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Basic Electronics

Basic electronic for all chip level courses:

ATOM: The smallest of an element which cannot exists in Free State

but

Takes part in chemical changes and possess all the properties of the

parent

Element is called an atom

It has three main parts. a) Neutron b) proton c) electron

Neutron: Neutron has no charge because it contains protons and

electrons in equal number.

Proton: the proton is relatively heavy art of an atom with a positive

charge

Electron: Electron in any is very light in comparison to protons

Current: The rate pf flow of electrons per second is called current

and it is measured in amperes ammeter or millimeter to measure.

Voltage: The potential difference between two end is called voltage

represented in ‘V’ voltmeter is used to millimeter.

Power: The total energy consumed by an electric or an electronic

device is called power and it is measured in watts it is abbreviated as

w.basic unites: watts (w).

Alternate Current (A.C): The rate of flow of current is in

bidirectional

Direct Current (D.C): The rate of flow of current is in direction.

Introduction:

The goal of this chapter is to provide some basic information about

electronic circuits. We make the assumption that you have no prior

knowledge of electronics, electricity, or circuits, and start from the

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basics. This is an unconventional approach, so it may be interesting,

or at least amusing, even if you do have some experience. So, the first

question is ``What is an electronic circuit?'' A circuit is a structure

that directs and controls electric currents, presumably to perform

some useful function. The very name "circuit" implies that the

structure is closed, something like a loop. That is all very well, but this

answer immediately raises a new question: "What is an electric

current?" Again, the name "current" indicates that it refers to some

type of flow, and in this case we mean a flow of electric charge, which

is usually just called charge because electric charge is really the only

kind there is. Finally we come to the basic question:

What is Charge?

No one knows what charge really is anymore than anyone knows

what gravity is. Both are models, constructions, fabrications if you

like, to describe and represent something that can be measured in the

real world, specifically a force. Gravity is the name for a force between

masses that we can feel and measure. Early workers observed that

bodies in "certain electrical condition" also exerted forces on one

another that they could measure, and they invented charge to explain

their observations. Amazingly, only three simple postulates or

assumptions, plus some experimental observations, are necessary to

explain all electrical phenomena. Everything: currents, electronics,

radio waves, and light. Not many things are so simple, so it is worth

stating the three postulates clearly.

Charge exists.

We just invent the name to represent the source of the physical force

that can be observed. The assumption is that the more charge

something has, the more force will be exerted. Charge is measured in

units of Coulombs, abbreviated C. The unit was named to honor

Charles Augustin Coulomb (1736-1806) the French aristocrat and

engineer who first measured the force between charged objects using

a sensitive torsion balance he invented. Coulomb lived in a time of

political unrest and new ideas, the age of Voltaire and Rousseau.

Fortunately, Coulomb completed most of his work before the

revolution and prudently left Paris with the storming of the Bastille.

Charge comes in two styles.

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We call the two styles positive charge, + , and (you guessed it)

negative charge, - . Charge also comes in lumps of 1.6 ×10-19C , which

is about two ten-million-trillionths of a Coulomb. The discrete nature

of charge is not important for this discussion, but it does serve to

indicate that a Coulomb is a LOT of charge.

Charge is conserved.

You cannot create it and you cannot annihilate it. You can, however,

neutralize it. Early workers observed experimentally that if they took

equal amounts of positive and negative charge and combined them on

some object, then that object neither exerted nor responded to

electrical forces; effectively it had zero net charge. This experiment

suggests that it might be possible to take uncharged, or neutral,

material and to separate somehow the latent positive and negative

charges. If you have ever rubbed a balloon on wool to make it stick to

the wall, you have separated charges using mechanical action.

Those are the three postulates. Now we will present some of the

experimental findings that both led to them and amplify their

significance.

Voltage

First we return to the basic assumption that forces are the result of

charges. Specifically, bodies with opposite charges attract, they exert

a force on each other pulling them together. The magnitude of the

force is proportional to the product of the charge on each mass. This

is just like gravity, where we use the term "mass" to represent the

quality of bodies that results in the attractive force that pulls them

together (see Fig. 4.1).

Figure 4.1: Opposite charges exert an attractive force on each other,

just like two masses attract. External force is required to hold them

apart, and work is required to move them farther apart.

