Method and system for detecting multiple touches on a touch-sensitive screen

A computer-readable medium containing computer-executable instruction for performing a method for indicating if a set of simultaneous contact points on a touch-sensitive screen contains a plurality of contact points, the method comprising:

• setting a multiple contact point discrimination threshold representing a minimum difference in voltage expected between conductors at opposing edges of the touch-sensitive when detecting multiple contact points are presented;
• setting a conductor on a first edge of the touch-sensitive screen to a first reference voltage;
• setting a conductor on a second edge of the touch-sensitive screen to a second reference voltage, the second edge being across the touch-sensitive screen from the first edge;
• taking a first measurement of a voltage associated with a conductor on a third edge of the touch-sensitive screen, the third edge being adjacent to the first and second edges;
• taking a second measurement of a voltage associated with a conductor on a fourth edge of the touch-sensitive screen, the fourth edge being adjacent to the first and second edges and across the touch-sensitive screen from the third edge;
• comparing the multiple contact point discrimination threshold with a difference between the first and second voltage measurements, the difference reflecting a difference in proximity between the set of simultaneous contact points and the third and fourth edges of the touch-sensitive screen;
• and
• if the difference between the first and second voltage measurements is greater than the multiple contact point discrimination threshold, then indicating that the set of simultaneous contact points contains a plurality of contact points.

A method for indicating if a set of simultaneous contact points on a touch-sensitive screen contains a plurality of contact points, the method comprising:

• setting a multiple contact point discrimination threshold representing a minimum combined difference in voltage expected between pairs of conductors at opposite edges of a touch-sensitive screen when multiple contact points are presented;
• setting a conductor on a first edge of the touch-sensitive screen to a first reference voltage;
• setting a conductor on a second edge of the touch-sensitive screen to a second reference voltage, the second edge being across the touch-sensitive screen from the first edge;
• taking a first measurement of a voltage associated with a conductor on a third edge of the touch-sensitive screen, the third edge being adjacent to the first and second edges;
• taking a second measurement of a voltage associated with a conductor on a fourth edge of the touch-sensitive screen, the fourth edge being adjacent to the first and second edges and across the touch-sensitive screen from the third edge;
• setting the conductor on the third edge of thee touch-sensitive screen to a third reference voltage;
• setting the conductor on the fourth edge of the touch-sensitive screen to a fourth reference voltage;
• taking a third measurement of a voltage associated with the conductor on the first edge of the touch-sensitive screen;
• taking a fourth measurement of a voltage associated with the conductor on the second edge of the touch-sensitive screen;
• combining a first difference between the first and second voltage measurements reflecting a difference in proximity between the set of simultaneous contact points and the third and fourth edges of the touch-sensitive screen with a second difference between the third and fourth voltage measurements reflecting a difference in proximity between the set of simultaneous contact points and the first and second edges of the touch-sensitive screen;
• comparing the multiple contact point discrimination threshold with a combination of the first and second differences;
• and
• if the combination of the first and second differences is greater than the multiple contact point discrimination threshold, then indicating that the set of simultaneous contact points contains a plurality of contact points.

A computer-readable medium containing computer-executable instructions for performing a method for indicating if a set of simultaneous contact points on a touch-sensitive screen contains a plurality of contact points, the method comprising;

• setting a multiple con-tact point discrimination threshold;
• setting a conductor on a first edge of the touch-sensitive screen to a first reference voltage;
• setting a conductor on a second edge of the touch-sensitive screen to a second reference voltage, the second edge being across the touch-sensitive screen from the first edge;
• taking a first measurement of a voltage associated with a conductor on a third edge of the touch-sensitive screen, the third edge being adjacent to the first and second edges;
• taking a second measurement of a voltage associated with a conductor on a fourth edge of the touch-sensitive screen, the fourth edge being adjacent to thee first and second edges and across the touch-sensitive screen from the third edge;
• setting the conductor on the third edge of the touch-sensitive screen to a third reference voltage;
• setting the conductor on the fourth edge of the touch-sensitive screen to a fourth reference voltage;
• taking a third measurement of a voltage associated with the conductor on the first edge of the touch-sensitive screen;
• taking a fourth measurement of a voltage associated with the conductor on the second edge of the touch-sensitive screen;
• combining a first difference between the first and second voltage measurements reflecting a difference in proximity between the set of simultaneous contact points and the third and fourth edges of the touch-sensitive screen with a second difference between the third and fourth voltage measurements reflecting a difference in proximity between the set of simultaneous contact points and the first and second edges of the touch-sensitive screen;
• comparing the multiple contact point discrimination threshold with a combination of the first and second differences;
• and
• if the combination of the first and second differences is greater than the multiple contact point discrimination threshold, then indicating that the set of simultaneous contact points contains a plurality of contact points.

