Energy Meter Load Control
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Transcript of Energy Meter Load Control
PORT1
8051
LevelConvert
er
SMS
GSM BASED ENERGY METERDSFDC Motor ControlDC Motor Control
GSM ENERGY METER
1
TABLE OF CONTENTS
INTRODUCTION
Introduction
Methodology
Scope of Work
Aims of the GSM Electronic Notice Board
Objectives of the GSM Home Appliance Control Device
Block diagram
Circuit diagram
Component list
THEORETICAL BACKGROUND AND LITERATURE REVIEW
Theoretical Background
GSM Architecture
Technical Details
Main Cellular Standards
GSM Frequencies
Network Structure
Subscriber Identity Module (SIM)
Literature Review
GSM Security
HARDWAR DISCRIPTION
DESIGN AND CONSTRUCTION
GSM Modem
Accessing GSM MODEM using Microsoft HyperTerminal
Testing of GSM Modem
2
List of Important AT Commands
Microcontroller – MODEM Interfacing
DTE and DCE
TESTS, RESULTS, AND DISCUSSION
Testing and Observations
Operational Flowchart
Initializations
Serial transfer using TI and RI flags
Validity Check
Display
Programmer
Simulator
Burner
RECOMMENDATION AND CONCLUSION
Conclusion
Problems Encountered
Future Improvement
Recommendation
REFERENCES AND TROUBLESHOOTING
3
INTRODUCTION
GSM and GPRS based Designs have developed another
innovative and Public utility product for mass communication
[1]. The purpose of this project is to remote monitoring and
control of the Domestic Energy meter. This system enables the
Electricity Department to read the meter readings regularly
without the person visiting each house. This can be achieved by
the use of micro controller unit that continuously monitors and
records the Energy Meter readings in its permanent (non-
volatile) memory location. This system also makes use of a
GSM modem for remote monitoring and control of Energy
Meter.
The Microcontroller based system continuously records
the readings and the live meter reading can be sent to the
Electricity department on request. This system also can be used
to disconnect the power supply to the house in case of non-
payment of electricity bills. A dedicated GSM modem with SIM
card is required for each energy meter.
4
The main aim of the project will be to design a SMS electronic
ENERGY METER toolkit which can replace the traditional
ENERGY METER. The toolkit send SMS to Electricity
Department number, The system is made efficient by SIMs so
that the SMS can be received by number of devices boards in a
locality using techniques of time division multiple access.
The main components of the toolkit include microcontroller,
GSM modem. These components are integrated with the device
board and thus incorporate the wireless features. The GSM
modem receives the SMS. The AT commands are serially
transferred to the modem. In return the modem transmits the
stored message through the wireless link. The microcontroller
used in this case is ATMEL AT89S52. SIMCOM 300 is used as
the GSM modem. In this prototype model, LCD display is used
for simulation purpose. The results presented in the thesis
support the proper functionalities and working of the system.
The timing diagram suggests the response of the modem to
various AT (attention) commands.
5
METHODOLOGY
The method used to carry out this project is the principle of
serial communication in collaboration with embedded systems.
This is a very good project for Industries. This project has a
GSM ENERGY METER, which will be used as the electronic
device, and also a GSM modem, which is the latest technology
used for communication between the mobile and the embedded
devices.
System will work like when the user wants to receive a
sms on the consumption of the engery in houses and offices; the
modem sent a message through the subscriber identity module
(SIM) which is inserted in the display system MODEM.
SCOPE OF WORK
I will use liquid crystal display for displaying the message; I will
also use GSM modem (Motorola W220) as an interface between
mobile and microcontroller. It will send message to any phone
irrespective of the GSM network through the modem connected
to the programmable device.
6
AIMS OF THE GSM ENERGY METER
Uses: This is every useful and innovative project.
We can use this to secure our houses and offices to save
power and money of the nation.
OBJECTIVES OF THE ENERGY METER
Programming of the mobile phone with AT (Attention)
command sequence
Interfacing the programming chip with the personal
computer
Interfacing the programmable chip with the DC Motor.
Interfacing of the mobile phone with the programmable
chip
Sending messages from the remote phone to control device.
7
BLOCK DIAGRAM
8
89S52
REGULATED POWER SUPPLY
GSM MODEM
LCD
APPLIANCES
MOBILE PHONES
RELAY
METER
CIRCUIT DIAGRAM
9
COMPONENT LIST
Meter Monitoring with Temper proof
Name Capacity Quantity Code
Regulator 7805 1 U1
Regulator 7812 1 U3
Capacitor 1000µf 1 C1
Capacitor 10µf 1 C2
Ceramic Capacitor 22pf 2 C3,C4
Diode 4 D1,D2,D3,D4
Push Button 1
Mobile Phone 1
Relay 1 RL1
LCD 16*2 1
40 Pin Base 1 U2
16 Pin Base 1 U5
ULN2003 1
8051(AT89S52) 1
Oscillator 11.0592mhz 1 X1
10
LED 2 D5,D7
Resistance 220Ω 3 R1,R4,R8
Resistance 1k 1 R3
Resistance 10k 2 R2,R5
Buzzer 1 BUZ1
BC547 1 Q1
Energy meter 1
11
THEORETICAL BACKGROUND AND
LITERATURE REVIEW
THEORETICAL BACKGROUND
GSM (Global System for Mobile communications: originally
from GROUPE Spécial Mobile) is the most popular standard for
mobile phones in the world. Its promoter, the GSM Association,
estimates that 80% of the global mobile market uses the
standard. GSM is used by over 3 billion people across more than
212 countries and territories [4]. Its ubiquity makes international
roaming very common between mobile phone operators
enabling subscribers to use their phones in many parts of the
world. GSM differs from its predecessors in that both signaling
and speech channels are digital, and thus is considered a second
generation (2G) mobile phone system [5]. This has also meant
that data communication was easy to build into the system.
