US20060227117A1 - Circular touch sensor - Google Patents

Abstract

A circular touch sensor has three or more sensors arranged in an iris pattern. Each pad is defined by continuous edges that spiral outward about a center point. The unique geometric shape allows measurement of relative amounts of contact on adjoining sensors. In one implementation, the sensors measure relative capacitance of two or more sensors, thereby enabling high precision identification of the point of contact. With as few as three pads, the circular touch sensor is less expensive than traditional 12-pad to 16-pad circular sensors.

Description

TECHNICAL FIELD
• This disclosure relates to touch sensors, and particularly circular touch sensors.
BACKGROUND
• Touch sensors are used in many electronic and computing devices. Many laptops, for example, are equipped with a rectangular touch sensor that functions like a computer mouse to control pointer positioning on a screen and permit entry of commands. The touch sensor detects the user's touch and generates signals representing a location of contact on the sensor.
• FIG. 1 shows a conventionallinear touch sensor100. For discussion purposes, thesensor100 is illustrated with four rectangular sensor pads102(1),102(2),102(3), and102(4) that are linearly aligned. This arrangement allows detection of a user's touch within four discrete zones1-4 that correspond with the four sensor pads102(1)-102(4).
• To increase precision, additional detection zones may be created by changing the shape of the sensor pads.FIG. 2 shows another conventionallinear touch sensor200 having five discrete sensor pads202(1)-202(5), where each sensor pad has a non-rectangular shape. Edges between adjacent sensor pads are discontinuous or jagged. This shape allows adjoining sensor pads to interlace with one another to define additional detection zones, so that there are more zones than sensor pads. In this example, there are nine detection zones1-9 for five sensor pads. With this arrangement, a single touch inzone2 is detected by adjacent sensor pads202(1) and202(2), whereas a touch inzone1 is detected solely by the top sensor pad202(1).
• Many devices today use non-rectangular touch sensors. For instance, some popular audio devices (e.g., MP3 players) employ circular touch sensors. These sensors have traditionally followed the same design as linear sensors, with multiple discrete sensor pads (e.g., 12-16 sensors) aligned side-by-side.FIG. 3 shows a conventionalcircular sensor300 having sixteendiscrete sensor pads302 extending radially outward from the center. To increase precision, the edges between the sensor pads may be made jagged.FIG. 4 shows one examplecircular sensor400 havingmultiple sensor pads402 with jagged edges. Sixteenpads402 are shown, but there may be fewer (e.g., 12).
• These conventional sensors detect presence or absence of a finger on each sensor pad. Past solutions to increase precision have been to increase the number of sensor pads or make the edges jagged to define extra detection zones. However, larger numbers of sensor pads requires more expensive and complex interfaces to convert the detection signals to a smaller number of output pins on circuit chips. Moreover, even as the number of sensor pads increase, the sensors still detect only a finite number of contact positions.
• In addition to precision, manufacturing cost is another important consideration for designers of touch sensors. These designers continually look for ways to reduce cost. Conventional circular touch sensors employ anywhere from 12 to 16 sensors, thereby increasing component costs.
• Accordingly, there remains a need for an improved circular touch sensor that is inexpensive to produce, yet provides high accuracy and precision similar to that of conventional 16-pad sensors.
SUMMARY
• A circular touch sensor has three or more sensors arranged in an iris pattern. Each pad is defined by continuous edges that spiral outward about a center point. The unique geometric shape allows measurement of relative amounts of contact on adjoining sensors. In one implementation, the sensors measure relative capacitance of two or more sensors, thereby enabling high precision identification of the point of contact. With as few as three pads, the circular touch sensor is less expensive than traditional 12-pad to 16-pad circular sensors.
BRIEF DESCRIPTION OF THE CONTENTS
• The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference numbers in different figures indicates similar or identical items.
• FIG. 1 illustrates a conventional linear touch sensor with straight edges between adjacent sensor pads.
• FIG. 2 illustrates a conventional linear touch sensor with jagged edges between adjacent sensor pads.
• FIG. 3 illustrates a conventional circular touch sensor with straight edges between adjacent sensor pads.
• FIG. 4 illustrates a conventional circular touch sensor with jagged edges between adjacent sensor pads.
• FIG. 5 illustrates a portable entertainment device that implements a circular touch sensor.
• FIG. 6 illustrates the circular touch sensor implemented in a system architecture, which may be implemented, for example, in the portable entertainment device ofFIG. 5. The circular touch sensor has three sensor pads arranged according to a first implementation.
• FIG. 7 illustrates the circular touch sensor ofFIG. 6 as it would appear if uncoiled and stretched out linearly.
• FIG. 8 illustrates a circular touch sensor in which the pad arrangement shown inFIG. 7 is replicated multiple times.
• FIG. 9 illustrates a circular touch sensor having three sensor pads arranged according to a second implementation.
• FIG. 10 illustrates the circular touch sensor ofFIG. 9 as it would appear if uncoiled and stretched out linearly.
• FIG. 11 illustrates a circular touch sensor in which the pad arrangement shown inFIG. 10 is replicated multiple times.
• FIG. 12 illustrates a circular touch sensor having four sensor pads.
• FIG. 13 illustrates the circular touch sensor ofFIG. 12 as it would appear if uncoiled and stretched out linearly.
• FIG. 14 is a flow diagram of a process for operating a circular touch sensor.
DETAILED DESCRIPTION
