title: Send iPhone Volume Up Signal Over USB/Headphone Jack
body: <p>In <code>iOS</code>, the <code>camera app</code> 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 <code>headphone port</code>.</p>
  
  <p>On the iPhone 7, the headphone port has been removed and effectively merged with the "<code>Lightning</code>" port. This feature still works. As a side-effect of this merge, <code>USB</code>s occupy the same space.</p>
  
  <p>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.</p>
  
  <p>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.</p>