Abstract:
A system detects presence of particles in the air of guest rooms of facilities such as motels and hotels for example that indicate that guests are engaged in recreational smoking. The system provides an indication to the facility manager of such behavior.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    A continuing problem for motels and hotels principally, but sometimes for other occupied spaces as well, are guests that smoke in non-smoking rooms. Usually but not always, guests smoke tobacco, but other products, often illegal, may be smoked as well. The term “recreational smoking” is intended to include tobacco smoke, marijuana smoke, and other types of substances legal and illegal, smoked by persons to alter their mood or because of an existing dependency. 
         [0002]    The problem also arises in schools where students smoke in rest rooms, etc., in facilities where smoking creates an immediate safety hazard, and possibly in other facilities as well. The problem is compounded by the fact that in motel, hotel, and rest room situations, camera surveillance is simply deemed unacceptable. 
         [0003]    Regardless of the type of recreational smoking product involved, the cost to clean and sanitize a room or other space after a guest has illicitly smoked in it can run to hundreds of dollars. The possible allergic reactions suffered by later occupants of a room in which someone has previously smoked may require that cleaning the residues of recreational smoking on drapes, carpeting, walls, and furnishings be very thorough. Further, even if there is no health issue, a motel or hotel that holds out a room as “No Smoking” must assure its guests that that room has not had a previous guest smoking in it. 
         [0004]    Even though terms of conduct for a guest may clearly state that no smoking is permitted in the particular room, a certain fraction of guests unfortunately believe that the requirement does not apply to them, or that they will not be caught if in breach of the requirement. Yet when illicit smoking occurs, it is difficult for the establishment to recover this loss from the responsible guest. The problems of proof and collection from the guest often make it simpler for the establishment to accept the loss. 
         [0005]    One can thus see that a system that can reliably detect most incidents of recreational smoking within a space with few or no false positives would pay high dividends in first of all, allowing the establishment to impose immediate sanctions on the guest, and secondly, allow charging the costs of cleaning the room back to the guest on a credit card. Further, knowledge by a guest that a reliable recreational smoking detector is present in the occupied room will serve as a significant deterrent to recreational smoking in the first place. 
         [0006]    Accordingly, a means for real time detection of illicit smoking with a high degree of accuracy is desirable. To date, such means are not available as far as is now known to the inventors. 
         [0007]    Available smoke detectors for room and structure fires are not suitable for distinguishing the combustion products of tobacco and other recreational smoking from a real fire. Combustion products produced by recreational smoking typically differ only slightly from those produced by the structure and its contents during an actual fire. 
         [0008]    Distinguishing recreational smoking combustion products from those of a real structure fire is therefore not easy. Yet, an establishment acting on a false positive will very likely create bad will on the guests&#39; part toward the establishment. False negatives will allow a smoking guest to avoid detection. At the same time, the establishment must be respectful of the guests&#39; privacy. 
         [0009]    These problems and the constraints on solutions to them have created problems for the hospitality industry. But detecting in real time in a room, the presence of recreational smoking has proven to be difficult. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0010]    The inventors find that presence in a room of air-borne particles with maximum dimensions of 100-300 nm is a reliable indicator of recreational smoking in that room. Further, the inventors have developed an inexpensive and reliable system for detecting the presence of such particles. 
         [0011]    Such a system can detect presence of recreational smoke in the air of first through nth individual rooms of a facility, each room having a unique room designator assigned thereto. 
         [0012]    The system comprises first through nth room sensors, each to be mounted on one of a wall and a ceiling of each of the first through nth rooms respectively. Each of said sensors provides a smoke level signal indicating the concentration of combustion products such as air-borne particles with maximum dimensions of 100-300 nm unique to recreational smoke in the air of the room in which the sensor is mounted. Each such room sensor further encodes in the smoke level signal, an identifier such as a room number assigned to the room in which the sensor is mounted. 
         [0013]    A monitor station receives and analyzes each smoke level signal, and provides a room status signal indicating that recreational smoke is present when that is the case. The monitor also encodes the room identifier in the smoke level signal. In one preferred embodiment, this functionality forms a part of the facility computer. 
         [0014]    A display unit forming a part of the facility computer provides the room number and the status of the room as having recreational smoking therein usually as a visual display signal but also potentially as an auditory signal. 
         [0015]    At least one of the room sensors may comprise a cylindrical chamber having a plurality of openings along the axial length thereof. A light source such as a laser diode is mounted at one end of the chamber to project a light beam through the chamber along a predetermined path. 
         [0016]    A light sensor having a sensing surface is mounted adjacent to the chamber with the sensing surface facing toward and spaced from the light beam path. The light sensor detects light scattered by recreational smoke in the chamber, and provides a sensor signal whose level is proportionate to the concentration of recreational smoke products in the air in the chamber. 
         [0017]    A signal analyzer receives the sensor signal and computes from it a numerical value indicating the concentration of recreational smoke combustion products in the air in the chamber. The signal analyzer then produces an analyzer signal encoding that numerical value. 
         [0018]    A transmitter receives the analyzer signal and providing the smoke level signal as well as a room sensor ID value associated with the room sensor. 
         [0019]    The light source in each room sensor may provide a light beam whose wavelength is in the range of wavelengths including about 650 nm. Although this is not an ideal wavelength since one prefers to closely match the wavelength to the maximum dimension of recreational smoking particles, which is on the order of 100-300 nm., it is adequate to detect most recreational smoking particles. A preferred light source is of the type producing a beam having substantial energy in the 100-300 nm. wavelength range, but the current cost of such a light source is too high for most applications. 
         [0020]    Preferably, the chamber has an interior wall having a reflective surface, and the light beam passes between the sensor and at least a part of the interior chamber wall, wherein the interior chamber wall reflects toward the light sensor&#39;s sensing surface, light impinging on the chamber wall. 
         [0021]    Preferably there is an optical filter within the chamber interposed between the light beam and the sensor. The optical filter preferably is of the type that blocks a greater fraction of light whose wavelength is above and below a range of wavelengths including a 650 nm. wavelength than is blocked within said range. 
         [0022]    The transmitter in the room sensors preferably comprises a RF transmitter, and the monitor station includes a RF receiver that receives the. 
         [0023]    The room sensor may include an enclosure having a plurality of walls and enclosing the chamber. The enclosure may include at least one baffle extending from an enclosure wall to the chamber. The interior surfaces of the enclosure may be light-absorbing. 
         [0000]    The room sensor may include an enclosure having a plurality of walls and enclose the chamber. At least one of these walls includes a vent in proximity to the openings in the chamber. Such a vent may comprise a grate having two series of oppositely oriented and linearly staggered fins. 
         [0024]    The room sensor may include a driver providing power voltage to the light source. The power voltage periodically varies between two levels. The light source receiving this power voltage provides a beam whose intensity is proportionate to the power voltage. The signal analyzer for such a room sensor includes a multiplier element receiving the power voltage and the sensor signal and providing a signal indicative of the product of a plurality of samples of each of the sensor signal level and the power voltage. An integrator receives the multiplier signal and integrating the values in the multiplier signal. 
         [0025]    Preferably the light source is a laser diode. Such a laser diode may provide a light beam having one of a wavelength of 100-300 nm. and a wavelength near 650 nm. 
         [0026]    The light source may be mounted to place the beam in closer proximity to the sensor&#39;s sensing surface than to an opposite wall of the chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a block diagram of the invention. 
           [0028]      FIG. 2  is a block diagram of a monitor unit for analyzing smoke level signals received from a room sensor. 
           [0029]      FIG. 3  is a perspective view of the circuit board in a room sensor including a recreational smoke detector as mounted on the circuit board. 
           [0030]      FIG. 4  is an edge elevation view of the circuit board in a room sensor including a recreational smoke detector mounted on the circuit board. 
           [0031]      FIG. 5  is an end projective view of the interior of an enclosure for a room sensor, including the circuit board and enclosure features. 
           [0032]      FIG. 6  is a block diagram of a room sensor showing the major elements thereof. 
           [0033]      FIGS. 7   a  and  7   b  are circuit diagrams of the driver for a light source used in the recreational smoke detector. 
           [0034]      FIG. 8  is a circuit diagram of the amplifier for the signals generated by the recreational smoke detector. 
           [0035]      FIG. 9  shows the connections to a microcontroller that provides many of the room sensor functions. 
           [0036]      FIGS. 10-12  define preferred locations of various discrete circuit components relative to other circuit components. 
           [0037]      FIG. 13  shows the transceiver used in both the room sensor and in the RF receiver that provides data to the monitor unit. 
           [0038]      FIG. 14  is a circuit diagram of a Wien oscillator that provides the signal controlling the frequency at which the amplitude of the light source output is modulated. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0039]    Turning first to  FIG. 1 , the block diagram therein shows the major elements of a recreational smoke detection system  10  for hospitality structures. Each room of a hospitality structure has mounted within it a room sensor  13   a - 13   n . The room sensor  13   a - 13   n  in a particular room electronically determines the level of recreational smoke products in the air within that room. Periodically, in one embodiment 0.5 sec., each room sensor  13   a - 13   n  provides on its associated path  16   a - 16   n , a smoke level signal as an output that encodes the level of detected recreational smoke products. 
         [0040]    Each room sensor  13   a - 13   n  has a dedicated data link  16   a - 16   n  that carries the smoke level signals a room sensor  13   a - 13   n  generates, to a monitor unit  20 . In some embodiments, a single data link may be shared by a number of the room sensors  13   a - 13   n . One preferred embodiment for the data links uses a RF connection having a MiWi connection, but the room sensors  13   a - 13   n  can be hard wired as well to the monitor unit  20 . MiWi is a proprietary RF communication system available from Microchip Technology, Chandler, Ariz. 
         [0041]    In any case, a smoke level signal must be associated in some way with the specific room sensor that generates that smoke level signal. In this embodiment, each room sensor  13   a - 13   n  has a pre-assigned sensor ID that is included with the smoke level signal from each room sensor  13   a - 13   n.    
         [0042]    An RF receiver  39  receives each transmission from each room sensor  13   a - 13   n  and provides the room sensor ID and smoke level signal from that room sensor  13   a - 13   n  to monitor unit  20  on the path labeled “42, 46.” 
         [0043]    In one preferred embodiment, monitor unit  20  and display unit  22  form a part of a facility computer  15  that executes suitable software to cause computer  15  to perform the functions of units  20  and  22 . 
         [0044]    The monitor unit  20  interprets the smoke level signals that each individual room sensor  13   a - 13   n  provides. When a smoke level signal value exceeds a preset value, this indicates that recreational smoke products are currently present in the air of the room in which the room sensor  13   a - 13   n  whose ID was encoded in the RF signal being processed. The management of the establishment can then take whatever steps are appropriate to address the situation. 
         [0045]      FIG. 2  is a more detailed block diagram of the monitor unit  20 . The RF receiver  39  provides to monitor  20  encoded in a signal carried on a path  42 , the room sensor ID provided by the current RF signal from a room sensor  13   a - 13   n . Similarly, the RF receiver  39  provides to monitor  20  on a path  46 , each smoke level carried by the current RF signal. 
         [0046]    Typically, the signals received by receiver  39  are spaced so far apart that they will not conflict, or to use the technical term, collide, and corrupt each other. The MiWi protocol has mechanisms to deal with collisions, but if for example each room sensor  13   a - 13   n  transmits for one millisecond every 5 seconds, one can see that even 200 room sensors will only rarely issue colliding signals. Even then, detecting colliding signals is easy to do, so no erroneous determination of presence of recreational smoke in a room occurs. The odds are extremely small that a single room sensor  13   a - 13   n  will experience two sequential collisions. 
         [0047]    In one embodiment, monitor unit  20  comprises a facility computer  15  that has many other functions, such as billing and reservations for example. The facility computer has software that performs the various functions forming a part of the invention. 
         [0048]    Each room sensor  13   a - 13   n  uses a microcontroller  200  (see  FIG. 9 ) that executes firmware to perform many of the functions in the individual room sensor  13   a - 13   n . When a microcontroller executes the invention&#39;s software or firmware, it becomes during that time, special purpose hardware dedicated to perform the computations that the system currently requires. In the example at hand, the software or firmware code that executes to allow a microcontroller to implement the invention may be considered to have been reconfigured as hardware elements whose components perform the computations that implement the invention. 
         [0049]    That is, the components (logic gates and memory elements) comprising a microcontroller  200 , while executing the firmware, actually change their physical structure. These altered components comprise nothing more than complex electrical circuitry that send and receive electrical signals exactly as would a non-programmable circuit that executes the invention&#39;s functions. In the course of this firmware execution, the components undergo many physical changes as signals pass into and from them. 
         [0050]    For example, at the elemental level, a logic gate within microcontroller  200  typically undergoes many physical changes while the microcontroller executes the invention&#39;s firmware. Such physical changes typically comprise changes in the level of electrons within the gate. These changes alter the impedance between the various terminals of the gate, in this way allowing the microcontroller  200  to execute individual instructions of the firmware. 
         [0051]    Another way to think of this is to consider the effect of executing the firmware code as setting literally tens of thousands of interconnected switches within the microcontroller to their on and off states. These switches then control changes in the state of other switches, so as to effect the computations and decisions typical of firmware to execute the algorithms of the invention. 
         [0052]    The mere fact that these microcontroller components are too small to be seen, or exist only for short periods of time while the relevant code executes is irrelevant as far as qualifying as patentable subject matter. Nothing in our patent law denies patent protection for inventions whose elements are too small to be seen or whose elements do not all exist simultaneously or for only short periods of time. 
         [0053]    Accordingly, claims defining this invention having elements formed by software or firmware execution in microcontroller  200  must be treated in the same way as an invention embodied in fixed circuit components on a circuit board. There is no reason to do otherwise. 
         [0054]    The monitor unit  20  of  FIG. 2  comprises a number of functional blocks within facility computer  15 . Each of these functional blocks comprises hardware element that performs the function specified for it by executing appropriate software. The arrows connecting them are data paths, with the arrows indicating the direction of data flow. In real life these arrows correspond to electrical paths within the microcontroller that carry signals encoding the data. As with microcontroller  200  for the room sensor  13   a - 13   n  functions, the facility computer  15  actually becomes each of the functional elements of  FIG. 2  for short periods of time. 
         [0055]    In  FIG. 2 , for each RF signal from a room sensor  13   a - 13   n , the signal path  42  carries the room sensor ID encoded in the room sensor signal to a room number lookup element  36 . A memory forming part of facility computer  15  includes a memory element  33  holding a room sensor ID/room number table  33  that associates each room sensor ID with the physical room in which the room sensor is located. 
         [0056]    Room number lookup element  36  uses the room sensor ID value to retrieve from element  33 , the room number of the room holding the room sensor  13   a - 13   n  supplying the signal currently being processed. The values in memory element  33  will typically be supplied by the user. The lookup element  36  places the room number of the room holding the room sensor whose RF signal is being processed on a data path  58 . 
         [0057]    Receiver  39  also decodes the portion of the RF signal carrying the smoke level value and places this value on a smoke level data path  46 . A comparator element  49  determines if the smoke level value on path  46  indicates a level of recreational smoke particles in the room creating a high probability that an occupant is smoking. If so, element  49  places a smoke sensed signal on a path  52 . 
         [0058]    A display unit  55  receives the smoke sensed signal and the room number, and responsive to the smoke sensed signal provides the room number and the status of the room encoded in at least one of a visual display signal and an auditory signal. 
         [0059]      FIGS. 3-5  show a module  70  forming a part of each room sensor  13   a - 13   n . A circuit board  73  carries electrical components  92  of the module  70 , only a few of these being shown. Conductors forming a part of circuit board  73  but not shown in  FIG. 3 , electrically interconnect the components  92 .  FIGS. 5-14  are schematics of the actual individual circuits forming module  70 . 
         [0060]    The module  70  detects recreational smoking within a room by detecting an excess of particles in the 100-300 nm size range in the air of the room. Tests suggest that presence of particles of this size in room air strongly correlates with tobacco smoke in that air. 
         [0061]    A hollow, cylindrical detector tube  105  is mounted on circuit board  73 . Tube  105  has a series of transverse slots  79  extending along the axis. The interior  88  of tube  105  should be highly reflective to increase the amount of light backscattered from recreational smoking particles. For example, the interior wall of tube  105  may be lined with highly reflective foil. 
         [0062]    A series of phototransistors  82  extend axially along and within tube  105  in general diametric opposition to slots  79 . Phototransistors  82  are connected to conductors in circuit board  73 . Other circuit components are shown generically at  92 . Phototransistors  82  have sensing surfaces generally facing the center of the detector tube  105 . 
         [0063]    A laser diode  95  is mounted on circuit board  73  using a bracket  97  and oriented to direct a light beam  102  through tube  105 . A small percentage of photons from beam  102  will be scattered or reflected toward phototransistors  82 . When a sufficient number of these photons is detected, one can conclude with a high degree of certainty that smoking is occurring in the room where circuit board  73  is mounted. 
