A small thermostat I built for a sodium persulfate PCB etching bath, controlling a heater originally intended for fish tanks (with the original temperature control removed). The temperature is fixed to 45–50 °C and power is provided for a small air pump. Schematics can be found here, PCB design files and MCU firmware here.
Recently, I needed a simple temperature switch which could withstand 400 °C. A thermocouple can easily manage this but its generated voltage is unpleasantly small. However, it turns out that a ATTiny216A’s integrated differential amplifier is absolutely sufficient for a, albeit not very accurate, measurement. Enough to determine if something is hot or not, at least.More details →
While restoring a milliohm meter made by Test Fuchs I could not find any information about, I traced its schematic. It can be found here in case anyone has the same instrument.
A useful thing to have for testing high voltage transformers is a simple chopper. This one switches a 600 V IGBT with an adjustable frequency between 50 Hz and 29 kHz (lower frequencies are possible with an external timing capacitor) and any duty cycle between 0 and 100%.More details →