Abstract:
Apparatus and associated methods relate to providing a constant-brightness lighting power to one or more interconnected light strings. A light string power controller draws operating power from a power source that has a variable voltage. The light string power controller supplies constant-brightness lighting power to the one or more interconnected light strings connected to a light-string connector. The constant brightness operating power is both independent of the variable voltage of the power source and independent of a number, up to a predetermined maximum number, of the one or more interconnected light strings connected to the light-string connector. Additional light strings can be connected to the one or more interconnected light strings without affecting a brightness of the one or more interconnected light strings. The brightness of the one or more interconnected light strings is similarly unaffected by voltage variations of the power source.

Description:
BACKGROUND 
     Decorative light strings are used to communicate a joy of a holiday season, to draw attention to merchandise, or to simply decorate or adorn an object. Decorative light strings have been used to adorn trees, shrubs, and houses. Decorative light strings are used both indoors and outdoors. In some lighting situations, power sources for such decorative light strings are difficult to tap or unavailable altogether. In such lighting situations, batteries can be used to provide power to light strings and to other decorative lights. 
     Batteries, however, may have a power supply capability that changes in response to changes in battery charge, ambient temperature, number of charge cycles, etc. When used to provide lighting power to decorative light strings, variations in the power supply capability of batteries can be manifest by variations in brightness of the decorative light strings. For example, the brightness of the decorative light string may decrease in response to charge depletion of the battery over time. The decorative light string may thus become less decorative over time. 
     SUMMARY 
     Apparatus and associated methods relate a constant-brightness lighting system including a light string having a plurality of LEDs distributed along a length of the light string. The constant-brightness lighting system also includes a light-string controller connected to a first end of the light string. The light-string controller includes a battery compartment configured to receive one or more batteries. The one or more batteries are configured to provide a battery voltage that varies in response to one or more battery conditions. The light-string controller includes a load sensor configured to sense a signal indicative of a brightness of the light string connected to the light-string controller. The light-string controller also includes a switching supply configured to draw operating power from the one or more batteries received by the battery compartment and to supply lighting power to the light string connected to the light-string controller. The switching supply supplies lighting power such that the sensed signal indicative of the brightness is within plus or minus 10% of a target signal indicative of a target brightness. The target signal is a constant and independent of the battery voltage. 
     In some embodiments, a modular constant-brightness lighting system includes a battery-module connector configured to electrically connect to one or more interconnected battery modules. The one or more interconnected battery modules are configured to provide a battery-module voltage that varies in response to one or more battery conditions. The modular constant-brightness lighting system includes a light-string connector configured to connect to one or more interconnected light strings. The modular constant-brightness lighting system includes a load sensor configured to sense a signal indicative of a brightness of the one or more interconnected light strings connected to the light-string connector. The modular constant-brightness lighting system also includes a switching supply configured to draw operating power from the one or more interconnected battery modules connected to the battery-module connector and to supply lighting power to the one or more interconnected light strings connected to the light-string connector. The supplied lighting power results in the sensed signal indicative of the brightness being within plus or minus 10% of a target signal indicative of a target brightness. The target signal is independent of the battery-module voltage. 
     Some embodiments relate to a method of controlling a constant brightness in a light string. The method includes providing one or more batteries. The one or more batteries are configured to provide a battery voltage that varies in response to one or more battery conditions. The method includes drawing operating power from the one or more batteries. The method includes providing a light string having a plurality of LEDs distributed along a length of the light string. The method includes supplying lighting power to the provided light string. The method includes sensing a signal indicative of a brightness of the provided light string. The method includes comparing the sensed signal indicative of the brightness to a target signal indicative of a target brightness. The method also includes adjusting the supplied lighting power based on the comparison of the sensed signal indicative of the brightness to the target signal indicative of the target brightness. The adjusted supplied lighting power results in the sensed signal indicative of the brightness being within plus or minus 10% of the target signal indicative of the target brightness. The target signal is independent of the battery voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a home decorated with various decorative light strings controlled by an exemplary lighting controller providing for constant brightness. 
         FIG. 2  is a block diagram of an exemplary modular lighting system. 
         FIG. 3  is a circuit schematic diagram of an exemplary constant-brightness decorative lighting system. 
         FIG. 4  is a block diagram of an exemplary constant-brightness decorative lighting system. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic view of a home decorated with various decorative light strings controlled by an exemplary lighting controller providing for constant brightness. In  FIG. 1 , home  10  has garden  12  with tree  14  and shrubs  16 ,  18 ,  20 . Tree  14  is decorated with decorative light string  22  and decorative illuminated star  24 . Shrubs  16 ,  18 ,  20  are decorated with decorative light strings  26 ,  28 ,  30 , respectively. Battery modules  32 ,  34  are interconnected with each other, and battery modules  32 ,  34  are coupled to lighting controller  36 . Decorative light strings  22 ,  26 ,  28 ,  30  and decorative illuminated star  24  are interconnected with one another, and interconnected decorative light strings  22 ,  26 ,  28 ,  30  and decorative illuminated star  24  are coupled to lighting controller  36 . 
     Lighting controller  36  may have an internal power source, but can also draw operating power from battery modules  32 ,  34  coupled to lighting controller  36 . Lighting controller  36  can provide constant-brightness lighting power to interconnected decorative light strings  22 ,  26 ,  28 ,  30  and decorative illuminated star  24 . Each of interconnected decorative light strings  26 ,  28 ,  30  is depicted as having first light-string connector  38  and second light-string connector  40  on opposite ends of light strings  26 ,  28 ,  30 . First light-string connectors  38 , second light-string connector  40  or both first and second light-string connectors  38 ,  40  may have additional connection ports to which additional light strings or other decorative lighting elements can be connected. 
     If additional decorative lighting elements are connected to interconnected decorative light strings  22 ,  26 ,  28 ,  30  and decorative illuminated star  24 , then lighting controller  36  adaptively provides additional power to the interconnected decorative light strings  22 ,  26 ,  28 ,  30  and decorative illuminated star  24  having such additional decorative lighting elements. Lighting controller  36  can sense a power drawn by interconnected decorative light strings  22 ,  26 ,  28 ,  30  and decorative illuminated star  24  having such additional decorative lighting elements. Lighting controller  36  can then source additional power to interconnected decorative light strings  22 ,  26 ,  28 ,  30  and decorative illuminated star  24  having such additional decorative lighting elements. 
     The amount of additional power sourced by lighting controller  36  is sufficient to maintain a constant brightness of interconnected decorative light strings  22 ,  26 ,  28 ,  30  and decorative illuminated star  24 . In other words, the power level provides by lighting controller  36  to light strings  22 ,  26 ,  28 ,  30  and decorative illuminated star  34  is maintained even though additional lighting elements are added. This maintained power level to light strings  22 ,  26 ,  28 ,  30  and decorative illuminated star  34  is achieved by lighting controller  36  sourcing additional lighting power. 
       FIG. 2  is a block diagram of an exemplary modular lighting system. In  FIG. 2  modular lighting system  42  include lighting controller  36 , first light-string  30 , second light string  28 , first battery module  32 , and second battery module  34 . First and second light strings  30 ,  28  are interconnected one to another. First and second light string  30 ,  28  each has first light-string connector  38  and second light-string connector  40 . Second light-string connector  40  of first light string  30  is electrically connected to first light-string connector  38  of second light string  28 . 
     First and second battery modules  32 ,  34  are interconnected to one another in a similar manner to the manner in which first and second light strings  30 ,  28  are interconnected to one another. In some embodiments, battery modules  32 ,  34  can be interconnected in a serial fashion. In some embodiments, battery modules  32 ,  34  can be interconnected in a parallel fashion. In some embodiments, battery modules  32 ,  34  can be interconnected in a daisy-chain fashion. 
     Lighting controller  36  includes: light string interface  44 ; battery module interface  46 , battery compartment  48 ; power conversion and distribution module  50 ; light string power controller  52 ; light string current sense module  54 ; timer  56 ; and user interface  60 . Interconnected first and second light strings  30 ,  28  are connected to lighting controller  36  via light string interface  44  and first light-string connector  38  of first light string  30 . Interconnected first and second battery modules  32 ,  34  are connected to lighting controller  36  via battery module interface  46 . 
