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How to Read a Schematic And Basic Electronics
We will begin at the beginning by discussing a little basic electronics. Don't worry. I've taught 10yearold girls and boys the same material as part of a church ministry, and they know pretty much everything you will read in this section. I hope there are other adults who will teach kids this material. Work through an organization where you can get a background check and go for it. It's worth the effort, even if you are a 72yearold like me. In my case it's because my kids need to know that education is the surest way out of their poverty. Maybe you know children in the same situation.
This web site covers the basic concepts of embedded and control systems. With that knowledge, a person can open the door to a career that represents the occupational future of this country. Run a search for "embedded and control systems salary survey" to see how well the effort pays off monetarily. Just as important is the pure joy of working with robots and other grown up toys.
So let's get started. In general terms, a circuit can be described as any group of electrical or electronic devices connected together by conductors. Conductors are most often metallic, and wires were the conductor of choice in the past. Old radios and other electronic equipment were often a rat's nest of wires, a little like the old Silvertone guitar amp I've been refurbishing:
Today, it's more common to find metallic
pathways, often called traces,
on a board constructed of a mixture of fiberglass and epoxy, such as the board for one of my products, The Listening Car (The video shows the board being used to drive a light box I built. It can also drive motors and other devices up to a little over 1 horesepower. The original idea was for it to drive lights under lowrider cars.) :
The terms board
and card
are synonymous in this context. You will often hear professionals use the initials P.C.B. (Printed Circuit Board).
A
schematic in electronics is a drawing representing a circuit. It uses
symbols to represent realworld objects. The most basic symbol is a
simple conductor, shown simply as a line. If wires connect in a
diagram, they are often shown with a dot at the intersection:
Conductors
that do not connect are shown without a dot, or with a bridge formed
by one wire over the other:
Among
the connections are power and ground, the high and low system
voltages respectfully. The 5 or 3 volt system power in the schematic
of a computer is shown simply as 5V or 3V. There is also a +12V
supply and a 12V supply. Ground, or 0 volts, has its own symbol:
A
switch
is
a device that is capable of allowing the user to make or break the
circuit as if the wire had been connected or broken. Its symbol
reflects this characteristic:
A
resistor
is
a device that resists the flow of charge. Its symbol reflects this
characteristic by making the line jagged:
Just
in case you have seen or heard "flow of current" elsewhere
rather than "flow of charge", see the definition of current
below.
The unit of resistance is the ohm, pronounced om with a long o. The K you will find in a lot of schematics stands for kilohm or thousands of ohms. 10K means the same as 10,000. Meg and sometimes M mean megohm or million ohms. 4.7Meg or 4.7M is the same as 4,700,000.
You will sometimes see two variations on resistors in some schematics. One is the
resistor array or network. It is commonly found in a Single Inline
Package (SIP) containing several resistors connected together. They
can be found in many configurations. One arrangement simply
connects one end of the resistors to each other and brings them out
to a common connection. The other end of each resistor is left free:
Another, more common variation is the variable resistor. It has a third contact
that can move along the resistor element to permit the values at that
point to be variable. The moveable part is called the wiper and is
shown as an arrow in a schematic:
There is a relationship between voltage, current and resistance that is expressed by Ohm's Law, which says that Voltage is equal to Current times Resistance, or:
V = I * R
V is voltage (often referred to as Electromotive Force where E rather than V is used), I is current and R is resistance. Current is expressed in Amperes, or amps for short. Very little current is used in typical electronic circuits, so milliamps, which means 1/1000 amp, is used. One milliamp = .001 amp. It's abbreviated ma, or sometimes MA.
To paraphrase a definition of charge from whatis.com :
"The coulomb (symbolized C) is the standard unit of electric charge in the International System of Units (SI). It is a dimensionless quantity. A quantity of 1 C is equal to approximately 6.24 x 10^{18}, or 6.24 quintillion."
"In
terms of SI base units, the coulomb is the equivalent of one
amperesecond. Conversely, an electric current of 1 amp represents 1
C of unit electric charge carriers flowing past a specific point in 1
second. The unit electric charge is the amount of charge contained in
a single electron. Thus, 6.24 x 10^{18}
electrons have 1 C of charge. This is also true of 6.24 x 10^{18}
positrons or 6.24 x 10^{18}
protons, although these two types of particles carry charge of
opposite polarity to that of the electron."
Since we deal mostly with electrons in electronics, 1 amp represents the effect of 6,240,000,000,000,000,000 electrons flowing past a point per second. Thus, since current is already defined as something flowing, to say "current flow" would be to say "..... flowing flow" which is incorrect because it is redundant.
