Chapter -1

ROBOTS

1.1 Introduction

Fig 1.1

A robot is a mechanical or virtual, artificial agent. It is usually a system, which, by its

appearance or movements, conveys a sense that it has intent or agency of its own. The

word robot can refer to both physical robots and virtual software agents, but the latter

are usually referred to as bots to differentiate

While there is still discussion about which machines qualify as robots, a typical robot

will have several, though not necessarily all of the following properties:

1.1 Is not 'natural' i.e. artificially created

1.2 Can sense its environment, and manipulate or interact with things in it

1.3 Has some ability to make choices based on the environment, often using

automatic control or a preprogrammed sequence

1.5 Moves with one or more axes of rotation or translation

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1.6 Makes dexterous coordinated movements

1.7 Appears to have intent or agency

1.2 Robot Fatalities

The first human to be killed by a robot was Robert Williams who died at a casting

plant in Flat Rock, MI (January 25, 1979).

A better known case is that of 37-year-old Kenji Urada, a Japanese factory worker, in

1981. Urada was performing routine maintenance on the robot, but neglected to shut it

down properly, and was accidentally pushed into a grinding machine.

Some examples of factory robots:

1.2.1 Car production: This is now the primary example of factory automation. Over

the last three decades automobile factories have become dominated by robots.

A typical factory contains hundreds of industrial robots working on fully

automated production lines - one robot for every ten human workers. On an

automated production line a vehicle chassis is taken along a conveyor to be

welded, glued, painted and finally assembled by a sequence of robot stations.

1.2.2 Packaging: Industrial robots are also used extensively for palletizing and

packaging of manufactured goods, for example taking drink cartons from the

end of a conveyor belt and placing them rapidly into boxes, or the loading and

unloading of machining centers.

1.2.3 Electronics: Mass produced printed circuit boards (PCBs) are almost

exclusively manufactured by pick and place robots, typically with SCARA

manipulators, which remove tiny electronic components from strips or trays,

and place them on to PCBs with great accuracy. Such robots can place several

components per second (tens of thousands per hour), far out-performing a

human in terms of speed, accuracy, and reliability.

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Fig 1.2

HelpMate trackless pharmacy bot navigates autonomously to transport drugs, lab

specimens, supplies and medical records.

1.2.4 Automated Guided Vehicles (AGVs): Mobile robots, following markers or

wires in the floor, or using vision[38] or lasers, are used to transport goods

around large facilities, such as warehouses, container ports, or hospitals.[39]

Early AGV-style robots were limited to tasks that could be accurately defined

and must be performed the same every time. Very little feedback or

intelligence was required, and the robots may need only the most basic of

exteroceptors to sense things in their environment, if any at all. However,

newer AGV's, such as the Speci-Minder, ADAM, Tug, and PatrolBot Gofer

qualify under the JARA definition of intelligent robots. They use some form

of natural features recognition to navigate. Scanning lasers, stereovision or

other means of sensing the environment in two- or three-dimensions is

combined with standard dead-reckoning calculations in a probabilistic manner

to continuously update the AGV's current location, eliminating cumulative

error. This means that the Self-Guided Vehicle (SGV) can navigate a space

autonomously once it has learned it or been provided with a map of it. Such

new robots are able to operate in complex environments and perform non-

repetitive and non-sequential tasks such as carrying tires to presses in

factories, delivering masks in a semi-conductor lab, delivering specimens in

hospitals and delivering goods in warehouses.

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Fig 1.3

The Roomba domestic vacuum cleaner robot does a menial job

There are many jobs which a human could perform better than a robot but for one reason

or another the human either does not want to do it or cannot be present to do the job. The

job may be too boring to bother with, for example domestic cleaning; or be too

dangerous, for example exploring inside a volcano. These jobs are known as the "dull,

dirty, and dangerous" jobs. Other jobs are physically inaccessible. For example, exploring

another planet, cleaning the inside of a long pipe or performing laparoscopic surgery.

1.2.5 Robots in the home: As their price falls, and their performance and

computational ability rises, making them both affordable and sufficiently

autonomous, robots are increasingly being seen in the home where they are

taking on simple but unwanted jobs, such as vacuum cleaning, floor cleaning

and lawn mowing. While they have been on the market for several years, 2006

saw an explosion in the number of domestic robots sold. By 2006, iRobot had

sold more than 2 million vacuuming robots. They tend to be relatively

autonomous, usually only requiring a command to begin their job. They then

proceed to go about their business in their own way. At such, they display a

good deal of agency, and are considered intelligent robots.

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Fig 1.4

A laparoscopic robotic surgery machine.

1.2.6 Telerobots: When a human cannot be present on site to perform a job because

it is dangerous, far away, or inaccessible, teleoperated robots, or telerobots are

used. Rather than following a predetermined sequence of movements a

telerobot is controlled from a distance by a human operator. The robot may be

in another room or another country, or may be on a very different scale to the

operator. A laparoscopic surgery robot such as da Vinci allows the surgeon to

work inside a human patient on a relatively small scale compared to open

surgery, significantly shortening recovery time. An interesting use of a

telerobot is by the author Margaret Atwood, who has recently started using a

robot pen (the Longpen) to sign books remotely. The Longpen is similar to the

Autopen of the 1800s. This saves the financial cost and physical

inconvenience of traveling to book signings around the world. At the other

end of the spectrum, iRobot ConnectR robot is designed to be used by anyone

to stay in touch with family or friends from far away. One robot in use today,

Intouchhealth's RP-7 remote presence robot, is being used by doctors to

communicate with patients, allowing the doctor to be anywhere in the world.

This increases the number of patients a doctor can monitor.

1.2.7 Military robots: Teleoperated robot aircraft, like the Predator Unmanned

Aerial Vehicle, are increasingly being used by the military. These robots can

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be controlled from anywhere in the world allowing an army to search terrain,

and even fire on targets, without endangering those in control. Many of these

robots are teleoperated, but others are being developed that can make

decisions automatically; choosing where to fly or selecting and engaging

enemy targets. Hundreds of robots such as iRobot's Packbot and the Foster-

Miller TALON are being used in Iraq and Afghanistan by the U.S. military to

defuse roadside bombs or Improvised Explosive Devices (IEDs) in an activity

known as Explosive Ordnance Disposal (EOD). Autonomous robots such as

MDARS and Seekur are being developed to perform security and surveillance

tasks at military facilities to address manpower shortages as well as keeping

troops out of harm's way. The Crusher Unmanned Ground Vehicle (UGV) is

being developed to perform military missions autonomously.

1.2.8 Elder Care: The population is aging in many countries, especially Japan,

meaning that there are increasing numbers of elderly people to care for but

relatively fewer young people to care for them. Humans make the best carers,

but where they are unavailable, robots are gradually being introduced.

1.3 Unconventional Robots

Much of the research in robotics focuses not on specific industrial tasks, but on

investigations into new types of robot, alternative ways to think about or design robots,

and new ways to manufacture them. It is expected that these new types of robot will be

able to solve real world problems when they are finally realized.

Fig 1.5

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A nanocar made from a single molecule

1.3.1 Nanorobots: Nanorobotics is the still largely hypothetical technology of

creating machines or robots at or close to the scale of a nanometer (10-9

meters). Also known as nanobots or nanites, they would be constructed from

molecular machines. So far, researchers have mostly produced only parts of

these complex systems, such as bearings, sensors, and Synthetic molecular

motors, but functioning robots have also been made such as the entrants to the

Nanobot Robocup contest. Researchers also hope to be able to create entire

robots as small as viruses or bacteria, which could perform tasks on a tiny

scale. Possible applications include micro surgery (on the level of individual

cells), utility fog, manufacturing, weaponry and cleaning. Some people have

suggested that if there were nanobots which could reproduce, the earth would

turn into "grey goo", while others argue that this hypothetical outcome is

nonsense.

1.3.2 Soft Robots: Most man-made machines are made from hard, stiff materials,

especially metal and plastic. This is in contrast to most natural organisms,

which are mostly soft tissues. Researchers at Tufts University recently

developed robots with silicone bodies and flexible actuators (air muscles,

electroactive polymers, ferrofluids). The control software emphasizes soft

behaviors using fuzzy logic and neural networks.

Soft-bodied robots can look, feel, and behave differently from traditional hard robots,

enabling new applications. Some of these robots are currently exhibited at the Museum of

Modern Art (MoMa) in New York City.

Fig 1.6

Molecubes in motion

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1.3.3 Reconfigurable Robots: A few researchers have investigated the possibility of

creating robots which can alter their physical form to suit a particular task,

like the fictional T-1000. Real robots are nowhere near that sophisticated

however, and mostly consist of a small number of cube shaped units, which

can move relative to their neighbours, for example SuperBot. Algorithms have

been designed in case any such robots become a reality.

Fig 1.7

A swarm of robots from the Open-source micro-robotic project

1.3.4 Swarm robots: Inspired by colonies of insects such as ants and bees,

researchers hope to create very large swarms (thousands) of tiny robots which

together perform a useful task, such as finding something hidden, cleaning, or

spying. Each robot would be quite simple, but the emergent behaviour of the

swarm would be more complex. The whole set of robots can be considered as

one single distributed system, in the same way an ant colony can be

considered a superorganism. They would exhibit swarm intelligence. The

largest swarms so far created include the iRobot swarm, and the Open-source

micro-robotic project swarm, which are being used to research collective

behaviors. Swarms are also more resistant to failure. Whereas one large robot

may fail and ruin the whole mission, the swarm can continue even if several

robots fail. This makes them attractive for space exploration missions, where

failure can be extremely costly.

1.3.5 Evolutionary Robots: is a methodology that uses evolutionary computation to

help design robots, especially the body form, or motion and behaviour

controllers. In a similar way to natural evolution, a large population of robots

is allowed to compete in some way, or their ability to perform a task is

measured using a fitness function. Those that perform worst are removed from

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the population, and replaced by a new set, which have new behaviors based on

those of the winners. Over time the population improves, and eventually a

satisfactory robot may appear. This happens without any direct programming

of the robots by the researchers. Researchers use this method both to create

better robots, and to explore the nature of evolution. Because the process often

requires many generations of robots to be simulated, this technique may be

run entirely or mostly in simulation, then tested on real robots once the

evolved algorithms are good enough.

1.3.6 Virtual Reality: Robotics also has application in the design of virtual reality

interfaces. Specialized robots are in widespread use in the haptic research

community. These robots, called "haptic interfaces" allow touch-enabled user

interaction with real and virtual environments. Robotic forces allow

simulating the mechanical properties of "virtual" objects, which users can

experience through their sense of touch.

1.4 Dangers and fears

Although current robots are not believed to have developed to the stage where they pose

any threat or danger to society, fears and concerns about robots have been repeatedly

expressed in a wide range of books and films. The principal theme is the robots'

intelligence and ability to act could exceed that of humans, that they could develop a

conscience and a motivation to take over or destroy the human race. (See The

Terminator, Runaway, Robocop, the Replicators in Stargate, the Cylons in BattleStar

Galactica, The Matrix, and I, Robot.) Robots could be dangerous if they were

programmed to kill or if they are programmed to be so smart that they make their own

software, build their own hardware to upgrade themselves or if they change their own

source code.

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Frankenstein (1818), often called the first science fiction novel, has become synonymous

with the theme of a robot or monster advancing beyond its creator. Probably the best

known author to have worked in this area is Isaac Asimov who placed robots and their

interaction with society at the center of many of his works. Of particular interest are

Asimov's Three Laws of Robotics. Currently, malicious programming or unsafe use of

robots may be the biggest danger. Although industrial robots may be smaller and less

powerful than other industrial machines, they are just as capable of inflicting severe

injury on humans. However, since a robot can be programmed to move in different

trajectories depending on its task, its movement can be unpredictable for a person

standing in its reach. Therefore, most industrial robots operate inside a security fence

which separates them from human workers. Manuel De Landa has theorized that humans

are at a critical and significant juncture where humans have allowed robots, "smart

missiles," and autonomous bombs equipped with artificial perception to make decisions

about killing us. He believes this represents an important and dangerous trend where

humans are transferring more of our cognitive structures into our machines.[75] Even

without malicious programming, a robot, especially a future model moving freely in a

human environment, is potentially dangerous because of its large moving masses,

powerful actuators and unpredictably complex behavior. A robot falling on someone or

just stepping on his foot by mistake could cause much more damage to the victim than a

human being of the same size. Designing and programming robots to be intrinsically safe

and to exhibit safe behavior in a human environment is one of the great challenges in

robotics. Some theorists, such as Eliezer Yudkowsky, have suggested that developing a

robot with a powerful conscience may be the most prudent course of action in this regard.

1.5 Early modern developments

An early automaton was created in 1738 by Jacques de Vaucanson, who created a

mechanical duck that was able to eat and digest grain, flap its wings, and excrete.

The Japanese craftsman Hisashige Tanaka, known as "Japan's Edison," created an array

of extremely complex mechanical toys, some of which were capable of serving tea, firing

arrows drawn from a quiver, or even painting a Japanese kanji character. The landmark

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text Karakuri Zui (Illustrated Machinery) was published in 1796. (T. N. Hornyak, Loving

the Machine: The Art and Science of Japanese Robots [New York: Kodansha

International, 2006])

In 1898 Nikola Tesla publicly demonstrated a radio-controlled (teleoperated) boat,

similar to a modern ROV. Based on his patents U.S. Patent 613,809   , U.S. Patent

723,188   and U.S. Patent 725,605   for "teleautomation", Tesla hoped to develop the

wireless torpedo into a weapon system for the US Navy. (Cheney 1989)

1.6 Modern Developments

In the 1930s, Westinghouse Electric Corporation made a humanoid robot known as

Elektro, exhibited at the 1939 and 1940 World's Fairs.

The first electronic autonomous robots were created by William Grey Walter of the

Burden Neurological Institute at Bristol, England in 1948 and 1949. They were named

Elmer and Elsie. These robots could sense light and contact with external objects, and use

these stimuli to navigate.

Fig 1.8

Unimate's PUMA arm

It wasn't until the second half of the twentieth century, when integrated circuits were

invented, and computers began to double rapidly in power (roughly every two years

according to Moore's Law), that it became possible to build robots as we imagine them.

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Until that time, automatons were the closest things to robots, and while they may have

looked humanoid, and their movements were complex, they were not capable of the self-

control and decision making that robots are today.

The first truly modern robot, digitally operated, programmable, and teachable, was

invented by George Devol in 1954 and was ultimately called the Unimate. It is worth

noting that not a single patent was cited against his original robotics patent (U.S. Patent

2,988,237   ). The first Unimate was personally sold by Devol to General Motors in 1960

and installed in 1961 in a plant in Trenton, New Jersey to lift hot pieces of metal from a

die casting machine and stack them.

1.7 Autonomous robot

Autonomous robots are robots which can perform desired tasks in unstructured

environments without continuous human guidance. Many kinds of robots have some

degree of autonomy. Different robots can be autonomous in different ways. A high

degree of autonomy is particularly desirable in fields such as space exploration, where

communication delays and interruptions are unavoidable. Other more mundane uses

benefit from having some level of autonomy, like cleaning floors, mowing lawns, and

waste water treatment.

Some modern factory robots are "autonomous" within the strict confines of their direct

environment. Maybe not every degree of freedom exists in their surrounding environment

but the work place of the factory robot is challenging and can often be unpredictable or

even chaotic. The exact orientation and position of the next object of work and (in the

more advanced factories) even the type of object and the required task must be

determined. This can vary unpredictably (at least from the robot's point of view).

One important area of robotics research is to enable the robot to cope with its

environment whether this be on land, underwater, in the air, underground, or in space.

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A fully autonomous robot has the ability to

1.7.1 Gain information about the environment.

1.7.2 Work for an extended period without human intervention.

1.7.3 Move either all or part of itself throughout its operating environment

without human assistance.

An autonomous robot may also learn or gain new capabilities like adjusting strategies for

accomplishing its task(s) or adapting to changing surroundings.

Fig 1.9

Exteroceptive sensors: 1) blue laser rangefinder senses up to 360 distance readings in a

180-degree slice; 2) 24 round golden ultrasonic sensors sample range readings in a 15-

degree cone; 3) ten touch panels along the bottom detect shoes and other low-lying

objects. 4) break beams between the lower and upper segments sense tables and other

mid-level obstacles. (Courtesy MobileRobots Inc)

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The first requirement for complete physical autonomy is the ability for a robot to take

care of itself. Many of the battery powered robots on the market today can find and

connect to a charging station, and some toys like Sony's Aibo are capable of self-docking

to charge their batteries.

