I am working on a Robotics project that involves using an otherwise expired Roomba as a base and using an old Powerbook as brains. I picked an 8/8/8 as the interface and am planning a two-relay-per-motor drive interface with switched electromechanical h-bridges. That leaves 4 outs for a primitive 1DOF arm with a gripper. I was planning on modifying servos to power the arm about the same way as the motors (except with stops.) It occurred to me that it might be possible to pulse the outs of the 8/8/8 directly to use the servos unmodified. Would it be possible to use two of the 8/8/8 outs, one as a V+ and one as the control to the servo white/yellow? What about using only one out as the control line with an external battery V+:would I risk frying the interface if I used an external power source and common ground to the control and power?
(Incidentally, here is a video of the robot with a primitive 2-nv brain installed. No arm yet and the eyes are now lit. May Benny Hill forgive me.)