修改至 http://ivmech.github.io/ivPID,使其可适配在MicroPython和mPython上。
Ivmech PID Controller is simple implementation of a Proportional-Integral-Derivative (PID) Controller in the Python Programming Language.
More information about PID Controller: http://en.wikipedia.org/wiki/PID_controller
Test PID with Kp=1.2, Ki=1, Kd=0.001 (test_pid.py)