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Touch screen problems

Discussion in 'General Electronics Chat' started by 2PAC Mafia, Jun 27, 2017.

  1. 2PAC Mafia

    2PAC Mafia Member

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    Hi guys,

    I´m trying to solve a problem with a marine display which uses touch screen. The unit was working switching on correctly but not reacting to touch screen so I replaced it and then it was working. After some days I received the phone call from my customer saying the touch screen was failing again.

    Now I took some measurements on the touch screen chip which is UCB1300. I measured resistence changes when I press between pin 27, 29 and pin 28, 30. If I measure at 28 or 30 against ground I see voltage from H to L, but when I measure at pin 27 or 29 I always see 0V.

    I don´t know if there is some way to measure output or if these values measured are OK, or the chip is failing. I read the datasheet but it´s a little bit confusing for me. Any help would be good. Thanks.
     
  2. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    Two things that happen to me...

    First! When I mounted the touch screen it worked really good.. But!! in the morning when cold it looked like it was failing... By 12 (ish) it was fine again.... I found the bezel was pressing on the touch panel... I hat to allow a clearance..

    Second! The port pin of my Pic32 kept on going low!! No idea to this day why.. I reprogram and its fine again... I have checked all errata's, but its still an ongoing issue... At first I thought that capacitance was locking up the gate latch... It'll come to light one day..
     
  3. 2PAC Mafia

    2PAC Mafia Member

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    Thanks. In my case it was working too but now is not working again, even if I wait time. My question is, are these values I´m measuring correct?

    I attach the datasheet, at page 14 starts touch screen section and at page 19 there is a table. I followed 4 of the 8 lines from touch screen directly to the chip, lines 27, 28, 29 and 30. Now I would like to know what should I expect on those pins when I touch the panel.

    As I understand, I should get some voltage value on pin 27 or 29 when I touch (position measurement), page 14.
     

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  4. dave

    Dave New Member

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  5. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    I write my own touch ( resistive ) driver... Two analogue pins and two digital pins are used..
    upload_2017-6-28_12-12-17.png

    If A = 3v3 and C = 0v then B will see 0~3v3v. ( Called Xval )
    If B = 3v3 and D = 0v then C will see 0~3v3v. ( Called Yval )


    BUT!! The read sequence is usually only initiated when the Zval is above a certain point.

    So when reading the live points you will need a scope...

    A will be 3.3v D will be 0 v and the two analogue pins C and B give the pressure ( Zval )
    This all happens quickly as C and B are tri stated several times during the reading process..
     
  6. 2PAC Mafia

    2PAC Mafia Member

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    Thanks, finally I discovered the problem comes when power supply is off. I was in WinCE system and made recalibration of touch screen, then everything worked again, I also replaced the UCB1300 chip. When I thought everything was solved I saw when I switched off and on again I had same problems, so same behavieur connecting a mouse on the system to recalibrate again the touch screen. It looses the calibration of position...
     
  7. Asa001

    Asa001 New Member

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    Useful topic! I solved my own touch screen issue !
     
    Last edited: Sep 28, 2017

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