>>   The external A/D converter is 12-bit; the internal, 8-bit.  It's a
>> question of granularity.  Do you want your altimeter to register 256
>> separate Feet (Meters) or 4,096 separate Feet (Meters) of altitude?
>
>It looks like I'm either going to have to either use external
>conditioning circuitry with the 8 bit 16C71 or an external (higher
>accuracy) A/D with the 16C84. Thanks for the reply

I'm also in the process of designing a PIC-based altimeter, requiring 12 bit
or greater resolution at 1 sample/sec.  It seems to me that this would be an
ideal application for the 14000.  However, the data sheet and application notes
are a little vague on how to achieve optimal analog performance.  AN624
mentions
that "A [resistive voltage] divider that results in an A/D input voltage that is
as near as possible to the bandgap reference voltage is normally selected, since
it reduces ratiometric errors during the calculation of the voltage."  The only
indication of what the nominal bandgap reference voltage tends to be is in
AN621,
where 1.1842 [volts] is given as a typical value of the bandgap reference
voltage
calibration constant.  Since the full-scale output voltage of a MPX5100A is 4.8
volts, this would imply that a voltage divider is, in fact, appropriate.

Has anyone used the 14000 for similar applications?
_____________________________
Marc Ramsey, marc@ranlog.com
http://www.ranlog.com/ramsey/