Capacitive touch control and display

• US 4,233,593 A
• Filed: 06/12/1978
• Issued: 11/11/1980
• Est. Priority Date: 06/12/1978
• Status: Expired due to Term

• Current Assignee: Ametek Aerospace Products, Inc. (Ametek Incorporated)
• Original Assignee: General Electric Company
• Inventors: Bigelow, John E.
• Primary Examiner(s): Caldwell, Sr., John W.
• Assistant Examiner(s): Groody, James J.
• Application Number:
  US05/914,373
• Time in Patent Office: 883 Days
• Field of Search: 340/365 C, 340/200, 340/365 S, 340/347 M, 340/347 P, 340/203, 200/DIG. 1, 200/52 R, 361/280, 361/292, 361/298, 361/299, 361/300, 361/287, 324/61 R, 324/60 C
• US Class Current: 341/15
• CPC Class Codes: G06F 3/03547 Touch pads, in which fingers can move on a surface
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 17/975 using a capacitive movable element
• CPC Class Codes: H03K 2017/9604 characterised by the number of electrodes
• CPC Class Codes: H03K 2217/94073 with capacitive detection

Abstract

A control for use upon a solid panel, devoid of control shaft apertures, allows data entry by rotational positioning of a sector-shaped electrode to vary the capacitance to at least one of a plurality of sector-shaped electrodes formed about a central disc upon an interior surface of the panel. A magnetizable disk is attached to the exterior of the panel, with the control knob having a magnetized member attracted to the disk for maintaining the control knob in proper position while allowing control knob rotational adjustments. Position-decoding electronics energize successive ones of the plurality of electrodes with successive phases of a master signal and recover zero-crossing information relating the phase of the signal returned from the control to the control position. A light-emitting display is positioned behind the panel to indicate the index of the control knob by a variable-length circular bar of light, a digitized display and the like.

Claims

1. A capacitive control assembly for use on a solid panel having front and rear surfaces, comprising:

a plurality (M) of input electrodes disposed about a common center and fabricated upon said panel rear surface;

the centers of adjacent input electrodes separated from one another by an angle about said common center substantially equal to (360/M) degrees, where M is an integer greater than one;

a movable electrode positioned adjacent to said panel front surface and rotationally alignable to overlap one portion of at least one of said input electrodes to vary the electrical capacitance between said movable electrode and those of said plurality of input electrodes overlapped by said movable electrode;

first means for producing a train of pulse signals at a frequency F;

second means receiving said train of pulses for producing a plurality (M) of square wave outputs each having a frequency (F'"'"') equal to (F/N), where N is an integer greater than one, and each successive one of said plurality of square waves having a phase difference of (360/M) degrees with respect to the next preceding and next subsequent square wave;

each successive square wave output of said second means being coupled to a successive one of said plurality of input electrodes, commencing at a particular one of said input electrodes associated with said reference point;

third means coupled to said movable electrode for recovering from the plurality of square waves capacitively coupled from said plurality of input electrodes a periodic waveform having a frequency equal to the frequency (F'"'"') of said square waves and crossing a predetermined level at a time, after a predetermined transition of the square wave coupled to the input electrode associated with said reference point, linearly related to the angular rotation of said movable electrode with respect to said reference point; and

fourth means coupled to said first and third means for counting the pulses from said first means during the time interval between said predetermined transition and said predetermined level crossing to obtain a digital representation of the angular rotation of said movable electrode with respect to said reference point.

2. The control assembly as set forth in claim 1, wherein said second means comprises a M-phase Johnson counter.

3. The control assembly as set forth in claim 2, wherein the number M of input electrodes, and the number of phases in said Johnson counter, is three.

4. The control assembly as set forth in claim 2, wherein said second means includes a counter coupled between said first means and said Johnson counter for dividing by an integer N the number of pulses received by said Johnson counter from said first means.

5. The control assembly as set forth in claim 4, wherein N=24.

6. The control assembly as set forth in claim 1, wherein said third means comprises a comparator having a first input receiving a reference level and a second input receiving a signal from said movable electrode.

7. The control assembly as set forth in claim 6, wherein said third means further comprises fifth means coupled between said movable electrode and said comparator second input for recovering only the fundamental sinusoidal component of the signal from said movable electrode.

8. The control assembly as set forth in claim 7, wherein said fifth means comprises an operational amplifier having an output and a summing junction input connected to said movable electrode and T-notch filter coupled to provide negative feedback between said operational amplifier output and said summing junction input.

9. The control assembly as set forth in claim 1, wherein said fourth means includes means for counting at least N consecutive pulses;

means for gating the pulse train from said first means to said counting means; and

means for enabling said gating means only in the time interval between said predetermined transition and said predetermined level crossing.

10. The control assembly as set forth in claim 9, wherein said counting means is reset to a predetermined count at the occurrence of said predetermined transition.

11. A capacitive control assembly for use on a solid panel having front and rear surfaces, comprising:

a plurality (M) of input electrodes disposed about a common center and fabricated upon said panel rear surface;

the centers of adjacent input electrodes separated from one another by an angle about said common center substantially equal to (360/M) degrees, where M is an integer greater than one;

a movable electrode positioned adjacent to said panel front surface and rotationally alignable to overlap one portion of at least one of said input electrodes to vary the electrical capacitance between said movable electrode and those of said plurality of input electrodes overlapped by said movable electrode;

means connected to each of said plurality of input electrodes and to said movable electrode for recognizing a change in differential capacitance between the movable electrode and each of the plurality of input electrodes to determine the rotational position of said movable electrode with respect to a reference point;

means magnetically attachable to and detachable from said panel front surface for supporting said movable electrode at a fixed distance parallel to said panel front surface during rotation of said movable electrode; and

a disk electrode positioned upon said panel rear surface and within the annulus formed by said plurality of input electrodes, said disk electrode being capacitively coupled to said movable electrode through said supporting means and directly coupled to said capacitance recognizing means.

12. The control assembly as set forth in claim 11, wherein each of said input electrodes is sector shaped and subtends an angle, about said common center, substantially equal to (360/M) degrees.

13. The control assembly as set forth in claim 12, wherein said movable electrode has substantially the same size and shape as each of said input electrodes.