Two-dimensional touch panel
A capacitive touch panel is provided capable of detecting multiple simultaneous touches. The touch panel delivers sets of capacitance signal values to a processor which computes the coordinates of single or multiple touch locations on the touch panel. The processing of each set is performed by (i) identifying the sensing element having the largest capacitance signal value; (ii) defining a region around that sensing element; and (iii) repeating the process iteratively, wherein each subsequent identifying step excludes signals that lie in previously defined regions. A multi-touch sensor is thus provided in which the signal processing is based on successive definition of regions or sub-blocks in the touch: panel. The touch location in each region can be determined more accurately by then applying interpolation between the adjacent signal values. This allows for position resolution at a finer scale than that defined by the touch panel's electrode patterning.
1. A method of processing signals from a touch-sensitive capacitive position sensor, the sensor having a touch panel having a plurality of sensing elements, the method comprising:
receiving a set of capacitance values, each capacitance value corresponding to a capacitance value for each of a respective one of the plurality of sensing elements;
defining an in-detect set of sensing elements from the plurality of sensing elements, the in-detect set comprising all of the plurality of sensing elements corresponding to capacitance values exceeding a threshold value;
identifying the sensing element in the in-detect set that has a received capacitance value that is the largest from among all capacitance values in the in-detect set, the identifying including comparing the capacitance value for each sensing element in the in-detect set to at least one other capacitance value in the in-detect set;
defining an area of the touch panel that includes the identified sensing element and at least the sensing elements adjacent to the identified sensing element;
selecting a sensing element from the sensing elements in the defined area to correspond to a touch in the defined area;
excluding the sensing elements in the defined area from the in-detect set of sensing elements;
repeating the identifying, defining an area of the touch panel, selecting, and excluding steps until the in-detect set of sensing elements has no sensing elements; and
interpolating each of the selected sensing elements corresponding to a touch in a respective defined area to find a touch position.
2. The method of claim 1 , wherein the identifying steps exclude from consideration any sensing elements with capacitance signal values that are not above a threshold value.
3. The method of claim 1 , wherein the sensing element in each region that has the largest capacitance value is taken to be the principally actuated sensing element of that region.
4. The method of claim 1 , wherein the sensing element in each region that is at the highest position on the touch panel among those sensing elements that have a capacitance signal value above a threshold value is taken to be the principally actuated sensing element of that region.
5. The method of claim 1 , wherein the touch location in each region is taken to be at the principally actuated sensing element.
6. The method of claim 1 , wherein the touch location in each region is determined by applying interpolation between the capacitance signal values of at least some of the sensing elements in that region.
7. The method of claim 6 , wherein the interpolation is limited to the sensing element identified as being the principally actuated sensing element of the region and its neighbors.
8. The method of claim 6 , wherein the interpolation includes all of the sensing elements in each region.
9. A 2D touch-sensitive capacitive position sensor comprising:
(a) a touch panel having a plurality of sensing elements distributed over at least a majority of the touch panel;
(b) a capacitance measurement circuit coupled to the sensing elements and operable repeatedly to measure sets of capacitance signal values, each set being made up of a capacitance signal value from each of the sensing elements; and
(c) a processor coupled to the capacitance measurement circuit, the processor operable to receive the sets of capacitance signal values and process each set to compute and output coordinates of single or multiple touch locations on the touch panel, the processing of each set being performed by:
determining a first set of sensing elements from the plurality of sensing elements;
identifying a sensing element from the first set of sensing elements having a largest capacitance signal value from among the sets of capacitance signal values;
defining a region of the touch panel including the sensing element corresponding to the largest capacitance signal value and selected ones of its neighbors;
selecting a sensing element from the sensing elements in the defined region to correspond to a touch in the defined region;
excluding the sensing elements in the defined region from the first set of sensing elements;
repeating the identifying, defining, selecting, and excluding until the first set has no sensing elements; and
outputting data indicating coordinates of a respective touch location in each defined region.
10. The sensor of claim 9 , wherein the identifying excludes from consideration any sensing elements with capacitance signal values that are not above a threshold value.
11. The sensor of claim 9 , wherein the sensing element in each region that has the largest capacitance value is taken to be the principally actuated sensing element of that region.
12. The sensor of claim 9 , wherein the sensing element in each region that is at the highest position on the touch panel among those sensing elements that have a capacitance signal value above a threshold value is taken to be the principally actuated sensing element of that region.
13. The sensor of claim 9 , wherein the touch location in each region is taken to be at the principally actuated sensing element.
14. The sensor of claim 9 , wherein the touch location in each region is determined by applying interpolation between the capacitance signal values of at least some of the sensing elements in that region.
15. The sensor of claim 14 , wherein the interpolation is limited to the sensing element identified as being the principally actuated sensing element of the region and its neighbors.
16. The sensor of claim 14 , wherein the interpolation includes all of the sensing elements in each region.