How To Chase The Beam With A Z80

The more accomplished 8-bit microcomputers of the late 1970s and early 1980s had a dedicated display chip, a CRT controller. This took care of all the jobs associated with driving a CRT display, generating the required timing and sequencing all the dots to make a raster. With a CRT controller on hand the CPU had plenty of time to do other work, but on some cheaper machines there was no CRT controller and the processor had to do all the work of assembling the display itself.

[Dr. Matt Regan] had a Sinclair ZX81 which relied on this technique, and he’s put up the first of what will become a series of videos offering a deep dive into this method of creating video. The key to its operation lies in very careful use of timing, with operations executed to keep a consistent number of clock cycles per dot on the display. He’s making a very low resolution version of the display in the first video, which he manages to do with only an EPROM and a couple of 74 logic chips alongside the Z80. We’re particularly impressed with the means of creating the sync pulses, using opcodes carefully chosen to do nothing of substance except setting a particular bit.

This method of assembling a display on such a relatively slow microprocessor has the drawback of no means of creating a grayscale, and of course it’s only available in glorious black and white. But it’s the system which gave a first experience of computing to millions, and for that we find the video fascinating. Take a look, below the break.

If this has caused you to yearn for all things Sinclair, read our tribute to the man himself.

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It’s Never Too Late To Upgrade Your ZX81 Keyboard

Sir Clive Sinclair’s ZX81 was a phenomenal sales success as one of the cheapest machines available in the early 1980s, but even its most fervent admirers will admit that it suffered heavily from the Sinclair economy drive. In particular that membrane keyboard was notorious for its lack of feedback, and a popular upgrade back in the day was a replacement keyboard. Now we can bring you what might be the ultimate in ZX replacement keyboards, in the form of [Brian Swetland]’s mechanical ZX81 keyboard.

The familiar 40-key layout is all there, using Cherry MX key switches and a beautiful set of custom-printed keycaps. There’s little more to a ZX keyboard than the matrix wiring, and in this case it’s all incorporated on a PCB. None of these techniques were readily available to individuals back in the ’80s, so a large piece of perfboard, key switches from an old terminal keyboard, and Letraset would have had to suffice.

We have to admit liking this project a lot, in fact we’re even tempted by a set of these keycaps for a regular keyboard just for old time’s sake. If you’re interested in the ZX81 then take a look at how we used one to help us through the pandemic.

Building A Sinclair ZX81 In 2022 With All New Parts

As the supply of genuine retrocomputers dwindles and their prices skyrocket, enthusiasts are turning their eyes in other directions to satisfy their need for 8-bit pixelated goodness. Some take the emulation route, but others demand a solution that’s closer to the original hardware. Following the latter path, [iNimbleSloth] is answering the question as to whether it’s possible to build a Sinclair ZX81 from all-new parts in 2022.

The ZX81 was Sir Clive’s second Z80-based computer, and its low price made it an instant success which paved the way for the legendary ZX Spectrum. From here in 2022 the original Ferranti ULA chip that contained all the logic is unobtainable except by raiding another ’81, so he’s using a design that has the same functionality in 74 series logic. The PCB is the same size as the original, and he’s paired it with a keyboard PCB using tactile switches. The video below the break is the first of what is to be a series, and he will be looking at a readily available 3D printed ZX81 case and the re-manufactured membrane keyboard.

For those of us who first learned to code in its meager 1k of memory the ’81 will always be a special computer. Sure it had many faults, but simply having an affordable real computer at all in 1981 was special. To see one being made from scratch is special then, and it would be nice to think that a few other people might learn how a computer works the Sinclair way.

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One Of The Worst Keyboards Ever, Now An Arduino Peripheral

For British kids of a certain age, their first experience of a computer was very likely to have been in front of a Sinclair ZX81. The lesser-known predecessor to the wildly-successful ZX Spectrum, it came in at under £100 and sported a Z80 processor and a whopping 1k of memory. In the long tradition of Sinclair products it had a few compromises to achieve that price point, the most obvious of which was a 40-key membrane keyboard. Those who learned to code on its frustrating lack of tactile feedback may be surprised to see an Arduino project presenting it as the perfect way to easily hook up a keyboard to an Arduino.

