My office was hot one day so I crafted a desk fan out of a 4 wire pc fan i salvaged out of an old computer. I cut the plug off of it and the barrel connector off of a 12V 1 amp wall wart and connected the positive and negative wires and it fired up. It's 4 wires red, black, blue, and white. Black and red are obvious, white is apparently rpm output signal, and blue is input for PWM. The way i had it connected was going full blast, which is way too much airflow. I found out searching online that if you connect the pwm wire to ground the fan will go to lowest setting. I did that and sure enough it did, but lowest setting isn't really enough. So i would just like to have a little controller on it.

From what i have gathered, since this type of fan has a circuit board you can't control it just via voltage control or something like that. Every project i find is some kind of voltage control, or soldering in a transistor, or multiple transistors with a selector switch or something. I was looking on ebay to see if i can find a simple pwm signal generator with a control knob but i'm not entirely sure what i'm looking at.

https://en.wikipedia.org/wiki/Computer_fan_control#Pulse-width_modulation
"The control signal is a square wave operating at 25 kHz, with the duty cycle determining the fan speed."

I found this controller, http://www.ebay.com/itm/PWM-0-90-Fr...941705?hash=item2ee145c549:g:uqYAAOSwBLlVUHVW

So I have some questions. If i am understanding things correctly, hertz and duty cycle are not the same thing, the duty cycle can vary while the hertz stays the same. This generator has 3 ranges of hertz adjustment controlled with a jumper, including 1khz- 100khz, which 25khz falls into, but does the board have to output at EXACTLY 25khz? There is a thing that says frequency adjustment, i assume that is the little brass slotted knob? I'm not sure how to measure when it's outputting 25khz without a piece of equipment i don't own. The big knob i guess adjusts the duty cycle. On the 4 pin connector, which pin should be blue wire connect to? +Out?

If you have a better controller to suggest, I'm all ears.

 

The average PC fan has a pole sensor and an IC to switch the internal BLDC signal, so also providing another external variable freq may not work, even a external PWM may not work out.
But I have never tested this in person.
Max..

 

The average PC fan has a pole sensor and an IC to switch the internal BLDC signal, so also providing another external variable freq may not work, even a external PWM may not work out.
But I have never tested this in person.
Max..

I've seen it demonstrated in a youtube video, using some large piece of equipment on a desk, that had an lcd screen, to output a pwm signal, and they had it connected to the pwm wire with an alligator clip. This obviously won't work for me as I don't have that piece of equipment i can only imagine costs hundreds of dollars, and I just want a simple little controller.

 

Yes, frequency and duty-cycle are two unrelated parameters.
The frequency is the cycles per second (Hertz) (how often the output goes from high to low and back in one second).
The duty-cycle determines how long the output stays high for each cycle.

I would say that the Ebay circuit you posted will do what you want.

 

Yes, frequency and duty-cycle are two unrelated parameters.
The frequency is the cycles per second (Hertz) (how often the output goes from high to low and back in one second).
The duty-cycle determines how long the output stays high for each cycle.

I would say that the Ebay circuit you posted will do what you want.

So as I was saying I don't have a way to measure the hertz. Is that what the little brass screw/knob is for, adjusting the frequency within the range that the jumper sets?
And is +Out the logical pin to connect the pwm wire to?
When i have ordered straight from china electronics in the past they either come with no instructions or instructions that might as well be written in ancient cuneiform script. "Please are make up wire connect in proper direction with gratitude for fun time."

 

t might as well be written in ancient cuneiform script. "Please are make up wire connect in proper direction with gratitude for fun time."

Been there a few times, it is called 'Chinglish'.
Max.

 

Yes, frequency and duty-cycle are two unrelated parameters.
The frequency is the cycles per second (Hertz) (how often the output goes from high to low and back in one second).
The duty-cycle determines how long the output stays high for each cycle.

I would say that the Ebay circuit you posted will do what you want.

This is the explanation. You need at least a little understanding of electrical engineering.
What is "frequency", "amplitude", "period", "duty cycle". You need to control these 4 things, if you can, than it wont be a problem.

 

Been there a few times, it is called 'Chinglish'.
Max.

I had 1964 Honda 305 motorcycle and the manual, extolling the virtues of it said "Pickups and hill climbs are no problem with a Honda."
The pickup part never worked that well for me.

 

I had 1964 Honda 305 motorcycle and the manual, extolling the virtues of it said "Pickups and hill climbs are no problem with a Honda."
The pickup part never worked that well for me.

You are the only one! It was probably the one statistically broken one !