Thanks very much for the help and explanation.  I really appreciate it.
=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.

This I get. The PWM simply sets the output high or low, with any =
combination of the high/low duration.  And we are working with the =
voltage of the PIC with is 0 to +5V.   =20


>=20
> That square wave consists of a 2.5 volt DC component plus a 1
> kHz
> sine wave of 5 volts p-p amplitude,=20
> 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.

I think I understand DC, and I think I understand AC, but this seems to =
be a mix of the two that I don't get.  I cannot even ask a question that =
would help me to understand better. =20

How can something be both AC and DC at the same time?

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=20

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