Pololu QTR-1RC Digital 1P Reflectance Sensor (2-Pack) ideal for line following Robots


This reflectance sensor is designed specifically for robotic line following applications, and you get two of them in each package (perfect for measuring differential reflectance), but these sensors can be used for a wide range of applications ranging from industrial to hobby designs.

Basically this sensor emits infrared light (IR) and uses a phototransistor to detect the amount of reflected light seen. You can access this data using a single digital IO pin in a similar way to how the PING and Virtuabotix Ultrasonic sensors are triggered then time high is measured (via pulsin). The time that the line stays high correlates to how reflective a material is. Highly reflective materials output a HIGH only briefly (microseconds sometimes), while non-reflective surfaces can take much longer (as much as a few milliseconds). The fact that this sensor can be read using a digital pin means that you don't have to sacrifice an Analog pin (or have one for that matter) just to use this sensor.

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Package Contents:

Pololu QTR-1RC Digital 1P Reflectance Sensor (2-Pack) ideal for line following robots


Dimensions: 0.3″ x 0.5″ x 0.1″ (without optional header pins installed)
Operating voltage: 5.0 V
Supply current: 17 mA
Output format: digital I/O-compatible signal that can be read as a timed high pulse
Optimal sensing distance: 0.125″ (3 mm)
Maximum recommended sensing distance: 0.375″ (9.5 mm)
Weight without header pins: 0.008 oz (0.2 g)
No analog-to-digital converter (ADC) is required
Improved sensitivity over voltage-divider analog output
Parallel reading of multiple sensors is possible with most microcontrollers

(Usage information and diagrams provided by Pololu)

Usage diagram:

QTR-1RC Reflectance Sensor recomended circuit

The diagram above shows roughly how this sensor operates (though this particular sensor using modified 1 wire digital protocols instead of analog output).

Reflectance is measured by setting the I/O line to an output and driving it high (for at least 10 uS), making the I/O line an input (high impedance), and measuring the time for the voltage to decay by waiting for the I/O line to go low. This can be done easily using the Arduino Pulsin function.


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