JPH10214090A - Buzzer driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the circuit reduced in the number of parts and reduced in the fluctuation of sound pressure and sound quality by connecting a switching transistor to a buzzer in series and driving the transistor with the PWM signals from a microcomputer. SOLUTION: A switching circuit 20 consists of resistors 11 to 13 and a switching transistor 14. The resistor 11 is connected between the PWM output terminal of a microcomputer 10 and the base terminal of the transistor 14. The resistor 12 is the bias resistor connected between the base terminal of the transistor 14 and a ground. When a switch SW is turned on, the microcomputer 10 repeatedly outputs pulse signals, in which the duty is changed in accordance with the characteristic, with a prescribed interval period, from the PWM output terminal for few times. In the pulse signals, the duty is continuously varied from 50% to 0% during a prescribed time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a buzzer that informs a person getting on or off a vehicle that he or she forgets to close a door or turn off a light.

[0002]

2. Description of the Related Art A conventional buzzer drive circuit is disclosed in
No. 8084, which will be described with reference to FIGS. When a switch (not shown) is turned on, the microcomputer 1 outputs an oscillation pulse having a constant frequency and a constant duty from one PWM output terminal to a positive power supply terminal of the buzzer 2 via a buffer and a diode. A trigger pulse having a frequency lower than the frequency of the oscillation pulse and a pulse width larger than the frequency of the oscillation pulse from another output terminal to a switching transistor 3 connected to the ground terminal of the buzzer 2 via a buffer and a bias resistor. Is output. As a result, a trigger pulse is supplied from the microcomputer 1 to the switching transistor 3, and during a short time during which the switching transistor 3 is turned on, the voltage of the oscillation pulse is directly applied between the terminals of the buzzer 2 via a buffer and a bias resistor. 2 sounds.

Thereafter, when the switching transistor 3 is turned off, the capacitor 4 is charged by the oscillation pulse from the PWM output terminal, and the voltage of the ground terminal of the buzzer 2 is determined by the resistor 5 and the capacitor 4 connected in series. The sound gradually rises at a constant rate, and the noise is gradually reduced. As a result, the buzzer 2 is continuously sounded as “pawn... Pawn”.

[0004]

However, the above-mentioned circuit has a problem that the number of parts increases and the cost increases because the time constant circuit including the resistor 5 and the capacitor 4 is used. . The capacitor 4
Must form a large-capacity capacitor such as an electrolytic capacitor, so that the capacitance value varies widely compared to a ceramic capacitor, etc., and the capacitance fluctuates greatly depending on the operating environment temperature. There was a problem that the variation was large.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a buzzer drive circuit having a small number of components and a small variation in sound pressure and sound quality.

[0006]

According to a first aspect of the present invention, there is provided a buzzer drive circuit for driving a buzzer by a PWM signal from a microcomputer.
A switching transistor is connected to the buzzer in series, and the switching transistor is driven by a PWM signal from the microcomputer.

A second invention is characterized in that the PWM signal output from the microcomputer according to the first invention has a duty continuously changing from a predetermined value to another predetermined value.

In a third aspect of the present invention, the duty in the second aspect of the invention changes at a first speed from a predetermined value to another predetermined value smaller than the predetermined value, and then gradually changes to 0% from the first speed. It is characterized by changing at a fast speed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 1 to 3 show an embodiment of the present invention.
This will be described below based on That is, in FIG.
Reference numeral 10 denotes a microcomputer. When a switch SW is turned on, a dashed line curve A shown in FIG.
A pulse signal (see FIG. 2) whose duty changes in accordance with the characteristic shown in FIG.
The output is repeated several times with a period of 5 sec). This pulse signal is a PWM signal having a frequency of 1 KHz and has a time T1 (T
1 <T2, T1 = 0.9 sec), duty 5
The duty is continuously changed from 0% to 0% duty. Fifteen
Denotes a buzzer, 20 denotes a switching circuit, and resistors 11 to 1
3, a switching transistor 14; a resistor 11 is connected between a PWM output terminal of the microcomputer 10 and a base terminal of the switching transistor 14;
4 is a bias resistor connected between the base terminal of No. 4 and the ground. The resistor 13 is a current limiting resistor connected between the collector terminal of the switching transistor 14 and the buzzer 15.

