Police Siren Circuit using 555 Timer IC | DIY Electronics Project
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✅ Introduction
Police sirens are widely used in security systems, emergency vehicles, and hobby electronics. In this blog post, we will show you how to build a police siren sound circuit using two 555 Timer ICs. The sound resembles the “wee-woo” effect of actual police sirens by modulating frequency.
This is a fun and beginner-friendly electronics project for anyone interested in sound circuits or learning 555 timer applications.
Materials for the Project
- 2x 555 TIMER IC
- 1x BD139 TRANSISTOR
- 2x 1N4007 DIODES
- 2x nF CAPACITORS
- 1x 10uF CAPACITOR
- 1x 47uF CAPACITOR
- 2x 100uF CAPACITORS
- 2x 1K RESISTORS
- 3x 10K RESISTORS
- 2x 47K RESISTORS
- 1x SWITCH (SPST)
- 1x SPEAKER
- VERO BOARD
- JUMPER WIRES
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Working Principle
This siren circuit uses two 555 Timer ICs in the following configuration:
1. IC1 (Tone Generator):
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Generates a base audio frequency (around 440 Hz to 1 kHz).
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Connected to the speaker.
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2. IC2 (Modulator):
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Modulates the frequency of IC1 slowly up and down.
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Creates a rising and falling tone—similar to police sirens.
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Download Circuit Diagram
Circuit Diagram
How It Works
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The first 555 Timer (IC2) is configured as a low-frequency oscillator.
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The second 555 Timer (IC1) produces a tone whose pitch is controlled by the output of IC2.
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As the voltage from IC2 varies, the frequency of IC1 increases and decreases, producing a siren-like sound.
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The signal is sent to a speaker or buzzer to generate the sound.
Output Sound
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The sound pattern mimics emergency vehicle sirens:
“WEEE-WOOO-WEEE-WOOO” -
You can change the resistor or capacitor values to:
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Slow down or speed up the siren
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Change pitch
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Make it more dramatic or subtle
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Power Supply Options
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9V battery
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5V USB power bank
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6V battery pack
Make sure your speaker matches your voltage supply to avoid distortion or damage.
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DIY security alarm systems
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Emergency sound simulators
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School science projects
Conclusion
Building a police siren using 555 timer ICs is a simple, affordable, and educational electronics project. It’s a great way to understand the power of 555 timers, frequency modulation, and audio generation. You can easily build it on a breadboard and even integrate it with motion sensors or lights for more advanced DIY projects.
For more DIY electronics circuits and tutorials, keep visiting SekhoHub.online—Pakistan’s growing platform for electronics learners and makers.