A very interesting project showing you how to turn on and off the power from your mains outlet through computer network. It is very well documented and very useful. Basically you could turn on or off any device from any location as long as you can connect to your network.
The on/off switching will be done by an Olimex AVR/IO board. This board is equipped with an ATmega16 microcontroller (with no initial software loaded), four low-voltage inputs, a serial interface and four 5A/250V SPDT relays. These relays can be controlled by serial, by the four inputs or both depending on the code you will write for the microcontroller. So it is a very versatile board and only your imagination is the boundary of it’s utility.
The four low-voltage inputs are optocoupler isolated so this input can accept signals with different ground. Also these inputs are very helpful if you want to use a wireless module like the XBee. A PNP transistor is used to drive these inputs without any trouble.
Each relay provides connections for both normally open and normally closed positions. The relay will be placed between the hot wire that comes from wall and the hot wire that goes into the outlet. This way it will open or close the circuit on your command. Be careful however of the power consumption of the device you plug in the outlet. The relays are rated at 5A but they can be changed if your requirements ask for it.
The network controller is the Atmel NGW100 and will allow you to control the Olimex board through the network. It has two ethernet ports, lots of GPIO ports and Linux with TCP/IP installed. Control of the GPIO ports can be a little tricky with the NGW100 but you will find the scripts in the project.
The next thing is to connect the NGW100 to the network. Once that is done you can access the NGW100 through the network and execute the scripts according to your desired action.