Photo coupler

The photocoupler has a built-in light emitting element and light receiving element.
The element can emit light by sending an electric signal to the light emitting element, and the light receiving element can output to the outside by receiving the light.

Unlike mechanical relays and general transistors, photocouplers are electrically isolated on the input side and output side, and can protect the device body from overcurrent and overvoltage from external devices connected to the output side.

As for the output, the current can flow in only one direction like the general transistor output.