A4988 

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http://www.instructables.com/id/Drive-a-Stepper-Motor-with-an-Arduino-and-a-A4988-/

http://documentation.echopen.org/CAT-daughter_board/DB-motor_control_v3/doc/pololu_a4988.pdf

http://howtomechatronics.com/tutorials/arduino/how-to-control-stepper-motor-with-a4988-driver-and-arduino/