I'd like to connect my own device (a device that can record the trace of the camera within the exposure time) with my SLR camera (a Canon EOS 5D markII) through the hot shoe. I need a signal to tell my device the shutter is pressed. Can the camera itself can generate a signal when I press the shutter? If not, how does the camera trigger the flash from the hot shoe?
According to Wikipedia, the hot shoe and the contact point are isolated when the shutter is not pressed and are shorted when the shutter is pressed. Is this still true for the Canon EOS 5D markII? Do I need to add external voltage to have that signal or is the signal generated by the camera itself? If I need to add external voltage, then what is the maximum voltage I can add?