# Circuit Idea/Technical University of Sofia
## A dedication to my students

I dedicate this exciting story to my students from Faculty of Computer Systems, Technical University of Sofia, spring 2008, that have inspired me to carry out this incredible experiment on the laboratory and to tell about it on Circuit idea wikibook. Cyril
I have been teaching analog circuitry for more than 20 years. During this period, my students and I have been carrying out many and many times an attractive computer-based experiment (it is my favorite experiment): visualizing the voltage distribution along a linear resistive film that is supplied by two voltage sources connected to the two sides of the resistor. For this purpose, we use all kinds of "resistors", some of them quite odd: resistive wires, pencil's graphites, conductive foam and rubber, and of course, opened potentiometers and the good old rheostats. By sliding on the resistive surface and varying consecutively the two supply voltages, we "invent" various legendary resistive devices: movement sensors, voltage dividers, resistive summers, subtractors, Wheatstone bridge, op-amp inverting, non-inverting and differential amplifier, etc.
In addition, this marvelous experiment presents in an attractive non-traditional way the famous Ohm's law, virtual ground concept, negative resistance phenomenon, etc. to curious students. It even shows directly in a "geometrical" way classical relations between the electrical quantities (I = V/R, U$_{OUT}$/V$_{IN}$ = -R$_2$/R$_1$, etc.) Furthermore, this experiment establishes a connection between the elementary passive resistive circuits (voltage divider, resistive summer, etc.) and the more sophisticated electronic op-amp circuits (non-inverting amplifier, inverting amplifier, etc.)
I have been having responsive, clever, curious and capable students that have been helping and inspiring me in my pursuit of revealing the truth about resistive circuits through these years. That is why, I have decided to place this experiment first on my site of circuit-fantasia.com and then on this wikibook.

## Implementation of the web experiment
### Students

During this term I teach basic circuitry (both lectures and laboratory exercises) to 150 students from Faculty of Computer Systems, Technical University of Sofia. They are divided into five groups (64, 65, 66, 67, 68), each of them containing 30 students. Further, for the purposes of the laboratory exercises, these groups are divided into sub-groups of 15 students. Each laboratory cycle lasts two weeks: the first five sub-groups (64a, 65a, 66a, 67a, 68a) conduct laboratory exercises during every even week; the other five sub-groups (64b, 65b, 66b, 67b, 68b) conduct laboratory exercises during every odd week. My general idea is to carry out the same experiment in the laboratory consecutively with all the student groups during the present cycle (March 17–29, 2008).

### Organization

Preparation. First, in the beginning of the week, I started this story on Circuit idea. For this purpose, I outlined briefly (about 25%) the future page: I traced out the contents by inserting the main subtitles; then, I placed semi-drawn pictures and a little explanatory text. By the way, it was very hard for me to refrain from making the whole page...
In the laboratory, I prepared all kinds of resistive elements (wires, pencil's graphites, conductive foam, etc.), power supplies, movements, VOM's, holders, etc. and arranged the laboratory equipment according to the future experiment's purposes.
I also prepared all kinds of recording equipment - a small solid state recorder (for quite a while I have recording my lessons, classes and laboratory exercises), camera and mobile phone. Maybe, next year I have to use a web camera:)?
I have also begun thinking who of famous web writers (mainly, university and college teachers) to invite to join this educational web initiative. For now, I have in mind Tony Kuphaldt (Lessons in electric circuits), Tom Hayes (Student manual for the art of electronics - great book!), William Beauty (Science hobbyist - great site!)...
Announcement. Then, in the lecture hall, I announced my intention to conduct such a web experiment to students and showed them how can we carry out it. I told them what is the great Wiki idea and how they can join the wikibook Circuit Idea. I suggested to students to choose meaningful user names consisting of student name and group number (thus I can observe their web achievements and add more credits to the rating).

## During the laboratory exercises

In the student group pages, my students and I describe step-by-step how the laboratory exercises have passed. The great mass of the written is extracted from the records but there is also some fragments that is written directly to this page in the laboratory during the exercises. Note that students make their reports in real time at the laboratory; I make also my "report" on the white board (ten times during the cycle!), snap it from time to time and write it on this page. Students and I make a lot of photos during the exercises; they show drafts on the whiteboard, screen shots, laboratory setups and, of course, the very students.
The idea is first to write up here chronologically what is done in the laboratory; then to systematize and polish these raw materials and place them in the main story. We will use here (and why not in the main page?) a quite informal style. I will mark student's insertions by italic to distinguish them from my teacher's text. Well, let's start!

## References

* ↑ Compound passive converters with voltage output