This 1967 Raytheon circuit uses a Raystor, an optical coupler with a lamp and an LDR. The circuit can be adapted to use another type of coupler.
We found this circuit in a 90s Popular Electronics. It increases the duration of a pulse in a...
This simple circuit detects when a conductive liquid reaches the sensors. The circuit has no...
This converter or inverter uses components that are still common. The transformer is the type...