Optoreflector

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Optoreflector sensors contain a matched infrared transmitter (LED) and infrared receiver (usually a phototransistor) pair. These devices work by measuring the amount of light that is reflected into the receiver. Because the receiver also responds to ambient light, the device works best when well shielded from abient light, and when the distance between the sensor and the reflective surface is small (the graph below shows how distance affects the output value). IR reflectance sensors are often used to detect white and black surfaces. White surfaces generally reflect well, while black surfaces reflect poorly.

Optoreflector distance.png

Application

In the mechatronics lab, we have the QRB1114 (datasheet) from Fairchild, shown below. It has four pins, with the first pair connected to the LED and the second pair connected to the phototransistor.

Optoreflectors.png

And below you will see a circuit schematic for using the QRB1114. The values of the resistors may need to be adjusted if you use a different device or depending on your usage.

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