JPS5811640B2 - Drive circuit for sound generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit for a coil-type sound generator which operates to produce a pleasant chime sound.

This drive circuit is particularly suitable for use in combination with a motor vehicle sound generator in that it is simple, inexpensive to manufacture and relatively insensitive to other electrical equipment.

Generally, the drive circuit of the present invention includes a high frequency oscillator and a low frequency oscillator.

The high frequency oscillator establishes the tone of the bell, and the low frequency oscillator gives the speed to "strike" the bell.

These oscillators include simple logic gate circuits that are used to generate a decaying sawtooth signal.

The outputs from the two oscillators are combined such that the high frequency signal is superimposed on the low frequency signal.

The resulting signal is pulse width modulated by passing it through a logic gate.

This modulated square wave signal is sent to the base of a drive transistor that controls the excitation of the coil.

Modulating the signal in this manner causes the transistor to cycle on and off such that the proportion of the transistor's on time is varied by the duty factor of the modulated waveform.

Therefore, when the impulse coefficient of this signal increases rapidly and gradually decreases, the sound generator produces a strike-decay, a strike-decay.

Further objects and advantages of the present invention will become apparent from the detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.

Referring now to FIG. 1, a circuit diagram of a drive circuit 10 according to the present invention is shown.

The present invention relates to a coil-driven acoustic generator such as that disclosed in U.S. Patent Application Ser. Applied in combination with a generator.

Generally, the drive circuit 10 includes a high frequency oscillator 12 and a low frequency oscillator 14, the outputs of which are combined at point 15 and applied to the base of a drive transistor 280, the output terminal of which is connected between the power supply VDD and ground. is connected in series to coil L1.

The combination of high frequency oscillator circuit 12 and low frequency oscillator circuit 14 causes the sound generator to produce a bell-like sound output rather than a constant sound.

In particular, high frequency oscillator 12 creates the tone of the acoustic output, and low frequency oscillator 14 provides the speed at which the bell is "struck."

The sound output produced by the sound generator therefore consists of a repetitive, pleasant sounding strike-decay, strike-decay.

High frequency oscillator 12 comprises a pair of logic gates, here inverters 16 and 18, which are connected in series with a capacitor C1 connected to the feedback loop of oscillator 12.

A resistor R5 and a diode D3 are connected in parallel between the midpoint of logic gates 16 and 18 and the feedback loop.

The values of resistor R5 and capacitor C1 are selected such that in this preferred embodiment, oscillator 12 oscillates at a frequency of approximately 1000 Hz.

The low frequency oscillator 14 also has a pair of inverter logic gates 20
and 22, the gates of which are connected in series with a capacitor C3 connected to the feedback loop of the oscillator 14.

A diode D2 is coupled between the midpoint of the two inverters 20 and 22 and the feedback loop, and a pair of series resistors R3 and R is coupled between the oscillator 140 input and ground.
4 is connected.

The values of resistors R3 and R4 and capacitor C3 are selected such that in this preferred embodiment, oscillator 14 oscillates at a frequency of approximately 1.2 Hz.

Since both oscillator circuits 12 and 14 work similarly, only the operation of high frequency oscillator 12 will be described.

A feedback capacitor C1, which causes the circuit to oscillate, is used to be charged in one direction via diode D3 and in the other direction via resistor R5.

Since resistor R5 provides a substantially greater resistance than diode T')3, capacitor C1 quickly charges positively through diode D3 and decays slowly negatively through resistor R5.

The signal at input point 21 thus has a sawtooth waveform with an exponentially decaying negative slope portion and a short positive slope portion.

It is important to note that the "output" signal from the oscillator 12 is actually derived from this input 21 of the oscillator 12.

The significance of this arrangement will become substantially clear from the following description of circuit 10.

In the low frequency oscillator circuit 14, resistors R3 and R4
The series-connected solid body performs the same function as the resistor R5 of the high frequency oscillation circuit 12.

However, resistors R3 and R4 are placed differently than in circuit 12 (although their effect on oscillator 14 remains the same).

This is because the voltage applied to inverter 24 needs to be stepped down.

Therefore, the required circuit resistance for oscillator 14 is 1
divided between the pair of resistors R3 and R4, and the 1
The output "is taken from the midpoint of this voltage divider network.

As mentioned above, the two oscillator circuits 12 and 14 function similarly.

The signal at the input point 23 of the oscillator 14 thus also includes a sawtooth waveform with an exponentially decaying negative-going portion and a short positive-going portion.

The relative output from the two oscillator circuits 12 and 14 is at point 1.
5, but in order to separate the high frequency oscillator 12 from the low frequency of the low frequency oscillator 14, the high frequency oscillator 12
The signals from are AC-coupled via capacitor C2.

