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
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:
- 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.
- Working from your plan, carefully assemble the circuit on a breadboard.
- Check and re-check all the connections.
- 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.
- Debug (identify problems and deal with them) if necessary.
- Again referring to your circuit plan, assemble the circuit on stripboard.
- 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
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
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!
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
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
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
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
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 prototype PWM controller |
 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
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
(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.)
 My 556 Circuit @ breadboard |
 Complete 556 circuit on a stamp-sized piece of stripboard |
 The box for the 556 circuit, complete with stylish aluminum pot and Molex connector for convenience |
 The business end of the controller - for me, two fan headers are plenty |
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)
Tags: air, Controller, Cooling, DIY, fan, PWM
01-17-11 12:07 PM
01-17-11 12:52 PM
Love the intro, and those illustrations too, thanks.
01-17-11 01:42 PM
01-17-11 02:51 PM
Thanks for writing this up.
01-17-11 03:16 PM
01-17-11 04:15 PM
01-17-11 04:45 PM
01-17-11 06:20 PM
01-17-11 11:54 PM
01-18-11 04:05 AM
01-18-11 04:22 AM
01-18-11 04:52 AM
Those fans are insane... i need a few to build a hovercraft with!
01-18-11 07:14 AM
Brings back great memories of when men were men, and we had to make our own controllers or do the 5V/7V tricks. (Back before Zalman and everybody else flooded the market with pre-made controllers.
Very nice design. Best -- Paul
01-18-11 09:30 AM
Paul - thanks, and it's nice to see somebody else putting Dundee on the map!!
01-19-11 08:50 AM
01-19-11 09:13 AM
Two configurations to think about:
(1) rheostat + thermistor in series: net resistance is additive
(2) rheostat + thermistor in parallel: net resistance is R1 * R2 / (R1 + R2)
Option (1) involves soldering your thermistor after or before P1.
Option (2) would be a matter of soldering the thermistor in parallel with potentiometer / rheostat R1.
There are pros and cons to both to think about. -- Paul
01-19-11 10:13 AM
The problem (you will find out if you read my whole thread) is with the stepping of those PWM circuits. This is where this controller comes in. In all honesty, you really only need about 3 or 4 speeds for this fan. Low/Med/High would work in almost all cases, except that different fans at this speed exhibit noises that can only be eliminated if you turn them up or down ~50 RPMs. In essence your are tuning them. It would be too much work to try to tune a 3 speed controller.
I run my fan daily at about 900 RPMs. I turn it up to about 2000 while gaming and then I turn it to 6000 while benching. All of these are +/- 50-100 rpms. You just can't do that with switches. Well actually, you could... on a non PWM, but then you would deal with Undervolting which would also produce annoying noises.
I could have built a thermistor into this circuit, but PWM really was probably overkill for most computer users, and a thermistor controlled PWM would be definitely overkill. Essentially a thermistor is just a variable potentiomter, just like the 10 or 100k Poti used in this circuit. So one would just replace the Poti with the thermistor.... Problem solved. You just have to tune it/
01-20-11 04:32 PM
This is interesting since as original circuit without the booster (inv sch buffer) couldn't drive even one as Brutal experience.
01-21-11 08:32 AM
I think I'll buy a cheap PSU specifically for testing the fans - don't want to short my system again!!
01-21-11 09:02 AM
But again, just take your time, no hurry, thanks in advance.
04-25-11 09:44 PM
The only issue is that the parts you suggested come up with many hits in digikey and I'm not sure which to get.
Can anyone provide digikey part numbers for the components?
Also, since this fan controller is for a fan that will not be in my computer, I wanted to make it temperature regulated. As for setting a thermistor in series or parallel, does anyone have a circuit diagram for that? Which thermistor and potentiometer set would work for that?
04-26-11 12:17 AM
04-26-11 10:33 AM
I google search for "diy pwm fan controller", and I always got this thread on the 1st page
04-16-12 09:06 AM
i just recently bought 6x Coolermaster xtraflo 120mm pwm fans for a 360 radiator (wanting to do a push pull setup)
my problem is i need to make a 4 pin pwm fan controller, do i need to use a 5v or 12v controller.
i have an existing Cooler Master Aerogate II Fan Controller is there a way to modify this to be compatiable with the 6 pwm fans .
i like this unit as it has the temps and rpm displayed.
if anyone could help this would be appreciated.
regards
zerocoolzmax
04-16-12 03:51 PM
Unless you're relatively good with electronics and quite handy with a soldering iron; modding that controller to send PWM out will be kind of hard. You do have an option though... The fans you bought; though PWM, can still be connected/controlled by that Aerogate II. The controller has 4 channels rated for 18W each; the fans take a max of 8.4W so you could connect two fans per channel and control them via voltage adjustment like normal fans and not lose any functionality on the controller.
12-07-12 08:33 PM
12-10-12 05:10 PM
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.