This relay board needs a power supply of 5VDC. The opto insulated input can handle 3-24VDC control voltage, with a maximum input current of 22mA at 24VDC. The input is LOW active. It means, the output of an micro controller (like Arduino or Raspberry) draws the input current to GND. The LOW level activates the relay, a high level (or open connection) deactivates the relay.