Abstract:
An emergency signaling system with integrated load management functionality is provided wherein the load management circuitry is alternatively operable in programming and operating modes. The system includes a keypad, control head, control unit and a plurality of signaling features selectively activated by the control unit in the operating mode. The load management circuitry automatically sheds loads from the signaling system in response to an indication from the electrical system powering the signaling system that an energy drain is occurring at the energy source that will cause disruption to other more important systems—e.g., the ignition system in a vehicle.

Description:
TECHNICAL FIELD OF THE INVENTION AND CROSS REFERENCE TO RELATED PATENT 
     The invention relates to the load management of accessories for emergency vehicles such as police cars, fire engines, ambulances and the like. 
     In the following description of the load management system of the invention, an exemplary emergency signaling system is described as part of the illustrated embodiment of the invention. This emergency signaling system is more completely described in U.S. Pat. No. 5,296,840, which is assigned to the same assignee as the present invention. U.S. Pat. No. 5,296,840 (hereinafter “the &#39;840 patent”) is incorporated herein by reference. 
     The reader should appreciate, however, that the invention is applicable to any accessory system of a vehicle. Those familiar with the products of the assignee Federal Signal Corporation will recognize the exemplary emergency signaling device described herein and described in the &#39;840 patent to be Federal Signal&#39;s SS2000 Smart Siren® system. The load management system of the invention has been implemented in circuitry and software that is an extension of the hardware and software in the existing SS2000 product. Thus, in some instances particular aspects of the implementation of the invention described herein have been primarily determined by the desire to not change the architecture of the existing product. As a result, a unique communication format was designed to provide data transfer between battery electrical load sensing and microcontroller operation. 
    
    
     BACKGROUND 
     There exist programmable signaling mechanisms, such as the Smart Siren® system marketed by Federal Signal Corporation, and disclosed in U.S. Pat. No. 5,296,840. The Smart Siren® system allows a user to selectively program desired signaling features, such as various lights and sirens, to activate in each of a number of user selectable modes. For instance, a user may use the Smart Siren® system keypad to program the vehicle&#39;s flashing lights to activate in a first mode, whereas in a second mode, additional lights are activated and in a third mode a siren is activated. In the Smart Siren®, a slide switch is provided to allow the user to quickly switch between modes. In addition to programming the desired signaling in each mode, the nature of the siren tone is also programmable through the same input keypad. For example, the siren tone may be programmed to be a yelp, wail, or air horn sound. Because of this programmability, this system has greatly reduced the workload on operators of emergency vehicles. 
     It is also known to provide a load shedding device to manage electrical loads in a vehicle. Existing load shedding devices may be placed in a vehicle and appropriately configured via dip switches or otherwise to provide a desired load shedding function. For example, such a device may measure vehicle battery voltage, and sequentially disable electrical loads, such as various lights, until the vehicle charging system is able to meet the electrical demands of the vehicle. 
     Users of emergency vehicles may desire to have both a smart signaling system such as the Smart Siren® and load shedding functionality on one vehicle. In such cases, the user has traditionally had to install two separate systems and user inputs. For example, a dash-mounted console is installed to operate the Smart Siren® system, while an additional dash-mounted console is required for the load manager. In addition, the load manager relay board must also be installed in the vehicle. These two systems are completely independent, must operate independently, and are independently programmed. This creates difficulties for users in that programming of both systems takes more time and is more complex due to the necessity of interacting with multiple user inputs. In addition, redundancy of parts, functions, and wiring in the two systems causes the price of such separate systems to be prohibitive for many applications. Also, the overall reliability and performance of such a system is compromised due to the complex wiring schemes involved in the installation. 
     An emergency signaling device is needed whereby the load managed enabling and disabling of external functionality, such as lights, and the provision of specific signal content, such as siren tone, are provided centrally through a consistent interface in a user-friendly and cost-effective manner. 
     SUMMARY OF THE INVENTION 
     The present invention solves the problems associated with the prior art by providing an integrated programmable siren control system and programmable load management system for use in emergency vehicles, wherein the integrated system may operate in either a programming or operating mode. The integrated system includes a control head with keypad, and a control unit. In the operating mode, portions of the keypad are usable to selectively enable various signaling devices. 
