• Creating the Lack Ping Pong LED Matrix

    arturo18206/02/2019 at 11:02 4 comments

    I've been wanting to create a LED Matrix of some kind for some time now, I even tried before with a laser cutter and a lack table, but it didn't turn out as well as I was hoping. Then I saw a project on /r/DIY that was using ping pong balls as LED diffusers and it clicked for me!

    Since I used a Lack table before and I live in Sweden (yay Ikea), it seemed fitting to use it again. The table is 55x55 cm and the balls are 4 cm in diameter, meaning I could make a 12x12 LED matrix easily. I was also using foam board as scaffolding for the matrix. For LEDs, I used a panel of fairly cheap and very popular WS2812b, they can be easily driven with a Raspberry Pi and the Satanic/Sexy/Stupid/Silly/Shiny LED matrix controller library.

    Let's get to the build!

    Here's most of the materials needed:

    As mentioned, the LEDs come in a PCB panel where you can snap off each PCB easily. Having them initially in a panel made the soldering easier.

    I started with drawing a 4cm x 4cm grid on the foam board, this is where each ball would go.

    Since I wanted to have the matrix not glued together as one piece but as two separate ones, I needed holes in the foam that would hold the ping pong balls so the LEDs could shine through. Enter the drill:

    The foam board used as A2-sized, which was not large enough for the 12x12 matrix, so I simply taped another board to it, extended the grid and drilled the rest of the holes. Note the vacuum in the back, the foam creates quite a mess so make sure to keep your workbench clean!

    After I was done with that part, I cut the foam to size and I had my ball scaffolding!

    I used a 10mm drill which was more than enough for the LEDs, one issue you might notice was that the foam didn't drill very cleanly, since it is just paper and foam. In hindsight, I would've used a hot soldering iron tip to burn the holes.

    Quick fit-test on the Lack and looks good!

    I then marked the Lack so I could route it. 12 x 4 cm = 48 cm, leaving us 3.5 cm each side.

    I moved over to the woodworking room and marked a hole in the corner for the router to enter.

    My initial try was with the narrow tool you can see in the photo below, however instead of routing it preferred to set the table on fire (I think it was too high rotation speed, but this router doesn't have speed control). So I switched to a v-score tool instead. That one worked great!

    Here's a quick video of me doing the routing, watch out, it gets loud. You may also notice I screwed up one side when the router got a bit off-side, I fixed that later bu routing that side again but a bit closer to the edge.

    And here we have all 4 sides routed, since I changed the tool to a wider one, I should've adjusted the margins a bit, so the actual frame I got was less than 3.5 cm, but it wasn't a big deal.

    If you've never seen a Lack table's insides, here's a video for you, it shows how Ikea can make them so cheap, there's actually very little wood in there:

    After that we had the frame almost ready. Notice the corners, there is still some particle board pieces in the corners that won't let the foam board go down.

    It took a while since I couldn't find a good way to do this, but eventually I got rid of the particle board in the corners and the Lack was ready!

    With that out of the way, I moved on to the LED part of the matrix. First, I needed a foam board...

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