Software PWM Problems

[Charles Linquis]

If you *REALLY* need smooth PWM out of your chip, it is possible.

One approach would be to set up a hardware timer to give you a constant period (say 100uSec), and then use an interleave-type A/D routine. You could do the conversions (and the math) on consecutive timer rollovers.

Using this technique you could get 8 bits of resolution and 0 to 100% duty cycle at 40Hz. Not great, but possibly usable.

[HenrikOlsson]

Hi,
(OK, just an idea here - worth a try)
With the AD result set to 8 bits your result will vary from 0 to 255. Try changing the line:

i = 256 - adval

to

i = 255 - adval

and see what happends. Even at full scale (adval=255) your i variable will be 10 if you subtract adval from 256. You will probably still get short glitches but hopefully you will end up closer to what you want.

/Henrik Olsson.