Turn on a little engine with the iPhone

I want to turn on a little engine with the iphone I mean, using the 30-pin cable and connecting some cables to the engine. Which is the code I have to write 开发者_运维问答to do that? And the most important, is that possible or is just a dream?

Perhaps you want the External Accessory Framework Reference?

The External Accessory framework provides support for communicating with external hardware connected to an iPhone OS–based device through the 30-pin dock connector or wirelessly using Bluetooth.

Also see Apple's landing page for accessory developers.

It's possible, but you have to convince Apple to let you do it. The connector itself is a proprietary design, and Apple's approval is required before Molex will sell it to you. Also, they're not really set up for hobbyists or experimenters; they want to deal with people making hardware add-ons to sell to the general public.