Input device having rotatable disk

An input device comprising:

• a casing comprising an annular area;
• a rotatable disk capable of rotating relative to the casing and surrounded by the annular area, the rotatable disk having a plurality of input modes for inputting characters of a plurality of character sets, the rotatable disk comprising a switch button for switching among the plurality of input modes, the rotatable disk further comprising a pointer;
• and
• a processor received in the casing;
• wherein the annular area has a plurality of input positions along a circumferential direction thereof, the plurality of input positions corresponds to characters of one of the plurality of character sets corresponding to a current input mode of the rotatable disk;
• wherein the processor is configured to generate a control signal according to a character corresponding to an input position when the pointer is aligned with the input position;
• wherein the rotatable disk comprises a first capacitor plate at the pointer, the annular area comprises a second capacitor plate at each of the plurality of input positions, the first capacitor plate and the second capacitor plate cooperatively generate a capacitance having a certain capacitance value each time the pointer is aligned with one input position, each of the plurality of input positions corresponding to one capacitance value, when the processor detects a capacitance value, the processor determines which input position is aligned with the pointer according to the detected capacitance value.