The information about which cameras can or cannot be electronically triggered seems incomplete . I have a Canon Powershot A590IS (which I got because somewhere on this site it is recommended specifically because it can be electronically triggered), and at first I could not find the info about triggering it. However, it is possible to trigger it with an appropriate remote, and this page - http://www.stereomaker.net/eng/sdm/quick.htm
- tells you more about that. (Scroll about 2/3 to 3/4 the way down the page to the title, "Preparing your switch unit and checking the batteries".)
In my case, I used SDM, rather than CHDK that it's based upon, as the control software for the camera. I suggest you use an SDHC card no larger than 4GB, as that can be formatted as one partition, whereas larger cards must be partitioned, which seems to be a headache. (I have yet to succeed with a 32GB SDHC card).
My switch works, but all is not quite well. I have yet to master SDM, largely because I am having difficulty plowing through the available information on it. However, the switch DOES work, so here's a description of my remote shutter trigger switch:
My switch provides 4.5V pulse. It was made from a 3-AAA-battery mini flashlight (http://www.harborfreight.com/3-1-2-half ... 97036.html
). I pressed the lens and LED's out and used that end for the USB cord (with mini plug that fits the camera on the other end).
A "fender" washer, of diameter slightly smaller than the ID of the flashlight body, holds a grommet, and a 1/4" diameter brass screw is inserted through the grommet such that on the head will contact the battery pack. The other end it is connected to the red lead of the USB cord by means of a 1/4" crimp lug, secured to the screw with a nut. (The battery pack must be inserted with the positive end against this contact. This has been indicated on the battery pack itself.)
The fender washer is drilled for a small sheet-metal screw, which in turn secures a small lug crimped to the black lead of the USB cable. The fencer washer makes contact with the aluminum flashlight housing, but to ensure against failure, I ran a screw into it through the flashlight body. I knotted the cord close in, then potted the knot, etc., in hot-melt adhesive.
The original switch on this flashlight is a pushbutton "toggle" switch which doesn't suit the purpose. Unfortunately, its design precluded easy conversion to a pulse pushbutton. After futile attempts to convert it, I replaced its guts with one of these mini pushbuttons: http://www.sparkfun.com/products/97
The contacts from this I soldered to the corresponding contacts from the original "toggle" switch, using very short copper leads. I used drops of hot melt adhesive to secure this switch and leads to the body of the original switch, as well as for electrical insulation. This modified switch mounts neatly in the modified outer half (i.e., nearer the button) of the original switch body (using pieces of the original push button), but the inner half could not be used as such, so pieces of it were used to secure the two original contacts, now soldered to the new switch. (Hot-melt glue would have worked as well.) A clearer description I can't really provide. The basic idea was to use the new switch in the old housing, and anything that accomplishes that will work.
This modified switch pressed back into the the original housing it came from, resulting in a pushbutton switch end that superficially looks unchanged from the original, and screws in just as the original switch did, making contact with the original spring to the negative end of the battery pack with one lead and to the aluminum flashlight case with the other.
Before using this switch, I tested it with a voltmeter.
As I said, my current problems are not with the switch but with the SDM software. I'm in the process of seeking answers for those.