I bought one of these from the states, in a (shamefully lazy) soldered, partly assembled kit form.
https://www.airgradient.com/indoor/Out of the box it worked, but pestered for being registered with it's cloud. I did note that all particulate mater values where 0.
I flashed it with ESPHome based firmware and it works even better now without no cloud... and MQTT data, command and control ala HomeAssistant style API.
Still however there are 0s and "NaN" values for the PM sensor.
I provoked it by lighting some cardboard on fire, then blowing it out and holding it directly under the sensor. (CO2 and VoC went nuts)... PM sensor read 0.
What I need to prove next is ... is that sensor duff or the combination of customizations on already 3rd party firmware.
I have two options.
Software: Add logging debug probes to the various layers ESPHome, PSMx driver, UART LL. Possibly even to the extent of running it in an Eclipse IDF with a JTag debugger...
Hardware: Solder 2 probe leads onto the Rx/Tx of the sensor and read it on the scope.
I'm thinking the later is a far better use of my Saturday morning.
Anyone any experiences with these?