Reliability Check: Consumer And Research-Grade Wrist-Worn Heart Rate Monitors

Wearables are ubiquitous in today’s society. Such devices have evolved in their capabilities from step counters to devices that measure calories burnt, sleep, and heart rate. It’s pretty common to meet people using a wearable or two to track their fitness goals. However, a big question remains unanswered. How accurate are these wearable devices? Researchers from the Big Ideas Lab evaluated a group of wearables to assess their accuracy in measuring heart rate.

Unlike other studies with similar intentions, the Big Ideas Lab specifically wanted to address whether skin color had an effect on the accuracy of the heart rate measurements, and an FDA-cleared Bittium Faros 180 electrocardiogram was used as the benchmark. Overall, the researchers found that there was no difference in accuracy across skin tones, meaning that the same wearable will measure heart rate on a darker skin-toned individual the same as it would on a lighter skin-toned. Phew!

However, that may be the only good news for those wanting to use their wearable to accurately monitor their heart rate. The researchers found the overall accuracy of the devices relative to ECG was a bit variable with average errors of 7.2 beats per minute (BPM) in the consumer-grade wearables and 13.9 BPM in the research-grade wearables at rest. During activity, errors in the consumer-grade wearables climbed to an average of 10.2 BPM and 15.9 in the research-grade wearables. It’s interesting to see that the research-grade devices actually performed worse than the consumer devices.

And there’s a silver lining if you’re an Apple user. The Apple Watch performed consistently better than all other devices with mean errors between 4-5 BPM during rest and during activity, unless you’re breathing deeply, which threw the Apple for a loop.

So, it seems as if wrist-worn heart rate monitors still have some work to do where accuracy is concerned. Although skin tone isn’t a worry, they all become less accurate when the subject is moving around.

If you’d like to try your own hand with fitness trackers, have a look at this completely open project, or go for the gold standard with a wearable DIY ECG.

Got Me Feeling Blue

Sleep schedules are an early casualty in the fight to be productive. Getting good sleep is an uphill battle, so anything that can help us is a welcome ally. We all know about the phone and computer settings that turn down the infamous blue hues at sunset, but what about when you want more blue light? Maybe you want to convince your body to stay awake to pre-acclimate for a trip across time zones. Perhaps you work or live in a place that doesn’t have windows. Menopause introduces sleep trouble, and that is a perilously steep hill.

[glowascii] takes the approach of keeping-it-simple when they arrange six blue LEDs under a flesh-tone patch, which isn’t fooling anyone and powers the lights with a USB power pack. Fremen jokes aside, light therapy is pricey compared to parts some of you have sitting in a drawer. Heck, we’d wager that a few of you started calculating the necessary resistor sizes before you read this sentence. Even if you don’t need something like this, maybe you can dedicate an afternoon to someone who does.

DIY therapy has a special place in our (currently organic) hearts, such as in this rehabilition glove or a robot arm.
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LED Shirt Does It With Tulle

Given that we are living in what most of humanity would now call “the future”, we really ought to start acting like it. We’re doing okay on the electric cars, but sartorially we’ve got some ground to make up. Helping with this effort is [Amy Goodchild], who put together a fancy LED shirt for all occasions.

The basis of the shirt is an ESP8266 running the FastLED library, hooked up to strings of WS2812B LEDs. It’s a great combination for doing quick and simple colorful animations without a lot of fuss. The LED strips are then fastened to the shirt by sewing them on, with heatshrink added to the strips to give the thread something to attach to. Tulle fabric is used as a diffuser, hiding the strips when they’re off and providing a more pleasant glowing effect. Everything is controlled from a small box, fitted with an arcade button and 7-segment display.

It’s a fun piece that’s readily achievable for the novice maker, and a great way to learn about LEDs and sewing. We’ve seen other similar builds before, such as this glowing LED skirt. Video after the break.

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Clean Air And A Gentle Breeze In Your Hoodie

Hoodies are great, and rightfully a hacker’s favorite attire: they shield you from the people around you, keep your focus on the screen in front of you, and are a decent enough backup solution when you forgot your balaclava. More than that, they are also comfortable, unless of course it is summer time. But don’t worry, [elkroketto] has built a solution to provide the regular hoodie wearer with a constant breeze around his face, although his Clean Air Bubble is primarily tackling an even bigger problem: air pollution.

