paho-mqtt library usage in Raspberry Pi

Introduction

The paho-mqtt library helps your Raspberry Pi talk to other devices using MQTT, a simple messaging system. It lets your Pi send and receive messages easily.

You want your Raspberry Pi to send sensor data to a server or another device.

You want your Raspberry Pi to receive commands from a phone or computer.

You want to connect multiple Raspberry Pis or devices to share information.

You want a lightweight way to communicate over the internet or local network.

You want to build smart home projects that talk to each other.

Syntax

Raspberry Pi

import paho.mqtt.client as mqtt

# Create a client
client = mqtt.Client()

# Connect to broker
client.connect('broker_address', 1883)

# Publish a message
client.publish('topic/name', 'message')

# Subscribe to a topic
client.subscribe('topic/name')

# Start listening for messages
client.loop_start()

The 'broker_address' is the server that handles messages.

'topic/name' is like a channel where messages are sent and received.

Examples

This example connects to a public MQTT broker and sends a message to the 'home/livingroom' topic.

Raspberry Pi

import paho.mqtt.client as mqtt

client = mqtt.Client()
client.connect('test.mosquitto.org', 1883)
client.publish('home/livingroom', 'Hello from Raspberry Pi!')

This example listens for messages on 'home/livingroom' and prints them when received.

Raspberry Pi

import paho.mqtt.client as mqtt

def on_message(client, userdata, message):
    print(f"Received message: {message.payload.decode()} on topic {message.topic}")

client = mqtt.Client()
client.on_message = on_message
client.connect('test.mosquitto.org', 1883)
client.subscribe('home/livingroom')
client.loop_start()

Sample Program

This program connects to a public MQTT broker, subscribes to 'test/topic', sends a message to the same topic, and prints any received messages.

Raspberry Pi

import paho.mqtt.client as mqtt
import time

def on_message(client, userdata, message):
    print(f"Received message: {message.payload.decode()} on topic {message.topic}")

client = mqtt.Client()
client.on_message = on_message
client.connect('test.mosquitto.org', 1883)
client.subscribe('test/topic')
client.loop_start()

# Publish a message
client.publish('test/topic', 'Hello MQTT!')

# Wait to receive messages
time.sleep(2)

client.loop_stop()

Important Notes

Always call loop_start() or loop_forever() to process network events and receive messages.

MQTT topics are case-sensitive and hierarchical, like folders.

Use public brokers for testing, but for real projects, use a private broker for security.

Summary

paho-mqtt lets your Raspberry Pi send and receive messages using MQTT.

You connect to a broker, publish messages, and subscribe to topics to listen.

Use callbacks to handle incoming messages and keep the client running with loop methods.