Quote Originally Posted by jalyst View Post
I didn't realise there are RPM reading problems or switching noise assoc. w/PWM!? (at least more so than LVC)
  • motor ticking noise when running at low PWM frequency. guess thats why intel specs use about 25kHz PWM frequency for PWM fan control.
  • high PWM frequency on the other hand, interferes with rpm readings as the fans internal rpm reading circuit is switched on and off at the PWM frequency, thus the rpm output is switched at the PWM frequency too. this interferes with the regular rpm pulses resulting in erratic rpm readings. this problem is primarily at lower rpm!


What are the main reasons you don't feel PWM should be part of your project?
as said before, i played around with it but was not able to control my fans the way i expected. the results varied from fan to fan. same fans could be controlled in the range from 80% up to 100% by varying PWM duty cycle from 5% to 10%. everything above 10% PWM duty cycle resulted in 100% rpm. thats not the way its supposed to be.

of course, all this problems are related to 3-pin fans only. bus as the PWM versions of gt's are not available till now i will focus on 3-pin fans.

anyway, my controller will definitely be able to use PWM control on 4-pin (real PWM) fans also.