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.
http://en.wikipedia.org/wiki/File:555_Pinout.svg


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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.

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General Purpose Alarm