An electronic component that can pass a signal via a light path, avoiding a direct electrical connection between two separate circuits. This will prevent voltage spikes generated in one piece of equipment from damaging another unit in the network, as well as breaking ground loops. The unit consists of a light source (an LED) and a light detector (a phototransistor) enclosed in a sealed box, the whole package looking IC-like. The part of the MIDI specification that deals with hardware requires that all MIDI In connections use an opto-isolator.