const int trigPin = 3;
const int echoPin = 4;
const int buzzerPin = 1;
const int led = 0;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(buzzerPin, OUTPUT);
  pinMode(led, OUTPUT);
  digitalWrite(buzzerPin, LOW);
}

void loop() {
  digitalWrite(buzzerPin, LOW);
  int duration, distance;
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance = duration / 58.2;

  if (distance > 1 && distance <= 80) {
      int freq_delay = map(distance, 0, 80, 30, 300);
      digitalWrite(buzzerPin, HIGH);
      digitalWrite(led, HIGH);
      delay(freq_delay);
      digitalWrite(buzzerPin, LOW);
      digitalWrite(led, LOW);
      delay(freq_delay);
  }
  else {
      digitalWrite(buzzerPin, LOW);
      digitalWrite(led, LOW);
  }
}