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JULY 2022 ISSN 1030-2662 07 9 771030 266001 $ 50* NZ $1290 11 INC GST e t i M o c i P VGA a powerfu l, bu t simple Raspberry Pi-based computer ANYCUBIC Photon Mono 3D Printer Review Build our Multimeter Calibrator & Checker INC GST Keep your electronics operating in IPX R ATEX D Harsh Conditions WATER RESISTANT SWITCH PANELS FOR BOATS OR RVS FROM 7495 $ Marine Switch Panels LOCKING LATCHES FOR EASY ACCESS • IP66 water resistant • Integrated 6-20A circuit breakers • LED illuminated switches • Pre-wired - easy install 4 Way SZ1906 | 6 Way SZ1907 Sealed Diecast Aluminium Boxes • IP65 dust and hoseproof • Internal guide slots • 6 sizes from 64Wx58Dx35Hmm to 222Wx146Dx55Hmm • Flanged versions available HB5030-HB5050 Industrial ABS Enclosures • IP66 weatherproof • Stainless steel hardware • Supports DIN rail components • 2 sizes HB6404-HB6412 FROM 1395 $ Switches for wet & dusty conditions 19 $ FROM 3695 $ STRONG, SAFE & SEALED 95 EA Durable Metal Pushbuttons • IP67 dust & waterproof • 12V LED illuminated (red, green or blue) • DPDT momentary action • SPDT with blue power symbol SP0800-SP0810 FROM 14 $ 95 Illuminated Pushbuttons • IP65 dust & water resistant • Momentary or On/Off • DPDT SP0741-SP0749 Explore our wide range of harsh environment products, in stock on our website, or at over 110 stores or 130 resellers nationwide. Other harsh environment products include: • 15 x Sealed IP65 Polycarbonate Enclosures • 14 x Sealed IP65 ABS Enclosures • 9 x ABS Instrument Cases with Purge Valves • Range of Waterproof Multi-pin Connectors, including Deutsch-type • Range of Sealed Rocker & Toggle Switches • 10 Waterproof Cable Glands jaycar.com.au/iprated 1800 022 888 Contents Vol.35, No.7 July 2022 14 IC Fabrication, Part 2 Shrinking node sizes and cutting-edge EUV (extreme ultraviolet) lithography machines are just a few of the topics covered in the next instalment of our series on how integrated circuits are made. By Dr David Maddison Semiconductors 41 Anycubic Photon Mono 3D printer This 3D printer from Anycubic is an affordable resin-based printer. The resin is cured by a UV light that passes through a 2K resolution LCD screen (4K in the new version). Resin is available in multiple colours and brands. By Tim Blythman & Nicolas Hannekum 3D printer review 68 Oatley Solar Charge Controller Oatley Electronics have two new solar charging kits which are suitable for charging 12V and 24V lead-acid batteries. Included with the controllers are a single 16W solar panel or two 16W panels respectively. By John Clarke Solar device review 83 PAS CO2 Air Quality Sensor In this article we cover the Infineon XENSIV PAS air quality sensor module. PAS (photoacoustic spectroscopy) sensors work by determining how gas particles absorb specific wavelengths of infrared light. By Jim Rowe Low-cost electronic modules 31 Multimeter Calibrator & Checker Our Multimeter Checker can verify how accurate your multimeters are. It can also be used to calibrate meters and adjust for drift. It can calibrate AC and DC voltage, direct current, frequency and resistance ranges. By Tim Blythman Test equipment project 52 VGA PicoMite With just a Raspberry Pi Pico and minimal extra components, you can build this amazingly capable BASIC computer. It has a 640 x 480 pixel VGA output, PS/2 keyboard input and uses an SD card for storage. By Geoff Graham & Peter Mather Raspberry Pi project 62 0-110dB RF Attenuator This 0-110dB RF Attenuator is designed to be used with the AM/FM Signal Generator from the May 2022 issue. Still, you can use it with just about any signal generator to provide output level adjustments in 1dB steps. By Charles Kosina Test equipment project 72 Secure Remote Mains Switch, Pt1 Our Remote Mains Switch has up to 68m line-of-sight range and can handle one to 16 transmitters per receiver. It can switch up to 30A at 250V AC, includes an adjustable timer and uses a secure UHF rolling code. By John Clarke Mains power project Multimeter -Checker -Calibrator Page 31 Page 62 110dB RF Attenuator Page 72 Secure Remote MAINS SWITCH 2 Editorial Viewpoint 4 Mailbag 78 Circuit Notebook 82 Product Showcase 86 Serviceman’s Log 93 Subscriptions 94 Vintage Radio 1. Switching on external devices via a TV 2. Variable L-pad speaker volume control 3. Transmitting in the FM broadcast band 4. Plugpack voltage and current monitor Astor CJ-12 car radio by Dr Hugo Holden 105 Ask Silicon Chip 106 Online Shop 111 Market Centre 112 Advertising Index 112 Notes & Errata 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 (resigned) 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 – M.Ed. 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 Low-cost UPSes are not worth the risk Ten or more years ago, purchasing an uninterruptible power supply (UPS) for a computer or other piece of critical equipment was quite expensive. Usually, you would have to buy a brand like APC. While their quality was reasonable, those units had very few features and cost a few hundred dollars for even a moderately-sized one. But more recently, many less-expensive units have come onto the market. These are very tempting because if you only need a basic UPS, you don’t want to pay hundreds of dollars more for what seems to be essentially the same thing. But these cheap units are usually too cheap. They come with low-quality batteries and have dumb charging schemes, often without proper battery management or thermal cut-outs. As a result, you’re lucky if the battery lasts more than a year or two. Even decent quality gel cell (SLA) batteries will generally not last more than a couple of years in these devices. When the battery inevitably fails, it can leak acid and overheat badly. While I haven’t heard of any such units catching fire, it doesn’t seem impossible. I had one of these fail on me, and it got stinking hot and reeked of acid. I had to disassemble the UPS to get the badly distorted and swollen battery out. More recently, I have heard from several other people who have had similar experiences with various low-cost UPS brands. I went into a bit more detail about my bad experience and what I did to prevent it from happening again in an article in the January 2020 issue titled “Emergency backup power during blackouts” (siliconchip.au/Article/12215). While it is a somewhat more expensive solution initially, buying an inverter/ charger and a separate, high-quality battery (AGM or LiFePO4) is much better. This approach lets you independently select the maximum power and backup time requirements. Battery replacement is easy, and the battery will last a lot longer. A decent AGM battery designed for standby use should have a useful life of at least five years, while a top-quality unit might last ten. Consider that most low-cost UPSes only offer a ‘runtime’ of around 10 minutes at full load. In contrast, the inverter/charger solution can maintain its output for hours without mains power. Even days, if that’s what you need. The long-term cost of this type of solution may not be that much higher than a cheap UPS because you won’t have to replace the battery as often. That means less maintenance and less chance of catastrophic battery failure. That’s partly because you aren’t stuck with gel cells but also because you can locate it outside the main unit, where cooling air can better circulate. If you must use a low-cost UPS, I suggest taking the battery out before you even use it and checking to see if it is a decent-quality unit. If not, immediately replace it with a higher-quality equivalent and either sell the battery that came with it or use it for another less-critical purpose. It would also be worth checking whether the UPS you buy has a thermal cutout to stop charging the battery if it fails. If you can’t see a temperature sensor near the battery, it probably doesn’t. I won’t suggest that you add a thermal cut-out if one is missing because I don’t have the space to describe how to do that properly. Ultimately, I think it isn’t worth dealing with a poorly-designed low-cost UPS. If possible, buy a better one or try the inverter-charger option I mentioned above. Ongoing mail delays Apologies to readers who received their May issues late (or not at all). They were mailed on-time but soon after came the Easter and Anzac Day public holidays, terrible weather and general postal chaos. Unfortunately, it seems that the postal system is not stable yet and might not be for some time. We mail out the magazines consistently in the middle of the previous month, but we are at the mercy of inconsistent delivery times. 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”. Reason for bundled mains cables On page 4 of the May 2022 issue, George Ramsey mentions bundled overhead mains cables. These cables have been in use in Victoria for at least two decades. They are used in areas of heavy forest or bushfire-prone areas. While installation may be cheaper, they are really used to increase safety. If a tree branch falls on open wires, they break and fall to the ground, leaving eight active wires, which can cause electrocution or start fires. If a branch falls on a bundled cable, it will break and fall, but the active ends will still be insulated, so the fallen cable is relatively safe. If the ends short, this will trip the circuit breakers and shut off the power. The chance of starting a fire from the ends is relatively small because the live area is so small. If exposed to fire, the insulation will melt and the exposed cables will short together, once again tripping the breakers. The cable may then break, but there is no danger of increasing the fire or harming people with no power applied. David Tuck, Yallourn North, Vic. More on bundled mains cables I’m writing regarding the letter from George Ramsay and the following comment in the May 2022 issue about aerial mains cables. We have had aerial bunched/bundled cables in Victoria for over 20 years. I think they were probably initially developed with bushfire areas in mind, to reduce the risk of sparking from open wire mains installations contacting vegetation. They also arguably have less visual impact; although the cable is much thicker, there are fewer cross-tees and insulators, along with less leakage and RF noise due to dust build-up on the insulators. They also allow for a somewhat reduced distance for vegetation clearance, which gained support from fringe Melbourne councils, concerned about severe tree pruning around power lines. John Anwin, Healesville, Vic. Vintage Test Gear giveaway Over many years, I have amassed quite a collection of ‘vintage’ test equipment, some made in Australia and some imported from overseas. They have all been acquired legally – some donated by friends, others salvaged from now-defunct magazines and companies, and some purchased by myself. I have now reached an age where I am happy to give these items away to anyone interested in taking them 4 Silicon Chip – to give them ‘a good home’. Here is the list of equipment on offer: 1 × Advance OS1000A analog CRO (2 × 20MHz?) 1 × Kikusui COS5100 analog CRO (2 × 100MHz) 1 × AWA analog CRO (5-inch) 1 × AWA F242A Distortion & Noise Meter 1 × AWA G-233 Ultra Low Distortion Audio Generator (10Hz to 110kHz) 1 × AWA Type 3R7231 RF Signal Generator SN 184 (big and very heavy) 1 × AWA Beat Frequency Oscillator Type R-7077 1 × Kikusui KSG4100 FM/AM Signal Generator2 x Palec SG-1 RF Signal Generators (SN 50, 269) 1 × Palec SA06-69 All Wave Oscillator 1 × Advance RF Signal Generator Type E Model 2 (100kHz to 100MHz) 1 × Advance Q-Meter Type T2 (SN443) 1 × B&K Model 1076-E-S Television Analyst 1 × Leader LAG-125 Low Distortion Audio Oscillator 1 × Lodestar LCR-3000A LCR Bridge 1 × GW GVT-417 AC Millivoltmeter 1 × Bird Model 612 RF Wattmeter (30 to 500MHz) 1 × AVO Electronic Test Meter 1 × AVO ‘Universal AVO Meter’ 1 × Simpson Model 260 Multimeter, with three adaptors: Battery Tester, Audio Wattmeter and Milliohm meter. They are located near Sydney Airport. If anyone is interested in taking them away, please send an e-mail to silicon<at>siliconchip.com.au Jim Rowe, Silicon Chip. Can you recharge disposable cells? I saw that Amazon is selling a battery charger designed by Popular Mechanics that claims to recharge just about any type of battery, including disposable types (https:// amazon.com/dp/B08KYK41PW). Reading between the lines, it does not really work. I doubt it is actually a Popular Mechanics design or product, or at least is not being used as intended. It might be a topic worthy of an article. David Mills, Oakleigh, Vic. Comment: We’ve published several articles on this subject in the past. It used to be well-known that primary batteries can be recharged a limited number of times. How well it works depends on the condition of the cells, their exact chemistry etc. This was explained in our recent All About Batteries Australia's electronics magazine siliconchip.com.au series (January-March 2022; siliconchip.au/Series/375) and the November 1994 Dry-Cell Battery Rejuvenator project (siliconchip.au/Article/5210). The latter article states that alkaline cells can be recharged about 7-8 times to 60% of the original capacity if you’re lucky, and zinc-­ carbon cells around 3-5 times. Touchscreen calibration varies I contacted you recently about a 2.8-inch touchscreen supplied in a kit that I thought was faulty. Upon building the kit and powering it up, I got a display on the screen but the touch function operated erratically. Swapping it for another 2.8-inch touchscreen I got in a different kit some time ago, it worked fine, making me think the first screen was faulty. When I asked about a replacement, you sent me an e-mail suggesting that I try recalibrating the touch function with that screen. I followed your instructions and I am glad to say everything is now working as it should. After accessing the Micromite console, I was able to calibrate the screen successfully. As a long-time subscriber, I appreciate you taking the time to provide me with the detailed instructions necessary for ILI9341 screen calibration. I have enjoyed and learned much from your publications over the years. The projects that you publish, as well as the “Vintage Radio” column, are of greatest interest to me. Greg Evans, Illawong, NSW. Comments: We’re glad you were able to get it to work. Sometimes the touchscreens can have a faulty touch controller, in which case the touch doesn’t work at all, and we have to replace them. But if the touch works erratically or oddly, that’s usually a sign that calibration is required. Unfortunately, it seems there are differences in the screens that sometimes mean the standard calibration works with one and not another. That’s despite them apparently being made by the same manufacturer etc. It might have to do with slight differences in how they are assembled or the parts they are made from. Small relays for Porsche electronic repairs I run an electronic repair business in Perth, mainly fixing home theatre equipment, turntables, cassette players and old-school stuff. Serviceman’s Log is the first section of the magazine I read. Regarding the item in February 2022 titled “Classically unorthodox car parts” on Porsche 928 electronic module repairs, I found some relays that would properly fit on his PCB. I had a similar problem with the electric window controller for my 1994 VW Golf; the relays were faulty. I fixed it using these relays from RS Components (shown adjacent): https://au.rs-online.com/web/p/automotiverelays/6995730/ They are surprisingly small for being 12V 30A SPDT relays. I could mount the relays on the board and still get the board to fit in the factory box. It does require some hard-wiring with tinned copper wire. I hope this information will help D. T. of Sylvania with his Porsche repairs. John Allen, Perth, WA. ago, I purchased a Li-ion battery (nominally 12V) with a capacity rating of 42,000mAh. Initially, I thought the battery was equivalent to 42Ah and considered it a large capacity battery in a relatively small package. But the label attached to the base also states 155Wh. So it seems that the mAh capacity is actually the sum of the mAh capacities of the cells, not the actual mAh capacity of the battery itself. The total charge capacity of a battery with all cells connected in parallel indicates the total lithium content. The number of cells, their charge capacity, and the battery’s configuration will determine the overall battery voltage and charge delivery. In simple batteries, this is a straightforward situation. However, ‘batteries’ with non-standard voltages (different to multiples of cell voltage), like 5V USB or 230V AC outputs, will contain internal electronics to produce these output voltages. The actual (as measured) charge capacity of such a ‘battery’ will now be altered. Still, assuming 100% efficiency, the battery will have the same energy capacity (Wh) regardless of its configuration or electronic conversions. Considering the above, there is little wonder that the general public can be confused about the charge capacity of lithium-ion batteries. Col Hodgson, Mount Elliot, NSW. Response: you may be right that manufacturers are adding up the mAh/Ah rating of all the cells to get the mAh/ Ah rating they put on the battery. The problem is that unless they are connecting all those cells in parallel, the resulting rating is wrong. Consider a battery with four 3Ah Li-ion cells in series. Each cell has a nominal voltage of 3.7V, so the battery has a nominal voltage of 14.8V. If the manufacturer labels the battery as 14.8V and 12Ah, that suggests we can draw 1.2A from it for 10 hours, but it will be flat in under three hours at that rate. The example you give shows how much confusion such incorrect ratings can cause. A 155Wh battery that’s nominally 12V can deliver at most 13Ah, not the 42Ah that your label states. We don’t think it’s a coincidence that this ‘confusion’ makes batteries sound like they have a much higher capacity than they actually do. The manufacturers know they are misleading consumers. They do it because labelling their products with misleading information makes them sell better. Misleading battery capacity ratings Concerning the letter on “Misleading battery capacity ratings” and your reply in the May 2022 issue, some time 6 Silicon Chip Australia's electronics magazine siliconchip.com.au KEEP PACE WITH AN EVER CHANGING MARKET, WORK WITH: • A global distributor of technology products, services and solutions that provides you with local support • A reliable partner that offers you a broad range of products • An industry leader providing access to specialised products Single Board Computing Leading distributor of cutting edge technology Semiconductors Over 120,000 semiconductors in stock at competitive prices Passives Over 140,000 passive products Electromechanical Over 60,000 electromechanical components Interconnect Over 550,000 connector, cable and wire products Test and Tools Full range of products to support electronic design and preventative maintenance Authorised distributor of Contact us now au.element14.com | 1300 361 005 By the way, the watt-hours rating of a Li-ion battery is also a pretty good indication of its lithium content. A tale of three pots The Ultra-Low Distortion Preamplifier with Tone Controls (March & April 2019; siliconchip.au/Series/333) was something for which I had been waiting for some time. I subsequently built the preamp and six-input switcher, which operated trouble-free for about a year, but then it started to make a crackling sound every time the motorised volume control pot operated. I tried to source a replacement in Australia but could not find any in stock. I had built a previous Silicon Chip preamplifier from an Altronics kit that had a 25kW dualgang motorised potentiometer. I salvaged this one and used it to replace the noisy pot. This second pot operated for a while, but then I lost one of the stereo channels, which I traced to a problem with the pot. I eventually turned to the internet and found one on eBay. It was rather expensive, but it seemed to be my only option to keep a good preamplifier going. The pot was an Alps RK27 Motor Potentiometer Double 5K from seller “bsitgoods”. It looked the same as the one it was to replace, so I ordered one, hoping it would fit the preamp PCB. The pot turned up a month later and, of course, it was not the same size as the original! It was longer, and the only pins that matched the holes in the PCB were the three pins of the front gang. After carefully determining the location of the other pot pins and the copper tracks on the PCB, I managed to drill holes to fit the new pot without cutting any tracks (shown below). The preamp is now back in operation and performing well. I should add that the Alps pot is very well constructed with what appears to be a diecast housing for the variable resistors. David Hebblethwaite, Mapleton, Qld. Comments: it’s a pity that sourcing motorised pots is difficult, but they are specialised parts. We’re glad you got the Alps pot working and that it seems to be of good quality. We’re moving to digital volume control for future remote-controlled preamps to solve this problem. After some searching, we discovered that Bourns Pro Audio has a 10kW dual-gang logarithmic motorised pot, part code PRM162-K420K-103A1, which should be a more direct replacement for the original part. It is not identical to the Alpha pots that Altronics used to sell, but it looks very close. We think it would fit the PCB with minor modifications (possibly by slightly enlarging the motor mounting post holes). Notably, the pinout of the pot part looks the same, and the motor appears to be roughly the same size and in roughly the same position, so hopefully, it won’t foul anything. Here is a potential source: siliconchip.au/link/abdh Long-range digital TV reception My TV automatically scans the channels periodically and includes any new ones it may find. I recently looked through the TV channels and was surprised to see some in the channel list from a tower that’s a long way away from me. I am in Melbourne, and the TV had picked up channels for Traralgon. The transmitter that services Traralgon is on Mt Tassie, approximately 175km away. I couldn’t get a video signal on those channels, so I think that the TV scanned for new channels at a time when atmospheric ducting was occurring; I might well have been able to watch the video had I been using the TV at the time. This led me to discover the following web page where people discuss long distance TV reception in Australia: siliconchip.au/link/abf3 DX TV as a hobby used to be a ‘thing’ with analog TV, but I wasn’t aware of it being practised or even possible with digital TV. Dr David Maddison, Toorak, Vic. Comment: with a sufficiently good/directional TV antenna with high gain and a masthead amplifier, the idea of receiving and decoding digital TV signals from 165km away or further does not seem impossible. It would depend on topography and, at that range, probably atmospheric reflection. As you suggest, that can vary with atmospheric conditions, including time of day. Another SMD holding tool I read with interest the letter regarding the clever SMD holding tool by Peter Gee of Inglewood in the Mailbag section of the May issue (page 10). It reminded me of the tool I saw on this website: siliconchip.au/link/abf1 The original source seems to be here: siliconchip.au/ link/abf2 Arden Clare, Mid North Coast, NSW. On power lines, electric cars and inverter generators I noted the Editor’s comment about the twisted bundle of power wires and their concern over insulation degradation. Almost thirty years ago, Energex replaced the connection wires of most houses with a twisted pair. The insulation appears to be the same and is withstanding the elements very well. In one of my earlier letters, I expressed my preference for stored hydrogen. I’d like to add that it should be very safe to place the storage cylinders at roof height. Leaking hydrogen or vented hydrogen due to over-heating would go upwards, unlike LPG, which pools. On the same topic, I came across this ATCO article: siliconchip.au/link/abez ATCO intends to build hydrogen generation and refuelling stations for locomotives in Canada. That is a really serious undertaking. siliconchip.com.au NEW PRODUCTS Introducing Control Products, Inc. (CPI) to our extensive product range. A great addition of Waterproof and Thermal switches designed for high demand Military and Industrial applications, where efficiency and reliability of machine operation is critically essential under harsh environmental conditions. WATERPROOF Switches THERMAL Switches CPI Waterproof Switches are fully waterproof and submersible. They are robustly designed to withstand harsh environmental conditions. Used in tough Military and Industrial applications. These switches are for control and sensing applications where hand actuation is preferred or configured with one of their many mounting brackets for mechanical actuation. CPI electro-mechanical Thermal Switches or their freeze switches are suitable for applications that require reliable and secure performance. Operates to high tolerances and programmable to set points of up to 954.4°C. Three Thermal switch types: SnapStat (-17.8°C to 148.8°C) PlugStat (-17.8°C to 343.3°C) Rod and Tube (-17.8°C to 954.4°C) DESIGNMEC 10X Keycap series MEC has launched their new Designmec 10X Keycap series. A new cap solution designed to allow you to use your own material insert and decorate your own cap design without tooling costs. Encounter a control panel that complements the environment, enchancing your overall user experience. Suitable with the Multimec 5G Series PCB mounted tactile switches. CUSTOM OPTIONS: • Ring: Metal or Coloured Plastics. • Decoration insert: Material of your choice. • Legends: UV Printed. • Bottom part: Black or Frosted white for illumination options. • Illumination: Integrated LED or Chips-LEDs on the PCB. CONTACT US Unit 13, 538 Gardeners Road, Alexandria NSW 2015 02 9330 1700 | sales<at>controldevices.net www.controldevices.com.au Helping to put you in Control N20K48 Modular Controller 230VAC NOVUS, proudly releases our N20K48 controller family. Base unit has universal input and relay and pulse output controller. Program via USB or smartphone bluetooth. A selection of micro modules can plug into the rear for additional I/O and comms. SKU: NOC-340 Price: $186.95 ea Fema I4L isolated signal converter for Load Cells Thhis converter can connect to 2 or 3 mV/V load cells. Features a display to show load. Configuration done by Keypad. 4-20mA/010V output. We have a service to configure the I4L for you if you require it. SKU: FMB-003 Price: $219.95 ea I3D Signal duplicator for process signals Accepts process signals in 4/20 mA and 0/10 Vdc, provides excitation voltage if needed. Dual output, with output 1 fixed to 4/20 mA, and output 2 configurable to 4/20 mA or 0/10 Vdc. Isolated 4 ways between power, input signal, output 1 and output 2. SKU: FMB-012 Price: $197.95 ea Signal Process Generator Pocket Precision Fixing an amplifier module and motorised pot The BRT LB02 Process Calibrator Resistance RTD TC mA mV signal generator is widely used as a precision multifunction process calibrator and multimeter, temperature calibrator, RTD PT100 simulator, loop calibrator, etc. SKU: HET-110 Price: $307.95 ea Adjustable 200mm Dual Float Switch Stainless steel vertically mount liquid level sensor, 200 mm in length. Floats can be adjusted to the desired length within the sensor’s overall length. SKU: HES-130 Price: $140.91 ea Mini Temperature and Humidity Sensor 0 to 10V output Panel mount Temperature (-20 to 80degc) and Humidity (0 to 100% non condensing) sensor, linear 0 to 10V output. Cable length 3 meters. SKU: EES-001V Price: $164.95 ea For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Silicon Chip Earlier this year, you gave me advice on repairing a blown SC200 amplifier module and problems with motorised potentiometers. The transistors for the SC200 arrived within six days of placing an order with Digi-Key, and the amplifier module is now back in service. I bought a 16mm 10kW dual-gang log pot from the local Jaycar store and successfully transplanted the track wafer assemblies into the faulty motorised pot shaft and body. Unfortunately, I lost the 3mm C-clip that holds the plastic gear onto the pot shaft. It took 12 long weeks for an eBay C-clip kit to arrive. Thankfully, the motorised pot is now working again. I have just finished building a Veroboard version of the October 2021 Active Crossover de-thumping circuit using 2N3906 and 2N3904 transistors. I used an 18V zener instead of the 5V zener and a 10μF capacitor instead of the 47μF capacitor. This gives a switch-on delay of about five seconds with a ±15V supply: no more massive switch-on or switch-off thumps. Dave Cole, Rotorua, New Zealand. Planned obsolescence or programmed obsolescence? Prices are subjected to change without notice. 10 Although I am not against EVs, I have previously expressed serious reservations about the change to only electric vehicles. I see many problems being pushed onto an ignorant public. One of these is already occurring in England. The following article concerns the overloading of the electrical supply: siliconchip.au/link/abf0 With the distinct possibility of future blackouts of the electrical system due to the closure of coal-fired power stations and the charging of electric vehicles at night, I bought a small petrol generator to keep my refrigerator running if things get really bad. I also purchased a new refrigerator with an inverter-type compressor, believing it should have a soft start. However, I thought I had made a mistake in buying my generator. It was stated that it is an inverter type generator, but it did not occur to me that the output might be pseudo-sinewave and not a true sinewave. To make matters worse, in reading the comments on some forums, it appears that certain inverter type refrigerators will not run from modified sinewave sources. If the refrigerator inverter used simple rectification of the mains power with storage capacitors, there should not be a problem, but I suspect that is not the case. To avoid the large current spikes that occur with simple rectification, the power supply probably takes power from over the whole of the mains sinewave. This is similar to the ‘Active PFC’ used in many computer power supplies. I made a capacitor-coupled resistive divider to safely view the generator’s AC waveform on my CRO to resolve this. The inverter proved to have a true sinewave output. Bunnings had plenty of petrol generators ‘shouting’ that they had sinewave inverters, but this $399 Ozito 2000W unit just declared that it was an inverter type. That is so strange in this age of over-the-top marketing. George Ramsay, Holland Park, Qld. Recently, my dishwasher stopped working. Since it was built in, I decided to see if I could get it repaired rather than try to find a replacement that would fit into Australia's electronics magazine siliconchip.com.au Stay connected with our 4G Antennas & adaptors Compatible with 2.4GHz & 4/5G networks for cross-compatibility 1 5dBi Antenna • Magnetic mount • Suitable for LTE, AMPS, GSM, PCS, UMTS and Wi-Fi • 2m lead with FME connector • 337mm long AR3340 ONLY $49.95 4 5m SMA Extension Lead 5 SMA to Induction 3G Plug 6 SMA to Modem Leads • Low loss • 50Ω coax • Flexible lead WC7824 ONLY $44.95 7dBi Antenna • Magnetic mount • 3m lead with FME connector • 435mm long AR3344 ONLY $69.95 2 • Adhesive backing AR3330 ONLY $19.95 7dBi Spring Mount Antenna • ½ wavelength design • 5m lead with FME connector • 740mm long AR3342 ONLY $129 3 3dBi Glass Mount Antenna • ¼ wavelength design • 3m lead with FME connector AR3338 ONLY $49.95 Range of leads that plug into the antenna socket on your USB modem. AR3332-AR3336 ONLY $19.95 EA SMA to Huawei E160/618 Plug AR3332 1 2 SMA to Sierra TS9 Plug AR3334 Telstra 4G USB Modem AR3336 We stock a great selection of Networking Antennas, Leads, Plugs, Sockets and Adaptors to improve the range and reliability of your wireless network. Explore our wide range of wireless networking products, in stock on our website, or at over 110 stores or 130 resellers nationwide. jaycar.com.au/4gwireless 1800 022 888 the cupboard space where the old one had resided. I found a company online, and the guy duly turned up and simply replaced the board with the control electronics. I asked him what had failed and why. He said his knowledge wasn’t that detailed; he just checks the error messages and almost always ends up changing the board. Then he told me that one of his fellow service personnel was deep into electronics and had taken several of the “failed” boards apart to see which components had failed. He often could not find any that could be identified as the cause of the failure. When a company rep came to give them a training course in servicing the latest model machines, he raised the issue with the guy. The rep replied that the machine was guaranteed for a number of years, during which the machine should have carried out a certain number of washes. After enough cycles, the computer chip shuts the machine down and refuses to work. Similar control boards were also employed in their clothes washing machines. So it was not planned obsolescence but programmed obsolescence. Cliff J. King, Oxley, Qld. Alternatives to subscription software Regarding your editorial in the May issue, I wonder if you are aware of the Affinity suite of applications from Serif in the UK. When Adobe suddenly switched to subscription software in 2012, a significant portion of their alleged 10 million user base (for Photoshop at least) refused to accept a de facto “Adobe Tax”. In my case, doing so would have doubled or tripled what I had been paying Adobe for periodic upgrades. Like many others, I stuck with Creative Suite version 6, which was perfectly serviceable, until something better came along. While there were some pretenders to the throne, nothing that could be called ‘professional’ standard existed until Serif in the UK released Affinity Designer, followed by Affinity Photo and finally, Affinity Publisher. The first two are serious contenders for replacing Photoshop and Illustrator, while Affinity Publisher is not yet mature enough to supersede InDesign for complex projects like magazines. Serif started with a clean slate circa 2010 and built a modern codebase common to all their applications. Hence, they have the same user interface (UI), document model and file format. The latter is a breath of fresh air after the limitations of Adobe’s historically fractured code bases and application-specific file formats. I documented my experience with these new applications in two blog posts: Starting the Gradual Move to Affinity: https://tdgq.com. au/design-publish/starting-move-to-affinity/ Innovations to Like in the Affinity Apps: https://tdgq. com.au/design-publish/innovations-to-like-in-affinityapps/ I realise that you may be more or less ‘locked in’ to CorelDraw, but I thought I should let you know about these apps in case you were not aware of them. They are not subscription-based, and the cost is remarkably low compared to Adobe’s equivalents. Paul Howson, Warwick, Qld. 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Simple & Quick Online Freight Rate Check! *DELIVERED TO YOUR DOOR! *Remote areas may require depot collection in your town DISCOUNT VOUCHERS VIEW AND PURCHASE THESE ITEMS ONLINE AT www.machineryhouse.com.au/SC0722 Specifications & Prices are subject to change without notification. All prices include GST and valid until 28-07-22 NSW (02) 9890 9111 QLD (07) 3715 2200 1/2 Windsor Rd, Northmead 625 Boundary Rd, Coopers Plains VIC (03) 9212 4422 4 Abbotts Rd, Dandenong WA (08) 9373 9999 11 Valentine Street Kewdale 05_SC_270622 LED Slim Rechargeable Handheld Work Light IC Fabrication Image Source: GlobalFoundries Inc. from inception to cutting-edge technology Last month, we covered the invention and history of integrated circuits (ICs) and the manufacturing process. Now we pick up where we left off, discussing how transistor counts keep increasing and feature sizes get smaller, culminating in the cutting-edge EUV technology. Part 2 – shrinking nodes, EUV, components – By Dr David Maddison T he technology generation in the semiconductor industry is referred to as a ‘technology node’ or a ‘process node’. It is a length measurement referring to the shortest transistor gate that could be fabricated with that particular technology node. But that has not been the case since about 1997, according to https://en.wikichip.org/ wiki/technology_node At about the 45nm technology node (around 2007), Intel used gate lengths 14 Silicon Chip of 25nm and no smaller, as undesirable results occurred otherwise. With the introduction of the 22nm process in late 2011, Intel fundamentally changed the design of the transistor with the introduction of the fin field-effect transistor (FinFET). This provided a higher transistor density without having to shrink the gate size. Thus, the feature size somewhat lost its meaning. Confusingly, today the technology Australia's electronics magazine node referred to is more a marketing term for new or improved fabrication processes with no specific relation to any physical feature size. However, the International Technology Roadmap for Semiconductors (ITRS) traditionally described the technology node in relation to the halfpitch between the smallest spacing of two metal conductors that could be made with a given fabrication process (see Fig.24). siliconchip.com.au The following process nodes are currently in use, depending upon a manufacturer’s capabilities and the devices being fabricated: 180nm, 130nm, 90nm, 65nm, 45/40nm, 32/28nm, 22/20nm, 16/14nm, 10nm, 8/7nm, 5nm. At present, only Samsung, TSMC (Taiwan Semiconductor Manufacturing Company) and Intel can use the three smallest nodes. Table 1 shows when each node was introduced. Microprocessor transistor count A common measure of the complexity of a CPU (central processing unit) or GPU (graphics processing unit) is the transistor count on the die. The transistors are usually Mosfets. The highest transistor counts currently for a variety of integrated circuits are shown in Table 2. The V-NAND (Vertical NOT-AND) flash memory chip, also known as 3D NAND by Samsung, is a 3D chip with 2000 billion transistors. This high transistor count is achieved by using many layers in the memory “stacks”. For example, a 128Gib V-NAND chip has 24 layers, and V-NAND chips with up to 160 layers are under development. 500+ layers are anticipated in the future. In 2019, Samsung had a 1024GB flash chip made from eight stacked 96-layer V-NAND chips; hence the huge transistor count – see Fig.25. We will discuss 3D chips further in the final article in this series. The Cerebras Systems Wafer Scale Engine 2 (WSE-2), designed for artificial intelligence, is the largest chip ever built, both by transistor count and physical size – see Fig.27. It contains 2.6 trillion transistors, 850,000 processor cores, has 40GB of on-chip memory, uses the 7nm technology node by TSMC and has an area of 46,225mm2 – that’s massive! A typical high-end processor is a bit larger than a postage stamp, around 1/100th that area. Moore’s Law The increase in IC component density with time has been observed to scale according to “Moore’s Law”. It is not a physical law but an observation reflecting improvements in technology and manufacturing processes. Gordon Moore was one of the founders of Fairchild Semiconductor. In 1965, Moore observed that the number of components on an integrated circuit siliconchip.com.au Fig.24: the traditional method by which technology nodes are named, according to the ITRS. Original source: https:// en.wikichip.org/wiki/ File:tech_node.svg (CC BY 3.0) Fig.25: how 3D NAND flash memory works, as distinct from 2D NAND. Original source: Wikimedia user NVMdurance Table 1 – process node introduction year Node Year Model 10µm 1971 Intel 4004 6µm 1973 Toshiba TLCS-12 3µm 1976 Intel 8085 1.5µm 1982 Intel 80286 1µm 1985 Intel 80386 800nm 1988 Cypress CY7C601 | Motorola 68030 (1987)? 600nm 1992 PowerPC 601 350nm 1995 Intel Pentium P54CQS 250nm 1997 Intel Pentium Katmai 180nm 1999 Intel Pentium III (Coppermine) 130nm 2001 Fujitsu SPARC64 V 90nm 2004 PowerPC 970FX 65nm 2006 Intel Pentium 4 Cedar Mill 45nm 2007 Panasonic UniPhier 32nm 2009 Intel Sandy Bridge (2nd-gen Core) 22nm 2011 Intel Ivy Bridge (3rd-gen Core) 14nm 2012 Samsung FinFET 14LPE 10nm 2016 Samsung 10LPE | TSMC 10FF 7nm 2018 TSMC N7 5nm 2019 Samsung 5LPE 3nm 2022 (estimate) 2nm 2024 (estimate) The years are mostly estimates for when nodes were first produced (we have primarily focused on microprocessors rather than including other ICs such as DRAM). Outlier examples include RCA’s CD4000 series which may have started 10μm production before Intel’s 4004; there’s also the Intel 1103 which was an 8μm process in 1970. Australia's electronics magazine July 2022  15 Table 2 – highest present transistor counts for various ICs Year IC type Model # of transistors 2020 AI processor Cerebras Wafer Scale Engine 2 2.6 trillion 2019 Flash memory Samsung V-NAND 2 trillion 2022 Processor Apple M1 Ultra 114 billion 2020 AI/deep learning Colossus Mk2 GC200 59.4 billion 2020 GPU 59 billion Alderbaran MI250X Table 3 – CPU transistor count over time was doubling every year. In 1975, he predicted that the number of components would double every two years – see Table 3. The second version of the law stayed true until around 2010, when a slowdown in the component count increase was observed. There is now a doubling approximately every two and a half years – see the full-page plot overleaf. Ultimately, there is a physical limit beyond which component density cannot increase. So improvements will have to come through better computing algorithms and different electronic architectures, such as optical computers or neural networks based on the structure of the human brain (Fig.26). Year Model Transistor count Node Area 1971 Intel 4004 2250 10μm 12mm2 1974 Motorola 6800 4100 6μm 16mm2 1974 Intel 8080 6000 6μm 20mm2 1975 MOS Tech. 6502 4528 8μm 21mm2 1979 Zilog Z8000 17,500 4μm(?) 35mm2(?) 1979 Intel 8088 29,000 3μm 33mm2 Silicon wafer size 1979 Motorola 68000 68,000 3.5μm 44mm2 Table 4 shows the evolution of standard silicon wafer size over the years (also see Figs.28 & 29). The larger the wafer, the more ICs can be made in one pass, so the more economical and cheaper the manufacturing process becomes, at least to a point. Standards have been established for 450mm wafers (see the “Global 450 Consortium (G450C) Program” at https://f450c.org/infographic/). But there is resistance to the uptake of that size due to the massive investment in new equipment and the questionable economics of using this size. It will probably be eventually adopted, though. 1982 Intel 80286 134,000 1.5μm 49mm2 1989 Intel 80486 1,180,235 1μm 173mm2 1993 Intel Pentium 3,100,000 800nm 294mm2 1998 Intel Pentium II 7,500,000 250nm 113mm2 1999 Intel Pentium III 9,500,000 250nm 128mm2 2000 Intel Pentium 4 42,000,000 180nm 217mm2 2003 AMD K8 105,900,000 130nm 193mm2 2006 Intel Pentium D 362,000,000 65nm 162mm2 2008 Intel Core i7 731,000,000 45nm 263mm2 2010 IBM POWER7 1,200,000,000 45nm 567mm2 2013 IBM POWER8 4,200,000,000 22nm 650mm2 2013 Xbox One (AMD) 5,000,000,000 28nm 363mm2 2015 Oracle SPARC M7 10,000,000,000 20nm 400mm2(?) 2018 Apple A12X 10,000,000,000 7nm 122mm2 2019 AMD EPYC Rome 39,540,000,000 7nm + 12nm 1008mm2 2021 Apple M1 Max 57,000,000,000 5nm ~432mm2 2022 Apple M1 Ultra 114,000,000,000 5nm ~864mm2 Table 4 – largest silicon wafer diameter by year Year Diameter Typical thickness 10×10mm dies per wafer 1960 25mm ? 2 1963 28mm ? 3 1969 50mm 275μm 9 1972 75mm 375μm 29 1976 100mm 525μm 56 1981 125mm 625μm 95 1983 150mm 675μm 144 1992 200mm 725μm 269 2002 300mm 775μm 640 Proposed 450mm 925μm 1490 Future 675mm >1mm(?) 3427 16 Silicon Chip Australia's electronics magazine Wavelength of light for lithography Over time, as the number of transistors on a chip has increased, lithography has required shorter and shorter wavelengths of light to produce the smaller IC feature sizes. According to the major equipment supplier, ASML (siliconchip.au/link/ abdu), their light sources changed over time as follows: • Early lithography systems used mercury lamps to produce blue light with a wavelength of 436nm, enabling feature sizes of 1000nm (1μm). • UV light sources with a wavelength of 365nm allowed feature sizes of 220nm. • KrF excimer laser light sources with a wavelength of 248nm allowed feature sizes of 80nm. • ArF excimer lasers with a wavelength of 193nm allowed feature sizes of 38nm. siliconchip.com.au Fig.27: the monster Cerebras Systems Wafer Scale Engine 2 (WSE-2) chip, the world’s largest integrated circuit both by physical size and transistor count. Fig.26: one possible way to improve performance beyond Moore’s Law and the physical limitations of semiconductors is using “neuromorphic” architecture to emulate the human brain but implemented in silicon. This is DANNA: Dynamic Adaptive Neural Network Arrays, a 2D grid representing neurons or synapses of the brain with programmable connectivity between them. Source: University of Tennessee (http://neuromorphic.eecs.utk.edu/ pages/research-overview/) • Extreme UV (EUV) uses light at 13.5nm, allowing feature sizes of around 3-7.5nm. Extreme UV lithography Traditionally, every new technology node decreased lineal feature dimensions by 30%, thus reducing IC area by 50% and power consumption also dropped correspondingly. This is known as Dennard or Mosfet Scaling. But this process has been slowing since around 2006, and the increase in transistor density has also not kept up with Moore’s law. As described last month, optical lithography has been moving to smaller wavelengths in the drive to smaller feature sizes. The most advanced commercially-­ made chips use extreme ultraviolet (EUV) lithography. Currently, only one company based in Veldhoven in the Netherlands can make the required machines: ASML (www.asml.com/ en/). It took them 10 years and US$25 billion to develop EUV machines, and siliconchip.com.au they charge up to US$200 million per machine. Despite this, there is a waiting list to purchase them. ASML has sold about 140 EUV machines in the last ten years. This machine is so advanced that it is regarded as strategically sensitive – see siliconchip.au/link/abdw These are among the most complicated machines ever manufactured. Quoting from the article at siliconchip. au/link/abdy: • One EUV system contains 100,000 parts and weighs approximately 180 tonnes. • An EUV system ships in 40 freight containers, spread over 20 trucks and three cargo planes. • The mirrors used in EUV systems are so flat that if one were to be blown up to the size of Germany, the biggest bump would be less than 1mm high. • An EUV system controls beams of light so accurately that it is equivalent to shining a torch from the Earth and hitting a 20 cent coin on the moon. Australia's electronics magazine Fig.28: 2-inch (51mm), 4-inch (100mm), 6-inch (150mm), and 8-inch (200mm) silicon wafers after they have been ‘diffused’. Each die visible on their surfaces will become a separate device once the wafer is sliced up. (GNU Free Documentation License) Fig.29: an Intel 300mm wafer with VLSI (very large scale integration) circuits fabricated onto it. The next phase would be testing; then, it would be cut up into individual dies (chips), ready for packaging. Source: Wikimedia user FxJ (public domain) July 2022  17 18 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.30: this plot shows that “Moore’s Law”, the prediction that the IC transistor count would double roughly every 18 months, was prescient. Source: https://ourworldindata.org/ uploads/2020/11/Transistor-Count-over-time.png (Max Roser, Hannah Ritchie, CC BY 4.0) Computers were once people! Integrated circuit manufacturer business models IC fabrication facilities or foundries are incredibly expensive to build and operate and must be kept running at maximum capacity to pay their bills. This is one of the reasons why some companies specialise in design while others provide fabrication services only. Some companies, known as integrated device manufacturers (IDMs), both design and manufacture devices. Examples of such companies are IBM, Intel, NEC, Samsung and Texas Instruments. Other ‘fabless’ (and possibly also fabulous) companies only design devices and get others to manufacture them. Examples include AMD (since 2008, when they sold their fab to GlobalFoundries), Apple, ARM, Broadcom, Marvell, MediaTek, Nvidia, Qualcomm and Xilinx. “Pure play” companies only manufacture devices that fabless companies design. Examples of pure play foundries include GlobalFoundries (headquartered in New York with fabs in various locations including Germany, Singapore, United States), TSMC (Taiwan) and UMC (Taiwan). The term “computer” was coined by English poet Richard Brathwaite (1588-1673), who published a book in 1613 called “Yong Mans Gleanings”. He used it to refer to a person who makes calculations. He wrote: I haue read the truest computer of Times, and the best Arithmetician that euer breathed, and he reduceth thy dayes into a short number: The daies of Man are threescore and ten. The unique mirrors in the EUV system are made of silicon and molybdenum, and are among the flattest in the world. Of course, a foundry needs more than just EUV machines. They need about 200 different large-scale machines, and the workflow through these has to be precisely coordinated. A vast number of supplies, processes and personnel work together to form a huge operation. ASML started as a subsidiary of Philips in 1984. Christophe Fouquet, its Executive Vice President, said that their first lithography machine “looked like a projector”. ASML is more valuable than some of its customers, such as Intel. They have come a long way from those early days. Only five chipmakers can afford to buy the most advanced machines. Its customers include Intel, Samsung and TSMC, who combined provided more than 84% of its business in 2021. There are thousands of chip foundries worldwide, so most cannot make the most advanced chips. The TWINSCAN NXE3600D is ASML’s most advanced EUV lithographic system and supports volume production at the 5nm and 3nm nodes for both logic and DRAM. It uses extreme UV of 13.5nm wavelength and can expose 160 300mm wafers per hour, with a maximum exposure field of 26mm x 33mm (see Fig.31). To produce the EUV light, a CO2 laser is fired into droplets of tin that vaporise and emit EUV light. The UV wavelength of 13.5nm is almost in the X-ray range. X-rays have a wavelength from 0.01nm to 10nm. The numerical aperture (see later) of the optics is 0.33. High-NA EUV A machine under development by ASML is the high-NA EUV machine which is expected to cost US$300 million. The numerical aperture (NA) is increased from 0.33 in the machines mentioned above to 0.55. These machines will be capable of producing both logic and memory chips in the 2nm technology node – see Fig.32. This machine is expected to be available from late 2023 for R&D customers and 2025 for volume manufacturers. Last month, we discussed multiple patterning and other lithographic techniques to achieve a smaller feature size. Foundries have to decide whether to continue with complicated multiple patterning with non-EUV lithography, or move to EUV lithography with simpler single-patterning. Reticle Optical Column Vacuum Chamber Wafer Handler Light Source Fig.31: part of an extreme UV (EUV) lithography machine from ASML with the covers removed, showing the optical path in purple. This image does not give credit to the size and complexity of the machine; it is roughly the size of a locomotive. Source: ASML siliconchip.com.au Australia's electronics magazine July 2022  19 Fig.32: ASML’s High-NA machine, which should allow even smaller feature sizes to be achieved, enabling the 2nm node. Wafer Stocker To support optimized FF thoroughput Mask Stage 4x increase in acceleration Lens & Illuminator • NA 0.55 for high contract • High transmission Horizontal Source (improved transmission) Compatible with future 0.33 NA sources, power improvements over time Improved Methodology 2~3x improvement in overlay/focus Wafer Stage 2x increase in acceleration Components on ICs Cooling Hood Mitigate wafer heating New Frames Improved thermal and dynamic control with larger optics Now that we’ve fully described how IC dies (also pluralised as dice) are made, let’s look at what they can contain. Apart from transistors and diodes, various other components can be fabricated onto integrated circuits. We will cover some common ones here but cannot possibly cover all existing types. While most of our readers will know how diodes and transistors work, especially if they have read our articles on the History of Transistors in the March, April & May issues (siliconchip.com. au/Series/378), we’ll start with a quick refresher. current to flow in one direction but not the other. As shown in Fig.33, with a reverse-­ biased voltage between the P-doped and N-doped semiconductor material, a depletion region at their junction prevents current from flowing. However, if the voltage is reversed and the device becomes forward biased, as in Fig.34, the depletion zone shrinks until current can flow between the terminals. A P-N junction can be formed in one layer of an IC by doping different areas with P-type and N-type dopants or between differently-doped layers in contact above and below. Diodes Transistors The simplest semiconductor device is the diode. It consists of adjoined areas of P-type and N-type semiconductors. It has the property of allowing A bipolar transistor can be constructed similarly to a diode in an IC but with an extra junction, forming P-N-P or N-P-N connections – see Fig.33: the depletion zone at the junction of P-doped and N-doped semiconductor material in a diode widens when a reverse bias voltage is applied. This blocks current flow. 20 Silicon Chip Fig.35. The emitter is usually doped more heavily than the collector, so those two P or N doped areas are typically created in separate steps. Mosfets are, in a sense, even simpler than bipolar transistors, needing just one type of doped semiconductor (P-type or N-type, depending on whether it’s a P-channel or N-channel Mosfet). The metal or semiconductor gate area is separated from the channel by a very thin insulating layer (usually silicon dioxide) – see Fig.36. The relative simplicity, straightforward biasing requirement and fast switching speeds are why Mosfets are almost exclusively used in digital circuits. JFETs are made similarly to Mosfets, but they do not need the insulating layer since the gate is differently-­ doped silicon, forming a diode junction that is normally reverse-biased Fig.34: with the bias voltage reversed, the diode is forwardbiased. The depletion zone essentially disappears and current can flow freely, with a small voltage drop. Australia's electronics magazine siliconchip.com.au Fig.35: a bipolar transistor can be formed by joining three differently doped areas of semiconductor material, either N-P-N or P-N-P. While the collector (top) and emitter (bottom) use similar material, the emitter is more heavily doped than the collector. Fig.36: Mosfets in ICs are usually 3D structures, but the general principle is the same as this 2D example; the electric field from the gate electrode influences current flow in the channel, between source and drain. Fig.37: an example of a diffused resistor within an IC. In this case, the resistor is diffused P-type material isolated from the substrate by an N-type material layer and covered with an insulating SiO2 layer. It is connected externally via terminals labelled 1 and 2. and hence does not conduct. JFETs are often used in audio ICs as they are low-noise, high-impedance devices. Resistors A resistor is fabricated on an integrated circuit utilising the resistivity of a volume of doped semiconductor or layers of a resistive material – see Fig.37. Resistance values from ohms to kilohms can be produced with a tolerance of about 5% to 20%. Some ICs need higher precision resistors than this (eg, instrumentation amplifiers). They typically use lasertrimmed thin film resistors (more on that below), measuring the resistor’s actual value and adjusting it to achieve the required precision. The resistance can be controlled by several methods such as: 1. A diffusion layer designed to have a particular resistivity. The length, width, diffusion depth and concentration of the layer determine the resistance. Only relatively low resistance values can be produced by this method, but they can be produced at the same time as transistors, so it is economical and common. Higher resistances can be produced by a zig-zag pattern in the diffusion region. Poly-silicon can also be used to create resistors. 2. An epitaxial resistor, used for higher resistance values, is made by depositing a layer on top of the substrate between two metal contacts. 3. A pinched resistor, where the cross-section of a diffused resistor is reduced to increase the resistance. 4. A thin film resistor is fabricated by depositing a resistive substance like Nichrome on the semiconductor substrate, making contact with it. Advantages include good high-frequency Fig.38: metal-insulator-metal (MIM) capacitor is built from layers of conductive metals and an insulating dielectric. siliconchip.com.au performance; the value can be adjusted by laser trimming; and a low tempco (temperature coefficient), meaning good stability. A disadvantage is additional processing steps. Capacitor There are several ways to make a capacitor in an integrated circuit. Some standard methods are as follows. 1. The most common capacitor is the MIM or metal-insulator-metal capacitor. It consists of two metal layers with a dielectric layer between them – see Fig.38. They require more process steps than some others to produce. 2. A similar capacitor to the MIM type is the MOM or metal-oxide-metal capacitor (Fig.39). It uses interdigitated electrodes, like two interlocking sets of fingers. The capacitance Fig.39: a metal-oxide-metal (MOM) capacitor can be fabricated in one plane (left) or multiple planes for higher capacitance in a similar area (right). Australia's electronics magazine July 2022  21 Fig.40: a trench capacitor in silicon. This example is a cross-section of a DRAM memory cell using 3D stack technology. The state of each bit in a DRAM memory chip is retained using a capacitor like this. The capacitor here is a polysilicon plate trench type. Original source: Wikimedia user Cepheiden (CC BY-SA 2.0 DE) is created by a dielectric between the fingers, but it can also have multiple layers, so there is capacitance in the vertical direction. The dielectric material is the oxide used in the processing of the IC, so they are typically cheaper and easier to make than MIM devices. 3. A trench capacitor is another way to implement a capacitor in an IC for use in memory devices, as shown in Fig.40. 4. Capacitors in ICs can utilise the properties of a P-N junction, as in diodes, transistors and other semiconductor devices. These are called junction capacitors because such junctions have capacitance. A junction capacitor is a reverse-­ biased P-N junction that can be formed simultaneously with transistors in the fabrication process. It comprises either the collector-base or emitter-base part of a transistor – see Fig.41. The capacitance is proportional to the junction area and inversely proportional to the thickness of the depletion region. The depletion region occurs at the site of the actual P-N junction. The capacitance is also voltage-­dependent, so these capacitors can be used like varicaps. Inductors Inductors are a challenging component to include in an integrated circuit. Firstly, chips don’t usually contain suitable core material. However, there are cases where magnetic materials such as ferrite can be deposited during the fabrication process (see Fig.42). Also, the limited space available makes for a small coil or spiral size and consequently, low values for both inductance and the quality factor or Q. Additional problems include the large chip area taken; the self-resonant frequency is affected by stray capacitance, but it can still be in the GHz range. On-chip inductors are not compatible with all fabrication processes. Coils or spirals on chips are typically 2D (see Figs.43-45), but bond Fig.43: a die micrograph of a planar spiral inductor on a silicon chip. Source: Michael S. McCorquodale et al. (www.researchgate.net/ publication/224169588_A_Silicon_ Die_as_a_Frequency_Source) wires can be used to make a pseudo-3D coil, as shown in Fig.47. Other devices (MEMS) Devices such as force sensors, gyroscopes and other sensors can be built into ICs using MEMS technology (micro electromechanical systems). For more details, see the Silicon Chip article on MEMS devices (November 2020; siliconchip.au/Article/14635). Connecting the chip to the outside world Traditionally, the chip is connected to a pre-fabricated ‘lead frame’. Connections are made from exposed metal areas on the die to those leads, usually via ‘bond wires’. Both the chip and lead frame are then encapsulated in plastic (or sometimes in a metal can, or even not at all). The bond wires that connect the silicon die (chip) to the package leads have traditionally been made of gold. Other possible materials are aluminium, copper and silver. 200μm 200μm Ferrite film (c) Coils Fig.41: this shows how a P-N junction can be used as a junction capacitor. The capacitor terminals are labelled 1 & 2. 22 Silicon Chip (a) (b) 4μm Fig.42: an on-chip inductor, without and with ferrite film, to act as the magnetic core. Source: https://doi.org/10.1155/2013/832401 (CC BY 3.0) Australia's electronics magazine siliconchip.com.au Fig.44: an annotated image of a chip that operates on the 2.4GHz ISM frequency band, showing on-chip inductors. Image source: H. Jhon et al. (https://ieeexplore.ieee.org/ document/4336140) Fig.45: a chip designed to operate at 390GHz, including tiny inductors. There are at least 14 inductor/transformer pairs in the section labelled “PA+Multiplier”. This die is about 2mm x 1mm. Source: A. Standaert et al. (https:// ieeexplore.ieee.org/document/9056947) Gold is now more expensive than ever, so copper is used for many bond-wire applications today. Still, it requires extra precautions such as an oxygen-free atmosphere to ensure the copper does not oxidise. Extra-highpurity copper is used as the hardness of regular copper is too high. As a lowcost alternative to gold, aluminium can also be used for wire bonding. Ball bonding is a variation of wire bonding. It is a process used to bond gold and copper wires with a combination of heat, ultrasonic energy and pressure. For aluminium wedge bonding, ultrasonic energy and pressure fuse the aluminium wires to aluminium pads (see Fig.46). Controlled collapse chip connection (C4) or ‘flip chip’ (see Figs.48 & 49) is another way a silicon die can be connected to other devices or a carrier package. Solder bumps are deposited onto the die, then the die is turned upside-down (hence “flip chip”) and aligned to corresponding ‘lands’ (pads). Heat is then applied to flow the joints. There are now also technologies that reduce the size of, or eliminate the need for solder bumps altogether. These are important for multi-chip module/chiplet technology, to be discussed next month. The carrier package to which the die is bonded typically is attached to a PCB via a ball grid array (BGA) – see Figs.49 & 50. With a BGA package, the entire area of the carrier package can be covered with connectors, not just along the edges as in more traditional siliconchip.com.au Fig.46: this image shows a chip where aluminium wedge bonding has been used to attach the leads to the chip. Source: Australian National Fabrication Facility, Queensland Node (https://anff-q.org.au/wire-die-bonding-technicalseminar/alu-wedge-bonding-on-chip/) Fig.47: a model of an inductor made on an IC with bond wires. Source: JongWan Kim et al. (www.mdpi.com/1424-8220/7/8/1387/htm – Open Access) Australia's electronics magazine July 2022  23 Fig.48: controlled collapse chip connection (C4). Original Source: Wikimedia user Twisp (public domain) Fig.49: an Intel Celeron CPU with the silicon die attached to the carrier via C4 bonding. The carrier is BGA soldered to the circuit board. Source: Wikimedia user Alecv (CC BY-SA 3.0) packages like dual in-line or quad flat-pack. Once the IC has been connected to the lead frame, a ceramic or plastic layer is often added to protect the die, leaving only the ends of the leads exposed. Plastic packages are now almost ubiquitous because they cost less than ceramic but still offer excellent protection. The plastic used is typically epoxy-cresol-novolak (ECN), as it is strong with very good heat and moisture resistance. The main advantage of ceramic packages is better heat dissipation; they act less like a heat insulator than plastic. In some very low-cost devices like calculators, rather than packaging the silicon die, it is glued to the PCB and bond wires are added to connect it directly to PCB tracks. For protection, a blob of molten plastic (possibly ECN) is deposited on top. This can be cheaper than packaging each individual IC for devices produced in very large numbers. Early IC packaging The first ICs, such as Fairchild’s Micrologic range, were housed in modified cylindrical transistor cans with extra leads added. This was not an efficient way to utilise space on PCBs. Then, in 1962, Yung Tao at Texas Instruments invented a 10-lead 6.4×3.2mm (1/4in x 1/8in) “flat pack” (Fig.51) to better utilise available space for aerospace equipment. These packages were derivatives of existing designs. Integrated circuits are still available in similar packages. That was followed by the development in 1965 of the ceramic dual in-line package by Don Forbes, Rex Rice and Bryant (“Buck”) Rogers at Fairchild Semiconductor. This is the familiar package with rows of pins on each side of a rectangular body, the pins being 0.1in (2.54mm) centre-­ to-centre and bending by 90° to meet the PCB. These dual-inline packages (DIP) revolutionised computer and circuit board manufacturing because they simplified the layout and enabled automatic insertion. This package type is still in common use, but its use has diminished this century due to the increasing use of surface-mounting packages, which do not require holes to be drilled in the PCB and can be soldered on both sides. Australian microchip fabrication There has been a surprising amount of semiconductor device manufacturing in Australia. A Philips factory opened in Hendon, South Australia, in 1947 (siliconchip. au/link/abdz), and IC manufacture started there in 1970. That business became known as Integrated Electronic Solutions Pty Ltd in 1997, then changed its name to Hendon Semiconductors Pty Ltd in 2007 (visit www. hendonsemiconductors.com.au). They no longer fabricate ICs but currently manufacture thick-film hybrid devices and provide other design and manufacturing services. In 1965 (some sources state 1964), Fairchild Semiconductor established a facility in Croydon, Victoria, to manufacture transistors and diodes and later, make ICs in ceramic dual in-line packages (an advert from Fairchild has been reproduced in Fig.52). Like most Australian electronic manufacturing, it closed in 1973 in part due to a cut in tariffs on imported electronic components. However, parts of it were spun off into Hybrid Electronics Australia which was still operating until a few years ago. Security of mask designs The security of IC mask design files has to be considered. They are possibly vulnerable to viruses if appropriate precautions are not taken and malicious parties are able to modify them. Quoting from the article at siliconchip.au/link/abeb: The possibility that an undetected piece of binary code can be inserted within an OASIS file with no restrictions on its size or its content, indicates an undeniable vulnerability to viruses, trojans and worms...there are already some cases where viruses have been propagated through pure data files because of lax security on the part of users. This could enable a hostile state actor to insert features into ICs to enable acts of espionage. There have been rumours that this may have already happened, but there is no confirmation as far as we know. For more information, see the research presentation PDF “Stealthy Dopant-Level Hardware Trojans” at siliconchip.au/link/abec 24 Silicon Chip Australia's electronics magazine Fig.50: a BGA footprint on a PCB after removal of an IC. Source: Wikimedia user Janke (CC BY-SA 3.0) siliconchip.com.au Fig.51: flat pack integrated circuits used in the Apollo guidance computer. This demonstrates that SMD packages have been around for a while! Source: NASA (public domain) Fig.52: a Fairchild Semiconductor advertisement for dual in-line package ICs from Electronics magazine, 13th of December 1965. AWA produced several devices at their factory in Rydalmere, NSW, but that facility was taken over by Philips in 1970 and closed. Silanna Group (https://silanna. com/) was founded in 2006 and is said to be Australia’s only semiconductor design and manufacturing company. To quote Silanna: With its head office in Brisbane and additional operational, manufacturing and design centres in Sydney, USA, UK and Singapore, Silanna supplies high-technology microelectronic chips to the global communications, space, defence and medical markets. The company’s silicon-on-sapphire radio-frequency antenna switch, for example, is used extensively in smart phones and space satellites, and in NASA’s Mars rovers. Unfortunately, Silanna did not respond to our request for more information about their activities in Australia. The Australian National Fabrication Facility (www.anff.org.au) was founded in 2007 “to provide access to micro and nanofabrication equipment, essential to Australia’s scientific future” … “and now represents an investment of more than $400m in research infrastructure made by Commonwealth and State Governments, as well as partner organisations”. The ANFF has 500 pieces of fabrication equipment for micro- and nano-scale devices over 20 sites. They employ 100 experts and help about 3000 users with various fabrication projects each year. For further information about transistor and integrated circuit manufacturing in Australia, refer to the article by Bernie O’Shannassy at siliconchip. au/link/abe0 – the rest of that website is also excellent. You can view an ABC Australia Four Corners program from the 25th of January, 1968, about the “computer age” and concerns about losing jobs to computers (online at https://youtu.be/ qKKMTm-ixZE). The Australian Computer Museum Society (ACMS) Sydney has a website at https://acms.org.au/ There is also the Museum of Computing History in Melbourne; website at siliconchip.au/link/abe1 Australia’s first homegrown stored memory computer, the fourth in the world, and the oldest surviving computer is CSIRAC in Melbourne, see siliconchip.au/link/abe2 The HP Computer Museum in Melbourne is unfortunately not open to the public, but you can see their website at www.hpmuseum.net/index.php Coming up The third and final article in this series next month will concentrate on the current state-of-the-art in integrated circuits, which is multi-chip modules. That is where multiple silicon dies are joined together in a single package to effectively form one very large ‘chip’. This allows for much more powerful devices, increases yields (reducing prices) and adds a lot of flexibility to manufacturing. Interesting links It is actually possible to “see” current flow in an integrated circuit die by observing its operation with an electron microscope. This technique is called voltage contrast. This is demonstrated in the first three points below: ● “Voltage Contrast in the Scanning Electron Microscope - Cambridge Instruments/BT” https://youtu.be/ NYyOphvd8eQ ● “Viewing an active electronic circuit with a scanning electron microscope” https://youtu.be/eoRVEw5gL8c ● Using the voltage contrast technique to see active electrical lines in a chip (PDF): siliconchip.au/link/abed ● “Zoom Into a Microchip (Narrated)” https://youtu.be/Knd-U-avG0c ● “Zoom in on the chip in your smartphone” https://youtu.be/2z9qme_ygRI ● “Catching a single Transistor - We’re looking inside the i9-9900K” https://youtu.be/WOZqoTuAGKY ● An excellent tour of one of Intel’s most advanced fabs (but highly censored): https://youtu.be/2ehSCWoaOqQ ● Here’s a fascinating YouTube channel about home-made ICs: www.youtube.com/c/SamZeloof ● The Computer History Museum in California (https://computerhistory.org/) contains much of the collection of the now-closed Computer Museum that was in Boston. There’s also the Intel Museum in Santa Clara, California; see siliconchip.au/link/abee siliconchip.com.au Australia's electronics magazine July 2022  25 Can you work out the circuit of a fabricated chip by looking at it? Supposing you were prepared to put a tremendous amount of work into ‘reverse engineer’ a chip, could you do it? According to Ken Shirriff, who does it as a hobby, you can, at least for older chips (his blog can be found at www. righto.com). He has developed his own methodology – see the video titled “Reading Silicon: How to Reverse Engineer Integrated Circuits” at https://youtu.be/aHx-XUA6f9g Using his techniques, Ken even managed to solve the mystery of how, in 1974, Sir Clive Sinclair took a simple fourfunction calculator chip from Texas Instruments, shown in Figs.53 & 54, and reprogrammed it to perform scientific calculations. The competing calculator, the HP-35, used five complex chips to do the same operations. Texas Instruments staff were amazed. It was the first affordable scientific calculator. See the story at siliconchip. au/link/abe3 The techniques shown would not likely work in modern high-density CPUs and GPUs because the feature size is much smaller than the wavelength of visible light, so you would not be able to resolve the features with a light-based microscope. An electron microscope would be another story, but how many people have one of those lying around? Also, modern chips have many more layers. The lower layers would not be visible, not to mention the staggering amount of work trying to work out what the billions of transistors and other components did. You can download many die photos for analysis from the following websites: ● https://zeptobars.com/en/ ● http://visual6502.org/ ● http://www.siliconpr0n.org/ You can see an extraordinary simulation of what happens inside a MOS Technology 6502 processor as it is executing code at http://visual6502.org/JSSim/index.html Also see the video titled “Reverse Engineering a simple CMOS chip” at https://youtu.be/FMdYuGpPicw Ken Shirriff has also reverse-engineered the 555 timer chip, said to be the world’s most popular IC, with billions of copies sold. He has identified the chip’s functional elements, as shown in Figs.55 & 56. He has also created an interactive explorer where you can click on parts of the chip, and the corresponding part of the circuit is highlighted. See siliconchip.au/link/abe4 Another example is when AMD reverse engineered Intel’s 80386 CPU to create the Am386 line, which was marketed SC as being 100% compatible with Intel’s processor. Comparator Current mirrors Discharge transistor Voltage divider Output driver Flip flop Comparator Fig.53: a labelled image of the TMS0805 chip used in the 1974 Sinclair Scientific Calculator. The mask was used to reverse-engineer the chip and its instruction code. Source: Ken Shirriff Metal lines Fig.54: a small portion of the instruction ROM of the TMS0805 chip used in the 1974 Sinclair Scientific Calculator, showing how the presence or absence of transistors stores individual bits. Ken Shirriff used this imagery to determine the brilliant code the calculator ran. Source: Ken Shirriff 26 Silicon Chip Transistors Silicon lines Figs.55 & 56: the functional blocks of an LMC555 chip, as determined by Ken Shirriff, and the corresponding internal circuit diagram (above). Australia's electronics magazine siliconchip.com.au Build It Yourself Electronics Centres® Spark Up a Winter project! Great build volume & features! K 8602 SAVE $260 639 $ urself. All the gear to make it yo t. 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Simple to connect modules with consistent sizing for easy stacking and experimenting. The PiicoDev system provides lots of creative freedom for hands on electronics building. Designed and developed by Core Electronics in Newcastle, NSW. Model Z 6419 Z 6590 Z 6591 Z 6580 Z 6581 Z 6582 Z 6583 Z 6584 Z 6585 Z 6596 Z 6597 Type Adapter Board for Raspberry Pi Pico Adapter Board for BBC micro:bit Adapter Board for Raspberry Pi GPIO TMP117 Precision Temperature Sensor BME280 Atmospheric Sensor VEM6030 Ambient Light Sensor VL53L1X Distance Sensor MPU6050 Motion Sensor MS5637 Pressure Sensor PiicoDev Cable 100mm PiicoDev Cable 200mm RRP $7.95 $5.80 $4.60 $9.95 $13.50 $4.60 $19.00 $9.25 $8.60 $1.10 $1.50 Western Australia Build It Yourself Electronics Centres Sale Ends July 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 Available now! 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/ Multimeter -CheckeR -Calibrator It’s amazing how handy even the cheapest multimeters can be. But did you ever stop to think about how accurate they are? With the Multimeter Checker, you can verify their accuracy. For meters that aren’t so cheap, it will also allow you to calibrate them and adjust for drift. Project by Tim Blythman ultimeters are indispensable tools; perhaps so necessary that we tend to take them, and their accuracy, for granted. Sometimes accuracy is not that important, but there are times when it is. Back in August 2015, we presented the Low-cost Accurate Voltage Current Resistance Reference (siliconchip.au/ Article/8801) and showed how to use it to check and calibrate multimeters (siliconchip.au/Article/8832). It provides a DC reference voltage of 2.5V ±1mV (±0.04%), a resistance of 1kW ±1W (±0.1%) and a current of 2.5mA ±3.5µA (±0.14%). The DC voltage reference comes from a precision voltage reference IC, and that plus a precision resistor provides the current reference. That precision resistor can also be used on its own as the resistance reference. The whole thing is compact and ran from a coin cell, perfect for keeping in the toolbox to be used whenever needed. It covers the most common measurements done with a multimeter. While that was great, it didn’t provide an AC voltage source, so not all of the typical multimeter ranges could be checked or calibrated. So we decided to develop a new design that adds that feature. For the new Multimeter Checker, we M siliconchip.com.au have a dedicated voltage reference IC providing 3.3V for DC calibration. This is also used with a precision resistor to provide an accurate 100mA current source. It has another precision resistor to act as a resistance reference. Importantly, for calibrating AC voltage ranges, it provides a precise 1V RMS AC sinewave at one of three frequencies: 50Hz or 60Hz (to match typical mains frequencies) or 100Hz. Different multimeters use different methods to measure AC voltage (and alternating current). That is why some multimeters are labelled as “True RMS” while others are not. True RMS multimeters give accurate AC voltage measurements, whatever the shape of the waveform. In contrast, some cheaper multimeters measure the peak voltage and multiply the reading by a factor of 0.71, on the assumption that the waveform is sinusoidal. Of course, this will not be accurate unless the waveform is close to being a sinewave. A square wave, for example, will give an artificially low reading as its peak is the same as its RMS value. Similarly, triangle and sawtooth waves will tend to give readings that are too high. Some other meters measure the average of the rectified AC voltage and assume a sinewave, which will have different error magnitudes for other waveforms. In our circuit, the AC voltage is generated by an analog circuit, so it does not have the digital artefacts that would be produced by a digital synthesis method. Its amplitude and frequency are checked and adjusted by a microcontroller, which compares Features & Specifications ∎ ∎ ∎ ∎ ∎ ∎ ∎ ∎ DC voltage reference: 3.3V ±0.1% AC voltage reference: 1V ±0.5% RMS Direct current reference: 100mA ±0.2% Resistance reference: 33W ±0.1% AC reference voltage frequency: 50Hz, 60Hz or 100Hz (±0.3%) AC reference frequency source: crystal oscillator AC reference harmonics: ≲40dBV Control: pushbuttons with LEDs, and over USB virtual serial port Australia's electronics magazine July 2022  31 these to the DC voltage reference and the frequency of a crystal oscillator. As well as enjoying the benefits of both analog and digital circuitry, this allows the AC voltage reference to be set to 50Hz, 60Hz or 100Hz. Circuit details The entire Checker/Calibrator circuit is shown in Fig.1. The DC references (voltage, current and resistance) on the Checker work much the same as in the earlier Low-cost Accurate Voltage Current Resistance Reference. Still, we’ll explain how they work together, because they are also an intrinsic part of the AC voltage reference. 5V USB power is applied to socket CON1 and powers, among other things, 3.3V precision voltage reference VREF1. This MCP1501 low-cost 3.3V precision reference is critical to the correct operation of all the other parts. It’s capable of supplying up to 20mA, which is vital to ensure that the accuracy of the reference is not affected by the connected loads, especially as the analog generation circuitry is powered from this 3.3V reference. VREF1 has a 100nF bypass capacitor at its positive supply, pin 1. The 3.3V output from pin 7 is connected to TP5 and can be compared with circuit ground at TP6; these two points are marked DCV on the PCB. The PCB has separate circuit traces from TP5 to REF1’s feedback (FB) pin 8. This ensures that the 3.3V is accurate at the test point, in spite of any loads. Precision reference current Dual low-voltage rail-to-rail op amp IC3 (MCP6272) is powered from the 3.3V output of VREF1 and has a 100nF supply bypass capacitor. One half of IC3 (IC3b) is used to drive the current reference. The 3.3V from VREF1 feeds into the non-inverting input of IC3b (pin 5) via a 1kW resistor. Its corresponding inverting input (pin 6) is fed (via another 1kW resistor) from the high side of a 33W precision resistor used to measure the reference current. Any current through this resistor causes a voltage to develop between TP4 and ground. The output of this op amp (pin 7) drives the base of NPN transistor Q1, acting as an emitter-follower, via a 100W resistor. Q1’s collector is connected to the 5V rail, and its emitter goes to TP3. TP3 and TP4 are thus the current reference terminals. When TP4 is below 3.3V, Q1 is fed current by the op amp. If TP4 starts to rise above 3.3V, the current drive to Q1 starts to get cut off. When TP4 is at 3.3V, 100mA must be flowing through the 33W resistor to ground. There will be a minuscule current flowing from TP4 into the op amp’s pin 6, but it is of the order nanoamps, so it is much less significant than the 0.1% precision component tolerances. Thus, the op amp’s feedback loop maintains 100mA between TP3 and TP4 when the two are connected by a multimeter measuring current. TP3 and TP4 are labelled on the PCB as the DCA reference points. This compact Checker provides outputs to check the most commonly used features on most multimeters. It delivers 3.3V DC, 100mA DC and a 1V AC RMS pure sinewave that can be set to 50Hz, 60Hz or 100Hz and is checked for both voltage and frequency by the onboard microcontroller. The USB interface can also be used to manually control the AC oscillator and set custom frequencies. Australia's electronics magazine The 1nF capacitor between pins 6 and 7 helps suppress any high-­ frequency oscillation that might occur due to the high gain of the op amp. With 3.3V across the 33W resistor plus the base-emitter drop of Q1 and perhaps 0.1V across the 100W base resistor, the op amp output is typically at 4V, giving about 1V of headroom below the 5V supply. So anything connected to the current reference must drop less than 1V or have less than 10W resistance for the current reference to work correctly. A second, identical 33W precision resistor is provided as the resistance reference, allowing the circuit to provide an independent set of test pads, TP7 and TP8, for the resistance feature. AC voltage reference Practically all of the remaining circuitry is used to provide the AC reference. Since this circuit operates from a single-ended 5V DC supply, we first need a nominal level around which the AC signal can swing. For this, we have chosen half of the 3.3V supply, which is derived by using a pair of 10kW resistors to divide the output from VREF1 to produce 1.65V. The resulting voltage is low-pass filtered by a 1μF capacitor and buffered by IC3a, with another 10kW resistor providing the unity-gain feedback. The output of this op amp (pin 1) sits at 1.65V, and this is our AREF rail. The AC signal is generated by a phase-shift oscillator based around another op amp, IC1 (another MCP6272), and IC2, an AD8403ARZ10 quad 10kW digital potentiometer. IC2 is powered by the 5V rail with a 100nF bypass capacitor. The analog ground pins 1, 5, 17 and 21 connect to circuit ground, along with its digital ground at pin 9, while the SHDN (shutdown) and RS (reset) pins are pulled up to 5V by 10kW resistors to allow normal operation of the digital potentiometer at all times. Op amp IC1 is powered from the 3.3V rail, with a 100nF bypass capacitor, to provide signal symmetry around the 1.65V AREF reference. This is one reason why we have chosen the MCP1501 reference, as it has a sufficient output current and suitable voltage to power these components. This is critical because one of IC1’s outputs saturates briefly on every cycle, so if it were powered from 5V, siliconchip.com.au Fig.1: most of the components in the circuit are to generate and monitor the AC waveform, including IC1, IC2 and IC4. IC1 and its connected components form the phase shift oscillator, with IC2’s potentiometer elements controlling its frequency and amplitude under the supervision of IC4. It measures the oscillator voltage using its ADC with reference to the 3.3V precision reference and adjusts the digital potentiometers to achieve very close to 1V RMS. Similarly, the AC signal frequency is adjusted using 16MHz crystal X1 as a reference. siliconchip.com.au Australia's electronics magazine July 2022  33 the saturation would occur differently on positive and negative swings, leading to harmonics (ie, frequencies above the selected 50/60/100Hz option) creeping into the output. A phase shift oscillator works by reinforcing a signal that is delayed by 360°. The delay is formed by several RC filter networks, which add up to 180° of phase shift, followed by inversion, equivalent to a further 180° phase shift. As the RC filter phase shift depends on frequency, it will only have a delay of precisely 360° at one specific frequency. Signal components at other frequencies are attenuated as they are delayed by a different amount and interfere destructively as they make their way around the circuit. The circuit elements also attenuate all frequencies to some extent, so one half of op amp IC1 provides the gain needed to overcome this, while the other half provides the phase inversion. Phase shift oscillator There are three phase-shift elements composed of three 1μF capacitors connected to IC2 and three of the digital potentiometer elements inside IC2 (numbered 1-3). These are all wired as variable resistors (rheostats) and can vary independently from near to 0W up to around 10kW. Imagine a fairly pure 50Hz 1V AC RMS signal at pin 1 of IC1; this is what is expected when the oscillator is working as designed and set to the 50Hz output. 