Canon CHDK - quick  guide.

CHDK is an alternative firmware for specific Canon Cameras models.  It includes functionality to run scripts (i.e intervalometers) or adds extra functionality such as bracketing. Not that hard to setup, but make sure you're camera is supported, or read in the discussion forum and se if a alpha version is available.

The software is placed solely on the Memory-Card, making it "safe" to install, and therefore run only in memory. The camera or software (rom) is not altered in anyway so it should  be practically impossible to brick the camera in anyway. 

Installation:

CHDK can run and be started with 2 methods.   1 is autostart whenever the camera starts, the other is thru a manual start.  Sometimes, only the autostart is the possible solution to run CDHK.

Installation consists of placing 1 or 2 files in the root-directory.   Disboot.bin and PS.FIR, but disk boot.bin is usually enough with the autostart version.

The CHDK directory is created during first run of CDHK.  Two methods/ways to run CHDK.  The Cards memory protection tab always have to be in the "locked" position, otherwise CHDK will not start.

1. Either run CHDK (start it) from the cameras menus by choosing firmware update menu. The choice is available if the Card has the .FIR file in the root directory.

2. Start CHDK with a bootable MemoryCard, and press the Alt (printer) button.  If a bootable card is present, the Camera will show CHDK during camera startup. It is then possible to automatically activate scripts, after a power outage for example. 

With the Camera startup method, 

1. Make the Card Bootable (i.e use cardtrick software on windows, format it and choose "make bootable").

2. Enable write protection with SD card, which is the "on" button for CHDK. The switch on SD-cards is only read by the SD-reader/Camera, and Write-priviliges has nothing to do with the card itself..   

Tested on Ixus SD40 (400),  and S80.