Wireless electronic notice board using gsm technolgy

[MGM’s COE NANDED] Page 1

WIRELESS ELECTRONIC NOTICE BOARD USING GSM TECHNOLGY

Chapter 1

INTRODUCTION

1.1 INTRODUCTION TO GSM

A digital mobile telephony system, which is globally accessed by more than 212

countries and territories. Global system for mobile communication is completely

optimized for full duplex voice telephony. Initially developed for the replacement of

first generation (1G) technology, now GSM is available with lots of salient features

with the constant up gradation of third generation (3G) technology. And now with the

alliance of microcontroller, GSM MODEM could be further tailor-made for some of

very innovative applications including GSM based Wireless electronic notice board ,

GSM based DC motor controller, GSM based home security system, GSM based

robot control, GSM based voting machine control, GSM based stepper motor

controller etc.

1.2 INTRODUCTION TO EMBEDDED SYSTEM

Embedded systems have grown tremendously in recent years, not only in their

popularity but also in their complexity. Gadgets are increasingly becoming intelligent

and autonomous. Refrigerators, air-conditioners, automobiles, mobile phones etc are

some of the common examples of devices with built in intelligence. These devices

function based on operating and environmental parameters.

The intelligence of smart devices resides in embedded systems. An embedded

system, in general, in co-operates hardware, operating systems, low-level software

binding the operating system and peripheral devices, and communication software to

enable the device to perform the pre-defined functions. An embedded system

performs a single, well-defined task, is tightly constrained, is reactive and computes

results in real time.

Let us take a detailed look at these features of embedded systems:

Single functioned: An embedded system executes a specific program repeatedly. For

example, a pager is always a pager. In contrast a desktop system executes a variety of

programs like spreadsheets, word processors, etc. However there are exceptions

where in an embedded system’s program is updated with newer program versions.

Cell phones are examples of being updated in such a manner.



Tightly constrained: All computing systems have constraints on design metrics but

those on embedded systems can be especially tight. A design metric is a measure of

an implementation’s features, such as cost, size performance and power.

Reactive and real time: Many embedded systems must continually react to changes in

the system’s environment and must compute certain results in real time without delay.

1.2.1 Embedded Hardware

All embedded systems need a microprocessor, and the kinds of

microprocessors used in them are quite varied. A list of some of the common

microprocessor families is the ZILOG Z8 family, Intel 805/80188/x 86 families,

Motorola 68k family and the PowerPC family.

1.2.2 Embedded Software

The software for the embedded systems is called firmware. The firmware will

be written in assembly languages for time or resource critical operations or using

higher-level languages like C or embedded C. The software will be simulated using

micro code simulators for the target processor. Since they are supposed to perform

only specific tasks these programs are stored in Read Only Memories (ROM’s).

1.2.3 Application areas for embedded systems

Embedded software is present in almost every electronic device you use today.

There is embedded software inside your watch, cellular phone, automobile,

thermostats, Industrial control equipment and scientific and medical equipment.

Defence services use embedded software to guide missiles and detect aircraft’s.

Communication satellites, medical instruments and deep space probes would have

been nearly impossible without these systems. Embedded systems cover such as broad

range of products that generalization is difficult.



1.2.4 Block diagram of Embedded System:

Figure 1.1: Embedded System Block Diagram

Software deals with the languages like ALP, C, and VB etc., and Hardware deals with

Processors, Peripherals, and Memory. Memory is used to store data or address.

Processor is an IC which is used to perform some task. There are four types of

processor Micro Processor (µp), Micro controller (µc),Digital Signal Processor

(DSP), Application Specific Integrated Circuits (ASIC).

Embedded

System

Software Hardware

o ALP

o C

o VB

Etc.,

o Processor

o Peripherals

o memory



CHAPTER 2

DESIGN OVERVIEW

2.1 BLOCK DIAGRAM OF GSM-BASED E-NOTICE BOARD:

Figure.2.1 Block diagram of wireless notice board

Figure.2.2 Basic Overview



2.2 HISTORY OF GSM

During the early 1980s, analog cellular telephone systems were experiencing rapid

growth in Europe, particularly in Scandinavia and the United Kingdom, but also in

France and Germany. Each country developed its own system, which was

incompatible with everyone else's in equipment and operation. This was an

undesirable situation, because not only was the mobile equipment limited to operation

within national boundaries, which in a unified Europe were increasingly unimportant,

but there was also a very limited market for each type of equipment, so economies of

scale and the subsequent savings could not be realized.

The Europeans realized this early on, and in 1982 the Conference of European

Posts and Telegraphs (CEPT) formed a study group called the Groupe Spécial

Mobile (GSM) to study and develop a pan-European public land mobile system. And

interaction with the Integrated service digital network (ISDN) which offers the

capability to extend the single-subscriber –line system with the various to a

multiservice system. The first commercial GSM system, called D2, was implemented

in Germany in 1982. This valuable channel of communication can equip us with a

powerful tool for controlling desired device or process parameter from distant

location, through electromagnetic waves. With a little effort logic can be setup to even

receive a feedback on the status of the device or the process being controlled.

2.3 SERVICES PROVIDED BY GSM

From the beginning, the planners of GSM wanted ISDN compatibility in terms of the

services offered and the control signalling used. However, radio transmission

limitations, in terms of bandwidth and cost, do not allow the standard ISDN B-

channel bit rate of 64 kbps to be practically achieved. Using the ITU-T definitions,

telecommunication services can be divided into bearer services, teleservices, and

supplementary services. The most basic teleservice supported by GSM is telephony.

As with all other communications, speech is digitally encoded and transmitted

through the GSM network as a digital stream. There is also an emergency service,

where the nearest emergency-service provider is notified by dialing three digits.



A variety of data services is offered. GSM users can send and receive data, at

rates up to 9600 bps, to users on POTS (Plain Old Telephone Service), ISDN, Packet

Switched Public Data Networks, and Circuit Switched Public Data Networks using a

variety of access methods and protocols, such as X.25 or X.32. Since GSM is a digital

network, a modem is not required between the user and GSM network, although an

audio modem is required inside the GSM network to interwork with POTS. Other

data services include Group 3 facsimile, as described in ITU-T recommendation T.30,

which is supported by use of an appropriate fax adaptor. A unique feature of GSM,

not found in older analog systems, is the Short Message Service (SMS). SMS is a

bidirectional service for short alphanumeric (up to 160 bytes) messages. Messages are

transported in a store-and-forward fashion. For point-to-point SMS, a message can be

sent to another subscriber to the service, and an acknowledgement of receipt is

provided to the sender. SMS can also be used in a cell-broadcast mode, for sending

messages such as traffic updates or news updates. Messages can also be stored in the

SIM card for later retrieval .

Supplementary services are provided on top of teleservices or bearer services.

In the current (Phase I) specifications, they include several forms of call forward

(such as call forwarding when the mobile subscriber is unreachable by the network),

and call barring of outgoing or incoming calls, for example when roaming in another

country. Many additional supplementary services will be provided in the Phase 2

specifications, such as caller identification, call waiting, multi-party conversations.

2.4 ARCHITECTURE OF THE GSM NETWORK

A GSM network is composed of several functional entities, whose functions and

interfaces are specified. Figure 1.1 shows the layout of a generic GSM network. The

GSM network can be divided into three broad parts. The Mobile Station is carried by

the subscriber. The Base Station Subsystem controls the radio link with the Mobile

Station. The Network Subsystem, the main part of which is the Mobile services

Switching Center (MSC), performs the switching of calls between the mobile users,

and between mobile and fixed network users. The MSC also handles the mobility

management operations. Not shown is the Operations and Maintenance Center, which

oversees the proper operation and setup of the network. The Mobile Station and the

Base Station Subsystem communicate across the Um interface, also known as the air



interface or radio link. The Base Station Subsystem communicates with the Mobile

services Switching Center across the A interface.

Fig. 2.3 General Architecture of a GSM Network

2.4.1 Mobile Station

The mobile station (MS) consists of the mobile equipment (the terminal) and a smart

card called the Subscriber Identity Module (SIM). The SIM provides personal

mobility, so that the user can have access to subscribed services irrespective of a

specific terminal. By inserting the SIM card into another GSM terminal, the user is

able to receive calls at that terminal, make calls from that terminal, and receive other

subscribed services. The mobile equipment is uniquely identified by the International

Mobile Equipment Identity (IMEI). The SIM card contains the International Mobile

Subscriber Identity (IMSI) used to identify the subscriber to the system, a secret key

for authentication, and other information. The IMEI and the IMSI are independent,

thereby allowing personal mobility. The SIM card may be protected against

unauthorized use by a password or personal identity number.



2.4.2 Base Station Subsystem

The Base Station Subsystem is composed of two parts, the Base Transceiver Station

(BTS) and the Base Station Controller (BSC). These communicate across the

standardized Abis interface, allowing (as in the rest of the system) operation between

components made by different suppliers. The Base Transceiver Station houses the

radio transceivers that define a cell and handles the radio-link protocols with the

Mobile Station. In a large urban area, there will potentially be a large number of BTSs

deployed, thus the requirements for a BTS are ruggedness, reliability, portability, and

minimum cost.

The Base Station Controller manages the radio resources for one or more

BTSs. It handles radio-channel setup, frequency hopping, and handovers, as described

below. The BSC is the connection between the mobile station and the Mobile service

Switching Center (MSC).

2.4.3 Network Subsystem

The central component of the Network Subsystem is the Mobile services Switching

Center (MSC). It acts like a normal switching node of the PSTN or ISDN, and

additionally provides all the functionality needed to handle a mobile subscriber, such

as registration, authentication, location updating, handovers, and call routing to a

roaming subscriber. These services are provided in conjuction with several functional

entities, which together form the Network Subsystem. The MSC provides the

connection to the fixed networks (such as the PSTN or ISDN). Signalling between

functional entities in the Network Subsystem uses Signalling System Number 7

(SS7), used for trunk signalling in ISDN and widely used in current public networks.

The Home Location Register (HLR) and Visitor Location Register (VLR),

together with the MSC, provide the call-routing and roaming capabilities of GSM.

The HLR contains all the administrative information of each subscriber registered in

the corresponding GSM network, along with the current location of the mobile. The

location of the mobile is typically in the form of the signalling address of the VLR

associated with the mobile station. The actual routing procedure will be described

later. There is logically one HLR per GSM network, although it may be implemented



as a distributed database. The Visitor Location Register (VLR) contains selected

administrative information from the HLR, necessary for call control and provision of

the subscribed services, for each mobile currently located in the geographical area

controlled by the VLR. Although each functional entity can be implemented as an

independent unit, all manufacturers of switching equipment to date implement the

VLR together with the MSC, so that the geographical area controlled by the MSC

corresponds to that controlled by the VLR, thus simplifying the signalling required.

Note that the MSC contains no information about particular mobile stations --- this

information is stored in the location registers.

The other two registers are used for authentication and security purposes. The

Equipment Identity Register (EIR) is a database that contains a list of all valid mobile

equipment on the network, where each mobile station is identified by its International

Mobile Equipment Identity (IMEI). An IMEI is marked as invalid if it has been

reported stolen or is not type approved. The Authentication Center (AuC) is a

protected database that stores a copy of the secret key stored in each subscriber's SIM

card, which is used for authentication and encryption over the radio channel.



CHAPTER 3

MICROCONTROLLER

Basically, a microcontroller is a device which integrates a number of the components

of a microprocessor system onto a single microchip. So a microcontroller combines

onto the same microchip. The components are CPU Core ,Memory (Both RAM and

ROM),Some Parallel Digital I/Os.The microprocessor is the integration of a number

of useful functions into a single IC package. Has the ability to execute a stored set of

instructions to carry out user defined tasks; also has ability to access external memory

chips to both read and write data from and to the memory.

Essentially, a microcontroller is obtained by integrating the key components of

microprocessor, RAM, ROM, and Digital I/O onto the same chip die. Modern

microcontrollers also contain a wealth of other modules such as Serial I/O, Timers,

and Analogue to Digital Converters. There are a large number of specialized devices

with additional modules for specific needs.

3.1 MICROCONTROLLER (AT89S52)

Microcontroller AT89S52 has following features ,Compatible with MCS-51 Products

8K Bytes of In-System Programmable (ISP) Flash Memory ,4.0V to 5.5V Operating

Range, Fully Static Operation: 0 Hz to 33 MHz, 256Bytes Internal RAM,32

Programmable I/O Lines,3 16-bit Timer/Counters, Full Duplex UART Serial

Channel.

