Scheduling of College Bell using Microcontroller
ABSTRACT
"Science is the study of the world as it is.
Engineering is the creation of the world tomorrow".
Science is basically "passive" observation of the universe, as it exists
to generate knowledge. Engineering is making use of that knowledge to
meet human needs by creating machine, systems, process and technologies
that have not previously existed.
Design and manufacturing are the synthetic part of engineering
practice. Manufacturer has received a lot of attention recently for very good
economic reasons.
Due to literacy awareness the number of colleges, schools and
institutions are rapidly increasing. In present system bells for periods or
recess are operated manually. After every class, one employee is engaged
into alarming bell. To avoid this, automisation of college bell is possible so
the bell would ring automatically at the scheduled time.
This project deals with the preparation of circuit for scheduling of
bell.
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Scheduling of College Bell using Microcontroller
INTRODUCTION
This Project takes over the task of ringing of the bell in colleges. It
replaces the Manual Switching of the Bell in the College. It has an Inbuilt
Real Time Clock (PCF 8583) which track over the Real Time. When this
time equals to the bell ringing time, then the relay for the bell is switched
ONN.
The Bell Ringing time can be edited at any Time, so that it can be
used at Normal Class Timings as well as Exam Times. The Real Time Clock
is displayed on four 7-segment display. The Microcontroller PIC16F877A is
used to control all the Functions, it get the time through the keypad and store
it in its Memory. And when the Real time and Bell time get equal then the
Bell is switched on for a predetermined time.
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LITERATURE REVIEW
An electric bell is a mechanical bell that functions by means of an
electromagnet.
Principle
In DC electric bells, when power is applied, current flows through the
coil. The coil becomes an electromagnet, attracting the metal strip. This
moves the clanger to hit the bell/gong, but also breaks the circuit. The coil is
no longer a magnet, so the clanger moves back. The circuit is thus restored.
The process repeats continuously until the power is removed.
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AC electric bells do not have interrupting contacts and their coils are
powered directly by the source. Their hammers vibrate at same frequency as
the frequency of voltage that they are powered by. Lack of contacts makes
them more reliable than DC bells.
Some electric bells have two cups which generate different tones.
When the hammer goes in one direction, it hits one cup, when it moves
back, it hits another cup. The sound of such two-tone electric bells is more
pleasant.
Applications
Two early applications of the electric bell were the telephone and
doorbell. Early telephones used electric bells to indicate that there was an
incoming call. Doorbells were used by visitors to indicate their presence at
the external door of a dwelling or business. Though still in use, the electric
bell mechanisms in both telephones and doorbells now compete with non-
mechanical noisemaking technologies including electronic oscillators and
digitally recorded sounds played back through a speaker.
A common style of doorbell uses an AC solenoid coil and a plunger.
When the doorbell button is depressed, the plunger is drawn into the
solenoid and strikes a gong; a shading coil on the solenoid prevents the
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Scheduling of College Bell using Microcontroller
plunger from vibrating at the same frequency as the power supply. When the
button is released, a spring retracts the plunger which then strikes a second
gong, giving a two-tone sound. A variant has a second solenoid which is
wired to the back door and only strikes one gong, allowing front or rear door
callers to be identified.
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COMPONENT LIST & DESCRIPTION
Component List
Microcontroller PIC 16F877A
Real Time Clock (RTC) PCF 8583
Transistor BC547
Relay 12v
LCD
Crystal 32.876
Keypad
Voltage regulator 7805
Transformer 09 750mA
Capacitor 1000mf, 25v
LED
Resistor 2.2K, 1K
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Microcontroller PIC 16F877A
PIC16F873A/876A devices are available only in 28-pin packages,
while PIC16F874A/877A devices are available in 40-pin and 44-pin
packages. All devices in the PIC16F87XA family share common
architecture with the following differences:
• The PIC16F873A and PIC16F874A have one-half of the total on-chip
memory of the PIC16F876A and PIC16F877A
• The 28-pin devices have three I/O ports, while the 40/44-pin devices
have five
• The 28-pin devices have fourteen interrupts, while the 40/44-pin
devices have fifteen
• The 28-pin devices have five A/D input channels, while the 40/44-pin
devices have eight
• The Parallel Slave Port is implemented only on the 40/44-pin devices
The available features are summarized in Table 1-1. Block diagrams
of the PIC16F873A/876A and PIC16F874A/877A devices are provided in
Figure 1-1 and Figure 1-2, respectively. The pinouts for these device
families are listed in Table 1-2 and Table 1-3. Additional information may
be found in the PICmicro Mid-Range Reference Manual (DS33023), which
may be obtained from your local Microchip Sales Representative or
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Scheduling of College Bell using Microcontroller
downloaded from the Microchip web site. The Reference Manual should be
considered a complementary document to this data sheet and is highly
recommended reading for a better understanding of the device architecture
and operation of the peripheral modules.
