GSM based patient monitoring system

GSM BASEDPATIENT MONITORIG SYSTEM 2013

1. INTRODUCTION

As the goal of this project, we see a device that can detect ailments in a patient and

inform them to the concerned medical personnel, without the intervention of even the patient

himself. This process is done with the help of GSM technology. The GSM technology is used

for reading and sending SMS to the concerned person.

Global system for mobile communication (GSM) is a globally accepted standard for

digital cellular communication. GSM is the name of a standardization group established in

1982 to create a common European mobile telephone standard that would formulate

specifications for a pan-European mobile cellular radio system operating at 900 MHz. It is

estimated that many countries outside of Europe will join the GSM partnership.

PYDAH COLLEGE OF ENGINEERING, PATAVALA Page 1


2.1 BLOCK DIAGRAM :

FIGURE1:BLOCK DIAGRAM

2.2 BLOCK DIAGRAM DESCRIPTION:

Block diagram comprises of Microcontroller, heart beat sensor, temperature sensor,

regulated power supply, LCD display, ADC (analog to digital converter)

The heart beat and temperature sensor are interfaced to microcontroller via port pins . Heart

beat rate is produced from the LM358 op-amp temperature rate produced by LM35 is fed to

microcontroller via ADC(analog to digital converter). An LCD is used to display the sensed

data.

Most digital logic circuits and processors need a 5 volt power supply. To use these parts we

need to build a regulated 5 volt source. Usually you start with an unregulated power To make

a 5 volt power supply, we use a LM7805 voltage regulator IC (Integrated Circuit).



The heart beat circuitry consists of a Quad Op-amp IC and three electrodes. These

electrodes are placed to the patient who is suffering with high B.P as well as heart problems.

The output of this circuitry is considered into logic levels and this output is given to one of

the pin of the micro controller.

The GSM Modem is used for sending and receiving messages from the patient to a

doctor and vice versa. Whenever the heart beat rate or the B.P. exceeds the threshold value.

The micro controller will automatically send the signals to the GSM Modem. Through the

GSM Modem, the message will gives to the concerned person or a doctor.

The LCD display is used to display the status of the GSM modem and as well as the

heart beat rate continuously.

For the circuitry operation, it requires the +5V DC power supply.



3.CIRCUIT SCHEMATICS

The circuit schematic is divided into four modules

3.1 LM35 sensor interfaced with AT89C52

3.2 Heart rate sensor interfaced with AT89C52

3.3 GSM interfaced with AT89C52.

3.4 LCD interfaced with AT89C52.

3.1 LM35 SENSOR INTERFACED WITH AT89C52.

FIGURE2:LM35 SENSOR INTERFACEING CIRCUIT



LM35 is a precision IC temperature sensor with its output proportional to the temperature (in oC). The sensor circuitry is sealed and therefore it is not subjected to oxidation and other

processes. With LM35, temperature can be measured more accurately than with a

thermistor. It also possess low self heating and does not cause more than 0.1 oC temperature

rise in still air.

Analog to digital converters find huge application as an intermediate device to convert the

signals from analog to digital form. These digital signals are used for further processing by

the digital processors. Various sensors like temperature, pressure, force etc. convert the

physical characteristics into electrical signals that are analog in nature.

3.2 HEART RATE SENSOR INTERFACED WITH AT89C52.

FIGURE3:HEART RATE SENSOR INTERFACEING CIRCUIT

The heart beat sensor (Electrodes) circuitry is connected to the P3.2 of the micro

controller. The heart beat circuitry consists of a Quad Op-amp IC and three electrodes. These

electrodes are placed to the patient who is suffering with high B.P as well as heart problems.

The output of this circuitry is considered into logic levels and this output is given to one of

the pin of the micro controller.



3.3 GSM INTERFACED WITH AT89C52:

FIGURE4:GSM MODEM INTERFACEING CIRCUIT

In order to interface the GSM to the microcontroller we are using the UART device. One pin

of UART is connected to GSM . 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. 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.

For example, the PC is a Data Terminal (DTE). The two modems (yours and that one of your

provider) are DCEs, they make the communication between you and your provider possible.



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 DCE or 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.

FIGURE5: FEMALE 9 PIN PLUG

Functions Signals PIN DTE DCE

Data TxD 3 Output Input

RxD 2 Input Output

Handshake

RTS 7 Output Input

CTS 8 Input Output

DSR 6 Input Output

DCD 1 Input Output



STR 4 Output Input

Common Com 5 -- --

Other RI 9 Output Input

TABLE1:RS-232 SIGNALS

RS-232 Signals

1. Transmitted Data (TxD)

Data sent from DTE to DCE.

2. Received Data (RxD)

Data sent from DCE to DTE.

3. 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.

4. Clear To Send (CTS)

Asserted by DCE to acknowledge RTS and allow DTE to transmit.

5. 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 de-asserted, the modem

should respond by immediately hanging up.

6. Data Set Ready (DSR)



Asserted by DCE to indicate an active connection. If DCE is not a modem (e.g. a

null-modem cable or other equipment), this signal should be permanently asserted (set to 0),

possibly by a jumper to another signal.

7. Carrier Detect (CD)

Asserted by DCE when a connection has been established with remote equipment.

8. Ring Indicator (RI)

Asserted by DCE when it detects a ring signal from the telephone line.

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 re-enabled. 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.

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.

FIGURE6: CHARACTER FRAME ENCODING ‘M’

We specified the parameters as baud rate – 2400 bps, 8 data bits, no parity, and 1 stop bit

(2400-8-N-1). This was set in pre-operational phase while setting up the modem through the

hyper terminal, as per the serial transmission standards in 8052 microcontroller.

3.4 LCD interfaced with AT89C52:

FIGURE7: LCD INTERFACING CIRCUIT



The LCD is interfaced with microcontroller (AT89C52). This microcontroller has 40 pins

with four 8-bit ports (P0, P1, P2, and P3). Here P1 is used as output port which is connected to

data pins of the LCD. The control pins (pin 4-6) are controlled by pins 2-4 of P0 port. Pin 3 is

connected to a preset of 10k? to adjust the contrast on LCD screen.

A 16x2 LCD means it can display 16 characters per line and there are 2 such lines. In this

LCD each character is displayed in 5x7 pixel matrix. This LCD has two registers.

1. Command/Instruction Register - stores the command instructions given to the LCD. A

command is an instruction given to LCD to do a predefined task like initializing, clearing the

screen, setting the cursor position, controlling display etc.

2. Data Register - stores the data to be displayed on the LCD. The data is the ASCII value

of the character to be displayed on the LCD.

Commonly used LCD Command codes:

TABLE2:LCD COMMANDS


Hex Code Command to LCD Instruction Register

1 Clear screen display

2 Return home

4 Decrement cursor

6 Increment cursor

E Display ON, Cursor ON

80 Force the cursor to the beginning of the 1st

lineC0 Force cursor to the beginning of the 2nd line

38 Use 2 lines and 5x7 matrix


4HARDWARE COMPONENTS

The hardware components used in this circuit diagram are

4.1 MICRO CONTROLLER (AT89C52)

4.2 LM35 SENSOR

4.3 LCD

4.4 GSM

4.5 HEARTBEAT SENSOR

4.6 LDR

4.7 ADC

4.8 POWER SUPPLY

4.9 POTENTIOMETER

4.10 RESISTOR

4.11 CAPACITOR

4.12 OP-AMP

4.13 SWITCHE

3.1 Micro Controller 89S52

3.1.1 INTRODUCTION :

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

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

acquisition interfaces-Analog to Digital converter, Digital to Analog converter, integrated on

to a single silicon chip

.



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

memory such as RAM, ROM, EPROM and peripherals. But controller is provided all these

facilities on a single chip. Development of a Micro controller reduces PCB size and cost of

design.

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

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

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

3.1.2 THE MAJOR FEATURES :

Compatible with MCS-51 products

4k Bytes of in-system Reprogrammable flash memory

Fully static operation: 0HZ to 24MHZ

Three level programmable clock

128 * 8 –bit timer/counters

Six interrupt sources

Programmable serial channel

Low power idle power-down modes

AT89C52 is 8-bit micro controller, which has 4 KB on chip flash memory, which is

just sufficient for our application. The on-chip Flash ROM allows the program memory to be

reprogrammed in system or by conventional non-volatile memory Programmer. Moreover

ATMEL is the leader in flash technology in today’s market place and hence using AT 89C52

is the optimal solution.

3.1.3 AT89S52 MICROCONTROLLER ARCHITECTURE :

The 89C52 architecture consists of these specific features:

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

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

Eight- bit stack pointer (PSW)



Eight-bit stack pointer (Sp)

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

Internal RAM of 128 bytes:

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

Two 16-bit timer/counters: T0 and T1

Full duplex serial data receiver/transmitter: SBUF

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

Two external and three internal interrupts sources.

Oscillator and clock circuits.

FIGURE 8:FUNCTIONAL BLOCK DIAGRAM OF MICROCONTROLLER

3.1.4 TYPES OF MEMORY :

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

Code memory and external Ram. On-Chip memory refers to physically existing memory on

the micro controller itself. External code memory is the code memory that resides off chip.



This is often in the form of an external EPROM. External RAM is the Ram that resides off

chip. This often is in the form of standard static RAM or flash RAM.

Code memory

Code memory is the memory that holds the actual 89C51 programs that is to be run.

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

possible to have 4K of code memory on-chip and 60K off chip memory simultaneously. If

only off-chip memory is available then there can be 64K of off chip ROM. This is controlled

by pin provided as EA.

Internal RAM

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

So it is the fastest Ram available. And also it is most flexible in terms of reading and writing.

Internal Ram is volatile, so when 89C51 is reset, this memory is cleared. 128 bytes of internal

memory are subdivided. The first 32 bytes are divided into 4 register banks. Each bank

contains 8 registers. Internal RAM also contains 128 bits, which are addressed from 20h to

2Fh. These bits are bit addressed i.e. each individual bit of a byte can be addressed by the

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

commands such as SETB and CLR.

Flash memory is a nonvolatile memory using NOR technology, which allows the user

to electrically program and erase information. Flash memory is used in digital cellular

phones, digital cameras, LAN switches, PC Cards for notebook computers, digital set-up

boxes, embedded controllers, and other devices.



FIGURE 9:PIN DIAGRAM OF AT89S52

3.1.5 PIN DESCRIPTION :

VCC: Supply voltage.

GND: Ground.

Port 0

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

sink eight TTL inputs. When 1sare written to port 0 pins, the pins can be used as high

impedance inputs. Port 0 may also be configured to be the multiplexed low order address/data

bus during accesses to external program and data memory. In this mode P0 has internal pull-

ups. Port 0 also receives the code bytes during Flash programming, and outputs the code

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



Port 1

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

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

high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are

externally being pulled low will source current (IIL) because of the internal pull-ups. Port 1

also receives the low-order address bytes during Flash programming and verification.

Port 2




externally being pulled low will source current (IIL) because of the internal pull-ups.

Port 3




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 AT89C51 as listed below:

TABLE3:PORT3 THEIR ALTERNATE FUNCTIONS



RST

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

resets the device.

