paho-mqtt library usage in Raspberry Pi - Mini Project: Build & Apply

Basic MQTT Messaging with paho-mqtt on Raspberry Pi

📖 Scenario: You have a Raspberry Pi connected to a local network. You want to send and receive simple messages using MQTT, a lightweight messaging protocol often used in IoT projects.MQTT messages are sent to topics on a broker. Your Raspberry Pi will publish a message to a topic and also subscribe to the same topic to receive messages.

🎯 Goal: Build a simple Python program using the paho-mqtt library that connects to a public MQTT broker, publishes a message to a topic, and subscribes to the same topic to receive messages.

📋 What You'll Learn

Create a client using the paho-mqtt library

Connect to the public MQTT broker at test.mosquitto.org

Subscribe to the topic 'test/topic'

Publish the message 'Hello from Raspberry Pi!' to 'test/topic'

Print any messages received on 'test/topic'

💡 Why This Matters

🌍 Real World

MQTT is widely used in IoT devices like sensors and smart home gadgets to send data efficiently over networks.

💼 Career

Understanding MQTT and paho-mqtt is useful for roles in IoT development, embedded systems, and network programming.

1

Import paho-mqtt and create MQTT client

Import the paho.mqtt.client module as mqtt and create a client object called client using mqtt.Client().

Raspberry Pi

# Import paho-mqtt and create client
# Your code here

Need a hint?

Use import paho.mqtt.client as mqtt to import the library.

Create the client with mqtt.Client().

2

Connect to MQTT broker and subscribe to topic

Use the connect method on client to connect to the broker at 'test.mosquitto.org' on port 1883. Then subscribe to the topic 'test/topic' using client.subscribe('test/topic').

Raspberry Pi

import paho.mqtt.client as mqtt

client = mqtt.Client()
# Connect to broker and subscribe to 'test/topic'
# Your code here

Need a hint?

Use client.connect('test.mosquitto.org', 1883) to connect.

Use client.subscribe('test/topic') to subscribe.

3

Define message callback and publish message

Define a function on_message that takes parameters client, userdata, and msg. Inside it, print the topic and payload as a decoded string. Assign this function to client.on_message. Then publish the message 'Hello from Raspberry Pi!' to 'test/topic' using client.publish.

Raspberry Pi

import paho.mqtt.client as mqtt

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

# Define on_message callback and publish message
# Your code here

Need a hint?

Define on_message to print the topic and decoded payload.

Assign it to client.on_message.

Publish with client.publish('test/topic', 'Hello from Raspberry Pi!').

4

Start the MQTT client loop and print output

Start the MQTT client network loop with client.loop_start(). Then add a print statement that outputs exactly "MQTT client started and waiting for messages...".

Raspberry Pi

import paho.mqtt.client as mqtt

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

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

client.on_message = on_message
client.publish('test/topic', 'Hello from Raspberry Pi!')

# Start client loop and print status
# Your code here

Need a hint?

Use client.loop_start() to run the MQTT client in the background.

Print the status message exactly as shown.