Phase 3 - ESP32 + WiFi MQTT Integration

📋 Topics Covered in Phase 3

1ESP32 MQTT connection setup

2Simple PubSubClient setup

3Relay control via MQTT topics

4Auto reconnection logic

5Multi-device architecture patterns

⚙️ Step 1: Arduino IDE Setup for ESP32

Add ESP32 Board Manager URL

Arduino IDE me ESP32 board support add karne ke liye:

# 1. Open Arduino IDE

# 2. Go to File → Preferences

# 3. Add this URL in "Additional Board Manager URLs":

https://dl.espressif.com/dl/package_esp32_index.json

Install ESP32 Board Package

# 1. Go to Tools → Board → Board Manager

# 2. Search for "ESP32"

# 3. Install "esp32 by Espressif Systems"

Install Required Libraries

MQTT communication ke liye PubSubClient library install karo:

# Go to Sketch → Include Library → Manage Libraries

# Search and install:

PubSubClient by Nick O'Leary

# Also install (for WiFi):

WiFi (built-in with ESP32 core)

⚠️

PubSubClient Configuration: Default MAX_PACKET_SIZE 128 bytes hai. Large payloads ke liye Header file me change karo:
#define MQTT_MAX_PACKET_SIZE 512

📶 Step 2: WiFi Connection Setup

Ye WiFi-only sketch Arduino IDE me direct compile/upload ho jayega. Current WiFi values already set hain.

// esp32-wifi-test.ino
#include <WiFi.h>

const char* WIFI_SSID = "Airtel_Yarana";
const char* WIFI_PASSWORD = "Abhishek@7052";
const int WIFI_LED = 2;
unsigned long lastWiFiRetry = 0;

void setup() {
  Serial.begin(115200);
  pinMode(WIFI_LED, OUTPUT);
  setupWiFi();
}

void loop() {
  if (WiFi.status() != WL_CONNECTED && millis() - lastWiFiRetry > 10000) {
    lastWiFiRetry = millis();
    Serial.println("WiFi disconnected. Connecting again...");
    setupWiFi();
  }
  delay(100);
}

void setupWiFi() {
  Serial.print("Connecting to WiFi: ");
  Serial.println(WIFI_SSID);
  digitalWrite(WIFI_LED, LOW);
  WiFi.mode(WIFI_STA);
  WiFi.disconnect();
  delay(500);
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);

  int attempts = 0;
  while (WiFi.status() != WL_CONNECTED && attempts < 30) {
    delay(500);
    Serial.print(".");
    attempts++;
  }

  if (WiFi.status() == WL_CONNECTED) {
    Serial.println();
    Serial.println("WiFi Connected!");
    Serial.print("IP Address: ");
    Serial.println(WiFi.localIP());
    digitalWrite(WIFI_LED, HIGH);
  } else {
    Serial.println();
    Serial.println("WiFi Connection Failed!");
  }
}
      
    

🔌 Step 3: MQTT Client Setup

ESP32 broker se connect hoga, command topic listen karega, aur received command ke according relay/status update karega.

        MQTT flow
        ESP32 WiFi se connect hone ke baad MQTT broker se connect hota hai.
ESP32 ek command topic subscribe karta hai.
Laptop/mobile app us topic par ON, OFF, TOGGLE ya STATUS message publish karta hai.
ESP32 command receive karke relay control karta hai aur status publish karta hai.

      

# Mac / MQTT broker IP

192.168.1.6

# ESP32 device IP from Serial Monitor

192.168.1.46

# MQTT commands me -h ke saath broker IP use hota hai

mosquitto_pub -h 192.168.1.6 -t "home/relay/esp32-001/command" -m "ON"

# Broker IP: laptop/server ka IP address

MQTT_BROKER = "192.168.1.6"

# Command topic: ESP32 isi topic ko listen karega

home/relay/esp32-001/command

# Status topic: ESP32 apna current status yahan publish karega

home/relay/esp32-001/status

Terminal 1: ESP32 status dekho

mosquitto_sub -h 192.168.1.6 -t "home/relay/esp32-001/#" -v

Terminal 2: ESP32 ko command bhejo

mosquitto_pub -h 192.168.1.6 -t "home/relay/esp32-001/command" -m "ON"

mosquitto_pub -h 192.168.1.6 -t "home/relay/esp32-001/command" -m "OFF"

mosquitto_pub -h 192.168.1.6 -t "home/relay/esp32-001/command" -m "TOGGLE"

mosquitto_pub -h 192.168.1.6 -t "home/relay/esp32-001/command" -m "STATUS"

💡

Result: ON command send karne par ESP32 Serial Monitor me received message dikhega. Terminal 1 me status/response publish hota hua dikhega.

