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.
Note: The QTR-1A reflectance sensor requires an analog input to take readings. The similar QTR-1RC reflectance sensor is available with a digital I/O-compatible output.
The Pololu QTR-1A reflectance sensor carries a single infrared LED and phototransistor pair. The phototransistor is connected to a pull-up resistor to form a voltage divider that produces an analog voltage output between 0 V and VIN (which is typically 5 V) as a function of the reflected IR. Lower output voltage is an indication of greater reflection.
The LED current-limiting resistor is set to deliver approximately 17 mA to the LED when VIN is 5 V. The current requirement can be met by some microcontroller I/O lines, allowing the sensor to be powered up and down through an I/O line to conserve power.
This sensor was designed to be used with the board parallel to the surface being sensed. Because of its small size, multiple units can easily be arranged to fit various applications such as line sensing and proximity/edge detection. For a line sensor with eight of these units arranged in a row, please see the QTR-8A reflectance sensor array. For a similar, smaller sensor with longer range, and intended for use with the board perpendicular to the surface, please see the QTR-L-1A reflectance sensor.
Interfacing with the QTR-1A Output
There are several ways you can interface with the QTR-1A output:
This last method will work if you are able to get high reflectance from your white surface as depicted in the left image, but will probably fail if you have a lower-reflectance signal profile like the one on the right.
Our Pololu AVR library provides functions that make it easy to use these sensors with our Orangutan robot controllers; please see the QTR Reflectance Sensors section of our library command reference for more information. We also have a Arduino library for these sensors.
This module has a single mounting hole intended for a #2 screw (not included); if this mounting hole is not needed, this portion of the PCB can be ground off to make the unit even smaller. The reflectance sensor ships with a 3-pin 0.1" header strip, which can be soldered in the conventional perpendicular orientation or parallel to the PCB, as shown below. You can also solder wires, such as ribbon cable, directly to the pads for the smallest installation.
People often buy this product together with: