I thought I’d learn Fritzing and post the circuit diagram of the modified Shinyei PPD42NS. The circuit is really quite simple. In the 42R, the Shinyei is connected to the Particle Photon which is a microcontroller with built-in Wifi and a cloud service. The Photon is shown below on the breadboard.
I played with the resistor value quite a bit, until I settled on 10K. In the Shinyei, there are two internal 82K resistors and so adding the external 10K, reduces the threshold to 0.47V
This modified threshold is measured at A4 in the Photon. So if you are reading 0.47V at A4, everything is OK. Else something is off. Reducing R3 to make the sensor more sensitive does not work well, there is a lot of noise.
Hope this helps!
indiaairquality 
I had a chance to open the dfrobots laser dust sensor. They seem to use some really sophisticated techniques. Idon’t entirely see though how they distinguish between mass and count and size of particles though. Will have a closer look later.
Hi A.J.,
Nice work with the PPD42N Fan+resistor.
But when there is a fan the dust is being introduced to the sensor. So I’m more interested in the setup with only the resistor on P2 pin.
Would you please provide formula with calibration for the setup of P2 resistor ?