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 oscillator pulses the crystal through a transistor power amplifier and step up transformer. That oscillator may be adjusted off the resonant frequency to reduce the output or a feedback path provided to lock the oscillator onto a resonant frequency.
A medical alert alarm is provided to enable an individual having a medical problem in the nature of a heart condition to alert bystanders of an impending attack. The alarm includes a compartment for storing medication, as well as means to identify the individual and the nature of the medical problem. An important feature of the invention relates to the small size of a housing used to contain components of the alarm. Very small components, including a small speaker and other audio oscillator circuitry, are used. In order to project an audible signal having desirable alerting characteristics, and still maintain a small housing size, a resonant cavity is employed. The dimensions of the resonant cavity are carefully selected so that the proper audible signal is produced. The invention also includes a clip and a switch positioned such that the alarm can be activated easily.
An electrically-energized horn is provided which is particularly suited for use in fire alarm and burglar alarm systems, and which includes a built-in solid state electronic drive circuit including a timer network for de-energizing the horn a predetermined time after it has been activated.
The present invention produces at least two sound signals such as warning signals or actuating signals by one sounder having a resonant frequency, wherein one of the sound signals is indicated by the resonant frequency of the sounder to enable a higher intensity sound to be produced.
An ultrasonic transducer has a pot-like housing with an annular wall and with a bottom surface serving as diaphragm. A piezo-element which is connected with connection lines is arranged at the inner side of the bottom surface. The edge remote of the bottom surface is surrounded by a decoupling ring which is formed as a holder for the connection lines.
A method and self-tuning circuit for tuning vibratory transducers, broadly including electroacoustic speakers and specifically including the speakers of common back-up alarms used for safety reasons on commercial vehicles and heavy equipment. The self-tuning circuit is physically coupled to the transducer's input terminals and operates by comparing the rising and falling edges of one period of a test waveform elicited from the transducer by the application of a test signal having a test frequency. Depending on the results of this comparison, the test frequency is adjusted by predetermined increments upward or downward until the transducer's resonance frequency has been tightly bracketed though not exactly pinpointed.
