// Requires NQC 2.2 or higher and RCX firmware 2.0
// Clock Reader, auto-synchronized
// With light sensor auto-calibration / raw mode (variation is inverted, less light -> higher readings)
// Next bit encoding depends on previous bit color
// State encoding :
// Present state     Encoding       Next State
//           0      Yellow = 0      2
//           0      Grey   = 1      1
//           1      Black  = 0      0
//           1      Yellow = 1      2
//           2      Black  = 0      0
//           2      Grey   = 1      1
 
#define Center 3

#define Light SENSOR_2
#define CardPresent SENSOR_1

int State;
int Value;
int Cpt;
int Aff;

// Threshold between black and grey
int BG;
// Threshold between grey and yellow
int GJ;

// Hysteresis
int Hyst=5;

int Yellow;
int Black;


task main()
{
  SetSensorType(Light,SENSOR_TYPE_LIGHT);
  SetSensorMode(Light,SENSOR_MODE_RAW);
  SetSensor(CardPresent,SENSOR_TOUCH);

  while (true)
  {
    until (CardPresent==1);
    Aff=0;
    SetUserDisplay( Aff, 0);
    OnFwd(OUT_C);
    GetValue(); 
    PlaySound(1);
    Aff=Value%10000;
    switch( Value/10000)
    {
      case 0:
        SetUserDisplay( Aff, 0);
        break;
      case 1:
        SetUserDisplay( Aff, 1);
        break;
      case 2:
        SetUserDisplay( Aff, 2);
        break;
      case 3:
        SetUserDisplay( Aff, 3);
        break;
    }
  }
}

void GetValue()
{
  Yellow = Light-10; // use -10 because of diffusing tape : background is farther thus darker
  BG = Yellow+30; // First approximation of Black/Grey threshold
  Value = 0;
  State = 0;
  Cpt=0;
  until (Light > BG + Hyst); // First plate is black
  Wait(Center);
  Black = Light; // Get Black value
  // Define Thresholds
  BG=Black-(Black-Yellow)*3/14;
  GJ=Yellow+(Black-Yellow)*2/7;

  do
  {
    Cpt++;
    Value *= 2;
    switch (State)
    {
    case 0:
    	until (Light < BG - Hyst);
	Wait(Center);
	if (Light < GJ)
	{
	  State = 2;
	}
	else
	{
	  Value += 1;
	  State = 1;
      }
      break;	

    case 1:
	until ((Light > BG + Hyst)|| (Light < GJ - Hyst));
	Wait(Center);
	if (Light > BG)
	{
	  State = 0;
	}
	else
	{
	  Value += 1;
	  State = 2;
      }
      break;	

    case 2:
	until (Light > GJ + Hyst);
	Wait(Center);
	if (Light > BG)
	{
	  State = 0;
	}
	else
	{
	  Value += 1;
	  State = 1;
      }
      break;	
    }
  } while ( Cpt < 15 );
  Wait(50);
  Float(OUT_C);
}