Abstract:
A retrofit energization arrangement especially suitable for an aircraft wherein original factory-placed wiring can be reused in common bus form for plural new loads in order to avoid the expense and hazard of disassembling original wiring bundles for new conductor incorporation. Serviceable wiring possibly earlier retired in place or becoming unneeded from equipment removal can, by way of the invention, be used for plural diverse new loads including loads of disparate operating cycle and current requirements for example, even though energized via a common bus. In the disclosed apparatus both energizing current and load control signals are transmitted via the same electrical bus between control location and load areas of the aircraft where control decoding and energy tap-off occur, the latter by switch mode power supply if needed. Control signals of sinusoidal waveform, minimal electromagnetic and radio frequency interference character and limited existing bus filtering attenuation are disclosed; these may be embodied as the Frequency Shift Keying (FSK) or Continuous Tone Coded Squelch System, CTCSS, frequencies used in the radio communication art. Loads of differing types are disclosed as examples in the described embodiment of the invention; additional loads are feasible. Use of the invention in land vehicles, watercraft and building structures is also contemplated.

Description:
RIGHTS OF THE GOVERNMENT 
   The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty. 

   BACKGROUND OF THE INVENTION 
   In the electrical energy conveyance art there is often a need to use existing inaccessible electrical wiring in order to achieve some new and originally unconsidered function. A “smart” ability to accomplish this new function can often save significant amounts of work and expense involved in a rework effort. This set of events is encountered in a plurality of differing applications of the electrical arts, i.e., in numerous fields of endeavor including buildings and transportation equipment of differing types. 
   One example of this situation is to be found in the electrical wiring of certain rooms in many homes especially in the United States but also other locations of the world. In these rooms, such as in a bedroom, there is originally provided a ceiling light fixture controlled by a wall mounted light switch located near the entrance door of the room. Energy for lighting the lamp of this fixture may be supplied to either of a small metal electrical box containing the wall switch or to the small metal electrical box used to mount the light fixture in the room ceiling. In either event the original house wiring often includes a single pair of lamp fixture controlling electrical conductors running between the two metal boxes, conductors that are buried and securely attached to structural members of the house before a wall covering such as plaster board or wet plaster is put in place. Such conductors are of course later inaccessible for enhancements such as an increase in conductor numbers without substantial destructive and reconstruction efforts. Local building codes in a few locations of the U.S. provide an exception to this general rule in requiring the use of “conduit” or pipe-like pathways and pulled-in conductors between these metal boxes and thus allow for new conductor retrofitting when needed. Communities around the city of Chicago, Ill. are for example known to have such local code rules. In most locations however original wiring is of the “Romex” or “BX” or even older “knob and tube” varieties and is thus rigidly attached to or passing through structural members of the house and is now inaccessible. 
   A problem with this usual wiring arrangement often arises when a new or additional usage of one or more of these boxes is contemplated, a use such as providing a combination electrical light and ceiling fan is desired in the room. When the box to box conductors are two in number, lie buried between wall surfaces and between first floor ceiling and second floor flooring and consist of flexible “Romex” or “BX” or other common two conductor residential wiring forms, the provision of a new third or additional electrical conductors for separate control of fan speed, fan direction and lamp intensities for example is a significant dilemma. 
   One clever solution to this electrical art dilemma has been provided by the Casablanca Fan Company located in California, USA. Combination fan and light fixtures provided by this supplier do in fact provide a plurality of differing fan speeds and directions and lamp illumination intensities all with use of only the two original conductors joining the ceiling and wall boxes! The Casablanca designers have accomplished this plurality of control functions through use of control signals coded into the sinusoid waveform of the supplied electrical energy wave. The Casablanca coding is embedded in the controlled energy wave near the sinusoid waveform zero voltage crossing points. Such coding is accomplished with wave slicing events performed by bidirectional semiconductor devices of the silicon controlled rectifier type, devices known in the art as “thyristors” or by other names proprietary to the device supplier. A more complete description of the Casablanca control is provided in a series of U.S. Patents including U.S. Pat. No. 4,716,409 issued to Casablanca designers, this and any other patent identified in this document are hereby incorporated by reference herein. 
   Although the Casablanca control and coding technique is elegant in design and performance it is limited by practicalities such as nearby lightning surges being often destructive of semiconductor devices when integrated into long house wiring runs, by switch contact resistance increasing over use lifetime, by generation of distorted sinusoid wave shapes (that are minimally diminished in electrical energy delivery effect but include high frequency harmonics, a possible source of radio frequency interference noise) and by the inherent applicability of the coding only to alternating current electrical energy sources. Generally it also may be stated that the Casablanca coding intentionally distorts an incoming sinusoidal wave in order to introduce the control coding as opposed to adding additional sinusoids to an incoming waveform in order to embed the control signals. The zero crossing coding of the Casablanca technique may nevertheless generally be considered as one clever and practical approach to communicating control signals by way of two energy delivery conductors and to the use of limited conductor existing wiring for new and more demanding applications. 
   As described herein there is additional need for arrangements somewhat of this nature in electrical applications outside of the house and building environment. It is for example particularly difficult to re-wire an aircraft in order to provide for new exterior or interior light sources or to energize other loads especially when such loads may necessitate physical dispositions at distant locations of a large airframe and thus require transmission of energy through hundreds of feet of integrally assembled and hidden factory installed wiring. Re wiring is of further increased difficulty when the wiring in an originally installed factory bundle is now characterized by electrical insulation degradation such as embrittlement or chafing or where the aircraft includes decorative or thermal insulation interior panels or other physical obstructions for examples. One needs only to consider the conclusions reached with respect to TWA flight 800 in New York to appreciate the significance of fragility in existing aircraft wiring. Aircraft rewiring is in fact so difficult and costly that the practice of “retirement in place” for original wiring has become commonplace in older aircraft, particularly in military aircraft. 
   In the art of improving existing aircraft with upgraded electronic systems, as has been practiced in several cycles in for example the fleet of B-52 bombers used by the U.S. Air Force since the mid 1950&#39;s, it may be convenient to reuse the electrical conductors of a somewhat large-conductor factory-wired bus of significant length and advantageous physical location for certain new equipment not in existence at the time of original aircraft fabrication. For example electronic equipment at the time of B-52 design was almost totally dependent on vacuum tubes and thus was characterized by low input to output efficiency, larger physical size and greater energy usage than is now experienced with integrated circuits and other semiconductor equipment. In a related manner smart missile weapons and global position system equipment for examples were completely unknown at the time of B-52 design but now are necessary additions for effective present day usage of such aircraft. 
   Similar examples involving the retrofitting of other aircraft are under current military consideration. The C-130 transport aircraft has been manufactured in several versions for years and certain of these versions are being considered for receipt of enhanced avionics equipment including cockpit displays and controls. Similarly the close ground support fighter aircraft commonly known as the A-10 and “warthog” has been in use for years and has also received modern equipment upgrades. The addition of night vision equipment and the provision of night vision equipment-compatible lighting both inside and outside the aircraft are additional areas of significant present military concern and are believed assisted by the present invention. 
   The present invention has been found especially useful in the modernization of tanker aircraft wherein both a replacement for incandescent filament lamps with light emitting diode elements and bus signal decoding electronics can all reside in the space reserved for original incandescent lamp fixtures. In such aircraft there exists, for example, a large number of light fixtures used in guiding an aircraft being refueled into correct position for engagement with the refueling boom. These fixtures are used under nighttime conditions and in both friendly and hostile airspace. Some of these guidance lamps now need to house covert or night vision related infrared characteristics in order to provide aircraft safety in hostile airspace. The present invention adds the capability to select between these multiple forms of signal illumination without need to provide additional lamp fixture wiring and other costly and time-consuming changes. 
   By way of capabilities achieved in the present invention an earlier provided electrical bus, as for old and now removed electronic equipment for example in an aircraft, may be re used to energize several present day loads while the application of energy to these loads is nevertheless individually controlled from the cockpit or from some other point of the aircraft, such as an operator station. Such technique may of course also be applied to newly installed wiring and equipment where it is desirable to reduce conductor numbers, weight or bundle size. According to this arrangement, a single electrical bus may be used to control a plurality of differing loads through signal coding communicated along the same bus conveying the controlled energy. For simplification purposes herein these multiple electrical loads may be represented by light sources of different character located throughout the aircraft and its exterior. Such light sources are of course also possible actual loads that may be energized in this manner, all as described subsequently below herein. 
   SUMMARY OF THE INVENTION 
   The present invention therefore provides for the re use of existing electrical wiring to supply electrical energy to a remote load device such as a lamp fixture or light emitting diode fixture or other load especially in an aircraft or other vehicle setting. 
   It is therefore an object of the present invention to provide bus energized individual load control arrangement responsive to control signals received via common energy bus conductors. 
   It is another object of the invention to provide remote load control signals that are sinusoidal in nature. 
   It is another object of the invention to provide remote control of individual electrical loads fed by a common bus. 
   It is another object of the invention to provide remote load control signals having a selectable plurality of simultaneous sinusoid frequencies. 
   It is another object of the invention to provide a remote load control arrangement of limited electromagnetic interference generation characteristics. 
   It is another object of the invention to provide a remote load control arrangement suitable for use with a variety of different load types and load environments. 
   It is another object of the invention to provide a remote load control arrangement usable to select a variety of characteristics in remote load devices. 
   It is another object of the invention to provide a remote load control arrangement usable in vehicular and building and other settings. 
   It is another object of the invention to provide a common bus remote load control arrangement having especially desirable utility in a large aircraft setting. 
   It is another object of the invention to provide an electrical load control arrangement that is suited for usage in new aircraft or in modernized older aircraft. 
   These and other objects of the invention will become apparent as the description of the representative embodiments proceeds. 
   These and other objects of the invention are achieved by aircraft electrical retrofit apparatus comprising the combination of: 
   a source of aircraft electrical load energization energy received in said aircraft; 
   an aircraft control location proximate source of selectable low level alternating current electrical load control signals impressed on an electrical output of said source of aircraft electrical load energization energy to form a modulated energy signal; 
   a newly added aircraft electrical energy load device remotely disposed in said aircraft with respect to said source of aircraft electrical load energization energy and said source of low level alternating current electrical control signals; 
   an electrical conductor within an undisturbed original wiring bundle of said aircraft said conductor being disposed between a combination of said source of aircraft electrical load energization and said control location proximate source of low level alternating current electrical load control signals at a first end thereof and a remote new load driver circuit at a second more remote aircraft location end thereof; 
   a load control signal decoder circuit disposed at said second more remote aircraft location and connected intermediate said second end of said electrical conductor and said remote new load driver circuit, said decoder circuit being responsive to said low level alternating current electrical load control signals received via said conductor and generating therefrom a remote load driver circuit controlling signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings incorporated in and forming a part of this specification, illustrate several aspects of the present invention and together with the description serve to explain the principles of the invention. In these drawings: 
       FIG. 1  shows a representative aircraft inclusive of a remote load control arrangement according to the present invention. 
       FIG. 2  shows a block diagram of a remote load control arrangement according to the present invention. 
       FIG. 3  shows a combined block diagram and fundamental schematic diagram of a remote load control arrangement according to the present invention. 
       FIG. 4  shows a simplified overall diagram of a remote load control arrangement according to the present invention. 
       FIG. 5  shows a block diagram of a remote load control signal encoder usable in the present invention. 
       FIG. 6  shows a block diagram of a remote load control signal decoder usable in the present invention. 
       FIG. 7  shows a block diagram of a controllable power supply usable with the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  in the drawings shows a representative larger size aircraft inclusive of a remote load control arrangement according to the present invention. In the  FIG. 1  drawing the aircraft  100  may be considered to be a B-52 or a C-5 or a C-17 or C-130 or a C-135 or A-10 or other aircraft. This aircraft is provided with the four jet type engines  102 ,  104 ,  106  and  108 , a fuselage  120 , wing sections  122 - 123 , an elevator assembly  110  and a rudder system  111 , all as are conventional for such aircraft. Attached to extremities of the wings  122  and  123 , the rudder system  111  and the fuselage  120  are aircraft external light source fixtures  112 ,  114 ,  116  and  118  that may serve as aircraft markers and for possible additional functions such as visual signal sources. 
