How can I identify the input and output pins of an optocoupler? Refer to the optocoupler's datasheet or a circuit diagram. Apply a varying voltage to the input pin. It typically consists of a light-emitting diode (LED) and a photodetector (such as a phototransistor, photodiode, or photothyristor) housed in. n this video, you will learn how to test an optocoupler (optoisolator) using a simple multimeter. An optocoupler is an essential electronic component that transfers signals without a direct electrical connection.