Column: Embedded design


Slave to the Blinkenlights By Myk Dormer, RF Engineer and Director, Smallwireless Limited I


t is unusually diffi cult to phrase the start of this article for several reasons, one being that about 50% of my readers will have no idea of what I’m talking about, with the rest feeling they have always known. It’s


also hard to fi nd words that don’t sound as if they come from a cult de-programming interview, or a confession to an addiction support meeting. So, let’s give it a try: “Despite being an RF engineer by trade,


I’m a retro-computing enthusiast.” “I design and build discrete-logic


CPUs out of TTL gates and registers – like it’s 1965!” It may sound an odd thing to be


doing, but the design and construction of CPUs and complete computer systems at the discrete gate level is actually quite a popular technical exercise and has been for decades. T ere are social media pages dedicated to it, many websites and Hackaday.io projects – and even a “web- ring”, when such things were common. T ese designs vary from pure theoretical models running on digital simulators, through FPGA- and CPLD-based realisations, to the logic gate based (very oſt en 74-series TTL) builds I favour. T ere are even braver souls, taking another step down into discrete transistor logic, as well as a few actual relay based computers. T ere is little uniformity in


architecture either, since you can fi nd anything from demonstration model 4-bit CPUs right up to powerful 16- and 32-bit “minicomputers”. T ey are sometimes supported by entire soſt ware ecosystems resembling the programming environments of the 1970s and 80s, oſt en including compilers and interpreters for


10 June 2026 www.electronicsworld.co.uk


high-level languages, with Forth and C being common choices. T e common thread is that these are


not a commercial microprocessor on a board. Each of these CPUs is pretty much unique, even though they show the obvious infl uences and borrowed concepts from “real” commercial machines. A lot of them implement a front panel


interface, comprising indicator lamps on every address and data bit, and data entry and machine control switches to allow (laborious) manual data entry: One


address word at a time – in binary! T is eff ort does raise a few questions,


with the most obvious being: “Why do it?”. For me it comes down to the joy of it.


No retro CPU designer is likely to come up with a totally new and commercially successful idea, so we are leſt with curiosity, mental exercise, education and an artful project. T at said, there is a very particular


satisfaction to seeing your processor successfully execute its fi rst op codes. The second obvious question linked


Figure 1: The 162 – a compact 16-bit bus width TTL processor


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