This is 4 Channel 5V Solid State Relay Module. A solid state relay (SSR) is just what it sounds like; an IC that acts like a mechanical relay. They allow you to control high-voltage AC loads from lower voltage DC control circuitry. They accomplish this by using infrared light as the ‘contact,’ a solid-state relay is really just an IR LED and a photo Triac sealed up into a little box. Solid-state relays have several advantages over mechanical relays.
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