On Mon, Aug 23, 2004 at 07:07:43PM -0400, Carey Fisher - NCS wrote:
> >Each will require a different amount of I/O
> >
> >1) The 4 individual keypads would require 32 I/O lines
> >2) The 8x8 would require 16 I/O lines.
> >3) The 4x16 would require 20 I/O lines.
> >
> >In each case a decoder and/or multiplexer can be used to reduce the lines
> to
> >the corresponding power of 2. So for the cost of a chip, you can greatly
> >reduce the number of lines required.
>
> Why don't you use 4 A/D channels where each A/D channel reads a whole 4x4
> keypad?  I've completed a project with a PIC18F452 where I read 8 switches
> with one A/D pin.  It's not hard. If interested, I send you a schematic...

Interesting idea. I presume that you tie different valued resistors across
the switches? That way you get a different voltage when the switch is pressed
as opposed to released?

But on a 4x4 how do you keep the different rows/cols from interacting. I
can see this for a single string of switches. But wouldn't pressing multiple
switches on a pad possible impact one another?

BAJ

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