Peripheral Features:
• Timer0: 8-bit timer/counter with 8-bit prescaler
• Timer1: 16-bit timer/counter with prescaler, can be incremented
during Sleep via external crystal/clock
• Timer2: 8-bit timer/counter with 8-bit period register, prescaler and
postscaler
• Two Capture, Compare, PWM modules
- Capture is 16-bit, max. resolution is 12.5 ns
- Compare is 16-bit, max. resolution is 200 ns
- PWM max. resolution is 10-bit
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Scheduling of College Bell using Microcontroller
• Synchronous Serial Port (SSP) with SPI™ (Master mode) and I
C™(Master/Slave)
• Universal Synchronous Asynchronous Receiver Transmitter
(USART/SCI) with 9-bit address detection
• Parallel Slave Port (PSP) – 8 bits wide with external RD, WR and CS
controls (40/44-pin only)
• Brown-out detection circuitry for Brown-out Reset (BOR)
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Block Diagram
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Pin Diagram
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RTC PCF 8583
GENERAL DESCRIPTION
The PCF8583 is a clock/calendar circuit based on a 2048-bit
static CMOS RAM organized as 256 words by 8 bits. Addresses and
data are transferred serially via the two-line bidirectional I2C-bus. The
built-in word address register is incremented automatically after each
written or read data byte. Address pin A0 is used for programming the
hardware address, allowing the connection of two devices to the bus
without additional hardware.
The built-in 32.768 kHz oscillator circuit and the first 8 bytes of the
RAM are used for the clock/calendar and counter functions. The next 8 bytes
may be programmed as alarm registers or used as free RAM space. The
remaining 240 bytes are free RAM locations.
FEATURES
I2C-bus interface operating supply voltage: 2.5 V to 6 V
Clock operating supply voltage (0 to +70 C): 1.0 V to 6.0 V
240 8-bit low-voltage RAM
Data retention voltage: 1.0 V to 6 V
Operating current (at fSCL = 0 Hz): max. 50 A
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Clock function with four year calendar
Universal timer with alarm and overflow indication
24 or 12 hour format
32.768 kHz or 50 Hz time base
Serial input/output bus (I2C)
Automatic word address incrementing
Programmable alarm, timer and interrupt function
Slave address:
– READ: A1 or A3
– WRITE: A0 or A2.
Block DiagramGovernment Polytechnic, Amravati 13
Scheduling of College Bell using Microcontroller
FUNCTIONAL DESCRIPTION
The PCF8583 contains a 256 by 8-bit RAM with an 8-bit auto-
increment address register, an on-chip 32.768 kHz oscillator circuit, a
frequency divider, a serial two-line bidirectional I2C-bus interface and a
power-on reset circuit. The first 16 bytes of the RAM (memory addresses 00
to 0F) are designed as addressable 8-bit parallel special function registers.
The first register (memory address 00) is used as a control/status register.
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The memory addresses 01 to 07 are used as counters for the clock function.
The memory addresses 08 to 0F may be programmed as alarm registers or
used as free RAM locations, when the alarm is disabled.
