// Security System Project with Ultrasonic Sensor, LEDs, and Buzzer

const int trigPin = 2;   // Ultrasonic sensor trig pin
const int echoPin = 3;   // Ultrasonic sensor echo pin
const int redLEDPin = 7;  // Red LED pin
const int yellowLEDPin = 8; // Yellow LED pin
const int greenLEDPin = 9;  // Green LED pin
const int buzzerPin = 4;  // Buzzer pin

void setup() {
  Serial.begin(9600);    // Initialize serial communication for debugging
  pinMode(trigPin, OUTPUT); // Set Ultrasonic sensor trig pin as OUTPUT
  pinMode(echoPin, INPUT);  // Set Ultrasonic sensor echo pin as INPUT
  pinMode(redLEDPin, OUTPUT); // Set Red LED pin as OUTPUT
  pinMode(yellowLEDPin, OUTPUT); // Set Yellow LED pin as OUTPUT
  pinMode(greenLEDPin, OUTPUT); // Set Green LED pin as OUTPUT
  pinMode(buzzerPin, OUTPUT); // Set Buzzer pin as OUTPUT
}

void loop() {
  long duration, distance;

  // Trigger the Ultrasonic sensor
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Measure the duration of the echo pulse
  duration = pulseIn(echoPin, HIGH);

  // Calculate the distance in centimeters
  distance = duration * 0.034 / 2;

  // Print the distance to the Serial Monitor
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Check the distance and set security status
  if (distance < 50) {
    // Motion detected, set security status to ALERT
    digitalWrite(redLEDPin, HIGH);
    digitalWrite(yellowLEDPin, LOW);
    digitalWrite(greenLEDPin, LOW);
    digitalWrite(buzzerPin, HIGH);
  } else {
    // No motion, set security status to OK
    digitalWrite(redLEDPin, LOW);
    digitalWrite(yellowLEDPin, LOW);
    digitalWrite(greenLEDPin, HIGH);
    digitalWrite(buzzerPin, LOW);
  }

  // Wait for a short time before taking the next measurement
  delay(500);
}