Note: Descriptions are shown in the official language in which they were submitted.
Technical Field
This inven~ion relat~s to musical instruments and
more part.icularly to an electronic harmonica which generates
electrical signals ~or controlling elec~ronic sound syn-
thesizing devices.
.
~ .
1- .
Backqround of the Inv2ntion
The variety of sounds and range of amplitudes
which can be produced with a traditional musical instrument
are circumscri~ed by its design and by the physical limita-
tions of the musician. Most conventional harmonicas, -for
example, are tuned to play a very limited range of full
tones and cannot produce sharp or flat half tones. An ex-
perienced player can Nbend~ the notes to approximate half
1~ tones, but the result is less ~han desirable. The volume or
amplitude of the tones produced ~y a conventional harmonica
is also limited by the lung capacity of the musician.
Mechanically modified harmonicas have been
designed to enable generation of half tones, as well as full
tones. U.S. Patent 2,565,100, issuad August 21, 1951 to J.
R. Tate, discloses one example. Such instruments typically
require the player learn new lip and hand movements that
di~fer substantially from conventional techniques for play-
ing a harmonica. These prior art instruments are also in-
capable of providing for other embellishments that would be
desirable, such as adding chords or ~ctave notes or changing
frequencies, key, scale tempo or the like.
Prior e~orts to increase ths ran~e of sound in-
tensitles obtainable from a harmonica have included instal-
lation of a microphone on the harmonica which is ~oupled to
a loudspeaker through an electrical amplifier, as ex-
empli~ied by the above ldenti~ied U.S. Patent 2,565,100.
- 2 -
% ~
This results in the production of the music at the harmonica
; itself accompanied by a repr~duction of the music at the
,~, .,
,~ loudspeaker location. Fee~back effects, in such an arrange-
~` ment, can disturb the musical performance. Such a system
; 5 also does not enable any embellishments of the musie
~! produced by the harmonica, other than volume amplification.
Recent deveLopments in electronie sound syn-
the~ r~ have overcome th~ limitations imposed by the
. . ,
desigll o~ tr~ditional musieal instruments and by the physi-
~' 10 cal eapabilities of the musician. Such systems, in the most
~, advaneed forms, are typically controlled by a digital
micxoprocessor be actuated with a keyboard or other input
deviee, to produce virtually any audible tone and to provide
any of a great variety of embellishments.
;, A harmonica construction eapable o~ eontrolling
il 15 sueh synthesizers signi~icantly enhanees the range o~ musi-
~'l eal options available to har~onica players. Preferably sueh
an infitrument should have the ~eel of the traditional in-
strument and not require any substantial alteration of the
~ eonventional teehniques ~or playing a harmoniea.
I,~ 20 Prior efforts to dispense with the reeds in the
' eonventional harmoniea and to substitute elee~rieal elements
for eontrolling an eleetrieal sound produeing d~vic~ hav~
not extended the eapabilities 9f the eonventional instxu-
ments~
. . ~ .
`
. . - ` : .
- 3 -
2 ~ ~. J F~ ~
u.S. Patent 2,455,032, issued Nove~ber 30, 1948 to
A. 0. Williams, describes a construction in which the reeds
are replaced with pressura~ensikive switches, each o~ which
can be operated by blowing into the harmonica and each o~
which causes a tone generator to produce a different one o~
a series of predeterminecl audio frequencies. The switches
are on-of~ d~vices which cannot detect variations in the
amplitude of notes that a musician generates.
U.S. Patent 3,516,320, issued ~une 23, 1970 to C.
A. Hillairet et al., also teaches the use of a series of air
flow actuated switches to d~tect air flow in any of the pas-
sages o~ a harmonica. Actuation of any of the switches
changes the output frequency of an electrical oscillator,
which is coupled to an audio speaker ~hrough an ampli~ier,
to produce the musical note which corresponds to the par-
ticular air passage. The circuit is an improvement of the
Williams device in that an air velocity detector modulates
the amplifier gain to vary the volume of the generated sound
in response to variations in the flow rate of the player's
breath. Additional controls enable the player to shift oc-
taves and to lntroduce effects such as tremolo an~ produc-
- tion of semi-tones.
However, the apparatus o~ U.S~ Patent 3,516,320
does not qenerate separate ele trical signals ~or each air
passage that are independent-of each other and which encode
both activation o~ the passage by the musician and also the
desired amplitude of the no~e. The note sensing switches
~ 4 -
'
.
2 0 ~
are interlinked at the single oscillator which cannot
respond accurately to simultaneous actuation of more than
one such switch. The separ~te amplitude detecting means is
a single detector which jointly monitors all air passages.
These characteristics do not pxovide the necessary ver-
satility for controlling a saund synthesizer.
A further characteristic of prior electronic har-
monicas is undesirable mechanical complexity and fragility
in the air flow sensing mechanisms. This makes such instru-
ments costly and prone to malfunc~ion from the e~fects of
saliva, dust, impacts or the liXe.
The present invention is directed to overcoming
one or more of the problems discussed above.
Summary of the Invention
In one aspect, the present invention provides an
electronic harmonica hav.ing a body with a plurality of air
passages each corresponding to a difPerent musical note, an
electrical power source and means for enabling an electri-
cally operated sound producing device to produce selected
sequences of the musical note signals in response to passage
of the player's breath through selected passages. The har-
monica includes air flow sensing means for produci~g
separate electrical signals in respons~ ~o air ~low through
each passage and for individually varying each of the sig-
nals in response to variations of air ~low rate and direc-
tion in the passage. This provides not characterizing sig-
. .
' ~'.
'
.
: '`.. .. . ; ' ' : ,
nals which identi~y notes ~ b played and also identi~y the
amplitude at which the note is to be played. The harmonica
further includes means fo~`transmitting each of the note
characteri~ing signals to the sound producing transducer.
In another aspect of the pr~sent invention, an
~, .
electronic harmonica for controlling a sound synthesizing
device that responds to control signals identifying musical
notes includes a body having a plurality of spaced apart air
passages and a plurality of electrical strain gages in the
n body. Each of the strain gages is positioned to ba flexed
by air flow in a separate one of the passages. The electri-
cal re istivity of each gage changes in response to such
flexing. Means are provided for producing the control sig-
nals by dPtec~ing air flow induced changes of the resis-
~, tivity of each of the strain gages.
In still another aspect, the invention provides an
electronic harmonica for generating and transmitting digital
control signals to a digital sound synthesizer. The har-
monica body has a plurality of spaced apaxt air passages
each corresponding to a different musical note and further
! components include a direct current electrical voltag~
supply and mPans for transmitting the digital control 5ig-
nals from the harmonica to the soun~ synthesiæer. A
plurality of strain gages are secured to the body and each
gag~ has a flexible resilient element exposed *o the air
flow within a separate one of the air ~assages, Each strain
-; gage has an electrical resistance which varies in response
- 6 -
,
,
.. .. .
".' . ' . . ,
, ~ '
2 ~
to flexing of the element a~d which is connected across the
voltage supply. Detector means sense changes of the resis-
tance of each strain gage and produces a plurality o~ analog
electrical signals, each of which indicates changes in the
resistance of a separate one of the strain gages. The har-
monica furkher includes means for repeti~ively generating a
sequence of digitally coded addresses that identify succes-
sive ones o~ the strain gages, an analog to digital con-
verter, and means for reading out repetitive sequences of
the analog signals from the detector means in response to
receipt of successive digitally coded addresses. The
resulting sequences of analog signals are directed to the
analog to digital converter to produce corresponding se-
quences of digital signal bytes that identify the amplitudes
of musical notes which are to be produced by the sound syn-
thesizer. Means are provided for adding address code bitsto each of the signal bytes to identify the musical note
which each byte characterizes. The sequences of bytes, in-
cluding the address code bits, are directed to the transmit-
ting means.
~0 The invention provides a mechanically simple and
damage resistant harmonica construction which greatly ex-
pands the range o~ musical effects which c~n be created by
the player of this novel instrument. The harmonica genera-
.
tes electrical signals which continually identify air flow
rate and direction in each air passage to enable an
electronic sound syntbeslser to producF the desired notes at
. . . : . :
.
- - .: ,
:' ' ' ' ' ' '
' ' ' ' . ' ', ' ` ' . :
2 ~ u ,~
the desired amplitude and, if desired, to modify, augment
and embellish the resulting music in wa~s that cannot }~e ac-
c o m p 1 i s ~' h e d w i t h
the conventional acoustic harmonica. In the
preferred form, the invention produces the electrical sig-
nals in a digital form which enables control of any of the
variety of digital sound synthesizing systems or instruments
that are equipped with the internationally standardized MIDI
(Music Instrument Digital Interface) ports.
Brief Description of the Drawinqs
Fig. 1 is a perspective view of the exterior of an
electronic harmonica in accordance with the preferred em-
bodiment of the invention.
Fig. 2 is a cross-section view o~ the harmonica of
,; 15 Fig. 1 taken along line 2-2 thereof.
Fig. 3 is a partial section view talcen along line
;; 3 3 oî Fig. 2 rurther depicting the internal construction of
the instrument.
;~ Fig. 4 is an exploded perspective view illustrat-
ing the principal components of the harmonica of the preced-
ing f igures ~
Fig. 5 is a circuit diagram depicting certain
. .
electrical components of the preîerred embodimentO
Fig. 6 lS a circuit diagram showing further com
ponents of the circuit which enable coupling of the har-
monica to a MIDI equipped digital sound synthesizer.
8 --
.
' - : - ' ' '
2 ~ ~ .3 ~
Fig. 7 is an electrical circuit diagram for
; another embodiment of the invention which is non-digital and
designed for controlling a~ess complex sound producing sys-
tem.
`; Detailed Description oE the Preferred Embodiment
~ R~erring initially to Fig. 1 of th,e drawings, an
,~ electronic harmonica 11 in accordance with this embodiment
o~ the invention may, if desired, have an external con-
; 10 ~iguration closely resembling that of a conventional instru-
ment and may be of more or less the same size. Major struc-
tural components include a flat body member 12 of rectan-
gular outline and cover plates 13 secured against each side
' of the body member.
,~ Referring to Figs. 1 and 2 in conjunction, the
forwar~ surface of body member 12 has rounded edges to
define a mouthpiece 14 and is transpierced by a row of
spaced apart wind'cell apertures 16 through which the musi-
cal can blow or draw air in the conventional manne.r. Each
such aperture 16 corresponds to a different not of the musi-
cal scale as in an acoustical harmonica. ~his embodiment
has twelve such apertures 16 to provide a chromatic har-
monica although the instrument can also be constricted with
other numbers of apertures. A diatonic harmonica, for ex-
- ample, requires only ten apertures.
,
'. . :
g_
.- . '
.: , ' ' : ' ' ~ ' -
. ..
With reference to Figs. 2 and 3, each wind c~l~
aperture 16 communicates with a separate one of a series of
parallel air ~low passages 17 within body member 12, which
passages extend through the back of the member. An im-
mulator flow restriction 18 at the back of each such passage
17 has an opening 19 which is smaller than the passage and
i5 sized to create the same degree of flow resistance that a
player experiences in the corresponding passage o a conven-
tional acoustic harmonica. This resistance progrPssively
decreases at successive ones of the passages 17 and thus the
opening~ 19 can be of progressively greater diameter at suc-
cessive ones of the passages in the direction of the left or
low note end o~ the instrument.
One of a series of electrical strain gages 21 ex~
tends into each passage 17 in order to sense air flow,
direc.tion and also the rate of the flow as will be further
discussed in connection with the electrical circuit of the
harmonica 11. Strain gages 21 may be of ~he known form
which have a flexible resilient backing 22 and a thin film-
like electrical resistor 23 adhered to the backing. Thus,
flexing of the backing tensions or compresses the resistor
to cause a detectable change of resistanca. The strain
t yages 21 of this particular example are of the form which
are pretensioned while being adhered to the backing 22.
Consequently, flexing of the gage 21 in one direction as il-
lustrated at 21a causes the electrical resistance to in-
crease as a function of the degree o~ flexing and movemen~
-- 10 --
~ a ~
in the opposite direction, as illustrated at 21b, causes a
progressive decrease in resistance. This enables sound
processing equlpment whlch~,may be coupled to the harmonica
ll to distinguish signals produced by blowing into ~he pas-
sage 17 from signals caused by drawing air through same pas-
sage. ~ir flow direction is sensed to provide two note sig-
;~ ~als from each passage.
Reerring a~ain to Fig. 1, the manually operated
controls 24 on the harmonica 11 o~ this particular embodi-
ment include two push button switches 24a and 24b that are
accessible at the central region of the top cover plate 13.
The switches 24 enable the player to signal th~ sound syn-
thesizer 26 to select the various alterations which such
systems are programmed to per~orm such as, for example, the
introduction of chords or simulation o~ the sound of another
, 15 musical instrument. Additional switches 24 may be provided
to increase the number of such options available to the har-
monica player of this novel instrument. Electrical connec-
tions to such switches will be hereinafter described.
Another push button 27 extends from the right side
` 20 of harmonica 11 for selectively causing the generation of
sharp or flat notes as will also be further discussPd. A
switch 2~ for turning the harmonica 11 on and off is
situated at the back of body member 12 in this example.
The harmonica 11 is Xurther provide~ with trans-
, 25 mitting means 29 for delivering signals to the remote sound
; synthesiz~r ~6. Such means 29 as depicted in Fig. 1 include
.
.~ :
a signal output port of jack 31 located at the left side2o~ ~
body member 1~ into which a multi-conductor electrical cable
32 can be plugged to condu~ signals to the synthesizer 26.
Other modes of signal transmission can also be used such as
fiber optic transmission of coded light signals. It is ad-
vantageous in many cases, such as in stage performances, to
dispense with any ~orm of cable 32. For this purpose, the
harmonica 11 may contain a small low power radio transmitter
33 having an antenna wire 3~ which extends for a short dis-
lo tance along the left side and back of the exterior of body
member 12~
Fig. 4 depicts a compact, and acceptable detailed
construction for the novel harmonica 11, although it should
be recognized that the components can have other configura-
tions and also may ~e differently arranged.
Body member 12 in this embodiment is a rectangular
frame having a series of spaced apart partitions 36 extend-
ing from front to back to define the side walls of the air
passages 17. Preferably, a pair o~ such partitions 36 are
disposed between each passage 17 and the ad]acent passages,
which pair o~ partitions axe slightly spaced apart as better
seen in Fig. 3. This provides a thin cushioning dead air
space 37 between successive passages 17 which prevents
cross-talk. Any flexing o~ the partition 36 at one passage
17 that may occur from changing air flow is not transferred`~
to the adjoining passages and thus doeæ not result in
spurious signals in adjoining passages.
- 12 -
-
2 ~
Xeferring again to Fig. 4, most of the components
of the electrical circuit of the harmonica 11 are attached
to or formed in a thin fl~t rectangular circuit board 38
which seats in a rectangular shelf 39 at the top of body
5member 12. Most such components, other than function
switches 24a, 24b, output port 31 and a vibrato/tremolo con-
trol 41, are not depicted in Fig. 4, as the scale of the
drawing does not permit such depiction and such components
will be hereinafter described with reference to circuit
10diagrams.
Another thin flat board ~2 similarly seats against
the underside of body member 12 and carries the sharp/flat
switch 27 and a rechargeable electrical battery 43 at op-
posite end locations where such components can be received
in the body men~er at opposite ends of the series of parti-
15tions 36. Battery 43 has projecting needle-like terminals
44 that penetrate into positive and negative power supply
terminal regions 46 of the circuit board 38 upon assembly of
the components. Body member 12 has an opening 47 located to
provide access to the recharging terminal port 48 for bat-
20tery 43~
The strain gages 21 in this embodiment are linked
together at the top by a continuous strip of material 49
which may b~ integral with the previously described backing
material 22 of the individual gagesO In the assembled har-
25monica 11, the gages 21 extend down into separate ones o~
the air passages 17 through a row of aligned slots 51 in the
.
- 13 -
' ' ~
circuit board 38. Referring again to Fig. 2, the strip por-
tion 49 of the strain gage 21 assembly is clamped between
two parallel insulative li~ear members 52 that are secured
to the top of circuit board 38. Needle-like contacts 53 are
penetra~ed through one such member 52 to provide for
electrical connections between the strain gayes 21 and other
circuit components.
Re~erring to Figs. 2 and 4 in conjunction, the im-
mulator flow reskriction openin~s 19 in this example are
formed in a slat-like member 54 which ~its into a slot 56
that extends along the back of body member 1~, successive
ones of the openings being located to register with succes-
sive ones of the air flow passages 17. Slat member 54 can
be replaced with another one having different sized openings
19 if it is desired to adjust the resistance to blowing or
drawing which the player experiences.
