This is a simple hack / add on to a great Eric Archer kit, Light2Sound, so I can make video recordings with my Iphone, using this board as the audio input - basically a few passive components that tell the phone when something is plugged in to its TRRS input.  The kit is essentially a photodiode circuit with some fancy auto gain circuitry.  Photodiodes convert light into current, so instead of an ac current coming from a microphone and going into a preamp, it's coming from a light source.