Bubble LED Display Module for HP 7400 Series 7 Segment DisplayDesigned by RFC2795 Ltd in United Kingdom
What is RC2014? RC2014 is a simple 8 bit Z80 based modular computer. It is inspired by the home built computers of the late 70s and computer revolution of the early 80s. It is not a clone of anythi...Read More…
RC2014 is a simple 8 bit Z80 based modular computer. It is inspired by the home built computers of the late 70s and computer revolution of the early 80s. It is not a clone of anything specific, but there are suggestions of the ZX81, UK101, S100, Superboard II and Apple I in here. It nominally has 8K ROM, 32K RAM, runs at 7.3728MHz and communicates over serial at 115,200 baud.
As a bare minimum, you will need a CPU, ROM, RAM, Clock and Input/Output module. The RC2014 is designed in such a way that you can build your own modules to expand it. As such, if you have access to similar components, or have specific needs, you might not need all the items I have on offer.
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.
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 shape 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 a 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 the pinout is the same too, so this should work, although at the moment this hasn’t been tested.
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, however, they can be fitted to a chip socket or soldered directly to a PCB with no problem at all. 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.
Please note that a few of the displays I have either have a leg or two cut too short, a faulty segment, or a chipped corner of glass. These B-Grade displays will be listed on Tindies Flea Market shortly. So if your budget is tight, you can save money by buying this kit without the displays, and picking up your displays in the Flea Market.
Of course, if you already have access a couple of these displays in your parts box, or know of a good source of them, you can go with the display-less option too.
RC2014 is a trademark of RFC2795 Ltd
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