After contemplating this design and even digging out a geared DC motor for it, I realized that the KK5.5 board I've been fiddling with could do the job with just a single servo and a 4cell NiCD pack for power. I did a bit of sketching and came up with a mechanical scheme I thought would work. But first, I spent some time on the software to make sure it would work as I intended. I am using a mechanical button press since my camera does not have any kind of electronic interface to the shutter button.

Here is the board and servo under test. The LED comes on when the servo moves. The 'roll' 'pitch' and 'yaw' pots are used to adjust timing. In this application, the gyros are not used at all.

In this image you can see the basic mechanical construction. I built this from a sketch and some TLAR measurements of the camera. All the aluminum bits were cut from scrap sheet about 2mm thick. I was careful to make sure that the holes in the vertical bits lined up. The horizontal lever is drilled for a 2:1 (in use) and a 3:1 ratio. After testing, I think I am going to move to the 3:1 ratio so the servo can move further with more precision, while retaining the short throw on the button press foot. As you can see I have used some old clevises but of course you can use Z bends or some other method of securing the push rod ends (even ball links). The presser foot has had some self-adhesive sponge tape added so that it does not slip off the camera button, which is at a slight angle.

Here is the entire rig. Had to take the photo with my cellphone so not very clear.
Back

Front

Bottom: showing the tripod mounting hole. The screw that holds the camera to the rig is a 1/4-20 nylon bolt more commonly used to hold wings. The hole in the wood is tapped 1/4-20 for the tripod screw.

The YAW pot is used to set the time interval from 5 to 30 seconds

PITCH pot is used to set the dwell delay length. The servo is moved about half it's travel and then delays this long before moving to the end of travel. This was an attempt to allow it to focus butin practise it is better to simply move the servo slowly in one continuous motion.

ROLL pot is used to set the servo traverse time, ie the total time it takes to travel from end to end.

Arduino basics

The Arduino is designed as a simple to use microcontroller project development environment. The software development environment works under Windows, Mac and Linux. I use it on Ubuntu Studio since that is what I have on my desktop. You can investigate Arduino for yourself HERE.

What I wanted and how I got it

I had just a few design requirements

1. Adjustable time interval
2. Adjustable servo movement speed

The time interval setting is simple enough, however I did find that the pots are the reverse of what one expects in that fully clockwise is a 0 reading. Since most of us are more used to having clockwise indicating an increasing reading, I invert the sense in the software:

g_pot = (1023-analogRead(POT_YAW));

(analogRead returns a value between 0 and 1023). After reading the value I scale it to the required range of seconds (in milliseconds):

nmseconds = map(g_pot,0,1023,5,30) * 1000;

The servo motion time is read from the ROLL pot using similar code except that the pot value isused directly as the delay in milliseconds.

The dwell delay time is not really required>

Mods

I have a few modifications planned:
Do away with the dwell and motion delays since in operation I have found it would be much more useful to use those pots to adjust the servo travel limits.

Make the minimum delay less than 5 seconds.

Download the software

The source interval.ino

The header for the KK board pin definitions: kk.h

I put the kk.h in the Arduino libraries folder so that it can be added to any sketch by using the usual library add menu item. I created this header file from the code at RCHacker