This optical coupler for short distances is powered by 12 V which is the voltage of the lamp and the relay. The circuit can also use emitting LEDs and the phototransistor can be of any type.
We found this circuit in a documentation from the 50s. It is based on CK722 germanium transistors. The...
Found in an English publication from the 1960s, this circuit uses period components, including the...
This oscillator can generate 2 to 10 MHz signals and was found in an American 1980s documentation. The...