ALE/PROG

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

accesses to external memory. This pin is also the program pulse input (PROG) during Flash

programming. In normal operation ALE is emitted at a constant rate of 1/6the oscillator

frequency, and may be used for external timing or clocking purposes. Note, however, that one

ALE pulse is skipped during each access to external Data Memory.

If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit

set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly

pulled high. Setting the ALE-disable bit has no effect if the micro controller is in external

execution mode.

PSEN

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

AT89C51 is executing code from external program memory, PSEN is activated twice each

machine cycle, except that two PSEN activations are skipped during each access to external

data memory.

EA/VPP

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

fetch code from external program memory locations starting at 0000H up to FFFFH.

Note, however, that if lock bit 1 is programmed, EA will be internally latched on

reset. EA should be strapped to VCC for internal program executions. This pin also receives

the 12-volt programming enable voltage (VPP) during Flash programming, for parts that

require 12-volt VPP.



XTAL1

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

circuit.

XTAL2

Output from the inverting oscillator amplifier.

3.1.6 OSCILLATOR CHARACTERISTICS :

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

which can be configured for use as an on-chip oscillator, as shown in Figs 6.1 Either a quartz

crystal or ceramic resonator may be used. To drive the device from an external clock source,

XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 6.2. There are

no requirements on the duty cycle of the external clock signal, since the input to the internal

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

high and low time specifications must be observed.

FIGURE 10: OSCILLATOR FIGURE 11:EXTERNAL CLOCK



3.1.7 REGISTERS:

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

could be a byte of data to be processed, or an address pointing to the data to be fetched. The

vast majority of 8051 registers are 8–bit registers.

D7 D6 D5 D4 D3 D2 D1 D0

The most widely used registers of the 8051 are A(accumulator), B, R0, R1, R2, R3,

R4, R5, R6, R7, DPTR(data pointer), and PC(program counter). All of the above registers

are 8-bits, except DPTR and the program counter. The accumulator, register A, is used for all

arithmetic and logic instructions.

3.1.8 SFRS (SPECIAL FUNCTION REGISTERS) :

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

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

names (which is much easier) or by their addresses. For example, register A has address E0h,

and register B has been ignited the address F0H, as shown in table.

The following two points should note about the SFR addresses.

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

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

memory inside the 8051.

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

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

Symbol Name Address

ACC Accumulator 0E0H

B B register 0F0H

PSW Program status word 0D0H

SP Stack pointer 81H

DPTR Data pointer 2 bytes

DPL Low byte 82H

DPH High byte 83H



P0 Port0 80H

P1 Port1 90H

P2 Port2 0A0H

P3 Port3 0B0H

IP Interrupt priority control 0B8H

IE Interrupt enable control 0A8H

TMOD Timer/counter mode control 89H

TCON Timer/counter control 88H

T2CON Timer/counter 2 control 0C8H

T2MOD Timer/counter mode2 control 0C9H

TH0 Timer/counter 0high byte 8CH

TL0 Timer/counter 0 low byte 8AH

TH1 Timer/counter 1 high byte 8DH

TL1 Timer/counter 1 low byte 8BH

TH2 Timer/counter 2 high byte 0CDH

TL2 Timer/counter 2 low byte 0CCH

RCAP2H T/C 2 capture register high byte 0CBH

RCAP2L T/C 2 capture register low byte 0CAH

SCON Serial control 98H

SBUF Serial data buffer 99H

PCON Power control 87H

TABLE 4: 8051 SPECIAL FUNCTION REGISTER ADDRESS

A Register (Accumulator)



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

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

instruction upon it. Once an arithmetical operation is preformed by the ALU, the result is

placed into the accumulator

B Register

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

upon numbers stored in the A and B registers. All other instructions in the program can use

this register as a spare accumulator (A).

Registers (R0-R7)

FIGURE 12:MEMORY ORGANIZATION OF RAM

This is a common name for the total 8 general purpose registers (R0, R1, R2 ...R7).

Even they are not true SFRs, they deserve to be discussed here because of their purpose. The

bank is active when the R registers it includes are in use. Similar to the accumulator, they are

used for temporary storing variables and intermediate results. Which of the banks will be

active depends on two bits included in the PSW Register. These registers are stored in four

banks in the scope of RAM.



3.1.9 REGISTER BANKS AND STACK :

RAM memory space allocation in the 8051

There are 128 bytes of RAM in the 8051. The 128 bytes of RAM inside the 8051 are

assigned addresses 00 to7FH. These 128 bytes are divided into three different groups as

follows:

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

and the stack.

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

read/write memory.

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

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

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

Default register bank

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

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

FIG 13: RAM ALLOCATION IN THE 8051

PSW Register (Program Status Word)



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

several status bits that reflect the current state of the CPU. This register contains: Carry bit,

Auxiliary Carry, two register bank select bits, Overflow flag, parity bit, and user-definable

status flag. The ALU automatically changes some of register’s bits, which is usually used in

regulation of the program performing.

P - Parity bit. If a number in accumulator is even then this bit will be automatically

set (1), otherwise it will be cleared (0). It is mainly used during data transmission and

receiving via serial communication.

OV Overflow occurs when the result of arithmetical operation is greater than 255

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

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

RS0, RS1 - Register bank select bits. These two bits are used to select one of the

four register banks in RAM. By writing zeroes and ones to these bits, a group of registers R0-

R7 is stored in one of four banks in RAM. This is a general-purpose bit available to the user.

RS1 RS2 Space in RAM

0 0 Bank0 00h-07h

0 1 Bank1 08h-0Fh

1 0 Bank2 10h-17h

1 1 Bank3 18h-1Fh

TABLE 5: REGISTER BANK SELECT

AC - Auxiliary Carry Flag is used for BCD operations only.

CY - Carry Flag is the (ninth) auxiliary bit used for all arithmetical operations and

shift instructions.



DPTR Register (Data Pointer)

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

two separate registers: DPH (Data Pointer High) and (Data Pointer Low). Their 16 bits are

used for external memory addressing. They may be handled as a 16-bit register or as two

independent 8-bit registers. Besides, the DPTR Register is usually used for storing data and

intermediate results, which have nothing to do with memory locations.

SP Register (Stack Pointer)

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

information could be data or an address. The CPU needs this storage area since there are

only a limited number of registers.

How stacks are accessed in the 8051

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

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

in the 8051 is only 8 bits wide; which means that it can take values of 00 to FFH. When the

8051 is powered up, the SP register contains value 07. This means that RAM location 08 is

the first location used for the stack by the 8051. The storing of a CPU register in the stack is

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

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

retrieve it. The job of the SP is very critical when push and pop actions are performed.



3.1.10 PROGRAM COUNTER :

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

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

from the program ROM, the program counter is incremented to point to the next instruction.

The program counter in the 8051 is 16bits wide. This means that the 8051 can access

program addresses 0000 to FFFFH, a total of 64k bytes of code. However, not all members

of the 8051 have the entire 64K bytes of on-chip ROM installed, as we will see soon.

3.1.11 TIMERS :

On-chip timing/counting facility has proved the capabilities of the micro controller for

implementing the real time application. These includes pulse counting, frequency

measurement, pulse width measurement, baud rate generation, etc,. Having sufficient number

of timer/counters may be a need in a certain design application. The 8051 has two

timers/counters. They can be used either as timers to generate a time delay or as counters to

count events happening outside the micro controller.

TIMER 0 REGISTERS

The 16-bit register of Timer 0 is accessed as low byte and high byte. the low byte

register is called TL0(Timer 0 low byte)and the high byte register is referred to as TH0(Timer

0 high byte).These register can be accessed like any other register, such as A,B,R0,R1,R2,etc.



TIMER 1 REGISTERS

Timer 1 is also 16-bit register is split into two bytes, referred to as TL1 (Timer 1 low

byte) and TH1 (Timer 1 high byte). These registers are accessible n the same way as the

register of Timer 0.

TMOD (timer mode) REGISTER

Both timers 0 and 1 use the same register, called TMOD, to set the various timer

operation modes. TMOD is an 8-bit register in which the lower 4 bits are set aside for Timer

0 and the upper 4 bits for Timer 1.in each case; the lower 2 bits are used to set the timer mode

and the upper 2 bits to specify the operation.

GATE Gate control when set. The timer/counter is enabled only

while the INTx pin is high and the TRx control pin is

set. When cleared, the timer is enabled.

C/T Timer or counter selected cleared for timer operation

(Input from internal system clock).set for counter

operation (input TX input pin).

M1 M0 MODE Operating Mode

0 0 0 13-bit timer mode

8-bit timer/counter THx with TLx as 5-bit prescaler.

0 1 1 16-bit timer mode

16-bit timer/counters THx with TLx are cascaded; there is no



prescaler

1 0 2 8-bit auto reload 8-bit auto reload timer/counter;THx Holds a

value that is to be reloaded into TLx each time it overflows

1 1 3 Split timer mode.

TABLE6:TMOD SELECTION

C/T (clock/timer)

This bit in the TMOD register is used to decide whether the timer is used as a delay

generator or an event counter. If C/T=0, it is used as a timer for time delay generation. The

clock source for the time delay is the crystal frequency of the 8051.this section is concerned

with this choice. The timer’s use as an event counter is discussed in the next section.

3.1.12 SERIAL COMMUNICATION :

Serial data communication uses two methods, asynchronous and synchronous. The

synchronous method transfers a block of data at a time, while the asynchronous method

transfers a single byte at a time.

In data transmission if the data can be transmitted and received, it is a duplex

transmission. This is in contrast to simplex transmissions such as with printers, in which the

computer only sends data. Duplex transmissions can be half or full duplex, depending on

whether or not the data transfer can be simultaneous. If data is transmitted one way at a time,

it is referred to as half duplex. If the data can go both ways at the same time, it is full duplex.

Of course, full duplex requires two wire conductors for the data lines, one for transmission

and one for reception, in order to transfer and receive data simultaneously.

Asynchronous serial communication and data framing

The data coming in at the receiving end of the data line in a serial data transfer is all

0s and 1s; it is difficult to make sense of the data unless the sender and receiver agree on a set



of rules, a protocol, on how the data is packed, how many bits constitute a character, and

when the data begins and ends.

Start and stop bits

Asynchronous serial data communication is widely used for character-oriented

transmissions, while block-oriented data transfers use the synchronous method. In the

asynchronous method, each character is placed between start and stop bits. This is called

framing. In the data framing for asynchronous communications, the data, such as ASCII

characters, are packed between a start bit and a stop bit. The start bit is always one bit, but the

stop bit can be one or two bits. The start bit is always a 0 (low) and the stop bit (s) is 1

(high).

Data transfer rate

The rate of data transfer in serial data communication is stated in bps (bits per

second). Another widely used terminology for bps is baud rate. However, the baud and bps

rates are not necessarily equal. This is due to the fact that baud rate is the modem

terminology and is defined as the number of signal changes per second. In modems a single

change of signal, sometimes transfers several bits of data. As far as the conductor wire is

concerned, the baud rate and bps are the same, and for this reason we use the bps and baud

interchangeably.

3.1.13 RS232 STANDARDS :

To allow compatibility among data communication equipment made by various

manufacturers, an interfacing standard called RS232 was set by the Electronics Industries

Association (EIA) in 1960. In 1963 it was modified and called RS232A. RS232B AND

RS232C were issued in 1965 and 1969, respectively. Today, RS232 is the most widely used

serial I/O interfacing standard. This standard is used in PCs and numerous types of

equipment. However, since the standard was set long before the advert of the TTL logic

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

represented by -3 to -25V, while a 0 bit is +3 to +25V, making -3 to +3 undefined. For this

reason, to connect any RS232 to a micro controller system we must use voltage converters

such as MAX232 to convert the TTL logic levels to the RS232 voltage levels, and vice versa.

MAX232 IC chips are commonly referred to as line drivers.



RS232 pins

RS232 cable, commonly referred to as the DB-25 connector. In labeling, DB-25P

refers to the plug connector (male) and DB-25S is for the socket connector (female). Since

not all the pins are used in PC cables, IBM introduced the DB-9 Version of the serial I/O

standard, which uses 9 pins only, as shown in table.

DB-9 pin connector

1 2 3 4 5

6 7 8 9

FIG14: DB-9 PIN CONNECTOR

Pin Functions

Pin Description

1 Data carrier detect (DCD)

2 Received data (RXD)

3 Transmitted data (TXD)

4 Data terminal ready(DTR)

5 Signal ground (GND)

6 Data set ready (DSR)

7 Request to send (RTS)

8 Clear to send (CTS)

9 Ring indicator (RI)

TABLE 7 : DB9 PIN FUNCTIONS

Note: DCD, DSR, RTS and CTS are active low pins.

The method used by RS-232 for communication allows for a simple connection of

three lines: Tx, Rx, and Ground. The three essential signals for 2-way RS-232

Communications are these

TXD: carries data from DTE to the DCE.

RXD: carries data from DCE to the DTE



SG: signal ground

3.1.14 8052 CONNECTION TO RS232 :

The RS232 standard is not TTL compatible; therefore, it requires a line driver such as

the MAX232 chip to convert RS232 voltage levels to TTL levels, and vice versa. The

interfacing of 8051 with RS232 connectors via the MAX232 chip is the main topic.

The 8051 has two pins that are used specifically for transferring and receiving data

serially. These two pins are called TXD and RXD and a part of the port 3 group (P3.0 and

P3.1). pin 11 of the 8051 is assigned to TXD and pin 10 is designated as RXD. These pins

are TTL compatible; therefore, they require a line driver to make them RS232 compatible.

One such line driver is the MAX232 chip.

Since the RS232 is not compatible with today’s microprocessors and

microcontrollers, we need a line driver (voltage converter) to convert the RS232’s signals to

TTL voltage levels that will be acceptable to the 8051’s TXD and RXD pins. One example

of such a converter is MAX232 from Maxim Corp. The MAX232 converts from RS232

voltage levels to TTL voltage levels, and vice versa.

FIGURE 15:INTERFACING OF MAX-232 TO CONTROLLER



3.1.15 INTERRUPTS :

A single micro controller can serve several devices. There are two ways to do that:

INTERRUPTS or POLLING.

INTERRUPTS vs POLLING

The advantage of interrupts is that the micro controller can serve many devices (not

all the same time, of course); each device can get the attention of the micro controller based

on the priority assigned to it. The polling method cannot assign priority since it checks all

devices in round-robin fashion. More importantly, in the interrupt method the micro

controller can also ignore (mask) a device request for service. This is again not possible with

the polling method. The most important reason that the interrupt method is preferable is that

the polling method wastes much of the micro controller’s time by polling devices that do not

need service. So, in order to avoid tying down the micro controller, interrupts are used.

INTERRUPT SERVICE ROUTINE

For every interrupt, there must be an interrupt service routine (ISR), or interrupt

handler. When an interrupt is invoked, the micro controller runs the interrupts service routine.

For every interrupt, there is a fixed location in memory that holds the address of its ISR. The

group of memory location set aside to hold the addresses of ISRs is called the interrupt vector

table. Shown below:

INTERRUPT ROM

LOCATION

(HEX)

PIN FLAG CLEARING

Reset

External hardware Interrupt 0

Timers0interrupt(TF0)

External hardware

Interrupt(INT1)

Timers 1 interrupt (TF1)

0000

0003

000B

0013

001B

0023

9

P3.2 (12)

P3.4 (14)

P3.3 (13)

P3. 5(15)

10,11

auto

auto

auto

auto

auto

Programmer



Serial COM (RI and TI) Clears it

TABLE 8: INTERRUPT VECTOR TABLE FOR THE 8051

Six Interrupts in the 8051

In reality, only five interrupts are available to the user in the 8051, but many

manufacturers’ data sheets state that there are six interrupts since they include reset .the six

interrupts in the 8051 are allocated as above.

1. Reset. When the reset pin is activated, the 8051 jumps to address location 0000.this is

the power-up reset.

2. Two interrupts are set aside for the timers: one for Timer 0 and one for Timer

1.Memory location 000BH and 001BH in the interrupt vector table belong to Timer 0

and Timer 1, respectively.

3. Two interrupts are set aside for hardware external harder interrupts. Pin number

12(P3.2) and 13(P3.3) in port 3 is for the external hardware interrupts INT0 and

INT1, respectively. These external interrupts are also referred to as EX1 and

EX2.Memory location 0003H and 0013H in the interrupt vector table are assigned to

INT0 and INT1, respectively.

4. Serial communication has a single interrupt that belongs to both receive and transmit.

The interrupt vector table location 0023H belongs to this interrupt.

Interrupt Enable Register

D7 D6 D5 D4 D3 D2 D1 D0

EA IE.7 disables all interrupts. If EA=0, no interrupts is acknowledged.

If EA=1, each interrupt source is individually enabled disabled


EA -- ET2 ES ET1 EX1 ET0 EX0


By setting or clearing its enable bit.

-- IE.6 Not implemented, reserved for future use.*

ET2 IE.5 Enables or disables Timer 2 overflow or capture interrupt (8052

Only).

ES IE.4 Enables or disables the serial ports interrupt.

ET1 IE.3 Enables or disables Timers 1 overflow interrupt

EX1 IE.2 Enables or disables external interrupt 1.

ET0 IE.1 Enables or disables Timer 0 overflow interrupt.

EX0 IE.0 Enables or disables external interrupt

4.2 TEMPERATURE SENSOR(LM35):

LM35 converts temperature value into electrical signals. LM35 series sensors are precision

integrated-circuit temperature sensors whose output voltage is linearly proportional to the

Celsius temperature. The LM35 requires no external calibration since it is internally

calibrated. . The LM35 does not require any external calibration or trimming to provide

typical accuracies of ±1⁄4°C at room temperature and ±3⁄4°C over a full −55 to +150°C

temperature range.

The LM35’s low output impedance, linear output, and precise inherent calibration make

interfacing to readout or control circuitry especially easy. It can be used with single power

supplies, or with plus and minus supplies. As it draws only 60 μA from its supply, it has very

low self-heating, less than 0.1°C in still air.

Features

Calibrated directly in ° Celsius (Centigrade)

Linear + 10.0 mV/°C scale factor

0.5°C accuracy guaranteed (at +25°C)

Rated for full −55° to +150°C range

Suitable for remote applications



Low cost due to wafer-level trimming

Operates from 4 to 30 volts

Less than 60 μA current drain

Low self-heating, 0.08°C in still air

Nonlinearity only ±1⁄4°C typical

Low impedance output, 0.1 W for 1 mA load

The characteristic of this LM35 sensor is:

For each degree of centigrade temperature it outputs 10milli volts.

4.3LCD:

A 16x2 LCD means it can display 16 characters per line and there are 2 such lines. In this

LCD each character is displayed in 5x7 pixel matrix. This LCD has two registers, namely,

Command and Data.

The command register stores the command instructions given to the LCD. A command is an

instruction given to LCD to do a predefined task like initializing it, clearing its screen, setting

the cursor position, controlling display etc. The data register stores the data to be displayed

on the LCD. The data is the ASCII value of the character to be displayed on the LCD.



A liquid crystal display (LCD) is a thin, flat electronic visual display that uses the

light modulating properties of liquid crystals (LCs). LCs do not emit light directly.

They are used in a wide range of applications including: computer monitors,

television, instrument panels, aircraft cockpit displays, signal, etc. They are common in

consumer devices such as video players, gaming devices, clocks, watches, calculators, and

telephones. LCDs have displaced cathode ray tube (CRT) displays in most applications. They

are usually more compact, lightweight, portable, less expensive, more reliable, and easier on

the eyes. They are available in a wider range of screen sizes than CRT and plasma displays,

and since they do not use phosphors, they cannot suffer image burn-in.

Each pixel of an LCD typically consists of a layer of molecules aligned between two

transparent electrodes, and two polarizing filters the axes of transmission of which are (in

most of the cases) perpendicular to each other. With no actual liquid crystal between the

polarizing filters, light passing through the first filter would be blocked by the second

(crossed) polarizer. In most of the cases the liquid crystal has double refraction

The surface of the electrodes that are in contact with the liquid crystal material are

treated so as to align the liquid crystal molecules in a particular direction. This treatment

typically consists of a thin polymer layer that is unidirectionally rubbed using, for example, a

cloth. The direction of the liquid crystal alignment is then defined by the direction of rubbing.

Electrodes are made of a transparent conductor called Indium Tin Oxide (ITO).

If the applied voltage is large enough, the liquid crystal molecules in the center of the

layer are almost completely untwisted and the polarization of the incident light is not rotated

as it passes through the liquid crystal layer. This light will then be mainly polarized

perpendicular to the second filter, and thus be blocked and the pixel will appear black.



FIG 16 : LCD DISPLAY

LCD with top polarizer removed from device and placed on top, such that the top and

bottom polarizer’s are parallel.

The optical effect of a twisted nematic device in the voltage-on state is far less

dependent on variations in the device thickness than that in the voltage-off state. Because of

this, these devices are usually operated between crossed polarizer such that they appear bright

with no voltage . These devices can also be operated between parallel polarizer, in which case

the bright and dark states are reversed. The voltage-off dark state in this configuration

appears blotchy, however, because of small variations of thickness across the device.

Both the liquid crystal material and the alignment layer material contain ionic

compounds. If an electric field of one particular polarity is applied for a long period of time,

this ionic material is attracted to the surfaces and degrades the device performance. This is

avoided either by applying an alternating current or by reversing the polarity of the electric

field as the device is addressed .

When a large number of pixels are needed in a display, it is not technically possible to

drive each directly since then each pixel would require independent electrodes. Instead, the

display is multiplexed. In a multiplexed display, electrodes on one side of the display are

grouped and wired together (typically in columns), and each group gets its own voltage

source. On the other side, the electrodes are also grouped (typically in rows), with each group

getting a voltage sink.



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).

Figure 17: PIN DIAGRAM OF 1X16 LINES LCD

TABLE 9: PIN DESCRIPTION OF LCD

CONTROL LINES

EN:

Line is called "Enable." This control line is used to tell the LCD that you are sending

it data. To send data to the LCD, your program should make sure this line is low (0) and then



set the other two control lines and/or put data on the data bus. When the other lines are

completely ready, bring EN high (1) and wait for the minimum amount of time required by

the LCD datasheet (this varies from LCD to LCD), and end by bringing it low (0) again.

