I want to make a toy car that follows a black line on the ground by using two sensor on the left and right sides of the car both pointing down. The sensor converts the light into a voltage that I will use to make the car turn left or right. I know that I can use batteries, but I am still very curious to find out if I could use my iPhone to power an Arduino because I also want to make a case with different sensors in it, and it would be thinner if I didn't have to put a 9V battery in the case.
If the phone has an accessible battery you could conceivably use the battery terminals to power a device such as Arduino. However, I think current smartphone batteries have complex monitoring circuits so this wont work.
If it doesn't, you'd be looking at using the USB/charger port on the phone.If your phone supports USB On-The-Go, I know that it allows phones to act as USB hosts, and according to USB-OTG specifications, the host must be able to supply at least 8mA of current between 4.4V and 5.25V.
If that's enough for you it could work.
For those coming here from Google.
The short answer is:
Yes you technically can, but it wont be dirt cheap or very pretty depending on your wallet and tastes/requirements.
I was researching the same thing. The problem is that Lightning connector is fairly complicated, and before it will start giving you power it requires software authentication by a chip that is built into the cable. That said you can use the USB camera connection kit or you can buy one of the IK Multimedia mini usb cables:
I have had success trying to tap into their cable for iRig Pro cause I happen to have one, and it gives out solid 3.3V on one of the pins which is good enough for my Arduino Mini Pro. But I would vouch that their full blown mini usb cable should be supplying regular 5V.