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Archive for the ‘Education’ Category

Digital filters :advantages disadvantages and uses and esign

January 18th, 2012 Remo No comments

Digital filter advantages
This type fof filter has the greater accuracy.Dital filters are comparatevity cheaper  than the digital filter.The ease of data storage is one of the main advantages of the digital fiters.Implementatipon ofsophisticated algorithm implementation is also very good for the the use of digital filters.Digital filter allows to use of sophisticated algorithm implementation.
Now what is the application of the VLF signals?What we can do in digital filter is that we can process very low frequency signals –signals which cannot be done with the analog filters.

Next we discuss what are the limitation of digital filters.
There is no doubt that digitals filters make the system more complex than the anlog filters.A/D and D/A converters are very much necessary for the application.Beacuse our real world is an anlog one.
For high frequency signals we need to sample as twice of the frequency in concern so because of nyquest criteria.So forhigh frequecy signals samplig frequency becomes a too large which may be a limitation for the A/D converters.

In digital filter the power consumption is more than the anlog filters.
Applications of digital filters:
Digital filters play a major role in thye filed of echo cancellation in telephone networks.In modems ,line repeaters ,channel multiplexing,video conferencing  digital filter has a major role in many application areas of modern days.
In the filed of consumer electronics Tv,radio mp3 player and many song or voice modifiaction applications there are many digital filters are applide.
I image processing application s also digital filters are used.Digital filters are also used iin image compression ,enhancement imeage analysis and recognistion of image s.
Speech processing is a field where digital filters are used .In military application  in radar signal processing the digital filter is an is an essential part.Sonar signal processing is also a place where digital signal processing and use of digital filters are used.
For secure and navigation  digital filters are also used.
Designing digital filters:
How to design a digital filter.Digital filter design is a very important topic in the filed of  digital signal processing.
Design of digital filter is very challenging in the filed of digital filter design.How the digital filters are classified ?
Digital filters are classified based on the fact that how they respond to a unit impulse.

IIR filter:
They are actually the digital counterpart of the analog filters.Thisn this type of filter uses feedback.This filters requires less resources than the FIR filters.

Now what are the problems of high order IIR filters?

The high order IIR filters have or may have problems with the instability,overflow for arith \matic operation.So in this IIR filter require carefulll design to avoid the problems of IIR filters in high order.

89C51/8051 based questions and notes

October 25th, 2011 Remo No comments

basic questions that can be asked at different interviews about 89c51.

89c51 based questions.

89C51 and 89S51 and 89S51 based questions.

8051 question papers that can be asked at different interviews .

What is a microcontroller .

How a microcontroller works at your own words.

What is the differnce between a 89c51 microcontroller and an 89S51 controller.

What is the memory available at AT89S51  and AT89C51 microcontroller.

What is the memory addressing instructions in case of 8051 core microcontroller.

What is the In system programming for a 89S51 microcontroller.

Is that ISP(in system programming possible for the  the AT89C51 /8051 microcontrollers.

How a 8051 microcontroller is different from a 8051 microcontroller.

What are the amount of programming memory available for  for the 89c51 microcontroller .

How ATMEGA 8 is different orm AT89C51 microcontroller.

Are the PIN diagram of AT89C51 microcontroller and the ATMEGA-8 is same.

How we can program an ATMEGA-8 microntroller.

Does a 8051 cose is license free.

What are the licensing options for A 8051 core.

How do you make interfacing of an 8051 microcontroller and the 8255 chip.

Can a 8051 microntrller be interfaced with a real time clock RTC module

What are the requirements to interface an 89c51 module for a RTC implementation

How to inteface a 89C51 /89S51 module with a clock

What are the serial communication baud rates of the 89c51 microcontroller

How to make an system which can do serial communication between 89c51 and the PC

PC and 89C51/89S51/8051 serial communication is that possible.

What is the role of MAX232 chip in case of AT89c51 and the PC serial comminication.

