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.
August 2017 - The new IXYS solid state relay CPC2907B from IXYS is currently in stock at Mouser...
This circuit was found in 1980s American documentation. The transducer is a piezoelectric capsule and the...
Using this circuit a low current switch can be used in the control of heavy duty loads, powered...