META-Electronics 101

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This will be an attempt at a basic, easy to understand electronics course. Feel free to contribute suggestions.

We will start at the beginning, Structure of Matter, work my way thru ohms law, resistance, capacitance, inductance, amplifiers, resonance, tubes and then transistors.

cj

Understanding electronics is easier if you have a basic knowledge of the chemistry and physyics involved, so I will start with a real simple lesson. I do not want to take too long on this becuase we want to get to the fun stuff right away, right?  This is the first lesson I had in my highschool electronics course.

Lesson 1: Structure of Matter

Matter- anything that takes up space and has mass

Matter is composed of atoms.

The Atom is composed of a Neutron, Proton and Electron.
The nucleus is the center of the atom and is always positive.
Protons and Neutrons are located in the nucleus of the atom.
The proton has a positive charge. The neutron is neutral-no charge.
Electrons orbit the nucleus.





Energy- the ability to do work

-----forms: heat, electrical, chemical, mechanical and atomic

Electron-gives us our energy
The electron has a negative charge.

An atom can have one or more orbits that are a fixed distance from the nucleus. These orbits can be filled partially or completely, depending on the number of electrons in the atoms. The first orbit can contain 2 electrons, the second 8, the third and fourth 18, etc.

Electronics is mainly concerned with the electrons in the outer shell (ring).
These are called valence electrons.

Elements are classified by the number of protons and electrons the have.
Atomic Number- the number of electrons and protons in the atom.
Elements are organized on the Periodic Table of the Elements  according to their atomic number.
Here is a link to the Periodic Chart.
You can click on the various elements to look at the atomic structure:

http://www.chemicalelements.com/show/electronconfig.html

Whenever an atom has just one electron in it's outer shell, it is unstable=conductor. Copper, Silver and Gold all have one electron in the outer orbits, which make them good conductors.

Here is a diagram of a copper atom.
Notice that it has only one electron in it's outer orbit:


Elements with their outer orbits filled are said to be stable. These are classified as insulators.

Elements with half of their outer orbits filled are called semi-conductors.
Example: Silicon and Germanium both have four out of eight electrons in their outer orbits-thus thay are semiconductors.

Here is a model of a Germanium atom. Notice that it has four valence electrons:



Law of Charges:

Like charges repel each other
Opposite charges attract each other

So electrons will repel each other.

We could get into ions, covalent and ionic bonds, energy levels, but I do not think it would be very benificial, so this is about as far as I want to go on the structure of matter.

------------Lesson 2-----Electricity--------------

Electricity is the flow of electrons.
Conductor-anything that will carry electrons.

Copper, silver, gold. and other good conductors of electricity have only one or two electrons in their valence ring. These atoms can be made to give up the electrons in their valence ring with little effort.

Since electricity is the movement of electrons from one atom to another, atoms that have one electron in their valence ring support electricity. They allow the electron to easily move from the valence ring of one atom to the valence ring of another atom. Therefore, if we have a wire made of millions of copper atoms, we have a good conductor of electricity. To have electricity, we simply need to add one electron to one of the copper atoms. Since like charges repel each other, that atom will shed the electron it had to another atom. which will shed its original electron to another, and so on. As long as we keep the electrons moving in the conductor, we have electricity.

In a conductor, the movement of the free electrons is hindered by collisions with the adjoining atoms of the element. This hindrance to movement is called RESISTANCE and it varies with different materials and temperatures. As temperature increases, the movement of the free electrons increases, causing more frequent collisions and therefore increasing resistance to the movement of the electrons.

To further understand this, imagine you are at a dance hall. If there is no music playing, nobody is dancing. You can walk across the dance floor with relative ease. Then all of a sudden the band starts playing and everybody starts moving. You now have a more difficult time trying to make it across the dance floor, as you have to constantly running into people. This is what happens when the tempeture increases in a conductor, such as a copper wire. The atoms start moving around like people on the dance floor.

Freezing a conductor with liquid nitrogen will lessen this effect. Superconductors are often made by taking a regular conductor and lowering it's tempeture with liquid nitrogen.

This movement of electrons is called electric CURRENT and is measured in amperes. When 6.28 billion, billion electrons pass a certain point in the circuit in one second, the amount of current flow is called one ampere.

The force or pressure which causes electrons to flow in any conductor (such as a wire) is called VOLTAGE. It is measured in volts and is similar to the pressure that causes water to flow in a pipe. Voltage is the difference in electrical pressure measured between two different points in a circuit. In a 12 volt system, for example, the force measured between the two battery posts is 12 volts.

