automatic railway gate controll

7/30/2019 Automatic Railway Gate Controll

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MICROCONTROLLER BASED AUTOMATIC RAILWAY GATE CONTROL

INTRODUCTION:-The objective of this paper is to provide an automatic railway gate at a

level crossing replacing the gates operated by the gatekeeper. It deals

with two things. Firstly, it deals with the reduction of time for which the

gate is being kept closed And secondly, to provide safety to the road

users by reducing the accidents.

By the presently existing system once the train leaves the station, the

stationmaster informs the gatekeeper about the arrival of the trainthrough the telephone. Once the gatekeeper receives the information, he

closes the gate depending on the timing at which the train arrives.

Hence, if the train is late due to certain reasons, then gate remain closed

for a long time causing traffic near the gates.

By employing the automatic railway gate control at the level crossing

the arrival of the train is detected by the sensor placed near to the gate.

Hence, the time for which it is closed is less compared to the manually

operated gates and also reduces the human labor. This type of gates canbe employed in an unmanned level crossing where the chances of

accidents are higher and reliable operation is required. Since, the

operation is automatic error due to manual operation is prevented.

Automatic railway gate control is highly economical microcontroller

based arrangement, designed for use in almost all the unmanned level

crossings in the country.

In this paper we are concerned of providing an automatic railway gate

control at unmanned level crossings replacing the gates operated by gate

keepers and also the semi automatically operated gates. It deals with two

things. Firstly, it deals with the reduction of time for which the gate is

being kept closed. And secondly, to provide safety to the road users by

reducing the accidents that usually occur due to carelessness of road

users and at times errors made by the gatekeepers.


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By employing the automatic railway gate control at the level crossing

the arrival of train is detected by the sensor placed on either side of the

gate at about 5km from the level crossing. Once the arrival is sensed ,

the sensed signal is sent to the microcontroller then MC activate the gate

motor to close the gate automatically after crossing the level cross at thattime train sensed the second sensor second sensor then sensor send a

signal to MC then MC again activate the motor to open the level

crossing gate.

BLOCK DIAGRAM OF THIS PROJECT


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This project contain 7 section ie

1.Power supply section

2.Motor driver section

3.Motherboard section

4.Relay driver section

5.Buzzer driver section

6.IR transmitter section

7.IR receiver section

8.NOT gate section


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COMPONENTS USED IN POWER SUPPLY CIRCUIT

COMPONENTS NAME SPECIFICATION

Diode IN4007

Capacitor 1000f,25V

Resistor 1.5k quarter watt

Regulator IC 7812,7805

COMPONENTS USED IN IR SENSOR


Transistor BC 547

IC LM393

Resistor 1K ,10K

PHOTO DIODE

LED


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COMPONENTS USED IN RELAY DRIVER CIRCUIT


Transistor BC 547

PCB PRINTED CKT BOARD

Resistor 1.5k

Diode IN4007

RELAY


Relay 12v,10amp

TRANSFORMER


Transformer Step down 230V-12V

0-12,1A


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CIRCUIT DESCRIPTION

4.1 POWER SUPPLY(+ive)

Circuit connection: - In this we are using Transformer (0-12) v,1Amp,LED & resistors. Here 230V, 50 Hz ac signal is given as

input to the primary of the transformer and the secondary of thetransformer is given to the bridge rectification diode.

Circuit Explanations: - When ac signal is given to the primary ofthe transformer, due to the magnetic effect of the coil magneticflux is induced in the coil(primary) and transfer to the secondarycoil of the transformer due to the transformer action. Transformeris an electromechanical static device which transformer electrical

energy from one coil to another without changing its frequency.Here the diodes are connected in a bridge fashion. Thesecondary coil of the transformer is given to the bridge circuit forrectification purposes. During the +ve cycle of the ac signal thediodes D2 & D4 conduct due to the forward bias of the diodes anddiodes D1 & D3 does not conduct due to the reversed bias of thediodes. Similarly during the ve cycle of the ac signal the diodesD1 & D3 conduct due to the forward bias of the diodes and thediodes D2 & D4 does not conduct due to reversed bias of thediodes. The output of the bridge rectifier is not a power dc alongwith rippled ac is also present. To overcome this effect, acapacitor is connected to the o/p of the diodes (D2 & D3). Whichremoves the unwanted ac signal and thus a pure dc obtained.Here we need a fixed voltage, thats for we are using ICregulators. The o/p of the bridge rectifier is given as input to theIC regulator through capacitor with respect to GND and thus afixed o/p is obtained. The o/p of the IC regulator (7805 & 7812) is

given to the LED for indication purpose through resistor. Due tothe forward bias of the LED, the LED glows ON state, and the o/pare obtained .


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POWER SUPPLY CIRCUIT


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4.2LED INDICATOR

The indicator section consists of a light emitting diode andits driver circuit is designed on the basis of current

required to glow the light emitting diode. Here the drivercircuit is required for the following functionality. TheMicrocontroller cannot provide adequate current forglowing the LED. The LEDs requires a current between10mA to 20mA of current to glow. The driver circuitprovides current to the load from a separate source, sothe load current used not pass through theMicrocontroller.


