The QTR-1A reflectance sensor carries a single infrared LED and phototransistor pair in an inexpensive, 
tiny 0.5" x 0.3" module that can be mounted almost anywhere and is great for edge detection and line following applications.

The reflectance measurement is output as an analog voltage.

Note: The QTR-1A reflectance sensor requires an analog input to take readings. 
The similar QTR-1RC reflectance sensor is available with a digital I/O-compatible output.

The Pololu QTR-1A reflectance sensor carries a single infrared LED and phototransistor pair. 
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 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.

Because of its small size, multiple units can easily be arranged to fit various applications such as line sensing and proximity/edge detection. 
For a line sensor with eight of these units arranged in a row, please see the QTR-8A reflectance sensor array.

Specifications

• Dimensions: 0.3" x 0.5" x 0.1" (without header pins installed)
• Operating voltage: 5.0 V
• Supply current: 25 mA
• Output format: analog voltage
• Output voltage range: 0  to supplied voltage
• Optimal sensing distance: 0.125" (3 mm)
• Maximum recommended sensing distance: 0.25" (6 mm)
• Weight without header pins: 0.008 oz (0.23 g)