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Circuit Idea/Group 65b

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65b Group Student Page

We are students from Faculty of Computer Systems, Technical University of Sofia. Our 65 group is divided into two sub-groups. We constitute the second one - 65b. Here are our names:

Svilen Peev, Tencho Petrov, Dimitar Shikov, Atanas Viyachki, Vladimir Konushliev,Galina Spasova,Silviya Karaivanova

The resistor as a component
What is resistor? It is defined by several parameters:

 * Resistance in Ohms (Ω)
 * Heat dissipation in Watts (W)
 * Manufacturing tolerance (%)

How to make a resistor? Electricity experimenters in the early 1800's used turns of wire of high resistance composition or compressed carbon granules to make resistances for their experiments.

What does resistor do? In electronics we use a resistor when we need to reduce the voltage applied to a circuit.

How does a resistor work? ... Silviya Karaivanova

Can a single resistor decrease voltage?
(try to explain the phenomenon) Circuit-fantasist (talk) 07:56, 28 April 2008 (UTC)

To decrease a voltage we need at least two resistors. Let's discuss the two possible cases.

R1 = 0. As we know:

Vout= (R2 /( R1+R2) )*Vin If   R1=0 -->       R2 / R2= 1

R2 = ∞. (explain...) Circuit-fantasist (talk) 12:42, 18 May 2008 (UTC)

So, we can finally conclude that one resistor couldn't decrease the voltage. We know that the resistor converts the current IIN into a proportional voltage VOUT. So,

VR=R*IIN and VIN=R*IIN   --> VR=VIN

The resistor R acts as a simple voltage-to–current converter.

Building a voltage divider by two resistors

Two resistors can be used to set a specific voltage. For example, if two resistors are connected as shown and a voltage of 10 volts is applied to the ends, then if both resistors are of equal value, the voltage at the middle point connection point will be 5 volts. The voltage is divided between the two resistors.

A three-terminal resistive voltage divider is sometimes also called a potentiometer. But what is potentiometer? Since it is a "meter", what does it measure? Circuit-fantasist (talk)

Basically a potentiometer is used to alter the potential difference in circuits. As we probably all know have so many definitions about the potentiometer. Some of them are:

1.	Potentiometer  is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider.

2.	Potentiometer is a measuring instrument for measuring direct current electromotive forces

3.	Potentiometer is a resistor with three terminals, the third being an adjustable center terminal; used to adjust voltages in radios and TV sets

4.	A device that controls the amount of current that flows through a circuit, such as a volume switch on a radio. Example: A volume control is usually a potentiometer.

5.	Potentiometer  is a variable resistor. It usually has three terminals: the two end terminals, across which the entire resistance appears, and a third terminal, the "wiper", which moves to a different spot on the resistor as the shaft is turned. ...

How a variable resistor works ? A variable resistor is a length of resistive material (wire, carbon, etc.) connected to the ends; a sliding connection makes the electrical connection. The resistance between the two connections is determined by the length of resistive material between the two connections. The closer the slider is to the end the lower the resistance is between this end and the slider and v.v.

A typical example is the volume control of audio equipment - there the resistive material is wrapped into an incomplete circle and the slider moves in an arc over the resistive material.

See also: |Voltage dividers

Silviya Karaivanova i Galina Spasova

Silviya, where have you taken these scans from? Don't you think we might have problems with Cambridge university press? Circuit-fantasist (talk) 15:21, 11 May 2008 (UTC)

Investigating the voltage divider

What do we need to carry out a computer-based experiment? First, we need a computer; after that we have only to connect to this computer a few analog-to-digital converters (ADC's) acting as analog inputs and a few digital-to-analog converters (DAC's) acting as analog outputs and our simple computer-based system Microlab is ready! Of course, we need the very voltage divider (or a potentiometer) that consists of at least two resistors. Silviya Karaivanova

Lab 2: The genuine Ohm's experiment.
Tuesday, March 25, 2008, 10.30 h

Lab 3: Transistor circuits (building the simplest transistor current source)
Tuesday, April 08, 2008, 10.30 h (extracted from the lab records made by a solid-state recorder) Circuit-fantasist 17:14, 28 May 2008 (UTC)

What a current source is

We begin our lab with general questions: "What is a current source? What do we want it to do?" How does a current source behave? How do we figure out that some device is a current source? How do we make a current source?" Simply speaking, we have to form a notion about constant current source.

What have you known about the current source from the basic course of electricity? Here is the well-known symbol of a current source (see the picture). How to make a good guess that it is a current source? If I give to you a (black) box with two leads and I say that it is a current source, how do you convince yourselves that it is really a current source? Vladimir: It will begin warming... Why do you think so? And what will happen, if we connect the two leads (a short circuit - case 1 on the picture)? Is it dangerous for the current source (comparing with a voltage one)? Vladimir: Yes, it is... Atanas: No, it isn't... Indeed, there is nothing dangerous for a current source, if we short its two leads. As the current source is designed for a given current, it keeps up (limits) the current thus protecting itself.

Then, maybe the opposite condition - an open circuit (case 3 on the picture) - will be dangerous as the current source will try to pass the same current as before. In this situation, the current source is misled: it doesn't see the open circuit; it "thinks" there is something connected there. It just "sees" that no current flows and raises its internal voltage up with the "hope" to pass a current through the harmful "thing". Of course, the current source does not manage to pass any current through the open circuit and reaches the final (compliance) voltage; a saturation and even a breakdown occurs. Thus, the compliance voltage represents the maximum voltage that the current source can reach when strives to produce the desired current.

Passive current source

Atanas has said that, if we connect a resistor in series to the voltage source there will no problem with the short connection. Well, let's place a resistor; thus we obtain the simplest current source. Choose for concreteness the favorite pretty values for the electrical quantities: V = 10 V and R = 10 kΩ to obtain I = 1 mA.

Ideal load. First, make a short connection at the output of the circuit. Since there is no voltage drop across the load, all the input voltage V is applied across the resistor R. As a result, the current is exactly as Ohm's law says:

I = V/R = 10 V/10 kΩ = 1 mA

Keeping a constant current by using an ideal current load Passive voltage-to-current converter (voltage causes current)

Imperfections. What are the problems of this humble circuit? Let's connect a load having some resistance to see what happens. As we can see, a voltage drop appears across the load and the current decreases.

The real load introduces some voltage drop VL, which affects the excitation voltage VIN. Now, not all the input voltage is applied across the current-setting resistor R but only the voltage difference VIN - VL. In other words, here the voltage difference VIN - VL determines the current IOUT instead the voltage VIN. As a result, the current decreases:

IOUT = (VIN - VL)/R = VIN/(R + RL)

This passive circuit is imperfect; it can't stand against the load "intervention" especially, if the load varies. It is a static, fixed, non-adaptable circuit... What do we do then?

Keeping a constant current by depreciating the load Passive voltage-to-current converter (voltage-controlled current source) Op-amp circuit builder (go to Stage 2 of this interactive flash movie)

Discovering the web
What a new idea might arise now? Maybe, we will find out it on the web? Then let's write "current source" in the Google window. No one knows why Google has chosen the Wikipedia page about current source from about 2,000,000 pages and put it at the first place. Well, open it to see what the truth about constant current source is. Alas! The page look quite cluttered and all that we can see here are definitions and specific circuit solutions. There is no philosophy; there are no basic ideas shown... For these cases they say, "Can't see the forest for the trees". Oh, the discussion page is quite more interesting! Even someone has suggested here a new structure of the page - the idea is first to reveal the basic idea and then to show the specific circuit solutions; that was in June, 2006...

Basic idea
Obviously, we have to reveal the truth by ourselves; let's then begin reasoning. The problem pops up when we connect a load and, what is worse, if we begin varying its resistance. Note the load may be not only a steady or varying resistor; it might be a capacitor that is charging, a diode (ordinary, zener, LED, base-emitter junction, etc.) or even a voltage source (e.g., a rechargeable battery)... It is not so important what exactly the load is; it is only important that a voltage drop appears across the load and this voltage drop confuses things.

If we look around, we can see that most things in this world are changeable, adaptable, dynamic... According to this observation, we have to make our current source react somehow to the load "intervention", to resist to its attempt to lower the current. That means something inside the current source has to change, in order to compensate the disturbing voltage drop across the load. What can change in this simple electric circuit?

Varying (dynamic) internal voltage

Vladimir: We might change the voltage... Yes, it is the one possible solution. Vladimir suggests, if the voltage drop VL across the load begins rising, the internal voltage VVAR of the current source to begin rising as well in the same direction with the same rate so that the difference VR between them to stay constant. This is the first idea: dynamic current source with following internal voltage. Till when will this magic continue? Of course, until VVAR finally reaches the positive supply rail. After that point, our wonderful "voltage-dynamic" current source becomes an ordinary passive one.

Have you heard the legend about Baron Munchhausen that was using his own boot straps to pull himself out of the sea? Our circuit is just one possible implementation of Munchhausen's bootstrapping idea in electronics.

Varying (dynamic) internal resistance

Do you have another idea? What else can change in this humble circuit when the voltage drop VL rises and, as a result, the current lowers? Atanas: Let's vary the resistance R... Great idea! The resistance R is another attribute that can change to keep the current constant.

Actually, we have to make the current source change its internal resistance so that to keep a constant sum R + RL; as a result, the current I = VREF/(R + RL) will stay constant. Again, till when will this magic continue? If RL rises, R will lower until it becomes finally zero. After that point, our wonderful "resistance-dynamic" current source becomes an ordinary one.

Since the resistor R has the property to keep up a constant current, they name it current-stable resistor. Let's realize this idea as it is simpler and more obvious than the idea of a dynamic voltage source considered above.