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IR TRANSMITTER (transmitter zone)

The IR LED is also light emitting diode but the

junction is made out of such material that the transitionof electron between the bands emits quanta of energy(

E=h) having a particular frequency which is having aparticular characteristic. When a diode emits aparticular characteristic signal having frequency in therange of infrared then, that diode is called a infraredemitting diode. The IR data transmitter is a highintensity IR signal transmitter. There are two diodes

connected in parallel to increase the intensity to avoiddata corruption receiver end. In this section our aim isto protect the zone/door/almira etc. from theunauthorized entry or interruption, for that we needsome element that should not be visible to theunauthorized person. For that we have taken elementsas IR LED as a source and photo diode as a

destination. Generally, we have taken IR because IR isinvisible to the eye, where as in case of LASER, whichis easily visible to the human eye by which will, alert theunauthorized person. That is why we have taken IR asa transmitter which will transmit a continuously IRsignal. At the receiver end the photodiode will receivethe IR signal. if somebody tries to interrupt the IR signal

at the transmitter end, the receiver will decide theabsence of the IR signal at the receiver end.


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Operation

IR transmitter consist of resister ,IR diode and connected

according above the fig. when the +Ve 12 V is fed to the IR

diode through 150E resistor ir diode get +ve from DC supply

and also IR diode get Ve from Ve terminal of DC voltage.

When IR diode gets +Ve andVE then it transmit a IR beam .


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4.2 IR RECEIVER

Introduction

A PHOTO DIODE is light sensitive device the junction ofthe photo diode is such that it generates carriers whenthe light falls on it. There are different type of diodes,which generates carriers in different magnitudes atdifferent frequency this depends on the nature and dopingof the junction. The liberation of carriers are very small in

magnitude which is very much dependant on thefrequency and intensity of the light signal falling on the

junction. In the forward biased condition the majoritycarrier current is so high that the current generated due tofall of light signal is very negligible. The photonbombardment cause the avalanche break down of the

junction and generate current which is in the order of 100s

micro ampere to few 10s of mA, due to the abovementioned causes the photo diodes to connected in thereverse biased condition. In the reverse biased conditionthe normal current is always in the order of fewmicroamperes, the current generated due to fall of lightsignal on the junction is also in the order of microampereso the net current through the diode is appreciablyincreased. The same current pass through the resistance

connected in series and drop across the resistance isincreased. There are two types of arrangements verymuch widely used in the circuits, as shown in the Fig.1and Fig.2.


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If the diode junction is exposed with visible light or invisiblelight like Infrared / Laser in the circuit shown in fig.2, thediode current will rise, possibly to as high as 1mA,producing a significant output across R. In use, thephotodiode is reversed biased and the output voltage istaken from across a series-connected load resistor.

CIRCUIT DIAGRAM OF IR RECEIVER

R

VCC

D1 Vout

D1

Vout

Fig.1

R

VCC

Fig.2


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Operation

In this project in the data receiving section, the photodiode

is used as signal (data) detector purpose to detect the IRsignal (data) from the IR transmitter LED section.Whenever the signal is transmitted from the IR transmitterLED, the signal is received at the photodiode receivingsection. The receiving signal is very weak in strength, forthat we used an amplifier. The output of the photodiode isgiven as input to the amplifier (Op-amp LM351) through a

filtering capacitor (0.01uF) which is configured as anComparator and the reference voltage is set at non-inverting terminal of the operational Amplifier. There is a10K variable resistor which is connected between +5 Voltand Ground and the variable terminal is connected to theOP-AMP for providing the Threshold value. The output ofthe LM351 swings in between +Vsat andVsat, even fora small variation of signal across the threshold value. Thatoutput signal is not Compatible with the Micro controllerbecause of the high current; that output from the Op-ampis given to the signal conditioning i.e. the signal is given tothe base of the Transistor through a base resistancebetween 1K 43K and the collector is connected to Vcc=+5Volt in series with a 10K resistance and the output istaken from the collector. The emitter is grounded. The

transmitted data is received at the receiving section. Thetransmitted signal must fall pin pointed to the photodiode

junction in order to receive the Signal.


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RELAY DRIVER :

A relay is an electrically operated switch. Many relaysuse an electromagnet to operate a switching mechanism, but

other operating principles are used. Relays find applications

where it is necessary to control a circuit by a low-power

signal, or where several circuits must be controlled by one

signal. The first relays were used in long distance telegraph

circuits, repeating the signal coming in from one circuit and

re-transmitting it to another. Relays found extensive use in

telephone exchanges and early computers to perform logical

operations. A type of relay that can handle the high power

required to directly drive an electric motor is called a

contractor. Solid-state relays control power circuits with no

moving parts, instead using a semiconductor device

triggered by light to perform switching. Relays with

calibrated operating characteristics and sometimes multiple

operating coils are used to protect electrical circuits fromoverload or faults; in modern electric power systems these

functions are performed by digital instruments still called

"protection relays".
http://en.wikipedia.org/wiki/Electrichttp://en.wikipedia.org/wiki/Electrichttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Contactorhttp://en.wikipedia.org/wiki/Contactorhttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Electric


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Relay Switch Characteristics

Relays provide a way for one electric current to

control another electric current.

