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 - STMicroelectronics' new T850 switches with triacs up to 8 A can be obtained from...
This circuit is from the 1990 Motorola Linear Databook. The circuit can be applied to other...
Found in documentation from the 90s, this circuit makes use of components from the time....