#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// ====== Konfigurasi Hardware ======
#define LED_PIN 2              // LED di pin D2
#define LDR_PIN A0             // LDR ke A0 (pakai keluaran analog AO)
#define SERIES_RESISTOR 2000   // Nilai resistor seri LDR (Ohm). Ganti ke 10000 jika pakai 10k

// ====== Konstanta Sensor LDR ======
// Model sederhana LDR: lux = (RL10*1000 * 10^GAMMA / R_LDR)^(1/GAMMA)
#define GAMMA 0.7              // Gamma LDR (contoh GL5528 ~ 0.7)
#define RL10 50                // Resistansi LDR pada 10 lux (kΩ)

// ====== LCD I2C ======
LiquidCrystal_I2C lcd(0x27, 20, 4); // Ganti 0x27->0x3F bila perlu, dan 20,4 ke 16,2 jika LCD 16x2

// Ambang lux untuk terang/gelap
float LUX_THRESHOLD = 50.0;

// Tegangan referensi ADC (Uno 5V)
const float VREF = 5.0;

void setup() {
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);

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

  Serial.begin(9600);
  Serial.println(F("Mulai: LDR + LCD I2C + LED"));

  lcd.setCursor(2, 0);
  lcd.print("Sensor Cahaya");
  lcd.setCursor(2, 1);
  lcd.print("LCD I2C Ready");
  delay(1200);
  lcd.clear();
}

void loop() {
  // ==== Baca analog ====
  int analogValue = analogRead(LDR_PIN);
  float voltage = analogValue * (VREF / 1023.0);

  // Hitung resistansi LDR dari pembagi tegangan:
  // Vout = VREF * (R_LDR / (R_LDR + RS))
  // => R_LDR = RS * Vout / (VREF - Vout)
  float rLdr = SERIES_RESISTOR * voltage / (VREF - voltage);

  // Cegah pembagian nol jika sangat gelap/terang
  if (rLdr < 1.0) rLdr = 1.0;

  // Hitung lux (model perkiraan)
  float lux = pow((RL10 * 1000.0 * pow(10.0, GAMMA)) / rLdr, (1.0 / GAMMA));

  // ==== Kendali LED ====
  bool isBright = (lux > LUX_THRESHOLD);
  digitalWrite(LED_PIN, isBright ? LOW : HIGH); // LED nyala saat gelap

  // ==== Tampilkan ke Serial ====
  Serial.print(F("ADC: ")); Serial.print(analogValue);
  Serial.print(F("  V: ")); Serial.print(voltage, 3);
  Serial.print(F("  R_LDR(ohm): ")); Serial.print(rLdr, 0);
  Serial.print(F("  Lux: ")); Serial.println(lux, 1);

  // ==== Tampilkan ke LCD ====
  // Baris 1: Lux
  lcd.setCursor(0, 0);
  lcd.print("Lux: ");
  lcd.print(lux, 1);
  lcd.print("           "); // padding agar bersih

  // Baris 2: Status
  lcd.setCursor(0, 1);
  lcd.print("Cahaya: ");
  if (isBright) {
    lcd.print("Terang     ");
  } else {
    lcd.print("Gelap      ");
  }

  // Baris 3: ADC & Volt (opsional informasi)
  lcd.setCursor(0, 2);
  lcd.print("ADC:");
  lcd.print(analogValue);
  lcd.print("  V:");
  lcd.print(voltage, 2);
  lcd.print("     ");

  // Baris 4: LED state
  lcd.setCursor(0, 3);
  lcd.print("LED: ");
  lcd.print(isBright ? "OFF (terang)" : "ON  (gelap) ");
  lcd.print("   ");

  delay(300);
}