class ServoController():
    """ Object that chats with controller over serial and sends him values
        with syntax: <value><servo_letter>"""

    def __init__(self, loop, tty):
        """ we need functional loop and tty we should connec to """
        self._s = serial.Serial(tty, 57600)
        self._tty_handle = pyuv.TTY(loop, self._s.fileno(), True)
        self._tty_handle.start_read(self._on_read)

    def _on_read(self, status_handle, data, error):
        """ callback called everytime that our pyuv.TTY receives something, in
            this case we didn't defined any response from controller!'"""
        pass

    def setPosition(self, position, letter):
        """sets servo to position based on it's letter'"""
        assert 500 <= position <= 2500

        position = str(position)
        string = position + letter

        self._tty_handle.write(string.encode('UTF-8'))
        print(("ServoController output: ", string))