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Thread: fast easy DAC with PIC
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face BY : Dan Michaels email (remove spam text)



Roman Black wrote:
.........
>Some people might initially think that varying PWM
>AND frequency to get the exact ratios might sound
>like butchery, but why not do it? It allows very
>fast PWM frequencies and very fine adjustment with
>quite a crude PIC.


Sounds like a classical accumulation algorithm. This is
probably good when you are running a motor and want to
even out the energy in the PWM wave, but for 10-bit PWM,
for instance, your "fundamental" frequency can vary by
up to 512:1, and this can cause problems in some cases.
[although, for a motor, it would never turn a lick with
PWM=1 part in 1024 anyway].

Varying fundamental would ruin operation of the PWM-controlled
LED intensity ckt I posted last week, where the fine point
of operation was the playoff between pulsewidth and rise time
of the RC filter.

- danM

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