Analog Vref Question

[shawn]

I have a little problem, and I would like to run my solution past you guys before I spend allot of time trying to make it work. I'm using a pic 18f458 in my project and I want to use 2 of the analog inputs. Problem is my Vref+ needs to be different for both of them. My simple thought was to use some transistors, off of outputs of the pic to change voltage levels to vref+. I think I could finagle that.
As the project grows I can see myself needing at least 2 more of the analog inputs. My next thought was to use a digital pot and just send values to the pot to change voltages to vref+. I should probalby use a standalone AD converter but I don't want to really. Do you guys have any tips or suggestions.
If both of these are bad Ideas does anyone know of easy to use 10bit I2C or SPI ad converter.Vref+ should probably be able to swing +- 15V maybe even 20. I bought a mpc3301 but vref+ is only good for 3 volts I think. I wish I would have noticed that before I bought it.
Ok I just looked at the data sheets for 18f458, am I looking at it right max vref+ is only 5 volts. IF this is the case I am going to have to use a standalone ad converter. Some advice please some one.
Thanks
Shawn

[mackrackit]

Yep, 5 volts is the max for these things.

As far as VREF goes, this may give you an idea or two.
http://www.picbasic.co.uk/forum/show...highlight=vref

[shawn]

Thanks Dave.
That was my exact question talked about in that post. I looked for hours and did not find that post. Sorry for starting a new thread I suck at searching on this forum for some reason.

Shawn

[mackrackit]

No problem. I kinda knew where it was.
And some times this help.
http://www.picbasic.co.uk/forum/showthread.php?t=4751