Introduction to Alarm

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INTRODUCTIONShadow Alarm is opto-sensitive circuit that sounds an alarm whenever a shadow

falls on it. When somebody approaches the unit, it will give a loud alarm to abort the

attempt of theft. Now a day it is widely used in aspects of security systems, where

security is our main concern .So it can be used at night by shopkeepers to protect thevaluables in their showrooms. It can also be used to provide security at warehouses (go-

downs) where storage and protection of various types of goods is main concern, and

works well for home-security too. A dim lighting in the room is necessary to detect the

moving shadow. Unlike opto-interruption alarms based on light-dependent resistors(LDRs), it does not require an aligned light beam to illuminate the photo-sensor. The

circuit uses the light sensing property of the Photo diode.

The circuit uses the light sensing property of the PIN Photodiode. The p-njunction of the photo diode gives light current when it is forward biased. IC1 is designedas a Voltage comparator. Its non inverting input is connected to a potential divider R1

and VR. By adjusting VR, input current to pin3 can be set to a reference level. The

inverting input of IC1 is connected to a photo diode. IC CA3130 is a 15 MHz Bi MOSOperational amplifier with MOSFET input sand bipolar output. The inputs contain

MOSFET transistors to provide very high inputimpedance and very low input current as

low as 10pA. It has high speed of performance and suitable for low input currentapplications. CA3130A and CA3130 are op amps that combine the advantage of both

CMOS and bipolar transistors. Gate-protected P-Channel MOSFET transistors are used

in the input circuit to provide very-high-input impedance, very-low-input current and

exceptional speed performance. The use of PMOS transistors in the input stage results incommon-mode input-voltage capability down to 0.5V below the negative-supply

terminal, an important attribute in single-supply applications. A CMOS transistor-pair,

capable of swinging the output voltage to within 10mV of either supply-voltage terminal,is employed as the output circuit. The CA3130 Series circuits operate at supply voltages

ranging from 5V to 16V, they can be phase compensated with a single external capacitor,

and have terminals for adjustment of offset voltage for application requiring offset-null

capability. Terminal provisions are also made to permit stroking of the output stage. TheCA3130A offers superior input characteristics over those of the CA3130. Normally in the

light Photodiode gives voltage to pin2 of IC1.Since this voltage is higher than the voltage

set by VR at pin3 ,output of IC1 remains low keeping LED and buzzer off. When a

person approaches the photodiode, the shadow causes a reduction in current through thephotodiode so that voltage at pin2 decreases below that of pin3. Output of IC1 then goes

high and Buzzer sounds.


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COMPONENTS DESCRIPTION:COMPONENTSLIST:

1. ICs1. IC1 741 1 No

2. IC2 NE555 1 No3. IC3 UM3561 1 No

2. TRANSISTORS1. T1 L14F1 1 No

2. T2 BC548 1 No

3. RESISTORS

1. 10 2Nos2. 100 K 1 No

3. 4.7K 1 No4. 100 Ohm 1 No

5. 680 Ohm 1 No6. 47 Ohm 1 No7. 1 Mega ohms 1 No

8. 220 K 1 No9.1 K 1 No

4. CAPACITORS1. 10UF 1 No

2. 0.01UF 1 No3. 47UF 1 No

5. PRESET 47K

6. LED 2Nos

7. ZENER DIODE 3.1V 1 No

8. SPEAKER8Ohms/0.5w 1 No

ICM7555 PIN DESCRIPTION:

The ICM7555 is a CMOS timer providing significantly improved performanceover the Standard NE/SE555 timer, while at the same time being a direct replacement for


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those devices in most applications. The ICM7555 is a stable controller capable ofproducing accurate time delays or frequencies

FEATURES:

Exact equivalent in most applications for NE/SE555

Low supply current: 80mA (typ)

Extremely low trigger, threshold, and reset currents: 20pA (typ) High-speed operation: 500 kHz guaranteed

Wide operating supply voltage range guaranteed 3 to 16V over full automotive

temperatures

Normal reset function; no crowbar ring of supply during output transition

Can be used with higher-impedance timing elements than the bipolar 555 for

longer time constants Timing from microseconds through hours Operates in both astable and monostable modes

Adjustable duty cycle

High output source/sink driver can drive TTL/CMOS Typical temperature stability of 0.005%/o C at 25C

Rail-to-rail output

OPERATION:In this mode of operation, the timer functions as a one-shot. See Figure 3. Initially

the external capacitor (C) is held discharged by a transistor inside the timer. Upon


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application of negative TRIGGER pulse to pin 2, the internal flip-flop is set whichreleases the short circuit across the external capacitor and drives the OUTPUT high. Thevoltage across the capacitor increases exponentially with a time constant t = RAC. When

the voltage across the capacitor equals 2/3 V+, the comparator resets the flip-flop, which

in turn discharges the capacitor rapidly and also drives the OUTPUT to its low state.TRIGGER must return to a high state before the OUTPUT can return to a low state.

APPLICATIONS:

Precision timing

Pulse generation

Sequential timing

Time delay generation

Pulse width modulation

Pulse position modulation

Missing pulse detector

The Operational Amplifier is probably the most versatile Integrated Circuit

available. It is very cheap especially keeping in mind the fact that it contains severalhundred components. The most common Op-Amp is the 741 and it is used in

many circuits. The OP AMP is a Linear Amplifier with an amazing variety of uses. Its

main purpose is to amplify (increase) a weak signal - a little like a Darlington Pair. The

OP-AMP has two inputs, INVERTING (-) and NON-INVERTING (+), and one output atpin 6.The 741 is used in two ways.


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1. An inverting amplifier. Leg two is the input and the output is always reversed. In aninverting amplifier the voltage enters the 741 chip through leg two and comes out of the741 chip at leg six. If the polarity is positive going into the chip, it negative by the time it

comes out through leg six. The polarity has been inverted.

2. A non-inverting amplifier. Leg three is the input and the output is not reversed. In a

non-inverting amplifier the voltage enters the 741 chip through leg three and leaves the

741 chip through leg six. This time if it is positive going into the 741 then it is still

positive coming out. Polarity remains the same.

FEATURES:

Short Circuit Protection Excellent Temperature Stability Internal FrequencyCompensation High Input Voltage Range Null of Offset

IC UM3561A DESCRIPTION:

FEATURES:

Four sounds can be selected Power on reset Typical 3V operating voltage A magnetic speaker can be driven by connecting 8-pin DIP package from an NPN

transistor


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PLAYING MODES:


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PASSIVE ELEMENTSRESISTORS

Resistors (R) are the most commonly used of all electronic components, to the

point where they are almost taken for granted. They are "Passive Devices", that is theycontain no source of power or amplification but only attenuate or reduce the voltage

signal passing through them. When used in DC circuits the voltage drop produced is

measured across their terminals as the circuit current flows through them while in ACcircuits the voltage and current are both in-phase producing0o phase shift. In all

Electrical and Electronic circuit diagrams and schematics, the most commonly used

resistor symbol is that of a "zigzag" type line with the value of its resistance given in

RESISTOR SYMBOL


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The symbol used in schematic and electrical drawings for a Resistor can either bea "zigzag type line or a rectangular box.

RESISTOR TYPES

All modern resistors can be classified into four broad groups;

Carbon Composition Resistor - Made of carbon dust or graphite paste, lowwattage values

Film or Cermets Resistor - Made from conductive metal oxide paste, very lowwattage values

Wire-Wound Resistors. - Metallic bodies for heat sink mounting, very highwattage ratings

Semiconductor Resistors - High frequency/precision surface mount thin filmtechnology

RESISTOR COLOUR CODEThe resistance value, tolerance, and watt rating of the resistor are generally printed onto

the body of the resistor as numbers or letters when the resistor is big enough to read the

print, such as large power resistors. When resistors are small such as 1/4W Carbon andFilm types, these specifications must be shown in some other manner as the print would

be too small to read. So to overcome this, small resistors use colored painted bands

to indicate both their resistive value and their tolerance with the physical size of the

resistor indicating its wattage rating. These coloured painted bands are generally knownas a Resistors Color Code.


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THE RESISTOR COLOUR CODE TABLE:


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VARIABLE RESISTOR:

Variable resistors consist of a resistance trackwith connections at both ends and a wiper

This moves along the track as you turn the spindle. The track may be made from carbon,cermets (ceramic and metal mixture) or a coil of wire (for low resistances). The track is

usually rotary but straight track versions, usually called sliders, are also available.

Variable are often called potentiometers in books and catalogues. They are specified by

their maximum resistance, linear or logarithmic track, and their physical size. The

standard spindle diameter is 6mm resistors may be used as a rheostat with two

connections (the wiper and just one end of the track) or as a potentiometer with all threeconnections in use. Miniature versions called presets are made for setting up circuits

which will not require further adjustment.


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RHEOSTAT:

This is the simplest way of using a variable resistor. Two terminals are used: one

connected to amend of the track, the other to the movable wiper. Tuning the spindlechanges the rheostat resistance between the two terminals from zero up to the maximum

resistance.

PRESET:These are miniature versions of the standard variable resistors. They are designed

to be mounted directly on to the circuit board and adjusted only when the circuit is built.A small screwdriver or similar tool is required to adjust the presets. Presets are much

cheaper than standard variable resistors so they are sometimes used in projects where astandard variable resistor would normally be used. Multi turn presets are used where very

precise adjustments must be made. The screw must be turned many times (10+) to move

the slider from one end of the track to the other, giving very fine control

Open style multi turn closed style

CAPACITORSINTRODUCTION:

Just like the Resistor, the Capacitor or sometimes referred to as a Condenser is a passive

device, and one which stores energy in the form of an electrostatic field which produces apotential(Static Voltage) across its plates. This flow of electrons to the plates is known as

the Charging Current and continues to flow until the voltage across the plates (and hence

the capacitor) is equal to the applied voltage Vic. At this point the capacitor is said to befully charged and this is illustrated below.


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CapacitorConstruction

Q = C * V

UNITS OF CAPACITANCE

-6 F

Nanofarad (nF) 1nF = 1/1,000,000,000 = 0.000000001 = 10-9 F

Picofarad (pF) 1pF = 1/1,000,000,000,000 = 0.000000000001 = 10-12 F

TYPES OF CAPACITORS

There are a very large variety of different types of Capacitors available in the market

place and each one has its own set of characteristics and applications from small delicatetrimming capacitors up to large power metal can type capacitors used in high voltage

power correction and smoothing circuits.

1. DIELECTRIC: Dielectric Capacitors are usually of the variable type such asused for tuning transmitters, receivers and transistor radios. They have a set of

fixed plates and a set of moving plates that mesh with the fixed plates and theposition of the moving plates with respect to the fixed plates determines the

overall capacitance. The capacitance is generally at maximum when the platesare fully meshed.


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Variable Capacitor Symbols

As well as the continuously variable types, preset types are also available

calledTrimmers. These are generally small devices that can be adjusted or "pre-set" to

a particular capacitance with the aid of a screwdriver and are available in very smallcapacitances of 100pF or less and are non-polarized.

2. FILM CAPACITORS: Film Capacitors are the most commonly available of alltypes of capacitors, consisting of a relatively large family of capacitors with thedifference being in their dielectric properties. These include polyester (Mylar),

polystyrene, polypropylene, polycarbonate, metalized paper, Teflon etc. Film type

capacitors are available in capacitance ranges from 5pF to 100uF depending uponthe actual type of capacitor and its voltage rating. Film capacitors also come in an

assortment of shapes and case styles which include: Wrap & Fill (Oval & Round) Epoxy Case (Rectangular & Round)

Metal Hermetically Sealed (Rectangular & Round)

3. CERAMIC CAPACITORS: Ceramic Capacitors or Disc Capacitors as they aregenerally called are made by coating two sides of a small porcelain or ceramic disc

with silver and are then stacked together to make a capacitor. For very low

capacitance values a single ceramic disco about 3-6mm is used. Ceramic capacitorshave a high dielectric constant (High-K) and are available so that relatively high

capacitances can be obtained in a small physical size. They exhibit large non- linear

changes in capacitance against temperature and as a result are used as de-coupling or

by-pass capacitors as they are also non-polarized devices. Ceramic capacitors havevalues ranging from a few Picofarads to one or two microfarads but their voltage

ratings are generally quite low. Ceramic types of capacitors generally have a 3-digit

code printed onto their body to identify their capacitance value. For example, 103

would indicate 10 x 103 PF


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4. ELECTROLYTIC CAPACITORS: Electrolytic Capacitors are generally usedwhen very large capacitance values are required. Here instead of using a very thinmetallic film layer for one of the electrodes, a semi-liquid electrolyte solution in

the form of a jelly or paste is used which serves as the second electrode (usually the

cathode). The dielectric is a very thin layer of oxide which is grown electro-chemically in production with the thickness of the film being less than ten microns.

