Method and apparatus for determining the coordinates of a contact point on a resistive type semianalog sensitive surface

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.

Claim 2

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.

Claim 10

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: 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.

Claim 11

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: 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.