USB communication with battery power

[mattomatto]

Hi all,

I'd like to know if I can power the Teensy with a battery, cut the VUSB trace so that the teensy can only be powered through the battery, and still communicate with a computer over USB?

I'm assuming this is the case because the following page states USB operation will work as low as 3.4v.
https://www.pjrc.com/teensy/external_power.html

Can I the also cut the USB GND connection?

My aim is to make a device that can communicate over usb but not use the bus power. This is because there are open +/- contacts on the device and CE/FCC guidelines wouldn't allow a product to have that whilst connect to a computer as it might damage it or cause a spark.

Side note: If anyone is particularly knowledgable on CE/FCC guidelines where open contacts on a PCB are concerned, I would really appreciate some guidance as it's been holding an otherwise complete product back for several months.

Thanks very much

 

[Theremingenieur]

As far as I know, the USB GND connection must not be cut because it serves as a reference potential for the 2 data lines. Out of that, common ground reduces the risk of electric discharge.

 

[clbphllps]

Yes, you can do that. Alternatively, I cut the red wire out of my USB cable since I seem to install the Teensy first without remembering to cut the VUSB trace.

 

[mattomatto]

Great, thanks both