This insulating layer is so thin that it is possible to make large value capacitors of a

small size. The majority of electrolytic types of capacitors are polarized, that is the

voltage applied to the capacitor terminals must be of the correct polarity as anincorrect polarization will break down the insulating oxide layer and permanent

damage may result. Electrolytic Capacitors are generally used in DC power supply

circuits to help reduce the ripple voltage or for coupling and decoupling applications.Electrolytes generally come in two basic forms; Aluminum Electrolytic andTantalum Electrolytic capacitors.

TRANSISTORA transistor is a semiconductor device used to amplify and switch electronic signals. It is

made of a solid piece of semiconductor material, with at least three terminals for

connection to an external circuit. A voltage or current applied to one pair of thetransistor's terminals changes the current flowing through another pair of terminals.

Because the controlled (output) power can be much more than the controlling (input)

power, the transistor provides amplification of a signal. Some transistors are packaged

individually but many more are found embedded in integrated circuits.


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PIN CONFIGURATION:

TRANSISTOR CHARACTERISTICS:

ADVANTAGESThe key advantages that have allowed transistors to replace their vacuum tube

predecessors in most applications are

Small size and minimal weight, allowing the development of miniaturized

electronic Devices.


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Highly automated manufacturing processes, resulting in low per-unit cost. Lower possible operating voltages, making transistors suitable for small,battery- Powered applications.

Lower power dissipation and generally greater energy efficiency.

Higher reliability and greater physical ruggedness. Extremely long life. Some transistorized devices have been in service for more

than 30 years.

LIMITATIONS:Silicon transistors do not operate at voltages higher than about 1,000 volts. In

contrast electron tubes have been developed that can be operated at tens of thousands of

volts.High power, high frequency operation, such as that can be used in over-the-air

television broadcasting, is better achieved in electron tubes due to improved electronmobility in vacuum.

LIGHT EMITTING DIODES:

A light emitting diode (LED) is a semi conductor light source. The LED is basedon semiconductor diode. When a light-emitting diode is forward biased (switched on),

electrons are able to recombine with electron holes within the device, releasing energy in

the form of photons. This effect is called electroluminescence and the color of the light(corresponding to the energy of the photon) is determined by the energy gap of the

semiconductor.


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The first commercial LEDs were commonly used as replacements forincandescent and neon indicator lamps, and in seven-segment displays, first in expensiveequipment such as laboratory and electronics test equipment, then later in such appliances

as TVs, radios, telephones, calculators, and even watches (see list of signal uses). These

red LEDs were bright enough only for use as indicators, as the light output was notenough to illuminate an area. Readouts in calculators were so small that plastic lenses

were built over each digit to make them legible. Later, other colors grew widely available

and also appeared in appliances and equipment. As LED materials technology grew more

advanced, light output rose, while maintaining efficiency and reliability at acceptablelevels. The invention and development of the high power white light LED to use for

illumination, which is fast replacing incandescent and fluorescent lighting... Most LEDs

were made in the very common 5 mm T1 and 3 mm T1 packages, but with rising poweroutput, it has grown increasingly necessary to shed excess heat to maintain reliability, somore complex packages have been adapted for efficient heat dissipation. Packages for

state-of-the-art high power LEDs bear little resemblance to early LEDs

Colors andmaterials:Conventional LEDs are made from a variety of inorganic semiconductor

materials; the following table shows the available colors with wavelength range, voltage

drop and material:

ADVANTAGES:

Size


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On/Off timeDimmingCycling

Efficiency

Cool lightSlow failure

Lifetime

DISADVANTAGES:High initial price

Temperature dependence

Voltage sensitivityLight quality.Area light source

Blue pollution

APPLICATIONS:

Application of LEDs falls into four major categories:

Visual signal application where the light goes more or less directly from the LEDto the human eye, to convey a message or meaning.

Illumination where LED light is reflected from object to give visual response ofthese objects.

Generate light for measuring and interacting with processes that do not involvethe human visual system Narrow band light sensors where the LED is operated inare verse-bias mode and is responsive to incident light instead of emitting light.