Referring again to Fig~ 4 in particular, insertion
of the immulator slat 54 into slot 56 is followed by inser-
tion of a small infrared light filter 57 into the end region
of the slot. Filter 57 seats over an infrared light window
58 in body member 12 which ~aces the vibrato/tremolo control
41. One portion of control 41 is an infrared light source
41a directed at window 58 and another portion of the contrQl
is an infrared detector 41b positioned to view the windowO
The player's hand is situated behind the window 58 and
reflects infrared from source 41a back to detector 41b. By
movement o~ tha hznd, the player =ay vary the amount of in-
- 14 -
.
,
frared light that is re~lected back to detector 41b and
thereby vary the output signal of the detector. As will
hereinafter be further descri~ed, this signal will cause the
sound synthesizer to oscillate a sound ~requency and thereby
cause a vibrato or ~rem~lo effect. The ~ilter 57 prevents
distortion of the desired signals by keeping al~bient visible
light awa~ ~rom detector 4lb.
Covers 13, which have a shallow dished shape, fit
against the top and bottom of hody member 12 to enclose the
internal components of the harmonica 11 and to define a hand
grip. Covers 13 have a pair of shallow notches 59 at each
end for, with reference to Fig. 1, receiving the ends of
U-shaped spring tensioned clips 61 which secure the as-
sembled components together. The components may also be
held together by other fasteners such as screws or by
adhesives if the instrument is not intended to be disas~
semble.
Referring now to Fig. 5, electrical components of
the harmonica receive D.C. operating voltage fxom the posi-
tive terminal B~ o~ a voltage xegulator 63 which also has
another terminal 69 de~ining a common conductor or chassis
ground. The battery 43 and on-off switch 2 ~ are connected
across the voltage regulator 63 input terminals ~3t in
series relationship vith each other.
The strain gages 21, the function control switches
such as 24a, the sharp/flat switch 27 and the
vi~rato/tremolo control 41 are each in a separa~e one o~
- 15 -
.
~ o ~ s~
sixteen signal channels 67 through a signal generating cir~
cuit 68. Channels 67 sequentially receive a momentary input
, ' voltage from a digital ,~`ddress decoder 64 which will
;, hereinafter be further discussed. The sequence of momentary
;" 5 applications of B-t vol~age to the input terminals 66 of
,' ` channels 67 is continually repeated, while the instrumant is
'',' in operation, preferably at a high repetition rate or fre-
quency which is 20 ~2 in this particular example. ~igh fre-
quency scanning of the channels 67 produces higher quality
;~ 10 sound as air flcw changes are detected more quickly and in
,'` smaller increments than is possible at lower frequencies.
Each s.rain ~age 21, of which only a single one is
` depicted in Fig. 5, is connected between the input terminal
~ 66 of a separate channel 67 and chassis ground in series
,1 relationship with a fixed resistor 71. Thus each such gage
21 and its associated resistor 71 functions as a voltage
~, divider and the voltage at the junction 72 between the gage
'' , and resistor, during successive energizations of the channel
67, varies in response to the changes of resistivity of the
gage that are caused by variations in air flow ra~e through
: !
~ 20 the corresponding one of the harmonica passages as previ-
,,~,' ~` ously descxibed. The varying voltage pulses from each such
`~``. circuit junction 72 are transmitted to a separate input ter-
`,~ minal 73 of a signal sensing circuit 74.
Within the signal sensing circuit 7~, each input
terminal 73 is connected to the nega~iv~ or inverting input
of a separate one of a series of voltage amplifiers 76
:
- 16 -
~ '
'
2 0 ~ J
through an input resistor 77, the positi~e or noninvertiny
input of the amplifier being connected to ground through
another resistor 78~ A feedback resistor 79 fixes the gain
of the amplifier 76 in the known mannèr.
Ou~put pulses ~rom ampli~ier 76 are transmitted to
a separate one of a series of output terminals 81 of the
sensing circuit 74 through one of a series of buffer
ampli~iers 82~ In particular, the output of amplifier 76 is
coupled to the noninverting input of buf~er amplifier 82
through a capacitor 83 which input is also connected to
ground through a resistor ~4. The inverting input of the
- bu~er amplifier 82 is connected to chassis ground through
another resistor 86 and to the output o~ the amplifier
through a feedback resistor 87. Thus, each ~uf~er amplifier
82 of the sending circuit 74 transmits a voltage pulse to
the associated out-terminal 81 each time decoder 64 ener-
gizes the associated signal channel 67, the amplitude of the
pulse being indicative o~ the momentary rate of air flow
thxough the corresponding one of the harmonica air passages
at the time of the strobe.
To generate the vibrato/tremolo signal within the
signal generating circuit 68, the in~rared lig~t detector
4lb is a photodiode connected between a decoder terminal 66
and chassis ground in series wi h a voltage droppi~g resis-
tor 89. The junction 91 between photodiode d2tector 41b and
resistor 89 is coupled to the associated separa~e one o~ th
outpu~ terminals 81 in sensing circuit 7~ through an
-- 17 --
,, '
: ' , '
amplifier circuit 92b which may bs similar to the circui~
92a described above wi~h refer~nce to the s~rain gage 21
signal ohannel. The inf~a~d light source 41a, which may be
a light emitting diode, is connected between the same input
terminal 66 and chassis ground.
Thus the diodes ~la and 41~ ara bokh momentarily
energized each time that decoder 64 applies a momentary
vol~age to the associated input terminal 66. The amount of
in~rared light from diode 41a that is received by diode 41b
is dependent on the harmonica player's hand movements in the
manner previously described. The diode detector 41b and
resistor 89 are in effect a voltage divider. Consequently,
as the resistance of diode 4lb varies in response to varia-
tions in the amount of infrared which it receives, the mag-
nitude of successive voltage p~lses at junction 91 and at
. . . .
~ 15 the associated output terminal 81 is varied in response to
; the player's hand movements. Oscillation o~ the player's
hand causes a similar oscillation oP the amplitude of suc-
cessive voltage pulses at the terminal 81.
Signals identiying the setting of the sharp/flat
selector switch 27 are generated in circuit 68 by a linear
potentiometer 93 having a resistive element 94 connected be-
tween the associated input terminal 66 and chassis ground
and having an adjustable tap 96 which is shiftable to any of
three positions along the resistiYe element by depresslo~ or
release of the actuator button 97.
~; - 18 -
. ~. .'. , . ' . ' '
' ' ' ' ': : '
Tap 96 is coupled to another of the sensing clr-
cuit output terminals 81 by another amplifier circuit 92c
similar to the previous~y,~escribed amplifier circuit 92a.
Thus, upon each energization of the potentiomater 93 by
decoder 64, a voltage pulse appears at the terminal 81 that
has one of three different magnitudes as determined by the
harmonica player. ~he highest magnitude vol~age, produced
when switch 27 is at its normal position, signals that
natural notes are to be played. Partial depression of the
actuator 97 to the intermediate position signals ~or sharp
notes and full depression indicates that flat notes are to
be synthesized.
In order to genera~e signals indicating the set-
ting of function selector switch 24a, a pair of fixed volt-
age divider resistors 98 and 99 are connected in series be-
tween the associated input terminal 66 and chassis ground.
the normally open function selector switch 24a bridges the
one of the resistors 98 that is directly connected to ter-
minal 66. The junction 101 between resistors 98 and 99 is
coupled to another output terminal 88 of sensing circuit 7~
through still another amplifier circuit 92d of the type pre-
viously described.
Thus repetitive voltages pulses having a ~irst
amplitude appear at the associated one of the sensing cir-
cuit output terminals 81 when switch 24a is in the normal
open condition and indicate hat the unction:aontrolled by
the switch iR not wanted. Cl~sing of th~ ~witch 24a by the
l9 _
::
' ' ' ' ,
2 0 ~
harmonica player causes higher voltaga pulses to appear at
- the terminal 81 to signal the sound synthesizer that the function is to be implemen~ed.
The circuit 68 has been described in detail with
respect to only one of the s~rain gage 21 channels and only
one o~ the function selector switch 2~a channels. It should
be understood that the circuit detail for each of the other
strain gages and th2 o~her ~unction selec~or switch may be
of sin~ilar conPiguration.
