ESP8266 Publishing DHT22 Readings with MQTT to Raspberry Pi

In this project you’ll create a standalone web server with a Raspberry Pi that displays temperature and humidity readings with a DHT22 sensor. You can also control two outputs from an ESP8266 using MQTT protocol.

In order to create the web server you will be using a Python microframework called Flask. Here’s the high level overview of the system:

Recommended resources:

Basic Raspberry Pi Setup

Before you continue reading this project, please make sure you have Raspbian Operating System installed in your Raspberry Pi.

You can read my Getting Started with the Raspberry Pi Guide to install Raspbian and complete the basic setup.

Run and install Mosquitto broker

The Raspberry Pi is going to interact with the ESP8266 with the MQTT protocol. Having Mosquitto broker installed, you need to have Mosquitto broker running on the background:

pi@raspberry:~ $ mosquitto -d

Installing Flask

We’re going to use a Python microframework called Flask to turn the Raspberry Pi into web server.

To install Flask, you’ll need to have pip installed. Run the following commands to update your Pi and install pip:

pi@raspberrypi ~ $ sudo apt-get update
pi@raspberrypi ~ $ sudo apt-get upgrade
pi@raspberrypi ~ $ sudo apt-get install python-pip python-flask git-core

Then, you use pip to install Flask and Paho MQTT:

pi@raspberrypi ~ $ sudo pip install flask
pi@raspberrypi ~ $ sudo pip install paho-mqtt

Installing SocketIO

This project uses SocketIO which allows you to create a Python Flask web page that can be asynchronously updated by your Python Flask application. This means that you don’t need to refresh the web page to see the latest readings, they are instantly updated. You’ll be installing the Flask SocketIO Python package.

pi@raspberrypi ~ $ sudo pip install flask-socketio

Creating the Python Script

This is the core script of our application. It sets up the web server and when these buttons are pressed it publishes an MQTT message to the ESP8266. It’s also subscribed to temperature and humidity MQTT topics to receive the readings.

To keep everything organized, start by creating a new folder:

pi@raspberrypi ~ $ mkdir web-server
pi@raspberrypi ~ $ cd web-server
pi@raspberrypi:~/web-server $

Create a new file called

pi@raspberrypi:~/web-server $ nano

Copy and paste the following script to your Raspberry Pi

# Created by Gnd_To_Vcc

import paho.mqtt.client as mqtt
from flask import Flask, render_template, request
from flask_socketio import SocketIO, emit

app = Flask(__name__)
app.config['SECRET_KEY'] = 'secret!'
socketio = SocketIO(app)

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))

    # Subscribing in on_connect() means that if we lose the connection and
    # reconnect then subscriptions will be renewed.

# The callback for when a PUBLISH message is received from the ESP8266.
def on_message(client, userdata, message):
    #socketio.emit('my variable')
    print("Received message '" + str(message.payload) + "' on topic '"
        + message.topic + "' with QoS " + str(message.qos))
    if message.topic == "/esp8266/temperature":
        print("temperature update")
	socketio.emit('dht_temperature', {'data': message.payload})
    if message.topic == "/esp8266/humidity":
        print("humidity update")
	socketio.emit('dht_humidity', {'data': message.payload})

mqttc.on_connect = on_connect
mqttc.on_message = on_message

# Create a dictionary called pins to store the pin number, name, and pin state:
pins = {
   4 : {'name' : 'GPIO 4', 'board' : 'esp8266', 'topic' : 'esp8266/4', 'state' : 'False'},
   5 : {'name' : 'GPIO 5', 'board' : 'esp8266', 'topic' : 'esp8266/5', 'state' : 'False'}

# Put the pin dictionary into the template data dictionary:
templateData = {
   'pins' : pins

def main():
   # Pass the template data into the template main.html and return it to the user
   return render_template('main.html', async_mode=socketio.async_mode, **templateData)

