Just wanted to share very simple thing with community. Sometimes you don't have step/dir motor driver to drive your unipolar motor right here right now. Temporary solution can be to use arduino as software step/dir driver.
I tried to google it somewhere, but couldn't find existing solution and wrote this very simple sketch. I hope it can help someone.
I have my step/dir drivers still somewhere in postman's satchel on the way from China. And I wanted to start using my cnc engraver made of scrap parts from old printers and dvd right now. I use GRBL on arduino as controller which supports only step/dir drivers, the only thing was missing - motor drivers themselves.
While waiting for drivers I just took spare arduino uno and made it work as step/dir driver for my unipolar motors. I used ULN2803/ULN2003 to drive motors. Its okay in case motors are not very powerful.
How to connect motor using uln2003/uln2803: example circuits
Sketch is on github: SoftwareStepDirUnipolarDriver
You are free to use it in any way you want.