>Either I'm not seeing it, or Microchip doesn't specify it, but I have a
>question that perhaps somebody in-the-know can answer (maybe by experience).

snip

>  Will my scheme work properly?

No.  But you can make it work quite simply: leave the input resistor as a
fairly high value, then switch in different values of resistors on the
bottom end of the divider.  The input to the a/d never exceeds maximum value
except when while determining what the voltage is.  Note: you can use either
straight digital outputs (LO or tristate only, never HI) or FETs *or* you
can use analog inputs turned into digital outputs (again, LO or tristate
only).  The neat things about using analog inputs as the range switching is
that the diginal inputs are disabled (no excessive currents due to biasing
the input in the linear region) *and* you can still use bsf / bcf on other
digital pins on that port: you always want the output driver for those
analog outputs to be Lo (any RMW instructions simply ensure that those pins
stay Lo).

Personally, I'd use other analog inputs as the range switching.

Concept:

       3-30V+
         |
         |
         R1
         |
         +------+------+--------> AN0 input
         |      |      |
         |      |      |
         R2     R3     R4
         |      |      |
         |      |      |
         D0     D1     D2
*or*
        AN1    AN2    AN3

dwayne


Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, Alberta, CANADA
(403) 489-3199 voice     (403) 487-6397 fax