int trigPin = 9;
int echoPin = 10;
int buzzerPin = 8;

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

void loop() {
  long duration, distance;
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = duration * 0.034 / 2;
  
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  if (distance <= 50) {
    int frequency = map(distance, 0, 50, 2000, 100);
    tone(buzzerPin, frequency);
  } else {
    noTone(buzzerPin);
  }
  delay(100);
}