 Vadvani Electronics Lab in the Electrical Engineering Department. This is the lab this complex of laboratories that you see all around here. They are collectively known as the Vadvani Electronics Lab. Vadvani was an alumnus of this department and made a special donation to upgrade the electronics laboratories in the department. So, you would notice that these all these rooms were done up and much of the equipment and so on have has been procured through a donation by Ramesh Vadvani. As a result actually we are able to have a fairly well equipped and roomy lab in which several experiments can run together and also by policy we run a 24 by 7 lab. We permit students with appropriately responsible people present. So, students can actually issue out keys and perform their experiments, projects or whatsoever on a 24 7 basis. So, that is possible because this lab has the wherewithal for doing most of that. I am by the way Dinesh Sharma my main line of work is in VLSI design and mixed signal design work in the micro electronics group of electrical engineering department here. And we are very lucky to have Madhumita Date here she is in charge of this lab generally we just tell her what we need to do and everything is ready and normally rather than we chasing her she is chasing us everything is ready she says this is ready should we do this or should we do that. She is done the same with today's experiment and the way we have structured the laboratory here is that as you would notice the experiments are very elementary. So, the idea is not to teach you about RLC circuits or combinator amplifiers and so on these are very basic. So, we I am sure you know the basic knowledge which underlies these experiments. The basic idea of this session is actually to learn about how to manage labs and how to run experiments for students. So, that there is a level of curiosity in them there is a willingness to learn and also on the management side how to manage lab. So, that they are efficiently run. So, I think it is this last topic that we will take up first please be interactive with Madhumita Date who manages this lab. So, I have requested her to interact with you she will first describe how we run the experiments here and then you know you may have a different setup you may have different rules and regulations and so on. So, we can have a little discussion on how to run similar labs here ok. So, with that I will hand over to Madhumita. Here as professor Sharma said this is a very important lab in our department because we not only cater to our department students, but to other department students also. Because mechanical metallurgy, engineering physics then chemical chemistry all these departments have at least one course in their curriculum in which they have to use electronics laboratory. So, even this they also come here to perform their experiments. Actually had you come on a working day to visit our lab you would have seen about 90 students in this this is well two well one we have five well labs five labs under Vadawani electronics laboratory. So, in these two labs we have at least 90 students perform together one single experiment. So, in order to perform one single experiment. So, exactly actually we need all identical instruments on the table. So, you will find all the instruments set of instruments is identical. So, all so CROs will also have the same specifications all meters, multimeters and power supplies everything. So, that when we have the first session very first session in the lab to introduce them to these equipments we can give common instructions otherwise the students if we had different models then they would like keep finding the knobs which is where and all. So, we have all identical instruments on all the tables. Now, maintaining as far as maintaining the lab is concerned we have the RAs who help us like research associates they are also doing part time m tech that means three years m tech program. So, because otherwise if there are some 90 plus students working here in the lab it is not possible for anybody I mean on I mean faculty as well as lab staff to conduct the entire show. So, we have teaching assistants as well as research associates to help us out. Normally the system is one TA that is teaching assistant or one RA who is conducting the lab one person is given assigned two groups here on these tables you will find the set of instruments group of three students work on each table. So, everybody I mean in a group there will be three students only. So, such two groups are handled by one TA. So, a closed supervision is possible here. So, what they do and what they are doing and what problems they are facing they are seen by the TAs and RAs the difference between the TA responsibilities and RAs is RAs basically they maintain the lab in the sense in order to run the show we have to see the health of each instrument and in order to conduct the lab effectively during the given session it is very important that all the instruments should be working and we frequently check the instruments so that the all the instruments are working at the time of the laboratory sessions. Of course, according to Murphy's law some instruments do malfunction, but then we have enough number of things to replace and then minor problems we can always take care of. Now, as far as the experiment is concerned we give them the handouts and in the handouts they they are supposed to come prepared for the lab it is not that they come here and do whatever is asked them to do mechanically they have something called as pre lab session. So, they are supposed to come prepared for the class because naturally whatever is going on in the class you cannot expect them to have things done in the class and then they come here to the lab with that background. So, theory and labs they do not go parallel most of the time so they have to come prepared and for that we give some basic reference material also if it is needed. The handouts are given at the time of the laboratory or now from last year onwards we have now uploaded all this material which they have to refer on the net. So, even in their hostels also whenever they have time they can refer to it and then they come prepared. So, there is pre lab session during the lab they have to conduct the I mean perform the experiment and then there is post lab session which is evaluated by the TAs. So, they come normally they come once in a week. So, if they are coming today next time then when they come they have to complete all their post lab session. Now, it is so happens that sometimes they do not get the correct results. So, if they find that they are not getting correct results whenever the lab is free and they are free they are free to come rather they should come then they perform the experiment and then when they come next time they have to have the correct results. So, we definitely encourage them to come for extra lab sessions. So, we can begin the experiment now you want to say how sometimes there are half way stops they are said do this calculation show it to the TA and then proceed. So, just go through the handout with that point of view and perform the experiment side by side just to get a feel of how the student goes through these machines. So, this is that time. So, identify the transistor there are detail instructions given there you would see a little diagram and the reason it amplifies is that the current which flows like this is much larger than and is controlled by the current which flows there. So, there are two sources of current in this this is the input and this is the output and this current is proportional to this current and that proportionality factor is what is being identified as beta in the handout for the transistor given to you it is about 150 that is by no means uncommon there are transistors with values from 100 to 1000. There are super beta transistors which have even higher values of beta what it means is that if one unit of current flows through this path then 150 units of current will flow through this path that is the part which helps us amplify the signal. Now, we make in the design calculations that you see we make use of the fact that the voltage difference between this point and this point is extremely insensitive to the amount of current flowing and therefore, can be taken to be a constant. So, even when relatively large current is flowing or small current is flowing this voltage difference more or less remains the same. So, since you are all anyway from a technical background the dependence is logarithm. So, therefore, it changes by 25 millivolts for every order of magnitude change in current 25 millivolts is a very small change. So, as a result we take this to be 0.6 volts that is given to you this is V BE this is the base this is the emitter and this is the collector. So, the voltage between the base and emitter irrespective of your operating conditions is about 0.6 volts or so. Now, for a good amplification to occur you can look up the characteristics of this transistor and for good amplification to occur this guy needs to be drawing about 1 milli ampere of current or so. So, the calculation which is given to you initially that is there to establish how to bias this transistor such that it draws about 1 milli ampere of current. So, we are told that our power supply is 6 volts that is in constant even we cannot control anything about that power supply is 6 volts. So, we have to design an amplifier which will use a 6 volt supply. Now, our first choice is at what voltage should this point there is some minor discussion there and we choose to keep it at about 3 volts. The reason for that is that as we apply a signal at the input we hope that the output will change by a large amount because there will be amplification. Now, when it changes it will go up as well as down and it should have as much head room above as below to provide you with maximum amplification. Is this part clear? We want to keep it somewhere midway so that there will be as much room to go above as there is to go below. So, therefore, it is conventional to design this voltage to be somewhere halfway between the power supply that is the reason ok. In fact, if you would notice that there is a question there saying what would happen if this voltage was much higher or much lower idea is to excite the student's mind to see suppose this voltage was much lower what would be the problem or if this voltage was much higher what would be the problem and this is the answer suppose I kept it at 5 volts then it cannot go above 6 volts. So, the head room available in the up direction is only 1 volt. So, it can go up only by 1 volt but down by 5 volts which is wasted because if we have some signal and it is 1 volt peak to peak if it is more than that it is anyway distorting clipping on the top. So, there is no point having more head room below. So, it is conventional to keep it at a voltage which is halfway. So, let us agree that we want to keep it at 3 volts. Now, we already know that 1 milliampere of current should be flowing through this transistor for good amplification to occur that we know from the characteristics of this transistor. So, now, the first calculation we can immediately do this point is at 6 volts, this point is at 3 volts and therefore, we want to drop 3 volts here. So, what should be this resistor 6 volts here, 3 volts here. So, a drop of 3 volts and 1 milliampere current. So, resistance is voltage divided by current 3 volts divided by 1 milliampere about 3 kilo volts. Now, these resistors come in discrete values not all values are available the closest value is 3.3 kilo volts. So, that is why we have chosen this to be 3.3 kilo volts. Now, this voltage is given to be 0.6 volts it does not change as I had said earlier. However, with temperature change with device to device variation and so on this is quite a small voltage and the variation of this is comparable to 0.6 volts. So, therefore, we like to drop some voltage across this which will absorb that variation and as a result I have put a resistor there and I have told you just for ease of design and calculation that we will drop about 0.4 volts across this. Now, because this current is very small the total current here is this current both are flowing through this, but this current is extremely small. Therefore, this current and this current are equal therefore, about 1 milliampere is flowing through this resistor voltage and because we have decided that we would like to keep this at about 0.4 volts. So, we need about 400 ohms 400 milli volts 1 milliampere. So, 400 milli volts divided by 1 milliampere gives you about 400 ohms and the nearest standard value of resistor is 390 ohms. How to establish the base voltage? This is at 0.4 volts we know that this drop is about 0.6 volts. Therefore, we want this to be at about 1 volt right this should this total voltage 0.4 plus 0.6 should be at 1 volt. That means, we need a voltage divider here which will divide this in the ratio of 1 is to 5 because 6 volts I want 1 volt here. So, 1 volt drops across this one and 5 volts drop across this one right. Since the same current flows through both therefore, their values should be in about 1 is to 5 ratio right. That is why we have chosen values again zap to the nearest values which is 10 k at 47. So, the ratio is nearly 5 not quite 5, but nearly 5 ok. That finishes the initial design of this, but remember we have made deviations from theoretically correct values like this is not 400, but 390 this is not 3 k, but 3.3 k this is not in a ratio of 5, but ratio of 4.7. So, you do expect some variation from ideal conditions. So, what we ask the students is that because of practical limitations availability of resistors and so on we have chosen these values. Now, back calculate what will be the voltages at different points and what will be the current through the transistor ok. So, that is first now to identify components resistors are identified by rings of different colors and it is to you can look up the colors it is too complicated I am sure you would not remember if I just wheeled out everything, but I will tell you just enough to do today's experiment ok. So, normally you have a format which is digit, digit and number of zeros. So, there are three rings which identify the first digit the second digit and the number of zeros. So, for example, the first digit here is 3 whose color is orange, the second digit is 9 which is white and number of zeros is 1 there is only one zero of the three and nine. So, one is brown. So, the resistor with an orange white and brown ring that is the 390 ohms resistors. Similarly, this is 3300 ohms 3.3 k is 3300 ohms. So, this is 3 you already know what 3 is ok. So, this is orange again 3. So, orange followed by 2 zeros. So, the color of 2 is red let us look at this 10 k. So, 10 k is 10000. So, first digit is 1 what should this be we have already we already have this information what should this be the second digit is 0 whose color is black it goes from black to white, black is 0 white is 9. So, second is black and how many zeros are there 3 what is the color of 3 orange. So, brown black orange that is the 10 k resistor the colors of 4 is yellow this is 47000. So, color for 4 is yellow color for 7 is violet anyway this color codes and so on when we do the experiments there is a display which is always available which is just put up. So, that students can look up at least initially they need this. So, color of 4 is yellow 7 is violet and then how many zeros orange what is the color for 3 orange. So, now you can look at all the colors ok. So, this will be yellow violet orange ok. So, now you build a circuit now the bread are you familiar with bread boards generally all of you how to use bread boards those lines are all shorted to each other ok. So, you plug in that way connections are already made for you and whatever is not already made you make by plugging in wires.