A transistor acting as a current-stable resistor

What electronic component has such a current-stable behavior? A student: The operational amplifier... No, no, it has to be a simpler element. Remember in this lab cicle we consider diode and transistor circuits; so, it has to be a diode or a transistor. A hint: the one has a behavior of a voltage source (more precisely, of a voltage-stable element); the other has a behavior of a current source (current-stable element). Well, which of the two behaves as a current-stable element? Of course, the transistor...

Well, let's then see why the transistor has such a behavior. You have already studied a subject about semiconductor elements; so, you have to know how it behaves. Do you have any reminiscence of it? What can a transistor do? A student: ...to amplify... No, it might sound paradoxical but the transistor does not amplify; it attenuates!?! The only thing that a transistor can do is to change its present resistance thus dissipating a power and, as a result, regulating the current through or the voltage across the load.

Here is an n-p-n transistor connected in series with a load RL and a power supply VCC. It is a three-terminal element (a triode) while a diode is a two-terminal element. A triode is too complicated for our reasoning:) so, we break down it into two two-terminal parts: an input base-emitter part and an output collector-emitter part. Each of them has an IV characteristic; now we are interested in the output characteristic of the collector-emitter part. Why they name it "IV characteristic"? Because we can do two things with it: to apply a voltage across it and to measure the current through it or to pass a current through it and to measure the voltage drop across it. Also, they name this curve output characteristic because it represents the output transistor's part. How does it look? Let's present the circuit operation graphically.

For this purpose, we have to superimpose two characteristics - one of the source and one of the load. First, let's draw the IV characteristic of the voltage source acting here as a power supply. What is it? It is a vertical line that is shifted with the magnitude of the voltage source VCC. Then, we have to show the presence of the load by inclining the line to the left according to the load resistance RL. The resulting curve represents an IV characteristic of a real voltage source having a voltage VCC and an internal resistance RL (they name it "load line"). After, we have to plot the transistor's output characteristic on the same coordinate system. The crossing point is known as an operating point; it represents the present magnitudes of the voltage and the current.

When we vary the load, the load line rotates and the operating point moves horizontally along the transistor's output characteristic. But why? How does it do this magic? What does the transistor actually do to achieve such an effect? Can someone explain? Let's try.

When we lower the load resistance the load line stands up; the transistor does the opposite - it increases its present collector-emitter resistance RCE (or just RT) so that to keep up a constant total circuit resistance. We may show RT by another line that begins from the coordinate system origin (the trick is to think of the present resistance RT as an ohmic one). So, this line will rotate around the origin and incline as well. As a result, the crossing point moves along a new almost horizontal line - the output transistor characteristic. This line is imaginary, unreal, artificial but we can see only this line; it represents the behavior of a current-stable resistor.

The text below is written by a student from this group:

The BJT transistor as a three-legged creature looks much like a light switch (2 legs for IN and OUT, and one for the ON/OFF button), and basically that's what it is - a switch. But this one here is like those fancy light switches with a rotating knob or even the more fancy ones - with a metal "touch-plate", which can be used to set a different light intensity in a continuous range by rotating the knob, or keeping your finger on the metal plate for a short time. But unlike these mechanically controlled switches, the transistor is an electrically controlled one - on this scheme the output collector-emitter(C-E) current is controlled by the input base current or the base voltage, whichever suits us more.

So here comes the simple idea - if we apply a constant base voltage, we will set a constant C-E current. When the C-E voltage increases (e.g. due to decrease in voltage on the load resistor Rl) the C-E resistance will increase too (remember we set the C-E current to constant using a constant base voltage). So what do we get - a dynamic varying resistor which keeps a constant current flow. In short - a current-stable resistor. Which is exactly what we need in order to make a constant current source.

This behaviour is shown on the IV diagrams below. They can be explained as a mechanism with the I line acting as a "fixed rail", on which the crossing of the two "pivots" - Rl and Rt lines - point A slides. As we decrease the load (Rl that is) point A slides down the Rl line, up the Rt line, and to the right on the I line. This means that the transistor resistance increases, so the whole resistance of the circuit remains the same, and therefore the current flow remains the same. As we do the opposite - guess what - exactly the opposite things happen ;)

--V.konushliev (talk) 08:42, 19 May 2008 (UTC)

Building a simplest transistor current source on the whiteboard
''Please, read carefully this story. IMO, this is the fanciest and the most incredible story about a transistor circuit that I have ever seen on the web! What do you think about this assertion?'' Circuit-fantasist (talk) 05:55, 20 May 2008 (UTC)

Looks scary at first sight :) But none of the elements involved bites, and everyone has it's role.

 * Maybe, it looks scary because we have placed here the final, complete and perfect circuit solution? Maybe, we would build it step-by-step snapping every drawing on the whiteboard to show the circuit evolution? Maybe... Circuit-fantasist (talk) 05:37, 20 May 2008 (UTC)

In the middle, surrounded by a blue line is the "boss" of the circuit - the varying load resistor Rl. It's he who leads the concert, and the whole circuit is built for him - to satisfy his needs and desires for constant current. The nameless resistor just beneath the boss is his "bodyguard" - just in case someone curious moves the slider of the "boss resistor" to its very end and try to short-circuit the power source through the transistor.

Everything outside the blue line is the BJT current source itself - a whole team of elements working for the "boss". There's the "hero" of the circuit - the workhorse - the mighty bipolar junction transistor (BJT), who does all the dirty job (donkey work:) of keeping the constant current. Connected to its base is his "manager" (modern heroes need to have managers), the varying resistor (potentiometer) P, who is basically a varying voltage divider, and by the means of base voltage Vb tells the transistor what to do. In this case - using a constant base voltage the manager tells him to keep the current flow at a constant rate. The "manager" also has a "bodyguard" - Rb keeping the power source safe from short-circuit's caused by someone playing with the potentiometer P.

Then there are our watchful eyes - the voltmeter V2, used to keep an eye on the voltage drop on the load resistor (the boss), another voltmeter V1, watching over the voltage drop on the transistor's collector-emitter junction, and an ammeter, which gives us a sneak-peak on the current flow.

Last, but not least - the power source VCC, who brings the whole circuit to life :) -- V.konushliev (talk) 13:22, 19 May 2008 (UTC)

Mounting the circuit on a PCB
It was easy so far but now we have to materialize the circuit on a prototyping printed circuit board. Can someone solder? If yes, please! Here are soldering iron and solder. How do we solder? Look at this links: 1, 2. You may use also various tools...

The transistor is n-p-n type packed in metallic body. The collector is connected to the body; so, you might measure the collector voltage by touching the body. You may supply the circuit by the computer or by an external power supply. What do you prefer? If you use the PC supply, there are two fixed voltages (+12 V and -12 V). Maybe, it is better to use the two varying lab supplies because we might provoke our transistor current source by varying the supply voltage. If you prefer, you might use a single power supply...

For our educational purposes it is preferable to arrange the elements in a similar way to the circuit diagram drawn on the whiteboard. For example, place the negative rail at the bottom and the positive one at the top; drive the transistor from the left and take the output from the right, etc. Now, let's make some photos..

What do we connect as a load? Let's it to be something varying - this 10 kΩ rotating "potentiometer" will suit us. Connect it as a rheostat (a two-terminal varying resistor). By the way, why the slider is connected to the one end? What is the idea of this connection? Also, as it is very likely someone to burn out it, connect a protecting resistor in series with the potentiometer.

How to set the input voltage? How to make a lower voltage by a higher one? Of course, by another potentiometer supplied by the same power supply (here it is connected as a real potentiometer).

Investigating the circuit...
In the beginning, we may draw and superimpose the current loops over the circuit diagram. Then, in order to measure the currents and voltages, we have to connect ammeters and voltmeters.

I have an idea for a synchronised presentation - I will "move" the slider of the input potentiometer on the whiteboard; at the same time, you will move the real slider on the PCB. In the beginning, the input voltage is 0 V; so, no any base current flows. The transistor is "closed". Increase carefully the input voltage and look at the input transistor characteristic; imagine we walk along it:) At some moment, a current will begin flowing through the base-emitter junction and β times bigger collector current will flows through the load.

What happens, if you go too far? The transistor will saturate. So, we have to stay in the middle where the transistor operates in the active region.

What elements constitute our current source? These are all the elements excluding the very load, of course... Well, now we have to see, if it is a constant current source. How? We have to disturb, "provoke" it and to observe its reaction to our "intervention". But let's afford an opportunity to Vladimir to tell what has happened in the laboratory (he can do it very well). Circuit-fantasist (talk) 19:41, 27 May 2008 (UTC)

The text below is written by a student from this group:

Everything here is based on the simple law of Ohm $$R=V/I$$

...by varying the load resistance RL...

... we observe a change in V1 and V2, but no change in the ammeter. We're happy: the current flow is constant :) How did that happen?

When we increase the load resistance Rl so does its voltage drop, which can be seen on voltmeter V2 (logically simple - more resistance generates more pressure). As V2 shows an increment, V1 respectively shows a decrement (their sum represents the voltage of the power source Vcc). Since we made the transistor act as a current-stable resistor, it "senses" the decrement of the C-E voltage drop and obediently reduces its resistance, so the sum of resistances in the circuit branch remains the same. Therefore the current flow remains the same too.

When we decrease the load resistance, exactly the opposite happens (V2 shows a decrement, V1 shows an increment, the transistor rises its resistance, the sum of resistance remains the same, and so does the current flow).

...by varying the supply voltage VCC
...we observe the same pleasing facts: no change in the ammeter, although V1 and V2 show changes. We're happy again: the current flow is still constant :)

This time both the voltmeters V1 and V2 showed increments of voltage drops, with the increment of the supply voltage Vcc. The transistor again "senses" the change in voltage drop and rises its resistance. But if the transistor reacts the same way as in the case above, how does the current remain the same, if there is no change in Rl? The difference comes with the fact, that the "manager" of the transistor tells him to rise it's resistance even more, by applying a larger base-emitter voltage (is it true? Circuit-fantasist). Of course this is due to the fact, that the "manager", as a simple voltage divider, divides a larger voltage (Vcc), and therefore gives a larger result (Vbe). At the end, the sum resistance of the circuit branch rises enough to compensate the increment in supply voltage Vcc and keep the current flow the same.

And again, with the opposite input (decrement of Vcc) the opposite phenomena is observed, but the result stays the same - constant current flow. A job well done by the BJT and it's "team" :) --V.konushliev (talk) 15:11, 19 May 2008 (UTC)

 * Vladimir, now I am realizing that I have misled you to some extent in this experiment. The circuit is not as correct as it seems. It would be more consistent, if we have made all the possible to make the input "manager" keep a constant voltage. Here we rely on the constant power supply; so, we shouldn't change its voltage. We should supply the potentiometer by another voltage source or replace the input voltage-divider circuit by a voltage-stabilizing one (e.g., by connecting a diode into the lower leg). This would be a prelude to the famous current mirror circuit (see group 66b and group 67b). Please, edit your explanation according to these circumstances.

 * Vladimir, I have a suggestion to. Would you contribute the Circuit idea story about the simplest transistor constant current source (and not only it)? Your writing style is unique; so, you might tell your lively story in a separate page as a different viewpoint at this famous circuit. Circuit-fantasist (talk) 06:46, 20 May 2008 (UTC)

 * I will try to contribute and help you with some pages, but this will be done after the exam session :) Time is running faster these days, unlike the current flow in the discussed circuit ;) Last week when we talked, you mentioned you'll be presenting your experience with involving students in web-based learning process on a conference before your colleagues. When will this conference be carried out? Cause i want to send you an e-mail with some feedback on your teaching style that might help you (or the opposite), so let me know the deadline. --V.konushliev (talk) 09:29, 28 May 2008 (UTC)

 * Hi Vladimir! Thank you for your willingness for contribution and giving me the so valuable feedback that I need. Frankly, I was surprised by your insertion since the term has passed over and the most of my students (including you:) are already rated. I know from my experience that, as a rule, students (even the best of them) loose interest in the subject after passing the examination. But obviously you are not one of them:)

 * Your remark sounds intriguing and I am eager to find out what you will send me as a feedback; I can only guess now. As for stories about the "Wikibooks student open project" that you, your colleagues and I, all together, have realized this term, I have started for discussion two Circuit idea stories:

 * Inducing Creativity in Students by Involving Them in Wikibooks - a general story,
 * Involving Students from Technical University of Sofia in Circuit Idea Wikibook - a concrete teacher's story.

 * As I have already said to you, I intend to present a paper version of the second story at the conference COMPUTER SCIENCE' 2008 that will be conducted during 18–19 September 2008 in Kavala, Greece. My idea is simple - to tell how I have managed to make students reason by involving them in Wikibooks. In this connection, I have a suggestion to you.

 * Why don't we (a teacher and a student) write this paper together? I will expose my teacher's viewpoint and you will show your student's viewpoint at the conducted web experiment. We might begin writing and developing the paper first on the talk page; then, we may use these drafts to create the main page and finally - the very paper. What do you think about my invitation? [mailto:cyril@circuit-fantasi.com Email] or call me to know more about the conference. Regards, Circuit-fantasist (talk) 19:05, 28 May 2008 (UTC)

Resources
Reinventing constant current source reveals the philosophy behind constant current source Understanding the simple BJT current source

Lab4: Op-amp circuits with parallel negative feedback
Tuesday, April 22, 2008, 10.30 h

Analogies
Driving: keeping up a constant speed, direction, temperature, volume... More negative feedback analogies: studying, teaching, keeping up a room temperature (body weight, mental equilibrium...) Thermostat control is a very popular example for using the negative feedback. When the temperature reaches certain value the heating (or the cooling) is switched on/off and soon we have again the temperature we want (Tencho65). In all these cases we do all that is possible to realize our goals, to move toward the goal...

Structure (block diagram)
So, the simplest negative feedback follower consists of only three components: power (energy) source E, regulating element R and a subtractor (-). Negative feedback connects the system output (inverted) with the system input. In response to some disturbance "attacking" the system, the negative feedback tends to re-establish equilibrium again. We can already draw a pretty block diagram. Tencho65

Operation
This humble device operates according to a simple algorithm: if X > Y, then increase Y; if X < Y, decrease Y; if X = Y, do nothing. As a result, always X = Y. So, this is an "active copying" principle and this device is an "active follower". This "algorithm" is so simple that humble devices (tubes, transistors, op-amps...) having no any intellect can perform it.

Advantages
Why do we make followers in this odd way? What are the advantages of this "negative feedback" approach?

What is op-amp?
How let's say some words about the main component of a negative feedback system - the operational amplifier (op-amp).

Inputs. Grounded voltage source... What is single-ended input? Floating voltage source... What is differential input? Why do we need a differential input? Input resistance... Do input currents flow? How does a non-inverting input behave? How does an inverting input behave? Can we use an op-amp with a differential input as an op-amp with single-ended (inverting or non-inverting) input? What do we do in these cases?

Output. How the op-amp output is made? What is the idea of a complementary, push-pull emitter follower? Output resistance...

Supplying. The idea of bipolar (split) supply (+12 V and -12 V here)... Why do we need a bipolar supply? Where currents flow? We can imagine the output part of the op-amp consists of two parts - a positive and a negative. Each of them works when its output voltage has the according polarity. By the way, is it possible to supply the op-amp with only one (e.g., positive) voltage and, at the same time, to obtain the opposite (negative) output voltage? And can the op-amp output voltage exceed the supply voltage? Maybe, it would be possible, if there were capacitive or inductive differentiating circuits inside the op-amp... But (for now) an op-amp contains only resistive and active components:(

Gain. Typical value is A > 200000. It seems too high. Can we manage to utilize all this gain? What is the maximum input voltage to keep the op-amp in the active region (assume 10 V maximum output voltage)? Can we use a bare op-amp as an amplifier? Or we can use it as another useful device having analog inputs and discrete output (write its name here)? We may conclude: If we use the op-amp as an amplifier, the voltage difference between its inputs is zero. But if we use it as a comparator, the input voltage might be whatever.

Transfer characteristic. Microlab can help us to obtain this curve on the screen. There is no time in this graphical presentation; there is only input and output quantities. We might discern three regions on this curve: negative saturation (large), active region (narrow) and positive saturation (large).

Generalization. What does the op-amp actually do? A possible answer is: an op-amp converts the steady power supply into varying voltage source; it acts as a voltage-controlled voltage source.

Passive electric follower

Now, we have only to convey this powerful idea from real life to electronics. Well, let's begin.

VIN will represent X in our electric follower; accordingly, VOUT will represent Y. But let's first persuade ourselves what is the use of building such an active follower instead a "passive" one.

What is the simplest voltage follower? Of course, a piece of wire can act as a humle voltage follower. It works perfectly, if there is no load (there is no current flowing). Only, is it still a follower, if we connect a big load at the end of the wire (especially, if it is a thin and long wire)? And imagine what happens, if the load and wire resistances vary... For example, the wire length can vary...

Another nasty problem of the passive voltage follower is that the load consumes energy from the input voltage source.; so, it droops when loaded.

Op-amp negative feedback inverter
What does the parallel inverter do? First,we use the resistive parallel amplifier.We use this component for comparing Uin and Uout voltages.It is the system with a negative feedback.There are two resistors wich are used for comparing voltages. If R1-R2=0 then Uout =Uin,but if R1 is not equal to R2 then the amplifier receives the difference between Vin and Vout on its input. And also if Vin is PLUS and Vout is MINUS then there is a "virtual ground". Uout/Uin=-R2/R1 --78.90.51.95 (talk) 15:36, 19 May 2008 (UTC)galina spasova

Building the circuit on the whiteboard

No, the bare wire is not a perfect follower in all the cases; so, it is worth the trouble to build an active negative feedback follower... Let's see how the students from group 65a, 66a and 67a have build such a follower by using an op-amp with differential input.

First, we connect a power supply - a voltage source V representing the power source E from the block diagram. We assume a bipolar input voltage; so, we get a bipolar (split) power supply. Then, we connect an op-amp OA acting as the regulating element R. Finally, we need a voltage subtractor to make the op-amp compare its output voltage VOUT with the input voltage VIN. Wh at is the simplest voltage subtractor? Of course, this is the bare loop (a piece of wire) according to Kirchhoff's voltage law (KVL). In other words, we have to connect the two voltage sources in series and in opposite directions (+ -, - +) traversing the loop, in order to subtract their voltages. Then, we have to cut the loop and to feed the op-amp input by the voltage difference.

But here we have a big problem: our op-amp has not a differential input; it has a single-ended input. How do we solve this problem?

It's time to remember the famous Ohm's experiment that we have conducted in our laboratory during Lab 2. See at the end of the page where we have invented the so useful parallel voltage summer (subtractor). Eureka! We can use it as a subtractor with single-ended inputs in our inverting circuit! Let's do it.

In practice, we usually connect separate resistors; thus we obtain the classic circuit diagram of the inverting amplifier. We have already known what the transfer ratio is:

$$\frac{Vout}{Vin}= - \frac{R2}{R1}$$

Investigating the circuit by Microlab

Explaining the circuit operation
(please, do it in a human-friendly manner!)

We are human beings, not computers... It seems strange but, in order to understand what the abstract op-amp really does in this circuit, we have to think of the op-amp as a "slow-thinking" device, not as a fast, non-inertial, instant device... From this human viewpoint, the op-amp compares continuously its output voltage VOUT with the input voltage VIN and changes VOUT in the right direction so that to keep almost zero difference VOUT - VIN = 0. It does exactly the same what we, human beings, were doing in all the analogies above.

