Intel's 4-pin "PWM" Connector

DIY Fan Controller for PWM Fans

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Intel's 4-pin "PWM" Connector

Intel's 4-pin "PWM" Connector

Introduction

I’m sure that most hardware enthusiasts are no strangers to dalliances with DIY, whether it be case modding, component modding, or custom cooling.  However, when it comes to building parts of your computer from scratch, the tally of enthusiasts who can claim this prestige most certainly diminishes.  Fortunately this neat fan controller project requires only a little time, expense, and commitment, and the circuit is relatively easy to build and very satisfying to use!

First Things First…What is PWM?

PWM stands for Pulse Width Modulation and is, among other things, a very clever means of controlling power to electrical devices: in our case a DC (direct current) fan motor.  Although you don’t need to understand the ins and outs of PWM, it helps to have an rough idea about how PWM works, so here’s a very quick explanation.

Think of a PWM signal as if it were a beating heart.  Rather than being powered by a continuous supply of power (which would ordinarily be the case) our DC fan motor is being fed with pulses of power; it is essentially being switched on and off very rapidly.  These on-off pulses are delivered to the motor several thousand times per second, and because the intensity (or width) of each pulse can be changed, so the speed at which the motor turns can be changed.  The image below shows how different pulse widths affect the resulting power of the PWM signal:

Three different PWM signals showing average voltage

PWM Controllers vs. PWM Fans

There are PWM controllers and there are PWM fans, but the way in which PWM is implemented in each differs greatly:  a standard PWM controller modulates the 12 V supply line of an “ordinary” 12 VDC motor. Conversely a PWM controller for PWM fans – such as the one featured in this article – doesn’t modulate the 12V supply line but instead sends a PWM signal along a different supply line (the magic “fourth wire”) to a more advanced 12 VDC motor, leaving the 12 V supply line uninterrupted.  Designated PWM fans not only have internal circuitry which differs from that of standard fans, but because they are designed with speed control in mind the motors themselves are usually more advanced (and expensive).  So, PWM speed control of a standard fan is indeed very different from PWM speed control of a PWM fan…  Nidec even goes so far as to say that modulating the main supply voltage is not advisable:

Pulse-width modulation of DC operating voltage to modify fan speed is not recommended. Transients generated by that approach can irreversibly damage motor commutation and control electronics and dramatically shorten the life of a fan.

The Circuit

Here is the circuit which was originally obtained from Nidec’s website, although I found it in the overclockers forum:

Nidec's Simple PWM Circuit

Nidec's Simple PWM Circuit

Components

  • 555 Timer IC (Integrated Circuit)
  • Capacitors:  C1 0.01 μF; C2 680 pF; C3 10 μF; C4 0.1 μF
  • Resistors:  R1 1k
  • Potentiometers:  P1 100k
  • Diodes: D1 & D2 1N4148

Building the Circuit

Now before you allow yourself to become intimidated by the above schematic and all these different components, make sure you are taking a calculated approach to the process of putting the circuit together.  The best thing to do is to take it one step at a time. Having done it myself (several times),  these are the steps that I find most conducive to hassle-free workflow:

  1. Plan your circuit on a piece of paper, familiarizing yourself with each component (learn what it looks like and what it does) and the layout of the circuit, and taking time to arrange it in such a way that it is clean and clear.
  2. Working from your plan, carefully assemble the circuit on a breadboard.
  3. Check and re-check all the connections.
  4. Connect the circuit to a power source – preferably a spare power supply that is not hooked up to a PC – and check to see if it works.
  5. Debug (identify problems and deal with them) if necessary.
  6. Again referring to your circuit plan, assemble the circuit on stripboard.
  7. Work on the presentation of your controller – eg., put it in a project box or into a drive bay.

Step 1:  Organize Your Components and Print a Plan of the Circuit

These are all of the components you need for the circuit

These are all of the components you need for the circuit

So, now you know what each component looks like.  Once you have your components arranged spaciously on an uncluttered flat surface (as above), get your breadboard ready!

