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BACKGROUND OF THE INVENTION
Musical instruments, and in particular percussion and string instruments,
require tuning in order to be played properly. Prior art methods of tuning
musical instruments require some sort of human intervention. Classically,
the piano tuner employs a tuning fork and his own hearing to tune a piano.
Likewise, one must rely upon his personal impression of a tone when tuning
a string instrument, such as a violin. Tuning gauges for percussion
instruments, such as kettledrums, have been developed. These tuning
gauges, however, only give an indication of the position of the adjustable
tuning member, and not the frequency of the tone produced by the vibrating
element or member of the musical instrument.
Not only must percussion and string instruments be tuned before a
performance, but sometimes must be returned during the performance. A
kettledrum must be tuned during the course of a performance. Typically,
kettledrums are arranged in groups of four. Each kettledrum has a
different tone range, which overlaps the tone range of its neighbor.
Usually, the complete tone range for all four kettledurms is about 1.5
octaves.
Key changes for string instruments, which are made while playing, usually
involve changing the effective length of the string by holding it immobile
at selected positions. Tuning of a string instrument involves changing the
restoring force of the vibrating member. Thus, key changing for stringed
instruments is comparatively easy since, effectively, one is changing the
boundary value conditions for a one-dimensional harmonic oscillator. Key
changes on a kettledrum, however, can only be performed by varying the
tension on the drumhead. Thus, a key change operation performed on a
kettledrum is identical to a tuning operation on the drum for that key.
Key changes for a kettledrum result from changing the coefficient of
restoring force of the drumhead. Practically speaking, it is very
difficult to change quickly and easily the boundary conditions for a
two-dimensional harmonic oscillator, as embodied in a circular drumhead.
During the course of a performance, a kettledrum is played in a number of
different keys. Thus, the musician must be able to adjust quickly and
easily the tension, and thereby the restoring force, on four drumheads
while the performance is being given.
Furthermore, as temperature, humidity and other external conditions change
during the performance, the tension on the vibrating element of the
musical instrument, whether the instrument is of the string or percussion
variety, changes. Thus, the instrument has a tendency to lose its tune
during the performance.
The tuning adjustment must also be performed in a darkened, and often
noisy, orchestra pit. Nevertheless, it is necessary that the musical
instrument be in tune and played in the proper key.
What is needed is a device which can tune a string or percussion instrument
to a selected frequency automatically, quickly and accurately. The tuning
device must be easy for a musician or non-technical person to operate. The
tuning device must also be non-responsive to extraneous sound.
SUMMARY OF THE INVENTION
The present invention provides a musical instrument tuning system having a
vibration sensor which optically senses movements of a vibrating sound
producing member of a musical instrument. In the present embodiment, the
musical instrument tuner is adapted to be used with a drum having a
drumhead as the vibrating sound producing member. The vibration sensor
produces a signal in response to the movement sensed. A compression
amplifier is connected to the vibration sensor, and receives the signal
from the vibration sensor. The compression amplifier maintains the
amplitude of the signal at a constant level. A digital counter is
connected to the compression amplifier to receive the constant amplitude
signal. The digital counter starts and stops in response to the period of
each signal cycle. A clock is also connected to the digital counter. The
clock provides a plurality of regular pulses, which are counted by the
digital counter while the digital counter is enabled in response to the
constant amplitude signal. A comparator is connected to the digital
counter. The comparator receives the count of the number of clock pulses
which occur during each signal cycle. An input encoder is also connected
to the comparator. The input encoder provides a digital encoder signal to
the comparator in response to a selected key for a period of the drumhead
fundamental frequency. The comparator generates a difference signal, which
is indicative of the difference between the count provided by the digital
counter and the digital encoder signal. The difference signal is
representative of the difference between the period of the desired
drumhead frequency and the period of the actual drumhead frequency. An
electric motor is connected to the comparator. The electric motor is also
connected, via a mechanical linkage of conventional tension lines, to the
drumhead. The electric motor, via the mechanical linkage, adjusts the
tension of the drumhead in response to the difference signal received from
the comparator. When the drumhead has been adjusted to the desired
drumhead fundamental frequency, no further signal will be received from
the comparator; and the electric motor will cease adjusting the tension of
the drumhead and lock in place.
