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CHAPTER 1

INTRODUCTION

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INTRODUCTION

The speed and direction control of DC motor is very important for various kind of uses.

Through all these years, there have been various attempts in finding different efficient solutions

for the speed and direction control of the DC motor.

History will recognize the vital role played by DC motors in the development of

industrial power transmission systems. The DC machine was the first practical device to convert

electrical power into mechanical power, and vice-versa in its generator form. Inherently

straightforward operating characteristics, flexible performance and high efficiency encouraged

the widespread use of DC motors in many types of industrial drive applications.

DC motors have been long been the primary means of Electrical traction. DC motor is

considered as a SISO system having torque/speed characteristics compatible with most

mechanical loads. Hence, DC motors are always a good ground for advanced theories because

the theory is extendable to other types of motors.

Wireless communication is the transfer of information between two or more points that

are not physically connected. Distances can be short, such as a few meters for television remote

control, or as far as thousands or even millions of kilometers. Among the various wireless

technologies like IR (Infra Red), Bluetooth and WLAN, we have chosen RF technology, the

main reason being it has a very long range of 3 KHz-300GHZ. It is also not affected by any

obstructions. Commercial applications for wireless are door announcers, security and access

systems, gate control, remote activation, score board and paging systems.

In this project we try to provide a similar approach by introducing the concept of radio

frequency technology.

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CHAPTER 2

WIRELESS COMMUNICATIONS

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WIRELESS COMMUNICATIONS

Wireless communication is the transfer of information over a distance without the use of

electrical conductors or "wires". The distances involved may be short (a few meters as in

television remote control) or long (thousands or millions of kilometers for radio

communications). Wireless communication is generally considered to be a branch of

telecommunications. It encompasses various types of fixed, mobile, and portable two-way

radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other

examples of wireless technology include GPS units, garage door openers and or garage doors,

wireless computer mice, keyboards and headsets, satellite television and cordless telephones.

Wireless operations permits services, such as long-range communications, that are

impossible or impractical to implement with the use of wires. The term is commonly used in the

telecommunications industry to refer to telecommunications systems (e.g. radio transmitters and

receivers, remote controls, computer networks, network terminals, etc.) which use some form of

energy (e.g. radio frequency (RF), infrared light, laser light, visible light, acoustic energy, etc.) to

transfer information without the use of wires. Information is transferred in this manner over both

short and long distances. In 1895, Guglielmo Marconi opened the way for modern wireless

communications by transmitting the three-dot Morse code for the letter ‘S’ over a distance of

three kilometers using electromagnetic waves. From this beginning, wireless communications

has developed into a key element of modern society. From satellite transmission, radio and

television broadcasting to the now ubiquitous mobile telephone, wireless communications has

revolutionized the way societies function.

Wireless communications and the economic goods and services that utilize it have some

special characteristics that have motivated specialized studies. First, wireless communications

relies on a scarce resource – namely, radio spectrum. Second, use of spectrum for wireless

communications required the development of key complementary technologies; especially those

that allowed higher frequencies to be utilized more efficiently. Finally, because of its special

nature, the efficient use of spectrum required the coordinated development of standards. Those

standards in turn played a critical role in the diffusion of technologies that relied on spectrum

use. Wireless operations permits services, such as long range communications, that are

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impossible or impractical to implement with the use of wires. The term is commonly used in the

telecommunications industry to refer to telecommunications systems (e.g. radio transmitters and

receivers, remote controls, computer networks, network terminals, etc.) which use some form of

energy (e.g. radio frequency (RF),acoustic energy, etc.) to transfer information without the use of

wires. Information is transferred in this manner over both short and long distances.

Wireless networking (i.e. the various types of unlicensed 2.4 GHz Wi-Fi devices) is used

to meet many needs. Perhaps the most common use is to connect laptop users who travel from

location to location. Another common use is for mobile networks that connect via satellite. A

wireless transmission method is a logical choice to network a LAN segment that must frequently

change locations. The following situations justify the use of wireless technology:

To span a distance beyond the capabilities of typical cabling,

To provide a backup communications link in case of normal network failure,

To link portable or temporary workstations,

To overcome situations where normal cabling is difficult or financially impractical, or

To remotely connect mobile users or networks.

The term "wireless" came into public use to refer to a radio receiver or transceiver (a dual

purpose receiver and transmitter device), establishing its usage in the field of wireless telegraphy

early on; now the term is used to describe modern wireless connections such as in cellular

networks and wireless broadband Internet. It is also used in a general sense to refer to any type of

operation that is implemented without the use of wires, such as "wireless remote control" or

"wireless energy transfer", regardless of the specific technology (e.g. radio, infrared, ultrasonic)

used.

2.1. PRINCIPLES OF WIRELESS COMMUNICATIONS:

Wireless communications begin with a message that is converted into an electronic signal

by a device called a transmitter. There are two types of transmitters: analog and digital. An

analog transmitter sends electronic signals as modulated radio waves. The analog transmitter

modulates the radio wave to carry the electronic signal and then sends the modified radio signal

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through space. A digital transmitter encodes electronic signals by converting messages into a

binary code, the series of zeros and ones that are the basis of all computer programming. The

encoded electronic signal is then sent as a radio wave. Devices known as receivers decode or

demodulate the radio waves and reproduce the original message over a speaker.

Wireless communications systems involve either one-way transmissions, in which a

person merely receives notice of a message, or two-way transmissions, such as a telephone

conversation between two people. An example of a device that only receives one-way

transmission is a pager, which is a high-frequency radio receiver. When a person dials a pager

number, the pager company sends a radio signal to the desired pager. The encoded signal triggers

the pager’s circuitry and notifies the customer carrying the pager of the incoming call with a tone

or a vibration, and often the telephone number of the caller. Advanced pagers can display short

messages from the caller, or provide news updates or sports scores.

Two-way transmissions require both a transmitter and a receiver for sending and

receiving signals. A device that functions as both a transmitter and a receiver is called a

transceiver. Cellular radio telephones and two-way radios use transceivers, so that back-and-

forth communication between two people can be maintained. Early transceivers were very large,

but they have decreased in size due to advances in technology. Fixed-base transceivers, such as

those used at police stations, can fit on a desktop, and hand-held transceivers have shrunk in size

as well. Several current models of handheld transceivers weigh less than 0.2 kg (0.5 lb). Some

pagers also use transceivers to provide limited response options. These brief return-

communication opportunities allow paging users to acknowledge reception of a page and to

respond using a limited menu of options.

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Fig2.1: Principle of wireless communications

2.2. TYPES OF WIRELESS COMMUNICATION:

1. Infrared Wireless Transmission- "Transmission of data signals using infrared-light

waves". These infrared-light waves are at a frequency too low for human eyes to receive

and interpret. Infrared ports can be found in digital cameras, laptops, and printers as well

as wireless mice.

2. Broadcast Radio- a wireless transmission medium that sends data over long distances

(regions, states, countries) at up to 2 megabits per second (AM/FM Radio).

3. Microwave Radio- Transmission of voice and data through the atmosphere as super high-

frequency radio waves called microwaves. These frequencies are used to transmit

messages between ground-based stations and satellite communications systems.

4. Communications Satellites- are microwave relay stations in orbit around the earth.

2.3. APPLICATIONS:

1. Broadcasting services: including short wave AM and FM radio as well as terrestrial

television.

2. Mobile communications of voice and data: including maritime and aeronautical mobile

for communications between ships, airplanes and land; land mobile for communications

between a fixed base station and moving sites such as a taxi fleet and paging services,

and mobile communications either between mobile users and a fixed network or between

mobile users, such as mobile telephone services

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3. Fixed Services: either point to point or point to multipoint services

4. Satellite: used for broadcasting, telecommunications and internet, particularly over long

distances.