Next, a method of generating a PWM signal in the microcomputer 10 will be described with reference to FIGS. 4 and 5. It is practical to change the duty along the curve A in FIG. Therefore, the generation of the straight lines B and C that approximate the curve A will be described. That is, when the switch SW is turned on, the clock pulse generating means 102 starts outputting the clock pulse A having a constant frequency, for example, 1 KHz (see FIG. 5A). The clock pulse A is supplied to the integrating means 103. The integrating means 103 has an F / V conversion function and outputs a voltage proportional to the number of the supplied clock pulses A. The integration constant is switched based on a switching signal B (see FIG. 5B) supplied from 104.
For example, while the high-level switching signal is being supplied, the resistance 103a (having a smaller resistance value than the resistance 103b) is changed by the switching contact piece 103d to the capacitor 103
c, and when the supply of the switching signal is stopped (low level in FIG. 5B), the switching contact piece 1
03d connects the resistor 103b to the capacitor 103c. As a result, as shown in FIG. 5C, the output from the integrating means 103 changes its voltage value linearly with time.

When the clock pulse is supplied from the clock pulse generating means 102 to the one-shot multivibrator means 105, the one-shot multivibrator means 105 has a pulse width proportional to the voltage value supplied from the integrating means 103. Pulse (See Fig. 5D)
Is output. That is, since the change of the integration output of the integration means 103 is large at first, the pulse width output from the one-shot multivibrator means 105 is sharply reduced by the approximate straight line B shown in FIG. 3 until time T3. (First speed), and thereafter, it switches to the approximate straight line C,
Until time T1, the pulse width gradually changes, and at time T1.
When it is 1, the pulse width becomes 0. This state of the pulse width 0 is maintained until time T2, and thereafter, the above operation is repeated again (see FIG. 5D).

Next, the operation of the above configuration will be described. When the switch SW is turned on, the microcomputer 10
From the PWM output terminal, a pulse signal whose duty is 50% is initially output as indicated by the approximate straight lines B and C in FIG. 3, and then changes along the approximate straight line such that the duty is reduced to 0%. It changes continuously until. As a result, the power gradually decreases and the sound also decreases. As a result, the buzzer 15 generates the same sound as “pawn... Pawn” as in the related art.

The duty characteristic of the trigger pulse output from the PWM output terminal is not limited to the one shown in FIG. 3, but may be any characteristic as long as the duty changes with time. It is needless to say that it may be a thing.

[0014]

As described above, according to the present invention, it is possible to obtain a buzzer drive circuit for generating a sound similar to the conventional one at low cost, with stable sound pressure and sound quality. You.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a buzzer drive circuit according to the present invention.

FIG. 2 is an explanatory diagram of a waveform of a PWM signal output from the microcomputer 10 of FIG. 1;

FIG. 3 is a characteristic diagram showing how the duty of the PWM signal shown in FIG. 2 changes.

FIG. 4 is a circuit diagram for explaining a method of creating a PWM signal in the microcomputer 10;

FIG. 5 is a waveform chart for explaining the operation of the circuit of FIG. 4;

FIG. 6 is an explanatory diagram of a conventional circuit.

FIG. 7 is a waveform chart for explaining the operation of the circuit shown in FIG. 6;

[Explanation of symbols]

 Reference Signs List 10 microcomputer 11, 12, 13 resistor 14 switching transistor 15 buzzer

Claims (3)

[Claims] 1. A buzzer driving circuit for driving a buzzer according to a PWM signal from a microcomputer,
A buzzer driving circuit, wherein a switching transistor is connected in series to the buzzer, and the switching transistor is driven by a PWM signal from the microcomputer. 2. The buzzer drive circuit according to claim 1, wherein a duty cycle of the PWM signal output from the microcomputer changes from a predetermined value to another predetermined value. 3. The method according to claim 1, wherein the duty changes at a first speed from a predetermined value to another predetermined value smaller than the predetermined value, and thereafter changes up to 0% at a slower speed than the first speed. 3. The buzzer drive circuit according to claim 2, wherein: