This autumn, I have to conduct with students of a new IT specialty a series of lab exercises related to study of basic semiconductor devices: ordinary, zener, light, tunnel and other diodes, bipolar and FET transistors, diode and transistor circuits... So, I temporarily leave the “kingdom” of my favorite analog circuitry where I deal with circuit systems and move to the lower level where I will reveal and show the secrets of circuit components. The problem that stands before me is how to do this in the best way...
I have unpleasant memories of the way they conducted laboratory exercises in this discipline in the 80's, when I studied in the same university. I remember that I had to perform a series of programmed actions on ready-made laboratory setups enclosed in boxes so their internal structure remained hidden for me...
That is why, I decided to conduct more interesting laboratory exercises with my students where they can conduct free experiments on flexible prototyping boards by all sorts of components instead of hard prepared experiments on closed laboratory setups. Thus I hope to motivate them by waking their curiosity and creativity.
My idea is first to pose the problem on the whiteboard, then to find the possible solutions and finally, to implement experiments in various ways. Students can investigate IV curves of diodes and transistors at four levels:
- manually - driving the circuit by a potentiometer and measuring the electrical quantities by digital multimeters or a digital oscilloscope in XY mode (shown in the first attached picture below)
- semiautomatically - driving the circuit by a functional generator or simply by a 50 Hz transformer, and measuring the quantities by an analog oscilloscope in XY mode (the second picture)
- automatically - by a data acquisition board equipped by an appropriate periphery (the third picture)
It would be interesting for me to know your opinion about such an educational experiment. Whether it would be feasible or would be extremely difficult for students and, as a consequence, for me?
See also:
https://www.researchgate.net/post/How_do_students_investigate_semiconductor_devices_in_the_lab-manually_or_automatically
https://www.researchgate.net/post/How_do_we_investigate_the_IV_curve_of_a_forward_biased_diode-by_current_voltage_or_real_source
Dear Cyril,
Dear colleagues,
Cyril is always worry about the students and how to present the scientific material to them. How to make the concepts clear and principles easy to grasp and understand.
He wants the student becomes aware with lessons with minimum effort, therefore he is always interested to propose and experience new education method.
As a teacher i would like to use the different methods proposed by Cyril. Thw manual methods comes at the basics and concepts of the course.
With advancement in the course such as the applications i would prefer to use semiautomatic experimentation methods.
For projects and advanced applications i would like to use the fully automated experimentation method like DAQ systems.
Best wishes
Thanks for the instant response, Vasile! It means a lot to me!
Of course, the idea of soldering always tempted me ... and I usually put (at least one soldering iron) during the laboratory exercises on analog, digital and microprocessor circuits. And now I still hesitate whether to include such experiments (for this purpose I have purchased a few prototype circuit boards and soldering irons for soldering)... and will probably do it. The only thing that stops me is the safety because these students do not have practical experience and can burn. I have the same concerns with regard to the sets of mounting tools (especially knives) that I will put on each work place.
About burned components... the more components are burned, the better for understanding:) I have stocked up a sufficient number of elements - except bought now, I dug out a pile of old but interesting elements of my past years as hobbyist:) Moreover, I intend to deliberately burn components:)
Very interesting observations during labs... I have similar ones accumulated during the years from 1986 up to now... and also use this monitorial system. Although I lecture, I prefer labs (with elements of classroom exercises and lectures)...
Interesting idea Cyril. I would be interested in the results of this experiment. I am also trying a new approach this year in the electrical engineering (circuits) labs. Also using breadboards so that the students will have to connect the circuits themselves. My idea is to give the students multiple tasks with increasing difficulty. The easy problems will be mandatory for all students, and the harder ones will be "For the motivated". Motivation is they key problem i try to deal with.
I am also considering to reserve the last 1-2 labs for the project of the course. The idea is to let the students implement their design tasks on the breadboards and see if they work as expected.
Dear Cyril,
Dear colleagues,
Cyril is always worry about the students and how to present the scientific material to them. How to make the concepts clear and principles easy to grasp and understand.
He wants the student becomes aware with lessons with minimum effort, therefore he is always interested to propose and experience new education method.
As a teacher i would like to use the different methods proposed by Cyril. Thw manual methods comes at the basics and concepts of the course.
With advancement in the course such as the applications i would prefer to use semiautomatic experimentation methods.
For projects and advanced applications i would like to use the fully automated experimentation method like DAQ systems.
Best wishes
Hi, Boris! Glad to see that there are enthusiastic young teachers who do not formally work in the laboratory. It would be interesting to exchange ideas during the experiments. I propose to do it here, in the RG forum, to gain more followers.
I wish you success!
Cyril
Cyril, you go back to your youth. I think that you have to follow the development cycle: design (short theory)->simulation (Spice,...)-> prototype (manually measurement). It may be that your students are not familiar with simulation environments, but for IT students it is not difficult to understand the simulation programs. The simulation helps in understanding of semiconductor theory and the manually measurement helps to fix them. Please keep us with your results.
You do not know guys how much joy I can get from reading the discussion. I suggest using a circuit simulator software in the first phase so students can get an overall idea to help them going to the second phase where they have to solder and to be aware about safety issues. Personal and component Safety ...
I prefer the Cyril's teaching style. A good teacher should motivate the students' enthusiasm first.
Dear Surducan,
A good theory is the best practice (Professor Hanganut ?). In my proposed cycle the simulation is an intermediate phase, the final phase is practical measurement. Fortunately we now have available the simulation environments, and the students have to understand that the simulation is mandatory in the new products development. But the simulation must be fallowed by practical measurements for a full understanding of simulated circuits.
I fully agree with Ioan Domuta! During simulation phase student may explore dc/ac analysis, transient simulation, parametric simulation, frequency response, sensitivity analysis, Monte Carlo simulation etc.
Dear Cyril,
as already commented by Abdelhalim Zekry and Mohammad Kazem Moravvey-Farshy, the most important think in higher education is the motivation of students for the given topic. As it concerns a truely basic course in semiconductor devices, I would prefer a practical appoach as already described. by youself. Very interesting is to offer the experiments in an open fashion and not enclosed in boxes. Also the preparation of the eperiments on whiteboards may activate the students. I am a bit suspicious about the discussion on device simulation in a basic course. In this case I agree Ion Domuda that simulation is a useful tool for circuit design. However, basic physical understanding of device properties is necessary to apply simulation tools caarefully.
On a side note, here is something about motivation. It's called "Theory of the flow". According to it in order to keep people (the students in our case) motivated you have to give them challenges which are neither too easy, nor too hard. The problem is every student has different level of expertise. That is why having an open type of lab where not everything is fixed should be able to improve the motivation.
https://upload.wikimedia.org/wikipedia/commons/thumb/6/6c/Flow_theory.jpg/300px-Flow_theory.jpg
Mr. Kamat,
I agree with your opinion, but the simulation should be completed by the physical measurements. The simulation is the same as you meet a person and the physical measurement is the same as you touch themselves. In the our designing activity it is a happy moment when the idea of complex circuit, the it's simulation an the final product working meet together. For the young students a semiconductor devices is a a complex circuit (and that is also true for us), and the simulation helps them the understand the semiconductor's behavior. Deep level modelling of semiconductor structure means that the simulation is not just a simulation, that means we can understand the circuits behavior on deep level.
Cyril, congratulations for the proposed discussion. From manually vs. automatically test, I am old fashion person, and I prefer manually measurements for students lab. This helps them in the understanding the concept of power source, generator or load.
Ioan, thank you for the colorful phrase, "The simulation is the same as you meet a person and the physical measurement is the same as you touch themselves"... it is very impressive and shows that you have a philosophy about the topic...
"Manually vs. automatically test" is also so important topic that deserves a separate question... But now I want to draw your attention to a practical issue related to experiments on this kind of prototyping boards - how to connect measuring instruments to the board. The problem is that standard probes are very rough and uncomfortable to use. Here is my solution, illustrated with the attached picture. Can you guess what is the "technology" of making such "probes"?
(Boris, I guess it would be interesting for you also.)
For connecting equipment to breadboards i made cables with "banana jack" on one side and "2.54 mm pin" on other side, taken from 40 Pin 2.54 mm Single Row Pin Header Strip. Other option would be to use appropriate single strand copper wire.
I agree with Boris ivanov Evstatiev that student should be given challenges to wake their curiosity & Creativity.
http://www.tme.eu/en/katalog/connectors_46/#id_category=112937&s_field=artykul&s_order=ASC&visible_params=2%2C6%2C422%2C152%2C7%2C9%2C426%2C412%2C418%2C1247%2C2555%2C11%2C419%2C424%2C328%2C43%2C32&used_params=412%3A24600%3B
In my opinion one of the main problems with breadboards is that there are no longer labeled resistors on the market. All resistors use color codes, which makes it hard (in certain situations) to verify the circuit and discover connection errors. Also if there are multiple resistors it's hard for the students to decide where to connect the measuring equipment. How do others deal with this problem?
Ioan, thanks for the info... but, as a man with good practice, I hope you will understand my next words...
There are two kinds of people in circuitry (and maybe, at all). The first (usually modern young people) blindly use conventional means to implement their purposes; but when there is no needed element, they are helpless (Boris is young but is not of them:)
The second (usually "old war horses" as me:) use their common sense, imagination, intuition and experience gained over the years, to solve problems in an inventive way (this does not exclude conventional means)...
That is why my multimeter 'probes' are so perfect that actually... there are no probes:)
Exactly, Boris... this is a problem for our purposes... To solve it, I use old resistors (usually Russian or Bulgarian MLT) with big power (size)... sometimes with giant dimensions (as shown in the second picture). Perhaps this is the only case in life (excluding wines:) when old does not mean bad...
Using old resistors is not sustainable (a modern word :D ). I like to think 10 years in advance and i cannot plan to use something which is no longer manufactured.
However while discussing this with you i think i may have just found the solution. The only resistors on the market which don't use color codes are the high power ones: 5 W and 9 W. The 9 W are way too large, however the 5 W ones may actually work. Now as i check an online shop, they sell such resistors up to 100k. Gonna check tomorrow if they fit into the breadboard.
Yes, I use such ceramic resistors (the white ones in the picture); they are labeled.
Hi Cyriil, Abdelhalim and Vasile,
Sorry I missed boarding the plane on the first call! Busy with the "DUTY FREE" (read as FREE DUTY) shopping of perfumes and candies (read as fumes due to Exams and results)!!!!!
Interesting discussion Cyril all the way.
Like you I have been very experimental in electronics since my school days in 80-90s, and as of today I am still continuing the same method in teaching my students and they enjoy both the theory class and the lab.
1) I make the lab compulsory, atleast 10 experiments and one lab per week!
2) Usually I follow the pattern of teaching the theory in the class and on the following day/s conduct the lab related to the topic taught in the classroom. That way students gain better understanding as their knowledge is "FRESH" and they apply the same during the lab.
3) In the lab I FIRMLY believe in "Hands-On" in both the solderless pin-up breadboard and at a later stage PCB soldering.
4) The BLACK BOX method of ready made lab solutions is CERTAINLY USELESS as the intended LEARNING OUTCOME is often not seen - students concentrate on following the instructions given in the manual to complete the experiment rather than learning the MAIN THEME of the lab work.
5) Particularly to the basic electronics/electricity experiments, I start with training the ENTRY level students with - a) Component Identification (R, L, C, Diodes, ICs, Transistors, resistor and capacitor marking codes etc. ), b) Introduction to Lab equipments such as power supply, oscilloscope, signal generator, multimeter etc and how to handle and use them.
6) For basic experiments like the Diode/ transistor characteristics, I prefer your First approach of MANUAL Method where students are not only trained in connecting the circuit properly, but also to set parameters precisely and note/observe the changes - and this requires patience. So students are trained to be attentive in the work. And I remain in the lab full time to SUPERVISE and ATTEND to any difficulties - so there are MORE SMILES than BURNS!!!!
6) The for each of the experiment they are asked to connect the circuit and take the measurements - the complexity of experiment increases as we move from first lab to the last (10 or 12).
7) By this way, the students attain high understanding of the concept and 100% success rate of both the experiments and the lab completion.
8) In case of soldering iron and the soldering practice, I think this is must - no question of burning if you illustrate them the proper technique once or twice, the students should be able to carry on - Its more of physics and heat transfer hidden in soldering than the soldering itself - A proper heating of the leads/wires results in perfect joint.
9) A prior explanation of the process to the students will yield better success than burns - These instructions with proper practical illustration would do the LIFE-LASTING impact
a) Both the surfaces should be cleaned from dust, oily and greasy material
b) Use sandpaper instead of sharp objects like knives and blades
c) Heat both the surfaces using the "iron TIP" - the component lead and the PCB pad or the other wire/lead and COUNT 1-2-3-4
d) DO NOT MELT Solder Wire on the TIP of the IRON !!!!!!
e) DO NOT PAINT the component leads/wires with SOLDER !!!!!!
f) Once heated, apply soldering material/wire and count 5-6-7
g) Withdraw soldering wire and count 8-9
h) Withdraw the soldering iron to count 10 and THERE YOU ARE.
10) Demonstrate to the students that if the leads or hands shake during the counts 5-6-7 then you get a DRY solder - the solder spot with DULL WHITISH glow
11) On the other hand, if it a perfect solder joint one can see BRIGHT SHINY GLOW on the joint. This the the TEST of a better solder joint.
12) Coming back to your question of MANUAL, SEMI and FULL AUTOMATIC, I think at undergraduate level, I would prefer MANUAL with higher classes (final year degree) of semi-automatic.
13) I have been working with PG and Doctoral students where the same I-V characteristics of a PN junction diode is needed - but the focus is not on the experiment but on testing many diodes (say Thin-Film). In that case, a FULLY AUTOMATIC method is adopted by changing the input Voltage/Current and recording the output Voltage/Current and quickly gain the feedback on the characteristics to optimize the thin-film process.
Therefore, the automatic method is more suitable for repeated measurements of same characteristics again and again.
Finally, I would like to give you a BIG THANKS to you Cyril for bringing out IMPORTANT TOPIC. Thank you all others for your valuable inputs. Indeed a NICE DISCUSSION.
Have a great time FOLKS!!!
-PRASANNA WAICHAL
Dear Prasanna,
Thank you for the comprehensive and in-depth comment, in which you make a very thorough analysis of laboratory activities and offer specific scenario for the implementation. It is a pleasure to receive such a response to the question being asked.
In this question, my idea was to discuss generally the implementing of more interesting laboratory exercises where students conduct flexible instead of hard prepared experiments on prototyping boards (following a free scenario). Then I asked the more detailed question about the nature of experiments (manual or automatic).
In this connection, I still hesitate whether students should make themselves the whole circuits on the prototyping boards or I should partially pre-wire them...
Thank you again for the responsiveness.
Cyril
Well Cyril,
Coming to the last part of your reply - Should the staff be involved in partially wiring or students be allowed to take the whore responsibility?
It all depends on the level and interest of the students but I would prefer let students carry on the whole thing. But before applying the power (and then expecting the Burns, Fumes and Sparks), we the teachers should inspect and check the connections properly. This way the students also learn if they have made any wrong connections. Our intervention should be limited only to guide and supervise and ensure that there is nothing adversely implemented.
Now the earlier part - whether students should wire the entire experiment/circuit on the breadboard or some pre-wired or automated systems be used.
Again I would suggest - "Let them build and connect the entire circuit" BUT in a STEP-BY-STEP approach with building stage-by-stage circuits. That way we are sure of not only the working of the circuit but the students also can understand how the entire circuit works and how to build and test such circuits.
Thus, if we have a FULLY AUTOMATED experimental setup, students will not learn how to wire a circuit, not will they understand how to take measurements. On the other hand, in MANUAL method, if the circuit is wired by the students themselves, they will also understand where and how to take measurements. This should later help in troubleshooting and fault-finding of the circuit should there be something wrong.
Well, that all my suggestion and the practice that I follow. It is robust but time consuming and demands hard efforts. But rewards are equally important too!
Thank once again for opening an excellent topic for discussion.
Regards,
Very nice response Prasanna, which give me much pleasure. I fully agree with what you said. Indeed, this is not a big problem in the laboratory of semiconductor devices because connections are very simple. But this issue is of interest to me in general, because I intend to use it in other disciplines.
Thank you again,
Cyril
Vasile, with your colorful language you bring a unique charm of this discussion and make it interesting for readers!
Maybe you guess that my intention is to consider these discussions during the laboratory exercises with my students (with the help of the multimedia projector and web)... to motivate them in this unusual way... and to make them generate new questions...
Great idea Cyril. But total freedom could have strange results. I do prefer to give some problems to the students... not structured circuits, no. Just a series of problems to solve; for instance, some arrangements of resistors, diodes and transistors are required to trigger certain inputs of an Arduino... or certain sensors require special resistors circuits to work properly. Hence, I am convinced that give a problem to the students is better than the situation in which they generate its own "problem". And they have to search for a solution. In my experience, they will learn searching, practicing, reading; not just making a circuit following instructions which someone wrote years ago. For instance, use https://learn.adafruit.com/downloads/pdf/force-sensitive-resistor-fsr.pdf.
Please, Cyril, let us keep posted regarding the results you are getting.
I am afraid that our teachers use certain methods because we did not have access to internet, books were scarce, and a data sheet was a sacred document. None of those restrictions are current in place. Then, new methods must be implemented. Good luck.
Hello Vasile, thanks for the question.
Not, not at all. I am referring to external circuits that you can connect to the digital or analog inputs of an Arduino. I am not intend that, at this stage, students will be able to handle some complicated issues from the very beginning; they should just learn from problems that increase its complexity as the lab is conducted.
Regarding data sheet, I was referred to 30 years ago, when you did not have access to internet, and you had to acquire certain books (in its physical form) from semiconductors manufacturers. We did not have (and we have not) any semiconductor manufacturer in Chile; hence, we relied on some minor distributors of semiconductors to have access to that precious and sacred "data sheets". And wait some month for new versions of that documents.
Finally, you are complete right: normal structure of the teaching-learning process is "teacher - content - problem"... in that order. Using structured problems at the end of the process, you test your students to find out if they "learn" the contents. Well, at the industry nobody gives you a structured problem: you have to formulate the appropriate "problem", its restrictions, etc. Also, at industry, and assuming you find out the adequate formulation of the problem, nobody gives you the "exact" content required to solve the problem. You have to search for the adequate data. The order of the component of this traditional and old structure (teacher - content - problem) respond to the scarce of contents before internet: teacher were the repository of "all of the knowledge".
Today, contents is ubiquitous and, in fact, teachers are not able to handle all of the contents and available knowledge. Hence, seems that traditional structure "teacher - content - problem" must be replaced by a new structure "teacher - problem - content". Please, notice the importance of the order. In this new structure, students learn from solving problems that teachers ask. How do students solve those problems? Learning from discussions, from interactions among peers, from squeezing internet and all of the creative methods to get necessary information to solve those problems.
New tools, new structures. Big challenge for teachers: they will not "teach" anymore... not as they are used to. Endless chats from teachers will disappear. Teachers should transform their slides of "specific contents" (that they are used to show at their chats and lectures); those slides are useless. All of that content is now available outside of the classroom. So, what do we do with teachers?. They have to evolve to a new rol. They will have to moderate the discussions among students, ask the appropriate questions to guide the process, teach how to pick up the appropriate information from massive amount of available data, motivate their audience... but they will not repeat year after year the same content... not anymore.
Best regards Vasile.
Great contribution, Sergio!
You greatly excited me with these beautiful thoughts on the new role of the teacher. How clever and precise you said it! I cannot stop to admire you!
Indeed, the teacher can no longer be just a reproducer of knowledge; the Web and Google deprived him of that opportunity. The teacher can not replace them; it can only supplement them with what they can not do - to explain, compare, summarize, advise, answer questions ... and motivate students through his/her own behavior ... The role of the teacher is to mediate between this huge mass of "dead" information and its living users - students...
According to me, the greatest obstacle to this new role of the teacher are the "dead" PP presentations, which totally replaced the traditional "live" means - the black and whiteboard. Interactive electronic boards are still expensive and for some reasons (unknown to me) are not loved by teachers. One of the most absurd situations I have seen in lecture halls, is a projection screen, descended before the black/whiteboard, which in practice makes it unusable...
My last observation in such a lecture hall was a blackboard, in front of which a projection screen was mounted. In the hall, there was no sink or even a bucket of water and sponge to erase the writing on the board. Apparently, the idea was not to write on the blackboard. In many other cases, whiteboards are used as projection screens instead of writing...
Thanks for your words Cyril, your compliment flatter me. Double honored coming from a teacher at University of Sofia (in Greek, Sofia means "wisdom").
I believe greatest obstacles are, ironically, teachers ourselves. We are used to talk and teach about "change", evolution, adaptive models and similar. But we never applied those lessons to us.
History of mankind is plenty of examples regarding evolution and changes. Not all of the "related parties" realize first signs that anticipate the phenomena; we are in the comfort zone..... I was always amazed by the story (history, in fact) of Mr. Frederic Tudor, the Ice King.
For other hand, teachers are responsible for "traditions" at our classroom. Hence, we are not very used to evolve. Maybe we have to listen more often a quote attributed to Mr. Gustav Mahler, "Tradition is not to preserve the ashes but to pass on the flame".
Regards Cyril, and keep us posted on your developments.
Vasile, I also scatter a number of components on the tables... and I am happy if they disappear. But unfortunately this happens rarely:) Electronic components and devices are of no interest for our IT students. Look, if this were smartphones, I might have better luck:)
I want to share one more practical observation during laboratory exercises in which I have used occasionally prototyping boards. I have noticed that students have difficulty about how to connect the contact points, although I have drawn a map of these connections. Perhaps the reason for this is that the board is a "black box". So, now I have opened one of the prototyping boards to show the internal connections.
Dear Cyril,
I believe you have clearly outlined how you can go about teaching your students. I have taught digital electronics and related stuff to undergrad IT students with bare minimum instruments and it was still interesting. In my opinion, your first consideration should be the level of the students. If they are undergrads, they must have a pretty good idea of basic circuits, breadboard etc. So that you can set up slightly advanced experiments. If they are freshers, the best way would be to use breadboards, multimeters and oscilloscopes. Setting up semiconductor experiments isn't complex at all. In fact its very interesting and can be done with just a few components in the lab. Dioes and transistors come cheap as also other passive components. If the students have knowledge of circuits and soldering, there is no point in making them go through it again. So you can choose a suitable method. if they dont, this would be a great way of teaching them. And as you mentioned later, your intro session should focus on precautions, handling of instruments, etc. Then coming to applications, you can set up simple experiments like transistor as a switch, diode as a rectifier, etc. Breadboards are the best, fastest, easiest and safest way of teaching electronics in schools and colleges these days. So bottomline is you can select the setup depending on the level of your students, their interest in the subject and what the curriculum demands.
Dear Ritendra,
Sorry that I answer your comment with such a delay but I was away ten days and now I read with interest this comment. Only if you know how I like the written by you, if I wrote it myself! How nice is to find an adherent even far away in this world! The paradox here is that our allies should be the people around us... but nowadays internet compensates for the lack of interest in them...
Thank you,
Cyril
Hey cyril,
You are most welcome. If there is anything more that I can help with, you can write to me at [email protected]. Anytime. Wish you all the best.
Thanks! Your response means a lot to me, Aparna! The simple is so complicated...
The "didactic" experiment in the laboratory continues... and, as I have already promised you, I periodically inform you about its progress...
The most striking for me after the three lab exercises was the large number of multimeters with blown fuses...
I had to stockpile large amounts of fuses and patience while open the multimeters to replace the blown fuses ... but finally I guessed to make students do this donkey work... and they imagine were happy:)
Thus finally I have extracted some very important "golden rules":)
Rule 1: If you give multimeters into the hands of students, always some of them will try to measure voltage by an ammeter:)
Rule 2: The number of multimeters with blown fuses is proportional to the number of students in the laboratory:)
Vasile,
Thank you for all the wisdom in your message above. Fortunately, there is a shop for electronic components at the first floor in the same building of the University:)
Well, fuses protect the low current range... but what will happen if they switch to the huge 10 A range? To clarify this situation, I open a multimeter and show to them the thick shunt wire.
Solderless bread boards are another reality that is very different than the "virtual reality" of the PP presentations:) It is hard to imagine what amazing connections can be done by people with no experience.
For example, although I even disassemble an exemplary bread board before my students, their favorite connection is to mount components in such a way that their terminals are shorted:) They do the same with multimeters...
Similarly, during the labs on Digital electronics, I have extracted more "golden rules":)
If you give integrated circuits having an output stage with open collector (drain) into the hands of students, always some of them will connect the collector (drain):
- Rule 3 - to VCC (in the case of n-p-n or NMOS transistor) or...
- Rule 4 - to ground (in the case of p-n-p or PMOS transistor:)
... abd the result is obvious...
Remember that the kernel components of all digital circuits are analog circuits ;-)
The first laboratory exercise (conducted with four student groupes) is completed. During labs, besides the usual introductory issues, I decided to start with the investigation of the static RD circuit and only after that to measure and examine the diode IV curve.
My observation is that this flexible way of conducting labs on solderless bread boards with free scenario is laborious but very useful for students.
Except that students had the first observations on the behavior of diodes, they saw in practice what happens if they measure the voltage by an ammeter... and if resistors can not dissipate the applied power...
I have noticed that after each lab exercise with my junior students I become more and more a "philosopher":)
For example, at the beginning of today's laboratory exercise I really did my best to explain to students what they should not do with a potentiometer...
...after which I disassembled the poor potentiometer to show them what happened inside it...
I told myself to mind, "It's so good that there is a big fire extinguisher in the laboratory":)
Thus I drew another golden rule:)
Rule 5: If you give a potentiometer in the hands of students, always one of them will connect its slider to VCC or ground... and will turn it completely to the ends:)
But despite these failures, they were very happy when saw the diode IV curve on the screen...
More experiments with various diodes - investigating LEDs in series and parallel...
Dear Aparna,
I am happy to see that someone is still interested in such basic questions... and does not consider them as irretrievably gone and useless... This keeps my desire to continue inventing more and more interesting experimental setups for studying all sorts of electrical and semiconductor elements...
Your question is very interesting and important; that is why I have dedicated a few questions to this topic. Here are the main of them:
https://www.researchgate.net/post/How_do_we_create_virtual_electrical_elements_in_electronics_Are_they_really_elements_or_circuits
https://www.researchgate.net/post/What_is_linear_and_what_is_nonlinear_Is_a_linear_resistor_static_and_a_nonlinear_dynamic_Is_a_nonlinear_resistor_a_dynamic_linear_resistor
I think you should use a software tool such as https://www.comsol.no/semiconductor-module
Interesting... and maybe useful... but I prefer real experiments with real components... This is my vocation... and I can do it best...
Before commenting on the Aparna's question, I would like to show you some interesting photos from today's laboratory exercise, during which my students studied all sorts of elements...
One task was to investigate the effect of temperature on the position of the IV curve of a germanium diode (base-collector junction of a germanium transistor). I was prepared as heaters powerful ceramic resistors... but it looked pretty boring and not attractive to my students. Then we used a hairdryer to heat up the transistor... but even it was not enough attractive... they wanted something more spectacular... And then a new idea was born - to bake the poor transistor with a cigarette lighter (under my control)...
Unfortunately, this proved to be a very robust Bulgarian transistor (SFT 323 manufactured by the factory plant in the Botevgrad city in the past)... which despite the diligence of my students, still revived... despite its IV curve shifted from the right side all the way to the left side of the screen...
This made me even I to change my bad opinion I had about germanium transistors to date.
Once contented their primary instinct to destroy:) my students calmed down and continued to explore, now much more peacefully, various semiconductor devices...
And when they finally asked me, "Hey what to record in our lab reports?", I replied simply, " Well, what you did - how you baked transistors":)
Maybe, that was an impressive example of how to motivate students in the lab despite serious but boring textbooks and laboratory manuals:
https://www.researchgate.net/post/How_do_we_motivate_students_in_the_laboratory_What_is_more_important_there-the_technical_equipment_or_the_teachers_skills
And I still can not stop admiring this amazingly simple handmade "curve tracer" consisting only of a transformer, resistor and XY oscilloscope (the diode is an external element under test)... It is not only extremely simple but, in addition, it is completely perfect...
But how to explain to my students this strange fact that there is no error in this so simple passive circuit? And why the scope's ground is connected between the two components?
Maybe the answer of the related question below can help?
https://www.researchgate.net/post/What_is_the_input_quantity_in_the_simplest_diode_IV_measuring_setup
Now about your question, "Can we replace the vertical part of the diode by a resistor with extremely low resistance?" It is too hard for me to answer this question...
On the one hand, we can think of the diode (in this part of its IV curve) as of a resistor... more precisely, as of a dynamic resistor... And indeed, it resists the current through it as a resistor... But what is confusing here is that it creates this resistance by means of oppositely directed electric field like a capacitor or an inductor...
From this "black box" perspective, it seems we can think of a capacitor as of a "resistor"... or of an inductor - as of another kind of a "resistor"... We can even consider an opposite dynamic voltage source as a "virtual resistor"... what looks quite strange...
This week we begin investigating transistor output characteristics by an oscilloscope...
:)
BTW "sce promeniate li toka, da, niet" means "Will you change anymore the current - yes/no?"
What about the setup on the blackboard?
It reminds you of your highschool moments since great ideas are eternal and immortal...There is many philosophy in this setup (if only you can see it:)...
For example, it is interesting to see why the resistor is connected in the emitter instead the collector... so this stage looks as an amplifier with emitter degeneration...
There was a mistake in the figure above (maybe some student had joked drawning the unnecessary and even harmful line on the top:) As a result, some pretty interesting effects were observed in the laboratory today ... maybe you will guess what ... Here is the right image below.
Yet why is the resistor connected in the emitter?
Thanks for the exotic suggestion... it is funny compared with boring IV curves... But is it academic enough:)?
Regarding the resistor... Really, its conventional place is in the collector to measure the collector current... but for some unknown reason (?) here it is inserted in the emitter...
By the way, I hastily fabricated this experimental set-up before the laboratory exercise dedicated to study of bipolar transistors. In fact, it combines both the experimental settings from the previous exercises dedicated to diodes - a DC type (left) and an AC type (right). The "flying" (galvanically isolated) power adapters and oscilloscope simplify connections.
My main problem during exercises is that some students with no prior experience make confused mounting with many cross links on boards (not orthogonal as it is customary to make)... In addition, they switch scope attenuators in various amazing combinations ... and then they simply say, "It does not work" .. . and I have to make it work... This is the price I have to pay for the freedom that I have given them during labs...
Hello ,Cyril
Is there any syllabus for the things your are planning? I can suggest you few if any.
Yes Vaibhav, there is... but my question is not about it... Thanks for the suggestion.
