This Massive Split

Aug 02, 2023

Split-flap displays are very cool — both because they have retro appeal and because they can show whatever pictographs you might want. But they're also very expensive. The Vestaboard is one example that caught a lot of attention recently, but it starts at $2,995 and that is far more money than most people are willing to spend just to display messages in a fancy way. Still, Dr. Tõnis was intrigued by the Vestaboard, so they built their own massive split-flap display that is endlessly versatile.

Every digit of a split-flap display is a rolodex-style wheel of cards. Pictographs (usually alphanumeric characters) sprawl across adjacent flaps, so stopping the wheel at any position will display that character. Put a whole bunch of those wheels together and you can combine strings of characters to form words and messages. It is also possible to show other symbols, or to use solid colored cards like pixels to form simple images.

In this case, the display built by Dr. Tõnis contains a total of 36 wheels arranged across three rows for a 3×12 grid. Each wheel contains 64 flaps, which is equal to the number of pictographs. Dr. Tõnis chose to use those for the full range of alphanumeric characters, several different punctuation marks, blank spaces, and a handful of solid colors. That provides quite a lot of variety, so this can display a huge range of different messages and imagery.

Dr. Tõnis designed the frame and mechanisms in Autodesk Fusion 360, then 3D-printed most of those parts. Small pancake stepper motors spin the flap wheels and every wheel needs its own motor. Dr. Tõnis developed custom driver PCBs and each of those can handle an entire row of 12 stepper motors. A Seeed Studio XIAO ESP32C3 development board controls the steppers through those driver boards. Simple digital Hall effect sensors help it find the wheel's home positions.

The current code is still a work in progress and Dr. Tõnis is working out the kinks, but the idea is to use this as a big clock. The development board can pull the network time or use a real-time clock. And because the ESP32 has Bluetooth and WiFi adapters, it would be possible to use either of those communication methods to set custom messages. This display could, for example, update to show the weather every now and then, or even news headlines.