ZENER DIODES:

Zener diode is a type of diode that permits current not only in the forward

direction like a normal diode, but also in the reverse direction if the voltage is larger than

the breakdown voltage known as "Zener knee voltage" or "Zener voltage. Aconventional solid-state diode will not allow significant current if it is reverse-biased

below its reverse breakdown voltage. When the reverse bias breakdown voltage is

exceeded, conventional diode is subject to high current due to avalanche breakdown.

Unless this currents limited by circuitry, the diode will be permanently damaged. In caseof large forward bias (current in the direction of the arrow); the diode exhibits a voltage

drop due to its junction built-in voltage and internal resistance. The amount of the voltage


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drop depends on the semiconductor material and the doping concentrations. A Zenerdiode exhibits almost the same properties, except the device is specially designed soapsto have a greatly reduced breakdown voltage, the so-called Zener voltage. By contrast

with the conventional device, a reverse-biased Zener diode will exhibit a controlled

breakdown and allow the current to keep the voltage across the Zener diode at the Zenervoltage. The Zener diode is therefore ideal for applications such as the generation of a

reference voltage (e.g. for an amplifier stage), or as a voltage stabilizer for low-current

applications.

The Zener diode's operation depends on the heavy doping of its p-n junction allowing

electrons to tunnel from the valence band of the p-type material to the conduction band of

then-type material. In the atomic scale, this tunneling corresponds to the transport of

valence band electrons into the empty conduction band states; as a result of the reducedbarrier between these bands and high electric fields that are induced due to the relatively

high levels of doping on both sides. The breakdown voltage can be controlled quite

accurately in the doping process.

PHOTO DIODE

A photodiode is a type of photo detector capable of converting light into either

current or voltage, depending upon the mode of operation. [1]The common, traditionalsolar cell used to generate electric solar power is a large area photodiode.

Photodiodes are similar to regular semiconductor diodes except that they may be either

exposed (to detect vacuum UV or X-rays) or packaged with a window or optical fiberconnection to allow light to reach the sensitive part of the device. Many diodes designed

for use specifically as a photodiode will also use a PIN junction rather than the typical

PN junction.


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Principle of operation

A photodiode is a PN junction or PIN structure. When a photon of sufficientenergy strikes the diode, it excites an electron, thereby creating a free electron (and a

positively charged electron hole). This mechanism is also known as the photoelectric

effect. If the absorption occurs in the junction's depletion region, or one diffusion lengthaway from it, these carriers are swept from the junction by the built-in field of the

depletion region. Thus holes move toward the anode, and electrons toward the cathode,

and a photocurrent is produced. This photocurrent is the sum of both the dark current

(without light) and the light current, so the dark current must be minimized to enhancethe sensitivity of the device.

FEATURESCritical performance parameters of a photodiode include:

Responsively: The ratio of generated photocurrent to incident light power, typicallyexpressed in A/W when used in photoconductive mode. The responsively may also be

expressed as a Quantum efficiency, or the ratio of the number of photo generated carriers

to incident photons and thus a unit less quantity.

Dark current:The current through the photodiode in the absence of light, when it is

operated in photoconductive mode. The dark current includes photocurrent generated by

background radiation and the saturation current of the semiconductor junction. Dark current must beaccounted for by calibration if a photodiode is used to make inaccurate optical power


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measurement, and it is also a source of noise when photodiode is used in an opticalcommunication system.

Noise-equivalent power: (NEP) The minimum input optical power to generate

photocurrent, equal to the rms noise current in a 1 hertz bandwidth. The relatedcharacteristic Directivity(D) is the inverse of NEP, 1/NEP;

And the specific directivityis the directivity normalized to the area (A) of the photo

detector; The NEP is roughly the minimum detectable input power of a photodiode.

ApplicationsP-N photodiodes are used in similar applications to other photo detectors, such

as photoconductors, charge-coupled devices, and photomultiplier tubes.Photodiodes are used in consumer electronics devices such as compact disc players,

smoke detectors, and the receivers for remote controls in VCRs and televisions.

In other consumer items such as camera light meters, clock radios (the ones that dim thedisplay when it's dark) and street lights, photoconductors are often used rather

than photodiodes, although in principle either could be used.

Photodiodes are often used for accurate measurement of light intensity in science and

industry. They generally have a better, more linear response than photoconductors.They are also widely used in various medical applications, such as detectors

for computed tomography (coupled with scintillates) or instruments to analyze samples

(immunoassay). They are also used in pulse dosimeters.

