Capacitive touch control and display

• US 4,264,903 A
• Filed: 05/07/1979
• Issued: 04/28/1981
• Est. Priority Date: 06/12/1978
• Status: Expired due to Term

• Current Assignee: LXD, Inc.
• Original Assignee: General Electric Company
• Inventors: Bigelow, John E.
• Primary Examiner(s): Groody, James J.
• Application Number:
  US06/036,558
• Time in Patent Office: 722 Days
• Field of Search: 340/365 R, 340/365 C, 340/365 S, 340/200, 340/347 P, 200/DIG. 1, 200/52 R, 361/280, 361/292, 361/298, 361/299, 361/300, 361/287, 178/19, 324/60 C, 324/61 R
• US Class Current: 341/1
• 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
• 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 2217/96066 Thumbwheel, potentiometer, scrollbar or slider simulation by touch switch

Abstract

A control for use upon a solid panel, devoid of control shaft apertures, allows data entry by rotational positioning of a human member, such as one'"'"'s finger, about a pattern of a plurality of interdigitated electrodes formed upon an interior surface of the panel. The position of the member varies the capacitance between adjacent ones of the electrodes, with position-decoding electronics energizing successive ones of the plurality of electrodes with successive phases of a master signal and recovering information relating the phase of the signal returned from the control to the position of the member. A light-emitting display may be 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 activatable by positional contact by a member having an impedance to electrical ground potential, comprising:

a solid panel having front and rear surfaces;

a plurality (M) of electrodes, where M is an integer greater than one, disposed along a preselected geometric curve and fabricated upon one of said panel surfaces;

each of said M electrodes insulated from the others of said electrodes;

means coupled to each electrode for providing one of a like plurality (M) of signals thereto;

each signal having the same frequency as all other signals and having a phase differing by (360/M) degrees from the phases of the signals coupled to adjacent electrodes;

said signal providing means including first means for producing a train of pulse signals at a frequency F,

second means receiving said train of pulse signals 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 electrodes, commencing at a particular one of said electrodes associated with a reference point; and

means connected to each of said plurality of electrodes for recognizing the phase of the summation of all of said square wave outputs after coupling to said electrodes to determine the location of said contact position of said member on said panel above said electrodes, with respect to said reference point;

said recognizing means including third means coupled to said electrodes for recovering from said electrodes a periodic waveform having a frequency equal to the frequency (F'"'"') of said square wave outputs and crossing a predetermined level at a time, after a predetermined transition of the square wave coupled to the electrode associated with said reference point, related to the position of said member contact 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 position of said member contact with respect to said reference point.

2. The control assembly of claim 1, wherein said plurality of electrodes are disposed about a common center, with a centerline of each pair of adjacent electrodes separated from one another by an angle about said common center substantially equal to (360/M) degrees.

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

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

5. The control assembly as set forth in claim 3, wherein said second means includes a counter coupled between said first means and said Johnson counter for dividing by an integer N the frequency of the first means pulse signals received by said Johnson counter.

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

7. 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 the summation of the square wave outputs of said second means after coupling to each of said electrodes.

8. The control assembly set forth in claim 7, wherein said third means further comprises fifth means, interposed between said electrodes and said comparator receiving the summation of the square wave outputs of said second means after coupling to each of said electrodes, for recovering only the fundamental sinusoidal component of the summed square wave outputs from said electrodes for couplng to said comparator second input.

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

10. 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.

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

12. The control assembly as set forth in claim 1, wherein each electrode has a plurality of finger portions, at least one finger portion of each electrode being interdigitated between finger portions of an adjacent electrode.

13. The control assembly as set forth in claim 12 wherein the number M of electrodes is at least three.

14. The control assembly of claim 12 wherein said electrodes are arranged in an annulus about said common center.