Abstract:
A system and method is provided for automatically connecting and disconnecting alternative power to intercom telephones without interfering or interacting with the power supplied or cancelled by the telephone company central office. Central Office power is continuously monitored by a sensing circuit to determine whether the service to that telephone is being activated or deactivated by the Central Office. When no Central Office power is detected, the system automatically supplies alternative operating power to the telephone, enabling it to initiate intercom phone calls. When a resumption of Central Office service is detected, the power supplied by the system is removed, and the Central Office power is supplied to the telephone.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit, under 35 U.S.C. § 119(e), of co-pending Provisional Application No. 60/694,771, Filed Jun. 28, 2005, the disclosure of which is incorporated herein by reference. 
     
    
     FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates generally to telephony, and more particularly to commercial intercom telephone systems with a “Call Down” feature. Additionally, this invention relates to commercial intercom telephone systems where a resident has chosen not to have traditional telephone services, but instead utilizes the standard building telephone wiring in order to be connected to a building intercom service. Even more specifically, this invention relates to telephone systems in which an intercom service is provided, and the resident telephone requires power in order to operate, and where there is also a requirement for this power to be automatically applied or removed when standard telephone service is activated or cancelled.  
         [0004]     No-phone-charge intercom systems in multi-resident buildings have existed for many years. The two primary systems are “hard wired” and “telephone intercoms”. The telephone intercom systems utilize the standard telephone wiring to each resident, so that the resident&#39;s standard telephone is used for both standard telephone service and intercom service. The primary function of the intercom system is to allow internal building communication in multi-resident structures without incurring charges from the telephone company. Currently there are two main types of telephone intercom systems. The first type is a “call up” telephone intercom system where the subscriber uses a telephone to provide visitors entry into the building without having to walk to the entrance and open the door. The second type is the “call up and call down” system where the subscriber not only uses a telephone to provide visitors entry into the building, but can also use the telephone to call down to another station to initiate an intercom telephone call with a limited number of door attendant/concierge/valet/management office telephones. Intercoms that allow the resident to initiate an intercom call require that the resident&#39;s telephone have a minimum operating voltage on its telephone line. Traditionally, a telephone company Central Office (CO) supplies this operating voltage.  
         [0005]     With the increasing popularity of cellular and broadband telephone services, it is becoming more commonplace for multiple resident buildings to have various forms of telephone services. If the resident is only using cellular telephone service, the intercom telephone system will no longer be supplied power from the CO. In order for the intercom call to be initiated by the resident, the resident&#39;s telephone must continually have a minimum amount of operating voltage across the phone line.  
         [0006]     In view of the above, a need exists for a system and method for connecting or disconnecting an alternative operating voltage power source to the resident phone line circuitry when needed.  
       SUMMARY OF THE INVENTION  
       [0007]     The general objective of the present invention is to provide an automatic fail safe method of connecting or disconnecting alternative power to standard resident telephones without interfering or interacting with the power supplied or cancelled by the telephone company central office. The method is implemented by an automated system in which an intercom power application is provided to supply an alternative operating voltage to resident telephone lines.  
         [0008]     The system includes a microprocessor, an alternative power source, a plurality of “voltage and current sensing circuits,” and a plurality of voltage selection switches. A voltage and current sensing circuit is individually coupled to each resident telephone line to monitor voltage and current levels provided by the telephone company central office. The microprocessor controls the voltage selection switches to connect or disconnect the alternative power source to and from the resident telephone line. The operation of the voltage selecting switches is based on signals received from the voltage and current sensing circuits. The microprocessor assures the proper timing of switching.  
