H bridge question (newbie)

[scott m]

Hello, I am working on a motor drive and using an h bridge which would require 8 inputs from my computers lpt port but I found this:

http://lathegear.com/174edc50.jpg

Supposedly only two transistors (1/2 of total circuit) need activation with this, which would require only four pins overall. I would like to include a photo instead of a link but can't find the buttons. I have highlighted the path I think the current would follow, one in blue and one in red. I think each part of the circuit would turn on the other transistor "by itself" and then continue on through the winding to ground. I would just build it and experiment but I am running out of transistors
8-). I hope I'm not too outrageously far off base (and confusing) but I am new to electronics. Thanks for any advise. Scott.

[sbrpollock]

What H-Bridge are you using that requires 8 inputs?

[pminmo]

The circuit you posted will have one coil always energized one power is applied. The are a host of ways to do a two input control H bridge. 3 inputs if you want an enable. But for a stepper you need 2 H bridges, is that why you are comming up with the larger number?

Phil

[scott m]

Precisely, a stepper motor, my fault for not stating that. I would rather use four inputs instead of eight. Will it work the way I think with that diagram? Just engergize the x or y? Thanks for the help. Scott.

[pminmo]

Well a one thing. That circuit is mean to be driver with open collector outputs. Some PC parallel ports have an active totem pole output.

Phil