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Claims  |
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I claim:
1. Compact portable apparatus for use in sensing and displaying in digital
terms the frequency of musical instrument strings vibrating in either
damped or undamped mode, and comprising in accordance with the invention:
(a) a housing for placement on the instrument in adjacency to a complement
of strings thereon;
(b) a vibration sensing probe constituting a movable part of said housing
and having a sensing head positionable relative to any selected string of
the complement;
(c) said head having respectively overlying and opposite underlying parts
adapted to straddle the selected string, one of said parts including a
light source and the other opposite part including optical slit means
positioned such that the selected string will vibrate crosswise of the
slit and substantially along the length thereof and modulate the source
light accordingly;
(d) photosensitive means positioned relative to said slit means such that
it is activated by the string-modulated source light;
(e) first circuit means in said housing activated by said photosensitive
means to produce frequency analogue signals from said string-modulated
source light;
(f) further circuit means in said housing converting said signals into
digital control signals;
(g) display means carried by said housing and activated by said digital
control signals to provide a luminous readout of the sensed string
frequency in digital notation;
(h) said probe including electromagnetic string-driving means having a
winding traversed by string-modulated photoelectric current and a salient
pole piece producing a string-vibrating flux varying with the existing
sensed string frequency located and disposed in driving adjacency to the
selected string as an incident to operative placement of the sensing head
relative to such string, whereby magnetically responsive strings will be
driven in sustained vibration at whatever sensed frequency the string
happens to be tuned.
2. A tuning aid of the photoelectric type for use with stringed musical
instruments wherein the vibration of a selected string modulates a light
source and photoelectric sensing and circuit means provided a visual
indication of some aspect of the rate of the string displayed as a visual
readout, characterized: in that a photoelectric sensor means is contained
in a sensing head constituting part of a motile probe which is a movable
component of an emplacement housing small in size and of configuration
suitable for emplacement upon the body of the musical instrument, said
head including a light source and photoelectric vibration sensor means
spaced therefrom to admit therebetween for free vibration however vibrated
whether plucked or power driven, a string selected by adjustment of said
probe to position said head relative thereto, said sensing head further
including optical aperture means in the form of an elongated slit of a
width approximating the width of the string to be sensed and of a length
many times greater than such width and interposed between the selected
string and said sensor means in a particular orientation consequent upon
adjustment of the probe as aforesaid, whereby the length of the slit is in
substantially parallel alignment with a lengthwise portion of the string
on a side thereof such that the string vibrates into the area of the slit
to modulate source light and produce an analogue vibration signal,
together with electronic digital readout display means carried by said
housing for displaying a readout of ambient string frequency in digital
numeric notation, and readout sub-circuit means responsive to said
analogue signals to activate said readout display means.
3. An electronic tuning aid as defined in claim 2 further characterized in
that said probe comprises an arm structure housing said photoelectric
sensor, aperture means and light source, together with means mounting the
arm structure for movement relative to the housing and disposition in
sensing relation with a selected string as aforesaid.
4. Apparatus as set forth in claim 3 further characterized in that said
mounting means disposes said arm structure for sliding movement relative
to the housing in a direction laterally of the length of the complement of
strings for disposition relative to a selected string as aforesaid.
5. Apparatus according to claim 3 wherein said probe arm structure
comprises two sections, one upper and one lower and spaced apart
vertically such that the upper section is adapted to overlie the string
complement including the selected string, and the lower section is adapted
to lie beneath said strings, the light source being located in one said
section and the photoelectric sensor in the other said section on the
opposite side of the selected string from said source, said aperture means
being interposed between the string and photoelectric sensor for
modulating obturation by vibratory movements of the selected string.
6. Apparatus according to claim 5 further characterized in that said
aperture means comprises a narrow elongated slit orientated with its
length paralleling a corresponding lengthwise portion of the selected
string such that vibration of the selected string tends to block and clear
the entire lengthwise and crosswise area of the slit for optical
modulation effects and sensitivity to string vibration of even slight
amplitude.
7. A tuning aid according to claim 5 further characterized in that that one
of said arm sections which is adapted to overlie the string complement, as
aforesaid, is pivotable relative to the other section enabling clearance
of the string complement and facilitating the selective positioning of the
probe relative to the desired string.
8. Apparatus according to claim 2 wherein said probe includes an
electromagnetic string driving means operative to drive
magnetically-attractable strings in sustained vibration at the tuned rate
thereof, said driving means including a pole piece located to lie at one
side of the selected string when the probe is oriented in sensing position
as aforesaid, together with an activating winding connected for pulsed
energization in synchrony with the string-modulated sensing current.
9. An electronic tuning aid according to claim 2 wherein said readout
subcircuit means comprises an amplifying subcircuit responsive to said
modulated sensing current and producing shaped sensing pulses
representative of the rate of string vibration; timing and differentiating
subcircuit means responsive to said pulses and connected to drive binary
digital counting means in timed counting cycles to produce an output
representative of the frequency of string vibration; and translating
subcircuit means including binary coded decimal conversion means connected
to translate the binary count into an equivalent digital count; and
luminous digital display means responsive to said digital count to display
the string frequency in digital form.
10. Apparatus according to claim 9 further characterized by the provision
of a blanking subcircuit cooperative with said digital counting means and
said display means to suppress unwanted digital zeros otherwise appearing
at the left of significant frequency digits in said digital frequency
display.
11. A unitary device for indicating the frequency of vibration of a
sound-producing string comprising: a photoelectric probe structure
positionable adjacent the string and including spaced members adapted in
positioning as aforesaid to straddle the string, one said member including
a light source directing light onto the string and the other said member
including a photoelectric sensor operative to produce sensing current
variations representative of the rate of vibration of the spring motion in
the path of said light; aperture means interposed between the string and
photoelectric sensor defining an elongated light-transmitting slit of
narrow width extending in the direction of the length of the string such
that the lengthwise extent of the aperture is several times greater than
the crosswise width thereof whereby vibratory movement of the lengthwise
portion of the string relative to the aperture will obturate a substantial
area of the aperture in maximum amplitude of vibration and appreciable
portions of such area at lesser marginal amplitudes including those near
and below the threshold of audibility for average normal hearing with
capability of producing modulated sensing current as aforesaid in both
ranges; together with circuit means connected for control by said sensing
modulations and operative in both ranges of amplitude aforesaid to provide
a visual display of the rate in vibrations per second of a vibrating
string with respect in which the probe is positioned as aforesaid. |
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Claims |
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Description |
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The invention relates to apparatus for sensing and indicating musical
pitch, and more particularly to that form thereof which is intended for
use in tuning musical instruments, the present improvements affording a
small electronic frequency-determining and indicating device having unique
structural and functional features especially adapting it to be
operational by placement on the body of a stringed instrument, such as the
guitar, with competence to sense and display the frequency of individual
strings in digital form.
Apparatus proposed heretofore for related purposes is unsuited to the
objectives and incapable of the performance afforded by the disclosed
device for reasons such as excessive bulk, mode of use, difficulty of
application to the musical instrument, and the complex character of the
circuit arrangements commonly relied upon with regard particularly to the
transducing methods employed for deriving an analogue pitch or tone signal
capable of actuating visual indicating means as, for example, in prior
systems such as referred to hereafter which rely upon microphone input and
its vulnerability to ambient noise, along with the necessity for operation
thereof in conjunction with a source of reference frequency and some
variation of comparator, discriminator, beat-frequency or peak-sensing
technique for actuation of one or another arrangement of blinking, steady
state, or null lamp means to indicate resonance or the tuned state.
An electronic tuning aid in accordance with the invention comprises a
photoelectric pitch-sensing probe which is immune to environmental noise
and constitutes a shiftable component of a compact unitary housing
containing the entire apparatus, and of a character to be operational by
placement on the body of an instrument such as a guitar, and including
digital readout subcircuit components activated by photoelectric sensing
means contained within the probe and utilizing an elongated optical slit
oriented lengthwise of the string for obturation by a lengthwise portion
thereof when vibrating, together with included amplifying, counting,
timing and translating subcircuit components providing a numeric display
of string frequency responsive to string vibration of only slight
amplitude, whether diminishing in the damped mode or sustained as in the
undamped mode.
In accordance with a further aspect of the invention, the probe includes
electromagnetic means for driving steel strings automatically in sustained
vibration by pulsed driving flux emanating from the pole piece of an
electromagnetic source disposed in close juxtaposition with whichever
string the probe is sensing, the electromagnetic source being part of a
reflex circuit arrangement responsive to the photoelectric current
modulations effected by the driven string.
The foregoing and other aspects of novelty and utility characterizing the
device will appear in greater detail in the following specification of a
preferred form thereof taken in view of the annexed drawing in which:
FIG. 1 is a perspective view of the complete tuning unit with instrument
strings shown fragmentally in operative relation thereto;
FIG. 2 is a perspective view of the device disposed in operative position
on an instrument such as a guitar;
FIG. 3 is a general functional diagram of structural and circuit components
shown in part schematically and in part by block diagram;
FIG. 4 is a detailed circuit schematic.
A preferred form of construction of the device, as depicted in FIG. 1,
comprises a unitary housing 10 sufficiently small to rest by placement on
the resonating body 11 of a stringed musical instrument, such as the
guitar illustrated in FIG. 2, in a position alongside the usual complement
of strings 12 which in some intruments may, as a matter of choice, be of
the steel type or in other instruments may be of natural gut or synthetic
material.
Provided as a unitized component along one side of the housing or
encasement 10 is a probe bed 14 in which is slideably seated the base
portion 15 of a chambered probe arm 16 pivotally supported thereon as at
17 to enable the arm to swing upwardly above the strings for positioning
thereover while the lower base portion slides beneath the strings in
positioning the sensing head 16X at the free end of the arm in overlying
juxtaposition with some particular string 12X as in FIGS. 1 and 3.
Disposed on the outer end of the slideable base portion 15 directly beneath
the sensing head 16X is a small chambered pad 20 adapted to underlie the
selected string and containing a light-sensitive element 22, which may be
a cadmium sulphide type of photoresistor, connected in a sensing circuit
to be described, and adapted to be excited by light from a small lamp
source 19 situated as shown in FIG. 3 in the head portion 16X, such light
being admitted to the pad through a very narrow and elongated optical slit
aperture 24 formed in a cover plate for the pad and having a width which
optimally does not exceed the diameter of the string, and oriented to
extend in a direction parallel to the length of the strings for an optimum
distance, for example about three-sixteenth (3/16) of an inch, such that
the total open area of the slit when obstructed is substantial relative to
its width to admit an optimal amount of light notwithstanding its narrow
lateral dimension, with regard also for the dimensional limitations
imposed by the small space available for placement of the probe.
When placed on the guitar, with reference to FIGS. 2 and 3, the probe is
positioned relative to some selected string 12X such that in its quiescent
state the string lies outwardly of and along one side of, but very close
to one edge margin of the slit aperture, so as to admit the maximum amount
of source light for excitation of the relatively small photocell, the
movements of the string when vibrating being effective to obscure the slot
in accordance with amplitude and rate thereof and vary the cell excitation
accordingly with modulation of the photoelectric current at whatever rate
the string is tuned to.
