Сирена 110 dB на микросхеме 74C14
This circuit uses a 74C14 to form a beeper that produces a 100 dB
tone. The feedback terminal of the piezoelectric device (Panasonic EFB-BD32B21)
is attached to a central region on the piezoelectric wafer. When the beeper is
driven at resonance, the feedback signal peaks. One inverter of the 74C14 is
wired as an astable oscillator. The frequency is chosen to be about 5 times
lower than the 3.2kHz resonant frequency of the piezoelectric device. Feedback
from the third pin of the beeper reinforces the correct drive frequency to
ensure maximum sound output. Four other inverter sections of the IC are wired to
form two separate drivers. The output of one section is crossed-wired to the
input of the second section. The differential drive signal that results produces
about 18 Vp-p when measured across the beeper. The last inverter section is
wired as a second astable oscillator with a frequency of about 2 Hz. It gates
the main oscillator on and off through a diode. For continuous tone, the
modulation circuit can be deleted.