S1  This nicad discharger circuit will automatically switch in a charger at the end of the discharge cycle. the charger to the nicad cells. Note that you cannot substitute an op amp for IC1 since S1 shorts the output to ground. This will cause no harm to an “open collector output” comparator but it will damage an op amp. P. Chen, Dundas, NSW. ($30) May 1995  25 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) TOTAL Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS ❏ New subscription – month to start­­___________________________ ❏ Renewal – Sub. No._______________   ❏ Gift subscription ☞ RATES (please tick one) Australia Australia with binder(s)* NZ & PNG (airmail) Overseas surface mail 2 years (24 issues) 1 year (12 issues) ❏ $A90 ❏ $A49 ❏ $A114 ❏ $A61 ❏ $A135 ❏ $A72 ❏ $A135 ❏ $A72 ❏ $A240 Overseas airmail ❏ $A120 *1 binder with 1-year subscription; 2 binders with 2-year subscription GIFT SUBSCRIPTION DETAILS Month to start__________________ Message_____________________ _____________________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) YOUR DETAILS Your Name_________________________________________________ (PLEASE PRINT) Address___________________________________________________ Address______________________ _____________________________ State__________Postcode_______ ______________________________________Postcode___________ Daytime Phone No.____________________Total Price $A __________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ Master Card 9am-5pm Mon-Fri. Please have your credit card details ready ______________________________ Card expiry date________/________ Card No. Phone (02) 9979 5644 Signature OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail coupon to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia May 1995  31 Build a mains music transmitter & receiver How many times have you wanted to listen to music while working in the garage or a room in the house but didn’t want to move the stereo speakers. With this system, you can listen to your music anywhere there is a power point. By JEFF MONEGAL This project is actually a variation of a mains intercom circuit. It consists of two parts: (1) a transmitter unit which is connected to the program source to feed the signal into the 240VAC mains wiring; and (2) a receiver which is plugged into another power point anywhere within your home. The transmitter is housed in a plastic box which has two RCA panel sockets for the input signal. It is powered from the mains supply and it couples its frequency modulated carrier signal into the 240VAC supply via its mains cord. The receiver is housed in another plastic box which is connected to the mains supply. On the front panel it has tone and volume controls and two LEDs, one to indicate that it is 32  Silicon Chip locked to the carrier signal and the other a power indicator. On the rear panel are a pair of screw terminals for connection of a loudspeaker to an internal 10W amplifier. Circuit description Let’s look at the circuit of the Music Transmitter which is shown in Fig.1. The heart of the circuit is IC2, a 4046 phase lock loop (PLL) IC. This oscillates at around 300kHz, as set by the 22kΩ resistor at pin 9 and the 100pF capacitor between pins 6 & 7. Pin 9 is the input to the voltage controlled oscillator (VCO) within IC2 and this is driven by IC1, a TL071 op amp con­nected as an inverting amplifier. This op amp has a gain of 4.7, as set by the 10kΩ and 47kΩ feedback resistors connected to pin 2. The input signal for IC1 comes via the volume control, VR1, which is preceded by a 0.1µF capacitor and two 1kΩ resistors which mix the left and right channels from the program source. This could be a CD player, tape deck, FM tuner or just the tape monitor output from your stereo amplifier. The latter gives access to all the program sources you have connected – pretty simple, really. The output of the VCO is at pin 4 of IC2 and it is used to drive the gate of Mosfet Q1. Q1 provides a high impedance buffer for the VCO and its drain drives both the Active and Neutral lines of the 240VAC mains supply via .01µF 5kV ceramic capaci­tors. IC1 is biased so that its output at pin 6 sits at half the supply rail of 8V (ie, at +4V), by virtue of the voltage divider consisting of R4 & R6. The voltage divider is bypassed by 10µF capacitor C3 and further supply de­ coupling is provided by resis­tor R8 and capacitor C5. The DC supply is provided by an 8V 3-terminal regulator and this feeds a bridge rectifier (BR1) and a 2200µF R8 1k C6 100pF C5 10 R4 47k RIGHT AUDIO INPUT LEFT C1 0.1 R1 1k R2 1k VR1 50k R6 47k IC1 2 TL071 4 6 R5 47k C3 10 +8V C7 10 6 CA 7 3 R3 10k C2 0.1 R11 270  7 16 R7 CB 3.3k 9 BIN 3 IC2 VCIN VC 4 4046 R1 INH OUT 11 8 5 R9 22k R12 100  R10 68  D G Q1 P222 S Fig.1: the circuit of the Music Transmitter. The 4046 is used as a voltage controlled oscillator to frequency modulate a 300kHz carrier. C4 330pF I GO A .01 5kV K A .01 5kV REG1 IN 7808 OUT 12.6V 240VAC GD S BR1 W04 T1 C12 2200 25VW N GND C10 10 C11 .0033 +8V A  LED1 K R13 560  E MUSIC TRANSMITTER filter capacitor from a 12.6VAC transformer. Music receiver While the Music Transmitter is fairly simple, the circuit for the receiver is a little more complicated, as shown in Fig.2. Again, the heart of the circuit is a 4046 PLL, IC1. This takes the FM signal which has been impressed onto the mains wiring and recovers the audio signal. In this case though, IC1 operates as a PLL and not simply as a VCO, as we shall see. Two .01µF 5kV capacitors couple the 300kHz FM carrier from the mains to the base of transistor Q1. Q1 is a common emitter amplifier roughly tuned to 300kHz by C1 and L1. The output signal from its collector is AC-coupled to the input of IC1. IC1 is also set to run at around 300kHz, as set by the 100pF capaci­tor between pins 6 & 7, and the 12kΩ resistor and 50kΩ trimpot (VR1) connected to pin 11. VR1 is set so that when a 300kHz carrier is present on the 240VAC mains, the PLL locks onto it. Resistor R3 and capacitor C7, connected to pins 2 & 9 respectively, form a filter which sets the “capture range” of the PLL; ie, the ease with which it locks to the incom­ing 300kHz carrier. When the VCO is locked to the incoming frequency, an error signal is generated by the PLL at pin 10. This voltage is propor­ tional to the difference between the free-running frequency of the PLL and the incoming carrier frequency. So as the incoming 300kHz carrier deviates from its nominal centre frequency, pin 10 generates a voltage which is proportional to the difference. The AC component of this error signal at pin 10 is actually the same as the modulating audio signal back at the transmitter. After filtering by R5 and C10, the signal is coupled via C9 to trimpot VR2. From there, the signal is fed to IC2, a TL071 op amp connected as an inverting amplifier with a gain of 10. Its frequency response is rolled off Where To Buy A Kit Of Parts A kit of parts for this project is available from CTOAN Electronics. The kits will be available in two forms with prices as follows: Kit 1 is a short form transmitter which contains the PC board and all onboard components excluding the power transformer. Price $ 20.00. Kit 2 is a short form receiver which contains the PC board plus all on-board components excluding the power transformer. Price $39.00. Kit 3 is a full transmitter kit containing all components, transformer, mains cord, case and adhesive front panel. Price $43.00. Kit 4 is a full receiver kit containing all components including the transformer, case, mains cord and adhesive panel. Price $65.00. All the above prices include postage within Australia. Kits may be ordered over the phone using a credit card or by sending a cheque or money order to CTOAN Electronics, PO Box 211, Jimboom­ba, Qld 4280. Phone (07) 297 5421. CTOAN Electronics will also be offering a repair service for this project. The cost will be $30.00 including return postage. Fully built and tested units will also be available. May 1995  33 L1 100uH C1 .0033 B E Q1 BC327 C R1 33k 3 BIN 14 AIN C5 .0033 C4 330pF 6 4 VC OUT D1 1N914 16 PCP Q2 LED1 BC558 E A B K  C 1 R6 22k CA C6 100pF 7 R3 120k 2 PC1 VCIN 9 R1 INH 11 5 SF R4 22k 8 R2 12k C9 0.1 R5 6.8k 10  K R8 470  C Q3 BC548 B E D2 1N914 C11 VR2 50k C10 .022 LOCKED LED2 R7 10k IC1 4046 CB C7 .001 A C8 10 0.1 VR1 50k R18 100  R11 22k R10 22k C12 47 R9 22k 3 R13 22k C13 47 2 7 IC2 TL071 6 C15 0.47 C18 0.47 C17 47 R14 10k R15 68k C20 0.1 C19 .047 4 R12 220k R16 33k C14 68pF C2 .01 5kV C3 .01 5kV A ZD1 12V C23 100 R17 68k C21 .047 C16 .0015 TONE VR3 50k VOLUME VR4 50k R19 47k C22 0.47 240V AC E C VIEWED FROM BELOW BR1 W04 12.6V N CASE  A K 34  Silicon Chip C28 1000 5 R23 10  8 C27 0.1 R21 1k C24 10 1 9 MUSIC RECEIVER Fig.2: the receiver circuit of the uses a 4046 PLL IC to recover the audio modulation on the 300kHz carrier which is picked up from the mains supply. above 10kHz by the 68pF feedback capaci­tor (C14). Immediately following IC2 we have a passive “twin-T” notch filter (C1921 & R15-17) which attenuates 50Hz, necessary in a system which is directly connected to the 50Hz mains supply. The output of the twin-T filter is connected to potentiometer VR3 which together with C18 forms a simple top-cut tone control. Potentiometer VR4 is the volume control. From here, the audio signal is coupled to IC3, a TDA1520 power amplifier which is capable of delivering 20W. In this cir- 4 R22 270  C26 680pF R20 47k R24 1.5k POWER LED3 E 6 IC3 9 TDA1520 2 +18V C29 2200 25VW 8 1 B T1 +18V C25 .0033 cuit though, the nominal supply rail of +18V means that it can only deliver about 3W, which is adequate for this applica­tion. Resistors R20 & R21 set the gain of IC3 to 48 while capaci­tor C24 sets the low frequency response of the amplifier to about 20Hz. The remaining components around the amplifier are for high frequency stability, while C28 is the output coupling capaci­tor. Power for the circuit comes from a 12.6V transformer driv­ing a bridge rectifier and 2200µF capacitor to give about +18V. This supplies the power amplifier directly and also feeds 12V zener diode ZD1 via a 100Ω resistor. The resulting +12V rail supplies IC1 and IC2. The remaining components to be discussed are those involved with Q2 and Q3. Q2’s job is to ensure that the audio path is disabled if the PLL loses lock at any time, as would be the case if the transmitter was switched off. In this situation, the PLL has no signal to lock onto and so the VCO will free run. This has the result of producing all sorts of noise and rubbish in the audio section and so it must be muted. This is done using the signal available at pin 1 of IC1. RCA SOCKETS 0.1 VR1 47k 1 A 10uF LED1 22k 68  100pF 3.3k IC2 4046 1 1k 270  K 10uF IC2 TL071 10k 47k 330pF 1k R IN 1k L IN 10uF .0033 10uF G D S Q1 2200uF REG1 BR1 100  SECONDARY Construction Let’s discuss the construction of the Music Transmitter first, since it is the most straightforward. It is assembled onto a PC board measuring 127 x 77mm and coded CE/MUSA/94. This is then mounted on the base of a standard plastic utility box using 9mm insulated spacers and secured using short screws. The component layout for the PC board is shown in Fig.3. After checking the PC board carefully for any defects, you can begin the assembly by installing PC stakes at the external wiring points for the RCA sockets and the LED. This done, install the resistors and capacitors, followed by the ICs and the 3-terminal regulator. Take care with the orientation of the semiconductors and electrolytic capaci­tors. The last component to be mounted is the small power trans­ former which is bolted to the board, along with a solder lug. The PC board can now be used as a template for drilling out its mounting holes in the base of the case. You will also have to drill holes for the RCA sockets, the LED and for the cordgrip grommet. Be sure to carefully shape the cordgrip grommet hole so that the grommet will be a tight fit. The mains cable should now be passed through the hole in the case and secured with the cordgrip grom­ met. Its Active and Neutral terminals can then be wired directly to the board, while the Earth lead is connected to a 47k 0.1 GND 560  When the system is in lock, pin 1 of IC1 is high. This high output is fed via D1 to R6 and is used to reverse bias LED1 and the base of Q2 so that the transistor is held in the off state. In this situation, the audio signal from volume control VR2 has an uninterrupted path to IC2 and IC3. The same voltage from pin 1 of IC1 turns on Q3 and so LED2 will be lit to indicate the “locked” condition. When the PLL loses the carrier signal, pin 1 will go low. Now base current for Q2 can flow via LED1 and R6 so that the transistor turns on. Its collector now pulls the non-inverting input of IC2 high, via diode D2 and R9. This is a rather brutal way of shutting down IC2 and thus prevents any extraneous signals from being fed to power amplifier IC3. Because pin 1 of IC1 is low, transistor Q3 will be off and LED2 will be extinguished. POWER TRANSFORMER .01 5kV PRIMARY A .01 5kV E ACTIVE BROWN Fig.3: this diagram shows the parts layout for the transmitter PC board. N EARTH GREEN/ YELLOW NEUTRAL BLUE CORD GRIP GROMMET The transmitter PC board is mounted on the base of the plastic case using 9mmlong insulated standoffs. Note that the mains cord must be anchored securely with a cordgrip grommet in the end of the case. May 1995  35 Fig.4: this is the component overlay for the receiver PC board. Note that LEDs 2 & 3 are actually mounted on the front-panel, while the output terminals (near IC3) go to an RCA socket on the rear panel – see photo. BR1 2200uF 100uF LED3 270  10  680pF .0033 Q1 12k 330pF 22k 33k IC1 4046 47uF 47k .047 VR3 68k 68k .047 .015 0.47 1 ZD1 IC2 TL071 0.1 .01 5kV 33k D1 10k 22k D2 A Q3 10uF LED1Q2 10k 22k 0.47 47uF .01 5kV 470  68pF E GREEN/YELLOW VR2 0.1 N 100pF 22k 22k BLUE 0.1 .001 1 6.8k A VR4 120k .0033 .022 BROWN VR1 220k PRIMARY 100 POWER TRANSFORMER 10uF A LED2 0.47 47uF L1 CORD GRIP GROMMET 0.1 A .0033 1000uF IC3 TDA1520 1.5k 47k 47k 1k OUTPUT solder lug – see Fig.3. An additional earth wire is then run from this solder lug to the earth terminal on the board. Finally, the board can be mounted in the case and the RCA sockets and LED connected using short lengths of hook-up wire. Music receiver The receiver board accommodates all the components, including the tone & volume control pots. Note the small aluminium heat­sink for the TDA1520 power amplifier IC. Use plastic cable ties to lace the primary leads of the power transformer so that there is no possibility of them coming adrift & contacting other parts. The low voltage wiring should also be secured with cable ties. 36  Silicon Chip The receiver is assembled onto a PC board measuring 137 x 117mm and coded CE/MUSB/94. The component layout is shown in Fig.4. With the exception of wires to the LEDs and rear speak­er terminals, all the wiring and components are on the PC board. Mount the small components first, such as resistors, ca­pacitors, diodes and transistors, followed by the ICs and induc­tor. The TDA1520 should be mounted on a small heatsink as shown in the photographs. We used a small scrap of 5mm aluminium. Drill a couple of mounting holes that correspond with the two mounting holes in the power amplifier. Bend the leads at right angles so that IC3 can mount flat on top of the heatsink. Be careful not to allow the leads to touch along the edge of the aluminium. The last component to be mounted is the small power transformer which is bolted to the board. The mains cable should be passed through a hole in the rear panel of case which is fitted with the correct size cordgrip grommet to anchor it. It can then be wired directly to the board. The board can then be mounted in the base of the case and the wiring completed. Fit cable ties to both the mains wiring and to the low-voltage wiring to prevent shorts if a wire comes adrift – see photo. Testing & setup The first step is to turn on the transmitter and check that the +8V supply is present at the output of the 3-terminal regulator and at pin 7 of IC1 & IC2. Similarly, turn on the receiver and check that +18V (or thereabouts) is present at pin 6 of IC3 and that +12V is present at pin 7 of IC1 & IC2. For the initial setup, turn VR1 in the transmitter fully anticlockwise. Connect an audio source to the input – a CD player or cassette deck will do. At the receiver, turn VR1 to mid-posi­tion and VR2 fully anticlockwise. Connect power and turn on. Do not plug the receiver into the same power point as the transmit­ter. If another GPO (mains power point) is not within reach then use an extension lead from another GPO. The power LED should light on the receiver and the locked LED may or may not come on. Turn up the volume control. You should hear some noise and hiss at full volume. Now slowly turn VR1 until the locked LED comes on. Remember that the transmitter must be on but a music source is not necessary as the receiver will lock onto the carri­er from the transmitter. When the receiver is not locked LED1 on the PC board should glow dimly and be out when it is in lock. Once the receiver is locked, turn on the music source to the transmitter. At the receiver, turn up the volume. If you are greeted with good clean music then no further adjustment is necessary. If not, then further adjustment of VR1 in the receiver is needed. At some point during the rotation of VR1 you should find that the receiv­er locks properly and produces good clean audio. If the audio is distorted, then reduce the level of audio at the transmitter by reducing VR1. This reduces the amount of modulation. VR2 in the receiver is set to give the PARTS LIST Transmitter 1 PC board, code CE/MUSA/94, 127 x 77mm 1 12.6V power transformer (Altronics Cat. M-2851) 1 plastic case, 158 x 95 x 55mm 1 3-core mains cord & moulded 3-pin plug 1 cordgrip grommet to suit mains cord 2 RCA panel sockets 1 50kΩ horizontal trimpot (VR1) 4 9mm tapped insulated standoffs plus 8 short screws to suit 1 5mm LED bezel 1 solder lug Semiconductors 1 TL071 FET-input op amp (IC1) 1 4046 phase lock loop (IC2) 1 P222 Mosfet (Q1) 1 7808 3-terminal regulator (REG1) 1 W04 1A bridge rectifier (BR1) 1 5mm red LED (LED1) Capacitors 1 2200µF 25VW electrolytic 4 10µF 16VW electrolytic 2 0.1µF monolithic 2 .01µF 5kV ceramic (do not substitute with lower rating) 1 .0033µF ceramic 1 330pF ceramic 1 100pF ceramic Resistors (0.25W, 5%) 3 47kΩ 1 560Ω 1 22kΩ 1 270Ω 3 10kΩ 1 100Ω 1W 1 3.3kΩ 1 68Ω 2 1kΩ Receiver 1 PC board, code CE/MUSB/94, 137 x 117mm 1 12.6V power transformer (Altronics Cat. M-2853) 1 plastic case, 152 x 64 x 158mm 1 100µH inductor (L1) 1 3-core mains cord and moulded 3-pin plug 1 cordgrip grommet to suit mains cord maximum recovered signal to IC2. To set it, set volume control VR4 to a low setting and then advance VR2 until the 2 knobs 1 set of speaker terminals 2 50kΩ horizontal trimpots (VR1,VR2) 2 50kΩ log PC mount potentiometers (VR3,VR4) 3 plastic cable ties Semiconductors 1 4046 phase lock loop (IC1) 1 TL071 FET-input op amp (IC2) 1 TDA1520 power amplifier (IC3) 1 BC327 PNP transistor (Q1) 1 BC558 PNP transistor (Q2) 1 BC548 NPN transistor (Q3) 2 1N914 signal diodes (D1,D2) 1 12V 1W zener diode (ZD1) 1 W04 1A bridge rectifier (BR1) 1 5mm yellow LED (LED1) 1 5mm green LED (LED2) 1 5mm red LED (LED3) Capacitors 1 2200µF 25VW electrolytic 1 1000µF 16VW electrolytic 1 100µF 25VW electrolytic 3 47µF 16VW electrolytic 2 10µF 16VW electrolytic 3 0.47µF monolithic 4 0.1µF monolithic 2 .047µF ceramic 1 .022µF ceramic 2 .01µF 5kV ceramic 2 .0047µF ceramic 2 .0033µF ceramic 1 .001µF ceramic 1 680pF ceramic 1 330pF ceramic 1 100pF ceramic 1 68pF ceramic Resistors (0.25W, 5%) 1 220kΩ 1 6.8kΩ 1 120kΩ 1 1.5kΩ 2 68kΩ 1 1kΩ 2 47kΩ 1 470Ω 2 33kΩ 1 270Ω 6 22kΩ 1 100Ω 1 12kΩ 1 10Ω 2 10kΩ Miscellaneous Scrap aluminium for heatsink (30 x 20 x 5mm), solder, hook-up wire. signal is overloaded. Finally, back off the trimpot to obtain a distortion-free SC signal. May 1995  37 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au Now you can practice your guitar at any time by using this low cost Guitar Headphone Amplifier. It provides ample power for headphones so that you can play to your heart’s content without disturbing the rest of the household or your neighbours. By JOHN CLARKE Build this guitar headphone amplifier Guitarists usually have their own amplifier and loudspeaker system but it is not always convenient to set it up when you want to practice on your own. Alternatively, you may not wish to disturb other memb­ers of your household. This is where this Guitar Head­phone Amplifier comes into play (pun intended). Capable of providing an output of one watt, it will deliver ear-splitting sound without disturbing anyone nearby. The Guitar Headphone Amplifier is housed in a small plastic case which clips onto your belt. It is powered from a 12VAC plugpack, so that you can play for as long as you like without fear of flattening batteries. The controls are simple and consist of an on/off switch and a volume control – just plug in your guitar and head­phones, adjust the volume and play. Note that while the amplifier is specified for use with 8-ohm stereo headphones, higher impedance types will also be quite satisfactory. How it works The circuit for the amplifier is shown in Fig.1. It uses the well-proven National Semiconductor LM386 amplifier (IC1) to drive the headphones directly. A 3-terminal regulator sets the supply voltage at 13.5V DC. Signal from the guitar is directly coupled to the 10kΩ volume control (VR1) and then AC-coupled to the non-inverting input of IC1 at pin 3. Additionally, the AC coupling minimises any offset at the output of the amplifier which will reduce the useable peak to peak Spec ificatio Power ns Output 0.9W in to a 16 -ohm lo Freque ad ncy Re sp -3dB po ints at 3 onse 0Hz an Total H d 70kH a z Typicall rmonic Disto rtion y less than .0 graph) 4% (se e Signalto-Nois 78dB e Ratio u 20kHz) n w e ig h t e d ( 20Hz to output; with respect 81dB A to the sam -weighte rated e cond d unde itions r Input s ensitiv ity 50mV; 10kΩ in put imp edance May 1995  41 +13.5V PARTS LIST 1 PC board, code 01305951, 60 x 70mm 1 front panel label, 125 x 65mm 1 plastic utility box, 130 x 68 x 41mm 1 belt clip 1 12VAC 5W plugpack with 2.5mm DC plug 1 stereo 6.5mm unswitched panel socket 1 mono 6.5mm unswitched panel socket 1 DC panel socket with 2.5mm pin 1 SPDT toggle switch (S1) 1 10kΩ log pot (VR1) 1 500Ω miniature horizontal trimpot (VR2) 1 knob 1 heatsink, 19 x 19 x 9.5mm 1 3mm screw & nut 1 40mm length of shielded cable 1 100mm length of yellow hookup wire 1 50mm length of red hookup wire 1 50mm length of blue hookup wire 1 20mm length of 0.8mm tinned copper wire 13 PC pins or stakes Semiconductors 1 LM386N-1 power amplifier (IC1) 1 LM317T 3-terminal adjustable regulator (REG1) 1 W04 1A 400V bridge rectifier (BR1) 1 1N4004 1A diode (D1) 100 GUITAR INPUT 0.22 VOLUME VR1 10k LOG 22 16VW 3 6 12VAC INPUT 1 7 47 16VW 4 0.1 330  IC1 LM386 2 POWER S1 8 5 470 16VW 16  L OAD OUTPUT .047 10  D1 1N4004 BR1 W04 REG1 LM317T IN 1000 25VW OUT ADJ 120  +13.5V 10 16VW 1k VR2 500W AO I GUITAR HEADPHONE AMPLIFIER Fig.1: the circuit is based on the well-proven LM386 power ampli­fier IC and drives the stereo headphones in series (16-ohm load) for optimum power and distortion performance. voltage. The pin 3 input impedance is 50kΩ and so the 0.22µF capacitor rolls off signals below 15Hz. The 0.1µF capacitor at pin 2 grounds this inverting input. The AC gain of the amplifier is set to 60 by the 330Ω resistor between pins 1 and 8 while the 22µF capacitor ensures that the DC gain is zero. The amplifier is internally biased so that its output at Capacitors 1 1000µF 25VW PC electrolytic 1 470µF 16VW PC electrolytic 1 100µF 16VW PC electrolytic 1 47µF 16VW PC electrolytic 1 22µF 16VW PC electrolytic 1 10µF 16VW PC electrolytic 1 0.22µF MKT polyester 1 0.1µF MKT polyester 1 .047µF MKT polyester Resistors (0,25W 1%) 1 1kΩ 1 120Ω 1 330Ω 1 10Ω Miscellaneous Pair of 8-ohm stereo headphones, heatsink compound, solder, etc. Fig.2: the power versus distortion characteristic of the head­phone amplifier. Distortion is typically below .04% at 1kHz. 42  Silicon Chip HEADPHONES POWER S1 VR2 10uF .047 10 REG1 LM317 1k 470uF 100uF 22uF 47uF 25VW IC1 LM386 330  120  1000uF 1 VR1 0.22 0.1 D1 BR1 POWER SOCKET GUITAR INPUT Fig.3: this is the component overlay for the PC board. Note that the 10kΩ volume control pot is secured to the board & not to the front panel. pin 5 sits at half the supply voltage for maximum output swing. Hence, a DC blocking capacitor of 470µF is required to couple the output signal to the 16-ohm load. This ca­pacitor rolls off frequencies below 21Hz. Power supply ripple rejection is vastly improved by including the 47µF capacitor between pin 7 and ground, while a 100µF capacitor is used to decouple the power supply pin (pin 6) to ground. A Zobel network comprising a .047µF capacitor and a 10Ω resis­tor connects to the amplifier output to prevent high frequency oscillation. Note that the stereo headphone socket is wired with the normal common ground connection open circuit. That is, the tip connection goes the amplifier output, the ring connection goes to ground and the sleeve connections is open-circuit. This effec­tively connects both 8Ω headphones in series to give a 16Ω load which enables much better performance in terms of power output and distortion than the LM386 is capable of into 8Ω or 4Ω loads. This series connection of the headphones also means that they are correctly in phase to give a centred sound image. As noted above, power for the circuit is derived from a 12V 300mA AC plugpack. Switch S1 applies power while the bridge (BR1) rectifies the AC. The resulting DC is filtered using a 1000µF capacitor. REG1 is an adjustable 3-terminal regulator which is set by trimpot VR2 to provide 13.5V DC. Construction Most of the components are mount­ed on a PC board coded 01305951 and measuring 60 x 70mm. The PC board mounts in the integral side clips of a plastic box measuring 130 x 68 x 41mm. We designed a front panel label measuring 125 x 65mm for the lid. Begin construction by inspecting the PC board for any de­fects in the copper pattern and, if necessary, make any repairs before fitting components. Start by installing PC pins The PC board clips into the bottom of the case. Note the small heatsink for the LM317 regulator. The unit is powered from a 12VAC plugpack. at the external wiring points, then fit the wire link and the resistors. This done, fit trimpot VR2, IC1, BR1 and diode D1. Be sure to orient IC1, D1 and BR1 correctly as shown on the overlay diagram. Install the capacitors next, taking care with the electrolytic capacitors which must be inserted with the correct polarity. Heatsinking The LM317 (REG1) is mounted onto a small heatsink using a nut and bolt to secure them to the PC board. Apply a smear of heatsink compound between the mating surfaces before mounting. VR1 mounts directly onto the PC board with the terminals solder­ing to the PC RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 Value 1kΩ 330Ω 120Ω 10Ω 4-Band Code (1%) brown black red brown orange orange brown brown brown red brown brown brown black black brown 5-Band Code (1%) brown black black brown brown orange orange black black brown brown red black black brown brown black black silver brown May 1995  43 on the case and clip the PC board into the box. Wire up the input socket to the PC board using shielded cable and use hook-up wire for the remaining wiring. Now attach the adhesive label to the front panel and drill the hole for the volume pot. You may also need to cut the shaft to length so that the knob will sit flush with the lid. Testing Apply power to the circuit and measure the voltage between a GND PC pin and the metal tab of REG1. Adjust Fig.4: this is the full-size etching pattern VR2 for a reading of +13.5V for the PC board. Check your board DC. Final testing can be done carefully for defects before installing with the guitar and head­ any of the parts. phones connected. Connect the lid to the case using the pins. Also solder the body of the pot four self-tapping screws and to the two adjacent PC pins located attach the knob. near the edge of the board to earth Now you can practice your the pot body and to aid in anchoring guitar without disturbing others, it in position. no matter what time it is. Note Drill holes in the plastic case for the that while any stereo headphones power switch (S1), the headphone and can be used, the best bass will be input sockets, and the power input obtained with those that fully socket. Holes will also be required for enclose the ears with well-fitting SC the belt clip. Mount these components surrounds. GUITAR INPUT 12VAC INPUT + MIN MAX VOLUME GUITAR HEADPHONE AMPLIFIER HEADPHONE POWER ON OFF Fig.5: the full-size front panel artwork. 20 Electronic Projects For Cars On sale now at selected newsagents or order your copy from Silicon Chip Yes! Please send me ___ copies of 20 Electronic Projects For Cars Enclosed is my cheque/money order for $­________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. Price: $8.95 (plus $3 for postage if ordering from Silicon Chip). Order by phoning (02) 979 5644 & quoting your credit card number; or fax the details to (02) 979 6503; or mail the coupon to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. 44  Silicon Chip Signature­­­­­­­­­­­­_________________________ Card expiry date_____/______ Name _________________________Phone No (_____)_____________ PLEASE PRINT Street ___________________________________________________ Suburb/town _____________________________ Postcode_________ SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au REMOTE CONTROL BY BOB YOUNG A 16-channel decoder for radio control This decoder is intended to be used with the 8-channel decoder published last month to give a total of 24 channels. It plugs into the 8-channel board and the piggyback AM receiver to give a very compact 24-channel receiver. The 16-channel expansion PC board is the third in the set for the Mk.22 receiver and in the following description will be termed PC board 3. The receiver board will be referred to as board 1 and the 8-channel decoder as board 2. To fit this expansion board to an existing 8-channel Mk.22 receiver, a new case bottom is required. The case lid remains the same although two additonal “U” shaped slots must be filed in the lid to accommodate the grommets for the first 8 channels which must now be on fly leads (see Fig.1). If the original 8-channel decoder has PC header pins for the servo connectors, these must be replaced with flyleads as there is no access to the PC pins once the third board is in place. The expansion port connector may also need to be fitted in addition to any missing servo connectors. The photograph of Fig.2 shows two prototype receivers, one 8-channel and the other a 24-channel. Note the lack of cover on the third PC board to highlight the similarity in receiver sizes. There is a surprisingly small difference in the size of the two receivers. The overall height of the 24-channel receiver is 39mm as against 29mm for the 8-channel receiver. The photo of Fig.3 shows the same 24-channel receiver with the cover removed. Note the location of the crystal and the 4-way header connector used to mate the receiver board to the 8-channel decod­er. The polarised servo connector access holes have not been punched in this case yet and the crystal access hole will not appear in the production 24-channel case. To show the progress in design over the years, the photo of Fig.4 shows an original 24-channel receiver supplied by Silver­ tone Electronics in about 1980. Note the large size and the original Mk.14 receiver module. NEW SLOTS PCB 1 PCB 2 PCB3 Circuit description If you wish to follow the circuit description, then I suggest you will also need to refer to page 71 of the April 1995 issue of SILICON CHIP. The basic circuit of Fig.5 consists simply of two additional shift registers (IC2 and IC3), with data, clock and enable being derived from PC board 2. The +4.8V and GND terminals are separate pads which are intended as the power input for the full 24-channel system with all 24 servos fitted. A “Y” lead made out of normal servo leads would not be at all adequate here, for the total current consump­tion of 24 servos could run up to 8A or more, if many servos were to switch simultaneously. The running current of a standard servo is about 100-150mA, so it is really only the start-up current that concerns us here. Fig.1: this exploded diagram shows how the three boards are assembled into the case. PCB1 is the receiver, PCB2 the 8-channel decoder & PCB3 the 16-channel decoder. These two inputs are connected directly to the servo power rails and power distribution to the 16 servos associated with this PC board is direct to the servos through TB11-26. TB27, the expansion port, provides May 1995  53 Fig.2: this photo shows two prototype receivers, one 8-channel & the other a 24-channel. Note the lack of cover on the third PC board to highlight the similarity in receiver sizes. the incoming data, clock and enable signal, as well as providing power to the receiver (PC board 1) and the 8-channel board (PC board 2). Resistors R19-R35 and capacitors C17-C32 form the noise filter networks (referred to last month) for the servo leads. R34 is a zero-ohm resistor and is used only as a jumper. C33 is a bypass capacitor for the power rail. In operation, the last channel (channel 8) on PC board 2 (IC1) is used as the data pulse for IC2 and is fed to pins 1 & 2 through jumper R34. The clock line is fed directly to pin 8 on each 74HC164 and the chip enable signal is again applied directly to pin 9 on both ICs. This voltage is derived from R13 & C13 on PC board 2. Thus, all three shift registers are running on commoned clock and enable lines, with the last output on each 74HC164 providing the data input (pins 1 & 2) for the following chip. Provided the signal conditions are correct on pins 1, 2, 8 and 9, the clock Fig.3: this photo shows the 24-channel receiver with the cover removed. pulses will be clocked through the shift reg­isters and an output pulse (high) will appear at each of the output pins, with a duration which is directly proportional to the control stick location. If all 24 channels are being trans­mitted, the sync pulse detector (R10, C10) on PC board 2 sets the data pins 1 & 2 on IC1 high after Fig.4: this photo clearly demonstrates the progress in design over the years. It shows an original 24-channel receiver supplied by Silvertone Electronics in about 1980. Note the large size & the original Mk.14 receiv­er module. 54  Silicon Chip about 6ms and the count begins again from channel 1. If less than 24 channels are being transmitted, then the pulse output after the last transmitted channel will be the sync pause. For example, a 6-channel transmitter with an 8ms sync pause will generate a high pulse on the channel 7 output which will be 8ms wide. Channel 8 will be a repeat of channel 1, channel 9 a repeat of channel 2 and so on, until channel 14 which will again be the sync pause (8ms). The sequence will repeat again until channel 21 which is the next sync pause and from there to channel 24 which will be a repeat of channel 3. At this point, the sequence stops until the next sync pause resets data high on IC1 and the se­quence begins all over. As a result of this train of events, a 24-channel decoder can be tested with a 2-channel transmitter, in which case the sync pause will appear at every third channel output. As long as the output goes high for the correct amount of time, then you know the decoder is working. If less channels are installed in the receiver than in the transmitter, then the count will proceed in an orderly manner until the last clock pulse and then wait until the sync pause appears, which will reset the data on channel 1 high and the count begins again. In other words, all outputs after the last clock pulse will remain low. Thus, a 7-channel receiver with a 16-channel transmitter will only give outputs on the first seven channels. As you can see from the foregoing, there does not need to be any compatibility between the channel counts on the transmit­ter and receiver. Any receiver will work on any transmitter as long as both are AM. The only difficulty that may arise is that the sync pause in some commercial brands of transmitters may be shorter than the time constant on the sync separator (R10, C10 on PC board 2). In this case, reduce the value of C10 until the correct time constant is arrived at. The waveshapes at the various key points on PC board 3 are all repeats of the waveshapes pictured last month. Pins 1 & 2 on IC2 receive the output of channel 8 which corresponds to Fig.5 on page 72 of the April issue. Pins 1 & 2 on IC3 receive the output of channel 16, so it is similar again to the preceding oscilloscope trace. The May 1995  55 R34 0 14 O3 O2 O1 O0 6 5 4 3 R19 1k R20 1k R21 1k R22 1k C32 .001 C17 .001 C18 .001 C19 .001 C20 .001 C21 .001 C22 .001 R25 1k C23 .001 R26 1k R24 1k R23 1k SILVERTONE MK22 24 CHANNEL DECODER 7 10 IC2 O4 1 74HC164 11 O5 A 12 2 B O6 13 O7 9 MR Fig.5: the 16-channel expansion board circuit consists simply of two additional shift registers, IC2 and IC3, with data, clock and enable being derived from the 8-channel decoder described last month. EXPANSION TB27 8 CLK CHANNEL 16 TB11 CHANNEL 15 TB12 CHANNEL 14 TB13 CHANNEL 13 TB14 CHANNEL 12 TB15 CHANNEL 11 TB16 CHANNEL 10 TB17 CHANNEL 9 TB18 14 O2 O1 O0 5 4 3 7 6 O3 10 IC3 O4 1 74HC164 11 O5 A 12 2 B O6 13 O7 9 MR 8 CLK C33 47 R35 1k R33 1k R32 1k R31 1k R30 1k C26 .001 C31 .001 C30 .001 C29 .001 C28 .001 C27 .001 R29 1k C25 .001 R28 1k C24 .001 R27 1k CHANNEL 24 TB26 CHANNEL 23 TB25 CHANNEL 22 TB24 CHANNEL 21 TB23 CHANNEL 20 TB22 CHANNEL 19 TB21 CHANNEL 18 TB20 CHANNEL 17 TB19 GND +4.8V TB11 TB12 TB13 TB14 TB15 TB16 TB17 TB18 TB27 J1 1 C32 IC3 74HC164 IC2 74HC164 R34 R26 C23 C21 C22 R25 R23 R24 C20 C19 R22 R21 C18 C17 R19 R20 J5 TB26 1 R35 TB25 J2 C31 R33 C29 C30 R32 C28 R31 R30 C27 R29 C26 C25 R28 C24 R27 C33 +4.8V GND TB19 TB20 TB21 TB22 TB23 TB24 Fig.6: both sides of the PC board are shown here. Note that C33, a tantalum capacitor, is quite large & must be laid on its side, as shown in Fig.7. clock pin (pin 8) on both IC2 and IC3 should correspond to Fig.3 from last month. The enable pin (pin 9) on each IC will again have a DC voltage with a shallow ripple. This voltage should be in the order of +4.5V. One final point on the servos themselves: servos designed for modelling applications are usually designed around a 14-20ms repetition (frame) rate and the pulse stretching capacitor in the servo is chosen accordingly. With all 24 channels being transmitted, the frame rate will be somewhat longer. The worst case will be with all channels at extreme width, which gives a frame rate of (24 x 2) + 8ms = 56ms. Some servos may begin to slow down at this frame rate and the pulse stretching capacitor must be increased to compensate. Assembly Begin by setting up the polarity of the servo rails. As delivered, the PC board is set up as centre-pin positive, which suits such sets as Futaba, JR and Hitech. To reverse the polarity of the system, simply cut the thin tracks connecting the compon­ ent supply rails to the power rails as shown in the component wiring diagram of Fig.6. This shows both sides of the PC board. There are small pads situated alongside the power rails for this purpose. Reconnect the supply rails to the power rails using 10A fuse wire or a thin component leg. Note that one pad is located on the top layer and the other on the bottom layer. Remember here that the same must be done to the 8-channel decoder PC board to keep 56  Silicon Chip the whole system compatible. Be sure to mark the finished receiver clearly, positive or negative centre-pin, when you have finished the receiver. Begin the assembly by tinning a single pad for each surface mount component as usual and mount all of the resistors and capacitors on the busy side of the board. When this is complete, turn the PC board over and place the two ICs and the three 1206 packages on the reverse side. Next, mount the required number of servo connectors in the appropriate locations. Once again, these are mounted from the busy side of the PC board with the plastic on the busy side and the long section of the servo pins going through the PC board. Solder the pins on the IC side of the PC board and snip them off flush. Now remove the plastic from the pins and you have a set of pins the correct length for servo connectors. You can build this PC board with only eight Receiver & Decoder Kit Availability Receiver PC board (double-sided with plated-through holes) ..........$11.50 Basic receiver kit: all parts except crystal .........................................$45.00 Built & tested AM receiver less crystal .............................................$59.00 Decoder PC board (double-sided with plated-through holes) ..........$11.50 8-channel decoder kit: all parts less servo pins or connec­tors .........$32.00 Built & tested 8-channel decoder but less servo plugs ....................$45.00 Expansion kit: all components to build the 16-channel decoder ......$42.00 Built & tested 16-channel decoder less servo connectors ...............$55.00 8-channel receiver case (includes labels) ........................................$11.50 16-channel receiver case (includes labels) ......................................$19.50 Machine wound RF coils ....................................................................$2.95 Machine wound IF coils ......................................................................$2.95 Crystals (AM) per pair ......................................................................$17.95 Servo header pins (each) ...................................................................$0.12 Futaba Ext lead ..................................................................................$3.40 J.R. Ext lead .......................................................................................$3.40 Sanwa Ext lead ..................................................................................$3.40 Notes: (1). When ordering crystals, do not forget to specify frequency. (2). All orders should add $3.00 for postage and packing. Payments may be made by cheque, money order, Bankcard, Visa Card or Mas­tercard. Send all orders to Silvertone Electronics, PO Box 580, Riverwood, NSW 2210. Phone (02) 533 3517. Fig.7: this photo shows the completed 16-channel expansion PC board from the servo connector side. Note the tantalum capacitor (C33) which must be laid over on its side. Fig.8 (right): this view shows the completed 24-channel receiver with the receiver deck removed. The receiver plugs into the 8-channel decoder board & this in turn plugs into the 16-channel decoder which sits in the bottom of the case. channels, in which case delete IC3 and all its associated components. Next, mount the 5-pin expansion socket which mounts on the opposite side of the PC board to the servo pins. Finally, mount the 47µF capacitor C33. This component must lay flat against the PC board, so bend its legs at right angles as close as possible to the capacitor body, taking care not to go too close to the enamel in order to avoid breaking the seal on the legs. Be careful to ensure the correct polarity before bend­ing. This completes the component assembly. Unfortunately, I had to use four jumpers on this PC board because of the lack of space. These must now be added. Use the wire-wrap wire supplied for J1 and J2 and the 5A hook-up wire for the two power rail jumpers J3 and J4. There are pads provided for J1 and J2 but J3 and J4 are soldered direct to the power rails. Finally, solder the two lengths of 8A hook-up wire into the power input pads, red for positive and black for negative (ground). Do not forget to reverse the order of these wires in the power input pads if Sanwa, KO or other centre-pin negative servos are to be used. Make sure here that the appropriate changes have already been made to the supply rails as described above. Fit the 8A connector provided, red closest to the triangular side of the housing and using the pins in this housing. That completes the assembly of the PC board. Testing Using a pre-tested receiver and 8-channel decoder, plug the 16-channel PC board into the expansion socket with the assembly out of the case. Great care must be exercised here to ensure the PC boards do not touch. A piece of cardboard inserted between the two will prevent shorts. Better still, make up an extension lead to separate the two PC boards so that you can work a lot more easily on both sides of the board. Switch on the transmitter and receiver and check the waveshapes at pins 1, 2, 8 and 9 on each IC and compare them with the oscilloscope photos in last month’s issue. Next, check each servo output and compare them with Fig.5 (last month). All 16 outputs should be more or less identical if a 24-channel transmitter is used. If a lesser number of channels is transmit­ted, see the above circuit description of where the sync pause will appear at the servo outputs. Do not plug a servo into this channel, as it will drive the servo hard against the gear stops and damage the servo gears. If you are using a transmitter with less channels than the receiver, be sure to cover these outputs to prevent accidentally plugging a servo into these channels. If all channels are working, it remains only to clip the three PC boards into the case bottom and the unit is complete. Debugging follows the same general pattern as that described last month. This PC board is very simple and few problems should be encountered if care is taken during assembly. The photo of Fig.7 shows the completed 16-channel expansion PC board from the servo connector side. The photo of Fig.8 gives an excellent view of the completed 24-channel receiver with the receiver deck removed. The original case lid is used but two additional slots must be filed into the case side to accommodate the grommets for the servo leads on PC board 2, which come out of the case side – see Fig 1. Congratulations, you now have a SC working 24-channel receiv­er. May 1995  57 BUILD AN FM RADIO TRAINER; PT.2 This second article on the FM Radio Trainer describes the construction & alignment. You do not need any special equip­ment for the job – just a soldering iron, multimeter, trimming tool & a simple alignment oscillator which you build yourself. By JOHN CLARKE The construction of the FM Radio Trainer includes the PC board assembly plus some coil winding. There is also a small amount of wiring to be installed on the underside of the PC board for the loudspeaker and volume control. To simplify construction, the board has a screen printed overlay to show 58  Silicon Chip the positions for the components – see photo. All you have to do is install the parts according to this overlay or you can follow Fig.8(a) which is a conventional parts layout diagram. As well as the usual parts, there are also four shield pieces soldered to PC stakes on the top of the board. These pro­ vide shielding for the tuned RF amplifier and mixer stages (Q1 & Q2). These shields are made from 19mmwide blank PC board materi­al. In addition, two baffles made from 25mm-wide PC board mate­rial are soldered to the underside of the board, adjacent to the loudspeaker. These enclose the loudspeaker along the edges of the board to improve the bass response. PC board assembly Before starting construction, it is a good idea to check the PC board for any shorts or breaks in the copper tracks. Repair any faults that you do find (generally, there will be none), then check the hole sizes as set out below. First, check that a pattern of 0.6mm holes has been drilled for the loud- SPEAKER 9V BATTERY HOLDER OFF 470uF SPEAKER +9V 10  .01 TP3 .01 +9V TP2 5.6k 5.6k ON S1 TP GND 100pF D2 1uF A VR1 B .0068 C 1 470uF IC4 1k 390pF 100uF 8.2k 68  47k 56pF .01 Q4 75  +9V 100  100  IC3 +9V TP GND .01 1 T1 100k 1uF .01 VC5 10pF .01 VC4 .01 Q3 3.9pF +9V +9V .01 10k VC3 39pF VC1 1k 47pF L1 TUNING SHIELD 27k 75  ANTENNA ANTENNA TP1 4.7pF L3 VC2 56pF 220pF .01 Q1 10k 47  330  RF1 18k L2 560  +9V 10k 470k .01 47W RF2 10k SHIELD 82pF .01 Q2 330  +9V 47k .01 SHIELD 68pF .01 47  +9V 330pF +9V 1 18k SHIELD IC1 .01 .01 T2 XF1 T3 .01 IC2 .01 .01 +9V 100  +9V SILICON CHIP FM RADIO TRAINER 100k .01 .01 270k +9V .01 330  Fig.7 (right): this is the pattern that’s screened onto the top of the PC board.The dotted lines connected to two of the terminals on the tuning gang (VC1/VC3) are actually tracks on the PC board. They are shown here so that you can see how the tuning gang is connected to the rest of the circuit. Note: pattern shown 67% of actual size – the full size pattern measures 563 x 115mm. VOLUME 47  .01 VC6 +9V 1 T4 TP4 1k 390pF 10uF 10  D1 .047 speaker and that 6.5mm holes have been drilled for the volume and tuning controls. The spindle hole for the VC1/VC3 tuning gang should be 7mm in diameter, the corner mounting screw holes should be 3mm in diameter, and the holes for the antenna PAL socket, switch S1 and the battery holder should be 2.5mm in diameter. Finally, check that 1.5mm holes have been drilled to accept the base and can pins of T1 and T4. You can do this by test fitting these two components. In most cases, the holes will all be correct but, if not, enlarge any undersize holes as necessary using the appropriate size drill bit. Once you are satisfied that all the hole sizes are correct, begin the assembly by installing PC stakes at the six shield mounting points, at test points TP1-TP4 & TP GND, and for the antenna socket earth – see Fig.8(a). This done, install the resistors at the locations indicated. Table 1 shows the resistor colour codes but it is also a good idea to check each resistor using a multi­meter, to make sure that you have the correct value. Diodes D1 and D2 can now be installed, followed by varicap diode VC1 and ceramic filter XF1. Make sure that the diodes are all correctly oriented (XF1 can go in either way around). VC1 has a similar appearance to D1 and D2, so be careful not to get them mixed up. Note also that D1 and D2 are specified May 1995  59 60  Silicon Chip TUNING VC3 VC1 39pF L1 1k RF1 27k 18k Q3 10k 560  .01 .01 47  L3 VC4 82pF .01 47  .01 VC5 1 T1 1uF .01 47k 330pF .01 68pF 10pF 330  Q2 SHIELD 10k RF2 4.7pF 10k SHIELD 470k TP1 VC2 3.9pF 330  .01 220pF Q1 L2 56pF .01 .01 47  18k TP GND 100k .01 1 .01 IC1 1 00  SHIELD 1 .01 T3 1 .01 1 IC2 .01 .01 1 .01 IC3 100  SILICON CHIP FM RADIO TRAINER T2 2 2 XF1 100  .01 .01 47  VOLUME VC6 Q4 56pF .01 75  330  .01 270k 100k 68  1 T4 .0068 GND Fig.8(b): this is the etching pattern for the PC board, shown here 67% of actual size. Check your finished board carefully against this pattern for possible etching defects before installing any of the parts. 1uF D2 8.2k TP4 TP 47k D1 100pF 100uF Fig.8(a): follow this parts layout diagram in conjunction with the layout pattern on the PC board when installing the various parts. Take care to ensure that all polarised parts are correctly oriented & keep all component leads as short as possible. The volume control (VR1) connects to points A, B & C to the left of IC4. 75  ANTENNA 47pF ANTENNA SHIELD 10k 5.6k .047 TP3 .01 .01 TP2 SPEAKER 470uF 10  10uF 5.6k 470uF 1k IC4 B C 1 10  VR1 A 390pF 390pF 1k ON S1 OFF SPEAKER 9V BATTERY HOLDER 5T 10T installed from the copper side of the PC board. Short lengths of tinned copper wire are then used to connect the tuning gang terminals to the PC board. Tuning dial 9mm By now, the PC board assembly will be substantially L1, L2, L3 1 : 2 com­ pleted, with only the 4.5T 0.8mm DIA ENCW T2 AND T3 coils, transformers and a few ON 5mm DIA MANDREL 0.25mm DIA ENCU WIRE ON sundry items to be installed. PHILIPS 4313 020 40031 BALUN CORE Before going further though, the tuning dial label should be fitted to the tuning wheel. To do this, first cut the label out in a neat circle CT using a pair of scissors, then 1 3mm 6 cut a neat central hole with a sharp utility knife. This 2mm done, remove the backing 2 5 sheet and fit the label over 56 5 the large spindle of the dial 1 with the numbers facing 4 3 1 the PC board (do not stick it down yet). 2 Next, secure the tuning BASE DIAGRAM TOP VIEW wheel to the tuning capacitor shaft with its screw and rotate it fully clockwise. The label should now be carefully 3 4 3 4 aligned so that “88” lines T1 T4 WINDINGS: PINS 4-5, 4T, WINDINGS: PINS 1-2, 30T, up opposite the edge of the 0.25mm DIA ENCU WIRE 0.125mm DIA ENCU WIRE. board. Now rotate the dial PINS 1-3, 30T, 0.125mm PINS 5-6, 10T BIFILAR, 0.25mm DIA ENCU WIRE fully in the opposite direcENCU WIRE. PIN 4-CT, 6T, 0.25mm DIA ENCU tion and check that “108” is WIRE WOUND OVER WINDING 1-2 now indicated. Fig.9: follow these winding diagrams & the instructions in the text carefully when If everything lines up making up the coils & IF transformers. In particular, make sure that all windings are correctly, stick the label to wound in the direction shown. the tuning wheel at the edges, then remove the tuning in the parts list as 1N4148s but you overdo it, otherwise you could dam- wheel and complete the job. Finally, can also use 1N914s. age the lead connections inside the re-attach the tuning wheel to the shaft. The four ICs can now be installed transistor. Coils on the board. These must be installed The remaining transistor (Q3 – with the notched ends oriented ex- BF199) is installed with the flat side Fig.9 shows the coil winding details. actly as shown on the overlay. Make of its body towards the tuning gang. The three air-cored coils, L1-L3, are sure that IC4 is the LM386 audio Splay its base lead so that it will fit identical and are made by winding amplifier. comfortably into the holes provided 4.5 turns of 0.8mm diameter enamThe next step is to fit the capacitors. and, as with the Mosfets, push it down elled copper wire onto a 5mm drill Table 2 lists the codes for the low-val- as far as it will comfortably go before bit. Before winding, stretch the wire ue polyester and ceramic types. The soldering its leads. slightly by clamping one end in a vyce electro­ lytic types are all polarised The two RF chokes, RF1 and RF2, and pulling the other end with a pair and must be oriented as shown on each consist of a short length of tinned of pliers. the overlay. copper wire which passes through the Be sure to wind these coils in the Once the capacitors are all in, you middle of a ferrite bead. Install these direction shown. If the coils are wound can install the three Mosfets (Q1, Q2 & now, then fit the three trimmer capac- in the wrong direction, they will not Q4). Each of these devices is installed itors (VC2, VC4 & VC6). VC2 and VC4 fit the holes in the PC board. with its metal tab towards the battery will have the same body colour, while After winding, install the coils on holder. Push each device down onto VC6 will be the odd one out. the board (push them all the way the board as far as it will comfortably The VC1/VC3 tuning gang is down) and trim their leads so that they go before soldering its leads but don’t mounted using two screws which are protrude through the board by about May 1995  61 This close-up view shows how the shield pieces are installed on the top of the PC board, around the RF amplifier & mixer stages. These shield pieces are supported by soldering them to PC stakes. 2mm. Note that the enamel insulation on the leads must be removed before they can be soldered. This can be done by applying heat from your soldering iron until the enamel melts, after which the leads can be soldered in the normal manner. Transformers T2 and T3 are wound onto the balun formers. These formers are oval in cross section and contain two holes. Begin by tightly winding 5 turns of 0.25mm ENCW on one former, making sure that both ends exit from the same side. Mark this side with a “1” using a lead pencil, then wind 10 turns of 0.25mm ENCW from the other side of the balun and mark this side with a “2”. The other balun is wound in identical fashion. After that, the two baluns can be installed on the PC board with the correct 1:2 and 2:1 ratios, as shown on Fig.8(a). Transformer T1 is made by winding two coils onto a minia­ture Neosid former. To wind this coil, first push the former into its 6-pin baseplate, then solder one end of the 0.125mm ENCW to pin 3 (see Fig.9). Now, starting from the bottom of the former, wind on 30 turns in the direction shown, with each turn adjacent to the previous turn (ie, the coil is close-wound). This done, terminate the free end of the winding on pin 1. The top winding is positioned 3mm above the bottom winding and consists of 4 turns of 0.25mm ENCW. Start by terminating one end of the wire to pin 5, then wind on four turns in the direc­tion shown and terminate the free end on pin 4. Finally, install the F29 screw core in the former. Transformer T4 is somewhat more complicated to wind than T1, so we’ll go through the procedure step-by-step. Begin by close-winding 30 turns of 0.125mm ENCW between pins 2 and 1 (note: this winding goes in the same direction as the 30-turn winding on T1). This done, connect a length of 0.25mm ENCW to pin 4 and wind 6 turns over the previous 30-turn winding as shown. Place some insulation tape over this winding to prevent it from unravelling. The top winding on T4 is bifilar wound; ie, it is wound using two lengths of wire that have been twisted together. To do this, first cut two 150mm lengths of 0.25mm ENCW, place them next to each other and clamp one end of each wire in a vyce. Secure the other ends of the wires in Table 1: RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  1 ❏  2 ❏  2 ❏  1 ❏  2 ❏  4 ❏  1 ❏  2 ❏  3 ❏  1 ❏  3 ❏  3 ❏  1 ❏  4 ❏  2 62  Silicon Chip Value 470kΩ 270kΩ 100kΩ 47kΩ 27kΩ 18kΩ 10kΩ 8.2kΩ 5.6kΩ 1kΩ 560Ω 330Ω 100Ω 75Ω 47Ω 10Ω 4-Band Code (1%) yellow violet yellow brown red violet yellow brown brown black yellow brown yellow violet orange brown red violet orange brown brown grey orange brown brown black orange brown grey red red brown green blue red brown brown black red brown green blue brown brown orange orange brown brown brown black brown brown violet green black brown yellow violet black brown brown black black brown 5-Band Code (1%) yellow violet black orange brown red violet black orange brown brown black black orange brown yellow violet black red brown red violet black red brown brown grey black red brown brown black black red brown grey red black brown brown green blue black brown brown brown black black brown brown green blue black black brown orange orange black black brown brown black black black brown violet green black gold brown yellow violet black gold brown brown black black gold brown the chuck of a hand drill, then wind the drill until there is about one twist every 2mm along the entire length. Next, solder one end of one lead to pin 5 of the base – see Fig.9. The other lead at this end goes to the centre-tap and can be stripped of the enamel insulation, so that it is ready to make the connection. This done, wind 10 turns onto the former in the direction shown, leaving a gap of about 2mm to the top of the previous winding. Once these turns have been wound on, you need to determine which free end goes to pin 6 of the former. This is done using a multimeter. Select a low “ohms” range, connect one probe to the already bared CT wire and measure the resistance to the free lead ends at the top of the coil. The end that gives a reading of zero ohms goes to pin 6, while the remaining lead goes to the centre-tap. Complete the winding by soldering all three CT leads to­gether, as shown in Fig.9. Trim off any excessive lead lengths here and push the CT connection as close to the former as possi­ ble, to ensure that it doesn’t end up shorting to the aluminium shield can. Cover the connection with insulation tape if neces­sary. Finally, complete the assembly by fitting the F29 screw core. T1 and T4 can be installed on the PC board, after which their shield cans can be installed. Make sure that the shield cans are centrally located over the formers and that they are pushed all the way down onto the PC board before soldering their pins. The loudspeaker is held in position using two copper wire straps which solder to the adjacent earth pattern on the PC board. Note the two baffle pieces. Installing the hardware Now that the coils are in place, the major hardware items can all be installed. Begin by mounting the external PAL antenna socket and note that its earth lug is soldered to an adjacent PC stake. The tuning control shaft is obtained by removing the cover, wiper and resistance sections from an old potentiometer. What remains is the pot shaft and its threaded bush. Cut the shaft to a length to suit the control knob, then install it from the underside of the PC board and secure it using a nut and starwasher. A round screw-on rubber foot is now pushed onto the underside of the pot shaft to provide a 3:1 reduction drive for the tuning wheel. The volume control potentiometer (VR1) is also installed from the under­ The reduction drive for the tuning wheel is made up using a control shaft & bush salvaged from an old potentiometer, together with a rubber foot which is simply pushed over the control shaft. side of the PC board (after first trimming its shaft). Fit the control knobs to the tuning and volume controls when they have been mounted. The volume control terminals are wired to points A, B & C on the PC board via a short length of 3-way rainbow cable. A short length of tinned copper wire should also be connected between the volume pot body and ground (the surrounding large copper area). This measure is necessary to prevent hum from being introduced into the amplifier when your hand is brought near the pot. The battery holder is secured in place using three 2mm screws and nuts. Do not forget to solder the battery terminals to the board. Switch S1 can then be mounted in position. Depending on the particular switch you are supplied with, you may need to bend its two outside terminals inwards slightly so that they line-up with the holes in the board. The loudspeaker is secured to the underside of the PC board (beneath its grille) using two thick (0.8mm) May 1995  63 Building The IF Alignment Oscillator This FM IF Oscillator generates a 10.7MHz square-wave signal & is used for aligning the IF stages of the FM Radio Trainer. It’s built on a small PC board, requires no adjustments & can be assembled in a few minutes. The circuit for the IF oscillator is based on a single high-speed (HC) CMOS NAND gate and a 10.7MHz ceramic filter. Fig.10 shows the details. IC1 is wired in a fairly standard oscillator configuration. One of its inputs, pin 9, is wired to the positive supply and so IC1 behaves as an inverter. It is biased in the linear mode using a 1MΩ feedback resistor between its pin 8 output and its remaining input (pin 10). the speci­fied 330Ω resistive load for XF1 because of the nominal 60Ω output impedance of IC1. The resulting 10.7MHz waveform at pin 8 is filtered using a 270Ω resistor and a 330pF capacitor to produce a reasonable sinewave signal. This is then fed to the output via level control VR1 and a .01µF capacitor. Although the nominal output frequency is 10.7MHz, it is in fact closer to 10.8MHz because of the phase characteristics of the ceramic filter. This 100kHz difference is of no consequence since the 10.7MHz ceramic filter used in the FM Radio Trainer has a bandwidth of 280kHz. Power for the circuit is derived from a 9V battery (eg, from the battery used in FM Radio Trainer or from a separate 9V battery). The 9V The 10.7MHz ceramic filter (XF1) is wired in parallel with the feedback resistor, along with a 15pF capacitor which provides the correct amount of capacitive loading. The associated 330Ω and 270Ω resistors provide the correct resistive loading for XF1. Note that the 330Ω resistor is AC-coupled to ground via a .01µF capacitor to prevent loading the DC voltages on pin 10. In addition, the 270Ω resistor at pin 8 is smaller than 15pF 56  1M 14 XF1 SFE10.7ML IC1 0.1 7 ZD1 4.7V 400mW +9V 0V 270  10 +4.7V 330  Fig.10 (right): this is the circuit for the IF alignment oscillator. It’s based on a single high-speed NAND gate IC (IC1) & a 10.7MHz ceramic filter. VR1 sets the output level, while ZD1 provides a regulated 4.7V supply to power the circuit. The completed PC board assembly is shown in the above photo. enamelled copper wire straps. These straps are soldered to the heavy earth track on the PC board (see photo). After mounting, connect the speaker terminals to the speaker pads on the PC board using a short length of figure-8 cable. Shield installation Refer now to the overlay diagram for the locations of the four blank PC board shield pieces. Three of these pieces are identical and measure 19 x 64  Silicon Chip 9 IC1 74HC00 8 270  330pF LEVEL VR1 1k .01 10.7MHz OUTPUT .01 70mm. Solder these to the PC stakes on the top of the board, taking care to ensure that their ends are all aligned about 2mm short of the edge of the main board. The 19 x 90mm shield piece is then soldered on the ends of these three shields. The two loudspeaker baffles are made from 25 x 90mm blank PC board material and are soldered to the underside the PC board as shown in one of the photos. This done, secure the six 25mm stand­offs to the underside of FM IF OSCILLATOR the PC board using 6mm-long x 3mm screws. Antenna Ideally, an external antenna should be used for best recep­tion and this can be plugged directly into the PAL socket. Alter­natively, if portability is a requirement, you can fit a tele­scopic antenna. The telescopic antenna used with the prototype has a hori­zontal hole drilled through the base of the unit. 15pF 0V 270  330  1M +9V 56  ZD1 XF1 .01 0.1 IC1 74HC00 270  330pF .01 VR1 OUTPUT GND 1 Fig.11(a): install the parts on the FM IF Oscillator board as shown here. Take care to ensure that IC1 is correctly oriented & insert PC stakes at the four external wiring points. The ceramic filter (XF1) can be installed either way around. Fig.11(b) at right shows the full-size etching pattern for the PC board. battery voltage is regulated to 4.7V using zener diode ZD1 and a 56Ω current-limiting resistor. Construction The FM IF Oscillator is built on a PC board coded 06304951 and measuring 76 x 39mm. Fig.11(a) shows the parts layout. Install the parts as shown, taking care to ensure that IC1 and ZD1 are both correctly oriented. PC stakes should be in­ stalled at the power supply and output wiring points, so that the unit can be easily connected to the receiver. To test the assembly, connect a 9V supply and check that the voltage across ZD1 is about 4.7V. If this is OK, PARTS LIST check that pin 8 is sitting at about 2.3V, as measured by a multimeter set to DC volts (note: this voltage represents the average level of the 10.7MHz signal from IC1). Alternatively, if a frequency meter is available, then the output can be directly checked for a 10.7MHz signal to ensure that the circuit is working correctly. CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ Value 0.1µF 0.01µF 330pF 15pF IEC 100n 10n 330p (n33) 15p EIA 104 103 331 15 1 PC board, code 06304951, 76 x 39mm 4 PC stakes 1 Murata SFE10.7ML ceramic filter (XF1) 1 1kΩ horizontal trimpot (VR1) Semiconductors 1 74HC00 high speed CMOS quad NAND gate (IC1) 1 4.7V 400mW zener diode (ZD1) Capacitors 1 0.1µF MKT polyester 2 0.01µF ceramic 1 330pF ceramic 1 15pF ceramic Resistors (0.25W, 1%) 1 1MΩ 2 270Ω 1 330Ω 1 56Ω 0.5W, 5% RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  1 ❏  2 ❏  1 Value 1MΩ 330Ω 270Ω 56Ω This is fitted with a 20 x 2mm screw and nut. Solder the nut in place to prevent it from coming loose, then bend the screw at right angles and feed it down the centre pin of the PAL plug (you will have to disassemble the PAL plug first). The antenna screw can now be clamped in position by doing up the plug’s anchor screw. Finally, reassemble the PAL plug, leaving out the top metal cable clamp section (this would short the antenna to the socket earth). 4-Band Code (1%) brown black green brown orange orange brown brown red violet brown brown green blue black brown 5-Band Code (1%) brown black black yellow brown orange orange black black brown red violet black black brown green blue black gold brown Another possibility is to leave the PAL socket out and use a telescopic antenna that can be bolted directly to the PC board. Initial tests Before installing the battery, check the assembly carefully to ensure that all parts are in their correct locations and are correctly oriented. The underside of the board should also be checked for missed solder joints and for shorts. Assuming that everything is correct, connect the negative lead of a multimeter set to 20V DC to test point TP1 and connect the positive lead to the positive battery terminal. If the bat­tery voltage drops by more than 1V when power is applied, switch off immediately and check the board for shorts or incor­ rect component orientation. Locate the source of the problem before switching on again. If nothing dramatic happens, you May 1995  65 The alignment oscillator is connected to the antenna input on the tuner board via two short wire links. Power for the oscillator is derived directly from the tuner board, although the actual connections (to the two PC stakes at top right) are not shown here. can proceed to make a series of voltage checks, as set out in Table 3. Note that these voltages are for guidance only and assume a 9V supply. They were measured on the prototype using a digital multimeter. If any measured voltages differ by more than 20% from the prototype, then there is probably an incorrectly placed component on the board. is 0.5mm below the top of can (use the trimming tool); (9). Adjust the core in T4 so that it is 4mm above the can; (10). Set VR1 fully anticlockwise for minimum volume. IF alignment The alignment procedure involves using the IF Alignment Oscillator de- Initial setup To minimise alignment adjustments, the circuit should ini­tially be set up according to the following procedure. Note that all adjustments to the trimmer capacitors and to the ferrite slugs in the coils must be carried out using a proper trimming tool. Do not use a screwdriver in the ferrite slugs, as this can easily crack them. Here is the initial setup: (1). Stretch coil L1 to 10mm; (2). Squeeze L2 to 8.5mm; (3). Squeeze L3 to 7mm; (4). Set VC2 to half mesh (ie, plates half open); (5). Set VC3 fully open (ie, plates fully out of mesh); (6). Set the trimmer capacitors on tuning gang VC1\VC3 to fully open; (7). Set VC6 to half mesh; (8). Adjust the core in T1 so that it 66  Silicon Chip TABLE 2: CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value .047µF .01µF .0068µF 390pF 330pF 220pF 100pF 82pF 68pF 56pF 47pF 39pF 10pF 4.7pF 3.9pF IEC 47n 10n 6n8 390p (n39) 330p (n33) 220p (n22) 100p (n10) 82p 68p 56p 47p 39p 10p 4p7 3p9 EIA 473 103 682 391 331 221 101 82 68 56 47 39 10 4.7 3.9 scribed in the accompanying panel. Its output is fed directly into the antenna input to the left of coil L1 on the FM receiver board. Don’t forget to connect the GND terminals of the two boards together as well (see photo). Power for the IF Alignment Oscillator can be derived di­rectly from the radio’s supply via a suitable length of hook-up wire. Alternatively, you can power the alignment oscillator from a separate 9V battery. Take care with the supply polarity. The step-by-step alignment procedure for the IF circuitry is as follows: (1). Apply power and connect a multimeter set to a low DC volts range between test points TP2 and TP3 (near the battery holder). Adjust trimpot VR1 on the IF oscillator for a multimeter reading of 1-3V. (2). Adjust the slug in T1 for a maximum reading, then adjust VC6 for a maximum reading. Note: at all times, make sure that the voltage does not go above 3V. Readjust VR1 if necessary. (3). Connect the multimeter between TP4 and TP GND (near the volume control) and adjust the slug in T4 for a 0V reading. (4). Reconnect the meter between TP2 and TP3 and readjust T1 and VC6. This done, reconnect the meter between TP4 and TP GND and readjust T4 for a 0V reading. (5). Remove the FM IF Oscillator board and attach the telescopic antenna to the PAL socket. That completes the alignment of the IF stages. The local oscillator and RF amplifier stages now require alignment. Only a few parts are mounted on the copper side of the PC board: the tuning assembly, volume control & loudspeaker. Note the short link that’s used to connect the body of the volume control pot to the adjacent earth track. TABLE 3: VOLTAGE CHART Device Expected Voltages Q1 G1 = 0V; G2 = 6.6V; S = 1.3V; D = 8.8V Q2 G1 = 0V; G2 = 5.1V; S = 1.3V; D = 8.8V Q3 C = 8.6V; E = 4.2V; B = 4.3V IC1, IC2, IC3 Pins 1 & 8 = 6.1V; Pin 2 = 0.9V; Pins 3, 4, 5 & 6 = 0V; Pin 7 = 2.8V Q4 G1 = 0V; G2 = 6.5V; S = 1.3V; D = 8.8V IC4 Pins 2, 3 & 4 = 0V; Pin 5 = 4.6V; Pin 6 = 8.9V VC5 Anode = 0V; Cathode = 1.4V (1). Connect a multimeter between TP2 and TP3 and adjust L2 for a maximum reading. If necessary, readjust L3 after each change to L2 (preferably using a frequency meter – see previous section) so that the local oscillator runs at the correct frequency. Note that the antenna should be shortened to reduce signal pickup if the reading on the multimeter goes above 3V. (2). Tune to a station around 104108MHz and adjust VC4 until the received frequency matches the indicated frequency. (3). Adjust VC2 for a maximum reading on the multimeter, again making sure again that the reading does not exceed 3V. Readjust the antenna length if necessary. (4). Repeat the three preceding steps (this is necessary, since adjustments at 6 . 108 90 88 10 3 95 92 101 100 97 Two methods are available for tuning the local oscillator, which is adjusted so that it runs 10.7MHz below the tuned signal. If you have access to a frequency meter, then follow this method: (1). Connect a 10:1 probe to TP1 (near coil L3) and connect the ground lead of the probe to TP GND. Set the tuning dial so that it shows 88MHz, then adjust L3 so that the frequency meter shows 77.3MHz. Note: squeeze the coil slightly (so that the turns are closer together) to lower the frequency, or stretch it to raise the frequency. (2). Set the tuning dial to 108MHz, then adjust VC4 for a reading of 97.3MHz on the frequency meter. Now return to the 88MHz tuning dial position and readjust L3 for 77.3MHz. This done, return to the 108MHz position and readjust VC4 for 97.3MHz. If you don’t have access to a frequency meter, then a com­mercial FM radio should be used for setting L3 as follows: (1). Tune in a station at about 95MHz on the commercial radio and make a note of the exact frequency. (2). Switch the commercial radio off and tune in the same station on the FM Radio Trainer. Note that it will probably not be any­where near the indicated dial frequency, since the local oscilla­tor has not yet been adjusted. (3). If the indicated frequency is too high, squeeze L3 so that its turns are closer together. Conversely, if the indicated fre­quency is too low, stretch L3 so that its turns are further apart. Continue this process until the indicated frequency match­es the station frequency. Don’t worry about adjusting VC4 at this stage. That step is covered in the next section. 10 Local oscillator adjustments RF amplifier adjustment The RF amplifier (Q1) is the next section to be adjusted. The procedure is as follows: Fig.12: this is the full-size artwork for the tuning dial. one end of the band also slightly affect the other end). (5). Tune to a station near 100MHz which gives a reading from 1-3V and readjust T1 for maximum signal. Now adjust L1 for a maxi­mum. (6). Tune to a station which gives a strong signal (above 1V on the multimeter) and adjust VC6 for a maximum reading. Now connect the multimeter between TP4 and TP GND and readjust T4 for a 0V reading. That completes the alignment procedure for the FM Radio Trainer. Check that it can tune stations across the entire FM band from 88-108MHz and that the dial calibrations are correct. Check also that no background noise is evident when you tune to strong local stations (a good antenna helps). If the dial calibrations are incorrect or local stations are noisy, go back and carefully repeat the alignment procedure. Finally, if you wish to operate the FM Radio Trainer for extended periods, you can power it from a 9V DC plugpack instead of a battery. Be sure to remove the battery before connecting the plugpack supply and check the polarity carefully before switching the SC receiver on. May 1995  67 Low cost transi & Mosfet tester base cur­rent from the DMM test circuit may be less than it should be, another source of inaccuracy. Another drawback involves power transistors. These typical­ ly require much more base current than small signal transistors and so beta tests of a power transistor using a DMM can often give misleading results. On the other hand, many of the top brand digital multimet­ers do not have a transistor test facility at all and this is where the SILICON CHIP transistor tester comes into its own. Plug this adaptor into your multimeter and measure the beta of power transistors, small signal types and small signal Darlingtons. In this case, the reading on the DMM indicates that the transistor has a beta of 81. Transistor gain This handy tester is designed to plug into a digital multimeter to provide an accurate measurement of transistor beta, to values up to 50,000 & more. You can use it to test small signal, power & Darlington transistors &, as a bonus, it will also check Mosfets. If you need to use transistors from your junk box for your projects, it is a good idea to test them before soldering them into circuit. Actually, this is a good idea even if you have just purchased the transistors because it can stop you from soldering the wrong type into circuit. But now that many digital multimet­ers incorporate a simple transistor tester, why would you want to build this adaptor? Well, there are several drawbacks to 68  Silicon Chip the typical “transis­tor test” facility in most digital multimeters. First, most will not measure transistor gains in excess of 1000. Most ordinary transistors have a beta of less than 1000 but many Darlington transistors have a beta far in excess of 1000 – up to 50,000 or more, in some cases. Also the fact that Darlington transistors have a base-emitter voltage drop of 1.2V or more and they incor­ porate internal base-emitter resistors means that the You can use the tester to match transistors for gain or to decide whether an unknown device is a Darlington (very high gain) or a standard transistor. You can also find out the transistor pin-outs by trying all connection possibilities until a valid gain measurement is found. Similarly, you can determine whether the device is NPN or PNP by finding the polarity which gives a gain reading. Mosfets are used extensively in SILICON CHIP circuits these days and testing them can be difficult. With this tester, you can obtain valuable information about the condition of a Mosfet. The test is not a gm measurement but it will give a good indication of Mosfet gain. The tester is housed in a small plastic case. Three flying leads with alligator clips are clipped to the device to be test­ed. On the underside of the case are two banana plugs which insert directly into the “VΩ” and “common” inputs. Main Features • Measure s beta fr om 1 to • Plugs dir over 50,0 ectly into 00 a digital • Measure multimete s NPN a r for beta nd PNP • Tests N-t readings transisto ype and rs P -t y • Two test pe Mosfe ts ba • High beta se currents: 10µA an d1 a • Battery o ccuracy and resolutio mA n at mea perated sured cu • Suitable rrent for high im pedance • Short in (>1 istor r for DMMs dication By JOHN CLARKE 0MΩ) mu ltimeters C +9V 1 There are two toggle switches; one is the NPN (N-type)/ PNP (P-type) switch to select the device polarity and the other is the 3-position range switch. The digital multimeter is turned on and a DC range selected, normally 2V to start. Then you press the button and the meter gives a reading. To convert the reading to beta, just take the reading in millivolts. For example, if you are on the 2V range and the reading is 0.695V or 695mV, the transistor beta is 695. Alternatively, if the 200mV DC range has been selected and the reading is 115mV, then the beta is 115. Power is consumed only while the Test button is pressed. If you want to hold the reading on your multimeter, press the “hold” button if it has one. That is how we stored the reading for the setup shown in the photograph accompanying this article. 1mA E1 TRANSISTOR UNDER TEST B R1 Q1 B2 Q2 D1 R2 E E Fig.1: this is the basic beta test setup with a fixed current supplied to the base of the transistor. If 100mV appears across the 1Ω resistor, the collector current is 100mA & the beta is 100. 1k NPN DARLINGTON Fig.2: typical Darlington power transistors have internal baseemitter resistors which means that a minimum base current of about 1mA is required to turn them on. Most beta testers in DMMs cannot supply this much base current. SHORT LED1  R2 C1 9V C2 R1 CURRENT SOURCE Multiplier switch The 3-position multiplier toggle switch needs some explana­tion. The position marked “X1 POWER” is used for testing power transistors and power Darlingtons. The other two settings are used for small signal transistors. The centre position marked “X1” gives a result as described; ie, the reading in mV is the beta. When on the “X100” setting, the readings are multiplied by 100 to give the actual result. This position is intended for small signal Darlington transistors which can typically have a beta of 30,000 or more. Mosfets are measured in a similar B C SWITCH B B TO MULTIMETER C TRANSISTOR UNDER E TEST SWITCH A PULSE GENERATOR Fig.3: this circuit shows the principle of operation of the Beta Tester. The current source is shunted to ground by switch A. When switch A opens, the current source drives the base of the tran­sistor & a voltage proportional to the collector current is developed across R1. Switch B & capacitor C2 form a “sample and hold” circuit which stores the voltage developed across R1 so that it can be read as a DC voltage by the multimeter. May 1995  69 SHORT LED1 1k TEST S1 A  K 120  1W 470 16VW +9V NPN (N-TYPE) 470 16VW S3a 4x1N4148 9V D3 D1 D4 D2 REF1 LM334Z 47  S2: 1 : x1 POWER 2 : x1 3 : x100 SMALL SIGNAL V+ 330k 7 1k 6 4 8 IC1 7555 2 3 IC2a 4053 S2b 1 2 V+ V- 2 3 1 0.1 100  IC2b 6.8k 16 by B 10 B 14 a ay 13 TO METER bx 2 100  15 b S2a 1 11 A ax 3 1 R 68  10 16VW PNP (P-TYPE) +V 10 16VW C DEVICE UNDER E TEST +9V S3b PNP NPN 6,7,8 0.1 A K R VV+ VIEWED FROM BELOW TRANSISTOR BETA AND MOSFET TESTER Fig.4: the circuit of the Beta Tester uses a 7555 astable mul­tivibrator (IC1) & a 4053 analog switch (IC2) to shunt the base current to the transistor. manner to power transis­tors. A good Mosfet will give a very high gain reading. If a device being tested has a short between collector and emitter, the “Short” LED will light. The LED will also light when the wrong polarity is selected for Mosfet and Darlington transis­tors. Test method Fig.1 shows the method of gain testing used in the circuit. The transistor under test is connected in a common emitter con­figuration with a 1Ω resistor for the collector load and a 1mA current source for the base drive. A transistor with a gain of 10 will produce a 10mV drop across the resistor. However, there are a few problems with this circuit. First­ly, for high gain transistors, a high current will be drawn from the supply and secondly, some transistors will not handle the The PC board is mounted on the lid of the case & secured to it using the switch nuts. Adjust the LED leads so that it just protrudes through the lid after it is placed in position. 70  Silicon Chip Pulse testing Because we cannot reduce the base current we need to modify the circuit in some other way to curb the excess current which will otherwise be drawn by high-gain transistors. Fig.3 shows how this is done by pulsing the base current with a short duty cycle. By having a long period between each base current pulse to the transistor, the average collector current can be reduced to only a few milliamps. Capacitor C1 lowers the supply impedance so that it can more easily deliver the required high current pulses. Switch A is normally held closed by the pulse generator and thereby shunts the current source to ground, preventing the transistor from turning on. When switch A opens, the current source drives the base of the transistor and a voltage propor­tional to the collector current is developed across R1. Switch B and capacitor C2 form a “sample and hold” circuit which stores the voltage developed D1 D3 S2 C IC2 4053 D4 D2 1 1 10uF 0.1 1k 470uF 120  1W 470uF 100  1 6.8k IC1 7555 10uF TO B DEVICE UNDER E TEST LED1 A K 0.1 TO 9V BATTERY 68  REF1 100  S1 NC NO C 47  330k 1k collector current without self-destructing. Simply reducing the base current and increasing the collec­tor resistor will drop the current but will not solve the prob­lem. This is because we need the 1mA base current to drive power transistors. Fig.2 shows the internal arrangement of power Dar­lington transistors. This entails two transistors with the emit­ter of the first transistor connected to the base of the second transistor. In addition, they also include base-emitter resis­tors. Resistor R1 can be as low as 1kΩ while R2 is generally smaller again. Since we must develop about 0.7V across the base and E1 of Q1 before transistor Q2 will switch on, the base cur­rent into Q1 must be at least 700µA. TO MULTIMETER S3 Fig.5: follow this parts layout diagram when installing the parts on the PC board. Note particularly the orienta­tion of the contacts on switch S1 – see text. across R1 so that it can be read as a DC voltage by the multimeter. Hence, when switch A opens, switch B closes and “samples” the resultant collector voltage. Resistor R2 is included for short circuit protection. If a transistor is connected incorrectly or if the collector and emitter leads are shorted together, excess current will otherwise flow. LED1 indicates whenever a short is present and also lights briefly each time the “TEST” button is pressed. The type of measurement used in B E C BC5xx BC3xx PLASTIC SIDE BCE "POWER" E C B E BC6xx B C "POWER" GD S MOSFET "POWER" E C (CASE) B "POWER" Fig.6: typical pin-outs for various case styles of transistor. the beta tester gives us the DC gain or hFE for the transistor. Mosfet devices are tested in a similar manner to transistors. The current source will charge up the gate to switch on the Mosfet and a voltage propor­tional to the Drain current will appear across resistor R1. Circuit operation The complete circuit for the Beta Tester is shown in Fig.4. IC1 is a 7555 CMOS timer connected as an astable multivibra­tor set to run at about 43Hz by the resistors and capacitor connected to pins 6 & 7. Its pulse train output at pin 3 is high for 23ms and low for 70µs. Pin 3 of IC1 controls IC2, a 4053 triple 2-channel demulti­ plexer. In our circuit we are using the 4053 as a 2-pole switch, with IC2a closed when IC2b is open, and vice versa. IC2a is used to alternately shunt the base current to the transistor under test, while IC2b is the sample-and-hold switch. A crucial part of the circuit is the 2-pole toggle switch, S3. S3a & and RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 2 1 2 1 1 1 Value 330kΩ 6.8kΩ 1kΩ 120Ω 100Ω 68Ω 47Ω 1Ω 4-Band Code (1%) orange orange yellow brown blue grey red brown brown black red brown brown red brown brown brown black brown brown blue grey black brown yellow violet black brown brown black gold gold 5-Band Code (1%) orange orange black orange brown blue grey black brown brown brown black black brown brown brown red black black brown brown black black black brown blue grey black gold brown yellow violet black gold brown brown black black silver brown May 1995  71 The banana plugs are mounted close to the end of the case & with a spacing of 19.5mm. Alternatively, set them at the spacing to match your multimeter. Fig.7 at right shows the full-size etching pattern for the PC board. S3b reverse the supply polarity to the transistor under test so that NPN and PNP devices can be tested. Since REF1, an LM334Z constant current source which supplies the base current, is a polarised device, a bridge rectifier consist­ ing of diodes D1-D4 ensures that it is correctly polarised, regardless of whether NPN or PNP devices are being tested. REF1 has its constant current programmed by the resistance connected between its R and V- pins. This is varied using 2-pole 3-position toggle switch S2. This is actually a “2-posi­ tion, centre-off” switch which is connected to vary both the base current and the collector load resistor for the device under test. Position 1 of S2a connects a 68Ω resistor in parallel with a 6.8kΩ resistor to provide a 1mA base current to the transistor under test. In position 2, the “centre-off” position, the 68kΩ resistor by itself sets the base current to 10µA. Positions 1 and 3 of S2b switch a 1Ω resistor in parallel with 100Ω, while the “centre off” position 2 leaves the 100Ω resistor by itself. Hence, for power transistors and small signal Darling­tons, the collector load resistor is 1Ω (shunted by 100Ω) while for small signal transistors the collector load is 100Ω. Power for the circuit is derived from a 9V battery which is applied via pushbutton S1 to S3 via a 120Ω resistor. This supply is decoupled with two parallel 470µF capacitors which provide the peak currents required. When S1 is open, the supply rail is discharged using the normally closed contact to prevent any voltage remaining on the circuit when the switch is released. When the switch is pressed, the 470µF capacitors are initially discharged and so LED1 lights momentarily. This provides a good indication of battery condition at the beginning of each test. Construction The Beta Tester is housed in a plastic utility case measuring 130 x 67 x 43mm. All the circuitry mounts on a PC board coded 04306951 and measuring 92 x 61mm. This is secured to the lid by the three switches. You can begin the construction by inserting PC stakes at the external wiring points. This done, install the resistors, links and diodes, followed by the capacitors and lastly, the integrated circuits. Make sure that the semiconductors and electrolytic capacitors are correctly polarised. The PC board is attached to the lid of the case and held in place by the nuts of the switches. Note that the LED lead length needs to be adjusted so that the lens of the LED just protrudes from the front panel. 72  Silicon Chip the E and C terminals and with S2 in the x1 power position check that LED1 lights. Now affix the Dynamark label to the front panel and drill the holes for switches S1-S3 and LED1. The four corner holes in SHORT the lid should also be drilled + out. One end of the case re­ quires separate holes for the three test leads which are fitted P-TYPE with crocodile clips. X1 POWER PNP Drill 3mm holes for the banana plugs so that they are + X1 + mounted as close to the end of the case as possible, 19.5mm X100 N-TYPE apart. The battery can be held NPN in place with a metal clamp or with Velcro®. You will need to remove the TRANSISTOR BETA & internal ribs of the case so there MOSFET TESTER is sufficient clearance for the PC board. You can do this job easily with a sharp chisel. + Now connect up wires on the board for the base, emitter and TEST collector test leads and for the banana plugs. Attach the PC board to the front panel by firstly placing a single nut on each switch bush about 5mm down from the top and then securing the panel with a second nut Fig.8: this full-size front-panel artwork for on each switch bush. The LED the Transistor Beta & Mosfet Tester can be should be adjusted in height so used as a drilling template for the case lid. that it sits correctly in the front panel hole. Next, the switches can be installed. Attach the meter output wires to Note that pushbutton switch S1 must the banana plugs and pass the B, C be oriented in a particular way. You and E wires through the holes in the will find that its three contacts are case. Terminate these wires to the labelled C (common), NO (normally alligator or easyhook clips. Fit the open; ie, when not pressed) and NC lid assembly into the case, attach (normally closed). The contact posi- the screws and the tester is ready tions should match the labelling on for service. the copper pattern side of the board (ie, NC contact toward the edge of Measurements the board). Use the centre-off switch Fig.6 shows typical pin-outs for for S2. various case styles of transistor. Use Finally, LED1 is inserted so that it this to help with identifying the correct sits at the same height as the switch pin arrangement. When testing small bushes. Do not cut its leads to length signal transistors, use the x1 and x100 yet, so that it can be set to the correct small signal setting for S2. height in the front panel later on. There will be some differences between readings on each range for Initial tests a given device under test. This is beAttach the battery clip leads to the cause transistor gain varies with base PC board and apply power. Connect current. a multimeter between the negative Mosfet “gain” values should be in battery lead and pin 8 of IC1 and check the region of 1000 or more and should that there is about +8V present when be tested on the x1 power position. S1 is pressed. Similarly, check for a The gate will only be pulled to about similar voltage on pin 16 of IC2. Short +6.5V due to the voltage drop across CBE DGS βΕΤΑ PARTS LIST 1 PC board, code 04306951, 92 x 61mm 1 plastic case, 130 x 67 x 43mm 1 front panel label, 64 x 124mm 1 9V 216 battery & battery clip 1 SPDT momentary pushbutton PC board mounting switch (S1) 1 DPDT centre-off PC mount toggle switch (S2) 1 DPDT PC-mount toggle switch (S3) 7 PC stakes 2 banana plugs 2 3mm x 10mm screws & nuts 3 crocodile clips 1 50mm length of green hookup wire 1 50mm length of red hookup wire 1 100mm length of black hookup wire 1 100mm length of blue hookup wire 1 100mm length of yellow hookup wire 1 100mm length of 0.8mm diameter enamelled copper wire Semiconductors 1 7555, TLC555CN or LMC555CN timer (IC1) 1 4053 triple 2-channel demultiplexer (IC2) 1 LM334Z current source (REF1) 4 1N4148, 1N914 signal diodes (D1-D4) 1 3mm red LED (LED1) Capacitors 2 470µF 16VW PC electrolytic 2 10µF 16VW PC electrolytic 2 0.1µF MKT polyester Resistors (0.25W 1%) 1 330kΩ 2 100Ω 1 6.8kΩ 1 68Ω 2 1kΩ 1 47Ω 1 120Ω 1W 1 1Ω REF1 and the bridge rectifier which is usually not sufficient to turn a Mosfet fully on. Consequently, the Mosfet will be operating in the linear region. Note that the polarity indication on the multimeter will differ, depending on the setting of the NPN/PNP switch SC (S3). May 1995  73 NICS O R T 2223 LEC 7910 y, NSW EY E OATLBox 89, Oa8t5leFax (02) 5s7a0 C a rd KITS & BITS i 9 PO 579 4 r C a rd , V e & fax ) 2 0 ( n e e Phon rd , M a s t with pho orders: a d c ed B a n k x accepte most mix 0. Orders $3; 50 x 72 x 3mm: $3. LINE GENERATING e r 1 OPTIC: makes a line out of a laser beam: & Am . P & P fo (airmail) $ s $5. LASER DIODE COLLIMATING LENS: order 4-$10; NZ world.net $4. PORRO 90 deg. PRISM: makes a $ <at> . y t e s l t u rainbow from white light: $10. PRECISION ROTATING a A AIL: o MIRROR ASSEMBLY: as used in levelling equipment, by EM needs small motor/belt, plus a laser beam, will draw a HIGH INTENSITY RED LEDs 550-1000mCd <at> 20mA, 100mA max, 5mm housing: 10 for $4, or 100 for $30. LOW COST IR ILLUMINATOR Employs 42 high output 880nM IR LEDs (30mW <at> 100mA ea.) & a seven transistor adjustable constant current driver circuit. Designed to be powered from 10-14V DC, current depends on power level setting: 5 - 600mA. The compact PCB is designed to replace the lid on a standard small 82 x 53 x 28mm plastic box. Good for illuminating IR responsive CCD cameras, IR & passive night viewers & medical use. The complete kit even includes the plastic box & is priced at a low: $40 MINIATURE FM TRANSMITTER Not a kit, but a very small ready made self contained FM transmitter enclosed in a small black metal case. It is powered by a single small 1.5V silver oxide battery, and has an inbuilt electret microphone. SPECIFICATIONS: tuning range: 88-108MHz, antenna: wire antenna - attached, microphone: electret condenser, battery: one 1.5V silver oxide LR44/G13, battery life: 60 hours, weight: 15g, dimensions: 1.3" x 0.9" x 0.4". $32. COLOUR MONITORS Used but guaranteed 12" colour computer monitors: $40 REEL TO REEL TAPES New studio quality 13cm-5" “Agfa” (German) 1/4" reel to reel tapes in original box, 180m-600ft: $8 ea. ARGON HEADS These low voltage air cooled Argon Ion Laser Heads are priced according to their hours of operation. They produce a bright BLUE BEAM (488nM) and a power output in the 10-100mW range - depending on the tube current. The head includes power meter circuitry, and starting circuitry. We provide a simple circuit for the supply. Limited supplies at a fraction of their real cost: $300 - $500. AC MOTOR Small but very powerful GEARED AC motor. 1 RPM/60Hz/24V/5watt. We supply a circuit diagram that shows how to power this motor from 12V DC: Variable speed/full power (bridge output). Bargain priced: $9 PCB and all on-board components kit for the 12V driver kit will be available late in May: $8 OPTICS BEAM SPLITTER for 633nM: $45. PRECISION FRONT SURFACE ALUMINIUM MIRRORS 200 x 15 x 3mm: 74  Silicon Chip line right around a room (360 deg.) with a laser beam: $45. LARGE LENS: out of a night viewer, can easily be pulled apart: $18. ARGON MIRRORS: high reflector and output coupler used to make an Argon tube: $50. POWER SUPPLIES Used but very clean non standard computer power supplies, enclosed in metal casing with perforated ends for air circulation, built in fan, IEC input connector and OFF-ON switch, “flying” DC output leads, overall dimensions: 87 x 130 x 328mm, 110-220V input, +5V/8A, +12V/3A, and -12V/0.25A DC outputs. BARGAIN PRICED: $18 ea. or 4 for $60. Used IEC lead with Australian plug $2.50 extra. TWO STEPPER MOTORS PLUS A DRIVER KIT This kit will drive two stepper motors: 4, 5, 6 or 8-wire stepper motors from an IBM computer parallel port. Motors require separate power supply. A detailed manual on the COMPUTER CONTROL OF MOTORS plus circuit diagrams/descriptions are provided. We also provide the necessary software on a 5.25" disc. Great “low cost” educational kit. We provide the kit, manual, disc, plus TWO 5V/6 WIRE/7.5 Deg. STEPPER MOTORS FOR A SPECIAL PRICE OF: $42. MAINS LASER SPECIAL Includes a compact potted US made power supply which can be powered from 110/220-240V AC, a 2-3mW He-Ne tube, a ballast resistor and instructions. The power supply requires 4-6V <at> 2mA DC enable to run. Brand new components. Giveaway price: $65 27MHz TRANSMITTERS These new Australian made transmitters are assembled (PCB and components) and tested. They are Xtal locked on 26.995 MHz and were originally intended for transmitting digital information. Their discrete component design employs many components, including 5 transistors and 8 inductors: circuit provided. A heatsink is provided for the output device. Power output depends on supply voltage and varies from 100mW to a few watts, when operated from 3-12V DC. These are sold for parts/experimentation/educational purposes, and should not be connected to an antenna as licensing may be required: $7 ea. or 4 for $20. 12V FANS Brand new 80mm 12V-1.6W DC fans. These are IC controlled and have four different approval stamps: $10 ea. or 5 for $40 CD MECHANISMS Used compact disc player mechanisms. Include IR laser diode, optics, small conventional DC motor, gears, stepping motor, magnets etc. Great for model railway hobbyists: The motor/gear assembly produces a linear movement of approx. 60mm. The whole assembly is priced at less than the value of the collimating lens, which is easy to remove: $6. We also have some similar CD assemblies that have linear motors. Used CD mechanisms with linear motors: $4. IMAGE INTENSIFIER TUBES Used but in excellent condition second generation image intensifier tubes. Can be used to make a small and very sensitive scope that can produce high resolution pictures in very low illumination. US made tubes that produce superior results! $650 We should have a complete kit of parts for a small scope available at the time of the publication of this advertisement: “Ring”. VIDEO TRANSMITTERS Low power PAL standard UHF TV transmitters. Have audio and video inputs with adjustable levels, a power switch, and a power input socket: 10-14V DC/10mA operation. Enclosed in a small metal box with an attached telescopic antenna. Range is up to 10M with the telescopic antenna supplied, but can be increased to approximately 30M by the use of a small directional UHF antenna. INCREDIBLE PRICING: $25. IR REMOTE SWITCH KIT Consists of a PCB and all on board components kit for an IR receiver with a toggle output, and a brand new commercial ready made slimline IR remote control transmitter, which was designed for a CD player. Simply press any button on the IR transmitter to toggle the output on the receiver. The system has up to 20M range and will also work from most other IR remote controls! Receiver uses an IC “front end”, has a toggle output, operates from 8-15V DC, and will drive a relay. Transmitter operates from two “AAA” batteries (not supplied). Unbelievable pricing: $18 For the slimline IR remote control transmitter and a kit for the IR receiver. Suitable 12V/8A relay with 4kV isolation: $3, 12V DC plugpack: $10. PRINTER MECHANISMS Brand new Epson dot matrix printer mechanisms: overall dimensions are 150 x 105 x 70mm. These are complete units and contain many useful parts: 12V DC motor (50mm long - 30mm diam.) with built in tachometer, gears, solenoid, magnet, reed switch, dot matrix print head etc.: $12. VISIBLE LASER DIODE MODULES Industrial quality 5mW/670nM laser diode modules. Overall dimensions: 11mm diameter by 40mm long. Have APC driver built in and need approximately 50mA from 3-6V supply. $60. SOLID STATE “PELTIER EFFECT” COOLER-HEATER These are the major parts needed to make a solid state thermoelectric cooler-heater. We can provide a large 3.4A Peltier effect semiconductor, two thermal cutout switches, and a 12V DC fan for a total price of: $35. We include a basic diagram/circuit showing how to make a small refrigerator-heater. The major additional items required will be an insulated container such as an old “Esky”, two heatsinks, and a small block of aluminium. 12V-4.5A Peltier device only: $25. DOT MATRIX LCDs Brand new Hitachi LM215 400 x 128 dot matrix Liquid Crystal Displays in an attractive housing. These have driver ICs fitted but require an external controller. Effective display size is 65 x 235mm. Available at less than 10% of their real value: $25 ea. or 3 for $60 VISIBLE LASER DIODE KIT A 5mW/670nM visible laser diode plus a collimating lens, plus a housing, plus an APC driver kit (Sept. 94 EA) UNBELIEVABLE PRICE: $35. The same kit is also available with a 3mW/650nM laser diode: $60. WELLER SOLDERING IRON TIPS New soldering iron for low voltage Weller soldering stations and mains operated Weller irons. Mixed popular sizes and temperatures. Specify mains or soldering station type: 5 for $10. $215 CCD VIDEO SECURITY SYSTEM Monochrome CCD Camera which is totally assembled on a small PCB and includes an auto iris lens. It can work with illumination of as little as 0.1Lux and it is IR responsive. This new model camera is about half the size of the unit we previously supplied. It is slightly bigger than a box of matches! Can be used in total darkness with Infra Red illumination. NEW LOW PRICE: $180 With every camera purchased we can supply an used but tested and guaranteed 12V DC operated Green computer monitor. We can also supply a simple kit to convert these monitors to accept the signal from the CCD camera: monitor $25, conversion kit $10. A COMPLETE 12V CCD VIDEO SECURITY SYSTEM FOR $215!! LOW COST 1-2 CHANNEL UHF REMOTE CONTROL A single channel 304MHz UHF remote control with over half a million code combinations which also makes provision for a second channel expansion. The low cost design includes a complete compact keyring transmitter kit, which includes a case and battery, and a PCB and components kit for the receiver that has 2A relay contact output!. Tx kit $10, Rx kit $20 additional components to convert the receiver to 2 channel operation (extra decoder IC and relay) $6. is available: suits 12-24V batteries, 0.1-16A panels, $27. Also available is a simple and efficient shunt regulator kit, $5. BLEMISHED 3 STAGE TUBES We have accumulated a good number of 40mm three stage fibre optically coupled 3 stage image intensifiers that have minor blemishes: similar to above but three tubes are supplied already bonded together: extremely high gain!! Each of these tubes will be supplied with the power supply components only. See SC Sept. 94. $200 For the 3 stage 40mm tube, supply kit. We can also supply the full SC Sept. 94 Magazine: $5 TDA ICs/TRANSFORMERS We have a limited stock of some 20 Watt TDA1520 HI-FI quality monolythic power amplifier ICs: less than 0.01% THD and TIM distortion, at 10W RMS output! With the transformer we supply we guarantee an output of greater than 20W RMS per channel into an 8ohm load, with both channels driven. We supply a far overrated 240V-28V/80W transformer, two TDA1520 ICs, and two suitable PCBs which also include an optional preamplifier section (only one additional IC), and a circuit and layout diagram. The combination can be used as a high quality HI-FI Stereo/Guitar/P.A., amplifier. Only a handful of additional components are required to complete this excellent stereo/twin amplifier! Incredible pricing: $25. For one 240V-28V (80W!) transformer, two TDA1520 monolythic HI-FI amplifier ICs, two PCBs to suit, circuit diagram/layout. Some additional components and a heatsink are required. RUBY LASER HEADS These complete and functional heads include a flash tube, mirrors, and 4" ruby rod! Produce a high intensity visible red beam! We should have suitable circuits - components to drive these available. Dangerous units with restricted sales. Limited quantity. $695 BIGGER LASER We have a good, but LIMITED QUANTITY of some “as new” red 6mW+ laser heads that were removed from new equipment. Head dimensions: 45mm diameter by 380mm long. With each of the heads we will include our 12V Universal Laser power supply. BARGAIN AT: $170 6mW+ head/supply ITEM No. 0225B INCREDIBLE PRICES: COMPLETE 1 CHANNEL TX-RX KIT: $30 COMPLETE 2 CHANNEL TX-RX KIT: $36 ADDITIONAL TRANSMITTERS: $10 We can also supply a 240V-12V/4A-5V/4A switched mode power supply to suit for $30. FIBRE OPTIC TUBES Originally designed for bicycles, but these suit any moving vehicle that has a rotating wheel! A nine function computer with speed, average speed, maximum speed, distance, odometer, timer, scan, freeze frame memory, and a clock. Its microprocessor based circuitry can be adapted to work with almost any wheel diameter. Simply divide the wheel diameter in millimetres by 6.8232, and program the resultant figure into the computer. We have a good supply of some tubes that may have a blemish which is not in the central viewing area! These produce a very high resolution image but would require IR illumination: !!ON SPECIAL!! $50 for a blemished 25 or 40mm (specify preference) image intensifier tube and supply kit. Matching good quality eyepiece lens only, $2 extra! That’s almost a complete night viewer kit for: $52. 12V-2.5 WATT SOLAR PANEL KITS These US made amophorous glass solar panels only need terminating and weather proofing. We provide terminating clips and a slightly larger sheet of glass. The terminated panel is glued to the backing glass, around the edges only. To make the final weatherproof panel look very attractive some inexpensive plastic “L” angle could also be glued to the edges with some silicone. Very easy to make. Dimensions: 305 x 228mm, Vo-c: 18-20V, Is-c: 250mA. SPECIAL REDUCED PRICE: $20 ea. or 4 for $60 Each panel is provided with a sheet of backing glass, terminating clips, an isolating diode, and the instructions. A very efficient switching regulator kit VEHICLE COMPUTERS $29.90 $70. SWITCHED MODE POWER SUPPLIES: mains in (240V), new assembled units with 12V-4A and 5V-4A DC outputs: $32. ELECTRIC FENCE KIT: PCB and components, includes prewound transformer: $40. PLASMA BALL KIT: PCB and components kit, needs any bulb: $25. MASTHEAD AMPLIFIER KIT: two PCBs plus all on board components, low noise (uses MAR-6 IC), covers VHF-UHF: $18. INDUCTIVE PROXIMITY SWITCHES: detect ferrous and nonferrous metals at close proximity, AC or DC powered types, three wire connection for connecting into circuitry: two for the supply, and one for switching the load, these also make excellent sensors for rotating shafts etc.: $22 ea. or 6 for $100. BRAKE LIGHT INDICATOR KIT: 60 LEDs, two PCBs and ten Rs, makes for a very bright 600mm long high intensity red display: $30. IEC EXTENSION LEADS: 2M long, IEC plug at one end, IEC socket at other end: $5. MOTOR SPECIAL: these permanent magnet motors can also double up as generators, type M9: 12V, I No load = 0.52A-15,800 RPM at 12V, 36mm diam.-67mm long: $5, type M14: made for slot cars, 4-8V, I No load = 0.84A at 6V, at max efficiency I = 5.7A-7500 RPM, 30mm diam.-57mm long: $5. EPROMS: 27C512, 512K (64k x 8), 150nS access CMOS EPROMS, removed from new equipment, need to be erased, guaranteed: $4. 40 x 2 LCD DISPLAY: brand new 40 character by 2 line LCD displays with built in driver circuitry that uses Hitachi ICs, easy to drive “standard” displays, brief information provided: $30 ea. or 4 for $100. MODULAR TELEPHONE CABLES: 4 way modular curled cable with plugs fitted at each end, also an 4M long 8way modular flat cable with plugs fitted at each end, one of each for: $2. POLYGON SCANNERS: precision motor with 8 sided mirror, plus a matching PCB driver assembly. Will deflect a laser beam and generate a line. Needs a clock pulse and DC supply to operate, information supplied: ON SPECIAL $15. PCB WITH AD7581LN IC: PCB assembly that amongst many other components contains a MAXIM AD7581LN IC: 8 bit, 8 channel memory buffered data acquisition system designed to interface with microprocessors: $20. EHT POWER SUPPLY: out of new laser printers, deliver -600V, -7.5kV and +7kV when powered from a 24V-800mA DC supply, enclosed in a plastic case: $16. MAINS CONTACTOR RELAY: has a 24V-250ohm relay coil, and four separate SPST switch outputs, 2 x 10A and 2 x 20A, new Omron brand, mounting bracket and spade connectors provided: $8. FM TRANSMITTER KIT - Mk.2: high quality - high stability, suit radiomicrophones and instruments, 9V operation, the kit includes a PCB and all the on-board components, an electret microphone, and a 9V battery clip: $11. FM TRANSMITTER KIT - Mk.1: this complete transmitter kit (miniature microphone included) is the size of a “AA” battery, and it is powered by a single “AA” battery. We use a two “AA” battery holder (provided) for the case and a battery clip (shorted) for the switch. Estimated battery life is over 500 hours!!: $11. BATTERY CHARGER S2: accessory set for Telecom Walkabout “Phones”. Includes cigarette lighter cable, fast rate charger, and desktop stand. Actually charges 6 series connected AA Nicad batteries: $27. LITHIUM BATTERIES: button shaped with pins, 20mm diameter, 3mm thick. A red LED connected across one of these will produce light output for over 72 hours (3 days): 4 for $2. SUPERCAPS: 0.047F/5.5V capacitors: 5 for $2. PCB MOUNTED SWITCHES: 90 deg. 3A-250V, SPDT: 4 for $2. 3-INCH CONE TWEETERS: sealed back dynamic 8-ohm tweeters: $5 ea. CASED TRANSFORMERS: 230V-11.7V 300mA AC-AC transformers in small plastic case with separate input and leads, each is over 2 metres long: $6. MORE KITS-ITEMS SINGLE CHANNEL UHF REMOTE CONTROL: SC Dec. 92, 1 x Tx plus 1 x Rx: $45, extra Tx $15. 4 CHANNEL UHF REMOTE CONTROL KIT: Two transmitters and one receiver: $96. GARAGE-DOOR-GATE REMOTE CONTROL KIT: SC DEC 93: Tx $18, Rx $79. 1.5-9V CONVERTER KIT: $6 ea. or 3 for $15. LASER BEAM COMMUNICATOR KIT: Tx, Rx, plus IR Laser: $60. MAGNETIC CARD READER: Professional assembled and cased unit that will read information from plastic cards, needs low current 12V DC supply-plugpack: MORE ITEMS AND KITS Poll our (02) 579 3955 or (02) 579 3983 fax numbers for instructions on how to obtain our Item and Kit lists. MANY MORE ITEMS AND KITS THAN ARE LISTED HERE!! You can also ask for a copy of these to be sent out with your next order. May 1995  75 SERVICEMAN'S LOG All it needs is a new fuse Some politician – whose name now escapes me – once decreed that “life wasn’t meant to be easy”. I don’t know who he was blaming for this situation but from where I stand, there are two who share some responsibility: TV set designers & customers. OK, so that’s a sweeping statement. Only a few customers make life less than easy and not all set designers are to be similarly condemned. But there are always some and when they get together on the one job, it is no longer “life wasn’t meant to be easy” – it is life was meant to be hard. What started this grouch? Answer: the bloke who designed a Mitsubishi projection TV set (model VS-360A) and the proprietor of the local pub, who owned the monster. And I use that word monster advisedly; Frank­ en­stein couldn’t have done better. Granted, projection TV sets are not my strong point. More correctly, I have never had to service one before this, which probably didn’t help. It all started about 12 months ago with a phone call from the aforementioned establishment, explaining that they needed to have the set serviced. And the caller added, in a most authorita­tive manner, that “all it needs is a new fuse”. Well, that started things off on the wrong foot. People who insist that they have diagnosed the fault, particularly as stupid­ly as this, really annoy me. I felt like saying, “well you re­place the fuse”. Instead, I replied that maybe a fuse had blown but that this would be only the result of a problem; the cause of the fuse blowing was the real problem. But no, he wouldn’t have a bar of that. All the set needed was new fuse and he wanted me to come up and fit it. Well, there was no way I was going to be in that. I knew the set well enough by sight and I can remember when it was installed, about 10 years ago. It is in one of the lounges and there was no way that one could work on it there due to the lighting and general at­ mosphere, to say nothing of the equipment that I might need. So I had to explain that the only way I could service the set was in the workshop. What’s more, he would have to arrange delivery. I wasn’t being hard to get on with, just practical; there simply wasn’t enough room in my own van for the monster. And, in any case, there was no way I could handle the thing at either end; it was far too big and heavy for one person. On the other hand, I knew that the hotel had a utility and plenty of manpower, so that it shouldn’t be a problem for them. Well, he hemmed and hawed about that. He insisted that all it needed was a fuse and that I should be able to fix it in a few minutes. But I stuck to my guns; it needed to be in the workshop if I was to service it. He said he would get back to me. The monster arrives Fig.1: the layout of the projection system in the Mitsu­bishi VS-360A, as given in the manual. The internal shelf is not shown. It runs from the back, about halfway to the front, above the projection tubes. 76  Silicon Chip That was the last I heard of the matter for about three months. Then suddenly, one morning, he turned up with the monster in the ute, along with a couple of brawny blokes from the local football club who manhandled it (the monster not the ute) into the shop. And he was still insisting that all the set needed was a fuse. This record was getting a bit worn by now and I asked him on what grounds he based this assertion. And then it came out. It appeared that after I had insisted that I could only service the set in the workshop, he had called one of my colleagues. He had agreed to go to the hotel, had found a blown fuse, and made the appropriate replacement. And the set had come to life. And that, of course, proved that all it needed was a fuse. The only snag was, it didn’t work for long. I don’t know for how long – he was a bit cagey about this – but I strongly suspect it was only for a few switch-on cycles. Anyway, all he wanted now was another fuse fitted. And try as I might, no expla­nation would convince him otherwise. So I said, “leave it with me.” And so it was that I found myself saddled with the monster. Initially, I wasn’t quite sure how best to get inside the cabi­net, or what I would find when I did. I had no technical data of any kind and only the vaguest idea of the likely layout. The most obvious entry point at this stage was a rear cover which extended from near the bottom of the cabinet to a point just below the bottom of the top mirror, as shown in Fig.1. All I had to do was remove the 16 screws holding it. This provided some access but it was still quite restrict­ed. The main restriction was a shelf running the width of the cabinet from the back, above the picture tubes, and about halfway towards the front. Its main role appeared to be to provide sup­port points for the three projection tubes. These are high intensity types, about 150mm in diameter, and are mounted in line. The various boards, including the power supply, were mounted on the cabinet floor or on the sides of the cabinet. To get any kind of view of these boards, I had to get my head halfway into the cabinet, after which I was able to see two fuses on the power supply board and, with some difficulty, was able to extract them. They were 2A slow blow types located in the mains leads and, yes, one was blown. I suspected that the fault might be intermittent – or had been – so I fitted a new fuse and applied power. But the result was an instant splat. So much for the amateur diagnosis. At this point it was obvious that I could go no further without a manual. I rang the Mitsubishi service department and contacted a very helpful staff member. He confirmed that a manual was available, price $36, plus $6 for postage. I also took the opportunity to discuss access from the front of the cabinet. I suspected that a front panel could be removed and, in fact, had noted that there seemed to be small cover missing from the bottom of the cabinet front and that there were two large bolt heads in this area. While it seemed likely that these were holding the front panel, their size suggested that they might be also May 1995  77 SERVICEMAN’S LOG – CTD Fig.2: this diagram shows the mains, power transformer & voltage selector wiring in the VS-360A. The voltage selector selects the appropriate tap on the power transformer. holding something larger. I had no desire to undo them and hear three picture tubes crash to the bottom of the cabinet. I needn’t have worried. The Mit­ subishi technician confirmed that these were to ones to unscrew. He then asked me what the problem was. When I explained that the set was blowing mains fuses, he didn’t seem all that surprised. And he went on suggest that I should check the power transformer for a brownish goo or varnish with which it might be covered. Apparently this substance can cause corrosion problems and, in fact, I can recall something similar which caused trouble in a video recorder. Anyway, he suggested that this may have caused a tracking problem and that it might be cured by scraping away any obvious track. Well, that was a help. I ordered a manual and, while wait­ing for it, took the technician’s advice and unscrewed the two bolts in the front. This freed the front panel which extends from the bottom up to various user controls beneath the screen area. This provided much better access but there was still a mass of boards, interconnecting cables, plugs and sockets, which I had to sort out. I put it aside until the manual arrived. 78  Silicon Chip When it did, I was able to sort things out in a little more detail. The horizontal and vertical output boards covered a large part of the cabinet floor. And, looking from the front, the power supply board was on the left, tucked in behind them. The main component, the power transformer, weighing several kilograms, was bolted to the cabinet floor. Other parts of the power supply were mounted on brackets. Screwed to the side of the cabinet, on the left, in front of the power supply, was a large board carrying the convergence circuitry, and screwed to the side of the cabinet on the right was the signal processing board. Power supply Having sorted all that out, I faced the real task of trying to track down what was obviously a short circuit. The accompany­ing circuit shows the relevant part of the power supply. To the right of centre is the power plug, a two pole on/off switch, and a plug/socket combination marked BA. Next in line are the two fuses already mentioned, while a voltage selector socket at extreme left connects to the transformer primary via plug/sockets BC and BB. There is also a second, smaller transformer at extreme right, which is fed via plug/socket BD. It is part of the remote control system. It was one of the first things to be unplugged. The main transformer primary is on the lower side of the core, with 200V, 220V, 240V and 260V tappings. The secondaries on the upper side connect to various plug/socket combinations. This arrangement of plugs and sockets was doubtless intend­ed to simplify assembly and servicing and it does up to a point. The difficulty was to identify all of these in cramped condi­tions, at least for someone tackling it for the first time. As a result, I spent considerable time and a fair amount of physical effort – to say nothing of scoring a few barked knuckles – sorting out all these connections and making sure everything was disconnected from the transformer secondary. When finally satisfied that this was so, I pulled plug/socket BB apart, which gave me direct access to the primary tappings. I then made up a dummy power lead, complete with fuse, and connected it directly to the common and 240V taps. An instant splat Then came the moment of truth. I plugged it in and switched on. Again there was an instant splat. And that settled it; it was the transformer and it had to come out. Whether it could be salvaged or not still had to be determined. Again, the problem was mainly physical. As already men­tioned, the transformer was bolted to the cabinet floor, which meant that I had to fit a spanner at both ends; one in the cabinet and one underneath it. There simply wasn’t enough space under the cabinet and I finished up having to tilt it and prop one side up on a couple of wooden blocks. Even then it a was tedious procedure but I eventually had it free and was able to pull it out and set it up on the bench. And the Mitsubishi technician was right; it was covered with a brown varnish and there was a dark patch between the primary terminal lugs. I spent some time scraping all this discoloured varnish away, then tried it again with the dummy lead. But it was no use; there was another splat and another fuse was written off. I A shocked customer I had some doubts as to whether the hotel would accept this. And I wasn’t far wrong. They were clearly shocked at the figure but I pointed out that there was really little option. If they were not prepared to spend that amount, then it was for the scrap heap. Finally, they said they would think about it. Well, they “thought about it” for some six or seven weeks and I was heartily sick of having the thing cluttering up the workshop. But finally they rang and said, “fix it.” So I ordered the replacement transformer, which arrived in about a week, then set about putting it all back together. This wasn’t quite so bad; after all I’d been there before and learned some of the tricks and traps. Then came the moment of truth; would it work? Well, it did and quite well in fact – for a projection system. I gave it a grey scale and convergence routine and the hotel sent down their ute and another team of footballers to take it home. And I made one final check when it was back in the lounge, giving the convergence a final tweak. It appears that this adjustment is quite sensitive and the journey in the ute had upset it a little. So they paid the bill – just on $600 – along with some general comments about how expensive everything is these days. Well, it was a pretty expensive fuse. The rejuvenated National My next story is about a National TV set, model TC-2138, using an M14H chassis. These sets first appeared SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. ORDER FORM PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏ 3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my Bankcard   ❏ Visa Card   ❏ MasterCard ❏ Card No. Signature­­­­­­­­­­­­_______________________________ Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ probed around a bit further but I was obviously flogging a dead horse. As far as I could see, the winding was damaged internally. Not only was it a write-off but I now felt quite sure that it had originally been intermittent, leading to the pointless replacing of fuses. So it was back to Mitsubishi to determine the availability of a new transformer and its price. I was concerned about this latter point, feeling that it would be quite costly. And I was right. It was available but the cost, including freight, was just short of $400. Add in the labour costs – what had been done and what was yet to be done – and it was making a mess of $600. May 1995  79 SERVICEMAN’S LOG – CTD somewhere around 1987 and this was one of that vintage. It belongs to a family that are long-standing customers and I have serviced it for a couple of routine faults over the years. It gave pretty good service until about 18 months ago. Then it failed completely, due to some minor fault, and landed on my bench. A dismal performance As I say, the basic fault was minor, and I soon had it up and running. But it gave a pretty dismal performance. In simple terms, the picture tube had “had it”. It was so bad that I felt there were only two possible approaches: to try rejuvenating it or, if that failed, fit a new tube. I talked it over with the customer and suggested that since the tube was so sick, there was little to lose by trying rejuvenation. Granted, there are always risks with this approach. One is that it simply won’t work; that the tube will be no better off after treatment. The other is that the tube may suffer further damage and be a complete write off. But, either way, the final result is much the same; a new tube will have 80  Silicon Chip to be fitted, if not immediately, then in a few month’s time when the user can no longer tolerate it. I explained all this to the customer and he saw the wisdom of rejuvenation. So I fished out the rejuvenator and went ahead with the job. Basically, it consists of applying 700-800V between grid 1 and cathode and this should, hopefully, blast any accumu­ lated rubbish off the cathode (usually with a display of fire­works). Of course, this is a somewhat simplified explanation but it will suffice for this story. And it worked this time. Granted, the performance was short of “as-new” but it was still a vast improvement on what it had been. And when the customer and his wife saw the result they were highly delighted; they had obviously forgotten what a good pic­ ture looked like. But I had to add a final word of warning; I had no idea how long the improvement would last. I’ve known it to last for a couple of years but I’ve also seen it pack up after a few months. There is no way to tell and the customer accepted this. With this in mind, I told him that if – or, really, when – it failed again, to bring the set back; that I could probably do a good deal on a picture tube, adding that I had one on hand from a wrecked set. And I emphasised that his set was otherwise in good condition and worthy of a replacement tube. The set that fell And that brings me to part two of the story – a part which has its humorous side. This started about five years previously. It concerns another TC-2138 set, only about 12 month’s old at the time, which belonged to a local club. This was located in a convenient viewing position on a small shelf, a couple of metres above the floor, in one of the club’s lounges. Don’t ask me how it happened – lots of strange things happen in such establishments – but someone knock­ ed it off the shelf. And apparently it landed on a pretty hard surface which, combined with the 2-metre drop, didn’t do it any good. The first I knew about this was when one of the club’s staff walked into the shop carrying the set’s original cardboard carton Naturally, I expected a TV set requiring conventional service. He put the carton on the counter and said. “Can you fix this for us – it’s had a fall.” Even then I didn’t wake up; I imagined it had been simply knocked over or, at worst, taken a gentle tumble due to someone losing their grip while carrying it. Until I opened the carton, that is. And what a sight. It was just a mass of bits. These sets are housed in the usual chipboard cabinet and all four sides were now separate pieces, the glued joints having failed. The plastic back was broken, as was the mask around the tube. And when I took a closer look at the innards, I realised that the mother board was cracked right across. It was all I could do not to burst out laughing; surely he was­­­n ’t serious? It reminded me of all the stories I’d heard about amateur clock repairers, who finish up with a cardboard box full of bits on the local jeweller’s counter. I never did believe those stories but here was something that would top them all. I’m afraid I recoiled in disbelief and this was probably obvious. “You don’t seriously expect me to repair this?” It was the customer’s turn to express disbelief. “Aw, y’should be able to glue the cabinet back together.” Well, I had to agree that, yes, one could probably glue the pieces back together but when I tried to explain about the cracked board and other obvious damage, I realised I was battling against the wind. So I took the diplomatic step of saying, “leave it with me, I’ll have a look at it”. That at least gave me time to think. A hopeless case In fact, I did go through the motions of taking another look. Of course, it was hopeless. The motherboard was cracked from front to back, taking an erratic path around the horizontal output transformer, with a number of secondary cracks radiating from this area. But these were only the visible faults. Even assuming they could be repaired – or replaced – there was always the risk that more damage would come to light as one progressed. And what about the picture tube? Strangely enough, it was physically intact but what had such a fall done to its insides? Even if it still func­tioned electrically, there was a real risk that the shadow mask had been distorted and it would also be a write off. So I rang the club, contacted someone who seemed better able to appreciate the seriousness of the accident, and laid it on the line. There was no way that the set could be repaired and they would be well advised to cut their losses and buy a new set. This advice was accepted and I was thanked me for my trouble. Well, that was the end of that part of the story, except that I was left with a carton of broken bits. There was almost nothing left worth salvaging and I sent most of it off to the tip. But I hung on to the picture tube. It was intact, the scan coils were still fitted (also apparently intact), and shaking it failed to reveal any internal rattles. And so I tucked it away under the bench, hoping that I might get another TC-2138 through the shop so that I could test it. Well, it was over a year later but such a set did turn up. And as soon as I had it working, I fished out the spare tube and propped it up on the bench with its back facing the back of the set. It was the simplest possible operation. All the set’s leads were long enough to reach my tube without any fiddling and, in no time at all, I had the whole arrangement up and running. And not only did the tube and assembly work but everything was spot on and the picture bright and sparkling. I gave it a purity check and even this failed to reveal any problems. So, not only did I have a spare tube in good condition, but one complete with deflection coils and all adjustments spot on. It was, literally, a perfect plug-in replacement. So it went back into stock and I thought no more about is until my aforementioned customer turned up with his sick tube, and I went through the rejuvenation process. Had this not worked, then the tube from the junked set was a good candidate. But it did work and I thought the customer might as well get his money’s worth for a few months. In fact, it was some 18 months before I heard from the family again. Then the wife was on the phone one morning and opened the conversation with the rather matter-of-fact statement that the old TV set had given up the ghost at last. But this was only a prelude to the main reason for the call, which was to ask my advice about buying a new set. Probing a little deeper, I learned that “we stuck the old set down in the garage because we can’t use it any more”. Apparently, my suggestion about a replacement tube had been forgotten. I imme­diately enquired as to whether the set was still actually working and was assured that it was, but that the picture was now quite unwatchable. I then reminded the lady about my offer of a replacement tube and suggested that they bring the set in and let me look at it. At the same time, I pointed out that I could probably restore the set for a good deal less than the $700 or more that they would be looking at for a new set. The set returns And so the set duly landed back on my bench again. A quick check confirmed the situation. Yes, the set was still working and yes, the picture was crook – real crook. I pulled the old tube out, fitted the spare tube and con­nected the various cables. The whole operation took less that half an hour and resulted in a firstrate picture. And, since the scan coils were still as originally assembled and adjusted, no convergence adjustments were required. All I had to do was reset the grey scale, these adjustments having been juggled for best results after the original tube had been rejuvenated. This turned out to be perfectly routine and the end result was excellent. When the owners came in to view the result and collect the set, they were delighted because the performance was virtually that of a new set. But I was perfectly honest with them, pointing out that it was a secondhand tube with about 12 month’s use. I also explained how I had acquired it. How much did it all cost? I charged them $150; $75 for the tube and $75 labour, which I felt was reasonable. And the custom­ ers thought so too; they were more than happy with the whole transaction. So everybody was happy; they had a first-class working set for a modest outlay and I had made a few dollars on a tube I had scored and carefully SC stored for several years. May 1995  81 VINTAGE RADIO By JOHN HILL A console receiver from junk Collecting old radios is a hobby that appeals to collectors in many different ways. For some, it’s the seeking & scrounging; for others, it’s the bartering & trading, or re­pairs & servicing, or the challenge of refurbishing old cabi­nets. One does not have to be a collector for very long before the miscellaneous bits and pieces start to build up. But not all old radios come complete and are easily restored. Indeed, col­lectors frequently encounter empty radio cabinets and odd chassis in various states of disrepair. Some have been smashed or canni­ balised and they appear to have little value. Never overlook these discarded wrecks, however, because they are the main source of much needed spare parts. As such, they should be kept or stripped of usable spares for future use. Parts such as valves, sockets, dials, speakers, knobs, escut­cheons and transformers can all be sourced from derelict receiv­ers. Speaking from my own experience, I must have stripped more than a hundred incomplete radios during the past decade. As no accurate count was taken, the figure could easily be considerably more. I have taken quite a few loads of bare chassis to the tip over the years. It may amuse readers to know that there have been occasions when some of my throw-outs have been returned to me a few days later by well-meaning people who “got onto” a few old radios for me. When the same stripped chassis comes back from the tip a second time, it can only go to show how many of my friends are “looking out” for me. Not all cabinets and chassis are broken or incomplete and quite sizable collections of each can soon accumulate. However, there seems to be a universal problem regarding these particular components. Almost never can similar makes and models be matched up to make a complete receiver. Invariably, the spare chassis will not fit the spare cabinets and the placement of controls and dials usually makes matching physically impossible. It’s Murphy’s Law at its best! Regular readers of Vintage Radio may recall a past story entitled “Realism Realised”. This particular article dealt with the fitting of a Precedent chassis and loudspeaker into a stylish turned-leg Precedent cabinet. In this instance, a complete legless console radio was bought just to supply the innards for the more elegant cabinet. The cannibalised radio was exactly the same apart from cabinet style. Even after the swap over, the resulting outfit was still the correct make and model and completely Precedent throughout. A real bitzer The tuning capacitor had to be raised by about 10mm so that the dial would line up with the dial escutcheon. 82  Silicon Chip Although the Precedent turned out to be a perfect match, this month’s story is about a similar transformation using odd bits and pieces of unknown origins. This time, I have taken an early 1930s console cabinet and mated it with an early 1930s 5-valve superhet chassis and a mid-1930s Rola electrodynamic loud­speaker. Coming up with a name for this creation of mine is rather difficult, as its parentage is decidedly suspicious to say the least. With a blank name space on the dial escutcheon and a The substitute chassis is considerably smaller than the original which took up nearly the full width of the cabinet. Even unmatched left-overs were used when building the cabinet, judging by the two side panels at the front. Despite the “bits & pieces” approach, the old outfit has turned out fairly well. Note the small turned feet fitted to the bottom of the cabinet. when the chassis is in place! Relocating the tuning shaft involved using spacers to lift the tuning capacitor above the chassis. This also realigned the dial with the escutcheon. The dial, by the way, was taken from the original chassis and it fitted in behind the escutcheon just like it always did. The chassis has the typical appearance of an early 1930s super­het, although the spun aluminium valve shields with their “acorn” shaped air vents are unusual. chassis that could have been made by anyone, it seems like a lost soul amongst the rest of my collection. I think I will call it “Claude”, just to identify it. The cabinet did have a chassis when I first acquired it but it had been extensively stripped of most of its parts with the exception of the tuner and dial. If I remember correctly, it was originally a battery set and the loudspeaker was also missing. What else can one do with such an incomplete receiver other than store it in a disused corner of the shed, hoping that, one day, something would come along and give it a new lease of life. That new lease of life became a reality when I was given a 5-valve chassis. And although this chassis was smaller and lacked the width of the original, the control positions at the front were fairly close to what was required. With just a little rear­ranging, they would fit the existing holes in the cabinet. To be more specific, the tuning control needed lifting about 10mm, while the two lower controls had to be moved up and slightly to the right. To align the two lower controls, the holes in the chassis were elongated with a round file until the control shafts lined up with the holes in the cabinet. In fact, these controls needed shifting a little further than I originally thought and a much neater job would have resulted by simply drilling new holes. Oh well, no one sees the job 1930s superhets This particular 5-valve chassis is a little better than most receivers of that vintage. Nearly all early 1930s super­hets were built to the unofficial standard of their day – autodyne mixer, 175kHz IF (intermediate frequency), an anode bend detector and a single output stage. My 5-valver has two significant dif­ferences to this set up. First, it uses a diode detector instead of the anode bend arrangement that is usually the case. Diode detection produces a cleaner sound with considerably less distortion. By the mid1930s, nearly all superhets had diode detection. And second, the intermediate frequency is a much higher 460kHz. The detection circuit makes use of a 2B7 valve, a semi-remote cutoff pentode with a pair of diodes. There is no AGC (automatic gain control) May 1995  83 This end of the chassis accommodates the 2A5 output valve (left) & the 80 rectifier (right). The 2B7 valve is one of the few early valves with built in diodes. Diodes are essential for low-distortion detection & automatic gain control (AGC). incorporated into the circuit but this feature could easily be added if desired and used in conjunction with the IF amplifier valve. Such an AGC setup works reasonably well, although not as effectively as when the frequency converter valve is also controlled. The 2.5V 2B7 valve was one of those “landmark” valves. It went on to become the 6B7, the 6B7S (remote cut- off) and the 6B8 (which is a 6B7S in octal form). Other valves in the line-up are also 2.5V types and include a 57 as an autodyne mixer and a 58 IF amplifier. The output is handled by a 2A5. Once again, these are all landmark valves, with some going on in other forms for many years after their concep­tion. 84  Silicon Chip The volume is controlled by a wirewound potentiometer in the cathode circuit of the IF amplifier valve. As usual, the volume control needed replacing and a 5kΩ 3W potentiometer of modern manufacture was used as a substitute. Restoration Restoration of the chassis was relatively straightforward, involving the usual replacement of all paper and electrolytic capacitors, plus a couple of valves and a wirewound resistor. All coils and transformers were serviceable and the general wiring was clean and corrosion free. And, as a bonus, there was no perished rubber cov­ered wiring, as all the underchassis hook- up wire was fabric covered. This receiver has no tone control, as was often the case in that era. Instead, the third control knob is for an on/off switch and this also needed replacing. The original switch had an unde­sirable internal resistance which would have caused trouble if it had been put back into service. Another electrical contact problem involved the tappings on the high-tension dropping resistor. This is not an uncommon fault to encounter and a thorough clean and re-tighten usually restores continuity. In this instance, however, the taps did not really need cleaning. Insufficient tension was the cause of the poor connections, as there was little or no pressure on the contact points. They had never been tightened properly in the first place! The chassis itself was a rather rusty looking mess on top, with some of the rust pits being quite deep. A bit of anti-rust treatment followed by a couple of coats of aluminium paint did much to improve its general appearance. A bit of experimenting (using various 20W wirewound resistors as field coil substitutes) indicated that a field resistance of 2kΩ would be a good choice. A spare 8-inch (200mm) Rola electrodynamic loudspeaker with a 2.2kΩ field coil was found in the spare parts department and it fitted the baffle board screw holes perfectly. The field coil drops the high tension to 240V after every­thing has warmed up to operating temperature. It was noted after the set was working that it could be used for 2-3 hour periods with the field winding only becoming only moderately warm during that time. This indicates that everything is normal in the high tension department. After the usual alignment procedure, the once derelict old chassis performed surprisingly well. It’s not often that they cannot be brought back from the dead! The cabinet The cabinet is typically early 1930s – big, square and with a fretwork loudspeaker opening. It also stands on short stubby little turned feet (legs?). Well, if they’re legs then they’re hippopotamus legs! Now I have always had trouble refurbishing timber radio cabinets. I have done many and most of them RESURRECTION RADIO VALVE EQUIPMENT SPECIALISTS Repairs – Restoration – Sales for RADIO & AUDIO Equipment S VE L VA This Rola K8 loudspeaker is the only brand-name component in the author’s “bits & pieces” console. The cabinet & chassis are of unknown manufacture. The speaker may be a few years younger than the rest of the outfit. BOUGHT SOLD   TRADED Send SSAE for Catalogue Visit our Showroom at 242 Chapel Street (PO Box 2029) PRAHRAN, VIC 3181 Tel: (03) 9510 4486; Fax (03) 9529 5639 Silicon Chip Binders This close-up view shows the controls. The new chassis lined up perfectly with the cabinet after a few minor adjust­ments. Note that there is no maker’s name on the dial escutcheon. look quite OK – but I find them a real humbug to do. As luck would have it, I have discovered someone who does an excellent job of cabinet repairs for a reasonable price and he transformed this particular cabinet of mine (which was a bit knocked around) to a thing of great beauty. It is said that “beauty is in the eye of the beholder!” Well, not everyone sees my cabinet that way and I have been told that it is big and ugly. What a nasty thing to say! As a matter of interest, the cabinet has been sprayed with a genuine nitrocellulose lacquer – the same sort of finishing treatment that was used in the 1930s. Personally, I would prefer an Estopol® type polyurethane finish, as it is far more durable. One unfavourable aspect of the nitrocellulose treatment is the fact that it goes white wherever it receives a knock. Well, there it is – a good-performing 1930s console radio that has been built up from odd parts. It looks good, sounds great and cost very little. It’s ancestry, on the other hand, is definitely suspect! But while it is a far cry from a brand-name collectable, it certainly looks the part – even if it has SC got hippopotamus legs! These beautifully-made binders will protect your copies of SILICON CHIP. They are made from a dis­tinctive 2-tone green vinyl & will look great on your bookshelf. Price: $A11.95 plus $3 p&p each (NZ $8 p&p). Send your order to: Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 979 6503; or ring (02) 979 5644 & quote your credit card number. May 1995  85 Silicon Chip July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3; All About Electrolytic Cap­acitors. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Rad­ios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.4. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Simple DTMF Encoder; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC. November 1989: Radfax Decoder For Your PC (Displays Fax, August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Wave Generator, Pt.2. RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. December 1989: Digital Voice Board (Records Up To Four Separate Messages); UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; Installing A Clock Card In Your Computer; Index to Volume 2. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. March 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Receivers From The 1920s. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Fitting A Fax Card To A Computer. September 1990: Music On Hold For Your Tele­phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; Using The NE602 In Home-Brew Converter Circuits. November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; Versatile 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages; Tasmania's Hydroelectric Power System. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; Build A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. ORDER FORM Please send me a back issue for: ❏ June 1989 ❏ July 1989 ❏ December 1989 ❏ January 1990 ❏ June 1990 ❏ July 1990 ❏ November 1990 ❏ December 1990 ❏ April 1991 ❏ May 1991 ❏ September 1991 ❏ October 1991 ❏ February 1992 ❏ March 1992 ❏ July 1992 ❏ August 1992 ❏ February 1993 ❏ March 1993 ❏ July 1993 ❏ August 1993 ❏ December 1993 ❏ January 1994 ❏ May 1994 ❏ June 1994 ❏ October 1994 ❏ November 1994 ❏ March 1995 ❏ April 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 September 1989 February 1990 August 1990 January 1991 June 1991 November 1991 April 1992 September 1992 April 1993 September 1993 February 1994 July 1994 December 1994 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ April 1989 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 May 1992 October 1992 May 1993 October 1993 March 1994 August 1994 January 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ May 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 June 1992 January 1993 June 1993 November 1993 April 1994 September 1994 February 1995 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 86  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Tuning In To Satellite TV, Pt.1. July 1991: Battery Discharge Pacer For Electric Vehicles; Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Step-By-Step Vintage Radio Repairs. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator For Model Railways Mk.II; Magnetic Field Strength Meter; Digital Alti­meter For Gliders & Ultralights, Pt.2; Getting To Know The Windows PIF Editor. November 1991: Colour TV Pattern Generator, Pt.1; Battery Charger For Solar Panels; Flashing Alarm Light For Cars; Digital Altimeter For Gliders & Ultralights, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Modifying The Windows INI Files. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Index To Volume 4. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Automatic Controller For Car Headlights; Experiments For Your Games Card; Restoring An AWA Radiolette Receiver. February 1992: Compact Digital Voice Recorder; 50-Watt/ Channel Stereo Power Amplifier; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; Designing A Speed Controller For Electric Models. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Direct­ories; Valve Substitution In Vintage Radios. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo Amplifier, Pt.2; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; Low-Cost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Multi-Station Headset Intercom, Pt.2; Electronics Workbench For Home Or Laboratory. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Electronically Regulated Lead-Acid Battery Charger. April 1994: Remote Control Extender For VCRs; Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Low-Noise Universal Stereo Preamplifier; Build A Digital Water Tank Gauge; Electronic Engine Management, Pt.7. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Two Simple Servo Driver Circuits; Electronic Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. February 1993: Three Simple Projects For Model Railroads; A Low Fuel Indicator For Cars; Audio Level/VU Meter With LED Readout; Build An Electronic Cockroach; MAL-4 Microcontroller Board, Pt.3; 2kW 24VDC To 240VAC Sine­ wave Inverter, Pt.5. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; An 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; A PC-Based Nicad Battery Monitor; Electronic Engine Management, Pt.9 March 1993: Build A Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders;A 24-Hour Sidereal Clock For Astronomers. July 1994: SmallTalk – a Tiny Voice Digitiser For The PC; Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. April 1993: Solar-Powered Electric Fence; Build An Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Step-Up Voltage Converter; Digital Clock With Battery Back-Up. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; The Micro­soft Windows Sound System. June 1993: Windows-Based Digital Logic Analyser, Pt.1; Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; Remote Volume Control For Hifi Systems, Pt.2 July 1993: Build a Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Windows Based Digital Logic Analyser; Pt.2; Quiz Game Adjudicator; Programming The Motorola 68HC705C8 Micro­controller – Lesson 1; Antenna Tuners – Why They Are Useful. August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Build a Nicad Zapper; Simple Crystal Checker; Electronic Engine Management, Pt.11. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Aircraft Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Electronic Engine Management, Pt.12. October 1994: Dolby Surround Sound – How It Works; Dual Rail Variable Power Supply (±1.25V to ±15V); Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Temperature Controlled Soldering Station; Electronic Engine Management, Pt.13. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits. November 1994: Dry Cell Battery Rejuv­enator; A Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems: How They Work; How To Plot Patterns Direct To PC Boards. September 1993: Automatic Nicad Battery Charger/ Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach; Servicing An R/C Transmitter, Pt.1. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford – A Pesky Electronic Cricket; Cruise Control – How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 2; Servicing An R/C Transmitter, Pt.2. January 1995: Build A Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Preamplifier; The Latest Trends In Car Sound; Pt1. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Electronic Engine Management, Pt.2; More Experiments For Your Games Card. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers , Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt2; Remote Control System For Models, Pt.2. December 1993: Remote Controller For Garage Doors; Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier Module; Peripherals For The Southern Cross Computer; Build A 1-Chip Melody Generator; Electronic Engine Management, Pt.3; Index To Volume 6. March 1995: 50W/Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras & Night Viewers; Remote Control System For Models, Pt.3; Simple CW Filter. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design For Beginners; Electronic Engine Management, Pt.4. April 1995: Build An FM Radio Trainer, Pt1; Photographic Timer For Darkrooms; Balanced Microphone Preamplifier & Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. February 1994: 90-Second Message Recorder; Compact & Efficient 12-240VAC 200W Inverter; Single Chip 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Electronic Engine Management, Pt.5; Airbags – How They Work. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, November 1988, December 1988, January, February, March and Aug­ust 1989, May 1990, and November and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear­sheets) at $7.00 per article (includes. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. March 1994: Intelligent IR Remote Controller; Build A 50W Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Electronic Engine Management, Pt.6. May 1995  87 PRODUCT SHOWCASE Epson’s LX-300 dot matrix printer has colour option Not everyone with a computer wants or needs an inkjet or laser printer. A dot matrix printer can do most print jobs and at price which is only a fraction of the fancier machines. And if you want to print in colour, a dot matrix unit like the Epson LX-300 can do it, by changing to a 4-colour ribbon. No-one denies that a laser printer or an inkjet can pro­duce a smart looking print job but for the home computer user or small business, they are often an expensive overkill. They are also expensive to run, with toner cartridges and drum renewals being very costly and while inkjet refills are cheaper, ribbons for dot-matrix printers are cheaper again and last longer. Another aspect to consider if you are using a laser printer is the disposal of the toner cartridge. Ideally, this should be recycled, both from the point of view of economics and the envi­ronment – toner cartridges should not go to the tip! All of which is a strong argument in favour of a low-cost dot matrix printer, such as the Epson LX-300. This has a 9-pin print head and prints on 80-column wide tractor-feed fan-fold paper or on single sheets (eg, A4-size) in friction-feed mode. By comparison with some inkjet 88  Silicon Chip printers, the LX-300 looks a little bulky but it is reasonably compact with dimensions of 385mm wide, 275mm deep and 130mm high, although the height is greater if the single-sheet feeder is in place. It weighs approx­ imately 4kg. As with many printers which can take single sheet or trac­tor feed paper, the LX-300 features “paper parking”. This allows you to have tractor-feed paper hooked up but by “parking” it, you can print one or more sheets using the friction feed. In fact, some readers may argue that the need for tractor feed paper is far less than it once was and that it is cheaper to use copy paper than fan-fold tractor feed paper. Both these comments are true but you still need the ability to handle tractor-feed paper if you want to print multi-part (e.g., original plus duplicate) forms such as invoices or computer labels. Printer fonts are selected by pushing the “font” button to light up the font LEDs in various combinations. By this means you have a choice of Roman, Sans Serif, Draft and Draft Condensed modes. The first two modes are classed as NLQ (near letter quali­ty) and the printer achieves this, in spite of only having a 9-pin print head, by making two passes for each line. In fact, if an underline is required for a line, the print head will make three passes. This requirement to make multiple passes means that the LX-300 is quite slow when printing in NLQ modes – the quoted figure is 44 characters/ second at 10 characters per inch and 53 cps at 12 cpi. In the draft modes, it is much faster: 264 cps at 10 cpi and 220 cps at 12 cpi. Feeding single sheet paper in is interesting. You just place the sheet into the feeder and push it down slightly until you feel resistance. The machine then feeds the paper round the platen and moves it backwards and forwards to find the top of sheet. This is good because you don’t have to line it up your­self. Another good feature is the way in which the printer cable and mains cord are plugged in underneath the machine. The cords are then routed out via both sides the case, so that they don’t interfere with tractor paper feed. Two interfaces are provided, a 36-pin Centronics socket and a 25-pin D-socket serial interface. In other respects, the LX-300 has all the normal features you would expect from a small dot-matrix printer and all of these are accessible via the Epson Esc codes. Mostly you never have to worry about these because it is all done by your printing soft­ware. You just tell the software that you are using Barcode time clocking An inexpensive time attendance system has been announced by AS Microcomputers. Designed and manufactured in Australia, the ZipNet Terminal is about the size of a standard mains power point. It is wall mounted, displays the time, has a slot for bar-coded cards and a socket for touch memory tags. Once a person has clocked in, the time recorded is stored for later collection by an administrative computer. For further information, contact an Epson LX-300 and the computer does the rest. We did not try the colour feature. This involves a special ribbon cartridge which is used by print ribbon shifting, again under the control of the printer and your software. The four colours of the ribbon are cyan, magenta, yellow and black (ie, CMYK, the standard four-colour printing process). ASP Microcomputers, 456 North Road, Ormond, Vic 3204. Phone (03) 578 7600. In conclusion, the Epson LX-300 is definitely worth consid­ering if your print jobs do not require laser or inkjet quality. It is cheap to run and cheap to buy. Our sample came from Rod Irving Electronics and they currently have it on sale, priced at $249 including sales tax. Rod Irving Electronics has a range of Epson printers available and more information is available at any of their stores. (L.D.S.) 20MHz Dual Trace Scope $795 100MHz Kikusui 5-Channel, 12-Trace 50MHz Dual trace Scope $1300 COS6100M Oscilloscope $990 These excellent units are the best value “near brand new” scopes we have ever offered. In fact, we are so confident that you’ll be happy, we will give you a 7-day right of refusal. Only Macservice can offer such a great deal on this oscilloscope . . . and you are the winners! 1. Power switch 2. LED 3. Graticule illumination switch 4. Trace rotation 5. Trace focus 6. Trace intensity for B sweep mode 7. Brightness control for spot/trace 8. Trace position 9/10/11. Select input coupling & sensitivity of CH3 12. Vertical input terminal for CH3 13. AC-GND-DC switch for selecting connection mode 14. Vertical input terminal for CH2 15/22. Fine adjustment of sensitivity 16/23. Select vertical axis sensitivity 17/24. Vertical positioning control 18/25/38. Uncal lamp 19. Internal trigger source CH1,CH2,CH3,ALT 20. AC-GND-DC switch for selecting connection mode 21. Vertical input terminal for CH1 26. Select vertical axis operation 27. Bezel 28. Blue filter 29. Display selects A & B sweep mode 30. Selects auto/norm/single sweep modes 31. Holdoff time adjustment 32/51. Trigger level adjustment 33/50. Triggering slope 34/49. Select coupling mode AC/HF REJ/LF REJ/DC 35. Select trigger signal source Int/Line/Ext/Ext÷10 MACSERVICE PTY LTD 36. Vertical input terminal for CH4 37. Trigger level LED 39. A time/div & delay time knob 40. B time/div knob 41. Variable adj of A sweep rate & x10 mag 42. Ready lamp Australia’s Largest Remarketer of Test & Measurement Equipment 20 Fulton Street, Oakleigh Sth, Vic., 3167. Tel: (03) 562 9500; Fax: (03) 562 9590 43. Calibration voltage terminals 44. Horizontal positioning of trace 45. Fine adjustment 46. Vertical input terminal for CH5 47. Delay time MULT switch 48. Selects between continuous & triggered delay 52. Trace separation adjustment 53. Ground terminal May 1995  89 Hand-held pH meter The model HH4-PH is a handheld pH meter with a 4-digit 12.7mm liquid crystal display. It has inputs for a pH electrode and a temperature sensor. A simple key­ pad allows the reading to be displayed in pH, milli­ volts or temper­ ature. Temperature com­pen­sation may be set manually or may be automatic via a sensor. A unique “electrode slope” display allows the condition of the pH electrode to be monitored, providing the user with an indication of wear. Calibration is carried out via a pushbutton procedure, with calibration data stored in non-volatile memory. Single point or 2-point calibration methods may be used. Additional features include a programmable automatic switch to prolong battery life and a programmable digital filter to reduce noise interference. A soft carry case, pH buffer solutions and a range of pH electrodes Cadjet plotter for large drawings Plotting up to A0 in size, Cadjet is ideal for mapping and CAD users to produce colour logos, titles, colour raster insets and small cross sections. Cadjet uses inkjet tech­nology to provide clean, reliable plotting with excellent line quality and a choice from a palette of 256 colours. Plots in A1 size monochrome draft quality are produced in less than 2.5 minutes and spot-colour draft quality in 10 minutes. Other features include automatic cut and stack in roll-feed mode, replot or multiple copies without the need for re-transmitting the vector file, and the ability to add an optional host-based spooler for convenient, productive unattended plot­ting. Print output may be on a variety of media including quality pen plotter bonds, vellums and film. There are seven “quick action” buttons on the control panel for frequently used instructions. In addition, there are five LED indicators and a liquid 90  Silicon Chip are available as options. For further information, contact Amalgamated Instrument Company Pty Ltd, 5/28 Leighton Place, Hornsby 2077. Phone (02) 476 2244. crystal display with an intuitive menu so that the unit can be used with minimal training. A black cartridge produces fast monochrome drawings at 300 x 300 dpi. There is also an option for 600 x 300 at a reduced speed. Adding colour is simple with the tri-chamber cyan-magenta-yellow cartridge which delivers 300 x 300 dpi printouts. The standard four megabyte plotter buffer handles most files and can be easily upgraded to 32 megabytes using standard SIMMs. The plotter emulates HP-GL, HP-RTL and HP-GL/2 so it works with a wide variety of CAD and mapping software. It also has the ability to combine vector drawings with raster images on the same page. The unit is available in A0 size or A1 size and comes stan­dard with a Windows 3.1 driver, AutoCAD/386 Release 12 ADI driver vector and raster versions. For further details contact Susan Barry, National Sales Manager, TCG, 30 Balfour St, Chippendale, NSW SC 2008. Phone (02) 698 5000. ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Troubleshooting the 1GHz frequency meter I have a problem with the 1GHz digital frequency meter, as published in the November 1987 issue of SILICON CHIP. It will not tune up via VR1 and will not trigger the Schmitt (IC2A). Also the LED above the period button will not work. We have checked the LED and it’s OK. We have been through the circuit so many times and everything checks out. We have been through the troubleshooting section several times but can find nothing wrong. It just does not want to work. We were wondering if you have met with this problem. If so, can you give us any information on how to get it working as it should? (J. B., Ardrossan, SA). • This project was featured in our first issue and has proved very reliable in Saving waste water with a diverter valve I would like to set up a system whereby I can divert used water from the washing machine, shower and bath, into a holding tank from which I could pump into a closed sprinkler system around my garden. My problem is that I require some sort of switching circuit that can switch on when the tank is full, thereby controlling a pump to feed the sprinkler system and then to switch off when the tank is empty. My guess would be to employ some type of sensor to detect full and empty which, in turn, controls relays to operate a standard “Davey” style 240V water pump. Could this idea be considered as an upcoming project by your excellent design team? Think of the water you would save! (J. E., Muswellbrook, NSW). • It seems likely that you could design your system around the the intervening years. The most common problems are missing segments due to solder bridges or missed solder joints. As far as your problems are concerned, we would again suspect soldering or even LEDs installed the wrong way around (embarrassing, but it happens to the best of us). It is possible to check the MC10116 (IC2) by measuring the voltages at its pins. Since it is an ECL device, the pins will sit at around +4.3V (high) or +3.4V (low). Pins 9 & 10 are biased at around +3.8V and the difference between them should be vari­able by trimpot VR1. Supersonic oscillation in audio amplifier I have a problem with a 300W amplifier module published about 15 years ago in another electronics magazine. sensors used in dishwashers. After all, these are designed to control 240VAC pumps and therefore are ideally suited to the job. However, it would not seem practical to have the unit pump out when the tank was full; after all, it could be raining! It would be better to have the diverter valve switch back to the sewer when the tank is full. If the diverter valve is electrically operated this would be a simple matter, using a standard water level sensor from a washing machine. At this stage though, we are reluctant to publish a design in the magazine as we understand that these water diverter valves are not legal and, in fact, people can be prosecuted for using them. On the other hand, if you know that they definitely are legal in some areas, we could certainly look at publishing a suitable circuit. We should also state that we think that this concept of water recycling must eventually be accepted by the authorities. I have had quite a bit of experience with many kits and can quite often nail tricky faults but not this one. Just recently I have built four of these modules and have only had success with one. I did noth­ing different at any of the four times. With no fuses present and no heatsink on the board, the power rails read ±70V DC. The voltage across the fuse clips ranges from 10.5V-35.8VDC according to the setting of the bias trim. There has been no load or input signal applied at this time. After about 15 seconds, with the bias trim at maximum resistance, the emitter resistors in the voltage amplifier stages both burn up. After this, checks on all output devices reveal that all the MJ15003, MJ15004s are OK. All the other transistors are fine also. I am testing these transistors by conventional resistance checks and a multimeter with hFE facility. I am unable to stop these resistors destroying themselves unless I bring the bias trim to a low resistance. At this stage I thought I was getting somewhere because I had no black parts but it was then I found I could not adjust the offset voltage at all. I then tried the module with the fuses in place and the bias pot at a low resistance. Nothing burned out but after about a minute the output devices were hot enough to fry an egg. At this stage, I went back to basics, I replaced all semiconductors and checked all my capacitors and resistors. My wire links are all correct and there were no shorts on the board. I tried again with the test procedures and had the same problems and results as before. I showed the modules to a friend who is a TV serviceman and he could find no solution to this problem. (D. W., Melbourne, Vic). • While we cannot be sure, it sounds as though your amplifier is oscillating supersonically, possibly at several hundred kilo­hertz although it could be a great deal higher than this, possi­bly at 10MHz or more. The best way to check for this is to use an oscilloscope which May 1995  91 Reversing an electric drill I have a 2-speed 240VAC electric drill. Could you explain how to modify the wiring to operate the drill in reverse direc­tion? Also, in a future publication, please explain the principle and concept of AC & DC motors. It would be useful for all read­ers. Recently, I built the UHF remote switch project (December 1989) and I experienced problems with the operational range. When I want to switch on the unit, I am able to operate the transmitter from 20m distance but when I go to switch off the unit, I need to come close to the receiver unit (less than 1m). Could you please explain to me why it’s happening or show any modification on the circuit? (C. M., Home­bush West, NSW) • Reverse direction in a universal motor, as used in electric drills, can only be achieved by reversing the connections to the field wind­ should ideally have a bandwidth of 20MHz or more. Your symptom of very hot output transistors certainly points to supersonic oscillation. The most likely cause of this problem is open circuit capacitors; eg, in the feedback circuit, between the base and collector of the voltage amplifier stage and in the Zobel network at the output. Electronic regulator for an alternator Since I retired a few years ago, I find that I use my car infrequently with the result that my battery does not get its regular dose of current each day. I thought that the solution to this would be to find one of my old PC boards on which I had built an adjustable regulator to control the current from the alternator to the battery. These circuits were around in the 1970s as we were still using electro-mechanical regulators on some cars. I had the same problem then; ie, not travelling enough distance to regularly charge the battery. After removing the internal epoxied 92  Silicon Chip ings with respect to the armature. Electrically, this is pretty simple since you only need to swap the connections to the brushes. Practically though, it could be quite difficult since you would need to install a double-pole changeover switch and there would be little space inside most appliances. We should also caution against running a drill in the re­verse direction because this will normally screw out the Jacobs chuck. In drills designed to be reversed, the chuck has a lefthand screw up the centre to stop it coming off. We are not sure why your UHF remote switch is hard to turn off but the most likely reason is that when the internal relay operates, the increased current drain from the supply means that the voltage to the regulator drops and causes more noise to be injected into the receiver. Hence, you need a stronger signal to turn it off. You may want to try another plugpack to check this suggestion. regulator inside the alternator and then replacing it with the externally mount­ed custom built unit, I was able to adjust the current to compensate. It worked so well, I used it for years and the battery was never flat although you had to remember to turn the pot back to normal before any long trips otherwise the battery would overgas. To my sorrow, I cannot find my old board unit or the cir­cuit. I noted the circuit in the “Circuit Notebook” pages of the September 1994 issue and reflected that I might use this for the job. However, I do remember that my old regulator used a 2N3055 attached to a heatsink and had a large 5W or 10W resistor plus a handy pot to adjust the voltage/current. Can you help with advice or one of those old circuits? (E. F., Watsons Bay, NSW). • While we cannot place your original regulator, the auto voltage regulator circuit in September 1994 can be made adjust­able simply by connecting a 5kΩ trimpot as a rheostat in series with the 1.5kΩ resistor and ZD1. Ideally, you could make the unit switchable so that the trimpot was switched out when you wanted the normal +14.2V cutout. Most of the components could be assem­bled onto a small piece of Veroboard and thereby replace your lost PC board. Increasing metal locator sensitivity I have constructed the induction balance metal detector that appeared in the May 1994 edition of SILICON CHIP. I pur­chased a kit from Jaycar in north Melbourne whilst on a recent trip to that area. I found the detector to be very good, doing everything it was supposed to do, but now I would like to experi­ment with larger coils to try for something deeper. I am not sure where to start and am wondering if you could give me some basic advice. The main questions that I would like some advice on are: (a) If I increase the size of the coil former, do I increase the number of turns of wire to make the coil, or do I use less? (b) Is there a formula, or some way of working this one out? (c) If I increase the size of the coil, do I have to use a different size of wire to wind it? When I opened the kit, it contained a short note from Jaycar stating that the reel of wire to wind the coil was not quite 37 metres in length, however, that would not make any difference to the coil, because a few turns either way would still let the coil operate normally. This I have found to be true. In other words, the number of turns is not critical. Howev­er, I am contemplating constructing a coil of around 20cm in diameter and this may make a great deal of difference. (B. D., Narooma, NSW). • As you have found, the number of turns on each coil is not critical. However, it is a good idea to use the same number of turns for both the transmit and receive inductors. The inductance of the coil will increase with the square of the radius and with the number of turns in a square-law fashion. So if you double the radius of the coil, reduce the number of turns to 0.7 of the original number. The wire diameter is not critical and we chose 0.6mm enamelled copper wire so that the coil was easy to wind and yet would support its own weight. Smaller diameter wire can also be used but be careful with the choice of baseplate so that it is stiff enough to prevent movement between the coils. I made an enquiry through my local wholesaler regarding the best FM antenna available and was told that the Hills 453FM was the top of the range. Having purchased a Tandy rotator, I would like to set up the best system to enable me to pull in distant FM stations in any direction. As some FM stations transmit horizontal and some vertical, would I gain anything by buying two FM antennas, placing one horizontal and one vertical, and coupling the two together? Should you feel that the two would be better, do you have any details such as the distance apart and is there a special coupler to marry the two in? Warilla is approximately 16km south of Wollongong and I intend putting the antenna/s up approximately 10 metres and installing my rotator so that I can direct the antenna to whatever signal I want to listen to. Do you have or can you advise me where I can get a complete list of Australian AM sta­tions, NSW FM & TV stations, their locations and power? Finally, I have connected into my 40W stereo amplifier a Tandy Realistic Cat 40:136 4-speaker control unit which allows my stereo to feed into four rooms. I would like to purchase another of these to give me a total of eight. Can I parallel the two switch boxes or do you have a circuit I can build to match the two in? (R. C., Warilla, NSW). • In general, you will obtain improved FM reception by having an antenna which matches the polarity of the transmitting sta­ tion. While the loss in signal reception from an incorrectly polarised antenna may not be important, the signal quality will also deteriorate due to worsened multipath (ie, ghosting) charac­teristics. Be that as it may, most car radios give quite good recep­tion from most stations (when stationary) even though their vertically polarised whip antenna may not match that of the signal. Our suggestion would be to install one antenna with its polarity matching the majority of stations you wish to receive. In practice, your installation of a rotator will possibly be more beneficial than polarity matching for all stations. If you wish to have two antennas, one vertical and one horizontal, you Using a multi-tap transformer T1 MM-2005 I am building the Rail­ 240VAC power Walkaround Throttle for Model Railroads and I have a problem. Your article specifies an M-2165 transformer from Altronics but I have been supplied with an equivalent 60VA transformer (Cat MM-2005) from Jaycar. Instead of two separate 12V windings which need to be connected in parallel, as per your article, this transformer appears to have all its secondary connections as part of one winding. The connections it provides are 0V, 9V, 12V, 15V, 18V & 24V. Do I just connect between the 0V and 12V terminals and ignore the others or is there more to it than that? (E. R., Cessnock, NSW). • You can get your circuit to work by connecting to the 0V and 12V winding taps as you suggest but it will not provide the full power output from the secondary winding. In effect, you will be extracting all the power from one half of the winding while the other half does nothing. If you try to draw the full rated power from 1N5404 24V 12V 0V 1N5404 2200 25VW 2200 25VW the transformer under these conditions, one half of the transformer secondary will tend to overheat and may even burn out. The solution is relatively easy and involves wiring the transformer as a centre-tapped secondary and omitting two of the diodes in the existing bridge rectifier. As shown in the accompa­ nying circuit diagram, the 12V terminal on the transformer becomes the centre-tap and this is connected to the negative side of the 2200µF 25VW electrolytic filter capacitors. The 0V and 24V connections of the transformer then connect to the anodes of the two diodes and these then connect to the positive side of the filter capacitors. The accompanying portion of the wiring diagram for the PC board shows how this wiring is accomplished. 12V 220uF 2x1N5404 24V AC CONNECTIONS ON TRANSFORMER 220uF 0V 2.2uF 2.2k Q7 2.2k Long distance FM reception +12V 10uF 7812 will inevitably have some signal loss by coupling their signals together in a combiner. The total installation will also be quite tall since the antennas should preferably be at least one metre apart if they are not to interact and mutually degrade their gain and back-to-front characteristics. Each year the Department of Communications publishes a handbook listing all television and radio broadcast stations in Australia. They should be available from the Government bookshop in your closest city. As far as your Tandy speaker control unit is concerned, we don’t think you can safely use two of these in parallel. You would be wise to consider having another amplifier to drive a separate SC room controller. May 1995  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES FOR SALE Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly in the space below or on a separate sheet of paper, fill out the form & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 979 6503. BUSINESS FOR SALE: vintage electronic repair business for sale. Established 6 years, includes over 10,000 valves, 100,000 capacitors, 200 radios and much more. Will sell with option of lease or freehold; will consider selling stock for relocation. Price $10,000 plus S.A.V. Enquiries to Howard Sheeran (060) 24 4558. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ MicroZed has stocks of NewMicro 68HC11F1 board, 20 I/O, 8ch A/D, Serial port, LCD I/F, 4x5 keypad I/F EEPROM Programs in FORTH, (in EPROM), BASIC, SMALL C, & Assembler. No books, documentation and programs on disk. Warning: you will need EPROM burner to use this one. 150mm x 100mm board, 18 by 36 pad work area, needs 5V-30Ma. For info, send 1 x 45c to MicroZed (see display advert p.95 for address). VALVE SPECIALS: 6V6GT $8.50, 6L6GC $10.00, ECC35 Mullard $22.00, 12AX7 $9.00, 12AT7 $10.00. High Voltage Caps: eg, 0.022uF 24c, 0.1uF 36c, 0.22uF 42c all 400V MKT. Call or send for list. RADIO RESTORATIONS (057) 26 1958. LEARN MICROCONTROLLER programming with our Motorola 68HC­ 705K1 & P9 Kits. All code fully commented, provided on floppy disk. Introduction to the K1 (reviewed in Everyday Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Card No. ✂ ❏ Bankcard   ❏ Visa Card   ❏ Master Card Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip RCS Radio Pty Ltd is the only company that manufactures and sells every PC board and front panel published in SILICON CHIP, ETI and EA. RCS Radio Pty Ltd, 651 Forest Rd, Bexley 2207. Phone (02) 587 3491 YUGA ENTERPRISE BA, LA, LB, LC, UPA, UPB, UPC, TA, Buy TBA, TDA, TEA, & 2SA, 2SB, 2SC, Sell ese 2SJ, 2SK, SAA, Japan STA, STK, STR, s IC & tors HA, AC, KA, KIA, Transis IX, LM, MN, PA TEL: (65) 741 0300 FAX: (65) 749 1048 705 Sims Drive #03-09 Shun Li Industrial Complex Singapore 1438 CTOAN ELECTRONICS PO Box 211, Jimboomba 4280. (07) 297 5421 New Kits Coming – Send For Details (1) Digital Speedo & Fuel Gauge (2) Digital Engine Temperature Gauge (3) Digital Battery Voltage Monitor (4) Automatic Pool Pump Controller (5) Main Connected Remote Control System (6) Bar Of Light Tachometer Electronics, 2/94), Reaction Timer (Electronics Australia, 3/94), Number Crunch­er (EA, 9/94), & Codepad (uses P9). DIY Electronics, phone/fax: (058) 62 1915. PELTIER EFFECT solid state modules 3cm x 3cm, 8V/5.4A. One side heats, the other cools. Up to 59 deg. C differential. Also 2.5mw, 635nm LASER DIODE modules, 10 times brighter than 670nm modules. HeNe replacement, 3V to 6V. 3-element glass collimating lens adjustable. DIY Electronics, tel/fax: (058) 62 1915. MicroZed has LCD drive board Serial in at 2400 Baud, drives your LCD with 44780 chipset. For info 1 x 45c to MicroZed (see display advert p.95 for address). 68705 DEVELOPMENT SYSTEM: In Circuit Simulator/Emulator and programmer board. Supports 68705 and 68HC705 series of Motorola micro controllers. Oztechnics, PO Box 38, Illawong, NSW 2234. Phone (02) 541 0310. Fax (02) 541 0734. Email oztec<at> ozemail.com.au. TECHNOLOGY BREAKTHROUGH: a $20 Programmer Kit for one of the newest, fastest, low power, single chip EEPROM micros available. The $15 PIC16C84 can be it’s own downloader Parallax Basic Stamp BS1-IC 8 I/O $49; Proto Board $17 Program in schoolboy level BASIC for SOPHISTICATED results. Send 4 x 45c stamps for application notes. Parallax technical support in Australia. MicroZed Computers PO Box 634 (296 Cook’s Rd), ARMIDALE 2350 V (067) 722 777 F (067) 728 987 Credit cards accepted. MEMORY & DRIVES PRICES AT APRIL, 1995 SIMM (all 70ns) Parity/No Parity 1Mb 30-pin $64/58 4Mb 30-pin $200/200 2Mb 72-pin $148/135 4Mb 72-pin $258/228 8Mb 72-pin $515/470 16Mb 72-pin $780/690 32Mb 72-pin $1560/1380 MAC 8Mb P’BOOK CO-PROCESSORS 387S/DX to 40 $405 $90 LASER PRINTER HP with 2Mb $200 COMPAQ CONTURA 8Mb $550 DRAM DIP 1Mb x 1 70ns DIP $7.80 256 x 4 70ns DIP $7.80 256 x 16 70ns SOJ $48.00 IBM PS.2 THINKPAD L40/N33 8Mb 4Mb $655 $275 TOSHIBA 3100SX 2100/50 4Mb 8Mb $255 $585 SUN SPARC 5 32Mb SPARC 10/20 64Mb $1780 $3696 DRIVES – SEAGATE 545Mb 14ms 3yr wty $335 1052Mb 9ms 5yr wty $550 2148Mb 9ms 5yr wty $1470 Sales tax 21%. Overnight delivery. Credit cards welcome. Ring for latest prices. We buy & trade RAM. 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Tel: (02) 980 6988 Fax: (02) 980 6991 PELHAM THIRD ELECTRONICS TECHNICIAN HEATSINKS GREG BALL ELECTRONICS UNIT 8, 9-11 ABEL STREET, PENRITH PH: (047) 31 5661 FAX: (047) 31 5982 development system as it will re-program 1Meg times, each time in 10 seconds. Send a $2 coin for my PROMO disk. Don McKenzie, 29 Ellesmere Crescent, Tullamar­ine 3043. Phone (03) 338 6286. UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar Invisibility, Surveillance, Self-Protection, Unusual Chem­ istry and more. For a complete catalog, send 95 cents in stamps to Vector Press, Dept S, PO Box 434, Brighton, SA 5048. C COMPILERS: everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC16, 8051/52, 8080/85, 8086 or 8096: $150.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $150 for the set. Debug monitors: $75 for 6 CPUs. All compilers, XASMs and monitors: $550. 8051/52 or 80C320 simulator (fast): $75. Demo disk: $5. Network Software: use serial, parallel, Required by large Sydney-based cinematography equipment supply house, due to industry expansion. Duties include maintenance and repair of 16 and 35mm movie cam­eras, battery chargers, high-power electronic lighting ballasts, specialised video equipment and a large range of accessories. Spacious air-conditioned smoke-free workshop, handy to Pacific Highway and Artarmon station, off-street parking provided. All tools and equipment supplied. Requirements: minimum 5 years electronics service experience. Good theoretical background and ability to work from first principles is essential due to wide range of equipment encountered. A strictly limited amount of on-the-job training will be provided. Hobbyist background and/or TV/video experience (particularly Video-8) advantageous. In first instance please send brief handwritten applications to: The Service Manager, PO Box 199, Artarmon 2064. Arcnet or Ethernet to share files and printers on your PCs. DOS and Windows compatible. $105 per net­work. All prices + postage. GRANTRONICS, PO Box 275, Wentworth­ville 2145. Ph/Fax (02) 631 1236. NEW SPRINKLER CONTROLLER KITS: RAIN BRAIN version uses ‘C8 and switch mode supply. Features galore!! Contact Mantis Micro Pro­ducts, May 1995  95 Microprocessor For Digital Effects Unit Microprocessor For Stereo Preamplifier Advertising Index Now available from SILICON CHIP: the 68HC705-C8P pre-programmed micro­pro­cessor IC for the Digital Effects Unit described in the Feb­ruary 1995 issue. Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Pub­lica­ tions, PO Box 139, Collaroy, NSW 2097. Phone (02) 979 5644; Fax (02) 979 6503. Now back in stock: the 68HC705-C8P pre-programmed micro­pro­cessor for the Infrared Remote Controlled Stereo Preamplifier (SILICON CHIP, Sept.Oct. 1993). This device also suits the Remote Volume Control published in May & June, 1993. Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. Phone (02) 9795644; Fax (02) 979 6503. Altronics ..........................IFC,38-40 38 Garnet St, Niddrie 3042. Phone/fax (03) 337 1917. Avico Electronics.........................90 Car Projects Book....................OBC Ctoan Electronics........................95 Dick Smith Electronics........... 12-15 Greg Ball Electronics...................95 Instant PCBs................................95 INFRARED AUDIO CONTROL KIT: based on the Intelligent Infrared Receiver kit (ref. Silicon Chip, March 94) to control volume, treble, bass, balance, mute and select between two inputs (CD, VCR, etc). Also available Intelligent Infrared Receiver kits and infrared transmitters, preprogrammed and learning models. For details call BENETRON P/L, phone (02) 837 3888 or (018) 200 108. MicroZed has eight Kilobyte of serial EEPROM data memory for Parallax Stamp! For info send 1 x 45c to Micro­Zed (see advert p.95 for address). VALVES: all types for radio, audio and industrial use. For sale and wanted to buy. SSAE for list. Electronic Valve and Tube Company, PO Box 381, Chad­ stone, Vic 3148. Fax (03) 571 1160. Ph (018) 557 380. Auto Switchers, Audio/Visual Intercoms, Observation Systems, Camera-TV/VCR Antenna Patch Links, Cordless Portable Camera-TV/VCR Links, Colour Modules/Cameras. TINY PINHOLE MODULES 32 x 32 x 15mm SEE through a 2mm hole from $239. Competitive Prices, Qty, Indent & Manufacturer Discounts. ALLTHINGS SALES & SERVICES Ph/Fax (09) 349 9413. DOS PROGRAMS: auto substitution databases, transistor $25, recti­fier $25, zener $25, signal $25, PCBCAD $25, SCHCAD $35, VGA Test $25. Order by M.O. payable to G. A. Georgopoulos, 34 Scouller St, Marrickville 2204. MicroZed has MicaSOFT Tutor Program. For demo send 4 x 45c to MicroZed (see display advert p.95 for address). TINY VIDEO CAMERAS from $199. MATCHBOX SIZE PCB MODULES 25 Types. Optional: Lenses, C Lens Mounts, Cases & Technical Manu­als. See p.90 SC Feb 1995. ALSO C.C.T.V. Std & Mini Cameras, Quad Splitters, PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. MicroZed has Parallax PIC Hobbiest Kit. For info, send 1 x 45c to MicroZed (see display advert p.95 for address).    SILICON CHIP BINDERS These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers, are made from a dis­tinctive 2-tone green vinyl & have the SILICON CHIP logo printed in gold-coloured lettering on the spine & cover. To order, just fill in & mail the order form on page 31, or phone or fax your order to: Silicon Chip Publications, PO Box 139, Collaroy Beach, 2097. Phone (02) 979 5644. Fax: (02) 979 6503. 96  Silicon Chip Av-Comm.....................................11 Jaycar ................................... 45-52 L & M Video...................................7 Macservice...............................3,89 MicroZed Computers...................95 Oatley Electronics.................. 74-75 Pelham........................................95 Railway Projects Book...............IBC RCS Radio ..................................94 Resurrection Radio......................85 Rod Irving Electronics .......... 26-30 Silicon Chip Back Issues....... 86-87 Silicon Chip Binders....................85 Silicon Chip Software..................79 Yuga Enterprise...........................95 _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. • H. T. Electronics, 35 Valley View Crescent, Hackham West, SA 5163. Phone (08) 326 5590. Especially For Model Railway Enthusiasts Order Direct From SILICON CHIP Order today by phoning (02) 9979 5644 & quoting your credit card number; or fill in the form below & fax it to (02) 9979 6503; or mail the form to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. This book has 14 model railway projects for you to build, including pulse power throttle controllers, a level crossing detector with matching lights & sound effects, & diesel sound & steam sound simulators. If you are a model railway enthusiast, then this collection of projects from SILICON CHIP is a must. Price: $7.95 plus $3 p&p Yes! Please send me _______ copies of 14 Model Railway Projects Enclosed is my cheque/money order for $­_________ or please debit my  Bankcard    Visa Card    Master Card Card No. Signature­­­­­­­­­­­­_________________________ Card expiry date_____/_____ Name _________________________Phone No (____)_____________ PLEASE PRINT Street ___________________________________________________ Suburb/town __________________________ Postcode____________