How to Build an Ultrasonic Mouse Repellent Circuit Using a 555 Timer

Mice are more than just annoying—they can be destructive. From gnawing on electric cables to damaging stored papers, rodents can cause serious harm to your home, office, or archives. Fortunately, you don’t need poison or traps to keep them away. A simple ultrasonic repellent circuit can do the job—and you can build it yourself.

🧠 How Does It Work?

The concept behind this mouse repellent is based on sound—ultrasonic sound, to be precise. Mice have very sensitive hearing and are irritated by high-frequency tones that humans can't hear.

This circuit generates a tone of around 50kHz, which is unpleasant for rodents but inaudible to humans. Once powered on, it continuously emits the ultrasonic signal to discourage mice from entering the area.

🔧 Key Components and Operation

The core of the circuit is a 555 timer IC, configured as an astable multivibrator. Here's how each part works:

Component	Function
IC 555 Timer	Generates a 50kHz square wave signal
C1 & C3	Determine the output frequency
SC1162 Transistor	Amplifies the output signal
Speaker	Converts the electric signal to ultrasonic sound
Power Source	9V or 12V DC supply

The output from the 555 timer is passed to a transistor amplifier, which then drives a piezoelectric speaker or high-frequency tweeter.

The frequency formula used is:
f = 1 / (0.693 × (R1 + 2 × R2) × C)
This setup is tuned to hit that irritating sweet spot—around 50kHz.

📘 Why Ultrasonic?

🐭 Mice find high frequencies painful or uncomfortable
👂 Humans can’t hear above 20kHz
🌿 No chemicals, no traps, no mess
💡 Works 24/7 once installed

Ultrasonic frequencies create an environment that mice naturally avoid. Over time, they will relocate without needing any direct intervention.

⚠️ Important Tips

Use a high-quality speaker that can handle ultrasonic ranges
Place the device in a closed space for better effectiveness
Don’t expect results instantly — ultrasonic deterrents often take a few days
This device doesn’t kill rodents; it only keeps them away

🛠️ Optional Enhancements

Add an ON/OFF switch or a light indicator
Integrate a motion sensor to activate it only when movement is detected
Enclose in a vented plastic case for safety and aesthetics
Add a solar panel to make it off-grid for outdoor use

🔌 Power Options

The circuit can be powered using a standard 9V battery, a 12V DC adapter, or even a USB-to-DC step-up converter.

🧰 Parts List

Item	Quantity
NE555 Timer IC	1
Resistors	2–3
Capacitors (C1, C3)	2
SC1162 Transistor (or similar NPN)	1
Speaker (Ultrasonic or Piezo)	1
Power supply	1

📍 Final Thoughts

Building a mouse repellent circuit is a smart and sustainable way to keep your space rodent-free. It’s cheap, efficient, and non-lethal. Plus, it's a great beginner-friendly electronics project using the timeless 555 timer.

If you have valuable files, electronics, or even food storage that needs protection, this ultrasonic mouse repeller is a practical and effective solution. Try it out and see the results for yourself!