Addressable LEDs From A Z80

If you buy WS2812s under the Adafruit NeoPixel brand, you’ll receive the advice that “An 8 MHz processor” is required to drive them. “Challenge Accepted!“, says [ShielaDixon], and proceeded to first drive a set from the 7.3 MHz Z80 in an RC2014 retrocomputer, and then repeat the feat from a 3.5 MHz Sinclair ZX Spectrum.

The demos in the videos below the break are all programmed in BASIC, but she quickly reveals that they call a Z80 assembler library which does all the heavy lifting. There’s no microcontroller behind the scenes, save for some glue logic for address decoding, the Z80 is doing all the work. They’re all implemented on a pair of RC2014 extension cards, a bus that has become something of a standard for this type of retrocomputer project.

So the ubiquitous LEDs can be addressed from some surprisingly low-powered silicon, showing that while it might be long in the tooth the Z80 can still do things alongside the new kids. For those of us who had the Sinclair machines back in the day it’s particularly pleasing to see boundaries still being pushed at, as for example in when a Z80 was (almost) persuaded to have a protected mode.

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A 3D-printed case for the ZX Spectrum with a mechanical keyboard

The ZX Spectrum Finally Gets A Proper Keyboard

The Sinclair ZX Spectrum is fondly remembered by many for being their first introduction into the wonderful world of computing. Its advanced capabilities coupled with a spectacularly low price made it one of the great home computers of the 1980s, at least in the UK and nearby countries. What was less spectacular about the Spectrum was its awful keyboard: although a step up from the flat membrane keyboards of earlier Sinclair computers, the Spectrum’s tiny rubbery keys made typing anything more than a few characters a bit of a chore.

If you’re planning to do any serious programming on your Spectrum, you might therefore want to check out [Lee Smith]’s latest project in which he redesigns the Spectrum’s case to include a proper mechanical keyboard. [Lee] got this idea when he was looking for ways to fix a few Spectrums with broken or missing cases, and stumbled upon several projects that aim to recreate classic Sinclair machines using modern components. He took a keyboard PCB meant for the ZX Max 128 project, populated it with some high-quality switches, and added a modified set of keycaps from the ManuFerHi N-Go.

A new ZX Spectrum case, opened to show the keyboard connecting to the mainboard
The new keyboard plugs into the original connectors and doesn’t require any board-level modifications.

Together, those parts formed a modern, comfortable keyboard that still had the proper labelling on all keys. This is rather essential on the Spectrum, since each key is also used to generate symbols and BASIC keywords: for instance, the “K” key also functions as LIST, +, LEN and SCREEN$.

With the keyboard design settled, [Lee] set to work on the rest of the case: he designed and 3D-printed a sleek enclosure that takes the new keyboard as well as an original Spectrum mainboard. The resulting system is called the ZX Mechtrum, and looks fabulous with its matte black exterior and the obligatory four-coloured rainbow. A replaceable rear panel also allows several board-level modifications, like composite video or VGA output, to be neatly incorporated into the design.

We wrote an extensive retrospect on the Spectrum on its 40th anniversary earlier this year. If, somehow, you actually like the Spectrum’s original rubbery keyboard, then you can also modify the whole thing to work with modern computers.

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Building A Replica Of An Obscure Romanian Computer

We’ve all seen emulated Apple II and Commodore 64 boards about the place. Few of us have heard of the Romanian ZX Spectrum clone known as the Cobra, let alone any efforts to replicate one. However, [Thomas Sowell] has achieved just that, and has shared the tale with us online.

The Cobra was named for its origins in the city of Brasov – hence, COmputer BRasov. The replica project was spawned for a simple reason. Given that sourcing an original Romanian Cobra would be difficult, [Thomas] realized that he could instead build his own, just as many Romanians did in the 1980s. He set about studying the best online resources about the Cobra, and got down to work.

The build started with board images sourced from, and these were used to get a PCB made. [Thomas] decided to only use vintage ICs sourced from the Eastern Bloc for authenticity’s sake, too. Most came from the former USSR, though some parts were of East German, Romanian, or Czechoslovakian manufacture. The project took place prior to the Russian invasion of Ukraine, so there weren’t any hassles shipping across borders.

With everything hooked up and the EEPROMs given a real Cobra ROM image, the computer burst into life. There were some hiccups, with an overheating video IC and some memory glitches. However, with some nifty tweaks and replacements subbed in, the computer came good. Other work involved adding a custom keyboard and modifying 3.5″ floppy drives to work with the system.

Overall, the build is a faithful tribute to what was an impressive piece of engineering from behind the Iron Curtain. [Thomas]’s work also embodies the DIY ethos behind many homebrew Cobra computers built back in the day.

If all this talk has got you curious about the full history of the Cobra and Romania’s underground computer movement, we have everything you’re looking for right here!

The Sinclair ZX Spectrum Turns 40

It’s an auspicious moment for retrocomputing fans, as it’s now four decades since the launch of the Sinclair ZX Spectrum. This budget British microcomputer was never the best of the bunch, but its runaway success and consequent huge software library made it the home computer to own in the UK. Here in 2022 it may live on only in 1980s nostalgia, but its legacy extends far beyond that as it provided an entire generation of tech-inclined youngsters with an affordable tool that would get them started on a lifetime of computing.

What Was 1982 Really Like?

Cover of Sincalir User, Sir Clive Sinclair as a magician
Sinclair User issue 3 captures the excitement surrounding the Spectrum launch.

There’s a popular meme among retro enthusiasts that the 1980s was a riot of colour, pixel artwork, synth music, and kitschy design. The reality was of growing up amid the shabby remnants of the 1970s with occasional glimpses of an exciting ’80s future. This was especially true for a tech-inclined early teen, as at the start of 1982 the home computer market had not yet reached its full mass-market potential. There were plenty of machines on offer but the exciting ones were the sole preserve of adults or kids with rich parents. Budget machines such as Sinclair’s ZX81 could give a taste of what was possible, but their technical limitations would soon become obvious to the experimenter.

1982 was going to change all that, with great excitement surrounding three machines. Here in the UK, the Acorn BBC Micro had been launched in December ’81, the Commodore 64 at the start of ’82, and here was Sinclair coming along with their answer in the form of first the rumour of a ZX82, and then the reality in the form of the Spectrum.

This new breed of machines all had a respectable quantity of memory, high-res (for the time!) colour graphics, and most importantly, sound. The BBC Micro was destined to be the school computer of choice and the 64 was the one everybody wanted, but the Spectrum was the machine you could reasonably expect to get if you managed to persuade your parents how educational it was going to be, because it was the cheapest at £125 (£470 in today’s money, or about $615). Continue reading “The Sinclair ZX Spectrum Turns 40”

A circuit board with a memory chip in a socket, and many memory chips in foam

Simple DRAM Tester Built With Spare Parts

Some of the most popular vintage computers are now more than forty years old, and their memory just ain’t how it used to be. Identifying bad memory chips can quickly become a chore, so [Jan Beta] spent some time putting together a cheap DRAM tester out of spare parts.

This little tester can be used with 4164 and 41256 DRAM memory chips. 4164 DRAM was used in several popular home computers throughout the 1970s and 1980s, including the Apple ][ series, Commodore 64, ZX Spectrum and many more. Likewise, the 41256 was used in the Commodore Amiga. These computers are incredibly popular in the vintage computing community, and its not uncommon to find bad memory in any of them.

With an Arduino at its core, this DRAM tester uses the most basic of electronic components, and any modest tinkerer should have pretty much everything in stock. The original project can be found here, including the Arduino code. Just pop the suspect chip into the ZIF socket, hit the reset switch, and wait for the LED – green is good, and red means it’s toast.

It’s a great sanity check for when you’re neck deep in suspect DRAM. A failed test is a sure sign that the chip is bad, however the tester does occasionally report a false pass. Not every issue can be identified with such a simple tester, however it’s great at weeding out the chips that are definitely dead.

If you’re not short on cash, then the Chip Tester Pro may be more to your liking, however it’s hard to beat the simplicity and thriftiness of building your own simple tester from spare parts. If you’re a little more adventurous, this in-circuit debugger could come in handy.

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When A Single Bit Was Enough, Into The Sound Of The ZX Spectrum

It’s normal for a computer in 2022 to come with a fully-featured sound card containing a complete synthesizer as well as high-quality PCM sound recording and playback. It’s referred to as a sound card after the way the hardware first appeared in the world of PCs, but in fact it’s now considered so essential as to be a built-in part of most mainboards. There was a time when computers boasted considerably less impressive sound hardware, and among the chorus of SIDs and AY chips of the perhaps the least well-featured was the original Sinclair ZX Spectrum. Its one-bit sound, a single line on an I/O port, is the subject of a thorough investigation from [Forgotten Computer]. It’s a long video which we’ve placed below the break, but for those with an interest in 8-bit music it should make a for a fascinating watch.

For Sir Clive Sinclair the 1-bit audio must have been welcome as it removed the need for an expensive sound chip and kept the Spectrum to its low price point, but on the face of it there was little more it could do than create simple beeps using Sinclair BASIC’s built-in BEEP command. The video gives us an in-depth look at how interleaving and PWM could be used to create much more complex sounds such as the illusion of multiple voices and even sampled sounds. In particular his technique of comparing the audio output with its corresponding pin on the Sinclair ULA shows the effect of the machine’s simple low-pass filter, though the music was often so close to the edge of what the interface could do that aliasing sounds are often very obvious.

As he demonstrates the various ingenious techniques that game and demo developers used to extract performance from such limited hardware that could even try to compete with the more sophisticated machines even at the same time as their code was running whatever was on the screen, it’s difficult not to come away with immense respect for their skills. If you’ve ever experimented with computer audio then you should try hardware this simple for yourself.

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A Redesigned ZX Spectrum Desktop Computer That Works Surprisingly Well

Retrocomputer enthusiasts will quite often be found pondering the great what ifs of their hobby. What if Commodore had had a half-way decent marketing division is a popular one, but the notoriously penny-pinching ways of Sinclair Research are also a plentiful source. What if Sinclair had won the competition for a computer in UK schools, not only the first time around when Acorn’s BBC Micro scooped the prize, but also what if they’d entered the fray once more in 1983 when there was another chance? [10p6] investigates this possibility, and comes up with a Spectrum desktop computer that you can see in the video below the break.

The first two-thirds of the video is devoted to renders which, while pretty to look at, offer nothing of substance. In the later part though we see a build, putting a Spectrum 48k board, Interface 1, and two Microdrives in a slimline case along with a power supply. Meanwhile a ZX rubber keyboard is mounted stand-alone on the end of a cable. It’s a computer that we know would have been an object of desire for many kids back in the day, and we agree with the video that it could have been integrated onto one board without the need for a separate Interface 1. We feel it’s inevitable though that Sinclair’s cost-cutting would have caused something to go astray and there would certainly have been only one Microdrive, even though we like that separate keyboard a lot.

They claim that the STLs will be available from a Facebook group, however unless you happen to have a set of Microdrives and an Interface 1 to go with your Spectrum that you’re prepared to butcher for the project we’re guessing that the chief interest lies in watching it unfold and that some of the ideas might translate to other platforms. Meanwhile if you’re interested in the Microdrive, we did a teardown on them last year.

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