QTR-8 Reflectance Sensor Array User's Guide

Table Of Contents

1. Overview and General Specifications

The Pololu QTR-8A [http://www.pololu.com/catalog/product/960] and QTR-8RC [http://www.pololu.com/catalog/product/961]

reflectance sensor arrays are intended as line sensors, but they can be used as a general-purpose proximity or

reflectance sensors. Each module is a convenient carrier for eight IR emitter and receiver (phototransistor) pairs

evenly spaced at intervals of 0.375" (9.525 mm). The outputs are all independent, but the LEDs are arranged in pairs

to halve current consumption. The LEDs are controlled by a MOSFET with a gate normally pulled high, allowing

the LEDs to be turned off by setting the MOSFET gate to a low voltage. Turning the LEDs off might be

advantageous for limiting power consumption when the sensors are not in use or for varying the effective brightness

of the LEDs through PWM control.

The LED current-limiting resistors for 5 V operation are arranged in two stages; this allows a simple bypass of one

stage to enable operation at 3.3 V. The LED current is approximately 20-25 mA, making the total board

consumption just under 100 mA. The schematic diagram of the module is shown below:

Specifications for the QTR-8x Reflectance Sensor Array

• Dimensions: 2.95" x 0.5"

• Operating voltage: 3.3-5.0 V

• Supply current: 100 mA

• Output format for the QTR-8A: 8 analog voltages ranging from 0 V to supplied voltage

• Output format for the QTR-8RC: 8 digital I/O compatible signals

• Optimal sensing distance: 0.125" (3 mm)

• Maximum recommended sensing distance for the QTR-8A: 0.25" (6 mm)

• Maximum recommended sensing distance for the QTR-8RC: 0.375" (9.5 mm)

• Weight without header pins: 0.11 oz (3.1 g)

1. Overview and General Specifications Page 2 of 9