Misc Hacks

4188 Articles

The Bose headphone plug in question, with reverse-engineered schematic of the filter overlaid.

This 3.5mm Cable Distorts Signals, Hides Audio-Filtering Circuit

April 10, 2022 by 57 Comments

[Avian]’s dad got a new ham radio transceiver with a 3.5 mm jack, and his pile-of-cables got him a headphone cable from Bose headphones. He built a DB9 to 3.5 mm adapter with that one – and it failed to let data through, outputting distorted garbage of a waveform instead. With a function generator and an oscilloscope, [Avian] plotted the frequency response of the cable, which turned out to be quite far from a straight line. What was up?

Taking the connector apart was a tricky job. A combination of blunt force and a nail polish remover soak didn’t quite get them all the way, so [Avian] continued to apply blunt force and took the jack apart with minimal casualties. Turned out that there was more to the 3.5 mm plug indeed — a whole PCB with a few resistors and capacitors, reverse-engineered into the schematic seen above.

Looks like Bose decided to tweak the audio characteristics of a specific pair of headphones, and an in-plug filter was, somehow, the most efficient solution. We probably shouldn’t expect to see this often, but it bears keeping in mind: next time your repurposed 3.5 mm cable doesn’t behave as expected, it would be prudent to do a capacitance test with your trusty meter or oscilloscope.

With how small MCUs have gotten, you can easily hide more than just a few capacitors! We don’t often see circuits built into cables, but when we do, it’s for malicious purposes.

Raspberry Pi Test Stand Tells You Which Glues To Use

April 7, 2022 by 6 Comments

Not all glues are created equal; or rather, not every glue is good for every application. But how is one to know which glue to use in which kinds of joints? The answer to that is not always clear, but solid numbers on the comparative strength of different glues are a great place to start.

To quantify what can ordinarily be a somewhat subjective process, there’s probably no one better than woodworker and hacker [Matthias Wandel], equipped as he is with his DIY strength-tester. Using its stepper-driven power to blast apart glued lap joints, [Matthias] measured the yield point of the various adhesives using a strain gauge connected to a Raspberry Pi.

His first round of tests had some interesting results, including the usually vaunted construction adhesive ending up in a distant last place. Also performing poorly, at least relative to its reputation and the mess it can cause, was the polyurethane-based Gorilla Glue. A surprise standout in overall strength was hot glue, although that seemed to have a sort of plastic yield mode. Ever the careful empiricist, [Matthias] repeated his tests using hardwoods, with remarkably different results; it seems that glues really perform better with denser wood. He also repeated a few tests to make sure every adhesive got a fair shake. Check out the video below for the final results.

It’s always good to see experiments like this that put what we often take for granted to the test. [John] over at the Project Farm channel on YouTube does this kind of stuff too, and even did a head-to-head test of epoxy adhesives.

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Rubber Band “Slide Rule” Doesn’t Slide, But Rotates

April 4, 2022 by 11 Comments

Around here we mostly enjoy slide rules. We even have our own collections including some cylindrical and circular ones. But [Mathologer] discusses a recent Reddit post that explains a circular slide rule-like device using a wheel and a stretchable rubber band. While it probably would be difficult to build the actual device using a rubber band, it can do wonders for your understanding of logarithms which still show up in our lives when, for example, you are calculating decibels. [Dimitri] did simulate the rubber band for you in software.

The idea is that a perfect rubber band has numbers from 0 to 10 evenly marked on it. As you rotate a wheel attached at the 10 mark, the rubber band stretches more and more. So the 10 and the 9 have relatively little space between them, but the 1 and the 2 are much further apart. The wheel’s circumference is set so that the 1 will exactly overlay the 10. What this means is that each spot on the wheel can represent any number that differs only by a decimal point. So you could have 3 mean 0.03, 300, or — of course — 3. Of course, you don’t need to build the wheel with a rubber band — you could just mark the wheel like a regular circular slide rule.

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Quick-Swap Socket For Stemma QT Experiments

April 4, 2022 by 6 Comments

[kmatch98] shares a quick hack with us over at Hackaday.io – a 3D-printed socket for Adafruit Stemma QT-based I2C modules. Since Adafruit has standardized the dimensions for their Stemma QT boards, it’s possible to make a socket that would fit many different sensors at once, where the board just slides in.