5. Professional LMR (Land Mobile Radio) and SMR (Specialized Mobile Radio) typically

used by business, industrial and Public Safety entities

6. Consumer Two Way Radio including FRS (Family Radio Service), GMRS (General

Mobile Radio Service) and Citizens band ("CB") radios.

7. Consumer and professional Marine VHF radios.

8. Cellular telephones and pagers: provide connectivity for portable and mobile

applications, both personal and business.

9. Global Positioning System (GPS): allows drivers of cars and trucks, captains of boats and

ships, and pilots of aircraft to ascertain their location anywhere on earth.

10. Cordless computer peripherals: the cordless mouse is a common example; keyboards and

printers can also be linked to a computer via wireless.

11. Cordless telephone sets: these are limited-range devices, not to be confused with cell

phones.

12. Satellite television: allows viewers in almost any location to select from hundreds of

channels.

13. Wireless gaming: new gaming consoles allow players to interact and play in the same

game regardless of whether they are playing on different consoles. Players can chat, send

text messages as well as record sound and send it to their friends.

14. Security systems: Wireless technology may supplement or replace hard wired

implementations in security systems for homes or office buildings.

15. Television remote control: Modern televisions use wireless (generally infrared) remote

control units. Now radio waves are also used.

16. Cellular telephony (phones and modems): These instruments use radio waves to enable

the operator to make phone calls from many locations world-wide. They can be used

anywhere that there is a cellular telephone site to house the equipment that is required to

transmit and receive the signal that is used to transfer both voice and data to and from

these instruments.

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17. Wi-Fi: Wi-Fi (for wireless fidelity) is a wireless LAN technology that enables laptop

PC’s, PDA’s, and other devices to connect easily to the internet. Technically known as

IEEE 802.11 a,b,g,n, Wi-Fi is less expensive and nearing the speeds of standard Ethernet

and other common wire-based LAN technologies

18. Wireless energy transfer: Wireless energy transfer is a process whereby electrical energy

is transmitted from a power source to an electrical load that does not have a built-in

power source, without the use of interconnecting wires.

2.4. ADVANTAGES AND DISADVANTAGES:

ADVANTAGES:

1. Anywhere, Anytime Work

2. Through wireless communication, working professionals and mobile workers can work

and access the Internet just about anywhere, anytime without the hassles of wires and

network cables.

3. Enhanced Productivity

4. Workers, students, professionals and others need not be constrained by wired Internet

connections or dial-up connectivity. Wireless Internet connectivity options ensures that

work and assignments can be completed anywhere and enhance overall productivity of all

concerned.

5. Remote Area Connectivity

6. Workers, doctors and other professionals working in remote-location hospitals and

medical centers can keep in touch with anyone through wireless communication. Non-

profit organization volunteers working in remote and underserved areas can stay

connected to the outside world with the help of wireless communication.

7. For those unable to keep away from their daily soap operas, reality-programs, online TV

shows and Internet surfing or download activities, wireless communication ensures an

entertainment bonanza on--demand and anytime.

8. Emergency Alerts

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9. Through wireless communication, many emergency situations and crisis situations can be

addressed quickly. Help and other assistance can reach affected areas quickly through

early alerts and warnings provided with the help of wireless communication.

DISADVANTAGES:

1. Wireless communications are limited by the range of the transmitter.

2. Cost of wireless communication system and components are high.

3. When transmitting data, users must sometimes send smaller bits of data so the

information moves more quickly. The size of the device that's accessing the information

is also still an issue.

4. Many applications need to be reconfigured if they are going to be used through wireless

connections.

5. Most client/server applications rely on a persistent connection, which is not the case with

wireless.

6. Since radio waves travel through the atmosphere they can be disturbed by electrical

interferences (such as lightning) that cause static.

2.5. RADIO FREQUENCY TECHNOLOGY:

RF refers to radio frequency, the mode of communication for wireless technologies of all

kinds, including cordless phones, radar, ham radio, GPS, and radio and television broadcasts.

RF technology is so much a part of our lives we scarcely notice it for its ubiquity. From baby

monitors to cell phones, Bluetooth® to remote control toys, RF waves are all around us. RF

waves are electromagnetic waves which propagate at the speed of light, or 186,000 miles per

second (300,000 km/s). The frequencies of RF waves, however, are slower than those of visible

light, making RF waves invisible to the human eye. Radio frequency (RF) is a frequency or rate

of oscillation within the range of about 3 Hz to 300 GHz. This range corresponds to frequency of

alternating current electrical signals used to produce and detect radio waves. Since most of this

range is beyond the vibration rate that most mechanical systems can respond to, it usually refers

to oscillations in electrical circuits or electromagnetic radiation.

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The frequency of a wave is determined by its oscillations or cycles per second. One cycle is one

hertz (Hz); 1,000 cycles is 1 kilohertz (KHz); 1 million cycles is 1 megahertz (MHz); and 1

billion cycles is 1 gigahertz (GHz).

2.5.1. BRIEF DESCRIPTION OF RF:

Radio frequency (abbreviated RF) is a term that refers to alternating current (AC) having

characteristics such that, if the current is input to an antenna, an electromagnetic (EM) field is

generated suitable for wireless broadcasting and/or communications. These frequencies cover a

significant portion of the electromagnetic radiation spectrum, extending from nine kilohertz (9

kHz),the lowest allocated wireless communications frequency (it's within the range of human

hearing), to thousands of gigahertz(GHz).When an RF current is supplied to an antenna, it gives

rise to an electromagnetic field that propagates through space. This field is sometimes called an

RF field, in less technical jargon it is a "radio wave." Any RF field has a wavelength that is

inversely proportional to the frequency. In the atmosphere or in outer space, if f is the frequency

in megahertz and s is the wavelength in meters, then s = 300/f.

The frequency of an RF signal is inversely proportional to the wavelength of the EM field

to which it corresponds. At 9 kHz, the free-space wavelength is approximately 33 kilometers

(km) or 21 miles (mi). At the highest radio frequencies, the EM wavelengths measure

approximately one millimeter (1 mm). As the frequency is increased beyond that of the RF

spectrum, EM energy takes the form of infrared (IR), visible, ultraviolet (UV), X rays, and

gamma rays.

Many types of wireless devices make use of RF fields. Cordless and cellular telephone,

radio and television broadcast stations, satellite communications systems, and two-way radio

services all operate in the RF spectrum. Some wireless devices operate at IR or visible-light

frequencies, whose electromagnetic wavelengths are shorter than those of RF fields. Examples

include most television-set remote-control boxes some cordless computer keyboards and mice,

and a few wireless hi-fi stereo headsets.

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2.5.2. PROPERTIES OF RF:

Electrical currents that oscillate at RF have special properties not shared by direct current

signals. One such property is the ease with which it can ionize air to create a conductive path

through air. This property is exploited by 'high frequency' units used in electric arc welding.

Another special property is an electromagnetic force that drives the RF current to the surface of

conductors, known as the skin effect. Another property is the ability to appear to flow through

paths that contain insulating material, like the dielectric insulator of a capacitor. The degree of

effect of these properties depends on the frequency of the signals.

Electric currents that oscillate at radio frequencies have special properties not shared by

direct current or alternating current of lower frequencies.

The energy in an RF current can radiate off a conductor into space as electromagnetic

waves (radio waves); this is the basis of radio technology.

RF current does not penetrate deeply into electrical conductors but flows along their

surfaces; this is known as the skin effect. For this reason, when the human body comes in

contact with high power RF currents it can cause superficial but serious burns called RF

burns.

RF current can easily ionize air, creating a conductive path through it. This property is

exploited by "high frequency" units used in electric arc welding, which use currents at

higher frequencies than power distribution uses.

Another property is the ability to appear to flow through paths that contain insulating

material, like the dielectric insulator of a capacitor. When conducted by an ordinary

electric cable, RF current has a tendency to reflect from discontinuities in the cable such

as connectors and travel back down the cable toward the source, causing a condition

called standing waves, so RF current must be carried by specialized types of cable called

transmission line.

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2.5.3. DIFFERENT RANGES PRESENT IN RF AND THEIR APPLICATION:

extremely low

frequency

3-30hz 10,000km-

100,00km

directly audible when converted to sound,

communication with submarines

super low

frequency

30-300hz 1000km-

10,000km

directly audible when converted to sound, ac

power grids

ultra low

frequency

300-

3000hz

100km-

1,000km

Directly audible when converted to sound,

communication with mines.

very low

frequency

3-30khz 10km-100km Directly audible when converted to sound.

low frequency 30-300khz 1km-10km Am broadcasting navigational beacons.

medium

frequency

300-

3000khz

100m-1km Navigational beacons, am broadcasting

maritime and aviation communication.

high frequency 3-30mhz 10m-100m shortwave, amateur radio, citizens’ band ratio

very high

frequency

30-300mhz 1m-10m fm broadcasting television., aviation

ultra high

frequency

300-

3000mhz

10cm- 100cm Broadcasting television, mobile telephones,

cordless telephones, wireless networking,

remote keyless entry for automobiles,

microwave ovens

super high

frequency

3-30ghz 1cm-10cm wireless networking, satellite links,

microwave links, satellite television, door

openers.

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Table 2.1. Different ranges present in RF and their applications.

2.5.4. RF ADVANTAGES AND DISADVANTAGES:

ADVANTAGES:

1. No line of sight is needed.

2. Not blocked by common materials: It can penetrate most solids and pass through walls.

3. Longer range.

4. It is not sensitive to the light.

5. It is not much sensitive to the environmental changes and weather conditions.

DISADVANTAGES:

1. Interference: communication devices using similar frequencies - wireless phones, scanners,

wrist radios and personal locators can interfere with transmission.

2. Lack of security: easier to "eavesdrop" on transmissions since signals are spread out in

space rather than confined to a wire.

3. Higher cost than infrared.

4. Federal Communications Commission (FCC) licenses required for some products.

5. Lower speed: data rate transmission is lower than wired and infrared transmission.

extremely high

frequency

30-300ghz 1 mm-10mm microwave data links, radio astronomy,

remote sensing advanced weapons systems.

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CHAPTER 3

DC MOTOR

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DC MOTOR

3.1. BASIC OPERATION OF DC MOTOR:

In any electric motor, operation is based on simple electromagnetism. A current-carrying

conductor generates a magnetic field; when this is then placed in an external magnetic field, it

will experience a force proportional to the current in the conductor, and to the strength of the

external magnetic field. Internal configuration of a DC motor is designed to harness the

magnetic interaction between a current-carrying conductor and an external magnetic field to

generate rotational motion.

Let's start by looking at a simple 2-pole DC electric motor (here red represents a magnet

or winding with a "North" polarization, while green represents a magnet or winding with a

"South" polarization).

Fig 3.1 : Parts of a DC motor

Every DC motor has six basic parts -- axle, rotor (a.k.a., armature), stator, commutator,

field magnet(s), and brushes. In most common DC motors, the external magnetic field is

produced by high-strength permanent magnets1. The stator is the stationary part of the motor --

this includes the motor casing, as well as two or more permanent magnet pole pieces. The rotor

(together with the axle and attached commutator) rotates with respect to the stator. The rotor

consists of windings (generally on a core), the windings being electrically connected to the

commutator.

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Fig 3.2: Operation of a DC motor

The direct current (DC) motor is one of the first machines devised to convert electrical

power into mechanical power. Permanent magnet (PM) direct current convert electrical energy

into mechanical energy through the interaction of two magnetic fields. One field is produced by a

permanent magnet assembly, the other field is produced by an electrical current flowing in the

motor windings. These two fields result in a torque which tends to rotate the rotor. As the rotor

turns, the current in the windings is commutated to produce a continuous torque output. The

stationary electromagnetic field of the motor can also be wire-wound like the armature (called a

wound-field motor) or can be made up of permanent magnets (called a permanent magnet

motor). In either style (wound-field or permanent magnet) the commutator acts as half of a

mechanical switch and rotates with the armature as it turns. The commutator is composed of

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conductive segments (called bars), usually made of copper, which represent the termination of

individual coils of wire distributed around the armature. The second half of the mechanical

switch is completed by the brushes. These brushes typically remain stationary with the motor's

housing but ride (or brush) on the rotating commutator. As electrical energy is passed through

the brushes and consequently through the armature a torsional force is generated as a reaction

between the motor's field and the armature causing the motor's armature to turn. As the armature

turns, the brushes switch to adjacent bars on the commutator. This switching action transfers the

electrical energy to an adjacent winding on the armature which in turn perpetuates the torsional

motion of the armature.

Permanent magnet (PM) motors are probably the most commonly used DC motors, but

there are also some other type of DC motors(types which use coils to make the permanent

magnetic field also) .DC motors operate from a direct current power source. Movement of the

magnetic field is achieved by switching current between coils within the motor. This action is

called "commutation". Very many DC motors (brush-type) have built-in commutation, meaning

that as the motor rotates, mechanical brushes automatically commutate coils on the rotor. You

can use dc-brush motors in a variety of applications. A simple, permanent-magnet dc motor is an

essential element in a variety of products, such as toys, servo mechanisms, valve actuators,

robots, and automotive electronics. There are several typical advantages of a PM motor. When

compared to AC or wound field DC motors, PM motors are usually physically smaller in overall

size and lighter for a given power rating. Furthermore, since the motor's field, created by the

permanent magnet, is constant, the relationship between torque and speed is very linear. A PM

motor can provide relatively high torque at low speeds and PM Field provides some inherent

self-braking when power to the motor is shutoff. There are several disadvantages through, those

being mostly being high current during a stall condition and during instantaneous reversal. Those

can damage some motors or be problematic to control circuitry. Furthermore, some magnet

materials can be damaged when subjected to excessive heat and some loose field strength if the

motor is disassembled.

High-volume everyday items, such as hand drills and kitchen appliances, use a dc

servomotor known as a universal motor. Those universal motors are series-wound DC motors,

where the stationary and rotating coils are wires in series. Those motors can work well on both

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AC and DC power. One of the drawbacks/precautions about series-wound DC motors is that if

they are unloaded, the only thing limiting their speed is the windage and friction losses. Some

can literally tear themselves apart if run unloaded.