Switches control the flow of electricity, and relays areswitches that are operated by the flow of electricity.

Relays are devices whereby one electric current can

control another electric current. The control part of a

relay is just an electromagnet. The switch part of the

relay is a metal piece that can be moved by the

electromagnet to close a circuit. Relays can becharacterized by poles and throws like any switch, as

well as by other characteristics.

Poles and Throws

Like all switches, relays are characterized by poles andthrows. Throws is really a way of saying how many

different circuits the relay can control. If there is onethrow, the relay opens and closes one switch, and

controls one circuit. Two throws indicates that the relay

opens and closes two mechanically linked switches, and

so controls two circuits. Poles are the number of current

carrying positions the switches can be in. A single pole

switch only opens and closes a circuit. A double pole

switch diverts a current into one of two possible paths.Both poles and throws are usually only one or two, but

higher numbers are sometimes seen.
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Normally Open or Closed

Single pole relays are characterized as normally open ornormally closed. This refers to the position of the switch

when the electromagnet is not activated. If the relay isnormally open, activating the electromagnet will close

the switch and activate another circuit. If the relay is

normally closed, some circuit is active and activating

the electromagnet will deactivate this previously active

circuit. Normally open relays are found when a tiny

current is used to control a bigger current; activating

the electromagnet closes the switch that carries thelarger current. Normally closed relays are found in

burglar alarms, with the circuits that controls the

electromagnet that holds the switch open running

through the doors and windows of a home. When a door

or window is opened, it stops the current to the

electromagnet which causes the switch to close and sets

off an alarm. Cutting the wires to this relay also sets offthe alarm.

Latching Relays

Latching relays are a way of making a switch with memory.The circuit that is controlled by a latching relay also runs

through the electromagnet. When the electromagnet operates

the normally open switch, it controls some circuit, but it also

energizes the electromagnet. If the electromagnet is activated,even by a single pulse, it latches so it stays closed even when

the original circuit that activated the switch is no longer active.

The only way to unlatch the switch is to break, even

temporarily, the circuit that includes the electromagnet.


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Latching relays are used when machines are turned on and off

by push buttons.

Relay driver sectionRelay driver is consists of capacitor 10f, diode IN4007,

resister and NPN transistor BC547 which is connected

according the below diagram. Before going to the relay

driver first we should know that about Relay. Relay is an

electrical and electronics SWITCH which is ON and OFF by

the help of voltage and current which depends upon

transistor switching circuit and digital IC. Here transistoracts as a switching circuit .when the high voltage is fed to the

base of the transistor through resister then the transistor is

ON that means it conducts and the relay coil get +12V from

the 12V power supply but it does not get the ve power

supply so it cant be ON. When the transistor is ON then the

relay gets VE power and the relay is ON. After getting VE

power relay come out from its normal condition to the ON

condition , which ON the device which is connected through

the relay in other words which depends on relay for ON and

OFF. Here diode and capacitor works for freewheeling

purpose.


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The above circuit is the relay driver by this above circuit we

can on or off the relay easily.

RELAY DRIVER

This application is in some ways a continuation of he

discussion introduced for diodes how the effects of inductive

kick can be minimized through proper design. In the below

figure (a), a transistor is used to established the current

necessary to energize the relay in the collector circuit. With no

input at the base of the transistor, the base current, collector

current, and the coil current are essentially 0A, and the relaysits in the unenergized state (normally open, NO).

However when a positive pulse is applied to the

base, the transistor turns ON, establishing sufficient current

through the coil of the electromagnet to close the relay.

Problem can be now develop when the signal is removed from

the base to turn OFF the transistor and de-energized the relay.

Ideally, the current through he coil and the transistor will

quickly drop to zero, the arm of the relay will be released, and

the relay will simply remain dormant until the next ON signal.

However we know from our basic circuit courses that the

current through the coil cannot change instantaneously, and in

fact the more quickly changes, greater the induced voltage

across the coil as defined by,

VL = L (diL / dt).

In this case, the rapid changing current through the coil will

develop a large voltage across the coil with the polarity shown


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in figure (a), which will appear directly across the output of the

transistor. The chances are likely that its magnitude will

exceeds the maximum ratings of the transistor, and the

semiconductor device will be permanently damaged. Thevoltage across the coil will not remain at its highest switching

level but will oscillate as shown until its level drops to zero as

the system settles down.

The destructive action can be subdued by placing a diode

across the coil as shown in below figure (b). During the ON

state of the transistor, the diode is back biased: it sits like an

open circuit and does not affect the thing. However, when thetransistor turns OFF, the voltage across the coil will reverse

and will forward biased the diode, placing the diode in its ON

state. The current through the inductor established during

ON state of the transistor can then continue to flow through

the diode, eliminating the severe change in current level.

