1. INTRODUCTION

The circuit basically works on the photo sensitive transistor which is the most sensitive photo

transistor. Unlike the conventional alarms which requires a constant aligned light beam source to

sound up that uses light dependent resistors (LDR’s) based on the opto-interruption technique. This

circuit works even in a dim lighting in the room or where ever the alarm is placed. The circuit is so

deigned that it can be used by the shopkeepers at night to avoid cases of theft and robbery with added

improvement in the circuit to operate a door using a dc motor.

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2. DECSRIPTION

2.1 CIRCUIT DIAGRAM

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FIG 2.1.1: Circuit diagram of Shadow alarm

2.2 CIRCUIT DESCRIPTION

The opto-sensitive circuit sounds up whenever a shadow falls on it. A dim lighting is required in the

room 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 has a 9

volt battery and uses most sensitive photo sensor to detect shadows. Op-amp μA741 (IC1) is used as a

voltage comparator. The inverting input of the IC1 is connected to the photo sensitive transistor and

the non-inverting input is connected to potential divider resistance (R2 ) and potentiometer (VR1).The

output of this IC (pin 6) is connected to pin 2 of IC2 which also connects resistance (R4 & R3) and

LED1. Pin 4 of IC2 is connected to resistance (R5) and capacitor (C1). Pin 6 and 7 is connected to

resistance (R6) and capacitor (C3). The output of Pin 3 is connected to the LED2 and further to the

piezoelectric buzzer which sounds whenever the circuit detects any shadow, also activating the dc

motor which pulls the door down.

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3. WORKING

In presence of ambient light in the room the phototransistor conducts the inverting input of IC1 (pin 2)

gets a low voltage than its non inverting input (pin 3) thus making the output of IC1 high and the

LED1 glows. When the photo transistor detects the shadows the output of IC1 is low and this low

pulse triggers IC2 which is designed for a delay of 51 sec using resistor (R6) and capacitor (C3). The

output of IC2 is used to light up the LED2 and sounds up the buzzer. The potentiometer can be

adjusted till the LED2 stops glowing and the buzzer stops beeping. This is the position of VR1 which

is to be maintained for that particular intensity of light.LED1 continues to glow even when the circuit

detects shadows which further provides a voltage to operate a dc motor to control the door.

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4. COMPONENTS

4.1 LIST OF COMPONENTS

S. No COMPONENTS QUANTITY SPECIFICATION

1 Photo sensor transistor

(L14F1)

1 Operating temp- -65-125 °C, VCEO 25 V

2 IC (741) 1 Input voltage 12-13 V,

3 IC (NE555) 1 4.5- 16 V supply, 3-6 mA

4 Potentiometer 1 47 K

5 LED 2 Red, Yellow

6 Resistor 7 1(100K),2(10 K),2(100Ω),1(4.7 K), 1(1M)

7 Capacitor 3 2(47µF), 1 (0.01µF)

8 Buzzer 1 Peizo electric

9 Battery 1 9V DC

10 Connecting wires 3

11 Switch 1 Simple On-Off

12 D C Motor 1 5-9 V

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8

7

6

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3

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4.2 COMPONENT DESCRIPTION

4.2.1 741 IC

Data Sheet

In the United States alone there are well over 30 IC manufacturers producing millions of ICs per year.

Each manufacturer uses a specific code and assigns a specific type number to the ICs it produces. For

example, the 741 type of internally compensated op-amp was originally manufactured by Fairchild and

is sold as the µA741 IC which we are using in our circuit.

The µA741 is a high performance monolithic operational amplifier constructed using the Fairchild

Planar epitaxial process. It is intended for a wide range of analog applications. High common mode

voltage range and absence of latch up tendencies make the µA741 ideal for the use as a voltage

follower. The high gain and wide range of operating voltage provides superior performance in

integrator, summing amplifier, and general feedback applications.

Absolute Maximum Ratings:

Supply Voltage= ±22V

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FIG 4.2.1.1: 741 IC

FIG 4.2.1.2: INTERNAL CIRCUITARY OF IC 741

Power Dissipation= 500 mW

Differential Input Voltage= ±30V

Input Voltage =±15V

Output Short Circuit Duration: Continuous

Operating Temperature Range =−55°C to +125°C

Storage Temperature Range= −65°C to +150°C

Junction Temperature= 150°C

Soldering Information:

N-Package (10 seconds) = 260°C

J- or H-Package (10 seconds) = 300°C

M-Package Vapor Phase (60 seconds) = 215°C

Infrared (15 seconds) = 215°C

Electrical Characteristics:

Input offset voltage= 0.8- 3.0 mV

Average input offset Voltage drift = 15 µV/ºC

Input offset Current = 3- 30 nA

Input Bais Current= 30- 80 mA

Input Resistance= 6 MΩ

Input Voltage range= ± 12- ±13 V

4.2.2 NE555 IC

Data Sheet

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The LM555/NE555/SA555 is a highly stable controller capable of producing accurate timing pulses.

With a mono stable operation, the time delay is controlled by one external resistor and one capacitor.

