Patent Publication Number: US-4321851-A

Title: Electronic musical instrument

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an electronic musical instrument, and more particularly a power supply circuit thereof. 
     For electronic musical instruments two types of power sources have been used, one a commercial AC source and the other a DC power source or a battery. In each type, the electronic musical instrument is constructed such that when a key is depressed after closing a source switch, a musical tone corresponding to the depressed key is produced. In such an electronic musical instrument, the performer often fails to open the power source switch after finishing the performance. This causes loss of power of a battery especially in a portable electronic musical instrument utilizing the battery as the power source. In the portable electronic musical instrument, unless the power consumption during performance is limited, the life of the battery will be shortened. This requires frequent renewal of the battery or use of a battery of a large capacity, so that use of a large battery increases the size and weight of the electronic musical instrument which makes it inconvenient to transport the same. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is the principal object of this invention to provide an electronic musical instrument capable of preventing undesirable power consumption when a performer forgets to open the source switch. 
     Another object of this invention is to provide an electronic musical instrument capable of reducing the power consumption during performance. 
     Still another object of this invention is to provide an improved electronic musical instrument of the portable type containing a small size DC power source and which can reduce the power consumption during performance. 
     A further object of this invention is to provide an electronic musical instrument in which the power supply is controlled in an interlocked relationship with a key depressing operation. 
     According to this invention there is provided an electronic musical instrument comprising a power source; a plurality of keys; key switch means including a plurality of key switches corresponding to respective keys; means for generating a signal corresponding to a note of a depressed key, the signal generating means including a source terminal adapted to be supplied with voltage of said power source and a control input terminal adapted to be supplied with a control input corresponding to the note of the depressed keys; power source switch means interposed between the power source and the source terminal and interlocked with a depression of the key; means responsive to the depression of the key for supplying a control signal corresponding to a musical tone signal to be produced to the control input terminal, and means for producing a musical tone in accordance with an output of the signal generating means. 
     The source switch means and the key switch means may be constructed as independent switch means or as a single common switch means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a connection diagram showing one embodiment of the electronic musical instrument according to this invention; 
     FIG. 2 is a perspective view showing the detail of a key switch unit shown in FIG. 1; 
     FIG. 3 is a connection diagram showing a modified embodiment of the electronic musical instrument according to the present invention; 
     FIG. 4 is a connection diagram showing a modified key switch unit; 
     FIG. 5 is a perspective view showing an actual construction of the key switch unit shown in FIG. 4; 
     FIG. 6 is a connection diagram showing still another modification of the key switch unit embodying the invention; 
     FIG. 7 is a perspective view showing an actual construction of the key switch unit shown in FIG. 6; 
     FIG. 8 is a connection diagram showing another modification of the key switch unit embodying the invention; and 
     FIG. 9 is a perspective view showing the actual construction of another modification of the key switch unit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the electronic musical instrument 100 according to this invention and shown in FIG. 1 utilizes an astable multivibrator and the oscillation frequency thereof is controlled by varying the resistance value of the resistor connected to the base electrode of one of the transistors of the oscillator. 
     A key switch unit 1 comprises a plurality of key switches 1-1 through 1-n respectively corresponding to keys 10-1 through 10-n (shown in FIG. 2) of the electronic musical instrument, and the key switches 1-1 through 1-n are ON-OFF controlled according to the operation of respective keys. Each key switch is provided with a movable contact and three-stationary contacts cooperating therewith. One of the stationary contacts is connected to one pole of a DC source, for example a battery 2 with the other pole grounded, whereas another one of the stationary contacts is connected to a source terminal 3a of an oscillator 3. Yet another stationary contact is connected to a control terminal 3b of the oscillator 3 through a frequency controlling resistor 4. Taking the key switch 1-1 as an example, a movable contact 1-1d is constructed to simultaneously engage all stationary contacts 1-1a, 1-1b and 1-1c. At this time, the stationary contact 1-1a is connected to the source 2, the stationary contact 1-1b is connected to the source terminal 3a of the oscillator 3 and the stationary contact 1-1c is connected to the control terminal 3b through an output line L 1  and the frequency controlling resistor 4. 
     One example of the actual construction of the key switch unit 1 is illustrated in FIG. 2 which shows only a key 10-1 corresponding to the highest tone pitch, and other keys 10-2 through 10-n are not shown. As shown, the key 10-1 is formed with a downwardly projecting actuator 10-1a and a resilient member 10-1b is secured to the lower end of the actuator 10-1a. A metal foil, for example, an aluminum foil acting as the movable contact 1-1d is bonded to the lower surface of the resilient member 10-1b. Stationary contacts 1-1a, 1-1b and 1-1c are mounted on a printed substrate 11 located beneath the movable contact 1-1d. Thus, when the key 10-1 is depressed it simultaneously engages the stationary contacts 1-1a, 1-1b and 1-1c, thus interconnecting the stationary contacts through the movable contacts. Accordingly, the source terminal 3a of the oscillator is connected to the source 2 to energize the oscillator 3. The control terminal 3b of the oscillator is also connected to the source 2 through the outut line L 1  and the frequency controlled resistor 4. By bonding the movable contact 1-1d to the resilient member 10-1b through the metal foil 1-1d, it is possible to reduce the contact resistance when the movable contact 1-1d is depressed against the stationary contacts 1-1a, 1-1b and 1-1c. 
