Abstract:
The present invention is a thermally activated electrical switch for use in simulating human activity. The invention is features dual heat sources enclosed in a thermally isolated chamber within the invention. Since the activation of the switch is dependent upon the ambient temperature of the environment, it opens and closes at sufficiently random intervals to simulate human activity. This embodiment includes the use of a photoelectric sensor to further vary timing of the switch actuation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND PATENTS 
   This Application claims priority as a CIP application based on prior Non-Provisional Application No. 10/906,489, filed Feb. 22, 2005, which is incorporated by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to the field of electrical security timers and more particularly relates to a randomized timer that is thermally and luminescently operated. 
   BACKGROUND OF THE INVENTION 
   Over the past 40 years, consumers, for the purpose of home security, have purchased millions of automatic switches, manufactured by several major manufacturers, for the purpose of simulating human activity in dwellings and other buildings to deter burglars when the occupants of the dwelling or building are away. Typical switches are clock operated. All of these clock-operated switches are settable to turn the light on or off, either on the hour or the half hour, two or more times in a 24-hour period. This practice of using a timer has become so widespread that it has become common knowledge that if the lights in a house switch on or off on the hour or the half hour, or at the same time on successive nights, that this is an indication that the owners are away and the house is unoccupied, indicating that a timer is being used to simulate occupancy. Even the popular movie of the late 1990&#39;s, entitled “Home Alone” has as a theme, the burglars who checked the time that the lights came on to determine that the owners were away on vacation. 
   The predictability of the timing of these devices has rendered them virtually counter-productive as burglar deterrents, as they now serve as much to inform the burglars of the absence of the occupants. In addition to the electromechanical clock types described, solid-state equivalent units are also available, also having the same inadequacies as the electromechanical types, for the purpose intended. 
   Notwithstanding their obsolescence as effective burglar deterrents due to their well known predictability, still they are continuously sold in all department stores, hardware stores, chain stores, discount stores and variety stores throughout North America, because no preferred alternative has been made available. It is the purpose of this invention therefore, to make available such alternative to better fill the need. 
   All clock operated timers and also the solid-state equivalent types, have three functional inadequacies which prevent them from being effective burglar deterrents. First, they are precisely predictable, because they operate at the same times, day after day. Second, they are vulnerable to power interruptions, which gets them “off-schedule” until manually reset by the owner, who may be away for days or weeks, or in the case of a vacation home, they can be off-schedule for months. Third, the setting of time of day, and programming the turning on and off of the lights is time consuming, complicated, and bothersome. 
   The present invention overcomes all 3 of the above inadequacies, as will be explained herein below. The present invention described herein controls the lights in a way that is completely unrelated to horological time. The present invention will never, or very rarely if ever, turn its load on or off at the same time as the previous day. The present invention is so unlikely to turn its load on or off at the same time as the previous day, that it is estimated by probability at one chance in approximately 500,000. 
   Second, because the present invention has no relationship to the horological clock, and has no horological schedule. Therefore, after a power interruption, and when the power is restored, the present invention continues turning its load on and off at intervals unrelated to horological timing, and therefore continues to serve the intended purpose just as effectively as if the power interruption had not occurred. Third, the present invention eliminates the need for any setting of time of day and time-of-operation programming. In contrast, a single switch, set to “security” position in an instant, is all that is needed to enable the invention to function for its intended purpose. 
   The invention herein described is designed to be useful in three different embodiments as herein below described. In its basic simplest form, the user simply turns this invention on or off by a single manual switch. The invention may also be combined with a day/night photoelectric sensor, which is well known in the art. In this embodiment the invention functions during the night, but not during the day. The invention may also be combined with a clock-operated switch, well known in the art, so as to function within selected hours only. In all three of the above embodiments the invention can be configured to plug directly into the wall outlet of the home, or fitted with a power cord and plug, and placed on any convenient table. It is available, therefore, as either “wall models” or “table models” for the convenience and preference of the user. 
