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bonestorm
Joined: 06 May 2001
Posts: 21
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 02 Oct 2004 16:00 Computer Case Fan |
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| Does anyone know the output of the third pin (white wire) from a PC case fan? Is it a PWM or voltage or a square wave that is proportional to the RPM of the fan?
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lvjrf
Joined: 25 Aug 2004
Posts: 19
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| 03 Oct 2004 14:31 Re: Computer Case Fan |
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| Its a square wave to control the speed of the fan
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bonestorm
Joined: 06 May 2001
Posts: 21
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| 03 Oct 2004 14:56 Re: Computer Case Fan |
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| Do you mean that the motherboard outputs a square wave to control the fan? Or do you mean that the fan outputs a square wave to indicate speed of the fan?
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FoxyRick
Joined: 09 Jan 2004
Posts: 598
Helped: 35
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| 03 Oct 2004 15:16 Re: Computer Case Fan |
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The fan outputs pulses to indicate speed. I think it is 2 pulses per revolution from an open collector output.
I don't know if they are squarewave, they don't need to be, just pulses.
I used to modify fans without a third wire by adding a diode and two resistors to give this output. That was in the days before they all had them.
FoxyRick.
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SPATAN
Joined: 17 Aug 2004
Posts: 135
Helped: 5
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| 04 Oct 2004 9:29 Re: Computer Case Fan |
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| It use for check speed fan. If speed slow then shutdown
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minaflying
Joined: 24 Sep 2004
Posts: 22
Helped: 2
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| 04 Oct 2004 12:37 Computer Case Fan |
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| I have designed a cpu fan driver IC,the output waveform is just a square wave ，it only indicate the speed of the fan,the cpu and motherboard don't control fan's speed by this pin.
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