14 Lab 3: MQTT Home Automation

14.1 Lab 3: MQTT Home Automation - Lights and Motion

Objective: Build a complete home automation system with motion detection and automated lighting control.

Materials:

• 2x ESP32 boards (one for motion sensor, one for light control)
• PIR motion sensor (HC-SR501)
• LED (or relay module for real lights)
• 220 ohm resistor
• Breadboard and wires

Circuit 1 - Motion Sensor (ESP32 #1):

PIR Sensor     ESP32
----------     -----
VCC    ------>  5V
OUT    ------>  GPIO 13
GND    ------>  GND

Circuit 2 - Light Control (ESP32 #2):

ESP32         LED
-----         ---
GPIO 2  ----> LED Anode (through 220 ohm resistor)
GND     ----> LED Cathode

Code for Motion Sensor (ESP32 #1):

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

const char* ssid = "YOUR_WIFI_SSID";
const char* password = "YOUR_WIFI_PASSWORD";
const char* mqtt_server = "test.mosquitto.org";

WiFiClient espClient;
PubSubClient client(espClient);

#define PIR_PIN 13
#define ROOM_ID "living_room"

char motion_topic[50];
char light_command_topic[50];

bool last_motion_state = false;
unsigned long motion_start_time = 0;
const unsigned long AUTO_OFF_DELAY = 30000; // 30 seconds

void setup() {
  Serial.begin(115200);
  pinMode(PIR_PIN, INPUT);

  sprintf(motion_topic, "home/%s/motion", ROOM_ID);
  sprintf(light_command_topic, "home/%s/light/command", ROOM_ID);

  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("\nWi-Fi connected");

  client.setServer(mqtt_server, 1883);
  reconnect();
}

void reconnect() {
  while (!client.connected()) {
    Serial.print("Connecting to MQTT...");
    if (client.connect("ESP32_MotionSensor")) {
      Serial.println(" Connected");
    } else {
      delay(5000);
    }
  }
}

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

  bool motion_detected = digitalRead(PIR_PIN) == HIGH;

  // Motion started
  if (motion_detected && !last_motion_state) {
    Serial.println("Motion detected!");
    client.publish(motion_topic, "true", true);

    // Turn on light
    client.publish(light_command_topic, "ON");
    motion_start_time = millis();
    last_motion_state = true;
  }

  // Motion stopped
  if (!motion_detected && last_motion_state) {
    Serial.println("   Motion cleared");
    client.publish(motion_topic, "false", true);
    last_motion_state = false;
  }

  // Auto turn off light after delay
  if (!motion_detected && (millis() - motion_start_time > AUTO_OFF_DELAY)) {
    client.publish(light_command_topic, "OFF");
    Serial.println("Auto turning off light");
    motion_start_time = millis() + 1000000; // Prevent repeated commands
  }

  delay(200);
}

Code for Light Control (ESP32 #2):

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

const char* ssid = "YOUR_WIFI_SSID";
const char* password = "YOUR_WIFI_PASSWORD";
const char* mqtt_server = "test.mosquitto.org";

WiFiClient espClient;
PubSubClient client(espClient);

#define LED_PIN 2
#define ROOM_ID "living_room"

char light_command_topic[50];
char light_state_topic[50];

void mqtt_callback(char* topic, byte* payload, unsigned int length) {
  String message = "";
  for (int i = 0; i < length; i++) {
    message += (char)payload[i];
  }

  Serial.print("Received command: ");
  Serial.println(message);

  if (message == "ON") {
    digitalWrite(LED_PIN, HIGH);
    client.publish(light_state_topic, "ON", true);
    Serial.println("Light turned ON");
  } else if (message == "OFF") {
    digitalWrite(LED_PIN, LOW);
    client.publish(light_state_topic, "OFF", true);
    Serial.println("Light turned OFF");
  }
}

void setup() {
  Serial.begin(115200);
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);

  sprintf(light_command_topic, "home/%s/light/command", ROOM_ID);
  sprintf(light_state_topic, "home/%s/light/state", ROOM_ID);

  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("\nWi-Fi connected");

  client.setServer(mqtt_server, 1883);
  client.setCallback(mqtt_callback);

  reconnect();
}

void reconnect() {
  while (!client.connected()) {
    Serial.print("Connecting to MQTT...");
    if (client.connect("ESP32_LightControl")) {
      Serial.println(" Connected");

      // Subscribe to light commands
      client.subscribe(light_command_topic);
      Serial.print("Subscribed to: ");
      Serial.println(light_command_topic);

      // Publish initial state
      client.publish(light_state_topic, "OFF", true);
    } else {
      delay(5000);
    }
  }
}

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

Expected Serial Output (Motion Sensor):

Wi-Fi connected
Connecting to MQTT... Connected
Motion detected!
   Motion cleared
Auto turning off light

Expected Serial Output (Light Control):

Wi-Fi connected
Connecting to MQTT... Connected
Subscribed to: home/living_room/light/command
Received command: ON
Light turned ON
Received command: OFF
Light turned OFF

Learning Outcomes:

Build the decision in sequence. Begin with Build multi-device MQTT communication. Then consider Implement automation logic with sensors and actuators. Then consider Use retained messages for state synchronization. Then consider Create topic naming conventions for home automation. Close by considering Handle timing and auto-off functionality.

Challenges:

Build the decision in sequence. Begin with Add manual control via MQTT (smartphone app or Node-RED). Then consider Implement brightness control with PWM. Then consider Add multiple rooms with independent control. Close by considering Create schedules (morning/evening modes).