QTRX-MD-13RC unusual reading

I am working on developing a line following robot using your QTRX-MD-13RC sensor and Arduino Uno R3. I ran your QTRRCRawValuesExample and all sensors return less than 200 readings for white background and 2500 reading for black line except for sensors 5 and 10. Sensors 5 and 10 return values ranging from 1700 to 2100 readings for black line. Is this normal? Don’t they also have to return 2500 for black line? Should the QTRX sensors be mounted exactly 10mm above the surface that they read or is there any mounting distance range for optimal readings?

Looking forward to hearing from you,


Are you looking at raw sensor measurements or calibrated ones? Some unit-to-unit variation with each sensor is expected, but that can normally be compensated for by calibrating the sensors well.

The 10mm optimal range mentioned on the product pages for the QTRX sensors is not a strict requirement. In general, the closer the object, the higher the contrast between light and dark readings, but the sensors’ performance (and optimal range) can depend on various aspects of each individual application like ambient lighting, the brightness level used, and presence of physical shrouding.

Also, if you have not done so already, I suggest testing your board with the example programs from our QTR reflectance sensors Arduino library with minimal modification.

- Patrick