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

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

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.

Raspberry Pi biosensor with screen-printed electrodes

Raspberry Pi And PpLOGGER Make A Low-Cost Chemiluminescence Detector

[Laena] and her colleagues at the La Trobe Institute for Molecular Science in Melbourne, Australia used a Raspberry Pi to make a low-cost electrochemiluminescence (ECL) detector to measure inflammation markers, which could be used to detect cardiovascular disease or sepsis early enough to give doctors a better chance at saving a patient’s life.

ECL reactions emit light as a result of an electrically-activated chemical reaction, making them very useful for detecting biochemical markers in blood, saliva, or other biological samples.  ECL setups are fundamentally fairly straightforward. The device includes a voltage reference generator to initiate the chemical reaction and a photomultiplier tube (PMT) to measure the emitted light. The PMT outputs a current which is then converted to a voltage using a transimpedance amplifier (TIA). That signal is then sampled by the DAQCplate expansion board and the live output can be viewed in ppLOGGER in real-time.

Using the RPi allowed the team to do some necessary, but pretty simple signal processing, like converting the TIA voltage back to a photocurrent and integrating the current to obtain the ECL intensities. They mention the added signal processing potential of the RPi was a huge advantage of their setup over similar devices, however, simple integration can be done pretty easily on most any microcontroller. Naturally, they compared their device to a standard ECL setup and found that the results were fairly comparable between the two instruments. Their custom device showed a slightly lower limit of detection than the standard setup.

Their device costs roughly $1756 USD in non-bulk quantities with the PMT being the majority of the cost ($1500). Even at almost $2000, their device provides more than $8000 in savings compared to ECL instruments on the market. Though cost is much more than just the bill of materials, we like seeing the community making efforts to democratize science, and [Laena] and her colleagues did just that. I wonder if they can help us figure out the venus fly trap while they’re at it?

Flexible, Thin-Film Biosensors

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”

Picture of NanoStat in 3D-printed enclosure with LiPo battery and US quarter for scale.

An ESP32-Based Potentiostat

Ever wanted to make your own wireless chemical sensor? Researchers from the University of California, Irvine (UC Irvine) have got you covered with their ESP32-based potentiostat.

We’ve talked about potentiostats here on Hackaday before. Potentiostats are instruments that analyze the electrical properties of an electroactive chemical cell. Think oxidation and reduction reactions (redox) from your chemistry course, if you can remember that far back. Potentiostats can be used in several different modes/configurations, but the general idea is for these instruments to induce redox reactions within a given electroactive chemical cell and then measure the resulting current produced by the reaction. By measuring the current, researchers can determine the concentration of a known substance within a sample or even determine the identity of an unknown substance, to name a few potential applications.

These instruments have become mainstays in research labs around the world and have incredible utility in the consumer space. Glucometers, devices used to measure blood glucose levels, are an example of technologies that have made their way into everyday life due to the advances made in electrochemistry and potentiostat research over the last few decades. Given their incredible utility to scientific research and medical technologies, a great deal of effort has gone into democratizing potentiostats, making them more available to the general public for educational and hobbyist purposes. Of course, any medical applications must go through rigorous testing and approvals by each country’s appropriate governing bodies. So we’re talking more non-medical purposes here.

The first popular open-source, DIY potentiostat was the CheapStat, which we’ve covered here on Hackaday before. Since then, developing newer and more advanced open-source potentiostats has become a popular endeavor within the scientific community. The researchers from UC Irvine wanted to put their own special spin on the open-source potentiostat craze and they did so with their inclusion of the ESP32 as their main processor. This obviously opens up them up do a whole host (see what we did there) of wireless capabilities that others before them have not explored.

With the ESP32, they developed a nice web-based GUI that makes controlling and collecting data from the potentiostat very seamless and user-friendly. You can imagine the great possibilities here. Teacher-led classroom demonstrations where the instructor can easily access each student’s device over the cloud to help troubleshoot or explain results. Developing soil monitoring sensors that can be deployed all around a farm to remotely collect data on feed, soil composition, and plant health. The possibilities here sure are promising.

We hope you’ll dive into their paper as it’s well worth a read. Happy hacking, Hackaday.

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

Breathe Through Your Ears?

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?”

TVout Library Brings Cardboard Arcade To Life

Recycling old CRTs is a true Hackaday tradition, and [Rob’s] mini arcade is sure to grab your attention.

First of all, you’ll probably appreciate [Rob] circumventing the supply shortage by getting all his components from recycled material. That’s probably the only way to get anything these days. He salvaged a small CRT from an old-school video intercom system and snagged the buttons, speakers, and switches from other unused devices laying around. Not all is lost, however, as [Rob] was able to purchase an Arduino Nano and a few resistors online. So maybe things are turning around in that category, who knows?

You’ll probably also appreciate how remarkably simple this hack is. No need for a Raspberry Pi as your standard 8-bit microcontroller will do the trick. And, fortunately, [Rob] found a nice library to help him generate the composite video signal, doing most of the work for him. All that was left to do was to build the arcade cabinet. Recreating the classic design was a pretty easy step, but you might opt for something a little nicer than cardboard though. But, hey, if it does the trick, then why not?

Cool project, [Rob]! We’re definitely happy to add this project to our retro collection here at Hackaday.

Continue reading “TVout Library Brings Cardboard Arcade To Life”

Infant is wearing sensor vest as she is held by her mom. ECG, respiration, and accelerometry data is also showing.

Open Source Wearables For Infants

We’ve seen plenty of hacks that analyze biometric signals as measures of athletic performance, but maybe not as many hacks that are trying to study behavior. Well, that’s exactly what developmental psychologists at Indiana University and the University of East Anglia have done with their open-source, wireless vest for measuring autonomic function in infants.

infant biosensor vest for heart rate, motion, and respiratory rateTheir device includes a number of components we’ve seen already. There is an HC-05 Bluetooth module, AD8232 electrocardiography (ECG) analog front-end, LIS3DH 3-axis accelerometer, MCP73831 LiPo charger, a force-sensitive resistor for measuring respiration, and a Teensy microcontroller. Given how sensitive an infant’s skin can be, they opted for fabric electrodes for the ECG instead of those awful sticky ones that we’re accustomed to. They then interfaced the conductive fabric with copper plates using snap fasteners (or press studs or snap buttons, whichever terminology you’re more familiar with). The copper plates were connected to the circuit board using standard electrical wire. Then, they embedded the sensors into a vest they sewed together themselves. It’s basically a tiny weighted vest for infants but it seems well-padded enough to be somewhat comfortable.

They did a short test analyzing heart and breathing rates during a period of “sustained attention,” basically when you’re quietly fixated on a single object or activity for a period of a few minutes or longer. They were really pleased with the vest’s ability to collect consistent data and noted that heart and respiratory rate variability decreased during the sustained activity test, which was an expected outcome. Apparently, when you’re pretty fixated on a singular task, your body naturally calms down, so to speak, and the variability in some of your physiological responses decreases. Well, unless someone slowly walks up behind you and pinches you, of course.

They provided detailed instructions for recreating the vest, so be sure to check those out. They probably want their device to look a lot less than body armor though. Maybe the Sewbo can help them out with their next iteration.