US 3180199 A
Description (OCR text may contain errors)
A ril 27, 1965 I J. R. ANDERSON ELECTRONIC TUNER FOR MUSICAL INSTRUMENTS Filed June 3, 1963 M.. m D N A R W MW 2 w United States Patent 3,180,199 ELECTRONIC TUNER FOR MUSICAL INSTRUMENTS John R. Anderson, 26279 Taatfe, Los Altos, Calif. Filed June 3, 1963, Ser. No. 235,451 6 Claims. (Cl. 84-454) This invention relates to electronic circuits which may be employed for tuning musical instruments, and more particularly to improvements therein.
The classic method for tuning musical instruments is to use a reference tone which is sought to be matched by the person tuning the musical instrument. The reference tone may be obtained by the note on a piano, by blowing on a pitch pipe, striking a tuning fork, or in the case of orchestras, a wind instdument such as the oboe, may provide the note. One of the problems with respect to striking thenote on the piano or with a tuning fork is that these are eifectively precussion instruments and if the person tuning the instrument is a bit slow the tone dies away and he must then energize the precussion instruments again. Also, at the time that the piano note or the tuning fork is struck, the person tuning the instrument, it alone, must stop tuning to perform this operation. This is a rather unfortunate and clumsy arrangement.
An object of this invention is the provision of an electronic circuit tuning arrangement which when energized stays energized as long as it is required in order to enable the user to tune his instrument.
Another object of this invention is to prow'de by electronic amplification a tuning note of sutlicient loudness to be heard by all members of a large or small instrumental group.
Still another object of this invention is to provide a simple and inexpensive electronic tuning arrangement which not only provides an accurate note for tuning, but also enables the user to detennine visually whether his instrument is properly tuned.
Yet another object of the present invention is to provide an electronic circuit which can furnish the proper notes for enabling the tuning of an instrument and also can serve as a metronome.
These and other objects of the invention may be achieved in an arrangement wherein there is provided a may also be employed to drive a visual indicator such as a meter to establish a standard output indication. Associated circuitry is then energized by the instrument being tuned. This circuitry in response to said energization drives the indicator to indicate whether or not the instrument causing such energization is higher or lower in pitch than the standard from which the standard reading of the indicator was established.
The novel features that are considered characteristic 3,189,199 Patented Apr. 27, 1965 FIGURE 2 is a circuit diagram for an alternative arrangement for an output indicator for use with the circuitry shown in FIGURE 1.
FIGURE 3 is a circuit diagram showing an alternative arrangement for obtaining an audio output.
Referring now to FIGURE 1, there may be seen a circuit diagram of an embodiment of this invention. This includes an arrangement whereby an oscillator, whose frequency may be changed, is used to provide an output frequency which is converted into an audio signal. The frequencies to which the oscillator may be switched comprise the frequencies of standard tones suitable for tuning instruments. In addition, a switch position is provided whereby the device acts as a metronome providing timing beats. For those persons having difliculty in determining whether, for example, a stringed instrument is below or above the requisite standard tuning, or even for singers, in order to train them to sing certain notes right on key, means are provided for visually indicating whether they are too low or too high. This diificulty is most apparent in tuning double stringed instruments such as the mandolin, where it is essential that both strings which are used for playing the same note must be tuned exacly alike. Students who are learning to play the instrument, for a considerable time, have dfiiculty in tuning the instrument properly.
In FIGURE 1 a source of potential 10 is connected,
when required, by means of a key 12, to the remainder of the circuitry. A constant potential source as well as one which is free from noise is provided by means of a filter section comprising a resistor 14 which is in series with the switch 12 and battery 10, and a capacitor 16 which is in shunt therewith. A Zener diode 18, which is connected across the capacitor assisits in maintaining voltage across the capacitor and load constant. As an alternative arrangement for this potential source, a single mercury battery having a constant reference potential can replace potential source 10, resistor 14, capacitor 16, and Zener diode 1 8.
The oscillator which provides the requisite frequencies, comprises a unijunction transistor 19 having its upper base 21 connected through a resistor 20 to the high potential side of the capacitor 16 and its lower base 23 connected through a resistor 22 to the ground side of the capacitor 1c. The emitter '25 of the unijunction transistor 19 is connected to the selector arm of a selector switch 24 and also to one side of a second timing capacitor 26. The other end of the timing capacitor 26 is connected to a second section 2t of the selector switch 24 which is ganged to be operable with the switch 24, and also is connected through a second resistor 30 to ground. There is a third section 32 for the selector switch which is ganged to be operable with the other two. That is, sections 24, 28 and 32, constitute three selector switch sections which are ganged to be operable together.
