Download - General Purpose Alarm
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Door knock alarm with timer
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Contents:-
AbstractIntroductionCircuit diagram
A)ConstructionB)Working
IC NE555A) Design
B) Operating mode
C) Pin Diagram of NE555
D) Specifications
IC UM66A)Pin diagramB)Melody generator circuitC)Applications
Transistor (BC547)A)Pin diagramB)Schematic symbol
ComponentsA)ResistorB)Capacitor
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C)BatteryD)SpeakerE)Piezo electric sensorF)Zener diode
ApplicationsConclusion
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I. ABSTRACT:-The alarm may be used in many ways, such as a sudden fear
or distressing suspense due to awareness of danger. It is an automatic
device that serves to warn of danger, as fire, to arouse someone from
sleep, or to call attention to a particular thing.
This circuit uses a thin piezoelectric sensor to sense the
vibrations generated by knocking on a surface. The piezoelectric element plate
is fixed at the centre of the door wing by using a cello tape. Apply a small
quantity of adhesive at the edges between the plate and the door. Extend wires
about 1-1.5 metres from the piezoelectric to the circuit. IC NE555 (IC1) is
configured in monostable mode. When it gets an input pulse its output goes high
for a period set by VR1, resistor R5 and capacitor C3. IC UM66 (IC2) is used as
a melody generator. When the door is knocked at, the piezo plate generates an
input pulse, which is amplified by transistor T1.
The amplified signal triggers the timer IC NE555 and its
output pin 3 goes high to enable the melody generator. Music is heard from the
speaker LS1. After the set time period, the melody sound stops. Assemble the
circuit on a general-purpose PCB and enclose in a suitable case. Fix the piezo
element at the door and place the speaker in a central room inside the house
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using long wires. The circuit works off 5-12V DC. The music time can be
adjusted through VR1 by changing the R-C time constant of the timer.
Introduction:-This circuit generates an alarm sensing the vibration
generated on knocking a surface. In some apartment buildings and class rooms
that are not equipped with a doorbell, it may be hard to hear someone knocking
on the front door. This circuit provides a means to activate a sound inside,
whenever someone knocks on the door from outside. It uses readily available,
low cost components whereas almost all commercial devices sold use a more
expensive and power consuming circuit.
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II. CIRCUIT DIAGRAM
Door knock alarm with timer:-
Circuit operation:-
Here a piezoelectric plate is used as the sensor. It can
convert any mechanical vibration into electrical signal. The piezoelectric sensor
plate is fixed at the centre of the door wing by using a cello tape. A small
quantity of adhesive is applied at the edges between the plate and the door.
Wires are extended from piezoelectric to the circuit.
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NE 555 IC is configured in monostable mode. When it
gets an input pulse, its output goes high for a period set by VR1, resistor R5 andcapacitor C. When door is knocked at, the piezoelectric plate generates an input
pulse, which is amplified by transistor T1.The amplified signal triggers the IC
555 and its output pin 3 goes high to enable the buzzer. After the set time
period, the alarm stops. The circuit works at 5v-12v dc supply. The alarm time
can be adjusted through VR1 by changing the RC time constant of the timer.
III. IC NE555III (i). Design:-
The IC was designed in 1971 by Hans R. Camenzind.
Depending on the manufacturer, the standard 555 package includes 25
transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin mini
dual-in-line package
The NE555 parts were commercial temperature range, 0 C to +70 C
Low-power versions of the 555 are also available, such as the 7555 and CMOS
TLC555.
The 7555 is designed to cause less supply noise than the classic 555 and the
manufacturer claims that it usually does not require a "control" capacitor and in
many cases does not require a decoupling capacitor on the power supply.
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III (ii).Pin Diagram of NE555:-
Pin Name Purpose
1 GND Ground, low level (0 V)
2 TRIG OUT rises, and interval starts, when this input
falls below 1/3 VCC.
3 OUT This output is driven to +VCC or GND.
4 RESET A timing interval may be interrupted by
Driving this input to GND.
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5 CTRL "Control" access to the internal voltage divider
(by default, 2/3 VCC).
6 THR The interval ends when the voltage at
THR is greater than at CTRL.
7 DIS Open collector output; may discharge
a Capacitor between intervals.
8 V+, VCC Positive supply voltage is usually between
3V and 15V.
III (iii).Operating mode of IC NE555:-
Schematic of a 555 in monostable mode
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In the monostable mode, the 555 timer acts as a "one-shot" pulse generator. The
pulse begins when the 555 timer receives a signal at the trigger input that falls
below a third of the voltage supply.
http://en.wikipedia.org/wiki/File:NE555_Monotable_Waveforms_(English).pnghttp://en.wikipedia.org/wiki/File:555_Monostable.svghttp://en.wikipedia.org/wiki/File:NE555_Monotable_Waveforms_(English).pnghttp://en.wikipedia.org/wiki/File:555_Monostable.svg -
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The width of the output pulse is determined by the time constant of an RC
network, which consists of a capacitor (C) and a resistor (R).
The output pulse ends when the voltage on the capacitor equals 2/3 of the
supply voltage.
The output pulse width can be lengthened or shortened to the need of the
specific application by adjusting the values of R and C.[5]
The output pulse width of time t, which is the time it takes to charge C to 2/3 of
the supply voltage, is given by
Where t is in seconds, R is in ohms and C is in farads.
While using the timer IC in monostable mode, the main
disadvantage is that the time span between the two triggering pulses must be
greater than the RC time constant.
III (iv).Specifications:-
These specifications apply to the NE555. Other 555
timers can have different specifications depending on the grade (military,
medical, etc.).
Supply voltage (VCC) 4.5 to 15 V
Supply current (VCC = +5 V) 3 to 6 mA
Supply current (VCC = +15 V) 10 to 15 mA
Output current (maximum) 200 mA
Maximum Power dissipation 600 mW
Power consumption (minimum operating) 30 mW@5V, 225 mW@15V
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Operating temperature 0 to 70 C
IV. UM66:-The UM66 is an electronic doorbell. It requires a botton for the door, a single
transistor, a battery and a speaker.
um66 is a melody generator cmos ic it is a three terminal ic pin no: 1 is set to
ground, and pin 2 is Vdd pin 3 is the output melody signal this ic generally
operates from 1.5 to 5 volts it is.
IV (i). Pin Diagram:-
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Pin Description: -
Pin No Function Name1 Melody output Output
2 Supply voltage (1.5V - 4.5V) Vcc
3 Ground (0V) Ground
IV (ii). Melody Generator:-
Circuit diagram
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Description:-
Here is a simple melody generator circuit you can make using an
IC. The UM66 series are CMOS ICs designed for using in calling bell, phone
and toys. It has a built in ROM programmed for playing music. The device has
very low power consumption. Thanks for the CMOS technology. The melody
will be available at pin3 of UM66 and here it is amplified by using Q1 to drivethe speaker. Resistor R1 limits the base current of Q1 within the safe values.
Capacitor C1 is meant for noise suppression.
IV (iii).Applications:-
It will generate a music signal by taking a less voltage at its input side.wecan use it in our commercial applications.
It placed inside a greeting card and operated off a single 3V flat buttoncell.
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V. Transistor:-
V (i). Pin diagram of BC547:-
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BC547 is an NPN bi-polar junction transistor. A transistor,
stands for transfer of resistance, is commonly used to amplify current. A small
current at its base controls a larger current at collector & emitter terminals.
BC547 is mainly used for amplification and switching
purposes. It has a maximum current gain of 800. Its equivalent transistors are
BC548 and BC549.
The transistor terminals require a fixed DC voltage to operate
in the desired region of its characteristic curves. This is known as the biasing.
For amplification applications, the transistor is biased such
that it is partly ON for all input conditions. The input signal at base is amplified
and taken at the emitter.
For switching applications, transistor is biased so that it
remains fully ON if there is a signal at its base. In the absence of base signal, it
gets completely OFF.
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V (ii). BC547 Transistor Circuit Schematic Symbol:-
FEATURES:-
Low current (max. 100 mA) Low voltage (max. 65 V).
Pin Description
1 Emitter
2 Base
3 collector
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APPLICATIONS:-
General purpose switching and amplification.
VI. Components:-
VI (i). Resistors
VI (ii).Capacitors
VI (iii).Battery
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VI (iv).speaker
VI (v).piezoelectric sensor
VI (vi).Zener diode
VI (i). Resistor:-
A RESISTOR is a component of an electrical
circuit that resists the flow of electrical current. A resistor has
two terminals across which electricity must pass, and is
designed to drop the voltage of the current as it flows from
one terminal to the next. A resistor is primarily used to create
and maintain a known safe current within an electrical
component.
The following table shows the colors used to identify resistor values:
COLOR DIGIT MULTIPLIERTOLERANCE TC
Silver x 0.01 10%
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Gold x 0.1 5%
Black 0 x 1
Brown 1 x 10 1% 100*10-6/K
Red 2 x 100 2% 50*10-/K
Orange 3 15*10-/K
Yellow 4 25*10-6/K
Green 5 0.5%
Blue 6 0.25% 10*10-/K
Violet 7 0.1% 5*10-/K
Grey 8
White 9 1*10-/K
VI (ii).capacitors:-
A CAPACITORS is a component that is used to store an
electrical charge. When power is supplied to a circuit the capacitor charges up.