It is a principal object of the present invention to provide a musical
instrument tuning device, which automatically adjusts the frequency of a
vibrating sound producing member while the musical instrument is being
played.
It is a further object of the present invention to provide a musical
instrument tuning device which is unresponsive to high-level extraneous
sounds.
It is another object of the instant invention to provide a musical
instrument tuning device which may be easily controlled by a musician or a
non-technical operator.
It is a still further object of the present invention to provide a musical
instrument tuning device which allows manual control of the timpani
tuning.
Other objects and uses of this invention will become readily apparent to
those skilled in the art upon a persual of the following specification in
light of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a conventional kettledrum;
FIG. 2 is a cutaway fragmentary view of a portion of the drum of FIG. 1,
showing details of the construction of the drumhead and a portion of its
associated mechanical linkage, and showing details of the vibration
sensor;
FIG. 3 is a plan view of a portion of the vibration sensor, showing details
of the photoresistors of the vibration sensor of FIG. 2;
FIG. 4 is a side view of the base portion of the drum of FIG. 1, having
portions broken away and showing details of a portion of the mechanical
linkage which adjusts the drumhead tension;
FIG. 5 is a schematic diagram of a portion of the circuitry of the musical
instrument tuning device;
FIG. 6 is a schematic diagram of another portion of the circuitry of the
musical instrument tuning device of FIG. 5;
FIG. 7 is a schematic diagram of the binary encoding matrix of the circuit
of FIG. 5; and
FIG. 8 is a block diagram of the musical instrument tuning device.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The specific embodiment of the present invention disclosed herein is
directed to a musical instrument tuning device for a kettledrum. Referring
now to the drawings, and especially to FIGS. 5, 6, 7 and 8, a musical
instrument tuning device 2 is generally disclosed therein. Musical
instrument tuning device 2 includes a tone sensor 3. A comparator 4 is
connected to tone sensor 3. A signal generator 6 is connected to
comparator 4. A tone adjustor 8 is also connected to comparator 4. Musical
instrument tuning device 2 is adapted to be used with a variety of
percussion and string instruments. Musical instrument tuning device 2 is
employed for tuning a drum 10, having a vibrating sound producing member
or drumhead 12. Drumhead 12 is fitted to a top of a kettle 13. A
conventional mechanical linkage 14 is connected to drumhead 12 to control
the tension of the drumhead, and thus its rate of vibration. Tone sensor 3
is connected to vibrating sound producing member 12. Tone adjustor 8 is
connected to vibrating sound producing member 12 through mechanical
linkage 14.
When vibrating sound producing member 12 is placed in vibrational motion,
tone sensor 3 senses the rate of vibration of the vibrating sound
producing member and produces a tone sensor signal indicative of the rate
of vibration. Signal generator 6 produces a selected frequency signal,
which is indicative of the frequency or key to which drum 10 is to be
tuned. Comparator 4 receives both the tone sensor signal and the selected
frequency signal, and produces an error signal indicative of the the
difference between the tone sensor signal and the selected frequency
signal. Tone adjustor 8 receives the error signal, and adjusts the rate of
vibration of vibrating sound producing member 12 in response thereto.
A vibration sensor, generally indicated by numeral 16, is located inside
kettle 13 under drumhead 12. Vibration sensor 16 is connected electrically
to a compression amplifier 18, as may be seen in FIGS. 5 and 8. A digital
counter 20 is connected to compression amplifier 18 to receive signals
from compression amplifier 18. A clock 22 is also connected to counter 20.
Clock 22 and digital counter 20 act as frequency-determining means. Tone
sensor 3 includes vibration sensor 16, compression amplifier 18, digital
counter 20 and clock 22.
A plurality of comparators 24 is connected to counter 20. Comparator 4
includes the plurality of comparators 24. An input encoder 26 is also
connected to comparator 24. Signal generator 6 includes input encoder 26.
An electric motor 28, which acts as electromechanical means, is connected
to the plurality of comparators 24 to receive an electrical output of the
plurality of comparators 24. Tone adjustor 8 includes electric motor 28.
