#define  ECHO_PIN 5
#define TRIG_PIN 4

void setup() {
  pinMode(13, OUTPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
}

float readDistanceCM() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  int duration = pulseIn(ECHO_PIN, HIGH);
  return duration * 0.034 / 2;
}

void loop() {
  float distance = readDistanceCM();

  if (distance < 10) {
    digitalWrite(13, HIGH);
    delay(100);
  }else {
    digitalWrite(13, HIGH);
    delay(100);
  }
}