The QTR-1A reflectance sensor carries a single infrared LED and phototransistor pair in an inexpensive, tiny 0.5" x 0.3" module that can be mounted almost anywhere and is great for edge detection and line following. The reflectance measurement is output as an analog voltage.
Documentation and other information
Pololu QTR Reflectance Sensor Application Note (Printable PDF: QTR_application_note.pdf)
Information about using the Pololu QTR-xA and QTR-xRC reflectance sensors, including sample oscilloscope screen captures of sensor outputs.
Pololu AVR C/C++ Library User’s Guide (Printable PDF: pololu_avr_library.pdf)
Information about installing and using the C/C++ libraries provided for use with Pololu products.
Arduino Library for the Pololu QTR Reflectance Sensors (Printable PDF: QTR_arduino_library.pdf)
Pololu AVR Library Command Reference (Printable PDF: avr_library_commands.pdf)
A reference to commands provided in the Pololu C/C++ and Arduino libraries for the AVR.