The section 24 of the selector switch, when in its first position, as shown in the drawing, connects to a potentiometer 34 which is connected through a resistor 36, to the source of operating potential 10. When in its second position switch 24 connects through a potentiometer 38 which is connected in series with the resistor 44 to the source of operating potential lil. When in its third position, the switch 24 connects to a potentiometer 40, which is connected in series with the resistor 42, which in turn is connected to the source of operating potential 10. When it is in its fourth position the selector switch 24 connects to a potentiometer 45 which is connected to the source of operating potential 11 Between the fourth contact positions of selector switch sections 24 and 23 there is connected a capacitor 46 in series with a potentiometer 48.
Each one of the resistors and potentiometers which are conductive.
pacitor as can charge up again.
beats of a metronome.
.quency by means of the potentiometer 44.
connected to the contacts of the selector switch section 24.
together with the capacitor 2s and the resist-or 3%, perform the usual relaxation oscillator function of determining the time required to charge up the capacitor 26 to a Value at which the unijunction transistor 19 is rendered At this time the capacitor 25 discharges through the unijunction transistor 19 The unijunction transistor 19 then is rendered nonconductive whereby ca- The frequency of oscillation of the relaxation oscillator arrangement described, is determined in accordance with well known principles and is adjusted precisely to the value desired by the trimming potentiometers 34, and iii. Therefore, by selecting one of these positions the oscillator will oscillate at the frequency determined by the circuit component values thereby used.
The fourth position of the selector switch sections is and is used for the purpose of compensating for variations which may occur in ditferent unijunction transistors and in diiferent values of capacitors used for capacitor 46 which latter components may have :10% tolerances.
The output of the relaxation oscillator which has a somewhat sawtooth shaped waveform, is applied to the base of a transistor 50. The transistor amplifies the signal and its collector is connected both to the selector arm of the selector switch 32 and to one end of an inductance 52. The other end of the inductance 52 is connected to the fourth contact terminal of the selector switch section =32, and to one end of the voice coil of a loud-speaker 54. The other end of the loud-speaker voice coil is connected through a switch S6 to a source of operating potential 58, for the transistor 50. The switch 56 may be ganged to operate together with the switch 12. That'is, whenever switch 12 is closed switch 56 is closed.
The first, second and third contacts of the selector switch section 32 are connected to first, second and third filter capacitor otl, s2, and 64. The purpose of the inductance 52 and therespective filter capacitors is to convert the sawtooth output signal of the relaxation oscillator to a sine wave signal which is then reproduced by the loudspeaker 54. No filtering and shaping action is pro- I vided when the selector switch is connected to its fourth position since, the waveform which is produced by the relaxation oscillator, when applied to the loud-speaker, sounds like the clicking sound of a metronome, which is exactly what is desired. A capacitor 64- is connected across the voice coil of the loud-speaker in order to bypass irritating high frequencies which may not be completely eliminated by the filter.
The circuit arrangement thus far described prov des audio output signals which comprise the notes or tones required for tuning instruments. arrangement provides an audio output consisting of the The required notes for tuning are initially established in, the instrument and then left unchanged. The metronome beats may be variedin fre- The instrument starts substantially immediately when the switches 12 and 5e are closed. The instrument maintains its output as long as switches 12 and 55 remain in their closed position. Thus, the person using the instrument need only start it after which he can tune his instrument and then turn off the device.
In addition to providing the functions of a metronome and an instrument tuner, the circuit shown may be combined with additional circuitry to provide the function of an indicator of whether a note being played is lower or higher than the standard tone provided by the circuit.
erating potentialand its second base connected through a resistor '73 to ground. Resistor 80 is connected in series wtih capacitor 82 which is connected in series with a potentiometer 84. The junction of resistor St and capacitor 32 is connected to the emitter of the unijunction transistor "F4. Operating potential charges up capacitor 82 until it reaches a value at which a breakdown of the unijunction transistor '74 occurs. However, the potentiometer 86 is connected between the junction of resistor 86 and capacitor $2 and ground, for the purpose of biasing the oscillator circuit just below the point of oscillation when no input signal is applied thereto through the diode 72. In the presence of such signal, the oscillator synchronizes therewith and oscillates at the same frequency as the incoming signal applied thereto.
