Touch control system

• US 5,867,111 A
• Filed: 11/01/1996
• Issued: 02/02/1999
• Est. Priority Date: 03/29/1993
• Status: Expired due to Fees

• Current Assignee: Donnelly Technology, Inc.
• Original Assignee: Donnelly Technology, Inc.
• Inventors: Caldwell, David W., Medendorp, Nicholas W.
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): WONG, ALBERT KANG
• Application Number:
  US08/740,701
• Time in Patent Office: 823 Days
• Field of Search: 341/33, 341/26, 341/72, 341/24, 341/195, 200/600, 200/5 A, 345/168, 345/173, 219/451, 362/32
• US Class Current: 341/33
• CPC Class Codes: F24C 7/083 on tops, hot plates
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard

Abstract

A touch control system that is responsive to a user input selection includes an electrically non-conducting substrate, such as glass ceramic, and at least one capacitive-responsive touch pad on the substrate. A source signal having a primary frequency that is greater than 150 kHz, and preferably in the range of between 150 kHz and 500 kHz, is applied to one portion of the touch pad. The touch pad couples the electrical signal to another portion of the touch pad in order to develop a detection signal, which is decoded in order to determine the presence of the capacitance of a user. The decoder preferably includes a peak detector composed of a low gain circuit in order to avoid distortion of the detection signal. Greatly improved performance in the presence of liquids, such as water, on the touch pad is provided. This is especially useful when the touch pad is applied to a horizontal surface, such as a cook top, upon which liquid spills may occur. A display is juxtaposed with the glass ceramic substrate and an optical correction material is provided between the display and the underlying modulated surface that imparts mechanical strength to the substrate. The optical correction material corrects optical distortion of the visual indications of the display caused by the modulated surface.

Claims

1. A moisture immune touch control circuit for use with a substrate comprising:

a touch responsive circuit including at least one touch pad which produces a detection signal in the presence of capacitance of a user at said touch pad, wherein said detection signal is substantially immune to the presence of moisture; and

a decoding circuit that responds to said detection signal in order to determine the presence of said capacitance of a user, said decoding circuit including a successive approximation register circuit in order to determine an amplitude of said detection signal.

2. The touch control circuit in claim 1 wherein said successive approximation register circuit includes a resistance network driven by a microcomputer to produce an approximation signal and a comparator to compare said detection signal with said approximation signal.

3. The touch control circuit in claim 2 wherein said successive approximation register circuit includes a scaling circuit to scale said approximation signal.

4. The touch control circuit in claim 1 including a carrier supporting and electrically interconnecting components defining said touch responsive circuit and said decoding circuit.

5. The touch control circuit in claim 1 wherein said decoding circuit has an input impedance of less than approximately 10 kohms.

6. The touch control circuit in claim 4 including an indicator mounted to said carrier for displaying outputs of said decoding circuit.

7. The touch control circuit in claim 6 wherein said carrier is a flexible carrier.

8. The touch control circuit in claim 4 wherein said carrier is a flexible carrier.

9. The touch responsive circuit in claim 1 wherein said at least one touch pad includes a pair of electrically conductive elements.

10. The touch responsive circuit in claim 9 including a signal generator for applying a signal to one of said elements, the capacitance of a user coupling said signal to the other of said elements as said detection signal.

11. The touch responsive circuit in claim 7 including an adhesive for affixing said flexible carrier to a substrate.

12. A moisture immune touch control circuit which is static electricity resistant for use with a substrate comprising:

a touch responsive circuit including at least one touch pad which produces a detection signal in the presence of capacitance of a user at said touch pad, wherein said detection signal is substantially immune to the presence of moisture; and

a decoding circuit the responds to said detection signal in order to determine the presence of said capacitance of a user, said decoding circuit comprising a low gain detector circuit, an amplifier and an impedance element, said detector circuit having an input coupled with said touch responsive circuit to receive said detection signal and an output coupled with said amplifier, said impedance element connected between said input and a ground providing an input impedance for said decoding circuit of less than approximately 10 kohms.

13. The touch control circuit in claim 12 including a carrier supporting and electrically interconnecting components defining said touch responsive circuit and said decoding circuit.

14. The touch control circuit in claim 13 including an indicator mounted to said carrier for displaying outputs of said decoding circuit.

15. The touch control circuit in claim 14 wherein said carrier is a flexible carrier.

16. The touch control circuit in claim 13 wherein said carrier is a flexible carrier.

17. The touch control circuit in claim 16 including an adhesive for affixing said flexible carrier to a substrate.

18. The touch control circuit in claim 12 wherein said detector circuit is a peak detector circuit.

19. The touch control circuit in claim 18 wherein said peak detector circuit has a substantially unity gain.

20. The touch control circuit in claim 12 wherein said detector circuit has a substantially unity gain.

21. The touch control circuit in claim 12 wherein said impedance element has an impedance value of less than approximately 10 kohms.

22. A touch control circuit for use with a substrate comprising:

a touch responsive circuit including at least one touch pad which produces a detection signal in the presence of capacitance of a user at said touch pad; and

a microcomputer having an output which operates a resistance network in order to produce an analog signal, a comparator which compares said analog signal with said detection signal and produces a digital signal which is supplied as an input to said microcomputer, said digital signal having a state which is a function of the relative amplitudes of said analog signal and said detection signal, wherein said microcomputer is programmed to adjust said output while monitoring said input in a manner which determines whether said detection signal represents the presence of capacitance of a user at said touch pad.

23. The touch control circuit in claim 22 wherein said decoding circuit has an input impedance of less than approximately 10 kohms.

24. The touch control circuit in claim 22 including a carrier supporting and electrically interconnecting components defining said touch control circuit.

25. The touch control circuit in claim 24 including an indicator mounted to said carrier for displaying outputs of said decoding circuit.

26. The touch control circuit in claim 25 wherein said carrier is a flexible carrier.

27. The touch control circuit in claim 24 wherein said carrier is a flexible carrier.

28. The touch control circuit in claim 27 including an adhesive for affixing said flexible carrier to a substrate.

29. The touch control circuit in claim 22 wherein said at least one touch pad includes a pair of electrically conductive elements.

30. The touch control circuit in claim 29 including a signal generator for applying a signal to one of said elements, the capacitance of a user coupling said signal to the other of said elements as said detection signal.