Fullscreen HTML5Med Res (??MB)HTML4

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 may edit and has the right to reproduce in electronic form and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman”. Cleaning silver with electricity By harnessing the power of electrons, silver cleaning can be quick, easy and efficient. The most popular way to clean tarnished silver and silver-plated objects is using a paste containing ammonia and a mild abrasive. But it gradually removes the silver, which is particularly bad for silver-plated items. Another method uses acidified thiourea, which tends to leave a yellowish residue. Alternatively, the silver object can be placed in direct contact with an aluminium pot or a sheet of aluminium foil, and immersed in a hot solution of sodium bicarbonate, setting up an electrolytic cell. While this method works quite well, it is fairly slow and works best with small objects. This method can be sped up enormously and made much more efficient by the simple application of an electric current, as explained in the video at https://youtu.be/57iwtmT4LNQ Tarnish is silver sulphide, generated over time by hydrogen sulphide in the air, or perhaps from contact with egg yolks. The reaction is: 4Ag + 2H2S + O2 → 2Ag2S + 2H2O The reaction can be reversed by electrons, with a reduction potential of -0.69V. In a mildly alkaline solution, the sulphide remains ionised and soluble in water: Ag2S + 2e− → 2Ag + S2− The reduction of aluminium ions involves a potential of -1.66V: Al3+ + 3e− → Al This reaction is also reversible under certain conditions. When these metals are in contact with each other in a mildly alkaline solution, an electrolytic cell is set up. The difference in reduction potential facilitates oxidation of aluminium and liberation of electrons to silver sulphide, forcing its reduction to metallic silver. The sulphide ions travel to the 4 Silicon Chip aluminium, which is converted into aluminium sulphide. The reaction can be greatly sped up with the help of a 6V battery. As before, the metals are placed in a solution of hot sodium bicarbonate and table salt, but the aluminium foil and the silver are not in contact with each other. The silver is connected to the negative terminal, and the aluminium is connected to the positive. The battery facilitates the movement of electrons out of the aluminium and into the silver. The result is dramatic. Within just a few seconds, the blackened silver turns shiny. The beauty of this method is that the silver sulphide is converted back to metallic silver and redeposited on the item. Since silver ions are positively charged, they can’t go anywhere else, and there is no risk of damage to the silver. But, beware – if you get the polarity mixed up, your precious ancestral silver will be rapidly stripped! The practical procedure is very simple. Fill a non-metallic bucket or dish with very hot tap water. Add a tablespoon of salt and a tablespoon of sodium bicarbonate (baking soda) and stir to dissolve. Place a sheet of aluminium foil overhanging the side and connect it to the battery’s positive terminal. Then connect the silver item to the battery’s negative terminal and dunk it in the liquid – keep the connection point dry and above the liquid. Fizzing will start, and within seconds, the tarnish will disappear, and the silver will be restored. When you are satisfied with the result, remove the silver item and invert it so that the half that was outside the liquid is now immersed. Then attach the negative end of the battery to the top of the silver item above the liquid. The remaining part will be cleaned in seconds. Australia’s electronics magazine Remove the item and give it a gentle rubdown with a damp cloth. Rinse it thoroughly with tap water to make sure that there is no residual salt. That’s all there is to it. Silver cleaning need no longer be drudgery! Jim Goding, Princes Hill, Vic. Pong in a picture frame Congratulations to Dr Hugo Holden on his Silicon Chip article on Arcade Mini Pong (June 2021; siliconchip. com.au/Article/14884) and on a neat board design. It’s a very nice and compact layout – at first glance, I thought he had switched to SMD chips to make it that small. Come to think of it, one could do that to take this even further. It would enable a discrete Pong PCB somewhere around the size of a postcard. With Chinese manufacturers like JLCPCB offering very affordable SMD assembly in small lots, a batch of pocket-sized Pong boards would be quite feasible. Hugo Holden’s circuit analysis has been invaluable for me when I got started with my “framed Pong” project. It took me a while to get hold of an original Pong board, and I started my upscaler