PC817 Optocoupler, Phototransistor Output

Transfers a signal across a complete electrical break using light: an internal LED shines onto a phototransistor, with no conductive path between the two sides at all. That isolation is what protects a microcontroller from mains-referenced circuits, breaks ground loops between separately powered systems, and keeps switching noise out of sensitive electronics. The isolation rating means the two sides can sit at very different potentials safely. Eight channels match a full byte or shift register output; Internal flyback diodes for inductive loads; 500 mA per channel from a logic-level input; Pairs naturally with a 74595 shift register