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If at resonance there is an insufficient voltage at TP1, you will need more secondary turns on the transformer (or take water out of the bath). The correct number of turns or amount of water is when the voltage at TP1 is close to 4.5V at resonance. This allows some leeway in frequency control to achieve 4.2V at TP1, for 36W into the transducer when slightly off-­ resonance. If the TP1 voltage when approaching resonance is too high (above 4.5V), Advertising Index Altronics....................... 7, 29-32, 41 Dave Thompson........................ 103 Emona Instruments.................. IBC Hare & Forbes............................... 9 Jaycar............................. IFC, 11-14 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.............OBC Mouser Electronics....................... 3 OurPCB Australia.......................... 6 PCBWay......................................... 5 PMD Way................................... 103 SC Dual Mini LED Dice.............. 103 SC Versatile Battery Checker..... 67 Silicon Chip PDFs on USB......... 47 Silicon Chip Shop.......... 61, 85, 99 Silicon Chip Subscriptions........ 15 The Loudspeaker Kit.com.......... 60 Wagner Electronics..................... 91 Errata and on-sale date Boeing 737 MAX & MCAS, August 2025: the MCAS system controlled the motors driving the trim tabs on the elevators, not the ailerons. Thin-Film Pressure Sensor, August 2025: in Fig.3 on p35, the S pin should go to A0 and the + pin to 5V. Next Issue: the October 2025 issue is due on sale in newsagents by Monday, September 29th. Expect postal delivery of subscription copies in Australia between September 26th and October 15th. 104 Silicon Chip reduce the number of secondary turns or use more water in the bath. 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, you will probably need to change the number of turns on the transformer secondary as described above. Once you get a reading of 4.5-4.7V with TP1 at resonance, the Cleaner should run correctly. Low-noise motor speed control wanted I am trying to find a project or kit for making a dual-thyristor speed controller that has very low noise and EMI, rather than a basic, noisy Triac-based speed controller. (P. F., New Zealand) ● We published a full-wave mains motor speed controller in the February & March 2014 issues (siliconchip. au/Series/195) that utilised a Mosfet instead of a Triac. Speed control is via pulse-width adjustment rather than phase control. The circuit essentially controls the motor with pulse-width modulated (PWM) DC that follows the envelope of a full-wave rectified mains voltage. In the past, for Triac-based dimmers controllers, we used a 100μH choke (in series with output) and a 10nF capacitor (from output to neutral) as an EMI filter. For controlling brush motors, any filtering of the Triac switching is totally masked by the EMI from the motor, so we don’t tend to use a filter in motor controllers. Connecting Frequency Relay to a fuel injector I have a Jaycar AA0377 Frequency Relay Module for Cars that I connected to my car’s injector signal wire and it worked perfectly. I then tried it on a Ford Falcon inline-six Barra engine’s injector signal wire, and that injector failed to work, resulting in the car misfiring while running. Removing the signal wire from the injector returned the engine running to normal. After some research, I found that the Falcon injectors are of the high-­ impedance type. I suspect that the loading of the Frequency Relay input circuit is stopping the ECU’s injector Australia's electronics magazine signal from getting to the injector or loading it down. Do you agree? If so, is there a way to match or reduce the Frequency Relay signal loading on the car’s injector circuit? I cannot use the ignition coil signal on this engine, as it produces three coil ignition pulses at idle. There is a tachometer signal, but it is a CAN bus signal that is not compatible with the Frequency Relay. Can you suggest a solution? I am trying to switch on a water pump above 4000 RPM. (M. S., Keilor Downs, Vic) ● Yes, the Frequency Relay input would be loading the injector signal. You could include an NPN transistor buffer, where the base of the transistor connects to the injector signal via a 10kW resistor. Another resistor (4.7kW) connects from the collector to the 0V supply. Then the emitter connects to ground (0V) and the collector connects to 12V via a 1kW resistor. The collector signal can then go to the Frequency Relay signal input. A BC337 would be suitable. EA Induction Loop projects are obsolete My question is regarding the Induction Loop TV Headphones published in Electronics Australia, October 1995, starting on page 68. I am looking for something cheap to build or purchase that will allow me to quickly check the status of a loop. Is this project for picking up sound from hearing aid loops, more commonly known as T-Loops? The circuit diagram shows inductor L1 is 800 turns on a 9 × 70mm ferrite rod. Where can I get this, or find a substitute for it? (B. A., Dee Why, NSW) ● The EA Induction Loop TV Headphones wasn’t designed to the standards of a T-coil hearing aid loop. Its output will be a low level if used with a hearing aid loop. It was meant for use with a small loop from a TV set’s audio signal, and is also very directional due to the long ferrite rod. The Jaycar LF1010 is a suitable replacement, and can be cut down to size if necessary. We published several projects that are compatible with T-Loops, including a Hearing Loop Receiver (September 2010; siliconchip.au/Series/11) and a Hearing Loop Level Meter (November & December 2010 issues; siliconchip.au/Series/15). You would be far better off building one of those to pick up signals from a T-Loop. SC siliconchip.com.au