Time lapse means pictures are taken at a specific interval of time. The time interval is adjustable over a wide range and it has an additional sensor, that interrupts the time lapse execution during the night, significantly reducing a large amount of black pictures. ;-)
What do you need:
a digital camera: Rollei 52 (although I guess it will work with most Rollei digital cameras)
a microcontroller (I used an Attiny24, but any other might do the same job)
a few electronics parts like transistors, resistors and connectors.
and a soldering iron like this one from craftsman for instance.
Step 1: Interface the camera
Most big SLRs have an existing interface where you can plug in a control unit. Most small size digicams don't even have an external shutter release interface.
So we have to built this by ourself. But keep in mind that you loose the warranty if you open the camera.
But you can install the interface it in a way, that you can still use the camera normally.