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MAY 2022 ISSN 1030-2662 05 The VERY BEST DIY Projects! 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST Heat pipes for cooling (or heating) devices from Laptops to large pipelines 500 POWER WATTS AMPLIFIER PART 2: BUILDING THE MAIN PCB 43 Precision AM-FM DDS Signal Generator with an output frequency of 100kHz-75MHz and an accuracy of 0.1Hz at 10MHz, this is the perfect addition for your workbench. OUR OW LD Y I N BU JACKPOT Build your own Power Usage Monitor This project will let you monitor and better manage the power consumption of devices running from low-voltage DC by letting you set notifications for their power usage. You can set a notification limit that gets automatically emailed to you when the power consumption reaches 50%, 75% and 100% of your set limit. This means you can better monitor and manage your power consumption on your next camping trip to ensure you don’t run your battery flat. SKILL LEVEL: BEGINNER CLUB OFFER BUNDLE DEAL For step-by-step instructions & materials scan the QR code. 3495 $ www.jaycar.com.au/arduino-power-monitor See other projects at SAVE 30% www.jaycar.com.au/arduino KIT VALUED AT $50.30 UP TO 25% OFF STACKABLE HEADERS SUITS MINI ESP (XC3802 $24.95) NOW 3 $ NOW 7 95 SAVE 20% Micro SD Card Shield for Wi-Fi Mini Level-up your projects with these stackable headers. Great for building custom shields. Includes: 1 x 10-pin & 6-pin, 2 x 8 pin and 1 x DIN 3-pin for ICSP. HM3208 100 $ gift card Awesome projects by On Sale 24 April 2022 to 23 May 2022 Add gigabytes of storage to your Wi-Fi Mini Main Board with this tiny shield and a microSD card (sold separately). Stackable headers pre-soldered to allow more shields to be added. XC3852 Got a great project or kit idea? NOW 14 95 $ 95 SAVE 20% Stackable Header Set SUITS UNO Board (XC4410 $29.95) $ SAVE 25% Data Logging Shield Know precisely what happened when! with this data logging, battery backed up, time stamped RTC (real time clock), full sized shield. Supports FAT 16 or 32 formatted SD card (sold separately). XC4536 If we produce or publish your electronics, Arduino or Pi project, we’ll give you a complimentary $100 gift card. Upload your idea at projects.jaycar.com Looking for your next build? Silicon Chip projects: jaycar.com.au/c/silicon-chip-kits Kit back catalogue: jaycar.com.au/kitbackcatalogue 1800 022 888 www.jaycar.com.au Shop online and enjoy 1 hour click & collect or free delivery on orders over $99* Exclusions apply - see website for full T&Cs. * Contents Vol.35, No.5 May 2022 19 All About Heat Pipes Air Quality Sensors page 70 Heat pipes, vapour chambers and thermosiphons are two-phase cooling (or heating) devices that are used to efficiently transfer heat. They are simple and inexpensive, commonly used on heatsinks in computers, greatly enhancing their performance. By Dr David Maddison Thermal management 30 The History of Transistors, Pt3 In this final instalment, we take an in-depth look at how bipolar junction transistors (BJTs) and both main types of field-effect transistors (JFETs and Mosfets) work at a fundamental level. There’s also a small section explaining the many different numbering schemes used for transistors. By Ian Batty Semiconductors 70 Air Quality Sensors OUR OW LD Y I N BU PAGE 76 Many new air quality sensor modules have been appearing on the market, some being surprisingly inexpensive. Here’s a quick rundown on what they do and how they work. Sensor types covered in this article include MOS, NDIR, PAS and PMC. By Jim Rowe Low-cost modules 43 AM-FM DDS Signal Generator This Precision DDS Signal Generator has an output frequency of 100kHz to 75MHz in 1Hz steps (with ±0.1Hz accuracy after calibration). It runs from a 5V, 140mA supply and has low RF leakage. By Charles Kosina Test equipment project 61 500W Power Amplifier, Part 2 This month we cover the assembly instructions for the Amplifier module PCB, which forms the largest single section of the project. We also provide some tips on how to wind the output filter inductor. By John Clarke Audio project 76 Slot Machine Real slot machines are an easy way to lose your money, so why not build your own! This Slot Machine has colour graphics and sound, and while it uses coins to play, you can get them back when you’re finished playing. The project is based on the Micromite Plus BackPack. By Gianni Palotti Game project 2 Editorial Viewpoint 4 Mailbag 85 Serviceman’s Log 97 Subscriptions 98 Circuit Notebook 1. Simple stereo microphone 2. A simple wireless charger 3. Li-ion battery reconditioner 4. Motion-triggered ESP32 WiFi camera 102 Vintage Radio 92 Oatley LED Lighting & Driver Kits 106 Online Shop Oatley has four low-cost, high-brightness LED kits which can be driven from the same general-purpose LED Driver via a 12V DC source. The LEDs supplied with the kits include one of: two 12W floodlights; two 0.6m 8W tubes; two 1.2m 18W tubes; or four 60W LED lamps. By John Clarke Lighting project 108 Ask Silicon Chip 111 Market Centre 112 Advertising Index Calstan 559M2 superhet by Fred Lever SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Nicolas Hannekum – Dip.Elec.Tech. Advertising Enquiries Glyn Smith Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Former Cartoonist Brendan Akhurst Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $65 12 issues (1 year): $120 24 issues (2 years): $230 Online subscription (Worldwide) 6 issues (6 months): $50 12 issues (1 year): $95 For overseas rates, see our website or email silicon<at>siliconchip.com.au Recommended & maximum price only. Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: Editorial Viewpoint Most software is a product, not a service Software offered “as a service” provides benefits almost entirely to the companies producing the software and not for their customers. I’ve complained about constant updates in this column before. Updates are a selling point of ‘software as a service’, but they rarely fix the bugs that are plaguing us or add valuable features. New features that are actually useful (the minority) could easily be rolled into a one-time annual or semi-annual update. I like having the option to decide if it is worthwhile to pay a couple of hundred dollars for the latest version of the software based on the claimed improvements. Why would I want to spend several times more for a “subscription” which provides very little real value? Anti-subscription rhetoric might seem odd from a magazine publisher. But keep in mind that you are genuinely getting something new each month when you subscribe to a monthly magazine, unlike most software where regular updates are just fixing things that shouldn’t have been broken in the first place. Take CorelDraw as an example. While we use it and mostly like it, CorelDraw suffers from terrible performance at times (a problem for at least a decade), and it’s too crash-prone for my liking. Still, it’s pretty decent overall, and we want to continue using it. They bring out one new version a year, with perhaps a mid-year update, but they rarely add or improve anything that makes upgrading worthwhile. Still, when we were offered an ‘upgrade protection plan’ (UPP) for around $130 per user per year to stay on the latest version, we accepted it. We recently received notification that they were ending that plan, forcing anyone who wants to use the latest version onto a $50 per month subscription ($600 per year). That’s nearly five times what we were paying. While you can still buy the software outright, it’s $1100 per copy with no apparent upgrade discount, making that about nine times as expensive as the upgrade plan. Even when we were paying for separate upgrades, we were not paying $600 per year. It isn’t worthwhile, given the marginal improvements with each version, and the lack of significant performance improvements or bug fixes. Does Corel realise that many people like us already have Adobe Creative Suite (including Adobe Illustrator) that we could switch to essentially for free? We don’t want to do that, but it’s an attractive option compared to another expensive subscription. While I don’t like paying $70-odd per month for Creative Suite, it includes several very useful packages, including Illustrator, Photoshop and InDesign, making it a far better value. Corel could have increased what they were charging us for the upgrade service, and we would probably have continued to pay it. But now we have cancelled all our UPPs and will stick with the 2022 version. They will get no more money from us; good job, Corel. It comes down to what users will tolerate. If most users say “no more” like we did and cancel, companies will get the message. But if enough users roll over and pay the exorbitant subscription fees, they’ll see that this scheme works and keep it up. This leaves the market open for a competitor to come along and offer a reasonable alternative without the subscription fee. Any such competitor would be guaranteed a portion of the market; those who don’t like subscription models. Also, the open-source (and free) software Inkscape is looking more attractive by the day... by Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Australia's electronics magazine siliconchip.com.au MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd has the right to edit, reproduce in electronic form, and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman’s Log”. Vale Brendan J. Akhurst I have been a reader of Silicon Chip (and Electronics Australia) for many decades now, but this is the first time I’ve been motivated to write (and it isn’t even about electronics...) I have just read Nicholas Vinen’s “Editorial Viewpoint” in the February 2022 issue and was very sad to learn of the passing of Brendan Akhurst, your long time contributing cartoonist. I first met “BJ” when I was just a lad and his father was my teacher at school. That was way back in 1969 – it was clear that he was a very talented artist even then. I have followed his work ever since. His distinctive style and gentle wit were always a highlight of your magazine for me – particularly when he added illustrations to your Serviceman’s Log section. I was surprised to learn from your editorial that he had also been a Police Officer, for I too had a career in Policing, but we never managed to cross paths again. Thanks to your editorial, I have passed on the news to Brendan’s former workmates in the NSW Police Force, and many of them have remembered him fondly. Please offer my sincerest condolences to his family and thank them for sharing him with us – your readers – for so many years. Bob Stephenson, Canberra, ACT. A collection of Brendan’s cartoons It is sad to note the passing of your cartoonist, B. J. Akhurst. Like you, I found his work highly amusing, especially the visual puns. His work will be missed. It was funny how he highlighted the fact that Dave Thompson is a New Zealander, with Kiwi birds and volcanoes in the distance. It would be nice if you could publish a “Best of Brendan” type of publication with some of his best efforts, although I would understand if you considered this is outside your brief as an electronics magazine. Ray Chapman, Pakenham, Vic. Comment: that is a good idea. We will certainly consider it. More on possible clone CP210x chips I read the letter on CP210x chips in Mailbag (April 2022) with some amusement; my brother gave me a USB/serial cable because it wouldn’t work on his Windows box, yet it worked just fine on my MacBook, FreeBSD server, and Linux laptop. He has another cable that works for him, so I assume it has the “correct” chip. There was a discussion on a private technical mailing list of which I am a member. The consensus was that 4 Silicon Chip Microsoft did indeed hobble the driver, given that a previous version is known to work with these devices. If it were a “driver bug”, as you postulate, surely it would have been fixed by now in one of their tedious “Patch Tuesday” updates. The story goes that the genuine chip has an undocumented feature (documentation available only under NDA) that makes it work faster to give it a competitive edge over clones. Dave Horsfall, North Gosford, NSW. Comment: this is just something to consider, but Microsoft has left serious bugs (including security holes) unpatched in Windows for long periods, see siliconchip.au/link/abdg Colour Maximite wanted Do any readers have a fully working Colour Maximite 2 (V1) they are willing to sell? The fully-assembled CMM2 I can purchase online is too expensive because they want to be paid in US dollars. Ric Mabury, Melville, WA. Twisted rather than separate mains supply lines Energex, the Queensland government corporation that owns the electricity network in SE Queensland, replaced the poles and wires in the eastern end of my street. They installed new poles several weeks ago and then, on Thursday, they replaced the wires. The contractors replaced the supply wires for more than twenty houses in just over four hours. The new poles and wires are totally different from the old system with cross-bars having four individual conductors supported on insulators. Instead, there is a single cable of four twisted wires, and the house supplies are connected via tapping blocks of some sort. I have never seen this system and when I looked around the neighbourhood, my street plus a side street are the only ones using it. I do not know if it is common in other areas. Perhaps electricity distribution methods might be another subject for an article considering that this method appears to be new technology. George Ramsay, Holland Park. Qld. Comment: we have seen that style of mains supply wires before (also called aerial bundled conductors). Presumably, it is quicker and easier to run because there is only one wire bundle, and it has better aesthetics. They must be confident that the inter-wire insulation is not going to degrade. Real-time clock option on Pico BackPack I have built two of your Pico BackPacks (March 2022; siliconchip.com.au/Article/15236) successfully according to the article. One useful minor amendment to add Australia's electronics magazine siliconchip.com.au to the list of commands in the third column on page 40 are these commands to configure the optional DS3231 real-time clock IC: RTC SETTIME 2022, 03, 10, 09, 00, 00 (change numbers to the current date & time) OPTION RTC AUTO ENABLE Mike Sunners, Nairne, SA. Why use a half-wave rectifier? In the Driveway Gate Remote Control article by Dr Hugo Holden (siliconchip.com.au/Article/15197), the circuit diagram on pages 80 & 81 shows the main rectifier for the motor as half-wave. This means that the transformer is subjected to a net DC through the windings, which will cause heavy saturation and exceptionally poor transformer utilisation. This is easily demonstrated, and I cannot imagine why a half-wave rectifier was specified. A single chassis-mount bridge would improve the DC output and greatly reduce the stress on the transformer and filter capacitor (which is also subjected to much greater ripple current). I realise that it’s only used intermittently, but half-wave rectification is the worst possible option. Transformers can tolerate severe overloads for a short time, but given the modest cost of a ‘proper’ bridge rectifier, there’s no reason not to have used one. Rod Elliott, Thornleigh, NSW. Response: If this was a clean-sheet design using all-new components, you are correct that it would be sensible to use a transformer only just large enough to power the gate motor with a bridge rectifier. That would be more cost-­efficient and power-efficient, although that’s hardly critical given its very intermittent usage. But consider that this project is designed to be retrofitted to a pre-existing gate controller. In many cases, the existing designs use a large power transformer with half-wave rectification. Then there’s no real advantage to changing that to full-wave rectification, as detailed in Dr Hugo Holden’s reply to your comments: Typical gate motors run at low average powers in the region of 10-30W. The large power transformers used in most gate controller boxes look good for at least 100W. It doesn’t excessively stress a transformer to draw current on half-cycles if the power drawn is well below the transformer’s rated power. And the gate is for intermittent use; it is not moving 24/7. When the gate is in motion, at a constant speed, the current requirement is in the region of an amp or so because the motor is only overcoming the friction of the moving parts, not accelerating a mass or lifting a weight against gravity. If we assume that the motor supply is around 22V (which it would be with the filter capacitor), motor power is in the region of 20W, but only for the time the gate is travelling. The whole thing has a very low duty in terms of motor on-time. Many low-power appliances use half-wave rectification. Car battery chargers with similar proportions are often based on half-wave rectifiers. There is no risk to the transformer if the power is below its maximum rating. It would work with a full-wave rectifier, but since there is no PWM controller to reduce the motor energy (as in 6 Silicon Chip some commercial controllers), the gate speed would be too high, at least for my gate. The controller I built for my gate doesn’t have the filter capacitor, and the speed is about right with half-wave power from the pre-existing transformer. It has been working like that for over 15 years. (End of Dr Holden’s reply) We agree that it would make sense for anyone who has to purchase a transformer for the Remote Gate Controller to add a bridge rectifier between the transformer secondary and CON4. In this case, for a 24V rated motor, a transformer with an 18V output under load plus a bridge rectifier might give about the right power to the motor (depending on the filter capacitor value). A large 24V transformer will probably deliver too much power to the motor if a bridge rectifier is used. Software obsolescence is a problem I read with interest your editorial in the February edition about devices that cease to work due to phone or PC operating system upgrades. I have had to throw out perfectly good (and expensive) equipment because it would no longer work with my PC or laptop computer. This includes a perfectly good laser printer, an expensive video capture card and an even more expensive WinRadio receiver, all due to the drivers not being updated to work with the latest versions of Windows. Also, I can no longer get data from my solar panels because the inverter manufacturer has gone away. I am now very wary of buying any equipment that requires a PC, laptop, phone or an internet connection to the manufacturer to operate. Mike Hammer, Mordialloc, Vic. Editorial on apps and obsolescence I read with a mixture of amusement and horror your editorial comments about the problem of devices that need apps. I have three internet radios that are now e-waste because Qualcomm pulled the plug on their so-called Aggregate website (Reciva, https://radios.reciva.com/index). All internet radios need such a site for listing and accessing the internet radio stations. I can now only receive the very few stations I had stored on buttons in the radios. I think this is, sadly, a case where it is difficult to follow your understandable advice that “all hardware devices should be able to be used in a standalone mode”. In the meantime, I have had to purchase yet another internet radio from a different company that uses a different aggregate page. Let’s hope that will be usable for a few more years. Christopher Ross, Tuebingen, Germany. Response: one of the aspects that bothers us the most is that it isn’t all that time-consuming or expensive to continue supporting many of these products. Website hosting doesn’t cost much, and the amount of labour required to maintain the site is minimal. It shows a lack of respect for the customers who purchased their products. Misleading battery capacity ratings My son-in-law recently asked me to look at a compact battery pack with USB outputs. He had bought it believing Australia's electronics magazine siliconchip.com.au Development tools in one location Thousands of tools from hundreds of trusted manufacturers Choose from our extensive selection au.mouser.com/dev-tools australia<at>mouser.com its 26,800mAh advertised capacity but found it could not recharge his Macintosh laptop more than once. I recharged it, and it took around 24,000mAh before the charge rate dropped. I then easily got more than 20,000mAh into a LED lamp. The reason for his problem then dawned on me. The ‘battery’ must be a single lithium-ion cell, nominally 3.7V. In converting that to the 5V USB output, he would not get more than 19,800mAh, even if the process was 100% efficient. Then there is the laptop battery, which is described as 10.8V and around 7,000mAh. To recharge that would require around 12.8V, so even at 100% efficiency, no more than 6,700mAh would be delivered. It seems to me that a better solution would be to buy a 12V battery booster with a USB output. So this was a cautionary tale in understanding battery capacity in the real world. Graham P. Jackman, Melbourne, Vic. Comment: giving battery mAh ratings is misleading as it is not a unit of energy. Units of energy are either joules (J), milliwatt-hours (mWh) or watt-hours (Wh). Milliamp-hours or amp-hours is only a useful metric if you want to know how much current a battery can deliver over a certain amount of time. It is not helpful in comparing the capacities of batteries unless you know they have the same voltages. The Wh figure for a battery can be easily estimated by multiplying the Ah capacity by the nominal battery voltage. But note that this will only ever be an estimate because the battery voltage won’t necessarily change linearly as it discharges. My adventures into SMDs When ordering the SMD Trainer kit from Silicon Chip, the gentleman asked if there was anything else that I wanted. When I said yes, he said, let me guess – the SMD Tweezers. No! I was after a Micromite LCD BackPack. After thinking this over for half an hour or so, I thought I was being silly, so I rang back and put the Tweezers on the same order. Over the years, I have built many projects. Apart from crystal sets, the first (in the late 1950s) was a five-band, five-valve radio. When the first stereo record came to town, I added a reel-to-reel tape recorder and turned it into a stereo system. That’s the sort of thing I’m used to building, so these new projects would be a game-changer for me due to the small parts. When the package arrived, I had to wait for some flux gel to arrive. As I usually work in a dusty old shed with a lathe, mill, welders, drills etc, I thought it wise to find a cleaner spot, so I cleared an area in my home office. I then had to make many trips back-and-forth for forgotten things (part of getting old). Was the soldering iron too big? A jeweller’s loupe OK? I was pretty keen to get started, but disaster struck as I opened the packet. Removing one part to try to determine what it was, it flicked out of my fingers and disappeared forever! I wonder what it was. The next trick was figuring out how to open the small packages. After fiddling for a long time and reading and asking Mr Google, I emailed Silicon Chip. The reply was to peel off the plastic layer, which I really hadn’t seen. I 8 Silicon Chip Australia's electronics magazine siliconchip.com.au was then able to extract one chip, but what was it? It had eight pins, so it had to be the 7555. I studied this for a long time to determine where the number one pin was. There was no dot in the corner, and no corner cut off. I woke in the middle of the night with the answer; the whole of one side may have a chamfer. This proved to be correct, but I found it was very subtle and hard to see. The next day, I decided to explore some more of the mysterious mini packages and had no idea what they were, so I decided to build the tweezers. Those worked first time, so I think I scored my first Brownie point. The next problem was to work out what size parts were in which packet, so I opened them and soldered them in the appropriate places. It wasn’t long before I had all the parts above the line in, including the 1μF, which is the one I lost and Silicon Chip kindly replaced. And it worked! I was starting to find that one and a half to two hours of concentration was enough, and as I had other projects on the go, it was a few days before I tackled the next bit. I next tackled the resistors and was quite pleased with my progress until I got to the M1005/0402. I managed to solder that one, but it was crooked. Still, I figured that it was too small for anyone to notice. The M0603/0201 was harder, though. I was still trying to get the plastic off and found it had dropped onto the desk, and then it stuck to the iron, but eventually, it made it into the board. I checked it with the tweezers and it looked good! Another Brownie point! After telling my friend how clever I was, I picked up the Trainer board and brushed my fingers over it, and the M0603 part fell off. 90 minutes later, I had managed to lose all the other M0603 resistors, either by having them stick to the iron and frying or losing them. Loss of all Brownie points! After spending some more hours, I managed to get a few LEDs flashing, so maybe I scored one back. The problem with the LEDs is that the green line is hard to see, especially when darkened on one end with heat from the iron. My recommendations from all this are, if you are serious, look at plenty of YouTube videos, buy two or three trainer kits or boards. Be prepared to destroy one, and buy plenty of spare components to replace the ones that get lost and destroyed. I found that Altronics have a list in their catalog. My conclusion is that I need a better iron, better lighting and a better magnifier (preferably a microscope with a screen). Better eyesight and steadier hands would be good too. I am certainly more confident with SMD parts; M2012/0805 may be my limit for reliable results. What a great project; thank you, Silicon Chip. I can now confidently tackle the Micromite BackPack. David Lloyd, Clare, SA. Comments: here at Silicon Chip, we were all initially hesitant to tackle SMD components as we feared working with them would be difficult. We mostly found that all but the smallest are manageable with a bit of practice. It helps to start when you are younger and still have reasonable eyesight. It also helps to work with smaller parts regularly to maintain that important close-up vision. You are correct that pin 1 can sometimes be hard to determine. We prefer it when there is a pin 1 dot or divot, but that isn’t always the case. And we too find that working siliconchip.com.au Helping to put you in Control LabJack T7 Data Acquisition Module A USB/Ethernet based multifunction data acquisition and control device. It features high data acquisition rates with a high resolution ADC of 4 ksamples/s at 18 bits to 50 ksamples/s at 16 bits. SKU: LAJ-045 Price: $902.00 ea + GST Temperature probe 5m Teflon Cable RTD probe with magnet fixing for surface temperature measurement. -50 to 200 ºC range and 5meter teflon cable. SKU: CMS-007T Price: $153.95 ea + GST J Thermocouple Temperature probe with magnet fixing This J type Thermocouple sensor has magnet fixing for surface temperature measurement. The 2 wire sensor has a silicone cable which is 3m long. Temperature range is -50 to 200 ºC. Class B. SKU: CMS-017J Price: $142.95 ea + GST 400W ACM Brushless AC Servo Motor Leadshine ACM604V60-T-2500 400W brushless AC servo motor with 2500 line encoder suitable to work with the ACS806 brush-less drive. SKU: MOT-450 Price: $347.60 ea + GST ACS806 Brushless Servo Motor Drive Brushless servo motor driver for 50 to 400 W, AC brushless motors with encoders. SKU: SMC-410 Price: $319.00 ea + GST LCD Temperature and Humidity Sensor The Pronem Midi from Emko Elektronik are microprocessor based instruments that incorporate high accurate and stable sensors that convert ambient temperature and humidity to linear 4 to 20 mA. Dimensions are only 60x 126 x 35mm. SKU: EES-020A Price: $241.95 ea + GST TxIsoloop-1 Single Loop Isolator Loop isolators provide signal protection by electrically isolating the 4-20mA input signal from the 4-20mA output. SKU: SIG-201 Price: $168.19 ea + GST For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Prices are subjected to change without notice. Australia's electronics magazine May 2022  9 with small parts can be fatiguing, and it’s essential to take breaks to avoid eye strain etc. Yes, M0603/0201 components are very difficult to hand-solder, but it can be done with some effort. It’s much better to destroy or lose parts in the Trainer kit than something more expensive. Some SMD micros can cost upwards of $20 each! We prefer to test the LEDs with a multimeter set on diode test mode rather than try to identify the anode and cathode visually. When they light up in that test, the red probe is on the anode and the black probe on the cathode. Clever SMD holding tool I see that you are including an increasing number of surface-mount devices in your projects. I am also finding that most of my personal projects and those for my small design business are forced to use more SMD components because they are all that is available. Recently, the component shortage has forced my hand even more into the SMD “corner”. With this came the realisation that SMD components not only are smaller but they can be mounted on either side of a PCB without interfering with the other side. This allows a doubling of component density and consequential reduction in overall size. My current project has over 120 SMDs. While I have the usual through-hole tools, including a magnifying lamp, I have added a hot air soldering station. Initially, dealing with tiny components was challenging enough without them getting blown away or flipped over by the airflow! Holding SMD transistors, diodes, resistors and capacitors accurately in place could be a problem. As a result, I developed this simple “holding tool”. It is made of 0.5mm steel plate with one edge folded by 90° for strength and springiness, and it articulates across the full extent of a 100 x 80mm board. It is temporarily secured to the PCB with an M3 threaded spacer with Nylon washers to allow movement while minimising slippage. Please refer to the attached photographs. I am in my mid-60s and can say that SMD is not just the domain of the youngsters! I even use QFN (quad, flat, no-leads) packages, although I extend the pads beyond the normal footprint of the chip to allow easier soldering and debugging. A hot-air station is essential for those chips. Peter Gee, Inglewood, WA. Comment: what an ingenious device, and simple too! We especially like how you use one of the existing mounting 10 Silicon Chip holes to attach it to the board. Some of the advantages of SMDs that you’ve noted, like being able to mount them on both sides of the board, are part of the reason they are so popular with manufacturers. We don’t always put parts on both sides just because it complicates assembly; we have some designs coming up where we do, though. Driving loudspeakers with a current source It is my assertion that, for voice coil speakers and ribbon tweeters, the use of voltage feedback is incorrect as this is affected by changes in impedance with frequency. The best result can be obtained by feeding back a voltage produced by sampling the current through the speaker and feeding back voltage proportional to the current. Simply a series resistor. It is also necessary to feed back the DC level to prevent DC from being fed through the speakers. You can find a simple design for this at www.inja.com. au/wp/ or www.inja.com.au/diy.php It can be proven that the magnetic force that applies in these speakers is proportional to current, not voltage, as follows. Wind two coils on two small diameter ceramic formers, one using Nichrome wire spaced to prevent shorted turns, the other with copper with the same number of turns and the same spacing (Jaycar WW4040 and WW4013). You will need an old compass. Connect the coils in series across a low-voltage supply so that they repel opposite ends of the compass. Now place the coils on the same side of the compass such that each coil is attempting to repel the opposite ends of the compass. You will notice that the forces are the same because the same current passes through identical coils. This shows that current, not voltage, determines the magnetic force in a coil as almost all the voltage is across the Nichrome coil with microvolts across the copper coil. If voltage caused the force, the end facing the Nichrome would have produced a much greater repelling force. John Cornwall, INJA Comment: We are publishing this letter in the spirit of open debate; we do not necessarily endorse its content. Note that we have never argued against the notion that magnetic field strength is related to the current through a coil. That is basic theory, and we are pretty sure that SC most speaker designers would agree. Australia's electronics magazine siliconchip.com.au Sale ends May 31st. n i a g r a B A g a B SALE Build It Yourself Electronics Centres® SAVE $100 399 $ IS PRICE! 20 SYSTEMS ONLY AT TH wer Gear to invent, po and create! Affordable 5 Megapixel CCTV Surveillance System. S 9901J No expensive cloud service required store footage on site. Simple to install with instructions supplied. Cameras can be remote viewed on iOS/ Android. Each pack includes: • Hybrid digital video recorder (IP camera ready!) • Pro grade 5MP (2K equivalent) resolution weatherproof cameras • 20m connection leads • Power supply • HARD DRIVES TO SUIT: 1TB $98 (D 5514), 2TB $125 (D 5516). No more eye strain! Amazing value under $100 109 $ X 4201 5 Dioptre X 4200 3 Dioptre Ultra-bright long life LED for fantastic clarity (plus no need to change a globe EVER!). Let “gadget” be your eyes. Identify those impossible to read miniature parts without straining your eyes. Great for collectors, model makers, jewellers etc. NEW! 99 SAVE $20 $ Q 1073A Premium Autoranging True RMS Multimeter Our first multimeter with wireless USB charging in-built! No more changing batteries. Includes top spec features such as illuminated sockets, LED torch, desk stand, True RMS, non contact voltage detection, frequency meter and relative mode. NEW! NEW! 349 229 $ $ S 9445 4K video surveillance anywhere you need it! 4K video or 30MP still shot resolution. Great for monitoring in remote locations, temporary CCTV monitoring etc. Runs off an internal battery so its quick & easy to set up anywhere you need to keep an eye on things. Weatherproof case with LCD screen. Requires SD card, DA0330 64GB $17.95. Throw away your old jumper leads! M 8195B SAVE 24% SAVE 24% 30 45 $ X 2312C 10W 69 $ X 2314C 20W Suits 12V battery vehicles. 20000mAh rated battery provides up to 2500A peak output when cranking. Three USB ports are provided for charging devices (like a giant battery bank!). It also has a super bright 1W LED torch in built. 192L x 90W x 36Dmm. 22 $ $ X 2318C 50W C 9032A Genlamp® LED Floodlights i12 Bluetooth® Earbuds Great for added security around the house, back shed or garage. Fitted with 240V 3 pin mains plug. Fully approved. Natural white. Rust free stainless steel brackets and hardware. IP65 rated. These affordable wireless Bluetooth 5.0 earbuds offer great sound for less! 2-3 hour listening time per charge. Compatible with iOS & Android devices. Bargain Walkie Talkie Package X 0669 Amazing value for money, these walkie talkies offer a great way to keep in touch on camping trips, hiking or offroad adventures! 16 channels with charging dock. Range up to 5km. Recharge your phone ANYWHERE Lithium-Ion Car Jump Starter SAVE 25% SAVE 23% A do-it-all USB power delivery charger (18W), Qi wireless charger and portable battery bank (6700mAh) for phones and tablets for use wherever you travel. Includes Australian, US, UK and European adaptors, plus carry case. *Phone for illustration purposes. 19.95 $ Triple USB Car Charger SAVE $29 50 $ M 8628B Keep everything charged up in the car with this handy 7.2A triple USB charger. Stylish carbon fibre look finish. rs! Handy gadget for travelle SAVE $39 A 0319* Your one-stop electronics shop since 1976. | Order online at altronics.com.au 50 $ Trim, crimp & screw it. T 1566A T 1528A T 1552A SAVE 15% SAVE 24% SAVE $25 90 33 $ Switch to Pass Thru RJ45 modular crimps and save time! Crimps and cuts in one ratchet action and works with industry standard connectors. All metal with ratchet action Combines a ratchet wire stripper, cutting blade & kwik crimper (red, blue and yellow sheaths). Suits 10-24 AWG cable. Crimps all standard “Kwik” connectors such as ring terminals, bullets and spades. Easy to identify red, blue, yellow jaws. SAVE 18% 20 20 60 $ Rust free stainless steel! T 2741 T 2735 T 2825A Precision Long Nose Pliers Electronics “Nipper” Side Cutters Stainless Steel Long Nose Pliers Super sharp with comfy handles for cutting component legs, wiring etc. 130mm Rust Resistant - great for the tackle box or use in moisture prone environments. 125mm. 30 17 $ T 2852 These heavy duty cutters will cut flexible copper or aluminium cable up 70mm2 (00AWG). 235mm length. 27 SAVE 10% 25 $ T 1489 12 $ 19.95 $ T 2350 4pc Pick & Scribe Set $ Strips cable of insulation at the flick of the wrist. Our best selling cable stripper of all time! A must have for any electronics enthusiast. Includes: • Side cutters. • Flat long needle nose pliers. • Flat bent needle nose pliers. • Long nose pliers/cutters. • Bull nose pliers/cutters SAVE 23% Nibbles holes in metal and plastic T 2758A 5pc Plier & Cutter Set Tough HRC 72° tungsten carbide construction for 5 times the life of standard side cutters. 130mm. SAVE 20% Ultra Fast Wire Stripper 29.95 $ Tungsten Carbide Side Cutters T 1522 Cut Large Core Cables Like Butter! BARGAIN! Stay sharp longer! SAVE 25% Super easy to use! The complete suite of tools for popular multipole DC connectors by Deutsch. Suits size 12, 16 and 20 DT series pins. Included in the kit are a terminal housing release tool, pin removal tool and screwdriver. SAVE 19% T 2749 $ $ $ Deutsch Connector Crimping Kit Spade, Ring & Lug Crimper 2 for SAVE 18% Includes carry case! Wire Stripper & Kwik Crimper SAVE 25% Premium quality 140mm precision pliers with jaw serrations for general electronics use. $ Toolbox space saver! RJ45 Pass Thru Crimper 25 119 $ Superb build quality! $ SAVE $30 35 $ SAVE 35% T 2196 T 2355 The Handy Nibbler Tool Suitable for cutting odd shaped holes in steel, plastic and aluminium. Steel: 1mm. Aluminium: 1.6mm. T 1489 High quality tool kit featuring straight, angled, curved and hook tips. 13 Piece Precision Knife Set Includes aluminium handle with 13 blades to suit different cutting jobs. Includes plastic carry case. SAVE 20% Great for repairing modern devices! 50 $ T 2183 SAVE 22% T 2168A Features 1/4” and 4mm drive handles 27 $ Jakemy® 106pc Precision Driver Set A workshop essential at a great price! An affordable do-it-all servicing set with 92 4mm chrome vanadium bits, flexible extension bar, tweezers & magnetiser ring. For repairing phones, laptops & more! 48pc Compact Servicing Kit T 2198B 11 Piece Screwdriver Set Quality set of flat blade and phillips screwdrivers for general repairs. Chrome vanadium. An aluminium driver handle with 48 4mm bits to open and repair all types of devices. Housed in an ultra slimline aluminium casing. 69pc Dual Ratchet Driver Kit SAVE 15% T 2185A 29 $ Superb quality ratchet driver with a wide selection of bits for most electronic jobs. Includes both a 1/4” adjustable angle (<90°) ratchet handle and a smaller 4mm ratchet handle. Great for the home handyman or enthusiast. Shop with us on eBay | www.ebay.com.au/str/altronicsaustralia Tool up your work space for less. Not just for desoldering works great as a regular hot air gun! 125 SAVE $100 275 $ Features 3 preset channels for quick temp selection. $ T 2460A T 2040 T 1289 SAVE $40 NEW! 119 $ SMD Hot Air Re-Work Desoldering Gun Micron® 68W Compact Soldering Station Provides 300W of hot air for quick and easy desolder and re-work of surface mount boards. 200-500°C adjustable. Includes desk stand - plus narrow, medium and wide nozzles for different tasks. This latest design benchtop soldering iron offers convenience and plenty of power for the enthusiast. Offers precise dial temperature control with temperature lock. In-built sleeper stand shuts down the unit when not in use saving on power costs. Includes a fine 1.2mm chisel tip, solder reel holder and tip sponge. Micron® Touchscreen Soldering Station A sturdy 100W benchtop soldering station featuring an all aluminium case and 2.8” touchscreen for quick temperature and preset selection. 100500°C temp range with slimline handle featuring burn resistant cable. T 2488 SAVE $22 Iroda® 3 Nozzle Blow Torch Kit 88 $ T 2098 300W Adjustable Solder Pot Tin multiple stranded hookup wires or remove multipin connectors from boards quickly and easily. Takes up to 1350g of solder. Stable temperature control: 200-480°C. Suitable for lead free and leaded work. 500g leaded solder bar $43.65 (T 1139A). 300W. Got Gas? 15 $ Ideal for trades requiring both precision brazing and high output wide spread flame jobs. Supplied in handy carry case with stable safety stand. 120 mins run time at mid setting. Includes carry case. 1500W Heat Gun Perfect for heatshrink - shrinks evenly without burning. Shifts paint, solvents from surfaces, makes plastics malleable, etc. 450L/min airflow. SAVE 30% SAVE $10 49 $ T 2110 Stock up on top notch scrubbed and triple filtered butane for reliable use in gas tools. The pocket rocket torch! Trade quality! Iroda® Mini Jet Blowtorch SAVE $76 Produces a powerful jet like flame - up to 1300°C! Refillable design is great for hobbyists. 149 $ T 2457 3 for $24 VE! STOCK UP AND SALY. ON TH ON M THIS 250ml can. T 2451. Normally $9.35ea Fume Extractor & Fan Whisk away solder/3D print fumes from your workspace! Also works as a fan. Adjustable speed. T 1296 SAVE 24% 60 $ SAVE 18% SAVE 22% T 1302A Dual Solder Reel Holder 19 $ Heavy weight base with solder guides. All metal construction. *Solder not included. SAVE 15% Never lose a tiny screw again! 29 $ T 4015A A 35x26cm heat resistant silicon work mat, plus a 25x20cm magnetic mat to keep screws and materials organised while you work. 69 $ T 2120 Cut, Polish, Grind, Sand & Carve. Perfect for odd jobs and hobbies. Powerful 130W motor with variable speed between 8000 and 33000 RPM. Included is a 172pc accessory kit of grinding wheels, drills, cutters, sanding discs, polishing pads and more. SAVE 23% 15 $ T 1460A Handy Desktop Holder The hobbyists dream - just like having an extra hand to get things done! Great for gluing, painting or soldering. Your one-stop electronics shop since 1976. | Order online at altronics.com.au Top deals on tech accessories. SAVE $50 Desk Monitor Mount SAVE 20% 50 65 $ H 8165A 32” to 70” Suits TVs up to 84” SAVE 22% $ 225 $ H 8126B Cantilever Arm TV Bracket H 8166A 60” to 100” Ultra Slim TV Wall Brackets Silky smooth cantilever adjustment, stays just where you want it to. It even has 14° of tilt adjustment! Engineered for flat screens up to 84” using 600 x 400mm VESA. Max weight, 45kg. Great value and build quality from one of the worlds leading AV mount suppliers. Two models covering TV sizes from 32” to 100”. Dual pull safety lock system. 59.95 Ideal for cars, caravans & boats! $ H 8195 Locking Swing Arm TV Bracket Regain precious desk space! • Easy adjust arms • Suits monitors up to 27” • Desk clamp installation. • Max 8kg. SAVE $44 Ideal for caravans - retaining pin keeps your TV locked against the wall when on the move. Suits 26” to 42” TVs. With pan and tilt adjustment. 15kg max. 55 $ H 8220A SAVE $40 159 $ NEW! Recharge anywhere! 69.95 $ D 2363A Perfect for the family ‘hot desk’ SAVE 24% 75 $ D 2358B USB C Network Hub 13 In 1 4K USB C Laptop Docking Station A handy laptop docking station hub for USB C type equipped laptops. Fitted with 3 x USB 3.0 ports, USB C 3.0 data port, SD & Micro SD card slot, mic & headphone jacks, gigabit wired ethernet port and VGA, HDMI & DisplayPort. Maximum 4K <at> 30Hz. One box for all your entertainment. D 2816 + A 0981 Provides HDMI (4K <at> 30Hz) connection, gigabit wired ethernet, plus three USB 3.0 ports, SD/Micro SD card slot and 60W power pass through - from a single USB C connection! SAVE $43.95 125 SAVE 24% 60 $ D 2359A Provides HDMI (4K <at> 30Hz) connection, plus dual USB 3.0 ports, SD/Micro SD card slot and 60W power pass through - all from a single USB C connection! SAVE 29% SAVE $36 49 79 $ $ D 2322 SAVE $50 79 An ultra-slim desk mount 10W wireless fast charger. Requires 60mmØ hole. Includes power supply & USB cable. Fits into a standard 60mm desk hole cutout to provide appliance power. Instant pop up design. 