USB 5V Blocker

This is my attempt to solve the problem of USB "vampire power". This occurs when joining two USB devices who both have their +5v rails present on the USB connector. The result is that if only one of the two devices is powered on, it will try to power the other device via the USB.

The most common example is when connecting an OctoPi server to your 3D printer. If the Octopi remains on and you power off the printer, its display and fans will remain running, as they are being powered by the Pi's USB. This is an unhealthy situation, as the Pi does not have enough current capacity on the USB to power your printer, nor does it have the additional 12v or 24v required by the steppers and heaters. The eventual end result, even if the printer remains idle, is a baked Pi.

My project applies a bit of garlic (to chase away the vampire, of course!) by interrupting the USB 5V pin and only allowing the ground and signal pins to pass through. My original thought was to modify the USB cable