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Electrical force, like gravity, also depends inversely on the distance

squared between the two bodies; short separation means big forces.

Thus it takes an opposing force to keep two charges of opposite sign

apart, just like it takes force to keep an apple from falling to earth. It

also takes work and the expenditure of energy to pull positive and

negative charges apart, just like it takes work to raise a big mass

against gravity, or to stretch a spring. This stored or potential energy

can be recovered and put to work to do some useful task. A falling

mass can raise a bucket of water; a retracting spring can pull a door

shut or run a clock. It requires some imagination to devise ways one

might hook on to charges of opposite sign to get some useful work

done, but it should be possible.

The potential that separated opposite charges have for doing work if

they are released to fly together is called voltage, measured in units of

volts (V). (Sadly, the unit volt is not named for Voltaire, but rather for

Volta, an Italian scientist.) The greater the amount of charge and the

greater the physical separation, the greater the voltage or stored

energy. The greater the voltage, the greater the force that is driving

the charges together. Voltage is always measured between two points,

in this case, the positive and negative charges. If you want to compare

the voltage of several charged bodies, the relative force driving the

various charges, it makes sense to keep one point constant for the

measurements. Traditionally, that common point is called "ground."

Early workers, like Coulomb, also observed that two bodies with

charges of the same type, either both positive or both negative,

repelled each other (Fig. 4.2). They experience a force pushing

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Figure 4.2: Like charges exert a repulsive force on each other.

External force is required to hold them together, and work is required

to push them closer.

them apart, and an opposing force is necessary to hold them together,

like holding a compressed spring. Work can potentially be done by

letting the charges fly apart, just like releasing the spring. Our

analogy with gravity must end here: no one has observed negative

mass, negative gravity, or uncharged bodies flying apart unaided. Too

bad, it would be a great way to launch a space probe. The voltage

between two separated like charges is negative; they have already

done their work by running apart, and it will take external energy and

work to force them back together.

So how do you tell if a particular bunch of charge is positive or

negative? You can't in isolation. Even with two charges, you can only

tell if they are the same (they repel) or opposite (they attract). The

names are relative; someone has to define which one is "positive."

Similarly, the voltage between two points A and B , VAB , is relative. If

VAB is positive you know the two points are oppositely charged, but

you cannot tell if point A has positive charge and point B negative, or

visa versa. However, if you make a second measurement between A

and another point C , you can at least tell if B and C have the same

charge by the relative sign of the two voltages, VAB and VAC to your

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common point A . You can even determine the voltage between B and

C without measuring it: VBC = VAC - VAB . This is the advantage of

defining a common point, like A , as ground and making all voltage

measurements with respect to it. If one further defines the charge at

point A to be negative charge, then a positive VAB means point B is

positively charged, by definition. The names and the signs are all

relative, and sometimes confusing if one forgets what the reference or

ground point is.

Current

Charge is mobile and can flow freely in certain materials, called

conductors. Metals and a few other elements and compounds are

conductors. Materials that charge cannot flow through are called

insulators. Air, glass, most plastics, and rubber are insulators, for

example. And then there are some materials called semiconductors,

that, historically, seemed to be good conductors sometimes but much

less so other times. Silicon and germanium are two such materials.

Today, we know that the difference in electrical behavior of different

samples of these materials is due to extremely small amounts of

impurities of different kinds, which could not be measured earlier.

This recognition, and the ability to precisely control the "impurities"

has led to the massive semiconductor electronics industry and the

near-magical devices it produces, including those on your

RoboBoard. We will discuss semiconductor devices later; now let us

return to conductors and charges.

Imagine two oppositely charged bodies, say metal spheres, that are

being held apart, as in Fig. 4.3.

Figure 4.3: Two spheres with opposite charges are connected by a

conductor, allowing charge to flow.

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There is a force between them, the potential for work, and thus a

voltage. Now we connect a conductor between them, a metal wire. On

the positively charged sphere, positive charges rush along the wire to

the other sphere, repelled by the nearby similar charges and attracted

to the distant opposite charges. The same thing occurs on the other

sphere and negative charge flows out on the wire. Positive and

negative charges combine to neutralize each other, and the flow

continues until there are no charge differences between any points of

the entire connected system. There may be a net residual charge if the

amounts of original positive and negative charge were not equal, but

that charge will be distributed evenly so all the forces are balanced. If

they were not, more charge would flow. The charge flow is driven by

voltage or potential differences. After things have quieted down, there

is no voltage difference between any two points of the system and no

potential for work. All the work has been done by the moving charges

heating up the wire.

The flow of charge is called electrical current. Current is measured in

amperes (a), amps for short (named after another French scientist

who worked mostly with magnetic effects). An ampere is defined as a

flow of one Coulomb of charge in one second past some point. While a

Coulomb is a lot of charge to have in one place, an ampere is a

common amount of current; about one ampere flows through a 100

watt incandescent light bulb, and a stove burner or a large motor

would require ten or more amperes. On the other hand low power

digital circuits use only a fraction of an ampere, and so we often use

units of 1/1000 of an ampere, a milliamp, abbreviated as ma, and

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even 1/1000 of a milliamp, or a microamp, μa . The currents on the

RoboBoard are generally in the milliamp range, except for the

motors, which can require a full ampere under heavy load. Current

has a direction, and we define a positive current from point A to B as

the flow of positive charges in the same direction. Negative charges

can flow as well, in fact, most current is actually the result of negative

charges moving. Negative charges flowing from A to B would be a

negative current, but, and here is the tricky part, negative charges

flowing from B to A would represent a positive current from A to B .

The net effect is the same: positive charges flowing to neutralize

negative charge or negative charges flowing to neutralize positive

charge; in both cases the voltage is reduced and by the same amount.

Batteries

Charges can be separated by several means to produce a voltage. A

battery uses a chemical reaction to produce energy and separate

opposite sign charges onto its two terminals. As the charge is drawn

off by an external circuit, doing work and finally returning to the

opposite terminal, more chemicals in the battery react to restore the

charge difference and the voltage. The particular type of chemical

reaction used determines the voltage of the battery, but for most

commercial batteries the voltage is about 1.5 V per chemical section

or cell. Batteries with higher voltages really contain multiple cells

inside connected together in series. Now you know why there are 3 V,

6 V, 9 V, and 12 V batteries, but no 4 or 7 V batteries. The current a

battery can supply depends on the speed of the chemical reaction

supplying charge, which in turn often depends on the physical size of

the cell and the surface area of the electrodes. The size of a battery

also limits the amount of chemical reactants stored. During use, the

chemical reactants are depleted and eventually the voltage drops and

the current stops. Even with no current flow, the chemical reaction

proceeds at a very slow rate (and there is some internal current flow),

so a battery has a finite storage or shelf life, about a year or two in

most cases. In some types of batteries, like the ones we use for the

robot, the chemical reaction is reversible: applying an external

voltage and forcing a current through the battery, which requires

work, reverses the chemical reaction and restores most, but not all,

the chemical reactants. This cycle can be repeated many times.

Batteries are specified in terms of their terminal voltage, the

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maximum current they can deliver, and the total current capacity in

ampere-hours.

You should handle batteries carefully, especially the ones we use in

this course. Chemicals are a very efficient and compact way of storing

energy. Just consider the power of gasoline or explosives, or the fact

that you can play soccer for several hours powered only by a slice of

cold pizza for breakfast. Never connect the terminals of a battery

together with a wire or other good conductor. The battery we use for

the RoboBoard is similar to the battery in cars, which uses lead and

sulphuric acid as reactants. Such batteries can deliver very large

currents through a short circuit, hundreds of amperes. The large

current will heat the wire and possibly burn you; the resulting rapid

internal chemical reactions also produce heat and the battery can

explode, spreading nasty, reactive chemicals about. Charging these

batteries with too large a current can have the same effect. Double

check the circuit and instructions before connecting a battery to any

circuit. More information on batteries can be found in Chapter 7.

Circuit Elements

Resistors

We need some way to control the flow of current from a voltage

source, like a battery, so we do not melt wires and blow up batteries.

If you think of current, charge flow, in terms of water flow, a good

electrical conductor is like big water pipe. Water mains and fire hoses

have their uses, but you do not want to take a drink from one. Rather,

we use small pipes, valves, and other devices to limit water flow to

practical levels. Resistors do the same for current; they resist the flow

of charge; they are poor conductors. The value of a resistor is

measured in ohms and represented by the Greek letter capital omega.

