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ABSTRACT
The various time essential for alarm system and control of various electric appliances in real time using programmable logic controller (PLC) has been accomplished in the present work. The real time system developed is highly effective, efficient and robust. The concept of automatic alarm system is to connect all the systems and devices to a central controller so that they can be controlled from anywhere and react to one another.
The work is based on an automatic alarm System where interface is by a Programmable Logic Controller. Implementing a PLC application which can handle various time. Now everything is going to be alarm using Programmable Logic Controller control techniques and vogue technology. The appliances can be connected with network grid and accessed using a PLC. This idea shall lead to the development of smart communities. The work illustrates how PLC’s can be used for control and alarm system. Automation and real time monitoring of inputs is easily accomplished. The idea of computerized control and its application saves precious time and manual effort, which can be utilized for better purposes. College automatic alarm convenient & elegant atmosphere for the family to compliment and match the lifestyle.
INTRODUCTION
1.1 Objective of the project:
This Automatic College BELL Electrical Student Project takes over the task of Ringing of the Bell in Colleges and replaces the Manual Switching of the Bell in the College. When time equals to the Bell Ringing time then the Relay for the Bell is switched on for a predetermined time and we can edit The Bell Ringing time any Time so it can be used at Normal Class Timings and even at Exam Times.
Everyone knows importance of time and everything should be done in time and accurately so we are here with this project. There are many types of digital clocks in the market readily available with bells but rings only at particular time. It is used in the college and school, during examinations, automatic scheduling, and time editable
The Real Time Clock is displayed on LCD display. The Microcontroller AT89S52 helps to control all the Functions to get the time by the keypad that stores in its Memory.
A 220V A.C. power supply is provided to the Step-Down Transformer that converts 220V A.C. into 12V A.C. and this 12V A.C. is converted into 12V D.C. by Full Wave Rectifier that consists of 2 Diodes & 2 Condensers.
1.2 Need For Automation:
Every thing must be done in time and accurately. Nowadays, school and college bells are operated manually and hence there is a necessity of accuracy, manpower and money. So we must use automatic control system that saves manpower, money and highest accuracy
OVERVIEW OF THE TECHNOLOGIES USED
Embedded Systems:
In this technologies in school and colleges automation is very attractive for many reasons. The wire way of communicating makes automatic and find out timings to ring the bell. Easily change the modification of mode change because exam time table and normal college working days.TO Prepare to easier, cheaper, and more flexible. bell to operate to easy technique by using plc alone. from this to save the man power and energy losses because easily started.
We are using in this project to easily hear bell sounds no man power losses and output executed the two modes of timings.
Hardware Implementation of the Project
This chapter briefly explains about the Hardware Implementation of the project. It discusses the design and working of the design with the help of block diagram and circuit diagram and explanation of circuit diagram in detail. It explains the features, timer programming, serial communication, interrupts of microcontroller. It also explains the various modules used in this project.
Project Design
The implementation of the project design can be divided in two parts.
Hardware implementation
Firmware implementation
Hardware implementation deals in drawing the schematic on the plane paper according to the application, testing the schematic design over the breadboard using the various IC’s to find if the design meets the objective, carrying out the PCB layout of the schematic tested on breadboard, finally preparing the board and testing the designed hardware.
The firmware part deals in programming the microcontroller so that it can control the operation of the IC’s used in the implementation. In the present work, we have used the Orcad design software for PCB circuit design, the Keil µv3 software development tool to write and compile the source code, which has been written in the C language. The Flash main programmer has been used to write this compile code into the microcontroller. The firmware implementation is explained in the next chapter.
The project design and principle are explained in this chapter using the block diagram and circuit diagram. The block diagram discusses about the required components of the design and working condition is explained using circuit diagram and system wiring diagram.
POWER SUPPLY UNIT
2.1 INTRODUCTION
Power supply is an integral parts a vital role in every electronic system and hence their design constitutes a major part in every application. In order to overcome mal-operation which results due to fluctuations in the load and discontinuity in the supply proper choice of power supply is indeed a great need in this hour.
The present chapter introduces the operation of power supply circuits built using filters, rectifiers, and then voltage regulators. Starting with an AC voltage, a steady DC voltage is obtained by rectifying the AC voltage, then filtering to a DC level, and finally, regulating to obtain a desired fixed DC voltage. The regulation is usually obtained from an IC voltage regulator unit, which takes a DC voltage and provides a somewhat lower DC voltage, which remains the same even if the input DC voltage varies, or the output load connected to the DC voltage changes.
A block diagram containing the parts of a typical power supply and the voltage at various points in the unit is shown in fig 19.1. The AC voltage, typically 120 V RMS, is connected to a transformer, which steps that AC voltage down to the level for the desired DC output.
A diode rectifier then provides a full-wave rectified voltage that is initially filtered by a simple capacitor filter to produce a DC voltage. This resulting DC voltage usually has some ripple or AC voltage variation. A regulator circuit can use this DC input to provide a DC voltage that not only has much less ripple voltage but also remains the same DC value
Even if the input DC voltage varies somewhat, or the load connected to the output
DC voltage.
2.1 POWER SUPPLY COMPONENTS
• TRANSFORMER
• FULLWAVE RECTIFIER
• VOLTAGE REGULATOR
• FILTER CIRCUIT
BLOCK DIAGRAM
The AC voltage, typically 220V RMS, is connected to a transformer, which steps that AC voltage down to the level of the desired DC output. A diode rectifier then provides a full-wave rectified voltage that is initially filtered by a simple capacitor filter to produce a DC voltage. This resulting DC voltage usually has some ripple or AC voltage variation.
