DIY Fan Controller for PWM Fans

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. inVain
    project "redemption" :salute:

    this is my 3rd attempt with extensive smd components.

    all my previous ones were FUBAR :chair:

    so, wish me luck guys :D


    Is that for 3 wire fans or 4 wire?
    project "redemption" :salute:

    this is my 3rd attempt with extensive smd components.

    all my previous ones were FUBAR :chair:

    so, wish me luck guys :D
    Bobnova
    Yeah, there are options. It looks like pin7 feeds into the collector of an NPN transistor, so leaving it floating shouldn't cause issues.


    That transistor is the discharge transistor, may want to connect it anyway.
    Bobnova
    Hmm, totally missed that. Looking at the 555 schematic it should still work. I'll have to breadboard it to make sure.


    If it don't work, after you solder the IC, you could use a piece of 30 gauge wire and connect pin 7 to the GND side of C2.
    Bobnova
    That's one of the great mysteries of life.

    I was wondering about that too, I have no idea. I think I must have plopped two through hole resistors down and then the pot, then realized I only needed one resistor.


    I also noticed that pin 7 is not connected to gnd that I can see, will it work with out that pin connected to gnd?
    That's one of the great mysteries of life.

    I was wondering about that too, I have no idea. I think I must have plopped two through hole resistors down and then the pot, then realized I only needed one resistor.
    Bobnova
    As soon as the parts get here, these will be in the classies as kits for learning SMD and building a fan controller!

    Definitely will still be cheaper to build your own, as you don't have to pay for my time packing things up, collecting parts, part shipping to me, etc.

    The kits should be pretty cheap though.

    Let this, and Whitehawk's boards, be an inspiration to people who want to make their own boards! I haven't had any formal training in this at all, you can learn it too :D

    The trick to 0805 soldering is, get good tweezers.

    Then you put solder on one pad, let it cool, get the part lined up with its pads but slid over enough that it is resting flat on the surface of the PCB, not on the little solder mound. Hold it with the tweezers, melt the solder and slide the part into it. Let the solder cool, then solder the other end.

    That goes for SMD chips, too. Do it with one pin, get the other pads aligned before you solder more than one pin, then you're home free.


    umm where is R2? :rofl:
    As soon as the parts get here, these will be in the classies as kits for learning SMD and building a fan controller!

    Definitely will still be cheaper to build your own, as you don't have to pay for my time packing things up, collecting parts, part shipping to me, etc.

    The kits should be pretty cheap though.

    Let this, and Whitehawk's boards, be an inspiration to people who want to make their own boards! I haven't had any formal training in this at all, you can learn it too :D

    The trick to 0805 soldering is, get good tweezers.

    Then you put solder on one pad, let it cool, get the part lined up with its pads but slid over enough that it is resting flat on the surface of the PCB, not on the little solder mound. Hold it with the tweezers, melt the solder and slide the part into it. Let the solder cool, then solder the other end.

    That goes for SMD chips, too. Do it with one pin, get the other pads aligned before you solder more than one pin, then you're home free.
    NiHaoMike
    Maybe design the board to be able to use either through hole or SMD? I sometimes see that approach on production hardware and whether they use SMD or through hole depends on component availability.


    Yep, great for manufacturing, but a pain from a design stand point, you have to find room for all the through and SMT parts in a small board.
    Maybe design the board to be able to use either through hole or SMD? I sometimes see that approach on production hardware and whether they use SMD or through hole depends on component availability.
    Yeah those are the ones.

    Forget the floor, if you drop them on a wood table you probably won't ever find them. You need a solid color very flat surface to find the damn things.

    I've stopped using them except when I have to, moved up to the much nicer 0603 and 0805 sizes :D

    0402 is a lovely size for 0.1µF decoupling caps though, you can plop 'em between 0.1" power/gnd pins and they have essentially zero trace length!
    Bobnova
    I thought about putting those on the 555 thing, but they're so big I could have done through-hole at that point :D

    I Did It Wrong and started with 0402. Those things are a pain.


    :rofl::rofl::rofl: There are some parts so small, if you drop them on the floor, don't bother looking for them :). Capacitor & Resistor sizes
    Bobnova
    I thought about putting those on the 555 thing, but they're so big I could have done through-hole at that point :D

    I Did It Wrong and started with 0402. Those things are a pain.


    :rofl::rofl::rofl: There are some parts so small, if you drop it on the floor, don't bother looking for it :)
    I thought about putting those on the 555 thing, but they're so big I could have done through-hole at that point :D

    I Did It Wrong and started with 0402. Those things are a pain.
    Bobnova
    Gotta learn SMD somehow. SOIC-8 and 0805 are good learning bits.

    I made mine SMD for just that reason, I'm going to see if I can sell a couple as "Learn SMD and build something useful" kits.

    They're also useful in that they can be run at 12V for switching MOSFETs if you don't want to control fans.


    Use 1206 to start with, 805 is small :) then as you get experience, you can go smaller.