Circuit fantasist5517Dec 6, 17:05TL Fong, thanks for the valuable thoughts! I completely share them; I have been using some of them for a long time. But in SE EE I had problems quoting my materials because they qualified it as “self-promotion”…Last night I wrote a short answer to your question where I explained the behavior of the tunnel diode in a fun way. I hope you like it. I will make a copy in my blog too. Cheers!  3 hours later… Circuit fantasistDec 6, 20:03Here is the copy – circuitstories.blogspot.com/…tlfong01Dec 6, 20:33@Circuitfantasist Ah, about self promotion, you remind me one thing related to Olimex: (1) fongheart.blogspot.com/2013/…, (2) tunneldiode.blogspot.com/2020/…. Question: I remember Olimex was established by some university academics in Bulgaria, but I forgot which University. Do you know which one? Circuit fantasistDec 6, 20:56Interesting… I have never heard about it… How could I have heard like me dealing with basic ideas from the 19th century and they with miracles from the 22nd:)?  15 hours later… tlfong014896Dec 7, 12:13@Circuitfantasist Well, when I was 10, I heard about scientists in 1600’s doing experiments with frogs, using electricity as a signal to move the frog’s legs. Fast forward to 2010’s I was curious to know what is ECG. So I went to a hospital to do ECG, and later I had the opportunity to play with handheld and desktop ECG machines, so I spent some two hobbyist weeks learning how to do ECG.At that time, I google for ECG toys, and found a startup project called Bulgaria Olimex was selling cheapy EKG board, which I think it the first of its kind. I bought two Olimex ECG board and learned about how they design circuits using virtual ground using human right leg, and how to use low pass filters to eliminate high frequency noises, … , tunneldiode.blogspot.com/2020/…***  10 hours later… Circuit fantasist5517Dec 7, 22:19TL Fong, I have no experience in ECG circuits but I know they are very sophisticated. But I would be happy to figure out the tricks used in them. Here is how I have explained, with a lot of imagination and intuition, the so-called right leg driven circuit…As you can see, the idea was rated with 0 reputations while the elite received a dozen of them for a dry and formal explanation… This is a good illustration of Einstein’s thought that I used as a motto at the top of my Wikipedia user page.  14 hours later… tlfong014896Dec 8, 12:42Ｙｏｕｒ　ｒｉｇｈｔ　ｌｅｇ　ｄｉｓｃｕｓｓｉｏｎ　ｉｓ　ｇｏｏｄ．　Ｉ　ｆｏｕｎｄ　Ｓｃｏｔｔ　Ｓｅｉｄｍａｎ＇ｐｒｏｆｉｌｅ　ｉｎｔｅｒｅｓｔｉｎｇ：electronics.stackexchange.com/…　Scott Seidman
top 0.80% overall
＊＊＊Engineering Educator＊＊＊, Biomedical Engineering, Bioinstrumentation, Embedded Systems, Medical Devices, Design tlfong014896Dec 8, 13:07I noticed one difference between the EE SE answers and mine is that I focus on module level, or system integration problems, almost always never at lower op amp level. Take the ECG Q&A as an example, you see that I give a lot of references, and debugged demo programs, and real life example python programs.(1) Raspberry Pi 3B+ interface with Heart Monitor AD8232 using MCP3008 and SPI pins – Asked 1 year, 7 months ago, Viewed 4k times
raspberrypi.stackexchange.com/…

(2) How can Rpi read the MAX30100 / MAX30102 Oximeter? Asked 7 months ago Active 1 month ago, Viewed 2k times
raspberrypi.stackexchange.com/…  9 hours later… tlfong014896Dec 8, 22:14Now I have set up the I2C AD5933 module and found Rpi4B can detect it without any problem. Next step is to write a little python to measure the impedance.

tlfong014896Dec 8, 22:42About the right leg circuit, I remember the first article I read about the 10 lead ECG is based on the Einthoven Triangle – Wikipedia
en.wikipedia.org/wiki/…. The very clever guy invented this triangle the late 1800’s, and got a Nobel prize in medicine. I remember I spent a couple of hours clarifying the basic things, and explain to a medi guy how the triangle works, and how to memorize the meaning of the names of the 10 leads. One thing I was very impressed is the following: The 12 leads are placed on the serface of the body, but what is interpreted is the h…(see full text)Ah bed time, call it a day, see you tomorrow.  18 hours later… Circuit fantasistWed 17:00OK, you made me think again about the exotic right leg circuit… I needed time to remember the idea behind this odd arrangement. I will reorganize my answer there and will create a post here about it. Now I’m moving to the blog to reply to your interesting comments there. Maybe I will redraw the conceptual circuit diagram…  1 hour later… tlfong014896Wed 18:00Yes, I think both of us need to take a break and look back what we have been chatting so far. I agree that you might need to redraw you conceptual diagrams, with more descriptions on the test setup etc (Step 2 of my selfie walkthrough below). The Right Leg cct might take you a long time, because it was designed more than one hundred years ago, and some terms are inconsistent with today’s usage.I agree with you saying that my blog is getting very messy, and it is difficult to search things. So I have decided to make a summary in the new post:tunneldiode.blogspot.com/2020/….I have been randomly hopping here and there, diverting aimlessly. Now I think your “Transformer + hand knob pot + scope” is in Lancaster’s Elegantly Simple style and indeed elegant, but it is difficult to understand. So if you can explain it with your new enhanced conceptual diagram should help tunnel diodes newbies a lot. In the mean time I hope my use of the triangular wave would hopefully get the picture as by Tektronix (Step 7).(removed)Ha, supper time. See you later.  2 hours later… Circuit fantasistWed 19:57TL Fong, It is a pleasure for me to read what you have written. I agree with it. You come out right – the right leg circuit takes time. I played with it because I lost something in my understanding. Here’s how I try to imagine it geometrically – photos.app.goo.gl/…, photos.app.goo.gl/….  9 hours later… Circuit fantasistThu 5:06TL Fong, I edited my answer to the question about the right leg driven circuit. It would be interesting to make some “discussion” there. Also, I will copy it in my blog…  4 hours later… tlfong01Thu 9:03Just a quick reply. Ah it would nice if you can copy it to your blog and I make comments there.  3 hours later… tlfong014896Thu 11:50As I said earlier, I am more interested in hobbyist style system integration, eg buying cheapy ECG modulde from Bulgaria Olimax, open source bio sensor board designed Analog Devices and other well known brands. Then I make workable devices for fun, or let the newbies know how me, the hobbyist developer follow the CMU research paper, use their recommended AD5399, make a real device helping disabled persons with bio sensors, and AI software, …I am not interested at all in low level at op amp ccts, otherwise I would invest tons of hours reading research papers like to following:

  3 hours later… tlfong014896Thu 15:06I ma reading you following answer on Schmitt ｔｒｉｇｇｅｒ　oscillator, because I am thinking of using the oscillator’s trnanglur ouput to power the tunnel diode when drawing the I-V curve.
electronics.stackexchange.com/…

I found you description of the amplifier too difficult for me. So I went to AAC (All About Circuits) for help. I found AAC good for low IQ guys like me　：）: tunneldiode.blogspot.com/2020/…(see full text)Circuit fantasistThu 15:28OK, I ам startинг now my online lection… I will write to you later…  2 hours later… Circuit fantasistThu 17:30“am starting”:)TL Fong, I have a feeling that you have some fear of the elite:)? tlfong01Thu 17:47Ha, yes, the real elites in Physics.StackExchange trigger my inferiority complex. 😦  1 hour later… Circuit fantasistThu 18:52circuitstories.blogspot.com/…  4 hours later… tlfong01Thu 22:54Then I will listen to some inferiority complex healing music, or find some ***fake elites*** to beat them up. 🙂
youtube.com/…  4 hours later… Circuit fantasistFri 3:19nice material about ECG  8 hours later… tlfong014896Fri 11:30@Circuitfantasist Just now I skimmed my ECG project log and found the whole documentation file is about 350MB large. I am thinking of using AD5933 impedance tester to confirm some of my old experiment results. I quickly skimmed the basic stuff to refresh my memory. I usually recommend fellow hobbyists to start with this very good tutorial:INTRODUCTION_TO_ECG_INTERPRETATION_V8_0_July_2012
academia.edu/11339390/…tlfong01Fri 11:47You might find more updated ECG materials from this Q&A site:
Medical Sciences Stack Exchange ECG
medicalsciences.stackexchange…  5 hours later… tlfong014896Fri 16:56Your Lancaster Simple Element circuit design method works simple and elegant. I designed and wired the Schmitt trigger oscillator and it works without any debugging.

