1. Introduction

This guide is for an older version of the QTRSensors Arduino library (3.1.0). The current version of the library can be found on GitHub, and its documentation is here.

QTR sensor size comparison. Top row: QTRX-HD-07, QTR-HD-07; middle row: QTR-3, QTR-1, QTR-L-1; bottom row: QTR-8.

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. 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 modules are available in two different output formats: the QTR-xA outputs an analog voltage between 0 and Vcc that can be measured by an analog-to-digital converter (ADC), and the QTR-xRC outputs require a digital I/O line capable of driving the output line high and then measuring the time for the output voltage to decay (which provides an analog measurement of reflectance).

QTR-L-1A reflectance sensor schematic diagram.

QTR-1A reflectance sensor schematic diagram.

QTR-1RC and QTR-L-1RC reflectance sensor schematic diagram.

Please see the product pages for more information on how these sensors work.

This document will explain how to install Arduino libraries for the Pololu QTR reflectance sensors, and it will provide sample sketches as well as links to library documentation. The libraries will give you everything you need to interface with a QTR-8x reflectance sensor array or multiple QTR-1x reflectance sensors, including advanced features like automatic calibration and, in the case of line detection, calculation of the line’s position.

New Products

Surplus SpringRC SM-S4303R Continuous Rotation Servo Pair (Two Servos)
DRV8874 Single Brushed DC Motor Driver Carrier
5V, 1.5A Step-Up/Step-Down Voltage Regulator S13V15F5
3pi+ 32U4 OLED Robot Kit with 15:1 HPCB Motors (Hyper Edition Kit)
Free Circuit Cellar magazine November 2021
9V Step-Up Voltage Regulator U3V40F9
Motoron M3H256 Triple Motor Controller Kit for Raspberry Pi
RoboClaw Solo 300A, 60VDC Motor Controller
DRV8256P Single Brushed DC Motor Driver Carrier
3pi+ 32U4 OLED Robot - Turtle Edition (75:1 LP Motors), Assembled
Log In
Pololu Robotics & Electronics
Shopping cart
(702) 262-6648
Same-day shipping, worldwide
Menu
Shop Blog Forum Support
My account Comments or questions? About Pololu Contact Ordering information Distributors