pulse oximeter as a small sticker that sticks on your fingernail and measures heart rate, motion, and blood oxygen

This Fingernail Sticker Can Detect When You Stop Breathing

January 1, 2023 by Orlando Hoilett 8 Comments

Sometimes we dig through the archives to see what kind of crazy hacks we can pull out of the depths of the world wide web and this one was worth sharing. Researchers at Northwestern University developed a sticker that’s applied to the fingernail and measures heart rate, motion, and blood oxygen, all without a battery.

The photoplethysmograph (PPG) system is similar to what we’ve covered before and the motion sensor is simply an accelerometer, so we won’t go over those aspects of the device. The parts of the device that did catch our attention were the battery-less operation as well as its size. It’s just so dang small! And fits snuggly on a fingernail or on even on your earlobe. The size here is actually a very interesting feature and not just a marketing plug. Because the device is so small and lightweight, it is very easy to adhere to the fingernail or skin with very little sensory perception. Basically, the person wearing the device won’t even notice it’s there. That’s definitely an advantage over the traditional, bulky, hospital-grade instruments we’ve grown accustomed to.

The device adheres really well given its small and lightweight design, so motion artifacts are significantly reduced. Motion artifacts in PPG-based devices are due to the relative motion between the optode (LED and photodiode) and the skin. The traditional approaches of ensuring the device don’t move are for the patient to keep very still during a recording, to wear the device tightly against the skin (think of how tightly you need to wear your smartwatch to get consistent readings), or use some seriously tough and uncomfortable adhesive as you may have done if you’ve ever gotten an electrocardiogram reading before. This device eliminates those three problems.

The other aspect of the device that caught our attention is its use of wireless power instead of a battery. In some senses, this could be seen as an advantage or as a disadvantage. The device relies on NFC for power and data transmission, a pretty common approach for devices that only need to be used intermittently. Wireless power could be a bit problematic for continuous monitoring devices which provide readings every second or several times a second. But who knows, wireless power seems to be everywhere these days.

Digging into the details a bit, the double-layer antenna is designed around the circumference of the device using wet etching to create traces on a copper polyimide foil. The team electroplated holes through the different layers of the device (optode layer, first antenna layer, polyimide, second antenna layer, component layer, protective top coat) connecting the antenna to the die pad NFC chip (SL13A, AMS AG). Connecting the chip requires some pretty fine-pitch soldering techniques, but nothing we’re not accustomed to here at Hackaday. Overall, they seemed pretty successful, obtaining a Q factor of 16 and a transmission distance of 30 mm using a smartphone and not some giant reader antenna.

Definitely, a really cool project that we recommend checking out.

Flexible, Thin-Film Biosensors

December 27, 2022 by Orlando Hoilett 6 Comments

We like to keep a pulse on the latest biosensor research going on around the world. One class of biosensors that have really caught our attention is the so-called thin-film sensors, pioneered by the Rogers Research Group at Northwestern University.

We’re no strangers to the flexible PCB here at Hackaday. Flexible PCBs have become increasingly accessible to small-scale developers and hobbyists, explaining why we’re seeing them incorporated into many academic research projects. The benefit of these types of sensors lies in the similarity of their mechanical properties to those of human skin. Human skin is flexible, so matching the flexibility of skin allows these thin-film sensors to adhere more comfortably and naturally to a person’s body. Continue reading “Flexible, Thin-Film Biosensors” →

Clever Design Technique Makes Flexible PCB Fit For A Queen

December 6, 2022 by Robin Kearey 11 Comments

Printed circuit boards can be square, round, octagonal, or whatever shape you desire. But there’s little choice when it comes to the third dimension: most PCBs are flat and rigid. Sure, you can make flexible PCBs like the kapton-backed ones you find inside electronic gadgets, but those are complicated to work with. As it turns out however, you can also make flexible boards using regular PCB material: check out [Rehana Al-Soltane]’s Flexible Crown PCB, a project she did as part of [Neil Gershenfeld]’s “How To Make (Almost) Anything” class at MIT.

The basic idea is to create flexures in the PCB by milling out several long slots with thin pieces connecting the two sides. [Rehana] got this idea from [Quentin Bolsée]’s flexible capacitive sensor project and applied it to make a crown-shaped PCB with sparkly LEDs. The crown can bend through 180 degrees and can actually be worn as a head ornament, with pin headers to clamp it down on the wearer’s hair.

[Rehana] used a tool called svg-pcb to design the board. This is an open source toolkit that lets you design PCBs by describing them in code, rather than drawing shapes by hand. Although this might look a bit odd if you’re used to working with traditional PCB design software, it’s ideal for making repetitive structures like the flexures in the crown: simply write a for loop and let the tool generate a perfect array of identical slots.

Fabricating the Flexible Crown posed a few difficulties of its own, because the PCB began to flex and wiggle itself loose before the milling process was finished. As it turned out, the trick was to cut all the slots on the interior first and only mill the board’s outline as the very last step.

Adding flexures to a PCB like this looks like a promising technique and we’ll keep an eye on further developments in this field. There are other ways of making bendy boards though: researchers at the University of Maryland used a laser engraver to make foldable PCBs. Our 2019 Flexible PCB Contest also yielded several impressive implementations.

Continue reading “Clever Design Technique Makes Flexible PCB Fit For A Queen” →

Miracle Of Science: Scotch Tape Improves Generator

December 4, 2022 by Al Williams 11 Comments

We were always amused that one of the biggest scientific discoveries of the recent past — graphene — was started with pencil lead and Scotch tape. Now, researchers at the University of Alabama in Huntsville have determined that double-sided Scotch tape can improve triboelectric power generators. Triboelectric generation, of course, is nothing new. These energy harvesters take mechanical and thermal energy and turn them into tiny amounts of electricity. What’s new here is that PET plastic, aluminum, and double-sided tape can make an inexpensive generator that works well.

Keep in mind we are talking about little bits of power. In the best scenario with the device stimulated at 20 Hz, the generator peaked at 21.2 mW. That was better than some designs that only got to 7.6 mW in the same configuration.

Continue reading “Miracle Of Science: Scotch Tape Improves Generator” →

Custom-designed photoplethysmogram designed to fit in ear like an ear bud

Breathe Through Your Ears?

December 4, 2022 by Orlando Hoilett 15 Comments

With all the attention given to heart rate monitoring and step counting, respiratory rate monitoring is often overlooked. Smartwatches are starting to incorporate respiratory rate monitoring more and more these days. However, current devices often simply look at breaths per minute without extracting more interesting features of the respiratory waveform which could give us more insight into our bodies than breaths per minute could alone. [Davies] and his team decided they wanted to change that by making an earbud that can measure respiratory rate. Continue reading “Breathe Through Your Ears?” →

I See By Your Tattoo That You Are A Hacker

November 28, 2022 by Anne Ogborn 38 Comments

We spotted [Segfault]’s new tattoo on a fast failing bird app a few days ago. We thought it was nice looking piece of skin art, but without a write up couldn’t cover it. The bearer of the tattoo pointed us to this blog post about the tattoo, and now we really like it.

It’s fun on it’s own, but when you start staring at it you realize it’s full of hidden jokes and meanings. If you like puzzles, go hunting for them before you read the blog post. We also liked the reminiscence about [Segfault]’s early electronics experimentation days, and how the 555 timer IC figured prominently in them.

We’ve not covered a lot of tattoos here at Hackaday. Mostly we cover the technology behind skin fused or embedded hacks. But occasionally some tattoo art catches our eye, as it did in this interesting barcode tattoo.

The project's wrist-worn heartrate sensor shown on someone's hand, Caption: Our device has three main components: watch electronics (arrow to watch display), organism enclosure (arrow to the 3D-printed case of the watch) and our living organism physarum polycephalum a.k.a slime mold.

What If Your Day-To-Day Devices Were Alive?

November 2, 2022 by Arya Voronova 9 Comments

We take advantage of a variety of devices in our day-to-day life, and we might treat them as just pieces of hardware, elements fulfilling a certain purpose — forgotten about until it’s time to use them. [Jasmine Lu] and [Pedro Lopes] believe that these relationships could work differently, and their recent paper describes a wearable device that depends on you as much as you depend on it. Specifically, they built wrist-worn heart rate sensors and designed a living organism into these, in a way that it became vital to the sensor’s functioning.

The organism in question is Physarum polycephalum, a slime mold that needs water to stay alive and remain conductive — if you don’t add water on a regular basis, it eventually dries out and hibernates, and adding water then will revive it. The heart rate sensor’s power rail is controlled by the mold, meaning the sensor functions only as long as you keep the mold alive and healthy. In their study, participants were asked to wear this device for one-two weeks, and the results go way beyond what we would expect from, say, a Tamagotchi — with the later pages describing participant reactions and observations being especially impressive.

For one, the researchers found that the study participants developed a unique sense of connection towards the slime mold-powered device, feeling senses of responsibility and reciprocity, and a range of other feelings you wouldn’t associate with a wearable. Page 9 of the paper tells us how one participant got sick, but still continued caring for the organism out of worry for its well-being, another participant brought her “little pet mold friend” on a long drive; most participants called the slime a “friend” or a “pet”. A participant put it this way:

[…] it’s always good to be accompanied by some living creature, I really like different, animals or plants. […] carrying this little friend also made me feel happy and peaceful.

There’s way more in the paper, but we wouldn’t want to recite it in full — you should absolutely check it out for vivid examples of experiences that you’d never have when interacting with, say, your smartphone, as well as researchers’ analysis and insights.

With such day-to-day use devices, developing a nurturing relationship could bring pleasant unexpected consequences – perhaps, countering the “kept on a shelf since purchase” factor, or encouraging repairability, both things to be cherished. If you’ve ever overheard someone talking about their car or laptop as if it were alive, you too might have a feeling such ideas are worth exploring. Of course, not every device could use a novel aspect like this, but if you wanted to go above and beyond, you could even build a lamp that needs to be fed to function.

Continue reading “What If Your Day-To-Day Devices Were Alive?” →