4 ms·

I used to design these things. Yes they are difficult to design in the sense of RF engineering to pump that much data on a data line, but the power end of it is

I used to design these things. Yes they are difficult to design in the sense of RF engineering to pump that much data on a data line, but the power end of it is a very simplest design. It has a current cap to prevent damage to the regulator circuit and USB regular spec is 0.5A. Which isn't very much if you've ever tried to charge a phone off of that. Without the inner pins it'll default to the low spec (on a well design USB Host) but no damage or risk to having those inner pins float since they have internal pull up resistors. If the device decides to provide more all the better for you as your device is what regulates how much current it wants when an infinite amount is available.

MertsA 13y ago
>If the device decides to provide more all the better for you as your device is what regulates how much current it wants when an infinite amount is available. If the host is capable of providing more power like 2.1A for example, how is that supposed to be signaled to the phone when the data lines are floating high? The way a USB charger that provides more current than the USB spec works is by pulling the data lines either to some voltage or shorting them together or to ground. Either way you need the data lines to negotiate that.
- megaframe 13y ago
  Yeah there's normally a negotiation via pins being grounded or through the level of resistance on that pull up which tells the device what spec is being used. That goes on to tell the device how much power it can pull without causing a power droop. If the pins are missing most devices won't try to pull more, like my phone won't... but I have a cheap external USB HDD enclosure that will pull what ever it needs from the line regardless of the pin setup. Most Mother Boards actually put out 1-2A on those lines so I can run the thing as normal, but the drive comes with this add on extension to hook it up to two USB lines to get around the 0.5A limit. So it'll depend on how nice of a device you have.
  - ambrop7 13y ago
    The "condom" can be designed to be transparent with regard to one or more kind of power negotiation, though this would require a microcontroller, and possibly some analog circuicity for proprietary resistance-based negotiations.
    - jessaustin 13y ago
      Then the condom would be a target for hacking! You've just added another layer to the problem...
      - runlevel1 13y ago
        That's kind of like arguing that seat belts can cause strangulation. There are always risks, so we just have to choose the less risky option available to us. So between these two... A. The black box charging station I know nothing about. B. The simple device that I brought from home whose single purpose is to limit my exposure to external risk. I'll take the latter. Odds are I'm no worse off than had I plugged directly into the charging station.
    - MertsA 13y ago
      A microcontroller actively doing the current negotiation would be nice (for things like working at the maximum power of both android and apple chargers) but a much simpler and dirt cheap solution would be to hook the data lines up so that they go through a simple filter that filters out everything other than the DC bias so power negotiation would work normally for chargers but no data could cross the cable.
    - kbaker 13y ago
      There are ICs that do this negotiation already. Like the MAX14636: http://www.maximintegrated.com/datasheet/index.mvp/id/7968 http://www.maximintegrated.com/datasheet/index.mvp/id/7968
  - peterwwillis 13y ago
    Or if you have a "nice" device like an Apple product, the voltages/resistances on the data lines will determine your charging speed. And then there's USB dedicated charging spec ports, like the ones that can put out 2100mA, but that's luckily out of scope of this device... http://www.extremetech.com/computing/115251-how-usb-charging-works-or-how-to-avoid-blowing-up-your-smartphone http://www.extremetech.com/computing/115251-how-usb-charging... http://learn.adafruit.com/minty-boost/icharging http://learn.adafruit.com/minty-boost/icharging

MertsA 13y ago

>If the device decides to provide more all the better for you as your device is what regulates how much current it wants when an infinite amount is available. If the host is capable of providing more power like 2.1A for example, how is that supposed to be signaled to the phone when the data lines are floating high? The way a USB charger that provides more current than the USB spec works is by pulling the data lines either to some voltage or shorting them together or to ground. Either way you need the data lines to negotiate that.

megaframe 13y ago
Yeah there's normally a negotiation via pins being grounded or through the level of resistance on that pull up which tells the device what spec is being used. That goes on to tell the device how much power it can pull without causing a power droop. If the pins are missing most devices won't try to pull more, like my phone won't... but I have a cheap external USB HDD enclosure that will pull what ever it needs from the line regardless of the pin setup. Most Mother Boards actually put out 1-2A on those lines so I can run the thing as normal, but the drive comes with this add on extension to hook it up to two USB lines to get around the 0.5A limit. So it'll depend on how nice of a device you have.
- ambrop7 13y ago
  The "condom" can be designed to be transparent with regard to one or more kind of power negotiation, though this would require a microcontroller, and possibly some analog circuicity for proprietary resistance-based negotiations.
  - jessaustin 13y ago
    Then the condom would be a target for hacking! You've just added another layer to the problem...
    - runlevel1 13y ago
      That's kind of like arguing that seat belts can cause strangulation. There are always risks, so we just have to choose the less risky option available to us. So between these two... A. The black box charging station I know nothing about. B. The simple device that I brought from home whose single purpose is to limit my exposure to external risk. I'll take the latter. Odds are I'm no worse off than had I plugged directly into the charging station.
  - MertsA 13y ago
    A microcontroller actively doing the current negotiation would be nice (for things like working at the maximum power of both android and apple chargers) but a much simpler and dirt cheap solution would be to hook the data lines up so that they go through a simple filter that filters out everything other than the DC bias so power negotiation would work normally for chargers but no data could cross the cable.
  - kbaker 13y ago
    There are ICs that do this negotiation already. Like the MAX14636: http://www.maximintegrated.com/datasheet/index.mvp/id/7968 http://www.maximintegrated.com/datasheet/index.mvp/id/7968
- peterwwillis 13y ago
  Or if you have a "nice" device like an Apple product, the voltages/resistances on the data lines will determine your charging speed. And then there's USB dedicated charging spec ports, like the ones that can put out 2100mA, but that's luckily out of scope of this device... http://www.extremetech.com/computing/115251-how-usb-charging-works-or-how-to-avoid-blowing-up-your-smartphone http://www.extremetech.com/computing/115251-how-usb-charging... http://learn.adafruit.com/minty-boost/icharging http://learn.adafruit.com/minty-boost/icharging