This reminds us of sci-fi datadisks, or, thinking of something more grounded in reality, game console cartridges – except that here, the fun you’re having is from exploring all the different devices you can get to speak I2C. To make such a socket, you only need to 3D-print two plastic parts, put a JST-SH plug between them, and screw them together – if you want to modify these to your liking, .f3d sources are available. Now you no longer have to use fingernails or tin snips to take the JST-SH plug out of your modules!

[kmatch98] is no stranger to sharing his projects on Hackaday.io with us, and we’ve covered some of his larger projects before, like this CircuitPython-powered cyber-duck cyberdeck, or the 3D-printable Maypole braider machine!

Hackaday Prize 2022: Solar Harvesting Is Better With Big Capacitors

March 30, 2022 by 26 Comments

The sun is a great source of energy, delivering in the realm of 1000 watts per square meter on a nice clear day. [Jasper Sikken] has developed many projects that take advantage of this power over the years, and has just completed his latest solar harvesting module for powering microcontroller projects.

The concept is simple. A small solar panel is used to charge up a lithium ion capacitor (LIC), which can then be used to power other projects. We first saw this project last year, when it was one of the winners of Hackaday’s 2021 Earth Day contest. Back then, it was only capable of dishing out 80 mA at 2.2V.

However, the latest version ups the ante considerably, delivering up to 400 mA at 3.3V. This opens up new possibilities, allowing the module to power projects using technologies like Bluetooth, WiFi and LTE that require more current to operate. It relies on a giant 250 F capacitor to store energy, and a AEM10941 solar energy harvesting chip to get the most energy possible out of a panel using Maximum Power Point Tracking (MPPT).

It’s a useful thing to have for projects that you’d like to run off the sun, and you can score one off Tindie if you don’t want to build your own. We’ve seen [Jasper] pull off other neat solar-powered projects before, too. Video after the break.

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Fancy Wire Loop Game Is A Beauty In Brass

March 30, 2022 by 4 Comments

The simple wire-loop game is often built as a fun project to teach students about electronics. [W&M Levsha] built their own version, showing off their fine crafting and machining skills and branding it as a sobriety test with the playful name “Breathalyzer.”

The mechanics of the game are quite simple. The player must guide a metal ring around the puzzle without touching it. A buzzer and light is used to indicate to the player when they’ve failed, with the project powered from a small lithium-polymer pouch cell charged via a USB port.

Where this build really shines is in the presentation, with [W&M Levsha] showing they really have what it takes to do great work in brass. Rather than a simple bent wire, we’re instead treated to a delicately-formed beam of rectangular cross-section hewn out of a single piece of metal. It’s paired with a nicely-crafted wand with a knurled handle.

We’ve seen similar displays of their exquisite craft before, too – such as with a bespoke toothbrush and a powder-powered lighter. Video after the break.

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Old Boat Becomes Toasty Floating Sauna

March 28, 2022 by 3 Comments

A sauna is a great place to feel warm and toasty and refreshed, but few of us have one at home. [Linus Strothmann] decided to build his own, using an old boat as the perfect base for his steamy build.

Finding the right boat was the first challenge; the vessel should be big enough to fully house the intended number of occupants, and be able to withstand sitting outside in the weather year-round. If it’s to be used in a place where it gets icy in winter, it’s best to go with a steel-hulled vessel.  [Linus] found a steel-hulled boat just under 8 m in length for less than 1000 Euros, and set to work on his project.

The boat was stripped out, and given high-quality glass windows capable of resisting the steam and high temperatures inside. A stove was installed for producing steam, and the boat-sauna was designed with multiple entries and exits for safety reasons. Insulation was also fitted to help keep heat in.

The result is a floating sauna that is an absolute pleasure to use in the winter months. Floating out on the lake, one can take in a steam, have a quick dip in the icy water, and then return to warm back up inside. [Linus] hopes to soon fit a small motor in order to allow the vessel to head out to the middle of the lake for an even better view during a steam session.

It’s not the first mobile sauna we’ve seen; a trailer-based design graced these pages last year. If you’re working on your own hot and steamy build, though, do share your work with us promptly!