The CO2 Canary Is an Ultra-Low-Power Espressif ESP32 ePaper Carbon Dioxide Monitor
Low-power sensor, low-power screen, and an energy-efficient firmware deliver a desktop CO2 sensor with months of battery life.
Pseudonymous maker "blinry" has released the design files for a compact, ultra-low-power, Espressif ESP32-controlled device designed to keep track of a room's carbon dioxide levels: the CO2 Canary.
"[I've] glued and soldered everything together," blinry writes of the project's status, which has been built in a fully-functional v0.1.0 guise. "Now it feels like a real device! I'm super happy! Thanks again to everyone who has helped me to get this far! I'm planning to write detailed instructions on how to order the required parts, so that you can get one yourself!"
The CO2 Canary is designed as a digital equivalent to the old canary-in-a-coalmine "sensor," though it tracks carbon dioxide concentrations with a claimed ±50 parts-per-million accuracy across a 400-10,000ppm range. Data gathered by the sensor, a low-power Sensair Sunlight CO₂ non-dispersive infrared (NDIR) carbon dioxide sensor, are charted on an electrophoretic ePaper display — requiring power only when it changes state, based on the value having changed substantially since the last reading 30 seconds ago.
The choice of low-power sensor and display indicates blinry's focus for the project: making something which is extremely low power, able to run for as long as possible on a single charge of the battery. "I need to make measurements on the new PCB," the maker admits, "but my prototype had a power draw of 93uA in deep sleep. One measurement + display refresh cycle drew 89mC, so on a 2,000mAh battery (~7200C) it should be able to do around 80,000 refreshes. I drew the conclusion that a many-month battery life is realistic."
More information on the project, which blinry estimates should cost around €60 (around $65) in parts based on building ten at a time, is available in blinry's Mastodon thread; design files and source code have been published to GitHub under the CERN Open Hardware License v2 and the GNU General Public License 3 respectively.
