Light beam musical instrument

A musical instrument is disclosed in which light beams striking a detector produce various tones and the loudness of the sounds produced is dependent upon the intensity of the light beam which can be changed by interrupting the beam or reflecting the light backwards to a detector situated next to the light source. A special amplifier circuit is provided which responds to both the amount of light beam interruption as well as the rapidity of interruption. The invention can be variously embodied in woodwind, string and percussion instruments and can also be used on a stage and controlled by moving dancers or musicians.

FIELD OF INVENTION 
The invention relates to musical instruments in which light beams striking 
detectors produce various tones. 
Description of the Prior Art 
In the past light beams have been used to produce musical sounds. 
Typically, the light shines on a series of photocells connected to an 
amplifier and speaker. When light strikes the cell a tone is produced or 
stopped. Most prior art light beam musical instruments utilize a shutter 
to control the light beam. However, Meissner in U.S. Pat. No. 3,038,363 
interrupts the light beam with a metal reed and Ferber in U.S. Pat. No. 
3,733,953 uses vibrating guitar strings. Yet, in all prior art light beam 
musical instruments interruption of the light beam stops or creates a 
sound. Volume is not controlled by the light beam. 
In the present invention the loudness of sounds produced is dependent upon 
the intensity of the light beam which can be changed by interrupting the 
beam or reflecting the light backwards to a detector situated next to the 
light source. To make the instrument respond to variations in light 
intensity I provide a special amplifier circuit which responds to both the 
amount of the light beam interruption as well as the rapidity of 
interruption. 
The present invention can be variously embodied for use in string, woodwind 
and percussion instruments. In addition, the invention can be embodied so 
that movement of dancers on a stage will control the loudness of the 
musical sounds. 
Other details, objects and advantages of the invention will become apparent 
from the following description of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 and 2 a light source 10 is provided which emits a 
light beam 12 toward detector 14. When light strikes the detector it emits 
a signal, shown as wave 114 in FIG. 2, which is amplified by amplifier 16 
into signal 116. If the light beam is blocked at interrupter 13 (shown in 
chain line) no signal will be emitted from the detector 14. The 
interrupter 13 could be an instrument key, a string, a finger or a body. 
After the signal is amplified it goes to a special amplifier 18 which 
responds to the amount of light beam interruption (indicated by the signal 
coming from detector 14) and the rapidity of the interruption. A signal 5 
(indicated as "V" in FIG. 1) entering this amplifier would be transformed 
into S+K ds/dt where K is a constant and dS/dt is the first derivative of 
S with respect to time. The transformed signal is shown as wave 118 in 
FIG. 2. Thus modified, the signal is applied to a voltage controlled 
amplitude modulator 20 to control the amplitude (and hence the loudness) 
of the signal which is supplied by a frequency generator 22. The signal 
emitted by the amplitude modulator 20, shown as wave 120 in FIG. 2, may be 
fed to a mixer 24 and there combined with other signals 25. The mixer 24 
can be attached to output controls 26 which may filter, color or amplify 
the output before it is fed to a speaker 28. 
The present preferred circuitry for the light detector 14, amplifier 16 and 
special amplifier 18 is shown in FIG. 3. As shown in FIG. 3, a light beam 
12 strikes a photo transistor 30. The operational amplifier 32 is driven 
at the output below ground level when the light beam is not interrupted. 
As the light beam begins to be interrupted the photo transistor supplies a 
positive signal which is greatly amplified due to the by-pass diode 
D.sub.1. When the signal crosses the ground level, D.sub.1 becomes reverse 
biased, and the amplification depends upon the setting of the variable 
resistor 34. The emerging output signal is coupled through diode D.sub.2 
so that only a positive ground-referenced portion is transmitted to the 
next stage. This second stage controls the rapidity of attack by 
differentiating the input signal S to output signal S.sub.o according to 
the formula: S.sub.o =S[1+(sRC)/(1+sTC)] where T represents the effective 
resistance of the control transistor 36, C is the capacitance of C, R is 
the resistance of R.sub.5, and s=j.omega.=j2.pi.f. Thus, if the transistor 
is kept non-conducting, T is very large and the transfer function is 
merely unity, the output signal emerges unaffected. However, if the 
transistor is brought into conduction through supplying a positive signal 
controlled by a foot pedal, then T becomes small and the output signal has 
a large differentiated component. The diode D.sub.3 cuts out the negative 
part of the derivative. The signal from operational amplifier 38 is then 
applied to a voltage controlled amplitude modulator (see FIG. 1) to 
control the volume of a tone supplied by a frequency generator as 
described above. 
In FIG. 4 the invention is applied to produce a harp-like instrument using 
light sources 41 and detectors 42. Each light source produces a beam of 
light 44 which can be interrupted with fingers. The light beams can be 
made of different colors in the spectrum to correspond to different notes. 
Each light detector is wired to an amplifier, special amplifier, amplitude 
modulator and frequency generator as shown in FIG. 1. The signals from all 
of the amplitude modulators can be mixed electronically and directed to a 
single output. In this instrument I prefer to use light beams in place of 
the strings of a harp because it would be expensive to produce a 
instrument containing strings and light source--light detector pairs 
associated with each string. However, one could use my invention in this 
manner. Alternatively, one could make a harp-like instrument containing 
various combinations of light source--light detector pairs and strings. 
For example, strings could be placed at octave intervals for a chosen note 
to indicate where the octave changes. 
A woodwind-like instrument employing another embodiment of the invention is 
shown in FIG. 5. The instrument has a mouthpiece 50, body 52 and bell 54. 
A plurality of keyholes 53 are provided along the body. A rib 56 runs 
through the center of the body and serves as a mounting for light sources 
58 and detectors 60. One light source 58 and one detector 60 is provided 
for each keyhole 58. When a finger 62, thumb 63 or instrument key (not 
shown) is positioned over a keyhole light 51 from the light source will be 
reflected back to the detector 58 which is wired as illustrated in FIG. 1. 
The reflected light will cause a signal to flow to the amplification, 
mixing and filtering circuits 64 and speaker 65 contained in the bell 54 
to produce sounds. A pressure transducer 66 that senses air pressure and 
attached sponge pad 67 for filtering noise are provided in the mouthpiece 
for overall volume control. Another embodiment for volume control can be 
implemented by pressing a transducer with the lips or teeth to change the 
signal flowing from the transducer 66 to the amplification, mixing and 
filtering circuits 64 thereby changing the volume. To eliminate the need 
for providing amplifiers and a speaker inside the instrument an output 
jack can be provided to connect the instrument to external amplifiers and 
speakers. This would enable the instrument to be connected to high quality 
external sound systems or recording devices. 
Referring now to FIGS. 6 and 7, a keyboard instrument is shown having a 
body 70 containing two keyboards 72. Each keyboard is comprised of a 
rectangular plate 73 having a series of slots 74 in it. A light source 75 
and optional lens 76 are positioned below each slot to direct light 
through the slot and focus it on a detector. A light detector 77 is 
positioned above each slot. The light detectors are wired to 
amplification, mixing and filtering circuits in a manner such that 
interruption of a given light source--light detector combination will 
produce a unique sound. Pedals 78 are provided for controlling overall 
loudness and to control the attack on transistor T in FIG. 3. 
A final preferred embodiment shown in FIG. 8 is comprised of light sources 
80 and light detectors 82 positioned on a stage 79. The light detectors 
are connected to other components as discussed above so that sounds will 
be produced by light beams 81 striking the detectors. Interruption of the 
light beams by a musician or dancer 84 will cause the tone to stop with 
the rapidity of interruption controlling the loudness. These arrangements 
on the stage can employ beams going in any direction vertically and 
horizontally, and both interrupting and reflecting schemes are 
conceivable. 
If desired, in certain uses, one may eliminate the specific amplitude 
modulator disclosed hereinbefore and modulate the light source. For 
example, in a clarinet type arrangement one might modulate a solid-state 
light source with the desired frequency from a frequency generator and 
thereby eliminate the need for a separate amplitude modulator. 
While I have illustrated and described certain present preferred 
embodiments of my invention it is to be distinctly understood that the 
invention is not limited thereto, but may be variously embodied within the 
scope of the following claims.