   For present invention purposes it is assumed that an electrical bus  126  of either one single conductor plus the common fuselage ground variety or of the two individually isolated conductors variety extends from the cockpit  124  to a point in the rear most or tail assembly area of the aircraft along with branches  128  and  130  extending to the extremities of the wing sections  122  and  123 . This bus  126  is used in the commonly fed but individually selectable energization of loads including the light sources  112 ,  114 ,  116  and  118  and other possible loads located in bus served extremity areas of the aircraft  100 . In keeping with one attribute of the present invention this bus may consist of conductors within a bundled existing assembly of wiring or may be of an individual and even newly added to the aircraft nature if desired. 
     FIG. 2  in the drawings shows in block diagram form several overall details of a control system according to the present invention. The  FIG. 2  details may be appropriate when the energy bus is installed in a vehicle or a building as well as in an aircraft  100 . At  200  in the  FIG. 2  drawing there is shown a plurality of possible main energy sources such as may be used to provide energization to the lamps or other loads attached to an existing conductor bus in for example the aircraft  100 . For lamp energization purposes it is often desirable to employ low voltage electrical energy in order to use heavier and vibration-tolerant filaments in incandescent lamps and light emitting diode devices that are directly operable from the available voltage. Fourteen volts is today popular for such usage in land vehicles, twenty eight volts has been popular for use in aircraft and in military vehicles and is therefore indicated in the  FIG. 2  drawing. 
   The bus energy sources shown at  200  in the  FIG. 2  drawing include three involving alternating current electrical energy; usually such sources as are available on larger aircraft or in ground based applications of the present invention. These sources are indicated at  201 ,  204  and  210  in the  FIG. 2  drawing and may involve either 400 Hertz or 60 Hertz energy or other alternating current sources. The two additional energy sources indicated at  206  and  208  in  FIG. 2  relate most directly to aircraft and other vehicles and are of a direct current nature. Each of the energy sources shown in  FIG. 2  is represented by a diamond shaped enclosure shown coupled to a succeeding rectangular block in which is disposed additional energy source components. These components may include the rectifier and energy storing capacitor at  204 , the switch mode power supplies represented by the abbreviation “SMPS” and shown at  201 , the low-pass filter represented by the abbreviation “LPF” and shown at  206  and  208  and the voltage changing transformer shown at  210 . To a large extent any of the  FIG. 2  rectangular block components may be used with any of the diamond shaped enclosure sources and may provide the fourteen or twenty eight volt direct current output energy shown at the right edge of the sources  202 . Generally any of the output energy forms shown at  200  in  FIG. 2  may be obtained from each combination of input energy form and rectangular block components with a suitable selection of components. 
   At  212  in the  FIG. 2  drawing there is represented a series of components used at the input or cockpit end of an electrical energy bus, such as the bus  126  in  FIG. 1 , for the purpose of supplying a remote load controlling signal on the bus. As provided in the present invention this control signal is used at remote locations along the bus in selecting load energization control variables such as ON and OFF status and energization level of a load element, a load element that is often of an energy transducer nature such as an electrical energy to radiant energy lamp or an electrical energy to thermal energy transducer (a detonator squib device for example). To accomplish these functions there is included at  212  an operator selection control  214 , a sinusoidal tone code signal source  216  and a mixer or modulating apparatus  218 . The sinusoidal tone code signal source  216  may be arranged to generate a variety of selectable control signal frequencies and frequency combinations, for example, frequency shift keying (FSK) or continuous tone coded squelch system frequencies. 