The operating temperature is upto +70°C with an astable operation, the frequency and duty cycle are

accurately controlled by two external resistors and one capacitor. It is available in two kinds 8-DIP and

8-SOP.

8-DIP

Features:

• High current drive capability (200mA).

• Adjustable duty cycle.

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8-SOP

FIG 4.2.2.1: TWO KINDS OF CONFIGURATIONS OF NE555 IC

• Temperature stability of 0.005%/°C.

• Timing from μ sec to hours

• Turn off time less than 2μ Sec

Applications:

• Precision timing

• Pulse generation

• Time delay generation

• Sequential timing

Absolute Maximum Ratings:

Supply Voltage =16 V

Lead Temperature (Soldering 10sec) = 300 °C

Power Dissipation = 600 mW

Operating Temperature Range = 0 ~ +70°C

Storage Temperature Range = -65 ~ +150 °C

Electrical Characteristics:

Supply Voltage= 4.5- 16 V

Supply Current= 3- 6 mA

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Control Voltage= 9- 11 V

Threshold Voltage= 10 V

Threshold Current=0.1- 0.25 µA

Trigger Voltage= 1.1- 2.2 V

Trigger Current= 0.01- 2 µA

Reset Voltage= 0.7V

Reset Current= 0.1 mA

Internal Block Diagram:

4.2.3 Potentiometer

1) It is a variable resistor

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FIG 4.2.2.2: INTERNAL BLOCK DIAGRAM OF NE555 IC

2) Wiper moves between two leads. Resistance between wiper and lead determines resistance

3) Resistance between leads is maximum resistance of potentiometer.

4) Comes in dial, slider, and trimpot form.

5) With linear pots resistance varies directly with the rotation of the knob.

6) With logarithmic pots resistance varies exponentially with the rotation of the knob.

7) Some other variable resistors include heat sensors, photoresistors and bend sensors.

4.2.4 LI4F1 PHOTO TRANSISTOR

Data Sheet

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FIG 4.2.3.1 : POTENTIOMETER

The L14F1/L14F2 are silicon photodarlingtons mounted in a narrow angle. They are also the most

sensitive photosensors which also detects the moving shadows. It’s tolerance limit is ±.010 with

operating temperature -65 to +125 °C. The collector to emitter breakdown voltage and collector to

emitter voltage both are 25 V.

FEATURES:

• Hermetically sealed package.

• Narrow reception angle.

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FIG 4.2.4.1: L14F1 PHOTO TRANSISTOR

Absolute Maximum Ratings:

Operating Temperature= -65 to +125 °C

Storage Temperature= -65 to +150 °C

Soldering Temperature (Iron) = 240 °C

Collector to Emitter Breakdown Voltage VCEO= 25 V

Collector to Base Breakdown Voltage VCBO= 25 V

Emitter to Base Breakdown Voltage VEBO= 12 V

Power Dissipation = 300 mW

Power Dissipation= 600 mW

Electrical Properties:

Collector-Emitter Breakdown Voltage=25 V

Emitter-Base Breakdown Voltage= 12 V

Collector-Base Breakdown Voltage= 25 V

Collector-Emitter Leakage Current=100 nA

Reception Angle at 1/2 Sensitivity θ = ±8 Degrees

On-State Collector Current = 7.5 mA

On-State Collector Current = 2.5 mA

4.2.5 DC MOTOR

Principle of operation

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In any electric motor, operation is based on simple electromagnetism. A current-carrying conductor

generates a magnetic field; when this is then placed in an external magnetic

field, it will experience a force proportional to the current in the conductor,

and to the strength of the external magnetic field.

The internal configuration of a DC motor is designed to harness the

magnetic interaction between a current-carrying conductor and an external magnetic field to generate

rotational motion.

Every DC motor has six basic parts -- axle, rotor (a.k.a., armature), stator, commutator, field

magnet(s), and brushes. In most common DC motors , the external magnetic field is produced by high-

strength permanent magnets. The stator is the stationary part of the motor -- this includes the motor

casing, as well as two or more permanent magnet pole pieces. The rotor (together with the axle and

attached commutator) rotates with respect to the stator. The rotor consists of windings (generally on a

core), the windings being electrically connected to the commutator. The above diagram shows a

common motor layout -- with the rotor inside the stator (field) magnets.

5. PRINTED CIRCUIT BOARDS

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FIG 4.2.5.1: DC MOTOR

The use of miniaturization and sub miniaturization in electronic equipment design has been

responsible for the introduction of a new technique in inters component wiring and assembly that is

popularly known as printed circuit.

The printed circuit boards (PCBs) consist of an insulating substrate material with metallic circuitry

photo chemically formed upon that substrate. Thus PCB provides sufficient mechanical support and

necessary electrical connections for an electronic circuit.

5.1 PCB MANUFACTURING PROCESS

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STAGE 1: PREPROCESSING

The first step to manufacture PCB requires a preparation of a layout. The layout can be prepared by

either using soft wares like PCB Artist or PCB Express or can be done manually on a plane paper

using marker with proper spaces between components.

NOTE: All the processes for the manufacture of lith film are performed in the dark room under

minimal amount of light. We can only use red light.

STAGE 2: LITH FILM MANUFACTURE

Before beginning with the steps we prepare 3 trays of solutions:

Tray 1: A+B tray which is Butyl + Sodium Carbonate with concentration 1 teaspoon in 1 litre of water

both added in same ratio.

Tray 2: Ordinary water

Tray 3: It consists of fixer (developer), the chemical is made by dissolving 2 teaspoons in 1 litre of

water.

1. Lith film is a sheet with two sides, one side is brown and the other is gray.

2. The lith film is now cut to an approximate size of the layout at least half cm more than the size

of layout.

3. The lith film is now placed in the lith making machine with readable part on the upper side.

4. The brown side of the lith film should touch the layout.

5. Now put the door of the machine down for not more than 8 seconds and push the switch ON.

6. Remove the lith film and wash it in the first tray continuously in movement till the complete

circuit is developed. Minimum time required is 2-3 minutes.

7. The circuit after the first tray appears transparent and the rest of the film turns black.

8. Now shift the lith film in second tray and wash it for 2-3 minutes.

9. Lastly wash the lith film in the fixer tray for the same time interval.

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10. Now, dry the film in air/oven at normal temperature say 40 degrees till the film dries.

The negative is ready to be processed further. PCB consists of an insulating substrate material.

STAGE 3: Photolithography

After preparing the negative, the next stage is photolithography. The steps performed under this are

mentioned below.

NOTE: All the processes for the manufacture of lith film are performed in the dark room under

minimal amount of light.

1. First of all we take a single sided copper clad board and cut it in size of the layout.

2. Clean it by metallic jute to see the shiny copper surface.

3. Now dip the PCB in the dip coating machine so that a layer photo resist material is coated on the

PCB. Photo resist is an organic solution which when exposed to light of particular wavelength

change their solubility in the developer. In dip coating copper clad board is clamped with the

machine and when the machine is switched on the copper clad gets dipped in the material.

4. After a layer of photo resist material is applied on the board surface, we dry the copper clad in

the oven at 50° c.

5. The basic purpose of applying photo resist material is that when this material is subjected

to UV light and the circuit gets imprinted on the board.

6. Now the copper clad board along with the layout is placed in the UV light machine to

film (lith film) kept in glass frame, for (2-3) minutes and after the time interval the circuit

becomes partially visible on the board.

7. Ultimately we drop the copper board in the machine which consists of white die and blue die in

separate tanks. We immerse the copper board first in white die for approximately one minute for

the visibility of the circuit.

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8. The next step is to wash the copper clad in simple water after which the circuit becomes

completely visible on the board.

9. After the above step, we put the copper board in blue dye for approximately one minute. The blue

dye covers the entire copper clad board.

STAGE 3: Etching

The next step after photolithography is etching

The etching process is performed by exposing the surface of the board to an etchant solution

which dissolves away the exposed copper areas other than the one deposited on the circuit .The

different solutions used are as etchants and the most commonly used is FeCl3.The steps

involved in etching are:

1. Switch on the etching machine, fix the sheet in the jaws and set the timer for 10 minutes

2. Now dip the prepared copper clad or the sheet in etchant.

3. After say about 8 minutes take out the sheet and check whether it’s is well etched or not. If

not then fix the sheet again and set the timer again

For 5 minutes.

4. Now wash the etched sheet in ordinary water and dry it in air for 10-15 minutes.

5. Extra copper is removed from the copper clad either manually or by a process called

tinning.

STAGE 4: Drilling

Drilling is used to create the component lead holes in a PCB .The drilling can be done before

or after the track defined for the components.

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STAGE 5: Component mounting and Soldering

Once the drilling has been done the components are mounted on their appropriate position and

the soldering is done.

STAGE 6: PCB Testing

After complete manufacturing PCB is tested for continuity.

5.2 PCB LAYOUT

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6. APPLICATIONS

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Shadow alarm features a very sensitive light sensor which helps the circuit to detect shadows. This

circuit may be very useful to guard some of the very costly belongings and it might be useful to the

shopkeepers who keep their jewelries in their shops.

The moment someone comes in between the light source and the sensor of the circuit which is placed

near the safe, it starts beeping, proving that someone is near and can be caught inside till some action

is taken.

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7. CONCLUSION

We were able to make the circuit of Shadow alarm. It is implemented and tested by casting shadow on

the sensor which makes the alarm run.

As a better implementation using a door with the alarm makes it more effective in serving the cause.

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8. REFERENCES

www.electronicsforyou.com/shadow alarm/images and components

www.google.com/circuit /circuit images/NE555/IC 741

www.wikipedia.com/electronic components/resistance,capacitance

www.electronicdesignworks.com/led,breadboards

Op-amps and linear integrated circuits (III edition), Ramkant A. Gayakwad Pearson

Publication, III edition Page No. 75 and 91

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