Q:

How to connect an iOS device to a custom USB device? 

I'm developing a custom electronic device - think of it as a special kind of data logger, and I need to connect a computer to it to configure it and to extract the data. 
I know I can do this without too much trouble on a PC, but I'd like to use an iOS device to do this. 
Two questions:
Can I do this with a regular dock connector / USB cable?   Will the EA framework let me do all the communicating? 
Once I have extracted the data, what's the best way to get that out of the iPad?   Make an email with it, save to a dropbox or something? 
Thanks! 

A:

Afaik, you need to join the MFi program to make USB accessories for iPad/iPhone.  That will give you all the technical resources needed. 
As for data transfer there are only "opinions", I say the more options of sending, the better.  Just don't force the user to choose more than once, then make it changeable in settings. 

A:

If you're doing very light communication, you might be able to get away with using the headphone jack. 

Apps communicate to the headphone port through the various audio frameworks on iOS.  AVFoundation is a high-level abstract framework to do various audio operations, but for fine-tuning the communication to a device over this interface, you will likely be using the C-language callback-based Audio Queue Services framework to do audio I/O.

This is nice because your device can be cross-platform (iOS, Android, Mac/PC) as long as you write the corresponding software, and because you don't need to go through Apple's MFi approval program.  Think like the Square credit card scanner.