Connecting Nodejs Backend with ESP32 via MQTT : A Step-by-Step Guide

MQTT (Message Queuing Telemetry Transport) is a lightweight messaging protocol ideal for the Internet of Things (IoT) due to its low bandwidth and fast, reliable communication. When combined with the ESP32 microcontroller, MQTT enables a wide range of applications requiring real-time updates.

This guide provides a clear, step-by-step process for connecting a Node.js backend with an ESP32 microcontroller using an MQTT broker. The example demonstrates how to set up a local Node.js server that communicates with an ESP32, sending and receiving data via MQTT. This setup is perfect for IoT applications, where devices need to exchange information seamlessly.

What You Need

• ESP32 Microcontroller
• MicroUSB to USB cable

Setting Up the MQTT Broker

We will use Mosquitto, a popular MQTT broker, for this example. You can set up Mosquitto locally or use a public broker like [test.mosquitto.org](https://test.mosquitto.org). Here are the steps to set up Mosquitto on your local machine.

Install Mosquitto

On Windows

1. Download the Mosquitto installer from the [Mosquitto website](https://mosquitto.org/download/).
2. Run the installer and follow the on-screen instructions.

On macOS

brew install mosquitto

Start the Mosquitto Broker

After installing Mosquitto, start the broker with the following command on the terminal

mosquitto

Node.js Backend Setup

Install Dependencies

Create a new directory for your project and initialize a new Node.js project

mkdir node-esp32-mqtt
cd node-esp32-mqtt
npm init -y
npm install mqtt express body-parser

Create ‘server.js’ File

Create a ‘server.js’ file with the following content

const mqtt = require('mqtt');
const express = require('express');
const bodyParser = require('body-parser');

const app = express();
const httpPort = 3000; 
const mqttClient = mqtt.connect({ host: 'test.mosquitto.org', port: 1883 });

app.use(bodyParser.json());


mqttClient.on('connect', () => {
    console.log('Connected to MQTT broker');
    mqttClient.subscribe('refrigerator/sensor1/temp');

    
    setInterval(() => {
        publishHardcodedData();
    }, 1000); 
});

mqttClient.on('message', (topic, message) => {
    console.log('Received message on topic', topic, ':', message.toString());
});

// Function to publish hardcoded data
function publishHardcodedData() {
    const hardcodedData = { "threshold": 25 };
    mqttClient.publish('refrigerator/config', JSON.stringify(hardcodedData), (err) => {
        if (err) {
            console.error('Failed to publish hardcoded data', err);
        } else {
            console.log('Hardcoded data published successfully');
        }
    });
}

// Start the server
app.listen(httpPort, () => {
    console.log(`Server is running on http://localhost:${httpPort}`);
});

This code sets up an MQTT client that connects to the MQTT broker and subscribes to all topics under ‘refrigerator/’. It also creates an HTTP endpoint ‘/publish’ to publish messages to specified MQTT topics.

ESP32 Setup

Next, we’ll set up the ESP32 to communicate with the MQTT broker.

Install Arduino Libraries

Ensure you have the following libraries installed in your Arduino IDE,

- WiFi
- PubSubClient
- ArduinoJson

ESP32 Code

Create a new sketch in the Arduino IDE and add the following code,

#include <WiFi.h>
#include <PubSubClient.h>
#include <ArduinoJson.h>

const char* ssid = "your_SSID";
const char* password = "your_PASSWORD";
const char* mqtt_server = "test.mosquitto.org";

WiFiClient espClient;
PubSubClient client(espClient);

void setup() {
    Serial.begin(115200);
    setup_wifi();
    client.setServer(mqtt_server, 1883);
    client.setCallback(callback);
}

void setup_wifi() {
    delay(10);
    Serial.println();
    Serial.print("Connecting to ");
    Serial.println(ssid);

    WiFi.begin(ssid, password);

    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial.print(".");
    }

    Serial.println("");
    Serial.println("WiFi connected");
    Serial.println("IP address: ");
    Serial.println(WiFi.localIP());
}

void callback(char* topic, byte* message, unsigned int length) {
    Serial.print("Message arrived [");
    Serial.print(topic);
    Serial.print("] ");
    for (unsigned int i = 0; i < length; i++) {
        Serial.print((char)message[i]);
    }
    Serial.println();
}

void reconnect() {
    while (!client.connected()) {
        Serial.print("Attempting MQTT connection...");
        String clientId = "ESP32Client-";
        clientId += String(random(0xffff), HEX); // Add a unique identifier to the client ID
        if (client.connect(clientId.c_str())) {
            Serial.println("connected");
            client.subscribe("refrigerator/config");
        } else {
            Serial.print("failed, rc=");
            Serial.print(client.state());
            Serial.println(" try again in 5 seconds");
            delay(5000);
        }
    }
}

void loop() {
    if (!client.connected()) {
        reconnect();
    }
    client.loop();

    // Publish temperature data
    StaticJsonDocument<200> doc;
    doc["temperature"] = random(20, 30);
    char buffer[256];
    serializeJson(doc, buffer);
    client.publish("refrigerator/sensor1/temp", buffer);

    delay(10000);
}

This code connects the ESP32 to the Wi-Fi network and the MQTT broker. It subscribes to the ‘refrigerator/config’ topic and publishes random temperature data to the ‘refrigerator/sensor1/temp’ topic every 10 seconds.

Running the Setup

Start the Node.js Server

Run the Node.js server by executing

node server.js

Your server should start and connect to the MQTT broker, displaying “Connected to MQTT broker” in the console.

Upload the Code to ESP32

Upload the ESP32 code to your ESP32 using the Arduino IDE. Open the Serial Monitor to check the connection status and messages being sent/received.

Happy Coding! Now you can play around.

For any projects involving MQTT, feel free to contact us; we can design and implement a custom system for your needs.

Protonest for more details.

Protonest specializes in transforming IoT ideas into reality. We offer prototyping services from concept to completion. Our commitment ensures that your visionary IoT concepts become tangible, innovative, and advanced prototypes.

Website: https://www.protonest.co/

Email: udara@protonest.co

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