This circuit triggers a relay when a light beam that hits the phototransistor is cut off. The circuit is from Electronics Now and the supply voltage depends on the relay voltage.
This circuit was found in the July 1992 issue of Radio Electronics magazine. The circuit is based...
This circuit was found in Electronics Today International of the 80's. The circuit uses still...
This circuit is from the National Semiconductor FET Databook. The coil data is provided with the...