Capacitive encoder

1. A human machine interface comprising:

a face plate;

a capacitive sensor disposed on an interior side of the face plate;

a control device rotatably coupled to the face plate and disposed on an exterior side of the face plate, the control device including at least one electrically conductive element, the control device being configured to rotate about an axis substantially perpendicular to the face plate such that the at least one electrically conductive element follows the rotation of the control device, wherein the capacitive sensor is configured to sense a rotational position of the at least one electrically conductive element;

a housing fixedly attached to the exterior side of the face plate, the housing including an annular lip, the control device being rotatably coupled to the housing; and

an annular detent sandwiched between the housing and the control device, the annular detent being attached to an interior side of the annular lip of the housing.

2. The interface of claim 1 wherein the control device comprises an annular bearing.

3. The interface of claim 1 wherein the annular detent comprises a first annular detent, the control device including a second annular detent engaging the first annular detent.

4. The interface of claim 1 wherein the at least one electrically conductive element comprises a disc.

5. The interface of claim 1 wherein the at least one electrically conductive element is disposed on an interior end of the control device.

6. The interface of claim 1 wherein the capacitive sensor has an annular shape.

7. The interface of claim 1 wherein the capacitive sensor comprises a capacitive circular switch pattern.

8. A method of operating a human machine interface, comprising the steps of:

providing a face plate including an exposed exterior side and an unexposed interior side;

providing a first capacitive sensor on the interior side of the face plate;

rotatably coupling a control device to the face plate, the control device including a first electrically conductive element, the control device being rotatable about an axis substantially perpendicular to the face plate such that the first electrically conductive element follows the rotation of the control device;

using the first capacitive sensor to sense rotational movement of the first electrically conductive element;

providing a second capacitive sensor on the interior side of the face plate;

slidably coupling a pushbutton to the control device, the pushbutton including a second electrically conductive element, the pushbutton being slidable along the axis substantially perpendicular to the face plate such that the second electrically conductive element follows the sliding of the pushbutton; and

using the second capacitive sensor to sense actuation of the pushbutton in axial directions toward and away from the face plate such that the second electrically conductive element follows the movement toward and away from the face plate, the second capacitive sensor sensing movement of the second electrically conductive element in the directions toward and away from the face plate.

9. The method of claim 8 comprising the further step of adjusting an operating parameter of an audio system, an HVAC system, or a navigation system of a motor vehicle, the adjusting being dependent upon a sensed rotational position of the control device.

10. The method of claim 8 wherein the at least one electrically conductive element is disposed on an interior end of the control device.

11. The method of claim 8 wherein the control device comprises an annular bearing.

12. The method of claim 8 wherein the capacitive sensor has an annular shape.

13. The method of claim 8 comprising the further steps of:

providing the control device with a detent; and

using the detent to provide a user with tactile feedback in response to the user rotating the control device about the axis.

14. A human machine interface comprising:

a face plate;

a first capacitive sensor disposed on an interior side of the face plate and having a substantially annular shape defining a central opening;

a second capacitive sensor disposed on the interior side of the face plate within the central opening of the first capacitive sensor;

a knob disposed on the exterior side of the face plate, the knob including:

a housing fixedly attached to the exterior side of the face plate;

a control device rotatably coupled to the housing and including at least one first electrically conductive element; the control device being configured to rotate about an axis substantially perpendicular to the face plate such that the at least one first electrically conductive element follows the rotation of the control device; and

a pushbutton disposed in the housing and movable in a first axial direction toward the face plate and a second axial direction away from the face plate;

a second electrically conductive element disposed within the housing and configured to follow the movement of the pushbutton; and

a spring disposed between the face plate and the pushbutton and configured to bias the pushbutton hi the second axial direction;

wherein the first capacitive sensor is configured to sense a rotational position of the at least one first electrically conductive element, and the second capacitive sensor is configured to sense an axial position of the second electrically conductive element.

15. The interface of claim 14 wherein the second electrically conductive element is disposed in a recess of the spring.

16. The interface of claim 14 wherein the second capacitive sensor is disposed in the central opening of the first capacitive sensor.

17. The interface of claim 14 wherein the second electrically conductive element is disposed at an interior end of the pushbutton.

18. The interface of claim 14 wherein the spring includes a frusto-conically shaped body and an annular base extending radially outwardly from an interior end of the body.

19. The interface of claim 14 further comprising:

a first detent on the knob housing; and

a second detent on an exterior end of the control device configured to engage the first detent and thereby provide a user with tactile feedback in response to the user rotating the control device.