V G <x.solarwind.x <at> gmail.com> writes:

>=20
> On Sat, Apr 7, 2012 at 7:36 PM, Sergey Dryga <sergey <at> dryga.us> wrote=
:
>=20
> >  Getting a clean pulse: use comparator, it will give you a clean digita=
l
> > signal.
> > It's possible to use a comparator in a PIC and do processing using the
> > same PIC.
> >
> > Extracting frequency is more problematic, but can be done in e.g. dsPIC=
, as
> > others suggested.  If you need to detect a specific frequency, LM565
> > phase-locked loop is good for audio frequencies.
> >
>=20
> I was thinking about the comparator, but since the amplitude of the signa=
l
> gradually falls over a period of a few seconds, how would I constantly
> follow and update the cutoff?
>=20

Set the trigger level at some low value which you would still consider to b=
e a
signal.  Anything above that level will produce "1", below - "0".  This way=
 you
eliminate the problem of decay in the amplitude.  For an AC-coupled signal
(through a capacitor) the level can be 1/2 V+.  Essentially, this will be a
zero-crossing detector.  If the noice is too high, increase the trigger lev=
el
just above the noise.=20

Sergey Dryga
http://beaglerobotics.com



--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.