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8/22/2019 Saii Iiiiii Final

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WIRELESS OPERATED WARFIELD LAND ROVER

PRAGATI ENGINEERING COLLEGE 1

CHAPTER 1


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INTRODUCTION

1.1 WHAT IS A ROBOT?

A robot is a mechanical or virtual, artificial agent. A robot is

usually an electro-mechanical system, which, by its appearance or movement,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 often referred to as

bots.

A typical robot must have several, but not all of the following properties:

Is not natural / has been artificially created.

Can sense its environment.

Can manipulate things in its environment.

Has some degree of intelligence or ability to make choices based on the

environment or automatic control / preprogrammed sequence.

Is programmable.

Can make with one or more axes of rotation or translation.

Appears to have intent or agency.

The appearance of agency is important when people are considering whether to

call a machine a robot. In general, the more a machine has the appearance of agency,the more it is considered a robot.

For robotic engineers, the physical appearance of a machine is less important than

the way its actions are controlled. The more the control system seems to have agency

of its own, the more likely the machine is to be called a robot. An important feature of

agency is the ability to make choice. So the ore a machine could feasible choose to do

something different, the more agencies it has.

The simple appearance of agency is not sufficient to be called a robot. A robot

must do something, whether it is useful work or not. So, for example, a rubber dog

chew, shaped like Asimo, would not be considered a robot.


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DEFINITIONS OF ROBOT:

International standard ISO 8373 defines a robot as:

An automatically controlled, reprogrammable, multipurpose, manipulator

programmable in three or more axes, which may be either, fixed in place or

mobile for use in industrial automation applications.

The Cambridge Online Dictionary defines robot as:

A machine used to perform jobs automatically, which is controlled by a

computer.

The Japanese Industrial Robot Association, (JIRA) does not provide a general

definition.

It distinguishes robot as per their performance and structure as follows:

1. Manipulator Robot2. Fixed sequence Robot

3. Variable sequence Robot

4. Play back Robot

5. Numerical control Robot

6. Intelligent Robot

The Robot Institute of America (RIA) defines a robot as:

A reprogrammable multifunctional manipulator designed to move and

manipulate material, parts, tools or specialized devices through variable

programmed motions for the performance of a variety of specific tasks.

1.2 REASONS FOR USING A ROBOT:

Over a period of years, need of a robot increased and technology

progressed with lots of research efforts taking place worldwide making robot as

on date as part and parcel of human, assisting them in several ways. The growing

areas of robots utilization are discussed here in a systematized way.

Hazards and Discomforts:

The first industrial application of robot took place in the year 1961,

which was used for loading and unloading a die casting machine, a particularly

unpleasant task for human operator. Infact, advent of robot was necessitated due


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to mans desire to free himself from high degree of hazardous and discomfort

jobs, especially in the areas of welding, painting, foundry operations etc. In the

earlier applications, this was the prime consideration for using a robot.

Increased productivity:

Third consideration for using industrial robot is its capability for

providing increased productivity. This is due to robots ability to work almost

continuously without breaks in comparision with human operartor. Robot

machine can work with no tiresomeness, doing job repetitively with no

grumbling. Human workers in contrast may not be so productive as well as

demanding more than due to them.

Better quality:

The fourth consideration in using a robot lies in its suitability in

handling repetitive jobs. Robots can be used to handle this type of tasks with high

degree of consistency, which in turn leads to improved product quality. This

improvement in quality justifies robots application in areas like spray painting,

welding, inspection etc.

The above four benefits, namely relieving human operator

from hazardous tasks, reduced costs, improved productivity and better quality,

primarily justify the reasons for using robots in industry. The way we listen,

research for a need based robot is being carried out producing robots that help

human in multiple ways.

1.3 CLASSIFICATION OF ROBOTS

In view of the definitions given, robots may be classified based on

generations, manipulators geometry and mobility.

1.3.1 Classification Based On Generations:

1. The first generation of robots mainly comprises of Manipulator, Fixed

sequence and Variable sequence types


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In manipulator type, the operator controls the transport arm directly

with or without power assistance depending on application. In Fixed

sequence type, a manipulator does the pre-set tasks repetitively as per

predetermined sequence, which cannot be altered. In contrast, a Variable

sequence type allows the sequence to be changed while doing the repetitive

job. Thus, the robots of the first generation are not capable of adapting to a

continuously changing environment.

2. The second generation of robots comprises of Playback and Numerical

control types. These are being provided with sensory inputs of rudimentary

nature such as vision and touch. These features enable them to respond to

the changing environment.

3. The third generation of robot is of intelligent type. In this generation of

robots, lot of refinements have been made in sensory devices, like visual,

acoustic and others implementing true adaptive control. This has resulted in

increased efficiency and precision.

1.3.2 Classification Based On Manipulator:

The robots have been also classified based on the construction of

manipulator arm. They are:

1. Cartesian type2. Cylindrical type

3. Spherical type

4. Anthropomorphic type

In Cartesian type of robots, the working head is manipulated along three

perpendicular tracks so as to achieve the required height, width and depth. The

base of manipulating robot may be positioned horizontally on the floor, or

may be suspended from a gantry or a travelling bridge.

In Cylindrical type of robots, the movements of the working head takes

place in a cylindrical volume for reaching any required height and azimuth.

This can be achieved by mounting an extendable arm on a central side, which

moves up and down and swivels on its base. This gives two longitudinal

movements with perpendicular axis and on rotational movement.


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In Spherical type of robots, the movement of working head takes

place in spherical range according to spherical coordinates. The manipulator is

provided with an extendable arm mounted on a central pivot, thereby allowing

rotations on a non-parallel axes.

In Anthropomorphic type of robots, the philosophy is based on the

human morphology, wherein the mechanical arm can be bent at an elbow

and swivel at ashoulder.

1.3.3 Classification Based On Mobility:

Yet another classification of robots can be based on the

mobility of the overall structure of the robot. While a universal robot is able

to undertake almost any task, a real robot can be performing a specific range

of tasks only as specified. In this context, two kinds of robots may be

highlighted, namely, Fixed robot and Mobile robot.

A Fixed robot, as the name signifies, has a defined

workspace and any manipulation task on a work-piece is done within the

defined workspace. This type of robot performs the following types of tasks:

Handling moving objects

Transformation of an object

Dismantling

Fixing

Measuring

A Mobile robot on the other hand has the ability to move to the

workspace, exceeding the dimensions set for the robot itself. Thus, it will be able to

do other tasks as well. Additionally, the mobile robot can do the following tasks:

Conveying

Exploration

Gathering

Tele-operation

This categorization gives us a feel of how complex is a real working

robot in relation to the simple robots.


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CHAPTER 2


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2. EMBEDED SYSTEMS

Embedded systems are electronic devices that incorporate microprocessors

with in their implementations. The main purposes of the microprocessors are to

simplify the system design and provide flexibility. Having a microprocessor in the

device helps in removing the bugs, making modifications, or adding new features

are only matter of rewriting the software that controls the device. Or in other

words embedded computer systems are electronic systems that include a

microprocessor to perform a specific dedicated application. The computer is

hidden inside these products. Embedded systems are ubiquitous. Every week

millions of tiny computer chips come pouring out of factories finding their way

into our everyday products.Embedded systems are self-contained programs that are embedded within a

piece of hardware. Whereas a regular computer has many different applications

and software that can be applied to various tasks, embedded systems are usually

set to a specific task that cannot be altered without physically manipulating the

circuitry. Another way to think of an embedded system is as a computer system

that is created with optimal efficiency, thereby allowing it to complete specific

functions as quickly as possible.

Embedded systems designers usually have a significant grasp of hardware

technologies. They use specific programming languages and software to develop

embedded systems and manipulate the equipment. When searching online,

companies offer embedded systems tools for use by engineers and businesses.

Embedded systems technologies are usually fairly expensive due to the necessary

development time and built in efficiencies, but they are highly valued in specific

industries. Smaller businesses may wish to hire a consultant to determine what

sort of embedded systems will add value to their organization.


