On 9/2/06, Darren Gibbs <tsquank@yahoo.com> wrote:
> For my LED-based lighting project, I'm using an 18F1320 to do 8
> channels of 9 bit PWM in software.  I have another PIC that generates
> lighting patterns and communicates with the PWM PIC using serial
> MIDI.  It works fine, but there is very noticeable (distracting)
> quantizing of the brightness steps at low brightness levels.  I've
> been experimenting with 10 or 11 bits of resolution, but the 40MHz
> PIC isn't fast enough to do it without the PWM frequency dropping to
> visible strobing.  I've been searching the web for other/better ways
> to do this, but so far I haven't found a part that seems
> appropriate.   In general pin count seems to go up with speed and I
> don't need giant amounts of I/O.  I did notice some future 28pin 8
> bit PICs on the Microchip webiste that run at 64MHz which is a step
> closer.  In my dreams is a 16bit, 80MHz MCU pin-compatible with the
> 18F1320.  Not holding my breath for that.  Does anyone have any
> suggestions a different MCU or different approach entirely?

You could try sigma-delta modulation instead of PWM.  In theory the
noise will be moved to higher frequencies where it is less
objectionable to the eye.  It practice, it may take a bit more math,
so the frequency may still be too low.

Regards,
Mark
markrages@gmail
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