Siren Generator Circuit Using UM3561 Ic With Bc 547 Transistor
by prem saini26 in Circuits > Electronics
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Siren Generator Circuit Using UM3561 Ic With Bc 547 Transistor

This is a simple yet very useful siren sound generator circuit built using the UM3561 IC, a BC547 transistor, a few resistors, and a buzzer. The circuit operates on a 3V DC battery and can generate police siren-like sounds. It’s widely used in toys, alarms, and learning projects.
Supplies

UM3561 IC
- Known as a "Multi-Sound Siren IC".
- It is capable of generating multiple siren tones.
- A 220KΩ resistor is connected between Pin 7 and Pin 8 to set the oscillation frequency.
BC547 NPN Transistor
- The output from UM3561 is very weak and cannot directly drive a buzzer.
- Therefore, the output pin (Pin 3) is connected to the base of the BC547 transistor via a 100Ω resistor.
- The transistor amplifies the signal and drives the buzzer with enough current.
Buzzer (or Small Speaker)
- The buzzer is connected between the battery and the transistor’s collector.
- When the transistor conducts, the buzzer produces loud sound based on the IC’s output.
3V DC Battery
- The circuit is low-power and works perfectly with a 3V supply (two AA cells).
- When the circuit is powered ON, the UM3561 IC generates siren tones internally.
- These audio signals are passed through the 100Ω resistor to the transistor’s base.
- The BC547 transistor amplifies the signal and makes it strong enough to drive the buzzer.
- The buzzer finally produces loud police siren-like sound.
Used in toys (police car sound, fire truck sound, etc.).
In security alarms and warning systems.
As a learning project for beginners in electronics.
For experiments and hobby electronics.
This siren generator circuit is low-cost, simple, and very effective. With just a handful of components, you can build your own police siren sound system. Since it works on only 3V, it is perfect for battery-powered