One Man’s Tale Of EMC Compliance Testing

October 9, 2017 by Jenny List 31 Comments

If you turn over almost any electronic device, you should find all those compliance logos: CE, FCC, UL, TÜV, and friends. They mean that the device meets required standards set by a particular region or testing organisation, and is safe for you, the consumer.

Among those standards are those concerning EMC, or ElectroMagnetic Compatibility. These ensure that the device neither emits RF radiation such that it might interfere with anything in its surroundings, nor is it unusually susceptible to radiation from those surroundings. Achieving a pass in those tests is something of a black art, and it’s one that [Pero] has detailed his exposure to in the process of seeing a large 3-phase power supply through them. It’s a lengthy, and fascinating post.

He takes us through a basic though slightly redacted look at the device itself, before describing the testing process, and the EMC lab. These are fascinating places with expert staff who can really help, though they are extremely expensive to book time in. Since the test involves a mains power supply he describes the Line Impedance Stabilisation Network, or LISN, whose job is to safely filter away the RF component on the mains cable, and present a uniform impedance to the device.

In the end his device failed its test, and he was only able to achieve a pass with a bit of that black magic involving the RF compliance engineer’s secret weapons: copper tape and ferrite rings. [Pero] and his colleagues are going to have to redesign their shielding.

We’ve covered our visits to the EMC test lab here before.

A Converter You Won’t Have: PS/2 Mouse To Serial Mouse

October 9, 2017 by Jenny List 68 Comments

When did you last buy a mouse? Did it have a little adapter in the box? There was a time when if you bought a USB mouse, in the box was also an adapter to allow it to be used with the older PS/2 interface. And if you were to go back a few more years into the past, you’d have found when you bought a mouse with a PS/2 connector fitted, it may well have come with an adapter for a 9-pin RS232 serial port. Those mice from a decade or more ago would have contained the software to recognise the interface into which they were plugged, and emulate it accordingly. It is unlikely then that you could take a modern USB-only device and an unholy chain of USB-to-PS/2-to-serial adapters, and have it work as a serial mouse. Want to run Windows 3.1 on a 386DX? You need a serial mouse.

Happily, [matze525] has come along with a solution for those of you with a need to drive an ancient PC with a serial mouse. He’s created a PS/2 to RS232 mouse converter, and it takes the form of a little PCB with an AT90S2313P microcontroller to do the translation and an RS232 level converter chip.

It might sound like a rather unexpected device to produce, but we can see it fills an important niche. In the early 1990s mice were not the reliable optical devices we have today, instead they had nasty mechanical connections inside, or if you were extremely lucky, optical encoder wheels. The supply of still-reliable RS232 mice must therefore be dwindling, and if you have a Windows 3.1 PC to keep alive then we can see the ability to use a more modern pointing device has a lot going for it.

If you have one of those machines from that era that came with proprietary interfaces, maybe you can make use of a USB to quadrature converter.

Your Hard Disk As An Accidental Microphone

October 8, 2017 by Jenny List 30 Comments

We’re used to attaching peripherals to our computers, when we have a need for them to interact with the world around them. An Arduino Uno needs a shield to turn on the lights, for example. Just sometimes though there is the potential for unintended interaction between a computer and the real physical world which surrounds it, and it’s one of those moments that [Alfredo Ortega] has uncovered in his talk at the EKO Party conference in Buenos Aires. He demonstrates how a traditional spinning-rust computer hard disk interacts with vibration in its surroundings, and can either become a rudimentary microphone, or be compromised by sound at its resonant frequency (PDF).

It seems that you can measure the response time of the hard drive head during a read operation without requiring any privilege escalation. This timing varies with vibration, so can be used to reconstruct the sound that the drive is facing. Thus it becomes a microphone, albeit not a very good one with a profoundly bass-heavy response. He goes on to investigate the effect of sound on the drive, discovering that it has a resonant frequency at which the vibration causes it to be unreadable.

Sadly the talk itself appears not yet to be online, but given that previous years’ EKO talks are on YouTube it is likely that when the dust has settled you will be able to see it in full. Meanwhile he’s posted a video demonstration which we’ve posted below the break.

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Radio Tuning The Quicksilver Way

October 7, 2017 by Jenny List 58 Comments

Modern radios are often digital affairs, in which the frequency is derived from a stable crystal oscillator and varied through a microprocessor controlled frequency synthesiser. It won’t drift, and it’s exactly on the frequency dialed in. Older radios though relied on a tuned circuit, a combination of capacitor and inductor, for their frequency selection. If you were curious enough to peer inside — and we know you were — you’d have seen the moving vanes of a variable capacitor controlled by the tuning knob.

Of course, there is another way to adjust a tuned circuit: by changing the value of the inductor. Older car radios for instance moved a ferrite slug inside a coil to tune from station to station. But that method is not good enough for [David Mills]. Being in possession of some finely graduated syringes he decided to try liquid tuning by increasing the volume within the coil.