Vibration sensor 16 is an optical vibration sensor, and has a pair of
photoresistors 30 and 32, respectively. Photoresistors 30 and 32 are
separated by an insulator strip 34. A light source 36 is positioned within
kettle 13 beneath drumhead 12. Light source 36 directs a beam of light 37,
through a focussing lens 39, against a reflective patch 38, which is
reflected onto photoresistors 30 and 32. Reflective patch 38 is affixed to
the inside of drumhead 12. Photoresistors 30 and 32 form two arms of a
conventional bridge circuit 40. The other two arms of the bridge circuit
are formed by a resistor 42 and a resistor 44. Bridge circuit 40 is
connected at a pair of points 46 and 48 to a voltage source. A contact
point 50, located between photoresistive elements 30 and 32, is connected
to ground. A contact point 52, located between resistors 42 and 44, is
connected to a lowpass filter 54.
Low-pass filter 54 has a plurality of ganged RC circuits. A resistor 56 is
connected to contact point 52. A capacitor 58 is connected between
resistor 56 and ground. A resistor 60 is connected to the junction of
resistor 56 and capacitor 58. A capacitor 62 connects resistor 60 to
ground. A resistor 64 is connected to the junction of resistor 60 and
capacitor 62. A capacitor 66 connects resistor 64 to ground. A resistor 68
is connected to the junction of resistor 64 and capacitor 66. A capacitor
70 connects resistor 68 to ground.
Compression amplifier 18 is connected to the junction of resistor 68 and
capacitor 70 of low-pass filter 54. Compression amplifier 18 includes a
controlled attenuator 72. Controlled attenuator 72 is connected to
low-pass filter 54. An amplifier 74 is connected to controlled attenuator
72. A detector 76 is connected in a feedback loop from amplifier 74 to
controlled attenuator 72.
A resistor 78 is connected to the junction of capacitor 70 and resistor 68.
An operational amplifier 80 is connected to resistor 78 at its
non-inverting terminal. A variable resistance 82 is connected from the
output terminal of operational amplifier 80 to the inverting terminal of
operational amplifier 80. A resistor 84 is connected between variable
resistor 82 and ground. Operational amplifier 80, variable resistor 82,
and resistor 84, comprise amplifier 74.
A capacitor 86 is connected to the output of operational amplifier 80. A
resistor 88 is connected between capacitor 86 and ground. A lead 89 is
connected to resistor 88. A resistor 90 is connected at the junction of
capacitor 86 and resistor 88. A diode 92 is connected in series with
resistor 90. A resistor 94 is connected to diode 92, opposite resistor 90
and parallel to resistor 88. A capacitor 96 is connected parallel to
resistor 94. A resistor 98 is connected in series with diode 92 at
capacitor 96. An NPN transistor 100, having a base 102, an emitter 104 and
a collector 106, is connected at base 102 to resistor 98. Emitter 104 is
connected to lead 89. Collector 106 is connected to a lead 107. A resistor
108 is connected to lead 89, adjacent emitter 104 of transistor 100. A
potentiometer 110 is connected in series to resistor 108. A resistor 112
is connected in series to potentiometer 110. Resistor 112 is connected at
point 114 to a positive voltage source, having a 15-volt potential. Lead
107 is connected, via a movable potentiometer tap 116, to potentiometer
110.
Capacitor 86, resistor 88, resistor 90, diode 92, resistor 94, capacitor
96, resistor 98, transistor 100, resistors 108 and 112, and potentiometer
110, all comprise detector 76.
Lead 107 is connected to an FET (Field Effect Transistor ) 118. FET 118 has
a gate 120, a drain terminal 122, and a source terminal 124. Gate 120 is
connected to lead 107. Source terminal 124 is connected to ground. Drain
terminal 122 is connected to the non-inverting terminal of operational
amplifier 80. FET 118 is the controlled attenuator 72.
A pulse generator 126 is connected to the output of operational amplifier
80. Included within pulse generator is a square wave generator 128. Square
wave generator 128 inludes a capacitor 130. Capacitor 130 is connected to
the output of operational amplifier 80. A resistor 132 is connected in
series with capacitor 130. Resistor 132 is connected to an inverting
terminal of an operational amplifier 134. A feedback resistor 136 is
connected between the output terminal of operational amplifier 134 and the
inverting terminal of operational amplifier 134. A resistor 138 connects a
non-inverting terminal of operational amplifier 134 to ground. Operational
amplifier 134 is connected at its output connection to a divide circuit
140. Divide circuit 140 is also part of pulse generator 126.
A resistor 142 is connected to divide circuit 140. A capacitor 144 is
connected between resistor 142 and ground.
