People frequently use mosquito repellents like coils, mats, liquid vaporizers, and creams in various settings. However, these repellents can pose a danger and harm humans. For instance, mosquito repellent creams and oils may cause adverse effects on the skin, such as allergic reactions. Coils and mats, when heated, can release hazardous fumes leading to respiratory problems, while heated liquid vaporizers can also emit harmful fumes.
To achieve effective results without any side effects, the most efficient approach is to create a basic electronic circuit with a few components that can generate an output to repel mosquitoes. In simple terms, this article will outline how to build a straightforward 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 have the ability to hear sounds within the range of 20 Hz to 20 kHz. Ultrasonic sound, characterized by a frequency greater than 20 kHz, is perceivable by various animals, including cats, dogs, insects, and mosquitoes. The existence of sensory structures in mosquito antennae accounts for this capability.
Male mosquitoes emit ultrasound, which female mosquitoes detect. However, post-breeding, female mosquitoes actively avoid ultrasound. Exploiting this behavior, one can generate ultrasound in a frequency range similar to that produced by male mosquitoes to repel them. The ultrasound stresses the antennae of mosquitoes.
In simpler terms, we design a straightforward circuit that actively produces ultrasound in the frequency range of 20 kHz to 38 kHz, effectively deterring mosquitoes.
Circuit Diagram of Electronic Mosquito Repellent Circuit:
- 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:
An electronic circuit that generates a pulsed output signal is called a multivibrator. Multivibrators are generally categorized based on the stability of their output.
- A multivibrator that possesses only one stable state is referred to as a monostable multivibrator and serves as a pulse generator.
- An astable multivibrator, which lacks a stable state, functions as an oscillator.
- A bistable multivibrator, with two stable states, is known as a Schmitt Trigger.
Our primary focus here is on the astable multivibrator. Astable multivibrators, acting as oscillators, do not rely on external triggering and can be implemented using transistors, operational amplifiers, or integrated circuits (ICs).
Mosquito Repellent Circuit Operation:
Once the switch is closed, the 555 timer circuit receives electrical power. As per the internal circuitry, the capacitor initially holds a voltage of 0, causing the threshold and trigger pins to register zero voltage. Eventually, as the capacitor charges through resistors Ra and Rb. There comes a point where the voltage at the threshold pin becomes lower than the capacitor voltage. This alteration triggers a change in the timer’s output.
Subsequently, the capacitor commences discharging through resistor Rb, designated as the discharge pin, and continues to discharge until the output voltage returns to its initial value. Consequently, the output signal becomes a 38 KHz oscillating signal. This oscillating signal drives a 38 KHz piezo buzzer in the astable multivibrator circuit, generating ultrasound at regular intervals. By adjusting the potentiometer’s value, the output frequency can be varied.
Applications of Mosquito Repellent Circuit:
As previously explained, one can utilize this circuit as a mosquito repellent. With specific adjustments and alterations to the resistor and capacitor values, the circuit can also function as an insect repellent for various pests. Furthermore, it has the capability to serve as a straightforward buzzer alarm circuit.
Mosquito Repellent Circuit Limitations
- Setting the frequency demands significant effort.
- Ultrasound signals emanate from the source at a 45-degree angle. If any obstacles obstruct their path, these signals either reflect or divert.
- It exhibits its efficacy when dealing with a smaller mosquito population.
