GRAPHICAL INPUT TABLET

• US 3,670,103 A
• Filed: 04/28/1971
• Issued: 06/13/1972
• Est. Priority Date: 04/18/1968
• Status: Expired due to Term

• Current Assignee: Larry K. Baxter, Shintaro Asano
• Original Assignee: Larry K. Baxter, Shintaro Asano
• Inventors: Baxter, Larry K., Asano, Shintaro
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Brauner, Horst F.
• Application Number:
  US05/138,203
• Time in Patent Office: 412 Days
• Field of Search: 178/18,19,20 331/35
• US Class Current: 178/18.07
• CPC Class Codes: G06F 3/0441 using active external devices, e.g. active pens, for receiving changes in electrical potential transmitted by the digitiser, e.g. tablet driving signals
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

An a-c potential field is established on an electrographic tablet. A stylus that may be used to write upon the tablet comprises a capacitive pickup to provide a potential representative of the stylus position. The potential field is alternately switched at a rapid rate between vertical equipotentials and horizontal equipotentials in synchronism with output analog switches coupled to the stylus to provide an X analog signal output and a Y analog signal output representative of the horizontal and vertical coordinates, respectively, of the stylus tip above the tablet.

Claims

1. In an electrographic apparatus having a conductive tablet, means for selectively establishing first and second orthogonal electric fields in said conductive sheet during mutually exclusive time intervals, and probe means for coupling a signal on a point of said tablet to first and second terminals, phase controlled detection electronics comprising, a difference amplifier means having a pair of input terminals coupled to said probe means, a multiplier having one input coupled from said difference amplifier, an output amplifier coupled from the output of said multiplier, and a phase controlled square wave generator coupled from said output amplifier and having an output that couples to another input of said multiplier.