One possibility is to integrate the square wave with an op-amp integrator,
yielding a triangle wave.  Then clip the peaks of the square wave producing
a pseudo-sine output.

If your application isn't too demanding this is a reasonable approach and
doesn't require elaborate filters.  And if you do decide to clean it up, you
can get by with less filtering than the brute force square wave --> low pass
filter = sine wave.

One simple example of the square wave --> integrator --> diode clipper =
sine approximation can be seen in the schematic and circuit description for
an inexpensive function generator kit at
http://electronics123.com/amazon/datasheet/k23.pdf




Jack



-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of John Nall
Sent: Friday, June 20, 2003 8:14 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC]: Square wave to sine wave - how?


I have a hunch that this is a stupid question to ask, and if so I may have
to endure a few sarcastic replies (or, even worse, no replies).  But since
I need to know, guess I just have to take that chance. :-)

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?

Thanks for any suggestions.

John

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