Is it possible to create an USB to micro USB (or lightning) cable that has storage built into it?

So if it's plugged into a computer with no phone, the computer recognizes it as a regular USB storage device. If it's plugged into a computer with a phone attached, it only acts as a regular USB data cable.

If is possible, is it difficult to do?

  • \$\begingroup\$ Certainly it's possible, and it should be no more difficult than any it her usb composite device-- straightforward if you have the right tools and experience, and difficult otherwise \$\endgroup\$ – Scott Seidman Oct 4 '15 at 14:53
  • \$\begingroup\$ @ScottSeidman Is there any way you could provide instructions on how to do it? \$\endgroup\$ – AGanz Oct 4 '15 at 16:02
  • \$\begingroup\$ As described, this is a bad idea, as connecting a phone while the storage volume is mounted would cause it to disappear without a chance for filesystem state to be flushed, which is likely to lead to data corruption sooner or later. Making a working product would require putting thought into the mode switch rules to avoid this type of issue. \$\endgroup\$ – Chris Stratton Oct 4 '15 at 18:06
  • \$\begingroup\$ @ChrisStratton Would there be any difference if I said that the cable didn't need to switch from being storage to a transfer cable when it's plugged into a phone, rather it can be both at the same time. (i.e. Is that any easier) \$\endgroup\$ – AGanz Oct 6 '15 at 22:58

Possible and difficult:

You will need an IC that can do USB storage, flash memory for that IC, and a USB switch IC. And then write some code that will switch the data lines from cable to storage IC.

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  • \$\begingroup\$ I noticed that this product has been able to do it: symlis.com/features ....do you think this was done via the method you described above? \$\endgroup\$ – AGanz Oct 4 '15 at 14:11
  • \$\begingroup\$ No idea - get one, open it, and let us know! \$\endgroup\$ – corecode Oct 4 '15 at 14:31
  • \$\begingroup\$ If you can find their patent they mention, it will describe how it's done. \$\endgroup\$ – pjc50 Oct 4 '15 at 15:47

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