4N35 Optocoupler — Galvanic Isolation Demo

An LED and a phototransistor in the same package transfer signals across an electrical no-man's-land — your first encounter with isolation.

Difficulty: Breadboard. Estimated build time: about 25 minutes. Estimated parts cost: about US$2.80. 5-part bill of materials with live supplier pricing. A logic-level signal that crosses an electrical isolation barrier through nothing but light.