Step 2:  Breadboarding

Components set out ready for breadboarding

Components set out ready for breadboarding

The wonderful thing about breadboarding is that it doesn’t have to be neat or tidy…or even compact.  The point of breadboarding a circuit is to give you, the “beta tester”, easy access to each and every component and connection, allowing you to quickly sort out problems and get your circuit up and running without having to worry about making permanent connections.  Here are a few simple pointers:

  • Take your time and keep your work area uncluttered.
  • Make sure your hands and fingers are clean before you start.
  • Use single-core wire for good connections to the breadboard tracks.
  • Leave some room around each connection/component to reduce the risk of shorting.
  • Remember to firmly press (but not force) the components and wires into place.

Step 3:  Check and Re-check the Connections

Carefully check that all terminals and pins are seated correctly

The reason this step is so important is that you are checking the connections solely with the power of observation; the breadboard should not be connected to a power source yet, and it is crucial that you carefully check each connection before the circuit gets anywhere near live wires.

Step 4:  Connect the Circuit to a Power Source and Test with a Fan

Breadboarding done and testing in progress!

Breadboarding done and testing in progress!

Connecting the breadboard to a live power source is, and always should be, the last thing you do (especially if you are a n00b, like me).  It is also advisable to use a spare/unconnected power supply, because if you happen to be so unfortunate as to cause a short circuit using the PSU that is connected to your computer, it may seriously damage the PSU and/or one of your PC components.  I can attest to this – my first attempt at a fan controller some weeks ago fried my treasured £300 Foxconn motherboard.  The PSU is fine (and has survived at least three further short circuits), however my experience tells me that even a good PSU like mine which has commendable SCP (short circuit protection) doesn’t guarantee the well-being of your components.  You have been warned!

And remember:  This circuit uses 5v, NOT 12v.

Step 5:  Debugging

Digital Multimeter - a must for testing circuits and components

Digital Multimeter - a must for testing circuits and components

Circuits generally don’t work the first time around, so be patient and acknowledge that you will probably have to do some debugging somewhere along the line.  It’s not a big deal, and although it may involve a fair bit of work, don’t worry about it – I had to debug my circuit (and in some ways I am still debugging it), and I had the overclockers.com forum community helping me every step of the way as I’m sure they will help anybody else who seeks assistance.  To make your life is a lot easier, get a digital multimeter if you don’t already have one.

Step 6:  Stripboard, Solder, and Sweat

My stripboard layout, created in MS Paint

My stripboard layout, created in MS Paint

When the time comes to make a proper circuit using scary grown-up tools like a soldering iron and a pair of wire cutters, it is definitely worth your while planning the layout of your circuit once again and trying to make it as compact as you can.  If you have space on your stripboard you might want to consider soldering a 4-pin fan header onto it to keep the controller tidy and practical.

The layout that I chose (above) is almost identical to the schematic of the circuit, which helped a great deal when the time came to put the circuit together and make sure all connections were made in the right place.  Stripboard has copper tracks that run along the underside of the board, so you must plan your circuit to accommodate these tracks and remember to break the tracks where necessary.  Here is a picture of the underside of my stripboard where the 555 IC is, hence the broken tracks:

Breaking tracks in the stripboard

Breaking tracks in the stripboard

Here is a picture of what is possible if components are extremely well laid out – this particular circuit was built by Martinm210 at overclockers.com forums and features a slightly different PWM generator using a 556 IC (two 555’s in one package) – see below for a schematic of this circuit:

Martinm210's PWM generator

Martinm210's PWM generator

Step 7:  Presentation

This is the icing on the cake.  You have finished your controller, but you don’t like the bedraggled morass of wires and terminals sitting beside your uber-modded and meticulously maintained gaming rig… so what should you do?  There are a number of answers, and it really comes down to what you want to use the controller for.  I use my controller for testing (well, playing with) very powerful PWM fans, so I packed it up inside a neat little project box to make it look a little more sophisticated and to make it more practical too:

The finished PWM controller

The prototype PWM controller

Project in a project box

Project in a project box

Developing the Circuit

As it is, the circuit should work well with most if not all PWM fans that you are likely to find in a hardware enthusiast’s box of tricks.  If, however, like me (and a few others) you want to engage in some turbulent tomfoolery with ludicrously powerful 12VDC fans (see below), you will need to boost the PWM signal or create a different PWM generator altogether which uses a 556 timer instead of a 555.  The circuits described below are featured in this exciting thread at overclockers.com forums.

Using Two 555 Timers

Here is a schematic of the dual-555 PWM generator.  This circuit boosts the existing PWM signal using an “inverted schmidt buffer” which was suggested by bing at overclockers.com forums:

A more powerful PWM generator

A more powerful PWM generator

Using the 556 Dual Timer

The 556 timer is a single 14-pin package which contains two 555s.  If you would rather build the more powerful 556-based PWM generator like the ones Martinm210 and Brutal-Force put together, here is the schematic (again, courtesy of bing):

556 Dual Timer circuit

556 Dual Timer circuit

(Components are identical to the 555 circuit but are labeled differently in this schematic:  C1 = 680pF; C2 = 0.01 μF; C3 = 0.1 μF; C4 = 10 μF, polarized.  There is also an extra resistor (R2) which has a value of 10K.)

The 556 Circuit on the breadboard

My 556 Circuit @ breadboard

Complete 556 circuit on a stamp-sized piece of stripboard

Complete 556 circuit on a stamp-sized piece of stripboard

Simple 4-pin Molex interface for the PWM controller

The box for the 556 circuit, complete with stylish aluminum pot and Molex connector for convenience

Two 4-pin fan headers for now

The business end of the controller - for me, two fan headers are plenty

Monstrous 260CFM 48W San Ace PWM Fan

Monstrous 260CFM 48W San Ace PWM fans

Final Thoughts and Video

First and foremost, make sure you take your time if you decide to build this (or any other) circuit for use with your system – working with electricity is hazardous (and if not for you, certainly for your hardware!) so be careful.  I’ve shorted my PC (yes, my entire system) no fewer than FOUR TIMES since I started messing around with DIY fan controllers, and unfortunately one of these shorts fried my prized Foxconn X58 motherboard.  Suffice to say, I have been more cautious since.

On the plus side, these fan controllers are a lot of fun and can be very useful if you regularly benchmark your system and require powerful cooling at the touch of a button (as I do).  Here’s a short video which shows the capabilities of the 556 circuit when paired with some seriously powerful 120mm fans…

Thanks

Primarily I’d like to thank I.M.O.G. for playing such an important role in my PWM fan projects (he organized the purchase and international shipping of the San Ace fans for me – top dude!) and for giving me the opportunity to write this article.  I’d also like to thank Brutal-Force for his videos and his thread which inspired me to make a PWM fan controller in the first instance, and resident electronics expert, bing, who freely shared his electronic expertise and offered valuable assistance throughout the learning process.

– Dave (LennyRhys)

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Discussion
  1. Sorry to resurrect this but does anyone know how I can go about building a PWM fan controller that adjusts the duty cycle based off of a thermistor? There would need to be a way of adjusting. I would want it to be as basic as possible as long is it achieved the ability to what resistance meant the lowest PWM signal and what meant the highest and that the controller had some sort of linear increase in duty cycle as the temperature went up.

    For example I would like the lowest duty cycle at 30C and the highest at 45C

    If anyone could answer this it would be great. I have a Corsair Link Mini and had the original and neither have ever worked properly at all. The Mini will not function when you assign an external temperature probe to the fan. Only software based temps for things like CPU, VGA, HD, MOBO etc. As soon as you set it to run the fan curve off an external probe it just goes to stays at one setting even though the software shows the probes are working and reporting accurate temperatures.

    Thanks guys
    WhitehawkEQ
    If your not going to use the PWM signal, then you realy don't need the 555 circuit, you can leave the PWM line not connected and the fan will run full speed.