PIN diodes are much faster and more sensitive than ordinary p-n junction diodes, andhence are often used for optical communications and in lighting regulation.

P-N photodiodes are not used to measure extremely low light intensities. Instead, if high

sensitivity is needed, avalanche photodiodes, intensified charge-coupled devicesor photomultiplier tubes are used for applications such as astronomy, spectroscopy, night

vision equipment and laser range finding.


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CIRCUIT DIAGRAM:

OPERATION:

The circuit is powered by a 9V PP3 battery and uses the most sensitive photo-sensor L14F1to detect shadows. It is portable and can be used at any place that is to be

monitored. Op-amp A741 (IC1) is used as a voltage comparator. Its inverting input is

biased by the voltage obtained from the junction of 100k resistor R1 and the collector of

phototransistor T1.The non-inverting input of IC1 gets a controlled voltage from potentialdivider R2 and VR1.In the presence of ambient light, the phototransistor conducts and the

inverting input (pin 2) of IC1 gets a lower voltage than its non-inverting input (pin 3).

This makes the output of IC1high, which is indicated by the glowing of LED1.When ashadow falls on the photo- sensor, the output of IC1 goes low. This low pulse triggers the

monostable (IC2) designed for a delay of 51 seconds using R6 and C3. The output of IC2

is used to light up LED2 and activate the alarm. Slide switch S2 is used to select eitherthe buzzer or siren. When it is towards left the buzzer beeps, and when it is towards right

IC UM3561 (IC3) activates to give a loud alarm simulating a police siren. Resistor R8

and zener diode ZD1 provide 3.1V DC to IC UM3561.The circuit is easy to assemble as

it requires only a few low-cost components. Enclose itin a cabinet with the photo-sensor

inside. Drill a 5mm hole on the front panel of the cabinet to let ambient light fall on the

photo- sensor. Adjust pot meter VR1 (47k) until LED2 stops glowing and the buzzerstops beeping whileLED1 glows. This is the posit ion of VR1 to be


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maintained for that particular intensity o f light.LED1 will continue to gloweven when a shadow is detected. The circuit is now ready to use. To test it, move apaper in front of the unit. If LED2 glows along with the beep of the buzzer, it means that

the photo-sensor has detected a shadow.

APPLICATIONS AND ADVANTAGES:The main application of this shadow alarm circuit is in the security system.

It is easy to understand that a security alarm system provides peace of mind whenyoure away from your place of business, and is there to meet insurance

requirements while minimizing burglary loss.

However, it is also a tool to protect your livelihood and that of your employees. Even if you have insurance to cover interruption of business, that wont help you

if your clients get comfortable using your competitor while you are closed due toa robbery or arson. Our security systems can help reduce inventory shrinkage andtheft, prevent break-ins, and when you consider what could happen to you or

your staff if you stumble into a crime scene you can understand one of the ways

it helps ensure employee safety.

It can be used at night by shopkeepers to protect the valuables in theirshowrooms.

It can also be used to provide security at warehouses where storage and protectionof various types of goods is main concern.

This circuit can also be used for home securities too. The main advantage of this circuit is that unlike opto-interruption alarm based on

light-dependent resistors (LDRs), it does not require an aligned beam toilluminate the photo-sensor.

This circuit is easy to implement and all the components used in this circuit areavailable in the market.

DISADVANTAGES:

Even though you may set your alarms when you leave, there is always that onechance that you may forget.

Most professional burglars are very familiar with home intruder alarms and knowexactly how to deal with them.

If the alarm is set and the burglar happens to trip it, he will immediately flee fromthe area and move on to a different home.


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CONCLUSION:The circuit has to found to have greater application in security reliable and less

expensive and is guaranteed to perform the best of the duration of their lifetime. Our team

effort and guidance of lecturers have helped us in completion of our project. This project

is accessible to anyone with an average expense and a bit of dedicated work, as we haverealized in materializing it. The project has been an enriching experience for us. We

conclude that this project will be useful to everyone.

FUTURE SCOPE:

In future we can develop more security systems with more reliability. We can also reduce man work. We can make it more economical.


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REFERENCES:www.electronicsforyou.com

www.howstuffworks.com

www.wikipedia.org

www.circuits-tody.com

www.freedatasheets.com

Introduction to Alarm

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