ABACUS INSTITUTE OF ENGINEERING & MANAGEMENT

MOSQUITO REPELLENT CIRCUIT TO GENERATE A FREQUENCY RANGE BETWEEN 20-38 kHz

BY

RAHUL NANDY,ROLL NO : 24000311034,REGISTRATION NO : 112400110096

REGISTRATION NO: 112400110107SOUMYAJIT DE,ROLL NO: 24000311034,

DEBJYOTI BISWAS,ROLL NO : 24000311015,REGISTRATION NO : 112400110077

REGISTRATION NO: 112400110096

REGISTRATION NO: 112400110096

ROLL NO : 24000311034,

ROLL NO: 24000311046,SOUNAK MAJUMDAR,

SAGNIK DASGUPTA,

Under The Supervision of

Assistant Professor ABACUS INSTITUTE OF ENGINEERING & MANAGEMENT Mrs. SUCHANDANA ROY

ACKNOWLEDGEMENT

First of all we would like to thanks all the member of Abacus Institute of Engineering & Management for helping us for the project and for her continuous guidance and support. We would like to thank others faculty members of our department.We would also like to thank everyone in the list. The developers of this project was also very helpful. Finally we would like to thank our family and friends for putting up with our constant moaning about the project and supporting us through the difficult times.

CONTEXT1. Abstract2. Acknowledgment

3. Theory behind the circuit 4. Circuit Diagram5. Equipment

6. Theory7. Use of 555 timer8. Astable Multivibrator9. Capacitor10. Resistor

11. Mosquito Repellent Circuit Limitations

Principle Behind Mosquito Repellent Circuit:

THEORY BEHIND THE CIRCUIT :

* Human beings can hear sound in the range of 20 Hz to 20 kHz

* Sound of any frequency above 20 kHz is termed as ultrasonic sound. Several animals like cats, insects, mosquitoes have the feature of being able to hear this ultrasonic sound. *Usually ultrasound is transmitted by male mosquitoes and received by female mosquitoes

*After breeding, female mosquitoes generally avoid the ultrasound and this fact can be used to produce ultrasound in a range similar to that produced by male mosquitoes and repel away the mosquitoes.

*In other words, a simple circuit is designed which can produce ultrasound in the frequency range of 20 kHz to 38 kHz, which can scare away mosquitoes.

Mosquito Repellent Circuit Operation:

1.Once the switch is closed, the 555 timer gets the power supply. 2.The inner circuit, initially the capacitor voltage will be zero and hence voltage at threshold and trigger pin will be zero. 3.The capacitor charges through resistors Ra and Rb, at a certain point voltage at threshold pin is less than the capacitor voltage. 4.This causes a change in timer output. 5.The capacitor now starts discharging through resistor Rb, i.e. the discharge pin and continues so until the output voltage is back to the original. 6.Thus the output signal is an oscillating signal with frequency 38 KHz.

7.The output from this astable multivibrator circuit drives a 38 KHz piezo buzzer, producing ultrasound at regular repetitions.

Circuit Diagram of Electronic Mosquito Repellent Circuit: 

Mosquito Repellent Circuit Design:

*The basic idea behind developing the circuit is to use a buzzer to produce ultrasound. The buzzer is driven by an oscillator circuit*A 555 Timer based astable multivibrator circuit as the

oscillator circuit. * The frequency of output signal produced by a 555 astable multivibrator is given by:

F = 1.44((Ra+Rb*2)*C) Ra =resistor between pin 7 and Vcc, Rb =resistor between pins 7 and 6

C =capacitor between pin 6 and ground. Let C = 0.01 microFarad ,F = 38 kHz

Let Duty Cycle, D = 60% This gives,Ra = 1.44(2D-1)/(F*C)And Rb=1.44(1-D)/(F*C) Substituting values of C, F and D, we get

Ra = 0.758 K Ohms, i.e. 758 Ohms and Rb = 1.52 K Ohms

Equipment:•An electrolyte capacitor of 0.01 micro Farad

• A ceramic capacitor of 0.01 micro Farad

•A resistor of 760 Ohms

•Another resistor of 1.5 K

•A 38 kHz pizzo buzzer

•A SPST switch

•A 5 V battery

•C.R.O

Theory:

*A multivibrator is an electronic circuit producing a pulsed output signal. Generally multivibrators are classified based on the nature of stability of output

*A multivibrator with one stable state is known as monostable multivibrator and is used as a pulse generator.

*A multivibrator with no stable state is known as an astable multivibrator and is used as an oscillator.

*A multivibrator with two stable states is known as a bistable multivibrator and is used as a Schmitt Trigger.

**Astable multivibrators do not require any external triggering and hence can be used as oscillators.

Use of 555 timer:The most common form of Astable multivibrator is 555 Timer IC. It is basically an 8 pin IC with the following pin description:

Pin1 – Ground pin, which is directly connected to the negative terminal of the battery.

Pin2- Trigger Pin. It is an active low pin. The timer is triggered when signal at this pin is less than one third of supply voltage. Pin 3 – It is the output pin.

