Notes

Quick and Dirty B–H Plots

While building solenoids, I needed a way to quickly judge the magnetic properties of some unknown steel. A simple analogue hall sensor IC works together with a controlled current source for the coil to drive a XY plotter (or oscilloscope in XY mode) and create simple B–H plots.

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RS232 Wiretap

If you need to monitor a RS232 line (or something else running through a D-Sub connector), use one of these open-style connectors. Their pins fit into a female D-Sub connector and provide ample space to attach probes.

PCB Etching Thermostat

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.

Thermocouple via Integrated Differential Amplifier

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.

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Milliohm Meter Test Fuchs MOM1

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.