// Define pins for the HC-SR04
const int trigPin = 13;
const int echoPin = 12;

// Define pin for the LED
const int ledPin = 11;

// Define distance threshold (in centimeters)
const int thresholdDistance = 100;

// Define variables
long duration;
int distance;

void setup() {
  // Start serial communication
  Serial.begin(9600);

  // Set pin modes
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  // Clear the trigger pin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  // Set the trigger pin HIGH for 10 microseconds
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

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

  // Calculate the distance
  distance = duration * 0.0344 / 2; // Speed of sound: 0.0344 cm/us, divided by 2 for the round-trip

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

  // Control the LED based on distance
  if (distance < thresholdDistance) {
    digitalWrite(ledPin, HIGH); // Turn LED ON
  } else {
    digitalWrite(ledPin, LOW);  // Turn LED OFF
  }

  // Wait before the next measurement
  delay(500);
}