There are many different ways to make a resistor. Some are just a coil

of wire made of a material that is a poor conductor. The most

common and inexpensive type is made from powdered carbon and a

glue-like binder. Such carbon composition resistors usually have a

brown cylindrical body with a wire lead on each end, and colored

bands that indicate the value of the resistor. The key to reading these

values is given in Chapter 2.

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There are other types of resistors in your robot kit. The potentiometer

is a variable resistor. When the knob of a potentiometer is turned, a

slider moves along the resistance element. Potentiometers generally

have three terminals, a common slider terminal, and one that exhibits

increasing resistance and one that has decreasing resistance relative

to the slider as the shaft is turned in one direction. The resistance

between the two stationary contacts is, of course, fixed, and is the

value specified for the potentiometer. The photoresistor or photocell

is composed of a light sensitive material. When the photocell is

exposed to more light, the resistance decreases. This type of resistor

makes an excellent light sensor.

Ohm's Law

Ohm's law describes the relationship between voltage, V , which is

trying to force charge to flow, resistance, R , which is resisting that

flow, and the actual resulting current I . The relationship is simple

and very basic: . Thus large voltages and/or low

resistances produce large currents. Large resistors limit current to

low values. Almost every circuit is more complicated than just a

battery and a resistor, so which voltage does the formula refer to? It

refers to the voltage across the resistor, the voltage between the two

terminal wires. Looked at another way, that voltage is actually

produced by the resistor. The resistor is restricting the flow of charge,

slowing it down, and this creates a traffic jam on one side, forming an

excess of charge with respect to the other side. Any such charge

difference or separation results in a voltage between the two points,

as explained above. Ohm's law tells us how to calculate that voltage if

we know the resistor value and the current flow. This voltage drop is

analogous to the drop in water pressure through a small pipe or small

nozzle.

Power

Current flowing through a poor conductor produces heat by an effect

similar to mechanical friction. That heat represents energy that comes

from the charge traveling across the voltage difference. Remember

that separated charges have the potential to do work and provide

energy. The work involved in heating a resistor is not very useful,

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unless we are making a hotplate; rather it is a byproduct of restricting

the current flow. Power is measured in units of watts (W), named

after James Watt, the Englishman who invented the steam engine, a

device for producing lots of useful power. The power that is released

into the resistor as heat can be calculated as P=VI , where I is the

current flowing through the resistor and V is the voltage across it.

Ohm's law relates these two quantities, so we can also calculate the

power as The power produced in a resistor

raises its temperature and can change its value or destroy it. Most

resistors are air-cooled and they are made with different power

handling capacity. The most common values are 1/8, 1/4, 1, and 2

watt resistors, and the bigger the wattage rating, the bigger the

resistor physically. Some high power applications use special water

cooled resistors. Most of the resistors on the RoboBoard are 1/8 watt.

Combinations of Resistors

Resistors are often connected together in a circuit, so it is necessary

to know how to determine the resistance of a combination of two or

more resistors. There are two basic ways in which resistors can be

connected: in series and in parallel. A simple series resistance circuit

is shown in Figure 4.4.

Figure 4.4: Two Resistors in Series

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Determining the total resistance for two or more resistors in series is

very simple. Total resistance equals the sum of the individual

resistances. In this case, RT=R1+R2 . This makes common sense; if

you think again in terms of water flow, a series of obstructions in a

pipe add up to slow the flow more than any one. The resistance of a

series combination is always greater than any of the individual

resistors.

The other method of connecting resistors is shown in Figure 4.5,

which shows a simple parallel resistance circuit.

Figure 4.5: Two Resistors in Parallel

Our water pipe analogy indicates that it should be easier for current

to flow through this multiplicity of paths, even easier than it would be

to flow through any single path. Thus, we expect a parallel

combination of resistors to have less resistance than any one of the

resistors. Some of the total current will flow through R1 and some will

flow through R2, causing an equal voltage drop across each resistor.

More current, however, will flow through the path of least resistance.

The formula for total resistance in a parallel circuit is more complex

than for a series circuit:

RT={1{1R1}+{1R2}...+{1Rn}} (1)

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Parallel and series circuits can be combined to make more complex

structures, but the resulting complex resistor circuits can be broken

down and analyzed in terms of simple series or parallel circuits. Why

would you want to use such combinations? There are several reasons;

you might use a combination to get a value of resistance that you

needed but did not have in a single resistor. Resistors have a

maximum voltage rating, so a series of resistors might be used across

a high voltage. Also, several low power resistors can be combined to

handle higher power. What type of connection would you use?