Self maintenance is based on "proprioception", or sensing one's own internal status. In

the battery charging example, the robot can tell proprioceptively that its batteries are low

and it then seeks the charger. Another common proprioceptive sensor is for heat

monitoring. Increased proprioception will be required for robots to work autonomously

near people and in harsh environments.

Fig 1.10

Robot GUI display showing battery voltage and other proprioceptive data in lower right-

hand corner. The display is for user information only. Autonomous robots monitor and

respond to proprioceptive sensors without human intervention to keep themselves safe

and operating properly. (Courtesy MobileRobots Inc)

1.8 Sensing the environment

Exteroception is sensing things about the environment. Autonomous robots must have a

range of environmental sensors to perform their task and stay out of trouble.

Common exteroceptive sensors are

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Electromagnetic spectrum

Sound

Touch

Smell, odor

Temperature

Range to things in the environment

Some robotic lawn mowers will adapt their programming by detecting the speed in which

grass grows as needed to maintain a perfect cut lawn, and some vacuum cleaning robots

have dirt detectors that sense how much dirt is being picked up and use this information

to tell them to stay in one area longer.

1.9 Task performance

The next step in autonomous behavior is to actually perform a physical task. A new area

showing commercial promise is domestic robots, with a flood of small vacuuming robots

beginning with iRobot and Electrolux in 2002. While the level of intelligence is not high

in these systems, they navigate over wide areas and pilot in tight situations around homes

using contact and non-contact sensors. Both of these robots use proprietary algorithms to

increase coverage over simple random bounce.

The next level of autonomous task performance requires a robot to perform conditional

tasks. For instance, security robots can be programmed to detect intruders and respond in

a particular way depending upon where the intruder is.

Fig 1.11

Indoor position sensing and navigation

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Robot interface GUI showing a robot building map with forbidden areas highlighted in

yellow on the right side of the screen. Defined task sequences and goals are in the second

column. Robots listed on the left side of the GUI can be selected by mouseclick. The

selected robot will then travel to any location clicked in the map, unless it is in a

forbidden area. For a robot to associate behaviors with a place (localization) requires it to

know where it is and to be able to navigate point-to-point. Such navigation began with

wire-guidance in the 1970s and progressed in the early 2000s to beacon-based

triangulation.

Current commercial robots autonomously navigate based on sensing natural features. The

first commercial robots to achieve this were Pyxus' HelpMate hospital robot and the

CyberMotion guard robot, both designed by robotics pioneers in the 1980s. These robots

originally used manually created CAD floor plans, sonar sensing and wall-following

variations to navigate buildings. The next generation, such as MobileRobots' PatrolBot

and autonomous wheelchair both introduced in 2004, have the ability to create their own

laser-based maps of a building and to navigate open areas as well as corridors. Their

control system changes its path on-the-fly if something blocks the way. Rather than climb

stairs, which requires highly specialized hardware, most indoor robots navigate

handicapped-accessible areas, controlling elevators and electronic doors. [2] With such

electronic access-control interfaces, robots can now freely navigate indoors.

Autonomously climbing stairs and opening doors manually are topics of research at the

current time.

As these indoor techniques continue to develop, vacuuming robots will gain the ability to

clean a specific user specified room or a whole floor. Security robots will be able to

cooperatively surround intruders and cut off exits. These advances also bring

concommitant protections: robots' internal maps typically permit "forbidden areas" to be

defined to prevent robots from autonomously entering certain regions.

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1.10 Outdoor autonomous position-sensing and navigation

Outdoor autonomy is most easily achieved in the air, since obstacles are rare. Cruise

missiles are rather dangerous highly autonomous robots. Pilotless drone aircraft are

increasingly used for reconnaissance. Some of these unmanned aerial vehicles (UAVs)

are capable of flying their entire mission without any human interaction at all except

possibly for the landing where a person intervenes using radio remote control. But some

drone aircraft are capable of a safe, automatic landing also.

Outdoor autonomy is the most difficult for ground vehicles, due to: a) 3-dimensional

terrain; b) great disparities in surface density; c) weather exigencies and d) instability of

the sensed environment.

Fig 1.8

The Seekur and MDARS robots demonstrate their autonomous navigation and security

capabilities at an airbase. (Courtesy of MobileRobots Inc)

In the US, the MDARS project, which defined and built a prototype outdoor surveillance

robot in the 1990s, is now moving into production and will be implemented in 2006. The

General Dynamics MDARS robot can navigate semi-autonomously and detect intruders,

using the MRHA software architecture planned for all unmanned military vehicles. The

Seekur robot was the first commercially available robot to demonstrate MDARS-like

capabilities for general use by airports, utilty plants, corrections facilities and Homeland

Security.

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Chapter-2

Dual-tone multi-frequency

Fig 2.1

A DTMF telephone keypad

2.1 Introduction

Dual-tone multi-frequency (DTMF) signaling is used for telephone signaling over the

line in the voice-frequency band to the call switching center. The version of DTMF used

for telephone tone dialing is known by the trademarked term Touch-Tone and is

standardized by ITU-T Recommendation Other multi-frequency systems are used for

signaling internal to the telephone network.

As a method of in-band signaling, DTMF tones were also used by cable television

broadcasters to indicate the start and stop times of local commercial insertion points

during station breaks for the benefit of cable companies. Until better out-of-band

signaling equipment was developed in the 1990s, fast, unacknowledged, and loud DTMF

tone sequences could be heard during the commercial breaks of cable channels in the

United States and elsewhere.

2.2 History

In the time preceding the development of DTMF, telephone systems employed a system

commonly referred to as pulse (Dial Pulse or DP in the U.S.) or loop disconnect (LD)

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signaling to dial numbers, which functions by rapidly disconnecting and connecting the

calling party's telephone line, similar to flicking a light switch on and off. The repeated

connection and disconnection, as the dial spins, sounds like a series of clicks. The

exchange equipment counts those clicks or dial pulses to determine the called number.

Loop disconnect range was restricted by telegraphic distortion and other technical

problems, and placing calls over longer distances required either operator assistance

(operators used an earlier kind of multi-frequency dial) or the provision of subscriber

trunk dialing equipment.

Dual Tone Multi-Frequency, or DTMF is a method for instructing a telephone switching

system of the telephone number to be dialed, or to issue commands to switching systems

or related telephony equipment.

The DTMF dialing system traces its roots to a technique AT&T developed in the 1950s

called MF (Multi-Frequency) which was deployed within the AT&T telephone network

to direct calls between switching facilities using in-band signaling. In the early 1960s, a

derivative technique was offered by AT&T through its Bell System telephone companies

as a "modern" way for network customers to place calls. In AT&Ts Compatibility

Bulletin No. 105, AT&T described the product as "a method for pushbutton signaling

from customer stations using the voice transmission path."

The consumer product was marketed by AT&T under the registered trade name Touch-

Tone. Other vendors of compatible telephone equipment called this same system "Tone"

dialing or "DTMF".

The DTMF system uses eight different frequency signals transmitted in pairs to represent

sixteen different numbers, symbols and letters - as detailed below.

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Fig 2.2

An Autovon telephone keypad with the four precedence levels

The engineers had envisioned phones being used to access computers, and surveyed a

number of companies to see what they would need for this role. This led to the addition

of the octothorpe number sign (#) and star (*) keys as well as a group of keys for menu

selection: A, B, C and D. In the end, the lettered keys were dropped from most phones,

and it was many years before these keys became widely used for vertical service codes

such as *67 in the United States and Canada to suppress caller ID.Public payphones that

accept credit cards use these additional codes to send the information from the magnetic

strip.

The U.S. military also used the letters, relabeled, in their now defunct Autovon phone

system. Here they were used before dialing the phone in order to give some calls priority,

cutting in over existing calls if need be. The idea was to allow important traffic to get

through every time. The levels of priority available were Flash Override (A), Flash (B),

Immediate (C), and Priority (D), with Flash Override being the highest priority. Pressing

one of these keys gave your call priority, overriding other conversations on the network.

Pressing C, Immediate, before dialing would make the switch first look for any free lines,

and if all lines were in use, it would disconnect any non-priority calls, and then any

priority calls. Flash Override will kick every other call off the trunks between the origin

and destination. Consequently, it is limited to the White House Communications Agency.