Where currents flow in this circuit? Draw them with whole loops in the two cases - at a positive and a negative input voltage. Remember: a current always arrives at the point from where it has gone. Another tip: in the two cases (at positive and negative input voltage) the load current will flow through different power supplies (accordingly, through the positive and negative voltage sources). Imagine also the complementary output emitter follower inside the op-amp: the upper n-p-n transistor will "blows" the output current when the op-amp "wants" to produce a positive voltage and the lower p-n-p transistor will "sucks" the output current when the op-amp "wants" to produce a negative voltage.

Disturbing the negative feedback inverter
Let's now make difficult the op-amp's action. How can we disturb it?

Explain here the unique property of all the negative feedback system to overcome various disturbances... See also how the "magicians" from group 68b have made almost ideal components by applying a parallel NFB. Circuit-fantasist (talk) 13:17, 28 April 2008 (UTC)

Converting the NFB follower into an amplifier
We have already seen how an op-amp overcomes various disturbances. Can we use its reaction to the disturbance as an output? Is this the idea needed to convert the inverter (K = -1) into an amplifier (K > -1)? Have you seen this phenomenon in your day's routine?

Resources
Operational amplifier

Differential and Single-Ended Inputs

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title: Circuit Idea/Group 65b


text:
Circuit Idea/Group 67b

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67b Group Student Page

We are students from Faculty of Computer Systems, Technical University of Sofia. Our 67 group is divided into two sub-groups; we constitute the first 67b one. Here are our names:

Dafar Shaban, Nikola Lambev, Kalina Domuschieva, Valeri Kirilov, Reneta Stoycheva, Sofiya Shtarbova, Kiril Rusev, Raya Yunakova,Ina Tacheva, Dimitar Mindalov (add your name here)

Lab 2: Computer-based Ohm's experiment
Tuesday, March 25, 2008, 16.45 h

In this lab exercise we tried to "invent" new analog devices using our knowledges for the famous Ohm's experiment. In order to see the graphics of our "new" devices, we used Microlab - PC Apple2 connected to 4 DACs and 4 ADCs. We made a couple of experiments and these are the schemes we were analysing. First the voltage source is connected only to the one end of the resistor and we measure the potential along the resistive layer(1st picture). Thus we make a linear transference-to-voltage converter.

In order to carry out Ohm's experiment, we needed some kind of resistive wire. Our teacher gave us a heater wire, so we start experimenting with it. When we connected it with conductors, power supply, voltmeter and an ammeter we start measuring its resistance. We were also using two kinds of voltmeters and ammeters - old-fashioned movement ones and new digital devices. After our successes in building and connecting the scheme, we were very excited to find it actually worked. The images around show our scheme and progress.

When there are two voltage sources, and both of them are with the same polarity, we have a parallel voltage summer.Here VOUT = r1/(r1+r2).VIN1 + r2/(r1 + r2).VIN1.

If we have voltages with different polarity and VIN1 and VIN2 are selected so that VOUT=0 (point known as "virtual ground") we have a comparing device,like in the scheme in the third picture:VIN2/VIN1 = -(r2/r1).To keep Vout = 0 we can use operational amplifier(down).Here I1.R1=(VIN/R1).R2 or VOUT/VIN=-R2/R1.

This lab report is made by Reneta Stoycheva, Sofiya Shtarbova, Ina Tacheva and Valeri Kirilov, Raya Yunakova,.

Lab 3: Transistor circuits ("inventing" a BJT current mirror)
Tuesday, April 08, 2008, 16.45 h (extracted from the lab records made by a solid-state recorder) Circuit-fantasist 05:43, 3 June 2008 (UTC)

Introduction
This Tuesday, three student groups in all are carrying out experiments in this laboratory dedicated to transistor circuits producing constant current. First, your colleagues from Group 65b were building and investigating the simplest transistor current source. The students from the next Group 66b continued their work trying to transform the simplest transistor current source into a BJT current mirror circuit. But they did not manage to do it since an accident happened at the end of the lab - the main transistor began to smoke and they had to find out why. The honor fell to your Group 67b to finish their work...

What the transistor is

We have to clarify some philosophical questions in the beginning of this lab. What is a transistor? What does it do? What notion do you have about the transistor? Is it a supernatural and "divine" device as they frequently present it and, for this purpose, they veil it by sophisticated equations and analyses? Or it is something simple, clear and intuitive that everyone (even a child) can understand?

A student: A transistor consists of two n-p junctions... But there are transistors without junctions (e.g., a MOS transistor does not contain junctions in the input part). Let's say it in a more general way. Another student: The transistor can amplify... But what does this mean? The student: If we apply an input signal, a large signal appears at the output. But this is impossible; there is no amplification in nature. We cannot amplify energy. I would like to say more precise that there is not amplification. We cannot obtain more energy from less energy; it is just impossible.

Then what does a transistor actually do? Well, look at the last picture (on the left) of your colleagues from the previous Group 66b. As you can see, we have drawn arrows going out of the transistor. They represent the heat that the transistor was dissipating since they were made a short connection in the collector circuit. So, I ask you again, "What does the transistor do? As you can see, we have broken the three-terminal transistor into two 2-terminal devices and now we discuss the one of them - the output collector-emitter "device". Here is this "device", I have held it. It has two leads and it is connected by these two leads in an electrical circuit... I ask you again, "What does it do in this circuit?", "What does the transistor do with its output part?"

A student: The transistor behaves as a resistor. Yes, it is exactly what I would like to hear - "resistor" in a broad sense of this word. Excepting the most popular sources, they usually do not explain the transistor in this manner; they refrain from giving such intuitive explanations (maybe, because a transistor behaves as a non-linear instead as an ohmic resistor). But yet, this is the simplest and the most powerful viewpoint at the transistor. So, if someone ask you what a transistor do or can do you can answer: the only thing that a transistor can do is to "insert" a resistance in the circuit where it is connected, to dissipate power, to throw out it in the space and, in this way, to impede the current, to regulate the load voltage, current and power. A transistor does not do anything else than this varying resistor (a rheostat) in front of us does. Of course, there is also a capacitance and an inductance but they are parasitic and negligible.

What are the differences between the transistor and the humble rheostat? First, a transistor is an electrically controlled resistor while the rheostat is a mechanically controlled one. There are also light-controlled resistors - photoresistors, sound-controlled resistors - carbon microphones, temperature-controlled resistors - thermoresistors, etc.) For example, connect this photoresistor to an ohmmeter and light up or shade it; thus you can measure the minimum (4 kΩ) and maximum (300 kΩ) resistance of this light-controlled resistor. In the same way we control the resistance of a transistor, only electrically.

Second, as we have mentioned above, the transistor is a non-linear current-stable resistor while the rheostat is an ohmic one. When they say "resistor" we implicitly understand "ohmic resistor"; so, the transistor is a resistor in a broad sense of the word. Well, let's draw the two kinds of characteristics. When we vary the resistance of an ohmic resistor, its IV characteristic inclines; when we vary the base-emitter voltage of a BJ transistor, its output characteristic moves vertically remaining parallel to itself.

A transistor acting as a current-stable resistor
Our final purpose is to create a current source controlled by another current. So, we have to understand how a transistor can keep up a constant current. We were considering this topic more consistently with your colleagues from group 65b a few hours ago. We began solving the problem "producing a constant current" by creating the simplest passive current source (a voltage source and a resistor connected in series). Then we ascertained how imperfect it is (if the load varies, the current varies as well). So, we began reasoning how to make a perfect constant current source. We remembered how they have solved this problem in electricity - by increasing the voltage and the resistance up to infinity so that to suppress the load influence. Only, we noted that this approach is imperfect since the resistor dissipated plenty of energy. Then, we moved in the area of electronics where this problem is solved more cleverly. Can you guess what the idea was?

Well, you have a circuit consisting of three connected in series elements: a voltage source, a current-setting resistor R and a load with varying resistance RL. As the load resistance varies, what do we have to do, in order to keep up a constant current? What is the clever idea? A student: ...transistor, op-amp... Maybe, but these are very concrete solutions; we are still at "idea" level. Another student: ...feedback... But we do not still know what a feedback is.

Let's continue reasoning in human friendly manner... For example, if the load resistance increases and, as a result, the current lowers, what do we do to restore the current? Students: ...we have to lower the current-setting resistor R! And vice versa, if RL decreases... Students: ...we have to increase R! It turns out a strange resistor stays at this place that have the unique property to change its resistance depending on the current flowing through it. The resistor R is not an ordinary "static" resistor; it is a kind of varying, dynamic resistor. It is still ohmic but varying ohmic resistor. They name such odd elements current-stable resistors.

We can see this dynamization idea everywhere in our human routine. Some people have a "static" behavior; they do not react to various interventions. Other people are more flexible, adaptable, dynamic; they win.

We begin looking for such an element. In electricity, a bulb has a similar behavior (there were so called barretters - thermistors having positive temperature coefficient of resistivity). In electronics, we find out that transistors (both BJT and FET) have such a behavior. See the picture where your colleagues have visualized how the transistor behaves. What is the idea of such a grapnical presentation? They have presented the output part of the circuit as two 2-terminal elements connected to each other - a real source and a load (according to the Thevenin's model, we can present every circuit in this manner). The real source is a compound one; it consists of two 2-terminal elements - an ideal voltage source VCC having a vertical IV characteristic and an internal resistance RL having an IV characteristic that is inclined to the right and begins from the coordinate origin. The difference between the two characteristics represents the effective IV characteristic of the compound real source. As you can see, it is shifted to the right by the magnitude of VCC and it is inclined to the left according to RL. It might seem strange but in this presentation the transistor plays the role of a load while RL plays the role of an internal source resistance?!? Do you agree to this viewpoint?

As you can see, the output transistor characteristic is similar to the characteristic of a constant current source. The crossing point of the two characteristics is named operating point; it represents the present voltage across and the current flowing through the two elements.

