Josh Koffman wrote:
> I'm going to be doing a project that requires me to use the ADC to
> read a bunch of pots.

If that's what you really want, connect the pots between the PIC Vdd and
ground.  The result will be ratiometric, so the actual power supply voltage
or any variations in it will cancel out.  It also nicely guarantees that yo=
u
can't drive the analog input outside their range.

> These will be putting out a 0-10V signal. In the
> future my board may be connected to another device which will source
> the 0-10V signal itself. This would be an 8 bit reading, I don't need
> anything higher.

So you really want to read 0-10 volt signals with the fact that they come
from pots being irrelevant?  In either case you need to know what the sourc=
e
impedance of the signal being measured will be.  If it's coming directly
from a pot with its ends at zero impedance nets like power and ground, then
the worst case impedance is 1/4 of the pot resistance.

> Analog design is far from being my forte. My current thought is to
> feed the signal into a resistor voltage divider which scales the
> voltage down to 0-5V. Then it would go into an op-amp voltage follower
> to buffer the signal.

Why do you think you need a buffer?  If the source signal impedance is low
enough, you can just feed the output of the resistor divider directly into
the PIC.

> If I go that route, I am considering using 10K resistors as the
> voltage dividers.

If your source signal is OK with a 20KOhm load, then most likely you can
feed the voltage divider output straight into the PIC A/D pin.

> The LM324 is cheap and available in a number of
> surface mount packages,

But will also add offset voltage and has common mode range issues.

> With that in mind, I know the PIC ADC has some parameters with
> respects to impedance of the voltage source.

Right, and for your PIC they are ...?  Read the datasheet (duh).  How do yo=
u
expect others to help when you don't tell us what this spec is for your PIC
nor the PIC you are using?


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