QTR-8RC 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 eight 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 coupled with the ability of QTR-8RC Reflectance Sensor Array to turn off LED power:
The outputs are all independent, but the LEDs are arranged in pairs to halve current consumption. The LEDs are controlled by a MOSFET with a gate normally pulled high, allowing the LEDs to be turned off by setting the MOSFET gate to a low voltage. Turning the LEDs off might be advantageous for limiting power consumption when the sensors are not in use or for varying the effective brightness of the LEDs through PWM control.
QTR-8A and QTR-8RC Reflectance Sensor Array User’s Guide: https://www.pololu.com/docs/0J12
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/961