Driving 32 Tiny Alphanumeric Bubble Displays
Eight HP bubble LED displays become a 16x2 serially addressable module.
Hacker sjm4306 found a number of HPDL-1414 four-digit bubble displays on AliExpress. These resemble tiny Nixie tubes, but are actually sets of 14-segment alphanumeric displays that apparently don’t require all the fiddling about with over 100VDC. Naturally he bought a number of them, and set to work on a method to string together eight of them to make a 16 x 2 serially addressable module.
The heart of this hack is a custom PCB to drive all of the boards together. Since each individual display requires 10 pins for control, he’s using shift registers to select each unit individually, feeding it the proper serial ASCII data. This all happens extremely quickly, so there’s little (if any) visual delay, and everything is controlled using just four logic pins from an Arduino Uno clone. This can be made even simpler if needed, as the fourth enable pin can be set to display at all times, or this can be used to vary the display brightness via PWM.
Board info is available here if you want to build your own, along with Arduino example code. The video is a great intro to these vintage displays. Sjm even goes over how much current these units draw, as well as the fact that you really shouldn’t use isopropyl alcohol to clean them!