> -----Original Message-----
> From: moonshadow [SMTP:moonshadow@NTLWORLD.COM]
> Sent: Monday, January 20, 2003 9:47 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Dual sine wave generation.
>
> I need to generate two sine waves. One fixed at 14 kHz and the other
> variable between 14 kHz and 14.250 kHz. I would prefer to use Crownhill's
> BASIC Compiler to do this.
>          Can anyone suggest how I ought to go about this please ?. I had
> thought to use the two internal  CCP modules and the PWM command. However
> both modules have the same output frequency.  Same with FREQOUT.
>
> John Kent.
>
What resolution do you need for the adjustable frequency?  How much jitter
can you tolerate?

 You can (maybe) use the hardware PWM, but not in the manner you are
thinking. One idea is to build a table of SIN values and step through the
table at a variable rate, outputing the table value to the CCP module.  The
PWM output would need to be low pass filtered to remove the PWM frequency
components.  This implies that the PWM frequency has to be significantly
higher than 14KHz.  The higher the PWM frequency the worse the PWM
resolution, which will affect the the quality (e.g. distortion) of your sine
wave.

Mike


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