Light Organ

Abstract

A system for energizing lights in response to sound intensity includes a microphone feeding a detector amplifier stage which generates a signal representative of sound intensity. The output of the amplifier stage controls the switching of a phase-controlled power switch connected across one of two lamp filaments connected in series. As the intensity of one lamp increases with sound intensity, the intensity of the other decreases. Automatic gain control circuitry adjusts the gain of the amplifier stages such that the lighting effect is substantially the same response for sound changes, and it is independent of ambient sound level.

Description

BACKGROUND OF THE INVENTION

This invention relates to a system for changing the intensity of lights so as to follow changes in intensity in sound.

Systems have been known for controlling lighting in response to sound. In one known system, a control element such as a silicon control rectifier is connected in series with a power source and lamps to be energized; and the power to the lamps is varied in response to an audio signal received from a microphone to control the conductivity of the silicon control rectifier and thus, to control the intensity of the lamps.

This prior system requires the use of a manual control element, such a potentiometer, to adjust the input to the silicon control rectifier in order to adapt the system to different ambient sound levels; and such manual adjustment is undesirable from the point of view of mass marketing such a system. Further, such control devices are usually more expensive than fixed components.

In addition, most prior lighting systems of the type with which the present invention is concerned illuminate one or more lamps in direct proportion to sound intensity. Some systems have a plurality of lamps all connected in parallel, and each lamp is provided with its own flicker switch so as to create very randomly changing lighting effects. Such random changes in lighting intensity, such as artificially induced flicker in addition to modulating filament current, may be acceptable in a system designed to create psychedelic effects, but it is undesirable for the type of instrument with which the present invention is concerned-- namely, a light organ which can be used in a home or recreation area and one which is easily transportable.

SUMMARY OF THE INVENTION

In the present invention, a crystal microphone is an integral part of the package, and it is responsive to a wide range of environmental sounds, ranging from low frequency voice sounds to higher frequency sounds of the type produced by string instruments. The microphone feeds detector amplifier stage which generates a signal representative of the sound intensity picked up by the microphone. The output of the amplifier stage controls the switching of a phase controlled power switch, such as a silicon control rectifier, connected across the higher resistance of two lamp filaments, the filaments being connected in series across a rectifier bridge energized by a 60-hertz, 117-volt power source as is available in an ordinary household supply wall socket.

As the instantaneous intensity of the sound increases, the phase switching of the silicon controlled rectifier advances, thereby causing the lower resistance lamp to become brighter and the higher resistance lamp to become correspondingly more dim. Automatic gain control circuitry adjusts the gain of the amplifier stages such that the lighting effect is substantially the same for changes in sound intensity independent of ambient sound level.

Thus, the present invention provides for a sound responsive light organ incorporating two separate lights. One of the lights increases in intensity in response to increases in sound intensity, and the other light decreases correspondingly. Further, the system is self-contained, requiring only that it be plugged into a conventional wall outlet. The circuitry is self compensating to provide proper response to musical rythmn and melody sequences without need for any adjustment by the user.

Other features and advantages in the present invention will be apparent to persons of ordinary skill in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing.

THE DRAWING

FIG. 1 is a block schematic diagram of a sound responsive light system according to the present invention;

FIG. 2 is a circuit schematic diagram of the system of FIG. 1; and

FIG. 3 is an idealized line diagram illustrating the phase-controlled switching of the lamps of the system of FIG. 1.

DETAILED DESCRIPTION

Turning first to FIG. 1, a microphone, which preferably is a small crystal microphone that does not display directional sensitivity and has a wide frequency response, is diagrammatically represented by the block 10; and it feeds a detector-amplifier stage 11. The output of the detector-amplifier 11 feeds a dc amplifier 12 which, in turn, controls the switching of a phase controlled power switch 13. The output of the phase controlled power switch 13 is connected to the junction between the filaments of two lamps designated respectively 14 and 15. The filaments of the lamps 14 and 15 are connected across a full-wave rectified ac power source, such as a 60-hertz, 117-volt source.

A reset circuit 16 resets the phase controlled power switch 13 every half cycle of the 60 cycle per second source. Automatic gain control circuitry 17, responsive to the output of the phase controlled power switch 13 adjusts the gain of the detector-amplifier 11 and the dc amplifier 12 to minimize the effect of changes in ambient sound level, thus rendering the system responsive only to changes in intensity of the type found in voice and music, for example.

In order to better understand the energizing of the lamps 14, 15, reference is made to FIG. 3 wherein the abscissa is time and the ordinate axis represents Voltage. The first three half cycles (or cusps) of full-wave rectified ac power are designated 18, and the second three cusps are designated 19. This represents the voltage fed to the lamp 14, assuming that the resistance of lamp 15 is greater. When the sound intensity sensed by the microphone 10 (less ambient sound level) is relatively low, the phase controlled power switch 13 is triggered at a relatively late phase angle in the cycle as represented by .phi..sub.1. When the power switch 13 is thus energized, it shorts out the filament of lamp 15 so that the entire ac voltage is applied across the filament of lamp 14. The shaded area beneath the cusps or envelopes 18 is, therefore, the amount of time during which no voltage is applied to the filament of lamp 15. Thus, the intensity of lamp 15 is slightly less than the case in which the phase control power switch 13 does not conduct at all. At the same time, however, the intensity of the lamp 14 has increased slightly for conduction at the angle .phi..sub.1.