         [0009]     This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiments thereof in connection with the attached drawings. Detailed descriptions of known functions and configurations incorporated herein have been omitted for clarity and conciseness. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0011]      FIG. 1  is a block diagram showing the architecture of an intercom power application system in accordance with the present invention;  
         [0012]      FIGS. 2A, 2B , and  2 C are schematic diagrams illustrating exemplary circuit implementations of the alternative power source, the microprocessor, and the sample timer, respectively, of the intercom power application system of  FIG. 1 ;  
         [0013]      FIG. 3  is a schematic diagram illustrating an exemplary circuit implementation of a current/voltage sensing circuit of the intercom power application system of  FIG. 1 ; and  
         [0014]      FIG. 4  is a flow chart illustrating the steps of a method for operating the intercom power application system of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.  
         [0016]     According to the present invention, a system and method for automatically connecting and disconnecting an alternative power source to and from intercom telephone lines is provided. Although the system and method of the present invention is described as being implemented in a multi-resident building, those skilled in the art will recognize that the principles and teachings described herein may be applied to a variety of structures using a commercial intercom telephone system, such as a hotel or ship.  
         [0017]     Turning to  FIG. 1 , a functional block diagram of an intercom power application system  100  that can be applied to both “call up” systems and “call up and call down” systems is shown. In a preferred embodiment of the present invention, the system  100  comprises an alternative power source  103  that, as will be described below, provides an alternative 24V DC power source for operating the intercom system. The power source  103  also supplies a 5V DC operating voltage to the components of the intercom power application system  100  of the present invention, which includes a microprocessor  101  providing operational control, a sample timer  107  controlling sampling rate, and a plurality of voltage/current sensing circuits  110 . A separate voltage/current sensing circuit  110  is connected to each resident telephone line  106  for sensing whether an operating voltage is provided by the CO.  FIG. 1  illustrates a representative voltage/current sensing circuit  110 . Although 12 resident telephone lines are shown, the system can have more or less resident telephone lines. If the CO is not providing the operating voltage, the alternative power source  103  provides 24V DC as an alternative intercom operating power source that is disconnected automatically when the CO power is restored, as discussed below.  
         [0018]     Telephone lines  105  from the CO are input into the voltage/current sensing circuit  10  which comprises a current-to-voltage converter  102 A for receiving a current signal from the CO and converting the current signal to a voltage signal, a signal amplifier  102 B for amplifying the voltage signal, and a voltage selection switch/latch  104  for connecting and disconnecting the alternative power source  103  to the resident telephone line  106 .  
         [0019]     The alternative power source  103  comprises a 24V AC power supply  118  and a DC converter power regulator  114 , such as a 78L05. The AC power supply  118  is conventional, and it may include a step-down transformer (not shown) that receives standard 110V AC voltage on its input side. The output of the AC power supply  118  is input into the DC converter power regulator  114 , which converts the 24V AC to 24V DC. The 24V DC is then supplied to a current limiter  117 , which, in turn, supplies a signal to the voltage selection switch  104 , causing the switch to position itself so that the alternative power source is connected to the resident line  106 . The microprocessor  101  continuously monitors the status of the operating voltage of the CO to the telephone line  106  by sampling the current flowing through an opto-coupler  111  (see  FIG. 3 ) in the current to voltage converter  102 A, using the sample timer  107 , and stores the sampling results.  
         [0020]     To ensure an accurate reading, the microprocessor  101  requires sixteen consecutive identical samples, with each sample taken at spaced intervals of approximately 3 seconds, before it initiates switching of the voltage selection switch  104 . This finite impulse response (FIR) filter type is provided to prevent glitches and non-representative signal changes from triggering the activation of the voltage selection switch  104 .  
         [0021]     The sample timer  107  determines the sampling rate of the microprocessor  101  by sending a timing signal to the microprocessor  101  via the latter&#39;s IRQ port, causing the microprocessor  101  to restart CO line scans. A light emitting diode LED 1   108  (such as a 1N914 as shown in  FIG. 2B ) is connected to an I/O port of the microprocessor  101 . Flashing of the light emitting diode  108  indicates the sampling rate and scan activation to service personnel.  