   While it is recognized, that the switching on and off of lamps and other electrical loads by electromechanical or electro-thermal means, as well as the timing of such switching, can be duplicated by solid state electronic means, using integrated circuits, triacs and other solid-state components, it should be noted that the use of solid state means, such as triacs, alters and distorts the waveform of the electrical current. This distortion is unsafe for any complex electrical device except an incandescent lamp. The present invention, as disclosed without solid state circuitry (though such circuitry may be used in controlling the actual switches and loads inside the device), does not distort the electrical waveform and is therefore safe for use with any electrical load, including consumer electronics and non-incandescent lamps. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing disadvantages inherent in the known types of security switches this invention provides an improved thermally activated security switch. As such, the present invention&#39;s general purpose is to provide a new and improved security switch that will operate independently from horological time. 
   The present invention is a thermally activated device for the simulation of human activity in an unoccupied dwelling. In its most basic embodiment, the invention utilizes a thermally sensitive switch, which when in use is electrically connected to a standard household electrical receptacle. Two heat sources are adjacent the switch, a primary resistor set and a secondary resistor. Both are connected to the electrical source in a parallel relation to the switch, but the primary, and significantly larger, resistor set is guarded by a triac gate in combination with a photo sensitive resistor, so that the gate is activated only when the resistor is not exposed to light and operating at a high resistance. All of the resistors and the switch are housed in a thermally insulating switch housing, which is in turn housed within an exterior housing. Exterior housing may feature an electrical receptacle and a primary bypass switch, allowing a user to bypass the thermal switch and maintain a continuous electrical current between the interface and receptacle. 
   In use, the device is plugged into a receptacle and a load, such as a lamp or television set, is plugged into the device&#39;s receptacle. For everyday use, the primary switch is left in a continuous “on” position, electrically bypassing the thermal switch. For security use, the primary switch directs current to the thermal switch and photocell and triac gate combination. Usually, the thermal switch is open, but as the resistors raise the surrounding temperature in the thermally insulated housing, the thermal switch is closed. The surrounding temperature drops slowly as secondary resistor is still providing heat and the thermally insulated housing slows heat transfer away from the switch. Eventually, the temperature cools to the point that the thermal switch again opens and allows current through. 
   The more important features of the invention have thus been outlined in order that the more detailed description that follows may be better understood and in order that the present contribution to the art may better be appreciated. Additional features of the invention will be described hereinafter and will form the subject matter of the claims that follow. 
   Many objects of this invention will appear from the following description and appended claims, reference being made to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views. 
   Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. 
   As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a circuit diagram of the present invention in open (off) mode. 
       FIG. 2  is a circuit diagram of the present invention in continuous on mode. 
       FIG. 3  is a circuit diagram of the present invention in security mode. 
       FIG. 4  is a cross sectional view of the thermally sensitive switch utilized in the invention in the open position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference now to the drawings, and with note that as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise, a preferred embodiment of the security switch is herein explained. As seen in  FIG. 1 , the device, in its preferred embodiment, consists of two parallel circuits; connected to a three-position manual control switch  4 , usually a Double Throw-Double Pole type, and power supply  3 . When switch  4  is in the continuously “on” position, shown in  FIG. 2  current flows into an indication circuit  10 , denoted with visible LED  8  and diode  6 , so positioned to protect LED  8  from excessive reverse voltage. Resistor  7  limits current to the LED  8 . Current also flows to load  14  through a parallel bypass circuit  12 . It should be noted that in the circuit drawings,  FIGS. 1-3 , the numerals  1  and  2  found along circuit components indicate current direction. 
   In  FIG. 3 , the switch  4  is set on security mode, activating the secondary heating circuit  22  and its associated parallel circuits. Secondary heat circuit  22  is a continuous circuit with small resistor  24  providing a constant heat source. The first parallel circuit is security indication circuit  20 , with LED  18 , Resistor  17 , and diode  16 , all serving similar function as described in indication circuit  10 . Security circuit  30  contains a solid state switching circuitry and two large resistors  26   a ,  26   b , in parallel and acting as a primary heat source. These resistors have a smaller combined resistance than resistor  24 . Resistance ratios are ideally that resistor  24  should have about 4 times the combined resistance of resistors  26   a ,  26   b.    
