Thanks!!!  Truthfully, I don't understand all of what you wrote, but I =
know the seeds of information are there.  It gives me what I need to go =
further.  I have much to give thought to.

Thanks again! Lindy.


=20
> >I remember LPF's and HPF's from studying about synthesizers.
> >Like, for instance, passing a noise through it and getting
> >a cymbal or drum sound.
> >
> >But you mention DC components.  I don't understand that.  What
> >does that have to do with the DC PWM signal?  Where was the AC
> >in the mix?
>=20
> Say I have a PIC with a PWM output that's running at 1 kHz with
> a
> 50% duty cycle; it produces a square-wave output which
> alternates
> between zero volts (logic "0", or ground) and 5 volts (logic
> "1"), spending half its time in each state.
>=20
> That square wave consists of a 2.5 volt DC component plus a 1
> kHz
> sine wave of 5 volts p-p amplitude, plus an infinite series of
> the odd harmonics of 1 kHz with amplitude inversely proportional
> to frequency.  Any of these components of the square wave-- as
> well as the DC average value-- can by isolated by an appropriate
> filter.
>=20
> >And most importantly, why or what about the PWM signal made it
> >necessary to low-pass-filter it?
>=20
> It looks to me like the PWM is being used as a digital-to-analog
> converter, where the analog output consists of the average value
> of the PWM's pulse train output.  The PWM output is a square
> wave, and the filter gets rid of everything but the DC part of
> it.
>=20
> >What where they trying to get by it?
>=20
> A smooth DC output voltage with little high-frequency "hash" or
> ripple on it, that can be adjusted simply by loading different
> numbers into the PIC's PWM registers.
>=20
> Hope this clarifies instead of obscures.  What might help is to
> just try it on the nearest handy PIC: put a single-stage RC
> filter on the PWM output (try a 10K resistor and a 10uF
> capacitor, for starters), stick your scope probe on the filter
> output and try adjusting the PWM register values.  See what you
> get.
>=20
> Dave D.
>=20

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=20

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