Unijunction oscillators have the unique feature that their output current is a linear function of the relaxation frequency. Thus, a direct current microamm eter or milliammeter can be used to indicate frequency, once a calibration point is established. The purpose of the diode capacitor circuit shown connected to the potentiometer 84, is to rectify the output pulses from the relaxation oscillator and to apply these to the meter 90. Thus, the sliding contact of the potentiometer 84 is connected through a diode 92 to one side of the meter. The other side of the meter 90 is connected to ground. A capacitor .94 connects across the meter. The output of the second oscillator circuit, which is synchronized with the first oscillator circuit is therefore rectified and applied to the I meter 90. The, potentiometer 84 is adjusted so that the In addition, the circuit reading on the meter is at center scale.
A microphone 96 is used to pick up the sound made by the person desiring to determine whetheror not-he is higher or lower than the standard note frequency selected by means of the selector switches 24, 28 and 32. The
the base of a transistor 102 to be amplified. The collector of the transistor T02 is connected to a source of operating potential through a resistor 164. Some feedback signal is applied between the collector and base of the transistor Th2 through a resistor 1%. The output of the transistor 102 is applied through a capacitor 108 to the base of a second amplifier transistor Elli). The collector of this transistor is connected through the primary winding 1121 of a transformer, the other end of which is connected to the source of operating potential. sistors 114, 116, which are connected across the operating potential source serve to apply a suitable cut-oif bias to transistor 119 so that it will only produce an output in the presence of an input and will disregard noise perturbations. The secondary winding 1128 of the transformer is connected to the second contact terminal 708 of selector switch '70. A load resistor 1 .18 and capacitor 119 are connected across the secondary winding 1128.
After the person using the embodiment of the invention has selected atone by means'ofthe selector switches 24, 28, 32, and'after he has centered the indicator on the meter 90 by means of the potentiometer 84,.he then actuates the switch 70 to the position at which it connects contact 70B to the rectifier 72. The switches 12, 56 may synchronized ordrivenby the signal applied to the micro Series re- 7 phone 96 and which is received through the secondary winding 112S of the transformer. The meter 90 will indicate whether or not the signal frequency is higher or lower than the frequency of the standard signal. In this way the person using the instrument is informed as to which direction his tuning must take, or his singing must take, in order to be at the correct frequency.
In FIGURE 2, the meter 100 may be a less sensitive meter than the milliammeter 90 represented in FIGURE 1. A transistor 102 is then required to drive this less sensitive meter. In place of the meter 90 shown in FIG- URE 1, the base of transistor 102 is connected to point B in the circuit shown in FIGURE 1, and point C of the circuit shown in FIGURE 2 is connected to point C of the circuit shown in FIGURE 1. A resistor 104 is connected between points B and C. The collector of the transistor 102 is connected to one side of the meter 100. The other side of the meter 100 is connected to an operating source of potential 106. The other side of the meter 100 is also connected to a resistor 108 whose other end is connected to the emitter of transistor 102. The emitter of transistor 102 is connected to ground through a potentiometer 110, which is made adjustable in order to establish the gain of the transistor 102.
It is obvious that the frequency metering techniques described above can also be applied to measuring 60 c.p.s. and 400 c.p.s. power line frequencies and to a variety of industrial applications.
FIGURE 3 shows a circuit diagram of an arrangement for obtaining an audio output using a hearing aid type of transducer instead of a loud-speaker. This both enables the device to be made smaller and more portable as well as enables its use, as a metronome for example, without disturbing others. In place of all of the transistor 50 and its following circuitry, there is connected instead an NPN transistor which has its emitter connected to the junction of capacitor 26 and resistor 30, its base connected to ground and its collector connected to a following volume control potentiometer 124 A hearing aid transducer 126 is connecetd between the potential source and the volume control 12. A capacitor 128 is connected between the transistor collector and ground.
The operation of the invention with the circuit shown in FIGURE 3 is the same as has been described previously. It performs as either a tuning aid or a metronome. The hearing aid transducer obviously is worn in the ear. The loudness level is adjusted by the potentiometer 124.
There has been described herein a novel, useful and unique arrangement for providing the notes required for tuning instruments, for operating as a metronome, and for indicating whether or not the instrument being tuned is higher or lower than the standard notes being provided. The circuit arrangement requires a minimum of circuit components while providing an optimum in accuracy of operation, as well as reliability.
