Stepper motor driver board mainly adopts ULN2003 chip. It is a seven-fold Darlington array. This circuit is the inverted output type, that is, its output terminal can be turned on to work only by inputting a low-level voltage. Onboard comes with 4 LEDs, so in this way you can know the state of input control pulse. In the experiment, we connect the stepper motor to its driver board, and then connect the drive board to microcontroller. The interface is anti-reversed type, so do not worry about the wrong connection.