Electronic Mosquito Repellent Circuit

Various mosquito repellent solutions like coils, liquid vaporizers, and creams, all have possible adverse effects to health. Then there are electronic mosquito repellents available in market which are equally efficient and relatively safer. The concepts of these mosquito repellers are simple and we can build a simple mosquito repellent circuit at home easily by using 555 timer IC and few other commonly available components. Let’s see the concept of mosquito repellent circuit in detail.

The concept that we are going to use in out circuit is related to ultrasound. A sound with frequency higher than 20 kHz is termed as “Ultrasound”. For we humans a sound only ranging between 20 Hz to 20 kHz frequency is audible, and any sound with frequency below or higher than this range wouldn’t be audible for us. But there are various animals and insects (including mosquitos) that could hear the ultrasound. Generally ultrasound in a range of 20 kHz to 40kHz is transmitted by male mosquitoes and received by female mosquitoes, however after breeding female mosquitoes tend to avoid male mosquitoes and so they tend to avoid ultrasound in that range. As we know that only female breeding mosquitoes bites humans, we can use this concept and can design a circuit which produces the ultrasound in frequency range specified above.

So here we are going to design a simple mosquito repellent circuit which will be producing a sound of approximately 40 kHz.

Required Components

555 Timer IC

Buzzer

Resistors - 1k and 1.3k (variable resistor of 10k)

Capacitor - 0.01µF

Battery - 9v

Breadboard and connecting wires

Circuit Diagram and Explanation

As shown in the above diagram, we have designed a circuit using 555 timer IC in Astable mode to produce 40 kHz frequency sound. We have connected Buzzer at the output (PIN 3) of the 555 timer IC so that a sound of desired frequency can be generated. We should note here that we need a HIGH frequency Piezo buzzer, so that a high frequency sound can be generated. Also note that we might not be able to hear the sound, generated by the circuit as it is beyond our audible range.

We can calculate the value of resistors and capacitor to produce oscillation of 40KHz frequency by given formulae:

F = 1.44 / ((R1+R2*2)*C)

In our case we have used:

R1= 1K

R2(RV1) = 1.3 K (variable resistor of 10k, set at 1.3K with the help of multimeter)

C = 0.01uF

So now

F = 1.44 / {(1 + 2*1.3)*1000} * 0.01uF

F = 1.44 * 100000 / 3.6 = 40000 = 40KHz

We can increase the value of resistor R1 or R2 to decrease the frequency.