This is a DIY controller for bipolar stepper motor from a 5-inch floppy disk drive. The logical part of the scheme borrowed from the Internet. Output npn and pnp transistors form a bridge circuit for each motor winding (50 Ohm, 25 mH).
Outputs is protected from bipolar surge voltage by diodes. LEDs show current direction in windings.
It is important to note that a powerful power supply must have an output voltage less than the supply voltage of the logical part in order for the output keys to work properly. In this case, 8V and 10V.
Middle logic source set direction of motor rotation.