If the sound intensity increases still further, so as to cause the phase control power switch 13 to conduct at an ever earlier phase angle, such as .phi..sub.2 for the envelopes 19 in FIG. 3, the filament of lamp 15 will be energized a correspondingly diminished amount of time; whereas the filament of lamp 14 will be energized by the full ac power an even longer time, and it will increase in intensity. By thus advancing the phase angle at which the power switch conducts in response to increases in intensity of the sound, the filament of one lamp is illuminated more intensely, whereas the filament of the other lamp becomes correspondingly less intense.

In a preferred embodiment, the lamp 14 has a lower resistance and thus a higher power rating than does the lamp 15, and the lamp 14 is colored a bright color, such as orange, whereas the lamp 15 is a blue color. With this combination, the brightness of the color of the lamp 14 and the increased intensity thereof in response to increases in sound intensity give an observer a feeling of increased excitement and activity; whereas, as the sound intensity diminishes, the predominance of the softer blue color gives the observer a more subdued, quiet feeling. With no sound changes, the lamps are both illuminated.

Turning now to the circuit schematic of FIG. 2, the 60-cycle per second ac source is connected to the terminals 20 which feed a full-wave rectifier bridge generally designated 21 and constructed according to conventional technique. One output of the bridge circuit 21 may be grounded, and the other output terminal is designated 22. The voltage appearing at the terminal 22 is, therefore, a full-wave rectified voltage such as that diagrammatically illustrated by the envelopes of the curves 18 and 19 in FIG 3. The filaments of lamps 14 and 15 are connected in series across the output terminals of the bridge 21, as illustrated.

A silicon control rectifier 23 has its anode and cathode terminals connected across the filament of lamp 15 for shorting that lamp out when rectifier 23 is in a conducting state. The gate lead of the silicon control rectifier 23 is connected to one terminal of a capacitor 24 having its other terminal grounded, and to the drain terminal of a field effect transistor (FET) designated 25. The other power terminal of the FET is grounded, and the gate lead thereof is connected to a voltage divider network including resistors 26 and 27, connected in series across the filament of lamp 15. The FET 25 is of the type commonly referred to a "p channel" field effect transistor. That is, the FET will be in a conductive state when the gate terminal is at a zero potential or negative with respect to the source terminal.

In operation, the gate lead of the FET 25 is at zero potential relative to its source terminal once every half cycle of the supply voltage-- namely, when the supply voltage returns to zero between adjacent cusps of the envelope shown in FIG. 3. At this time, the FET 25 conducts and discharges the capacitor 24 to ground.

The silicon control rectifier 23 together with the capacitor 24 thus perform the function of the phase control power switch 13 of FIG. 1, and the FET 25 and its associated circuitry form the reset circuit 16 of FIG. 1.

Turning now to the lefthand portion of the schematic of FIG. 2, the crystal microphone is again designated 10 and shown in schematic form. The output of the microphone 10 is coupled through a capacitor 29 to the base of an NPN transistor 30, having its emitter grounded. A resistive voltage divider network including a resistor 31 and a resistor 32, connected in series between a terminal 33 and ground, bias the transistor 30 near the cutoff region. That is to say, the transistor 30 amplifies positive half cycles of the ac voltage generated by the microphone 10, but it does not amplify negative half cycles.

The terminal 33 is connected to the junction between the filaments of the lamps 14, 15 by means of a resistor 34 which is a relatively large resistor, of the order of two megohms. A capacitor 35, also of a large value, is connected between the terminal 33 and ground. The large resistance 34 serves two functions: first, to reduce the average voltage used for biasing in the amplifying stages, and secondly, to inhibit rapid charge of capacitor 35. For example, whereas the average voltage between the filaments of lamps 14, 15 is of the order of 60-70 volts, the average voltage at the terminal 33 is of the order of 10 volts. Further, the time constant for discharge of charge accumulated at the terminal 33 by the capacitor 35 is of the order of a few seconds for the reason that the automatic gain control circuitry is responsive only to relatively long term changes in the ambient sound level, but is insensitive to changes in sound intensity such as occur in speech and music.

The collector of the transistor 30 is connected by means of a series circuit including resistors 37 and 38 to the terminal 33. A capacitor 39 is connected parallel with the resistor 37. A PNP transistor 40 has its emitter connected to the terminal 33, its base connected to the junction between resistors 37, 38, and its collector connected by means of a resistor 41 to the gate of the silicon control rectifier 23.