It may be noted, with refer~nce jointly to Figs. 2
and 5, that voltage pulses of a predetermined amplitude will
appear at sensing circuit output terminals 81 when there is
no air flow in the harmonica passages 17 and tha strain
gages 21 are in the unflexed state. Flexing of the strain
gages 21 in one direction 21a causes the pulse amplitudes to
rise from this normal value by an amount dependent on the
' degree of flexing and thus the rate of air flow. Flexin~ of
~, the gages 21 in the opposite direction 21b causes a lowering
of pulse amplitudes to a degree dependent on the magnitude
of the flexing. The normal pulse voltage that is produced
under conditions of no air flow is in~erpreted by the signal
utilizing system as calling for an off or no sound signal.
Increasing or dPcreasing voltage~ Prom any of the strain
gage channels 67 are interpreted as calling ~or syntheslzing
of the particular musical note to which that channel cor-
~ 25 responds at an amplitude or volume dependen~ on the amount
'` of the voltage increase or decrease. The fact that the
.1 .
20 -
..
', ' '
:: ' ' ' -
.
2 0 ~
pulse amplitudes may either increase or decrease from the no
air flow value, depending on direction o~ air flow, enables
definition be~ween notes ~oduced by blowing into the har-
monica 11 and notes producing by drawing or sucking on the
5harmonica.
Th~ circuit described above causes momentary volt-
age pulses to appear sequentially at the sixteen output ter-
minals 81 of the sensing circuit 74 in a repetitive cycle,
each pulse being an analog signal which characterizes what
10the harmonica player desires at that instant with respect to
a particular musical note or with respect to a particular
control function. These signals may be used in any of
various way for controlling known forms of sound synthesiz-
ing apparatus.
For example, with reference to Fig. 6, the analog
15signals from sensing circui~ output terminals 81 may be
digitized and transmitted to one or more digital sound syn-
thesizers 102 oE the type having a MIDI signal interface 103
and which are typically controlled by a computer or
microprocessor 104. ~he construction and operation of such
20sound generating equipment 106 are well understood in the
art and widely employed in apparatus ranging from electronic
keyboards sold for amateur use to complex, costly ins~alla-
tions for professional synthesizing of music or other acous-
tical effects. Typically such apparatus incIudes a function
25selector console 107 by which an operator can condi~ion the
microprocessor 104 to augment to modify the oriqinal notes
2 0 ~
produced by the musician in any of a variety of ways, ln-
cluding, among many other ~xamples, addition of chords, con-
version of musical key, substitution of sharp or flat
notes or simulation of the sound of some instrument other
than the one at which the signals actually originate.
The signals from the outputs 81 o~ sensing circuit
74 can be transmitted to the receiving e~uipment 106 over
sixteen separate lines or radio channels but this complica-
tion can be avoided by serializing the data for transmission
by a single channel. For this purpose, a multiplexer 108
reads out the voltages from each term.inal 81 in sequence and
`` delivers corresponding signal voltages to an analog to digi-
tal signal converter 109 in serial form through a single
signal channel 111. Multiplaxer 108 receives the same ad-
dress signals as decoder 64 and thus repetitively reads out
".;~ 15 the sequence of signals in synchronism with the energizing
, of the channels 67 by decoder 64.
`,, The repetitive sequence of digital address codes
for cycling decoder 64 and multiplexer 108 and clock signals
` for repetitively enabling such components can be generated
;. 20 by circuits of the type specifically designed ~or the pur-
pose but it is advantageous to use a microprocessor 112,
coupled to a random access memory 113, read only memory 114
and address latch 116, for these purposes. Programming o~ a
~- microprocessor 112 to repetitlvely ~read out a~serLe of
stored digital address~d ~rom memory 114 and to generate
.
'`
- 22 -
!.
_ . ~
'
2 ~
cyclical enabling signals for peripheral components 64, 108,
los and 112 is a relatively simple operation well understood
in the art.
Analog to digital converter 109 converts each suc-
cessive signal voltage received on channel 111 to a multibit
digital byte or word that identifies the magnitud~ of the
voltage and thus the momentary amplitude of the musical note
that the h~rmonica player desires. Converter 109 produces
ten bit digital words in this example in order to provide 60
dB of dynamic range which exceeds that of an acoustic har-
monica.