MAX 232 chip and 89C51 interfacing and connection diagram

what are the ports available for the 89C51 microcontroller

What are the serial ports available for 89C51 microcontroller

Operation of the monostable pulse generating circuit using OPAMP

September 27th, 2011 Remo No comments



Monostable generation

Here in this circuit the circuit generates a quasi-stable state transition from the stable state.Say the output of the V0= L+ I mean HIGH or Vsat.Now feedback fraction=b=R1/(R1+R2).Now as the output voltage is L+ then voltage at the C terminal is bL+.And as the diode D1 is getting High voltage at the P side so diode D1 is ON.So the voltage at the terminal B is just one dide drop say VD1.So the output remains at L+(I mean HIGH).So thisnis the stable state.BUT diode D2 is OFF as R4 is high.So this is the stable state of the monostable multivibrator.

How we go from stable state to quasi-stable state?

We apply a pulse at the trigger terminal. So then diode D2 will now conduct and the voltage at the C terminal will drop. Now when the voltage at the C terminal drops below voltage at B terminal then the output changes to L- or LOW state so this way HIGH to LOW(quasi-stable) state transition occur.

When back to stable state again from quasi-stable state.

Answer is when the output is at Low voltage (L-) then the voltage at terminal C is bL-.Now as the trigger is removed (because trigger is a very short duration pulse).So now as the diode D1 p-sde has low voltage so DIO D1 will be OFF and the capacitor C1 will try to charge towards L-.So a time will come when the voltage at the B terminal will be less than bL- and then output of the OPAMP go to L+ state again. But still this is not the stable state. Stable state will be achieved when the diode D1 will be On again.

What is recovery time

When the capacitor C1 will discharged as output (point A ) is L+. So C1 will discharge first and then when voltage at point B is more than diode potential barrier then diode D1 will be ON and then current will be flown via A to D1 and voltage at point B is again one diode drop.So stable state achieved. The time required to discharge the C1 is called recovery time.

Mono stable Multivibrator using IC 555:Details

September 27th, 2011 Remo No comments



See the figure and I will explain that to you.

First initially the SR Flip flop is in RESET state. Those who donot know what a flip flop is just keep remembering that it has 2 inputs named S and R and two outputs named as Q and Q_bar.If Q is HIGh then Q_BAR is low and vice versa. Note. Whan S=1 R=0 Then Q=HIGH and when S=0,R=1 Then Flip flop is in reset state. And When S=0,R=0 Then it is in no change state and Q and Q_bar value remains at it was earlier for other values of S and R. Here S-R kind of flip flop is being used.

So initially the flip flop is in reset state that means Q=LOW and the output of the Flip flop may be thought as HIGH ,another thing need to remember is that The trigger PIN is initially kept at a voltage higher than the VTL. So when the situation is like this then as VTH=2/3VCC and VTL=1/3VCC(because of the voltage divider network –voltage VCC is divided in three parts by using 3 equal registers).So What is the output of comparator1 :It is LOW.Why ?Because as Q is LOW so the Q_Bar is HIGH and this turns ON the transistor and as the point C is connected with the collector of the transistor so the voltage is zero there. Now consider the comparator 1 output ,it has Voltage LOW at +ve terminal than the voltage at the –ve terminal so output is LOW. For comparator 2 as the –ve terminal is maintained at a voltage more than VTL so the output is also LOW. So what we got –the outputs of the both comparators are low-So SR flip flop state remains unchanged –that means output will be at stable stage LOW.

What happens when we apply a trigger:

When we apply a trigger at the trigger terminal having pulse height lesser than VTL then output of comparator 2 is HIGH and output of comparator 1 is LOW, So this combination of S and R will set the flip-flop and so the output is HIGH now. So Q_bar is LOW and then and transistor goes OFF. So this way we reached at Quasi-stable state from the stable state.

How long to stay at Quasi-stable state ?

