detecting rpm from pwm powered case fan

Thread Starter

b0red

Joined Dec 17, 2009
12
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.
 
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