Dust Sensor  http://store.linksprite.com/dust-sensor/

Sharp’s GP2Y1010AU0F is an optical air quality sensor, designed to sense dust particles. An infrared emitting diode and a phototransistor are diagonally arranged into this device, to allow it to detect the reflected light of dust in air. It is especially effective in detecting very fine particles like cigarette smoke, and is commonly used in air purifier systems.

The LED pin has to be modulated with a cycle of 1ms as discussed in the datasheet.
The LED seems to use a PNP transistor so to power on, the LED pin must actually recieve a lower voltage.

Ok, you should now have every thing connected:

the author is  Paul  http://sensorapp.net/?p=479