     Battery compartment  48  can receive one or more batteries. Power conversion and distribution module  50  receives power from interconnected first and second battery modules  32 ,  34  or from battery compartment  48  or from both interconnected first and second battery modules  32 ,  34  and battery compartment  48 . Power distribution and control module  50  then generates one or more supply levels for use by various components of lighting controller  36 . 
     Light string power controller  52  receives operating power from power conversion and distribution module  50 . Light string power controller  52  provides constant-brightness lighting power to interconnected first and second light strings  30 ,  28  via light string interface  44 . The constant-brightness lighting power is substantially independent of a first voltage that varies with a charge of a battery received in battery compartment  48 , and independent of a second voltage that varies with a charge of first and second battery modules  32 ,  34 , and independent of a number (e.g., two in the depicted embodiment), up to a predetermined maximum number, of interconnected light strings connected to the light-string connector. In some embodiments, the predetermined maximum number of interconnected light strings to which lighting module  36  can supply constant-brightness lighting power is constrained by a maximum power rating of light string power controller  52 . In various embodiments the maximum power rating of light string power controller  52  is capable of providing illuminative power to 2, 3, 5, 8 or 10 light strings. 
     Constant-brightness lighting power is defined to mean lighting power that is within a limited range of predetermined power level. For example, constant-brightness lighting power can mean a lighting power within plus or minus 15%, 10%, 6%, or about 3% of a target lighting power, for example. In some embodiments, constant-brightness lighting power can mean lighting voltage within plus or minus 12%, 10%, 5%, or about 3% of a target lighting voltage, for example. 
     Light string current sensor  54  can sense a current drawn by interconnected first and second light strings  30 ,  28 . Light string current sensor can then generate a signal indicative of the sensed current drawn by interconnected first and second light strings  30 ,  28 . Light string current sensor can then output the generated signal indicative of the sensed current drawn by interconnected first and second light strings  30 ,  28  to light string power controller  52 . Light string power controller  52  can then change, if necessary, a lighting power so as to maintain the constant-brightness lighting power provided to the first and second light strings  30 ,  28 . 
     Such adaptive control of lighting power can maintain constant brightness of first and second light strings  30 ,  28  even should some LEDs of first and second light strings fail. Such adaptive control of lighting power can maintain constant brightness of first and second light strings  30 ,  28  even should additional light strings be added. Such adaptive control of lighting power can maintain constant brightness of first and second light strings  30 ,  28  even should one of first and second light strings  30 ,  28  be removed. 
     Adaptive control of lighting power has other advantages. For example, adaptive control of lighting power can maintain a constant brightness of light strings  30 ,  28  through changes in an ambient temperature. For example, a current-voltage relation in a light string can change in response to a changing ambient temperature. If the current-voltage relation of a light string changes, open loop power control can result in non-constant brightness of the light string. But by sensing both a current drawn by the light string and a voltage across the light string, a power can be measured. In some embodiments, the power can then be adaptively controlled to maintain constant brightness in the light string. 
     Timer  56  can generate timing signals and provide such timing signals to light string power controller  52 . Light string power controller  52  can respond to such timing signals, for example, by turning on first and second light strings  30 ,  28 , turning off first and second light strings  30 ,  28 , dimming first and second light strings  30 ,  28 , etc. Such timing signals may be used to change colors of first and second light strings  30 ,  28 , for example. In some embodiments, such timing signals may be used to make first and second light strings  30 ,  28  flash on and off in some predetermined fashion. Timer  56  may generate a command signal indicative of a specific lighting command and/or function. 
     User interface  60  may include user output devices and/or user input devices. Examples of output devices can include a display device, a sound card, a video graphics card, a speaker, a cathode ray tube (CRT) monitor, a liquid crystal display (LCD), a light emitting diode (LED) display, an organic light emitting diode (OLED) display, or other type of device for outputting information in a form understandable to users or machines. Examples of input device(s)  48  can include a mouse, a keyboard, a microphone, a camera device, a presence-sensitive and/or touch-sensitive display, or other type of device configured to receive input from a user. 
