Convert PWM Frequency

Just found this. Thought it could be useful to someone here: http://letsmakerobots.com/node/17095

OddBot obviously does not come here much.

http://www.picaxeforum.co.uk/showthread.php?t=8533
See post #14
You should be able to PWM down to 5Hz with an 08M.
And you will have much better control of the duty as well.

So, it changes D-A and then uses simpe threshold to set it back to PWM.
I'm sure it works but it sounds like it would lack precision.

Looks like it is based on the old triangle-wave/comparator method of generating PWM using 2 op-amp stages.

If you can't get direct PWM of a low enough frequency there are a number of chips that can do this without going to all that effort - and with far greater accuracy.
Or, do like I did, write a serially controllable PWM generator.