#4.3.1.2. 예제 

int trigPin = 13; 

int echoPin = 12;

int greenLed = 2;

int yellowLed = 3;

int redLed = 4;

void setup() {

  pinMode(echoPin, INPUT); 

  pinMode(trigPin, OUTPUT);

  pinMode(greenLed, OUTPUT);

  pinMode(yellowLed, OUTPUT);

  pinMode(redLed, OUTPUT);

}

void loop() {

  digitalWrite(trigPin, LOW);

  delayMicroseconds(2);

  digitalWrite(trigPin, HIGH);

  delayMicroseconds(10);

  digitalWrite(trigPin, LOW);

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

  if (dist < 10) {

    digitalWrite(greenLed, LOW);

    digitalWrite(yellowLed, LOW);

    digitalWrite(redLed, HIGH);

  } else if (dist < 20) {

    digitalWrite(greenLed, LOW);

    digitalWrite(yellowLed, HIGH);

    digitalWrite(redLed, LOW);

  } else if (dist < 30) {

    digitalWrite(greenLed, HIGH);

    digitalWrite(yellowLed, LOW);

    digitalWrite(redLed, LOW);

  } else {

    digitalWrite(greenLed, LOW);

    digitalWrite(yellowLed, LOW);

    digitalWrite(redLed, LOW);

  }

}