Now let's say we have a 10K resistor and 2 milliamps of current. The voltage across the resistor will be:
V = I * R = .002 * 10,000 = 20 volts
We can use the original Ohm's Law equation and a little simple algebra to generate an equation for each of the three variables. It would be a good idea to learn the following well, as knowing at least some simple algebra will be necessary in electronics. It requires remembering just two things:
1. It's OK to do something to one side of an equation as long as the same thing is done to the other side. The two sides will remain equal.
2. Anything divided by itself is equal to 1.
Start
with the original equation:
V = I * R
Now divide both sides
by R. Since R/R = 1, the right side now becomes I * 1 which is simply
I, giving us V/R = I. If we switch sides and put the I on the left we
end up with:
I = V/R
Again,
start with the original Ohm's Law equation:
V = I * R
Now
divide both sides by I. Since I/I = 1, the right side now becomes R *
1 which is simply R, giving us V/I = R. If we switch sides and put
the R on the left we end up with: R = V/I
Thus,
all three equations are:
V = I * R
I = V/R
R = V/I
Always
work a problem by writing down the equation first. For example,
What
is I if V = 10 and R = 5?
Write
down the equation:
I = V/R
Now
plug in the values, so here's what you get:
I
= V/R = 10/5 = 2 Amps
One way to remember the three equations is to say, "The Vulture looks down and sees the Iguana and the Rabbit side by side (V = I * R), the Iguana sees the Vulture over the Rabbit (I = V/R) and the Rabbit sees the Vulture over the Iguana (R = V/I)." But please learn the algebra. It will serve you well in the future.
A very common circuit is a voltage divider. An example might be like the following:
Two components connected endtoend, such as the resistors above, are said to be connected in series.
Here, the total resistance is simply the sum of the two. In this case, it
would be 22000 + 33 = 22033 ohms. If 1 volt is applied to the open
end of the 22K resistor, the current through the whole circuit would
be I = V/R = 1/22033 or .00004538646576 amps, or about .05
milliamps.
The
voltage across the 33 ohm resistor is then
V = I * R =
.00004538646576 * 33 = .00149775337 volts, or about 1.5 millivolts
(1/1000 volt).
Resistors are also often connected in parallel , such as below:
The
value of the above parallel network is:
R = 1/(1/R1 + 1/R2 +
1/R3)
The equation is good for any number of resistors. There's more on parallel resistors below.
The following shows the symbols and units for voltage, resistance and current. Power is also shown since it can be found from the other quantities: P = VI:
Quantity 
Symbol 
Unit 
Voltage or Electromotive Force 
V or E 
Volts 
Resistance 
R 
Ohms 
Current 
I 
Ampere or Amp (often milliamp in electronics) 
Power 
P 
Watts 
A
color code is used to determine the value of a resistor:
The following will help you remember the colors:
Number 
Color 
Memory Word 
0 
Black 
Bad 
1 
Brown 
Boys 
2 
Red 
Rob 
3 
Orange 
Our 
4 
Yellow 
Young 
5 
Green 
Girls 
6 
Blue 
But 
7 
Violet 
Violet 
8 
Gray 
Gives 
9 
White 
Willingly 
5% or .1 multiplier 
Gold 

10.00% 
Silver 

To determine the value, first write down the first 2 numbers from the first two colors. Then put the number of 0s indicated by the third color after the first 2 numbers.
Consider these examples:
The above is yellow, violet, brown. Yellow=4, Violet=7 and Brown=1, so the first two digits are 47 and we put 1 zero on the end to make 470 ohms.
Or this:
This one is gray, red and black. The last color indicates the temperature coefficient. Gray=8, Red=2 and Black=0, so the first two numbers are 82 and there are no zeros on the end, so it's 82 ohms. You can see the gold tolerance band a little better here, which means the resistor is 82 ohms +/ 5%.
Download my free ColorCode program HERE to help you learn the code. There are some other applications there that might be useful as well.
Capacitors are devices which have metal plates separated by an insulator. They are used to temporarily store an electrical charge. Their symbol reflects their construction:
The
unit of capacitance is the Farad, but it's so large that the
microfarad
is used in practice. Microfarad means millionths of a Farad. It's
often abbreviated mf, MF or some variation, although the correct
abbreviation is µF. A value without a designator is assumed to
be in microfarads. For example, in a schematic you might see several
capacitors simply designated .1, but they are actually .1µF capacitors.
Some capacitors must have their leads connected to the positive or negative side of a circuit. They are polarized capacitors. When that is the case, one side will be shown with a + sign where the positive side must be, or a  sign where the negative side must be, or both.
It's also very common to see picofarads abbreviated pf in some schematics. A picofarad is 10^{12} Farad, and is sometimes called a micro microfarad.
A diode permits the flow of charge in only one direction. Its symbol reflects this characteristic, but with a slight problem:
Anode Cathode
The
slight problem comes from the fact that flow of charge, at least in a
wire, is from where there are a greater number of electrons to where
there are fewer. Electrons are negatively charged. Thus, electrical
flow of charge is from negative to positive in a wire. The problem
with the symbol is that the cathode, not the anode, is the negative
side. Electrical flow of charge is from the cathode to the anode,
against the direction of the arrow. It's backwards because Benjamin
Franklin thought the flow of charge was from positive to negative. A special
kind of diode is the Light Emitting Diode (LED), shown as a diode
with lines representing light waves:
Integrated
Circuits contain many individual components. They, in
turn, usually form several functional blocks. For example, the
following page shows a pinout for the 74LS08 Quad 2 Input AND gate,
along with its truth table. VCC is the 5 volt supply, and GND is
ground. Sometimes ground is shown as VSS. The gate inputs are the As
and Bs, and the outputs are the Ys. Thus, the inputs to gate 1 are 1A
and 1B, and the output is 1Y. You will see variations on these
conventions, but they hold true in many cases.
An
Operational
Amplifier
also contains many individual components, but is not a digital
circuit. It looks a little like a buffer which can be found in the
Boolean Logic section, but has 2 inputs:
You
can find a more detailed treatment of operational amplifiers on the
Internet. For a simplified coverage of the subject, look at the
circuit below:
An OpAmp has many important characteristics. One of them is that the above circuit, called an inverting amplifier, attempts to prevent any current through the inverting () input. In this circuit, Rin connects to the inverting input. Rfb also connects to the inverting input, with its other end connected to the output. Rfb is called the feedback resistor. Let's attempt to drive a current through the inverting input by placing 1V on the unconnected end of Rin and assume that the right end has 0 volts on it. If Rin == 1K, the current will be Iin = V/Rin = 1/1K = 1ma
The output will try to counter this by driving a current of the opposite polarity through the feedback resistor into the inverting input. With a 10K feedback resistor, the required voltage to do that will be: V = (I * Rfb) = (1ma * 10K) = 10V.
Thus,
we get a voltage to current conversion, a current to voltage
conversion, a polarity inversion and, most importantly,
amplification. Amplification or gain is commonly labeled G. In the
case of the inverting amplifier,
G = (Feedback Resistor / Input
Resistor)
In this case, it's G = (Rfb/Rin) = 10.
Since the feedback cancels out the input, there is no voltage at the inverting input. It is said to be at virtual ground .
Now look at the circuit below taken out of a schematic from one of my projects:
The
gain is a little over 1000 in order to provide enough amplification
for the lowlevel output of a microphone. The signal is not only
amplified but inverted because we are going into the inverting input.
The inversion however, is not quite the same as it is in a digital
device. Here, we are talking about an audio analog signal that, once
transformed into an electrical signal by the microphone, moves
smoothly and continuously in the negative and positive voltage
directions. Inversion here means that when the input moves in the
positive direction, the output moves in the negative direction. When
the input goes toward negative, the output goes toward positive. C1
prevents DC voltages from even getting into the circuit. This
blocking action will be discussed in a future section.
The noninverting side is designated by the +. It is there that a positive offset voltage is applied. If R1 were not connected to C1 but rather to ground, the noninverting side would exhibit a gain of (R2/R1)+1 for the bias voltage. With C1 however, there is no DC gain for the noninverting side, and AC is effectively shorted to ground by C2. The result is a gain of 1 on the noninverting side for DC voltages.
The following is a selftest over this section. You will find other, shorter tests in various sections below. It would be a very good idea to make sure you know the answers to all of the questions in this document since the sections that follow will build on this one.
1. _____ is a drawing that represents a circuit.