1V RMS is around 2.8V peak-to-peak. Op amp IC1b acts as an inverting amplifier with a gain of 1.5 times. So the output at pin 7 is expected to be an inverted version of IC1a’s pin 1 signal, but with a 4.2V peak-to-peak value. Since IC1 is fed from a 3.3V supply, the output saturates at 3.3V peak-to-peak. The resulting waveform is between a sinewave and a square wave, so it will also have some odd harmonics of 50Hz present, the first of which is at 150Hz. Fig.2 shows the spectrum of the oscillator’s output at 50Hz. You can see that the only significant harmonic is the third harmonic at 150Hz, although its level is down by over 40dB compared to the fundamental. Note that we will still get a 3.3V peak-to-peak output from IC1b even if the signal from IC1a’s pin 1 output 34 Silicon Chip Fig.2: this spectral analysis of the Checker’s AC output shows that the strongest harmonic is the third, over 40dB below the frequency of interest. The peak at 0Hz is due to the DC offset and using a grounded oscilloscope, instead of referring the signal to the 1.65V test point, TP2. drops as low as around 0.8V AC RMS or if it was higher than 1V AC RMS due to the saturation effect. This amplified signal from IC1b (at pin 7) passes through the three RC lowpass filter stages. If the digital potentiometers are set to around 5.5kW, each stage will cause a 60° delay to the 50Hz component and approximately halve its AC amplitude (as measured at each successive capacitor). Other, higher-frequency components will be delayed more and attenuated even more. For example, the third harmonic of 50Hz at 150Hz will be phase-shifted by around 80° and be reduced to about a fifth of its original amplitude by each stage. The three stages interact to a degree, so a simple mathematical analysis of each stage separately does not quite match what happens when they are combined. Before building the prototype, we had to simulate the entire circuit to determine the required component values. The result is a relatively pure 50Hz signal, but with quite a low amplitude coming into pin 3 of IC1a. But as long as the pin 7 output of IC1b is saturated on each cycle, the level is steady. IC1a acts as a non-inverting amplifier with a gain set by the ratio of the 330W fixed resistor and the fourth variable resistor in IC4. This gain is selected to bring the attenuated signal from the RC filter stages back up to 1V RMS and is fed to TP1 via a 100W resistor to protect IC1 from external short circuits. TP2 is connected to the 1.65V reference so that the sinewave between TP1 and TP2 can be measured without a DC offset. So, the AC signal frequency can be changed by adjusting the three variable Australia's electronics magazine resistor elements in the three RC networks. Similarly, the amplitude can be varied by adjusting the fourth variable resistor value. The resulting waveforms are shown in Scope 1. The primary output signal is the blue trace, while the red trace is the saturated output at IC1b’s pin 7. Note that it is inverted compared to the blue trace. You can see that the orange, yellow and green traces are phase-shifted and attenuated by each successive RC stage. The green trace is amplified to become the blue trace, thus completing the feedback loop. Control circuitry IC4 is a PIC16F1459 microcontroller that adjusts and monitors the AC reference for accuracy, among other tasks. It is powered from the 5V USB supply with a 100nF bypass capacitor between pin 1 (5V) and pin 20 (ground). A 10kW resistor between pins 1 and 4 pulls up the MCLR pin to allow normal operation when the circuit is powered. IC4 needs both an accurate voltage and frequency reference to do its job. The 3.3V output of VREF1 goes to JP1, and with the appropriate jumper fitted (in the ‘Run’ position), it feeds through to pin 16 (AREF+) of IC4. Since pin 16 also provides the PGD programming function, JP1’s other jumper position (marked ‘Prog.’) connects to programming header CON2. The other programming signals from IC4 are also connected to CON2. This includes MCLR, 5V, ground and PGC at IC4’s pin 15. Pins 13 and 14 connect to the AC reference output at TP1 and the 1.65V AREF signal, respectively. These are monitored by the ADC (analog to siliconchip.com.au Scope 1: the blue trace is the AC output signal at TP1, while the red trace is measured at output pin 7 of IC1b. The orange, yellow and green traces are measured at the top of each 1μF capacitor to the left of IC1a in Fig.1, from left to right. digital converter) peripheral in IC4 to check the frequency and amplitude of the output signal. The frequency reference comes from 16MHz crystal X1, connected to IC4’s pins 2 and 3 (CLKIN and CLKOUT). A 15pF load capacitor connects from each side of the crystal to circuit ground so it will oscillate correctly. Three LEDs, LED1-LED3, connect to IC4 via 10kW series resistors. The LED cathodes are grounded, so the LEDs illuminate when pins 8-10 are pulled high. Two tactile pushbuttons, S1 and S2, connect to pins 11 and 12. The other side of each switch is grounded while the pins are internally pulled up, allowing the micro to detect when the button is pressed. These LEDs and buttons provide a basic control interface for operating the Multimeter Checker. Control of digital potentiometer IC2 is over an SPI serial interface, with pins 5, 6 and 7 of IC4 being connected to pins 14, 12 and 11 of IC2. These lines have the roles of SCK (clock), SDI (data) and CS (chip select), respectively. Since IC2 uses an unusual 10-bit interface and a high data rate is not needed, the SPI commands are sent via bit-banged GPI/O operations. This also allowed us to simplify the PCB layout as we did not need to use the dedicated SPI (MSSP peripheral) pins, but could use any digital I/O pins. Pins 17, 18 and 19 are associated with IC4’s USB peripheral, so pins 18 and 19 are taken to the CON1 USB socket, and pin 17 is fed 3.3V from REF1. This means that the Multimeter Checker can be controlled and monitored by being connected to a computer’s USB port too. The PIC16F1459 was chosen as a siliconchip.com.au suitable part because we could not quite fit the necessary features onto a 14-pin microcontroller. But the presence of the USB interface means that we can add some other interesting and valuable features too. Finally, we get to the power supply. We’ve chosen a USB supply for its ubiquity. The 5V supply also gives more headroom than the 3V coin cell from the earlier design. After all, the 3.3V voltage reference would not function from a 3V cell. It also allows us to produce a higher test current than a coin cell could supply. LED4 and a 10kW series resistor are connected across the incoming 5V supply to show that power is present. There is no onboard 5V regulator; we rely on the USB source to be within the normal 4.5-5.5V range. All of the onboard components running from the 5V rail can handle that. Firmware The firmware program that runs on IC4 has three main aspects. The first is the fairly straightforward task of monitoring the buttons S1 and S2 and controlling LEDs LED1-LED3, providing a basic user interface. The second is the USB interface. This appears as a virtual serial port when connected to a computer. Keystrokes from the computer are stored in a buffer and handled much like button presses, but with extra functions. There is also the option of ‘printing’ status updates to the serial port, so the Multimeter Checker can provide more detailed information via the virtual serial port than can be displayed with the LEDs. Finally, IC4 is responsible for setting and monitoring the AC reference voltage output. It has no control over Australia's electronics magazine the DC voltage or current references, although it uses the DC voltage reference to check the AC voltage. The crystal oscillator used for IC4’s timebase ensures that all timing is accurate, particularly in measuring the frequency. The microcontroller samples the AC voltage waveform and checks its period (and thus its frequency), peakto-peak amplitude and average absolute amplitude (with reference to the 1.65V midpoint). Since the 3.3V reference is used as the scale for the ADC peripheral, the absolute digital value of the peak-topeak and average amplitude values are known and fixed in the program. The sampling works as follows. A timer interrupt fires 6000 times every second and takes a sample of the AC waveform. We chose this rate to allow integer divisions of 50Hz, 60Hz and 100Hz into that timer. Although that is not critical, it makes the calculations simpler. Just over 240 samples are taken, corresponding to two complete cycles at 50Hz. This is so that we can ensure that at least two positive-going zero crossings occur within each sample set; these are the points between which the period is measured. While 120 samples for a cycle at 50Hz does not seem like much precision, the firmware interpolates where the zero crossings occur to within 1/16th of a sample. It does this by calculating how much the samples before and after the zero-crossing are above or below the zero point. This way, the period can be measured with a resolution of around one part in 960 for a 100Hz signal, or better for lower frequencies. Sampling must occur without July 2022  35 interruption, so a set of samples is taken and then processed. Adjustments are made if necessary; then it goes back to sampling. By taking both the peak-to-peak and average amplitude, the Checker can also confirm that the waveform is sinusoidal, as a waveform with a different shape will not be able to match both. Oscillator adjustments The four digital potentiometers each have 256 steps. This is what limits the amplitude accuracy to 0.5% (about 1 part in 200), as the steps are about that far apart. In practice, a small amount of dithering occurs, so the average over several cycles will be closer to the target, close to the accuracy of the 3.3V reference. The frequency can be controlled more closely than the amplitude, as three potentiometers are involved. Rather than stepping all three together, each is incremented in turn, giving almost three times as many steps. This resolution results in steps of around 0.1Hz at 50Hz up to 0.3Hz at 100Hz, around 0.3% in the operating range. Like the amplitude, dither over several cycles improves the longer-­term average accuracy of the frequency. We’ll mention the full details of the USB interface a bit later. It provides a manual mode that allows direct control of the digital potentiometers. Construction The Multimeter Checker is built on a small PCB, 65 × 58.5mm, coded 04107221 – see Fig.3. It is mainly populated with surface mounting parts, although they are all pretty large and easy to work with. The only part with a smaller pin pitch than 1.27mm is the USB socket, and all passives are M3216/1206 parts at around 3.2 × 1.6mm. We’ll assume you have flux, solder wick, tweezers and all the other gear for working with these sorts of parts. Fume extraction is a good idea when working with flux too. Start by fitting the USB socket, CON1. Apply flux to the pads on the PCB and insert the socket’s locating posts into their holes on the PCB. Clean the iron’s tip and add fresh solder. Carefully apply the tip to each lead in turn without touching the metal shell. After soldering each pin, use a magnifier to check that there are no solder bridges, and if there are, use the wick to remove them. If you can’t see, clean off the flux residue with alcohol or a flux cleaner. Parts List – Multimeter Checker & Calibrator 1 double-sided PCB coded 04107221, 65 × 58.5mm 1 mini USB Type B socket (CON1) 1 5-pin right-angle header (CON2; optional; only needed for in-circuit programming) 1 3-pin header and jumper shunt (JP1) 2 small SMD two-pin tactile switches (S1, S2) 1 16MHz low-profile HC-49 crystal (X1) Semiconductors 2 MCP6272 or MCP6L2 dual low-power rail-to-rail op amps, SOIC-8 (IC1, IC3) 1 AD8403ARZ10 4-channel 10kW digital potentiometer, wide SOIC-24 (IC2) 1 PIC16F1459-I/SO microcontroller programmed with 0410722A.HEX, wide SOIC-20 (IC4) 1 MCP1501T-33E/SN 3.3V voltage reference, SOIC-8 (REF1) 4 green LEDs, 3mm through-hole or M3216/1206 SMD (LED1-LED4) 1 BC817 50V 800mA NPN transistor, SOT-23 (Q1) Capacitors (all 10V+, X7R or C0G ceramic, SMD M3216/1206 or M2012/0805) 4 1μF 5 100nF 1 1nF 2 15pF Resistors (all M3216/1206 1% 1/8W except as noted) 1 15kW 12 10kW 2 1kW 1 330W 2 100W 2 33W 0.1% Complete Kit: includes all the parts listed above and is available for $45 + P&P, Cat SC6406 36 Silicon Chip Australia's electronics magazine If you find a solder bridge, apply fresh flux to the leads and press the wick against the bridge using the iron, then carefully pull both away. When the smaller leads look tidy, solder the larger pads for the shell, turning up the heat if necessary. Fit the four ICs and REF1 next. These are all SOIC (small outline IC) parts of various sizes, but don’t mix up REF1, IC1 and IC3 as they all have eight pins. Note that IC3 and REF1 face in opposite directions too. Check the part markings against the parts list and PCB silkscreen as you go, making double sure that pin 1 is correctly orientated in each case before soldering any pins. For each part, apply flux, then tack one lead in place, ensuring the correct orientation by checking the silkscreen dot and IC markings. If the pads are all well aligned, solder the remaining pins; otherwise, adjust as needed by reapplying heat from the iron. Like with CON1, check for solder bridges and remove them as needed. It’s usually easier to solder all the pins before removing any bridges. Q1 is the only transistor on the board, and it should be fitted as shown in the photos and overlay. It’s the smallest part overall, so be careful not to lose it. But as the leads are widely spaced, it should not be difficult to solder. Install the capacitors next. The values will not be marked on the parts themselves, so work with one value at a time. The values required for each location are shown in Fig.3. Solder one lead, check that the part is square, flat and even within its pads and then solder the remaining lead. Refresh the first lead if necessary. Remember to add flux to the PCB pads as you go, regularly cleaning the iron tip and then adding fresh solder. The resistors should be marked with codes representing their values. They are all the same size; check Fig.3 or the PCB silkscreening to see which values go where. We used larger pads for the 33W precision resistor in case part shortages meant that we couldn’t get the high-­ accuracy parts in an M3216/1206 size, so don’t be concerned that the part is much smaller than the pads. Now fit the four LEDs. They are all in one corner of the PCB and have their cathodes to the right, as indicated by the cathode symbol on siliconchip.com.au Fig.3: most components are relatively easy to solder; the USB socket is a bit tricky because its pins are pretty close together. During assembly, the most critical thing to check is that all ICs are orientated correctly, with their pin 1s in the positions shown. Also ensure that the solder makes contact with the pad and pin of each device and check carefully for solder bridges between pins when you’ve finished. the silkscreen. You can use either M3216/1206 surface-­mounting types or 3mm through-hole LEDs. For through-hole LEDs, the anode lead is usually longer. If using SMD LEDs, they should have green cathode markings, but it’s pretty easy to check them with a DMM set on diode test mode. Hold the probes on either side of the LED (making sure it doesn’t fly away!). If the LED lights up, the red probe is on the anode and the black probe on the cathode. The two tactile switches mount near the LEDs. Install these in the same fashion as the other two-lead parts. That completes the surface-mounted parts, so you can now clean off the flux residue. The remaining components are all through-hole types, and some are optional. Fit crystal X1 next. You should not need an insulating pad under the metal case as the two mounting pads are covered with solder mask on the top of the PCB. However, if the solder mask in that area is damaged, add an insulator or mount it off the PCB surface. Regardless, verify after soldering it that its case is not shorted to either pad underneath. If you have a pre-programmed microcontroller (IC4), you don’t need to fit CON2, the in-circuit programming header. In this case, you could also replace JP1 with a short wire link across the pair of pads on the “R” side of the jumper. Otherwise, fit both headers and install the jumper shunt initially in the “P” position for programming. Although we have not used them on our prototype, we’ve scattered a few 3mm holes around the PCB to fit standoffs if you want to mount the Checker to something. siliconchip.com.au Programming If you don’t have a pre-programmed microcontroller, you will have to program it now. The Silicon Chip Online Shop offers a complete kit for this project; if you’re using that, the micro will be programmed, and you won’t have to worry about this step. Using a PICkit 3, PICkit 4 or Snap connected to CON2, load the 0410722A.HEX file onto IC4 using the Microchip IPE (integrated programming environment). If you are using a Snap, you likely will need to supply power to the board; this can be done using a USB lead connected to CON1. When power is applied, LED4 will light up. So if you don’t see LED4 illuminated, check for power and that the circuit has been built correctly before proceeding. After programming, disconnect the programmer and move JP1 from the “P” (program) position to the “R” (run) position. Testing When the unit is powered up, it will start in 50Hz mode, and LED1 should be solidly lit to indicate this. Pressing S1 will cycle through the 50Hz, 60Hz and 100Hz modes. LED1-LED3 light up in turn to show the current mode. Pressing S2 switches between the default pure sinewave to a more saturated waveform. You can use this to check how the multimeter responds to AC waveforms that are not pure sinewaves. In this mode, the amplitude is set to a high level (causing saturation of the op amp output and clipping). The LEDs indicate this mode by flickering rapidly. This waveform may be easier to verify during initial testing, as it does not depend on the microcontroller correctly detecting the amplitude. Australia's electronics magazine If the LEDs are flashing slowly (around 1Hz), the Checker has not been able to verify that the output frequency and amplitude are correct. They might flash briefly on a mode change, but there is a problem if they continue flashing for more than a few seconds. In this case, first double-check that JP1 is in the run position. This connects the 3.3V reference to the microcontroller, so if it is still in the programming position or not fitted, the micro cannot confirm the AC output level. One bad solder joint, especially around IC1 and IC2, will be enough to corrupt the waveform, so check those areas too. If you have an oscilloscope, you can verify that the waveform at TP1 is a 1V RMS sinewave offset by 1.65V DC. The DC level can be eliminated by using AC coupling on the ‘scope. Be careful not to ground TP2 unless the supply to the Checker is floating (for example, it is powered by a USB battery pack). USB control Connecting the USB interface to a computer will provide a lot more information, so do this if possible, especially if you are troubleshooting. The Checker should not need USB drivers on recent operating systems, and you can simply use a serial terminal program to communicate. We usually use TeraTerm on Windows, but programs like Putty, the Arduino Serial Monitor or MMEdit can also be used. On Linux, minicom is one option. Find out what serial port has been allocated and open this with your terminal program. You will not need to set a baud rate as it is a virtual serial port. July 2022  37 Typing “1”, “2” or “3” will change the mode to 50Hz, 60Hz or 100Hz. You will see the LEDs change as the mode changes. Pressing “S” selects the sinewave mode, while the “R” key sets the saturated output (think “rectangular wave”). Pressing the space bar will produce a status report over two lines; this can be seen at the top of Screen 1. The first line shows the current control variables; “A” controls the amplitude and “F” controls the frequency. The second line shows the reported amplitude (V) and frequency (F). Pressing “M” sets manual control mode. All three LEDs will light together in this case, and you can set the A and F parameters manually. The A parameter is changed with the full stop and comma keys (think of the <> above them on the keyboard). Increasing the A parameter will decrease the output amplitude. Once the output voltage drops below 0.8V AC RMS, it may drop off altogether as there is insufficient gain around the feedback loop to maintain oscillation. Still, it will recover once a valid setting is selected. You can change the frequency with the “−” and “+” (or “=”) keys. The F parameter can span between 1 and 750, corresponding to approximately 45Hz to over 1kHz. The Checker cannot accurately display frequencies over about 600Hz, so the use of this end of the range is not recommended. Manual mode is terminated by pressing S1 on the board, or selecting the 50Hz, 60Hz or 100Hz modes from the USB interface using the 1-3 keys. Using it Before you start using our Checker, you should refer to the calibration section in its manual (if present). When using our Checker, you can check or calibrate a multimeter in the following modes: • DC voltage – connect the probes between TP5 and TP6 on a range like 20V DC and check/adjust for 3.300V. • AC voltage – connect the probes between TP1 and TP2 on a range like 2V AC and check/adjust for a reading of 1.00V. This should be correct regardless of whether the meter is a True RMS type or not, as it is a pure sinewave. • Direct current – connect the probes between TP3 and TP4 on a range like 200mA and check/adjust for 100mA output. TP3 is the current source and TP4 is the sink, so you might get a negative reading unless the red probe goes to TP3. • Alternating current – connect the probes between TP1 or TP2 with a 100W 1% or 0.1% resistor in series. Set it for a low range and check for a reading of 10mA. • Resistance – connect the probes between TP7 and TP8 on a range like 200W and check/adjust for a reading of 33.00W. • Frequency – connect the probes between TP1 and TP2 on a range like 200Hz and check for a reading of 50Hz, 60Hz or 100Hz (set using pushbutton S1 and LEDs1-3). For best results, press S1 until LED3 lights and check/adjust for 100.0Hz. • Duty cycle – connect the probes between TP1 and TP2 and check for a Here we are probing TP1 & TP2 (ACV) with an Agilent (now Keysight) U1252A DMM. This result is within 0.03% of the expecting value, which shows that the meter’s calibration is still good, and demonstrates the accuracy of the Multimeter Checker & Calibrator. 38 Silicon Chip Screen 1: a typical output from the USB serial port. You can trigger the two-line reports shown here by pressing the space bar, while the single-line entries are due to manual changes in the amplitude and frequency settings. Mode changes do not produce any output but will be seen in changes to the illuminated LEDs on the Checker. reading of 50%. For best results, press S1 until LED3 lights. • True RMS readings – press S2 to activate the modified wave mode and check the AC voltage reading between TP1 and TP2. The displayed voltage should be above 1V RMS; our prototype produces 1.27V RMS in this mode. A higher reading suggests your meter uses the average method. In comparison, a lower reading suggests it uses the peak method (as the peakto-peak voltage in this mode is 3.3V, a peak-reading multimeter will generally show around 1.17V). Summary While we set out to add an AC voltage and frequency reference to an otherwise straightforward DC reference design, we think that being able to control the operation of the AC source manually will be a handy feature that many people will use. The USB interface also gives this handy little device a range of possible uses. One thing to watch out for is noisy USB charger power supplies; they can cause frequency measurements of the ACV output to be unstable. In that case, the best solution is to power it from a USB power bank. A laptop USB port usually provides enough clean power to get stable readings from the Multimeter Checker. SC Australia's electronics magazine siliconchip.com.au ONLY 249 $ QM1493 Specialty meters combined with multimeter functions. HIGH VOLTAGE INSULATION TESTING "MEGGER" • MULTIMETER FUNCTIONS • DIGITAL DISPLAY • ANALOGUE BARGRAPH • DATAHOLD ONLY 89 $ TAKE EASY ENVIRONMENTAL MEASUREMENTS • MULTIMETER FUNCTIONS • SOUND LEVEL • LIGHT LEVEL • INDOOR TEMP • HUMIDITY TEST WIRING INSULATION 95 ONLY 139 $ QM1594 TEST ALMOST ANYTHING! QM1632 CONTACTLESS HIGH CURRENT MEASUREMENTS • MULTIMETER FUNCTIONS • TRUE RMS • AUTORANGING • CAPACITANCE • NON-CONTACT VOLTAGE MEASURE HIGH CURRENT ALL MODELS FEATURE: • AUTORANGING • AUDIBLE CONTINUITY • MAX / DATA HOLD DETECT OPEN, SHORT OR MISS-WIRED LAN CABLES • MULTIMETER FUNCTIONS • PINOUT INDICATOR ONLY 8995 $ XC5078 GREAT FOR I.T. TECHNICIANS Multi-function Meters Saves you money and provides the convenience to carry just one tester in your toolbox. Specialty Function Display (Count) QM1632 QM1493 XC5078 QM1594 Clamp Meter up to 600A AC/DC Insulation Test up to 4000MΩ LAN Cable Test with pinout indicator Sound, Light, Humidity & Temp 4000 4000 2000 4000 Security Category Cat III 600V Cat III 1000V Cat III 600V/Cat II 1000V Cat IV 600V/Cat III 1000V Voltage 600V AC/DC 750V AC / 1000V DC 600V AC / 600V DC 600V AC / 600V DC 40MΩ 4000MΩ 20MΩ True RMS • Current 600A AC/DC Capacitance 100mF Resistance Frequency 200mA AC/DC 10A AC/DC 1000°C Non Contact Voltage • • 40MΩ 100µF 10MHz Temperature Relative Measurement • 10MHz 750°C • • • Explore our great range of multimeters, in stock on our website, or at over 110 stores or 130 resellers nationwide. • www.jaycar.com.au/specialtydmm 1800 022 888 Create highly detailed prints with Our Newest 4K 3D Printer The new Anycubic Photon Mono 4K resin printer is great value and perfect for any maker, from hobbyist to professional. J US IN! T • MAKE MODELS UP TO 165(H) X 132(W) X 80(D)mm • FAST 1.5 SEC LAYER CURE • REPLACEABLE ANTI-SCRATCH FILM • COMPATIBLE WITH PHOTON MONO FEP SHEETS • 2.8" TOUCH SCREEN • RESIN FILL INDICATOR • 10-50µm LAYER HEIGHTS • 6.23” 4K MONOCHROME LCD • 35µm XY RESOLUTION BRINGS VIVID DETAILS • 400:1 CONTRAST RATIO FOR SHARP & CLEAR EDGES • UV BLOCKING COVER • AUTO PAUSE IF COVER REMOVED MID-PRINT JUST 599 $ TL4419 Shop Jaycar for your 3D Printing needs: • 2 Models of Resin Printer, with over 45 types of resin • 8 Models of Filament Printer, with over 50 types of filament and counting! • Massive range of 3D Printer spare parts & accessories • In-stock at over 110 stores or 130 resellers nationwide Order yours today: www.jaycar.com.au/resinprinters Phone: 1800 022 888 LCD type printer review by Tim Blythman & Nicholas Hannekum ANYCUBIC Photon Mono Resin-based 3D Printer Resin-based 3D printers have been around for a while, but it’s only in the last few years that we have seen them experience a boom in popularity and availability. We tested this model (available from Jaycar) to see how it shapes up, especially compared to filament-based 3D printing. W e previously looked at several filament-based 3D printers, including the UP! in August 2011 (siliconchip.au/Article/1132), the RapMan in the December 2012 issue (siliconchip.au/Article/450) and the Vellemann K8200 in October 2014 (siliconchip.au/Article/8040). The Vellemann K8200 was available from both Jaycar and Altronics as a kit. Since then, pre-assembled filament-based 3D printers are much more prevalent and can be purchased even more cheaply than the kits from less than 10 years ago. We also covered other 3D printing technologies in detail in January 2019 (siliconchip.com.au/Article/11367). That article covered 3D printers that siliconchip.com.au use a plastic filament, also called material extrusion, fused deposition modelling (FDM) or fused filament fabrication (FFF). It also described other technologies, including binder jetting, directed energy deposition, material jetting, powder bed fusion, sheet lamination and vat photopolymerisation. The last of those is also commonly known as resin 3D printing. Like filament 3D printing, the technologies needed for resin 3D printing have been known and patented for around 30 years. The recent expiry of these patents has allowed the unencumbered use of these technologies, resulting in machines that you can now purchase at quite reasonable prices. Australia's electronics magazine Resin 3D printing While the term vat photopolymerisation is a bit unwieldy, it does sum up how resin 3D printing works. The raw resin in a vat is photopolymerised, which means that it is hardened by the selective application of light. This is done in layers to build up the object (see Fig.1). Vat polymerisation can be broken down into three major subsets: SLA, DLP & LCD printing. The main difference between each type of printing is the type of light source used: • SLA (stereolithography) is the most common form, whereby a UV ‘laser’ is used to trace each layer of resin. July 2022  41 Cover Vat detail Z lead screw Platform securing knob Platform bracket Spout Printing platform Frame Vat retaining screw Resin vat USB port Fig.1: the basic principles of resin 3D printing are shown. Many smaller printers use an LCD panel to project an entire layer rather than scanning with a laser or DLP device. Source: “Digital Fabrication Techniques for Cultural Heritage: A Survey” • DLP (digital light processing) instead uses a single UV projector with the light selectively directed to process a whole layer at once. • LCD (liquid crystal display) is nearly identical to DLP except it uses an array of LEDs as the UV light source which is imaged via an LCD panel. There are quite a few parallels to filament-based 3D printing, including the use of ‘slicer’ software to process computer models into the printer’s working files. There are also several significant differences, which we’ll discuss in detail later. In practically all cases, the resin hardens when exposed to a UV light. The resin consists of photosensitive compounds which release free radicals on exposure to specific wavelengths of light. These free radicals cause other substances in the resin to combine into the final, solid resin polymer. A movable platform, analogous to the print bed on a filament-based 3D printer, moves away from the panel to create the third axis perpendicular to the platform surface. Anycubic Mono UV Photon The Anycubic Mono UV Photon is reasonably representative of the resin 3D printers that use an LCD panel. 42 Silicon Chip Touschscreen FEP film Power switch UV LCD screen (under vat) Fig.2: the main parts of the Mono. The FEP Film is a thin transparent plastic film that allows the UV light to pass through and cure the resin. Some larger 3D printers use the scanning laser technique, but otherwise, the parts and operation will be similar for the commonly available consumer resin 3D printers. We purchased our unit from Jaycar Electronics (Cat TL4422). Note that it will be discontinued as there is a higher-­resolution “4K” version replacing it (Cat TL4419). You might still be able to pick up one of the reviewed printers from Jaycar if you are quick. These printers are very similar and you can expect everything we say about the review unit to apply to the 4K version, with the benefit of finer details on the newer version. Returning to the printer we’re reviewing, It has a nominal print area of 80 × 130 × 165mm. Many resin 3D printers use a similar LCD screen to a mobile phone, which helps to explain those relatively small dimensions. The availability of off-the-shelf screens such as these is part of why prices for such 3D printers have dropped. The overall size of the printer is 222 × 227mm at the base and it is 383mm tall. So it’s quite compact. The nominal resolution is 0.01mm (10μm) on the vertical (Z) axis and 0.051mm (51μm) on the horizontal (X and Y) axes. The horizontal resolution is due to the LCD itself, while Australia's electronics magazine the motion hardware limits the vertical resolution. All of these figures are much finer than commonly found on filament-based 3D printers. We’ll refer to it as the Mono, as Photon is the name Anycubic appears to give to all its resin 3D printers, and we feel that the UV label is implicit. It’s called the Mono because it uses a monochrome LCD panel. Many other similar printers use commonly available RGB panels, resulting in longer print times as the RGB panels do not pass as much light as monochrome panels. Fig.2 shows the main parts of this type of printer. In operation, the Z lead screw moves the platform vertically. The hex screws on the platform allow it to be adjusted correctly when the Z-axis is at its bottom home position. During printing, the Z-axis moves upwards as successive layers are exposed. One side effect of this motion is that the object is printed upside-down (compared to a filament-based 3D printer), leading to some subtle and interesting side effects. Setting it up Naturally, we dove straight into trying the 3D printer out. Here’s our experience of starting to use the Mono. siliconchip.com.au We expect many similar printers are much the same. We started with a 500mL bottle of Anycubic clear resin (Jaycar Cat TL4427) as the clear resin would let us inspect the interior of 3D printed parts. We also printed some parts with grey resin, as you can see from our photos. We had no trouble with the quickstart guide, although the instructions are brief. There are a couple of presliced files on the included USB stick, so you don’t even need to install the software to start printing. We simply plugged in the USB stick to the Mono. We later switched to a shorter USB stick so that it didn’t protrude as far from the printer’s body, reducing the risk of it getting damaged. We found that even a 1GB stick was ample, with most sliced files coming in under 10MB. After unpacking and assembling, the essential preliminary step is to set the platform using the four hex head screws. There is a piece of paper included specifically for this purpose. Like a filament-based printer, the ideal gap between the platform and the UV LCD screen is about the thickness of a sheet of paper. In the case of the Mono, this gives space for the thin film of the resin bath. There aren’t too many functions on the Mono’s touch screen, so it’s easy enough to navigate. Still, the “Home” option, which we expect would be used regularly, is quite deep in the menu structure. After the platform is homed, the hex head screws are tightened to fix this positioning. The instructions say to press the “Z=0” button before continuing. After this, the platform moves up to allow the resin vat to be inserted. While it appears that the thin FEP (fluorinated ethylene propylene) membrane of the resin vat would be a suitable thickness for calibration (and we did use it on occasion when the vat and platform were wet with resin), we can see a good reason for removing the vat. A common catastrophic failure mode is for the platform to be driven into the UV LCD screen with something solid hidden in the resin. This cracks and damages the LCD (fortunately available as a spare part). This is more likely than you might think, as many failed prints result from the printed object detaching from the platform and falling into the resin. Even using clear resin doesn’t help siliconchip.com.au much, as a transparent object is practically invisible in clear resin! Accessories and safety The Mono includes several tools in the box. There are two scrapers, a plastic mask, some gloves, a handful of filter funnels and three hex wrenches (Allen keys). The manual also notes that safety glasses should be worn when handling the resin. The mask, gloves and filter funnels should be considered consumables. There is some discussion online that the mask supplied (which appears to be the type used for protection against dust) will not block the resin fumes, and we found that to be the case. The most common advice is to work in a well-ventilated area, such as near an open window. However, consider that sunlight (which includes a significant amount of UV) should be kept away from the printer to prevent the resin from being prematurely cured! The gloves and glasses are to prevent skin and eye contact with the resin; the MSDS lists irritation as a side-­effect of skin contact. We didn’t notice any discomfort when we did get resin on our skin, although this will vary from person to person. Thorough rinsing and washing with soap and water is the recommended way to remove resin on the skin. The most extreme cases of exposure involve the resin being retained in the skin and slowly hardening. We imagine that this would be nasty if you got it in your eye. Fortunately, the resin is safe after it hardens, so the general advice for disposing of surplus liquid resin is to leave it in the sun to harden. not necessary if you take care, but you must wear safety glasses as this is when the resin could easily splash. The inside of the vat is marked with graduations in millilitres as well as a MAX marker. Filling above the MAX marker might cause the vat to overflow when the platform is lowered into the vat. The slicer program reports an estimate of the resin volume needed, although this will vary with resin type, temperature and even the degree of exposure selected. We found that we needed an excess of at least 10mL to avoid running out. Since there will be an excess of resin needed in any case, we found it easiest to be generous, as the resin can be later reclaimed using the filter funnels. The printing process The “Print” menu item simply lists the available files on the USB stick, including a name and a thumbnail that looks like the view from the slicing software. Play and pause buttons control the process. A remaining time display is shown Adding resin The last step before printing is to add resin to the vat. Wearing gloves is probably This 3D printer also comes in a 4K resolution model called the Mono 4K (twice the standard resolution). Australia's electronics magazine July 2022  43 during printing. We found it was pretty accurate but consistently underestimated by about a minute for every hour of printing time. What you have read so far may lead you to believe that resin 3D printing is quite simple. Of course, there is some subtlety to the way the Mono (or, we expect, any other resin 3D printer) does its job. ‘Exposure time’ is a critical parameter for resins. It varies from resin to resin and needs to be longer for thicker layers. Critically, it is not the only time that is spent by the printer on each layer. The default exposure time for the Anycubic resin is two seconds per 50μm layer. But the actual cycle time per layer is on the order of 10 seconds as other things need to happen. When the printer is ready to start its exposure time for a layer, it passes the image to the LCD, turns on the UV backlight and counts down the exposure time. It then turns off the backlight and clears the LCD. There may now be an ‘off’ period, where everything is left as-is for a few seconds, allowing the freshly exposed resin to settle. Both the absorbed UV light and the chemical reaction it triggers can generate heat, so this period also allows the heat to dissipate. The printer then lifts the platform to detach the freshly printed layer from the FEP film. While FEP is a similar material to Teflon, the resin still sticks to it quite well. The tearing/popping sound it makes is disconcerting, but perfectly normal. The Mono’s default setting is for a lift of 6mm at 4mm/s, so it takes a few more seconds to lift the platform clear of the FEP and then reposition it for the next layer. The platform returns to a point that is higher by the layer thickness, to allow the next layer to be printed. After the printing sequence, the platform is moved upwards, although items close to the Mono’s height limit might not clear the resin vat. The printed object can be left to allow any excess uncured resin to drip for a few minutes. Fig.3: these small, inexpensive UV nail lamps work well for the final curing step. As with any UV source, we recommend wearing eye protection while using such devices. the bed, any supports are removed; that is usually enough for most designs. For a resin printer, the part needs to be removed from the platform and then any excess liquid resin must be rinsed off by solvent washing and possibly mechanical cleaning. After removing the supports, the part undergoes further UV exposure to ensure that the resin is fully cured and hardened. Not only are there more steps, but they are also much messier due to the sticky liquid resin. Anycubic also sells a ‘wash and cure’ machine, which can help with some of these steps. It’s at this point that gloves are needed. An organised (and, if possible, spacious) workspace is imperative, as you do not want to be moving things around while wearing sticky gloves. We recommend employing a large work area with a lip (to contain liquid resin) to remove the part from the platform, alongside two containers of cleaning solvent and next to another open area where clean parts can be placed to dry. We kept the Mono on a large plastic tub lid to provide a ‘catchment’ for leaks. It certainly helped with the occasional drip while removing parts Post-processing from the printer. One crucial way the resin 3D printThe most common arrangement uses ing process differs from filament two tubs of cleaning solvent. One is 3D printing is in the manual post-­ used for the first pass, to remove the processing steps. For a filament 3D bulk of the excess resin, and the secprinter, after removing the part from ond to finish. The solvent from the 44 Silicon Chip Australia's electronics magazine second tub can be recycled to be used in the first step. We’ve even seen some people use a third tub to clean the platform, keeping it out of the way while the parts are cleaned. So despite it being a small machine, you’ll probably still need a good amount of nearby space in which to work. To remove the printed part from the printer, the screw on the platform is loosened to detach the platform, and the platform is rested on its edge. The metal scraper can then be used to separate the part from the platform. Substantial force might be needed, potentially making this step messy if the part flies off. The part is placed in the first solvent tub, which is agitated to remove the uncured resin. It is then moved to the second tub to remove any remaining resin. It’s then placed on a flat surface to allow the excess solvent to evaporate. This last step is critical. It should be left until no shiny spots remain. Resin mixed with solvent stays sticky, even after the next curing step, and can only be removed with further solvent processing. Solvent options We tried three different solvents. While some people swear by isopropyl alcohol, we found that they all were quite capable of doing the job. Isopropyl alcohol was actually the last we tried because it still appears to be in short supply and, where available, it siliconchip.com.au least compared to the Anycubic resin. It tended to end up with a slightly yellow tint and did not seem to be as dimensionally stable as the Anycubic resin. We suspect that is due to the heating and expansion that occurs during the UV curing process. Some resins also expand as they solidify. On the other hand, we found that this resin needed slightly less exposure time, so we could print a bit quicker with it. The cured eSun resin also had a very odd bluish cast in sunlight. We suspect that is due to the photoreactive compounds present in the resin fluorescing in the presence of UV light. Resin exposure range finder Fig.4: a sample print of the Resin exposure range finder (R_E_R_F) test file. Different parts are printed with varying exposure times to hone in on the ideal exposure setting. There are several different features to compare, and your choice might depend on whether you are printing coarse or finely detailed objects. is much more expensive. We first tried methylated spirits as it is the cheapest. It worked fine for dissolving the leftover resin, but