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Modbus TCP↔RTU gateway for bioreactor control

An M-Duino exposes the whole plant over Modbus TCP and drives chillers, variable frequency drives and flow meters over RS485.

Runs on: M-Duino — Arduino sketches (.ino).

The application

A bioprocess laboratory needed to control two fermenters (temperature, agitation and flow) from its SCADA without wiring every device to the network. An M-Duino acts as a gateway: upstream it is a Modbus TCP slave (port 502) with a single register map for the whole plant; downstream it is a Modbus RTU master over RS485 driving 2 chillers, 2 variable frequency drives and 2 flow meters, plus physical I/O for sensors and pilot lights.

Architecture

• SCADA ↔ Modbus TCP (single map: coils, holding and input registers)
• M-Duino as Modbus RTU master at 9600 over half-duplex RS485
• Chillers: run command and temperature setpoint (reg. 0x06/0x0A)
• Drives: RPM setpoint (0x0144) and 32-bit actual speed reading (0x2149)
• Flow meters: 32-bit totalizer (0x100) with remote reset

Bill of materials

• M-Duino — Industrial Shields controller
• 2× thermoelectric Modbus chiller — thermal control
• 2× Modbus variable frequency drive — agitation
• 2× Modbus flow meter — accumulated litres

What is in the pack

• chiller-control-rtu.ino
• flow-meter-reading.ino
• gateway-modbus-tcp-rtu.ino
• modbus-register-map.ino
• vfd-rpm-control.ino
• Bill of materials + README