code: public function sendMessage($str, $waitForReply = 0.1)
      {
          $this->_buffer .= $str;
  
          if ($this->autoFlush === true) {
              $this->serialflush();
          }
  
          usleep((int) ($waitForReply * 1000000));
      }
docs: Sends a string to the device
  
  @param string $str          string to be sent to the device
  @param float  $waitForReply time to wait for the reply (in seconds)