We found this circuit in a Radio Electronics from October 1976. The components are still common, but the circuit applies to older car models with contact breaker ignition.
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...