Counter function modes
When the control/status register is programmed, a 32.768 kHz clock
mode, a 50 Hz clock mode or an event-counter mode can be selected. In the
clock modes the hundredths of a second, seconds, minutes, hours, date,
month (four year calendar) and weekday are stored in a BCD format. The
timer register stores up to 99 days. The event counter mode is used to count
pulses applied to the oscillator input (OSCO left open-circuit). The event
counter stores up to 6 digits of data.
When one of the counters is read (memory locations 01 to 07), the
contents of all counters are strobed into capture latches at the beginning of a
read cycle. Therefore, faulty reading of the count during a carry condition is
prevented. When a counter is written, other counters are not affected.
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Alarm function modes
By setting the alarm enable bit of the control/status register the alarm
control register (address 08) is activated. By setting the alarm control
register a dated alarm, a daily alarm, a weekday alarm or a timer alarm may
be programmed. In the clock modes, the timer register (address 07) may be
programmed to count hundredths of a second, seconds, minutes, hours or
days. Days are counted when an alarm is not programmed.
Whenever an alarm event occurs the alarm flag of the control/status
register is set. A timer alarm event will set the alarm flag and an overflow
condition of the timer will set the timer flag. The open drain interrupt output
is switched on (active LOW) when the alarm or timer flag is set (enabled).
The flags remain set until directly reset by a write operation.
When the alarm is disabled (Bit 2 of control/status register = 0) the alarm
registers at addresses 08 to 0F may be used as free RAM.
Control/status register
The control/status register is defined as the memory location 00 with
free access for reading and writing via the I2C-bus. All functions and
options are controlled by the contents of the control/status register.
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Pinning
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Voltage Regulator 7805
General Description
The LM7805 series of three terminal regulators is available with
several fixed output voltages making them useful in a wide range of
applications One of these is local on card regulation eliminating the
distribution problems associated with single point regulation The voltages
available allow these regulators to be used in logic systems instrumentation
HiFi and other solid state electronic equipment Although designed primarily
as fixed voltage regulators these devices can be used with external
components to obtain adjustable voltages and currents.
The LM7805 series is available in an aluminum TO-3 package which
will allow over 10A load current if adequate heat sinking is provided
Current limiting is included to limit the peak output current to a safe value
Safe area protection for the output transistor is provided to limit internal
power dissipation If internal power dissipation becomes too high for the heat
sinking provided the thermal shutdown circuit takes over preventing the IC
from overheating.
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Considerable effort was expanded to make the LM7805 series of
regulators easy to use and mininize the number of external components It is
not necessary to bypass the output although this does improve transient
response Input bypassing is needed only if the regulator is located far from
the filter capacitor of the power supply
For output voltage other than 5V, 12V and 15V the LM117 series
provides an output voltage range from 12V-57V.
Features
Output current in excess of 1A
Internal thermal overload protection
No external components required
Output transistor safe area protection
Internal short circuit current limit
Available in the aluminum TO-3 package
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Transformer 09, 750mA
A transformer is a device that transfers electrical energy from one
circuit to another through inductively coupled electrical conductors. A
changing current in the first circuit (the primary) creates a changing
magnetic field. This changing magnetic field induces a changing voltage in
the second circuit (the secondary). This effect is called mutual induction.
If a load is connected to the secondary circuit, electric charge will
flow in the secondary winding of the transformer and transfer energy from
the primary circuit to the load. In an ideal transformer, the induced voltage
in the secondary winding (VS) is a fraction of the primary voltage (VP) and
is given by the ratio of the number of secondary turns to the number of
primary turns:
By appropriate selection of the numbers of turns, a transformer thus
allows an alternating voltage to be stepped up — by making NS more than
NP — or stepped down, by making it less.
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Transformers come in a range of sizes from a thumbnail-sized
coupling transformer hidden inside a stage microphone to huge units
weighing hundreds of tons used to interconnect portions of national power
grids. All operate with the same basic principles, although the range of
designs is wide. While new technologies have eliminated the need for
transformers in some electronic circuits, transformers are still found in
nearly all electronic devices designed for household ("mains") voltage.
Transformers are essential for high voltage power transmission, which
makes long distance transmission economically practical.