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2.1 CHARACTERISTICS

Two major areas of differences are cost and power consumption. Since many

embedded systems are produced in tens of thousands to millions of units range,

reducing cost is a major concern. Embedded systems often use a slow processor

and small memory size to minimize costs. The slowness is not just clock speed.

The whole architecture of computer is often intentionally simplified to lower

costs. For examples, embedded systems often use peripherals controlled by

synchronous serial interfaces, which are ten to hundreds of times slower often run

with real time constrains with limited hardware resources : often there is no disk

drive, operating system, keyboard or screen may be used instead of a PCs

keyboard and screen.

2.2 EMBEDDED SYSTEMS CONSTRAINTS

An embedded system is software designed to keep in view three constraints:

Available system memory

Available processor speed

The need to limit the power dissipation

2.3 WHAT MAKES EMBEDDED SYSTEMS DIFFERENT

Real-time operation

Size

Cost

Time

Reliability

Safety

Energy

Security


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2.4 CLASSIFICATIONS OF EMBEDDED SYSTEM

1. Small Scale Embedded System

2. Medium Scale Embedded System

3. Sophisticated Embedded System

SMALL SCALE EMBEDDED SYSTEM

Single 8 bit or 16bit Microcontroller.

Little hardware and software complexity.

They May even be battery operated.

Usually C is used for developing this system.

The need to limit power dissipation when system is running continuously.

Programming tools:

Editor, Assembler and Cross Assembler

Fig:2.4.1

MEDIUM SCALE EMBEDDED SYSTEM Single or few 16 or 32 bit microcontrollers or Digital Signal Processors (DSP) or

Reduced Instructions Set Computers (RISC).

Both hardware and software complexity.

Programming tools:

RTOS, Source code Engineering Tool, Simulator, Debugger and Integrated

Development Environment (IDE).

Fig:2.4.2


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SOPHISTICATED EMBEDDED SYSTEM

Enormous hardware and software complexity

Which may need scalable processor or configurable processor and programminglogic arrays

Constrained by the processing speed available in their hardware units.

Programming Tools:

For these systems may not be readily available at a reasonable cost or may not be

available at all. A compiler or retarget able compiler might have to be developed

for this.

Fig:2.4.3


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CHAPTER 3


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3. MICROCONTROLLER

Microcontroller as the name suggests are small controllers. They are like

single hip computers that are often embedded into other systems to functions as

processing/controlling unit. For example the remote control you are using

probably has micro controllers inside that do micro wave ovens, toys etc.,

where automation is needed.

Micro controllers are useful to the extent that they communicate with other

devices, such as sensors, motors, switches, keypads, displays, memory and even

other microcontrollers. Many interface methods have been developed over the

years to solve the complex problem of balancing circuit design criteria such as

features, cost, size, weight, power consumption, reliability, availability,manufacturability. Many microcontroller designs typically mix multiple

interfacing methods. In a very simplistic form, a micro controller system can be

viewed as a system that reads from (monitors) inputs, performs processing and

writes to (controls) outputs.

Embedded system means the processor is embedded into the required

application. An embedded product uses a microprocessor or microcontroller to do

one task only. In an embedded system, there is only application software that is

typically burned into ROM. Example: printer, keyboard, video-game player.

Microprocessor -A single chip that contains the CPU or most of the computer

Microcontrollers - A single chip that controls other devices.

Microcontroller differs from a microprocessor in many ways. First and the most

important is its functionality. In order for a microprocessor to be used, other

components such as memory, or components for receiving and sending data must be

added to it. In short that means the microprocessor is the main heart of the computer.

On the other hand, microcontroller is designed to be all of that in one. No other

external components are needed for its application because all necessary peripherals

are already built into it. Thus we save time and space needed to construct devices.


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3.1 MICROPROCESSOR VS MICROCONTROLLER

MICROPROCESSOR

CPU is stand-alone, RAM, ROM, I/O, timer are separate.

Designer can decide on the amount of RAM, ROM and I/O ports.

Expensive

Versatility general-purpose

MICROCONTROLLER

CPU, RAM, ROM, I/O and timer are all on a single chip.

Fix amount of on chip ROM,RAM,I/O ports

For applications in which cost, power and space are critical

Single purpose.

3.2MICRO CONTROLLER 89C51

3.2.1 INTRODUCTION

A Micro controller consists of a powerful CPU tightly coupled with memory,

various I/O interfaces such as serial port, parallel port timer or counter, interrupt

controller, data acquisition interfaces-Analog to Digital converter, Digital to

Analog converter, integrated on to a single silicon chip.

If a system is developed with a microprocessor, the designer has to go for

external memory such as RAM, ROM, EPROM and peripherals. But controller is

provided all these facilities on a single chip. Development of a Micro controller

reduces PCB size and cost of design.

One of the major differences between a Microprocessor and a Micro controller

is that a controller often deals with bits not bytes as in the real world application.

Intel has introduced a family of Micro controllers called the MCS-51.

3.2.2 THE MAJOR FEATURES:

Compatible with MCS-51 products

4k Bytes of in-system Reprogrammable flash memory

Fully static operation: 0HZ to 24MHZ


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Three level programmable clock

128 * 8 bit timer/counters

Six interrupt sources

Programmable serial channel

Low power idle power-down modes

AT89C51 is 8-bit micro controller, which has 4 KB on chip flash memory,

which is just sufficient for our application. The on-chip Flash ROM allows the

program memory to be reprogrammed in system or by conventional non-volatile

memory Programmer. Moreover ATMEL is the leader in flash technology in

todays market place and hence using AT 89C51 is the optimal solution.

3.2.3 AT89C51 MICROCONTROLLER ARCHITECTURE

The 89C51 architecture consists of these specific features:

Eight bit CPU with registers A (the accumulator) and B

Sixteen-bit program counter (PC) and data pointer (DPTR)

Eight- bit stack pointer (PSW)

Eight-bit stack pointer (Sp)

Internal ROM or EPROM (8751) of 0(8031) to 4K (89C51)

Internal RAM of 128 bytes:

Thirty two input/output pins arranged as four 8-bit ports:p0-p3

Two 16-bit timer/counters: T0 and T1

Full duplex serial data receiver/transmitter: SBUF

Control registers: TCON, TMOD, SCON, PCON, IP, and IE

Two external and three internal interrupts sources.

Oscillator and clock circuits.


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Fig 3.1: Architecture of micro controller

3.2.4 TYPES OF MEMORY:

The 89C51 have three general types of memory. They are on-chip memory,

external Code memory and external Ram. On-Chip memory refers to physicallyexisting memory on the micro controller itself. External code memory is the code

memory that resides off chip. This is often in the form of an external EPROM.

External RAM is the Ram that resides off chip. This often is in the form of

standard static RAM or flash RAM.

a) Code memory

Code memory is the memory that holds the actual 89C51 programs that is to

be run. This memory is limited to 64K. Code memory may be found on-chip or

off-chip. It is possible to have 4K of code memory on-chip and 60K off chip

memory simultaneously. If only off-chip memory is available then there can be

64K of off chip ROM. This is controlled by pin provided as EA.


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b) Internal RAM

The 89C51 have a bank of 128 of internal RAM. The internal RAM is found

on-chip. So it is the fastest Ram available. And also it is most flexible in terms of

reading and writing. Internal Ram is volatile, so when 89C51 is reset, this memory

is cleared. 128 bytes of internal memory are subdivided. The first 32 bytes are

divided into 4 register banks. Each bank contains 8 registers. Internal RAM also

contains 128 bits, which are addressed from 20h to 2Fh. These bits are bit

addressed i.e. each individual bit of a byte can be addressed by the user. They are

numbered 00h to 7Fh. The user may make use of these variables with commands

such as SETB and CLR.

Flash memory is a nonvolatile memory using NOR technology, which allowsthe user to electrically program and erase information. Flash memory is used in

digital cellular phones, digital cameras, LAN switches, PC Cards for notebook

computers, digital set-up boxes, embedded controllers, and other devices.

Fig 3.2: - Pin diagram of AT89C51


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3.2.5 PIN DESCRIPTION:

VCC: Supply voltage.

GND: Ground.

Port 0:

Port 0 is an 8-bit open-drain bi-directional I/O port. As an output port, each

pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be

used as high impedance inputs. Port 0 may also be configured to be the

multiplexed low order address/data bus during accesses to external program and

data memory. In this mode P0 has internal pull-ups. Port 0 also receives the code

bytes during Flash programming, and outputs the code bytes during program

verification. External pull-ups are required during program verification.

Port 1:

Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1

output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins

they are pulled high by the internal pull-ups and can be used as inputs. As inputs,

Port 1 pins that are externally being pulled low will source current (IIL) because

of the internal pull-ups. Port 1 also receives the low-order address bytes during

Flash programming and verification.

Port 2:





of the internal pull-ups.

Port 3:





of the pull-ups.


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Port 3 also serves the functions of various special features of the AT89C51 as

listed below:

Tab 1 Port pins and their alternate functions

RST:

Reset input. A high on this pin for two machine cycles while the oscillator is

running resets the device.

ALE/PROG:

Address Latch Enable output pulse for latching the low byte of the address

during accesses to external memory. This pin is also the program pulse input

(PROG) during Flash programming. In normal operation ALE is emitted at a

constant rate of 1/6the oscillator frequency, and may be used for external timing

or clocking purposes. Note, however, that one ALE pulse is skipped during each

access to external Data Memory. If desired, ALE operation can be disabled by

setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a

MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting

the ALE-disable bit has no effect if the micro controller is in external execution

mode.

PSEN:

Program Store Enable is the read strobe to external program memory. When

the AT89C51 is executing code from external program memory, PSEN is

activated twice each machine cycle, except that two PSEN activations are skipped

during each access to external data memory.


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EA/VPP:

External Access Enable. EA must be strapped to GND in order to enable the

device to fetch code from external program memory locations starting at 0000H

up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be

internally latched on reset. EA should be strapped to VCC for internal program

executions. This pin also receives the 12-volt programming enable voltage (VPP)

during Flash programming, for parts that require 12-volt VPP.

XTAL1:

Input to the inverting oscillator amplifier and input to the internal clock

operating circuit.

XTAL2:

Output from the inverting oscillator amplifier

OSCILLATOR CHARACTERISTICS:

XTAL1 and XTAL2 are the input and output, respectively, of an inverting

amplifier, which can be configured for use as an on-chip oscillator, as shown in

Figs 6.1 Either a quartz crystal or ceramic resonator may be used. To drive the

device from an external clock source, XTAL2 should be left unconnected while

XTAL1 is driven as shown in Figure 6.2. There are no requirements on the duty

cycle of the external clock signal, since the input to the internal clocking circuitry

is through a divide-by-two flip-flop, but minimum and maximum voltage high and

low time specifications must be observed.

Fig 3.3 Oscillator Connections Fig 3.4 External clock drive Configuration


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3.2.6 REGISTERS:

In the CPU, registers are used to store information temporarily. That

information could be a byte of data to be processed, or an address pointing to the

data to be fetched. The vast majority of 8051 registers are 8bit registers. .

D7 D6 D5 D4 D3 D2 D1 D0

The most widely used registers of the 8051 are A (accumulator), B, R0, R1,

R2, R3, R4, R5, R6, R7, DPTR (data pointer), and PC (program counter). All of

the above registers are 8-bits, except DPTR and the program counter. The

accumulator, register A, is used for all arithmetic and logic instructions.

SFRs (Special Function Registers):

In the 8051, registers A, B, PSW and DPTR are part of the group of registers

commonly referred to as SFR (special function registers). The SFR can be

accessed by the names (which is much easier) or by their addresses. For example,

register A has address E0h, and register B has been ignited the address F0H, as

shown in table.

The following two points should note about the SFR addresses.

1.The Special function registers have addresses between 80H and FFH. These

addresses are above 80H, since the addresses 00 to 7FH are addresses of RAM

memory inside the 8051.

2.Not all the address space of 80H to FFH is used by the SFR. The unused

locations 80H to FFH are reserved and must not be used by the 8051 programmer.

Symbol Name Address

ACC Accumulator 0E0H

B B register 0F0H

PSW Program status word 0D0H

SP Stack pointer 81H


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DPTR Data pointer 2 bytes

DPL Low byte 82H

DPH High byte 83H

P0 Port0 80H

P1 Port1 90H

P2 Port2 0A0H

P3 Port3 0B0H

IP Interrupt priority control 0B8H

IE Interrupt enable control 0A8H

TMOD Timer/counter mode control 89H

TCON Timer/counter control 88H

T2CON Timer/counter 2 control 0C8H

T2MOD Timer/counter mode2 control 0C9H

TH0 Timer/counter 0high byte 8CH

TL0 Timer/counter 0 low byte 8AH

TH1 Timer/counter 1 high byte 8DH

TL1 Timer/counter 1 low byte 8BH

TH2 Timer/counter 2 high byte 0CDH

TL2 Timer/counter 2 low byte 0CCH

RCAP2H T/C 2 capture register high byte 0CBH

RCAP2L T/C 2 capture register low byte 0CAH

SCON Serial control 98H

SBUF Serial data buffer 99H

PCON Power control 87H

Table: 2 8051 Special function register Address


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ARegister(Accumulator):

This is a general-purpose register, which serves for storing intermediate results

during operating. A number (an operand) should be added to the accumulator

prior to execute an instruction upon it. Once an arithmetical operation is

preformed by the ALU, the result is placed into the accumulator.

B REGISTER:

B register is used during multiply and divide operations which can be

performed only upon numbers stored in the A and B registers. All other

instructions in the program can use this register as a spare accumulator (A).

Registers (R0-R7)

Fig3.5: Memory organization of RAM

This is a common name for the total 8 general purpose registers (R0, R1, R2

...R7). Even they are not true SFRs, they deserve to be discussed here because of

their purpose. The bank is active when the R registers it includes are in use.

Similar to the accumulator, they are used for temporary storing variables and

intermediate results. Which of the banks will be active depends on two bits

included in the PSW Register. These registers are stored in four banks in the scope

of RAM.


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8051 REGISTER BANKS AND STACK:

RAM memory space allocation in the 8051

There are 128 bytes of RAM in the 8051. The 128 bytes of RAM inside the8051 are assigned addresses 00 to7FH. These 128 bytes are divided into three

different groups as follows:

1. A total of 32 bytes from locations 00 to 1FH hex are set aside for register

banks and the stack.

2. A total of 16 bytes from locations 20 to 2FH hex are set aside for bit-

addressable read/write memory.

3. A total of 80 bytes from locations 30H to 7FH are used for read and write

storage, or what is normally called Scratch pad. These 80 locations of RAM are

widely used for the purpose of storing data and parameters nu 8051 programmers.

Default register bank

Register bank 0; that is, RAM locations 0, 1,2,3,4,5,6, and 7 are accessed with

the names R0, R1, R2, R3, R4, R5, R6, and R7 when programming the 8051.

FIG 3.6: RAM Allocation in the 8051

PSW REGISTER (Program Status Word)


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This is one of the most important SFRs. The Program Status Word (PSW)

contains several status bits that reflect the current state of the CPU. This register

contains: Carry bit, Auxiliary Carry, two register bank select bits, Overflow flag,

parity bit, and user-definable status flag. The ALU automatically changes some of

registers bits, which is usually used in regulation of the program performing.

P - PARITY BIT:

If a number in accumulator is even then this bit will be automatically set (1),

otherwise it will be cleared (0). It is mainly used during data transmission and

receiving via serial communication.

OV OVERFLOW:

occurs when the result of arithmetical operation is greater than 255 (decimal),

so that it cannot be stored in one register. In that case, this bit will be set (1). If

there is no overflow, this bit will be cleared (0).

RS0, RS1 - REGISTER BANK SELECT BITS:

These two bits are used to select one of the four register banks in RAM. By

writing zeroes and ones to these bits, a group of registers R0-R7 is stored in one of

four banks in RAM.

RS1 RS2Space in

RAM

0 0Bank0 00h-

07h

0 1Bank1 08h-

0Fh

1 0Bank2 10h-

17h

1 1 Bank3 18h-

Table3


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F0 - FLAG 0: This is a general-purpose bit available to the user.

AC - AUXILIARY CARRY FLAG: Ac is used for BCD operations only.

CY - CARRY FLAG: CY is the (ninth) auxiliary bit used for all arithmetical

operations and shift instructions.

DPTR REGISTER (Data Pointer):

These registers are not true ones because they do not physically exist. They

consist of two separate registers: DPH (Data Pointer High) and (Data Pointer

Low). Their 16 bits are used for external memory addressing. They may be

handled as a 16-bit register or as two independent 8-bit registers. Besides, the

DPTR Register is usually used for storing data and intermediate results, which

have nothing to do with memory locations.

SP REGISTER (Stack Pointer):

The stack is a section of RAM used by the CPU to store information

temporarily. This information could be data or an address. The CPU needs this

storage area since there are only a limited number of registers.


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3.3 HOW STACKS ARE ACCESSED IN THE 8051:

If the stack is a section of RAM, there must be registers inside the CPU to

point to it. The register used to access the stack is called the SP (Stack point)

Register. The stack pointer in the 8051 is only 8 bits wide; which means that it

can take values of 00 to FFH. When the 8051 is powered up, the SP register

contains value 07. This means that RAM location 08 is the first location used for

the stack by the 8051. The storing of a CPU register in the stack is called a

PUSH, and pulling the contents off the stack back into a CPU register is called a

POP. In other words, a register is pushed onto the stack to save it and popped off

the stack to retrieve it. The job of the SP is very critical when push and pop

actions are performed.

3.4 PROGRAM COUNTER:

The important register in the 8051 is the PC (Program counter). The program

counter points to the address of the next instruction to be executed. As the CPU

fetches the opcode from the program ROM, the program counter is incremented to

point to the next instruction. The program counter in the 8051 is 16bits wide.

This means that the 8051 can access program addresses 0000 to FFFFH, a total of

64k bytes of code. However, not all members of the 8051 have the entire 64K

bytes of on-chip ROM installed, as we will see soon.


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CHAPTER 4


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4. ZIGBEE TECHNOLOGY

4.1 Zig-bee:

Fig 4.1 Zibee

Zig-bee is a specification for a suite of high level communication protocols

using small, low-power digital radios based on the IEEE 802.15.4,2006 standard for

wireless personal area networks (WPANs),

such as wireless headphones connecting with cell phones short-range radio.

The technology defined by the Zig-bee specification is intended to be simpler and less

expensive than other WPANs, such as Bluetooth. Zig-bee is targeted at radio-

frequency (RF) applications that require a low data rate, long battery life, and securenetworking.

Zig-bee is a low data rate, two-way standard for home automation and data

networks. The standard specification for up to 254 nodes including one master,

managed from a single remote control. Real usage examples of Zig-bee includes

home automation tasks such as turning lights on, setting the home security system, or

starting the VCR. With Zig-bee all these tasks can be done from anywhere in the

home at the touch of a button. Zig-bee also allows for dial-in access via the Internet

for automation control.

Zig-bee protocol is optimized for very long battery life measured in months to

years from inexpensive, off-the-shelf non-rechargeable batteries, and can control

lighting, air conditioning and heating, smoke and fire alarms, and other security

devices. The standard supports 2.4 GHz (worldwide), 868 MHz (Europe) and 915

MHz (Americas) unlicensed radio bands with range up to 100 meters.


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IEEE 802.15.4

IEEE 802.15.4 is a standard which specifies the physical layer and medium access

control for low-rate wireless personal area networks (LR-WPAN's).This standard was

chartered to investigate a low data rate solution with multi-month to multi-year

battery life and very low complexity. It is operating in an unlicensed, international

frequency band. Potential applications are sensors, interactive toys, smart badges,

remote controls, and home automation.

802.15.4 Is part of the 802.15 wireless personal-area network efforts at the IEEE? It is

a simple packet-based radio protocol aimed at very low-cost, battery-operated widgets

and sensors (whose batteries last years, not hours) that can intercommunicate and

send low-bandwidth data to a centralized device.

As of 2007, the current version of the standard is the 2006 revision. It is maintained

by the IEEE 802.15 working group.

It is the basis for the Zig-bee specification, which further attempts to offer a complete

networking solution by developing the upper layers which are not covered by the

standard.

802.15.4 Protocol

Data rates of 250 kbps with 10-100 meter range.

Two addressing modes; 16-bit short and 64-bit IEEE addressing.

CSMA-CA channel access.

Power management to ensure low power consumption.

16 channels in the 2.4GHz ISM band.

Low duty cycle - Provides long battery life.

Low latency.

Support for multiple network topologies: Static, dynamic, star and mesh. Up to 65,000 nodes on a network.

Comparison with other technologies

Zig-Bee enables broad-based deployment of wireless networks with low-cost, low-

power solutions. It provides the ability to run for years on inexpensive batteries for a

host of monitoring applications: Lighting controls, AMR (Automatic Meter Reading),


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smoke and CO detectors, wireless telemetry, HVAC control, heating control, home

security, Environmental controls and shade controls, etc.

Why is Zigbee needed?

There are a multitude of standards that address mid to high data rates for voice, PC

LANs, video, etc. However, up till now there hasnt been a wireless network

standard that meets the unique needs of sensors and control devices. Sensors and

controls dont need high bandwidth but they do need low latency and very low

energy consumption for long battery lives and for large device arrays.

There are a multitude of proprietary wireless systems manufactured today to solve

a multitude of problems that also dont require high data rates but do require low

cost and very low current drain.

These proprietary systems were designed because there were no standards that met

their requirements. These legacy systems are creating significant interoperability

problems with each other and with newer technologies.

4.2 Zigbee/IEEE 802.15.4 - General Characteristics

Dual PHY (2.4GHz and 868/915 MHz).

Data rates of 250 kbps (@2.4 GHz), 40 kbps (@ 915 MHz), and 20 kbps

(@868 MHz).

Optimized for low duty-cycle applications (


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ZIGBEE NETWORK TOPOLOGY:

Fig 4.2 Zigbee network topology

Three devices in network:

1. Zigbee PAN coordinator (MASTER)

2. Zigbee router (full function device)

3. Zigbee end device (reduced function device)

Star Topology

PAN

Full function device Communications flow

Peer to Peer topology Cluster Tree Topology

Reduced Function Device


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4.3 ZIGBEE PROTOCOL STACK

Fig 4.3 Zigbee protocol stack

PHYSICAL LAYER

The physical layer was designed to accommodate the need for a low cost yet

allowing for high levels of integration. The use of direct sequence allows the analog

circuitry to be very simple and

The PHY provides two services: the PHY data service and PHY management

service interfacing to the physical layer management entity (PLME). The PHY data

service enables the transmission and reception of PHY protocol data units (PPDU)

across the physical radio channel. The features of the PHY are activation and

deactivation of the radio transceiver, energy detection(ED), link quality indication

(LQI), channel selection, clear channel assessment (CCA) and transmitting as well as

receiving packets across the physical medium.


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The standard offers two PHY options based on the frequency band. Both are

based on direct sequence spread spectrum (DSSS). The data rate is 250kbps at

2.4GHz, 40kbps at 915MHz and 20kbps at 868MHz. The higher data rate at 2.4GHz

is attributed to a higher-order modulation scheme. Lower frequencies provide longer

range due to lower propagation losses. Low rate can be translated into better

sensitivity and larger coverage area. Higher rate means higher throughput, Lower

latency or lower duty cycle.

There is a single channel between 868 and 868.6MHz, 10 channels between 902.0

and 928.0MHz, and 16 channels between 2.4 and 2.4835GHz.

MAC LAYER

The media access control (MAC) layer was designed to allow multiple

topologies without complexity. The power management operation doesnt require

multiple modes of operation. The MAC allows a reduced functionality device

(RFD) that neednt have flash nor large amounts of ROM or RAM. The MAC

was designed to handle large numbers of devices without requiring them to be

parked.

MAC Primitives:

MAC Data Service

MCPS-DATA exchange data packets between MAC and PHY.

MCPS-PURGE purge an MSDU from the transaction queue.

MAC Management Service

MLME-ASSOCIATE/DISASSOCIATE network association.

MLME-SYNC / SYNC-LOSS - device synchronization.

MLME-SCAN - scan radio channels.

MLME- COMM-STATUS communication status.

MLME-GET / -SET retrieve/set MAC PIB parameters.

MLME-START / BEACON-NOTIFY beacon management.

MLME-POLL - beaconless synchronization.

MLME-GTS - GTS management.


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MLME-RESET request for MLME to perform reset.

MLME-ORPHAN - orphan device management.

MLME-RX-ENABLE - enabling/disabling of radio system.

Network Layer

The responsibilities of the Zigbee NWK layer include:

Starting a network: The ability to successfully establish a new network.

Joining and leaving a network: The ability to gain membership (join) or relinquish

membership (leave) a network.

Configuring a new device: The ability to sufficiently configure the stack for

operation as required.

Addressing: The ability of a Zigbee coordinator to assign addresses to devices

joining the network.

Synchronization within a network: The ability for a device to achieve

synchronization with another device either through tracking beacons or by polling.

Security: applying security to outgoing frames and removing security to

terminating frames

Routing: routing frames to their intended destinations.

Network Routing Overview

Perhaps the most straightforward way to think of the Zigbee routing algorithm is as a

hierarchical routing strategy with table-driven optimizations applied where possible.

NWK uses an algorithm that allows stack implementers and application developers

to balance unit cost, battery drain, and complexity in producing Zigbee solutions to

meet the specific cost-performance profile of their application.

Started with the well-studied public-domain algorithm AODV and MotorolasCluster-Tree algorithm and folding in ideas from Ember Corporations GRAD.


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Network Summary

The network layer builds upon the IEEE 802.15.4 MACs features to allow

extensibility of coverage. Additional clusters can be added; networks can be

consolidated or split up.

Application layer

The Zigbee application layer consists of the APS sub-layer, the ZDO and the

manufacturer-defined application objects. The responsibilities of the APS sub-layer

include maintaining tables for binding, which is the ability to match two devices

together based on their services and their needs, and forwarding messages between

bound devices. Another responsibility of the APS sub-layer is discovery, which is the

ability to determine which other devices are operating in the personal operating space

of a device. The responsibilities of the ZDO include defining the role of the device

within the network (e.g., Zigbee coordinator or end device), initiating and/or

responding to binding requests and establishing a secure relationship between network

devices. The manufacturer-defined application objects implement the actual

applications according to the Zigbee-defined application descriptions

Zigbee Device Object

Defines the role of the device within the network (e.g., Zigbee coordinator or

end device)

Initiates and/or responds to binding requests

Establishes a secure relationship between network devices selecting one of

ZigBees security methods such as public key, symmetric key, etc.

Application Support Layer:

This layer provides the following services:

Discovery: The ability to determine which other devices are operating in the

personal operating space of a device.

Binding: The ability to match two or more devices together based on their

services and their needs and forwarding messages between bound devices.


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APPLICATIONS OF ZIGBEE TECHNOLOGY

Typical application areas include

Home Entertainment and Control Smart lighting, advanced temperature

control, safety and security, movies and music

Home Awareness Water sensors, power sensors, energy monitoring,

smoke and fire detectors, smart appliances and access sensors

Mobile Services m-payment, m-monitoring and control, m-security and

access control, m-healthcare and tele-assist

Commercial Building Energy monitoring, HVAC, lighting, access control

Industrial Plant Process control, asset management, environmental

management, energy management, industrial device control, machine-to-

machine (M2Mcommunication.

Zigbee vs. Bluetooth

Zigbee looks rather like Bluetooth but is simpler, has a lower data rate and spends

most of its time snoozing. This characteristic means that a node on a Zigbee network

should be able to run for six months to two years on just two AA batteries. The

operational range of Zigbee is 10-75m compared to 10m for Bluetooth (without a

power amplifier).

Zigbee sits below Bluetooth in terms of data rate. The data rate of Zigbee is 250kbps

at 2.4GHz, 40kbps at 915MHz and 20kbps at 868MHz whereas that of Bluetooth is

1Mbps.

Zigbee uses a basic master-slave configuration suited to static star networks of many

infrequently used devices that talk via small data packets. It allows up to 254 nodes.

Bluetooths protocol is more complex since it is geared towards handling voice,

images and file transfers in ad hoc networks. Bluetooth devices can support scatter

nets of multiple smaller non-synchronized networks (piconets). It only allows up to 8

slave nodes in a basic master-slave piconet set-up.

When Zigbee node is powered down, it can wake up and get a packet in around 15

msec whereas Bluetooth device would take around 3sec to wake up and respond.


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ZIGBEE MODULE:

Comparison with other technologies

StandardZigbee

802.15.4

Wi-Fi

802.11b

Bluetooth

802.15.1

Transmission Range

(meters)

1 100* 1 100 1 10

Battery Life (days)100 1,000 0.5 5.0 1 - 7

Network Size (# of nodes)> 64,000 32 7

Application

Monitoring &

Control

Web, Email,

Video

Cable

Replacement

Stack Size (KB)4 32 1,000 250

Throughput kb/s)20 250 11,000 720

Zigbee-compliant products operate in unlicensed bands worldwide, including 2.4GHz

(global), 902 to 928MHz (Americas), and 868MHz (Europe). Raw data throughput

rates of 250Kbps can be achieved at 2.4GHz (16 channels), 40Kbps at 915MHz (10

channels), and 20Kbps at 868MHz (1 channel). The transmission distance is expected

to range from 10 to 100m, depending on power output and environmental

characteristics. Like Wi-Fi, Zigbee uses direct-sequence spread spectrum in the

2.4GHz band, with offset-quadrature phase-shift keying modulation. Channel width is

2MHz with 5MHz channel spacing. The 868 and 900MHz bands also use direct-

sequence spread spectrum but with binary-phase-shift keying modulation.

ZIGBEE MODULE SPECIFICATION:

Performance: XBee

Power output:: 1mW (+0 dBm) North American & International version

Indoor/Urban range: Up to 100 ft (30 m)

Outdoor/RF line-of-sight range: Up to 300 ft (90 m)


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RF data rate: 250 Kbps

Interface data rate: Up to 115.2 Kbps

Operating frequency: 2.4 GHz

Receiver sensitivity: -92 dBm

Performance: XBee-PRO

Power output:

63 mW (+18 dBm) North American version

10 mW (+10 dBm) International version

Indoor/Urban range: Up to 300 ft (90 m)

Outdoor/RF line-of-sight range: Up to 1 mile (1.6 km) RF LOS

RF data rate: 250 Kbps

Interface data rate: Up to 115.2 Kbps

Operating frequency: 2.4 GHz

Receiver sensitivity: -100 dBm (all variants)

Networking

Spread Spectrum type: DSSS (Direct Sequence Spread Spectrum)

Networking topology: Point-to-point, point-to-multipoint, & peer-to-peer

Error handling: Retries & acknowledgements

Filtration options: PAN ID, Channel, and 64-bit addresses

Channel capacity:

XBee: 16 Channels

XBee-PRO: 12 Channels

Addressing: 65,000 network addresses available for each channel

Power

Supply voltage:

XBee: 2.8 - 3.4 VDC

XBee-PRO: 2.8 - 3.4 VDC

XBee Footprint Recommendation: 3.0 - 3.4 VDC


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Transmit current:

XBee: 45 mA (@ 3.3 V) boost mode 35 mA (@ 3.3 V) normal mode

XBee-PRO: 215 mA (@ 3.3 V)

Receive current:

XBee: 50 mA (@ 3.3 V)

XBee-PRO: 55 mA (@ 3.3 V)

Power-down sleep current:

XBee:


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CHAPTER 5


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5. WORKING FLOW OF THE PROJECT

5.1 BLOCK DIAGRAM:

CONTROL SECTION:

Fig 5.1 Control Section

ROBOT SECTION:

Fig 5.2 Robot Section

ZIGBEE TRANSCEIVERPERSONAL COMPUTER

RF RECEIVER

ZIGBEE

TRANSCEIVER

8051

MICRO CONTOLLER

HBRIDGEMAX 232

MOTORS

LCD

ULTRA SONIC SENSOR

METAL DETECTING

SENSOR

BUZZER

POWER SUPPLY

CAMERA


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CIRCUIT DISCRIPTION:

In this project, there are two sections (control section & robot section) as

shown in the block diagrams. The instructions such as Left, Right etc are processedand are given by the person by operating PC. So based upon input of PC the following

output will be seen i.e. left or right. In control Section, the instructions are delivered

to Zigbee transceiver from which is connected to the PC. This information is

processed and is sent to the receiver section via wireless.

The signals from the control section are received by the Zigbee

transceiver, in the Robot section and are sent to the controller as input. Controller

processes this data and controls the Robot direction according to the instruction given

at the control section. It has a camera which records audio and video of the

surrounding environment and it transmits those signals to control section via wireless.

So we can monitor the robot and basing upon that, we can give instructions from

control section. Then the Robot will move in a particular direction for the given

instruction. Similarly if any metal is detected, the buzzer will make a beep sound

which is audible at control section using RF receiver. This robot section also has a

ultrasonic sensor which is used to detect any obstacles. If it detects any obstacle, it

gives output to microcontroller, then that micro-controller processes that signal and

automatically rotates the robot right.

5.2 POWER SUPPLY

The input to the circuit is applied from the regulated power supply. The a.c.

input i.e., 230V from the mains supply is step down by the transformer to 12V and is

fed to a rectifier. The output obtained from the rectifier is a pulsating d.c voltage. So

in order to get a pure d.c voltage, the output voltage from the rectifier is fed to a filter

to remove any a.c components present even after rectification. Now, this voltage is

given to a voltage regulator to obtain a pure constant dc voltage.


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5.2.1 BLOCK DIAGRAM:

Fig 5.2.1: Block diagram

THE POWER SUPPLY MAINLY CONSISTS OF THREE PARTS:

Step down transformer.

Full wave rectifier (Bridge rectifier).

Regulator LM 7805.

Entire circuit works on a supply of +5v.Transformer 12-0-12 volts/1amp

rating is used. Bridge rectifier for 7805 power regulator is used. it is a three pin

package .first pin for input ,second pin for ground, third pin for output. First pin is

connected to 1000uf/25v capacitor positive terminal. Second pin is connected to

ground terminal. Third pin is connected to output pin to provide 5v supply for

micro controller board.

5.2.2 STEP DOWN TRANSFORMER:

A transformer is an electrical device which is used to convert electrical power

from one electrical circuit to another without change in frequency.

Transformers convert AC electricity from one voltage to another with little

loss of power. Transformers work only with AC and this is one of the reasons why

mains electricity is AC. Step-up transformers increase in output voltage, step-

230V AC

50Hz

D.C

Output

Step down

transformer

Bridge

rectifier

FilterRegulator


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down transformers decrease in output voltage. Most power supplies use a step-

down transformer to reduce the dangerously high mains voltage to a safer low

voltage. The input coil is called the primary and the output coil is called the

secondary. There is no electrical connection between the two coils; instead they

are linked by an alternating magnetic field created in the soft-iron core of the

transformer. The two lines in the middle of the circuit symbol represent the core.

Transformers waste very little power so the power out is (almost) equal to the

power in. Note that as voltage is stepped down current is stepped up. The ratio of

the number of turns on each coil, called the turns ratio, determines the ratio of the

voltages. A step-down transformer has a large number of turns on its primary

(input) coil which is connected to the high voltage mains supply, and a small

number of turns on its secondary (output) coil to give a low output voltage.

Fig 5.2.2: An Electrical Transformer

Turns ratio = Vp/ VS = Np/NS

Power Out= Power In

VS X IS=VP X IP

Vp = primary (input) voltage

Np = number of turns on primary coil

Ip = primary (input) current

5.2.3 RECTIFIER:

A circuit, which is used to convert a.c to dc, is known as RECTIFIER.

The process of conversion a.c to d.c is called rectification.


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TYPES OF RECTIFIERS:

Half wave Rectifier

Full wave rectifier

1. Center-tap full wave rectifier.

2. Bridge-type full bridge rectifier.

BRIDGE RECTIFIER:

Most of electronic device and circuits need a DC source for the

operation. So it is necessary to convert AC to DC. The process of converting AC

to DC is called rectification. This can be achieved with a rectifier, filter and

voltage regulator.A rectifier is defined as an electronic device used for converting AC

voltage current into unidirectional voltage and current. The rectifiers are classified

in two types:

1. Half wave rectifier.

2. Full wave rectifier.

5.2

.4 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.

CAPACITOR FILTER:

We have seen that the ripple content in the rectified output of half wave

rectifier is 121% or that of full-wave or bridge rectifier or bridge rectifier is 48%

such high percentages of ripples is not acceptable for most of the applications.

Ripples can be removed by one of the following methods of filtering:


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(a) A capacitor, in parallel to the load, provides an easier by pass for the ripples

voltage though it due to low impedance. At ripple frequency and leave the d.c.to

appears the load.

(b) An inductor, in series with the load, prevents the passage of the ripple current

(due to high impedance at ripple frequency) while allowing the d.c (due to low

resistance to d.c)

(c) Various combinations of capacitor and inductor, such as L-section filter

section filter, multiple section filter etc. which make use of both the properties

mentioned in (a) and (b) above. Two cases of capacitor filter, one applied on half

wave rectifier and another with full wave rectifier.

Filtering is performed by a large value electrolytic capacitor connected across the

DC supply to act as a reservoir, supplying current to the output when the varying

DC voltage from the rectifier is falling. The capacitor charges quickly near the

peak of the varying DC, and then discharges as it supplies current to the output.

Filtering significantly increases the average DC voltage to almost the peak value

(1.4 RMS value).

To calculate the value of capacitor(C),

C = *3*f*r*Rl

Where,

f = supply frequency,

r = ripple factor,

Rl = load resistance

Note: In our circuit we are using 1000 microfarads.

5.2.5 VOLTAGE REGULATOR:

Voltage regulator ICs is available with fixed (typically 5, 12 and 15V) orvariable output voltages. The maximum current they can pass also rates them.

Negative voltage regulators are available, mainly for use in dual supplies. Most

regulators include some automatic protection from excessive current ('overload

protection') and overheating ('thermal protection'). Many of the fixed voltage

regulators ICs has 3 leads and look like power transistors, such as the 7805 +5V


48/86



1A regulator shown on the right. The LM7805 is simple to use. You simply

connect the positive lead of your unregulated DC power supply (anything from

9VDC to 24VDC) to the Input pin, connect the negative lead to the Common pin

and then when you turn on the power, you get a 5 volt supply from the output pin.

Fig 5.2.3: A Three Terminal Voltage Regulator

78XX:

The Bay Linear LM78XX is integrated linear positive regulator with three

terminals. The LM78XX offer several fixed output voltages making them useful

in wide range of applications. When used as a zener diode/resistor combination

replacement, the LM78XX usually results in an effective output impedance

improvement of two orders of magnitude, lower quiescent current. The LM78XX

is available in the TO-252, TO-220 & TO-263packages,

FEATURES:

Output Current of 1.5A

Output Voltage Tolerance of 5%

Internal thermal overload protection

Internal Short-Circuit Limited

No External Component

Output Voltage 5.0V, 6V, 8V, 9V, 10V, 12V, 15V, 18V, 24V

Offer in plastic TO-252, TO-220 & TO-263

Direct Replacement for LM78XX


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PRAGATI ENGINEERING C

5.3 MAX 232:

5.3.1 RS-232 WAV

Fig 5

The diagra

when using the common

Bit. The RS-232 line, wh

with a start bit which is (

The LSB (Least Signific

the signal to make up the

The data se

framed between a Start a

RS-232 Voltage leve

+3 to +25 volts to

-3 to -25 volts for

Any voltage in be

undefined.

WIRELESS OPERATED

OLLEGE

FORM

.3.1:TTL/CMOS Serial Logic Waveform

m above shows the expected waveform from th

8N1 format. 8N1 signifies 8 Data bits, No Parit

en idle is in the Mark State (Logic 1). A transm

ogic 0). Then each bit is sent down the line, o

nt Bit) is sent first. A Stop Bit (Logic 1) is then

transmission.

nt using this method, is said to be framed. That

d Stop Bit.

s

signify a "Space" (Logic 0)

a "Mark" (logic 1).

tween these regions (i.e. between +3 and -3 Vol

WARFIELD LAND ROVER

49

UART

and 1 Stop

ssion starts

e at a time.

appended to

is the data is

ts) is


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The data byte i

The bits are tra

rate of the serial signal.

computer, shown below.

5.3.2 RS-232 LEVEL

Standard serial

Standard device, requires

purpose. It provides 2-ch

The driver requi

Fi

WIRELESS OPERATED

OLLEGE

always transmitted least-significant-bit first.

smitted at specific time intervals determined b

his is the signal present on the RS-232 Port of

Fig 5.3.2: RS-232 Logic Waveform

CONVERTER

nterfacing of microcontroller (TTL) with PC or

TTL to RS232 Level converter . A MAX232 is

annel RS232C port and requires external 10uF

es a single supply of +5V.

5.3.3 MAX 232 IC Configurations

WARFIELD LAND ROVER

50

the baud

our

any RS232C

sed for this

apacitors.


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MAX-232 includes a Charge Pump, which generates +10V and -10V from a single 5v

supply.

5.3.3 Serial communication

When a processor communicates with the outside world, it provides data in

byte sized chunks. Computers transfer data in two ways: parallel and serial. In parallel

data transfers, often more lines are used to transfer data to a device and 8 bit data path

is expensive. The serial communication transfer uses only a single data line instead of

the 8 bit data line of parallel communication which makes the data transfer not only

cheaper but also makes it possible for two computers located in two different cities to

communicate over telephone.

Serial data communication uses two methods, asynchronous and

synchronous. The synchronous method transfers data at a time while the

asynchronous transfers a single byte at a time. There are some special IC chips made

by many manufacturers for data communications. These chips are commonly referred

to as UART (universal asynchronous receiver-transmitter) and USART (universal

synchronous asynchronous receiver transmitter). The AT89C51 chip has a built in

UART.

In asynchronous method, each character is placed between start and stop

bits. This is called framing. In data framing of asynchronous communications, the

data, such as ASCII characters, are packed in between a start and stop bit. We have a

total of 10 bits for a character: 8 bits for the ASCII code and 1 bit each for the start

and stop bits. The rate of serial data transfer communication is stated in bps or it can

be called as baud rate.

To allow the compatibility among data communication equipment made

by various manufacturers, and interfacing standard called RS232 was set by the

Electronics industries Association in 1960. Today RS232 is the most widely used I/O

interfacing standard. This standard is used in PCs and numerous types of equipment.

However, since the standard was set long before the advent of the TTL logic family,

its input and output voltage levels are not TTL compatible. In RS232, a 1 bit is

represented by -3 to -25V, while a 0 bit is represented +3 to +25 V, making -3 to +3

undefined. For this reason, to connect any RS232 to a microcontroller system we must


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use voltage converters such as MAX232 to connect the TTL logic levels to RS232

voltage levels and vice versa. MAX232 ICs are commonly referred to as line drivers.

Fig 5.3.4: Serial communication process

The RS232 cables are generally referred to as DB-9 connector. In labeling, DB-9P

refers to the plug connector (male) and DB-9S is for the socket connector (female).

The simplest connection between a PC and microcontroller requires a minimum of

three pin, TXD, RXD, and ground. Many of the pins of the RS232 connector are used

for handshaking signals. They are bypassed since they are not supported by the UART

chip.

IBM PC/ compatible computers based on x86(8086, 80286, 386, 486 and

Pentium) microprocessors normally have two COM ports. Both COM ports have

RS232 type connectors. Many PCs use one each of the DB-25 and DB-9 RS232

connectors. The COM ports are designated as COM1 and COM2. We can connect the

serial port to the COM 2 port of a PC for serial communication experiments. We use a

DB9 connector in our arrangement.


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5.4 H-BRIDGE:

DC motors are typically controlled by using a transistor

configuration called an "H-bridge". This consists of a minimum of four mechanical or

solid-state switches, such as two NPN and two PNP transistors. One NPN and one

PNP transistor are activated at a time. Both NPN and PNP transistors can be activated

to cause a short across the motor terminals, which can be useful for slowing down the

motor from the back EMF it creates.

Basic Theory:

H-bridge. Sometimes called a "full bridge" the H-bridge is so named because

it has four switching elements at the "corners" of the H and the motor forms the cross

bar.

The key fact to note is that there are, in theory, four switching elements within

the bridge. These four elements are often called, high side left, high side right, low

side right, and low side left (when traversing in clockwise order).

The switches are turned on in pairs, either high left and lower right, or lower

left and high right, but never both switches on the same "side" of the bridge. If both

switches on one side of a bridge are turned on it creates a short circuit between the

battery plus and battery minus terminals. If the bridge is sufficiently powerful it will

absorb that load and your batteries will simply drain quickly. Usually however the

switches in question melt.

To power the motor, you turn on two switches that are diagonally opposed. In

the picture to the right, imagine that the high side left and low side right switches are

turned on.

The current flows and the motor begins to turn in a "positive" direction. Turn on the

high side right and low side left switches, then Current flows the other direction

through the motor and the motor turns in the opposite direction.

Actually it is just that simple, the tricky part comes in when you decide what

to use for switches. Anything that can carry a current will work, from four SPST


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switches, one DPDT switch, relays, transistors, to enhancement mode power

MOSFETs.

One more topic in the basic theory section, quadrants. If each switch can be

controlled independently then you can do some interesting things with the bridge,

some folks call such a bridge a "four quadrant device" (4QD get it?). If you built it out

of a single DPDT relay, you can really only control forward or reverse. You can build

a small truth table that tells you for each of the switch's states, what the bridge will do.

As each switch has one of two states, and there are four switches, there are 16

possible states. However, since any state that turns both switches on one side on is

"bad" (smoke issues forth: P), there are in fact only four useful states (the four

quadrants) where the transistors are turned on.

High Side Left High Side Right Low Side Left Low Side Right Quadrant Description

On Off Off On Forward Running

Off On On Off Backward Running

On On Off Off Braking

Off Off On On Braking

Table 5.4.1

The last two rows describe a maneuver where you "short circuit" the motor

which causes the motors generator effect to work against itself. The turning motor

generates a voltage which tries to force the motor to turn the opposite direction. This

causes the motor to rapidly stop spinning and is called "braking" on a lot of H-bridge

designs.

Of course there is also the state where all the transistors are turned off. In this

case the motor coasts freely if it was spinning and does nothing if it was doing

nothing.


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5.4.1 Implementation of H-bridge

1. Using Relays:

A simple implementation of an H Bridge using four SPST relays is shown.

Terminal A is High Side Left, Terminal B is High Side Right, Terminal C is

Low Side Left and Terminal D is Low Side Right. The logic followed is

according to the table above.

Warning: Never turn on A and C or B and D at the same time. This will lead

to a short circuit of the battery and will lead to failure of the relays due to the

large current.

Fig 5.4.1: Implementation using relalys

2.Using Transistors:

We can better control our motor by using transistors or Field Effect

Transistors (FETs). Most of what we have discussed about the relays H-Bridge

is true of these circuits. See the diagram showing how they are connected. You


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should add diodes across the transistors to catch the back voltage that is

generated by the motor's coil when the power is switched on and off. This fly

back voltage can be many times higher than the supply voltage!

Warning: If you don't use diodes, you could burn out your transistors. Also the

same warning as in the diode case. Don't turn on A and C or B and D at the

same time.

Fig 5.4.2: Implementation using transistors

Transistors, being a semiconductor device, will have some resistance,

which causes them to get hot when conducting much current. This is called not

being able to sink or source very much power, i.e.: Not able to provide muchcurrent from ground or from plus voltage.

Mosfets are much more efficient, they can provide much more current

and not get as hot. They usually have the fly back diodes built in so you don't

need the diodes anymore. This helps guard against fly back voltage frying

your ICs.

To use Mosfets in an H-Bridge, you need P-Channel Mosfets on top

because they can "source" power, and N-Channel Mosfets on the bottom

because then can "sink" power.

It is important that the four quadrants of the H-Bridge circuits be

turned on and off properly. When there is a path between the positive and

ground side of the H-Bridge, other than through the motor, a condition exists


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called "shoot through". This is basically a direct short of the power supply and

can cause semiconductors to become ballistic, in circuits with large currents

flowing. There are H-bridge chips available that are much easier, and safer, to

use than designing your own H-Bridge circuit.

3.Using H-Bridge Devices:

The L293 has 2 H-Bridges (actually 4 Half H-Bridges), can provide

about 1 amp to each and occasional peak loads to 2 amps.

The L298 has 2 h-bridges on board, can handle 1amp and peak current

draws to about 3amps. The LMD18200 has one h-bridge on board, can handle

about 2 or 3 amps and can handle a peak of about 6 amps. There are several

more commercially designed H-Bridge chips as well.

Once a Half H-bridge is enabled, it truth table is as follows:

INPUT

A

OUTPUT

Y

L L

H H

Table5.4.2

So you just give a High level when you want to turn the Half H-

Bridge on and Low level when you want to turn it off. When the Half H-

Bridge is on, the voltage at the output is equal to Vcc2.If you want to make a

Full H-Bridge, you connect the motor (or the load) between the outputs of twoHalf H-Bridges and the inputs will be the two inputs of the Half H-Bridges.

Suppose we have connected Half H-Bridges 1 and 2 to form a Full H-

Bridge. Now the truth table is as follows:


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INPUT

1A

INPUT

2A

OUTPUT

1Y

OUTPUT

2Y Description

L L L LBraking (both terminals

of motor are Gnd)

L H L H Forward Running

H L H L Backward Running

H H H HBraking (both terminals

of motor at Vcc2

Table 5.4.3

5.4.2 L293D Motor Driver IC:

Since two motors are used to drive The back wheels of the robot

independently, there is a need for Two H-bridges. Instead of implementing the above

H-bridge controlCircuit twice, an alternative is to use an integrated circuit (IC), which

Provides more than one

H-bridges. One such IC is L293D, which has 2 H-Bridges in it. It can supply

600Ma continuous and 1.2A peak Currents. It is suitable for switching applications up

to 5 kHz. These Features make it ideal for our application. Another option is to use

IC L298, which can drive 2A continually and 3A peak currents. The Diagram of

L293D is shown in Figure. It can be observed from the figure that L293D has asimilar configuration to the circuit in h bridge.


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Fig 5.4.3 L293 Motor Driver IC

Motor Driver Connections:

The motor driver requires 2 control

inputs for each motor. Since we drive 2 motors, we need 4 controls

Inputs from the microcontroller. Since it has many pins which can be

configured as outputs, there are many options for implementation.For example, in our

robot the last 4 bits of Port B (RB4, RB5, RB6,RB7 - Pins 37 to 40) are used to

control the rotation direction of the motors . The enable pins of the motor driver are

connected to the PWM outputs of the microcontroller (Pins 16and 17). This is

because, as was mentioned above, by changing the width of the pulse (implying

changing the enable time of the driver) one can change the speed of the motor. The

truth table for motor driver is as shown in Table II, where H = high, L = low, and Z

=high output impedance state.

Since the motors are reverse aligned, in order to have the robot Move forward they

must be configured such that one of them turns forward and the other one turns


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backward. In case of any requirement for the robot to move backward, it is sufficient

to just reverse the

THE TRUTH TABLE OF THE MOTOR DRIVER

input enable output

H H H

L H L

H L z

L L z

Table 5.4.4

DRIVER CONTROL INPUTS

Direction Input 1 Input 2 Input 3 Input 4

Forward H L L H

Backward L H H L

Table 5.4.5

Outputs of the control pins. For example, in our robot while moving forward, inputs

of the motor driver have states shown in the first row Of Table III, whereas for

backward movement, the states shown in the second row of Table III is applied.


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5.5 DC MOTORS

DC motors are configured in many types and sizes, including brush less,

servo, and gear motor types. A motor consists of a rotor and a permanent magnetic

field stator. The magnetic field is maintained using either permanent magnets or

electromagnetic windings. DC motors are most commonly used in variable speed and

torque.

Motion and controls cover a wide range of components that in some way are

used to generate and/or control motion. Areas within this category include bearings

and bushings, clutches and brakes, controls and drives, drive components, encoders

and resolves, Integrated motion control, limit switches, linear actuators, linear and

rotary motion components, linear position sensing, motors (both AC and DC motors),

orientation position sensing, pneumatics and pneumatic components, positioning

stages, slides and guides, power transmission (mechanical), seals, slip rings,

solenoids, springs.

Motors are the devices that provide the actual speed and torque in a drive

system. This family includes AC motor types (single and multiphase motors,

universal, servo motors, induction, synchronous, and gear motor) and DC motors

(brush less, servo motor, and gear motor) as well as linear, stepper and air motors, and

motor contactors and starters.

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. As you are well aware of

from playing with magnets as a kid, opposite (North and South) polarities attract,

while like polarities (North and North, South and South) repel. The 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).


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Fig 5.5.1: Block Diagram of the 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 (and all that

Beamers will see), 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. The above diagram shows a common motor layout -- with the rotor

inside the stator (field) magnets

The geometry of the brushes, commutator contacts, and rotor windings are

such that when power is applied, the polarities of the energized winding and the stator

magnet(s) are misaligned, and the rotor will rotate until it is almost aligned with the

stator's field magnets. As the rotor reaches alignment, the brushes move to the next

commutator contacts, and energize the next winding. Given our example two-pole

motor, the rotation reverses the direction of current through the rotor winding, leading

to a "flip" of the rotor's magnetic field, and driving it to continue rotating.

In real life, though, DC motors will always have more than two poles

(three is a very common number). In particular, this avoids "dead spots" in the

commutator. You can imagine how with our example two-pole motor, if the rotor is

exactly at the middle of its rotation (perfectly aligned with the field magnets), it will

get "stuck" there. Meanwhile, with a two-pole motor, there is a moment where the

commutator shorts out the power supply (i.e., both brushes touch both commutator

contacts simultaneously). This would be bad for the power supply, waste energy, and

damage motor components as well. Yet another disadvantage of such a simple motor


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