WiFi

 WI-FI -Wireless Fidelity.

Using Wi-Fi your information will fly in air and reach your computer.
Now-a-days, many people use wireless networking also called as Wi-Fi or 802.11 networking.
It uses radio waves to transfer data and uses two frequency levels either 2.4 GHz or 5 GHz.
HOTSPOTS: Hotspots are simply areas where Wi-Fi can be accessed.

HOW IT WORKS???

To use Wi-Fi connection one's computer should have wireless adapter.
Let us see the working in two ways. One is from client to server and other is from server to client.
CLIENT TO SERVER:
Adapter translates data into radio signals and transmits it to the space using an antenna.
A wireless router receives the signal and decodes it.
The router sends the information to the internet using wired Ethernet connection.
SERVER TO CLIENT:
Router receives information from the internet, translates it to radio signal and transmit it.
Wireless adapter receives the signal and decode it.

VARIOUS STANDARDS OF WIFI:

Its transmission frequency is either 2.4 GHz or 5 GHz, which is higher than frequencies used for mobile phones, television, etc.
Due to high frequency it carries large data.
It has several standards which are explained below:
    802.11a - It transmits data at 5 GHz and move up to 54 megabits of data per second.
          It uses Orthogonal Frequency Division Multiplexing (OFDM), a technique that splits radio signals into sub-signals. This reduces interference.
    802.11b - It transmits data at 2.4 GHz and move up to 11 megabits of data per second.
          It is developed for low cost communication. Also it is slower than the predecessor.
    802.11g - It transmits data at 2.4 GHz and move up to 54 megabits of data per second.
          It is same as 802.11b but speed is somewhat better.
    802.11n - This is the most widely used standard.
          It transmits data at 2.4 GHz and move up to 140 megabits of data per second.
          It can transmit data up to four streams.
    802.11ac - It the newest standard developed recently in 2013.
           It transmits data at 5 GHz and move up to 140 megabits of data per second.
           It is not yet widely used.

ULTRASONIC TOOTHBRUSH

 ULTRASONIC TOOTHBRUSH

Many of you may have heard this name "Ultrasonic Brush" or may not.
This is the brush of latest technology which is used to reduce our strain ever for brushing.
It is a kind of electrical toothbrush because it works on current.
When it is switched ON it produces ultrasonic waves so that its bristles vibrate at ultrasonic frequency.
That vibration creates small bubbles, which ignites normal brushing action.
The lathers created are used to clean our teeth in the nooks and crevices.
Usage of this brush is not like ordinary brushing in circular brushing motion.
Unlike that it should be drawn across the teeth in a slow, straight line, back and forth manner.
It uses normal AA or AAA sized battery.
Another kind of brush uses coiled wiresfor charging; when the handle of the brush is brought near the charger the energy transferred to the battery and recharges it.
The charge can lasts for one week.
These kinds of brushes are more expensive.
It is specially designed for the elders who are not even able to do ordinary simple work.

BLUETOOTH

BLUETOOTH - A WIRELESS NETWORK

Have you ever thought about the working of Bluetooth, a wonderful networK???
Read this post you will get clear idea about its working..........

WHY IT IS CALLED AS BLUETOOTH???

Bluetooth was named after a king in Denmark "HARALD BLUETOOTH", who got his name because of his fondness for blueberries, which stained his teeth.
He was famous for uniting the warring tribes of Scandinavia, just like our Bluetooth protocol, uniting different technologies.
Hence the name Bluetooth came.

WHAT IS THE NEED FOR BLUETOOTH???

When two devices need to talk with each other either it should have wired connection or wireless connection.
Wired connection increases cabling, cost and complexity.
Compared to wired, wireless is advantageous but it need more power for transmission.
Bluetooth offers a solution to this problem.

GENERATION OF BLUETOOTH:

Now Bluetooth is in its second generation.
First generation Of Bluetooth 1.0 has maximum data transfer speed of 1 Mbps.
Second generation- Bluetooth 2.0 has transfer rate of 3 Mbps.

HOW BLUETOOTH CREATES A CONNECTION???

Bluetooth takes small networking area and keeps transmission power extremely low.
It consumes just 1 milliwatt of power, thereby saving cell phone charges.

HOW BLUETOOTH OPERATES???

