Audio Circuit Diagrams

Wailing Siren Circuit

There are different circuits designed to produce a variety of sounds, and this particular circuit is designed for creating a wailing siren sound. The primary function of this circuit is to generate a wailing siren effect. It achieves this using the astable mode of the 555 timer IC. When the switch is pressed, the speaker emits a high-pitched siren sound, and when the switch is released, the pitch gradually decreases, eventually turning off after a 30-second duration.


  • Wailing Siren Circuit Diagram:
    • Wailing Siren Circuit Design:
    • How Wailing Siren Circuit Works?
    • Wailing Siren Circuit Applications:
      • Limitations of this Circuit:
    • Project Output Video

Wailing Siren Circuit Diagram:

Wailing Siren

Circuit Components:

  • 555 timer IC
  • NPN transistor  Q1, Q2
  • Resistors
  • Capacitors
  • Speaker

Wailing Siren Circuit Design:

The central component of this circuit is the 555 timer IC, featuring a total of eight pins. Pins 2 and 6 are connected together. Pin 2 is linked to ground via a 10nF capacitor to provide stability, while pin 5 is connected to ground with a 10nF capacitor to facilitate oscillations. A 22K ohms resistor is connected in series with the switch.

A 100uF capacitor is connected in series with a 100k ohms resistor, which in turn is connected to the base of the transistor. The collector of the 555 timer IC is connected to the power supply voltage, and the emitter is also connected to the supply voltage.

The transistor used in this setup is the BC547, which is an NPN transistor. Initially, it remains in an open circuit state. NPN transistors start conducting when a voltage is applied to the base. In this configuration, a BC547 transistor drives the speaker. Another NPN transistor, the BC557, is employed to power the 555 timer IC.

In this example, a 555 timer is configured in astable mode, and pins 2 and 6 are shorted to enable continuous triggering of the circuit. The output of the 555 timer is connected to the speaker through a transistor. A resistor links the positive terminal of the speaker to the power supply voltage.

A speaker with an 8-ohm impedance is used in this experiment. Inside the speaker, you will find a voice coil, diaphragm, and magnet. When electrical pulses are applied to the voice coil, it generates electromagnetic waves that interact with the magnetic field of the permanent magnet. This interaction causes the voice coil to move back and forth, creating vibrations in the diaphragm. These vibrations produce sound.

How Wailing Siren Circuit Works?

  • To begin, power the circuit with a 6 volt supply.
  • Press the S1 switch now.
  • The speaker can be seen making a wailing siren sound.
  • When the transistor conducts and the base voltage is attained, the capacitor C1 begins charging and discharging to the 555 timer IC’s supply pin.
  • When the 555 timer IC’s supply voltage is introduced, the capacitor C1 begins to charge.
  • When the capacitor hits 2/3rds of VCC, it begins to discharge.
  • When this reaches 1/3rd of VCC, the capacitor begins to charge in order to generate the pulses.
  • Because the transistor is connected to the output, it is only connected to the ground when it begins to conduct.
  • Finally, the speaker begins to emit a wailing sound.
  • Now release the switch, siren is decreased and stops after about 30 seconds

Wailing Siren Circuit Applications:

  • This circuit with slight modifications can be used at the time of  disaster to warn.
  • This can also be used  in security applications. For simple and good security alarm circuits, click here.
  • This can also be used in toys.

Limitations of this Circuit:

This can not be used in applications where the sound is required to switch off instantaneously.

Project Output Video


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