That doesn't look like it's a valid curve. A smoke density of 3ppm can be indicated by six different voltages.Where did you get that curve from?Pete
It is not that simple. First, the MQ-2 is not a smoke sensor, it is a gas sensor that works mainly for detecting H2, LPG, CH4, CO and alcohol. It needs to be "burned in" and calibrated properly to measure anything.The MAX30105 is also not a smoke sensor. It measures backscattering of light from particles in the air, and the quantity measured does not have a simple relationship to whatever you think the "PPM of smoke" might be.