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Thread: [Need advice] USB OTG + Charging

  1. #1
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    [Need advice] USB OTG + Charging

    There are people which achieved it using this cable but there are also a lot of people which say that it's not working.
    While googling I found this schematic and I can't really figure out why this should not work



    I also had an idea about a separate charger for phone and usb device, here's my schematic, I do not know if it this can work but I really cannot see why



    What do you think? Did you managed to build your own OTG-Charger cable?
    Last edited by Andre91; 09-27-2014 at 07:39 AM.

  2. #2
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    your pictures are not showing to me.... What do you want to achive?? being able to use an external USB device, AND charge the tablet at the same time?

    if its that, i also had tried to manage it once, but it turns out that its very dependended on the tablet... (untill i see someone who has actually managed it, i beliave it cant be done). The reason i found out was this : The USB cable has 4 wires. +5v,GND,D1,D2. as you can imagine D1,D2 are used to transmit the serial data.... The problem is, that newer chargers, use the D1,D2 with a constant 2v on them. that way, if the "tablet" sees 2v on those lines, instead of pulses, it understands its being charged, and switches the internals, so it can receive more than 500mA...

    What usb device you wanna use ??

  3. #3
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    Quote Originally Posted by settra View Post
    your pictures are not showing to me.... What do you want to achive?? being able to use an external USB device, AND charge the tablet at the same time?

    if its that, i also had tried to manage it once, but it turns out that its very dependended on the tablet... (untill i see someone who has actually managed it, i beliave it cant be done). The reason i found out was this : The USB cable has 4 wires. +5v,GND,D1,D2. as you can imagine D1,D2 are used to transmit the serial data.... The problem is, that newer chargers, use the D1,D2 with a constant 2v on them. that way, if the "tablet" sees 2v on those lines, instead of pulses, it understands its being charged, and switches the internals, so it can receive more than 500mA...

    What usb device you wanna use ??
    I want to use a mouse and a keyboard (custom board) while charging my phone.
    I modified the pic in the open post please take a look, the second pic should solve our problem but it will require of two charger but it's better than nothing

  4. #4
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    One note about your second picture...

    You need to attach the black wire to all of your connections...

    I have tested that you can run the positive off a different source than the PC like your drawing but you MUST share the ground or you will blow up something...

    Plus I have not seen mention of a 5th line that you are showing. I was under the impression you just short the data pins for high power charging.

    I plan to use a double throw double pull relay in my truck. When I want to have it charging and not tied to the PC I will have it one way.


    Rodney
    Last edited by redheadedrod; 09-27-2014 at 04:32 PM.

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