//The active wire is connected to Normally Open and common
//****************************************************************************
int relayPin = 8;    // 5V relay module attached to digital pin D8 of Arduino Uno
int PIRInterrupt = 2;// PIR Motion Sensor attached to digital pin D2 of Arduino Uno
int LDRPin = A0;     // LDR pin attached to Analog pin A0 of Arduino Uno
int LDRReading;      // LDR value is stored on LDR reading
int LDRThreshold = 300;// LDR Threshold value
// Timer Variables:
long lastDebounceTime = 0;  
long debounceDelay = 10000;

volatile byte relayState = HIGH;

void setup() {
  Serial.begin(115200);// Initialize serial communication at 115200 bps
  pinMode(relayPin, OUTPUT);   // Set relayPin as output
  digitalWrite(relayPin, LOW);// By default set relayPin to HIGH
  pinMode(PIRInterrupt, INPUT);// PIR motion sensor set as an input
  // Triggers detectMotion function on rising mode to turn the relay on, if the condition is met
  attachInterrupt(digitalPinToInterrupt(PIRInterrupt), detectMotion, RISING); 
}

void loop() {
  // If 10 seconds have passed, the relay is turned off
  if((millis() - lastDebounceTime) > debounceDelay && relayState == LOW){
    digitalWrite(relayPin, LOW);
    relayState =HIGH;
    Serial.println("Lamp is OFF");    
  }
  delay(50);
}

void detectMotion() {
  Serial.println("Motion detected");
  LDRReading = analogRead(LDRPin);  
  Serial.print("Photocell reading = ");
  Serial.println(LDRReading); // LDR Reading value is printed on serial monitor - easy to get your LDRThreshold 
  if(LDRReading > LDRThreshold){// Only turns the Relay on if the LDR reading is higher than the LDRThreshold
    if(relayState == HIGH){
      digitalWrite(relayPin, HIGH);
    }
    relayState = LOW;  
    Serial.println("Lamp is ON");
    lastDebounceTime = millis();
  }
}