The triangular wave is sharp and stable, much better than that much more complicated and unstable ICL8038 and NE555 circuits.Next step is to use this triangular wave voltage to power the tunnel diode and see if I can watch the electrons swimming through the tunnel. 🙂 Many thanks for your inspiring suggestion. Ah, jogging and supper time. See you later. Cheers.  2 hours later… Circuit fantasist5517Fri 18:52OK, this is a possible solution. In the Lancaster’s “elegant simplicity”, a neon lamp serves as 7414. You can see the general idea in many everyday situations. Now, you need my 90’s V-to-I module – a buffered inverting amplifier with a tunnel diode in the place of R1. I will publish a paper and post about it… also, about the “simplest IV curve tracer”…  23 hours later… tlfong014896Sat 17:39I am still confused of the operation of a curve tracer (for a tunnel diode) I know the classical tracer is to show the I-V characteristic of a BJT transistor, using a scope. I think the curve tracer for a diode, including the tunnel diode, also needs a scope. The scope’s X-axis is voltage V, and Y-axis is current I.Now my very first I-V curve plotting experiment does NOT use any scope. I just vary the voltage source to the tunnel diode with a protecting, series current limiting resistor. I use a manual, two push button presses to adjust the voltage value. I use a DMM to measure the voltage across the diode, and another DMM to measure the current through the diode, and also through the resistor. After all the measurements, I use the Excel worksheet to plot the I vs V curve.The problem of using the above manual, adj PSU, and voltage and current DMM is that it is tedious to make the not too accurate DMM measurements. And it would be even more tedious to find the series/external resistance and inductance to avoid the switching/jumping over the NDR region, as described by the GE’s 1962 TD User Manual, in my BlogSpot post below.tunneldiode.blogspot.com/2020/….Ah, jogging and supper time! See you later. Cheers.  1 hour later… tlfong014896Sat 19:10The pcf8951 DAC/ADC is only 8 bit resolution. So I am not sure I need higher resolution ADC, such as 10 bit MCP3008, 12 bit MCP3208, or even higher.

  2 hours later… Circuit fantasistSat 21:04Okay, I’ll explain but I have to do something first and I suspect that when I’m done it will be time to go to bed there … tlfong01Sat 21:20nothing urgent. You can do it in two weeks, which is what I need to sort all the ADC, DAC stuff. I just found two more old PCF8951 ADC/DAC’s in my junk box. Usually I need two or three same modules for swap testing or troubleshooting. Good night. Cheers.  5 hours later… Circuit fantasistSun 2:16OK, I will comment in your blog – tunneldiode.blogspot.com/2020/….  2 hours later… Circuit fantasistSun 4:22I have appended my comments in you blog also to my answer to your question in CD.  6 hours later… tlfong014896Sun 9:55@Circuitfantasist Your suggestions in my tunneldiode.blogspot.com are inspiring. Let me make some quick and dirty follow up replies.Your first suggestion summarized: (1) “Let’s see what is the most important to measure the tunnel diode IV curve. IMO this is not the scope. You have to see that when increasing the voltage across the diode, the current through it decreases. …”Yes, I very much agree that the scope cannot measure the tunnel diode’s current and voltage characteristics, though it is very useful, to give a very vivid picture that the I-V curve has a mysterious gap (NDR or Twilight Zone) where the electrons. split itself into two parts, like the Schrodinger Cat, with one part jail breaking, disappearing into the Bermuda Triangle, and reappearing in the free world, …So let us forget the scope for a while and focus on how to do the I, V measurements using adj UPS, DMMs, opAmps (which I try to avoid for now, because my audiences are the U15 hobbyists in our local maker’s club) etc, …Wow, your following story is amazing: “… I think the best way to measure and plot IV curves is based on a computer. Apple II was very suitable for this purpose with its graphic features. The monitor software had a function “plot a point” that could be used by an additional program written in Assembler. In this way, in the late 80s, a few students and I created MICROLAB system, …”/ continued from above: “… The AD periphery consisted of 12-bit DAC and ADC. Later, one of these capable students, created MICROLAB BASIC – an expansion to the embedded BASIC. It consisted of a set of assembler drivers called by commands like “IN”, “OUT”, “PLOT”, etc…”So your MicroLab’s (tunnel) diode I-V plotting equipment using Apple 2 and 12-bit ADC/DAC is 20 years ahead of my 64-bit Raspberry Pi and 8-bit DAC/ADC. For our non realtime project, Rpi’s 64-bit processing is not relevant, but 12 bit resolution might be just appropriate technology, while my 8-bit PCF8951 ADC/DAC might be too weak.Your zero resistance stuff is a bit too hard for a Sunday morning reading. Anyway, it is now tea time, So see you later. Cheers. tlfong014896Sun 10:53Oh my goodness, so your MicroLab I-V curve plotter is 20 years ahead of mine. I need to skip my lunch to catch up!