Varying the load resistance
Let's now begin reasoning what happens when we begin varying RL. If we decrease it, the source curve rises and v.v., if we increase the resistance, the source curve lies down. And, as they usually say in classical electronics courses, since the transistor's output characteristic is almost horizontal the operating point moves almost horizontally along it; the current variations are insignificant. This explanation works of a sort but we would like to know how the transistor actually does this magic; how its output characteristic is obtained. But nobody answers these questions...

See the second picture on the right above. What is shown there? We can see another line beginning from the coordinate origin. What is this line? What does it represent? As you probably quess it represents the present ohmic transistor's resistance. Remember how we presented the transistor above - as a varying resistor having a present ohmic resistance RT = VCE/IC. And if you begin decreasing RL, this "resistor" begins increasing its resistance and v.v. So, it behaves as a varying ohmic resistor. It is not a static but a dynamic, a self-changing resistor and it does it in such a way so that the crossing (operating) point moves along an almost horizontal line - the output characteristic. This line represents the trajectory of the operating point; it is an unreal, an imaginary, an artificial curve. Only the two crossing lines are real.

This explanation was an attempt to explain what a dynamic (non-linear) resistor is. So, let's draw a conclusion: a dynamic (non-linear) resistor is actually a "self-varying" ohmic resistor. The current flowing through it or the voltage across it changes its present resistance.

Other elements (e.g., diodes) have the opposite characteristic. When we vary RL, such an element would change its present resistance in the same direction so that to keep a constant voltage. So, they behave as voltage-stable elements.

Varying the supply voltage
According to the explanations above, if we begin varying the supply voltage, the current would stay constant: if we increase the voltage, the transistor will increase its present resistance so that the ratio I = VCC/RT to stay constant as well and v.v. But it does not stay constant. Why? What is wrong in this arrangement? A student: ...the input voltage varies as well... Yes, that is right. Your colleague feels the things very well... Obviously, the problem is that we have taken the input (reference) voltage from the same voltage source instead from a separate one. This is incorrect and the result is obvious: when we vary the supply voltage, the "reference" voltage varies as well.

It turns out that in practice, there is no separate source or, what occurs more frequently, we prefer to use a common source (for example, a car has only one battery supplying a lot of electric and electronic devices). Obviously, we have to arrange things so that when the supply voltage varies, the input (reference) base-emitter voltage does not change.

Building the simplest transistor current source
Look at the picture below to see how we began solving this problem with your colleagues from Group 66b. What is the problem? What do we want to keep constant? We want to keep up a steady base-emitter voltage even if the supply voltage varies because the horizontal output BJT characteristic is at given base-emitter voltage. So far, a voltage divider produces this voltage; but a voltage divider is a proportional device. Then, what kind of device do we need?

Looking at a new circuit we discern more familiar "sub-devices"; here, we identify the well-known voltage divider. Only, we want to make it does not change its output voltage when its input voltage varyes. In other words, we have solved the problem keeping up a steady current; now, we have to solve the problem keeping up a steady voltage. Let's generalize these thoughts.

The simplest transistor current source exploits the inherent ability of the transistor to stabilize the current when the base-emitter voltage is fixed. What do we need to build the simplest transistor current source according to this idea? First, we have to set a constant voltage to the base-emitter junction; so, we need a constant voltage source. Your colleagues from group 65b have made it by a voltage divider. Note that there is also a protecting resistor (3.9 kΩ) connected in series with the potentiometer; it limits the base current (up to 3 mA) in a case when someone moves the slider to the end of the rheostat. This humble resistive circuit allows us to set some input voltage and, in this way, to move the output characteristic to a given position. Thus we make the transistor pass the desired current through the load and keep it constant according to the explanations above. The transistor opposes to our intervention by changing its present resistance, by a dynamic resistance connected in series to the load. The total resistance and the supply voltage stay constant; as a result, the current stays constant as well. In this way, in electronics we are smart enough to make perfect current sources.

A true diode sets the input current
So, we need a voltage-stable element, we need a diode to obtain the needed voltage drop. How do we connect it? A student: it has to be forward-biased... Before we had to adjust the voltage; now it is axactly as much as we need. More precisely speaking, we will adjust it by changing the current flowing through it; this voltage will vary slightly when we change the current significantly.

Your colleagues from Group 66b have found the same solution in Tony Kuphaldt's page about current mirrors.

Replacing the true diode by a base-emitter transistor junction

But we need not only an output current; we need a mirror output current whose magnitude is equal to the input current. Thinking about the problem we realize the two elements have to have identical characteristics. As soon as the input behaves as a p-n junction don't we use another p-n junction to set the voltage? For this purpose, we may use the base-emitter junction of another transistor as such an element. As in the "diode" case above, there isn't need to adjust the reference voltages as we had to do that in the case of voltage divider. The technology of integrated circuit manufacturing allows to make the two elements absolutely identical.

So, the better solution is to connect the base-emitter junction of an identical transistor (leaving the collector no connected).

A problem appears

Only, a problem appears - the output transistor is saturated! Why? Let's see again the Tony Kuphaldt's page about current mirrors and try to find the answer of this question. Tony claims that the output current flowing through the load is equal to the input current flowing through the diode: "Current through resistor Rload is therefore a function of current set by the bias resistor, the two being nearly equal." He think the two output currents are equal because the two input base-emitter voltages are equal. But is it true? We have to prove this ascertion here...

What do you think, are the two currents equal? Obviously, the input voltages are equal as the two base-emitter junctions are connected in parallel. But does it mean the two output currents are equal? We can find out the current-setting diode diverts only "one" base current Ib = V/2Rbias and the corresponding collector current of T2 is β/2 times bigger - Ic = IL = β.V/2Rbias.

We can conclude that the "diode" current mirror acts as a current amplifier (IOUT > IIN) but not as a true current mirror (IOUT = IIN)!

Now let's remember the beginning of our exercise and clarify the role of the potentiometer by reazoning as follows. Imagine we connect two identical resistors - a base resistor Rb and a load resistor RL = Rb. As a result we get a current amplifier (Ic = βIb) instead the desired current mirror (Ic = Ib). Then, let's connect a second resistor (actually, a potentiometer) in parallel to the base-emitter junction to divert the excessive current from the base to the ground.

Well, let's continue developing the current mirror circuit...

A negative feedback transistor "diode" sets the input current
Thus we arrive at the powerful idea to connect the non-used collector to the transistor bases with the purpose to divert the excessive base current to the ground.

Drawing the diagram on the whiteboard

In this way, we have revealed the role of the input current-setting transistor T1; it take away the great amount -- (1 + β)Ib—from the input current and leaves only the small Ib for the output transistor T2. As a result, the input and the output currents are almost identical.

Eureka! We have "invented" the famous but never explained circuit of BJT current mirror! We have even disprove a widespread misconception about the simple BJT current mirror - the possibility to set the input current by a forward-biased diode or a base-emitter junction!

Investigating the circuit

Resources
How to Reverse Current Direction is another Circuit idea story about basic current mirror. Current mirrors is a popular exposition of the current mirror topic written by the well-known web author Tony Kuphaldt

Lab 4: Endowing circuits with memory
Tuesday, April 22, 2008, 16.45 h

In this exercise we are going to reinvent legendary circuits - flip-flops. First, we will reveal the general idea of memorizing; then, we will build an RS flip-flop by using NPN transistors and an op-amp flip-flop. In order to do this, we need to know what flip-flops can be used for and how we want our "invention" to work. I am sure that every student at the Technical University is familiar with these devices but since this book is meant to explain the idea of electronics to everyone who is interested I will provide some general information on the subject.

What a flip-flop is (a conventional viewpoint)

Flip-flops (FFs) are devices used in the digital field for a variety of purposes. When properly connected, flip-flops may be used to store data temporarily, to multiply or divide, to count operations, or to receive and transfer information. Every FF has two to five inputs depending on its type. What is common for all types of FFs is that they have two distinct outputs usually marked Q and /Q. They can either have a "0" state or "1" state and should always be complementary. This means that if the state of Q is "1" the /Q's state is "0" and vice versa. The RS flip-flop in particular is used to temporarily hold or store information until it is needed. A single RS FF will store one binary digit, either a 1 or a 0. It has two standard inputs - R, which stands for "reset" and sets the Q output in "0", and S, which stands for "set" and sets the Q output in "1" (Raya Yunakova, 67).

We can see on the picture above the inputs and the outputs but we are not able to understand how the flip-flop actually works. Our main goal in this exercise is to reveal what's in that "black box". Basically RS flip-flop is the simplest practical memory device based on NOR gates connected in a feedback configuration. Anyone in TU knows the truth table of that flip-flop so we are not going to bore you with that stuff. The general question is: How to make something "remember", "memorize"? If we find that answer, then we will know the exact mechanism of creating any kinds of flip-flops.(Reneta Stoycheva and Sofiya Shtarbova)

The basic idea behind memorizing: positive feedback
Describe here situations (analogies) derived from our human daily routine where someone (something) having no memory begins memorizing. Examples: a dog bitten its tail:), an enraged man working himself into a fury:), a snow avalanche, etc. Circuit-fantasist (talk) 16:14, 18 May 2008 (UTC)

Building a transistor switch

Here is where we start. We have a bipolar junction transistor, whose emitter is common to both the input and the output. The input is controlled by the transistor's base and its collector serves as the output. We control the input with the button marked with *. When the button is pressed the input circuit is closed and the transistor is active. When the button is not pressed the transistor is inactive and we can not get any output signal.

Making the transistor switch memorize

Structure. This is the normal working routine of a BJT. In our case however, this is not good enough since our goal is to "invent" a device which doesn't change its state when there is no input. But how? It is obvious that we need to add something to our circuit that will keep influencing the input (base) of the transistor. What if we get a second transistor and connect it to the first one like this?

