The Air Quality Egg uses the Grove dust sensor – a Shinyei Model PPD42NS
I wanted to see if the values I have been getting from the AQE could be verified by a simple test where I plugged the Dust Sensor directly into a Arduino and used the Arduino sketch from Seed Studios wiki – found here.
The setup looked like this :
The shoe is there to hold the shield upright.
And the values I got out looks like this :
They are in columns :
lopulseoccupancy – a count of how many times we counted a low on the output pin
ratio – a percentage
concentration – a approximation of the sensor sensitivity as based on the calibrated curve in the data sheet.
So in other words somewhere between 0.6 to 4 % – if I understand the AQE calculations then the RAW figure is in tenth of a percent.
Btw. – read this to get a better understanding of the sensor – http://forums.parallax.com/archive/index.php/t-139538.html
It turn out that there is a resistor at the bottom of the sensor (can be seen if you look in to the plastic enclosure) – this heats up air to cause airflow into the chamber (the foil covered bit in the upper left hand corner). So this is the reason the sensor has to be positioned in a upright manner.