This module allows two HP 5082-7400 series bubble LED displays to be controlled by a RC2014 computer. Two ports are used (Port 0 and Port 2) for the digits and segments respectively, and a full display of 8 characters can be achieved by strobing the digits. Simple software routines for BASIC, Z80 Assembly and FORTH are available on the RC2014 GitHub page, although they can be controlled by any language that can access the Z80 I/O ports.
What are the HP Bubble LEDs
These fantastic looking 7 segment LED displays were used in iconic devices of the 1970s such as the Sinclair Black Watch, several classic calculators and HP test equipment. The individual 7 segment displays are tiny, so the bubble acts as a magnifying glass to make them more readable. See the photo above with a Lego MiniFig for scale.
This module is designed around the 5082-7414 which is a 4 digit display. It will also work with the 5082-7412 and 5082-7413, which both have 3 active digits in a 4 digit case (aligned to the right and left respectively). These other models will work exactly the same, although obviously nothing will display if the nonexistent digit is selected. There are also 5082-7415 and 5082-7405 which are a 5 digit displays, but these will not work with this module.
The HP QDSP-6064 is a later model which looks very similar to the 5082-7414 and has the same pinout. This should work, although at the moment this hasn’t been tested.
Are these Displays New-Old-Stock?
No. Some NOS displays are available online, but they are very rare, and thus very very expensive. I managed to get hold of a handful of used displays which have been cut from a PCB. Therefor the legs are shorter than new ones. They can be fitted to a chip socket or soldered directly to a PCB with no problem though. Every display I include with this kit will have been tested and visually inspected so that you know that you’re getting good working displays with your kit.
I also offer the option of buying the kit without the display modules. If you already have some of these displays, or have access to a cheaper source of Bubble LED displays than I do, you are probably better off doing this.
For PCB Only option, see Expansion Module PCB listing