// Define pins for the ultrasonic sensor and LED
const int trigPin = 12;
const int echoPin = 11;
const int ledPin = 2;

// Define variable to store the distance
long duration;
int distance;

// Define the distance threshold for detecting an object
const int thresholdDistance = 20; // in centimeters

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

  // Set the trigPin as an OUTPUT
  pinMode(trigPin, OUTPUT);

  // Set the echoPin as an INPUT
  pinMode(echoPin, INPUT);

  // Set the ledPin as an OUTPUT
  pinMode(ledPin, OUTPUT);
}

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

  // Set the trigPin on HIGH state for 10 microseconds
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read the echoPin and return the sound wave travel time in microseconds
  duration = pulseIn(echoPin, HIGH, 30000); // 30ms timeout (approx 510cm)

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

  // Print the duration and distance to the Serial Monitor for debugging
  Serial.print("Duration: ");
  Serial.print(duration);
  Serial.print(" us | Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Check if the distance is less than the threshold
  if (distance < thresholdDistance) {
    // Turn the LED on
    digitalWrite(ledPin, HIGH);
  } else {
    // Turn the LED off
    digitalWrite(ledPin, LOW);
  }

  // Add a delay before the next measurement
  delay(500);
}