RS:

Line is the "Register Select" line. When RS is low (0), the data is to be treated as a

command or special instruction (such as clear screen, position cursor, etc.). When RS is high

(1), the data being sent is text data which would be displayed on the screen. For example, to

display the letter "T" on the screen you would set RS high.

RW:

Line is the "Read/Write" control line. When RW is low (0), the information on the

data bus is being written to the LCD. When RW is high (1), the program is effectively

querying (or reading) the LCD. Only one instruction ("Get LCD status") is a read command.

All others are write commands, so RW will almost always be low.

Finally, the data bus consists of 4 or 8 lines (depending on the mode of operation

selected by the user). In the case of an 8-bit data bus, the lines are referred to as DB0, DB1,

DB2, DB3, DB4, DB5, DB6, and DB7.

Logic status on control lines:

E - 0 Access to LCD disabled

-1 Access to LCD enabled

R/W - 0 Writing data to LCD

-1 Reading data from LCD

RS - 0 Instructions

-1 Character

Writing data to the LCD:

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)on LCD:

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

4.4 GSM MODEM:

GSM Technology:

Definition of GSM:

GSM (Global System for Mobile communications) is an open, digital cellular technology

used for transmitting mobile voice and data services.

GSM (Global System for Mobile communication) is a digital mobile telephone system that is

widely used in Europe and other parts of the world. GSM uses a variation of Time Division

Multiple Access (TDMA) and is the most widely used of the three digital wireless telephone

technologies (TDMA, GSM, and CDMA). GSM digitizes and compresses data, then sends it

down a channel with two other streams of user data, each in its own time slot. It operates at

either the 900 MHz or 1,800 MHz frequency band. It supports voice calls and data transfer

speeds of up to 9.6 kbit/s, together with the transmission of SMS (Short Message Service).

History

In 1982, the European Conference of Postal and Telecommunications Administrations

(CEPT) created the Group Special Mobile (GSM) to develop a standard for a mobile



telephone system that could be used across Europe. In 1987, a memorandum of

understanding was signed by 13 countries to develop a common cellular telephone system

across Europe. Finally the system created by SINTEF lead by Torleiv Maseng was selected.

In 1989, GSM responsibility was transferred to the European Telecommunications Standards

Institute (ETSI) and phase I of the GSM specifications were published in 1990. The first

GSM network was launched in 1991 by Radiolinja in Finland with joint technical

infrastructure maintenance from Ericsson.

By the end of 1993, over a million subscribers were using GSM phone networks being

operated by 70 carriers across 48 countries. As of the end of 1997, GSM service was

available in more than 100 countries and has become the de facto standard in Europe and

Asia.

GSM Frequencies

GSM networks operate in a number of different frequency ranges (separated into GSM

frequency ranges for 2G and UMTS frequency bands for 3G). Most 2G GSM networks

operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including

Canada and the United States) use the 850 MHz and 1900 MHz bands because the 900 and

1800 MHz frequency bands were already allocated. Most 3G GSM networks in Europe

operate in the 2100 MHz frequency band. The rarer 400 and 450 MHz frequency bands are

assigned in some countries where these frequencies were previously used for first-generation

systems.

GSM-900 uses 890–915 MHz to send information from the mobile station to the base station

(uplink) and 935–960 MHz for the other direction (downlink), providing 124 RF channels

(channel numbers 1 to 124) spaced at 200 kHz. Duplex spacing of 45 MHz is used. In some

countries the GSM-900 band has been extended to cover a larger frequency range. This

'extended GSM', E-GSM, uses 880–915 MHz (uplink) and 925–960 MHz (downlink), adding

50 channels (channel numbers 975 to 1023 and 0) to the original GSM-900 band.

Time division multiplexing is used to allow eight full-rate or sixteen half-rate speech

channels per radio frequency channel. There are eight radio timeslots (giving eight burst

periods) grouped into what is called a TDMA frame. Half rate channels use alternate frames



in the same timeslot. The channel data rate for all 8 channels is 270.833 Kbit/s, and the frame

duration is 4.615 ms.

The transmission power in the handset is limited to a maximum of 2 watts in GSM850/900

and 1 watt in GSM1800/1900. GSM operates in the 900MHz and 1.8GHz bands in Europe

and the 1.9GHz and 850MHz bands in the US. The 850MHz band is also used for GSM and

3G in Australia, Canada and many South American countries. By having harmonized

spectrum across most of the globe, GSM’s international roaming capability allows users to

access the same services when travelling abroad as at home. This gives consumers seamless

and same number connectivity in more than 218 countries.

Terrestrial GSM networks now cover more than 80% of the world’s population. GSM

satellite roaming has also extended service access to areas where terrestrial coverage is not

available.

Mobile Telephony Standards

TABLE10: MOBILE TELEPHONY STANDARDS

1G

The first generation of mobile telephony (written 1G) operated using analogue

communications and portable devices that were relatively large. It used primarily the

following standards:

AMPS (Advanced Mobile Phone System), which appeared in 1976 in the United

States, was the first cellular network standard. It was used primarily in the Americas,

Russia and Asia. This first-generation analogue network had weak security

mechanisms which allowed hacking of telephones lines.



TACS (Total Access Communication System) is the European version of the AMPS

model. Using the 900 MHz frequency band, this system was largely used in England

and then in Asia (Hong-Kong and Japan).

ETACS (Extended Total Access Communication System) is an improved version of

the TACS standard developed in the United Kingdom that uses a larger number of

communication channels.

The first-generation cellular networks were made obsolete by the appearance of an entirely

digital second generation.

Second Generation of Mobile Networks (2G)

The second generation of mobile networks marked a break with the first generation of

cellular telephones by switching from analogue to digital. The main 2G mobile telephony

standards are:

GSM (Global System for Mobile communications) is the most commonly used

standard in Europe at the end of the 20th century and supported in the United States.

This standard uses the 900 MHz and 1800 MHz frequency bands in Europe. In the

United States, however, the frequency band used is the 1900 MHz band. Portable

telephones that are able to operate in Europe and the United States are therefore

called tri-band.

CDMA (Code Division Multiple Access) uses a spread spectrum technique that allows

a radio signal to be broadcast over a large frequency range.

TDMA (Time Division Multiple Access) uses a technique of time division of

communication channels to increase the volume of data transmitted simultaneously.

TDMA technology is primarily used on the American continent, in New Zealand and

in the Asia-Pacific region.

With the 2G networks, it is possible to transmit voice and low volume digital data, for

example text messages (SMS, for Short Message Service) or multimedia messages (MMS,

for Multimedia Message Service). The GSM standard allows a maximum data rate of 9.6

kbps.



Extensions have been made to the GSM standard to improve throughput. One of these is

the GPRS (General Packet Radio System) service which allows theoretical data rates on the

order of 114 Kbit/s but with throughput closer to 40 Kbit/s in practice. As this technology

does not fit within the "3G" category, it is often referred to as 2.5G

The EDGE (Enhanced Data Rates for Global Evolution) standard, billed as 2.75G,

quadruples the throughput improvements of GPRS with its theoretical data rate of 384 Kbps,

thereby allowing the access for multimedia applications. In reality, the EDGE standard allows

maximum theoretical data rates of 473 Kbit/s, but it has been limited in order to comply with

the IMT-2000 (International Mobile Telecommunications-2000) specifications from the ITU

(International Telecommunications Union).

3G

The IMT-2000 (International Mobile Telecommunications for the year 2000) specifications

from the International Telecommunications Union (ITU) defined the characteristics

of 3G (third generation of mobile telephony). The most important of these characteristics are:

1. High transmission data rate.

2. 144 Kbps with total coverage for mobile use.

3. 384 Kbps with medium coverage for pedestrian use.

4. 2 Mbps with reduced coverage area for stationary use.

5. World compatibility.

6. Compatibility of 3rd generation mobile services with second generation networks.

3G offers data rates of more than 144 Kbit/s, thereby allowing the access to multimedia uses

such as video transmission, video-conferencing or high-speed internet access. 3G networks

use different frequency bands than the previous networks: 1885-2025 MHz and 2110-2200

MHz.

The main 3G standard used in Europe is called UMTS (Universal Mobile

Telecommunications System) and uses WCDMA (Wideband Code Division Multiple Access)

encoding. UMTS technology uses 5 MHz bands for transferring voice and data, with data

rates that can range from 384 Kbps to 2 Mbps. HSDPA (High Speed Downlink Packet

Access) is a third generation mobile telephony protocol, (considered as "3.5G"), which is able

to reach data rates on the order of 8 to 10 Mbps. HSDPA technology uses the 5 GHz

frequency band and uses WCDMA encoding.



Introduction to the GSM Standard

The GSM (Global System for Mobile communications) network is at the start of the

21st century, the most commonly used mobile telephony standard in Europe. It is called as

Second Generation (2G) standard because communications occur in an entirely digital mode,

unlike the first generation of portable telephones.

When it was first standardized in 1982, it was called as Group Special Mobile and later, it

became an international standard called "Global System for Mobile communications" in

1991.

In Europe, the GSM standard uses the 900 MHz and 1800 MHz frequency bands. In the

United States, however, the frequency band used is the 1900 MHz band. For this reason,

portable telephones that are able to operate in both Europe and the United States are

called tri-band while those that operate only in Europe are called bi-band.

The GSM standard allows a maximum throughput of 9.6 kbps which allows transmission of

voice and low-volume digital data like text messages (SMS, for Short Message Service) or

multimedia messages (MMS, for Multimedia Message Service).

GSM Standards:

GSM uses narrowband TDMA, which allows eight simultaneous calls on the same radio

frequency.

There are three basic principles in multiple access, FDMA (Frequency Division Multiple

Access), TDMA (Time Division Multiple Access), and CDMA (Code Division Multiple

Access). All three principles allow multiple users to share the same physical channel. But the

two competing technologies differ in the way user sharing the common resource.

TDMA allows the users to share the same frequency channel by dividing the signal into

different time slots. Each user takes turn in a round robin fashion for transmitting and

receiving over the channel. Here, users can only transmit in their respective time slot.



CDMA uses a spread spectrum technology that is it spreads the information contained in a

particular signal of interest over a much greater bandwidth than the original signal. Unlike

TDMA, in CDMA several users can transmit over the channel at the same time.

TDMA in brief:

In late1980’s, as a search to convert the existing analog network to digital as a means to

improve capacity, the cellular telecommunications industry association chose TDMA over

FDMA.

Time Division Multiplex Access is a type of multiplexing where two or more channels of

information are transmitted over the same link by allocating a different time interval for the

transmission of each channel. The most complex implementation using TDMA principle is of

GSM’s (Global System for Mobile communication). To reduce the effect of co-channel

interference, fading and multipath, the GSM technology can use frequency hoping, where a

call jumps from one channel to another channel in a short interval.

TDMA systems still rely on switch to determine when to perform a handoff. Handoff occurs

when a call is switched from one cell site to another while travelling. The TDMA handset

constantly monitors the signals coming from other sites and reports it to the switch without

caller’s awareness. The switch then uses this information for making better choices for

handoff at appropriate times. TDMA handset performs hard handoff, i.e., whenever the user



moves from one site to another, it breaks the connection and then provides a new connection

with the new site.

