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Mobile Device Port - USB

Discussion in 'General Electronics Discussion' started by Stef Corn, Aug 23, 2015.

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  1. Stef Corn

    Stef Corn

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    Aug 23, 2015
    Hello,

    I have a mobile device that runs windows, and has a port on the back to connect extra accessories like an extra battery or a smart card and RFID reader. I hope this question is in the right section...

    I am trying to figure out:
    - What kind of port would this be? (probably a custom one as you can also connect extra batteries)
    - Can I connect other USB based accessories on this port?
    - or do i need to add a USB Hub in between?
    - can I connect a device with a UART interface?

    and finally (and why I am asking this question here): are there any circuits that I would need to enable me to connect other USB devices on this port?

    This is the port viewed from the back of the device:
    Tablet Conn.jpg

    This is the PCB of the smart card reader that is clicked on the back of the device:
    PCB.jpg

    And this is the IC at the top of the connector (GL852G):
    HUB.jpg

    The GL852G is a 4-port USB hub and from the PCB you can actually also read "USB-" and "USB+" printed on the PCB. The smart card reader has a contacted smart card and a contactless one. All checks out in terms of addresses on the IC and what the Device Manager shows me in windows.

    Now I want to connect another USB device. I have tried to connect a memory stick with an external 5V (the mobile device only gives 3.3V), and connect the USB+ and USB- pins to the connector, but the USB stick does not show up. I assume that the USB+ and USB- pins of the connector are the upstream connectors of the IC.

    My Windows device manager shows 1 USB Host Controller, and 2 Generic USB hubs by default without the external reader. When I connect the external card reader, an extra "Generic USB HUB" shows up, and when looking at the device ID's of this hub, it is indeed the GL852G from the PCB that is detected.

    Kind regards,
    Stef Corn
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    you have USB+ and USB- (the data pins). All you need to do is to find +5V and ground to complete the 4 USB connections.
     
  3. Stef Corn

    Stef Corn

    5
    0
    Aug 23, 2015
    The USB ports of this IC are fine, the module works, although I can only measure 3.3V on the connector. The circuit itself works fine at this voltage. But this IC is not the issue.
    I want to create my own board with a 14 pin interface, that has other USB accessories on it (like a USB memory key) or a card reader with a UART interface. Hence I was wondering if the USB+ and USB- of the 14-pin connector on the device itself are exactly the same as the USB+ and USB- from a normal USB port. I thought it could be deduced from the IC of the card reader.

    Kind regards,
    Stef
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    not sure. Can you find a datasheet for this chip?
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    From the look of it, this chip has a 5V and 3.3V power requirements.

    If there is no 5V output on the connector then presumably the plug in modules don't require it. You would have to grab this via some other means.
     
  6. Stef Corn

    Stef Corn

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    Aug 23, 2015
    Thanks Steve, much appreciated!

    So you think I should be able to connect a USB device directly to these data pins if I get power from somewhere else? This would mean there is no difference in data ports between the USB controller and a hub...

    It is so hard to find any specific information on this for USB due to the overload of info on consumer USB on the internet...

    Thanks again!
    Stef
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,259
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    Jan 21, 2010
    Well, any source of 5V will need to share a common ground with that of this device. I'm assuming that this device is a USB host as the chip seems to belong to a family which can support several ports. This makes no sense unless it is a host (or hub)
     
  8. Stef Corn

    Stef Corn

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    Aug 23, 2015
    I will try to connect an external 5VDC with common ground and get it working this way.
    Thank you for your time!
     
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