Resistors 2.2K, 1K
A resistor is a two-terminal electronic component designed to oppose
an electric current by producing a voltage drop between its terminals in
proportion to the current, that is, in accordance with Ohm's law: V = IR. The
resistance R is equal to the voltage drop V across the resistor divided by the
current I through the resistor.
The primary characteristics of resistors are their resistance and the
power they can dissipate. Other characteristics include temperature
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coefficient, noise, and inductance. Practical resistors can be made of
resistive wire, and various compounds and films, and they can be integrated
into hybrid and printed circuits. Size, and position of leads are relevant to
equipment designers; resistors must be physically large enough not to
overheat when dissipating their power. Variable resistors, adjustable by
changing the position of a tapping on the resistive element, and resistors
with a movable tap ("potentiometers"), either adjustable by the user of
equipment or contained within, are also used.
Resistors are used as part of electrical networks and electronic
circuits.
There are special types of resistor whose resistance varies with
various quantities, most of which have names, and articles, of their own: the
resistance of thermistors varies greatly with temperature, whether external or
due to dissipation, so they can be used for temperature or current sensing;
metal oxide varistors drop to a very low resistance when a high voltage is
applied, making them suitable for over-voltage protection; the resistance of a
strain gauge varies with mechanical load; the resistance of photoresistors
varies with illumination; the resistance of a Quantum Tunnelling Composite
can vary by a factor of 1012 with mechanical pressure applied; and so on.
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Transistor BC 547
In electronics, a transistor is a semiconductor device commonly used
to amplify or switch electronic signals. A transistor is made of a solid piece
of a semiconductor material, with at least three terminals for connection to
an external circuit. A voltage or current applied to one pair of the transistor's
terminals changes the current flowing through another pair of terminals.
Because the controlled (output) power can be much larger than the
controlling (input) power, the transistor provides amplification of a signal.
The transistor is the fundamental building block of modern electronic
devices, and is used in radio, telephone, computer and other electronic
systems. Some transistors are packaged individually but most are found in
integrated circuits.
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How transistor works?
The essential usefulness of a transistor comes from its ability to use a
small signal applied between one pair of its terminals to control a much
larger signal at another pair of terminals. This property is called "gain". A
transistor can control its output in proportion to the input signal; this is
called an "amplifier". Or, the transistor can be used to turn current on or off
in a circuit like an electrically controlled "switch", where the amount of
current is determined by other circuit elements.
The two types of transistors have slight differences in how they are
used in a circuit. A bipolar transistor has terminals labelled base, collector
and emitter. A small current at base terminal can control or switch a much
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larger current between collector and emitter terminals. For a field-effect
transistor, the terminals are labelled gate, source, and drain, and a voltage at
the gate can control a current between source and drain.
The image to the right represents a typical bipolar transistor in a
circuit. Charge will flow between emitter and collector terminals depending
on the current in the base. Since internally the base and emitter connections
behave like a semiconductor diode, a voltage drop develops between base
and emitter while the base current exists. The size of this voltage depends on
the material the transistor is made from, and is referred to as Vbe.
Capacitor 1000mf, 25v
A capacitor or condenser is a passive electronic component consisting
of a pair of conductors separated by a dielectric. When a voltage potential
difference occurs between the conductors, an electric field occurs in the
dielectric. This field can be used to store energy, to resonate with a signal, or
to link electrical and mechanical forces.
Capacitors are manufactured as electronic components for use in
electrical circuits, but any two conductors linked by an electric field also
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display the fundamental property of capacitance. The effect is greatest
between wide, flat, parallel, narrowly separated conductors.
An ideal capacitor is characterized by a single constant value,
capacitance. This is defined as the ratio of the amount of electric charge in
each conductor to the potential difference between them. The unit of
capacitance is thus coulombs per volt, or farads. Higher capacitance
indicates that more charge may be stored at a given voltage. In practice, the
dielectric between the plates passes a small amount of leakage current. The
conductors add an additional series resistance (specifically called equivalent
series resistance), and the dielectric has an electric field strength limit
resulting in a breakdown voltage.
