E4 Empatica device for measuring location, temperature, skin conductance, sleep, etc. on arm

Choosing The Optimal Sampling Rate For Your DIY Heart Rate Monitor

September 3, 2020 by Orlando Hoilett 19 Comments

With wearables still trying to solidify themselves in the consumer health space, there are a number of factors to consider to improve the reliability of such devices in monitoring biometrics. One of the most critical such parameters is the sampling rate. By careful selection of this figure, developers can minimize errors in the measurement, preserve power, and reduce costs spent on data storage. For this reason, [Brinnae Bent] and [Dr. Jessilyn Dunn] wanted to determine the optimal sampling rate for wrist-worn optical heart rate monitors. We’ve shared their earlier paper on analyzing the accuracy of consumer health devices, so they’ve done a lot of work in this space.

The results of their paper probably don’t surprise anyone. The lower the sampling rate, the lower the accuracy of the measurement, and the higher the sampling rate the more accurate the measurement when compared to the gold standard electrocardiogram. They also found that metrics such as root mean square of successive differences (RMSSD), used for calculating heart rate variability, requires sampling rates greater than 64 Hz, the nominal sampling rate of the wearable they were investigating and of other similar devices. That might suggest why your wearable is a bit iffy when monitoring your sleeping habits. They even released the source code for their heart rate variability analysis, so there’s a nice afternoon read if you were looking for one.

What really stood out to us about their work is how they thoroughly backed up their claims with data. Something crowdfunding campaigns could really learn from.

World’s Only Flying Twin Mustang Goes On Sale

September 3, 2020 by Tom Nardi 18 Comments

Given the incredible success of the P-51 Mustang during the Second World War, it’s perhaps no surprise that the United States entertained the idea of combining two of the iconic fighters on the same wing to create a long-range fighter that could escort bombers into Japan. But the war ended before the F-82 “Twin Mustang” became operational, and the advent of jet fighters ultimately made the idea obsolete. Just five examples of this unique piece of history are known to exist, and the only one in airworthy condition can now be yours.

Assuming you’ve got $12 million laying around, anyway. Even for a flyable WWII fighter, that’s a record setting price tag. But on the other hand, you’d certainly be getting your money’s worth. It took over a decade for legendary restoration expert [Tom Reilly] and his team to piece the plane, which is actually a prototype XP-82 variant, together from junkyard finds. Even then, many of the parts necessary to get this one-of-a-kind aircraft back in the sky simply no longer existed. The team had to turn to modern techniques like CNC machining and additive manufacturing to produce the necessary components, in some cases literally mirroring the design in software so it could be produced in left and right hand versions.

Recovering half of the Twin Mustang in 2008.

We first covered this incredible restoration project back in 2018, before the reborn XP-82 had actually taken its first flight. Since then the plane has gone on to delight crowds with the sound of two counter-rotating Merlin V-12 engines and win several awards at the Oshkosh airshow. The listing for the aircraft indicates it only has 25 hours on the clock, but given its rarity, we can’t blame [Tom] and his crew for keeping the joyrides to a minimum.

As important as it is to make sure these incredible pieces of engineering aren’t lost to history, the recent crash of the B-17G Nine-O-Nine was a heartbreaking reminder that there’s an inherent element of risk to flying these 70+ year old aircraft. A world-class restoration and newly manufactured parts doesn’t remove the possibility of human error or freak weather. While we’d love to see and hear this beauty taxiing around our local airport, it’s a warbird that should probably stay safely in the roost. Hopefully the $12 million price tag will insure whoever takes ownership of the world’s only flying F-82 treats it with the respect it’s due.

A 3D Printed Magnetic Stirrer For Your DIY Chemistry Projects

September 3, 2020 by Zoe Skyforest 20 Comments

When mixing or agitating delicate solutions in the chemistry lab, a magnetic stirrer is often the tool of choice. They’re able to be easily sterilized and cleaned, while maintaining isolation between the mechanical parts and the solutions in question. While they can be purchased off the shelf, [Max Siebenschläfer] whipped up a design that can easily be built at home.

The build consists of a 3D printed base, containing a simple brushed motor. This is hooked up to a motor controller fitted with a simple potentiometer for adjusting the speed of rotation. The motor is then fitted with a small 3D printed spinner containing two magnets. A similar 3D printed part acts as a stirrer, and is fitted with a matching pair of magnets, and dropped into the solution. The magnets in the stirrer are attracted to the ones on the end of the motor, and so when the motor spins, the stirrer spins in the solution, with no physical contact required.

It’s a simple way to build a magnetic stirrer at home without having to shell out big money for a laboratory grade unit. We imagine this could be put to fun use for stirring coffee or cocktails, too – if built with a food-grade spinner. More advanced designs are also possible for the eager home scientist. Video after the break.

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Cerebral Palsy Tool Assistant

September 3, 2020 by Brian McEvoy 2 Comments

We all deserve to create. Some people seem to have the muses hidden in their pocket, but everyone benefits when they express themselves in their chose art form. Each of us has tools, from Dremels to paintbrushes, and many folks here build their own implements. Even if we don’t have our macro-enabled mechanical keyboard or a dual-extrusion printer, we can make due. But what if you couldn’t operate your drill, or mouse, or even a pencil? To us, that would be excruciating and is the reality for some. [Laura Roth] and [Christopher Sweeney] are art teachers designing a tool holder for their students with cerebral palsy so that they can express themselves independently.

