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Introduction to Robotics with
CADARA




Electronic concepts




Active and Passive Components



2.1 Electronics Components

Electronics deals with flow of electrons through nonmetal

conductors or

semi conductors. Electrical refers to the

flow of charge through metal conductors. Flow of charge

through Germanium, which is not a metal, would come

under electronics. The study of new semiconductor

devices and related technology

is a branch of physics

whereas the design and construction of electronic circuits

to solve practical problems comes under electronics

engineering.

An electronic component is an entity in an electronic

system, who serves the purpose of changing, the nature

of charges in accordance with the purpose of the

electronic system as a whole. Components are generally

used to create an electronic circuit with a particular

function
(for

example an amplifier, radio receiver, or

oscillator). Some common electronic components are

capacitors, resistors, diodes, transistors etc.


2.2

Active and Passive Components


The main

components used in electronics are of two
general types:
passive (e.g. resistors and capacitors) and
active (e.g. transistors and
integrated circuits).

• Passive components are those that do not have


gain or directionality. They req
uire power from


outside to operate.

• Active components are those that have gain or


directionality. They can amplify signals on their


own.


2.2.1
Passive Compone nts



The following section outlines the commonly used passive
components.






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2.2.1.1

Resistors


2.2.1.2

Measurement of Resistance Values


Resistance values can be identified manually by using
color codes.
The value of most resistors is shown by a
pattern of coloured rings.
These are read starting from
the band closest to an end. The colours are
internationally defined as listed below.

A brief illustration of how the color code is read is shown
in the figure
below.

The First band is red and it stands for two, violet for

seven, orange for three and gold for tolerance of 5%.

Therefore, the total value of resistance is 27*10
3

with 5%

tolerance.


This value is commonly specified as 27kΩ.












Figure: 2.1

















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There are two classes of resistors; fixed resistors and the

variable resistors. They are also classified according to

the material from which they are made. The typical

resistor is made of either carbon film or metal film. There

are other types

as well, but these are the most common.


The resistance value of the resistor is not the only thing
to consider when
selecting a resistor for use in a circuit.
The "tolerance" and the electric
power ratings of the resistor are also important.

The tolerance of a resistor denotes how close it is to the
actual rated
resistance value. For example, a
±5%
tolerance would indicate a
resistor that is within ±5% of
the specified resistance value.

The power rating indicates how much power th
e resistor can safely
tolerate. Just as if you would not use a 6
-
volt
flash

light lamp to replace
a burned out light in your
house, you would not use a 1/8 watt resistor
when you
should be using a 1/2 watt resistor.

The maximum rated power of the

resistor is specified in

Watts. Power is calculated using the square of the current
(I
2
) multiplied
by the resistance value
(R) of the resistor. If the
maximum rating of
the resistor is exceeded, it will
become extremely hot and even burn.























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Resistors in electronic circuits are typically rated 1/8W,

1/4W, and 1/2W. 1/8W is usually used in signal circuit

applications.

When powering a light emitting diode, a comparatively

large current flow through the resistor, so you need to

consider the power rating of the resistor you choose.



1/8W


Figure: 2
.2

1/4W



1/2W





2.2.1.3

Calculation of Resistances in circuits


Resistances come in standard values. Therefore, to
customize the
value of resistance needed resistances are
connected in series or parallel
in a circuit. This section
describes how to calculate the value of
resistances connected in series or parallel.









Figure: 2.3













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2.2.1.4 Series Connection


In a series circuit, the current flowing is the same at all

points. The circuit diagram shows two resistors connected

in series with a 6 V battery: The total resistance in this

circuit is the sum of both the resistances R1 and R2.

R total = R1 + R2 = 2

kΩ (As shown in figure 2.3)


The current can be hence measured as


V/R = 6v/ 2kΩ= 6 (2*10
3
) = 3 * 10
-
3

Or 3mA (milli
Ampere)



2.2.1.5
Parallel Connection


In parallel connection, the potential drop is constant in all

the branches, but the current varies in accordance to the

value of resistances in each branch. The total resistance is

calculated as R total = (R1 * R2)/ (R1+R2) =1*1/ (1+1)

= 0.5kΩ




Figure: 2.4








The current can be hence measured as V/R = 6v/ 0.5kΩ=

6 / (0.5*10
3
) = 12 * 10
-
3
Or 12mA (milli Ampere).

In general, if there are ‘n’ Resistors connected in parallel
then total
resistance is calculated by the formula

1/Rtotal = 1/R1 + 1/R2 + …….. + 1/Rn




2.2.1.6

Special Kinds of Resistors

Some Resistors have values which changes according to

the environmental parameters. Most common amongst


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this

category is the LDRs (Light dependent Resistors) and
Temperature
dependent resistors commonly called as
Thermistors (Thermally
sensitive Resistors).


2.2.1.6.1 Light Dependent Resistor (LDR)



A photo resistor or Light Dependent Resistor or CdS

()
Cell is a
resistor whose resistance decreases with
increasing incident light
intensity. It can also be referred
to as a photoconductor.

A photo resistor is made of a high resistance

semiconductor. If light falling on the

device is of high

enough frequency, photons absorbed by the

semiconductor give bound electrons enough energy to

jump into the conduction band. The resulting free electron

(and its hole

partner) conduct electricity, thereby lowering

resistance.


A photoelectric device can be either intrinsic or extrinsic.

An intrinsic semiconductor has its own charge carriers and

is not an efficient semiconductor, e.g. silicon. In intrinsic

devices, the only available electrons are in the valence

band, and hence the photon must have enough energy to

excite the electron across the entire band gap. Extrinsic

devices have impurities, also called dopants, added whose

ground state energy is cl
oser to the conduction band;

since the electrons do not have, as far to jump, lower

energy photons
(i.e., longer wavelengths and lower

frequencies) are sufficient to trigger the device. If a

sample of silicon has some of its at
oms replaced by

phosphorus atoms (impurities), there will be extra

electrons available for conduction. This is an example of

an extrinsic semiconductor.


Photo resistors come in many different types. Inexpensive
cadmium
sulfide cells can be

found in many consumer
items such as camera
light meters, streetlights, clock radios, security alarms, and outdoor
clocks.










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2.2.1.7 Thermister


The resistance value of the
thermistor changes according
to temperature.




Figure: 2.5





This part is used as a temperature sensor.



Figure: 2.6

Symbol for Thermistor


2.2.1.8

Capacitors

A capacitor is a passive electrical component that can

store energy

in the electric field between a pair of

conductors
(called "plates"). The process of storing

energy in the capacitor is known as "charging", and

involves electric charges of equal magnitude, but opposite

polarity, building up on each plate. A capacitor's ability to

store charge is measured by its capacitance, in units of

farads.


Figure: 2.7





Capacitors are often used in electric and electronic circuits

as energy
-
storage devices. Capacitors are

occasionally

referred to as condensers. A wide variety of capacitors

have been invented, including small electrolytic capacitors

used in electronic circuits, basic parallel
-
plate capacitors,

mechanical variable capacitors, and the early Leyden jars,

among numerous other types of capacitors.




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The symbol

is used to indicate a capacitor in a circuit

diagram.

Generally, capacitors have two leads. Some are axial
leaded, like
resistors, and others are radial leaded, with
both leads at one end. Unlike
resistors, some capacitors
are polarized, with positive and negative
leads: the voltage across such capacitors must agree with the polarity
of the leads. Take care to orient polarized
capacitors correctly in a
circuit.


A capacitor acts as a charge store. It contains a pair of

metal plates separated by a thin sheet of insulating

material. Left to them the plates is electrically neutral
-

the number of positive protons in each exactly equals the

number of nega
tive electrons. However, if we connect

wires to the plates and apply and external voltage we can

drag electrons off one plate and push them on to the

other. This takes energy, i.e. we have to do work

charging the capacitor. The result is a capacitor with one

plate positively charged and the other negatively charged.

