Audio Responsive Intensity Modulator For Fluorescent And Like Lamps

Abstract

The intensity of a fluorescent, ultraviolet or other gas discharge lamp is modulated in response to the amplitude of an audio signal. A dimmer or blinking ballast transformer is connected to the lamp. Power from an ac source is conducted to the ballast transformer via a controlled rectifier for a portion of each ac half cycle. The phase angle at which the controlled rectifier is fired is established by trigger means responsive to the instantaneous amplitude of the audio signal, thereby producing interesting optical effects directly correlated to that audio signal.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to apparatus for modulating the intensity of a fluorescent or like lamp in response to an audio signal. This is achieved by utilizing the audio signal to vary the firing angle of a controlled rectifier supplying power to the lamp via a ballast transformer.

2. Description of the Prior Art

Devices which produce an optical display synchronized with music or other audio signals have gained widespread popularity. Such devices literally add a new dimension to the enjoyment of music, by appealing to the visual as well as aural sense of the listener.

Most prior art audio responsive light displays employ incandescent lamps driven by the output of an audio amplifier. By passing the audio signal to each lamp through a high, low or band pass filter, a frequency responsive display is achieved. Variety is added by shining each bulb through a different colored filter.

Some interesting effects are achieved, but the effectiveness of the display is limited by two factors inherent to incandescent bulbs. First, each bulb represents essentially a point source of light, making it difficult to implement displays requiring uniform illumination of a large area. Second, since incandescent lamps have inherently slow response, it is almost impossible to achieve very rapid light intensity modulation. The incandescent lamp intensity is determined by the audio signal amplitude as averaged over a duration commensurate with many cycles of the ac power source. The music or audio signal may have very rapid changes in amplitude, easy to detect aurally, but due to the slow response, the incandescent lamp brightness will remain more or less constant while these short term musical effects are occurring. The resultant optical display is of limited interest.

The use of fluorescent, ultraviolet or other gas discharge lamps presents the possibility of providing a diffuse, rather than point light source, and of permitting more rapid light variation. The present invention provides simple control circuits which facilitate very rapid intensity modulation of a fluorescent, ultraviolet or like lamp in response to an applied audio signal.

Such short term intensity changes are implemented by controlling the phase angle at which power is supplied to the lamp each ac half cycle. The lamp intensity thus is substantially related to the instantaneous amplitude of the audio signal, rather than to the average or rms level. Accordingly, much more interesting visual effects are achieved as compared with incandescent lamp displays.

Moreover, by using such instantaneous amplitude control, occasional beat effects are experienced between the audio signal and the frequency of the ac power source. As a result, actual blinking of the fluorescent lamp may occur from time to time, causing unusual stroboscopic effects. Such effects further are enhanced by using the lamp to illuminate a moving object such as a rotating disc carrying a geometric pattern.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided an apparatus for modulating the intensity of a fluorescent, ultraviolet or other gas discharge lamp in response to the substantially instantaneous amplitude of an audio signal. The audio signal is used to establish the phase angle at which a controlled rectifier supplying power to the lamp is triggered during each ac half cycle. Interesting optical effects are achieved which may include blinking at beat frequencies between the audio signal and the ac power source.

In preferred embodiments, the apparatus uses a dimming or blinking ballast transformer operatively connected to the lamp. A triac or one or more silicon controlled rectifiers (SCRs) conduct power to the ballast for a portion of each ac half cycle established by triggering means responsive to the audio signal. The triggering means may employ an audio transformer to supply directly the SCR gate signal, or a phase control circuit of the ramp and pedestal type, wherein the audio signal controls ramp parameters establishing the controlled rectifier triggering angle. Alternatively, a zero crossing switch or a audio responsive light source and photosensor combination may provide the triggering signals.

Unusual stroboscopic effects result when the inventive apparatus is used to illuminate a moving object such as a rotating geometric pattern.

Thus, it is an object of the present invention to provide an improved audio responsive light modulator for controlling the intensity of a fluorescent or like lamp in rapid response to an audio signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed description of the invention will be made with reference to the accomplanying drawings wherein like numerals designate like parts in the several figures.