leaves more residue that takes longer to evaporate. We suspect this is due to the additives or the small amount of water usually present in methylated spirits. Still, the results are satisfactory as long as the part is left to dry completely. We also tried acetone. It’s much more aggressive than either of the other two solvents and also evaporates quite quickly. Being more aggressive, you should ensure that your gloves can withstand it. Because it evaporates so quickly and thus cools, we suspect that water was condensing on the parts when it was humid. That water needs to evaporate before the part can be cured. The isopropyl alcohol works much the same as the methylated spirits, although there’s a bit less residue and, as we noted, is more expensive at the time of writing. fingernail polish and gels). They run from USB power, and the style we purchased costs around $10 from a local eBay seller, shown in Fig.3. The UV lamp has collapsible legs that can make it taller than small parts, and the timer runs for about 60 seconds. We found that using this lamp for a minute on each side of the part was enough to cure it fully. Resin choices There are a rapidly growing number of resins now available. Apart from the obvious choice of different colours, different material properties are also possible. Many quote strength, density and hardness, although the standard resins often seem to be the strongest. Subjectively, we felt that the standard Anycubic resins gave the best results. We tried the eSun eResin-PLA from Jaycar, also in the clear variety, although it comes in a handful of colours. It claims to be ‘low smell’, and we found that to be the case, at One of the files on the USB stick is called R_E_R_F.pwmo (.pwmo is the file type of the ‘sliced’ file used by the Mono). This special file is used to help calibrate the exposure time. When this file is printed, different parts are printed at different exposure times to allow the optimum time to be found. Fig.4 shows a sample print of this file, and you can see that the part at lower right is obviously underexposed. Not as evident in the two adjacent parts is that the small pillar features are missing, so the optimum setting is towards the middle of this print. See the later panel for further discussion on what resins are available. Software At a bare minimum, you will need to use the Photon Workshop software to ‘slice’ models into a format suitable for printing. There was a version on the USB stick, but we downloaded a later version, 2.1.24, from siliconchip. com.au/link/abet It’s common to work with .stl files, but .obj model files are also supported, as well as several sliced formats (see Fig.5). We found this handy when trying a model from www.thingiverse. com in the .obj format. Curing The last step is to use UV light to fully cure the resin. The wash and cure machine has a turntable that evenly exposes the part to UV light, but we found that simply leaving the part outside in the sun for half an hour, while turning it over occasionally, was adequate. We also tried a small UV lamp of the type sold as a UV nail lamp (for curing siliconchip.com.au Fig.5: raw mesh files in .stl and .obj formats can be loaded into Photon Workshop, as can pre-sliced files of the various types shown. Loading pre-sliced files will not give as many printing options, as you cannot change aspects such as the layer height. Australia's electronics magazine July 2022  45 Fig.6: the Photon Workshop application, showing a 3DBenchy loaded. The 3DBenchy test object (by www.creativetools. se) can be downloaded from www.thingiverse.com/thing:763622 At left are the various transforms that can be applied to rotate, move and scale objects, while the slicer settings are at right. Supports can be created using a second tab on the right. If you are designing your own files for printing on a filament 3D printer, much the same process will apply, except for using a different slicer program. For example, we use OpenSCAD to design .stl files for filament printing, and you could use those same .stl files on the Mono. As long as you can export .stl files from your 3D design package, you can import these into Photon Workshop. Fig.6 shows the Photon Workshop software. Most of the transform options on the left will be familiar to those who have used a slicing program from filament 3D printers. These allow loaded objects to be rotated, sized, moved and adjusted. At right are the exposure and printing settings. The program defaults to two-second exposures for 0.05mm layers, but we mostly used five-­second exposures with 0.1mm layers to speed up printing slightly. Note how the time more than doubles going from 0.05mm to 0.1mm, presumably due to the UV light being attenuated as it passes through thicker layers. We also did some prints with much thicker layers to improve the printing time and found that 0.3mm per layer, with around 15s exposure, tended to be the limit. After this, the lift and peel 46 Silicon Chip time becomes less significant. In any case, 0.3mm is getting into the layer heights commonly found on filament printers, resulting in prints with noticeable jagged layer artefacts that begin to show the resin curing unevenly. Fig.7 shows a pair of test cubes, one printed with a 0.3mm layer height and the other with a 0.1mm layer height. Resin printing specifics Supports are common in filament printing, but are used in a slightly different way with resin printers. The general advice is that all resin 3D prints should use supports. This is primarily due to the way that parts adhere to the platform, but also because of the high forces that occur on each layer lift. Using supports means that the part can be printed on a detachable raft that can bear the scraper’s brunt while the part is being removed from the platform. The raft can also be expanded to provide a greater area to affix to the platform, reducing the probability of it detaching mid-print. Another factor is that the first layers (by default, six with the Mono) are overexposed to ensure good platform adhesion. This means that they will Australia's electronics magazine tend to be over-dimensioned unless compensation is made. Using supports means that the actual 3D model does not start until these early layers have been printed, meaning that they do not suffer from overexposure. There are some artefacts at the points where the supports contact the object, but we found that they snap off quite cleanly, and a light touch with sandpaper removes all traces. Fig.8 shows a part with a raft and supports; you can see how the supports taper to narrow points that make for clean breaks. siliconchip.com.au Fig.7: the left-hand cube was printed at 0.3mm layer height, while we printed the right-hand cube with 0.1mm layers. The staircase effect is much more pronounced at 0.3mm. Note how it is more prominent on the top half of the object. This is due to the way that the resin cures more the closer it is to the UV source, producing unevenness within thick layers. The holes visible are part of the punch and hollow features which can be used to reduce the amount of resin needed. We should point out that while Photon Workshop can produce supports and a raft, the ones shown in this image were done by a separate program. We tried PrusaSlicer from Prusa Research (www.prusa3d.com). Prusa Research has a substantial background in filament printers, but they also design and sell resin printers. Importantly, PrusaSlicer can export a 3D model (such as an .stl file) with supports added, allowing the now-­ supported model to be sliced by Photon Workshop. We just had to choose an appropriate Prusa Research printer, and the SL1 has a similar build size. Fig.8: the narrowing of the support pillars near where they join the model means they snap apart easily. Removing supports from resin prints is easier than on parts printed with a filament printer. It isn’t evident that the raft has an angled edge, which makes it possible to wedge the scraper underneath it to help remove the part from the platform. It might seem like an unnecessary extra step, but we found that the supports broke off more cleanly, and it was also a bit more intuitive to manually place support points using the PrusaSlicer program. Hollow and punch In the world of filament 3D printing, a partial infill is very common, with figures around 25%, allowing parts to be both light and strong. Various patterns are used, with trade-offs in print speed, strength and, in some cases, interior support. With filament printing occurring in the air, air fills the voids and it is trapped when the top layers are printed. Since resin printing occurs under the surface of a liquid resin bath, empty spaces are liable to be left full of the same. So the reasons and strategies for infill treatment are very different for resin printing; simply choosing an infill option is not enough to guarantee a hollow part. Both Photon Workshop and Prusa­ Slicer have a “Hollow” option that allows a wall thickness to be set, which is simple enough, leaving the remaining space inside the model hollow. Fig.9: the narrow pillars in this model boat are 0.3mm in diameter. You can just make out the 0.1mm layer lines below and the aliasing due to the 0.051mm pixels. With such fine details, the extreme forces that occur during each layer lift mean that such delicate parts must be designed with care and with an appreciation for the printing process. siliconchip.com.au Australia's electronics magazine July 2022  47 What resin is available? There are quite a few different resins available to use with the Anycubic Mono. The default type of resin is sold by Jaycar and comes in a 500g bottle with black, grey, clear, blue and green as available colours (Jaycar Cat TL4425-9). Anycubic also sells a more expensive, plantbased version (made from soybean oil) in 1kg bottles. It’s marketed as having less odour and shorter curing time at 50-60s exposure for the bottom layer and 8-10s exposure for other layers. It comes in translucent green, clear, grey, black and white colours, and it can be purchased online from websites such as Amazon. Third-party resins In terms of third-party resins, many should work if they’re suited for DLP or LCD printing and are rated with a UV wavelength around 410nm. We have only fully tested the eSun range, which is available from Jaycar. They sell a standard 1kg resin (Jaycar Cat TL44439), and PLA (polylactic acid) resin (Jaycar Cat TL4433-9) which can be cleaned with isopropyl alcohol. Both are available in red, yellow, white, black, grey, blue (sky blue for the standard resin) and clear. There’s also a water-washable version, which has the highest density range of the eSun resins, but in exchange has the lowest tensile strength (Jaycar Cat TL4450-3). Sadly they don’t list whether any of the above resins can be painted over, as that can be a nice feature if you’re assembling a garage kit or similar. Your best bet is to use clear resin when available as it should have less pigment, making it easier to paint. Monocure 3D from Australia also make resin that is suitable for the Photon Mono. You can find a list of compatible products on their website: https:// monocure3d.com.au/printers/photon-mono-x/ While not directly related to this printer, Formlabs have a very nice document listing all the different types of resins they sell along with their specifications; you can find this document at: siliconchip.au/link/abeu You can also find a general guide on 3D printing by Formlabs at https:// formlabs.com/asia/blog/3d-printing-materials/ But the model then needs to have holes added so that any liquid can be drained out of the model after printing. It’s possible to leave the resin inside, but that has no real advantage over simply printing the model solid in the first place. Since some resins can expand on curing, this could cause the model to swell and rupture if curing continues later. The “Punch” option adds holes, and they are simply placed by clicking on the model’s surface. More holes should be better, to allow air to enter and excess resin to leave, but they will also mar the model’s surface. Wall thicknesses of around 3mm are the default, with a similar size for the 48 Silicon Chip punched holes. The test cubes shown in Fig.7 were printed with 3mm walls and 3mm punched holes to test these features out. Draining the liquid resin from a model is another messy step that is added to the process, followed by the need to rinse and drain the cleaning solvent. We think that if it makes sense for you to print hollow objects, the best results will come from designing them to be hollow from the start. Most of the objects that we printed were relatively small, so the potential resin savings were not worth the trouble and effort. You’ll also find that objects printed in clear resin will show the outline of the hollowing, so there might also be Australia's electronics magazine cosmetic reasons why hollow objects are undesirable. Dimensionality We found the dimensions of printed objects to be very accurate, which is to be expected when two of the dimensions are created from a fixed-sized LCD screen, and the third is set by the steps and pitch of a worm gear driven by a stepper motor. One test model we printed had a 5mm square hole and a series of different sized holes. We found that the post had to be 4.9mm or smaller to fit in the hole. This is around two pixels of difference on the LCD screen! Unsurprisingly, the pixels tend to spread by a small amount. If they didn’t, adjacent pixels wouldn’t merge to become a solid object. But this effect is relatively minor. Fig.9 shows a printed model with some fine details, including pillars only 0.3mm across. Of more serious concern are the forces that distort an object as it is printed. As we mentioned, there are substantial forces involved as each layer is lifted up and away from the FEP film. The fine pillars in Fig.9 have only been printed successfully as they are vertical and the handrail is horizontal. Such fine elements would probably not have printed well if they were not aligned with the axes. You could add supports to the side of objects, but they will be of limited use on such small objects. We found that a good rule of thumb was to align an object so that it has a long vertical axis. Such alignment ensures a small footprint and thus suffers less lifting forces. This will also tend to result in the longest printing time. On a similar note, we found that thin sheet-like areas (even vertical) did not always print well. We suspect that the lifting forces cause stretching, leading to deformation as subsequent layers are printed and joined together. One upside of the whole layer being printed simultaneously is that multiple objects can be printed in the same amount of time as a single object, provided they fit in the print area. Impressions At the time of writing, we’ve used about three litres of resin, and the FEP film is looking noticeably worn and siliconchip.com.au scratched, although this doesn’t seem to be affecting the print quality. Spare FEP films for the Mono are available (Jaycar Cat TL4502), as are complete resin vats (Jaycar Cat TL4504). The LCD screen used for projecting the UV image onto the resin is also available as a spare part (Jaycar Cat TL4506). We’ve heard figures of around 1000 hours of operation before replacement is needed; that works out to about six weeks of continuous printing. It appears that the UV light eventually degrades the LCD to the point that it no longer blocks the UV light and needs to be replaced, although we haven’t seen any signs of this happening. Resin printing with the Mono is simple enough, although it can sometimes get messy. The resolution and detail are impressive. As you can see from our photos, the finish of the prints is very matte and almost has a texture like velour, although the layer and pixel artefacts might be visible, depending on the lighting. So models printed with the clear resin will not have a glassy finish, although a gloss lacquer can generally improve transparency on clear models and hide layer lines. Summary We’re impressed with the fine detail that the Mono can produce and how easy it is to use. Printing with it can get quite messy, but with the proper space and tools, it is manageable. There are a few consumables involved, and we suspect that the cost of these will add up after a few years. The print volume is smaller than most filament 3D printers, but we expect that the fine detail will appeal to those making smaller miniatures and other parts. We’ve found at least one other use for the Mono – see our panel on “3D Printing PCBs… sort of” for more information. We suspect there are other UV reactive substances (UV ink is one that we know of) that might be used in combination with the Mono. We haven’t tried it, but it might also be a handy way to erase EPROMs in a pinch! As noted earlier, the Anycubic Mono UV Photon resin 3D printer and select spare parts are available from Jaycar (www.jaycar.com.au/). SC siliconchip.com.au 3D Printing PCBs... sort of We covered using 3D printers as part of a home workshop process to make prototype PCBs in our “Modern PCBs – how they’re made” article from July 2019 (siliconchip.au/Article/11700). That article mentioned techniques like printing a thin layer of filament onto copper-clad fibreglass to act as an etch resist, or even directly printing conductive filament onto a substrate. But YouTuber Thomas Sanladerer demonstrates another use for a resin 3D printer that actually comes very close to how the professional PCB fabricators work at https://youtu.be/RudStbSApdE The technique uses the 3D printer’s UV LCD to selectively cure the photosensitive resist on a coated copper clad board, before the resist is fixed, and then the board is etched in the usual fashion. The results are both fast and remarkable. The photo below shows his first test PCB using this technique. That video screenshot also demonstrates the importance of the difference between positive and negative resist boards! He notes an exposure time of 60-90 seconds, although that will probably vary between printers and resist compounds. Given that the Mono’s resolution in the horizontal plane is around 50μm, 10mil traces (which are about the minimum that we typically design for) are about five pixels wide. In other words, it should be possible to create very fine PCB detail with this technique. The trick is converting Gerber files into something that the slicer program can process for the printer. Our Making PCBs article has more information about Gerber files. We don’t have access to the software that Thomas uses. Still, it appears that there are numerous ways to convert an image file to an .stl file, including via several online tools, so it shouldn’t be an insurmountable obstacle. Thomas also shows etching an image of a leaf onto a piece of copper-clad board, so it appears that there are many uses for this technique. With the existence of UV-curing inks, it may be possible to ‘print’ PCB silkscreen overlays too. This is something we’ll be trying out soon. Perhaps it won’t be long until we’re all making factory-quality PCBs ourselves! YouTuber Thomas Sanladerer (https://youtu.be/RudStbSApdE) shows how to use the UV LCD of a resin 3D printer to selectively cure photosensitive resist, producing home-made PCBs. Like him, you will have to be careful of the differences between positive and negative resist boards! Australia's electronics magazine July 2022  49 Make amazing prints with our wide range of Resin & Filament for 3D Printers 0 OV E R 2 I N S RE S CK & IN S TO G! IN COUNT FROM 3995 $ EA AVAILABLE IN 500G OR 1KG HIGH QUALITY RESIN Made specifically for colour or mono LCD/LED light source printers. 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IN COUNT PLA+ 1KG 3995 $ EA TL4454-TL4464 1KG 3995 $ EA TL4465-TL4471 EXOTIC RANGE INCLUDES RAINBOW 1KG FROM 39 $ 95 EA TL4477-TL4480 Are 100% bio-degradable and FDA food safety approved. • 10 times stronger than regular PLA • Smoother prints • Low material shrinkage rate • No cracking or brittle issues • 12 colours to choose from PETG Stronger than regular PLA • Smooth & delicate prints • Low material shrinkage rate • No cracking or brittle issues • 7 colours to choose from eSILK Made from a special mix of PLA+ and certain additives to give a glossy and slightly transparent appearance when printed. • Choose from Gold, Silver, Copper and Rainbow colours ABS+ 1KG 3995 $ EA TL4472-TL4475 HIGH QUALITY FILAMENT Are extremely durable, lightweight alternatives to PETG and PLA. Able to withstand heat and stress without cracking or weakening, finished prints will hide blemishes & minor print issues. • Durable and lightweight • No cracking or brittle issues • Highly resistant to chemicals • 4 colours to choose from High quality 3D filament, known for producing smoother prints & better adhesion. Our expanded range of filament colours and types includes some new exotics to help ensure we have the right filament for your next work of art. Explore our wide range of resins, filaments and accessories, in stock on our website, or at over 110 stores or 130 resellers nationwide. jaycar.com.au/3dprinting 1800 022 888 e t i M o c i P A VG to a powerful, bu t simple ‘boot BASIC’ computer With the low-cost Raspberry Pi Pico board, a handful of standard components and our new firmware, you can build this amazingly capable ‘boot to BASIC’ computer. It has a 16-colour VGA output, a PS/2 keyboard input, runs programs from an SD card and can be built in no time. And it uses our popular fullyfeatured MMBasic interpreter. A fter the fun of building it, you can have even more fun writing programs to track your expenses, teach children about computing, play simple computer games and calculate the positions of the planets (to name a few possible activities). ‘Boot to BASIC’ computers were popular in the early 1980s – think of the Tandy TRS-80, Vic 20, Commodore 64 and 128, Apple II, Amigas and many others. After turning them on, within a fraction of a second, you have access to the built-in BASIC language, where you can test commands, then enter or load a program and run it. The operating system is built-in. Developing a program is fast and stress-free. You use the editor to enter the program into memory and run it with one keystroke. If there is an error in your program, you get a plain English message pointing to the problem. With another keystroke, you will be taken back into the editor with the cursor placed on the line that caused the error, ready to be fixed. If this sounds familiar, that’s because this computer is the latest of a series that we have published over the years, starting with the monochrome Maximite (March-May 2011; siliconchip. com.au/Series/30) and including the Colour Maximite 2 (July & August 2020; siliconchip.com.au/Series/348 and August & September 2021; siliconchip.com.au/Series/368). What sets this one apart is that it is so simple. The Raspberry Pi Pico module costs less than $10, and with just a few other components, you have a fully working computer. While it is simple, it does not lack performance. It runs a dual-core 32-bit CPU with a clock speed of up to 252MHz, has 103KB of program memory, a 640 x 480 pixel VGA output and stores programs and data on standard Words and MMBasic by Geoff Graham 52 Silicon Chip SD cards. To put that into perspective, it is about 100 times faster and more capable than the Apple II computer that was so popular in its heyday, yet costs about 1/100th as much! This firmware is derived from the PicoMite firmware for the Raspberry Pi Pico that we described in the January 2022 issue (siliconchip.com.au/ Article/15177). In this version, we have removed the ability to drive LCD panels and replaced it with the ability to produce a colour VGA signal. Other than this, the two versions are identical. VGA output The VGA output is generated within the Raspberry Pi Pico, a considerable feat for a low-cost processor without any specialised hardware for the task. It is derived from work by Miroslav Nemecek in the Czech Republic, ported by Peter Mather in the UK. VGA PicoMite firmware by Peter Mather Australia's electronics magazine siliconchip.com.au The Raspberry Pi Pico (shown 50% larger than real life) is a popular and cheap microcontroller module with plenty of memory, speed and I/O capability. With our VGA PicoMite firmware, you can easily program it in BASIC with a VGA monitor, keyboard and SD card storage support and access to all the Pico’s features. The VGA signal is generated using the second CPU in the RP2040 processor on the Raspberry Pi Pico plus one PIO channel. Because of this, it does not affect the performance of the BASIC interpreter, which runs unimpeded at full speed on the first CPU. The video signal is in the standard VGA format with a pixel rate of 25.175MHz and a frame rate of 60Hz, so you get a stable video output that is supported by all VGA monitors. In monochrome mode, the resolution is 640 x 480 pixels, while in colour mode, the pixels are doubled horizontally and vertically to give an effective resolution of 320 x 240 pixels. Regardless of the mode, the monitor still receives a 640 x 480 pixel image, and virtually all monitors support this mode. The colour mode uses four bits to define the colour of each pixel, giving a total of sixteen (24) colours (including black). One bit is assigned to red, two bits for green and one bit for blue. While this is not very good for displaying photographs, it is great for games, graphs and brightening up the output of your programs. The graphics driver includes some of the features of the Colour Maximite 2. So, in addition to drawing lines, boxes, etc, you can also have multiple fonts and create fast animations with the BLIT command. You can load images from the SD card for display on the video screen, and you can save an image of the current screen to the SD card (ie, take a screenshot/screengrab). The hardware to generate the VGA signal only uses eight resistors and two diodes to generate the correct signal levels. These components can be assembled on a piece of perforated stripboard (eg, Veroboard), but we felt that many people would like the convenience of building it on a PCB, so we have designed a simple board that includes the VGA output and the keyboard and SD card interfaces. siliconchip.com.au But, if you want to build it on an extreme budget, the stripboard solution will work fine. Keyboard and SD card The VGA PicoMite firmware supports standard PS/2 keyboards. While they are less popular today than USB keyboards, there are still plenty to be found, and many wired USB keyboards come with a PS/2 adaptor. These work perfectly with the VGA PicoMite. The keyboard is fully supported; auto-repeat and the arrow and function keys work as expected. The PS/2 standard uses 5V signal levels, but the Raspberry Pi Pico is strictly limited to a maximum of 3.6V, so level shifting is required to interface the Pico with the keyboard. This is done using four resistors and two Mosfets. Like the VGA interface, this could be built on a perforated stripboard if you do not want to use our PCB (although it isn’t exactly expensive). SD cards use 3.3V signal levels, so they can connect directly to the Raspberry Pi Pico with no interface components required. The firmware supports cards up to 32GB, formatted with a FAT16 or FAT32 file system. MMBasic supports long file names, hierarchical folders etc. You can save, load and run BASIC programs from the card as well as read/write data files to it. The file system is compatible with Windows, Linux and macOS, so it is easy to use an SD card to transfer data back and forth between the VGA PicoMite and a computer or laptop. However, an SD card is not necessary as the firmware reserves eight ‘slots’ for BASIC programs in the Pico’s flash memory. So you can save or retrieve up to eight separate programs there if you wish. If you are just casually playing with this computer, that could be all you need. Regardless, adding SD card support is so easy that we have included it on our PCB. Australia's electronics magazine The firmware supports many other devices that can be connected, including infrared (IR) remote control receivers, stereo audio output, distance sensors, a real-time clock, temperature sensors and so on. We did not clutter up the PCB with these, but you can easily connect external circuitry to the 40-pin header on the rear of the board. These pins mimic the I/O pins on the Raspberry Pi Pico (including the VGA and keyboard connections), so you can add almost whatever you want via that connector. MMBasic None of this can work without the firmware and MMBasic. We have described MMBasic many times before, so it is sufficient to say that it is a full-featured version of the BASIC computer language designed to be easy to use. As mentioned before, the firmware includes a built-in editor with a colour-coded display plus support for all the peripherals described above (and more). On the VGA PicoMite, programs can be as large as 108KB. The amount of RAM available for buffers, arrays, etc is even larger at 140KB, so you can have very large data arrays. By default, the CPU runs with an instruction clock of 126MHz, but you can switch it to 252MHz. This is ‘overclocking’ the RP2040 processor used in the Raspberry Pi Pico, which has a specified top speed of 133MHz. However, nearly all the Picos we have tested run fine at this speed, so it is a viable option if you want to go mad with the performance. One feature that will be appreciated by people who played with the early computers of the 1980s is that MMBasic saves the program to flash memory, not RAM. When you edit a program, it is saved to flash, and when you run it, it runs from flash. Because flash memory is non-volatile, July 2022  53 you will not lose your program, even if you accidentally restart the device or interrupt the power – something that happened distressingly often with the early computers that stored programs in volatile RAM. Circuit details Fig.1 is the straightforward circuit of the VGA PicoMite. The VGA output from the Raspberry Pi Pico uses six digital signals – one for red, two for green, one for blue and one each for horizontal and vertical synchronisation. For the red and blue signals, the digital output levels are simply clipped by the 1N4148 diodes to 0.7V, the correct level for full brightness in the VGA standard. The green output also has a resistor network providing four intensity levels from completely off to full brightness. The 200W multi-turn trimming potentiometer lets you adjust for a balanced white output without needing precision resistors with hard-tofind values. The horizontal and vertical sync signals use standard TTL signal levels, so they directly connect to the monitor. The keyboard interface consists of just two signals, the clock and the data lines, which are bi-directional. Each signal is level-shifted using two resistors and a small 2N7000 Mosfet. There are many ways to implement level shifting, but this is cheap and uses common components. In the idle state, the outputs from the Pico and the keyboard are pulled high to 3.3V and 5V respectively, by 10kW pull-up resistors. When the Pico wants to send a signal, it pulls its output low, causing the Mosfet to conduct because its gate is held at +3.3V. This means that the keyboard’s corresponding pin is also pulled low. When the keyboard wants to signal, it pulls its pin low, and that causes the substrate diode in the Mosfet to conduct and also pull the Pico’s corresponding pin low. There is very little to the SD card interface. All the SD card signal lines connect directly to the Raspberry Pi Pico as both the SD card and the Pico use 3.3V logic signalling. This SPI serial bus consists of four signals: • Chip select (CS), which is pulled low by the Pico when it wants to communicate. • The clock, generated by the Pico. • Master out slave in (MOSI), which carries data from the Pico (the master) to the card. • Master in slave out (MISO), which carries data from the card to the Pico. The card socket also has switches to indicate when a card is inserted and whether it is write-protected, but these are not used to keep the maximum number of the Pico’s I/O pins free. Instead, the card’s insertion and removal are detected by ‘polling’ the SD card (ie, periodically checking if it is present). The Raspberry Pi Pico itself is powered via its micro USB connector, which provides 5V for the PS/2 Fig.1: the VGA PicoMite circuit mainly comprises the components necessary to convert the Raspberry Pi Pico’s signal levels to that required by the PS/2 keyboard and VGA monitor. It could be assembled on a piece of perforated stripboard, but the commercial PCB doesn’t cost that much, makes construction much easier and gives a more professional-looking result. 54 Silicon Chip Australia's electronics magazine siliconchip.com.au keyboard. The output of the Pico’s onboard 3.3V regulator is used to power the processor and flash memory, and is also fed to the SD card. For maximum flexibility, all 40 pins on the Raspberry Pi Pico are routed to the 40-way connector on the rear of the PCB in the same configuration as that used by the Pico. This makes it easy to connect external devices using jumper wires, as you can consult the Pico pinout diagram and then select the corresponding pins on the 40-way connector. Taking into consideration the I/O pins reserved for the VGA output, keyboard and SD card, there are still 14 I/Os available for interacting with external circuitry. Construction The simplest way to source the components is to purchase a kit from the Silicon Chip Online Shop, which includes everything except a power supply and a case. But if you decide to source the parts yourself, you might have some difficulties due to current shortages, especially with the VGA and SD card connectors. It can help to use a parts search site like https://octopart.com to identify suppliers that currently have stock of a given part. Populating the PCB is straightforward (see Fig.2). As usual, start with the low-profile components and work upward. Preferably, your soldering iron should be temperature-controlled and have a chisel or conical tip with a diameter of 1.7mm or thereabouts. You can get away with other sizes, but some of the pads (for example, on the VGA connector) are close together, meaning a smaller tip will be easier to use. Note the choice of mounting a vertical or right-angle 2x20-pin header for CON4 depending on whether you’re using a case or not. The SD card socket is surface-­ mounted and, because you need space to get your soldering iron close to it, you should start with that. Begin by applying a thin layer of flux paste on all its pads. It has two small posts on the underside that click into matching holes in the PCB to ensure perfect alignment. With the socket in position, solder the two tabs on the right side of the socket (viewed from the front) and the five on the left side. Now that the siliconchip.com.au Parts List – VGA PicoMite 1 double-sided PCB coded 07107221, 124mm x 69mm 1 Raspberry Pi Pico 1 right-angle PCB-mount DE15 (VGA) socket (CON1) [TE Connectivity 1-1734530-1 or Multicomp SPC15430; Mouser, element14, RS] 1 right-angle PCB-mount 6-pin mini-DIN socket (CON2) [Altronics P1106 or element14 1200113] 1 Hirose DM1AA-SF-PEJ(72) or DM1AA-SF-PEJ(82) SD card connector (CON3) [Mouser, Digi-Key, element14, RS] 1 2×20-pin header, 2.54mm pitch (CON4) OR 1 2×20-pin right-angle box header, 2.54mm pitch (CON4) (for installation in a case) 1 4-pin vertical short actuator tactile switch (S1) [Altronics S1120 or element14 4511189] 1 200W multi-turn top-adjust trimpot (VR1) [Altronics R2372A or element14 9353569] 2 2N7000 60V 200mA N-channel Mosfets, TO-92 (Q1, Q2) 2 IN4148 diodes (D1, D2) 1 100nF 50V+ multi-layer ceramic or MKT capacitor Resistors (all through-hole 1/4W 5%) 4 10kW metal or carbon film resistors 7 220W metal or carbon film resistors Optional parts 1 71 × 130 × 30mm grey ABS instrument case [Altronics H0376] 4 No.2 × 4-5mm self-tapping screws (if mounting PCB in case) 4 stick-on rubber feet or short tapped spacers with M3 machine screws (if using PCB without case) 2 20-pin SIL headers, 2.54mm pitch (to make Pico module pluggable) 2 20-pin SIL header sockets, 2.54mm pitch (to make Pico module pluggable) Kit: a mostly complete kit for the VGA PicoMite is available from the Silicon Chip Online Shop (Cat SC6417 SC6417) for $35. It includes the PCB and everything that mounts on it. You just need to add a USB power supply, keyboard, monitor and optionally an SD card. This can be mounted in a case although you’ll also need a different header for CON4 and some self-tapping screws. Fig.2: assembling the VGA PicoMite is easy; just fit the parts as shown here, starting with the lower-profile components and working up to the taller ones. The diodes, Mosfets & Pico must be orientated correctly. The main options to consider are whether you’re using headers for the Pico and the type of connector you’re using for CON4. Australia's electronics magazine July 2022  55 The Raspberry Pi Pico can be directly soldered to the PCB, or you can solder pin headers to the Pico and then plug this assembly into matching SIL header sockets soldered to the PCB, as shown in the adjacent photo. Using the sockets is the safest option as you can then easily replace the Pico if you suspect that it has been damaged. Housing the VGA PicoMite If you want to house the VGA PicoMite in a box, the board is sized to fit in the Altronics H0376 snap-together case. The Raspberry Pi Pico can be directly soldered to the PCB, or you can solder pin headers to the Pico and then plug this assembly into two matching 20-pin single-in-line (SIL) header sockets installed on the PCB. Using headers means that you can easily replace the Pico if it fails. socket is secured, you can solder the nine pins on the rear. For each pin, slide the tip of your iron over the solder pad towards the connector so that the tip hits the connector’s pin. Within half a second, the solder should magically flow around the pin, and you can withdraw the iron. If you get a solder bridge, don’t worry and carry on with the other pins. Finally, examine your soldering using a powerful magnifier and check for any bridges (especially to the connector’s shield) and remove them using more flux paste and solder wick. Be careful here, as the solder wick can suck up all the solder, so you should recheck the joint after using it (although it usually leaves a sufficient amount behind). We expect that most readers will put rubber feet on the bottom of the PCB and use it as is (‘naked’). Another option for feet is tapped spacers via the mounting holes. Still, if you want to house it in a box, the board is sized to fit in a small 71 x 130 x 30mm instrument case (Altronics H0376). Incidentally, this is the same case that was used for the first ‘boot to BASIC’ computer we published, the original Maximite, back in 2011. If you are planning to house the PCB in this, you can replace the vertical 40-way pin header on the rear of the PCB with a right angle shrouded IDC connector so that you can use a ribbon cable to connect to any external circuits. See Fig.3 for the front and rear panel‘s drilling diagram to suit the Altronics H0376 case. Loading the firmware Loading the firmware onto the Raspberry Pi Pico is quick and easy, thanks to the bootloader built into the Pico. All you need to do is hold down the white button on the top of the Pico while plugging its USB connector into your computer. The Raspberry Fig.3: use these front & rear panel cutting diagrams/ templates to locate and size the holes in the case. The central cut-out in the front is to plug a cable into the USB socket on the Pico. Use the upper, dashed cut-out if you’ve mounted the Pico on headers. Either way, it might need enlarging depending on the size of the plug on your USB cable. The distance between the dashed cutout on the front panel and the cutout below it is 5mm. 56 Silicon Chip Australia's electronics magazine siliconchip.com.au Pi Pico will appear as a pseudo USB flash drive onto which you copy (eg, drag and drop) the “PicoMiteVGA.uf2” firmware file. This will upload the file to the Pico and program it into its flash memory. Following this, the Raspberry Pi Pico will drop the USB connection and reconnect as a virtual serial port over USB. But you can ignore that for the moment, as it will also come up driving the VGA output and looking for an attached keyboard. If you have a VGA monitor attached, you will see the MMBasic copyright message (as shown in Screen 1) and, if you have a keyboard attached, you can try typing in a command. For example, try “PRINT 2 + 2” and, unless your computer failed kindergarten, it will display the number 4. The only adjustment needed is the 200W trimpot for the white balance. To correctly set this, you should display a large area of white. You can do this by entering the following line at the command prompt: CLS RGB(white) This will clear the screen to a white background, and you can then adjust the trimpot for a neutral white colour without a tint. Fault finding If you do not see anything on your monitor after loading the firmware, start by checking the green LED on the top of the Raspberry Pi Pico. It should be slowly flashing off/on with a period of about a second and a half. This indicates that the Pico is correctly programmed with the firmware and is running MMBasic. If you do not see the LED flashing, reprogram the Raspberry Pi Pico and make sure that it completes successfully. Also make sure that you used the VGA PicoMite firmware and not the standard PicoMite firmware without the VGA capability – that will also flash the LED but not provide the VGA output. If the Raspberry Pi Pico is OK, you will then need to resort to standard fault-finding procedures. Carefully check all solder joints with a magnifier, look for solder bridges, check all components and their values and make sure that the orientations of the diodes and Mosfets are correct. It is also worth checking your monitor, keyboard and connecting cables. siliconchip.com.au PicoMiteVGA MMBasic Version 5.0.7.04b8 Copyright 2011-2021 Geoff Graham Copyright 2016-2021 Peter Mather > Screen 1: after loading the firmware, the VGA PicoMite will restart, activate the VGA output and look for an attached keyboard. With a VGA monitor connected, you will see this copyright message, and if you have a keyboard attached, you can try typing in a command or two. Do they work with other devices? The cables can be a problem; in the past, some constructors have been baffled by the lack of video only to discover that their VGA cable was faulty. SD card The VGA output and keyboard interfaces automatically operate after the firmware is installed, but the interface to the SD card needs to be configured before it can be used. This is done with the following command, entered on one line at the MMBasic command prompt: OPTION SDCARD GP13, GP10, GP11, GP12 This tells the firmware that the SD card socket is connected and what I/O pins are used for chip select (CS), clock, MOSI and MISO respectively. Entering this option will cause the VGA PicoMite to reboot, but from then on, the setting will be remembered, even after power off. So you only have to enter it once. After setting it up and inserting an SD card, you can test it by entering the command “FILES” at the prompt, and it should list the files and directories found on the card. If you had a BASIC program on the SD card, you could load it with the command: LOAD "filename" Then, if you edit it within MMBasic, you can save it back to the SD card with the command: SAVE "filename" The double quotes around the filename are required – you will get an error if they are not used. As mentioned earlier, the SD card is not strictly necessary. The firmware reserves eight ‘slots’ in the Raspberry Pi Pico’s flash memory for program storage on the chip. So, if you have entered a program, you could save it into (for example) slot 6 with the command “FLASH Australia's electronics magazine SAVE 6”. Later, you can load it back into program memory with the “FLASH LOAD 6” command. What next? To get a feel for the VGA Pico­Mite, you can enter the following short program. Start the process with the “EDIT” command. This is described in the user manual but, for the moment, all that you need to know is that in the editor, anything that you type will be inserted at the cursor, the arrow keys will move the cursor and backspace will delete the character before the cursor. At the command prompt, type EDIT followed by the Enter key. The editor should start up, and you can type the following four lines: DO INPUT "What is your name? ", N$ PRINT "Hello, " N$ LOOP Then press the F1 key on the keyboard. This tells the editor to save your program and exit to the command prompt. At the command prompt, type RUN and press the Enter key. Your new computer should ask for your name, and when you type it in (followed by the Enter key), it will reply with a greeting. To break out of the program and return to the prompt, press Ctrl-C. There you are; you have just written and run your first program on the VGA PicoMite. If you type EDIT again, you will be taken back into the editor, where you can change or add to your program. You will probably have many questions at this point, and we have written a detailed user’s manual to answer them. You can download this for free from the Silicon Chip website or the author’s web page (https://geoffg.net/ picomitevga.html). It should cover everything that you need to know. July 2022  57 If you are new to BASIC programming, open up this manual and check out Appendix G (Programming in BASIC – A Tutorial) near the end. This comprehensive tutorial on the language will take you through the fundamentals of programming in BASIC in an easy-to-read format with lots of examples. When you have finished, you will be a ‘gung-ho’ BASIC programmer! Tetris To test out this new computer, we decided to write a program to play the game of Tetris. Tetris is well-known and has been ported to over 65 platforms, a Guinness world record. We were hoping to make it 66, but it turns out that the name and the game are copyrighted, so we developed something similar that we called Blocks, which we believe is just as much fun to play – see Screen 2. It is not a huge program (about 475 lines), and it uses just the basic graphics commands (line, box etc), so there is nothing special here. Anyone could program this game with a bit of familiarity with BASIC, and you can easily dig into the code to see how it works. On the VGA PicoMite, Blocks runs very fast, and it uses only 15% of the available program memory. This illustrates the capability of this little computer and underlines the fact that you can aim big with it, and it will not let you down. The Blocks program is included in the VGA PicoMite firmware download so all you need to do is copy it to an SD card, then transfer that card to the VGA PicoMite and enter the command: RUN "Blocks.bas" Screen 2: Blocks is a BASIC game that runs on the VGA PicoMite. It is colourful and fast, and it uses only 15% of the available program memory, so you can have fun adding to it if you wish. It will also run on the Colour Maximite 2. Screen 3: The output of the “Colours.bas” program, included with the VGA PicoMite firmware download. It shows all the colours the VGA PicoMite can generate. Run it on your computer to see the true colours as the printing press cannot reproduce all the colours accurately. 58 Silicon Chip Australia's electronics magazine Incidentally, Blocks will also run on the Colour Maximite 2, so if you have built that computer, you can try playing it on that. There are two additional programs in the firmware download package. The first is “Fonts.bas”, which will display the various fonts that come built into MMBasic on your monitor. This is handy when you are writing a program and need to select a suitable font. The second program is called “Colours.bas” and it displays all 16 colours that the VGA PicoMite can generate on the monitor, including the codes to use in your BASIC program. Screen 3 shows what its output looks like, but the printing press will not accurately reproduce the colours, so run it on your VGA PicoMite to see the true set of colours. So there you have it, one of the simplest ‘boot to BASIC’ computers possible. To keep up with firmware updates, including early ‘beta’ releases, check out the author’s website at https:// geoffg.net/picomitevga.html It’s also a good idea to visit the Back Shed forum (see www.thebackshed. com/forum/Microcontrollers) where there are many MMBasic fans swapping ideas and offering help to newcomers. SC siliconchip.com.au BEST COMPATIBILITY WITH SHIELDS, SENSORS & MODULES BEST SELLER BREADBOARD FRIENDLY FOR EASY PROTOTYPING ARDUINO® COMPATIBLE NANO ONLY ARDUINO® COMPATIBLE UNO XC4414 OUR MOST POPULAR DEVELOPMENT BOARD. 29 $ COMPACT DESIGN WITH SIMILAR FEATURES TO THE UNO 95 FROM 2995 $ XC4410/11 FOR MORE ADVANCED PROJECTS THAT REQUIRE MORE I/O & PWM PINS EMULATE A USB KEYBOARD, MOUSE, JOYSTICK, ETC. 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Range 100-450°C 150-450°C 150-450°C 160-480°C 50-480°C Soldering 100-500°C Hot Air 200-480°C Display Digital Digital Digital ESD Safe • • • $159 $249 $329 Price $34.95 $59.95 $119 *Temperature rating is set by the soldering iron tip. ESD means Electro Static Discharge Shop Jaycar for your soldering essentials: • 6 Soldering stations • 12 Electric handheld irons • Over 12 gas powered irons • Classic 60/40, lead-free, silver & paste solder options • Multiple desolder braid and tools • Wide range of stands, cleaners and PCB holders By Charles Kosina Features & Specifications Usable frequency range: DC to 100MHz Input & output impedance: 50W Attenuation range: 0dB to -110dB in 1dB steps up to 2MHz; reduced maximum attenuation at higher frequencies (see Fig.2) Attenuation error: typically ≤0.5dB (see Fig.1) Power supply: 5V/100mA Fits in the same diecast case as the AM/FM Signal Generator from last month 0-110dB RF Attenuator for Signal Generators This Attenuator was designed to accompany my recently published AM/FM Signal Generator design (May 2022; siliconchip.au/Article/15306). However, you could combine it with just about any signal generator to provide easy output level adjustment over a wide range. W e often need a very low amplitude RF signal to test, align or adjust a radio. Unless you buy an expensive signal generator, the chances are that your generator’s output level is far too high for such a task. My recent AM/FM Signal Generator design has an output near 0dBm, which translates to about 220mV into a 50W load. To reduce this to 1µV RMS (eg, for testing a radio’s sensitivity), we need 107dB of attenuation. The simplest way to achieve this is to buy off-the-shelf fixed attenuators. These are available from 1dB to 40dB and cost about $5 each. They have SMA connectors on either end, and you screw them together to give the required attenuation. Variable digital attenuators are also available, as reviewed by Silicon Chip last year (October & November 2021; siliconchip.com.au/Article/15067 & siliconchip.com.au/Article/15100). These have a maximum attenuation of about 30dB and can be adjusted in small steps, eg, 1dB or 0.5dB. Combining one of these with a few fixed 62 Silicon Chip attenuators is one possible solution. However, I decided to design my own attenuator as it is pretty straightforward; it’s basically just a string of fixed attenuators, each consisting of three resistors, selected in combinations using relays. This works fine at low frequencies, eg, below 2MHz, but once we get much higher than that, the signal will sneak through by various paths to make a 1µV output difficult to achieve. Does this Attenuator achieve such a task? Yes and no. At 2MHz and below, the maximum attenuation is 110dB, but once we get to 75MHz, the attenuation is only 81dB. So for a 0dBm input, the lowest output level is 20µV RMS. However, adding one fixed 30dB attenuator to its output lets us get to 110dB and still gives quite a bit of adjustment range, so I consider that reasonably good. This is because, at higher frequencies, stray capacitance and inductance become more significant. In addition, circuit board tracks act as antennas and radiate energy that is picked up further Australia's electronics magazine downstream in the attenuator string. Professional signal generators with attenuators use extensive internal shielding to reduce such effects. For home-built equipment, this is somewhat impractical. That is why I did not build the Attenuator into the Signal Generator but rather in a separate diecast aluminium enclosure. There is far too much RF floating around in the signal generator which would make it difficult to isolate the attenuator section. Fig.3 shows the attenuator circuit. The signal is fed in via CON4 then passes through ten switched attenuator sections using DPDT relays RLY1 to RLY10 before reaching output connector CON5. These sections attenuate by 1dB, 2dB, 3dB, 5dB, 10dB (twice) and 20dB (four instances). The ideal resistance values for these attenuators are not in the standard range, so I have chosen the closest standard values, resulting in slight inaccuracies. With a relay de-energised, the signal just passes through the normally-closed siliconchip.com.au Parts List – 110dB RF Attenuator 1 double-sided plated-through PCB coded CSE211003, 76 x 95.5mm 1 diecast aluminium enclosure, 119 x 93.5 x 34mm [Jaycar HB5067 or Altronics H0454] 1 5V 100mA+ regulated DC power supply (eg, USB charger with adaptor cable) 1 0.96in OLED screen module with I2C interface and SSD1306 controller (OLED1) 1 mechanical rotary encoder with integrated pushbutton switch and 20mm total height (RE1) [eg, Bourns PEC11R-4215F-S0024] 10 EC2-5NU DPDT 5V coil relays (RLY1-RLY10) 1 10μH axial RF inductor (L1) 1 28-pin DIL IC socket (optional, for IC1) 1 PCB-mount DC barrel socket with 2.1mm or 2.5mm inner pin diameter (CON1) 1 2-pin, 2.54mm pitch polarised header and matching plug with pins (CON2) 1 3-pin, 2.54mm pitch polarised header (CON3) ● 2 SMA edge connectors (CON4, CON5) 2 2x3-pin header (CON6; optional, for programming IC1) 1 4-way female header socket (CON7; for OLED1) 1 large knob to suit EN1 4 12mm-long M3 tapped metal spacers 2 10mm untapped spacers sets of contacts. If it is energised, the signal instead passes through the resistive attenuator section. A rotary encoder is used to adjust the amount of attenuation required, in either 1dB or 5dB steps, toggled by pressing the encoder’s integral pushbutton switch. The firmware in the ATMega168 or ATMega328 microcontroller translates the attenuation to switch in the appropriate set of relays. For example, to select 35dB, relays 3, 6 and 7 would be energised. To prevent relays chattering while the shaft encoder is turned, there is a short delay after the number is selected before the appropriate relays are turned on and off. Each relay’s coil is switched using a small signal Mosfet. You might have noticed that there are no diodes to absorb the backEMF of the relay coils at switch-off at Fig.1: the attenuation settings are very accurate at low frequencies down to about 90dB, with a maximum error of only 1dB. The +0.5dB blip between 6dB and 8dB could be due to measurement error. siliconchip.com.au 4 M3 x 6mm panhead machine screws 4 M3 x 8mm countersunk head machine screws 2 M2 x 16mm or M2.5 x 16mm panhead machine screws and nuts (to match OLED mounting holes) 4 M3 flat washers Semiconductors 1 ATmega168 or ATmega328 8-bit microcontroller programmed with CSE211003.hex, DIP-28 (IC1) 1 LP2950-3.3 or similar 3.3V LDO regulator, TO-92 (REG1) 10 PMV15UNEA, PMV19XNEA or similar avalancherated N-channel Mosfets, SOT-23 (Q1-10) [Mouser Cat 771-PMV15UNEAR or element14 Cat 3268027] 2 2N7000 N-channel Mosfets, SOT-23 (Q11-Q12) ● Capacitors (SMD 0805 6.3V+ X7R ceramic unless stated) 1 10μF M3216/1206-size 1 1μF 4 100nF 3 10nF Resistors (all SMD M2012/0805 1% thick film) 5 18kW 2 4.7kW 1 1kW ● 2 820W 2 470W 2 270W 4 220W 2 180W 4 100W 2 68W 8 56W 1 33W 1 18W 1 12W 1 5.6W ● omit if the debugging interface is not needed SC6420 kit ($75): a short form kit is available that includes most parts. See page 106 for more details. switch-off. This is a bit unusual, but it does cut back on the number of components. This only works if the Mosfets are rugged enough to withstand the voltage spikes caused by the relay coil magnetic fields dissipating. See the section below on “Avalanche-rated Mosfets” for more details on this. As with my other designs, I have added a simplified RS-232 interface for debugging using Mosfets Q11 and Fig.2: the actual attenuation for a selected value of 110dB between 2MHz and 75MHz. As the signal frequency increases, parasitic capacitances on the circuit board result in more of the input signal leaking through to the output. Australia's electronics magazine July 2022  63 Q12. These may be omitted unless you plan to use that interface. The Attenuator is powered from a standard 5V DC mobile phone charger (or other USB power source). While this could be obtained from an output socket on the Signal Generator, I decided to use a separate supply to reduce potential RF leakage. You will note that the photos show an additional DC socket. This is for powering 64 Silicon Chip an external amplifier that was used for measurement. Inductor L1 is in series with the incoming supply to further reduce any outside RF. This seems to be effective as powering it from a battery of three AA cells made no measurable difference in readings. The same 0.96in SSD1306-based OLED screen is used to display the attenuation value as in the Signal Australia's electronics magazine Generator. A 3.3V regulator generates the OLED supply rail. The I2C interface requires pull-up resistors to +3.3V. As the SDA and SCL outputs on PC4 and PC5 of IC1 are open drain, there is no problem with the 5V-powered micro interfacing with the OLED. I chose NEC EC2-5NU relays. They are DPDT types with 5V DC rated coils. These are readily available and have good isolation. The measured siliconchip.com.au capacitance between open contacts is 1pF, which does not sound like much. Still, the reactance at 75MHz is -j × 2122W, which is effectively in parallel with the 220W resistor in the 20dB sections, slightly reducing the attenuation. The measured attenuation tracks the set attenuation fairly closely at 2MHz and below, as is shown in Fig.1. I took these readings with the tinySA spectrum analyser. The noise floor of the tinySA is about -90dBm, so I used a 30dB low-noise amplifier (LNA) to measure down to -110dBm. The measured value varied slightly on each pass, so I averaged several readings. Once the frequency gets above 2MHz, the accuracy drops off, and Fig.2 shows the maximum attenuation achievable up to 75MHz. To get a lower signal level at the higher frequencies, Fig.3: the entire circuit of the 110dB Attenuator. The main section consists of 10 switched attenuators, each made from three resistors, one relay (RLY110) and one Mosfet (Q1-Q10) to drive the relay. The transistors are driven by microcontroller IC1, which also monitors the rotary encoder and pushbutton, and communicates with the OLED to show the current attenuation setting. you will need to put a fixed 30dB attenuator on the unit’s output. Avalanche-rated Mosfets Avalanche-rated Mosfets (such as those specified in the parts list) must be used to ensure longevity. This is easy to check by searching the device data sheet for the avalanche energy rating (usually expressed in mJ). When a Mosfet’s drain-source rating voltage is exceeded, it can enter avalanche breakdown, similar to a zener diode. In this mode, the channel conducts current until the voltage drops. The problem with this is that a typical Mosfet is made of many (usually thousands of) cells, and there’s no guarantee that each cell will break down at the same voltage. That means the energy may pass through a very small proportion of the Mosfet area, causing intense local heating and possibly failure. Also, the avalanche current is not conducted through the normal channel but rather through a ‘parasitic bipolar transistor’ formed by two semiconductor junctions within the Mosfet. This also has the effect of concentrating the current into a smaller area than usual. Avalanche-rated Mosfets solve this by two methods. Firstly, they are designed and manufactured in such a way to minimise the variation in breakdown voltages between individual cells so that the current is spread out. Secondly, after being manufactured, they are tested by being forced into avalanche breakdown with a pulse of energy at least as high as specified in the data sheet. Any ‘weak’ devices that cannot handle this fail and are discarded. Only the survivors go on to be sold. We’ve calculated the energy pulse from the relay coils in this design at around 1mJ. The Mosfets we have specified have single-pulse ratings of around 15mJ. They only need to handle one pulse every few seconds, so this should be well within their capabilities. If substituting Mosfets, choose types with a minimum avalanche rating of 10mJ. For more information about this topic, see the excellent PDF from Infineon at siliconchip.com.au/link/ abdb Construction The unit is built into a standard aluminium diecast box, available from siliconchip.com.au Australia's electronics magazine July 2022  65 Fig.4: the front panel label for the Attenuator. The number and size of cutouts have been minimised to prevent RF leakage into or out of the case. Fig.5: luckily, there aren’t too many holes that need to be cut in the diecast case. They can all be drilled, except for the rectangular OLED hole. There are various ways to make that; just be sure to do it slowly to avoid it becoming jagged or oversized. 66 Silicon Chip Australia's electronics magazine Jaycar and Altronics (the same one used for the recently-described AM/ FM Signal Generator). It’s best to prepare this before assembling the PCB. I sprayed mine black to improve its appearance. I printed the label (Fig.4) on photographic paper and added a 1.5mm-thick protective clear polycarbonate sheet on top, cut to the same size as the label. You can download this artwork from siliconchip.com.au/ Shop/11/6419 The PCB attaches to the inside of the case using 12mm threaded spacers. If you can’t get these, use 10mm threaded spacers with an added nut to extend them to 12mm. I also sprayed the screws through the front panel black to improve the overall appearance. The required cutouts in the enclosure are shown in Fig.5. For best accuracy, locate the reference point in the bottom left and drill this to 3mm diameter. Then attach the blank PCB to use as a template. Square it up, drill the opposite corner and secure it with another screw. Now drill the other mounting holes. The encoder location on the PCB has a small hole in the centre on the PCB. Drill the panel through this using a 1.5mm diameter drill bit, then drill holes in the case corresponding to the four OLED mounting holes to 2.5mm. Remove the PCB and enlarge the hole for the shaft encoder to 14mm siliconchip.com.au diameter. It needs to be that large so that the PCB can be manoeuvred into position. Increase the size of the OLED mounting holes to 4mm and use the outside of these to mark the cutout needed. How you make the cutout depends on the equipment and skills that you have. Perhaps the simplest approach is to drill a series of reasonably small (say 3-4mm) holes around the inside of the perimeter. Join these with a file until the centre part drops out, then use a larger flat file to smooth the edges until they are straight and the hole is just large enough. Finally, drill two 7mm holes for the SMA connectors on the front and a hole for the DC connector on the back. There is not much room for this connector; it should be 7mm up from the bottom of the case. I also placed a small toggle switch next to the DC connector for the power, but that is optional. PCB assembly Most of the components mount on a double-sided PCB coded CSE211003 that measures 76 x 95.5mm. Fig.6 shows where the parts go. The resistors and capacitors are mostly SMD M2012/0805 or M3216/1206 size, while the transistors are in SOT-23 packages. Solder all the SMDs first, followed by the throughhole components, then the SMA connectors, and the rotary encoder last. siliconchip.com.au Fig.6: the resistors, capacitors and Mosfets all come in SMD packages but are pretty easy to solder. The micro, regulator, relays, headers and rotary encoder are through-hole parts. Fit all the SMDs first, then the through-hole parts from lowest profile to tallest, with the edge connectors last. Be careful to orientate the microcontroller and regulator as shown. There are options for other 3.3V regulators if the LP2950-3.3 regulator is not available. Some have different pinouts, so check this if substituting. If your replacement regulator has a reversed pinout, you can mount it on the opposite side of the board. The OLED screen plugs into a 4-pin socket strip. Although four mounting holes are provided, attaching it with two screws and two 10mm spacers is adequate. The holes in the OLED may be either 2mm or 2.5mm, so use either Australia's electronics magazine M2 x 16mm or M2.5 x 16mm machine screws and nuts. Using it It’s about as easy as it gets. Simply power the unit up, use the rotary encoder to dial in the amount of attenuation required while checking the screen display, then ensure your input and output cables are connected to the correct sockets. Remember that pushing down on the rotary encoder knob switches between adjustment steps of 1dB and 5dB. SC July 2022  67 Review by John Clarke Solar Charger Controller from Oatley Electronics Oatley Electronics (www.oatleyelectronics.com) has two new solar packages suitable for charging 12V and 24V lead-acid batteries. These can be used to maintain battery charge where mains power is not available, or as the basis of a solar power supply system for lighting or other low-voltage loads. F or the 12V package, you get a single 16W solar panel, while for the 24V package, two 16W solar panels are included. These two panels, connected in series, form a 24V, 32W equivalent panel. The same solar charge controller is included in either package, and it operates with either 12V or 24V batteries and matching solar panels. Both packages include 5m of 15A-rated figure-8 wire to connect the battery to the load and/or extend the solar panel wiring. The pricing of both kits is very reasonable, as detailed at the end of this article. The charger itself is only suitable for lead-acid batteries such as flooded cell (standard liquid acid), absorbed glass mat (AGM) or gelled acid (gel cell/SLA) types. However, note that some lithium-based rechargeable batteries claim to be directly compatible with lead-acid chargers. Possibly the most pressing need for a solar charger is to maintain the 68 Silicon Chip charge in batteries that see infrequent use. If a lead-acid battery is left to self-discharge over time, its life will be reduced, and it can be permanently damaged. Where available, you can use a mains-powered trickle charger to maintain the charge, although it will draw power from the mains all the time. In more remote places, using mains power is either inconvenient, dangerous or non-existent. Solar charging is more practical there, especially on boats, in sheds, on farms, and at campsites. Even for locations where mains power is available, the long-term cost of using a solar charger is likely lower than paying for mains power. This system doesn’t cost much more than a mains-powered trickle charger, but there is no ongoing cost. Each 1W of continuous power drawn from the mains adds up to 8.76kWh per year or around $3 at current prices. One practical use for the solar Australia's electronics magazine charger is to maintain the charge in a vehicle battery when it is not used often or stored for an extended period. That includes classic and vintage vehicles, farm tractors, ride-on petrol mowers (especially when unused during a drought) or spare vehicles. When used as a solar lighting system or for any other application where power is being drawn from the battery, the solar charger includes features to prevent discharging the battery to the point where its life will be reduced. This includes dusk-to-dawn operation (suiting outdoor lighting) with a timer and an adjustable switch-off voltage when the battery is deemed discharged. The battery capacity used with this system (measured in amp-hours [Ah]) needs to be considered based on the power that will be drawn from it over the day and night, and the number of days in a row that available solar power might be insufficient to recharge the battery. siliconchip.com.au The solar panel(s) The supplied solar panel consists of an aluminium frame surrounding amorphous poly-crystalline solar cells sealed within a clear glass cover. These TUV NORD BL16P-12 panels measure 355 × 355 × 25mm and weigh 1544g. The maximum power output is 16W in full sunlight at 1000W/m2. At least with these solar panels, you know you are getting what you expected; we’ve published multiple letters from readers who purchased a panel rated at a particular power level when they could never achieve that! We’ve tested these, and they actually exceed their specifications. Their electrical specifications are an open-circuit voltage of 21.6V and a short circuit current of 0.97A. These two parameters are easily measured using a multimeter. The short-circuit current is measured by setting the multimeter to measure current and connecting the probes to the solar panel leads. The open-circuit voltage is a simple voltage measurement between the wires. Both are measured in full sunlight. Maximum power from the panel is specified as 18V and 0.89A (18V × 0.89A = 16.02W). The solar panel is supplied with a 650mm length of dual-core cable attached. Fig.1 shows the power curve for the solar panel. The red curve is the quoted specifications, while the blue curve is what we measured at midday in early April. The sample panel produced 17.6W, 10% higher than the specified 16W. It could produce a bit less on a sweltering day, so that is likely why the rating is conservative. For the type of solar charger supplied, the usable power region of the panel is shown shaded. This covers the region where the panel is used to charge a battery from near-flat to full charge. So with these packages, the maximum power available from the panel is between 10.1W (at 11V) and 13.5W (at 15V), assuming the panel follows the specified curve. Power and voltage is doubled for two series-­ connected panels for 24V use. Note that if a (presumably more expensive) maximum power point tracking (MPPT) charger were used, it would maintain the operating point at 18V/36V to take full advantage of the available power from the panel(s). But for maintenance charging or applications where you’re going to plug in a siliconchip.com.au Fig.1: the specified I/V curve for the supplied TUV NORD BL16P-12 panel compared to our measurements, made in full sun in early April. The mauve shaded area shows on which part of these curves the supplied charger will typically operate. Australia's electronics magazine July 2022  69 Six screw terminals are available on the side of the solar charger module for connecting solar panels, batteries and loads. flat battery and come back days later, it won’t make much difference. Solar charge controller This controller is quite small at 133.5 × 70 × 35mm and very light at 130g. Its model code is W88-C. The controller automatically detects and operates with either a 12V or 24V battery. As mentioned above, this is not an MPPT controller. Instead, it connects the solar panel to the battery using two paralleled Mosfets driven using pulse-width modulation (PWM). The Mosfets are switched with a variable duty cycle to maintain the required battery voltage. When a discharged battery is connected, the solar panel is connected continuously to the battery until the required end-point voltage is reached (typically around 14.4V or 28.8V). The duty cycle of the Mosfets is then reduced to a point where this voltage is maintained. Two USB Type-A ports are provided, rated at 5V <at> 2.5A total. But our tests showed that the maximum current that could be obtained before voltage dropped below 4.5V was 600mA. The short-circuit current is just 780mA. So the 2.5A seems ‘optimistic’. Still, they would be better than nothing if you had a flat phone battery and no mains power available. As the two USB ports are connected in parallel, if you are drawing 500mA from one, you can’t really use the other. Still, the second one might be useful to plug in a small LED light or similar. Connections to the solar panel, battery and load are via screw terminals along one side of the controller. The battery must be connected first before connecting the solar panel and load; disconnection is done in the reverse order. 70 Silicon Chip Reverse-polarity protection is included for the solar charge controller, and it uses Mosfets instead of diodes. These Mosfets are connected as ‘ideal diodes’ with a low drain-tosource resistance (Rds) of less than 11mW, so there is minimal voltage loss and heat produced. The same type of Mosfet is used for the charging connection from the panel to the battery, and the battery to the load. Heat dissipation The rear panel of the Solar Charger is the heatsink for the six Mosfets. These are pressed against the steel rear panel with adhesive thermal tape. This charger is likely to become very hot if used at its full ratings, but with the 16W or 32W panels supplied, the temperature rise is negligible, even with 10A drawn via the load connection. User interface A small LCD screen (34 × 22mm) shows the battery voltage at the top with solar panel, battery and load discharge icons below. An arrow between the solar panel icon and battery icon flashes during charging. Similarly, an arrow between the battery and load (shown as a light bulb) appears when the load is on. The battery voltage is shown to the nearest 100mV. The solar panel icon shows when a panel is connected and producing an output. The battery voltage icon is interesting in that it has five bars to show the state of battery charge, in addition to the voltage reading. There are three push-button controls on the front panel for Menu, Up and Down. The Down button also doubles as a load on/off switch. The display usually shows the battery voltage and returns to this screen automatically if the Menu button or Up/Down buttons are not pressed within five seconds. Australia's electronics magazine You can step through each menu item by pressing the Menu button. It cycles through the main display (showing battery voltage), the full charge voltage, the discharge reconnect voltage, the discharge disconnect voltage, load connect timer options (called the work mode) and finally, the battery type. To change any of these settings, press the Menu button to access that setting, then press it again and hold it for ~5s until the value flashes. The value can then be adjusted using the Up or Down buttons. Another long press of the Menu button is required to store the new value. Load output While you could connect a load directly to the battery, the load output on the charge controller provides valuable features. As mentioned, the load can be manually switched on and off with the right-hand push-­button except when making adjustments, when this button decreases the value. The maximum current that can be drawn from the load output is 10A. The main feature is that this load output will switch off the load when the battery charge falls below a preset voltage, thus saving the battery from damage due to over-discharge. The second feature is that the load can be switched off with an adjustable timer that starts counting down from dusk. Full voltage The full voltage setting is in the second menu and sets the voltage at which you want the battery to stop charging. Once the battery is charged up to this voltage, it is maintained at that same voltage. This is the only setting related to charging voltage. The battery is initially charged at a rate determined by the solar panel, until the battery reaches the full voltage. Typically the current needed to maintain the charge termination voltage is just that required to counteract the self-discharge current of the battery and any standby drain of the charge controller. That amounts to around 10mA. The specifications for the full voltage default values (double that provided when using a 24V battery) are somewhat confusing as they quote these as equalisation voltages. The default voltage is one of three values siliconchip.com.au depending on the type of battery selected. According to the user manual, they are for AGM batteries (B1), initially set at 14.4V; gel cell batteries (B2), initially set at 14.2V; and flooded batteries (B3), initially set at 14.6V. These voltages are too low for equalisation and are instead the full charge voltages. Typically, for equalisation, the charge voltage would be increased above 15V to ensure each cell in the battery becomes fully charged. This can produce a lot of gassing, so equalisation shouldn’t run very often. The so-called ‘equalisation’ voltage mentioned appears to be a misnomer in the user manual. The charger performs no equalisation. The full voltage for each battery type mentioned above is adjustable. However, we found a discrepancy in the B2 setting: we found that it was set by default at 12.6V and could only be adjusted downward from this to 11.5V, but not above 12.6V. By contrast, the B1 value could be adjusted between 14.4V and 13V and the B3 value from 14.6V to 13V. So if you are using an SLA (gel) battery, it would be better to use the B1 or B3 selection and set the full charge voltage to a more appropriate value like 14.2V. Note that the B1-B3 selections do not necessarily have to be used for AGM, gel and flooded batteries in that order. The selections are arbitrary and are determined by the voltage set for the connected battery type. You will probably need to compromise with the voltage settings. When charging a battery, typically, the voltage is raised until it reaches the bulk charge end-point voltage (around 14.0-14.6V) and then the charging current decreases to a low level. The charging voltage then drops to the float or trickle charge level, usually around 13.0-13.8V. However, that is not the case with this solar charge controller, as the full voltage is maintained. Many batteries have a maximum specified time at the bulk charge voltage (usually no more than eight hours), after which damage can occur due to outgassing etc. That is why a more advanced charger will drop the voltage once the battery is fully charged. Of course, with a solar charger, the maximum charge time is limited by the number of daylight hours available. But that could easily exceed siliconchip.com.au eight hours, and some batteries could have much shorter specifications for the amount of time they can spend above 14V. But with this charger, there is no other charging state. So you either set the charge voltage to the bulk charge level to fully charge the battery, or set it at the float level for the battery for long-term use. A higher voltage setting will have the battery charged closer to 100%, while a lower voltage will be more suited to lower float (maintenance charge) requirements. However, setting it to terminate at the float value will prevent the battery from reaching full charge if it is ever discharged. So if you are using the charger to maintain charge rather than for charging, set the voltage value to the recommended float voltage for the type of connected battery. Alternatively, if using the charger with a load such as solar lights, it may be better to set the full voltage to the recommended bulk charge voltage (or full charge voltage) for your battery type. So the setting really depends on your application. It would be wise to check the manufacturer’s specifications for your battery before making that setting. Load reconnect The next three menus are related to the load output. They set how the load is connected based on the battery voltage and light level, and for how long. The load reconnect menu selects the battery voltage that the load will be reconnected after being disconnected by a low battery level (see the next menu). It is initially set at 12.6V and can be adjusted between 10V and 13V. This setting should be high enough that the battery gains some extra charge from the solar panel if the load is disconnected, before reconnection. Load disconnect The next menu is similar to the above menu, except it sets the voltage below which the load disconnects. Initially, it is set at 10.7V, but you can adjust it between 11.5V and 8V. Ideally, this should be set to a higher value than 10.7V, as the battery would be almost fully discharged at this level and possibly already damaged. Around 11.5V would be a more practical value to prevent excessive battery discharge. Australia's electronics magazine For more information regarding battery voltage for charging and discharging, see: deepcyclebatterystore.com/ how-to-maintain-batteries/ Work mode This mode is for the load switching settings. This is initially set for 24H, meaning the load can be switched on at any time and will remain on continuously. Other options switch on the load from dusk for a set period in hours. When the time is set between one hour and 23 hours (1H to 23H), the load is powered for that period beginning at the onset of dusk. If you select the hours as zero (0H), the load is switched on over the entire dusk until dawn period. This is distinct from the 24H setting, when the load can also be on during the daytime. The controller detects dusk and dawn by monitoring the solar panel voltage, with 8V as the threshold voltage (or 16V for a 24V panel). Below 8V is dusk to dawn, whereas above 8V is daytime. Battery type Finally, the last mode before the main display reoccurs is the battery type. This is selected as B1-B3. You can set a different full voltage for each battery selection as detailed above. The maximum charging current for the controller is 30A. It will not come anywhere near this limit with the supplied panels. You would need over 300W of 12V panels or 600W of 24V panels to exceed it. Conclusion While the charger is a bit basic, these solar packages from Oatley Electronics are excellent value if you are looking for a solar charging system with around 12-24W of power, such as for some small outdoor lights or maintaining an infrequently used leadacid battery. The two packages are ● IT159PK1 with one 16W solar panel, the 30A regulator and 5m of Fig.8 cable, suiting 12V lead-acid battery charging: $39 plus P&P. ● IT159PK2 with two 16W solar panels, the 30A regulator and 5m of Fig.8 cable, suiting 24V leadacid battery charging: $54 plus P&P. For more information or to order these packages, visit Oatley’s website siliconchip.au/link/abes SC July 2022  71 Secure Remote Receiver 68m line-of-sight range Up to 16 remotes per receiver Mains-powered, quiescent power typically 0.8W Relay contact rating: 30A at 250V AC, meaning it can switch large mainspowered devices like pumps Relay on-timer ranges: 250ms to 60s or 60s to 4.5h (see Tables 3 & 4) Brownout protection: 192V AC switch off, 220V AC switch on DC supply current: 17mA with relay off, 100mA with relay on Part one: by John Clarke T HE SECURE REMOTE CONTROLLED MAINS SWITCH (we’ll call it the Switch from now on) is ideal for switching motor loads such as pool pumps, water pumps and any number of applications where you find it convenient to switch power to an appliance remotely. The high security of this design means that it can be used for remote-controlled doors, gates and door strikes, maintaining the security of your home or premises. As is typical for security remote controls, the handheld unit is pocket-sized. Many commercially-made remotecontrolled mains switches are available, such as Jaycar Cat MS6148 and Altronics Cat A0345. Wi-Fi controlled mains switches are also available, like the Blaupunkt smart Wi-Fi plug BSP2EM. These rely on a mobile phone app for control. These are all fine for their intended purpose, but the relays they use to switch mains power are not suitable for appliances that include motors. While rated at 10A, the relay contacts will quickly be destroyed when used to power items such as a pool pump. Also, controllers relying on a mobile phone app could become obsolete 72 Silicon Chip should support for that app be dropped or become incompatible with newer phones. We covered this phenomenon in the February 2022 editorial. Secure codes The use of secure codes is not only necessary for security applications; it is also very useful to ensure that a neighbour or passer-by using a similar remote control does not inadvertently switch your appliance on or off while controlling their own equipment. Editor’s note: our motorised security shutters have rolled up or down more than once when we were nowhere near the remote control! So this is not just a theoretical risk, and it definitely has security implications. The security of this design also means that you can build more than one Switch without being concerned about interference between them. The unique transmission code ensures that the Switch receiver will not be activated by anything other than one of the paired handheld remote controls. Rolling codes for high security The remote control code sent by the handheld remote units can be Australia's electronics magazine considered an electronic lock similar to a physical key. This key is a specific code sent by the transmitter to the receiver; it is a long sequence of on and off signals sent in a particular order and over a set period. The code must be correct for the receiver to respond. With a fixed remote control code, an intending thief can receive and store the code sent by the remote control and re-transmit it in an attempt to operate the receiver. However, with a rolling code, the reused code will not trigger the receiver. That’s because the receiver requires a different code each time. Each code that’s transmitted differs markedly from one transmission to the next. The codes sent are based on an algorithm (calculation) that both the transmitter and receiver have in common, based on a unique numerical value that is stored within ICs in both the remote control and the receiver. The handheld remote will have a unique identifier different from any other handheld remote. The code possibilities of a rolling code system run into the trillions. This renders any attempt to break the code by sending out guessed codes totally unrealistic. The odds of picking a siliconchip.com.au MAINS SW TCH Transmitter Professional-looking key-fob enclosure Powered by a 3V CR2032 lithium cell, 200mAh+ recommended, giving more than two years of life with typical use Standby current: typically 60nA (526μAh/year) Active (transmitting) current: 10mA average over 160ms (900nAh / transmission) Registration current: 10mA average over 2.75s (15.5μAh per registration) Transmission rate: 976.5 bits/s (1.024ms per bit) Data encoding: Manchester code with a transmission time of 82ms Unique code generation: secure UHF rolling code control with 48-bit seed, 24-bit multiplier and 8-bit increment value This remote mains power switch uses secure wireless transmission so that nefarious people can’t intercept the commands and override your control. It can also switch high current loads and includes an adjustable timer. Up to 16 separate handheld remotes can control the same receiver. correct code at random for our rolling code transmitter, for example, is one in 2.8 trillion. Even then, the code needs to be sent at the correct data rate, with the correct start and stop bit codes and other transmission requirements, including data scrambling that changes for each transmission. Other features Our Switch comprises two parts: a professional key-fob-style transmitter and a separate receiver. The key-fob has three pushbutton switches and an acknowledge LED that briefly lights up each time one of the switches is pressed. Up to 16 different key-fob transmitters can be used with one receiver. The receiver has a 30A mains relay making it suitable for switching power to motors. The relay can be switched on or off, or switched on for a fixed time, using the remote control or a switch on the receiver. The on-period can be adjusted from 1/4 second to 4.5 hours in two ranges. Another feature is brownout detection; it automatically switches off should a brownout occur. This is when the mains voltage drops to a siliconchip.com.au lower than normal level, usually because of a supply fault. This lower voltage can cause motors to overheat and burn out. Motor burn-out occurs because the current through a motor’s induction windings increases when it is not spinning at its correct speed, which is likely when the supply voltage is low. During severe brownouts, the voltage can be so low that the motor will not turn at all, but current is still flowing in its windings. In that situation, the motor will quickly overheat and suffer permanent damage. The brownout detection protects the motor by switching off its power if the supply voltage falls below a preset value. Brownout detection is vital for mains-powered water pumps. Security and registration Each key-fob transmitter must be allocated an Identity number from 0 to 15, set by coding links on the PCB. Each transmitter is registered to the receiver by sending a synchronising code to the receiver when the receiver is in registration or learning mode. A facility is included to lock out a particular transmitter after registration. This is useful if a transmitter Australia's electronics magazine has been lost. If the lost transmitter is found, it can be easily re-registered. If the identity of the lost transmitter is not known, all transmitters can be locked out, and the ones that are still in use can be re-registered. The data is transmitted using UHF ASK as Manchester code. A zero bit is sent as a 512µs period of no transmission followed by a 512µs burst of 433.9MHz carrier. In contrast, a one bit is transmitted as a 512µs burst of 433.9MHz carrier followed by a 512µs period of no signal. Each transmission consists of four start bits, an 8-bit identifier, a 48-bit code and four stop bits, for a total of 64 bits. The start bits include a 16.4ms gap between the second start bit and the third start bit, while the code scramble value is altered on each transmission with 32 variations. Unique codes are generated using a 48-bit seed, 24-bit multiplier and 8-bit increment value initially set by a unique identifier within IC1 on the transmitter. The registration code is sent as two blocks. Block 1 sends four start bits, the 8-bit identifier, a 32-bit seed code and four stop bits. Block 2 sends four start bits, the 24-bit multiplier, the July 2022  73 8-bit increment and 8-bit scramble values and four stop bits. Again, the start bits include a 16.4ms gap between the second start bit and the third start bit. Circuitry The transmitter circuit is shown in Fig.1. It mainly comprises microcontroller IC1 and a 433.9MHz UHF transmitter. For IC1, the PIC16LF15323 was chosen for its very low standby current and the inclusion of a unique identifier called the Microchip Unique Identifier (MUI). We use the MUI to generate a rolling code sequence that is unique to the IC and thus the transmitter. IC1 is usually kept in sleep mode with its internal oscillator stopped and most of its internal circuitry switched off. In this state, it draws a typical standby current of 60nA from the 3V cell. You can verify this by connecting a 100kW resistor in series with the 3V supply with a switch across it. Apply power with the switch closed. After about 10 seconds, when the micro goes to sleep, open the switch and measure the voltage across the resistor. We measured 6mV, indicating a sleep current of 60nA. Switches S1 to S3 connect to the RA4, RC3 and RC1 digital inputs of IC1 while the Identity switches (1, 2, 4 & 8) connect to the RA0, RA1, RA2 and RC0 digital inputs, respectively. The Identity inputs are used to differentiate between different transmitters for a given receiver. If only one transmitter is used, it can be set for Identity 0, and none of the Identity pins need to be connected to circuit ground. At power-up, each Identity input is held high by pull-up resistors to the 3V rail that is inside IC1. The software then disables the pull-up resistor for any identity input that is kept low. That prevents that pull-up continuous sourcing current, which would otherwise be 25-200µA drawn from the cell per low input. The pull-ups for pushbutton switches S1-S3 are left on since they are only pressed momentarily. In contrast, at least one of the Identity inputs is always held low for Identity settings other than 0. IC1 is programmed to wake up from its sleep condition when any one of switches S1-S3 is pressed, and that corresponding input changes from high to a low. It then runs the program to send the rolling code for the function associated with the pressed switch. The rolling code and registration codes are sent via the 433.9MHz transmitter module. This module is powered via the paralleled RC5 and RC4 outputs of IC1, which go high to provide a nominal 3V to the Vcc input of the module. This way, it only draws current from the cell when in use. The code is applied to the data input of the module from the RA5 output of IC1. The antenna is a coiled length of wire. Fig.1: the transmitter circuit is quite simple, primarily comprised of a PIC16LF15323 microcontroller and a 433.9MHz UHF transmitter module. 