Sparkfun Electronics Digital IR Line Sensor - QRE1113

This is the Digital IR Line Sensor - QRE1113 . This version of the QRE1113 breakout board features a digital output, using a capacitor discharge circuit to measure the amount of reflection. This tiny board is perfect for line sensing when only digital I/O is available, and can be used in both 3.3V and 5V systems. The board's QRE1113 IR reflectance sensor is comprised of two parts - an IR emitting LED and an IR sensitive phototransistor. When you apply power to the VCC and GND pins, the IR LED inside the sensor will illuminate. A 100 Ohm resistor is on-board and placed in series with the LED to limit current. The output of the phototransistor is tied to a 10nF capacitor. The faster that capacitor discharges, the more reflective the surface is.