A)
Switch
B) Schematic
C) Ground
D) Diagram
2. A _____ is a device that allows the user to break the circuit.
A)
Scissors
B) Schematic
C) Resistor
D) Switch
3. A _____ is a device that resists the flow of charge.
A)
Resistor
B) Buffer
C) Diode
D) Microfarad (or µF)
4. The unit of resistance is the ____ . The relationship between voltage, current, and resistance is expressed by ____ .
A)
Buffer B) Ohm's Law C) Amplifier D) Capacitors
E) Ohm F) Diode G)
Circuits H) Switch
5. The ____ is the unit of current. If there is very little current, it is expressed as ____, which means 1/1000th.
A) Amperes (or Amps) B) Volts C) Millivolts
D) Picofarads (or pf) E) Milliamps (or Ma or ma)
F) Microfarads (or µF;) G) Amplifier, Circuits
6. _____ are devices which have metal plates separated by an insulator. They temporarily store an electrical charge.
A)
In Series
B) Cathode
C) Capacitors
D) Microfarad
7. What permits the flow of charge in only one direction?
A)
Anode
B) Diode
C) Cathode
D) Schematic
8. _____ contain many individual components and usually form several functional blocks.
A)
Schematics
B) Diodes
C) Amplifiers
D) Integrated Circuits
9. The _____ also contains many components, but is not a digital device.
A)
Inverting Amplifier
B) Operational Amplifier
C) Volt
D)
Electron
10. This is _________________________________________
11. This is ___________________________________
12. This is __________________________________________
13. This is _______________________________________
14. This is ________________________________________
15. This is _________________________________________
16. This is _________________________________________
17. Ohm's Law: ________________________________________
18. I = 4, R = 10 so V = ________________ = ________________
19. V = 12, R = 6 so I = ________________ = ________________
20. I = 75, V = 150K Volts so R = ________________ = ________________
21. What's the power for 20?: P = ________________ = ________________
22.
The value of the following is
______________
Resistors that are connected
endtoend are in series with each other. They are not a series
circuit since the ends are not connected. Remember the phrase “series
circle” to get an idea of what a series circuit looks like. The
following resistors are connected in series, but are not a series
circuit since there is no “circle”:
Remember the two rules about a series circuit:
The current at all points of a series circuit is the same.
The voltage drops of the parts of a series circuit add up to the source voltage (the battery voltage in this case).
To start with an easy
circuit, look at the following. To find the total resistance of
resistors connected in series, just add the values:
So,
the total resistance in the above circuit = ___________ ____________ (there are two blanks because both the value and units should be included)
Now, remember that the current in a circuit = I = V/R.
The voltage is ____________ ____________
So, remembering to write the equation first, plug in the values to get the current:
I = ____________ =
____________ = ____________ ____________
To measure the voltage drop
across a resistor, just put your meter wires on each end of the
resistor:
You can get a meter for about $6 at Harbor Freight and probably at other stores. I got one for each of the kids in my class:
Since all three resistors are 1000 ohms in the above circuit, there is a total of 3000 ohms, and I = 3/3000 = 1ma. Remember, ma means milliamps or thousandths of an amp, so 1ma is the same as 1/1000^{th} of an amp. Now, to find the voltage across each 1K resistor, use V = IR.
So, the calculated voltage across each resistor =
V = IR = ____________ = ____________ ____________
This one is a little more
complicated:
To
find the total resistance of resistors connected in series, just add
the values. So the total resistance is 1000 + 2200 + 470 = 3670 ohms.
Then the current for the whole circuit is I = V/R = 3/3670 = about .8ma.
In this experiment, you will
use a breadboard:
The holes outlined in green are connected to each other. That's true of all of the vertical rows of holes in the center section, and the horizontal rows of holes on the outside edges. Horizontal holes in the center section and vertical holes in the outside sections are not connected to each other.
So, if three resistors are
plugged like this, they are connected endtoend:
If you connect a 3 volt battery pack to
the left and right end of the whole circuit, you will have the series
circuit above with the three resistors in series with the 3 volt battery:
Now do this experiment. Connect three resistors in series with each other and a battery to make a series circuit like the one above. Pick the resistors so that they are not the same values and add up to a total resistance between 1000 and 10000 ohms.
Would including a 10K resistor work? ________. Why? ________________________
R1 = ________ ________
R2 = ________ ________
R3 = ________ ________
Calculate (don't measure, calculate) the total of the series resistance.
Total Series Resistance: ______________ Ohms
Now, measure (don't just read it off of the battery) your source voltage.
Source Voltage (Battery): ____________ Volts
Again, remember the two rules for a series circuit:
1. The current at all points of a series circuit is the same.
2. The voltage drops of the parts of a series circuit add up to the source voltage (the battery voltage in this case).
Calculate the current in the circuit. Remember, I = V/R, where V is the battery voltage and R is the total series resistance. Remember, enter the equation first, then plug in the numbers, then the answer.
