Intro to Electronics

    Let us travel back to the early 1700's. There were some scientists who knew of electricity. The word electricity was first applied in its modern usage by William Gilbert, a physician who experimented with static electricity in amber. [1] Then, in 1752, a philosopher, scientist, and writer named Benjamin Franklin took a kite with a key attached into an electrical storm and created sparks, thus proving his theory that lightening is electric. [2] Franklin is credited with having invented the lightning rod and numerous other electrical apparatuses like an electric motor. [3][4] He also left behind an important theory which said that electricity is composed of two charges, a positive and a negative. He believed that the positive charge must flow toward the negative. This was later proven wrong, as we will see, but it was nevertheless an important milestone in electronics history. For the next 250 or so years, Franklin's theory of electricity would be taught in schools all over the world, sparking interest in the subject of electronics.

Voltage and Current

    We don't know exactly what electricity is, though we have many theories based on prediction and observation which are most likely fact. Electricity is energy that works by way of attraction, charge, and movement in and between atoms. [5] There are two very important aspects to electricity, voltage and current, that must be understood before anything else.
Voltage
    Voltage is another word for potential. The more voltage there is between two points the higher the electric force there will be between them. It is the desire to expend energy. [6] Voltage is not a measurement of actual electric movement, only the potential for electric movement. Voltage is measured in volts. A volt is the potential difference across a conductor when a current of one amp dissipates one watt of power. [7]
Current
    Current is a measurement for electric movement or flow. More specifically, it is the waves and cycles of moving electrons. Current is measured in amperes (amps). It can be calculated with the equation I=Q/t where Q is the electric charge in coulombs and t is the time in seconds. [8]

Circuits

    Electronics work by way of circuits, which enable electricity to flow. Electricity must come out of one pole, or terminal, and eventually connect to another pole. This creates a closed circuit. [9] Along the way there can be electronic components that are supplied with power. In fact, it is very important to have various things placed along the circuit or else the circuit would serve no real purpose. It may even result in a short circuit. A short circuit means that a route in the circuit was created with very low resistance, which allows current to travel very fast. [10]  Short circuits result in damage when too much current is pushed through from one pole to the other at a fast rate, causing the entire design to malfunction. To prevent such malfunctions, things like resistors, fuses, and circuit breakers are placed along the route of electricity. Electrons will always travel the path of least resistance, so it is important to understand what you're doing when you design a circuit so that you don't cause a 'short'. [11]
Oscillators
    Electronic oscillators are circuits which oscillate, or repeat signals over and over and form sign or square waves. [12]
Rectifiers
    Rectifier circuits are able to convert AC current to pulsating DC. [13]

Components

    There are many different electronic components. This knol will not be covering all of them, but it will introduce the most commonly used and oft-considered 'important' ones.

Resistors

    It isn't hard to understand what resistors do when the explanation is the root of their name. To put it simply, they resist, or hold back, electric current. [14] Another word to explain the blocking, slowing down, or opposing of electricity is impedance, which takes into account both resistance and capacitance. [15] Resistors block or slow electricity in electronic circuits so that malfunction does not occur, and because certain parts of a circuit might not need as much voltage as the current would deliver. Resistance is measured in ohms.

    To know how many ohms a resistor is, one must learn how to read the color bands that are printed along the sides. As you can see in the image above, there are four bands on this 1K ohm resistor. To read the bands and arrive at an ohm measurement, a chart is used. [16]

Color Codes
Band Color	1st Band #	2nd Band #	*3rd Band #	Multiplier x	Tolerances  ± %
Black	0	0	0	1
Brown	1	1	1	10	± 1%
Red	2	2	2	100	± 2 %
Orange	3	3	3	1000
Yellow	4	4	4	10,000
Green	5	5	5	100,000	± 0.5 %
Blue	6	6	6	1,000,000	± 0.25 %
Violet	7	7	7	10,000,000	± 0.10 %
Grey	8	8	8	100,000,000	± 0.05 %
White	9	9	9	1,000,000,000
Gold				0.1	± 5 %
Silver				0.01	± 10 %
None					± 20 %

    First, make sure you are looking at the resistor so that the collection of bands is facing left. Now look at the first color band, which is brown in this case. Looking at the chart we see that brown is 1. Black is 0. This gives us the number 10. Now take the number 10 and multiply it by the color red and its multiplier number-- 100. This gives us 1,000, or 1K. The band to the far right will tell us the tolerance level of the resistor. [17] Since the 1K resistor has a gold band, it means that the it will resist plus or minus 5% of 1K.
    There are some resistors, called potentiometers, that are able to change resistance level.

