Audio Circuit Diagrams

Wailing Siren Circuit

There are various types of circuits that generate various types of sounds. This is a basic circuit for making a wailing siren. This circuit’s main purpose is to generate a wailing siren. The astable mode of the 555 timer IC is used. When the switch is pressed, the speaker emits a high-pitched siren; when the switch is released, the pitch drops and the speaker turns off after 30 seconds.


  • 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 555 timer IC is the heart of this circuit. It has a total of eight pins. The second and sixth pins have been shorted. The second pin is connected to ground via a 10nF capacitor. For oscillations, the 5th pin is linked to ground through a 10nf capacitor. A 22K ohms resistor is attached to the switch.

A 100 uF capacitor is connected in series with the 100 kOhm resistor attached to the transistor’s base. The 555 timer IC’s collector is connected to the supply voltage, while the emitter is connected to the supply voltage.

The BC547 transistor is an NPN transistor. It is initially open circuited. NPN transistors begin to conduct when a cutoff voltage is applied to the base. The Speaker is driven by a BC547 transistor in this setup. Another NPN transistor, the BC557, is utilised to power the 555 timer IC.

A 555 timer is wired in astable mode in this example. To enable continuous triggering of the circuit, the 2nd and 6th pins are shorted. The 555 timer’s output pin is connected to the speaker via a transistor. A resistor connects the speaker’s positive terminal to the supply voltage.

A speaker with an impedance of 8 ohms was employed in this experiment. A voice coil, diaphragm, and magnet will be found inside the speaker. Electromagnetic waves are formed around the voice coil when electrical impulses are applied to it, and they interact with the permanent magnet’s magnetic field.As a result, the permanent magnet and the induced magnetic field repel and attract each other, changing the polarity of the electric signal. As a result of this electric signal, the coil moves back and forth. As the diaphragm moves continually, vibrations are created. These vibrations are what cause sound to be produced.

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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