Building the LED-strip display

Building the display was a lot of work. And I really mean A LOT of work. It started off with having to solder some wires to the 42 individual strips. Each strip needing 3 wires on one side, and 2 on the other. So about 200 wires in total. Having not much soldering experience before this project, you could definitely see my soldering work increase with quality the more time I spent doing the soldering. Of course I ended up re-doing a bunch of the first LED-strips, because I was not happy with how they turned out. All part of the learning process!

Next step. We stick all the LED-strips on a big wooden plate. In hindsight, it would have been a better idea to find a metal plate to stick the strips on for better heat-conductivity, as the display currently does get warm (40–50°C) when doing full-brightness for about an hour. But this doesn’t happen too often anyway. So not a big deal. However, it is something I would change if I attempt this for a second time.

Next up, we attach some larger diameter wires to all the positive and negative wires of the LED strips. Making sure the large wires are rated to be able to supply the max 100A safely. To be extra sure, we also add a 15A fuse for each display section.

At this point, we are able to start making our first attempts at controlling the display. After a lot of failure and tinkering with software settings and wires. I was finally able to display a solid color on the display without any distortion or interference. This took me a long time, and it was still far from perfect. I continued having problems with distorted signals for a while, until I posted a question about it on electronics.stackexchange.com. The very nice people over there helped me diagnose the problem. I still don’t fully understand the problem, but attaching negative leads directly alongside the data-lines from the MCU-ground to the ground terminal next to the data-input on the strips solved the issue. Since then, we never had any distortion problems anymore on the display.

As seen in the illustration from before, we have 2 layers of material that go on top of the LED strips.

For the material on top of the grid, we need something that is strong, transparent but also diffusing. However I did not want to use glass, as it is expensive and easy to break. I decided to go for general purpose clear polystyrene. To make it diffuse the light, I sanded it with fine sandpaper to the point where you can’t see through it anymore. Simple as that.

It took me a lot more effort to build the grid that sits directly on top of the strips. I considered ordering a custom build grid with the right specifications directly, but I was quoted around 500 euro. Which was not worth it in my opinion. So we have to build it ourselves. In order to do this, we need thin (max 2mm thick), strong, opaque, white plastic strips. Quite a lot of requirements. So it took me a while to find the right material. Turns out, old sun-blocking window slats which we had lying around were the perfect kind of material.

First, we made a little jig to make consistent straight cuts on the wide slats. This resulted in just enough smaller strips of plastic. Now, we need to cut notches halfway through each strip at the exact right positions. This is necessary to put the pieces of plastic together to form a grid. This is what I was doing in the third picture. Before you do this, you have to be sure that the width of the saw is the same or a little bit wider than the width of the strip that you are cutting into. Otherwise you will not be able to put the puzzle together later on. In our case, a metal cutting saw turned out to be the perfect width.

On the fourth picture you can see the result after putting all the strips together to form the grid. This was very frustrating tedious work, but the grid turned out very sturdy. The squares generally also look like they are about the same size. No big inconsistencies between square sizes, which would look odd on the display, so that turned out pretty good. Happy with the grid.

Now, we added a wooden ring around the grid which has multiple purposes. First of all, it holds down the clear polystyrene plate on top of the grid. It makes sure the grid does not shift position. And the wooden ring also presses down on the wires so that they are more secure, less likely to accidentally tear off (which did happen a couple times while moving the display).

In this picture, the polystyrene plate on top of the grid is dulled with fine sandpaper. Notice how you can barely see the grid anymore, this is exactly the effect we are looking for.

After spending hours on hours of experimenting with how to properly control the display, we finally got it working. Maintaining signal integrity was a huge problem. But like I said earlier, the community at electronics.stackexchange helped me out!

The display is bright, a lot more bright than I expected. I should have seen it coming though, when ordering a 100A power supply to run the display.

As mentioned multiple times already. We are using the FastLED library to control the LEDs. What I did not mention before is that I also use a modified version of Jürgen Skrotzky’s FastLED-GFX library (which in itself is a port of the Adafruit-GFX-Library) to easily draw shapes and whatnot on the display. The modification to this library is minor, but necessary to make the interpreter talk to the library in a nice way.