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Thread: USB double adaptor question

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    Default USB double adaptor question

    Ok here is what I am trying to do. I have a cheap Chineese Android tablet that does not have an internal GPS. I have a GPS dongle that I have working on it with OZI Explorer. The problem is that the dongle is connected via the only usb port on the tablet. What I want to be able to do is supply dc power to the tablet via the usb port to charge it while collecting data from the GPS dongle. I think it should be possible i just need to find a double adapter that has a male usb plug (either micro usb or standard usb) with 2 usb sockets wired in parallel. Does such a thing exist or am I going to have to make one?

    I have tried a powered hub plugged in, but it does not charge the tablet.

    thanks in advance
    Mike



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    Quote Originally Posted by motocross_mike View Post
    Ok here is what I am trying to do. I have a cheap Chineese Android tablet that does not have an internal GPS. I have a GPS dongle that I have working on it with OZI Explorer. The problem is that the dongle is connected via the only usb port on the tablet. What I want to be able to do is supply dc power to the tablet via the usb port to charge it while collecting data from the GPS dongle. I think it should be possible i just need to find a double adapter that has a male usb plug (either micro usb or standard usb) with 2 usb sockets wired in parallel. Does such a thing exist or am I going to have to make one?

    I have tried a powered hub plugged in, but it does not charge the tablet.

    thanks in advance
    Mike
    I think you may find that your hub is charging the tablet, but at a rate that is insufficient to have the charging indicator come on. To check this, let the battery discharge for a while. Plug the hub back in and note the % charge of the battery. Come back in a couple of hours and see if the % charge has increased.

    If the hub is connected and powered most of the time, this might be acceptable.

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    Thanks for the advise, I will give it a try.
    I must admit that when I first tried the powered hub I did it for only a few minutes.
    Thanks again

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    well I took the hub apart and checked things out and there is definitely voltage supplied to the male usb that you would plug into the tablet when the hub is powered by an external source. So now I will check if there is enough current getting to the tablet to keep it charged or to charge it up when discharged...

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    I have done some more reading since my last post and it appears that resistors of various values are used across the data pins (pins 2 and 3) to tell the devise that you plug it into to act as a charging cable. The resistor value determines the current that the devise will allow to charge the battery. Without a resistor across the data pins the cable acts as a OTG cable and will power the external devise from the tablet/ phone etc and send and receive data from that devise. So it appears that the cable determines if you can charge the devise or it is a OTG cable but not both. There does seem to be a USB standard that will allow the connection of a OTG devise and still charge your tablet/ phone, but this needs to be controlled by the devise you plug the cable into and seems that is not something you have any control over it is done at the manufacturing level.

    I saw one claim that a Nexis tablet would do this, but I am not convinced.

    So it looks like I will have to rethink my plans....

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    Quote Originally Posted by motocross_mike View Post
    it appears that resistors of various values are used across the data pins (pins 2 and 3) to tell the devise that you plug it into to act as a charging cable
    I think you'll find that connecting resistors between pins 2 and 3 of the USB cable is a peculiarly Apple thing. Just one way that Apple bastardise industry standards to make their users buy Apple's over-priced chargers.

    My experience is that Android devices simply look for pins 2 and 3 of the charging cable being connected together.

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