555 Timer Based Mosquito Repeller
Basically this circuit will produce an ultrasound of around 40KHz which will be not audible by human but this frequency is generally used in electronic mosquito repellers to scare away the mosquitoes.
Concept of this mosquito repellent circuit is quite simple. 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.