74 Silicon Chip Australia's electronics magazine The transmit indicator, LED1, is driven via the RC2 output of IC2 through a 220W current-limiting resistor and is modulated at the code transmission rate of about 1kHz. After sending the code, IC1 powers down the UHF transmitter and returns to sleep mode. During transmission, the current draw from the cell briefly rises to about 10mA. If you keep holding one of the buttons down after the transmission is complete, the current will drop to about 220µA until the button is released. This is due to the current flow in the switch pull-up resistor. Considering the quiescent current and intermittent bursts of higher current when transmitting, cell life should be more than two years with typical use. Receiver circuit The receiver (see Fig.2) uses a PIC16F1459-I/P microcontroller (IC1) and UHF receiver module with an onboard coiled wire antenna input to provide a very good reception range. When no signal is present, the receiver’s output signal is random noise since the module’s automatic gain control (AGC) is at its maximum. Upon reception of a 433.9MHz signal, the receiver gain is reduced for best reception without overload, and the coded signal from the data output of the module is delivered to the RC7 digital input of IC1. The Acknowledge LED (LED2) indicates whenever a valid signal is received. The RC5 digital output of IC1 drives NPN transistor Q1, which switches the relay coil. When RC5 goes high, it delivers current to transistor Q1’s base and Q1 powers RLY1. Diode D5 clamps the back-EMF that causes a voltage spike at the collector of Q1 as the relay switches off. The relay contacts are rated at 30A and 250V AC. The unit can be set up to power the relay for a fixed period or just switch it on or off continuously. There are two ways to toggle the relay on and off. The operation of switch S1 on the receiver depends on jumper JP3. When JP3 is open, the relay switches on with one press and off on the next. When JP3 is bridged and S1 is pressed, the relay is switched on for a fixed time and switches off at the end of this period, or when S1 is pressed again – see Table 1. siliconchip.com.au Fig.2: UHF transmissions are fed to microcontroller IC1 on the receiver, which decodes them. If they are valid, it controls the mains relay by changing the level at digital output RC5, which drives NPN transistor Q1 to power the relay coil. Table 1 – JP3 settings Table 3 – JP1 timer settings JP3 in/out Receiver switch S1 function JP1 in/out Timer period Out Off if already on, otherwise on with a timer, range per JP1 Out 0.25-60s (1x) In Toggle on/off In 1m-4.5h (255x) Table 2 – transmitter switch functions Table 4 – Nominal period versus TP1 voltage Switch Function with JP2 out Function with JP2 in TP1 Time with JP1 out Time with JP1 in S1 Relay on with a timer, range per JP1 Relay on with a timer, 0.25-60s 0V 0.25s 1m S2 Relay on continuously Relay on with a timer, 1m-4.5h 1.25V 15s 1h 7.5m 2.5V 30s 2h 15m S3 Relay off Relay off 3.75V 45s 3h 22.5m 5V 60s 4h 30m siliconchip.com.au Australia's electronics magazine July 2022  75 433.9MHz receiver module, while the +12V rail powers the relay. The outputs of REG1 and REG2 are filtered and stabilised using 100µF capacitors. A 100nF capacitor further decouples the 5V supply for IC1. Brownout detection The receiver fits into an IP65 sealed ABS plastic case, so it could be installed in a pool house or similar, to control a pool pump, among other possible uses. Being splashproof could also come in handy if it’s controlling a gate or garage door. It should be installed out of the elements, as the sockets and switches are not sealed. The remote control has three buttons, and usually, S1 on the remote switches the relay on with the timer to switch it off, S2 switches it on continuously (or for a much longer time if JP2 is inserted), and S3 switches it off. See Table 2 for more details. The timer period is set using trimpot VR1. The trimpot wiper can be adjusted from 0V through to 5V. This voltage is monitored at the AN6 analog input of IC1, which converts the voltage into a period from 0.25 seconds to 60 seconds. IC1’s digital input RA4 has an internal pull-up current from IC1. If JP1 is inserted, this pin is pulled low instead. In that case, the timing period ranges from one minute to 4 hours and 30 minutes – see Table 3. You can monitor the timer setting voltage at test point TP1. Table 4 shows the typical periods for selected trimpot positions. Identity The Identity selection is made using a BCD rotary switch (S4) with 16 positions, labelled 0-9 and A-F (for 10-15). This switch is only applicable to the lockout selections; it plays no part in the key-fob transmitter registration. S4’s four contacts connect to the RB7, RB6, RB5 and RB4 digital inputs 76 Silicon Chip of IC1. When the BCD switch is set at 0, all four inputs are high. Position 1 on the switch has the ‘1’ output at RB7 pulled low, while Position 15 (or F) sets all switch outputs at 0V. S3 provides the lockout or deregistering function for a transmitter. Pressing S3 will prevent the transmitter from operating the receiver identified by the number selected with the BCD switch. The Learn switch (S2) tells the program within IC1 to be ready to accept the synchronising signal from a handheld remote. While waiting for a signal from the remote unit, the Learn LED (LED1) stays lit. The Learn LED extinguishes once the synchronising signal has been received. Power supply Power for the receiver comes from the mains via transformer T1. The transformer’s 12V secondary voltage is full-wave rectified using diodes D1-D4 and filtered with a 470µF electrolytic capacitor at 3-terminal regulator at REG1’s input plus another 100µF capacitor at REG2’s input. The result is a pulsating 17V DC rail applied to REG1 & REG2, which in turn provide regulated +12V DC and +5V DC rails, respectively. The +5V rail is used to power IC1 and the Australia's electronics magazine IC1’s AN8 analog input is used for brownout detection. This input samples the 17V DC rectified rail via a voltage divider consisting of a 22kW resistor and trimpot VR2. VR2’s wiper voltage is filtered using a 10µF capacitor (to smooth out 100Hz ripple and transients) and applied to the AN8 input via a 1kW resistor. During the set-up procedure, VR2 is adjusted so that the voltage at AN8 is a DC voltage that is 1/100th that of the mains AC voltage. For example, the voltage is set to +2.35V if the mains voltage is 235V AC. If a brownout occurs and the mains voltage drops below about 192V AC, the voltage applied to AN8 will fall below 1.92V DC. This is detected by microcontroller IC1, which then switches the relay off to disconnect power from the mains output. The relay can only be switched on again manually when the mains voltage returns to normal. One small problem with monitoring the 17V rail is that while it does vary with mains voltage, it also varies with load. RLY1 has a coil resistance of 120W, so there is an extra 100mA drawn from the 17V rail when the relay is on. As a result, this rail drops when the relay is powered. Therefore, VR2 is adjusted while the relay is on, so the brownout voltage detection threshold is accurately set. When the relay is off, the voltage is expected to rise by about 3V as the relay load on the supply is removed. However, as the relay is latched off by a brownout and must be manually switched on again, that doesn’t matter. Next month We still have quite a bit of ground to cover as, besides assembling the two PCBs, we also need to describe how to fit them into their respective cases. Then we’ll go over the testing procedure, set-up, remote registration and de-registration and some more advice for using the Secure Remote Mains Switch. All of that will be in the second and final article in this series, next month. SC siliconchip.com.au Parts List – Secure Remote Mains Switch Receiver 1 double-sided plated-through PCB coded 10109211, 159 x 109mm, 1.6mm thick 1 IP65 ABS enclosure, 171 x 121 x 55mm [Jaycar HB6248, Altronics H0478] 1 433.9MHz UHF ASK receiver (RX1) [Jaycar ZW3102, Altronics Z6905A or equivalent] 1 3VA PCB-mounting 12V mains transformer (T1) [Altronics M7012A] 1 12V DC coil, 250V AC 30A contact SPST relay (RLY1) [Jaycar SY4040 or equivalent] 1 momentary push-to-close 250V AC panel-mount mains switch (S1) [Jaycar SP0716, Altronics S1080] 2 SPST PCB-mount tactile micro switches (S2, S3) [Jaycar SP0600, Altronics S1120] 1 4-bit DIL BCD PCB-mount rotary switch (S4) [Jaycar SR1220, Altronics S3000A] 1 SPST mains rocker switch (S5) [Jaycar SK0984, Altronics S3210] 1 10A mains panel socket with side wire entry [Jaycar PS4094, Altronics P8241] 1 panel-mount IEC mains socket with integral fuse holder [Jaycar PP4004, Altronics P8324] 1 M205 10A fast-blow fuse (F1) 1 10A IEC mains cord 1 panel-mount 230/240V AC neon lamp 2 2-way screw terminals, 5.08mm pitch (CON1) 1 3-way screw terminal, 5.08mm pitch (CON2) 3 2-way pin headers, 2.54mm pitch (JP1-JP3) 3 jumper shunts (JP1-JP3) 1 20-pin DIL IC socket (for IC1) Hardware 2 M4 x 6mm panhead machine screws and nuts (for relay mounting) 2 M3 x 10mm panhead Nylon machine screws (for IEC connector mounting) 6 M3 x 6mm panhead machine screws 4 M3 nuts 2 150mm cable ties (to hold down transformer) Wiring 1 20mm length of 3mm diameter red heatshrink tubing 1 400mm length of 10A light blue mains-rated wire ● 1 400mm length of 10A brown mains-rated wire ● 1 200mm length of 10A green/yellow mains-rated wire ● 1 400mm length of 7.5A brown mains-rated wire 1 170mm length of 1mm diameter enamelled copper wire 1 50mm length of 10mm diameter red heatshrink tubing 1 100mm length of 5mm diameter red heatshrink tubing 1 25mm length of 5mm diameter blue heatshrink tubing 1 25mm length of 5mm diameter green heatshrink tubing 12 100mm cable ties ● can be stripped from a length of 3-core 10A mains flex siliconchip.com.au Semiconductors 1 PIC16F1459-I/P microcontroller, DIP-20, programmed with 1010921R.HEX 1 7805 5V 1A regulator, TO-220 (REG1) 1 7812 12V 1A regulator, TO-220 (REG2) 1 BC337 500mA NPN transistor, TO-92 (Q1) 5 1N4004 400V 1A diodes, DO-41 (D1-D5) 2 3mm high-brightness red LEDs (LED1, LED2) Capacitors 1 470μF 25V PC electrolytic 1 100μF 25V PC electrolytic 2 100μF 16V PC electrolytic 2 10μF 16V PC electrolytic 2 100nF MKT polyester (code 104 or 100n) Resistors (all 1/4W, 1% metal film) 1 22kW 5 10kW 1 1kW 2 560W 1 330W 1 10kW miniature single turn top-adjust trimpot (code 103) (VR1) 1 10kW top-adjust multi-turn trimpot (code 103) (VR2) Transmitter (up to 16 per receiver) 1 double-sided plated-through PCB coded 10109212, 30 x 45mm, 1.0mm thick 1 RF Solutions ENCL_KIT3 3-switch key-fob enclosure [RS Components 4510674, Mouser 223-ENCL-KIT3] 1 Renata HU-2032-LF PCB-mount cell holder (BAT1) [element14 1319749, Mouser 614-HU2032-LF] 1 CR2032 3V lithium cell (BAT1) 1 433.9MHz UHF ASK transmitter (TX1) [Jaycar ZW3100, Altronics Z6900 or equivalent] 3 SPST two-pin momentary PCB-mount tactile switches (S1-S3) [Jaycar SP0611, Altronics S1127] 1 PIC16LF15323-I/SL microcontroller, SOIC-14, programmed with 1010921A.HEX (IC1) 1 3mm high-brightness red LED (LED1) 2 100nF 50V through-hole ceramic 1 220W 1% SMD resistor, M3216/1206 size 1 162mm length of 0.5mm diameter enamelled copper wire Resistor Colour Codes Australia's electronics magazine July 2022  77 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. Switching on external devices via your TV This circuit was designed to power on auxiliary devices such as external amplifiers, lighting, modems etc that are connected to a TV set. It works by sensing an audio signal from the TV’s audio line output or headphone output port. The presence of that signal triggers it to turn on the accessories after a few seconds. When the TV is switched off, the audio signals stop and mains power to the accessories is cut off after about 40 seconds. There needs to be a delay as some program content can have quiet periods. The audio signal fed into CON2 is AC-coupled to the base of NPN transistor Q1, which acts as a common-­ emitter amplifier with a high AC gain as its emitter resistor is bypassed with a 10μF capacitor. I measured the audio output of several TVs at normal listening settings as being from 6mV to 80mV. As the rest of the circuit requires at least 0.5V to trigger the relay, a preamp with an AC gain of at least 100 is needed, and Q1 does that job. The amplified signal drives a charge pump consisting of diodes D2 & D3 and two 4.7μF capacitors. When a signal is present, the 4.7μF capacitor in parallel with the 2.2MW resistor is rapidly charged up to several volts. When the signal goes away, it is slowly discharged by its parallel resistor over about 40s. You can adjust this delay by changing the value of the 2.2MW resistor. For example, 1MW will give a 20 second turnoff time. The voltage from this capacitor is applied to the pin 3 inverting input of comparator IC1. A ~0.6V reference voltage is generated at its pin 2 non-­ inverting input by the forward voltage of diode D4, fed with about 0.1mA by the 100kW resistor from the positive supply. Therefore, when the voltage across the 4.7μF charge pump capacitor exceeds 0.6V, output pin 7 of IC1 goes low, forward-biasing the base of PNP transistor Q3. When Q3 switches on, it powers the coil of mains-rated relay RLY1, switching on the devices plugged into the mains socket. A 22nF X2-class safety capacitor across its contacts prevents arcing during switching, while diode D5 absorbs the back-EMF current pulse when the relay switches off. LED2 is wired in parallel with the coil to show when it is energised. A switch-on delay is provided by NPN transistor Q2 and the 22μF capacitor in its base bias network. At switch-on, this capacitor is discharged so Q2’s base is at around 0.7V, holding it on and effectively shorting out the 4.7μF charge pump capacitor. The 22μF capacitor charges through the 1kW series resistor until the voltage at Q2’s base drops enough that it switches off, enabling normal operation. Power is supplied by a 9-12V DC plugpack. This circuit will work fine with a 6V plugpack, but the relay will need to be a 6V type with suitable contact ratings. I cut into the insulation of a mains extension lead to expose the active wire, then cut it and wired it to the relay contacts. All the mains wiring must be securely anchored and fully insulated. Warwick Talbot, Toowoomba, Qld. ($100) WARNING! – this circuit involves mains wiring and contact with live components is potentially lethal 78 Silicon Chip Australia's electronics magazine siliconchip.com.au Variable L-Pad volume control for loudspeakers This network adjusts the volume of an extension speaker. Unlike many commercial resistive volume controls, it adds damping-reducing resistance that is not more than 2W. This does not significantly alter the alignment of a loudspeaker system with a rated impedance of at least 8W. The minimum load of the pad and speaker presented to the amplifier is 4W. Thus, you cannot connect another speaker in parallel with the extension speaker without risking damage to the amplifier. A pair of toggle switches are used to vary the attenuation because rotary switches with adequate current capacity are costly and not readily available. The switch positions for the five different attenuation levels are straightforward and shown with the circuit diagram. With both toggle switches down, attenuation is at a maximum. Pushing the toggle of switch S1 upwards decreases the attenuation in two steps, each of approximately 6dB. Then moving S2 upwards reduces the attenuation in a further two steps. The other four combinations of toggle switch positions should not be used as they can result in a load slightly below 4W being presented to the amp, or an increased damping resistance of about 3W. However, if these settings are inadvertently selected, they will not cause damage or much distortion. U S B siliconchip.com.au The required resistance for R5 is calculated using the formula R5 = k × Z x Rt ÷ [Z × (k − 1) − Rt] = 5.3W where k is 10dB ÷ 20, Z is the rated impedance of the speaker and Rt is the damping resistance. Here, k = 2 (-6dB attenuation), Z = 8W and Rt = 2W. For -6dB of attenuation, we calculate the equal values for R1 and R2 using the formula R1 || R2 = Rt × R5 ÷ (R5 − Rt), so R1 & R2 = 6.4W. The value of resistor R4 is selected to produce attenuation close to 12dB when S1 is up and S2 is down. Similarly, the value of R3 is chosen to give about 24dB attenuation with both toggle switches down. The way R1 and R2 connect to S2 prevents resistors R3 and R4 from being switched in parallel or series with the speaker. That would present a 2W load to the amplifier. The power ratings for resistors R1-R5 and current ratings of switches S1 & S2 are based on the output of the amp and the power delivered to the speaker not exceeding its 15W rating. Duplicating the network using DPDT switches in place of SPDT yields a stereo two-channel volume control. With the wattage ratings of the resistors as shown, you can build the stereo version for under US$40. Peter H. Lehmann, Newburgh, Maine, USA ($120). Cable Tester 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 Australia's electronics magazine July 2022  79 Transmitting in the FM broadcast band with the MC2833 NBFM chip This circuit was designed to transmit audio within my house so I could receive it using an ordinary FM radio. I am using the MC2833P IC, which usually employs a quartz crystal to set the carrier frequency, thus avoiding drift or complicated adjustments. However, this chip is designed to produce narrowband FM signals, ie, weakly modulated signals with a similar bandwidth to an HF AM signal (5kHz). Wideband FM receivers picking up such a signal would produce an unacceptably low sound level. To increase the bandwidth and operate within the broadcast band (87.5-108MHz in my country), I added the ICS2494N IC, a PLL-based frequency multiplier for computer applications with an output of up to 135MHz. The ICS2494N produces two outputs, simultaneously multiplying the input frequency by two values out of 20 fixed factors. These factors depend on the version of the IC, which is indicated by the last three digits of the part number. I am using the ICS2494N-244 here, set to multiply the input frequency by 4.889 times at one of its outputs; the other outputs are not used. I also replaced the quartz crystal with a Murata CERA­ LOCK 18MHz ceramic resonator (CSTLS18M0X51-A0). I tested some CERALOCK ceramic resonators of other frequencies (8MHz, 16MHz, 16.9MHz), and in all cases, the circuit worked satisfactorily on its corresponding frequency. In all cases, the carrier wave output of the MC2833P did not coincide precisely with the nominal resonator frequency. In the case of the 18MHz resonator, it produced 17.98MHz. 17.98MHz × 4.889 = 87.9MHz, a broadcast frequency that is unused at my location. The audio input, which may come from a microphone, is applied to the internal audio amplifier in IC1 via pin 5. The gain of this stage is adjusted by varying VR1 so that the maximum frequency deviation is achieved without distortion. If applying higher-level audio signals, such as from a CD/DVD/Blu-ray player or DAC, increase the value of the 2.7kW resistor to avoid overloading the amplifier. 80 Silicon Chip The audio signal is then used by IC1 to modulate the reactance at pin 1. This modulates the frequency of the internal Colpitts oscillator, with a frequency also determined by inductor L1, the 18pF & 56pF capacitors and the ceramic resonator. IC1 has two internal RF transistors, which I used in this circuit to amplify the RF signal before applying it to IC2’s input. IC2, the ICS2494N-244, has several parallel digital inputs that configure the factors by which the internal PLLs will multiply the input frequency. FS3 (the most significant bit) to FS0 (the least significant bit) establish the multiplication factor for the VCLK output (pin 19), along with strobe (pin 6), which enables that selection. In this case, the binary word “1001” is used. Inputs MS1 and MS0 (pins 11 & 9 respectively), define the factor for the MCLK output, which is not used in this circuit. The FM RF signal from the VCLK output through a 47pF capacitor is about 5V peak-to-peak. For short-distance transmissions, it can be applied to an antenna without amplification. Different ICS2494N versions (with different multiplication factors) can also be used. For example, by using a CSTLS16M9X54 resonator (16.9MHz), I obtained a 16.92MHz output from IC1. If the ICS2494N-325 were used with the binary word “1011” for FS3-FS0 (which establishes a factor of 5.378), the output carrier frequency would be 90.1MHz. I also tested an SFE10.7MA5-A 10.7MHz ceramic filter and got 10.959MHz at IC1’s output. By employing an ICS2494N-281 and the binary word “1110”, the output carrier frequency would be 99.5MHz. To compare the frequency deviation at IC1’s output using the 18MHz ceramic resonator, the SFE10.7MA5-A ceramic filter and an 18MHz quartz crystal, I disconnected the capacitor from pin 3 of IC1 and applied an adjustable DC voltage to pin 3. This produced the frequency-­voltage plot shown at right. I made the curves intersect at V = 0.95V, which is the voltage that gave approximately the same frequency as no Australia's electronics magazine siliconchip.com.au modulation. It is also the midpoint of the range considered (0.65-1.25V), which is the range at pin 3 when an 8mV peak-to-peak 1kHz audio signal is applied to the circuit with VR1 at its maximum value. You can see that the ceramic devices produce higher frequency deviations than the quartz crystal. The ceramic resonator gives a change in frequency about six times that of the crystal, and the ceramic filter, despite its lower frequency, almost doubles that number. They all become non-linear at the lowest voltages but the audio quality is still good. I have seen VFOs or modulable oscillators employing ceramic resonators before, but never using the MC2833. Since the frequency multiplication to VHF is made inside the ICS2494N, non-integer factors are available, and the use of coils and the need for adjustment are avoided, simplifying the circuit. Ariel G. Benvenuto, Paraná, Argentina. ($120) Simple plugpack voltage & current monitor When checking the voltage of a plugpack, it is tricky to hold the probes just right to make reliable contact. It’s even more difficult to measure the voltage and current simultaneously. This power meter allows you to do that quickly and easily. It also allows you to see the output voltage of the plugpack while under load, which a simple test with a multimeter would not show. I recently came across a “Multi-Function Digital Power Meter” sold by Altronics (Cat Q0589). I thought it would make a useful meter for checking plugpack power supplies and the equipment they power. Jaycar sells a similar DC Power Meter (Cat QP2320), which seems to have the same specifications, although I have not tried it. Not only does the Q0589 show the output voltage and load current, but it also calculates and displays the instantaneous power and energy consumption over time. As 2.1mm and 2.5mm DC connectors are pretty common these days, I have fitted it with both sizes of input and output, but other types could be used or added. The power monitor has been designed to use with plugpacks that have a negative barrel and positive tip, as they are now the most common type. The hardest part of making it is cutting the opening for the panel mount meter in the plastic siliconchip.com.au box; the rest is straightforward. The whole project can be completed in a couple of hours. The two DC input sockets are wired in parallel with the intention that one is used at a time. Similarly, the two output plugs are also wired in parallel, again with the intent to use one at a time (although you could use both if your plugpack is up to it). Rather than making up the two output plugs and leads, it is easiest Australia's electronics magazine to obtain these from old plugpacks that are no longer required. It can measure from 6.5V to 100V DC and up to 20A. If high currents (>3A) are to be measured, use sufficiently thick wires. I fitted a warning label to the device to indicate that it is for use with positive-tip DC supplies only. I also marked the sizes of the plugs and sockets for convenience. John Louttit, Stafford, Qld. ($60) July 2022  81 PRODUCT SHOWCASE CPI waterproof switches Control Devices has added CPI waterproof switches to their product line. CPI switches are designed to cater to demanding Industrial and Defence applications, where efficiency and reliability of machine operation is essential under severe environmental conditions. Based on the users’ set parameters, the switches can qualify for an IP68 rating. They are protected with a thermoplastic or neoprene rubber cover, and are fully submersible – splashproof, waterproof and wash-down resistant. They perform under exposure to water, salt water, oil, sand, dirt, humidity, vibration, shock and temperature extremes. They also come in a selection of styles ranging from a pendant, rocker, plunger, limit and ball. Momentary and maintained functions are available. For installation, the switches can be mounted into a bracket to fit into confined spaces or a switch panel unit. Control Devices Unit 13, 538 Gardeners Road Alexandria NSW 2015 Phone: 02 9930 1700 sales<at>controldevices.net www.controldevices.com.au WBZ451 and PIC32CX-BZ2 early access development kit Take your multi-protocol wireless design to the next level with the PIC32CX-BZ2 family of wireless microcontrollers and WBZ451 modules. They feature the low-energy Bluetooth 5.2 specification, industry-leading security and a proven Zigbee stack. Based around an ARM Cortex-M4, the PIC32CX-BZ2 integrates a high-­performance 2.4GHz radio and supports a wide temperature range in a stand-alone package making it wellsuited for industrial applications such as industrial lighting and remote factory/building control. Home automation is at your fingertips with the PIC32CX-BZ2. It can be used to turn on living room lights, lock your front door and control your blinds remotely. You can even use Bluetooth to set up a Zigbee network and control it from your smartphone. The applications for this exciting new solution are endless. Be one of the first to get early access to Microchip’s development kit, user guides and example demos. The EA71C53A is an early access development kit for developers who want to explore and develop applications with Microchip’s upcoming Bluetooth 5.2 and Zigbee wireless solution. The kit is available now for US$88. To get started visit GitHub here: https://github.com/MicrochipTech/ EA71C53A Microchip Technology 2355 West Chandler Blvd, Chandler Arizona 85224-6199 USA Phone: (480) 792 7200 www.microchip.com Bosch BMP390 pressure sensor now available at Mouser Mouser Electronics is now stocking the BMP390 barometric pressure sensor from Bosch. The BMP390 is an ultra-small, low-power and lownoise 24-bit barometric pressure sensor with vertical (z-axis) capabilities that enable accurate indoor localisation with smartphones in case of emergencies. The Bosch BMP390 barometric pressure sensor offers a pressure range of 300hPa to 1250hPa at 0°C to 65°C with typical relative accuracy of ±0.03hPa. The sensor features low 82 Silicon Chip power consumption of 3.2µA at 1Hz and a small 2 × 2 × 0.75mm form factor, making it ideal for a wide range of lowpower, altitude-tracking applications in smartphone and wearable devices. For development, Mouser also stocks the BMP390 Shuttle Board and the Application Board 3.0. Designed to be used together, the Application Board and Shuttle Board enable access to the BMP390 sensor’s pins to build prototypes. The minuscule, single-package BMP390 solution enhances design Australia's electronics magazine flexibility to allow easy integration, including Internet of Things (IoT) devices, smartphones, GPS modules, wearables, hearables and drones. Visit www.mouser.com/new/bosch/ bosch-bmp390-pressure-sensor to learn more about the Bosch BMP390 sensor. Mouser Electronics Inc. 1000 North Main St, Mansfield, TX 76063 USA Phone: (852) 3756 4700 www.mouser.com siliconchip.com.au Using Cheap Asian Electronic Modules By Jim Rowe PAS CO2 Air Quality Sensor Module Continuing our series of articles describing low-cost air quality sensors (LCAQS), this month, we take a close look at a sensor module based on photoacoustic spectroscopy or PAS. It’s the Infineon XENSIV PAS CO2 mini-board. P AS (photo-acoustic spectroscopy) sensors take advantage of the way molecules of a particular gas absorb specific IR wavelengths according to the Beer-Lambert law. In PAS sensors, the degree of absorption is measured using a phenomenon Alexander Graham Bell discovered in 1880. When a thin metal disc is exposed to pulses of sunlight (Bell used a rotating slotted wheel), it emits sound. Later, Bell showed that materials exposed to the non-visible wavelengths in sunlight (like infra-red/IR and ultraviolet/UV) also emit sound. The basic structure of a PAS sensor is shown in Fig.1. On the left is the pulsed IR light source (generally an array of LEDs), with an optical filter passing only the wavelengths absorbed by the gas to be detected - in this example, 4.2μm for the detection of CO2. At the far end of the chamber, there is 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. The whole sensor 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 seems to be the XENSIV PAS CO2 sensor from Infineon Technologies (an offshoot of Siemens in Munich, Germany). This comes on a very compact module measuring only 14 x 13.8 x 7.5mm, combining the PAS sensor with a Fig.1: the basic structure of a PAS sensor. A pulsed IR LED emits light through a filter leaving only wavelengths of light that the gas to be detected can absorb. A MEMS microphone then detects low-frequency audio that is emitted by the gas, which can be measured to provide the amount of gas in the cell. siliconchip.com.au Australia's electronics magazine dedicated microcontroller unit (MCU) running advanced compensation algorithms and providing a choice of three different data interface ports. It is currently available from suppliers like element14 for around $50 or Mouser Electronics for about $78. Inside the module Fig.2 shows a functional block diagram of the XENSIV PAS CO2 sensor module. At the top is the PAS measurement cell, with its gas inlet pipe on the right, the MEMS IR emitter in the centre and the MEMS LF microphone on the left. Then in the lower part of the diagram are the microcontroller and memory, the light source driver and the circuit that measures the voltage of the external 12V DC supply used to power the IR emitter. Labels for the pin connections are available on the module underside. July 2022  83 but I suspect it is only functional when the UART or PWM interfaces are being used. The actual pin connections for the PAS CO2 mini-board are shown in Fig.3, which is a simplified top view of the module. There are six pins on each side, but the two lowest pins, labelled SWD and SWCLK, are for testing during manufacture and should not be connected when the module is being used. All of the remaining pins correspond to those shown in Fig.2. Trying it out Fig.2: a functional block diagram of the XENSIV PAS sensor module. As mentioned above, the PAS CO2 sensor mini-board provides a choice of three different data interfaces for communicating with an external MCU: I2C, asynchronous serial (UART) and PWM (pulse-width modulation). Which one to be used is chosen by setting the logic level on the PSEL and PWM_DIS control pins. To use the I2C interface, the PWM_ DIS and PSEL pins must be pulled down to GND. For the UART interface, PWM_DIS is pulled down while PSEL is pulled up to logic high (3.3V) instead. Finally, if you want to use the PWM interface, the PWM_DIS pin is pulled to logic high (3.3V). When the I2C interface is selected, the SDA/TX pin is used for the data line and the SCL pin for the clock line. When using this interface, both the SDA/TX and SCL pins need to be fitted with 10kW pull-up resistors to the +3.3V supply. When the UART interface is selected, the SDA/TX line is used as the serial data output and the RX pin for serial data input. But when the PWM interface is selected, the width-modulated pulses emerge from the PWM pin. The INT pin is an output to allow the internal MCU to indicate when it has finished a measurement. I could not find much information on this, Once I had obtained a sample XENSIV PAS CO2 mini-board module, the challenge was to discover how to connect it to a standard low-cost MCU like an Arduino Uno. Luckily, I found this information on the Infineon website. Although Infineon only provides specific information on connecting the module to either a PSoC 6 WiFi-BT Pioneer Kit or an up-market Arduino Due, I was able to glean enough from the latter option to work out how to connect it to an Uno or similar. This turned out to be relatively straightforward, as you can see from Fig.3, which shows how to connect the module to an Arduino Uno via I2C. The 3.3V logic supply comes from the +3.3V output of the Uno, while the SCL Fig.3: connecting the PAS sensor to an Arduino board is straightforward. Note that we have tied the PWM_DIS and PSEL pins to GND so that the module is in I2C mode. Useful links PAS modules: • https://au.element14.com/3779651 • https://au.mouser.com/ProductDetail/726-PASCO2V01AUMA2 • www.infineon.com/cms/en/product/sensor/co2-sensors/#!products Software libraries (or download through the Arduino IDE Library Manager): • https://github.com/Infineon/arduino-pas-co2-sensor • www.arduino.cc/reference/en/libraries/pas-co2-sensor/ Photoacoustic spectroscopy: • https://w.wiki/4wsX 84 Silicon Chip Australia's electronics magazine siliconchip.com.au and TX/SDA pins connect to the Uno’s SCL and SDA pins and a pair of 10kW pull-up resistors. The PWM_DIS and PSEL pins are tied to ground for I2C mode, as mentioned earlier. Since the module also needs a 12V DC supply to provide power for the IR LED, this can come from a separate plugpack supply. It can be a small supply, since the average current is less than 600μA with brief pulses of around 20mA. Three bypass capacitors on the 12V supply line provide smoothing. Of course, we need a software library to send commands to and receive data from the sensor, plus a sketch to use the library. After a bit of searching on the Arduino website in the “reference/en/ libraries” section and then in the list of 900-odd contributed libraries for communicating with sensors, I found one called “PAS CO2 Arduino Library v1.0.3”. When I clicked on that one, it took me to github.com, where I discovered that the library was provided by and maintained by Infineon! So it was obviously the right one to download. I downloaded the library zip file and added it to my Arduino IDE’s list of installed libraries. I then discovered that it came with 12 example sketches – four of which are for using the module’s PWM interface mode, while the Fig.4: sample output 15:37:04.303 15:37:09.505 15:37:14.520 15:37:19.487 15:37:24.502 15:37:29.516 15:37:34.483 15:37:39.498 15:37:44.466 15:37:49.480 15:37:54.448 15:37:59.462 15:38:04.477 15:38:09.444 15:38:14.459 15:38:19.426 15:38:24.441 -> -> -> -> -> -> -> -> -> -> -> -> -> -> -> -> -> pas co2 co2 co2 co2 co2 co2 co2 co2 co2 co2 co2 co2 co2 co2 co2 co2 co2 ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm serial intialized value : 633 value : 623 value : 621 value : 611 value : 609 value : 610 value : 649 value : 1018 value : 1255 value : 1254 value : 1256 value : 1317 value : 1409 value : 1418 value : 1405 value : 1392 other eight are for the serial interface modes (ie, I2C or UART). The latter had the following titles: • serial-alarm • serial-api-test • serial-calibrate • serial-device-id • serial-diagnosis • serial-oneshot • serial-periodic • serial-reset I decided to try “serial-oneshot.ino”, and when I loaded it, compiled it and then uploaded it to the Arduino and opened virtual serial port COM3, it all sprang into life. The PAS sensor measures 14 x 13.8mm, making it tiny in comparison to the enlarged photo shown here. Fig.4 shows the output in the Arduino IDE Serial Monitor following the startup of the serial-oneshot sketch. The first line indicates that the PAS CO2 and its I2C serial port have been initialised, while the following lines show the measured CO2 levels in ppm (parts per million). These measurements are about five seconds apart, as you can see from the timestamps. The other thing to note from Fig.4 is that the initial seven readings are all between 610ppm and 649ppm, whereas the eighth reading suddenly jumps up to 1018ppm and then following readings move up to 1418ppm before starting to fall again. At about 15:37:40, I exhaled towards the PAS CO2 sensor. So it was responding to the sudden increase in CO2 level, as it’s supposed to. Encouraged by this initial success, I then tried loading, uploading and running the “serial-calibrate.ino” example sketch. This sketch ran very quickly, simply giving a “sensor now calibrated” message before ending. Summary Despite being very compact, the Infineon XENSIV PAS CO2 sensor mini-board is a good performer. As it uses a standard I2C interface, it is compatible with just about any microcontroller, including virtually all Arduinos. No doubt it would work with a Micromite as long as it was set up to send the correct I2C commands. Although it is priced higher than the MOS sensors we’ve looked at previously, and it needs a 12V supply, it is a good choice if you want a small and accurate CO2 sensor. SC siliconchip.com.au Australia's electronics magazine July 2022  85 SERVICEMAN’S LOG Trail camera fun Dave Thompson Sometimes when you’re presented with a faulty device with no obvious symptoms, you have to take an educated guess and repair the bit you think is most likely to fail. That’s what I did this time, and while it was a bit of a circuitous path, it eventually led me to the right conclusion. Sometimes, you just need to trust your gut instinct. Remote cameras have been used in sports and wildlife photography for decades, but they have increasingly become both much more advanced and affordable recently. One particular use of them that has grown hugely in the last few years is in the great outdoors. Hunters, nature photographers and conservationists are all big users of so-called trail cameras (sometimes called hunting cameras). These devices use increasingly modern technology to allow users to ‘set and forget’ camera traps out in the wild that (hopefully) capture images and videos of animals or natural activity that is rarely seen. The basic idea is