Aqui is an open-source, do-it-yourself monitor that shows real-time PM2.5 and PM10 readings on an Android phone. It is built around the SDS011 laser particle sensor, which connects to the phone through a USB serial cable and a USB-C OTG adapter. The phone supplies the power, processing and display, so the monitor needs no microcontroller, battery, screen or wireless module. The whole monitor is 75 × 80 × 28 mm, about half the footprint of the phone it plugs into, and there is nothing to charge: it draws power from the phone and starts reading as soon as it is connected.
The system comprises an open-source companion Android app, which shows PM2.5 with its air quality category, PM10 and a running average of recent readings; printable STL files and an editable STEP model of the enclosure; a parts list; and demonstration and assembly videos. Low-cost optical sensors of this kind degrade under continuous operation, so Aqui is designed for intermittent, hyperlocal spot measurements: comparing a busy road with a park 50 metres away, checking conditions before going outdoors, or testing whether an air purifier works. It is meant for citizens, students and researchers who want their own local readings where government monitoring stations are sparse, relocated or offline. All designs and code are released under the Creative Commons CC0 public domain dedication. An earlier version was described on the LEAP Blog.
Citation:
Patnaik, Ayush (2026). Aqui: A frugal DIY air quality monitor. XKDR Forum
