GB2101452A

GB2101452A - Buzzer

Info

Publication number: GB2101452A
Application number: GB08217522A
Authority: GB
Inventors: Noriaki Fujita; Yukio Sakano
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1981-06-19
Filing date: 1982-06-17
Publication date: 1983-01-12
Also published as: DE3222843A1; JPS57210395A

Abstract

A drive system for a piezoelectrically operated buzzer (30) employs means for modulating a buzzer drive signal (SD) with a frequency (SM) which is lower than the frequency of the buzzer drive signal and lies within an audible frequency band. <IMAGE>

Description

SPECIFICATION Drive system for piezoelectrically operated buzzer Background of the invention The present invention relates to a system for driving a piezoelectrically operated buzzer.

Means heretofore known for driving buzzers of the type described may be typified by a drive circuit which is a sort of oscillation circuit. The drive circuit is supplied with a constant voltage from a d.c. constant voltage source and, for the duration of a supply of the voltage, it feeds to a buzzer a drive signal whose frequency is constant and equal or substantially equal to the resonance frequency of the buzzer.

However, such a buzzer drive means cannot sound the buzzer but with a single pitch and tone which is predetermined by the constant frequency of the output of the drive circuit. Sounding of the buzzer always at a given pitch and tone may not always be pleasant to the auditory sense or may not meet a desired application.

Summary of the invention A drive system for a piezoelectrically operated buzzer embodying the present invention includes drive means which produces a drive signal having a constant frequency while a constant voltage is applied by a constant voltage source to drive the buzzer. The drive signal from the drive means is modulated by modulator means.

In accordance with the present invention, a drive system for a piezoelectrically operated buzzer employs means for modulating a drive signal with a frequency which is lower than the frequency of the drive signal and lies within an audible frequency band.

It is therefore an object of the present invention to provide a drive system for a piezoelectrically operated buzzer which is capable of driving the buzzer while selectively varying the pitch and tone of the sounding.

It is another object of the present invention to provide a generally improved drive system for a piezoelectrically operated buzzer.

Other objects, together with the foregoing, are attained in the embodiments described in the following description and illustrated in the accompanying drawings.

Brief description of the drawings Figure 1 is a block diagram of a prior art drive system for a piezoelectrically operated buzzer; Figures 2a and 2b are timing charts demonstrating the operation of the prior art drive system; Figures 3a and 3b are timing charts representing the operation of a drive system embodying the present invention; Figures 4a and 4b are timing charts showing an alternative embodiment of the present invention; Figure 5 is a block diagram of a practical circuit arrangement which is applicable for practicing the present invention; and Figures 6a-6c are timing charts demonstrating the operation of the arrangement shown in Figure 5.

Description of the preferred embodiments While the drive system for a piezoelectrically operated buzzer of the present invention is susceptible of numerous physical embodiments, depending upon the environment and requirements of use, substantial numbers of the herein shown and described embodiments have been made, tested and used, and all have performed in an eminently satisfactory manner.

Referring to Figure 1 of the drawings, a prior art drive system for a buzzer of the type concerned employs a drive circuit 20 which is a kind of oscillation circuit. The drive circuit 20 has an input terminal connecting to a d.c. constant voltage source 10 and an output terminal connecting to a buzzer 30. When supplied with a constant voltage Vc from the voltage source 10, the driver 20 supplies the buzzer 30 with a drive signal SD for the same duration as the supply of the constant voltage in order to cause it to produce sound. The drive signal SD has a predetermined frequency f, which is identical or substantially identical with the resonance frequency of the buzzer 30. Waveform A shown in Figure 2a represents oscillation of the buzzer 30 which occurs in response to the drive signal SD.

Though waveform A is rectangular in Figure 2a, it may not always be rectangular in practice. The basic frequency of waveform A is equal to the frequency f, of the drive signal SD. Shown in Figure 2b are the levels of the d.c. constant voltage Vc coupled from the voltage source 10 to the driver 20. Thus, while the voltage Vo remains high (ON) level, the buzzer 30 continuously emits sound.

