Kishan Pratap Singh built AirSense, a DIY air purifier controlled by an ESP32 that monitors what comes out of the filter, not just what goes in. Sensors along the exhaust path measure PM2.5 dust concentration, AQI, temperature, humidity, and atmospheric pressure, displayed live on an LCD.
The hardware is a 150mm exhaust fan mounted in a 3D-printed cap, pulling air through a cylindrical Xiaomi HEPA filter housed inside a perforated metal trash can. The ESP32 and LCD live in the same cap, keeping the footprint tight. Singh runs it continuously, but the original writeup on Instructables raises a real design question: whether demand-triggered operation could save power on time-of-use electricity plans, and what sensor repositioning that would require.
The full build log is worth reading for the sensor placement decisions and the tradeoffs in exhaust-path measurement. The Xiaomi HEPA filter has appeared before in hacks targeting its filter DRM and in Naomi Wu's open-source purifier design, making this part of a longer conversation about consumer hardware repurposed for serious air quality work.
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