A coordinate reader comprises a coordinate detector body having at least one excitation line, at least one detection line, an exciting circuit connected to the excitation line for supplying an exciting signal, a signal processing circuit connected to the detection line for receiving an induction signal generated in the detection line and outputting a signal containing amplitude information of the induction signal, and a control circuit for receiving the signal outputted by the signal processing unit and outputting an excitation control signal to the exciting circuit. A coordinate indicator indicates position information obtained from the induction signal induced in the detection line. A phase detecting circuit detects a phase difference between the excitation signal and the induction signal generated in the detection line. By this structure, an induction signal component due to the direct electromagnetic coupling between the excitation line and the detection line is eliminated, the required accuracy in calculation of the coordinates is ensured, and the read invalid region can be further reduced.

A system and a method for sensing the location of a remote object relative to a base object involve integrating inductive loop antennas with variable loop density into the base object and utilizing the antennas to transmit energy to and receive energy from an LC resonant circuit that is integrated into the remote object. The amplitude of a signal generated by the inductive loop antennas in response to energy received from the LC circuit identifies the location of the LC circuit relative to the antennas. Preferably, the sensing system is integrated into an electronic percussion instrument, where the keys of the instrument are formed with overlapping inductive loop antennas and the mallets used to activate the keys are formed with LC resonant circuits integrated into the mallet heads. In an enhanced version of the instrument, each antenna can be driven at multiple frequencies and made responsive to frequency-specific mallets, thereby creating an instrument that has continuous responsiveness over at least one lateral dimension of each key.

A position detecting apparatus capable of detecting position pointing devices of any combination simultaneously out of plural position pointing devices, thereby providing a user a friendly apparatus. A frequency of a resonance circuit provided inside a position pointing device is set by a command signal transmitted from a tablet, causing plural position pointing devices placed on the tablet to have a different frequencies, thereby suppressing electromagnetic interference among position pointing devices on the tablet, so that a simultaneous detection becomes available.

A digitizer for use as an input device for a computer system is provided. The digitizer is of the passive type, having a coordinate board for use as an input board which does not include any power sources or active circuit elements. In the coordinate board there is configured a plurality of resonant loop coils along each of two coordinate axes, whose resonant frequencies are mutually different. A position indicating device, exemplified by a hand-held pointer, includes an antenna coil electromagnetically coupled with any of the loop coils disposed in the coordinate board. AC power supplied to the antenna coil has a frequency which is varied to match the resonant frequencies of each of the plurality of loop coils. An AC signal generated by the induction effect due to the electromagnetic coupling is generated in the antenna coil, is outputted to a processing unit, and coordinate values of the position indicating device are calculated based on the output AC signal. Further, a method for detecting positions performed in the digitizer is described.

A coordinate defining signal is applied to an counter electrode in a period different from a writing period of voltages to pixel electrodes, and detected by way of an electrostatic capacitive coupling to determine a coordinate. Concurrently, to avoid a malfunction due to noises, gate and source drivers have their operations interrupted in the non-writing period. To prevent a variation of the coordinate defining signal due to capacitance variations of liquid crystal, an output of a driver for a scan or signal line is subjected to a high impedance in the non-writing period to isolate scan lines or signal lines. A light weight compact device is implemented.