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Thursday, August 9, 2012

IR Sensor based Visitor Counter


Visitor counting is simply a measurement of the visitor traffic entering and exiting offices, malls, sports venues, etc. Counting the visitors helps to maximise the efficiency and effectiveness of employees, floor area and sales potential of an organisation.
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 hiring human auditors to stand and manually tally 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.
Two IR transmitter-receiver pairs are used at the passage: one pair comprising IR transmitter IR TX1 and receiver phototransistor T1 is installed at the entry point of the passage, while the other pair comprising IR transmitter IR TX2 and phototransistor T2 is installed at the exit of the passage. The IR signals from the IR LEDs should continuously fall on the respective phototransistors, so proper orientation of the transmitters and phototransistors is necessary.
Circuit description

Two similar sections detect interruption of the IR beam and generate clock pulse for the microcontroller. The microcontroller controls counting and displays the number of persons present inside the hall. above figure shows the circuit of the microcontroller-based visitor counter, wherein the transmitter and the receiver form the IR detection circuit. Control logic is built around transistors, operational amplifier LM324 (IC1) and flip-flop (IC2). When nobody is passing through the entry/exit point, the IR beam continuously falls on phototransistorT1. Phototransistor T1 conducts and the high voltage at its emitter drives transistor T3 into saturation, which makes pin 3 of comparator N1 low and finally output pin 1 of comparator N1 is high. Now if someone enters the place, first the IR beam from IR TX1 is interrupted and then the IR beam from IR TX2. When the beam from IR TX1 is interrupted, phototransistor T1 and transistor T3 cut-off and pin 3 of comparator N1 goes high. The low output (pin 1) of comparator N1 provides negative trigger pulse to pin 1 of J-K flip-flop IC2(A). At this moment, high input at ‘J’ and ‘K’ pins of flip-flop IC2(A) toggles its output to low. On the other hand, the low input at ‘J’ and ‘K’ pins of IC2(B) due to clock pin 1 of IC2(A) and ‘J’ input (pin 9) and ‘K’ input (pin 12) of IC2(B) are connected to pin 1 of comparator N1. The negative-going pulse is applied to clock pin 6 of IC2(B) when the person interrupts the IR beam from IR TX2. There is no change in the output of IC2(B) flip-flop. This triggers the external interrupt INT0 (pin 12) of microcontroller AT89C52. The AT89C52 is an 8-bit microcontroller with 8 kB of flash-based program memory, 256 bytes of RAM, 32 input/output lines, three 16-bit timers/counters, on-chip oscillator and clock circuitry. A 12MHz crystal is used for providing clock. Ports 0, 1 and 2 are configured for 7-segment displays. Port-0 pin is externally pulled up with 10-kilo-ohm resistor network RNW1 because port-0 is an 8-bit, open-drain, bidirectional l, input/output (I/O) port. Port-1 andport-2 are 8-bit bidirectional I/O ports with internal pull-ups (no need of external pull-ups). Port pins 3.0 and 3.1 are configured to provide the set pulse to J-K flip-flops IC2(A) and IC2(B), respectively. External interrupts INT0 and INT1 receive the interrupt pulse when the person interrupts the IR beams. Resistor R9 and capacitor C5 provide power-on-reset pulse to the microcontroller. Switch S1 is used for manual reset. When the microcontroller is re- s e t , t h e flip-flops are b r o u g h t i n ‘ s e t ’ s t a t e through the microcontroller at software run time by making their ‘set’ pin high for a moment. The value of the counter increments by ‘1’ when the interrupt service routine for INT0 is executed .The output of the corresponding J-K flip-flop is set to ‘high’ again by making its ‘set’ input pin low through the microcontroller. The micro-controller is configured as a negative-edge triggered interrupt sensor. Similarly, if somebody exits the place, first the IR beam from IR TX2 is interrupted and then the IR beam from IR TX1. When the beam from IR TX2 is interrupted, output pin 7 of comparator N2 goes low. This provides clock pulse to pin 6 of J-K flip-flop IC2(B).
   
At  this  moment,  the  high  input at ‘J’ and ‘K’ pins of  flip-flop IC2(B) toggles its output to low. On the other hand, the low input at ‘J’ and ‘K’ pins of IC2(A) due to clock pin 6 of IC2(B) and ‘J’ input (pin 4) and ‘K’ input (pin16) of IC2(A) are connected to pin 7 of comparator N2.
The  negative-going  pulse  is  ap- plied to clock pin 1 of IC2(A) when the person interrupts the IR beam from IR TX1. There is no change in the output of  IC2(A)  flip-flop. This  triggers  the external  interrupt  INT1  (pin  13)  of microcontroller  AT89C52.  The  value of the counter decrements by ‘1’ when interrupt service routine for INT1 is ex- ecuted. The output of the correspond ing J-K flip-flop is set to ‘high’ again by making its ‘set’ input pin low through the microcontroller.

The  circuit  is  powered  by  regulated 5V. Above figure shows the  circuit of the power supply. The  AC mains is stepped down by  transformer X1 to deliver  secondary  output  of  7.5V,
250mA, which is rectified by  bridge rectifier BR1, filtered by capacitor C6 and regulated by  IC 7805 (IC4). Ca- pacitor C7 bypasses any ripple in the regulated output.

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