It operates in Radio frequency range. Its transmission frequency is 2.45 Gigahertz (actually between 2.402 GHz & 2.480 GHz).
Here you should ask a query... Many devices in our home operate in radio frequency region but Bluetooth doesn't interfere with those gadgets why?
The answer is here, there is more chance of interference yet it won't interfere because of low power consumption. As the transmission power is very low it restricts the usage of Bluetooth within 10 meters (32 feet). So it won't affect any other electronic gadgets.
Bluetooth can connect up to 8 devices simultaneously within 10 meters range.
You should ask another query here...  If many devices turned ON Bluetooth at a time and transfers data, won't they interfere with each other because all are working in same frequency range?
To solve this problem Bluetooth uses a technique called SPREAD-SPECTRUM FREQUENCY HOPPING.
SPREAD-SPECTRUM FREQUENCY HOPPING means jumping of data from one frequency to another.
Not clear....??? When a device transfers data via Bluetooth it will select particular frequency between 2.402 GHz & 2.480 GHz.
If some other device working nearby also took the same frequency data collision may occur.
In order to avoid that Bluetooth keep on jumping from one frequency to another called frequency hopping. (HOP-jump)
By this technique a device can use 79 individual frequencies and it will jump to other frequency 1600 times per second.
Due to this jumping other devices can also use the slice of frequencies without any trouble.
This device reduces collision because it is very rare for any two devices to use the same frequency. If it happens that is also not a problem because every device lasts in particular frequency only for a fraction of second.

SECURITY IN BLUETOOTH:

Usually wireless communication is not safer. Most of the devices grab radio waves in air automatically. But Bluetooth communication is secured one.
Before connecting to any device the Bluetooth will ask for permission to the user else it will ask for code.
After the establishment of connection only it will start transferring data. All these securities are made in software level.
A user can put his device in non-discoverable mode thereby preventing any other devices to identify it.

Bluetooth is a wonderful small network discovered to transfer data with low power... Make use of it....!!!

DAY 9 OF ELECTRONICS

METAL OXIDE SEMICONDUCTOR FIELD EFFECT TRANSISTOR (MOSFET)

MOSFETs are another category of FETs. It also has three terminals drain, source and gate.
It is similar to that of JFET except that the Gate is insulated from the channel; as a result it doesn't form a P-N junction.
Because of this MOSFET is also called as IGFET (Insulated Gate Field Effect Transistor).
The Gate is insulated from channel by means of introducing a layer of silicon dioxide in between Gate and channel.
There are two types of MOSFETs:
    1. Depletion MOSFET (D-MOSFET)
    2. Enhancement MOSFET (E-MOSFET)
It also has N-channel and P-channel. Normally we use N-channel in most of the cases.

1. DEPLETION MOSFET (D-MOSFET):

CONSTRUCTION:

An N-channel D-MOSFET consists of highly doped P-type substrate.
In this substrate, two heavily doped N-regions are diffused.
These two regions are used as Source and Drain.
A thin layer of silicon dioxide is applied on the surface of this structure. An ohmic contact brought out from this layer called as Gate.
This SiO2 layer acts as a insulator between Gate and the Channel.
It should be noted that the gate and channel do not form PN junction as like in other cases, because the Gate is insulated from channel by means of SiO2 layer.
Hence it is named as Insulated Gate Field Effect Transistor (IGFET).
The construction of P-channel D-MOSFET is also similar to that of N-channel, with the difference that the substrate is of N-type and heavily doped region is P-type.

OPERATION:

 

As the Gate is separated by means of insulating material, the Gate and channel acts as two plates of a parallel-plate capacitor.
The SiO2 layer acts as dielectric between these two plates.
When a voltage of particular polarity is applied to the gate, the charges with opposite polarity are induced in the channel by the principle of parallel-plate capacitor.
The voltage may be either +ve or -ve, hence two modes are possible
        Depletion mode - for negative gate voltage
        Enhancement mode - for positive gate voltage

DEPLETION MODE - If negative voltage is applied to the gate, then D-MOSFET operates in depletion mode.
The negative voltage at the gate produces positive charges on another plate called channel.
Due to this the channel is depleted of electrons (i.e. positive charges produce) and current flow reduces.
If Drain-Source voltage is applied the positive charges near channel are influenced towards drain.
As the negative voltage near gate increases, positive charge near channel keeps on increasing. This reduces drain current.
ENHANCEMENT MODE - If positive voltage is applied to the gate, then D-MOSFET operates in enhancement mode.
The positive voltage at the gate produces negative charges on channel.
Due to this more and more electrons produced in the channel and the current flow enhances.
Hence this mode is called as enhancement mode.

