Capacitive touch switch, circuit configuration for a capacitive touch switch and control device for an electronic domestic appliance with at least one capacitive touch switch

• US 20070181412A1
• Filed: 01/26/2007
• Published: 08/09/2007
• Est. Priority Date: 02/06/2006
• Status: Active Grant

• Current Assignee: Diehl AKO Stiftung & Company KG
• Original Assignee: Diehl AKO Stiftung & Company KG
• Inventors: Raunig, Bernd
• Granted Patent: US 7,851,720 B2
• Time in Patent Office: Days
• US Class Current: 200/310
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2017/9613 using two electrodes per touch switch
• CPC Class Codes: H03K 2217/960755 Constructional details of capacitive touch and proximity switches
• CPC Class Codes: H03K 2217/96076 with spring electrode
• CPC Class Codes: H03K 2217/960765 Details of shielding arrangements

Abstract

A capacitive touch switch which is used, for example, in a control device for an electronic domestic appliance, includes a sensor area as part of a capacitive sensor element having a capacitance which changes when touched. A measuring electrode, which is coupled to the sensor area, is disposed on a printed circuit board and is at a first potential. An additional electrode, which is disposed near the measuring electrode, likewise on the printed circuit board, is electrically insulated from the measuring electrode and is at a second potential, which is different from the first potential. The additional electrode brings about a shielding of the measuring electrode and thus an output signal of an associated sensor circuit that is less sensitive to interference. A circuit configuration for a capacitive touch switch and a control device for an electronic domestic appliance, are also provided.

Claims

1. A capacitive touch switch, comprising:

a sensor area being part of a capacitive sensor element having a capacitance changing when touched;

a printed circuit board;

a measuring electrode being disposed on said printed circuit board, coupled to said sensor area and at a first potential; and

an additional electrode being disposed on said printed circuit board near said measuring electrode, electrically insulated from said measuring electrode and at a second potential different from said first potential.

2. The touch switch according to claim 1, wherein said measuring electrode and said additional electrode are disposed on the same side of said printed circuit board.

3. The touch switch according to claim 2, wherein said additional electrode surrounds said measuring electrode with at least one shape selected from the group consisting of strip-shaped and areal-shaped.

4. The touch switch according to claim 1, wherein said measuring electrode is disposed on one side of said printed circuit board and said additional electrode is disposed on another side of said printed circuit board opposite said measuring electrode.

5. The touch switch according to claim 4, wherein said additional electrode corresponds to said measuring electrode in terms of size or has a larger area than said measuring electrode.

6. The touch switch according to claim 4, wherein said additional electrode is also disposed on the same side of said printed circuit board as said measuring electrode and surrounds said measuring electrode with at least one shape selected from the group consisting of strip-shaped and areal-shaped.

7. The touch switch according to claim 5, wherein said additional electrode is also disposed on the same side of said printed circuit board as said measuring electrode and surrounds said measuring electrode with at least one shape selected from the group consisting of strip-shaped and areal-shaped.

8. The touch switch according to claim 1, wherein said additional electrode and said measuring electrode have corresponding contours.

9. The touch switch according to claim 1, wherein said second potential of said additional electrode is different from ground.

10. The touch switch according to claim 1, which further comprises an elastic compression element electrically conductively connecting said measuring electrode to said sensor area.

11. The touch switch according to claim 1, which further comprises an electrically insulating, at least partly light-transmissive control panel plate behind which said sensor area is disposed.

12. A circuit configuration for a capacitive touch switch, the circuit configuration comprising:

a sensor circuit including;

a first pnp transistor having a base, an emitter and a collector, a first resistor connected between the base of said first pnp transistor and said measuring electrode of said touch switch according to claim 1, a second resistor connected between the base of said first pnp transistor and an operating voltage from a first voltage source, a third resistor connected between the emitter of said first pnp transistor and the operating voltage, and the collector of said first pnp transistor being connected to said additional electrode of said touch switch according to claim 1 and receiving a pulse voltage from a second voltage source; and

a second pnp transistor having a base, an emitter and a collector, the base of said second pnp transistor being connected to the emitter of said first pnp transistor, the collector of said second pnp transistor being connected to a reference potential, a parallel circuit connected between the emitter of said second pnp transistor and the operating voltage, said parallel circuit having a fourth resistor and a capacitance, and the emitter of said second pnp transistor supplying an output signal of said sensor circuit; and

an evaluation circuit receiving the output signal of said sensor circuit for determining whether or not said touch switch is actuated.

13. The circuit configuration according to claim 12, wherein said sensor circuit is one of a plurality of sensor circuits each being associated with a respective touch switch.

14. A control device for an electronic domestic appliance, the control device comprising at least one capacitive touch switch according to claim 1.

15. A control device for an electronic domestic appliance, the control device comprising a circuit configuration according to claim 12 for at least one capacitive touch switch.