void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(5, OUTPUT); //trigger
  pinMode(18, INPUT); // echo
  pinMode(13, OUTPUT); //led
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(5, LOW);
  delayMicroseconds(3);
  digitalWrite(5, HIGH);
  delayMicroseconds(10);
  digitalWrite(5, LOW);
  double tiempo = pulseIn(18, HIGH);
  double distancia = tiempo/58;
  Serial.println(distancia);
  if (distancia <= 30){
    digitalWrite(13, HIGH);
    delay(2000);
  }else {
    digitalWrite(13, LOW);
    delay(2000);
  }
  delay(2000);
}