This circuit was found in the Electronics Experimenter Handbook from 1991. The sensor is a diode and the circuit has a relay according to the voltage used in the supply.
We found this circuit in the 1994 Linear Applications Handbook from National Semiconductor. The...
This circuit is from an Electronics World of 1968. The transistors are of the time and the power...
This circuit checks the infrared emission of a common remote control. We found it in the March 1993...