This circuit was originally intended for reading movie soundtracks. The circuit is from 1967 and was found in an English publication. The sensor is semiconductor type.
We found this circuit in the May 1972 issue of Radio Electronics magazine. Its purpose is to teach...
This circuit is from 1985 documentation. The integrated circuit used is not very common today, but...
This circuit consists of a simple continuity test with two transistors forming a relaxation...