2. ENHANCEMENT MOSFET (E-MOSFET):

Construction:

 

An N-channel E-MOSFET consists of highly doped P-type substrate.
In this substrate, two heavily doped N-regions are diffused.
These two regions are used as Source and Drain.
A thin layer of silicon dioxide is applied between two N-regions. An ohmic contact brought out from this layer called as Gate.
The construction of E-MOSFET and D-MOSFET are similar. The only difference is that in E-MOSFET a channel is not formed as in the case of D-MOSFET.

OPERATION:

 

The operation of E-MOSFET is similar to that of enhancement mode of D-MOSFET.
The difference is the induced negative charge on the other side forms channel between two N-regions.
After the formation of channel only the current starts to flow before that current will be zero.
So that other operations are similar to that of D-MOSFET.

DAY 8 OF ELECTRONICS

FIELD EFFECT TRANSISTOR

Invention of Field Effect Transistor is the starting point of electronic journey towards digital....
FET is a three terminal device and unipolar because current conduction is only by one carrier either electron or hole.
In FET current is controlled by electric field. Hence we can say this as field-dependent device.
FET is classified into two types
        1. Junction FET (JFET)
        2. Metal Oxide Semiconductor FET (MOSFET)
            2a) Depletion type MOSFET (D-MOSFET)
            2b) Enhancement type MOSFET (E-MOSFET)

1. Junction FET (JFET)

FET has three terminals namely Drain, Source and Gate.
N-channel JFET: It consists of N-type semiconductor with two heavily doped P-type regions. Current is produced by electrons in it.
P-channel JFET: It consists of P-type semiconductor with two heavily doped N-type regions. Current is produced by holes in it.

Construction:

Usually the P-type and N-type region combined together to form PN junction for both N & P channels.
In N-channel heavily doped P-type regions at both sides are internally connected and an ohmic contact is brought out called as GATE.
Also two ohmic contacts are brought out at other opposite sides (from N-channel) called as Source and Drain.
In the similar way P-channel JFET also constructed but replacing N-type by P-type and P-type by N-type.

Operation of JFET:

The current conduction in JFET is from Source to Drain. That current is named as Drain current.
There are two terminal voltages one is between drain & source (Vdd) and the other is between gate & source (Vgg).
In Gate-source terminals, Negative terminal of battery is connected to gate and positive to source. Similarly in Drain-source terminals, Positive terminal is connected to drain and negative to source.
When DC voltages are applied to the terminals of JFET, a depletion region is formed between two PN junctions.
If Gate-source voltage is the only voltage then the width of depletion region is uniform.
If another voltage (Drain-Source voltage) is applied the depletion region extends towards drain under the influence of +ve voltage.
If Gate-Source voltage is not applied, the electrons near source move towards drain (because of -ve voltage) and electrons near drain move towards +ve terminal. This forms a closed loop for current flow. This current is called as drain current.
After applying Gate-Source voltage the depletion region produces this reduces the width of the channel i.e. the channel become narrow.
Hence eventual decrease in current flow because of reduced electron flow towards drain. It's observed from this that if Gate-Source voltage is increased drain current decreases.
If Gate-Source voltage is continuously increased, after a certain stage it will reach high voltage called as Pinch-off voltage.
Under pinch-off voltage there will be no electrons to cross the channel (current is zero). But in practical case small current will flow.
If Gate-Source voltage is further increased beyond pinch-off voltage then the P-N junction breaks down. And the drain current shoots up to large value.
This is the basic principle of operation of JFET.

