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 using only transistors was obtained from Ferranti's 1969 documentation. It can be...
This sensitive circuit can be designed with FETs such as BF245 and MPF102. The sensor is a silicon...
Found in Popular Electronics from the 90s, this circuit generates two tones that are selected by a...