576 Ping Pong Balls Form Gigantic “Hard Disk Defrag Visualiser”

Manoj Nathwani and his brother Dhiresh came up with a really neat display for EMF Camp 2016 using WS2811 LED strips, ping pong balls, and a wooden fiberboard backing with a huge number (i.e. 576) of holes in it to form a grid. Like many projects, actually documenting it was a to-do item for some time, but as 2019 crawls to its end, Nathwani decided to finally write it up.

The display was cleverly divided into two 16x8 halves for easy transportation, and after quite a bit of gluing, cutting, and wiring work, the brothers hooked each assembly up to a NodeMCU for testing. Things looked great, so they proceeded to camp where they would assembly the device for display in all its glory…

Unfortunately, they found that things don’t always work the same way in the real world as in a controlled environment, and after hooking it up, it didn’t behave as planned. It could start to run though a color wipe display, but at around 200 LEDs in, things got a bit wonky. Even after swapping out the NodeMCU for an Arduino Uno and checking connections, it still misbehaved, but after analysis, they realized that by daisy chaining all of these strips together they were transmitting on an effective cable length of 48 meters.

The solution would have been to add a new data cable incrementally throughout the setup, or to use a specialized LED strip driver such as FadeCandy from Adafruit. The good news, however, is that people still seemed to still love this glitchy display, especially after jokingly renaming it “Hard Disk Defrag Visualiser.”

Setting aside the issues around not being able to fully program the matrix to display what we wanted this was still a super fun project to work on! There’s something really enjoyable about building a large physical installation for a festival and sharing your creations with others who really take time to appreciate what you’ve built. There’s also something therapeutic about drilling 576 holes in a wooden board, carefully cutting an X onto a ping pong ball and then feeling an LED into it piece-by-piece. The end result was also really pretty to look at, especially outdoors at night and it really came out much better than we originally imagined. At some point in the future I’ll likely take out the LEDs strips again and get all 48 meters of it to correctly work!