         [0064]      FIG. 5  shows a room sensor  13   a - 13   n  as comprising the module  70  and an enclosure  108 .  FIG. 5  presents a view of the interior of enclosure  108  perpendicular to the laser beam, and in which module  70  is mounted. Enclosure  108  may be generally rectangular with six walls. Top  117  and two side walls  120  may be solid. 
         [0065]    Enclosure  108  has a bottom wall having a grille or grate  114  with slots  123  that allow air potentially carrying recreational smoke particles to enter enclosure  108 . Two end walls  119  of which only one is shown may have vents or slots  125 . Vent slots  125  may also enhance circulation of air through enclosure  108 . Improved circulation may improve speed and accuracy of recreational smoking detection. However, preliminary experiments suggest that forced convection through enclosure  108  may not be beneficial in improving sensitivity. 
         [0066]    A room sensor  13   a - 13   n  normally will be mounted on a ceiling of a room, and oriented as shown in  FIG. 5  with top  117  against the ceiling and grate  114  facing downwardly. In general, it seems best to mount enclosure  108  approximately in the center of the room. This has not yet been fully resolved however, and it may be that one or more room sensors  13   a - 13   n  mounted on one or more walls of the room involved will yield improved detection. 
         [0067]    The sensitivity and reliability of smoke detection is enhanced by taking a number of steps in the design of module  70  and enclosure  108 . It is likely but not certain that sensitivity of detection is improved by mounting laser diode  95  to cause beam  102  to pass in closer proximity to sensors  82  than to an opposite wall of the chamber.  FIGS. 4 and 5  show beam  102  closer to phototransistors  82  than to the center of tube  105  for example. 
         [0068]    Sensitivity also improves if the wavelength of beam  102  closely matches the size of the smoke particles. Unfortunately, at this time a laser diode  95  that produces a beam  102  with a wavelength in the range of 100-300 nm typical of recreational smoke particles is too expensive to be practical. Tests show however, that inexpensive laser diodes that produce a beam in the range of 640-655 (650 nominal) nm still yield adequate detection of particles whose size is in the range of 100-300 nm. 
         [0069]    Sensitivity is further improved by limiting the amount of parasitic or exterior light that strikes phototransistors  82 . To this end the interior of enclosure should be painted a matte, light-absorbing black. Grate  114  is shown as having two series or rows of oppositely oriented and linearly staggered fins  123  to limit the influx of light to the interior of enclosure  108  from the room itself. Vent slots  125  may have the form of a similar double row of fins. 
         [0070]    An optical filter  90  excludes from reaching phototransistors  82 , most light other than that in a fairly narrow range centered on the wavelength of laser diode  95 . For example, a suitable filter  90  may exclude almost all light having a wavelength outside a range of 600-700 nm from reaching phototransistors  82 . 
         [0071]    A pair of interior baffles  111  that extend from sides  120  to detector tube  105 , form another feature that improves sensitivity and reliability of the room sensors  13   a - 13   n . Baffles  111  may well direct particles-bearing air drifting through grate  114  more directly into detector tube  105 . The pair of baffles  111  limit the volume within enclosure  108  that entering air must occupy, thereby concentrating the number of smoke particles within tube  105 . Vents  125  may also improve circulation, and thereby increase speed and accuracy in detecting recreational smoke 
         [0072]    The block diagram of  FIG. 6  shows the major functional elements of a room sensor  13   a - 13   n  as comprising a beam generator element  130  and a detector  150 . Beam generator  130  includes a Wien bridge oscillator  60  that provides a signal to a laser driver circuit  80 , and the laser diode  95 . 
         [0073]    Detector  150  comprises the phototransistors  82 , an amplifier  160  receiving the digitized phototransistors  82  output, and a set of firmware functions implemented by microcontroller  200 . As previously explained, microcontroller  200  physically becomes for brief periods, each of the hardware elements that perform these firmware functions. 
         [0074]    The attached firmware source code as executed by microcontroller  200  forms the best mode known at this time for this implementation. It is likely that this firmware may not function as well or at all in other than the designated Microchip Technology microcontroller. 
         [0075]    As is true for most microcontrollers, microcontroller  200  has an on-board A/D converter that digitizes both the amplifier  160  and the oscillator  60  outputs. These two signals are then multiplied and integrated according to well-known signal processing methods. 
         [0076]    These elements comprise:
       an analog to digital converter  168   a  that digitizes the phototransistor transistor  82  output and transmit in a digitized phototransistor output signal   an analog to digital converter  168   b  that digitizes the Wien bridge output and transmit in a digitized Wien bridge oscillator  60  output signal   a multiplier element  163  receiving the Wien bridge oscillator  60  and the amplifier  160  output signals and providing a multiplier signal, and   an integrator  166  receiving the multiplier signal from the multiplier element and providing an integration signal.       
 