The described optics of the probe means afford a highly sensitive reponse
to very slight string displacement owing to the lengthwise extent of the
aperture as against its lateral restriction and the photosensitive area to
be affected, in relation to the thickness of the strings, and the
effective lengthwise extent thereof available to reduce the open area
significantly by even slight string movement beyond the margin of the
slit, with consequent advantages in that vibration of little amplitude, as
when the vibratory motion is diminishing progressively in damped
vibration, will be effective to actuate the readout means even when the
sound is no longer detachable by the ear, in consequence of which a
readout of appreciable duration will be produced even if a string is
plucked only one, this being an important advantage since many instruments
will not employ the magnetically-attractable type of string responsive to
the electromagnetic driving means. Satisfactory results are obtainable
with an aperture width ranging between 0.031 and 0.008 inch, the latter
being smaller than the diameter of the smallest string commonly used, and
a preferred width where ambient light is strong.
Continuing with reference to FIG. 3, the fluctuations of the
string-modulated photoelectric current effectuated by the described probe
means, are amplified and converted into shaped pulses by the indicated
photoelectric (PEC) Amplifying Means 30 providing square-wave output
pulses as current analogues of the string vibrations which are then
further amplified by Driving Transistor Means 32 (T-3) connected to
energize the coil of the string-driving electromagnet 34, such pulses also
being utilized to activate associated frequency readout subcircuit
components included within the device and collectively represented by
Block 40 in FIG. 3 to include solid state counting, integrating, timing,
blanking and binary conversion and translating means actuating a 3-digit
luminous readout unit, as indicated in Block 60, and situated on the top
wall of the unit housing 10, FIG. 1.
Operating power for the apparatus is self-contained and derived primarily
from an Internal Power Supply 50 in the form of a battery source indicated
schematically at 50A in FIG. 4, and preferably comprising rechargeable
batteries of the nickel-cadmium type accommodated within the housing 10
(not seen) and cooperative with an internal voltage-regulating circuit
means and distributing network to be described hereafter, both effectively
terminating in a jack J-1 accessible on a wall portion of the housing (not
seen) for optional plug-in connection with an external source of Auxiliary
Operating and Charging Power 70.
In use, with further reference to FIG. 3, the operation of the device is
such that when the unit is disposed in operative position on the musical
instrument, as described above, and assuming such instrument is equipped
with steel strings, the selected string relative to which the probe has
been positioned will begin to vibrate automatically the moment the master
operating switch 28 is moved to the "ON" position owing to the provision
of appropriate bias voltage operative in the PEC Amplifier system to
maintain the Driving Transistor T-3 in conductive state in the absence of
string movement in order to energize the driver coil 34, as will more
fully appear, in consequence of which the quiescent string will be
deflected at once when the switch is turned on, with the result that the
Driving Transistor turns off and the string is relaxed, this process
continuing with the string driving means operating as a form of oscillator
deflecting and releasing the string in step with the vibratory
displacements thereof occurring at the rate at which the string happens to
be tuned, with reflexive variation of the driving flux from the pole piece
36.
More detailed aspects of the foregoing circuit arrangements are depicted in
FIG. 4 wherein the several subcircuit components described generally in
view of FIG. 3 are grouped for convenient reference in functional blocks
designated I through VI, Block I reproducing the probe components shown in
FIG. 3 in accompaniment with circuit details of the PEC Amplifying Means
30.
The light-modulated output from photocell 22 is applied via conductor 27 as
input to cascaded amplifying transistors T-1 and T-2 and the driving
transistor T-3 (also indicated generally at 32) to provide square-wave
output pulses at a level suitable for energization of the string-driving
means 34. A variable resistor R-8 in the base circuit of T-3 affords a
calibrating control for the operating bias of this transistor effective in
the "ON" condition of switch 28 to set the quiescent string vibrating
automatically, as previously explained, and effective to adjust the pulse
output in step with string displacement and fluctuation of the PEC input.
This adjustment also operates to clip stray light signals and amplifier
noise when the string is not vibrating.