📝 Step 4: Complete ESP32 MQTT Sketch

Complete working ESP32 sketch jisme WiFi + MQTT + Relay Control + Telemetry sab kuch hai:

// esp32-mqtt-relay-complete.ino
// Complete ESP32 MQTT Control with Relay

// ===========================================
// INCLUDES
// ===========================================
#include <WiFi.h>
#include <PubSubClient.h>

// ===========================================
// CONFIGURATION - CHANGE THESE!
// ===========================================

// WiFi
const char* WIFI_SSID     = "Airtel_Yarana";
const char* WIFI_PASSWORD = "Abhishek@7052";

// MQTT Broker
const char* MQTT_BROKER    = "192.168.1.6";
const int   MQTT_PORT        = 1883;
const char* MQTT_USER       = "";      // Leave empty if no auth
const char* MQTT_PASSWORD   = "";

// Device ID - MUST BE UNIQUE per device
const char* DEVICE_ID = "esp32-001";

// MQTT Topics
const char* TOPIC_CMD       = "home/relay/esp32-001/command";
const char* TOPIC_STATUS    = "home/relay/esp32-001/status";
const char* TOPIC_TELEMETRY = "home/relay/esp32-001/telemetry";
const char* TOPIC_RESPONSE  = "home/relay/esp32-001/response";

// Hardware Pins
const int RELAY_PIN = 26;      // Relay signal pin
const int LED_PIN   = 2;      // Built-in LED

// ===========================================
// GLOBAL OBJECTS
// ===========================================
WiFiClient espClient;
PubSubClient mqttClient(espClient);

// State variables
bool relayState = false;
unsigned long lastTelemetry = 0;
unsigned long lastWiFiRetry = 0;
const int TELEMETRY_INTERVAL = 30000;  // Send telemetry every 30 seconds

// ===========================================
// SETUP
// ===========================================
void setup() {
  Serial.begin(115200);
  Serial.println("ESP32 MQTT Relay Starting...");

  // Configure pins
  pinMode(RELAY_PIN, OUTPUT);
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(RELAY_PIN, LOW);  // Relay OFF at start
  digitalWrite(LED_PIN, LOW);

  // Connect to WiFi
  setupWiFi();

  // Setup MQTT
  mqttClient.setServer(MQTT_BROKER, MQTT_PORT);
  mqttClient.setCallback(mqttCallback);

  Serial.println("✅ Setup Complete!");
}

// ===========================================
// MAIN LOOP
// ===========================================
void loop() {
  if (WiFi.status() != WL_CONNECTED) {
    if (millis() - lastWiFiRetry > 10000) {
      lastWiFiRetry = millis();
      Serial.println("WiFi disconnected. Connecting again...");
      setupWiFi();
    }
    delay(100);
    return;
  }

  // Maintain MQTT connection
  if (!mqttClient.connected()) {
    reconnectMQTT();
  }
  mqttClient.loop();

  // Send telemetry periodically
  if (millis() - lastTelemetry > TELEMETRY_INTERVAL) {
    sendTelemetry();
    lastTelemetry = millis();
  }

  delay(10);  // Small delay to prevent watchdog
}

// ===========================================
// WiFi Setup
// ===========================================
void setupWiFi() {
  Serial.print("Connecting to WiFi: ");
  Serial.println(WIFI_SSID);

  WiFi.mode(WIFI_STA);
  WiFi.disconnect();
  delay(500);
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);

  int attempts = 0;
  while (WiFi.status() != WL_CONNECTED && attempts < 30) {
    delay(500);
    Serial.print(".");
    digitalWrite(LED_PIN, millis() % 1000 < 500 ? HIGH : LOW);
    attempts++;
  }

  if (WiFi.status() == WL_CONNECTED) {
    Serial.println();
    Serial.println("WiFi Connected!");
    Serial.printf("IP: %s\n", WiFi.localIP().toString().c_str());
    Serial.printf("RSSI: %d dBm\n", WiFi.RSSI());
    digitalWrite(LED_PIN, HIGH);  // LED ON when connected
  } else {
    Serial.println();
    Serial.println("WiFi Failed!");
  }
}

// ===========================================
// MQTT Reconnection
// ===========================================
void reconnectMQTT() {
  while (!mqttClient.connected()) {
    Serial.print("MQTT connecting...");

    // Create unique client ID
    char clientID[50];
    snprintf(clientID, sizeof(clientID), "%s-%d", DEVICE_ID, millis());

    // Connect with or without auth
    bool connected;
    if (strlen(MQTT_USER) > 0) {
      connected = mqttClient.connect(clientID, MQTT_USER, MQTT_PASSWORD);
    } else {
      connected = mqttClient.connect(clientID);
    }

    if (connected) {
      Serial.println(" Connected!");
      mqttClient.subscribe(TOPIC_CMD);
      Serial.printf("Subscribed: %s\n", TOPIC_CMD);

      // Publish online status (retained)
      mqttClient.publish(TOPIC_STATUS, "{\"state\":\"online\"}", true);
    } else {
      Serial.printf(" Failed (rc=%d)\n", mqttClient.state());
      delay(5000);
    }
  }
}

