C. Scott Ananian Turns a Watchy Smartwatch Into a Wearable CO₂ for COVID-19 Safety Monitoring

Designed to detect when ventilation is needed, this wearable sensor aims to reduce your risk of contracting COVID-19.

Maker and former One Laptop Per Child staffer C. Scott Ananian has turned a Watchy open-hardware smartwatch into a wearable environmental sensor, designed to highlight air quality issues that could lead to increased risk of contracting COVID-19.

"The relationship of CO₂ [carbon dioxide] sensing to COVID safety can be found at a number of places," Ananian explains. "Briefly, CO₂ levels measure the amount of human breath in your vicinity which is a reasonable proxy for the number of particles of an infectious airborne pathogen potentially in your vicinity. There are some caveats, mostly related to indoor air filtration systems which can potentially remove (very small) virus particles but not (much smaller) CO₂ molecules, but it's still a reasonably interesting parameter to monitor when you're in a new or unusual setting."

There's been plenty of interest in using CO₂ sensors in rooms as a means of determining when ventilation is required, but less work on the personal front — which is where Ananian's project comes in. Designed as a replacement case and add-in board for the open source, Arduino-compatible Watchy smartwatch, the board adds temperature, humidity, and carbon dioxide sensing — with live and historical graphing.

Built around the Sensiron SCD40/41 carbon dioxide sensor, the add-in board solders onto the Watchy PCB in order to add sensing capabilities. An open-source watch face provides access to the data as a line chart and current reading in parts per million, and a 3D-printable case holds everything together — with surprisingly little added bulk over the Watch on its own.

"This board will work with the lower-cost SCD40 sensor, and gets about a day of battery life in this configuration, with the stock Watchy battery, reading CO₂ levels every 30 seconds," Ananian writes. "The slightly more expensive SCD41 sensor has the exact same pinout and footprint, but contains a lower-power mode where it can read the sensor every 5 minutes instead, and power consumption drops from 3.2mA to 0.5mA."

The board design files, case design files, and source code are all available on Ananian's GitHub repository under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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