Hardware for using ModbusRTU with RS-485 on Arduino
Why Modbus Hardware is Required for Arduino
The Modbus RTU logical communication protocol is typically transmitted using the physical RS-485 serial communication signaling standard.
Arduino-framework micro-controllers, on the other hand, transmit serial signals using transistor-to-transistor logic, or TTL serial.
Therefore, most sensors using this library will need to an RS485-to-TTL adapter module to communicate. Also, most Modbus sensors require 5-12V of power, so a separate step-up power converter may be necessary to run it off a 3.3V Arduino micro-controller. Last, the electrical "logic level" signals returned from a sensor will typically have a HIGH (or "1") returned at the same voltage that powers the sensor, which means that a logic-level shifter/converter is required to ensure that communication signals being received by the Arduino micro-controller are 3.3V. Luckily, most RS485-to-TTL adapter modules also perform logic-level voltage conversions.
For all these reasons, additional hardware is usually required to interface a Modbus sensor with an Arduino micro-controller.
We have developed some guidance, designs and documentation different interface hardware solutions that have worked for us. This information is now available in the EnviroDIY/
