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CO2 sensors


(German below)

We have two Sensirion SCD41 sensors in the space. One is on top of the on top of the shelves between the seats and the couch in main room, and other is in the soldering workshop (aka e-workshop, lötschlauch, clean workshop). Locations may change as we figure out a mostly-permanent place for them, this page should be updated accordingly.

Accessing the data:

The data is available through Club Assistant (use trusted networks to log in, on the top, switch to the tab with the sensor icon), and through an RGB LED on the boards themselves.

The LED changes between green and yellow between 400-1000 PPM, yellow and red between 1000-2000 PPM and stays red above 2000 PPM. This can give a quick overview of how fresh the air in the room is, however, you should apply your own safety model to the values.

In my personal (ave) experience, due to the size of the room and leaky windows, the main room rarely goes above 2000PPM, but it is also really hard to lower the level when there's a large amount of people in there. The soldering workshop, when the door and windows are closed, has its CO2 values go up very fast, you should pay attention to air it regularly when it is crowded.

A quick rundown of how to interpret the values:

CO2 ppm Associated effect
~420 Outdoor CO2 level as of early 2024.
~1000 slightly stuffy air, reduced cognitive functionality (~15%)
~1500 somewhat stuffy air, significantly reduced cognitive functionality (~50%)
~2000-5000 stuffy air, significantly reduced cognitive functionality, reduced ability to focus, headache, sleepiness

A meta analysis of the research on CO2's effects on human cognitive health can be found on this paper (large part of the table above is based on this).

As a note, while air filters we have in the room make the air feel a bit fresher (due to reducing VOCs) and reduce the covid risk, they do not lower the CO2 levels. You should open the windows to air the room as appropriate.

Technical notes:

The sensors are connected to an ESP8266 with an 8mm PL9823 RGB LED (which uses WS2812B protocol, except it's RGB, not GRB). They're wired up on a (very annoyingly: double-sided) perfboard. There's a logic level shifter for the data pin of the RGB LED, circuit diagrams will be posted at some point.

The ESP8266 runs esphome, the configs are available on our esphome instance. For some reason it cannot connect to the devices, so you'll still want to flash them through your computer or something (for now I'm using it as just a config storage).

For sensor choice justification see this fedi post, TL;DR: NDIR sensors are the only cheap, small and good way to get CO2 data currently, and many other cheaper options require a lot more maintenance due to their calibration logic being worse.

German goes here

infrastructure/co2_sensors.txt · Last modified: 2024-02-07 09:38 UTC by ave

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