JP2931594B2 - Buzzer drive circuit - Google Patents

Description

Description of the Invention [Object of the Invention] (Industrial application field) The present invention relates to a buzzer drive circuit for driving a piezoelectric buzzer.

(Related Art) In recent years, buzzers are often used in electronic devices. Among these buzzers, piezoelectric buzzers are used in various electronic devices because they consume little current, are thin, and have little electrical influence on circuits. For example, it is widely used as a time notifying means in an electronic alarm clock or the like, a state checking means in a calculator, a camera, or the like, an alarming means in a kind sensor, an alarm device, or the like.

The piezoelectric buzzer directly uses a flexural vibrator obtained by bonding a thin plate formed by a piezoelectric element to a metal vibrator or the like, and sounds when driven by an AC voltage having an audible frequency. Therefore, in order to make the piezoelectric buzzer sound, the piezoelectric buzzer must be driven by an AC voltage such as a sine wave voltage or a rectangular wave voltage by any method. In recent years, there are many cases in which a digital circuit such as a microcomputer drives directly.

By the way, the volume of the piezoelectric buzzer is usually single. However, depending on the electronic device, it may be preferable to change the volume. For example, in an electronic device used both indoors and outdoors, it is generally preferable that the volume can be set higher when used outdoors than when used indoors.

The sound pressure of the piezoelectric buzzer can be changed by an applied voltage, that is, a drive voltage, as the name implies. Therefore, to change the volume of the piezoelectric buzzer, the drive voltage of the piezoelectric buzzer may be changed.

FIG. 4 shows a generally conceivable configuration for changing the drive voltage.

The illustrated buzzer drive circuit drives the piezoelectric buzzer 13 at its resonance frequency by turning on and off the common emitter transistor 12 by a pulse signal having the same frequency as the resonance frequency of the piezoelectric buzzer 13 output from the pulse generation circuit 11 In this configuration, a plurality of power supplies 14, 15, and 16 having different power supply voltages are prepared, and these can be selectively connected to the piezoelectric buzzer 13 by a switch 17.

According to such a configuration, at both ends of the piezoelectric buzzer 13,
_A rectangular voltage having peak values of the power supply voltages V _A , V _B , and V _C is applied. Therefore, the driving voltage of the piezoelectric buzzer 13 is set to the fifth voltage depending on which power supply 14, 15, 16 is connected to the piezoelectric buzzer 13.
It can be changed as shown in the figure. As a result, the piezoelectric buzzer 13
The sound pressure changes as shown in FIG. 6, and the piezoelectric buzzer 13 sounds at a different volume.

Reference numeral 18 denotes a basic clock generation circuit that generates a basic clock used as a reference when the pulse generation circuit 11 generates a pulse signal. Reference numeral 19 denotes a microcomputer that controls a pulse generation operation of the pulse generation circuit 11.

In the above configuration, the driving voltage of the piezoelectric buzzer can be changed by a simple configuration in principle.
Since 4, 15 and 16 are required, there is a problem that it is difficult to actually design and commercialize the apparatus in terms of cost and the like.

(Problems to be Solved by the Invention) As described above, when changing the volume of the piezoelectric buzzer,
In general, it is conceivable to change the power supply voltage. However, such a configuration requires a plurality of power supplies, so that it is difficult to actually design and commercialize the device, although the basic configuration is simple. There is.

Accordingly, it is an object of the present invention to provide a buzzer drive circuit that can change the volume of a piezoelectric buzzer with a single power supply and that is easy to actually design and commercialize.

[Means for Solving the Problems] To achieve the above object, according to the present invention, the sound pressure of the piezoelectric buzzer is increased to the amplitude of a component having a frequency near the resonance frequency of the piezoelectric buzzer at the driving voltage. Focusing on the dependence, a means that can selectively output a plurality of pulse signals having a frequency higher than the resonance frequency of the piezoelectric buzzer and having different duties is provided. The gate is gated by a pulse signal having substantially the same frequency as the resonance frequency, and the piezoelectric buzzer is driven by the gate output.

(Operation) According to the above configuration, at the driving voltage of the piezoelectric buzzer,
Since the amplitude of the component having a frequency near the resonance frequency can be changed by the duty of the pulse signal having a higher frequency than the pulse signal having substantially the same frequency as the resonance frequency, depending on which duty pulse signal is selected, The volume of the piezoelectric buzzer can be changed. Thus, with a single power supply, without having to facilitate multiple power supplies,
The volume of the piezoelectric buzzer can be changed.

In particular, since the alternatively output pulse signal is gated with a pulse signal having substantially the same frequency as the resonance frequency,
The gate output always has the spectrum of the resonance frequency. For this reason, the plurality of pulse signals having different duties can be set irrespective of the resonance frequency as long as the condition that the pulse signal has a frequency higher than the resonance frequency of the piezoelectric buzzer is satisfied. Can be increased, and the configuration can be made very advantageous, such as generation from an arbitrary existing clock, which is practical.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration of one embodiment of the present invention.

In FIG. 1, reference numeral 21 denotes a clock generation circuit for generating a basic clock. 22 is this basic clock generation circuit
This is a pulse generation circuit that generates a pulse signal P having the same frequency as the resonance frequency of the piezoelectric buzzer 31 according to the basic clock output from 21. 23, 24, 25 are the basic clock generator 21
This is a pulse generation circuit that generates pulse signals PA, PB, and PC having a frequency higher than the resonance frequency of the piezoelectric buzzer 31 and different duties from each other in accordance with the basic clock output from. Reference numeral 26 denotes a pulse selection circuit that selectively selects the pulse signals PA, PB, and PC output from the pulse generation circuits 23, 24, and 25 according to a control signal from the microcomputer 27. Reference numeral 28 denotes a pulse signal P output from the pulse generation circuit 22 and a pulse signal P selected by the pulse selection circuit 26.
AND gate circuit. 30 is this AND circuit 28
Is a common-emitter transistor which receives the gate output of the transistor through the resistor 29 and is turned on and off by the gate output. Reference numeral 32 denotes a resistor inserted between the collector of the transistor 30 and the power supply 33 in parallel with the piezoelectric buzzer 31.

 The operation of the above configuration will be described.

Assuming that a pulse-like drive voltage applied to both ends of the piezoelectric buzzer 31 is y (t), if y (t) is a periodic function of the resonance period T of the piezoelectric buzzer 31, the following equation (1) is used. Can be expanded to a Fourier series.

y (t) = A ₁ sinωt + A ₂ sin2ωt + A ₃ sin3ωt +... B ₀ + B ₁ cosωt + B ₂ cos2ωt + B ₃ cos3ωt +... (1) where ω: 2π / T , Greatly depends on a component having a frequency near the resonance frequency. That is, at the drive voltage y (t) regarded as a periodic function of the resonance period T, A ₁ sinωt and B ₁ cos
Since the sum with ωt indicates the level of the component having the resonance frequency, it may be considered that the volume of the piezoelectric buzzer 31 is governed by this sum component.

For the sake of simplicity, the duties of the pulse signals PA, PB, and PC output from the pulse generation circuits 23, 24, and 25 are respectively changed as shown in FIGS. 2 (a), (b), and (c). 1,1 / 2,
1/4.

When the pulse signal PA is selected by the pulse selection circuit 26 under the control of the microcomputer 27, a driving voltage having a waveform as shown in FIG. 3A is applied to both ends of the piezoelectric buzzer 31. At this time, if the time axis is taken as shown in FIG.
Since B ₁ = 0, A ₁ indicates the amplitude of a component having substantially the same frequency as the resonance frequency. In this case, A ₁ is calculated as follows.

Here, if the collector-emitter voltage V _CE when the transistor 30 is turned on is neglected, since V = α, it is almost the same as when a sine wave having a frequency of 1 / T and oscillating 2V / π is applied. Volume is obtained.

