What would it take to get an iOS device to talk to an arduino?

(Over USB, specifically. Though WiFi might be workable for a game controller.)

There's an iOS to RS232 cable I've wanted to play with for a while: http://www.redpark.com/c2db9.html

Sorry if you meant specifically using USB

Is this something that Apple would approve?

Unlikely. It requires use of private API on the Mac, or direct USB communication with the device using an undocumented/private protocol.

That private API appears to be usbmux which iTunes uses to create tunnels to the device: http://www.theiphonewiki.com/wiki/index.php?title=Usbmux

Inquiring minds want to know, I would love to write a true DSLR tethered shooting app for IOS.

seconding this question.

My obvious need would be a version of "air display" that worked over usb, but when i looked into it 2 years ago talking over usb wasn't allowed except for certified products.

If you have a device that supports tethering, you can do that today. Turn on tethering, plug in the device, and they'll get a mini-LAN running over the USB connection.

If you have a WiFi-only device, or a cell plan that doesn't allow tethering, then this won't work, sadly.

thanks for the tip! I may start looking for an old ipad 3g then.

Also going to look and see if you can just enable usb tether with jailbreak.

Who cares?! You bought the device. It's yours not Apple's.

But you can't publish the app in the store, so few people can use it. Closed ecosystem :(

So distribute it some other way. If it's a great app and lots of people have a use for it, they will find a way to get it. You have the greatest distribution channel known to man at your disposal which NO ONE, not even the mighty Apple, truly controls: the internet.

Apple is just one company... which happens to spend an inordinate amount of money on marketing and an incredible amount of effort trying to control people through the lure of nice form factor and a graphical interface.

But there's more to computing than form factor and GUI. Lots more.

How does iOS and USB mix? Is it just a TCP protocol and the real USB i/o happens on a mac?