A brushless motor operates much in the same way as a traditional brush motor. However,

as the name implies there are no brushes (and no commutator). The mechanical switching

function, implemented by the brush and commutator combination in a brush-type motor, is

replaced by electronic switching in a brushless motor. In a typical brushless motor the

electromagnetic field, created by permanent magnets, is the rotating member of the motor and is

called a rotor. The rotating magnetic field is generated with a number of electromagnets

commutatated with electronics switches (typically transistors or FETs) in a right order at right

speed. In a brushless motor, the trick becomes to know when to switch the electrical energy in

the windings to perpetuate the rotating motion. This is typically accomplished in a brushless-type

motor by some feedback means designed to provide an indication of the position of the magnet

poles on the rotor relative to the windings. A Hall Effect device (HED) is a commonly used

means for providing this positional feedback. In some applications brushless motors are

commutated without sensors or with the use of an encoder for positional feedback. A brushless

motor is often used when high reliability, long life and high speeds are required. The bearings in

a brushless motor usually become the only parts to wear out. In applications where high speeds

are required (usually above 30,000 RPM) a brushless motor is considered a better choice

(because as motor speed increases so does the wear of the brushes on traditional motors). A

brushless motor's commutation control can easily be separated and integrated into other required

electronics, thereby improving the effective power-to-weight and/or power-to-volume ratio. A

brushless motor package (motor and commutation controller) will usually cost more than a

brush-type, yet the cost can often be made up in other advantages. Brushless motors are seen

nowadays in very many computer applications, the disk drives.

Sometimes the rotation direction needs to be changed. In normal permanent magnet

motors, this rotation is changed by changing the polarity of operating power (for example by

switching from negative power supply to positive or by inter-changing the power terminals going

to power supply). This direction changing is typically implemented using relay or a circuit called

an H bridge. There are some typical characteristics on "brush-type" DC motors.

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When a DC motor is straight to a battery (with no controller), it draws a large surge

current when connected up. The surge is caused because the motor, when it is turning, acts as a

generator. The generated voltage is directly proportional to the speed of the motor. The current

through the motor is controlled by the difference between the battery voltage and the motor's

generated voltage (otherwise called back EMF). When the motor is first connected up to the

battery (with no motor speed controller) there is no back EMF. So the current is controlled only

by the battery voltage, motor resistance (and inductance) and the battery leads. Without any back

emf the motor, before it starts to turn, therefore draws the large surge current. When a motor

speed controller is used, it varies the voltage fed to the motor. Initially, at zero speed, the

controller will feed no voltage to the motor, so no current flows. As the motor speed controller's

output voltage increases, the motor will start to turn. At first the voltage fed to the motor is small,

so the current is also small, and as the motor speed controller's voltage rises, so too does the

motor's back EMF. The result is that the initial current surge is removed, acceleration is smooth

and fully under control.

3.2. TYPES OF DC MOTORS:

3.2.1. Shunt Wound DC Motors:

Shunt wound DC motors provide medium starting torque, 125% to 200% full load, and

are capable of delivering 300% of full load torque for short periods. With excellent speed

control, shunt wound motors generally drive loads requiring speed control and low starting

torque.

Some applications include fans, blowers, centrifugal pumps, conveyors, elevators,

printing presses, woodworking machines, and metalworking machines.

There are two basic types of shunt wound DC motors. Self-excited shunt wound motors have a

shunt field and armature connected to the same power supply.

In separately excited shunt wound motors, shunt field and armature connect to separate power

supplies.

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3.2.2. Series Wound DC motor:

A series wound DC motor has its armature and field connected in a series circuit. These

type motors normally drive loads that require high torque and do not require precise speed

regulation. Series DC motors are ideal for traction work where the load requires a high

breakaway torque. Such are locomotives, hoists, cranes, automobile starters, or oil drilling rig

applications.

Starting torque developed in series motors normally ranges between 300% and 375% of

full load, but attains 500% of full load torque. These motors deliver this high starting torque

because their magnetic field operates below saturation.

An increase in load results in an increase in both armature and field current. As a result, the

armature flux and field flux increase simultaneously. Since the torque developed in DC motors is

dependent upon the interaction of armature and field flux, torque increases by the square of

current increase.

Speed regulation in series motors is inherently less precise than in shunt motors. If motor

load diminishes, current flowing in both the armature field circuits reduces as well, effecting a

reduction in flux density.

This results in a greater increase in speed than realized in shunt motors. Removal of

mechanical load from series motors results in indefinite speed increase whereby centrifugal

forces generated by the armature eventually destroy the motor.

Fig 3.3: Series wound DC motor

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3.2.3. Compound Wound DC motors:

Whenever an operation requires speed regulation characteristics unavailable in series or

shunt motors, compound wound motors perform well. With medial starting torque capability,

between 180 and 260% of full load, they deliver constant operating speeds under any percentage

of full loads. This characteristic is a result of placing part of the field circuit in series with that of

the armature. When under load, increased series winding current raises the level of field flux.

Enlarged field flux in compound wound motors yields greater reduction in speed than in a shunt

motor.

The compound wound DC motor comprises both series and shunt windings. The shunt

winding connects in parallel with armature and series windings. Some associated applications

include punch presses, shears, crushers, and reciprocating compressors.

Fig 3.4: Compound wound DC motor

3.2.4. Permanent Magnet DC motor:

Permanent magnet motors are well fit for use where response time is a factor. Their speed

characteristics are similar to those of shunt wound motors. Built with a conventional armature,

they use permanent magnets rather than windings in the field section. DC power is supplied only

to the armature.

Permanent magnet motors are not expensive to operate since they require no field supply.

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The magnets, however, lose their magnetic properties over time and these effects less than rated

torque production. Some motors have windings built into the field magnets that re-magnetize the

cores and prevent this from happening.

Automobiles have installed DC permanent magnet motors that control power seats,

windows, and windshield wipers. DC permanent magnet motors produce high torque at low

speed, and are self-braking upon disconnection of electrical power. Permanent magnet motors

cannot endure continuous operation because they overheat rapidly, destroying the permanent

magnets.

Fig 3.5 : Permanent magnet DC motor

3.2.5. Universal DC Motors-

Universal motors seldom exceed one horsepower, and do not run at constant speeds. The

speed of a universal motor varies with its load. Among the applications using these motors are

vacuum cleaners, food mixers, portable drills, portable power saws, and sewing machines.

In most cases, little more than a few hundred rpm is reached with heavy loads. When the

motor operates with no load, the speed may attain 15,000 rpm.

The universal series motor differs in design from a true induction motor. The rotor of a universal

motor is made of laminated iron wound with wire coils. The ends of the coils, or loops, connect

to a commutator. Electric current in the motor flows through a complete circuit formed by the

stator winding and rotor winding. Brushes ride on the commutator and conduct the current

through the rotor from one stator coil to the other. Directed by these brushes the rotor current

24

interacts with the magnetic field of the stator causing the rotor to turn. When the direction of

current flow changes in the stator, it changes in the rotor. Since the magnetic field is reversed,

the rotor continues to turn.

Universal motors have series wound rotor circuitry similar to that of DC motors. They

have high starting torque and high starting current. The name universal derives from the motor's

capability of operating on either AC or DC power sources.

Universal, variable speed motors slow down with increased loads. High horsepower-to-size ratio

is characteristic of their design. Due to the brush/commutator setup, universal motors require

more maintenance than other motor designs.

3.3. SPEED CONTROL METHODS OF DC MOTOR:

Fig 3.6: Speed control of a DC motor

Basically, there are three ways to vary the speed of DC motors:

1. With the use of mechanical gears to achieve the desired speed.

2. Reducing the motor voltage with a series resistor. However this is inefficient ( energy wasted

in resistor) and reduces torque. The current drawn by the motor increases as the load on the

motor increases. More current means a larger voltage drop across the series resistor and

therefore less voltage to the motor. The motor now tries to draw even more current resulting

in the motor “stalling”.

25

3. By applying the full voltage supply to the motor in bursts or pulses, eliminating the series

dropping effect. This is called the pulse width modulation (PWM). Shorter pulses means the

motor runs slowly, longer pulses make the motor run faster.

