Thanks Scott,
Lookup table and filter is a great reccomendation. Thanks. By the way, great
website -- I did some looking around.
Shawn
----- Original Message -----
From: Scott Dattalo <scott@DATTALO.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, March 20, 2002 6:00 PM
Subject: Re: [PIC] Sine wave oscillator


> On Wed, 20 Mar 2002, shawn wrote:
>
> > I'm looking for some opinions and perhaps suggestions. I would like to
> > replace a 625Hz analog sine wave oscillator with a low-end PIC
> > microcontroller -- say 16F84 or 8-pin model. Is it better to use a
> > look-table approach to replicate the sine wave or can excellent
> > results be achieved by generating a square wave then filtering? Any
> > advice on the second approach would be appreciated. And finally, would
> > the answer change if I were generating say a 1MHz wave?
>
> First question: lookup table plus filter is definitely better.
>
> Second question: yes, if you want to use a PIC. It's quite easy to
> generate a pulse train devoid of the 2nd, 3rd and 4th harmonics. This
> greatly reduces the filter requirements (suppressing the 3'rd harmonic of
> a square wave without affecting the fundamental is practically
> impossible). You can continue with an optimized pulse stream to minimize
> the first N harmonics. Or you can increase the complexity of the pulse
> stream and suppress the 2nd,3rd, 5th and all multiples of them.
>
> Check out:
> http://www.dattalo.com/technical/theory/sqwave.html
>
> and specifically usage number 011.
>
> This pulse stream, btw is devoid of 2nd, 3rd, and 4th harmonics. I don't
> recall how big the 5'th is.
>
>  ^ v(t)
>  |
> A|  +--+  +--+                          +--+
>  |  |  |  |  |                          |  |
> -+--+  +--+  +-----------------------T--+  +-----> t
>  0  1  2  3  4  5  6  7  8  9 10 11  0  1  2  3
>
>
> The idea is to run this through a cheesy low pass filter and you have a
> sine wave!
>
> Scott
>
> --
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>
>

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