FPGA development before I had an actual board, based on his documentation. The detailed analysis also gave me the confidence to buy a non-working Pong board, since I had all the information needed to fix it. Thank you very much for sharing your knowledge! I wrote up my project at www. e-basteln.de/arcade/pong/pong/ Jürgen Müller, Hamburg, Germany. DAC chip has a fault in one channel I built the USB SuperCodec by Phil Prosser published in the August to October 2020 issues (siliconchip.com. au/Series/349), and while it generally worked, I found that the performance siliconchip.com.au of one channel was much worse than the other, with a much higher noise floor and a distortion figure 20-30dB higher. With further analysis, I discovered that it was one DAC channel that was not up to scratch. To investigate, I disconnected the four 240W resistors from pins 19, 20, 23 & 24 of IC9 to the op amps and swapped the channels over. The high distortion remained with the same DAC channel, ruling out the op amps or associated components as the culprits. So it looked like I had a faulty DAC chip. Not having the tools or skills to remove the SMD, I sent the board over to Phil Prosser, who graciously offered to swap the chip for a new one. That fixed it. Phil pointed out that a static discharge on one of the output pins could have damaged the faulty channel. Thanks to Phil for fixing it. Stephen Gordon, Thurgoona, NSW. DAB+ radio updates On May 18th, the ABC/SBS digital radio signal quality was adjusted. ABC Classic has been increased from 80kbit/s to 120kbit/s. After all the initial sound quality complaints, it will be interesting to see if anyone notices. ABC Jazz has been increased slightly to 88kbit/s, which is not likely to make a noticeable difference. The losers are ABC country, triple j and triple j Unearthed, reduced from 80kbit/s to 72kbit/s. This is interesting because triple j’s younger audience should have better hearing! ABC Kids Listen has also been reduced from 72 to 64kbit/s. The ABC local radio for each capital city is transmitted in 64kbit/s stereo, despite their AM transmitter radiating in mono except for Darwin, which is in FM stereo. SBS is unchanged, meaning that Chill and Pop Asia are still 72kbit/s stereo. All these channels use HE-AAC V2 compression. There is now an even more efficient compression called xHE AAC, but current DAB+ receivers cannot handle it yet. A Government DAB+ transmitter carries 18 programs. The commercial/ community DAB+ transmitters are carrying up to 32 programs each. There is an opportunity for regional areas to roll out DRM+ using the vacant analog TV channels 0-2, that can cover 6 Silicon Chip a much larger area than DAB+, which uses higher-frequency channels, increasing line-of-sight losses by 12 times. This could replace many AM and FM broadcasts. One DRM+ transmitter can carry the pair of programs from commercial broadcasters, and there is now a six-channel modulator that can transmit the 18 ABC/SBS programs using a single antenna. 2.8 million DAB+ receivers have been sold to date in Australia, and 77% of new cars have DAB+ receivers. Alan Hughes, Hamersley, WA. Secondary circuit breaker recommended with variacs Dr Hugo Holden’s Variac-Based Mains Regulator article (May 2021; siliconchip.com.au/Article/14856) is a great idea. I’ve had a commercial version protecting my small collection of vintage electronic equipment for 15 years, and it has been invaluable. We live a long way up a country road, where electricity is supplied by the proverbial “thin piece of wet string”, meaning that the mains voltage varies widely (far outside the nominal statutory limits) depending on farm loads, domestic cooking times and so on. Modern appliances with switchmode power supplies take it all in their stride, but it is a different story for the old-time stuff. As just one familiar example, until the advent of LED lamps, globe life in our home was very short indeed! However, I have a recommendation for anyone who decides to build one. If the variac of choice does not already have one as an OEM fitting (they usually don’t, in my experience), I suggest a thermal overload should be inserted in the secondary between the variac and the outlet socket, rated at the nameplate current of the variac. It is very easy to damage a variac by inadvertently overloading it, and a simple thermal circuit breaker or overload will prevent much heartache. They are readily available, small in size, moderately priced, and do a better Australia’s electronics magazine job than a secondary fuse because they will trip on small sustained overloads, which can damage the carbon brush. A photo is shown below of a typical thermal overload