Neat idea.  However, by losing the LM317 and using the keypad and resitors
with the single slope converter in AN512 (Microchip App Note), the method
could be used on low end parts without an AD converter with just a small
software overhead.  I suspect you wouldn't even need the reference resistor
described in the app note, simplifying things even more.

A nice compact routine that chooses the closest value in a lookup table
would be nice, to allow for drift etc.  My asm is not great so I'll leave
that to the rest of the gurus on here.

Regards

Mike Rigby-Jones

> ----------
> From:         Tony Nixon[SMTP:Tony.Nixon@ENG.MONASH.EDU.AU]
> Sent:         03 February 1999 03:37
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      1 wire keypad
>
> Hi all,
>
> I just posted a simple circuit for reading a keypad with 1 PIC pin.
> Nothing too elaborate, but it will work with hobby projects etc.
>
> http://www.picnpoke.com/projects/keypad.html
>
> --
> Best regards
>
> Tony
>
> Multimedia 16F84 Beginners PIC Tools.
> ** NEW PicNPro Programmer and Port Interface **
>
> http://www.picnpoke.com
> Email picnpoke@cdi.com.au
>