Forearm Muscle Contraction Sensor Is Useful Component For Open Source Prosthetics

October 20, 2022 by 2 Comments

Being able to actuate parts of a prosthetic limb can make it much more useful. To help in this goal for partial arm or hand amputees, [TURFPTAx] has developed a sensor for detecting forearm muscle contractions. 

The sensor itself is cost-effective and simple to build.

The build is part of the Open Prosthetics project, which aims to offer open designs for various types of prosthetic devices. It apes common commercial designs using a simple electromechanical system.

The build relies on magnets mounted on twelve pistons that move when the muscles contract under the skin. The pistons are sprung to allow them to follow the expansion and contractions of the muscles, and the motion of the magnets is detected by hall effect sensors. The system is bulkier than some other solutions, but has the benefit of clean output and the ability to detect the movement of several distinct muscle groups. The data is all collected by an ESP32 which is then sent wirelessly to a computer for measurement, with [TURFPTAx] using the PyGame library to plot the sensor data.

[TURFPTAx] notes that the output of the sensors would be perfect to input into a machine learning system. Video after the break.

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Retrotechtacular: The Original Weather Channel

October 20, 2022 by 22 Comments

The Weather Channel has decided to pull the plug on its automated weather display, a favorite experience for weather geeks everywhere. However, it wasn’t the original weather nerd TV station.  Early cable TV networks had their own low-tech versions of this much longer ago than you might expect. For example, check out the video below which shows one of these weather stations back in 1975.

The audio was from a local FM station and you can enjoy handwritten public service announcements, as well.

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Render Yourself Invisible To AI With This Adversarial Sweater Of Doom

October 20, 2022 by 57 Comments

Ugly sweater season is rapidly approaching, at least here in the Northern Hemisphere. We’ve always been a bit baffled by the tradition of paying top dollar for a loud, obnoxious sweater that gets worn to exactly one social event a year. We don’t judge, of course, but that’s not to say we wouldn’t look a little more favorably on someone’s fashion choice if it were more like this AI-defeating adversarial ugly sweater.

The idea behind this research from the University of Maryland is not, of course, to inform fashion trends, nor is it to create a practical invisibility cloak. It’s really to probe machine learning systems for vulnerabilities by making small changes to the input while watching for changes in the output. In this case, the ML system was a YOLO-based vision system which has little trouble finding humans in an arbitrary image. The adversarial pattern was generated by using a large set of training images, some of which contain the objects of interest — in this case, humans. Each time a human is detected, a random pattern is rendered over the image, and the data is reassessed to see how much the pattern lowers the object’s score. The adversarial pattern eventually improves to the point where it mostly prevents humans from being recognized. Much more detail is available in the research paper (PDF) if you want to dig into the guts of this.

The pattern, which looks a little like a bad impressionist painting of people buying pumpkins at a market and bears some resemblance to one we’ve seen before in similar work, is said to work better from different viewing angles. It also makes a spiffy pullover, especially if you’d rather blend in at that Christmas party.

Catch The Stick Game Is A Tidy Build

October 20, 2022 by 10 Comments

There are many different ways to test one’s reaction times; a simple way is to simply drop a ruler and see how far it falls before you can catch it. Take that same concept to a greater level, and you get this impressive “Catch The Stick” game.

The creation of one [Romain Labbe], the build has a wooden frame that holds up several sticks roughly seven feet off the ground. When the game is triggered, a beeper counts down, and then sticks start dropping. Each stick is held in place with a small solenoid-controlled latch, and the game simply energizes the solenoids in turn to drop the sticks randomly. On easier modes, the sticks are released gently, one at a time. On higher difficulty levels, they’re released in a near-continuous stream that would tax even a team of several players.

It’s not a complicated build, but it is very nicely executed. It certainly looks to be good fun to play with friends. Alternatively, you could try out this more distributed-style build. Video after the break.

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Permeability Tuned Oscillators Made Stable With A Glue Stick

October 19, 2022 by 18 Comments

For over a century now, radio amateurs have made tuned circuits using a coil of wire and a variable capacitor. In recent decades the supply of variable capacitors has dwindled, as SDR technology has supplanted the traditional tuning capacitor. No more tuned circuits for the radio amateurs? Not quite, as [Bill Meara N2CQR] shows us in the video below the break by making variable inductors using permeability tuning. This is hardly high-tech, the major component is as simple as a glue stick.

A permeability tuned inductor has a core that is moved in and out of its center by means of a screw. A glue stick has a glue core on a lead screw from a knob at its end, so an old glue stick with the glue replaced by a ferrite ring makes a reasonable permeability tuned former. The coil is wound on its outside, and when assembled into an oscillator it gives a useful tuning range. This is hardly a new idea as permeability tuning could be found in car radios and TV tuners among other applications back in the day, but it’s still a good trick to bear in mind.

We’ve featured plenty of Bill’s videos before here at Hackaday, most recently tracking down an unusual early TV.

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Rubber Stamping Your Way To Custom PCBs

October 19, 2022 by 22 Comments

Many of us now outsource PCB production to board houses overseas, which offer high-quality boards with increasingly impressive turnaround times. You might still brew up your own PCB, though, and a reader found this great old hack from [William Hare] that might be worth a look.

Forget toner transfer or marker pens — this build is all about speed. [William] decided to use a rubber stamp to quickly transfer ink to a copper board that can then be etched to produce a PCB. It’s simple and straightforward enough. We’ve used the same technique for silkscreen and pad art, but never as an etch resist.

The trick is to make several rubber stamps with different circuit elements, though. The genius part is that you can then assemble a PCB by simply stamping down the various circuit components you need. The boards will still need to be drilled if you’re working with through-hole parts, but tipster [Shri] notes that the technique is super useful for producing single-sided surface mount boards.

We’ve seen some other unique methods to producing PCBs at home, such as using a 3D printer to help out. If you’ve got your own innovative homebrew PCB hacks, be sure to drop us a line!

Thanks [Shri Hari Ram] for the tip!

A 3D Printer With Quadruple The Output

October 19, 2022 by 8 Comments

While the polygraph is colloquially associated with pseudoscientific lie detector tests, the actual invention of the first polygraph was designed to mechanically duplicate the pen strokes of someone writing. Famously, a polygraph was used by former US President Thomas Jefferson in his “modern office”, a replica of which still sits in the Smithsonian museum. Few of us have a need for a pen-based polygraph anymore, but inspiration from the centuries-old invention can still be gleaned from the machine, like in this 3D printer which can output four identical prints at once.

The printer is a Core XY design with four separate print heads, which are all locked together. The printer behaves as if there is a single print head which keeps it simpler than it otherwise could be. Some extra consideration needs to be paid to the print bed to ensure it’s level and flat, and it also includes a unique Z-axis designed to prevent Z-banding from poor quality leadscrews. It has a fairly wide print area, but a noticeable restriction is that it’s essentially quartered, so while it can produce many parts at once, it can’t produce a single part that uses the entire area of the print bed.

Every printed part used to make this printer was designed by [Rick] in OpenSCAD. He also built a custom electronics board with the printer drivers, and all other associated circuitry in KiCad. For anyone who prints large volumes of parts, this might be just the trick to increase output without having to manage more printers. If you already have more printers and need an easier way to manage them all, take a look at this dedicated Raspberry Pi set up to do just that.

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