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Circuits designed by David Johnson, P.E.
Last Updated on:
Saturday, December 23, 2017 03:21 PM
List of Dave's Circuit Designs
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More
Alarms Beepers
Sirens |
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3v Sweeping
Siren Alarm
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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. |
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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 Drawing Below to view PDF version of Schematic |
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