Lesson 3-----Basic Electrical Circuits-----------

Electricity always flows in a circle. If you apply voltage with a car battery to one end of a wire and the other end goes nowhere, you will not have current flow. You need a complete circuit in order to have current. The electrons in the wire need to have a path back to the battery.

There are three types of basic circuits:

1. Series
2. Parallel
3. Series-Parallel

Let's look at a simple series circuit first.

Here is a battery, a switch and a lightbulb. We can put a current meter, or ammeter, whatever you want to call it, in series with the circuit in order to measure current. When the switch is off, the electricity does not have a complete path to flow in, therefore, we will have no current:



Notice that when you close the switch to complete the electrical circuit, the electrons start moving and the ammeter indicates that there is current flowing in this circuit. Also notice that the light bulb begins to glow. This happens because the electrons moving through the tiny wires in the bulb (or filament) make them become so hot that they glow.



This is called a series circuit because there is only one path for the electrons to take between any two points in this circuit. In other words, the components, which are the battery, the switch, the ammeter, and light, are all in ?series? with each other.

One of the properties of the series circuit is that the current will always be the same everywhere in the circuit. This is because there is only one path for the electrons to take. So if you were to move that ammeter to a different location in the circuit, it would still read the same.

Note that the ammeter must be placed in series with the circuit. If you were to place it across the battery terminals, you would fry it like bacon.

The light bulb is considered a load in this circuit. You might think of a load as anything that is using the energy that is being delivered by the electric current in a circuit. It could be anything from a light bulb to a computer to a washing machine and so on.

Let?s build another series circuit, but this time we will use some resistors instead of a light bulb. Resistors are components that are used to control that amount of current flowing in a circuit. The light bulb in the first circuit was actually acting like a resistor because it only allowed a certain amount of current to flow through it. If there are no resistors or components that act like resistors to slow the flow of electrical current, too much current may flow through the circuit and damage its components or wires. Too much current flowing through a component results in the generation of heat that can melt the conductive path through which the electrons are flowing. This in known as a short circuit and is the reason fuses or circuit breakers are often included in a circuit.



We cannot see any work being done since there is no light bulb, but there is current actually flowing inside. We know the current is flowing because the ammeter is indicating this. It is important to know that we may not be able to tell whether current is flowing through a circuit without test equipment, such as our ammeter connected to the circuit.

Question: Is the current the same in each one of the resistors?
Answer: Yes. Series circuit=current the same everywhere.

OK, lets check out a parallel circuit:

Like the series circuit, parallel circuits also contain a voltage (current) source as well as wires and other components. The main difference between a series circuit and a parallel circuit is in the way the components are connected. In a parallel circuit the electricity has several paths that it can travel.



In our series circuit, all the electrons flowed through all the components in order. With the parallel circuit, some electrons go through one load and some go through the other load, all at the same time. At point A, the total current splits up and takes different paths before the circuit joins back together again at point B.

A parallel circuit exists whenever two or more components are connected between the same two points. Those two points in this circuit are points A and B. Both resistors connect to both points A and B.

Each parallel path is called a branch of the parallel circuit.



This parallel circuit contains 3 branches (two resistors and a voltmeter), which means the electron current goes through all three branches at the same time. We put a voltmeter on this second circuit to show an important fact. Ammeters must always be placed in series in a circuit, otherwise they will not work. The voltmeter we added in the last circuit has a different requirement in order to work. Voltmeters must be placed in parallel with the circuit in order to work. This is because voltage meters measure the difference in electromagnetic force (EMF) from one area to another. They are used to measure the difference in EMF on one side of a component compared to the other side of the component. In our homes, most circuits contain 120 volts of EMF.

You can see that the voltage across each of the resistors in the above circuit will be the same. This is one of the properties of a parallel circuit. The voltage across any of the componentes will be the same.

Summary:
The current thru any component in a series circuit will always be the same.
The volatge across any component in a parallel circuit will always be the same.

The ammeter goes in series with the components in the circuit.
The voltmeter is placed in parallel, or across the components in the circuit.

OK, the last part of this lesson is the series/parallel circuit.

When we have a circuit in which some of the components are in series and others are in parallel, we have a series/parallel circuit.




