Question : Problem: DIY USB "Y" Cable

Hello,

I have a stack of usb cables and want to make a "Y" cable,  something like this:

Computer ------------------------  Peripheral
                         |
                         -----------------   USB Power supply

So in this instance, the "computer" does not have enough power on its usb port to power "peripheral", so I need the volts from a usb power supply, which is providing 5v

Currently, I have the white and green data cables between the computer and peripheral straight through.

I have the ground from all three connected together, and the red 5v line from the USB power supply connected to the red 5v line to the peripheral.

The final red 5v from the "computer" is not connected to anything.

With this configuration, the computer recognises the peripheral, but I get "rejected 1 configuration due to insufficient available bus power"

I have confirmed the 5v is present from the USB power supply.  It appears that the usb host on the computer doesn't recognise it is getting power from elsewhere.

I have guessed at how to wire the voltage together.  Is there something else I need to do to get this working?

Answer : Problem: DIY USB "Y" Cable

Well, the answer was "yes" the cable is correct.  And the way to get it to work in this scenario was to disable power management for the usb port

echo -n "1" > /sys/bus/usb/devices//bConfigurationValue

Don't try this at home unless you know that the power is present...