Building A Replica Of An Obscure Romanian Computer

September 29, 2022 by Lewin Day 5 Comments

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 Cobrasov.com, 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

April 26, 2022 by Jenny List 68 Comments

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

February 27, 2022 by Chris Wilkinson 13 Comments

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.

Continue reading “Simple DRAM Tester Built With Spare Parts” →

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

January 20, 2022 by Jenny List 8 Comments

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.

Continue reading “When A Single Bit Was Enough, Into The Sound Of The ZX Spectrum” →

A Redesigned ZX Spectrum Desktop Computer That Works Surprisingly Well

October 17, 2021 by Jenny List 20 Comments

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.

Continue reading “A Redesigned ZX Spectrum Desktop Computer That Works Surprisingly Well” →

How To Get Into Computer Game Development In 1982

September 26, 2021 by Jenny List 16 Comments

If you are a follower of retrocomputing, perhaps you caught the interactive Black Mirror episode Bandersnatch when it came out on Netflix. Its portrayal of a young British bedroom coder finding his way into the home computer games industry of the early 1980s was of course fictional and dramatised, but for those interested in a real-life parallel without the protagonist succumbing to an obsession with supernatural book there’s a recent epic Twitter thread charting an industry veteran’s path into the business.

An acceptance letter like this from Artic Software would have been the wildest dream of any early-80s bedroom coder.

[Shahid Kamal Ahmad] now has an impressive portfolio spanning his his nearly four decades at the forefront of gaming, but his story starts in 1982 as a diabetic British Pakistani teenager from a not-privileged background in London writing in BASIC on his Atari 400. His BASIC games are good, but not good enough to gain acceptance from a publisher, so he sells his prized BMX bicycle to buy books on Atari 6502 assembler, a coffee percolator, and for curiosity’s sake, [Rodnay Zaks’] Programming the Z80. An obsessive three-month learning of 6502 programming and the Atari’s architecture ensues, and his game Storm in a Teacup sells to Artic Software. He’s a professional game developer.

We follow him through a couple more projects until he arrives at Software Projects in Liverpool to try to sell his game Faces of Haarne, which he secures publishing for but also lands the opportunity of a lifetime. Jet Set Willy is the smash hit of the year on the ZX Spectrum, and they urgently need a Commodore 64 port. Can he do it in four weeks, with a bonus if he manages three? The subsequent descent into high-pressure assembly coding and learning the quirks between two completely different 8-bit architectures is an epic in itself, but he manages it in just a shade over the three weeks and they pay him the bonus anyway. His career in the computer game industry is cemented.

Through this tale the reminders of 1980s Britain are everywhere, far from bring a retro paradise it was a place hollowed out by industrial decline, with very little for those at the bottom of society to be optimistic about. His descriptions of casual racism are hard-hitting, but the group of computer-addicted friends at school is probably something that all teenagers of the era whose interests lay in that direction can relate to. The real hero of the story is probably his mother, who somehow found the resources for that Atari 400 and who provided him with much-needed support and encouragement.

This thread captures a unique and never-to-be repeated era in which a teenager could master an emerging technology and make a living in it without an expensive education. Like Bil Herd’s description of his career at Commodore in the same period, it’s well worth a read.

Farewell Sir Clive Sinclair; Inspired A Generation Of Engineers

September 16, 2021 by Jenny List 74 Comments

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.

Continue reading “Farewell Sir Clive Sinclair; Inspired A Generation Of Engineers” →