• This disclosure is directed to circular touch sensors. The circular touch sensor has three or more sensor pads arranged in an iris pattern. The sensor pads measure relative presence of a user's finger (or other pointing member) on adjoining sensor pads. The sensor pads may measure, for example, relative capacitance or pressure on adjoining pads, although other technologies that output variable signals indicative of the degree of contact may be used. The unique geometric shape and measurement of relative contact position on adjoining sensor pads enables high precision detection with far fewer sensor pads than the traditional 12-pad to 16-pad sensors. Since the sensor can be implemented with as few as three sensors, the circular touch sensor is less expensive than the conventional circular sensors.
• For discussion purposes, the circular touch sensor is described in the context of consumer electronic devices, such as portable entertainment devices, portable digital assistants (PDAs), cellular phones, audio players, video players, notebook computers, digital cameras, laptop computers, and the like. One example implementation is shown below inFIG. 5. However, the circular touch sensor can be implemented in other types of devices and in different environments.
• Portable Entertainment Device
• FIG. 5 shows aportable entertainment device500 configured as a Portable Media Center™ device supported by Microsoft Corporation. Thedevice500 is a multifunction device having memory and processing capabilities to play music and videos, depict still images, download content from the Internet, and the like.
• Device500 has a body or casing502 and adisplay panel504 mounted centrally of thecasing502. Thedisplay panel504 is a flat panel, color display with sufficient resolution to depict digital images or motion video. The display panel may be optionally implemented with a touch screen overlaying the display to facilitate user input. The display panel may be implemented using different technologies, including LCD (liquid crystal display) and OLED (organic light emitting diode).
• Acircular touch sensor506 is positioned left of thedisplay panel504 to support user control of thedevice500.Shuttle control buttons508 are positioned right of thedisplay panel504 to control video playback. One or more other buttons may also be provided to facilitate other control functions, such as volume, brightness, contrast, and so forth. It is noted that thedevice500 is just one exemplary implementation, and that other configurations and layouts, with more or less buttons and features, may be used.
• Thecircular touch sensor506 has three or more sensor pads arranged in a geometric pattern with continuous, arcuate edges. This allows the sensor pads to measure a ratio of finger contact across adjoining pads. While thetouch sensor506 is illustrated in a circular shape, it is noted that thesensor506 may take on other non-circular shapes. Possible example shapes include ovals, star-like patterns, and polygons.
• Sensor
• FIG. 6 shows a circular touch sensor in asystem architecture600 that might be implemented, for example, in theportable entertainment device500. Thecircular touch sensor506 is coupled to a microcontroller or CPU (central processing unit)602 viacapacitance detection circuitry604 and aninterface606. Theinterface606 may be implemented as software running on theCPU602 or as a hardware interface. When a user or other object (e.g., stylus) contacts thecircular touch sensor506, thecapacitance detection circuitry604 detects changes in capacitance as an indication of contact. Thecircuitry604 generates signals that are passed to theCPU602 for determination of a location of the touch on thecircular sensor506.
• Thecircular touch sensor506 is illustrated with three sensor pads A, B, C and acenter region610. The pads A, B, C are arranged in a geometric pattern about a center point within thecenter region610. Each pad is defined by continuous, arcuate edges that spiral from aninner boundary612 defined by thecenter region610 outward to anouter boundary614 of thesensor506. In this arrangement, the sensor pads A, B, C form an iris pattern, where each sensor pad defines or covers approximately one-third of a contact region defined between the inner and outer boundaries.
• The sensor pads A, B, C overlap one another such that any radius from the sensor's center crosses over at least two sensor pads. In this example, each pad edge originates at a first point on theinner boundary612 and terminates at a second point on theouter boundary614, where the first and second points are approximately 180° apart. For instance, an edge separating pads A and B originates at a point on theinner boundary612 at 0° and terminates at a point on theouter boundary614 at 180°. In this manner, a user's finger is likely to contact two adjoining sensor pads at any point on thecircular touch sensor506.
• For capacitance detection, the pads A, B, C are formed of metal or other electrically conductive material. Contact with pad A causes a capacitance change that is detected by an associatedcapacitance meter620 of thecapacitance detection circuitry604. Similarly, contact on pads B and C induce capacitance changes that are detected by associatedcapacitance meters622 and624, respectively. The capacitance meters620-624 generated values indicative of capacitance (or capacitance change), which are passed to theinterface606.
• With the iris-pattern arrangement, the user is likely to touch two pads concurrently. Theinterface606 and/orCPU602 determines the position of the user's finger on thecircular touch sensor506 based on the values from the capacitance meters620-624 associated with the pads A-C. Theinterface606 and/orCPU602 computes a ratio of values generated by pads being contacted. The ratio accurately identifies the angle at which contact is made on the circular sensor. In this manner, theCPU602,circuitry604, andinterface606 define a means for detecting contact made to one or more of the sensors and determining a location of the contact.
• As one example technique, there is a baseline value when no finger or pointing mechanism is present on the sensor pads. The baselines value can be established at design, or set through a calibration process. When a finger or pointing mechanism comes in contact with the sensor arrangement, there is an increase in capacitance across all sensors above the baseline value. The position of contact is determined by comparing the relative contribution of each sensor pad to the total capacitance increase across all sensors above the baseline value. A table may be compiled with various sensor values for corresponding finger positions, and theinterface606 may look up the position from the values in table 1 below.

