PC2PC Mini Project Documentation

Wireless network between two computers using Radio Frequency

Chapter one

Introduction

Problem Outline

Objective

Motivation

Thesis Outline

Department of ECE, Adam’s Engineering college, Paloncha Page 1


1.0 Introduction

The project report describes on the design development and fabrication of one demo

unit of the project work “Implementation of wireless communication between computers”.

Now a day, with the advancement technology, particularly in the field of Micro-controllers,

all the activities in our daily living have become a part of Information Technology and we

find micro-controllers in each and every application. Thus, trend is directing towards

Microcontrollers Based Project works. However, in this project work, the transferring of

data serially is monitored. Subsequently, after serial processing, these signals are encoded.

This information is transmitted through radio frequency (RF) transmitter. The received

information (using suitable RF receiver) is again decoded into digital signal at the receiver

end. Then the decisions are taken with the help of micro-controllers and associated

software.

In this project we are developing a system such that providing wireless

communication between computers. this is very useful in case of communication between

two building networks. If you connecting the wire network between these two networks the

problems are mainly cost, security, flexibly of routing wires and maintains. So, we are

going to wireless technology such as RF, which is purely depending on radio technology. It

has its own benefits.”RF wireless technology is an open specification for a low-cost, low-

power, short-range radio technology for ad-hoc wireless communication of voice and data

anywhere in the world.”

1.1 Problem outline

Now a day, with the advancement technology, particularly in the field of Micro-

controllers, all the activities in our daily living have become a part of Information

Technology and we find micro-controllers in each and every application. Thus, trend is

directing towards Microcontrollers Based Project works. However, in this project work, the

transferring of data serially is monitored without using microcontroller. Subsequently, after

serial processing, these signals are encoded. This information is transmitted through RF

transmitter.



The received information (using suitable radio frequency receiver) is again decoded

into digital signal at the receiver end. Then the decisions are taken with the help of

associated software.

In this project, the data is transferred only when the frequencies of both transmitter

and receiver are equal.

1.2 Objective

In this project work, the transferring of data serially is monitored without using

microcontroller. Subsequently, after serial processing, these signals are encoded. This

information is transmitted through RF transmitter. The received information (using suitable

RF receiver) is again decoded into digital signal at the receiver end.

RF transmitter is used to transmit the information with constant frequency i.e equal

to 433.3MHz.

Max232 is used as voltage level converter i.e RS232 level to TTL level and vice

versa.

RF receiver is used to receive the information with constant frequency i.e equal to

transmitter frequency.

1.3 Motivation

Wireless communications between two computer’s using radio frequencies one of

the most active areas of technology development of our time. This development is being

driven primarily by the transformation of what has been largely a medium for supporting

voice telephony into a medium for supporting other services, such as the transmission of

video, images, text, and data. Although there are, of course, still a great many technical

problems to be solved in wireless communications like internet, bluetooth, wi-fi

technologies demands for additional wireless capacity can be fulfilled largely with the

addition of new private infrastructure, such as additional routers and so on. On the other

hand, the traditional resources that have been used to add capacity to wireless systems are

radio bandwidth and transmitter power.



Unfortunately, these two resources are among the most severely limited in the

deployment of modern wireless networks: radio bandwidth because of the very tight

situation with regard to useful radio spectrum, and transmitter power because mobile and

other portable services require the use of battery power, which is limited. These two

resources are simply not growing or improving at rates that can support anticipated

demands for wireless capacity.

But still there are so many villages which does not having these technologies. The

developers are not spreading these technologies into villages because of higher cost.

So, In this project we are developing a new technology to transfer data from one

computer to another computer. It is also a wireless technology, by using radio frequencies

and antennas the data is transferred. In this new technology there is no need of internet,

bluetooth, wi-fi technologies

.

1.4 Thesis outline

Chapter2

This chapter describes about literature survey of the project.

Chapter3

This chapter describes about project introduction, principle of operation, details about radio

frequencies, block diagram description and serial communication.

Chapter4

This chapter describes about circuit diagram, transmitting unit, receiving unit, power

supply, max232 connector and 9pin and 25pin connector.

Chapter5

This chapter describes about software used and coding.

Chapter6

This chapter describes about result, merits, demerits, future scope and conclusion.



Chapter two

Literature Survey



2.0 Literature survey

Internet starts in the 1950s and 1960s with the development of computers. This

began with point to point communication between mainframe computers and terminals,

expanded to point-to-point connections between computers and then early research into

packet switching. Packet switched networks such as ARPA net, Mark I at NPL in the UK,

CYCLADES, Merit Network, Tymnet, and Telenet, were developed in the late 1960s and

early 1970s using a variety of protocols. The ARPANET in particular led to the

development of protocols for internetworking, where multiple separate networks could be

joined together into a network of networks.

Method 1

In 1982 the Internet Protocol Suite (TCP/IP) was standardized and the concept of a

world-wide network of fully interconnected TCP/IP networks called the Internet was

introduced. Access to the ARPANET was expanded in 1981 when the National Science

Foundation (NSF) developed the Computer Science Network (CSNET) and again in 1986

when NSFNET provided access to supercomputer sites in the United States from research

and education organizations. Commercial internet service providers (ISPs) began to emerge

in the late 1980s and 1990s. The ARPANET was decommissioned in 1990. The Internet

was commercialized in 1995 when NSFNET was decommissioned, removing the last

restrictions on the use of the Internet to carry commercial traffic.

Since the mid-1990s the Internet has had a drastic impact on culture and commerce,

including the rise of near instant communication by electronic mail, instant messaging,

Voice over Internet Protocol (VoIP) "phone calls", two-way interactive video calls, and the

World Wide Web with its discussion forums, blogs, social networking, and online

shopping sites.

The research and education community continues to develop and use advanced

networks such as NSF's very high speed Backbone Network Service (vBNS), Internet2,

and National LambdaRail. Increasing amounts of data are transmitted at higher and higher

speeds over fiber optic networks operating at 1-Gbit/s, 10-Gbit/s, or more. The Internet


http://en.wikipedia.org/wiki/National_LambdaRail

http://en.wikipedia.org/wiki/Internet2

http://en.wikipedia.org/wiki/VBNS

http://en.wikipedia.org/wiki/Online_shopping

http://en.wikipedia.org/wiki/Online_shopping

http://en.wikipedia.org/wiki/Social_networking

http://en.wikipedia.org/wiki/Blogs

http://en.wikipedia.org/wiki/Discussion_forums

http://en.wikipedia.org/wiki/World_Wide_Web

http://en.wikipedia.org/wiki/Video_chat

http://en.wikipedia.org/wiki/Voice_over_Internet_Protocol

http://en.wikipedia.org/wiki/Instant_messaging

http://en.wikipedia.org/wiki/E-mail

http://en.wikipedia.org/wiki/Internet_service_providers

http://en.wikipedia.org/wiki/Supercomputer

http://en.wikipedia.org/wiki/NSFNET

http://en.wikipedia.org/wiki/CSNET

http://en.wikipedia.org/wiki/National_Science_Foundation

http://en.wikipedia.org/wiki/National_Science_Foundation

http://en.wikipedia.org/wiki/Internet_Protocol_Suite

http://en.wikipedia.org/wiki/Internetworking

http://en.wikipedia.org/wiki/Communications_protocol

http://en.wikipedia.org/wiki/Telenet

http://en.wikipedia.org/wiki/Tymnet

http://en.wikipedia.org/wiki/Merit_Network

http://en.wikipedia.org/wiki/CYCLADES

http://en.wikipedia.org/wiki/National_Physical_Laboratory_(United_Kingdom)

http://en.wikipedia.org/wiki/Mainframe_computers


continues to grow, driven by ever greater amounts of online information and knowledge,

commerce, entertainment and social networking.

It is estimated that in 1993 the Internet carried only 1% of the information flowing

through two-way telecommunication, by 2000 this figure had grown to 51%, and by 2007

more than 97% of all telecommunicated information was carried over the Internet.

Method 2

One computer to another computer communication is also done by using Infrared.

Here we are using infrared rays to communicate with each other. Electromagnetic

frequencies currently have little legal status for protection and as such, can be freely

intercepted by motivated individuals. This doesn't mean wireless transmission is easily

breached, as security varies by the type of wireless transmission method. As presented

earlier in the advantages and disadvantages of infrared versus radio frequency transmission,

what might be considered an advantage to one method for transmission could turn out to be

a disadvantage for security. Because infrared is line-of-sight it has less transmission range

but is also more difficult to intercept when compared to radio frequency.

Method 3

In this project, one computer to another computer communication is done by using

radio frequencies. It is implemented to overcome the drawbacks of Infrared. RF technology

is not effected due to line of sight and it is not light sensitive.


http://en.wikipedia.org/wiki/Telecommunication

http://en.wikipedia.org/wiki/Social_networking


Chapter three

Introduction of wireless network

Principle of Operation

Details about Radio Frequencies

Description of Block diagram of wireless

network

Functional units

Max 232 connector

Power Supply

Serial Interface

Transmitter

Receiver

Antenna

Description of Serial Communication



3.0 Introduction of wireless network

Now a day, with the advancement technology, particularly in the field of Micro-

controllers, all the activities in our daily living have become a part of Information

Technology and we find micro-controllers in each and every application. Thus, trend is

directing towards Microcontrollers Based Project works. However, in this project work, the

transferring of data serially is monitored. Subsequently, after serial processing, these

signals are encoded. This information is transmitted through RF transmitter. The received

information (using suitable RF receiver) is again decoded into digital signal at the receiver

end. Then the decisions are taken with the help of micro-controllers and associated

software.

Now coming to the project work, to obtain the parameter (transferring of data

serially between to computers) from transmitter to the receiver, where the serial data

transfer is monitored, the radio transmission technique is incorporated in the design. For

this Radio transmission, there are number of mechanisms by which Radio waves may

travel from a transmitting to a receiving antenna. The terms, GROUND WAVES, SKY

WAVES and SCOPE or TROPOSHERIC WAVES designates the more important of these.

The ground wave can exist when the transmitting and receiving are close to surface

of the earth and are vertically polarized. The sky wave represents that reaches receiving

antenna as a result of a bending of the wave path introduced by the ionization in the upper

atmosphere. The space wave represents energy that travels from the transmitting to the

receiving antenna in the earth troposphere. The radio transmission at frequencies above

about 30MHz is normally the space wave propagation. The transmitters that are frequency

modulated find extensive use at frequencies use at frequencies above 40MHz. In this

project we are developing a system such that providing wireless communication between

computers. This is very useful in case of communication between two building networks. If

you connecting the wire network between these two networks the problems are mainly

cost, security, flexibly of routing wires and maintains. So, we are going to wireless

technology such as blue tooth, which is purely depending on radio technology.



It has its own benefits.”Blue tooth wireless technology is an open specification for a

low-cost, low-power, short-range radio technology for ad-hoc wireless communication of

voice and data anywhere in the world.”

In this project we provide flexible range compare to blue tooth technology and we

can transfer data from one computer to another computer with adjustable range using FM

communication.

In this project we are developing a system such that providing wireless

communication between computers. This is very useful in case of communication between

two building networks. If you connecting the wire network between these two networks the

problems are mainly cost, security, flexibly of routing wires and maintains. So, we are

going to wireless technology such as RF, which is purely depending on radio technology. It

has its own benefits.”RF wireless technology is an open specification for a low-cost, low-

power, short-range radio technology for ad-hoc wireless communication of voice and data

anywhere in the world.”

Embedded Systems

A system is something that maintains its existence and functions as a whole through

the interaction of its parts. E.g. Body, Mankind, Access Control, etc A system is a part of

the world that a person or group of persons during some time interval and for some purpose

choose to regard as a whole, consisting of interrelated components, each component

characterized by properties that are selected as being relevant to the purpose.

• Embedded System is a combination of hardware and software used to achieve a

single specific task.

• Embedded systems are computer systems that monitor, respond to, or control an

external environment.

• Environment connected to systems through sensors, actuators and other I/O

interfaces.

• Embedded system must meet timing & other constraints imposed on it by

environment.



3.1 Principle of operation

In this project we have two sections, one for transmitting and other for receiving.

In transmitting section we transmit the data of computer1 with the help of RF. Here we

collect the data from computers serial port and we convert computer compactable signal

(RS232) to TTL logical signal by level converter IC 232. The o/p of the 232 is connected to

i/p of ASK transmitter. With ASK transmitter the signal is keyed with 433MHz carrier

signal.

At other end receiving section, RF receiver is tuned to 433MHz for faithfully

reception of data from transmitter to receiver. After decoding, the signal is amplified and

fed to RS232 and here also we used RS232 for level converting. I.e. we must change TTL

level signal to RS232 level signal for computer compactable signal. This signal is feed to

system 2 through serial port and system program recover the data and display as

transmitted at the transmitter system.

3.2 Details about Radio Frequencies

A radio wave is an electromagnetic wave propagated by an antenna. Radio waves

have different frequencies, and by tuning a radio receiver to a specific frequency you can

pick up a specific signal.

Radio is a technology that allows the transmission of signals by modulation of

electromagnetic waves with frequencies those of light.

In today’s economy, people are demanding more and more mobility to function

efficiently. To address this demand, companies are moving data by air instead of wire.

There are many applications in which it is more efficient to move data wirelessly.

For this reason, it is necessary to make communications between two computers as

easy as possible by allowing people to move computers without moving wires. A

communication client program will interface with the user’s computer to send data to the

wireless data link. On the opposing end, a different user will use the second

communications program to receive the data from their data link. The data itself will be

sent by RF waves from a transmitter device to a receiver device



The RF transmission will be transparent to the user’s computers as if they were

directly connected to each other using a RS232 crossover cable.

Short for radio frequency, any frequency within the electromagnetic spectrum

associated with radio wave propagation. When an RF current is supplied to an antenna, an

electromagnetic field is created that then is able to propagate through space. Many wireless

technologies are based on RF field propagation.

These frequencies make up part of the electromagnetic radiation spectrum:

Ultra-low frequency (ULF) -- 0-3 Hz

Extremely low frequency (ELF) -- 3 Hz - 3 kHz

Very low frequency (VLF) -- 3kHz - 30 kHz

Low frequency (LF) -- 30 kHz - 300 kHz

Medium frequency (MF) -- 300 kHz - 3 MHz

High frequency (HF) -- 3MHz - 30 MHz

Very high frequency (VHF) -- 30 MHz - 300 MHz

Ultra-high frequency (UHF)-- 300MHz - 3 GHz

Super high frequency (SHF) -- 3GHz - 30 GHz

Extremely high frequency (EHF) -- 30GHz - 300 GHz

Implementation

To implement the wireless RS232 interface two different circuit boards will be

designed. The two boards will consist of a transmitter and receiver. The transmitter will

accept data from a RS232 (9-pin) of a computer port and transfer the information to RF

signal.

The receiver will capture the RF signal, transferring it back to a digital signal, and

finally import it into the RS232 (9-pin) port of a computer. The purpose of the rest of this

document is to specify the integration of this RF technology.


http://www.webopedia.com/TERM/R/RF.html


Units

As the unit of frequency is the hertz (Hz), frequencies shall be expressed:

in kilohertz (kHz), up to and including 3000 kHz;

in megahertz (MHz), above 3 MHz, up to and including 3000 MHz;

in gigahertz (GHz), above 3 GHz, up to and including 3000 GHz.

3.3 Description of Block diagram of wireless network between two computers

Transmitter

Figure 3.1: Block diagram of Transmitter of wireless network


PowerSupply

RFTransmitter

RS 232

230V AC +5V

COMPUTER

PC


Receivers

Figure 3.3: Block diagram of receiver of wireless network

The Block diagram of the project work “Implementation of Wireless

Communication between two Computers” is explained. For better understanding, the total

block diagram is divided into two various blocks and each block explanation is provided in

this chapter. The complete block diagram consists of the following blocks.

Functional Units

MAX232 Connector

Power Supply

Serial Interface

Transmitter

Receiver

Antenna

3.3.1 Functional units

The above figure conceptually displays the proposed system architecture for our

project. Each box represents a different functional unit. Each box will be described below

to give the reader a better understanding of this system.


RS 232RF

Receiver

PC


3.3.2 MAX232 Connector

The MAX232 connector will be used to transfer data from the MAX232 (16-pin)

port of a computer to the input line converter. The connector will be a 90-degree flat mount

design that will allow the pins of a serial connection to be transferred to data lines in a

computer board. A typical model would be 182-09F-ND Right Angle D-Sub connector

made by Norcomp.

3.3.3 Power supply

Power supply unit provides +5V-regulated power to the system. It consists of two

parts Rectifier and Monolithic IC voltage regulators. Here the step down transformer of

voltage ratio 230V/9-0-9V steps down 230VAC primary to 9–0–9V secondary and gives

the secondary current up to 500mA, to the Rectifier. The output voltage of the rectifier

then regulated to +5V using LM7805 monolithic IC voltage regulators.

3.3.4 Serial Interface

The serial interface on the transmitter will accept a data line from the MAX 232

connector and transfer it to TTL/CMOS standard logic level. The TTL/CMOS signal will

then be sent on a data line to the Encoder/Buffer.

The serial interface on the receiver accept a data from the Decoder/Buffer and

transfer it to TTL/CMOS standard logic level. The TTL/CMOS signal will then be sent on

a data line to the MAX232 Connector.

3.3.5 Transmitter

The transmitter will be an AM hybrid transmitter that operates at a frequency of

433.92 MHz. The transmitter accepts a TTL/CMOS signal on a data line from the

Encoder/Buffer and will output a signal to an antenna. The proposed transmitter is

manufactured in Italy by Telecontrolli s.p.a and supplied by Okwelectronics; part number

AMRT4-433.



3.3.6 Receiver

The receiver will be a AM SuperRegen Receiver Module that operates at a

frequency of 433.92MHz. The receiver accepts a signal from an antenna and will output

TTL/CMOS signal on a data line to the Decoder/Buffer. The proposed receiver is

manufactured in Italy by Telecontrolli s.p.a and supplied by Okwelecronics; part number

AMHRR3-433.

3.3.7 Antenna

User defined depending on required signal distance / power.

3.4 Description of Serial Communications

Data transfer within a system is generally in parallel. All the bits of the data word

are transferred in parallel at the same instant. In some cases, particularly in transferring

data over long distances, it is preferred to transfer the data in serial form.

The data word from a transmitting system is converted to stream of bits by parallel

to serial conversion, and one bit at a time is transferred on a single line to a receiving

system. At the receiving end, the word is reconstructed by serial to parallel conversion.

The speed of data transfer in serial communication is specified by baud. All IBM

compter and compatible computers are typically equipped with two serial ports and one

parallel port.

Although these two types of ports are used for communicating with external devices,

they work in different ways. A parallel port sends and receives data eight bits at a time over

8 separate wires. This allows data to be transferred very quickly; however, the cable

required is more bulky because of the number of individual wires it must contain. Parallel

ports are typically used to connect a computer to a printer and are rarely used for much

else. A serial port sends and receives data one bit at a time over one wire. While it takes

eight times as long as to transfer each byte of data this way, only a few wires are required.

In fact, two-way (full duplex) communications is possible with only three separate wires-

one to send, one to receive, and a common signal ground wire.



Bi-directional communications

Communicating by bits

The Parity Bit

Cable lengths

DCE And DTE devices

Synchronous and Asynchronous Communications.

Bi-directional Communications

The serial port on your computer is a full-duplex device meaning that it can send

and receive data at the same time. In order to be able to do this, it uses separate lines for

transmitting and receiving data. Some types of serial devices support only one-way

communications and therefore use only two-wires in the cable – the transmit line and the

signal ground.

Communicating by bits

Once the start bit has been sent, the transmitter sends the actual data bits. There

may either be 5,6,7, or 8 data bits, depending on the number you have selected.

Both receiver and the transmitter must agree on the number of data bits, as well as

the baud rate. Almost all devices transmit data using either 7 or 8 data bits.

Notice that when only 7 data bits are employed, you cannot send ASCII values

greater than 127. Likewise, using 5 bits limits the highest possible value to 31.

After the data has been transmitted, a stop bit is sent. A stop bit has a value of 1- or

a mark state- and it can be detected correctly even if the previous data bit also had a value

of 1. This is accomplished by the stop bit’s duration.

The Parity Bit

Besides the synchronization provided by the use of start and stop bits, an additional

bit called a parity bit may optionally be transmitted along with the data. A parity bit affords



a small amount of error checking, to help detect data corruption that might occur during

transmission.

Cable Lengths

The MAX-232 standard imposes a cable length limit of 50 feet. You can usually

ignore this “standard”, since a cable can be as long as 10000 feet at baud rates up to 19200

if you use a high quality, well shielded cable. The external environment has a large effect

on lengths for unshielded cables.

DCE and DTE devices

Two terms you should be familiar with are DTE and DCE. DTE stands for Data

Terminal Equipment, and DCE stands for Data Communication Equipment.

These terms are used to indicate the pin-out for the connectors on a device and the direction

of the signals on the pins. Your computer is a DTE device, while most other devices are

usually DCE devices.

If you have trouble keeping the two straight then replace the term “DTE device”

with your computer and the term DCE device with “remote Device” in the following

discussion.

The RS-232 standard states that DTE devices use a 25-pin male connector, and DCE

devices use a 25-pin female connector. You can therefore connect a DTE device to a DCE

using a straight pin-for-pin connection. However, to connect two like devices, you must

instead use a null modem cable. Null modem cables cross the transmit and receive lines in

the cable.

The DTE device puts this line in a mark condition to tell the remote device that it is

ready and able to receive data. If the DTE device is not able to receive data (typically

because its receive buffer is almost full), it will put this line in the space condition as a

signal to the DCE to stop sending data. When the DTE device is ready to receive more data

it will place this line back in the mark condition.

The complement of the RTS wire is CTS, which stands for Clear to Send. The

DCE device puts this line in a mark condition to tell the DTE device that it is ready to



receive the data. Likewise, if the DCE device is unable to receive data, it will place this line

in the space condition. Together, these two lines make up what is called RTS/CTS or

“hardware” flow control.

Software flow control uses special control characters transmitted from one device

to another to tell the other device to stop or start sending data. With software flow control

the RTS and CTS lines are not used.

DTR stands for Data Terminal Ready. Its intended function is very similar to the

RTS line. DSR (Data Set Ready) is the companion to DTR in the same way that CTS is to

RTS.

Some serial devices use DTR and DSR as signals to simplify confirm that a device

is connected and turned on. The software wedge sets DTR to the mark state when the serial

port is opened and leaves it in that state until the port is closed. The DTR and DSR lines

were originally designed to provide an alternate method of hardware handshaking.

Synchronous and Asynchronous Communications

There are two basic types of serial communications, synchronous and

asynchronous. With synchronous communications, the two devices initially synchronize

themselves to each other, and then continually send characters to stay in sync.

Even when the data is not really being sent, a constant flow of bits allows each

device to know where the other is at any given time. That is, each character that is sent is

either actual data or an idle character.

Synchronous communications allows faster data transfer rates than asynchronous

methods, because additional bits to mark the beginning and end of each data byte are not

required. Asynchronous means no “synchronization”, and thus does not require sending

and receiving idle characters. However, the beginning and end of each byte of data must be

identified by start and stop bits. The start bit indicates when the data byte is about to begin

and the stop bit signals when it ends. The requirement to send these additional two bits

causes asynchronous communication to be slightly slower than synchronous has the

advantage that the processor does not have to deal with the additional idle characters.



Chapter four

Design and Implementation of wireless

network between two computers

Circuit Diagram of wireless network between

two computers

Description of Transmitting unit of wireless

network

PC block

RS 232

RF transmitter

Power Supply

Transformer

Rectifiers

Filters

Voltage regulator

Description of Receiving unit of wireless

network

RF receiver

Description of MAX 232 connector

9 pin and 25 pin connector

Advantages and disadvantages



4. Design and Implementation of wireless network between two computers

4.1 Circuit Diagram of wireless network between two computers

C 7

1 u F

7

U 1

M A X2 3 2

134526

1 29

1 11 0

1 38

1 47

C 1 +C 1 -C 2 +C 2 -V +V -

R 1 O U TR 2 O U T

T1 I NT2 I N

R 1 I NR 2 I N

T1 O U TT2 O U T

C 21 0 0 u F

D 2

1 N 4 0 0 7

C 11 0 0 0 u F

C 3

1 u F

8

C 5

1 u F

D 3

7 8 0 5

1 3V I N V O U T

6

3

5 V

4

2

1

5

T2

2 3 0 V , 5 0 H z

1 5

6

4 8

D 1

1 N 4 0 0 7

9

C 6

1 u F

Figure4.1: Transmitting unit circuit diagram of wireless network



C 7

1 u F

7

U 1

M A X2 3 2

134526

1 29

1 11 0

1 38

1 47

C 1 +C 1 -C 2 +C 2 -V +V -

R 1 O U TR 2 O U T

T1 I NT2 I N

R 1 I NR 2 I N

T1 O U TT2 O U T

C 21 0 0 u F

D 2

1 N 4 0 0 7

C 11 0 0 0 u F

C 3

1 u F

8

C 5

1 u F

D 3

7 8 0 5

1 3V I N V O U T

6

3

5 V

4

2

1

5

T2

2 3 0 V , 5 0 H z

1 5

6

4 8

D 1

1 N 4 0 0 7

9

C 6

1 u F

Figure4.2: Receiving unit circuit diagram of wireless network



4.2 Description of Transmitting unit of wireless network

4.2.1 PC Block

The PC is having various I/O peripherals such as parallel port, serial (COM) port,

USB port, modems etc. For this project we have taken serial (COM) port because in

monoplex mode of communication, only one wire is sufficient. Here we can transmit single

wire information, so we have chosen this port. A nine pin D – type connector is placed at

the rear panel of the computer through which we take data using an interfacing cable. For

taking commands and transmitting the data, ‘C’ language is used. An user friendly menu is

created for better operation.

Figure4.3: Schematic diagram of transmitting unit of wireless network

4.2.2 RS232

The MAX232 family of line drivers/receivers is intended for all EIA/TIA-232E and

V.28/V.24 communications interfaces, particularly applications where ±12V is not


Power supply

RFTransmitter

RS 232

230V AC +5V

COMPUTER

PC


available. These parts are especially useful in battery-powered systems, since their low-

power shutdown mode reduces power dissipation to less than 5µW. the features of these

I.C. are Superior to Bipolar, Operate from Single +5V Power Supply, Meet All EIA/TIA-

232E and V.28 Specifications, Multiple Drivers and Receivers, 2-State Driver and Receiver

Outputs.

4.2.3 RF Transmitter

This block generates a continuous frequency of 433MHz, which is used to form a

permanent link between the transmitter and receiver, and this is known as carrier

frequency. The output serial port is fed to this RF transmitter. This is a frequency

modulated radio transmitter. The radiating power of the transmitter is 20mw, and it is

designed using BC 494 B high frequency switching transistor.

Low Cost solution for Telemetry and Radio control. We have mini size transmitter

TWS434 and receiver RWS434 at frequencies. The transmitter speed is up to 3Kbps (uses

SAW device) and the receiver is 5Kbps (LC superregen). The operation range is up to 200

feet (70mts).

433MHz RF Transmitter

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

range is required. The transmitter operates from 1.5-12V supply, making it ideal for

battery-powered applications. The transmitter employs SAW-stabilized oscillator, ensuring

accurate frequency control for best range performance. Output power and harmonic

emissions are easy to control, making FCC and ETSI compliance easy. The manufacturing-

friendly SIP style package and low-cost make the STT-433 suitable for high volume

applications.



Figure4.4: 433MHz RF transmitter

Features

· 433.92 MHz Frequency

· Low Cost

· 1.5-12V operation

· 11mA current consumption at 3V

· Small size

· 4 dBm output power at 3V

Applications

· Remote Keyless Entry (RKE)

· Remote Lighting Controls

· On-Site Paging

· Asset Tracking

· Wireless Alarm and Security Systems

· Long Range RFID

· Automated Resource Management



Specifications

Table4.1: specifications of RF transmitter

Parameter Symbol Min Type Max Unit

Operating voltage Vcc 1.5 3.0 12 Volts Dc

Operating Current

Data=VCC

Icc - 11mA@3V

59mA@5V

- mA

Operating Current

Data=GND

Icc - 100 - uA

Frequency

Accuracy

TOL fc -75 0 +75 KHz

Center Frequency Fc - 433 - MHz

RF output power - 4dBm@3V(2mW)

16dBm@5V(39mW)

dBm/mW

Data Rate 200 1K 3K BPS

Temperature -20 60 Deg.C

Power up delay 20 ms

RFID

RFID or Radio Frequency identification is a technology that enables the tracking or

identification of objects using IC based tags with an RF circuit and antenna, and RF readers

that "read" and in some case modify the information stored in the IC memory.

Radio frequency identification (RFID) is a general term that is used to describe a system

that transmits the identity (in the form of a unique serial number) of an object wirelessly,

using radio waves. RFID technologies are grouped under the more generic Automatic

Identification (Auto ID) technologies.



The RF tags could be divided in two major groups

Passive tags

The power to activate the tag microchip is supplied by the reader through the tag

antenna when the tag is in the interrogation zone of the reader, as is the timing pulse

Active Rfid tags

Active RFID tags have a battery in them and are therefore more capable in terms of

range and data handling.

Frequency use

There are four commonly used frequencies: low frequency (LF) 125/134.2 kHz,

high frequency (HF) 13.56 MHz, ultra high frequency (UHF) (including 869 and 915

MHz) and microwave (at 2450 MHz, a band familiar to ISPs).

4.3 Power Supply

Power supply unit provides +5V-regulated power to the system. It consists of two

parts Rectifier and Monolithic IC voltage regulators. Here the step down transformer of

voltage ratio 230V/9-0-9V steps down 230VAC primary to 9–0–9V secondary and gives

the secondary current up to 500mA, to the Rectifier. The output voltage of the rectifier

then regulated to +5V using LM7805 monolithic IC voltage regulators.

Power Supply circuit diagram

Figure4.5: Circuit diagram of power supply



The AC main Block is the power supply which is of single phase 230V ac. This

should be given to step down transformer to reduce the 230V ac voltage to low voltage.

i.e., to 6V or 12V ac this value depends on the transformer inner winding. The output of the

transformer is given to the rectifier circuit. This rectifier converts ac voltage to dc voltage.

But the voltage may consist of ripples or harmonics.

To avoid these ripples the output of the rectifier is connected to filter. The filter thus

removes the harmonics. This is the exact dc voltage of the given specification. But the

controller operates at 5V dc and the relays and driver operates at 12V dc voltage. So we

need a regulator to reduce the voltage. 7805 regulator produces 5V dc and 7812 regulator

produces 12V dc. Both are positive voltages.

A 5V regulated power supply system as shown below:

Figure4.6: Block diagram of power supply



The power supplies are designed to convert high voltage AC mains electricity to a

suitable low voltage supply for electronic circuits and other devices. A RPS (Regulated

Power Supply) is the Power Supply with Rectification, Filtering and Regulation being done

on the AC mains to get a Regulated power supply for Microcontroller and for the other

devices being interfaced to it. A power supply can by broken down into a series of blocks,

each of which performs a particular function. A d.c power supply which maintains the

output voltage constant irrespective of a.c mains fluctuations or load variations is known as

“Regulated D.C Power Supply”

4.3.1 Transformer

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

from one Electrical circuit to another without change in frequency.

The Step down Transformer is used to step down the main supply voltage from

230V AC to lower value. This 230 AC voltage cannot be used directly, thus it is stepped

down. The Transformer consists of primary and secondary coils. To reduce or step down

the voltage, the transformer is designed to contain less number of turns in its secondary

core. The output from the secondary coil is also AC waveform. Thus the conversion from

AC to DC is essential. This conversion is achieved by using the Rectifier Circuit/Unit.

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-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. Note that as voltage is stepped down

current is stepped up.



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.

Figure4.7: 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

4.3.2 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”. The Rectifier circuit is used to convert the

AC voltage into its corresponding DC voltage. There are Half-Wave, Full-Wave and bridge

Rectifiers available for this specific function.

The most important and simple device used in Rectifier circuit is the diode. The

simple function of the diode is to conduct when forward biased and not to conduct in

reverse bias.

The Forward Bias is achieved by connecting the diode’s positive with positive of

the battery and negative with battery’s negative. The efficient circuit used is the Full wave



Bridge rectifier circuit. The output voltage of the rectifier is in rippled form, the ripples

from the obtained DC voltage are removed using other circuits available. The circuit used

for removing the ripples is called Filter circuit.

Types of Rectifiers

Half wave Rectifier

Full wave rectifier

1. Centre tap full wave rectifier.

2. Bridge type full bridge rectifier.

Full-wave Rectifier

From the below comparison we came to know that full wave bridge rectifier as

more advantages than the other two rectifiers. So, in our project we are using full wave

bridge rectifier circuit.

Bridge Rectifier

A bridge rectifier makes use of four diodes in a bridge arrangement to

achieve full-wave rectification. This is a widely used configuration, both with individual

diodes wired as shown and with single component bridges where the diode bridge is wired

Internally.

Figure4.8: Circuit diagram of Bridge rectifier



A bridge rectifier makes use of four diodes in a bridge arrangement as shown in

fig (a) to achieve full-wave rectification. This is a widely used configuration, both with

individual diodes wired as shown and with single component bridges where the diode

bridge is wired internally.

Operation

During positive half cycle of secondary, the diodes D2 and D3 are in forward

biased while D1 and D4 are in reverse biased as shown in the fig(b). The current flow

direction is shown in the fig (b) with dotted arrows.

Figure4.9: Bridge rectifier when D2,D3 in forward bias and D1,D4 in reverse bias

During negative half cycle of secondary voltage, the diodes D1 and D4 are in

forward biased while D2 and D3 are in reverse biased as shown in the fig(c). The current

flow direction is shown in the fig (c) with dotted arrows.

Figure4.10: Bridge rectifier when D1,D4 in forward bias and D2,D3 in reverse bias



Comparison of rectifier circuits

Table4.2: Comparison of rectifiers circuits

Parameter

Type of Rectifier

Half wave Full wave Bridge

Number of diodes

1 2 4

PIV of diodesVm 2Vm Vm

D.C output voltageVm/ 2Vm/ 2Vm/

Vdc,at no-load0.318Vm 0.636Vm 0.636Vm

Ripple factor1.21 0.482 0.482

Ripple frequencyF 2f 2f

Rectification

efficiency 0.406 0.812 0.812

Transformer

Utilization

Factor(TUF)0.287 0.693 0.812

RMS voltage Vrms Vm/2 Vm/√2 Vm/√2



4.3.3 Filter

A Filter is a device which removes the a.c component of rectifier output but

allows the d.c component to reach the load. Capacitors are used as filter. The ripples from

the DC voltage are removed and pure DC voltage is obtained. And also these capacitors are

used to reduce the harmonics of the input voltage. The primary action performed by

capacitor is charging and discharging. It charges in positive half cycle of the AC voltage

and it will discharge in negative half cycle. So it allows only AC voltage and does not

allow the DC voltage. This filter is fixed before the regulator. Thus the output is free from

ripples.

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.

(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 appear at 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 = ¼√3frRl

Where,

f = supply frequency,

r = ripple factor,

Rl = load resistance

Note: In our circuit we are using 1000µF hence large value of capacitor is placed to reduce

ripples and to improve the DC component.

Output Filter

The Filter circuit is often fixed after the Regulator circuit. Capacitor is most often

used as filter. The principle of the capacitor is to charge and discharge. It charges during

the positive half cycle of the AC voltage and discharges during the negative half cycle.

So it allows only AC voltage and does not allow the DC voltage. This filter is fixed

after the Regulator circuit to filter any of the possibly found ripples in the output received

finally. Here we used 0.1µF capacitor. The output at this stage is 5V and is given to the

Microcontroller.

4.3.4 Voltage Regulator

Voltage regulator ICs is available with fixed (typically 5, 12 and 15V) or variable

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 have 3 leads and look like power

transistors, such as the 7805 +5V 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.

Figure4.11: A Three Terminal Voltage Regulator

Regulator regulates the output voltage to be always constant. The output voltage is

maintained irrespective of the fluctuations in the input AC voltage. As and then the AC

voltage changes, the DC voltage also changes.

Thus to avoid this Regulators are used. Also when the internal resistance of the

power supply is greater than 30 ohms, the output gets affected. Thus this can be

successfully reduced here. The regulators are mainly classified for low voltage and for high

voltage.

Further they can also be classified as:

i) Positive regulator

1---> input pin

2---> ground pin

3---> output pin



It regulates the positive voltage.

ii) Negative regulator

1---> ground pin

2---> input pin

3---> output pin

It regulates the negative voltage.

7805 Regulator

The Bay Linear LM7805 is integrated linear positive regulator with three terminals.

The LM7805 offer several fixed output voltages making them useful in wide range of

applications. When used as a zener diode/resistor combination replacement, the LM7805

usually results in an effective output impedance improvement of two orders of magnitude,

lower quiescent current. The LM7805 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

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

4.4 Description of receiving unit

.4.1 RF receiver

The RF receiver is designed with IC CXA1619, which is AM/FM Radio receiver

IC, operates at a local oscillator of 88 - 108MHz and is tuned with the transmitter. This IC

consists of built in RF amplifier, a double balanced mixer, local oscillator, a two stage IF

amplifier, a quadrature demodulator for a ceramic filter and an automatic frequency



control. The built in RF amplifier, a part from the amplification of received RF signal, it

also reduces the Noise figure, which could otherwise be a problem because of the large

band widths needed for RF. It also matches the input impedance of the radio receiver with

the antenna.

In this block diagram also we are using one computer and RS232 interfacing

circuit, which we have already discussed in transmitting section

Figure4.12: Schematic diagram of receiving unit of wireless network

433MHz RF Receiver

The STR-433 is ideal for short-range remote control applications where cost is a

primary concern. The receiver module requires no external RF components except for the

antenna. It generates virtually no emissions, making FCC and ETSI approvals easy. The

super-regenerative design exhibits exceptional sensitivity at a very low cost.

The manufacturing-friendly SIP style package and low-cost make the STR-433

suitable for high volume applications.


RS 232

RFReceiver

PC


Figure4.13: 433MHz RF receiver

Features

· Low Cost

· 5V operation

· 3.5mA current drain

· No External Parts are required

· Receiver Frequency: 433.92 MHZ

· Typical sensitivity: -105dBm

· IF Frequency: 1MHz

Applications

· Car security system

· Sensor reporting

· Automation system

· Remote Keyless Entry (RKE)

· Remote Lighting Controls

· On-Site Paging

· Asset Tracking

· Wireless Alarm and Security Systems

· Long Range RFID



Specifications

TABLE4.3: SPECIFICATIONS OF RF RECEIVER

Parameter Symbol Min Type Max Unit

Operating Voltage Vcc 4.5 5.0 5.5 VDC

Operating Current Icc - 3.5 4.5 mA

Reception

Bandwidth

BW rx - 1.0 - MHz

Center Frequency Fc - 433.92 - MHz

Sensitivity - - -105 - dBm

Max Data Rate - 300 1K 3K Kbits/s

Turn On Time - - 25 - ms

Operating

Temperature

Top -10 - +60 0C

4.5 MAX232 Connector (Voltage Converter)

Since the RS232 is not compatible with todays microprocessors and micro

controller, we need line driver to convert the RS232 signals to TTL voltage levels that will

be acceptable to the 8051’s TXD and RXD pins. One example of such a converter is MAX

232 from maxim corp.

The MAX 232 converts from RS232 voltage levels to TTL voltage levels, and vice

versa. One advantage of MAX232 chip is that it uses a +5V power source. In other words,

with a single +5v power supply we can power the MAX 232. The MAX 232 requires four

capacitors ranging from 1 to 22 microfarad. The most widely used value for this capacitor

is 22microfarad.



Pin Diagram Of MAX232:

Figure4.14: Pin diagram of max232

RS-232 logic levels are indicated by positive and negative voltages, rather than by

the positive-only signals of 5V TTL and CMOS logic. At an RS-232 data output (TD), a

logic 0 is defined as equal to or more positive than +5V, and a logic 1 is defined as equal to

or more negative than –5V. In other words, the signals use negative logic, where the more

negative voltage is logic 1.

The control signals use the same voltages, but with positive logic. A positive

voltage indicates that the function is on, or asserted, and a negative voltage indicates that

the function is off, or not asserted.

RS-232 interface chips invert the signals. On a UART’s output pin, a logic-1 data

bit or an off control signal is near 5V, which results in a negative voltage at the RS-232

interface. Logic – 0 data bit or on control signal is near 0V, resulting in a positive voltage

at the RS-232 interface.

Because an RS-232 receiver may be at the end of a long cable, by the time the

signal reaches the receiver, its voltage may have attenuated or have noise riding on it. To

allow for this, the minimum required voltages at the receiver are less than at the driver. An



input more positive than +3V is a logic 0 at RD, or On at a control input. An input more

negative than –3V is a logic 1 at RD, or Off at a control input. According to the standard,

the logic level of an input between –3V and +3V is undefined.

The MAX232 connector will be used to transfer data from the MAX232 (16-pin)

port of a COMPUTER to the input line converter. The connector will be a 90-degree flat

mount design that will allow the pins of a serial connection to be transferred to data lines in

a computer board.

Circuit Diagram Of MAX232

Figure4.15: Circuit diagram of max232



RS – 232 Serial Interface

The MAX232 I.C convert input TTL level into RS-232C standard level and

connected to COMPUTER through 9-pin D-type connector. Now discuss about standards

of RS232 and Serial communication through RS232.

RS-232 logic levels are indicated by positive and negative voltages, rather than by

the positive-only signals of 5V TTL and CMOS logic. At an RS-232 data output (TD), a

logic 0 is defined as equal to or more positive than +5V, and a logic 1 is defined as equal to

or more negative than –5V. In other words, the signals use negative logic, where the more

negative voltage is logic 1.

The control signals use the same voltages, but with positive logic. A positive

voltage indicates that the function is on, or asserted, and a negative voltage indicates that

the function is off, or not asserted.

RS-232 interface chips invert the signals. On a UART’s output pin, a logic-1 data

bit or an off control signal is near 5V, which results in a negative voltage at the RS-232

interface. Logic – 0 data bit or on control signal is near 0V, resulting in a positive voltage

at the RS-232 interface. Because an RS-232 receiver may be at the end of a long cable, by

the time the signal reaches the receiver, its voltage may have attenuated or have noise

riding on it.

To allow for this, the minimum required voltages at the receiver are less than at the

driver. An input more positive than +3V is a logic 0 at RD, or On at a control input. An

input more negative than –3V is a logic 1 at RD, or Off at a control input. According to the

standard, the logic level of an input between –3V and +3V is undefined.

The noise margin, or voltage margin, is the difference between the output and input

voltages. RS-232’s large voltage swings result in a much wider noise margin than 5V TTL

logic. For example, even if an RS-232 driver’s output is the minimum +5V, it can attenuate

or have noise spikes as large as 2V at the receiver and still be a valid logic 0.

Many RS-232 outputs have much wider voltage swings: 9 and 12V are

common. These in turn give much wider noise margin. The maximum allowed voltage

swing is 15V, though receivers must handle voltages as high as 25V without damage.



Two other terms used in relation to RS-232 are Mark and Space. Space is logic 0,

and Mark is logic 2. These refer to the physical marks and spaces made by the mechanical

recorders used years ago to log binary data.

TIA/EIA-232 includes both minimum and maximum timing specifications. All of

the many RS-232 interface chips meet these specifications. The specified slew rate limits

the maximum bit rate of the interface. Slew rate is a measure of how fast the voltage

changes when the output switches and describes an output’s instantaneous rate of voltage

change.

The slew rate of an RS-232 driver must be 30 Volts per microsecond or less. The

advantage of limiting slew rate is that it improves signal quality by virtually eliminating

problems due to voltage reflections that occur on long links that carry signals. With fast

rise and fall times. But the slew rate also limits a link’s maximum speed. At 30 V/s, an

output requires 0.3 microsecond to switch from +5V to –5V. RS-232’s specified maximum

bit rate is 20 kbps, which translates to a bit width of 50 microseconds, or 166 times the

switching time at the fastest allowed slew rate.

In reality, because UARTs read inputs near the middle of the bit, and because most

timing references are very accurate, you can often safely use bit widths as short as 5 to 10

times the switching time. Taking these into account, some interface chips allow bit rates of

115 kbps and higher, even though this violates the standard’s recommendations. Besides

having a maximum switching speed, RS-232 drivers must also meet minimum standards to

ensure that signals dont linger in the undefined region between logic states. For the control

signals and other signals of 40 bps and lower, the line must spend no more than 1

millisecond in the transition region between a valid logic 0 and logic 1.



Null Modem

Figure4.16: The connections of the Null modem using RS-232D connecter

Null modem is used to connect two DTE's together. This is used to transfer files

between the computers using protocols like Zmodem protocol, xmodem protocol, etc.,

Above-mentioned figure shows the wiring of the null modem. The main feature indicated

here is that the to make the computer to chat with the modem rather than another computer.

The guest & host computer connected through the TD, RD, and SG pins. Any data that is

transmitted through TD line from the Host to Guest is received on RD line.

The Guest computer must have the same setup as the Host. The signal ground (SG)

line of the both must be shorted so that grounds are common to each computer. The Data

Terminal Ready (DTR) is looped back to Data Set Ready and Carrier Detect on both

computers. When the Data Terminal Ready is asserted active, then the Data Set Ready and

Carrier Detect immediately become active.

At this point, the computer thinks the Virtual Modem to which it is connected is

ready and has detected the carrier of the other modem. All left to worry about now is the

Request to Send and Clear To Send. As both computers communicate together at the same

speed, flow control is not needed thus these two lines are also linked together on each

computer. When the computer wishes to send data, it asserts the Request to Send high and

as it is hooked together with the Clear to Send, It immediately gets a reply that it is ok to

send and does so.



The Ring indicator line is only used to tell the computer that there is a ringing

signal on the phone line. As we do not have, a modem connected to the phone line this is

left disconnected.To know about the RS232 ports available in your computer, Right click

on "My Computer", Goto 'Properties', Select tab 'Device Manager', go to Ports( COM &

LPT ), In that you will find 'Communication Port(Com1)' etc. If you right click on that and

go to properties, you will get device status. Make sure that you have enabled the port( Use

this port is selected).

4.6 9-PIN and 25-PIN Connector

Connectors a 25-pin D-type connector (DB-25) and a 9-pin D-type connector (DB-

9). The type of serial communications used by COMPUTERs requires only nine pins, so

either type of connector will work equally well. Since modern COMPUTERs employ only

9-pinD-type connectors, only this configuration has been discussed in this article,

including connections and programming.

The RS-232D has existed in two types. i.e., D-TYPE 25 pin connector and D-TYPE

9 pin connector, which are male connectors on the back of the COMPUTER. You need a

female connector on your communication from Host to Guest computer.

The below shown connector known as 9-pin, D-type male connector is used for

RS232 connections.

Figure4.17: Pin diagram of 9-pin D-type connector



Build that 9 pin connector

First you have to take 3 pin connector with long wires. Strip the other end of wire

with cutter and then tream it. As you can see wire i m using is 3 color wire which is

generally used for servo connection. Terminology for this wire here is

1 >> BLACK = Ground

2 >> RED = TX of module

3 >> YELLOW = RX of module

so now first make a cable for UART. You will need one 9 pin female connector , plastic

casing of same ,3 pin connector with cable ,soldering iron and some soldering metal.

First solder the 3 ends of wire to 9 pin connector as shown in figure as you can see

Figure4.18: DB-9 connector

pin number 2,3 and 5 are connected to 3 pin connector

pin number 2 is connected to Yellow wire that is RX of module

pin number 3 is connected to Red wire that is TX of module

and pin number 5 is connected to black wire that is Ground

solder all three wires with soldering iron as shown in figure and then mount plastic

casing on it so your serial connector will be ready to use


http://robosoftsystems.co.in/blog/wp-content/uploads/2009/09/how-to-connect-RFmodule-to-PC-9.JPG


The pin description is given in the following table:

Table4.4: Pin descriptions of rs232

Pin

number

Common

Name

RS232

name

Description Signal

direction

1 /CD CF Received line signal

detector

IN

2 RXD BB Received data IN

3 TXD BA Transmitted data OUT

4 /DTR CD Data terminal ready OUT

5 GND AB Signal ground --

6 /DSR CC Data set ready IN

7 /RTS CA Request to send OUT

8 /CTS CB Clear to send IN

9 -- CE Ring indicator IN

We cannot simply connect our system to this terminal without providing proper

hand shaking signal. For communicating with RS-232 type equipment, the /RTS of the

connector is simply looped into the /CTS, so /CTS will automatically be asserted when

/RTS is asserted internally. Similarly the /DTR is looped into /DSR and /CD, so when

COMPUTER asserts its /DTR output the /DSR and /CD inputs are automatically be

asserted.

These connections do not provide for any hardware hand shaking. They are

necessary to get the COMPUTER and our system talk each other.



The connection diagram is shown below.

Figure4.19: Connection diagram of db-9 and rs232

Table 4.5: pin functions of max232


Tx 3 Rx 2 /CTS 8

/

RTS 7

/DSR 6

/DTR 4 /CT 1

GND 5

2 Rx3 Tx

5 GND


Abbreviation Full name Function

TD Transmit Data Serial Data Output (TXD)

RD Receive Data Serial Data Input (RXD)

CTS Clear to Send This line indicates that the

Modem is ready to exchange

data.

DCD Data Carrier Detect When the modem detects a

"Carrier" from the modem at

the other end of the phone

line, this Line becomes

active.

DSR Data Set Ready This tells the UART that the

modem is ready to establish

a link.

DTR Data Terminal Ready This is the opposite to DSR.

This tells the Modem that

the UART is ready to link.

RTS Request To Send This line informs the

Modem that the UART is

ready to exchange data.

RI Ring Indicator Goes active when modem

detects a ringing signal from

the PSTN.

4.7 Advantages and disadvantages



Advantages

1. Not line of sight.

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

walls.

3. Longer range.

4. Not light sensitive.

5. Not as sensitive to weather/environmental conditions.

Disadvantages

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

scanners, wrist radios and personal locators can interfere with transmission.

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

out in space rather than confined to a wire.

3. Higher cost than infrared.

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

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



Chapter five

Result and Discussions



5.0 Result and Discussion

The main aim of this project is to transfer information from one computer to

another computer by using RF. BIOSCOM is one of the method used in TURBO C. It is

also performance important role in this project. First, design the circuits in one procedure.

This project contains two circuit sections one is transmitter section and another is receiver

section. Now, transmitter section is connected to one computer by using db9 pin and

receiver section is connected to another computer by using another db9 pin.

Before sending the information first install the TURBO C software in both

computers. TURBO C is divided into two methods. Here we are using bioscom method.

After installation run the desired program then it displays empty screen. Now type the

information.

For example, in transmitting computer type “HELLO WORLD” .Now, the desired

information is transmitted to transmitter circuit with the help of db9. Transmitter circuit

contains RS232 and RF transmitter.

RS 232 send the data serially and RF transmitter is used to send data with constant

frequency i.e 433.3 MHz. Now this data sends to given antenna.

The transmitting signals by the transmitting antenna are taken by the receiving

antenna. The received signals are sends to RF receiver and to RS232 devices.RS232 sends

the data to computer serially. Now, the required information “HELLO WORLD” is

displays on screen.



Chapter six

Conclusion and Future Scope

Conclusion

Future Scope



6.1 Conclusion

It allows communicating with the computer. The thought would be to have the

transmitter connected to the transmitter and the receiver connected to the computer. In that

way it detects something and notifies the computer. The computer would monitor the serial

port and then do an action based on the values passed.

The above project has shown the successful implementation of wireless

communication using RF. A Transmitter kit is developed and connected to computer to

receive the character, the character is then encoded and transmitted through radio

frequency.

At the end of receiver section the decoder will decode the encoded data. The

receiver data is then transmitted to another computer. This concludes the communication of

data from computer to computer.

6.2 Future scope

In this project we just construct a small prototype model, which is having one-way

communication that means the data or information is transferred from transmitter to

receiver only and there is no chance to receiver to send data to the receiver. So, in future by

using of transceivers in place of transmitter and receiver we can overcome the above

problem.

Antennas used in this project are having strength to transmit and receive signals

below 50meters distance only. In future, there is a chance to increase the capacity of

antennas for longer distance communications.



References

Books

C programming for embedded systems- Kirk Zurell

Teach yourself electronics and electricity- Stan Giblisco

Embedded Microcomputer system- onathan w.Valvano(2000)

Telecommunication and computer by Martin

Web sites

www.Microchips.com

http://www.mikroelektronika.co.yu/english/product/books/PICbook/

0_Uvod.htm

www.how stuff works.com

www.texasinstruments.com

www.nationalsemiconductors.com

www.fairchildsemiconductors.com


http://www.fairchildsemiconductors.com/

http://www.nationalsemiconductors.com/

http://www.texasinstruments.com/

http://www.mikroelektronika.co.yu/english/product/books/PICbook/0_Uvod.htm

http://www.mikroelektronika.co.yu/english/product/books/PICbook/0_Uvod.htm

Documents

PC2PC Mini Project Documentation