No information is given on the transformer in this circuit that we found in an American 1967 documentation. The power transistors are of the time and mounted on a plug-in module.
The purpose of this circuit is to allow common analog multimeters to measure low resistances, on...
We found this circuit in a Radio Electronics issue from July 1969. The lamp remains on until C1...
This circuit was found in a 90s Popular Electronics. The sensor can be any phototransistor. ...