Looking for edge or line sensor? You are at the right place. This QTR-1A reflectance sensor carries a single infrared LED and phototransistor pair in an inexpensive, tiny 0.5" x 0.3" module that can be mounted almost anywhere. The reflectance measurement is output as an analog voltage. This sensor is sold in packs of two units.
This QTR-1A reflectance sensor carries a single infrared LED and phototransistor pair. 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 parallel to the surface being sensed. Because of its small size, multiple units can easily be arranged to fit various applications such as line sensing and proximity/edge detection.
- Dimensions: 0.3" x 0.5" x 0.1" (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
- Optimal sensing distance: 0.125" (3 mm)
- Maximum recommended sensing distance: 0.25" (6 mm)
- Weight without header pins: 0.008 oz (0.2 g)
Interfacing with the QTR-1A Output:
There are several ways you can interface with the QTR-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 I/O line of a microcontroller.
- Connect the output directly to the 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 this image.
But will probably fail if you have a lower-reflectance signal profile like this result.
The Pololu AVR library provides functions that make it easy to use these sensors with Orangutan robot controllers; please see the QTR Reflectance Sensors section of the library command reference for more information. There is also Arduino library for these sensors.
- Pololu QTR Reflectance Sensor Application Note (pdf)
- Datasheet of Fairchild's QRE1113GR sensor (pdf)
- Pololu AVR library
- Arduino library
- 2 x QTR-1A board
- 2 x 3-way straight header pin
- 2 x 3-way right angle header pin