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The QTR-3A reflectance sensor array is intended as a line sensor, but it can be used as a general-purpose proximity or reflectance sensor. The module is a convenient carrier for three IR emitter and receiver (phototransistor) pairs. With sensors spaced at intervals of 0.375″ (9.525 mm) along of the board’s longer axis, this array works well as a minimal detector for line-following robots, as line-following courses are commonly made using 3/4″ (19 mm) black electrical tape. The middle sensor is slightly offset along the short axis of the board.
Each phototransistor is connected to a pull-up resistor to form a voltage divider that produces an analog voltage output between 0 V and VCC (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 resistors are set to deliver approximately 17 mA to the LEDs when VCC is 5 V, making the total board consumption just over 50 mA.
This module has two mounting holes intended for #2 screws (not included); if the mounting holes are not needed, the ends of the PCB can be ground off to make the unit even smaller (less than 1″ wide). The reflectance sensor array ships with a 1×5 straight male header strip and a 1×5 right-angle male header strip. You can also solder wires, such as ribbon cable, directly to the pads for the smallest installation.
5VDC Operating Voltage
50mA Supply Current
Analog I/O Compatible
Optimal Sensing Distance: 0.125” (3mm)
32 x 8 x 2.54 mm