8x8x8 RGB-LED-Cube


The 8x8x8 RGB-LED-Cube is the biggest project of legl-electronics so far. We are still working on it and there will probably always be something to improve on. Furthermore, we are also permanently looking for innovations and ideas for new animations.

Special thaks to Kevin Darrah who inspired me to built a cube. I used his cube as role model and of course there are many accordances, so please visit also his website.

Links to other parts:

How does it work?

First of all: how are the LEDs wired? multiplex The figure above shows our cube in front view. Overall, the cube comprises 8 plates. All the cathodes of the LEDs are wired together horizontally (red wire). All the anodes are wired together vertically (green wire).

How can you turn on a single LED?
This can be done by putting voltage to the anode wire and the cathode wire the LED is connected to.

But then you cannot control all individually LEDs at the same time!
Sadly, that is right; We cannot, e.g., turn on all LEDs with different colors at the same time. Nonetheless, we can apply a different solution. The method we use is called multiplexing. We put voltage to the lowest anode and to the cathodes of the LEDs we want to turn on. Since the other anodes do not have any voltage the other LEDs stay off. Then we put the voltage to the second anode, then to the third etc. until we reach the top and start the whole process at the bottom all over again. Using this method, every LED can only be on 1/8 of the time. However, it looks like as if they were on all the time and they are still very bright.

Why do you use this method?
If we wired every LED we would get [4(red, green, blue, common anode/cathode of each LED)*8*8*8=] 2048 wires. Yes, you heard right: Then there would be 2048 wires. With the multiplexing we have, the number of wires remains at a solid [8*8*3(all the cathodes)+8(all the anodes)=] 200. At this point we have to add that all the anodes in one level are connected together; therefore, there is only one anode for each horizontal layer.

Now we know how to control the LEDs, but how do you control the colors?
Every color is a mixture of the red, green and blue light of the RGB-LED. Because of that we can create each color by controlling the red, green and blue LED inside the RGB-LED individually. To control the brightness of the LEDs we use bit angle modulation.

How does this bit angle modulation work?
We use a 4-bit bit angle modulation. This gives us the opportunity to control the LEDs in 15 different levels of brightness plus (of course) the “off”-state. Each bit represents its decimal value of runs (bit 1 = 1, bit 2 = 2, bit 3 = 4, bit 4 = 8). In this case one run is one loop of multiplexing (each level was lit once). We take the decimal value from 0 to 15 and convert it into a binary number. If the bit (for example 3) is on, the LED is going to be on for four runs (because it is the third bit which represents 4). In the graphic you can see some examples: blue would be a brightness of 9, red would be 6, and green would be 5.

bam


More will follow soon




Creative Commons License
8x8x8 RGB-LED-Cube by Fabian Legl is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.



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