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.
An inproved version of the circuit CIR129E is shown here. The resistorR1 must be at least 5 times...
A bridge with greater sensitivity and, therefore, lower consumption for the microcontroller...
This circuit is from a 1965 Argentine publication (Radio Chassis Television). The original...