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USB Condom (take 2)

Discussion in 'Electronic Design' started by Oppie, Oct 4, 2013.

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  1. Oppie

    Oppie Guest

    Tried to post this through Teranews.com and it seems to have gotten stuck
    somewhere. Trying again now through eternal-september.

    I recently saw an advertisement for a USB Condom that, essentially breaks
    the data path between a computer used for charging and the peripheral
    device. I tried making one of these with a chopped off Type A connector from
    a A/B cable.
    Colors I got (looking into mating face with logo side up) of the USB Type A
    cable connector were as follows:
    Pin 4 Blk common (to left side)
    Pin 3 Grn D-
    Pin 2 Wht D+
    Pin1 Red Vbus (5v) (to right side)

    Used a Molex 87520-0010BLF PWB through-hole type A connector as my socket.
    Connecting 1:1 confirms that this does work as an extension cable.

    Using my 5th generation iPod/touch (with lightning cable) as a test, just
    connecting the Vbus and common weren't enough to cause a charge condition.
    By trial and error, found that connecting on receptacle (peripheral) side, a
    10K from Vbus to D+ and leaving the data lines otherwise disconnected would
    cause the iPod to charge.

    iOS7, by the way now warns when you plug into a computer, "do you trust this
    computer?" as data theft from plugging into charging kiosks has become
    increasingly a threat.

    Oppie
     
  2. Tim Williams

    Tim Williams Guest

    Came through here, oddly (also ES).

    Tim
     
  3. Oppie

    Oppie Guest

    Take2 was sent through ES and showed up on Teranews almost immediately.
    Original post is stuck in tera's input filter somewhere. Also tried
    responding to several posts through tera. Some propagated and others didn't.

    Thanks for the heads-up.
     

  4. That sound about right, My Motorola V Rzr has the pullup on its
    charger plug (mini usb)

    Cheers
     
  5. Guest

    Yes, disconnect the D+ and D- wires at the the power source end of the cable and link them together at the client end. Its all in the USB standard which is downloadable free.

    If you use such a cable to get power from a PC, it may only deliver 100mA, depending on how strictly the PC interprets the USB standard. If it is connected to a suitable 5V power supply, then much higher currents are available.

    Old USB devices from the days when there was no standard for "dumb charging" look for a combination of pullup and pulldown resistors on D+ and D-. Apple used a different configuration from nearly everybody else. Yet anothernon-standard method used a long time ago by Motorola was to have a link between D+ and D- and a resistor to ground connected to the sense pin of a mini-USB the value of which controlled charging and backlight status.

    John
     
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