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
3V Siren Alarm 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 3V Siren Alarm 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.
The 3V Siren Alarm 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).
3V Siren Alarm schematic here:
3V Siren Alarm figure