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- Manufacturer: Pololu
- Order number: EXP-R25-291
- Manufacturer part number: 2459
- Availability: 4
- country of origin: US
- HS code: 90275000
- Weight (kg): 0.001
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.
For a line sensor with eight of these units arranged in a row, please see the QTR-8RC reflectance sensor array; for a similar array of three slightly different sensor components, see the QTR-3RC. For a similar, smaller sensor with longer range, and intended for use with the board perpendicular to the surface, please see the QTR-L-1RC reflectance sensor.
QTR sensor size comparison. Clockwise from top left: QTR-3RC, QTR-1RC, QTR-L-1RC, QTR-8RC.
- 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: digital I/O-compatible signal that can be read as a timed high pulse
- Optimal sensing distance: 0.125" (3 mm)
- Maximum recommended sensing distance: 0.375" (9.5 mm)
- Weight without header pins: 0.008 oz (0.2 g)
QTR-1RC output (yellow) when 1/8" above a black line and microcontroller timing of that output (blue).
- No analog-to-digital converter (ADC) is required
- Improved sensitivity over voltage-divider analog output
- Parallel reading of multiple sensors is possible with most microcontrollers
- 1. Set the I/O line to an output and drive it high
- 2. Allow at least 10 us for the 10 nF capacitor to charge
- 3. Make the I/O line an input (high impedance)
- 4. Measure the time for the capacitor to discharge by waiting for the I/O line to go low
With a strong reflectance, the discharge time can be as low as several dozen microseconds; with no reflectance, the discharge time can be up to a few milliseconds. The exact time of the discharge depends on your microcontroller’s I/O line characteristics. Meaningful results can be available within 1 ms in typical cases (i.e. when not trying to measure subtle differences in low-reflectance scenarios), allowing up to 1 kHz sampling.
Our Pololu AVR library provides functions that make it easy to use these sensors with our Orangutan robot controllers; please see the QTR Reflectance Sensors section of our library command reference for more information. We also have a Arduino library for these sensors.
- Size: 0.3″ × 0.5″ × 0.1″1
- Weight: 0.2 g2
- 1. Without optional included header pins.
- 2. For a single sensor without included optional header pins.