#define TRIG 5     // D3 = GPIO5
#define ECHO 6     // D4 = GPIO6
#define BUZZER 7   // D5 = GPIO7

void setup() {
  Serial.begin(115200);
  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);
  pinMode(BUZZER, OUTPUT);
}

void loop() {

  // Ultrasonic pulse
  digitalWrite(TRIG, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);

  long duration = pulseIn(ECHO, HIGH, 30000);

  if (duration == 0) return;

  float distancia = duration * 0.0343 / 2;

  Serial.print("Distance: ");
  Serial.println(distancia);

  if (distancia <= 20) {
    digitalWrite(BUZZER, HIGH);   // sound ON
  } else {
    digitalWrite(BUZZER, LOW);    // sound OFF
  }

  delay(200);
}