#define TRIG_PIN 7
#define ECHO_PIN 8

void setup() {
  Serial.begin(9600);
  pinMode(TRIG_PIN, OUTPUT);
  digitalWrite(TRIG_PIN, LOW);
  pinMode(ECHO_PIN, INPUT);
}

void loop() {

  unsigned long duration;

  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  duration = pulseIn(ECHO_PIN, HIGH);
  Serial.print(duration / 58.77);
  Serial.println("cm");

  delay(100);

}