Uni-Directional OPC UA to MQTT Publisher in Python with JSON Payload

Last Code Revision Date: 03-Sep-2025

OPCUA to MQTT Bridge

This project connects to an OPC UA server, reads values from specified nodes, and publishes their values as a JSON payload to a single MQTT topic. It is useful for integrating industrial data into IoT platforms via MQTT.

Project Features

• Reads values from multiple OPC UA nodes and publishes them as a single JSON object to an MQTT topic.
• Publishes only when node values change (reduces traffic).
• Robust reconnection logic for both OPC UA and MQTT connections.
• Configuration via config.json (server, broker, topic, nodes, interval).
• Clean shutdown on keyboard interrupt.
• Initial values are published on startup.

Requirements

Install dependencies:

python -m pip install -r requirements.txt

Configuration

Edit config.json to set your OPC UA server, MQTT broker, topic, nodes, and interval:

{
    "opcua_server_url": "opc.tcp://DESKTOP-FAFB2HS:53532/OPCUA/SimulationServer",
    "mqtt": {
        "broker": "127.0.0.1",
        "port": 1883,
        "master_topic": "OPC_UA_Nodes"
    },
  "nodes": {
    "Counter": "ns=3;i=1002",
    "Random": "ns=3;i=1003",
    "Sawtooth": "ns=3;i=1004"
  },
  "interval": 5,
  "reconnect_delay": 5
}

Usage

Run the main script:

python main.py

How It Works

1. Loads configuration from config.json.
2. Connects to the OPC UA server and MQTT broker (with auto-reconnect).
3. Reads initial values from configured OPC UA nodes and publishes as JSON to the MQTT topic.
4. Periodically checks for changes in node values and publishes updates only when values change.
5. Handles connection loss and attempts to reconnect automatically.
6. Clean shutdown on keyboard interrupt.

File Overview

• main.py: Main script for OPC UA to MQTT bridge.
• config.json: Configuration file for server, broker, nodes, and interval.
• requirements.txt: Python dependencies.

main.py

The main.py script loads configuration from config.json, connects to the OPC UA server and MQTT broker, reads values from configured OPC UA nodes, and publishes their values as a JSON object to a single MQTT topic. It supports both asynchronous and synchronous OPC UA/MQTT clients (as listed in requirements), and only publishes updates when node values change, reducing unnecessary traffic.