The Pololu QTR-L-1RC reflectance sensor carries a right-angle infrared LED and a right-angle phototransistor, both pointing toward the front edge of the board. The phototransistor uses a capacitor discharge circuit that allows a digital I/O line on a microcontroller to take an analog reading of reflected IR by measuring the discharge time of the capacitor. Shorter capacitor discharge time 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 perpendicular to the surface being sensed, and narrow-angle lenses built into the infrared LED and phototransistor packages allow it to be effective to a range of about 1? (25 mm). Because of its small size, multiple units can easily be arranged to fit various applications such as line sensing and proximity/edge detection. The QTR-L-1RC is sold in packs of two units.

Specifications:

Dimensions: 0.3? ? 0.35? ? 0.12? (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? to 0.25? (3 mm to 6 mm)

Maximum recommended sensing distance: 1? (25 mm)