WiFi Direct: wireless LAN standard for file sharing

So, you want to share large folders like videos, photos fast but without wires??

Creating a wireless LAN to share files between computer was difficult and almost impossible for non-geeks.

Few months back I wanted to share 5 GB of photos in my laptop with a friend. Few minutes later I was disappointed to know that its impossible over existing WiFi architecture. The other option was bluetooth, but it is very slow. Finally I used to the old method of transferring files using a flash drive.

But wireless file sharing over WiFi is now possible using the WiFi direct standard.

Wi-Fi Direct acts like a software hotspot (software access point, or "soft AP"), for any device that wishes to support it. All Wi-Fi Direct connections are protected by the recent WPA2 security standard. When a device enters the range of the Wi-Fi Direct host, they can connect using the existing ad-hoc protocol and create a connection.

Atleast one Wi-Fi Direct enabled device is needed to perform the task. Any Wi-Fi Direct enabled device can connect to other non Wi-Fi Direct certified devices to perform the task.

Turn off Bluetooth by default in Linux

Many people noticed that bluetooth is switched on by default laptop on a laptop running Ubuntu. One method on internet is to stop bluetooth module from loading, but that method prevents from using bluetooth when needed. This can also be used on other Debian based Linux distros with bluetooth enabled by default.

Lets see how to configure it.

Open the Terminal (Applications -> Accesories -> Terminal)

At the prompt, type

sudo nano /etc/rc.local

add following line before the last line exit 0 (highlighted in the screenshot).

rfkill block bluetooth

 

This is how it works:

Scripts  in file /etc/rc.local are executed at the end of all the multi-user boot levels.

Adding

rfkill block bluetooth

turns off bluetooth after the OS starts it.

rfkill provides a generic interface to disabling any radio transmitter in the system.

 

This helps in reducing the power consumption of a computer  and also protects us from wireless radtion.

Switch (Basics)

Switch is an electrical component that can make or break an electrical circuit. It has conductive pieces (often metal) called contacts or terminal that touch to close (make) or open (break) a connection.

A pair of contacts is closed (switched on) when current can flow from one contact to other. When the contacts are separated by an air gap, they are open (switched off) and no current can flow between them.

Switches used for home wiring are mechnical switches and have an internal arrangement as shown below.

Electromechanical switches like relay are used for specialized operations.

Note: The representation shown below is the technical representation (used in diagrams) followed by some actual switches used.

Technically, based on the number of contacts, switches can be classified as:

• SPST (Single pole, single throw)

It is a simple on-off switch. The two terminals are either connected together or disconnected from each other.

For Ex: light switch in homes.

     

 

• SPDT (Single pole, double throw)

It has a common contact C (COM) connected to either of two other contacts A or B.

  

 

• SPCO (Single pole, centre off)

Equivalent to SPDT switch, only that it has a centre off position.

   

 

 

• DPST (Double pole, single throw)

Equivalent to two SPST switches controlled by a single mechanism.

   

 

 

• DPDT (Double pole, double throw)

Equivalent to two SPDT switches controlled simultaneoulsy.

   

A is connected to either B or C, D is connected to either E or F.

 

• DPCO (Double pole, centre off)

Equivalent to a DPDT switch, it has a stable off position in the centre.

   

 

Switches derived from above are switches are

• Push-to-make

A push-to-make switch returns to its normally open (off) position when you release the button, this is shown by the brackets around ON.

For Ex: Doorbell switch.

   

 

 

• Push-to-break

A push-to-break switch returns to its closed (on) position when you release the button.

   

 

Source: Wikipedia