Random Nerd Tutorials

MicroPython – Getting Started with MQTT on ESP32/ESP8266


In this tutorial, we’ll show you how to use MQTT to exchange data between two ESP32/ESP8266 boards using MicroPython firmware. As an example, we’ll exchange simple text messages between two ESP boards. The idea is to use the concepts learned here to exchange sensor readings, or commands.

MicroPython Getting Started with MQTT on ESP32/ESP8266

Note: this tutorial is compatible with both the ESP32 and ESP8266 development boards. 


Before continuing with this tutorial, make sure you complete the following prerequisites:

MicroPython firmware

To program the ESP32 and ESP8266 with MicroPython, we use uPyCraft IDE as a programming environment. Follow the next tutorials to install uPyCraft IDE and flash MicroPython firmware on your board:

MQTT Broker

To use MQTT, you need a broker. We’ll be using Mosquitto broker installed on a Raspberry Pi. Read How to Install Mosquitto Broker on Raspberry Pi.

If you’re not familiar with MQTT make sure you read our introductory tutorial: What is MQTT and How It Works

Parts Required

For this tutorial you need two ESP32 or two ESP8266 boards:

You also need a Raspberry Pi and the following accessories:

You can use the preceding links or go directly to MakerAdvisor.com/tools to find all the parts for your projects at the best price!

Project Overview

Here’s a high-level overview of the project we’ll build:


  • ESP#1 publishes messages on the hello topic. It publishes a “Hello” message followed by a counter (Hello 1, Hello 2, Hello 3, …). It publishes a new message every 5 seconds.
  • ESP#1 is subscribed to the notification topic to receive notifications from the ESP#2 board.
  • ESP#2 is subscribed to the hello topic. ESP #1 is publishing in this topic. Therefore, ESP#2 receives ESP#1 messages.
  • When ESP#2 receives the messages, it sends a message saying ‘received’. This message is published on the notification topic. ESP#1 is subscribed to that topic, so it receives the message.

Preparing ESP#1

Let’s start by preparing ESP#1:

  • It is subscribed to the notification topic
  • It publishes on the hello topic

Importing umqtttsimple library

To use MQTT with the ESP32/ESP8266 and MicroPython, you need to install the umqttsimple library.

1. Create a new file by pressing the New File button.

2. Copy the umqttsimple library code into it. You can access the umqttsimple library code in the following link:

3. Save the file by pressing the Save button.

4. Call this new file “umqttsimple.py” and press ok.

5. Click the Download and Run button.

6. The file should be saved on the device folder with the name “umqttsimple.py” as highlighted in the figure below.

Now, you can use the library functionalities in your code by importing the library.


Open the boot.py file and copy the following code to ESP#1.

How the Code Works

You need to import all the following libraries:

import time
from umqttsimple import MQTTClient
import ubinascii
import machine
import micropython
import network
import esp

Set the debug to None and activate the garbage collector.

import gc

In the following variables, you need to enter your network credentials and your broker IP address.


For example, our broker IP address is:

Note: read this tutorial to see how to get your broker IP address:

To create an MQTT client, we need to get the ESP unique ID. That’s what we do in the following line (it is saved on the client_id variable).

client_id = ubinascii.hexlify(machine.unique_id())

Next, write the topic the ESP#1 is subscribed to, and the topic it will be publishing messages:

topic_sub = b'notification'
topic_pub = b'hello'

Then, create the following variables:

last_message = 0
message_interval = 5
counter = 0

The last_message variable will hold the last time a message was sent. The message_interval is the time between each message sent. Here, we’re setting it to 5 seconds (this means a new message will be sent every 5 seconds). The counter variable is simply a counter to be added to the message.

After that, we make the procedures to connect to the network.

station = network.WLAN(network.STA_IF)

station.connect(ssid, password)

while station.isconnected() == False:

print('Connection successful')


In the main.py file is where we’ll write the code to publish and receive the messages. Copy the following code to your main.py file.

How the code works

The first thing you should do is creating a callback function that will run whenever a message is published on a topic the ESP is subscribed to.

Callback function

The callback function should accept as parameters the topic and the message.

def sub_cb(topic, msg):
  print((topic, msg))
  if topic == b'notification' and msg == b'received':
    print('ESP received hello message')

In our callback function, we start by printing the topic and the message. Then, we check if the message was published on the notification topic, and if the content of the message is ‘received’. If this if statement is True, it means that ESP#2 received the ‘hello’ message sent by ESP#1.

Basically, this callback function handles what happens when a certain message is received on a certain topic.

Connect and subscribe

Then, we have the connect_and_subscribe() function. This function is responsible for connecting to the broker as well as to subscribe to a topic.

def connect_and_subscribe():

Start by declaring the client_id, mqtt_server and topic_sub variables as global variables. This way, we can access these variables throughout the code.

global client_id, mqtt_server, topic_sub

Then, create a MQTTClient object called client. We need to pass as parameters the cliend_id, and the IP address of the MQTT broker (mqtt_server). These variables were set previously on the boot.py file.

client = MQTTClient(client_id, mqtt_server)

After that, set the callback function to the client (sub_cb).


Next, connect the client to the broker using the connect() method on the MQTTClient object.


After connecting, we subscribe to the topic_sub topic. Set the topic_sub on the boot.py file (notification).