simple: set up one or more cameras in an area of interest, and anything that meanders past, day or night, will trigger the camera into action. Most of the latest devices can record both high-resolution video and still images, with the captured data stored on a built-in memory card. In some models, it is also transmitted via SMS/ MMS to a mobile phone. Most of these cameras also have night-vision capability, using arrays of high-intensity infrared LEDs to provide a wide area of night-time illumination, even in complete darkness. The advantages of this scheme should be obvious; a standard flashgun would work, but would scare off (not to mention temporarily blind) any detected game. However, the invisible-to-most-eyes infrared flash or flood would not reveal the presence of anything out of the ordinary to the quarry. I first heard about these cameras many years ago, after one of our cats went missing, and I looked into buying one because reported sightings were coming in. We wanted some way of knowing if he was turning up to these people’s places. He also may have been coming back home after dark. Either way, we wanted to know. I did my ‘due diligence’ and purchased a mid-priced unit from a reputable brand at a local retailer. This model had a 2-inch (5cm) screen for reviewing footage and a range of functions we’d likely never use, all in a relatively compact, camouflage-motif case. I had a good play with it before deploying it, and it lived up to the bumf. The photo quality was especially good, even in complete darkness, though this was monochrome – during the day, it took the usual full-colour snaps. Then again, one would expect decent quality with a purported 12-megapixel sensor and a fixed-focus lens. The camera used the older SD card format for data storage, and even a relatively-small 4GB card was enough for a lot of photos. However, if the video recording option was enabled, it used up the storage space pretty quickly, so I stuck with stills initially. Its battery life was good, but this model also had a ‘backpack’ battery holder, meaning an extra four AA-size cells could be fitted, giving the camera a significant amount of unattended operation capability. The whole idea is to ‘set and forget’ and come back in a few days, weeks or months to download what the camera has captured in the meantime. I soon learned that trawling through a thousand almost-identical images was a considerable time investment! Leaves, wind, birds, hedgehogs, cats, dogs, mice and bugs could set it off – and often, the image would show nothing but a slight ‘spot’ in range of the PIR sensors. Ah well, we don’t get anything for nothing! Enter the customer My point – as usual, a long time coming – is that a customer recently brought in one of these cameras for me to look at. Ironically, he’d brought one into my workshop a few years previously (a considerably older model) that he’d been given but did not work. When I cracked the case open, I could see why; someone had stored it long-term with batteries in place, and they had 86 Silicon Chip Australia's electronics magazine siliconchip.com.au Items Covered This Month • • • • • Messing around with a trail camera The dilapidated pair of touch lights The compact fault whisperer Follow-up to Clenergy 1.5kW solar inverter Repairing a lathe’s motor speed controller 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 leaked – badly. The entire area of PCB beneath the battery holder had corroded away, and the device was completely dead. Even if I could see any tracks (or remains of tracks), it would have been impossible to repair them. He was philosophical about it – he’d been given it after all – and used that as a premise to buy a fancy new one. It was this new model that brought him back this time. It had worked hard for several years, usually mounted out by a run on his rural property, monitoring for feral cats and any other predators that were breaking into the run and decimating his chicken population. This had become an essential piece of kit in preventing animals from poaching his stock, and he was keen to get it back to work. This meant that it had spent all of its working life sitting in weather, ranging from far below freezing to baking in the scorching summer heat. I was surprised it had lasted this long! I hated to think what it was like inside, IP66 rating or not! The problem was that while it appeared to be working (various lights on power-up etc), it was not taking any new photos, the last one having been several weeks previously. Something had happened in the meantime, although on careful questioning, he did say that he had changed batteries ‘around’ that time. This was a clue, perhaps. Getting it open was no challenge. Six screws held it all together, and after removing them, I could gently ease the case apart. It was pretty tight, which was caused (it turned out) by the weather seals holding on tightly. Each screw turret had a rubber seal between it and the back of the case, and there was a large, embedded ‘o’ ring in a channel around the very edge of the case. This is flattened slightly by the screw pressure on the other half of the case, and should have kept the inside weatherproofed. I was expecting carnage inside, given its working history, but it was actually pristine. That weatherproofing did its job well! The only real possibility of water/environment ingress into the case would be through the hinged access panel. When the camera is sitting normally, it is at the very bottom. That puts it out of any real weather just by being where it is, and that trapdoor has a seal on it as well. Popping that hatch open reveals all the main controls, including an Off/On/Test switch, external power and video out connectors and mini-USB and SD card sockets. The screen is on the rear of the device, covered by the backplate in normal use, and below that are membrane-style siliconchip.com.au shuttle buttons for manually taking photos or movies and for captured video and stills playback. This allows it to essentially operate like a standard digital camera. Usually, in ‘test’ mode, the screen is activated, and we can alter camera settings and preview captured data; but that was no longer happening. Turning the camera ‘on’ using that switch would usually result in a red LED embedded within the LED array flashing for 10 seconds before going dark, indicating the camera is ‘armed’ and ready to detect any movement. The delay gives the operator time to shut the hatch and exit the area without taking any accidental selfies. Pushing the switch further to ‘Test’ mode also fires up the red LED, and then a blue one next to it lights up when the two PIR sensors detect any movement. This allows more accurate positioning of the camera’s detection area, similar to a ‘walk’ test we do for home alarm PIR sensors. As I mentioned earlier, the screen didn’t light up in Test mode. Neither did the blue LED activate. All roads led to Test mode not being entered at all, and on top of that, even in normal operating mode, the camera no longer wrote anything to the SD card. Something seems fishy I suspected the switch itself. It didn’t ‘feel’ right when actuated, and as one of the very few moving parts, it was at risk of wearing out. Getting to it was not easy; the PCB, which is stuffed with electronics, sits sandwiched between the moulded battery holder and the hard-plastic back half of the case. Space is very tight, though the PCB screws and clips would be relatively easy to access with a small screwdriver once the battery holder was removed. Still, the battery holder – a separate and quite-complex plastic moulding – could only be removed once the power connections to the PCB were de-soldered. These connections were actually extensions of the battery spring connectors, and they were press-fitted into the plastic holder. I had to be careful not to go too heavy on the heat and melt them out of the housing! Some deft soldering iron work and pump/wick application soon had the leads out and clear; the holder assembly could then Australia's electronics magazine July 2022  87 be unscrewed and unclipped from the PCB. Now I had better access to the PCB screws and could take that away from the case shell. This gave me direct access to the switch. I was hoping it was the switch because, if not, there would likely be little more I could do with it. As is typical, there are no circuits or schematics available anywhere for these cameras and, even if I did have one, troubleshooting something with this many tiny SMDs is no fun at all. The other thing I had to consider is that a very similar – if not better – camera is available from my favourite online shopping site for under a hundred bucks. So any fix on this would have to be pretty easy and inexpensive to make it even worth repairing. Partly out of curiosity (and the Serviceman’s Curse, obviously), I wanted to see if I could get it working. The switch is a reasonably standard-looking triple-pole, triple-throw sliding type. As is becoming more usual, the metal outside case is soldered to pads on the PCB, along with the six soldered pins. Taking mounted components like this off a PCB can be a chore, especially on multilayer boards. That is, unless you don’t want them any longer, in which case just cutting off what we can with a Dremel or good side-cutters is the easiest way. Then it is just a matter of extracting the cut-off legs and whatever else remains behind. Rudimentary tests in-circuit weren’t that conclusive as to whether it was making the right contacts or not, so I decided just to cut the switch away and replace it with an identical one. I have boxes full of new-old-stock switches but nothing (of course) with the same dimensions and pinout as the one I removed, so I hit the usual electronics suppliers to see what they had. Anyone who has used those websites knows it can be tricky to find what we want among the gazillions of possible options. The use of specific search parameters is essential, but it can still take time to wade through the results. I eventually found one identical in every 88 Silicon Chip respect. While not expensive, there was a minimum order amount, so I usually try to find some small hand tools to top up the order amount. It’s a tough job, but someone has to do it! The switch arrived a few days later, and fitting it was much easier than removing the old one! I temporarily reassembled the board and battery holder on the bench and powered it up. I’d like to report that I had fixed the problem, but I’d be lying. It did precisely the same thing as before. Oh well; that wasn’t the first time I’d been well wide of the mark. On to plan B, then. The SD card slot is the only other part that gets accessed from the outside of the case, besides the battery holder and on/off switch. While modern versions of these cameras use MicroSD cards (which can be found up to 2TB [yes, that’s 2000GB] these days!), older cameras like this one utilise the older and considerably physically-bigger SD cards. They are still viable; many laptops come with card readers that can accept this type of media. The customer had a 16GB card in this one and swapped it out with another identical card when he went to service the camera every week or so. That meant the cards got a fair bit of use, as did the card socket inside the camera. I tried using one of my own cards. While most cameras can accept Windows/FAT32-formatted cards, for whatever reason, they typically recommend that any ‘new’ card be formatted by the camera itself. As I couldn’t get to the display, I couldn’t format it, and as his card worked fine via a card-reader on my workshop computer, I made the educated guess that it was likely OK. The user manual states that if a card is faulty, everything will power on, but a ‘card error’ message is displayed. Australia's electronics magazine Doing some micro-surgery Taking all that into account, I turned my attention to the socket itself. As I mentioned earlier, the camera’s interior was pristine, and nothing was floating around inside it, but I put the board under the scope anyway for a look. The soldering was not bad siliconchip.com.au overall, but a few spots looked dodgy up close. A quick going over soon had those looking better. I paid particular attention around the SD socket, as several of the pins looked a bit light on solder as well. And if I flexed the socket slightly, one pin, in particular, appeared to be lifting away from the solder pad. It was difficult to see, even with the microscope, but I decided to re-do the whole row of solder joints as a precaution. Pushing the media in and taking it out puts a fair amount of stress on those joints and, unlike the switch body, the flimsy metal frame of this connector was not well-­ soldered to the board, with just a couple of tiny tabs on either side of the socket near the pins anchoring it down. Many SD connectors are (by design) very lightweight and made to fit in very tight places. Given that one has to ‘push to click’ the media in, then push again to remove it, it stands to reason that some wear and tear is inevitable. I gave each pad a decent sweat of flux and solder, and it looked much better. I couldn’t see anything else evident on the PCB, so this was as far as I would go with it. I reassembled it properly; if it didn’t work now, at least it would be in one piece for the customer. Getting the battery holder back in was a bit of an act, but it was straightforward enough. I loaded up the batteries and hit the switch to ‘Test’. Imagine my surprise when the display lit up straight away! I could surf for files on the media, and I could now adjust settings and do a walk test, noting the blue LED indicating the PIRs detecting my presence. I set the switch to ‘On’ and, after the ‘get away’ period, did several walk-pasts. I’m not much of a runway fashion model, but it did result in photos of me appearing on the card, so I was happy with that. It’s always worth giving a repair a go; after all, it just might work! Return of the dilapidated gear B. P., of Dundathu, Qld is at it again, fixing up someone else’s discarded gear and getting it to work again. It’s certainly cheaper than buying brand new... I bought a pair of touch lights at the local tip shop, assuming they wouldn’t be working. The lights are ‘antique style’ and were in reasonably good condition, apart from some corrosion from age and some of the parts in the shades being loose. So they had nothing major wrong, appearance-wise. After bringing them home, I removed the shades, put 3W LED globes in them, plugged one in and touched it. Nothing happened, so I tried the second one, and it also did not work. I guess this is why the previous owner had discarded the lights. I took the base plates off both lights and opened the black boxes that house the electronics. The first thing I noticed was that both lights had two bad electrolytic capacitors on the circuit boards. I found equivalents in my salvaged capacitors collection. After that, one light stayed on all the time while the other light only worked sometimes, after multiple touches. So there was something else wrong. I could see that these lights used a BT136-600 Triac and a TT6061 IC. I thought I would swap over the Triacs between the two lights to see what would happen. Now neither light worked, indicating that both components were faulty in both lights. This was likely caused by the bad electrolytic capacitors. As I did not have either component in stock, I ordered them on eBay. They weren’t available from Australian sellers, so I had to order both parts from China. Once they arrived, I fitted them and set the lights up for testing again. Now both lights worked. However, one feature of the lights did not work correctly with the LED globes. The first touch is supposed to turn the light on to a dull setting, but they were obviously designed for incandescents and the LED globes flicker badly. Touching the light a second time changes it to bright mode, and the LED globes no longer flicker. Touching the light again returns the light to dull mode, but there is now very little flickering. Another touch turns the light off. So the lights were now working correctly, other than the problem with using LED globes. The best solution is just to touch the lamp twice to turn it to bright mode straight away. There isn’t much difference in brightness with the LED globes between the two settings anyway. I was able to screw the bases back onto the lights after finally completing the repairs. After that, I gave them a good wipe down with a damp cloth. Because the lights are made from brass-plated steel, the surface cannot be cleaned too aggressively; otherwise, it will be further damaged. The slightly deteriorated look of the lights adds to the antique appearance. Even though they are modern lights, they look a lot older than they are, both with the style and the ‘aged patina’. Upon opening the base of the touch lights two bad electrolytic capacitors were immediately noticeable. siliconchip.com.au Australia's electronics magazine July 2022  89 Turning my attention to the shades, I straightened the bent parts on the brackets, tightened the screws and cleaned them with a damp cloth. The shades were actually in quite good condition with all the parts being present and nothing broken or chipped. Then I refitted the shades and screwed the decorative nut on firmly. So for a few dollars for the lights and around $7 in parts (I bought 10 of each component), I now have two working touch lights. So that’s about $5 each in total. I looked online to see if I could find the same light, and I found a similar lamp for $220 for just one! It’s handy to be able to fix things that someone else has thrown away. The fact that these items can be purchased cheaply at the tip shop means that they can be recycled or repaired. Not to mention the massive saving compared to buying new lights. The fault whisperer J. W., of Hillarys, WA ran into that strange situation where he managed to fix a faulty device but isn’t really sure how he did it. Oh well, a win is a win... I was talking to a friend who worked as an audio specialist (now retired) at a Perth radio station about all the equipment he used to work with. He mentioned that he had a Studer A730 Professional CD player that had not worked for a couple of years and asked if I could try to get it going again. I told him I would take a look at it, so it ended up in my workshop with the complete service manual. Upon powering it up, there were no signs of life on the front panel and a strange clicking noise emanating from within. It seemed like a power supply problem to me. I removed the six screws holding the front panel, although one was difficult and had to be drilled out. I was then presented with the main board with approximately 60 ICs, including two microprocessors. With the front panel moved out of the way, I could hear that the noise was not coming from the CD mechanism but seemed to be a relay trying to operate at the rear of the main board. I checked the service manual and found there should be four power supply rails: +5V, -5V, +12V and -15V. The latter three were produced using LM317 and LM337 linear regulators and tested OK. An L296 switching regulator generated the +5V supply, but the output only measured about 0.4V. I downloaded the data sheet for the L296 and found that the current was set to be limited to about 4A. With my CRO connected to the +5V line, I found that it was trying to start but being shut down by its over-current protection. I disconnected the front panel and audio output boards but found the +5V was still not present. I then removed the main board from the case and made a cable for the secondary of the power transformer, so that An exterior (left) and interior (right) shot of the Studer A730 CD player. 90 Silicon Chip Australia's electronics magazine siliconchip.com.au I could run it away from the case where the mains transformer was situated. Now I could move the board around and give it a good visual inspection; nothing seemed to be getting hot or looked damaged. I manipulated the board and then tapped around with a probe, producing no change in the situation. I decided to start trying to isolate sections of the main board and see if the +5V would come to life. After cutting several tracks to no avail, I discovered that the board was multi-layered with a least one copper plane not accessible, so I could not isolate any more sections. I decided to remove the output inductor from the switching regulator and use my high-current linear power supply to replace the +5V supply. This way, I might be able to produce some evidence of overheating from the faulty component. I set my supply to 5V and 4A and powered up the player and my supply. The current hit its limit at the 4A setting, delivering about 2.5V. I then started to feel each component to see if it was getting hot. While doing that, its output voltage increased to 4.1V, with the current still at 4A. A short time later, I noticed that the voltage had gone up to 5V and the current had dropped to 900mA, so the overload had cleared. I then tried to bring the fault back by tapping each component and flexing the board, but it did not fail again. Had the problem disappeared entirely, or was it intermittent? I reconnected the original power and was greeted with a steady 5.1V. After connecting the front panel and audio boards back up, I powered the player up again and was greeted with NO DISC showing on the front panel display. I inserted a CD and pressed play; the player was now working properly. I let it run for a few days before ringing my friend to tell him the news. Two days later, I walked into the workshop to find smoke streaming from the back of the player, although the CD was still playing. I turned it off and lifted the front panel to find the mains filter and switch assembly was quite hot, but the mains transformer was not. I removed the mains filter and noticed some smelly liquid coming from the power switch. It looked like the mains suppression circuit had failed. I ordered a replacement unit and connected the mains transformer to a spare power cord so I could let the system run again. The player ran flawlessly until the replacement mains filter arrived. I fitted that and screwed the front panel back in place. After letting it run for another few days, I rang my friend. He was delighted and told me he thought the player was still worth a few thousand dollars. I saw one on eBay for €3000 – over $4000! It has been a few months now, and the player is still working fine. I never found out what had caused the +5V line to be overloaded. Perhaps it was some sort of ‘tin whisker’ that burned away when I applied 4A continuously. Follow-up to the Clenergy 1.5kW solar inverter R. S., of Figtree Pocket, Qld has a follow-up to the Clenergy 1.5kW solar inverter repair storage that we published on page 101 of the May 2021 issue (siliconchip.au/Article/ 14862)... The “Ground I Fault” message is caused by drift in the Hall Effect based current sensor, which monitors any current difference (caused by faulty panel insulation) between siliconchip.com.au Australia's electronics magazine July 2022  91 The exterior and interior of the motor controller are shown above, while the underside of the replacement motor controller is shown below. It worked fine for a few weeks, but then blew up, fusing one of the tracks (marked in red). the inverter AC output Active and Neutral lines. The sensor is in the bottom-left corner of the inverter and looks like a toroid. There is more than one version of this sensor. The later versions are more stable, so the newer inverters do not have this fault. There does not seem to be an easy way to adjust for the drift. It might be that the only way to fix an inverter giving this message is to replace that sensor with the latest version. Repairing a lathe’s motor speed controller While repairing a motor speed controller, D. S., of Maryborough, Qld discovered a horribly flawed design. Had the controller not failed, it might have been a lethal hazard... B. P.’s repair in the November 2021 Serviceman’s Log column reminded me of a service call I made to a local woodcarver. He called me and said that his wood lathe had gone bang. Being a mains-powered lathe, I advised him to switch off the power and wait for me to get there. When I checked out the lathe, nothing seemed amiss – no damaged wiring, no burn marks on the motors or any other signs of a problem. I switched the power back on and re-checked the lathe. The spindle motor worked correctly, as did the speed controller for it. However, this lathe has a small secondary motor. It is much smaller than the main spindle motor and has a small drill chuck fitted to the end. This auxiliary motor can be used to carve various patterns into the spinning workpiece by adjusting speeds and the cutting bit. This motor did not work at all. There were no voltages present anywhere. I had to remove the top shield over the main motor controls to access the smaller motor controls. This smaller motor is an add-on and was modified to fit the existing lathe. But it seems that its speed controller decided to die a couple of weeks earlier, after giving several years loyal service. The owner decided that he would find a replacement controller on eBay. He did find one and at a fraction of the cost of the original. As the replacement unit had the same connections as the previous one, he fitted himself. It 92 Silicon Chip worked fine for a couple of weeks, then boom! This damage was actually a godsend. As you can see from the photo of the underside, one of the mains tracks intersects a mounting hole that has a metal screw going through it and the metal shield around the whole thing. The separation is so minimal that the vibration of normal work eventually caused the track to short against the shield, causing the track to vaporise. Neither of the onboard fuses blew, and the safety switch for the workshop did not trip off. I checked the Earth circuit from the lathe to the power board and found it safe, and a quick safety switch check revealed a normal trip current of 30mA. So at least the proximity of that track to the shield would not have caused the frame of the lathe to become live, although I don’t know why the safety switch did not trip. I replaced this unsafe device with a new controller made in Australia. Although a bit more expensive, it is a lot safer. Please be very careful buying mains-powered items from eBay. Cheap units are flooding the market, and a considerable number of them are simply not safe! If you have any SC doubts, please consult a licensed electrician. 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To start your subscription go to siliconchip.com.au/Shop/Subscribe Vintage Radio 1966 Astor “Diamond Dot” CJ-12 Car Radio By Dr Hugo Holden This car radio is a piece of Australian history. It was in such poor condition that I almost threw it away, but it has cleaned up a treat. True to its name, it has a fake diamond-like ‘jewel’ embedded in the front panel. Perhaps the most fascinating aspect is that most of its components, including the transistors, were locally made! I was cleaning out my shed and found a very old and rusty MW-band (AM) car radio with missing knobs and a broken and yellowed dial. I had acquired it for my 1966 Triumph TR4A, as it was period correct. But I ended up fitting a Motorola AM radio with an FM converter instead, and had forgotten all about this Astor radio. It had what looked like a diamond set into the metalwork. It is not a real diamond, of course; it is more like a costume jewellery variant, but it still gives the front escutcheon an eye-catching look. The radio was in such poor condition that I almost threw it away, as I was in the process of a big cleanup. But I decided to take a closer look. The 94 Silicon Chip more I looked at it, the more interesting it became, so I decided it was worthy of a complete restoration. It turned out very nicely, as I think you’ll agree from the photo. The radio’s dial is quite a piece of Australian broadcasting history, with rows of station IDs for different states: TAS, NSW, VIC, SA, NT, WA and QLD. I noticed one of my favourite radio stations listed as KQ, which is 4KQ in Brisbane. Obviously, this radio was intended to be used anywhere in Australia (given that cars were not only sold throughout Australia but also mobile, that makes perfect sense). Car radio design history I have always found the design of car Australia's electronics magazine radios interesting, especially because they commonly use permeability tuning, which permits easy pushbutton station selection. Also, my very first job out of school in the 1970s was working at a car radio factory called “Aerial Radio” in Auckland. That is where I learned about car radios. I worked in a final testing station, putting the radios through their paces and fixing any assembly errors before they were boxed up for sale. Car radios made before 1955 used valves (vacuum tubes). Generally, the HT supply was provided by a vibrator and step-up transformer; the tube anode voltages were similar to those in a line-powered domestic radio, in the 200-300V range. siliconchip.com.au In the mid-to-late 1950s, valves that required only 12V at the anode, such as the EF98 and ECH83, were devised. These were usually combined with a single germanium power transistor, typically a 2N441, in a class-A audio output stage with a collector choke. This ‘hybrid’ design was very popular until the early 1960s. The low HT voltage tubes eliminated the need for the vibrator. The hybrid radio audio stage generally used one EF98, and with a 10MW input grid resistance, this would drive a 23:1 transformer. That fed the base-emitter junction of the 2N441 power transistor, which would have a choke as the collector load, with the speaker connected directly across the choke, or to a tap on it. This hybrid design resulted in an audio amplifier system that required about 2-3V peak for full volume, with an output power of around 4-5W. Having an input impedance of 10MW at the grid and an output impedance of 4-8W was impressive, especially for just one valve and one transistor. However, it was not energy-­ efficient, and the transistor required moderate heatsinking. After all, in class-A, the idle power consumption is often a similar value to the maximum audio output power. In 1955, the first ‘all-transistor’ car radio appeared on the scene in the USA. This was the Mopar (Chrysler) model 914HR. Hybrid radios were still prevalent at that time. The 914HR was made possible by some revolutionary new surface barrier radio frequency transistors, with very low base to collector feedback capacitances. These were rivalled perhaps only by germanium RF transistors such as the OC169, which appeared later, in 1960. There is an interesting YouTube video about this revolutionary Mopar radio at https://youtu.be/Qz3JkFnvBuA Mopar all-transistor radios were fitted to the 1956 Chrysler and Imperial car models. It took about five years for other manufacturers to catch up, before the all-transistor car radios took over. So the Mopar 914HR was some years ahead of the times. By the early 1960s, most countries started mass producing all-­transistor car radios. By the mid-1960s, not only were most car radios of this type, but in keeping with other transistor radios, the audio output stages had siliconchip.com.au Fig.1: the damaged dial from the Astor “Diamond Dot” radio. Fig.2: this is what the radio looked like after being disassembled, just before commencing restoration. moved to push-pull class-AB designs. These had significantly improved efficiency over the class-A designs of hybrid radios. These class-AB designs were essentially class-B amplifiers but with enough initial bias to overcome crossover distortion. This cut the radio’s power consumption to the point that you could get away with accidentally leaving your car radio on overnight and just be able to start your car in the morning. The initial push-pull audio output stage designs used a driver and output transformer. Later, a split driver transformer was used, eliminating the output transformer and saving the cost and weight of the iron core. The speaker was coupled to the power output transistors via a capacitor. Then, with an abundance of good silicon NPN and PNP power output transistors, totally transformerless circuit topologies with complementary audio output transistors appeared. After the mid-1970s, the entire audio stages often were replaced by a single Australia's electronics magazine IC, as was the trend in many domestic radios. Therefore, one could expect a transistor car radio from the mid-1960, like the Astor Diamond Dot, to be sporting a push-pull output stage, probably with coupling transformers. And that is indeed what it has. But what about the transistors? What was Astor using, and where did they come from? Inspecting my radio, I immediately noticed two grey ceramic transistors with black resin tops with the part numbers AX1130 on their sides. I was about to learn more about the sadly lost and once amazing Australian transistor manufacturing industry (more on this in the panel near the end of the article). Restoring the radio There were some interesting problems to solve in the restoration, mainly related to oxidised metalwork, missing front panel retaining nuts and missing knobs. Fig.2 shows the radio in a state of disassembly before restoration. July 2022  95 Fig.3: the radio originally used two Anodeon AT-1138 (shown opposite) transistors. Those were replaced with AD149 germanium transistors, as shown in the photo. Fig.4: The rusted Anodeon AT-1138 transistors were painted and stored in case they were ever needed later. Fig.5: I machined two new hex nuts to mount the front escutcheon. Disassembly required removing several rivets (later replaced) to separate the audio amplifier heatsink assembly from the metal lid. The dial was yellowed through its entire thickness, except where it was shaded from sunlight along its upper and lower edges. It had hardened and cracked. The metal had pitted due to surface rusting, more on the top of the radio than the bottom. The stripping processing before re-electroplating eliminates all the rust crystals. This must be done because ‘rust never sleeps’, and when I see radios that have supposedly been “restored” by painting over the rust, it makes me cringe. After electroplating, the metal pits remain, but at least the surface is plated and no longer rusting. The radio used quite a few self-threading screws, all very rusty. I replaced the common ones (eg, garden size #4 and size #6) with new screws, but for the special low-profile countersunk head types that are hard to get, I had to send those to the electroplater to be re-plated. I was able to replace all the rivets with identical geometry rivets, except for the two small ones above the AD149 on the left. I had to replace those with small stainless steel screws. The two original germanium output transistors, the Anodeon AT-1138 types, had rusted. So I replaced these with a very well-matched pair of AD149 germanium transistors with equally good performance, if not superior (see Fig.3). I kept the original Anodeon transistors and painted them, in case somebody would prefer to use them later (shown in Fig.4). The special nuts which secured the front escutcheon were missing. I searched and could not find any, so I machined two from hexagonal brass bar on my mini-lathe (Fig.5). The thread is 3/8in diameter, 32 threads per inch (TPI), and I was able to get those taps on eBay. An 8.5mm drill worked well. I took the fibre washers from some panel-mount fuse holders I had in my junk box. As for the knobs, I bought some plastic replica knobs on eBay but was disappointed with the quality. Fig.6: knobs from another Astor car radio were modified to fit the Diamond Dot. 96 Silicon Chip Australia's electronics magazine I eventually found some original metal knobs from another model of Astor transportable car radio. They were almost perfect, but the centre knob was designed to push onto a ¼in shaft. This radio had 3/16in shafts for the centre knob, so I machined brass inserts to fit into the centre knobs to make them compatible. These inserts are visible in Fig.6. The ARTS&P sticker on the radio body was moderately marked, so I scanned it (Fig.7) and made a replica. The photo in Fig.8 was taken near the end of the rebuild, after the metalwork came back from the electroplater. The upper panel (radio’s lid, #1 in Fig.8) holds the audio amplifier assembly, and a leash of wires linked it to the main radio board. For ease of restoration, I cut the wires and inserted 0.9mm gold-plated pins and sockets (from Jaycar) to make it easy to separate the audio amplifier and top plate assembly. #2 in Fig.8 points to the two interesting Australian-made Fairchild AX1130 transistors. These act as drivers for the two germanium output Fig.7: the original ARTS&P sticker, which shows the model number. A replica was made of this sticker. siliconchip.com.au transistors, in the Darlington configuration. This reduces the required drive current to the output stage. When I first powered the radio, one of these transistors was defective, so I desoldered it from the PCB. All transistors on the main board in this radio had sleeved leads, so the lead wires were not directly visible. The transistors are interesting as, in common with many of the Fairchild types of the time, they have gold-plated steel lead wires. I found that the defective AX1130 had one lead wire that was totally rusted through. But there was enough of it projecting from the transistor body to save the transistor by joining another wire. I decided to inspect the other transistors on the main board in the radio frequency sections. All the lead wires had grossly rusted, extending right up to the transistors’ plastic bodies. Ultimately, I elected to replace all of them with high-quality mil-spec 2N2222A transistors to avoid any future troubles. This radio must have been in a very moist environment, possibly even saturated with water at one point. After replacing the radio’s electrolytic capacitors, powering the radio and adjusting the output’s stages quiescent current, I tested the audio output stages with a signal generator. I then moved onto the radio-frequency sections. The radio was stone dead, with just a faint hiss from the speaker. I quickly determined that the local oscillator (LO) was not operating. I checked the transistors’ DC conditions, and they were normal. I worried that the oscillator coil in the permeability tuning unit could have gone open-circuit. Testing showed that the oscillator started when a 47pF capacitor was placed in parallel with the existing 56pF feedback capacitor in the oscillator circuit (#3 in Fig.8). Fig.9 shows this capacitor in the circuit. It provides positive feedback from the tank circuit to maintain oscillation. At first, I thought that the requirement for more feedback capacitance indicated the transistor stage gain had dropped or the coil losses had increased. I tested the 56pF polystyrene capacitor shown in Fig.11; it had zero leakage and read 57pF on my YF-150 capacitance meter. Yet, I found when I replaced it with a new 50pF capacitor that the oscillator ran normally. How could that be when the 56pF capacitor tested fine? I siliconchip.com.au #1 #2 #3 #4 Fig.8: the internal topside of the chassis is marked with four locations: #1 radio lid and audio amplifier assembly; #2 two Australian-made Fairchild AX1130 transistors; #3 local oscillator; #4 permeability tuning mechanism. Fig.9: a section of the oscillator circuit with a 56pF capacitor shown. This 56pF capacitor provides feedback from the tank circuit. Australia's electronics magazine July 2022  97 Fig.10 Fig.11: the 56pF capacitor from the radio was faulty, despite having zero leakage and reading fine on a capacitance meter. It was replaced with a new 50pF capacitor. have never seen this defect in a polystyrene capacitor before. Of course, when a technician finds a faulty part, it most often gets thrown in the bin, as it is not cost-effective to investigate it. But I decided to attempt to find out what was wrong with this 56pF capacitor, in light of the disturbing fact that it tested as normal on my meters but didn’t work. Testing it with a signal generator and a scope, I determined that its ESR had increased massively, to around 22kW. Of course, ESR meters cannot measure low-value capacitors like this. I then tried measuring known-good lowvalue capacitors in the range of 50 to 100pF with 22kW resistors in series on my YF-150 capacitance meter; it was unable to detect the significant series resistance. Presumably, inside the capacitor, the bonds or connections between the lead-in wires and the foils have become oxidised or corroded. The implications of this sort of failure are interesting. If a capacitor with this fault were used instead in a tuned circuit in an RF amplifier, it would not throw the centre frequency off to any significance. Still, it would certainly lower the circuit Q, lowering the gain and increasing the bandwidth. Since, after alignment, this radio is now working properly and is sensitive, I have not removed any of the other polystyrene capacitors for testing. The permeability tuning mechanisms of vintage car radios (#4 in Fig.8) are fascinating. They have continuous tuning by the control knob and preset pushbutton tuning, which acts as mechanical memory for preferred stations. When a button is pushed, a sliding arm disengages a clutch mechanism to mechanically isolate the tuning knob. With time, these rubber clutches have a habit of slipping, even with an otherwise well-lubricated mechanism. The rubber ages and hardens, its surface becomes glazed and the metal disc it runs against can become quite polished. Disassembling it and replacing the rubber disc requires pressing off a gear from the assembly’s shaft, which is better avoided. Cleaning the rubber disc with isopropyl alcohol (IPA) helps but often won’t solve the problem. I developed a method to fix these clutches using some very thin cardboard, similar to thin transformer card with an adhesive on one side. A washer is made the same size as the rubber disc, and the central hole is opened to the disc perimeter. The clutch is opened manually or by pushing a button, and the disc is inserted with the adhesive facing the metal disc surface, and it sticks to that. The rubber face then runs on the card face rather than the shiny metal surface, increasing the friction and preventing slipping. As an aside, my view is that the continuously variable tuning knob is the safest method to use a radio while driving a car. The driver could keep their eyes on the road while turning a knob, and stop on the station they liked the sound of. Other radio tuning methods could require the driver to take their eyes off the road. Circuit diagram The circuit diagram (Fig.10) and PCB layout (Fig.12) are reproduced here. This diagram, the manual for this radio and other relevant documentation is available from Kevin Chant’s website at siliconchip.au/link/abek The transistors were drawn in a way typical of some early 1960s vintage Australian transistor manufacturing Bardeen, Brattain and Shockley invented the point-contact transistor at Bell Labs in December 1947 and announced it to the world in 1948. Shockley’s junction transistor was also announced that year. Within a decade, four companies came to invest in Australian transistor manufacturing: AWA, STC, Philips and Ducon. All came to manufacture germanium-alloy junction transistors in Australia in the late 1950s to early 1960s. But what about silicon transistors, specifically, the AX1130 in the 1966 Astor radio? I looked in my parts inventory for similar transistors and came up with the devices shown in the accompanying photo. These transistors, all with the A prefix, were manufactured by Fairchild’s Australian division. They are relatively rare now, unlike most transistor types. If you search for them on eBay trying to find a spare part, you do not get any hits, as these transistors are ‘unique Australiana’. In June 1964, Radio Television