Description
This page is about a low-cost system that can remotely reboot a PC placed anywhere in the world with GSM signal coverage. To switch off or on the PC, all you need is to give a missed call to the phone. The beauty of the system is that dose not require any hardware intervention neither on PC site nor phone site. All the elements of the system are shown in figure 1. 
The system is composed from the following components:
1 – Mobile phone – in this case a Nokia 2630. It is used to receive the off/on command through GSM network.
2 – Signal cable – transmits the command received by the phone to the off/on box.
3 – off/on box – this box is built around PIC12F510 microcontroller which decodes the command from the mobile phone and toggles a relay cutting off and on the power to remotely restart the PC.
4 – Power cables – used to supply the off/on box and the PC that needs to be remotely restarted.
How it works?
The mobile phone is an usual phone that supports mp3 songs as ring-tones. A special song was composed for this application and uploaded on the phone. The song is a 17 Hz sinusoidal waveform. You can download the song from here (you will need to change the file extension from pdf to mp3). To allow just authorized people to toggle your PC state the 17 Hz sinusoidal waveform song was set as ring-tone just for those people phone number. This way, every time when an authorized number will call the mobile phone the 17 Hz waveform song will be played in phone speakers and will be transmitted trough the hands-free cable if this is present. Because the frequency of the song is 17 Hz this will be an unhearble noise for human beings..
1
The signal cable is a nonstandard cable which has attached at one end a 2.5 mm jack nokia hands-free connector which is connected to the phone through. At the other end has a BNC male connector witch is connected to the on/off box through. This cable is used to transfer the ring-tone signal from the phone to the on/off box.
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The off/on box. The main components of the box are the PIC12F510 microchip microcontroller and a relay. The PIC12F510 decodes the signal coming from the phone and commands the relay. The relay is used to interrupt the cable that supplies the PC.
As can be seen on the right side image there are four sockets on the back panel of the off/on box. Three of those sockets are power sockets and the other one is a signal socket.
About the sockets and their usage:
Socket number 1 – is a power socket and is used to supply with power the electronics from the box.
Sockets number 2 and 3 – is a pair (male -female) of sockets. This pair of sockets is used to disconnect the PC from the power supply grid. Inside the box, the socket 2 is connected to socket 3 through the relay contacts. That means, that if the contacts of the relay are closed, the power that comes in the socket 2 reach the socket number 3; and if the contacts of the relay are opened, the electrical circuit from socket 2 to socket 3 is broken.
Socket number 4 – is a BNC female signal input socket. Through this socket, the microcontroller receives the reset signal from the phone.
The front panel of the off/on box:
As can be seen in the image, on the front panel of the off/on box are: a switch, a push button, a green LED and an orange LED.
The switch is used to power on/off the off/on box.
The push button is used to toggle the relay state. That means, that if the contacts of the relay are closed (there is electrical connection between socket 2 and socket 3), a push on to the switch will open the contacts of the relay (the electrical connection between socket 2 and 3 will be broken).
The green LED is used to signal the state of the relay contacts. If the green LED is on, that means that the contacts of the relay are closed. If the green LED is off, that means that the contacts of the relay are opened.
The orange LED is used to indicate when there is activity on the signal input.
The power cables. The system requires three power cables. Two cables as cable 1 on the right image. One of those cables is used to supply the off/on box with power. One end of this cable is connected to the AC grid and the other end is connected to the socket 1 of the off/on box.
Together, cable 1 and cable 2 are used to supply the PC with power. Cable 1 is connected with one end to the AC grid and with the other end to the off/on box at socket 2. Cable 2 is connected with one end to the off/on box to socket 3 and with the other end to the power socket of the PC.
The PC is the target item of the system, but can easily be noticed that the role of the PC can be played by any item that needs to be remotely turned off and on. Of course this will work only for those items that can be turned on simply by connecting them to the power grid.
As default the PC will not start if it is connected to the power grid. To make the system work with a PC is required to modify one of the BIOS settings of your PC. Ther should be an option that says something as: “Reboot on power failure” and this needs to be ON to permit the PC to start.
The electronic scheme
download schematic in pdf format
Note: The cable from schematic is a more complex cable that this project requires. I used this cable because I was forwarding skype calls over the GSM network.
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