Abstract: A pressure sensitive pointing device or pen is described for use with an electronic tablet that determines the position of the pointing device on the surface of the tablet. The pointing device incorporates a variable reluctance circuit responsive to the force exerted on the pen point for modulating a radiating frequency, emanating from the pen, in proportion to the force.

Abstract: A position resolving system is described incorporating a cordless pointing instrument such as a pen having an oscillator and battery supply therein. Electromagnetic radiations from the pen are directed onto a tablet grid having a plurality of grid loops therein. When the pen is in contact with the tablet, signals of maximum amplitude are radiated; when the pen is raised out of contact with the tablet, signal radiation is maintained but at a decreased amplitude for a predetermined time and then reduced to zero. Each loop is formed of parallel conductors joined at one end thereof by an end conductor; each loop is placed adjacent corresponding loops in the X and in the Y directions. The electromagnetic radiations are non-coherently amplitude detected to select the grid loop in the X direction and the grid loop in the Y direction having the maximum amplitudes thereon.

Abstract: A digitizing system includes a tablet and a cordless pointing device including a plurality of data grid conductors in the tablet and a plurality of clock grid conductors in the tablet, all receiving a magnetic field signal transmitted by the pointing device. A data channel circuit includes a differential amplifier and demodulating and filtering circuitry coupled to an output of the differential amplifier, having a clock input. An A/D converter has an input coupled to an output of the demodulating and filtering circuitry. Multiplexing circuitry selectively couples various grid conductor signals to the data channel circuit. A clock recovery circuit responsive to the clock grid conductors includes a phase-locked-loop circuit that generates a recovered clock signal which is synchronous with the magnetic field signal and is used as a reference for demodulating the phase and amplitude of signals multiplexed from the data grid conductors to the data channel circuit.

Abstract: A digitizing system includes a differential noise reduction technique wherein spaced parallel grid conductors in a tablet are differentially sensed in order to cancel out locally induced noise signals. Grid conductors also are sensed in a single ended fashion to initially locate a grid conductor conducting a larger induced carrier signal amplitude than any other grid conductor and produce amplitude data that is used to eliminate ambiguities arising from differential sensing of pairs of spaced grid conductors.

Abstract: A cordless four button cursor unit for accurately digitizing points along a digitizing tablet surface has an insulative housing including four buttons, each shaped as a quadrant of a circle and arranged about a hub. The hub acts as a stationary support from which an operator's fingers can conveniently "roll" to actuate any of the buttons. An antenna loop integral with a printed circuit board extends forward of the housing and subtends a cross hair on the bottom surface of a transparent substrate. A pair of conductive touch plates on opposite sides of the housing are short circuited by the resistance of an operator's hand, enabling an oscillator to effectuate operation of the cursor unit, causing the antenna to transmit electrostatic signals of frequencies representing button commands. The capacitance of the operator's body adds to the ground plane capacitance, so that transmission of electrostatic signals by the ground plane to the digitizing tablet is avoided.

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.

Abstract: A graphic tablet and method is described having a plurality of orthogonally related sensing conductors imbedded in the surface of a tablet. The imbedded sensing conductors thus form an X and Y grid for receiving signals from a signal radiating pen. The signals induced in the imbedded sensing conductors are detected, operated upon, and digitized to form an address of the radiating pen. The sensing conductors are formed of three conductors for each of the X and Y directions; the conductors extend across the pad in a given direction and are then redirected back across the pad in the opposite direction. Each of the X and Y sensing conductors thus extend back and forth across the pad forming parallel adjacent segments. A plurality of auxiliary conductors are each connected through resistors to a respective sensing conductor at spaced points along the sensing conductors length. Signals induced in the sensing conductor thus result in auxiliary signals in the auxiliary conductor.

Abstract: A writing tablet system is disclosed incorporating a plurality of parallel conductors imbedded beneath the surface thereof arranged in two groups in orthogonal relationship with respect to each other. The conductors form an antenna grid for receiving radiated electric signals generated remote from the tablet and supplied to a pen, or cursor, acting as a signal radiating means. The radiated signals generate signals of varying amplitude in the respective grid conductors. Each of the conductors in each of the X and Y directions are interconnected at one end thereof by resistances. The opposite ends of each of the conductors are either connected to a signal sensing circuit or are left unconnected. The unconnected conductors, or minor conductors, are arranged between the connected (or major) conductors such that radiated signals received by the antenna grid are received by all conductors but only those signals appearing on the major conductors are utilized in the determination of pen position.

Abstract: A writing tablet is disclosed incorporating a plurality of conductors imbedded beneath the surface thereof in orthogonal relationship with respect to each other. The conductors form a grid for receiving radiated electric signals generated remote from the tablet and supplied to a pen acting as a radiating antenna. The radiated signals generate signals of varying amplitude in the respective grid conductors; the grid conductors in each of the X and Y directions are interconnected by resistors; terminals are provided at the outside conductors in the X and Y directions. The terminals are sequentially connected to a detector which in turn provides input signals to a dual slope integrator for ratioing the amplitude of the signal appearing at selected terminals. The output of the integrator is a timed wave form having a time value proportional to the position of the pen on the tablet surface.

Abstract: Graphic communication apparatus for electronically writing information and transmitting includes a pen having a pair of windings disposed in a predetermined angular relation with respect to each other, and a writing surface having a plurality of windings arranged substantially parallel to each other for sensing the presence of the pen from the magnetic fields of the pen coils to provide differential outputs over the writing surface with respect to the windings of the pen apparatus, and the differential outputs being located with respect to the writing surface in an X--Y orientation.