Now when it goes to quasi-stable state then as point C is no longer connected to ground via the transistor as transistor is OFF NOW so the capacitor begins charging so voltage at point C go on increasing ,as the capacitor will try to charge towards VCC so a time will come when the voltage at point C will exceed the VTH , Then the output of the comparator1 will go HIGH and the comparator 2 has LOW output because triggering pulse gone. So this is the RESET condition and the Flip flop will reset and the Q=LOW again. Q_bar is HIGH and transistor will be ON and then voltage at point C will now go towards zero after discharge of the charge capacitor stored the voltage at C is completely zero and so recovery done and multivibrator is aging at the stable state LOW.

Motor control using simple Schmitt trigger.

September 27th, 2011 Remo No comments


Hello here we will see how we can control the speed of a DC motor by using a Schmitt trigger IC.Note the speed of the motor can be controlled by various ways ,may be by reducing the DC voltage across the motor etc .

But here we will follow the most conventional way of reducing/increasing the speed of the motor.The basic principle is if say the motor operates at speed 5 V DC then if this is done by sending a pulse of period say x with x/2 ti,e it has 5V and x/2 time it has 0 V. That means we are sending a square wave with 50% duty cycle.Because 50% of the time period we have HIGH voltage across the Motor(5V) and 50% of the time period we have 0 V across the motor.So what will be the result?

The answer is motor will rotate no doubt.But if we increase duty cycle more ? then ? then the speed of the motor will increase because the motor will now have the DC voltage across it more time,because we increased the duty cycle.How we increased te duty cycle ?simple just now we made a square wave such that 75% of time now there is HGH voltage across the motor and 25% of time there is 0V across the motor.So on the average the motor is getting more voltage in the sense that within one time period of the pulse that is being applied then motor is getting more average voltage when the dutry cycle is HIGH.

Actually what we do is that we configure an astable mutivibrartor such a way that its duty cycle can be varied using a potentiometer. So as the duty cycle can be varied then how this is used with the motor? The answer is the motor is connected with a transistor and the astable output is given at the base of transistor. So the transistor will be made on/off based on the duty cycle that way the Motor will be connected or unconnected with the supply at the same rate as the transistor will be ON/OFF. So this way the speed of the motor can be increased and decreased.

More full projects at


Tips to get success in Joint entrance examination

February 27th, 2011 Remo No comments

As we all know that getting success in   exam like JEE or WBJEE can change your life.If the score is high I man if the ranking is good then you may get chance to a reputed college or university and can have an engineering degree. Now how to prepare for that exam.Here are some tips and suggestions that will help you if you want to get success to the JEEE examination. First   of all as you need to prepare the JEE or WBJEE or AIEEE examination during your study. So fix a time for the study of the Higher secondary examinations.


Now How to be prepared when you are studying the   as well ? So try to understand the concepts of the things when you study because if you just remember the problems etc and the solutions so that will not make you a better problem solver (by problem I mean the may be problems associated with physics chemistry or associated with mathematics)

So try to understand them well and see how the formulas etc are used and at which situation the formulas need to used. That can only be achieved via practice.

So when ever you find similar situation then you can apply those formulas.

A problem solving mind :try to grow within yourself.

For example when ever a problem given say a physics related problem is given :first see what are the given information in that problem then apply the appropriate formulas and then try to solve.It is worthy to note that you have to have keep in mind the formulas. Some may argue that we can derive some formulas when needed,so why to remember them-For them I will say time is a very critical factor in competitive examinations. So be aware of that.

Next Try to devote a fixed amount of time each day on the preparation of specifically    for the preparation of WB-JEE examination(Joint entracnce examination)..

Then practice regularly the problem sets.

Many people ask me is that is it   worthy to go for WB-JEE coaching for high price ?Really speaking they may help or may not be as helpful as you think.

