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4 wire resistive touch screen

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amsbhole07

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Can anyone tell me how this 4 wire resistive touch screen work
 

ckshivaram

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firstly Is it connected in matrix form.
then it is working as a keypad matrix. the rows and columns are connected to port pins.then when the intersection of 2 wires are touched the logic level is pulled to low or high ( depending on the logic)
If you can visualise keypad interface to 8051, it is replica of that technique
 

mandar_mahajan

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The four wire Touch pad firstly works on SPI Protocol with the driver IC(if u r using). U can read the data from that IC say ADS7843 through spi engine of by bit bang method & can simulate the results either on ur display of on hiper terminal.

Mandar
 

FvM

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Resistive touch screens are operating based on the voltage divider principle. Imagine two resistive sheets, one terminated at the left and right side, the other on the top and bottom side. The sheets touch at one point. The point detection is a two step process. First you apply a voltage difference to one resistive sheet, say spanned in the x direction, e.g. 0 and 5V. You can measure a voltage at the unloaded terminals of the other sheet, representing the x-position. Then you reverse the connection (supply voltage to the y-direction sheet, measure at x terminals) and get the y position.

To drive a 4 wire touch screen, you either use dedicated chips, as the said ADS7843, or general purpose processors with analog ports, e.g. a PIC.
 

amsbhole07

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Hi,

Please explain how we can do with PIC microcontroller
 

ckshivaram

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please indicate to which of the 3 posts are you referring to. Which answer is the nearest to your question. Based on that the implementation will be told by concerned person.
 

amsbhole07

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FvM
Re: 4 wire resistive touch screen

Resistive touch screens are operating based on the voltage divider principle. Imagine two resistive sheets, one terminated at the left and right side, the other on the top and bottom side. The sheets touch at one point. The point detection is a two step process. First you apply a voltage difference to one resistive sheet, say spanned in the x direction, e.g. 0 and 5V. You can measure a voltage at the unloaded terminals of the other sheet, representing the x-position. Then you reverse the connection (supply voltage to the y-direction sheet, measure at x terminals) and get the y position.

To drive a 4 wire touch screen, you either use dedicated chips, as the said ADS7843, or general purpose processors with analog ports, e.g. a PIC.

Hi,

Please explain how we can do with PIC microcontroller
 

FvM

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I think, my previous post already sketches the basic algorithm. It's talking about using 4 PIC port pins, two of them with ADC input function. If you can't figure it out yourself, you'll find masses of code examples at the internet, e.g. at compiler specific sites like CCS forum.
 

mhjedaboard

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hi everybody
i have a problem with touch.
the touch x and y is being read well . but the x and y parameter is (somehow) related together .
for example four corner of touch have this output :
(1,1)----------------(45, 1)
|--------------------------|
|--------------------------|
|--------------------------|
(1,27)--------------(60,52)

as you see the last coordinate (60,52) should be (45,27) !
anyone can help?
 

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