"Description":"Wheel encoders use non-contact methods to give rotation information. This sensor was developed for the DFRobot Wheel Encoder, though it could be used for any counting time-based task. When you instantiate a class of this type, the gpio pin specified is connected to an interrupt. Whenever a low to high transition occurs on the gpio pin, the internal counter is incremented by one. This class also includes a millisecond counter, so that you can correlate the number of counts to a time period for calculating an RPM or other value as needed.",