Alright, I know very little about what I am currently asking about, but here is the gist of it:
I want to build a cnc machine out of some old floppy drives. I purchased a couple L293D dual H-bridge ICs to drive the stepper motors, and I want to interface with grbl. The problem I seem to be having in designing a proper circuit for this is the circuits for driving stepper motors with the L293D all involve two inputs, one for each direction, and grbl seems to only use one Arduino pin for direction for each axis.
So what I've thought up is using a pnp and an npn transistor to act as a kind of two way switch, when I apply voltage one goes on, other goes off, and vice versa, so that basically 1's and 0's are controlling which way the motor will spin, and the "step pulse" will provide the actual motor power to move it in that direction.
My question is: will this work, or is what I said complete non-sense? I only understand pnp and npn transistors to be something like a "usually on" or "usually off" logic switch, basically, so that's where I've come up with that... Kinda like how an H-bridge works in the first place.
Thanks for taking the time, the diagrams I'm looking at are:
grbl to Arduino pins: http://www.electrodragon.com/w/images/e/e7/Grbl_Pin_Layout.png
L293D driving a stepper motor: http://arduino.cc/en/uploads/Reference/bipolar_stepper_two_pins2.png