Notice in this series/parallel circuit that the resistors R1, the switch, the battery, and the ammeter are in series with each other while resistors R2 and R3 are in parallel with each other. We might also say that the R2/R3 combination is in series with the rest of the components in this circuit. This is a very common circuit configuration. Many circuits have various combinations of series and parallel components.

If we apply Ohm?s law to any of these series or parallel circuits, we can calculate the current flowing at any point in the circuits. We will also be able to come up with additional characteristics of series and parallel circuits.

Lesson 4------------Ohm's Law-------------

Probably the most important mathematical relationship between voltage, current and resistance in electricity is something called ?Ohm?s Law?. A cat named George Ohm published this formula in 1827 based on his experiments with electricity. This formula is used to calculate electrical values so that we can design circuits and use electricity in a useful manner. Ohm's Law is shown below.

OHM'S LAW where E = voltage, I = current, and R = resistance:

E =I x R or, Volts equals Current time Resistance.

Depending on what you are trying to solve we can rearrange it two other ways.

I = E/R or, Currents equals Volts divided by Resistance.

R = E/I or, Resistance equals Volts divided by current.

If any two of the quantities are known the other can be calculated.

Note: You might see Ohm's Law written as V=IR. V is commonly used in place of E. It's the same law, no matter which letter you use. E stands for Electromotive Force.


As you can see, voltage, current, and resistance are mathematically related to each other. We cannot deal with electricity without all three of these properties being considered.


OK, here's your first quiz:





------------------------------------------------------------(ans-spelled backwards: pma eno)

Lesson 5    Ohm's Law Exercises

Let's do some lab problems with resistors.

Before we do some problems, lets learn how to read resistor color codes.

Most of the time you will probably use resistors with 4 bands in their color code.  Here is a typical resistor:


This happens to be a 1000 ohm resistor, or commonly referred to as a "1K"
The brown band stands for 1, the black band stands for 0, and the red band means you put 2 zeros after the first two digits: 1-0-00 or 1,000 ohms.
Resistors are usually never the exact value as the color code indicates so the manufacture uses the fourth band to indicate the tolerance of the resistor. In theis case, the silver band corresponds to a 10 percent tolerance. It is pretty rare to find a 10 percent tolerance on a resistor nowdays. Most resistors nowdays carry a 5 percent tolerance which corresponds to a gold band.

Precision resistors are sometimes used in critical locations. They use a 5 band color coding system, but we won't worry about those right now.

To calculate the value of a resistor using the color coded stripes on the resistor, use the following procedure.

"Step One: Turn the resistor so that the gold or silver stripe is at the right end of the resistor.

Step Two: Look at the color of the first two stripes on the left end. These correspond to the first two digits of the resistor value. Use the table given below to determine the first two digits.

Step Three: Look at the third stripe from the left. This corresponds to a multiplication value. Find the value using the table below.

Step Four: Multiply the two digit number from step two by the number from step three. This is the value of the resistor in ohms. The fourth stripe indicates the accuracy of the resistor. A gold stripe means the value of the resistor may vary by 5% from the value given by the stripes."

Here is a color code chart. It's funny, but just about every tutorial I have seen fails to mention one very important memorization fact: The color code is arranged like the colors of the rainbow! The last two bands, gold and silver, do not apply to this. I usally forget the order of the green and blue color bands all the time, so I have to revert back to the rainbow. Green comes before blue:



Resistors do not come in an ifinite number of values, so eventually, you will be able to recognize their value at fisrt sight, without having to do the math in your head. This is especially true with common values like 100 ohms, 1 K, 10 K, 100 K,  1 Meg (Meg=million ohms), 47 K, etc.

Grab about ten different resistors and practice the color code. Verify your guesses with an ohm meter. You will get it down pretty quickly. And remember the rainbow trick!

An easier way to use the third band which is the multiplier, is to just add the number of zeros that the band corresponds to after you figure out the first two digits. Example: Brown-Black-Orange corresponds to a 10 with an "orange" amout of zeros after it. Orange corresponds to 3 on the color code chart, so you have a 10 with 3 zeros after it, which is, of course, 10,000, or a 10 K resistor.. Thie eliminates they typical multiplication method, which is a pain in my opinion.

Here is a resistance calculator. You can play around with it to get familiar with color codes. You can pull down different colors from the menus at the top:



OK, lets solve a series circuit problem.