An exclusive OR gate 146, having a pair of input terminals 148 and 150, is
connected at terminal 148 to the junction of resistor 142 and capacitor
144. A lead 152 is connected between clock 140 and resistor 142. A lead
154 is connected between lead 52 and terminal 150. Exclusive OR gate 146
has an output terminal 156, to which is connected a lead 158.
A pulse delay circuit 160 is connected to pulse generator 126. Pulse delay
circuit 160 includes a resistor 162, connected to lead 152. A capacitor
164 is connected between resistor 162 and ground. A resistor 166 is
connected to lead 152, in parallel with resistor 162. A capacitor 168
connects resistor 166 to ground. An exclusive OR gate 170, having a pair
of input terminals 172 and 174, and an output terminal 176, is connected
at input terminal 172 to the junction of resistor 162 and capacitor 164.
Likewise, exclusive OR gate 170 is connected at input terminal 174 to the
junction of resistor 166 and capacitor 168.
Resistors 162 and 166, capacitors 164 and 168, and exclusive OR gate 170,
form pulse delay circuit 160. A lead 178 is connected to output terminal
176 of exclusive OR gate 170.
A twelve-bit binary counter 20, having a clock terminal 180, a reset
terminal 182, and a plurality of output terminals 186, 188, 190, 192, 194,
196, 198, 200, 202, 204 and 206, is connected at reset terminal 182 to
output terminal 176 of exclusive OR gate 170.
A lead 208 is connected to lead 158. A resistor 210 is connected in series
with lead 208. A capacitor 212 connects resistor 210 to ground. A NOR gate
214, having a pair of input terminals 216 and 218, and an output terminal
220, is connected to resistor 210 at input terminal 216. NOR gate 214 is
connected at its output terminal 220 to clock terminal 180 of twelve-bit
binary counter 20. Lead 178 is connected to reset terminal 182 of digital
counter 20.
Clock 22 is connected to input terminal 218 of NOR gate 214. Clock 22
includes a NOR gate 222, having input terminals 224 and 226, and an output
terminal 228. Input terminal 226 of NOR gate 222 is connected to ground.
Output terminal 228 and input terminal 224 have a resistor 230 connected
thereacross. A resistor 232 is connected to resistor 230. A quartz crystal
234 is connected between resistors 230 and 232. A capacitor 236 connects
the junction of quartz crystal 234 and resistor 230 to ground. A capacitor
238 connects the junction of quartz crystal 234 and resistor 232 to
ground. A NOR gate 240, having a pair of input terminals 242 and 244, and
an output terminal 246, is connected at its input terminal 242 to output
terminal 228 of NOR gate 222. Input terminal 244 of NOR gate 240 is
connected to ground. Output terminal 246 is connected to input terminal
218 of NOR gate 214.
A latch 248 is connected to counter 20 and pulse generator 246. Latch 248
includes a plurality of separate latches 250, 252 and 254. Latch 250 has a
plurality of input terminals 256, 258, 260 and 262, which are respectively
connected to output terminals 184, 186, 188 and 190 of digital counter 20.
Latch 250 also has an enable terminal 264. By the same token, latch 252
has a plurality of input terminals 266, 268, 270 and 272, which are
respectively connected to output terminals 192, 194, 196 and 198 of binary
counter 20. Latch 252 also has an enable terminal 274. Latch 254 has a
plurality of input terminals 276, 278, 280 and 282, which are respectively
connected to output terminals 200, 202, 204 and 206 of twelve-bit binary
counter 20. Latch 254 has an enable terminal 284. Lead 158 is connected in
parallel to enable terminals 264, 274 and 284 of latches 250, 252 and 254,
respectively.
Latch 250 has a plurality of output terminals 286, 288, 290 and 292,
respectively. Latch 252 has a plurality of output terminals 294, 296, 298
and 300, respectively. Latch 254 has a plurality of output terminals 302,
304, 306 and 308, respectively.
