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320*240 resistive touch screen calibration problem

Hi every one.

I have 320*240 LCD with resistive touch screen and touch screen controller of AD7843 ( All is together in one LCD from topway: KM2088S). I want to know what is the best way to calibrate the touch screen? when I push the touch screen a little bit it shows me a number, but when I push it harder it shows me a different number!! how can I solve it? Is it going to solve by calibration? I really appreciate if you guys can help me.

Regards

Arash

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  • Hi Arash,

    Nice to hear from you.

    AN-1021 describes the calibraion for the mechanical misalignments and scaling factors of resistive-type touch screens which will affect the X and Y coordinates produced by the touch screens. That is different issue from your problem.

    Per my personal understanding, AD7843 is an ADC to sample the voltage output of the resistor divider (resistive touch screen is basically a resistor divider). So your problem is that when you touch the small point on touch screen, touch presure will affect the X/Y coordinates. It is because that the high touch pressure will make a big contact of the two layer of touch screen and affect the resistor value. In other word, high touch pressure doesn't touch only one point, it touches a big area, and make an ambiguity output.

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  • Hi Arash,

    Nice to hear from you.

    AN-1021 describes the calibraion for the mechanical misalignments and scaling factors of resistive-type touch screens which will affect the X and Y coordinates produced by the touch screens. That is different issue from your problem.

    Per my personal understanding, AD7843 is an ADC to sample the voltage output of the resistor divider (resistive touch screen is basically a resistor divider). So your problem is that when you touch the small point on touch screen, touch presure will affect the X/Y coordinates. It is because that the high touch pressure will make a big contact of the two layer of touch screen and affect the resistor value. In other word, high touch pressure doesn't touch only one point, it touches a big area, and make an ambiguity output.

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