On either side of this banner image, you can see pencil drawings from [Sara], who has spastic cerebral palsy. She made these drawings while wearing the tool holder modeled after her hand. Now, that design serves other students and is part of the 2020 Hackaday Prize. The tool holder wraps around the wrist like a wide bracelet. Ribbing keeps its shape, and a tube accepts cylindrical objects, like pencils, styluses, and paintbrushes.The result is that the tip of the pencil is not far from where it would have been if held in the hand, but this sidesteps issues with grip and fine control in hands and fingers.

The print is available as an STL and should be printed with flexible filament to ensure it’s comfortable to wear. Be mindful of digital styluses which may need something conductive between the barrel and user.

Hackers are familiar with the challenges of cerebral palsy, and we’ve enjoyed seeing a variety of solutions over the years like door openers, camera gimbals, and just being altogether supportive.

The Astronomical Grit Of Ronald McNair

September 3, 2020 by Kristina Panos 23 Comments

There is more than one way to lead a successful life. Some people have all the opportunity in the world laid out before them, and it never does them any good. Others have little more than the determination and desire they’ve dredged up within themselves, and that grit turns out to be the abrasive that smooths the path ahead.

Ronald McNair succeeded despite poverty, racism, and an education system designed to keep Black people down. He became an accidental revolutionary at the age of nine, when he broke the color barrier in his small South Carolina town via the public library. This act of defiance in pursuit of education would set the course for his relatively short but full life, which culminated in his career as a Space Shuttle mission specialist.

Rule-Breaker with a Slide Rule

Ronald McNair was born October 21, 1950 in Lake City, South Carolina, the second of three sons, to Pearl and Carl McNair. His mother was a teacher, and encouraged his love of reading. Ronald’s father, Carl was an auto mechanic who never finished high school and always regretted it. Though the family was poor, Ron grew up surrounded by books, music, and support.

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Linux Fu: Moving /usr

September 3, 2020 by Al Williams 83 Comments

Linux has changed. Originally inspired by Unix, there were certain well understood but not well enforced rules that everyone understood. Programs did small things and used pipes to communicate. X Windows servers didn’t always run on your local machine. Nothing in /usr contributed to booting up the system.

These days, we have systemd controlling everything. If you run Chrome on one display, it is locked to that display and it really wants that to be the local video card. And moving /usr to another partition will easily prevent you from booting up, unless you take precautions. I moved /usr and I lived to tell about it. If you ever need to do it, you’ll want to hear my story.

A lot of people are critical of systemd — including me — but really it isn’t systemd’s fault. It is the loss of these principles as we get more programmers and many of them are influenced by other systems where things work differently. I’m not just ranting, though. I recently had an experience that brought all this to mind and, along the way, I learned a few things about the modern state of the boot process. The story starts with a friend giving me an Intel Compute Stick. But the problems I had were not specific to that hardware, but rather how modern Linux distributions manage their start-up process.

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COVID-tracing Framework Privacy Busted By Bluetooth

September 3, 2020 by Elliot Williams 60 Comments

[Serge Vaudenay] and [Martin Vuagnoux] released a video yesterday documenting a privacy-breaking flaw in the Apple/Google COVID-tracing framework, and they’re calling the attack “Little Thumb” after a French children’s story in which a child drops pebbles to be able to retrace his steps. But unlike Hänsel and Gretl with the breadcrumbs, the goal of a privacy preserving framework is to prevent periodic waypoints from allowing you to follow anyone’s phone around. (Video embedded below.)

The Apple/Google framework is, in theory, quite sound. For instance, the system broadcasts hashed, rolling IDs that prevent tracing an individual phone for more than fifteen minutes. And since Bluetooth LE has a unique numeric address for each phone, like a MAC address in other networks, they even thought of changing the Bluetooth address in lock-step to foil would-be trackers. And there’s no difference between theory and practice, in theory.

In practice, [Serge] and [Martin] found that a slight difference in timing between changing the Bluetooth BD_ADDR and changing the COVID-tracing framework’s rolling proximity IDs can create what they are calling “pebbles”: an overlap where the rolling ID has updated but the Bluetooth ID hasn’t yet. Logging these allows one to associate rolling IDs over time. A large network of Bluetooth listeners could then trace people’s movements and possibly attach identities to chains of rolling IDs, breaking one of the framework’s privacy guarantees.

This timing issue only affects some phones, about half of the set that they tested. And of course, it’s only creating a problem for privacy within Bluetooth LE range. But for a system that’s otherwise so well thought out in principle, it’s a flaw that needs fixing.

Why didn’t the researchers submit a patch? They can’t. The Apple/Google code is mostly closed-source, in contrast to the open-source nature of most of the apps that are running on it. This remains troubling, precisely because the difference between the solid theory and the real practice lies exactly in those lines of uninspectable code, and leaves all apps that build upon them vulnerable without any recourse other than “trust us”. We encourage Apple and Google to make the entirety of their COVID framework code open. Bugs would then get found and fixed, faster.

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