“We’ve made all manner of LED displays over the years. Some simple, some complex, some tiny, some huge. But no other has been such a culmination of all the skills we’ve learned over the years. We call it the Bixel, for Button/Pixel.
Ok, so we’re bad at naming things. Moving on…
Every time we show off our work at Maker Faire or SparkCon we get great response from all the displays, but none more so than the interactive ones. There’s just something about a blinky thing you can reach out and touch that really attracts people’s attention. With that in mind, we have wanted to build an interactive display where each pixel hides a button so that people can directly touch and manipulate the pixels.
For those that are already screaming “just give me the sweet, sweet video!”, see below for a wonderful time-lapse build. Otherwise, read on!
Originally the plan was to find some arcade buttons with built-in RGB LEDs as they are literally designed to do what we want. However, the cheapest we could find was more than $2 per button and for a 16x16 display that’s over $500 just for the buttons alone.
Beyond just the cost, arcade buttons posed another problem; every one we could find simply had LED wires for Ground, Red, Green, and Blue. This meant that we would need to drive the full 16x16 array with some sort of multiplexing scheme. Not impossible, by any means, but it makes both the code and the PCB layout considerably more complicated.
Even still, we had originally assumed that multiplexing the LEDs would be the cheapest way to go. But after much research and some discussion with our LED supplier in China, we came to the realization that we could use standard digital, chainable LEDs which would simplify the code and the PCB while being far cheaper than the arcade buttons. This was even when our new plan required an enormous PCB, but more on that later.
Typically something like this would just use the bare LED modules (SK9822, an APA102 clone, in our case) soldered directly to the PCB. But besides the fact that these would need to be expertly hand soldered or preferably reflow soldered to the massive PCB, we’ve had exceptionally poor luck with using these LEDs in the past. They are extremely heat and moisture sensitive and prone to failure during the soldering process. However, once soldered with the right equipment they seem bulletproof.
So with this in mind, we fell upon a novel solution; we would simply purchase full strips of LEDs, cut them up into the individual pixel sections, and then solder those directly to the PCB. All it took was creating a custom component footprint in KiCad. As you can see below, “