Capacitive sensing control knob

1. A method comprising:

receiving a plurality of signals from a sensor array disposed on a side wall of a non-movable, non-mechanical protrusion, wherein the protrusion is integrated into a surface of a control panel of a device as one integrated piece and physically resembles a mechanical knob that protrudes from the surface of the control panel of the device, wherein the protrusion extends out from the surface of the control panel such that a user's hand can at least grab an outer surface of the protrusion or move over the outer surface to operate the device and includes an opening on a back side of the protrusion that allows access to the side wall of the protrusion; and

detecting interaction of the user's hand with the sensor array based on the plurality of signals when the user's hand grabs the protrusion or moves over the outer surface;

wherein detecting the interaction comprises:

detecting presences of multiple conductive objects on the sensor array;

determining positions of the multiple conductive objects; and

identifying one of the multiple conductive objects as a finger and isolating the finger as a reference indicator based on the positions of the multiple conductive objects,

wherein identifying one of the multiple conductive objects as the reference indicator comprises:

determining a distance between each directly adjacent position of the multiple conductive objects based on a capacitance maximum for each of the multiple conductive objects, wherein each capacitance maximum corresponds to the positions of the multiple conductive objects; and

identifying a reference position using two greatest distances between the directly adjacent positions of the multiple conductive objects, wherein the one of the multiple conductive objects that is located at the reference position is identified as the finger.

2. An apparatus comprising:

a control panel having a non-movable, non-mechanical protrusion integrated with a surface of the control panel, as one integrated piece, that physically resembles a mechanical knob protruding from the surface of the control panel, wherein the protrusion is cylindrical or conical, wherein the protrusion extends out from the surface of the control panel such that a user's hand can interact with at least a portion of an outer surface of the protrusion to operate the control panel and includes an opening on a back side of the protrusion that allows access to a side wall of the protrusion;

a sensor array disposed on a side wall of the protrusion to detect the interaction of the user's hand with the sensor array when the user's hand grabs the protrusion or moves over the outer surface; and

a processing device coupled to the sensor array to detect the interaction of the user's hand with the sensor array by:

detecting presences of multiple conductive objects on the sensor array;

determining positions of the multiple conductive objects; and

identifying one of the multiple conductive objects as a finger and isolating the finger as a reference indicator based on the positions of the multiple conductive objects,

wherein identifying one of the multiple conductive objects as the reference indicator comprises:

determining a distance between each directly adjacent position of the multiple conductive objects based on a capacitance maximum for each of the multiple conductive objects, wherein each capacitance maximum corresponds to the positions of the multiple conductive objects; and

identifying a reference position using two greatest distances between the directly adjacent positions of the multiple conductive objects, wherein the one of the multiple conductive objects that is located at the reference position is identified as the finger.

3. The apparatus of claim 1 , further comprising a display disposed on a top surface of the protrusion to indicate the interaction of the user with the control panel.

4. The apparatus of claim 1 , further comprising an external indicator to indicate the interaction of the user with the control panel.

5. The apparatus of claim 1 , wherein the apparatus is an electrical appliance, and wherein the processing device, protrusion, and sensor array operate as a control knob of the electrical appliance.

6. The apparatus of claim 2 , further comprising a moveable part disposed on the protrusion and configured to engage the protrusion such that the moveable part moves with reference to the protrusion, while the sensor array and protrusion remain in fixed, non-moveable locations.

7. An apparatus, comprising:

a processing device to receive a plurality of signals from a sensor array, wherein the sensor array is disposed on a side wall of a non-movable, non-mechanical protrusion integrated with a surface of a control panel of a device as one integrated piece, wherein the protrusion extends out from the surface of the control panel such that a user's hand can interact with at least a portion of an outer surface of the protrusion to operate the device and includes an opening on a back side of the protrusion that allows access to the side wall of the protrusion;

wherein the processing device is configured to detect the interaction of the user's hand with the sensor array based on signals received from the sensor array by:

detecting presences of multiple conductive objects on the sensor array;

determining positions of the multiple conductive objects; and

identifying one of the multiple conductive objects as a finger and isolating the finger as a reference indicator based on the positions of the multiple conductive objects,

wherein identifying one of the multiple conductive objects as the reference indicator comprises:

determining a distance between each directly adjacent position of the multiple conductive objects based on a capacitance maximum for each of the multiple conductive objects, wherein each capacitance maximum corresponds to the positions of the multiple conductive objects; and

identifying a reference position using two greatest distances between the directly adjacent positions of the multiple conductive objects, wherein the one of the multiple conductive objects that is located at the reference position is identified as the finger.

8. The apparatus of claim 7 , wherein the processing device comprises:

a capacitance sensor to measure a capacitance on the sensor array; and

a selection circuit coupled to a plurality of sensor elements of the sensor array and the capacitance sensor, wherein the selection circuit is configured to select each of the plurality of sensor elements to measure the capacitance on each of the plurality of sensor elements.

9. The apparatus of claim 8 , wherein the capacitance sensor is a relaxation oscillator, and wherein the relaxation oscillator is coupled to a digital counter.

10. The apparatus of claim 8 , wherein the capacitance sensor includes a sigma-delta modulator circuit, and wherein the sigma-delta modulator circuit is coupled to a digital filter to measure a ratio of pulse widths of an output of the sigma-delta modulator circuit.