Pin 4 – It is the reset pin. It is an active low pin. It is usually connected to positive rail of the battery

Pin 5 – It is the control pin and is seldom used. For safety purpose, this pin is connected to ground through a 0.01microFarad ceramic capacitor.

Pin 6 – It is the threshold pin. The timer output is back to its stable state when voltage at this pin is greater than or equal to two-third of supply voltage.

Pin 7 – It is the discharge pin and provides the discharge path for the capacitor.

Astable Multivibrator (AMV):

*In the 555 Oscillator circuit above, pin 2 and pin 6 are connected together allowing the circuit to re-trigger itself on each and every cycle allowing it to operate as a free running oscillator.

*During each cycle capacitor, C charges up through both timing resistors, R1 and R2 but discharges itself only through resistor, R2 as the other side of R2 is connected to the discharge terminal, pin 7.

*Then the capacitor charges up to 2/3Vcc (the upper comparator limit) which is =0.693(R1+R2)C combination and discharges itself down to 1/3Vcc (the lower comparator limit)= 0.693(R2.C) combination.

*Output waveform whose voltage level is approximately equal to Vcc – 1.5V and whose output “ON” and “OFF” time periods are determined by the capacitor and resistors combinations

BATTERY: *An electric battery is a device

consisting of two or more electrochemical cells that convert stored chemical energy into electrical energy.

*Each cell contains a positive terminal, or cathode, and a negative terminal, or anode. *Electrolytes allows ions to move between the electrods & terminals,which allows current to flow out of the battery to perform work.Resistors:

There is always some resistance in every circuit.

• A circuit is always made up of some wire, so there will be some resistance there.

• Even the battery has parts that offer resistance to the flow of electrons.

• The only circuits that come near to zero resistance are superconductors.

This resistance that is from the parts of the circuit itself (especially the battery) is called internal resistance.

Capacitor:

*A ceramic capacitor is a fixed value capacitor in which ceramic material acts as the dielectric. *It is constructed of two or more alternating layers of ceramic and a metal layer acting as the electrodes.

Ceramic capacitors are divided into two application classes:• Class 1 ceramic capacitors offer high stability and low losses for resonant circuit applications.

• Class 2 ceramic capacitors offer high volumetric efficiency for buffer, by-pass, and coupling applications.

*Ceramic capacitors, especially the multilayer style (MLCC), are the most produced and used capacitors in electronic equipment

*Ceramic capacitors of special shapes and styles are used as capacitors for RFI/EMI suppression, as feed-through capacitors and in larger dimensions as power capacitors for transmitters.

ceramic capacitor:

Electrolytic capacitor:

Electrolytic capacitors is the generic term for three different capacitor family members: • Aluminum electrolytic capacitors, Tantalum electrolytic capacitors and Niobium electrolytic capacitors

All electrolytic capacitors (e-caps) are polarized capacitors whose anode electrode (+) are made of a special metal on which an insulating oxide layer originates by anodically oxidation (forming), which acts as the dielectric of the electrolytic capacitor The large capacitance of electrolytic

capacitors makes them particularly suitable for passing or bypassing low-frequency signals up to some mega-hertz and storing large amounts of energy. Electrolytic capacitors are polarized components by the manufacturing principle and may only be operated with DC voltage. Voltages with reverse polarity, or voltage or ripple current higher than specified, can destroy the dielectric and thus the capacitor.

SPST switch: A Single Pole Single Throw (SPST) switch is a switch that only has a single input and can connect only to one output. This means it only has one input terminal and only one output terminal. 

A Single Pole Single Throw (SPST) switch serves in a circuit as on off witchs.

38 kHz piezo buzzer: *Piezo buzzer is an electronic device commonly used to produce sound.

*Light weight, simple construction and low price make it usable in various applications like car/truck reversing indicator, computers, call bells etc

*It is the phenomena of generating electricity when mechanical pressure is applied to certain materials and the vice versa is also true.

*Such materials are called piezo electric materials.

Mosquito Repellent Circuit Limitations:

•It requires a lot of frequency setting.

•Ultrasound signals travel at an angle of 45 degrees from the source. In case of any obstacles in the path, the signals get reflected or diverted.

•It shows effect for lesser mosquito population.

Progress of The Project :IN PROJECT I :

we had collect all the information of the project and the equipments then we design the circuit using pspice and run it and got the graph which generate frequency near about 38khz.And we also made a power point presentation on our project and displayed it in PROJECT I lab. Exam.

IN PROJECT II:

This semester we make the circuit in hardware using Resistor,Capacitance,555 timer,SPST Switch,Power supply 5V,CRO.we obtain the frequency using CRO using make the circuit in bread board.

CONCLUSIONS:

We conclude that the experimental values is near about the theoretical values. the frequency generate near 38khz not properly. the circuit is successfully done and get the expected result approximately.

References:

All the information about the circuit ,equipment ,theory behind the circuit and the circuit diagram we got from the book “ELECTRONICS Fundamental and Applications” written by D.Chattopadhyay and P.C.Rakshit. Also our respective mam Mrs. Suchandana Roy and all the assistant professors of ECE department of Abacus Institute of Engineering and Management help us to get success in our project.