Finally, print a message and return the client:

print('Connected to %s MQTT broker, subscribed to %s topic' % (mqtt_server, topic_sub))
return client

Restart and reconnect

We create a function called restart_and_reconnect(). This function will be called in case the ESP32 or ESP8266 fails to connect to the broker.

This function prints a message to inform that the connection was not successful. We wait 10 seconds. Then, we reset the ESP using the reset() method.

def restart_and_reconnect():
  print('Failed to connect to MQTT broker. Reconnecting...')

Receive and publish messages

Until now, we’ve created functions to handle tasks related with the MQTT communication. From now on, the code will call those functions to make things happen.

The first thing we need to do is to connect to the MQTT broker and subscribe to a topic. So, we create a client by calling the connect_and_subscribe() function.

  client = connect_and_subscribe()

In case we’re not able to connect to the MQTTT broker, we’ll restart the ESP by calling the restart_and_reconnect() function

except OSError as e:

In the while loop is where we’ll be receiving and publishing the messages. We use try and except statements to prevent the ESP from crashing in case something goes wrong.

Inside the try block, we start by applying the check_msg() method on the client.


The check_msg() method checks whether a pending message from the server is available. It waits for a single incoming MQTT message and process it. The subscribed messages are delivered to the callback function we’ve defined earlier (the sub_cb() function). If there isn’t a pending message, it returns with None.

Then, we add an if statement to checker whether 5 seconds (message_interval) have passed since the last message was sent.

if (time.time() - last_message) > message_interval:

If it is time to send a new message, we create a msg variable with the “Hello” text followed by a counter.

msg = b'Hello #%d' % counter

To publish a message on a certain topic, you just need to apply the publish() method on the client and pass as arguments, the topic and the message. The topic_pub variable was set to hello in the boot.py file.

client.publish(topic_pub, msg)

After sending the message, we update the last time a message was received by setting the last_message variable to the current time.

last_message = time.time()

Finally, we increase the counter variable in every loop.

counter += 1

If something unexpected happens, we call the restart_and_reconnect() function.

except OSError as e:

That’s it for ESP#1. Remember that you need to upload all the next files to make the project work (you should upload the files in order):

  1. umqttsimple.py;
  2. boot.py;
  3. main.py.

After uploading all files, you should get success messages on: establishing a network connection; connecting to the broker; and subscribing to the topic.

ESP #2

Let’s now prepare ESP#2:

  • It is subscribed to the hello topic
  • It publishes on the notification topic

Like the ESP#1, you also need to upload the umqttsimple.py, boot.py, and main.py files.

Importing umqttsimple

To use MQTT with the ESP32/ESP8266 and MicroPython, you need to install the umqttsimple library. Follow the steps described earlier to install the umqttsimple library in ESP#2.

You can access the umqttsimple library code in the following link:


Copy the following code to the ESP#2 boot.py file.

This code is very similar with the previous boot.py file. You need to replace the following variables with your network credentials and the broker IP address.


The only difference here is that we subscribe to the hello topic and publish on the notification topic.

topic_sub = b'hello'
topic_pub = b'notification'


Copy the following code to the ESP#2 main.py file.

This code is very similar with the main.py from ESP#1. We create the sub_cb(), the connect_and_subscribe() and the restart_and_reconnect() functions. This time, the sub_cb() function just prints information about the topic and received message.

def sub_cb(topic, msg):
  print((topic, msg))

In the while loop, we check if we got a new message and save it in the new_message variable.

new_message = client.check_msg()

If we receive a new message, we publish a message saying ‘received’ on the topic_sub topic (in this case we set it to notification in the boot.py file).

if new_message != 'None':
  client.publish(topic_pub, b'received')

That’s it for ESP#2. Remember that you need to upload all the next files to make the project work (you should upload the files in order):

  1. umqttsimple.py;
  2. boot.py;
  3. main.py.

The ESP32/ESP8266 should establish a network connection and connect to the broker successfully.


After uploading all the necessary scripts to both ESP boards and having both boards and the Raspberry Pi with the Mosquitto broker running, you are ready to test the setup.

The ESP#2 should be receiving the “Hello” messages from ESP#1, as shown in the figure below.

On the other side, ESP#1 board should receive the “received” message. The “received” message is published by ESP#2 on the notification topic. ESP#1 is subscribed to that topic, so it receives the message.

Wrapping Up

In this simple example, you’ve learned how to exchange text between two ESP32/ESP8266 boards using MQTT communication protocol. The idea is to use the concepts learned here to exchange useful data like sensor readings or commands to control outputs.

If you like MicroPython with the ESP32/ESP8266, you may also like:

Learn ESP32 with Arduino IDE

This is our complete guide to program the ESP32 with Arduino IDE, including projects, tips, and tricks! The registrations are open, so SIGN UP NOW »

Recommended Resources

Home Automation using ESP8266 »
Build IoT projects and home automation gadgets with the ESP8266 Wi-Fi module.

Build a Home Automation System »
Learn how to build a automation system using open-source hardware and software from scratch.

Arduino Step-by-Step Projects »
Build 25 cool Arduino projects with our course even with no prior experience!

Leave a Comment:

Add Your Reply

Enroll in our Electronics and Programming Courses:

ESP32, ESP8266, Arduino and much more.