Abstract:
This invention relates generally to monitoring systems and more particularly concerns devices and systems used to monitor patients lying in hospital beds or in other care giving environments. According to a first aspect of the instant invention, a microprocessor based patient monitor is disclosed which includes a loudspeaker driven by a power amplifier responsive to an input signal derived from a programmable volume control. The microprocessor synthesizes any one of multiple alarm sounds under software control, operates the programmable volume control of the alarm system and activates and deactivates the alarm in response to the electronic signals received from the sensor and a user interface. An electrically erasable programmable read-only memory accessible by the processor stores data which can be modified to tailor the operations of the monitor to suit a variety of different needs. According to still another aspect of the instant invention, a microprocessor-based patient monitor is disclosed which has a personality that is defined by software that is resident in modifiable nonvolatile memory, which software can thus be altered to change the programmed responses of the monitor. Finally, a software and hardware system is provided for reading information from and writing information to modifiable nonvolatile RAM within a microprocessor-based patient monitor. This information might be parameter settings, data values, or computer instructions.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 09/031,363, filed on Feb. 26, 1998, now U.S. Pat. No. 6,111,509, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to monitoring systems and more particularly concerns devices and systems used to monitor bed patients in hospital or other care giving environments. 
     It is well documented that the elderly and post-surgical patients are at a heightened risk of falling. There are many reasons for this but, broadly speaking, these individuals are often afflicted by gait and balance disorders, weakness, dizziness, confusion, visual impairment, and postural hypotension (i.e., a sudden drop in blood pressure that causes dizziness and fainting), all of which are recognized as potential contributors to a fall. Additionally, cognitive and functional impairment, and sedating and psychoactive medications are also well recognized risk factors. 
     A fall places the patient at risk of various injuries including sprains, fractures, and broken bones—injuries which in some cases can be severe enough to eventually lead to a fatality. Of course, those most susceptible to falls are often those in the poorest general health and least likely to recover quickly from their injuries. In addition to the obvious physiological consequences of fall-related injuries, there are also a variety of adverse economic and legal consequences that include the actual cost of treating the victim and, in some cases, caretaker liability issues. 
     In the past, it has been commonplace to treat patients that are prone to falling by limiting their mobility through the use of restraints, the underlying theory being that if the patient is not free to move about, he or she will not be as likely to fall. However, research has shown that restraint-based patient treatment strategies are often more harmful than beneficial and should generally be avoided—the emphasis today being on the promotion of mobility rather than immobility. Among the more successful mobility-based strategies for fall prevention include interventions to improve patient strength and functional status, reduction of environmental hazards, and staff identification and monitoring of high-risk hospital patients and nursing home residents. 
     Of course, monitoring high-risk patients, as effective as that care strategy might appear to be in theory, suffers from the obvious practical disadvantage of requiring additional staff if the monitoring is to be in the form of direct observation. Thus, the trend in patient monitoring has been toward the use of electrical devices to signal changes in a patient&#39;s circumstance to a caregiver who might be located either nearby or remotely at a central monitoring facility, such as a nurse&#39;s station. The obvious advantage of an electronic monitoring arrangement is that it frees the caregiver to pursue other tasks away from the patient. Additionally, when the monitoring is done at a central facility a single nurse can monitor multiple patients which can result in decreased staffing requirements. 
     Generally speaking, electronic monitors work by first sensing an initial status of a patient, and then generating a signal when that status changes, e.g., he or she has sat up in bed, left the bed, risen from a chair, etc., any of which situations could pose a potential cause for concern in the case of an at-risk patient. Electronic bed and chair monitors typically use a pressure sensitive switch in combination with a separate monitor/microprocessor. In a common arrangement, a patient&#39;s weight resting on a pressure sensitive mat (i.e., “sensing” mat) completes an electrical circuit, thereby signaling the presence of the patient to the microprocessor. When the weight is removed from the pressure sensitive switch, the electrical circuit is interrupted, which fact is sensed by the microprocessor. The software logic that drives the monitor is typically programmed to respond to the now-opened circuit by triggering some sort of alarm—either electronically (e.g., to the nursing station via a conventional nurse call system) or audibly (via a built-in siren). Some examples of devices that operate in this general fashion may be found in U.S. Pat. Nos. 4,484,043, 4,565,910, 5,554,835, and 5,634,760, the disclosures of which are incorporated herein by reference. 
     That being said, patient monitoring systems that rely on sensing mats to detect the presence of a patient in a bed suffer from a variety of drawbacks. For example, the bed monitoring systems currently available in the marketplace feature externally accessible configuration switches that allow the caregiver to reconfigure the device at will and to adjust parameters such as the duration of the alarm, and the time lapse between the sensing of the “empty bed” condition and the sounding of an alarm. External switching makes tampering with the system extremely easy and makes it more difficult to establish and maintain a hospital-wide policy with respect to monitor settings. 
     A further problem with conventional bed monitoring systems is that they use oscillating transducers in their alarm audio circuits, resulting in single frequency audio alarms. Since bed monitor alarms are frequently employed in environments in which a multiplicity of other problems might also trigger audio alarms, if the single alarm sound provided by the bed monitor happens to be similar to one or more other alarm sounds heard in response to different monitors, confusion and consequential lengthened response times to patient monitor alarms may result. 
     Those skilled in the art know that there are many nurse call station configurations and it is to the economic advantage of a manufacturer to be able to accommodate all of them. However, another problem with the present state-of-the-art in bed monitoring systems is that they are typically pre-configured internally at the factory for one particular type of nurse call station. Thus, if the unit is misconfigured when it arrives at an installation, it may be necessary to summon a medical technician to reconfigure it, since internal modifications to the unit are required to adapt it to different call station types. This can result in additional expense and delay in getting the unit correctly configured and into operation. Further, there are many hospitals that use multiple incompatible nurse call system types, each having been separately added as a new building or wing was constructed. The inability to quickly and reliable move electronic monitors between these systems means that the hospital will generally be required to maintain excess inventory of each type of compatible monitor, a result that ultimately adds to the health care costs borne by the consumer/patient. 
     Still another failure in known bed monitoring systems is that they do not provide a method of accumulating statistical data relating to the operation of the unit including, for example, the response times of the caregiver to alarm conditions. This sort of information could be very helpful to the maintenance and proper operation of the monitor, and for caregiver quality control purposes. 
     It is, therefore, a primary object of this invention to provide a patient monitor that is microprocessor-based so as to be reconfigurable by the uploading of configuration data to an electronically erasable programmable read only memory accessible by the microprocessor. A further object of this invention is to provide a microprocessor based patient monitor which synthesizes multiple alarm sounds in software for selection by the caregiver. It is also an object of this invention to provide a microprocessor based patient monitor having a nurse call interface allowing interconnection with any nurse call station without modification of the monitor. Yet another object of this invention is to provide a microprocessor based patient monitor having an electrically erasable programmable read only memory accessible by the microprocessor for logging statistical data with respect to the use of the monitor and the response time of the caregiver using the monitor. Another object of this invention is to provide a microprocessor based bed patient monitor which permits the downloading of the logged statistical data to a host microprocessor connected to the system. It is still another object of the instant invention to provide a system for configuration of monitor parameters and for recalling and analyzing statistical data accumulated therein. 
     Heretofore, as is well known in the bed monitor arts, there has been a need for an invention to address and solve the above-described problems. Accordingly, it should now be recognized, as was recognized by the present inventor, that there exists, and has existed for some time, a very real need for a electronic patient monitor that would address and solve the above-described problems. 
     Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a patient monitor is provided in which a processor receiving electronic signals from a sensor indicating the presence on the sensor and absence from the sensor of a patient is combined with an alarm system which includes a loudspeaker driven by a power amplifier which responds to an input signal derived from a programmable volume control to produce an aural alarm. The processor synthesizes at least one and preferably multiple alarm sounds under software control, operates the programmable volume control of the alarm system to select the decibel level of the alarm and activates and deactivates the alarm in response to the electronic signals received from the sensor and a user interface. An electrically erasable programmable read-only memory accessible by the processor stores a plurality of alarm sounds for selection by the processor for synthesis of the selected alarm sound. In addition, the electrically erasable programmable read-only memory stores multiple decibel levels for selection by the processor of the desired decibel level of the alarm sound. In the preferred embodiment, the patient monitor will be used to sense the presence of patient who is lying in a bed, however, it should be noted and remembered this monitor could also be used in other sorts of applications, including with chair and toilet monitors. 
     Preferably, the electrically erasable programmable read-only memory also permits storage of a plurality of options for the delay time between initiation of the absence of a patient from the sensor and the activation of the alarm by the processor. Furthermore, the monitor is preferably provided with an external switch connected to the processor for caregiver selection of the delay time from the plurality of delay time options. 
     It is also preferred that the electrically erasable programmable read-only memory log usage data with respect to the monitor including the total hours of use of the monitor, the total time of alarms sounded by the monitor, the total number of alarms sounded by the monitor and the response time between the most recent sounding of an alarm and a subsequent operation of the monitor by the caregiver. The monitor will include a port for downloading the log usage data to a host computer. 
     The monitor also includes a nurse call interface having a relay which is energized when the power amplifier is de-energized and which has a normally opened contact, a normally closed contact and a common contact for interconnecting the monitor to a nurse call system to one of the normally opened and normally closed contacts so that the monitor requires no modification to accommodate the type of nurse call station with which the monitor is used. 
     According to still another aspect of the instant invention, there is provided a bed monitor/computer system which allows easy on-site configuration of a monitor to work with different nurses stations. In more particular, the monitor of the instant invention is designed to be reconfigured through the use of a host computer, which obviates the need for internal modifications of monitor parameters through the use of dip switches, rotary dials, etc., which are commonly used in the industry. In the preferred embodiment, a standard computer interface, such as serial interface, is provided as a means for communication between the monitor and a separate host computer. This allows the unit to be readily reprogrammed without risking the exposure of the internal electronic components to the environment. 
     According to still a further aspect of the instant invention, there is provided a software system for providing the monitor with new programming instructions or a new “personality” which will enable it to operate with potentially any plug-compatible nurse call station. In the preferred embodiment, the internal operating logic and various parameters which change the operation of the device to match a particular nurse call station are preferably stored in nonvolatile flash-type RAM which is RAM that can be modified on demand through the use of a host computer-to-patient monitor transfer. One obvious advantage of this arrangement is that it eliminates the many problems associated with mechanical configuration switches, such as dip switches and rotary dials, while providing an easy, inexpensive, and reliable way of upgrading or otherwise modifying the functionality of a monitor while it is in the field. 
     The foregoing has outlined in broad terms the more important features of the invention disclosed herein so that the detailed description that follows may be more clearly understood, and so that the contribution of the instant inventor to the art may be better appreciated. The instant invention is not to be limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. Rather, the invention is capable of other embodiments and of being practiced and carried out in various other ways not specifically enumerated herein. Additionally, the disclosure that follows is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. Further, it should be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting, unless the specification specifically so limits the invention. 
     While the instant invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
     FIG. 1 is a block diagram illustrating a preferred embodiment of the monitor; 
     FIG. 2 is a schematic diagram illustrating a portion of a preferred embodiment of the processor of the monitor; 
     FIG. 3 is a schematic diagram illustrating a portion of a preferred embodiment of the processor of the monitor; 
     FIG. 4 is a schematic diagram illustrating a preferred embodiment of the user interface of the monitor; 
     FIG. 5 is a schematic diagram illustrating a preferred embodiment of the audio section of the monitor; 
     FIG. 6 is a schematic diagram illustrating a preferred embodiment of the signal condition circuit of the monitor; 
     FIG. 7 is a schematic diagram illustrating a preferred embodiment of the non-volatile memory of the monitor; 
     FIG. 8 is a schematic diagram illustrating a preferred embodiment of the nurse call interface of the monitor; 
     FIG. 9 is a schematic diagram of a preferred embodiment of the power supply of the monitor; 
     FIG. 10 is a flow diagram illustrating a preferred embodiment of a cold start routine of the monitor; 
     FIG. 11 is a flow diagram illustrating a preferred embodiment of the executive routine of the monitor; 
     FIG. 12 is a flow diagram illustrating a preferred embodiment of the hold mode routine of the monitor; 
     FIG. 13 is a flow diagram illustrating a preferred embodiment of the monitor routine of the monitor; 
     FIG. 14 is a flow diagram illustrating a preferred embodiment of a portion of the alarm mode of the monitor; 
     FIG. 15 is a flow diagram of another portion of the alarm mode routine of the monitor; 
     FIG. 16 is a flow diagram illustrating a portion of a preferred embodiment of the program mode of the monitor; 
     FIG. 17 is a flow diagram illustrating a portion of a preferred embodiment of the program mode of the monitor; 
     FIG. 18 is a flow diagram illustrating a portion of a preferred embodiment of the program mode of the monitor; 
     FIG. 19 is a flow diagram illustrating a preferred embodiment of the data logger subroutine of the monitor; and 
     FIG. 20 is a flow diagram illustrating a preferred embodiment of the pull-out protection subroutine of the monitor. 
     FIG. 21 contains an illustration of the general environment of the instant invention, wherein a host computer is connected to the monitor for purposes of data transfer. 
     FIG. 22 illustrates the main hardware elements of the reprogrammable monitor embodiment. 
     FIG. 23 contains a flow chart that illustrates the principle computer steps in the personality loading routine. 
     FIG. 24 is a flow chart of the principle steps in the parameter recall routine, wherein data is passed from the monitor to the host CPU. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Microprocessor-Based Patient Monitor 
     According to a first aspect of the instant invention, there is provided a microprocessor based patient monitor that offers improved functionality in comparison with known control units by introducing added features and improvements in the intuitiveness of the operation. As is illustrated in FIG. 1, a preferred embodiment of the instant monitor hardware has seven functional blocks including a processor  10 , a user interface  40 , an audio section  70 , a signal conditioning circuit  100 , a non-volatile memory  130 , a nurse call interface  160  and a power supply  190 . 
     As is made clear in FIG. 1, the microprocessor  10  is responsible for various functions within the monitor including managing its user interface  40 , communicating with the nurse call interface  160 , and controlling the signal condition circuit  100 /audio section  70 . Additionally, the processor  10  is able to retrieve from and store to non-volatile memory  130  as needed. 
     As shown in FIGS. 2 and 3, the processor  10  includes a microcontroller  11 , a latching display driver  13  and a latch  15 . Since the microcontroller  11  is synthesizing the alarm sound in software, it is important to run the microcontroller  11  at its maximum operating speed. The microcontroller  11  preferably has fourteen general purpose I/O pins grouped into a port A and a port B and one interrupt request input IRQ. The pins of the microcontroller  11  are preferably utilized as follows: 
     Port A Bit  0 : via a multifunction bus  17  to D 1  of the latch  15 , A IN  of the latching display driver  13 , INC of a volume control  71  in the audio section  70 , via a diode  25  to U 111  of the user interface  40  and via a resistor R 1  to VCC; 
     Port A Bit  1 : via the multifunction bus  17  to D 2  of the latch  15 , B IN  of the latching display device  13  and U/D of the volume control  71 , via a diode  27  to UI 12  of the user interface and via a resistor R 2  to VCC; 
     Port A Bit  2 : via the multifunction bus  17  to D 3  of the latch  15  and C IN  of the latching display driver  13 ; 
     Port A Bit: via the multifunction bus  17  to D 4  of the latch  15  and D IN  of the latching display driver  13 ; 
     Port A Bit  4 : to Key Input Enable of the user interface  40 ; 
     Port A Bit  5 : via the multifunction bus  17  to D 6  of the latch  15 ; 
     Port A Bit  6 : to LE of the latching display driver  13 ; 
     Port A Bit  7 : to CLK of the latch  15 ; 
     Port B Bit  0 : to SDA of the non-volatile memory  130  (EEPROM Data), via a resistor R 3  to VCC and the power supply  190 ; 
     Port B Bit  1 : to SCL of the non volatile memory  130  (EEPROM clock), via a resistor R 6  to VCC and the power supply  190 ; 
     Port B Bit  2 : to the nurse call interface  160  (pull out detection); 
     Port B Bit  3 : to CS of the volume control  71  (volume); 
     Port B Bit  4 : to VH of the volume control  71  (audio out); 
     Port B Bit  5 : to the signal condition circuit  100  (mat detection); 
     IRQ: (Interrupt Request) to the signal condition circuit  100  (mat input); 
     Reset: to VCC through the time delay R 13 /C 13 ; and 
     OSCI &amp; OSC 2 : to the master clock for the microcontroller  11 . 
     Additionally, the remaining pins of the latching display driver  13  are preferably used as follows: 
     A OUT : Via a resistor R 4  to UI 1  of the user interface  40 ; 
     B OUT : Via a resistor R 5  to UI 2  of the user interface  40 ; 
     C OUT : Via a resistor R 7  to UI 3  of the user interface  40 ; 
     D OUT : Via a resistor R 8  to UI 4  of the user interface  40 ; 
     E OUT : Via a resistor R 10  to UI 5  of the user interface  40 ; 
     F OUT : Via a resistor R 11  to UI 6  of the user interface  40 ; 
     G OUT : Via a resistor R 12  to UI 7  of the user interface  40 ; and LT and B 1 : to VCC 
     The remaining pins of the latch  15  are preferably used as follows: 
     Q 1 : via a resistor R 14  to UI 8  of the user interface  40 ; 
     Q 2 : via a resistor R 15  to UI 9  of the user interface  40 ; 
     Q 3 : via a resistor R 16  to UI 10  of the user interface  40 ; 
     Q 4 : to the nurse call interface  160 ; 
     Q 5 : unused; 
     Q 6 : to the nurse call interface  160 ; and 
     D 5  and CLR: to VCC. 
     The multifunction bus  17  to D 1 ,  2 ,  3 ,  4  and  6  of the latch  15  capitalizes on the bidirectional feature of the microcontroller  11  to create a local data bus. This allows the associated pins PA 0 ,  1 ,  2 ,  3  and  5  of the microcontroller  11  to be used for several functions, reducing the total number of I/ 0  pins required and allowing for a smaller, less expensive microcontroller  11  to be used. The multifunction bus  17  sources information for a numeric display  41  via the latching display driver  13 , selects annunciators  43  to be illuminated via the latch  15 , energizes the nurse call relay K 1  via the latch  15 , provides up/down information for the programmable volume control  71  and inputs the status of the keypad  45 . Operation of the multifunction bus  17  is purely under software control. The microcontroller  11  contains internal RAM  19 , EPROM  21 , and a Timer  23 . One suitable hardware choice for the microcontroller  11  is a Motorola MC68HC705J2, the latching display driver  13  is a Motorola 74HC4511 and the latch  15  is a Motorola 74HC 1 174. 
     A resistor R 13  and capacitor C 13  connected between the power source VCC and the RESET port of the microcontroller  11  provide time delay at initialization and a typical clock circuit is connected to the OSC 1  and OSC 2  ports of the microcontroller  11 . 
     Turning to FIG. 4, the user interface  40  preferably consists of the numeric display  41 , an annunciator bank  43  including a HOLD annunciator  47 , a MON annunciator  49  and an ALARM annunciator  51  and the keypad  45  including a reset switch  53  and a delay adjust switch  55 . Needless to say, many other arrangements of the control switches and displays are possible and are well within the capability of one of ordinary skill in the art to devise. 
     The numeric display  41  is a seven segment display driven by the latching display driver  13 . The preferred latching display driver  13 , such as the Motorola 74HC4511, takes Binary Coded Decimal (BCD) in and decodes it into the appropriate segments to display the desired number. The BCD input is provided by D 1 -D 4  of the multifunction bus  17 . The information is latched into the latching display driver  13  by Port A Bit  6 . The latching operation frees up the multifunction bus  17  for other purposes while maintaining a stable display. The latching display driver  13  provides a blanking function, a totally dark display, by writing a number greater than nine to the BCD input. Four bits of data provide 16 possible combinations ( 0 - 15  ), while only ten combinations are defined in BCD ( 0 - 9  ). The other six combinations ( 10 - 15  ) result in turning off all of the display segments. The numeric display  41  is used to display the seconds of delay which precede an alarm in normal operation of the monitor. In addition, the display  41  is used to show selected options during the local programming mode, as is hereinafter further described in relation to the monitor software. All three annunciators,  43 ,  45  and  47 , are LED&#39;s driven by the latching display driver  13 . The preferred latching display driver  13 , a Motorola 74HC4511, is capable of sourcing 20 milliamps per output  50 . No additional drive is necessary to each LED. The driver  13  has a hex latch (six individual D flip/flops with a common clock line). Only five latch outputs are implemented and one of those is unused in the current software. Q 1  through Q 3  are used for the annunciators  47 ,  49  and  51 , respectively. By using a latch  15  with sufficient drive capability, the latching display driver  13  provides the source current to illuminate each LED and also latches the data so that the annunciators  43 ,  45  and  47  remain stable while the multifunction bus  17  is used for other purposes. To turn on a particular annunciator  47 ,  49  or  51 , the processor  10  raises the appropriate bit of the multifunction bus  17 , D 1  for ALARM  47 , D 2  for MON  49  or D 3  for HOLD  51 , and then toggles Port A Bit  7  to latch the data. Operating characteristics for each mode are hereinafter described in relation to the monitor software. The reset switch  53  and delay adjust switch  55  are inputted to the processor  10  on bits D 1  and D 2  of the multifunction bus  17 . The two switches  53  and  55  share a common select line so a read of either switch  53  or  55  always reads both switches  53  and  55 . To accomplish a read, the processor  10  must make Port A Bit  0  and Port A Bit  1  inputs. The switches  53  and  55  are then read by taking Port A Bit  4  low. The two inputs are pulled up by resistors R 1  and R 2  and these two bits may be pulled low through diodes D 1  and D 2  respectively. This can only happen if the appropriate switch  53  or  55  is closed and the key enable line is low. 
     Looking now at FIG. 5, the audio section  70  consists of a programmable volume control  71 , a power amplifier  73  and a loudspeaker  75 . The audio is a single bit square wave generated by the processor  10  under software control. The audio signal is divided to the requested volume by the programmable volume control  71 , the power amplified to a sufficient level to drive the loudspeaker  75 , and converted to audio by the loudspeaker  75 . 
     The volume control  71  is preferably a Xicor Corporation X9314 digital potentiometer. This integrated circuit performs the same function as a potentiometer except the wiper position VW is digitally positioned to any one of 32 (i.e., 0-31) possible steps. The circuit is designed such that position zero corresponds to a minimum volume (no sound) and position  31  is maximum volume. To control the volume chip select CS, which is connected to VCC via a pull-up resistor R 32 , is set low (Port B Bit  3  ), the up-down pin U/D (mfb D 1 ) is set low to reduce volume or high to increase volume, and the increment-decrement INC pin (mfb D 0 ) is toggled the appropriate number of times to reach the new wiper position. 
     The multifunction bus  17  is used for the U/D control and for the INC control since these signals have no effect on the chip in the absence of a valid chip select signal. Therefore, using mfb D 1  and mfb D 2  will not effect the volume when used for other purposes and the chip select signal (active low) is high. The output of the programmable volume control  71  is AC coupled by a resistor R 33  and capacitor C 5  and directed to the input of the audio power amplifier  73 . 
     The power amplifier is preferably a National Semiconductor LM388 audio amplifier which has adequate drive for the required volume levels and requires relatively few discrete components to produce a viable audio amplifier. It is used in its simplest configuration and directly drives the unit&#39;s loudspeaker  75 . It preferably has a fixed gain of 20 and a resistor R 26  scales the audio appropriately for the desired maximum output level. 
     The loudspeaker  75  is preferably a simple two inch polycone speaker. However, it should be noted that other arrangements are certainly possible and it is within the ordinary skill of in the art to devise. By way of example only, the loudspeaker element might be a piezoelectric device capable of generating an audible alarm signal. Thus, when the term “loudspeaker” is used hereinafter, that term should be construed in the broadest possible sense to include any device capable of emitting an audible alarm signal under the control of the microprocessor  10 . Additionally, when loudspeaker is used herein that term should also be taken to include an associated power amplifier, if one is necessary from the context of its use (as it usually will be). Finally, it should also be noted that it is, not an essential element of the instant invention that the loudspeaker  75  be found within the body of the monitor. The speaker  75  could also be mounted externally thereto, and, as an extreme example, might by located in an adjacent hallway or at the nurses station. 
     The signal conditioning circuit  100 , shown in detail in FIG. 6, filters noise from the mat inputs JR 1 - 1  and  2  and provides a reasonable degree of protection to the monitor from static discharge. Filtering at one input JR 1 - 2  is accomplished by a single RC circuit including resistors R 20  and R 21  and a capacitor C 6  and at the other input JR 1 - 1  by a simple RC circuit including resistors R 9  and R 31  , and a capacitor C 3 . This eliminates some noise and assists in increasing the immunity from static discharge. A static discharge to the monitor passes through the RC filters and is then clamped by surge limiting devices, RV 1  and RV 2  of FIG.  6 . The combination of the first input components R 20 , R 21 , C 6  and RV 2  and the second input components R 19 , R 31 , C 3  and RV 1  should provide static protection far in excess of known monitors. 
     The non-volatile memory  130  illustrated in FIG. 7 includes a 1 Kbit (128×8) electrically erasable programmable read only memory EEPROM  101 . It is connected via resistors R 25  and R 27  to the power supply interface connections J 3 - 4  and J 3 - 5 . The actual IC chip is preferably a Microchip X24LC01 which uses a two wire serial interface to communicate with the processor  10 . The interface is based on the I 2  C bus which has become the predominant standard for low cost inter-chip communications (i.e., “Inter-IC” bus, which is a standard means of providing a two-wire communication link between integrated circuits). Detailed information on the chip and the I 2  C bus may be found in the Microchip Nonvolatile Memory Products databook. The EEPROM  101  is used to store operating characteristics, usage information and device specific information such as a repair log and unit serial number. The operating characteristics are defined, in part, by a collection of user-modifiable parameters that control various aspects of the monitor&#39;s operations, including, for example, the type of alarm tone (e.g., FIG. 15, item  329  ), the relay action, the hold time delay, and the volume of the alarms. These memory locations may be modified either through use of the front panel control switches or, as hereinafter described, via a computer program that is executing on a remote host connected to the monitor via an electronic interface, such as a serial port. Usage information might consist, by way of example only, of an hour meter which logs total hours of use of the monitor, the total time alarming, the total number of alarms, the response time to the last alarm, and/or the date and time of past alarms (the calendar date and time being provided by, for example, a date/time chip  595  of the sort illustrated in FIG.  22 ). 
     Downloading usage information to a host computer allows a number of diagnostic statistics to be calculated, including the “average time to respond”. This information is preferably only be written by the monitor, and read only to an inquiring host computer. Read only status is purely a software function of the host. Device specific information would typically not be used by the monitor and is never written to or read by the monitor. It is preferably written only at the time of manufacture or time of repair by an external host computer. The information is intended for use by the factory, a repair station, or a facilities biomedical staff and might include, for example, the date of the last ten repairs and corresponding work order numbers and the unit&#39;s serial number. 
     Turning now to FIG. 8, the nurse call interface  160  uses a relay K 1  to provide isolation between the monitor circuitry and the nurse call system. A normally open contact  161 , a normally closed contact  163  and a common contact  165  of the relay K 1  are connected to a connector J 2 . The nurse call cord (not shown) plugs into this connector J 2  and would typically be an RJ-45 or similar connector. Since there is always a potential for inadvertent disconnection of a connector J 2 , two additional pins J 2 - 4  and  5  are used in the connector J 2  to provide a continuity loop. By monitoring this loop, the processor  10  can detect a pulled-out nurse call cord. If this condition is detected, a distinct in-room alarm is sounded. Pull-out protection may be disabled via the profile stored in the nonvolatile memory  130  when the system is used in a facility without a nurse call system or in a home. The relay K 1  is energized in the non-alarming state. This effectively reverses the contacts  161  and  163  so that the normally open contact  161  appears to be normally closed and vice versa. Thus, a nurse call is issued whenever power is interrupted to the monitor. This provides a fail safe on the power supply  190  and its interconnects. A single RC filter consisting of a resistor R 18  and a capacitor C 4  provides static protection for the processor  10 . The relay K 1  is turned on by the transistor Q 1  via a current limiting resistor R 23  and a diode D 3  which absorbs the inductive kick which occurs when the relay K 1  is de-energized. 
     As shown in FIG. 9, the power supply  190  includes an external connector J 3 . The connector J 3  includes a transformer (not shown) connected between two pins J 3 - 1  and J 3 - 2  of the connector. Power VCC is brought into the monitor through a voltage regulator  191  connected to the first connector pin J 3 - 1 . Two additional pins J 3 - 4  and  5  of this connector J 3  are used for the read/write interface of the external EEPROM  101 . Filter capacitors C 11  and C 12  are preferably connected on either side of the voltage regulator  191 . 
     Monitor Front Panel Control Functions 
     The internal software allows the monitor to perform a variety of f unctions. As illustrated in FIG. 4, the user interface  40  includes inputs allowing a user to modify control unit actions via the reset button  53  and to adjust the delay via the delay adjust button  55  and outputs for controlling operation of the 0 through 9 numeric display  41 , the status annunciators  43  and various aural signals. 
     An idle mode (HOLD), which is active when the monitor is not monitoring, enables automatic advancement to the monitor mode, manual override for immediate advancement to the monitor mode, adjustment of the delay time, aural indications of any unsafe conditions and logging of hours in use. The monitor mode (MON) enables monitoring of the patient for activity within the bed which could be a precursor for a bed evacuation, adjustment of the delay time, manual return to the idle mode (HOLD), automatic advancement to the alarm mode (ALARM), aural indications of an y unsafe hardware conditions and logging of hours in use. The alarm mode (ALARM) enables generation of a nurse call through the nurse call system  160 , aural in-room alarm, manual return to the idle mode (HOLD) and logging of response time and total alarm time. A program mode enables the user to customize the features of the monitor and to update the non-volatile memory  130  with user selected parameters. 
     All functions which utilize the user interface  40  are consistent with the nomenclature which the user sees on the labels of the buttons  53  and  55  and on the numeric display  41 . For example, any features which use the reset button  53  have an intuitive connection to the word “reset”. Likewise, the delay adjust button  55 , which preferably features a triangle pointing up, causes an upward adjustment in the numeric display  41  with appropriate roll over at a maximum value. 
     Internal Software/Logic Functions 
     FIG. 10 illustrates the main steps that are executed within the monitor as part of a power-up (i.e., cold start) sequence. In the preferred embodiment, a cold start  201  will cause the processor  10  to automatically enter into the HOLD mode as part of step  201 . Then, the system initialize hardware  203  and variables  205 , after which it will then set the I 2 C interface to inputs  207  to determine whether the interface is already being used, for example to change the programs in the EEPROM  101 . An inquiry is then made as to whether the I 2 C is busy  209 . If the response to this inquiry is “YES,” then the inquiry is repeated until the response is “NO.” If a “NO” response is received, the system proceeds to recall parameters stored previously within EEPROM  213 . The system will next inquire as to whether the delay time equals nine (step  215  ). If the response to this inquiry is “YES,” the system will next inquire as to whether the reset is pressed  217 . If the response to either the inquiry as to whether the delay time equals nine  215  or whether the reset is pressed  217  is “NO,” then the system proceeds to go to executive routine  219 . If the response to the inquiry as to whether the reset is pressed  217  is “YES,” the system proceeds to go to local configuration  221 . 
     As is illustrated in FIG. 11, if the system has gone into executive  223  mode, the system will again inquire as to whether the I 2 C is busy  225 . If the response to this inquiry is “YES,” the system will continue to inquire as to whether the I 2 C bus is still busy  227 . As long as the response to this inquiry is “YES,” the inquiry continues. If the response to the inquiry as to whether the I 2 C bus is still busy  227  is “NO,” then the system will go to cold  229  and resume from the cold start  201  as shown in FIG.  10 . If, however, on inquiry as to whether I 2 C is busy  225  the response is “NO,” the system proceeds to display delay time  231  on the display  41  and will turn on hold annunciator light  233  which is an indication to the caregiver that there is no weight on the mat used to monitor the patient&#39;s presence. The system then inquires as to whether it is time to log (step  235  ). In the preferred embodiment, every six minutes or {fraction (1/10)}th of an hour the system will log the lapse of an increment so as to maintain a record of total hours of use of the monitor. If six minutes have not elapsed, the response to the inquiry is “NO” and the system proceeds to inquire as to whether the delay adjust switch is pressed  237 . If six minutes have elapsed, the response to the inquiry as to whether it is time to log  235  is “YES” and the system will proceed to call data logger  239  so as to register this increment. The system then continues to the delay adjust switch pressed inquiry  237  until another six minute interval has elapsed and the call data logger  239  is again cycled. If the response to the inquiry as to whether the delay adjust switch is pressed  237  is “NO,” the system proceeds to inquire as to whether the mat is pressed  241 . If the response to the inquiry as to whether the delay adjust switch is pressed  237  is “YES,” the system proceeds to increment delay  243  by stepping to the next of the nine increments available for delay as hereinbefore discussed and then inquires as to whether the mat is pressed  241 . If the response to the mat pressed inquiry  241  is “NO,” the system will recycle to the time to log inquiry  235  and continue the process until the response to the mat pressed inquiry  241  is “YES,” indicating that a patient is on the sensing mat. If the response to this inquiry is “YES,” the system then proceeds to go to hold delay  245 . 
     Turning now to FIG. 12, representing the transient condition between the hold mode  201  and the monitor mode  273 , when the monitor is at hold delay  247 , the system will initialize hold timer to program value  249 . Generally, the hold timer will permit selection by the caregiver of from 1 to 20 seconds as the interval that the patient&#39;s weight must be on the sensing mat before monitoring of the patient&#39;s presence is initiated. In the preferred embodiment described herein, this available time interval is in a range of 1 to 9 seconds. The system then proceeds to initialize flasher timer  251 . The flasher timer establishes the flash interval for the attenuator indicating that a patient&#39;s weight is on the sensing mat. With the timers initialized, the system proceeds to get keys  253  by examining the switches  53  and  55  of the keypad  45 . Inquiry is first made as to whether the caregiver has operated the delay adjust  255 . A “YES” response indicating that the delay adjust switch  55  is depressed will result in an increment change  257 . If the response to the delay adjust inquiry  255  is “NO” or the increment change  257  is made, the system continues on to inquire as to whether the reset is pressed  259 . If the response to this inquiry is “NO,” the system proceeds to inquire as to whether the hold time is expired  261 . If the response to this inquiry is “NO,” the system inquires as to whether the flash time has expired  263 . If the flash time has expired, providing a YES response, the system will toggle the hold light and reset the timer  265 . If the flash time has not expired or has been reset, the system will proceed to inquire as to whether there is a weight on the mat  267 . If the response to this inquiry is “NO,” the system will go to executive  219 , returning to the loop illustrated in FIG.  11 . If the response to the weight on mat inquiry  267  is “YES,” the system will perform a pullout check  269  to determine if there is an improper connection in the system. After performing the pullout check  269 , the system will return to the get keys step  253  of the hold delay loop  247 . If, in the operation of the hold delay loop  247 , the response to the reset pressed inquiry  259  or the hold time expired inquiry  261  is “YES,” then the system will go to monitor  271 , as will hereinafter be described. 
     The HOLD mode  235  is characterized by a continuous hold indicator  47  and the number of seconds of delay time is displayed on the numeric display  41 . The nurse call relay K 1  is energized (non-alarming state). There is no testing of the sensor validation input, there is no pull-out detection, and the keypad  45  is monitored at least 20 times per second except during tone generation. Upon pressing the delay adjust button  55 , the delay is bumped by one second and the display  41  is updated with the new delay time. After nine seconds, the delay time resets to one second. If the reset button  53  is pressed, a ½ second tone at 1 kHz is generated. Software exits this loop and enters the pre-monitor phase of the monitor mode MON when weight is detected on the mat (IRQ goes low). During the hold mode HOLD, logging of hours in use occurs every {fraction (1/10)}th of an hour (six minutes). 
     The main monitor routine is illustrated in FIG.  13 . When the system goes to monitor  273 , it will change the annunciator condition by turning on MON and turning off HOLD  275 . Thus, the HOLD annunciator  47  will be de-energized and the monitor annunciator  49  energized. The system will then inquire as to whether it is time to log  277 , as has been hereinbefore explained. If the response to this inquiry is “YES,” then the system will call data logger  279  to log the expiration of the six minute increment. If the answer to the inquiry as to time to log  277  is “NO,” or if an increment has been logged, the system will proceed to a get keys status  281 . The system will inquire as to whether the delay adjust switch is pressed  283 . If the response to this inquiry is “YES,” an increment change  285  will be made in the time delay. If the response to the delay adjust inquiry  283  is “NO” or the increment change  285  has been made, the system will proceed to inquire as to whether the reset is pressed  287 . If the response to this inquiry is “YES,” the system will go to executive  289  and perform the loop illustrated in FIG.  11 . If the response to the reset pressed inquiry  287  is “NO,” the system will proceed to call pull-out  291  to determine whether there is an electrical connection failure in the system. The system then inquires as to whether there is a weight on the mat  293 . If the response to this inquiry is “YES,” the system will return to the time to log step  277  of the monitor loop  273 . If the response to the inquiry as to weight on the mat  293  is “NO,” the system will proceed to go to alarm  295 . 
     The monitor mode  273  has a transient pre-monitor phase shown in FIG. 12 and a steady-state monitor phase shown in FIG.  13 . The pre-monitor state is characterized by a flashing hold indicator  47 . The LED flash period is 0.2 seconds on and 0.2 seconds off. During the pre-monitor phase, the nurse call relay K 1  is energized (non-alarming state), nurse call pull-out protection is active, the sensor input is validated, the numeric display  41  continues to display delay time, and the keypad  45  is polled at least 20 times per second. If the software detects an improperly inserted nurse call connector, a tone will be generated, preferably sixteen cycles of 400 Hz followed by 42 msec of silence, repeated four times, followed by a minimum of 320 msec of silence before repeating the entire process. Pressing the delay adjust button  55  will increment the delay time one second up to a maximum of nine seconds. The delay time then resets to one second. The numeric display  41  is updated with each change in the delay time. Pressing the reset button  53  will cause the monitor to immediately proceed to the monitor phase  273 . This mode expires after a programmable hold time. The hold time defaults to ten seconds but may be programmed by the user for any time from 1 to 10 seconds. Upon expiration of the hold time or upon pressing the reset button  53 , the software advances to the monitor phase  273 . The software will return to the hold mode  247  if weight is removed from the mat prior to entering the monitor phase  273 . 
     The monitor phase of the monitor mode  273  is characterized by a solid monitor status indicator  49 . During this phase, the sensor is monitored for weight on mat, the nurse call relay K 1  is energized (non-alarming state), nurse call pull-out protection is active, the numeric display  41  continues to display the delay time, and the keypad  45  is polled at least 20 times per second. If an improperly inserted nurse call cord is detected, the unit will sound an alarm as described in the pre-monitor phase. Pressing the delay adjust button  55  will advance the delay time one second up to a maximum of nine seconds. The delay time then resets to one second. The numeric display  41  is updated with each change in the delay time. Pressing the reset button  53  will return the software to the hold mode  247 , allowing removal of the patient from the bed. Since there must be weight on the mat to be in this mode  247 , the hold mode  247  will automatically advance to the pre-monitor phase of the monitor mode  273 . To improve functionality, the hold time will temporarily be set to 25 seconds when this path is taken to allow sufficient time to remove the patient from bed. If weight is removed from the mat, the software advances to the pre-alarm phase of the alarm mode  302 . That parameter “hours in use” is logged/incremented every {fraction (1/10)}th of an hour. 
     The alarm mode  301  illustrated in FIG. 14 consists of a transient re-alarm phase and a steady state alarm phase. The pre-alarm phase is characterized by a flashing alarm indicator  51 . The flash period is 0.2 seconds on and 0.2 seconds off. During the pre-alarm phase the nurse call relay K 1  is energized (non-alarming state), the mat input is monitored, and the keypad  41  is polled at least 20 times per second. Returning weight to the mat will cause the software to return to the monitor mode  273 . Pressing the delay adjust button  55  has no effect. Pressing the reset button  53  will return the software to the hold mode  247 . Since this mode  247  is only active with weight off the mat, the monitor will remain in hold upon returning to the hold mode  247 . This mode  247  expires after the number of seconds displayed in the numeric display  41  and then enters the alarm phase. 
     The alarm phase of the alarm mode  301  is characterized by a solid ALARM indicator  51  and an audible alarm. During this mode the nurse call relay K 1  is operated in accordance with a pre-programmed protocol and the keypad  41  is polled at least 20 times per second. Pressing the delay adjust button  55  has no effect. The audible alarm will continue to sound until the reset button  53  is pressed, returning the unit to the hold mode  247 . The alarm preferably provides one of six possible user selectable alarms (see, for example,  329  ) including a 1 kHz beep in intervals of 0.5 seconds on and 0.5 seconds off, a 1 kHz beep in intervals of 0.25 seconds on and 0.25 seconds off, a 1 kHz beep in intervals of 1 second on and 1 second off, 16 cycles at 400 Hz followed by 18 cycles at 440 Hz repeated 12 times followed by one second of silence, a rising whoop or a stepped alarm providing four alarms at 320 Hz in intervals of 28 cycles and 28 cycles off, four alarms at 392 Hz in intervals of 32 cycles on and 32 cycles off, four alarms at 277 Hz intervals of 24 cycles on and 24 cycles off with ½ second of silence. It is also possible to have no audible alarm. The nurse call relay K 1  has three possible operating modes to accommodate various nurse call systems including continuous closure, one-shot and asynchronous  331 . At the termination of the ALARM mode  301 , the response time is written to the EEPROM  101 , the stored number of alarms is bumped by one and rewritten to the EEPROM  101  and the current response time is added to the total alarm time and the EEPROM  101  is updated with the new value. 
     In the alarm mode  301  the system will initialize flash timer  303  and change the annunciator status to turn on alarm and turn off HOLD  305 . The system then inquires as to whether reset is pressed  307  and, if the response to this inquiry is “YES,” the system will go to executive  309  and repeat the executive loop  223  illustrated in FIG.  11 . If the response to this inquiry is “NO,” the system will proceed to inquire as to whether the flash timer has expired  311 . If the response to this inquiry is “YES,” the system will toggle the alarm light  313  and reset the timer  315 . If the response to the flash timer expired inquiry  311  is “NO” or the timer is reset  315 , the system will proceed to inquire as to whether there is weight on mat  317 . If the response to this inquiry is “YES,” the system will go to monitor  319  and repeat the monitor loop  273  illustrated in FIG.  13 . If the response to the weight on mat inquiry  317  is “NO,” the system will inquire as to whether the delay timer expired  321 . In this step, the system determines whether the time selected by the caretaker to elapse after weight has left the mat and before weight has returned to the mat has expired. If the response to this delay time expired inquiry  321  is “NO,” the system will return to the reset pressed inquiry  307  of the alarm loop  301 . If the response to the delay timer expired inquiry  321  is “YES,” the system proceeds to loop A  323  of the alarm mode illustrated in FIG. 15 to provide the audio alarm. In this phase of the alarm mode  301 , the system will set the volume  325  and initialize the alarm variables  327  established by the caregiver for the system. The system then dispatches for selected tone  329 , causing the monitor to give the audio tone selected from the six audio tones available to the caregiver. The system will also exercise relay per selected option  331 , causing the nurse call station relay K 1  to function according to one of the four alternatives selected by the caregiver for the system. The system will next inquire as to whether the reset is pressed  333 . If the reset button  53  has not been operated by the caregiver, the response to the inquiry is “NO” and the system will return to the dispatch for selected tone  329  step of the alarm loop  301  and continue to provide the selected audio alarm. If the response to the reset press inquiry  333  is “YES,” the system will bump event counter, save response time and total response  335  in which the system makes a record of the responses and response times of the caregiver. When this has been completed, the system will go to executive  337  and return to the executive loop  223  illustrated in FIG.  11 . 
     The local configuration or program mode  341  provides the user with a means to select various user options and save these selections in the non-volatile memory  131 . To enter this mode  341 , the delay time is set to nine seconds. The monitor is then powered down. The monitor then is re-powered up with the reset button  53  pressed. The software will then illuminate multiple annunciators to indicate the particular phase of the programming mode  341  which has been entered. There are four phases of the program mode  341  including tone select, relay action &amp; pull-out detection enable, hold time select and volume adjust. The tone select phase will display the last tone selected in the numeric display  41 . A new tone may be chosen by cycling through the available options with the delay adjust button  55 . Preferably, the default for the first time to apply power is the 1 kHz beep at 0.5 second intervals mentioned above. The relay action phase will display the current relay action in the numeric display  41 . A different action may be chosen by cycling through the available options with the delay adjust button  55 . The default for the first time to apply power is continuous operation. The available relay options are discussed above in relation to the alarm mode  301 . Programming to a three will disable the pull-out detection. This allows the unit to be used in facilities which do not have a nurse call system or choose not to connect to the nurse call system. Programming this to a zero, one, or two enables the pull-out detection. The hold time phase allows the user to adjust the time delay between a patient placing weight on the mat and the beginning of monitoring. The default is preferably 10 seconds. The user may select 1 to 10 seconds. A zero in the numeric display  41  represents 10 seconds. The volume adjust allows the user to select one of ten possible volume levels. The alarm is silent when set to zero and at full volume when set to nine. The software translates 1 through 9 into actual steps (0-31) of the wiper control VW of the programmable volume control  71 . When programmed from the external interface, all 32 steps are available. The default volume is seven (numeric displayed value) which translates to a wiper position of 25. For all of the above, a value is accepted and the next phase is entered by pressing the reset button  53 . After the programming of the volume control  71 , the monitor enters the hold mode  247 . If power is removed during the programming process, the new values up to the last time reset  53  was pressed will be saved. 
     In the local configuration loop  341 , the system will first turn on hold, monitor and alarm lights, load tone selection and output to numeric display  343 . The system then proceeds to get keys  345  as earlier discussed with respect to other system loops, inquiring as to whether the delay adjust is pressed  347 . If the response to this inquiry is “YES,” the system will increment the toning selection  349  and then inquire as to whether the tone is greater than five  351 . This relates to the sequence of six tones earlier referenced in relation to the alarm mode  301 . If the response to this inquiry  351  is “YES,” the system will reset the alarm mode to zero  353 . If, after incrementing tone selection  349  the tone is not greater than five  351  or is set to zero  353 , the system returns to the turn-on hold, monitor and alarm lights, load current tone selection and output numeric display step  343 . If the response to the delay adjust pressed inquiry  347  is “NO,” the system next inquires as to whether the reset is pressed  355 . If the answer to this inquiry  349  is “NO,” the system returns to the get keys step  345 . If the response to this inquiry  349  is “YES,” the system will save tone to EEPROM  357 . When the tone has been saved in EEPROM  101 , the system will , beep  359  to indicate this status. The system will then turn off alarm light, load current relay action and output to numeric display  361  and again proceed to get keys  363 . The system again inquires as to whether the delay adjust is pressed  365 . If the response to this inquiry  365  is “YES,” the system will increment relay action  367  according to the sequence discussed in relation to the alarm mode  301 . The system will inquire as to whether the relay is greater than three  369 , determining which increment of the relay options the system will select. If the response to this inquiry  369  is “YES,” indicating that the option will be greater than three, the system sets to zero  371  to begin a recycle of available selections. If the answer to the inquiry  369  is “NO” or if the selection is set to zero  371 , the system returns to the turn off alarm light, load current relay action and output to numeric display step  361 . If the response to the delay adjust pressed inquiry  365  is “NO” the system proceeds to inquire as to whether the reset is pressed  373 . If the answer to this inquiry is “NO,” the system returns to the get keys step  363 . If the answer to this inquiry is “YES,” the system proceeds to point B  375  of FIGS. 16 and 17. Looking at FIG. 17, if the reset pressed inquiry  373  response is “YES,” the system will save relay to EEPROM  377 , storing the selected relay position in the EEPROM  101 . The system then proceeds to beep  379  to advise the caregiver of the status. The system then turns on the alarm annunciator, turns off the monitor annunciator, loads the current hold time and outputs to numeric display  381 . The system then again proceeds to get keys  383 , first inquiring as to whether the delay adjust is pressed  385 . If the response to this inquiry is “YES,” the system will increment hold time  387 . Inquiry is made as to whether the hold is greater than nine  389  and if the response to this inquiry is “YES,” the system will set to zero  391 . If the response to the inquiry  389  is “NO,” or the system has been set to zero  391 , the system will return to the turn-on alarm enunciator, turn-off monitor enunciator, load current hold time and output numeric display  381 . If the response to the delay adjust pressed inquiry  385  is “NO,” the system will then inquire as to whether the reset is pressed  393 . If the response to this inquiry is “NO,” the system returns to the delay adjust pressed inquiry  385 . If the response to the inquiry  393  is “YES,” the system will save hold time to EEPROM  395 , storing the selected delay time in the EEPROM  101 . The system will then provide a beep  397  to indicate the status and will then turn off the HOLD annunciator, turn on monitor annunciator, load, e.g., 7 as the volume and output to the numeric display  399 . That is, of the ten volume increments selectable, the system will automatically proceed to the seventh increment level. The system then proceeds through point C  401  as illustrated in FIG. 18 to get keys  403  and inquire as to whether the delay adjust is pressed  405 . If the response to this inquiry  405  is “YES,” the system will increment volume  407  and inquire whether the volume is greater than nine  409 . If the response to this inquiry  409  is “YES,” the system will reset volume to zero  411 . If the response to the volume greater than nine  409  is “NO,” or the system has set the volume to zero  411 , the system then returns through point D  413  to turn-off HOLD annunciator, turn-on monitor annunciator, load 7 as volume and output to numeric display  399  as shown in FIG.  17 . Returning to FIG. 18, if the response to the delay adjust pressed inquiry  405  is “NO,” the system proceeds to inquire as to whether the reset is pressed  415 . If the response to this inquiry  415  is “NO,” the system returns to the get key step  403 . If the response to the inquiry  415  is “YES,” the system proceeds to look up actual volume  417 . The system then writes the volume to EEPROM  419 , storing the selected volume in the EEPROM  101 , and then goes to cold  421 , returning to the cold start  201  illustrated in FIG.  10 . 
     The data logger subroutine  431  illustrated in FIG. 19 is used by the system at the call data logger steps  239  and  279  of the executive loop  223  illustrated in FIG.  11  and the monitor mode  273  illustrated in FIG. 13, respectively. In the data logger sub routine  431 , the system will read hours from RAM  433  and write hours to EEPROM  435 , storing the number of hours that the system has operated in EEPROM  101 . The system will then read minutes from RAM  437  and write minutes to EEPROM  439  to store any portion of an hour not already stored in EEPROM  101 . The system will then reset 0.1 hour timer  441  and return  443  to the routine making the data logger demand. 
     The pull-out protection sub routine  451  illustrated in FIG. 20 is used by the system at the call pull-out steps  269  and  291  of the hold delay mode  247  illustrated in FIG.  12  and the monitor mode  273  illustrated in FIG. 13, respectively. In the pull-out protection subroutine  451 , the system will read the output Q 6  of the latch and read the status of Bit  2  of Port B  455 . The system will then inquire as to whether PB 2  is high  457 . If the response to this inquiry is “NO,” the system will sound alarm  459  and return  461  to the pull-out protection step  451 . If the response to this inquiry is “YES,” the system will proceed to return  461  to the routine making the pullout protection demand without sounding the alarm. 
     In summary, the monitor will preferably conform to the following specifications: 
     
       
         
               
               
               
               
               
             
           
               
                   
               
               
                 Specification 
                 Min: 
                 Max: 
                 Units 
                 Tolerance 
               
               
                   
               
             
             
               
                 Delay Time 
                 1 
                 10  
                 seconds 
                 +/−5% 
               
               
                 Hold Time 
                 1 
                 10  
                 seconds 
                 +/−5% 
               
               
                 Relay One-shot Duration 
                   0.5 
                 5 
                 seconds 
                 n/a 
               
               
                 Relay Asynchronous On 
                   0.25 
                 2 
                 seconds 
                 n/a 
               
               
                 Relay Asynchronous Off 
                   0.25 
                 2 
                 seconds 
                 n/a 
               
               
                 Tone Programming 
                 0 
                 7 
                 n/a 
                 n/a 
               
               
                 Relay Programming 
                 0 
                 2 
                 n/a 
                 n/a 
               
               
                 Pull-out Programming 
                 0 
                 1 
                 n/a 
                 n/a 
               
               
                 Hold Time Programming 
                 0 
                 9 
                 n/a 
                 n/a 
               
               
                 Warning Frequencies 
                 n/a 
                 n/a 
                 Hertz 
                  +/−10% 
               
               
                 Tone Durations 
                 n/a 
                 n/a 
                 seconds 
                  +/−10% 
               
               
                   
               
             
          
         
       
     
     Microprocessor-Based Monitor with a Modifiable Personality 
     According to a second aspect of the instant invention, there is provided a microprocessor based monitor substantially as described above, but wherein the software that controls the actions of the monitor is stored within modifiable nonvolatile memory (e.g., flash-RAM) within the device, so as to be modifiable to create a patient monitor that has different personalities, depending on the needs of a particular application. More specifically, it is contemplated that much, if not all, of the software illustrated in FIGS. 10 to  20 —the software that controls the personality/functionality of the unit—will be stored within the monitor in a form that can be modified to suit the requirements of any site or individual patient (per doctor&#39;s orders) and, more particularly, the needs of the particular nurse call station to which the monitor is connected. 
     Turning first to FIG. 21 wherein the general environment of the instant invention is broadly illustrated, in the preferred embodiment the reprogrammable monitor  550  is connected to sensing mat  500  by way of an RJ-11 connector  525 . As has been discussed previously, the RJ-11 connector  525  provides the internal microprocessor  10  access to the state of the patient detector circuit within the mat  500 . During normal operations, power line  565  would be plugged into monitor  550  to provide a source of external power to the unit. However, FIG. 21 illustrates the preferred configuration of the monitor  500  and a interconnected computer host  570  during exchange of information. Interface unit  560  is designed to act as a data conduit and pass serial information along line  580  from the host computer  570  to the monitor  550  and back again on demand from the host  570  or monitor  550 . Additionally, the instant interconnection incorporates a power line into the serial line  590  for use by the monitor  550  during programming. It is not essential that the power be incorporated into the interconnecting line  590 , but it is part of the presently preferred embodiment that it be so designed. In the event that a source of power is not needed via line  590 , that line could take the form of a simple parallel serial, USB, etc. cable and interface unit  560  could then be a standard computer port (serial, parallel, etc.). Additionally, it should be noted that, although the interface unit  560  is pictured as being a separate device that is external to both the monitor  550  and the host  570 , it might easily be incorporated into one unit, or the other, or both. 
     In the preferred embodiment, the lines  580  and  590  that interconnect the host computer  570  and electronic monitor  550  are serial lines, and the data communications protocol used is the I 2 C standard. However, those skilled in the art will recognize that there are many other standard and non-standard communications protocols that could be used in the alternative. For example, the instant inventors specifically contemplate that the interconnecting communications lines ( 580  and  590 ) could be parallel cables. Further, it might prove to be desirable in some cases to put a separate data port on the monitor  550  which might be, for example, a serial or parallel connector and which is dedicated for use in communications with a host computer  570 , i.e., it does not share the responsibility of conveying power to the unit during data transfer. Finally, it specifically contemplated by the inventors that it would even be possible to communicate with a remotely positioned monitor  550  through nurse call interface  130  (FIG.  1 ), thereby eliminating the need to physically bring together the host computer  570  and monitor  550 , it being well within the capability of one of ordinary skill in the art to modify the invention-as-disclosed to implement this variation. 
     Within the monitor  550  and as is illustrated in FIG. 22, data sent from the host computer  570  are received by the CPU  620  of the microprocessor  10  and then subsequently stored, preferably within a local flash RAM  610 . As is well known to those skilled in the art, many other similar arrangements might be used instead that would be functionally equivalent to using flash RAM, including using conventional RAM with battery backup, EEPROM ; a local disk drive, etc, the key feature being that—what ever type of storage is used—it should be at least relatively nonvolatile for purposes of the instant embodiment and, most importantly, modifiable under local program control. Thus, in the text that follows the phase “modifiable nonvolatile RAM” will be used in the broadest sense to refer to the type of storage just described. Additionally, it is anticipated that CPU  620  will be provided with some amount of ROM  130  or other storage type for permanently storing information and which could contain, for example, the serial number of the unit, date of manufacture, and the code that would control the basic operations of the CPU  10  during cold starts, resets, personality uploads, etc. 
     During operation, the monitor  550  could use the flash RAM  620  as storage for various data parameter values including accumulated performance statistics, data/time stamps of alarm events, patient identification numbers, hold delay, delay time, speaker volume, type of alarm tone (i.e., what sort of alarm will be sounded—e.g., fast beep, slow beep, whoop, etc.), relay action type (e.g., continuous, one-shot, asynchronous, etc.), total time in service, date of last bio-med check,total number of alarms sounded, response time to last alarm, average response to last four alarms, alarm history (e.g., response times for the last fifteen or so alarms and time/date of alarm occurrence), repair history, hospital equipment identification number (e.g., asset number), or a current time/date stamp. Additionally, this same connection could be used to read parameters from the monitor  550  such as total time in service ; date of last biomedical check, the unit serial number, etc. 
     However, the main anticipated use for the flash RAM  620  is for storage of the operating personality of the unit. In particular, FIGS. 10 to  20  discussed previously are implemented within the monitor in the form of assembly language computer instructions which are stored in and read from ROM memory  130 , thereby making those program steps immutable, unless the memory chip containing them is replaced. In the instant embodiment, it is anticipated that much of the functionality of the software illustrated in those figures would be stored in a form that can be modified to suit the requirements of a particular nurse call station, or hospital environment, e.g., within flash RAM  620 . 
     As is broadly illustrated in FIG. 23, the personality loading program  700  within the a monitor  550  is preferably initiated through the use of a non-maskable interrupt  705  (defined as a “master mode” interrupt) as is provided for by the I 2 C communications standards. In more particular, when the CPU  610  senses an interrupt on the pins associated with port  593 , it preferably enters a slave mode, wherein the host computer  570  completely controls its operations. The host computer  570  then directs the monitor CPU  610  to begin receiving “data”  715  and storing that data  725  at predetermined locations within the flash RAM  620 , which data may be parameter values as discussed previously or, preferably, binary computer instructions that define the personality/operations of the unit. 
     At the conclusion of the loading process, the host computer will preferably require the monitor to execute a cold start  735 , after which the monitor will continue execution as before, only this time using the various aspects of the new personality stored  740  in flash-RAM. Of course, the obvious advantage of an arrangement such as this is that it permits the functionality of the monitor to be modified to suit specific applications and, indeed, makes it possible for a single monitor to function with multiple nurse call station formats with only minimal effort. 
     System for Programming a Reprogrammable Monitor 
     According to still a further aspect of the instant invention, there is provided a monitor/host software combination that allows the end-user to make personality changes in the software that controls the monitor. Additionally, this same system provides a means for the user to read and/or modify data values that are maintained in the nonvolatile memory of the patient monitor. In the preferred embodiment, the software that manages the user interface would run on a host computer  570  such as a lap top computer. As is well known to those skilled in the art, the software embodying the instant invention might be conveyed into the computer that is to execute it by way of any number of devices  571  including, for example, a floppy disk, a magnetic disk, a magnetic tape, a magneto-optical disk, an optical disk, a CD-ROM, flash RAM, a ROM card, a DVD disk, or loaded over a network. 
     As is broadly illustrated in FIGS. 21 through 23 and as has been discussed previously, a preferred embodiment of the instant invention uses a host computer  570  to load operating parameters and executable instructions into the monitor. Additionally, this same connection is used to retrieve statistical and other information from the monitor. Further, cumulative statistical values such as total time spent in an alarm condition, alarm history, etc., can -be reset (e.g., made equal to zero) by this same process. 
     As is illustrated in FIG. 24, the host control program for parameter and operating statistics recall  800  preferably begins by generating a non-maskable interrupt  805  which results in monitor  550  passing operating control to the host computer  570 . The host computer  570  then instructs the monitor CPU  610  to pass the contents of specific memory locations (steps  815  to  830 ) back to itself. The data returned from the monitor  550  are then presented to the user for review. Needless to say, once the data have been collected additional analysis of the resulting information would certainly be useful in some situations and that additional step has been specifically contemplated by the instant inventors. 
     Conclusions 
     Although the preceding text has occasionally referred to the electronic monitor of the instant invention as a “bed” monitor, that was for purposes of specificity only and not out of any intention to limit the instant invention to that one application. In fact, the potential range of uses of this invention is much broader than bed-monitoring alone and might include, for example, use with a chair monitor, a toilet monitor, or other patient monitor, each of which is configurable as a binary switch, a binary switch being one that is capable of sensing at least two conditions and responding to same via distinct electronic signals. In the preferred embodiment, those two embodiment, other types of switches could work as well for some applications. Additionally, it should be noted that the use of the term “binary” is not intended to limit the instant invention to use only with sensors that can send only two signal types. Instead, binary switch will be used herein in its broadest sense to refer to any sort sensor that can be utilized to discern whether a patient is present or not, even if that sensor can generate a multitude of different of signals. 
     Thus, it is apparent that there has been provided, in accordance with the invention, a monitor and method of operation of the monitor that fully satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art and in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit of the appended claims.