Conductors, Insulators, and Resistors.

Conductors and Insulators

Because of the distribution of electrons in the VALENCE RING of a

natom, some elements will allow electrical current to flow easier than

others. Materials which easily allow the flow of electric current are

called CONDUCTORS . CONDUCTORS do not hold tightly to the

electrons in their VALENCE RING, and are said to have a large

number of FREE ELECTRONS . Some examples of good conductors

are Gold, Silver, Copper, Aluminum, Zinc, and Carbon. Other

elements do not allow electrical current to flow easily, and these are

called INSULATORS . INSULATORS tend to hold tightly to the

electrons in their VALENCE RING, and do not want to share with

other atoms. Some examples of good insulators are Quartz,

Mica,Teflon, Polystyrene, and Water. (Yes, water is an insulator.... not

a conductor. This will be explained later in more detail).

Resistors and Resistance:

If water is moving through a hose,

we say that it has FLOW .

If we restrict the flow, by pinching

the hose, we are causing friction at

the point of restriction. This friction

can be said, is resistance to the flow

of the water.

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Electricity, according to Benjamin Franklin, acts like a fluid. It flows

and has a measurable CURRENT . We can restrict its flow by adding

electrical friction. We say that the restriction of electrical flow is

called RESISTANCE and that a device which causes such

RESISTANCE is called a RESISTOR . All materials, even the very best

CONDUCTORS demonstrate a certain amount of RESISTANCE to

electron flow.

In order to compare the resistance of various materials, we need to

have some standard unit of measurement. The unit of measurement

for resistance is called the Ohm , and is indicated by the Greek letter

Omega ( Ω ).

One Ω is defined as the amount of resistance that a 1000 foot piece of

#10 copper wire has. A 3000 foot piece of #10 copper wire would

have 3 Ohms of resistance. A 500 foot piece of #10 copper wire would

exhibit 1/2 an Ohm, etc. Although Ohm is the basic unit, KiloOhm

and MegOhm are frequently used. 1 KiloOhm (K Ω) is equal to 1

thousand Ω. 1 MegOhm (M &Omega) is equal to 1 million Ω.

There are 4 factors that determine the resistance of a material:

(1) Type of Material

The resistance of various types of materials are different.

For instance, gold is a better conductor of electricity than

copper, and therefore has less resistance.

(2) Length

The resistance of a material is directly proportional to it's

length. The longer the material is, the more resistance it

has. This is because the electrons must flow through more

material, and therefore meets more friction over the

entire distance.

(3) Cross Sectional Area

The resistance of a material is inversely proportional to

the cross sectional area of the material. This means that

the thicker the substance is across, the lower the

resistance. This is because the larger the cross sectional

area is, the less friction there is over a given length.

(Picture in your mind, if you will, that a fire hose will pass

more water than a garden hose, because the wider the

pipe, the less resistance it has).

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(4) Temperature

In various types of materials, resistance can vary inversely

or directly with the temperature. This is because of the

chemical properties of the material. In Carbon, for

instance, the resistance decreases as the temperature

rises. So we say it varies inversely. In copper, however, the

opposite is true, with the rise in temperature, we have a

rise in the resistance.

Resistance then, is basically a form of friction which restricts the flow

of an electrical current. In basic science class, you learned that by

putting your hands together, and rubbing them quickly, your hands

get warm. This is because friction generates heat. Electrical friction -

RESISTANCE - also generates heat.

So not only can resistance change with heat, but causes heat as well.

An important point to remember when working with resistors,

especially in high power circuits.

Schematic Symbols

Sometime over the years, some bright soul determined that it would

be difficult to draw a picture of every component that you decided to

put into a circuit. However, they needed a way to tell their colleagues

about discoveries and accomplishments. So a system was developed

that was a sort of "electrical shorthand". They call it a SCHEMATIC

DIAGRAM and the individual component representations are called

SCHEMATIC SYMBOLS .

Throughout the course, I will be introducing you to the various

SCHEMATIC SYMBOLS one by one. This lesson will take you through

the first two symbols, and describe how they are used in a circuit.

