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Digital Visitor Counter :
It 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 LCD. Visitor counting is simply a measurement of the visitor traffic entering and exiting. Offices, malls, sports, venues etc. Counting the visitors helps to maximize the efficiency and effectiveness of employees, floor area and sales potential of an organization.
Visitor counting is not limited to the entry/exit point of a company but has a wide range of applications that provide information to management on the volume and flow of people throughout a location. A primary method for counting the visitors involves sharing human auditors to standard manually tallies the number of visitors who pass by a certain location. But human-based data collection comes at great expense. Here is a low-cost microcontroller based visitor counter that can be used to know the number of persons at a place. All the components required are readily available in the market and the circuit is easy to build.
Basic principle :
When somebody enters into the room then the counter is incremented by one. The total number of persons inside the room is displayed on LCD .The microcontroller does the above job , it receives the signals from the sensors, and these signals operated under the control of software which is stored in ROM.
Microcontroller AT89s52 continuously monitors the sensor, when any object or person passes through the sensor then the light rays falling on the sensor are obstructed, this obstruction is sensed by the Microcontroller. When sensor is obstructed, then the Microcontroller will increment the counter by 1 in the display.
Circuit Diagram :
Components Used :
1. 555 Timer IC
2. LCD [16*2]
3. Microcontroller [ AT89s52]
4. Frequency Crystal [11.0592 MHz]
6. Voltage regulator 
Description of components :
The components are as follows
The 555 Timer IC is an integrated circuit (chip) implementing a variety of timer and multivibrator applications. It has been claimed that the 555 got its name from the three 5 kΩ resistors used in typical early implementations,
Pin diagram :
The connection of the pins is as follows:
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.
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 3 and 15 V.
Operating Modes :
The 555 has three operating modes:
1. Monostable mode: In this mode, the 555 functions as a "one-shot". Applications include timers, missing pulse detection, bouncefree switches, touch switches, frequency divider, capacitance measurement, pulse-width modulation (PWM) etc
2. Astable mode / Free running mode: The 555 can operate as an oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation, etc.
3. Bistable mode or Schmitt trigger: The 555 can operate as a flip-flop, if the DIS pin is not connected and no capacitor is used. Uses include bouncefree latched switches, etc.
1.Monostable mode :
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. The width of the output pulse is determined by the time constant of an RC network, which consists of a capacitor © and a resistor ®. The output pulse ends when the charge on the C 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.
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
t = 1.1RC
where t is in seconds, R is in ohms and C is in farads.
2.Bistable Mode :
In bistable mode, the 555 timer acts as a basic flip-flop. The trigger and reset inputs (pins 2 and 4 respectively on a 555) are held high via pull-up resistors while the threshold input (pin 6) is simply grounded. Thus configured, pulling the trigger momentarily to ground acts as a 'set' and transitions the output pin (pin 3) to Vcc (high state). Pulling the reset input to ground acts as a 'reset' and transitions the output pin to ground (low state). No capacitors are required in a bistable configuration. Pins 5 and 7 (control and discharge) are left floating.
3.Astable mode :
In astable mode, the 555 timer puts out a continuous stream of rectangular pulses having a specified frequency. Resistor R1 is connected between VCC and the discharge pin (pin 7) and another resistor (R2) is connected between the discharge pin (pin 7), and the trigger (pin 2) and threshold (pin 6) pins that share a common node. Hence the capacitor is charged through R1 and R2, and discharged only through R2, since pin 7 has low impedance to ground during output low intervals of the cycle, therefore discharging the capacitor.
2.LCD Display [16*2] :
A liquid crystal display (LCD) is a thin, flat electronic visual display that uses the light modulating properties of liquid crystals (LCs). LCs do not emit light directly.They are used in a wide range of applications including: computer monitors, television, instrument panels, aircraft cockpit displays, signage etc. They are common in consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephones. LCDs have displaced cathode ray tube (CRT) displays in most applications. They are usually more compact, lightweight, portable, less expensive, more reliable, and easier on the eyes.They are available in a wider range of screen sizes than CRT and plasma displays, and since they do not use phosphors, they cannot suffer image burn-in.
LCDs are more energy efficient and offer safer disposal than CRTs. Its low electrical power consumption enables it to be used in battery-powered electronic equipment. It is an electronically-modulated optical device made up of any number of pixels filled with liquid crystals and arrayed in front of a light source (backlight) or reflector to produce images in colour or monochrome. The earliest discovery leading to the development of LCD technology, the discovery of liquid crystals, dates from 1888. By 2008, worldwide sales of televisions with LCD screens had surpassed the sale of CRT units