To provide ~or transmission of the data to the
remote receiving equipment 106 over a single channel, the
digital words produced by converter 109 are serialized prior
to delivery to the transmitter 33. While a separate paral-
lel to ,serial signal converter can be used for the purpose,
this is preferably done by the microprocessor 112 which also
transmits the address bits with each such word to identify
the note which the word characterizes. Similarly, a
separate serial to parallel converter may be provided be-
tween the received 105 and sound synthesizer 102 to reparal-
lelize the successive signal bytes but this is more con-
veniently done by the receiver microprocessor 104.
The signal generating harmonica is not limited to
production of digital signals for transmission to a MIDI
e~uipped sound synthesizing device 106 of the above
described kind and can be adapted to~control a variety of
- 23 -
2011~
other sound generating devices. For example, with reference
to Fig. 7, the harmonica can be used to selectively actuate
any of a series of electri~l oscillator circuits 117 of the
type that gen~rate an audio fre~uency output in response to
a control signal voltage and at an amplitude that is propor-
tional to the magnitude of the control signal voltage. Each
such oscillator 117 may have a di~ferent frequency cor-
responding to the frequency of a di~ferent musical note.
i Each such oscillator 117 may be coupled to an audio speaker
lo 118 through a separate one of a series of bu~fer amplifiers
119. Thus the speaker 118 produces sounds having audio fre-
quencies corresponding to ~he electrical frequency received
from any of the oscillators 117.
; Modifications of the harmonica circuits for this
purpose include connecting the battery 43 and on-off switch
28 to a D.C. power supply 63a of the bipolar type which has
~..
both positive and negative output terminals B+ and B-. A
pair of equa`l resistances 121 are connected in series across
~ the B+ and B- terminals and the junction between the two
; resistances define the chassis ground for the circuit. Thus,
~ 20 the positive and negative voltages provided by the power
.t~ .
` supply 63a have equal magnitudes relative to ground but are
of opposite polarities.
Each strain gage 21 is connected across the power
supply terminals B+, B- in series with one of a group of
; 25 resistors 122 each of which has a re istance equal to that
~; of the strain gage when it is in the relaxed o~ unflexed
:; :
i - 24 -
~ .
. ~ . .
.. ~ ...~.
.
!
,
' '
., condition. Thus, the junctions 123 between the resistors
~, 122 and strain gages 21 are at ground potential when the
gages are in the unflexe~ state and no output signal is
' present. As each strain gage 21 and the associated resistor
; 5 122 is in effect a voltage divider, an increase of the
resistance of the gage caused by flexing results in a posi-
tive voltage at junction 1~3 that is proportional to the
amount oP ~lexing. Similarly, a ~ecrease of the strain gage
` ! resistance caused by flexing in the opposite direction
produces a proportionate negative voltage at junction 123.
ach junction 123 is connected to chassis ground
through a first diode 124 and resistor 126 and also through
~l~ a second diode 127 and resistor 128, the two diodes being
oppositely oriented to conduct positive and negative volt-
.
` ages respectively. The junction 129 between first diode 124
: 15 and resistor 126 is coupled to the control input of a first
~; o~ the oscillators 117 through a D.C.amplifier 131 and the
',~ junction 132 between second diode 127 and resistor 128 is
`, coupled to another of the oscillators 117 through a separate
D.C.amplifier 133. Amplifier 133 is a polarity inverting
amplifier as the oscillators 117 of this embodiment all
raspond to control voltages of the same polarity. While ~he
- connections to only two of the strain qages 21 are depicted
f in Fig. 7, each of the other s rain gages in the harmonlca
is similarly connected to a separate pair o~ the oscillators
117.
!
2 5
.,'~1~
. ~
Thus blowing into any selected air passage of the
harmonica actuates a corresponding one of the oscillators
117 resulting in generat~n of the corresponding musical
note at speaker 11~. Sucking or drawing air through the
same passage actuates a different oscillator 117 t.o produce
a different musical note. If it is desired that the system
produce the same musical note in response to air flow in a
particular harmonica passage without regard to the direction
of flow, the D.C. amplifiers 131 and 133 may be coupled to
the same oscillator 117.
While the invention has been disclosed with
respect to certain particular embodiments for purposes of
example, many variations and modifications are possible and
it is not intended to limit the invention except as de~ined
in the following claims.
.
- 26 -
'
_.
. . .
' " ' ', '. ' .: ' ' ,', ", ' ' ''. '. '" '. . , " ., ' ~ ' " ~
, . .. ~ . . . . .
