void setup() {
  pinMode(12, OUTPUT);
  pinMode(13, INPUT);
  pinMode(2, OUTPUT);
  digitalWrite(2, HIGH);
  Serial.begin(9600);

}

void loop() {
  digitalWrite(12, LOW);
  delayMicroseconds(2);
  digitalWrite(12, HIGH);
  delayMicroseconds(10);
  digitalWrite(12, LOW);

  pulseIn(13, HIGH);

  Serial.print("pulse in: ");
  Serial.println(100);
  delay(1000);
  Serial.flush();
}