microcontrolller based digital visitor counter

MICROCONTROLLER BASED DIGITAL VISITOR COUNTER

1. INTRODUCTIONDigital visitor counter is a reliable circuit that takes over the task of counting number

of Persons/ Visitors in the Room very accurately. When somebody enters into the Room then

the Counter is Incremented by one. The total number of Persons inside the Room is displayed

on the seven segment display module. The microcontroller does the above job it receives the

signals from the sensors, and this signals operated under the control of software which is

stored in ROM. This counter we will create counter system for apply. The total number of

object is displayed on the seven segment displays. The system is fully controlled by the 8 bit

microcontroller AT89C2051 which has a 2Kbytes of ROM for the program memory. A

counter that can change its state in either direction, under control of an up–down selector

input, is known as an up–down counter.

The circuit given here can count numbers from 0 to 9999 in up and down modes

depending upon the state of the selector. It can be used to count the number of persons

entering a hall in the up mode at entrance gate. In the down mode, it can count the number of

persons leaving the hall by decrementing the count at exit gate. It can also be used at gates of

parking areas and other public places. This circuit divided in three parts: sensor, controller

and counter display. The sensor would observe an interruption and provide an input to the

controller which would run the counter in up/down mode depending upon the selector setting.

The same count is displayed on a set of 7-segment displays through the controller.

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2. DESCRIPTION

2.1. BLOCK DIAGRAM :

Fig.2.1: Block Diagram

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2.2. CIRCUIT DIAGRAM :

Fig.2.2: Circuit Diagram

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2.2.1. Components Details:a) Resistor:

Resistor is a component that resists the flow of direct or alternating electric circuit.

Resistors used in electric circuits are cylindrical. They are often color coded by three or four

color bands that indicate the specific value of resistance. Resistors obey ohm’s law, which

states that the current density is directly proportional to the electric field when the

temperature is constant.

b) Capacitor:

Capacitor or electric condenser is a device for storing an electric charge. When one

plate is charged with electricity from a direct current or electrostatic source, the other plate

have induced in it a charge of the opposite sign; that is, positive if the original charge is

negative and negative if the original charge is positive. Capacitors are produced in a wide

variety of forms. Air, Mica, Ceramics, Paper, Oil, and Vacuums are used as dielectrics

depending on the purpose for which the device is intended

c) Transistor:

Transistor is a device which transforms current flow from low resistance path to high

resistance path. It is capable of performing many functions of the vacuum tube in electronic

circuits, the transistor is the solid state device consisting of a tiny piece of semi conducting

material, usually germanium or silicon, to which three or more electrical connections are

made.

2.3. MICROCONTROLLER AT89C2051:

2.3.1. Features:

Compatible with MCS®-51Products

2K Bytes of Reprogrammable Flash Memory

2.7V to 6V Operating Range

Fully Static Operation: 0 Hz to 24 MHz

Two-level Program Memory Lock

128 x 8-bit Internal RAM

15 Programmable I/O Lines

Two 16-bit Timer/Counters

Six Interrupt Sources

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Programmable Serial UART Channel

Direct LED Drive Output

On-chip Analog Comparator

Low-power Idle and Power-down Modes

Green (Pb/Halide-free) Packaging Option

2.3.2. Block diagram:

Fig.2.3: Block diagram of AT89C2051

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2.3.3. Description:The AT89C2051 is a low-voltage, high-performance CMOS 8-bit microcomputer

with 2K bytes of Flash programmable and erasable read-only memory (PEROM). The device

is manufactured using Atmel’s high-density nonvolatile memory technology and is

compatible with the industry-standard MCS instruction set. By combining a versatile 8-bit

CPU with Flash on a monolithic chip, the Atmel AT89C2051 is a power-full microcomputer

which provides a highly-flexible and cost-effective solution to many embedded control

applications. The AT89C2051 provides the following standard features: 2K bytes of Flash,

128 bytes of RAM, 15 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt

architecture, a full duplex serial port, a precision analog comparator, on-chip oscillator and

clock circuitry. In addition, the AT89C2051 is designed with static logic for operation down

to zero frequency and supports two software selectable power saving modes. The Idle Mode

stops the CPU while allowing the RAM, timer/counters, serial port and interrupt system to

continue functioning. . The power-down mode saves the RAM contents but freezes the

oscillator disabling all other chip functions until the next hardware reset.

