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Powering U3 and tablet

USB power supply

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5 replies to this topic

#1 Aro

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Posted 03 March 2015 - 09:36 AM

I have a question regarding power and splicing USBs.  We have a 5VDC, 3.5Amp power supply we would like to use to power both the U3-LV and the tablet computer we are using to control it (that way we don't have to worry about battery life).  I've wired the +5V from the power supply to both the U3 and the tablet USB jack, and the power supply ground to both the U3 and tablet USB jack.  Then I wired the two signal wires from the tablet USB jack to the U3.  When the tablet is plugged into the jack and the device turned on, the U3 is powerd (though I cannot tell if its drawing from the power supply or the tablet) and is able to communicate with the tablet, but the tablet will not charge.  I've double checked to ensure all the wires are connected to the proper pins, but still nothing.  Any help would be most appreciated.



#2 LabJack Support

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Posted 03 March 2015 - 09:49 AM

Are you saying the tablet has only 1 USB port that is used for charging the tablet (power input to the tablet) and also can be used as a host port (to talk to a device)?



#3 Aro

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Posted 03 March 2015 - 10:13 AM

Yes, the tablet only has one USB micro port.  It can be used for charging and hosting.



#4 Aro

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Posted 03 March 2015 - 12:31 PM

Never mind.  Turns out it was the USB micro to female A converter wire that was the problem.  It must only be wired for communication and not power (not sure why some one would make it that way).  Thanks for your help anyway.



#5 LabJack Support

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Posted 03 March 2015 - 03:37 PM

So did you get it working?  I'm not sure if USB spec requires (or even allows) an on-the-go (USB OTG) port to accept input current for charging while acting as a host port.



#6 Aro

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Posted 17 March 2015 - 03:12 PM

Sorry for the delay in responding.  So the tablet battery icon shows that it is charging and the screen gets brighter as if it were plugged into a wall receptacle, but it doesn't appear to actually build charge.  However, it doesn't seem to loose charge either.  The tablet has about an 8hr battery life and we had it running our device for well over that and yet the battery life never changed, up or down.  You maybe right about USBs not being able to charge and be a host at the same time, but it seems like it can power itself and act as a host at the same time.  Which is good enough for our application.

 

Thanks again for you help





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