FIG. 1 is an electrical schematic diagram of a lamp intensity modulating circuit in accordance with the present invention.

FIG. 2 is a simplified electrical schematic diagram of a lamp modulating circuit employing optical coupling.

FIG. 3 is an electrical block diagram illustrating utilization of a zero crossing switch as a component of the invention.

FIG. 4 is an electrical schematic diagram of another lamp intensity modulator utilizing a phase control circuit.

FIG. 5 is a graph illustrating operation of a portion of the circuit of FIG. 4.

FIG. 6 is a perspective view of a rotating geometric pattern illuminated by a lamp modulated in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description is of the best presently contemplated modes of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

Structural and operational characteristics attributed to forms of the invention first described shall also be attributed to forms later described, unless such characteristics are obviously inapplicable or unless specific exception is made.

Referring now to the drawings, and particularly to FIG. 1 thereof, there is shown a circuit 10 for modulating the intensity of a fluorescent, ultraviolet or like gas discharge lamp 11 in response to an audio signal supplied via a line 12. To accomplish such modulation, the lamp 11 is powered via a ballast transformer 13 having windings 14, 15, each provided with autotransformer taps 14a, 15a supplying power to the respective lamp heaters 11a, 11b. The winding 14 is connected via the terminals 16 across an ac power source. When the leads 14b, 15b of the respective windings 14, 15 are connected together, the windings 14, 15 together function to supply across the lamp 11 a sufficiently high voltage so as to turn on the lamp 11 to a nominal maximum intensity level.

To modulate the intensity of the lamp 11, suitable switching means are provided. In this instance, the switching means comprises a pair of silicon controlled rectifiers 17, 18. Mechanical switches such as reed relays could be used instead. The SCRs are parallel connected, in opposite polarity, between the leads 14b and 15b. The SCRs 17, 18 respectively receive gating signals supplied by the output windings 19, 20 of a toroidal transformer 21 driven by the amplified audio signal. Specifically, the audio signal on the line 12 is amplified by an amplifier 22 and provided via the lines 23a, 23b and an inductor 24 to the input winding 25 of the toroidal transformer 21.

With this arrangement, the voltages induced in the transformer windings 19, 20 will gate on the respective SCRs 17, 18 at some time during respective alternate half cycles of the ac power source. The particular firing angle or time of occurrence of triggering during each ac half cycle will depend on the amplitude of the audio signal occurring during that half cycle. Thus, the duty cycle of each SCR 17, 18, and hence the intensity of the lamp 11, will be substantially instantaneously related to the amplitude of the audio signal provided via the line 12. The resultant visual display thus will be synchronous with the sound produced by the speaker 27 also driven by the amplifier 22.

A resistor 28 (FIG. 1) connected between the leads 14b and 15b causes some current flow between the transformer windings 14, 15 even when the SCRs 17, 18 both are off. This produces some voltage across the lamp 11, thus establishing the minimum brightness or intensity of that lamp.

The inductor 24 functions as a low pass filter, to prevent high frequency audio components from reaching the transformer 21. Such high frequency components may trigger the SCRs 17, 18 at the beginning of each ac half cycle, causing the lamp 11 to remain on continuously. By passing only low frequency components to the transformer 21, more interesting displays are achieved as the SCRs 17, 18 are switched on at audio related times during each ac cycle. The audio signal supplied to the transformer 21 may include frequency components which beat with the ac line frequency; blinking of the lamp 11 may then occur. Other effects can be achieved by utilizing windings 19, 20 of different size; the individual SCRs 17, 18 will fire at different phase angles for a like audio signal.

The transformer 21 isolates the amplifier 22 and the speaker 27 from the lamp 11 circuitry. Impulsive noise spikes or transient voltages may be generated as the SCRs 17, 18 are triggered or as the lamp 11 is modulated. These spikes are prevented from being fed back to the audio lines 23a, 23b by the toroidal transformer 21.