The energy used to move charge is stored by this

imbalance. If we connect two plates together with a

resistor, the el
ectrons 'rush back home' releasing their

energy again. The voltage between the plates of a

charged capacitor is proportional to the amount of charge

moved. The charge/voltage ratio for any specific capacitor

is called its capacitance.









Figure: 2.8












Breakdown voltage


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When using a capacitor, you must pay attention to the

maximum voltage, which can be used. This is the

"breakdown voltage." The breakdown voltage depends on

the kind of capacitor being used. You must be especially

careful with electrolytic capacitors because the breakdown

voltage is comparatively low. The breakdown voltage of

electrolytic

capacitors is

displayed as Working Voltage.

The breakdown voltage is the voltage that when exceeded

will cause the dielectric (insulator) inside the capacitor to

break down and conduct. When this happens, the failure

can be catastrophic.


Different types of cap
acitors.


Electrolytic Capacitors (Electrochemical type capacitors)


Aluminum is used for the electrodes by using a thin

oxidization membrane. Large values of capacitance can be

obtained in comparison with the size of the capacitor,

because the dielectric used is very thin. The most

important characteristic of electrolytic capacitors is that

they have polarity. They have a positive and a negative

electrode. [Polarized] This means that it is very important

which way

round they are connected. If the capacitor is

subjected to voltage exceeding its working voltage, or if it

is connected with incorrect polarity, it may burst. It is

extremely dangerous, because it can quite literally

explode. Make absolute
ly no mistakes.





Figure: 2.9




Generally, in the circuit diagram, the positive side is
indicated by a
"+" (plus) symbol.

Electrolytic capacitors range in value from about 1µF to

thousands of µF. mainly this type of capacitor is used as a

r
ipple filter in a power supply circuit, or as a filter to

bypass low frequency signals, etc. Because this type of

capacitor is comparatively similar to the nature of a coil in

construction, it is not possible to use for high
-
frequency


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circuits.

(It is said that the frequency characteristic is

bad.)


Tantalum Capacitors

Tantalum Capacitors are electrolytic capacitor that use a

material called tantalum for the electrodes. Large values

of capacitance similar to aluminum electrolytic capacitors

can be obtained. In addition, tantalum capacitors are

superior to aluminum electrolytic capacitors in

temperature and frequency characteristics. When

tantalum
powder is baked in order to solidify it, a crack

forms inside. An electric charge can be stored on this

crack.

These capacitors have polarity as well. Usually, the "+"

symbol is used to show the positive component lead. Do

not make a mistake with the
polarity on these types.

Tantalum capacitors are a little bit more expensive than

aluminum electrolytic capacitors. Capacitance can change

with temperature as well as frequency, and these types

are very stable. Therefore, tantalum capacitors are used

for circuits, which demand high stability in the

capacitance values. In addition, it is said to be common

sense to use tantalum capacitors for analog signal

systems, because the current
-
spike noise that occurs with

aluminum

electrolytic capacitors does not appear.

Aluminum electrolytic capacitors are fine if you do not use

them for circuits, which need the high stability

characteristics of tantalum capacitors.





Figure: 2.10












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2.2.1.8.1
Capacitors in Series



Figure: 2.11





1/C total = 1/C1 + 1/C2




2.2.1.8.2
Capacitors in parallel







Figure: 2.12

C

total=C1 + C2


]

2.2.1.9

Inductor

An inductor is a passive electrical component designed to
provide
inductance in a circuit.

Inductors store energy in a magnetic field created when

an electric current flows through them. Some sort of

coiled conductive winding usually implements them. The

winding may surround a magnetic core, in which case it is

called a ferromagnetic
-
core or iron
-
core inductor. Large

inductors used at low frequencies may have thousands of

turns of wire around a
n iron core; however even a

straight piece of wire (i.e., with turns and core reduced to

zero) has significant inductance.





Figure: 2.13




An "ideal inductor" has inductance, but no resistance or

capacitance, and does not dissipate
energy. A real

inductor is equivalent to a combination of inductance,



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some resistance due to the resistivity of the wire, and

some capacitance. At some frequency, usually much

higher than the working frequency, a real inductor

behaves as a resonant circuit
(due to its self
-

capacitance). In addition to dissipating energy in the

resistance of the wire, magnetic core inductors may

dissipate energy in the core due to hysteresis, and at high

currents may show other departures from ideal behavior

due to nonlinearity.




Figure: 2.14






Inductors are used extensively in analog

circuits and

signal processing. Inductors in conjunction with capacitors

and other components form tuned circuits, which can

emphasize or filter out specific signal frequencies. This

can range from the use of large inductors as chokes in

power supplies, which in conjunction with filter capacitors

remove residual hum or other fluctuations from the direct

current output, to such small inductances as generated by

a ferrite bead or torus around a cable to prevent radio

frequency interferen
ce from being transmitted down the

wire. Smaller inductor/capacitor combinations provide

tuned circuits used in radio reception and broadcasting,

for instance.


Two (or more) inductors, which have coupled magnetic

flux, form a transformer,

which is a fundamental

component of every electric utility power grid. An inductor

is used as the energy storage device in some switched
-

mode power supplies. Inductors are also employed in

electrical transmission systems, where they are u
sed to

depress voltages from lightning strikes and to limit

switching currents and fault current. In this field, they are

more commonly referred to as reactors.


As inductors tend to be larger and heavier than other

components, their u
se has been reduced in modern

equipment; solid
-
state switching power supplies eliminate



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large transformers, for instance, and circuits are designed
to use only
small inductors, if any; larger values are simulated by use of gyrator
circuits.


2.2.1.10

Diodes



A diode is a semiconductor device, which allows current to
flow through it
in only one direction. Although a transistor
is also a semiconductor
device, it does not operate the way a diode does. A diode is specifically
made to allow
current to flow through it in only one direction.

A diode can be used as a rectifier that converts AC
(Alternating
Current) to DC (Di
rect Current) for a power
supply device.


Diodes can be used as an on/off switch that controls

current. This symbol

is used to indicate a diode in a

circuit diagram. The meaning of the symbol is

(Anode)
(Cathode). Current flows

from the anode

side to the cathode side. Although all diodes operate with

the same general principle, there are different types

suited to different applications. For example, the following

devices are best used for the applications noted.


Voltage regulation diode (Zener Diode)


The circuit symbol is




It is used to regulate voltage, by taking advantage of the

fact that Zener diodes tend to stabilize at a certain

voltage when that voltage is applied in the opposite

di
rection.

Diodes that can be made to conduct backwards. This

effect, called Zener breakdown, occurs at a precisely

defined voltage, allowing the diode to be used as a

precision voltage reference. In practical voltage reference,

circuits Zener and switching diodes are connected in

series and opposite directions to balance the temperature

coefficient to near zero.







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2.2.1.11
Light emitting diode [LED]



The circuit symbol is


This type of diode emits light when current flows through
it in the
forward direction. (Forward biased.)

In a diode formed from a direct band
-
gap semiconductor,

such as gallium arsenide, carriers that cross the junction

emit pho
tons when they recombine with the majority

carrier on the other side. Depending on the material,

wavelengths (or colors) from the infrared to the near

ultraviolet may be produced. The forward potential of

these diodes depen
ds on the wavelength of the emitted

photons.

2.2.1.12
Variable capacitance diode


The circuit symbol is

The current does not flow when applying the voltage of

the opposite direction to the diode. In this condition, the

diode has a capacitance like the capacitor. It is a very

small capacitance. The capacitance of the diode changes

when changing voltage. With the change of this

capacitance, the frequency of the oscillator can be

changed.