3.4. GEAR DC MOTOR:

A gear motor is a type of electrical motor. Like all electrical motors, it uses the

magnetism induced by an electrical current to rotate a rotor that is connected to a shaft. The

energy transferred from the rotor to the shaft is then used to power a connected device.

3.4.1 DESCRIPTION AND OPERATION:

In a gear motor, the energy output is used to turn a series of gears in an integrated gear

train. There are a number of different types of gear motors, but the most common are AC

(alternating current) and DC (direct current). DC gear motors are configured in many types and

sizes, including brushless and servo. They consist of a rotor and a permanent magnetic field

stator and an integral gearbox. They are used in variable speed and torque applications. Direct

motors are most common in industrial robots.

In a gear motor, the magnetic current (which can be produced by either permanent

magnets or electromagnets) turns gears that are either in a gear reduction unit or in an integrated

gear box. A second shaft is connected to these gears. The result is that the gears greatly increase

the amount of torque the motor is capable of producing while simultaneously slowing down the

motor's output speed. The motor will not need to draw as much current to function and will move

more slowly, but will provide greater torque. The gearbox increases the torque generating ability

of the motor while simultaneously reducing its output speed. The main advantage of a gearmotor

is that the driving shaft may be coupled directly to the driven shaft. Belts, pulleys, chains, or

additional gearing to step down motor speed are needed. Also, coupling or belting of a motor to a

separate speed-reducer unit is eliminated.

The reduction gear trains used in gear motors are designed to reduce the output speed

while increasing the torque. The increase in torque is inversely proportional to the reduction in

speed. Reduction gearing allows small electric motors to move large driven loads, although more

26

slowly than larger electric motors. Reduction gears consist of a small gear driving a larger gear.

There may be several sets of these reduction gear sets in a reduction gear box.

Finally its nothing but a small motor (ac induction, permanent magnet dc, or brushless

dc) designed specifically with an integral (not separable) gear reducer (gear head). The end

shield on the drive end of the motor is designed to provide a dual function. The side facing the

motor provides the armature/rotor bearing support and a sealing provision through which the

integral rotor or armature shaft pinion passes. The other side of the end shield provides multiple

bearing supports for the gearing itself, and a sealing and fastening provision for the gear housing.

Gear motors are complete motive force systems consisting of an electric motor and a

reduction gear train integrated into one easy-to-mount and easy-to-configure package. This

greatly reduces the complexity and cost of designing and constructing power tools, machines and

appliances calling for high torque at relatively low shaft speed or RPM. Gear motors allow the

use of economical low-horsepower motors to provide great motive force at low speed such as in

lifts, winches, medical tables, jacks and robotics. They can be large enough to lift a building or

small enough to drive a tiny clock.

Important performance specifications to consider when searching for gear motors include

shaft speed, continuous torque, continuous current, and continuous output power. The terminal

voltage is the design DC motor voltage. The continuous torque is the output torque capability of

the motor under constant running conditions. Continuous current is the maximum rated current

that can be supplied to the motor windings without overheating. Continuous output power is the

mechanical power provided by the motor output.

Speed Reduction

Sometimes the goal of using a gear motor is to reduce the rotating shaft speed of a motor

in the device being driven, such as in a small electric clock where the tiny synchronous motor

may be spinning at 1,200 rpm but is reduced to one rpm to drive the second hand, and further

reduced in the clock mechanism to drive the minute and hour hands. Here the amount of driving

force is irrelevant as long as it is sufficient to overcome the frictional effects of the clock

mechanism.

27

Torque Multiplication

Another goal achievable with a gear motor is to use a small motor to generate a very

large force albeit at a low speed. These applications include the lifting mechanisms on hospital

beds, power recliners, and heavy machine lifts where the great force at low speed is the goal.

Motor Varieties

Most industrial gear motors are AC-powered, fixed-speed devices, although there are

fixed-gear-ratio, variable-speed motors that provide a greater degree of control. DC gear motors

are used primarily in automotive applications such as power winches on trucks, windshield wiper

motors and power seat or power window motors.

3.4.2. APPLICATIONS:

Gear motors have a variety of successful applications. They are used in packaging and

labeling, case erectors, box taper, hot melt glue pumps, heat shrink tunnels, tape dispensers and

conveyor drives. They are also used in food processing industry. They are used in ice making

machines, weigh checking, baking machinery, meat slicing, cooker drive, and breading

equipment. In transport equipment they are used in wheelchairs, stair lifts, golf carts and pipeline

crawlers. In machine tools they are used in drill heads, rotary table drives, and hardness test. The

power can openers, garage door openers, stair lifts, rotisserie motors, timer cycle knobs on

washing machines, power drills, cake mixers and electromechanical clocks have in common is

that they all use various integrations of gear motors to derive a large force from a relatively small

electric motor at a manageable speed. In industry, gear motor applications in jacks, cranes, lifts,

clamping, robotics, conveyance and mixing are too numerous to count.

3.4.3. GEAR MOTOR BENEFITS:

Using the right sized motor and gear head combination for an application helps to

prolong gearmotor life and allows for optimum power management and power

utilization. Traditionally, design engineers oversized motors and gear heads to add

“safety factors” — Bodine “factory matched” gear motors consistently deliver rated

performance.

28

Quieter operation due to integral castings and integral pinion, ground on the armature

or rotor shaft. Fewer parts requiring assembly resulting in “near perfect” alignment of

the rotor, pinion and gear train.

Minimum risk of lubricant leakage, because of “O-ring” and lip seal construction. The

design can be more compact and the lubrication can be controlled better (for various

mounting configurations).

Gear motors eliminate the need for motor/gear head couplings and eliminate any

potential bearing alignment problems, common when a motor and gear head are

bolted together by an end-user (separable gear heads). Misalignment can result in

bearing failure due to fretting corrosion.

Separable motor and gear head solutions make more sense in larger integral

horsepower (>1 HP) applications. For example, when a 100-pound motor is mounted

to a 500-pound gear head.

3.5. SPECIFICATIONS OF DC MOTOR:

Fig 3.7: Gear DC motor

Table 3.1: Technical parameters

DC Micro Motor RF-500TB Technical Parameter

Model

Voltage No-Load At Maximum Efficiency Stall

Operating

Range Nominal

Speed Current Speed Current Torque Output

Power Torque Current

r/min A r/min A g.cm mN.m W g.cm mN.m A

RF-

500TB-

12560

1.5-6 6V 2700 0.020 2200 0.070 10 0.98 0.23 60 5.88 0.35

29

CHAPTER 4

CIRCUIT DESCRIPTION

30

CIRCUIT DESCRIPTION

4.1. CIRCUIT SCHEMATIC DIAGRAMS:

4.1.1. POWER SUPPLY CIRCUIT :

Fig 4.1: Power supply circuit

4.1.2. TRANSMITTER CIRCUIT:

Fig 4.2: Transmitter circuit

31

4.1.3. RECEIVER CIRCUIT:

Fig 4.3: Receiver circuit

4.1.4.FOUR RELAY CONTROL:

Fig: Four relay control

32

4.1.5. RELAY OPERATION:

Fig4.5: Relay operation

4.2. CIRCUIT OPERATION:

4.2.1. POWER SUPPLY SECTION:

Fig 4.6 : Block diagram of power supply

This section consists of the rectifier, filter and voltage regulator.

Rectifier:

The output from the transformer is fed to the rectifier. It converts A.C. into pulsating

D.C. The rectifier may be a half wave or a full wave rectifier. In this project, a bridge rectifier is

used because of its merits like good stability and full wave rectification.

