const int TRIG_PIN = 2;
const int ECHO_PIN = 4;
//const int LED_PIN = 16;
//const int DISTANCE_THRESHOLD = 100;
float distance;
long duration;
void setup() {
Serial.begin(115200);
delay(1500);
pinMode(TRIG_PIN, OUTPUT);
pinMode(ECHO_PIN, INPUT);
//pinMode(LED_PIN, OUTPUT);
}
void loop() {
digitalWrite(TRIG_PIN,LOW);
delayMicroseconds(10);
digitalWrite(TRIG_PIN, HIGH);
duration = pulseIn(ECHO_PIN, HIGH);
distance = 0.017 * duration;
 //if(distance < DISTANCE_THRESHOLD)
   // digitalWrite(LED_PIN, HIGH); // turn on LED
  //else
    //digitalWrite(LED_PIN, LOW);  // turn off LED

  // print the value to Serial Monitor
  Serial.print("distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  delay(1000);
}