Pencept, Inc.

Thomas C Prentice

Barry A Blesser

A digitizing tablet is disclosed in which two multiplexors are connected to alternate conductive loop elements in each plane of elements. The two multiplexors are connected to a differential amplifier. The signals from the differential amplifier are demodulated. The demodulated signal is provided to an integrator. A microprocessor controlled reset switch is connected across the integrator to reset the integrator after the completion of each measurement. Grounded copper strips are used in the space formed within and between the conductive loop elements of the digitizing tablet to shield the loop elements from capacitive interference.

Digitizing tablet system

A position indicating implement is disclosed having a first coil connected to a current source and a second coil inductively coupled with the first coil. A capacitor is connected in series with the second coil so that the current in the first coil induces a phase shifted current in the second coil. A tip extends from the barrel of the position indicating implement of the present invention. The tip is designed for placement on and movement over a digitizing tablet. A switch has been located near the tip so that it is easily accessible to a user's finger while holding the implement. The power source providing an alternating current to the first coil includes a digital switching circuit for producing a step function which approximates a sine wave and lacks any components at the second, third, fourth, fifth and sixth harmonics. The step function is filtered to produce a sine wave for delivery to the first coil. The switch near the tip of the implement may be used as a mouse switch so that the position indicating implement may be used as a mouse to indicate relative position rather than absolute position. Remote signaling may be accomplished by providing a switch in the circuit of the second coil. Calibration of the phase shift between the fields of the two coils may be accomplished by providing a line from the circuit of the second coil.

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Milford, MA, United States of America

Thomas C Prentice