418 Automatic Railway Gate Control System

1.ABSTRACT

OBJECTIVE: The aim of this project is to Automate unmanned railway gate using mechatronics.

PROJECT DEFINATION:

The objective of this project is to manage the control system of railway gate using the microcontroller. When train arrives at the sensing point alarm is triggered at the railway crossing point so that the people get intimation that gate is going to be closed. Then the control system activates and closes the gate on either side of the track. once the train crosses the other end control system automatically lifts the gate. For mechanical operation of the gates 1.8 step angle stepper motors are employed. Here we are using embedded controller built around the 8051 family (AT89C52) for the control according to the data pattern produced at the input port of the micro controller, the appropriate selected action will be taken.. The logic is produced by the program written in Embedded C language. The software program is written, by using the KEIL micro vision environment. The program written is then converted in HEX code after simulation and burned on to microcontroller using FLASH micro vision.

WORKING METHODOLOGY: 

Present project is designed using 8051 microcontroller to avoid railway accidents happening at unattended railway gates, if implemented in spirit. This project utilizes two powerful IR transmitters and two receivers; one pair of transmitter and receiver is fixed at up side (from where the train comes) at a level higher than a human being in exact alignment and similarly the other pair is fixed at down side of the train direction. Sensor activation time is so adjusted by calculating the time taken at a certain speed to cross at least one compartment of standard minimum size of the Indian railway. We have considered 5 seconds for this project. Sensors are fixed at 1km on both sides of the gate. We call the sensor along the train direction as ‘foreside sensor’ and the other as ‘after side sensor’. When foreside receiver gets activated, the gate motor is turned on in one direction and the gate is closed and stays closed until the train crosses the gate and reaches aft side sensors. When aft side receiver gets activated motor turns in opposite direction and gate opens and motor stops. Buzzer will immediately sound at the fore side receiver activation and gate will close after 5 seconds, so giving time to drivers to clear gate area in order to avoid trapping between the gates and stop sound after the train has crossed.

GATE CONTROL

Railways being the cheapest mode of transportation are preferred over all the other means .When we go through the daily newspapers we come across many railway accidents occurring at unmanned railway crossings. This is mainly due to the carelessness in manual operations or lack of workers. We, in this project has come up with a solution for the same. Using simple electronic components we have tried to automate the control of railway gates. As a train approaches the railway crossing from either side, the sensors placed at a certain distance from the gate detects the approaching train and accordingly controls the operation of the gate. Also an indicator light has been provided to alert the motorists about the approaching train.

2.INTRODUCTION

Introduction:The objective of this project is to manage the control system of railway gate using

the microcontroller. When train arrives at the sensing point alarm is triggered at the railway crossing point so that the people get intimation that gate is going to be closed. Then the control system activates and closes the gate on either side of the track. once the train crosses the other end control system automatically lifts the gate. For mechanical operation of the gates 1.8 step angle stepper motors are employed. Here we are using embedded controller built around the 8051 family (AT89C52) for the control according to the data pattern produced at the input port of the micro controller, the appropriate selected action will be taken.. The logic is produced by the program written in Embedded C language. The software program is written, by using the KEIL micro vision environment. The program written is then converted in HEX code after simulation and burned on to microcontroller using FLASH micro vision.

AT89C51 Microcontroller

The Micro controller (AT89C51) is a low power; high performance CMOS 8-bit micro controller with 4K bytes of Flash programmable and erasable read only memory (PEROM). The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional non-volatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C51 is a powerful microcomputer, which provides a highly flexible and cost-effective solution to many embedded control applications. By using this controller the data inputs from the smart card is passed to the parallel port of the pc and accordingly the software responds. The IDE for writing the embedded program used is KEI L software.

Keil Micro vision Integrated Development Environment.

Keil Software development tools for the 8051 micro controller family support every level of developer from the professional applications engineer to the student just learning about embedded software development.The industry-standard Keil C Compilers, Macro Assemblers, Debuggers, Real-time Kernels, and Single-board Computers support ALL 8051-compatible derivatives and help you get your projects completed on schedule.

The source code is written in assembly language .It is saved as ASM file with an extension. A51.the ASM file is converted into hex file using keil software. Hex file is dumped into micro controller using LABTOOL software. At once the file is dumped and the ROM is burnt then it becomes an embedded one.

Step Motor Advantages :

Step motors convert electrical energy into precise mechanical motion. These motors rotate a specific incremental distance per each step. The number of steps executed controls the degree of rotation of the motor’s shaft. This characteristic makes step motors excellent for positioning applications. For example, a 1.8° step motor executing 100 steps will rotate exactly 180° with some small amount of non-cumulative error. The speed of step execution controls the rate of motor rotation. A 1.8° step motor executing steps at a speed of 200 steps per second will rotate at exactly 1 revolution per second.Step motors can be very accurately controlled in terms of how far and how fast they will rotate. The number of steps the motor executes is equal to the number of pulse commands it is given. A step motor will rotate a distance and at a rate that is proportional to the number and frequency of its pulse commands.

Step motors have several advantages over other types of motors. One of the most impressive is their ability to position very accurately. NMB’s standard step motors have an accuracy of +/-5%. The error does not accumulate from step to step. This means that a standard step motor can take a single step and travel 1.8° +/-0.09°. Then it can take one million steps and travel 1,800,000° +/-0.09°. This characteristic gives a step motor almost perfect repeatability. In motor terms, repeatability is the ability to return to a previously held position. A step motor can achieve the same target position, revolution after revolution.

3.CIRCUIT DIAGRAM

4.COMPONENTS

The project consists of three main parts:

8051 microcontroller IR Transmitter IR Receiver Stepper Motor Circuit 8051 CONTROLLER

The I/O ports of the 8051 are expanded by connecting it to an 8255 chip. The 8255 is programmed as a simple I/O port for connection with devices such as LEDs, stepper motors and sensors.

The following block diagram shows the various devices connected to the different ports of an 8255. The ports are each 8-bit and are named A, B and C. The individual ports of the 8255 can be programmed to be input or output, and can be changed dynamically. The control register is programmed in simple I/O mode with port A, port B and port C (upper) as output ports and port C (lower) as an input port.

IR CIRCUITS

This circuit has two stages: a transmitter unit and a receiver unit. The transmitter unit consists of an infrared LED and its associated circuitry.

IR TRANSMITTER The IR LED emitting infrared light is put on in the transmitting unit. To generate IR signal, 555 IC based astable multivibrator is used. Infrared LED is driven through transistor BC 548. IC 555 is used to construct an astable multivibrator which has two quasi-stable states. It generates a square wave of frequency 38kHz and amplitude 5Volts. It is required to switch ‘ON’ the IR LED.

IR RECEIVER: The receiver unit consists of a sensor and its associated circuitry. In receiver section, the first part is a sensor, which detects IR pulses transmitted by IR-LED. Whenever a train crosses the sensor, the output of IR sensor momentarily transits through a low state. As a result the monostable is triggered and a short pulse is applied to the port pin of the 8051 microcontroller. On receiving a pulse from the sensor circuit, the controller activates the circuitry required for closing and opening of the gates and for track switching. The IR receiver circuit is shown in the figure below.

STEP MOTOR ADVANTAGESStep motors convert electrical energy into precise mechanical motion. These

motors rotate a specific incremental distance per each step. The number of steps executed controls the degree of rotation of the motor’s shaft. This characteristic makes step motors excellent for positioning applications. For example, a 1.8° step motor executing 100 steps will rotate exactly 180° with some small amount of non-cumulative error. The speed of step execution controls the rate of motor rotation. A 1.8° step motor executing steps at a speed of 200 steps per second will rotate at exactly 1 revolution per second.Step motors can be very accurately controlled in terms of how far and how fast they will rotate. The number of steps the motor executes is equal to the number of pulse commands it is given. A step motor will rotate a distance and at a rate that is proportional to the number and frequency of its pulse commands.

Step motors have several advantages over other types of motors. One of the most impressive is their ability to position very accurately. NMB’s standard step motors have an accuracy of +/-5%. The error does not accumulate from step to step. This means that a standard step motor can take a single step and travel 1.8° +/-0.09°. Then it can take one million steps and travel 1,800,000° +/-0.09°. This characteristic gives a step motor almost perfect repeatability. In motor terms, repeatability is the ability to return to a previously held position. A step motor can achieve the same target position, revolution after revolution.

5.EMBEDDED SYSTEMS

Introduction:

An Embedded system is a combination of computer hardware and software, and

perhaps additional mechanical or other parts, designed to perform a specific function.

Embedded systems are usually a part of larger, complex system. Dedicated

applications, designed to execute specific activities, are implemented and embedded in

systems. These embedded applications are required to collaborate with the other

components of an enclosed system. Embedded application components interact mostly

with the non-human external environment. They continuously collect data from sensors

or other computer components and process data within real-time constraints. Embedded

systems are usually associated with dedicated hardware and specific software.

Embedding an application into system

Application and system are closely tied together

Collaborative application

Dedicated H/W and specific S/W

Interaction with non-human external environment

Real-time systems are embedded systems

5.1 EMBEDDED PRODUCT DEVELOPMENT LIFE CYCLE

5.2 DESIGN CONSIDERATIONS FOR AN EMBEDDED SYSTEM

Understand user requirements

Understand user requirements

Choose optimum electronic chip

Choose optimum electronic chip

HLL/ALLHLL/ALL

AlgorithmAlgorithm

Coding/Editing Compiling/Assembling

Coding/Editing Compiling/Assembling

DebuggingDebugging

TestingTesting

SimulatorSimulator

S/WS/W

PCB Layout designPCB Layout design

Assembling components

Assembling components

TestingTesting

H/WH/W

ICE (In Circuit Emulator)

ICE (In Circuit Emulator)

Embedded ProductEmbedded Product

S/W Side H/W Side

DOWNLOAD

ProcessorProcessor

MemoryMemory

InputsInputs OutputsOutputs

Introduction:

Unlike software designed for general-purpose computers, embedded software

cannot usually be run on other embedded system without significant modification. This is

mainly because of the incredible variety in the underlying hardware. The hardware in

each embedded system is tailored specifically to the application, in order to keep system

costs low. As a result, unnecessary circuitry is eliminated and hardware resources are

shared whenever possible.

In order to have software, there must be a place to store the executable code and

temporary storage for runtime data manipulation. These take the form of ROM and

RAM, respectively. All embedded systems also contain some type of inputs and outputs.

It is almost always the case that the outputs of the embedded system are a function of its

inputs and several other factors. The inputs to the system usually take the form of sensors

and probes, communication signals, or control knobs and buttons. The outputs are

typically displays, communication signals, or changes to the physical world.

Example of an Embedded System

Other common design requirement include -

Processing power

Memory

Development cost

Number of Units

Expected Lifetime

Reliability

Processing power

This is the amount of processing power necessary to get the hob done. A common

way to compare processing power is the MIPS (millions of instructions per second)

rating. Other important features of the processor need to be consider is register width,

typically ranges from 8 to 64 bits.

Memory:

The amount of memory (ROM and RAM) required holding the executable

software and data it manipulates. The amount of memory required can also affect the

processor selection. In general, the register width off a processor establishes the upper

limit of the amount of memory it can access.

Development cost:

The development cost of the hardware and software design processes is a fixed,

one-time cost, so it might be that money is no object or that this is the only accurate

measure of system cost.

Number of units:

The tradeoff between production cost and development cost is affected most by

the number of units expected to be produced and sold.

Expected lifetime:

This indicates how long must the system continue to function? This affects all

sorts of design decisions from the selection of hardware components to how much the

system may cost to develop and produce.

Reliability:

How reliable must the final product be? If it is a children’s toy, it doesn’t always

have to work right, but if it is part of a space shuttle or a car, it had sure better do what it

is supposed to each and every time.

The Basic Design – REALTIME:

Designing Embedded systems is a challenging task. Most of the challenge comes

from the fact that Embedded systems have to interact with real world entities. These

interactions can get fairly complex. A typical Emebbed system might be interacting with

thousands of such entities at the same time. For example, a telephone switching system

routinely handles calls from tens of thousands of subscriber. The system has to connect

each call differently. Also, the exact sequence of events in the call might vary a lot.

Embedded systems have to respond to external interactions in a predetermined

amount of time. Successful completion of an operation depends upon the correct and

timely operation of the system. Design the hardware and the software in the system to

meet the Realtime requirements. For example, a telephone switching system must feed

dial tone to thousands of subscribers within a recommended limit of one second. To meet

these requirements, the off hook detection mechanism and the software message

communication involved have to work within the limited time budget. The system has to

meet these requirements for all the calls being set up at any given time.

The designers have to focus very early on the Realtime response requirements.

During the architecture design phase, the hardware and software engineers work together

to select the right system architecture that will meet the requirements. This involves

deciding inter connectivity of the processors, link speeds, processor speeds, etc.

The main queries to be asked are:

Is the architecture suitable? If message communication involves too many

nodes, it is likely that the system may not be able to meet the Realtime

requirement due to even mild congestion. Thus a simpler architecture has a better

chance of meeting the Realtime requirements.

Are the processing components powerful enough? A CPU with really high

utilization will lead to unpredictable Realtime behavior. Also, it is possible that

the high priority tasks in the system will starve the low priority tasks of any CPU

time. This can cause the low priority tasks to misbehave.

Is the Operating System suitable? Assign high priority to tasks that are involved

in processing Realtime critical events. Consider preemptive scheduling if

Realtime requirements are stringent. When choosing the operating system, the

interrupt latency and scheduling variance should be verified. 

o Scheduling variance refers to the predictability in task scheduling times.

For example, a telephone switching system is expected to feed dialtone in

less than 500 ms. This would typically involve scheduling three to five

tasks within the stipulated time. Most operating systems would easily meet

these numbers as far as the mean dialtone delay is concerned. But general

purpose operating systems would have much higher standard deviation in

the dialtone numbers.

o Interrupt Latency refers to the delay with which the operating system can

handle interrupts and schedule tasks to respond to the interrupt. Again,

Embedded Systems based on real-time operating systems would have

much lower interrupt latency.

6.MICROCONTROLLER

Introduction:

Microcontrollers are "embedded" inside some other device (often a consumer

product) so that they can control the features or actions of the product. Another name for

a microcontroller, therefore, is "embedded controller."

Microcontrollers are dedicated to one task and run one specific program. The

program is stored in ROM (read-only memory) and generally does not change.

Microcontrollers are often low-power devices.

A microcontroller has a dedicated input device and often (but not always) has a

small LED or LCD display for output. A microcontroller also takes input from the

device it is controlling and controls the device by sending signals to different

components in the device.

For example, the microcontroller inside a TV takes input from the remote control

and displays output on the TV screen. The controller controls the channel selector,

the speaker system and certain adjustments on the picture tube electronics such as

tint and brightness. The engine controller in a car takes input from sensors such as

the oxygen and knock sensors and controls things like fuel mix and spark plug

timing. A microwave oven controller takes input from a keypad, displays output on

an LCD display and controls a relay that turns the microwave generator on and off.

A microcontroller is often small and low cost. The components are chosen to

minimize size and to be as inexpensive as possible.

A microcontroller is often, but not always, ruggedized in some way.

On the other hand, a microcontroller embedded inside a VCR hasn't been

ruggedized at all.

The actual processor used to implement a microcontroller can vary widely.

Atmel 89c51 Microcontroller Description

The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer

with 4K bytes of Flash programmable and erasable read only memory (PEROM) based

on the famous 8051 architecture. The device is manufactured using Atmel’s high-density

nonvolatile memory technology and is compatible with the industry-standard MCS-51

instruction set and pinout. The on-chip Flash allows the program memory to be

reprogrammed in-system or by a conventional nonvolatile memory programmer. By

combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C51 is

a powerful microcomputer which provides a highly-flexible and cost-effective solution to

many embedded control applications.

Features

The AT89C51 provides the following standard features:

Compatible with MCS-51 Products

Endurance: 1,000 Write/Erase Cycles

4K Bytes of In-System Reprogrammable Flash Memory

128 bytes of Internal RAM (128 x 8-bit)

32 Programmable I/O Lines

Two 16-bit Timer/Counters

Five vector two-level interrupt architecture

A full duplex serial port

Three-level Program Memory Lock

Six Interrupt Sources

BLOCK DIAGRAM:

Figure: Block Diagram of AT89c51 Microcontroller

PIN CONFIGURATIONS:

Figure: PDIP Type AT89c51 Pin Diagram

PIN DESCRIPTION

VCC Supply voltage.

GND Ground.

Port 0:

Port 0 is an 8-bit open-drain bi-directional I/O port.

As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins,

the pins can be used as high impedance inputs. Port 0 may also be configured to be the

multiplexed low order address/data bus during accesses to external program and data

memory. In this mode P0 has internal pull-ups. Port 0 also receives the code bytes during

Flash programming, and outputs the code bytes during program verification. External

pull-ups are required during program verification.

Port 1

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

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

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

Port 1 pins that are externally being pulled low will source current (IIL) because of the

internal pull-ups. Port 1 also receives the low-order address bytes during Flash

programming and verification.

