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Wailing Siren Circuit

There are different types of circuits that produce different kinds of sounds. Here is a simple circuit that produces wailing siren. The main principle of this circuit is to produce a wailing siren. The 555 timer IC is operated in astable mode. When the switch is pressed, speaker produces high pitch siren and when it is released, its pitch decreases and is switched off after 30 seconds.

Wailing Siren Circuit Diagram:

Circuit Diagram of Wailing Siren
Circuit Diagram of Wailing Siren

Circuit Components:

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

Also Read the Post – How to Design a Police Siren Circuit using NE555 Timer.

Wailing Siren Circuit Design:

This circuit mainly consists of  555 timer  IC. It has 8 pins. Sixth and second pins are shorted. Second pin is connected to ground through a capacitor of 10nf. 5th pin is connected to the ground through a 10nf capacitor for providing oscillations. Switch is connected to 22K ohms resistor.

A 100uf capacitor is connected in series to the 100 Kohm resistor which is connected to the base of the transistor. Collector is connected to the supply voltage and emitter is connected to the supply voltage of 555 timer IC.

BC547 is an NPN transistor. Initially, it is open circuited. When the based is applied with some cut off voltage, NPN transistor starts conducting. In this circuit BC547 transistor is used for driving the Speaker. Another NPN transistor BC557 is used for providing supply to the 555 timer IC.

Here 555 timer is connected in astable mode. The 2nd and 6th pins are shorted to provide continuous triggering of the circuit. Output pin of the 555 timer is connected to the speaker through a transistor. Positive terminal of the speaker is connected to the Supply voltage through a resistor.

Speaker used here is a 8ohms speaker. Internally, speaker will have voice coil, diaphragm and magnet. When the electrical signals are applied to the voice coil electromagnetic waves are generated around the coil and it interacts with the magnetic field of the permanent magnet. Thus the permanent magnet and the induced magnetic field repel and attract each other and thus producing the electric signal changing its polarity. Thus the coil moves back and forth as a result of this electric signal. Thus this creates vibrations as the diaphragm moves continuously. These vibrations are responsible for producing sound.

How Wailing Siren Circuit Works?

  • Initially power the circuit with a supply of 6v.
  • Now, press the switch S1.
  • One can observe the speaker producing wailing siren sound.
  • The capacitor C1 starts charging and discharging to the supply pin of the 555 timer IC as the transistor conducts when base voltage is reached.
  • When the 555 timer IC is applied with its supply voltage, the capacitor C1 starts charging.
  • When it reaches  2/3rd of VCC capacitor starts discharging.
  • When this is at 1/3rd of VCC capacitor starts charging to produce the pulses.
  • As transistor is connected to the output, it is connected to the ground only when transistor starts conducting.
  • And finally, speaker starts producing wailing sound.
  • Now release the switch, siren is decreased and stops after about 30 seconds

Wailing Siren Circuit Applications:

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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