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TCA8418: pull up resistors on row

ajayt
Genius 9555 points
Part Number: TCA8418

Hi,  Had a working key pad solution, then added a static shield over the swith domes, which caused the buttons on row one to misread-  

We added a pull up 10k to Row 0 and the issue is resolved.

Do you see any possible issue with adding pull up to that row? Can we add pull up to all rows? Do you know the ideal resistor value for that?

  • 0
    TI__Guru 72161 points

    Hello Ajayt,

    My guess is that what you added ended up adding capacitance on the rows which caused the keypad scanner to register multiple key presses anytime one key was pressed. The solution to this is to add external pull up resistors to help the internal pull up resistor to drive the signal high before the next row is strobed.

    "Do you see any possible issue with adding pull up to that row?"

    No, this is what we recommend if the problem is there is too much capacitance on the rows.

    "Can we add pull up to all rows?"

    Yes, that is recommended if all the rows have a lot of capacitance due to the shield.

    "Do you know the ideal resistor value for that?"

    10k should be fine.

    Thanks,

    -Bobby