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 ...

This Arduino Uno setup can be powered by a 6F22 9V battery or ... A few more significant details about this Chinese “2 Relay Module” are worth noting, especially if you are using it for the first time ...

The Arduino acts as the brains of the operation while an off-the-shelf NFC/RFID reader module is used to read ... the Arduino triggers a relay which can then be used to control just about anything.