Even Amstrad Spectrums Need Their Bugs Fixing

April 6, 2023 by Jenny List 2 Comments

The history of the Sinclair ZX Spectrum is one that mirrors the fortunes of the British home computer industry, one of an early 8-bit boom followed by a sharp decline as manufacturers failed to capitalise on the next generation of 16-bit machines. The grey ZX Spectrum on [Keri Szafir]’s bench is one that encapsulates that decline perfectly, being one of the first models produced under the ownership of Amstrad after Sir Clive’s company foundered. Amstrad made many improvements to the Spectrum, but as she demonstrates, there are still some fixes needed.

The machine came her way because of a hum from the tape deck circuitry. The read amplifier was picking up electrical noise, and she fixed it without mods to the circuit but with the simple expedient of powering the analogue circuit from the tape motor switch so it only works when needed.

Beyond that, this machine demonstrates another ’80s innovation, the SCART/Peritel AV connector. These first appeared on early-80s French TV sets, but by the later half of the decade had made it to the UK where Amstrad included support for an adapter cable from the DIN socket on the back of their Spectrum. Even then they didn’t get it quite right, and she modifies some links on the board to better support it.

Sinclair were famous for on-board bodges, and even in new ownership continued. There’s a reversed transistor and at least one bodged-on component, but of course, it wouldn’t be a Spectrum without bugs, would it!

Continue reading “Even Amstrad Spectrums Need Their Bugs Fixing” →

Digitizing Sound On An Unmodified Sinclair ZX81

March 25, 2023 by Jenny List 27 Comments

Whatever the first computer you used to manipulate digital audio was, the chances are it came with dedicated sound hardware that could play, and probably record, digitized audio. Perhaps it might have been a Commodore Amiga, or maybe a PC with a Sound Blaster. If you happen to be [NICKMANN] though, you can lay claim to the honor of doing so on a machine with no such hardware, because he managed it on an unmodified Sinclair ZX81.

For those of you unfamiliar with the ZX, it embodied Clive Sinclair’s usual blend of inflated promises on minimal hardware and came with the very minimum required to generate a black-and-white TV picture from a Zilog Z80 microprocessor. All it had in the way of built-in expansion was a cassette interface, 1-bit read and write ports exposed as 3.5 mm jacks on its side. It’s these that in an impressive feat of hackery he managed to use as a 1-bit sampler with some Z80 assembler code, capturing a few seconds of exceptionally low quality audio in an ’81 with the plug-in 16k RAM upgrade.

From 2023 of course, it’s about as awful as audio sampling gets, but in 1980s terms it’s pulling off an almost impossible feat that when we tried it with a 1-bit PC speaker a few years later, we didn’t succeed at. We’re impressed.

The ’81 may be one of the simplest of the 8-bit crop, but in its day it set many a future software developer on their career path. It’s still a machine that appears here today, from time to time.

Building A Sinclair ZX81 In 2022 With All New Parts

November 10, 2022 by Jenny List 50 Comments

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.

Continue reading “Building A Sinclair ZX81 In 2022 With All New Parts” →

Loki Is Part Cyberdeck, Part Sinclair Spectrum, And Pretty Tricky

August 11, 2022 by Dan Maloney 5 Comments

You’ve got to watch out for Loki — he’s a trickster, after all, and he might make you think this semi-cyberdeck mash-up machine is named after him, when the backstory on this build is more interesting than anything in the current Marvel scene.

According to [Steve Anderson], Loki was the name of a mocked-up machine that Sinclair teased in the mid-1980s as a competitor for the Amiga. [Steve] coveted the vaporware machine and never quite got over it, but rather than pine for something that never existed, he created his own Loki. He only loosely qualifies the machine as a cyberdeck — it has some features of the genre, like a Raspberry Pi and a cast-off iPad screen for a display, but isn’t really intended to be as portable as a real cyberdeck. To scratch his Sinclair itch, the machine also includes a ZX Uno, which is an FPGA emulator of the Sinclair Spectrum. The keyboard is hand-wired using mechanical switches, and is backed up by a Pico running custom software so it can talk both USB and PS/2.

[Steve] has much more detail on Loki and his other cyberdeck builds over on his blog, which you should probably check out. Somewhat surprisingly, it doesn’t look like he’s entered Loki in our new Cyberdeck Contest that just launched. Hopefully that’s just an oversight.

Reviving A 1974 Sinclair Scientific Calculator

May 8, 2022 by Jenny List 6 Comments

When a treasure of retrotechnology fails to work, the natural next step is to have a go at repairing it. [Adam Wilson] found himself in this position when he acquired a 1974 Sinclair Cambridge Scientific calculator, and his progress with the device makes for an interesting read.

First up is something of value to all old Sinclair enthusiasts, he’s found a solution to the original battery connectors being prone to failure. A couple of parts stocked by RS can be used as replacements, which should save quite a lot of Sinclairs with crusty connectors.

Saving the connectors should have fixed the calculator, but only served to reveal that it had an electronic fault. Some detective work traced this to the power supply, which is a small switching circuit. The 1974 chip and associated coil had both failed, which rather drew the project to a halt. A second repair-or-spares Cambridge Scientific was sourced, and by good luck it happened to have a working PCB. So [Adam] got a working calculator, and we hope he’ll succumb to the temptation to shoehorn in a PSU from 2022 to get the other one working.

Anyone curious about this slightly unusual calculator should take a look at our teardown of one.

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 Sinclair ZX81 Clone Still Has The Power To Fascinate

March 15, 2022 by Jenny List 26 Comments

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.