I’ve got one of the SN-GCJA5 particle sensors, and the readings coming out of it seem way off. I’m in Boulder where the air quality is pretty abysmal right now, and my Plantower PMS5003 is reading a PM2.5 of 100ug/m^3. The SN-GCJA5 in the same location is reading only 70 (I’m assuming also ug/m^3, though the datasheet never mentions it). The Plantower reading seems to line up with purpleair (which also uses the Plantower sensor) and also IQAir.
Am I assuming wrong that the the SN-GCJA5 directly gives ug/m^3? It seems to always read much lower than what I’d expect.
I’m adding support for the SN-GCJA5 to the OpenLog Artemis. I can confirm the particle mass density reading is in ug/m^3.
All I can suggest is:
Please make sure you are using getPM2_5() to read the 2.5 micron density. There are matching functions for 1.0 and 10 micron: getPM1_0() and getPM10().
Please check the photodiode, laser diode and fan status using getStatusPD() , getStatusLD() and getStatusFan() . These will return non-zero values if the status is abnormal. In particular, please check the fan status.
Please check you are powering the sensor from 5V. (The I2C and UART signals are 3.3V though.)
Page 6 in the communication specification contains more information on the status:
I’ve got the SN-GCJA5 working with the OpenLog Artemis. Just for info, it seems quite happy if I power the OLA from USB (5V) and then power the SN-GCJA5 from the MEAS/VIN pin.
I have noticed that the particle counts and densities reset every time you read them. E.g. if you read one of the counts, the value that is returned is the count since you last read the values. I’m wondering if your reading interval is maybe a bit short? Do the readings agree more closely with your other sensors if you take readings perhaps once per minute?