A quick Google search leads me to the GP2Y1010AU0F Compact Optical Dust Sensor[1][2], which you can get on ebay for cheap. Hope that helps! [1] http://sharp-wo

A quick Google search leads me to the GP2Y1010AU0F Compact Optical Dust Sensor[1][2], which you can get on ebay for cheap. Hope that helps! [1] http://sharp-world.com/products/device/lineup/data/pdf/datasheet/gp2y1010au_e.pdf http://sharp-world.com/products/device/lineup/data/pdf/datas... [2] http://sensorapp.net/?p=479 http://sensorapp.net/?p=479