In India there are 6 seasons, one season almost covers 3 months. The Rainy and summer season is a recall for newborn insects to come out on the earth surface. As the rain continue the water get collected in streets or in small pits near houses. And cause insect night out on these places. We can’t kill every mosquito but we can mark the prohibited area. So, let’s build a circuit to repel the mosquitoes and see how it works.
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Which mosquito bites:
Male mosquitoes feed only on plant juices, such as nectar, to get the sugar they need for energy and survival. As males do not bite, they cannot transmit diseases.
Female mosquitoes, on the other hand, need protein from blood for the development of their eggs. Only female mosquitoes bite people and animals to get a blood meal. Even the blood meal taking process in female mosquitos start after meeting with male mosquitoes. And after that female mosquito doesn’t bear and male mosquito near her.
How repellent works:
Male mosquito emits ultrasonic waves to in the search of food. When these waves came in contact with any female mosquito, she find a place to hide or to fly back to other area. Using the same idea we can create a repellent circuit which can produce ultra sound of the desirable frequency to repel the female mosquito. Therefore, No need to kill the mosquitoes anymore.
Here we are using low power animal hearing range ultrasound to repel the mosquitos because they are affected under a ultrasonic range of 22khz to 40khz. So, please don’t use this circuit if you are a pet owner.
1) NE 555 timer ic
2) Passive buzzer
3) 220R, 2K and 18K resistor
4) 10k Potentiometer
5) 10nf capacitors
6) Tactile switch
7) 5V- 9v power supply/ battery
8) Custom PCB from JLCPCB
We are using timer 555 ic which can be operated as multi vibrator and for this circuit we are using this in astable configuration. This astable multivibrator can provide the desirable frequency range under its capabilities without any external trigger pulse. So, it is a free running self-triggered mode rectangular oscillator circuit. This one has two quasi stable states (high and low). Frequency and duty cycle can be adjusted using 2 resistor and capacitors. The circuit can be tuner by performing different tests. Passive buzzers are made to work with triggered frequency, so the output of 555 is connected with it.
Basic circuit diagram:
Here in the circuit diagram 100k resistor is R2 and 1K resistor is R1. C is the electrolytic capacitor connected at pin 2 of the IC.
Time for the output should be high: 0.693*(Rt1+Rt2) *Ct
Time for the output of oscillator is low: 0.693* Rt2*Ct
I designed the schematics and PCB using EasyEda. The circuit is quite simple either you can use this design from here or build your own using the circuit diagram given above.
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The concept of working is quite simple, through the 555 multi vibrator we are getting a square wave of adjustable frequency. which can be tuner as per area requirements. A passive buzzer is connected to the output of 555 which directly trigger it and thus produce a ultrasound.
This sound is out of human audible range so there is no effect of that sound on human ears. If you can hear the sound that means the circuit is not tuned properly in ultrasound range. See the video and have a look on those crazy waveforms.