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 have other circuits like this on the website. This is from a 1967 Electronics World. The Triac...
We found this circuit in an integrated circuit cookbook from 1974. The circuit can provide larger...
This circuit was found in a 1977 Radio Shack documentation. The unijunction transistor can be...