Volume Control Apparatus

1. Field of the Invention

This invention relates to a volume control apparatus using an electronic attenuator, and more particularly to a volume control apparatus which is capable of adjusting the speed of volume control, i.e., volume increase or decrease rapidly or slowly according to operation of an operating knob.

2. Description of Prior Art

There has been widely known a volume control apparatus using an electronic attenuator as illustrated in FIG. 1. In the figure, 1 is an electronic attenuator having an audio input terminal IN, an audio output terminal OUT and a control terminal C, 2 is a D/A converter for applying a control analog signal to the control terminal C, and 3 is an up/down counter for applying a digital signal to the D/A converter 2 which has a clock input terminal CL, an up/down control terminal U/D and a carry terminal CA where an output appears at a maximum count value and at a minimum count value. 4 is a volume increasing switch comprised of a normally opened contact which is grounded at one end thereof and connected at another end thereof to a power souce B through a resistor R.sub.1. 5 is a volume decreasing switch comprised of a normally opened switch which is grounded at one end thereof and connected at another end thereof to the power source B through a resistor R.sub.2. Junction points between the resistor R.sub.1 and the switch 4 and between the resistor R.sub.2 and the switch 5, respectively, are coupled to input terminals of a logic circuit (NAND circuit) 6, respectively. An output terminal of this logic circuit 6 is coupled to an input terminal of an oscillatory circuit 8 through an inverter 7. An output terminal of this oscillatory circuit 8 is coupled to the clock input terminal CL of the up/down counter 3 through an inverter 9. A junction point between the volume decreasing switch 5 and the logic circuit 6 is coupled to the up/down control terminal U/D of the up/down counter 3. The oscillatory circuit 8 includes a NAND circuit 81 and is adapted to stop oscillation where a signal from the carry terminal CA of the up/down counter 3 is applied to the NAND circuit 81.

The operation of this conventional volume control apparatus will now be described. When the volume increasing switch 4 is closed, a level of an input to the logic circuit 6 becomes low and a level of an output of the logic circuit 6 becomes high. This output is made low by the inverter 7 so that the oscillatory circuit 8 starts oscillation to apply an oscillation output to the clock input terminal CL of the up/down counter 3. The up/down control terminal U/D is at a high level so that the up/down counter 3 counts the oscillation output in the adding direction. The count output is converted into an analog output by the D/A converter 2. A voltage of a signal to the control terminal C of the electronic attenuator 1 is increased and an amount of attenuation by the attenuator 1 is decreased, so that an output from the audio output terminal OUT is increased. On the other hand, when the volume decreasing switch 5 is closed, the oscillatory circuit starts oscillation to apply an oscillation output to the clock input terminal CL and render the up/down control terminal U/D to be of low level. As a result, the up/down counter 3 counts the oscillation output in the subtracting direction. A voltage of a signal to the control terminal C of the electronic attenuator 1 is decreased and the amount of attenuation is increased, so that an output from the audio output terminal OUT is decreased.

As apparent from the foregoing description, in the conventional volume control apparatus, the counting speed of the up/down counter 3 is determined by an oscillation period of the oscillatory circuit 8 and the amount of volume increase or decrease depends upon the closing time of the volume increasing or decreasing switch 4 or 5. Thus, it has not been able for the operator to attain quick or slow volume control as desired.

It is therefore an object of the present invention to provide an improved volume control apparatus which is capable of obviating the aforesaid disadvantage of the conventional volume control apparatus.

It is another object of the present invention to provide an improved volume control apparatus which is capable of effecting quick or slow volume control by operating a volume control operating knob.

In accordance with the present invention, there is provided a volume control apparatus which comprises:

an up/down counter having a clock input terminal and an up/down control terminal;

a D/A converter for converting a digital output from said counter into an analog output;

an attenuator responsive to said analog output for controlling an attenuation amount of an input signal;

a pulse generator having a first output terminal, a second output terminal and a pulse generating amount control means and adapted to produce a pulse from said first or second output terminal according to the operating direction of said pulse generation amount control means every given operation amount of said means; and

a logic circuit coupled to said first and second output terminals of the pulse generator for supplying a pulse from either one of said output terminals to said clock input terminal of said counter and supplying an up/down control signal to said up/down control terminal in response to the pulse appearing at said first or second output terminal.

