I realized I should probably better define what I'm looking for, so I 
can get more useful answers.  I guess this is one area where I can't 
just say "how do I isolate an analog input".   Not to say that the 
answers so far haven't be useful, as they have pointed me in some 
directions I haven't thought about - for instance both the V/F and the 
Instrument amplifier are good ideas which I will delve into further.

That said, what I really need to be able to do is have a half dozen or 
so "voltmeters" which are attached to the PIC18F*J60.  Cost is 
definately an object in this case.    Although I will need to deal with 
different scales so that a 2V signal can be read with enough resolution, 
on the high end I need to measure up to about 60VDC.  The input can 
swing either way.  These will be used to measure things like battery 
voltage level (typically the *same* array that the unit is powered from, 
but not always), charge/discharge current measured as shunt voltage (may 
be on the + or - side of the bat), and other inputs such as fuel level, 
valve positions, etc.  

In many cases I could say "everything is measured in relation to 
ground/Vss", and this wouldn't pose a problem.  In others, this would be 
an issue.   In an ideal world, the inputs would be completely isolated 
from each other and from ground/Vss.  That is, work just like multiple 
battery powered voltmeters.   I realize that this may be unworkable or 
significantly expensive.   As a result, the needs may be able to be 
redefined such that everything must be ground referenced.  However, 
being able to measure voltages where the input is below Vss is important 
since one of the main applications for this device is to monitor battery 
utilization.

Hopefully this rambling helps describe what I'm trying to figure out.  
I'm at the "we need to be able to measure x, and what are our options to 
do so" stage so I really don't want to through any ideas out at this 
point, even if they don't fully meet my ideal situation.

-forrest






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