QTR-8 Reflectance Sensor Array User's Guide

7. Additional Considerations
As the sensing distance of your sensors increases, the distinction between black and white surfaces starts to
decrease. This problem can be exacerbated by infrared components of ambient lighting. The QTR-8x PCB was
designed to help shield the sensors from ambient IR, but this may not be sufficient for areas with unusually high
ambient IR or in cases where you need to mount your QTR-8x higher than the recommended 0.25" maximum. In
these situations, you might fight it helpful to use shielding (e.g. a skirt around your robot) to block ambient IR.
When troubleshooting your QTR-8x, a digital camera can be useful in determining whether the IR LEDs are
functioning as expected. Many older/cheaper digital cameras lack IR filters (most cell phone cameras fit in this
category) and can therefore be used to determine if the LEDs are on or off. However, some cameras (usually more
expensive ones) have better filters that block IR. In the picture below, a point-and-shoot camera shows the IR LEDs
of our IR Beacon [http://www.pololu.com/catalog/product/701] shining (in purple) but the DSLR with which the picture is
taken does not show the LEDs.
QTR-8A and QTR-8RC Reflectance Sensor Array User's Guide © 2001–2009 Pololu Corporation
7. Additional Considerations Page 9 of 9