Figure 1: Reflectance sensors
The reflectance sensors in figure 1 are used to measure reflectance as the wheel rotates during travel time. As pictured in figure 2, the wheel has a reflective tape attached to it and each time the reflective tape passes the sensor to the non-reflective surface; a low voltage signal is then interpreted into the form of marks. The Arduino microcontroller will record eight marks as one full wheel revolution which is approximately 3.9 inches.
Figure 2: Wheel with reflective tape
Figure 3 represents how imperative it is to have the reflectance sensors as close as possible to the wheel with reflective tape. The further the wheel is away from the tire, the greater the chance that light pollution will degrade the reading of the reflectance sensor. Erroneous data has been collected from the reflectance sensor with the wheel being only 3/8 inches away from the sensors.
Figure 3: Wheel attached for reflectance sensor to detect