A plurality of comparators 24 is connected to latch 248; and is made up of
comparators 310, 312 and 314, which are respectively connected to latches
250, 252 and 254. Comparator 310 has a plurality of latch input terminals
316, 318, 320 and 322, which are respectively connected to output
terminals 286, 288, 290 and 292 of latch 250. Comparator 310 has a
plurality of encoder input terminals 324, 326, 328 and 330. Comparator 310
has a plurality of input side terminals 332, 334 and 336. Terminals 332
and 336 are connected to ground. Terminal 334 is connected to a resistor
338. Resistor 338 is connected to a voltage source. Comparator 310 has a
plurality of output side terminals 340, 342 and 344.
Comparator 312 has a plurality of latch input terminals 346, 348, 350 and
352, which are respectively connected to latch output terminals 294, 296,
298 and 300. Comparator 312 has a plurality of encoder input terminals
354, 356, 358 and 360. Comparator 312 has a plurality of input side
terminals 362, 364 and 366. Terminals 362 and 366 are connected to ground.
Terminal 364 is connected to a resistor 368. Resistor 368 is connected to
a potential source. Comparator 312 has a plurality of output side
terminals 370, 372 and 374.
Comparator 314 has a plurality of latch input terminals 376, 378, 380 and
382, which are respectively connected to output terminals 302, 304, 306
and 308 of latch 254. Comparator 314 has a plurality of encoder input
terminals 384, 386, 388 and 390. Comparator 314 also has a plurality of
input side terminals 392, 394 and 396, which are respectively connected to
output side terminals 370, 372 and 374 of comparator 312. Comparator 314
also has a plurality of output side terminals 398, 400 and 402.
A NAND gate 404, having a plurality of input terminals 406, 408 and 410,
and an output terminal 411, is connected at input terminal 406 to output
terminal 344 of comparator 310. Input terminal 408 is connected to output
terminal 400 of comparator 314. Input terminal 410 of NAND gate 404 is
connected to lead 411. Lead 411 is connected to an AND gate 414 at an
output terminal 416. AND gate 414 has a pair of input terminals 418 and
420. A switch 422 is connected to lead 418. A capacitor 424 is connected
to lead 418, and in parallel with switch 422. Capacitor 424 is also
grounded. A resistor 426 is connected to capacitor 424 in series with
input terminal 418 of AND gate 414. A first level detector 428 is
connected to resistor 426. A second level detector 430 is connected to
input terminal 420 of AND gate 414.
An operational amplifier 432, having a non-inverting input terminal 434, an
inverting input terminal 436 and an output terminal 438, is connected via
output terminal 438 to resistor 426. Inverting terminal 436 is connected
to lead 107. Non-inverting terminal 434 is connected to a potentiomenter
440 via a tap 441. Potentiometer 440 is connected to a resistor 442 and a
resistor 444. Resistor 442 is connected to a fifteen-volt positive voltage
source at a point 446. Resistor 444 is grounded; and is connected in
parallel to a resistor 448. A potentiometer 450, having a movable tap 452,
is connected to resistor 448. A resistor 454 is connected to potentiometer
450. Resistor 454 is connected at a point 456 to a fifteen-volt positive
potential. Movable tap 452 is connected to an operational amplifier 458.
Operational amplifier 458 has an inverting terminal 460, a non-inverting
terminal 462 and an output terminal 464. Inverting terminal 460 is
connected to movable tap 452. Noninverting terminal 462 is connected to
lead 107. Output terminal 464 is connected to input terminal 420 of AND
gate 414.
Resistors 442 and 444, potentiometer 440, and operational amplifier 432,
comprise first level detector 428. Resistors 448 and 454, potentiometer
450, and operational amplifier 458, comprise second level detector 430.
A transistor 466, having a base 468, an emitter 470 and a collector 472, is
connected at base 468 to lead 412. Emitter 470 is connected to a
light-emitting diode 474. Light-emitting diode 474 is, in turn, connected
to a resistor 476. Resistor 476 is connected at a point 478 to a positive
potential. Collector 472 is connected to ground.
