TechyMagThings

A pyrotechnic charge is set off by passing a high voltage through a filament within it, melting the filament and igniting the charge. We could think of a variety of circuits that could do this, but perhaps we wouldn’t have come up with [Michał Słomkowski]’s solution. He’s used the ringer crank generator from an old military field telephone. It’s an old project he’s shared with us due to its recent republishing on his website.

The basic principle is simple enough, winding the generator charges a capacitor bank through a bridge rectifier. Then a thyristor is used as the trigger device, dumping the contents of the capacitor into the filament. But the full circuit has a couple of refinements. There’s a charge indicator circuit using a couple of Zener diodes and an LED, and a filament tester which passes a non-triggering current through the filament from a 9 volt battery. We like the use of an over-the-top high-current thyristor, no doubt what he had in his junk box.

Perhaps it’s a symbol of how far technology has moved, that today it’s surprisingly rare to find a bridge rectifier or a thyristor, and building this device today would involve a microcontroller and probably an AliExpress inverter module as a matter of course.

Meanwhile, should field telephones interest you, we’ve been there before.

[Matt Lenhard] has an interesting writeup explaining exactly how fraudsters offer access to cutting-edge AI models at a tenth of the price. Perhaps unsurprisingly, the secret is to get tokens for free from anywhere they can and by any means necessary. Then wrap them in a pretty relay API, and sell access to it.

Relaying tokens is not by itself a shady practice. That distinction belongs to services that obtain tokens fraudulently, opening the door to selling them at rates far below market value. This practice is widespread and profitable, in part because the abuse is so hard to pin down and stop.

One source of tokens is free credits on new accounts. New accounts are spooled up as fast as possible, hammered until they’re empty, then it’s done all over again. Another method is to sign up as pay-after, possibly with a stolen card, and simply ensure the account has no valid payment method once the bill comes due. Or set up a temporary card, pay some minimum up front and consume as much as possible, then initiate a chargeback. It doesn’t matter if individually each of these doesn’t amount to much before they get flagged, because it’s being leveraged relentlessly on a massive scale by automated systems.

There are the shadier methods, too. Fraudsters don’t just target providers directly. Consumer software products with AI features get reverse-engineered, then the back ends hammered for all they are worth. Poorly-coded support chatbots can be highjacked into serving fraudsters’ traffic instead of just their own. It doesn’t actually matter where the tokens come from, after all. As long as the fraudsters are obtaining them for free (or at least below their costs) then it’s profit.

That last point is one [Matt] zeroes in on with advice on how to mitigate this abuse. He goes into detail in his writeup but what it comes down to is recognizing that it’s a numbers game. Fraudsters depend entirely on obtaining tokens for free, or nearly free. So just like using an AI to keep phone scammers tied up, anything that raises friction increases the fraudster’s costs, in turn encouraging them to find an easier target.

Fluid simulations are one of the “killer apps” of high-performance computing, but if you can’t afford the performance, they can take a depressingly long time to run. Depending on your use case, as long as you keep the Reynold’s number in mind– or are just looking for a qualitative look at pretty flows–you might be able to get away with purely-practical simulations using rheoscopic fluid, as [Visual Thinker] demonstrates in a recent video.

The fluid, as you can guess from the name, lets you scope out rheos— that’s flow, for those of you didn’t take Greek. Making it is as simple as you could ask for: get some mica flakes, which are readily available to add ‘sparkle’ to cosmetics, and mix with water and a drop of soap. The soap isn’t always necessary, but depending on your mica it helps keep it in suspension and avoid clumping– [Visual Thinker] found it helped him a good deal. Being flat plates of reflective material, the mica flakes catch the light and sparkle beautifully– and since they align with the fluid shear, they show you exactly what’s going on in your ‘simulation’.

[Visual Thinker] isn’t starting with serious simulations; the first thing he tries is essentially a toy that lets him see fluid flow around a Benchy by sticking magnets in it and using it to move a cross-section of its hull though a thin layer of fluid sandwitched betwixt pieces of laser-cut acrylic. We don’t call it a toy to disparage it, though– we totally want one. [Visual] mentions the idea of a coffee table combining the concept with the kind of underslung mechanism we see in sand drawing tables, which sounds dangerously hypnotic. If any of you build one, please try and tear your eyes away long enough to let us know.

He has another beautiful piece that make the video worth watching: a wind-tunnel, again made of laser-cut acrylic and printed parts. With careful consideration of the scale and flow speeds, that one might actually prove useful– and even if it doesn’t, it’s pretty enough that it doesn’t really matter. Beauty has its own utility sometimes.

Most wind tunnels we see around here use actual wind, but rheoscopic fluid was invented for this sort of thing, even if it does make for pretty baubles.

