Quote Originally Posted by malc-c View Post
Darrel,

Thanks for the advice, never thought that the scope / soundcard software would cause that issue...

I've not given up entirely on using a PIC, as I feel they offer a lot more and simpler than using descrete components. I'll keep plugging away and see what I come up with.

I assume that using a 100 Hz frequency for the PWM would be ideal... what PIC did you use, and is having an internal clock an issue (I'm using a 12F675 for experimential use)
I've ran a heater blower motor on a car at ~4khz and unless I strained to hear it, there wasn't much to hear. I know it's a different motor, but still, quite a current draw and I switched the power with MOSFETs. Initially, I ran it with somewhere around 62hz...lots of noise! Both audible and almost a vibration...not to mention the noise coming thru the stereo (which may have just been a bad ground somewhere).
The 12F675 can run 4mhz on the internal clock. You should be able to easy incorporate the TMR0 interrupt and make a software PWM output that'll run at 3.9khz (which should be plenty high enough) and use the A/D input to set the duty cycle on that PWM. I suppose the easy way to do it would be to take the 10bit A/D input, divide it by 4, giving you 8 bits and use that as the basis for the software PWM.
Are you familiar with doing software PWM based on interrupts?