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1519 Posts

Posted - 18 Dec 2002 :  18:31:30  Show Profile  Email Poster
Trouble with your touch panel and/or cable?

Here are some tips and tricks to find the source:
  • Probe each of the touch panel signals.
    You should see pulses of data on each line when the touch panel is pressed.
    The pulses should change height as you move your finger along the X or Y axis.

  • Enable debug output from the driver (if using CE, see this topic)

  • Compare problem against these results:
    A recent pin removal test of the GC Plus (same driver GMaster and Bitsy) using CE drivers gave the following results:
    Disconnected pin 1 (X+/"right"): X approx 1015, Y data ok
    Disconnected pin 2 (X-/"left"): X approx 25, Y approx 1015
    Disconnected pin 3 (Y+/"bottom"): X approx 770, Y approx 25
    Disconnected pin 4 (Y-/"top"): no touch data out; only pin 3 changes electrically when panel touched

For further reading about touch panels on ADS products, see the touch panel topic index.

Drew Kidder
ADS Technology Transfer


47 Posts

Posted - 10 Jan 2008 :  13:43:59  Show Profile

Testing the Touch Panel

The touch panel can also have a problem, either inherently or due to damage. Follow the steps below to test a four-wire touch panel connected to an ADS device with a 4 pin header:
  • Disconnect the cable from the device, but leave it attached to the touch panel.

  • Using an Ohm meter measure the resistance between pins 1 and 2 (X+ and X-). It should be somewhere between 300 and 800 ohms and should not change when the panel is touched.

  • Similar results should be obtained from measuring pins 3 and 4 (Y+ and Y-).
    The ratio of the resistance between each pair should be similar to the aspect ratio of the touch panel.

  • Measure the resistance from pin 1 to pin 3. It should be an open circuit unless the panel is being touched. The resistance should be lower the harder you press on the panel.
If these results are not obtained there is a problem with either the panel or the cabling. To find out which, try a similar test directly at the panel connector, keeping in mind that the pinout may be different for that connector.

Touch panels with characteristic impedances outside the 300-800 ohm range may be difficult for the touch panel controller to read, and may result in reduced sensitivity or unexpected behavior.

Edited by akidder 28-jul-08: Added title and introductory and closing paragraphs.
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