A control panel having a touch sensitive position sensor and at least one mechanical switch located within a sensitive area of the position sensor is provided. The position sensor comprises a capacitive position sensing element coupled to position sensing circuitry operable to determine the position of a capacitive load, such as a finger, positioned adjacent to the sensitive area of the position sensing element. The mechanical switch has an open state and a closed state and is arranged such that a contact of the switch is selectively electrically coupled to or decoupled from the position sensing element depending on whether the switch is in the open or closed state. A compact and robust control panel can thus be provided in which the presence of the mechanical switch within the sensitive area of the position sensor does not significantly effect its sensitivity.
1. A control panel comprising:
a capacitive position sensing element arranged on a surface of the substrate and coupled to a position sensing circuit operable to determine the position of a capacitive load applied to the position sensing element; and
at least one mechanical switch positioned on the surface of the substrate within a sensitive area of the position sensing element, wherein the switch has an open state and a closed state and is arranged such that a switched contact of the switch is electrically coupled to the position sensing element when the switch is in the closed state and is electrically decoupled from the position sensing element when the switch is in the open state.
2. The control panel of claim 1 , wherein the switched contact is electrically coupled to a system ground potential.
3. The control panel of claim 1 , further comprising a capacitor wherein the switched contact is electrically coupled to the capacitor.
4. The control panel of claim 1 , further comprising a switch sensing circuit coupled to the switched contact and wherein the position sensing circuit includes a drive circuit operable to apply drive signals to the capacitive position sensing element, the switch sensing circuit being operable to determine whether the drive signals are applied to the switched contact.
5. The control panel of claim 1 , wherein the capacitive position sensing element comprises a plurality of sense electrodes and the position sensing circuit is operable to measure a capacitance of each sense electrode to a system ground potential.
6. The control panel of claim 1 , wherein the capacitive position sensing element comprises a continuous resistive sensing path and wherein the position sensing circuit is operable to determine a capacitance between the resistive sensing path and a system ground potential at a plurality of locations along the resistive sensing path.
7. The control panel of claim 6 , wherein the switch comprises a deformable diaphragm having a resistivity substantially the same as that of the resistive sensing path.
8. The control panel of claim 1 , wherein the position sensing element is operable to determine the position of an object in a sensing direction and wherein the mechanical switch has a greater extent in a direction orthogonal to the sensing direction than in a direction along the sensing direction.
9. The control panel of claim 1 , further comprising a surface panel overlaying the position sensing element, wherein the surface panel has a wall defining an opening through which the mechanical switch passes.
10. The control panel of claim 9 , further comprising a protective flexible membrane overlaying the surface panel.
11. The control panel of claim 1 , wherein the mechanical switch comprises a deformable diaphragm overlaying the switched contact, and wherein the switch is operable to be changed between the open state and the closed state by pushing on the deformable diaphragm.
12. The control panel of claim 1 , wherein the position sensing element is arranged around a closed path.
13. The control panel of claim 1 , wherein the position sensing circuit comprises a charge transfer capacitance measurement circuit.
14. A device having a control panel comprising:
a capacitive position sensing element arranged on a surface of the substrate and coupled to a position sensing circuit operable to determine the position of a capacitive load applied to the position sensing element; and
at least one mechanical switch positioned on the surface of the substrate within a sensitive area of the position sensing element, wherein the switch has an open state and a closed state and is arranged such that a switched contact of the switch is electrically coupled to the position sensing element when the switch is in the closed state and is electrically decoupled from the position sensing element when the switch is in the open state.