FPGA Raises Component Video From A Sinclair ZX Spectrum

An abiding memory of the early-80s heyday of 8-bit computing for many is operating their computer from the carpet in front of the family TV. While the kids in the computer adverts had parents who bought them a portable colour telly on which to play Jet Set Willy, the average kid had used up all the Christmas present money on the computer itself. The cable would have been an RF connection to the TV antenna socket, and the picture quality? At the time we thought it was amazing because we didn’t know any different, but with the benefit of nearly 40 years’ hindsight, it was awful.

For ZX Spectrum owners in 2020 a standard modification is to bring out a composite video signal, but [c0pperdragon] has gone a step or two beyond that with a component video interface. And this isn’t a mod in which the signals are lifted from the Spectrum’s colour encoder circuitry, instead it uses an FPGA hooked directly to the ULA chip to generate the component video itself.

The Altera chip sits on a little PCB designed to occupy the footprint of the original Astec modulator, and sports a neat bundle of wires hooked up to the various Spectrum signals it needs. There are a couple of jumpers to select the output type and resolution, it supports YPbPr or RGsB outputs and both 288p and 576p. If you think perhaps it looks a little familiar, that’s because it’s the sister project of an earlier board for the Commodore 64. So if you have a Spectrum and are annoyed by UHF and PAL, perhaps it’s worth a look.

The Primordial Sinclair ZX Spectrum Emerges From The Cupboard

The Centre for Computing History in Cambridge, UK, receive many donations from which they can enrich their collection and museum displays. Many are interesting but mundane, but the subject of their latest video is far from that. The wire-wrapped prototype board they reveal with a flourish from beneath a folded antistatic mat is no ordinary computer, because it is the prototype Sinclair ZX Spectrum.

It came to the museum from Nine Tiles, a local consultancy firm that had been contracted by Sinclair Research in the early 1980s to produce the BASIC ROM that would run on the replacement for their popular ZX81 home microcomputer. The write-up and the video we’ve placed below the break give some detail on the history of the ROM project, the pressures from Sinclair’s legendary cost-cutting, and the decision to ship with an unfinished ROM version meaning that later peripherals had to carry shadow ROMs with updated routines.

The board itself is a standard wire-wrap protoboard with all the major Spectrum components there in some form.  This is a 16k model, there is no expansion connector, and the layout is back-to-front to that of the final machine. The ULA chip is a pre-production item in a ceramic package, and the keyboard is attached through a D connector. Decent quality key switches make a stark contrast to the rubber keys and membrane that Spectrum owners would later mash to pieces playing Daley Thompson’s Decathlon.

This machine is a remarkable artifact, and we should all be indebted to Nine Tiles for ensuring that it is preserved for those with an interest in computing to study and enjoy. It may not look like much, but that protoboard had a hand in launching a huge number of people’s careers in technology, and we suspect that some of those people will be Hackaday readers. We’ll certainly be dropping in to see it next time we’re in Cambridge.

If you haven’t been to the Centre for Computing History yet, we suggest you take a look at our review from a couple of years ago. And if prototype home computers are your thing, this certainly isn’t the first to grace these pages.

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Bringing Back A Spectrum’s Rails

The Sinclair ZX Spectrum was to most Brits the computer to own in the early 1980s, it might not have had all the hardware features of its more expensive competitors but it had the software library that they lacked. Games came out for the Spectrum first, and then other platforms got them later. If you didn’t have a rubber keyboard and a Sinclair logo, you were nothing in the playground circa 1984. That low price though meant that in true Sinclair tradition a number of corners had been cut in the little micro’s design. Most notably in its power supply, all the various rails required by the memory chips came from a rather insubstantial single-transistor oscillator that is probably the most common point of failure for these classic machines.

[Tynemouth Software] had an Issue 2 Spectrum with a missing -5V rail, and has detailed both the power supply circuit used on these machines and the process of faultfinding and repairing this one. A single transistor oscillator drives a little ferrite-spool transformer from which the various supplies are rectified and filtered. Similar circuits appear in multiple generations of Sinclair hardware, where we might nowadays use a little switching regulator chip.

We’re taken through the various stages of faultfinding this particular circuit, and the culprit is found to be a faulty Zener diode. It’s certainly not the last dead Spectrum that will cross an enthusiast’s bench, but at least in this case, the fault was less obtuse than they sometimes can be in this much-loved but sometimes frustrating machine.

Sinclair enthusiasts might also appreciate the great man’s earliest work.

Someone’s Made The Laptop Clive Sinclair Never Built

The Sinclair ZX Spectrum was one of the big players in the 8-bit home computing scene of the 1980s, and decades later is sports one of the most active of all the retrocomputing communities. There is a thriving demo scene on the platform, there are new games being released, and there is even new Spectrum hardware coming to market.

One of the most interesting pieces of hardware is the ZX Spectrum Next, a Spectrum motherboard with the original hardware and many enhancements implemented on an FPGA. It has an array of modern interfaces, a megabyte of RAM compared to the 48k of the most common original, and a port allowing the connection of a Raspberry Pi Zero for off-board processing. Coupled with a rather attractive case from the designer of the original Sinclair model, and it has become something of an object of desire. But it’s still an all-in-one a desktop unit like the original, they haven’t made a portable. [Dan Birch has changed all that, with his extremely well designed Spectrum Next laptop.

He started with a beautiful CAD design for a case redolent of the 1990s HP Omnbook style of laptop, but with some Spectrum Next styling cues. This was sent to Shapeways for printing, and came back looking particularly well-built. Into the case went an LCD panel and controller for the Next’s HDMI port, a Raspberry Pi, a USB hub, a USB to PS/2 converter, and a slimline USB keyboard. Unfortunately there does not seem to be a battery included, though we’re sure that with a bit of ingenuity some space could be found for one.

The result is about as good a Spectrum laptop as it might be possible to create, and certainly as good as what might have been made by Sinclair or Amstrad had somehow the 8-bit micro survived into an alternative fantasy version of the 1990s with market conditions to put it into the form factor of a high-end compact laptop. The case design would do any home-made laptop design proud as a basis, we can only urge him to consider releasing some files.

There is a video of the machine in action, which we’ve placed below the break.

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