The properties of capacitors in a circuit may determine the resonant
frequency and quality factor of a resonant circuit, power dissipation and
operating frequency in a digital logic circuit, energy capacity in a high-
power system, and many other important aspects.
The capacitor has become ubiquitous within electronic and electrical
systems.
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Theory of operation
A capacitor consists of two conductors separated by a non-conductive
region. The non-conductive substance is called the dielectric medium,
although this may also mean a vacuum or a semiconductor depletion region
chemically identical to the conductors. A capacitor is assumed to be self-
contained and isolated, with no net electric charge and no influence from an
external electric field. The conductors thus contain equal and opposite
charges on their facing surfaces, and the dielectric contains an electric field.
The capacitor is a reasonably general model for electric fields within electric
circuits.
An ideal capacitor is wholly characterized by a constant capacitance
C, defined as the ratio of charge ±Q on each conductor to the voltage V
between them:
Sometimes charge buildup affects the mechanics of the capacitor,
causing the capacitance to vary. In this case, capacitance is defined in terms
of incremental changes:
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In SI units, a capacitance of one farad means that one coulomb of
charge on each conductor causes a voltage of one volt across the device.
Crystal 32.876
A crystal or crystalline solid is a solid material whose constituent
atoms, molecules, or ions are arranged in an orderly repeating pattern
extending in all three spatial dimensions. The scientific study of crystals and
crystal formation is crystallography.
The word crystal is derived from the ancient Greek word (krustallos),
which had the same meaning, but according to the ancient understanding of
crystal. At root it means anything congealed by freezing, such as ice. The
word once referred particularly to quartz, or "rock crystal".
Most metals encountered in everyday life are polycrystals. Crystals
are often symmetrically intergrown to form crystal twins.
For cost reason using an overtone crystal is 5 to 6 times cheaper than
a fundamental one. Using this type of crystal is slightly different comparing
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to a fundamental one . The frequency of an overtone crystal is adjusted on
the fundamental one and this one must be trapped by a LC pass–band filter.
The typical schematic is shown below.
Liquid Crystal Display (LCD) 16 x 2
A liquid crystal display (LCD) is an electronically-modulated optical
device shaped into a thin, flat panel made up of any number of color or
monochrome pixels filled with liquid crystals and arrayed in front of a light
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source (backlight) or reflector. It is often utilized in battery-powered
electronic devices because it uses very small amounts of electric power.
A comprehensive classification of the various types and electro-optical
modes of LCDs is provided in the article LCD classification.
In recent years LCD is finding wide spread use replacing 7 segment
LEDs or other multisegment LEDs. This is due to following reasons:
The declining process of LCDs.
The ability to display numbers, characters, graphics. This is in
contrast to LEDs. Which are limited to numbers and a few characters.
In corporation of a refreshing controller into the LCD, thereby
relieving the CPU of the task of refreshing LCD. In contrast the LED
must be refreshed by the CPU to keep displaying the data.
Ease of programming for characters and graphics.
LCD better known as alpha-numeric modules, display
characters, numbers, symbols and some limited graphics.
Interface is achieved via a bi-directional, parallel ASCII
data bus necessary features such as character generation
Display RAM addressing, cursor scrolling Blanking, and
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Handshake are call included user programmable fonts are
supported summary
Pin no Symbol Description
1 Vss Ground potential
2 Vcc Power supply for logic LCD (+)
3 Vo Constant adjustment
4 RS Resistor select pin
5 Riw Read write
6 E Enable pin
7 Dbo Code I/O data LSB
8 Db1 Code I/O data 2nd bit
9 Db2 Code I/O data 3rd bit
10 Db3 Code I/O data 4th bit
11 Db4 Code I/O data 5th bit
12 Db5 Code I/O data 6th bit
13 Db6 Code I/O data 7th bit
14 Db7 Code I/O data MSB
15 VLED Power supply for LED backlight
16 VLSS VLED –5V, VLSS –0V
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Interfacing of LCD
LED
A light-emitting diode (LED) is an electronic light source. The LED
was discovered in the early 20th century, and introduced as a practical
electronic component in 1962. All early devices emitted low-intensity red
light, but modern LEDs are available across the visible, ultraviolet and infra
red wavelengths, with very high brightness.
