A position determining device for a control knob includes a relative position
determiner
and an absolute position determiner. The standard output data of the potentiometer
corresponding to the rotational limits of the control knob is recorded in a ROM
during manufacturing of the device. Since the device is activated until the potentiometer
reaches one of the limits, the operating amount of the control knob is determined
in accordance with absolute position data outputted from the potentiometer. When
the potentiometer reaches one of the rotational limits of the control knob, the
standard data corresponding to the rotational limits is read from the ROM and set
as an initial value for the determination by the rotary encoder. Thereafter, the
operated amount of the control knob is determined in accordance with relative position
data outputted from the rotary encoder.
