Graphical input terminal

• US 3,959,585 A
• Filed: 02/01/1974
• Issued: 05/25/1976
• Est. Priority Date: 02/01/1974
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Inventors: Mattes, Hans George, Torok, Gabor Peter
• Primary Examiner(s): Robinson, Thomas A.
• Application Number:
  US05/438,723
• Time in Patent Office: 844 Days
• Field of Search: 178/18, 178/19, 178/20, 338/90, 33/1 M, 33/1 SD, 340/347 AD, 35/61-67, 346/21
• US Class Current: 178/18.05
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

A graphical input terminal includes a pair of resistive sheets separated by an air gap. An energizing voltage is alternately applied to each sheet while an output voltage representative of the position of contact between the sheets caused by the pressure of a stylus, is derived from the nonenergized sheet. A circuit for indicating stylus up/stylus down status without undue interference from capacitively induced voltages is also provided.

Claims

1. Apparatus for generating an electrical representation of the location of a stylus on a writing area, comprising

first and second resistive sheets overlapping in a common writing area and spaced apart from each other by a gap, said sheets adapted for contact with each other at a point on said writing area under the pressure of said stylus,

a source of energizing potential having high and low outputs,

first means for connecting said high and low outputs across said first resistive sheet to generate a first voltage gradient across said first sheet in a first direction,

second means for connecting said high and low outputs across said second resistive sheet to generate a second voltage gradient across said second sheet in a second direction different from said first direction,

each point on said writing area thereby being uniquely defined by a unique combination of voltages on said first and second resistive sheets at said point,

third means for alternately actuating said first and second means, thereby defining alternate time intervals during which one of said resistive sheets is energized and the other one of said resistive sheets is nonenergized,

an output circuit, and

fourth means for connecting said nonenergized resistive sheet to said output circuit during at least one portion of said time interval in which said sheet is nonenergized, wherein said gap includes a layer of material which is an electrical insulator in the absence of pressure applied thereto and an electrical conductor in the presence of pressure applied thereto.

2. The invention defined in claim 1 wherein

said high and low outputs of said source of energizing potential are both above ground potential.

3. The invention defined in claim 2 further including fifth means for connecting said nonenergized resistive layer to ground potential during another portion of said time interval in which said layer is nonenergized.

4. Apparatus for providing an electrical indication of the position of a stylus on a writing area, comprising

first and second spaced apart resistive sheets overlapping in said writing area and adapted for contact with each other under the pressure of said stylus applied at a point on said area,

first means for alternately energizing said first and second sheets to alternately establish a voltage gradient on each of said sheets in a different direction, so that said point on said writing area is represented by a unique pair of voltages on said first and second sheets,

an output circuit adapted to receive said electrical indication, and

second means cooperating with said first means for connecting the nonenergized one of said sheets to said output circuit,

wherein said apparatus further includes at least one row of flexible material positioned around the perimeter of said writing area for generally maintaining said first and second sheets in spaced relation, and

wherein at least one of said resistive sheets is a composite structure comprising a central polyester sheet, a resistive layer formed on one side of said polyester sheet, and a layer of chalkboard paint formed on the other side of said polyester sheet.

5. The invention defined in claim 4 wherein said resistive layer comprises a conductive ink reverse rolled onto said polyester sheet.

6. Apparatus for providing an electrical indication of the position of a stylus on a writing area, comprising

first and second spaced apart resistive sheets overlapping in said writing area and adapted for contact with each other under the pressure of said stylus applied at a point on said area,

first means for alternately energizing said first and second sheets to alternately establish a voltage gradient on each of said sheets in a different direction so that said point on said writing area is represented by a unique pair of voltages on said first and second sheets,

an output circuit adapted to receive said electrical indication, and

second means cooperating with said first means for connecting the nonenergized one of said sheets to said output circuit,

wherein said apparatus further includes at least one row of flexible material positioned around the perimeter of said writing area for generally maintaining said first and second sheets in spaced relation, and

wherein said flexible material comprises a cylindrical neoprene tube.