Low power, high resolution digitizing system with cordless pen/mouse

Abstract

A cordless pen emits a directional electric field from the tip of a conductive pen cartridge. The pen tip is capacitively coupled to embedded major X and major Y conductors in a digitizer tablet, which are scanned to determine which three X conductors and which three Y conductors have the greatest resulting signal levels. A microprocessor calculates the precise pen location from the three largest X signals and the three largest Y signals. A resistive path to ground is provided for each X and Y conductor. A plurality of minor conductors are disposed between each pair of X and Y conductors. A resistive divider circuit linearly distributes the voltage across the pair of conductors among the minor conductors therebetween, and improves the capacitively coupled signal levels and also 'localizes' noise signals. The frequency of the pen signal is modulated by several pen switches. Circuitry in the digitizing tablet discriminates the pen frequency to decode the commands represented by switch closures between data scanning operations. In one embodiment of the invention a keyboard is placed on the digitizer tablet. The keyboard includes a groud plane through which a plurality of conductive tips actuated by keys extend to capactively couple an electrical signal to embedded X and Y conductors. The microprocessor interprets the scanned data to determine the identity of each depressed key.