Because the inductive current is switched to diode almost

instantaneously after the OFF state is established, the diodemust have a current rating to match the current through the

inductor and the transistor when is in ON state. Eventually,

because of the resistive elements in the loop, including the

resistance of the coil windings and the diode, the high

frequency (quickly oscillating) variation in voltage level across

the coil will decay to zero and the system will settle down.


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Overload Relays

SIRIUS overload relays with screw-type, spring-loaded or

ring cable lug connections reliably protect loads as well as

other switching and protective devices in the respective load


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feeder against overload, phase imbalance and phase failure.

Thanks to ATEX certification, they can be used in many

different applications, even under the particularly harsh

conditions of the process industry. The overload relays caneasily be used with the contactors of the modular SIRIUS

system.There are two versions of overload relays: thermal

and electronic.

In the main circuit, the SIRIUS 3RU thermal overload

relays are responsible for current-dependent overload

protection of electrical loads (e.g. motors). The 3RU2

overload relays are available with spring-loaded, screw-type

and ring cable lug connections - for a particularly flexible

implementation. In the 3RU2 overload relays, the power

losses are 5 to 10 % lower than for the previous models

thanks to a new bimetal technology. Therefore, the

temperature within the control cabinet can be reduced as

well.

The 3RB electronic overload relay ensures real commercial

added value: In the main circuit, the electronic overload

relays for standard applications are responsible for current-

dependent overload protection of electrical loads (e.g.

motors). Due to the wide current setting ranges, completeseries of motors are covered with just a few types. An

electrical remote reset has been added to the already

extensive basic functions of the 3RB31 version.


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For demanding applications, a modular variant of the

electronic overload relay even offers full motor protection

by also sensing the temperature of the motor.

In addition, optimized, uniform accessories are available for3RU2 and 3RB3. This reduces the costs for the ordering

process and for maintaining stocks.

Electronic overload relay SIRIUS 3RB24 for IO-Link

With the new communication-capable electronic

overload relay SIRIUS 3RB24 for IO-Link you can easily

connect your load feeder to a higher-level control and

therefore its integration in your automation environment. As

the electronic overload relay supports the transmission of

analog process variables like currents, system processes can

be optimized, e.g. through load monitoring.Moreover, you will profit from an increased system

availability and easier system documentation thanks to

integrated diagnostic functions and readable parameter

assignment. In combination with contactors, the overload

relay can also be employed as direct, reversing and star-

delta starter.


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NOT GATE

SIGNAL CONDITIONING

The output form the input signal i.e. comparator or any

other external circuit must be compatible with the -controller,

because the -controller can takes 5V as input voltage and gives

a 5V as output voltage. That for we need a signal conditioning

circuit as given in the below figure.


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(SIGNAL CONDITIONING)

fig..1:1

In the fig1: 1, whenever the base voltage is HIGH the

transistor comes to saturation condition i.e. the collector current

flows to the emitter which gives a high voltage at the outputcorresponding to Vcc given at the collector. The output is taken

from the emitter junction through a current limiting resistance

and the output signal is given to the - controller or any other

circuit which needs a compatible (5V) voltage. Similarly,

whenever the base voltage is LOW the emitter current flows

from the emitter junction of the transistor, which gives a low

voltage at the output corresponding to GND. The output is taken

from the emitter junction through a current limiting resistance

and the output signal is given to the - controller or any other

circuit which needs a compatible (5V) voltage.

fig..1:0

BC5471.5k

10k

(1:0)

CC= +5vCC= +5v

(1:1)

INPUT

1.5k

OUTPUT

10kOUTPUT

BC547

INPUT


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In the fig1: 0, whenever the base voltage is HIGH the

transistor comes to saturation condition i.e. the emitter current

flows to the collector which gives a low voltage at the output

corresponding to GND. The output is taken from the collectorjunction through a current limiting resistance and the output

signal is given to the - controller or any other circuit which

needs a compatible (5V/0V) voltage. Similarly, whenever the

base voltage is LOW the collector current flows from the

collector junction of the transistor, which gives a high voltage at

the output corresponding to Vcc. The output is taken from the

emitter junction through a current limiting resistance and theoutput signal is given to the - controller or any other circuit

which needs a compatible (5V/0V) voltage.

The application of the transistors is not limited solely to the

amplification of the signals. Through proper design transistors

can be used as switches for computers and control applications.

The network of figure-01 (a) can be employed as an inverter in

computer logic circuitry. Note that the output voltage Vc is

opposite to the applied to the base or input terminal. In

addition note the absence of dc supply connected to the base

circuit. The only dc source is connected to the collector or

output side, and for computer applications is typically equal to

the magnitude of the high side of the applied signal in this

case 5V.

IN

Rc

OUT

Vcc = +5V

Rb Q1

BC547

Vi

t

5v

0v

Vc

t

5v

0v


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OPERATION:

Proper design for the inversion process requires that the

operating points switch from cut-off to saturation along the

load line depicted in above figure (b). For our proposes we will

assume that IC = ICEO = 0mA, when IB = 0A (an excellent

approximation in light of improving construction techniques),

as shown in above figure (b). In addition, we will assume that

VCE = VCE sat = 0V.

