When using a slow shutter speed, the camera should be as steady as possible, in order to not blur the picture. The common rule states that if you are using a focal length of, say, 125 mm, the shutter speed should be 1/125 or faster if you hand-held the camera. For slower shutter speeds, your camera should be on a tripod. But in many cases this is not enough, because the vibration you cause when pressing the shutter may suffice to blur the picture. To avoid this in a classic, film SLR, you would use a (mechanical) shutter cable release.
But in modern digital cameras, the situation is not that simple. In particular, the Nikon Coolpix line requires a device intelligent enough to "speak" with the camera, just to do the same job that the old-fashioned cable release (crazy!). I developed kShutter, an electronic circuit based on a microcontroller (a simple but full computer in a single chip) and programmed it to send the appropriate messages to the camera to take a shot whenever a button is pressed.
The main component is a PIC16F628A microcontroller, which reads the button state and speaks with the camera through a serial RS-232 port. In order to adapt PIC voltage levels to those of RS-232, a MAX3323 is used. You will need a serial Nikon SC-EW3 cable (or equivalent) to connect this circuit to the camera. One end of the SC-EW3 is a DB9 connector (that goes to CON1, see the schematic) the other is the proprietary design used for the camera. As the SC-EW3 only has 3 wires, for my implementation I cut the DB9 end and replaced it by a stereo jack, which is less bulky that the DB9 (accordingly, I used a stereo female jack instead of CON1 on my kShutter). As 3V power supply, you can use a CR2032-type button cell battery which is very compact in size.
If you want to know more about the communications protocol used by the camera, have a look at Vladimir Vyskocil's (unofficial) specification.
If you want intervalometer functionality, try kShutter2.