USB Questions

Discussion in 'General Electronics Discussion' started by Shre, Jan 5, 2017.

  1. Shre


    Jan 5, 2017
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    Can micro USB be soldered to a USB and be able to provide adequate power to two devices- one plugged into the USB and one being supplied directly by the micro USB?
    Shre, Jan 5, 2017
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  2. Shre

    Harald Kapp Moderator Moderator

    Nov 17, 2011
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    Germany-Europe-Earth-Sol System-Milky Way-Laniakea
    Micro USB is electrically the same as USB, only smaller. Therefore you can use the two of them interchangeably, provided plug and receptacle match in size.
    It maybe difficult to manually solder the thin wires used in typical USB cables.
    Powering more than one device from a single USB source is not an issue as long as the max. current is not exceeded (depending on the version of USB you're using). You may not, however, connect the data lines in parallel. This is not allowed by theUSB spec. And this is where you'll probably run into problems: A USB host that conforms to the standard will allow only 100 mA unless a higher power has been negotiated between the USB host and slave. Negotiating wil not be possible with at least one of the devices connected to your setup as only one USB connector may have the data lines serviced.
    See here for more info.
    Harald Kapp, Jan 5, 2017
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  3. Shre


    Oct 14, 2014
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    It will depend a lot on the devices you're hooking up and the host port you're using. FWIW, it's actually the device that determines how much current to draw. They decide how much to draw based on what they see on the data lines (either voltage levels or actual communication). This tells the device how much current it is allowed to draw. It's up to the host to protect itself from having too much current drawn and I'm not sure there's a standard for that. As Harald pointed out this is unlikely to work correctly with two devices in parallel off the same data lines unless the current drawn by both devices is small.

    The worst case is you'll hook up two devices to that one port, they'll both try to pull the max current that port can supply and you'll blow out your USB port.
    garublador, Jan 5, 2017
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