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 obtained in a manual of the used old operational amplifier. However, the same...
Other series amplifiers such as the MC3301, MC3401 and LM2900 can be used on this circuit. We...
The circuit is from an 80's publication, but the components are current, only special type diodes...