Application Notes

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Table Of Contents

Pololu QTR Reflectance Sensor Application Note
- 1. QTR-xRC Sensor Output (Intended for Digital I/Os)
- 2. QTR-xA Sensor Output (Analog Voltages)

Pololu QTR Reflectance Sensor

Application Note

1. QTR-xRC Sensor Output (Intended for Digital I/Os) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2. QTR-xA Sensor Output (Analog Voltages) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

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Summary of content (5 pages)

PAGE 1
Pololu QTR Reflectance Sensor Application Note © 2001–2009 Pololu Corporation Pololu QTR Reflectance Sensor Application Note 1. QTR-xRC Sensor Output (Intended for Digital I/Os) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. QTR-xA Sensor Output (Analog Voltages) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Pololu QTR Reflectance Sensor Application Note © 2001–2009 Pololu Corporation 1. QTR-xRC Sensor Output (Intended for Digital I/Os) Each QTR-1RC [http://www.pololu.com/catalog/product/959] and QTR-8RC [http://www.pololu.com/catalog/product/961] reflectance sensor phototransistor output is tied to a capacitor discharge circuit as shown on the right, which allows a digital I/O line on a microcontroller to take an analog reflectance reading by measuring the discharge time of the capacitor.
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Pololu QTR Reflectance Sensor Application Note QTR-1RC output (yellow) when 3/8" above a white surface and microcontroller timing of that output (blue). QTR-1RC output (yellow) when 3/8" above a white/black interface and mcu timing of that output (blue). © 2001–2009 Pololu Corporation QTR-1RC output (yellow) when 3/8" above a black line and microcontroller timing of that output (blue).
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Pololu QTR Reflectance Sensor Application Note © 2001–2009 Pololu Corporation 2. QTR-xA Sensor Output (Analog Voltages) Each QTR-1A [http://www.pololu.com/catalog/product/958] and QTR-8A [http://www.pololu.com/catalog/product/960] reflectance sensor phototransistor output is connected to a pull-up resistor as shown below to form a voltage divider that produces an analog voltage output that ranges between 0 V and the supplied voltage (which is typically 5 V).
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Pololu QTR Reflectance Sensor Application Note © 2001–2009 Pololu Corporation between the three captures is the distance from the sensor to the disk: ~1/8" in the first capture, ~1/4" in the second capture, and ~3/8" in the third capture. QTR-1A output 1/8" away from a spinning white disk with a black line on it. QTR-1A output 1/4" away from a spinning white disk with a black line on it. QTR-1A output 3/8" away from a spinning white disk with a black line on it.