QTR-3RC Reflectance Sensor Array is intended as a line sensor, but it can be used as a general-purpose proximity or reflectance sensor. The module is a convenient carrier for three IR emitter and receiver (phototransistor) pairs evenly spaced at intervals of 0.375" (9.525 mm). To use a sensor, you must first charge the output node by applying a voltage to its OUT pin. You can then read the reflectance by withdrawing the externally supplied voltage and timing how long it takes the output voltage to decay due to the integrated phototransistor. Shorter decay time is an indication of greater reflection. This measurement approach has several advantages, especially when multiple units are used:
The LED current-limiting resistors are set to deliver approximately 17 mA to the LEDs when VCC is 5 V, making the total board consumption just over 50 mA.
Pololu QTR Reflectance Sensor Application Note: https://www.pololu.com/docs/0J13
Pololu AVR C/C++ Library User’s Guide: https://www.pololu.com/docs/0J20
Arduino Library for the Pololu QTR Reflectance Sensors: https://www.pololu.com/docs/0J19
Pololu AVR Library Command Reference: https://www.pololu.com/docs/0J18
Pololu Web Site: https://www.pololu.com/product/2457