A NAND gate 480, having a plurality of input terminals 482, 484 and 486,
and an output terminal 488, is connected at input terminal 482 to output
side terminal 340 of comparator 310; is connected at input terminal 484 to
output terminal 400 of comparator 314; and is connected at input terminal
486 to lead 411. A NAND gate 490, having a pair of input terminals 492 and
494, and an output terminal 496, is connected at input terminal 492 to
output terminal 402 of comparator 314; is connected at input terminal 402
of comparator 314; and is connected at input terminal 494 to lead 412. A
NAND gate 498, having a pair of input terminals 500 and 502, and an output
terminal 504, is connected at input terminal 500 to output terminal 398 of
comparator 314. NAND gate 498 is connected at its input terminal 502 to
lead 411.
Referring now to FIG. 7, input encoder 26 is shown therein. Input encoder
26 is a binary encoding matrix. Binary encoding matrix 26 has a plurality
of columns 506, 508, 510, 512, 514, 516, 518, 520, 522, 524, 526 and 528.
In this embodiment, encoding matrix 26 has plurality of rows 530, 532 and
534. Rows 530, 532 and 534 each have a respective switch 536, 538 and 540
which is selectively connectable to ground. Each of columns 506, 508, 510,
512, 514, 516, 518, 520, 522, 524, 526 and 528 has a respective identical
resistance 542, 544, 546, 548, 550, 552, 554, 556, 558, 560, 562 and 564
in series with it. Resistances 542 through 564 are connected in parallel
to a potential source connection point 566, which is connected to a
positive potential. Row 530 has a plurality of shorting diodes 568, 570,
572, 574, 576 and 578 connected to columns 506, 508, 510, 512, 514 and
518, respectively. Row 532 has a plurality of shorting diodes 580, 582,
584, 586, 588, 590 and 592 connected respectively to columns 506, 508,
510, 512, 514, 516 and 522. Row 534 has a plurality of shorting diodes
594, 596, 598 and 600 connected respectively to columns 506, 508, 514 and
524.
Columns 506, 508, 510 and 512 are respectively connected to input encoder
terminals 324, 326, 328 and 330 of comparator 310. Columns 514, 516, 518
and 520 are respectively connected to input encoder terminals 354, 356,
358 and 360 of comparator 312. Columns 522, 524, 526 and 528 are
respectively connected to input encoder termnals 384, 386, 388 and 390 of
comparator 314.
A four-bit comparator and digital-to-analog converter 602 is connected to
latch 248 and input encoder 26. Comparator and digital-to-analog converter
602 includes a plurality of exclusive OR gates 604, 606, 608 and 610.
Exclusive OR gate has a pair of input terminals 612 and 614, and an output
terminal 616. Exclusive OR gate 606 has a pair of input terminals 618 and
620, and an output terminal 622. Exclusive OR gate 608 has a pair of input
terminals 624 and 626, and an output terminal 628. Exclusive OR gate 610
has a pair of input terminals 630 and 632, and an output terminal 634.
Input terminals 612, 618, 624 and 630 are respectively connected to output
terminals 286, 288, 290 and 292 of latch 250. Input terminals 614, 620,
626 and 632 are respectively connected to columns 506, 508, 510 and 512 of
encoding matrix 26. Output terminals 616, 622, 628 and 634 are
respectively connected to a plurality of diodes 636, 638, 640 and 642.
A resistor 644 is connected to diode 636. A resistor 646 is connected to
diode 638. A resistor 648 is connected to doide 640. A resistor 650 is
connected to diode 642. Resistors 644, 646, 648 and 650 are connected in
parallel to a lead 652. Lead 652 is connected to a voltage point 654. A
positive voltage is applied at point 654. A resistor 656 is connected to
lead 652 at point 654. A back-biased Zener diode 658 is connected to
resistor 656. Back-biased Zener diode 658 is grounded.
