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Auditorium Attendance Counter


Price : INR 5,450.00


Auditorium Attendance Counter is very useful for counting the number of people in a hall or in a conference room. You can use it at any place. Auditorium Attendance Counter will count the difference between the number of people leaving the room and entering the room.

 

Auditorium Attendance Counter is based on IR interruption to detect the object. Two IR circuits are used for detecting the object moving in forward and reverse direction. Associated logic circuit makes the count up or down depending upon the direction. Two up/down counter ICs are used for counting up/down pulse. For display the count, two BCD to seven segment display driver and two common cathode displays are used. The circuit will count maximum 99 objects. Logic circuit is designed using Schmitte trigger inverter, NAND Gate, and timer circuit. The power supply section comprises mains step down transformer, full wave rectifier, 12V regulator IC and filter capacitors.


About the Circuit :

Two IR sensors detect the movement of object. It comprises two IR transmitters and associated receiver module.

The simple transmitter circuit is shown in figure. It consists of 555 Timer connected as an astable multivibrator driving an output transistor which switches the IR emitter ON and OFF. The duration of the transmitted light pulses is about 10ms and the repetition rate is just less than 1 KHz. The average current drawn by the circuit is about 12mA and the peak current through the IR diode is around 700mA.

The power supply for the transmitter is not critical provided the output voltage is not greater than 9V as this could result in the maximum current rating of IR diode.

 

The receiver circuit is shown in figure. An infrared photodiode is operated in the reverse bias mode. The leakage current of this diode varies with the light received from the transmitter, which causes a varying voltage to appear across the resistor of the transistor T1. The signal appearing at the collector T1 is fed to IC1, which is used as an amplifier and limiter. P1 varies the sensitivity by altering the reverse bias voltage of the diode D1.

When light pulses are being received from the transmitter a negative going pulse train with amplitude in excess of 1V peak to peak appears at the output of IC1 (pin8). This turns T2 ON and OFF continuously, charging up C11. T3 is thus always turned on T4 is turned OFF.

When the light beam between the transmitter and receiver is interrupted, the amplitude of the pulse train from the output of IC1 will fall. T2 will be cut OFF, C11 will discharge, T3 will turn OFF, and T4 will turn ON. This energizes the relay. Once the light beam is restored the relay will of course, drop out again but can be made to hold in for several seconds after the light beam has been restored by adding the components shown dotted. R12 and C12 are designed according to holding time. Alternatively latching arrangement may be used that will hold the relay on a reset button is pressed.

Initially consider the object is moving from A to B. When first IR beam is interrupted, transistor T4 is turned ON and logic ‘0’ is fed to pin1 of IC1(A), which is a Schmitte trigger inverter. The high output at pin2 of IC1(A) is given to the inputs of NAND Gate IC2(A). The output of NAND Gate is zero and this output is given to trigger pin2 of timer IC3. The output of NAND gate acts as a trigger input to timer. The output of timer remains high depending on the setting time, which varies from 1sec to 100sec. The requirement is that the timer output remains high until second IR beam is interrupted. This timer output acts as one of the input of NAND gate IC2(C). When the second IR beam is interrupted, second IR receiver is triggered. The output transistor turns on shortly and a short low pulse acts as another input of NAND Gate IC2(C). Thus, output of this NAND Gate IC2(C) becomes shortly low and acts as a UP pulse to counter IC6 (40192). Thus, counter is incremented and the count is displayed on seven-segment display. The output of 40192 is in BCD format. For converting BCD input to seven-segment code BCD to seven-segment decoder IC 4055 is used, which drives seven-segment display. Here maximum count is 99, which can be increased by cascading more counter and display stages.

When object is moving from B to A, the same operation is repeated as above. The low pulse at output of NAND Gate IC2 (D), acts as a down pulse to counter IC. Thus, the counter is decrement by one. The resultant count is displayed on two seven-segment displays.
 
Installation :
Install the two IR transmitter detector pairs and connect them to the respective logic circuit. The first IR pair comprises IR LED1 and PHOTODIODE1. The second pair comprises IR LED2 and PHOTODIODE2. Orient the two IR LED transmitters such that their IR beams fall on the respective detector. Also, ensure that the IR beam off one pair doesn’t affect the other pair’s IR beam.

Counter will count will only when somebody interrupts IR rays of the first pair and then second pair sequentially. It will count down when second IR rays interrupted first and then first IR beam.





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