Capacitive touch-activated transducer system including a plurality of oscillators

• US 4,103,252 A
• Filed: 11/26/1976
• Issued: 07/25/1978
• Est. Priority Date: 11/26/1976
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Bobick, Thomas W.
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US05/744,907
• Time in Patent Office: 606 Days
• Field of Search: 331/65, 331/108 D, 331/111, 331/48, 331/55, 331/56, 307/116, 328/1, 328/5, 324/61 R, 324/61 P, 340/200, 340/258 C, 340/324 A, 340/324 AD, 340/365 R, 361/181, 361/203, 361/280, 200/52 R, 200/DIG. 1, 200/DIG. 2
• US Class Current: 331/48
• CPC Class Codes: G06F 3/03547 Touch pads, in which fingers can move on a surface
• CPC Class Codes: H03K 17/962 Capacitive touch switches

Abstract

A human touch on an etched copper electrode produces a capacitive change to vary the time constant of an RC network as a part of an oscillator. The variation in the capacitance of the sensor changes the time constant of the RC network which results in a change in frequency of the output signal of the oscillator. This change in frequency thus varies with the human touch to the copper electrode. To develop a directional indication of the touch position, four electrodes are arranged in opposed pairs along orthogonal axes. Each electrode is part of an RC network connected to an oscillator with each of the four oscillators identified with one of the four positions along the orthogonal axes. The output signal from each of the oscillators is transmitted to timing and control circuitry that generates four separate pulse trains, one pulse train identified with each of four positions along the orthogonal axis.

Claims

1. A capacitive activated transducer, comprising:

a sensor responsive to a touch by a human operator to generate a change in capacitance,

an oscillator connected to said sensor and generating a signal at a frequency varying with the capacitance of said sensor, and

means for gating a pulse train signal to an output terminal, said means connected to said oscillator and responsive to a time window varying with the frequency of said oscillator.

2. A capacitive activated transducer as set forth in claim 1 wherein said oscillator includes an integrated circuit generating pulse signals at a repetition rate related to the capacitance of said sensor.

3. A capacitive activated transducer as set forth in claim 2 wherein said gating means is responsive to the output of said integrated circuit and to enabling pulses.

4. A capacitive activated transducer as set forth in claim 1 wherein said sensor includes a substrate of an electrically insulating material with an etched copper pattern overlaying said substrate connected to said oscillator and responsive to a touch by a human operator.

5. A capacitive activated transducer, comprising:

a sensor having a plurality of electrodes, each responsive to a touch by a human operator to generate a change in capacitance at each electrode, and

a plurality of oscillators equal in number to said plurality of electrodes, each oscillator connected to one of said electrodes and generating a signal at a frequency related to the capacitance of said electrode, and

timing and control means connected to said plurality of oscillators for gating a pulse train signal to an output terminal for a preset time window varying with the frequency signal from said oscillators.

6. A capacitive activated transducer as set forth in claim 5 wherein each of said oscillators includes an integrated logic circuit generating pulse signals at a repetition rate related to the capacitance of the electrode connected thereto.

7. A capacitive activated transducer as set forth in claim 5 wherein said sensor consists of two pairs of opposed electrodes oriented along orthogonal axes.

8. A capacitive activated transducer as set forth in claim 7 including a finger electrode extending inward from each of said electrodes toward the intersection of the orthogonal axes.

9. A capacitive activated transducer as set forth in claim 5 wherein said sensor includes a substrate of an electrically insulating material with the electrodes consisting of a copper pattern on said substrate.

10. A capacitive activated transducer as set forth in claim 9 including a protective shield overlaying said copper electrodes.

11. A sensor for a capacitive activated transducer, comprising:

a first pair of opposed electrodes positioned along a first of two orthogonal axes and spaced an equal and predetermined distance from the intersection of said orthogonal axes, each electrode of said first pair having a shape symmetrical with said first orthogonal axis, and

a second pair of opposed electrodes positioned along the second of said two orthogonal axes and spaced an equal and predetermined distance from the intersection of said orthogonal axes, each electrode of said second pair having a shape symmetrical with said second orthogonal axis and positioned with respect to the adjacent electrodes of said first pair such that a predetermined portion of the periphery of said electrode is spaced a predetermined distance from a corresponding portion of said adjacent electrodes,

whereby a change in capacitance may be sensed with respect to the two orthogonal axes when the sensor is touched by a human operator.

12. A sensor for a capacitive activated transducer as set forth in claim 11 wherein said first and second pairs of electrodes have a shape whose outer peripheries form a ring-shaped configuration.

13. A sensor for a capacitive activated transducer as set forth in claim 12 wherein the radius of the outer edge of the ring-shaped configuration is substantially constant.

14. A sensor for a capacitive activated transducer as set forth in claim 11 including a finger electrode extending toward the intersection of said orthogonal axes from each of said electrodes.

15. A sensor for a capacitive activated transducer as set forth in claim 14 wherein each finger electrode is oriented along one of the two orthogonal axes.

16. A sensor for a capacitive activated transducer, comprising:

a substrate of an electrically insulating material,

a first pair of opposed electrodes formed on said substrate along a first of two orthogonal axes and spaced an equal and predetermined distance from the intersection of said orthogonal axes, each electrode of said first pair having a shape symmetrical with said first orthogonal axis, and

a second pair of opposed electrodes formed on said substrate along the second of said two orthogonal axes and spaced an equal and predetermined distance from the intersection of said orthogonal axes, each electrode of said second pair having a shape symmetrical with said second orthogonal axis and positioned with respect to the adjacent electrodes of said first pair such that a predetermined portion of the periphery of said electrode is spaced a predetermined distance from a corresponding portion of said adjacent electrodes,

whereby a change in capacitance may be sensed with respect to the two orthogonal axes when the sensor is touched by a human operator.

17. A sensor for a capacitive activated transducer as set forth in claim 16 wherein said electrodes comprise an etched copper pattern overlaying said substrate.

18. A sensor for a capacitive activated transducer as set forth in claim 17 including a protective shield overlaying said copper pattern.

19. A sensor for a capacitive activated transducer as set forth in claim 17 wherein said first and second pairs of copper electrodes have a shape whose outer peripheries form a ring-shaped configuration.