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Author Topic: 4 pin PWM fans and Arduino Uno not playing nice.  (Read 1120 times)
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Hi everyone, first post on here. I've been following arduino's for awhile now and decided to get one today for a project I wanted to do. I write .net code and also mess around with small electronic projects from time to time but this thing has got me stumped. I've scoured the web and tried various pieces of code to no avail. Here is my problem.

All I want to do is be able to change the speed of a 4-pin PWM 12v fan. I've seen some pretty elaborate setups on line but there has to be a simpler way. I have connected the fan to an external power source which powers the fan and it is running at a slow speed which is what I would expect. I then connected the Blue wire to various PWM pins on the arduino and tried using the analogWrite method but no go. I've also tried utilizing some code chunks that change the pin frequency to 25khz on pin 10 ect.. Still no go.

I have also tried all of these options with and without the ground from the fan connected to the GND pin located next to pin 13. I know I must be missing something. Do i need to utilize the Yellow wire (rotation speed) somehow. Hopefully one of you Arduino experts can assist.

Thanks
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Boston
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What fan are you using?
Do you have a link to the datsaheet for the fan?
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Here is the fan i am trying to use. I have 4 of them but I am only trying to get one going for now until I am better aquainted with the arduino.

http://www.newegg.com/Product/Product.aspx?Item=N82E16835553002

I couldn't find any better specs on the Mfg site either.

Am i wiring correctly for this type of fan. ?
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This is a guess, but could it be that the pwm fan input is expecting a 12V signal? If so, the arduino output is going to register as low whether it is 5V or 0 - hence no effect.
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The spec for 4pin fan pwm states:
Quote
2.1.1 Fan Input Voltage
Fan operating voltage shall be within the range 12 V ±5% V.
...
2.1.4 PWM Control Input Signal
PWM Frequency: Target frequency 25 kHz, acceptable operational range 21 kHz to 28 kHz
Maximum voltage for logic low: VIL = 0.8 V
Absolute maximum current sourced: Imax = 5 mA (short circuit current)
Absolute maximum voltage level: VMax = 5.25 V (open circuit voltage)
This signal must be pulled up to a maximum of 5.25V within the fan.

http://formfactors.org/developer/specs/4_Wire_PWM_Spec.pdf
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Still scratching my head on this one. Been playing around with it all morning and nothing seems to work. Anyone have a link to a post or video showing a PWM fan working in this manner.
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Anyone. ?

I see a few PWM threads around here but they all seem to either go unanswered or have some laundry list of things to do just to PWM a fan. Shouldn't be this difficult.
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Problem has been solved.

Self inflicted. When using a 4 pin molex connector for power always remember the yellow is 12v and the red is 5v. Had it tied to the 5v which is why it would never go any faster than it's slowest speed.  smiley-red
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