const int trigPin = 2;    // Ultrasonic sensor trig pin
const int echoPin = 3;    // Ultrasonic sensor echo pin
const int ledPin = 13;    // LED pin

void setup() {
  Serial.begin(9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  long duration, distance;
  
  // Send ultrasonic pulse
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  // Measure the echo pulse
  duration = pulseIn(echoPin, HIGH);
  
  // Calculate distance
  distance = duration * 0.034 / 2;
  
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Turn on LED if distance is less than 20cm
  if (distance < 20) {  // Adjust this threshold as needed
    digitalWrite(ledPin, HIGH); // LED ON (lid closed)
  } else {
    digitalWrite(ledPin, LOW); // LED OFF (lid open)
  }

  delay(1000);  // Adjust delay as needed
}