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 circuit applies to other operational ones, other than the one indicated. The formulas next to the...
This circuit can source 3 to 12 V with currents up to 500 mA depending only on the transformer....
This relay circuit is intended for reversing small DC motors. The circuit is from an old...