     The oscillator 3 shown in FIG. 1 comprises an astable multivibrator which produces a musical tone signal having a frequency corresponding to the tone pitch of the depressed key. The oscillation frequency of the oscillator 3 is controlled by the resistance value of the frequency controlling resistor 4. More particularly, the frequency controlling resistor 4 is constituted by a plurality of serially connected resistors defined by a plurality of intermediate taps, and respective key switches 1-1 through 1-n are connected to intermediate taps of the resistor 4 where the resistance values between respective key switches 1-1 through 1-n and the control terminal 3b of the oscillator 3 assume the values corresponding to the tone pitches of respective keys. Assume now that the resistance between one of the depressed key switches 1-1 through 1-n and the control terminal 3b is denoted by Rn and that the elements (resistor and capacitor) constituting the oscillator 3 have values as shown in FIG. 1, the period T 1  of the musical tone signal produced by the oscillator 3 is expressed by the following equation. 
     
         T.sub.1 =0.7 Cb.sub.2 ·Rb.sub.2 +0.7 Cb.sub.1 ·(Rn+Rb.sub.1) 
    
     The musical tone signal generated by the oscillator 3 is applied directly, or through a suitable tone color filter (not shown), to a loudspeaker 7 via a transistor 5 and a resistor 6 to be produced as a musical tone. A light emitting diode (LED) 8 is connected between the loudspeaker 7 and the ground to display a state of a performance. Where the key 10-1 of the highest tone pitch is depressed, the movable contact 1-1d of the key switch engages the stationary contacts 1-1a, 1-1b and 1-1c to apply the source voltage to the source terminal 3a of the oscillator 3 while a control voltage is applied to the control terminal 3b to produce a musical tone signal from the oscillator 3 corresponding to the depressed key 10-1 thus producing a musical tone from the loudspeaker 7. 
     In a modified embodiment of this invention shown in FIG. 3, the oscillation frequency is controlled by varying the base voltage of an astable multivibrator and in FIG. 3, elements corresponding to those shown in FIG. 1 are designated by the same reference charactors. 
     In the modification shown in FIG. 3, although the oscillator 3A comprises an astable multivibrator in the same manner as that shown in FIG. 1, its oscillation frequency is controlled according to its base voltage V BB  which is supplied from a frequency controlling resistor 4A. More particularly, this resistor 4A is made up of a plurality of resistors having values corresponding to the tone pitches of keys so that the voltage supplied from the source 2 via a depressed key switch (one of the switches 1-1 through 1-n) is adjusted to a voltage corresponding to the tone pitch of the depressed key and the voltage V BB  thus produced is applied to the control terminal 3b of the oscillator 3A. Denoting the base voltage by V BB , the base-emitter voltage by V BE , and the collector voltage by V CC  and suppose that the resistor and the capacitor have values shown in FIG. 3, the period T 2  of the musical tone signal generated by the oscillator 3A is expressed by the following equation. ##EQU1## 
     With this construction, where either one of the keys is depressed, the voltage of the source 2 would be applied to the source terminal 3a of the oscillator 3A while at the same time, a voltage corresponding to the tone pitch of the depressed key would be applied to the control terminal 3b so that the oscillator 3A produces a musical tone signal having a frequency corresponding to the tone pitch of the depressed key and the musical tone signal is produced as a musical tone by the loudspeaker 7. 
     Although in the foregoing embodiment each key switch is constituted by one movable contact and three stationary contacts (with reference to key switch 1-1, one movable contact 1-1d and three stationary contacts 1-1a, 1-1b and 1-1c) the key switch may be constructed as a key switch unit 1A shown in FIG. 4 in which elements corresponding to those shown in FIG. 1 are designed by the same reference characters. 
     In the modification shown in FIG. 4, one end of the movable contact 1-1d is normally connected to the stationary contact 1-1a so that when the key 10-1 is depressed, the movable contact 1-1d engages the stationary contacts 1-1b and 1-1c. Actually, the switch unit 1A is constructed as shown in FIG. 5. More particularly, only a resilient member 10-1b is secured to the lower end of the actuator 10-1a of the key 10-1 and the stationary contacts corresponding to the stationary contacts 1-1b and 1-1c shown in FIG. 4 are mounted on the printed substrate 11 and one end of the movable contact 1-1d in the form of a leaf spring is secured to the printed substrate 11 such that its other end will be positioned above the stationary contacts 1-1b and 1-1c. 
     The voltage of the source 2 is applied to the movable contact 1-1d. Thus, as the key 10-1 is depressed, the movable contact 1-1d bridges the stationary contacts 1-1c and 1-1b to supply the source voltage to the source terminal 3a of the oscillator 3. At the same time, the source voltage is supplied to the control terminal 3b of the oscillator 3 via the movable contact 1-1a, the stationary contact 1-1c and the frequency control resistor 4. As a consequence, the oscillator 3 produces a tone source signal having a frequency corresponding to the tone pitch of the depressed key 10-1, and the signal is converted into a musical tone by the loudspeaker 7. 