When Vi = 5v, the transistor will be ON and design must

insured that the network is heavily saturated by a level of IB

greater than that associated if the IB curve appearing near the

saturation level. In the above figure (b), this requires that IB >

50A.

IB = 0A

IB = 10A

IB = 20A

IB = 40A

IB = 60AIB = 80A

Vcc = 5VVCE

(b)

IC sat = 6mA

IC (mA)


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The saturation level for the collector current for the circuit is

defined by,

IC= VCC/ RC

The level of IB in the active region just before saturation resultscan be approximated by the following equation,

IBmax ICsat / dc

For the saturation level we must therefore insure that the

following condition is satisfied:

IB max >ICsat / dc

For the network of the above figure (b), when Vi = 5v the

resulting level of IB isIB = Vi0.7 / RB= 5v 0.7 / 1.5k

= 2866A

ICsat = VCC /RC

= 5v / 10k

= 0.5mA

Testing the above equation gives:IB =2866A > ICsat / dc = 0.5mA / 300

Which is satisfied. Certainly any level of IB greater than 2866A

will pass through a Q- point on the load line that is very close to

the vertical axis.

INVERTER EXAMPLEAt saturation,

ICsat = VCC/ RC

10mA = 5V / RC

RC = 5V / 10mA = 500


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At saturation,

IB ICsat / dc= 10mA / 300 = 33 A

Choosing IB = 60A to ensure saturation and using,

IB = Vi0.7V / RB

RB = Vi 0.7V / IB

= 5v 0.7v / 60A or 80A

= 716k or 537k

Choose RB = 720k or 560k which is a standard value. Then,

IB = Vi0.7V / RBIB= Vi 0.7V / 720k or 560k

= 4.3V / 720k or 560k

= 59A or 76 A

PIEZO ELECRTIC BUZZER:

It is a device that converts electrical signal to an audible

signal (sound signal).The Microcontroller cannot drive directly

to the buzzer, because the Microcontroller cannot give sufficientcurrent to drive the buzzer for that we need a driver transistor

(BC547), which will give sufficient current to the

buzzer.Whenever a signal received to the base of the transistor

through a base resistance (1.5k) is high, the transistor comes to

saturation condition i.e. ON condition thus the buzzer comes to

on condition with a audible sound. Similarly, whenever the

signal is not received to the base of the transistor, thus thetransistor is in cut-off state i.e. is in OFF state thus the buzzer

does not gets activated.


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3 MOTHER BOARD:

The motherboard of this project is designed with a MSC 51core compatible micro controller. The motherboard is designed

on a printed circuit board, compatible for the micro controller.

This board is consisting of a socket for micro controller, input

/output pull-up registers; oscillator section and auto reset circuit.

Microcontroller core processor:

Introduction

Despite its relatively old age, the 89C51 is one of the most

popular Micro controller in use today. Many derivatives Micro

controllers have since been developed that are based on--and

compatible with--the 8051. Thus, the ability to program an

BUZZER DRIVER

1.5K

BC547

DATA

INPUT

BUZZER

VCC


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89C51 is an important skill for anyone who plans to develop

products that will take advantage of Micro controller.

Many web pages, books, and tools are available for the 89C51

developer.

The 89C51 has three very general types of memory. To

effectively program the 8051 it is necessary to have a basic

understanding of these memory types.

The memory types are illustrated in the following graphic. They

are: On-Chip Memory, External Code Memory, and External

RAM.

Fig-9 (Memory structure of Microcontroller)

On-Chip Memory refers to any memory (Code, RAM, or other)

that physically exists on the Microcontroller itself. On-chip

memory can be of several types, but we'll get into that shortly.

External Code Memory is code (or program) memory that

resides off-chip. This is often in the form of an external

EPROM.


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External RAM is RAM memory that resides off-chip. This is

often in the form of standard static RAM or flash RAM.

Code Memory

Code memory is the memory that holds the actual 8051 program

that is to be run. This memory is limited to 64K and comes in

many shapes and sizes: Code memory may be found on-chip,

either burned into the Microcontroller as ROM or EPROM.

Code may also be stored completely off-chip in an external

ROM or, more commonly, an external EPROM. Flash RAM isalso another popular method of storing a program. Various

combinations of these memory types may also be used--that is to

say, it is possible to have 4K of code memory on-chip and 64k

of code memory off-chip in an EPROM.

When the program is stored on-chip the 64K maximum is often

reduced to 4k, 8k, or 16k. This varies depending on the versionof the chip that is being used. Each version offers specific

capabilities and one of the distinguishing factors from chip to

chip is how much ROM/EPROM space the chip has.

However, code memory is most commonly implemented as off-

chip EPROM. This is especially true in low-cost development

systems and in systems developed by students.

Programming Tip: Since code memory is restricted to 64K,

89C51 programs are limited to 64K. Some assemblers and

compilers offer ways to get around this limit when used with

specially wired hardware. However, without such special

compilers and hardware, programs are limited to 64K.


