#4.5.5.1. 예제 

int ldrPin = A0;

int ledPin = 13;

int threshold = 500;

void setup() {

  pinMode(ledPin, OUTPUT);

}

void loop() {

  int ldrValue = analogRead(ldrPin);

  if (ldrValue < threshold) {

    digitalWrite(ledPin, HIGH);

  } else {

    digitalWrite(ledPin, LOW);

  }

  delay(100);

}