JPH0477318B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a volume control circuit for an electronic music box.

An object of the present invention is to provide a volume control circuit that is inexpensive and easy to electronically control in an electronic music box that uses a lingering waveform based on an RC discharge curve.

2. Description of the Related Art With the recent advances in electronic technology, electronic devices that generate music, voice, etc. by driving speakers using electronically synthesized signals are rapidly becoming popular.

The volume control circuit of such electronic devices is structured to mainly adjust the amplification factor of the amplifier circuit, but in the case of an electronic music box with simple sound quality,
A circuit as shown in FIG. 1 is also used, and FIG. 2 is a timing chart for explaining its operating principle.

The rhythm signal shown in FIG. 21 is input to FIG. 1A. Transistor T becomes conductive only when rhythm signal 1 is at H level, and capacitor C
to charge. The electric charge charged in capacitor C is
While the rhythm signal 1 is at L level, it is gradually discharged through the resistor R, and a lingering waveform 2 whose time constant is determined by R×C is obtained.

In FIG. 1B, a melody signal having a frequency determined by the pitch of the note as shown in FIG. Therefore, there is a second point at point P in Figure 1.
A modulation waveform shown in 4 in the figure appears.

If this modulation waveform 4 is appropriately divided into resistances by the variable resistor VR, and the divided waveform 5 is input into the amplifier circuit AMP to drive the speaker SP, the variable resistor VR
You can adjust the volume by changing the division ratio.

The disadvantage of this type of volume control circuit is that it uses a variable resistor, which is a relatively expensive component that costs about 100 yen.
It may not be suitable for automatic volume adjustment according to ambient noise, or for all-electronic volume adjustment required for alarm clocks that gradually become louder.

The present invention eliminates these drawbacks.

FIG. 3 is a circuit diagram of an embodiment of the present invention in which the amount of charge to the capacitor C is adjusted by changing the equivalent resistance value when the transistor that charges the capacitor C is in a conductive state using a rhythm signal.

In the case of a loud sound, rhythm signal 1 in FIG. 4 enters A ₁ and A ₂ in FIG. 3 at the same time to create reverberation waveform 2, and modulation waveform 4 enters amplifier circuit AMP.

Rhythm signal 1' for a small sound has the same pulse width as rhythm signal 1 for a loud sound, but is input only to _A1 and not to _A2 , so only transistor _T1 becomes conductive.

In this case, the equivalent resistance is higher than when T ₁ and T ₂ are in a conductive state in parallel, so with the same pulse width, a reverberation waveform 9 with a short fall width is obtained, and a small sound is generated. .

By the way, control to input rhythm signals of the same pulse width to _A1 and _A2 at the same time or only to _A1 in Fig. 3 requires mechanical operation by combining known techniques. This can be achieved without using any variable resistors or switches.

Therefore, the present invention eliminates the need to use relatively expensive components such as variable resistors and switches, and at the same time realizes a volume control circuit that does not require mechanical operations and is easily electronically controlled.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of the part of an electronic music box that uses a conventional method to form a lingering waveform, modulate the melody signal with it, adjust and amplify the volume, and emit sound from the speaker. FIG. 2 is a timing chart for explaining the operation of the circuit shown in FIG. Third
The figure is an example of a circuit diagram when the same part as in FIG. 1 is improved according to the present invention. FIG. 4 is a timing chart for explaining the operation of the circuit shown in FIG.

Claims (1)

[Claims] 1. An electronic music box that adjusts the volume based on a lingering waveform output from a CR circuit formed by connecting a capacitor and a resistor in parallel. An electronic music box characterized by comprising a charging circuit for the capacitor, which has a case in which the first and second transistors are conductive and a case in which the first transistor is conductive.