Touch sensitive liquid crystal switch

• US 4,529,968 A
• Filed: 11/10/1982
• Issued: 07/16/1985
• Est. Priority Date: 11/16/1981
• Status: Expired due to Term

• Current Assignee: The secretary of state for defence in her Britannic Majesty's Government of the United Kingdom of Great Britain And Northern Ireland
• Original Assignee: The secretary of state for defence in her Britannic Majesty's Government of the United Kingdom of Great Britain And Northern Ireland
• Inventors: Hilsum, Cyril, Raynes, Edward P.
• Primary Examiner(s): Groody, James J.
• Application Number:
  US06/440,590
• Time in Patent Office: 979 Days
• Field of Search: 340/365 C, 340/712, 340/784, 340/765, 200/DIG. 1, 361/287, 361/288, 361/290, 361/291, 400/479.1
• US Class Current: 340/635
• CPC Class Codes: H03K 17/962 Capacitive touch switches

Abstract

A touch sensitive switch with a liquid crystal cell and a circuit for measuring capacitive changes when the cell is deformed by touch. The cell has a layer of a liquid crystal material between slides bearing electrodes. Capacitive changes are detected for example by a comparator or by a bridge circuit which includes one or more cells. Touching one cell unbalances the bridge. The area of cell that is touched may be coincident with or separate from a display area. For some types of cells extra sensitivity is achieved by maintaining a voltage across the cell between a critical and saturation value.

Claims

1. A touch sensitive switch comprising:

a liquid crystal cell formed by a layer of liquid crystal material contained between two electrode bearing slides,

means for applying a voltage to the electrodes above a threshold value at which liquid crystal molecules begin to rotate under the effect of the electric field caused by the applied voltage,

means for detecting a change in cell capacitance between said electrodes when the cell is deformed, and

means for producing a signal indicating said detected capacitance change.

2. The switch according to claim 1 wherein the cell is arranged to change displayed information in at least a part of the cell area.

3. The switch according to claim 2 wherein that part of the cell displaying information is arranged to be deformable by an operators touch.

4. The switch according to claim 2 wherein that part of the cell displaying information is separate from that part deformable by an operators touch.

5. The switch according to claim 1 wherein the means for detecting a change in capacitance includes a balanced bridge circuit which is unbalanced on deformation of the cell which forms a part of the bridge.

6. The switch according to claim 5 wherein a plurality of cells are connected into the bridge circuit.

7. The switch according to claim 1 wherein the liquid crystal material is a nematic material.

8. The switch according to claim 1 wherein the liquid crystal material is a cholesteric material.

9. The switch according to claim 1 wherein an amount of a dye is dissolved in the liquid crystal material.

10. The switch according to claim 1 wherein the facing surfaces of the slides are treated to align contacting liquid crystal molecules at an angle to the surfaces.

11. The switch according to claim 1 wherein the means for detecting a change in capacitance includes means for supplying a voltage across the cell and a reference capacitor connected together in series, and a comparator for comparing the voltage developed across the cell with a reference voltage.

12. A touch sensitive switch comprising:

a liquid crystal cell formed by a layer of liquid crystal material contained between two electrode bearing slides, the slides being surface treated to give a molecule tilt above 10°

to the liquid crystal molecules at the slide surface,

means for detecting a change in cell capacitance between said electrodes when the cell is deformed, and

means for producing a signal indicating said detected capacitance change.