Power supply to all sections

Step

down

T/F

Bridge

Rectifier

Filter

Circuit Regulator

33

Filter:

Capacitive filter is used in this project. It removes the ripples from the output of rectifier

and smoothens the D.C. Output received from this filter is constant until the mains voltage and

load is maintained constant. However, if either of the two is varied, D.C. voltage received at this

point changes. Therefore a regulator is applied at the output stage.

Voltage regulator:

As the name itself implies, it regulates the input applied to it. A voltage regulator is an

electrical regulator designed to automatically maintain a constant voltage level. In this project,

power supply of 5V and 12V are required. In order to obtain these voltage levels, 7805 is used.

The first number 78 represents positive supply and the numbers 05 represent the required output

voltage levels.

The power supply board initially has the 230v/9v transformer. Single phase ac supply of

230v is taken and given to the center tapped transformer. This transformer steps down the

voltage to 9v AC. The 9 volts AC voltage is converted to dc voltage by a bridge rectifier. The

terminals 1 and 3 are given to the transformer and terminals 2 and 4 give the dc voltage. The dc

voltage obtained is about 12v which contains ripples. So to remove such disturbances, ripples a

capacitor of 1000 micro farad , 35v rating is used which filters them out and gives pure 9v dc

supply. This capacitor also helps in maintaining a constant voltage input to the regulator. Then a

voltage regulator is used to get a 5v dc supply.

4.2.2. TRANSMITTER SECTION:

Fig 4.7: Block diagram of transmitter section

34

This section consists Encoder HT640, RF Transmitter 434 MHz, 9v battery, voltage

regulator, switches, and antenna.

The switches are placed at the encoder side. The encoder converts digital to analog signal

and is given to the transmitter. The transmitter sends this analog information through

electromagnetic waves (radio frequency) to the receiver section. The receiver section receives

this data through the receiver. The power supply to the transmitter section is a 9v battery. The

switches used here are manually operated. SW-1 represents forward direction control switch,

SW-2 represents reverse direction control switch, SW-3 represents high speed control switch,

SW-4 represents medium speed control switch. The switches used here are four-legged. \

4.2.3. RECEIVER SECTION:

Fig 4.8 : Block diagram of receiver section

The receiver section consists of the HT648L decoder, receiver STT-433 MHz, supply

5v.The supply of 5v is taken from the power supply section. The decoder decodes the analog

signal to the digital signal and this data is collected for the driver circuit. Here the data is initially

received by the receiver STT-433 MHz The data from the decoder is received by the resistors

(1Kohm) and then depending on the activation of the particular transistor, that particular relay

gets activated. The transistors used here is BC 547. LED’s are also used on the board to notify

the operation on the board.

35

4.2.4. RELAY OPERATION:

Refer to fig 4.5 for the relay operation. In this the relay one and relay two have the direction

control over the DC motor whereas the relay 3 and relay 4 provide the speed control.

4.3. CIRCUIT COMPONENTS:

S.NO. EQUIPMENT RANGE/TYPE QUANTITY

1. Transformer 23OV/ 9V Center

tapped transformer

1

2. Diodes IN 4007 8

3. Capacitor 1000 microF, 35V 1

4. Voltage regulator LM 7805 2

5. Relays 2CO 4

6. Transistors BC547 5

7. Encoder HT640 1

8. Decoder HT648L 1

9. LEDS Red color 9

10. Resistors 15k/2W

33K/2W

1K 11

390K 3

11. Push buttons 4

12. DC Motor Gear DC motor, 100

rpm

1

13. Transmitter , receiver STT-433 MHz 1 pair

14. Antenna 1

15. PCB 5

16. Cardboard 1

Table 4.1: Circuit component

36

4.4. COMPONENT DESCRIPTIONS:

4.4.1. VOLTAGE REGULATOR:

The 78XX (sometimes LM78XX) is a family of self-contained fixed linear voltage

regulator integrated circuits. The 78xx family is commonly used in electronic circuits requiring a

regulated power supply due to their ease-of-use and low cost. For ICs within the family, the xx is

replaced with two digits, indicating the output voltage (for example, the 7805 has a 5 volt output,

while the 7812 produces 12 volts). The 78xx line are positive voltage regulators: they produce a

voltage that is positive relative to a common ground. There is a related line of 79xx devices

which are complementary negative voltage regulators. 78xx and 79xx ICs can be used in

combination to provide positive and negative supply voltages in the same circuit.

78xx ICs have three terminals and are commonly found in the TO220 form factor,

although smaller surface-mount and larger TO3 packages are available. These devices support an

input voltage anywhere from a couple of volts over the intended output voltage, up to a

maximum of 35 or 40 volts, and typically provide 1 or 1.5 amperes of current (though smaller or

larger packages may have a lower or higher current rating).

Advantages

7805 ICs do not require additional components to provide a constant, regulated source of

power, making them easy to use, as well as economical and efficient uses of space. Other

voltage regulators may require additional components to set the output voltage level, or to

assist in the regulation process. Some other designs (such as a switching power supply) may

need substantial engineering expertise to implement.

7805 ICs have built-in protection against a circuit drawing too much power. They have

protection against overheating and short-circuits, making them quite robust in most

applications. In some cases, the current-limiting features of the 7805 devices can provide

protection not only for the 7805 itself, but also for other parts of the circuit.

37

Disadvantages

The input voltage must always be higher than the output voltage by some minimum amount

(typically 2 volts). This can make these devices unsuitable for powering some devices from

certain types of power sources (for example, powering a circuit that requires 5 volts using 6-

volt batteries will not work using a 7805).

As they are based on a linear regulator design, the input current required is always the same

as the output current. As the input voltage must always be higher than the output voltage, this

means that the total power (voltage multiplied by current) going into the 78xx will be more

than the output power provided. The extra input power is dissipated as heat. This means both

that for some applications an adequate heat sink must be provided, and also that a (often

substantial) portion of the input power is wasted during the process, rendering them less

efficient than some other types of power supplies. When the input voltage is significantly

higher than the regulated output voltage (for example, powering a 7805 using a 24 volt power

source), this inefficiency can be a significant issue.

Even in larger packages, 78xx integrated circuits cannot supply as much power as many

designs which use discrete components, and are generally inappropriate for applications

requiring more than a few amperes of current.

4.4.2. TRANSMITTER:

The transmitter module used here is the RF TRANSMITTER STT-433MHz.

The STT-433 is ideal for remote control applications where low cost and longer range is

required.

The transmitter operates from a1.5-12V supply, making it ideal for battery-powered

applications.

The transmitter employs a SAW-stabilized oscillator, ensuring accurate frequency control for

best range performance.

38

The manufacturing-friendly SIP style package and low-cost make the STT-433 suitable for

high volume applications.

Features

433.92 MHz Frequency

Low Cost

1.5-12V operation

Small size

Fig 4.9: STT-433MHz Transmitter

Pin description:

GND -Transmitter ground. Connect to ground plane.

DATA -Digital data input. This input is CMOS compatible and should be driven with CMOS

level inputs.

VCC-Operating voltage for the transmitter. VCC should be bypassed with a .01uF ceramic

capacitor and filtered with a 4.7uF tantalum capacitor. Noise on the power supply will degrade

transmitter noise performance.

ANT- 50 ohm antenna output. The antenna port impedance affects output power and harmonic

emissions. Antenna can be single core wire of approximately 17cm length or PCB trace antenna.

39

4.4.3. RF RECEIVER:

Fig 4.10:STR-433MHz Receiver

The data is received by the RF receiver from the antenna pin and this data is available on

the data pins. Two Data pins are provided in the receiver module. .