12
GSM ARCHITECTURE
GSM is a complex system and difficult to understand. The
Mobile Station (MS) refers to the mobile equipment [6]. The
Base Station Subsystem controls the radio link with the Mobile
Station. The Network Subsystem performs main functions such
as switching of calls between mobile users, mobility
management operations, and proper operation and setup of a
network [7]. These functions are controlled by the Mobile
Services Switching Center (MSC).
TECHNICAL DETAILS
GSM is a cellular network, which means that mobile phones
connect to it by searching for cells in the immediate vicinity.
MAIN CELLULAR STANDARDS
13
YEAR STANDARD MOBILE
TELEPHONE
SYSTEM
TECHNO
LOGY
PRIMARY
MARKETS
1981 NMT540 NORDIC MOBILE
TELEPHONY
ANALOG
UE
EUROPE,MIDDL
E EAST
1985 TACS TOTAL ACCESS
COMMUNUNICATION
SYSTEM
ANALOG
UE
EUROPE AND
CHINA
1986 NMT900 NORDIC MOBILE
TELEPHONY
ANALOG
UE
EUROPE,
MIDDLE EAST
1991 GSM GLOBAL SYSTEM FOR
MOBILE
COMMUNICATION
DIGITAL WORLD-WIDE
1991 TDMA TIME DIVISION
MULTIPLE ACCESS
DIGITAL AMERICA
1993 CDMA CODE DIVISION
MULTIPLE ACCESS
DIGITAL NORTH
AMERICA,
KOREA
1992 GSM 1800 GLOBAL SYSTEM FOR
MOBILE
COMMUNICATION
DIGITAL EUROPE
1994 PDC PERSONAL DIGITAL
CELLULAR
DIGITAL JAPAN
1995 PCS 1900 PERSONAL
COMPUTER SERVICES
DIGITAL NORTH
AMERICA
2001 GSM 800 GLOBAL SYSTEM FOR
MOBILE
COMMUNICATION
DIGITAL NORTH
AMERICA
2006-TILL
DATE
GSM 450 GLOBAL SYSTEM FOR
MOBILE
DIGITAL WORLD-WIDE
14
COMMUNICATION
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 [9]
NETWORK STRUCTURE
The network behind the GSM seen by the customer is large and
complicated in order to provide all of the services which are
required.
The Base Station Subsystem (the base stations and their
controllers).
15
The Network and Switching Subsystem (the part of the
network most similar to a fixed network). This is
sometimes also just called the core network.
The GPRS Core Network (the optional part which allows
packet based Internet connections).
All of the elements in the system combine to produce many
GSM services such as voice calls and SMS.
SUBSCRIBER IDENTITY MODULE (SIM)
One of the key features of GSM is the Subscriber Identity
Module, commonly known as a SIM card. The SIM is a
detachable smart card containing the user's subscription
information and phone book. This allows the user to retain his or
her information after switching handsets [10]. Alternatively, the
user can also change operators while retaining the handset
16
simply by changing the SIM. Some operators will block this by
allowing the phone to use only a single SIM, or only a SIM
issued by them; this practice is known as SIM locking, and is
illegal in some countries [11].
LITERATURE REVIEW
This project is an implementation to the idea of the wireless
communication between a mobile phone and a microcontroller.
Currently the main work that has been done on this proposed
system is through serial port to the computer but not wireless. If
they want to switch on and off the appliance, they have to go to
the remote area and one /off the appliance. But in this new
design, the systems need not be reprogrammed to control
another home appliance without changing the programming of
microcontroller. The user will send SMS from his phone and he
will be able to control the appliance.
17
GSM SECURITY
GSM was designed with a moderate level of security. The
system was designed to authenticate the subscriber using a pre-
shared key and challenge-response. Communications between
the subscriber and the base station can be encrypted.
Fig. 2.2 Block Diagram
18
As we see in the above figure, there are at least three interfacing
circuits, MAX-232 with Microcontroller, LCD display with
microcontroller, and MAX-232 with GSM MODEM.
19
HARDWARE DISCRIPTION
POWER SUPPLY:
Power supply is a reference to a source of electrical power. A
device or system that supplies electrical or other types of energy
to an output load or group of loads is called a power supply
unit or PSU. The term is most commonly applied to electrical
energy supplies, less often to mechanical ones, and rarely to
others.
Here in our application we need a 5v DC power supply for all
electronics involved in the project. This requires step down
transformer, rectifier, voltage regulator, and filter circuit for
generation of 5v DC power. Here a brief description of all the
components is given as follows
TRANSFORMER:
A transformer is a device that transfers electrical energy from
one circuit to another through inductively coupled conductors —
the transformer's coils or "windings". Except for air-core
transformers, the conductors are commonly wound around a
20
single iron-rich core, or around separate but magnetically-
coupled cores. A varying current in the first or "primary"
winding creates a varying magnetic field in the core (or cores) of
the transformer. This varying magnetic field induces a varying
electromotive force (EMF) or "voltage" in the "secondary"
winding. This effect is called mutual induction.
If a load is connected to the secondary circuit, electric charge
will flow in the secondary winding of the transformer and
transfer energy from the primary circuit to the load connected in
the secondary circuit.
The secondary induced voltage VS, of an ideal transformer, is
scaled from the primary VP by a factor equal to the ratio of the
number of turns of wire in their respective windings:
21
By appropriate selection of the numbers of turns, a transformer
thus allows an alternating voltage to be stepped up — by making
NS more than NP — or stepped down, by making it
BASIC PARTS OF A TRANSFORMER
In its most basic form a transformer consists of:
A primary coil or winding.
A secondary coil or winding.
A core that supports the coils or windings.
Refer to the transformer circuit in figure as you read the
following explanation: The primary winding is connected to a
60-hertz ac voltage source. The magnetic field (flux) builds up
(expands) and collapses (contracts) about the primary winding.
The expanding and contracting magnetic field around the
primary winding cuts the secondary winding and induces an
alternating voltage into the winding. This voltage causes
alternating current to flow through the load. The voltage may be
stepped up or down depending on the design of the primary and
secondary windings.
22
THE COMPONENTS OF A TRANSFORMER
Two coils of wire (called windings) are wound on some type of
core material. In some cases the coils of wire are wound on a
cylindrical or rectangular cardboard form. In effect, the core
material is air and the transformer is called an AIR-CORE
TRANSFORMER. Transformers used at low frequencies, such
as 60 hertz and 400 hertz, require a core of low-reluctance
magnetic material, usually iron. This type of transformer is
called an IRON-CORE TRANSFORMER. Most power
transformers are of the iron-core type. The principle parts of a
transformer and their functions are:
23
The CORE, which provides a path for the magnetic lines of
flux.
The PRIMARY WINDING, which receives energy from
the ac source.
The SECONDARY WINDING, which receives energy
from the primary winding and delivers it to the load.
The ENCLOSURE, which protects the above components
from dirt, moisture, and mechanical damage.
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.
24
BASIC OPERATION
According to the conventional model of current flow originally
established by Benjamin Franklin and still followed by most
engineers today, current is assumed to flow through electrical
conductors from the positive to the negative pole. In actuality,
free electrons in a conductor nearly always flow from the
negative to the positive pole. In the vast majority of
applications, however, the actual direction of current flow is
irrelevant. Therefore, in the discussion below the conventional
model is retained.
In the diagrams below, when the input connected to the left
corner of the diamond is positive, and the input connected to the
right corner is negative, current flows from the upper supply
terminal to the right along the red (positive) path to the output,
and returns to the lower supply terminal via the blue (negative)
path.
25
When the input connected to the left corner is negative, and the
input connected to the right corner is positive, current flows
from the lower supply terminal to the right along the red path to
the output, and returns to the upper supply terminal via the blue
path.
In each case, the upper right output remains positive and lower
right output negative. Since this is true whether the input is AC
or DC, this circuit not only produces a DC output from an AC
26
input, it can also provide what is sometimes called "reverse
polarity protection". That is, it permits normal functioning of
DC-powered equipment when batteries have been installed
backwards, or when the leads (wires) from a DC power source
have been reversed, and protects the equipment from potential
damage caused by reverse polarity.
Prior to availability of integrated electronics, such a bridge
rectifier was always constructed from discrete components.
Since about 1950, a single four-terminal component containing
the four diodes connected in the bridge configuration became a
standard commercial component and is now available with
various voltage and current ratings.
OUTPUT SMOOTHING
For many applications, especially with single phase AC where
the full-wave bridge serves to convert an AC input into a DC
output, the addition of a capacitor may be desired because the
bridge alone supplies an output of fixed polarity but
continuously varying or "pulsating" magnitude (see diagram
above).
27
The function of this capacitor, known as a reservoir capacitor (or
smoothing capacitor) is to lessen the variation in (or 'smooth')
the rectified AC output voltage waveform from the bridge. One
explanation of 'smoothing' is that the capacitor provides a low
impedance path to the AC component of the output, reducing the
AC voltage across, and AC current through, the resistive load. In
less technical terms, any drop in the output voltage and current
of the bridge tends to be canceled by loss of charge in the
capacitor. This charge flows out as additional current through
the load. Thus the change of load current and voltage is reduced
relative to what would occur without the capacitor. Increases of
voltage correspondingly store excess charge in the capacitor,
thus moderating the change in output voltage / current.
28
The simplified circuit shown has a well-deserved reputation for
being dangerous, because, in some applications, the capacitor
can retain a lethal charge after the AC power source is removed.
If supplying a dangerous voltage, a practical circuit should
include a reliable way to safely discharge the capacitor. If the
normal load cannot be guaranteed to perform this function,
perhaps because it can be disconnected, the circuit should
include a bleeder resistor connected as close as practical across
the capacitor. This resistor should consume a current large
enough to discharge the capacitor in a reasonable time, but small
enough to minimize unnecessary power waste.
Because a bleeder sets a minimum current drain, the regulation
of the circuit, defined as percentage voltage change from
minimum to maximum load, is improved. However in many
cases the improvement is of insignificant magnitude.
The capacitor and the load resistance have a typical time
constant τ = RC where C and R are the capacitance and load
resistance respectively. As long as the load resistor is large
enough so that this time constant is much longer than the time of
29
one ripple cycle, the above configuration will produce a
smoothed DC voltage across the load.
In some designs, a series resistor at the load side of the capacitor
is added. The smoothing can then be improved by adding
additional stages of capacitor–resistor pairs, often done only for
sub-supplies to critical high-gain circuits that tend to be
sensitive to supply voltage noise.
