I've used this approach a couple times. In one case with 15 buttons. I did
a single string of identical resistors (resistor network) between ground
and +5V. The NO contact of each switch picked a point off the series
string. The NC contact of one switch drove the common of the next switch.
This gave a priority order to the switches and prevented invalid voltages
when more than one switch was pressed.

Harold


> Hi all,
>
> I have only 1 pin available in a PIC16F micro but need to read 5-10
> momentary buttons, and do not want to use any other additional external
> IC.
> I figured out a way to work this out using 1 single A/D pin to
> differentiate
> each button from the rest, provided I have different R-R bridge for each
> button, therefore if no button is pressed the A/D should read 5V, but as
> soon as a button is pressed, a R would move that to, say, 2.8V. If all the
> resistor combination are different and I can work with at least
> 0.25Vdistance between them (
> e.g. 0.25V, 0.50V, 0.75V, 1V, etc), looks like a robust and solid solution
> to me.
>
> Only drawback I can see is no multiple buttons can be pressed at a time
> and
> give a valid value, but this is not a requirement.
>
> Do you see any problem with this approach? Anybody used something like
> this
> before? Any other option you can suggest for multiple buttons, 1 pin and
> no
> additional circuitry?
>
> Thanks in advance.
>
> --
> Ariel Rocholl
> Madrid, Spain
> --
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