Raliway Requirement Board (RRB)

RRB announce vacancies for  following posts for more than 18000 posts across India.

Filling up online form start on  26/12/2015 to 25/01/2016 only through below link

RRB

All are nontechnical posts.

1. Commercial Apprentice (CA) - 703 Posts
2. Traffic Apprentice (TA)- 1645 Posts
3. Enquiry cum reservation clerk (ECRC) -127 Posts
4. Goods Guard - 7591 Posts
5. Junior Account Assistant cum typist (JAA) - 1205 Posts
6. Senior clerk cum typist (SCT) - 869 Posts
7. Assistance Station Master (ASM) - 5942 Posts 
8. Traffic Assistance (TA) - 166 Posts
9. Senior Time Keeper (STK)- 04 Posts

Education details - Any graduates can apply .(T&C apply)

Exam details:

• Exam is objective paper 
• 100 Questions 
• 90 minutes
• 1/3 negative marks

General Knowledge

• Current Affairs  india and international 
• World general science 
• Indian economy 
• Indian culture
• Science technology

Arithmetic Ability 

• Percentage
• Time & Work
• Boats & Steams
• Time & Distance
• Interest 
• Profit & Loss
• Averages
• Problems on Age

General Intelligence 

• Analogies
• Similarities 
• Problem solving
• Relationship concepts
• Decision making
• Judgement 
• Visual memory discrimination 

General Science 

• Physics
• Environmental Studies
• Chemistry
• Biology

LiFi technology

What is LiFi ?

LiFi is a wireless optical networking technology that uses light emitting diodes (LEDs) for data  transmission.

LiFi is designed to use LED light bulbs similar to those currently in use in many energy conscious homes and offices. However , LiFi bulbs are outfitted with chip that modulates the light imperceptibly for optical data transmission . LiFi data is transmitted by the LED bulbs and received by photoreceptors.


LiFi early developmental models were capable of 150 Mbps. Some commercial kits enabling that speed have been released . In the lab with stronger LEDs and different technology , researchers have enabled 10 gigabits per second which is faster than 802.11ad.

Base of Digital electronics

1. AND Gate


2. OR Gate


3. NOT Gate


4. NAND Gate


5 NOR Gate


6. EX-OR Gate


7. EX-NOR Gate

EX-NOR Gate

The Exclusive NOR Gate function is a digital logic gate that is the reverse or complementary form of the EX-OR function. Basically the EX-NOR is a combination of EX-OR Gate and NOT Gate but has a truth table similar to the standard NOR Gate in that it has an output that is normally at logic level "1" and goes LOW to logic level "0"  when any of its inputs are at logic level "1".

Above is how EX-OR Gate  form using other Gates .

EX-OR Gate

There are two other types of digital logic gates which although they are not a basic gate in their own right as they are constructed by combining together other logic gates, their output boolean function is important enough to be considered as complete logic gates. These two logic gates called Exclusive-OR (EX-OR) Gate and its complement the Exclusive NOR Gate.

Above shows EX-OR Gate and its truth table.

By using basic gates and Universal gate we make EX OR Gate

OR Gate

In this gate any of the input is 1 so output is 1. This is basic function of this gate. Basically it will add all the input and gives output. figure below is 2 input OR gate.

Truth table of 2 input OR gate

Basically how it will work like a parallel circuit

NOT Gate

This gate is basically a inverse gate . It have only one input and one output. It just inverse the input
Given below symbol and truth table.

Transistor circuit of NOT gate.

IN this circuit NOT gate in IC . generally 6 gates are included in one IC, it is more than AND & OR gate because it has only one input and one output.





Other Gates
AND Gate

OR Gate

NAND Gate

NOR Gate

AND Gate

1. AND Gate

Symbol of AND gate

Above the basic operation for 2 input AND gate.(multiply system)

If both  A &  B are true than answer will be TRUE 

Above is the 2 and 3 input AND gate.

NOR Gate

The logic NOR gate is a combination of the digital logic OR gate with that of an inverter NOT gate connected togather in series.

" If both A & B are Not true , than Q is true."

NAND Gate

The NAND function is a combination of two separate gates  function AND & NOT .
NAND function is a series combination of series AND gate and NOT gate.
The logic function of NAND gate in Boolean algebra is   A.B.

Above figure is for symbol of NAND gate.

Above figure is how we get output of NAND gate .

Truth table for NAND Gate.

Other  Gates

AND Gate

OR Gate

NOT Gate

NOR Gate

Automatic night light using 555 timer

Description 
A cheap and simple  automatic night light using few transistors and NE555 timer is shown here . The circuit will automatically switch on the AC lamp when night falls and the lamp will automatically switched off after a preset time.


The working of this night light circuit very simple. An LDR is used as the sensor here. At day time the resistance of the LDR will be low and so do the voltage drop across it, the transistor Q1 will be in conducting mode . When darkness falls the resistance of LDR increases and so do the voltage across it. This makes the transistor Q1 OFF.  Base of Q2 is connected to the emitter of Q1 and so Q2 is biased on which in turn power IC1.



NE 555 is wired as monostable multivibrator that is automatically triggered at power ON . This automatically triggering is achieved with the help of capacitor C2. The  output of IC1 remains high for   a time determined by resistor R5 and capacitor C4 . When output of IC1 goes high transistor Q3 is switched ON which triggers triac T1 and the lamp glows . A 9V battery is included in the circuit in the order to power the timer circuit during power failures . Resistor R1 and diode D1 , capacitor C1 and Zener D3 forms the power supply section of the circuit . R7 and R8 are current limiting resistors.



Notes:

• The circuit can be assembled on a very board.
• Preset R2 can used to adjust sensitivity of the circuit.
• Preset R5 can be used to adjust the ON time of the lamp.
• The wattage of L1 must nor exceed 200W
• Heat sink is recommended for BT136.

for more information about 555 timer IC

more information about 555 IC

Silicon Controlled Rectifier

What is SCR ?

It is Silicon Controlled Rectifier , use in power electronic device. It use as a switching devices in many high voltages area and high temperature .

figure shows physical diagram and symbol of SCR.
SCR is well known member of thyristor family, although there are many different members are available in thyristor family but SCR are so widely used that as if thyristor and SCR become synonymous.


If we see from the constructional and operation point of view , it is a four layer (PNPN) three terminals (anode,cathode, gate) semiconductor device. This device has two states ON and OFF. We can turn it ON by sending gate current signal between second P layer and cathode. But we cannot turn OFF by control signal. That means we have control upon its turn ON, once it goes to conduction mode , we lose control over it.

It can block both forward and reverse voltage but can conduct only in one direction.It use in high power application like AC -DC converter etc.

SCR V-I Characteristic 

Images electronics figure, circuit diagram chart

Mobile  to Smart phone of popular companies 

Apple

Samsung

Nokia

Lumia series 

old nokia

TV from 1970 to 2015

In 1970

In 1980

In 1990

In 2001

In 2005

GPS

What is GPS ?

The Global Positioning System (GPS) is a satellite base navigation system . It is maintained by united states government and was originally designed for soldiers and army vehicle,but now it available freely to all.  

The satellite work on solar power and also backup batteries when solar light is not available.   

Working principal

There are six GPS satellite in each 4 orbit of earth, they are arrange in such a way that minimum 4 of them cover any point of the globe.

The GPS satellite transmit signals to receivers.

Figure below show how GPS work

Frequency use in GPS