Stoatwblr
commented
1 month ago "I suspect "A" is an unused input"
Nope. It's required for calculations B = Vo and A=Voc on the VOC sensor
In essence, TVOC reporting is dynamic due to the heating element and potential contamination of the MEMS sensor. What matters for reporting purposes is "B-A"
I think that the reason they're reported separately is that doing so allows in-cloud/app calculation of HCHO(formaldahyde) and eCO2 assuming human origin of the VOCs (which is theoretically plausible but only valid in a sterile indoor environment. Best to just dump these and report VOCs)
This seems to follow the same pattern as the Sharp sensor, although Sharp's Vo/Voc handling is internal to U5
From the Sharp GP2Y1010AU0F application note
6-3 Basic output handling ・The output voltage Vo of this sensor is the sum of output voltage at no dust Voc and output proportional to dust density ΔV. Output proportional to dust density ΔV is shown as follows. ΔV = Vo - Voc (Vo : monitor value)
・Output voltage at no dust Voc is caused by the stray light ocuurring in this sensor. This sensor makes Voc voltage even at dust density 0mg/m3. If dust attached within this sensor increases, Voc becomes bigger. On the other hand, if dust attached within this sensor decreases, Voc becomes smaller.
・To store Voc in the memory of application is necessary to calculate ΔV from monitor value Vo. If monitor value Vo lower than the memorized Voc appears, this monitor value Vo should be stored in the memory of application as a new Voc.
・If monitor value Vo maintains a bigger value than the memorized Voc for a certain period of time, this monitor value Vo should be stored in the memory of application as a new Voc.
Section 7 has a table of density vs Vo - Not that it's linear from 0-0.45mg/m^3 and then tapers off rapidly, pinning at about 0.55mg/m^3
Hiya
I suspect "A" is an unused input
B is a direct reading of the TVOC device Vout in mV - it goes down the more alcohol/formaldyhyde is around. Looking at the datasheets, converting this to VOC is highly dependent on device temperature (which is where the heater matters and seems to sit around 35C internally)
Pm2.5 is in units of 100uV ("500" = 50mV), which will need converting to ug/m3, however I'm not sure if this is better done in HA than onboard. It absolutely maxes out at "1955" (tested with a smoke source - pinned the adjacent meter at 1000ug/m^3)
(on my unit, 420 ~=0, ~600 ~=20ug/m^3, ~500 ~=10ug/m^3, ~450 ~=5ug/m^3 - Supposedly the Sharp modules have a linear response)
Is https://wiki.dfrobot.com/Sharp_GP2Y1010AU or https://www.howmuchsnow.com/arduino/airquality/ of any use?