The Pololu QTR-1RC reflectance sensor carries a single infrared LED and phototransistor pair. 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 20-25 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.
Due to its small size, multiple units can easily be arranged to fit various applications such as line sensing and proximity/edge detection.
Check out this awesome tutorial using an Arduino.
- Dimensions: 0.3" x 0.5" x 0.1" (without header pins installed)
- Operating voltage: 5.0 V
- Supply current: 25 mA
- Output format: digital I/O compatible
- Optimal sensing distance: 0.125" (3 mm)
- Maximum recommended sensing distance: 0.375" (9.5 mm)
- Weight without header pins: 0.008 oz (0.23 g)