The idealized waveforms shown above are seen for both voltage
and current when the load on the bridge is resistive. When the
load includes a smoothing capacitor, both the voltage and the
current waveforms will be greatly changed. While the voltage is
smoothed, as described above, current will flow through the
bridge only during the time when the input voltage is greater
than the capacitor voltage. For example, if the load draws an
average current of n Amps, and the diodes conduct for 10% of
the time, the average diode current during conduction must be
10n Amps. This non-sinusoidal current leads to harmonic
distortion and a poor power factor in the AC supply.
In a practical circuit, when a capacitor is directly connected to
the output of a bridge, the bridge diodes must be sized to
30
withstand the current surge that occurs when the power is turned
on at the peak of the AC voltage and the capacitor is fully
discharged. Sometimes a small series resistor is included before
the capacitor to limit this current, though in most applications
the power supply transformer's resistance is already sufficient.
Output can also be smoothed using a choke and second
capacitor. The choke tends to keep the current (rather than the
voltage) more constant. Due to the relatively high cost of an
effective choke compared to a resistor and capacitor this is not
employed in modern equipment.
Some early console radios created the speaker's constant field
with the current from the high voltage ("B +") power supply,
which was then routed to the consuming circuits, (permanent
magnets were then too weak for good performance) to create the
speaker's constant magnetic field. The speaker field coil thus
performed 2 jobs in one: it acted as a choke, filtering the power
supply, and it produced the magnetic field to operate the
speaker.
31
REGULATOR IC (78XX)
It is a three pin IC used as a voltage regulator. It converts
unregulated DC current into regulated DC current.
Normally we get fixed output by connecting the voltage
regulator at the output of the filtered DC (see in above diagram).
It can also be used in circuits to get a low DC voltage from a
high DC voltage (for example we use 7805 to get 5V from 12V).
There are two types of voltage regulators 1. fixed voltage
regulators (78xx, 79xx) 2. variable voltage regulators (LM317)
In fixed voltage regulators there is another classification 1. +ve
voltage regulators 2. -ve voltage regulators POSITIVE
VOLTAGE REGULATORS This include 78xx voltage
32
regulators. The most commonly used ones are 7805 and 7812.
7805 gives fixed 5V DC voltage if input voltage is in (7.5V,
20V).
THE CAPACITOR FILTER
The simple capacitor filter is the most basic type of power
supply filter. The application of the simple capacitor filter is
very limited. It is sometimes used on extremely high-voltage,
low-current power supplies for cathode ray and similar electron
tubes, which require very little load current from the supply. The
capacitor filter is also used where the power-supply ripple
frequency is not critical; this frequency can be relatively high.
The capacitor (C1) shown in figure 4-15 is a simple filter
connected across the output of the rectifier in parallel with the
load.
Full-wave rectifier with a capacitor filter.
33
When this filter is used, the RC charge time of the filter
capacitor (C1) must be short and the RC discharge time must be
long to eliminate ripple action. In other words, the capacitor
must charge up fast, preferably with no discharge at all. Better
filtering also results when the input frequency is high; therefore,
the full-wave rectifier output is easier to filter than that of the
half-wave rectifier because of its higher frequency.
For you to have a better understanding of the effect that filtering
has on Eavg, a comparison of a rectifier circuit with a filter and
one without a filter is illustrated in views A and B of figure 4-
16. The output waveforms in figure 4-16 represent the unfiltered
and filtered outputs of the half-wave rectifier circuit. Current
pulses flow through the load resistance (RL) each time a diode
conducts. The dashed line indicates the average value of output
voltage. For the half-wave rectifier, Eavg is less than half (or
approximately 0.318) of the peak output voltage. This value is
still much less than that of the applied voltage. With no
capacitor connected across the output of the rectifier circuit, the
waveform in view A has a large pulsating component (ripple)
compared with the average or dc component. When a capacitor
34
is connected across the output (view B), the average value of
output voltage (Eavg) is increased due to the filtering action of
capacitor C1.
UNFILTERED
Half-wave rectifier with and without filtering.
FILTERE
D
35
The value of the capacitor is fairly large (several microfarads),
thus it presents a relatively low reactance to the pulsating current
and it stores a substantial charge.
The rate of charge for the capacitor is limited only by the
resistance of the conducting diode, which is relatively low.
Therefore, the RC charge time of the circuit is relatively short.
As a result, when the pulsating voltage is first applied to the
circuit, the capacitor charges rapidly and almost reaches the
peak value of the rectified voltage within the first few cycles.
The capacitor attempts to charge to the peak value of the
rectified voltage anytime a diode is conducting, and tends to
retain its charge when the rectifier output falls to zero. (The
capacitor cannot discharge immediately.) The capacitor slowly
discharges through the load resistance (RL) during the time the
rectifier is non-conducting.
The rate of discharge of the capacitor is determined by the value
of capacitance and the value of the load resistance. If the
capacitance and load-resistance values are large, the RC
discharge time for the circuit is relatively long.
36
A comparison of the waveforms shown in figure 4-16 (view A
and view B) illustrates that the addition of C1 to the circuit
results in an increase in the average of the output voltage (Eavg)
and a reduction in the amplitude of the ripple component (Er)
which is normally present across the load resistance.
Now, let's consider a complete cycle of operation using a half-
wave rectifier, a capacitive filter (C1), and a load resistor (RL).
As shown in view A of figure 4-17, the capacitive filter (C1) is
assumed to be large enough to ensure a small reactance to the
pulsating rectified current. The resistance of RL is assumed to be
much greater than the reactance of C1 at the input frequency.
