You may be better off using a comparator instead of A/D
converter.  If all you want is frequency counting, then you
don't need to know the analog value of the signal at lots of
points in time, you just need to know how often it passes a
certain value.  Using a PIC with an internal comparator and
voltage reference (like the 12F675), you can do just that.

---- Original message ----
>Date: Fri, 27 Sep 2002 05:16:49 -0600
>From: Nate Duehr <nate@NATETECH.COM>
>Subject: [PIC] A/D vs. Counting Pulses - Design Question
>To: PICLIST@MITVMA.MIT.EDU
>
>Hi all,
>
>Working on getting my head "around" the PIC a bit here, and
have a
>generic design question that may or may not come off as
really dumb.
>
>Not an EE here, so take any incorrect terminology with a
grain of salt.
>
>I'm looking to take an audio input to a PIC, first bandpass
filtering it
>heavily so that only the 50-300 Hz range is left over after
a filter
>(call it an anti-aliasing filter if you like) and then
present that to
>the PIC to do a frequency count.
<snip>
--
Mike P.
MTP Technologies
KC0LLX

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