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External RAM

As an obvious opposite of Internal RAM, the 89C51 also

supports what is called External RAM. As the name suggests,

External RAM is any random access memory which is found

off-chip. Since the memory is off-chip it is not as flexible in

terms of accessing, and is also slower. For example, to

increment an Internal RAM location by 1 requires only 1

instruction and 1 instruction cycle. To increment a 1-byte value

stored in External RAM requires 4 instructions and 7 instruction

cycles. In this case, external memory is 7 times slower!

What External RAM loses in speed and flexibility it gains in

quantity.While Internal RAM is limited to 128 bytes (256 bytes

with an 8052), the 8051 supports External RAM up to 64K.

Programming Tip: The 8051 may only address 64k of RAM.

To expand RAM beyond this limit requires programming and

hardware tricks. You may have to do this "by hand" since many

compilers and assemblers, while providing support for programsin excess of 64k, do not support more than 64k of RAM. This is

rather strange since it has been my experience that programs can

usually fit in 64k but often RAM is what is lacking. Thus if you

need more than 64k of RAM, check to see if your compiler

supports it-- but if it doesn't, be prepared to do it by hand.

On-Chip Memory

As mentioned at the beginning of this chapter, the 89C51

includes a certain amount of on-chip memory. On-chip memory

is really one of two types: Internal RAM and Special Function


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Register (SFR) memory. The layout of the 89C51's internal

memory is presented in the following memory map:

As is illustrated in this map, the 8051 has a bank of 128 bytes of

Internal RAM. This Internal RAM is found on-chip on the 8051

so it is the fastest RAM available, and it is also the most flexible

in terms of reading, writing, and modifying its contents.

Internal RAM is volatile, so when the 8051 is reset this memoryis cleared.

The 128 bytes of internal ram is subdivided as shown on the

memory map. The first 8 bytes (00h - 07h) are "register bank 0".

By manipulating certain SFRs, a program may choose to use

register banks 1, 2, or 3. These alternative register banks are

located in internal RAM in addresses 08h through 1Fh. We'll

discuss "register banks" more in a later chapter. For now it is

sufficient to know that they "live" and are part of internal RAM.

Bit Memory also lives and is part of internal RAM. We'll talk

more about bit memory very shortly, but for now just keep in


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mind that bit memory actually resides in internal RAM, from

addresses 20h through 2Fh.

The 80 bytes remaining of Internal RAM, from addresses 30h

through 7Fh, may be used by user variables that need to beaccessed frequently or at high-speed. This area is also utilized

by the Microcontroller as a storage area for the operating stack.

This fact severely limits the 8051s stack since, as illustrated in

the memory map, the area reserved for the stack is only 80

bytes--and usually it is less since this 80 bytes has to be shared

between the stack and user variables.

SFR Descriptions

There are different special function registers (SFR) designed in

side the 89C51 micro controller. In this micro controller all the

input , output ports, timers interrupts are controlled by the

SFRs. The SFR functionalities are as follows.

This section will endeavor to quickly overview each of thestandard SFRs found in the above SFR chart map. It is not the

intention of this section to fully explain the functionality of each

SFR--this information will be covered in separate chapters of the

tutorial. This section is to just give you a general idea of what

each SFR does.

P0 (Port 0, Address 80h, Bit-Addressable): This is

input/output port 0. Each bit of this SFR corresponds to one ofthe pins on the Microcontroller. For example, bit 0 of port 0 is

pin P0.0, bit 7 is pin P0.7. Writing a value of 1 to a bit of this

SFR will send a high level on the corresponding I/O pin whereas

a value of 0 will bring it to a low level.


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Programming Tip: While the 8051 has four I/O port (P0, P1, P2,

and P3), if your hardware uses external RAM or external code

memory (i.e., your program is stored in an external ROM or

EPROM chip or if you are using external RAM chips) you may

not use P0 or P2. This is because the 8051 uses ports P0 and P2

to address the external memory. Thus if you are using external

RAM or code memory you may only use ports P1 and P3 for

your own use.

SP (Stack Pointer, Address 81h): This is the stack pointer of theMicrocontroller. This SFR indicates where the next value to be

taken from the stack will be read from in Internal RAM. If you

push a value onto the stack, the value will be written to the

address of SP + 1. That is to say, if SP holds the value 07h, a

PUSH instruction will push the value onto the stack at address

08h. This SFR is modified by all instructions which modify the

stack, such as PUSH, POP, LCALL, RET, RETI, and wheneverinterrupts are provoked by the Microcontroller.

Programming Tip: The SP SFR, on startup, is initialized to 07h.

This means the stack will start at 08h and start expanding

upward in internal RAM. Since alternate register banks 1, 2, and

3 as well as the user bit variables occupy internal RAM from

addresses 08h through 2Fh, it is necessary to initialize SP in

your program to some other value if you will be using the

alternate register banks and/or bit memory. It's not a bad idea

to initialize SP to 2Fh as the first instruction of every one of

your programs unless you are 100% sure you will not be using

the register banks and bit variables.


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DPL/DPH (Data Pointer Low/High, Addresses 82h/83h): The

SFRs DPL and DPH work together to represent a 16-bit value

called the Data Pointer. The data pointer is used in operations

regarding external RAM and some instructions involving codememory. Since it is an unsigned two-byte integer value, it can

represent values from 0000h to FFFFh (0 through 65,535

decimal).

Programming Tip: DPTR is really DPH and DPL taken together

as a 16-bit value. In reality, you almost always have to deal with

DPTR one byte at a time. For example, to push DPTR onto the

stack you must first push DPL and then DPH. You can't simply

plush DPTR onto the stack. Additionally, there is an instruction

to "increment DPTR." When you execute this instruction, the

two bytes are operated upon as a 16-bit value. However, there

is no instruction that decrements DPTR. If you wish to

decrement the value of DPTR, you must write your own code to

do so.

PCON (Power Control, Addresses 87h): The Power Control SFR

is used to control the 8051's power control modes. Certain

operation modes of the 8051 allow the 8051 to go into a type

of "sleep" mode, which requires much, less power. These

modes of operation are controlled through PCON. Additionally,

one of the bits in PCON is used to double the effective baud

rate of the 8051's serial port.

TCON (Timer Control, Addresses 88h, Bit-Addressable):The Timer Control SFR is used to configure and modify the way

in which the 8051's two timers operate. This SFR controls

whether each of the two timers is running or stopped and


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contains a flag to indicate that each timer has overflowed.

Additionally, some non-timer related bits are located in the

TCON SFR. These bits are used to configure the way in which

the external interrupts are activated and also contain the externalinterrupt flags which are set when an external interrupt has

occurred.

TMOD (Timer Mode, Addresses 89h): The Timer Mode SFR

is used to configure the mode of operation of each of the two

timers. Using this SFR your program may configure each timer

to be a 16-bit timer, an 8-bit auto reload timer, a 13-bit timer, or

two separate timers. Additionally, you may configure the timersto only count when an external pin is activated or to count

"events" that are indicated on an external pin.

TL0/TH0 (Timer 0 Low/High, Addresses 8Ah/8Ch): These

two SFRs, taken together, represent timer 0. Their exact

behavior depends on how the timer is configured in the TMOD

SFR; however, these timers always count up. What is

configurable is how and when they increment in value.

TL1/TH1 (Timer 1 Low/High, Addresses 8Bh/8Dh): These

two SFRs, taken together, represent timer 1. Their exact

behavior depends on how the timer is configured in the TMOD

SFR; however, these timers always count up. What is

configurable is how and when they increment in value.

P1 (Port 1, Address 90h, and Bit-Addressable): This isinput/output port 1. Each bit of this SFR corresponds to one of

the pins on the Microcontroller. For example, bit 0 of port 1 is



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SCON (Serial Control, Addresses 98h, Bit-Addressable): The

Serial Control SFR is used to configure the behavior of the8051's on-board serial port. This SFR controls the baud rate of

the serial port, whether the serial port is activated to receive

data, and also contains flags that are set when a byte is

successfully sent or received.

Programming Tip: To use the 8051's on-board serial port, it is

generally necessary to initialize the following SFRs: SCON,TCON, and TMOD. This is because SCON controls the serial port.

However, in most cases the program will wish to use one of the

timers to establish the serial port's baud rate. In this case, it is

necessary to configure timer 1 by initializing TCON and TMOD.

SBUF (Serial Control, Addresses 99h): The Serial Buffer SFR is

used to send and receive data via the on-board serial port. Any

value written to SBUF will be sent out the serial port's TXD pin.Likewise, any value which the 8051 receives via the serial port's

RXD pin will be delivered to the user program via SBUF. In other

words, SBUF serves as the output port when written to and as

an input port when read from.

P2 (Port 2, Address A0h, and Bit-Addressable): This is

input/output port 2. Each bit of this SFR corresponds to one ofthe pins on the Microcontroller. For example, bit 0 of port 2 is





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Programming Tip: While the 8051 has four I/O port (P0, P1, P2,

and P3), if your hardware uses external RAM or external code

memory (i.e., your program is stored in an external ROM or

EPROM chip or if you are using external RAM chips) you maynot use P0 or P2. This is because the 8051 uses ports P0 and P2

to address the external memory. Thus if you are using external

RAM or code memory you may only use ports P1 and P3 for

your own use.

IE (Interrupt Enable, Addresses A8h): The Interrupt Enable SFR

is used to enable and disable specific interrupts. The low 7 bits

of the SFR are used to enable/disable the specific interrupts,

where as the highest bit is used to enable or disable ALL

interrupts. Thus, if the high bit of IE is 0 all interrupts are

disabled regardless of whether an individual interrupt is

enabled by setting a lower bit.

