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Microcontroller
Selection Criteria
1. The first and the foremost criterion for selecting a microcontroller is that it must meet
the task at hand efficiently and cost effectively. In analyzing the need of a
microcontroller based project we must see whether an 8 bit, 16 bit, 32 bit
microcontroller can best handle the computing need of the task most efficiently.
Among other consideration in this category are speed, power consumption, amount of
on chip RAM and ROM, the number of sufficient I/O ports and cost per unit.
2. Second how easy is it to develop product around it. Key considerations are the
availability of an assembler, debugger, emulator and technical support.
3. Its ready availability in needed quantity, both now and in future.
Taking all these considerations we have chosen “ATMEL 89C51” microcontroller.
2.3.1.2 Brief History of 8051
In 1981, Intel Corporation introduced an 8 bit microcontroller called 8051, this
had 128 bytes of RAM, 4 bytes of on chip ROM, two timers, one serial port, and 4
ports each 8 bits wide all on a single chip. At this time it was referred to as “system on
chip”. The 8051 is an 8 bit processor meaning that the CPU can work only on 8 bit at a
time. Data larger than 8 bit has to be broken up into 8 bit pieces to be processed by the
CPU.
The 8051 became widely popular after Intel allowed other manufacturers to make
and market any flavor of 8051 with the condition that they remain code compatible
with 8051. This has lead to many versions of 8051 with a different speed and amount of
on chip ROM marketed by different companies.
Software
As our project required involved the application of software, on consulting with our
project guide we came to the conclusion that we shall use Embedded C for
programming utilizing the Keil software
Use of embedded processors cars, mobile phones, medical equipment, aerospace
systems etc is widespread. The applications of embedded C are exploited through the
Keil software. Keil was founded in 1986 to market add on products for development
tools provided by many of the silicon vendors. It soon became evident that there was a
void in the market placethat must be filled with quality software development tools. It
was then that Keil introduced the first C compiler designed from the ground-up
specifically for 8051 microcontroller.
The literature about Keil was collected from the net as well as some e-books via
the internet. http://www.keil.com/company is the link of the site from which the basics
of the software was taken.
Chapter 3. ADOPTED METHODOLOGY
Planning in phases:
Before commencement of the project it was decided to plan the project in phases so the
following are the phases in which the project will be done:
The very first phase was planning the project and getting the concepts right about the
project.
This involved lot of reading and understanding about the core concepts and the
applications of our project.
Getting to know about the features of various components present in the circuitry.
Learning about various softwares like keil , Eagle 4.11 etc that will be used in our
project.
Procuring the various components required for the project.
Creating the PCB (printed circuit board) for our project.
Interfacing the monitoring system with GSM module.
Implementing the entire project.
Testing the working of the final monitoring system.
3.3TUTORIAL ON MICROCONTROLLER
The 89C51 microcontroller is from the 8051 family of microcontrollers. The basis
features of all the controllers in this family are the same, except for a few differences
from device to device. The features of the Atmel IC 89C51 is discussed in detail below.
below.
3.3.1
Memory Organization
The basic block diagram of the family of the 80x51 is as shown below in the
figure.
Fig. 3.8
All 80x51 devices have separate address spaces for program and data memory.
The logical separation of program and data memory allows the data memory to be
accessed by 8-bit addresses, which can be quickly stored and manipulated by an 8-bit
CPU. Program memory (ROM, EPROM) can only be read, not written to. There can
be up to 64k bytes of program memory. In the 89C51,there is 4K Bytes of
Reprogrammable Flash Memory(Program Memory) and 128 x 8-bit Internal RAM
(Data Memory).
3.3.2
Special Function Registers
3.6.2.1 Description
Special Function Registers (SFRs) ate area of memory that control
functionality of the processor. SFRs are accessed as if they were normal Internal
RAM. The only difference is that Internal RAM is from address 00h through 7Fh
whereas SFR registers exist in the address range of 80h through FFh. Each SFR has
an address (80h through FFh) and a name. The following chart provides a graphical
presentation of the 80C51's SFRs, their names, and their address.
Fig. 3.9
As you can see, although the address range of 80h through FFh offer 128 possible
addresses, there are only 19 SFRs in a standard 80C51. All other addresses in the SFR
range (80h through FFh) are considered invalid. Writing to or reading from these
registers may produce undefined values or behavior. There are 3 categories of SFR’s
namely I/O, control and other.
Whether a given I/O line is high or low and the value read from the line are
controlled by the I/O SFRs. The control SFRs in some way control the operation or
the configuration of some aspect of the 80x51. For example, TCON controls the
timers, SCON controls the serial port.The remaining SFRs, are "other SFRs." These
SFRs can be thought of as auxillary SFRs in the sense that they don't directly
configure the 80x51 but obviously the 80x51 cannot operate without them. For
example, once the serial port has been configured using SCON, the program may read
or write to the serial port using the SBUF register.
3.6.2.2 Overview of all SFR’s
This section will endeavor to quickly overview each of the standard SFRs
found in the above SFR chart map. This section is to just give you a general idea of
what each SFR does.
SP (Stack Pointer, Address 81h): This is the stack pointer of the
microcontroller. This SFR indicates where the next value to be taken from the stack
will be read from in Internal RAM. If you push a value onto the stack, the value will
be written to the address of SP + 1. That is to say, if SP holds the value 07h, a PUSH
instruction will push the value onto the stack at address 08h. This SFR is modified by
all instructions which modify the stack, such as PUSH, POP, LCALL, RET, RETI,
and whenever interrupts are provoked by the microcontroller.
DPL/DPH (Data Pointer Low/High, Addresses 82h/83h): The SFRs DPL and
DPH work together to represent a 16-bit value called the Data Pointer. The data
pointer is used in operations regarding external RAM and some instructions involving
code memory. Since it is an unsigned two-byte integer value, it can represent values
from 0000h to FFFFh (0 through 65,535 decimal).
PCON (Power Control, Addresses 87h): The Power Control SFR is used to
control the power control modes. Certain operation modes allow the to go into a type
of "sleep" mode which requires much less power. These modes of operation are
controlled through PCON. Additionally, one of the bits in PCON is used to double the
effective baud rate of the serial port.
TCON (Timer Control, Addresses 88h, Bit-Addressable): The Timer Control
SFR is used to configure and modify the way in which the two timers operate. This
SFR controls whether each of the two timers is running or stopped and contains a flag
to indicate that each timer has overflowed. Additionally, some non-timer related bits
are located in the TCON SFR. These bits are used to configure the way in which the
external interrupts are activated and also contain the external interrupt flags which are
set when an external interrupt has occured.
TMOD (Timer Mode, Addresses 89h): The Timer Mode SFR is used to
configure the mode of operation of each of the two timers. Using this SFR your
program may configure each timer to be a 16-bit timer, an 8-bit autoreload timer, a
13-bit timer, or two separate timers. Additionally, you may configure the timers to
only count when an external pin is activated or to count "events" that are indicated on
an external pin.
TL0/TH0 (Timer 0 Low/High, Addresses 8Ah/8Ch): These two SFRs, taken
together, represent timer 0. Their exact behavior depends on how the timer is
configured in the TMOD SFR; however, these timers always count up. What is
configurable is how and when they increment in value.
TL1/TH1 (Timer 1 Low/High, Addresses 8Bh/8Dh): These two SFRs, taken
together, represent timer 1. Their exact behavior depends on how the timer is
configured in the TMOD SFR; however, these timers always count up. What is
configurable is how and when they increment in value.
P1 (Port 1, Address 90h, Bit-Addressable): This is input/output port 1. Each bit
of this SFR corresponds to one of the pins on the microcontroller. For example, bit 0
of port 1 is pin P1.0, bit 7 is pin P1.7. Writing a value of 1 to a bit of this SFR will
send a high level on the corresponding I/O pin whereas a value of 0 will bring it to a
low level.
SCON (Serial Control, Addresses 98h, Bit-Addressable): The Serial Control
SFR is used to configure the behavior of the on-board serial port. This SFR controls
the baud rate of the serial port, whether the serial port is activated to receive data, and
also contains flags that are set when a byte is successfully sent or received.
SBUF (Serial Control, Addresses 99h): The Serial Buffer SFR is used to send
and receive data via the on-board serial port. Any value written to SBUF will be sent
out the serial port's TXD pin. Likewise, any value which it receives via the serial
port's RXD pin will be delivered to the user program via SBUF. In other words,
SBUF serves as the output port when written to and as an input port when read from.
IE (Interrupt Enable, Addresses A8h): The Interrupt Enable SFR is used to
enable and disable specific interrupts. The low 7 bits of the SFR are used to
enable/disable the specific interrupts, where as the highest bit is used to enable or
disable ALL interrupts. Thus, if the high bit of IE is 0 all interrupts are disabled
regardless of whether an individual interrupt is enabled by setting a lower bit.
P3 (Port 3, Address B0h, Bit-Addressable): This is input/output port 3. Each bit
of this SFR corresponds to one of the pins on the microcontroller. For example, bit 0
of port 3 is pin P3.0, bit 7 is pin P3.7. Writing a value of 1 to a bit of this SFR will
send a high level on the corresponding I/O pin whereas a value of 0 will bring it to a
low level.
IP (Interrupt Priority, Addresses B8h, Bit-Addressable): The Interrupt Priority
SFR is used to specify the relative priority of each interrupt. An interrupt may either
be of low (0) priority or high (1) priority. An interrupt may only interrupt interrupts of
lower priority. For example, if we configure so that all interrupts are of low priority
except the serial interrupt, the serial interrupt will always be able to interrupt the
system, even if another interrupt is currently executing. However, if a serial interrupt
is executing no other interrupt will be able to interrupt the serial interrupt routine
since the serial interrupt routine has the highest priority.
PSW (Program Status Word, Addresses D0h, Bit-Addressable): The Program
Status Word is used to store a number of important bits that are set and cleared by
instructions. The PSW SFR contains the carry flag, the auxiliary carry flag, the
overflow flag, and the parity flag. Additionally, the PSW register contains the register
bank select flags which are used to select which of the "R" register banks are
currently selected.
ACC (Accumulator, Addresses E0h, Bit-Addressable): The Accumulator is
one of the most-used SFRs, since it is involved in so many instructions. The
Accumulator resides as an SFR at E0h, which means the instruction MOV A,#20h is
really the same as MOV E0h,#20h. However, it is a good idea to use the first method
since it only requires two bytes whereas the second option requires three bytes.
B (B Register, Addresses F0h, Bit-Addressable): The "B" register is used in
two instructions: the multiply and divide operations. The B register is also commonly
used by programmers as an auxiliary register to temporarily store values.
3.6.3 Timers/Counters
3.6.3.1 General Description
The MCS-51 has two 16 bit Timer/ Counter register Timer 0 and Timer 1. Both
can be configured to operate either as timers or event counter. Microcontroller can be
used as timer or counter as you need. Microcontroller will act as timer when switch
position on upper and microcontroller will act as counter when switch position on
lower by controlling C/T bit on TMOD register. The diagram below shows the logic
of the timer/counter circuit.
Fig. 3.10
The timer/counter is controlled by the two registers TMOD and TCON. Both the
timers share these registers. The layout of both these registers is given below.
Timer/ Counter Mode Control ( TMOD ) Register
TIMER 1
GATE
C/T
TIMER 0
M1
M0
GATE
C/T
M1
M0
GATE: Gating control when set. Timer/ Counter X is enabled only while INTx
pin is high and TRx control pin is set
C/T : Timer or Counter Selector cleared for Timer operation (input from internal
system clock) and set for counter operation (input from Tx input pin)
M0 M1 : Indicates the mode of the Timer/ Couner
Timer/ Counter Control ( TCON ) Register
MSB
TF1
LSB
TR1
TF0
TR0
IE1
IT1
IE0
IT0
TFx: Timer overflow flag. Set by hardware on Timer/Counter overflow. Cleared
by hardware when processor vector to interrupt routine, or clearing the bit in
software.
TRx: Timer Run control bit . Set/ cleared by software to turn Timer/ Counter
on/off
IEx: Interrupt Edge flag. Set by hardware when external interrupt edge detected.
Cleared when interrupt processed.
ITx: Interrupt type control bit. Set/ cleared by software to specefy falling edge/
low level trigerred external interrupts
3.6.3.2 Modes of the timer
M1
M0
0
0
0
1
1
0
Operating
13 bit Timer, TLx serves as 5 bit prescaler
16 bit Timer/Counter THx and TLx are cascaded, there is no
prescaler
8 bit auto reaload Timer/ Counter THx holds a value which is
tobe reloaded into TLx each time it overflows
(Timer 0) TL0 is an 8 bit Timer/ Counter controlled by the
1
1
standard timer 0 control bits
(Timer 1) Timer/ Counter 1 stopped
Mode 0 (13-bit Timer mode) :
Figure shows the Mode 0 operation as it applies to Timer 1. In this mode,
the Timer register is configured as a 13-bit register. As the count rolls over from all
1s to all 0s, it sets the Timer interrupt flag TF1. The counted input is enabled to the
Timer when TR1 = 1 and either GATE = 0 or INT1 = 1. (Setting GATE = 1 allows
the Timer to be controlled by external input INT1, to facilitate pulse width
measurements). The 13-bit register consists of all 8 bits of TH1 and the lower 5 bits
of TL1. The upper 3 bits of TL1 are indeterminate and should be ignored. Setting the
run flag (TR1) does not clear the registers. Mode 0 operation is the same for the
Timer 0 as for Timer 1.
Fig. 3.11
Mode 1 (16-bit Timer mode) :
Mode 1 is the same as Mode 0, except that the Timer register is being run
with all 16 bits.
Fig. 3.12
Mode 2 (8-bit Auto Reload):
Mode 2 configures the Timer register as an 8-bit Counter (TL1) with
automatic reload, as shown in Figure. Overflow from TL1 not only sets TF1, but also
reloads TL1 with the contents of TH1, which is preset by software. The reload leaves
TH1 unchanged.
Fig. 3.13
Mode 3 (2 8-bit Counter/Timer):
Timer 1 in Mode 3 simply holds its count. The effect is the same as setting
TR1=0. Timer 0 in Mode 3 establishes TL0 and TH0 as two separate counters. The
logic for Mode 3 on Timer 0 is shown in Figure. TL0 uses the Timer 0 control bits:
C/T, GATE, TR0, INT0, and TF0. TH0 is locked into a timer function (counting
machine cycles) and takes over the use of TR1 and TF1 from Timer 1. Thus, TH0
now controls the “Timer 1” interrupt. Mode 3 is provided for applications requiring
an extra 8-bit timer on the counter. With Timer 0 in Mode 3, an 80C51 can look like
it has three Timer/Counters. When Timer 0 is in Mode 3, Timer 1 can be turned on
and off by switching it out of and into its own Mode 3, or can still be used by the
serial port as a baud rate generator, or in fact, in any application not requiring an
interrupt.
Fig 3.14
3.7 SERIAL COMMUNICATION :
3.7.1 Serial Port in 89C51
The serial port is full duplex, meaning it can transmit and receive
simultaneously. It is also receive-buffered, meaning it can commence reception of a
second byte before a previously received byte has been read from the register.
The serial port receive and transmit registers are both accessed at Special Function
Register SBUF. Writing to SBUF loads the transmit register, and reading SBUF
accesses a physically separate receive register.
Fig. 3.15
The serial port can operate in 4 modes:
Mode 0:
Serial data enters and exits through RxD. TxD outputs the shift clock. 8
bits are transmitted/received (LSB first). The baud rate is fixed at 1/12 the oscillator
frequency.
Mode 1:
10 bits are transmitted (through TxD) or received (through RxD): a start
bit (0), 8 data bits (LSB first), and a stop bit (1). On receive, the stop bit goes into
RB8 in Special Function Register SCON. The baud rate is variable.
Mode 2:
11 bits are transmitted (through TxD) or received (through RxD): start bit
(0), 8 data bits (LSB first), a programmable 9th data bit, and a stop bit (1). On
Transmit, the 9th data bit (TB8 in SCON) can be assigned the value of 0 or 1. On
receive, the 9th data bit goes into RB8 in Special Function Register SCON, while the
stop bit is ignored. The baud rate is programmable to either 1/32 or 1/64 the oscillator
frequency.
Mode 3:
11 bits are transmitted (through TxD) or received (through RxD): a start
bit (0), 8 data bits (LSB first), a programmable 9th data bit, and a stop bit (1). In fact,
Mode 3 is the same as Mode 2 in all respects except baud rate. The baud rate in Mode
3 is variable.
In all four modes, transmission is initiated by any instruction that uses SBUF as a
destination register. Reception is initiated in Mode 0 by the condition RI = 0 and
REN = 1. Reception is initiated in the other modes by the incoming start bit if REN =
1.
3.7.2 RS232 Standards :
In telecommunications, RS-232 (Recommended Standard 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. The RS-232 standard defines the voltage levels that correspond
to logical one and logical zero levels. The standard has been renamed several times
during its history as the sponsoring organization changed its name, and has been
variously known as EIA RS 232, EIA 232, and most recently as TIA 232. Valid
signals are plus or minus 3 to 15 volts. The range near zero volts is not a valid RS232 level; logic one is defined as a negative voltage, the signal condition is called
marking, and has the functional significance of OFF. Logic zero is positive, the signal
condition is spacing, and has the function ON. The standard specifies a maximum
open-circuit voltage of 25 volts. The region -3 to +3 is called as a dead band, since
the voltages are undefined in this region. For this reason to use RS232 to any
microcontroller we must first use voltage converters like MAX232 to convert TTL
logic to RS232 logic and vice versa. Such chips are commonly known as line drivers.
3.7.3 MAX232
A standard serial interfacing for PC, RS232C, requires negative logic, i.e.,
logic '1' is -3V to -12V and logic '0' is +3V to +12V. To convert a TTL logic, say,
TxD and RxD pins of the uC chips, thus need a converter chip. A MAX232 chip has
long been using in many uC boards. It provides 2-channel RS232C port and requires
external 10uF capacitors. This I.C. also includes two receivers and two transmitters in
the same package. This is useful in many cases when you only want to use the
Transmit and Receive data Lines. You don't need to use two chips, one for the receive
line and one for the transmission.
Fig. 3.16
Chapter 4. ANALYSIS EXPERIMENTATION AND
RESULTS
4.1 IC DESCRIPTION
4.1.1 MICROCONTROLLER ATMEL AT89C51
4.1.1.1 Features

