PIC A/D and Voltage Divider

Started by Max March 19, 2011
Or you could use higher value resistors with a very low power voltage follower, but that could be expensive if you need accuracy or speed, and could end up using more power in the end.  If you can live with lower speed or lower accuracy the 10k limit can be raised.  There should be a formula for sample time versus input resistance.
My software has no bugs, only undocumented features.
You should be able to use a fairly large, low-leakage capacitor on the
input of the A/D. This will, of course, limit how fast you can see
changes in the input voltage, but if you are simply measuring DC, then
that shouldn't be a problem. The capacitor will charge to the divided
voltage, and provide current while the A/D is sampling. Accuracy and
low power at the same time.
The cap will also filter out any noise that is induced into the
high-impedance voltage divider.

Charles Linquist.