US Patent 8253702 Position detecting apparatus and position pointer

In a position detecting apparatus, electric power of a position pointer is turned on only when the position pointer is put within a particular range from a tablet to minimize consumption of a battery disposed in the position pointer. When the position pointer is brought close to the tablet, a control signal transmitted from the tablet is detected by a resonant circuit of the position pointer, and MOSFETs serving as a power switch are turned on by the detected signal. In response, electric power is supplied from a battery via the MOSFETs to circuit elements of the position pointer, and thus an operation of the position pointer starts.