MQTT

MQTT Environment for PLC and HMI Simulation

This repository demonstrates a simple MQTT-based simulation environment consisting of three main components:

• Mosquitto Broker: Acts as the central MQTT broker that routes messages between clients.
• PLC (Publisher): A Python script that simulates a PLC by publishing sensor values (randomly generated) to an MQTT topic.
• HMI (Subscriber): A Python script that simulates an HMI by subscribing to that MQTT topic and displaying the received sensor values.

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How It Works

1. Mosquitto Broker
   Mosquitto is a lightweight MQTT broker that listens on the default MQTT port (1883). It handles connections from both the PLC and the HMI. When the PLC publishes a sensor value to the MQTT topic (in this case, plc/sensor), Mosquitto forwards that message to all clients subscribed to that topic.

2. PLC (Publisher)
   The PLC script (plc_mqtt.py) simulates a real PLC by publishing a new random sensor value (an integer between 0 and 100) every 2 seconds to the MQTT topic plc/sensor. This mimics a PLC sending periodic sensor readings.

3. HMI (Subscriber)
   The HMI script (hmi_mqtt.py) acts as an MQTT subscriber. It connects to the broker, subscribes to the topic plc/sensor, and displays the sensor values it receives on the console.

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Installing Mosquitto

1. Update your package lists and install Mosquitto along with its client tools:

   sudo apt update
   sudo apt install mosquitto mosquitto-clients

2. Start the Mosquitto service:

   sudo systemctl start mosquitto

Running the Python Scripts

1. Running the PLC (Publisher) Open a terminal and navigate to the directory containing plc_mqtt.py.

Run the script:

python3 plc_mqtt.py

• The PLC script connects to the MQTT broker at localhost:1883 and publishes a random sensor value (0–100) to the topic plc/sensor every 2 seconds.

2. Running the HMI (Subscriber) Open another terminal and navigate to the directory containing hmi_mqtt.py.

Run the script:

python3 hmi_mqtt.py

• The HMI script connects to the broker, subscribes to the topic plc/sensor, and prints the sensor values as they are received.

Monitoring MQTT Traffic with Wireshark

To verify that MQTT messages are transmitted correctly:

1. Open Wireshark.
2. Set a display filter to capture MQTT traffic on port 1883:

tcp.port == 1883

3. You should see MQTT packets with proper MQTT headers (including message types, topics, etc.), confirming that the PLC and HMI are correctly using the MQTT protocol.