Calculated Current: I = _____________ = _____________ = _____________
Measure (don't calculate) the voltage drops across each resistor:
R1 voltage drop: _____________ Volts
R2 voltage drop: _____________ Volts
R3 voltage drop: _____________ Volts
Sum of Voltage Drops: ____________ Volts
Now that you know the voltage across each resistor and the value of each resistor, calculate the current for each. Remember, enter the equation first, then plug in the numbers, then the answer:
R1 Current: I = ____________ = ____________ = ____________ ____________
R2 Current: I = ____________ = ____________ = ____________ ____________
R3 Current: I = ____________ = ____________ = ____________ ____________
Now look at this:
Most LEDs need 2 volts at
20ma (.02 amps) as shown in the following:
What is your power supply voltage? ____________
What is the required voltage drop across R? ___________
So what is the value needed for R?
R = ____________ = ____________ = ____________
For younger learners and those who might be a little rusty on the subject, we will be talking here about raising a number to a power. It's not hard. A number raised to a power is shown with two parts. The base is the big number (5 in the example below) and the exponent is the little number (7 in the example below). The exponent is the power to which a number is raised. To raise a number to a power, just write it down the exponent number of times and multiply. In the following example, we would say that 5 is raised to the power of 7:
5^{7}
One way to recognize an
exponent is by the fact that it is ^{raised}
when written:
5^{2} =
5 * 5 = 25
2^{3} = 2
* 2 * 2 = 8
4^{4} = 4
* 4 * 4 * 4 = 256
The number raised, such as the 5, 2 and 4 above, is called the base. Humans have used a base of 10 for thousands of years, probably because we have 10 fingers.
Each position has a weight.
For all numbering systems I am aware of, the number on the right end
of a whole number (a number without a decimal fraction) is known as
the 1's place. There, the weight is equal to the base
raised to the power of 0.
Any number
raised to the power of 0 is equal to 1.
The exponent is increased by
1 with each move to the left. Thus, the second place from the right
in a whole number has a weight equal to the base raised to the power
of 1.
Any number raised to the power
of 1 is equal to itself.
We were taught that the second place from the right is the 10's place. That's because we were using a base of 10 and we were raising it to the power of 1.
We can also raise our base to a negative power. This gives us decimal fractions when using the base of 10.
So
we have this:
10 Raised to a Power
10^{3}
10^{2}
10^{1}
10^{0}
10^{1}
10^{2}
10^{3}
Weight (place)
1000
100
10
1
.1
.01
.001
Weight as Fraction
1000/1
1000/1
10/1
1/1
1/10
1/100
1/1000
Place in words
Thousands
Hundreds
Tens
Ones
Tenths
Hundredths
Thousandths
For example, many times you will have a lot less current than 1 amp. In fact, most of the time in electronics you have only milliamps, abbreviated ma. A milliamp is one thousandth of an amp. For example, one of the circuits above was found to have a current of about .8ma. You might see 8.174386921^{4} on one calculator, or 817.4386921 x 10^{6 }on another (it might show e6 rather than x 10^{6}). To find the number of amps, just move the decimal the number of places shown by the power number. In the above cases, that's four or six places to the left, since the power is negative. Both give you a little over .0008 amps, or about .8ma. If the power number is positive, move the decimal to the right. Remember that a whole number has an imaginary decimal on the right end. So 54, 54.0 and 54. are the same thing.
Study the chart above a little and you will also notice that the weight in a position is the weight of the place to its right times the base.
Try these for practice:
1,385,247 ^{0} = ________________
1 X 10^{3 = _____________________}
.1ma = ______________ amps
10^{1} = _______________
10^{4} = _______________
For the number 432.178,
the 4 is in the ____________s place,
the 7 is in the ____________s place, and
the 8 is in the ____________s place.
And for a bit of a head scratcher:
x^{y0} = x
raised to the power of y which is raised to the power of 0 =
_______________
Just take it one step at a time from right to left.
When
you connect polarized devices, such as batteries, diodes, etc. in
series, the voltages add. You connect them positive to negative. So,
two 3 volt battery packs would be connected in series like the
following. Since they are 3 volts each, the total series voltage is 6
volts:
In
a problem above, you were supposed to figure out what size of
resistor you needed to power a LED. You learned that the LED needs 2
volts at 20ma. You also know that the current is the same everywhere
in s series circuit, and that the voltage drops add up to the source
voltage. So this is what happens if you use your two battery packs in
series:
You need to find the value of the resistor you need to do the job, which is easy. Just remember that the equation for resistance is R = V/I (or the Rabbit sees the Vulture over the Iguana). Now plug in the numbers, and you get R = 4/.02 (.02 is the same as 20ma, and 4 is the voltage drop you need). So, R = 4/.02 = 350 ohms.
