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DiscoverCircuits.com
-- Hobby Corner
"Hobby Circuits for
your Hobby Projects"
Last Updated on:
08/31/2008 02:26:32 AM
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3v
Sweeping Siren Alarm
designed by David A. Johnson, P.E. |
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June
24, 2008 |
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A while back I was
challenged by a visitor to the website. He needed a very loud sweeping
siren type audio sound generator powered by 3v. He tried some of the
commercial sirens but they were not very loud when powered by 3v. He
also said that those devices demanded much higher current than he wanted
to use. I gave this problem some thought and came up with a design
below. |
| The circuit
uses a LTC1799 precision frequency generator from Linear Technology.
A 74HC14 hex Schmitt trigger from Texas Instruments is also used to
perform several other functions. One section is wired as a simple
7Hz square wave oscillator. The triangle waveform across that capacitor
generates the low frequency sweeping signal for the siren. Two
resistors bias the LTC1799 for a center frequency of about 2KHz. A flyback DC to DC converter circuit, produces a 40v peak signal, which is
turned on and off according to the output of the LTC1799. |
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The output is connected to a quality
piezoelectric beeper, which has a resonant frequency of about 2.5KHz.
The result is a siren which is quite loud but draws only 40ma from a 3v
supply. A piezoelectric device from Kobitone, part number
254-PB515-ROX, (Mouser part number 245-PB516) shown above works well.
If you want something much smaller, although
not quite as loud, try the Murata PKM17EPP-2002-BO shown above (Digikey
part number 490-4688). |
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Click on Schematic below to view PDF version of this Circuit |
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