Dennis J. Murray wrote:
>
> Olin - I'm not entirely sure I agree with multiple keypresses showing as the
> highest priority keypress.  Maybe I missed the original post, but I didn't
> read where he described the actual wiring.  IF he's using the resistor
> ladder as nothing more than a multi-tap voltage divider and the switches do
> nothing more than route a particular tap to the A/D input, then multiple
> keypresses will short out part of the ladder, giving you an A/D input not
> representative of either valid keypress.
>
> Do you disagree?



I do, the switches go from each ladder rung to
ground. The uppermost switch pressed has priority.
It requires one R for each sw, the ADC tap is
taken after the top R, at the point where the top
sw connects. This system can use identical R values,
and still provide safe (ie large) boundaries with
an 8bit ADC.
-Roman

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