   Use of an array of frequencies identified by the name of “Continuous Tone Coded Squelch System” or “CTCSS” frequencies is considered one possibility for frequencies usable at  216  in the  FIG. 2  drawing for present invention load coding purposes. The “CTCSS” coding concept is believed to originate with Motorola Inc. where it has been used in the two-way radio field to provide privacy among plural users of a shared same radio frequency voice channel. This privacy is achieved by identifying each user&#39;s communication with a differing sub audible encoding tone. Each such CTCSS tone is one of about 30 to 50 possible tones, a tone often lying between 67 Hertz and 5 kilohertz in frequency for example. In such radio communication usage when an appropriate tone signal is present in a received signal the receiver muting or squelch function is disabled and the incoming signal reproduced for hearing. The audio signal band pass of a receiver accommodating such CTCSS coded signals, a voice communication receiver, may be limited in low frequency range in order to exclude the CTCSS control signal from listener detection-even though the control signal may otherwise fall within the human detectable frequency range. 
   “CTCSS” related concepts have also become known in the art by the name of “private line” or “PL” and by other names used by suppliers other than Motorola. The concept has also been adopted in the amateur radio equipment field and is applied there to unlock repeater equipment and for other control purposes. For “CTCSS” use the original tone frequencies were selected to provide harmonic signal separation benefits. The present invention may thus be viewed as a new use for “CTCSS” like frequency array signals, however, it is not necessary that only these frequencies be employed for present invention purposes. 
   It is notable with respect to the present invention that the CTCSS array of frequencies envelop or come close to the frequencies often encountered in alternating current energy distribution systems e.g., the frequency of 400 Hertz in aircraft energy sources and the frequency of 50 or 60 Hertz in ground based energy sources. In instances wherein the present invention control system is used with one of these energy frequencies it is of course necessary to distinguish between the energy frequency and nearby control signal frequencies in a control signal receiver apparatus. Various forms of signal frequency selection such as electrical wave filters and phase locked loop systems may be used for these purposes as are known in the art. 
   In the block  218  of  FIG. 2  the mixing of synthesized “CTCSS” or FSK code signals with the bus energy is accomplished. In other words sinusoidal control signals are impressed on the bus input energy in the block  218  notwithstanding which of the possible combinations of input energy, rectangular block processing and output energy from the processing at  202  is employed. Impression of the control signals on the direct current energy supplied to the bus can be accomplished in the manner described in subsequent drawings herein. In situations where rapidity of response of the controlled load is required, frequency shift keyed control signals may be used advantageously in place of CTCSS signals in the interest of faster response times. 
   The low pass filtering shown at  219  in the  FIG. 2  drawing allows the load energization energy and the impressed control signals to pass while attenuating undesired higher frequency components that if present could radiate from the bus  126  into the  FIG. 1  aircraft or beyond. The output of the low pass filter at  219  may be connected directly to an input port along the bus  126  as is indicated by the double identification numbers of the filter output at  222  and  126  in the  FIG. 2  drawing. 
     FIG. 3  in the drawings shows at  300 , in block diagram form, an array of components usable to decode the sinusoidal signals impressed on energy bus  126  in  FIG. 1  at each possible load location along this bus; i.e., one of a plurality of such decoding and energy coupling circuits desired for aircraft  100  usage of the present invention. In the  FIG. 3  apparatus the coded and energy delivery components of an input signal received from bus  126  are segregated by a low pass filter  301  into direct current energy at  302  and sinusoidal control signals at  303 . The direct current energy is sent to for example lamp or light emitting diode driver circuits  316  and  318  through the current sensing series connected resistors  312  and  314 . The sinusoidal control signals are sent to a tone decoder circuit  304  for identification and conversion into a form usable to enable the error amplifiers  308  and  310  and the switching mode power supplies (SMPS)  306  and  307 . 
   By way of sensing voltage drop across the series connected current sensing resistors  312  and  314  the error amplifiers  308  and  310  maintain the for example lamp or light emitting diode load elements represented at  316  and  318  in  FIG. 3  in a desired range of illumination current in closed loop fashion. This energization provides a selected one of visible output from one aircraft mounted light emitting diode fixture  316  and limited spectrum covert output from an alternate aircraft mounted light emitting diode fixture, the covert emission fixture  318 . A selected one of or both of these fixtures can be energized at any given instant in an operating scene in order to provide a desired identification/marking of an aircraft such as the aircraft  100  in  FIG. 1 . 
   Notwithstanding this illumination flexibility, both the energy and the control signals for such fixtures can be communicated via a single electrical bus according to the present invention. Moreover according to the invention this single electrical bus can be simultaneously controlling and energizing other loads at different locations along the bus  126  by way of additional of the  FIG. 3  circuits. The illuminations at  316  and  318  may be coincident in time or in time sequence with the addition of appropriate time related signals to the error amplifiers  308  and  310  or at other points in the  FIG. 3  system. This load control flexibility can of course extend to intentionally intermittent energization of a load when needed; input of an intermittent control signal to one position of selector switch  214  for example can be used for this purpose. 
   A selected encoding of sub audible tones provides a possible error resistant addition to the heretofore described present invention. Coding of this nature is resistant to errors such as may be caused by induced interference from other systems or from electromagnetic interference and radio frequency interference sources in an aircraft for example. Golay coding is for example a branch of the applied mathematics art and is an error prevention code of the desired type. Golay coding is discussed in a plurality of technical publications including the article “Golay Codes” authored by Melissa Kanemasu and appearing in the MIT Undergraduate Journal of Mathematics. This article and numerous others concerning Golay codes are available through use of the World Wide Web and a search engine inquiry regarding the topic. 
     FIG. 4  in the drawings shows a combination block and schematic diagram for a single load remote load control arrangement according to the present invention. In the  FIG. 4  drawing the  FIG. 2  signal source apparatus at  216  appears approximately at  400  and the signal decoding apparatus at  300  in  FIG. 3  appears approximately at  402 . In the  FIG. 4  diagram a source of electrical energy  404  is coupled through a circuit breaker  406  to a control signal injection transformer  408  and then to an aircraft wiring conductor  414 . The transformer  408  provides a coupling of load control signals, preferably sinusoidal signals, generated at  412  in  FIG. 4  and amplified at  410  onto the electrical energy conveyed along the aircraft conductor  414 . The conductor  414  may thus be considered to convey energy signals that are modulated by low level control signals of the CTCSS, FSK, or other types. 
   The electrical size of the transformers  408  and  416  in the  FIG. 4  circuit as well as the current rating and output impedance characteristics of the amplifier  410  are quantitative considerations in assembling the  FIG. 4  components of an invention embodiment. These considerations are of course primarily dependent on the level of load energization current flow in the conductor  414  as well as on the attainable sensitivity of the control signal buffer amplifier  418 , the prevailing system environment noise level and other secondary considerations. An additional factor to be considered in selecting these components is the nature of the load energization energy i.e., whether it is of the direct current nature shown herein or of the also feasible alternating current nature. Clearly for example a physically smaller transformer at  408  and at the below discussed transformer  416  location are realistic if the load energization energy is of 400 Hertz frequency than if it is of 60 Hertz nature. Additionally with use of larger sized power transistors, suitable feedback arrangements and a low output impedance in the output stage of the amplifier  410  the coupling of load current components backward through the transformer  408  can be limited and an impression of sufficient control signal amplitude onto the conductor  414  assured regardless of the small or larger aircraft load to be driven by the  FIG. 4  circuit. 
   In the load end circuits  402  of the signal conductor  414  the transformer  416  recovers the sinusoidal control signal injected at  408  in  FIG. 4  and couples this control signal to the decoder circuits  420  by way of the amplifier  418 . Following the signal recovery in transformer  416  the remaining load energization energy is conveyed along the path  424  to a load or light power supply  422 . Functional operation of this power supply both with respect to load ON or OFF state and load energization level is determined by way of the decoded control signal from block  420 . This signal is again preferably sinusoidal in nature and may be of the decoded CTCSS signal(s) nature. Additional information regarding the block  420  circuit and other  FIG. 4  circuits is disclosed in the ensuing paragraphs and drawings herein. 