Now, figure out how to use your 6 volt source with no resistor but with more LEDs. Hint: the sentence that's talking about polarized devices above will help a lot.
Another
way to connect things is to wire them in parallel. It might help to
understand what a parallel circuit looks like by thinking of a
railroad track. A railroad track has two steel beams running along
side (in parallel with) each other. The wheels of a train roll on the
beams, called rails, which are kept the correct distance apart by
railroad ties. The rails are held down on the ties with metal plates
and spikes (large nails). The whole thing sits on a bed of gravel or
other material called a ballast:
A parallel circuit looks a lot like the railroad track's rails and ties. Components (parts) of the circuit are connected across two conductors like the ties from rail to rail. You will even find the term railtorail in some electronics documents. A simple parallel circuit using just resistors follows.
Remember the two rules about a series circuit:
1. The current at all points of a series circuit is the same.
2. The voltage drops of the parts of a series circuit add up to the source voltage (usually the battery voltage in our experiments).
The parallel circuit also has two rules:
1. The current through each component can be different, but the sum of the current through all components add up to the source current.
2. The voltage across each component is the same as the source voltage.
The
usual way to calculate the combined resistance in a circuit like the
above is to use this equation:
R_{total}
= 1/(1/R1 + 1/R2 + 1/R3) = 1/(1/30K + 1/300 + 1/3K).
But since you know the voltage, you can use the rules for a parallel circuit and Ohm's law for resistance and current. So calculate the following. Remember, the voltage is 3 volts across each resistor. Also remember to write Ohm's law for current first, which is ___________ :
Current through R1: _________ = __________ = __________ __________
Current through R2: _________ = __________ = __________ __________
Current through R3: _________ = __________ = __________ __________
Total current through all 3 = __________ __________
Since you know the source voltage is 3 volts and you know the total current, you can calculate the combined resistance using Ohm's law for resistance, which is _____________ :
R_{total} = __________ = ____________ = ____________ __________
Now look at this circuit:
Notice
the three LEDs. They are in series with each other, but the three of
them together are in parallel with the resistors and light bulb. The
group of parallel components are in series with the power source and
switch. This makes a parallelseries or seriesparallel circuit. You
can say it either way. Both are correct.
Such
circuits are very common. Any room in a house that has more than one
light controlled by a single switch is usually a parallelseries
circuit.
If you are working on this material in a classroom setting, then draw a schematic diagram of the seriesparallel lighting system in a room as a team project. You could also work on it alone, but the point is that a lot, maybe even most, engineering is done in teams. You will use the power that is supplied by the electric company, which is about 120VAC. VAC means volts, alternating current, which will be discussed shortly. You will use 4 lighting units, each of which needs 120VAC to power it. Finally, you will use a switch to turn on all 4 lights at once. Use engineering grid paper for rough drawings and a white board for the final drawing if available. Use any symbols you like for the different parts. Some ideas are below:
When
you use a battery, you are using something called DC, or direct
current. The positive stays positive and the negative stays negative.
But that's not the same with AC (alternating current). With AC, the
voltage moves from 0 to a maximum positive value, back to 0, then
down to a maximum negative value. If you could see it, it might look
like a sine wave:
You
can see the above wave form with an oscilloscope:
The
AC wave form shown above is an example of an analog signal. Not all
analog signals look like a sine wave. Some, such as the human voice,
are full of different widths and heights all mixed together. The
oscilloscope display of a voice pattern can be seen by amplifying the
signal from a microphone, then connecting the signal to an
oscilloscope. What's being seen is not the actual sound wave. A sound
wave can be visualized as bursts of compressed air particles. The
darker areas below represent the compressed parts of a sound wave:
What
is seen on the oscilloscope is the sound wave converted to an
electrical signal. Most computers, however, work with signals that
are either on of off.
The
next section will begin the programming part of the tutorial. We will
eventually work with on/off signals, which are called digital
signals. When we reach the point where we are attempting to look at
analog signals we will need to convert them to digital patterns that
the computer can work with.
But
for now, let's just talk about basic programming in the next section.
Table
Of Contents
Answers
to The Questions in this Section
Next: Programming Part 1
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