New PCB Revives Ancient Bubble LED Displays

For those of us who remember LED calculators, the HP 5082-7400 series red “bubble” displays hold a special charm. Available in 3, 4, or 5-digit varieties, these multiplexed 7-segment displays provided countless hours of entertainment to those who would spell upside-down words on their pocket calculators. In case you happen to be lucky enough to have access to a few of these beautiful vintage display sticks, [Gigawipf] has designed a small driver PCB that lets you easily interface them to a modern microcontroller.

At the heart of the board, aimed at either the 5082-7405 or 5082-7415 5-digit modules, are a pair of 74HC595 shift registers in tiny QFN packages. Five lines from one register drive one of the common cathodes for the selected digit, while the other register drives the eight anode lines through 330-Ohm resistors. The boards are slightly smaller than the width of the displays allowing you to stack them seamlessly for more digits, and eight header pins on each allow you to plug them into solderless breadboards for prototyping. The result is easy to drive with some simple code, and [Gigawipf] provides an example for Arduino as part of the project. The Eagle design files are supplied, as well as Gerbers for those who just want to have some boards made. This sounds like a great way to get some of these vintage displays going again.

If you can’t find any of these displays to play, with, you can try making some larger digits from individual surface-mount LEDs.

Large Seven-Segment Clock Build Takes Time To Perfect

[Kevin Rye] built a discrete TTL based seven-segment clock, and he wasn’t too happy with the ugly insides compared to the nice enclosure he built for it. He embarked on creating another large seven-segment clock to put inside that enclosure.

Clocks, and specifically seven-segment based ones, aren’t anything new to write about. This particular project, which is still work in progress, is interesting. [Kevin] is an experienced hacker, but the problems he encountered and resolved along the way could prove useful to a fellow hacker someday.

To start with, he tried rectifying his old build. But in his own words “You can polish a turd, but it’s still a turd.” Five years later, he’d had enough. He’s built a lot of other clocks, but rather than repurposing them, he decided to start from scratch. He quickly breadboarded an Arduino, some displays and drove them using the Multiplex7seg library. That library supports only four characters, so he was back to the drawing board. With a fresh start, his design is now moving along nicely. For now, he’s designed three boards for the display, two boards for the colons between digits, the main Arduino-clone controller board and a 3D printed front frame to hold the displays. It will be nice to finally see that enclosure receive some fitting occupants and bring this build to closure.