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# shekhar_dandya

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1. ## Cutoff frequency and 3dB points

Hi All, I may not be 100% correct,but,a loss of 3db in gain does not hamper the overall response of the amplifier.i.e this loss is unnoticable in the o/p of amplifier.But we get higher bandwidth at peak- 3db gain,compared to bandwidth obtained considering only the flat portion of the gain-frequency plot. I would like someone to give more explanation of it.
2. ## Set up time and Hold time

Hi Shiva, The set up and hold requirements stem from the fact that if 2 logic signals change simultenously at the input of a digital sequential circuit there is a possiblity of metastability.Which physical phenomenon is responsible for that I still don't know,if anybody on the forum knows,I will be glad to understand. But,what is metastability?A metastable state is a stable state between logic 1 and logic 0.A digital sequential circuit has not 2 but 3 stable states where it can reside for indefinite time.So if circuit resides in this metastable state i.e between 1 & 0,for eternity,the further logic computation will hamper.Both Q and nQ o/p's of a flipflop assume same value which dose'nt correspond to valid 1 or valid 0. Theorotically a circuit resides in this state for eternity,practically,due to noise,which adds to say,Q output of a flip flop and subtracts from nQ output or vice versa,and due to positive feedback,circuit comes out of metastable state and Q assumes a logic 1 and nQ assumes a logic 0 or vice versa. mathematically,the equation for a stable state is satisfied at logic 1,logic 0 and at a voltage midway between 1 & 0. So to avoid metastability,one input is allowd to change first and second later,giving rise to set up and hold times.These have to be kept to minimum to increase speed,so datasheets specify a min value for both. more inputs from other members of the forum welcomed. Shekhar
3. ## Understanding test conditions in any Datasheet

I went through the pdf.It definitely helped me. comming back to the question, So should I take these "test conditions" in my design and calculate other parameters of my circuit?
4. ## Understanding test conditions in any Datasheet

Hi H.W.Wizard, I did not get you. ???Can you be more elaborate?
5. ## Understanding test conditions in any Datasheet

Generally all parameters of a device in any datasheet are specified at certain test conditions. my question is : 1) How are these test conditions chosen?what criteria? 2)What is their importance? 3) What values of parameters should we select if these test conditions do not exsist in our circuit?
6. ## Basic Transistor Circuits questions

But How does one decide Q point Ic i.e dc Ic?I find many students assuming Ic of 1 mA,just because its fairly a reasonable value. So,when to use say,Ic of 1mA when to use Ic of 10mA or 100mA?
7. ## Basic Transistor Circuits questions

While designing a transistorised circuit,say a voltage divider bias,an amplifier etc,should we select the transistor first and then decide the Q-point characterstics based on its datasheet or we establish the q-point characterstics and then select a suitable transistor? If condition2 is correct,then what values to select for Ic for say a CE voltage amplifier?deciding that Vce = 1/3 Vcc?leaving 1/3Vcc across Rc and 1/3Vcc across Re?
8. ## when should use FPGA?

Ante, If this is meant to be only for MCU's then plz create a forum for
9. ## How to make RPM counters

This method will work for slower RPM, for faster ones? I think then one can measure no. of revs in say 10 sec and then calculate for 1 min? what do you say?
10. ## How to make RPM counters

How to make an RPM counter? Assuming you have some sensing mechanism,say a flywheel with a slit to pass the light beam that is sensed by a photosensor at reciever end and which is attached to a transistor driver that gives you square pulses for every cut. How to process the rest of the signal using a microcontroller? One way is to use interrrupt pin to interrupt the MCU every time the pulse comes and increment a variable in the ISR. use a timer to generate a delay of 1 min.read the counter variable before starting the timer and after 1 min.take the difference and display. Is there any more better way? How are commercial RPM counters/taechometers made? I feel they don;t wait for 1 min to gather the # of revs in a minute. How do they work?
11. ## 'potential Difference' questions

So,motion of electrons constitute current.Hence its current that creates "potential Difference",right?or is it that "potential difference" causes current?Is this that-first egg or chicken problem? BTW I still don't understand the basic origin of Energy in a battery,exactly which chemical energy is released to convert to potential energy? What is EMF?What is its cause?I learned this concepts in junior college but never thought on it deeply,so forgotten.can ne1 explain?
12. ## 'potential Difference' questions

If voltage is potential Energy difference,where does this potential energy come from in batteries or cells?If the answer is "chemical reactions" then which chemical reactions/physical phenomenon(bonding,thermodynamics?) is responsible to impart this "potential energy" to electrons?
13. ## International Physics olympiad problem

solve this international olympiad prob suppose a cylinder of weight 20N is rolling on ground in right direction.if half of length of cylinder is positively charged,and it is placed in magnetic field whose dirction is inward to plane of rolling and if a charged particle is placed at distance 10m from cylinder .and magnitude of electrical interacton is 10N and magnitude of magnetic field force is 31N. will cylinder fly? if yes ..then in which direction ? I tried to solve this: Basically the cylender will fly if normal component of net force acting on cylender is > 20N. I found many things missing in the above problem or they need to be assumed: 1.Polarity and magnitude of charge(+ve/-ve)? if we use F = q1q2/r2(coloumb's law) how to find q1,q2? 2.Placement of charge in 3-D space? 3.The mechanical force acting on the cylender due to magnetic field: F = BILsin(x). How to find B from magnetomotive force? B = uH H = mmf/(leghth of coil).How to find this? 4.The velocity at which cylender is rolling?From this we could find the current i.e rate at which charge is moving. I think x = 90 deg so sin(x) = 1. Any thoughts? -Shekhar
14. ## Voltage

"Potential" of a point in space,as I was taught in school, is energy spent in bringing a charge from infinity to that point within the vicinity of test charge,which is exerting the force on our charge. So energy spent is stored as
15. ## Simulation Models Creation...

Try downloading Labcenter electronics evaluation version Proteus software from their website.It internally uses PSpice.I foud it very handy for microcontroller based simulations...hope you will also find it useful.
16. ## USB for Real time applications?

Has anyone tried to drive a real time embedded system(Say motor or LCD)on USB? Does anyone know of any commercial application of USB in Real time system? As far as I know whatever USB applications we see in today's market(e.g camera,flashcard,Scanners etc) use USB for data transfer and not for processing in real time as can be done using printer port. I want to compare Processing using USB in real time vs processing using parallel port in real time on timing basis.I found that USB is slower than LPT under Windows 2000.(for toggling a bit USB took 2ms while LPT took 5us)Does the drivers or the O.S influence this timing? Does the protocol influence the timing? Thoughts welcomed.
17. ## Simple battery charger

Hi All, I think the voltage rating and the charging current to be applied is written on the battery.It is recomended that charging current should not be exceeded. Why not design a constant current source,so that the charging current does not exceed?Why people go for constant voltage source? A constant current source can be designed with a vlotage divider bias with zener between base and ground and battery in collector load.Again Why go for complex circuits? -Shekhar
18. ## What is an electric field?

How are they different? my question again, How does the capacitor works?
19. ## What is an electric field?

So,If we consider electrons as particles,then is the energy stored as potential energy in electrons? When the battery pushes the electrons from the -ve terminal(i.e electrons start disssipiating their potential energy aquired from battery charging),those electrons gather on one plate of capacitor,increasing the charge of that plate. Now what causes the electrons from other plate to travel to +ve terminal of the battery,which is in fact at lower potential?i.e how is potential difference established inside the capacitor? Please,if whatever written above sounds too clumsy,provide me a simpler understanding of "how capacitor works" .Also invited,"how inductor works". What makes capacitor store energy and resistor dissipiate the same energy?
20. ## basics of electrical supply

Hi, Iam back again with my original question. Suppose I remove the ground plate that's buried under my building in a 5 feet deep ditch.keep the earth terminal floating in air.ie don't use it. Now expt #1: I hold the live wire.Do I get a shock? expt#2:A person besides me on the same ground now holds the neutral and I hold the live.Now we both get shocked.right? Are my observations correct? What's the conclusion? If U remove ground,no shock as far as one person is concerned. When 2 persons hold,circuit gets completed and we both have a shock. So what is the importance of ground?
21. ## What is an electric field?

What is an electric field? Is it matter?Does it have mass? If no then how does it store energy in a capacitor?Since to store energy,there must be prescence of matter. e.g: If I lift a block of metal,energy is transffered from one matter(namely me)to another matter(namely block)and the block stores it as potential energy. how do U explain it in terms of electric or magnetic fields?
22. ## Von neumann vs Harvard architectures

HI All, What is the difference between Von neumann architecture & harvard architecture? Is it that von neumann has unique address space where all the instructions,data & peripherals are mapped whereas,harvard has seperate address spaces for instructions & (data + peripherals).WHat about the address & data busses? Is it that von neumann has only one address and data bus whereas harvard has 2 address& 2 data busses? please clarify my confusion. -Shekhar
23. ## basics of electrical supply

I think my basic question remains unanswered as far as theory goes: "But,if neutral is not connected to ground,and there is no special protection circuits around,is it that we never will get shocked when we hold a live wire? "
24. ## basics of electrical supply

But,if neutral is not connected to ground,and there is no special protection circuits around,is it that we never will get shocked when we hold a live wire?
25. ## basics of electrical supply

Hi All, I wanted to know that is neutral wire connected to earth at some point ? If not then how do we get shocked,since to get shocked,current must flow from live to neutral? -Shekhar
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