#define TRIG 5
#define ECHO 18
#define ALERT_PIN 13 // LED or buzzer

float binHeight = 400.0;        // total bin height in cm
float alertThreshold = 80.0;   // alert when fill% > 80

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

  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);
  pinMode(ALERT_PIN, OUTPUT);
  digitalWrite(ALERT_PIN, LOW); // start with alert OFF
}

// Get distance from ultrasonic sensor
float getDistance() {
  digitalWrite(TRIG, LOW);
  delayMicroseconds(2);
  
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);

  long duration = pulseIn(ECHO, HIGH, 30000); // 30 ms timeout

  if (duration == 0) return binHeight; // no echo, assume empty

  float distance = duration * 0.0343 / 2; // convert to cm

  // Safety clamp
  if (distance > binHeight) distance = binHeight;
  if (distance < 0) distance = 0;

  return distance;
}

void loop() {
  float distance = getDistance();
  float fill = ((binHeight - distance) / binHeight) * 100.0;

  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.print(" cm | Fill: ");
  Serial.print(fill);
  Serial.println("%");

  // ALERT LOGIC
  if (fill >= alertThreshold) {
    Serial.println("ALERT! Bin is almost full!");
    digitalWrite(ALERT_PIN, HIGH); // LED ON / buzzer ON
  } else {
    digitalWrite(ALERT_PIN, LOW);  // LED OFF / buzzer OFF
  }

  delay(1000); // 1 second between measurements
}