Pin description:

ANT -Antenna input

GND- Receiver Ground. Connect to ground plan

VCC (5V) -VCC pins are electrically connected and provide operating voltage for the receiver.

VCC can be applied to either or both. VCC should be bypassed with a .1μF ceramic capacitor.

Noise on the power supply will degrade receiver sensitivity

DATA-Digital data output.

This output is capable of driving one TTL or CMOS load. It is a CMOS compatible output.

4.4.4. DECODER:

Features

Operating voltage: 2.4V~12V.

Low power and high noise immunity CMOS technology.

Low standby current.

Capable of decoding 18 bits of information.

40

Pairs with HOLTEK’s 318 series of encoders.

8~18 address pins.

0~8 data pins.

Fig 4.11: HT648L Decoder

WORKING OF DECODER:

The 3^18 decoders are a series of CMOS LSIs for remote control system applications. They

are paired with the 3^18 series of encoders.

For proper operation, a pair of encoder/decoder pair with the same number of address and

data format should be selected.

The 3^18 series of decoders receives serial address and data from that series of encoders that

are transmitted by a carrier using an RF medium.

41

A signal on the DIN pin then activates the oscillator which in turns decodes the incoming

address and data.

It then compares the serial input data twice continuously with its local address.

If no errors or unmatched codes are encountered, the input data codes are decoded and then

transferred to the output pins.

The VT pin also goes high to indicate a valid transmission. That will last until the address

code is incorrect or no signal has been received.

The 3^18 decoders are capable of decoding 18 bits of information that consists of N bits of

address and 18–N bits of data.

Table 4.2:HT648L Pin detail

4.4.5. ENCODER:

WORKING OF ENCODER:

The 318 (3 power of 18) series of encoders begins a three-word transmission cycle upon

receipt of a transmission enable (TE for the HT600/HT640/HT680 or D12~D17 for the

HT6187/HT6207/HT6247, active high). This cycle will repeat itself as long as the transmission

enable (TE or D12~D17) is held high. Once the transmission enable falls low, the encoder output

completes its final cycle and then stops as shown below.

42

Fig 4.12: Working of encoder

Address/data programming (preset)

The status of each address/data pin can be individually preset to logic high, logic low, or

floating. If a transmission enable signal is applied, the encoder scans and transmits the status of

the 18 bits of address/data serially in the order A0 to AD17.

Fig 4.15: Encoder Address/data programming

Transmission enable

For the TE trigger type of encoders, transmission is enabled by applying a high signal to

the TE pin. But for the Data trigger type of encoders, it is enabled by applying a high signal to

one of the data pins D12~D17.

43

Fig 4.16: HT640 Encoder

Table 4.3:HT640 Pin details

44

4.4.6. RELAYS:

A relay is an electrically operated switch. Many relays use an electromagnet to operate a

switching mechanism mechanically, but other operating principles are also used. Relays are used

where it is necessary to control a circuit by a low-power signal (with complete electrical isolation

between control and controlled circuits), or where several circuits must be controlled by one

signal. The first relays were used in long distance telegraph circuits, repeating the signal coming

in from one circuit and re-transmitting it to another. Relays were used extensively in telephone

exchanges and early computers to perform logical operations.

A type of relay that can handle the high power required to directly control an electric

motor is called a contactor. Solid-state relays control power circuits with no moving parts,

instead using a semiconductor device to perform switching. Relays with calibrated operating

characteristics and sometimes multiple operating coils are used to protect electrical circuits from

overload or faults; in modern electric power systems these functions are performed by digital

instruments still called "protective relays".

BASIC DESIGN AND OPERATION:

A simple electromagnetic relay consists of a coil of wire surrounding a soft iron core, an

iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and

one or more sets of contacts (there are two in the relay pictured). The armature is hinged to the

yoke and mechanically linked to one or more sets of moving contacts. It is held in place by a

spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this

condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open.

Other relays may have more or fewer sets of contacts depending on their function. The relay in

the picture also has a wire connecting the armature to the yoke. This ensures continuity of the

circuit between the moving contacts on the armature, and the circuit track on the printed circuit

board (PCB) via the yoke, which is soldered to the PCB.

When an electric current is passed through the coil it generates a magnetic field that

attracts the armature and the consequent movement of the movable contact either makes or

45

breaks (depending upon construction) a connection with a fixed contact. If the set of contacts

was closed when the relay was de-energized, then the movement opens the contacts and breaks

the connection, and vice versa if the contacts were open. When the current to the coil is switched

off, the armature is returned by a force, approximately half as strong as the magnetic force, to its

relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in

industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage

application this reduces noise; in a high voltage or current application it reduces arcing.

When the coil is energized with direct current, a diode is often placed across the coil to

dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise

generate a voltage spike dangerous to semiconductor circuit components. Some automotive

relays include a diode inside the relay case. Alternatively, a contact protection network

consisting of a capacitor and resistor in series (snubber circuit) may absorb the surge. If the coil

is designed to be energized with alternating current (AC), a small copper "shading ring" can be

crimped to the end of the solenoid, creating a small out-of-phase current which increases the

minimum pull on the armature during the AC cycle.

A solid-state relay uses a thyristor or other solid-state switching device, activated by the

control signal, to switch the controlled load, instead of a solenoid. An opt coupler (a light-

emitting diode (LED) coupled with a photo transistor) can be used to isolate control and

controlled circuits.

TYPES OF RELAYS:

1. Latching Relay

Latching relays are also called impulse relays. They work in the bistable mode, and thus

have two relaxing states. They are also called keep relays or stay relays because as soon as the

current towards this relay is switched off, the relay continues the process that it was doing in the

last state. This can be achieved only with a solenoid which is operating in a ratchet and cam

mechanism. It can also be done by an over-centre spring mechanism or a permanent magnet

mechanism in which, when the coil is kept in the relaxed point, the over-centre spring holds the

46

armature and the contacts in the right spot. This can also be done with the help of a remanent

core. In the ratchet and cam method, power consumption occurs only for a particular time. Hence

it is more advantageous than the others.

2. Reed Relay

These types of relays have been given more importance in the contacts. In order to

protect them from atmospheric protection they are safely kept inside a vacuum or inert gas.

Though these types of relays have a very low switching current and voltage ratings, they are

famous for their switching speeds.

3. Polarized Relay

This type of relay has been given more importance on its sensitivity. These relays have

been used since the invention of telephones. They played very important roles in early telephone

exchanges and also in detecting telegraphic distortion. The sensitivity of these relays are very

easy to adjust as the armature of the relay is placed between the poles of a permanent magnet.

4. Buchholz Relay

This relay is actually used as a safety device. They are used for knowing the amount of

gas present in large oil-filled transformers. They are designed in such a way that they produce a

warning if it senses either the slow production of gas or fast production of gas in the transformer

oil.

5. Overload protection Relay

As the name implies, these relays are used to prevent the electric motors from damage by

over current and short circuits. For this the heating element is kept in series with the motor. Thus

when over heat occurs the bi-metallic strip connected to the motor heats up and in turn releases a

spring to operate the contacts of the relay.

47

6. Mercury Wetted Relay

This relay is almost similar to the reed relay explained earlier. The only difference is that

instead of inert gases, the contacts are wetted with mercury. This makes them more position

sensitive and also expensive. They have to be vertically mounted for any operation. They have

very low contact resistance and so can be used for timing applications. Due to these factors, this

relay is not used frequently.

