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 is better than the previous one in that the control is isolated by a transformer. The...
This circuit was found in American documentation from the 1980s. The integrated circuit used is...
This oscillator takes advantage of the 2000 ohms headphone inductance as the oscillator circuit coil....