Solutions of salts made little difference, so he reached for some mercury. The result is an RF inductor wound round a syringe body, with a body of mercury whose position can be adjusted by the plunger. He measures the Q factor of the coil with air core or mercury core, and as the inductance decreases with more mercury, so does the Q.

We see home-made parts from time to time, and there’s nothing too special about permeability tuning. However, this unusual take on the matter makes this one rather special. We doubt we’ll see its like very often in the future.

Tape Cutting Bot Trims The Tedium

October 6, 2017 by Jenny List 12 Comments

If you have ever had to assemble a batch of electronic kits, you will know the tedious nature of cutting the tape containing your components. It’s easy enough to count four or five surface-mount resistors and snip them off with a pair of scissors once or twice, but when you are faced with repeating the task a hundred or more times, its allure begins to pale.

[Overflo] faced just such a problem when assembling hundreds of kits for a workshop at the upcoming 34C3 event in Germany. The solution? A tape-cutting robot, of course! (YouTube video, embedded below.)

At the heart of the machine is a pair of scissors operated by a stepper motor, snipping away at the component tape fed by another stepper. An infra-red light barrier sensor counts sprocket holes, and the whole is under the control of an Arduino Pro Mini. An especially clever trick is that the strip passes over a marker pen, allowing different components in a kit to be identified by a color code.

This isn’t the first such approach to this problem we’ve encountered, here’s one that cuts component tape with a laser.

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The Cambridge Z88 Lives! (As A USB Keyboard)

October 5, 2017 by Jenny List 19 Comments

What did [Clive Sinclair] do next? After his line of home computers including the iconic ZX Spectrum hit the buffers and was sold to Amstrad, that is. No longer in the home computer business, he released a portable computer for the business market. The Cambridge Z88 had a Z80 at its heart, a decent keyboard, a text-only LCD display, and ran for an impressively long time on a set of AA alkaline cells. It made a handy portable word-processor, or a serial terminal thanks to its rare-for-the-time RS232 port. And it’s that port that [Spencer Owen] made use of his Z88 in a modern setting, using it as a USB keyboard.

It’s a few years old, so he used a Minimus AVR microcontroller board to provide a serial-to-USB HID keyboard interface, and to keep things tidy he’s made a poor man’s enclosure for it using Sugru. It’s not quite an amazing hardware hack, but we’re featuring it simply for its use of a Z88. Retro computers used as keyboards are a common theme, but a Z88 is a particularly eclectic choice.

If you’re not British you may only know the name [Sinclair] through Brits on the Internet waxing lyrical about their ZX Spectrum computers, but in fact the man behind them is a serial electronics entrepreneur whose career has continued since the 1960s and has touched fields as diverse as portable television and bicycles aside from the computers he is best known for. Often his products took technology to the limit of practicality, but they were and continue to be the ones to watch. If [Clive Sinclair] is working in a field his products may not always hit the right note when released, but you can guarantee that you’ll be buying the same thing from the big boys within a few years. The Z88 is a classic Sinclair product, a little before its time in 1988 and pushing the technology a little too far, but delivering a truly portable and capable computer with a meaningful battery life a couple of decades before you’d find the same attributes from all but a few other niche manufacturers.

Not had enough USB HID devices? How about a Morse key? And if [Spencer] rings a bell, he’s the originator of the RC2014 retrocomputer we reviewed last year.

A 3D Printer Alone Doesn’t Make A Hackspace

October 5, 2017 by Jenny List 75 Comments

There was a time when hackspaces were few and far between — legendary environments that you’d read about online, where amazing projects were made by people who had come together to form communities of creative technology enthusiasts. Of course, they were always in places far afield, California, or Germany, never in provincial England where I call home. Eventually our movement spread its tentacles into the county towns, and several years later with a stint as a hackspace director behind me I sense that it is on the cusp of escaping its underground roots. Every month seems to bring news of yet another organisation wanting to open a makerspace of their own, be they universities, co-working spaces, enterprise centres, libraries, or even banks. It’s evident that our movement has attracted an aura of edginess when it comes to getting things done, and that these entities are anxious to secure a little piece of that for themselves.

So within a few miles of most hackspaces will be several places where you can find a 3D printer, maybe a vinyl cutter, a CAD workstation, and a soldering iron. There will be a fancy hipster coffee machine and some futuristic furniture, and probably some kind of enclosed meeting pod of dubious design. All of which can no doubt be viewed through a glass wall, so that people in suits can watch all that raw #innovation sizzling away.

Viewed from within the movement, it’s easy to see all this activity on the edges of the world of making as a threat. A struggling community organisation survives on its wits alone, it doesn’t have a multi-million pound (or dollar) university or investor behind it. Its tools are hard-won and patched up, and its coffee machine is a battered electric kettle and a jar of supermarket instant coffee. When it comes to gleaming innovation spaces, a group of assorted makers simply can’t compete. Surely the arrival of these spaces will tempt members away, and the hackspace will inevitably wither, and die.

It’s worth taking a step back at this point, and considering what makes a hackspace. Specifically, what makes a good hackspace.

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