Similarly, when the pulse signal PB shown in FIG. 2B is selected, the drive voltage y (t) applied to the piezoelectric buzzer 31
Is as shown in FIG. 3 (b), A ₁ is calculated as follows.

Therefore, in this case, a sound volume that is 1/2 of that obtained when the pulse signal PA is selected is obtained.

The driving voltage y when you select pulse signal PC shown in FIG. 2 (c) (t) is as shown in FIG. 3 (c), the amplitude of A ₁ has omitted the detailed calculations , Pulse signal PA
It is about 24.5% of the case where is selected.

As can be seen from the above considerations, since the power supply voltage V is constant, when a certain pulse signal is selected, the sound volume is However, N: the number of ON periods in one cycle ∫ _n dt: It is considered that the applied sound volume is almost equal to the volume when a sine wave having the amplitude of the integrated value of the ON period is applied.

Therefore, if the desired sound volume is a sound volume when a sine wave having an amplitude β is applied, an equivalent sound volume can be obtained by selecting a pulse signal that has been divided into sections so as to satisfy Expression (4).

As described above, this embodiment focuses on the fact that the volume (sound pressure) of the piezoelectric buzzer 31 greatly depends on the amplitude of the frequency component near the resonance frequency 1 / T of the drive voltage y (t). The pulse signals PA, PB, and PC having frequencies higher than / T and having different duties are gated by the pulse signal P having the same frequency as the resonance frequency 1 / T, and the piezoelectric buzzer 31 is driven by this gate output. It was made.

According to such a configuration, in the drive voltage y (t), the amplitude of the component having the same frequency as the resonance frequency 1 / T changes according to the duty of the pulse signals PA, PB, and PC. The volume of the buzzer 31 can be changed. Therefore, the actual design and commercialization of the buzzer drive circuit are facilitated.

Also, since the volume can be changed simply by changing the duty of the pulse signal, fine and highly accurate volume adjustment can be relatively easily realized.

Although one embodiment of the present invention has been described in detail, the present invention is not limited to such an embodiment.

For example, in the above-described embodiment, the case where the frequency of the pulse signal is made completely equal to the resonance frequency of the piezoelectric buzzer has been described.

Further, in the above-described embodiment, the number of pulse signals having different duties is set to three. However, it goes without saying that a plurality of other pulse signals may be used.

In addition, it goes without saying that the present invention can be variously modified without departing from the scope of the invention.

[Effects of the Invention] As described above, according to the present invention, since the volume of the piezoelectric buzzer can be changed with a single power supply, it is easy to design and commercialize a buzzer drive circuit capable of adjusting the volume. Can be.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing the configuration of one embodiment of the present invention, and FIG.
FIGS. 3 and 3 are signal waveform diagrams for explaining the operation of FIG. 1, FIG. 4 is a circuit diagram showing a configuration generally considered as a buzzer drive circuit having a volume control function, and FIG. 4 is a signal waveform diagram for explaining the operation of FIG. 4, and FIG. 6 is a characteristic diagram for explaining the operation of FIG. 21 Basic clock generation circuit 22, 23, 24, 25 Pulse generation circuit 26 Pulse selection circuit 27 Microcomputer 28 AND circuit 29 Resistance 30 Emitter ground Transistor, 31 Piezoelectric buzzer, 32 Resistor, 33 Power supply.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G10K 9/12

Claims (1)

(57) [Claims] A first pulse generating means for generating a pulse signal having substantially the same frequency as a resonance frequency of a piezoelectric buzzer; a frequency higher than a pulse signal output from the first pulse generating means; A second pulse generating means capable of selectively generating a plurality of pulse signals different from each other, and a pulse signal output from the second pulse generating means being a pulse signal output from the first pulse generating means. A buzzer drive circuit comprising: gate means for gate; and buzzer drive means for driving the piezoelectric buzzer according to a gate output of the gate means.