Testimonials Testimonials

QTR-3A Reflectance Sensor Array

QTR-3A Reflectance Sensor Array

£4.31 incl VAT
(£3.59 exc. tax)
Price in points: 718 points
2.00 g.
In stock
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.


  • 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.


Manufacturer's Details

Manufacturer's SKU :

No posts found

Write a review

No FAQ found

£8.63 incl VAT (£7.19 exc. tax)
This sensor module has 8 IR LED/phototransistor pairs mounted on a 0.375" pitch, making it a great detector for a line-following robot. Pairs of LEDs are... read more
In stock
Price in points: 1438 points

£3.67 incl VAT (£3.06 exc. tax)
The QTR-1A reflectance sensor carries a single infrared LED and phototransistor pair in an inexpensive, tiny 12.7mm x 7.62mm module that can be mounted... read more
In stock
Price in points: 612 points

Customers also bought....

£2.16 incl VAT (£1.80 exc. tax)
White Plastic Mod 0.5 Rack 4x6x250mm. For dimensions and product description, click button below. We source our special order products from the largest... read more
In stock

£0.22 incl VAT (£0.18 exc. tax)
5 off 1N4001 1A 50V Rectifier Diodes A 1A plastic moulded diode 5mm long x 2.5mm diameter with a 0.6mm lead diameter. read more
In stock
Price in points: 36 points

£3.05 incl VAT (£2.54 exc. tax)
Motor Driver L293D The Device is a monolithic integrated high voltage, high current four channel driver designed to accept standard DTL or TTL logic levels... read more
Out of stock
Price in points: 508 points

£0.22 £0.19 incl VAT (£0.16 exc. tax)
A miniature slide switch with solder tag connections and break before make DPDT contacts. Contacts rated at 0.3A, 125V AC Fixing centres 19mm... read more
Out of stock
Price in points: 32 points

£0.43 incl VAT (£0.36 exc. tax)
Non-latching push button action Rated 250mA 125V AC Panel hole diameter 7mm Overall dimensions 28mm long, 10.5mm diameter read more
In stock
Price in points: 72 points