There is a Sony RX10 III camera which also has a external trigger for it. The goal is to send a signal from a micro-controller (Arduino & optocoupler in between) to release the shutter. I thought I could just short the GND to the shutter pin like with older cameras, but with this particular camera it didn't work. You can see the pin-outs made by some nice people here. I dismantled the external trigger and de-soldered the USB connector cables, but it seems there is more to it than just shorting.
I don't know what the circuitry is doing. From testing I was able to figure out, that the Green wire seems to do the focusing; this leaves the white for shutter. Just shorting doesn't work here though. I have read in the post I linked that there is resistors used sometimes for some custom protocol.
Here is a picture showing my interpretation on what is connected to what.
I hope some of you can help me figure this out. Unfortunately I only rarely have access to the camera, so I would like to do this with as little trial and error as possible. If more info is required please ask. Thank your for your help.