#7.4.10. 초음파 센서 + 피에조 부저

#define ECHO 3

#define TRIG 4

void setup() {

  pinMode(ECHO, INPUT);

  pinMode(TRIG, OUTPUT);

  Serial.begin(9600);

}

void loop() {

  digitalWrite(TRIG, LOW);

  delayMicroseconds(2);

  digitalWrite(TRIG, HIGH);

  delayMicroseconds(10);

  digitalWrite(TRIG, LOW);

  long dist = (pulseIn(ECHO, HIGH)) / 56.2;

  Serial.println(dist);

  if (dist < 10) {

    tone(11, 362, 100);

    delay(100);

  } else if (dist < 20) {

    tone(11, 362, 100);

    delay(250);

  } else if (dist < 30) {

    tone(11, 362, 100);

    delay(500);

  } 

    noTone(11);

  }

}