DIY Mosquito Repellent Circuit

Mosquitoes are a common nuisance, especially in warmer climates, and finding effective ways to repel them can make a big difference in comfort. One innovative method to tackle this problem is using an electronic circuit that generates sound waves to deter mosquitoes. Here, we’ll explore a DIY mosquito repellent circuit based on an astable multivibrator, a simple yet effective solution.

Understanding the Astable Multivibrator Circuit

An astable multivibrator is a type of oscillator circuit that continuously switches between its high and low states, generating a square wave output. This circuit can be built using various components, but for this mosquito repellent application, we'll use transistors to create a sound frequency that repels mosquitoes.

Components Needed

  • Transistors: BC547 (or similar NPN transistors)
  • Resistors: Collector resistors, base resistors
  • Capacitors: For timing and frequency setting
  • Piezo Buzzer: To produce the sound
  • Power Supply: 9V battery or equivalent

Circuit Design

The core of the circuit is an astable multivibrator built with two BC547 transistors. Here's a basic overview of how to set it up:

  1. Transistors: The BC547 transistors will act as the switching elements in the circuit.
  2. Resistors: Use collector resistors (R1 and R2) and base resistors (R3 and R4) to control the timing and frequency of the oscillation.
  3. Capacitors: Cross-coupled capacitors (C1 and C2) are connected to the collectors of the transistors and set the frequency of the oscillation.
  4. Piezo Buzzer: Connected across the collectors of the transistors to emit sound at the desired frequency.

To design a mosquito repellent circuit using an astable multivibrator, you will want to set the frequency to a value that is effective for repelling mosquitoes. Common frequencies used are in the ultrasonic range, typically between 20 kHz and 65 kHz. Let’s assume you want to design the circuit to operate at 38 kHz, which is a frequency often cited for mosquito repellents.

See the following DIY Mosquito Repellent Circuit diagram.

DIY Mosquito Repellent Circuit

Calculating Component Values

1. Determine the Frequency Formula

For an astable multivibrator using NPN transistors, the frequency f of oscillation is given by:

f1.44(R1+R2)(C1+C2)f \approx \frac{1.44}{(R1 + R2) \cdot (C1 + C2)}

2. Choose Capacitor Values

Assume you choose capacitors C1 and C2 as:

  • C1=C2=100 nF which is 0.1μF

3. Calculate the Total Capacitance

For simplicity, if C1C and C2C2 are equal:

Ctotal=C1+C2=0.1μF+0.1μF=0.2μFC_{total} = C1 + C2 = 0.1 \mu F + 0.1 \mu F = 0.2 \mu F

4. Calculate the Resistor Values

Rearrange the frequency formula to solve for R1+R2R1 + R2:

R1+R2=1.44fCtotalR1 + R2 = \frac{1.44}{f \cdot C_{tot

Substitute the values:

R1+R2=1.4438 kHz0.2μFR1 + R2 = \frac{1.44}{38 \text{ kHz} \cdot 0.2 \

Convert the units to get the result in ohms:

f=38 kHz=38×103 Hzf = 38 \text{ kHz} = 38 \times 10^3 \text{ Hz} Ctotal=0.2μF=0.2×106 FC_{total} = 0.2 \mu F = 0.2 \times 10^{-6} \text{ F} R1+R2=1.4438×103×0.2×106R1 + R2 = \frac{1.44}{38 \times 10^3 \times 0.2 \times 10^{-6}} R1+R2=1.440.0076R1 + R2 = \frac{1.44}{0.0076} R1+R2189.5 kΩR1 + R2 \approx 189.5 \text{ k}\Omega

5. Select Resistor Values

Choose resistor values that add up to approximately 189.5 kΩ. For instance:

  • R1=100 kΩ
  • R2=90 kΩ

You can use standard resistor values close to these numbers or use a potentiometer for fine-tuning.

Summary

For a mosquito repellent circuit designed to oscillate at 38 kHz:

  • Capacitors: C1=C2=100 nF(0.1 µF)
  • Resistors: R1=100 kΩ, R2=90 kΩ (or resistors adding up to approximately 190 kΩ)

You may need to adjust component values slightly during testing to fine-tune the frequency.

Learning More About Astable Multivibrators

To build a deeper understanding of the astable multivibrator and its variations, you might find these resources helpful:

  Video Demonstration: See how the DIY Mosquito Repellent Circuit works,

Conclusion

Creating your own mosquito repellent circuit using an astable multivibrator is a practical and engaging project. By understanding and utilizing the principles of oscillation and sound frequency, you can effectively deter mosquitoes and enjoy a more comfortable environment. Experiment with different component values and configurations to fine-tune your circuit and achieve the best results.

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