By adding the two signals, the high frequency waveform is effectively superimposed on the low frequency waveform A, as shown by curve B in FIG. 2.For clarity, the signal diagram in FIG. Note that it does not accurately represent the relative frequency difference between the two oscillator signals.

The combined signal at point 15 is applied to a logic switching element, here an inverter 24, which performs a pulse width modulation function.

In particular, inverter 24 is associated with a specific switch level of 2 to 3 volts, typically about 2.5 volts, which controls the logic state of its output.

In particular, when the magnitude of the input signal is greater than the switch level of inverter 24, the output of inverter 24 assumes a logic low or 0 volt state.

Conversely, when the magnitude of the input signal is less than the switch level of inverter 24, the output of inverter 24 switches to a logic high state, ie, 5 volts.

Thus, as shown in FIG. 2, inverter 24 acts as a pulse width modulator by providing a pulsed output signal whose pulse width is proportional to the instantaneous magnitude of the decaying sawtooth signal at point 23. Proportional.

In fact, C in the signal diagram of FIG. 2 represents the output of inverter 26 rather than inverter 24.

Inverter 26 simply inverts the output of inverter 24, and the reason this inverter 26 is included is that it constitutes the sixth logic gate of the IC package and is an NPN transistor rather than an expensive PNP transistor.
This is simply because it allows the type drive transistor 28 to be used.

The signal applied to the base of transistor 28 therefore consists of a pulse signal whose pulse width narrows as the magnitude of the decaying sawtooth waveform at point 15 decreases.

Thus, drive transistor 28 is caused to cycle on and off, with the percentage of its on time determined by the impulse coefficient of the signal applied to its base.

By driving the coil L1 in this manner, the sound generator is caused to produce a striking-damped repeating sound output, as described above, and the frequency of the low frequency oscillator determines the speed of the striking, The frequency of the high-frequency oscillator then determines the tone of the bell.

At this point, the significance of connecting oscillators 12 and 14 so that an "output" signal is taken from the input will be explained.

It is clear from FIG. 2 that inverter 24 requires an attenuating ramp signal of the type appearing at summing point 15 to provide its modulation function.

However, although the signals at the conventional outputs of oscillators 12 and 14, i.e., the signals at the outputs of inverters 16 and 20, respectively, consist of square wave pulse signals, these signals are effectively reduced by feedback capacitors C1 and C3. is integrated to produce a decaying ramp signal at the oscillator inputs 21 and 23.

Thus, if oscillators 12 and 14 were connected in the conventional manner and their output pulse signals were summed and provided to inverter 24, inverter 24 would simply invert the pulses without modulating the signals. That is clear.

Therefore, the desired bell sound effect will be lost.

Although the above description relates to preferred embodiments of the invention, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the scope of the invention.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of one driving circuit according to the present invention, and FIG. 2 is a signal diagram showing how to pulse width modulate a synthesized waveform. 10...Drive circuit according to the present invention, 12...High frequency oscillator, 14...Low frequency oscillator, 16°18...Inverter, 20, 22...Inverter, 24.26...Inverter, 28...Drive transistor.

Claims (1)

[Claims] 1. In a sound generator drive circuit that causes the sound generator to generate an acoustic output similar to the sound of a bell, a first circuit that generates a relatively high frequency signal having attenuated amplitude characteristics. means for varying the relatively high frequency signal according to a relatively low frequency pattern having an attenuated amplitude characteristic;
circuit means for generating a pulse width modulated substantially square wave drive signal at a frequency associated with the relatively high frequency signal and having an impulse coefficient that varies in accordance with the amplitude characteristics of the relatively low frequency pattern; A drive circuit comprising: third circuit means for. 2. The drive circuit of claim 1, wherein the pulse width modulated signal is a digital square wave signal having a logic high amplitude level or a logic low amplitude level. 3. The drive circuit of claim 2, wherein said second circuit means includes an oscillator circuit for generating a signal at said relatively low frequency. 4. The drive circuit of claim 3, wherein the relatively low frequency signal generated by the oscillator circuit has attenuated amplitude characteristics. 5. said second circuit means further configured to control said relatively low frequency signal and said relatively high frequency signal such that said relatively high frequency signal is effectively superimposed on said relatively low frequency signal; 5. A drive circuit as claimed in claim 4, including means for combining the signals. 6. The drive circuit according to claim 1, wherein said third circuit means includes a transistor whose collector and emitter terminals are connected between said acoustic generator and ground potential. 7. The drive circuit according to claim 6, wherein the third circuit means further includes logic gate means connected to the output side of the second circuit means. 8. The drive circuit according to claim 7, wherein the output side of the logic gate means is connected to the base of the transistor.