This version of the SparkFun Line Sensor Breakout – QRE1113 (Analog) features an easy-to-use analog output, which will vary depending on the amount of IR light reflected back to the sensor. This tiny board is perfect for line sensing applications 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 power is applied to the VCC and GND pins the IR LED inside the sensor will illuminate. A 100Ω resistor is on-board and placed in series with the LED to limit current. A 10kΩ resistor pulls the output pin high, but when the light from the LED is reflected back onto the phototransistor the output will begin to go lower. The more IR light sensed by the phototransistor, the lower the output voltage of the breakout board.