@tridge Many thanks !
I have an Omnibus F4 pro v3, so parameters you are talking about is for f405 wing.
So for others parameters to trigger a camera with Omnibus f4 pro v3 is that (tested on arduplane 3.9.2) :
BRD_PWM_COUNT = 2
RELAY_PIN = 15 # for output 5
I found PWM hardware definition here :
So if we want to trigger on pwm 6 we have to set RELAY_PIN = 41. Pretty tricky but when you found how it works it’s really nice !