Here:
http://www.stellarjourney.com/index....uipment_onstep
In my implementation, Arduino MEGA is in the box with buttons, Pololu drivers and motors are in the mount (so I can have any sort of electronics, including Bartels - which is still superior to other solutions in terms of functionality, but not in terms of portability).
The box itself works without laptop as well.
If you use Howard's Sky planetarium, only one USB cable is sufficient even if guiding used.