JP2914663B2 - Sound signal formation circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for generating an acoustic signal such as a so-called chime sound used as a calling signal of an intercom apparatus. 2. Description of the Related Art As one of intercom devices, there is a so-called intercom device for making a call between a dwelling unit or a resident in a room and a visitor at an entrance or an entrance. In such an intercom apparatus, a call switch is provided on a door phone, which is a loudspeaker handset installed at an entrance or the like, and the user speaks when the call switch is pressed at a predetermined time interval or when the call switch is pressed. Time 2
Each time, a ringing sound called a chime sound, which sounds like "Peen" or "Pawn", is generated from a speaker installed in a room or the like. Conventionally, such a chime sound has been formed by amplitude-modulating a rectangular wave signal having an audible frequency with a triangular wave-like low-frequency envelope signal that attenuates exponentially at a relatively long period from a predetermined amplitude. FIG. 3 shows a conventional swing modulation circuit used for generating a chime sound. FIG. 2 (a) shows a modulation using a diode. An envelope signal is applied to the anode of the diode via a resistor, an audible frequency rectangular wave is applied to the cathode, and an amplitude modulation signal as a chime sound signal is applied from the anode. I try to take it out. FIG. 2B shows the modulation using a transistor. The rectangular wave is applied as a modulated wave to the collector of the transistor Tr1, the envelope signal is applied to the base, and the chime signal is extracted from the emitter. Like that. FIG. 4 shows an envelope signal generating circuit for generating an envelope signal for the modulation circuit of FIG. In the figure, reference numeral 1 denotes a Schmitt trigger circuit for shaping a long-width rectangular pulse generated by turning on and off a call switch SW, and 2 denotes a rising edge of the rectangular pulse upon switch-on, which corresponds to the "pean" portion. A first differentiating circuit for generating an envelope signal is provided at the falling edge of the rectangular pulse when the switch is turned off.
A second differentiating circuit 4 for generating the envelope signal of the portion is a positive signal synthesizing circuit for synthesizing only the positive side of the outputs of the differentiating circuits 2 and 3. Further, Japanese Utility Model Application No. 49-41218 (Japanese Utility Model Application No. 50-131965)
(Prior Art Document) discloses a signal generation circuit for generating a pseudo chime sound. This document describes a so-called envelope waveform that attenuates with a curve of a time constant determined by a capacitor and a resistance, based on a monostable multivibrator activated by reciprocating operation of a call push button. Then, the positive portion of this waveform is applied to the balanced modulation circuit B1, and is modulated into an audio frequency signal of frequency f1. Further, the negative portion of the waveform is applied to the balanced modulation circuit B2, and is modulated into an audio frequency signal having a frequency f2. As a result, a two-frequency chime sound is obtained. Also, in this document, during the operation of the monostable multivibrator driven by the reciprocating operation of the call push button,
To the balanced modulation circuits B1 and B2, audio frequency signals of frequencies f1 and f2 are constantly applied by an oscillator A1 generating a frequency f1 and an oscillator A2 generating a frequency f2, respectively. In these modulation circuits, as shown in FIG.
It is necessary to provide the polarity of the two envelope signals for the "Peen" sound and the "Pawn" sound with respect to the ground potential (GND), which complicates the configuration of the envelope circuit as shown in FIG. There was a defect. Further, in the above-mentioned conventional literature, during the generation of the envelope waveform, the balanced modulation circuits B1 and B2 are respectively provided with the frequency.
Oscillator A1 for generating f1 and oscillator for generating frequency f2
A2 always applies audio frequency signals of frequencies f1 and f2. Therefore, the oscillator A1 that generates the “peep” sound and the oscillator A2 that generates the “pawn” sound are simultaneously generating audio frequency signals of the frequencies f1 and f2. This means that the “pawn” sound is pronounced as the “pean” sound becomes smaller,
Behind the sound, a relatively small "peen" sound is produced simultaneously. Even if such a relatively small “peen” sound is output from a speaker via an amplifier, it becomes noise and the “pawn” sound becomes less clear. An object of the present invention is to provide an acoustic signal generating circuit capable of obtaining a clear chime sound with a simple circuit configuration. Means for Solving the Problems An acoustic signal forming circuit according to the present invention comprises an envelope wave generating circuit for alternately generating positive and negative low frequency envelope signals, an oscillating circuit for generating an audible wave signal, and a base. The audio signal is applied, and the envelope signal is applied to a collector or an emitter via an impedance, and the transistor has an emitter or a collector grounded, and the positive and negative envelopes are driven by the audio signal. A bidirectional switching circuit for turning on / off a signal and outputting the signal. According to the present invention, positive and negative low-frequency envelope signals are alternately generated, and the envelope signal is turned on and off in response to the generated low-frequency envelope signal. The number of points can be reduced, and a chime sound with less noise can be generated. An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 shows an amplitude modulation circuit and an envelope wave generation circuit according to an embodiment of the present invention. The amplitude modulation circuit shown in FIG.
