With this arrangement you will need some unusual switches (three
terminal make-make)

And with the conventional method it is also possible to detect multiple
simultaneous presses.


Isaac


Em 3/4/2013 19:25, Allen Mulvey escreveu:
> Thank you all for the excellent information and resources. I
> had checked Microchip and MikroElektronica sites and found
> nothing. I missed the significance of the current rating for
> the internal pullups.
>
> I have been experimenting with a slightly different kind of
> matrix keypad. Instead of shorting row and column, it
> grounds both. This eliminates the need to scan and allows
> the selection of multiple key presses although not all may
> be unique. I think much of the problem I have seen has been
> caused by capacitance. Earlier I didn't think about the R-C
> timer effect. If I connect the keypad with a foot of cat-5
> cable the 20k resistors work fine. If I use 6" of ribbon
> cable 20k is too big but 4k7 or slightly less works fine.
> There also appears to be a difference depending on which end
> of the cable the resistors are attached although I have not
> tested this very well.=20
>
> Thanks again,
> Allen
>
>
>

--=20
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