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A device for detecting the position of a human finger or other object on a touch-sensitive scrolling pad. Dual independent oscillators may be used to generate two pulse trains at frequencies dependent upon the capacitance of two conductors resulting from the position of the finger on the conductors.

A device for detecting the position of a human finger or other object on a touch-sensitive scrolling pad. Dual independent oscillators may be used to generate two pulse trains at frequencies dependent upon the capacitance of two conductors resulting from the position of the finger on the conductors. The pulses from each oscillator may be counted over a time interval. A ratio-metric measurement may be taken by calculating the ratio of the two counts, and a sum may also be calculated. The ratio of the two counts relates to finger position on the device, and their sum relates to finger pressure upon the device.

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1. A device for measuring a position of a pointing member, comprising:a first oscillator including a first capacitive node having a first capacitance depending upon the position of the pointing member relative to the first capacitive node, the first oscillator generating a first signal having a firs

1. A device for measuring a position of a pointing member, comprising:a first oscillator including a first capacitive node having a first capacitance depending upon the position of the pointing member relative to the first capacitive node, the first oscillator generating a first signal having a first frequency depending upon the first capacitance; a second oscillator including a second capacitive node having a second capacitance depending upon the position of the pointing member relative to the second capacitive node, the second oscillator generating a second signal having a second frequency depending upon the second capacitance; and a frequency ratio determinator determining first and second characteristics associated with the first and second frequencies, respectively, and determining a ratio of the first and second characteristics. 2. The device of claim 1, wherein the frequency ratio determinator includes a counter configured to count a number of pulses in the first and second signals over a certain time interval in order to determine the first and second frequencies, the first characteristic being the number of pulses over the time interval in the first signal, the second characteristic being the number of pulses over the time interval in the second signal.3. The device of claim 1, wherein the frequency ratio determinator is configured to measure the first and second frequencies directly, the first and second characteristics being the first and second frequencies, respectively.4. The device of claim 1, wherein the first and second capacitive nodes each comprises a conductive plate.5. The device of claim 1, wherein the first and second capacitive nodes each comprises an etched conductive tracing on a substrate.6. The device of claim 2, wherein the first and second oscillators are each configured to be disabled while the other oscillator is enabled, and wherein the counter is configured to count the number of pulses in the first signal over a first time interval and the number of pulses in the second signal over a second non-overlapping time interval.7. The device of claim 2, wherein the counter is configured to count the number of pulses in the first and second signals over a time interval that is substantially less than a period of ambient alternating current power.8. The device of claim 2, wherein the frequency ratio determinator is further configured to determine a sum of the pulses counted from both the first and second signals, thereby allowing a pressure of the pointing member to be determined.9. The device of claim 1, further including an interface configured to send data representing the ratio of the first and second frequencies to another device.10. The device of claim 1, wherein the first oscillator further includes a third capacitive node and the second oscillator further includes a fourth capacitive node, the first, second, third, and fourth capacitive nodes being interdigitated with each other.11. A method for measuring a position of a pointing member, comprising the steps of:determining a first capacitance of a first capacitive node, the first capacitance depending upon the position of the pointing member; determining a second capacitance of a second capacitive node, the second capacitance depending upon the position of the pointing member; generating a first signal having a first frequency depending upon the first capacitance; generating a second signal having a second frequency depending upon the second capacitance; counting a number of pulses over a certain time interval from each of the first and second signals; and determining a ratio corresponding to a ratio of the first and second frequencies, the position of the pointing member being indicated by the determined ratio, wherein the step of determining the ratio includes determining the ratio as being a ratio of the number of pulses counted from the first signal and the number of pulses counted from the second signal. 12. The method of claim 11, wherein the step of counting includes counting the number of pulses of the first signal over a first time interval and counting the number of pulses of the second signal over a second non-overlapping time interval.13. The method of claim 12, wherein the step of counting includes enabling a first oscillator that generates the first signal during the first time interval while disabling a second oscillator that generates the second signal, and then disabling the first oscillator while enabling the second oscillator during the second time interval.14. A device for measuring a position of a pointing member relative to the device, comprising:a first capacitive node and a second capacitive node each commonly coupled to a first circuit node; and a third capacitive node and a fourth capacitive node each commonly coupled to a second circuit node, the first, second, third, and fourth capacitive nodes being disposed so as to be adjacent and interdigitated, wherein the pointing member interacts with at least one of the first, second, third, and fourth capacitive nodes, wherein the first circuit node is part of a first oscillator and the second circuit node is part of a second oscillator, the first oscillator generating a first signal with a frequency depending upon a combined capacitance of the first and second capacitive nodes, the second oscillator generating a second signal with a frequency depending upon a combined capacitance of the third and fourth capacitive node. 15. A device for measuring a position of a pointing member relative to the device only in a single dimension, comprising:a first capacitive node and a second capacitive node each commonly coupled to a first circuit node; a third capacitive node and a fourth capacitive node each commonly coupled to a second circuit node; an insulating material disposed over the first and second circuit nodes; and a groove formed in the insulating material and running axially in the single dimension, the first, second, third, and fourth capacitive nodes being disposed so as to be interdigitated, wherein the pointing member interacts with at least one of the first, second, third, and fourth capacitive nodes. 16. A device for measuring a position of a pointing member, comprising:a first oscillator including a first capacitive node, the first oscillator being configured to generate a first signal having a first characteristic depending upon the capacitance of the first capacitive node, the capacitance of the first node depending upon the position of the pointing member; a second oscillator including a second capacitive node, the second oscillator being configured to generate a second signal having a second characteristic depending upon the capacitance of the second capacitive node, the capacitance of the second node depending upon the position of the pointing member; and a processor configured to determine a ratio of the first and second characteristics. 17. The device of claim 16, further including an insulating material disposed over the first and second capacitive nodes.18. The device of claim 17, wherein the insulating material has a groove running in an axial direction, the first and second capacitive nodes also extending in the axial direction.