FIG. 2 shows an alternative circuit 30 for triggering a pair of SCRs 17', 18' in response to an audio signal provided via the lines 23'. The audio signal is supplied via an isolation transformer 31 and a constant current source 32 to a light-emitting diode 33. The light emitted by the diode 33 is related to the amplitude of the supplied audio signal.

A light dependent resistor 34 is connected between the gates of the SCRs 17', 18', and is positioned to receive the light emitted by the diode 33. Light activated switching devices could be substituted for the SCRs and the resistor 34. Accordingly, SCR gate triggering signals will be provided by the light-dependent resistor 34 in response to the audio signal. The SCRs 17', 18' are connected across the ballast transformer leads 14b, 15b in place of the transformer-driven SCR circuit shown in FIG. 1, so as to modulate the lamp 11.

A triac may be substituted for the SCRs in the circuits described above. Another triac control circuit is shown in FIG. 3, wherein a triac 36 is connected across the ballast transformer leads 14b, 15b. The trigger signal for the triac 36 is provided by a zero crossing switch 37 receiving the audio signal from the line 12. Such a circuit 37 provides a triac trigger pulse each time the audio signal goes through zero. Audio responsive lamp intensity modulation results.

An alternative lamp intensity control circuit 40 is shown in FIG. 4. A conventional dimming ballast transformer 41 is operatively connected to a lamp 11' and receives ac power via the terminals 42 and a triac 43. The firing angle of the triac 43 is established in response to an audio signal supplied via the lines 44a, 44b by means of a phase control circuit 45. The circuit 45 preferably comprises a General Electric monolithic integrated phase control trigger circuit sold commercially under the designation PA 436. The encircled numerals in FIG. 4 designate connections to that GE device.

During each ac half cycle, the phase control circuit 45 produces a ramp voltage typically illustrated by the waveform 47 of FIG. 5. This ramp voltage 47 is developed across a capacitor 48, which rapidly is charged to a pedestal level established by the voltage present on the line 49. The voltage across the capacitor 48 then decreases in value and eventually crosses a reference level 50. At the time of crossover, indicated by the line 51 of FIG. 5, the phase control circuit 45 supplies a trigger signal via the line 52 to fire the triac 43.

The triac firing angle is established by the audio signal received on the lines 44a, 44b by superimposing the audio on a dc voltage provided to the line 49. This dc level is set by a voltage divider comprising the resistors 53, 54, 55 series connected across the lines 56, 57 supplying a fixed dc voltage. The audio signal is connected via a potentiometer 58 and an isolation transformer 59 across the resistor 55.

Thus the audio output of the transformer 59 is added algebraically to the voltage across the resistor 55, producing a corresponding voltage change on the line 49. Since the line 49 voltage determines the ramp 47 pedestal level, the instantaneous amplitude of the input audio signal will control the phase angle of the triac 43 trigger signal. The desired lamp intensity modulation is achieved over a very wide dynamic range of audio levels.

The ramp amplitude (FIG. 5) may be controlled by a potentiometer 61 associated with the phase control circuit 45. Optionally, the audio input signal may be combined with the voltage developed across the potentiometer 61 so as to modulate the ramp amplitude, and thereby control the triac 43 triggering angle.

Positive triggering of the triac 43 is achieved by precharging a capacitor 62 and discharging this capacitor via the line 52 at the instant when the ramp 47 crosses the reference level 50. Generation of the ramp 47 in synchronism with each ac half cycle is achieved by providing an ac feedback signal to the circuit 45 via the resistor 63. Power to the phase control circuit 45 is supplied via the resistor 64.

Unique visual effects are achieved by using the audio modulated lamps to illuminate a moving object. Thus in FIG. 6, a lamp 11" is mounted on a fixture 71 and used to illuminate a rotating disc 72 containing a geometric pattern of differently colored designs 73, 74. The disc 72 is driven by a motor 75 and a shift 76 at either a constant or variable speed. The lamp 11" is powered via the lines 77 from any of the circuits 10, 30, 35, or 40. The lamp intensity, and hence the amount of light reflected from the disc 72, will correspond to the supplied audio signal.

