Classic LED Bubble Displays Ride Again

November 17, 2024 by Dan Maloney 17 Comments

Hewlett-Packard used to make some pretty cool LED displays, many of which appeared in their iconic pocket calculators back in the 1970s and 1980s. [Upir] tracked down some of these classic bubble displays and used them with a microcontroller. We love the results!

The displays featured here, the HPDL-1414, aren’t quite what would have been found in an HP-35, of course. These displays have 16 segments for reasonably legible approximations of most of the ASCII character set. Also, these aren’t just the displays; rather, a pair of the bubble-topped displays, each with four characters, is mounted to a module that provides a serial interface. [Upir] found these modules online, but despite the HP logo on the PCB silkscreen, it’s not really clear who made them. The documentation was a bit thin, to say the least, but with a little translation help from Google, he figured out the serial parameters and the character encoding. The video below shows him putting these modules through their paces.

Unusually for [upir], who has made a name for himself hacking displays to do things they weren’t designed to do, he stuck with the stock character set baked into this module. We think it would be fun to get one of these modules and hack the firmware to provide alternative character sets or even get a few of the naked displays and build a custom interface. Sounds like a fun rainy-day project.

This reminded us of another HP display project we saw a while back. Or, roll your own displays.

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Chaining Together A 16×2 Bubble LED Display

December 10, 2019 by Tom Nardi 27 Comments

We’ve recently noticed an uptick of interest in so-called “bubble displays”: vintage alphanumeric LEDs which are probably best remembered as being used in watches and calculators before the LCD took over. Today they’re available as surplus or even salvage for literally pennies, but unfortunately they only provide four or five characters to work with. Or rather they did, until [sjm4306] built a board that chains them into a 16×2 array.

For the princely sum of 71 cents each, [sjm4306] picked up ten HPDL-1414 displays, each capable of showing four characters. He then designed a PCB that would accept eight of the displays at once, and even thought ahead to use headers so they could be pulled out and swapped as needed. Of course mounting them is only half the battle, you still need to drive the things.

Each display has its own dedicated driver chip on board, but trying to address each one individually would take far too many pins. So [sjm4306] opted to use a trio of 74HC595 shift registers, allowing him to toggle the three dozen pins necessary over SPI from a microcontroller. He’s even written up a little library and some example code that you can grab on the project’s Hackaday.io page.

Unfortunately, after all his hard work, tragedy struck. As these displays were a couple decades old given their date code, [sjm4306] thought he would clean them up with a bit of alcohol before their big video debut. But whatever plastic the clear panels are made of didn’t take kindly to the IPA, and they all shattered. They still work, but it’s definitely a quirk to keep in mind if you pick up some of these vintage displays to play with yourself.

In the past we’ve seen a much smaller PCB that allowed similar displays to more easily be interfaced with modern microcontrollers; perfect if you just want to bang out a few retro LED characters with a minimum of fuss.

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