Some properties of Series Circuits:

1. Current only has one path.

2. Current is the same everywhere.

3. Voltage drop across each resistor in a series circuit depends on the value of the resistor. The higher the value, the higher the voltage drop.

4. The sum of all the voltage drops across the resistors in a series circuit is equal to the applied voltage from the power supply or battery.

Connecting resistors in a string one pigtail to another is called connecting them in series.  When connected this way the resistance of one resistor adds to the next in line.  For example a 100 ohm resistor in series with a 500 ohm resistor is the same as having a 600 ohm resistor.

OK, lets do a series circuit problem. Here is the circuit. Just a battery and two light bulbs in series:



Light bulbs are nothing more than resistors that put out light. So we can re-draw the circuit and just denote the light bulbs as resistors. We will also use the symbol for a battery. By the way, the larger bar of a battery symbol always denotes the positive terminal:



OK, so lets do a little math using Ohm's law and the properties of a series circuit to analyze this thing.

Ohm's Law: E=IR. where E equals voltage. I is current, and R is resistance.

Lets find the current flowing thru this circuit. Remember that the current flowing thru a series circuit is always the same. So if we find the total current, we will have the current flowing thru both of the resistors. To find the current, we need to know the voltage applied to the circuit, and the total resistance of the circuit. In a series circuit, we simply add up the resistances. In this case, the total resistance is 9 ohms plus 6 ohms equals 15 ohms total. Now we have enough variables to compute the current, as the battery voltage has been given as 30 volts.

Ohm's Law: E=IR  We want to find the current in this circuit, so let's put the current variable on one side of the equation:

I=E/R,  punching in our numbers we have I = 30/15 = 2 Amps.

Here is the equivalent of our lightbulb circuit:



Let's figure out a few more things about this circuit. That 30 volts from the battery has to be chewed up by the two resistors. But which resistor do you think chews up the most voltage? We can find out by using the fact that current is always the same in a series circuit, and with ohm's law.

The voltage across the resistors is going to be E=I x R, so lets punch in the values to get some answers: For the 9 ohm resistor, the voltage across it will be the current thru it times it's resistance, so E = 2 amps x 9 ohms, which is 18 volts.

The voltage across the 6 ohm resistor will be caculated the same way, so E = I x R, so E = 2 amps x 6 ohms, which is 12 volts.

Now since the two resistors have to chew up the 30 volts from the battery, adding up the two different voltage drops across them should give us the battery voltge: 18 + 12 is indeed, 30 volts! So we know we have done our math right.

Notice that the 9 ohm resistor chews up more voltage than the 6 ohm resistor, as it offers more opposition to the 30 volt battery.

By the way, which resistor do you think is going to get hotter? We have not studied the power formula, but we should still be able to make a guess; Well, both resistors have the same amount of current flowing thru them because they are in series. But one is only holding back 12 volts, and the other has to hold back 18 volts. Which one do you think has to work the hardest?

You can practice your Ohm's Law by changing the values of the above circuit and re-computing. Then, add more resistors and do some more problem solving.

Let's do a Parallel Circuits problem.



Properties of Parallel Circuits:


1. Voltages is the same.
2. Current varies.
3. Total resistance decreases with more resistance.

A parallel circuit is a current divider.
In this illustration you can see that the sum of the individual currents, Ib, Ic and Id, will add up to the total current, Ia:




Here is a parallel circuit.

In this case, the two resistors have the same value, 10 ohms each. We would expect the current flowing in the circuit to be divided equally among the two resistors, no? We can also speculate that the power disapated by each resistor would also be equal. We can use Ohm's Law to calculate the total current flowing in this circuit, just like we did in the series circuit, but there is a twist. How do we calculate the total resistance?

Well, since the electrons have two paths they can take back to the battery, and each of these paths are ten ohms, the total resistance of this circuit is five ohms. What if we were to add a couple more ten ohm resistors in parallel?  Well, the total resistance would be 10 ohms divided by four, which is 2.5 ohms.




In fact, if the resistors in a parallel circuit are all the same value, then you can compute the total resistance by simply taking the value of one of the resistors and dividing it  by the number of resistors there are in the circuit.


So if you had ten ea.  100 ohm resistors in parallel, the total resistance would be 100 ohms/10 ea.,  which is 10 ohms.
If you had 50 ea. 1 ohm resistors in parallel, you would have 1 ohm/50 ea. = 1/50 th of an ohm.

So the formula for like resistors in parallel is:

R-total = any R/no. of R's.

