Pen status system for digitizer pen

Abstract

A pen status indicating system for a digitizer pen utilized in conjunction with a digitizer having a grid of spaced conductors positioned beneath a writing surface. The digitizer includes an electronic system which scans the spaced conductors and senses signals produced in the spaced conductors by a transmitting coil located near the writing tip of a pen used to write on the writing surface. The pen status indicating system senses whether the writing tip of the pen is pressed against the writing surface. The pen status indicating system includes a split inductor having a movable core coupled in direct communication with a pen cartridge having the writing tip connected thereto. When the pen is raised, the movable core occupies a first position relative to the secondary winding of the split inductor windings and when the pen is lowered, the movable core is caused to occupy a second position relative to the split inductor windings, causing a phase reversal in a signal produced on a center tap conductor of the split inductor. A sensing circuit including a phase sensitive detector, a filter, and a comparator produces a pen status output signal in response to the signal on the center tap conductor.