  TABLE 1
  Position	A	B	C	TOTAL	A %	B %	C %

  0	1.00	0.00	0.50	1.50	0.667	0.000	0.333
  10	1.00	0.08	0.42	1.50	0.667	0.056	0.278
  20	1.00	0.17	0.33	1.50	0.667	0.111	0.222
  30	1.00	0.25	0.25	1.50	0.667	0.167	0.167
  40	1.00	0.33	0.17	1.50	0.667	0.222	0.111
  50	1.00	0.42	0.08	1.50	0.667	0.278	0.056
  60	1.00	0.50	0.00	1.50	0.667	0.333	0.000
  70	0.92	0.58	0.00	1.50	0.611	0.389	0.000
  80	0.83	0.67	0.00	1.50	0.556	0.444	0.000
  90	0.75	0.75	0.00	1.50	0.500	0.500	0.000
  100	0.67	0.83	0.00	1.50	0.444	0.556	0.000
  110	0.58	0.92	0.00	1.50	0.389	0.611	0.000
  120	0.50	1.00	0.00	1.50	0.333	0.667	0.000
  130	0.42	1.00	0.08	1.50	0.278	0.667	0.056
  140	0.33	1.00	0.17	1.50	0.222	0.667	0.111
  150	0.25	1.00	0.25	1.50	0.167	0.667	0.167
  160	0.17	1.00	0.33	1.50	0.111	0.667	0.222
  170	0.08	1.00	0.42	1.50	0.056	0.667	0.278
  180	0.00	1.00	0.50	1.50	0.000	0.667	0.333
  190	0.00	0.92	0.58	1.50	0.000	0.611	0.389
  200	0.00	0.83	0.67	1.50	0.000	0.556	0.444
  210	0.00	0.75	0.75	1.50	0.000	0.500	0.500
  220	0.00	0.67	0.83	1.50	0.000	0.444	0.556
  230	0.00	0.58	0.92	1.50	0.000	0.389	0.611
  240	0.00	0.50	1.00	1.50	0.000	0.333	0.667
  250	0.08	0.42	1.00	1.50	0.056	0.278	0.667
  260	0.17	0.33	1.00	1.50	0.111	0.222	0.667
  270	0.25	0.25	1.00	1.50	0.167	0.167	0.667
  280	0.33	0.17	1.00	1.50	0.222	0.111	0.667
  290	0.42	0.08	1.00	1.50	0.278	0.056	0.667
  300	0.50	0.00	1.00	1.50	0.333	0.000	0.667
  310	0.58	0.00	0.92	1.50	0.389	0.000	0.611
  320	0.67	0.00	0.83	1.50	0.444	0.000	0.556
  330	0.75	0.00	0.75	1.50	0.500	0.000	0.500
  340	0.83	0.00	0.67	1.50	0.556	0.000	0.444
  350	0.92	0.00	0.58	1.50	0.611	0.000	0.389
  360	1.00	0.00	0.50	1.50	0.667	0.000	0.333