  1 hour later… tlfong014896Sun 11:59When browsing you the links you just gave me, I suddenly remember that my original question in CD is very long, including a couple of your references, and pictures stating that origins are are from you Wikibooks. But my very long question has been condensed to CD’s standard format of 70 words, so many of my references I wish my readers/answers are removed. Anyway, I recovered part of the contents from the Cd’s history files, but the formats are incompatible to EE，tunneldiode.blogspot.com/2020/…Ｆｕｎｎｙ　ｃｈａｒ　ａｇａｉｎ，　ｎｅｅｄ　ｔｏ　ｔａｋｅ　ａ　ｂｒｅａｋ　ｔｏ　ｆｉｘ　ｔｈｅ　ｐｒｏｂｌｅｍ．  1 day later… tlfong01yst 13:24So this morning I have placed an order for the current sensor amplifier max4172:tunneldiode.blogspot.com/2020/…  1 hour later… Circuit fantasistyst 14:44… instead to make it yourself? In general, this is the better solution if your goal is the element under test… tlfong014896yst 15:14I didn’t catch you. I order the 8 pin SOP chip, so I need to use the SOP 8 top DIP 8 adapter board and hand solder the SOP chip to adapter. I forgot where I placed my SOP to DIP board, so I need to order some more, in case I could not find my old ones. I will also order ICL8038 through hole chips and DIY a fixed triangle sig gen, instead of using the bigger, hard to adjust module. tlfong01yst 15:43This is the adapter board for max4172:SOP8 to DIP8 adapter board
item.taobao.com/…tlfong01yst 15:56This is the order for MCP4725:tunneldiode.blogspot.com/2020/…  1 hour later… Circuit fantasistyst 17:16OK, I will look at them after my on-line meeting with my students where we are making “ideal diodes”:) See en.wikibooks.org/wiki/… and en.wikibooks.org/wiki/….  4 hours later… tlfong014896yst 21:10Ha, I watch your students doing the lab, and then more realized why I have an inferior complexity when talking to the real EE pros. I need to first introduced my background, when I studied the EE diploma in a sort of community college to be trained as a technician repairing radios in a Philips radio manufacturing factory, or American semiconductor testing plants. In short we learned more practical things, and not emphasizedon theories.So, as I often said, after the EE diploma, I still don’t know the meaning of opAmp virtual ground. I also don’t know the deeper meaning of positive and negative feedback. Also we almost only used the locally made cheap equipment for repairing radios and the more expensive equipment was always locked in the cabinets. (1) So my first surprise was seeing your students can actually hands on, touching the high class equipment which I think are for industrial grade R&D labs.So, as I often said, after the EE diploma, I still don’t know the meaning of opAmp virtual ground. You should remember that not too long ago, I mentioned that I was very grateful for the two YouTube guys D Jones and the other name I forgot, explaining the meaning of virtual ground. I never dreamed that I can “investigate” the deep practical virtual ground.(2) The other things is about dressing code. I must first mention that in those days in my city, a large proportion of people are refugees. So when I looked back, I should be dressed as a refugee in college. I still remember that I only had two cheapy coats and two jumpers which I wore for the whole winter. So I was so surprised to see your students/tutors dressed so smartly and fashionable in the lab.Of course many years later our community collage upgraded a polytechnic and had business and even fashion design departments. Well, I am not complaining, because in those years only less than 3% of those eligible to enter a university, and perhaps 5% could go to a technical college. So fast forward decades, you should see why now I am so keen to make a (tunnel) diode oscillator, playing with opamps and ADC/DAC etc.It is sort of a healing process, or repairing of my broken dream of not being able to go to America to study EE in a University. HongKong EE/ME industries did not go well after my graduation and technician years. Luckily I had other chances to study IT and software engineering and can still earn a decent living. Now the time has come to show off my software engineering knowledge and skills.For the MCP4725 12-bit ADC, I am using high class programming techniques call “Data Driven Programming” style to power the tunnel diode to hopefully force it to enter the Negative Dynamic Resistance region.Just thinking aloud, sorry for all the typo errors. Almost bed time, see you tomorrow. Cheers.  9 hours later…

