I need a flash extender or flash adapter with the option of connecting a cable to trigger a flash at a distance from the camera. I'm considering the JJC Standard Hot Shoe Adapter. However, when looking at the pictures, I see that it has only one electrical connection to the central pin of the camera's hot shoe mount as is shown in the picture below:
However, if I understand the workings of the hot shoe, the trigger signal consists of creating an electrical connection between the central pin and ground, which corresponds to the metallic structure that makes the mount as described in this figure (taken from this post).
Therefore, with only one connection, this adapter shouldn't be able to pass the triggering signal to the flash connected on the top of it or to others connected through the cables. If it does pass the triggering signal (as this video seems to suggest), how does that work? Is there an electrical connection hidden somewhere under that plastic plate surrounding the central contact on the first figure? Or am I missing something?
Side note: I'm really after capturing the triggering signal from an automated camera controller I have designed with an Arduino. This would serve as feedback to confirm that the camera indeed shoot the picture. And I need the adapter or extender to properly gain access to the hot shoe contacts.