Touch Screen False Coordintes


I’m developing my first touch screen application with the FEZ Cobra and the 3.5" touch screen module (EMX Firmware Version I have found that when touching controls, sometimes other controls get selected (always above and to the left of the touched control).

To investigate I ran the Ink Canvas sample and found that a firm press draws in the correct place. However if you use a soft touch or are slow in applying the touch the resulting coordinates returned by the touch screen are somewhere between the touched location and the top left of the screen.

To me this sounds like an issue with the resistive touch screen and/or the touch screen’s A to D converters. My question is, has anyone else experienced this issue and is there anything I can do about it in code?

Any help would be greatly appreciated.


have you calibrated your screen?

Using stylus?

Thanks for the quick response.

I haven’t calibrated the screen. I assumed (probably incorrectly) that as a firm touch was giving an accurate location I didn’t need to. Will calibration help to filter out the inaccurate soft touches?

This is resistive touch screen and using something pointy is required

Unfortunately our application needs to work with fingers. I guess if there’s no way to filter out the inaccurate coordinates we would have to look at using a capacitive screen. Would anyone be able to offer any advice on sourcing/interfacing with a capacitive touch screen. Is there one that can be easily connected to the FEZ Cobra board? What drivers would be required? etc

Sorry about all the questions, I’m a software guy so not too familiar with the hardware side.

Capacitive screens are very expensive and you will not find “easy to use” capacitive touch display. I would suggest no to bother and look.

The good news is that GHI has been communicating with multiple sources and have some samples already so this will be an option in near future.

i also prefer to use the touch with fingers. At the chipworkX dev kit the Button (Glide) shows a reaction by pressing with finger, but the window/system don’t change. I Have to press with pointed stylus about 1 second until the program change the screen/window.

Is it possible to change the touch configuration / response characteristic. Or disable/change the soft touch filter?


Note: I experiment with the multiple window glide example:

Capacitive touch is the way to go