I am using a 18F252 that can output two PWM waveforms each with it's own
duty cycle.  However, I need three for my project.

The hardware PWM works great as you can see from this image, where it
smoothly blends one color into another...

  http://www.ian.org/HD-Clock/HDC-BG-PWM.jpg


I tried doing the PWM in software and it worked.. but not well.  I could
only get a few bits of resolution and it ate up all the CPU cycled because
of the high speed it needs, even with the PIC running at 40MHz.  The
minimum period I need to use is 25us.  Higher and there is visible
interference patterns from the PWM wave.  Just too fast to bit-bang and
leave room for much else.

Are there any PICs that can output more than two duty cycles?  I have seen
some PICs have four outputs but they are just for driving h-bridges and
still only let you set two duty cycles.

I suppose I could use a 2nd PIC like a 16F86 but I'd prefer internal PWM
since it works so well for the 2 channels I have.

Thanks!

--
Ian Smith
www.ian.org
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