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CFAF320240F-035T-TS touch screen

learner71

New member
Dear Sir/Mam,
I have read CFAF320240F-035T-TS is 4 wire touch screen, but when i am reading its datasheet. I have not found any four pins for getting the touch screen status. if it is not touch screen, kindly tell me the touch screen.
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learner71

New member
But i have not seen any 4-wire in the datasheet of CFAF320240F-035T-TS for touch screen. I am not getting the complete information about touch screen? tell me is it really touch screen,then where is the 4 wire,where will be get position of touch screen. As you are talking about touch screen controller,where user has to connect separate touch screen controller or is it inbuilt into the lcd.
 

CF Support2

Administrator
Our touch panels are "Analog 4-wire". There is no controller on board.

The pin out for the touch panel is on page 12 of the CFAF320240F-032-T-TS datasheet.

The touch screen must be driven in one direction, then read in the other direction. TI makes a low-level part that has the drivers and ADC built into one part. Some micros have analog inputs that may work directly. Microchip has some high level touch panel support available:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2599#P118_1746
<http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2599#P118_1746>

Basically you put a gradient across one set of electrodes (both set as digital outputs, drive one high and the
other low), then you look at either of the other set of electrodes (both set as inputs, at least one analog). The analog input will pick up the voltage of the gradient at the contact point. To read the other channel, you just rotate the whole process 90 degrees:

<http://www.elotouch.com/Technologies/AT4/howitworks.asp>

This description is just a conceptual outline, I am sure there are many other nuances to be addressed (references, calibration, drift, non-contact,detecting "taps" and "double-taps").

Some information on the structure of a resistive touch screen:

http://www.dmccoltd.com/english/tecnical/logs/tec20041126_a.asp
<http://www.dmccoltd.com/english/tecnical/logs/tec20041126_a.asp>

Here is a bunch of book-marks on touchscreen controllers:

<http://www.howstuffworks.com/question716.htm>
<http://www.microtouch.com/mthtml/03h_specs.htm>
<http://www.analog.com/en/analog-to-digital-converters/touchscreen-controllers/products/index.html>
<http://www.idt.com/?id=5433>
<http://www.maxim-ic.com/view_press_release.cfm/release_id/663>
<http://focus.ti.com/docs/prod/productfolder.jhtml?genericPartNumber=ADS7843>
<http://focus.ti.com/docs/prod/productfolder.jhtml?genericPartNumber=TSC2003>
<http://focus.ti.com/docs/prod/folders/print/tsc2003.html>

Third party software graphics driver libraries:

<http://www.crystalfontz.com/forum/showthread.php?t=6073>
 
Last edited:

mpholmes

New member
I'm interested in slightly more detail about how the 4 wires work. I noticed that there is -x, +x, and -y, +y. So, what voltage range do I give +x and -x, for it to be considered "driven high"? And if both -y and +y are configured as inputs, at least one of them analog, how specifically does the analog input correspond to the coordinates on the screen? Let's say I touched the top of the screen, what voltage would be seen by the analog input? And if I touched the bottom of the screen, what voltage would been seen by the analog input? The datasheet is incredibly sparse with respect to the touch screen implementation.

And what is the point of 2 inputs for -y and +y? If only one of them has to be an analog input, what is the function of the digital input?

By the way, this is for the CFAF320240F-T (or its replacement).
 
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