Multi-Channel Smart Home Automation System with Relays & Sensors

/*
 * Project: Smart Home Automation System with 4-Channel Relays
 * Author: ElectronLab STEM Curriculum
 */

const int RELAY_LIGHT = 4;
const int RELAY_FAN   = 5;
const int PIR_PIN     = 2;
const int LDR_PIN     = A0;

// Relays are typically Active-LOW (LOW = ON, HIGH = OFF)
#define RELAY_ON  LOW
#define RELAY_OFF HIGH

unsigned long motionOffTime = 0;
const unsigned long AUTO_OFF_DELAY = 10000; // 10 seconds timeout

void setup() {
  Serial.begin(9600);

  pinMode(RELAY_LIGHT, OUTPUT);
  pinMode(RELAY_FAN, OUTPUT);
  pinMode(PIR_PIN, INPUT);

  // Initialize all appliances to OFF
  digitalWrite(RELAY_LIGHT, RELAY_OFF);
  digitalWrite(RELAY_FAN, RELAY_OFF);

  Serial.println("Smart Home Controller Online!");
}

void loop() {
  int motionDetected = digitalRead(PIR_PIN);
  int lightLevel = analogRead(LDR_PIN); // Lower value = Darker room

  if (motionDetected == HIGH) {
    Serial.println("Motion in Room -> Turning Appliances ON");
    
    // Turn ON light only if it's dark
    if (lightLevel < 400) {
      digitalWrite(RELAY_LIGHT, RELAY_ON);
    }
    digitalWrite(RELAY_FAN, RELAY_ON);
    
    motionOffTime = millis() + AUTO_OFF_DELAY;
  }

  // Check if room has been vacant past delay timeout
  if (millis() > motionOffTime) {
    digitalWrite(RELAY_LIGHT, RELAY_OFF);
    digitalWrite(RELAY_FAN, RELAY_OFF);
  }

  delay(200);
}