2.3.4. Pin Description:

Fig.2.4: Pin Configuration of AT89C2051

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2.2.5. Pin Description:1. Vcc:

Supply voltage

2. GND:

Ground

3. Port 1:

Port 1 is an 8-bit bi-directional I/O port. Port pins P1.2 to P1.7 provide internal pull-

ups. P1.0 and P1.1 require external pull-ups. P1.0 and P1.1 also serve as the positive input

(AIN0) and the negative input (AIN1), respectively, of the on-chip precision analog

comparator. The Port 1 output buffers can sink 20 mA and can drive LED displays directly.

When 1s are written to Port 1 pins, they can be used as inputs. When pins P1.2 to P1.7 are

used as inputs and are externally pulled low, they will source current (IIL) because of the

internal pull-ups. Port 1 also receives code data during Flash programming and verification.

4. Port 3:

Port 3 pins P3.0 to P3.5, P3.7 are seven bi-directional I/O pins with internal pull-ups.

P3.6 is hard-wired as an input to the output of the on-chip comparator and is not accessible as

a general purpose I/O pin. The Port 3 output buffers can sink 20 mA. When 1s are written to

Port 3 pins they are pulled high by the internal pull-ups and can be used as inputs. As inputs,

Port 3 pins that are externally being pulled low will source current (IIL) because of the pull-

ups.

Table 2.1: Special features of AT89C2051 serve by Port 3

5. RST:

Reset input. All I/O pins are reset to 1s as soon as RST goes high. Holding the RST

pin high for two machine cycles while the oscillator is running resets the device. Each

machine cycle takes 12 oscillator or clock cycles.

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6. XTAL1:

Input to the inverting oscillator amplifier and input to the internal clock operating

circuit.

2.3.6. Oscillator Characteristics:The XTAL1 and XTAL2 are the input and output, respectively, of an inverting

amplifier which can be configured for use as an on-chip oscillator, either a quartz crystal or

ceramic resonator may be used. To drive the device from an external clock source, XTAL2

should be left unconnected while XTAL1.There are no requirements on the duty cycle of the

external clock signal, since the input to the internal clocking circuitry is through a divide-by-

two flip-flop, but minimum and maximum voltage high and low time specifications must be

observed.

2.3.7. Restrictions on Certain Instructions:The AT89C2051 and is an economical and cost-effective member of Atmel’s growing

family of microcontrollers. It contains 2K bytes of flash program memory. It is fully

compatible with the MCS-51 architecture, and can be programmed using the MCS-51

instruction set. However, there are a few considerations one must keep in mind when utilizing

certain instructions to program this device. All the instructions related to jumping or

branching should be restricted such that the destination address falls within the physical

program memory space of the device, which is 2K for the AT89C2051. This should be the

responsibility of the software programmer. For example, LJMP 7E0H would be a valid

instruction for the AT89C2051 (with 2K of memory), whereas LJMP 900H would not.

2.3.8. Branching Instructions:LCALL, LJMP, ACALL, AJMP, SJMP, JMP @A+DPTR These unconditional

branching instructions will execute correctly as long as the programmer keeps in mind that

the destination branching address must fall within the physical boundaries of the program

memory size (locations 00H to 7FFH for the 89C2051). Violating the physical space limits

may cause unknown program behavior. CJNE [...], DJNZ [...], JB, JNB, JC, JNC, JBC, JZ,

JNZ With these conditional branching instructions the same rule above applies. Again,

violating the memory boundaries may cause erratic execution. For applications involving

interrupts the normal interrupt service routine address locations of the 80C51 family

architecture have been preserved.

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2.3.9. MOVX-related Instructions, Data Memory: The AT89C2051 contains 128 bytes of internal data memory. Thus, in the

AT89C2051 the stack depth is limited to 128 bytes, the amount of available RAM. External

DATA memory access is not supported in this device, nor is external PROGRAM memory

execution. Therefore, no MOVX [...] instructions should be included in the program. A

typical 80C51 assembler will still assemble instructions, even if they are written in violation

of the restrictions mentioned above. It is the responsibility of the controller user to know the

physical features and limitations of the device being used and adjust the instructions used

correspondingly

2.4 IR SENSOR:

Description The TSOP17.. – series are miniaturized receivers for infrared remote

control systems. PIN diode and preamplifier are assembled on lead frame, the epoxy package

is designed as IR filter. The demodulated output signal can directly be decoded by a

microprocessor. TSOP17.. is the standard IR remote control receiver series, supporting all

major transmission codes.

