#define ECHO_PIN 8
#define TRIG_PIN 7

float X=400/397.63;
void setup() {
  Serial.begin(9600);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
}

void loop() {
  //Generate ultrasonic signal
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  
  //Read ultrasonic signal
  float duration = pulseIn(ECHO_PIN, HIGH);
  float distance = (duration * 0.034 * X) / 2;

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

  delay(100);
}