Such a buzzer drive means, however, involves the problem previously discussed. Due to the constant frequency f, of the drive signal SD, the buzzer 30 cannot emit sound but that of predetermined loudness and tone which are not always pleasant to the ears.

Referring to Figures 3a and 3b, a buzzer drive system embodying the present invention is represented by waveforms A' and Vc'. In accordance with the present invention, when a constant voltage Vc' is supplied from the d.c.

voltage source 10 to the driver 20 so as to drive the buzzer 30 by an output SDI of the driver 20, as discussed with reference to Figure 1, the constant voltage Vc' is controlled ON and OFF repeatedly with an audible frequency f2 (2 < f) to modulate the output SDI of the driver 20. Thus, the buzzer 30 is driven with oscillation waveform A' whose basic frequency is f1. Sounding of the buzzer 30 is not of intermittent nature but of continuous one and, since f2 < f1, lower in pitch than in the case of waveform A shown in Figure 2a. While the repetition frequency is f2, oscillation waveform A' is a frequency modulated version of waveform A by waveform Vc' and, therefore, the resulting tone is also different from one attainable with the waveform A.For example, where the frequency f1 is 5 kHz, desired one of do, re, mi, fa, sol, la and si of the musical scale can be selected merely by employing a corresponding frequency f2. Apart from the pitch, the tone will be more favorable to the auditory sense due to the high frequency component contained in waveform A'.

The ON-OFF control of the constant voltage from the voltage source 10 may be performed to any desired time ratio other than that shown in Figures 3a and 3b. For instance, as indicated in Figures 4a and 4b, the constant voltage may be controlled ON and OFF as represented by waveform Vc" so that the buzzer 30 is sounded according to waveform A" despite the same repetition frequency, f2. It will be seen that the sounding A" is identical in pitch (basic frequency) with the sounding A' but different in tone.

Thus, the buzzer drive system of the present invention permits the buzzer 30 to sound with a desired pitch and tone by, while causing the drive circuit 20 to operate at or substantially at the resonance frequency of the buzzer 30, modulating an output of the drive circuit 20 with an audible frequency which Is lower than the resonance frequency.

Referring to Figure 5, another and more concrete means for modulating the drive signal having the frequency f1 is shown. A NAND gate 50 is connected at one input to the buzzer driver 20 and at the other input to an oscillator 40 which oscillates a modulating signal SM of a frequency f2. The output of the NAND gate 50 is connected to the buzzer 30. With this arrangement, instead of the foregoing ON-OFF control of the constant voltage Vc, the NAND gate 50 is opened and closed in accordance with the modulating signal SM to modulate the drive signal SD frorn the driver 20. Hence, the output frequency of the driver 20 can be modulated, with the constant voltage Vc continuously coupled to the driver 20. It will be noted that the oscillator 40 may be driven in a manner to put the drive signal SD and modulating signal SM under a given synchronous relation or under an asynchronous relation.

In summary, it will be seen that the present invention provides a buzzer drive system which allows a buzzer to sound with a pitch and tone which are variable as desired.

Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.

Claims

1. A drive system for a piezoelectrically operated buzzer comprising: drive means for producing a drive signal having a constant frequency while a constant voltage is applied by a constant voltage source to drive the buzzer; and modulator means for modulating the drive signal.

2. A drive system as claimed in claim 1, in which the constant frequency is substantially equal to the resonance frequency of the buzzer.

3. A drive system as claimed in claim 1, in which the modulator means is constructed to control on and off the constant voltage repeatedly with a given frequency.

4. A drive system as claimed in claim 3, in which the given frequency is higher than the constant frequency.

5. A drive system as claimed in claim 3, in which the given frequency is substantially equal to the constant frequency.

6. A drive system as claimed in claim 3, in which the given frequency lies within an audiable range.

7. A drive system as claimed in claim 1, in which the modulator means comprises an oscillator for producing a modulating signal having a given frequency and gate means responsive to the drive signal and the modulating signal to produce a modulated drive signal.

8. A drive system as claimed in claim 7, in which the gate means comprises a NAND gate.

9. A drive system as claimed in claim 7, in which the given frequency is substantially equal to the constant frequency.

1 0. A drive system as claimed in claim 7, in which the given frequency lies within an audible range.