This blog provides a step-by-step guide on how to test an optocoupler with a multimeter, focusing on the PC817 model. In this guide, we will delve into the intricacies of this essential electronic device, exploring its technical specifications, applications, and the multitude of advantages it offers. The article highlights key testing procedures and common signs of a faulty optocoupler. The 817C optocoupler is a common opto-isolator, consisting of a light-emitting diode ( LED ) and a photosensitive transistor (phototransistor) with an input and an output. 817C optrons are a crucial type of electronic component that are utilized in many circuits for voltage shifting and signal. Part #: CT817C. Manufacturer: CT Micro International Corporation.