MarkT:
What are you trying to do with this motor? If you only need slow rotation you should
have bought a high-impedance unipolar stepper and driven with a ULN2803, much
simpler.If you want high performance from a stepper you just will not get it with H-bridge driver,
you need a current-controlling chopper driver for that application.
I need to rotate the motor on a slow move, but still need to have a good torque since is going to open or close a curtain, and an ULN2803 only provides 500mA.