Capacitors

    Capacitors are electronic components that store energy. Inside of them there are two metal plates that sandwich a dielectric. The metal plates conduct electricity while the dielectric does not. The dielectric material can be any kind of nonconducting material like air, mylar, glass, or ceramic. [18] The level of capacitance, or the amount of energy a capacitor can hold, depends on the dielectric material used and the size of the metal plates. [19] Current travels into the capacitor's first metal plate. Since there is a gap (the dielectric) between this piece of metal and the next, charge can not pass through and it builds up in the plate. [20] The more surface area the metal plates have, the more electricity they will be able to hold.
    When the plate inside of the capacitor has taken up a large amount of electrons it will have a very strong charge. The plate will take on a negative charge at this time. All of this charge can eventually be released back into the circuit by reversing the polarity. The electrons on the plate will be thrown out into the circuit at a net charge that is much greater than the charge of the current which originally brought them there. Capacitors have a rating (measured in Farads) which tells what they are capable of storing. [21] If current is applied to the capacitor which exceeds this rate then the capacitor can blow up and/or your circuit can be fried. Resistors and capacitors work together to create an overall level of impedance on the circuit.

Transistors

    Whereas resistors will decrease a current, transistors will amplify it. [22] Before transistors there were vacuum tubes. Vacuum tubes were highly unreliable and enormous. Transistors were invented and are much smaller. They act as either switches or amplifiers, meaning they can direct traffic of current or increase the level of current. They can create signals of their own or mesh signals together. [23]
Bipolar Transistors (NPN and PNP)

    A transistor with three sections of semiconductor and two P-N junctions is called a bipolar resistor. An NPN transistor has a P (positive) type semiconductor layer that is in between two N (negative) type semiconductor layers. The above picture shows the standard symbol for an NPN transistor. The arrow on an NPN transistor symbol will never be pointing in toward the center of the circle, which should help you distinguish. This transistor has three leads: a base, collector, and emitter. [24] The P type layer, at the center, is the base. Then there are two other semiconductors, one of which is the thin emitter and the other is the thick collector. The base is also called the control because the current of electricity through the entire transistor depends on the current that is coming in at the emitter-base function.
    Normally the emitter will be negative and the collector will be positive when DC is being applied to an NPN transistor.

    A PNP transistor is an N type layer in between two P type layers. Usually a NPN transistor can take the place of a PNP transistor and vice-versa should one of them break. [23] The arrow pointing inward is located at the emitter. Naturally, polarity of the PNP is the reverse of the NPN.
Zero Bias - Bipolar transistors are at zero bias when they are not connected to anything or when they are short-circuited to the emitter.
Forward Bias - If the bias at the base of the NPN transistor is positive in relation to the emitter then it has forward bias.

Integrated Circuit

    Integrated circuits (IC's) are small electronic circuits that are imprinted and placed on a thin semiconductor plate. [25] They are most commonly used to store information and/or perform specific tasks in order to aid in the overall functioning of a larger circuit. They are used for things like microprocessors, automobiles, and audio and video equipment. [26] Integrated circuits can either be bipolar, which means they have bipolar transistors, or Metal-oxide-semiconductor (MOS), which means they have MOS transistors. [27]
    Integrated circuits are categorized by size, or the number of transistors they can hold.
SSI (Small-Scale Integration) - 100 transistors or less
MSI (Medium-Scale Integration) - 100 to 3,000 transistors
LSI (large-scale integration) - 3,000 to 100,000 transistors
VLSI (very large-scale integration) - 100,000 to 1,000,000 transistors
ULSI (ultra large-scale integration) - 1,000,000 transistors or more
    Modern computer processors have many millions of transistors. For example, the Intel Core 2 Quad QX9650 has about 820 million transistors. [28] The first semiconductor chips held only 1 transistor each. Talk about growth!

Inductors

    Inductors are electronic components that create a significant magnetic field (have inductance). They are simply coils of wire wrapped around a ferromagnetic core, which create a magnetic field because of the properties of coil. [29] An inductor is essentially an electromagnet that can store energy in its magnetic field. When current first runs through an inductor, the inductor will impede on the current's flow. Once the magnetic field is established, current will go through the inductor at a normal rate. The field will stay for a short period of time even after the power (current) is taken away. Inductance is measured using the henry. [30]

Amplifiers

    An amplifier is an electronic component that increases the amplitude of an electric signal like voltage or current. [31] More specifically, they can increase the loudness of an audio-frequency or radio-frequency. They are commonly used in electronics like televisions, computers, CD players, radios, and anything that uses a speaker. They are not strictly limited to changing audio decibel, as they can be used to increase amplitude of any electrical signal.

Fuses

    A fuse is used to make sure that a circuit breaks if the current exceeds a certain level. [32] A soft piece of wire, the fuse melts if current gets to hot. This helps prevent destruction to other components in the circuit. Fuses can be replaced after short circuits or overloads. There are two types of fuses. A quick-break fuse is nothing but a straight wire while a slow-blow fuse is a straight wire with spring as well. [23]

Circuit Breakers

    A circuit breaker is a lot like a fuse because it is designed to cut power off from a circuit if the current gets too high. [33] Circuit breakers, however, do not need to be replaced after every overload. Instead, a switch can be flipped which resets the circuit breaker and allows the circuit to resume normal function. Sometimes a circuit breaker will automatically switch itself after a certain length of time.

Diodes

    Diodes are made from semiconductor material (usually silicon) and work by way of a P-N Junction. A P-N Junction consists of an N (negative) type piece of semiconductor placed directly beside a P (positive) type piece of semiconductor. [34] The two must physically touch. The N type contains many electrons and the P type has many holes. The N type material will usually be the cathode while the P type material is the anode. [35] When the negative terminal of a battery is connected to the anode and the positive terminal is connected to the cathode then current will be able to flow in a condition known as forward bias. Electrons from the N type material will go over and fill the holes in the P type material. If the terminals were reversed, then the electrons in the N type material will travel away from the P type material, and the holes in the P type material will move away from the N type material. This results in impedance of conduction and is called a reverse bias condition.
Forward Breakover Voltage
    In order for the diode to conduct a certain amount of voltage is required. This minimum voltage is called the forward breakover voltage, and usually ranges from 0.3V to 1V. [23]
Zener Diode
    Zener diodes are capable of maintaining a fixed voltage. They are therefore used to regulate voltage in electrical circuits. [36]
Rectification
    A rectifier diode is constructed in such a way that current can only pass in one direction, which is helpful when changing alternating current (AC) to direct current (DC)-- both of which are explained in the next few sections of this knol. The process of changing AC to DC is called rectification. [37]

Direct Current (DC)

    Electrons that move in one unchanging direction create an electric flow called direct current (DC). [38] Power supplies for things like radios and computers often use direct current. In fact, most computers and electronics will require DC. In a DC circuit, electrons will flow from a negative pole toward a positive pole. DC can either be pure, which means that it keeps a constant voltage, or it can vary in voltage intensity. Sometimes DC will change in amplitude at a rapid pace, which causes it to look a lot like an alternating current (AC). This is called pulsating DC.
Ohm's Law
    DC circuits involve three main aspects. There is the source of voltage, the current, and the resistance. An equation called Ohm's law allows a person to find any one of these aspects so long as the other two are known. [39] The equation is E=IR, where E is the voltage, I is the current, and R is the resistance running through the electrical circuit. The voltage must be in volts, the current in amperes, and the resistance in ohms for the equation to work. [23] From ohm's law we can deduce two other formulas: I=E/R and R=E/I.
Power Formula
    To calculate electrical power dissipated in a DC circuit, the formula P=EI is used. P stands for power whereas E is the voltage from the battery, and I is the current. If E is unknown, then the formula P=I²R can be used so long as R (resistance) and I are known. [40] P=E²/R can also be used to find the amount of power in the circuit, which is measured in watts.