A PNP transistor 660, having a base 662, an emitter 664 and a collector
666, is connected at its base 662 to resistor 656. Emitter 664 is
connected to the junction of resistors 644 and diode 636. Collector 666 is
connected to a lead 668. A lead 670 is also connected to resistor 656. A
PNP transistor 672, having a base 674, an emitter 676 and a collector 678,
is connected by its base 674 to lead 670. Emitter 676 is connected to the
junction of resistor 646 and diode 638. Collector 678 is connected to lead
668. A transistor 680, having a base 682, an emitter 684 and a collector
686, has its base 682 connected to lead 670. Emitter 684 is connected to
the junction of resistor 648 and diode 640. Collector 686 is connected to
lead 668. A PNP transistor 688, having a base 690, an emitter 692 and a
collector 694, is connected by its base 690 to lead 670. Emitter 692 is
connected to the junction of resistor 650 and diode 642. Colllector 694 is
connected to lead 668. A resistor 696 is connected to the junction of
collector 694 and lead 668. Resistor 696 is also grounded.
An operational amplifier 698, having a non-inverting terminal 700, an
inverting terminal 702 and an output terminal 704, is connected at its
non-inverting terminal 700 to lead 668. A resistor 706 is connected
between output terminal 704 and inverting terminal 702. A resistor 708 is
connected to resistor 706 and inverting terminal 702. Resistor 708 is
grounded. A resistor 710 is connected to resistor 708, in parallel with
resistor 708. Resistor 710 is connected to an operational amplifier 712,
having a non-inverting input terminal 714, an inverting input terminal 716
and an output terminal 718. Resistor 710 is connected to non-inverting
terminal 714. A resistor 720 is connected between output terminal 718 and
inverting input terminal 716. A resistor 722 is connected between the
junction of resistor 720 and inverting terminal 716 and lead 668. A
resistor 724 is connected to output terminal 704. A resistor 726 is
connected to output terminal 718.
Resistor 726 is connected to a P-channel FET 728, having a gate 730, a
source 732 and a drain 734. Resistor 726 is connected to source 732. Gate
730 is connected to output terminal 412 of NAND gate 404. Drain 734 is
connected to a lead 736.
Resistor 724 is connected to a P-channel FET 738, having a gate 740, a
source 742 and a drain 744. Resistor 724 is connected to source 742. Gate
740 is connected to output terminal 488 of NAND gate 480. Drain 744 is
connected in parallel to drain 742 with lead 736. A P-channel FET 746 is
connected to lead 736. FET 746 has a gate 748, a source 750 and a drain
752. Drain 752 is connected to lead 736. Source 750 is connected to a
resistor 754. Resistor 754 is connected to a voltage source at a point
756. Gate 748 is connected to output terminal 466 of NAND gate 490.
A P-channel FET 758, having a gate 760, a source 762 and a drain 764, is
connected to lead 736 at drain 764. Source762 is connected to a resistor
766. Resistor 766 is connected to a voltage source at a point 768. Gate
760 is connected to output terminal 504 of NAND gate 498. A motor control
amplifier 765 is connected to lead 736. Motor control amplifier 765
includes an operational amplifier 767, having a non-inverting input
terminal 769, an inverting input terminal 770 and an output terminal 772.
Operational amplifier 767 is connected at its inverting terminal 770 to
drain 764 of FET 758. A resistor 774 is connected between output terminal
772 and inverting terminal 770. A resistor 776 is connected to inverting
terminal 770. A resistor 778 is connected between resistor 776 and
non-inverting input terminal 769. Resistors 776 and 778 are also connected
to ground. A meter 780 is connected to output terminal 772. A resistor 782
is connected to meter 780. Resistor 782 is grounded.
Motor control amplifier 765 further includes an operational amplifier 784,
having an inverting terminal 786, a noninverting inverting input terminal
788 and an output terminal 790. Operational amplifier 784 is connected at
its inverting terminal 786 to output terminal 772 of operational amplifer
769. A resistor 792 is connected to non-inverting terminal 788 of
operational amplifier 784. Resistor 792 is grounded.