When the circuit is energized, the diode conducts on the positive
half cycle and current flows through the circuit, allowing C1 to
charge. C1 will charge to approximately the peak value of the
input voltage. (The charge is less than the peak value because of
the voltage drop across the diode (D1)). In view A of the figure,
the heavy solid line on the waveform indicates the charge on C1.
As illustrated in view B, the diode cannot conduct on the
negative half cycle because the anode of D1 is negative with
respect to the cathode. During this interval, C1 discharges
37
through the load resistor (RL). The discharge of C1 produces the
downward slope as indicated by the solid line on the waveform
in view B. In contrast to the abrupt fall of the applied ac voltage
from peak value to zero, the voltage across C1 (and thus across
RL) during the discharge period gradually decreases until the
time of the next half cycle of rectifier operation. Keep in mind
that for good filtering, the filter capacitor should charge up as
fast as possible and discharge as little as possible.
Figure 4-17A. - Capacitor filter circuit (positive and negative
half cycles). POSITIVE HALF-CYCLE
Figure 4-17B. - Capacitor filter circuit (positive and negative
half cycles). NEGATIVE HALF-CYCLE
38
Since practical values of C1 and RL ensure a more or less
gradual decrease of the discharge voltage, a substantial charge
remains on the capacitor at the time of the next half cycle of
operation. As a result, no current can flow through the diode
until the rising ac input voltage at the anode of the diode exceeds
the voltage on the charge remaining on C1. The charge on C1 is
the cathode potential of the diode. When the potential on the
anode exceeds the potential on the cathode (the charge on C1),
the diode again conducts, and C1 begins to charge to
approximately the peak value of the applied voltage.
After the capacitor has charged to its peak value, the diode will
cut off and the capacitor will start to discharge. Since the fall of
the ac input voltage on the anode is considerably more rapid
than the decrease on the capacitor voltage, the cathode quickly
39
become more positive than the anode, and the diode ceases to
conduct.
Operation of the simple capacitor filter using a full-wave
rectifier is basically the same as that discussed for the half-wave
rectifier. Referring to figure 4-18, you should notice that
because one of the diodes is always conducting on. either
alternation, the filter capacitor charges and discharges during
each half cycle. (Note that each diode conducts only for that
portion of time when the peak secondary voltage is greater than
the charge across the capacitor.)
Figure 4-18. - Full-wave rectifier (with capacitor filter).
40
Another thing to keep in mind is that the ripple component (E r)
of the output voltage is an ac voltage and the average output
voltage (Eavg) is the dc component of the output. Since the filter
capacitor offers relatively low impedance to ac, the majority of
the ac component flows through the filter capacitor. The ac
component is therefore bypassed (shunted) around the load
resistance, and the entire dc component (or Eavg) flows through
the load resistance. This statement can be clarified by using the
formula for XC in a half-wave and full-wave rectifier. First, you
must establish some values for the circuit.
41
42
\As you can see from the calculations, by doubling the
frequency of the rectifier, you reduce the impedance of the
capacitor by one-half. This allows the ac component to pass
through the capacitor more easily. As a result, a full-wave
rectifier output is much easier to filter than that of a half-wave
rectifier. Remember, the smaller the XC of the filter capacitor
with respect to the load resistance, the better the filtering action.
Since
the largest possible capacitor will provide the best filtering.
Remember, also, that the load resistance is an important
consideration. If load resistance is made small, the load current
increases, and the average value of output voltage (Eavg)
decreases. The RC discharge time constant is a direct function of
the value of the load resistance; therefore, the rate of capacitor
voltage discharge is a direct function of the current through the
load. The greater the load current, the more rapid the discharge
of the
43
capacitor, and the lower the average value of output voltage. For
this reason, the simple capacitive filter is seldom used with
rectifier circuits that must supply a relatively large load current.
Using the simple capacitive filter in conjunction with a full-
wave or bridge rectifier provides improved filtering because the
increased ripple frequency decreases the capacitive reactance of
the filter capacitor.
CIRCUIT DIAGRAM OF POWER SUPPLY
44
[
RELAY
The relay takes advantage of the fact that when electricity flows
through a coil, it becomes an electromagnet. The
electromagnetic coil attracts a steel plate, which is attached to a
switch. So the switch's motion (ON and OFF) is controlled by
the current flowing to the coil, or not, respectively.
A very useful feature of a relay is that it can be used to
electrically isolate different parts of a circuit. It will allow a low
voltage circuit (e.g. 5VDC) to switch the power in a high
voltage circuit (e.g. 100 VAC or more).
The relay operates mechanically, so it can not operate at high
speed.
45
Internal circuit of Relay
Relays
There are many kind of relays. You can select one according to
your needs. The various things to consider when selecting a
relay are its size, voltage and current capacity of the contact
points, drive voltage, impedance, number of contacts, resistance
of the contacts, etc. The resistance voltage of the contacts is the
maximum voltage that can be conducted at the point of contact
in the switch. When the maximum is exceeded, the contacts will
spark and melt, sometimes fusing together. The relay will fail.
The value is printed on the relay
46
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. Like a GSM mobile phone, a GSM modem requires a
SIM card from a wireless carrier in order to operate [11].
