# USB data transfer without charge

This is a total hardware noob question, but I really need an answer to this one:

I have 2 devices, A & B that are both self-powered. I would like to disable the +5VDC cord inside USB port, but still send data between devices through Data+ & Data- cables. Can this be done?

• Google for USB data link. The ones I know have proprietary protocols when used on Windows, and offer a regular TCP/IP link on Linux. – jippie Jul 1 '15 at 18:30
• Oh the short answer is: without special hardware in the cable: No. – jippie Jul 1 '15 at 18:32
• I don't get it. Are devices A and B both hosts, or are the USB devices, or what? If one is a host and one is a device, there is no reason you can't hook them together. But if they are both the same type, then I don't think it will work. You could read up on USB OTG if you are interested. Also not clear on what you mean by diabling +5VDC cord. Why would you do that? – mkeith Jul 1 '15 at 19:07
• We have a HDMI connection on the B (slave) device that switches off the HDMI feed as soon as it detects voltage on USB port. If the +5VDC cord is cut (physically), the HDMI feed continues to run. As we cannot modify hardware on slave device, we're wondering if modification on master or cable is possible. – Gal Jakič Jul 1 '15 at 20:01

If you want to stay compliant with the USB standard without transferring power, then you can use a USB Isolator, either as a chip that must be included on your PCB for about $7 plus a few passives or as a prefab unit for about$40. (U.S. dollars)