Port 2

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

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

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

Port 2 pins that are externally being pulled low will source current (IIL) because of the

internal pull-ups. Port 2 emits the high-order address byte during fetches from external

program memory and during accesses to external data memory that uses 16-bit addresses

(MOVX @ DPTR). In this application, it uses strong internal pull-ups when emitting 1s.

Port 3

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

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

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

Port 3 pins that are externally being pulled low will source current (IIL) because of the

pull-ups.

Port 3 also serves the functions of various special features of the AT89C51 as listed

below:

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)

P3.6WR (external data memory Write

strobe)

P3.7RD (external data memory read

strobe)

Port 3 also receives some control signals for Flash programming and verification.

RST

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

running resets the device.

ALE/PROG

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

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

Flash programming.

In normal operation ALE is emitted at a constant rate of 1/6 the oscillator frequency, and

may be used for external timing or clocking purposes. Note, however, that one ALE pulse

is skipped during each access to external Data Memory. If desired, ALE operation can be

disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during

a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the

ALE-disable bit has no effect if the microcontroller is in external execution mode.

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

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

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

external data memory.

/VPP

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

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

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

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

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

require 12-volt VPP.

XTAL1

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

circuit.

XTAL2

Output from the inverting oscillator amplifier

7.HARDWARE DISCRIPTION

7.1 STEPER MOTOR

Introduction:

Stepper motors convert electrical energy into precise mechanical motion. These

motors rotate a specific incremental distance per each step. The number of steps executed

controls the degree of rotation of the motor’s shaft. This characteristic makes step motors

excellent for positioning applications. For example, a 1.8° step motor executing 100 steps

will rotate exactly 180° with some small amount of non-cumulative error. The speed of

step execution controls the rate of motor rotation. A 1.8° step motor executing steps at a

speed of 200 steps per second will rotate at exactly 1 revolution per second.

Stepper motors can be very accurately controlled in terms of how far and how fast

they will rotate. The number of steps the motor executes is equal to the number of pulse

commands it is given. A step motor will rotate a distance and at a rate that is proportional

to the number and frequency of its pulse commands.

Basic Stepper Motor System

The diagram above shows a typical step motor based system. All of these parts

must be present in one form or another. Each component’s performance will have an

effect on the others. By altering the frequency of the pulse train, the pulse generator can

instruct the motor to accelerate, run at a speed, decelerate or stop. A pulse generator must

be present otherwise the motor will not move. Next is the motor driver.

The driver takes the pulses from the pulse generator and determines how and

when the windings should be energized. The windings must be energized in a specific

sequence to generate motion. Finally there is the step motor itself. A step motor has two

primary parts; the rotor, the moving piece, and the stator, the stationary piece. The stator

contains coils of wire called windings. The rotor spins on bearings or bushings inside the

stator. All step motors operate through the principle of the rotor following a rotating

magnetic field created by sequencing the flow of current through the stator windings.

Each NMB step motor has two phases, which are groups of electrically connected

windings. As current is passed through each phase, the motor takes “steps” or small

movements to keep in synchronism with the magnetic field. The degree of rotation per

step depends on the style of driver used and the construction of the motor.

Step Motor Advantages:

• Accuracy & Repeatability – Ability to position accurately.

• Responsiveness & Quick Acceleration – Step motors have low rotor inertia,

allowing them to get up to speed quickly. This makes step motors an excellent choice for

short, quick moves.

• Excellent torque for their size – Step motors have the highest torque per cubic

inch of any motor.

• Positioning Stability – Unlike other types of motors, step motors can be held

completely motionless in their stopped position.

Construction and Operating the Hybrid STEP MOTOR

Figure 1a depicts a 1.8° hybrid step motor. The rotor contains a permanent

magnet similar to those found in permanent magnet step motors. Hybrid rotors are axially

magnetized, one end polarized north and the other polarized south. Both the rotor and the

stator assemblies of hybrid motors have tooth-like projections. To understand the rotor’s

interaction with the stator, examine the construction of a 1.8° (the most common

resolution) hybrid step motor.

The two cups are oriented so that the teeth of the top cup are offset to the teeth of

the bottom cup by 3.6°. Second, the stator has a two-phase construction. The winding

coils, 90° apart from one another, make up each phase. Each phase is wound so that the

poles 180° apart are the same polarity, while the poles 90° apart are the opposite polarity.

