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)
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.