Circuit Stories

Посвещавам тази забавна история на най-малката си внучка Катерина (участник в експеримента:-), която днес има имен ден. -------------------------------- В предишната си история от серията "Ако не можеш да обясниш нещо на 6-годишно дете..." ви разказах как с моя 7-годишен внук Алекс пресъздадохме един интересен физически експеримент. С него изследвахме действието на атмосферното налягане върху водата, налята в обърната чаша. Това вероятно е възбудило неговия интерес и той прояви желание да направим още подобни експерименти с вода. Така възникна идеята да разберем как древногръцкият учен Архимед е успял да докаже, че златната корона на царя е фалшива. Честно да си призная, и аз не се бях замислял какво точно е направил, за да го установи, макар че често съм използвал възклицанието "Еврика!" в моите схемни истории. Скромните ми познания бяха, че Архимед се потопил във ваната, видял че водата се покачила, идеята го осенила и хукнал гол, крещейки "Еврика!" Явн...

I  answered  this  SE EE question  a few hours ago. The challenge It just so happened that while explaining the role of the common resistor Rgain in the input stage of the three op-amp instrumentation amplifier in a related question , I came here on this two op-amp circuit with a common gain-setting resistor Rg. Drawn in this perplexing manner, it appeared to me perfectly unfamiliar, and this caused me to try to discover what idea was hidden in it. The common idea Today, I thought about it almost all day and finally managed to see the general idea that connects the seemingly different circuit solutions of instrumentation amplifiers: The input part of op-amp instrumentation amplifiers consists of two non-inverting amplifiers coupled by Rg. The implementation In the three op-amp circuit, the bottom resistors of the voltage dividers constituting the negative feedback network are connected by Rgain (Rg) "in series" while in the two op-amp circuit they are connected "in p...

I answered this SE EE question a few hours ago. My answer The idea The role of the common resistor Rgain is essential to the circuit operation. Connected in this way, the input amplifier stages can interact with each other and behave differently depending on the mode. The voltage of the midpoint inside the resistor Rgain indicates the mode. So it is important to monitor it and this is achieved by "split" Rgain in two or "assemble" it from two resistors Rgain/2 in series. Operation In the common mode, the midpoint follows the variations of the two input voltages. Figuratively speaking, it "moves" with them and acts as a "movable ground". The two input stages cooperate and act as voltage followers; so the input signal is not amplified. In the differential mode, the midpoint "freezes" and acts as а "fixed" or "virtual" ground. The two stages counteract each other and function as non-inverting amllifiers; so the input ...

I  answered  this  SE EE question  two hours ago. My answer A very popular (especially in the past) application of this phenomenon is the neon-lamp line tester . Its operation is surprising and incomprehensible to many people, because at first glance it does the impossible - it measures the voltage with just one probe! For the participants in this discussion, the answer is clear - a very weak (but enough to light the neon lamp) current flows mainly through the capacitive coupling and leakage of the human body to the ground . So the human body acts as the other probe. See also How does a "neon tester" work? I remember that in the past I had noticed an interesting detail - the tester did not work well (the neon lamp glowed very dimly) when I tried to measure the voltage while standing on a ladder. Guessing about its operation principle then I used a simple trick - I touched my other hand to the wall... and the lamp glowed brightly. But later I realized that this is dan...

I  answered  this  SE EE question  an hour ago. My answer You can get a good intuitive idea of ​​what a "voltage drop" is from Ohm's famous experiment in 1826 where he studied the voltage distribution along a resistive wire. Also, fluid and other analogies that allow us to transfer our ideas from life to abstract electrical phenomena, are very useful. See, for example, the Wikibooks story about the voltage drop phenomenon that my students and I created in 2008 where we investigated voltage drops across various resistive materials. In 2013, I dedicated a special question in ResearchGate to "voltage drop" compared with "voltage"; I hope it will be interesting for you. You also asked: "How can I use a single resistor to drop the voltage to 3 V?" You can... but a more sophisticated trick is to use a "non-linear voltage-stabilizing resistor", e.g. a diode with 2 V forward voltage. And since there is no such a diode, you can make one by...

I answered this SE EE question  just now. My answer You have to solve two tasks: to coarsen the sensitivity (to enlarge the range) of the available 1 mA ammeter to 5 mA to convert the available 1 mA ammeter into a 20 V voltmeter You can solve the first task using the "current divider" device by connecting a resistor ("shunt") in parallel with the ammeter. You can solve the second task using the "voltage divider" device by including a ("ballast") resistor in series with the ammeter. -------- BTW this technique of converting an ammeter to a voltmeter was used in the 19th and maybe until the middle of the 20th century because back then they didn't have voltmeters, only ammeters. Now we have very good voltmeters (ADCs) and so we use the reverse technique to convert a voltmeter into an ammeter - by connecting a resistor ("current-to-voltage converter") in parallel to the voltmeter. See also my two stories in Circuit Idea  wikibook: Pass...

I answered this SE EE question a few hours ago. My answer In one of your comments, you (OP) said:  "The power adaptor doesn't have a magical changing resistor inside it." But the power adaptor does have a "magical changing resistor" inside it! Let's see what this "magic" is with the help of a simple electrical experiment. It is so simple that it could have been carried out in the middle of the distant 19th century (for example, by Ohm and Thevenin:-) without knowing what a "transistor" or "negative feedback" is. We can call it a "man-controlled power adapter". To make it, we need only four elements - a simple voltage source V, a variable resistor R (rheostat) in series, a voltmeter at the output and, of course, someone willing to turn the resistor wiper. Ok, I agree to do it for free and with pleasure:-) We can load the "adapter" by another variable resistor RL (another rheostat) in series to R. I assume yo...

  I answered this SE EE question yesterday. My answer 1. Real circuit. The diode D and 4 V voltage source are shown on the schematic but they do nothing during the "negative half cycle". More precisely speaking, the total resistance of the two elements in series is much larger than the resistance R1. A voltage divider with a transfer ratio of about 1 is formed. 2. Circuit with "redundant" elements removed . So we can remove (erase) the redundant elements from the schematic. 3. Circuit with zeroed resistance. Also, the resistor R1 does nothing during the "negative half cycle"; it behaves like a piece of wire so we can replace it by a piece of wire on the schematic. More precisely speaking, the resistance R1 is much less than the load resistance (not shown in the diagram). A voltage divider with a transfer ratio of about 1 is formed.

I answered this SE EE question just a few minutes ago. My answer Let's finally summarize all these specific explanations in a "current source philosophy". The problem is how to interrupt (stop) the current produced by an (almost) ideal current source, which here is a charged coil. The answer is the current cannot be stopped by breaking (opening a series-connected switch); current can be stopped only by diverting (closing a parallel-connected switch). In short, the rule is: Current is stopped not by interrupting but by diverting. The "current steering" observed in transistor differential amplifier stages is a typical application of this rule.

By the mid-1990s, I had already developed my own philosophy about electronic circuits, and I decided it was time to share it with my colleagues. In the spring of 1997, I presented a series of three papers at the XXXII Scientific Conference on Communication, Electronic and Computer Systems at the Technical University of Sofia. The first of these was devoted to my heuristic course on analog circuits , in which I had implemented my circuit philosophy. There I shared my idea of building circuits for the purposes of understanding, presenting and inventing  circuits. In this post, I will tell you about this venture of mine. The Idea The idea of ​​the building approach is to use the elementary electrical devices as a kind of "cubes" to "build" the more complex electronic devices. Examples We can "assemble" a ''parallel voltage summer'' from the elementary electrical ''voltage-to-current converters'', ''current summer'...

