Hey, have you ever been kept awake by that annoying buzz of mosquitoes around your ear, or woken up with itchy bites all over? If you’re into DIY electronics like I am, you might want to try building this simple circuit that’s designed to keep those pests at bay. The image shows a basic electronic mosquito repellent setup using the CD4047 IC, which generates a sound frequency meant to drive mosquitoes away. I’ll walk you through the analysis of the diagram, explain how it works, list the parts, show you the math behind the frequency, and give you step-by-step instructions to build it. We’ll also talk about the science and whether these things actually do the job, based on what I’ve dug into. Let’s get started.
Understanding the Circuit’s Purpose
This circuit is all about creating an ultrasonic or high-frequency sound that mosquitoes supposedly hate. The idea is that female mosquitoes, the ones that bite, avoid certain frequencies because they mimic the wing beats of male mosquitoes or predators like dragonflies. The diagram labels it as an “Electronic Mosquito Repellent,” and it uses a piezo buzzer to emit the sound. It’s powered by 12V DC, which makes it suitable for battery operation or even plugging into a car’s power outlet for outdoor use.
From what I see in the image, the core is the CD4047 IC, a versatile CMOS chip that can act as an astable multivibrator to produce oscillating signals. The output drives a pair of transistors in a push-pull configuration to amplify the signal for the piezo buzzer. There’s also a decoupling capacitor to smooth the power supply. It’s a compact design, probably from a hobbyist site like A2a Electronics, and it’s meant to be low-cost and easy to assemble.
Components You’ll Need
The diagram keeps it simple with just a few parts. Here’s the list based on what’s shown:
- CD4047 IC: This is the main chip, a low-power multivibrator that generates the square wave signal.
- R1: 10K ohm resistor: Connected to the timing pins to set the oscillation frequency.
- C1: 4.7nF capacitor: Works with R1 for timing the oscillations.
- C2: 22uF, 16V electrolytic capacitor: Likely for power supply decoupling to filter noise and stabilize the 12V input.
- Transistors: Two NPN transistors (they look like BC547 or similar in the diagram, though not explicitly labeled). They’re arranged in a push-pull setup to drive the buzzer efficiently.
- Piezo Buzzer: The output device that converts the electrical signal into sound waves.
- Power Supply: +12V DC source, such as a battery or adapter.
- Miscellaneous: Breadboard for prototyping, jumper wires, and perhaps a small PCB if you want a permanent build.
You can grab these from any online electronics store or your local hobby shop. The total cost should be under $5 if you skip the fancy enclosures. Make sure the transistors can handle the current for the buzzer – the 2N3055 from your previous flasher project would be overkill here, but something small like BC547 works fine.
How the Circuit Works
Let’s break down the diagram step by step. The CD4047 is wired in astable mode, which means it continuously flips between high and low states without any external trigger. That’s perfect for generating a steady tone.
Power comes in at +12V DC, connected to pin 14 (VDD) of the IC, with ground at pin 7 (VSS). C2, the 22uF cap, sits across the power rails to keep things stable and prevent voltage spikes from messing with the oscillations.
The timing components are R1 (10K) and C1 (4.7nF). In the standard astable configuration for CD4047, the capacitor C1 connects between pins 1 and 3, and the resistor R1 between pins 2 and 3. The diagram shows this setup, though the lines are a bit crowded. Pins 4, 5, and 6 are configured to enable astable operation (pin 5 high, pin 4 low, etc.).
The outputs are at pins 10 (Q) and 11 (/Q), which are complementary – when one is high, the other is low. These drive the bases of the two transistors. The transistors are in a push-pull arrangement, meaning one pulls the buzzer high while the other pushes it low, effectively doubling the voltage swing across the piezo for louder output without needing a higher supply voltage.
The piezo buzzer connects between the collectors of the transistors, with emitters to ground or power as needed. When the IC oscillates, it creates a square wave that makes the buzzer vibrate at the set frequency, emitting sound waves. No fancy amplifiers here – the transistors handle the power directly.
Calculating the Frequency
One of the cool parts about this circuit is tweaking the frequency to target mosquitoes. The formula for the output frequency at Q (pin 10) in astable mode is f = 1 / (4.4 * R * C), where R is in ohms and C in farads. Some sources note that the oscillator frequency (at pin 13) is twice that, but since we’re using Q and /Q, the buzzer sees the Q frequency.
Plugging in the values: R = 10,000 ohms, C = 4.7 × 10^-9 F.
First, calculate 4.4 * R * C = 4.4 * 10,000 * 4.7 × 10^-9 = 4.4 * 4.7 × 10^-5 = 20.68 × 10^-5 = 0.0002068.
Then, f = 1 / 0.0002068 ≈ 4,836 Hz, or about 4.8 kHz.
That’s in the audible range for most people – think of it as a high-pitched whine. If you want to push it into ultrasonic territory (above 20 kHz), you could swap C1 for a smaller value, like 0.47nF, which would give f ≈ 48 kHz. Or add a potentiometer in series with R1 to adjust on the fly. The diagram sticks to fixed values, but experimenting is half the fun.
Step-by-Step Guide to Building It
Building this is straightforward, even if you’re new to soldering. Start on a breadboard to test.
- Place the CD4047 IC on the breadboard. Connect pin 14 to +12V and pin 7 to ground.
- Add C2 (22uF) across +12V and ground – positive leg to +12V.
- For timing: Connect C1 (4.7nF) between pins 1 and 3. Connect R1 (10K) between pins 2 and 3.
- Set up astable mode: Connect pin 5 to +12V, pin 4 and pin 6 to ground (or follow the exact ties in the diagram – pins 4,5,6 might have specific connections, but standard is pin 4 low, pin 5 high).
- Wire the outputs: Pin 10 (Q) to the base of one transistor via a small resistor if needed (diagram shows direct, but 1K can protect). Pin 11 (/Q) to the other transistor’s base.
- Transistors: Collectors to the piezo buzzer terminals, emitters to ground for one and +12V for the other? Wait, in push-pull, typically both emitters to ground, collectors to buzzer ends, with buzzer center-tapped or direct. The diagram shows the buzzer connected across the transistors.
- Power it up with 12V. You should hear a tone from the buzzer. If not, check connections – the CD4047 is sensitive to static, so handle carefully.
- For a permanent version, solder on a perfboard, add a switch, and enclose in a small box. Test outdoors to see if mosquitoes steer clear.
If the sound is too loud or annoying, enclose the buzzer or adjust the components. Remember, at 4.8 kHz, you and your neighbors might hear it, so ultrasonic tweaks could help.
The Science Behind Mosquito Repellents Like This
Now, let’s get real about whether this works. The theory is that mosquitoes detect sound vibrations through their antennae and avoid frequencies that signal danger. Some sources suggest 38-44 kHz repels them, mimicking bat echolocation or other threats. Others point to 15-25 kHz as effective. There’s even talk of lower frequencies like 5-7 kHz mimicking male wing beats, which mated females avoid.
But here’s the catch: A lot of studies show these ultrasonic devices don’t do much. A 2010 review of 10 field tests found no effect on mosquito bites. The BBC reported in 2012 that there’s “no scientific evidence whatsoever” for ultrasound repelling mosquitoes. More recent takes, like a 2023 Reddit discussion and a 2020 study, echo that – mosquitoes might hear, but they don’t flee from these sounds long-term. Even as of 2025, sources like Forbes and PubMed studies confirm they’re ineffective, with pests habituating quickly.
On the flip side, some Amazon products in 2025 claim success with 20-60 kHz ranges, and anecdotal reports exist. But that’s marketing – the FTC has cracked down on false claims. In my view, this circuit is more of a fun project than a reliable solution. Pair it with proven methods like DEET sprays, nets, or eliminating standing water for better results.
Variations and Improvements
If 4.8 kHz isn’t cutting it, modify! Replace R1 with a 100K pot to tune from low audible to higher frequencies. For true ultrasonic, drop C1 to 1nF for about 23 kHz. You could add a 555 timer for dual tones or use a microcontroller like Arduino for programmable sweeps.
Some circuits use 555 IC instead, but CD4047 is efficient for battery life. For power, switch to 9V if 12V is too much, or add solar for outdoor setups.
Safety Considerations
This is low-voltage, so no big shocks, but be careful with the power supply – don’t short the battery. The sound might annoy pets or kids with sensitive hearing, especially if audible. If modifying to ultrasonic, test that it doesn’t interfere with devices like hearing aids. And remember, this isn’t a substitute for medical advice on mosquito-borne diseases like malaria – use it as a supplement.
Final Thoughts
There you go – a complete rundown on this electronic mosquito repellent circuit. It’s a neat way to dip into multivibrators and audio generation, even if the repelling effect is debatable. Build it, test it in your backyard, and see for yourself. If mosquitoes still crash the party, at least you’ll have learned something. Drop me a line if you tweak it or find a better frequency. Stay bite-free!
