Bringing Back A Spectrum’s Rails

June 2, 2018 by Jenny List 10 Comments

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.

Clive Sinclair, The Other Author

April 12, 2018 by Jenny List 51 Comments

A reasonable selection of the Hackaday readership will have had their first experiences of computing on an 8-bit machine in a black case, with the word “Sinclair” on it. Even if you haven’t work with one of these machines you probably know that the man behind them was the sometimes colourful inventor Clive (now Sir Clive) Sinclair.

The finest in 1950s graphic design, applied to electronics books.

He was the founder of an electronics company that promised big results from its relatively inexpensive electronic products. Radio receivers that could fit in a matchbox, transistorised component stereo systems, miniature televisions, and affordable calculators had all received the Sinclair treatment from the early-1960s onwards. But it was towards the end of the 1970s that one of his companies produced its first microcomputer.

At the end of the 1950s, when the teenage Sinclair was already a prolific producer of electronics and in the early stages of starting his own electronics business, he took the entirely understandable route for a cash-strapped engineer and entrepreneur and began writing for a living. He wrote for electronics and radio magazines, later becoming assistant editor of the trade magazine Instrument Practice, and wrote electronic project books for Bernard’s Radio Manuals, and Bernard Babani Publishing. It is this period of his career that has caught our eye today, not simply for the famous association of the Sinclair name, but for the fascinating window his work gives us into the state of electronics at the time.

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Someone’s Made The Laptop Clive Sinclair Never Built

January 21, 2018 by Jenny List 42 Comments

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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Romania’s 1980s Illicit DIY Computer Movement

November 7, 2017 by Steven Dufresne 51 Comments

In Western countries in the early 1980s, there was plenty of choice if you wanted an affordable computer: Apple, Atari, TRS-80, Commodore and Sinclair to name a few. But in communist-ruled Romania, mainly you’d find clones of the British Sinclair ZX Spectrum, an 8-bit computer built around the Zilog Z80A, using a CRT TV as display and a BASIC interpreter as UI. The Cobra was one such Romanian Sinclair clone. However, most people couldn’t afford even that, which lead to hackers building their own versions of the Cobra.

Making these clones was highly illegal. But that didn’t stop students at the Politehnica University of Bucharest. They made them for themselves, family and friends, and even sold them at well under market price. To keep people from building radio transmitters, the Communist government kept electronics prices high. So instead, parts smuggled from factories could be paid for with a pack of cigarettes.

Look inside an old Apple II and you’ll see a sea of chips accomplishing what can be done with only a few today. The Cobra clones looked much the same, but with even more chips. Using whatever they could get their hands on, the students would make 30 chips do the job of an elusive $10 chip. No two computers were necessarily alike. Even the keyboards were hacked together, sometimes using keys designed for mainframe computers but with faults from the molding process. These were cleaned up and new letters put on. The results are awesome hacks which fit right in here on Hackaday.

Sadly though, it often takes harsh necessity to make a culture where these inspiring hacks thrive in the mainstream. Another such country which we’ve reported on this happening in is Cuba, which found the necessity first when the U.S. left Cuba in the 60s and again when the Soviet Union collapsed in the 90s, reducing the availability of many factory produced items needed for daily life, and creating a DIY society.

Build A Calculator, 1974 Style

November 6, 2017 by Jenny List 10 Comments

Last month we touched upon the world of 1970s calculators with a teardown of a vintage Sinclair, and in the follow-up were sent an interesting link: a review of a classic Sinclair calculator kit from [John Boxall]. It’s a few years old now, from 2013, but since it passed us by at the time and there was clearly some interest in our recent teardown, it’s presented here for your interest.

It seems odd in 2017 that a calculator might be sold as a kit, but when you consider that in the early 1970s it would have represented an extremely expensive luxury purchase it makes some sense that electronics enthusiasts who were handy with a soldering iron might consider the cost saving of self-assembly to be worthwhile. The £24.95 price tag sounds pretty reasonable but translates to nearly £245 ($320) in today’s terms so was hardly cheap. The calculator in question is a Sinclair Cambridge, the arithmetic-only predecessor to the Sinclair Scientific we tore down, and judging by the date code on its display driver chip it dates from September 1974.

As a rare eBay find that had sat in storage for so long it was clear that some of the parts had suffered a little during the intervening years. The discrete components were replaced with modern equivalents, including a missing 1N914 diode, and the display was secured in its flush-fitting well in the board with wire links. The General Instrument calculator chip differs from the Texas Instruments part used in the Scientific, but otherwise the two calculators share many similarities. A full set of the notoriously fragile Sinclair battery clips are in place, with luck they’ll resist the urge to snap. A particularly neat touch is the inclusion of a length of solder and some solder wick, what seems straightforward to eyes used to surface-mount must have been impossibly fiddly to those brought up soldering tube bases.

