FOr an example, this is done for switch decoding on the Pocket Programmer (a
good PIC programmer).  The schematics are at www.bubblesoftonline.com, and
show a schematic for four button control.  It dooes indeed use a resistor
ladder to determine the voltage input to a single A/D port on the PIC.

Rgs
Ian.



-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Olin Lathrop
Sent: Thursday, 27 February 2003 12:57 am
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: A to D convertor use for switch decoding


> Not necessarily. It is potentially (no pun intended) possible to detect
> any and all switch states.

Yes, if you use R/2R ladder.  However, that severly limits the number of
switches based on the accuracy of the resistors, as you pointed out.

I straight muli-tap divider allows for more switches with lower tolerance
parts, but does have the priority issue.


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