Turning Your ESP32 into a MQTT Broker: A Hands-On Tutorial

This tutorial assumes a basic familiarity with electronics and programming microcontrollers like the ESP32.

Requirements

• ESP32 development board
• Micro-USB cable
• Computer with Arduino IDE installed
• Basic programming knowledge (especially in C++/Arduino)

Step 1: Setting Up Arduino IDE for ESP32

1. Install Arduino IDE: If you haven’t already, download and install the Arduino IDE from the official Arduino website.
2. Add ESP32 Board to Arduino IDE:
   • Open Arduino IDE, go to File > Preferences.
   • In the “Additional Board Manager URLs” field, add this URL: https://dl.espressif.com/dl/package_esp32_index.json
   • Click OK.
   • Go to Tools > Board > Boards Manager, search for ESP32, and install it.

Step 2: Connect Your ESP32

• Plug your ESP32 board into your computer using the Micro-USB cable.
• Select the correct board and port in Arduino IDE:
  • Go to Tools > Board and select your ESP32 model.
  • Go to Tools > Port and select the COM port your ESP32 is connected to.

Step 3: Install MQTT Broker Library

• In the Arduino IDE, go to Sketch > Include Library > Manage Libraries.
• Search for and install the uMQTTBroker library.

Step 4: Write the Code

1. Start a New Sketch: Go to File > New in the Arduino IDE to open a new sketch.
2. Include the Required Libraries:

#include <WiFi.h>
#include <uMQTTBroker.h>

3. Setup Wi-Fi Credentials:

const char* ssid = "yourSSID";
const char* password = "yourPASSWORD";

4. Initialize the Wi-Fi and MQTT Broker:

void setup() {
  Serial.begin(115200);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(100);
    Serial.print(".");
  }
  Serial.println("Connected to WiFi");

  // Start the MQTT Broker
  MQTT_server_start();
}

5. Handle Client Connections:

class MyBroker: public uMQTTBroker {
public:
  virtual bool onConnect(IPAddress addr, uint16_t client_count) {
    Serial.println(addr.toString() + " connected");
    return true;
  }

  virtual bool onAuth(String username, String password) {
    return true; // Allow all clients
  }

  virtual void onData(String topic, const char *data, uint32_t length) {
    char message[length + 1];
    memcpy(message, data, length);
    message[length] = '\0';
    Serial.println("Received message: " + String(message));
  }
} myBroker;

6. Main Loop:

void loop() {
  // MQTT broker loop
}

7. Upload the Code: Press the upload button in Arduino IDE.

Step 5: Test Your MQTT Server

1. Use an MQTT Client: You can use any MQTT client (like MQTTBox, Mosquitto client, etc.) to connect to the IP address of your ESP32.
2. Subscribe to a Topic: In your MQTT client, subscribe to a topic.
3. Publish to the Topic: Send messages to the topic from the MQTT client and observe the serial monitor of Arduino IDE for incoming messages.

Conclusion

This basic setup turns your ESP32 into a simple MQTT broker. Remember, the ESP32 is suitable for handling only a small number of clients and messages due to its limited resources. For more complex applications, consider using a dedicated MQTT broker.