Why ? The reason there is no other alternative except hard work if you want to stick to a life of honesty. So donot think that if your child is not well in study and I mean not studious and will get a best result just by spending 10 -15 thousand rupees ,then either you are never did well in study or just prefer to buy a rank –but that is not possible(as I think and if the system OK).What   I mean that tutorial center may show just a way –they have some teachers but do you really think they have the best teachers or the good quality teachers than school. I don’t think so –so teach your son/daughter how to get best help from the teachers available at school. Believe me many teachers are there if they found that your  son/daughter is good in behavior and   studious they will help a lot.


So you must be studious to get a good rank inWb-JEE or JEE or AIEEE or Joint entrance examination.


Operation of n-channel enhancement type MOSFET :Device operation of MOSFET

February 27th, 2011 Remo No comments

To understand that first note that enhancement MOSFETs are normally OFF device. Now what is meant by normally off device?
Means if we apply a source to drain voltage then no current will flow.
The reason behind  is that  
There are 3 regions based o the application of gate to source voltage.
Suppose we are considering the n-channel enhancement type MOSFET.
For that n-channel enhancement type MOSFET there are 3 regions and they are accumulation, depletion and the inversion.
Now suppose for the n-channel enhancement type MOSFET we applied a fixed drain to source voltage and we are varying the  gate to source voltage -2,-1,0,1,2,3,4,5.
Now what will happen when the gate to source voltage is-2 volt. Suppose source is at potential 0V and drain is at potential 5 volt.
Now when the source voltage is at zero volt and gate to source voltage is -2 volt then what happens inside the device. At gate the voltage is now-2 Volt. So at the one end of the insulator(silicon di-oxide) there is now  -ve   induced charges and at the other end(insulator –semiconductor interface at the insulator side).
Then as the induced charges at the insulator-semiconductor interface(at the insulator side) in negative now so at the semiconductor side positive holes will be attracted or accumulation region results.
This is called accumulation because its is actually the accumulation of holes for n-channel device(I mean n-channel MOSFTET).Then when we apply  a positive voltage say 1 V at the gate terminal then due to positive charges induced at the semiconductor and gate and at the insulator and semiconductor interface positive charges induced and due to that fact  there will be a depletion of the positive holes at the interface as the holes will now be repelled from the surface of insulator-semiconductor at the semiconductor site and the minority electrons  will be attracted ,  for that when minority electrons are get at attracted towards that interface say still that number of electrons are not   sufficient to from the channel. So still we will not get any drain to source current .This is depletion region(we call).Now when the gate to source voltage is greater than  the threshold voltage of the device then the device will be on and at that time inversion will occur and a channel will be induced ,this is electrically induced channel not the channel present by structure as in depletion type MOSFET.

Now what is meant by inversion ?
The  answer is that the p region in between the source an the drain will be inverted and will form a n-channel.
Say for example the device has the threshold voltage say 2 V.
So if gate to source voltage is greater than 2 volt then inversion will occur and we will get a current flowing from drain to source.

What is MOSFET: an Note on MOSFET: MOSFET Operation and details

February 26th, 2011 Remo No comments

First what is MOSFET: MOSFET stands for Metal Oxide Semiconductor FET. This device has same characteristics about FET i.e. same as FET but having a MOS structure. For MOSFET there are 2 types. One is enhancement type MOSFET and other is Depletion type MOSFET.

Depletion type MOSFET are normally ON device and Enhancement type MOSFET are normally OFF device and we can make enhancement MOSFET ON after we apply some voltage at the gate terminal greater than threshold voltage of the device. So the minimum voltage required to make the device On is called the Threshold voltage of the device. Now Depletion type of MOSFET is just the reverse of that ,this device is normally ON

device and by proper gate voltage this device can be made OFF.

About the structure of the MOSFET.

