> The challenge is then to get a 2.5V reference.... ;-)

Fortunately 2.5V is a standard reference. Microchip do the
MCP1525 (I use occassionally), and there's AD, LM, MAX,
REF-, TL, ZRC etc. Those are from the RS catalogue, I'm
sure Mouser or Digikey will have similar

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist