Patent Publication Number: US-6657544-B2

Title: Apparatus and method for electronic exclusion and confinement of animals relative to a selected area

Description:
This application is a continuation-in-part of application Ser. No. 09/128,246 filed Aug. 3, 1998, now abandoned, which is a continuation of application Ser. No. 08/796,986, filed Feb. 7, 1997, now U.S. Pat. No. 5,787,841 which is a continuation-in-part of application Ser. No. 08/741,852, filed Oct. 29, 1996, now U.S. Pat. No. 5,794,569. 
    
    
     FIELD OF THE INVENTION 
     This invention relates in general to a method and apparatus for controlling movement of an animal and, in particular, to a method and apparatus for electronically preventing an animal from approaching an area to be protected from intrusion by the animal. 
     BACKGROUND OF THE INVENTION 
     Electronic animal control systems commonly either contain an animal within a perimeter delineated by a wire, or are of the form of an “electronic tether.” When using a typical perimeter device, the animal is deterred from crossing the perimeter by applying an electronic correction signal to the animal after it approaches within a preselected distance of the wire. Detecting the proximity of the wire is typically performed by use of a sensor on a collar unit provided on the animal, where the sensor senses an electromagnetic field around the wire. The electronic correction is supplied by the collar unit and is typically either an acoustic signal or an electric shock. 
     “Electronic tether” systems use a similar collar unit but, in this case, the electronic correction is applied to the animal when the distance between a collar unit and a central transmitter is too great, as measured by the strength of a received electromagnetic signal. The animal receives correction when it has strayed too far from the central transmitter. 
     These electronic animal control systems are relatively unsophisticated devices, and are not well suited to use indoors. For example, it would appear that an outdoor perimeter device could be used indoors to deter an animal from approaching a door, thus keeping the animal in the room. However, such a perimeter unit requires that a perimeter wire be laid around the entire room, which significantly reduces the area within the room in which the animal may roam without receiving correction. Additionally, present electronic control systems are unable to distinguish which of several animals requires attention, assuming that more than one animal is provided with a collar unit, and the control systems, therefore, treat all animals in the same manner. Typically, no record is kept of animal activity, for example how many corrections the animal received in any particular time period. 
     A conventional collar unit is generally an autonomous unit which is battery powered. The lifetime of the battery is affected by many factors, including the number of corrections which are provided to the animal. The user is not provided with information regarding the number of corrections the animal receives, nor with the current state of the battery. Thus, the user may be unaware that the battery has lost charge, and the user has to guess when a new battery is needed in the collar unit. Additionally, a conventional collar unit is provided with metal contact pins of fixed length. These pins, typically of fixed length, may have to be changed according to the thickness of the coat of the animal. For example, a dog with a thin coat, such as Doberman Pinscher, requires shorter pins, while a dog with a long coat, such as an English Sheepdog, requires longer pins. Current collar units provide the user with a number of sets of pins, which the user has to connect manually to the collar unit. The pins would require changing if, for example, a collar unit normally used on a dog with a thin coat, were to be used on a dog with a thicker coat. 
     Indoor pet control systems are available which repel a pet from a prescribed area. Such systems typically use ultrasonic transmitters to generate a continuous repulsion signal. The animal is dissuaded from entering the area simply because the volume of the ultrasonic signal is uncomfortably high. Systems of this type suffer from several deficiencies, including a lack of intelligence, so the system cannot distinguish between different animals which may approach the protected area. Since the ultrasonic signal is generally continuous, the animal is subjected to constant annoyance, even when outside the area being protected. 
     Therefore, there is a need for an electronic animal control system which does not confine an animal to only a portion of a room when the desired restriction is simply to prevent it from leaving the room. There is also a need for a more sophisticated system which is able to warn the user when an animal receives correction or when the battery in the collar unit is low. There is a general need for a more sophisticated approach to electronically controlling an animal which can provide the user with many advanced features not available with current systems, including the management of a number of containment spaces, and where each containment space may be pre-programmed to be applicable to each particular animal present. There is also a need for a collar unit having improved metal contact pins which do not require repeated adjustment or reinstallation by the user. 
     SUMMARY OF THE INVENTION 
     To overcome the limitations in the prior art, such as those described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is directed to a method and apparatus for communicating signals directly to the portable unit other than through the energy used to created the exclusion area or the bounded area. 
     The invention may be viewed as a portable unit for providing a correction to an animal. The portable unit includes a sensor configured to detect a first signal indicating that the animal has approached an inappropriate location. The portable unit includes a transmitter configured to provide a second signal indicating information about the portable unit. The portable unit also includes a receiver configured to detect a third signal having an instruction for the portable unit. 
     The invention may also be viewed as a method for providing correction to an animal. The method involves providing a second signal from the portable unit to send information about the portable unit to a controller unit. The second signal is received at the controller unit and an appropriate correction is determined. A third signal is provided from the controller unit to the portable unit to indicate the correction. The third signal is received at the portable unit to provide the appropriate correction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings in which like reference numbers represent corresponding parts throughout: 
     FIG. 1 illustrates an apparatus for providing electronic exclusion of animals according to the principles of the present invention; 
     FIG. 2 illustrates a magnetic field around an electronic exclusion apparatus; 
     FIG. 3 illustrates a block diagram schematic of a portable unit of an electronic exclusion apparatus; 
     FIG. 4 illustrates a block diagram schematic of an antenna system provided in a portable unit; 
     FIG. 5 illustrates a block diagram schematic of a controller unit of an electronic exclusion apparatus; 
     FIG. 6 illustrates a block diagram schematic of an exclusion unit of an electronic exclusion apparatus; 
     FIG. 7 illustrates waveforms generated by an exclusion unit; 
     FIGS. 8A-8B illustrate waveforms detected and analyzed by a portable unit; 
     FIG. 9 illustrates two exclusion units operating in tandem; 
     FIG. 10 illustrates a cross-section through a portable unit; 
     FIG. 11 illustrates an apparatus for providing electronic confinement of animals according to the principles of the present invention; 
     FIG. 12 illustrates a block diagram schematic of a transmitter unit of an electronic confinement apparatus; 
     FIG. 13 illustrates a segmented collar for a portable unit; and 
     FIG. 14 illustrates a segment for a segmented collar. 
     FIG. 15 illustrates a block diagram schematic of a portable unit of an electronic exclusion apparatus having a receiver in addition to an antenna system; 
     FIG. 16 illustrates a magnetic field around an electronic exclusion apparatus whereby the controller unit communicates directly with the portable unit; 
     FIG. 17 illustrates a bounded area generated by a power unit; 
     FIG. 18 illustrates waveforms generated by the power unit; 
     FIG. 19 illustrates a block diagram schematic of an antenna system provided in a portable unit having inbounds/out-of-bounds detection ability; 
     FIGS. 20A-20E illustrates alternative waveforms generated by the power unit and waveforms produced by the antenna system in response to the power unit waveforms. 
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     In the following description of the illustrated embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration, various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     The present invention is directed to an apparatus for electronically controlling the movement of an animal with respect to a prescribed area. Typically, the animal may be a pet, and the prescribed area, such as an exclusion area, may be a portion of a front or back yard, or may be an area within a house, such as an area around a doorway or close to selected items of furniture which the owner wishes to protect. Unlike prior methods of electronically controlling the movement of animals, the present invention allows the animal to roam freely outside the exclusion area, and provides a warning to the animal when the animal approaches the exclusion area. The warning typically includes a correction, preferably in the form of an audible signal or an electric shock, in order to dissuade the animal from making any further approach to the exclusion area. The invention is particularly effective in preventing an animal from approaching a doorway or archway in a house, which represents an important capability when electronically restricting the movement of a pet within a house. The illustrated embodiments are discussed in terms of protecting doorways and archways within a house, but the invention is not restricted to such use, as is discussed hereinbelow. 
     Referring now to FIG. 1, which shows an animal control apparatus  19 , an exclusion area  20  associated with exclusion unit  22  is located close to a doorway  24  of a room  27 . The exclusion area  20  is an area around the exclusion unit  22  which deters the animal from approaching the exclusion unit  22 . By positioning the exclusion unit  22  close to the doorway  24 , the doorway  24  is included within the exclusion area  20 . Thus, the animal  30  is deterred from approaching the doorway  24  and is contained within the room  27 . 
     The exclusion unit  22  is controlled by a control unit  26  which is connected to a computer  28 . The control unit  26  may be a stand alone unit, connectable to an external computer, or may be an integral part of the computer, for example a board plugged into one of the extension slots of the computer  28 . The following description refers to the first exclusion area  20  and exclusion unit  22 , but may be applied equally to a second exclusion area  21  and second exclusion unit  23  positioned so as to deter the animal  30  from approaching, for example, an item of furniture  25 . The animal  30  is provided with a portable unit  32 . The portable unit  32  is attached to the animal  30  by use of a collar  31  placed around the animal&#39;s neck, but may also be attached by use of a belt around the animal&#39;s abdomen or leg, or attached to the animal in a similar way. 
     The exclusion unit  22  typically produces a modulated magnetic field. The portable unit  32  includes a magnetic sensor to detect the modulated magnetic field produced by the exclusion unit  22 , and is generally sufficiently sensitive to provide a positive detection of the electromagnetic field at a distance ranging from approximately two to six feet from the exclusion unit  22 . It is understood that the detection range from the exclusion unit may be larger than six feet. The portable unit  32  includes a radio transmitter which transmits a signal to the control unit  26  indicating that an attempt has been made by the animal  30  to enter a particular exclusion area. If the portable unit  32  or control unit  26  determines that the animal  30  has entered the exclusion area  20 , then the control unit  26  may activate an alarm  33  which alerts the owner or guardian of the animal  30  to the animal&#39;s intrusion into the exclusion area  20 . 
     The portable unit  32  is provided with a sensor which senses the strength of the electromagnetic field produced by the exclusion unit  22 . The strength of the electromagnetic field is determined by the distance from the exclusion unit  22  to the portable unit  32 . 
     FIG. 2 illustrates the formation of the exclusion area  20  by the exclusion unit  22  close to a doorway  24 . The exclusion unit  22  is preferably mounted close to the door jamb of the doorway  24 , and is powered by household electric power from the wall socket  41 . The exclusion unit  22  generates an electromagnetic field  34 , preferably using a coil having an air-core or a ferrite-core, or using other radiation antennas. The exclusion unit  22  is at an originating point within the exclusion area  20 , and does not peripherally generate an electromagnetic field surrounding an essentially field free region where the animal  30  may be located. The resulting electromagnetic field  34  has a dipole-type profile, and contours of increasing electromagnetic field strength  36 ,  38 ,  40  and  42  lie increasingly closer to the exclusion unit  22 . It is understood that the shape of the exclusion area  20  is dependent on the source used for generating the electromagnetic field  34  included in the exclusion unit  22 . It may be useful, for example in protecting a table, to employ an electromagnetic field  34  which is more circular than the electromagnetic field  34  illustrated. A differently shaped field may be generated, for example, using an antenna having a different configuration, or by including additional elements to shape the field. 
     Different zones A, B, C, D, and E, marked by respective letters within circles, represent areas of decreasing electromagnetic field strength. Zone E is outside the exclusion area  20 . When the animal  30  enters the exclusion area  20 , for example by passing from zone E to zone D, the portable unit  32  detects an increase in electromagnetic field strength and transmits a signal, indicative of the electromagnetic field strength relative to the animal&#39;s position within the exclusion area  20 , to the control unit  26 . The control unit  26  responds by selecting an appropriate, selectable level of correction for the animal, typically an audible signal or an electric shock, depending on which zone (A-D) the animal  30  has entered or on the length of time for which it has failed to respond to the applied correction. If the control unit  26  is programmed to exclude the animal  30  from the exclusion area  20 , the control unit  26  transmits a correction control signal to the exclusion unit  22 . The correction control signal is encoded on the electromagnetic field  34  generated by the exclusion unit  22 . The portable unit  32  detects the encoded electromagnetic field  34  and provides correction to the animal  30  in accordance with the received correction signal. 
     In FIG. 3, there is illustrated a block diagram of one embodiment of the portable unit  32 . A similar embodiment is discussed with reference to FIG. 15, but includes transceiving abilities that the embodiment of FIG. 3 does not provide. Power is applied to the portable unit  32  by the battery power supply  50 . The battery power supply  50  includes a battery  52 , such as a lithium, coin-shaped battery. A battery  52  of this type advantageously reduces the profile of the portable unit  32  and the period between battery changes. The voltage output from the battery  52  is regulated by a regulator circuit  54 , including a regulator such as one from the MICREL 2570 or from the Linear Tech LT 1307 series of regulator chips, so as to give a regulated output of approximately 3 or 3.3 Volts. The regulator circuit  54  ensures that the output from the battery power supply  50  is maintained at approximately 3 or 3.3 Volts, even when the voltage derived from the battery  52  is greater or less than approximately 3 or 3.3 Volts. The regulator circuit  54  detects when the voltage of the battery  50  has fallen below a pre-selected acceptable level, typically around 1 Volt. When such a low battery voltage condition is detected, the regulator circuit  54  directs a low battery voltage signal  56  to a portable unit processor  58 . On receiving the low battery voltage signal  56 , the portable unit processor  58  transmits a low battery voltage message over the data line  61  to the radio transmitter  63 . The radio transmitter  63  then transmits a low battery voltage message to the control unit  26  to alert the user of the low battery voltage condition of the portable unit  32 . 
     The antenna system  60  preferably includes two orthogonal antennas, such as antennas  112  and  114  of FIG. 4, for detecting the electromagnetic field  34  produced by the exclusion unit  22 . The portable unit processor  58  transmits an antenna sampling signal  62  to the antenna system  60  to sample the signals received from one of the antennas. If more than two antennas are used, the sampling signal selects one antenna from all the antennas present. The portable unit processor  58  may also adjust the sensitivity of the antenna system through use of a sensitivity adjust signal  66 , as is described hereinbelow. 
     A tilt switch array  68 , which may be of the ball bearing type, is provided on the portable unit  32 . The tilt switch array  68  serves several functions, including the determination of activity of the animal  30 , and directing orientation information to the portable unit processor  58  regarding the orientation of the portable unit  32 . Since the tilt switches in the tilt switch array  68  are sensitive to movement, the movement of the animal  30  acts to repeatedly switch the tilt switches in the tilt switch array  68  between on and off states. A power-up signal  70  is fed from the tilt switch array  64  to the regulator circuit  54  in the battery power supply  50  in response to this activity. The regulator circuit  54  powers up the regulated approximately 3 or 3.3 Volt output when activity is detected by the tilt switch array  68 . When no animal activity has been detected from the tilt switch array  68  for a timeout period, the portable unit processor  58  provides a no-activity signal  59  to power down the regulated approximately 3 or 3.3 Volt output until the activity signal  70  again signals when the tilt switch array  68  senses animal activity and powers up the approximately 3 or 3.3 Volt output. Before powering itself down, the portable unit processor  58  sends a notice of power down over the data line  61  to the radio transmitter  63 . The radio transmitter  63  then transmits a notice of power down to the control unit  26  so as not to cause a lost animal alarm. As such, this power conservation scheme results in a greatly extended battery life. 
     An important aspect of the invention is that the control unit  26  may select an appropriate form of correction given to the animal  30  in response to the distance between the animal  30  and the exclusion unit  22 . When the portable unit  32  has detected that the animal  30  is approaching the exclusion unit  22 , a signal is transmitted from the portable unit  32  to the control unit  26  by the radio transmitter  63 . The transmitted signal indicates the distance separating the animal  30  from the exclusion unit  22 . The control unit  26  then determines what kind of correction should be applied to the animal  30  according to the separation distance. For example, the correction may be an acoustic signal, a low-level electric shock, or a high-level electric shock. Once the control unit  26  has selected the applicable correction, the control unit  26  then directs the exclusion unit  22  to generate coded pulses on the electromagnetic field  34  which are received by the antenna system  60  of the portable unit  32 . The coded pulses include instructions for correcting the animal  30 . 
     For example, if the instructions received from the control unit  26  indicate that the animal  30  should be corrected by an acoustic alarm, then an alarm signal  71  is directed to an acoustic signal device  72 . The acoustic signal device  72  may be an intermittent buzzer, operating at audible frequencies or at ultra-sonic frequencies particularly detectable by the animal  30 . If the instructions received from the control unit  26  indicate that the animal  30  should be corrected by the application of an electric shock, then the portable unit processor  58  activates the shock correction system  74 . The shock correction system  74  generates an electrical shock signal  84  which is typically applied to the animal by a pair of contact pins. The shock correction system  74  includes a capacitive precharge and switching circuit  76  which is charged according to a precharge signal  78 . After a predetermined charging time, the portable unit processor  58  directs a discharge signal  80  to the capacitive precharge and switching circuit  76 . The capacitively stored energy is preferably discharged through a pulse transformer  82  to generate an electrical shock signal  84  which is applied to the animal  30 . The voltage generated by the capacitive precharge circuit  76  is generally around 3 or 3.3 Volts, and the pulse transformer typically increases the voltage of the electrical shock signal  84  to approximately 1,000 Volts. The duration of the charging cycle determines the amount of charge capacitively stored in the capacitive precharge and switching circuit  76 . The intensity of the electrical shock signal  84  applied to the animal  30  may be controlled by selected variation of the duration of the precharge cycle according to instructions received from the control unit  26 . 
     With refernce to FIGS. 10 and 13, the electrical shock is preferably applied to the animal  30  by a pair of sprung contact pins  322  extending from the portable unit  32 . FIG. 10 illustrates a cross section through a typical portable unit  32  where the sprung pins  322  are backed by springs  324  in a well  326  (one contact pin  322  is shown fully extended and the other fully retracted). The use of springs  324  to spring-load the contact pins  322  advantageously allows the sprung contact pins  322  to adjust in length automatically in response to the thickness of the animal&#39;s fur or hair. The contact pins  322  may then form an electrical contact with the animal&#39;s skin sufficient to close the electrical circuit. The compressibility of the springs  324  is preferably selected to minimize discomfort to the animal  30 . The use of spring-loaded contact pins  322  obviates requiring the user to manually replace one pin set with another in order to adapt the pin length to the thickness of the animal&#39;s fur or hair, as is the case in conventional devices. The spring-loaded contact pins  322  advantageously maintain consistent contact with the animal  30  when the animal  30  is in motion, or when the animal&#39;s body swells during periods of high activity. 
     An important feature of the present invention is that the control unit  26  is programmed to provide the level of correction to be applied to the animal  30  in response to changes in the separation distance between the animal  30  and the exclusion unit  22 . As the animal  30  moves closer to the exclusion unit  22 , the level of correction may be increased. For example, the first level of correction applied to the animal on entering zone D may be a soft acoustic correction signal  73  generated by the acoustic signal device  72 . As the animal moves closer to the exclusion unit  22 , for example into zone C, then a low-level electrical shock signal  84  may be applied by the shock correction system  74 . An increased electrical shock signal  84  may be applied as the animal  30  approaches closer to the exclusion unit  22 , for example from zone C to zone B. Alternative correction strategies may be programmed into the control unit  26 . For example, if the exclusion unit  22  is protecting a piece of furniture, then it may be preferable to supply a low-level acoustic warning when the animal  30  enters zone D, a higher level acoustic warning when the animal  30  enters zone C, a low-level electric shock when the animal  30  enters zone B, and a higher level electric shock when the animal  30  enters zone A. Alternatively, only acoustic correction may be applied to the animal  30 , irrespective of how close the animal  30  approaches the exclusion unit  22 . Additionally, both an electrical shock signal  84  and an acoustic signal  73  may be applied to the animal  30  simultaneously. This combination may be used for training the animal  30  to respond to an acoustic signal  73 . 
     If the animal  30  approaches within a certain distance of the exclusion unit  22  so as only to initiate an acoustic alarm, but does not retreat from the exclusion unit  22  within an acceptable time, then the control unit  26  may be programmed to direct the portable unit  32  to apply an increased level of correction, such as a low-level electrical shock until the animal  30  retreats from the exclusion area  20 . 
     The portable unit processor  58  is preferably adapted to control the battery power supply  50  so as to reduce the possibility of radio frequency (RF) interference from the regulator circuit  54  interfering with the electromagnetic field  34  detected by the antennas  100  and  102  in the antenna system  60 . The portable unit processor  58  turns the regulator circuit  54  off by the regulator standby signal  57  so as to reduce RF interference. Turning the regulator circuit  54  off results in a loss of regulated voltage applied to the other elements of the portable unit  32 . By maintaining a storage capacitor across the output of the battery power supply  50  in the portable unit  32 , the regulator circuit  54  may be periodically turned off, for example around 2 milli-seconds at a time. After a 2 milli-second time off interval, the regulator circuit  54  is reactivated by the regulator standby line  57  and a approximately 3 or 3.3-Volt regulated signal re-applied to each of the elements in the portable unit  32 , so as to recharge the storage capacitors. 
     FIG. 4 illustrates a block schematic diagram of the antenna system  60 . Two antennas  100  and  102  are illustrated, but three or more may also be used. Antenna one  100  and antenna two  102  are preferably oriented so that their respective directions of maximum sensitivity are orthogonal, and that the plane defined by the directions of maximum sensitivity for each antenna is a horizontal plane extending around the animal  30 . 
     Each of the antennas is selected in sequence by the antenna select signal  62  received from the portable unit processor  58 . The output A from the antenna thus selected is directed through a signal attenuator formed by switchable resistors  112  and  114  coupled to a gain module  104 . The gain module  104  typically includes an operational amplifier operating in the linear region. The output  106  from the gain module  104  is directed to a comparator  108  which compares the gain module output  106  with a reference signal voltage  110 . The sensitivity adjust signal  66  selects programmable resistors  112  and  114  in the signal attenuator so as to vary the amplitude of the input to the gain module  104 . The use of two programmable resistors  112  and  114  results in four sensitivity settings for the gain module output, resulting in a comparator  108  output  109  indicative of the levels of electromagnetic field shown as  36 ,  38 ,  40  and  42  around the exclusion unit  22 . When the comparator output  109  is high, even though the programmable resistors  112  and  114  are switched so as to produce the smallest gain module output  106 , then the animal has entered zone A, closest to the exclusion unit  22 . If, on the other hand, there is a zero output signal  109  from the comparator  108  for all levels of gain module output signal  106 , the animal  30  is assumed to be outside the exclusion area  20 , i.e. in zone E. An alternative approach to determining in which zone the animal  30  is located is to maintain the input to the gain module  104  with a single sensitivity and to sample different reference voltages  110 . In another alternative approach, the programmable signal attenuator, including the switchable resistors  112  and  114 , and the comparator  108  may be included with the portable unit processor  58  in a single chip. 
     The comparator output  109  is directed to a low pass filter  116 . The output from the low pass filter  116  is directed to the portable unit processor  58  as the data out signal  64 . 
     Once the portable unit processor  58  has processed the data out signal  64  from the antenna system  60 , the appropriate information data packet is transferred to the radio transmitter  61  for transmission to the control unit  26 . The information packet transmitted by the radio transmitter  61  typically includes a code identifying which portable unit  32  transmitted the signal and data indicating in which zone the portable unit  32  is currently located. 
     A block diagram schematic of the control unit  26  is illustrated in FIG.  5 . The radio signals  65  transmitted by the radio transmitter  63  in the portable unit  32  are received by the radio receiver  150  in the control unit  26 . The radio signals are decoded and the data transferred via the data input line  152  to the central processor  154 . 
     The central processor  154  includes non-volatile memory, program memory, and data memory, and controls operating functions of the animal control apparatus  19 . 
     When the portable unit  32  determines that the animal  30  has entered one of the zones A-D in the exclusion unit  22 , the portable unit  32  identifies which zone the animal  30  is located in and transmitting identification codes to the control unit  26  identifying which exclusion unit  22  generated the electromagnetic field  34  which was detected and the portable unit  32  transmitting the message. The central processor  154  in the control unit  26  includes program memory so that the user may program the animal control apparatus  19  to provide different levels of correction according to which zone A-D the animal  30  has entered or, alternatively, to provide no correction at all for the animal  30  on entering the exclusion area  20 . When the central processor  154  receives the zone information from the portable unit  32 , the central processor  154  transmits a correction instruction appropriate to the zone currently occupied by the animal  30 . The correction instruction is directed to the radio transmitter  158  via the data output line  156 . The radio transmitter  158  transmits the instructions to the exclusion unit  22  which then encodes correction commands modulated on the electromagnetic field  34 , as discussed hereinbelow. After the portable unit  32  receives and decodes these correction commands, the desired correction is applied to the animal  30 . 
     The control unit  26  may control the operation of a number of exclusion units  22  and  23 , allowing the user to control the movement of one or more animals by employing a number of exclusion areas  20  and  21 . Thus, the user may position exclusion units  22  at several doorways through the house so as to allow the animal  30  to range within several rooms. 
     If the radio transmitter  63  of the portable unit  32  transmits a low battery voltage signal to the control unit  26 , the central processor  154  may warn the user of the low battery condition by directing a low battery voltage signal to the information display  170  through one of the LED select lines  168  and  169 . 
     The central processor  154  monitors the distance between the animal  30  and the exclusion unit  22  by monitoring which zone is occupied by the animal  30 . The central processor  154  may be programmed to increase the level of correction to the animal  30  if the animal  30  does not move away from the exclusion unit  22  in a timely manner, for example within about 3-5 seconds of correction starting. Increasing the level of correction may include changing the sound of the acoustic signal, changing from an acoustic signal to an electrical shock signal, and/or increasing the intensity of the electrical shock signal. Additionally, the central processor  154  may measure the time for the animal  30  to move from one zone to the next and, if it determines that the animal is approaching the exclusion area  20  above a preselected speed, the central processor  154  may apply a level of correction higher than would be applied if the animal  30  were approaching the exclusion area  20  at a lower speed. 
     The central processor  154  may further be programmed to cease the application of correction if the animal  30  does not respond to the increased level of correction within a certain time, for example approximately 10 seconds, since the animal  30  may be caught in the zone and be unable to move away from the exclusion unit  22 . Following a rest period of approximately 10 seconds, correction may then be reapplied for another period of approximately 10 seconds. If the animal  30  still does not move out of the exclusion zone  20 , then correction ceases and the central processor  154  may then warn the user that the animal has become caught close to the exclusion unit  22 . The user may be warned through one of the acoustical signal source  162 , the information display  170 , and a warning directed to the computer  28  through the computer interface  166 . 
     The control unit  26  may be used to create an historical log of the encounters of the animal  30  with the exclusion unit  22 . This is preferably achieved by connecting the control unit  26  to a computer  28  via the computer interface  166 , and transferring information from the central processor  154  to the computer  28  for storage. Such historical information may include the time of an incursion event, the zone which the animal  30  penetrated and the correction strategy employed. 
     Whenever the portable unit  32  is not in a powered-down mode, it transmits a regular handshake signal to the control unit  26  to confirm that the portable unit  32  is operative. Failure by the control unit  26  to receive a regular handshake signal within a preselected timeout period, and without receiving a power-down notice from the portable unit  32 , may result in a warning to the user that the portable unit  32  is faulty, or that the animal  30  is lost. 
     The pet control apparatus  19  may be used for containing more than one animal at a time, and may be programmed to provide customized levels of correction to a number of animals. The central processor  154  is programmable to determine a level of correction according to the zone the animal  30  enters and which particular portable unit  32  is associated with a specific animal  30 . 
     For example, the central processor  154  may be programmed to provide high levels of correction to a disobedient animal or one which is at an early training stage, so that an electrical shock correction is applied whenever the animal reaches any zone within the exclusion zone  20 . The central processor may be programmed to command electrical shocks of increasing intensity as the animal  30  approaches the exclusion unit  22 . The central processor  154  may also be programmed to respond differently to a second animal which, for example, is well trained or unable to withstand severe correction. The central processor  154 , for example, may be programmed to command only an audible warning to the second animal, irrespective of how closely the second animal approaches the exclusion unit  22 . Alternatively, the central processor  154  may be programmed to permit the second animal to pass through a first exclusion zone  20 , for example allowing the second animal to move from one room to a second room, while barring a first animal from entering the exclusion zone  20 . The central processor  154  may also be programmed to exclude both the first and second animals from a second exclusion area  21  generated by a second exclusion unit  23 . 
     The correction strategy for each animal is updatable by reprogramming the programmable memory in the central processor  154 . For example, a young animal being introduced to the animal control system  19  may initially require high levels of correction, but the programmed correction levels may be changed so as to reduce the level of correction necessary to keep the animal within the bounds of the system  19  as the animal  30  becomes trained. In order for the control unit  26  to determine which animal of a number of animals is approaching the exclusion unit  22 , each portable unit  32  is provided with a unique identifying code which is transmitted to the central processor  154 . The control unit  26  is thus able to establish which animal  30  approaches the exclusion unit  22 . 
     An input keypad  172  is provided to facilitate programming of the central processor  154  by the user. The input keypad  172  is connected to the central processor via key select lines  174  and key pressed lines  176 . A user may employ the input keypad  172  for entering such information as, for example, the levels of correction associated with each portable unit  32  for each zone, or the length of time that correction is applied to the animal  30  in a single zone before increasing to a next level of correction, or ceasing correction altogether. 
     The computer interface  166  permits connection of the pet control apparatus  19  to a computer  28  for remote control and monitoring of the pet control apparatus  19  and for logging activity of the animal  30 . For example, user-friendly control software may be provided on the computer  28  to allow the user to remotely program the control unit  26 , rather than using the input keypad  172 . Monitoring software provided on the computer  28  may allow the user to record the activity of the animal  30 , including periods of inactivity and incursions to the exclusion zones  20  and  21 . The monitoring software may also allow an automatic alarm signal to be sent via telephone line to a remote location when specific events occur, such as loss of contact with a portable unit  32 . 
     The control unit  26  is provided with a power supply  178  to provide power to all the control unit&#39;s components at appropriate voltage levels. 
     The control unit  26  may be configured to catch certain information, such as a low battery warning or a missing portable unit  32 , so that such information is not lost in the event that power to the control unit  26  is shut off. 
     FIG. 6 illustrates a block diagram schematic of the exclusion unit  22 . A radio receiver  200  receives control signals  190  transmitted from the control unit  26 . The received control signals are directed on control signal line  202  to the exclusion unit processor  204  where the received control signals are processed. After processing, the exclusion unit processor  204  directs control signals  206  to the electromagnetic field generator  208  which produces the electromagnetic field  34 . 
     The exclusion unit  22  is provided with a power supply  214  which preferably generates three separate DC voltage levels. The approximately 3 Volt DC level is used for powering the radio receiver  200 . The 5 Volt DC level is used in powering the central processor  204 . The electromagnetic field generator  208  is typically powered at a 12 Volt DC level. A power/status LED display  216  may indicate the present power status, for example whether the power unit is functioning normally or to indicate that there is an exclusion unit processor  204  fault, or that there is no power. 
     The modulated electromagnetic field  34  generated by the exclusion unit  22  and detected by the portable unit  32  is discussed with reference to FIGS.  7  and  8 A- 8 B. The electromagnetic field  34  is time-encoded with information, such as data or commands, from the control unit  26 . 
     The following discussion describes, an approach in accordance with one embodiment, to modulating the electromagnetic field  34  for information transfer from the control unit  26  to the portable unit  32 , although other approaches may be employed. FIG. 7 illustrates the signal transmitted by the exclusion unit  22 . The signal includes a frame  250 , where the frame is a binary word having four distinct components. The first component is the frame start  252  which includes a “1” and a “0”. The second component is the system code, typically comprising three bits, and which indicates a code number related to the control unit  26 . The system code  254  is used, for example, to distinguish between different pet control systems operating in adjacent apartments. Following the system code  254  is the command data component  256 , typically comprising 8 bits. The command data component  256  may include a header indicating which portable unit  32  out of a plurality of portable units the following command is directed to. The remainder of the command data component  256  includes an identification of which exclusion unit  22  out of a number of exclusion units is transmitting the frame  250 , and the instructions for the particular portable unit  32 , such as correction commands. The final component of the frame is stop bit  258 , which is a “1” followed by a variable dormant period. 
     The digits in the binary frame  250  are produced by burst width modulation of electromagnetic field reversals having a period of approximately 10 KHz. For example, a “1” may typically be represented by a 4 millisecond burst at 10 KHz, and “0” may typically be represented by a 6 millisecond burst at 10 KHz. The standard separation between bits is 2 milliseconds. The length of the frame  250  can vary, depending on the number of zeros present in the frame  250 . The separation between adjacent frames may be varied so that the time lapse between frame starts is constant from one frame to the next. It is understood that the frequency of the bursts may be at frequencies other than 10 KHz. 
     FIG. 8A illustrates a portion of the signal received by one of the antennas  100  and  102 , as would be detected at position A in FIG.  4 . FIG. 8B shows the same signal once it has been transmitted through the comparator  108 , at point B. The comparator  108  produces a logic high whenever the incoming signal is above the reference signal voltage  110 . The signal of FIG. 8B is then passed through a low pass filter to remove the 10 KHz carrier frequency, and is decoded by the portable unit processor  58 . Changing the sensitivity in terminals  112  and  114  results in the signal shown in FIG. 8B growing or shrinking in amplitude. If the animal  30  is sufficiently far away and does not register in a particular zone, the signal in FIG. 8B is flat (zero level). 
     With reference to FIG. 9, two exclusion units,  22   a  and  22   b , may be used in combination to provide an exclusion area across a wide opening, where a single exclusion unit operating alone is not able to provide an exclusion area sufficiently large as to cover the whole opening. Such an opening may be an archway, as is typically found between a living room and a dining room in many houses. The opening  300  is positioned between opposing wall sections  302 . The first exclusion unit  22   a  is positioned on the left side of the opening  300  and the second exclusion unit  22   b  is positioned on the right side of the opening  300 . The electromagnetic fields radiated into the opening  300  by the exclusion units  22   a  and  22   b  are preferably synchronized to be out of phase with each other by 180°. Thus, as the first exclusion unit  22   a  radiates a first polarity into the opening  300 , the second exclusion unit  22   b  radiates the opposite polarity into the opening  300 . Preferably the two exclusion units  22   a  and  22   b  are synchronized to present oppositely polarized electromagnetic fields to each other, so that the combined electromagnetic field  304  reaches across the opening  300  between the two exclusion units  22   a  and  22   b.    
     The exclusion units  22   a  and  22   b  may operate in synchronism where each is provided with a high frequency clock  218 , such as a quartz clock, for running the respective exclusion unit processors  204 , and by initializing the exclusion units  22   a  and  22   b  to operate together. For example, during an initial setup, the exclusion units  22   a  and  22   b  may be programmed to operate from the same control signal  190  received from the control unit  26 , and for both to generate an electromagnetic signal following, for example, a selected number of cycles of the clock  218  after receipt of the control signal  190 . The first exclusion unit  22   a  may be programmed to generate its electromagnetic signal starting with a first polarity, while the second exclusion unit  22   b  is programmed to generate its electromagnetic signal starting with the opposite polarity. Such a system relies on the clocks  218  in each exclusion unit  22   a  and  22   b  keeping close time so as to commence transmission of each frame  250  in synchronism, and to maintain synchronism throughout the duration of the frame  250 . Thus, in such an approach, the clock may be regarded as being a synchronization circuit. 
     Other schemes for operating the two exclusion units  22   a  and  22   b  in synchronism include a master/slave approach, where, for example, exclusion unit  22   a  operates as a master and the exclusion unit  22   b  operates as a slave. The electromagnetic signal generated by the slave exclusion unit  22   b  is thus slaved to the electromagnetic signal generated by the master exclusion unit  22   a  to ensure synchronism. This approach requires transmission of a synchronization signal from the master exclusion unit  22   a  to the slave exclusion unit  22   b  using, for example, a radio transmitter or an infrared transmitter or the electromagnetic signal  34  generated by the master exclusion unit  22   a.    
     Another embodiment of the invention, illustrated in FIG. 11, operates on an alternative principle, as discussed in U.S. Pat. No. 5,067,441 which is incorporated herein by reference, where the animal  230  is given increasing correction as it moves away from a transmitter  220 , rather than when moving towards a transmitter. This approach results in confining the animal  230  to a confinement area  222 , rather than excluding the animal  230  from an exclusion area  22 . The animal control system  219  includes a portable unit  232  on the animal, a control unit  226  and a transmitting unit  220 . The transmitting unit  220  transmits an electromagnetic signal  234 . The strength of the electromagnetic signal  234  received by the portable unit  232  reduces as the animal  230  moves away from the transmitter  220 . The portable unit reports the strength of the detected electromagnetic signal  234  to the control unit  226 , which is programmed to determine a degree of correction to be applied to the animal  230  in response to the separation between the animal  230  and the transmitter  220 . The control unit  226  transmits control information to the transmitter  220 , and the control information is then retransmitted by the transmitter  220  on the electromagnetic signals  234  to be detected by the portable unit  232 . 
     The portable unit  232  is similar to that shown in FIGS. 3 and 4, except that the antennas  100  and  102  are tuned to the frequency of the electromagnetic signal  234  transmitted by the transmitter  220 . The portable unit may be programmed to provide correction to the animal  230  when no signal  234  is detected, indicating that the animal  230  has left the confinement area  222 . Such correction may be terminated if the animal  230  has not returned to the confinement area  222  within a timeout time, since the animal  230  may have become trapped and be unable to re-enter the confinement area  222 . 
     The control unit  226  is similar to that shown in FIG. 5, except that it is programmed to generate a correction signal when the detected electromagnetic signal  234  reduces in amplitude, rather than increases. For example, the control unit  226  may be programmed to provide an acoustic correction signal to the animal  230  when it passes from zone A to zone B, and increasing levels of electric shock correction when it passes from zone B to zone C and from zone C to zone D. The control unit  226  is programmable to control the movement of more than one animal within the confinement area  222  around the transmitter  220 , so that different animals may receive different levels of correction for a given separation distance from the transmitter  220 . In addition, the control unit  26  may control more than one transmitter  220  in the animal control system  19 . Multiple transmitters  220  may have overlapping confinement areas  222 , so that the animal  30  may pass from one confinement area  222  to the next, and thus enjoy a greater range of freedom, without receiving correction. Alternatively, multiple confinement areas  222  may be separated so that animals  230  may be confined to their respective confinement areas  222  without being able to pass to a neighboring confinement area  222 . 
     The transmitter  220  is illustrated in FIG.  12 . The transmitter  220  is related to the exclusion unit  22  illustrated in FIG. 6. A radio receiver  200  receives input transmitted by the control unit  226 , and the received digital data  202  thus received are passed to the transmitter processor  242 . The transmitter processor decodes the signals received from the control unit  226  and directs the radio transmitter  240  to transmit electromagnetic signals  234  with instructions for the portable unit  232  encoded thereon. The transmitter  220  may be provided with a power/status LED  216  to inform the user of the power status, or useful information. The transmitter processor  242  may be driven by a clock  218 , such as a quartz clock. The power supply  244  provides D.C. voltage levels for powering the components of the transmitter  220 , for example a 5 V level for the transmitter processor  242  and approximately a 3 V level for powering the radio receiver  200  and the radio transmitter  240 . 
     The portable unit  32  may be attached to the animal  30  by any method which ensures that contact is maintained between the contact pins  322  and the animal&#39;s skin. Prior approaches have employed a webbing collar, to which the collar unit is attached, and placing the collar on the animal&#39;s neck. 
     An alternative approach, illustrated in FIG. 13 is to use a segmented strap, such as a segmented collar  340  attached to the portable unit  32 . The segmented collar  340  may include two parts  342  and  344 , where the first part  342  is terminated at one end by an insertion portion  346  and the second part  344  is terminated at one end by a receptacle portion  348 . The insertion portion  346  and the receptacle portion  348  may be of a familiar type of plastic buckle. The other ends of the first and second parts  342  are attached to either side of the portable unit  32 . Each part  342  and  344  is formed from a series of connectable segments  350  made, for example, from molded plastic. The segments  350  are formed to allow a user to assemble the first and second parts  342  and  344  by fitting one segment  350  into another. This allows the user to adjust the lengths of the first and second parts  342  and  344  to form a close fitting collar  340  when the insertion portion  346  and the receptacle portion  348  are joined. Adjacent segments  350  may “snap fit” together so as to provide hinged attachment therebetween. One approach to forming attachable segments, illustrated in FIG. 14, is to provide a segment  350  with a bar  352  along a portion of one side and a hooked portion  354  along a complementary portion of the other side. The hooked portion  354  of a first segment  350  may snappingly fit over the bar of an adjacent segment  350  so as to provide hinged attachment between adjacent segments  350 . Alternatively, the first and second parts  342 ,  344  may be of fixed length and adjustments may be made by adding segments  350  to either or both the insertion portion  346  and receptable portion  348 . 
     A segmented collar  340  of this sort advantageously provides support to the maintain the portable unit  32  in position and orientation against the animal  30  so as to maintain electrical contact between the contact pins  322  and the animal&#39;s skin. The segmented collar  340  also provides the user with a wide range of adjustment in collar length to accommodate a wide range of animal sizes. The segmented collar may also be used with the portable unit  232 . It is understood that such a segmented strap may be used to attach a portable unit to a portion of the animal  230  other than its neck, such as a leg. 
     The following paragraph describes some alternative methods of accomplishing the same objects of the present invention. The portable unit  32  may be adapted to operate autonomously, without interacting with a control unit  26 . In such a case, the exclusion unit  22  would be adapted to produce a electromagnetic field  34  from which the portable unit  32  would be able to provide an appropriate correction. The portable unit  32  could be programmable so as to store information regarding, for example, which level of correction is desired for each zone (A-D) in the exclusion zone  20 . 
     The comparator  108  may be provided with a different number of reference signal voltage levels, for example 8, thus permitting detection of the animal in 8 different zones, rather than 4. 
     The information transmitted from the control unit  26  to the portable unit  32  could be encoded using a protocol different from the one described with reference to FIGS.  7  and  8 A- 8 B. For example, a pulse position modulation technique could be used, rather than pulse width modulation. The frame could be configured to include more bits for carrying more information. Also, bidirectional radio communications could take place between the control unit  26  and the portable unit  32 , in which case the exclusion unit  22  could generate unencoded electromagnetic signals  34 . 
     FIGS. 15 and 16 illustrate an additional embodiment of the portable unit  532  whereby bidirectional communication may be established between the controller unit  526  and the portable unit  532 . This may be useful for reasons such as transmitting commands to the portable unit  532  directly from the controller unit  526  so that the animal may stray from the exclusion unit  520 , or the peripheral wire  622  (FIG.  17 ), yet remain in communication with the controller unit  526 . 
     In FIG. 15, there is illustrated a block diagram of one embodiment of the portable unit  532  that is similar to the embodiment shown in FIG. 3 but in this embodiment the unit  532  has transceiving capabilities permitting bi-directional communications. Power is applied to the portable unit  532  by the battery power supply  450 . The battery power supply  450  includes a battery  452 , such as lithium, coin-shaped battery. A battery  452  of this type advantageously reduces the profile of the portable unit  532  and the period between battery changes. The voltage output from the battery  452  is regulated by a regulator circuit  454 , including a regulator such as one from the MICREL 2570 series of regulator chips or from the Linear Tech LT1307 series, so as to give a regulated output of approximately 3 Volts or alternatively 3.3 Volts. The regulator circuit  454  ensures that the output from the battery power supply  450  is maintained at approximately 3 or 3.3 Volts, even when the voltage derived from the battery  452  is greater or less than approximately 3 or 3.3 Volts. The regulator circuit  454  detects when the voltage of the battery  450  has fallen below a pre-selected acceptable level, typically around 1 Volt. When such a low battery voltage condition is detected, the regulator circuit  454  directs a low battery voltage signal  456  to a portable unit processor  458 . On receiving the low battery voltage signal  456 , the portable unit processor  458  transmits a low battery voltage message over the data line  461  to a radio transceiver  463 . The radio transceiver  463 , typically operating in the 900 MHz band, then transmits a low battery voltage message to a control unit  526  (shown in FIG. 16) to alert the user of the low battery voltage condition of the portable unit  532 . 
     The antenna system  460  preferably includes two orthogonal antennas for detecting the electromagnetic field  434  produced by the exclusion unit  520  (and/or for detecting the magnetic field produced by power unit  624  of FIG.  17 ). The portable unit processor  458  transmits an antenna sampling signal  462  to the antenna system  460  to sample the signals received from each antenna. If more than two antennas are used, the sampling signal selects one antenna from all the antennas present. The portable unit processor  458  may also adjust the sensitivity of the antenna system through use of a sensitivity adjust signal  466 , as is described hereinbelow. 
     A tilt switch array  468 , which may be of the ball bearing type, is provided on the portable unit  532 . The tilt switch array  468  serves several functions, including the determination of activity of the animal  530 , and directing orientation information to the portable unit processor  458  regarding the orientation of the portable unit  532 . Since the tilt switches in the tilt switch array  468  are sensitive to movement, the movement of the animal  530  acts to repeatedly switch the tilt switches in the tilt switch array  468  between on and off states. A power-up signal  470  is fed from the tilt switch array  464  to the regulator circuit  454  in the battery power supply  450  in response to this activity. The regulator circuit  454  powers up the regulated approximately 3 Volt output when activity is detected by the tilt switch array  468 . When no animal activity has been detected from the tilt switch array  468  for a timeout period, the portable unit processor  458  provides a no-activity signal  459  to power down the regulated approximately 3 Volt output until the activity signal  470  again signals when the tilt switch array  468  senses animal activity and powers up the approximately 3 Volt output. Before powering itself down, the portable unit processor  458  sends a notice of power down over the data line  461  to the radio transceiver  463 . The radio transceiver  463  then transmits a notice, such as through signal  465 , of power down to the control unit  526  so as not to cause a lost animal alarm. As such, this power conservation scheme results in a greatly extended battery life. 
     One potential aspect of this embodiment of the invention is that the control unit  526  may provide information for a profile table stored in the portable unit&#39;s memory that can be referenced by the processor  458  to determine the appropriate correction to apply to the animal  530 . This profile table information may be received through the transceiver  463 , and then a confirmation signal may be transmitted from the transceiver  463  to the control unit  526  to indicate that the portable unit  532  received the profile table information and a resend is unnecessary. Alternatively the control unit  526  may select an appropriate form of correction given to the animal  530  in response to the transceiver  463  communicating the distance between the animal  530  and the exclusion unit  520  to the control unit  526 , such as through signal  465 . The control unit  526  may communicate the correction to the central processor  458  of the portable unit  532  through the transceiver  463 , such as by signal  486 , or alternatively through the antenna system  460 . When the portable unit  532  has detected that the animal  530  is approaching the exclusion unit  520 , a signal is transmitted from the portable unit  532  to the control unit  526  by the radio transmitter portion of transceiver  463 . Alternatively, a separate receiver and transmitter may be used in place of the transceiver  463 . The transmitted signal indicates the distance separating the animal  530  from the exclusion unit  520 . The control unit  526  then determines what kind of correction should be applied to the animal  530  according to the separation distance. For example, the correction may be an acoustic signal, a low-level electric shock, or a high-level electric shock. Once the control unit  526  has selected the applicable correction, the control unit  526  then transmits a coded signal that is received by the transceiver  463  of the portable unit  532 . The coded signal includes instructions for correcting the animal  530 . 
     For example, if the instructions received from the control unit  526  indicate that the animal  530  should be corrected by an acoustic alarm, then an alarm signal  471  is directed to an acoustic signal device  472 . The acoustic signal device  472  may be an intermittent buzzer, operating at audible frequencies or at ultra-sonic frequencies particularly detectable by the animal  530 . If the instructions received from the control unit  526  indicate that the animal  530  should be corrected by the application of an electric shock, then the portable unit processor  458  activates the shock correction system  474 . The shock correction system  474  generates an electrical shock signal  484  which is typically applied to the animal by a pair of contact pins. The shock correction system  474  includes a capacitive precharge and switching circuit  476  which is charged according to a precharge signal  478 . After a predetermined charging time, the portable unit processor  458  directs a discharge signal  480  to the capacitive precharge and switching circuit  476 . The capacitively stored energy is preferably discharged through a pulse transformer  482  to generate an electrical shock signal  484  which is applied to the animal  530 . The voltage generated by the capacitive precharge circuit  476  is generally around 3 or 3.3 Volts, and the pulse transformer typically increases the voltage of the electrical shock signal  484  to approximately 1,000 Volts. The duration of the charging cycle determines the amount of charge capacitively stored in the capacitive precharge and switching circuit  476 . The intensity of the electrical shock signal  484  applied to the animal  530  may be controlled by selected variation of the duration of the precharge cycle according to instructions received from the control unit  526  or from reference to the profile table stored in memory as previously discussed. 
     The profile table may be arranged such that one section of the table contains a correction bit for each exclusion unit  520  the animal may approach where the correction bit&#39;s value determines whether the animal receives correction for a particular exclusion unit  520 . The next section of the profile table contains a value indicative of the correction to be applied to the animal for a given exclusion unit  520 . This value may then be multiplied by a multiplier whose value is dependent upon the strength of the received signal in the antenna system  460  to find a product that is used to trigger a correction signal, whether it be audible or a shock. Alternatively, the control unit  526  may maintain a similar table for each portable unit  532  under its control and may communicate specific correction instructions to the collar. 
     This profile table of either the portable unit  532  or the control unit  526  may also be configured such that its bit values change depending upon the time of day. For example, a particular exclusion unit  520  may guard a room entrance where the room contains the animal&#39;s food. The profile table may be configured so that this exclusion unit  520  causes correction to be applied until a certain time of day, when the exclusion unit&#39;s signal may be ignored so that the animal may enter the room and eat. Detecting that the animal has passed by the exlcusion unit  520  again, indicating that the animal left the room, may be used as a trigger to reset the profile table so that the signal from the exclusion unit  520  guarding the room again results in correction when detected by the portable unit  532 . The exclusion unit  520  may be provided its own table so that it provides an indication to the animal  530  that it may pass by the exclusion unit  520  without receiving correction during the appropriate time of day. The indication may be visual, such as a blinking light, or audible, such as a beep, or a combination of both. 
     Because the portable unit  532  is capable of directly receiving communication from the controller unit  526 , the exclusion unit may provide only its code to the portable unit  532  through the magnetic signal  522 . Furthermore, the controller unit  526  may also contain a transceiver to communicate with the portable unit&#39;s transceiver  463  or it may contain an additional transmitter for transmitting commands to the transceiver  463  in addition to a transmitter configured to transmit information to the exclusion unit  520 . 
     The portable unit processor  458  is preferably adapted to control the battery power supply  450  so as to reduce the possibility of radio frequency (RF) interference from the regulator circuit  454  interfering with the electromagnetic field  522  detected by the antennas  600  and  602  in the antenna system  660  of FIG.  19 . The portable unit processor  458  turns the regulator circuit  454  off by the regulator stand by signal  457  so as to reduce RE interference. Turning the regulator circuit  454  off results in a loss of regulated voltage applied to the other elements of the portable unit  532 . By maintaining a storage capacitor across the output of the battery power supply  450  in the portable unit  532 , the regulator circuit  454  may be periodically turned off, for example around 2 milli-seconds at a time. After a 2 milli-second off interval, the regulator circuit  454  is reactivated by the regulator standby line  457  and an approximately 3 or 3.3-Volt regulated signal is re-applied to each of the elements in the portable unit  532 , so as to recharge the storage capacitors. 
     FIG. 16 further indicates that the various zones as previously discussed may be created for the embodiment including the portable unit  532  and the controller unit  526 . The strength of the magnetic field decreases with distance from the exclusion unit  520 . The portable unit  532  may be configured to detect the variation in magnetic field strength, such as for zones A, B, C, and D, and correction associated with the particular zone may then be applied, as a result of the portable unit  532  receiving an instruction from the control unit  526  or from referencing the on-board profile table. The portable unit  532  may also detect that it is located in the outer zone E where the animal is free to roam, and therefore, no correction may be applied. As shown, the controller unit receives signals from the portable unit  532  and provides signals back to the portable unit  532  for reception by the transceiver  463 . 
     It may also be desirable for the exclusion unit  520  to act as a repeater for the bi-directional communications between the portable unit  532  and the controller unit  526 . In this case, the exclusion unit  520  (such as the exclusion unit shown in FIG. 6) may contain a radio transceiver in place of the radio receiver  200  of FIG. 6 wherein the radio transceiver is similar to or the same as the transceiver  463  of the portable unit shown in FIG.  15 . Alternatively, the exclusion unit  520  may utilize the radio receiver  200  and a separate transmitter. Because the animal may stray farther away from the controller unit  526  than from the exclusion unit  520 , the exclusion unit may serve to extend the range of the portable unit&#39;s communication with the controller unit  526  by receiving the radio signal from the controller unit  526  and relay the signal to the portable unit  532 . In the same fashion, the exclusion unit  520  may receive the radio signal from the portable unit  532  and relay the signal to the controller unit  526 . 
     Referring now to FIG. 17, an additional confinement system is shown wherein the animal may be included or excluded from an area defined by a peripheral boundary. FIG. 17 shows an animal control apparatus  619  and selected spaces  620  and  621  that are surrounded by buried wires  622  and  623  respectively, each buried wire  622  and  623  typically located a few inches below the surface and forming the peripheral boundary. The perimeters of the selected spaces may be defined in some other way, for instance the wire may not be buried, or the electrical conductor may not be in the form of a wire. The buried wires  622  and  623  are respectively powered by power units  624  and  625 . The power units  624  and  625  are controlled by a controller  626  which is preferably connected to a computer  628  for maintaining an activity log. The following description refers to buried wire  622  and power supply  624 , but may be applied equally to buried wire  623  and power supply  625 . The animal  630  contained within the selected space  620  is provided with a portable unit  632 . The portable unit  632  is preferably in the form of a collar placed around the animal&#39;s neck, but may also be a belt around the animal&#39;s abdomen or leg, or attached to the animal in a similar way. 
     The power unit  624  typically transmits a series of electrical pulses around the buried wire  622 , so as to produce a modulated magnetic field in an area close to the buried wire  622  that weakens with distance from the wire. As mentioned, the portable unit  632  includes a magnetic sensor, such as antenna system  460 , to detect the magnetic field produced by the buried wire  622 , and is typically sufficiently sensitive to provide a positive detection of the magnetic field at a distance ranging between approximately four to six feet from the buried wire  622 . The antenna system  460  may employ variable sensitivity, as previously discussed, to permit the creation of zones around the wire such as those created around the exclusion unit  520  of FIG.  16 . 
     The portable unit  632  may include a radio transceiver  463 , as previously described, which transmits a signal to the controller  626  indicating that a magnetic field of a given strength has been detected and receives a signal from the controller  626  indicating the type of correction to apply. Alternatively, the controller  626  may provide a signal to the power unit  624  which is then encoded in a signal provided on the wire  622  and received by the portable unit  632 . Another alternative is for the portable unit  632  to reference an on-board profile table. If the portable unit  632  or controller  626  determines that the animal  630  has crossed the buried wire  622  so as to escape from the selected space  620 , then the controller  626  may activate an alarm  634  which indicates to the owner or guardian of the animal  630  that the animal  630  has left the selected space  620 . 
     As discussed, the portable unit  632  is provided with a magnetic field sensor which senses the strength and direction of the magnetic field. The strength of the magnetic field is determined by the distance from the buried wire  622  to the portable unit  632 . The direction of the magnetic field is determined by whether the animal  630  is approaching the buried wire  622  from within or outside the selected space  620 . One potential aspect of this embodiment of the present invention is that if an animal  630  is intended to be confined to the space  620  but has escaped, then the portable unit  632  is operable so as not to provide correction to the animal  630  if the animal subsequently attempts to re-enter the selected space  620  by crossing the buried wire  622  from the outside. Similarly, if the animal is to be excluded from the space  620  but has entered into it, then the portable unit  632  is operable so as not to provide correction to the animal  630  if the animal subsequently attempts to exit the selected space  620 . 
     The signals transmitted by the power unit  626  and received by the portable unit  632  are discussed with reference to FIGS.  18  and  20 A- 20 E. The power unit  626  transmits a series of current pulses around the buried wire  622  to generate the magnetic field  644  detected by the portable unit  632 . The current pulses may be encoded with information, such as data or commands, from the controller  626  if the portable unit  632  is not provided with a transceiver for communicating with the controller  626 . With or without the transceiver  463 , the portable unit  632  of this embodiment utilizes a magnetic field receiver for detecting the proximity to the wire  622 . The pulses on the wire  622  may also be encoded with a code for the power unit  624 . The following discussion describes a preferred approach to encoding the current pulses and decoding them with the portable unit  632  so as to detect whether the animal is inside or outside of the bounded area. 
     FIG. 18 illustrates one example of a signal transmitted by the power unit  624  along the buried wire  622 . In this example, the signal may include a frame  750 , where the exemplary frame is a binary word having four or more distinct components. The first component is the frame start  752  which includes a “1” and a “0”. The second component is the system code, typically comprising three bits, and which indicates a code number related to the controller unit  626 . The system code  754  is used, for example, to distinguish between pet containment systems operating in neighboring back yards. A similar signal may be transmitted by an exclusion unit  520  of FIG. 16 and a system code  754  may be used to distinguish between pet containment systems operating in adjacent living spaces such as neighboring apartments. 
     Following the system code  754 , may be the command data (not shown), typically comprising 8 bits. The command data component may include a header indicating which portable unit  632  out of a plurality of portable units the following command is directed to. The remainder of the command data component may also include the instructions for the particular portable unit  632 , such as correction commands or profile table information. As mentioned, the command data may be transmitted from a radio transmitter or transceiver of the controller  626  to a radio transceiver or radio receiver of the portable unit  632 , and therefore, not be included in the frame  650 . The next component of the frame is stop bit  756  which is a “1” that is followed by the last component, a polarity pulse  758 . 
     The digits in the binary frame  650  of this example may be produced by burst width modulation of approximately 10 KHz bursts. For example, a “1” may typically be represented by a burst of a few milliseconds at 10 KHz, and “0” may typically be represented by a longer burst at 10 KHz. A standard separation between bits of a few millisecond is provided. Other schemes, such as Manchester encoding may be used as well, as shown in FIG. 20A, whereby burst width modulation of the data is not used but the Manchester encoded data is carried by 10 KHz bursts. Manchester encoding may be desired due to the balanced nature of the resulting signal. 
     When using burst width modulation, as shown in FIG. 18, the length of the frame  250  can vary, depending on the number of zeros present in the frame  250 . The separation between adjacent frames may be varied so that the time lapse between frame starts is constant between all frames. The stop bit  756  transmitted by the power unit  624  of this embodiment includes a burst followed by a polarity pulse. The polarity pulse is a unipolar pulse without 10 KHz modulation, the width of which is typically about 3.5 seconds when Manchester encoding is used for the data. It is understood that the frequency of the bursts may be at frequencies other than 10 KHz for burst width modulation, Manchester encoding, or other data transfer methods. 
     FIG. 19 illustrates a block schematic diagram of the antenna system  660  (such as antenna system  460  of FIG. 15) used by the portable unit  632 . Antenna one  600  and antenna two  602  are oriented so that their respective directions of maximum sensitivity are orthogonal. Additional antennas may be used, and a third antenna may be implemented so that its maximum sensitivity is orthogonal to both the maximum sensitivity of antenna one  600  and antenna two  602 . The antennas  600  and  602  are preferably oriented on the animal  630  so that the plane defined by the directions of maximum sensitivity for each antenna is a vertical plane extending forward from the animal  630 . For example, if the animal  630  is a dog, then the plane defined by antenna one  600  and antenna two  602  is a vertical plane parallel to the dog&#39;s spine, and dividing the dog into right and left halves. A third antenna could be added to account for three-dimensional space rather than a vertical plane. Each antenna  600  and  602  has associated with it one or more tilt switches in the tilt switch array  468  (FIG.  15 ). These associated tilt switches indicate the orientation of the antenna, so that the portable unit processor  658  (such as processor  458  of FIG. 15) may determine the attitude of each antenna  600  and  602  and subsequently determine which side of the buried wire the animal  630  is on, as described hereinbelow. 
     The output A from both antennas  600  and  602  is directed to a gain module  604 , which is typically an operational amplifier operating in the linear region. The output  606  from the gain module  604  is directed to a comparator  608  which compares the gain module output  606  with a reference signal voltage  610 . The sensitivity adjust signal  666  selects programmable resistors  612  and  614  in the signal attenuator so as to vary the amplitude of the input to the gain module  604 . The use of two programmable resistors  612  and  614  results in four sensitivity settings for the gain module output, resulting in a comparator  608  output  609  indicative of the level of magnetic field around the periphery wire  622 . Other signal attenuator configurations may be used as well, such as using 3 programmable resistors to set up eight detectable zone. Furthermore, the resistors may be connected to addressable ports of the central processor  658  rather than to programmable switches as shown. When the comparator output  609  is high, even though the programmable resistors  612  and  614  are switched so as to produce the smallest gain module output  606 , then the animal has entered the zone closest to the wire  622 . If, on the other hand, there is a zero output signal  609  from the comparator  608  for all levels of gain module output signal  606 , the animal  630  is assumed to be adequately distanced from the wire  622 . An alternative approach to determining in which zone the animal  630  is located is to maintain the input to the gain module  604  with a single sensitivity and to sample different reference voltages  610 . In another alternative approach, the programmable signal attenuator, including the switchable resistors  612  and  614 , and the comparator  608  may be included with the portable unit processor  658  in a single chip. 
     The output from the comparator  608  is directed to a rising edge detector  616  in this embodiment. The output from the detector  616  is directed to the portable unit processor  658  as the data out signal  664 . The portable unit processor  658  samples the signal from one antenna at a time using the antenna sampling signal  662 . 
     Once the portable unit processor  658  has processed the data out signal  664  from the antenna system  660 , the processed data, including an out of bounds signal, is transferred to the radio transceiver  463  for transmission to the controller  626 . The information packet transmitted by the radio transceiver or separate transmitter typically includes a code identifying the portable unit  632 , data indicating which zone the portable unit  632  is in, and the out of bounds signal. 
     FIG. 20A further illustrates the signal carried by the periphery wire  622  that uses Manchester encoding whereby the encoded data is carried by 10 KHz square bursts. As shown, the encoded signal has a carrier burst frequency of 2F. The ending portion (i.e. high signal value) of the stop bit is shown, where the stop bit is defined as a logic one which has a zero signal amplitude (not shown) followed by the high signal value. Assuming a 10 KHz carrier, the complete high signal value portion of the stop bit as shown consists of 4 bursts having a period of 0.1 msec/burst for a total bit duration of 0.8 msec. Other bit durations and carrier frequencies are possible as well. The stop bit is followed by a gap and then a polarity pulse is provided. The duration of the last carrier burst of the stop bit plus the gap is X (e.g. 5 milli-seconds). The width of the polarity pulse is given by W (e.g. 3.5 milli-seconds). 
     FIG. 20B illustrates the signal received by the antenna system  660  as it exists at point A of FIG.  19 . The antenna  600  or  602  may be configured so that positively oriented pulses are generated for each rise of the carrier burst and negatively oriented pulses are generated for each fall for a given portable unit orientation and for a given side of the boundary wire  622 . Portable unit orientation refers to whether an antenna  600  or  602  that is closest to parallel to the vertical component of the magnetic field around boundary wire  622  is upward or downward. The tilt switch array  468  detects the antenna closest to parallel to the vertical component and also detects whether the orientation of that antenna is upwards or downwards. 
     It may be chosen that when the receiving antenna  600  or  602  is upwards and when the vertical component of the magnetic field is upwards on the side of boundary wire  622  where the portable unit  632  is located, the waveform shown in FIG. 20B would result. In this waveform, a signal rise from the wire results in a positively oriented pulse received by the receiving antenna  600  or  602  while a signal fall results in a negatively oriented pulse. If the receiving antenna  600  or  602  becomes downwardly oriented while the animal remains on the same side of the bounded area or if the animal moves to the other side of the boundary wire  622  while the antenna  600  or  602  remains upwards, then the received signal at point A of FIG. 19 is inverted, as is shown in FIG.  20 D. 
     For the waveform of FIG. 20B, after the signal has been amplified by gain module  604  of FIG. 19, it is passed to the comparator  608  that allows only the positively oriented pulses to pass through. The positively oriented pulses are then supplied to the rising edge detector  616 , such as a one-shot multivibrator. For each rising edge, the detector  616  outputs a detector pulse having a time constant large enough to maintain an output pulse width (A of FIG. 20C) with a duration longer than the positive pulse separation from the comparator. For burst width modulation (such as shown in FIG.  18 ), the time constant may be set so that a rising edge of a “1” results in one output pulse while rising edges of a “0” results in an output pulse consisting of two continuous output pulses which processor  658  may then interpret. For Manchester encoding, this output pulse width maintains an output pulse having a width approximately that of the high value portion of the encoded stop bit and enables the processor  658  to interpret the Manchester encoded data. The output of the detector  616 , as shown in FIG. 20C, results from the received waveform in FIG.  20 B. The output of the detector  616 , as shown in FIG. 20E, results from the received waveform in FIG. 20D, which was the inverted version of the received waveform in FIG.  20 B. 
     As is shown in FIGS. 20B and 20C, the polarity pulse created by the wire  622  results in one received positive pulse and one received negative pulse at point A of FIG.  29 . For a given antenna convention and current direction, FIG. 20B indicates an animal within the bounded area and FIG. 20D indicates an animal outside of the bounded area. In FIG. 20B, the positive pulse received due to the polarity pulse occurs first and passes through the comparator  608  while the received negative pulse is blocked. The detector  616  then produces a detector pulse having Δ width in response to the received positive pulse. The detector pulse from the detector  616  begins at (X−Δ) time from the termination of the last received pulse resulting from the stop bit. 
     In FIG. 20D, the negative pulse received at point A due to the polarity pulse occurs before the received positive pulse, since the vertical component of the field has the opposite direction on the outside of the bounded area. This received negative pulse at point A is blocked by the comparator  608 . The received positive pulse at point A due to the polarity pulse is delayed by the polarity pulse width W relative to the received positive pulse at point A for the waveform of FIG.  20 C. The detector  616  therefore does not produce a detector pulse in response to the received positive pulse until (X−Δ+W−F) time from the termination of the pulse generated from the stop bit. Thus, the received positive pulse occurs later in time by (W−F) than it does for the situation of FIG.  20 C. 
     The central processor  658  may determine whether the animal is inside or outside of the bounded area by knowing the orientation of the receiving antenna from the tilt switch and by knowing whether the final pulse from the detector  616  for a received frame had a delay of (X−Δ) or the longer delay of (X−Δ+W−F). For example, the processor may be programmed for a first sign convention (i.e., a particular direction is considered upward for an antenna) and for a first current direction (i.e., counter-clockwise) for the polarity pulse in the boundary wire  622 . If the processor  658  detects that the receiving antenna is upwardly oriented and that the final detector pulse had a short delay, then the animal is assumed to be inside the bounded area. If the processor  658  detects that the receiving antenna is downwardly oriented and that the final detector pulse has a short delay, then the animal is assumed to be outside the bounded area. If the processor  658  detects that the receiving antenna is upwardly oriented and that the final detector pulse had a long delay, then the animal is assumed to be outside the bounded area. Finally, if the processor  658  detects that the receiving antenna is downwardly oriented and that the final detector pulse has a long delay, then the animal is assumed to be inside the bounded area. 
     The processor may be programmed for a second sign convention (i.e. opposite direction is considered up for an antenna) for the first polarity pulse current direction in the boundary wire  622 . In that case, the result is reversed so that the animal is determined to be on the opposite side of the wire  622  for the same antenna orientation and detector pulse delay from the example above. Likewise, if the processor is programmed for the first sign convention but the polarity pulse current direction is reversed in the boundary wire  622 , the animal would be determined to be on the opposite side of the wire  622 . A truth table, table 1, is provided below to illustrate these variations. 
     Thus, the portable unit  532  should be placed on the animal in a given orientation to produce the correct detection of being out of bounds. The proper orientation may be found by using a calibration technique whereby the installer approaches the boundary while in-bounds with the portable unit  532  to determine whether the portable unit responds with a correction. If not, then reversing the orientation of the portable unit  532  by flipping it over will result in the correct orientation for the portable unit  532  to be placed on the animal  530 . 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
            
               
                   
                 Tilt Switch Result 
               
            
           
           
               
               
               
            
               
                 First Convention 
                 Up 
                 Down 
               
               
                   
               
               
                 First Current Direction 
               
               
                 Short Delay 
                 Inside 
                 Outside 
               
               
                 Long Delay 
                 Outside 
                 Inside 
               
               
                 Opposite Current Direction 
               
               
                 Short Delay 
                 Outside 
                 Inside 
               
               
                 Long Delay 
                 Inside 
                 Outside 
               
               
                   
               
               
                 Opposite Convention 
                 Up 
                 Down 
               
               
                   
               
               
                 First Current Direction 
               
               
                 Short Delay 
                 Outside 
                 Inside 
               
               
                 Long Delay 
                 Inside 
                 Outside 
               
               
                 Opposite Current Direction 
               
               
                 Short Delay 
                 Inside 
                 Outside 
               
               
                 Long Delay 
                 Outside 
                 Inside 
               
               
                   
               
            
           
         
       
     
     Once the portable unit  632  has determined that the animal is inside or outside, this information along with the zone may be transmitted back to the controller unit  626 . The controller unit  626  may then determine the appropriate correction. The correction instruction can then be transmitted back to the portable unit  632 , such as by modulating the command into the magnetic field generated by the wire  622 , Manchester encoding the command into the signal on the wire  622 , or by transmitting the command through radio signals received by the portable unit&#39;s transceiver  463 , if any. Alternatively, the portable unit  632  may reference the profile table to determine the appropriate correction based on the zone and in/out of bounds information. 
     In summary, an electronic system for deterring an animal from entering an exclusion area or entering or leaving a bounded area has been described. The system also provides important information to the user, such as battery level condition, provides an optional alarm when the animal enters an exclusion area or is trapped in an exclusion area, and allows the user to maintain a log of animal activity and behavior. 
     The foregoing description of the various embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.