One good thing to remember about parallel resistance problems is that the total resistance is ALWAYS less than the value of the smallest resistor.  You can use this fact as a quick reality check when you do a parallel resistance problem.

Computing the total resistance of a parallel circuit with resistors of different values is a bit more tricky than a problem with like value resistors. Here is parallel resistance problem with unlike resistors.
Notice that there is twice as much current flowing thru the resitor with half as much resistance. That makes sense, right? There is half as much resistance, therefore twice as much current.  Note from the picture that both resistors have 30 volts across them.

Let's use Ohm's Law to make sure that the values on that drawing are correct. We use the same Ohm's Law formula that we used for series circuits, E=IR.

Since the voltage across resistors in a parallel circuit is the same, we use 30 volts for both calculations:

30V/3 Ohms is 10 amps, and 30V/6 ohms is 5 amps.

So the total current flowing is found by adding up the individual currents in the two branches: 10 plus 5 is 15 amps total.


So what is the total resistance of this circuit? We can use the total current and the total voltage applied:

30V/15 amps is 2 ohms total.
Notice that the total resistance of 2 ohms is less than the smallest resistor in the circuit.

There is a formula for calculating total resistance in a parallel circuit:



Let's use it in a couple of examples.

To find the equivalent resistance (the total resistance offered to the flow of current) we invert the values and add them. Then we invert the result.

For example take 2 ohms and 4 ohms in parallel.

Inverted 1/2 +1/4 = 3/4

Invert this 4/3 = 1.33 ohms

A quick check on your answer is that it should be smaller in value than the value of the smallest resistor.

Let's try it out on one more problem:

3 Ohms and 6 ohms in parallel:

Inverted 1/3 + 1/6 = 1/2.

Invert this 2/1 = 2 Ohms. Hey, that's the answer to the problem we did up above, right? (the one with the blue background)
So we know the formula works.

Remember:

Resistors in parallel are connected across one another.
They all have the same voltage across them.

The good news about parallel resistance problems is that in real life, you will seldom encounter problems with more than two resistors in parallel. So practicing on a problem like this is good exercise, but not really necessary, but just in case, let's just do one last problem to make sure we have this down. Here it is. What is the total resistance from A to B?
Try it yourself before you look at the answer.









1/2 + 1/3 + 1/6 + 1/1 = 2.  Invert this 1/2 = 0.5 ohms.

Here is a link to a Parallel Resistance Calculator:

http://www.1728.com/resistrs.htm

One last tip for parallel circuits:

If one resistor is at least ten times the value of the smaller resistor in a parallel circuit, it can sometimes be ignored.

Example: If a  10 ohm resistor is in parallel with a 100 ohm resistor, the total resistance is  about 9.1 ohms.

Lesson 6    Watt's Law

The movement of electrons through resistive circuits generate heat.  This is normally an unwanted result but meets conservation of energy laws.  The power dissipation in a resistor is expressed by Watt's law.  The law has three forms:

P = V x I  (my favorite), P = I^2 R, (engineers favorite) 

and  P = V^2/R (nobody's favorite :grin: )

where P is power in Watts, V is Volts, I is Current, and R is Resistance.

If any two of the quantities are known the other can be calculated.

Power Rating of Resistors

As current flows through a resistor it converts the electrical energy in to mechanical energy in the form of heat. The power rating of a resistor is a measure of the maximum power the resistor can dissipate without being damaged. The rating is determined by physical characteristics rather than by the resistive values. The larger the surface area of the resistor the more power it can dissipate.



The surface area of a cylindrical shaped resistor equals l x c. The larger this value the more power the resistor can dissipate without being damaged. Resistors are available in the following powering ratings.

1/8 W, 1/4 W, 1/2 W, 1W and 2W.

Power resistors are available with power ratings from 10 W up to 225 W.

When designing circuits attention must be give to the power rating of a resistor and the amount of power it will see in a circuit. If the amount of power in a resistor exceeds the power rating then the resistor can become damaged.

Let's play around with Watt's Law to make sure it really works!

Here is a simple series circuit with just one resistor:




We have all the variables needed to use the above formulas except the total current, so let's find that first before we compute the power used up by the resistor.
You should be able to figure out the current flowing in this circuit by using Ohm's Law, which was covered earlier.

E = I x R, so  10 Volts divided by 100 ohms is 0.100 amps. Simple enough, eh?