ACCESSING GSM MODEM USING MICROSOFT
HYPERTERMINAL
Microsoft HyperTerminal is a small program that comes with
Microsoft Windows. We use it to send AT commands to the
GSM modem. It can be found at Start -> Programs ->
Accessories -> Communications -> HyperTerminal. Before
programming our SMS application, it is required to check if the
GSM modem and SIM card are working properly first [12]. The
MS HyperTerminal is a handy tool when it comes to testing the
GSM device. It is a good idea to test the GSM devices
beforehand. When a problem occurs, sometimes it is difficult to
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tell what causes the problem. The cause can be the program, the
GSM device or the SIM card. If GSM device and SIM card with
MS HyperTerminal are operating properly, then it is very likely
that the problem is caused by the program or other hardware
[12]. For Linux users, Mincom can be used instead of
HyperTerminal.
TESTING OF GSM MODEM
To use MS HyperTerminal to send AT commands to the GSM
modem, the following procedure is followed
1. I put a valid SIM (MTN) card into the GSM modem. I obtain
a SIM card by subscribing to the GSM service of a wireless
network operator.
2. No need to install any driver for the GSM modem
3. Then I set up MS HyperTerminal by selecting Start ->
Programs -> Accessories -> Communications ->
HyperTerminal.
4. In the Connection Description dialog box (as shown in the
screenshot given below), I enter any file name and choose an
icon I like for the connection. Then I click the OK button.
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. In the Connect To dialog box, choose the COM port that your
mobile phone or GSM modem is connecting to in the Connect
using combo box. I choose COM1 because my mobile phone is
connected to the COM1 port. Then click the OK button. Type
"AT" in the main window. A response "OK" will be returned
from the mobile phone or GSM modem. Type "AT+CPIN?" in
the main window. The AT command "AT+CPIN?" is used to
query whether the mobile phone or GSM modem is waiting for a
PIN (personal identification number, i.e. password). If the
response is "+CPIN: READY", it means the SIM card does not
require a PIN and it is ready for use. If my SIM card requires a
PIN, you need to set the PIN with the AT command
"AT+CPIN=<PIN>".
[
LIST OF IMPORTANT AT COMMANDS
After successfully testing the MODEM for its correct
operational state, I then set the MODEM parameters like Baud
rate, Echo off etc to enable easier access via a microcontroller
which I used in this project. The following are the
ATCOMMAND used for programming the gsm modem
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Example: Changing and saving parameters
AT+IPR=9600[Enter] Transfer rate to 9600bps
AT&W [Enter] save parameters
AT+CMGF means convert the message to machine instruction
format
AT+CPMS means selection of SMS memory
AT+CMGR means read message from a given memory location
AT+CMGD means delete message from a given memory
location.
Microcontroller – Modem Interfacing
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. Let's say I have a computer
on which wants to communicate with the Internet through a
modem and a dial-up connection. To get to the Internet I tell my
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modem to dial the number of my provider. After my modem has
dialed the number, the modem of the provider will answer my
call and I will hear a lot of noise. Then it becomes quiet and I
see my login prompt or my dialing program tells me the
connection is established. Now I have a connection with the
server from my provider and I can surf the Internet [13].
MICROCONTROLLER – LCD INTERFACING
Above is the quite simple schematic. The LCD panel’s Enable
and Register Select is connected to the Control Port. The
Control Port is an open collector / open drain output. Therefore
by incorporating the two 10K external pull up resistors, the
circuit is more portable for a wider range of computers, some of
which may have no internal pull up resistors. I make no effort to
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place the Data bus into reverse direction. Therefore I had wire
the R/W line of the LCD panel, into write mode. This will cause
no bus conflicts on the data lines. As a result I cannot read back
the LCD’s internal Busy Flag which tells us if the LCD has
accepted and finished processing the last instruction [20]. This
problem is overcome by inserting known delays into my
program. The 10k Potentiometer controls the contrast of the
LCD panel. Nothing fancy here.
I used a power supply of 5volt. The user may select whether the
LCD is to operate with a 4-bit data bus or an 8- bit data bus. If a
4-bit data bus is used, the LCD will require a total of 7 data
lines. If an 8-bit data bus is used, the LCD will require a total of
11 data lines [20]. LCD with 8-bit data bus is used for this
design. The three control lines are EN, RS, and RW. EN line
must be raised/lowered before/after each instruction sent to the
LCD regardless of whether that instruction is read or write text
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or instruction. In short, I manipulate EN when communicating
with the LCD.
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TESTING AND OBSERVATIONS
After inclusion of the validation module in the program code, I
test the module with the device called universal programmer. In
this prototype I used only one valid number. With more memory
available three or four valid numbers can be included. When a
message is sent to number carried by the SIM of the MODEM,
the validation module of the program checks character by
character the sender’s number with the number stored in the
memory as the valid or authentic number. I then look for signals
on the TX and RX lines. What you see below on the left are the
signals on these lines with the ECHO being ON (ATE1). The
corresponding picture on the right depicts the modem response
after about 460 ms (variable as per message length: D) delay
with the new message
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Test Result
12345 Please submit your
thesis
Please submit your thesis
12345 there will be a
meeting by 2pm
There will be a meeting by
2pm
12345 I want to see Mr.
Musa
I want to see Mr. Musa
12345 I will not come to
school today
I will not come to school
today
12345 please enemy alert Please enemy alert
12345 I am in India I am in India
12345 please hurry up Please hurry up
1234 I will be in office in
the next 30 minute
I will be in office in the next
30 minute
12345 is the password of the GSM electronic notice board.