     The load management feature automatically causes the shedding of electrical loads in a pre-programmed sequential manner when it detects that the vehicle battery voltage is lower than certain threshold levels, and that the vehicle is in a PARK condition. This ensures that more critical electrical systems, such as vehicle engine ignition and radio functionality, remain uncompromised. The integrated functions are programmable from a centralized location readily accessible to the vehicle operator, avoiding the need to control functions from separate locations through separate user inputs. 
     In addition to managing these relay outputs, the load manager also controls the fast idle of the vehicle in low-battery situations as an initial attempt to prevent draining of the battery by the loads of the emergency system. Loads are shed in response to a low-battery-voltage condition if the fast idle condition does not stop the deterioration of the battery voltage. An audible beep may be generated each time a load is turned off. All previously shed loads will be restored at 0.5 seconds interval with reversed sequence as they were shed when the vehicle shifts out of PARK. 
     Battery voltages above the reference point will not restore previously shed loads. Only after the PARK has been released and engaged again will the load manager be reset. This portion of the load manager for a specific load can also be turned off through programming to prevent load shedding under certain operational conditions. 
     As soon as the vehicle shifts out of PARK, the HIGH IDLE output will be turned off immediately. HIGH IDLE will also be turned off if the battery voltage returns to a user-programmable point above the reference voltage (e.g. 13.8V). 
     Other objects and advantages will become apparent upon reference to the following detailed description when taken in conjunction with the drawings. 
     While the invention will be described in connection with a preferred embodiment, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications, and equivalents falling within the spirit and scope of the invention as defined by the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevated perspective view of an emergency vehicle incorporating a signaling/load management system according to the invention, where the standard vehicle construction is shown in broken lines in order to highlight the system; 
     FIG. 2A is a schematic diagram of the signaling/load management system of FIG. 1, illustrating the load management function incorporated into a control unit that is programmable by way of a control head preferably mounted at a location convenient to a driver of the vehicle shown in FIG. 1; 
     FIG. 2B is a perspective view of the control head of the signaling/load management system including a keypad for programming and operating the system in keeping with the invention; 
     FIG. 3A is a schematic diagram of the control unit for the signaling/load management system of the invention, which illustrates the voltage sensing circuitry that measures battery voltage and provides the measurement to a microprocessor of the control unit for the purpose of managing the emergency loads placed on the power system of the vehicle; 
     FIG. 3B is a circuit diagram of the load management circuitry that is schematically illustrated in FIG. 3A; 
     FIG. 4 is a schematic diagram of the circuitry comprising the control head of the signaling/load management system; 
     FIG. 5 is a flow diagram of a program executed by the microcontroller of the control unit in response to an interrupt request generated by the load management circuitry for shedding loads in response to low voltage at the vehicle&#39;s battery; 
     FIG. 6 is a map relating the several programming modes of the signaling/load management system, including the mode for programming the load management function; and 
     FIGS. 7A,  7 B,  7 C and  7 D are four images of the panel of the control head illustrating a sequence of keystrokes that serve to program the load management circuitry so that its load shedding function can be tailored to the vehicle. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Those familiar with emergency signaling systems for vehicles will appreciate that such systems create a substantial load on the electrical system of a vehicle such as the vehicle  11  illustrated in FIG.  1 . The signaling/load management system described herein and shown in FIGS. 1-7 includes signaling devices which are illustrative only and intended merely to aid in explaining how the system manages loads placed on the electrical system of the vehicle  11  when the vehicle is operating under emergency conditions. More important to the invention is the cooperative operation and load management of the lights and siren of the emergency signaling devices on the vehicle by a single-processor system whose operational and load shedding characteristics are independently programmable from a single convenient location, as will be discussed. 
     Thus, the reference in this description to particular loads comprising emergency signals is not intended to limit the scope of the invention to the illustrated or similar systems. To the contrary, the invention is applicable to all systems that are intended to provide a comprehensive emergency signaling system for a vehicle. 
     In the following detailed description, the signaling system is described in general terms to provide a context for the description of the load management function. A complete detailed description of the emergency signaling functions can be found in the &#39;840 patent. 
     The exemplary signaling system illustrated in FIG. 1 is installed in a vehicle  11  shown in broken lines. The system includes a conventional light bar  13  that incorporates a speaker  15  and a plurality of lights. In such a light bar, the lights are typically arranged in three groups—i.e., flashing lights, rotator lights and other lights such as take-down and alley lights. In the illustrated light bar, two pairs of three (3) lights are arranged on both sides of the centrally located speaker  15 . Although actual light bar configurations of the system including flashing lights, rotators and beacons may be different than that illustrated, for convenience of reference and illustration, the inner light  17  or  17 ′ of each pair is considered herein to be a rotator, the central light  19  or  19 ′ is considered to be a flasher and the outer light  21  or  21 ′ is considered to be a beacon. 
     Control of the groups of lights  17 - 21 ,  17 ′- 21 ′ and the speaker  15  comprising the light bar  13  is provided by a control unit  23  and control head  25 . The control head  25  is mounted in the interior area of the vehicle  11 , preferably on the dashboard/instrument panel area  27  just to the right of the steering wheel  29  for easy access by the operator of the vehicle. Typically associated with the control head  25  is a two-way radio  31 . As is well known with respect to these types of signaling systems, the control unit  23  may rebroadcast radio signals over the speaker  15 , and a microphone  33  of the two-way radio may function as a microphone for a public address (PA) function implemented by the speaker  15 . Activation of either of these features is accomplished by way of keystrokes to a keypad  35  incorporated in the control head  25 . 
     The emergency signaling system may include other switches activated manually, or by the horn, and so on. Signals from these switches are received by the control unit  23 , which responds by controlling the operation of the light bar  13  and siren/speaker  15  in a predetermined manner. 
     Referring to FIGS. 2A and 2B, the control unit  23  of FIG. 1 receives power from a battery  43  of the vehicle by way of an ignition circuit  45  in a conventional manner. Because of the power requirements of the lights  17 - 21 ,  17 ′- 21 ′ of the light bar  13  of FIG. 1, they receive power from the battery  43  through a separate circuit that includes relays  119 , which are associated with the control unit  23  as illustrated in more detail in FIG.  3 B. 
     The control unit  23  is programmable by way of the keypad  35  of the control head  25  to provide a mechanism for modifying the manner in which the system manages its load on the vehicle&#39;s electrical system. Selected keystrokes to the keypad  35  place the control unit  23  into a programming mode wherein the load shedding characteristics of the system may be changed. In an installed system, the shedding function is tailored by first causing the control unit  23  to enter a program mode by way of keystrokes to the keypad  35  and then programming either or both of the load shedding sequence and the threshold voltages for the load management function, as will be described hereinafter. 
     Before describing the programming of the system in further detail, the operation of the system&#39;s load management function is described. For ease of understanding, the following description of the operation of the signaling/load management system is undertaken from the frame of reference of an operator. In other words, the operation will be described with respect to system responses to keystrokes to the keypad  35 . 
     Referring to the illustration of the control head  25  in FIG. 2B, when a slide switch  74  is in its “OFF” position, the control unit  23  assumes an idle mode condition, meaning the system is not operating the lights and speaker. Moving the slide switch  74  on the control head  25  to one of the positions marked “1”, “2” or “3” transfers the system from this idle mode to one of the operating modes. In an operating mode, the system may activate either the lights or the speaker or both. Also, a keystroke to the “RADIO” key  70  will transfer the system to a radio-rebroadcast mode. A second keystroke to any of these keys will return the system to the mode identified by the slide switch  74 . Referring to FIG. 2A, communications between the control head  25  and the control unit  23  is by way of hardwired serial communications lines  53 , one for transmitting and a second for receiving. 
     As mentioned, placing the slide switch  74  into any one of the positions “1”, “2” and “3” places the system into one of its signaling operating modes. Each of these operating modes is intended for particular types of emergency situations. Typically, the operating modes are configured to provide a range of signaling intensity. For example, operating mode  1  may provide low intensity signaling such as flashes only and no siren. Operating mode  2  may activate a more intense signaling configuration such as the simultaneous operation of the flashing lights and rotators. Operating mode  3  may activate the most intense signaling configuration, one that is usually used for pursuing a vehicle and similar extreme emergency situations. In operating mode  3 , the system may be configured to simultaneously operate the flashing lights  17 ,  17 ′, the rotators  19 ,  19 , the beacons  21 ,  21 ′ and the speaker  15 . The siren tone generated in operating mode  3  may be either a wail, yelp or high/low sound. Sounds in each of the modes are programmable via control head  25  as described in the &#39;840 patent. 
     Certain keys of the keypad  35  control auxiliary functions that may be activated in any of the operating modes or also in the “OFF” position of the slide switch  74 . Examples of auxiliary functions for these keys are as follows: “LEFT ALLEY” light  21 ; “RIGHT ALLEY” light  21 ′; and “TAKE-DOWN” light  21 ′. A keystroke to any of these keys will activate the associated auxiliary function. 
     Each of the control circuit  23  and the control head  25  of the signaling/load management system includes a microprocessor, preferably the MC68HC05C9, manufactured by Motorola, Inc. of Austin, Tex. The microprocessor  75  of the control unit  23  is illustrated in FIG.  3 A. It and the microprocessor  77  of the control head  25  (FIG. 4) are in a conventional master/slave configuration, where the microprocessor  75  of the control unit  23  is nominally the master. The program executed by the control unit&#39;s microprocessor  75  is stored in a ROM  79  internal to the microprocessor  75 . The programming of the signaling system is stored in an EPROM  81  that is connected to the SPI input of the microprocessor in a well-known manner. A listing of the program stored in the ROM  79  for controlling the emergency lights is contained in Appendix A of the &#39;840 patent. On the receive input (RDI) of each microprocessor  75  and  77 , an opto-isolator circuit  83  and  85 , respectively, protects the receive inputs by isolating them from the noise of the power and ground of the system. The transmit output (TDO) of each microprocessor  75  and  77  is associated with a buffer/inverting amplifier  87  and  89 , respectively. 
     One of three sources of audio signals may be provided to the speaker  15  via an analog switch  91  in response to control signals from the microprocessor  75 . The first source is one of the tone signals (i.e., peak-and-hold, yelp, wail, high/low, air horn) generated by the microprocessor  75  when the system is in operating mode  3  or when the appropriate one of the auxiliary functions is selected. The second source of audio signals for the speaker  15  is the microphone  33  for execution of the PA function. The third source is the output of the two-way radio  31  for execution of the radio rebroadcast function. The analog switch  91  is a commercially available device such as MC 14066B switch/multiplexer, manufactured by Motorola of Phoenix, Ariz. The particular audio source presented to the speaker  15  is determined by selective activation by the microprocessor  75  of the three control lines “SIREN”, “PA” or “RADIO.” In response to an active control line, one of the audio signals is passed from the inputs of the analog switch  91  to its output labeled “OUT.” 
     The bank of relays  119  of the control unit  23  is responsive to control signals generated on control lines  121  by the microprocessor  75  in response to keystrokes to the keypad  35  of the control head  25  and signals on the PARK/NEUTRAL/SAFETY line. Power to the relays  119  is provided directly from the battery  43  of the vehicle  11  in order to provide the needed power to the devices attached to the outputs  123  of the relays. The bank of relays  119  includes a latch and driver for each relay as described more fully in connection with FIG.  3 B. The control signals are strobed into the latch by way of a “STROBE” signal  124  from the microprocessor  75 . 
     The outputs  123  of the relays  119  provide selective power to the lights  17 - 21  and  17 ′- 21 ′ of the light bar  13 . The outputs may also control conventional gun lock and/or trunk release mechanisms. The control lines  121  are under program control and each of the control lines can be programmed in the program mode for tailoring various operating modes of the loads connected to the lines. Each control line is associated with a power circuit controlled by one of the relays  119 . One of the control lines  121  for example, may energize one of the relays  119  that completes the power circuit for the flashing lights  17  and  17 ′. Another one of the control lines  121  may energize one of the relays  119  that completes the power circuit for the rotators  19  and  19 ′. Another one of the control lines  121  may energize one of the relays  119  that completes the power circuit for the lights  21  and  21 ′. 
     Referring to FIG. 3B, in order to monitor the voltage at the battery  43 , an analog to digital converter (ADC) circuit  100  provides a digital signal to the microprocessor  75 . A zener diode  102  ensures that the voltage introduced to the measurement system is no more than its breakdown voltage, here about 27V. Diodes  104  and  106  provide a voltage drop of 1.4V taken together, while diode  108  provides a voltage drop of 8.2V. Thus, the battery voltage variations of interest, which cover the range of approximately 10 to 15 Volts, are mapped to a range of approximately 0 to 5 volts, an appropriate range matching the ADC input range of 0 to 5 volts. Temperature compensation is fortuitously accomplished by the pairing of diodes  106  and  108 , by virtue of the fact that temperature-induced variations in the performance of one diode will be offset by a similar change in the other, which is oriented with an opposite polarity. 
     A microcontroller  100  includes analog-to-digital conversion functionality and communicates with the main microprocessor  75  via a data bus  110  for controlling the relays. A programmable logic device (PLD)  112  serves as a latch for capturing control signals from the microprocessor  75  and for isolating the data bus so that battery voltage data from the ADC microcontroller  100  is not passed downstream to the relays  119 . The data bus  110  is multiplexed with signals that control the relays  119  and signals that describe the voltage at the battery  43 , briefly as follows: Microcontroller  100  takes control of bus  110  pursuant to a simulated “request to send” signal on line  114  to the interrupt input of microcontroller  100 , which also connects to the clock input of PLD  112 . The relay enablement data is latched to the right of PLD  112  by the rising edge of this signal, while the microcontroller  100  routine is triggered by the falling edge. Microcontroller  100  asserts a low value (CheckBit) on line  116  to control the bus  110  and disable the gate signal (G) of the PLD  112 . Lines  118  and  120  are then used to signal and send the actual digitized voltage data while microcontroller  100  controls the bus. 
     The generation of emergency sounds and other real-time signal processing on the data bus takes priority over communicating the battery voltage back to the microprocessor  75 . Moreover, the time required for the microprocessor  75  to communicate with peripherals should be as short as possible. The data bus  110  to the relays  119  operates in a parallel mode, which makes the time between successive signals to the relays relatively short compared to the time needed for a serial communication. 
     Noise level is controlled through several approaches. The power ground including relay coil is separated from signal ground. There are two significant considerations in splitting them. One consideration is the electrical current and the other consideration is coil inductance. The inductance (L) plus PCB inherent capacitance (C) forms resonant circuitry induces signal oscillations in some specific frequencies. This noise interferes with the lights, relays and communication bus lines. Separate ground lines solve the problem. 
     The slave microprocessor  77  of the control head  25  executes a program stored in a ROM  127  internal to the microprocessor as shown in FIG.  4 . Input ports “A” to the microprocessor  77  receive keystroke signals from the keypad  35 . The keypad  35  is laid out as a four-by-four matrix that is buffered by a conventional buffer  131  such as a 74LS240 manufactured by Texas Instruments, Dallas, Tex. The microprocessor  77  identifies keystrokes to the keypad  35  and transmits the information to the microprocessor  75  from its TDO output. The functioning of keypad  35  is described in greater detail in the &#39;840 patent which has been incorporated by reference. 
     In the following paragraphs, the operating and programming of the load manager of the invention is described. As mentioned, a more detailed description of the operating and programming of the signaling system is found in the aforementioned &#39;840 patent, which has been incorporated herein by reference. 
     In the operating mode, in order to facilitate the operation of the load management system, an interrupt routine is periodically executed by the microprocessor  75 . In a conventional manner, the microprocessor  75  responds to a timer based interrupt request to service a software-based routine stored in the ROM  79 . A flow-chart describing this routine appears in FIG.  5 . Initially, in step  1 , the routine determines whether the vehicle is in PARK. If it is not, then a check is made for previously shed loads, which are turned back on in reverse order preferably with a short delay, such a as 0.5 seconds, between them, and the routine is exited. If the vehicle is in PARK, then in step  2  it is determined whether the battery voltage has been less than 12.8 volts for more than 30 seconds. If no, the routine branches to point c 2 , to be discussed below. If yes, a check is made in step  3  whether high idle has been turned on. If it has, then a load is shed according to the programmed sequence, and if the low voltage alarm is on, the routine is exited. If the alarm is not on, the routine branches to node c 4 . If high idle was not on in step  3 , then it is turned on and the routine branches to node c 4 . 
     In step  4 , it is determined whether the battery voltage has been less than 11.8V for 30 seconds or more. If yes, the low voltage alarm is turned on. At this point, at node c 1  and c 2 , the voltage is checked in step  5 , and if it is found to be greater than 12.8V for 30 seconds or more, then the low voltage alarm, if on, is turned off. If it is not found to be greater than 12.8V for 30 seconds or more, then status flags are updated and the routine exited. In step  6 , if the battery voltage is found to be greater than 13.8V for 30 seconds or more, then the high idle, if on, is turned off. If it is not found to be greater than 13.8V for 30 seconds or more, then status flags are updated and the routine exited. 