Like many retrocomputing parts, the ZX81 ‘board has been re-manufactured, to the joy of many a Sinclair enthusiast. It’s thus readily available and relatively cheap (we think they can be found for less than the stated 20 euros!), so surprisingly it’s a reasonable choice for an Arduino project. The task of trying to define by touch the imperceptible difference in thickness of a ZX81 key will bring a true retrocomputing experience to a new generation. Perhaps if it can be done on an Mbed then someone might even make a ZX81 emulator on the Arduino.

We’re great fans of the ZX81 here at Hackaday, for some of us it was that first computer. Long may it continue to delight its fans!

A Sinclair ZX81 Clone Still Has The Power To Fascinate

The golden age of 8-bit computing brought us pixelated graphics in bright colours, accompanied of course by chiptune music. This aesthetic is strong enough to define a collective image of a generation’s youth, even if the 1980s reality had much more of the tired 1970s leftovers about it.  The truth was that not all popular 8-bit machines had colour, sound, or good graphics, and among these limited-capability machines was Sir Clive Sinclair’s ZX81. With a Z80, 1k of RAM, a membrane keyboard, and not much else, it helped set the stage for the hugely popular ZX Spectrum which followed it. The fun’s not over though, as [Augusto Baffa] demonstrates with his modern recreation of a machine that can switch between the ’81 and its less-popular ZX80 predecessor.

Rather than a Eurocard-sized mainboard and membrane keypad, this clone copies the ZX80 with a full-sized mainboard the front of which carries the keyboard contacts. It also eschews the ULA found in the ’81 for discrete TTL. It’s based upon the venerable Grant Searle design for a homebuilt Sinclair computer, and all of the files for this version can be found in a GitHub repository.

There is a lot to be said for the ZX81 as a model for retrocomputer experimentation, because of its extreme simplicity. It may have been no great shakes in the computing department compared to many of its competitors, but it remains possibly one of the easiest of the bunch whose operation to completely understand. Also we like it for that paltry 1k of memory, teaching kids about memory constraints is a good thing in our book.

We’ve featured the diminutive ZX more than once, including a couple of years ago in our April Fools coverage.

Farewell Sir Clive Sinclair; Inspired A Generation Of Engineers

It is with sadness that we note the passing of the British writer, engineer, home computer pioneer, and entrepreneur, Sir Clive Sinclair, who died this morning at the age of 81 after a long illness. He is perhaps best known among Hackaday readers for his ZX series of home computers from the 1980s, but over a lifetime in the technology industry there are few corners of consumer electronics that he did not touch in some way.

Sinclair’s first career in the 1950s was as a technical journalist and writer, before founding the electronics company Sinclair Radionics in the 1960s. His output in those early years was a mixture of miniature transistor radios and Hi-Fi components, setting the tone for decades of further tiny devices including an early LED digital watch at the beginning of the 1970s, miniature CRT TVs in the ’70s and ’80s, and another tiny in-ear FM radio which went on sale in the ’90s.

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Examples of ZX81 computer game screens

The Labor Of Love That Is Recovering Lost Software

At the beginning of the home computer revolution, the humble compact cassette was far and away the most popular choice for microcomputer data storage, especially on the European continent. As a volunteer at the Museum of Computing, [Keith] was instrumental in recovering and archiving the early works of Roger Dymond, a pioneering developer of early computer software in the United Kingdom.

In his video, [Keith] goes to great lengths detailing the impact that Roger Dymond had on the early home computing scene. After being let go from his council apprenticeship, Roger turned his attention to developing games for the ZX81, and later the ZX Spectrum. With the help of his family, he went on to run a moderately successful mail-order games publishing venture for several years. Increasing advertising costs and a crowded development scene saw Roger’s business become nonviable by 1983, but not before developing several gambling-style games and a standout Space Invaders clone.

Fast forward to 2021, and while some of Roger’s Spectrum software had been archived, much had been marked as ‘missing’ by online archivists. After further research, [Keith] realized that another potentially important tape had been forgotten about. ‘Games Compendium’ for the ZX81 had been completely lost to time, with the only evidence that it had ever existed coming from a 1983 advert in ‘Sinclair User’ magazine. Being written for the earlier model ZX81, the compendium would undoubtedly be of interest to software archivists and game historians.

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