I think I'm missing something very fundamental about H bridges but I'm a total electronics newb so some help would be really, really appreciated.
So I've set up an L293D on a breadboard exactly as Tom Igoe shows in his excellent "Physical Computing" book. It's also actually on his stepper motor web page...can't post the link as this is my first post and the forum won't let you post links on your first post, to stop spam I guess.
My setup is as per the 3rd diagram down (for bipolar steppers). I got the motor spinning, thought "great!" but then went to disconnect the motor power supply and guess what?...the stepper carried on spinning. Now I can only assume this is because it's somehow taking power from the Arduino...but I really don't get it. I thought the whole point was that the Arduino can't supply much in the way of current and the H bridge acts like a switch for the higher current supply. It makes no difference to the motor if the motor power is connected or not. For motor power, I'm using a 3x1.5V AA battery pack. If anyone can explain what's going on here and what I actually should be doing then I'd be very grateful!