Note:   When you receive this sensor, the surface is covered with a blue protective film. When you peel off the film, you can see the stainless steel case.     Working principle:  This sensor uses the principle of light scattering. That is, the illuminates the suspended particles in the air to generate scattering, and at the same time, the scattered light is collected at a certain angle to obtain a curve in which the intensity of the scattered light changes with time. Furthermore, the microprocessor uses an algorithm based on the MIE theory to obtain the equivalent particle size of the particles and the number of particles of different particle sizes per unit volume.     Output results:  The main output is the unit concentration of the mass concentration of each concentration in the unit volume: micrograms per cubic meter.  The output is divided into two states: active output and passive output. After the sensor is powered on, the default state is active output, that is, the sensor actively sends serial data to the host at a time interval of 200~800ms. The higher the concentration of particulate matter in the air, the shorter the time interval. The active output is divided into two modes: smooth mode and fast mode.  Package includes:  1 x PM2.5 Sensor Module