Fig.2.5: IR Sensor

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2.4.1 Features:

Photo detector and preamplifier in one package

Internal filter for PCM frequency

Improved shielding against electrical field disturbance

TTL and CMOS compatibility

Output active low

Low power consumption

High immunity against ambient light

Continuous data transmission possible (up to 2400 bps)

Suitable burst length ≥10 cycles/burst

2.4.2 Sensor Description:

The circuit of the TSOP17.. is designed in that way that unexpected output pulses due

to noise or disturbance signals are avoided. A band pass filter, an integrator stage and an

automatic gain control are used to suppress such disturbances. The distinguishing mark

between data signal and disturbance signal are carrier frequency, burst length and duty cycle.

The data signal should full fill the following condition: • Carrier frequency should be close to

center frequency of the band pass (e.g. 38kHz).

• Burst length should be 10 cycles/burst or longer.

• After each burst which is between 10 cycles and 70 cycles a gap time of at least 14

cycles is necessary.

• For each burst which is longer than 1.8ms a corresponding gap time is necessary at some

time in the data stream. This gap time should have at least same length as the burst.

• Up to 1400 short bursts per second can be received continuously. Some examples for

suitable data format are: NEC Code, Toshiba Micom Format, Sharp Code, RC5 Code,

RC6 Code, R–2000 Code, Sony Format (SIRCS). When a disturbance signal is applied

to the TSOP17.. it can still receive the data signal. However the sensitivity is reduced to

that level that no unexpected pulses will occure. Some examples for such disturbance

signals which are suppressed by the TSOP17..

• DC light (e.g. from tungsten bulb or sunlight)

• Continuous signal at 38kHz or at any other frequency

• Signals from fluorescent lamps with electronic ballast (an example of the signal

modulation is in the figure below).

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2.5. Timer IC (555):

It is a highly stable device for generating accurate time delays or oscillation.

Additional terminals are provided for triggering or resetting if desired. In the time delay

mode of operation, the time is precisely controlled by one external resistor and capacitor. For

astable operation as an oscillator, the free running frequency and duty cycle are accurately

controlled with two external resistors and one capacitor. The circuit may be triggered and

reset on falling waveforms, and the output circuit can source or sink up to 200mA or drive

TTL circuits.

Fig.2.6: Pin Diagram of Timer IC

2.5.1. Features:

Direct replacement for SE555/NE555

Timing from microseconds through hours

Operates in both astable and monostable modes

Adjustable duty cycle

Output can source or sink 200 mA

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Output and supply TTL compatible

Temperature stability better than 0.005% per °C

Normally on and normally off output

2.5.2 Applications:

Precision timing

Pulse generations

Sequential timing

Time delay generation

Pulse width modulation

Pulse position modulation

Linear ramp generator

2.5.3. Monostable Mode:

As the name suggests; in this mode the output is stable in only one (mono) state i.e.

‘off’ state. Thus it can stay only for a finite time, if triggered, to the other state i.e. ‘on’ state.

This time can be set choosing appropriate values of resistances in the formula:

T=1.1XR1XC1

Fig.2.7: Monostable Circuit

2.5.4 Astable Mode

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In this mode; the output is stable neither in ‘high’ state nor in ‘low ’ state. Hence it

oscillates from one state to another giving us a square wave or clock. We can set the clock

frequency and Duty cycle D by the formulae:

Fig.2.8: Astable mode

2.6. SEVEN SEGMENT DISPLAY:

An LED or Light Emitting Diode, is a solid state optical PN-junction diode which

emits light energy in the form of “photons” when it is forward biased by a voltage allowing

current to flow across its junction, and in Electronics we call this process

electroluminescence. The actual colour of the visible light emitted by an LED, ranging from

blue to red to orange, is decided by the spectral wavelength of the emitted light which itself is

dependent upon the mixture of the various impurities added to the semiconductor materials

producing it.

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Light Emitting Diodes have many advantages over traditional bulbs and lamps, with

the main ones being their small size, long life, various colours, cheapness and are readily

available, as well as being easy to interface with various other electronic components and

digital circuits. But the main advantage of light emitting diodes is that because of their small

die size, several of them can be connected together within one small and compact package

producing what is generally called a 7-segment Display.

The 7-segment display, also written as “seven segment display”, consists of seven

LEDs (hence its name) arranged in a rectangular fashion as shown. Each of the seven LEDs

is called a segment because when illuminated the segment forms part of a numerical digit

(both Decimal and Hex) to be displayed. An additional 8th LED is sometimes used within the

same package thus allowing the indication of a decimal point, (DP) when two or more 7-

segment displays are connected together to display numbers greater than ten.