As for the "emitter resistor" ... it is actually a collector resistor because it measures exactly the collector current... not the emitter current... It is a collector resistor connected in the emitter... But why?
You can answer this question if you analyze the sighs of voltage drops across the collector-emitter junction and resistor... and if we know the specifics of these old analog Tektronix scopes...
Hi Cyril
I suggest first experiment you are planning shall be introduction to semiconductor components. Remember if you give them 100% the will prepare 60 % and so on!!!
you take various components , there data sheets(you need to teach them how to use data sheets), and let them identify device, its terminals, type , other parameter from the no specified
1) example: BC107 A. It is a transistor. Then it is of NPN type. B: Silicon if A: germenium, C: Audio range or small signal general purpose transistor, 107 is registration no. A is family having some parameters different than B, or C (usually IC and hfe). similarly do this for JFET, MOSFET NPN and PNP , Si or Ge.
2) Take a diode switching diode(1N4148), rectifier diode(1N4001-4007), zener diode(1N4728), LEDs etc.Explain how they are different even though all are diodes
Verify this terminals using DMM (digital multimeter).
make them simulate using suitable software (Multisim, Orcad etc)
Take a simple DC circuit to understand biasing methods. (Fixed, collector to base bias, voltage divider)
let them design one one biasing circuit provide them VCC, RE, hfe, ICQ, VCEQ, VBE find all resistances. Help them in finding right transistor (i.e select a transistor from available many transistors see data sheets).
explain them theoretical calculation in class and verify that by SW and HW implementations.also explain necessity of biasing.
find Q point parameters (ICQ and VCEQ), plot characteristics...
this all stuff is done with DC power supply. Avoid adapters.
**second lab can be different configurations CE, CB, CC. Same DC circuit ask them to connect in other configuration. From this all experimenting they should conclude that Q point is not disturbed event though configuration changes. Second thing they should know the relation ships between IC, IB, IE
IC= beta x IB or hfe x IB
IE = IB+IC i.e why IC approximately = IE
I hope this will help you plan first two experiments. please tell students that we are there to help you but not there to correct the connections.
An excellent and extremely useful (especially for me) exposition of the topic, Vaibhav! I will comment on it in more depth later. Thank you very much!
(the attached photo is taken during the yesterday's lab)
Cyril
Is this the picture you wanted to see, Vasile? I have arranged the laboratory specially to make it for you:)
On Saturday I went to the lab and prepared some experiments for my favorites for the next cycle of lab exercises; they are dedicated to various applied diode and transistor circuits.
First, I mounted a parallel diode limiter and investigated the circuit by an oscilloscope (YT mode)...
Besides the photos above, I made also a small demo movie to show what they will do during the first part of the next lab...
https://drive.google.com/open?id=0B45uRPpHPD9hdFhJRGM2XzRPd2M
Then I prepared an experiment with a classic AC common-emitter stage where they can observe the effect of biasing:
- without clipping...
Of course, I accomplished these photos by another demo movie.
https://drive.google.com/open?id=0B45uRPpHPD9hdmhZUnN2eUlnN2s
Besides these "mandatory experiments", I intend to offer them a variety of amusing and even frivolous experiments with various types of sensors (microphones, photo and thermo resistors, sensor "buttons"...) and loads (LEDs, relays, motors...). Thus I will try to turn this dry matter into an entertaining activity... such as it was for me in my childhood in the distant 60's...
.
Cyril:
.
It appears you are on top of the originally-stated problem.
But it might be advisable to initially avoiding dragging "T"
onto the scene but instead to stick strictly to X-Y plots. In
fact, if you don't have one already, try to find a Tektronix
575 or 576 curve-tracer; see the link below. But I expect
you know already about these nice pieces of machinery.
.
Barrie
http://www.ebay.com/gds/Guide-to-Tektronix-Transistor-Curve-Tracers-/10000000001641251/g.html
Dear Barrie Gilbert,
Thanks again for the suggestion; the RG forum is unique in that you can get valuable tips from famous personalities...
I have realized the need of a curve tracer during the first labs where my students have to measure IV curves. The final labs are dedicated to basic diode and transistor applcations and circuit concepts; that is why I intend to use mainly the YT mode of the scope. Maybe diode limiters are one exception where the XY mode is useful. I have also realized that if we drive the device by a triangle (ramp) input signal, both the transfer and time characteristics are equal...
Thank you again,
Cyril
The approach is nice and the efforts as well as curiosity towards better understanding of the real world is appreciated.Try to obtain the characteristics with DC circuit and observe the behavior with AC i.e Amplitude as well as frequency response.
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