The Opto-coupler Plug v2 is a small board containing a dual opto-coupler. It can be used to detect the presence of low DC voltages (a few dozen volts) and currents (milliamps) without creating a direct electrical connection to any other circuits. It can also be used as an output driver, say to drive small DC relays.
Note: Because the chip must be reversed, to switch from input to output, that the Opto-coupler Plug cannot be used as both input and output at the same time.
Both input circuits consist of a built-in LED which must be driven with ≈ 3-55 mA of current. Two 1K Ω series resistors are included, which allow using this board with 3-12V DC sources. Other resistor values can be used for higher or lower voltages.
In theory, this plug could be used to detect AC mains power, when part of a suitable circuit. In practice, you should only consider this if you know exactly what you’re doing, and have taken all the necessary safety precautions. The 1K resistors are not in any manner appropriate for mains voltages and should not be used. High voltages can be lethal – proceed at your own risk!
The PCB Only version contains just the printed circuit board for the Optocoupler Plug. No parts, no headers.
The documentation and full design details are freely available.