LEDs are based on the semiconductor diode. When the diode is
forward biased (switched on), electrons are able to recombine with holes and
energy is released in the form of light. This effect is called electrolumine
scence and the color of the light is determined by the energy gap of the
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semiconductor. The LED is usually small in area (less than 1 mm2) with
integrated optical components to shape its radiation pattern and assist in
reflection.
LEDs present many advantages over traditional light sources
including lower energy consumption, longer lifetime, improved robustness,
smaller size and faster switching. However, they are relatively expensive
and require more precise current and heat management than traditional light
sources.
Applications of LEDs are diverse. They are used as low-energy
replacements for traditional light sources in well-established applications
such as indicators and automotive lighting. The compact size of LEDs has
allowed new text and video displays and sensors to be developed, while their
high switching rates are useful in communications technology.
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Construction of LED
Types of LEDs
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LEDs are produced in an array of shapes and sizes. The 5 mm
cylindrical package (red, fifth from the left) is the most common, estimated
at 80% of world production.[citation needed] The color of the plastic lens is
often the same as the actual color of light emitted, but not always. For
instance, purple plastic is often used for infrared LEDs, and most blue
devices have clear housings. There are also LEDs in SMT packages, such as
those found on blinkies and on cell phone keypads.
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CIRCUIT DIAGRAM & WORKING
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R1
4.7k
2
1
+ C1
470uF/16V
So1
LCD_12
RS
LCD_14E
VCC
D5
1N4148
J1
CON4
1234
D3 LED
R7
10K
2
1
VCC
+ 12vu
R810K
2
1
PC_RXD
X1
4MHz
So1
Q1BC547
VCC
RS
LCD_11
LCD_12
D2
LED
Q2BC557
VCC
D4 LED
R5 15E21U2
PIC16F877
918
1920
2930
31
40
1
2345678
2122
23242526
2728
10
1112
13
14
151617
39383736353433
32
RE1/AN6/W RSCK/SCL/RC3
PSP0/RD0PSP1/RD1
PSP6/RD6PSP7/RD7
GN
D
PGDA/RB7
MC
LR_
RA0/AN0RA1/AN1RA2/AN2/VREF-RA3/AN3/VREF+RA4/TOCK1RA5/AN4/SSRE0/AN5/RD
PSP2/RD2PSP3/RD3
SDL/SDA/RC4SD0/RC5
TX/CK/RC6RX/DT/RC7
PSP4/RD4PSP5/RD5
RE2/AN7/CS
+V
EG
ND
OSC1/CLKIN
OSC2/CLKOUT
T1OS0/T1CK1/RC0T1OS1/CCP2/RC1
CCP1/RC2
PGCLK/RB6RB5RB4
PGM/RB3RB2RB1
INT/RB0+
VE
+ 12vu
PC_TXD
PC_TXD
J7
CON3
123
LCD_14
R6
10K
2 1
VCC
C3
33pF1
2
VCC
So1
R2
100E
2
1
VCC
LCD_13LCD_13
CONT
C6
100uF
TEMP
CON3
123
R4 1.5K
21
U1LM7805C/TO220
1 3
2
IN OUT
GN
D
RXD
PC_RXD
R9
10K
2
1
R3 1.5K21
J5
CON8
12345678
VCC
TXD
J2
CON3
123
J4
CON10
123456789
10
RRST
1k
2
1
LCD_11
CONT
E
-+
D1
BRIDGE
1
4
3
2
J6
CON12
123456789
101112
VCC
C433pF
1
2
VCC
R10
10K
21
RXD
+ C2
1uF
TXD
J3
CON12
123456789101112
VCC
36
Scheduling of College Bell using Microcontroller
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Scheduling of College Bell using Microcontroller
WORKING
The main working of the project is based on real time clock ie PCF
8583. Interfacing of microcontroller chip with this RTC is done by IIC
protocols. In this protocol there are only two lines connected to the
microcontroller ie SCL (Serial Clock) and SDA (Serial Data). The start and
stop conditions of PCF 8583 is shown below
For the initialization of RTC, send the control word to the RTC bit by
bit serially. In start we edit the actual time in the RTC register. And then
scheduling register is used for schedule. In this RTC there are several
registers (eg. Hrs, min, sec, day, year, month). The alarm register is same as
this register. When we schedule the alarm register, it equals with the main
register and if it equals the interrupt is generated. This interruption is read by
the microcontroller and according to process schedule the bell is ring.