         [0081]    The multiplier element  163  and the integrator  166  form a signal analyzer. 
         [0082]    Wien bridge oscillator  60  provides an offset sine wave of 1 khz to laser driver  80  and to multiplier  163 . A part of the circuitry of microcontroller  200  and the firmware recorded in the microcontroller  200  memory forms multiplier  163  and integrator  166 . 
         [0083]    In one embodiment, over an interval of 11.278 ms, each of the Wien bridge oscillator  60  output and the amplifier  160  output are sampled 300 times at nearly identical times. Each value is converted to digital by A/D converters  168   a  and  168   b . Each pair of digital values sharing the identical time of sampling are multiplied and recorded. 
         [0084]    The multiplier  163  computations so recorded are provided to integrator  166  that integrates the values in the multiplier  163  output signal. In one embodiment, this integration comprises a summation of the multiplier  163  output for a sampling interval of 11.278 ms. The sampling interval length is not critical, but should be roughly an order of magnitude longer than a single cycle time of the Wien bridge oscillator  60  output. 
         [0085]    The output signal of integrator  163  is normalized to a value falling between 1 and 24 and encoded in a smoke level signal. In one embodiment, a value of the smoke level signal between 1 and 5 indicates an insignificant concentration of recreational smoke particles in the room air, 6-9 indicates a low level of such particles, and any value above 10 indicates a significant level of such particles. 
         [0000]    The smoke level signal from integrator  163  and a signal encoding the room number associated with the room sensor ID are supplied to the facility computer  15 .  FIG. 2  shows that the facility computer  15  tests the normalized integrator value to determine whether recreational smoking has occurred in the room with the encoded room number. If recreational smoking is detected, the facility system can provide a human-detectable indication of this situation. Receiver  39  may connect to the facility system with a USB cable. 
         [0086]    The circuits that  FIGS. 7   a ,  7   b , and  8 - 14  show comprise a number of microcircuits of various types as well as discrete components. In general, the discrete components can be inexpensive ±10% devices, available from a variety of sources. Individuals with minimal knowledge of electrical engineering will be easily able to construct the hardware portions of this invention with these circuit diagrams and the following information. 
         [0087]    Certain of the microcircuits are single source items, which are here identified by source and part number. 
         [0000]    
       
         
               
               
               
               
             
               
             
               
               
               
               
             
               
             
               
               
               
               
             
           
               
                   
               
               
                 Drawing 
                   
                   
                   
               
               
                 ID 
                 Item 
                 Source 
                 Part No. 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Room Sensor 
               
             
          
           
               
                 U1 
                 microcontroller 
                 Microchip Tech. 
                 PIC18F26K80-I/SS 
               
               
                 U2 
                 operational 
                 Intersil 
                 CA3240EZ 
               
               
                   
                 amplifier 
               
               
                 U3 
                 operational 
                 Texas Insts. 
                 LMV796MF/NOPB 
               
               
                   
                 amplifier 
               
               
                 U4 
                 operational 
                 Diodes, Inc. 
                 APX321WG-7 
               
               
                   
                 amplifier 
               
               
                 U5 
                 volt. regulator 
                 Fairchild Inst. 
                 LM317LZ 
               
               
                 U6 
                 transceiver 
                 Microchip Tech. 
                 MRF24J40MA 
               
               
                 U7 
                 3.3 v. regulator 
                 Microchip Tech. 
                 MCP1700T-3302E/TT 
               
               
                 ZD1, 
                 Zener, 5.6 v. 
                 ON Semiconductor 
                 MMSZ5V1T1G 
               
               
                 ZD2 
               
               
                 LD 
                 650 nm laser 
                 Lasermate Group 
                 LD65010A 
               
               
                   
                 diode 
               
             
          
           
               
                 Receiver 39 
               
             
          
           
               
                 U1 
                 microcontroller 
                 Microchip Tech. 
                 PIC18F26K80-I/SS 
               
               
                 U6 
                 transceiver 
                 Microchip Tech. 
                 MRF24J40MA 
               
               
                   
               
             
          
         
       
     
         [0088]    U 1  and U 6  cooperate in each of a room sensor  13   a - 13   n  and in receiver  39  to control transmission and reception of data signals. Microchip Technologies have proprietary protocols that allow a user to for the most part ignore the RF signal generation and reception details, and simply insert into and extract from the RF signal, the desired information to be communicated from the data source (room sensor  13   a - 13   n  here) and provided to facility computer  15  by receiver  39 . 
         [0089]    Respecting transceiver  39 , the firmware to cause U 1  and U 6  to operate as described is deemed so simple for someone familiar with these Microchip Technology devices and having minimal technical expertise in these electronic arts to develop, that it has not been included in this description. 
         [0090]      FIGS. 7   a  and  7   b  together show the circuitry for the two stages of the driver for laser diode  95 . Stage  1  receives output from the Wien bridge oscillator  60  terminal B. The output of stage  1  of driver  80  is at terminal A, which is connected as shown to stage  2 . 
         [0091]    The intensity of the light beam that diode  95  provides is proportionate to the voltage across the HI and LO terminals of diode  95 . Thus, the light intensity has a sine wave pattern with a 1 khz frequency. 
         [0092]      FIG. 8  is the circuitry of the amplifier  160  that amplifies the phototransistors  82  output and supplies this amplified voltage in a PD-OUT signal to pin  2  of U 1 , microcontroller  200 . Microcontroller  200  performs calculations on the signal that amplifier  160  provides that cause microprocessor  200  to function as multiplier  163  and integrator  166 . 
         [0093]      FIG. 9  shows the microcontroller  200  and the connections to it. Microcontroller  200  receives the input at PD-OUT (pin  2 ) from amplifier  160  and digitizes it. Microcontroller  200  then functionally becomes the multiplier  163  and integrator  166  as it processes the signal that the amplifier  160  and the Wien bridge oscillator  60  provide. 
         [0094]    Microcontroller  200  then provides room sensor ID and smoke level outputs to the transmitter portion of transceiver  39 , see  FIG. 13 . These outputs eventually become the room sensor ID signal on path  42  and the smoke level signal on path  46 , as  FIG. 2  shows. 
         [0095]      FIG. 10-12  show preferred placements of various capacitors. These placements will likely reduce noise and improve operation of the circuits. 
         [0096]      FIG. 13  shows the details of transceiver  39 . Microcontroller  200  provides all of the signal inputs to transceiver  39 , but note that some of the transceiver  39  pins are connected to power and ground. 
         [0097]      FIG. 14  shows the details of the Wien bridge oscillator  60 . The output at terminal B is a sine wave that oscillates between about 0 and 3 v at 1 khz. The output of oscillator  60  forms the inputs to laser driver  80  ( FIG. 7   a ) and to microcontroller  200 , pin  3 , for the multiplication function. The 1 khz frequency is chosen to be far from most light noise source frequencies, such 60 hz power. 
         [0098]    The source code attached hereto as Appendix A when compiled using a standard C compiler, produces object code that causes microcontroller  200  to operate in a way that implements certain of the functions of the room sensors  13   a - 13   n.