There are n-channel enhancement type MOSFET and p-channel enhancement type MOSFET.For n-Channel enhancement type MOSFET there is a p-substrate and within the p substrate there are 2 n+ regions are diffused .These 2 n+ regions will be source and drain. In between the source and drain there is a gate region. The structure of gate is Metal/Polysilicon then oxide and then p substrate.

Now the characteristics curve for the n-channel MOSFET are same as that of FET only in the curve there is a voltage at which gate to source voltage the device will remain in off state- I mean no current will flow when the device have gate to source voltage below the threshold voltage.

Now for the depletion type MOSFET there is a pre-existed channel in between the source and drain so forming a channel.There is a preexisted channel between the source and the drain that’s why when there is no gate to source voltage still we will get some current if some drain to source voltage applied.So this device is normally ON device.

Now there in depletion mode transistor say for n-channel depletion mode transistor FET i.e. MOSFET there is preexisted channel , this channel is made by ion implantation to implant some ions /electrons within the channel region that’s why the device is normally ON. Now when the proper gate to source voltage is applied then the device can be made OFF.

Method-3:Finger print recognition project

February 26th, 2011 Remo No comments

Now this method is a little bit harder. But what are the advantage if you can do this hard part then what are the advantages ?
According to me the advantage is tremendous.
You can have your own web shop/business etc shop for selling the authentication devices, attendance systems etc.
But what are the hard parts ?
What are the price ?
Hard parts are that you need to be expert with microcontroller and interfacing and need to be a good student with a capability to read and learn almost any circuit ,computer programming etc terms by yourself without anybody’s help, because at this level almost nobody will help you as this may be an industrial product and when the term comes money then nobody will give you the code etc and  t even not tell anything about that.
I am here giving a rough idea  about what you  need and how to do that..
You need to have a camera (  not web cam rather small standalone camera chips or image sensor chips ) then image sensor chips driver need to be written for  microcontroller. May be you need to go for a better microcontroller like PowerPc or ARM etc. Then after that on that microcontroller you need to implement the finger print algorithm .
So this is the way. The  price of single camera chip not so low, may be more that $30.
Then you need to learn the microcontroller because some advanced microcontroller needed in this case.

Is there any other way ?
Instead of microcontroller you can use DSP chips may be TMS 6711 chips by Texas instruments and write a camera driver in code composer studio and also implement the algorithm for finger print in that TMS series DSP chips.


FPGA based approach:
In this  approach of the design we need to learn Verilog language very well. Then apply the hardware knowledge to design the  finger print recognizer engine. Then implement the algorithm using verilog  compiler and the use a CPLD/FPGA to download the code to.You may use Xilinx ISE webpack to download your code to the FPGA kits manufactured Xilinx corporation. Now obviously you need to write the camera driver if you use standalone camera for that.
Other Links for same project implementation



Finger print recognition :Method 2 of implementation

February 26th, 2011 Remo No comments

Now in this method of implementation you can do this by DSP processor.

So what are the things required here ?

Obviously you need to study and understand the algorithm very well. Then you require the DSP processor for as a hardware. Now Texas instruments DSK board can serve well for this purpose.

There is also a software comes with the DSK board called code composer studio, so within that code composer studio you can write the finger print recognition algorithm in C and then can download that code to the DSK board.

The DSK board contains the DSP processor and many other peripherals.

So what are the things you need?

Your DSK board should interface with the PC and via PC you will take the image of finger via web cam and the send that image to DSK board and then recognition tasks are done by the DSK board and you may glow a red LED on when there is a mismatch and a green LED when there is a match.

Now a little bit more deep. Explanation ?how DSK board will communicate with the PC ?If you see the code composer manual you can easily found the code to communicate between PC and DSK board via serial or parallel port.

Now take a snapshot or image via the web cam software and save that to some where. Then code composer studio environment run the program to read that that file and extract the raw image pixels and then those raw datas are send to DSK board to process(i mean the finger print recognition processing).

So this way using DSK board you can recognize finger print.

For method 3 see the next article.

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