I'm making some changes to the rig I use for doing kite aerial photography, and realized that one of the changes has some wider application to other folks who are using CHDK on their Canons:
The GentLED-CHDK and GentLED-CHDK2 are devices developed by James Gentles for interfacing an RC receiver to a CHDK-enabled camera. Brooks Leffler is the North American supplier I bought mine from.
The GentLED-CHDK monitors one channel on an RC receiver, and when that channel swings from one extreme to the other, it puts a +5V pulse down the +5V line of the USB cable.
The GentLED-CHDK2 monitors two channels on an RC receiver. It will send a pulse down the +5V line of the USB cable with one of six durations, depending on the state of the two channels. Most builds of CHDK let you find out the duration of a pulse to the +5V line, so essentially this lets you send one of six commands to the camera, depending on what you do with those two RC channels.
Dave Mitchell has written a scripting guide for using the GentLED-CHDK2. It touches on the basic theory of reading input from the GentLED-CHDK2, and includes a script that lets you zoom the camera in and out, and trip the shutter using an RC radio.
When I started this whole switch-over, I was mostly looking for a way to remotely trigger my A650IS without using a servo as a "finger" to hit the shutter button. (This is how I'm currently doing it.) But the added functionality of the GentLED-CHDK2 was just too good to pass up. I'm still not sure what I'll use it for, but I'm sure I'll come up with something.
One non-aerial application I could see for this would be a pan-tilt-zoom rig with wireless video feedback for doing wildlife photography, potentially with the ability to switch from stills to video without having to touch the camera.
Another potential application would be for remote sensing in locations where a person just can't fit. Lots of possibilities.
Anyway, figured I'd share. Pictures to follow once I've had a chance to test it in the field.
6:16PM, 5 January 2009 PST