| 摘要 |
1537555 Piezoelectric sound generators WARD & GOLDSTONE Ltd 4 Aug 1977 [11 Aug 1976 20 Oct 1976] 33341/76 and 43466/76 Heading G5J A sound generator includes a piezoelectric crystal 6 and an oscillator operative to pulse the crystal. The crystal may be attached by solder or conductive epoxy resin to the inside or outside of a closed end of a cylindrical can 5 which also contains the oscillator. The oscillator comprises a first integrated CMOS circuit IC1 including a driving oscillator including NAND gates G3, G4 for driving the crystal 6 via a transistor T1 and a transformer, and a modulating oscillator for the driving oscillator including gates G1, G2. The modulating oscillator is switchable on or off so that a continuous or a modulated tone is generated. A further integrated CMOS circuit IC2 including gates G5-G8 is also switchable on or off, the gates forming an oscillator which charges and discharges a capacitor C4 supplying power to the integrated circuit IC1 so that a siren effect may be produced. In Fig. 5 (not shown) a feedback signal is taken from the crystal to stabilize the oscillator. In Fig. 6 (not shown) the oscillator includes inverters instead of NAND gates. In Fig. 7 (not shown) the cylindrical can containing the crystal and oscillator is mounted on a support by means of an intermediate ring formed of highly-compliant closed cell expanded plastics foam to form a watertight enclosure. The sound generator may be employed in fire alarm or security installations. |