As software updates cease for operating systems, they eventually begin to lose access to parts of the LAN and internet due to out of date encryption features, as well as the inability to handle file sharing protocols like SBM3, which is somewhat of a necessity if you have e.g. a NAS on the LAN. Such too was the case with [watermark_hd]’s 20-year old PowerPC Macs and their installations of OS X Tiger and Leopard.

Cue Aqualink, a native SMB3 client for these older OS X versions that uses [Ronnie Sahlberg]’s libsmb2 server/client library for SMB2 and SBM3. The source code can be found over on GitHub, along with a Japanese translation. By using a local WebDAV server Tiger’s built-in mount_webdav feature can be used to mount these remote volumes.

While you can often still use SMB1 even on modern Windows and Linux/BSD via Samba, allowing even retro systems like these PowerMacs to speak SMB3 is at least a great boost for network security, even if the aforementioned encryption shortcomings mean that you cannot quite run encrypted file shares yet.

Although OS X eventually began to adopt modern SMB versions, some of us may remember how incredibly buggy they were, to the point that us OS X users often had to fall back to CIFS (SMB 1.0), so this is another potential use for this Aqualink application.

Hypoesthesia, more commonly referred to as numbness, is one of the more distressing ailments that can affect us humans, primarily because it reminds us of just how much we rely on our sensation of touch in daily life. From experiencing the world around us, handling objects, noticing when you just bumped into that side table again and the comforting hug of a fellow human being, touch is perhaps the most important of our senses.

In that regard the recently published research by [Haofeng Chen] et al. on giving robots a skin that can experience touch seems rather important as it would give especially humanoid robots a more natural way to interact with their environment, using feedback from touch.

One of the essential parts of biological skin is that it is teeming with sensors, at a density level that provides excellent resolution as required, down to sensing e.g. small surface imperfections with one’s finger tips. Replicating this with an artificial skin for robotics has always been a problem, due to the wiring and/or reliability nightmare this poses with typical approaches. Instead of focusing on many individual sensors, [Chen] et al. focused on effectively creating the equivalent of a resistive touch screen in skin format.

The basic principle underlying the demonstrated artificial skin is electrical impedance tomography (EIT), which uses surface electrodes to form a tomographic image based on measures electrical resistivity. Core here is the flexible TPU layer with electrodes and the conductive fabric patches attached to the top TPU cover layer. The electrodes continuously measure the resistivity, with disturbances from those patches due to touch events on the cover layer altering these values. From this EIT can be used to reconstruct the location and strength of the touch event.

The results from the created prototypes were promising, with only 16 electrodes sufficing to create a fairly accurate pressure map. Hardware-wise this makes it thus quite uncomplicated, with the characterization of the TPU porosity and such along with the EIT algorithm (provided in the paper) probably being the biggest hurdles for hobbyist recreations.

The AM29000 series of processors were AMD’s entry into the world of super-fast next-generation silicon of the late 1980s. It was a time when ARM was still a niche architecture in a British educational computer, the 68000 series was still a major player, and it was by no means certain that the x86 would maintain its position. It therefore wasn’t an unreasonable choice for someone building a high performance computer at the time, which is what [Oscar Toledo G.] and his father did. If that wasn’t enough, he went on to write an operating system for it in AM29000 assembly, complete with a GUI, a C compiler, and an up-to-date web browser for the late 1990s. The story makes for an engaging read.

It’s written across two parts, with the first looking at the computer and the early software development, and the second at the C compiler and web browser. It’s a tale of epic mastery of the machine, and something we remember ourselves, piecing together knowledge in a time before the Internet placed it all at our fingertips. Tales such as hand porting — we can’t really say compiling — C code into AM29000 machine code are completely next-level. You have to read these two write-ups, and there’s even an in-browser emulator should you want to try it.

Meanwhile, in case you think something is a little familiar here, he’s the same person who brought us a Transputer in the browser.

It’s likely that even those of us who have never picked up a guitar in our lives will recognize the sound of an electric guitar with a fuzz box effects pedal. The raspy distorted sound has been at the heart of so many very well known recordings. Behind it is a distortion circuit, or as [Bill Jehle’s Mad Scientist Guitar Lab] is here to tell us, eight different circuit topologies.

The result is a fascinating trip through the evolution of rock music through the 1960s, as he examines circuits from simple diode clippers through to frequency doublers and phase shifters. He’s provided a playlist as an accompaniment so you can even have an immediate listen to each sound. It’ll mess up our YouTube recommendations, but worth it for the informative journey.

It’s also a window into a lost period in electronics where all they practically had was the transistor, so each device had to put in the maximum work for a living. Designing circuits like these called for intimate knowledge of the device characteristics, and just how they could be safely exceeded. The video is below the break, and well worth a watch.

If clever transistor music circuits interest you, you’ll love the flawed devices that gave the Roland 808 its sound.