This circuit can modulate a laser rate at frequencies of 50 kHz. We found the old documentation. The bipolar transistors can be the BD135 and 136 and the FET admits equivalent.
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. ...