3 outlets plus dual USB port charging. Great for any work space. Handy air mouse for presentations. In-built laser pointer. Plug & play, no drivers required for Mac or Windows. Includes battery. With the latest QC 3.0 charging & 18W USB-C PD output, this enormous 20,000mAh power bank will keep your devices charged anywhere. With laser pointer! SAVE 35% D 4238 8K DisplayPort Switch $ or 2 for $120 Charges a laptop, a phone & tablet at the same time! Handy pop-up power board Presentations made simple! Jumbo QC3.0/USB C Power Bank 22 $ D 2323 P 8146 Build wireless charging into your desk D 0511B Wireless Magnetic Power Bank Iphone 12 for illustration purposes. USB C Expansion Hub FREE! 63 $ D 0515A* Charge your phone on the go with this MagSafe compatible wireless charging battery bank. 10,000mAh. 20W USB C PD in/out. *Shown with compatible $ Make your TV even Smarter! Stream direct to your TV from streaming services, plus play games and connect to local media on your home network. Capable of streaming stunning 4K videos <at> 60fps! 4GB ram with 32GB on board storage. Requires 2A USB power supply. Includes FREE A 0981 trackpad/keyboard valued at $29.95. SAVE 20% Switch between two PC sources to DisplayPort monitors. Supports 4K <at> 120Hz or 8K <at> 30Hz. 39.95 $ 55 $ A 3091 Multi Voltage PoE+ Splitter Provides 5, 9 or 12V output over ethernet for PoE compatible devices such as IP cameras, access points etc. Desk Mount Laptop Charger A 96W USB type C charger, plus dual QC 3.0 USB charging in the one compact near flush mount unit. 60mmØ mounting hole. Includes power supply. SAVE $19 D 4226A Shop with us on eBay | www.ebay.com.au/str/altronicsaustralia Get started in 3D Printing. Need help with 3D printing? SAVE $70 399 $ Ask our friendly staff in store for guidance on how to start, recommended software, tips & tricks! K 8600 30 x 30 x 40cm build volume for larger prints The worlds best selling 3D printer! Over 800,000 sold worldwide. SAVE $351 K 8606 Print bigger with the Creality® CR-10 V2 3D Printer Creality® ‘Ender 3’ 3D Printer The CR-10 offers reliable large volume printing up to 30Wx30Dx40Hcm! The dual port fan cooled hot end offers reliable and precise print quality whilst the triangular design provides excellent stability. Heated print bed reduces warping, ensuring great prints every time. This printer is great for anyone who needs to print larger designs such as cosplay parts, architectural models & replacement parts. Creality’s top selling 3D printer is here! The Ender 3 is a compact 3D printer offering excellent print quality with a build volume of 22Wx22Dx25Hcm and is compatible with ABS, PLA and TPU filaments. Supplied mostly assembled and can be up and running within an hour. Creality® Premium PLA Filament ABS Filament We’re now stocking Creality’s premium 1.75mm PLA designed for use in many brands of 3D printer on the market. Creality have focused on making top quality non toxic filaments with a tolerance of just 0.02mm. Each filament is 100% bubble free and offers excellent tensile strength & fluidity. This all adds up to more reliable prints and less waste! 1kg rolls. SAVE $10 Made from high quality materials for less brittle filament breakages. 39 $ n K 8387A Silver n K 8388A Gold n K 8389A Pink n K 8391A Orange n K 8392A Green n K 8393A Yellow n K 8394A Purple n K 8395A Blue n K 8396A Red n K 8397A Black n K 8398A Grey n K 8399A White High Temperature Polyimide Tape SAVE 15% Rare Earth Magnets Quality rare earth magnets. Great for building into 3D print designs. Model Type 2 FOR T 1464 25x5mm Countersunk T 1465 25 x 5mm Solid T 1466 10 x 3mm 4 pack T 1467 5 x 6mm 8 pack $18 $16 $14 $15 799 $ Great for 3D printing and other electronics applications. Leaves no residue in high temperature masking applications. Model Width NOW T 2971A 8mm T 2972A 12mm $9 $12 $13.50 $15 $17 $25 T 2973A 16mm T 2974A 19mm T 2975A 24mm T 2976A 36mm NEW! Quality ABS filament for those requiring added durability. 1kg rolls. SAVE $9.95 n K 8383A White $ n K 8384A Black 35 Fluoro Filament A translucent fluoro yellow coloured PLA for brightly coloured prints! 1kg roll. SAVE $10 47 $ K 8390A T 2370 18 $ .50 Deburring Hand Tool Remove rough edges and neaten up prints with this comfort grip external chamfer tool. .75 SAVE 12% 15 $ 5 Piece Needle File Set T 2352 Accurate Digital Vernier Calipers Precision measuring with ease! 150mm length, suitable for measuring internal, external and depth dimensions. 0.01mm, 0.0005” and 1/128th” display. Fine edge files for smoothing 3D prints. Shop with us on eBay | www.ebay.com.au/str/altronicsaustralia SAVE 24% 44 $ T 2247A Stay powered up, anywhere! Power mains appliances from your car or auxiliary battery. 155 $ Pure Sine Wave M 8060 300W 54.95 $ M 8050 150W Modified Sine Wave 79 $ 289 $ M 8051 300W 99 M 8062 600W $ 429 $ M 8054 600W 209 M 8064 1000W $ 625 $ M 8056 1000W 299 M 8065 1500W Pure Sine Wave BlackMax Inverter - Ultimate in portable power. Housed in a rugged aluminium extrusion, this new range delivers robust reliability and unwavering performance - even under severe operating conditions. For peace of mind all models have been certified to Australian Standard AS/NZS 4763.2011. Ideal for tricky loads, such as laptops, TVs & game consoles. Perfect for 4WDs, campers, caravans & trade vans. 219 $ Going bush? Have power wherever you go on your next 4WD/camping adventure. Includes 130W panel, solar regulator, battery connection cables and canvas carry case. 3 stage solar charger. Adjustable stand for best sun placement. 664x631x75mm (folded). N 2087 20A Powerhouse® Solar DC-DC Battery Chargers 345 $ N 2089 40A This dual input design connects to a solar panel and your cars alternator (12 or 24V) to provide charging for secondary batteries such as those used in campers, caravans and trades service vans/trailers. Suitable for Lead Acid, AGM and Lithium Fe PO4 batteries. Powerhouse® Portable Power Battery Box Fits a standard 90-120Ah automotive battery for powering appliances at your camp site - a totally self contained power unit! Fitted with 2.4A USB charger, dual Anderson sockets, volt meter, car acc. socket & battery terminals, plus 2x50A fuses for added safety. SAVE $30 SAVE $40 99 $ T 5098 .95 SAVE $110 139 $ An all round portable charging device - plus vehicle jump starter! Not just for car battery emergencies, this high capacity battery bank also wirelessly charges your phone, powers laptops etc. Jumpstarts most 4-6 cyl vehicles. M 8193 & USB Keeps devices charged with wireless SAVE 24% P 0698 P 0697 30 36.95 $ $ Handy Power Panels For Cars & Caravans These panels can be easily surface mounted to custom panels to provide power to your devices & portable appliances. 15A DC breaker. P 0697: 50x130x70mm. P 0698: 50x187x70mm. 209 $ N 1130F Includes canvas carry case. car battery topped up! Heading away? Keep the 49 $ Power your camping fridge without risk of draining your battery! Portable Battery Bank Jump Starter Fitted with secure lid clips & colourful LED voltmeter M 8057 1500W The same top notch quality and safety features as our popular Black Max inverter series (left), with a modified sine wave design to bring 240V power to any vehicle at a fantastic price. Models up to 600W have USB and auxiliary 3A 12V DC output for powering devices. 240V outlet runs most simple appliances such as power tools, pumps, lights, fans and heater elements. 130W Remote Power Folding Solar Panel NEW! $ The affordable portable power solution for any vehicle. Top up your batteries with solar power. N 0700A This compact 5W solar panel is designed for keeping your vehicle batteries topped up when parked - ideal for when you head off on summer holidays. Suits permanent outdoor install. charging! Colourful Anderson Style Plugs More colours in the popular SB50 size reversible plugs. 50A rated. Includes crimps. P 7761 Red P 7762 Green P 7763 Blue P 7764 Black P 7765 Yellow Your one-stop electronics shop since 1976. | Order online at altronics.com.au 6 $ .95 Tinker, Design & Build. Arduino UNO & Ethernet Board SAVE $31 Control more with 2 shields! Connect your Arduino design to the internetof-things with this handy W5500 ethernet board with atmega328p SAVE $23 on board. Fully UNO compatible with USB $ download & micro SD slot. Z 6467 79 $ Z 6310 45 SAVE $30 TOP VALUE! 109 $ MK2 Arduino MegaBox Kit by Altronics. K 9670A ATDev Shield for ATTiny Kit A powerful and versatile programming and breakout shield for ATtiny. Combine with a UNO for instant programmer and debugging. Arduino Tinker Kit Includes a huge array of parts for learning with the Arduino UNO (board included). Also includes proto-shield, LED matrix, 7 segment displays, two breadboards, stepper motor, servo, IR remote, connection leads and a variety of parts, LEDs, buttons and sensors. Developed in house by Altronics, this MegaBox has space for two shields, plus five 2A 5V relay outputs and eight opto isolated outputs. All UNO/ Mega pins are broken out to header sockets for easy connection to other breakouts. A small 160 hole prototyping area is included for connecting to other sensors. *Arduino board & shields not included. SAVE 20% K 9815 18 $ SAVE 48% SAVE 34% SAVE 35% 5 $ ea Colourful Arcade Gaming Switches Jumbo arcade machine momentary switches with 12V illumination and customisable button plate. 25mmØ hole. S 0910 Red S 0911 Green S 0912 Blue S 0913 Yellow S 0914 White S 1148A S 1147 15 $ Heavy Duty Arcade Joystick USB Interface For Joystick & Buttons NEW! 15 $ NEW! 14 19.95 .95 $ $ K 9642 Great for retro gaming projects or for direction control in serious projects. Adjustable plate allows 2, 4 or 8 way control. 95x59mm mounting plate. A handy interface board for a joystick and up to 12 arcade buttons. Includes pre-terminated cables. Must have for Arduino builders! Z 0003 Jumper Header Kit LED Assortment Pack Single row header connectors. Includes male & female pin headers, plus 2.54mm housings. 3mm and 5mm LEDs in green, red, blue, yellow and white. 300pcs. Z 6387 SAVE 22% SAVE 26% 50 $ ‘Due’ Development Board Z 6244 The first Arduino board based on a 32 bit ARM core microcontroller for added power. Ideal for projects that need higher speed processing. 54 digital in/outs, 12 analog inputs & 4 UARTs. 3.3V shield/sensor compatible. SAVE 22% $ per 1m ESP32 Camera Board An ultra compact ESP32 based module with on-board camera, Bluetooth BLE & 802.11n Wi-Fi. Ideal for building your own IoT smart device projects. 5V input. Create Amazing LED Light Effects! 5050 size LEDs for superior light output! 23 25 $ X 3222A 1m length of addressable RGB 5050 LED strip - this means you can program the colour of every individual LED using an Arduino/Raspberry Pi. 60 LEDs per m. WS2812B chip on board. 10mm width, adhesive backed. 5V, 3.6A/m (max). Z 6442 LN298 Dual Motor Module A complete and self-contained WiFi network solution that can operate independently or as a slave on other host MCUs. 3.3V input. designed to drive inductive loads, such as relays, solenoids, DC and stepping motors. 2 channels. 5V input. 26 $ 14 12 $ ESP8266EX Mini Wi-Fi Module P 1018A 350pc $ 22 $ Z 6441 SAVE 15% P 1014A 140pc Prototyping Wire Packs Handy packs of pre cut and trimmed solid core wire for breadboarding your next design! 10 $ SAVE 30% SAVE 20% SAVE 24% 3 Axis Accelerometer Z 6321 Low power, high resolution ADXL345 accelerometer for tilt and movement sensing projects. 3-5V input. Breadboards for big designs! Huge breadboards with aluminium bases for those designs that are beyond the scope of your average breadboard! Easy power connection via binding posts. SAVE 28% 35 $ P 1012A 1660 Hole SAVE 26% 40 $ P 1015A 2309 Hole Your one-stop electronics shop since 1976. | Order online at altronics.com.au Must have for the electronics maker! Make your home smarter. Wi-Fi RGB Strip Lighting Kit X 3227* Answer the door when you’re not home! SAVE $15 60 This kit includes 5m of RGB strip lighting, power supply, controller unit and IR remote control allowing you to create colourful lighting effects around your home. Music sensor input allows the lighting to trigger to music being played in the room. Works with Alexa and Google Assistant. 60 LEDs per metre. $ SAVE $50 Music sensor can trigger lights to the beat! SAVE 24% 99 Wi-Fi Video Doorbell with Tuya smartphone app control and 2 way audio. This stylish doorbell connects to your wi-fi and notifies your mobile phone when a person arrives at your doorstep. Great for telling the postie where to put packages. • Security camera mode • Motion detect notification • Includes power supply and indoor doorbell ringer unit. $ 2 For 30 $ S 9455A P 8149 HOT PRICE! Automate heaters & lamps! Switch any connected appliance on or off remotely from anywhere in the world. Set schedules, monitor and control via the Tuya Android/iOS app. Maximum 10A 2400W. Works with Google Home and Alexa What is Tuya® Smart Home? Tuya is a common application for thousands of products from the worlds leading Smart Home suppliers. It provides a single point of control for home security, lighting and appliance power allowing you to control everything you need from a the one smartphone app. The Tuya IoT platform powers over 250,000 home automation products across the globe! All of our Tuya compatible cameras below provide 1080p HD with audio and can be easily located anywhere! Camera measures just 10mm across SAVE $20 69 S 9846 Wi-Fi HD Camera Clock • Internal battery - set it up anywhere! • Day/night with IR • USB rechargeable • 100 mins motion activated recording time. • Ultra compact module can be built into custom enclosures • Completely wireless - set it up anywhere! • USB rechargeable • 100 mins motion activated recording time. Cable Free Wi-Fi Surveillance This handy 1080p camera can be installed just about anywhere indoors or out and has an in-built battery so you don’t need to run any cables! Offers 4-6 months of motion detect recording. When it’s flat, just take it off the wall & recharge via USB. Suits sheltered outdoor use. S 9850 S 9844 Wi-Fi Camera Module Also includes ball joint bracket. SAVE $40 159 $ S 9843B • Real alarm clock function • Two-way audio (mic & speaker) • Motion detect recording • USB or battery powered (S 4736 x 2 $18.50ea) *Note: We encourage this item be used responsibly for legitimate CCTV use. Outdoor Pan & Tilt Wi-Fi Camera S 9020 SAVE $44 Provides extra coverage to your outdoor spaces with motorised pan (355°) and tilt (100°). Auto-tracks moving objects within the frame. Constructed from UV stabilised plastic with weatherproof rating to IP66. 2-way audio with mic and speaker. 30m IR night time coverage. Requires 5V 2A USB power supply. 95 $ Sale Ends May 31st 2022 Phone: 1300 797 007 Fax: 1300 789 777 Mail Orders: mailorder<at>altronics.com.au » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd Outdoor Solar Powered Camera • IP66 rated for outdoor use • Two-way audio (mic & speaker) • Motion detect recording • 2MP 1080p HD sensor • Day/night operation with IR • Battery powered (included) with solar recharging - mounts anywhere! Indoor Pan & Tilt Wi-Fi Camera Makes a great baby or pet monitor, this camera features intelligent tracking of moving objects within the frame. 2-way audio with mic and speaker. 5m IR night time coverage. Requires 5V 1A USB power supply. Western Australia Build It Yourself Electronics Centres $ $ $ Mini Wi-Fi Cube Camera 159 139 69 $ SAVE $40 S 9845A SAVE $30 SAVE $20 HOT PRICE! SAVE $10 69 $ S 9017A Victoria 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 New South Wales » Auburn: 15 Short St 02 8748 5388 Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 South Australia » Prospect: 316 Main Nth Rd 08 8164 3466 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. © Altronics 2022. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0091 Find a local reseller at: altronics.com.au/storelocations/dealers/ Heat pipes, vapour chambers and thermosiphons Heat pipes, vapour chambers and thermosiphons are “two-phase” cooling (or heating) devices that transfer heat from one place to another very efficiently. They are simple and inexpensive, with no moving parts and do not require external power. Yet they conduct heat so much better than metals like aluminium or copper that they can be considered ‘heat superconductors’. T he t e r m i n o lo g y regarding these devices is somewhat confusing. According to some definitions, vapour chambers and thermosiphons are simply variations of the standard heat pipe. That is logical since they all operate on the same principle. For clarity, we will refer to the most common type of heat pipe as a constant conductance heat pipe (CCHP), to distinguish it from the other types of heat pipe such as the thermosiphon and vapour chamber. These devices all operate on similar principles, with some differences as follows: • CCHPs can operate in any orientation, transferring heat from one place to another and are generally in the form of a cylindrical pipe. • Thermosiphons are similar to CCHPs but operate with the assistance of gravity, and thus can only work correctly in a particular orientation. • Vapour chambers distribute heat evenly over an area instead of transferring heat from one location to another. In their modern form, CCHPs were initially developed for space applications but are now widely used in many areas, especially electronics. As computer chip component density and speed becomes higher and higher, the amount of heat generated becomes difficult to remove, even with huge aircooled or liquid-cooled solid copper or aluminium heat sinks. Consider that an integrated circuit like the Nvidia GA102, with over 28.3 billion transistors onboard, has an area of just 628mm2 – about the size of a postage stamp – yet dissipates up to 450W in operation! Traditional heatsinks have no hope of removing that much heat without the silicon junction temperature greatly exceeding 100°C, therefore another solution is needed. Enter heat pipes Heat pipes are used either when a traditional heatsink cannot efficiently remove the heat from a device or when weight or size targets can’t be met with conventional heatsinks. Commonly, these considerations apply to modern computers. Water cooling (via a water block, pump and radiator with fans) is another possible solution in some cases. Still, it introduces complications like pumps, pump noise, potential pump failures and the possibility of water leaks. These problems do not occur with By Dr David Maddison siliconchip.com.au Australia's electronics magazine May 2022  19 heat pipes which are now important elements of the CPU (central processing unit) and GPU (graphics processing unit) cooling assemblies in many desktop and laptop computers, plus many other electronic devices. Heat pipes and vapour chambers are even used in some smartphones. Without adequate cooling, modern CPUs and GPUs would be destroyed in seconds if they didn’t have internal overheating protection to shut them down. Two-phase cooling devices are also used for high-power IGBTs (insulated-­ gate bipolar transistors) in wind turbines, electric vehicles, data centres and solid-state lasers, among other applications. Heat pipe construction Constant conductance heat pipes, vapour chambers, thermosiphons and related two-phase devices are sealed hollow metal tubes or cavities that have been evacuated of most air (to a low pressure), into which a tiny amount of liquid has been placed. Some of this liquid evaporates to its vapour form given the low pressure inside the tube. Depending upon the application, the typical liquids used are water, ammonia, alcohols such as methanol or ethanol, R134a refrigerant or liquid alkali metals such as sodium. We will Expansion Vessel Furnace Coils heat source by capillary action, gravity or some other force, and the process is endlessly repeated, removing heat from the object to be cooled. Heat pipes such as CCHPs and thermosiphons are typically used for cooling as described above, but the process is equally applicable to supplying heat to an area. It depends on which end of the heat pipe the object to be heated or cooled is located. In the case of vapour chambers, they can be used to evenly distribute heat as well as cold. History of heat pipes Initial Venting Filling Fig.1: the Perkins System of heating from British Patent 6146, dated 30th July 1831. later discuss what liquids are used in different applications. Heat pipe operation During operation, liquid at the heat source (evaporator end) absorbs heat and evaporates. The vapour migrates to another area of the pipe (usually the other end, called the condenser). There, it condenses into a liquid and releases ‘latent heat’ (described later) into the surrounding environment. This latent heat represents a large amount of energy. The liquid then migrates back to the Angier March Perkins (son of Jacob) invented what was to become the antecedent of the heat pipe and obtained US Letters Patent No. 888 in 1838 and UK Patent No 6146 for his invention (see siliconchip.com. au/link/abd5). Later, he and his son, Loftus Perkins, invented a hermetically-sealed boiler tube with water or another liquid as the working fluid. It was a heat transfer device; however, it was single-phase (liquid-only) and operated at high pressure (about 20 atmospheres) and high temperature (150°C or more). By comparison, a modern heat pipe uses two phases, eg, water and steam. It was highly successful for about 100 years and was known as the “Perkins System of Heating”. Many of these systems are still in use today in Fig.2: a steam locomotive built by Jacob Perkins in 1836 using his sealed steam tube patent of that same year. The device became known as the Perkins Tube. Fig.3: a Perkins steam oven displayed at the Paris Exhibition of 1867 that used a Perkins Tube. 20 Silicon Chip Fig.4: an advertisement for a Perkins steam baking oven, probably from the 1890s. Australia's electronics magazine siliconchip.com.au southern England and Wales; some are 160 years old. The chronology of heat pipe development is confusing because an important patent of Jacob Perkins from 1836 is widely misquoted as having been awarded in 1936. This is British Patent No 7059, 12th April 1836, “Steam engines; generating steam; evaporating and boiling fluids for certain purposes”. This device was a sealed vertical tube filled with water that passed over an evaporator and then a condenser. It relied on gravity for the cooled condensate to return to the heat source (see Figs.1-4) and became known as the Perkins Tube. As this device contained both water and steam, it was a twophase device, like a modern heat pipe. Perkins Tubes were first used in locomotive firebox superheaters. Another important use was “stoppedend steam tubes” in bread-making ovens, patented by Loftus Perkins in 1865. These were adopted by the British Army some years after difficulties encountered feeding troops in the Crimean War (which ended in 1856). The ovens contained a multiplicity of slightly sloping tubes above and below where the bread was baked, each hermetically sealed and filled with distilled water. The lower end of each tube was immersed in the furnace. The ovens were widely acclaimed because of the even, continuous heat they supplied, plus their economical operation. The Perkins Tube relied on gravity to return the condensed liquid; today, they would be known as a two-phase Fig.5: F.W. Gay’s thermosiphon heat pipe invention, as disclosed in US Patent 1,725,906. siliconchip.com.au thermosiphon. Later, we will discuss the various types of heat pipes in greater detail. For more on the engineering genius of the Perkins family, see siliconchip. com.au/link/abd6 Later developments In 1942, F. W. Gay developed a finned heat pipe gas-to-gas heat exchanger in the form of a thermosiphon to exchange heat between a flow of hot air and cold air (see Fig.5). The main problem with thermosiphons is that they rely on gravity, so they only operate in a particular orientation. But this problem can be solved by using very small diameter pipes called capillaries. The flow is then dominated by capillary action, which can act in opposition to the force of gravity. Simple examples of capillary action are the way paint is drawn into the bristles of a paintbrush, or how water soaks upwards in tissue paper. This action occurs because intermolecular forces dominate the liquid’s smallscale behaviour, rather than gravity. A capillary-based heat transfer device was the subject of the 1942 patent application of Richard S. Gaugler of General Motors (awarded in 1944) for a “Heat Transfer Device” – see siliconchip.com.au/link/abd7 However, nothing seems to have come of it at the time. The idea of the patent was that, unlike a thermosiphon, his capillary-based heat transfer device (which today would be called a heat pipe) could function in any orientation. Independently of Gaugler’s work, and seemingly without prior knowledge of it, in 1963 George M. Grover of the US Los Alamos National Laboratory independently discovered the heat pipe and filed a patent which was awarded in 1966 for an “Evaporation-­ Condensation Heat Transfer Device” – see siliconchip.com.au/link/abd8 He coined the term “heat pipe”, mentioned in the patent application. Apparently, the patent examiner was aware of Gaugler’s work (citing it) but awarded the patent anyway. Both inventions are almost identical, using materials such as metal powders attached to the inside of capillary tubes to enhance the capillary action by the wicking effect. But while Gaugler’s was not widely known or put to use, Grover’s was, and he became known as the “father of the heat pipe”. Grover’s work saw the heat pipe put to use in space applications by NASA. Latent heat To further understand the operation of heat pipes and related devices, we must first discuss latent heat. Latent heat is the release (or absorption) of heat that occurs during a ‘phase transition’ such as between solid, liquid and gaseous states (see Fig.6). It can also be released or absorbed due to structural changes within a material, such as changing from one crystal structure to another. For example, consider that if you had ice at 0°C and you added heat to it, it would melt and become liquid water, but the water could still be at Fig.6: water’s energy content vs its temperature at atmospheric pressure. Energy added or removed can either change the temperature or change the phase. The change in phase at constant temperature is indicated by the horizontal areas of the graph and is due to latent heat. The sloping areas of the graph indicate changes in temperature (sensible heat). Original source: Wikimedia user Cawang (CC BY-SA 3.0) Australia's electronics magazine May 2022  21 0°C. Where did that heat energy go? It is the heat of fusion and is returned when the liquid water is re-frozen. Similarly, if you heat liquid water, you get steam at 100°C, with the added energy being the heat of vapourisation. That energy is returned when the steam condenses as the heat of condensation (making steam burns even worse than they already are). Another example is the process of sweating, which results in the body being cooled due to energy removed in the latent heat of vaporisation of water as the sweat evaporates (swamp coolers use the same effect). During the release or absorption of latent heat, two phases of the substance coexist, such as liquid water and ice or liquid water and water vapour. There is a lot of energy associated with these transitions, which is why ice keeps a drink much colder for longer than simply having the drink at a temperature close to freezing. Similarly, there is a lot more energy in steam than there is in water close to the boiling point, which is part of the reason why steam is effective for powering steam engines or turbines in power stations. Latent heat versus sensible heat for cooling Because of the large amount of energy associated with latent heat, it is much more efficient than traditional sensible heat cooling. Latent heat is shown as the horizontal regions in Fig.6, while sensible heat corresponds to the sloped sections. Note how the heat of vaporisation is considerably higher than the energy required to raise water temperature from 0°C to 100°C! Table 1: typical working fluids for heat pipes & their operating ranges. Working fluid Operating temperature range Silicon Chip Operating temperature range Helium -271°C to -269°C Ammonia -75°C to +125°C Hydrogen -260°C to -230°C Methanol -75°C to +120°C Neon -240°C to -230°C Acetone -48°C to +125°C Oxygen -210°C to -130°C Water +1°C to +325°C Nitrogen -200°C to -160°C Caesium +350°C to +925°C Methane -180°C to -100°C Potassium +400°C to +1025°C Ethane -150°C to +25°C Propylene -150°C to +60°C Pentane -125°C to +125°C Methylamine -90°C to +125°C To put it another way, it takes much less energy to boil a kettle full of water starting at 0°C than it does to convert all that boiling water into steam. You can easily observe this yourself if you force a kettle to stay on after the water is boiled for a period equal to the boiling time. Most of the water will still be liquid by the end. Elements of a heat pipe Heat pipes, and similar, essentially comprise a container (often a tube but not necessarily), a working fluid and possibly a wick or capillary structure – see Fig.7. The container must: • be easy to fabricate • be chemically compatible with the working fluid • be wettable by the working fluid • have sufficient strength and good thermal conductivity • in cases like spacecraft applications, be light Common materials used for heat pipes are copper, aluminium and stainless steel. More exotic materials Fig.7: the operation of a heat pipe. The working fluid evaporates at the hightemperature end and absorbs energy (1). It then migrates along the cavity to the low-temperature end (2) and condenses, releasing its latent heat (3). The liquid is absorbed by the wick structure and migrates back to the high-temperature end (4), repeating the cycle. Original source: Wikimedia users Zootalures & Offnfopt (CC BY-SA 3.0) 22 Working fluid Australia's electronics magazine NaK +425°C to +825°C Sodium +500°C to +1225°C Lithium +925°C to +1825°C Silver +1625°C to +2025°C such as tungsten, molybdenum, niobium and Inconel are used for the highest-­temperature applications. Among other characteristics, the working fluid must: • be able to wet any wicking material present • be able to wet the container walls • be chemically & thermally stable • have a high latent heat • have high thermal conductivity • be able to exist as a liquid and vapour over the desired temperature range • have a high surface tension to drive capillary action • have low vapour and liquid viscosity to aid flow The working fluid used chiefly depends on the desired temperature range of the heat pipe. Water is the most common working fluid, with an operating temperature range of +1°C to 325°C. The lowest temperature heat pipe uses helium for a range of -271°C to -269°C and the highest temperature pipe uses silver for an operational Fig.8: several basic, straight, constant conductance heat pipes (CCHPs) of the type that can be bought online very... siliconchip.com.au range of +1625°C to +2025°C. See Table 1 for other working fluids. Correct selection of the working fluid is essential; if the temperature is too high for the fluid, it will be all gas, and if too low, it will freeze. The temperature range must accommodate the coexistence of both liquid and vapour of the chosen fluid. The velocity of vapour in a heat pipe is surprisingly high, approaching the speed of sound. The return liquid flow is at about walking speed. Figs.9(a) & (b): a CCHP with a metal sintered powder wick opened up. Source: Thermolab (http://thermolab.co.kr/) Wicks One of the defining features of a heat pipe compared to a vapour chamber or thermosiphon is the presence of a wick or wicks. The function of a wick is to transport working fluid from the condenser back to the evaporator by capillary action. Wicks come in various forms, such as sintered metal powder, grooves in the tube, a screen mesh or other porous or fibrous wicking structures, such as carbon fibre or ceramic fibres. For some examples of wicks, see Figs.9-11. Sintering is when small particles of metal are fused by heat and pressure, forming a porous solid structure with a very high surface area. Figs.10(a) & (b): a CCHP with a grooved metal wick opened up. Source: Thermolab (http://thermolab.co.kr/) Heat pipe types There are many variations on heat pipes, but we’ll concentrate on describing the more common types. Standard heat pipe (CCHP) Figs.11(a) & (b): CCHP with a metal mesh wick opened up. Source: Thermolab (http://thermolab.co.kr/) The constant conductance heat pipe (CCHP) is the most common type of heat pipe and is ‘simply’ a partially evacuated, sealed tube with a wicking material and a working fluid inside (see Figs.8 & 12). It transfers Fig.12: the operation of a typical constant ► conduction heat pipe. Heat applied to one end causes the working fluid to evaporate and flow along the centre of the tube to the cold end. It then condenses and flows back to the hot end, along the capillary wick, and the process repeats. ...inexpensively for experimentation. Other CCHPs may have bends and attachments to suit. siliconchip.com.au Australia's electronics magazine May 2022  23 Fig.13: a CPU cooling assembly (known as a “tower cooler”) with six heat pipes. Note how they are flattened to make good thermal contact with a CPU. Heat is removed from the ‘cold end’ of the heat pipes via fin stacks and one or more fans, blowing air between the fins. In this case, one fan is mounted in the middle of the two fin stacks. heat energy from the ‘hot end’ to the ‘cold end’. While a CCHP can work in any orientation, the maximum distance it can work against gravity is about 250mm for a copper/water heat pipe. In many cooling applications such as computer CPU coolers, fins are added to the heatsink, and possibly fans, to dissipate that heat (Fig.13). While some lower-end modern CPUs can be cooled with a standard finned heatsink and fans, that is not good enough at the high levels of heat generated by many modern CPUs, some of which can exceed 200W under full load. To allow transfer into and out of the heat pipe, sections of the tube can be flattened, as shown in Fig.13. These flattened sections can then be laid side-by-side and machined to form rectangular areas which make Fig.15: a Dynatron-brand R15 vapour chamber base with a copper stacked fin heatsink, recommended for use with certain CPUs in server applications. It is capable of dissipating 165W. Despite the relatively small source area (typically around 200mm2), the vapour chamber ensures an even distribution of heat across the heatsink. Source: Dynatron Corporation 24 Silicon Chip Fig.14: the structure of a vapour chamber. Note the support structure made from numerous solid copper pillars to resist the high clamping force. intimate contact with either the heat source (eg, the flat surface of a silicon chip) or the heat removal system (eg, a set of metal fins). As long as the sections are not flattened so much that they pinch off the inside of the pipe, this has little impact on their performance. Vapour chambers A vapour chamber can be thought of as a type of flattened and square CCHP (see Fig.14). Its purpose is to distribute heat uniformly, remove hot spots, and transfer high heat from a smaller area such as CPU or GPU to a larger heatsink such as the finned assembly. That finned assembly can then deal with the lower heat flux, as seen in Figs.15 & 16. A vapour chamber is constructed much the same as a heat pipe. But in addition to the capillary material lining the interior chamber, there may also be internal support posts to allow for the high clamping pressures involved. These are from the need to firmly attach the heatsink and vapour chamber to the device to be cooled, so that it has sufficient thermal conductivity to the vapour chamber. An advantage of a vapour chamber is that the cooling assembly can be larger and therefore quieter than a traditional heatsink, the latter of which may require very powerful and noisy fans to remove a high heat load. (Have you ever heard a modern computer server working? They sound like a plane about to take off!) Note that heat pipes used in coolers have a similar role; they spread the heat out to a much larger area than the source, allowing many more fins to conduct the heat into the air, and larger (and thus slower spinning and Fig.16: an illustration of vapour chamber arrangement as used on a reference Nvidia GTX580 graphics card. The function of the vapour chamber is to spread heat evenly to the finned heatsink. The condensed liquid is returned via a wick structure. “GPU” is the graphics processing unit chip. Australia's electronics magazine siliconchip.com.au Fig.17: a video frame showing a vapour chamber from Razor Phone 2 with the chamber cut open to reveal the wicking and support structure. From the video titled “Razer Phone 2 Teardown - The Vapor Chamber is Incredibly Cool” at https://youtu.be/UGsICbmmfws quieter) fans to assist in that transfer. The quietness of these designs is a particular advantage for computer gamers who want quiet machines that must run for long periods under heavy 3D graphics computational loads. Another advantage of vapour chambers is that they can be used in height-sensitive devices like phones and laptops as they can be made as thin as one millimetre, much thinner than a heat pipe in the same application (see Fig.17). In such applications, heat can be distributed and ‘diluted’ elsewhere in the device, or removed via a flat outside surface such as the back cover. In a sense, this means that rather than your phone or tablet CPU getting hot under load and throttling back its frequency, the whole phone/tablet instead becomes somewhat warm. That’s because the same amount of energy is spread over a wider area, lowering the temperature and improving thermal transfer to the surrounding air. Thermosiphons Thermosiphons can be thought of as wickless heat pipes (see Figs.18 & 19) and were the subject of the original invention of Perkins. While they do not have a wick, sometimes they have grooves on the pipe’s interior walls to increase the surface area and facilitate the return of the working fluid to the evaporator. Unlike CCHPs, they rely on gravity, not capillary action, for the return of the working fluid. Therefore, they can only be used with the heat moving siliconchip.com.au from a lower area to a higher location, since gravity can only return the condensate to a lower area. So why use thermosiphons instead of CCHPs that can be used in any orientation? The advantage of thermosiphons is that they have about three times the heat transfer capacity for the same pipe diameter. They can also transfer heat over distances of tens of metres. Since thermosiphons will remove heat from the bottom of the pipe to the top, but won’t transfer heat from top to bottom, they can be thought of as analogous to a diode. This type of thermosiphon should not be confused with the natural convention and circulation of water without a pump that occurs in some solar hot water systems or older internal combustion engines. While those are classified as thermosiphons, they are not heat pipes. One variation is the loop thermosiphon, where the liquid return and vapour paths are separated. This has the advantage of removing any restriction caused by the liquid and vapour flowing in the same pipe in different directions. Fig.18: the operation of a thermosiphon heat pipe. This one is embedded in the ground and is designed to prevent the permafrost from melting around buildings in cold climates like Alaska or northern Canada. The thermosiphon can also be designed to support structures. Original source: www.researchgate. net/publication/266672789_Review_ of_Thermosyphon_Applications Thermosiphons in building construction While not a problem in Australia or New Zealand, there is permanently frozen ground known as permafrost in the far north of North America, Europe, and Russia. Any attempt to build on permafrost will result in heat from the building causing the permafrost to thaw, thus Australia's electronics magazine Fig.19: a heat pipe loop thermosiphon. Source: Celsia, Inc May 2022  25 Fig.20: thermosiphon support structures hold up the Trans-Alaska Pipeline System (TAPS). Without them, heat from the pipeline would cause the permafrost to melt, and the pipeline supports would sink into the ground. Note the finned condensers. These heat pipes use ammonia as the working fluid and steel for the pipes. Source: Dave Bezaire & Susi HavensBezaire (CC BY-SA 2.0) destabilising the foundations of the structure. The solution is to either drive piles deeply into the ground and build on top of those, build on a thick gravel pad, or use heat pipe technology to keep the ground frozen, as shown in Figs.20 & 21. In cases where the ground has thawed, it may be re-frozen and kept frozen using a variation of a thermosiphon called a thermoprobe, such as from Arctic Foundations of Canada (http://arcticfoundations.ca/). How good are heat pipes? Excellent passive heat conductors such as pure copper, aluminium, graphite, and diamond have a thermal conductivity between 250W/m.K and 1500W/m.K. In comparison, heat pipes have a thermal conductivity in the range of 5000W/m.K to 200,000W/m.K. So they range from being around three times better heat conductors to being 800 times better than solid metal! Variable conductance heat pipe (VCHP) Fig.21: a diagram showing how the Trans-Alaska Pipeline System thermosiphons shown in Fig.20 are made. 26 Silicon Chip Australia's electronics magazine Constant conductance heat pipes are linear devices in which the temperature at the evaporator end (the source of heat where evaporation occurs) drops proportionally to the difference in temperature between the evaporator end and the condenser end. Situations where the heat source is not generating much heat and/or the condenser ambient temperature is low can result in the device being excessively cooled. A variable conductance heat pipe can prevent that. In a variable conductance heat pipe, the device being cooled is, by design, kept at a relatively constant temperature even when heat dissipation from the device changes or the ambient temperature of the condenser end changes (see Figs.22 & 23). This is done by adding a non-condensable gas (NCG) to the heat pipe, in addition to the working fluid. A gas reservoir is also added at the condensing end of the heat pipe (the end remote from the heat source). When there is significant heat to be moved and the ambient temperature is not too low, the working fluid vapour pressure pushes the NCG back into the reservoir. The heat pipe then works in the usual manner, as shown at the top of Fig.22. siliconchip.com.au But when the dissipation from the device being cooled is low and/or the ambient temperature is low, meaning the device could be excessively cooled, the working fluid has a lower pressure and cannot push back the NCG as much. As shown at the bottom of Fig.22, less condensing area is exposed, and therefore, the device is not cooled as much and stays at an appropriate temperature. A VCHP can maintain the temperature of the evaporator end to within 1-2°C of the desired temperature. This is despite significant variations in the heat being dissipated by the device at the evaporator end and the ambient temperature at the condenser end. Loop heat pipes The loop heat pipe is based on the CCHP and is like a loop thermosiphon. But unlike a thermosiphon, it does not rely on gravity. Loop heat pipes can transfer more heat over longer distances than CCHPs can. They can be used in conjunction with CCHPs and VCHPs. Applications include spacecraft, avionics cooling in aircraft and aircraft de-icing – see Fig.24. Rotating heat pipes Fig.23: a variable conductance heat pipe from a spacecraft. The bulbous structure is the gas reservoir, and the distant end is the evaporator. The condenser portion is the long flange. The valve and pressure gauge are removed when the device is put into service. Source: Advanced Cooling Technologies, Inc (CC BY-SA 3.0) Fig.24: a commercial loop heat pipe system for NASA spacecraft designed by Advanced Cooling Technologies. The titanium/water heat pipes operate from 70°C to 250°C. Spacecraft heat pipes can have multiple evaporators and condensers. Source: Advanced Cooling Technologies ► Fig.25: rotating heat pipes work similarly to other heat pipes, but they use centripetal/centrifugal forces along with a tapered profile to return the working fluid after it has condensed. ► A rotating heat pipe (Fig.25) is designed to cool rotating machinery such as motors or RF rotary joints, as used in telecommunications. They work much like a CCHP, but they rely on centrifugal forces instead of relying on capillary action for the condensate return. They do this either via a tapered wall with a smaller diameter at the condenser end or by having spiral grooves similar to a rifle barrel to convey the condensate back to the evaporator. Heat can only flow in one direction in a rotating heat pipe, so it is again analogous to a diode. Fig.22: how a variable conductance heat pipe (VCHP) works. The top diagram shows its operation under optimal conditions, while at the bottom, it has reduced heat dissipation at the evaporator end (where the device being cooled is located) due to less heat being produced. This is because non-condensable gas migrates down the tube, blocking some of the condenser area and reducing its capacity. Oscillating and pulsating heat pipes Oscillating or pulsating heat pipes (OHP), are relatively new members of the heat pipe family, having been invented in the 1990s. They comprise a continuous loop of pipe or pipe-like shape laid out in a serpentine manner, containing alternating pockets of liquid ‘slugs’ and vapour bubbles which move back and forth in relation to the condenser area as they are alternatively heated or cooled – see Fig.26. siliconchip.com.au Australia's electronics magazine May 2022  27 They are often machined into a bottom plate, and a smooth top plate is bonded to that, with the item to be cooled attached to the top plate. In Fig.26, the OHP is said to be bonded to a battery pack but it could be just about anything that generates heat. A video of how an oscillating heat pipe works can be seen, titled “Pulsating Heat Pipe (PHP)/Oscillating heat pipe (OHP) -CFD analysis | Animation” at https://youtu.be/ glYguHLKRL0 Direct liquid cooling of ICs Fig.26: an oscillating heat pipe for cooling an electric vehicle battery. Original source: www.mdpi.com/1996-1073/11/3/655 Fig.27: a silicon chip with an onboard microfluidic cooling system, developed by the Swiss Federal Institute of Technology in Lausanne. The fluid inlet and outlet can be seen at the top of the device. 