And an audible frequency rectangular wave signal is applied to the base of the collector, and a chime sound signal as an amplitude-modulated wave is extracted from the collector. Comparing this with the conventional circuit of FIG. 3 (b), it can be seen that the signals applied to the collector and base of the transistor Tr1 have been switched. That is, in this circuit, the concept of the conventional modulated wave and the modulated wave is reversed,
The envelope signal that was originally a modulated wave is input as a modulated wave to the collector that can process both positive and negative signals, and the audible wave signal that was originally a modulated wave is input as a modulated wave to a base that can process only one polarity. I am trying to do it. As a result, both positive and negative envelope signals can be used, the envelope wave generating circuit is simply configured as shown in FIG. 1B, and the circuit configuration of the entire chime sound generating circuit is simplified. be able to. FIG. 2 shows a chime sound generation circuit using the amplitude modulation circuit and the envelope wave generation circuit of FIG. In the figure, parts common or corresponding to FIG. 3 are denoted by the same reference numerals. 2 is a Schmitt trigger circuit 1 which shapes a voltage change generated by turning on and off a call switch SW to form a rectangular pulse having a time width from on to off, and a rectangular output from the circuit 1. A CR differentiating circuit 2 having a relatively long time constant (for example, 1 second) for differentiating a pulse, an oscillating circuit (astable multivibrator circuit) 5 for generating a rectangular wave signal in an audible number band, and a transistor Tr1 as a bidirectional switching circuit Have. The resistor R20 of the differentiating circuit 2 also serves as the protective resistor R22 of the inverter A12 in FIG. 1B and the resistor R1 as a part of the switching circuit in FIG. 1A. is there. Next, the operation of the chime sound generating circuit of FIG. 2 will be described. In the figure, when the call switch SW is turned on, the voltage at the input terminal of the Schmitt trigger circuit 1 goes to the “H” level, and operating power is supplied to the oscillation circuit 5 via a control circuit (not shown). As a result, the output of the Schmitt trigger circuit 1 rises from "L" to "H", and the oscillation circuit 5 operates to generate a rectangular wave signal of an audible frequency. Transistor Tr1
Is applied to the base of this rectangular wave signal, and is turned on (conducting state) and off (non-conducting state) at the audible frequency. On the other hand, the differentiating circuit 2 differentiates the rising edge of the output of the Schmitt trigger circuit 1 to form an envelope signal of the first half of the chime sound, and supplies the envelope signal to the collector of the transistor Tr1 which is turned on and off at the audible frequency. Accordingly, a signal as shown in the figure is generated at the collector of the transistor Tr1 by dividing the envelope signal by the output resistance determined by the resistors R20 and R21 and the equivalent resistance between the collector and the emitter of the transistor Tr1. This signal is the signal of the "Peen" part of the chime ("Peen Pawn" sound). This signal is extracted from an output terminal OUT connected to the collector of the transistor Tr1, amplified by a power amplifier (not shown), and emitted from a speaker (not shown). Next, when the call switch SW is turned off and the input voltage of the Schmitt trigger circuit 1 changes from "H" to "L", the falling is differentiated by the differentiating circuit 2, and the signal and polarity at the time of the rising are changed. An inverted negative envelope signal is generated and supplied to the collector of the transistor Tr1. At this time, in conjunction with the turning off of the call switch SW, the audible frequency rectangular wave signal generated from the oscillation circuit 5 causes a "pawn" portion of a frequency different from that when the call switch SW is turned on, that is, a chime sound. It is modulated to a frequency for generation. In FIG. 2, this modulation circuit is omitted. The transistor Tr used in the present embodiment
In the case of 1, when the voltage between the base and the emitter is constant, the impedance between the collector and the emitter varies depending on the direction of conduction, but the impedance difference does not substantially matter in a region where the voltage between the collector and the emitter is extremely small. Since the peak value of the envelope signal is extremely small so as not to be affected by the characteristics of the transistor Tr1, the same switching operation is performed even when the potential between the collector and the emitter is inverted. Therefore, the negative envelope signal is also processed in the same manner as when the positive envelope signal is formed, and the transistor Tr1
, A signal of the latter half of the illustrated waveform, that is, the "pawn" portion of the chime sound is formed. Thus, in the circuit of FIG.
Signals of "Peen" and "Pawn" sounds, that is, "Peen Pawn" chime sound signals are formed in accordance with the ON and OFF operations of the SW. According to the present invention, positive and negative low frequency envelope signals are alternately generated, and the envelope signal is turned on / off and output in response to the low frequency envelope signal. This is simplified, the number of components can be reduced, and a chime sound with less noise can be generated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an amplitude modulation circuit and an envelope wave generation circuit according to one embodiment of the present invention. FIG. 2 is a circuit diagram of a chime sound generation circuit using the amplitude modulation circuit and the envelope wave generation circuit of FIG. 1; FIG. 3 is a circuit diagram of a conventional amplitude modulation circuit. FIG. 4 is a circuit diagram of a conventional envelope wave generating circuit. [Description of Signs] 1 ... Schmitt trigger circuit 2 ... Differentiation circuit 5 ... Audio frequency oscillation circuit Tr1 ... Transistor R20 ... Resistance

Claims (1)

(57) [Claims] An envelope wave generating circuit for alternately generating positive and negative low frequency envelope signals; an oscillating circuit for generating an audible wave signal; and the envelope signal through an impedance applied to a base and an impedance to a collector or an emitter. And a bidirectional switching circuit driven by the audible signal to turn on and off the positive and negative envelope signals. An acoustic signal forming circuit characterized by: 2. The envelope wave generating circuit includes a rectangular pulse generating circuit that generates a rectangular pulse having a relatively long cycle, and a CR differentiating circuit having a relatively large time constant that differentiates the rectangular pulse. The acoustic signal forming circuit according to claim 1. 3. 3. The sound signal forming circuit according to claim 2, wherein said rectangular pulse generating circuit is a Schmitt trigger circuit for shaping a DC voltage signal for sound generation command.