I've done this for card node I.D. no problem but my I had plenty of  1%
metal film resistors handy, so I used those in the a/d environment.
I also compared and verified the a/d result with a couple of hits.  As a
decoupling capacitor, I used a 0.01uF in order not to affect the response
time as much. {slewrate}

----- Original Message -----
From: "Eric Bohlman" <ebohlman@EARTHLINK.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, February 26, 2003 3:45 AM
Subject: Re: [PIC]: A to D convertor use for switch decoding


> 2/25/03 11:27:14 PM, Michael Reid <mikecreid@MSN.COM> wrote:
>
> >Does anyone have any experience in using an A to D input with a ladder
> >resistor array of 8 resistors and 8 switches to allow for the 8 switches
to
> >be used without taking up more than 1 I/O into the processor?
>
> There are a couple examples on Microchip's site; the one I remember
offhand was in the "tips and
> tricks" document for the 12F629/675.
>
> >If the resistors are all 1k in value then the input voltage will
correspond
> >to whichever button is pressed?  Is this a practical route to explore?
> >
> >We are designing a keypad for a control system and I/O's are at a
premium.
> >We need a 1 or 2 color LED per switch so that will use a mess of I/O's.
>
> Sounds reasonable, but read the application notes; you'll want to watch
out for noise pickup and for
> boundary ambiguity.

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