DAY 7 OF ELECTRONICS

BJT CIRCUIT CONFIGURATION

In any circuit, two terminals are required for input and two terminals are required for output.
Therefore, totally four terminals are required for both input and output sides.
But in a transistor only three terminals are there.
So in order to overcome this problem one terminal should be kept common to both input and output.
This is the need for transistor circuit configuration.
Based on the common terminal the transistor can be configured in three ways....
        Common-Base (CB)
        Common-Emitter (CE)
        Common-Collector (CC)

Let us see the working of both PNP & NPN transistors in all the three circuit configurations.
In circuit configuration we are going to see about current flow & voltage.
(NOTE: The current considered here is electron current)

RULES:

There are two currents & two voltages one is actual & other is conventional.
        Actual: True behavior of the circuit.
        Conventional: universally accepted behavior of the circuit.
RULE 1: Assume all the currents entering into transistor as positive. If the actual direction coincides with the conventional direction, then it is taken as positive. Otherwise take is as negative.
RULE 2: Assume voltage near the common terminal as negative or low potential. If the actual voltage coincides with the conventional voltage, then it is taken as positive. Otherwise take is as negative.

COMMON-BASE CONFIGURATION (CB):

In this configuration, the base is common to both input and output terminals. The input terminals are Emitter-Base and the output terminals are Collector-Base.
EMITTER CURRENT:
    NPN: Actual emitter current is output from the terminal because electrons (majority carriers) move towards base. The actual direction doesn't coincide with the above rule. Hence emitter current is taken as negative.
    PNP: Actual emitter current enters into terminal because electrons (minority carriers) move towards positive terminal. The actual direction coincides with the above rule. Hence emitter current is taken as positive.
BASE CURRENT:
    NPN: Actual base current enters into base region. It coincides with the above rule. Hence base current is taken as positive.
    PNP: Actual base current comes out from base region. It doesn't coincide with above rule. Hence base current is taken as negative.
COLLECTOR CURRENT:
    NPN: Actual collector current enters into transistor because electrons come out under the influence of positive potential. The actual direction coincides with the above rule. Hence collector current is taken as positive.
    PNP: Actual collector current comes out of the transistor because electrons move inward under the influence of negative potential. The actual direction doesn't coincide with the above rule. Hence collector current is taken as negative.
EMITTER-BASE VOLTAGE:
    NPN: The DC voltage is connected so as to make emitter terminal negative and base terminal positive such that emitter is having low potential. These polarities don't coincide with above rule. Hence Emitter-Base voltage is negative.
    PNP: The DC voltage is connected so as to make emitter terminal positive and base terminal negative such that emitter is having high potential. These polarities coincide with above rule. Hence Emitter-Base voltage is positive.
COLLECTOR-BASE VOLTAGE:
    NPN: The Dc voltage is connected so as to make collector terminal positive and base terminal negative such that collector is having high potential. These polarities coincide with above rule. Hence Collector-Base voltage is positive.
    PNP: The DC voltage is connected so as to make collector terminal negative and base terminal positive such that collector is having low potential. These polarities don't coincide with above rule. Hence Collector-Base voltage is negative.

COMMON-EMITTER CONFIGURATION (CE):

In this configuration, the emitter is common to both input and output terminals. The input terminals are Base-Emitter and the output terminals are Collector-Emitter.
EMITTER CURRENT, BASE CURRENT and COLLECTOR CURRENT are same as that of common base. The change only will be in voltage.
BASE-EMITTER VOLTAGE:
    NPN: The DC voltage is connected so as to make base terminal positive and emitter terminal negative such that base is having high potential. These polarities coincide with above rule. Hence Base-Emitter voltage is positive.
    PNP: The DC voltage is connected so as to make base terminal negative and emitter terminal positive such that base is having low potential. These polarities don't coincide with above rule. Hence Base-Emitter voltage is negative.
COLLECTOR-EMITTER VOLTAGE:
    NPN: The Dc voltage is connected so as to make collector terminal positive and emitter terminal negative such that collector is having high potential. These polarities coincide with above rule. Hence Collector-Emitter voltage is positive.
    PNP: The DC voltage is connected so as to make collector terminal negative and emitter terminal positive such that collector is having low potential. These polarities don't coincide with above rule. Hence Collector-Emitter voltage is negative.