The first transistor's output is connected to the second transistor's input (its base) whose output is connected to the first one's input. The collectors of both elements are connected to a constant voltage source through resistors. The emitters are grounded. (Raya Yunakova, 67)

Operation. How does our circuit operate? When we put the circuit into operation the transistor on the left is inactive. However, current which is high enough to activate the transistor on the right flows through resistor Rc1 (remember we've connected a voltage source). Its emitter-base junction is forward biased and therefore we have output which is equal to the ground potential. This output influences the first transistor's input but it is not high enough to activate the first element. We continue to have a logical "1" on its output which keeps the situation in our circuit exactly the same as it was before. And wasn't that what we wanted to happen in the first place?

It seems that we have completed our goal and we have made the transistor "remember"! Using this approach we can create almost any kind of memory device to serve our purposes. We have actually implemented a mechanism called "positive feedback". It is largely used in electronics to change the parameters of an amplifier like voltage gain, input and output impedance, stability and bandwidth.(Raya Yunakova, 67)

A problem: a voltage conflict
Describe here what the problem was and how we have solved it. Circuit-fantasist (talk) 17:29, 18 May 2008 (UTC)

Visualizing the operation by voltage diagram
Describe here what we have done. Circuit-fantasist (talk) 17:24, 18 May 2008 (UTC)

Making the op-amp Schmidt trigger memorize

More pictures

Left picture shows our first try to make the scheme which occurred to be incorrect :( After that with team work we managed to do it the right way.

This lab report is made by Reneta Stoycheva and Sofiya Shtarbova.

Updated by Raya Yunakova.

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license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Circuit Idea/Group 67b


text:
Talk:Editing Wikitext/Pictures/The Quick Course

I note from the history page and the resulting conflict that it created that a user has vandalised the entire page. All content was removed.

The page was restored from a backup in its original form.

Armchair (talk) 17:19, 2 April 2008 (UTC)


text: User talk:68.193.26.170

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title: User talk:216.61.101.247


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User talk:Madhumohan

Welcome, Madhumohan!

Come introduce yourself at the new users page. If you have any questions, you can ask there or contact me personally.--Whiteknight (Page) (Talk) 18:04, 2 April 2008 (UTC)

title: User talk:Madhumohan


text: User talk:Kyle 706

title: User talk:Kyle 706


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User:Dgroseth

 * My Editing Notes
 * My External Links
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 * w:Wikipedia:Cheatsheet
 * Editing_Wikipedia
 * Wikipedia:Help:Editing
 * Wikipedia:Help:Interwiki_linking

Pages, Projects and Portals

 * AppleScript_Programming
 * Celestia - Computer software

title: User:Dgroseth


text:
Fundamentals of Transportation/Queueing/Problem1

 Problem: Application of Single-Channel Undersaturated Infinite Queue Theory to Tollbooth Operation. Poisson Arrival, Negative Exponential Service Time
 * Arrival Rate = 500 vph,
 * Service Rate = 700 vph

Determine

 * Percent of Time operator will be free
 * Average queue size in system
 * Average wait time for vehicles that wait

Note: For operator to be free, vehicles must be 0

 * Solution

/Problems


text:
Fundamentals of Transportation/Queueing/Solution1

 Problem: Application of Single-Channel Undersaturated Infinite Queue Theory to Tollbooth Operation. Poisson Arrival, Negative Exponential Service Time
 * Arrival Rate = 500 vph,
 * Service Rate = 700 vph

Determine

 * Percent of Time operator will be free
 * Average queue size in system
 * Average wait time for vehicles that wait

Note: For operator to be free, vehicles must be 0

 Solution: $$ \rho = \frac{\lambda }{\mu } = \left( {\frac} \right) = 0.714 \,\!$$

$$ P\left( n \right) = \rho ^n \left( {1 - \rho } \right) = \left( {0.714} \right)^0 \left( {1 - 0.714} \right) = 28.6\% \,\!$$

$$ Q = \frac = \frac = 2.5 \,\!$$

$$ w = \frac{\lambda } = \frac = 0.003571hours = 12.8571\sec \,\!$$

$$Q= \lambda w =500*0.00357=1.785\,\!$$

$$ ServiceTime = \frac{1}{\mu } = \frac{1} = 0.001429\ hours = 5.142\sec \,\!$$

$$ t = \frac{1} = \frac{1} = 0.005\ hours = 18{\rm{seconds}} \,\!$$

/Solutions


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Fundamentals of Transportation/Queueing/Problem2

 * Solution

/Problems


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Fundamentals of Transportation/Queueing/Solution2

/Solutions


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Fundamentals of Transportation/Queueing/Problem3

 * Solution

/Problems


text: User talk:165.138.232.2

title: User talk:165.138.232.2


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Fundamentals of Transportation/Queueing/Solution3

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Category:Book:Fundamentals of Transportation/Problems

Problems in the  book.


text:
Proteomics/Proteomics and Drug Discovery/Protein Aggregation

Chapter written by: Ashlee Benjamin and Rhea Sanchez

Contact amb4541@rit.edu or ris6859@rit.edu for contributions

This Section:

Introduction to Protein Aggregation
Protein Aggregation has become a topic of growing interest in recent years, especially in pharmaceutical research. Protein aggregation is often encountered during late research stages or manufacturing of biopharma. The presence of aggregates often leads to an immune response to reject the product, and can sometimes interfere with the body’s vital functions. Aggregation causes several serious diseases such as Alzheimer’s and Type II Diabetes. Antibodies or other small molecules that are developed for research can sometimes aggregate when over-expressed costing companies’ time and money. Many companies are taking advantage of bioinformatics techniques to predict aggregation. Such approaches are just predictions, but are still very useful for analyses during research and development.

Aggregation and Amyloid Fibrils
Protein aggregation can be described as the fibrilization or formation of insoluble structures from completely or partially unfolded peptides. A peptide can bind to itself or to other proteins in the cell in an unnatural way. This often occurs when proteins are over-expressed. There is more than one type of protein aggregation; however the best-studied type is amyloid fibrilization. Amyloid fibrils are primarily composed of beta sheets and the main chain dominates the protein’s structure. These fibrils are highly organized structures stabilized by hydrogen bonds. Amyloid fibrils are usually 10nm in diameter and consist of approximately 2-6 “protofibrils” twisted around one another. Protofibrils are the precursors to amyloid fibrils and are the most toxic to the cell. The protofibrils are made up of a cross-beta structure. In a cross-beta structure, beta sheets are assembled from beta strands that run perpendicular to the fibrils. An image of an amyloid fibrils is shown in Figure 1.

Figure 1: Small Amyloid Fibril

The native state of a protein that yields proper function is usually the most energetically favorable form of the protein at environmental conditions. Protein aggregation occurs when inter-chain contacts with other parts of that protein or other proteins. Because of this, these aggregates are thought to be as energetically favorable or more energetically favorable than the native state. There are several diseases linked to protein aggregation. This discussion will examine Alzheimer's disease and Transthyretin related diseases.

Different Types of Aggregates
Many different types of aggregation can occur. They are classified based on types of interactions and solubility. Soluble aggregates are invisible particles and cannot be removed with a filter. Insoluble aggregates can be removed by filtration and are often visible to the human eye. Both types of aggregates cause problems in biopharma development. Covalent aggregates arise from the formation of a covalent bond between multiple monomers of a given peptide. Disulfide bond formation of free thiols is a common mechanism for covalent aggregation. Oxidation of tyrosine residues can lead to formation of bityrosine which often results in aggregation. Reversible protein aggregation typically results from weaker protein interactions. The reversibility of this type of aggregation can change when environmental factors such as protein concentration, salt concentration, or pH are varied.

Advancements in Understanding of Protein Folding
In order for us to understand protein aggregation, we need to understand more about protein folding in general. It would not be feasible to understand and account for all factors involved in aggregation when developing a prediction tool. However, the more that is understood about such factors, the better a prediction model may be. Advances have been made in understanding the protein folding process. These advances can help us to understand how the process "goes wrong" and results in aggregation. Figure 2 shows an image of an unfolded peptide chain and its corresponding native folded state peptide.

Figure 2: Protein Folding

The general folding process of a protein can be described as a “stochastic search” for the native state. The native state is usually a stable, low energy conformation. More specifically, smaller proteins fold by a nucleation-condensation mechanism, and larger proteins fold in modules or smaller parts. Nucleation-condensation is the formation of a folding nucleus, about which the rest of the structure condenses or collapses. As more is understood about the folding process, the less need there will be for prediction models such as these. However, in the mean time such models can be created to increase the understanding of aggregation and perhaps protein folding in general.

Factors Affecting Aggregation
It has been suggested that a few general principles or protein characteristics may govern aggregation and fibrilization. Although it has been shown that any generic protein under suitable external conditions has the ability to form aggregates resembling amyloid fibrils, aggregation depends on characteristics of the sequence as well. Aside from external conditions such as temperature and characteristics of the sequence itself, characteristics of peptide monomers may not give insight into the aggregation propensity of their polymer versions because interpeptide chain interactions may cause conformational changes. Regardless of all factors involved, much is known about what factors can be utilized to predict aggregation. Known intrinsic properties that can effect aggregation include charge, hydrophobicity, hydrophobic/hydrophilic patterns, and secondary structure propensities.

Hydrophobic surfaces that become exposed upon denaturation are highly vulnerable to promiscuous interactions that can lead to protein aggregation. These surfaces act as "sticky" spots and try to interact with whatever they can. High helix secondary structure propensities significantly decrease the probability of aggregation, whereas high beta sheet propensities significantly increase aggregation. Charged residues have also been shown to decrease aggregation. Extrinsic factors such as ionic strength, temperature, pH, protein concentration, chaperones, quality control, and pressure have been shown to have an effect of aggregation. The presence of some ligands and ions, can increase aggregation. Stress applied to the protein can result in denaturation which can lead to subsequent aggregation. Some of these stresses include freezing, exposure to air, or interactions with metal surfaces – many of which are involved in development of biopharma. Because of the involvement of these stresses in drug development, the more we understand aggregation, the better control we have in drug development. Physicochemical properties such as polar or non-polar accessible surface areas, dipole moment, and aromatic residues are also important. It has been shown that inward pointing charged residues and fewer dangling hydrogen bonds will decrease the amount of protein aggregation. Utilizing all of this knowledge, we can determine how likely a given protein is to aggregate. These factors can, and have been utilized to predict protein aggregation.

When a protein is being expressed, drastic increases in protein concentration can lead to intracellular aggregation. This is either due to interactions of unfolded protein molecules or poor recognition of the nascent chain by molecular chaperones.

Of course, there is still the problem of the natural means by which an organism prevents aggregation. Chaperones proteins assist in the folding of proteins. Gatekeeper residues may also help prevent aggregation. Extrinsic factors such as these are nearly impossible to utilize when creating a prediction model.

Alzheimer’s Disease
Alzheimer's disease is a neurodegenerative disease caused by the aggregation of the beta-amyloid peptide. Beta–amyloid peptide is prone to aggregation in the human body as well as in experimental conditions. The native state of this peptide is relatively unstable leading to aggregation. Aggregation of this peptide in the brain leads to the formation of aggregate plaques. Figure 3 shows these plaques in the cerebral cortex of an Alzheimer’s patient.

Figure 3: Beta-amyloid Plaques

Beta-amyloid monomers are thought to form a hexagonal arrangement, and then proceed to form amyloid fibrils. The exact structure of the intermediate steps has not been determined.

TTR-related Diseases
Transthyretin, or TTR, is a protein that when aggregated causes senile systemic amyloidosis, familial amyloidotic neuropathy, and some other rare neurodegenerative diseases. Transthyretin is found in the Central nervous system. TTR is a serum protein in the cerebrospinal fluid and carries thyroxine, a thyroid hormone. In the blood, albumin usually carries out this function, but albumin is not present in cerebrospinal fluid. Many of the TTR diseases have been shown to be caused by point mutations in the peptide sequence. These mutations change the intrinsic properties of the sequence increasing the propensity for aggregation. TTR is a tetramer and aggregation begins when the tetramer dissociates. After the separation, the peptide chains make energetically favorable contacts that favor fibrilization. From this point, aggregation of the TTR monomers proceeds rapidly. The intermediate structures have not been determined with TTR aggregation.

Created Prediction Models
In an effort to better understand and predict protein aggregation, several research groups have been developing predictive models based on different principles.

The prediction method created by Tartaglia et al. is based on physicochemical properties. The method is an ab initio prediction method based on polar and non-polar accessible surface areas, dipole moment, charge, aromatic residues, and beta-sheet propensity. The prediction gives an aggregation rate and “amyloid spectrum.” This method scans each sequence with a determined window size, moving the window one amino acid at a time. Each stretch is ranked using the aggregation propensity. The positions of the three highest ranking stretches are stored. This method yielded an impressive 95% correlation with experimental aggregation rates.

The AGGRESCAN method is based on experimentally derived aggregation propensities of individual amino acids. A sliding window is used to calculate the average aggregation propensity of the window and the value is assigned to the center amino acid. This gives a profile of “hot spots” for aggregation. The method gives a graphical representation of the aggregation profile including hot spots, peak areas, and aggregation values.

The TANGO method is a statistical mechanisms algorithm that identifies regions of a sequence that are prone to aggregation. The method considers several different types of intrinsic structural tendencies of the polypeptide sequence and determines which is the most likely conformation for a sliding window of varying length. This method was between 87-92% correct for the prediction of aggregation in general but like most aggregation prediction tools does not distinguish amyloid formation from amorphous aggregation. .

The method created by Pawar et al. uses intrinsic properties of a sequence to find aggregation prone and aggregation susceptible areas. The method utilizes alpha-helix propensity, beta-sheet propensity, charge, hydrophobicity, and hydrophobic/hydrophilic patterns to predict aggregation prone and aggregation susceptible areas of a sequence. An overall aggregation propensity, z-score for propensity, aggregation rate, and rate or propensity profile can be calculated with this method. When calculating a profile, each amino acid is mutated to all other possibilities and the rate or propensity is calculated. The maximum, minimum and wild type values are stored and these profiles are smoothed over a sliding window of 7 amino acids.

Can the sequence characteristics of a peptide provide insights into the sites that harbor amyloid tendencies? Known diseases associated with aggregation give us a research basis upon which to start pattern searching. From what has been seen with bioinformatics approaches in this area so far, sequence characteristics do tell us a lot about the aggregation of a protein. However, no perfect model has been built, so it is clear that we do not understand every aspect of protein aggregation. The hope is to understand protein aggregation and to learn how to prevent it.


text:
Category:Book:Fundamentals of Transportation/Solutions

Solutions to Problems in the  book.

/Problems


text:
Fundamentals of Transportation/Conclusions

Transportation is multi-modal, multi-disciplinary field that requires the efforts of people from a spectrum of backgrounds. Planners, engineers and policy makers are the primary groups, but architects, economists, and operations researchers serve in roles that benefit the industry. In order for an idea to become a road, it must go through several planning and design stages. This section serves as a conclusion for this wikibook as well as a summary of the building process for a roadway.

Connecting Places

 * Planning
 * Assessing Needs: Testing Alternatives (Hypotheses)
 * Predicting Demand
 * Trip Generation
 * Trip Distribution
 * Mode Choice
 * Route Assignment

Determining Road Capacity (Width)

 * Level of service

 * Design to satisfy standard
 * Understand implications of traffic (queues, shockwaves, congestion)

Determining Road Alignment (Length)

 * Properties of drivers, vehicles, roadway
 * Maximum grade associated with speed, vehicle type
 * Stopping sight distance
 * Vertical alignment (sags & crests)
 * Horizontal alignment

Determining Road Strength (Depth)

 * Given load on the road, how long can the road hold up.
 * Design pavement depth to satisfy predicted traffic.

Putting it together
Planning determines origin/destination demand by vehicle type … feeds into Level of Service
 * LOS feeds into in-depth traffic analysis and determines number of lanes
 * Truck demand determines maximum grade
 * Stopping sight distance determines horizontal and vertical curvatures.
 * Truck demand determines pavement thickness

Implications
Fraction of demand (trucks) is determining design characteristics (grade, depth)

Fraction of demand (peak hour traffic) is determining width.

1. Financing should consider this

2. Design should consider this. Maybe cars and trucks should have separate routes. (car-only highways would be cheaper, separation would be safer).

3. We don’t ask one building to serve all needs, why should one road?

Thought Question
How does an idea become a road? Explain how an idea becomes a road. Illustrate your explanation with a consistent set of examples for all of the major steps of analysis that are required (i.e. the output of one example should be the input to the next example).


title: User:ChessCreator/Invite1


text:
Fundamentals of Transportation/Sight Distance

Sight Distance is a length of road surface which a particular driver can see with an acceptable level of clarity. Sight distance plays an important role in geometric highway design because it establishes an acceptable design speed, based on a driver's ability to visually identify and stop for a particular, unforeseen roadway hazard or pass a slower vehicle without being in conflict with opposing traffic. As velocities on a roadway are increased, the design must be catered to allowing additional viewing distances to allow for adequate time to stop. The two types of sight distance are (1) stopping sight distance and (2) passing sight distance.

Stopping Sight Distance

Stopping Sight Distance (SSD) is the viewable distance required for a driver to see so that he or she can make a complete stop in the event of an unforeseen hazard. SSD is made up of two components: (1) Braking Distance and (2) Perception-Reaction Time.

For highway design, analysis of braking is simplified by assuming that deceleration is caused by the resisting force of friction against skidding tires. This is applicable to both an uphill or a downhill situation. A vehicle can be modeled as an object with mass $$m$$ sliding on a surface inclined at angle $$\theta$$.

While the force of gravity pulls the vehicle down, the force of friction resists that movement. The forces acting this vehicle can be simplified to:

$$ F = W\left( {\sin \left( \theta \right) - f\cos \left( \theta  \right)} \right) \,\!$$

where
 * $$W = mg\,\!$$ = object’s weight,
 * $$f \,\!$$ = coefficient of friction.

Using Newton’s second law we can conclude then that the acceleration ($$a$$) of the object is

$$ a = g\left( {\sin \left( \theta \right) - f\cos \left( \theta  \right)} \right) \,\!$$

Using our basic equations to solve for braking distance ($$d_b\,\!$$) in terms of initial speed ($$v_i\,\!$$) and ending speed ($$v_e\,\!$$) gives

$$ d_b = \frac \,\!$$

and substituting for the acceleration yields

$$ d_b = \frac \,\!$$

For angles commonly encountered on roads, $$\cos(\theta)\approx1$$ and $$\sin(\theta)\approx \tan(\theta)=G$$, where $$G$$ is called the road’s grade. This gives

$$ d_b = \frac \,\!$$

Using simply the braking formula assumes that a driver reacts instantaneously to a hazard. However, there is an inherent delay between the time a driver identifies a hazard and when he or she mentally determines an appropriate reaction. This amount of time is called perception-reaction time. For a vehicle in motion, this inherent delay translates to a distance covered in the meanwhile. This extra distance must be accounted for.

For a vehicle traveling at a constant rate, distance $$d_r$$ covered by a specific velocity $$v$$ and a certain perception-reaction time $$t_r$$ can be computed using simple dynamics:

$$ d_r = \left( vt_r \right) \,\!$$

Finally, combining these two elements together and incorporating unit conversion, the AASHTO stopping sight distance formula is produced. The unit conversions convert the problem to metric, with $$v_i$$ in kilometers per hour and $$d_s$$ in meters.

$$ d_s= d_r + d_b  = 0.278t_r v_i  + \frac \,\!$$

A Note on Sign Conventions
We said $$ d_b = \frac \,\!$$

Use: $$ (f - G) \,\!$$ if going downhill and $$ (f + G) \,\!$$ if going uphill, where G is the absolute value of the grade

Passing Sight Distance
Passing Sight Distance (PSD) is the minimum sight distance that is required on a highway, generally a two-lane, two-directional one, that will allow a driver to pass another vehicle without colliding with a vehicle in the opposing lane. This distance also allows the driver to abort the passing maneuver if desired. AASHTO defines PSD as having three main distance components: (1) Distance traveled during perception-reaction time and acceleration into the opposing lane, (2) Distance required to pass in the opposing lane, (3) Distance necessary to clear the slower vehicle.