Precedence dialing is still done on the military phone networks.

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2.3 AUDIO SAMPLE

2.3.1 Dtmf push to talk id

Present-day uses of the A, B, C and D keys on telephone networks are few, and exclusive

to network control. For example, the A key is used on some networks to cycle through

different carriers at will (thereby listening in on calls). Their use is probably prohibited

by most carriers. The A, B, C and D tones are used in amateur radio phone patch and

repeater operations to allow, among other uses, control of the repeater while connected to

an active phone line.

DTMF tones are also used by some cable television networks and radio networks to

signal the local cable company/network station to insert a local advertisement or station

identification. These tones were often heard during a station ID preceding a local ad

insert. Previously, terrestrial television stations also used DTMF tones to shut off and

turn on remote transmitters.

DTMF tones are also sometimes used in caller ID systems to transfer the caller ID

information, however in the USA only Bell 202 modulated FSK signaling is used to

transfer the data.

2.3.2 Keypad

The DTMF keypad is laid out in a 4×4 matrix, with each row representing a low

frequency, and each column representing a high frequency. Pressing a single key (such as

'1' ) will send a sinusoidal tone of the two frequencies (697 and 1209 hertz (Hz)). The

original keypads had levers inside, so each button activated two contacts. The multiple

tones are the reason for calling the system multifrequency. These tones are then decoded

by the switching center to determine which key was pressed.

DTMF keypad frequencies (with sound clips)

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1209 Hz 1336 Hz 1477 Hz 1633 Hz

697 Hz 1 2 3 A

770 Hz 4 5 6 B

852 Hz 7 8 9 C

941 Hz * 0 # D

Table 2.1

DTMF event frequencies

Event Low frequency High frequency

Busy signal 480 Hz 620 Hz

Dial tone 350 Hz 440 Hz

Ringback tone (US) 440 Hz 480 Hz

Table 2.2

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The tone frequencies, as defined by the Precise Tone Plan, are selected such that

harmonics and intermodulation products will not cause an unreliable signal. No

frequency is a multiple of another, the difference between any two frequencies does not

equal any of the frequencies, and the sum of any two frequencies does not equal any of

the frequencies. The frequencies were initially designed with a ratio of 21/19, which is

slightly less than a whole tone. The frequencies may not vary more than ±1.8% from their

nominal frequency, or the switching center will ignore the signal. The high frequencies

may be the same volume or louder as the low frequencies when sent across the line. The

loudness difference between the high and low frequencies can be as large as 3 decibels

(dB) and is referred to as "twist". The minimum duration of the tone should be at least 70

msec, although in some countries and applications DTMF receivers must be able to

reliably detect DTMF tones as short as 45ms.DTMF can be decoded using the Goertzel

algorithm.

2.4 DTMF Generator/Decoder

The photo depicts a DTMF generator/decoder pair you can build in an afternoon or two.

Dual-tone-multi-frequency (DTMF, also known as touch-tone) are the audible sounds

you hear when you press keys on your phone.

The tone generator (top) uses the 5589 chip and a DIP switch. You can actually hear the

tones through the speaker. The bottom circuit uses the 8870 to decode a tone and display

its associated number on the 7-segment LED.

Touch-tone is familiar to many (telephone), it is a mature technology, and readily

available with off-the-shelf, single-chip, low-cost components. For these reasons DTMF

is often used in remote control applications that typically use telephones (e.g. accessing

your messages from an answering machine, retrieving your account balance info from

your bank's database).

This tutorial will not discuss telephone interfacing. Rather it will give you a basic

working foundation which you can build upon. The generator/decoder above are tethered

23

together by a single wire. But you can expand upon this foundation for wireless remote

control using a microphone. For longer distances maybe you can add a pair of walkie-

talkies, generating audible tones into one, and decoding with the other.

Another possibility is to use infrared (IR). Since tones are just electrical pulses, you can

replace the speaker with an IR emitter and add an IR detector to the decoder.

Yet another experiment is to interface either the generator or the emitter or both to a PC

or embedded microprocessor (e.g. 8051, PIC or Stamp). In this scenario, the PC or a

peripheral, through touch-tones, can respond and control.

If you are familiar with how telephones work, the basic circuit might also help you to

build devices the respond to your call. For example, you can build upon the decoder and

add relays to control household devices that respond when you call your home.

Well hopefully I got you motivated. The bottom line is that DTMF was designed for

optimal performance with each tone being very distinct. This makes decoding the tone

very easy even in surrouding noise. It is this performance that makes DTMF ideal for

clear transmission and reception in remote control (wireless or through phone lines)

applications.

Parts List and Potential Vendor Source Below are parts I used for constructing my DTMF

generator/decoding pair. Additionally, I list the source from which I bought it from, along

with the vendor part number and cost (in 1998). Note: I have no association with these

vendors. I tend to buy parts from these US-based electronic mail-order companies. They

usually have items in stock. When Jameco (reasonable prices) doesn't have a part, I then

look at Digikey and JDR and Radio Shack. Additionally, I used a combination of

soldering and wirewrapping on a prototyping board (Radio Shack). Part placement is not

critical.

TABLE 2.3: DTMF Generator

24

PART DESCRIPTIONVENDOR

PART

PRICE

(1998)QUANTITY

TCM5589N TONE GENERATOR

16-PIN DIP

JAMECO

#328033.95 1

3.579545 MHZ CRYSTALJAMECO

#145331.05 1

8 OHM SPEAKERJAMECO

#884101.95 1

16-PIN WIREWRAP SOCKETJAMECO

#374791.35 2

8-POSITION DIP SWITCHJAMECO

#388420.79 3

TIP31 NPN TRANSISTORJAMECO

#330480.49 1

TABLE 2.4: DTMF Decoder

PART DESCRIPTION VENDOR PARTPRICE

(1998)QUANTITY

8870 DTMF DECODER 18-PIN

DIPsee below 1

3.579545 MHZ CRYSTALJAMECO

#145331.05 1

7-SEG DISPLAY COMMON

CATHODE

JAMECO

#247820.99 1

74LS48 7-SEG DRIVER 16-PIN

DIP

JAMECO

#478110.89 1

16-PIN WIREWRAP SOCKET JAMECO 1.35 1

25

#37479

18-PIN WIREWRAP SOCKETJAMECO

#381481.35 1

0.1 uF CAPACITORJAMECO

#1511160.15 2

100 KOHM RESISTOR 2

300 KOHM RESISTOR 1

Teltone offers the 8870 chip. This part can be ordered from Component

Distributors, Inc. They sell Teltone's M-8870-01 (18-pin DIP package) unit for

about $1.50 in single quantities and can ship internationally. They have local

offices around the US. Check out their webpage for locations. (Added the

following 08/13/99) One visitor alerted me to B.G. Micro. This mail-order house

sells the 8870 for $2.25 and the 5089 for $1.25. They are based in Dallas, Texas:

Telephone: 1-800-276-2206.

It has also come to my attention that there are similar DTMF decoding chips.

Namely Harris Semiconductor's CD22202. JDR Microdevices offers this chip. It

is not pin-compatiable with the 8870 but functions in the same way. The JDR part

number is CD22202E and costs $3.99. Please note that I have not used the

CD22202E. I imagine that if you wire it up taking into account that the pin-

numbers differ with those of the 8870, your decoder should still work.

26

2.5 Theory of Operation

2.5.1 So what are these tones?

In DTMF there are 16 distinct tones. Each tone is the sum of two frequencies: one

from a low and one from a high frequency group. There are four different

frequencies in each group.

Your phone only uses 12 of the possible 16 tones. If you look at

your phone, there are only 4 rows (R1, R2, R3 and R4) and 3

columns (C1, C2 and C3). The rows and columns select

frequencies from the low and high frequency group

respectively. The exact value of the frequencies are listed in

Table 3 below:

TABLE 2.5: DTMF Row/Column Frequencies

LOW-FREQUENCIES

ROW # FREQUENCY (HZ)

R1: ROW 0 697

R2: ROW 1 770

R3: ROW 2 852

R4: ROW 3 941

HIGH-FREQUENCIES

COL # FREQUENCY (HZ)

C1: COL 0 1209

C2: COL 1 1336

C3: COL 2 1477

C4: COL 3 1633

C4 not used in phones

27

Thus to decipher what tone frequency is associated with a particular key, look at

your phone again. Each key is specified by its row and column locations. For

example the "2" key is row 0 (R1) and column 1 (C2). Thus using the above table,

"2" has a frequency of 770 + 1336 = 2106 Hz The "9" is row 2 (R3) and column 2

(C3) and has a frequency of 852 + 1477 = 2329 Hz.

The following graph is a captured screen from an oscilloscope. It is a plot of the

tone frequency for the "1" key:

Fig 2.3

You can see that the DTMF generated signal is very distinct and clear. The

horizontal axis is in samples. The frequency of the tone is about 1900 Hz - close

to the 1906 Hz predicted by Table 3 (697+1209).

2.6 Construction

This section is organized as follows:

o Schematics

o Construction Hightlights

28

2.6.1 Schematics

The schematic in the figure below is relatively straightforward. I

recommend that you use a combination of soldering and wirewrapping

using sockets for all IC component placement.

2.6.2 Tone Generator

Fig 2.4

2.6.3 Tone Decoder

The schematic for the DTMF decoder in the figure below. Again you can

use a combination of wirewrapping and soldering. Part placement is not

critical.

29

Fig 2.5

2.7 Construction Highlights

2.7.1 Tone Generator

The DTMF generator circuit is straight forward to construct. Only 3 of the

5089's 4 column pins (3,4,5) and all 4 row pins (11 to 14) were used. Thus

it uses only 12 of the 16 touch tones (just like your phone). In this

schematic you'll note the "/" in front of column and row pin labels (e.g.

/C1). This means that these pins are active low. In other words, a pin is

enabled when it is grounded. When the circuit is powered on, these pins

normally high (+5V). C1-C3 and R1-R4 are wired to an 8-position DIP

switch. In a single-package this DIP contains 8 single-pole-single-throw

(SPST) switches. It is much cheaper to use than 8 real SPST switches.

You slide a DIP position to open or close its switch. When closed that

particular switch connects its associated column or row pin to ground and

makes it active.

You could use a 12-key keypad available from many surplus or electronics

mail-order companies. But you must be aware of what you buy. Not all

30

keypads can be used with the 5089. I think the proper keypad will have 9

pins: 8 (for 4 rows plus 4 columns) plus 1 for a common which you'd

connect to ground. Often surplus keypads do not come with techsheets,

and you will have to manually figure out which pin is associated with

which row or column. I found to my surprise that my particular surplus

12-key keypad (from Electronic Goldmine) did not have this common pin

and so I resorted to using a DIP.

In this photo DIP positions 1 and 4 (C1 and R1 respectively) are in their

ON positions. C1 and R1 is "1" on your phone's keypad. The speaker will

emit the touch-tone associated with the "1" key (see Table 4)

The speaker is driven through the TIP31 transistor. Note: the labels 1, 2

and 3 that refer to the base, collector and emitter pins respectively in the

schematic are not standard. Be sure to check your spec sheet for your

TIP31.

TABLE 2.6: DIP SWITCH POSITIONS

(1) DIP: 1+4 (2) DIP: 2+4 (3) DIP: 3+4

(4) DIP: 1+5 (5) DIP: 2+5 (6) DIP: 3+5

(7) DIP: 1+6 (8) DIP: 2+6 (9) DIP: 3+6

(*) DIP: 1+7 (0) DIP: 2+7 (#) DIP: 3+7

Table 4 shows the DIP positions that will activate the tone associated with

the key. The numbers in bold and parenthesis are your desired key tone

(like your phone). Thus if you wanted to dial a "0", you would slide only

positions 2 and 7 on the DIP switch.

2.7.2 Tone Decoder

31

The decoder circuit is also easy to construct. You will have to physically

wire (using alligator clips for instance) the TONE OUT pinout from the

generator to the TONE IN pinout of the decoder.

Once physically wired together, the 7-segment display will light up the

number associated with the touch-tone you activate with the DIP switch.

Note: A "0" tone lights up as "[" and not zero. This is because, "0" key's

tone is actually a ten in binary (1010). Because the 7-segment displays

only a single digit, ten is displayed as a "[". Similarly, the "*" (binary

1011) and "#" (binary 1100) light up as "]" and "U" respectively.

32

CHAPTER 3

VARIOUS DEVICES USED

3.1 RESISTOR :

3.1.1 Introduction

A resistor is a two-terminal electrical or electronic component that opposes an electric

current by producing a voltage drop between its terminals in accordance with Ohm's law:

The electrical resistance is equal to the voltage drop across the resistor divided by the

current through the resistor while the temperature remains the same. Resistors are used as

part of electrical networks and electronic circuits.

Fig 3.1

Axial-lead resistors on tape. The tape is removed during assembly before the leads are

formed and the part is inserted into the board.

Fig 3.2

Three carbon composition resistors in a 1960s valve radio.

33

3.1.2 Identifying resistors

Most axial resistors use a pattern of colored stripes to indicate resistance. Surface-mount

resistors are marked numerically. Cases are usually brown, blue, or green, though other

colors are occasionally found such as dark red or dark grey.One can also use a multimeter

or ohmmeter to test the values of a resistor.

3.1.3 Four-band axial resistors

Four-band identification is the most commonly used color coding scheme on all resistors.

It consists of four colored bands that are painted around the body of the resistor. The

scheme is simple: The first two numbers are the first two significant digits of the

resistance value, the third is a multiplier, and the fourth is the tolerance of the value (e.g.

green-blue-yellow red : 56 x (10^4) ohms = 56 x 10000 ohms = 560 kohms ±2%). Each

color corresponds to a certain number, shown in the chart below. The tolerance for a 4-

band resistor will be 1%, 5%, or 10%.

Color1st

band2nd band

3rd band

(multiplier)

4th band

(tolerance)

Temp.

Coefficient

Black 0 0 ×100    

Brown 1 1 ×101 ±1% (F) 100 ppm

Red 2 2 ×102 ±2% (G) 50 ppm

Orange 3 3 ×103   15 ppm

Yellow 4 4 ×104   25 ppm

34

Green 5 5 ×105 ±0.5% (D)  

Blue 6 6 ×106 ±0.25% (C)  

Violet 7 7 ×107 ±0.1% (B)  

Gray 8 8 ×108 ±0.05% (A)  

White 9 9 ×109    

Gold     ×10-1 ±5% (J)  

Silver     ×10-2 ±10% (K)  

None       ±20% (M)  

Table 3.1

3.1.4 Preferred values

Resistors are manufactured in values from a few milliohms to about a gigaohm; only a

limited range of values from the IEC 60063 preferred number series are commonly

available. These series are called E6, E12, E24, E96 and E192. The number tells how

many standardized values exist in each decade (e.g. between 10 and 100, or between 100

and 1000). So resistors conforming to the E12 series, can have 12 distinct values between

35

10 and 100, whereas those confirming to the E24 series would have 24 distinct values. In

practice, the discrete component sold as a "resistor" is not a perfect resistance, as defined

above. Resistors are often marked with their tolerance (maximum expected variation

from the marked resistance). These E numbers correspond to the formula R= 10^(N/E),

So for an 1.21 ohm E96 series resistor, N=8 and 10^(8/96)=1.21 ohm. Each multiple of

96 added to the remainder gives the next decade. So a 12.1 ohm resistor would have a N=

8+96 = 104. N can also be found by using the formula E*LOG10(R) = N.

3.1.5 Power dissipation

The power dissipated by a resistor is the voltage across the resistor multiplied by the

current through the resistor:All three equations are equivalent. The first is derived from

Joule's law, and other two are derived from that by Ohm's Law.

The total amount of heat energy released is the integral of the power over time:

If the average power dissipated exceeds the power rating of the resistor, the resistor may

depart from its nominal resistance, and may be damaged by overheating. Significantly

excessive power dissipation may raise the temperature of the resistor to a point where it

burns out, which could cause a fire in adjacent components and materials.

3.1.6 Series and parallel circuits

Resistors in a parallel configuration each have the same potential difference (voltage). To

find their total equivalent resistance (Req):

The parallel property can be represented in equations by two vertical lines "||" (as in

geometry) to simplify equations. For two resistors,The current through resistors in series

stays the same, but the voltage across each resistor can be different. The sum of the

potential differences (voltage) is equal to the total voltage.

To find their total resistance:

36

A resistor network that is a combination of parallel and series can sometimes be broken

up into smaller parts that are either one or the other. For instance,However, many resistor

networks cannot be split up in this way. Consider a cube, each edge of which has been

replaced by a resistor. For example, determining the resistance between two opposite

vertices requires matrix methods for the general case. However, if all twelve resistors are

equal, the corner-to-corner resistance is 5⁄6 of any one of them.

3.2 CAPACITOR

3.2.1 Introduction

A capacitor is an electrical/electronic device 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.

Capacitors are often used in electric and electronic circuits as energy-storage devices.

They can also be used to differentiate between high-frequency and low-frequency signals.

This property makes them useful in electronic filters.

Capacitors are occasionally referred to as condensers. This is considered an antiquated

term in English, but most other languages use an equivalent, like "Kondensator" in

German, "Condensador" in Spanish, or "Kondensa" in Japanese.

3.2.2 Physics

Diagram of a parallel-plate capacitorA capacitor consists of two conductive electrodes, or

plates, separated by a dielectric.

3.2.3 Capacitance

The capacitor's capacitance (C) is a measure of the amount of charge (Q) stored on each

plate for a given potential difference or voltage (V) which appears between the plates:

37

In SI units, a capacitor has a capacitance of one farad when one coulomb of charge is

stored due to one volt applied potential difference across the plates. Since the farad is a

very large unit, values of capacitors are usually expressed in microfarads (µF),

nanofarads (nF), or picofarads (pF).

When there is a difference in electric charge between the plates, an electric field is

created in the region between the plates that is proportional to the amount of charge that

has been moved from one plate to the other. This electric field creates a potential

difference V = E·d between the plates of this simple parallel-plate capacitor.

The capacitance is proportional to the surface area of the conducting plate and inversely

proportional to the distance between the plates. It is also proportional to the permittivity

of the dielectric (that is, non-conducting) substance that separates the plates.

The capacitance of a parallel-plate capacitor is given by:

where ε is the permittivity of the dielectric (see Dielectric constant), A is the area of the

plates and d is the spacing between them.

In the diagram, the rotated molecules create an opposing electric field that partially

cancels the field created by the plates, a process called dielectric polarization.

3.2.4 Stored energy

As opposite charges accumulate on the plates of a capacitor due to the separation of

charge, a voltage develops across the capacitor due to the electric field of these charges.

Ever-increasing work must be done against this ever-increasing electric field as more

charge is separated. The energy (measured in joules, in SI) stored in a capacitor is equal

to the amount of work required to establish the voltage across the capacitor, and therefore

the electric field. The energy stored is given by:

where V is the voltage across the capacitor.

38

The maximum energy that can be (safely) stored in a particular capacitor is limited by the

maximum electric field that the dielectric can withstand before it breaks down. Therefore,

capacitors made with the same dielectric have about the same maximum energy density

(joules of energy per cubic meter), if the dielectric volume dominates the total volume.

3.2.5 Capacitor types

Fig 3.3

Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum

at top right; through-hole electrolytic at bottom right. Major scale divisions are cm.

Fig 3.4

Various types of capacitors. From left: multilayer ceramic, ceramic disc, multilayer

polyester film, tubular ceramic, polystyrene, metallized polyester film, aluminium

electrolytic. Major scale divisions are cm.

Fig 3.5

39

3.3 CRYSTAL OSCILLATOR

Fig 3.6

3.3.1 Introduction

A miniature 4 MHz quartz crystal enclosed in a hermetically sealed HC-49/US package,

used as the resonator in a crystal oscillator.

A crystal oscillator is an electronic circuit that uses the mechanical resonance of a

vibrating crystal of piezoelectric material to create an electrical signal with a very precise

frequency. This frequency is commonly used to keep track of time (as in quartz

wristwatches), to provide a stable clock signal for digital integrated circuits, and to

stabilize frequencies for radio transmitters/receivers.

Fig 3.7

Inside construction of a modern high performance HC-49 package quartz crystal

40

3.3.2 Operation

A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a

regularly ordered, repeating pattern extending in all three spatial dimensions.

Almost any object made of an elastic material could be used like a crystal, with

appropriate transducers, since all objects have natural resonant frequencies of vibration.

For example, steel is very elastic and has a high speed of sound. It was often used in

mechanical filters before quartz. The resonant frequency depends on size, shape,

elasticity, and the speed of sound in the material. High-frequency crystals are typically

cut in the shape of a simple, rectangular plate. Low-frequency crystals, such as those used

in digital watches, are typically cut in the shape of a tuning fork. For applications not

needing very precise timing, a low-cost ceramic resonator is often used in place of a

quartz crystal.

When a crystal of quartz is properly cut and mounted, it can be made to distort in an

electric field by applying a voltage to an electrode near or on the crystal. This property is

known as piezoelectricity. When the field is removed, the quartz will generate an electric

field as it returns to its previous shape, and this can generate a voltage. The result is that a

quartz crystal behaves like a circuit composed of an inductor, capacitor and resistor, with

a precise resonant frequency. (See RLC circuit.)

Quartz has the further advantage that its elastic constants and its size change in such a

way that the frequency dependence on temperature can be very low. The specific

characteristics will depend on the mode of vibration and the angle at which the quartz is

cut (relative to its crystallographic axes)1 Therefore, the resonant frequency of the plate,

which depends on its size, will not change much, either. This means that a quartz clock,

filter or oscillator will remain accurate. For critical applications the quartz oscillator is

mounted in a temperature-controlled container, called a crystal oven, and can also be

mounted on shock absorbers to prevent perturbation by external mechanical vibrations.

Quartz timing crystals are manufactured for frequencies from a few tens of kilohertz to

tens of megahertz. More than two billion (2×109) crystals are manufactured annually..

41

3.4 VOLTAGE REGULATOR

3.4.1 Introduction

A voltage regulator is an electrical regulator designed to automatically maintain a

constant voltage level.

It may use an electromechanical mechanism, or passive or active electronic components.

Depending on the design, it may be used to regulate one or more AC or DC voltages.

With the exception of shunt regulators, all modern electronic voltage regulators operate

by comparing the actual output voltage to some internal fixed reference voltage. Any

difference is amplified and used to control the regulation element. This forms a negative

feedback servo control loop. If the output voltage is too low, the regulation element is

commanded to produce a higher voltage. For some regulators if the output voltage is too

high, the regulation element is commanded to produce a lower voltage; however, many

just stop sourcing current and depend on the current draw of whatever it is driving to pull

the voltage back down. In this way, the output voltage is held roughly constant. The

control loop must be carefully designed to produce the desired tradeoff between stability

and speed of response.

3.4.2 Voltage Regulator 7805

The Digilab board can use any power supply that creates a DC voltage between 6 and 12

volts. A 5V voltage regulator (7805) is used to ensure that no more than 5V is delivered

to the Digilab board regardless of the voltage present at the J12 connector (provided that

voltage is less than 12VDC). The regulator functions by using a diode to clamp the output

voltage at 5VDC regardless of the input voltage - excess voltage is converted to heat and

dissipated through the body of the regulator. If a DC supply of greater than 12V is used,

excessive heat will be generated, and the board may be damaged. If a DC supply of less

than 5V is used, insufficient voltage will be present at the regulators output.

42

Fig 3.8

If a power supply provides a voltage higher than 7 or 8 volts, the regulator must dissipate

significant heat. The "fin" on the regulator body (the side that protrudes upward beyond

the main body of the part) helps to dissipate excess heat more efficiently. If the board

requires higher currents (due to the use of peripheral devices or larger breadboard

circuits), then the regulator may need to dissipate more heat. In this case, the regulator

can be secured to the circuit board by fastening it with a screw and nut (see below). By

securing the regulator tightly to the circuit board, excess heat can be passed to the board

and then radiated away.

Fig 3.9

43

3.5 Soldering

Fig 3.10

(De)soldering a contact from a wire.

Soldering is a process in which two or more metal items are joined together by melting

and flowing a filler metal into the joint, the filler metal having a relatively low melting

point. Soft soldering is characterized by the melting point of the filler metal, which is

below 400 °C. The filler metal used in the process is called solder.

Soldering is distinguished from brazing by use of a lower melting-temperature filler

metal; it is distinguished from welding by the base metals not being melted during the

joining process. In a soldering process, heat is applied to the parts to be joined, causing

the solder to melt and be drawn into the joint by capillary action and to bond to the

materials to be joined by wetting action. After the metal cools, the resulting joints are not

as strong as the base metal, but have adequate strength, electrical conductivity, and water-

tightness for many uses. Soldering is an ancient technique mentioned in the Bible and

there is evidence that it was employed up to 5000 years ago in Mesopotamia.

3.5.1 Applications

The most frequent application of soldering is assembling electronic components to

printed circuit boards (PCBs). Another common application is making permanent but

reversible connections between copper pipes in plumbing systems. Joints in sheetmetal

objects such as food cans, roof flashing, rain gutters and automobile radiators have also

historically been soldered, and occasionally still are. Jewelry and small mechanical parts

44

are often assembled by soldering. Soldering is also used to join lead came and copper foil

in stained glass work. Soldering can also be used to effect a semi-permanent patch for a

leak in a container cooking vessel.

3.5.2 Solders

Soldering filler materials are available in many different alloys for differing applications.

In electronics assembly, the eutectic alloy of 63% tin and 37% lead (or 60/40, which is

almost identical in performance to the eutectic) has been the alloy of choice. Other alloys

are used for plumbing, mechanical assembly, and other applications.

A eutectic formulation has several advantages for soldering; chief among these is the

coincidence of the liquidus and solidus temperatures, i.e. the absence of a plastic phase.

This allows for quicker wetting out as the solder heats up, and quicker setup as the solder

cools. A non-eutectic formulation must remain still as the temperature drops through the

liquidus and solidus temperatures. Any differential movement during the plastic phase

may result in cracks, giving an unreliable joint. Additionally, a eutectic formulation has

the lowest possible melting point, which minimizes heat stress on electronic components

during the soldering process.

Lead-free solders are suggested anywhere children may come into contact (since children

are likely to place things into their mouths), or for outdoor use where rain and other

precipitation may wash the lead into the groundwater. Common solder alloys are

mixtures of tin and lead, respectively:

3.1 63/37: melts between 180–185 °C (356–365 °F)

3.2 60/40: melts between 183–190°C (361–374 °F)

3.3 50/50: melts between 185–215°C (365–419 °F)

Lead-free solder alloys melt around 250 °C (482 °F), depending on their composition.

For environmental reasons, 'no-lead' solders are becoming more widely used.

Unfortunately most 'no-lead' solders are not eutectic formulations, making it more

45

difficult to create reliable joints with them. See complete discussion below; see also

RoHS.

Other common solders include low-temperature formulations (often containing bismuth),

which are often used to join previously-soldered assemblies without un-soldering earlier

connections, and high-temperature formulations (usually containing silver) which are

used for high-temperature operation or for first assembly of items which must not

become unsoldered during subsequent operations. Specialty alloys are available with

properties such as higher strength, better electrical conductivity and higher corrosion

resistance.

in stained glass work.

3.5.3 Desoldering and resoldering

Used solder contains some of the dissolved base metals and is unsuitable for reuse in

making new joints. Once the solder's capacity for the base metal has been achieved it will

no longer properly bond with the base metal, usually resulting in a brittle cold solder joint

with a crystalline appearance.

It is good practice to remove solder from a joint prior to resoldering—desoldering braids

or vacuum desoldering equipment (solder suckers) can be used. Desoldering wicks

contain plenty of flux that will lift the contamination from the copper trace and any

device leads that are present. This will leave a bright, shiny, clean junction to be

resoldered.

The lower melting point of solder means it can be melted away from the base metal,

leaving it mostly intact though the outer layer will be "tinned" with solder. Flux will

remain which can easily be removed by abrasive or chemical processes. This tinned layer

will allow solder to flow into a new joint, resulting in a new joint, as well as making the

new solder flow very quickly and easily.

46

3.5.4 Soldering defects

Various problems may arise in the soldering process which lead to joints which are non

functional either immediately or after a period of use. The most common defect when

hand-soldering results from the parts being joined not exceeding the solder's liquidus

temperature, resulting in a "cold solder" joint. This is usually the result of the soldering

iron being used to heat the solder directly, rather than the parts themselves. Properly

done, the parts to be connected are heated by the iron, which in turn melts the solder,

guaranteeing adequate heat in the joined parts for thorough wetting.

An improperly selected or applied flux can cause joint failure, or if not properly cleaned

off the joint, may corrode the metals in the joint over time and cause eventual joint

failure. Without flux the joint may not be clean, or may be oxidized, resulting in an

unsound joint.

Movement of metals being soldered before the solder has cooled will cause a highly

unreliable cracked joint.

3.6 Printed circuit board

Fig 3.11

Part of a 1983 Sinclair ZX Spectrum computer board; a populated PCB, showing the

conductive traces, vias (the through-hole paths to the other surface), and some mounted

electrical components

47

Fig 3.11

PCB Layout Program

A printed circuit board, or PCB, is used to mechanically support and electrically

connect electronic components using conductive pathways, or traces, etched from copper

sheets laminated onto a non-conductive substrate. Alternative names are printed wiring

board (PWB),and etched wiring board. A PCB populated with electronic components

is a printed circuit assembly (PCA), also known as a printed circuit board assembly

(PCBA).

PCBs are rugged, inexpensive, and can be highly reliable. They require much more

layout effort and higher initial cost than either wire-wrapped or point-to-point constructed

circuits, but are much cheaper and faster for high-volume production. Much of the

electronics industry's PCB design, assembly, and quality control needs are set by

standards that are published by the IPC organization.

3.6.1 Materials

Conducting layers are typically made of thin copper foil. Insulating materials have a

wider scale: phenolic paper, glass fibre and different plastics are commonly used. Usually

PCB factories use prepregs (short for preimpregnated), which are a combination of glass

fibre mat, nonwoven material and resin. Copper foil and prepreg are typically laminated

together with epoxy resin. Well known prepreg materials used in the PCB industry are

FR-2 (Phenolic cotton paper), FR-3 (Cotton paper and epoxy), FR-4 (Woven glass and

epoxy), FR-5 (Woven glass and epoxy), FR-6 (Matte glass and polyester), G-10 (Woven

48

glass and epoxy), CEM-1 (Cotton paper and epoxy), CEM-2 (Cotton paper and epoxy),

CEM-3 (Woven glass and epoxy), CEM-4 (Woven glass and epoxy), CEM-5 (Woven

glass and polyester). Other widely used materials are polyimide, teflon and some

ceramics.

Fig 3.12

A PCB as a design on a computer (left) and realized as a board assembly with populated

components (right). The board is double sided, with through-hole plating, green solder

resist, and white silkscreen printing. Both surface mount and through-hole components

have been used.

49

Chapter 4

MT 8870 IC

4.1 Features

• Complete DTMF Receiver

• Low power consumption

• Internal gain setting amplifier

• Adjustable guard time

• Central office quality

• Power-down mode

• Inhibit mode

• Backward compatible with

MT8870C/MT8870C-1

4.2 Applications

• Receiver system for British Telecom (BT) or

CEPT Spec (MT8870D-1)

• Paging systems

• Repeater systems/mobile radio

• Credit card systems

• Remote control

• Personal computers

• Telephone answering machine

50

4.3 Description

The MT8870D/MT8870D-1 is a complete DTMF integrating both the

bandsplit filter and

digital decoder functions. The filter section uses witched capacitor

techniques for high and lowgroup filters; the decoder uses digital counting

techniques to detect and decode all 16 DTMF tonepairs into a 4-bit code.

External component count is minimized by on chip provision of a

differential input amplifier, clock oscillator and latched three-state bus

interface

4.4 Functional Description

The MT8870D/MT8870D-1 monolithic DTMF receiver offers small size, low power

consumption and high performance. Its architecture consists of a bandsplit filter section,

which separates the high and low group tones, followed by a digital counting section

which verifies the frequency and duration of the received tones before passing the

corresponding code to the output bus.

51

Fig 4.1

52

4.5 MT8870D/MT8870D-1 ISO2-CMOS

18 PIN CERDIP/PLASTIC DIP/SOIC

Fig 4.2

20 PIN SSOP/TSSOP

53

Fig 4.3

4.6 PIN DESCRIPTIONS:-

Table 4.1

54

4.7 Functional Description

The MT8870D/MT8870D-1 monolithic DTMF receiver offers small size, low power

consumption and high performance. Its architecture consists of a bandsplit filter section,

which separates the high and low group tones, followed by a digital counting section

which verifies the frequency and duration of the received tones before passing the

corresponding code to the output bus.

4.8 Steering Circuit

Before registration of a decoded tone pair, the receiver checks for a valid signal duration

(referred to as character recognition condition). This check is performed by an external

RC time constant driven by ESt. A logic high on ESt causes vc to rise as the capacitor

discharges. Provided signal condition is maintained (ESt remains high) for the validation

period (tGTP), vc reaches the threshold (VTSt) of the steering logic to register the tone

pair, latching its corresponding 4-bit code into the output latch. At this point the GT

output is activated and drives vc to VDD. GT continues to drive high as long as ESt

remains high. Finally, after a short delay to allow the output latch to settle, the delayed

steering output flag (StD) goes high, signalling that a received tone pair has been

registered. The contents of the output latch are made available on the 4-bit output bus by

raising the three state control input (TOE) to a logic high. The steering circuit works in

reverse to validate the interdigit pause between signals. Thus, as well as rejecting signals

too short to be considered valid, the receiver will tolerate signal interruptions (dropout)

too short to be considered a valid pause. This facility, together with the capability of

selecting the steering time constants externally, allows the designer to tailor performance

to meet a wide variety of system requirements.

55

Basic steering circuit

Fig 4.4

4.9 Filter Section

Separation of the low-group and high group tones is achieved by applying the DTMF

signal to the inputs of two sixth-order switched capacitor bandpass filters, the bandwidths

of which correspond to the low and high group frequencies. The filter section also

incorporates notches at 350 and 440 Hz for exceptional dial tone rejection (see Figure 3).

Each filter output is followed by a single order switched capacitor filter section which

smooths the signals prior to limiting. Limiting is performed by high-gain comparators

which are provided with hysteresis to prevent detection of unwanted low-level signals.

56

The outputs of the comparators provide full rail logic swings at the frequencies of the

incoming DTMF signals.

Filter response

Fig 4.5

4.10 Guard Time Adjustment

In many situations not requiring selection of tone duration and interdigital pause, the

simple steering circuit shown in Figure is applicable. Component values are chosen

according to the formula:

tREC=tDP+tGTP

tID=tDA+tGTA

57

The value of tDP is a device parameter (see Figure 11) and tREC is the minimum signal

duration to be recognized by the receiver. A value for C of 0.1 μF is recommended for

most applications, leaving R to be selected by the designer.

Different steering arrangements may be used to select independently the guard times for

tone present (tGTP) and tone absent (tGTA). This may be necessary to meet system

specifications which place both accept and reject limits on both tone duration

and interdigital pause. Guard time adjustment also allows the designer to tailor system

parameters such as talk off and noise immunity. Increasing tREC improves talk-off

performance since it reduces the probability that tones simulated by speech will

maintain signal condition long enough to be registered. Alternatively, a relatively short

tREC with a long tDO would be appropriate for extremely noisy environments where fast

acquisition time and immunity to tone drop-outs are required. Design information for

guard time adjustment is shown in Figure .

Fig 4.6

58

4.11 Differential Input Configuration

The input arrangement of the MT8870D/MT8870D-1 provides a differential-input

operational amplifier as well as a bias source (VRef) which is used to bias the inputs at

mid-rail. Provision is made for connection of a feedback resistor to the op-amp output

(GS) for adjustment of gain. In a single-ended configuration, the input pins are connected

as shown in Figure with the op-amp connected for unity gain and VRef biasing the input

at 1/2VDD. Figure shows the differential configuration, which permits the adjustment of

gain with the feedback resistor R5.

Fig 4.7

59

4.12 Crystal Oscillator

The internal clock circuit is completed with the addition of an external 3.579545 MHz

crystal and is normally connected as shown in Figure (Single- Ended Input

Configuration). However, it is possible to configure several MT8870D/MT8870D-1

devices employing only a single oscillator crystal. The oscillator output of the first device

in the chain is coupled through a 30 pF capacitor to the oscillator input (OSC1) of the

next device. Subsequent devices are connected in a similar fashion. Refer to Figure for

details. The problems associated with unbalanced loading are not a concern with the

arrangement shown, i.e., precision balancing capacitors are not required.

Fig 4.8

oscillator connections

60

Fig 4.9

Single ended input configuration

4.13 resonator specifications recommendation

Table 4.2

61

4.14 Absolute maximum condition

Table 4.3

4.15 Recommended operation conditions

Table 4.4

62

4.15 DC Electrical characterstics

Table 4.5

63

4.16 Operating characterstics

Table 4.6

4.17 Operating AC characterstics:-

Table 4.7

64

4.18 Applications

The purpose of this Application Note is to provide information on the operation and

aplication of DTMF Receivers. The MT8870 Integrated DTMF Receiver will be

discussed in detail and its use illustrated in the application examples which follow.

More than 25 years ago the need for an improved method for transferring dialling

information through the telephone network was recognized. The traditional method, Dial

pulse signalling, was not only slow, suffering severe distortion over long wire loops,but

required a DC path through the communications channel. A signalling scheme was

developed utilizing voice frequency tones and implemented as a very reliable alternative

to pulse dialling. This scheme is known as DTMF (Dual Tone Multi- Frequency), Touch-

Tone™ or simply, tone dialling. As its acronym suggests, a valid DTMF signal is the sum

of two tones, one from a low group (697-941Hz) and one from a high group (1209-

1633Hz) with each group containing four individual tones. The tone frequencies were

carefully chosen such that they are not harmonically related and that their

intermodulation products result in minimal signaling impairment (Fig. 1a). This scheme

allows for 16 unique combinations. Ten of these codes represent the numerals zero

through nine, the remaining six (*,#,A,B,C,D) being reserved for special signalling.

Most telephone keypads contain ten numeric push buttons plus the asterisk (*) and

octothorp (#). The buttons are arranged in a matrix, each selecting its low group tone

from its respective row and its high group tone from its respective column .

The DTMF coding scheme ensures that each signal contains one and only one component

from each of the high and low groups. This significantly simplifies decoding because the

composite DTMF signal may be separated with bandpass filters, into its two single

frequency components each of which may be handled individually. As a result DTMF

coding has proven to provide a flexible signalling scheme of excellent reliability, hence

motivating innovative and competitive decoder design.

65

DTMF Spectrum

Fig 4.10

66

CHAPTER-5

L293D

5.1Features

5.1.1 600mA OUTPUT CURRENT CAPABILITY PER CHANNEL

5.1.2 1.2A PEAK OUTPUT CURRENT (non repetitive) PER CHANNEL

5.1.3 ENABLE FACILITY OVER TEMPERATURE PROTECTION

5.1.4 LOGICAL”0” INPUT VOLTAGE UP TO 1.5 V (HIGH NOISE IMMUNITY)

5.1.5 INTERNAL CLAMP DIODES

Fig 5.1

67

5.1Description

The Device is a monolithic integrated high voltage, high current four channel driver

designed to accept standard DTL or TTL logic levels and drive inductive loads (such as

relays solenoids, DC and stepping motors) and switching power transistors.

To simplify use as two bridges each pair of channels is equipped with an enable input. A

separate supply input is provided for the logic, allowing operation at a lower voltage and

internal clamp diodes are included.

This device is suitable for use in switching applications at frequencies up to 5 kHz. The

L293D is assembled in a 16 lead plastic package which has 4 center pins connected

together and used for heatsinking.

The L293DD is assembled in a 20 lead surface mount which has 8 center pins connected

together and used for heatsinking.

68

5.2 Block Diagram

Fig 5.2

69

5.3 Absolute Maximum Ratings

Table 5.1

5.4 PIN CONNECTIONS (Top view)

Fig 5.3

70

5.5 ELECTRICAL CHARACTERISTICS (for each channel, VS = 24 V,

VSS = 5 V, Tamb = 25 °C, unless otherwise specified)

Table 9.2

71

5.6 TRUTH TABLE (one channel)

Table 9.3

Z = High output impedance

(*) Relative to the considered channel

5.7 Switching Times

Fig 5.4

5.8 THERMAL DATA

Table 5.4

72

Junction to ambient thermal resistance vs. area on board heatsink

(SO12+4+4 package)

Fig 5.5

73

5.9OUTLINE AND MECHANICAL DATA

Power dip 16

Fig 5.5

Power dip 16 package mechanical data

Table 5.5

74

Table 5.6

75