Checksum fail after concentration larger than 600(sometimes 1000 cannot confirm this at the moment)

[joshishrey]

Checksum fails by 2 or 4 when the concentration of aerosols get high. I have a hunch this happens when the concentration is more than the measuring limit. Is this the outcome that is expected when the concentration is too high?

[jeffeb3]

I think the issue is here:
https://github.com/Electronza/HPMA115S0/blob/master/src/hpma115s0.cpp#L95
The modulo is % 0xFF and the data sheet says it should be modulo 256, which is % 0x100. So if that number is greater than 255, then this modulo is wrong.