The first three SCHEMATIC SYMBOLS you will be introduced to are

the lamp, battery and resistor.

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Remember that a resistor is

any device which causes

electrical friction. In

electronics, the resistor can be

substituted for any current load. The

schematic symbol for a battery can

likewise be substituted for any direct

current supply voltage. So, in

essence, we could theoretically use our battery and resistor to

represent our light bulb circuit.

You will notice that the picture on the left is the same one we just

looked at. The one on the right actually has two schematic diagrams.

The schematic on the left is an exact representation of the picture on

the left. The schematic on the right we say is an ELECTRICAL

EQUIVILANT circuit for the one on the left. Any circuit, no matter

how complex, can be broken down to being a source and a load. The

resistor represents the light bulb, which is the load of the circuit.

Anytime you are having a problem figuring out how a circuit works, it

can be helpful to break it down to an ELECTRICAL EQUIVILANT

circuit.

The SCHEMATIC SYMBOL for the light bulb is pretty self

explanatory. The Schematic for the resistor looks like a series of sharp

turns. Just remember that on a road, you have to slow down at sharp

turns, and electrical flow (current) has to slow down at a resistor. The

battery needs a little explanation. The lines represent the electrodes

of a battery. Note that the SHORT line is always the NEGATIVE

terminal, and the longer line is always the POSITIVE terminal.

Also along the way, I will try to give

you an idea of what certain types of

electronic components look like,

although there are so many shapes out

there, I can not possibly cover them

all.

I am fairly certain you already know

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what a battery and a light bulb look like, but you may never have seen

a resistor. There are many types of resistors, but some of the most

common types are shown in the picture to the left.

The top one is a ceramic coated " wirewound ", which, as its name

implies, consists of a winding of wire, cut to a certain length to create

a certain amount of resistance. The second is a carbon composite, and

the third is a metal film or metal oxide, which has very tight

resistance tolerances.

Note that on wirewound resistors, the values are printed on the side,

whereas the carbon and metal types have their values painted on as

color coded bands around the resistor.

EXTRA CREDIT

Not a required part iof the course, but if you wish to pursue

electronics, you should probably memorize the resistor color code. It

will be used throughout your career.

THE RESISTOR COLOR CODE

Many resistors that are produced are very small. In addition, resistors

can get extremely hot with use. So hot, in fact, that they will often

burn off any small lettering that may be printed on them. For this

reason, resistors have been made with colored bands painted onto

them. These bands conform to a universal color code, which identifies

the value and tolerance of the resistor. Each of the colors below,

correspond to a particular number.

For the purpose of memorization, I was taught a MNEMONIC to

remember the colors and their related numbers. However, for reasons

of political correctness, I can not teach you the same mnemonic. The

mnemonic procedure, though, is still valid, so I will present you with

a new - more politically correct one. If you memorize this phrase, you

will never forget the resistor color code:

Black Bunnies Run Over Your Greens But People Get Wise - Ripe

Golden Squash Now

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If you remember this mnemonic, you will not only know the values of

resistors on sight, but also their tolerances. Here's how it works:

Using the above phrase, it will indicate the following numbers:

BLACK BROWN RED ORANGE YELLOW GREEN BLUE PURPLE GREY WHITE

0 1 2 3 4 5 6 7 8 9

color value multiplier tolerance

Black 0 0

Brown 1 1

Red 2 2

Orange 3 3

Yellow 4 4

Green 5 5

Blue 6 6

Violet 7 7

Gray 8 8

White 9 9

Gold

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Silver

Resistors may have anywhere from 3 to 6 colored bands on them. As a

rule, the first two bands are the "value bands", so the color directly

corresponds to the value. In the example, we are using a 27,000 Ohm

( or 27K Ohm ) resistor. The first two colors are RED and PURPLE,

indicating the numbers 2 and 7. This is where things get tricky. On

the 3 an 4 band resistors, the third band, called the "MULTIPLIER" -

in this case being Orange, indicates that the 27 is followed by THREE

zeros ( 000 ). So in this case, we have 27 followed by 000 or a 27,000

Ohm resistor.

If there are only 3 bands, then we are done. 2 Questions arise though:

1. Why did we memorize the "Ripe Golden Squash Now" portion

of the mnemonic? We already have all 10 numbers!

2. What about the 4th band?