When the current in a phase is reversed, is the polarity, meaning that any winding coil

can be either a north pole or a south pole. As shown in fig. 1b below, when phase A is

energized, the windings at 12 o’clock and 6 o’clock are north poles and the windings at 3

o’clock and 9 o’clock are south poles.

The windings at 12 and 6 would attract the teeth of the magnetically south end of

the rotor, and windings at 3 and 9 would attract the teeth of the magnetically north end of

the rotor.

.

7.3 POWER SUPPLY:

CIRCUIT DIAGRAM:

POWER SUPPLY:

To run the electronic gadget at home it is provided by some power supply. The

microcontroller used (at89c51) requires 12v D.C supply. The DTMF receiver used

(mt8870) requires 5v D.C. so design of these regulated power supply is also an important

part in hardware design. The A.C power supply from mains is taken and regulated using

the rectifiers.

For design of a regulated power supply components used are:

Transformer.

Diodes.

Rectifiers.

Regulated IC chips.

Capacitive filters.

Trans former:

A transformer is required to couple the mains to the actual power supply circuit.

This is required to isolate the mains from the actual regulated power supply circuit and

the other part of the kit. This isolation eliminates the dame of the kit to any power supply

variations or from a faulty shock.

IN4007

0

1

2

7805

LED

1

2

1000uf

TRANSFORMER

6

8

1IN4007

5

1k

2

1100uf

230 V AC

SUPPLY

50 HZ

4

For a transformer shown below:

:

Diodes:

In bride rectifier four diodes are used. The specifications of diodes are chosen

as:

PIV > input voltage.

Si diode is better.

Power dissipation is kept fixed with respect to current through the diode.

Junction capacitance need not be considered for frequencies <1 kHz.

RECTIFIERS:

Rectification is a process of conversion of AC to DC. Here, the AC of transformer

output is given to the rectifier input, which converts it to DC output. Basically, bridge

rectifiers or diodes arranged in bridge called Diode arrangement are used for power

supply design.

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

V1 V2

i1 i2

V1 = i2 = n1V2 i1 n2

Current Flow in the Bridge Rectifier

For both positive and negative swings of the transformer, there is a forward path

through the diode bridge. Both conduction paths cause current to flow in the same

direction through the load resistor, accomplishing full-wave rectification.

While one set of diodes is forward biased, the other set is reverse biased and

effectively eliminated from the circuit.

Diode Bridge:

A diode bridge is an arrangement of four diodes connected in a bridge circuit as

shownbelow, that provides the same polarity of output voltage for any polarity of the

input voltage. When used in its most common application, for conversion of alternating

current (AC) input into direct current (DC) output, it is known as a bridge rectifier. The

diagram describes a diode-bridge design known as a full-wave rectifier or Graetz circuit.

This design can be used to rectify single phase AC when no transformer center tap

is available

Bridge Rectifier Circuit:

The essential feature of this arrangement is that for both polarities of the voltage

at the bridge input, the polarity of the output is constant.

Capacitors:

Capacitive filters are used stabilized or perfect regulation of the voltage. The

capacitive filters are opted because, they are more efficient. But they are also more

costly.

Different types of capacitors are:

1. Ceramic capacitors.

2. Electrolyte capacitors.

3. Paper/Mica capacitors.

4. Silver capacitors.

5. Tantalum capacitors.

Ceramic, Paper/Mica, Silver are nonpolarized capacitors. Electrolyte and Tantalum

are polarized capacitors. For high frequency, Ceramic capacitors are used. For low

frequencies, Electrolyte capacitors are used.

Linear regulated IC’s:

Linear regulated IC’s are used for best regulated output. The output from these

regulated IC’s is given to microcontroller and DTMF receiver. These linear regulated

IC’s are self protective (any accidental shot circuit in the IC is grounded automatically).

78xx series ICs are used for ‘+ve’ supply.

79xx series ICs are used for ‘-ve’ supply.

78xx and 79xx series ICs are fixed voltage regulators. LM 317 is a variable

voltage regulator.

CONCLUSION:

HENCE THE UNMANNED RAILWAY GATES PERATE ACCORDING TO THE DATA INPUT FROM

SENSORS TO MICROCONTROLLER. FIRST AN ALARM IS TRIGGERED AND THEN THE GATE IS

OPERATED.