Compatible with MCS®51 Products

4K Bytes of Reprogrammable Flash Memory

2.7V to 6V Operating Range

Fully Static Operation: 0 Hz to 24 MHz

Two-level Program Memory Lock

128 x 8-bit Internal RAM

15 Programmable I/O Lines

Two 16-bit Timer/Counters

Six Interrupt Sources

Programmable Serial UART Channel

Direct LED Drive Outputs

On-chip Analog Comparator

Low-power Idle and Power-down Modes

Brown-out Detection

Power-On Reset (POR)

Green
(Pb/Halide-free/RoHS
Compliant)
Packaging
– Endurance: 1,000
Write/Erase Cycles
4.1.1.2.Description
The AT89C51 is a low-voltage, high-performance CMOS 8-bit
microcontroller with 4K bytes of Flash programmable and erasable read-only
memory. The device is manufactured using Atmel’s high-density nonvolatile
memory technology and is compatible with the industry-standard MCS-51
instruction set. By combining a versatile 8-bit CPU with Flash on a monolithic
chip, the Atmel AT89C51 is a powerful microcontroller which provides a highlyflexible and cost-effective solution to many embedded control applications.
The AT89C51 provides the following standard features: 4K bytes of
Flash, 128 bytes of RAM, 15 I/O lines, two 16-bit timer/counters, a five-vector,
two-level interrupt architecture, a full duplex serial port, a precision analog
comparator, on-chip oscillator and clock circuitry. In addition, the AT89C51 is
designed with static logic for operation down to zero frequency and supports two
software-selectable power saving modes. The Idle Mode stops the CPU while
allowing the RAM, timer/counters, serial port and interrupt system to continue
functioning. The power-down mode saves the RAM contents but freezes the
oscillator disabling all other chip functions until the next hardware reset.
4.1.1.3. Pin Diagram
Fig. 4.1
4.1.1.4. Internal Block Diagram
Fig. 4.2
4.1.1.5. Pin Description
VCC
Supply voltage.
GND
Ground.
Port 1
Port 1 is an 8-bit bi-directional I/O port. Port pins P1.2 to P1.7 provide internal
pullups. P1.0 and P1.1 require external pullups. P1.0 and P1.1 also serve as the
positive input (AIN0) and the negative input (AIN1), respectively, of the on-chip
precision analog comparator. The Port 1 output buffers can sink 20 mA and can
drive LED displays directly. When 1s are written to Port 1 pins, they can be used
as inputs. When pins P1.2 to P1.7 are used as inputs and are externally pulled low,
they will source current (IIL) because of the internal pullups. Port 1 also receives
code data during Flash programming and verification.
Port 3
Port 3 pins P3.0 to P3.5, P3.7 are seven bi-directional I/O pins with internal
pullups. P3.6 is hard-wired as an input to the output of the on-chip comparator
and is not accessible as a general- purpose I/O pin. The Port 3 output buffers can
sink 20 mA. When 1s are written to Port 3 pins they are pulled high by the
internal pullups and can be used as inputs. As inputs, Port 3 pins that are
externally being pulled low will source current (IIL) because of the pullups. Port 3
also serves the functions of various special features of the AT89C51 as listed
below: Port 3 also receives some control signals for Flash programming and
verification.
Port
Pin
Alternate Functions
P3.0
RXD
(serial input port)
P3.1
TXD
(serial output port)
P3.2
INT0
(external interrupt 0)
P3.3
INT1
(external interrupt 1)
P3.4
T0
(timer 0 external input)
P3.5
T1
(timer 1 external input)
RST
Reset input. All I/O pins are reset to 1s as soon as RST goes high. Holding the
RST pin high for two machine cycles while the oscillator is running resets the
device. Each machine cycle takes 12 oscillator or clock cycles.
XTAL1
Input to the inverting oscillator amplifier and input to the internal clock operating
circuit.
XTAL2
Output from the inverting oscillator amplifier.
4.1.2 MAX232
4.1.2.1 Features

Meets or Exceeds TIA/EIA-232-F and ITU Recommendation V.28

Operates From a Single 5-V Power Supply With 1.0-uF Charge-Pump
Capacitors

Operates Up To 120 kbit/s

Two Drivers and Two Receivers

±30-V Input Levels

Low Supply Current . . . 8 mA Typical

ESD Protection Exceeds JESD 22-2000-V Human-Body Model (A114-A)

Upgrade With Improved ESD (15-kV HBM)and 0.1-_F Charge-Pump
Capacitors is available With the MAX202

