#include <LiquidCrystal_I2C.h>

#define LDR_PIN A0
#define LED 3
#define PIR_PIN 4

// LDR Characteristics
const float GAMMA = 0.7;
const float RL10 = 50;

LiquidCrystal_I2C lcd(0x27, 20, 4);

void setup() {
  pinMode(LDR_PIN, INPUT);

  lcd.init();
  lcd.backlight();
}

void loop() {
  int analogValue = analogRead(LDR_PIN);
  float voltage = analogValue / 1024. * 5;
  float resistance = 2000 * voltage / (1 - voltage / 5);
  float lux = pow(RL10 * 1e3 * pow(10, GAMMA) / resistance, (1 / GAMMA));

  lcd.setCursor(2, 0);
  lcd.print("Room: ");
  if (lux > 50) {
    lcd.print("Terang!");
    digitalWrite(LED, LOW);
  } else {
    lcd.print("Gelap  ");
    if (digitalRead(PIR_PIN) == HIGH)
      digitalWrite(LED, HIGH);
  }

  lcd.setCursor(0, 1);
  lcd.print("Lux: ");
  lcd.print(lux);
  lcd.print("          ");

  delay(100);
}