As has already been explained, the signal at the collector of transistor 30 has an average value or dc level which changes in proportion to the intensity of sound sensed by the microphone 10. The transistor 30 acts as a detector-amplifier stage. As the sound intensity increases, the average voltage level at the collector of transistor 30 decreases, and this in turn, causes the transistor 40 to become more forwardly biased, thereby transmitting a relatively larger current through the resistor 41 to charge the capacitor 24 to a slightly higher voltage. The resistor 41 serves as a current limiting resistor. As the voltage level across the capacitor 24 increases, the phase angle at which the silicon control rectifier conducts will also be advanced, in a manner explained in connection with FIG. 3. Thus, as sound intensity increases, the firing angle or conduction phase angle of the silicon control rectifier is advanced, thereby shorting out the filament of lamp 15 for a proportionately greater time. This, in turn, dims the bulb 15 and causes the source voltage to be applied directly across the filament of lamp 14 for a longer proportionate period of each half cycle of source voltage.

At the end of each half cycle (i.e., between the adjacent cusps of FIG. 3) the voltage at the base of the field effect transistor 25 becomes zero, thereby causing it to conduct and discharging capacitor 24 so that operation may resume similar to that which has just been described.

The operation of the automatic gain control circuitry will now be described. When power is first applied to the terminals 20, a dc charge accumulates on capacitor 35 to supply voltage to bias the transistors 30 and 40; and this takes a few seconds because of the fact that the time constant associated with charging and discharging the capacitor 35 is well outside of the audio frequency range. As the average sound level increases, the silicon controlled rectifier 23 will fire at an earlier conduction angle, as already described. Therefore, the average value of the voltage appearing at its anode (namely, at the junction between the filaments of lamps 14, 15) will decrease. It is, however, this voltage which charges the capacitor 35. Therefore, the charge accumulated on the capacitor 35 will decrease thereby causing the transistors 30 and 40 to be biased still further into the cutoff region and reducing the gain of the pre-amplifier and dc amplifier stages.

Correspondingly, as the ambient sound level decreases, the average voltage at the anode of the switch 23 increases. This will increase the voltage across the capacitor 35 which will bias the transistors 30 and 40 more toward the active region, thereby increasing the gain of those stages.

Thus, the present system modulates the intensity of the lamp 14 proportional to the intensity of sensed sound in the voice frequency range, and it modulates the intensity of the lamp 15 inversely proportional to that sound. Further, by means of the automatic gain control circuitry described, the system automatically adjusts itself to a wide range of environmental sound levels without the need for manual adjustment.

Modifications may be made to the illustrated system, for example, a resistor could be substituted for the filaments of either one of the lamps 14 or 15 if it were desired to use only a single lamp. If it were desired to have the light intensity proportional to sound, a resistor would be substituted for the filament of lamp 15; and if it were desired to have the light intensity be inversely proportional to the sound, a resistor could be substituted for the filament of lamp 14. However, as has already been mentioned, it is preferred to have both lights operating in the manner disclosed to achieve the desired results. Further, other power switches could be substituted for the silicon control rectifier 23 as well as for other circuit elements. It is, therefore, intended that all such modifications and substitutions be covered as they are embraced within the spirit and scope of the appended claims.

Claims

I claim:

1. In a light organ for modulating light intensity in response to changes in intensity of sound, the combination comprising: an electrical power supply, electric load means in circuit with said power supply, means productive of electrical signals representative of instantaneous sound intensity, detector-amplifier means for converting said sound representative signals into pulse signals of individually varying widths, phase-controlled switch means in circuit with said detector-amplifier means and said load means and operable to control power supplied to said load means from said power supply in accordance with the signal output of said detector-amplifier means; and control means in feedback circuit with said detector-amplifier means and said switch means for automatically varying the gain of said detector-amplifier means in inverse relation to average sound intensity.

2. The invention of claim 1 wherein said load means comprises an incandescent lamp, and said phase-controlled switch means controls energization of said load means for varying time intervals to correspondingly vary the illumination intensity thereof.

3. The invention of claim 1, wherein said load means comprises at least two independent load elements in series circuit relation, said switch means being in parallel circuit relation with one thereof whereby energization of said one load element is inversely proportional to said signal output and energization of the other thereof as directly proportional to said signal output.

4. The invention of claim 1, wherein said load means comprises at least two independent incandescent lamps in series circuit relation, said switch means being in parallel circuit with at least one thereof whereby energization of said one lamp is inversely proportional to said signal output and energization of the other thereof is directly proportional to said signal output.

5. The invention of claim 1, wherein said phase-controlled switch means comprises a silicon controlled rectifier.

6. The invention of claim 1, in which said power supply comprises full wave alternating current rectifier circuit means, and said switch means is periodically operable to control power supplied to said load means by varying the amount of time in each half cycle of full wave rectified alternating current during which voltage is supplied thereto.

7. The invention of claim 1, in which said control means operatively regulates the individual width of each of said pulse signals in said inverse relation to average sound intensity.