28 Silicon Chip Australia's electronics magazine All the above-mentioned types of heat pipes can be used to cool electronics or other devices. But a heat pipe can only ever contact the exterior of a chip or electronic device package and often requires a thermal interface material to achieve sufficient thermal conductivity between the two. That material always has some sort of thermal resistance, though. Another way to cool silicon chips that does not involve heat pipes, currently under development, is to build liquid cooling channels into the chip itself (see Fig.27). This technology is under development at the Swiss Federal Institute of Technology in Lausanne under the leadership of Professor Elison Matioli. In this case, liquid-carrying microchannels are fabricated in the silicon substrate. The size of the channels vary according to the cooling required in a particular area of the device. The channel size varies because if they were all of the same small size, a large amount of energy would be required to pump the fluid. So, like a human circulatory system to which the cooling channels have been likened, the channels are only narrow in the areas where the cooling is needed most. Cooling channels of the small size involved come under the general area of microfluidics, which we covered in the Silicon Chip article on Fluidics in the August 2019 issue (siliconchip. com.au/Article/11762). This type of system has been shown to be capable of removing 1700W/cm2 with the chip temperature limited to 60°C. That’s about ten times more effective than external liquid cooling or cooling using heat pipes. The work is significant because, until now, semiconductor device fabrication and cooling have been siliconchip.com.au considered two separate areas of design. This approach integrates the two areas. Ice cream scoops One application you might not have considered for heat pipes is ice cream scoops! Heat is transmitted from the hand via a heat pipe in the handle to the scoop, where it melts the ice cream, making it easier to scoop out (Fig.28). You can view the US Patent for this vital technology at siliconchip.com. au/link/abda Related videos ● “What’s Inside the Worlds’ Fastest Heat Conductor?” – https://youtu.be/ OR8u_ _Hcb3k ● “Liquid Crystals Painted on Heat Pipes” – https://youtu.be/Y6K7h9tbD_s ● “Heat Pipe Basics and Demonstration Video” – https://youtu. be/2vk5B6Gga10 ● “How Copper Heatpipes Are Made | China Factory Tour (Cooler Master)” – https://youtu.be/AD-4WKwCAfE Fig.29: heat pipes (labelled) as used on a NASA Kilopower experimental reactor proposed, for use in space, on the Moon and on Mars. Source: NASA Heat pipe limits Limitations are imposed on the operation of heat pipes by several factors. These include: 1) the capillary limit, where capillary action in the returning liquid is not fast enough to support the evaporation rate in the opposite direction 2) the entrainment limit whereby the velocity of the vapour near the wick is enough to restrict the return flow of the liquid 3) the sonic limit, where the vapour cannot exceed the speed of sound at the pressure inside the heat pipe whereby a shockwave may be created 4) excessive heat, causing the liquid in the wick to evaporate Conclusion Heat pipes are a vital technology for today’s high-density semiconductors. They allow waste heat to be removed to a sufficiently large fin stack for the semiconductor device to remain at a reasonable operating temperature, without the additional complexity, cost or size of a standard liquid-­cooling system. With the density of digital semiconductors continuing to increase, and greater demand for high-efficiency power semiconductors in renewable energy systems and electric vehicles, they have become an essential part of SC modern technology. Fig.28: a Thermoworks ice cream scoop that uses a heat pipe to assist in scooping the ice cream. It appears to be no longer manufactured. siliconchip.com.au Australia's electronics magazine May 2022  29 The History of Transistors Part 3: by Ian Batty Left: a Texas Instruments SN7400 quad NAND gate die after its plastic encapsulation was dissolved. Source: https://w.wiki/4mri Below: the 2N2222 50V NPN bipolar junction transistor. Source: https://w. wiki/4pAP Over the last two months, I described the invention of transistor technology and the subsequent innovations and improvements that led to the current transistor technology. In this third and final instalment, we take a more in-depth look at how transistors work, including bipolar junction transistors (BJTs) and both main types of fieldeffect transistors (JFETs and Mosfets). T he previous two articles in this series covered the history of transistor development, from the first-­ generation point-contact transistors to the modern epitaxial planar type. More advanced types exist but are relatively uncommon. Descriptions of devices such as heterojunction and unijunction transistors are available online. Wikipedia is a good starting point; see https://w.wiki/4SJw Those articles described the physical 30 Silicon Chip construction of transistors, their manufacturing processes and the details of how and when they were invented. This one will concentrate on explaining how they behave, starting with some basic semiconductor physics. After that will come information on performance limitations, the origin of the circuit symbol and some typical model numbering schemes. We’ll also cover field-effect transistors (FETs) in some detail, including Australia's electronics magazine junction FETs (JFETs) and metal-oxide semiconductor FETs (Mosfets), used individually and in CMOS (complementary Mosfet) ICs. Let’s start with some fundamental semiconductor theory. Semiconductor physics We’re accustomed to electric current as a flow of electrons. Electrons flow freely in most metals, which is why they are conductive. Fig.43 shows siliconchip.com.au how metal atoms allow electrons from their outer shells to leave the influence of the nucleus and ‘wander about’ in the metal’s crystalline structure. These outer electrons are known as valence electrons. Although electron-deficient atoms become positively-charged ions, the net charge in the metal is zero; the positive and negative charges still balance. The population of free electrons is sometimes known as the ‘electron gas’. Metals have so many free electrons that they are not suitable for the active parts of transistors. We want to influence the conductivity of a transistor’s structure, and metals are already such good conductors that transistor action is impossible only with metals. Fig.43: in conductive metals like copper, the valence electrons are free to roam among the lattice of atoms and hence provide high conductivity. Fig.44: silicon has four valence electrons and forms a very regular crystal with those electrons more-or-less trapped between each pair of adjacent silicon atoms. It therefore has poor natural conductivity, so it is classed as a semiconductor. Semiconductors For simplicity, I’m going to use the atomic model that was standard prior to quantum physics, considering atoms and electrons as distinct objects. Fig.44 shows a crystal of silicon, but the following applies equally well to germanium. With four valence (outer) electrons, pure silicon/germanium crystals form very regular lattices with near-perfect atom-to-atom bonds. These perfect bonds mean that few free electrons can exist. This scarcity of free electrons explains silicon’s poor natural conductivity – it’s a semiconductor. Pure silicon is better known as intrinsic silicon. Its four outermost (valence) electrons class it as a tetravalent element. This tetravalent nature allows silicon atoms to form tight, perfect bonds between each other. Ideally, each set of covalent bonds completely ‘captures’ the electrons in each atom’s outer shell and binds them tightly between their parent atom and its neighbours. The bonding is not totally perfect, however. Some electron motion is possible, which gives silicon a resistance much higher than a true metal such as copper, but less than that of a true insulator such as sulfur. It’s possible to add small amounts of impurity atoms to the crystal to tailor conductivity very exactly. The improved conductivity that comes from this doping by impurities is at the heart of semiconductor technology of all kinds. The effect of doping is to create free charge carriers that are not tightly bound into the silicon-to-­ silicon lattice. siliconchip.com.au Fig.45: when impurities are introduced into the silicon crystal (it’s ‘doped’), in this case, a phosphorus atom, the situation changes. The phosphorus atom has five valence electrons, so one is left free to roam the crystal, giving it a permanent negative charge (making it N-type) and increasing its conductivity. Fig.45 shows the result of heating the silicon to melting point and adding a tiny amount of phosphorus. With five valence electrons, the phosphorous atoms will slot into the crystal structure on solidification, but with only four of each set of five phosphorus electrons taken up into the crystal lattice. Now, each phosphorus atom’s excess electron is free to drift about in the doped silicon crystal. In a true metal, each free electron Australia's electronics magazine leaves behind a positively charged metal ion in the crystal so that the charges balance out over the entire piece. But our doped N-type silicon has a permanent negative charge of electrons. Remember that, although a metal does have free electrons, these are not a permanent surplus. The metal is electrically neutral. Phosphorus, a pentavalent element, is a donor impurity – the “n” in donor reminds us that by phosphorus’ May 2022  31 donation of an electron, the intrinsic semiconductor becomes N-type. Current would flow in this material, pretty much as in a metal. The main difference is that we have exact control over the N-type silicon’s conductivity; heavier phosphorous doping gives more conductivity, light doping gives less conductivity. This helps explain the near-fanatical search for silicon (and germanium) of near-absolute purity. Any ‘foreign’ atoms can have a dramatic and uncontrolled effect on a semiconductor, considering that the doping ratios are so tiny: some as low as one part in 107 (one in 10,000,000). Unwanted contamination must be much less to give reliable doping effects. What if we dope with aluminium, as in Fig.46? It’s a trivalent element, and with only three electrons, there will be a net loss of charge as one silicon atom cannot achieve its preferred ‘take-up’ of four valence electrons. A loss of negative charge must be a supply of positive charge, and this is a positive ‘hole’ – the opposite of an electron. Aluminium, a trivalent element, is an acceptor impurity, with the “p” reminding us that, by aluminium’s acceptance of an electron, the intrinsic semiconductor becomes P-type. If an electron escapes an adjacent atom, it may wander in and fill the hole, but that will leave another hole behind. Thus, the P-type silicon has a permanent net positive charge and is also conductive to an extent determined by the doping concentration. Do holes really exist? Are holes really only a flow of electrons in the opposite direction? This was a critical step in the understanding of semiconductor physics. The way that holes flow is different enough from that of electrons that we are justified in describing hole flow as a distinct kind of current flow. One critical difference is diffusion/flow speed. Holes move more slowly than electrons, and this accounts for NPN transistors having better high-frequency characteristics than PNPs. Electron flow in the N-type emitter and collector of an NPN transistor (the bulk of the entire transistor) is faster than hole flow in the P-type emitter and collector of a PNP transistor. Hole flow actually already exists in some metals, it is just much less common than electron flow. It seems no sooner had we discounted ‘current from positive to negative’ by the discovery of electrons than we needed to call it back from obscurity. Be aware, though, that this is not the conventional current flow model, which – coming so many decades before the identification of hole flow as a real-but-uncommon phenomenon – did not include current carriers. It’s now clear why semiconductor action was initially so hard to describe and understand. Valve theory can be handled pretty well with classical Newtonian physics and the conventional ‘tiny solar system’ model of the atom with electrons orbiting the central nucleus. But semiconductor theory is impossible without delving into the weird world of quantum physics. It’s that complexity which bedevilled Welker, Mataré, Bardeen, Brattain, Shockley and all of the other physicists, chemists and engineers who brought us the transistor. Majority & minority carriers The description so far has shown the intended result of doping: a surplus of electrons in N-type, a surplus of holes in P-type. These are the ‘majority carriers’. In reality, thermal agitation of the crystal lattice (occurring at all temperatures above absolute zero, -273.15°C) will liberate some charges of the opposite polarity to those created by doping; N-type semiconductors will exhibit a small numbers of holes while P-type will exhibit a small numbers of electrons. These are ‘minority carriers’. We might expect minority carriers to be obliterated by the overwhelming number of majority carriers. But in practice, new minority carriers are continually being generated by thermal agitation. Because they are thermally generated, they increase with temperature. Germanium is especially productive in this regard and this is why leakage currents (which are caused by minority carriers) are so troublesome in germanium semiconductors. The combination of high leakage currents and an inability to operate over about 75°C contributed to silicon’s supplanting of germanium in semiconductor devices. This is also the basis of thermal runaway, where leakage at high temperatures causes increased current flow, which causes increased heating and possibly, eventual self-destruction. The semiconductor diode Fig.46: in contrast to phosphorus, aluminium has three valence electrons, so when a silicon crystal is doped with aluminium, it obtains a permanent positive charge (P-type). This results in a ‘hole’ (lack of electron) that can also roam the crystal lattice, albeit with lower mobility than an electron. 32 Silicon Chip The following figures show holes and electrons travelling in straight lines – this simplicity makes the drawings easier to understand. Be aware that, in reality, their paths are random and wandering. Let’s take two pieces of doped semiconductor: N-type and P-type. If we join them, as in Fig.47, we find the junction region ‘populated’ with both holes (P-type) and electrons (N-type). We now have a two-element device – a diode. Holes in the P material and electrons in the N material are mutually attracted and will flow to the junction. On crossing the junction, holes will meet the excess electrons in the N material and will recombine with them. Likewise, electrons crossing the junction will meet excess holes in the P material and recombine with them. Australia's electronics magazine siliconchip.com.au This means that a small region on each side of the junction will contain only the crystal lattice, with the formerly-­ polarised atoms (whether originally P or N) neutralised by the inflow of opposite-polarity charge carriers – see Fig.48. In practice, the ‘rush’ of charge happens progressively in a diffused device, as the top layer diffuses into the bulk of the substrate. The depletion zone will assume a small potential dependent on the type of semiconductor. As this potential prevents charge carriers from crossing it, it appears that any applied voltage must exceed this depletion zone’s effective potential before current can flow. Fig.49 shows that making the P-type more negative and the N-type more positive will cause holes to move to the negative end and electrons to move to the positive end. This is reverse bias for the diode; the depletion zone widens, and no current flows. Minority carriers will cross the depletion zone, and these constitute the diode’s leakage current. As noted above, minority carriers increase with temperature, and occur in much higher numbers in germanium than silicon. If the reverse bias is excessive, minority carriers can reach such high numbers and travel so quickly that they collide with the crystal lattice and ‘knock off’ extra charge carriers. This is the avalanche effect, and it can cause reverse current to skyrocket, destroying the diode through overheating. Alternatively, with a limited current applied as in the case of a zener diode, it is the intended operating mechanism. At least, this is the case for zeners above about 5.1V; they conduct in avalanche mode, whereas below 5.1V, a different conduction mechanism (tunnelling) is used. Fig.50 shows that applying the opposite polarity to the diode (negative to the N-type, positive to the P-type) creates a forward bias. Electrons move away from the negative terminal and towards the depletion zone. Likewise, holes move towards the depletion zone. As the forward bias increases, the depletion zone narrows and is eventually overcome. Current flows through the diode, with a small voltage drop in the depletion zone. Electrons and holes meet and recombine at the junction, and this recombination allows current to flow continuously. Fig.50 appears to show two ‘channels’ in the diode: one for electrons and the other for holes. In reality, it’s a mess. Holes and electrons move like clouds – chaotic when you look closely, but with an overall, predictable direction. For germanium, current flow begins at around 0.1V for junction construction or around 0.4V for alloy-diffused construction. For silicon, it’s around 0.6V for common types. Germanium’s low forward voltage drop was its only real advantage over silicon. Silicon devices such as the schottky diode (using a metal-­semiconductor junction) have lower forward drops of about 0.3-0.4V. This is about half that of a P-N junction diode because the depletion zone is about half as wide; the metal side of the diode has no depletion zone. Schottky diodes withstand lower reverse bias voltages though (for a similar reason) and also have higher leakage currents. The maximum forward current is principally limited by heating in the diode junction due to Ohm’s Law losses. A silicon diode passing a current of 1A will drop as much as one volt, thus converting about 1W of the electrical energy to infrared emissions and heat. The diode must be siliconchip.com.au Fig.47: when N-type and P-type doped silicon crystals meet, the roaming electrons and holes are attracted to each other and ‘cancel out’. Fig.48: the cancellation noted in Fig.47 results in a “depletion zone” forming at the junction of the two zones, where there are neither free-roaming electrons nor holes, thus blocking the flow of current between the zones. Fig.49: by applying a reverse-biased voltage across this PN junction, the depletion zone widens, so current will still not flow. However, that would change if the bias voltage was increased to the point of avalanche breakdown, at which point a high current would suddenly start to flow. Fig.50: on the other hand, if a forward-biased voltage is applied to the PN junction, the depletion zone shrinks, and if the bias voltage is high enough, it is eliminated and the roaming electrons and holes can once again meet. The result is that current will flow, with a slight voltage loss as it crosses the junction (the diode’s forward voltage). Australia's electronics magazine May 2022  33 capable of dissipating this without melting its junction. To handle higher currents, the junction and/or package have to be increased in size, a heatsink needs to be attached or a schottky type (with a lower forward voltage and thus dissipation) used – or a combination of all three. Now for amplification Fig.51: the basic structure of an N-channel JFET. The negatively doped (N-type) channel is connected to the drain and source electrodes on either side via ohmic contacts. The P-type gate(s) form diode junctions with the channel. In operation, a negative voltage is applied to the gates relative to the drain/source, so these junctions are reverse-biased and virtually no current flows. Fig.52: if the negative bias on the JFET gate is high enough, the depletion zone extends all the way through the channel, ‘pinching off’ the current flow between drain and source. Fig.53: with a less negative JFET gate bias, the depletion zone still narrows the conducting channel, decreasing its conductivity, but current can now flow between the source and drain. Fig.54: even with zero gate bias, a depletion zone still exists. This narrows the channel, so a JFET typically does not allow a high current to flow. This property is taken advantage of in ‘current regulator diodes’ (a component you don’t often see these days). 34 Silicon Chip Next, let’s look at the field-effect transistor (FET), the device patented in 1925 by Julius Lilienfeld, and the device that William Shockley and his team tried and ultimately failed to develop. Lilienfeld’s 1925 patent provided a starting point for William Shockley’s efforts at Bell Labs in the 1940s. After much frustration and with only very weak demonstrations of any effect, Shockley’s team (led by Bardeen and Brattain) abandoned the field-effect approach and successfully embarked on point-contact and then junction transistor research. Looking back, it appears that Shockley’s efforts were frustrated by the imperfect nature of his feedstock. Without germanium of near-perfect purity, and without a crystal surface of near-perfect regularity and alignment, his intended electrostatic influence could not penetrate the chaotic and tangled surface of what would be the conducting channel. Ironically, Shockley could well have succeeded had he listened to Gordon Teal’s insistence on using feedstock of the highest possible purity and regularity. Shockley’s field-effect efforts were frustrated by the poorly-understood concept of surface states, the understanding of which eventually led to the successful construction of FETs. Remarkably, this device’s operation is very similar to a triode valve, as had been Shockley’s aim. The FET has a single conducting path between its source (‘cathode’) and its drain (‘anode’), and it presents a very high input impedance at its gate (‘grid’). Two major FET technologies exist. The junction FET (JFET) uses a diode structure for its gate. During regular operation, the diode is reverse-biased, so it allows minuscule current to flow, in the low nanoamps (1/1000 of a microamp) and presents impedances easily exceeding 1000MW. This contrasts with vacuum tubes, where grid currents due to emission and gas effects are commonly in the low microamps range, to give input impedances well under 100MW. JFETs are suitable as low-noise amplifiers, gain control devices and radio-frequency amplifiers into the hundreds of megahertz. Working models were presented in 1953 by George F. Dacey and Ian M. Ross (see http://en.wikipedia. org/wiki/JFET). Actual operation is simplicity itself. Let’s say we use an N-type channel, as in Fig.51. Electrons flow into the channel via the source connection. This is a simple ohmic connection, not a diode junction, so the electron flow continues as electrons; ideally, there are no holes to recombine or carry current in an N-channel FET’s conducting channel. This differs both from the junction transistor and from the vacuum triode. Junction transistors and triodes both create a space charge, either within the base (transistor) or surrounding the hot cathode (vacuum triode). The junction FET needs neither forward bias (transistor action) nor a heated cathode (triode action) to permit conduction. Australia's electronics magazine siliconchip.com.au Fig.55: you can see here how insensitive the JFET’s is to changes in drain-source voltage above a few volts; the channel current remains more-or-less constant, determined mainly by the gate bias. A current-regulator diode is just a JFET with its gate permanently connected to the source, so it always has 0V bias. You can see from this plot how they provide a semi-constant current. Current flows through the channel towards the drain. Again, this is a simple ohmic connection. The device so far appears to be simply a resistor, its initial resistance controlled by the amount of doping in the semiconductor channel. With the N-type channel, a P-type gate is added to the side of the channel. A negative voltage will act as a reverse bias on the P-N diode, so current flow between gate and channel is virtually zero, as shown in Fig.52. The bias penetrates the full depth of the channel and forces current flow to stop. In a valve, we would call it cut-off. In the JFET, this is pinch-off. Fig.53 shows the JFET with a reduced negative bias while Fig.54 shows it with zero bias. There is some depletion zone effect even at zero bias, since the right-hand end of the channel becomes more positive with respect to the zero voltage bias at the gate is closer to the positive drain connection voltage. This makes the gate progressively negative compared to the channel. JFET operation is similar to valve action: with zero bias, about 10mA flows. As the negative bias increases, current falls until the point where the bias voltage causes current flow to cease. If we think of the JFET’s channel as a resistor, it’s having its cross-sectional area reduced. This increases its resistance. For the valve, the effect is like a resistor of constant cross-sectional area but of poorer conductivity (higher ‘natural resistance’) with increasing bias. Remember that the junction transistor has its current carriers diffusing slowly and randomly across the base region. In contrast, the FET’s channel experiences a significant voltage difference (similar to the anode-cathode field in a vacuum tube) that does accelerate current carriers in their path from source to drain. Because the JFET’s gate is not within the channel’s current flow, we don’t get anything similar to the Edison effect we see in valves, where the grid is naturally weakly negative. With the moderate negative bias shown in Fig.54, the depletion zones widen, restricting current flow and the –3V bias reduces the drain current to 2.5mA, ¼ of maximum. siliconchip.com.au So the JFET shows a non-linear transfer characteristic: 50% of cut-off bias allows only 25% of zero-bias current. The curves flatten off to an almost constant current after a few volts are applied across the device, as shown in Fig.55. At lower voltages, the gate voltage to drain current relationship is not linear. The JFET’s curves, in valve terms, are most similar to those of a remote-cutoff pentode. The JFET has no semiconductor junctions in its conduction path, so there is no ‘noisy’ recombination of holes and electrons. Lacking a heated cathode, electron flow does not suffer thermal agitation, so internal noise is low. The JFET is a naturally low-noise device, with noise figures less than 1dB for many types. Unlike valves (but like bipolar transistors), FETs are made in both polarities: a P-channel FET would give exactly the same characteristics as those above, but would be pinched off by a positive gate voltage relative to the source. The JFET’s gate-channel junction overcomes the surface-­ state problem that frustrated Shockley: its reverse-biased diode readily accepts a control voltage and widens its barrier region in response. Mosfets The metal-oxide semiconductor (silicon) FET (Mosfet), also known as the insulated gate FET (IGFET), uses a thin insulating layer between the gate connection and the bulk of the device. Fig.56 shows a simplified version. These FETs offer impedances in the millions of megohms with gate leakage currents below 1nA. As well as high-impedance, radio-frequency and low-noise applications, Mosfet technology is used in high-power switching and linear devices such as for RF and audio power amplifiers, and DC applications such as power controllers in electric cars and switch-mode power supplies. The greatest usage of Mosfets is found in the millions of active sites in microprocessors, where it is known as CMOS (complementary metal-oxide semiconductor) due to the use of both N-channel and P-channel devices. Again, Shockley’s surface-state problems are averted. The semiconductor-insulator interface is a continuation of the highly-regular, highly purified silicon lattice. It’s just that the channel is doped (and is therefore conductive), while the oxide layer is not (and is thus a very good insulator). The bias voltage field is propagated across the oxide layer by the ordinary process of dielectric strain, and is Fig.56: a Mosfet is similar to a JFET, but instead of using a reverse-biased PN junction to isolate the gate from the channel, it uses an extremely thin layer of semiconductor oxide; typically silicon dioxide, SiO2, basically glass – an excellent insulator. The gate’s electric field typically enhances electron/hole flow in the channel when applied; it is pinched off otherwise. These are thus known as ‘enhancement mode’ devices. Australia's electronics magazine May 2022  35 Fig.57: a dual-gate Mosfet is pretty much what you’d expect, like a regular Mosfet but with two separate gate terminals. They are useful as mixers or variable-gain amplifiers. Fig.58: a simplified model of a bipolar junction transistor (BJT) operating as a common-emitter. Note how the emitter current (Ie) is the sum of the collector current (Ic) and the base current (Ib). Here beta or hfe = 50 (50mA ÷ 1mA). Not exactly a tetrode: the dual-gate Mosfet Fig.59: we’ve removed the collector from consideration so we can examine what is happening in the base. Holes from the emitter enter the base region, but the base’s light doping means that few of them recombine with base electrons, leaving a surplus “space charge” of holes in the base. It’s this space charge that will become collector current. 36 Silicon Chip thus able to directly influence charge carriers in the channel; the interfering jumble of irregular surface states that bedevilled Shockley is absent. FETs offer transconductances in the 1000~10,000μS (microsiemens) range, roughly the same as valve tetrodes and pentodes. Despite this, FETs are rarely used in the main parts of audio or RF amplifiers, where bipolar junction transistors (BJTs) are most common. Since BJTs offer transconductances some ten times that of FETs, FETs need very high load resistances to give comparable gains. But you will find FETs of all kinds as low-noise “front ends” and in amplifiers, especially op amps. Various sub-types exist, and it’s possible to build depletion-­mode Mosfets that require bias to reduce current to give operational usefulness (like the vacuum triode), or enhancement-mode types that must have bias applied to conduct at all (just like bipolar transistors!). William Shockley’s foundation patent described the familiar ‘triode’ transistor. But he also described a multilayer device (mentioned in the first article of this series) intended for use as a mixer. So, why not a multi-gate Mosfet? The dual-gate Mosfet looks like a tetrode – one source/drain pair and one channel with two independent gates (see Fig.57). The extra gate, however, does not act as does the screen grid in a valve tetrode. It gives little if any increase in gain, and little if any reduction of output-input feedback capacitance in most circuits. The second gate’s effective transconductance is about that of the first gate. The dual-gate Mosfet can have gain control voltages applied to its second gate, and the device is often used in the famous ‘cascode’ circuit at VHF and in high-voltage wideband video amplifiers. This gives high gain with virtually no troublesome feedback, especially the Miller Effect that limits gain at higher frequencies in conventional single-stage amplifiers. The dual-gate device is also close to being an ideal mixer. The remainder of this article details operation of the ‘transistor’ as we usually think of it – the bipolar junction transistor or BJT. The BJT behaves unlike any thermionic device that came before, and is also completely unlike its later solid-state ‘cousin’, the field-effect transistor already described. The transistor Let’s consider the most common real-world BJT circuit, the common-emitter amplifier. Fig.58 shows a BJT with bias applied. It’s a PNP device (P-type emitter and collector, N-type base) like the BC107 (silicon) or OC71 (germanium). Notice that the emitter current (51mA) is the base current (1mA) plus the collector current (50mA). This gives a base-to-collector current gain of 50mA ÷ 1mA = 50. Considering the OC71, the transistor has a typical input resistance at low frequencies of around 500~5000W. Let’s say it’s 1kW. Its output resistance is much higher, but let’s say 10kW for simplicity, and let’s use quite a small input signal of just 1μA AC. A quick back-of-the envelope calculation shows this: 1μA into 1kW ohms is 1nW (10-9W). This is the signal’s input power to the transistor. Australia's electronics magazine siliconchip.com.au A current gain of 50 means the collector signal current is 1μA × 50 = 50μA. Now, 50μA in the output resistance of 10kW gives us 25mW (2.5 × 10-5W). This is the potential output power delivered to the next amplifying stage. The power gain works out to 2500 times or around +44dB. This is around the theoretical maximum for the venerable OC71, but given that the common BC107 has a current gain around 250 with an output impedance of up to 50kW, you can see that a modern transistor’s maximum power gain is quite impressive. Power gain derives from two main factors: the current gain, and the fact that the transistor’s output resistance is considerably higher than its input resistance. These combine to give high power gains. How is this possible? With sufficient negative bias on the base, electrons are attracted out (down) from the P-type emitter, liberating holes that flow upwards to cross the bulk of the emitter and enter the base-emitter junction. Arriving in the N-type base, the holes meet the resident majority electrons. This sounds like diode action, and it is. But it’s a pretty poor diode, because the base is very lightly doped, and has very few electrons compared to the flood of holes entering. Fig.59 shows the movement of holes in the emitter and their interaction with electrons within the base, but with no collector voltage. Electrons leaving the emitter connection to flow to the battery’s positive pole liberate holes in the emitter region. Electrons enter at the base from the battery’s negative pole to recombine with holes in the base region, thus forming the base current. The few electrons that do meet holes and recombine with them become the base current in the base lead. Since there are many more holes than the base electrons can recombine with, the base electrons form a positive ‘cloud’ similar to the space charge that forms around a thermionic valve’s filament, with the important difference that the valve’s space charge only ever consists of electrons. Notice, though, that the base is at pretty well the same potential throughout; there is no powerful electric field to either attract or repel the cloud of holes in the base. The holes naturally repel each other and diffuse throughout the base. This diffusion is augmented by more and more holes flooding in to the base. Some holes diffuse all the way across to the base-­ collector junction, and more particularly, to the base-­ collector depletion zone, changing the effective base width, as shown in Fig.60. With the base at about 0.3V and the collector at 10V, there is a powerful electric field across the extremely thin depletion zone – it’s probably a micrometre or less in width. As soon as holes diffuse into the depletion zone, they rapidly cross the collector’s P-type material. Reaching the collector connection, they recombine with “incoming” electrons to become collector current. Or, in point form: 1. Holes cross the emitter-base junction and enter the base according to the amount of bias applied. 2. With enough bias, holes enter the base region and combine with the resident electrons to form the base current. Since the base doping is light, there are not many electrons available to do this. siliconchip.com.au Fig.60: this plot illustrates how the effective base width is reduced at higher collector voltages, providing shorter transit times for electrons and holes. 3. Holes in the base overwhelm the few electrons, so a space charge of holes floods the base. 4. The holes, by mutual repulsion, diffuse to fill the base region. 5. Some holes diffuse all the way to the base-collector junction’s depletion zone. 6. Once holes diffuse into the depletion zone, they encounter a powerful electric field and become collector current. 