QTR-3A Reflectance Sensor Array

List price: £7.56
£5.28
(£6.34 UK, incl VAT) You save: £2.28 (30%)
Price in points: 1056 points
2110-628
2 g
3 item(s)
End of Line
+
Add to wish list

This compact module packs three IR LED/phototransistor pairs onto a 1.25″ × 0.3″ board. The sensors are mounted on a 0.375″ pitch, making this array a great minimal sensing solution for a line-following robot. Each sensor provides a separate analog voltage output.

Functional Description

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″ (9.525mm) 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″ (19mm) 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 17mA to the LEDs when VCC is 5V, making the total board consumption just over 50mA. The schematic diagram of the module is shown above.

For an alternative array with eight sensors and the ability to turn off the IR LEDs to limit power consumption, consider our QTR-8A reflectance sensor array. For individual reflectance sensors, consider our QTR-1A and QTR-L-1A.

Specifications

  • Dimensions: 1.25″ × 0.3″ × 0.1″ (32 × 8 × 3mm) (without header pins installed)
  • Operating voltage: 5.0V
  • Supply current: 50mA
  • Output format: 3 analog voltages
  • Output voltage range: 0V to supplied voltage
  • Optimal sensing distance: 0.125" (3mm)
  • Maximum recommended sensing distance: 0.25" (6mm)
  • Weight without header pins: 0.02 oz (0.6g)

Interfacing with the QTR-3A Outputs

There are several ways you can interface with the QTR-3A outputs:

  • Use a microcontroller’s analog-to-digital converter (ADC) to measure the voltages.
  • Use a comparator with an adjustable threshold to convert each analog voltage into a digital (i.e. black/white) signal that can be read by the digital I/O line of a microcontroller.
  • Connect each output directly to a digital I/O line of a microcontroller and rely upon its internal comparator.

This last method will work if you are able to get high reflectance from your white surface as depicted in the left image, but will probably fail if you have a lower-reflectance signal profile like the one on the right. (Please note that the images above show the output of a QTR-1A, which uses a sensor with slightly different characteristics than the ones on the QTR-3A.)

Included Components

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 a1×5 right-angle male header strip as shown above. You can also solder wires, such as ribbon cable, directly to the pads for the smallest installation.

Downloads

Customers also bought....

2110-631
£3.63 £2.42 (£2.90 UK, incl VAT)
2110-631
The QTR-1RC reflectance sensor carries a single infrared LED and phototransistor pair in an inexpensive, tiny 12.7mm x 7.62mm module that can be mounted...
12 item(s)
End of Line

2110-634
£4.86 £3.24 (£3.89 UK, incl VAT)
2110-634
The QTR-L-1A reflectance sensor incorporates a right-angle infrared LED and a right-angle phototransistor in an inexpensive, tiny...
4 item(s)
End of Line

7700-102
£2.48 (£2.98 UK, incl VAT)
7700-102
White Plastic Mod 0.5 Rack 4x6x250mm. For dimensions and product description, click button below. We source our special order products from the largest...
Out of stock

1613-400
£0.18 £0.14 (£0.17 UK, incl VAT)
1613-400
Height above PCB 4.3mm. Each switch has a body size of 6 x 6mm square, the height figure is the height from the PCB to the top of the switch 'knob'....
In Stock

Minimum quantity for "Tactile Switch PCB Mounting 6x6x4.3mm" is 5.


4611-014
£3.28 £2.60 (£3.12 UK, incl VAT)
4611-014
This custom-designed plastic wheel by Pololu has a rubber tyre measuring (42 mm) in diameter and is designed to fit the output shafts on our model geared...
15 item(s)
End of Line