This relay board needs a power supply of 5VDC. The opto insulated inputs can handle 3-24VDC control voltage, with a maximum input current of 22mA at 24VDC. A jumper can switch between 2 modes: If the jumper cap is set to VCC and JD-VCC, relays and opto inputs are using the same 5VDC power supply. If the jumper is open, a separated 5VDC power supply can drive the relays and the inputs are open for voltages up to 24VDC. The inputs are LOW active. It means, the output of an microcontroller (like Arduino or Raspberry) draws the input current to GND. The LOW level activates the relay, a high level (or 3-state level) deactivates the relay.