   Security circuit  30 , its components demarcated within the dashed box in  FIG. 3 , contains a both a primary resistor  31  in series with a photocell resistor  32  which connects back into the secondary heat circuit  22 . When exposed to light, the resistance in the photocell resistor  32  approaches zero and allows current to pass back into the secondary heat circuit  22 . When not exposed, resistance in the photo cell  32  increases to an extreme amount, effectively cutting off the sub-circuit. Branching parallel to the photocell  32  is a secondary resistor  33 , which divides the voltage along the circuit. Between the primary  31  and secondary resistors  33  is a diac  35 , in parallel to the secondary resistor  33  and serving as a trigger for the gate of triac  36 , in series with diac  35  and heating resistors  26   a ,  26   b . Capacitor  34 , bridging the secondary heating circuit  22  and the security circuit  30  at the location where secondary resistor  33  separates in parallel, is provided to store energy for the triggering function. The primary and secondary resistors provide different voltage across the circuit so as to operate the diac  35 . Current flows to resistors  26   a ,  26   b  after the gate of the triac  36  is activated, generating heat. Ideally, the physical position of these resistors are opposite each other and proximate the thermally sensitive switch  30 . A feedback resistor  38  bridges the secondary heat circuit  22  and the security circuit  30  between the diac  34  and triac  35  to prevent false triggering of triac  35 , which is also connected to secondary heat circuit  22 . 
   When sufficiently heated, switch  28  closes. As shown in  FIG. 4 , the switch  28  is activated by a bimetal disc  43  opening and closing the connection between the electrical contacts  48  in the switch  28 . Switch  28  comprises a movable arm  40  and a stationary arm  41 , held in place by retainer  46 , said movable arm  40  in operable connection to an actuating pin  45 , which is moved by the contortions of bimetal disc  43 . Bimetal disc  43  inherently has two metals with different expansion rates and thermal conductivity. As such, one metal will expand greatly when another does not, thus bending the disc  43  and moving the actuating pin so that movable arm  40  connects and disconnects contacts  48 , opening and closing the circuit. Ideally, spacer  42  is provided to allow room for disc contortion and a sensing cap  44  closely covers the disc  43 , allowing for thermal interaction, and the rest of the switch assembly in case  49 . Also ideally, case  49  is riveted  51  to a terminal backing  50 . It should be noted that the switch may just as easily be manufactured for either a default (room-temperature) open or closed state. In this application, the switch is described in a default open position, but the use of a default closed switch would be perfectly within the scope of this invention as it would only require an adjustment of components to have the same effect. Since the switch physically opens and closes, the waveform of electrical input is unaltered; therefore, the timer according to the present invention is safe for all types of electrical devices. 
   Referring to  FIG. 3 , input power is supplied to the output load  14  when switch  28  is closed. Ideally, the output load includes a lamp or other light generating device and such device is then turned on. The new ambient light is received by photocell  32  and its resistance plummets to near zero ohms again, thus closing the triac  35  gate and the rest of the security circuit  30 . Secondary heat circuit  22  remains energized to slow provide current to resistor  24  and slow the cooling of thermally sensitive switch  28 . Once sufficiently cooled, switch  28  opens, repeating the periodic on-off cycles again and again until manual switch  12  is set to “Continuous” or “Off” by the user. An enclosure isolates switch  28  and resistors  24 ,  26   a ,  26   b  from the exterior environment, further ensuring that the cooling process is slowed down. Likewise, an external casing, enclosing the entirety of device components, provides further thermal insulation. 
   Total thermal mass would include the material from which the external casing, enclosure and interior components are manufactured and any optional thermal mass added inside the enclosure and external casing to slow both the heating cycle and the cooling cycle. The optional thermal mass can be the addition of any thermally conductive material, including epoxy resin inserted into the timing module, or a thick steel disc inserted inside the enclosure on top of the thermally sensitive switch  28 . 
   Although the present invention has been described with reference to preferred embodiments, numerous modifications and variations can be made and still the result will come within the scope of the invention. As an example, solid-state circuitry may be used to achieve the same effect as the resistors and other circuitry in this disclosure. No limitation with respect to the specific embodiments disclosed herein is intended or should be inferred.