The first distance component $$d_1$$ is defined as:

$$ d_1 = 1000t_1 \left( u - m + \frac \right) \,\!$$

where
 * $$t_1\,\!$$ = time for initial maneuver,
 * $$a \,\!$$ = acceleration (km/h/sec),
 * $$u \,\!$$ = average speed of passing vehicle (km/hr),
 * $$m \,\!$$ = difference in speeds of passing and impeder vehicles (km/hr).

The second distance component $$d_2\,\!$$ is defined as:

$$ d_2 = \left(1000ut_2\right) \,\!$$

where
 * $$t_2\,\!$$ = time passing vehicle is traveling in opposing lane,
 * $$u \,\!$$ = average speed of passing vehicle (km/hr).

The third distance component $$d_3\,\!$$ is more of a rule of thumb than a calculation. Lengths to complete this maneuver vary between 30 and 90 meters.

With these values, the total passing sight distance (PSD) can be calculated by simply taking the summation of all three distances.

$$ d_p = \left( d_1 + d_2 + d_3 \right) \,\!$$

Demonstrations

 * GIF animation: Stopping Sight Distance on Flat Surface (contributed by Oregon State University faculty and students)
 * GIF animation: Stopping Sight Distance on Downhill Grade (contributed by Oregon State University faculty and students)
 * Flash animation: Bicycle Crash Type (contributed by Oregon State University faculty and students)
 * Video: Vertical Alignment and Sight Distance

Thought Question
Problem

If the coefficient of friction is 0 (zero) and the grade is 0, how long does it take a moving vehicle to stop?

Solution

Forever

Note, the design conditions for roads are wet, i.e. a lower coefficient of friction

Sample Problem
Problem (Solution)

Additional Questions

 * Homework
 * Additional Questions

Variables

 * $$d_s$$ - stopping (sight) distance (m)
 * $$d_r$$ - perception reaction distance (m)
 * $$d_b$$ - braking distance (m)
 * $$d_p$$ - passing distance (m)
 * $$v_i$$ - initial speed (km/h)
 * $$t_r$$ - perception/reaction time (seconds)
 * $$f$$ - AASHTO stopping friction coefficient (dimensionless)
 * $$G$$ - roadway grade (dimensionless)

Key Terms

 * SSD : Stopping Sight Distance
 * PSD : Passing Sight Distance
 * PRT : Perception-Reaction Time


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User talk:Kickme~enwikibooks

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Hello,

The developer team at Wikimedia is making some changes to how accounts work, as part of our on-going efforts to provide new and better tools for our users like cross-wiki notifications. These changes will mean you have the same account name everywhere. This will let us give you new features that will help you edit and discuss better, and allow more flexible user permissions for tools. One of the side-effects of this is that user accounts will now have to be unique across all 900 Wikimedia wikis. See the announcement for more information.

Unfortunately, your account clashes with another account also called Kickme. To make sure that both of you can use all Wikimedia projects in future, we have reserved the name Kickme~enwikibooks that only you will have. If you like it, you don't have to do anything. If you do not like it, you can pick out a different name.

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User talk:Great Legacy~enwikibooks

Your account will be renamed
Hello,

The developer team at Wikimedia is making some changes to how accounts work, as part of our on-going efforts to provide new and better tools for our users like cross-wiki notifications. These changes will mean you have the same account name everywhere. This will let us give you new features that will help you edit and discuss better, and allow more flexible user permissions for tools. One of the side-effects of this is that user accounts will now have to be unique across all 900 Wikimedia wikis. See the announcement for more information.

Unfortunately, your account clashes with another account also called Great Legacy. To make sure that both of you can use all Wikimedia projects in future, we have reserved the name Great Legacy~enwikibooks that only you will have. If you like it, you don't have to do anything. If you do not like it, you can pick out a different name.

Your account will still work as before, and you will be credited for all your edits made so far, but you will have to use the new account name when you log in.

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text: User talk:Sjakkalle

title: User talk:Sjakkalle


text:
Fundamentals of Transportation/Sight Distance/Problem

 * Solution

/Problems


text:
Wikijunior:Famous Inventors/Inventors in Communication/Alexander Graham Bell

When, Where, and to whom was he or she born?
Alexander Bell was born in Edinburgh, Scotland on March 3, 1847

What was his or her childhood like?
 Did You Know?
 * First interesting fact.
 * Another interesting fact.
 * Yet another interesting fact.

The family home was at 16 South Charlotte Street, Edinburgh and has a commemorative marker at the doorstep, marking this as Alexander Graham Bell's birthplace.

Why did this person become interested in science?
As a child, young Alexander displayed a natural curiosity about his world, resulting in gathering botanical specimens as well as experimenting even at an early age.

Where did this person go to school?
As a young child Bell, like his brothers, received his early schooling at home from his father. Later he went to a college in London. He went to school for 5 years.

What problem did he or she uncover that needed solving?
His efforts resulted in a remarkably lifelike head that could "speak," albeit only a few words.

What solutions had already been tried that did not solve the problem? Why wasn't it working?
Bell continued to experiment with a live subject, the family's Skye terrier, "Trouve"

How did the invention solve the problem?
He thought he could harness the new electronic technology by creating a machine with a transmitter and receiver that would send sounds telegraphically to help people hear.

How has this inventor changed people and the world?
It allowed people from all over the world to keep in touch regardless of distance.

What happened to this inventor in the end?
Bell died of diabetes on 2 August 1922, at his private estate, Beinn Bhreagh, Nova Scotia, at age 75.

If you could ask this inventor one question, what would you ask?
How did you make the telephone?

If you could bring this inventor to today and tell him or her one thing, what would you tell him or her about the effect of his or her invention?
How easy was it to make the telephone?


text:
Fundamentals of Transportation/Sight Distance/Solution

/Solutions


text:
User:Xania/temp

LATIN SCRIPT - XANIA CYRILLIC SCRIPT - ЗAНИA

LATIN SCRIPT - XANUCIA CYRILLIC SCRIPT - ЗAНУСИA

title: User:Xania/temp


text:
Wikijunior:Famous Inventors/Inventors in Everyday Uses/Thomas Edison

When, Where, and to whom was he or she born?

Thomas Edison was born in Milan, Ohio, (on February 11, 1847) and was raised in Port Huron, Michigan. He was the seventh and last child of Samuel Ogden Edison, Jr. (1804–1896) (born in Marshalltown, Nova Scotia, Canada) and Nancy Matthews Edison née Elliott (1810–1871). His family was of Dutch origin.

What was his or her childhood like?
In school, Thomas Edison wasn't a really good student. People think this may have been partly because he couldn't hear well, so that he didn't pay attention to the teacher as much as he should have. Also, in those days some teachers thought students shouldn't ask questions, and apparently he asked a lot of questions. His teacher said he was "addled". He only stayed in school for three months; after that, his mother taught him.

Why did this person become interested in science?
Thomas Edison loved to read and he became interested in science from books. At the age of 10, he set up a small Laboratory in his room. He spent most of his time reading or trying out a new experiment.

Where did this person go to school?
He went to school in Port Huron, Michigan. But he only went to school for three months.

What problem did he or she uncover that needed solving?
The problem he needed solving is that how to make the electric light bulb last longer than the ones that other inventors invented.  Did You Know?
 * He helped create over 1,000 inventions!
 * He produced the first talking motion picture.
 * He worked for the navy in World War I.

What solutions had already been tried that did not solve the problem? Why wasn't it working?
The solutions that had already been tried that did not solve the problem are that he used platinum and other filaments that did not work, he tried many times and every one, failed. After many Failures he used a carbon filament and it lasted 40 hours.

What did this person invent?

Thomas Edison invented the phonograph. The phonograph was the first invention that could record the sound of someone's voice and play it back to them. In 1877 he recited the poem "Mary had a little lamb" and the phonograph played it back to him.

He solved the problem of providing light for the world.

How has this inventor changed people and the world?
He helped in the creation of the light bulb. If he hadn't helped we probably wouldn't have long lasting light bulbs like we do now. It gave light to the world.

If you could ask this inventor one question, what would you ask?
If I could ask this inventor one question, I would ask him how he was inspired to be an inventor.

If you could bring this inventor to today and tell him or her one thing, what would you tell him or her about the effect of his or her invention?
Was it hard work?


text:
Wikijunior:Famous Inventors/Inventors in Communication/Samuel Morse

Link to Samuel F. B. Morse's Wikipedia entry

When, Where, and to whom was he or she born?
Samuel F.B. Morse was born on April 27, 1791 in Charlestown, Massachusetts. His father was Jedidiah Morse and his mother was Elizabeth Ann Breese Morse.

What was his or her childhood like?
After going to a private school in Massachusetts.

 Did You Know?
 * Sam Morse was raised strictly religious.
 * Sam Morse was a very talented painter.

Why did this person become interested in science?
Sam Morse became interested in science when taking a trip on a ship. There, he talked to another man interested in electronics, magnets and telegraphs.

Where did this person go to school?
Sam went to Yale College to learn religious philosophy, math and science of horses. He also learned about electricity. He graduated in 1810.

What problem did he or she uncover that needed solving?
Before Sam Morse invented Morse Code, people had trouble communicating with others who were far away. Important messages that needed to be delivered quickly couldn't be.

What solutions had already been tried that did not solve the problem? Why wasn't it working?
Other people invented telegraph machines that did not work as well as Sam Morse's.

How has this inventor changed people and the world?
With Morse Code, communication became easier all over the world.