Alternating Current (AC)

    When electrons of a current move in one direction for a certain length of time, then reverse, and reverse again over and over at a steady rate it is called an alternating current. [41] The back and forth motion occurs about 60 times per second in most United States AC utility circuits. AC can reverse billions of times per second, though, like in the case of some radio transmitters and receivers. Most all of the electricity offered in homes and businesses is AC, and converted by many electronics to be DC. [42] This is because AC is much more efficient than DC in high power applications.
Sine Wave

    Alternating current usually produces a sine-wave, which is sinusoidal in shape. [43] If you've ever taken a trigonometry or calculus course then you should be familiar with the sine-wave. Sine waves can be observed using electronic tools called oscilloscopes. An oscilloscope is a tool that displays electronic signals on a screen where the horizontal axis is time and the vertical axis is amplitude. [44] Signals can look like perfect sine-waves but they are not. Nevertheless, these imperfect signals are still called sine-waves.
Square and Rectangular Waves

    A 'perfect' square wave is composed of two different sets of dash lines that are parallel to one another across the horizontal axis. [45] One set of lines has positive polarity while the other set of lines has negative polarity. The picture above gives an example of what a square wave might look like. Square AC waves can be symmetrical or asymmetrical. [23] A symmetrical square wave will have the same positive and negative amplitude (voltage) difference. For instance, the positive peak would be +5 and the negative would be -5. An asymmetrical square wave has different amplitudes. For example, the positive could be +6 volts while the negative is -2 volts. If the time that the signal is negative does not match the time that the signal is positive, then it is called a rectangular wave. [46]
Sawtooth Waves

    A sawtooth wave is looks like the sharp teeth of a saw, hence the name. [47] When the positive slope on the graph raises very very fast and high, while the negative slope of the graph decreases at a slower speed or to a lesser degree then it is called a fast-rise. The sawtooth wave can also rise gradually and decrease suddenly, which is called a slow-rise or ramp wave.
Complex and Irregular Waves

    Waves that don't necessarily fit into any of the aforementioned wave forms are called complex or irregular. Complex waves look like they are many different sine waves all meshed together into one. There is no definitive pattern or shape in a complex wave.

Power Supplies

    A power supply has the ability to convert AC to DC current, which is important since electronics need DC while the outlets in the United States and most of the world supply AC. [48] This is why you can find power supplies in every personal computer, speaker system, radio, and more.
Transformers
    A power-supply transformer can either decrease (step-down transformer) or increase (step-up transformer) AC voltage. [49]

Batteries

    Electrochemical cells, or cells, are the basis for batteries. [50] These cells provide DC power and can be connected together to create a battery. Batteries are used in many electronics since they allow for voltage to occur independently of utility systems. One example of a battery is the lead-acid cell, which is made by putting an electrode of lead and an electrode of lead dioxide into a sulfuric-acid solution. [51] Potential energy in the acid is converted into DC electric energy. The cell can be recharged after all of the voltage has been drained by connecting it to an external power source with the same voltage. Cells such as the lead-acid that can be recharged are called secondary cells. [52] Cells that cannot be recharged are called primary cells.

Conclusion

    This was just a crash course in electronics and there are many more subjects to research and learn about. The world of electronics and technology is huge and always growing. They have definitely become fundamental parts of all of our lives. We are enmeshed with electronics and this connection will only become stronger as new electronics are created. Nanotechnology, biotechnology, wireless implementations, and more are all paving the way for new and exciting advancements that will undoubtedly change the industry forever.