The pulse output from driving transistor T-3 is also applied via conductor
38 to clock a 3-digit binary coded decimal counter I-2 in Block III, which
may be an McMOS low power complementary BCD counter of the MC14553 type
with internal latch means, low-frequency scanning clock, and multiplexing
means, serving as a frequency counter cooperatively with timing and
differentiating means, as shown in Block II, and comprising a timer I-1 of
the 555 or Mc1555 type to supply triggering and resetting pulses for the
counter cooperatively with differentiating network means C-7, R-12.
The Binary Count of I-2 is translated to digital equivalent by application
of the counter outputs via conductors 48 to a Binary Decoding and Driving
Means I-4, as shown in Block IV, which may be in the form of a BCD to
7-segment decoder-driver of the 7448 type, the outputs of which are
supplied to a luminous readout display unit 60, such as an NSN33 or a
DL33B type of DIP multiplexing readout located on the unit housing 10 and
affording a 3-digit LED display, also designated D-I, Block IV.
Unwanted zeros to the left of the significant digits, which would otherwise
appear automatically in such a readout system, are suppressed by means of
a blanking circuit, such as depicted in Block V, comprising a 2-input
position NAND gate 80 of the 7400 type with internal connections as shown
and blanking outputs extended via transistors T-4 and T-6, and conductors
82 and 83 to the display unit 60.
For practical use with instruments such as the guitar, it is sufficient to
provide a readout capacity of only three significant figures with omission
of fractional values, since it is virtually impossible to tune the usual
instrument of this class closer than 1 Hz to any given frequency, and the
range of the usual complement of strings will not require more than the
three-digit capacity provided, it being understood nevertheless that the
competence of the photoelectric sensing means is entirely adequate to
permit expansion of the readout capacity to include fractional values as
well as an extended digit range for use with other types of stringed
instrument of greater or different frequency range.
Space is provided within the unit housing 10 (not shown) to accommodate
five small series-connected nickel cadmium battery cells of the AA type,
indicated schematically at 51 in FIGS. 3 and 4 and affording a nominal
terminal voltage of 6.25 volts, constituting the normal source of working
power for completely portable use.
The internal battery 51 is connected as shown in Block VI, FIG. 4, to float
across an internal voltage-regulating and charging circuit governing the
voltage level of the battery source as well as that of an auxiliary
external operating source indicated at 70 in FIG. 3 and of a type capable
of delivering rectified DC for connection by plug and jack means P-1, J-1,
FIG. 3, the jack being accessible on the rear side of the unit housing 10
(not seen) and having its tip contact, FIG. 4, connected via limiting
resistor R-16 and diode D2 and the master control switch 28 to the system
bus terminal indicated at 52, and also connected to the input terminal 1
of an integrated voltage regulating circuit unit VR with output extended
from regulator terminal "OUT" via diode D1 to said terminal 52, the
negative terminal of the battery being connected to the common terminal 4
of the regulator at 53A. The regulator VR may be of the uA78MGT2C type.
Control voltage for the regulator is derived from a voltage divider R17-R18
shunted across the system bus terminals at 53A, 55, the diode D2 blocking
feedback of battery power directly to the input jack J-1 but passing
current from the external source, if and when plugged in, to the extent
governed by limiting resistor R16. A storage capacitance C6 of about 33
mfd. is shunted across the system terminals, and a stabilizing capacitance
C8 of about 10 mfd. is connected across the regulator input. The internal
power network will thus have the advantage of supplying requisite working
voltage when any conventional external source of rectified DC of
appropriate voltage (not shown) is plugged into jack J-1, for example when
the device is required to operate over long periods, in which case
charging current will be supplied concurrently to the battery to the
extent of its acceptance from time to time; or, with the tuning aid turned
off, a depleted battery may be brought up to charge whenever necessary,
the voltage being regulated and overcharge avoided in each case.
Calibration of the device is easily checked and quickly adjustable by
exposing the photocell through the slit aperture directly to light from a
lamp powered by the usual a.c. utility lines at 60 Hz or other known line
frequency and observing the readout. If this readout is different from
120, correction can be made by adjustment of variable resistor R15, Block
II.
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Description |
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