This simple tester was found in a Popular Electronics from the 90s. The circuit is powered by two 9 V batteries since it requires a symmetrical source.
This circuit is from a Linear Technology manual from the 90's. The integrated circuit is from the...
The original design of this circuit is from a 1978 publication. The circuit can be implemented with a...
The PNP transistor can be a BC548 and the NPN any common phototransistor. The circuit is from 1968...