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.

Abstract: A method and apparatus are provided for converting a position of a pen to a digital number representing the pen position with respect to a grid of conductors. A coil disposed above the tip of the pen is driven by a continuous AC input voltage of fixed frequency and amplitude, thereby inducing corresponding signals in each of the conductors of the grid. Scanning circuitry sequentially scans the grid conductors, first in the X direction and then in the Y direction, thereby sequentially coupling the induced signals to the input of a differential amplifier. A position counter is reset at the beginning of scanning in each direction and is incremented at a rate proportional to and greater than the scanning rate. The outputs of the differential amplifier are inputted to a phase sensitive detector producing a characteristic output which changes polarity as grid conductors on opposite sides of the pen tip location are sequentially scanned.

Abstract: A system is disclosed for converting the location and movement of a manually controlled instrument into corresponding electrical signals. The manually controlled instrument responds to the phase and frequency of an electrical field that varies to represent position information on an orthogonal writing grid. A single, phase-locked loop is utilized to produce both a first signal corresponding to the instrument location along an x-axis and a second signal corresponding to the instrument location along a y-axis. The first and second signals both represent the differential between pairs of related absolute signals. The differential signals are independent of normal signal variations and other error sources. The field is generated by first selecting sets of conductors that are positioned orthogonally with respect to each other. Signals are then applied to the respective sets of conductors to thus generate an electric field at the location of the intersection of the orthogonal sets.

Abstract: A system is disclosed for converting the location and movement of a manually controlled instrument into corresponding electrical signals. The manually controlled instrument responds to the phase and frequency of an electrical field that varies to represent position information on an orthogonal writing grid. A single, phase-locked loop is utilized to produce both a first signal corresponding to the instrument location along an x-axis and as second signal corresponding to the instrument location along a y-axis. The first and second signals both represent the differential between pairs of related absolute signals. The differential signals are independent of normal signal variations and other error sources.