The build raises an interesting question: is it sacrilege to take a rare survivor like this kit, and assemble it? Would you do it? We’d hesitate, maybe. But having done so it makes for a fascinating extra look at a Sinclair Cambridge, so is definitely worth a read. If you want to see the calculator in action he’s posted a video which we’ve put below the break, and if you need more detail including full-resolution pictures of the kit manual, he’s put up a Flickr gallery.

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Teardown With A Twist: 1975 Sinclair Scientific Calculator

November 1, 2017 by Jenny List 78 Comments

When writing a recent piece about Reverse Polish Notation, or RPN, as a hook for my writing I retrieved my Sinclair Scientific calculator from storage. This was an important model in the genesis of the scientific calculator, not for being either a trailblazer or even for being especially good, but for the interesting manner of its operation and that it was one of the first scientific calculators at an affordable price.

I bought the calculator in a 1980s rummage sale, bodged its broken battery clip to bring it to life, and had it on my bench for a few years. Even in the early 1990s (and even if you didn’t use it), having a retro calculator on your bench gave you a bit of street cred. But then as life moved around me it went into that storage box, and until the RPN article that’s where it stayed. Finding it was a significant task, to locate something about the size of a candy bar in the storage box it had inhabited for two decades, among a slightly chaotic brace of shelves full of similar boxes.

The Sinclair's clean design still looks good four decades later. — The Sinclair’s clean design still looks good four decades later.

Looking at it though as an adult, it becomes obvious that this is an interesting machine in its own right, and one that deserves a closer examination. What follows will not be the only teardown of a Sinclair Scientific on the web, after all nobody could match [Ken Shirriff]’s examination of the internals of its chip, but it should provide an insight into the calculator’s construction, and plenty of satisfying pictures for lovers of 1970s consumer electronics.

The Sinclair is protected by a rigid black plastic case, meaning that it has survived the decades well. On the inside of the case is a crib sheet for its RPN syntax and scientific functions, an invaluable aid when it comes to performing any calculations.

It shares the same external design as the earlier Sinclair Cambridge, a more humble arithmetic calculator, but where the Cambridge’s plastic is black, on the Scientific it is white. The LED display sits behind a purple-tinted window, and the blue-and-black keyboard occupies the lower two-thirds of the front panel. At 50 x 111 x 16 mm it is a true pocket calculator, with an elegance many of its contemporaries failed to achieve and which is certainly not matched by most recent calculators. Good industrial design does not age, and while the Sinclair’s design makes it visibly a product of the early 1970s space-age aesthetic it is nevertheless an attractive item in its own right.

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One Chip, Sixteen Times The RAM

October 20, 2017 by Jenny List 16 Comments

Have you ever upgraded your computer’s memory sixteen-fold, with a single chip? Tynemouth Software did for a classic Sinclair micro.

For owners of home computers in the early 1980s, one of the most important selling points was how much RAM their device would have. Sometimes though there just wasn’t much choice but to live with what you could afford, so buyers of Sinclair’s budget ZX81 computer had to put up with only 1 kiB of memory. The system bytes took up (by this writer’s memory) around 300 bytes, so user programs were left with only around 700 bytes for their BASIC code. They were aided by Sinclair’s BASIC keywords stored as single bytes, but still that was a limit that imposed coding economy over verbosity.

Sinclair sold a 16 kiB upgrade, the so-called “Rampack”, which located on the ’81’s edge connector and was notorious for being susceptible to the slightest vibration. Meanwhile the mainboard had provision for a 2 kiB chip as a drop-in that was never sold in the UK, and enterprising users could fit larger capacities with soldered combinations of other chips piggybacking the original. And this is what the Tynemouth people have done, they’ve replaced their machine’s dual 1 kiB x 4 chips with a single 62256, and with a bit of pin-bending they’ve managed to do it without the track-cutting that normally accompanies this mod.

Adding chips to a 36-year-old home computer for which there are plenty of available Rampacks might seem a bit of a niche, but in doing so they’ve made a standalone ’81 that’s just a little bit more useable. They’ve also brought a few other components up-to-date, with a composite video mod, switching regulator, and heatsink for the rare ULA chip. If you are of a Certain Generation, it might just bring a tear to your eye to see a ZX81 being given some love.

Did you lose your ZX81 along the way? How about emulating one in mbed?