• From table 1, a point of contact is deemed to be positioned at 60° when the contribution of pad A to the total increase above the baseline is approximately ⅔ (0.667) and the contribution of pad B to the total increase above the baseline is approximately ⅓ (0.333). Additionally, theinterface606 can use the table to interpolate between listed positions. Thus, the point of contact is deemed to be positioned at 55° on the circular touch sensor when pad A's contribution is approximately 0.667 to the total capacitance increase above the baseline, pad B's contribution is approximately 0.305, and pad C's contribution is approximately 0.028. With interpolation, thecircular touch sensor506 essentially functions as an infinitely variable sensor that senses infinitely many finger positions.
• Center region610 may also define a fourth pad. In this implementation,circuitry604 is equipped with a fourth capacitance meter to detect contact with thecenter region610. Thecenter region610 may be associated with a “select” or “OK” command.
• FIG. 7 shows the pads A-C of thecircular touch sensor506 uncoiled and stretched out linearly. Theinner boundary612 extends along the bottom and theouter boundary614 extends along the top. This illustration demonstrates the overlapping relationship of the pads. Contact sensed at a position of 0° is manifest by pad A contributing ⅔ (0.667) to the total increase above the baseline and pad C contributing ⅓ (0.333) to the total capacitance increase above the baseline. Contact sensed at a position of 240° is manifest by pad C contributing ⅔ (0.667) to the total increase above the baseline and pad B contributing ⅓ (0.333) to the total increase above the baseline.
• Notice also that there are locations on the sensor where three pads may detect presence of the user's finger, such as positions between 0° and 60°, and between 120° and 180°, and between 240° and 300°. As the user's finger moves along the sensor pads, the ratios of capacitance values generated by adjoining pads in contact with the finger vary continuously, providing very accurate position detection. The continuous ratio variance results from the smooth arcuate edges that spiral outward from the center region. This arrangement allows the circular touch sensor to effectively detect infinitely many positions, which is an improvement over discrete sensors that are capable of detecting only a finite number of positions.
• One particular implementation for detecting position using variable ratios of adjoining pads is described in U.S. patent application Ser. No. 09/820747, which was filed 03/30/2001, and is assigned to Microsoft Corporation. This Application is hereby incorporated by reference. Additionally, the above implementation is described as measuring capacitance to detect position. It is noted that the circular sensor may be implemented using other technologies, including pressure sensing technology. The circular sensor with an iris-shaped pad arrangement may be implemented with essentially any technology that measures variability of contact (e.g., 0→1), as opposed to a binary determination of presence or non-presence (e.g., 0 or 1).
• The pad layout shown inFIGS. 6 and 7 is one possible layout, and suitable for sensors having a radial width between theinner boundary612 and theouter boundary614 that is approximately the size of the user's finger. If the radial width is greater than a finger width, the pattern may be repeated radially to avoid affecting any measurement that might be caused by radial movement of the finger.
• FIG. 8 shows a linear version of acircular touch sensor800 where the iris pattern of three pads is repeated multiple times in the radial direction. In this example, the iris pattern of pads A-C, as represented in the linear version shown inFIG. 7, is repeated four times as represented by horizontal bands802(1),802(2),802(3), and802(4). Each band is set apart by intermediate boundaries, such that within each band between boundaries, the iris pattern is preserved. Here, two bands802(1) and802(3) are identical to that ofFIG. 7, while the other two bands802(2) and802(3) are inverted or mirrored. In each band, the sensor pads have side edges that spiral about the center point outward from one intermediate boundary to the next.
• As shown inFIG. 8, the resulting sensor pad layout defines a zigzag pattern in the vertical direction. When a user touches the sensor, two or three of the pads will generate capacitance signals used to determine the finger position. InFIG. 8, a user's finger (represented by dashed circle804) contacts three pads A, B, and C, although predominantly on pad A.
• Alternative Designs
• The circular touch sensor may be implemented in any number of different ways. For instance, the pads may be arranged with different iris patterns that generate different capacitance values for various contact positions.
• FIG. 9 shows acircular touch sensor900 having three pads A, B, and C. In this example, each pad edge originates at a first point on theinner boundary902 and terminates at a second point on theouter boundary904, where the first and second points are approximately 120° apart. For instance, an edge separating pads A and B originates at a point oninner boundary902 at 0° and terminates at a point onouter boundary904 at 120°. As a result, there are contact positions that can be sensed by a single sensor, rather than two or more sensors. Notice that contact positioned along radial paths906 (at 0°),908 (at 120°), and910 (at 240°) might be detected solely or predominantly by corresponding pads A, B, and C.
• Theinterface606 determines the contact position based on relative values generated by the capacitance meters620-624 associated with the pads A-C. Theinterface606 may use a table to look up contact position given the relative values, similar to that described above with respect to table 1.
• As above, theinterface606 can interpolate between the positions using a table, such as one similar to table 1, to detect any number of finger positions on the circular touch sensor.
• FIG. 10 shows the pads A-C of thecircular touch sensor900 when uncoiled and presented as a linear version. Notice that positions 0°, 120°, and 240° have no overlapping pads. Thus, unlike the layout ofFIG. 7, at most only two pads are contacted at any one time. As contact occurs at various positions on the circular sensor, ratios of capacitance values generated by two adjoining pads are used to identify the contact location. The arcuate edges of the pads enable continuously changing ratios as the user's finger slides around the sensor, thereby allowing infinitely many detection locations. For instance, as the user slides her finger from 0° to 120°, the contribution value ratio of pad A to pad B varies continuously from 1:0 to 0:1.
• FIG. 11 shows a linear version of acircular sensor800 where the iris pattern of three pads is repeated four times in the radial direction, as represented by horizontal bands1102(1),1102(2),1102(3), and1102(4). Two bands1102(1) and1102(3) are identical to that ofFIG. 10, while the other two bands1102(2) and1102(3) are inverted or mirrored.
• The sensors described above have three conductive pads. However, more than three conductive pads may be implemented in the circular touch sensor. More generally, the pad assembly for the touch sensors has N sensor pads arranged about a center point, where N≧3. Each sensor pad defines approximately 1/N of a contact region defined between the inner and outer boundaries.
• FIG. 12 shows an exemplarycircular touch sensor1200 having four pads A, B, C, and D arranged about acenter region1202. The pads A-D are arranged in a geometric iris-shaped pattern with continuous, arcuate edges spiraling outward from thecenter region1202. In this arrangement, the sensor pads A-D overlap one another such that any radius from the sensor's center crosses over at least two sensor pads and more often over three sensor pads. In this manner, a user's finger is likely to contact two or three adjoining sensor pads at any point on thecircular touch sensor1200.
• FIG. 13 shows the four pads A-D stretched out linearly. This illustration demonstrates the overlapping relationship of the four pads. At 60°, the contribution of pad B to the total increase above the base line is approximately ⅓ (0.333), the contribution of pad A is approximately ½ (0.500), and the contribution of pad D is approximately ⅙ (0.167).
• Operation
• FIG. 14 shows aprocess1400 for operating a circular touch sensor. Theprocess1400 is illustrated as a collection of blocks in a logical flow graph, which represent a sequence of operations that can be implemented in hardware, software, or a combination thereof. In the context of software, the blocks represent computer instructions that, when executed by one or more processors, perform the recited operations.
• For discussion purposes, theprocess1400 is described with reference to thesystem architecture600 shown inFIG. 6. It is noted that theprocess1400 may be implemented by other sensors and architectures.
• Atblock1402, contact on one or more pads of a circular touch sensor is detected. The contact may be from human touch, such as a finger, or a pointing device, such as a stylus or the like. In one implementation, the contact is detected by sensing capacitance change of one or more metal sensor pads, such as pads A, B, and C ofsensor506. The capacitance meters620-624 sense the capacitance change and pass values indicative of capacitance (or capacitance change) to theinterface606.
• Atblock1404, a location of contact on the circular touch sensor is determined. With respect tosystem600, theinterface606 and/orCPU602 interpret the values from the capacitance meters to identify a precise location that the user touched thesensor506. As one example, theinterface606 and/orCPU602 computes a ratio among the two or more pads receiving the contact. The computation may involve use of a table, such as tables 1 or 2 above, and interpolation between values listed in the table. The ratio accurately identifies the location of contact on the circular sensor in terms of angular position.
• Atblock1406, the identified location of contact is used to effectuate an operation. For instance, theCPU602 uses the location to ascertain a command intended by the user when contacting the circular touch sensor. Suppose, for example, that the device is operating in an audio player mode, and playback functions such as play, stop, skip ahead, and skip back are associated with locations on the circular sensor. When the user touches a position that aligns approximately with the “play” function, theCPU602 understands the identified location as the user's instruction to initiate play of the song title.
• Conclusion
• Although the invention has been described in language specific to structural features and/or methodological acts, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the claimed invention.

Claims (20)

1. A touch sensor, comprising:

multiple sensor pads arranged about a center point in an iris pattern, where each sensor pad has at least one associated edge that spirals about the center point to a boundary; and

circuitry coupled to the sensor pads to detect contact to one or more of the sensor pads.

2. A touch sensor as recited inclaim 1, wherein the multiple sensor pads comprises not more than four sensor pads.

3. A touch sensor as recited inclaim 1, wherein the multiple sensor pads are electrically conductive.

4. A touch sensor as recited inclaim 1, wherein:

the multiple pads are electrically conductive; and

the circuitry comprises capacitance meters to sense capacitance change in the multiple sensor pads.

5. A touch sensor as recited inclaim 1, wherein the circuitry senses pressure applied to one or more of the sensor pads.

6. A touch sensor as recited inclaim 1, wherein the circuitry generates values indicative of relative amounts of contact among the sensor pads.

7. A touch sensor as recited inclaim 1, wherein the multiple sensor pads are arranged with in multiple, repeating iris patterns set apart by intermediate boundaries, such that within each pattern, each sensor pad has at least one associated edge that spirals about the center point to the intermediate boundary.

8. A system comprising:

the touch sensor as recited inclaim 1; and

means for determining a location of the contact on the touch sensor.

9. A system comprising:

the touch sensor as recited inclaim 1, wherein the circuitry generates values representative of the contact to one or more of the sensor pads; and

means for determining a location of the contact on the touch sensor from the values by deriving a ratio indicative of relative contact among the one or more sensor pads, the ratio being used to ascertain the location of the contact on the touch sensor.

10. An electronics device comprising the touch sensor as recited inclaim 1.

11. A pad assembly for a touch sensor, comprising:

N sensor pads arranged about a center point; and

each sensor pad defining approximately 1/N of a contact region defined by first and second boundaries, where the second boundary is farther from the center point than the first boundary, and said each sensor pad having at least one associated edge that originates at the first boundary and spirals about the center point through the contact region to the second boundary.

12. A pad assembly as recited inclaim 11, wherein the sensor pads consist of three sensor pads (N=3).

13. A pad assembly as recited inclaim 11, wherein the sensor pads are made of an electrically conductive material.

14. A pad assembly as recited inclaim 11, wherein sensor pads are arranged such that the second boundary forms a circle.

15. A pad assembly as recited inclaim 11, wherein the edge originates at a first point on the first boundary and terminates at a second point on the second boundary, wherein the first and second points are at least 120° apart.

16. A pad assembly as recited inclaim 11, wherein the edge originates at a first point on the first boundary and terminates at a second point on the second boundary, wherein the first and second points are approximately 180° apart.

17. A pad assembly as recited inclaim 11, further comprising a center pad defined within the first boundary.

18. A sensor system, comprising:

the pad assembly as recited inclaim 11; and

circuitry coupled to the sensor pads to detect contact to one or more of the sensor pads.

19. A sensor system, comprising:

the pad assembly as recited inclaim 11; and

means for detecting contact to one or more of the sensors and determining a location of the contact.

20. A device, comprising:

a processor; and

a circular touch sensor coupled to provide user input controls to the processor, the circular touch sensor comprising:

multiple sensor pads arranged about a center point; and

each sensor pad having at least one associated edge that originates at a first boundary and spirals about the center point to a second boundary, where the second boundary is farther from the center point than the first boundary.

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