#define ECHO_PIN 2
#define TRIG_PIN 3
#define BUZZER_PIN 4
#define LED_PIN 13 // Assuming the built-in LED is connected to pin 13
#define DISTANCE_THRESHOLD 20

void setup() {
  Serial.begin(115200);
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
}

float readDistanceCM() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  int duration = pulseIn(ECHO_PIN, HIGH);
  return duration * 0.034 / 2;
}

void loop() {
  float distance = readDistanceCM();

  bool isNearby = distance < DISTANCE_THRESHOLD;
  digitalWrite(LED_PIN, isNearby);

  static bool wasNearby = false; // Variable to track previous state

  if (isNearby) {
    // Turn on the buzzer when an object is within the specified threshold distance
    digitalWrite(BUZZER_PIN, HIGH);
    wasNearby = true; // Update the previous state
  } else if (wasNearby) {
    // Turn off the buzzer if no object is detected within the threshold distance
    digitalWrite(BUZZER_PIN, LOW);
    wasNearby = false; // Update the previous state
  }

  Serial.print("Measured distance: ");
  Serial.println(distance);

  delay(100);
}