int data[4] = {0,0,0,0};
int frame[7] = {0,0,0,0,0,0,0};
int i = 0;
int state = 5;
int photoPin = A2;
int pv;   //τιμη που διαβάζεται από την φωτοαντίσταση
int b;  // bit που λήφθηκε (προκύπτει από την pv)
int count = 0;
void setup() {
  Serial.begin(9600);


}

void loop() {
  pv = analogRead (photoPin);
  //Serial.println(pv);

  if (pv <= 150)
    b = 0;
  else
    b = 1;

  
  switch(state){
    case 0:
     
      if (b==0)
     {
      
      Serial.println(b);
        state = 1;
     }
      break;
      
    case 1:
      //Serial.println("state 1");
      if(b == 1)
      {

        
      Serial.println(b);
      state = 2;
      }
      else
        state = 0;
      break;
      
    case 2:
      //Serial.println("state 2");
      if(b == 0)
      {
        Serial.println(b);
        state = 3;
        }
      else
        state = 0;
      break;
      
    case 3:
      //Serial.println("state 3");
       if(b == 1)
       {
        Serial.println(b);
        state = 4;
        i = 0;}
      else
        state = 0;
      break;

    case 4:
      Serial.println(b);
      frame[i] = b;
      i++; 
      if ( i == 7 )
      {
        i=0;
        boolean rc = checkParity(); 
        if (rc == false )
          state =5; //0;
        else
        {
          extractData();
          state = 5; //0;     
        }
      }
      
      break;

     case 5:
        if (b==1)
        {
          count++;
          if (count >= 3)
            state = 0;
        }
        else
          count = 0;
        break;
    
    }

    delay(500);
}

boolean checkParity()
{
  int s1 = frame[0] + frame[2] + frame[4] + frame[6];
  int s2 = frame[1] + frame[2] + frame[5] + frame[6];
  int s3 = frame[3] + frame[4] + frame[5] + frame[6];
  if (s1 %2 ==0 && s2 %2 ==0 && s3 %2 ==0 )
  return true;
  else 
  return false;
    
}


void extractData()
{
  data[0] = frame[2];
  data[1] = frame[4];
  data[2] = frame[5];
  data[3] = frame[6];
}