breaker, stocked by a reputable NZ supplier (mytools.co.nz). John Reid, Tauranga, New Zealand. Eliminating transformers in the IMSC I was interested in reading the recent advice you gave to a correspondent who wanted to run the Silicon Chip Induction Motor Speed Controller (IMSC) from 115V AC (April 2021, Ask Silicon Chip, p110). I have built a couple of them to run my pool filter and bench drill (both from 230V), and they work very well. I have made some modifications to the circuit for improved performance that would also enable 115V AC operation. It does require some repackaging of the unit and is a project for the experienced constructor, but the results are beneficial. I replaced both the transformerbased high-side and low-side 15V and 12V DC power supplies entirely with a couple of 12V 1A switchmode supplies from eBay (intended for the LED Christmas lights market). Many sellers have them. These supplies are enclosed, small in size and have a wide input AC voltage range, operating from 90V AC to over 240V AC. They allow the unit as a whole to run from 115V AC since the high voltage part of the circuit will be unaffected, as noted in your advice. However, as you mention, the low voltage protection circuitry will require modification. I could have used a 5V DC switchmode supply for the cold side, but chose 12V to standardise on one DC supply type. This means I had to add a small flag heatsink to REG1. I changed the output voltage of the high-side supply to the recommended 15V by replacing just one resistor in the switchmode supply. By coincidence, I saw later (after I had traced out the circuit) that Oatley Electronics had posted the procedure to change the output voltage of this generic power supply on its website. Notably, instead of powering the switchmode supplies directly from 230V AC, I used the mains rectified 325V DC bus that powers the 3-phase VFD chip. The same AC input terminals to the switchmode can be used, and they are polarity independent. siliconchip.com.au Ready for Tomorrow Over new brands * added PROCESS & ANALYTICAL INSTRUMENTS pi 3g p .pi3g.com Inventory increased by 25% SBC +64% Semiconductors +6% Passives +12% EMECH +202% Interconnect +16% Test and Tools +18% Contact us now Phone: 1300 361 005 Sales: au-sales<at>element14.com Quotes: au-quotes<at>element14.com au.element14.com/ready4tomorrow *from July 2019 POWER SUPPLIES PTY LTD ELECTRONICS SPECIALISTS TO DEFENCE AVIATION MINING MEDICAL RAIL INDUSTRIAL Our Core Ser vices: Electronic DLM Workshop Repair NATA ISO17025 Calibration 37 Years Repair Specialisation Power Supply Repair to 50KVA Convenient Local Support SWITCHMODE POWER SUPPLIES Pty Ltd ABN 54 003 958 030 Unit 1 /37 Leighton Place Hornsby NSW 2077 (PO Box 606 Hornsby NSW 1630) Tel: 02 9476 0300 Email: service<at>switchmode.com.au Website: www.switchmode.com.au 8 Silicon Chip This modification has significant advantages for me. Since the switchmode supplies operate down to below 100V, when power is switched off to the unit, the control circuitry remains powered along with the VFD chip, so the unit will continue to drive the load until the DC bus drops below 100V, or until the undervoltage protection kicks in (I don’t know which happens first). When powering a 1500W pool pump, this process takes less than a second. Even when the motor stops drawing its load current, the switchmode supplies continue to discharge the DC power supply capacitors until the DC rail is well below 100V. This means that the load resistors across the high voltage caps for safety are not required, so a major source of heating in the enclosure is eliminated. I was surprised to note another benefit. Builders of the IMSC will have noticed that when the power to the original unit is disconnected, the motor being driven stops completely with a jerk. Another reader reported this phenomenon some time ago and asked a question as to why this happens. The answer proposed that the integral protection diodes in the VFD chip were shorting the motor and acting like a dynamic brake. I haven’t tested this or other theories (I don’t have the HV test equipment or the courage) but, when the switchmode DC power supplies are introduced, this effect disappears, and the motor runs down smoothly. I think the IMSC is one of the most useful projects presented by Silicon Chip. An industrial electronics-scale project was a welcome addition to the project stable. It’s a shame that packaged kits are no longer available for this and, for that matter, most Silicon Chip construction projects – an unfortunate sign of these ‘maker’ times. David Hainsworth, Westlake, Qld. More on software for 3D printers Thanks for your advice on software for 3D printers (Ask