By the mid-1990s, I had already developed my own philosophy about electronic circuits, and I decided it was time to share it with my colleagues. In the spring of 1997, I presented a series of three papers at the XXXII Scientific Conference on Communication, Electronic and Computer Systems at the Technical University of Sofia. The first of these was devoted to my heuristic course on analog circuits , in which I had implemented my circuit philosophy. There I shared my idea of reinventing circuits  for the purposes of understanding, presenting and inventing  circuits. In this post, I will tell you about this venture of mine. The Idea The idea of ​​the heuristic approach in circuitry is simple - ''instead of presenting the circuits in their complete and perfect form, we reinvent them''. Thus, we can delve deeply into the essence of phenomena, realize the meaning of technical solutions and develop heuristic thinking. This will allow us not only to analyze the operation of el...

  By the mid-1990s, I had already developed my own philosophy about electronic circuits, and I decided it was time to share it with my colleagues. In the spring of 1997, I presented a series of three papers at the XXXII Scientific Conference on Communication, Electronic and Computer Systems at the Technical University of Sofia. The first of these was devoted to my heuristic course on analog circuits, in which I had implemented my circuit philosophy. There I shared my idea of combining and varying electrical quantities for the purposes of understanding, presenting and inventing  circuits. In this post, I will tell you about this venture of mine. The Idea A large part of electronic devices we can "invent" by combining and varying with the parameters of the studied object. For this purpose, in a series of experiments, we choose successively an independent and a dependent variable, keeping the other quantities constant. We then begin to vary the independent variable and obser...

By the mid-1990s, I had already developed my own philosophy about electronic circuits, and I decided it was time to share it with my colleagues. In the spring of 1997, I presented a series of three papers at the XXXII Scientific Conference on Communication, Electronic and Computer Systems at the Technical University of Sofia. The first of these was devoted to my heuristic course on analog circuits , in which I had implemented my circuit philosophy. There I shared my idea of using cause and effect relationships for the purposes of understanding, presenting and inventing  circuits. In this post, I will tell you about this venture of mine. Revealing causality As a rule, classil electronics courses do not reveal ''cause and effect relations'' in electronic circuits. For example, who cares if there is a causality and what causes what (what quantity is an input and what an output) in Ohm's law? Authors just suppose that voltage and current change simultaneously; they do n...

By the mid-1990s, I had already developed my own philosophy about electronic circuits, and I decided it was time to share it with my colleagues. In the spring of 1997, I presented a series of three papers at the XXXII Scientific Conference on Communication, Electronic and Computer Systems at the Technical University of Sofia.  The first of these was devoted to my  heuristic course on analog circuits , in which I had implemented my circuit philosophy. There I shared  my idea of using analogies for the purposes of understanding, presenting and inventing  circuits. In this post, I will tell you about this venture of mine. What are analogies? We begin learning from the day we are born. In this way, in the early years of our childhood, we accumulate a knowledge of life for visible (mechanical, hydraulic, pneumatic, social, etc.) phenomena of our world. But this world is arranged so interesting that apparently different phenomena obey the same laws; they are ana...

Тази есен преподавателската ми дейност със студентите  от Техническия университет приключи и аз с удоволствие се върнах към творческата си дейност в уеб (електронната книга Circuit Idea , моя блог Circuit Stories и форумите ResearchGate , StackExchange и Codidact ). Наистина, в началото чувствах някакъв вакуум, но след това започнах да усещам облекчение, защото вече беше почнало да ми омръзва насила да уча ИТ студентите на нещо  (схемотехника) , което малко ги интересуваше.  Сега от моите идеи в уеб можеха да се възползват любознателни "онлайн студенти" от цял свят (включително и някои от бившите ми студенти), които действително се интересуват от схемите. И тук изненадващо за мен се появи един съвсем реален "студент", който прояви желание да направим интересни технически (физически) експерименти. Това беше моят 7-годишен внук Алекс, който само от месец е първокласник. Аз знаех, че е "много напред с материала", защото можеше да чете и пише свободно, с лек...