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Is the level of ground at GPIO Pins 9 et al. the same as ground of the micro USB input?

I am building an application where multiple GPIO pins will output voltage, and I do not want to send the current of multiple GPIO pins through one ground GPIO pin.

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It is unlikely that the device can source more current than a single ground return pin can handle. And cabling over to the USB would be even higher impedance. –  Chris Stratton Nov 29 '12 at 21:44
    
I will not use a standard USB cable but use a fixed voltage regulator connected to USB plus and ground. –  Residuum Nov 30 '12 at 23:12
    
Doesn't really matter. The lowest impedance at high frequency would be the physically closest connection, so for a GPIO signal that would be the GPIO ground reference. In terms of DC supply limits, the input PTC fuse is the greater limitation than the physical header pin. Not running the supply for a high current peripheral through the pi at all would however be a potential improvement. –  Chris Stratton Nov 30 '12 at 23:27
    
I am trying to close several relays with drivers, i.e. using circuits of a BC337 transistor, a 270 Ohm resitor and a 1N4148 diode (mikrocontroller.net/articles/…). The question was about simplifying ground connections of the circuits, so I do not have to connect them back to the GPIO ground. –  Residuum Dec 1 '12 at 12:34
    
I'd misread and through you were going to pull power from the USB output. At any rate, you don't really want the relay power running through the pi board at all, but rather separately connected to the same power supply - or to a different supply, with the GPIO ground furnishing the common reference (though at the low frequencies involved in your case, any of the grounds on the board should be fine for reference purposes). –  Chris Stratton Dec 1 '12 at 15:58
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1 Answer

up vote 2 down vote accepted

They are the same ground as you can see here:

The Micro USB input:

USBInput

The GPIO Output:

P1-GPIO-Output

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