When power is turned off the capacitor discharges its electrical charge slowly.
Capacitor Colour Code Table
ColourDigit
A
Digit
B
Multiplier
D
Tolerance
(T) > 10pf
Tolerance
(T) < 10pf
Temperature
Coefficient
(TC)
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Black 0 0 x1 20% 2.0pF
Brown 1 1 x10 1% 0.1pF -33x10-
Red 2 2 x100 2% 0.25pF -75x10-
Orange 3 3 x1,000 3% -150x10-6
Yellow 4 4 x10,000 4% -220x10-
Green 5 5 x100,000 5% 0.5pF -330x10-6
Blue 6 6 x1,000,000 -470x10-
Violet 7 7 -750x10-
Grey 8 8 x0.01 +80%,-20%
White 9 9 x0.1 10% 1.0pF
Gold x0.1 5%
Silver x0.01 10%
VI(iii).Battery:-
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The battery has both terminals in a snap connector on
one end. The smaller circular (male) terminal is positive, and the
larger hexagonal or octagonal (female) terminal is the negative .
A ninevolt battery also called PP3 battery. This is a
rectangular prism shape with rounded edges and a polarized snap
connector at the top.
Applications:-
It is commonly used in pocket radios, smoke detectors, carbon monoxidealarms, guitar effect units, and radio-controlled vehicle controllers.
VI (iv). Speaker:-
http://en.wikipedia.org/wiki/Battery_terminalshttp://en.wikipedia.org/wiki/Smoke_detectorhttp://en.wikipedia.org/wiki/Carbon_monoxidehttp://en.wikipedia.org/wiki/Guitar_effecthttp://en.wikipedia.org/wiki/Radio_controlhttp://en.wikipedia.org/wiki/Radio_controlhttp://en.wikipedia.org/wiki/Guitar_effecthttp://en.wikipedia.org/wiki/Carbon_monoxidehttp://en.wikipedia.org/wiki/Smoke_detectorhttp://en.wikipedia.org/wiki/Battery_terminals -
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Speaker is used to here the noise of the alarm . speakers are found in
devices such as radio and TV receivers, and many forms of music
players.
VI(v).piezo electric sensor:-
The Piezoelectric effect is an effect in which
energy is converted between mechanical and electrical forms. An
example of this can be seen in piezoelectric speakers. (These are the
cause of those annoying system beeps that are all too common in today's
computers).
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Piezoelectric sensor act as transducers which
turn force, or mechanical stress into electrical charge which in turn can be
converted into a voltage
The sensor can be attached to a door, a cash
box, cupboard, etc using adhesive.Piezo elements come in handy when
you need to detect vibration or a knock. You can use these for tap or
knock sensors pretty easily by reading the voltage on the output. They
can also be used for a very small audio transducer such as a buzzer.
VI (vi).zener Diode:-
A Zener Diode is a special kind of diode which
permits current to flow in the forward direction as normal, but will also allow it
to flow in the reverse direction when the voltage is above a certain value -
the breakdown voltage known as the Zener voltage.
A typical diode functions only in one direction
(forward-bias). When subjected to reverse-bias, the junction will eventually
break down under high enough voltage.
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VII. Uses:-
Whenever AC mains supply fails, this circuit alerts you by sounding analarm. It also provides a backup light to help you find your way to the
torch or the generator key in the dark
LPG gas is supplied in pressurized steel cylinders. As this gas is heavierthan air, when it leaks from a cylinder it flows along floor and tends to
settle in low spots such as a basement. This can cause fire or suffocation
if not dealt with. Here is a circuit that detects the leakage of LPG gas and
alerts the user through audio-visual indications.
If the fridge door is left open for too long or hasn't closed properly, tostop food from spoiling. There are lots of other uses as well. A
refrigerator or freezer door that is left open or ajar may cause the food
contents to spoil.
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Conclusion:-
Using a melody generator IC, like UM66, at the output of
timer we can hear a melodious music when someone knocks the door. This
circuit uses a piezoelectric plate to sense any mechanical vibration. Hence it
avoids false triggering. The plate can be fixed on a door, cash box, cupboard etc
using adhesive. With some small modifications this can also be used as burglar
alarms and to safeguard motor vehicles. If a burglar touches the outside door
knob this circuit will instantly emit a loud alarm to scare him away and alert
you of the attempted entry.