INTRODUCTION
The electronic gadgets made the human life comfortable, systematic, more predictable for the future. The data collection for assessment of needs, requirements, deliverables lead to better planning and development.
The counter is, though, a small gadget yet it helps to count the public entered to any of the service delivery center or to a ware house where from supplies are made either in bulk to keep the “enter” and “exit” record.
A shepherd with larger number of cattle in a herd to drive may use it to keep his cattle counting true and systematic which bring them out for grazing and back from the yard to the barn ()باڑہ. The gadget can be used in almost all spheres of life.
The report on project “Visitors’ Counter” covers the gadget objectives, its uses, the diagram, lay out, design, component, power supplies, etc.
The method of originating the gadget, and problems faced are also highlighted in the report. There are many different ways to design a circuit for counting device but before discussing that we need to understand the components used for its circuit.
1. SOURCE: As we are designing a digital circuit and we have idea that all digital circuits requires 5v maximum. So to provide 5v we had used the regulator IC7805 and connected it to the 9v battery. By doing so, we had connected the output and ground from IC7805 to our circuit. The pin configuration of the IC7805 is shown in fig-1.
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2.
INFRARED TRANSMITTER AND RECIVER:
The infrared transmitters and receiver are used to sense the object that passes through it. The IR transmitter is forward biased with 5 volt source and 120 ohm resistor. In the circuit we had used two IR led to extend the range of rays. The IR receiver is reverse biased with 5v source and a 10k current limiting resistor. When IR rays from transmitter falls on receiver. The resistance of the IR receiver decreases and the voltage drop across the 10k resistor increases. From the positive end of the 10k resistor we had in turn taken a connection for pin-2 (non-inverting pin) of IC 358.
1- OPERATIONAL AMPLIFIER LM358: In our circuit we had used the op-amp 358 as comparator i.e. the non-inverting pin is connected to the positive side of 10k resistor of IR receiver and the inverting pin is connected to the potentiometer. We use the potentiometer to set such a reference point at which the comparator gives zero output voltage when some object has blocked the IR rays coming from transmitter.The pin configuration of lm358 is shown in fig-3.
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2- NE555 TIMER/OSCILLATOR: To understand 555 timers IC, let us see the fig below that illustrates its pin configuration.
Pin1. - The ground pin that connects the 555 timer to negative of power supply. • Pin2. –
Trigger The negative input to comparator No 1. A negative pulse on this pin “sets” the internal Flip-flop when the voltage drops below 1/3Vcc causing the output to switch from a “LOW” to a “HIGH” state.
• Pin3. –
Output, The output pin can drive any TTL circuit and is capable of sourcing or sinking up to 200mA of current at an output voltage equal to approximately Vcc – 1.5V so small speakers, LEDs or motors can be connected directly to the output.
• Pin4. –
Reset, This pin is used to “reset” the internal Flip-flop controlling the state of the output, pin 3. This is an active-low input and is generally connected to a logic “1” level when not used to prevent any unwanted resetting of
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the output.
• Pin5. –
Control Voltage, This pin controls the timing of the 555 by overriding the 2/3Vcc level of the voltage divider network. By applying a voltage to this pin the width of the output signal can be varied independently of the RC timing network. When not used it is connected to ground via a 10nF capacitor to eliminate any noise.
• Pin6. –
Threshold, The positive input to comparator No 2. This pin is used to reset the Flip-flop when the voltage applied to it exceeds 2/3Vcc causing the output to switch from “HIGH” to “LOW” state. This pin connects directly to the RC timing circuit.
• Pin7. –
Discharge, The discharge pin is connected directly to the Collector of an internal NPN transistor which is used to “discharge” the timing capacitor to ground when the output at pin 3 switches “LOW”.
• Pin8. –
Supply +Vcc, This is the power supply pin and for general purpose TTL 555 timers is between 4.5V and 15V.
The 555 Timers name comes from the fact that there are three 5kΩ resistors connected together internally producing a voltage divider network between the supply voltage at pin 8 and ground at pin 1. The IC555 is the most known and has many applications in electronics. The 555 timer can be used in three different ways. Those are:
a. Astable mode b. Monostable mode c. Bistable mode In our counter device we used 555 in monostable mode. So here we will only discuss monostable mode.
