The QTR-HD-09A Reflectance Sensor Array is a 9-sensor array for 1D line-following applications from Pololu. The array contains an array of 9 infrared (IR) reflectance sensors, each composed of an IR emitter and an IR detector. The sensors are arranged on a 0.375" spacing. When a bright surface is brought close to the sensor, the reflected IR light is detected by the IR detector and the corresponding sensor outputs a high logic level. A dark surface will cause the corresponding sensor to output a low logic level. The sensor array works with any microcontroller or microcomputer with digital I/O pins, including the Zumo robot and Arduino boards. It helps users build projects that can make line-following robots, edge detection devices, and more. It is easy to assemble and connects with a three-pin IDC-10 connector. The sensor is capable of operation up to 100 cm away.