unsigned int a, twelve = 0b1000000000000000;
void setBit(unsigned int &target, uint16_t x, bool set) {  
  if (set)
    target |= (1 << x);
  else
    target &= ~(1 << x);

  target &= 0b0000111111111111; // cut 4 upper bits -> 12 bit
}
// -----------------------------------------------------

void setup() {
  Serial.begin(115200);
  
  int16_t special[] = {230, 248, 229};
  int16_t i, n = 0;
  
  int16_t numbers[30];
  char letters[30];

  Serial.println("int16_t letters[] = {");
  for (i=97; i<123; i++)
    numbers[n] = i,
    letters[n++] = (char)i;

  for (i=0; i<3; i++)
    numbers[n] = special[i],
    letters[n++] = (char)special[i];

  
  for (i=0; i<29; i++) {
    Serial.print("  "),
    Serial.print(i), Serial.print(" "),
    Serial.print(i%7), Serial.print(" -> "),
    Serial.print(numbers[i]),
    Serial.print(",\t// "), 
    Serial.println((char)(numbers[i]));
    //Serial.println((char)(numbers[i]-32));
  }
  Serial.println("};");
    /*
    //c = toupper(c);
    Serial.print(i); Serial.print(" "); 
    Serial.print(c); Serial.print(" "); 
    Serial.println(toupper(c));
    */
  
  for (;;);
  /*
  230: æ
  248: ø
  229: å
  198: Æ
  216: Ø
  197: Å
  */
  for (int16_t i=197; i<249; i++) {
    char c = (byte)i;
    char b = (byte)(i-32);
    if (
      (i == 197) ||
      (i == 198) ||
      (i == 216) ||
      (i == 229) ||
      (i == 230) ||
      (i == 248) 
    ) {
      Serial.print(i); Serial.print(" : "); Serial.write(c); 
      Serial.print(" "); Serial.println(b);
    }
  }
}
// -----------------------------------------------------


void Serial2Ints() {
  String s = Serial.readStringUntil('\n');
    char   c = s[0];
    int    i = s.substring(0, 2).toInt(); i = (i>16) ? 16 : i;

    setBit(twelve, i, ( twelve & (1 << i) ) ? false : true);
    
    Serial.print(c); Serial.print(" -> "); Serial.println(i);
    uint32_t bitmask = 0b0000111111111111;
    //for (; bitmask; bitmask >>= 1) Serial.print(bitmask & twelve ? '1' : '0');
    Serial.println(twelve, BIN);
}

void loop() {
  if (Serial.available()) 
    Serial2Ints();
}