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Monostable mode: The figure below shows a simple monostable arrangement. When a negative ( 0V ) pulse is applied to the trigger input (pin 2) of the Monostable configured 555 Timer oscillator, the internal comparator, (comparator No1) detects this input and “sets” the state of the flip-flop, changing the output from a “LOW” state to a “HIGH” state. This action in turn turns “OFF” the discharge transistor connected to pin 7, thereby removing the short circuit across the external timing capacitor, C1. This action allows the timing capacitor to start to charge up through resistor, R1 until the voltage across the capacitor reaches the threshold (pin 6) voltage of 2/3Vcc set up by the internal voltage divider network. At this point the comparators output goes “HIGH” and “resets” the flip-flop back to its original state which in turn turns “ON” the transistor and discharges the capacitor to ground through pin 7. This causes the output to change its state back to the original stable “LOW” value awaiting another trigger pulse to start the timing process over again. Then as before, the Monostable Multivibrator has only “ONE” stable state. The Monostable 555 Timer circuit triggers on a negative-going pulse applied to pin 2 and this trigger pulse must be much shorter than the output pulse width allowing time for the timing capacitor to charge and then discharge fully. Once triggered, the 555 Monostable will remain in this “HIGH” unstable output state until the time period set up by the R1 x C1 network has elapsed. The amount of time that the output voltage remains “HIGH” or at a logic “1” level is given by the following time constant equation.
Where, t is in seconds, R is in Ω’s and C in Farads.
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Use of 555 IC in counter device: As mention before that in our circuit we are using 555 timer as monostable mode i.e. the trigger pin of the IC is connected to the 5V supply through a 10k resistor and to ground through a 120 ohm resistor and led(we use led for indication purposes). The trigger pin is also connected to the pin 1 (output pin) of IC lm358. When the 555 timer receive low pulse (0V) it gives a high output for the time of 51.7 millisecond. The output of the IC is connected to the ground through a resistor of 120 ohm and led (just for induction of high pulse) and to the clock pin of 4026 IC.
5. COUNTER IC 4026: The counter IC is used to count the number of high pulse and display it on 7 segment display. To understand the IC4026 see the pin configuration and description shown below.
PIN IC4026:
DISCRIPTION OF
1. Pin 1 or clock pin- It receives clock signals, and at every positive clock and counter advances one by one. We can provide clock with the switch, 555 timers or with the help of logic gates. In short high pulse on this input increments the counter.
2. Pin 2 or disable clock (clk inhibit) pin- 4026 counter advances one by one by receiving positive pulse at this time for this clock inhibit pin should be grounded. If it is connected to
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supply than counter advancement will be inhibited means there will be no meaning of clock pulse.
3. Pin 3 or enable display (En in) pin- It enable the 7 segment display to display the numeric value. It should be kept high for enabling the display. Mean output goes high when only when display enable is high.
4. Pin 4 or enable out- It Enables the carry out pin. In our circuit we have left this pin unconnected.
5. Pin 5 or divide by 10 outputs- It is used to complete one cycle for every 10 clock input cycle and it also used to cascade more IC's.
6. Pin 6, pin7 and Pin9 to pin 13 - These are 7 decoded output from a to g used to illuminates the corresponding segment of 7 segment display to display the digit from 0 to 9.
7. Pin 14 or not 2 output (UNGATED "C" SEGMENT) signals- They are not gated by the Display clock and therefore are available continuously. This feature is a requirement in implementation of certain divider function such a as divide by 60 and divide by 12.
8. Pin 15 or Reset pin- It is used to reset the counter. When it receives high it clears the counter and counting again starts from zero. One important thing reset pin should again made low to start the counter once again.
9. Pin 8 or ground pin and Pin 16 known or Vdd it should be connected to power supply.
In our circuit we had used two 4026 ICs to display the two digit 7-sigment display. We may use more IC to represent the greater than two digits by cascading.
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6. 7-SEGMENT DISPLAY: The 7-segment display is used to display the number of objects that it had counted we had use two 7-sigment display to count up to 99. The fig shows 7-segment display and its pin configuration. In our circuit we had used common cathode 7-seg display. The pin3 and 8 are shorted and grounded while the rest are connected with corresponding pins of IC 4026.
CIRCUIT THAT I HAD STUDIED DURING THIS PROJECT
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To understand the concept of astable mode of 555 tmer Astable mode of 555 timer
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Monostable mode of 555 timer
Transmitter circuit that produce 38 KHz frequency By using 555 timers in astable mode. It was really hard for me to adjust the frequency of the circuit for me.
Receiver circuit that receives the signals of 38 KHz.
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Simple visitor counter circuit using L.D.R. as receiver and led as transmitter
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REFERANCES: http://www.madlab.org/electrnx/lesson7.html http://www.circuitsgallery.com/2015/11/visitor-counter-circuit.html http://circuitdigest.com/electronic-circuits/555-timer-seven-segment-counter-circuit http://circuitdigest.com/electronic-circuits/object-counter-circuit-diagram http://www.engineersgarage.com/contribution/anjali/counter-using-ic-4026
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