A new project I’ve just finished using an Arduino Mega, Lithium battery pack, TL230R frequency to light convertor IC and the DS1307 RTC and a 20x4 LCD display. It uses non-blocking timing code and and an interrupt with MsTimer2 so that the buttons remain fully functional when taking images rather than using the easier delay() function. It’s been done a thousand times before but as a photographer I do like the control this system is giving me when using the camera in bulb mode and modifying the pulse length to adjust the shutter speed.
It is based on a system developed on the OpenMoco site but I’m very pleased with the end result. It can also be used as a simple intervalometer with interval and pulse adjustments.
Details can be seen here http://www.photosbykev.com/wordpress/2010/05/20/arduino-intervalometer-for-digital-cameras/