         [0022]     When the microprocessor  101  detects a change of CO power, it initiates a process to change the position of the voltage selection switch  104 . This process includes changing the I/O configuration and asserting predetermined logic values to a relay coil terminal of the voltage selection switch  104 , while observing a predetermined sequence of operation to avoid timing conflicts. Following a system power-up, the voltage selection switches  104  are in their default position, connecting CO power to a resident phone line  106 . To change a voltage selection switch  104  from CO power to alternative power requires energizing the relay coil of the voltage selection switch by asserting logic “1” on a relay line (e.g., the line RLY 1  in  FIGS. 2B and 3 ) and logic “0” on a sense line (e.g., the line SENSE 1  in  FIGS. 2B and 3 ), energizing a relay  109  ( FIG. 3 ) in the voltage selection switch  104  to perform switching. (The sense lines and relay lines are respectively labeled “SENSE LINES” and “RELAY LINES” in the block diagram of  FIG. 1 .) Once the switch  104  changes its position, it maintains that position until signal polarity changes on its relay coil.  
         [0023]     As best shown in  FIG. 3 , in a non-CO power position, the voltage selection switch  104  disconnects CO lines from the resident telephone line  106  and connects the alternative 24V DC from the alternative power source  103  to its “Tip line” via a current limiting resistor R 43   117 , and it connects the “Ring line” to ground (GND). In this position, the resident phone is disconnected from the CO, while the current loop is maintained from the CO&#39;s “Ring line” to its “Tip line” through a serially connected opto-coupler  111  and a resistor R 56   116 . When CO power is restored, current in the current loop increases, turning transistor Q 1   113  “on,” and asserts logic “0” on a “sense line,” thereby indicating the presence of CO power to the microprocessor  101 .  
         [0024]      FIG. 2A  is a schematic diagram of the alternative power source  103 . The alternative power source  103  includes a line transformer (not shown) providing 24V AC to a rectifier bridge  119  via a power input  118 . The rectified 24V DC is used to provide the alternative voltage to each resident telephone line  106  via a current limiting resistor  117  ( FIGS. 1 and 3 ). The 24V DC is converted further by a DC Converter  114  to supply 5V DC to the microprocessor  101 , to the sample timer  107  and to the signal amplifier  102 B in each of the sensing circuits  110  (one for each telephone line).  
         [0025]      FIG. 2B  is a schematic diagram of an exemplary implementation of the microprocessor  101 . A MC68HC7059A Micro-Processor Unit (MPU)  139  or the equivalent, such as or a 68705C9 micro-controller, is preferably used in the present invention. The MPU  139  operates with 5V DC supplied by the alternative power source  103 , with a capacitor C 5   121  as a decoupling capacitor. A tank circuit formed by a 2 MHz quartz-crystal X 1   124 , a resistor R 41   123 , and capacitors C 2   122  and C 3   125 , connected to pins  38  and  39  of the MPU  139  and sets the internal clock of the MPU  139  to 2 MHz. Power-on reset is applied to the MPU  139  by an RC network comprising a resistor R 42   126  and a capacitor C 1   127 . The LED  108  is connected to an I/O port of the MPU  139  via a current limiting resistor R 37   128 . A pull-up resistor R 38   129 , connected to another I/O port of the MPU  139 , allows the MPU  139  to recognize the IRQ signal. A jumper JP 1   120  is advantageously provided, which, when shorted, results in IRQ requests being ignored. Furthermore, during a system test performed by shorting the jumper JP 1   120 , the microprocessor  101  is put into a continuous mode of operation, allowing for quick diagnostics.  