     FIG. 6 illustrates another modification of a key switch unit 1B. In this modification, one end of the movable contact 1-1d is normally connected to the stationary contact 1-1c so that when the key is depressed the movable contact 1-1d engages the stationary contacts 1-1a and 1-1b. The actual construction of the key switch unit 1-B is shown in FIG. 7. Thus, a resilient member 10-1b is attached to the lower end of the actuator 10-1a of the key 10-1 and the stationary contacts 1-1a and 1-1b are mounted on the printed substrate 11. One end of the movable contact 1-1d in the form of a leaf spring is secured to the printed substrate 11 such that its other end is positioned above the stationary contacts 1-1a and 1-1b. The voltage of the source 2 is applied to the stationary contact 1-1c. Upon depression of the key 10-1, the movable contact 1-1d is caused to engage stationary contacts 1-1a and 1-1b to apply the source voltage to the source terminal 3a of the oscillator 3 via these movable and stationary contacts. At the same time, the source voltage is applied to the control terminal 3b of the oscillator via the stationary contact 1-1a, the movable contact 1-1and the frequency controlling resistor 4 with the result that the oscillator 3 produces a tone source signal having a frequency corresponding to the tone pitch of the depressed key 10-1 thus producing a musical tone by the loudspeaker 7. In FIG. 7, an insulating strip 15 is provided for clamping one end of the movable contacts 1-1d, 1-2d-1-nd to the printed substrate 11. 
     Alternatively, as shown in FIG. 8, the movable contact 1-1d may be normally connected to the stationary contact 1-1b. 
     FIG. 9 illustrates still another modification of this invention. In a key switch unit 10 shown in FIG. 9, a single source switch is commonly used for respective keys. Thus, the key switch unit 10 including key switches 1-1 through 1-n is also provided with a source switch 1-Z, which are arranged on the printed substrate 11 as shown. A supporting bar 21 is mounted on the substrate 11 for supporting keys corresponding to respective key switches. For the sake of simplicity, only one key 20-i is shown. One end of this key 20-i is supported by a spring 23 with its lower end anchored by the substrate 11. Downwardly projecting actuators 20-1a and 20-1b are provided for the key 20-i at portions beyond the supporting bar 21. A resilient member 20-1c is secured to the lower end of the actuators 20-1a, and the movable contact 1-id is bonded to the lower surface of the resilient member 20-1c. The movable contact 1-id may be made of a foil of metal, aluminum for example and stationary contacts 1-ia and 1-ic are mounted on the substrate 11 to confront the movable contact 1-id. The stationary contact 1-ic is connected to the frequency controlling resistor 4 having the same construction as that shown in FIG. 1 and its output is coupled to the control terminal 3b of the oscillator 3. The other actuator 20-1b engages a U shaped bar 28 rotatably mounted on the substrate 11 and normally biased upwardly by springs 26a and 26b. A metal plate 1-Zd constituting the movable contact of the source switch 1-Z is secured to a suitable portion of the bar 28. Stationary contacts 1-Za and 1-Zb are secured to the substrate 11 to oppose the metal plate 1-Zd. The stationary contact 1-Za is connected to the source 2 while contact 1-Zb is connected to the source terminal 3a of the oscillator 3. 
     In this modification as the key 20-i is depressed, the bar 28 is rotated downwardly to cause the movable contact 1-Zd to engage with the stationary contacts 1-Za and 1-Zb to supply the source voltage to the source terminal 3a of the oscillator 3. At the same time, the movable contact 1-id of the key switch 1-i engages the stationary contacts 1-ia and 1-ic to connect the source 2 to the frequency controlling resistor 4. As the key is released it is raised by spring 23 to open key switches 1-ia and 1-iz. As above described the key and the source switch are interlocked. 
     It should be understood that the invention is not limited to the specific embodiments described above and that many changes and modifications may be made without departing the spirit and scope of the invention. For example instead of using an astable multivibrator as an oscillator any other variable frequency oscillator may be used, for example a resistance controlled LC oscillator or a voltage controlled oscillator. Although in FIG. 1, a source switch is also used as a stationary contact for connecting a source, four independent stationary contacts can also be used. Further instead of using a single oscillator actuated by respective key switches a plurality of independent oscillators corresponding to respective key switches can be used. In addition, it is also possible to provide an oscillator for the highest octave and to divide the output frequency of the oscillator where a key of a lower octave is depressed. 
     A mechanical switch shown in the drawings may be substituted by a pressure sensitive switch, a photoswitch, a reed switch and any other well known switch, or a combination of switches having different performances, and a battery may be substituted by a commercial AC source. 
     As above described, according to this invention, a key switch is interlocked with a source switch or constructed to act also as a source switch so as to supply the source voltage to a musical tone producing circuit only when the key switch is closed. As a consequence it is possible to prevent power consumption caused by the failure of a performer to open the source switch.