There are a lot of documentation online about how to build a
remote trigger for the Canon EOS 350d digital SLR camera,
e.g. this one.
Not only is the necessary circuit very simple, but perhaps
even more important is that the connector that plugs into the camera
is a standard 2.5mm TRS plug, and is
easy to procure,
compared to the various proprietary connectors
used for other models and brands.
ready for action
As the intended use for this trigger is to serve as the
shutter control in a stop-motion setup I chose to do an electronic
build instead of using manually operated switches. As
dmx512usb board was developed to be useful in more than
its original context the final trigger assembly was designed
to neatly connect to the GPIO pins on the board—with the right
firmware—usb trigger control, or for that matter, the possibility
to trigger it over DMX512.