This circuit, with printed circuit board, is from an article in Radio Electronics magazine from May 1971. The circuit uses the C106 which was already a common component at the time.
In the figure we have the way to use a stepper motor as an encoder. Operational amplifiers can be of...
Placed inside the refrigerator, this circuit triggers an oscillator when the part is opened...
We found this circuit in an old documentation from the 70s, but it can be assembled with more...