1. An electronic'tuning aid and metronome comprising a first variable oscillator, audio transducer means to which oscillations from said first oscillator are applied to be rendered audible, a second oscillator, visual indicator means connected to the output of said second oscillator to provide an output representative of its frequency of oscillation whereby an instrument may be tuned, means for synchronizing the frequency of oscillation of said second oscillator responsive to an applied signal, and switch means having a first position for connecting said means for synchronizing to said first oscillator output to synchronize said second oscillator frequency therewith whereby said visual indicator means provides a first indication thereof, and having a second position for connecting said means for synchronizing to said audio transducer means output to synchronize said second oscillator frequency therewith whereby said visual indicator means provides a second indication which if different from said first indication enables the user to determine how to correct his tuning.
2. An electronic tuning aid as recited in claim 1 wherein said visual indicator means includes a meter, and potentiometer means coupled between the output of said second oscillator and said meter for adjusting the reading of said meter to provide a predetermined reading in response to said second oscillator output when it is synchronized with said first oscillator output.
3. An electronic tuning aid as recited in claim 1 wherein said first and second oscillators each comprises a relaxation oscillator including a unijunction transistor having a first and second base and an emitter electrode, two resistors, a capacitor, means connecting in series said capacitor between said two resistors, means connecting the emitter of said unijunction transistor to the connection between one of said two resistors and said capacitor, a source of operating potential, means for applying operating potential from said source across said unijunction transistor first and second base, means for applying operating potential from said source across said series connected two resistors and capacitors, and means for deriving an output from the other of said two resistors.
4. An electronic tuning aid and metronome comprising a variable reference oscillator comprising a unijunction transistor having a first and second base and an emitter, a capacitor, a resistor connected in series with said capacitor, and a first, second and third selector switch each having a plurality of contacts and a selector arm movable to connect to a different one of said contacts, means connecting the selector arm of said first selector switch to said unijunction emitter and to said capacitor, a plurality of resistors a different one of which has one end connected to a different one of said first selector switch contacts, a source of operating potential means for applying operating potential from said source across said unijunction transistor first and second bases and to the other ends of said plurality of resistors whereby said reference oscillator oscillates at a frequency determined by the one of said plurality of resistors which is selected by said first selector switch, another capacitor and another resistor connected in series between the last of said first and second selector switch contacts, an inductive irnpedance, a loud-speaker connected to one end of said inductive impedance, means connecting the selector arm of the third selector switch to the other end of said inductive impedance, means connecting the last contact of said third selector switch to the loud-speaker, a plurality of filter capacitors a separate one of which is connected to a different one of the remaining contacts of said third selector switch, and means for applying output signals from said variable oscillator to said other end of said inductive impedance.
5. An electronic tuning aid and metronome comprising a reference oscillator, means for varying the frequency of said reference oscillator to have a predetermined value, an audio transducer, a synchronized oscillator circuit comprising a unijunction transistor having an emitter, two resistors, a capacitor, means connecting in series said capacitor between said two resistors, means connecting said emitter to the connection between one of said two resistors and said capacitor, yet another resistor connected between said connection between said one of said two resistors and said capacitor and said other of said two resistors for preventing said synchronized oscillator circuit from oscillating in the absence of an input synchronizing signal, means for applying a synchronizing signal to said synchronized oscillator including a first contact connected to the output of said reference oscillator, a second contact connected to the output of said audio-electric transducer, and a swinger arm for alternatively connecting to said first or second contact, means connecting said swinger arm to said connection between said one of said two resistors and said capacitor, an output indicator connected to said other of said two resistors, and means for establishing said output indicator in a reference indicating position when said swinger arm is connected to said first contact whereby when said swinger arm is connected to said second contact said output indicator indicates the frequency of any output from said audioeelectric transducer. 1
6. An electronic tuning aid and metronome comprising a variable reference oscillator comprising a unijunction transistor having a first and second base and an emitter, a capacitor, a resistor connected in series with said capacitor, and a first and second selector switch each having a plurality of contacts and a selector arm movable to connect to a different one of said contacts, means connecting the selector arm of said first selector switch to said unijunction emitter and to said capacitor, a plurality of resistors a different one of which has one end connected to a different one of said first selector switch contacts, a source of operating potential, means for applying operating potential from said source across said unijunction transistor first and second bases and to the other ends of said resistors whereby said reference oscillator oscillates at a frequency determined by the one of said plurality of resistors which is selected by said first selector switch, another capacitor and another resistor connected i References Cited by the Examiner UNITED sr r' s PATENTS oTrr R "REFERENCES Garner, In, Radio and Television News (pages 50, 51,
' 158), January 1954.
Primary Examiner I V Publication:A Transistor fMetrbnomefi by Loui's E.