// ===========================================
// MQTT Message Handler
// ===========================================
void mqttCallback(char* topic, byte* payload, unsigned int length) {
  // Convert payload to string
  char msg[length + 1];
  memcpy(msg, payload, length);
  msg[length] = '\0';

  Serial.printf("[%s]: %s\n", topic, msg);

  // Parse command
  if (strcmp(msg, "ON") == 0) {
    relayState = true;
    digitalWrite(RELAY_PIN, HIGH);
    digitalWrite(LED_PIN, HIGH);
    Serial.println("Relay: ON");
    mqttClient.publish(TOPIC_RESPONSE, "{\"result\":\"ok\",\"relay\":\"on\"}");
    publishStatus();
  }
  else if (strcmp(msg, "OFF") == 0) {
    relayState = false;
    digitalWrite(RELAY_PIN, LOW);
    digitalWrite(LED_PIN, LOW);
    Serial.println("Relay: OFF");
    mqttClient.publish(TOPIC_RESPONSE, "{\"result\":\"ok\",\"relay\":\"off\"}");
    publishStatus();
  }
  else if (strcmp(msg, "TOGGLE") == 0) {
    relayState = !relayState;
    digitalWrite(RELAY_PIN, relayState ? HIGH : LOW);
    digitalWrite(LED_PIN, relayState ? HIGH : LOW);
    Serial.printf("Relay: %s\n", relayState ? "ON" : "OFF");
    char response[100];
    snprintf(response, sizeof(response),
      "{\"result\":\"ok\",\"relay\":\"%s\"}", relayState ? "on" : "off");
    mqttClient.publish(TOPIC_RESPONSE, response);
    publishStatus();
  }
  else if (strcmp(msg, "STATUS") == 0) {
    Serial.println("Status requested");
    publishStatus();
  }
}

// ===========================================
// Publish Device Status
// ===========================================
void publishStatus() {
  char payload[200];
  snprintf(payload, sizeof(payload),
    "{\"device\":\"%s\",\"relay\":%s,\"rssi\":%d,\"uptime\":%lu,\"ip\":\"%s\"}",
    DEVICE_ID,
    relayState ? "\"on\"" : "\"off\"",
    WiFi.RSSI(),
    millis() / 1000,
    WiFi.localIP().toString().c_str()
  );
  mqttClient.publish(TOPIC_STATUS, payload, true);
  Serial.printf("Status: %s\n", payload);
}

// ===========================================
// Send Telemetry Data
// ===========================================
void sendTelemetry() {
  char payload[200];
  snprintf(payload, sizeof(payload),
    "{\"device\":\"%s\",\"rssi\":%d,\"uptime\":%lu,\"freeheap\":%lu}",
    DEVICE_ID,
    WiFi.RSSI(),
    millis() / 1000,
    (unsigned long) ESP.getFreeHeap()
  );
  mqttClient.publish(TOPIC_TELEMETRY, payload);
  Serial.printf("Telemetry: %s\n", payload);
}
      

💡

Testing the ESP32:
1. Upload sketch to ESP32
2. Open Serial Monitor at 115200 baud
3. From another terminal: `mosquitto_pub -h 192.168.1.6 -t "home/relay/esp32-001/command" -m "ON"`
4. ESP32 will respond and relay will activate!

🏢 Step 5: Multi-Device Topic Pattern

Agar same project me multiple ESP32 devices hon, to har device ka ID aur topic unique rakha jata hai.

# Pattern

home/relay/DEVICE_ID/command

home/relay/DEVICE_ID/status

# Example device 1

home/relay/esp32-001/command

home/relay/esp32-001/status

# Example device 2

home/relay/esp32-002/command

home/relay/esp32-002/status

        Multiple ESP32 setup
        ESP32-001 ke code me DEVICE_ID = esp32-001 rakho.
ESP32-002 ke code me DEVICE_ID = esp32-002 rakho.
Dashboard ya terminal jis device ko control karega, usi device ke command topic par message publish karega.
Status dekhne ke liye same device ka status topic subscribe kiya jayega.

      

📋 Quick Test Commands

brew services start mosquitto

lsof -nP -iTCP:1883 -sTCP:LISTEN

nc -vz 192.168.1.6 1883

mosquitto_sub -h 192.168.1.6 -t "home/relay/esp32-001/#" -v

mosquitto_pub -h 192.168.1.6 -t "home/relay/esp32-001/command" -m "ON"

mosquitto_pub -h 192.168.1.6 -t "home/relay/esp32-001/command" -m "OFF"

mosquitto_pub -h 192.168.1.6 -t "home/relay/esp32-001/command" -m "TOGGLE"

mosquitto_pub -h 192.168.1.6 -t "home/relay/esp32-001/command" -m "STATUS"

# Serial Monitor output
WiFi Connected
IP Address: 192.168.1.46
MQTT Connected
Subscribed: home/relay/esp32-001/command
Message received: ON
Relay: ON
Status published: home/relay/esp32-001/status
      