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Advertising Index Altronics.................................31-34 Blackmagic Design....................... 9 Control Devices........................... 85 Dave Thompson........................ 103 DigiKey Electronics....................... 3 Emona Instruments.................. IBC Hare & Forbes............................ 6-7 Icom Australia............................. 14 Jaycar........................IFC, 11, 15-17 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.............OBC Mouser Electronics....................... 4 OurPCB Australia........................ 10 PCBWay....................................... 13 PMD Way................................... 103 Rohde & Schwarz........................ 83 SC Ideal Bridge Rectifiers kits.... 57 SC GPS Clock kit......................... 60 SC Advanced Tweezers kit......... 93 Silicon Chip Shop.......... 69, 82, 84 Silicon Chip Subscriptions........ 30 The Loudspeaker Kit.com.......... 12 Wagner Electronics..................... 91 Silicon Chip Binders REAL VALUE AT $21.50 PLU S P&P Order online from www.siliconchip. com.au/Shop/4 or call (02) 9939 3295. Next issue of Silicon Chip Next Issue: the July 2025 issue is due on sale in newsagents by Thursday, June 26th. Expect postal delivery of subscription copies in Australia between June 23rd and July 11th. 104 Silicon Chip Australia’s demise. I have been involved in the electronics industry, servicing, building and importing components since the days of Mullard’s transistors (half of which did not function). I have built a number of circuits published in Silicon Chip and would like to congratulate you on your persistence in encouraging young minds to delve into both analog and digital electronics. The shrinking size of components will not help, especially for old guys like me. I have a question about John’s Multi-Spark CDI design (December 2014 & January 2015; siliconchip.au/ Series/279). I want to be able to trigger up to six spark plugs simultaneously while revving to high RPMs. Rather than building six complete units, would the output from the inverter be sufficient for one inverter to supply six individual trigger systems? (K. S., Dunedin, New Zealand) ● Thank you for your words of appreciation for Silicon Chip magazine. Regarding the Multi-Spark ignition, the coil driver section comprising IC2, Q3, Q4 and the 1μF capacitor and associated components would need to be duplicated six times for six separate ignition coils. The 300V DC generator comprising IC1, Q1, Q2, T1, the D2-D5 full-wave rectifier and associated components should be able to drive all six output circuits with the 300V DC. If the 300V is not maintained with the six outputs connected and running at high RPM, you may need to build another 300V DC section so that each will only drive three output circuits. RIAA preamp wanted for record player I have been asked to restore an old 1950s chest-type valve radiogram that has great sentimental significance to its owner. Unfortunately, the existing Collaro record changer looks to be beyond help, with perished rubber parts. The only solution I have is to retrofit a newer turntable/record changer unit. I envisage using something like a later model Garrard obtained second-hand, fitted with a magnetic cartridge. The radiogram won’t have sufficient audio gain to be driven directly from a magnetic cartridge, but I can easily add a solid state preamp, hidden inside the cabinet. Have you published a design for a mono (or stereo) RIAA magnetic phono Australia's electronics magazine preamp that can provide an output of up to 300-400mV? If so, do you have PCBs available for it? (P. W., Pukekohe, New Zealand) ● We have published a Magnetic Cartridge Preamplifier (August 2006; siliconchip.au/Article/2740). It is a stereo preamplifier with a gain that should be suitable for your application. Its output level depends on the cartridge signal output with record groove modulation. The PCB is still available from our Online Shop (siliconchip.au/Shop/?article=2740). Bouncing Kelvin causes the eyes to light up My son and I enjoyed building the Kelvin the Cricket project (October 2017; siliconchip.au/Article/10828) and would love to learn more about two aspects of his design and function. 1. If I bounce Kelvin, his eyes light up, even with the batteries out and the jumper removed. I’ve only tried this on dark rooms because the LED is too dim to see in well-lit rooms. I’ve tried leaving Kelvin alone for an hour in case there was a charged capacitor. I’ve tried different locations in case there was a strong magnetic field. Sometimes both LEDs glow, sometimes one does. 2. Do you have the PIC code in C# or pretty much any other language other than assembly, so I can learn how the functions were implemented? (B. B., via email) ● The interesting effect where the LEDs light when Kelvin is dropped is due to the piezo transducer producing a voltage when flexed. Since the transducer is in parallel with the LEDs and their current limiting resistors, they light up when this happens, but for extremely brief periods and very low currents. Piezo materials flex when a voltage is applied (producing a sound) but they also do the reverse, ie, if flexed they will produce a voltage. The dropping of Kelvin the Cricket causes piezo movement when it hits the ground, as it experiences inertial forces. The piezo element will probably ring (oscillate) with the initial abrupt stop when hitting the ground and drive the LEDs alternately as the AC waveform from the transducer changes polarity on each ringing cycle. Sorry, we don’t have C source for the software as it was written in assembly language. SC siliconchip.com.au