Circuit fantasist6:35Hi Fong, Again, I admire your gift for expressing yourself warmly and in such a human way. This is very rare on the web … as if people there have lost their ability to communicate naturally … 

Circuit fantasist55176:51Regarding the emphasis on “theories”… Maybe the reason is in me simply because I was created that way – to look for the idea and after revealing it, to explain it to others. At the same time, I am a practitioner…For example, yesterday I changed the timer of the stair lighting in the building where I live. For this purpose, I did some experiments with the buttons on the floors to find out if they are working. Also, I had to figure out the idea of ​​the timer to make sure it was damaged. Of course, these are simple but still practical skills that require some intuition and experience … especially since it is not safe … 

Circuit fantasist

7:43Virtual ground… It is a simple but difficult to understand concept. I myself continue to look for an even simpler explanation of this phenomenon … but in a more general form …  9 hours later…

 Circuit fantasist551716:24

Ok, let’s try to explain it in a simple possible way:

“Virtual ground” is simply a “voltage copy” of the real ground; this is the essence of the virtual ground phenomenon…

So, to create such a “copy”, you simply need a voltage follower. Connect its input to the real ground and take the virtual ground from its output.

The simplest voltage follower is an op-amp whose output is connected to its inverting input.

Thus, the output voltage is subtracted from the input voltage at the non-inverting input… the difference is amplified many times and appears at the output… and so on so forth…

This can be explained in a human-friendly manner by personalizing the op-amp.

Figuratively speaking, the op-amp “compares” the voltage at the non-inverting input with the voltage of the inverting input and changes it until the former becomes equal to the latter…

Read the latter as: Figuratively speaking, the op-amp “compares” the voltage at the inverting input with the voltage of the non-inverting input and changes it until the former becomes equal to the latter. 

Circuit fantasist551716:39

From this perspective, every op-amp circuit with negative feedback contains a follower (another wisdom which cannot be found in “reputable” sources).

Even the inverting amplifier contains a non-inverting follower inside – the voltage of the inverting inputs, as above, copies the voltage of the non-inverting input…

and, if the latter is zero (real ground), the former will be zero as well (virtual ground)…

If we put a resistor (R2) in the connection (negative feedback loop) between the output and the inverting input, the op-amp will continue keeping a zero voltage of the virtual ground…

But where is the input voltage here? We include it to this following system as a “disturbance” (another wisdom).

For this purpose, we connect the “disturbing” input voltage source through a resistor (R1) to the virtual ground. The op-amp reacts to this “intervention” by raising its output voltage… and we use its “reaction” as an amplified output voltage.

But there is a virtual ground as before…

Ohh… I have to prepare for the next meeting with my favorites. We will discuss, as yesterday, diode circuits… a very interesting topic… Nice to see you later…  3 hours later… 

Circuit fantasist551720:06

The equipment in my lab is quite old. There is a need for modern digital oscilloscopes and functional generators.

But because I am an “old war horse”, I can handle any situation…

In terms of dressing, these students now have the freedom to dress as they wish. And at the time I dressed modestly. But in general, Bulgarians and especially women pay attention to their appearance … also to the home and the car … I think this is typical for small nations …

.END