# QTR-L-1A Reflectance Sensor (2-Pack) **Type:** Product page · **SKU:** POLOLU-2454 · **Brand:** [Pololu](https://core-electronics.com.au/brands/pololu-australia) **Page:** https://core-electronics.com.au/qtr-l-1a-reflectance-sensor-2-pack.html ([markdown](https://core-electronics.com.au/qtr-l-1a-reflectance-sensor-2-pack.html.md)) ## Retired product This product is retired and no longer available for purchase. Search the catalogue for an alternative. ## Description **Note:** The QTR-L-1A reflectance sensor requires an analog input to take readings. The similar [QTR-L-1RC reflectance sensor](https://core-electronics.com.au/qtr-l-1rc-reflectance-sensor-2-pack.html) is available with a digital I/O-compatible output. **Functional Description** | ![](https://a.pololu-files.com/picture/0J4433.227.png?e738d61d87595c2b0ece249fc21fb152) | |---| The Pololu QTR-L-1A reflectance sensor carries a right-angle infrared LED and a right-angle phototransistor, both pointing toward the front edge of the board. 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 17 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. This sensor was designed to be used with the board perpendicular to the surface being sensed, and narrow-angle lenses built into the infrared LED and phototransistor packages allow it to be effective to a range of about 1" (25 mm). Because of its small size, multiple units can easily be arranged to fit various applications such as line sensing and proximity/edge detection. The QTR-L-1A is sold in packs of **two** units. For a similar sensor that can be used with the board parallel to the surface, but with shorter range, please see the [QTR-1A reflectance sensor](https://core-electronics.com.au/qtr-1a-reflectance-sensor-2-pack.html). Pololu also offer arrays of three and eight sensors: the [QTR-3A reflectance sensor array](https://core-electronics.com.au/qtr-3a-reflectance-sensor-array.html) and the [QTR-8A reflectance sensor array](https://core-electronics.com.au/qtr-8a-reflectance-sensor-array.html). | [![](https://a.pololu-files.com/picture/0J4642.400.jpg?9ae24a3959a88fee8dd66d333023e2dc)](https://a.pololu-files.com/picture/0J4642.1200.jpg?9ae24a3959a88fee8dd66d333023e2dc) | |---| | QTR sensor size comparison. Top row: QTRX-HD-07, QTR-HD-07; middle row: QTR-3, QTR-1, QTR-L-1; bottom row: QTR-8. | **Specifications** | [![](https://a.pololu-files.com/picture/0J4431.300.jpg?1b1eede3eca29b69a1b826f7db69323c)](https://a.pololu-files.com/picture/0J4431.1200.jpg?1b1eede3eca29b69a1b826f7db69323c) | |---| - Dimensions: 0.3" × 0.35" × 0.12" (without optional header pins installed) - Operating voltage: 5.0 V - Supply current: 17 mA - Output format: analog voltage - Output voltage range: 0 to supplied voltage (dependent on operating environment) - Optimal sensing distance: 0.125" to 0.25" (3 mm to 6 mm) - Maximum recommended sensing distance: 1" (25 mm) - Weight without header pins: 0.006 oz (0.2 g) **Interfacing with the QTR-L-1A Output** There are several ways you can interface with the QTR-L-1A output: - Use a microcontroller’s analog-to-digital converter (ADC) to measure the voltage. - Use a comparator with an adjustable threshold to convert the analog voltage into a digital (i.e. black/white) signal that can be read by the digital input line of a microcontroller. - Connect the output directly to the digital input 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 (so that there is a large output voltage difference over black and white surfaces), but will probably fail if you have a lower-reflectance signal profile. The following table shows some typical output voltages from the sensor over different surfaces and at different distances: | | White surface | 3/4" black electrical tape | |---|---|---| | 0.25" distance | 0.2 V | 3.8 V | | 1" distance | 2.4 V | 3.5 V | Ambient light, especially sunlight, can affect the sensor readings significantly. If the output voltage from the QTR-L-1A is consistently low, you might need to add shielding around the sensor or mount it in a different location to reduce interference from outside light sources. Pololu's Pololu AVR library provides functions that make it easy to use these sensors with Pololu's [Orangutan robot controllers](https://core-electronics.com.au/category/8/robot-controllers); please see the QTR Reflectance Sensors section of Pololu's library command reference for more information. Pololu also have a Arduino library for these sensors. **Included Components** Each pack of two reflectance sensors includes sets of [straight male header strips](https://core-electronics.com.au/0-100-2-54-mm-breakaway-male-header-1x40-pin-straight.html) and [right-angle male header strips](https://core-electronics.com.au/0-100-2-54-mm-breakaway-male-header-1x40-pin-right-angle.html), which allow you to mount them in the orientation of your choice. You can also solder wires, such as ribbon cable, directly to the pads for the most compact installation. | \| [![](https://a.pololu-files.com/picture/0J4434.300.jpg?5502acfb8dfeeb48866b1b9de114a262)](https://a.pololu-files.com/picture/0J4434.1200.jpg?5502acfb8dfeeb48866b1b9de114a262) \| \|---\| \| QTR-L-1A or QTR-L-1RC reflectance sensor (2-pack) with included header pins. \| | \| [![](https://a.pololu-files.com/picture/0J4432.300.jpg?2318f2abcb3577ccfcf6b7114bcdec6c)](https://a.pololu-files.com/picture/0J4432.1200.jpg?2318f2abcb3577ccfcf6b7114bcdec6c) \| \|---\|---\| \| QTR-L-1A and QTR-L-1RC reflectance sensors plugged into a breadboard in two possible orientations. \| | |---| **People often buy this product together with:** | [![QTR-8A Reflectance Sensor Array](https://a.pololu-files.com/picture/0J615.100.jpg?ef5903b25450c25de151ed9b43d1fce3)](https://core-electronics.com.au/qtr-8a-reflectance-sensor-array.html) | [QTR-8A Reflectance Sensor Array](https://core-electronics.com.au/qtr-8a-reflectance-sensor-array.html) | |---|---| | [![QTR-L-1RC Reflectance Sensor (2-Pack)](https://a.pololu-files.com/picture/0J4429.100.jpg?36c064268d187fa85c0720fa7556e1af)](https://core-electronics.com.au/qtr-l-1rc-reflectance-sensor-2-pack.html) | [QTR-L-1RC Reflectance Sensor (2-Pack)](https://core-electronics.com.au/qtr-l-1rc-reflectance-sensor-2-pack.html) | |---|---| | [![QTR-3A Reflectance Sensor Array](https://a.pololu-files.com/picture/0J4634.100.jpg?0f0149ee8924596844aa274cc0b34632)](https://core-electronics.com.au/qtr-3a-reflectance-sensor-array.html) | [QTR-3A Reflectance Sensor Array](https://core-electronics.com.au/qtr-3a-reflectance-sensor-array.html) | |---|---| **Identifying markings** | Other PCB markings: | 0J7200 | |---|---| **Documentation and other information** - ![](https://a.pololu-files.com/picture/0J641.100.jpg?08dbaf9dd44b994eb477f4effaecdd1b)**Pololu QTR Reflectance Sensor Application Note (Printable PDF)** Information about using the Pololu QTR reflectance sensors, including differences between A-type and RC-type sensors and sample oscilloscope screen captures of sensor outputs. - ![](https://a.pololu-files.com/picture/0J820.100.jpg?a44d405951389e985b1535132805f6e9)**Pololu AVR C/C++ Library User’s Guide (Printable PDF)** Information about installing and using the C/C++ libraries provided for use with Pololu products. - ![](https://a.pololu-files.com/picture/0J741.100.jpg?725d319fb76b96a96ebbb756122b54b3)**Pololu AVR Library Command Reference (Printable PDF)** A reference to commands provided in the Pololu C/C++ and Arduino libraries for the AVR. - ![](https://a.pololu-files.com/picture/0J865.100.jpg?139f815df6176d87af70e9c26db8a4fd)**Building Line Following and Line Maze Courses (Printable PDF)** Step-by-step instructions for building your own line-following courses. **File downloads** - **Drill guide for QTR-L-1A and QTR-L-1RC Reflectance Sensor (13k dxf)** This DXF drawing shows the locations of all of the board’s holes. - **Dimension diagram of the QTR-L-1x Reflectance Sensor (119k pdf)** - **3D model of the QTR-L-1A Reflectance Sensor (2MB step)** - **Guide utilisateur du senseur QTR (suiveur de ligne) (1MB pdf)** Un guide utiliser et exploiter un senseur QTR (détecteur de ligne) (version 0.1). **Note:** This French translation of Pololu's QTR sensor documentation was made by Pololu's distributor MCHobby. **Recommended links** - **[mbed library for QTR sensors](https://os.mbed.com/users/phillippsm/code/PololuQTRSensors/)** Matthew Phillipps ported Pololu's [Arduino Library for the Pololu QTR Reflectance Sensors](https://github.com/pololu/qtr-sensors-arduino) to the [mbed](https://core-electronics.com.au/arm-mbed-nxp-lpc1768-development-board.html) platform. The Arduino library is designed to work with [Pololu QTR reflectance sensors](https://core-electronics.com.au/category/123/pololu-qtr-reflectance-sensors), so the mbed library should too, but Matthew points out he only tested it with the analog sensors. This library was not written and is not maintained by Pololu. - **[Arduino library for the Pololu QTR Reflectance Sensors](https://github.com/pololu/qtr-sensors-arduino)** This library for [Arduino](https://core-electronics.com.au/hardware.html) makes it easy to interface with Pololu [QTR Reflectance Sensors](https://core-electronics.com.au/category/123/pololu-qtr-reflectance-sensors). ## Images - [Product image 1](https://core-electronics.com.au/media/catalog/product/q/t/qtr_l_1a_reflectance_sensor__2_pack___pololu_2454__00.jpg)