> Clearly, generating a square wave from a PIC is a piece of cake.  But I
> need to generate a sine wave and am not sure how to do it.  Is there an
> IC around that  takes a square wave as input and outputs a sine
> wave?   Perhaps an AF amplifier or something like that?

There are many ways to do this.  The best approach depends many parameters
including frequency, frequency range, allowable distortion, amplitude and
frequency accuracy, etc.

The simplest solution is to passively low pass filter a square wave.  This
can result in arbitrarily low distortion, but only works well for a
previously known narrow frequency range.  More complex on the fly
filtering allows for broader frequency range.  Function generator chips
work over wide frequency ranges, but the distortion is somewhat higher.
For low frequencies, you could compute the sine in firmware and output to
PWM or D/A, followed by passive low pass filter.

There are too many approaches to talk about until you provide some more
specifics.


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