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:

**Transistors**: The BC547 transistors will act as the switching elements in the circuit.**Resistors**: Use collector resistors (R1 and R2) and base resistors (R3 and R4) to control the timing and frequency of the oscillation.**Capacitors**: Cross-coupled capacitors (C1 and C2) are connected to the collectors of the transistors and set the frequency of the oscillation.**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.

### Calculating Component Values

### 1. **Determine the Frequency Formula**

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

$f \approx \frac{1.44}{(R1 + R2) \cdot (C1 + C2)}$### 2. **Choose Capacitor Values**

Assume you choose capacitors $C1$ and $C2$ as:

- $C1=C2=100\text{nF}$ which is $0.1\mu F$

### 3. **Calculate the Total Capacitance**

For simplicity, if $C$ and $C2$ are equal:

$C_{total} = C1 + C2 = 0.1 \mu F + 0.1 \mu F = 0.2 \mu F$### 4. **Calculate the Resistor Values**

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

$R1 + R2 = \frac{1.44}{f \cdot C_{tot$Substitute the values:

$R1 + R2 = \frac{1.44}{38 \text{ kHz} \cdot 0.2 \$Convert the units to get the result in ohms:

$f = 38 \text{ kHz} = 38 \times 10^3 \text{ Hz}$ $C_{total} = 0.2 \mu F = 0.2 \times 10^{-6} \text{ F}$ $R1 + R2 = \frac{1.44}{38 \times 10^3 \times 0.2 \times 10^{-6}}$ $R1 + R2 = \frac{1.44}{0.0076}$ $R1 + R2 \approx 189.5 \text{ k}\Omega$### 5. **Select Resistor Values**

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

- $R1=100\text{k}\mathrm{\Omega}$
- $R2=90\text{k}\mathrm{\Omega}$

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**: $C1=C2=100\text{nF}$(0.1 µF)**Resistors**: $R1=100\text{k}\mathrm{\Omega}$, $R2=90\text{k}\mathrm{\Omega}$ (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:

- Astable Multivibrator Using Transistors: A detailed guide on building an astable multivibrator with transistors.
- Astable Multivibrator with E-MOSFET: Explore how MOSFETs can be used in an astable multivibrator configuration.
- Transistor Astable Multivibrator: A comprehensive look at designing and implementing a transistor-based astable multivibrator.
- Astable 555 Timer as Siren or Alarm: Learn about using the 555 timer IC in an astable mode for sound generation.
- 555 Timer Online Calculator: An online tool for calculating component values for 555 timer circuits.
- Video Demonstration: See how the works,

** 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.