Learn to build an Optocoupler Test Circuit to verify switching and electrical isolation. Step-by-step DIY guide, working principle, diagram, and components included. Their ability to provide electrical isolation between two circuits while maintaining data transfer is crucial for safety and preventing ground loops. This isolation is achieved through the use of. Optocoupler is one type of ICs, It isolates input and output section by using optical technology this feature increase safety of circuit. They may look fine from the outside, but the internal LED or photo part may not function properly. Guessing. In this episode #0018 of Electronic Components Testing, we reveal how to test an optocoupler (optoisolator) using a digital multimeter step by step.