An audible alarm device comprising a transducer which resonates at its natural frequency in an alarm mode to produce an alarm tone, this same transducer being driven, e.g. in a "ready" mode, by a non-resonant background signal generator in the manner to produce background sound of relatively low intensity which can indicate that the alarm circuit is functioning but is not in its alarm mode.

A piezoelectric transducer and a voltage doubling means are utilized in conjunction with a power supply means, a pulsator means, an amplifier means, and an acoustical loading means to produce an efficient high output audible alarm device. The voltage doubling means and the acoustical loading means enhance the audible output of the alarm device while increasing the overall electroacoustical efficiency of the alarm.

A warning device for incorporation in the handle-bar of a bicycle has a casing with a tubular portion and a head portion. The tubular portion fits inside the end of the handle-bar while the head portion abuts the end of the handle-bar. A flat spring member with an arc-like configuration extends longitudinally outside the tubular portion to engage the inside of the handle-bar and retain the casing in its installed position. There is a battery cell within the tubular portion as well as circuitry. ...

An electronic sound generating apparatus includes a housing having a closed end and a sidewall defining a cavity. The sidewall also includes a series of radially arrayed sound radiating ports. A circuit board with power source, a sound generating element electronically connected to the circuit board and a sound reflector are all received in the cavity. The sound reflector includes a substantially conical face axially aligned within the cavity and directed toward the sound generating element. Thi...

An electroacoustic sound generator of the type having a diaphragm vibrating in the audio frequency range is described. The diaphragm is mounted in a housing which is constructed to form first and second volumes, the former being smaller than the latter. The housing has channels formed therein for communicating sonic energy to the exterior from the first interior volume portion. The first volume portion together with the channels form a Helmholtz resonator tuned to the frequency of the sonic ener...

A smart card comprising: a memory for storing information; at least one transmitting or receiving antenna; and a low frequency circuit, for handling information associated with said antenna and said memory, which information is modulated at a modulation frequency of between 5 kHz and 100 kHz. Preferably the antenna is an acoustic antenna.

An audible indicator circuit including a piezoelectric crystal and transistor device, that is of extremely simple and inexpensive construction and has its on-off operation selectively controlled in response to an automatic or manually applied control signal. The piezoelectric crystal is connected between the collector and emitter electrodes of the transistor, so that with an "on" control signal applied to the base electrode and a supply voltage of magnitude that exceeds the collector to emitter ...

An open ended can has a piezoelectric crystal attached to its closed end face and contains within it the battery supply and circuitry operative to cause the can to resonate. The can is attached at its open end to a back board through a ring of closed cell foamed synthetic plastics material to form a waterproof enclosure for battery and circuitry. The circuitry is based on one or more CMOS integrated circuits having gates or inverters connected to form one or more oscillators and one of the oscil...

A highly reliable annunciator circuit which is immune from spurious signals generated in an elevator environment is provided. The circuit employs an input condition verification network which performs in conjunction with low true logic two-bit inputs by carrying out switching only when those inputs fall below a preset control value, highly enhanced performance is achieved. Volume control over the piezoelectric output developing a chime or gong sound is achieved through a variable impedance contr...

A piezoelectric buzzer comprises: a piezoelectric transducer; a casing comprising a hollow body having one end closed by a perforated end wall, a lid adapted to close the other end of the hollow body, and an annular groove defined on the inner peripheral surface of the open end of the hollow body for loosely receiving the peripheral portion of the lid. The annular groove and the lid are so dimensioned and so shaped as to avoid any undesired suppression of the frequency of resonance of the casing...