FIG. 1 is a circuit diagram of a conventional volume control apparatus; and

FIG. 2 is a circuit diagram of a volume control apparatus in accordance with the present invention.

Referring now to FIG. 2, there is illustrated a preferred embodiment of the present invention. In FIG. 2, the same or similar parts or portions as or to those in FIG. 1 are designated by the same or similar references.

10 is a rotary pulse generator which generates a low-level pulse output at either a first output terminal 11 or a second output terminal 12 according to a direction of rotation of a slide terminal 10a by an operating knob (not shown). This pulse output is generated every rotational angle of the operating knob. The rotary pulse generator 10 may be a pulse generator commonly used for manual tuning in a PLL synthesizer type electronic tuning radio. The first output terminal 11 of this rotary pulse generator 10 is coupled to an input terminal of an NAND circuit 6 through a capacitor C.sub.1, and the second terminal 12 is coupled to an up/down control terminal U/D of an up/down counter 3 and further to another input of the NAND circuit 6 through a capacitor C.sub.2. Opposite ends of each of the cpacitors C.sub.1 and C.sub.2 are coupled to power sources B, respectively, through resistors R.sub.3 and R.sub.4 and resistors R.sub.5 and R.sub.6, respectively. An output terminal of the NAND Circuit 6 is coupled to an input terminal of another NAND circuit 13. Another input terminal of this NAND circuit 13 is coupled to a carry terminal CA of the up/down counter 3. An output terminal of the NAND circuit 13 is coupled to a clock input terminal CL of the counter 3 through an inverter 9.

With the arrangement as described above, the volume control apparatus of the present invention operates as will be described hereinafter.

When the operating knob of the rotary pulse generator 10 is rotated clockwise, a low-level pulse output appears at the first output terminal 11. This output is inputted to the NAND circuit 6 through the capacitor C.sub.1 and applied to the clock input terminal CL of the up/down counter 3 through the NAND circuit 13 and the inverter 9. The up/down control terminal U/D is not applied with a pulse (up/down control signal) and is thus kept at a high level. As a result, the up/down counter 3 counts the output pulse in an adding direction. When the operating knob of the rotary pulse generator 10 is rotated in the opposite direction, counter-clockwise, a low-level pulse output appears at the second output terminal 12. This output is applied to the clock input terminal CL through the capacitor C.sub.2, the NAND circuti 6, the NAND circuit 13 and the inverter 9 and is also applied to the up/down control terminal U/D. Thus, since the low-level pulse is concurrently applied to the clock input terminal CL and the up/down control terminal U/D, the up/down counter 3 counts the pulse output in a subtracting direction.

When the operating knob of the rotary pulse generator 10 is rotated rapidly, a pulse output appears thickly so that a count output of the up/down counter 3 changes quickly. On the other hand, when the operating knob is rotated slowly, the pulse output appears thinly so that the count output from the up/down counter 3 is changed slowly. Thus, the volume obtained at the audio output terminal OUT of an electronic attenuator 1 in response to the count output from the up/down counter 3 can be changed rapidly or slowly according to the operation of the operating knob.

When the up/down counter 3 reaches a maximum count value or minimum count value, a low level signal (inhibiting signal) appears at the carry terminal CA to close a gate of the NAND circuit 13. Thus, the pulse output from the rotary pulse generator 10 is prevented from being inputted to the up/down counter 3, so that the up/down counter 3 maintains the maximum count value or the minimum count value.

A plurality of rotary pulse generators may be employed. For example, in case where the volume control apparatus of the present invention is used for a car acoustic equipment, one of the rotary pulse generator 10 may be mounted in a body of the acoustic equipment so that the car driver may carry out a volume control operation, and another rotary pulse generator 10' may be provided at a rear seat so as to allow the occupant of the rear seat to carry out volume control, too.

The rotary pulse generator employable in the present invention is not limited to that described above, but it may be any type of pulse generator which has a pulse generation amount control means and is capable of producing a pulse from the first or second output terminal according to the operation direction of the means, by every given operation amount.

As described above, according to the present invention, volume increase or decrease can be carried out rapidly or slowly according to necessity by the operation of the operating knob of the rotary pulse generator.