    This was a stupid question actually. 100% speed PWM signal is simply continuous ('a flatliner') so there's no difference between such state and e.g. the PWM cable cut out and PWM 555 module ripped out from the board. :) Anyway, I think having ON/OFF switches for every single fan is very useful.

    In the light of this I guess the answer to the question #2 is: "cut the 5V supply to the 555 PWM control circuit".
    NiHaoMike
    PC fans are not classical DC motors. They're actually synchronous AC motors with integrated inverters. Some of those inverters accept a logic level PWM signal for speed control.


    That still doesn't answer the question. The output of the transistor will be logic level, so long as the voltage input to the transistor is 5v (or whatever the logic voltage is at). I was curious about this as well. The circuit in the original link is rather odd and I've never seen one like it before. Usually the pot controls the RC timing circuit of the 555 and the output is sent through a transistor. This has the pot on the output. A very odd circuit.
    Bucic
    Two more questions.

    1. If a fan is going to operate at full speed, does it make sense to feed it with PWM signal at all?

    2. Regardless of the above. If I'd like to disable the PWM signal, can I simply cut the 5V supply to the 555 PWM control circuit or is cutting off the PWM signal wire off using a switch the only option?


    If your not going to use the PWM signal, then you realy don't need the 555 circuit, you can leave the PWM line not connected and the fan will run full speed.
    Two more questions.

    1. If a fan is going to operate at full speed, does it make sense to feed it with PWM signal at all?

    2. Regardless of the above. If I'd like to disable the PWM signal, can I simply cut the 5V supply to the 555 PWM control circuit or is cutting off the PWM signal wire off using a switch the only option?
    Bucic
    Thank you. But what about those controllers with transistors that are intended for PC fans? The proponents are actually not that savvy?


    Some older PC type fans are designed to be PWMed just like an actual DC motor. Or voltage modulated with a buck converter. Nowadays, logic level PWM is the recommended way as it gives the best control.

    BTW, while standard PC fans with PWM are designed for about 25kHz noninverted, that's not the case for some fans designed for other applications like A/C indoor units. I have a 120mm Delta that was intended for a small Daikin mini split unit and not only is the PWM signal inverted, it works erratically at 25kHz PWM frequency. I don't have the indoor unit it is intended for but some experimentation with the 555 circuit gave pretty good control at about 1kHz. (In summary, if you have a fan that works erratically with the 555 controller, try lowering the frequency.)
    NiHaoMike
    PC fans are not classical DC motors. They're actually synchronous AC motors with integrated inverters. Some of those inverters accept a logic level PWM signal for speed control.


    Thank you. This (with some explication by Wikipedia) finally explains our fans.
    NiHaoMike
    PC fans are not classical DC motors. They're actually synchronous AC motors with integrated inverters. Some of those inverters accept a logic level PWM signal for speed control.


    Thank you. But what about those controllers with transistors that are intended for PC fans? The proponents are actually not that savvy?
    PC fans are not classical DC motors. They're actually synchronous AC motors with integrated inverters. Some of those inverters accept a logic level PWM signal for speed control.
    Can anyone please explain why most of 555-based PWM controllers use transistors but the one linked in the article in the OP doesn't?

    See for example http://www.555-timer-circuits.com/motor-pwm.html
    Bucic
    I've just finished re-creating the controller in Fritzing. Change the file extension from 7z to fzz. This is not an archive. Then I'm going to also use Fritzing to create my multi-fan controller by cloning as many of the 555 PWM controllers as needed alongside headers regulated using regular potentiometers only for 3-pin non-PWM fans.

    Fritzing also exports bill of materials etc.

    PS. There are no mobo fan headers etc. in the Fritzing library so I've used whatever similar components there were. I couldn't even find single terminals. Also, this is my first elec project so expect everything.


    C1 is .01uf or 10nf not 10pf.
    I've just finished re-creating the controller in Fritzing. Change the file extension from 7z to fzz. This is not an archive. Then I'm going to also use Fritzing to create my multi-fan controller by cloning as many of the 555 PWM controllers as needed alongside headers regulated using regular potentiometers only for 3-pin non-PWM fans.

