Yes, grounding is a must, expecially if you are drawing power from two different power supplies, but I wonder if you are using one of those auto-adjusting TTL interfaces , see here: it is possible that if you supply 5V to the interface you get the "wrong" TTL levels in output. Hello again. Here is how i managed it: http://yfrog.com/5cesquemagj The usb gives 3,3 v, but i read that it must be connected to the 5v on TTL, but i can put it on 3,3 v if you think it's better. Is it connected in the right way? I don't know if the TTL is auto-adjusting, you can see how it is at the picture attached. Maybe you will know it.... TTL gives power to HDD through TX? I can use a Polymeter to check the output... Thanks, thanks, thanks!!!