I've seen this method used. The issue that presented itself at the time was
that multiple button presses could be detected as a single button press. I'm
not sure how the issue was resolved.

David
 

> -----Original Message-----
> From: Ariel Rocholl [mailto:foros@arocholl.com] 
> Sent: Thursday, June 28, 2007 8:20 PM
> To: Microcontroller discussion list - Public.
> Subject: [PIC] Multiple momentary button in 1 single pin
> 
> 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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