COMMON-COLLECTOR CONFIGURATION (CC):

In this configuration, the collector is common to both input and output terminals. The input terminals are Base-Collector and the output terminals are Emitter-Collector.
EMITTER CURRENT, BASE CURRENT and COLLECTOR CURRENT are same as that of common base. The change only will be in voltage.
BASE-COLLECTOR VOLTAGE:
    NPN: The Dc voltage is connected so as to make base terminal positive and collector terminal negative such that base is having high potential. These polarities coincide with above rule. Hence Base-Collector voltage is positive.
    PNP: The DC voltage is connected so as to make base terminal negative and collector terminal positive such that base is having low potential. These polarities don't coincide with above rule. Hence Base-Collector voltage is negative.
EMITTER-COLLECTOR VOLTAGE:
    NPN: The Dc voltage is connected so as to make emitter terminal positive and collector terminal negative such that emitter is having high potential. These polarities coincide with above rule. Hence Emitter-Collector voltage is positive.
    PNP: The DC voltage is connected so as to make emitter terminal negative and collector terminal positive such that emitter is having low potential. These polarities don't coincide with above rule. Hence Emitter-Collector voltage is negative.

DAY 6 OF ELECTRONICS

BIPOLAR JUNCTION TRANSISTOR (BJT)

BJT is also called as junction transistor.
It consists of two P-N junctions.
The junctions are arranged in such a way that one type of semiconductor material is common to both the junctions.
In that way, it provides two possible types to construct a transistor.
        NPN transistor
        PNP transistor

NPN: One P-type semiconductor is sandwiched between two N-type semiconductors.
PNP: One N-type semiconductor is sandwiched between two P-type semiconductors.

THREE TERMINALS:

It has three terminals Emitter, Base and Collector.
EMITTER: This region is on one side of transistor and it is heavily doped. In NPN emitter is of N-type and in PNP emitter is of P-type.
BASE: This region is in middle of transistor and it is lightly doped. In NPN base is of P-type and in PNP base is of N-type.
COLLECTOR: This region is on other side of transistor and its doping lies between emitter and base. In NPN collector is of N-type and in PNP collector is of P-type.
The junction between Emitter and Base is called as Emitter-base junction. And junction between Collector and Base is called as Collector-base junction.

WORKING:

UNBIASED TRANSISTOR:

An unbiased transistor is called as open-circuited transistor.
Under unbiased condition diffusion of majority carriers takes place across two junction due to concentration gradient (i.e. to achieve equilibrium)
Due to diffusion of majority carriers depletion region is formed.
The diffusion of carriers continues and finally attains equilibrium condition. Thus thereafter no diffusion of carriers takes place.

BIASED TRANSISTOR:

When two junctions are biased using external DC voltages, the transistor is called biased transistor.
As there are two junctions, two Dc sources are required.
Based on the biasing a transistor have three modes of operation.
    Active mode
    Saturation mode
    Cut-off mode
(NOTE: All the modes are explained here with NPN transistor)

ACTIVE MODE:

In this junctions are biased as, Emitter-base junction: Forward-biased & Collector-base junction: Reverse-biased.
The negative potential between emitter-base causes the electrons to flow towards base. This constitutes emitter current.
The electrons that enter into the base recombine with holes and constitute base current.
However, only few electrons recombine with holes and remaining crosses the junction enters into collector region due to the fact that the base is lightly doped.
The electrons that entered into the collector region + electrons already exist in the collector region get attracted towards the positive terminal because of reverse bias.
So that it produces collector current. Also there will be a continuously flow of current from one terminal to another such that forming closed loop.
The current will flow without any interruption for this reason only this is called as active mode.

SATURATION MODE:

In this junctions are biased as, Emitter-base junction: Forward-biased & Collector-base junction: Forward-biased.
The negative potential between emitter-base cause electrons to flow towards base. This constitutes emitter current.
Likewise negative potential between collector-base cause electrons in collector region to flow towards base.
Because of flow of both the region's electrons towards base more recombination takes place and this abruptly increases base current. The width of junctions is small.
Hence there will be high current. The transistor in this mode is used for closed switch.

CUTOFF MODE:

In this junctions are biased as, Emitter-base junction: Reverse-biased & Collector-base junction: Reverse-biased
The positive potential between emitter-base and collector-base causes electrons to flow towards the terminal. This increases the width of the junction.
Hence there will be no chance of recombination and no current flow.
The transistor in this mode is used for open switch.

(NOTE: Normally the operation of transistor will be explained in active mode)