P3 (Port 3, Address B0h, and Bit-Addressable): This is

input/output port 3. Each bit of this SFR corresponds to one ofthe pins on the Micro controller. For example, bit 0 of port 3 is





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Fig-10 (Structural Hierarchy)


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Auto reset Circuit:

Fig-11 (Connection of Relay with microcontroller)

RST10uF

22pF

22pF

8.2k

4 - 12Mhz

VCC=+5vdc

AT89C51

9

1819

2930

31

1

2

3

4

5

6

7

8

2122

23

24

25

26

27

28

10

11

12

13

14

15

16

17

3938

37

36

35

34

33

32

RST

XTAL2

XTAL1

PSEN

ALE/PROG

EA/VPP

P1.0

P1.1

P1.2

P1.3

P1.4

P1.5

P1.6

P1.7

P2.0/A8

P2.1/A9

P2.2/A10

P2.3/A11

P2.4/A12

P2.5/A13

P2.6/A14

P2.7/A15

P3.0/RXD

P3.1/TXD

P3.2/INT0

P3.3/INT1

P3.4/T0

P3.5/T1

P3.6/WR

P3.7/RD

P0.0/AD0

P0.1/AD1

P0.2/AD2

P0.3/AD3

P0.4/AD4

P0.5/AD5

P0.6/AD6

P0.7/AD7

MICROCONTROLLER


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The auto reset circuit is a RC network as shown in the mother

board circuit diagram. A capacitor of 1-10mfd is connected in

series with a 8k2 resister the R-C junction is connected to the

micro controller pin 9 which is reset pin. The reset pin is onewhen ever kept high( logic 1) the programme counter (PC)

content resets to 0000h so the processor starts executing the

programme. from that location. When ever the system is

switched ON the mother board gets power and the capacitor acts

as short circuit and the entire voltage appears across the resistor,

so the reset pin get a logic 1 and the system get reset, whenever

it is being switched ON.


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Pull-UP Resisters:

FIG-12 (Pin configuration of AT89C51 microcontroller)

The PORT0 and PORT2 of the MCS-51 architecture

is of open collector type so on writing logic 0 the pins are

providing a perfect ground potential. Where as on writing logic

1 the port pins behaves as high impedance condition so putting apull-up resister enables the port to provide a +5volt( logic 1).

Port1 and Port3 are provided with internal pull-ups. A pull-up

resister is normally a 10K resistance connected from the port pin

to the Vcc (+5) volt.

AT89C51

9

18

19

29

30

31

1

2

3

4

5

6

7

8

21

22

23

24

25

2627

28

10

11

12

13

14

15

16

17

39

38

37

36

35

3433

32

RST

XTAL2

XTAL1

PSEN

ALE/PROG

EA/VPP

P1.0

P1.1

P1.2

P1.3

P1.4

P1.5

P1.6

P1.7

P2.0/A8

P2.1/A9

P2.2/A10

P2.3/A11

P2.4/A12P2.5/A13

P2.6/A14

P2.7/A15

P3.0/RXD

P3.1/TXD

P3.2/INT0

P3.3/INT1

P3.4/T0

P3.5/T1

P3.6/WR

P3.7/RD

P0.0/AD0

P0.1/AD1

P0.2/AD2

P0.3/AD3

P0.4/AD4P0.5/AD5

P0.6/AD6

P0.7/AD7

10k

PORT-0

VCC=+5V


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Crystal Oscillator

The 8051 family microcontroller contains an inbuilt crystal

oscillator, but the crystal has to be connected externally. This

family of microcontroller can support 0 to 24MHz crystal andtwo numbers of decoupling capacitors are connected as shown

in the figure. These capacitors are decouples the charges

developed on the crystal surface due to piezoelectric effect.

These decoupling capacitors are normally between 20pf to 30pf.

The clock generator section is designed as follows,

Fig-13 (Crystal oscillator)

The Microcontroller design consist of two parts

1) Hardware2) Software

.


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HARDWARE:

The controller operates on +5 V dc, so the regulated + 5v is

supplied to pin no. 40 and ground at pin no. 20. The controller is

used here need not required to handle high frequency signals, soas 4 MHz crystal is used for operating the processor. The pin no.

9 is supplied with a +5V dc through a push switch to reset the

processor .As prepare codes are store in the internal flash

memory the pin no. 31 is connected to + Vcc

4.6-IC 7805

ITs one of the most famous regulator IC to make theripple in wave form smooth.when we convert AC to DCwe need to use like this IC to regulate the voltage andcurrent.78 mean that it works with + polarity and 05 meansit produce +5 volts for u regulated and without ripple. if wewant to have the higher voltage u should use

7805,7806.7812,78XXand for the negative polarityuse 7905,7912,79XX is positive type.


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Features

Output Current up to 1A

Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V

Thermal Overload Protection

Short Circuit Protection

Output Transistor Safe Operating Area Protection

Description

The KA78XX/KA78XXA series of three-terminal positiveregulator are available in the TO-220/D-PAK package andwith several fixed output voltages, making them useful inwide range of applications. Each type employs internalcurrent limiting, thermal shut down and safe operatingarea protection, making it essentially indestructible. If

adequate heat sinking is provided, they can deliver over1A outpu current. Although designed primarily as fixedvoltage regulators, these devices can be used withexternalcomponents to obtain adjustable voltages andcurrents.


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automatic railway gate controll

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