         [0026]      FIG. 2C  is a schematic diagram of an exemplary implementation of the sample timer circuit  107 . The sample timer circuit  107  employs a timer U 26   133 , preferably an MC 1455 or LM555 timer or the equivalent. The timer  133  is operated with the 5V DC supply, using a capacitor C 7   132  as a decoupling capacitor. Resistors R 40   130  and R 39   131 , together with a capacitor C 6   132 , determine the cycle time of the timer circuit  107 . The cycle time is calculated by Equation (1):
   T   cycle =0.693× C 6×( R 40+2× R 39)  Equation (1): 
         [0027]     The internal circuitry of each of the voltage/current sensing circuits  110  is illustrated in  FIG. 3 . During normal operation (i.e. the CO is supplying operating voltage to the resident lines  106 ), current from a CO Ring line R C  flows through a current loop back to a CO Tip line T C . The current loop is formed by serially connecting the opto-coupler  111 , such as a H11AA, one side of the voltage switch  104 , and a resident telephone via resident Tip and Ring lines (T R  and R R , respectively). The current loop is coupled to the signal amplifier  102 B, comprised of a transistor Q 1   113 , such as a 2N2222, and a collector resistor R 13 , via a base resistor R 25   112 , for amplifying the current. The collector of the transistor Q 1   113  is connected to an I/O port of the microprocessor  101  (shown in  FIG. 2B ) through a resistor R 1   115  via a sense line S, asserting logic “0” indicating the presence of CO service, i.e. the resident telephone  106  is operating normally with CO provided power. When CO power is removed or unavailable, current flowing through the opto-coupler  111  decreases to a predetermined value (determined by the respective gains of the opto-coupler  111  and the transistor Q 1 ), forcing the signal amplifier  102 B to output a logic “1” on the sense line S, which is input to the microprocessor  101 .  
         [0028]     Table 1 below identifies the preferred values of the resistors and capacitors (described above) in a preferred embodiment of the present invention.  
                                                                             TABLE 1                                       R1    20K           R13   470K           R25   100K           R38    2K           R39   220K           R40   100K                R41   10   M                R42    10K                R43   680   ohms           R56   5.1   M           C1   4.7   uF           C2   33   pF           C3   33   pF           C5   4.7   uF           C6   10   uF           C7   0.1   uF                      
 
         [0029]      FIG. 4  is a process flowchart illustrating the steps of an automatic method for operating the intercom power application system  100  in accordance with the present invention. The operation of intercom power application system  100  is controlled by the microprocessor  101  (see  FIG. 1 ) that manages the functions and timing of the intercom power application system  100 . The microprocessor  101  stores and retrieves multiple data sets and the operating software that controls the system. In the following description only basic operations that are necessary to understand the automatic application or removal of alternative power are described.  
         [0030]     In step S 201 , at first power up, the voltage selection switches  104  default all channels (e.g., twelve channels) to the CO mode.  
         [0031]     In step S 202 , the sample timer  107  is armed (automatically reset), and the LED  108  indicator is turned off.  
         [0032]     In steps S 203  and S 204 , the system  100  is idling for 3 seconds.  
         [0033]     In step S 205 , the telephone line sampling process begins, and the LED  108  indicator is turned on.  
         [0034]     In steps S 206  thru S 209 , lines are sampled sequentially, and the results of the last 16 samples for each of the twelve lines, designated as ‘N’ channels, get stored in the microprocessor  101 .  
         [0035]     In step S 210 , it is determined if the last 16 samples were all the same. If the samples were all the same, the process continues at step S 211 . Otherwise, the process proceeds to step S 203  if the samples are inconsistent.  
         [0036]     In step S 211 , it is determined if a change occurred in CO service status by testing it against the previous known state of the relay, such as a G6KU-2F in the voltage selection switch  104 . If there is a change, the microprocessor  101  initiates switching of the appropriate voltage selection switch  104  in step S 212 . Otherwise, the process proceeds to step S 213 .  
         [0037]     In step S 212 , a voltage selection switching is performed to match line service requirements.  
         [0038]     In step S 213 , it is determined whether all 12 telephone lines were scanned. If scanning is incomplete, the next phone line is scanned in step S 207 . Otherwise, the process proceeds to step S 202  to arm a new scan cycle.  
         [0039]     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.