http://www.geeetech.com/wiki/index.php/Stepper_Motor_5V_4-Phase_5-Wire_%26_ULN2003_Driver_Board_for_Arduino#Interfacing_circuits
http://www.jangeox.be/2013/10/stepper-motor-28byj-48_25.html
http://www.jangeox.be/2013/10/change-unipolar-28byj-48-to-bipolar.html