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Scheduling of College Bell using Microcontroller
LCD 16x2 is used for editing time, scheduling and actual time
displaying. This LCD have 16 pins. First pin is used for ground, second is
for Vcc. Third is used for contrast control. Forth is for RS bit. Fifth is for
read/write bar, so we have connected fifth pin directly to ground. Sixth pin is
used for enabling data/command. Pin 7-14 is used for data/command bus. 15
and 16 pin is used for back LED. If RS bit is in high condition then LCD
treat as data and if RS bit is low LCD treat it as a command byte. Firstly, to
interface to the LCD the first command of ‘CLEAR DISPLAY’ should be
sent by microcotroller for clearing the display.
The second command is cursor movement ie left to right/right to left
according the our application. Next command should be sent for location
selection in which we can display the data to that location. But the
microcontroller works on hex and LCD works on ASCII so giving data
should be in hex to ASCII conversion form.
Keyboard is used for editing the time which is directly connected with
microcontroller port pins. Particular subroutine is called according to the pin
which goes low.
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For ONN/OFF the AC bell, the relay is used. Relay requires 12v. The
driving capability of the microcontroller and voltages is less than 12v relay
so we use the transistor for the driving of relay. When the microcontroller
pin gets high the relay becomes ONN and bell starts ringing. When pin of
microntroller gets low, the relay becomes OFF to stop the bell.
The power supply of the whole circuit is 5v and 12v for relay. For this
we have used step down transformer but output of the transformer is AC so
we use bridge for DC source and capacitor for filter.
7805 is used for 5v regulator. LCD, microcontroller, PCF 8583
requires 5v which is supplied by voltage regulator 7805.
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PCB DESIGN
INTRODUCTION
Printed circuit board is a piece of art. The performance of an
electronic circuit depends upon the layout and design of PCB. The PCB
design of the circuit operation should be very precise to work it properly.
The soldered point should be small enough so that any stray between these
points should not exist. Also high package density of components can
produce stray which should be avoided by proper circuit designing and
components should be spread in such a way that two-component produce
minimum stray. Also the track of the PCB, soldering points and components
mounting should be very correct and that will be of great help to success the
project.
Making such precise PCB is easy. For preparing the PCB
layout, we used the PCB layout manufacturing by the Vega company with a
help of computerized equipment. We can not use readymade PCB for our
project. The trackside of the PCB is shown in figure.
To make the PCB with professional touch, the general method
that should be carried out is as follows.
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LAYOUT PLANNING:
The layout of the PCB has to incorporate all information on the
board, before one can proceed further for the artwork preparation. This
planning procedure depends on many factors.
LAYOUT SCALE:
Depending upon the accuracy required artwork produced
should be at 1:1 or 2:1 scale. Accordingly the size of the artwork will be
equal to four times or sixteen times of that actual PCB. The layout is best
prepared on the same scale as artwork.
LAYOUT SKETCH:
The end produced of the layout design is the pencil sketched
component and conductor driving, which is called layout sketch. It contains
all relevant information for preparation of artwork.
Besides the components outlines, components holes and
interconnection line (patterns) the layout should also include the information
on.
Diameter of component hole, IC transistor pads.
Minimum spacing between the conduction lines that must produced.
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Bottom Layer
Top Layer
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ARTWORK:
Preparation of artwork is considered as first step in preparation
of PCB. Following steps are included while designing the artwork. A
polyester foil and tracing paper may be used. Basic methods of preparing
artwork are:
Ink the drawing.
Using block tapes and sticking patterns.
Using red and blue transparent tapes.
The artwork is then converted to photonegative of proper size.
