Two dollar variable fan controller

Well – given current exchange rate, AU 2.59 = USD 2.33.. So it’s not quite a two dollar product, but pretty close. And “2.33 dollar fan controller” did not make for a nice subject line…

After the earlier post about variable 12V fan controllers, it might be worth looking at what is available on Ebay. Turns out you can get a variable controller delivered anywhere in the world for USD 2.33 – pretty amazing! It looks deceivingly like the Zalman Fan Mate 2 too:

Zalman Fan Mate 2 (left, USD 7) and eBay ditto (right, USD 2.3)
Zalman Fan Mate 2 (left, USD 7) and eBay ditto (right, USD 2.3)

The eBay controller only has one 3-pin male connector (where the fan connects), and then a soldered in wire with a 3-pin female connector, for attaching to the PC or other equipment.

The Zalman on the other hand has a 6-pin male connector on one end, a special Y-cable (it comes with the Fan Mate 2) is then needed to hook up the controller to fan and PC. Both variants of course work, the Zalman approach is maybe slightly better, as it allows the controller to be mounted closer to an inside corner, without the cables being in the way. Not a major difference though.

Looking inside the eBay controller, it is obviously different from the Zalman. For starters, it has a NEC B772 P PNP medium effect transistor in there, rather than a voltage regulator. I could not find a datasheet for that particular NEC device, but I am pretty sure it is more or less identical to ST’s 2SB772.

There is also a TL431 adjustable voltage regulator in there, together with a second SOT23 transistor market J6, it might be a S9014 NPN transistor (or equivalent).

So, in essence the eBay controller is also a linear regulator, but based off an adjustable regulator (rather than the fixed-voltage 7805 that the Zalman uses), with an extra power transistor to boost current. The extra transistor is needed, as the TL431 can only sink 100 mA on its own.

All good so far. But when reverse engineering the eBay controller, the schematic just doesn’t add up. Below is what the eBay controller looks like, with the above assumptions on components – and this is not a working circuit, as far as I can tell (or is it? Feel free to add your expertise in the comments!).

eBay variable fan controller - except that the circuit is a bit weird.. Need to re-check those PCB traces!
eBay variable fan controller – except that the circuit is a bit weird.. Need to re-check those PCB traces!

So…. either I made incorrect assumptions regarding what SMD components are used in the eBay controller, or I just didn’t check closely enough how the PCB traces were connected. Time to bring out the multimeter to check those traces – more to come on this topic.

Fritzing vs circuits.io vs Eagle – comparing schematics editors

During the recent work on the one dollar variable fan controller, I looked into options for documenting the work.

I have never really used CadSoft Eagle enough to get comfortable with it, and whenever I used it it seemed to be overkill for what I wanted to do. Still, it is usually still seen as the best software for this kind of work.

But maybe there are other options.. In particular I thought the more basic editors sounded promising – let’s give them a try. Disclaimer: Nothing near a full review was made of the different services. The verdicts below are instead based on 15-20 minutes use of each service, and no reading of any manuals or help pages.

Circuits.io

This would be the new kid on the block. Mix schematic editor with GitHub and you get something like Circuits.io. You can follow circuits created by other people, fork your own variants of other people’s circuits etc. Very nice concept, but it also seemed to have a lot of limitations..

circuits.io one dollar fancontroller
Circuits.io used to create a one dollar variable fan controller

For example, I failed mirroring the 7805 in the circuit to the right. Having the output to the left feels very awkward.. I am sure there are ways around it, but even though I really searched for it, I also failed to find a traditional 7805 symbol such as the one in the second image, and was left with the one used in the top schematic. Fail.

Traditional 7805 symbol
Traditional 7805 symbol

There for sure are nice things about circuits.io though. Having an entirely browser based editor is a very nice concept. It might be too early days for it now, but good things come to those who wait… I also liked the feature where you, given a PCB board design, can get files for 3D printing or milling a custom case for your board. Nice!

The fan controller project can be found at http://www.circuits.io/circuits/4841. Go fork it!

Fritzing

This is also a pretty new project, with a lot of promise. It is obviously geared towards hobbyists that might not have a ton of experience in electronics design, but it is still kind of nice.

