Tiny Wearable Turns Thumbnail into Trackpad

Wearable technology is on the rise, particularly with regard to fitness trackers and health monitors. However, these wearable technologies make for somewhat bulky wristbands, necklaces, or other devices that hang from the human body.

Researchers at the MIT Media Laboratory are blurring the boundary between the physical and digital worlds with the development of a nail-mounted gestural input surface called NailO.

According to Cindy Hsin-Liu Kao, an MIT graduate student and lead author of NailO: Fingernails as an Input Surface, a paper describing the system, the technology could allow users to control wireless devices when their hands are full. “For example, if both your hands are busy cooking, but you need to navigate a mobile device, NailO could be used like a third hand,” says Kao.

The researchers drew inspiration from decorative nail stickers found in the cosmetic industry. “We were motivated by fashion trends in East Asian countries, where decorative art stickers are very popular,” explains Kao. “So instead of having everything on your wrist, we’re making it more discrete in the form factor of a cosmetic product.”

NailO involves multilayered miniaturized hardware that wirelessly transmits data via Bluetooth to a mobile device or PC. The hardware is then mounted on the thumbnail with cosmetic nail tape.


Kao and Artem Dementyev, a fellow graduate student and the paper’s co-author, began work on their first prototype in August 2014. After finishing a rigid circuit board design by the end of September, the two began work on a second version – a flexible circuit board.

Kao and Dementyev’s project is supported by their advisors Chris Schmandt, principal research scientist, and Joe Paradiso, an MIT professor of media arts and science.

The researchers designed NailO to use projected capacitance to sense finger touch gestures, in which the capacitance is measured on each electrode independently. When touched, a capacitor is formed between the finger and the sensing electrode, and capacitance is sensed indirectly by charging and discharging a resistor-capacitor (RC) circuit.

“The electrodes are optimized specifically for touch,” explains Dementyev. “The capacitive touch doesn’t pick up anything non-conductive, like your sleeve.”

For the first prototype, the team constructed its sensors by printing copper electrodes on sheets of flexible polyester. The process allowed them to experiment with a range of electrode layouts; however, they are currently using off-the-shelf sheets of electrodes comparable to those found in some touchpads.


NailO is a stacked device, consisting of four unique layers. The top layer is an interchangeable, decorative nail sticker for users to customize sensor appearance. “Because the appearance is so malleable with NailO, you can easily adjust it to how you want it to look,” explains Kao.

Shown here is the first NailO prototype with Rigid PCB and copper printed electrodes. The 4 layers are shown individually, stacked on top of each other. (All images courtesy of the MIT Media Lab)

The second layer comprises the matrix of sensing electrodes connected to the printed circuit board underneath it, and the third layer is made up of an ATmega328 (Atmel) microcontroller and MTCH6102 (Microchip) capacitive touch controller.

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“The microprocessor is doing all the calculations and linking everything together,” says Kao. “Then we have the capacitive sensing chip, which links to the electrodes and enables the device to detect if someone is touching it or not.” The samples are then transmitted to a laptop or phone using a Bluetooth Low Energy chip nRF8001 (Nordic).

Beneath the circuit board is a 10 mAh lithium-polymer battery, which powers the circuit. According to the researchers, the battery layer was the primary challenge in terms of miniaturization. “Its current battery life is two hours,” explains Dementyev. “Instead of running the device all the time, we think we could have it sleeping most of the time, and have a special activation gesture to wake it up.”

The current battery has a mean power consumption of 4.86 mA; however, Dementyev believes that, with the right battery, it would be possible to get the device running for up to one week without recharging. The researchers have been in discussions with several battery manufacturers. In fact, they think they have found a technology that could produce a battery that fits in the space of a thumbnail, but is only half a millimeter thick.


The nail-mounted device currently recognizes five gestures. “Once you put NailO on your thumb, you can use your index finger to swipe left/right, top/down, and perform a long press,” says Dementyev. “You control the device using the small trackpad like a cursor.”

In order to embed the software on-chip for future iterations, the researchers chose a thresholding algorithm over machine learning for a lightweight solution. However, after conducting various pilot studies, they found that the baseline capacitive sensor values differed between users, prompting the researchers to include an initial calibration phase to find the best parameters for each user.

The system then feeds the optimal parameters to the gesture detection algorithm after calibration, and the software proceeds to read in sensor data at approximately 30 frames per second, feeding it into the algorithm.

In a user study testing the five gestures, NailO detected gestural inputs in real time with more than 92 percent accuracy. Ten users (five male, five female) were asked to perform the swipe gestures with their middle finger.

“We designed NailO for the thumb, because it has more space, and it’s easier for us to prototype,” says Kao. “But a lot of people who tested our device wanted to put it on different fingers, and some people wanted to put it on all their fingers so they could use it like a scrollbar.” The researchers plan to eventually manufacture the sensor for all ten fingers and print electrode substrates in different sizes to fit different users.

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Applications for the device can be broken down into two categories. The first application would use NailO like a remote control. “Imagine when both your hands are busy cooking, and you need to look at a recipe on your mobile device – NailO could help you navigate and scroll through it.”

In addition, she believes the users would be eager to advantage of the device’s small form factor. “For if you’re in a meeting, but you happen to get message that your child is sick, and you need to NailO is a very discrete way to send a reply.”

Despite what Kao describes as an unlimited number potential applications, it will take a couple of years the device can be brought to the market due to in current battery manufacturing technology. The researchers realize that NailO must be able to accidental false positives. As a solution, Kao a two-second activation press before any gestures can be performed.

“At the MIT Media Lab, we try to imagine what the future of technology might look like 10 to 20 years out, and we don’t just imagine it – we build prototypes to give the world a glimpse of the possible future,” says Kao. “We really feel that, with technology getting closer to the human body, it is getting more important to think about personalization in a deeper sense.”

NailO works as an X-Y coordinate touchpad on your fingernails and allows for swipe gestures.


Posted from: http://www.pddnet.com/article/2015/11/tiny-wearable-turns-thumbnail-trackpad

Author: Kaylie Duffy

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