SOLDERING AND SOLDERING TECHNIQUE
There are basically two types of soldering techniques:
Manual soldering with iron.
Mass soldering.
SOLDERING:
Soldering is a process used for jointing metal parts. It is necessary to
use molten metal known as solder.
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During soldering, relative positioning of the surfaces to be joined,
wetting of this surface with molten solder and cooling time for solidification
is important. The various types of soldering are
Mass soldering:
Dip soldering:
Wave soldering:
PRINTING OF PCB
The drawing so prepared has to imposed over the glass epoxy. Take a
PCB terminated sheet and cut the of required size of PCB by using hacksaw
place the glass epoxy plate sheet on a table, keeping the glass epoxy side on
rub away the dirt, grease and oxide wish a sand paper. Now keep carban
paper of the same size on PCB taking glass epoxy surface on the top carban
paper. Since the tracing paper is transparent you can now reproduce carbon
print over the PCB. After tracing the PCB layout now paint the tracks wish
the help of oil paint and brush, keep plate in open to dry. After the paint on a
copper side has dried, check the drawing carefully, excess paint should be
scratched off wish of a blade.
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Scheduling of College Bell using Microcontroller
ETCHING OF PCB
In a tray, take water and mix a few tea spoons of ferric chloride
powder and few drop of HCL. Immerse/dip the PCB in this solution keep the
PCB in this solution for about 40-50 min.
Reaction - 2FeC13+2Cu=2CuC12+Fe2Cl
Observe the changing color of copper surface. Take out the PCB from
the solution only when the unmarked portion of copper is completely
dissolved in this solution wash the PCB wish water. After washing PCB,
remove the paint with a soft piece of cloth or cotton. Now the plate is what
we call it as printed circuit board.
DRILLING, MOUNTING AND SOLDERING.
After the etching process drilling is done for mounting the compo-
nents. Drill the board by using hand drill or machine drill. Before inserting
the leads of the components are placed on the irrespective position
(according to the circuit Diagram) this process is called as component
mounting.
Now the next process is soldering. In this process, the leads of compo-
nents are joined/ soldered with the copper tracks of PCB. For this tussible
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alloy metal which is known as 'SOLDERING WIRE1 is required soft solder
has 37% of lead and 63 % of zinc and is used because of its excellent drying
action. Its melting point is very low. It gives mechanically strong point for
soldering the components, soldering gun is used. Flux is used as an
inorganic solvent.
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ADVANTAGES
1) Automatic scheduling of college bell is possible
2) The components used for the assembling of this circuit are very cheap
and are easily available in the market. Hence the initial cost of setting
up the circuit is minimal.
3) Compact in size so takes less space.
4) Easy to install.
5) This project is much suitable college, schools, institutions etc.
6) Time editable facility is available.
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CONCLUSION
Present day manual operation for ringing the bell in colleges or
schools are carried out. The main disadvantage of this is one person is to be
keep alert for this. At the same time during that time he could not be engage
in another task.
To overcome from this, we have decided to prepare the circuit which
will be operated automatically and the ringing of bell will start by its own
time. The time input can be edited as per requirements.
This circuit is simple to prepare and easy to install. We can say that it
will be much useful for colleges or schools or other educational institutions.
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REFERENCES
Books :
1. “Intel’s MCS 51 Data Book ”, Intel Inc.
2. Joan B. Peatman, “Design with Microcontroller”, Mc Graw Hill.
3. V. K. Mehta & Rohit Mehta “Principle of Electronics”
Websites :
www.datasheet4u.com
www.wikipedia.org
www.google.com
www.sciencetoday.com
www.crutchfield.com
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CONTENTS
1. ABSTRACT..........................................................................1
2. INTRODUCTION.................................................................2
3. LITERATURE REVIEW......................................................3
4. COMPONENT DESCRIPTION...........................................6
5. CIRCUIT DIAGRAM & WORKING.................................36
6. WORKING..........................................................................37
7. PCB DESIGN......................................................................40
8. ADVANTAGES..................................................................47
9. CONCLUSION...................................................................48
10. REFERENCES....................................................................49
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