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Original question:

TCA8418 appears to be giving false touches when membrane is touched

TCA8418: Does not report button presses after a while

Raphael Zahnd1
Prodigy 20 points
Part Number: TCA8418

Hi,

After a while of usage and pressing multiple keys very quickly after each other the TCA8418 goes into a "locked" state where it does not report any interrupts any more.

Reading back all the registers it looks all fine but pressing any button does not set the interrupt flag in the IN_STAT register. The only way to recover from this state is to power cycle the chip.

Is this a known issue of the TCA8418 or are what can be done to prevent this?

Many thanks,

Raphael

  • 0
    TI__Guru 72621 points

    Hey Raphael,

    Can you do a register read of all of the readable registers and provide them in a follow up post?

    I'd like to review this to see if anything looks funny/off.

    "Is this a known issue of the TCA8418 or are what can be done to prevent this?"

    The only time I've heard of something like this occurring is when customers do testing with our device for ESD/Emissions while the device is powered on.

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 20 points

    Hi Bobby,

    Thanks for the answer. Please see attached the PDF file with register values in "Sticky notes".

    Many thanks,

    RaphaelTI_TCA8418_Keypad_Scanner_Chip_with_I2C_Interface.pdfTI_TCA8418_Keypad_Scanner_Chip_with_I2C_Interface.pdf

  • 0 in reply to Raphael Zahnd1
    TI__Guru 72621 points

    Hey Raphael,

    Thanks for the additional information.

    I didn't see anything out of the normal in the register reads.

    Can you do a register write to address 0x03h (just write 0x00h). Then try pressing the keypad again? I'm wondering if the keypad is being locked and it's not being registered. (I suspect this isn't the case but it wouldn't hurt to try).

    What Vcc range are you using this device at?

    Can you probe the Rows on an o-scope? Verify each row is pulled high to Vcc

    Please probe the Columns as well. I suspect they should be GND and in the 'idle' mode.

    Afterwards, try to tie GND to one of the Rows then press one of the switches again. This should pull the device from idle mode to scan mode.

    -Bobby