Yes, i understand it is too old for a CHDK support, but can i remote control it without CHDK? I can control the shutter from a PC through the USB port, what protocol does it use there?
The IXUS 400 is equipped with a DIGIC I image processor, therefore it will never be supported by CHDK.
Most probably the camera use the PTP protocol to transfer images and to control the camera remotely; since this protocol needs "external logic" like a computer with the adequate software, i guess there isn't a simple way to build an external remote switch like CHDK provides it for some cameras.
CHDK remotes do not use any protocol at all, the running CHDK on the camera just detects the voltage of the USB power lines.
To do something similar without CHDK, first you must be able to run your own code on the camera...
