PURPOSE: To find out a precise coordinate by applying a part of a signal added to a board to a writting tool, informing the holding of a pen by the writting tool to a control part, and finding the difference between the coordinate detected by a sensor of the tool and an original coordinate.
CONSTITUTION: The output of an oscillator OSC is inputted to frequency dividers J, N and shift registers SFT1WT2 and the frequency divider N divides frequency by N to input a driving pattern SIN to both shift registers SFT1WT2 and then divides the frequency by M and 1/2 to input the divided results to the shift registers as XY switching signals. A pen PE is fitted to a pen holder PH having a sensor SEN, a magnetic field on the board B is detected by the sensor SEN, amplified A, an unnecessary band is filtered F, and the filtered signal is supplied with A/D conversion. The output of the AD converter is inputted to a processing part PRO by using an output from the frequency divider J. Signals ix, iy to be applied to the coils CXi, CYi of the board B are branched and inputted to a coil CO. Said signal is compensated by the difference between the phase of the magnetic field inputted to the processing part PRO and the logical phase R. Thus, the precise coordinate can be found out.
IWAKI HIROSHI
OOYA NOBUMASA
