detecting rpm from pwm powered case fan

Discussion in 'The Projects Forum' started by b0red, Dec 26, 2009.

  1. b0red

    Thread Starter New Member

    Dec 17, 2009
    Hello ! Is it possible to clean up the pwm noise on rpm sense pin of 3-wire pwm powered case fan to get a clear rpm signal ?

    Do 4-wire fans designed to operate with pwm have a clear rpm reading on their sense pin ?

    I made a 555 pwm supply for my standard 3-wire fan and eliminated the whining noise by connecting a huge 1000uF eletrolytic cap across it's terminals to smooth out the voltage. So i'm wondering if this change in (otherwise typical) design may affect any possible solutions to my problem.