2.2.2


Active Components


A transistor is a semiconductor device commonly used to

amplify or switch electronic signals. A transistor is made

of a solid piece of a semiconductor material, with at least

three terminals for connection to an external circuit. A

voltage or current applied to one pair of the transistor's

terminals changes the current flowing through another

pair of terminals. Because the controlled (output) power

can be much larger th
an the controlling (input) power,

the transistor provides amplification of a signal. The

transistor is the fundamental building block of modern

electronic devices, and is used in radio, telephone,

computer and other electronic syst
ems. Some transistors


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are packaged individually but most are found in
integrated
circuits.



Figure: 2.15










2.2.2.1

Bipolar Junction Transistor

A Bipolar Junction Transistor essentially consists of a pair

of PN Junction Diodes that are joined back
-
to
-
back. This

forms a sort of a sandwich where one kind of

semiconductor is placed in between two others. There are

therefore two kinds of bipolar sandwich, the NPN and PNP

varieties. The three layers of the sandwich are

conventionally called the Collector, Base, and Emitter. The

reasons for these names will become clear later once we

see how the trans
istor works.





Figure: 2.16







A transistor may be used to switch or to amplify. The image to the
right represents a typical transistor in a
circuit. Its three components are
the base, emitter and
collector, which correspond to regions of the
mixed
semiconductors from which the transistor is made.
Current
may flow from the emitter to the collector
depending on the voltage
applied to the base, but only if
this voltage exceed a certain value:








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Transistor as a switch

Once the base voltage reaches a certain level, no more

current will flow and the output will be held at a fixed

voltage. The transistor is then said to be saturated.

Hence, values of input voltage can be chosen such that

the output is either completely off, or completely on. The

transistor is acting as a switch, and this type of operation

is common in di
gital circuits where only "on" and "off"

values are relevant.







Figure: 2.17









Transistor as an amplifier

A varying base voltage, V
in
, as long as it exceeds V
be
,

controls current through the transistor and thus

influences the output voltage V
out
. The slope of the graph

is such that small swings in V
in

will produce large changes

in V
out
.



Types of transistor

This occurs because the base voltage controls how much

of the power supply voltage V
cc

causes current through

the transistor itself, and how much of it causes current

through a load driven by V
out
. It is important that the

operating parameters of the transistor are chosen and the

circuit designed such that as far as possible the transis
tor

operates within a linear portion of the graph, such as that

shown between A and B, otherwise the output signal will

suffer distortion.





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Semiconductor material: germanium, silicon, gallium arsenide, silicon

carbide, etc.



Structure

--



Polarity

--


Maximum power rating

--





Maximum
operating
--
frequency






Application

--




Physical packaging

--





BJT, JFET, IGFET

(MOSFET), IGBT,
"other types"


NPN, PNP (BJTs); N
-
channel, P
-
channel
(FETs)


Low, medium, high



Low, medium, high, radio frequency

(RF),

microwave

(The maximum

effective frequency of a transistor is

denoted by the term fT, an abbreviation

for "frequency of transition". The

frequency of transition is the frequency

at which the transistor yields unity

gain).


wa
tch, general purpos
e, audio, high voltage,
super
-
beta, matched pair



Through hole metal, through hole
plastic,
surface mount, ball grid array,
power modul

Introduction to Robotics with
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2.2.2.2

Operational amplifiers



An operational


amplifier

(4/15/2009) is a high
-
gain

electronic

voltage amplifier. An Op
-
amp

has two inputs

and one output. The output of the Op
-
amp is high since

the high gain of the Op
-
amp drives the output value into

saturation. So in order to control the output voltage,

Feedbacks are provided.
Feedbacks are of two type,

posi
tive feedback and negative feed
back. Negative feed
-


back helps in stabilizing the gain. Depending on whether

the feedback is there or not, the op
-
amp configurations

are classified into open loop and
closed loop

configurations.











Figure: 2.18







Op
-
amps are among the most widely used electronic

devices. The simplicity and the integrated circuitry help it

to be used in vast consumer electronic devices and other

applications.












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