A system for indicating if a set of simultaneous contacts points on a touch-sensitive screen contains a plurality of contact points, the touch-sensitive screen comprising first, second, third, and fourth edges, each edge comprising a conductor, the first edge being across the touch-sensitive screen from the second edge, the third and fourth edges each being adjacent to the first and second edges, and the third edge being across the touch-sensitive screen from the fourth edge, the system comprising:

• a multiple contact paint discrimination threshold representing a minimum combined difference in voltage expected between airs of conductors at opposite edges of a touch-sensitive screen when multiple contact points are presented;
• a voltage source for setting the first edge conductor to a first reference voltage and for setting the second edge conductor to a second reference voltage;
• a voltage measurement circuit with an input, and an output;
• a multiplexor for connecting the input of the voltage measurement circuit alternatively to the third edge conductor and to the fourth edge conductor;
• a comparator for comparing the multiple contact point discrimination threshold with a difference between a value produced on the output of the voltage measurement circuit when its input is connected to the third edge conductor and a value produced on the output of the voltage measurement circuit when its input is connected to the fourth edge conductor the difference reflecting a difference in proximity between the set of simultaneous contact points and the third and fourth edges of the touch-sensitive screen;
• and
• an indicator for indicating that the set of simultaneous contacts points on the touch-sensitive screen contains a plurality of contact points, the indicator set based on an output of the comparator.

A system for indicating if a set of simultaneous contacts points on a touch-sensitive screen contains a plurality of contact points, the touch-sensitive screen comprising first, second, third, and fourth edges, each edge comprising a conductor, the first edge being across the touch-sensitive screen from the second edge, the third and fourth edges each being adjacent to the first and second edges with the third edge being across the touch-sensitive screen from the fourth edge, the system comprising:

• a multiple contact point discrimination threshold representing a minimum combined difference in voltage expected between pairs of conductors at opposite edges of a touch-sensitive screen when multiple contact points are presented;
• a first voltage source for setting the first edge conductor to a first reference voltage and for setting the second edge conductor to a second reference voltage;
• a first voltage measurement circuit with an input and an output;
• a first multiplexor for connecting the input of the first voltage measurement circuit alternatively to the third edge conductor and to the fourth edge conductor;
• a first calculator for calculating a first difference between a value produced on the output of the first voltage measurement circuit when its input is connected to the third edge conductor and a value produced on the output of the first voltage measurement circuit when its input is connected to the fourth edge conductor, the first difference reflecting a difference in proximity between the set of simultaneous contact points and the third and fourth edges of the touch-sensitive screen;
• a second voltage source for setting the third edge conductor to a third reference voltage and for-setting the fourth edge conductor to a fourth reference voltage;
• a second voltage measurement circuit with an input and an output;
• a second multiplexor for connecting the input of the second voltage measurement circuit alternatively to the first edge conductor and to the second edge conductor;
• a second calculator for calculating a second difference between a value produced on the output of the second voltage measurement circuit when its input is connected to the first edge conductor and a value produced on the output of thee second voltage measurement circuit when its input is connected to the second edge conductor, the second difference reflecting a difference in proximity between the set of simultaneous contact points and the first and second edges of the touch-sensitive screen;
• a comparator for comparing the multiple contact point discrimination threshold with a combination of the first and second differences;
• and
• an indicator for indicating that the set of simultaneous contacts points on the touch-sensitive screen contains a plurality of contact points, the indicator set based on an output of the comparator.