     FIG. 5  in the drawings herein shows additional details of the control signals determination apparatus  500  as generally appears at  400  in the  FIG. 4  drawing. In the  FIG. 5  circuit apparatus the selector switch  214 , first appearing in the  FIG. 2  drawing, is again shown. This switch provides ability for a pilot or other person at the sending end of the electrical bus  126 / 414  to choose one of or a combination of load controlling coded sinusoid signals for communication along the electrical bus  126  and select the one or plurality of aircraft loads for current time energization. The switch  214  chosen code signals are generated in the block  502  of  FIG. 5  where circuitry fabricated around a Motorola MCL 68HC705 integrated circuit device for example may be used for control signal tones generation. The generated tone signals are amplified and provided with the low output impedances discussed previously in the amplifier  410 / 504  shown connected with the tone generator at  502 . A power line filter shown at  506 , generally a multiple poled low pass filter, can be used to attenuate undesired noise or other spurious signals tending to communicate in either direction with the bus  126  in the  FIG. 5  circuit. 
     FIG. 6  in the drawings shows details of an embodiment of the control tone decoder circuit represented at  420  in the  FIG. 4  drawing. In the  FIG. 6  circuit  600  another filter circuit  602 , generally of the same type as described at  506  in  FIG. 5 , may be used the couple the electrical bus  126 / 414  to a tone signal decoder circuit  604  where one or multiple tone signals impressed on the electrical bus  126 / 414  cause activation of one or more of the individual load selector output signals indicated at  606  in  FIG. 6 . The tone signal decoder circuit  604  may for example include a phase locked loop circuit and a series of comparator circuits, one for the output signal at  608  and each of the other output circuits at  606 . Generally each of these comparator circuits maintains one of output signals  606  in the active state so long as the related tone control signal can be detected on the electrical bus  126 / 414 . 
     FIG. 7  in the drawings shows details of an embodiment of the light power supply circuit represented at  422  in the  FIG. 4  drawing. In the  FIG. 7  circuit  700  a digital to analog converter apparatus represented at  702  may be used to generate an analog signal at  710  for driving for example the dual current mode power supply represented at  704 . Each output  706  and  708  of the power supply  704  may be coupled to an individual one of the remotely located load devices of the aircraft  100  in  FIG. 1 . As shown in the  FIG. 7  drawing the remotely located load devices are represented as one visible light emitting diode external fixture of the aircraft  100  and one covert, e.g. infrared light emitting diode external fixture, of the aircraft  100 . Other load devices such as weapons dispensers or defensive device dispensers for examples may be controlled by the circuit  704  or by the plurality of such circuits contemplated in a large aircraft use of the present invention. 
   Plural present invention improvements result from use of sinusoidal tones communicated over existing conductors conveying power to the remote devices to command changes in the performance of the remote devices. Since the frequency of the tones is low and waveforms are sinusoidal in nature, such tones will readily pass through filter networks that may already exist in the lighting or power systems of vehicles for example; filters that would otherwise block higher frequency tones. In view of the tones readily passing through any such filters no additional or dedicated conductors for carrying control signals are needed between control point location(s) and controlled light fixture locations nor do existent filter networks otherwise needed for other functions need to be changed. As a result of the sinusoidal waveform used little or no electromagnetic interference and very little or no radio frequency interference is generated. Such interference is undesirable and often intolerable in many military vehicle and aircraft situations since it may, for example, interfere with “intercom” operations as well as limit aircraft stealth characteristics. The use of sinusoidal tones for control is thus believed a significant improvement in the control art. 
   Thus the present invention provides for the control of light source fixture operation and other loads on for example aircraft and on other vehicles or on stationary structures where intensity and other operating parameters are to be controlled from a remote location such as elsewhere in the vehicle through use of existing power conductors. An advantage of the invention is that it is flexibly adaptable to function with systems having widely different energy supply characteristics, e.g. direct current or alternating current at low or high voltages and large or small load current levels while at the same time avoiding the need for destruction and reconstruction of existing wiring arrangements, being free of large electromagnetic interference generation and enabling control of multiple and diverse loads. 
   While the apparatus and method herein described constitute a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus or method and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.