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Electronic Mosquito Repellent Circuit

Mosquito repellent such as coils, mats, liquid vaporizers, and creams are frequently utilised in a variety of settings. They are, nevertheless, prone to being lethal and can injure humans. Mosquito repellent creams and oils, for example, might have negative side effects on the skin, such as allergic responses. When heated, coils and mats can emit hazardous fumes that can cause respiratory problems, whereas heated liquid vaporisers can also emit fumes.

The most efficient option for efficient outcomes without any side effects is to create a basic electronic circuit with few components that can produce output to repel mosquitoes. In basic terms, this article will outline a simple mosquito repellent system.

Outline

  • Principle Behind Mosquito Repellent Circuit:
  • Circuit Diagram of Electronic Mosquito Repellent Circuit: 
  • Components Required
  • Mosquito Repellent Circuit Design:
  • Theory Behind the Circuit:
  • Mosquito Repellent Circuit Operation:
  • Applications of Mosquito Repellent Circuit:
  • Mosquito Repellent Circuit Limitations

Principle Behind Mosquito Repellent Circuit:

Humans can hear sounds in the 20 Hz to 20 kHz range. Ultrasonic sound is defined as sound with a frequency greater than 20 kHz. Several animals, including cats, dogs, insects, and mosquitoes, have the ability to perceive ultrasonic sound. This characteristic is due to the existence of sensory structures in mosquito antennae.

Male mosquitoes transmit ultrasound, which is received by female mosquitoes. Female mosquitoes, on the other hand, avoid ultrasound after breeding, and this feature can be exploited to produce ultrasonic in a range similar to that produced by male mosquitoes and hence repel mosquitoes. The mosqui’s antennae are stressed by the ultrasound.

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.

Circuit Diagram of Electronic Mosquito Repellent Circuit:

Mosquito Repellent
  • 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. For astable operation this pin is connected directly to pin no.6
  • 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. For astable operation, this pin is shorted to pin 2 and connected to pin 7 using a resistor.
  • Pin 7 – It is the discharge pin and provides the discharge path for the capacitor.

Components Required

  • 555 timer
  • 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
  •  piezo buzzer
  • A SPST switch
  • A 5 V battery

Mosquito Repellent Circuit Design:

The primary concept behind the circuit is to generate ultrasound using a buzzer. An oscillator circuit powers the buzzer. As the oscillator circuit, we’re utilising a 555 Timer based astable multivibrator circuit.

The circuit requires the creation of an astable multivibrator circuit. In general, the frequency of a 555 astable multivibrator’s output signal is provided by:

F = 1.44((Ra+Rb*2)*C)

Here Ra is the value of resistor between pin 7 and Vcc, Rb is value of resistor between pins 7 and 6 and C is value of capacitor between pin 6 and ground.

Let C = 0.01 microFarad

F = 38 kHz

Let Duty Cycle, D = 60% (It is not possible to get 555 timers to produce signal with 50% duty cycle.

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

Thus, we can use a resistor of 760 Ohms and another resistor of 1.5 K. Here a potentiometer of 1.5 K is used.

Theory Behind the Circuit:

  • 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.

Here we are mainly concerned about Astable multivibrator. Astable multivibrators do not require any external triggering and hence can be used as oscillators. They are realized using transistors, operational amplifiers or ICs.

Mosquito Repellent Circuit Operation:

The 555 timer receives electricity once the switch is closed. According to the inner circuit, the capacitor voltage will be 0 at first, resulting in zero voltage at the threshold and trigger pin. At some time, the voltage at the threshold pin is smaller than the capacitor voltage as the capacitor charges through resistors Ra and Rb. The output of the timer changes as a result of this. The capacitor now begins to discharge through resistor Rb, i.e. the discharge pin, and continues to discharge until the output voltage returns to its original value. As a result, the output signal is a 38 KHz oscillating signal.The output from this astable multivibrator circuit drives a 38 KHz piezo buzzer, producing ultrasound at regular repetitions. On varying the value of potentiometer, the output frequency can also be varied.

Applications of Mosquito Repellent Circuit:

As described, this circuit can be used as a mosquito repellent. By certain modifications and changes in the value of resistors and capacitor, the circuit can also be used as other insect repellent. Further, it can also be used as a simple buzzer alarm circuit.

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.
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