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In iOS, the camera app has a feature where it takes a picture when it receives a volume up signal in landscape layout. This feature is used by devices such as "selfie sticks" to trigger the camera from a distance by sending the "volume up" signal through the headphone port.

On the iPhone 7, the headphone port has been removed and effectively merged with the "Lightning" port. This feature still works. As a side-effect of this merge, USBs occupy the same space.

As it's possible to send the volume up signal with an not-internally-powered headphone set, I believe (but I'm not sure), that the signal is fairly simple.

Thus follows my question: How do I replicate sending this signal over USB? I want to control the shutter of the camera app through interaction with a laptop.

Cheeezburger
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  • In the case of a simple headphone, the volume button simply puts a specific resistance between ground and the remote control pin. Presumably the lighting headphone adapter interprets this resistance just like the phone used to and sends that command over the lightning data channel. I doubt you can do this from a laptop since a laptop doesn't look like a lightning headphone adapter to the phone; it looks like a computer. – Paulw11 Feb 10 '17 at 00:37
  • In that case, is it possible to control the USB connection computer-side to make it look like a headphone adapter? Because, as far as I know, the headphone to lightning adapter itself doesn't have any computing capability built into it. – Cheeezburger Feb 10 '17 at 04:10
  • It would require some pretty low-level programming to make a computer look like a USB peripheral rather than a host. The lighting headphone adapter will definitely have a chip in it. It needs to implement the lighting protocols, peripheral authentication and digital/analogue and analogue/digital conversion for the headphones and microphones. – Paulw11 Feb 10 '17 at 04:16
  • Would it be more feasible to program a "fake" adapter, or use an actual adapter and string it up with the sound output of a laptop via a double ended 3.5mm jack? – Cheeezburger Feb 10 '17 at 04:21
  • Nope, the lighting connector is totally different to the old 30 pin connector. You can see the signals on the Lighting connector here - https://en.wikipedia.org/wiki/Lightning_(connector). Two power pins, two identification pins and two differential digital IO channels (2 pins each). Compare with the 30 pin connector - http://pinouts.ru/PortableDevices/ipod_pinout.shtml where there are discrete analog pins for audio in/out and video. – Paulw11 Feb 10 '17 at 04:21
  • Possibly - You just need to switch a 4.7k resistance across ground and the control pin - http://david.carne.ca/shuffle_hax/shuffle_remote.html. It wouldn't be too hard to create a USB controllable device that does that – Paulw11 Feb 10 '17 at 04:23
  • you can use a VNC server like *Veency* on the iphone and a client (Chicken of the VNC) on the mac to control the phone – ralf htp Feb 10 '17 at 08:59

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