Browse Prior Art Database

Single Plane Tablet Using Resistive Wedges

IP.com Disclosure Number: IPCOM000048422D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Dym, H: AUTHOR

Abstract

A single-layer capacitive tablet in which electrodes provide capacitive coupling with a pen to produce signals which correspond to the X and Y dimensions of the position of the pen on the tablet is described in U.S. Patent 4,087,625. To achieve position signals for two orthogonal axes from one conductive pattern, one axis uses the geometry of wedge-shaped conductors to produce a variable coupling to the sensing pen and the other axis uses a conventional voltage gradient applied by a separate external voltage divider.

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Single Plane Tablet Using Resistive Wedges

A single-layer capacitive tablet in which electrodes provide capacitive coupling with a pen to produce signals which correspond to the X and Y dimensions of the position of the pen on the tablet is described in U.S. Patent 4,087,625. To achieve position signals for two orthogonal axes from one conductive pattern, one axis uses the geometry of wedge-shaped conductors to produce a variable coupling to the sensing pen and the other axis uses a conventional voltage gradient applied by a separate external voltage divider.

A low cost version of the above-described tablet is made using copper as the conductive pattern, and process techniques used in fabricating printed circuit boards. The wedge pattern is modified because of the high conductivity of copper. As shown in the figure, each wedge 10 is formed with a fine line split 11 from the center of the base 12 to just below the top 13 so that the wedges are capable of providing a resistor divider function. The effect of the split 11 is to form a long continuous conductive path between the end contact points 14, and
15. With this serpentine path, a resistance on the order of 100 ohms is obtained, which is a suitable value as a load for commercially available signal drivers.

With an AC signal 16 applied to contact point 14, and contact point 15 grounded by the switch control 17, a pen will sense a linear voltage amplitude gradient when moving across the wedges even though the vol...