# The function below is executed when someone requests a URL with the pin number and action in it:
def action(board, changePin, action):
   # Convert the pin from the URL into an integer:
   changePin = int(changePin)
   # Get the device name for the pin being changed:
   devicePin = pins[changePin]['name']
   # If the action part of the URL is "1" execute the code indented below:
   if action == "1" and board == 'esp8266':
      pins[changePin]['state'] = 'True'
   if action == "0" and board == 'esp8266':
      pins[changePin]['state'] = 'False'
   # Along with the pin dictionary, put the message into the template data dictionary:
   templateData = {
      'pins' : pins
   return render_template('main.html', **templateData)

@socketio.on('my event')
def handle_my_custom_event(json):
    print('received json data here: ' + str(json))

if __name__ == "__main__":, host='', port=8181, debug=True)

Creating the HTML File

 Keeping HTML tags separated from your Python script is how you keep your project organized.Flask uses a template engine called Jinja2 that you can use to send dynamic data from your Python script to your HTML file.

Create a new folder called templates:

pi@raspberrypi:~/web-server $ mkdir templates
pi@raspberrypi:~/web-server $ cd templates
pi@raspberrypi:~/web-server/templates $

Create a new file called main.html.

pi@raspberrypi:~/web-server/templates $ nano main.html

Copy and paste the following template to your Pi:

<!DOCTYPE html>
   <title>RPi Web Server</title>
   <!-- Latest compiled and minified CSS -->
   <link rel="stylesheet" href="" integrity="sha384-1q8mTJOASx8j1Au+a5WDVnPi2lkFfwwEAa8hDDdjZlpLegxhjVME1fgjWPGmkzs7" crossorigin="anonymous">
   <!-- Optional theme -->
   <link rel="stylesheet" href="" integrity="sha384-fLW2N01lMqjakBkx3l/M9EahuwpSfeNvV63J5ezn3uZzapT0u7EYsXMjQV+0En5r" crossorigin="anonymous">
   <!-- Latest compiled and minified JavaScript -->
   <script src="" integrity="sha384-0mSbJDEHialfmuBBQP6A4Qrprq5OVfW37PRR3j5ELqxss1yVqOtnepnHVP9aJ7xS" crossorigin="anonymous"></script>
   <script src="" integrity="sha256-hVVnYaiADRTO2PzUGmuLJr8BLUSjGIZsDYGmIJLv2b8=" crossorigin="anonymous"></script>
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <script type="text/javascript" src="//"></script>
   <script type="text/javascript" charset="utf-8">
      $(document).ready(function() {
      	var socket = io.connect('http://' + document.domain + ':' + location.port);
      	socket.on('connect', function() {
          socket.emit('my event', {data: 'I\'m connected!'});
      	socket.on('dht_temperature', function(msg) {
	  var nDate = new Date();
          $('#readingsUpdated').text(nDate.getHours() + 'h:' + nDate.getMinutes() +
             'm:' + nDate.getSeconds() + 's').html();
      	socket.on('dht_humidity', function(msg) {

   <h1>RPi Web Server - ESP8266 MQTT</h1>
   {% for pin in pins %}
   <h2>{{ pins[pin].name }}
   {% if pins[pin].state == 'True' %}
      is currently <strong>on</strong></h2><div class="row"><div class="col-md-2">
      <a href="/esp8266/{{pin}}/0" class="btn btn-block btn-lg btn-default" role="button">Turn off</a></div></div>
   {% else %}
      is currently <strong>off</strong></h2><div class="row"><div class="col-md-2">
      <a href="/esp8266/{{pin}}/1" class="btn btn-block btn-lg btn-primary" role="button">Turn on</a></div></div>
   {% endif %}
   {% endfor %}
   <h3>DHT Readings (updated <span id="readingsUpdated"></span>)</h3>
   <h3>Temperature: <span id="temperature"></span>ºC</h3>
   <h3>Humidity: <span id="humidity"></span>%</h3>

Programming the ESP8266

For the ESP8266 to interact with the Raspberry Pi web server, you need to install PubSubClient library. This library provides a client for doing simple publish/subscribe messaging with a server that supports MQTT (basically allows your ESP8266 to talk with Python web server).

