A little clock/display thing made from a pair of HPDL-1414 displays and an Arduino Pro Micro clone

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I started this well over three years ago, in my previous job. I frequently missed office chat messages so I thought I'd build a display that would show a clock most of the time but could have alerts flashed to it over serial/USB. When I left that job at the end of 2016, I lost this board in the process, but found it again a couple of weeks ago!

Sadly the code has long gone, so I've started from scratch, this time programming it using PlatformIO via VS Code. (It's sooooo much nicer than the Arduino IDE!)

I really like these 'smart' LED bubble displays. They look fantastic and the HPDL-1414 variety are available on your favourite online marketplaces for next to nothing (seriously, they're cheap enough for me to have given loads of them away to maker friends). They're nice and easy to drive as well - select a character address with two pins, give it an ASCII-derived character code on the seven data pins, then strobe the write pin. For each extra display module you just need one more pin from your microcontroller to act as that module's write pin, and everything else is parallel. Dead simple.

They're quite wide, due to the 90s circuitry inside, but one day I realised the Arduino Pro Micro board had the same pitch, and inspiration kicked in. Vcc and Gnd are at the same end of the module, and could dangle off the end of the Arduino so that the essential control pins would be aligned purely over the IO of the board, and the power and ground handled with bodge wires. That's good for one module, but I wanted more!

A scrap of protoboard was cut and sanded so that it could sit flush to the end of the Arduino and dangling legs of the first display would fit in the first holes of the protoboard. Add a little superglue and to the protoboard's edge, solder in the dangling legs and it held fine! (This isn't getting sold to anyone - have you SEEN the soldering?! - so it's good enough for me at least.) One more HPDL-1414 went on the protoboard, and it got wired up as necessary.

  • 1 × Arduino Pro Micro, 5V (or clone thereof)
  • 1 × DS3231 breakout board
  • 2 × HPDL-1414 display module (or clone thereof)
  • 1 × Small 2-pin tact switch
  • 1 × various bits of wire

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