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TCA8418 appears to be giving false touches when membrane is touched

Gary Cochran
Intellectual 295 points
Other Parts Discussed in Thread: TCA8418

Hi e2e,

Our customer is having problems with the TCA8418, it is giving false touches when the membrane is touched and the snap domes are not depressed and it is locking up if too many keys are pressed.  Can you pleased assist, please see full description from customer below.

The two problems are as follows:

 

1.)  We are getting false key presses when rubbing the keypad membrane while our processor board is plugged into a power source. Our keypad normally runs on a battery and we do not see false key presses when Keypad is not plugged in.

 

2.)  We are experiencing a stuck key every so often. Normally this occurs when multiple buttons are pressed at the same time. We believe this to be an issue with the resistance of the pull-up on the interrupt and reset pins.

  • 0
    Prodigy 20 points
    To expand on the second issue, I believe the stuck key behavior may be a result of the TCA8418 somehow getting frozen or locked up when mashing buttons on the keypad.

    We're seeing interrupts occur during a key press and then another when the key is released. However, the stuck key is a side effect of a press interrupt occurring and no corresponding release interrupt. Once it's in this state, pressing other keys won't result in any further interrupts and the TCA is completely unresponsive.

    Rebooting the computer doesn't solve the issue, and the only way to get the TCA8418 to trigger interrupts again is by completely cutting the power and resetting everything.

    Enabling/disabling features like overflow and keypad locks doesn't seem to help at all.
  • 0 in reply to Andrew Langley
    Prodigy 20 points

    Here some more information: We appear to be getting these errors from the tca8418 Linux driver:

    overflow occured
    unable to clear REG_INT_STAT