Silicon Chip, June 2021, p108). I tried OpenSCAD (https://openscad.org/) initially, and that worked so well that I didn’t explore alternatives. It is easy to use, with a very good Wiki-style user manual. It is one of few software products that didn’t provoke me to put fists through computer screens. I noticed three quirks, but these are more amusing than annoying. It is a programming language, not an interactive pointand-click tool. Although that might seem odd in modern times, it leaves a record of what I’ve done and allows me to leave comments for myself. So if I don’t get my clever gadget perfect the first time, which I didn’t, I can read what I’ve done and fix it. It resembles languages like LISP more than procedural languages like BASIC or C, and everything felt back-tofront for a while. A bit like the German language it is, with verbs at the end of the sentences. That encouraged me to define my gadget using modules so that each module, Module N, had a pattern like: Use Module N-1 Add these bits Remove these other bits Once I got the hang of it, I produced modules that were quite pleasing and reliable. Although its documentation mentions variables, it also warns that they aren’t Australia’s electronics magazine siliconchip.com.au Our capabilities CNC Machining UV Colour Printing Enclosure Customisation Cable Assembly *** Box Build *** System Assembly Ampec Technologies Pty Ltd Australia’s electronics magazine siliconchip.com.au Tel: (02) 8741 5000 Email: sales<at>ampec.com.au Web: www.ampec.com.au FEBRUARY 2021 37 variables, but more like constants. For a proper programming language, this would create huge problems, but for doing what OpenSCAD does, it is no worse than a mildly irritating curiosity. I sent my clever design to KAD3D, and they turned it into a gadget that looks like the gadget I drew. Keith Anderson, Kingston, Tas. Historical articles enjoyed First off, let me thank you for the effort that you have put into the magazine over the years. Good work! Your article on the humble three-pin Aussie plug and socket was very interesting, and someone had done a lot of research into it; a great read (September 2020; www.siliconchip. com.au/Article/14573). Same with the articles on the VCR and its not so humble beginnings (March-June 2021; siliconchip.com.au/ Series/359). Coming from the electronics service industry, now retired and living in Tasmania, that article series brought back a whole lot of memories from a bygone era, including my studies at the local TAFE. Would it be possible to publish an article on the Compact Disc, DVDs, LaserDisc etc and the problems and formats that this medium provides? I find that type of article interesting and a good read. I re-read one of your articles from May 2019 (p104) on The History of Stromberg Carlson, and Admiral Television. This was a blast from the past. My family had one of these Admiral televisions (Imperial 800), and I can still remember the set being delivered around 1958/9. I was just a little kid at the time. This set was still going up until my parents purchased a colour television; whatever happened to that set, I do not know! I remember that when Channel 0 started transmission (later to become Channel 10), these and a lot of other sets needed the “0” biscuit modified to receive the new channel. The other time the set was repaired was when the flyback transformer failed. That, the horizontal output valve (6DQ6) and damper diode (6AX4) were all replaced during a house call. When I started working, I was lucky enough to land an apprenticeship as a radio and television trainee. I had not long turned 15 at the time, and I worked in the television reconditioning section. Many of these Admiral TVs were traded in at the time, and a lot were passed over as being too hard to work on due to the “new” printed circuit boards they used. I think that was before solder wick and solder suckers. The standard iron at the time was the old scope 300W iron, with no temperature control, and using one on printed boards was a real learning curve. Too much heat and the copper track would lift off the board. One soon learned. Television techs of that era enjoyed point-to-point wiring, and the ease with which those sets could be repaired. How soon that was to pass! I had a soft spot for our own Admiral set and soon took to several of the Admiral sets that were traded in. One Admiral set I remember also had a radiogram in the bottom of the cabinet. This pulled out like a drawer in a cupboard. I remember that the radiogram had push-pull output valves (possibly 6AQ6s) in the audio output stage. Stephen Gorin, Mildura, Vic. SC 10 Silicon Chip Australia’s electronics magazine siliconchip.com.au