automatic railway gate controll
TRANSCRIPT
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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
COMPONENTS NAME SPECIFICATION
Transistor BC 547
IC LM393
Resistor 1K ,10K
PHOTO DIODE
LED
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COMPONENTS USED IN RELAY DRIVER CIRCUIT
COMPONENTS NAME SPECIFICATION
Transistor BC 547
PCB PRINTED CKT BOARD
Resistor 1.5k
Diode IN4007
RELAY
COMPONENTS NAME SPECIFICATION
Relay 12v,10amp
TRANSFORMER
COMPONENTS NAME SPECIFICATION
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
pin P1.0, bit 7 is pin P1.7. Writing a value of 1 to a bit of this
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SFR will send a high level on the corresponding I/O pin whereas
a value of 0 will bring it to a low level.
SCON (Serial Control, Addresses 98h, Bit-Addressable): The
Serial Control SFR is used to configure the behavior of 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
pin P2.0, bit 7 is pin P2.7. 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 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
pin P3.0, bit 7 is pin P3.7. Writing a value of 1 to a bit of this
SFR will send a high level on the corresponding I/O pin whereas
a value of 0 will bring it to a low level.
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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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