Let's plug some of these numbers into the equations from above:

First, lets use P = I x V:    P = 0.100 Amps x 10 Volts  = 1 Watt

Let's try the other two formulas just to make sure this Watt guy ain't pullin our leg:

P = I^2 x R,  P = 0.100^2 x 100,  so P = .01 x 100 = 1 Watt.

OK so far, now the last one:

P = V^2/R,  P = 10^2/100, so P = 100/100 = 1 Watt! 

OK, everything is cool. Or hot. Or whatever. :grin:

CJ:

Sorry to intrude on your tutorial, but I wonder if you could address a topic that I'm having a hard time with, that hasn't really been addressed in the book/web reading I've been doing.

When dealing with power and loads, we need to consider the whole circuit to calculate current, resistance, voltage drops, etc.

But what about the OTHER part of audio circuits: the audio path! ICs can boost, phase invert, etc. the signal, and I assume that resistors can pad the signal, but there's generally so much more going on in the audio path and I can't follow it. What's going on there?

Thanks for a great post btw.

I see your point.
Since the audio signal is ac, whatever current you have suppling the audio chain will rise with a positive signal, and drop with a negative signal. Most of the time this tends to cancel out current draw, as the plus and minus averages out. Power amplifiers might be a difernt story. They chew up many more times power than a line level piece of equipmemt.

CJ, awesome lesson! I may have missed it above, but a reminder that all of the above formulas apply only to DC circuits. AC analysis is a whole other ballgame! [Especially if there's caps and inductors in the circuit(s).]

If I did miss it, just smack me, and pretend you didn't see me! :green:

[quote author="The Kid"]CJ, awesome lesson! I may have missed it above, but a reminder that all of the above formulas apply only to DC circuits. AC analysis is a whole other ballgame! [Especially if there's caps and inductors in the circuit(s).]

If I did miss it, just smack me, and pretend you didn't see me! :green:[/quote]

AC theory comes later, although from a resistive standpoint, all of the above applies to AC as well. I think the tact CJ is taking is good for the beginner; better to learn to walk first than to run and trip!

better to learn to walk first than to run and trip!

Click to expand...

Yeah, good to know what you're gonna run into, though! :twisted:

Here is an interesting pdf file that details the use of the oscilloscope.

Its in the form of a quiz. Being the newb I am, I'm not able to supply each correct answer. Any how maybe this would be helpful to folks.

http://www.ibiblio.org/obp/books/socratic/output/scope1.pdf

Denny

thanks, and i will get going on the ac section.
i have been stealing clip art and things, so am ready.

I just purchased a scope and a function generator.
I'd love to learn exactly how to take common measurements related to audio circuits.
Perhaps some written basics here, or some pertaining links ?
It's killing me, knowing there is much to be had by these machines, that the basic manuals don't reveal to the beginner. Often the manuals tell you how to get a reading, but not how that reading is usefull to me.

I'll start. I found two links, for a new scope owner. One is an online college course guide. Start at Experiment 1, and move on:

http://www.colorado.edu/physics/phys3330/PDF/

Experiment #1 Electronic Instruments
Experiment #2 DC Measurements, Voltage Dividers, and Bridges
Experiment #3 Filters and Waveform Shaping
Experiment #4 Operational Amplifiers and Negative Feedback
Experiment #5 Positive Feedback and Oscillators
Experiment #6 LEDs, Photodiodes, and Lock-in Amplifiers
Experiment #7 Bipolar Transistors
Experiment #8 Field Effect Transistors and Noise
Experiment #9 Digital Electronics I: Logic, Flip-Flops, and Clocks
Experiment #10 Digital Electronics II: Microcontrollers

(quote)
"The main textbook for the course is Horowitz and Hill, The Art of Electronics, 2nd edition, Cambridge University Press (1989). This is one textbook that you will use long after the course is over. "

and another:
http://www.doctronics.co.uk/scope.htm
http://www.doctronics.co.uk/signals.htm

=FB=

Something very basic for most around here, but I found this helpful. It's about AC and DC coupling on a scope:
http://zone.ni.com/devzone/cda/ph/p/id/9

Nice website with interactive examples, but in french, but with interactive examples:
http://www.univ-lemans.fr/enseignements/physique/02/electro/mnueltro.html

Thanks guys!
I think I finally will have some time this Thanksgiving vacation to put down the second section.

http://www.allaboutcircuits.com/vol_1/index.html

Thanks! Good stuff, workin on it..