Home > Circuit Blox > Warbler Siren
UPDATED:.13:35 29 June 2014

This circuit produces a loud tone that changes pitch rapidly ideal for a warning device.

It is advised to use a paper or mylar cone speaker of at least 1W. Do not use high quality speakers for home entertainment systems.

Circuit Voltage: 6 to 12 volts

Set the Range 2 - (31Hz-850Hz) and use VR1 to change frequency.
Range 3 - (700Hz-18KHz) can also produce some very piercing sounds)

Adjust the warble rate using VR1. Start with VR1 set at minimum, fully anti-clockwise.

The Triangle Wave Astable produces a wave that ramps up and down evenly.

The output is fed to the Frequency Modulation input of the Astable which causes the output frequency to vary in proportion with the voltage at any one point. The more voltage, the more deviation from the original frequency creating a rapidly rising and falling tone.

The output from the Astable is connected to the Darlington Driver whihch boosts current for the speaker.

By turning VR1 on the Triangle Wave Astable gradully clockwise, the speed of the warbling will increase to a point where it matches the frequnecy of the second astable. This can produce some very unusual sounds. For a standard siren, turn VR1 fully anti-clockwise

Topics could include:
  • Frequency Modulation and associated terminology
  • Principle of radio transmission
  • AM - Amplitude Modulation.

    The circuit makes a good siren for any alarm system or warning system. Combined with another form of control it could be used for:
    • Fire Alarm
    • Elderly Panic Alarm
    • Attack Alarm

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