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.
I found this circuit in an English magazine from July 1982. The circuit is still viable as all...
The circuit is from the 1990 Motorola Linear Databook. The circuit can be implemented with other...
This indicator makes use of an LM339 voltage comparator circuit that contains 4 internal...