Canon CHDK - Manual (Page 57)

USB Remote notes
USB Remote Cable
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 can 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, ie. wireless IR or RF.
In order to trigger a CHDK camera remotely, you will need to connect a suitable triggering device to the
USB socket of the camera, ensure "Enable remote" is selected in CHDK, select a shoot mode (i.e. not
playback mode, movie mode, alt mode, etc) with CHDK still running, operate the trigger!
Triggering devices
The 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 can risk damage to your camera), but which must be greater than or equal to
the minimum voltage specified on the Camera-Features page. This is a low power circuit, ~0.5mA, and
only requires light duty components.
See
:- http://chdk.wikia.com/wiki/CameraFeatures
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. Recent cameras have a combined USB and AV connector, a "splitter" type cable & connector is
required.
Note that the 3V CR2032 battery might not be enough to trigger the camera, if not, you may need to use a
different power source, e.g. three 1.5V AAA cells connected in series.
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