25-08-2017, 09:32 PM
PROJECT REPORT ON AUTOMATIC COLLEGE BELL
AUTOMATIC COLLEGE BELL.pdf (Size: 1.12 MB / Downloads: 19)
ABSTRACT
Manual operation of school bell / college bell creates lot of disturbances
caused by human errors. If the bell operator forgets to ring the bell for a
specific period, or delayed to ring the bell, it creates disturbances for
entire the institution. All the classes on that day will be completely
disturbed. This problem is more present if the bell operator is on leave.
Automatic Periodic College Bell is the only solution to avoid all these
problems.
This project is very useful in schools, colleges and educational / academic
institutions for automation of periodic class bell. This bell rings only at
preprogrammed timings. When we provide power supply to 555 IC which
is in Astable mode, then it generates the Clock pulse. The input from this
IC goes to BCD counter.and the another input goes to the another 555 IC
which works in Monostable mode.The input high pulse of the clock goes
to BCD counter which is connected to BCD decoder (HD74LS248P).The
HD74LS248 activates the seven segment display, whereas the input low
pulse goes to 555 timer which is in monostable mode. The 555 timer
which is in monostable mode activates the buzzer.
INTRODUCTION
In today’s life, everyone gives importance to time. Time does not wait for
anybody. Everything should be performed in time & accurately. Now a day’s
school/college bells are manually operated. Hence there is a big question of accuracy.
Also there is necessity of manpower and money. Hence here we should use automatic
control system, which saves our manpower and money & also highest accuracy.
Hence we have selected the project.
What is our System?
In market there many digital clocks available with bells but rings only at
specific time. For e.g. Alarm Clock and some bells that ring after some time intervals
and that cannot stop after specific time. For e.g. Musical Clock But all these limitation
have been removed by our project. It rings only according to our college time table.
Our Project takes over the task of Ringing of the Bell in Colleges. It replaces
the Manual Switching of the Bell in the College. 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
BCD TO SEVEN SEGMENT DECODER
The HD74LS248 is electrically and functionally identical to the HD74LS48,
respectively, and has the same pin assignments as its equivalents. It can be used
interchangeably in present or future designs to offer designers a choice between two
indicator fonts. The HD74LS48 composes the 6 and the 9 without tails and the
HD74LS248 composes the 6 and the 9 with tails. Composition of all other characters,
including display patterns for BCD inputs above nine, is identical. The HD74LS248
features active-low outputs designed for driving indicators directly. All of the circuits
have full ripple-blanking input / output controls and a lamp test input. Segment
identification and resultant displays are shown below. Display patterns for BCD input
count above 9 are unique symbols to authenticate input conditions. This circuit
incorporates automatic leading and / or trailing-edge zero-blanking control (RBI and
RBO).
Lamp test (LT) of this type may be performed at any time when the BI / RBO node is
at a high level. This type contains an overriding blanking input (BI) which can be
used to control the lamp intensity be pulsing or to inhibit the outputs.
TRANSFORMER
Definition
The transformer is a static electro-magnetic device that transforms one alternating
voltage (current) into another voltage (current). However, power remains the some
during the transformation. Transformers play a major role in the transmission and
distribution of ac power.
Principle
Transformer works on the principle of mutual induction. A transformer consists of
laminated magnetic core forming the magnetic frame. Primary and secondary coils are
wound upon the two cores of the magnetic frame, linked by the common magnetic
flux. When an alternating voltage is applied across the primary coil, a current flows in
the primary coil producing magnetic flux in the transformer core. This flux induces
voltage in secondary coil.
TRANSISTORS
A transistor consists of two junctions formed by sandwiching either p-type or n-type
semiconductor between a pair of opposite types. Accordingly, there are two types of
transistors namelyAn n-p-n transistor is composed of two n-type semiconductors separated by a thin
section of p type. However two p sections separated by a thin section of n-type
form a p-n-p transistor.
A transistor raises the strength of a weak signal and thus acts as an amplifier. The
weak signal is applied between emitter base junction and output is taken across the
load Rc connected in the collector circuit (in common emitter configuration). In order
to achieve faithful amplification, the input circuit should always remain forward
biased. To do so, a dc voltage is applied in the input in addition to the signal. This dc
Voltage is known as biasing voltage and its magnitude and polarity should be such
that it always keeps the input circuit forward biased regardless of the polarity to the
signal to be amplified
SEVEN SEGMENT DISPLAY
A seven segment display, as its name indicates, is composed of seven elements.
Individually on or off, they can be combined to produce simplified representations of
the Arabic numerals. Often the seven segments are arranged in an oblique (slanted)
arrangement, which aids readability. Each of the numbers 0, 6,7and 9 may be
represented by two or more different glyphs on seven-segment displays
BUZZER
A buzzer or beeper is an audio signalling device, which may be mechanical,
electromechanical, or piezoelectric. Typical uses of buzzers and beepers include alarm
devices, timers and confirmation of user input such as a mouse click or keystrok
Electromechanical buzzer
Early devices were based on an electromechanical system identical to an electric bell
without the metal gong. Similarly, a relay may be connected to interrupt its own
actuating current, causing the contacts to buzz. Often these units were anchored to a
wall or ceiling to use it as a sounding board. The word "buzzer" comes from the
rasping noise that electromechanical buzzers made
LAYOUT DESIGN
When designing the layout one should observe the minimum size (component body
length and weight). Before starting to design the layout we need all the required
components in hand so that an accurate assessment of space can be made. Other space
considerations might also be included from case to case of mounted components over
the printed circuit board or to access path of present components.
It might be necessary to turn some components around to a different angular position
so that terminals are closer to the connections of the components. The scale can be
checked by positioning the components on the squared paper. If any connection
crosses, then one can reroute to avoid such condition.
All common or earth lines should ideally be connected to a common line routed
around the perimeter of the layout. This will act as the ground plane. If possible try to
route the outer supply line to the ground plane. If possible try to route the other supply
lines around the opposite edge of the layout through the center. The first set is tearing
the circuit to eliminate the crossover without altering the circuit detail in any way
ETCHING PROCESS
Etching process requires the use of chemicals. Acid resistant dishes and running water
supply. Ferric chloride is mostly used solution but other etching materials such as
ammonium per sulphate can be used. Nitric acid can be used but in general it is not
used due to poisonous fumes. The pattern prepared is glued to the copper surface of
the board using a latex type of adhesive that can be cubed after use. The pattern is laid
firmly on the copper using a very sharp knife to cut round the pattern carefully to
remove the paper corresponding to the required copper pattern areas. Then apply the
resistant solution, which can be a kind of ink solution for the purpose of maintaining
smooth clean outlines as far as possible. While the board is drying, test all the
components.
Before going to next stage, check the whole pattern and cross check with the circuit
diagram. Check for any free metal on the copper. The etching bath should be in a
glass or enamel disc. If using crystal of ferric- chloride these should be thoroughly
dissolved in water to the proportion suggested. There should be 0.5 lt. of water for
125 gm of crystal.
COMPONENT ASSEMBLY
From the greatest variety of electronic components available, which runs into
thousands of different types it is often a perplexing task to know which is right for
a given job.
There could be damage such as hairline crack on PCB. If there are, then they can
be repaired by soldering a short link of bare copper wire over the affected part.
The most popular method of holding all the items is to bring the wires far apart
after they have been inserted in the appropriate holes. This will hold the
component in position ready for soldering.
Some components will be considerably larger .So it is best to start mounting the
smallest first and progressing through to the largest. Before starting, be certain that
no further drilling is likely to be necessary because access may be impossible
later
WORKING
When we provide power supply to 555 IC which is in Astable mode, then it generates
the Clock pulse. The input from this IC goes to BCD counter. (The 4510 is a BCD, or
Binary Coded Decimal counter with four outputs capable of counting up or down,
following the BCD pattern, according to the logic states of various inputs, when a
source of pulses is connected to the CLOCK input) and the another input goes to the
another 555 IC which works in Monostable mode (Chapter 3.2.12). The input high
pulse of the clock goes to BCD counter which is connected to BCD decoder
(HD74LS248P).
The HD74LS248 features active-low outputs designed for driving indicators directly.
All of the circuits have full ripple-blanking input / output controls and a lamp test
input.
The HD74LS248 activates the seven segment display, whereas the input low pulse
goes to 555 timer which is in monostable mode. The 555 timer which is in monostable
mode activates the buzzer.