I wanted to smooth noise of the airflow produced by the case-fan of my PC.
I made a simple circuit with a PIC12F683, a temperature sensor as
inpout and a PWM signal as output to control the speed of the fan.
That works, but now the fan produces a mechanical noise, apparently
with the PWM frequency. I have tried PWM frequencies between 60 and
500 to see if I just hit a resonance frequency of the fan, but the
noise remains.
Any suggestion (where to find info) on how to smooth this noise?

Regards, Rob.

-- 
Rob Hamerling, Vianen NL (http://www.robh.nl/)
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