MQTT Communication

MQTT (Message Queue Telemetry Transport) is a protocol for machine-to-machine communication that is popular in IoT (Internet of Things) networks. The broker manages data transport from clients that publish or subscribe to updates. It was created around 1998 and has increased in popularity with the increase of IoT devices. It is especially good for ad hoc networking of devices that have varying levels of latency and communication bandwidth. MQTT typically runs over TCP/IP for bi-directional and lossless connections.

MQTT Broker (Server)

The MQTT broker can be in the cloud or hosted locally. The amqtt library is a lightweight Python option for hosting a broker locally.

pip install amqtt
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Create the MQTT broker with the following Python script. This script runs indefinitely to manage the publish/subscribe requests from clients.

Run MQTT Broker

import asyncio
import os
from amqtt.broker import Broker

config = {
    "listeners": {
        "default": {
            "type": "tcp",
            "bind": "0.0.0.0:1883",
        },
        "ws-mqtt": {
            "bind": "127.0.0.1:8080",
            "type": "ws",
            "max_connections": 10,
        },
    },
    "sys_interval": 10,
    "auth": {
        "allow-anonymous": True
    },
    "topic-check": {"enabled": False},
}

broker = Broker(config)

async def test_coro():
    await broker.start()

if __name__ == "__main__":
    asyncio.get_event_loop().run_until_complete(test_coro())
    asyncio.get_event_loop().run_forever()
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Another broker option is to download Eclipse Mosquitto or use the online MQTT broker.

MQTT Client with Local Broker

The paho-mqtt package is a popular Python MQTT client. Paho also provides MQTT client libraries for other languages as well. Install the Paho client with pip. Also install the tclab library to provide an Internet of Things (IoT) device or emulator.

pip install paho-mqtt
pip install tclab
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This example uses the amqtt local broker with the paho client. Use tclab.TCLab() if a TCLab physical device is connected. Otherwise, use the TCLab digital twin with tclab.TCLabModel().

Client to Publish Temperature to Local Broker

import paho.mqtt.client as mqtt
import time
import tclab

mqttBroker ='127.0.0.1'
client = mqtt.Client('TCLab')
client.connect(mqttBroker,port=8080)

with tclab.TCLabModel() as lab:
    lab.Q1(70) # set heater 1 to 70%
    # cycle 30 sec, publishing temperature
    for i in range(30):
        client.publish('T1', lab.T1)
        print('Published ' + str(round(lab.T1,2)))
        time.sleep(1)
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MQTT Client with Cloud Broker

This example uses the online MQTT broker provided by Eclipse Mosquitto from the Eclipse Foundation. It is an open-source message broker that can also be installed locally. There are also premium services such as Cedalo and Streamsheets for dashboarding. Test simple MQTT clients that publish and subscribe to the Eclipse Mosquitto public MQTT broker.

Client to Publish Temperature to Cloud Broker

import paho.mqtt.client as mqtt
import time
import tclab

mqttBroker ='mqtt.eclipseprojects.io'
client = mqtt.Client('TCLab')
client.connect(mqttBroker)

# use tclab.TCLab() if physical device connected
#   otherwise use digital twin tclab.TCLabModel()
with tclab.TCLabModel() as lab:
    lab.Q1(70) # set heater 1 to 70%
    # cycle 30 sec, publishing temperature
    for i in range(30):
        client.publish('T1', lab.T1)
        print('Published ' + str(round(lab.T1,2)))
        time.sleep(1)
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Client to Subscribe to Temperature through Cloud Broker

import paho.mqtt.client as mqtt
import struct

def on_message(client, userdata, msg):
    print(f'Temperature: {float(msg.payload)}')

mqttBroker ='mqtt.eclipseprojects.io'
client = mqtt.Client('IoT_Display')
client.on_message = on_message
client.connect(mqttBroker)
client.subscribe('T1')
client.loop_forever()
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✅ Knowledge Check

1: What does MQTT stand for?

A. Message Queue Text Transfer
Incorrect. MQTT stands for Message Queue Telemetry Transport, not Message Queue Text Transfer.
B. Message Queue Telemetry Transport
Correct. MQTT stands for Message Queue Telemetry Transport.
C. Message Quality Test Transfer
Incorrect. MQTT stands for Message Queue Telemetry Transport, not Message Quality Test Transfer.
D. Machine Queue Transfer Type
Incorrect. MQTT stands for Message Queue Telemetry Transport, not Machine Queue Transfer Type.

2: Which library can be used to host an MQTT broker locally in Python?

A. paho-mqtt
Incorrect. While paho-mqtt is a popular MQTT client library, it does not provide the ability to host an MQTT broker.
B. Eclipse Mosquitto
Incorrect. Eclipse Mosquitto is an open-source message broker, but it is not a Python library.
C. amqtt
Correct. The amqtt library is a lightweight Python option for hosting an MQTT broker locally.
D. tclab
Incorrect. tclab is a library for controlling the TCLab device and not for hosting an MQTT broker.
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