Wanting to block out any environmental factors from the air he breathes, [elkroketto] got himself a thrift store hoodie to cut holes in the back, and attach two radial fans that suck in the air through air filtering cloths. A 3D printed air channel is then connected to each fan, and attached on the inside of the hood, blowing the filtered air straight into his face. Salvaging a broken drill’s battery pack as power supply and adding a 3D printed clip-in case for the step-up converter, the fans should provide him a good 5 hours of fresh air. Of course, one could also add a solar charging rig if that’s not enough.

Keep in mind though, while a wearable air filter might sound particularly useful in current times, [elkroketto] specifically points out that this is not for medical use and won’t filter out any airborne diseases.

Werewolf Ears With A Sense For Danger

When walking down a dark street, it’s common to get a sense that one is being followed. It pays to check, of course, but what if we could get better data than simply a vague feeling from the unknown? [caitlinsdad] built a project that can do just that, with a cute pair of ears to boot.

The werewolf ears claim to be ISO Standard, though we’re yet to see the relevant documents to bear that out. Regardless, they use an Adafruit Gemma M0 microcontroller to run the show, hooked up to an infrared proximity sensor to detect movement. When triggered, the Gemma responds to the signal by twitching the wolf ears attached to a headband, alerting the wearer that someone is closing in.

Built and calibrated properly, this could be a useful invention for those who regularly find themselves followed by those skulking on the sidewalk and for whom moving to another neighbourhood is a more expensive option. We’ve seen other responsive wearables, too. Video after the break.

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Stylish Outfit Packs A Solar Charging Rig

Being out and about with your devices rapidly running out of battery power can rapidly turn into a sticky situation. Suddenly you find yourself unable to hail rideshares and incapable of transferring money around. For the fashion conscious who wish to avoid this, [Kitty Yeung]’s design may be a valuable addition to their summer closet.

The project starts with [Kitty] sewing an elegant bodice and shorts out of a silky silver material. This fabric tends to fray when cut, so fabric glue and iron-on tape was used to protect the edges. This also makes sure the garment doesn’t fall to pieces when washed or worn often. Ribbons, pockets, and other features were designed into the garments to integrate them with hardware to enable the garments to act as a portable charging solution. 3D-printed brackets are affixed to the shoulders, holding a solar panel in an upward-facing angle to catch a good amount of sun. The panel chosen integrates circuitry to output a nice, clean 5V output for charging devices over USB.

It’s a fashionable outfit that also packs useful hardware, and we agree with [Kitty] that it really would be perfect for Burning Man. The cone hat was a nice touch, too. It’s not the first time we’ve heard from [Kitty] either – she appeared as a speaker at 2018’s Hackaday Superconference, too!

Pavlok Gets A Literally Shocking Teardown

Apparently, there is a wrist-mounted device that delivers electric shocks to the wearer when it receives the appropriate command over Bluetooth. No, it’s not part of some kind of house arrest program. If you can believe it, the gadget is actually intended to help break bad habits or wake up exceptionally deep sleepers. We don’t know which of those problems [Becky Stern] has, but we’re glad to see she decided to take hers apart before the 21st century self-flagellation started.

Called the Pavlok and available for $180 USD from various online retailers, the device looks like a chunky fitness tracker. But in place of the screen that would show you how many steps you’ve taken or your current heart rate, there’s a lighting bolt button that you can press when you want to shock yourself. With the smartphone application, you can control the device remotely with a handy desktop widget that allows you to select the intensity of the shock. No, we aren’t making any of this up. Check out the video after the break to see it in action.

When [Becky] tried to take the Pavlok apart, she found that it was nearly impossible to handle it without inadvertently triggering a shock. So until she could get the case open and physically disconnect the battery, all she could do was turn the intensity down in the application and work through the occasional jolts from the device. We can only hope that more devices don’t adopt a similar sense of self-preservation.

Once inside she found mainly the same kind of hardware you’d expect in a standard, non-masochistic, fitness wearable. There’s a nRF52832 Bluetooth SoC, a MMA8451Q accelerometer, a PCF85063A I2C RTC, and a FXAS21002C gyroscope. What you’re somewhat less likely to find inside your FitBit however is the LPR6235 coupled inductor and beefy capacitors which are used to build up a high-voltage charge from the standard 3.7 V LiPo battery.

We’ve been very interested in the recent projects which are creating custom firmwares for commercially available fitness wearables, as it could be an express route to a hacker-friendly smartwatch. While the Pavlok has some compelling hardware, and the programming header [Becky] identified looks interesting, we don’t like the idea of being one misplaced if statement away from riding the lightning.

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