AC Freezer Question: PWM Control

[BillytheImpaler]

Definitive source: http://www.formfactors.org/developer\specs\REV1_2_Public.pdf (pdf warning)

Pin  Function  Wire Color
1    GND       Black
2    12 V      Yellow
3    Sense     Green
4    Control   Blue

The PWM input shall be delivered to the fan through the control signal on Pin 4 (see Section 2.4).
Fan speed response to this signal shall be a continuous and monotonic function of the duty cycle
of the signal, from 100% to the minimum specified RPM. The fan RPM (as a percentage of
maximum RPM) should match the PWM duty cycle within ±10%. If no control signal is present
the fan shall operate at maximum RPM. See Figure 2.

Pin 4 is essentially communicating with a relay in the motor that is switching the power on and off as it specifies by switching itself on and off.

 

[Big.Wayne]

Ta

 

[Snapshot]

Ok, I didn't take my 'new' mobo out the box yet and look, but I never saw a 4-pin fan header before? What mobo you using?

Gigabyte GA945P-S3 but I believe it came in with Intel's LGA775 and all LGA775 mobo's certainly have it now. I don't know about the AMD side of things.

 

[Big.Wayne]

I don't know about the AMD side of things.

I'm 99% sure no socket939 mobos have a 4-pin cpu-fan-header (none I seen anyway) but I suspect its a socket AM2 thing maybe?