#define ECHO_PIN 2 
#define TRIG_PIN 3
void setup() {
  Serial.begin(115200);
  pinMode(13, OUTPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  // put your setup code here, to run once:

}

  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();
    bool isNearby = distance < 100;
    digitalWrite(13,  isNearby );
    Serial. print("Measured distance : ");
    Serial. println(readDistanceCM());
    delay(100);
  }

  // put your main code here, to run repeatedly: