int cm;
 unsigned long pulso;
void setup() {
  Serial.begin (9600);
  pinMode(2,INPUT);  // Echo a pin2
  pinMode(3,OUTPUT); // Trigger pin3
}

void loop() {
  delay(100);
  digitalWrite(3, LOW);
  delayMicroseconds(2);
  digitalWrite(3, HIGH);
  delayMicroseconds(10);
  digitalWrite(3, LOW);
  pulso = pulseIn(2, HIGH); //tiempo del Echo en ms
  cm = pulso / 29 / 2;  // Convertir pulso en cm
  Serial.println(cm);
}