Интернет-магазин оборудования для спутникового телевидения www.agsat.com.ua: спутниковые HDTV ресиверы Dreambox, GI, Openbox, Vu+.
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.