One dollar variable fan controller, using Fritzing
One dollar variable fan controller, using Fritzing

With a slogan of “from prototype to product” it is clear that the Fritzing team is trying to cover it all. Not sure I would want to go this route with a full project though – I always get suspicious about software that offer a link to some third party service (in this case for manufacturing of PCBs). It probably works perfectly fine – I just feel left without the control I want to have.

Breadboard view in Fritzing
Breadboard view in Fritzing

The schematics editor is nice (better than circuits.io), and I even like the slightly silly feature where you can get a breadboard view of the circuit. Probably not a bit useful for an experienced electronics hacker, but still kind of cute.

The fan controller project can be found at http://fritzing.org/projects/one-dollar-variable-fan-regulator

Eagle

CadSoft Eagle is a professional schematics editor and PCB layout tool. The free version does have some limitations (PCB size and # layers, among others), but they are pretty generous and won’t cause any problems for most hobbyist projects.

The UI feels a bit dated, to be honest. But also quite efficient, given the vast number of components available. Seems lots of people also create their own Eagle libraries with various components, so there is a good chance you can find, download, install and use existing libraries. Otherwise it’s not too hard to create your own, half an hour of fiddling around with libraries left me with a working one. Nice!

Of the three tools Eagle is by far the best, even when considering the somewhat steep learning curve. Give it an hour and you will be able to create fairly complex circuits. PCB layout is still a bit of an art, no matter what product you use – you just have to learn as you go along, and from mistakes. Eagle does have some nice tools for eliminating the most obvious errors though – once again, nice.

All in all, going forward Eagle will (still) be the preferred solution around here.

One dollar variable fan controller

2013-08-09_22-06-40_copyWhile trying out various computer and network gear, I quite often find the fans too loud. They are of course there for a good reason, but experience tells that the device usually works just fine with less cooling. Best case one or more fans can be removed altogether, even though that is typically not recommended. They are of course put there for a good reason..

Anyway, I have repeatedly found myself looking for an easy solution to control the speed of regular 12V fans. Something that is just plug-and-play. Ideally also cheap or even free.

Going through a 7805 data sheet for other reasons, I suddenly realised that a 7805 set up in variable voltage configuration (figure 4 in the data sheet) should work great as a fan controller. These 12V fans usually run just fine down to 5-6 volts, but at lower rpms, and thus quieter. Just what was needed!

The circuit is quite basic:

7805 based variable fan controller
7805 based variable fan controller

The circuit is pretty clever – by shifting the ground to a higher level than the common ground/0V level, we get the voltage regulator to output between ca 6V and 10.5V. The component values were ones I had in my junk box, making a point of only using scavenged parts (don’t forget a heat sink for the 7805!) plus a little piece of strip board, the cost for me was actually zero. Nice!

A possible drawback of the design is the fact that a linear regulator like the 7805 will get rid of all (well… most anyway) excess energy as heat. A proper heat sink is thus definitely needed. An option would be to use some kind of low drop-out voltage controller (to get the upper limit closer to 12V), but it would have the same issue with heat dissipation. A better/easiesr option is probably to use one of the many PWM fan controller ICs available (here is Maxim’s list, there are plenty others too), it deals with at least some of the heat waste issues. You might be able to get some free samples too if you just want to play around with them. Most of them are not too expensive though.

All working well thus, and the story could have ended there.. However, a week or two later i was pulling apart an old PC when I found a couple of Zalman Fanmate 2 controllers… Too much of a coincidence not to see what made them tick.

Zalman Fan Mate 2, variable fan controller
Zalman Fan Mate 2, variable fan controller

After pulling one apart it turns out it is using exactly the same circuit as above! They did go a bit cheap and skipped the smoothing caps though, seems to work fine anyway – the fans won’t care much about some noise on their power line.

Also, the heat sink seems quite small and the controller is only specced to 6W, which is half of what the 7805 should be able to handle (it can handle 1A, so 1A*12V = 12W max power, with a proper heat sink).

Interestingly enough the Zalman controller costs ca USD 7 – not a huge amount of money, but one dollar to buy the components of your own (or even zero!) is a lot better..

Some additional shots of the Zalman controller: