Help running 2-wire stepper motor

Hi, I'm looking at this method of running a 2-wire Biolar stepper motor ( http://www.tigoe.net/pcomp/code/category/arduinowiring/51 ) specifically credited to Sebastian Gassner. My question is that the diagram shows a NPN transistor but does specify what type. Can anyone help? Does it depend on the stepper motor itself? How do I calculate it? Thanks!

The transistors are simply inverters so any NPN type will do in this case.

You need to choose a transistor that can sink (or source) enough current to run the specified motor.

/me

You need to choose a transistor that can sink (or source) enough current to run the specified motor.

No if you look at the circuit in the link you will see it just generates complementary control signals to the driver chip.

That's true sorry. Wasn't looking at the right diagram!

/me

So using a BC547 is fine? I'm guessing both of them would have to be the same, right? Thanks again!

Yes, two BC547 transistors should work in this circuit.

I'm guessing both of them would have to be the same, right?

No they could be different types it's not critical at all.