PORTA set as ADC is terribly easy to be
damaged. So far, this is what I found.

pin shearing can do saving pin, also.





----- Original Message -----
From: "Carey Fisher - NCS" <careyfisher@ncsradio.com>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Friday, July 01, 2005 9:34 PM
Subject: RE: [PIC] 1-pin 16 key analog keypad


>
>   I once saw a
>    > "16-button analog keypad" circuit which used 1 pic i/o pin
>    > configured as
>    > analog input, (obviously) 16 momentary switches and some
>    > resistors.  The
>    > theory behind it was that for each key pressed, a different
>    > voltage would
>    > be present to the analog input and the pic could tell what key was
from
>    > that voltage.
>    >
>
>    > -Mario
>
> Mario,
> Here www.ncsradio.com/schematics/keypad.pdf is an Eagle schematic
>  .pdf showing an 8 switch version of what you want.  The signal
>  labelled PIC_AD_SW is tied to an A/D input pin on the PIC.
>   If you calculate the voltages for each switch pressed,
>  you'll see how this works.  I use a table of the mid
> voltage between adjacent switches as the decision point
> for which switch is pressed.  One feature of this design
> is that multiple switches pressed at the same time will
> not be confused with other switches; the lower number
> switch always has priority.  If you want some more info
> on the algorithm I use for this design, let me know.
> Carey
>
> --
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