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.

Calculating Component Values

1. Determine the Frequency Formula

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

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:

4. Calculate the Resistor Values

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

Substitute the values:

Convert the units to get the result in ohms:

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,