Installing the PubSubClient library

1) Click here to download the PubSubClient library. You should have a .zip folder in your Downloads folder

2) Unzip the .zip folder and you should get pubsubclient-master folder

3) Rename your folder from pubsubclient-master to pubsubclient

4) Move the pubsubclient folder to your Arduino IDE installation libraries folder

The library comes with a number of example sketches. See File > Examples > PubSubClient within the Arduino IDE software.

Installing the DHT sensor library

The DHT sensor library provides an easy way of using any DHT sensor to read temperature and humidity with your ESP8266 or Arduino boards.

1) Click here to download the DHT sensor library. You should have a .zip folder in your Downloads folder

2) Unzip the .zip folder and you should get DHT-sensor-library-master folder

3) Rename your folder from DHT-sensor-library-master to DHT

4) Move the DHT folder to your Arduino IDE installation libraries folder

5) Then, re-open your Arduino IDE

Uploading sketch

Finally, you can upload the full sketch to your ESP8266 (replace with your SSID, password and RPi IP address):

 All the resources for this project:


// Loading the ESP8266WiFi library and the PubSubClient library
#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include "DHT.h"

// Uncomment one of the lines bellow for whatever DHT sensor type you're using!
//#define DHTTYPE DHT11   // DHT 11
//#define DHTTYPE DHT21   // DHT 21 (AM2301)
#define DHTTYPE DHT22   // DHT 22  (AM2302), AM2321

// Change the credentials below, so your ESP8266 connects to your router
const char* ssid = "YOUR_SSID";
const char* password = "YOUR_PASSWORD";

// Change the variable to your Raspberry Pi IP address, so it connects to your MQTT broker
const char* mqtt_server = "YOUR_RPi_IP_Address";

// Initializes the espClient
WiFiClient espClient;
PubSubClient client(espClient);

// Connect an LED to each GPIO of your ESP8266
const int ledGPIO5 = 5;
const int ledGPIO4 = 4;

// DHT Sensor
const int DHTPin = 14;

// Initialize DHT sensor.

// Timers auxiliar variables
long now = millis();
long lastMeasure = 0;

// Don't change the function below. This functions connects your ESP8266 to your router
void setup_wifi() {
  // We start by connecting to a WiFi network
  Serial.print("Connecting to ");
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
  Serial.print("WiFi connected - ESP IP address: ");

// This functions is executed when some device publishes a message to a topic that your ESP8266 is subscribed to
// Change the function below to add logic to your program, so when a device publishes a message to a topic that 
// your ESP8266 is subscribed you can actually do something
void callback(String topic, byte* message, unsigned int length) {
  Serial.print("Message arrived on topic: ");
  Serial.print(". Message: ");
  String messageTemp;
  for (int i = 0; i < length; i++) {
    messageTemp += (char)message[i];

  // Feel free to add more if statements to control more GPIOs with MQTT

  // If a message is received on the topic home/office/esp1/gpio2, you check if the message is either 1 or 0. Turns the ESP GPIO according to the message
      Serial.print("Changing GPIO 4 to ");
      if(messageTemp == "1"){
        digitalWrite(ledGPIO4, HIGH);
      else if(messageTemp == "0"){
        digitalWrite(ledGPIO4, LOW);
      Serial.print("Changing GPIO 5 to ");
      if(messageTemp == "1"){
        digitalWrite(ledGPIO5, HIGH);
      else if(messageTemp == "0"){
        digitalWrite(ledGPIO5, LOW);

// This functions reconnects your ESP8266 to your MQTT broker
// Change the function below if you want to subscribe to more topics with your ESP8266 
void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
     To change the ESP device ID, you will have to give a unique name to the ESP8266.
     Here's how it looks like now:
       if (client.connect("ESP8266Client")) {
     If you want more devices connected to the MQTT broker, you can do it like this:
       if (client.connect("ESPOffice")) {
     Then, for the other ESP:
       if (client.connect("ESPGarage")) {
      That should solve your MQTT multiple connections problem

