QTR-1A Reflectance Sensor 2-Pack
The Pololu QTR-1A reflectance sensor carries a single infrared LED and phototransistor pair. The phototransistor is connected to a pull-up resistor to form a voltage divider that produces an analog voltage output between 0 V and VIN (which is typically 5 V) as a function of the reflected IR. Lower output voltage is an indication of greater reflection.
The LED current-limiting resistor is set to deliver approximately 17 mA to the LED when VIN is 5 V. The current requirement can be met by some microcontroller I/O lines, allowing the sensor to be powered up and down through an I/O line to conserve power.
This sensor was designed to be used with the board parallel to the surface being sensed. Because of its small size, multiple units can easily be arranged to fit various applications such as line sensing and proximity/edge detection.
For a line sensor with eight of these units arranged in a row, please see the QTR-8A reflectance sensor array; for a similar array of three slightly different sensor components, see the QTR-3A. For a smaller sensor with longer range, and intended for use with the board perpendicular to the surface, please see the QTR-L-1A reflectance sensor.
Interfacing with the QTR-1A Output
There are several ways you can interface with the QTR-1A output: