solarwind wrote:
> This is the thing - I don't know much about analog circuits, but I
> want to learn.
> http://en.wikipedia.org/wiki/Analog-to-digital_converter
> the wikipedia article says that the voltage resolution is equal to
> overall range divided by the discrete intervals (2^10 in this case)?
> But I don't know what the voltage range of the ADC in the PIC is.

The PIC A/D makes a number proprotional to where the input voltage is within
the Vref- to Vref+ range.  For now keep things simple by not using separate
Vref inputs.  This means the A/D input range will be ground to Vdd.  Use a
5V regulator to make Vdd and you'll be all set for the purposes of your
experiment.

>> Depending on what your experiment is about, you may be better off
>> using the 8-bit mode so you wouldn't have to worry as much about
>> dealing with noise.
>
> Question: how does using 8 bit mode (for the ADC?) help with dealing
> with noise?

Short answer: Not very well.  See my other post.

> I'm planning to make some sort of a bandpass filter to
> filter out high frequency noise.

You only need a low pass filter for that.  Since this is inherently a AC
signal, you do need one high pass filter stage somewhere, but that is really
just to block DC.  In practise, your circuit will need to block DC in the
front end to keep the DC from overwhelming later stages.  Then it needs to
add Vdd/2 DC offset at the end to keep the signal centered in the A/D input
range.  Your firmware will need to remove this offset, probably right up
front by only passing the difference signal to the rest of the system.
Technically that's a filter, but your "real" filter will probably be two or
three poles of low pass with the rolloff frequency carefully chosen.


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