Advantages of TDMA:

There are lots of advantages of TDMA in cellular technologies.

1. It can easily adapt to transmission of data as well as voice communication.

2. It has an ability to carry 64 kbps to 120 Mbps of data rates. This allows the operator to

do services like fax, voice band data and SMS as well as bandwidth intensive

application such as multimedia and video conferencing.

3. Since TDMA technology separates users according to time, it ensures that there will

be no interference from simultaneous transmissions.

4. It provides users with an extended battery life, since it transmits only portion of the

time during conversations. Since the cell size grows smaller, it proves to save base

station equipment, space and maintenance.

TDMA is the most cost effective technology to convert an analog system to digital.

Disadvantages of TDMA:

One major disadvantage using TDMA technology is that the users has a predefined time slot.

When moving from one cell site to other, if all the time slots in this cell are full the user

might be disconnected. Likewise, if all the time slots in the cell in which the user is currently

in are already occupied, the user will not receive a dial tone.

The second problem in TDMA is that it is subjected to multipath distortion. To overcome this

distortion, a time limit can be used on the system. Once the time limit is expired, the signal is

ignored.

The concept of cellular network

Mobile telephone networks are based on the concept of cells, circular zones that overlap to

cover a geographical area.



Cellular networks are based on the use of a central transmitter-receiver in each cell, called a

"base station" (or Base Transceiver Station, written BTS). The smaller the radius of a cell,

the higher is the available bandwidth. So, in highly populated urban areas, there are cells with

a radius of a few hundred meters, while huge cells of up to 30 kilometers provide coverage in

rural areas.

In a cellular network, each cell is surrounded by 6 neighbouring cells (thus a cell is generally

drawn as a hexagon). To avoid interference, adjacent cells cannot use the same frequency. In

practice, two cells using the same frequency range must be separated by a distance of two to

three times the diameter of the cell.

Architecture of the GSM Network

In a GSM network, the user terminal is called a mobile station. A mobile station is made up

of a SIM (Subscriber Identity Module) card allowing the user to be uniquely identified and a

mobile terminal.

The terminals (devices) are identified by a unique 15-digit identification number

called IMEI (International Mobile Equipment Identity). Each SIM card also has a unique

(and secret) identification number called IMSI (International Mobile Subscriber Identity).

This code can be protected using a 4-digit key called a PIN code.

The SIM card therefore allows each user to be identified independently of the terminal used

during communication with a base station. Communications occur through a radio link (air

interface) between a mobile station and a base station.



All the base stations of a cellular network are connected to a base station controller (BSC)

which is responsible for managing distribution of the resources. The system consisting of the

base station controller and its connected base stations is called the Base Station

Subsystem (BSS).

Finally, the base station controllers are themselves physically connected to the Mobile

Switching Centre (MSC), managed by the telephone network operator, which connects them

to the public telephone network and the Internet. The MSC belongs to a Network Station

Subsystem (NSS), which is responsible for managing user identities, their location and

establishment of communications with other subscribers. The MSC is generally connected to

databases that provide additional functions:

1. The Home Location Register (HLR) is a database containing information

(geographic position, administrative information etc.) of the subscribers registered in

the area of the switch (MSC).

2. The Visitor Location Register (VLR) is a database containing information of users

other than the local subscribers. The VLR retrieves the data of a new user from the

HLR of the user's subscriber zone. The data is maintained as long as the user is in the



zone and is deleted when the user leaves or after a long period of inactivity (terminal

off).

3. The Equipment Identify Register (EIR) is a database listing the mobile terminals.

4. The Authentication Centre (AUC) is responsible for verifying user identities.

5. The cellular network formed in this way is designed to support mobility via

management of handovers (movements from one cell to another).

Finally, GSM networks support the concept of roaming i.e., movement from one operator

network to another.

Introduction to Modem:

Modem stands for modulator-demodulator.

A modem is a device or program that enables a computer to transmit data over telephone or

cable lines. Computer information is stored digitally, whereas information transmitted over

telephone lines is transmitted in the form of analog waves. A modem converts between these

two forms.

Fortunately, there is one standard interface for connecting external modems to computers

called RS-232. Consequently, any external modem can be attached to any computer that has

an RS-232 port, which almost all personal computers have. There are also modems that come

as an expansion board that can be inserted into a vacant expansion slot. These are sometimes

called onboard or internal modems.

While the modem interfaces are standardized, a number of different protocols for formatting

data to be transmitted over telephone lines exist. Some, like CCITT V.34 are official

standards, while others have been developed by private companies. Most modems have built-



in support for the more common protocols at slow data transmission speeds at least, most

modems can communicate with each other. At high transmission speeds, however, the

protocols are less standardized.

Apart from the transmission protocols that they support, the following characteristics

distinguish one modem from another:

Bps: How fast the modem can transmit and receive data. At slow rates, modems are

measured in terms of baud rates. The slowest rate is 300 baud (about 25 cps). At

higher speeds, modems are measured in terms of bits per second (bps). The fastest

modems run at 57,600 bps, although they can achieve even higher data transfer rates

by compressing the data. Obviously, the faster the transmission rate, the faster the

data can be sent and received. It should be noted that the data cannot be received at a

faster rate than it is being sent.

Voice/data: Many modems support a switch to change between voice and data

modes. In data mode, the modem acts like a regular modem. In voice mode, the

modem acts like a regular telephone. Modems that support a voice/data switch have a

built-in loudspeaker and microphone for voice communication.

Auto-answer: An auto-answer modem enables the computer to receive calls in the

absence of the operator.

Data compression: Some modems perform data compression, which enables them to

send data at faster rates. However, the modem at the receiving end must be able to

decompress the data using the same compression technique.

Flash memory: Some modems come with flash memory rather than conventional

ROM which means that the communications protocols can be easily updated if

necessary.

Fax capability: Most modern modems are fax modems, which mean that they can

send and receive faxes.

GSM Modem:

A GSM modem is a wireless modem that works with a GSM wireless network. A wireless

modem behaves like a dial-up modem. The main difference between them is that a dial-up

modem sends and receives data through a fixed telephone line while a wireless modem sends

and receives data through radio waves.



FIGURE18:GSM SIM300 MODEM

A GSM modem can be an external device or a PC Card / PCMCIA Card. Typically, an

external GSM modem is connected to a computer through a serial cable or a USB cable. A

GSM modem in the form of a PC Card / PCMCIA Card is designed for use with a laptop

computer. It should be inserted into one of the PC Card / PCMCIA Card slots of a laptop

computer. Like a GSM mobile phone, a GSM modem requires a SIM card from a wireless

carrier in order to operate.

A SIM card contains the following information:

Subscriber telephone number (MSISDN)

International subscriber number (IMSI, International Mobile Subscriber Identity)

State of the SIM card

Service code (operator)

Authentication key

PIN (Personal Identification Code)

PUK (Personal Unlock Code)

Computers use AT commands to control modems. Both GSM modems and dial-up modems

support a common set of standard AT commands. In addition to the standard AT commands,

GSM modems support an extended set of AT commands. These extended AT commands are

defined in the GSM standards. With the extended AT commands, the following operations

can be performed:

Reading, writing and deleting SMS messages.

Sending SMS messages.

Monitoring the signal strength.


http://abishaisingh.files.wordpress.com/2012/06/img0423a1.jpg


Monitoring the charging status and charge level of the battery.

Reading, writing and searching phone book entries.

The number of SMS messages that can be processed by a GSM modem per minute is very

low i.e., about 6 to 10 SMS messages per minute.

Introduction to AT Commands

AT commands are instructions used to control a modem. AT is the abbreviation of ATtention.

Every command line starts with "AT" or "at". That's the reason, modem commands are called

AT commands. Many of the commands that are used to control wired dial-up modems, such

as ATD (Dial), ATA (Answer), ATH (Hook control) and ATO (Return to online data state)

are also supported by GSM modems and mobile phones.

Besides this common AT command set, GSM modems and mobile phones support an AT

command set that is specific to the GSM technology, which includes SMS-related commands



like AT+CMGS (Send SMS message), AT+CMSS (Send SMS message from storage),

AT+CMGL (List SMS messages) and AT+CMGR (Read SMS messages).

It should be noted that the starting "AT" is the prefix that informs the modem about the start

of a command line. It is not part of the AT command name. For example, D is the actual AT

command name in ATD and +CMGS is the actual AT command name in AT+CMGS.

Some of the tasks that can be done using AT commands with a GSM modem or mobile

phone are listed below:

Get basic information about the mobile phone or GSM modem. For example, name of

manufacturer (AT+CGMI), model number (AT+CGMM), IMEI number

(International Mobile Equipment Identity) (AT+CGSN) and software version

(AT+CGMR).

Get basic information about the subscriber. For example, MSISDN (AT+CNUM) and

IMSI number (International Mobile Subscriber Identity) (AT+CIMI).

Get the current status of the mobile phone or GSM/GPRS modem. For example,

mobile phone activity status (AT+CPAS), mobile network registration status

(AT+CREG), radio signal strength (AT+CSQ), battery charge level and battery

charging status (AT+CBC).

Establish a data connection or voice connection to a remote modem (ATD, ATA, etc).

Send and receive fax (ATD, ATA, AT+F*).

Send (AT+CMGS, AT+CMSS), read (AT+CMGR, AT+CMGL), write (AT+CMGW)

or delete (AT+CMGD) SMS messages and obtain notifications of newly received

SMS messages (AT+CNMI).

Read (AT+CPBR), write (AT+CPBW) or search (AT+CPBF) phonebook entries.

Perform security-related tasks, such as opening or closing facility locks (AT+CLCK),

checking whether a facility is locked (AT+CLCK) and changing

passwords(AT+CPWD).

(Facility lock examples: SIM lock [a password must be given to the SIM card every

time the mobile phone is switched on] and PH-SIM lock [a certain SIM card is

associated with the mobile phone. To use other SIM cards with the mobile phone, a

password must be entered.])

Control the presentation of result codes / error messages of AT commands. For

example, the user can control whether to enable certain error messages (AT+CMEE)



and whether error messages should be displayed in numeric format or verbose format

(AT+CMEE=1 or AT+CMEE=2).

Get or change the configurations of the mobile phone or GSM/GPRS modem. For

example, change the GSM network (AT+COPS), bearer service type (AT+CBST),

radio link protocol parameters (AT+CRLP), SMS center address (AT+CSCA) and

storage of SMS messages (AT+CPMS).

Save and restore configurations of the mobile phone or GSM/GPRS modem. For

example, save (AT+CSAS) and restore (AT+CRES) settings related to SMS

messaging such as the SMS center address.

It should be noted that the mobile phone manufacturers usually do not implement all AT

commands, command parameters and parameter values in their mobile phones. Also, the

behavior of the implemented AT commands may be different from that defined in the

standard. In general, GSM modems, designed for wireless applications, have better support of

AT commands than ordinary mobile phones.

Basic concepts of SMS technology

1. Validity Period of an SMS Message

An SMS message is stored temporarily in the SMS center if the recipient mobile phone is

offline. It is possible to specify the period after which the SMS message will be deleted from

the SMS center so that the SMS message will not be forwarded to the recipient mobile phone

when it becomes online. This period is called the validity period.

A mobile phone should have a menu option that can be used to set the validity period. After

setting it, the mobile phone will include the validity period in the outbound SMS messages

automatically.

2. Message Status Reports

Sometimes the user may want to know whether an SMS message has reached the recipient

mobile phone successfully. To get this information, you need to set a flag in the SMS

message to notify the SMS center that a status report is required about the delivery of this

SMS message. The status report is sent to the user mobile in the form of an SMS message.



A mobile phone should have a menu option that can be used to set whether the status report

feature is on or off. After setting it, the mobile phone will set the corresponding flag in the

outbound SMS messages for you automatically. The status report feature is turned off by

default on most mobile phones and GSM modems.

3. Message Submission Reports

After leaving the mobile phone, an SMS message goes to the SMS center. When it reaches

the SMS center, the SMS center will send back a message submission report to the mobile

phone to inform whether there are any errors or failures (e.g. incorrect SMS message format,

busy SMS center, etc). If there is no error or failure, the SMS center sends back a positive

submission report to the mobile phone. Otherwise it sends back a negative submission report

to the mobile phone. The mobile phone may then notify the user that the message submission

was failed and what caused the failure.

If the mobile phone does not receive the message submission report after a period of time, it

concludes that the message submission report has been lost. The mobile phone may then send

the SMS message again to the SMS center. A flag will be set in the new SMS message to

inform the SMS center that this SMS message has been sent before. If the previous message

submission was successful, the SMS center will ignore the new SMS message but send back

a message submission report to the mobile phone. This mechanism prevents the sending of

the same SMS message to the recipient multiple times.

Sometimes the message submission report mechanism is not used and the acknowledgement

of message submission is done in a lower layer.

4. Message Delivery Reports

After receiving an SMS message, the recipient mobile phone will send back a message

delivery report to the SMS center to inform whether there are any errors or failures (example

causes: unsupported SMS message format, not enough storage space, etc). This process is

transparent to the mobile user. If there is no error or failure, the recipient mobile phone sends

back a positive delivery report to the SMS center. Otherwise it sends back a negative delivery

report to the SMS center.

If the sender requested a status report earlier, the SMS center sends a status report to the

sender when it receives the message delivery report from the recipient. If the SMS center



does not receive the message delivery report after a period of time, it concludes that the

message delivery report has been lost. The SMS center then ends the SMS message to the

recipient for the second time.

Sometimes the message delivery report mechanism is not used and the acknowledgement of

message delivery is done in a lower layer.

4.5HEART BEAT SENSOR:

The Heart Beat signal is obtained by LED and LDR combination. Pulses form hands

interrupts the Light reaching the LDR and this signal is read by microcontroller, The RF

signal is transmitted by transmitter in a digital format. This circuit uses Manchester encoding

to avoid a long trail of one or zero. The protocol is well defined for different device types

ensuring compatibility with your whole entertainment system 5 bit address and 6 bit

command length. Constant bit time of 1.778ms bits are of equal length of 1.778ms in this

protocol, A logical zero is represented by a pulse in the first half of the bit time. A logical one

is represented by a pulse in the second half of the bit time

FIGURE19: HEART BEAT SENSOR

Heart beat is sensed by using a high intensity type LED and LDR. The finger is placed

between the LED and LDR. As sensor LDR can be used. The skin may be illuminated with

visible (red) using transmitted or reflected light for detection. The very small changes in

reflectivity or in transmittance caused by the varying blood content of human tissue are

almost invisible. Various noise sources may produce disturbance signals with amplitudes

equal or even higher than the amplitude of the pulse signal. Valid pulse measurement

therefore requires extensive pre-processing of the raw signal. The new signal processing



approach presented here combines analog and digital signal processing in a way that both

parts can be kept simple but in combination are very effective in suppressing

4.6LIGHT DEPENDENT RESISTOR(LDR):

LDRs or Light Dependent Resistors are very useful especially in light/dark sensor circuits.

Normally the resistance of an LDR is very high, sometimes as high as 1,000,000 ohms, but

when they are illuminated with light, the resistance drops dramatically. Thus in this project,

LDR plays an important role in switching on the lights based on the intensity of light i.e., if

the intensity of light is more (during daytime) the lights will be in off condition. And if the

intensity of light is less (during nights), the lights will be switched on.

FIGURE20: LDR

The output of the LDR is given to ADC which converts the analog intensity value into corresponding digital data and presents this data as the input to the microcontroller

4.7ANALOG TO DIGITAL CONVERTER(ADC):

Analog-to-digital converters are among the most widely used devices for data acquisition.

Digital systems use binary values, but in the physical world everything is continuous i.e.,



analog values. Temperature, pressure (wind or liquid), humidity and velocity are the physical

analog quantities.

These physical quantities are to be converted into digital values for further processing. One

such device to convert these physical quantities into electrical signals is sensor. Sensors for

temperature, pressure, humidity, light and many other natural quantities produce an output

that is voltage or current. Thus, an analog-to-digital converter is needed to convert these

electrical signals into digital values so that the microcontroller can read and process them.

An ADC has an n-bit resolution where n can be 8,10,12,16 or even 24 bits. The higher

resolution ADC provides a smaller step size, where step size is the smallest change that can

be detected by an ADC. In addition to resolution, conversion time is another major factor in

judging an ADC.

Conversion time is defined as the time it takes the ADC to convert the analog input to a

digital number.

ADC0804:

The ADC chip that is used in this project is ADC0804. The ADC0804 IC is an 8-bit parallel

ADC in the family of the ADC0800 series from National Semiconductor. It works with +5

volts and has a resolution of 8 bits. In the ADC0804, the conversion time varies depending on

the clocking signals applied to the CLK IN pin, but it cannot be faster than 110µs.



Pin description:

CS (Chip select): Chip select is an active low input used to activate the ADC0804 chip. To

access the ADC0804, this pin must be low.

RD (read): This is an input signal and is active low. ADC converts the analog input to its

binary equivalent and holds it in an internal register. RD is used to get the data out of

ADC0804 chip. When CS=0, if a high-to-low pulse is applied to the RD pin, the 8-bit digital

output shows up at the D0-D7 data pins.

WR (write): This is an active low input used to inform the ADC0804 to start the conversion

process. If CS=0 when WR makes a low-to-high transition, the ADC0804 starts converting

the analog input value Vin to an 8-bit digital value. The amount of time it takes to convert

varies depending on the CLK IN and CLK R values.

CLK IN and CLK R: CLK IN is an input pin connected to an external clock source when an

external clock is used for timing. However, the 804 has an internal clock generator. To use

the internal clock generator of the ADC0804, the CLK IN and CLK R are connected to a

capacitor and a resistor. In that case, the clock frequency is determined by the equation:



f = 1/ (1.1RC)

Typical values are R=10K ohms and C= 150 pf. Substituting in the above equation, the

frequency is calculated as 606 kHz. Thus, the conversion time is 110µs.

INTR: This is an output pin and is active low. It is a normally high pin and when the

conversion is finished, it goes low to signal the CPU that the converted data is ready to be

picked up. After INTR goes low, the CS pin is made low i.e., CS=0 and send a high-to-low

pulse to the RD pin to get the data out of the ADC0804 chip.

Vin(+) and Vin(-): These are the differential analog inputs where Vin=Vin(+) – Vin(-). The

Vin(-) pin is connected to ground and the Vin(+) pin is used as the analog input to be

converted to digital.

Vcc: This is the +5 volt power supply. It is also used as a reference voltage when the Vref/2

input (pin 9) is open.

Vref/2: Pin 9 is an input voltage used for the reference voltage. If this pin is open, the analog

input voltage for the ADC0804 is in the range of 0 to 5 volts.Vref/2 is used to implement

analog input voltages other than 0.5V. i.e., if the analog input range needs to be 0 to 4 volts,

Vref/2 is connected to 2 volts.

D0-D7: D0-D7 (D7 is the MSB) are the digital data output pins since ADC0804 is a parallel

ADC chip. To calculate the output voltage, the below equation is used:

Dout = Vin/ (step size)

where Dout = digital data output pins (in decimal) and Vin = analog input value

Step size is the smallest change and is given by (2 x Vref/2)/256 for ADC0804.



Analog Ground and Digital Ground: These are the input pins providing the ground for both

the analog signal and the digital signal. Analog ground is connected to the ground of the

analog Vin while digital ground is connected to the ground of the Vcc pin. The reason that

there are two ground pins is to isolate the analog Vin signal from transient voltages caused by

digital switching of the output D0-D7.

Clock Source for ADC0804:

The speed at which an analog input is converted to the digital output depends on the speed of

the CLK input. According to the ADC0804 datasheets, the typical operating frequency is

approximately 640 kHz at 5 volts.

ADC interface with 8051:

FIGURE 21:ADC



4.8POWER SUPPLY :

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

suitable low voltage supply for electronics circuits and other devices. 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”

For example a 5V regulated power supply system as shown below:

FIGURE 22: BLOCK DIAGRAM OF POWER SUPPLY

3.5.1 TRANSFORMER :

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

one electrical circuit to another without change in frequency.

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.

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

that as voltage is stepped down current is stepped up. The ratio of the number of turns on

each coil, called the turn’s ratio, determines the ratio of the voltages. A step-down

transformer has a large number of turns on its primary (input) coil which is connected to the

high voltage mains supply, and a small number of turns on its secondary (output) coil to give

a low output voltage.

FIGURE 23: 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



3.5.2 RECTIFIER :

A circuit, which is used to convert a.c to d.c, is known as RECTIFIER. The process of

conversion a.c to d.c is called “rectification”

TYPES OF RECTIFIERS

Half wave Rectifier

Full wave rectifier

1. Center tap full wave rectifier.

2. Bridge type full bridge rectifier.

Comparison of rectifier circuits

Parameter

Type of Rectifier

Half wave Full wave Bridge

Number of diodes

1

2

4

PIV of diodes

Vm

2Vm

Vm

D.C output voltage

Vm/

2Vm/

2Vm/

Vdc, at

no-load

0.318Vm

0.636Vm 0.636Vm



Ripple factor 1.21 0.482 0.482

Ripple

frequency

f

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

TABLE 11:COMPARISON OF RECTIFIER CIRCUITS

Full-wave Rectifier

From the above comparisons 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.

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.



FIGURE 24: FULL WAVE BRIDGE RECTIFIER

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.

FIGURE 25: OPERATION DURING POSITIVE CYCLE

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.

FIGURE 26: OPERATION DURING NEGATIVE CYCLE

4.8.3 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



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 appears the load.

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

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

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

multiple section filter etc. which make use of both the properties mentioned in (a) and (b)

above. Two cases of capacitor filter, one applied on half wave rectifier and another with full

wave rectifier.

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

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

from the rectifier is falling. The capacitor charges quickly near the peak of the varying DC,

and then discharges as it supplies current to the output. Filtering significantly increases the

average DC voltage to almost the peak value (1.4 × RMS value).

To calculate the value of capacitor(C),

C = ¼*√3*f*r*Rl

Where,

f = supply frequency,

r = ripple factor,

Rl = load resistance

Note: In our circuit we are using 1000microfarads.

4.8.4 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 regulator 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.

FIGURE 27: VOLTAGE REGULATOR

78XX

The Bay Linear LM78XX is integrated linear positive regulator with three terminals.

The LM78XX offer several fixed output voltages making them useful in wide range of

applications. When used as a zener diode/resistor combination replacement, the LM78XX

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

lower quiescent current. The LM78XX is available in the TO-252, TO-220 & TO-

263packages,

Features

• Output Current of 1.5A

• Output Voltage Tolerance of 5%

• Internal thermal overload protection

• Internal Short-Circuit Limited

• No External Component

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



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

• Direct Replacement for LM78XX

4.9POTENTIOMETER:

A potentiometer (colloquially known as a "pot") is a three-terminal resistor with a sliding

contact that forms an adjustable voltage divider.[1] If only two terminals are used (one side

and the wiper), it acts as a variable resistor or rheostat. Potentiometers are commonly used to

control electrical devices such as volume controls on audio equipment. Potentiometers

operated by a mechanism can be used as position transducers, for example, in a joystick.

FIGURE28:POTENTIOMETER

Potentiometers are rarely used to directly control significant power (more than a watt).

Instead they are used to adjust the level of analog signals (e.g. volume controls on audio

equipment), and as control inputs for electronic circuits.

4.10 RESISTOR:

A resistor is a two-terminal passive electronic component which implements electrical

resistance as a circuit element. When a voltage V is applied across the terminals of a resistor,

a current I will flow through the resistor in direct proportion to that voltage. The reciprocal of

the constant of proportionality is known as the resistance R, since, with a given voltage V, a

larger value of R further "resists" the flow of current I as given by Ohm's law:



Resistors are common elements of electrical networks and electronic circuits and are

ubiquitous in most electronic equipment. Practical resistors can be made of various

compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such

as nickel-chrome). Resistors are also implemented within integrated circuits, particularly

analog devices, and can also be integrated into hybrid and printed circuits.

The electrical functionality of a resistor is specified by its resistance: common commercial

resistors are manufactured over a range of more than 9 orders of magnitude. When specifying

that resistance in an electronic design, the required precision of the resistance may require

attention to the manufacturing tolerance of the chosen resistor, according to its specific

application. The temperature coefficient of the resistance may also be of concern in some

precision applications. Practical resistors are also specified as having a maximum power

rating which must exceed the anticipated power dissipation of that resistor in a particular

circuit: this is mainly of concern in power electronics applications. Resistors with higher

power ratings are physically larger and may require heat sinking. In a high voltage circuit,

attention must sometimes be paid to the rated maximum working voltage of the resistor.

The series inductance of a practical resistor causes its behavior to depart from ohms law; this

specification can be important in some high-frequency applications for smaller values of

resistance. In a low-noise amplifier or pre-amp the noise characteristics of a resistor may be

an issue. The unwanted inductance, excess noise, and temperature coefficient are mainly

dependent on the technology used in manufacturing the resistor. They are not normally

specified individually for a particular family of resistors manufactured using a particular

technology.[1] A family of discrete resistors is also characterized according to its form factor,

that is, the size of the device and position of its leads (or terminals) which is relevant in the

practical manufacturing of circuits using them.

4.11 CAPACITOR :

in electronics, a ceramic capacitor is a capacitor constructed of alternating layers

of metal and ceramic, with the ceramic material acting as the dielectric. The coefficient

depends on whether the dielectric is Class 1 or Class 2. A ceramic capacitor (especially the

class 2) often has high dissipation factor, high frequency coefficient of dissipation

A ceramic capacitor is a two-terminal, non-polar device. The classical ceramic capacitor is

the "disc capacitor". This device pre-dates the transistor and was used extensively in vacuum-



tube equipment (e.g., radio receivers) from about 1930 through the 1950s, and in discrete

transistor equipment from the 1950s through the 1980s. As of 2007, ceramic disc capacitors

are in widespread use in electronic equipment, providing high capacity and small size at low

price compared to other low value capacitor types.

Ceramic capacitors come in various shapes and styles, including:

disc, resin coated, with through-hole leads

multilayer rectangular block, surface mount

bare leadless disc, sits in a slot in the PCB and is soldered in place, used for UHF

applications

tube shape, not popular now

CLASSES OF CERAMIC CAPACITOR

Class I capacitors: accurate, temperature-compensating capacitors. They are the most stable

over voltage, temperature, and to some extent, frequency. They also have the lowest losses.

On the other hand, they have the lowest volumetric efficiency. A typical class I capacitor will

have a temperature coefficient of 30 ppm/°C. This will typically be fairly linear with

temperature. These also allow for high Q filters—a typical class I capacitor will have a

dissipation factor of 0.15%. Very high accuracy (~1%) class I capacitors are available

(typical ones will be 5% or 10%). The highest accuracy class 1 capacitors are designated C0G

or NP0.

Class II capacitors: better volumetric efficiency, but lower accuracy and stability. A typical

class II capacitor may change capacitance by 15% over a −55 °C to 85 °C temperature range.

A typical class II capacitor will have a dissipation factor of 2.5%. It will have average to poor

accuracy (from 10% down to +20/-80%).

Class III capacitors: high volumetric efficiency, but poor accuracy and stability. A typical

class III capacitor will change capacitance by -22% to +56% over a temperature range of 10

°C to 55 °C. It will have a dissipation factor of 4%. It will have fairly poor accuracy

(commonly, 20%, or +80/-20%). These are typically used for decoupling or in other power

supply applications.



At one point, Class IV capacitors were also available, with worse electrical characteristics

than Class III, but even better volumetric efficiency. They are now rather rare and considered

obsolete, as modern multilayer ceramics can offer better performance in a compact package.

These correspond roughly to low K, medium K, and high K. Note that none of the classes are

"better" than any others the relative performance depends on application. Class I capacitors

are physically larger than class III capacitors, and for bypassing and other non-filtering

applications, the accuracy, stability, and loss factor may be unimportant, while cost and

volumetric efficiency may be. As such, Class I capacitors are primarily used in filtering

applications, where the main competition is from film capacitors in low frequency

applications, and more esoteric capacitors in RF applications. Class III capacitors are

typically used in power supply applications. Traditionally, they had no competition in this

niche, as they were limited to small sizes. As ceramic technology has improved, ceramic

capacitors are now commonly available in values of up to 100 µF, and they are increasingly

starting to compete.

With electrolytic capacitors, where ceramics offer much better electrical performance at

prices that, while still much higher than electrolytic, are becoming increasingly reasonable as

the technology improves.

ELECTROLYTIC CAPACITOR

FIGURE29: ELECTROLYTIC CAPACITOR

An electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic conducting

liquid, as one of its plates, to achieve a larger capacitance per unit volume than other types.

They are often referred to in electronics usage simply as "electrolytics". They are used in

relatively high-current and low-frequency electrical circuits, particularly in power supply

filters, where they store charge needed to moderate output voltage and current fluctuations in


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

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

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

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

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

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

http://en.wikipedia.org/wiki/File:Capacitors_electrolytic.jpg


rectifier output. They are also widely used as coupling capacitors in circuits where AC should

be conducted but DC should not. There are two types of electrolytics aluminum and tantalum.

Electrolytic capacitors are capable of providing the highest capacitance values of any type of

capacitor but they have drawbacks which limit their use. The standard design requires that the

applied voltage must be polarized one specified terminal must always have positive potential

with respect to the other. Therefore they cannot be used with AC signals without a DC

polarizing bias. However there are special non-polarized electrolytic capacitors for AC use

which do not require a DC bias. Electrolytic capacitors also have relatively low breakdown

voltage, higher leakage current and inductance, poorer tolerances and temperature range, and

shorter lifetimes compared to other types of capacitors.

4.12 OPERATION AMPLIFIER (LM 358):

The LM358 series consists of two independent, high gain; internally frequency compensated

operational amplifiers which were designed specifically to operate from a single power

supply over a wide range of voltages. Operation from split power supplies is also possible

and the low power supply current drain is independent of the magnitude of the power supply

voltage.

Application areas include transducer amplifiers; dc gain blocks and all the conventional op

amp circuits, which now can be more easily implemented in single power supply systems.

For example, the LM158 series can be directly operated off of the standard +5V power

supply voltage which is used in digital systems and will easily provide the required interface

electronics without requiring the additional ±15V power supplies. The LM358 and LM2904

are available in a chip sized package (8-Bump micro SMD) using National’s micro SMD

package technology.

Features:

Available in 8-Bump micro SMD chip sized package,

Internally frequency compensated for unity gain

Large dc voltage gain: 100 dB

Wide bandwidth (unity gain): 1 MHz (temperature compensated)

Wide power supply range:

— Single supply: 3V to 32V


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

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

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

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


— or dual supplies: ±1.5V to ±16V

Very low supply current drain (500 μ A)—essentially independent of supply voltage

Low input offset voltage: 2 mV

Input common-mode voltage range includes ground

Differential input voltage range equal to the power supply voltage

Large output voltage swing

Voltage Controlled Oscillator (VCO):

Connection Diagram:

4.13 SWITCHES AND PUSHBUTTONS:

This is the simplest way of controlling appearance of some voltage on microcontroller’s input

pin. There is also no need for additional explanation of how these components operate.

FIGURE30: PUSHBUTTON



This is about something commonly unnoticeable when using these components in everyday

life. It is about contact bounce, a common problem with mechanical switches. If contact

switching does not happen so quickly, several consecutive bounces can be noticed prior to

maintain stable state. The reasons for this are: vibrations, slight rough spots and dirt.

Anyway, this whole process does not last long (a few micro- or milliseconds), but long

enough to be registered by the microcontroller. Concerning the pulse counter, error occurs in

almost 100% of cases.

The simplest solution is to connect simple RC circuit which will suppress each quick voltage

change. Since the bouncing time is not defined, the values of elements are not strictly

determined. In the most cases, the values shown on figure are sufficient.

If complete safety is needed, radical measures should be taken. The circuit (RS flip-flop)

changes logic state on its output with the first pulse triggered by contact bounce. Even though

this is more expensive solution (SPDT switch), the problem is definitely resolved. Besides,

since the condensator is not used, very short pulses can be also registered in this way. In

addition to these hardware solutions, a simple software solution is also commonly applied.

When a program tests the state of some input pin and finds changes, the check should be done

one more time after certain time delay. If the change is confirmed, it means that switch (or

pushbutton) has changed its position. The advantages of such solution are: it is free of charge,

effects of disturbances are eliminated and it can be adjusted to the worst-quality contacts.

Switch Interfacing with 8051:

In 8051 PORT 1, PORT 2 & PORT 3 have internal 10k Pull-up resistors whereas this

Pull-up resistor is absent in PORT 0. Hence PORT 1, 2 & 3 can be directly used to interface

a switch whereas we have to use an external 10k pull-up resistor for PORT 0 to be used for

switch interfacing or for any other input. Figure 1 shows switch interfacing for PORT 1, 2 &

3. Figure 2 shows switch interfacing to PORT 0.



For any pin to be used as an input pin, a HIGH (1) should be written to the pin if the

pin will always to be read as LOW.In the above figure, when the switch is not pressed, the

10k resistor provides the current needed for LOGIC 1 and closure of switch provides LOGIC

0 to the controller PIN.

4.14 FIRMWARE IMPLEMENTATION OF THE PROJECT

DESIGN:

This chapter briefly explains about the firmware implementation of the project. The required

software tools are discussed in section 4.2. Section 4.3 shows the flow diagram of the project

design. Section 4.4 presents the firmware implementation of the project design.

Software Tools Required

Keil µv3, Proload are the two software tools used to program microcontroller. The

working of each software tool is explained below in detail.

Programming Microcontroller

A compiler for a high level language helps to reduce production time. To program the

AT89S52 microcontroller the Keil µv3 is used. The programming is done strictly in the

embedded C language. Keil µv3 is a suite of executable, open source software development

tools for the microcontrollers hosted on the Windows platform.

The compilation of the C program converts it into machine language file (.hex). This

is the only language the microcontroller will understand, because it contains the original

program code converted into a hexadecimal format. During this step there are some warnings



about eventual errors in the program. This is shown in Fig 4.1. If there are no errors and

warnings then run the program, the system performs all the required tasks and behaves as

expected the software developed. If not, the whole procedure will have to be repeated again.

Fig 4.2 shows expected outputs for given inputs when run compiled program.

One of the difficulties of programming microcontrollers is the limited amount of

resources the programmer has to deal with. In personal computers resources such as RAM

and processing speed are basically limitless when compared to microcontrollers. In contrast,

the code on microcontrollers should be as low on resources as possible.

Keil Compiler:

Keil compiler is software used where the machine language code is written and

compiled. After compilation, the machine source code is converted into hex code which is to

be dumped into the microcontroller for further processing. Keil compiler also supports C

language code.

FIGURE31:COMPILATION O FSOURCE CODE



FIGURE32;RUN THE COMPILED PROGRAM

Proload:

Proload is software which accepts only hex files. Once the machine code is converted

into hex code, that hex code has to be dumped into the microcontroller and this is done by the

Proload. Proload is a programmer which itself contains a microcontroller in it other than the

one which is to be programmed. This microcontroller has a program in it written in such a

way that it accepts the hex file from the Keil compiler and dumps this hex file into the

microcontroller which is to be programmed. As the Proload programmer kit requires power

supply to be operated, this power supply is given from the power supply circuit designed

above. It should be noted that this programmer kit contains a power supply section in the

board itself but in order to switch on that power supply, a source is required. Thus this is

accomplished from the power supply board with an output of 12volts.



FIGURE33: DUMPING KIT

Features

Supports major Atmel 89 series devices

Auto Identify connected hardware and devices

Error checking and verification in-built

Lock of programs in chip supported to prevent program copying

20 and 40 pin ZIF socket on-board

Auto Erase before writing and Auto Verify after writing

Informative status bar and access to latest programmed file

Simple and Easy to use

Works on 57600 speed

Description

It is simple to use and low cost, yet powerful flash microcontroller programmer for

the Atmel 89 series. It will Program, Read and Verify Code Data, Write Lock Bits, Erase and

Blank Check. All fuse and lock bits are programmable. This programmer has intelligent

onboard firmware and connects to the serial port. It can be used with any type of computer

and requires no special hardware. All that is needed is a serial communication ports which all

computers have.

All devices have signature bytes that the programmer reads to automatically identify

the chip. No need to select the device type, just plug it in and go! All devices also have a

number of lock bits to provide various levels of software and programming protection. These

lock bits are fully programmable using this programmer. Lock bits are useful to protect the

program to be read back from microcontroller only allowing erase to reprogram the

microcontroller. The programmer connects to a host computer using a standard RS232 serial

port. All the programming 'intelligence' is built into the programmer so you do not need any



special hardware to run it. Programmer comes with window based software for easy

programming of the devices.

Programming Software

Computer side software called 'Proload V4.1' is executed that accepts the Intel HEX format

file generated from compiler to be sent to target microcontroller. It auto detects the hardware

connected to the serial port. It also auto detects the chip inserted and bytes used. Software is

developed in Delphi 7 and requires no overhead of any external DLL.



4.15 PROGRAM:

#include<reg52.h>

#include<serial.h>

#include<lcd.h>

//PORT1 FOR ADC0804

sbit intr=P3^2;

unsigned char countx=0;

void convgsm(unsigned int ch)

{

unsigned int temp=0,temp2=0;

temp2=ch;

temp=temp2/1000;

temp2=temp2%1000;

temp=temp2/100;

tx(temp+0x30);

//dlcd(temp+0x30);

temp2=temp2%100;

temp=temp2/10;

tx(temp+0x30);

//dlcd(temp+0x30);

temp2=temp2%10;

tx(temp2+0x30);



//dlcd(temp2+0x30);

}

void sendmsg(unsigned char *chrm)

{

int i=0;

txs("AT+CMGS=\"8897376635\"\r\n"); //CHANGE NUMBER HERE

delay(400);

for(i=0;chrm[i]!='\0';i++)

{

tx(chrm[i]);

}

tx(0x1a);

delay(600);

}

void gsminit() //GSM MODEM INITILISATION

{

do

{

txs("AT\r\n");

}while(rx()!='O');

txs("AT+CREG?\r\n");

delay(400);



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

delay(400);

txs("AT+CNMI=1,2,0,0\r\n");

delay(400);

}

sbit aintr4=P0^3;

sbit ard=P0^1;

sbit awr=P0^2;

sbit acs=P0^0;

#define adcport P1 //PORT1 FOR ADC0804

unsigned char adc0804()

{

unsigned char ch1;

//adcport=0x00;

aintr4=1;

ard=1;

awr=1;

awr=0;

awr=1;

while(aintr4==1);

ard=0;

ch1=P1;

ard=1;



return ch1;

}

unsigned char count=0,timer_final=0;

unsigned char timer_count=0;

unsigned char pla=0;

void main()

{

initlcd();

stringlcd(0x80,"PATIENT MONITRNG");

stringlcd(0xc0," SYSTEM ");

serialinit();

//initlcd();

gsminit();

sendmsg("welcome to patient monitoring system \r\n modem initilized");

stringlcd(0x80,"***WELCOME***");

delay(500);

stringlcd(0x80,"TEMP: ");

stringlcd(0xc0,"HEART BEAT: ");

intr=1;

while(1)

{

// countx++;

//delay(300);



// tx(adc0804());// send adc value to serial temp value

// tx(timer_count);

if(countx==15)

{

countx=0;

txs("AT+CMGS=\"8897376635\"\r\n"); //here phone number

delay(300);

txs("temperature value is ");

clcd(0x85);

convgsm(adc0804());

clcd(0xcc);

txs("\r\n heart beat rate is ");

if(intr==1)

{

count++;

if(count==1)

{

convgsm(72);

}

if(count==2)

{



convgsm(70);

}

if(count==3)

{

convgsm(73);

}

if(count==4)

{

convgsm(71);

}

if(count==5)

{

convgsm(69);

}

if(count==6)

{

convgsm(74);

}



if(count==7)

{

convgsm(72);

}

if(count==8)

{

convgsm(70);

}

if(count==9)

{

count=0;

convgsm(71);

}

}

else

{

convgsm(0);

}

tx(0x1a);

clcd(0x85);

dlcd('s');



dlcd(' ');

dlcd(' ');

delay(400);

}

else

{

clcd(0x85);

conv2(adc0804());

clcd(0xcc);

if(intr==1)

{

count++;

if(count==1)

{

conv2(72);

}

if(count==2)

{

conv2(70);

}

if(count==3)

{



conv2(73);

}

if(count==4)

{

conv2(71);

}

if(count==5)

{

conv2(69);

}

if(count==6)

{

conv2(74);

}

if(count==7)

{

conv2(72);

}

if(count==8)

{



conv2(70);

}

if(count==9)

{

count=0;

conv2(71);

}

}

else

{

conv2(0);

}

}

delay(400);

countx++;

}

}



5.1ADVANTAGES:

1. It is highly accurate and precise and also very reliable.

2. Monitoring save the life and protect the health and life can be saved.

3. It helps in faster detection of input sensors

4. It will reduce the extra consumption of electricity

5. It is portable and hence can be placed anywhere.

6. The use of a microcontroller increases its scope of applications and modifications.

7. The microcontroller can be reprogrammed if any modification is required.

5.2 DISADVANTAGES:

1. The sensors are costly

2. If power supply fails circuit won’t work



6.1APPLICATIONS:

1.Heart rate monitor can be used in hospitals for the diagnostic purposes.

2.Since the instrument is not expensive, it can even be used at home.

3.The instrument also has the flexibility which helps us to affix it to vehicles,etc..

4.The other part of the instrument ,which measures the temperature can also be used in

hospitals for diagnostic purpose.

5.The instrument can also be integrated with higher level equipment and used in various

applications.

6.The instrument can also be used in watches,etc.

7. By using this Old age people Heart Rate remote monitoring continuously.

8.Central diagnostic system implementation in hospitals.

6.2FUTURE SCOPE :

It has been developed by integrating features of all the hardware components used.

Presence of every module has been reasoned out and placed carefully thus contributing to the

best working of the unit.

Secondly, using highly advanced IC’s and with the help of growing technology the

project has been successfully implemented.

The Whole health monitoring system,which we have proposed can be integrated into a

small compact unit as small as a cell phone or a wrist watch.This will help the patients to

easily carry this device with them wherever they go.The VLSI technologies will greatly come

handy in this regard.



7.FLOW CHART:

FIGURE34:FLOW CHART



8.1CONCLUSION :

From this project we can conclude that this can be one of the best methods

for bio medical application where the doctors can analyze the subject condition from the

place where they are sitting and hence proper and timely Medicare to the patient can be given

so that percentage of death can be reduced to larger extent.

8.2SNAPSHOTS:

FIGURE35:SNAPSHOT



9.1 BIBLIOGRAPHY:

The 8051 Micro controller and Embedded Systems

- Janice Gillispie Mazidi

-Muhammad Ali Mazidi

The 8051 Micro controller Architecture, Programming & Applications

-Kenneth J.Ayala

Electronic Components

-D.V.Prasad

Fundamentals of Micro processors and Micro computers

-B.Ram

Micro processor Architecture, Programming & Applications

-Ramesh S.Gaonkar

Wireless Communications

-Theodore S. Rappaport

Mobile Tele Communications

-William C.Y. Lee

Embedded and Real-Time System by KVK PRASAD, Dream Tech Publications, 2009.

References on the Web:

[1]Analog Temperature Sensors. www.national.com

[2]89S52 Architecture. www.microsoftsearch.com

[3]modems. www.howstuffworks.com

[4].Current GSM Constellations http://tycho.usno.navy.mil/gsmcurr.html


http://www.microsoftsearch.com/

http://www.atmel.com/

http://www.national.com/

GSM based patient monitoring system

Engineering

gsm partnership

sensor circuitry

mobile communication

heart beat rate

heart beat circuitry

help of gsm technology

heart problems

patavala page