     Note that the load shedding sequence can be overridden or reversed manually by pushing a key on keypad  35  associated with a particular load. Thus, in addition to the steps shown in FIG. 5, the load shedding routine checks for such manual indications. If a manual indication is received which corresponds to a potentially or previously shed load, that load is not shed, or, if previously shed, is restored, regardless of the programmed load shedding sequence. Additionally, the high idle and low voltage alarm functions may also be overridden manually in a similar manner. 
     In addition to the monitoring activity shown in FIG. 5, it is also preferable to monitor the voltage of the vehicle&#39;s battery during non-emergency driving, such as when the vehicle is not in PARK, and the siren is not on. The control processor  23  of FIG. 2A has access to the information regarding the gear that the vehicle is in through the PARK/NEUTRAL/SAFETY line, and is also aware of the status of the siren since enablement of the siren is through the control processor  23 . Thus, if the sensed battery voltage while the vehicle is being driven and the siren is off falls below a preset threshold, the audible low voltage alarm is sounded. This allows the driver of the vehicle to manually remove electrical loads, and/or to cease operation of the vehicle in a safe manner, being forewarned. Numerous conditions could cause such a situation, including alternator failure, various wiring failures, and so on. 
     The programming mode of the control head  25  is preferably entered via selected actions or keystrokes by the user. Once in the programming mode, the control head  25  may appear as shown in FIG.  7 A. 
     There are five program levels indicated by keys  10 ,  11 ,  12 ,  13  and  14  as shown in FIG.  7 A. The configuration tree corresponding to these levels is shown in FIG.  6 . Programming the emergency loads for normal operation according to levels  1 - 4  is described in detail in the &#39;840 patent. Essentially, the first four levels enable the programming of the functionality and/or default condition of the keyboard, keys, and switches, as well as the parameters of the Horn Ring function. The Programming Level  5  exposes the load management functionality of the system. As shown, many parameters and functions related to load management can be accessed and adjusted from this programming level. 
     The configuration mode of the system may be entered by simply executing the following steps: 
     1. Power up the system and wait for startup to finish. 
     2. Unplug the control head  25 . 
     3. Press SAVE (key  9 ) and continue to hold. 
     4. Plug the control head  25  back in while continuing to hold SAVE. 
     5. Release the SAVE key. The “MAIN MENU” shown in FIG. 7A will come up on the keyboard as soon the configuration mode is entered. Keys  10 ,  11 ,  12 ,  13 , and  14  are preferably solidly illuminated at this juncture. From the menu, there are six choices: 
     Key  9 —SAVE 
     Key  10 —ENTER PROGRAMMING LEVEL  1   
     Key  11 —ENTER PROGRAMMING LEVEL  2   
     Key  12 —ENTER PROGRAMMING LEVEL  3   
     Key  13 —ENTER PROGRAMMING LEVEL  4   
     Key  14 —ENTER PROGRAMMING LEVEL  5   
     Pressing “SAVE” (Key  9 ) will save the present configuration to permanent memory, end the programming session, and put the system into operation mode. In the current embodiment, the Slide Switch is preferably left in the OFF position while reconfiguring the system. 
     From the MAIN MENU, a keystroke to key  14  places the system into the fifth programming level, which is the programming mode for the load manager as discussed above. In order to inform the user that the system is in the programming mode for the load manager, the keys  10 ,  11 ,  15  and  16  are illuminated as shown in FIG.  7 B. 
     Keystrokes to each of the four illuminated keys  10 ,  11 ,  15  and  16  in FIG. 7B will display the shed sequence, voltage threshold, high idle control, and low alarm control, respectively. Programming of each of these is as follows: 
     A keystroke to key  10  arms the control head  25  for programming the shed sequence. The control head  25  should appear as shown in FIG.  7 C. 
     Keys,  4 ,  5 ,  6 ,  7 ,  8   10 ,  11  and  12  are illuminated in FIG.  7 C and they correspond to relays A, B, C, D, E,  1 ,  2  and  3 , respectively. Of course, there can be any number of relays, and corresponding illuminated keys, subject to the load manager. In a preferred embodiment, only those identified in the load shedding sequence will be shed by the manager if the battery voltage falls below the threshold level. 
     While the control head  25  is in the programming mode illustrated in FIG. 7C, sequential keystrokes to the keys  4 ,  5 ,  6 ,  7 ,  8 ,  10 ,  11  and  12  are preferably interpreted as the sequence in which the loads are to be shed. For example, keystrokes in the sequence of keys  4 ,  5 ,  6  and  8  causes the sequence of load shedding to be relays A, B, C and E. The loads corresponding to the rest of the relays will not be shed during load management. 
     Also in the programming mode of FIG. 7C, key  16  resets the shed sequence to a default of null. That is, during operation the status of all relay outputs will now be maintained regardless of the condition of the battery voltage. After a load shedding sequence has been entered, a keystroke to key  9  will save the sequence. The control head  25  display then returns to the configuration in FIG. 7B, which will indicate to the user that the sequence has been accepted. 
     From the state of the control head  25  shown in FIG. 7B, a keystroke to the key  11  causes the system to enter the programming or configuration mode for the voltage thresholds for load shedding, and causes the control head  25  to change the display to that illustrated in FIG.  7 D. 
     The High Idle Control Voltage Threshold, Load Shedding Voltage Threshold, and Low Battery Voltage Alarm Voltage Threshold are programmable as follows: The voltage thresholds are set to some default settings during manufacturing. The voltage threshold programming can be performed only when key  15  in FIG. 7D is pressed and the LED of key  15  turns on. To perform the voltage threshold programming, an adjustable DC power supply and a voltmeter replace the battery  43 . All switches are left off and the output of the DC power supply is adjusted to 14 volts. All of these adaptations should be done before enter the programming mode to adjust the voltage thresholds. 
     At this point, the power supply may be adjusted to 11.8 volts or any other desired voltage. A keystroke to key  4  then reads the voltage into the system memory as the voltage threshold for detecting a “low alarm” condition. Next, the variable source is adjusted to 12.8 volts or any other desired voltage. A keystroke to the key  5  causes the voltage to be read into system memory as the voltage to trigger the load shedding sequence. For the third threshold voltage, the variable voltage source is adjusted to 13.8 volt or any other desired voltage. A keystroke to the key  6  causes the voltage to be read into system memory as the voltage threshold for triggering the disabling of the high idle signal. A keystroke to key  9  after the voltage thresholds have been set will return the system to the state displayed in FIG.  7 B. 
     In the programming mode and with the control head  25  in the state shown in FIG. 7B, keystrokes to key  15  toggles the high idle control between enabled and disabled conditions. The high idle control operates in conjunction with the PARK input. If the vehicle is shifted out of PARK, the high idle control will not turn on. The key  15  is preferably illuminated when the high idle control is enabled and off when high idle control is disabled. 
     From the menu presented in FIG. 7B, a keystroke to key  16  “Low Voltage Alarm Enable” enables/disables the Low Voltage Alarm. The Low Voltage Alarm turns on if the system senses that the battery voltage is below the low voltage threshold for 30 seconds or more. The LED for key  16  is preferably on when the Low Voltage Alarm is enabled and off when the Low Voltage Alarm is disabled. 
     A keystroke to key  9  exits the configuration mode for programming the load manager and returns the keypad to the condition illustrated in FIG.  7 A. Another keystroke to key  9  will cause the system to exit the program mode and save the new settings. 
     From the foregoing, it will be appreciated that a programmable integrated load management and emergency signaling system has been described. Parameters of the load shedding system such as voltages, sequence and timing of load shedding can be programmed by way of keystrokes to the keypad  35  after the system has been installed. Using the same keypad, the parameters of emergency signaling devices such as sirens may also be configured. In this regard, the entire signaling system and load management functionality can be controlled from the keypad  35  without necessitating any disassembly of the system, and without requiring an operator to locate and use different user inputs for the various functions. 
     In view of the many possible embodiments to which the principles of this invention may be applied, it should be recognized that the embodiment described herein with respect to the drawing figures is meant to be illustrative only and should not be taken as limiting the scope of invention. For example, those of skill in the art will recognize that the elements of the illustrated embodiment can be modified in arrangement and detail without departing from the spirit of the invention. Therefore, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and equivalents thereof.