Quote Originally Posted by Charles Linquis View Post
The thing most people ignore is the quality of their reference and dividers. They try to get 10-12 bits (or more) of resolution when using Vcc as the reference voltage. That just doesn't work. We use an LM4120-4096 (4.096V) reference with 0.2% accuracy. All voltage dividers use 0.1% resistors.
If the thing you are reading also operates with a Fixed Reference, then sure ... you should use a reference on the A/D.

But most things are "Ratiometric" and a fixed reference will transfer any ripple on the power supply straight into your A/D readings. And regulators like 7805's that can't keep a constant voltage will make the readings wander all over the place.

References have their place, but I believe you should not use them unless the right conditions are met.

0.1% resistors ... gotta agree with that though.
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