I had someone ask me the other day about "dust / smog" detection.  They=20
wanted to automatically close some windows when the outside air quality=20
was poor (lots of particulates).

My initial thought was a simple IR LED + photo diode pair to sense a=20
reduction in emission.  I then pulled a photo electric smoke alarm apart=20
to look at the optical chamber.  It uses an IR LED and photo transistor,=20
but set at 90=B0 to each other.  The smoke particles cause a reflection as=
=20
opposed to beam interference.

A quick look online for commercial sensors only seemed to reveal ones=20
designed for clean rooms (BIG $$), or actual smoke alarms.  Has anyone=20
been down this path before?
David...

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___________________________________________
David Duffy        Audio Visual Devices P/L
Unit 8, 10 Hook St, Capalaba 4157 Australia
Ph: +61 7 38235717      Fax: +61 7 38234717
Our Web Site: www.audiovisualdevices.com.au
___________________________________________

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