Patent ID: 8355009
Filing Date: 2013-01-15
Classification: G06F

Abstract:
1. A method for determining coordinates of simultaneous touches on a touch sensor pad, the touch sensor pad including a first plurality of resistive sensor strips on a first resistive sheet and a second plurality of resistive sensor strips on a second resistive sheet, the method of determining comprising the steps of: determining coordinates of each of the multiple locations of touch independently of other touches, the determining step for a touch comprising: identifying a first strip of the first plurality of resistive sensor strips of the first resistive sheet that is physically contacting a second strip of the second plurality of resistive sensor strips of the second resistive sheet in response to the touch; identifying the second strip; energizing terminals of the first strip to a first terminal voltage to generate a voltage gradient along the first strip; determining a first offset voltage by assigning each of the second plurality of resistive sensor strips a sequential index value wherein the first offset voltage is a function of the first terminal voltage times an index value of the second strip divided by a number of the second plurality of resistive sensor strips; determining a first measured voltage wherein the first measured voltage is the voltage of the second strip applied by the first strip while in contact with the second strip in response to the touch minus the first offset voltage; clearing the voltages; energizing terminals of the second strip to a second terminal voltage to generate a voltage gradient along the second strip; determining a second offset voltage by assigning each of the first plurality of resistive sensor strips a sequential index value wherein the second offset voltage is a function of the second terminal voltage times an index value of the first strip divided by a number of the first plurality of resistive sensor strips; determining a second measured voltage wherein the second measured voltage is the voltage of the first strip applied by the second strip while in contact with the first strip in response to the touch; minus the second offset voltage; determining coordinates of the touch based on the first measured voltage, taken together with the index value of the second strip, the second measured voltage, and the index value of the first strip.