QTR-L-1A Reflectance Sensor (2-Pack) Note: The QTR-L-1A reflectance sensor requires an analog input to take readings. The similar QTR-L-1RC reflectance sensor is available with a digital I/O-compatible output. Functional Description The Pololu QTR-L-1A reflectance sensor carries a right-angle infrared LED and a right-angle phototransistor, both pointing toward the front edge of the board. 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 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- 1A is sold in packs of two units. For a similar sensor that can be used with the board parallel to the surface, but with shorter range, please see the QTR-1A reflectance sensor. We also offer arrays of three and eight sensors: the QTR-3A reflectance sensor array and the QTR-8A reflectance sensor array.QTR sensor size comparison. Clockwise from top left: QTR-3RC, QTR-1RC, QTR-L-1RC, QTR-8RC. Specifications Dimensions: 0.3 0.35 0.12 (without optional header pins installed) Operating voltage: 5.0 V Supply current: 17 mA Output format: analog voltage Output voltage range: 0 to supplied voltage (dependent on operating environment) Optimal sensing distance: 0.125 to 0.25 (3 mm to 6 mm) Maximum recommended sensing distance: 1 (25 mm) Weight without header pins: 0.006 oz (0.2 g) Interfacing with the QTR-L-1A Output There are several ways you can interface with the QTR-L-1A output: Use a microcontrollers analog-to-digital converter (ADC) to measure the voltage. Use a comparator with an adjustable threshold to convert the analog voltage into a digital (i.e. black/white) signal that can be read by the digital input line of a microcontroller.