In the previous part of the blog post series you’ve constructed the actual 8x8x8 LED cube itself and mounted it onto the mould you used or the build. In this section I’ll show you how to wire up the cube.
A first question is why did I choose this dimension for the cube? You can build a cube of any size you like: 4x4x4, 7x7x7, 12x12x12, … It doesn’t matter. The only thing you have to keep in mind is that the complexity grows exponentially when moving to a bigger dimension. I mean, with an 8x8x8 cube you already have to work with 521 LEDs. If you would create a 9x9x9 cube, the number of LEDs would already be 729.
8×8 pixels is also the smallest usable dimension to display text. If you want to do that, an 8x8x8 is the minimum. And of course I also chose this dimension because it is quite handy for wiring, because then you can simply use UTP cables, which have 8 wires.
Wiring the cube
First, you need to understand how you are going to program the cube’s animations. Since the cube contains 512 LEDs you will have to be able to control 521 individual outputs. Or so you might think, because you can simplify this a whole lot by using multiplexing. What is this? Well, multiplexing is a way of programming that switches only some of the LEDs on or off at the same time. Then you quickly move to another set of LEDs and then another and so on. By doing this very quickly the yes cannot keep up and it will appear as though you are turning all of them on when in fact only 64 LEDs will be turned on at any given time. You can see a good demonstration of this principle in the YouTube video below, where the switching is gradually increased in speed.
In our specific cube the multiplexing will go per vertical plane. That means that all the horizontal layers can be turned on at the same time and one vertical row of 8 LEDs as well. So 8 rows in a plane times 8 layers equals 64 LEDs. This system also keeps the power consumption really low as well.
The first thing you need to do is create some wires. You simply cut off a piece of UTP cable about 20-25cm long and remove the outer layer for about 5cm on one end and about 10cm on the other end. Then you unwind the inner wires and place then in a fixed order. I used brown – brown/white – orange – orange/white – green – green/white – blue – blue/white. But you can choose any order you want. Just make sure that for each cable the order is the same to avoid mixups afterwards. You’ll need 9 of these cables: one for each plane and one for the layers.
The next thing you need to do is to solder the female headers to the shortest end. This in not an easy thing to do when you do it freehand soldering, so if you have a “third hand” device lying around, please use that. If you don’t, you can also use a pair of pliers to hold the female headers in place so you have both hands free for soldering. I know the picture below is a little bit dark, but you can clearly see the end result of this operation.
The last thing you have to do is to solder the other end in the same order to on of the rows of LED legs that are sticking out through the bottom of your mould. It is also a good idea to label the cables to make it easier later on to connect the proper cable to the proper IC.
Once you’ve done this, you simply do follow the same procedure for the other rows and one last time for controlling the layers. The bottom of your mould should now look something like this.
In the next section I’ll cover the brains of this thing and we’ll be making the prototype board