Home Engineering Insights Building Industrial IoT Telemetry Systems: Modbus RS485 to MQTT Cloud Gateways
Industrial IoT & Automation

Building Industrial IoT Telemetry Systems: Modbus RS485 to MQTT Cloud Gateways

BCNT Hardware & Firmware Team September 03, 2026 6 min read

Learn how to bridge legacy plant machinery running RS485 Modbus RTU to modern MQTT cloud brokers using custom microcontrollers and encrypted Node-RED flows.

Many manufacturing plants across India operate legacy machinery with RS485 Modbus communications. While reliable on the shop floor, these isolated PLCs lack native cloud connectivity for predictive maintenance and remote dashboard monitoring. ### The Architecture: RS485 Modbus to MQTT To digitize plant operations without replacing million-dollar capital equipment, we deploy edge IoT telemetry gateways: 1. **Modbus Master Polling**: An embedded STM32 or ESP32 microcontroller polls slave PLC registers over RS485 differential lines (9600/115200 baud). 2. **Payload Parsing & JSON Formatting**: Raw integer values (temperature, current draw, vibration RMS) are parsed and packed into lightweight JSON strings. 3. **TLS Encrypted MQTT Transmission**: The gateway connects via cellular 4G or Wi-Fi to transmit JSON payloads over port 8883 to an EMQX or Mosquitto MQTT broker. 4. **Node-RED & Web Dashboard**: Incoming MQTT streams update real-time gauges, log database records in PostgreSQL, and trigger automated WhatsApp/SMS alerts when thresholds exceed safe limits. Through custom PCB hardware design and low-latency MQTT architecture, BCNT Technologies enables factory managers in Pune, Chennai, and Coimbatore to monitor plant OEE in real time.

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