We found this circuit in a 1985 documentation. The transformer is an old TV flyback that has an exposed part of the core, where 10 to 20 turns of common wire are wrapped.
This very simple circuit uses a phototransistor and a very sensitive relay (reed type) being used...
We found this circuit in Radio Electronics magazine from January 1958. It uses a neon lamp as the...
The integrated circuits in this application are not very common today. One consists of an A / D...