7. Machine Tool Relay

This is one of the most famous industrial relay. They are mainly used for the controlling

of all kinds of machines. They have a number of contacts with easily replaceable coils. This

enables them to be easily converted from NO contact to NC contact. Many types of these relays

can easily be setup in a control panel. Though they are very useful in industrial applications, the

invention of PLC has made them farther away from industries.

8. Contactor Relay

This is one of the most heavy load relay ever used. They are mainly used in switching

electric motors. They have a wide range of current ratings from a few amps to hundreds. The

contacts of these relays are usually made with alloys containing a small percentage of silver. This

is done so as to avoid the hazardous effects of arcing. These type of relays are mainly

categorized in the rough use areas. So, they produce loud noises while operated and hence cannot

be used in places where noise is a problem.

9. Solid State relay

SSR relays, as its name implies are designed with the help of solid state components. As

they do not have any moving objects in their design they are known for their high reliability.

48

10. Solid State Contactor Relay

These relays combine both the features of solid state relays and contactor relays. As a

result they have a number of advantages. They have a very good heat sink and can be designed

for the correct on-off cycles. They are mainly controlled with the help of PLC, micro-processors

or microcontrollers.

SOME FEATURES OF RELAYS USED IN THIS PROJECT:

De-spiking Diode Relays

A diode in the reverse-biased position is connected in parallel with the relay coil. As

there is no flow of current due to such a connection, an open circuit of the relay will cause the

current to stop flowing through the coil. This will have effect on the magnetic field. The

magnetic field will be decreased instantly. This will cause the rise of an opposite voltage with

very high reverse polarity to be induced. This is mainly caused because of the magnetic lines of

force that cut the armature coil due to the open circuit. Thus the opposite voltage rises until the

diode reaches 0.7 volts. As soon as this cut-off voltage is achieved, the diode becomes forward-

biased. This causes a closed circuit in the relay, causing the entire voltage to pass through the

load. The current thus produced will be flowing through the circuit for a very long time. As soon

as the voltage is completely drained, this current flow will also stop.

De-spiking Resistor Relays

A resistor is almost efficient as that of a diode. It can not only suppress the voltage spikes

efficiently, but also allows the entire current to flow through it when the relay is in the on

position. Thus the current flow through it will also be very high. To reduce this, the value of the

resistance should be as high as 1 Kilo Ohm. But, as the value of the resistors increases the

voltage spiking capability of the relay decreases.

49

Fig 4.15 : De-spiking diode and resistor relays

RELAY USED IN THIS PROJECT:

Main features:

2CO electromechanical relay

92/8 gold silver alloy on silver palladium contact type is suitable for

low level switching application. Fig4.16 2CO relay

Small size and light weight can provide high density.

2.54mm terminal pitch

Low coil power consumption of GS-T type and high coil power consumption of GS-D type

available.

Plastic epoxy resin sealed type.

Table 4.4: 2CO relay parameters-contact rating

50

Applications:

Telecommunications, domestic appliances, office machine, audio equipment, remote control, etc.

Specifications:

1. Contact resistance….. 100mohm

2. Operate time ……GS-D 6msec , GS-T 8msec

3. Release time…… 4msec

4. Insulation resistance….. 100megaohm

5. Weight….. about 4.8 g

Fig 4.5: 2CO relay- coil specification

4.5. OPERATING PROCEDURE:

1. Initially the 230v AC supply is given to the center tapped transformer.

2. The bridge rectifier gives an output of 9v dc after filtering out the ripples.

3. The voltage regulator further gives 5v dc supply to the entire set-up.

4. A battery of 9v is attached to the transmitter section.

51

5. Suppose we want the motor to rotate in clockwise direction with high speed then the SW-1

and SW-3 is pressed manually.

6. We see that the transmitter transfers the data to the receiver section through electromagnetic

waves and the receiver obtains this data.

7. We see that the relay transistor 1 gets activated and so the relay one gets activated.

8. Suppose we want the motor to rotate in anti-clockwise direction, the SW-2 and SW-3 are

pressed.

9. In case we want the motor to rotate with a medium speed in clockwise direction then SW-1,

SW-3, SW-4 is pressed.

10. Accordingly we see the motor rotating in clockwise, anti-clockwise directions with medium

and high speeds.

Table 4.6: Relay operating procedure

RELAY1 RELAY2 RELAY3 RELAY4 MOTOR OPERATION

1 0 X X CLOCKWISE DIRECTION

0 1 X X ANTI-CLOCKWISE DIRECTION

0 0 X X OFF

1 1 X X OFF

X X 1 0 MEDIUM SPEED

X X 0 1 HIGH SPEED

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CHAPTER 5

RESULTS AND APPLICATIONS

53

RESULTS AND APPLICATIONS

Fig 5.1: Complete Circuit

Hence, the speed and direction control of a DC motor using a geared DC motor has been

controlled through a wireless communicating technology i.e., the radio frequency technology

widely known as the RF method.

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Observations:

PRESSING SW-1 AND SW-3 CLOCKWISE, HIGH SPEED ROTATION

OF MOTOR

PRESSING SW-2 AND SW-3 ANTI-CLOCKWISE, HIGH SPEED

ROTATION OF MOTOR

PRESSING SW-1, SW-3, SW-4 CLOCKWISE, MEDIUM SPEED

ROTATION OF MOTOR

PRESSING SW-2, SW-3 AND SW-4 ANTI-CLOCKWISE, MEDIUM SPEED

ROTATION OF MOTOR

Table 5.1: Project observations

The speed and direction can be controlled over a wide range nearly 360 degrees around

the set-up with the help of the antenna in the transmitter section. Therefore, this project is

advantageous is providing speed and direction control from a remote place and also has proved

to be more reliable and easy to operate.

Some of its applications include:

Industries are using RF solutions for monitoring, process, control, inventory tracking, data

links and bar code reading devices.

Commercial wireless applications such as door announcers, security and access systems, gate

control, remote activation, score board and paging systems.

Automotive companies employing RF for wireless remote control, remote keyless entry and

safety applications.

Consumer products including electronic toys, home security, gate and garage door openers,

intercom, fire and safety systems and irrigation controllers

Medical products like patient call and monitoring, handicap assistance device, surgery

communication system, remote patient data logging and ECG monitor

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CHAPTER 6

CONCLUSION

56

CONCLUSION

The wireless communications have always proved a boon in this century. It has

been helpful is solving many intricate of satellite communication, telecommunications,

etc. Among its various methods, radio frequency technology has provided us with

accurate, easy, simpler, faster method of communication compared to the classical

approach. This project brings out one such wireless communication application. It shows

how a dc motor can be controlled wirelessly by the radio frequency technology.

Among all the speed control techniques, a DC geared motor speed is controlled by

using a simple relay driver circuit. Thus, we can obtain variable speeds with clockwise or

anti-clockwise direction of motor. For further use, a microcontroller can be used in this

set up. A potentiometer can also be included to have different speed levels. Tachometer

can also be developed to measure the speed using reed switch.

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CHAPTER 7

REFERENCES

58

REFERENCES

WEBSITES:

1. http://www.circuitstoday.com/types-of-relays

2. www.howstuffworks.com

3. www.answers.com

4. www.radiotronix.com

5. www.WineYardProjects.com

6. http://gearmotorblog.wordpress.com/2009/08/13/what-is-a-gearmotor/

7. http://kontakt-t.narod.ru/catalog/file/relay_goodsky/en_GS.pdf

MAGAZINES:

1. Electronics for you magazine

2. Electrikindia magazine

3. Go Wireless magazine

BOOKS:

1. Radio Frequency Applications By Morris Hamington

2. Working with Radio Frequency By Cruis Leanardo