Ok and if I manage it to last longer, lets say for about a second (like I was trying to ground it using a wire)
set it up as a camera feedback pin that will be able to handle the short 2ms inputs that your looking to record.
Oh I’m already using the camera feedback on AUX4
I just realized you are the same person that posted about using 2 hotshoes before.
Yes, but I understand that it is impossible to record two cameras feedback (am I right?) so i’m trying to log the event in other ways and I thought using another aux input for that
as far as I know yes, currently you can only use one hotshoe pin. A long way around would just be to carry a second pixhawk but that is an expensive way to do it.
Yes, another pixhawk is too much for that 
But if I mange to make the event last longer, for a second (or what is the minimum for the btn to work?), so it can be a solution for me
I just take the BTN events from the log then
