The modules come as compact, single-sensor units ( QTR-1A and QTR-1RC QTR-L-1A and QTR-L-1RC), 3-sensor arrays ( QTR-3A and QTR-3RC), or as 8-sensor arrays ( QTR-8A and QTR-8RC) that can be optionally split into a 2-sensor array and a 6-sensor array.
The Pololu QTR reflectance sensors carry infrared LED and phototransistor pairs that can provide analog measurements of IR reflectance, which makes them great for close-proximity edge detection and line-following applications. Top row: QTRX-HD-07, QTR-HD-07 middle row: QTR-3, QTR-1, QTR-L-1 bottom row: QTR-8. The current version of the library can be found on GitHub, and its documentation is here. This guide is for an older version of the QTRSensors Arduino library (3.1.0).
