magsense

Open-souce low-cost vibro-magnetic wearables for hand-to-face contact prevention.

“Don’t touch your face!”

It is a seemingly simple advice. Since coronaviruses are stable for days on many surfaces 🦠, a person can get COVID-19 by touching a contaminated handle or object and then touching their own mouth, nose, or possibly eyes. But quitting is far easier said than done. Most people touch their face frequently throughout the day, usually without thinking about it—it’s a very difficult habit to break and requires a surprising amount of conscious effort.

The MIT Media Lab is advancing Saving Face: a suite of easily scaled technologies to help people fight the pandemic by warning them when they’re about to touch their faces. As one of the solutions, we have designed magsense, a wearable device that vibrates when the hand and face get too close, based on magnetic field sensing. Magnetic rings or bracelets on both hands are detected by a magnetometer worn around the neck as a necklace or a clip-on. Since it is based on a field sensing, the necklace or clip-on can also be hidden under a shirt. We provide two approaches in deploying magsense wearables by assembling off-the-shelf components or manufacturing our customized hardware.

Magsense node, necklace, and clip-on with magnet rings

Electronics/ - Hardware PCB files for the customized magsense board in Autodesk Eagle

Mechanical/ - Hardware STL files for 3D-printing packaging, necklace and clip-on version

Libraries/ - Collection of the Arduino libraries required for the sensor

Firmware/ - Firmware for magsense

Getting started

To quickly prototype magsense, you can use a small microcontroller such as Trinket M0, ATtiny85, or Arduino/Adafruit Gemma. Connect the microcontroller to a high-performance magnetometer breakout (in this case LIS2/3MDL, with +/- 50 gauss magnetic range and 1.5 mgauss sensitivity) through I2C lines. Connect one digital output of the microcontroller to drive a vibration motor through a transistor with a base resistor (see Electronics/ hardware PCB schematic for connections). Finally, plug in a rechargeable Li-Poly battery, download and move corresponding libraries (Libraries/) to the Arduino libraries folder, and upload the sketch (Firmware/) through Arduino IDE. All of these components can be found in Adafruit, SparkFun, Amazon, or eBay easily. You can also print the packaging and clip-on structure (Mechanical/) if you have access to a 3D printer and purchase or make your own necklace cord.

We have also designed a miniaturized customized hardware (Electronics/) that will significantly reduce the cost and form-factor of magsense. This development is meant for large-scale manufacturing and deployment.

Customized hardware PCB design

Firmware

After plugging a micro-USB cable to both computer and microcontroller and moving the LIS2/3MDL libraries (Libraries/) to your Arduino libraries, you can select your corresponding Board, Port, and Programmer in Arduino IDE/Tools. For ATtiny85 boards, use USBTinyiSP, for M0 use ArduinoISP in the Programmer. Push the reset button in your Trinket/Gemma, wait for the programming LED to blink, and then upload the sketch (Firmware/).

Known issues

Try to use Neodymium magnets. The stronger the magnet, the easier it is for the magnetometer to detect its presence and the higher its sensing range. Neodymium magnet rings work well, but ensure that they have the right magnet orientation. For different magnet rings and bracelets, you need to calibrate your own threshold by changing the values of the variables provided in Firmware/.

Manufacturing

There are three parts needed for manufacturing magsense: production of the printed circuit boards, sourcing the electronic parts, and assembly (soldering components and packaging). We encourage manufacturing magsense from the source files (/Electronics and /Mechanical). There are numerous board houses local and international that you can use (sugh as OSHpark or seeedstudio) and rigid PCBs are very affordable now even in small to mid-quantities. Note that the prices in the US are relatively higher than in China.

The electronic parts can be purchased from large electronic component distributors such as Digikey or Mouser. You can also check Alibaba for a cheaper price. You usually get discount for large quantities. The assembly can be also done by a factory, using high-throughput machines. It is possible to pick-and-place and solder manually, but it requires a lot of patience and a good reflow oven with a temperature distribution profile. There are several assembly houses in the US, such as Advanced Circuits or PCBway. There are also many in China that are significantly cheaper, but they are more difficult to connect with. For more than 1000 productions, for example, we can estimate each magsense with the rings would cost approximately $5 to $7.

Acknowledgements

Saving Face Team: Irmandy Wicaksono, Camilo Rojas, Cedric Honnet, Niels Poulsen, Zhi Wei Gan, Eyal Perry, and Tomas Vega.

Advisors: Kevin Esvelt, Joe Paradiso, Pattie Maes, and Fadel Adib.

Video and Content Editting: Guadalupe Babio and Nicolas Ayoub.

longcnn/magsense