Fig.2.9: Seven Segment Display

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http://www.amazon.in/s/?field-keywords=Light-Emitting%20Diodes


3. POWER SUPPLYIn this ,we have power supplies with +5V & -5V option normally +5V is enough for

total circuit. Another (-5V) supply is used in case of OP amp circuit .Transformer primary

side has 230/50HZ AC voltage whereas at the secondary winding the voltage is step downed

to 12/50hz and this voltage is rectified using two full wave rectifiers. The rectified output is

given to a filter circuit to filter the unwanted ac in the signal after that the output is again

applied to a regulator LM7805 (to provide +5v) regulator .Whereas LM7905 is for providing

–5V regulation. (+12V circuit is used for stepper motors, Fan and Relay by using LM7812

regulator same process like above supplies.)

3.1 TRANSFORMER:

3.1.1 Description:

A transformer is a device that transfers electrical energy from one circuit to another

through inductively coupled conductors the transformer's coils. A varying current in the first

or primary winding creates a varying magnetic flux in the transformer's core, and thus a

varying magnetic field through the secondary winding. This varying magnetic field induces a

varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is

called mutual induction. The transformer symbol is as shown in below fig.3.1.

Fig.3.1: Transformer Symbol

Transformer is a device that converts the one form energy to another form of energy

like a transducer. The transformer is as shown in fig.3.2.

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Fig.3.2: Transformer

3.1.2 Basic Principle of Transformer:

A transformer makes use of Faraday's law and the ferromagnetic properties of an iron

core to efficiently raise or lower AC voltages. It of course cannot increase power so that if the

voltage is raised, the current is proportionally lowered and vice versa. As shown in below

fig.3.3.

Fig.3.3: Basic Principle of Transformer

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3.1.3 Transformer Working:

A transformer consists of two coils (often called 'windings') linked by an iron core, as

shown in below fig.3.4. There is no electrical connection between the coils, instead they are

linked by a magnetic field created in the core.

Fig.3.4: Basic Transformer

Transformers are used to convert electricity from one voltage to another with minimal

loss of power. They only work with AC (alternating current) because they require a changing

magnetic field to be created in their core. Transformers can increase voltage (step-up) as well

as reduce voltage (step-down).

Alternating current flowing in the primary (input) coil creates a continually changing

magnetic field in the iron core. This field also passes through the secondary (output) coil and

the changing strength of the magnetic field induces an alternating voltage in the secondary

coil. If the secondary coil is connected to a load the induced voltage will make an induced

current flow. The correct term for the induced voltage is 'induced electromotive force' which

is usually abbreviated to induced e.m.f.

The iron core is laminated to prevent 'eddy currents' flowing in the core. These are

currents produced by the alternating magnetic field inducing a small voltage in the core, just

like that induced in the secondary coil.

Transformers have two great advantages over other methods of changing voltage:

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1. They provide total electrical isolation between the input and output, so they can be

safely used to reduce the high voltage of the mains supply.

2. Almost no power is wasted in a transformer. They have a high efficiency (power out /

power in) of 95% or more.

3.1.4 Classification of Transformer:

Step-Up Transformer

Step-Down Transformer

3.1.5 Step-Down Transformer:

Step down transformers are designed to reduce electrical voltage. Their primary

voltage is greater than their secondary voltage. This kind of transformer "steps down" the

voltage applied to it. For instance, a step down transformer is needed to use a 110v product in

a country with a 220v supply.

Step down transformers convert electrical voltage from one level or phase

configuration usually down to a lower level. They can include features for electrical isolation,

power distribution, and control and instrumentation applications. Step down transformers

typically rely on the principle of magnetic induction between coils to convert voltage and/or

current levels.

Step down transformers are made from two or more coils of insulated wire wound

around a core made of iron. When voltage is applied to one coil (frequently called the

primary or input) it magnetizes the iron core, which induces a voltage in the other coil,

(frequently called the secondary or output) as shown in fig.3.5. The turn’s ratio of the two

sets of windings determines the amount of voltage transformation.

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Fig.3.5: Step-Down Transformer

3.1.6 Step-Up Transformer:

A step up transformer has more turns of wire on the secondary coil, which makes a

larger induced voltage in the secondary coil. It is called a step up transformer because the

voltage output is larger than the voltage input as shown in below fig.3.6.

Fig.3.6: Step-Up Transformer

Step-up transformer 110v 220v design is one whose secondary voltage is greater than

its primary voltage. This kind of transformer "steps up" the voltage applied to it. For instance,

a step up transformer is needed to use a 220v product in a country with a 110v supply.

A step up transformer 110V, 220V converts alternating current (AC) from one voltage

to another voltage. It has no moving parts and works on a magnetic induction principle; it can

be designed to "step-up" or "step-down" voltage. So a step up transformer increases the

voltage and a step down transformer decreases the voltage.

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The primary components for voltage transformation are the step up transformer core

and coil. The insulation is placed between the turns of wire to prevent shorting to one another

or to ground. This is typically comprised of Mylar, nomex, Kraft paper, varnish, or other

materials. As a transformer has no moving parts, it will typically have a life expectancy

between 20 and 25 years.

3.1.7 Uses and Applications:

It can be used to prevent DC from passing from one circuit to the other.

It can isolate two circuits electrically.

Generally these Step-Up Transformers are used in industries applications only.

3.2 RECTIFIER:

The purpose of a rectifier is to convert an AC waveform into a DC waveform (OR)

Rectifier converts AC current or voltages into DC current or voltage. There are two different

rectification circuits, known as 'half-wave' and 'full-wave' rectifiers. Both use components

called diodes to convert AC into DC.

In this digital counter we are using bridge rectifier. The main advantage of this bridge

circuit is that it does not require a special centre tapped transformer, their by reducing its size

and cost. The single secondary winding is connected to one side of the diode bridge network

and the load to the other side as shown below.

3.2.1 Diode Bridge Rectifier:

The four diodes label led D1 to D4 are arranged in "series pairs" with only two

diodes conducting current during each half cycle. During the positive half cycle of the

supply, diodes D1 and D2 conduct in series while diodes D3 and D4 are reverse biased and

the current flows through the load as shown in fig.3.7.

Fig.3.7: Bridge Rectifier

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3.2.2 Positive Half-Cycle of Bridge Rectifier:

Fig.3.8: Positive Half Cycle of Bridge RectifierThe positive half cycle of bridge rectifier as shown above fig.3.8. During the positive

half cycle of the supply, diodes D1 and D2 conduct in series, but diodes D3 and D4switch

"OFF" as they are now reverse biased. The current flowing through the load is the same

direction as before.

3.2.3 Negative Half-Cycle of Bridge Rectifier:

Fig.3.9: Negative Half Cycle of Bridge Rectifier

The negative half cycle of bridge rectifier as shown in above fig.3.9 the current

flowing through the load is unidirectional so the voltage developed across the load is also

unidirectional the same as for the previous two diode full-wave rectifier, therefore the

average DC voltage across the lot is 0.637Vmax. However in reality, during each half cycle

the current flows through two diodes instead of just one so the amplitude of the output

voltage is two voltage drops (2 x 0.7 =1.4V) less than the input VMAX amplitude. The ripple

frequency is now twice the supply frequency. (e.g. 100Hz for a 50Hzsupply)

3.2.4 Typical Bridge Rectifier:Although we can use four individual power diodes to make a full wave bridge

rectifier, pre-made bridge rectifier components are available "off-the-shelf" in a range of

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different voltage and current sizes that can be soldered directly into a PCB circuit board or be

connected by spade connectors.

The image to the right shows atypical single phase bridge rectifier with one corner cut

off. This cut-off corner indicates that the terminal nearest to the corner is the positive or +Ve

output terminal or lead with the opposite (diagonal) lead being the negative or -Ve output

lead.

3.3 FILTER:

Filtering is performed by a large value electrolytic capacitor connected across the DC

supply to act as a reservoir, supplying current to the output when the varying DC voltage

from the rectifier is falling. The below fig.3.10 shows the unfiltered varying DC (dotted line)

and the filtered DC (solid line). The capacitor charges quickly near the peak of the varying

DC, and then discharges as it supplies current to the output.

Fig.3.10: Charging and Discharging of a Capacitor

3.4 REGULATOR:

A voltage regulator is an electrical regulator designed to automatically maintain a

constant voltage level. It may use an electromechanical mechanism, or passive or active

electronic components. Depending on the design, it may be used to regulate one or more AC

or DC voltages. Voltage regulator having three pins like input, ground and output as shown in

fig.3.11.

This is a simple DC regulated supply seminar using 7805 voltage regulator to obtain a

variable DC voltage range from 5V to15V.

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Fig.3.11: Voltage Regulator

As the name itself implies, it regulates the input applied to it. A voltage regulator is an

electrical regulator designed to automatically maintain a constant voltage level. In this

technique, power supply of5Vand12Vare required. In order to obtain these voltage levels,

7805 and 7812 voltage regulators are to be used. The first number78 represents positive

supply and the numbers 05, 12 represent the required output voltage levels. The L78xx series

of three-terminal positive regulators are available in TO-220, TO-220FP, TO-3, D2PAK and

DPAK packages and several fixed output voltages, making it useful in a wide range of

applications.

The regulators can provide local on-card regulation, eliminating the distribution

problems associated with single point regulation. Each type employs internal current limiting,

thermal shut-down and safe area protection, making it essentially in destructible. If adequate

heat sinking is provided, they can deliverover1Aoutput current. Although designed primarily

as fixed voltage regulators, these devices can be used with external components to obtain

adjustable voltage and currents.

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4. APPLICATIONS1. Digital Visitor Counter can be used in various rooms like seminar hall, conference

hall where the capacity of room is limited and should not be exceeded. it will display

actual number of persons inside the room.

2. “Automatic Room light Controller with Visitor Counter” can be used in class

rooms, study rooms in colleges.

3. This digital counter can also be used in industries.

4. This digital counter can also be used in our home because many times we come out of

our bedroom or any other room and we forgot to turn off the room light.

5. This digital counter can be used in Cinema halls, multiplex, malls as well as in

temples to count the number of person entering inside. So that these places should not

get over crowded to avoid congestion.

6. This circuit can be used domestically to get an indication of number of persons

entering a party

7. It can be used at official meetings.

8. It can be used at homes and other places to keep a check on the number of persons

entering a secured place.

9. It can also be used as home automation system to ensure energy saving by switching

on the loads and fans only when needed.

10. Used in parking lot

11. Low cost

5. ADVANTAGES & DISADVANTAGES

ADVANTAGES:

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1. Main advantage of this seminar is that it helps in energy conservation. Because when

there is nobody inside the room then lights are automatically turned off.

2. Human efforts to count the number of persons are eliminated. Since this seminar does

the automatic person counting with the help of two sensors installed on door frame.

3. Whole system will work automatically so it reduces the human work.

4. High precision and accuracy can be achieved through it.

5. Used in elevator to prevent the maximum limit of weight.

DISADVANTAGES:

1. IR sensor cannot detect if lot of people are entering at one time.

2. When microcontroller fails then the entire system fail.

6. FUTURE SCOPE

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Voice alarm system can be added to indicate that room is full & persons can’t enter

inside.

We can increase the maximum number of persons that can be counted by

implementing the external EEPROM ic.

We can send this data to a remote location using mobile or internet

We can interface GSM modem to send this data through SMS

7. CONCLUSION

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This seminar provides enriched learning experience to count the number of visitor in

any particular location.

Thus the concept entitled digital visitor counter helps to measure visitor entering and

exiting a particular way .The circuit counts both entering and exiting visitor and displays the

number of visitors present inside the wall visitor counting not limited to the entry/exit point

of a company but has a wide range of applications that provide the information to the

management on the volume flow of a people throughout the location.

It can also be enhanced for long and accurate sensing range using a laser torch instead

of IR transmission circuit. Thus the circuit can be used to monitor visitor flow in effective

manner, where the visitors have to counted and controlled.

8. BIBLIOGRAPHYREFERENCE BOOKS:

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1. "Synchronous counter", Digital, Play hookey.

2. Singh, Arun Kumar (2006). Digital Principles Foundation of Circuit Design and

Application. New Age Publishers

3. Horowitz, Paul; Hill, Winfield (1989). The Art of Electronics. Cambridge

University Press.

4. Graf, Rudolf F (1999). Modern Dictionary of Electronics.

5. "Atmel’s Self-Programming Flash Microcontrollers" Retrieved 2008-10-25. by

Odd Jostein Svendsli 2003

REFERENCE WEBSITES:

en.wikipedia.org

www.atmel.com

www.slideshare.com

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http://www.atmel.com/

http://books.google.com/books?id=uah1PkxWeKYC&pg=PA401&dq=moebius+ring+counter+johnson

http://books.google.com/books?id=bkOMDgwFA28C&pg=PA667&dq=ring+counter+walking

http://books.google.com/books?id=13Wi37h2A-oC&pg=PA113&dq=switchtail+ring+counter+johnson

http://books.google.com/books?id=13Wi37h2A-oC&pg=PA113&dq=switchtail+ring+counter+johnson

http://www.play-hookey.com/digital/synchronous_counter.html

microcontrolller based digital visitor counter

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