    Fritzing also exports bill of materials etc.

    NOTE 1: There are no mobo fan headers etc. in the Fritzing library so I've used whatever similar components there were. I couldn't even find single terminals. Also, this is my first elec project so expect everything.

    NOTE 2: I have only edited the basic parameters of the components used. For example with a capacitor I only edited its capacitance without altering its maximum voltage, current or anything else.
    This circuit seems to be quite good and can provide great accuracy of timing. Thanks for publishing it.

    Do you only need the application of the two diodes because of the easier timing, or do they also enhance the stability of the a-stable circuit?

    Best regards,

    chey
    After checking out several DIY PWM controllers on the internet I have finally found this one. About time because it started to get ridiculous. Every second of such projects had fundamental errors pointed out in comments, other projects made by guys who don't impress me as someone who knows what he's doing. So, thank you for the article and thanks to those who helped you!

    Seebs
    One million Watts... :)

    Now; for the serious answer.

    The PWM controllers that this article refers to don't actually power the fans. The fans are powered straight from the PSU (12V) all the time and the controller simply sends ON/OFF signals to a circuit on the fan that switches power ON/OFF very fast (the standard is 25KHz, but some fans work on other frequencies).

    So since the fans are not being powered from the controller; the answer to your question is that you can run whatever fans you want (no watts limitation); provided your PSU can power them.


    I was also under the impression you need the 556 variant for 12V fans. It would be great if the article was supplemented with the information, highlighted.

    Speaking of which. Could anyone please try to explain what specific fan configuration would require the 556 variant and why?

    Even though I'm a electrion00b I plan to build a controller based on this one (555) with the following minimum features:

    - 4 fans in total, two of which controlled in pair (common control signal)

    - on/off switches (not integrated in potentiometers)

    - optional: full RPM startup capacitors

    - optional: 'fan not operating' leds

    - optionsl: integrate the PWM controller with a standard potentiometer-only controller for 3-wire fans sporting the same features as listed above

    Few basic questions:

    1. You've mentioned short circuits during your work. Why didn't you use a circuit breaker?

    2. How many fans can be connected to the common control line with the 555 controller?

    3. Does anyone have schematics for any variant of the controller for 2 fans controlled separately?
    NiHaoMike
    Some variable speed ("PWM") fans do interpret 10% and below as a command to turn off. There are also some that will just go full speed if it gets 0% or very close to it, as a safeguard against the the line becoming shorted to ground. It all depends on what the OEM programmed into the inverter.


    If they turn off they do not follow the specification. All PWM controlled stuff should go to 100% if PWM signal gets too low or is missing eetirely..

    Some have a lower limit at like 30 %, and can't be tweaked lower, while others have a "soft" limit at 30 % (like my new noctua industrial fan), but can actual be turned down much farther with some controllers.

    (I might remember the above slightly wrong, but it is about right)
    Some variable speed ("PWM") fans do interpret 10% and below as a command to turn off. There are also some that will just go full speed if it gets 0% or very close to it, as a safeguard against the the line becoming shorted to ground. It all depends on what the OEM programmed into the inverter.
    hyperplane
    Ok that sounds right.

    For the record I have a NOCTUA NF-B9 PWM fan and when I turn down to 0% it stops spinning. I don't actually know if it goes to max speed when turned to 100% but anyway my goal was to set it to "the maximum speed that makes no noise". Moreover it turns out that that speed is enough to keep the attached heat-sink at a low temperature.


    that looks strange to me.

    take a look at this:

    http://www.noctua.at/main.php?show=productview&products_id=44&lng=en&set=1

    given the worst -20%, the fan should spins at ~240 rpm @0% (slow but it should be keep spinning).

    you might want to recheck your controller, or a least add another 555 as shown on the "mega thread"; sorry for the no-link, since I've lost all of my bookmarks.

    but if you already happy with it, you can use it anyway :thup: