Surface capacitance with area gestures
A surface capacitance touch sensitive surface (or “surface cap panel”) suitable for use in a touch screen or touchpad, wherein the surface cap panel has a substantially even coating of a conductive material on a non-conductive substrate and then covering the conductive material with a dielectric material, wherein a novel current measuring circuit reduces the effect of stray capacitance on the accuracy of a current measurement so that the relative X and Y position of an object on the surface cap panel can be determined using simple ratio equations, and wherein measuring the charge transfer rate in a measuring circuit, in addition to the total charge transfer for each toggle event, enables the location of two objects to be identified on the surface cap panel, wherein the charge transfer rate is used to determine the distance between two points of contact on the surface cap panel, and wherein height and width information related to the distance between the two points of contact can now be determined by doubling the number of electrodes at the corners of the surface cap panel.
1. A method for measuring the position of a plurality of pointing objects on a surface capacitance touch panel (surface cap panel), said method comprising:
1) providing a surface capacitance touch sensitive surface comprised of a surface cap panel having an insulating substrate, a resistive material disposed on the substrate and formed as a single and planar sheet, and a dielectric disposed on the resistive material;
2) connecting a first capacitor to opposite edges of the surface cap panel while simultaneously connecting a second capacitor to different opposite edges and measuring current across the surface cap panel using a current measuring circuit in different directions across the surface cap panel, and for different time apertures, and making current measurements in a group of first time apertures and in a group of shorter time apertures relative to the first time apertures; and
3) triangulating a position of the multiple pointing objects using the measurements obtained above.
2. The method as defined in claim 1 wherein the method further comprises the step of providing a known voltage charge on the first and second capacitors in order to determine how much current is being drained from the surface of the touch panel by the presence of the each of the multiple pointing objects.
3. The method as defined in claim 1 wherein the method further comprises performing the following measurements for the first time aperture:
1) Drive electrodes at the bottom and detect electrodes at the top of the surface cap panel;
2) Drive electrodes at the top and detect electrodes at the bottom of the surface cap panel;
3) Drive electrodes at the left side and detect electrodes at the right side of the surface cap panel; and
4) Drive electrodes at the right side and detect electrodes at the left side of the surface cap panel.
4. The method as defined in claim 3 wherein the method further comprises performing the following measurements for the shorter time aperture:
1) Drive electrodes at the bottom and detect electrodes at the top of the surface cap panel;
2) Drive electrodes at the top and detect electrodes at the bottom of the surface cap panel;
3) Drive electrodes at the left side and detect electrodes at the right side of the surface cap panel; and
4) Drive electrodes at the right side and detect electrodes at the left side of the surface cap panel.
5. The method as defined in claim 4 wherein the method further comprises the step of using the 8 current measurements to determine the location of the plurality of pointing objects on the surface cap panel.
6. The method as defined in claim 1 wherein the method further comprises the step of creating a linear voltage gradient across the surface cap panel using the first and the second capacitors.
7. The method as defined in claim 6 wherein the method further comprises the step of refreshing the first capacitor and the second capacitor to a known voltage in order to maintain the voltage gradient across the surface cap panel.
8. The method as defined in claim 1 wherein the method further comprises the step of increasing accuracy of the method for measuring the position of the plurality of pointing objects on the surface cap panel by only allowing the current to drain to the plurality of pointing objects and to the current measurement circuit.