// ****** LDR Pin Definition *********************************************
#define LDRanalog  27   // Analog input pin for LDR
#define LDRdigital 26   // Digital input pin for LDR

// ****** LDR Lux Calculation Constants ***********************************
const float GAMMA = 0.7;   // LDR gamma characteristic constant
const float RL10  = 50;    // LDR resistance (kΩ) at 10 lux

void setup() {
  // Initialize serial monitor at 115200 baud
  Serial.begin(115200);
  pinMode(25, OUTPUT);  // Pin 25 = LED output (street light)
}

void loop() {
  // ===== READ LDR =====
  int digitalValue = digitalRead(LDRdigital);   // Digital: 0 (dark) or 1 (bright)
  int adcValue     = analogRead(LDRanalog);     // Analog: 0 to 4095 (12-bit ADC)

  // ===== CALCULATE VOLTAGE, RESISTANCE, LUX =====
  // Step 1: Convert ADC value to voltage (assuming 5V reference)
  float voltage = adcValue * 5 / 4095.0;

  // Step 2: Calculate LDR resistance using voltage divider formula
  //         R_LDR = (R_fixed * V_ldr) / (Vcc - V_ldr)
  //         Here R_fixed = 2000 ohms, Vcc = 5V
  float resistance = 2000 * voltage / (1 - voltage / 5);

  // Step 3: Convert resistance to lux using LDR characteristic curve
  //         lux = (RL10 * 1000 * 10^GAMMA / R_LDR) ^ (1/GAMMA)
  float lux = pow(RL10 * 1e3 * pow(10, GAMMA) / resistance, (1 / GAMMA));

  // ===== PRINT TO SERIAL MONITOR =====
  Serial.print("Digital Value = ");
  Serial.println(digitalValue);
  Serial.print("ADC Value     = ");
  Serial.println(adcValue);
  Serial.print("Lux           = ");
  Serial.println(lux);
  Serial.print("Voltage       = ");
  Serial.println(voltage);

  // ===== AUTOMATIC STREET LIGHT LOGIC =====
  // If ADC >= 2000 → bright environment (daytime) → turn OFF the light
  // If ADC <  2000 → dark environment (nighttime) → turn ON the light
  // This mimics a real street light that activates automatically at night.
  if (adcValue >= 2000) {
    digitalWrite(25, LOW);   // Daytime: LED OFF (save power)
    Serial.println("Status: DAYTIME  → Light OFF");
  } else {
    digitalWrite(25, HIGH);  // Nighttime: LED ON (street light active)
    Serial.println("Status: NIGHTTIME → Light ON");
  }

  Serial.println("----------------------------------");
  delay(500);
}