3.2 DESCRIPTION OF MICROCONTROLLER AT 89S52:

The AT89S52 is a low-power, high-performance CMOS 8-bit micro controller with

8Kbytes of in-system programmable Flash memory. The device is manufactured

using Atmel’s high-density non-volatile memory technology and is compatible with

the industry-standard 80C51 micro controller. The on-chip Flash allows the program

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

programmer. By combining a versatile 8-bit CPU with in-system programmable flash



one monolithic chip; the Atmel AT89S52 is a powerful micro controller, which

provides a highly flexible and cost- effective solution to many embedded control

applications.

Fig. 3.1 Block Diagram of AT 89S52 microcontroller



Fig.3.2 pin configuration

The AT89S52 provides the following standard features: 8K bytes of Flash, 256

bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit

timer/counters, full duplex serial port, on-chip oscillator, and clock circuitry. In

addition, the AT89S52 is designed with static logic for perationdown to zero

frequency and supports two software selectable power saving modes. The Idle

Mode stops the CPU while allowing the RAM timer/counters, serial port, and

interrupt system to continue functioning. The Power-down mode saves the RAM

contents but freezes the oscillator, disabling all other chip functions until the next

interrupt or hardware reset.



3.3 PIN DESCRIPTION OF MICROCONTROLLER AT89S52

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 1sare written to port 0 pins, the pins

can be used as high impedance inputs. Port 0 can 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. In addition,

P1.0 and P1.1 can be configured to be the timer/counter 2 external count input

(P1.0/T2) and the timer/counter 2 trigger input P1.1/T2EX), respectively, as shown in

the following table. Port 1 also receives the low-order address bytes during flash

programming .

Table.3.1 Port 1 functions

Port 2: Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2

output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins,

they are pulled high by the internal pull-ups and can be used as inputs. Port 2 emits

the high-order address byte during fetches from external program memory and during

accesses to external data memory that uses 16-bit addresses (MOVX @DPTR). In this



application, Port 2 uses strong internal pull-ups when emitting 1s. During accesses to

external data memory that use 8-bit addresses (MOVX @ RI), Port 2emits the

contents of the P2 Special Function Register. Port 2 also receives the high-order

address bits and some control signals during Flash programming and verification.

Port 3:Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 3

output buffers can sink/source four TTL inputs. When 1s are written to Port 3

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

inputs, Port 3 pins that are externally being pulled low will source current (IIL)

because of the pull-ups. Port 3 also serves the functions of various special

features of the AT89S52, as shown in the following table. Port 3 also receives

some control signals for Flash programming and verification.

Table. 3.2 port 3 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 (ALE) is an 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 of1/6 the 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 (PSEN) is the read strobe to external program

memory. When the AT89S52 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.

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. A should be strapped to VCC for internal program

executions. This pin also receives the 12-voltProgramming enables voltage (VPP)

during Flash programming.

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 that can be configured for use as an on-

chip oscillator, as shown in Figure 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 2.

Fig.3.3 circuit diagram of crystal oscillator



3.4 Microcontroller – MODEM Interfacing

3.4.1 DTE and DCE

The terms DTE and DCE are very common in the data communications market. DTE

is short for Data Terminal Equipment and DCE stands for Data Communications

Equipment. But what do they really mean? As the full DTE name indicates this is a

piece of device that ends a communication line, whereas the DCE provides a path for

communication. Let's say we have a computer on which wants to communicate with

the Internet through a modem and a dial-up connection. To get to the Internet you tell

your modem to dial the number of your provider. After your modems has dialed the

number, the modem of the provider will answer your call and your will hear a lot of

noise. Then it becomes quiet and you see your login prompt or your dialing program

tells you the connection is established. Now you have a connection with the server

from your provider and you can wander the Internet. In this example you PC is a Data

Terminal (DTE). The two modems (yours and that one of your provider) are DCEs,

sthey make the communication between you and your provider possible. But now we

have to look at the server of your provider.

Is that a DTE or DCE? The answer is a DTE. It ends the communication line between

you and the server. When you want to go from your provided server to another place

it uses another interface. So DTE and DCE are interfacing dependent. It is e.g.

possible that for your connection to the server, the server is a DTE, but that that same

server is a DCE for the equipment that it is attached to on the rest of the Net.

3.4.2 RS-232

In telecommunications, RS-232 is a standard for serial binary data signals connecting

between a DTE (Data terminal equipment) and a DCE (Data Circuit-terminating

Equipment). It is commonly used in computer serial ports. In RS-232, data is sent as a

time-series of bits. Both synchronous and asynchronous transmissions are supported

by the standard. In addition to the data circuits, the standard defines a number of

control circuits used to manage the connection between the DTE and DCE. Each data

or control circuit only operates in one direction that is, signaling from a DTE to the

attached DCEor the reverse. Since transmit data and receive data are separate circuits,

the interface can operate in a full duplex manner, supporting concurrent data flow in



both directions. The standard does not define character framing within the data

stream, or character encoding.

Fig 3.4 Female 9 pin plug

Table.3.3 RS232 signals

3.4.3 RS-232 Signals

Transmitted Data (TxD) :Data sent from DTE to DCE.

Received Data (RxD) :Data sent from DCE to DTE.

Request To Send (RTS) :Asserted (set to 0) by DTE to prepare DCE to receive data.

This may require action on the part of the DCE, e.g. transmitting a carrier or reversing

the direction of a half-duplex line.



Clear To Send (CTS): Asserted by DCE to acknowledge RTS and allow DTE to

transmit.

Data Terminal Ready (DTR): Asserted by DTE to indicate that it is ready to be

connected. If the DCE is a modem, it should go "off hook" when it receives this

signal. If this signal is deasserted, the modem should respond by immediately hanging

up.

Data Set Ready (DSR): Asserted by DCE to indicate an active connection. If DCE is

not a modem (e.g. anull-modem cable or other equipment), this signal should be

permanently asserted (set to 0), possibly by a jumper to another signal.

Carrier Detect (CD): Asserted by DCE when a connection has been established with

remote equipment.

Ring Indicator (RI) :Asserted by DCE when it detects a ring signal from the

telephone line.

3.4.4 RTS/CTS Handshaking

The standard RS-232 use of the RTS and CTS lines is asymmetrical. The DTE asserts

RTS to indicate a desire to transmit and the DCE asserts CTS in response to grant

permission. This allows for half-duplex modems that disable their transmitters when

not required, and must transmit a synchronization preamble to the receiver when they

are reenabled. There is no way for the DTE to indicate that it is unable to accept data

from the DCE. A non-standard symmetrical alternative is widely used: CTS indicates

permission from the DCE for the DTE to transmit, and RTS indicates permission from

the DTE for the DCE to transmit. The "request to transmit" is implicit and continuous.

The standard defines RTS/CTS as the signaling protocol for flow control for data

transmitted from DTE to DCE. The standard has no provision for flow control in the

other direction. In practice, most hardware seems to have repurposed the RTS signal

for this function. A minimal “3-wire” RS-232 connection consisting only of transmits

data, receives data and ground, and is commonly used when the full facilities of RS-

232 are not required. When only flow control is required, the RTS and CTS lines are

added in a 5-wire version. In our case it was imperative that we connected the RTS

line of the microcontroller (DTE) to ground to enable receipt of bit streams from the

modem.



3.4.5 Specifying Baud Rate, Parity & Stop bits

Serial communication using RS-232 requires that you specify four parameters: the

baud rate of the transmission, the number of data bits encoding a character, the sense

of the optional parity bit, and the number of stop bits. Each transmitted character is

packaged in a character frame that consists of a single start bit followed by the data

bits, the optional parity bit, and the stop bit or bits. A typical character frame encoding

the letter "m" is shown here. Character Frame Encoding ‘m’ We specified the

parameters as baud rate – 4800 bps, 8 data bits, no parity, and 1 stop bit. This was set

in pre-operational phase while setting up the modem through the hyper terminal, as

per the serial transmission standards in 8051 microcontroller.

Fig.3.5 Character Frame Encoding ‘m’

3.4.5.1. DCE Baud Rates

110,300,1200,2400,4800,9600,19200,38400,57600,115200,230400,460800,921600

(Possible Baud Rates)

Baud Rate Used Power on default rate



3.5 Microcontroller – LCD Interfacing

Fig.3.6 LCD Interfacing

Above is the quite simple schematic. The LCD panel’s Enable and Register Select is

connected to the Control Port. The Control Port is an open collector / open drain

output. While most Parallel Ports have internal pull-up resistors, there are a few which

don’t. Therefore by incorporating the two 10K external pull up resistors, the circuit is

moreportable for a wider range of computers, some of which may have no internal

pull up resistors. We make no effort to place the Data bus into reverse direction.

Therefore we hard wire the R/W line of the LCD panel, into write mode. This will

cause no bus conflicts on the data lines. As a result we cannot read back the LCD’s

internal Busy Flag which tells us if the LCD has accepted and finished processing the

last instruction. This problem is overcome by inserting known delays into our

program. The 10k Potentiometer controls the contrast of the LCD panel. Nothing

fancy here. As with all the examples, I’ve left the power supply out. You can use a

bench power supply set to 5v or use a onboard +5 regulator.The user may select

whether the LCD is to operate with a 4-bit data bus or an 8- bit data bus. If a 4-bit

data bus is used, the LCD will require a total of 7 data lines. If an 8-bit data bus is

used, the LCD will require a total of 11 data lines. The three control lines are EN, RS,

and RW. Note that the EN line must be raised/lowered before/after each instruction

sent to the LCD regardless of whether that instruction is read or write text or

instruction. In short, you must always manipulate EN when communicating with the

LCD. EN is the LCD’s way of knowing that you are talking to it. If you don’t

raise/lower EN, the LCD doesn’t know you’re talking to it on the other lines.



3.6 LIQUID CRYSTAL DISPLAY

A liquid crystal display (LCD) is a thin, flat display device made up of any number of

color or monochrome pixels arrayed in front of a light source or reflector. Each pixel

consists of a column of liquid crystal molecules suspended between two transparent

electrodes, and two polarizing filters, the axes of polarity of which are perpendicular

to each other. Without the liquid crystals between them, light passing through one

would be blocked by the other. The liquid crystal twists the polarization of light

entering one filter to allow it to pass through the other.For an 8-bit data bus, the display

requires a +5V supply plus 11 I/O lines. For a 4-bit data bus it only requires the supply

lines plus seven extra lines. When the LCD display is not enabled, data lines are tri-state

and they do not interfere with the operation of the microcontroller.

Data can be placed at any location on the LCD. For 16×2 LCD, the address

locations

First

line

80 81 82 83 84 85 86 through 8F

Second

line

C0 C1 C2 C3 C4 C5 C6 through CF

Table. 3.4 Address location for a 2/16 line LCD

3.6.1 SIGNAL TO LCD

The LCD also requires 3 control lines from the microcontroller:

A. Enable:This line allows access to the display through R/W and RS lines. When

this line is low, the LCD is disabled and ignores signals from R/W and RS. When

(E) line is high, the LCD checks the state of the two control lines and responds

accordingly

B. Read/Write(R/W):This line determines the direction of data between the

LCD and microcontroller.When it is low, data is written to the LCD. When

it is high, data is read from LCD.

C. Register select(RS):With the help of this line, the LCD interprets the type of

data on data lines. When it is low, an instruction is being written to the LCD.



3.6.2 writing and reading the data from LCD

Writing data to the LCD is done in several steps:

1) Set R/W bit to low

2) Set RS bit to logic 0 or 1 (instruction or character)

3) Set data to data lines (if it is writing)

4) Set E line to high

5) Set E line to low Read data from data lines (if it is reading)

1) Set R/W bit to high

2) Set RS bit to logic 0 or 1 (instruction or character)

3) Set data to data lines (if it is writing)

4) Set E line to high

5) Set E line to low

3.7 PIN DESCRIPTION

Most LCDs with 1 controller has 14 Pins and LCDs with 2 controller has 16 Pins

(two pins are extra in both for back-light LED connections).

Fig.3.7 Basic LCD Interfacing Circuit



Table.3.5 Pin Configuration of 16X2 Lcd



Table 3.5 Control Codes of LCD



CHAPTER 4

HARDWARE PROFILE

4.1 BLOCK DIAGRAM OF WIRELESS NOTICE BOARD

Fig.4.1 block diagram of wireless notice board



4.2 POWER SUPPLY

The power supply unit is used to provide a constant 5V of DC supply from a 230V of AC

supply. These 5V DC will acts as power to different standard circuits. It mainly consists of

follwing blocks.

Fig. 4.2 Block Diagram Of Power Supply

4.2.1 BRIDGE WAVE RECTIFIER

A rectifier is an electrical device that converts alternating current (AC) to direct current

(DC), a process known as rectification. The term rectifier describes a diode that is being

used to convert AC to DC. A bridge-wave rectifier converts the whole of the input

waveform to one of constant polarity (positive or negative) at its output. Bridge-wave

rectifier converts both polarities of the input waveform to DC (direct current), and is more

efficient. However, in a circuit with a center tapped transformer (9-0-9) is used.

Fig.4.3 Bridge Wave Rectifier

For single-phase AC, if the transformer is center-tapped, then two diodes back-to-back(i.e.

anodes-to-anode or cathode-to-cathode) can form a full-wave rectifier. Many windings are

required on the transformer secondary to obtain the same output voltage.



In this only two diodes are activated at a time i.e. D1 and D3 activate for positive cycle

and D2 and D4 activates for negative half cycle. D2 and D4 convert negative cycle to

positive cycle as it as negative supply and negative cycle as positive cycle at its output.

4.2.2 VOLTAGE REGULATOR

This is most common voltage regulator that is still used in embedded designs.

LM7805 voltage regulator is a linear regulator. With proper heat sink these LM78xx

types can handle even more than 1A current. They also have Thermal overload

protection, Short circuit protection. This will connect at the output of rectifier to get

constant Dc supply instead of ripple voltages. It mainly consists of 3 pins That are

input voltage, ground, output voltage. For some devices we require 12V/9V/4V Dc

supply at that time we go for 7812/7809/7804 regulator instead of 7805 regulator. It

also have same feature and pins has 7805 regulator except output is of 12V/9V/4V

instead of 5V.The general circuit diagram for total power supply to any embedded

device is as shown below.

Fig.4.4 general circuit diagram for total power supply



4.3 UART

Fig.4.5 UART Block Diagram

Atmel microcontroller features a full duplex (separate receive and transmit registers)

Universal Asynchronous Receiver and Transmitter (UART).The main features are

Baud rate generator that can generate a large number of baud rates (bps) , High baud

rates at low XTAL frequencies, 8 or 9 bits data, Noise filtering, Overrun detection

Framing Error detection, False Start Bit detection,Three separate interrupts on TX

Complete, TX Data Register Empty and RX Complete.The alternative function of

portd0, portd1 is UART. Portd0 is the receiver pin and portd1 is the transmitter pin.

Here we are using IC MAX232 as a UART driver.This micro controller board

contains max232 IC which is used as a voltage converter.



Fig.4.6 Max 232 Schematics

The output supply of computer will be 10V and we require 5V of supply for our

microcontroller board.When we want to take some input from the computer to the

micro controller, then we require some means in order to down convert that 10V to

5V. This is done through max232 IC. Similarly, when we are reading some thing from

the micro controller in to the micro controller, then we need some up converter that

converts 5V to 10V to the computer. This is also done through max232 only.This all

work is done through the 4 capacitors present near the max232. These capacitors

provide charge when required and store the charge when not required.So, Max232

requires power supply of 5V,2 RS232 Drivers,4 External Capacitors of 1micro farad

Dual charge pumps DC-DC voltage converters ,Receiver and Transmitter Enable

control pins.Temperature of 00to +70

0 . The transmit pin of the micro controller [txd]

pin 11 is connected to pin no 10 of MAX 232 IC. The receive pin of the micro

controller [rxd] pin 10 is connected to pin no 9 of MAX 232 IC. In the DB9 connector

pin no 5 is GROUND. Pin no 2 is receive pin. Pin no 3 is Transmit pin.



4.4 NULL MODEMS

A Null Modem is used to connect two DTE's together. This is commonly used as a

cheap way to network games or to transfer files between computers using Zmodem

Protocol, Xmodem Protocol etc. This can also be used with many Microprocessor

Development Systems.

Fig.4.7 Null Modem Wiring Diagram

Above is my preferred method of wiring a Null Modem. It only requires 3 wires (TD,

RD & SG) to be wired straight through thus is more cost effective to use with long

cable runs. The theory of operation is reasonably easy. The aim is to make to

computer think it is talking to a modem rather than another computer. Any data

transmitted from the first computer must be received by the second thus TD is

connected to RD. The second computer must have the same set-up thus RD is

connected to TD. Signal Ground (SG) must also be connected so both grounds are

common to each computer.

The Data Terminal Ready 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's

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

send and does so.



4.5 GSM MODEM

GSM Modem Product, from Sparr Electronics limited (SEL), provides full functional

capability to Serial devices to send SMS and Data over GSM Network. The product is

available as Board Level or enclosed in Metal Box. The Board Level product can be

integrated in to Various Serial devices in providing them SMS and Data capability

and the unit housed in a Metal Enclosure can be kept outside to provide serial port

connection. The GSM Modem supports popular "AT" command set so that users can

develop applications quickly. The product has SIM Card holder to which activated

SIM card is inserted for normal use. The power to this unit can be given from UPS to

provide uninterrupted operation. This product provides great feasibility for Devices in

remote location to stay connected which otherwise would not have been possible

where telephone lines do not exist.

The GSM module offers the advantages as, Ultra small size (22x22x3 mm),

lightweight (3.2 g) and easy to integrate, Low power consumption,R&TTE type

approval plus CE, GCF, FCC,PTCRB, IC, Full RS232 on CMOS level with flow

control (RX,TX, CTS, RTS, CTS, DTR, DSR, DCD, RI) High performance on low

price

Product Features are,

A. E-GSM 900/1800 MHz and GSM 1800/1900 with GSM Phase 2 / 2+

B. Control via AT commands (ITU, GSM, GPRS and manufacturer supplementary)

C. Supply Voltage range: 3.22 V - 4.2 V,nominal:3.8V

D. Power consumption: Idle mode: <1.8 mA, speech mode: 200 mA (average)

Figure.4.8 Connection Diagram



4.5.2 GSM MODULE WITH RS232

Full Type Approved Quad Band Embedded GSM Module (GSM 850/900 1800/1900)

with AT command set and RS232 interface on CMOS level shown in figure 2. This

GSM wireless data module is the ready a solution for remote wireless applications,

machine to machine or user to machine and remote data communications in all

vertical market applications. A range of dual band GSM radio modems, which give

compatible mobile devices wireless connectivity using the GSM900/1800 cellular

networks. Each modem interfaces to the host via a Universal Synchronous /

Asynchronous Serial Receiver-Transmitter (USART), which is automatically detected

by the operating system and easily configured using standard operating system

drivers.The modems are controlled by industry standard AT commands

Figure.4.9 GSM modem



CHAPTER 5

SOFTWARE PROFILE

5.1 User Perspective

Figure 5.1 User Perspective Flowchart

The above given flowchart gives the end user perspective on the control flow. During

normal operations the LCD reads a message from a fixed memory location in the

Microcontroller and displays it continuously, until a new message arrives for

validation. It is then when a branching occurs basing on the validity of the sender’s

number and further taking into account the priority assigned to the new message in

comparison to the previous one.



Figure 5.2 operational flowchart

5.2. Control Flow in Code

5.2.1. Initializations

The baud rate of the modem was set to be 4800 bps using the command

AT+IPR=4800.The ECHO from the modem was turned off using the command

ATE/ATE0 at the hyper terminal. For serial transmission and reception to be possible

both the DTE and DCE should have same operational baud rates. Hence to set the

microcontroller at a baud rate of 4800bps, we set terminal count of Timer 1 at 0FFh

(clock frequency = 1.8432). The TCON and SCON registers were set accordingly.



5.2.2. Serial transfer using TI and RI flags

After setting the baud rates of the two devices both the devices are now ready to

transmit and receive data in form of characters. Transmission is done when TI flag is

set and similarly data is known to be received when the Rx flag is set. The

microcontroller then sends an AT command to the modem in form of string of

characters serially just when the TI flag is set. After reception of a character in the

SBUF register of the microcontroller (response of MODEM with the read message in

its default format or ERROR message or OK message), the RI flag is set and the

received character is moved into the physical memory of the microcontroller.

5.2.3. Validity Check

After serially receiving the characters the code then checks for start of the sender’s

number and then compares the number character by character with the valid number

prestored in the memory. Since we are employing just one valid number, we are able

to do the validation process dynamically i.e. without storing the new message in

another location in the memory. For more than one valid numbers we would require

more memory locations to first store the complete (valid/invalid) message in the

memory and then perform the comparison procedure.

5.2.4 Display

After validity check the control flow goes into the LCD program module to display

the valid message stored in the memory. In case of multiple valid numbers all invalid

stored messages are deleted by proper branching in the code to the “delete-message”

module.

5.3 SHORT MESSAGE COMMANDS

5.3.1READ MESSAGE +CMGR

5.3.1.1 Description

This command allows the application to read stored messages. The messages are read

from the memory selected by +CPMS command.



5.3.1.2 Syntax

Command syntax : AT+CMGR=<index>

Response syntax for text mode:

+CMGR : <stat>,<oa>,[<alpha>,] <scts> [,<tooa>,<fo>,

<pid>,<dcs>,<sca>,<tosca>,<length>] <CR><LF> <data> (for SMS

MS MS-DELIVER only)

+CMGR : <stat>,<da>,[<alpha>,] [,<toda>,<fo>,<pid>,<dcs>, [<vp>], <sca>,

<tosca>,<length>]<CR><LF> <data> (for SMS-SUBMIT only)

+CMGR : <stat>,<fo>,<mr>,[<ra>],[<tora>],<scts>,<dt>,<st> (for SMS SMS

STATUS-REPORT only)

5.3.2Response syntax for PDU mode :

+CMGR: <stat>, [<alpha>] ,<length> <CR><LF> <pdu>

A message read with status “REC UNREAD” will be updated in memory with the

status “REC READ”.

5.3.2.1 SEND MESSAGE +CMGS Description :

The <address> field is the address of the terminal to which the message is sent. To

send the message, simply type, <ctrl-Z> character (ASCII 26). The text can contain

all existing characters except <ctrl-Z> and <ESC> (ASCII 27). This command can be

aborted using the <ESC> character when entering text. In PDU mode, only

hexadecimal characters are used (‘0’…’9’,’A’…’F’).

5.3.2.2 Syntax

Command syntax in text mode:

AT+CMGS= <da> [ ,<toda> ] <CR>

text is entered <ctrl-Z / ESC >

Command syntax in PDU mode :

AT+CMGS= <length> <CR>

PDU is entered <ctrl-Z / ESC >



COMMAND POSSIBLE RESPONSE

AT+CMTI:”SM”,1

Note: New message received

AT+CMGR=1

Note: read the message

+CMGR :”REC UNREAD”,”0146290800”,

“98/10/01;18:22:11+00”,<CR><LF>

ABcdefGH

Ok

AT+CMGR=1

Note: read the message again

+CMGR:”REC UNREAD”,”0146290800”,

“98/10/01,18:22:11+00”,<CR><LF>

ABCdefGHI

OK

Note: message is read now

AT+CMGR=2

Note :Read at a wrong index

+CMS ERROR:321

Note : Error : invalid index

AT+CMGF=0 : +CMGR=1

Note :In PDU mode

+CMGR: 2,<Length><CR><LF><pde>

OK

Note :Message is stored but unsent, no

<alpha>field

AT+CMGF=1;+CPMS+”SR”;+CNMI=…2

Reset to text mode ,set read memory to

“SR”,and allow storage of further SMS

Status Report into”SR”memory

OK

AT+CMSS=3

Send an SMS previously stored

+CMSS :160

OK

+CDSI :”SR”,1

New SMS Status Report Stored in “SR”

Memory at index 1

AT+CMGR=1

Read the SMS Status Report

+CMGR :’READ’,6,160,

“+33612345678’,129,”01/05/31,15:15:09

+00’,’01/05/31,15:15:09+00”,0

OK

Table 5.1 Example for CMGR command



Command Possible response

AT+CMGS=”+33146290800”<CR>

Please call me soon, fred. <ctrl.z>

Note: send a message in text mode.

+CMGS;<mr>

Ok

Note:successful transmission

AT+CMGS+<length><CR><pdu><ctrlz>

Note: Send a message in pdu mode.

+CMGS;<mr>

Ok

Note:Sucessful transmission.

Table 5.2 Examples for CMGS commands



PROGRAM CODING

1. LCD coding

#include<reg52.h>

#include<intrins.h>

#include<string.h>

#include "lcd.h"

sbit BZ=P1^1;

bit flag = 0;

bit r_flag = 0;

bit sucess = 0;

sbit AB = P3^2;

int i=0;

char idata buff[150];

//char idata num[12];

char idata mes[60];

void send_chr(unsigned char);

bit vl=0,li=0;

void serial_intr(void) interrupt 4

{

if(TI==1)

{

TI=0;

flag=1;

}



else

{

RI=0;

r_flag=1;

if(i<150)

buff[i++]=SBUF;

}

}

void print(char *str)

{

while(*str)

{

flag=0;

SBUF=*str++;

while(flag==0);

}

}

void transmit(unsigned char *s)

{

while(*s)

{

SBUF=*s++;

delay_ms(40);

}



}

unsigned char m;

void main()

{

int I;

char t=0;

TMOD=0x21;

SCON=0x50;

TH1=0XFD;

TR1=1;

IE=0X92;

TH0=0X00;

TL0=0X00;

init_lcd();

display_lcd("GSM BASED");

cmd_lcd(0XC0);

display_lcd("MESSAGE DISPLAY");

delay_ms(3000);

cmd_lcd(0x01);

display_lcd("INITIALIZING");

i=0;

print("AT+CMGF=1\r\n");

delay_ms(100);

sucess=0;

do



{

strcpy(buff," ");

r_flag=0;

i=0;

print("AT+CMGD=1,4\r\n");

while(i<16)

delay_ms(100);

cmd_lcd(0xc0);

display_lcd("MODEM CONNECTED");

// display_lcd(buff);

delay_ms(1000);

I=0;

while(buff[I]!='\0')

{

if(buff[I++]=='E')

sucess=1;

}

delay_ms(1000);

}while(sucess!=1);

while(1)

{

AB=1;

sucess=0;

do



{

i=0;

strcpy(buff,'"');

r_flag=0;

do

{

i=0;

//

//

strcpy(buff,'"');

}

while(r_flag==0);

delay_ms(100);

if(buff[2]=='+')

sucess=1;

} while(sucess!=1);

cmd_lcd(0x01);

display_lcd("MESSAGE RECEIVED");

BZ=0;

delay_ms(2000);

BZ=1;

i=0;

strcpy(buff,'"');

print("AT+CMGR=1\r\n");



delay_ms(1000);

I=0;

while(buff[I++]!=',');

// cmd_lcd(0x01);

//display_lcd("CELL NO:");

//cmd_lcd(0xc0);

//I=I+4;

t=0;

while(buff[I]!='"');

buff[I++];

do

{

buff[I++];

//num[t++]=buff[I++];

delay_ms(50);

}


//num[t]='\0';

// cmd_lcd(0x01);

//display_lcd(num);

//delay_ms(1000);

cmd_lcd(0x01);

cmd_lcd(0xc0);



while(buff[I]!='"')

(buff[I++]);

while(buff[I]!='"')

(buff[I++]);

while(buff[I++]!=0x0d);

cmd_lcd(0x01);

display_lcd("MESSAGE:");

cmd_lcd(0xc0);

//buff[I++];

//write_lcd(buff[I]);

do

{

mes[t++]=buff[I++];

// delay_ms(50);

}

while(buff[I]!=0x0d);

mes[t]='\0';

delay_ms(1000);

cmd_lcd(0X01);

// cmd_lcd(0X18);

display_lcd(mes);

cmd_lcd(0XC0);

delay_ms(2000);

sucess=0;

do



{

strcpy(buff," ");

r_flag=0;

i=0;


while(i<14);

delay_ms(100);

I=0;


{

if(buff[I++]=='E')

sucess=1;

}

delay_ms(500);

}while(sucess!=1);

// cmd_lcd(0x01);

}

}

void send_chr(unsigned char c)

{

flag=0;

SBUF=c;

while(flag==0);

}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////



//lcd.h

#include <reg52.h>

#define LCD P2

sbit RS=P0^0;

sbit RW=P0^1;

sbit EN=P0^2;

void delay_ms(unsigned int i)

{

unsigned int j;

while(i-->0)

{

for(j=0;j<500;j++)

{

;

}

}

}

void cmd_lcd(unsigned char c)

{

RS=0;

RW=0;

EN=1;

LCD=c;

delay_ms(10);



EN=0;

delay_ms(10);

}

void init_lcd(void)

{

delay_ms(10);

cmd_lcd(0x38);

delay_ms(10);

cmd_lcd(0x0c);

delay_ms(10);

cmd_lcd(0x06);

delay_ms(10);

cmd_lcd(0x01);

}

void write_lcd(unsigned char c)

{

RS=1;

RW=0;

EN=1;

LCD=c;

delay_ms(10);

EN=0;

delay_ms(10)

}

void display_lcd(unsigned char *s)



{

while(*s)

write_lcd(*s++);

}

2.MAIN EMBEDDED C CODE

#include<reg52.h>

#include<intrins.h>

#include<string.h>

#include "lcd.h"

sbit AB = P3^2;

bit flag = 0;

bit r_flag = 0;

bit sucess = 0;

int i=0;

char idata buff[140];

char idata num[12];

char idata mes[20];

void send_chr(unsigned char);

void transmit(unsigned char *t_data)

{



while(*t_data!='\0')

{

SBUF = *t_data;

t_data++;

delay_ms(30);

}

}

void serial_intr(void) interrupt 4

{

if(TI==1)

{

TI=0;

flag=1;

}

else

{

RI=0;

r_flag=1;

if(i<160)

buff[i++]=SBUF;

}



}

void print(char *str)

{

while(*str)

{

flag=0;

SBUF=*str++;

while(flag==0);

}

}

unsigned char m;

void main()

{

int I;

char t=0;

TMOD=0x21;

SCON=0x50;

TH1=0XFD;

TR1=1;

IE=0X90;

init_lcd();

display_lcd("GSM SCROLLING");

cmd_lcd(0XC0);



display_lcd("LED DISPLAY SYS");

delay_ms(3000);

AB=0;

cmd_lcd(0x01);

display_lcd("INITIALIZING");

i=0;

print("AT+CMGF=1\r\n");

delay_ms(100);

sucess=0;

do

{

strcpy(buff," ");

r_flag=0;

i=0;


while(i<16)

delay_ms(100);

I=0;


{

if(buff[I++]=='E')

sucess=1;

}

delay_ms(1000);

}while(sucess!=1);



cmd_lcd(0x01);

display_lcd("MODEM CONNECTED");

delay_ms(1000);

cmd_lcd(0x01);


cmd_lcd(0XC0);


delay_ms(1000);

while(1)

{

AB=0;

sucess=0;

init_lcd();


cmd_lcd(0XC0);


delay_ms(200);

do

{

i=0;

strcpy(buff,'"');

r_flag=0;

do

{

i=0;



strcpy(buff,'"');

}

while(r_flag==0);

delay_ms(100);

if(buff[2]=='+')

sucess=1;

} while(sucess!=1);

cmd_lcd(0x01);

display_lcd("MESSAGE RECIVED");

delay_ms(1000);

i=0;

strcpy(buff,'"');

print("AT+CMGR=1\r\n");

delay_ms(1000);

I=0;

while(buff[I++]!=',');

cmd_lcd(0x01);

display_lcd("CELL NO:");

cmd_lcd(0xc0);

//I=I+4;

t=0;


buff[I++];

do



{

//buff[I++];

num[t++]=buff[I++];

delay_ms(50);

}


num[t]='\0';

cmd_lcd(0xc0);

display_lcd(num);

delay_ms(1000);

while(buff[I]!='"')

(buff[I++]);

while(buff[I]!='"')

(buff[I++]);

while(buff[I++]!=0x0d);

cmd_lcd(0x01);

display_lcd("MESSAGE READING");

cmd_lcd(0xc0);

buff[I++];

//write_lcd(buff[I]);

//delay_ms(1000);

t=0;

//while(buff[I]!='"');

//buff[I++];



do

{

mes[t++]=buff[I++];

delay_ms(5);

}

while(buff[I]!=0x0d);

mes[t]='\0';

delay_ms(200);

cmd_lcd(0x01);

display_lcd(mes);

delay_ms(2000);

if(strcmp(mes,"FORMAT") == 0)

{

AB = 1;

cmd_lcd(0x01);

display_lcd("MESSAGES DELETED");

delay_ms(100);

send_chr('#');

delay_ms(1000);

send_chr('4');

delay_ms(1000);

send_chr('6');

delay_ms(5000);

AB=0;



}

else

{

AB=1;

// EA=0;

cmd_lcd(0x01);

display_lcd("DISPLAY SETTING");

delay_ms(100);

send_chr('*');

delay_ms(2000);

transmit("<M ");

transmit(mes);

transmit(" ><S 1><D L1>\r\n");

send_chr(0x0d);

delay_ms(3000);

send_chr(0x0d);

delay_ms(5000);

EA=1;

AB = 0;

}

//delay_ms(2000);

send_chr(0x0d);

print("AT+CMGD=1\r\n");

delay_ms(1000);




delay_ms(1000);


delay_ms(1000);

cmd_lcd(0x01);

}

}

void send_chr(unsigned char c)

{

flag=0;

SBUF=c;

while(flag==0);

}



CONCLUSION

The project “wireless electronic notice board using GSM technology” has been

successfully completed and tested with integration of the features of every hardware

component for its development. Presence of every block has been reasoned out and

placed carefully thus contributing to the best working of the unit.

The project was finished using very simple and easily available components

making it lightweight and portable. This helps for wireless notice board application

with the help of GSM Technology. We believe that our step is towards complete

automation for notice board application which can be used in colleges,

Finally we can conclude that this project application gives a very good feature

and there is huge scope for further research and development for using the same with

the help of advanced technology.



FUTURE IMPROVEMENTS

The use of microcontroller in place of a general purpose computer allows us to

theorize on many further improvements on this project prototype. Temperature

display during periods wherein no message buffers are empty is one such theoretical

improvement that is very possible.

The ideal state of the microcontroller is when the indices or storage space in

the SIM memory are empty and no new message is there to display. With proper use

of interrupt routines the incoming message acts as an interrupt, the temperature

display is halted and the control flow jumps over to the specific interrupt service

routine which first validates the sender’s number and then displays the information

field. Another very interesting and significant improvement would be to

accommodate multiple receiver MODEMS at the different positions in a geographical

area carrying duplicate SIM cards.

With the help of principles of TDMA technique, we can choose to simulcast

and /or broadcast important notifications. After a display board receives the valid

message through the MODEM and displays it, it withdraws its identification from the

network & synchronously another nearby MODEM signs itself into the network and

starts to receive the message. The message is broadcast by the mobile switching

center for a continuous time period during which as many possible display board

MODEMS “catch” the message and display it as per the constraint of validation.

Multilingual display can be another added variation of the project.

The displayboards are one of the single most important media for information

transfer to the maximum number of end users. This feature can be added by

programming the 40 microcontroller to use different encoding decoding schemes in

different areas as per the local language. This will ensure the increase in the number

of informed users. Graphical display can also be considered as a long term but

achievable and target able output. MMS technology along with relatively high end

microcontrollers to carry on the tasks of graphics encoding and decoding along with a

more expansive bank of usable memory can make this task a walk in the park.



REFERENCES

Literature

A. 8051 Microcontroller and Embedded Systems – Muhammad A. Mazidi

B. MATRIX SIMADO GDT11 GSM MODEM Manual

C. Frank Vahid, Embedded system design, Tata Mc Graw hill, 3 Edition, 1995.

D. Raj Kamal, Embedded Systems, JWE, 4 Edition, 2000.

Links

MAX – 232 data sheet from Texas Instruments

A. http://www.datasheetcatalog.com

B. http://www.8052.com

C. www.wikipedia.org

D. www.keil.com/forum/docs

E. www.embeddedrelated.com

Business

Wireless electronic notice board using gsm technolgy