int trigger = 4;
int echo = 5;
int ledPin = 13;        // LED as indicator (object detected)

int thresholdDistance = 15;   // cm (bin full / object near)

void setup() {
  Serial.begin(115200);

  pinMode(trigger, OUTPUT);
  pinMode(echo, INPUT);
  pinMode(ledPin, OUTPUT);

  Serial.println("Ultrasonic Object Detection System Started");
}

// Function to find distance
int finding_distance() {
  digitalWrite(trigger, LOW);
  delayMicroseconds(2);
  digitalWrite(trigger, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigger, LOW);

  long duration = pulseIn(echo, HIGH);
  int distance = duration * 0.034 / 2;

  return distance;
}

void loop() {

  int distance = finding_distance();

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

  // Object detection logic
  if (distance > 0 && distance <= thresholdDistance) {
    digitalWrite(ledPin, HIGH);
    Serial.println("Object Detected → LED ON");
  } else {
    digitalWrite(ledPin, LOW);
    Serial.println("No Object → LED OFF");
  }

  delay(500);
}