A subtly obvious e-paper room air monitor (Part 1: Why?)

Summary

TL;DR – In the cold season we tend to keep the windows closed. The air gets "stale": humidity often rises above 60 %, which can harm our wellbeing and promote mould. At the same time the CO₂ level in the air increases, which impacts our ability to concentrate. So I built a room air monitor that stays unobtrusive as long as everything is in the green zone, but becomes deliberately noticeable once thresholds are exceeded. For my personal love of statistics I also visualise the measurements in a clear dashboard. Note: This English version was created with the help of automated translation and I am not a native English speaker. If you notice any unclear or incorrect wording, feel free to point it out in the comments or reach out via e-mail so I can improve the text. Why this project? When windows stay closed for longer periods, the air indoors quickly becomes “stale”. Both humidity and the CO₂ level rise. CO₂ is measured in parts per million (ppm) – essentially “CO₂ molecules per one million air molecules”. This makes it easy to compare how much more CO₂ is present indoors compared to fresh outdoor air. At elevated levels, the following issues can occur: CO₂ level Meaning / possible effects around 400-450 ppm (typical outdoor air) Baseline for fresh air. up to ~1 000 ppm Often used as an upper limit for good ventilation. Values above ~1 000 ppm indicate insufficient ventilation. about 1 000-1 500 ppm Concentration rises – reduced performance, concentration problems and tiredness become more likely. > 1 500 ppm or more Very poorly ventilated room. Health and comfort issues become more frequent. Extreme values (e.g. > 5 000 ppm) Severe symptoms possible, e.g. shortness of breath or loss of consciousness. Very rare in normal indoor environments. Source: ASHRAE (2022). ASHRAE Position Document on Indoor Carbon Dioxide – PDF Humidity that is too high or too low is also unhealthy. If it is too low, this leads to dry mucous membranes, irritated skin and a higher susceptibility...