and Hobbies magazine carried the following announcement: “A new Australian company to produce heat resisting silicon transistors has been formed in Melbourne. An offshoot of the Fairchild Camera and Instrument Corporation of New York, the Australian company will be known as Fairchild Australia Pty Ltd”. siliconchip.com.au In 1966, the company opened its laboratory facilities (see the EA article on page 102). The factory closed in 1973, and the AY/AX series of transistors unique to Fairchild in Australia became obsolete. For more on the history of transistor manufacturing in Australia, see this fascinaring website: http://siliconchip. au/link/abel A short list of some Australian-made transistors from Fairchild Semiconductors. Australia's electronics magazine July 2022  99 Fig.12 radios. One interesting thing is that the audio driver transformer does not have a primary winding. Due to the Darlington output devices made from the combination of the AX-1130 and AT-1138 transistors, the output stage has a fairly high impedance. Therefore, the driver transistor can simply capacitively couple into one side of the driver ‘transformer’, which is essentially a centre-tapped choke, and acts like an auto-transformer. Upper transistor #144 gets its drive directly from the previous stage (via an AC-coupling capacitor) while lower transistor #144 gets its phase-inverted drive from the other end of the centre-­ tapped autotransformer. The centre tap is held at a mid-rail voltage point due to the action of Vbe multiplier transistor #143. I measured the properties of this transformer, as well as the output transformer, in case others need to wind replacements for faulty units. The driver transformer is bifilar wound on a 7.5 x 7.5mm cross-section core and each winding measured 195W and 2.3H. The output transformer is designed for a 15W speaker and it is wound using 0.5mm diameter enamelled copper wire on a 15.4 x 15.4mm cross-section core. Its two primary windings measured 1W & 66.5mH with the single secondary measuring 2W & 190mH. The windings ratio is 1.7:1. Performance This radio is a good performer, sensitive in the RF circuitry due to a tuned RF stage, one mixer stage, separate local oscillator injection and two IF stages. On the audio side, it’s a good performer with a push-pull class-AB output stage, with plenty of audio output power for use in a car. The audio amp in the Astor radio is pretty good. The use of a 15W speaker is unusual in latter days for a car radio; most became 4W. But of course, when you have an output matching transformer, it is easy to use higher-­ impedance speakers, if more costly. Astor don’t mention the maximum audio output power in their manual. With a 12V supply, you end up with about 10-11V swing before peak clipping in the collector load (half of the output transformer primary) because of the collector-emitter saturation voltage of the Darlington pair, and their emitter resistors. siliconchip.com.au Fig.13: the internal underside of the chassis shows just a few discrete components attached via point-to-point wiring. So the power delivered to the 15W speaker just on clipping can be calculated as about 6-7W, allowing for transformer losses. It is more like 8W, given that the radio’s supply voltage creeps closer to 14V while driving, as the battery is charging. That is plenty of audio power, even in a noisy car. It is physically very well made, and rivals any MW-band car radio made in any other country. I am glad I could see the potential in this radio, to become something beautiful again and took the time to restore it. It would make a fine addition to a vintage car of the same period. This radio is a reminder of how advanced Australian electronics and transistor manufacturing was in the Australia's electronics magazine mid-1960s. This saddens me, as we were once able to make our own transistors and ICs. The worst thing about this is the strategic significance of this, with the inability to build our own electronics, and the impact of disrupted supply chains for electronics, medicines and other vital products that is now quite apparent. This has exposed how dependent we have become on overseas-­made products. When high-tech manufacturing infrastructure and ability is lost, it takes decades to rebuild it. The human skill-base and required engineering experience get lost along with it. The problem goes much deeper than derelict factories and unemployment. SC July 2022  101 Fairchild now making TO-92 plastic transistors in Australia A new manufacturing line for moulded plastic transistors in the Jedec TO-92 package is now in full production at Fairchild Australia’s plant in Croydon, Victoria. Most of the production equipment used in the new line has been made by Australian manufacturers. The new line has been turning out commercial quantities of TO-92 moulded plastic devices for some weeks now. Most of the output has been going in large orders to commercial customer, but the products are being released to the general market this month. Approximately 10 different types of product are currently being made in the TO-92 package, including both bipolar transistors and JFETs. In most cases the new devices are electrically identical with existing devices marketed in the familiar TO-5 and TO-18 metal can or epoxy “glob-top” packages. As far as the end user is concerned, the main difference is that they come in a characteristic moulded silicone package, which is halfround in cross section and roughly the same size as a TO-18 device. From the manufacturing viewpoint, there are more important differences between 102 Silicon Chip TO-92 devices and metal can or epoxy types. For economical plastic moulding, devices must be grouped together in batches rather than handled separately; this dictates a lead-frame approach to device fabrication, where the devices progress through most of the manufacturing steps in multiple strips or frames. The frames are formed by the metal lead header assembly of the individual devices, held together by metal links which are punched away only at the end of the production process. A big advantage of the lead-frame approach is that it cuts down on the handling time required for most manufacturing steps. Operations like die-attachment and wire bonding can thus be made more speedy and efficient, with the operator no longer having to load and unload individual devices. Lead frames also lend themselves far more readily to process automation, both because the Australia's electronics magazine This is a cleaned-up reproducion of an article from the February 1973 issue of Electronics Australia. It is relevant to two articles in this issue: 1. Dr Hugo Holden’s Vintage Radio column on the Astor Diamond Dot. 2. Dr David Maddison’s article on IC Fabrication. by JAMIESON ROWE headers are uniformly spaced and orientated, and because the frames are readily indexed and incremented. In their new line Fairchild are using 50-device lead frames, measuring about 285mm in length. The frames are punched and formed overseas from a special copper alloy, selected for its low thermal resistance, and are gold-plated locally before use. The use of a relatively long frame permits production rates of typically 600 devices per hour for die attachment, 400 per hour for wire bonding, more than 5,000 per hour for plastic moulding and 12,000 per hour for final cropping apart. Fairchild Australia’s production engineer Frank Fimmel designed the new TO-92 line and supervised all aspects of its setting-up. When I talked to him recently at the Croydon plant, Frank was justifiably proud of the project, for two main reasons. One was that he had been able to set up the line in siliconchip.com.au Picture at top of opposite page shows the main bonding and assembly lines at Fairchild’s plant in Croydon. The lines which have been converted for TO-92 are at extreme right. At left on this page is a close-up of a wire bonding station, showing a leadframe under way. Above is the cropping and shearing press, which divides the frames up into individual devices at the rate of 12,000 per hour. Below is the moulding press, with frame preheater at left and dielectric heater for the moulding pellets at right. a considerably shorter time than similar overseas lines, and for a cost only a third as great. The other reason was that he had been able to obtain most of the new equipment from Australian manufacturers. The plastic moulding press was manufactured by Archer Hydraulics, of Stanmore in Sydney; the impregnation equipment by Dynavac, and the de-flashing equipment by O. Granowski, both of Melbourne; and the cropping and separation press by John Heine, of Sydney. All of these manufacturers had made similar equipment before, although this was the first time that each had made equipment for transistor manufacture. Early production steps such as die attachment and wire bonding are much the same for TO-92 devices as for metal can types. siliconchip.com.au except that the operations are carried out on the lead frames. After wire bonding the frames are thoroughly cleaned by washing in de-ionised water, which prepares them for plastic moulding. Fairchild’s moulding press handles two lead frames at once – i.e., it moulds 100 devices at a time. The frames are supported in carriers, and are pre-heated in the carriers Australia's electronics magazine prior to loading in the press. Pellets of the special silicone moulding compound used in the press are preconditioned in a 1kW dielectric heater, which reduces them to the consistency of soft putty. They are then inserted into the injection system of the press, after the moulding dies are closed around the transistor lead frames. The moulding itself then takes place after July 2022  103 Impregnation with silicone resin, for hermetic sealing. the operator activates dual interlock buttons, which are designed to prevent accidents. Following moulding the frames are baked in an oven at 200 degrees C to harden the encapsulation, and de-flashed by blasting with a stream of crushed walnut shell particles. After this they undergo a pressure impregnation process, in which a special silicone resin is forced into the moulded plastic under high pressure to ensure hermeticity. The special silicone resin used for the impegnation is imported and very expensive – $90 per gallon. After impregnation the frames are baked a second time to cure the resin and complete the hardening of the encapsulation. Final step in the actual manufacture of the devices is cropping, performed by a very accurate punch and die set in a mechanical press. Here the metal links which joined the leads of the devices together in the lead frame are sheared away, separating them into individual units at a rate of 200 per minute. As with other devices, the TO-92 transistors then progress to the testing and sorting section, where automated testing equipment under computer control sorts them into the various device categories corresponding to programmed parameter range combinations. They then pass through Quality Assurance to final marking and packing ready for despatch. In getting their TO-92 line going, Fairchild have had to master the two main problems associated with plastic moulded semiconductor devices. The first of these is protection of the actual device chip and its wire leads, both during the moulding process and the subsequent curing. There is a tendency for the wire leads especially to be “washed away” by the flow of plastic during the moulding, and also for the leads to be broken by strain produced by plastic shrinkage during the curing. Part of Fairchild’s solution to the washaway problem is the detailed design of their lead frame, which has the chip sited on top of a small horizontal bracket formed at the top of the collector lead. Besides supporting the 104 Silicon Chip At top right is the deflashing station, where excess plastic swarf is removed by blasting with walnut shell powder. At right is a die attachment station. chip and helping to lock the assembly inside the moulded package, the bracket also tends to deflect the flow of plastic away from the chip and its leads. But Frank Fimmel tells me that the shape of the lead frame is only part of the story. The exact design of the moulding die is quite critical, together with the temperature and pressure used. And the composition of the moulding compound is also critical, not only with regards to wash-away but also to minimise shrinkage strain. It is not surprising that the silicone moulding compound used is actually the most expensive part of a TO-92 device, in terms of actual material cost. The second problem which has traditionally plagued moulded plastic devices is the difficulty in obtaining true hermeticity. Fairchild are confident that they have licked the problem with their pressure impregnation process, and extensive testing by their Q & A department justifies their confidence. Naturally most of the answer must lie in the impregnation resin, and they aren’t giving away any secrets; but it must be a rather special brew at $90 per gallon! Apart from involving mastery of the two traditional problems associated with moulded plastic devices, Fairchild believe their TO-92 devices are exceptionally rugged both in the mechanical and electrical senses. Some moulded packages have been notorious for either losing leads completely, or allowing sufficient lead movement to cause Australia's electronics magazine faulty operation. To obviate this problem Fairchild have designed their lead frame so that each of the three leads for a device is doubly locked into the final moulding, and prevented from being withdrawn and from moving. The special copper alloy used for the leads and the carefully tailored thermal coefficients of the materials in the overall package make Fairchild’s TO-92 package particularly rugged in the electrical sense compared with a comparable size device such as the TO-18 globtop. Normal dissipation tests have shown that short-term overloads of much higher magnitude can be carried without damage. Some devices have operated at 2.5 watts for more than 3 hours before finally succumbing! Fairchild are predicting that globtop devices will be progressively phased out by TO-92 products within the next 2-4 years, and that the lower production costs of TO-92 compared with metal can products will result in eventual domination of the low power discrete market. In short, the future of TO-92 seems very bright. Although they have announced general plans to expand the range of TO-92 products as the market develops, Fairchild aren’t commenting on other possibilities for plastic moulded devices. No doubt the current deliberations of the Tariff Board will influence future plans, but my guess is that plastic moulded ICs might be next. Reproduced from Electronics Australia, February 1973. siliconchip.com.au 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 Substitute transformer for 500W Amplifier I have a question regarding the toroidal transformer used in the 500W Amplifier (April-June 2022; siliconchip.au/Series/380). The recommended transformer is RS Components Cat 1234050 ($420) with two 110V primary windings, two 55V secondary windings and an 800VA rating. element14 has a toroidal 2 × 55V transformer rated at 625VA for $151. Is that a possible substitute for the specified transformer without losing much performance? (J. C., via email) ● The overall continuous output power from the Amplifier would be lower compared to the 800VA transformer. You could use the VTX-146625-155 625VA toroidal transformer (element14 Cat 1675103) instead of the specified transformer. However, under normal listening conditions and program material, it would be difficult to notice the difference without a side-by-side comparison between two amplifiers with each transformer. You might prefer the VTX-146-625255 (element14 Cat 2817718) with two 115V primary windings (like the one we specified from RS components) that can be used in series for 230V mains. It’s cheaper again by $30. Note that the wiring colours for the primary and secondary windings on the transformer appear to be the same as the transformer we used. Take care when doing the wiring to ensure you have the correct windings connected. Where to start with getting into electronics? I am considering a career change and thought about getting into electronics. I have not had much to do with electronics, just doing a bit of wiring. Can you recommend books or courses to get me started? (J. W., via email) ● There are many different approaches to learning electronics. You have obviously seen our magazine. While some of the content will be over your head at this stage, you will still pick up a lot by reading it, especially sections like Circuit Notebook and the simpler project articles. We also have some articles on fundamental electronics like the following: • All About Capacitors – March 2021 (siliconchip.au/Article/14786) • The History of Op Amps – August 2021 (siliconchip.au/Article/14987) • LTspice tutorials – June, August & September 2017 (siliconchip.au/ Series/317) • How Switchmode Controllers Work – February 2011 (siliconchip. au/Article/910) • Low-cost Electronic Modules – October 2016 to the present (siliconchip.au/Series/306) Other things you can try include: 1. Buy an Arduino kit that includes an Arduino board and other components. There are a vast number of Arduino projects on internet sites that you can try. 2. Check out Rod Elliott’s website at https://sound-au.com – while he specialises in audio, he also has free articles on many general electronics topics, such as the following: • https://sound-au.com/articles/ 555-timer.htm • https://sound-au.com/articles/ comparators.htm • https://sound-au.com/articles/ fet-applications.htm • https://sound-au.com/articles/ variac.htm • https://sound-au.com/articles/ relays.htm 3. Download and read device data sheets. These often contain example circuits. You can buy the devices, build the circuits and try them out. For example: • www.ti.com/lit/gpn/lm317 • www.ti.com/lit/ds/symlink/ lm3914.pdf • www.ti.com/lit/ds/symlink/ lm555.pdf Running a 60Hz clock from 50Hz mains I do volunteer repairs and check electronic/electrical items donated to an op shop. Someone donated a very valuable kinetic sculpture clock but continued on page 108 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 July 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. 07/22 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) Si473x FM/AM/SW Digital Radio (Jul21), 110dB RF Attenuator (Jul22) 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) 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 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 20A DC Motor Speed Controller (Jul21) Fan Controller & Loudspeaker Protector (Feb22) Secure Remote Mains Switch Receiver (Jul22) PIC16F1459-I/SO Multimeter Calibrator (Jul22) PIC16F15214-I/SN Improved SMD Test Tweezers (Apr22) PIC16F1705-I/P Flexible Digital Lighting Controller Slave (Oct20) Digital Lighting Controller Translator (Dec21) PIC16LF15323-I/SL Secure Remote Mains Switch Transmitter (Jul22) ATSAML10E16A-AUT PIC16F18877-I/P PIC16F88-I/P High-Current Battery Balancer (Mar21) USB Cable Tester (Nov21) UHF Repeater (May19), Six Input Audio Selector (Sep19) Battery Charge Controller (Dec19 / Jun22) 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) GPS-Synched Frequency Reference (Nov18), Air Quality Monitor (Feb20) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) $20 MICROS ATmega644PA-AU PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT PIC32MX795F512H-80I/PT AM-FM DDS Signal Generator (May22) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) Touchscreen Audio Recorder (Jun14) dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) $25 MICROS $30 MICROS PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC VGA PICOMITE KIT (CAT SC6417) (JUL 22) MULTIMETER CALIBRATOR KIT (CAT SC6406) (JUL 22) 110dB RF ATTENUATOR SHORT-FORM KIT (CAT SC6420) (JUL 22) Complete kit with everything needed to assemble the board, you just require a few external parts such as a power supply, keyboard and monitor $35.00 Complete kit with everything needed to assemble the board Includes the PCB, programmed micro, OLED and all other on-board parts BUCK-BOOST LED DRIVER KIT (CAT SC6292) (JUN 22) SPECTRAL SOUND MIDI SYNTH KIT (CAT SC6261) (JUN 22) SLOT MACHINE (MAY 22) 500W AMPLIFIER HARD-TO-GET PARTS (CAT SC6019) (APR 22) 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 everything needed to assemble the board Complete kit including all programmed PICs (no case or power supply) - 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) $45.00 $75.00 $80.00 $200.00 $45.00 $5.00 $10.00 All the parts marked with a red dot in the parts list, 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 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 siliconchip.com.au/Shop/ 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 SMD TRAINER COMPLETE KIT (CAT SC5260) (DEC 21) USB CABLE TESTER KIT (CAT SC5966) (NOV 21) MICROMITE LCD BACKPACK V3 KIT (CAT SC5082) (AUG 19) Includes PCB & all on-board components, except for a TQFP-64 footprint device Short form kit with everything except case and AA cells $20.00 $110.00 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) $12.50 - DS3231 real-time clock SOIC-16 IC (Cat SC5103) $7.50 - 23LC1024 1MB RAM (SOIC-8) (Cat SC5104) $6.00 - 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) $2.00 VARIOUS MODULES & PARTS - 70W LED panel (cool white, SC6307 | warm white, SC6308) - 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-16 IC (Pico BackPack, Mar22) - DS3231MZ real-time clock SOIC-8 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) $19.50 $10.00 $3.00 $7.50 $10.00 $1.00 $10.00 $35.00 $15.00 $3.00 $25.00 *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 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 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 DATE 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 NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 PCB CODE Price 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 16109201 $12.50 16109202 $12.50 16110201 $5.00 16110204 $2.50 11111201 $7.50 11111202 $2.50 16110205 $5.00 CSE200902A $10.00 01109201 $5.00 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT 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) AM-FM DDS SIGNAL GENERATOR SLOT MACHINE HIGH-POWER BUCK-BOOST LED DRIVER ARDUINO PROGRAMMABLE LOAD SPECTRAL SOUND MIDI SYNTHESISER REV. UNIVERSAL BATTERY CHARGE CONTROLLER DATE 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 MAY22 MAY22 JUN22 JUN22 JUN22 JUN22 PCB CODE 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 CSE211002 08105221 16103221 04105221 01106221 04107192 Price $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 $7.50 $5.00 $5.00 $5.00 $7.50 $7.50 VGA PICOMITE SECURE REMOTE MAINS SWITCH RECEIVER ↳ TRANSMITTER (1.0MM THICKNESS) MULTIMETER CALIBRATOR 110dB RF ATTENUATOR JUL22 JUL22 JUL22 JUL22 JUL22 07107221 10109211 10109212 04107221 CSE211003 $5.00 $7.50 $2.50 $5.00 $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 unfortunately, it is designed for 60Hz mains, so it runs very slowly on 50Hz. Changing the voltage from 230V AC to 115V AC is not a problem. Would it be possible to make a low-power 230V 50Hz to 115V 60Hz converter for this type of thing? The company who made the clock will service it and put in a 50Hz motor (but still 115V AC) or change a gear, but they want US$1500, including postage! (D. M., Toorak, Vic) ● We suspect it will run fine from a 110V 60Hz pure sinewave inverter. They’re about $50 from AliExpress or eBay. Given the clock’s low power demands, you should be able to power the inverter from a 12V DC plugpack. Its frequency accuracy may not be as good as the mains, but the inverter likely contains a quartz crystal, so it should be pretty good. The clock may need adjustment once every few months. We also published a 50/60Hz Turntable Driver which will work (May 2016; siliconchip.au/Article/9915). Different servo motors with same model code I built two Model Railway Semaphores (April 2022; siliconchip.au/ Article/15273), but neither stops at 45° regardless of the positions of VR1 or VR2. They just keep on rotating either forward or backward, depending on the switch position. It seems like the chip is not counting the pulses. I used DF9GMS servos from Core Electronics (360° micro servo). What’s going on? (D. Y., Wyelangta, Vic) ● Looking into this, we found two different servos on the Core Electronics website with the same model number! The one that we linked to in the Semaphore article is the correct 180° type that Les used: siliconchip.au/link/abf4 A different item comes up if you search for “DF9GMS” on the Core Electronics website (and the correct one is not listed): siliconchip.au/link/abf5 That one clearly states it is a 360° type that is unsuitable for this project. We think its full model number should be DF9GMS-360, as distinct from the DF9GMS that the design needs. Please be sure to use the 180° servo via the link we provided in the article. Dual Hybrid Supply has flashing “V” I built the Dual Hybrid Supply (February & March 2022; siliconchip. au/Series/377) and, after reading the Notes & Errata in the May issue, I put the control board jumper in the correct position and it started working. But I still have one problem: on the display set screen, the “V” is flashing along with the decimal digits in the righthand section. Do you have a solution? (J. A., Townsville, Qld) ● It seems that you have not set the transformer voltage high enough in the setup menu. The V flashes when the output voltage is too close to the calculated maximum output voltage. Go into the setup menu and check the voltage you have set; try setting the transformer voltage higher. That should stop the flashing. The video you sent showing that also indicated a residual measured current on each output. Have you gone through the calibration procedure? If not, do that after adjusting the transformer voltage. A larger bath for the Ultrasonic Cleaner I am building the High Power Ultrasonic Cleaner (September & October 2020; siliconchip.au/Series/350) and have a 1/2 GN stainless steel Gastronorm, 150mm high. This has an 8L capacity which is twice the volume recommended in the article. How much of an impact would this larger size have on its performance? I purchased this because I might want to clean something large. I could probably use the 150mm-high 1/3 GN Gastronorm instead, but it was out of stock when I bought the larger one. Thanks for your advice, and keep up the good work with the magazine. (G. G., Knoxfield, Vic) ● Seeing you have the 8L tank, you could try using it with the Ultrasonic Cleaner, clamping the transducer to a flat portion outside of the tank. Most of the time, you could use less fluid than the full tank capacity for better penetration of the ultrasonic waves. Generally, with a larger tank, more The kinetic sculpture clock. 108 Silicon Chip Australia's electronics magazine siliconchip.com.au ultrasonic energy is required to produce a satisfactory cleaning effect. Our Ultrasonic Cleaner cannot provide an increased output power above the original design limit. Ultrasonic Cleaner not reaching full power I built the High-Power Ultrasonic Cleaner (September & October 2020; siliconchip.au/Series/350) and am having some trouble making it work. First, I measured just over 2V at TP1 with the transformer wound as per the article. I added about 20 turns with the rest of the enamelled wire I had left, and was able to get up to 3.1V. After completely rewinding the transformer with 40 more turns on the secondary than specified, I am now able to get 4.2V at TP1 for a resonance frequency of about 37.2kHz. The piezo is glued to a stainless steel tray of similar dimensions as yours using epoxy resin. Now, when I set the power to 100% and start the device, it goes slowly down to 10% (or between 10 and 25%) before stabilising (LED ON lit). So it looks like it does not find the resonance frequency. Once I run the diagnosis and find the maximum voltage at TP1, what should I do? How does the cleaner memorise this value? Do I need to validate the result somehow? I can adjust the low/ high frequency bounds so that the pot is set right in the middle at resonance. I measure around 130V AC at the piezo connector. When I find the resonance during the diagnostic procedure, I can hear the water making some noise. I hope you can give me some direction. (O. A., Singapore) ● The resonance point is not precisely stored as it can vary over a range of frequencies. The general resonant point region is stored, and the frequency is varied at start-up to find the resonance point (or off-resonance for lower power). When you find the frequency range in diagnostic mode and get the maximum peak at 4.6V, try to set it to the next lower frequency and perform the calibration. If that is not effective, try again with the next higher frequency from the peak value. If that’s unsuccessful, try rerunning the diagnostics and sweeping the frequencies to find the maximum current siliconchip.com.au by measuring the voltage at TP1. If this voltage goes over the 4.8V overload point, reduce the number of secondary turns on the transformer. The turns need to be so that current overload isn’t reached at resonance. This is the only way to find the transducer resonance frequency correctly. The cleaner should then run correctly, and you can then achieve the ultimate power by increasing or reducing the transformer’s secondary windings by only a few turns. Switching between battery & mains supply Have you published a circuit that can switch between a battery power source and a mains-based power supply quickly without interruption? I had in mind a 12V DC battery supply that might go dead, so it would need a mains supply to come online immediately. (F. C., Maroubra, NSW) ● We haven’t published exactly what you are after, although the DIY UPS design in the May-July 2018 issues (siliconchip.au/Series/323) is somewhat similar. Also see our article on battery backup power supplies in the January 2020 issue (“What do to before the lights go out...”, siliconchip.au/ Article/12215). We are not sure how much current you require. We have published several battery protectors that disconnect a battery from a load when the battery discharges. These include including the Dual Battery Lifesaver from the December 2020 issue (siliconchip. au/Article/14673); and the LifeSaver from September 2013 (siliconchip.au/ Article/4360). If the battery is switched off, a mains supply could be switched in to take over. These projects can handle a load of about 10A. The mains supply could be switched in using a part of the circuit in the Protector to drive a relay or relay switcher like the DC Relay Switch (December 2006; siliconchip. au/Article/2813). You may need to add a transistor driven by the Protector circuit to power the relay coil, or use a solid-state relay that does not require much drive current (Jaycar SY4093). Another (probably simpler) way of doing this is to permanently connect a mains charger to the battery to prevent it from discharging when used. That way, it shouldn’t go dead. Australia's electronics magazine Remote control for electric fence I am wondering about the practicality of signalling via the hot wire of an electric fence to toggle it on and off as required. Something akin to the switching technology power companies use to switch on/off off-peak power etc. I am often a kilometre or so from the electric fence generator, and travelling back and forth is often impractical. I still have an electric fence tester built back in the ETI days, and it works well. I have only replaced the battery twice in at least 20 years, so no complaints on that! The ideal device I am looking for would encompass a tester and signal sender in a handheld unit, with a receiver at the fence energiser to switch the mains power on/off. This way, I can test and fix a fence remotely without receiving the usual jolt. Currently, it is a two-person job via a mobile phone, and often the person and the network may not be available simultaneously. (C. G., Yakamia, WA) ● You could switch an electric fence on and off remotely via a 4G mobile network without needing a helper using our 4G Remote Monitoring Station (February 2020; siliconchip. au/Article/12335) together with the Opto-Isolated Mains Relay (October 2018; siliconchip.au/Article/11267). That would let you switch the electric fence on and off with SMSes, with acknowledgement messages being returned. It would also allow you to query it about whether the fence is on at any particular time. The last electric fence tester project published in Silicon Chip was in May 1999 (siliconchip.au/Article/4559). It includes three designs, each of which simply flashes a lamp to indicate that the fence is working. The second version also indicates the voltage. Alternative Mosfets for DC Speed Controller I am trying to build the High Power DC Motor Speed Control (January & February 2017; siliconchip.au/ Series/309). The IPP023N10N5AKSA1 Mosfets were out of stock with a delivery date in the not too distant future. However, after I ordered them, that date came and went, and now the July 2022  109 supplier says they “will advise” a delivery date. I suspect that means I will not be getting them any time soon, if ever. I did a bit of searching and found that the FDP2D3N10C is available. I think it is a reasonable substitute with the same package and voltage rating, similar on-resistance, similar threshold voltage, similar switching times, slightly lower gate charge, higher current rating and sufficient power rating (214W vs 375W in the original). Can I make that substitution? (E. Z., Turramurra, NSW) ● Yes, those Mosfets would be fine in the DC Speed Controller. The power rating is not so critical as we are switching them on and off rather than using them in linear mode, where power dissipation would be high. So the 214W rating is more than sufficient. Tweaking Automotive Sensor Modifier range I have just finished building the Automotive Sensor Modifier project (December 2016; siliconchip.com.au/ Article/10451), but I can’t figure out the value of R1 to use. My input signal will be from a MAP (manifold absolute pressure) sensor that delivers 1.13V with zero boost and 2.7V up to 20PSI. I only need to alter about 50 sites. Please help. (G. C., Beaudesert, Qld) ● If you want to be able to adjust over the entire range (eg, change an input of 1.13V to an output of up to 2.7V), that’s a maximum 1.57V change. When R1 is 15kW, you can adjust by 1.3V (not enough), while when it is 24kW, you can adjust up to 2V (too much, although that will only mean there are wider adjustment steps than desired). A resistance between 15kW and 24kW will provide a better resolution while still providing sufficient range. With R1 at 18kW, that would give a 1.53V range, which should be adequate, while 20kW would give a 1.68V range. leakage measurements. There needs to be an adjustment to three-phase readings because the three phases are 120° out of phase. Without accounting for that, the leakage reading will be higher. Additionally, if any of the line phase currents differ, there will be a resulting ‘leakage’ reading simply due to the imbalance of the phases. For a three-phase Y connection, assuming identical voltages in each phase, pure sinewaves and 120° phase differences, the leakage reading would need to be divided by √3 (~1.732) for the equivalent single-phase leakage. Testing three-phase gear for Earth leakage Lower value coil for Multi-Spark CDI? Having successfully built and tested your Appliance Earth Leakage Tester project (May 2015 issue; siliconchip. au/Article/8553) with single-phase devices, I tried it with three-phase. I did this simply by feeding the three live conductors and the Neutral conductor through the current transformer. It reads significantly higher than a comparable calibrated meter that I usually use when measuring a threephase drill press. Are three-phase Earth leakage measurement with this circuit feasible? If so, why did I get a higher-than-normal reading? (B. T., New Zealand) ● The Appliance Earth Leakage Tester was only intended for single-phase Does the coil for the Multi-Spark Capacitor Discharge Ignition system project (December 2014 & January 2015; siliconchip.com.au/Series/279) need to be a 4W type? Those coils are mostly for single-cylinder applications such as motorcycles, while my application is a V8 engine. Would a 1.5-2W coil work? (P. H., St Pierre sur Orthe, France) ● The main thing is to limit maximum current. The dwell needs to be limited to prevent a high saturation current (highest when the coil is charged). The lower the coil impedance, generally, the shorter the maximum dwell. A 1.5-2W coil will be OK if this is set correctly. continued on page 112 SMD Test Build it yourself Tweezers Improved ● Resistance measurement: 10W to 1MW ● Capacitance measurements: ~10pF to 150μF ● Diode measurements: polarity & forward voltage, up to about 3V ● Compact OLED display readout with variable orientation ● Runs from a single lithium coin cell, ~five years of standby life ● Can measure components in-circuit under some circumstances 110 Silicon Chip Complete Kit for $35 Includes everything pictured (plus tips), except the lithium button cell. October 2021 issue siliconchip.com.au/Article/15057 SC5934: $35 + postage siliconchip.com.au/Shop/20/5934 Australia's electronics magazine siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE FOR SALE 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 LEDsales SILICON CHIP LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au 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 KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com 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 LEDs and accessories for the DIY enthusiast VISIT THE NEW TRONIXLABS parts clearance store for real savings on new parts at clearance prices, with flat rate express delivery Australia-wide – go to https://tronixlabs.com Email for a postage quote, quote the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au Issues Getting Dog-Eared? Keep your copies safe with these handy binders Order online from www.siliconchip.com.au/Shop/4 see website for overseas prices or call (02) 9939 3295. REAL VALUE A T $19.50* PLUS P&P 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 July 2022  111 Advertising Index Altronics.................................27-30 Control Devices............................. 9 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 element14..................................... 7 Emona Instruments.................. IBC Hare & Forbes............................. 13 Jaycar.........................IFC,11,39-40, ..................................... 50-51,59-61 Keith Rippon Kit Assembly....... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.................. 5 Mouser Electronics..................OBC Ocean Controls........................... 10 SC Pico BackPack.................... 105 SC SMD Test Tweezers............ 110 SC USB Cable Tester.................. 79 Silicon Chip Binders................ 111 Silicon Chip Shop............ 106-107 Silicon Chip Subscriptions........ 93 The Loudspeaker Kit.com.......... 91 Tronixlabs.................................. 111 Errata and Next Issue Wagner Electronics..................... 12 112 Where to get inductors for Battery Zapper I want to build the Lead-Acid Battery Zapper & Desulphator Mk.3 (July 2009; siliconchip.au/Article/1500), but both kits have been discontinued, and the specified 220μH and 1mH aircored inductors are no longer available from Jaycar. Do you know where I can get them? ● You have a few options. Air-cored inductors are often used for crossovers, and ‘crossover inductors’ are available from other sources. The Jaycar inductors used 20AWG wire (0.8mm diameter). We found an Australian website called Speakerbug with 220μH and 1mH air-cored inductors at reasonable prices, wound with either 18AWG or 21AWG wire. 18AWG would be preferable, but either should work; see: siliconchip. au/link/abex Another option would be to wind your own. There are online calculators that tell you how many turns of what diameter wire on what sized former are needed to make a specific inductance value. If you have an LC meter, you can also keep winding until you reach the desired inductance value. You might even find that reels of enamelled copper wire have close to the correct inductance by just using the whole reel or unwinding a part of it. We used that approach in the Easyto-build Bookshelf Speaker System (January-March 2020; siliconchip.au/ Series/341), which used reels of ECW as 390μH and 900μH inductors. 900μH is probably close enough to 1mH for the Battery Zapper, and for the 220μH inductor, you could use the same reels of ECW that measured 390μH for the Bookshelf Speakers but MOS Air Quality Sensors, June 2022: in the Useful Links box, the secondlast link should be https://fs.keyestudio.com/KS0457 Railway Semaphore Signal, April 2022: be aware that some vendors are selling DF9GMS-360 360° servos under the same model code as the DF9GMS 180° servos specified for this project. The 360° servo motors will not work. You need to use a 180° servo. High Power DC Motor Speed Control, January & February 2017: the IPP023N10N5AKSA1 Mosfets specified are currently unobtainable. Constructors can substitute the FDP2D3N10C, which is available at the time of writing. Next Issue: the August 2022 issue is due on sale in newsagents by Thursday, July 28th. Expect postal delivery of subscription copies in Australia between July 27th and August 12th. Silicon Chip Australia's electronics magazine unwind some turns (probably about 1/3 of them) to get a value closer to 220μH. MC34063 regulator chips failing I have just built the Pocket TENS Unit (January 2006; siliconchip.au/ Article/2532), and I have had problems with the repeated failure of the MC34063 chip. When setting the inverter output voltage, the IC fails. I can get the output close to 60V before that happens. I got the MC34063s from eBay. As for the toroidal transformer, I could not find the original Neosid core, so I used another of unknown origin but with the same physical dimensions. Do you have any ideas? (M. A., Wurtulla, Qld) ● The MC34063 is generally very reliable, but it is a ubiquitous chip, and we suspect there are plenty of clones on the market, some of which might be dodgy. We suggest trying an MC34063 from Jaycar (Cat ZK8837) or Altronics (Cat Z2750). For the ferrite core, use Jaycar Cat LO1234. Those combinations seem to be reliable. High voltage track clearances I designed a new PCB for the Multi Spark CDI System (September 1997; siliconchip.au/Article/4837) with a full ground plane and am having some problems. Would a ground plane cause any problems? I set the track clearance at 0.305mm. Do you think that’s enough? (J. M., New Haven, USA) ● For tracks with up to 300V between them, more clearance would be preferable. Arc-over would be likely at 0.305mm, especially without a solder mask layer. The IPC-2221 standards require 1.25mm or more (see www.smps.us/pcbtracespacing.html). Clearance may not be your only problem, though, and maybe photos of the PCB could help us see where problems might lie. Note that we published a CDI design much more recently (December 2014 & January 2015; siliconchip. au/Series/279), and we can supply both the PCB and hard-to-get parts for that project. These are available from our website at: siliconchip.au/Shop/? article=8120 SC siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! Ex GST RIGOL DS-1000E Series RIGOL DS-1000Z/E - FREE OPTIONS RIGOL MSO-5000 Series 450MHz & 100MHz, 2 Ch 41GS/s Real Time Sampling 4USB Device, USB Host & PictBridge 450MHz to 100MHz, 4 Ch; 200MHz, 2CH 41GS/s Real Time Sampling 424Mpts Standard Memory Depth 470MHz to 350MHz, 2 Ch & 4Ch 48GS/s Real Time Sampling 4Up to 200Mpts Memory Depth FROM $ 429 FROM $ ex GST 649 FROM $ ex GST 1,569 ex GST Multimeters Function/Arbitrary Function Generators New Product! 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