#define TRIG_PIN 9
#define ECHO_PIN 8

float distance;
unsigned long duration;

void setup() {
  Serial.begin(9600);

  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);

  digitalWrite(TRIG_PIN, LOW);

  Serial.println("HC-SR04 Distance Sensor");
  Serial.println("-----------------------");
}

void loop() {

  // สร้าง Trigger Pulse 10 us
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);

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

  digitalWrite(TRIG_PIN, LOW);

  // อ่านเวลา Echo
  duration = pulseIn(ECHO_PIN, HIGH, 30000UL);

  if (duration == 0) {
    Serial.println("Out of Range");
  }
  else {
    // คำนวณระยะทาง หน่วย cm
    distance = duration * 0.0343 / 2.0;

    Serial.print("Distance: ");
    Serial.print(distance, 2);
    Serial.println(" cm");
  }

  delay(200);
}