7. Arriving at the collector terminal (connection), holes recombine with entering electrons which form the external collector current. The base current may be one-fiftieth, or as little as one-thousandth, of the emitter current. The collector current is almost the same as emitter current (it’s the emitter current minus the much smaller base current). Therefore, this device has high current gain. Compared to valves, BJTs have very high mutual transconductance (gm). This is the ratio of change in collector (or anode) current to the change in base (or grid) voltage that caused it, and is measured in microsiemens (or micromhos for us “oldies” – mho is ohm backwards, and this is the inverse of resistance). The iconic 6AC7 set a benchmark gm of 9000μS in valve technology (you may know this as 9mA/V). A grid voltage swing of 1V would cause the anode current to change by 9mA. The humble germanium OC70 has a gm of around 30,000μS or 30mS; a base voltage swing of only 100mV gives a collector current swing of 3mA. A silicon BC109 transistor has a gm of about 90mS or 90mA/V. Australia's electronics magazine May 2022  37 Table 1 Common emitter Common base Common collector (emitterfollower) Voltage gain High, 30~1000 High, 30~1000 Low, 0.95~0.999 Current gain High, 30~1000 Low, 0.95~0.999 High, 30~1000 Power gain Up to 1,000,000x Up to 1000x Up to 1000x Input impedance Medium, 500W~5kW Low, 10~50W High, 5kW~1MW Output High, 30kW+ High, 30kW+ impedance Feedback impedance Signal inversion Low Greatest effect Least effect Not usually considered Yes No No Properties of different transistor circuit configurations Fig.61: a bipolar transistor’s collector-emitter current flow mostly depends on the base-emitter current flow and not the collector-emitter voltage. This is a valuable property as it means they provide substantially constant collector current regardless of collector voltage. In this sense, they operate similarly to a pentode valve, not a triode. However, bipolar transistors are not commonly characterised for transconductance (although FETs often are). The most useful single parameter for a BJT is base-to-­collector current gain, written as β (beta), hfe (h parameter, Forward, common Emitter) or h21 (h parameter, output current to input current). Beta values range from around 30 (OC70) to 900 (BC109) in small-­signal transistors, and from about 150 down to only about 12 in power transistors; for example, a 2N3055 has a typical hfe of 120 at 0.3A Ic and 12 at 10A The 2SD2153 high-gain transistor has a specified hfe at 500mA of between 560 and 2700. Plotting collector current against base current (for differing collector voltages) gives the curves in Fig.61. Notice that, like the field-effect transistor, the bipolar transistor has a ‘pentode characteristic’: at any collector voltage above a few volts, collector current is pretty much independent of collector voltage. In other words, the bipolar transistor has a high output resistance. However, unlike the FET’s non-linear voltage-current characteristic, the BJT’s base current to collector current characteristic is quite linear. This means that the base-to-collector current gain (β, hfe) is pretty much the same over a range of collector currents. Outside that range, though, hfe varies considerably. It usually falls off as the collector current approaches the transistor’s maximum, and can sometimes drop off a little at very low currents, although some transistors maintain their mid-current hfe down to basically leakage current levels. Many other transistor performance parameters exist. Some of the most useful are maximum collector-emitter voltage, collector current and power (dissipation), Vce (the collector-emitter saturation voltage), the transition frequency (Ft), input resistance and capacitance, output Fig.62: three different ways to use a PNP transistor as an amplifier. Each has its advantages and disadvantages. Commonbase has the best high-frequency performance but a low input impedance and low current gain. Common-emitter has the highest power gain but suffers from feedback capacitance. Common-collector (emitter-follower) provides a high current gain but low voltage gain. 38 Silicon Chip Australia's electronics magazine siliconchip.com.au resistance and capacitance & feedback resistance and capacitance. Some of these depend on the circuit configuration. Transistor circuit configurations The first circuit generally used was common base, shown in Fig.62(a). The signal is coupled to the emitter, the output comes from the collector and the base is held at a constant bias voltage. This was, and still is, used to give maximum gain at the upper end of a transistor’s frequency capabilities, as with thermionic triodes in grounded grid configuration. Notice that the example circuit uses transformer coupling to match the transistor’s low emitter and collector impedances. Shown in Fig.62(b), common-emitter gives the highest power gain with moderately high input impedance. As with thermionic triodes in common cathode, it’s the most commonly-used configuration. Common collector, Fig.62(c) is like common anode/ cathode follower for thermionic triodes. This gives very high input impedance and very low output impedance, useful for driving low-impedance loads. Table 1 summarises the performance of small-signal transistors in these three configurations. The upside-down world Fig.62 is drawn using PNP transistors. NPN is the structure of preference for very high and ultra-high frequencies, and for high powers; electrons travel more quickly than holes throughout the transistor. The configurations for an NPN transistor would be identical but with the voltages inverted. PNP-NPN combinations (complementary designs) are common in transformerless power output stages. Mosfets and JFETs are also available in complementary designs, and are used similarly to complementary BJTs. Like BJTs, N-channel Mosfets are closer to ideal than P-channel. Using bipolar transistors for gain control Many valve radios used automatic gain control (AGC) circuitry to control RF amplifier/converter/IF amplifier stage gains, allowing full gain when needed to amplify weak signals, but reducing it to prevent overload with strong input signals. This was reverse AGC: a stronger signal would push the valve to a lower anode current, so the gain was reduced. Junction transistors had similar characteristics, as shown in Fig.63, with stage gains dropping to zero at low currents (in the μA range). Thus, designers applied reverse AGC to bipolar transistors as had been done with valves, reducing device current to reduce gain. However, modern planar transistors have much flatter hfe vs Ic curves. For example, the BF115 has an hfe of around 150 at 1mA, dropping to only about 50 at 10μA. That is not enough for any useful gain control, and some newer transistors such as the BC807 have an essentially flat hfe curve from about 20mA down into the microamps range. All transistors show some drop in gain at high collector currents, so it’s possible to reduce stage gain by pushing the collector current above the usual operating point. This is forward gain control, where a stronger signal increases the device current to reduce stage gain. Like the availability of PNP-NPN complements, it’s another fundamental difference between valves and planar transistors. So for planar transistors, gain control is usually implemented using forward gain control. In other words, the DC bias is increased until the hfe drops. Lower-current transistors or specially-designed transistors exaggerate this effect, so are very useful for gain-control applications. For example, the BF167 is specified for forward AGC. It has a transducer gain of some +28dB at low collector currents, dropping to around -32dB at a high collector current. That means that, used in a radio, they can give an AGC control range of 60dB in one stage (see Fig.64). The more traditional (reversed) method struggles to better 30dB gain control per stage. Factors limiting performance With valves, the ‘flight time’ between cathode and anode (transit time) sets an absolute limit to operating frequency. Extremes of triode valve technology, with cathode-anode spacings in the sub-millimetre range, reach their limits at about 5GHz. We would like the transistor to be perfect: a simple input resistance (rb) and an output current generator with Fig.64: planar transistors don’t suffer from such a large hfe drop at low currents as junction transistors (if at all). So forward gain control is used, reducing the stage gain by increasing the collector current. Fig.63: the dB gain of a junction transistor as a function of its DC collector current. Like valves, junction transistors can have their gain reduced by dropping the bias current below the optimum value. siliconchip.com.au Australia's electronics magazine May 2022  39 Transistor Family Tree Metal Semiconductor All-Semiconductor Point Contact Junction Diffused Micro-Alloy Grown Junction Drift-Field Base Micro-Alloy Diffused Alloyed Junction Alloy-Diffused This family tree serves to demystify the history of semiconductors and how they developed as one fabrication method superseded another. a current (β × ib) directly proportional to the input current. The output should appear as a current generator shunted by the output resistance (rc). The output resistance is very high because the transistor draws a nearly constant current regardless of the collector voltage. Similarly, its signal output current is nearly independent of the load resistance. Combining these elements, Fig.65 is pretty much the same as a simplified model of the tetrode/pentode valve. Could transistors, with their micrometre-wide base regions, also suffer from transit time effects? Yes. There are two principal effects even at relatively low frequencies. Firstly, unlike valves, transistors have no powerful accelerating field to sweep charge carriers across the entire device. Once charge carriers enter the base region and form a space charge, they only move by diffusion, a slow process. Very narrow base regions help to reduce diffusion times, yet these remain finite, rather like the transit time in a valve. Secondly, and more frustratingly, reducing diffusion times by using a very thin base gives a fairly high spreading resistance from the contact side across to the other extreme of the base. This comes from two factors: the base is very thin, and it has quite low doping compared to the emitter and collector regions. Any thin conductor will have high resistance, and a poor conductor (the result of low base doping) compounds the problem. This is rbb, the base spreading resistance. This is not simply the base lead resistance, it’s in the base itself, so it’s impossible to eliminate rbb – it can only be minimised. Unlike the valve’s grid, where one can expect any voltage Fig.65: a very straightforward model of the bipolar transistor – this is how we’d like an ideal bipolar transistor to behave, but in reality, they are not this simple. 40 Silicon Chip Multi-Diffusion Mesa Planar Epitaxial Epitaxial Mesa Planar change on the connecting terminal to appear almost instantaneously at every point across the entire grid, there can be a significant time lag across the expanse of a transistor’s base at radio frequencies. Complicating this, the considerable base-emitter capacitance must be charged and discharged by the base voltage. The base spreading resistance limits the maximum charge/ discharge rate of the base as a whole, and thus contributes to limiting high-frequency performance. We can now create a more realistic common-emitter transistor model, shown in Fig.66. The input is partly composed of the internal base-emitter resistance (rb’e), the result of bias voltage and base current. But there is also the base spreading resistance (rbb), and the base-emitter capacitance (ce). This last feature seems odd. The base-emitter is forward-­ biased and should surely appear as a resistance. Why do we appear to have a capacitance? This is due to complex hole (or electron) generation in the base and emitter areas and the hole-electron recombinations. These effects can be described mathematically, and the maths reduces to a non-resistive, reactive component: capacitance. This can be over 400pF, as the data for the OC44 germanium transistor shows. The output circuit is more like our expectations: the current generator (β × ib) is shunted by the transistor’s high output resistance (rc) and its output capacitance (cc). Finally, we must expect some collector-base feedback. This is essentially capacitive, but transit time effects change it according to frequency. For an AF118, the phase Fig.66: a more comprehensive transistor model, including the parasitic resistances and capacitances that limit their performance. Australia's electronics magazine siliconchip.com.au 99mm 193mm Fig.67: ‘pallet’ amplifiers like this are used for high-power RF transmitters. This board uses two Ampleon BLF989 900W RF Mosfets to provide 1000W of peak analog power for digital TV broadcasts at 470-705MHz (the Mosfets are rated to 860MHz). The voltage gain is 19dB and the cost is ~US$1200. Source: https://broadcastconcepts.com/180wuhf-digital-400w-analog-tv-pallet-amplifier.html angle (in common-emitter configuration) ranges from the expected 270° at 455kHz to around 210° at 100MHz. The complex nature is represented by rb’c and cb’c. We might have expected the tiny dimensions of transistor construction to free us from the tyranny of high-­ frequency limits. Alas, not so. Recent developments, however, have yielded transistors with impressively high frequency limits, in the hundreds of gigahertz; frequencies simply impossible with triode valves. High power and frequency? Returning to the field-effect transistor, its conducting channel does provide an accelerating field for charge carriers. This ‘valve-like’ characteristic allows FETs to be the device-of-choice at ultra-high and microwave frequencies. Gallium arsenide (GaAs) FETs can easily give noise figures of 0.2dB at 432MHz, a barely measurable contribution to the theoretical minimum noise figure. Power FETs are used in ‘pallet’ amplifiers of powers up to around one kilowatt (see Fig.67)! Want more power? Just put some in parallel. High-power solid-state transmitters at HF, VHF & UHF do this; a 20kW transmitter might use twenty individual 1kW pallets, paralleled and combined to deliver the final output. Transistor devices have replaced virtually all valve designs. A few niches, such as megawatt, gigahertz radars still use the powerful magnetron. But its microwave fellows, such as low-power klystrons and travelling-wave tubes, are obsolete in new equipment. That circuit symbol The semiconductor diode symbol had been in existence for some time when the transistor was invented, so it made sense to adopt it. Since the emitter admits current to the transistor, it was denoted as an arrow that indicated the direction of current flow. Engineers accepted conventional current (positive to negative) as the direction of current flow, so the emitter arrow obeys this convention. The shape of the circuit symbol represents the physical construction of a point-contact transistor – see Fig.68(a). Point-contact devices had become obsolete by the 1960s, so attempts were made to refashion the symbol to more siliconchip.com.au Fig.68: the standard PNP and NPN transistor symbols, shown at the top, are based on the physical configuration of point-contact transistors. The symbols at the bottom, designed to look more like a junction transistor, never really caught on even though they would probably make circuit drawings neater. closely represent the junction transistor, as shown in Fig.68(b). Wireless World and our own Radio, TV and Hobbies carried the charge, but the rest of the publishing world did not adopt their more rational and descriptive form. Interestingly, current mesa and planar transistor technologies have reverted to a physical structure more similar to point-contact technology. Type numbering As with valves, US manufacturers took a haphazard approach to numbering. The Joint Electron Devices Engineering Council (JEDEC) simply numbered junctions: 1N for diodes, 2N for triode transistors, 3N for the now obsolete junction tetrodes and current dual-gate Mosfets, and 4N for optocouplers. JEDEC’s 2N series were issued in order of application, with no indication of function. The 2N1066 is a germanium PNP RF type rated at 240mW, 80V and 120MHz in a four-wire TO-33 case. The 2N1067 is an NPN silicon power transistor rated at 5W, 60V and 1.5MHz in a threelead TO-8 package. Like JEDEC, the Japanese Industrial Standards Committee’s JIS numbers were simply allocated in order of registration with no indication as to application or voltage/power rating. Frequency ratings and polarity can be deduced to some extent by the prefix (see Table 2). For example, the 2SA120 is a high-frequency PNP, akin to a higher-power OC170, while the 2SD43 is a low-power NPN audio type. Australian transistors, either licence-manufactured or local types, took a bit from everywhere. We have a mess. The saying goes, “the great thing about standards is that there are so many to choose from”. Table 2 – JIS transistor code categories 2SA high-frequency PNP BJTs 2SB audio-frequency PNP BJTs 2SC high-frequency NPN BJTs 2SD audio-frequency NPN BJTs 2SJ P-channel FETs (both JFETs and Mosfets) 2SK N-channel FETs (both JFETs and Mosfets) Australia's electronics magazine May 2022  41 • AWA’s licensing from RCA produced many 2N types, plus their own AS series. • Ducon licensed from Compagnie Générale de Télégraphie Sans Fil (CSF), producing SFD diodes and SFT transistors. • Electronic Industries Ltd (EIL) owned Radio Corporation Pty Ltd, makers of Astor brand radios and TVs, and Eclipse Radio Pty Ltd, makers of Peter Pan and Monarch radios. They made semiconductors under their Anodeon brand: 2N series and their own AT and AX series. • Devices from, or licensed from, General Electric in the UK use the GET prefix. • Fairchild Australia produced 2N series devices and their own, unique, SE, AX and AY series. • Early Philips/Mullard devices followed their European parents, adopting O (for ‘no heated cathode’), using OA for diodes and OC for transistors. Like the JEDEC series, device numbers were allocated on demand, running to at least OC977 and with very little indication of device type. The OC45 is a low-performing version of the OC44 PNP germanium converter, but the OC16 is a 10W germanium power transistor. Between the OC44/45 and OC70/71 junction transistors we find the (then) obsolete OC50/51 point-contact types. The OC206 is PNP silicon with a cutoff frequency of 850kHz. • Standard Telephones and Cables released their own TS series. • As with valves, the European Electronic Component Manufacturers Association (EECA) Pro Electron system took an organised approach and provided semiconductor type and intended application via the type number. Notable Australian adopters, Philips and Mullard, deserve praise for adopting Pro Electron which aids in decoding those metal and plastic devices that populate transistor radios. The first letter shows the type of semiconductor: A for germanium, B for silicon, C for gallium arsenide (GaAs). The second letter shows device type (see Table 3), followed either by a three-digit code (such as AF118, BC107 etc), or a third letter (X, Y or Z) and a two-digit code for professional devices, such as AFY40, BUX84 and BCZ10. Pro Electron also includes diodes, with the second letter: A = signal diode, B = varicap diode, X = varactor/ step recovery diode, Y = power diode and Z = zener/ reference diode. Table 3 – Pro Electron transistor prefixes AC Germanium small-signal AF transistor AD Germanium AF power transistor AF Germanium small-signal RF transistor AL Germanium RF power transistor AS Germanium switching transistor AU Germanium power switching transistor BC Silicon small-signal transistor (‘general purpose’) BD Silicon power transistor BF Silicon RF (high-frequency) BJT or FET BS Silicon switching transistor (BJT or Mosfet) BL Silicon high-frequency, high-power (for transmitters) BU Silicon high-voltage (eg, for CRT horizontal deflection circuits) CF GaAs small-signal microwave transistor (MESFET) CL GaAs microwave power transistor (FET) This series is extracted from Chapters 1 to 4 of How Your Transistor Radio Works by Ian Batty. The remaining nine chapters cover transistor receivers – from biasing and power supplies, through converters, RF/IF amplifiers and demodulation, audio amplifiers, to detailed analysis of actual circuits, including AM/FM radios. How Your Transistor Radio Works contains 102 pages of valuable information in the one volume – you won’t find a better combination of basic theory and practical circuit description anywhere. It’s available through the HRSA’s Valve Bank at the very reasonable price of $20.00 (plus postage). Visit https://hrsa.org.au/training-manuals/ to order this and other fine HRSA books. Joining the HRSA gives you access to our Valve Bank, and you’ll get our quarterly magazine, Radio Waves with 60 pages packed full with everything from Marconi radios and restorations of Australian classics to helpful contacts around Australia. And while you’re there, consider Ian’s previous How Your Radio Works, which covers similar topics in the Valve Universe. At only $12.00 (plus postage), it’s a must have for any restorer of valve radios from TRF sets to modern SC superhets. Raspberry Pi Pico BackPack With the Raspberry Pi Pico at its core, and fitted with a 3.5inch touchscreen. It's easy-to-build and can be programmed in BASIC, C or MicroPython. There's also room to fit a real-time clock IC, making it a good general-purpose computer. This kit comes with everything needed to build a Pico BackPack module, including components for the optional microSD card, IR receiver and stereo audio output. $80 + Postage ∎ Complete Kit (SC6075) siliconchip.com.au/Shop/20/6075 The circuit and assembly instructions were published in the March 2022 issue: siliconchip.au/Article/15236 Australia's electronics magazine siliconchip.com.au By Charles Kosina ∎ Output Frequency: 100kHz to 75MHz in 1Hz steps ∎ Frequency Accuracy: ±0.1Hz immediately after calibration against a precise standard ∎ Output Level: 0dBm +0,-0.5dB 100kHz to 55MHz; +0,-3dB 55-75MHz ∎ Modulation: none, AM or FM ∎ AM: 50Hz-10kHz, 50% modulation ∎ FM: 50Hz-1kHz; 2.5kHz, 5kHz or 10kHz deviation ∎ 5V, 140mA power supply ∎ Digital frequency readout ∎ low RF leakage Precision AM-FM DDS Signal Generator This signal generator aims to provide very high calibrated accuracy with an error of just ten parts in a billion (108), which translates to 0.1Hz at 10MHz. It also has plenty of features, including amplitude and frequency modulation. N umerous cheap signal generators are available online but their accuracy leaves a lot to be desired. So I decided that if I wanted to have a maximum error of 0.1Hz at 10MHz, which would be ideal, I would have to design one. The first decision I had to make was what I wanted it to look like. This would determine the type of enclosure needed, the display and the controls. With the current worldwide shortage of many components, choosing these parts can be difficult. There is no escaping the fact that most advanced components are only available in surface-­ mount packages, some with very small lead pitch. Good shielding is essential for a signal generator. You want the signal to be via the output connector and not radiated from the device itself. For this reason, I chose a diecast aluminium box with a minimum number of apertures that need to be cut. The largest of these is for the display, and by using a small OLED module, RF leakage is cut down substantially. Next, I had to decide whether to use siliconchip.com.au ready-made modules or individual parts. Let’s take the frequency generating chip, the Analog Devices AD9851. This is available on a prebuilt module with its own clock generator and output filtering. Those have several problems, starting with the crystal oscillator module, which is just a standard cheap 30MHz unit. The accuracy and temperature stability is dubious and does not fit my design criteria. Yes, you can remove it and add a wire link to an accurate temperature-­ compensated crystal oscillator (TCXO) on the main board. Applying amplitude modulation requires access to the RSET pin on the AD9851 chip, meaning another wire link to the main board. The type of output I want to use requires a wideband transformer from two pins on the DDS chip. This is now getting into the too hard category and is the final reason for rejecting the prebuilt module. The cheapest Arduino modules mostly use an ATMega328 chip running at 16MHz. All the I/O pins are Australia's electronics magazine brought out, so there are no changes needed. But with my design, the number of pins available from the ATmega328 are inadequate, so a fancy pin-sharing arrangement would be necessary. Also, much processing is needed to apply frequency modulation, and the 16MHz clock speed is marginal for this. So instead, I am using a 44-pin ATmega644. This gives me more than enough I/O pins and I can arrange for it to run at 20MHz for a 25% boost in processing power. The display needs to convey lots of information, but a large screen is ruled out by the need for a small cutout to give low RF leakage. That’s why I chose a 0.96in (24mm) diagonal OLED. It does have rather small characters, but conveys all the needed information. By eliminating ready-made modules, the final PCB size (and thus enclosure required) is much smaller. Diecast boxes are expensive, so using the smaller one makes it considerably cheaper. The final major component needed is another DDS chip, the AD9833. This May 2022  43 Fig.1: the signal generator circuit is based on three main chips: IC1, the AD9833 DDS that’s used for the AM signal; IC2, the ATmega644 microcontroller; and IC3, the AD9851 DDS that produces the output signal. IC3 is clocked by the high-precision 30MHz TCXO, while IC1 & IC2 are both clocked by the same 20MHz crystal (X1) driven by IC2’s internal amplifier. Microcontroller IC2 also monitors user controls EN1, VR1 & VR2. comes only in a tiny 10-pin MSOP package but it is available on a small, ready-made module. I was tempted to use such a module in my design, and could have fitted it in, but I did not want yet another oscillator running in the unit (the module has an onboard 25MHz oscillator). 44 Silicon Chip So I am just using the bare chip. It gets its 20MHz clock source from the clock output pin on the ATmega644 processor. Component Selection Given the present severe shortage of electronic components, I paid Australia's electronics magazine particular attention to being able to source parts from several suppliers. The AD9851 DDS chip is available from several suppliers on AliExpress for about US$14 (around $20) delivered. The AD9833 DDS chip is also available for about US$3.50 ($5) from numerous AliExpress sellers. siliconchip.com.au If you want to stick to a more reputable supplier, Digi-Key has the AD9851 for $56.76 and the AD9833 for $14.95. The ATmega644 chip is another matter. I could only find one supplier on AliExpress who charged US$2.05 each plus US$5.26 shipping, for a total of around $11. Similarly, I could only find one supplier on eBay with a ridiculously high price. But Silicon Chip will have these chips available pre-programmed. Wherever you get it, make sure it’s the 20MHz, 44-pin TQFP variant. The 30MHz TCXO is best obtained from AliExpress, and the delivered price is about $15. I have found none suitable at Mouser, Digi-Key or element14. The OLED is a 0.96in, 128 x 64 pixel type with the SSD1306 controller. There are multiple suppliers for this, and it comes in different colours. The one I have has the top quarter yellow and the rest blue, and this highlights the set frequency, but you can choose whatever colour combination pleases you. Likewise, the potentiometers and the encoder are standard items. Make sure that they are the same size. The distance from the PCB to the end of the shaft should be about 25mm. That leaves the magnetic components. The output transformer is made by Coilcraft, with the PWB-16-BL giving the best result. siliconchip.com.au M3216/1206-size chip inductors are suitable for the remaining inductors. These have pretty close tolerances, far better than trying to wind your own. At 85MHz, the low-pass filter (LPF) for the RF output needs three 120nH coils. These are readily available at element14, although they can also be sourced from AliExpress. I paid $2.80 for 100, with free postage, and by some miracle, they arrived from China in two weeks. The rest of the components are standard resistors and capacitors, almost all in the standard M2012/0805 SMD size. The toggle switches can be bought from Jaycar and Altronics, as can the diecast box. The full parts list will come later in this article. Circuit details The complete circuit is shown in Fig.1. The microcontroller IC1 drives the two Analog Devices direct digital synthesis (DDS) chips. The AD9851 (IC3) generates frequencies from 100kHz to 75MHz, while the second DDS chip (IC1, AD9833) provides the amplitude modulation (AM) from 50Hz to 10kHz. The SSD1306 OLED screen (OLED1) shows the current status. The reference clock for the AD9851 is a 30MHz TCXO which is multiplied by the AD9851 to 180MHz. The output frequency is adjusted by an incremental shaft encoder (EN1) in steps set by its integral pushbutton Australia's electronics magazine switch. Pressing it cycles through step sizes from 1Hz to 1MHz. Potentiometers VR1 and VR2 are connected to two of IC2’s analog inputs. One sets the modulating frequency for both AM and FM. Rather than have a continuous range of frequencies, I instead opted for 11 separate frequencies. The other adjusts the FM deviation and also for calibration. Three-position toggle switch S2 selects between AM, CW and FM. Almost everything that I design includes a simplified RS232 serial port using transistors Q2 and Q3. I find this an invaluable tool for debugging while developing the code. It could also be used for controlling the unit from a PC as part of a future upgrade. The two DAC outputs from the AD9851 are connected to centre-­ tapped RF transformer T1, which has a 7th-order Chebyshev low-pass filter connected to its secondary to reduce harmonics and spurs. With a clock frequency of 180MHz, it is possible to generate frequencies up to the Nyquist limit of 90MHz, but the waveform is extremely distorted by then. I set the limit at 75MHz and, with the output filter, it does not contain too many spurs even at that frequency. The unit draws 140mA from a 5V DC supply. I find that a mobile phone charger is ideal for powering it. I must have at least ten of these; I am sure most people have lots of spares. As mentioned earlier, the whole May 2022  45 thing fits in a standard diecast box, making it quite robust and providing good shielding. Tuning The shaft encoder used to adjust the output frequency is available from numerous suppliers on eBay and AliExpress as well as Digi-Key, Mouser, element14 and others. They come in different shaft lengths and prices; choose one with a 20mm shaft length. I have added pull-up resistors on all the pins. There are weak internal pullups in IC2, but I have found the lower value external resistors plus capacitors to ground (for contact bounce filtering) give far more reliable operation. You want the frequency to increase when you wind the knob clockwise but depending on the shaft encoder, it can operate either way. To solve this, a jumper placed between pins 4 & 6 of the programming header will reverse the encoder direction. The firmware detects this by enabling a pull-up and checking the level on the MOSI SPI programming pin (PB5, pin 1 of IC2). With the jumper on, this pin is low; otherwise, it is high. The interrupt handler tests the state of the PB5 and selects the rotation direction based on this. With a range of 100kHz to 75MHz, you don’t want to turn the knob millions of times to set the frequency. This is where its integral pushbutton switch comes into use. Pressing it cycles through step sizes of 1Hz, 100Hz, 1kHz, 10kHz, 100kHz and 1MHz. 0.1Hz at 10MHz. More on this later. The FTW can be loaded into the AD9851 using serial or parallel methods. Serial loading takes far too much time and would make FM virtually impossible. Hence, I’m using parallel loading with five bytes transferred: one control byte plus four for the FTW (4 × 8 = 32 bits). You can see in the circuit diagram that I have split this up into four bits from two separate ports on microcontroller IC2. I did this because I can’t use all of Port A as I need two analog inputs, and the only available analog inputs are on Port A. Port B has the 20MHz clock output required by the AD9833 (PB1), so that’s ruled out. Port C has dedicated SDA and SCL pins for the I2C interface to the OLED, and I want to use INT0 and INT1 on port D for the shaft encoder. Therefore, I couldn’t dedicate all eight lines of one port for loading the FTW. So I split up the parallel interface into four bits from Ports C and D. The extra few lines of code required to do this don’t slow things down very much. Once the byte is set up, it is clocked in by the WCLK pin, and after all five bytes have been sent, the FQUD pin is pulsed to update the AD9851’s internal latch. RF output There are two outputs from the DAC (digital-to-analog converter) on the AD9851. Application note AN-423 from Analog Devices suggests using a wideband transformer to couple these two outputs to the external load. This makes for clean amplitude modulation (AM), also described in the note. The transformer in their example is 1:1 centre tapped, which for a 50W load, reflects 25W to the DAC outputs. I used a Coilcraft transformer with this ratio and found it to be most unsatisfactory. The 25W load on the DAC outputs is far too low in impedance; it reduced the output levels, and the waveform became very noisy. I feel that specifying such a transformer is an error. Experimenting with other Coilcraft transformers, I found the best results were with the PWB-16-BL with a 16:1 impedance ratio that reflects 400W to each DAC output; a far more satisfactory value. The transformer -3dB bandwidth is 75kHz to 90MHz, so there is a slight drop in level at 100kHz and 75MHz. This gave me an output close to 0dBm over much of the range (Fig.2). Output Filter Without a low-pass filter on the output, there will be many undesirable harmonics and spurs. While it is feasible to use some of these spurs for frequencies well above the Nyquist limit, for simplicity, I decided not to use this approach. Filter design is so easy these days. Rather than ploughing through some complex s-parameter mathematics, there are online calculators. The one I used to work out the C and L values for a 7th-order Chebyshev low-pass AD9851 interface The AD9851 has a 32-bit Frequency Tuning Word (FTW) that controls the output frequency. There is a handy online tool for calculating the required value at siliconchip.com.au/link/abc8 For a 1MHz output, FTW = 23860929, which is 16C16C1 in hexadecimal. The actual frequency with this FTW is 999.999982305kHz, an error of about 0.02Hz. But this assumes that the TCXO is exactly 30.000000MHz. The ones that I have bought from AliExpress have been within about 10Hz. Is that good enough? It depends on your application, but with some of the digital communication techniques used, an error of just a few hertz can make message decoding impossible. So I developed a calibration technique that reduces this error to less than 46 Silicon Chip Fig.2: the Signal Generator’s output level varies by about 1/4dB between 100kHz and 55MHz, except for a dip at -1/2dB between about 10MHz and 22MHz. It’s usable up to 75MHz, although the level drops considerably above 55MHz, reaching nearly -3dB at 70MHz. Australia's electronics magazine siliconchip.com.au Fig.3: here’s what the 100kHz output signal looks like with 5kHz AM (yellow). The AM signal output from the AD9833 is shown below (cyan). filter with 85MHz cutoff and 0.5dB passband ripple is at https://rf-tools. com/lc-filter/ The output of this calculator can be exact or standard values; the difference in performance between the two is minimal. The choice of inductors was discussed above in the component selection section. Amplitude modulation The ATmega644 processor (IC2) could generate amplitude modulation, but why bother with the complicated coding involved when we can use a second low-cost DDS chip instead? The AD9833 (IC1) can run at clock speeds of up to 25MHz. It is a tiny 10-pin chip with a three-wire serial control interface. Rather than having a separate clock generator, I use the 20MHz clock out pin on PB1 (pin 41) of IC1. The output of the AD9833 is applied to the gate of Mosfet Q1 via a 10kW trimpot, and this controls the RSET pin on the AD9851 as per the aforementioned application note AN-423. Rather than having a separate knob on the front panel, I preset the modulation level to about 50%. Potentiometer VR1 sets the modulation frequency. The voltage read using the 10-bit analog-to-digital converter (ADC) in IC2 is converted by software into the tuning word required by the AD9833. I could have had a continuous range but found that setting the frequencies was very fiddly. I decided instead on dividing the ADC reading into 11 distinct values: 50Hz, 100Hz, 200Hz, 400Hz, 1kHz, 2kHz, 3kHz, 5kHz, 6kHz, 8kHz and 10kHz. Fig.3 shows a 100kHz generated signal with 50%, 5kHz amplitude siliconchip.com.au Fig.4: as expected, the spectrum of the signal from Fig.3 has a single prominent peak at 100kHz with two smaller peaks, 5kHz on either side (ie, at 95kHz and 105kHz). modulation on channel 1, with the sinewave modulation signal on channel 2. The spectrum of this signal is shown in Fig.4. Frequency modulation Applying FM proved to be the trickiest part of the design. To approximate a sinewave, we have to change the AD9851 output frequency continuously. This sinewave is divided into 24 samples, each 15° apart. Taking the sine of that angle and multiplying it by the maximum deviation gives the instantaneous deviation for that sample. For example, if the maximum deviation is 3kHz, sin(30°) = 0.5, so we add a value to the FTW equivalent to 1.5kHz (3kHz x 0.5). The numbers become negative past 180° and subtract from the frequency. This takes quite a bit of processor time; so much that the maximum modulation frequency possible is 1000Hz. At this frequency, the micro’s timer generates 24,000 interrupts per second, and each triggers a new FTW value to be calculated and sent. For other modulation frequencies, the timer interrupt is 24 times the modulation frequency. See Table 1 for the values that are added and subtracted to the FTW to give ±2.5kHz deviation. The available modulation frequencies are 50Hz, 100Hz, 200Hz, 400Hz, 500Hz, 600Hz, 700Hz, 800Hz, 900Hz and 1kHz. There are ways of getting a higher modulation frequency. If we can stand having a rougher sinewave, we could have samples 30° apart, which would allow a maximum frequency of 2kHz. The spectrum of an FM signal is far more complex; advanced mathematics is needed to derive it. It has sidebands that go on forever, but their amplitude decreases rapidly so that only the first few are important. For more details visit: https://w.wiki/4eC$ Table 1 – frequency modulation FTW offsets for ±2.5kHz deviation angle θ sin(θ) Δf (Hz) ΔFTW angle θ sin(θ) Δf (Hz) ΔFTW 0° 0 0 0 180° 0 0 0 15° 0.259 647 15,437 195° -0.259 -647 -15,437 30° 0.500 1250 29,825 210° -0.500 -1250 -29,825 45° 0.707 1767 42,160 225° -0.707 -1767 -42,160 60° 0.877 2192 52,301 240° -0.877 -2192 -52,301 75° 0.966 2415 57,622 255° -0.966 -2415 -57,622 90° 1.000 2500 59,650 270° -1.000 -2500 -59,650 105° 0.966 2415 57,622 285° -0.966 -2415 -57,622 120° 0.877 2192 52,301 300° -0.877 -2192 -52,301 135° 0.707 1767 42,160 315° -0.707 -1767 -42,160 150° 0.500 1250 29,825 330° -0.500 -1250 -29,825 165° 0.259 647 15,437 345° -0.259 -647 -15,437 Australia's electronics magazine May 2022  47 Display Screen 1: this shows the screen layout during normal operation. The output frequency (in Hz) is at the top, the step size and FM deviation on the second line and the amplitude and frequency modulation signal frequencies on the last two lines. Screen 2: calibration mode is entered by rotating the Function knob fully clockwise; the bottom two lines of the display change, with the last line showing the FTW. If you have the right gear, you can get the output frequency within 0.1Hz. The OLED module has an SSD1306 controller and a resolution of 128 x 64 pixels. My original design used an 8 x 8 font which gave eight lines each of 16 characters. This allowed for a fair bit of information to be displayed but with rather tiny characters. I changed it to a 16 x 16 font, which is much easier to read, but this gives only four lines of eight characters. So I had to considerably simplify what is displayed. Screen 1 shows the unit’s normal display. The top line readout is the frequency in Hz, while the second has the frequency adjustment step size. Line 3 shows the AM frequency, one of 11 fixed frequencies from 50Hz to 10kHz. Line 4 shows the FM frequency, which steps through 11 fixed settings from 50Hz to 1kHz. With the Function knob fully clockwise, the unit enters calibration mode, shown in Screen 2. The modulation frequencies are replaced with line 3 showing “Calib” and line 4 showing the Frequency Tuning Word (FTW). The calibration procedure is explained later in the article. Power supply Fig.5: use this PCB overlay diagram to help with board assembly. Remember to link out REG1 and note that Q2, Q3, and associated 15kW & 1kW resistors are only needed if you will use the serial debugging interface. Make sure that the three ICs, D1, REG2, T1, TCXO1 and VR1 are orientated as shown. Note that the orientation of REG2 is swapped in the prototype, this is because regulator that was used has a different pinout than the one specified in the parts list. 48 Silicon Chip Australia's electronics magazine Many readers would have numerous mobile phone chargers lying around, left over from generations of phones. Most of them deliver a nominal 5V at up to 2A. The maximum current drawn by the Generator is about 140mA, well within the capability of all chargers. I included a schottky diode in the design as reverse polarity protection. This drops the supply voltage by about 0.37V. The charger that I used had an output of 5.2V, dropping to 4.85V through the diode. It’s a simple matter of cutting off the connector on the cable and replacing it with a DC barrel plug to suit your DC socket (either 2.1mm or 2.5mm inner pin diameter). The PCB design includes another regulator, REG1, so that a higher supply voltage could be used. However, this is probably not necessary, so it’s just linked out in the final design. I have connected another DC socket, CON6, in parallel with CON5. This is for powering the companion Attenuator, to be described in a future article. The OLED requires 3.3V, and this is supplied by a TO-92 low-dropout linear regulator, which draws from the 5V supply. The open-drain SDA and SCL pins for driving the OLED are pulled siliconchip.com.au up to 3.3V by a pair of 4.7kW resistors. Construction The Signal Generator is built on a double-sided PCB coded CSE211002 that measures 100 x 78.5mm. Refer to the PCB overlay diagram, Fig.5, as a guide during construction. It shows which components go where. Most of the parts on the PCB are surface-­mounting types, and two of them are very fine-pitch ICs. These are the two DDS chips, and you should start with these. Soldering them accurately and without short circuits between the pins takes some skill. It helps to spread a little flux paste on the pads before placing the ICs and ensure they are aligned with their pads on both sides after tacking the first pin and before soldering any others. Also, be careful to check that their pin 1s are located correctly before soldering more than one pin! Rather than trying to solder the pins without bridges, concentrate on making sure that each pin gets enough solder and that it flows down onto the corresponding PCB pad. Try to avoid getting any solder high up on the pins, where it is harder to fix bridges. After soldering all the pins, it’s then just a matter of spreading some more flux paste over them and carefully using a length of solder wick to remove any excess solder, including that which might be bridging adjacent pins. Clean off the flux residue with some flux cleaner or alcohol, then inspect the IC leads to make sure all the solder joints look good and there are no remaining bridges. If you find anything that looks suspect, add a dab of flux paste, heat the offending pin(s) and use solder wick if necessary. Repeat this process as many times as needed until you have nicely soldered ICs. Following these, mount the ATmega644 chip (with wider pin spacings than the first two, but pins on four sides), again being careful with its pin 1 orientation, followed by all the other SMD components. The orientation of SMD transformer T1 also matters. Then give the board a good clean to remove flux residue. Now fit the through-hole parts from lowest profile to tallest. Be careful to orientate diode D1, the TCXO, VR3, and REG2 as shown. Don't forget the wire link across REG1, which can be made from a component lead off-cut. siliconchip.com.au Parts List – AM-FM DDS Signal Generator 1 double-sided plated-through PCB coded CSE211002, 100 x 78.5mm 1 diecast aluminium enclosure, 119 x 93.5 x 34mm [Jaycar HB5067 or Altronics H0454] 1 0.96in OLED display module with I2C interface and SSD1306 controller (OLED1) 1 mechanical rotary encoder with integrated pushbutton switch and 20mm total height (RE1) [Bourns PEC11R-4215F-S0024] 2 10kW PCB-mount vertical 10mm 20mm-tall linear potentiometers (VR1, VR2) [Alpine RK09K1130AH1] 1 10kW side-adjust multi-turn trimpot (VR3) [Altronics R2361] 1 large knob to suit RE1 2 medium knobs to suit VR1 & VR2 1 20MHz 18pF 30ppm crystal resonator, HC-49 (X1) 1 30MHz 20 x 12mm TCXO module (TCXO1) [aliexpress.com/item/32719087266.html] 1 Coilcraft PWB-16-BL SMD wideband transformer (T1) 3 Coilcraft 1206CS-121XJEC 120nH chip inductors or equivalent, M3216/1206 size (L1-L3) 1 3x2 pin header, 2.54mm pitch (ICSP) (optional; for programming IC1) 1 2-pin polarised locking header with matching plug, 2.54mm pitch (CON1) 1 3-pin polarised header with matching plug, 2.54mm pitch (optional; CON3) 1 panel-mount BNC socket (CON4) 2 panel-mount DC barrel sockets (CON5, CON6) 1 4-way female header socket (for OLED1) 1 SPDT panel-mount switch (S1) [Altronics S1310] 1 SPDT panel-mount centre-off switch (S2) [Altronics S1330] 1 tactile pushbutton switch (S3) 4 12mm-long M3 tapped metal spacers 2 10mm untapped spacers 4 M3 x 6mm panhead machine screws 4 M3 x 8mm countersunk head machine screws 2 M2 x 12mm panhead machine screws and nuts 4 M3 flat washers Semiconductors 1 AD9833 12.5MHz DDS generator, MSOP-10 (IC1) 1 20MHz ATmega644 microcontroller in TQFP-44 (eg, ATMEGA644PA-AN or ATMEGA644PA-AU) programmed with CSE21100A.hex (IC2) 1 AD9851BRS 180MHz DDS generator, SSOP-28 (IC3) 1 LP2950CZ-3.3 3.3V low-dropout linear voltage regulator, TO-92 (REG2) 3 2N7002 60V 2A N-channel 3.3V drive Mosfets, SOT-23 (Q1-Q3) 1 1N5819 40V 1A schottky diode (D1) Capacitors (all SMD M2012/0805 size unless otherwise stated) 1 100μF 6.3V X5R ceramic, M3216/1206 size 3 10μF 6.3V X5R ceramic 1 220nF 50V X7R ceramic 10 100nF 50V X7R ceramic 2 10nF 50V X7R ceramic 2 100pF 50V NP0/C0G ceramic 2 68pF 50V NP0/C0G ceramic 2 22pF 50V NP0/C0G ceramic Resistors (all SMD M2012/0805 size 1% thick film unless otherwise stated) 6 27kW 2 15kW ERRATA: the gate bias for Mosfet Q1 is fixed at 1.5V, which might not suit all 2N7002 devices. If there is no output from 2 4.7kW IC3, the bias might be too low, in which case the 3.3kW 1 3.9kW resistor can be changed to 4.7kW (1.8V) or 6.2kW (2.0V). If 1 3.3kW there is output from IC3, but the modulation is weak, the bias 1 1.5kW might be too high, in which case the 3.3kW resistor can be 1 1kW changed to 1.8kW (1.05V). 