Applications :TIA/EIA-232-F, Battery-Powered Systems, Terminals,
Modems, and Computers
4.1.2.2 Description
The MAX232 is a dual driver/receiver that includes a capacitive
voltage generator to supply TIA/EIA-232-F voltage levels from a single 5-V
supply. Each receiver converts TIA/EIA-232-F inputs to 5-V TTL/CMOS levels.
These receivers have a typical threshold of 1.3 V, a typical hysteresis of 0.5 V,
and can accept ±30-V inputs. Each driver converts TTL/CMOS input levels into
TIA/EIA-232-F levels. The driver, receiver, and voltage-generator functions are
available as cells in the Texas Instruments LinASIC™ library.
4.1.2.3 Pin Diagram
Fig. 4.3
4.1.2.4 Interfacing Diagram
The diagram below shows the interfacing pin configuration of the IC
MAX232 with the DB9 (Female) serial port connector and the Microcontroller.
16X2 LCD DISPLAY
4.1.5.1 Features

Maximum input voltage: 5.3VDC

Operating input voltage: 5VDC

8-bit interface data bus

Controller: HD47780 equivalent

Character font size: 0.125"W x 0.200"H

16 pin/terminals

Display size: 2.5"L x 0.7"W

Module size: 3.4"L x 1.2"W x 0.5"T
4.1.5.2 Description
This is a 16 character by 2 line display, with the standard HD44780
chipset. It works great with any microcontroller and it is very easy to interface. This LCD
has 8-bit parallel interface. It is possible to use all 8 bits plus 3 control signals or 4 bits
plus the control signals.
4.1.5.3 Pin Diagram
Fig. 4.6
Fig. 4.7
4.1.5.4 LCD Interfacing diagram
The diagram below gives the interfacing configuration of the LCD with
the microcontroller.
Energy Metering Circuit:
This enrgy meter is manly built around the IC 7751, an ANALOG DEVICE
ELECTRONIC ENERGY METERING IC, which converts the analog input energy
reading into output as pulse for displaying the count value which is equivalent to the
energy consumption. In addition to monitoring the energy consumption and data
transmission & reception, the meter also provides protection against high voltage, over
current and theft by immediately disconnecting metering circuit from the supply and
altering the consumer by giving an audible alarm, so that the consumer or maintenance
personal to take corrective action.
This circuit takes two current samples in terms of voltage form then takes one voltage
sample, and then generates a series of pulses depending upon the load connected.
It contains analog to digital converter section internal to it, and it also ahs its own
reference, it work s on the fixed frequency source generated by the crystal connected to it
externally.
There is also fault detection facility provided in the metering IC, So whenever the two
currents i.e. Phase and neutral, differs by the value more than 12% fault indication is
provided.
2.1 ENERGY MEASUREMENT BLOCK:
This block takes the proportional voltage, proportional current in a fixed duration
so that the energy consumed V*I*t. To obtained the voltage supply 230V is potentially
dived with the help of respective network and thus part of AC voltage under
measurement is obtained. Similarly, to obtain the current measurement differential input
signals are taken using current transformers.
These two signals (V & I) are fed to AD 7751. This IC internally multiply current
and voltage signal and generate instantaneous power signal. This signal is low pass
filtered and converted to frequency F1 and F2 using digital to frequency converter, these
signals are taken across pin no 23 and 24. Thus the o/p is a frequency signal proportional
to the consumed energy.
The internal block diagram schematic of the 7751 is shown below,
Opto Coupler Ic :
Is is a 4 termianl device,it provides isolation between two different circuits, it enables in
sending the information through optical medium,
What it does is it provides isolation from the electrical circuit which is having the AC gnd
and the micro controller circuit which is having DC gnd.
If isolation was not there then because of presence of neutral as AC Gnd, which would
have been get combined with the DC gnd, then it would have created the short circuit the
complete damaging of the digital circuitry.
That is why there exits a opto coupler.
Two numbers of opto couplers are used in cascade manner that is in series so that both
the get the same pulse at the same time.
One opto coupler sends pulses to the stationary counting micro controller circuit and
other sends signal to remote station.
Micro controller block:
This block contains the main circuitry which measures the enrgy in terms of the
pulses,here micro controller AVR is configured as counting the in put pulses as well as
diplaying the reading on the back light LCD.
Mocro contreoller is to be configured as a counter by putting the appropriate vlue in its
TMOD register,sele cting the preticular timer as a counter and selecrting the particular
poin as input pin for receiving the pulses.then also configure the modes aof the operation
of the counting, mode 0 is selcted inthis application,as it has 8 bit wide register it counts
upto 255 and with 5 bit prescaler so combining both we get the last counting value upto
1fffh.it counts in mod32 manner.So if 1kwhr=3200 pulses then 100 count of the 32 is to
be displayed o the LCD display.
Display:Display section include 16*1 back light LCD interfaced with the microcontroller. It has
own processor to control the display information. So the interfacing of the LCD is done
same as peripherals. It has own commands, addresses for the different locations on
different lines. Here 16 character one line LCD with 5 * 7 dot matrix pattern LCD is used
it require 5v supply for operation & same 5v for back light LED. The back light is having
greenish yellow shade of light. It has 8 data lines for sending the data over it & 3 control
lines to communicate with the LCD. Before reading & writing to LCD its busy status
need to be checked.
LCD gives more advantages & as compaired to the LED 7 segment displays. They are as
follows
1) The decline in price of LCD
2) The ability to display number, character & graphics. This is in contrast to LED which
are limited to numbers & few character.
3)In corporation of refreshing controller into the LCD, thereby relieving the CPU of the
task of refreshing the LDC. In contrast, the LED must be refreshed by the CPU (or in
some other way) to keep displaying the data.
4)Ease of programming for characters & graphics.
LCD:
It is a back light LCD, It has its own processor so it can be called as intelligent LCD. It is
treated as other peripheral device. So it needs to be interfaced like any other device.
It has 8 data lines and 3 control lines,
Using these 3 control lines one can read and write into the LCD, it also has internal
RAM.
IT also has address location specifying the particular location on particular lines. For 1
line the address starts from 80H through 8F so one can specify the location of the
character or number be displayed.
These 3 control lines are R/S: register select
R/W: read Write
E:
Transmitter:-
Enable
It contains the GSM module for transmission of the data in the form of SMS.SMS is send
to the user informing him about the update.GSM module SIM 300 is used in this
project.It is interfaced with the microcontroller using serial communication i.e. RS232
protocol.
Receiver Block:
The transmitted data is received by the mobile phone of the user whose number is fed
into the data base. So that information in the form of SMS is send.
Power Supply:For our all IC we require 5V D.C. supply which can be generated by step
down transformer, full wave bridge rectifier, filter condenser & voltage
regulator IC7805.
12V supply for relay is generated separately using the same procedure as
above.
Chapter 4 : Design Details
5.1
Power supply design
Power supply is the first and the most important part of our project. For our
project we require +5V regulated power supply with maximum current rating
500mA Following basic building blocks are required to generate regulated power supply.
Step-down
transformer
Mains 230 V
A.C.
Rectifier
Filter
Ckt.
Three
Terminal
Voltage reg.
Regulated O/P
Voltage
Step Down Transformer :-
Step down transformer is the first part of regulated power supply. To
step down the mains 230V A.C. we require step down transformer.
Following are the main characteristic of electronic transformer.
1) Power transformers are usually designed to operate from source of low
impedance at a single freq.
2) It is required to
construct with sufficient insulation of necessary
dielectric strength.
3) Transformer ratings are expressed in volt–amp. The volt-amp of each
secondary winding or windings are added for the total secondary VA. To
this are added the load losses.
4) Temperature rise of a transformer is decided on two well-known factors
i.e. losses on transformer and heat dissipating or cooling facility provided
unit.
Rectifier Unit :-
Rectifier unit is a ckt. which converts A.C. into pulsating D.C.
Generally semi-conducting diode is used as rectifying element due to its
property of conducting current in one direction only. Generally there are two
types of rectifier.
1) Half wave rectifier
2) Full wave rectifier
In half wave rectifier only half cycle of mains A.C. is rectified so its
efficiency is very poor. So we use full wave bridge type rectifier, in which
four diodes are used. In each half cycle, two diodes conduct at a time and we
get maximum efficiency at o/p.
Following are the main advantages and disadvantages of a full-wave
bridge type rectifier ckt.
Advantages:1) The need of center tapped transformer is eliminated.
2) The o/p is twice that of center tap circuit for the same secondary voltage.
3)The PIV rating of diode is half of the center tap circuit.
Disadvantages:-
1) It requires four diodes.
2) As during each half cycle of A.C. input, two diodes are conducting
therefore voltage drop in internal resistance of rectifying unit will be
twice as compared to center tap circuit.
Filter Circuit :-
Generally a rectifier is required to produce pure D.C. supply for using
at various places in the electronic circuit. However, the o/p of rectifier has
pulsating character i.e. if such a D.C. is applied to electronic circuit it will
produce a hum i.e. it will contain A.C. and D.C. components. The A.C.
components are undesirable and must be kept away from the load. To do so
a filter circuit is used which removes (or filters out) the A.C. components
reaching the load. Obviously a filter circuit is installed between rectifier and
voltage regulator. In our project we use capacitor filter because of its low
cost, small size and little weight and good characteristic. Capacitors are
connected in parallel to the rectifier o/p because it passes A.C. but does not
pass D.C. at all.
Three terminal voltage regulator :-
A voltage regulator is a ckt. that supplies constant voltage regardless of
change in load current. IC voltage regulators are versatile and relatively
cheaper. The 7800 series consists of three terminal positive voltage
regulator. These ICs are designed as fixed voltage regulator and with
adequate heat sink, can deliver o/p current in excess of 1A. These devices
do not require external component. This IC also has internal thermal
overload protection and internal short circuit and current limiting
protection. For our project we use voltage regulator Ics 7812 & 7805.
Design of Step down Transformer:The following information must be available to the designer before he
commences for the design of transformer.
1) Power Output.
2) Operating Voltage.
3) Frequency Range.
4) Efficiency and Regulation.
Size of core
Size of core is one of the first considerations in regard of weight and volume of
transformer. This depends on type of core and winding configuration used. Generally
following formula is used to find area or size of core.
P1
Ai
=
----------0.87
Ai
= Area of cross - section in Sq. cm. and
P1
= Primary voltage.
In transformer
P1 = P2
For our project we required +5V regulated output. So transformer secondary
rating is 12V, 4A
So secondary power wattage is,
P2
= 12 x 4 w.
= 48w
48
So Ai = 0.87
= 7.427
Generally 10% of area should be added to core to accommodate all turns for
low Iron losses and compact size.
So
Ai
= 8.1697
Turns per volt
Turns per volt of transformer are given by relation
10,000
Turns / Volt
= ----------------------4.44 f Bm Ai
Here,
f is the frequency in Hz
Bm is flux density in Wb/m2
Ai is net area of cross section.
Following table gives the value of turns per volt for 50 Hz frequency.
Flux
density
1.14
1.01
0.91
0.83
0.76
40/Ai
45/Ai
50/Ai
55/Ai
60/Ai
Wb/m2
Turns per volt
Generally lower the flux density better be quality of transformer.
For project for 50 Hz the turns per Volt for 0.91 Wb/m2 from above table.
Turns per Volt
= 50 / Ai
50
= 8.1697
 6.13
Thus for Primary winding
= 220 x 6.13 = 1346.43.
& for Secondary winding
= 12 x 6.13 = 74
Wire size
As stated above size depends upon the current to be carried out by the
winding, which depends upon current density of 3.1 A/mm2. For less copper
losses 1.6 A/mm2 or 2.4 A/mm2 may be used. Generally even size guage of
wire are used.
Rectifier Design
R.M.S. Secondary voltage at secondary of transformer is 12V.
So maximum voltage Vm across Secondary is
= Rms. Voltage x 2
= 12 x 2
= 16.97
D.C. O/p Voltage at rectifier O/p is
2 Vm
Vdc
=
---------
2 x 16.97
= ----------------------
=
10.80 V
PIV rating of each diode is
PIV = 2 Vm.
= 2 x 16.97
= 34 V
& maximum forward current which flow from each diode is 500mA.
So from above parameter we select diode IN 4007 from diode selection
manual.
Design of Filter Capacitor
Formula for calculating filter capacitor is,
1
C =
---------------------43 r f RL.
r
= ripple present at o/p of rectifier.
(Which is maximum 0.1 for full wave rectifier.)
F
= frequency of mains A.C.
RL
= I/p impedance of voltage regulator IC.
1
C =
-----------------------------43 x 0.1 x 50 x 28
= 1030 f
 1000 f.
And voltage rating of filter capacitor is double of Vdc i.e. rectifier o/p which
is 20V. So we choose 1000 f / 25V filter capacitor. [ Ref : 6 ]
IC 7812 (Voltage Regulator IC.)
Specifications :
Available o/p D.C. Voltage
= +12V.
Line Regulation
= 0.03
Load Regulation
= 0.5
Vin maximum
= 35 V
123
Ripple Rejection = 66-80 (db)
IC 7805 (Voltage Regulator IC.)
Specifications :
Available o/p D.C. Voltage
= + 5V.
123
Line Regulation
= 0.03
Load Regulation
= 0.5
Vin maximum
= 35 V
Ripple Rejection = 66-80 (db)
Chapter 2 : Technical Details
IC 78XX (Voltage Regulator IC )
 OUTPUT CURRENT UP TO 1.5 A
 OUTPUT VOLTAGESOF 5; 5.2; 6; 8; 8.5; 9;
 12; 15; 18; 24V
 THEOVERLOADPROTECTION
 SHORT CIRCUIT PROTECTION
 OUTPUT TRANSITION SOA PROTECTION
DESCRIPTION
The L7800 series of three-terminal positive regulators is available in TO-220
TO-220FP TO-3 and D2PAK packages and several fixed output voltages,
making it useful in a wide range of applications. These regulators can
provide local on-card regulation, eliminating the distribution problems
associated with single point regulation. Each type employs internal current
limiting, thermal shut-down and safe area protection, making it essentially
indestructible. If adequate heat sinking is provided, they can deliver over 1A
output current. Although designed primarily as
Electrical Characteristic :
PCB DESIGNING AND FABRICATION
Introduction to printed circuit boards:
It is called PCB in short; printed circuit pattern applied to one or both sides
of an insulating base, depending upon that, and it is called single sided PCB
or double-sided PCB.
Conductor materials available are silver, brass, aluminum and copper;
copper is most widely used which is used here as well. The thickness of
conducting material depends on the current carrying capacity of the circuit.
The printed circuit board usually serves three functions:
1.
It provides mechanical support to the components mounted on it.
2.
It provides necessary electrical interconnection.
3.
It acts as heat sink, i.e., it provides a conduction path leading to
removal of most of the heat generated in the circuit.
Cu clad
The base of laminate is either paper of glass fiber cloth. Cu foil, which is
produced by the method of electroplating, is placed on laminate and both are
kept under hydraulic pressure for proper adhesive pressure for proper
adhesive. These Cu clad are easily available in the market.
Types of Laminates
National Electrical Manufactures Association (NEMA) has various grades of
laminates that are obtained by different resins and filters.
1.
Phenol
Phenol and Formaldehyde produce phenolic paper base laminate it has
phenolic resins with proper filter. This is Brown in color and opaque.
Disadvantage is poor moisture resistance.
2.
Epoxy Laminates
Epoxy paper that is also paper based but impregnated with epoxy resin,
yellowish white and translucent.
Epoxy Glass; This base material has high mechanical strength and good
electrical properties usually green in color and semitransparent.
There are a variety of laminates available. We have selected Fiber Glass
epoxy laminate.
PCB fabrication includes following steps:
1)
Layout of the circuit
2)
Artwork designing
3)
Printing
4)
Etching
5)
Drilling
6)
Mounting of components and soldering
7)
Finishing
1.
Layout
The layout of a PCB has to incorporate all the board before one can
go onto the all work preparation. Detailed circuit diagram, the design
concept and the philosophy behind the equipment are very important for the
layout.
Layout Scale
Depending on the accuracy required artwork should be produced at a 1:1 or
2:1 or even 4:1 scale. The layout is best prepared on the same scale as the
artwork to prevent the entire problem, which might be caused by redrawing
of the layout to the artwork scale. The layout/ artwork scale commonly
applied is 2:1 with a 1:1 scale, no demanding single sided boards can be
designed but sufficient care should be taken, particularly during the artwork
preparation.
Procedure
The first rule is to replace each and every PCB layout as viewed from
the component side. This rule must be strictly followed to avoid confusion,
which would otherwise be caused.
Another important rule is not to start the designing of a layout unless an
absolutely clear circuit diagram is available.
Among the components, the larger ones are placed first and the space in
between is filled with smaller ones. Components requiring input/output
connecting come near the connector. All components are placed in such a
manner that de-soldering of other components is not necessary if they have
to be replaced.
Layout sketch
The end product of the layout designing is the pencil sketched
component and conductor drawing which is caller ‘layout sketched’. It
contains all the information for the preparation of the network.
Component holes
In a given, PCB most all the holes required are one particular
diameter. Holes of a different are shown with a code in the actual layout
sketch.
Conductor Holes
A code can be used for the conductor with a special width. Minimum
spacing should also be provided.
A) Holes
Standard holes
1.1 mm
1.5 mm
3.2 mm
B) Conductor Widths
Standard width, 0.5 mm
1 mm
2 mm
4 mm
2) Artwork
The generation of PCB artwork should be considered as the first step of the
PCB manufacturing process. The importance of a prefect artwork should not
be under estimated. Problems like inaccurate registered, broken annular
rings or too critical spacing are often due to bad artwork. And even with the
most sophisticated PCB production facilities, PCB can be made better than
the quality of the artwork used.
Basic Approaches
For ink drawing on white cardboard paper, good quality Indian ink and
ink-pen set are minimum requirements.
Drawing practice ---drawing procedure is very at-least by 0.1 – 0.2, and
solder pad locations.
And conductors can be easily displaced by 0.3 – 0.5 mm
3) Screen Printing
The process of screening – printing is well known to the printing
industry because of its inherent capabilities of printing a wide range of inks
on almost any kind of surface including glass, metal, plastic fabrics etc.
Found their way into an extremely broad field of applications.
Screen-printing offers the advantage of wide control on the ink deposition,
thickness though the selection of suitable mass density and composition. In
the production of PCB’s, it is successfully employed in printing of

Etch resists

Plate resists

Solder stop lacquers

Notation printing
In its basic form, the screen-printing process is very simple. A screen fabric
with uniform meshes and opening is stretched and fixed on a solid frame of
metal or wood. The circuit pattern area open, while the meshes in the rest of
the area is closed.
In the actual printing step, ink is forced by the moving squeeze thorough the
open meshes onto the surface of the material to be printed.
The ink deposition, in a magnified cross section, shows the shape of a
trapezoid.
Pattern transfer onto the Screen
There are two different methods in use, and each method has its own
advantages and disadvantages.
With the direct method, the screen is prepared by coating a photographic
emulsion directly onto the screen fabric and exposing it in the pattern area.
The indirect method makes use of a separate screen process film, supported
on a backing sheet. The film on its backing sheet that is there after pressed
onto the screen fabric and sticks there. Finally, the backing sheet is peeled
off, opening all those screen meshes, which are not covered by the film
pattern.
The direct method provides very durable screen stencils with a higher
dimensional accuracy but the finest details are not reproduced. The indirect
method is more suitable for smaller series and where the finest details to be
reproduced. The indirect method is faster but dimensionally less accurate
and the screen stencils are less durable, more sensitive to mechanical
damages and interruption in printing.
4) Etching
In all subtractive PCB process, etching is one of the most important steps.
The final copper pattern is formed by selective removal of all the unwanted
copper, which is not protected by an etching unit.
Solutions, which are used in etching process, are known as enchants.
I)
Ferric Chloride
II)
Cupric Chloride
III)
Chromic Acid
IV)
Alkaline Ammonia.
Of these Ferric Chloride is widely used because it has short etching time and
it can be stored for a long time. Etching of PCBs as required in modern
electronic equipment production, is usually done in spray type etching
machines.
Tank or bubble etching, in which the boards kept in tank, were lowered and
fully immersed into the agitated, has almost disappeared.
5) Component Mounting
Careful mounting of components on PCB increases the reliability of
assembly.
1)
The leads must be cleaned before they are inserted in PCB holes.
Asymmetric lead bending must be avoided; the ENT leads must fit into
holes properly so that they can be soldered.
2)
When space is to be saved then vertical mounting is to be preferred.
The vertical leads must have an insulating sleeve.
3)
Where jumper wire crosses over conductors, they must be insulated.
4)
For mounting of PCBs, TO5, DIP packages special jigs must be used
of easy insertion.
5)
While mounting transistors, each lead must insulating sleeve. All the
flat radial components such as resistors, diodes and inductors are mounted
and soldered. Then IC bases are soldered. The vertical components such as
transistors, gang condenser and FET are mounted & soldered.
6) Soldering
The next process after the component mounting is soldering; solder pint is
achieved by heating the solder and base metal about the melting point of the
solders used.
The necessary heat depends upon:
1)
The nature and type of joints
2)
Melting temperature of solder
3)
Flux
Soldering techniques are of so many types but we are using iron soldering.
Iron soldering
Soldering iron consists of an insulating handle connected through a metal
shaft, of a bit accurately makes contact with the component parts of the joint
and solder and heats them up. The electrical heating element is located in the
hollow shank or handle to heat the bit.
Functions of the Bit
It stored heat and convey it from the heat source to the work. It may be
required to store surplus solder from the joint. It may be required to store
molten solder and flux to the work.
The surface must be lined and wetted; this encourages flow of solder into the
joint. When the surface of the work becomes tested by the solder, a
continuous flow of liquid metal between the bit and the work provides a path
of high thermal conductivity through which heat can flow into the work
piece.
Solder bit are made up of copper; this metal has good wetting property, heat
capability and thermal conductivity. Tin-lead solder affects copper during
soldering operation. Production of copper bit can be made with thick iron
coating followed by Ni/Tin plating. The life of the bit is increased by a
factor of 10 to 15. Solder irons are specified in terms of wattage. Depending
on heat input intended for working and types of work ( continuous or
individual) the choice of the solder iron can be made.
Procedure of Soldering
The points to be joined must be cleaned first and fluxed. The hard solder
iron and solder wire is applied to the work. The melted solder becomes
bright and fluid. The iron must be removed after sufficient time and joint is
allowed to coal.
At the end, finishing is done.
PCB, Designing using computer aided designing (CAD):
CAD has many advantages over manual designing, important among then is:
1)
Changes can be easily made because we don’t have to erase our pencil
work on paper repeatedly.
2)
Time is saved.
3)
Before taking printout we can have preview of the design etc.
The software which we have used is Quick-route.
Circuit diagram
Layout