#include <LiquidCrystal.h>

/* General constants */
const int VSUPPLY = 5;

/* Display */
LiquidCrystal lcd(7, 6, 5, 4, 3, 2);

/* LDR */
const float GAMMA = 0.7;
const float RL10 = 50;
const int REF_RESISTANCE = 10000;
const int LDR_PIN = A0;

float readLDRSensor() {
  int analogValue = analogRead(LDR_PIN);
  const float refVoltage = analogValue / 1024. * 5;
  const float ldrResistance = REF_RESISTANCE * (refVoltage / (VSUPPLY - refVoltage));

  return pow(RL10 * 1000 * pow(10, GAMMA) / ldrResistance, (1 / GAMMA));
}

void showLuxValue(float lux)
{
  lcd.clear();
  lcd.setCursor(2, 0);
  lcd.print("Light level:");
  lcd.setCursor(3, 1);
  lcd.print(String(lux, 2) + " lux");
}

void setup() {
  lcd.begin(16, 2);
  lcd.print("This is a test!");
}

void loop() {
  float roomLux = readLDRSensor();
  showLuxValue(roomLux);
  delay(1000);
}