The above described circuits may cause blinking of the lamp 11" at audio frequencies which beat with the ac line frequency. This will produce stroboscopic or "stop-motion" effects when used to illuminate the rotating disc 72. The use of an ultraviolet lamp 11' and phosphorescent colors for the patterns 73, 74 can produce even more unusual visual effects.

Claims

Intending to claim all novel, useful, and unobvious features shown or described, the applicant claims:

1. Apparatus for modulating the intensity of a gas discharge lamp in response to an audio signal, comprising:

a ballast transformer having primary and secondary windings, said primary winding being connected directly across an ac power source, said discharge lamp being connected in an operating circuit between one terminal of said primary winding and one terminal of said secondary winding,

controlled rectifier means connected between the other terminal of said primary winding and the other terminal of said secondary winding for effectuating autotransformer connection of said ballast transformer to energize the arc of said discharge lamp for the portion of each ac half cycle when said rectifier means is triggered on, and

trigger means for establishing the phase angle at which said rectifier means is triggered on in response to the amplitude of said audio signal.

2. Apparatus according to claim 1 wherein said trigger means comprises a toroidal transformer having a primary winding receiving said audio signal and at least one secondary winding for coupling said audio signal to said controlled rectifier means for triggering thereof.

3. Apparatus according to claim 2 wherein said controlled rectifier means comprises first and second silicon controlled rectifiers parallel connected in opposite polarity, and wherein said toroidal transformer has first and second secondary windings respectively providing triggering signals to the gates of said first and second silicon controlled rectifiers.

4. Apparatus according to claim 3 wherein said first and second windings are of different size, thereby causing said first and second silicon controlled rectifiers to trigger on at different phase angles in response to like audio signals.

5. Apparatus according to claim 2 further comprising resistor means across said controlled rectifier means for effectuating current-limited autotransformer connection of said ballast transformer to bias on said lamp to a minimum intensity.

6. Apparatus according to claim 2 further comprising a low pass filter in circuit with the primary of said toroidal transformer.

7. Apparatus according to claim 2 wherein said ballast transformer comprises a blinking ballast transformer having tapped windings for energizing the heaters of said lamp.

8. Apparatus according to claim 1 wherein said trigger means comprises a zero crossing switch, said switch providing a trigger signal to said controlled rectifier means upon detection of a zero crossing of said audio signal.

9. Apparatus according to claim 1 wherein said trigger means comprises a photosensor connected to provide a trigger signal to said controlled rectifier means when the light incident on said photosensor exceeds a selected level, and a light source driven by said audio signal and illuminating said photosensor.

10. Apparatus according to claim 9 wherein said photosensor comprises a light-dependent resistor, and wherein said light source comprises a light-emitting diode.

11. Apparatus according to claim 1, in combination with a moving object illuminated by said lamp.

12. Apparatus for modulating the intensity of gas discharge lamp in response to an audio signal, comprising:

a ballast transformer operatively connected to said lamp,

controlled rectifier means for conducting power from an ac source to said ballast for the portion of each ac half cycle when said rectifier means is triggered on, and

triggering means for establishing the phase angle at which said rectifier means is triggered on in response to the amplitude of said audio signal, said trigger means comprising:

a phase control circuit for providing a trigger to said controlled rectifier means when a ramp voltage crosses a reference level, and

means for changing a phase-angle-establishing parameter of said ramp voltage in response to said audio signal.

13. Apparatus according to claim 12 wherein said phase control circuit includes means for setting the pedestal level of said ramp voltage in response to a control voltage, and wherein said means for changing comprises means for algebraically adding said audio signal to said control voltage.

14. Apparatus according to claim 12 wherein said controlled rectifier means comprises a triac, and wherein said ballast transformer comprises a dimming ballast.

15. Apparatus according to claim 14 wherein said means for changing further comprises a toroidal transformer having a primary winding receiving said audio signal and a secondary winding supplying said audio signal to said means for changing, said toroidal transformer providing electrical isolation for the source of said audio signal.