const int trig = 8;
const int echo = 9;
void setup() {
  Serial.begin (9600);
  // put your setup code here, to run once:
  pinMode(trig, OUTPUT);
  pinMode(echo, INPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(trig, HIGH);
  delayMicroseconds(3);
  digitalWrite(trig, LOW);

  float duration_us = pulseIn(echo, HIGH);

  float distance_cm = 0.017 * duration_us;

  Serial.print("distance: ");
  Serial.print(distance_cm);
  Serial.println(" cm");

  delay(500);
}