Any message a user want to send has to be preceded by 12345
spaces the message. A user will then send the message to the
GSM number that is inside the Motorola c168
INITIALIZATIONS
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The baud rate of the modem was set to be 9600 bps using the
HyperTerminal, The ECHO from the modem was turned off
using the command ATE0 at the HyperTerminal. For serial
transmission and reception to be possible both the DTE and
DCE should have same operational baud rates. Hence to set the
microcontroller at a baud rate of 9600bps, I set terminal count of
Timer 1 at 0FFh (clock frequency = 1.8432). The TCON and
SCON registers were set accordingly.
SERIAL TRANSFER USING TI AND RI FLAGS
After setting the baud rates of the two devices both the devices
are now ready to transmit and receive data in form of characters.
Transmission is done when TI flag is set and similarly data is
known to be received when the Rx flag is set. The
microcontroller then sends an AT command to the modem in
form of string of characters serially just when the TI flag is set.
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After reception of a character in the SBUF register of the
microcontroller (response of MODEM with the read message in
its default format or ERROR message or OK message), the RI
flag is set and the received character is moved into the physical
memory of the microcontroller [22].
VALIDITY CHECK
After serially receiving the characters the code then checks for
start of the sender’s number and then compares the number
character by character with the valid number pre stored in the
memory. Since we are employing just one valid number, we are
able to do the validation process dynamically i.e. without storing
the new message in another location in the memory. For more
than one valid numbers we would require more memory
locations to first store the complete (valid/invalid) message in
the memory and then perform the comparison procedure.
DISPLAY
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After validity check the control flow goes into the LCD program
module to display the valid message stored in the memory. In
case of multiple valid numbers all invalid stored messages are
deleted by proper branching in the code to the “delete-message”
module.
PROGRAMMER
When we have to learn about a new computer we have to
familiarize about the machine capability we are using, and we
can do it by studying the internal hardware design (devices
architecture), and also to know about the size, number and the
size of the registers.
A microcontroller is a single chip that contains the processor
(the CPU), non-volatile memory for the program (ROM or
flash), volatile memory for input and output (RAM), a clock and
an I/O control unit. Also called a "computer on a chip," billions
of microcontroller units (MCUs) are embedded each year in a
myriad of products from toys to appliances to automobiles. For
example, a single vehicle can use 70 or more microcontrollers.
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The following picture describes a general block diagram of
microcontroller.
89S52: The AT89S52 is a low-power, high-performance
CMOS 8-bit microcontroller with 8K bytes of in-system
programmable Flash memory. The device is manufactured using
Atmel’s high-density nonvolatile memory technology and is
compatible with the industry-standard 80C51 instruction set and
pin out. The on-chip Flash allows the program memory to be
reprogrammed in-system or by a conventional nonvolatile
memory pro-grammar. By combining a versatile 8-bit CPU with
in-system programmable Flash on a monolithic chip, the Atmel
AT89S52 is a powerful microcontroller, which provides a highly
flexible and cost-effective solution to many, embedded control
applications. The AT89S52 provides the following standard
features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines,
Watchdog timer, two data pointers, three 16-bit timer/counters, a
six-vector two-level interrupt architecture, a full duplex serial
port, on-chip oscillator, and clock circuitry. In addition, the
AT89S52 is designed with static logic for operation down to
zero frequency and supports two software selectable power
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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
con-tents but freezes the oscillator, disabling all other chip
functions until the next interrupt
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The hardware is driven by a set of program instructions, or
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software. Once familiar with hardware and software, the user
can then apply the microcontroller to the problems easily.
The pin diagram of the 8051 shows all of the input/output pins
unique to microcontrollers:
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The following are some of the capabilities of 8051
microcontroller.
Internal ROM and RAM
I/O ports with programmable pins
Timers and counters
Serial data communication
The 8051 architecture consists of these specific features:
16 bit PC &data pointer (DPTR)
8 bit program status word (PSW)
8 bit stack pointer (SP)
Internal ROM 4k
Internal RAM of 128 bytes.
4 register banks, each containing 8 registers
80 bits of general purpose data memory
32 input/output pins arranged as four 8 bit ports: P0-
P3
Two 16 bit timer/counters: T0-T1
Two external and three internal interrupt
sources Oscillator and clock circuits.
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SIMULATOR
KEIL Micro Vision is an integrated development environment
used to create software to be run on embedded systems (like a
microcontroller). It allows for such software to be written either
in assembly or C programming languages and for that software
to be simulated on a computer before being loaded onto the
microcontroller. The software used is c programming
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μVision3 is an IDE (Integrated Development Environment)
that helps write, compile, and debug embedded programs. It
encapsulates the following components:
A project manager.
A make facility.
Tool configuration.
Editor.
A powerful debugger.
To create a GSM ENOTICE board project in uVision3:
1. Select Project - New Project.
2. Select a directory and enter the name of the project file.
3. Select Project –Select Device and select a device from
Device Database.
4. Create source files to add to the project
5. Select Project - Targets, Groups, and Files. Add/Files,
select Source Group1, and add the
Source files to the project.
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6. Select Project - Options and set the tool options. Note that
when the target device is selected from the Device
Database all-special options are set automatically. Default
memory model settings are optimal for most applications.
7. Select Project - Rebuild all target files or Build target.
To create a new project, simply start micro vision and
select “Project”=>”New Project” from the pull–down menus.
In the file dialog that appears, a filename and directory was
chosen for the project. It is recommended that a new directory
be created for each project, as several files will be generated.
Once the project has been named, the dialog shown in the
figure below will appear, prompting the user to select a target
device. The chip being used is the “AT89S52,” which is listed
under the heading “Atmel”.
Next, Micro Vision was instructed to generate a HEX file
upon program compilation. A HEX file is a standard file format
for storing executable code that is to be loaded onto the
microcontroller. In the “Project Workspace” pane at the left,
right–click on “Target 1” and select “Options for ‘Target 1’
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”.Under the “Output” tab of the resulting options dialog, ensure
that both the “Create Executable” and “Create HEX File”
options are checked. Then click “OK”.
Next, a file must be added to the project that will contain
the project code. To do this, expand the “Target 1” heading,
right–click on the “Source Group 1” folder, and select “Add
files…” Create a new blank file (the file name should end in
“.c”), select it, and click “Add.” The new file should now appear
in the “Project Workspace” pane under the “Source Group 1”
folder. Double-click on the newly created file to open it in the
editor. To compile the program, first save all source files by
clicking on the “Save All” button, and then click on the
“Rebuild All Target Files” to compile the program as shown in
the figure below. If any errors or warnings occur during
compilation, they will be displayed in the output window at the
bottom of the screen. All errors and warnings will reference the
line and column number in which they occur along with a
description of the problem so that they can be easily located
[23].
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When the program has been successfully compiled, it can
be simulated using the integrated debugger in Keil Micro
Vision. To start the debugger, select “Debug”=>”Start/Stop
Debug Session” from the pull–down menus.
At the left side of the debugger window, a table is
displayed containing several key parameters about the simulated
microcontroller, most notably the elapsed time (circled in the
figure below). Just above that, there are several buttons that
control code execution. The “Run” button will cause the
program to run continuously until a breakpoint is reached,
whereas the “Step Into” button will execute the next line of code
and then pause (the current position in the program is indicated
by a yellow arrow to the left of the code).
PRO51 BURNER SOFTWARE
PRO51 BURNER provides you with software burning tools for
8051 based Microcontrollers in their Flash memory. The 51
BURNER tools, you can burn AT89C/SXXXX series of
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ATMEL microcontrollers.
CONCLUSION
The prototype of the GSM based display electronic notice board
was efficiently designed. This prototype has facilities to be
integrated with a display board thus making it truly mobile. The
toolkit accepts the SMS, stores it, validates it and then displays
it in the LCD module. The SMS is deleted from the phone each
time it is read, thus making room for the next SMS. The major
constraints incorporated are the use of ‘*’ as the termination
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character of the SMS and the display of one SMS as at a time.
These limitations can be removed by the use of higher end
microcontrollers and extended RAM. The prototype can be
implemented using commercial display boards. In this case, it
can solve the problem of instant information transfer in this
campus(federal university of technology MINNA).
5.2 Problem Encountered
During soldering, many of the connection become short
cktd. So we desolder the connection and did soldering
again.
A leg of the crystal oscillator was broken during mounting.
So it has to be replaced.
LED`s get damaged when we switched ON the supply so
we replace it by the new one.
TROUBLESHOOT
Care should be taken while soldering. There should be no
shorting of joints.
Proper power supply should maintain.
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FUTURE IMPROVEMENT
In my project I am sending messages through GSM network
and Control the home device by utilizing AT
(ATTENTION) commands. The same principle can be
applied to display the message on electronics display board
appliances at a distant location.
Robots can be controlled in a similar fashion by sending the
commands to the robots. These commands are read by using
AT commands and appropriate action is taken. This can be
used for spy robots at distant locations, utilized by the
military to monitor movement of enemy troops.
Currently farmers have to manually put on or off pumps,
drippers etc by using electric switches. Using the principle of
AT commands we can put on or off these appliances
remotely.
RECOMMENDATION
It is highly recommended that electronic board should be
constructed for this new system (GSM electronic notice board
REFERENCES
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1. The 8051Microcontroller by Kenneth J. Ayala
2. The 8051 Microcontroller and Embedded Systems by
Muhammad Ali Mazidi.
3. Principles and Applications of GSM by Vijay Garg.
4. Artificial Intelligence – Elain Rich & Kevin Knight, Tata Mc
Graw Hill, 2nd Edition.
5. Artificial Intelligence – A Modern approach – Slaurt Russel
and Peter Norving, Pearson Education, 2nd Edition.
6. Introduction to Robotics – P.J.Mc Kerrow, Addisson Wesley,
USA, 1991 Bernard Sklar, Digital Communications:
Fundamentals and Applications, Prentice Hall, 2001.
7. A. Clark and R. Harun, Assessment of kalman-_lter channel
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8. ETS 300 502. European Digital Cellular Telecommunication
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Handbook of RF and Wireless
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10. GSM Multiple Access Scheme,
http://www.eecg.toronto.edu/~nazizi/gsm/ma/ William
Stallings Data and Computer Communications 7th Edition:
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465/lectures/09-SpreadSpectrum-new.ppt
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13. Jörg Eberspächer and Hans-Jörg Vögel. GSM switching,
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AN/GSC-10/KATHRYN variable rate data modem for HF
radio," IEEE Trans. Commun.Techn., vol. CCM15,16
19. Hardware and user manuals of the modem from
MOTOROLA C168
http://developer.motorola.com/getDocument.do?docId=65054
20. http://www.mobilegpsonline.com/downloads/GM28-
29%20Datasheet%20R1G.pdf
21. http://www.mobilegpsonline.com/GSMJC01Spec.pdf
22. http://www.visualgsm.com/wire_sms_index.htm
23. http://en.wikipedia.org/wiki/Gsm
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