// Define pin numbers for ultrasonic sensor
const int trigPin = 9;
const int echoPin = 10;

// Define pin numbers for buzzer and LED
const int buzzerPin = 8;
const int ledPin = 12;

// Variables to store duration and distance
long duration;
float distance;
const float thresholdDistance = 100.0; // Threshold in cm to trigger the alarm

void setup() {
  // Set up Serial Monitor for debugging
  Serial.begin(9600);

  // Initialize ultrasonic sensor pins
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  
  // Initialize LED and buzzer pins
  pinMode(buzzerPin, OUTPUT);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  // Send a trigger pulse to the ultrasonic sensor
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read the echo pin and calculate the duration
  duration = pulseIn(echoPin, HIGH);

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

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

  // If an object is within the threshold distance (person detected)
  if (distance < thresholdDistance && distance > 0) {
    // Turn on LED and buzzer
    digitalWrite(ledPin, HIGH);  // Turn ON LED
    digitalWrite(buzzerPin, HIGH);  // Turn ON buzzer
    tone(buzzerPin, 31);
  } else {
    // Turn off LED and buzzer
    digitalWrite(ledPin, LOW);  // Turn OFF LED
    digitalWrite(buzzerPin, LOW);  // Turn OFF buzzer
    noTone(buzzerPin);
  }

  // Delay before the next reading
  delay(1000);
}