> The first cardinal rule of using an A/D: you always use an analog filter
> from the signal going to the pic set so that any frequencies you aren't
> interested in are attenuated.

No, only the frequencies that cause aliasing at your sample rate.  There is
nothing wrong with filtering a signal digitally as long as it is not
aliased.  Digital filters are more accurate and can often be free by using
cycles and memory that were available anyway.

> One of the reasons so many people do averaging after they have measured
> the signal is that they don't understand the importance of this initial
> low pass filter.

Or perhaps they understand both analog and digital signal processing very
well and chose the most effective solution for their problem.  Perhaps you
didn't mean to, but your statements leave the impression that analog is the
"right" way to filter, while digital is only done by those that don't know
better.  That is certainly NOT the message newcomers should be getting.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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