In the 1970s, most calculators had HP bubble displays, which were made up of miniature LEDs on a PCB with plastic bubble lenses on top to magnify them.
Now, as we approach 2025, such displays are rare, although they have been used in a digital clock built by Joshua Coleman, who has documented the process in a blog post.
Inside the 3D-printed case is an ESP32 microcontroller to drive the display, which is powered by an 18650 battery with associated charging circuitry.
Coleman uses two 74HC595 shift registers to drive the display, which is fastened into the case using thermal glue.
He apologises for using US date formats, but points out that Hackaday has previously advocated the ISO 8601 format as the best way to avoid the date format trap.
