Dust Sensor based on Sharp optics works well in detecting very delicate particle, like cigarette smoke, is a commonly used system of air purifier. This device contains IR LED and photoeletric transistor. Arranging them with across corners can detect the reflected light of dust in the air. It has a ultra-low power consumption(Max at 20mA, Typical at 11mA ), and can be equipped with sensors up to 7VDC. Analog voltage is proportional to measured concentration of dust , and sensitivity is 0.5V/0.1mg/m3.