CK II PWM Fanbus – Hardware

When speaking of fan control, there are generally 2 ways of doing it, linear control, and pulse-width control. The linear control is the most common. The idea is to decrease the voltage to the fan. If the fan is specified to 12 volts, in most cases you can lower the voltage to 6-7 volts. But if you want to go lower, the result is often that your fans won’t even start.
Another issue is step less regulation. This requires a variable resistor (rheostat) or a control circuit, using transistors. If you want to run a fan at 7 volts, the remaining 5 volts will have to be burned of as heat in the control circuit or rheostat.

Pulse width control, or commonly referred to as PWM (Pulse Width Modulation), is a great alternative to the linear control.
The linear control supplies the fan with a constant voltage. But the PWM control generates rapid 12 volt pulses, and the “on” and “off” timing determines the overall speed of the fans.

Here’s the linear control illustrated:

The voltage is, as we can see, constant at approx. 6 volts.

This is a PWM controlled output at 6 volts:

The voltage rises to 12 volts, but only for 50% of the period. In the remaining 50%, the voltage is 0, and this causes the fan to run at 6 volts.

The real assets of PWM is:
- Low power loss in the control circuit. Almost no heat is dissipated.
- You get the option of decreasing the voltage to a very low value, often 15-20%.

The major con about PWM control, is that the RPM signal telling the fan speed, is useless.
But if you can live with that, PWM is far superior to linear control.

The hardware part

Until now, the construction of a PWM circuit has been pretty tricky. It requires an advanced circuit to control the different time constants. But with CKControl II, all timing signals are controlled via the software, allowing us to utilize the PC parallel port as 8 individual, fully controllable PWM outputs.
The only thing needed is an amplification of the signals, as the data pins isn’t capable of driving just one single fan.

You can use the outputs for not only fans, but all kinds of things – including Lazer LED’s, Cold Cathode lights – as long as the maximum current output doesn’t exceed 0,8 A for each channel. You could even add a relay and make the software turn your coffee machine on and off!

How many fans can we add to the circuit, then? That depends on the fans used. The electronic components used are specified to 1 Ampere per channel. With that in mind, we should stay below 0,8 Ampere, or approx. 10 Watt per channel. A standard 80mm fan typically uses 0,14 – 0,18 mA (1 mA = 1/1000 Ampere). That makes 5 fans per channel – a total of 40 fans for all 8 channels. But that’s a rather theoretical value; as 40 fans would demand a heavy duty power supply, as well as thick wires and PCB tracks. In addition, considerably few of us uses 40 fans in our desktop computers..

In general, a fan’s current is proportional to it’s size. But in order to determine a fans current value, read the printed label on the fan.
You can’t use this circuit to control your CPU or GPU cooler. To increase stability, the fans won’t start running until Windows is loaded and CKControl II is initialised.
We’ve included the opportunity to set some or all outputs high via a switch, if required – even if CKII isn’t started.

The construction should be made on a printed circuit board, PCB. That gives us multiple choices:

1) A so-called Vero board uses horizontal copper tracks, tied together. This makes you able to build smaller constructions, fairly easy, but it takes a certain amount of patience, and is only suitable if you are an experienced hobby-electronics builder.

2) By means of a PCB-pen, it is possible to literally draw insulating tracks on raw copper-plates, and then etch the remaining naked copper away. It’s an easy way of creating PCB’s, but even with a steady hand, the overall outcome may not look so nice. It also takes some technique and experience to draw a circuit like this by hand.

3) Another method called photo print, gives you industry like quality. It is done by exposing a photosensitive copperplate to UV-light, masking the layout with a transparent paper copy, and then applying developing fluids and finally etching. It’s quite expensive, but also gives you the finest results.

The drawback of method 2 and 3 is that you have to drill the PCB holes yourself.

4) For this project, we have constructed a PCB with the holes already drilled. The PCB is designed to be mounted on the backside of a 5,25” front bezel. The PCB can be bought from us, and is an easy solution if you’re not into etching and drawing yourself. See the contact info on the last page.

Our PCB layout:

In the following guide, we have used this PCB.

Circuit diagram:

”12V” is +12 volts from an unused hard drive-power connector in the computer, and GND is ground, or (-) from the same connector.

The dots marked with D0 to D7 are the data inputs from the parallel port. If we take a look at a drawing of the port, we’ll notice that D0 to D7 is pin 2 to pin 9:

STROBE is pin 1 on the parallel port.

SW1 is an ”override” switch which, if required, forces 12V to certain fan outputs – depending on how you’ve made your circuit.

The 2 AUX outputs is not controlled by the override switch. They are supposed to be connected to lights, lazer-LED’s and so on. We’ve chosen to make 6 fan outputs and 2 auxiliary outputs, but that choice is fully yours. The rectifiers marked by a dashed line, decides whether the regarding output is “override-able”. If they are mounted, the output can be overridden. If the rectifier isn’t mounted, the output will not respond to the override switch.

Components:

In case you shouldn’t know anything about electronics, let’s have a brief look at the components:
Transistor:
 

The transistors must be mounted correctly. If disoriented, the transistors are likely to be permanently damaged.
Here’s the pin-out for the 3 different transistor types used in this circuit:
 

 

Capacitor:

The capacitor to the right must be mounted correctly (the black line to ground), while the capacitor to the left has no particular orientation.

Resistor:


Can not be disorientated.

Rectifier:



The rectifier must be mounted correctly. The cathode (K) is usually marked by a white ring.

Parts list:
 

PCB components:

8 pcs. 220 ohm 1 W resistors app. 9 DKK.
9 pcs. 10 Kohm ¼ W resistors app. 1 DKK.
1 pcs. 470 ohm ¼ W resistor app. 1 DKK.
1 pcs. 680 ohm ¼ W resistor app. 1 DKK.
9 pcs. BC547C NPN transistor app. 4 DKK.
8 pcs. BD136 PNP transistor app. 52 DKK.
1 pcs. BD135 NPN transistor app. 6 DKK.
23 pcs. 1N4004 1A rectifier app. 6,50 DKK.
1 pcs. 100 nF capacitor app. 1,50 DKK.
1 pcs. 10 uF / 50V capacitor app. 1,50 DKK.
30 PCB-connectors app. 2 DKK.


Misc. components:

3mm blue LED, app. 12,50 DKK.
LED holder LDC300 app. 0,50 DKK.
8 * 2 pcs. Terminal connectors app. 15 DKK.
1 pcs. 1 pole switch, 80W app. 20 DKK.
1 pcs. 4 pin Molex harddrive connector app. 11 DKK.
1 pcs. 25 pinD-SUB connector app. 11 DKK.

Misc.:  Wires, fuse and fuse holder, soldering machine, soldering wire, wire cutter, measuring tools, pencil, soft eraser and a printer extension cord.

Price:
The parts and components are approx. 21,00 EUR / 24 USD total.