#define VW_ID 54424

uint16_t _crc_ccitt_update (uint16_t crc, uint8_t data){
#define lo8(x) ((x)&0xff)
#define hi8(x) ((x)>>8)
  data ^= lo8 (crc);
  data ^= data << 4;
  return ((((uint16_t)data << 8) | hi8 (crc)) ^ (uint8_t)(data >> 4)
          ^ ((uint16_t)data << 3));
}

uint8_t vw_send(uint8_t* buf, uint8_t len){
#define VW_SPEED 500
#define GPIO_TX 0 // GPIO передатчика
#define VW_HEADER_LEN 8
#define VW_MAX_MESSAGE_LEN 40
#define VW_MAX_PAYLOAD VW_MAX_MESSAGE_LEN-3
  static uint8_t vw_tx_buf[(VW_MAX_MESSAGE_LEN * 2) + VW_HEADER_LEN]
    = {0x2a, 0x2a, 0x2a, 0x2a, 0x2a, 0x2a, 0x38, 0x2c};
  const uint8_t symbols[] =
  {
    0xd,  0xe,  0x13, 0x15, 0x16, 0x19, 0x1a, 0x1c,
    0x23, 0x25, 0x26, 0x29, 0x2a, 0x2c, 0x32, 0x34
  };

  // Number of symbols in vw_tx_buf to be sent;
  uint8_t vw_tx_len = 0;
  uint8_t i;
  uint8_t index = 0;
  uint16_t crc = 0xffff;
  uint8_t *p = vw_tx_buf + VW_HEADER_LEN; // start of the message area
  uint8_t count = len + 3; // Added byte count and FCS to get total number of bytes

  if (len > VW_MAX_PAYLOAD)
    return false;
  // Encode the message length
  crc = _crc_ccitt_update(crc, count);
  p[index++] = symbols[count >> 4];
  p[index++] = symbols[count & 0xf];

  // Encode the message into 6 bit symbols. Each byte is converted into
  // 2 6-bit symbols, high nybble first, low nybble second
  for (i = 0; i < len; i++)
  {
    crc = _crc_ccitt_update(crc, buf[i]);
    p[index++] = symbols[buf[i] >> 4];
    p[index++] = symbols[buf[i] & 0xf];
  }

  // Append the fcs, 16 bits before encoding (4 6-bit symbols after encoding)
  // Caution: VW expects the _ones_complement_ of the CCITT CRC-16 as the FCS
  // VW sends FCS as low byte then hi byte
  crc = ~crc;
  p[index++] = symbols[(crc >> 4)  & 0xf];
  p[index++] = symbols[crc & 0xf];
  p[index++] = symbols[(crc >> 12) & 0xf];
  p[index++] = symbols[(crc >> 8)  & 0xf];

  // Total number of 6-bit symbols to send
  vw_tx_len = index + VW_HEADER_LEN;
  cli();
  uint8_t vw_tx_bit = 0, vw_tx_index = 0;
  for (; vw_tx_index < vw_tx_len;)
  {
    digitalWrite(GPIO_TX , vw_tx_buf[vw_tx_index] & (1 << vw_tx_bit++));
    if (vw_tx_bit >= 6)
    {
      vw_tx_index++;
      vw_tx_bit = 0;
    }
    delayMicroseconds((1000000 / VW_SPEED));
  }
  digitalWrite(GPIO_TX , 0);
  sei();
  return true;
}
uint8_t countsend;

void setup(){
  pinMode(GPIO_TX, OUTPUT);
}

void loop(){
  int16_t hum = 610; // 60.0%
  int16_t temp = 253; // 25.3 С
  uint8_t msg[] = {26, VW_ID & 255, VW_ID / 256, countsend,
                   1, temp & 255, temp / 256, // датчик температуры
                   1, hum & 255, temp / 256, // датчик температуры
                   1, temp & 255, temp / 256, // датчик температуры
                   1, hum & 255, temp / 256, // датчик температуры
                   2, hum & 255, hum / 256 // датчик влажности
                  };
  vw_send((uint8_t *)msg, sizeof(msg));
  countsend++; // счетчик передач
  delay(5000);
}