     In some embodiments, user interface  60  may be in a form of a communications port. User interface  60 , in one example, utilizes one or more communication devices to communicate with external devices via one or more networks, such as one or more wireless or wired networks or both. User interface  60  can be a network interface card, such as an Ethernet card, an optical transceiver, a radio frequency transceiver, or any other type of device that can send and receive information. Other examples of such network interfaces can include Bluetooth, 3G, 4G, and WiFi radio computing devices as well as Universal Serial Bus (USB). 
       FIG. 3  is a circuit schematic diagram of an exemplary constant-brightness decorative lighting system. In  FIG. 3 , light string power controller  52  includes battery B 1 , LED lighting controller U 1 , switching power supply U 2 , current sense resistor R SENSE , and light string LS. Output V OUT  of switching power supply U 2  provides operating power to light string LS. Output V OUT  of switching power supply U 2  is also coupled to node V SENSE  of LED lighting controller U 1 . A voltage across current sensing resistor R SENSE  is indicative of the current through light string LS. The voltage across R SENSE  is provided to node I SENSE  of LED lighting controller U 1  and node I SENSE  of switching power supply U 2 . In some embodiments, switching power supply U 2  uses the I SENSE  signal for fast, closed-loop control of the LED current. In some embodiments, lighting controller U 1  uses the signal for fine-tuning of the LED current and/or to detect low-battery charge conditions. 
     LED lighting controller U 1  generates control signal V CTRL , based on the signals received on nodes V SENSE  and/or I SENSE . The generated control signal V CTRL  is then output to input pin V IN  of switching power supply U 2 . Control signal V CTRL  is indicative of a desired lighting power. Switching power supply U 2  receives the control signal V CTRL  indicative of the desired lighting power on node V IN . Switching power supply U 2  generates a constant-brightness lighting power and supplies the constant-brightness lighting power to light string LS via output node V OUT . Both switching power supply U 2  and LED lighting controller U 1  receive operating power from battery B 1 . 
     Various embodiments can use various means for providing constant-brightness lighting power to an interconnected number of light strings. In some embodiments, light string power controller  52  can generate and provide constant-brightness lighting power. In some embodiments, light string power controller  52  can include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other equivalent discrete or integrated logic circuitry. In some embodiments, light string power controller  52  may generate a digital signal indicative of a constant-brightness lighting power. A digital-to-analog converter can then convert the digital signal indicative of the constant-brightness lighting power to an analog power signal supplying the constant-brightness lighting power. 
       FIG. 4  is a block diagram of an exemplary constant-brightness lighting system. The constant-brightness lighting system depicted in  FIG. 4  is a simplified version compared with the modular lighting system depicted in  FIG. 2 . In  FIG. 4 , constant-brightness lighting system  54  includes light string  56  and light-string controller  58 . Light string  56  is connected to light-string controller  58  at first end  60  of light string  56 . At second end  62  of light string  56  is light string connector  64 . Light string connector  64  is configured to connect to additional interconnected lighting elements. 
     Light-string controller  58  has battery compartment configured to receive one or more batteries. The received batteries can provide operating power to light-string controller  58  which provides a portion of such operating power to light string  56  in the form of lighting power. Light-string controller  58  includes switching supply  66 , load sensor  68 , and memory module  70 . Switching supply  66  and load sensor  68  are in electrical communication with light string  56 . Load sensor  68  is configured to sense a signal indicative of a brightness of light string  56 . Load sensor  68  may provide the sensed signal indicative of the brightness of light string  56  to switching supply  66 . In some embodiments, load sensor  68  can generate a new signal indicative of the brightness of light string  56  and provide the generated new signal to switching supply  66 . For example, load sensor may amplify and/or filter the sensed signal before providing the generated new signal to switching supply  66 . 
     Switching supply  66  can compare the received signal indicative of the brightness with a target signal  72 . Target signal  72  can be retrieved from memory  58  and/or it can be calculated by switching supply  66 . In some embodiments, target signal  72  can be calculated based on the received signal indicative of the lighting brightness. For example, the signal indicative of the lighting brightness may include a signal indicative of a number of lighting elements. The target brightness may be calculated to vary in response to the number of lighting elements, for example. For example, a sensed voltage can be indicative of a lighting brightness, and a sensed current can be indicative of a number of lighting elements. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.