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Last Post 23 Oct 2015 09:56 AM by  bradb
Spurious Touch Screen Presses
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chad.grant
New Member
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Posts:18


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23 Oct 2015 08:34 AM

    Are there any known issues with the TSC2004 giving spurious touch events?

    We are using the DM3730 in a custom board with WinCE 6.0 and we will sporadically get fake touch events from the touch screen.

    Here are things we've tried:

    • Put .01uf filtering capacitors on the touch lines.
    • Tried various different timing values by modifying touchscreen.cpp.
    • Gone so far to even try running the TSC2004 in chip controlled mode instead of host controlled.

    Some things have seemed to work better than others but we have gotten fake events with all of these. When we put an oscilloscope on the line it seems that at times the X+ (or whichever line is responsible for triggering touch detect) will start to drift instead of remain high. If it wanders low enough we get an interrupt and then we start measuring to see where we have pressed - all of this happens without anyone pressing it. If we do press it then it reads properly and if we press in the correct spot (usually lower right corner) it seems to actually help the X+ stay high when it isn't pressed - at least for a few seconds.

    The touch screen we are using has worked fine for us with the iMX31 SOM - we never had a problem with fake events.

    Do you guys have any idea as to what could be causing this, or any way of mitigating it - either through code or hardware changes, or both?

    Thanks,

    Chad

    Stephen Bell
    New Member
    New Member
    Posts:5


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    23 Oct 2015 08:59 AM
    I had the same problem with a capacitive touch screen connected to the DM3730. In my case, the problem was caused by the particular DC wall adapter I was using. To be certain, rig up some batteries to power your circuit instead.

    If the problem disappears when you're battery powered, then your DC adapter is causing your issues. In my case, simply switching to an adapter that was earth ground shielded solved my problems.

    (more info: http://electronics.stacke...e.com/a/167425/6494)
    bradb
    Basic Member
    Basic Member
    Posts:203


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    23 Oct 2015 09:56 AM
    Chad,

    We haven't seen this issue with the DM37x SOM-LV or Torpedo development kits.  Please verify you have the latest WinCE touch driver (v3.0.2 BSP) and that you have a similar connection as seen on the DM37x SOM-LV development kit.

    For others reading this response, must have a Logic PD account and registered your DM37x SOM-LV and/or development kit to access the previous links.

    Another source of noise might be the LCD itself.  Since you are using a different LCD controller, you might consider noise from the LCD panel.  A quick test would be to disable the LCD controller and allow the OS to boot.  If you are no longer getting spurious interrupts you might consider adjusting the LCD timings. 

    If you need additional assistance you might consider having us debug the issue through one of the Logic PD support contracts.

    Best Regards,

    Brad

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