An audible signalling system utilizes a piezoelectric transducer to produce a chime tone audible signal. The system includes audible signalling circuitry, circuitry for driving the audible signalling circuitry to provide a pulsed audible signal, and circuitry for exponentially decaying the pulsed audible signal to produce a chime tone audible signal.

A multifrequency piezoelectric sound-generating system is provided with a piezoelectric vibrator for generating audible sound at two or more resonance frequencies, an oscillator circuit connected to the piezoelectric vibrator for oscillating at one of the resonance frequencies, and a modulator circuit connected to the oscillator circuit for amplitude-modulating the oscillator circuit with a modulating frequency substantially equal or close to a frequency separation between the resonance frequencies to energize the piezoelectric vibrator with frequency-modulated waves to generate multifrequency audible sound. The modulator circuit may have a frequency divider that is operative in response to an oscillating frequency in the oscillator circuit for dividing or counting down the oscillating frequency into the modulating frequency to modulate the oscillator circuit therewith. The piezoelectric vibrator may include a diaphragm, a generally rectangular metal sheet which is smaller in size than the diaphragm and mounted on the diaphragm, and a sheet of a piezoelectric material mounted on the metal sheet.

Audio frequency signal generator to generate signals in a selected band of audio frequencies to generate a noise having an amplitude pattern which simulates the noise generated by a selected occurrence which can be utilized for setting the actuation range of an audio actuated alarm device which is capable of discriminating the noise generated by such an occurrence where the generated frequency of the sound and amplitude of the sound waves can be varied selectively to simulate the pattern of the sound waves emanating from the selected occurrence.

An electrical short circuit protection device for an electric trailer brake controller includes a fuse connected between the controller and the trailer brakes and an acoustic piezoelectric transducer connected across the fuse. Upon a short circuit fault developing in the trailer brakes, the fuse opens and the transducer generates an audio warning signal.

A microcontroller is used to drive a piezoelectric transducer. Certain pins on the microcontroller are indicative of selection signals. The selector can be activated either by a user directly (e.g., by pushing buttons), by an offboard actuator (e.g., another microcontroller), or by any method known in the art for activating switches. In one embodiment, an output pin of the microcontroller acts as output for a high-low oscillator. The oscillation amplitude toggles between 0 and 5 volts in a square wave fashion. The output pin is coupled to the base of a bipolar junction transistor so that the transistor turns on and off as a switch in response to the high-low oscillations. As the transistor turns on and off, supply voltage is routed through a network of logic inverters, after first passing through a current limiting impedance means such as a resistor, to the piezoelectric transducer in a manner designed to provide a voltage swing at the transducer on the order of two times the supply voltage for each oscillation. In another embodiment, instead of using a single pin on the microcontroller to alternately forward and reverse bias a single transistor, the microcontroller actuates predetermined pins that are connected to different RC oscillators. The RC oscillators are then connected to the driving circuit. The circuit includes a voltage regulator connected at an input to the supply voltage and at an output to the power supply pin of the microcontroller.