Arduino As PC Fan Controller

Hello,

Honestly, the 8-bit microcontroller in Arduino won't have enough resources to do that. It only has 2 8-bit counters and one 16 bit counters. If you want to monitor 4 fans independently, you need at least 4 counters that are able to capture external triggers (count edges from the microcontroller's pins), however, you also need 4 counters (or 1 counter with 4 period comparations) to independently drive them.

I would recommend using a PSoC for this (32-bit core, Cortex M0), here is an ultra cheap kit: http://www.cypress.com/documentation/development-kitsboards/psoc-4-cy8ckit-049-4xxx-prototyping-kits

It features a ready made component "FanController" with 4 channels, which allow you to independently control and monitor 4 fans (and I think there can be more of these components put into a design).

Before you start, make sure you know your fans.

Two wire fans: DC brush fans, can be driven at constant voltage and regulated using a PWM (pulsing the power pin). They provide no feedback, however, you can externally monitor the current going through the coil.

Three wire fans: DC brushless fan, can be regulated using a variable DC voltage. The additional pin is for monitoring the revolutions (provides pulses that can be count). (They have some electronics circuitry inside.)

Four wire fans: DC brushless fan, need constant voltage, but are provide one pin for driving using PWM (usually 25 kHz) and one pin for monitoring (the "same" as a three wire fan).

If you want to build your own controller, then Arduino and one fan is OK.

If you want to build something reliable (embedded PID regulation, error handling, etc), go for the PSoC (or similarly powerful MCU).

David

Hi Nicolas,

If you want to do it accurately, as David says, you'll need different hardware. According to the link here: How PC Fans Work the three-wire fan uses it's third wire to provide speed feedback (tacho). For something that could perhaps work with the Arduino, you could build a circuit to convert the tacho output into a voltage, and read it via the ADC. A 555 would do it (google '555 monostable' and append an RC integrator to it). But it is effort that may not be needed, if you don't care about the precise speed, and just want to have a slow fan, or a fast fan. It would likely be cheaper and easier to buy the fan controller. Also, I'm not sure it is good to play with fan speeds because I think usually the PC will do that, to keep itself cool, and also to power off if the fan fails.

Anyway if you really do want to control the speed yourself, as mentioned the 4-pin option is easiest, otherwise you could use a MOSFET to chop the power (i.e. use PWM library on the Arduino) to the red and black wires on the 3-wire fan. For an example circuit (there are many ways to do it, this is just one example), see here:

The recommended part is IRLD120PBFIRLD120PBF.

Tach outputs on fans are open collector transistor pulse outputs (usually one or two pulses per revolution). The only

  circuit they need is a pull up resistor (I used 4.7K on a 6 input fan monitor I built using a AT89c51) to +5V.

Yeah, I think the issue is with the coding. Sure you can do it, but this is a beginner asking how to do this with Arduino - nothing is impossible to code, even video output with an Arduino! but it's not pretty with the limited resources on the Arduino.

And furthermore, technically it's not even needed, to meet the actual goal in the question "add some modes like gaming for full speed, office use for lower rpm and less noise". Context is everything.

"Yeah, I think the issue is with the coding."

The original post is clearly hardware oriented and does not ask about the coding to do it. Your response is also hardware oriented with no mention at all about an issue with coding.

"And furthermore, technically it's not even needed, to meet the actual goal in the question "add some modes like gaming for full speed, office use for lower rpm and less noise". Context is everything."

From the original post:

"Can I control (4 fans) with an Arduino and get feedback from them about the RPM and the voltage if it possible(have it connected with USB on my computer and read the output in Arduino IDE)?

I directly responded to your reply about "extra circuitry needed to provide speed feedback (tacho)" so context was fully observed.

As you mention a commercial fan controller is by far the easiest but I do not know if any of them offer a way to do the gaming/office mode selection Nicolas asks about. It would seem like something

obvious to add to a standard fan controller.

"Also, I'm not sure it is good to play with fan speeds because I think usually the PC will do that, to keep itself cool, and also to power off if the fan fails."

As far as I know the only situation normally used to power down a PC is when the CPU overheats which relies on the CPU temperature sensor. Fan failure usually generates an audio alarm via the

PC speaker and usually displays a fan failure message during boot unless fan monitoring is turned off in BIOS.

Getting RPM feedback actually isn't the end goal. Why not sometimes actually try to understand the requirement, and form a more complete answer that helps the user? Just an opinion I've formed over the years seeing your replies.

While this sounds like a great project, I'm surprised by the application.

Most PC motherboards have fan control built in.

They require a 3 wire fan (as you have identified), and control the speed according to the PC needs rather than the application.

Most Video card fans are the same, they control the speed to suit the cooling need of the chip.

I recently had a issue with killing hard drives in a box that had speed controlled fans.

I switched to a Fractal R3 where the drives are across the front just behind the fans.

Fractal Design

You can't hear them running and there are zero temperature issues, which is good.

So IMO it is better to allow the motherboard to dictate the speed, rather than the application.

This will also allow for a speed hike if the heatsinks are getting blocked with dust, etc.

Mark

"Getting RPM feedback actually isn't the end goal"

I never said it was, but it was clearly listed as something that he wanted to do (if possible, and it is) and you spent

a full paragraph of your response on it. I replied to that response from you simply to point out what the tach output

actually was and what kind of external circuit was needed to sense it. And for some inexplicable reason you have a

problem with that.

"Why not sometimes actually try to understand the requirement, and form a more complete answer that helps the user?

Just an opinion I've formed over the years seeing your replies."

Despite your "opinion" otherwise I had no problem understanding the requirements and I'm sure the description of the

motor tach output did indeed help the user, please notice 4 of 4 people found it useful. Somehow I don't think you

did. I will withhold any opinions I've formed over the years from your responses (especially to me, see first paragraph

above) as I don't really see how it is any more relevant than yours is to this discussion.

P.S. the circuit you gave to control the fan motor will not work very well. For many years now PC fans have used

brushless motors with their own internal motor controller ICs and rapidly turning the voltage to the motor controller

on and off as would happen with the circuit you gave is in general not a good idea and will almost certainly cause

the fan motor to "rattle". This was a common complaint with some early commercial fan controllers. If you want

to PWM a fan that does not have a PWM input you need to integrate the output of the transistor circuit to produce

a variable the voltage to the motor. This has a limited range as most fan motors will not run below around 5V and

they may require the full 12V to start. Still it would probably be good enough to fit the requirement given.

You should be able to do this from the system bus controller itself. For an idea of how to control a PC pan, I have a blog post (on my personal) blog that shows how to PWM a 3-pin PC fan with an Arduino.

If you are serious about doing this yourself, instead of letting SMBUS handle it, this will give you an idea of what is involved. That said, that post was meant to show why you should use a 4-pin fan when you want to control via PWM. (The 4-pin PC fans are designed to be controlled by PWM. 3-pin fans aren't.)

What's with the quote-marks around "opinion" : ) I didn't ask you for your formed opinion, nor to withhold it. Open up and release it if you like. It's your choice.

Here's mine: Gary, you've always had issues. Not just with me, but others who have sadly left over the years too.

Just an example - it's clear what your opinion is/was of your peers here - this was one of your very first interactions on the forum with your peers or inmates at the asylum as you termed them: