This very simple circuit uses a phototransistor and a very sensitive relay (reed type) being used over short distances with a lens system. The circuit is from a 1967 Japanese publication.
This low drift or offset circuit is from an 80's documentation. The configuration can be made with...
We found this circuit in a 1956 Sylvania publication. It serves to monitor telegraph transmissions being...
This circuit activates an incandescent lamp at dusk and goes out at dawn. The sensor is an LDR and...