Welcome to my fanbus page! This isn't a walk-through on how to build one, just a description of what I did and how I did it. Hopefully I'll be able to give some of you some ideas or a place to start from on building your own.
All the images should be clickable, bringing you to their full uncropped, unresized (and probably blurry) glory. They'll be 900x600, so don't get impatient.
Let's start off with what the thing looks like and what it does.
All the unit does is control 4 power plugs, which in my case (heh) are used for my 5 case fans. The 4 black switches control the on-off state of each power plug, while the red switch determines the voltage going to the plugs. The four LED's indicate the state of each plug, on or off.
As you can see I used a blank 5.25" faceplate to mount the switches in. As my case (Addtronics 6896A) uses screw-on metal blanks rather than the pry-off kind, I was able to use one as the mounting point for the whole unit, not just the plastic faceplate. Here's a picture of how it mounts to the case.
Here's a picture of the back of the unit, so you can see the two metal plates that screw onto the case.
Onto the plates I mounted the breadboard, which we'll get to later. It's kind of hard to see with all the wires in the way, but the faceplate is attached to the plates with two wood spacers. Then two little angle brackets attach the plates to a long piece of scrap metal, which hold the breadboard. Here's a shot of the underside which show this more clearly.
Now let's get to the interesting part, the workings of the unit. Here's a PSpice schematic of the whole thing.
Before I get into the workings of the unit, let's go over what a DPDT switch is. It stands for "Double Pole, Double Throw". What that means is that there are two sets of contacts to work with (it's like having 2 switches in one), and the double throw part means that a common contact is switched between two other contacts. A single throw switch simply opens and closes a set of contacts. In the schematic, each box is a separate switch, with the two sets of contacts being on the top and bottom. The common contact is always in the middle.
The unit uses the +12V line for all operations. Let's look at what the left-most (red) switch is doing, first. Yes, this switch corresponds to the red one on the faceplate. One of its common contacts feeds the fans, while the other goes to the status LEDs. The bottom common contact goes to the fans, while the top one goes to the LED's. Notice that the 12V line goes directly into one of the switched contacts on the bottom of the first switch. The other switched contact hooks up with the small circuit in the upper left. What is that thing? It's a variable voltage regulator. The box marked "LM317T" is the heart of the regulator, and the values of the two resistors control the supplied voltage. The resistor marked "POT" and with the arrow is a variable resistor (potentiometer) that allows you to tweak the voltage to your heart's content. Here's a picture of the LM317T and the pot. Note that PSpice doesn't have an LM317T part built-in. I just drew a box and stuck a label inside of it. The switches are fake, too. I have information on simulating the circuit here.
I got the heatsink a while after I built the unit, as I burnt my finder on the regulator while running 5 fans off of it. Here's a picture of the regulator and heatsink.
By the way, here's a link to the LM317T's datasheet.
So now we have some voltage on the bottom common contact, which goes out to the top common contact on each of the 4 black switches. As you can probably see, the fans are alternated between that voltage and nothing.
Before I get into the LED's, note that while I have two separate LED's for each switch on the schematic, there's only one LED for each switch on the unit. That's because they're common-cathode bi-color LED's, which are basically two LED's in one package.
Looking back at the red switch, you can see how only a 12V signal will be on the top common contact. Right down the line is a 120 ohm resistor, which prevents the LED's from frying. This is because the LED's only drop around 2V apiece, leaving ~10V to be dropped along the rest of the wire. Because most wire has a pretty low resistance, you're going to get an assload® of current through the wire, and thusly the LED. LED's don't like a lot of current. Anyway, that current-limited line goes out to the bottom common contact of the black switches, where is it alternated between the two colors.
Well, that's about all the explanation this thing needs. Here's a list of parts that I used.
I'll just post the non-shitty pictures I took here. Don't mind the hard drive; it's awaiting its new drive cage as I write this.
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Last Updated: 3/3/2002
