Interface for the encoder of the red fischertechnik motors

Dependencies:   NeedfulThings

Simple Interface for the simple encoder of the red fischertechnik motors.

The interface counts both, rising and falling edges, resulting in 150 counts per revolution. The interface also provides a speed measurement updated with each edge.

Connect the green wire to GND, the red one to +3.3V and the black signal line to any of mbed numbered pins. Additionally connect the signal line via a pullup resitor to +3.3V. A 10K resistor works fine.