Motor control amplifier 765 also includes an NPN transistor 794, having a
base 796, an emitter 798 and a collector 800. NPN transistor 794 is
connected by its base 796 to output terminal 790 of operational amplifier
784. Emitter 798 of transistor 794 is connected to a resistor 802. Emitter
798 is also connected to an NPN transistor 804, having a base 806 and a
collector 810. Base 806 of transistor 804 is connected to emitter 798 of
transistor 794. Collector 800 of transistor 794 is connected to a positive
voltage source. Collector 810 of transistor 804 is also connected to a
positive voltage source. A PNP transistor 812, having a base 814, an
emitter 816 and a collector 818, is connected by its base 814 to output
terminal 790 of operational amplifier 784. A resistor 820 is connected
between emitter 816 and resistor 802. A PNP transistor 822, having a base
824, an emitter 826 and a collector 828, is connected by its base 824 to
the junction of emitter 816 and resistor 820. Emitter 826 of transistor
822 is connected to emitter 808 of transistor 804. Collector 818 is
connected to a negative voltage source. Collector 828 is also connected to
a negative voltage source. A lead 830 is connected to the junction of
resistors 802 and 820. Lead 830 is also connected to the junction of
emitters 808 and 826. Lead 830 is connected to motor 28. A tachometer 832
is connected to motor 830. A lead 834 is connected from tachometer 832 to
non-inverting input terminal 788 of operational amplifier 784. A lead 836
is connected to motor 28. A lead 838 is connected to tachometer 832. Leads
836 and 838 are connected in parallel to ground.
Referring now to FIGS 1, 2 and 4, motor 28 can be seen in FIG. 4. Motor 28
is contained in a base 840 of drum 10. Motor 28 is carried on a shaft arm
842. Shaft arm 842 has a pair of spaced tongues 844 and 846, extending
perpendicularly from the body of shaft arm 842. Shaft arm 842 is pivotedly
connected to an arm support 847. Arm support 847 is fixedly connected to
the inside of base 840. A gear 848 is rotatably mounted between tongues
844 and 846, and is connected drivingly to motor 28. A gear 849 meshingly
engages gear 840. Gear 849 is rotatably mounted between spaced tongues 844
and 846. Gear 849 is threadedly connected to a threaded rod 850. Threaded
rod 850 is, in turn, part of mechanical linkage 14. Base 840 has a foot
pedal 852 pivotedly attached thereto. Foot pedal 852 is connected to a
hinge 854. Hinge 854 is connected to base 840. A push rod 856 is connected
to foot pedal 852; and, via a link 858, to shaft arm 842.
Mechanical linkage also includes a central pivot head 860, connected to the
end of threaded rod 850, as is conventional in the construction of
kettledrums. Pivot head 860 is connected, via a plurality of tension lines
862, 864, 866 and 868, to a plurality of hinges, one of which is shown as
hinge 870. Hinge 870 is mounted in a leg 872 of kettledrum 10. Hinge 870
is linkingly connected to a push rod 874. Leg 872 and a plurality of legs
876, 878 and 880 are connected to base 840. In addition, legs 872, 876,
878 and 880 are supportively connected to kettle 13. Leg 880 has a tension
line 882 mounted therein. Tension line 882 is hingledly connected to
tension line 862. Tension line 882 is connected to a hinge 884, which has
a pivot 886 and a pivot 888. Pivot 886 is connected to leg 880. Pivot 888
is connected to a support rod 890. A counter hoop 892 is connected to rod
890. Counter hoop 892 is of a circular configuration; and surrounds
drumhead 12. A flesh hoop 894 is clamped under counter hoop 892. Drumhead
12 is fixedly attached to flesh hoop 894.
In operation, drum 10 is struck off-center on drumhead 12 to produce a
desired tone. Drumhead 12 vibrates, as is shown in FIG. 2. The vibration
produces both a fundamental tone and harmonics. At the time the drumhead
is struck, and immediately thereafter, the drumhead generates a large
percentage of harmonics and noise. The harmonics and noise decay more
rapidly than the fundamental tone. Thus, the tone becomes more pure with
time. The typical decay time for a tone generated by a twenty-six-inch
kettledrum is on the order of two seconds. The vibration of drumhead 12
carries reflective patch 38 through a similar vibration. Light 36 projects
light beam 37 against reflective patch 38. As reflective patch 38 moves,
light beam 37 swings through a portion of an arc, across photoresistors 30
and 32.
Optical vibration sensor 16, as was set forth above, is comprised of two
photoresistors 30 and 32, which are connected in a Wheatstone bridge
circuit 40. Optical vibration sensor 16, of which Wheatstone br | | |
