I would like to get some input on using the Shinyei Model PPD42NS particle sensor.
Basically, its data is read by measuring the proportion of time a low pulse is sensed out of a 30 second window duration. An example sketch is here: http://www.seeedstudio.com/wiki/Grove_-_Dust_sensor
On my sensors (yes, tested several), I could find long periods of time (say 3 minutes) where my Arduino Uno doesn't even measure a single low pulse. Yes, I know, perhaps the there's really no dust particles to sense? I think not. Because, occasionally, the sensor does register an appreciable count that's nowhere near to zero.
Now, I've found that if I move the sensor, or if I gently encourage some air to flow through/around the sensor, the sensor does register an appreciable count too.
This gets me thinking. Is it necessary for some air flow to be encouraged through the sensor? I know there's already a heat resistor in it, and that's supposed to create some convection air flow. But somehow I get the sense that it's not causing enough flow for me.
If you've also worked with this particle sensor, I would greatly appreciate some input on using it! Thank you :)