From CHDK Wiki

Using a USB cable, a low voltage power supply, and a push button switch, you can construct a device that will allow you to remotely trigger the shutter of your CHDK-enabled camera. Remote triggers are most often used in low-light situations when pressing the shutter button on the camera could introduce picture spoiling camera shake, but may also be useful in other circumstances - for instance if you wish to trigger the shutter with your foot, or with an electronic signal from another device.

In order to trigger your CHDK camera remotely, you will need to:

install CHDK on your camera;
connect a suitable triggering device to be connected to the USB socket of your camera;
ensure "Enable remote" to have been selected in CHDK;
run a suitable script (see example below);
place your camera in shoot mode (i.e. not playback mode, movie mode, alt mode, etc) with CHDK still running;
operate the trigger!

[edit] Triggering devices

Your triggering device should incorporate a power supply - a battery, for instance - that has its negative (or ground) terminal connected to pin 4 of a mini-USB cable and its positive terminal connected to pin 1 of a mini-USB cable via a momentary push-to-make switch. The power supply should provide a voltage that is no greater than 5V (or you may damage your camera), but which must be greater than or equal to the minimum voltage specified on the CameraFeatures page.

The power supply does not need to be able to supply a high current. (For reference, an IXUS 80 being triggered with a device drawing power from a bench PSU set to 4.62V drew a maximum of 0.4mA from the trigger circuit during triggering.)

[edit] Homemade USB remote cable

A popular method for remotely triggering CHDK-enabled cameras involves constructing a simple triggering device from a 3V CR2032 coin battery, a USB extension cable, and a push switch. The camera's USB cable is then attached to the camera at one end and to the triggering device by the other end.

Below is a circuit diagram of such a switch.

If you are cutting up a commercially-made USB extension cable, then wires 1 and 4 are red and black, respectively, according to the USB standard. It seems that even cheaply made USB cables follow this standard.

Note that the 3V CR2032 battery might not be enough to trigger your camera; if not, you may need to use a different power source, e.g. three 1.5V AAA cells connected in series.

[edit] USB bus-powered remote cable

A computer's USB port incorporates a 5V power supply. This can be used in place of a battery, which could be useful for photo sessions that require the trigger to be operated more times than a battery's limited capacity will permit.

To build a USB-powered remote cable, obtain a USB-A to mini-USB cable and follow the instructions above, but instead of replacing one end of the cable with a battery, leave the USB-A plug connected. Now simply splice the push-switch into the cable's +5V wire, leave the ground wire connected, and disconnect the other two wires. Voila!

Note: an incorrectly-constructed cable could damage your computer's USB port, your camera, or both, so test it with a continuity checker before using it, to ensure you haven't made a mistake. You try this kind of USB remote trigger out at your own risk!

[edit] Enable built-in CHDK remote support

First, ensure you are running a reasonably up-to-date CHDK build. Some early builds did not support remote shutter release control via USB.

Now enable remote support via the CHDK menu: Main Menu > Miscellaneous Stuff > Remote Parameters > Enable Remote

NB. If you enable the "Sync Delay" then the shutter will release after you stop the voltage to the USB port. This was done because it was found they could sync the shutters on 2 cameras for stereo imagery much better as the voltage dropped. (It can also be useful if your switch uses poor-quality contacts, in which case the rise in voltage when it closes may not occur quickly enough to trigger CHDK's remote function.) Under most single-camera circumstances, however, you won't need this unless you need to sync the shutter release more accurately to your voltage trigger signal for specialized reasons.

[edit] Simple Remote script

Now that you've enabled the remote function via CHDK's menu, you'll need a script to be running which will recognize when the remote trigger has been operated and which will then operate the shutter.

You can use this small script to trigger the shutter:

Script Code

@title Remote button
while 1
  wait_click 1
  if is_key "remote" then shoot
wend

end

Save it as "remote.bas" to your /CHDK/SCRIPTS/ folder, and then access it using CHDK's menu.

Now you should be all set to attach your triggering device to your camera and use it to take some pictures!

[edit] Links

[edit] Remote hardware

Usb Remote Shutter using Linear Voltage regulator (Forum)
DIY wireless remote with a chinese door ring bell (Forum)
CHDK Remote Shutters "temporarily unavailable" 2009-05-03
GentLedIR (scripting info)
Confirmed the Ricoh CA-1 cable release works for the Canon SX10. Tested Single shot only; not continuous or zoom.
building usb-remote-cable(Forum)
http://www.flickr.com/groups/chdk/discuss/72157612167472551/
http://www.instructables.com/id/Amiga_Joystick_USB_Camera_Cable_Release/ (Instructable for creating cable release from an Amiga Joystick)
https://sites.google.com/site/canonremotehowto/ Short directions for building a cable release using an LED keychain flashlight

[edit] Remote Scripting

USB Remote Cable