     THE SECTION IN loop() function should match your device name
    if (client.connect("ESP8266Client")) {
      // Subscribe or resubscribe to a topic
      // You can subscribe to more topics (to control more LEDs in this example)
    } else {
      Serial.print("failed, rc=");
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying

// The setup function sets your ESP GPIOs to Outputs, starts the serial communication at a baud rate of 115200
// Sets your mqtt broker and sets the callback function
// The callback function is what receives messages and actually controls the LEDs
void setup() {
  pinMode(ledGPIO4, OUTPUT);
  pinMode(ledGPIO5, OUTPUT);
  client.setServer(mqtt_server, 1883);

// For this project, you don't need to change anything in the loop function. 
// Basically it ensures that you ESP is connected to your broker
void loop() {
  if (!client.connected()) {
     To change the ESP device ID, you will have to give a unique name to the ESP8266.
     Here's how it looks like now:
     If you want more devices connected to the MQTT broker, you can do it like this:
     Then, for the other ESP:
      That should solve your MQTT multiple connections problem

     THE SECTION IN recionnect() function should match your device name
  now = millis();
  // Publishes new temperature and humidity every 10 seconds
  if (now - lastMeasure > 10000) {
    lastMeasure = now;
    // Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
    float h = dht.readHumidity();
    // Read temperature as Celsius (the default)
    float t = dht.readTemperature();
    // Read temperature as Fahrenheit (isFahrenheit = true)
    float f = dht.readTemperature(true);

    // Check if any reads failed and exit early (to try again).
    if (isnan(h) || isnan(t) || isnan(f)) {
      Serial.println("Failed to read from DHT sensor!");

    // Computes temperature values in Celsius
    float hic = dht.computeHeatIndex(t, h, false);
    static char temperatureTemp[7];
    dtostrf(hic, 6, 2, temperatureTemp);
    // Uncomment to compute temperature values in Fahrenheit 
    // float hif = dht.computeHeatIndex(f, h);
    // static char temperatureTemp[7];
    // dtostrf(hic, 6, 2, temperatureTemp);
    static char humidityTemp[7];
    dtostrf(h, 6, 2, humidityTemp);

    // Publishes Temperature and Humidity values
    client.publish("/esp8266/temperature", temperatureTemp);
    client.publish("/esp8266/humidity", humidityTemp);
    Serial.print("Humidity: ");
    Serial.print(" %\t Temperature: ");
    Serial.print(" *C ");
    Serial.print(" *F\t Heat index: ");
    Serial.println(" *C ");
    // Serial.print(hif);
    // Serial.println(" *F");


To complete this project you need these next components:

  • 1x ESP8266 12E – read Best ESP8266 Wi-Fi Development Boards
  • 1x DHT22 Sensor 
  • 1x 4700 Ohm Resistor
  • 2x 470 Ohm resistors
  • 2x LEDs

Note: other DHT sensor types will also work with a small change in the code.

Here’s the schematics:

Important: the DHT sensor requires 5V to operate properly, so make sure you use the Vin pin from your ESP8266 that outputs 5V.

Launching the Web Server

To launch your Raspberry Pi web server move to the folder that contains the file

pi@raspberrypi:~/web-server/templates $ cd ..

Then, run the following command:

pi@raspberrypi:~/web-server $ sudo python

Your web server should start immediately on port :8181!


Open your Raspberry Pi address in your browser by entering its IP address, in my case:

Note: you must enter your IP address followed by :8181

Wrapping up

In the next blog post, we will publish sensor readings with the ESP8266 to the Python web server, but those readings are going to be stored in an SQLite database.

Thanks for reading.

Published by Gnd_To_Vcc

Here to spread my knowledge . Knowledge should always be spread not stored.

5 thoughts on “ESP8266 Publishing DHT22 Readings with MQTT to Raspberry Pi

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