Dodecahedron

I was shown a dodecahedron with LEDs inside. Looked great, so decided to have a go.

The principle is not that hard - a PCB strip on the inside of each edge with WS2812 style LEDs, and solder pads on the ends, then a triangle corner piece on each vertex soldered to the strips.

The challenge is making it one continuous LED chain for WS2812. As you can guess - 3 way vertices makes that tricky.

After sleeping on it, I realised I need two types of corner.

First off, the strips, I made the ends consistent.

The idea is the strip has two lanes - one goes through all the LEDs (left to right on that image), and the other just connects from one side to the other with no LEDs. So instead of each edge being one way, it is a two lane road. This allows loops around the edges of the dodecahedron.

Now for the corners - after some thought I decided I need two types, I called Y and C.

The Y type feed each lane to its left. The C type link left and top both ways, and loopback the right. I then designed it so it is just one PCB, with Y one side and C the other side.

If you made all vertices Y then it would be a loop around each pentagon.

But the logic is pretty simple. If you put a dodecahedron on a flat base, you have a bottom, middle, and top.

The middle 10 you put Y corners, and top and bottom you put C corners with the C facing sideways to the next edge around. The effect is a loop or Ys around the middle, with each vertex taking a detour up to the top or bottom and then one edge around the top or bottom before looping back to continue around the middle.

You will see two issues with this.

1. It is two loops, a top hemisphere and a bottom hemisphere, not joined.
2. It is a loop, but WS2812 is a string.

First issue is solved by changing one of the Y middle pieces to a C, facing the C sideways. This C links the two sides making a loop for the entire thing.

Finally the C has an extra pad, and an area where you see to cut a track. Cutting the track breaks the loop, and the pad is where you inject the WS2812 signal.

The exact mapping will depend which C you tapped in to (the obvious one is the extra one on the middle row), and which way around each LED strip is fitted - either work, just change where it is on the string.

Final step was designing a support as a 3D model, 30 pieces that fit together to hold the PCBs. That involved far too much trigonometry for my liking but I worked it out.