1 51W Australia's electronics magazine May 2022  49 You can safely omit Q2, Q3, the two adjacent resistors and CON3. These are the simplified RS232 interface and are used as a debugging aid. The OLED screen plugs into a fourpin socket strip and is held in place by two screws and standoffs. Rather than cutting down an 8-pin strip that I already had, I just removed four pins. Depending on the OLED, the mounting holes may be either 2mm or 2.5mm in diameter. While M2 screws are not as easy to find as M3, I bought some from eBay. Some larger online electronics retailers also stock M2 screws and nuts. Don’t try to drill the holes out on the OLED to bigger screw sizes! There are four screw holes provided but two are adequate. The potentiometers and encoder should be installed last, after cleaning off any flux residue on the board. Preparing the case The adjacent photo shows the diecast box with the board already mounted in the base. The positions of the required holes are shown in the drilling and cutting template/ guide, Fig.6. The raw aluminium is not very attractive, so I sprayed it with three coats of matte black paint. I used the blank circuit board as a template to accurately drill the mounting holes and the holes for the control shafts. There are small holes on the PCB in the centre of the controls for this purpose. Once the PCB has been mounted in the case and the wire to the BNC socket soldered, all you need to do is wire up and plug in the DC socket. You only need one, as shown here, but if you’re thinking of building the upcoming matching attenuator, add a second socket in parallel so you can daisy-chain the power. It takes a bit of care to make the rectangular cutout. There are various ways of doing it. If you have a milling machine, that’s great, but very few readers would possess one. I started by drilling a circular hole of 25mm diameter centred on the rectangle with a step drill. Then I filed it out into the required 26 x 28mm rectangle. It takes a bit of time but results in a neat finish. You will also need to drill two holes in the side of the base, near the lid, to accept the barrel sockets. Make sure they are placed so that they will not foul the PCB assembly once it’s dropped in. You might also want to drill a hole in the side so that you can access VR3 (the AM depth adjustment trimpot) once the board has been mounted in the case. Fig.6: this template shows the cutouts on the diecast box. This template can be downloaded from the Silicon Chip website and then printed at actual size. You can also use the blank PCB to mark the hole positions. Fig.7: the front panel label for the ► Precision DDS Signal Generator. 50 Silicon Chip Australia's electronics magazine siliconchip.com.au A ‘sneak peak’ at the companion attenuator PCB that we will describe in an upcoming issue. The panel label shown in Fig.7 can be downloaded from the Silicon Chip website and printed onto photographic paper. Make the OLED and shaft cutouts with a sharp scalpel or hobby knife. I cut a piece of 1mm-thick clear acrylic to 112 x 86 mm to protect the label, again using the blank PCB as a template to drill the holes. Attach the PCB to the front panel siliconchip.com.au using 12mm threaded spacers with countersunk screws on the outside. Add a washer under each spacer to slightly increase the distance. Now it’s time to install the panel-­ mount connectors. It turned out to be too difficult to mount the BNC connector on the PCB itself. Connect a 50mm length of stiff wire to the connector and pass this through Australia's electronics magazine the centre hole of the BNC connector location on the PCB. Once the board is attached to the box, cut off the excess and solder it. To remove the board, you will have to desolder this one wire. After the PCB has been fitted, connect the DC sockets in parallel, then wire them to the matching plug for CON1. Make sure the wires are the right length to reach CON1. Also, ensure the polarity is correct. You can check this by testing for continuity between the barrel socket’s tip and one end of power switch S1, and also continuity from the outer barrel (with a plug inserted) to PCB ground. Apply power and check that everything works before fitting the lid to the box with the supplied screws. You should get a sensible display on the OLED as soon as it’s switched on. Check that you can adjust all the parameters with the knobs. If you run into any problems, remove the PCB and have a good look at it. Check that all the solder joints look good, especially on the SMDs, and that everything is where it should be, referring to Fig.5. Calibration Without calibration, the accuracy of the signal generator is entirely dependent on the TCXO. The best calibration procedure requires a two-channel oscilloscope, a GPS-disciplined 10MHz reference and a high-precision frequency counter (which might be built into some higher-end oscilloscopes). Set the three-position switch to “CW” and the output frequency to 10000000Hz (10MHz). Rotate the Function knob fully clockwise and adjust the tuning knob to get FTW = 23860929. This is the value needed if the TCXO has an output of precisely 30MHz. If you have no other equipment available, press the tuning button to save that value into EEPROM and turn the Function knob back a bit. If you have an accurate frequency counter, repeat above but adjust the FTW for exactly 10MHz on the frequency counter, and save it into EEPROM as before. For best accuracy, first, adjust the frequency using the counter as above. Then connect the GPS disciplined reference 10MHz signal to one channel of a two-channel oscilloscope, and trigger on that channel to produce a stationary display. Set the signal May 2022  51 A 300kHz signal with 10kHz amplitude modulation applied, resulting in smaller peaks 10kHz on either side of the carrier wave. Here frequency modulation has been applied. This results in many small peaks of all sorts of multiples of modulating waves either side of the carrier wave, but this spectrum analyser doesn't have the resolution to separate them. generator to 10MHz and connect it to the other scope channel. If the frequencies are identical, the signal generator waveform will be steady. But this will hardly ever be the case; it will drift left or right. Set the Function knob fully clockwise, and using the tuning knob, adjust the FTW for minimum drift. Typically, the drift will take 10 or more seconds across one complete cycle. The 10 seconds corresponds to an error of 0.1Hz at 10MHz. Press the frequency button to save the calibrated FTW value into the EEPROM. The calibrated frequency may hold for several hours depending on temperature fluctuations; the TCXO is by no means perfect. Do the calibration just before you want to do any seriously accurate work. There is a multi-turn trimpot accessible through a hole in the left side of the case. Setting the amplitude modulation level is best done using an oscilloscope. Still, if you loosely couple the output to an AM receiver, you can simply adjust the level for a clear tone. It will overmodulate and create lots of spurious and harsh harmonics if you wind it up too much. A matching attenuator Spectral analysis of a 75MHz output signal. Because of how a DDS works, you not only get spurious peaks at multiples of the signal frequency but also at fractions. The most significant in this case is at 30MHz, 35dB below the fundamental. Given the relatively small enclosure size, it was impractical to fit an attenuator into the same housing. There have been various RF attenuators described in Silicon Chip in the past, but the maximum attenuation has been about 30dB. I have designed a separate attenuator in another identical enclosure with an attenuation range from 1dB to 110dB in 1dB steps. As the output of the Signal Generator is about 0dBm, this means the lowest signal level that the pair can generate is around -110dBm. The photo on the previous page shows a preview of the attenuator, to be described in an upcoming SC article. ► A 100kHz output signal modulated by 1kHz at 10kHz deviation. 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We apologise for factors out of control which may result in some items may not being available on the advertised on-sale date of the catalogue. Affordable Storage Media 30mm FROM 119 $ 79 $ 100mm SSD Hard Drives with USB Type-C ONLY ULTRA HIGH SPEEDS UP TO 10GBPS (NVME) OR 6GBPS (SATA) USB Type-C External M.2 SATA/NVME SSD Case Ultra slim, ultra portable storage. Super-fast transfer speeds up to 440MB/s via USB Type-C. 500GB XC5920 $119 1TB XC5922 $199 Ultra portable storage solution, fits any M.2 NVMe or SATA SSD drive and supports ultra high speeds up to 10Gbps(NVMe) via USB3.1 USB C. XC5908 SDXC Class 10 microSD Memory Cards FROM 12 95 $ M.2-2280 95 NVMe/PCIe SSD FROM 69 $ Perfect for phones, tablets, action cameras etc. Allows you to maximise the performance of your device with their ultra-fast read write speeds. 16GB to 512GB capacity available. XC5015-XC5020 Super fast & reliable. Reads/write up to 2500/1900MB/s. 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Prices and special offers are valid from 24.04.2022 - 23.05.2022. 500 POWER WATTS AMPLIFIER PART 2 BY JOHN CLARKE Having described our new 500W Amplifier Module last month, giving its performance details and describing the circuit, we follow on this month with the amplifier construction, beginning with the PCB (Amplifier Module) assembly. Next month, we’ll build this into a complete amplifier along with fan cooling, a speaker protector and a clipping detector. T he 500W Amplifier has four main components: the Amplifier Module, its power supply, the Fan Cooling & Loudspeaker Protector board and the Clipping Indicator board. The last two of those have already been described in the January & February issues. This article will concentrate on the assembly of the Amplifier Module, its circuit having been described last month. Next month, the final article will detail the power supply, the chassis, and the final assembly and wiring, bringing all those parts together. Now let’s move on to building the all-important Amplifier Module. siliconchip.com.au Construction The 500W Amplifier Module is built on a double-sided, plated-through PCB coded 01107021 that measures 402 x 124mm. Refer to Fig.6, the parts layout diagram during construction. Before starting, it’s a good idea to inspect the board carefully. This will familiarise you with its layout and reveal any defects (however unlikely that is). Start construction by fitting transistors Q1 and Q2. These are small SOT23/TO-236 surface-mounting transistors. They are relatively easy to solder due to their widely spaced pins, but you might need the aid of a magnifying Australia's electronics magazine glass and strong light if your vision is not perfect. First, align Q1 onto the pads, holding it with tweezers, and solder one of the pins to the PCB. Check that it is correctly aligned with the other pads, reheating the solder joint to realign if necessary. Then solder the remaining pins. Mount Q2 similarly. Don’t worry if you add so much solder that the joints on these SOT-23 parts look like small silver balls. This is unlikely to cause any problems; we want to joints to be shiny, and adding a bit too much solder is better than not adding enough! If you feel the need to remove the May 2022  61 Fig.6: all the parts for the amplifier module mount on this somewhat large PCB. As usual, take care with the orientations of the transistors, diodes, LEDs and electrolytic capacitors and don’t get similar-looking parts mixed up. Note the two wire links required in the middle of the board. You should sleeve them with insulation just to be safe. This overlay is shown split at actual size. excess solder, add a little bit of flux paste and touch the join with a clean soldering iron tip. Now mount the small (1/4W or 1/2W) resistors. Check each value using a digital multimeter set to read ohms before soldering in place. Don’t rely on the colour bands to determine the value, as these can be difficult to read accurately. 62 Silicon Chip Note that there are two pairs of resistors labelled R1 and R2 on the PCB; they don’t have associated values. The nominal values required for these resistors (which define the SOA protection curves) are R1 = 35.328kW and R2 = 204.8W. We can’t get these exact values, but there are two ways we can get close. We can use E96 value resistors, with Australia's electronics magazine R1 = 35.7kW (+1%) and R2 = 205W (+0.1%). That is the easy method, and if you buy the set of hard-to-get parts from us, you’ll get the 35.7kW and 205W resistors. A slightly more precise method for R1 & R2 is to use paralleled pairs of resistors, one fitted to the top side of the PCB as normal, and the other soldered across the pads underneath siliconchip.com.au afterwards. These are 62kW || 82kW for R1 giving 35.3kW (-0.08%) and 390W || 430W giving 204.5W for R2 (+0.15%). We don’t think the +1% error using 35.7kW for R1 matters; the current-­ sensing 0.47W resistors have 5% tolerances, and the protection curves have a built-in safety margin. Still, if you’re concerned about it, you can use the parallel pairs instead. siliconchip.com.au Fit these resistors now, in the eight positions, using whichever method you prefer. Now install the two small 1N4148 diodes (D1 and D2) with their striped ends (cathodes) as shown on the overlay diagram and PCB silkscreen. Next, fit the BAV21 diode (D3) with the cathode facing the same way. The UF4003 diodes (D4-D7) can go Australia's electronics magazine in next. They are not all orientated the same so check Fig.6 and the PCB silkscreen. There are two wire links in the middle of the PCB above Q7 and Q9. Make these using 0.7mm diameter tinned copper wire covered in 1mm heatshrink tubing over most of their lengths, leaving just the very ends exposed. May 2022  63 L1 Winding Jig 1 2 These photos show how 4 the winding jig is used to make the 2.2μH inductor. F First, the bobbin is slipped over the collar on the bolt (1), then an end cheek is attached and the wire threaded through the S exit slot (2). The handle is then attached and the coil tightly wound onto the bobbin using 13.5 turns of 1.25mm-diameter enamelled copper wire (3). The finished coil (4) is secured using a couple of layers of insulation tape and a band of heatshrink tubing. 3 Wind wire on bobbin clockwise T he winding jig consists of a 70mm M5 bolt, two M5 nuts, an M5 flat washer, a piece of scrap PCB material or similar measuring 40 x 50mm approximately and a scrap piece of timber (about 140 x 45 x 20mm) for the handle. In use, the flat washer goes against the bolt’s head, after which a collar is fitted over the bolt to take the bobbin. This collar should be slightly smaller than the inner diameter of the bobbin and can be made by winding insulation tape onto the bolt, or from tubing. The collar needs to be of sufficient diameter for the bobbin to fit snugly without being too tight. Drill a 5mm hole through the centre of the scrap PCB material, plus a 1.5mm exit hole about 8mm away that will align with one of the slots in the bobbin. The bobbin can Continue by mounting the 1W resistors, again being careful to check the values. For the 56W resistors near speaker connector CON3, four mount on the top side of the PCB and four on the underside. The PCB screen printing shows the resistor positions on both sides. Fit the small-signal transistors in TO-92 packages next. These are Q3 and Q4 (BC546) plus Q5 and Q6 (BC556). Leave Q25 and Q26 off at the moment, 64 Silicon Chip be slipped over the collar, after which the scrap PCB end cheek is slipped over the bolt, ie, the bobbin is sandwiched into position between the washer and the scrap PCB. Align the bobbin so that one of its slots lines up with the exit hole in the end cheek, then install the first nut and secure it tightly. Next, fit the handle by drilling a 5mm hole through one end, slipping it over the bolt and installing the second nut. These photos show how the winding jig is used to make the 2.2μH inductor. First, slip the bobbin over the collar on the bolt (1), then attach the end cheek and thread the wire threaded through the exit slot (2). Next, attach the handle and wind the coil tightly onto the bobbin using 13.5 turns of 1.25mm-­diameter enamelled copper wire (3). Finally, secure the finished coil (4) around the outside using 20mm diameter heatshrink tubing. as these need to be mounted against the heatsink. However, you can fit the two TL431 references now, also in TO-92 packages (REF1 and REF2). Read the device markings carefully, and be sure to install the correct type at each location. The three LEDs are mounted about 5mm off the PCB, taking care to orientate them correctly and using the green LED for LED1. The longer lead is the anode, and this position is marked Australia's electronics magazine with an “A” on the board. Fit the 75pF 200V capacitor now, along with the 1nF, 10nF, 100nF, 470nF and 1μF MKT capacitors. Follow with trimpot VR1, then VR2 with its adjustment screw towards the bottom of the board as shown (right edge in Fig.6). The four M205 fuse clips are next. Press them down fully onto the board before soldering and ensure that the retention clips are on the outside. The best approach to make sure the siliconchip.com.au fuse clips are aligned correctly is to firstly fit a fuse to hold the fuse clips in position, then solder to the pads on the underside of the PCB. You can now solder in the 12 0.47W 5W resistors. These should be mounted about 2mm proud of the PCB so that air can circulate beneath them for cooling. A cardboard spacer slid under the resistor bodies before soldering their leads can be used to ensure consistent spacing. Now fit the connectors, ie, the RCA socket (CON1), the two-way socket for the loudspeaker connection (CON3) and the 6-way power connector (CON2). For CON3, first insert the terminal block plug into the socket and then install the socket into the PCB holes with the wire entries toward the outside edge of the PCB. Now mount the 100nF X2 class capacitor located near CON3. The 47μF, 470μF and 2200μF electrolytic capacitors can then go in. The 47μF NP (non-polarised) electrolytic can go in either way around, but the others must all be orientated correctly. Note that the 47μF capacitor above Q5 and Q6 must be rated to handle at least 50V (eg, a 63V type would be acceptable). Mini heatsinks Before fitting Q7 and Q9, you must first attach the heatsinks. Do this by inserting the mounting posts into the PCB holes and soldering these to the underside of the PCB. These will require a lot of heat from your soldering iron before the solder will successfully melt to secure the heatsink. Take care to avoid burning yourself on the hot heatsinks; wait until they are cool before mounting Q7 and Q9. Now tackle Q7 (FZT558). It would help to spread a little flux paste on all four of its pads before placing the part. Align the device with the PCB pads and solder one of the pins to the PCB. Check for alignment and reheat the solder to realign if necessary. Then solder the remaining pins. The metal tab needs to be soldered to the PCB right next to the heatsink. Again, you will need to heat it with your iron for an extended period due to the heatsink drawing heat away. Once the solder melts, though, solder the tab as quickly as possible to avoid overheating the device. Now install transistor Q9 (FZT458) in the same manner. siliconchip.com.au Use a cable tie to secure the 2.2μH inductor L1 to the board. Winding inductor L1 The inductor (L1) is wound using a 2m length of 1.25mm diameter enamelled copper wire on a plastic bobbin. Use a winding jig as shown opposite. Without it, it’s a much more difficult procedure, and you risk damaging the relatively fragile bobbin. Attach the bobbin to the jig, then wind 13.5 turns of 1.25mm diameter wire in the clockwise direction as shown, leaving about 20mm free at each end. When finished, secure the winding with a narrow strip of insulation tape, then slip a 15mm length of 20mm diameter heatshrink tubing over the bobbin and heat it gently (be careful to avoid melting the bobbin). Next, use a small, sharp hobby knife to scrape away the enamel from the protruding lengths of wire around the whole circumference and tin the exposed copper at the ends, ensuring the solder sticks. The inductor can then be installed on the PCB, orientated as shown. Secure it with a cable tie over the top of the winding and through to the underside of the PCB. Preparing the main heatsink The next step is to drill the heatsinks using the drilling templates provided (Fig.7). It is essential to place the holes accurately, so they are centred between the heatsink fins. That way, the screw heads will fit neatly between the fins. Before drilling the heatsink, you will have to carefully mark out the A close-up of the mounting arrangement of the transistors to the heatsink. Australia's electronics magazine May 2022  65 Fig.7: drill the two side-by-side heatsinks as shown here. You can drill the transistor mounting holes through the heatsink using a 3mm bit and then mount the transistors using screws, nuts and washers. The underside edge is drilled to 2.5mm and tapped for M3 in two places on each heatsink so that it can be mounted to the chassis. 66 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.8: use this diagram as a guide for mounting the various devices to the heatsink. Note the use of silicone insulating washers for all the large devices (no need for Mica given how spread out the heat load is) and the plastic bushes for the TO-220 devices with fully exposed metal tabs. hole locations using a very sharp pencil, then use a centre punch (or hammer and nail) to mark the hole centres. Next, drill 3mm holes at all the marked positions. It is best to use a drill press as it’s challenging to get the holes perfectly perpendicular to the mounting face otherwise. Use a small pilot drill to begin with (eg, 1.5mm), then step up the drill size to either 2.5mm or 3mm. Use a suitable lubricant when drilling the holes. Kerosene is the recommended lubricant for aluminium, but we found that light machine oil (eg, Singer or 3-in-1) also works well for jobs like this. The holes have to go between the fins, so check that the hole positions are correct before drilling them. Don’t try drilling each hole in one pass. When drilling aluminium, it’s important to regularly remove the bit from the hole and clear away the metal swarf. If you don’t do this, the aluminium swarf has a nasty habit of jamming the drill bit and breaking, it and can also scratch the heatsink face. Relubricate the hole and the bit each time before you resume drilling. At this stage, 2.5mm holes can be drilled in the bottom edge of the heatsink, ready to be tapped with an M3 thread. Do this at two places along the bottom edge on each heatsink. This siliconchip.com.au is for mounting the heatsinks to the chassis later. Tapping To tap the underside mounting holes, you will need an M3 intermediate (or starting) tap (not a finishing tap). The trick here is to take it nice and slowly. Keep the lubricant up and regularly wind the tap out to clear the metal swarf from the hole. Relubricate the tap each time before resuming. Do not apply undue force to the tap. It’s all too easy to break a tap in half if you are heavy-handed. Similarly, if you encounter any resistance when undoing the tap from the heatsink, gently rotate it back and forth and let it cut its way back out. In short, don’t force it, or it will break. Finally, lightly deburr hole edges using an oversized drill bit and clean off any aluminium particles or swarf. Check that the area around the holes is perfectly smooth, or the insulating washers could be damaged. Scrub the heatsink thoroughly using water and detergent and allow it to dry. Final assembly Fig.8 shows the transistor mounting details. Start by mounting transistors Q13 to Q24, noting that Q13-Q18 are the MJW21196 transistors while Q19Q24 are the MJW21195 transistors. Australia's electronics magazine Q13-Q18 are mounted on the left-hand heatsink and Q19-24 on the right-hand heatsink. The locations for these are shown in Fig.7 (you can also refer to Fig.6). These all mount with a silicone insulating washer between each transistor and the heatsink face. They are secured using M3 x 20mm machine screws inserted between the heatsink fins and a flat metal washer and M3 nut against the transistor face. Do not tighten the screws yet, so you can move the insulation washers and transistors to allow mounting onto the PCB. Q12 (the MJE15034) on the left-hand heatsink and Q11 (the MJE15035) on the right-hand heatsink need silicone TO-220 insulating washers and an insulating bush inserted into the device’s tab hole before being secured with an M3 x 15mm screw and M3 nut. Also leave these loose for the moment. Q10, the BD139, mounts with the metal face toward the heatsink and a TO-220 silicone washer between the heatsink and transistor. Attach it May 2022  67 When finished, our 500W Amplifier will have fans attached at the back of the heatsink via a metal bracket on the base of the case. with an M3 x 15mm screw and M3 nut and again, leave the screw connection loose. Now mount the PCB on six M3-tapped 9mm spacers and sit it on a flat surface. Lower each heatsink, one at a time, inserting the transistor leads through the appropriate holes. Once they’re in, push the board down so that all four spacers (and the heatsink) are in contact with the benchtop. This adjusts the transistor lead lengths and ensures that the bottom of the board sits exactly 9mm above the bottom edge of the heatsink. Check that the correct transistor is in each position and adjust the PCB assembly horizontally so that each extends an equal 1mm beyond the side of the heatsink. Now tighten all the transistor screws just enough that they are held in place while keeping the insulating washers correctly aligned. The rear of each heatsink should be flat against the transistor mounting edge of the PCB. The next step is to lightly solder the transistor leads from the top of the PCB, or at least as many leads as you can easily access from the top. Then carefully turn the whole assembly upside down and prop the front edge of the board up by placing books 68 Silicon Chip or something similar under the board so that the PCB is maintained at right angles to the heatsink. If you don’t have anything handy that you can stack to a suitable height, you can cut a couple of cardboard cylinders to 63mm (eg, from discarded paper towel rolls) to use as temporary supports. If you don’t do this, it will sag under its own weight and remain in this condition after the leads are soldered. Now you can solder the remaining transistor leads and add extra solder to any that need it. Make sure the joints are good since they can carry many amps at full power. When finished, trim the leads and turn the board rightway-up again. Next, tighten the transistor mounting screws to ensure good thermal coupling between the devices and the heatsink. They need to be tight, but don’t get out your breaker bar or impact driver. Checking device isolation Now check that the transistors are all electrically isolated from the heatsink. Do this by switching your multimeter to a high ohms range and measuring the resistance between the heatsink mounting surface and the Australia's electronics magazine collectors of the heatsink-mounted transistors. For transistors Q13-Q24, it’s simply a matter of checking between each of the fuse clips closest to the heatsink and the heatsink itself on each side of the Amplifier. That’s because the device collectors in each half of the output stage are connected together and run to their respective fuses. You should get a reading above 10MW, and quite likely “OL” as it should be too high for your DMM to read. Testing shorts for transistors Q10 (the Vbe multiplier), Q11 and Q12 is different. In this case, you have to check for shorts between the centre (collector) lead of each device and the heatsink. If you do find a short, undo each transistor mounting screw in turn until the short disappears. It’s then simply a matter of locating the cause of the problem and remounting the offending transistor. Be sure to replace the insulating washer if it has been damaged in any way (eg, punched through). Q25 (BC546) and Q26 (BC556) can be mounted now. These are held in position using transistor clamps attached to the heatsink by 15mm M3 screws and nuts. Apply a smear of heatsink compound to the flat face of each, mount the transistor clamps and position each transistor so the clamps will hold them in place at approximately the centre of the transistor body. Then tighten the screws. Turn the PCB assembly upside-down and solder and trim the transistor leads. Now you must remove the three support spacers from the edge of the board adjacent to the heatsink. This edge of the board must be supported only by the heatsink transistor leads. This avoids the risk of eventually cracking the PCB tracks and pads around the heatsink mounted transistors due to thermal expansion and contraction as the assembly heats up and cool down. Coming up next That completes the assembly of the Amplifier Module. Next month we will describe the power supply, how to power up and test the Amplifier and give full details on building the Amplifier into a vented aluminium metal case (shown above and with its lid removed) and keeping it cool, even under full load conditions. SC siliconchip.com.au Parts List – Complete 500W Amplifier 1 assembled 500W Amplifier Module (see Silicon Chip, April & May 2022) 1 assembled Amplifier Clipping Indicator set up for ±80V DC supplies (see Silicon Chip, March 2022) 1 assembled Fan Controller & Loudspeaker Protector with three 120mm PWM fans (see Silicon Chip, February 2022) 1 12V 15W switch-mode mains supply [Jaycar MP3296, Altronics M8728] Chassis 1 3U Aluminium rack enclosure, 558.80mm x 431.80mm x 133.35mm, made from: 1 Bud Industries RM-14222 Rackmount Chassis Kit (front, back & sides) [Digi-Key 377-1392-ND] 1 Bud Industries TBC-14253 Solid Rackmount Cover (for base) [Digi-Key 377-1396-ND] 1 Bud Industries TBC-14263 Perforated Rackmount Cover (for lid) [Digi-Key 377-1397-ND] 4 equipment mounting feet [Jaycar HP0830/HP0832, Altronics H0890] 1 400mm length of 20 x 20mm x 3mm aluminium angle [hardware store] 1 220 x 60mm front panel label Power Supply 1 800VA toroidal mains transformer with 2 x 115V AC and 2 x 55V AC windings [RS Components 1234050] 1 toroidal transformer mounting disc (drill hole out to 8mm diameter) [RS Components 6719202] 2 Neoprene washers for toroidal transformer [RS Components 6719218] 1 35A 400V bridge rectifier (BR1) [MB354, KPC3504 or similar] 1 208 x 225 x 0.8mm insulating sheet (Prespahn, Elephantide or similar) [Jaycar HG9985] 1 295 x 125 x 3mm plastic sheet (Perspex, Polycarbonate, PVC, acrylic or similar) 1 IEC mains input connector with fuse [Jaycar PP4004, Altronics P8324] 1 IEC mains connector insulating boot [Jaycar PM4015] 1 IEC mains power cord 1 M205 3.15A slow-blow fuse (F3) 1 DPDT mains switch with red neon lamp (S1) [Jaycar SK0982, Altronics S3242B] 1 3-way 6A mains-rated terminal strip [Jaycar HM3194, Altronics P2130A] 8 10,000μF 100V electrolytic capacitors [Jaycar RU6712 with mounting brackets] 6 15kW 1W resistors 2 5mm LEDs (LED4, LED5) 6 5mm yellow insulated crimp eyelets [Jaycar PT4714, Altronics H2061B] 6 6.3mm blue insulated female spade crimp connectors [Jaycar PT4625, H1996B] 10 150mm cable ties 7 adhesive panel mount cable anchors assortment of heatshrink tubing siliconchip.com.au Wire and cable 300mm of 7.5A or 10A Earth wire (green/yellow striped) [can be sstripped from three-core mains flex] 1 1.5m length of twin-core 7.5A sheathed mains cable 5m of 0.5mm diameter copper wire (eg, copper picture frame wire) 400mm of dual-core shielded microphone cable (or single-core if RCA input socket is used) 2m of red 25A-rated hookup wire, 2.9mm2 [Jaycar WH3080] 2m of black 25A-rated hookup wire, 2.9mm2 [Jaycar WH3082] 1m of figure-8 wire, 2.93mm2 per conductor [Jaycar WB1732] 1m of figure-8 wire, 2.5mm2 per conductor [Jaycar WB1712] 2m of figure-8 wire, 0.76mm2 per conductor [Jaycar WB1708] 1m of figure-8 wire, 0.44mm2 per conductor [Jaycar WB1704] Hardware, including screws 2 No.4 x 6mm self-tapping screws (or two M2 x 6mm machine screws and two M2 nuts) 1 M8 x 75mm bolt, M8 hex nut and washer for transformer [hardware store] 8 M4 x 50mm machine screws 1 M4 x 20mm machine screw 3 M4 x 15mm machine screws 22 M4 x 10mm machine screws 4 M4-tapped joiners 39 M4 hex nuts 3 M4 star washers 2 M3 x 15mm machine screws 4 M3 x 12mm countersunk head machine screws 10 M3 x 10mm machine screws 11 M3 x 9mm Nylon standoffs 2 M3 x 6mm machine screws 22 M3 x 5mm machine screws 12 M3 hex nuts Other parts 1 SPDT 30A relay, 12V coil (RLY1) [Altronics S4211] 3-pin female XLR panel connector [Jaycar PS1054, Altronics P0903] (or insulated panel-mount RCA socket) 1 panel-mount pair of heavy-duty loudspeaker terminals [Jaycar PT0457, Altronics P9257A] 1 RCA line plug 1 panel-mount bezel for 5mm LED [Jaycar SL2610, Altronics Z0220] 3 6.3mm yellow insulated female spade crimp connectors [Jaycar PT4725, Altronics H1842A] 1 560nF 100V MKT capacitor 2 10kW lug-mount NTC thermistors [Altronics R4112] Here is the complete parts list for the 500W Amplifier. While we aren’t describing its assembly in this article (just the module), it will give potential constructors time to order and receive the parts, ready for the final constructional article next month. Australia's electronics magazine May 2022  69 Air Quality Sensors Many different air quality sensors and sensing modules have appeared on the market, some of them surprisingly low in cost. Here’s a quick rundown of what they do and how they work. By Jim Rowe I Image Source: www.pexels.com/photo/white-clouds-and-blue-sky-907485/ nterest in air quality sensors and monitors has grown steadily, especially during bushfires when there’s a lot of smoke in the air, or for people who live in countries with factories near urban areas that cause poor air quality. Air filters and air quality sensors are now an essential part of the air conditioning systems in office buildings, hospitals and factories. But the filters and sensors developed for these ‘large scale’ applications are generally rather expensive. Then when the COVID-19 virus and its growing family of mutants appeared in late 2019 and were soon found capable of spreading via aerosol droplets, interest in air quality sensors almost exploded. It soon became apparent that smaller and lower-cost sensors were needed to sense and control the air quality in ‘smaller scale’ environments like homes, retail stores and schools. To meet this challenge, designers worldwide soon came up with many different kinds of low-cost air quality sensors and modules. There are so many that it can be daunting to pick the sensor or module best suited for your particular application. This article will describe the main types of low-cost air quality sensors and explain what each type does and how they work. There are quite a few acronyms commonly used in this area, and you’ll find the more common ones explained in the Glossary sidebar. Before getting to the sensors, let’s look at the undesired matter that can be in the air we breathe. What’s in the air There are three main types of harmful components in the air we breathe: particulate matter, volatile organic compounds and toxic gases like sulfur dioxide, nitrogen dioxide, ozone, carbon monoxide and carbon dioxide – the last of which we exhale ourselves. Particulate matter includes smoke and smog particles, which have long been recognised as a health risk. It also includes liquid aerosol droplets, which may contain things like viruses and bacteria. Currently, there are three official categories of airborne particulate matter, specified according to particle size and diameter: PM10, PM2.5 and PM1.0. PM10 refers to particles less than 10 micrometres (μm) in diameter, PM2.5 to particles less than 2.5μm in diameter and PM1.0 to particles less than 1μm in diameter. To put these numbers in perspective, the diameter of human hair is typically between 50μm and 70μm. Particles with a diameter of less than 10μm are small enough to pass through our nostrils and throat and enter our lungs. Once inhaled, these particles can remain in our lungs and contribute to serious health problems like emphysema and lung cancer. Even smaller particles with a diameter of less than 2.5μm can pass through the lung tissues and enter our bloodstream, where they can cause even more serious problems in organs like Nine of the low-cost MQ-series MOS gas sensors made by Hanwei Electronics in Henan, China and widely available on the internet. 70 Silicon Chip Australia's electronics magazine siliconchip.com.au the heart, liver and kidneys. This also applies to particles with a diameter of less than 1μm. PM1.0 is arguably a less useful criterion than the other two as the effect of these particles is similar to PM2.5. It’s almost impossible to have totally clean air, especially in an urban environment. So what levels of airborne particulate matter are regarded as relatively ‘safe’? The current guidelines are: • PM10 particles should not exceed 20μg per cubic metre (μg/m3) averaged over a year, or 50μg/m3 mean over 24 hours. • PM2.5 particles should not exceed 10μg/m3 averaged over a year, or 25μg/m3 mean over 24 hours. As for volatile organic compounds (VOCs), these are vapours emitted by many of the materials used in building our homes and offices, and many of the products we have and use in them. Common VOCs that may be present in the indoor air are benzene, ethylene glycol, formaldehyde, methylene chloride, tetrachloroethylene, toluene, xylene and 1,3-butadiene. By the way, “organic” means that they contain carbon molecules (like our organs, hence the name), not that they have been grown without synthetic fertiliser or pesticides. VOCs come from paints, varnishes, vinyl flooring, adhesives and composite wood products. Many can cause health problems in people with asthma and similar breathing problems, as well as people with specific allergies. Currently, there aren’t many ‘safe level’ guidelines for VOCs, though, and the general advice seems to be that they should be kept as low as possible – especially over the long term. Now we come to toxic gases. The most common of these in our homes and offices is carbon dioxide (CO2) because we exhale this ourselves. The best way to keep the CO2 level reasonable is to provide adequate ventilation. Still, it is also the major component of combustion gases, along with water vapour (but water is generally harmless). Other examples of toxic gases are sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO) and ozone (O3). Luckily, since CO is produced mainly by imperfect combustion, there shouldn’t be much of it in the air inside our homes and offices. But if you work in or adjacent to a siliconchip.com.au vehicle repair facility or parking garage or have an unflued gas heater, it may well be of concern. Historically, SO 2 pollution has been associated with the combustion of wood or fossil fuels like coal. So nowadays, in urban areas, this should not be a serious problem – unless you live near a coal-fired power station or prefer an old-fashioned wood fire to heat your home. Like CO, NO2 is generally produced as a result of combustion. Motor vehicles are the main source outdoors. Indoors, the primary sources are gas, wood, oil, kerosene, coal-burning fires and heaters, and tobacco smoke. Ozone can be emitted by office equipment involving high voltage, like laser printers and photocopiers. It is also generated by arcing within brushed motors. Safety guidelines for some of these gases are currently: • SO2: less than 40μg/m3 averaged over one hour. • NO2: less than 10μg/m3 average over a year, or 200μg/m3 over one hour. • O3: less than 60μg/m3 mean over eight hours. Types of air quality sensor Currently, there are four main types of air quality sensor: the metal oxide semiconductor (MOS) type, the non-dispersive IR sensor (NDIR) type, the photo-acoustic spectroscope (PAS) type and the particulate matter counter (PMC) type. Let’s now look at how these work. MOS sensors Sometimes called MOx sensors, these rely on the behaviour of particles of a metal oxide (usually tin oxide) when heated in the presence of air and/ or other gases. The basic principle of a MOS sensor is shown in Fig.1, which shows a cross-section of a MOS sensor. The silicon substrate of the sensing chip has a thin layer of tin oxide on the top, placed there by chemical vapour deposition. Electrodes at each end allow its resistance to be measured. On the underside of the chip is a heater element, used to heat the oxide layer to around 200-250°C, to speed up the sensor’s response. When the oxide layer is heated in the presence of clean air, donor electrons in the oxide attract oxygen molecules from the air and they are ‘captured’ by the oxide particles. As a result, a depletion layer forms on the surface of the oxide layer, and its electrical resistance rises. But if reducing gases such as carbon monoxide (CO) and some VOCs are present in the air, oxygen molecules in the surface of the oxide are released, and the depletion layer becomes thinner. As a result, the effective resistance of the oxide layer is reduced. So the current passed by the oxide layer varies proportionally with the amount of reducing gas in the air surrounding the oxide layer. The higher the reducing gas level, the higher the current. MOS sensors can detect specific VOCs by ‘doping’ the oxide layer with various chemicals. This is done in the MQ-series of sensors made by Hanwei Electronics Group in Henan, China. For example, their MQ-3 sensor is designed to detect alcohol vapour, so it’s suitable for use in a ‘breathalyser’. On the other hand, their MQ-5 sensor is designed to detect natural gas, LPG and coal gas, so it’s suitable for use in gas leak detectors. The other sensors in this series are designed for sensing: • MQ-4: methane gas • MQ-6: LPG, iso-butane & propane Fig.1: the basic principle of a MOS sensor. Australia's electronics magazine May 2022  71 • MQ-7: carbon monoxide (CO) • MQ-8: hydrogen (H2) • MQ-9: methane (CH4), LPG & CO • MQ-135: ammonia (NH3), nitrous oxides (NOx), carbon dioxide (CO2), alcohol, benzene and smoke Many of the Hanwei MQ-series sensors are used in many low-cost gas sensing modules available on the internet. They are all in a cylindrical six-pin package, either 17mm or 20mm in diameter and 10mm or 15mm high. Most of these modules simply take the analog current output from the sensor and convert it to a proportional voltage using an op amp buffer. The output voltage can then be measured using a digital multimeter (DMM) or fed into one of the ADC inputs of a microcontroller unit (MCU). SGX Sensortech Other MOS sensors found in lowcost air/gas sensing modules are the MiCS-5524 and the MiCS-4514, both made by SGX Sensortech (an Amphenol company) in Switzerland. These are much smaller than the MQ-series sensors, being in an SMD package measuring only 7 x 5 x 1.6mm. The MiCS-5524 detects CO, ethanol, hydrogen, ammonia and methane, while the MiCS-4514 has a second MOS sensor that detects nitrogen dioxide (NO2). The MiCS-5524 sensor is used in a gas sensing module with the same name, available from various internet suppliers, including Banggood, which currently has it priced at US$11.00 plus free shipping. This module measures only 18 x 13mm. The MiCS-4514 sensor is used in a fancier and slightly larger module (23 x 14mm) called the MiCS-VZ89TE, provided by SGX Sensortech itself and available from suppliers like Two more low-cost modules using the CCS811 MOS sensor made by ScioSense BV in Eindhoven. The one on the left is the Geekcreit CJMCU-811, available from Banggood, while the one on the right is Duinotech SEN-CCS811, available from Jaycar (Cat XC3782). element14 for around $25 plus shipping. This module incorporates its own ADCs (analog-to-digital converters), together with a dedicated MCU with detection algorithms. This module can provide CO2 equivalent and TVOC (isobutylene equivalent) readings via both PWM outputs and over an I2C serial bus. ScioSense BV Yet another MOS sensor found in low-cost air/gas sensing modules is the CCS811, made by ScioSense BV in Eindhoven, The Netherlands. Like the MiCS devices, the CCS811 is in a tiny SMD package, but it’s even smaller at just 4 x 3 x 1.2mm. Despite this, the CCS811 incorporates both an ADC and a dedicated MCU with built-in conversion algorithms, plus an I2C digital interface to link directly to a PC or an MCU. ScioSense describes it as an “ultralow-power digital gas sensor” and is claimed to detect a range of VOCs, providing both eTVOC (equivalent total VOC) and eCO2 (equivalent CO2) levels. The CCS811 sensor is used in several air quality sensing modules, including the Keyestudio KS0457 Two low-cost modules using the MiCS5524 MOS gas sensor made by Swiss firm SGX Sensortech. The module on the left is available from Banggood (probably made by Geekcreit), while the one on the right is the MiCS-VZ-89TE provided by SGX Sensortech itself, with a built-in MCU. 72 Silicon Chip Australia's electronics magazine CO2 Air Quality module, the Duinotech SEN-CCS811 Air Quality Sensor module (Jaycar Cat XC3782), the Adafruit CCS811 Air Quality Sensor and the CJMCU-811 CO2, Temperature and Humidity Sensor from Banggood. We’ll have a lot more details on MOS/MOx air quality sensors in a follow-up article next month, which will also show how to hook them up to microcontroller modules. NDIR sensors Another type of gas sensor is the non-dispersive infrared (NDIR) type, which, as the name suggests, makes use of IR light. It’s a simple kind of spectrophotometer that does not use any ‘dispersive’ elements like a prism or diffraction grating to separate the various wavelengths. Instead, it uses optical filters and/or a narrow-band infrared light source like LEDs or a semiconductor laser. It was discovered some time ago that molecules of different gases absorb light of specific IR (and near-IR) wavelengths. Pierre Bouguer discovered the general principle before 1729, and it was later elaborated on by Johann Lambert in 1760 and August Beer in 1852. Nowadays, it’s known as the Beer-Lambert law or the Beer-­LambertBouguer law. So by passing light of a specific wavelength through an air/gas mixture, the degree to which the light is attenuated indicates the amount of that gas present. The absorption spectra of various gases are shown in Fig.2. Carbon dioxide (CO2) absorbs light with a wavelength of 4.26μm (red lines) and also at a group of wavelengths around 15μm. Similarly, ozone (O3) absorbs light at wavelengths between 9.4-10μm (dark green lines), while carbon monoxide (CO) absorbs light at wavelengths between siliconchip.com.au Fig.2: the absorption spectra of various gases that can be detected by some of the sensor modules. 4.6-4.8μm (purple lines) and nitrogen dioxide (NO2) absorbs light between 6.17-6.43μm (light green lines). The operating principle of a simple NDIR sensor is shown in Fig.3. The IR light comes from the LED on the left, while there are two IR detectors on the right, behind separate optical filters. One filter passes only light of the wavelength corresponding to the gas to be detected. In contrast, the other filter passes either all other wavelengths or else the wavelength absorbed by a gas like nitrogen, which is the major component of air. By comparing the output of the two IR detectors, it can determine the proportion of the gas you want to detect in the chamber. NDIR detectors have been used in heating, ventilation, and air conditioning (HVAC) systems for years. However, they have tended to be large and relatively expensive – until recently, when IR LEDs and IR detectors based on micro-electromechanical systems (MEMS) have allowed them to be made smaller and for somewhat lower in cost. They still haven’t appeared widely in the low-cost air quality sensor (LCAQS) market, however. wavelengths in sunlight (like IR and ultraviolet or UV) also emit sound. The basic structure of a PAS sensor is shown in Fig.4. On the left again is the pulsed IR light source (generally a MEMS LED array), with an optical filter to its right passing only light of the wavelength absorbed by the gas to be detected; in this example, the wavelength of 4.2μm for detection of CO2. Then at the far end of the chamber, there’s a MEMS microphone, optimised to detect low audio frequencies. When the detected sound level is amplified, it can be converted into a figure corresponding to the amount of CO2 present in the cell. Note that the sensor as a whole is enclosed in an acoustic insulation layer, to reduce the influence of external sound. LCAQS sensors using the PAS principle have only appeared in the last couple of years because their development has depended on MEMS technology. The only one currently available is the XENSIV PAS CO2 sensor from Infineon Technologies (an offshoot of Siemens in Munich, Germany). This comes in a very compact PCB ‘mini board’ module measuring only 14 x 13.8 x 7.5mm, which combines the PAS sensor with a dedicated MCU running advanced compensation algorithms. The Infineon XENSIV PAS CO2 sensor mini-board module is currently available from suppliers like element14 and Mouser Electronics for around $48. Particulate matter sensors The fourth kind of air quality sensor is particulate matter or ‘PM’ sensors or counters. These can fall into three groups depending on the size of the particles they are designed to detect: less than 10μm (PM10), less than 2.5μm (PM2.5) and less than 1μm (PM1.0). However, some of them provide several ‘channels’ to deal with particles of different sizes. Currently, the PM2.5 type is the most common in the low-cost section of the market, so we will concentrate on this type. The basic principle of this type of PM sensor is shown in Fig.5. A small fan pulls air from the environment into a channel which passes through a sensing chamber. A small Fig.3: how a simple NDIR (non-dispersive infrared) sensor works. PAS sensors Another kind of gas sensor is the Photo-Acoustic Spectroscopy or PAS sensor, which again makes use of the way specific IR wavelengths can be absorbed by molecules of a particular gas (according to the Beer-Lambert law). But in PAS sensors, the degree of absorption is not measured directly. Instead, they make use of a phenomenon first discovered by Alexander Graham Bell in 1880: that when a thin disc is exposed to pulses of sunlight (using a rotating slotted wheel), it emits sound. Later, Bell showed that materials exposed to the non-visible siliconchip.com.au Fig.4: the basic structure of a PAS (photoacoustic spectroscopy) sensor. Australia's electronics magazine May 2022  73 laser sends a focused beam of light through the chamber, where any particles of matter in the air will scatter the light towards the sides. One or more photodiodes in the sides of the chamber detect this scattered light. Any light that is not scattered by PM particles passes through the chamber to be absorbed by the ‘beam dump’. By controlling the fan speed and thus moving the air through the sensing chamber at a known rate of volume, together with measuring the output of the photodiodes, the concentration of particles in the air can be calculated. The result is in units of μg/m3 (micrograms per cubic metre). Note that the traditional and most accurate way of measuring PM is the ‘gravimetric’ method, using a preweighed clean filter to collect particles from the air over a 24-hour sampling period, then weighing the filter again to determine the total mass of the accumulated particles, in micrograms. The concentration is obtained by dividing this figure by the volume of air that passed through the filter during the 24-hour sampling period. There are several low-cost PM2.5 sensors currently available, including the Grove-Laser PM2.5 Sensor module based on the Seeed Studio HM3301 sensor from Shenzen, China; the SN-GCJA5 sensor made by Panasonic Photo and Lighting Co. in Osaka, Japan; and the SPS30 PM sensor from Sensirion in Staefa, Switzerland. Fig.5: the basic operating principle of a PM (particulate matter) sensor. The Seeed Studio HM3301 sensor is inside a compact plastic and metal case measuring 38 x 40 x 15mm. In addition to the fan, laser and photodiodes, it has built-in electronics which provide fan control, photodiode signal amplification, filtering, multichannel data acquisition and an MCU for data processing. The output is via an I2C interface. In the Grove-Laser PM2.5 module, the HM3301 sensor is mounted on a PCB measuring 80 x 40mm, with a four-pin connector at one end for connection to a 3.3-5V power supply and the I2C lines for connection to a PC or external MCU. The effective PM2.5 The Grove Laser PM2.5 air sensor module is based on the Seeed HM3301 particulate matter sensor. The sensor itself measures only 38 x 40 x 15mm, and the module comes with a cable to connect to an Arduino or similar MCU. 74 Silicon Chip measuring range of the module is 1-500μg/m3, although it can measure up to a maximum level of 1000μg/m3. This module is available from Australian distributor Pakronics in Rosanna, Victoria for around $50 plus shipping. The Panasonic SN-GCJA5 PM2.5 sensor is again inside a compact moulded plastic box, measuring 37 x 37 x 12mm and weighing 13g. Like the HM3301 sensor, it includes all electronics to control the fan speed, amplify and filter the signals from the photodiodes, and an MCU for data processing. The Panasonic SN-GCJA5 PM2.5 particulate matter sensor comes in a small moulded plastic case measuring 37 x 37 x 12mm. In addition to the fan, laser and photodetector, it contains all electronics and provides both I2C and UART digital outputs. Australia's electronics magazine siliconchip.com.au The output is via either an I2C or a UART TX (serial) terminal. The effective measuring range of this module is 0-2000μg/m3. The Panasonic SN-GCJA5 PM2.5 sensor is currently available in Australia from element14 for around $37 plus delivery. It comes in a compact plastic-and-metal case measuring 41.2 x 41.2 x 12.3mm and weighing only 26.3g. As with the other two, it includes all the electronics to control the fan speed, amplify and filter the photodiode signals, together with an MCU for data processing. The output is via either an I2C interface or a UART TX/RX interface (selectable). The effective PM2.5 measuring range is 0-1000μg/m3. By the time you read this article, the Sensirion SPS30 PM sensor should also be available in Australia from element14, for around $60 plus shipping. I will review some of the sensors described here, and show how to use them in a future series of articles. Glossary of terms ADC Analog-to-Digital Converter – a device that converts a current or voltage into a digital value (usually an integer) eCO2 A concentration of CO2 in the air inferred by measuring the concentration of VOCs (see below) COPD Chronic Obstructive Pulmonary Disease – includes asthma, emphysema, asbestosis, etc IAQ Indoor Air Quality LCAQS Low-Cost Air Quality Sensors – officially defined as sensors costing less than US$500(!) MCU Microcontroller Unit – a small processor with onboard memory and peripherals MEMS Micro ElectroMechanical Systems – devices fabricated like an IC but with mechanical elements. See our November 2020 feature article (siliconchip.com.au/ siliconchip.com.au/ Article/14635) for details Article/14635 MOS Metal Oxide Semiconductor – a type of semiconductor that varies its resistance depending on the concentration of reducing gases it is exposed to, allowing it to detect CO and some VOCs MOx Another name for MOS NDIR Non-Dispersive Infrared (IR) sensor NOx The oxides of nitrogen, NO2 & NO3, generally created when air is heated to very high temperatures (eg, inside an internal combustion engine, especially diesel engines) PAS Photo Acoustic Spectroscopy – gas molecules exposed to IR pulses produce sound which can be used to determine the gas concentration Manufacturers: www.infineon.com www.sgxsensortech.com siliconchip.com.au/link/abcv siliconchip.com.au/link/abcw PMC Particulate Matter Counter – a device which counts the number of particles in an air sample PM10 Particulate matter in the air, including only particles less than 10μm in diameter PM2.5 Particulate matter in the air, including only particles less than 2.5μm in diameter Retailers: www.jaycar.com.au https://au.element14.com/3523840 www.pakronics.com.au www.banggood.com siliconchip.com.au/link/abcx SC PM1.0 Particulate matter in the air, including only particles less than 1μm in diameter tVOC A VOC reading (see below) equivalent to a reference concentration of isobutylene (a VOC) VOCs Volatile Organic Compounds – a large group of chemicals within many of the products we have in our homes and offices; their vapours can form a health risk if breathed in U Cable Tester S B Test just about any USB cable! USB-A (2.0/3.2) USB-B (2.0/3.2) USB-C Mini-B Micro-B (2.0/3.2) Reports faults with individual cable ends, short circuits, open circuits, voltage drops and cable resistance etc November & December 2021 issue siliconchip.com.au/Series/374 DIY kit for $110 SC5966 – siliconchip.com.au/Shop/20/5966 Everything included except the case and batteries. Postage is $10 within Australia, see our website for overseas & express post rates siliconchip.com.au Australia's electronics magazine May 2022  75 U O R OW Y D L I N U B GIANNI PALOTTI’S JACKPOT A slot machine is a game where you insert a coin, and the machine randomly chooses a combination of symbols. Depending on what symbols turn up, you might get a payout; rare combinations could net you many times what you put in. They can be fun to play but it gets expensive if you’re using real money. Why not build this machine with colour graphics and sound; it’s just as fun to play, but you can’t lose your shirt! T his slot machine displays four virtual wheels, each with 17 symbols drawn from a set of six: cherries, a bell, a bar, the number seven, a lemon and a bonus starburst (see Fig.1). It is based on a Micromite Plus LCD BackPack, producing colour graphics and sound. To keep things simple, this Slot Machine differs a little from a real slot machine that has the symbols in a fixed order on the wheels. Instead, it randomly selects one of the six symbols for each wheel over the 17 ‘runs’ or ‘loops’. Each symbol showing at the end of each cycle therefore has six possibilities. Still, as this is updated over 17 cycles, the possibility of repeating the same symbol too often is avoided. The design includes a 5c coin input slot; this gives the player a more realistic ‘casino’ feeling when compared to a typical downloadable slot machine game. The standalone cabinet also makes it more interesting than any old app. I made the coin input from a funnel with a reflective photosensor. Every time a coin passes through, a highto-low signal transition is sent to the Micromite Plus LCD BackPack around which the game is based, and it adds one credit in response. It has a limit Fig.1: the six possible symbols that randomly appear on the four ‘wheels’ during play. The payout varies depending on what combination is shown in Fig.2. of three credits (coins) per spin, and wins are calculated accordingly, based on the chart shown in Fig.2. You could use a pushbutton instead of a coin slot, but that would remove some of the fun. An add-on module offers the possibility of a solenoid-operated ‘kicker’ to eject any coins collected into the coin tray. This can be done by operating a tilting table, or the coins can be ejected into a thin tube (with an internal diameter slightly bigger than the 5c coins) located under the coin input funnel. However, the details of those options are not described here and will be left as an exercise for the reader. Some changes to the overall case dimensions would be necessary to implement either option. Operation Once power is switched on, the program starts an initialisation routine which sets up the sound module and loads images from an SD card using the BLIT READ command available on the Micromite Plus. Once the initialisation is complete, the gamer can insert coins into the slot. The first coin will activate the “PlayReady” LED, and the “Play 1 Coin” button becomes active. You can choose the number of coins you would like to play by continuing to push this button or hold it down until no more coins are transferred from the “CREDITS” box into the “COINS IN” box. The maximum number of coins you can play for each spin is three. When “Spin Wheel” is pushed, it changes the symbols displayed on the screen using the “BLIT WRITE” command, based on random numbers generated by the RND(TIMER) function, which tells the computer to use its internal clock value as a random seed. This number is then further processed Slot Machine Payouts ● ● ● 1 ● ● ● 2 ● ● 3 ● 5 ● 5 ● 8 Values above the red line are multipled by the amount of coins inserted (up to three coins). 10 ● 18 20 ● 25 30 ● 50 JACKPOT Fig.2: the payouts that are given depend on the result of the spin. For example, if you get “7 cherry lemon cherry”, that’s two cherries, so you get a payout of three if one coin was inserted, six if two were inserted or nine if three were inserted. siliconchip.com.au Australia's electronics magazine May 2022  77 Fig.3: the circuit of the Slot Machine is simple as most of the work is done by the Micromite. It triggers audio playback by sending commands to the DFPlayer Mini module, which connects to the loudspeaker via CON1. The rest of the circuit is mostly a power supply and a way to interface to the pushbuttons, LED and coin sensor. to achieve an almost-random value from 1 to 6. The process is then repeated 17 times to simulate the wheels spinning, after which the result is analysed and any payout is processed, as per Fig.2. The addition of sound effects makes this unit more fun and adds to the 78 Silicon Chip reality of the game. After all, the point of playing slots is to have fun! Circuit details The main circuit is shown in Fig.3. It’s based around the Micromite Plus LCD BackPack (November 2016 issue; siliconchip.com.au/Article/10415). Australia's electronics magazine This has a powerful onboard PIC32MX470F512H 32-bit 120MHz processor plus a 320x240 pixel colour touchscreen that’s used as the display and for user input. The touchscreen has a 3.2-inch (8cm) diagonal measurement compared to the 2.8-inch (7cm) screen siliconchip.com.au Parts List – Slot Machine 1 Micromite Plus LCD BackPack (without touchscreen) loaded with SlotMachine V10.bas [Silicon Chip Cat SC6211] 2 microSD cards loaded with sounds & images 1 3.2-inch LCD touchscreen with ILI9341 controller 1 4-pin female header (to mount the touchscreen to the BackPack) 1 double-sided PCB coded 08105221, 76 x 53mm 1 DFPlayer Mini audio player module [Silicon Chip Cat SC4789] 1 5V DC coil SPDT relay (RLY1) [Omron G5LE-5V or CIT J107F1CS125VDC] ● 7 2-pin headers, 2.54mm pitch (CON1, CON3, CON9-CON13) 1 4-pin header, 2.54mm pitch (CON2) 1 PCB-mount DC barrel socket (CON4) 1 2-pin polarised header and matching plug, 2.54mm pitch (CON5) 2 8-way female headers, 2.54mm pitch (CON6, CON7) 1 18-way male or female header, 2.54mm pitch (CON8) 1 9V battery clip to barrel plug (optional) 1 3W 4W miniature loudspeaker 1 grille to suit the loudspeaker 1 panel-mount slide or toggle switch (power on/off) 3 square miniature panel-mount pushbuttons (Collect, Spin & Play Coin buttons) [Jaycar SP0716 or Altronics S1080] ▲ 1 red panel-mount LED in a square housing [eBay item #353825669342] 1 PS126EL1 paper sensor (optional, for coin sensing) various jumper wires various M3 machine screws, nuts, washers and spacers (for mounting the PCBs, coin sensor etc) Hardware 1 300 x 350mm sheet of 7mm plywood 1 136 x 95mm sheet of 14mm plywood 1 150 x 130mm sheet of 3mm black perspex/acrylic ■ 3 65 x 52mm sheets of 3mm black perspex/acrylic ■ 1 100mm length of 20 x 12mm aluminium angle 2 M5 x 15mm hex socket cap head machine screws 4 No.4 x 10mm self-tapping black screws for mounting the front panel 4 M4 x 10mm panhead machine screws & nuts 3 M4 x 6-7mm panhead machine screws 2 M3 x 20mm panhead machine screws & nuts 14 No.4 x 15mm wood screws Semiconductors 1 7805 5V 1A linear regulator (REG1) 1 2N2222A 40V 600mA NPN transistor (Q1) ● 1 1N4004 400V 1A diode (D1) ● Capacitors 2 100μF 10V electrolytic 2 100nF multi-layer ceramic Resistors (all 1/4W 5%, small body types if possible) 2 10kW 1 2.4kW ● 6 1kW 2 1kW ● 1 120W ▲ add one more button if a coin sensor is not being fitted ■ or purchase laser-cut pieces from the Silicon Chip Online Shop (Cat SC6181) ● these components are only needed for the optional ‘coin kicker’ normally used for this BackPack. That larger size makes it better suited to the Slot Machine. Since it has the same number of pixels as the 2.8-inch screen and a compatible controller chip, it’s a direct swap; the only consideration is that the mounting holes no longer line up with the BackPack PCB. siliconchip.com.au Because of this, I glued a 4-pin female header to the outer side of CON4 on the BackPack to provide extra anchorage for the screen. The components besides the BackPack and LCD are hosted on another PCB that adds just a few things to the BackPack: Australia's electronics magazine • • • • a simple linear power supply some buttons and LEDs the coin sensor a DFPlayer Mini digital audio player, described in the December 2018 issue (siliconchip.com. au/Article/11341). This PCB concentrates all the extra connections into two sets of wires, one 9-way and one 3-way, that emanate only from one side of the BackPack. The DFPlayer Mini is responsible for producing all the sounds. It is wired to a miniature 73 x 51mm 4W 3W speaker mounted in the back of the Slot Machine. Power comes from a 9-12V DC plugpack or battery through a DC barrel jack or direct USB input to the BackPack. Micromite control Programming the Micromite Plus LCD BackPack is easy as it is done in BASIC. The software configures the COM port required to control the DFPlayer Mini music player module (COM2), sets the correct music files source (micro SD slot) and sets the volume to the required value (20). The BASIC code can be downloaded from the Silicon Chip website and loaded into the BackPack in the usual manner, eg, using TeraTerm or MMEdit to load the software into the BackPack over its USB virtual serial port. Once running, the coin input generates an INTH command which runs a routine where the number of coins inserted is registered without affecting other operations or music playback. The rest of the code is based on which button is pressed and how much credit is available at the time. In addition to loading this software, you must load each audio file on the micro SD card in the correct order. The sound effects are also part of the download package, although the ‘background music’ is not included as it depends on your taste. Select a music track and convert it to a 44.1kHz 16-bit stereo WAV file. The files must then be copied into a folder named “mp3” on the micro SD card in the following order: 1. Background music track 2. Coinin.wav 3. Play1Coin.wav 4. RunArm.wav 5. SpinWheel.wav 6. NoWin.wav 7. Jackpot.wav May 2022  79 The main screen for the Slot Machine indicates your total winnings (or losses!) To get the files in the correct order, it’s best to copy them one at a time. However, you can prefix the files with a four-digit number, to guarantee the correct playback order. We have done this for the supplied files. For example, the first file would be prefixed with 0001, the second file with 0002 etc. This is because the DFPlayer only plays a file based on its order in the file system and does not look at the actual file name, unless it has a numeric prefix as mentioned above. The image files must be loaded on a separate micro SD card in the BackPack slot. These files are named “SlotScreen1.bmp”, “SlotScreen2. bmp” and “PayOutChart.bmp” and are included in the download package. Most of the parameters in the code can be easily modified to suit your preferences. This includes the ‘rewards’. Note that any code changes to PAUSE(delay) commands can alter Fig.4: assembly of this add-on PCB is straightforward; start by soldering the lowestprofile components and then work your way up to the taller types. As most of the headers connect elsewhere via jumper wires, you could substitute male for female headers or vice versa, depending on what jumper wires you have. * only for the coin kicker the coordination between the sound and program sequence. Electronic assembly Build the Micromite Plus LCD BackPack as per the instructions in the November 2016 issue (link above) and, once it’s up and running, load the BASIC code (“SlotMachine V10.bas”) onto it as explained earlier. Next, build the extra circuitry on the PCB coded 08105221 (76 x 53mm). Follow the overlay diagram, Fig.4. There isn’t much to it – solder the resistors as shown (use small body resistors or bend the leads close to the bodies), followed by diode D1 orientated as shown, then transistor Q1 and the two 100nF non-polarised capacitors. Then fit the headers, including the two 8-way female headers CON6 and CON7 (not visible in Fig.4 as they are under the DFPlayer Mini module). Note that you can use a male or female header for CON8 depending on what type of header you have fitted to the BackPack, and what sort of jumper wires you intend to use to join the two boards. Follow with the DC socket, then the electrolytic capacitors with their positive (longer) leads towards the bottom or right side of the PCB, as shown. Then mount REG1 with its tab towards the edge of the PCB, followed by RLY1 if you are using the coin kicker option. Finally, plug the DFPlayer into its socket with the micro SD card socket entry towards the nearest board edge. Note that if you’re using the coin sensor, the 120W and 1kW resistors specified may be suitable, or they might need to be changed, with either possibly being a higher value. For this reason, extra 1kW and 2.4kW resistors are specified in the parts list. You can swap them out later if you find the coin sensor doesn’t work well with the initial resistor values. The wiring is relatively straightforward, with most connections running between the two main boards. Coins are ejected via the underside of the Slot machine, so you might want to put a small tray underneath it to catch them. 80 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.5: cut the plywood shapes as shown. Note the dotted outlines that show how the various parts fit together. Don’t forget that the ‘floor’ is made from thicker (14mm) plywood. You could use other materials such as MDF or even acrylic. Chassis assembly Now we move on to building the cabinet. It’s mostly made from plywood and perspex, with a couple of metal brackets. The plywood cutting details are shown in Fig.5, while the perspex and metal pieces are shown in Fig.6. To save some effort, we can supply laser-cut perspex pieces made from 3mm-thick black acrylic (see the parts list); or download the templates from siliconchip.com.au/Shop/11/6443 Fig.5 also shows how some of the siliconchip.com.au other pieces mount to the side panel. So once you’ve made all these pieces and cut and drilled the holes, assemble them as per Fig.5 and the photos. The 3mm black perspex front panel is where the coin slot, LED screen, three pushbuttons and LED are mounted. This panel can be made of two separate components or formed from a larger piece, by bending it at the required point to a 110° angle after heating it (eg, with a hot air gun). If bending it, make the cut-outs after the panel is formed to avoid them distorting. Australia's electronics magazine Our laser-cut front panels are supplied as two separate pieces. You could fill the joint with black silicone after assembly if you want to. The 5¢ coin input unit is made from the same material as the front panel. Our laser-cut set includes these four pieces, which are assembled as shown on the right side of Fig.6. The correct location of the sensor opening must be worked out according to the final sensor or microswitch selected. Once all the pieces are ready, ...continued on page 84 May 2022  81 Fig.6: the front panels (upper left) can be made from two flat pieces or one bent piece, as depicted at right. Making the metal brackets is simply a matter of cutting the aluminium angle to length and drilling some holes. The four remaining acrylic pieces shown opposite are assembled to form the coin chute as depicted at lower right. The Micromite Plus LCD BackPack that controls the whole Slot Machine is based on Geoff Graham's Explore 64 (shown at actual size). 82 Silicon Chip Australia's electronics magazine siliconchip.com.au We will be supplying a double-sided PCB for the add-on module of the Slot Machine from our Online Shop. This is the 3W speaker I used. It works well and I recommend it, but there are plenty of other options. siliconchip.com.au Australia's electronics magazine May 2022  83 Fig.7: here is how to wire it all up. Switch S4 is not needed if you’re using the coin sensor and vice versa (although you could have both if you want). The power switch can be any type that can handle the current. Take extra care with the wiring between the add-on board and the BackPack, especially the GND, 5V & 3V3 cables or you could fry something! If using the optional switch (S4) for Coin In instead of the coin sensor then you will need an additional cut-out for another pushbutton on the lower front panel. The dimensions of this will be provided in the download for the front panels on the Silicon Chip website. assemble the cabinet using small 3mm wood screws, ensuring that each holding hole is fully pre-drilled so that the plywood does not split. Once complete, the box can be primed and painted as required. To allow coins to slide out of the base, glue a thin section of material (preferably perspex) to the top face of the floor. You can use any metal or plastic lid from any suitable container for the 84 Silicon Chip coin catching tray. I was fortunate to find one of exact size that only needed to be cut around the edges to make a suitable shape. Use the small black self-tapping screws to attach the front panel on either side. Wiring After the chassis has been assembled, you’re ready to mount the BackPack, control board and other Australia's electronics magazine electronic components and wire it up. See the photos, which show where the various parts go. Those photos should also help you figure out the wiring, but for clarity, we’ve also provided a full wiring diagram in Fig.7. Double-check the wiring between the control board and the BackPack before powering the Slot Machine up since a mistake there could cause damage to either or both boards. SC siliconchip.com.au SERVICEMAN’S LOG Where there’s a weld, there’s a way Dave Thompson It has always been my dream to build my own car. I worked on aeroplanes for many years, and if I could do that, surely a more terrestrial vehicle would be a doddle! Still, such an undertaking is a major project, which is why I have been working on it for around 15 years and still haven’t finished... It was either that or build an aeroplane; kit planes exist, but they are pretty expensive, and my garage isn’t exactly hangar-sized, so building a car is a somewhat more realistic goal. When I started those 15 years ago, my circumstances allowed me to indulge in this dream. It was all triggered when I came across a book on making a Lotus 7 replica using standard Ford parts for systems like steering, suspension and drivetrain, as manufacturing these critical parts is tricky for the home builder. There were a few problems, of course. Firstly, I’d need to find those parts – or suitable equivalents. Secondly, I’d need many tools I didn’t already have. First and foremost among those, I’d need a decent welder and some skills to go along with it. Dad was a pretty good welder – he wasn’t qualified, but learned by doing, and over the years, I spent many hours watching him use his trusty arc welder (called a ‘stick welder’ in some parts) to fuse metals together. I inherited his welder and accessories, which now sit under my bench. But I’ve never used them. MIG vs TIG The Lotus 7 replica was based on a tubular steel spaceframe chassis. To put it together and have it certified, I’d need to use either a MIG (metal inert gas) or TIG (tungsten inert gas) welder. Back when I started all this, TIG welders were expensive, and from the research I’d done, it was a much harder skill to acquire, so I decided to go with MIG. The principle of welding is simple; heat the metal joint (and filler rod) enough and, under the right circumstances, it will literally fuse together. In contrast, soldering ‘glues’ components electrically but gives no real strength, which is why solder alone should never be used for joints where physical strength is required. In electrical engineering terms, an arc welder is the simplest way to fuse metal. All you have to do is pass a huge alternating or direct current (AC/DC – rock on!) through the metal to be joined to heat it up. One of the electrodes is a flux-coated rod to assist sweating everything into a nice seam. While simple in theory, in practice, it takes a lot of skill and knowledge to know which rods to use, how much current to apply, how fast to move the rod along the seam, how fast to feed it in, and many other variables that only experience and practice can teach. A MIG welder is theoretically a lot easier to use for beginners. Instead of a solid flux, an inert gas (usually Argon, CO2 or a mixture of both) is used to isolate the weld as it happens. This prevents air from oxidising the joint at the high working temperatures, which would otherwise make it messy and not structurally sound. This all happens at the nozzle end of the welding torch. It is hollow and has an aperture for the gas to flow through, while a wire is power-fed to the joint down the centre. Pressing the trigger on the torch does three things. Firstly, a valve opens so gas can flow out the end of the torch. Secondly, a motor starts feeding wire out of the nozzle at a pre-determined rate and lastly, lots of current is applied to that wire. The circuit is completed by clipping a heavy-duty Earth Items Covered This Month • • • • • When there’s a weld, there’s a way Magnifying viewer repair Smeg dishwasher repair Troubleshooting a BWD 525 oscilloscope Fixing a pool chlorinator Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Cartoonist – Louis Decrevel Website: loueee.com siliconchip.com.au Australia's electronics magazine May 2022  85 clamp to the work to be welded. Wherever the wire from the torch touches the metal, the circuit is completed, and welding occurs. As you can imagine, there is a lot going on, but the variables are all easily adjusted on the welder itself. Gas flow can be changed by tweaking the regulator, wire speed is controlled by a potentiometer and the output current by either a pre-set switching arrangement or a continuously variable current regulator. The performance between different welding rigs varies enormously, as does the price. Hobby welders are notoriously cheap and often not designed for any serious work. All welders have a stated duty cycle, and this is usually part of the numbers one looks at when buying a welder, along with the maximum output current. Welders can only be used for so long at full noise before having to ‘rest’ and cool down. The standard ‘period’ is 10-minute units, so if the duty cycle on a 100A welder is 30%, it can theoretically be run at 100A for three minutes before either shutting down due to overheating, or the operator stops welding and waits out the remaining seven minutes. Obviously, there are variables in this; if you make a weld and then stop for a while before making another one, you can go for longer as it’s only the on-time that matters. Also, running it at a lower current will usually allow you to have a higher duty cycle. But that number does provide a good indication of the practical use of the product, and should be taken into account when shopping. Another consideration is the device’s build quality; many inexpensive machines use aluminium windings in the main transformer, usually one of the most critical components of any welder. Aluminium is cheaper than copper, so cheaper machines tend to use transformers wound with it. Much internet argument rages over the pros and cons of either material, and whether square or round-wound coils on the transformer core are better. Still, in practice, most serious welding machines use very beefy, copper-wound, iron-cored transformers. I mention this backstory because recently, a neighbour brought in a dead MIG welder to my workshop, asking if I could repair it. When plugged in and powered on, the cooling fan ran, gas flowed and the wire was fed at a pull of the torch’s trigger. However, there was no output voltage 86 Silicon Chip (typically 23-26V DC on a smaller MIG like this), and it wouldn’t weld when the circuit was completed. This didn’t bode well; I suspected several possible reasons. On many such welders, there is a massive full-bridge rectifier mounted to the case, while in others, a ‘driver’ PCB controls the current delivery. This rectifier (or any of the components on a driver board) could have failed. Many welders also use the same PCB (or sometimes separate smaller PCBs) to hold components for controlling the fans, electronic gas switching and wire-feed speeds. Still, as these features all appeared to be working, failure here was unlikely (though possible, of course). Depending on the type of thermal cut-out device employed, this may have also failed, preventing power output. While some machines use bi-metal thermal switches, others use simple single-use thermal ‘fuses’. Either can kill power to the whole machine, or only prevent the high-­ current side of things operating and keep the fans running to assist cooling. And if none of those things turns out to be the problem, it might be the transformer itself, which would put a whole different light on things. Either way, I’d have to open it up and take a look. I could see the bottom of a PCB through the vented case, so I would start by looking at that. This welder is a 180A ‘prosumer’ level gas/gasless machine with a claimed duty cycle of 60%; not too shabby, considering it was purchased many years ago. It can also weld aluminium (with the right welding wire fitted and the polarity to the torch reversed). Interestingly, the owner uses a large SodaStream CO2 gas bottle mounted to it for the inert gas supply, through a converter valve commercially made for that purpose. I wish I’d known about this when I got my MIG, as it is substantially cheaper to swap these bottles out than rent even the smallest one and get it filled from the local industrial gas suppliers. It is also much more portable than having a large gas cylinder to tote around. Opening it up There are few jobs easier than disassembling a welder. There is usually a side panel that can be unscrewed or simply unlatched to change wire spools and access the power leads to the torch and other interior components. Chunky PK-style screws hold the rest of the metal and plastic bits together, and it takes literally five minutes to strip the whole caboodle down to spare parts. The main transformer is the star of the show and takes up a good amount of space inside the box. It also makes up the vast majority of the weight of the machine. A large 100mm cooling fan sits near the back of the compartment, and the spool and wire-feeder mounts at the front, behind the control panel (such that it is). More modern ‘inverter’ type welders get away with a lot less electrical mass. While they typically do an excellent job, they tend to cost a lot more. The PCB I saw earlier was easy enough to remove, and as far as I could ascertain, there was nothing untoward with it. No electrical smell or signs the ‘magic smoke’ had escaped. The pot that controlled wire speed felt smooth, and a meter across it showed no signs of worn-out tracks when I slowly rotated the pot through its range. There is a fuse mounted on the PCB, and that tested OK. There is also a smaller mains to 12V transformer mounted on Australia's electronics magazine siliconchip.com.au this board; I tested it for continuity, and both primary and secondary looked good, with no shorts to ground anywhere. 12V DC applied briefly to the relay coil saw it pulling in and letting go properly, and the contacts also rang out OK. None of this was much of a revelation as this board controls the fan, gas valve and wire feeder – all of which I knew still worked. Moving on then. A bi-metal type thermal switch was mounted to a bracket that pressed the face of the switch to the coils of the transformer. If the coils got too hot, the switch would trip and interrupt power, preventing welding until it cooled again. Testing the switch was straightforward; after removing it from the bracket, I used a multimeter to measure the resistance across the terminals (with the leads disconnected from the rest of the circuit). The reading was almost 0W. I then used my hot air gun to carefully apply heat to the face of the switch, and it opened at around 50°C, or as near as I could measure it anyway. That seemed about right; if the outside of the coil were at around 50°C, the centre would be hotter, and that’s as hot as I’d want it to get. The final discrete component was the large industrial-­ sized bridge rectifier mounted to a metal block, which was then mounted to the steel case (for better cooling, I assume). Measuring across all points with my diode tester showed there were no shorted or open-circuit diodes. That left the main transformer. While it was possible the switch in the torch handle was failing, the rest of it was working when the trigger was pulled, so I suspected it was not the problem. Preliminary measurements across the primary of the transformer were encouraging. However, after further testing, I discovered that one of the two secondary windings was open-circuit. After disconnecting all the wires, I pulled the transformer out for better access, noting carefully where everything went so I could put it back together later. It certainly wouldn’t help if I wired it back up incorrectly! My fears were confirmed with one of the secondary windings appearing open, and it was the one that went off to the rectifier. That explains the lack of output to the wire. It was also possible that this welder was branded and marketed under one name by one company but sold by other companies (even in the same country) under another name, with the same (or very similar) hardware. A quick look on the Interweb brought up literally hundreds of very similar welders, but very little information on the parts inside or even who made them. Besides, I didn’t exactly have any part numbers emblazoned over anything in this machine either. I don’t relish making phone calls like this to clients, but sometimes these things don’t work out. But in this case, the client mentioned that when he bought his welder, an old friend of his had also purchased the same one. That one had fallen off the back of a ute at a job site years ago and no longer worked. The client reckoned his mate might still have it lying around (like many of us, he didn’t throw anything away either!), and if so, perhaps he could acquire it and I could burgle it for parts. Even better, I said, it might be easier to repair than this one! Sure enough, a few days later, the client turned up with his mate and his mate’s dead welder in tow. One look at the wreck told me that it wasn’t going to be repairable! It looked like it had been run over; I guess when heavy objects fall onto hard ground, they don’t usually fare well! However, transformers don’t bend easily, and as it is mounted in the dead centre of the case (to balance the weight and make it easier to move about, I suppose), it is about as protected as something could be in a relatively flimsy stamped metal case. In-situ measurement (once I’d bent a few things out of the way) proved it was still alive, so after some serious panel beating to get stuff out of the way, I was able to extract the transformer from the dead machine. Reassembling it into the original chassis was as straightforward as wheelbarrow mechanics. Once I made sure that Bringing it back to life This caused somewhat of a quandary; buying a new transformer, or having one made specially if we couldn’t find a replacement, would likely cost the lion’s share of a new, more modern welder. I’m in the very fortunate position to have a commercial-grade transformer-winding machine and ample copper wire stocks, but I’d have to face a couple of problems before I could re-wind it. For one, I’d have to break down the old, dead transformer to salvage the E and I iron core laminations from it – I have some NOS (new old stock) cores in stock but nothing that large. And for two, at the moment, that machine is buried under a household’s worth of junk in storage. Getting it out (very much a two-person job) and setting it up to re-wind one transformer (even a monster one) wasn’t going to fly. That was a shame, really, as it would have been a very interesting project for my machine. Oh well, such is life. A quick call-around for potential replacement transformers came up empty. This brand of welder was no longer made or sold, so it meant finding another one from another manufacturer – that is, if the customer wanted to go ahead with a repair. siliconchip.com.au Australia's electronics magazine May 2022  87 everything was in its proper place and wired in correctly, I held my breath and plugged it in. A quick brush of the wire to a scrap of metal held into the earth clamp proved that we now had plenty of juice at the torch. The moral of the story? It’s always good to have a spare! “Magnifying viewer” repair B. G., of St Helens, Tasmania has a short story about repairing a somewhat unusual device... A friend called me seeking help to repair a “magnifying viewer” for a vision-impaired friend. I duly picked up the unit and was told that it failed to switch on and ruined the RCD in his switchboard, which had to be replaced. I gathered from the weight that it contained an old CRT. The item to be viewed was placed in a tray under the tube, then adjusting the magnification and focus knobs provided a clear and magnified display of the object on the screen. I cautiously plugged the power plug into my test outlet, which has an incandescent globe in series with the Active line. The globe pulsed for some seconds, then tripped my circuit breaker. The unit was made by Telesensory Systems, a US company that now appears to be non-existent. So I had to trace the circuit. There was a nice toroidal power transformer with no markings, a regulator board with +16V DC and +12V DC outputs, CRT drive circuits, a small ‘vidicon’ camera underneath and two of the smallest fluorescent tubes I have ever seen. I discovered that the two 12V regulators had failed and replaced them. I couldn’t make much sense of the transformer; a mate suggested that I temporarily try one he had, to no avail. I checked for shorts on the mains side, but it seemed all right. Undoing an insulated cover on the left side, I found another board labelled “fluoro lamp driver” with a 4060 IC, some large capacitors, relays and transistors and a large black inductor. The inductor and the board were connected to the mains Active input and were easily unplugged. The unit powered up now; this time, a dim raster was visible, so perhaps the original power transformer was OK. I then realised that the large inductor was the ballast for the fluoro tubes. It measured open-circuit, and I bet it was breaking down with voltage applied. An internet search failed to find anything suitable like a 4W ballast, and given that it was not producing a dull picture, I fitted a string of white LEDs under the CRT. This allowed it to produce a very reasonable magnified display. I left it like that, and my friend was delighted to have it returned in working order. Smeg off and buy a new capacitor R. W., of Hadspen, Tas managed to repair a dishwasher for a grand total of $6. That’s less than 1% of what he was quoted for a new control board without installation... When we moved to Tasmania, our new house had a Smeg DWA U214X dishwasher installed, matching the kitchen cabinetry. It was about three years old, appeared to be in good condition, and worked reliably until one day, a year and a half later, it refused to start. This “magnifying viewer” utilised a large CRT display. It was made by a company called Telesensory Systems who specialised in making devices to help visually impaired people. 88 Silicon Chip Australia's electronics magazine siliconchip.com.au This unit has a large pushbutton switch that controls the mains supply. Upon switching it on, the machine gave a beep, but none of the LEDs illuminated. It would generally flash the two right-most LEDs to indicate completion of the previous cycle. Selecting a program would typically show the corresponding LED, but nothing happened. Cycling the power gave the same initial beep but no further activity. I trawled the internet and found that this was a common problem with Smeg dishwashers of this age, but no one had documented a repair. Some of the suggestions were entirely unhelpful, stating things like “you need a new keyboard for it”. I was able to find an assembly diagram but sadly, not a schematic. The next day, I again tried to operate the machine and was greeted with the same result. I was called away for an hour or so and, after returning, I realised that I had left it switched on and now the end-of-cycle LEDs were flashing. After selecting a program, it operated normally. The next day, the fault returned, but it worked after being left on for an hour. I contacted a local supplier of appliance spares, and they were able to find a replacement board, but it was over $650. Even second-hand items on auction sites weren’t cheap and certainly not guaranteed to work. This effectively wrote off the dishwasher, but I decided to attempt a repair as I had nothing to lose. I thought that faulty capacitors were the likely culprits, possibly not resetting the microprocessor, causing the switchmode supply not to start or limiting the available current. I retrieved the control board, and there were no tell-tale signs of failure or bulging electrolytics. There was a 22nF X2 capacitor to drop the mains voltage, and I remembered reading in a past Serviceman’s Log column that these had caused some problems in ageing equipment. I decided to replace it and all of the accessible electros too. A quick trip to Jaycar, and I had five capacitors for about $6. Some like the X2 were an exact fit, while others were larger, and I used a leaded 100μF electro to replace an SMD type. However, when I desoldered one leg of the SMD capacitor, it took part of the PCB track with it! I was able to delicately solder the lead to the remaining piece of track. Not ideal, but it worked. The PCB is sandwiched in two half-shells that mount in the dishwasher and guide the edge connectors. I had to make a hole in one side to accommodate the 450V electrolytic, as the original 400V unit was smaller. Smoke test time – it worked faultlessly. The LEDs appeared brighter than I recall, indicating that the X2 capacitor was indeed not passing sufficient current for the power supply to start. So a dishwasher was saved from the junk heap for just $6, one hundred times cheaper than a new board and many hundreds cheaper than a new dishwasher. Troubleshooting a BWD 525 oscilloscope J. D., of Crows Nest, NSW has an electrical engineering degree but wound up working in IT instead. He has kept his workbench going with the odd repair and project, but mainly in the digital electronics, low voltage space... High voltage for me meant mains power, and even then, it was only to step it down. But then, I got the opportunity siliconchip.com.au Australia's electronics magazine May 2022  89 to purchase an Australian-made analog BWD 525 cathode ray oscilloscope (CRO). It was already close to 40 years old by then. It worked great until one day, my single trace became multiplied, roughly 10 scan lines high. I thought I’d have a go at diagnosing the problem. I started by checking the various dials. The focus dial ‘worked’, meaning the multiple scan lines did all go in and out of focus but remained 10 high. Next, I fed in a 1kHz 4V peakto-peak square wave, and the 10-high scan lines remained, but the Y deflection seemed to be working. The X&Y controls moved my waveform as expected. Luckily, I had the service manual, and it included the complete circuit, with expected waveforms and voltages at various points. Vaguely remembering how to discharge a CRT, I opened the CRO, revealing discrete components – including capacitors as big as cans. I started looking at the focus circuit, which has -1450V DC applied to a series resistor string of 1.5MW, a 2.5MW pot and two 3.9MW to ground. The pot’s wiper went into the CRT terminal marked “focus”. This was somewhere to start. There’s also a bypass capacitor between the pot and the CRT. I measured the resistor values and disconnected the bypass cap; they seemed all good. One problem was that my multimeter had a maximum rating of 1000V DC, so I couldn’t directly measure the -1450V rail. There were even higher voltages marked on the circuit. I creatively measured the focus voltage by adding a resistor in series with my DMM’s input resistance and calculated that the focus voltage was somewhere between 800V and 1200V. The horizontal amplifier looked like it was working too; there was a 7400 TTL NAND gate doing some tricky switching, but roughly measuring the voltage and waveforms, it seemed to all be correct. The horizontal amp circuit also does the blanking among some other functions such as “alt” and “add” (dual-display/add the signals together) – I couldn’t find any faults there. Looking at the capacitors, nothing seemed strange; there were no bulges or anything like that. Also, the diodes and the bipolar transistors all seemed to be conducting correctly. 90 Silicon Chip The repaired BWD 525 oscilloscope displaying a nondistorted trace. Working around 8600V made me a little nervous. Next, I thought I’d check the power supplies. The 135V rail showed a whopping 9V ripple before getting clipped by a zener diode – which reduced it to 25mV. So I ordered and then installed some new unique-valued capacitors because they didn’t seem to be filtering the supply rails very effectively any more. I then calculated that I could directly measure the voltage at the CRT focus pin with the potentiometer set halfway; it should just be within range of my multimeter. Doing this, the scan lines decreased to 5 high. So I was definitely in the right area. Eagerly, I continued to measure. I measured across one of the 3.9MW series resistors, expecting to get a reading around 480V. Instead, it went to 1000V+, then the multimeter promptly failed. I confirmed that the resistor was open-circuit, replaced it and the original, crisp traces returned. But wait, didn’t I measure the resistor values before? That’s a real headscratcher. With newfound confidence (and a new multimeter), I wanted to tackle another problem that I’ve always had with this scope. The horizontal trace never made it all the way to the right edge of the screen. It would cut off about 2.5cm before reaching the right edge. Looking at the circuit, the horizontal deflection amp was made of pair of matching high-voltage BD115 transistors with their collectors connected to the left and right horizontal deflection plates on the CRT. Their bases were connected to identical pairs of emitter followers; that made sense. As they are mirror images, I compared and measured them. All the voltages for those transistors matched perfectly and were as shown in the manual. I then checked the emitter-followers, and I got twice the voltages specified in the manual. I measured -3.5V to -4.15V Australia's electronics magazine siliconchip.com.au instead of -2V to -2.8V. However, the voltage at the BD115s still measured perfectly. This was a mystery. The coarse & fine horizontal adjustments worked – scrolling left, it scrolls off the left side, as you would expect, but when scrolling to the right, it always clipped 2.5cm before hitting the right-hand edge. I started to look at the trace as it reached its end before the right edge and couldn’t see any distortion in the trace. It was as if the blanking/retrace circuit kicked in too early. So I swap the connections to the BD115s. My theory was that if it was the blanking circuit, the ‘cut off’ would also switch to the left side. It didn’t! It was still cut off on the right side, as if there was an invisible wall. While off, I carefully placed the CRO on its side, the right side down, thinking that whatever is obstructing is probably extending too far left from the right side. After all, I was running out of ideas. I banged the table, switched it on, and the trace moved closer to the right side! I banged some more, and it moved some more until it was back to normal – happy days. So now I have a fully working 45-year-old Australian-­ made CRO and a new multimeter. Pool chlorinator problems C. F., of Duncraig, WA had a problem with an AstralPool Viron eQuilibrium pool chlorinator. Luckily, the control board had relatively few parts and identifying the one which was not doing its job was not overly tricky... One day, I noticed the chlorinator pump was not operating at the usual time. We had some wild weather with occasional blackouts, so I thought the timer had been reset. I checked it, and the time displayed was 00:00. I set the time, checked the timer setting (which was fine) and put it in automatic mode. I was expecting the pump to start, but nothing happened. The display cycles through screens showing pool chemistry, chlorine production, the current time and timer status. When the clock display appeared again, the time was 00:00. My first thought was that I had stuffed up when setting the time, so I tried again, with the same result. I reset the system, but that didn’t help either. Each time after cycling back to the clock display, the time showed midnight and did not advance with passing minutes. I called the manufacturer support line but they couldn’t help me; all the person could tell me was how to set the clock, which was not the problem. As the controller is out of warranty, I decided to have a look inside. I disconnected the controller and brought it to my workbench. Removing four screws opened it up. Inside is a large PCB with a couple of transformers, a few relays and power transistors. A ribbon cable connects it to another PCB at the front panel. I took out four more screws to remove this PCB. It has the display, three ICs – one square with 64 pins and two eight-pin types, all SMD. The board is coated in a protective lacquer. This is good as the controller lives near the pool, potentially exposed to the elements and pool chemicals. However, it makes readings the IC markings a bit challenging. Eventually, I got the details by using a magnifying glass and illuminating the board with a torch from different angles. One of the eight-pin ICs is a 5V regulator, the 64-pin is the PIC microcontroller (a PIC18F6XK22) and the siliconchip.com.au Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column in SILICON CHIP? If so, why not send those stories in to us? It doesn’t matter what the story is about as long as it’s in some way related to the electronics or electrical industries, to computers or even to cars and similar. We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. other 8-pin IC is a Microchip MCP7940N real-time clock. I checked its supply voltage, and it was correct. The clock chip is equipped with an I2C serial interface and the PIC microcontroller also has I2C lines. Following the tracks, I could see the connections between them. So it looks like the PIC microcontroller ‘outsources’ timekeeping to the clock chip. I used an oscilloscope to check what was happening on the I2C serial clock and serial data pins. As expected, there was activity on setting the time, and each time the display entered the clock and timer status display. I checked the external oscillator pin and the signal looked OK. Since, apart from the clock, all other functions seemed to be working, I thought the clock chip was not doing its job. If it were the PIC microcontroller, I would have no hope as I don’t have the software to program a new one, but I thought that replacing the clock chip would fix the problem. I ordered a compatible MCP79400 in the SOIC package. After replacing the chip on the PCB, I connected the ribbon cable to the power board and plugged in the unit. I entered the time and waited for the display to circle to show the clock and timer. The clock did not return to 00:00, the time was now correct, and after a minute, it advanced. So the clock was now working. All that was left was to apply some protective lacquer over the new chip and put the controller back together, which was the reverse of the disassembly procedure. I was pleased that I saved the controller from ending up a junk SC pile in this ‘throw-away society’. The AstraPool pool chlorinator is now keeping the correct time after replacing the MCP7940N/MCP79400 real-time clock/calendar (RTCC) IC. Australia's electronics magazine May 2022  91 By John Clarke LED Lighting & Driver Kits from Oatley Electronics Oatley has four LED kits that can be driven from the one generalpurpose LED Driver, using a 12V DC source such as a battery. Battery-powered LED lighting is ideal for outdoor use, such as camping, in sheds or on small boats, where mains power is not available. Different lighting options suit various purposes ranging from wide coverage to more concentrated floodlighting. T he Oatley Electronics K491 LED Driver runs from a 12V supply and is included in one of four kits: K491PK1, K491PK2, K491PK3 or K491PK4. All four kits include various combinations of white LEDs. The K491 LED Driver is supplied as a kit in all four cases. It needs to be assembled by mounting the supplied components onto the PCB. There are not many parts to install, and the inductor is prewound, so it all goes together pretty quickly. Then it’s just a matter of wiring the Driver up to the supplied white LED lamps. Lighting options The four kits are as follows: 1) K491PK1 This kit includes the Driver plus four LED lamps in conical aluminium housings with reflectors to concentrate the light, as shown above. The four lamps are connected in parallel and driven at 35W total (or 8.75W per lamp). Because they are rated at 60W each, they are significantly under-driven, which means that they run cool and the lamp life should be very long. 2) K491PK2 This kit includes the Driver plus two 1.2m-long 18W tubes, similar in appearance to fluorescent tubes but containing strings of white LEDs instead. Again, they are driven in Table 1 – kit LED lighting options Kit Driver LEDs supplied LED connection Driven power Driving voltage Inductor tap R1 value K491PK1 K491 Four 60W LED lamps parallel 35W 20V DC 16 turns 0.05W K491PK2 K491 Two 1.2m-long 18W LED tubes parallel 28W 33V DC 12 turns 0.05W K491PK3 K491 Two 0.6m-long 8W LED tubes parallel 14W 50V DC 16 turns 0.1W K491PK4 K491 Two 12W LED floodlights parallel 20W 50V DC 16 turns 0.05W 92 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.1 (above): this circuit shows the basic operating principle of a DC-DC converter. Fig.2 (right): the block diagram of the Motorola MC34063 DC-DC converter, which is used in the LED driver. parallel but a bit closer to their ratings at 28W total (14W per tube). Still, they are under-driven, so they run relatively cool and should last a while. 3) K491PK3 This is similar to K491PK2, but you get the Driver plus two shorter 0.6m-long tubes rated at 8W each. They are driven in parallel at 14W, so 7W per lamp, just a bit under their rated power. 4) K491PK4 This version has the Driver plus two 12W LED floodlights. These are IP65 rated, so they can be left out in the weather. They include substantial heatsinking and adjustable mounting brackets. They are rated at 12W each and are driven at 20W total or 10W per lamp, so again, they are not being run at full power, extending their lifespans, while still providing a decent amount of light. Table 1 summarises these four configurations and has a few extra details that are needed to customise the Driver for each set of lamps. K491 LED Driver The K491 LED Driver is used in all four kits. The Driver can be set up for each lamp type by setting the tapping on the inductor with a wire bridge, and by changing the value of resistor R1 on the PCB. This LED Driver is designed to drive 10-40W of LED lighting from a 12V supply. It is a DC-DC boost converter based around an MC34063 controller IC. The LED lamps can comprise between three and 15 LEDs connected in series. The LEDs may be combined into a cluster, with a combination of series and parallel connections. White LEDs light up with around 3.0-3.3V across their terminals. When siliconchip.com.au connected in series, the overall voltage to drive them increases accordingly, with between 9V and 9.9V required to drive three LEDs in series. This rises to between 45V and 49.5V for 15 LEDs in series. Fig.1 shows the basic operating principle of the DC-DC converter. It incorporates an inductor, a diode, a switch and a capacitor. When switch S1 is closed, current flows through the inductor L1 and S1. L1 stores energy in its magnetic flux. When S1 opens, that energy is transferred, via diode D2, to the output filter capacitor and the load. In practice, the switch is a transistor or Mosfet, and the on and off times of the transistor’s conduction are varied to maintain the desired load voltage or current. The internal details of the Motorola MC34063 DC-DC converter controller IC are shown in Fig.2. It contains all the necessary circuitry to produce a step-up, step-down or inverting DC-to-DC converter. Its internal components comprise a 1.25V reference, a comparator, an oscillator, an RS flipflop and output transistors Q1 and Q2. The switching frequency is set by the capacitor connected to pin 3 of this IC. A 330pF capacitor sets it at about 90kHz (measured as 96kHz on our prototype). The oscillator is used to drive the flip-flop which, in turn, drives the output transistors. The inductor current is sensed at pin 7. When this reaches its peak, the flip-flop and the output transistors are switched off. The time for which the output transistors are switched on is determined by the comparator, which monitors the output voltage. When the pin 5 comparator input exceeds the 1.25V Australia's electronics magazine reference, indicating that the output voltage exceeds the required level, the comparator goes low. This resets the flip-flop, holding the transistors off. Conversely, if the output voltage is too low, the inverting input of the comparator will be below the 1.25V reference, so the output transistors can be toggled on by the RS flip-flop at the rate set by the oscillator. In voltage-regulation mode, the target output voltage is set using a voltage divider that applies a fixed fraction of the output voltage to feedback pin 5. However, if the circuit is configured so that the target output voltage is never reached and voltage to pin 5 is always below the reference, the circuit then operates in current-limited mode. In this case, the peak current sets the duty cycle, and this plus the inductance of L1 sets the average current delivered to the load. Circuit details The complete circuit of the Driver is shown in Fig.3. The internal transistors of IC1 are connected as a 93 The assembled Driver has just four wires connected: two for power in (at right) and two going to the LEDs (at left). Darlington to drive the gate of Mosfet Q2 high via diode D1, to switch it on. Q2 acts as the switch (S1) shown in Fig.1. When pin 2 of IC1 goes low to turn off Mosfet Q2, PNP transistor Q1 switches on to discharge Q2’s gate capacitance, giving a rapid turn-off. When Q2 is on, current begins to flow in inductor L1. Resistor R1 (0.1W or 0.05W) between pins 6 & 7 of IC1 sets the peak current delivered to the inductor. IC1 does this by switching off Q2 when the voltage across R1 reaches 0.33V. So the peak current is limited to 3.3A when R1 is 0.1W or 6.6A when it is 0.05W. Each time Q2 is switched off, the voltage at its drain rises because of the energy stored in inductor L1. As the current can no longer flow in Q2, it is diverted through diode D2 instead, flowing into the two 100μF 63V electrolytic capacitors, the 47nF ceramic capacitor and the load. Diode D2 is a schottky type with a fast response to cope with the high switching frequency of about 96kHz. It also has a low forward voltage, reducing power dissipation and improving efficiency. Voltage regulation is provided by the feedback network from the output to pin 5, mainly the 43kW resistor from the output and the 1kW resistor to ground. The output voltage is maintained when the voltage at pin 5 equals the internal reference of 1.25V. The 43kW and 1kW resistors reduce the voltage by a factor of 44 ([1kW + 43kW] ÷ 1kW). So the output voltage is limited to 1.25V × 44 = 55V. This voltage regulation protects the Mosfet (Q2) and the output capacitors from excessive voltage should the LED lamp load become disconnected or if the circuit is run without a load. Power for the circuit is from a 12V DC supply, with supply filtering provided by another two 100μF 63V electrolytic capacitors plus a second 47nF ceramic capacitor. Power delivery Remember that the average current delivered to the load via diode D2 is less than the peak current in L1, and power to the load depends on the value of the inductor and the peak current. For this circuit, the inductor is tapped to select an inductance that provides a suitable power output for the particular LED lighting load that’s connected. Fig.3: the circuit diagram for the LED driver kit from Oatley Electronics. 94 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.5: the overlay diagram of the LED Driver. Note that one of the resistors near IC1 is marked as 39kW on the PCB silkscreen but should be 43kW as shown here. L1 has taps at four, eight, 12 and 16 turns. The power versus LED voltage graph (Fig.4) shows the typical power levels for various configurations. Note that the power shown in this graph is the power drawn from the battery and not that delivered to the load. The efficiency of the circuit is high, so the graph gives a reasonable idea of the power delivered to the load. Construction Construction involves inserting and soldering the parts onto the PCB. Follow the overlay diagram, Fig.5, for the correct placement of each component. Begin with the 1/4W resistors, including the 0W resistor (used as a wire link). The colour coding for these is shown in the parts list, but you should check each value with a multimeter to ensure each is placed in the correct position. Note that R4 on the PCB screen print is marked as a 39kW resistor, but it should be 43kW. Fit diode D1 next, noting that the cathode (striped end) is to the left. IC1 can also be mounted now, taking care to orientate it as shown. Fig.4: the typical power level for various configurations of the LED cluster. Note that this graph shows the power drawn from the battery. siliconchip.com.au Australia's electronics magazine R1 is installed as either one or two 0.1W 1W resistors (R1a & R1b), with two resistors giving the 0.05W total resistance. There are four sets of holes for these resistors. For the K491PK3 kit requiring 0.1W, install either R1a or R1b but not both. You can use straight leads. For the other kits, fit both resistors and bend the leads, as shown in Fig.5. Install inductor L1 next. You can check that it is in the correct orientation by verifying that the lower five sets of pins on the right-hand side have wires attached to them on the former. If not, you need to rotate it by 180°. Solder all the pins of L1 and then fit transistor Q1, taking care to orientate it correctly. Follow with the four ceramic capacitors, which are not polarised, then the four 100μF electrolytic capacitors, which are polarised. Ensure that each electrolytic capacitor’s positive side (with the longer lead) goes in the top PCB hole in all cases. Next, install diode D2. If an SR1060 is supplied, this will come in a TO-220 package, and it must be fitted with the metal tab towards the top of the board. However, our sample kit came with an SR350 in an axial package. In this case, it is mounted vertically, with the cathode (striped end) to the left. The anode should be placed in the right PCB hole, with the diode body upright and the cathode lead bent over by 180° to insert into the left PCB hole. Leave the diode body about 5mm above the PCB for improved cooling. Mosfet Q2 comes in a TO-220 package, and it is mounted with the tab toward the edge of the PCB, and with the mounting hole 15mm above the May 2022  95 PCB. After soldering it, slip the heatsink over it; it is secured with spring pressure. You could add an M3 x 6mm screw and nut to further secure it if you want to. Inductor tap selection On the underside of the PCB are the tapping selections for inductor L1, shown at the right of Fig.5. You need to connect a wire link from pin 13 on the underside of L1 to the COM connection. Then, connect either the 12T tap or 16T tap (see Table 1) by soldering in one of the dashed wire links. Only one of these should be fitted. The power input is via wires or pins soldered to the +12V IN and GND terminals at the upper right and lower right of the PCB, respectively. It is crucial to connect the input supply with the correct polarity to the K419 Driver, as there is no reverse polarity protection. Also ensure that you connect the LED arrays with the right polarity, with all the common anodes to the V+ OUT terminal at upper left, and the common cathodes to the GND terminal at lower left. If soldering the input and output wires directly to the PCB (as we expect most constructors would), it’s good practice to add some form of strain relief to prevent the solder joints from fracturing. Parts List – Oatley LED Kits 1 set of LED lights (see Table 1 for kit options) 1 single-sided PCB coded K419, 92 x 64mm 1 prewound multi-tapped inductor (L1) 1 TO-220 clip-on heatsink Semiconductors 1 MC34063AP DC-DC converter, DIP-8 (IC1) 1 C8550 PNP transistor, TO-92 (Q1) 1 IRFZ44Z 55V 31A 13.9mW N-Channel Mosfet, TO-220 (Q2) 1 1N5817, 1N5818 or 1N5819 1A 20-40V schottky diode, DO-41 (D1) 1 SR350 50V 3A schottky diode, DO-41 (D2) OR 1 SR1060 60V 10A schottky diode, TO-220-2 (D2) Capacitors 4 100μF 63V electrolytic 3 47nF ceramic disc 1 330pF ceramic disc Resistors (all 1/4W, 1% unless otherwise noted) 1 43kW 2 1kW 1 22W 2 0.1W 1W 1 0W You could do this by adding a reasonable amount of neutral cure silicone sealant around each wire, holding them to the PCB while limiting the amount of flexing that can occur. Preparing the tubes The K491PK3 kit contains two 0.6m-long tubes. As supplied, they include an internally-installed LED driver that was designed for use with AC mains voltage. This needs to be removed by undoing the screws that hold the end caps in position and removing the end caps. Then, cut the white wires so that the installed driver module can be removed. Next, cut the red and black wires that connect between the LEDs and the driver module near to the Driver, and drill holes in the end cap so these red and black wires can pass through. Then replace the end caps. The red and black wires connect to the K419 driver output, red to V+ OUT and black to GND. Availability & pricing At the time of writing, the K491PK4 kit is $42, K491PK2 is $40, and the other two kits are $30 each. Postage is around $10 in most cases, although it might be a bit more depending on how many you order. You can order these kits and more details on the Oatley Electronics site: SC siliconchip.com.au/link/abd1 The K491PK4 version of the kit comes with these two 12V floodlights instead of the LED lamps. The K491PK2 version comes with the two 1.2m 18W tubes shown below, while the PK3 instead comes with the shorter 0.6m 8W tubes. 96 Silicon Chip Australia's electronics magazine siliconchip.com.au Subscribe to APRIL 2022 ISSN 1030-2662 04 9 771030 266001 $ 50* NZ $1290 11 500 INC GST INC GST POWER WATTS AMPLIFIER The History of Transistors Australia’s top electronics magazine DELIVERS 500W RMS INTO A 4Ω LOAD Geiger Counters and Measuring Radioactivity Part two Silicon Chip is one of the best DIY electronics magazines in the world. Each month is filled with a variety of projects that you can build yourself, along with features on a wide range of topics from in-depth electronics articles to general tech overviews. Rosehill GaRdens , sydney – 5-6 a pRil Published in Silicon Chip If you have an active subscription you receive 10% OFF orders from our Online Shop (siliconchip.com.au/Shop/)* Rest of World New Zealand Australia * does not include the cost of postage Length Print Combined Online 6 months $65 $75 $50 1 year $120 $140 $95 2 years $230 $265 $185 6 months $80 $90 1 year $145 $165 2 years $275 $310 6 months $100 $110 1 year $195 $215 2 years $380 $415 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. Try our Online Subscription – now with PDF downloads! Geiger Counters and Measuring Radiation; April 2022 500W Power Amplifier; April 2022 History of Transistors; March 2022 An online issue is perfect for those who don’t want too much clutter around the house and is the same price worldwide. Issues can be viewed online, or downloaded as a PDF. To start your subscription go to siliconchip.com.au/Shop/Subscribe CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Simple stereo microphone This design lays little claim to originality but might inspire some legendary recordings. I plugged it into a CD-quality digital stereo dictation device (at a low gain selected) to record the echo of Cape Town’s noonday gun rolling off Table Mountain. When heard on a hifi stereo system, the final result is stunning. The originality of the design does not lie in the circuit itself. Two omnidirectional microphone inserts are mounted half a metre to one metre apart, pointed in opposite directions. This makes a very noticeable difference over a typical stereo microphone, where two electret microphones are often mounted quite close together (such microphones fail to take basic psychoacoustics into account). This circuit gives the most striking results with fairly sharp sounds—the noonday gun, or dogs barking, or a clap of thunder. More confusing sounds, such as crickets chirping, city traffic, or children playing, may not produce the most striking stereo result. I used a dual low-noise JFET input op amp for gain. The result is extremely sensitive, pushing against the bounds of the possible. You can reduce its sensitivity by lowering the values of the 10kW feedback resistors. Be sure to use a good-quality screened microphone cable and solder the screen to 0V. A useful wireless charger Wireless chargers have many applications apart from charging phones and toothbrushes, but standard “Qi” power transmitters and receivers have disadvantages – limited power and the inability to drive low-impedance loads. I wanted to charge two 10F 2.7V supercapacitors in series, which act as a 5F, 5.4V capacitor. This load looks like a short circuit to a Qi chipset and it will go into overload shut-down protection mode. A non-Qi wireless charger is much easier to design, and a push-pull configuration uses fewer components than a full bridge. However, it does require a centre-tapped output coil. An approximate sinewave results if the output 98 Silicon Chip filter capacitor is 220nF, but the Mosfets and the 220nF capacitor get hot. Therefore, I am using 47nF, which is enough for spike suppression to protect the Mosfets. This capacitor and the Mosfets only get warm when charging a discharged 5F capacitor to 5V in less than 30 seconds. With a minimal air gap, it will charge in 15 seconds. I am not using resonant charging, so a sinewave is not necessary. A suitable matching wireless power receiver circuit is shown. I bought Qi charger modules from AliExpress only for the coils – they are amazingly cheap. The method of making a centre-tapped coil from two standard coils is shown in my Australia's electronics magazine The circuit draws less than 2mA, so battery life is of little concern. An audio editor may be used to reduce hiss in the recording if desired. Thomas Scarborough, Cape Town, SA. ($75) YouTube video (https://youtu.be/ xnIhMQ2O7C4). The UCC2808-2 driver IC will run from 5V and has push-pull outputs which directly drive logic-level Mosfets, as shown in its typical application circuit. A helpful website to refer to when designing wireless chargers is www. wirelesschargingcoil.com There are also two interesting, related videos. One is about designing a 3.3kW wireless inductive power transfer system with 95% efficiency over a 10cm air gap (https://youtu. be/xEUnBNL8Dyk). The other is on DIY wireless energy transfer systems (https://youtu.be/3E5PUnYlaTM). John Russull, Kratie, Cambodia. ($120) siliconchip.com.au Lithium-ion battery reconditioner A lot of modern gadgets are discarded that contain perfectly good Li-ion batteries. This project allows you to give those batteries a new life and use them in your projects. It is based on a Micromite LCD BackPack with a touchscreen and supports 1-4 cell batteries. After carefully removing the battery from the device, fit a protection circuit if it doesn’t already have one. These are available on eBay for a few dollars with different modules to manage different numbers of cells. They monitor the voltages of each cell, and if a cell is overcharged, overdischarged or excessive current is drawn, the whole battery is disconnected. These are good for the safety and longevity of the cells, but they do not balance the cells. This circuit is not designed to charge cells rapidly; instead, it charges and discharges the cells slowly and safely. In discharge mode, it monitors the cell voltage and disconnects it when it reaches 3.6V. There is also a 12-hour timer to limit the maximum discharge time. When charging, a regulated 4.2V supply with current limiting is used. The voltage and current are monitored, and charging stops when the current drops to around 50mA, but a timer will also stop the charging after 24 hours. When the circuit is first powered, it cycles through the cells continuously to check the voltages. If you want to determine the capacity of a cell, select the cell and then press Discharge. The circuit will connect an 8.2W resistor across the cell and discharge it until it reaches 3.6V. A graph is displayed showing the last two minutes (or so) of the discharge history, with separate lines for voltage (blue) and current (red) – see the screen photo. It disconnects the cell and provides an estimate of the capacity in mAh. If you select a cell and then press Charge, the cell will be charged until the charge current drops to around 50mA, after which the charger is disconnected. A graph shows the charge current and voltage for the last two minutes or so. The Charge All and Discharge All buttons do the same but for all the cells in the battery, in sequence. Measuring the capacity of the cells allows you to create batteries with cells of similar capacity. By charging each cell individually, you can ensure the battery is correctly balanced and provides maximum capacity. The circuit is powered by a 12V DC plug pack; 1A should be sufficient. The core of the circuit is an LM317 regulator set to 4.2V by the ratio of the 110W resistor and the 100W resistor in series with the trimpot. The 1N5404 diode ensures the circuit will power off correctly if the power is disconnected while charging. The 0.1W sense resistor limits the current that can be supplied but is also used to monitor the charge current, by measuring the voltage across it. The pairs of 100kW/47kW resistors reduce Transmitter Receiver siliconchip.com.au Australia's electronics magazine May 2022  99 the monitored voltages to levels that can be safely applied to the Micromite analog inputs. For typical Li-ion cells, the charge current will start at about 0.5A and drop to 50mA when fully charged. If the cell is short-circuited, the LM317 will supply up to about 1.5A. A heatsink is required as the regulator drops around 8V at around 0.5A. You could reduce power dissipation by using a 7.5V supply. The regulator operates as a single-­ cell charger but is switched to each individual cell using the relays in an 8-channel relay module. This can be 100 Silicon Chip purchased from eBay or Jaycar (Cat XC4418), and is a cheap way to get many relays, but it also has additional isolation and driver circuitry. RLY1 allows the cells to be connected either to the charger regulator or across an 8.2W 10W resistor (5W is sufficient but 10W is better). RLY2 isolates the cells from the load or charger. The cells are disconnected when it is off, but their voltage can still be monitored. Relays 3-8 are used to switch between the four cells. The Micromite Backpack displays the curves and provides the user interface. Any version of the BackPack with Australia's electronics magazine a 320x240 pixel screen should work. Power for the BackPack is derived from the incoming 12V DC using a prebuilt DC-DC converter with a 5V output. The software is written in Micromite BASIC, making it easy to change parameters like timeout values. It is named “Lithium-ion Battery Reconditioner.bas” and is available for download from siliconchip.com.au/ Shop/6/6366 The timeouts and other parameters are clearly marked in the source if you wish to tailor them to suit your requirements. Dan Amos, Macquarie Fields, NSW. ($110) siliconchip.com.au Motion-triggered ESP32-based WiFi camera captures intruders The ESP32-CAM is a small module you can buy with an onboard ESP32 with WiFi plus a camera. By adding a small PIR sensor, you can set it up to take pictures of intruders secretly. By the nature of the module, very few I/O pins are free. IO4 is used to enable an onboard bright LED that acts as an extra light source for the camera. GPIO13 is used as the trigger input pin for taking pictures, either by pressing pushbutton S1 or when triggered by the passive infrared (PIR) motion detector. When a photo is taken, the program stamps the time on the filename and then stores it serially on the onboard siliconchip.com.au micro SD card. The ESP32 is then put into deep sleep mode after taking a picture. GPIO13 is used to trigger wake-up from deep sleep mode. This allows the device to be battery-powered, preserving battery power during the idle time when no picture is being taken. GPIOs 1 & 3 are used to drive an I2C serial bus that connects to the OLED display and the DS3231 realtime clock. Note that you will need a PIR sensor that can run from 5-9V. The bottom part of the circuit diagram shows how to configure the ESP32-CAM to take photos when motion is detected. The real-time Australia's electronics magazine clock is used to timestamp the photos while the display lets you check that the camera is working correctly as it displays status messages each time it is triggered. The display could be left out, or unplugged after the unit is set up, as it will work without it. As mentioned earlier, the module is woken up and triggered by pulling GPIO13 to ground. It’s essential that this happens reliably, and I’ve found the best way to do it is via an optoisolator. The opto-isolator connection to the PIR sensor is easy and works perfectly every time. You can download the software from siliconchip.com.au/Shop/6/6440, then compile and upload it to the module using the Arduino IDE. As the ESP32CAM does not have a built-in USB interface, a USB-to-serial adaptor is required to upload the sketch, connected as shown in the top section of the circuit diagram. GPIO0 needs to be pulled to ground to enable uploading, which is the purpose of switch S3. The module’s onboard button should be pressed during the first few seconds of uploading, then released. Bera Somnath, Vindhyanagar, India. ($120) May 2022  101 101 Vintage Radio Calstan Model 559M2 AM/SW superhetrodyne By Fred Lever This set is an important part of Australian radio history, yet it’s a bit of a mystery. I can find little information on this model and it looks very hastily made, especially the timber cabinet, which seems to have been thrown together. However, it’s a decent performer and mostly just needed cosmetic repairs. I purchased this radio (serial number 10538) from eBay in a non-­ working condition. From the photos in the eBay listing, I could see that some of the knobs and back-plate were missing and the dial was not in good condition. In summary, the radio was looking a bit sad (see Figs.1 & 2), so I decided to rescue it. My first move was to remove the chassis and have a closer look (Fig.3). The chassis was complete, with 1960s style components and no thought given to neatness; it was just wired point-to-point (see Fig.4). The first repair I undertook was to sort out the dial stringing, as the pointer had fallen off the top of the dial and was hanging loose. All that I really needed to do was free up the seized spindle and pulleys and put the pointer back where it came from; that returned it to operating condition. Unable to find any details of this model, I sketched the circuit diagram (Fig.5) and found it to be close to that of a previous model 549 but with an updated IF valve, changed from the 6BA6 type to a 6N8. The type of components used suggests the set was made in the late 1960s or early 1970s. The Rola 7000/3-5 output transformer has a date stamp of 30 October 1968 (Fig.6), and there are plenty of model numbers on the chassis, but there is no ARTS&P sticker. The set uses an MSP 8C oval speaker, labelled MSP 6.4/M A/3 50018. Who was Calstan? Calstan was a brand name for testing equipment designed and made by Charles Slade pre-1939 for the radio Figs.1 & 2: the Calstan (also known as Slade) 559M2 radio was initially provided in ‘worn’ state, with some knobs missing and the dial a bit scuffed. 102 Silicon Chip Australia's electronics magazine siliconchip.com.au industry. It is said that the name Calstan is short for “Calibrated Standard”, which suits the excellence of the products made by Slade. Neville Williams wrote an article for Electronics Australia about Charles Slade (November 1992, pages 14-17). Post-war, Slade concentrated on selling radios from Slade Radio Pty Ltd in Lang St, Croydon in Sydney (near Burwood and, interestingly, quite close to the site of a Jaycar store today). It is said that the Zenith Radio Company were also involved, and there are references to later Calstan radios being produced by Zenith. Whoever made it, this radio is a sound design electronically, but the cabinet is very crude with no frills in the design or construction. It does not look like a receiver Zenith would have made. The whole thing shouts low-volume and possibly even madeto-order. Fig.4: the underside of the chassis had been assembled using pointto-point wiring, despite the radio looking like it was produced in the 1960s. Getting it going This set had not been powered for a long time, so it took some time to reform the filter capacitors using a low applied AC voltage via a variac. With that done, the set worked, but it had very weak volume. A simple resistor check revealed that the 470kW plate resistor on the 6AV6 was open-circuit. It was one of those tiny half-watt IRC carbon resistors, so I replaced it with a 1W resistor. The set then worked normally. Its performance is quite good; I didn’t measure its sensitivity, but the set is very lively and capable of generating Fig.3: a quick look at the topside of the chassis showed that it was complete, without any parts noticeably missing. siliconchip.com.au Australia's electronics magazine May 2022  103 Fig.5: this circuit diagram for the Calstan model 559M2 is very similar to the previously released model 549 from 1954. Note the available connections for both an internal and external speaker. up to 18V on the AGC line, with an ample sound level. Luckily, that was the only electronic repair I had to make. The converter is a conventional set-up using a 6BE6 pentagrid with tuning gang control and a changeover switch to select between the AM (broadcast) and SW (shortwave) bands. The full valve lineup is 6BE6, 6N8, 6AV6, 6AQ5 and 6V4. The intermediate frequency transformers (IFTs) are AP1008 52 types. I noted that the IFTs have damping resistors on the primaries; presumably, that was done to broaden the response of the coils by lowering their Q figures. The first three valves run with grounded cathodes and bias is applied by the AGC feedback line to all control grids. The intermediate frequency (IF) amplifier valve is a 6N8, using the pentode section with the two internal diodes unused. The set has a simple AGC system, with the voltage derived from the diodes residing in the 6AV6 audio amplifier that also demodulate the IF to produce the audio signal. Audio is fed, via the volume control, to the 6AV6. That then feeds a self-biased 6AQ5 which drives the 7kW coupling transformer. The tone control circuit is quite complicated, being part of the negative feedback loop with both low-volume bass boost and a top-cut roll-off control. A phono/radio switch is fitted, allowing for a ‘pickup’ feed-in socket. The power supply is standard, with a 6V4 full-wave rectifier feeding a ‘T’ filter with two RC pi filters to smooth the 180V HT supply and Fig.6: the output transformer had the date 30 October 1968 stamped on it. Fig.7: the words “WARD 1. P.P.C” can be seen pencilled into the case. Fig.8: I cleaned and re-glued the cabinet as it was showing its age. Circuit design 104 Silicon Chip Australia's electronics magazine siliconchip.com.au also a 220V tap-off point to power the output stage. Repairing the cabinet With the set going, I turned my attention to the cabinet. It is just a timber box with no frills, 350mm wide and 200mm high. It’s possible that there never was a rear panel as the whole thing looks “cheap as”. I found the inside of the box was interesting as the maker had pencilled markings on it and did not bother to remove them, including one mysterious label which reads “WARD 1. P. P. C.” (Fig.7). Some of the plies were separating from the base timber, so I added some strengthening bits, glued the lifting plies down, bogged it up and sanded the whole thing back – see Fig.8. The front cloth cleaned up nicely with fabric cleaner, looking almost new. I applied a turps-based sealer and, once dry, a same-brand gloss coat to the timber. The wretched thing fish-eyed with something leeching through the sealer, disturbing the gloss coat badly (Fig.9). Talk about disasters in the paint shop! While that was drying, I brushed a turps-based black coat on the inside (Fig.10). I finished it off by spraying the knobs gold and cutting a piece of scrap Perspex for a back panel to prevent burnt fingers (shown below). I tarted the chassis and speaker up a bit by cleaning them and applying some gloss spray, then reassembled the set. The gloss coat took about a month to harden, so that was another painting disaster! I still need to add Letraset labels for the controls onto the front of the refinished cabinet. The knob functions from left-to-right are tone control, volume control, power switch, band switch and tuning. I have seen pictures of Calstan radios with white letter transfer legends above the controls and a cast gold-coloured metal logo, but this set had neither. I’ll have to put something on the controls, but I won’t worry about the logo as the dial has the Calstan logo at the top. Fig.9: a fabric cleaner was used on the front panel cloth, and a gloss coat to the timber cabinet. Fig.10: a black coat of paint was then applied to the inside, and the front knobs sprayed gold. Fig.11: the chassis was then remounted inside the cabinet with the MSP speaker, measuring 9 x 6-inches and rated at 15W. After mounting the chassis, the rear of the cabinet was sealed with a piece of clear Perspex as a safety measure (see the photograph below). Conclusion I think this set is an important part of Australian radio history. I have not seen another one of this model. It was probably among the last made with the Calstan name, possibly from leftover stock and scrap parts, hence the awful woodwork. Still, it’s worth preserving, I think. SC siliconchip.com.au Australia's electronics magazine May 2022  105 SILICON CHIP .com.au/shop ONLINESHOP HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 139, COLLAROY, NSW 2097 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 05/22 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS 24LC32A-I/SN ATmega328P ATmega328P-AUR ATtiny85V-10PU ATtiny816 PIC10F202-E/OT PIC10LF322-I/OT PIC12F1572-I/SN PIC12F617-I/P Digital FX Unit (Apr21) RF Signal Generator (Jun19), Si473x FM/AM/SW Digital Radio (Jul21) RGB Stackable LED Christmas Star (Nov20) Shirt Pocket Audio Oscillator (Sep20) ATtiny816 Development/Breakout Board (Jan19) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) Range Extender IR-to-UHF (Jan22) LED Christmas Ornaments (Nov20; versions), Nano TV Pong (Aug21) Car Radio Dimmer (Aug19), MiniHeart Heartbeat Simulator (Jan21) Refined Full-Wave Universal Motor Speed Controller (Apr21) Model Railway Level Crossing (two required – $15/pair) (Jul21) Range Extender UHF-to-IR (Jan22) PIC12F617-I/SN Model Railway Carriage Lights (Nov21) PIC12F675-I/P Motor Speed Controller (Mar18), Heater Controller (Apr18) Useless Box IC3 (Dec18) PIC12F675-I/SN Tiny LED Xmas Tree (Nov19) PIC16F1455-I/P Microbridge (May17), USB Flexitimer (June18) Digital Interface Module (Nov18), GPS Finesaver (Jun19) Digital Lighting Controller LED Slave (Dec20) PIC16F1455-I/SL Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) PIC16F1459-I/P Ultrasonic Cleaner (Sep20), Electronic Wind Chime (Feb21) 20A DC Motor Speed Controller (Jul21) Fan Controller & Loudspeaker Protector (Feb22) PIC16F15214-I/SN Improved SMD Test Tweezers (Apr22) PIC16F1705-I/P Flexible Digital Lighting Controller Slave (Oct20) Digital Lighting Controller Translator (Dec21) ATSAML10E16A-AUT PIC16F1459-I/SO PIC16F18877-I/P PIC16F88-I/P High-Current Battery Balancer (Mar21) Four-Channel DC Fan & Pump Controller (Dec18) USB Cable Tester (Nov21) UHF Repeater (May19), Six Input Audio Selector (Sep19) Battery Charge Controller (Dec19), Railway Semaphore (Apr22) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21) Touchscreen Digital Preamp [2.8in/3.5in version] (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) PIC32MX795F512H-80I/PT Touchscreen Audio Recorder (Jun14) $20 MICROS ATmega644PA-AU dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT AM-FM DDS Signal Generator (May22) 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) $30 MICROS PIC32MX695F512L-80I/PF Colour MaxiMite (Sep12) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC SLOT MACHINE (MAY 22) - Micromite Plus BackPack kit without touchscreen (Cat SC6211) - DFPlayer Mini module (Cat SC4789) - Set of laser-cut 3mm acrylic pieces for front panel & coin slot (Cat SC6181) 500W AMPLIFIER HARD-TO-GET PARTS (CAT SC6019) $45.00 $5.00 $10.00 (APR 22) All the parts marked with a red dot in the parts list (see p32), including the 12 output transistors, driver transistors, VAS transistors, input pair (2SA1312), BAV21 & UF4003 diodes, TL431 ICs, 75pF capacitor, E96 series resistors and 10kW 1W resistor $200.00 IMPROVED SMD TEST TWEEZERS KIT (CAT SC5934) (APR 22) RASPBERRY PI PICO BACKPACK KIT (CAT SC6075) (MAR 22) CAPACITOR DISCHARGE WELDER (MAR 22) INTELLIGENT DUAL HYBRID POWER SUPPLY (FEB 22) Complete kit with PCBs, all onboard parts, new microcontroller and gold-plated header pins to use for the tips. Does not include a lithium coin cell $35.00 Complete kit, includes all parts except the optional DS3231 IC $80.00 Parts for the Power Supply – includes the power supply PCB, IC1-3, D1, the 1W shunt and sole SMD capacitor (Cat SC6224) $25.00 Parts for the ESM – includes one ESM PCB, IC8, Q3 & Q4 (IRFB7434G), D9 plus the SMD capacitors and resistors (Cat SC6225) → 8-14 sets typically needed $20.00ea Hard-to-get parts for the regulator module – all the ICs & regulators ◉ needed to build one module, plus the schottky diode, 10μH inductor, 4700μF 50V capacitors, 1W shunts and SMD capacitors – does not include PCB (Cat SC6096) $125.00 ◉ does not include the LM2575T as it comes with the CPU module parts Hard-to-get parts for the CPU module – most of the required parts, including programmed PIC32MZ, EEPROM, LM2575T, LM317 & LD1117V regulators etc. You just need the PCB, headers, a ferrite bead, trimpot and electrolytic capacitors (Cat SC6121) $60.00 IR-TO-UHF MODULE FOR RANGE EXTENDER (CAT SC5993) (JAN 22) SMD TRAINER COMPLETE KIT (CAT SC5260) (DEC 21) HUMMINGBIRD AMPLIFIER (CAT SC6021) (DEC 21) PCB and all SMDs (including the programmed micro) for the IR-to-UHF module Includes PCB & all on-board components, except for a TQFP-64 footprint device Hard-to-get parts includes: two 0.22W 5W resistors; plus one each of an MJE15034G, MJE15035G, KSC3503DS & 220pF 250V C0G ceramic capacitor $25.00 $20.00 $15.00 siliconchip.com.au/Shop/ USB CABLE TESTER KIT (CAT SC5966) (NOV 21) MODEL RAILWAY CARRIAGE LIGHTS KIT (CAT SC6027) (NOV 21) NANO TV PONG SHORT FORM KIT (CAT SC5885) (AUG 21) MICROMITE LCD BACKPACK V3 KIT (CAT SC5082) (AUG 19) Short form kit with everything except case and AA cells Includes PCB, IC1 (programmed), IC2, D1, L1, SMD capacitors and resistors. Does not include reed switch, magnet, LEDs or through-hole parts PCB and all onboard parts only (does not include controllers) $110.00 $25.00 $17.50 Includes PCB, programmed micros, 3.5in touchscreen LCD, UB3 lid, mounting hardware, Mosfets for PWM backlight control and all other mandatory on-board parts $75.00 Separate/Optional Components: - 3.5-inch TFT LCD touchscreen (Cat SC5062) $35.00 - DHT22 temp/humidity sensor (Cat SC4150) $7.50 - BMP180 (Cat SC4343) OR BMP280 (Cat SC4595) temp/pressure sensor $5.00 - BME280 temperature/pressure/humidity sensor (Cat SC4608) $10.00 - DS3231 real-time clock SOIC-16 IC (Cat SC5103) $4.00 - 23LC1024 1MB RAM (SOIC-8) (Cat SC5104) $5.00 - AT25SF041 512KB flash (SOIC-8) (Cat SC5105) $1.50 - 10µF 16V X7R through-hole capacitor (Cat SC5106) $2.00 - MCP1700 3.3V LDO regulator (suitable for USB M&K Adapator, Feb19) $1.50 VARIOUS MODULES & PARTS - 0.96in SSD1306-based yellow/blue OLED (AM-FM DDS, May22, SC6421) - Pulse-type rotary encoder (AM-FM DDS, May22, SC5601) - DS3231 real-time clock SOIC-8 IC (Pico BackPack, Mar22) - DS3231MZ real-time clock SOIC-16 IC (Pico BackPack, Mar22) - 4-pin PWM fan header (Fan Controller, Feb22) - 64x32 pixel white 0.49in OLED (SMD Test Tweezers, Oct21) - pair of AD8403ARZ10 (Touchscreen Digital Preamp, Sep21) - Si4732 radio IC (Si473x FM/AM/SW Radio, Jul21) - EA2-5NU relay (PIC Programming Helper, Jun21) - VK2828U7G5LF GPS module (Advanced GPS Computer, Jun21) - MCP4251-502E/P (Advanced GPS Computer, Jun21) - pair of Signetics NE555Ns (Arcade Pong, Jun21) - 2.8-inch touchscreen LCD module (Lab Supply, May21) - Spin FV-1 digital effects IC (Digital FX Unit, Apr21) $10.00 $3.00 $4.00 $7.50 $1.00 $10.00 $35.00 $15.00 $3.00 $25.00 $3.00 $12.50 $25.00 $40.00 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # P&P prices are within Australia. Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT 3.5-INCH LCD ADAPTOR FOR ARDUINO DSP CROSSOVER (ALL PCBs – TWO DACs) ↳ ADC PCB ↳ DAC PCB ↳ CPU PCB ↳ PSU PCB ↳ CONTROL PCB ↳ LCD ADAPTOR STEERING WHEEL CONTROL IR ADAPTOR GPS SPEEDO/CLOCK/VOLUME CONTROL ↳ CASE PIECES (MATTE BLACK) RF SIGNAL GENERATOR RASPBERRY PI SPEECH SYNTHESIS/AUDIO BATTERY ISOLATOR CONTROL PCB ↳ MOSFET PCB (2oz) MICROMITE LCD BACKPACK V3 CAR RADIO DIMMER ADAPTOR PSEUDO-RANDOM NUMBER GENERATOR 4DoF SIMULATION SEAT CONTROLLER PCB ↳ HIGH-CURRENT H-BRIDGE MOTOR DRIVER MICROMITE EXPLORE-28 (4-LAYERS) SIX INPUT AUDIO SELECTOR MAIN PCB ↳ PUSHBUTTON PCB ULTRABRITE LED DRIVER HIGH RESOLUTION AUDIO MILLIVOLTMETER PRECISION AUDIO SIGNAL AMPLIFIER SUPER-9 FM RADIO PCB SET ↳ CASE PIECES & DIAL TINY LED XMAS TREE (GREEN/RED/WHITE) HIGH POWER LINEAR BENCH SUPPLY ↳ HEATSINK SPACER (BLACK) DIGITAL PANEL METER / USB DISPLAY ↳ ACRYLIC BEZEL (BLACK) UNIVERSAL BATTERY CHARGE CONTROLLER BOOKSHELF SPEAKER PASSIVE CROSSOVER ↳ SUBWOOFER ACTIVE CROSSOVER ARDUINO DCC BASE STATION NUTUBE VALVE PREAMPLIFIER TUNEABLE HF PREAMPLIFIER 4G REMOTE MONITORING STATION LOW-DISTORTION DDS (SET OF 5 BOARDS) NUTUBE GUITAR DISTORTION / OVERDRIVE PEDAL THERMAL REGULATOR INTERFACE SHIELD ↳ PELTIER DRIVER SHIELD DIY REFLOW OVEN CONTROLLER (SET OF 3 PCBS) 7-BAND MONO EQUALISER ↳ STEREO EQUALISER REFERENCE SIGNAL DISTRIBUTOR H-FIELD TRANSANALYSER CAR ALTIMETER RCL BOX RESISTOR BOARD ↳ CAPACITOR / INDUCTOR BOARD ROADIES’ TEST GENERATOR SMD VERSION ↳ THROUGH-HOLE VERSION COLOUR MAXIMITE 2 PCB (BLUE) ↳ FRONT & REAR PANELS (BLACK) OL’ TIMER II PCB (RED, BLUE OR BLACK) ↳ ACRYLIC CASE PIECES / SPACER (BLACK) IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION USB SUPERCODEC ↳ BALANCED ATTENUATOR SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS DATE MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 JUN19 JUN19 JUN19 JUN19 JUL19 JUL19 JUL19 AUG19 AUG19 AUG19 SEP19 SEP19 SEP19 SEP19 SEP19 SEP19 OCT19 OCT19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 DEC19 JAN20 JAN20 JAN20 JAN20 JAN20 FEB20 FEB20 MAR20 MAR20 MAR20 APR20 APR20 APR20 APR20 MAY20 MAY20 JUN20 JUN20 JUN20 JUN20 JUL20 JUL20 JUL20 JUL20 JUL20 JUL20 AUG20 NOV20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 PCB CODE Price 24111181 $5.00 SC5023 $40.00 01106191 $7.50 01106192 $7.50 01106193 $5.00 01106194 $7.50 01106195 $5.00 01106196 $2.50 05105191 $5.00 01104191 $7.50 SC4987 $10.00 04106191 $15.00 01106191 $5.00 05106191 $7.50 05106192 $10.00 07106191 $7.50 05107191 $5.00 16106191 $5.00 11109191 $7.50 11109192 $2.50 07108191 $5.00 01110191 $7.50 01110192 $5.00 16109191 $2.50 04108191 $10.00 04107191 $5.00 06109181-5 $25.00 SC5166 $25.00 16111191 $2.50 18111181 $10.00 SC5168 $5.00 18111182 $2.50 SC5167 $2.50 14107191 $10.00 01101201 $10.00 01101202 $7.50 09207181 $5.00 01112191 $10.00 06110191 $2.50 27111191 $5.00 01106192-6 $20.00 01102201 $7.50 21109181 $5.00 21109182 $5.00 01106193/5/6 $12.50 01104201 $7.50 01104202 $7.50 CSE200103 $7.50 06102201 $10.00 05105201 $5.00 04104201 $7.50 04104202 $7.50 01005201 $2.50 01005202 $5.00 07107201 $10.00 SC5500 $10.00 19104201 $5.00 SC5448 $7.50 15005201 $5.00 15005202 $5.00 01106201 $12.50 01106202 $7.50 18105201 $2.50 04106201 $5.00 04105201 $7.50 04105202 $5.00 08110201 $5.00 01110201 $2.50 01110202 $1.50 24106121 $5.00 16110202 $20.00 16110203 $20.00 16111191-9 $3.00 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE BK1198 AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION ADVANCED GPS COMPUTER PIC PROGRAMMING HELPER 8-PIN PCB ↳ 8/14/20-PIN PCB ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) + 2 JOINERS ↳ JOINER ONLY (1pc) TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR 2-/3-WAY ACTIVE CROSSOVER TELE-COM INTERCOM SMD TEST TWEEZERS (3 PCB SET) USB CABLE TESTER MAIN PCB ↳ FRONT PANEL (GREEN) MODEL RAILWAY CARRIAGE LIGHTS HUMMINGBIRD AMPLIFIER DIGITAL LIGHTING CONTROLLER TRANSLATOR SMD TRAINER 8-LED METRONOME 10-LED METRONOME REMOTE CONTROL RANGE EXTENDER UHF-TO-IR ↳ IR-TO-UHF 6-CHANNEL LOUDSPEAKER PROTECTOR ↳ 4-CHANNEL FAN CONTROLLER & LOUDSPEAKER PROTECTOR SOLID STATE TESLA COIL (SET OF 2 PCBs) REMOTE GATE CONTROLLER DUAL HYBRID POWER SUPPLY SET (2 REGULATORS) ↳ REGULATOR ↳ FRONT PANEL ↳ CPU ↳ LCD ADAPTOR ↳ ACRYLIC LCD BEZEL RASPBERRY PI PICO BACKPACK AMPLIFIER CLIPPING DETECTOR CAPACITOR DISCHARGE WELDER POWER SUPPLY ↳ CONTROL PCB ↳ ENERGY STORAGE MODULE (ESM) PCB 500W AMPLIFIER MODEL RAILWAY SEMAPHORE CONTROL PCB ↳ SIGNAL FLAG (RED) DATE NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 JUN21 JUN21 JUN21 JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 AUG21 SEP21 SEP21 OCT21 OCT21 OCT21 NOV21 NOV21 NOV21 DEC21 DEC21 DEC21 JAN22 JAN22 JAN22 JAN22 JAN22 JAN22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 MAR22 MAR22 MAR22 MAR22 MAR22 APR22 APR22 APR22 PCB CODE 16109201 16109202 16110201 16110204 11111201 11111202 16110205 CSE200902A 01109201 16112201 11106201 23011201 18106201 14102211 24102211 10102211 01102211 01102212 23101211 23101212 18104211 18104212 10103211 05102211 24106211 24106212 08105211 CSE210301C 11006211 09108211 07108211 11104211 11104212 08105212 23101213 23101214 01103191 01103192 01109211 12110121 04106211/2 04108211 04108212 09109211 01111211 16110206 29106211 23111211 23111212 15109211 15109212 01101221 01101222 01102221 26112211/2 11009121 SC6204 18107211 18107212 01106193 01106196 SC6309 07101221 01112211 29103221 29103222 29103223 01107021 09103221 09103222 Price $12.50 $12.50 $5.00 $2.50 $7.50 $2.50 $5.00 $10.00 $5.00 $2.50 $5.00 $10.00 $5.00 $12.50 $2.50 $7.50 $7.50 $7.50 $5.00 $10.00 $10.00 $7.50 $7.50 $7.50 $5.00 $7.50 $35.00 $7.50 $7.50 $5.00 $15.00 $5.00 $2.50 $2.50 $5.00 $1.00 $12.50 $2.50 $15.00 $30.00 $10.00 $7.50 $5.00 $2.50 $5.00 $5.00 $5.00 $5.00 $7.50 $2.50 $2.50 $7.50 $5.00 $5.00 $7.50 $20.00 $25.00 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $2.50 $5.00 $5.00 $5.00 $25.00 $2.50 $2.50 AM-FM DDS SIGNAL GENERATOR SLOT MACHINE MAY22 MAY22 CSE211002 08105221 $7.50 $5.00 NEW PCBs We also sell an A2 Reactance Wallchart, RTV&H DVD, Vintage Radio DVD plus various books at siliconchip.com.au/Shop/3 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. Send your email to silicon<at>siliconchip.com.au Capacitor options for the CD Welder Regarding the Capacitor Discharge Spot Welder project in the March 2022 edition (siliconchip.com.au/ Series/379), can I use a Maxwell 16V 500F supercapacitor bank with your design? The capacitor bank is made of six 2.7V 3000F capacitors connected in series. They are said to have a low ESR, and these banks are being marketed for vehicle engine starting instead of a conventional lead-acid battery. I have one of these capacitor banks on hand and am wondering if I could use it to handle the power delivery. The weld pulse duration may have to be considerably shortened. (C. B., Bonville, NSW) ● The design of the CD Welder is based on using a relatively large number of capacitors because each ESM with 2-3 capacitors also has a pair of Mosfets. This way, the Mosfets only have to switch relatively low currents (around 50A each or 100A per ESM). What you have is effectively one large capacitor. That means you need a single ‘switch’ that can handle something in the region of 1000A. When we designed the CD Welder, we spent a lot of time ensuring that it could safely switch the currents. The spreadsheet providing this analysis is available for download from our website, as it forms an important part of the design, even if not great reading. Note that as your supercapacitor has 500 times the capacitance of our bank, there will be significant safety issues in the case of failure of the switching system, as it stores 500 times the energy. To use your supercapacitor as the basis of a CD Welder, you could use our Controller Module as-is and take inspiration from the switching part of the Energy Storage Module to make a switching module that can handle switching your supercapacitor into a low resistance. You will likely need ten sets of Mosfets and associated switching drivers. So yes, it probably is possible, but it will require a redesign. 108 Silicon Chip If you do this, we strongly recommend that you download that spreadsheet and build a model of the system, as the cost of getting this sort of design wrong is high! HDMI-based projects are not practical Could you please tell me if you have ever done a composite or component video to HDMI project? I have a couple of old DVD/VHS players, which I would like to be able to feed to the TV via an HDMI input. I believe this would make an interesting project, especially if it could be adapted to different requirements with inputs/outputs such as HDMI, composite, component, S-video, VGA etc. I have been a subscriber for many years and look forward to receiving my copy each month. (B. S., Kogarah, NSW) ● We agree that it could be an interesting project, but unfortunately, the licensing requirements for HDMI and the HDCP protocol make it impossible. The licensing feed for HDMI alone for low-volume production is US$5000 per year plus $1 per unit. HDCP costs are on top of that. Your best bet is to buy something like Altronics A3503 or Jaycar AC1722. It’s doubtful that even if we could design such a device, we could do it with a total parts bill less than either of those devices. Pico BackPack troubleshooting I built the Pico BackPack kit (March 2022; siliconchip.com.au/Article/ 15236), but I have a problem with the TFT touch function using PicoMite Basic. The calibration function fails with a hardware error message when the second target location is touched during the GUI Calibrate procedure. If I load the MicroPython demo, none of the touch buttons work. Loading “PicoMite DemoV5.uf2” only shows a blank screen. Unfortunately, Australia's electronics magazine I don't have another touchscreen to substitute. Please help me to resolve this problem. (A. E., Colyton, NSW) ● Check the soldering on the micro SD card socket. A short circuit on the socket will interfere with the touch functions as they share the same SPI bus. Check for continuity between all the pairs of SPI pins, and each SPI pin to ground. If you find a short, that will explain your problem. It’s also a good idea to examine all the solder joints under magnification, looking for solder bridges. Most likely, the fault is with the MISO line since a fault on any other SPI line would almost certainly prevent the TFT from showing an image. If you still can’t see anything wrong with it, try removing the socket (eg, with hot air) as you could have solder or something else conductive under the socket, shorting out its pins. Note that the Micromite Plus BackPack (November 2016; siliconchip. com.au/Article/10415) and the D1 Mini LCD PackPack (October 2020; siliconchip.com.au/Article/14599) have similar designs, so they too can have touchscreen problems if the micro SD card socket has a soldering problem. Remote Control Range Extender fixed Thanks for your advice on troubleshooting my Remote Control Range Extender (January 2022; siliconchip. com.au/Article/15182) that you published in Ask Silicon Chip, April 2022 (page 116). I followed those steps but still can’t figure out why it isn’t working. I think there might be something wrong with the programming of the PIC12F617 in the UHF-to-IR receiver. Can you look at my unit and check if that chip has been correctly programmed? (R. M., Ivanhoe, Vic) ● We received the device sent by R. M. and got it working. We found that the UHF receiver (RX1) was installed backwards, so the data and antenna connections were grounded. siliconchip.com.au We de-soldered it, flipped it around, re-soldered it, and the unit started working. Interestingly, the receiver used appears to be the Altronics Z6905A, but it looks somewhat different from the Altronics receivers we have purchased in the past. The trimmer is in the centre of the UHF module while it is offset on the photo on the Altronics website. Also, the unit we were sent lacks the pin labels shown in the photo on their website. We noticed another difference: this receiver has a fast-operating automatic gain control (AGC) return. Full sensitivity is achieved between repeated remote control codes, causing more noise in the reception. We were initially concerned about this, but further testing revealed that it works just as well as the Jaycar receivers, even though they have a slower AGC function. We also checked the programming of the three PIC12F617s sent to us, along with the PIC10LF322 on the transmitter, and all were correct. Note that for the transmitter, the value of the 100kW pull-down resistor we specified (but not installed in this unit) turned out to be a bit high. We now recommend using a 1kW pulldown resistor instead, to ensure the pull-up is disabled when this resistor is fitted. SD cards and keyboard for Colour Maximite 2 I believe the SD card is obsolete. So, what type of SD cards can be used on the Colour Maximite 2 (August & September 2021; siliconchip.com.au/ Series/368), and can you use a micro SD card with an adaptor? My second question is, what types of USB keyboards are guaranteed to work on the CMM2? Can I use a USB to PS/2 adaptor to use a USB keyboard on the original Colour Maximite? (R. M., Melville, WA) ● Geoff Graham replies: while micro SD cards are now more common, neither full-size nor micro SD cards are obsolete. You can use a full-size SD card or a micro SD card with an adaptor (often supplied with the card) on the CMM2. Both work equally well. A typical keyboard that works well is the Logitech K270, which is wireless and low in cost. Other keyboards that have been tested and work include: Logitech K120, K400+ or K800; HP siliconchip.com.au SK2885; Lenovo KU-0225; and Microsoft 600. Keyboards with a built-in mouse function (ie, a trackpad) will not work because they have a built-in USB hub, and the CMM2 keyboard port does not support hubs. It is also possible that some regular keyboards will not work. This is rare, and the reason for it is not clear, so it would be worthwhile trying a few different ones if you run into problems. All of this is covered in the user manual: siliconchip.com.au/link/abdj Waterproofing jet ski ignition system Recently, you helped with recommendations for a Capacitor Discharge Ignition system on a two-cylinder, two-stroke jet ski from the 1980s I am rebuilding, a project still underway. One of the challenges is waterproofing or potting the circuits to ensure they survive the wet areas. Initially, I need the circuits open and modifiable as I merge and adapt cabling, trigger coils, the CDI etc. But as soon as possible, I want to protect the circuits with a water barrier. Have you covered the options for water protection, limitations or risks around digital or higher-frequency circuits and keeping the circuits removable and repairable? What are the options for sealing connectors (like dielectric grease) in hostile environments like boat motors? (L. C., Donvale, Vic) ● The easiest way to waterproof electronics is to house it within an IP67 enclosure. IP65 or IP66 will probably not be sufficient for a jet ski due to the water pressure involved. These are available made from ABS, polycarbonate or diecast aluminium. The diecast versions are ideal where heat needs to be dissipated or RF shielding is required. Any cable entry to the enclosure should be made using IP68 cable glands (Jaycar Cat HP0720, HP0724 etc) or IP67 connectors (Jaycar Cat PP1000 etc). Neutral-cure silicone can be used for extra waterproofing around seals and wire entry points, although this can be hard to remove once cured. Potting electronics is not ideal, reducing heat dissipation and practically eliminating any hope of repairs. Unless the circuit is low in cost or needs to be operated in extremely Australia's electronics magazine harsh conditions, we don’t recommend potting. For operation under extreme conditions, potting may be the only solution to preventing damage to the electronics. A full seal around the closing edges (using silicone if necessary) is better than potting since it’s easier to reverse. It would also be a good idea to spray both sides of the boards with a conformal coating before placing them in the enclosures so that if a little bit of water does get in, it’s less likely to cause damage. You can usually solder through these coatings to make changes or repairs. Our experience using IP65 enclosures underwater shows that water will creep inside any cabling that lies in the water, allowing water to enter the enclosure, corroding the wiring and electronics inside. The water eventually penetrates the outer cable sheath and runs along the inside. So waterproofing the cable sheath is necessary. PVC tubing can be used for this. Some cable types can also be purchased with a gel filling to help prevent water penetration. Omitting designators from circuits I have a question for you, although I think I know the answer. Why don’t you number resistors and capacitors? It would be much easier to say “R1” instead of something like “the resistor from the input to 0V”. I’m guessing it’s because there’s not enough room on the PCBs for both component numbers and values, and it was decided that having values on the PCB would result in fewer errors. (D. H. Sorrento, WA) ● Your assumption is basically correct. There are obvious advantages to numbering resistors and capacitors, but there are disadvantages too. As you point out, there often isn’t room to print both designators and values on a PCB, so if we chose to print the designators, constructors would need to refer to a parts list for the value of every single component. That will slow down assembly and increase the chance of mistakes. So the initial assembly becomes more difficult. Having the designators definitely helps with troubleshooting, but since most boards assembled ought to work first time (given that we’ve already tested the designs), we’d be optimising the less common scenario. May 2022  109 Also, adding designators to circuit diagrams makes them significantly more cluttered and harder to follow. That was probably the main reason we stopped doing it. We would certainly print designators if we were producing commercial products assembled by machines. In that case, we would only need to refer to the printed labels for troubleshooting and repairs. Reducing air compressor power I bought a small air-bed compressor to drive my melodica (a sort of winddriven keyboard). I want to reduce the airflow to suit this task as I am too asthmatic to blow into it for more than a minute or so. It's rated at 2.5A/600W, but I don't want to pull it apart in case something goes "sproing!" and is lost forever. Short of tying a knot in the hose or otherwise blocking it (which could damage the compressor), would a 240/120V stepdown transformer with an adaptor work, or perhaps one of your motor speed controllers? There are no further specs about the motor of any use. (D. H., North Gosford, NSW) ● It’s hard to say without knowing much about the motor, but we think the motor speed would likely be reduced by decreasing the supply voltage. So you could probably use a variac, step down transformer or our Refined Full-Wave Motor Speed Controller (April 2021; siliconchip.com. au/Article/14814). There also appear to be much lower power air pumps available that would be more suited to powering your melodica without having to alter the pump motor speed. For two more methods of powering a melodica that we definitely don’t recommend, see the video at https:// youtu.be/8_9C3Q9AAEc Arduino LC Meter not calibrated correctly I have built your Arduino-based Inductance/Capacitance Meter (June 2017; siliconchip.com.au/Article/ 10676). It works perfectly in both modes (L/C), but inductance mode only works correctly if the variable "CF" is removed from this line of code: CXval = C1val * CF * (float(F1sqrd/F3sqrd) - 1.0); 110 Silicon Chip Without this change, only the frequency is shown correctly; the inductance is always displayed as "Over Range!". Are you help me? (A. Z., via email) ● CF is the calibration factor. It seems as if that variable does not have a compatible value. This suggests that your problem may be due to one of the following causes: 1. you did not perform the calibration procedure when you first powered up the project; 2. when you attempted calibration, you may have forgotten to insert the jumper shunt LK1 first; 3. you did not fit a low-inductance shorting bar across the test terminals before performing calibration; 4. you did not remove the jumper shunt from LK1 immediately after performing calibration (before powering the unit up again). Any of these could result in the calibration factor (CF) having a value that is not compatible with the meter’s operation. Balancing lithium-ion batteries I have a device with two Li-ion cells in series driving a DC-DC boost converter giving 14V output to drive a circuit (up to 0.7A peak for less than three seconds). I’d like to charge the batteries while they are still in the device using a three-pin connector and external charger. I’m currently using two Li-ion 18650s, but I’d also like to try LiFePO4. I’ve noticed some voltage differences between the two cells, so a simple 8.4V (7.2V for LiFePO4) charger might not always be safe. Is it practical to have a plug-in power supply with positive and negative outputs, so both cells can be charged independently while connected in series inside the device? The charger output should be able to deliver up to 0.8A but a maximum of 0.5A would be safer, to suit 16003000mAh cells. I don’t want the cells to be shorted out or overcharged in the process. This would save me unscrewing the box and removing batteries to go into the usual one- or two-cell chargers. (T. C., Penrith, NSW) ● Balance-charging Li-ion cells is very common and there are many products on the market to do it, both as standalone chargers and as Battery Australia's electronics magazine Management Systems (BMSs) that you can leave permanently connected to the cells. Because these are so common and cost so little, it doesn’t make much sense for us to design one. Having said that, we have published at least two Cell Balancers to date, and we’re working on another one. You could consider building the Battery Pack Cell Balancer from March 2016 (siliconchip.com.au/Article/9852), although it’s probably overkill for your application. We sell the PCBs and all the parts for that project: siliconchip. com.au/Shop/?article=9852 You could also consider simply purchasing a balance charger like the iMax B3, available for under $20 on eBay with free delivery. It could be wired up via a 3-pin plug and socket. However, probably the simplest and cheaper option is to fit one of the many 2S Li-ion protection/cell balance/BMS boards available for just a few dollars. For example, see www.ebay.com.au/ itm/253968033970 Many of these claim to balance the cells during charging. Then you just need to apply the 8.4V or 7.2V charging voltage and let the BMS equalise the cell voltages. How mains capacitor/ zener supplies work Have you ever considered doing an article on capacitor-drop power supplies? I recently repaired the infrared-­ controlled three-speed fan in my workshop and found it to be a frustrating experience due to my lack of knowledge. The problem was that after switching it on with the remote, the fan locked up and could only be switched off at the mains. Many would argue that with the low cost of replacement, why bother? But as a hobby, the enjoyment of repairing such a thing is hard to beat. I have a mains isolation transformer that made the job a lot easier. The fault was with the 1μF X2 capacitor; it was down to a very low value. I know that you have done many projects using such power supplies in the past. (P. W., Montmorency, Vic) ● We went into detail on how this type of power supply works on pages 32, 34 & 35 of the April 2012 issue (siliconchip.com.au/Article/705). That article described a mains-powered Soft continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip FOR SALE FOR SALE KIT ASSEMBLY & REPAIR LEDsales DAV E T H O M P S O N (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, NZ but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDs and accessories for the DIY enthusiast PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. SILICON CHIP ASSORTED BOOKS FOR $5 EACH Selling assorted books on electronics and other related subjects – condition varies. Some of the books may have already been sold, but most are still available. Bulk discount available; post or pickup. All books can be viewed at: siliconchip.com.au/link/aawx Email for a postage quote, quote the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au TRONIXLABS PTY LTD would like to thank all of our customers for their support and feedback. For any enquiries or customer technical support, please email support<at>tronixlabs.com KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com Lazer Security For Quality That Counts... QUALITY LED PRODUCTS + MORE The parts clearance sale continues, but stock is limited, this month check out the freebies – go to lazer.com.au PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. 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 Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine May 2022  111 Advertising Index Altronics.................................11-18 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Hare & Forbes..........................OBC Jaycar.............................. IFC,53-60 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.................. 5 Mouser Electronics....................... 7 Ocean Controls............................. 9 PMD Way................................... 111 SC USB Cable Tester.................. 75 Silicon Chip Pico BackPack...... 42 Silicon Chip Subscriptions........ 97 Silicon Chip Shop............ 106-107 The Loudspeaker Kit.com.......... 89 Tronixlabs.................................. 111 Wagner Electronics....................... 8 Starter we designed that used that type of power supply, and it explained how it worked. Fundamentally, they are pretty simple. At a fixed frequency (50Hz for our mains supply), the impedance of a capacitor is inversely proportional to its value. So with a capacitor connected in series with the supply, the current drawn depends on the capacitor value; double the value, and you roughly double the current that the device draws. The capacitor applies the mains voltage waveform to a bridge rectifier, with its output voltage being clamped by a zener diode or similar to produce a DC rail. Since the capacitor limits the current being fed in, the zener is not destroyed and the desired supply voltage is achieved. So the capacitor value is chosen based on how much current the circuit will consume; making it larger than necessary will just waste power, and if it's too small, the desired supply voltage will not be achieved. So any significant drop in capacitance is likely to stop the device from working. The only solution is to replace that capacitor. Unfortunately, it is not uncommon for X2 capacitors to lose capacitance over time. Money and space pressure sometimes cause manufacturers to choose capacitors that are physically too small to be reliable. Also, by the nature of the way X2 safety capacitors are designed, being exposed to voltage spikes (eg, caused by nearby lightning) will often cause them to lose capacitance. Question about an old project I can’t find anything on your website about the PCB used in the September 1992 LCD Readout. I have the used PCB here for testing; the code on it is 00921. I’d love to make a spare as this unit has become well worn. Mostly I use it for testing displays before fitting them to other equipment. Is this PCB pattern available? I have been subscribed since the early 1980s. I may be able to find the magazine in my attic storage, it would take some time, and it’s hot up there. (J. P., Shailer Park, Qld) ● 00921 does not look like a Silicon Chip PCB code as our codes are usually eight digits long. We can’t find any projects in September 1992 called “LCD Readout”, but there is a General-Purpose 3 1/2Digit Panel Meter project (siliconchip.com.au/Article/5520) that uses an LCD screen. Presumably, that is the one you are referring to. Its PCB code is 04110921, similar to the code you provided. We don’t sell many PCBs from that long ago (as there is virtually no demand), nor do we have any CAD or other computer files for that designs before about 1995. The pattern was published in the article on page 85. It looks like it was made with tape, not on a computer, which is likely why we don’t have any files from back then. We have scanned the PCB pattern, cleaned it up, and added the image to our website’s PCB Patterns download section (siliconchip.com.au/ Shop/10/6329). SC Notes & Errata Dual Hybrid Power Supply part two, March 2022: in Fig.11 on page 85, the metal sheet for the heatsink folds up where shown, not down. Also, the hole in the heatsink should be drilled 25mm from the left edge, not 30mm. Note that link LK1 on the control board, shown in Fig.13 on page 86, needs the shorting block in the upper RDO position, not the lower SDO4 position. Finally, instead of the 15μF tantalum capacitors specified, non-polarised 15μF 50V X7R M5750/2220 ceramics can be used. We supply those in the kits as they are superior to the tantalum caps in virtually every way. Remote Control Range Extender, January 2022: if needed, the optional pull-down resistor at pin 1 of the IC1 (PIC10LF322) on the transmitter should be 1kW rather than 100kW as originally specified. This lower value ensures the resistor is reliably detected and the internal pull-up is always disabled. Programmable Hybrid Lab Supply with WiFi, May & June 2021: on p74 of the June issue, Fig.7 shows the copper layers swapped and thus the SMD components are shown placed on the wrong side of the board and mirrored. The actual locations of some of these parts can be seen in the photo at the bottom of p75 of the same issue, and the diagram has been corrected in the June 2021 online issue. This means that two 1.8kW resistors are under the ESP-32 module. The June 2022 issue is due on sale in newsagents by Thursday 26th of May. Expect postal delivery of subscription copies in Australia between May 24th and June 10th. 112 Silicon Chip Australia's electronics magazine siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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