Simply, it’s an Arduino library for communicating with Modbus slaves over RS232/485 via RTU (remote terminal unit) protocol. In conclusion, the Modbus 2-channel 5V relay module is a very useful device ...

If so, remember to connect the VCC pin to 5V of the Arduino board to enable the control input pins IN1 and IN2. Also note at this point that, if you want perfect galvanic-isolation, do not link ...

The 5.2V is safe for all 5V-powered electronics like Arduino, Raspberry Pi, or Beagle Bone while preventing icky brown-outs during high current draw because of USB cable resistance.