Method and apparatus for determining the coordinates of a contact point on a resistive type semianalog sensitive surface
First Claim
1. A method for determining the coordinates of a conductive object on a sensitive surface, wherein said surface is in the form of an insulating support carrying a grid formed by two terminals between which resistant strips are connected in parallel and conductive strips placed between said resistant strips, said conductive strips individually connected to a selection means which successively samples the voltage of each conductive strip, said method comprising the steps of:
- determining a digital coordinate during a first phase by;
polarizing said two terminals in phase with a clock signal;
sampling the voltage of each conductive strip separately during the on and off periods of said clock signals;
averaging the samples separately for said on and off periods;
comparing the averages for said on and off periods for each conductive strip to locate which conductive strip has a large difference between the averages and to indicate which conductive strip is in contact with said resistant strip;
determining the digital coordinate to be the number of the located conductive strip; and
determining an analog coordinate during a second phase by;
leaving the selection means in contact with the located conductive strip;
polarizing said two terminals in opposite phase with the clock signal to create current in each direction alternately in each resistant strip;
sampling the voltage of each conductive strip separately during each current direction;
averaging the sample separately for each current direction;
taking the difference of said averages to compute the analog coordinate.
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Accused Products
Abstract
A method and apparatus for determining the coordinates of a point of contact of an object on a semianalog sensitive surface. The coordinates are of a zone of contact of a conductive object such as a finger on a sensitive surface. The surface consists of an insulating support having a grid formed by two terminals between which a certain number of emitting resistant strips are connected in parallel and detecting conductive strips, placed between the resistant strips. The conductive strips are connected separately to a selection switch making it possible successively to sample the voltage of each detecting strip. The operation is performed in two phases by polarizing the two terminals of the grid, first in phase, then in opposite phase, and in each phase of the process the averages are taken of a certain number of synchronous samples which make it possible to determine the two coordinates.
35 Citations
11 Claims
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1. A method for determining the coordinates of a conductive object on a sensitive surface, wherein said surface is in the form of an insulating support carrying a grid formed by two terminals between which resistant strips are connected in parallel and conductive strips placed between said resistant strips, said conductive strips individually connected to a selection means which successively samples the voltage of each conductive strip, said method comprising the steps of:
determining a digital coordinate during a first phase by; polarizing said two terminals in phase with a clock signal; sampling the voltage of each conductive strip separately during the on and off periods of said clock signals; averaging the samples separately for said on and off periods; comparing the averages for said on and off periods for each conductive strip to locate which conductive strip has a large difference between the averages and to indicate which conductive strip is in contact with said resistant strip; determining the digital coordinate to be the number of the located conductive strip; and
determining an analog coordinate during a second phase by;leaving the selection means in contact with the located conductive strip; polarizing said two terminals in opposite phase with the clock signal to create current in each direction alternately in each resistant strip; sampling the voltage of each conductive strip separately during each current direction; averaging the sample separately for each current direction;
taking the difference of said averages to compute the analog coordinate.- View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A device for determining the coordinates of a conductive object contacting a semianalog sensitive surface, said surface having a grid formed by two terminals between which are connected in parallel a plurality of resistant strips and detecting strips placed between said resistant strips and individually connected to a selection means, said device comprising:
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a clock signal generator; reversing switch means coupled to said clock signal generator for switching each of said two terminals between a polarization voltage and ground after each clock cycle of said clock signal generator, so that the terminals are connected in phase or in opposite phase to said clock signal; sampling means for sampling the voltage on said detecting strips in synchronism with the clock signal; averaging means for determining the average of a number of samples separately for each half of the clock signal; and logic means for controlling said reversing switch means, said selection means and sampling means, for counting said samples and for calculating the values of said coordinates. - View Dependent Claims (10, 11)
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Specification