Iot-protocolsHow-ToBeginner · 4 min read

How to Use MQTT on Raspberry Pi: Simple Setup and Example

To use MQTT on Raspberry Pi, first install an MQTT broker like mosquitto and a Python client library such as paho-mqtt. Then write Python scripts to publish and subscribe messages using paho-mqtt to communicate over MQTT.

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Syntax

MQTT communication on Raspberry Pi typically involves these parts:

Broker: The server that routes messages (e.g., mosquitto).
Client: The device or script that sends (publishes) or receives (subscribes) messages.
Topics: Named channels where messages are sent and received.
QoS: Quality of Service level for message delivery (0, 1, or 2).

Python client code uses paho.mqtt.client with methods like connect(), publish(), and subscribe().

python

import paho.mqtt.client as mqtt

client = mqtt.Client()
client.connect("broker_address", 1883, 60)

client.publish("topic/name", "message")
client.subscribe("topic/name")

client.loop_forever()

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Example

This example shows how to install the MQTT broker and client, then run a simple Python script to publish and subscribe messages on Raspberry Pi.

bash/python

# Step 1: Install Mosquitto broker and client
sudo apt update
sudo apt install -y mosquitto mosquitto-clients python3-pip

# Step 2: Install Python MQTT client library
pip3 install paho-mqtt

# Step 3: Python script to subscribe and publish

import paho.mqtt.client as mqtt
import time

# Callback when a message is received
def on_message(client, userdata, msg):
    print(f"Received message: {msg.payload.decode()} on topic {msg.topic}")

client = mqtt.Client()
client.on_message = on_message
client.connect("localhost", 1883, 60)
client.subscribe("test/topic")
client.loop_start()

# Publish messages every 2 seconds
for i in range(3):
    message = f"Hello MQTT {i}"
    client.publish("test/topic", message)
    print(f"Published: {message}")
    time.sleep(2)

client.loop_stop()
client.disconnect()

Output

Published: Hello MQTT 0 Received message: Hello MQTT 0 on topic test/topic Published: Hello MQTT 1 Received message: Hello MQTT 1 on topic test/topic Published: Hello MQTT 2 Received message: Hello MQTT 2 on topic test/topic

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Common Pitfalls

Broker not running: Forgetting to start mosquitto causes connection errors.
Wrong broker address: Using incorrect IP or hostname prevents connection.
Not subscribing before publishing: Subscribers must be active to receive messages.
Firewall blocking port 1883: Ensure port 1883 is open for MQTT traffic.

bash/python

## Wrong way: Not starting broker
client.connect("localhost", 1883, 60)  # Fails if mosquitto not running

## Right way: Start broker first
sudo systemctl start mosquitto
client.connect("localhost", 1883, 60)  # Connects successfully

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Quick Reference

Command	Description
sudo apt install mosquitto mosquitto-clients	Install MQTT broker and clients
sudo systemctl start mosquitto	Start MQTT broker service
pip3 install paho-mqtt	Install Python MQTT client library
client.connect('broker', 1883, 60)	Connect Python client to broker
client.publish('topic', 'message')	Send message to topic
client.subscribe('topic')	Listen for messages on topic

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Key Takeaways

Install mosquitto broker and paho-mqtt client on Raspberry Pi to use MQTT.

Run the broker before connecting clients to avoid connection errors.

Use Python scripts with paho-mqtt to publish and subscribe messages easily.

Always subscribe before expecting to receive messages on a topic.

Check network and firewall settings to allow MQTT traffic on port 1883.