Links to read about "The Theory"

[rtek1000]

• PID Autotune Library: http://brettbeauregard.com/blog/2012/01/arduino-pid-autotune-library/

  https://playground.arduino.cc/Code/PIDAutotuneLibrary/

• PID Library: https://playground.arduino.cc/Code/PIDLibrary/

  https://github.com/br3ttb/Arduino-PID-Library/

  http://brettbeauregard.com/blog/2011/04/improving-the-beginners-pid-introduction/