WORKING PRINCIPLE
BRIDGE RECTIFIER
When four diodes are connected as shown in figure, the circuit is called as bridge rectifier. The input to the circuit is applied to the diagonally opposite corners of the network, and the output is taken from the remaining two corners.
Let us assume that the transformer is working properly and there is a positive potential, at point A and a negative potential at point B. the positive potential at point A will forward bias D3 and reverse bias D4.
The negative potential at point B will forward bias D1 and reverse D2. At this time D3 and D1 are forward biased and will allow current flow to pass through them; D4 and D2 are reverse biased and will block current flow.
The path for current flow is from point B through D1, up through RL, through D3, through the secondary of the transformer back to point B. this path is indicated by the solid arrows. Waveforms (1) and (2) can be observed across D1 and D3.
One-half cycle later the polarity across the secondary of the transformer reverse, forward biasing D2 and D4 and reverse biasing D1 and D3. Current flow will now be from point A through D4, up through RL, through D2, through the secondary of T1, and back to point A. This path is indicated by the broken arrows. Waveforms (3) and (4) can be observed across D2 and D4. The current flow through RL is always in the same direction. In flowing through RL this current develops a voltage corresponding to that shown waveform.
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One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit.
This may be shown by assigning values to some of the components shown in views A and B. assume that the same transformer is used in both circuits. The peak voltage developed between points X and Y is 1000 volts in both circuits. In the conventional full-wave circuit shown—in view A, the peak voltage from the center tap to either X or Y is 500 volts. Since only one diode can conduct at any instant, the maximum voltage that can be rectified at any instant is 500 volts.
The maximum voltage that appears across the load resistor is nearly-but never exceeds-500 volts, as result of the small voltage drop across the diode. In the bridge rectifier shown in view B, the maximum voltage that can be rectified is the full secondary voltage, which is 1000 volts. Therefore, the peak output voltage across the load resistor is nearly 1000 volts. With both circuits using the same transformer, the bridge rectifier circuit produces a higher output voltage than the conventional full-wave rectifier circuit.
VOLTAGE REGULATOR
Voltage regulator is a device, which provides a stable and a constant D.C. voltage irrespective of the change in the load current. Stable and constant D.C, output voltage necessities the usage of voltage regulator in this power section.
They are of many types namely:
• Fixed voltage Regulator
• Adjustable voltage Regulator
• Switch Regulator
•
IC VOLTAGE REGULATORS:
Voltage regulators comprise a class of widely used ICs. Regulator IC units contain the circuitry for reference source, comparator amplifier, control device, and overload protection all in a single IC. Although the internal construction of the IC is somewhat different from that described for discrete voltage regulator circuits, the external operation is much the same. IC units provide regulation of either a fixed positive voltage, a fixed negative voltage, or an adjustably set voltage.
A power supply can be built using a transformer connected to the AC supply line to step the AC voltage to desired amplitude, then rectifying that AC voltage, filtering with a capacitor and RC filter, if desired, and finally regulating the DC voltage using an IC regulator. The regulators can be selected for operation with load currents from hundreds of milli amperes to tens of amperes, corresponding to power ratings from milli watts to tens of watts.
THREE-TERMINAL VOLTAGE REGULATORS:
Fig shows the basic connection of a three-terminal voltage regulator IC to a load. The fixed voltage regulator has an unregulated DC input voltage, Vi, applied to one input terminal, a regulated output DC voltage, Vo, from a second terminal, with the third terminal connected to ground.
For a selected regulator, IC device specifications list a voltage range over which the input voltage can vary to maintain a regulated output voltage over a range of load current. The specifications also list the amount of output voltage change resulting from a change in load current (load regulation) or in input voltage (line regulation)
GENERAL DESCRIPTION
The LM 78xx series of three terminal regulators is available with several fixed output voltages making them useful in a wide range of applications. One of these is local on card regulation, eliminating the distribution problems associated with single point regulation.
The voltages available allow these regulators to be used in logic systems, instrumentations, HiFi, and other solid state electronic equipment.
Although designed primarily as fixed voltage regulators these devices can be used with external components to obtain adjustable voltages and currents.
The LM78xx series is available in an aluminium T0-3 package which will allow over 1.0A load current. Current limiting is included to limit the peak output current to a safe value. Safe area protection for the output transistor is provided to limit internal power dissipation.
If internal power dissipation becomes too high for the heat sinking provided, the thermal shutdown circuit takes over preventing the IC from overheating. Considerable effort was expanded to make the LM78xx series of regulators easy to used and minimize the number of external components. It is not necessary to bypass the output, although this does improve transient response. Input by passing is needed only if the regulator is located far from the filter capacitor of the power supply. For output voltage other than 5V, 12V, 15V, the LM117 series provides an output voltage range from 1.2V to 57V.
FEATURES
• Output current in excess of 1A
• Internal thermal overload protection
• No external components required
• Output transistor safe area protection
• Internal short circuit current limits
• Available in the aluminium T0-3 package.
Voltage Range
• LM 7805 C – 5V
• LM 7812 C – 12V
• LM 7815 C – 15 V
In many low current application, compensation capacitors are not required. However, it is recommended that the regulated input be bye passed with the capacitor if the regulator is connected to the power supply filter with long wire lengths are if the output load capacitance is large. An input bypass capacitor made of ceramic is chosen to provide good frequency characteristics to ensure stable operation under all load condition. The bypass capacitor mounted with the shortest possible leads directly across the regulators input terminals.
FILTER CIRCUIT
The output of the voltage regulator is given to this filter unit. Filters are frequency selective electronic circuitry, which allows certain specified band of frequency and attenuate frequencies other than the specified frequencies. Here capacitor is used to short the ripple with frequency of 120 Hz to ground. It is also called bypassing capacitor or decoupling capacitor, which acts as surge arrestors.