docs: def _hm_send_msg(self, message):
          """This is the only interface to the serial connection."""
          try:
              serial_message = message
              self.conn.write(serial_message)   # Write a string
          except serial.SerialTimeoutException:
              serror = "Write timeout error: \n"
              sys.stderr.write(serror)
          # Now wait for reply
          byteread = self.conn.read(159)
          # NB max return is 75 in 5/2 mode or 159 in 7day mode
          datal = list(byteread)
          return datal