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Archive for the ‘Simple Electronics notes’ 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


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.

FET:Field effect transistor some questions

January 28th, 2011 admin No comments

Some questions i am asking and i am expecting some body to answer it or get the
answers from your teacher

Q1. Why it is called field effect?
Q2. What is the field mentioned here ,how the field mentioned here and is it related with the voltage
Q3. if related with the voltage with which voltage
Q4. What is our aim for studying the transistors
Q5. How FET transistors are different form those  of BJTS
Q6. Which one is better BJT or FET
Q7. In which application scenarios we use FET
Q8. What is unipolar and bipolar device
Q9. In FET Characteristic curve why after pinch-off the current saturates
Q10. What is the reason behind the saturation because as the channel get constricted then why current remain saturated
Q11. What are the applications where the saturation property of FET can be utilized.
Q12. What are the source and drain and how do we identify them though the device is a symmetrical device.
Q13. FET and MOSFET how they are different
Q14. FET and BJT which one consumes less power.

Now to answer those questions what bare things you need to read.

Must read the basic device of FET from any text book and then try to answer those.

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Communication and Modulation

January 28th, 2011 admin No comments


Telecommunication is the transmission of signals over a distance for the purpose of communication. In modern times, this process typically involves the sending of electromagnetic waves by electronic transmitters, but in earlier years it may have involved the use of smoke signals, drums or semaphore.

In a broadcast system, a central high-powered broadcast tower transmits a high-frequency electromagnetic wave to numerous low-powered receivers. The high-frequency wave sent by the tower is modulated with a signal containing visual or audio information. The antenna of the receiver is then tuned so as to pick up the high-frequency wave and a demodulator is used to retrieve the signal containing the visual or audio information. The information signal can be either analog (signal is varied continuously with respect to the information) or digital (information is encoded as a set of discrete signal values).

Basic elements: Each telecommunication system consists of three basic elements:

a transmitter that takes information and converts it to a transmit signal

a transmission medium over which the signal is transmitted

a receiver receives the transmit signal and converts it back into usable information

In this project only one way communication is taken into account. So this communication system falls under the category of Simplex.

Communication is simply the process of conveying message at a distance or communication is the basic process of exchanging information.

Information source produces required message which has to be transmitted.

Input transducer is a device which converts one form of energy to another form of energy. It converts information source output to a electrical signal.

What is Modulation:-

Modulation may be defined as a process by which some characteristics of a signal known as carrier is varied according to the instantaneous value of another signal known as modulating or base band signal. The signals containing intelligence or information to be transmitted are called the modulating signals. The carrier frequency is much greater than the base band signal frequency.

In the context of using antennas to radiate the transmitter output, modulation is used since we know that for efficient radiation

antenna height (l) = (wave length) / 4= velocity of light/(4*frequency).

That’s why modulation is done when audio frequency is transmitted using a radio frequency carrier in the MHz range, so antenna height is reduced.

Transmitter is used to modulate a carrier signal to produce a transmit signal.

Communication channel is the medium (e.g. optical fiber, free space etc.) through which the transmit signal travels from transmitter to receiver. Noise is unwanted signals which tend to interfere with the required signal.

Receiver reproduces the message signal in electrical form from noisy & distorted received signal.

Destination is the final stage which is used to convert an electrical message signal into its original form.