Method and apparatus for coordinate detection

Telegraphy – Systems – Position coordinate determination for writing

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G08C 2100

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active

056591543

ABSTRACT:
A digitizing tablet includes stacked X and Y coordinate resistance boards (X-board and Y-board) with insulating beads therebetween. A CPU controls input and grounding switches of both X- and Y-boards and a selector switch. The selector switch connects an A/D converter input to grounding electrodes of the X and Y boards. The input switch of the X-board applies a supply potential to an input electrode of the X-board while a grounding electrode of the X-board is disconnected from ground by the grounding switch. The Y-board is grounded at a grounding electrode while the input electrode of the Y-board floats. The A/D converter monitors a voltage at the grounding electrode of the X-board to detect a drop in potential from the supply potential. When contact pressure is applied to the digitizing tablet, current flows from the supply potential, through the X and Y boards via a contact point, and into ground via the Y-board grounding switch. The potential appearing at the grounding electrode of the X-board drops thus signaling contact. The CPU reads this change in potential and initiates a coordinate determination process. An alternate embodiment employs a voltage dropping resistor, in supply leads to the X and Y boards, which turns on a switching transistor when current is drawn, signaling an interrupt to the CPU, and initiating coordinate determination.

REFERENCES:
patent: 5245139 (1993-09-01), Protheroe et al.
patent: 5274362 (1993-12-01), Potvin
patent: 5324895 (1994-06-01), Inamori

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