EL817 optoisolator

These are one of the most common optoisolators, consisting of a simple LED and phototransistor pair. They feature 5kV of isolation, and either open collector or open emitter operation. Standard 4-pin DIP package.

They are ideal for anywhere that two DC circuits need to be electrically isolated, such in power supplies, logic controlled circuits etc.

Made by Everlight, part number EL417. Datasheet is here.