Abstract:
A device for rerouting the report call of an alarm system to another telephone number through the interruption of the alarm system&#39;s out-dialing process, includes two electronically controlled switching devices that allow the device to momentarily isolate the alarm from the phone line. Switches are operated under microprocessor control, for causing dialing of the new phone number by the generation of DTMF tones by a DTMF generator operating under microprocessor control. Triggering of the report call rerouting process is keyed to the presence of two conditions: one being loss of voltage from the handset lines, and the other being presence of dialing activity, either DTMF tones or pulse-dialing pulses on the telephone line. The device will reset itself after the telephone has been held in the on-hook condition for a predetermined interval by the alarm system, to allow the device to reroute subsequent report call attempts if initial attempts to connect are unsuccessful.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to security systems, and more particularly to security systems which communicate with a central monitoring station via a telephone line. 
     BACKGROUND OF THE INVENTION 
     Present day security systems (i.e. intrusion and/or fire alarm systems) typically include a telephone dialer which is coupled to the alarm system and to a telephone line at the protected premises. When an alarm system is “tripped” (i.e. intrusion, fire), the alarm system dials the telephone number of a central monitoring station. Upon answering by the central monitoring station, the alarm system transmits information to the central monitoring station so that police and/or firefighters may be dispatched to the protected premises. Many of the alarm systems&#39; telephone dialers are typically limited to the telephone number programmed by the vendor or installer. Therefore, users of such alarm systems are limited in choosing their central monitoring service provider. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a method and apparatus for rerouting the report call of an alarm system to a telephone number different from the preprogrammed one. 
     It is a further object of the invention to provide the user of the alarm system an option to choose any desired central monitoring station service provider without having to program the alarm system itself. 
     With these and other objects in mind, the present invention provides for a detector means for sensing both the voltage drop across a telephone handset line and the presence of dialing activity from the alarm system, whereupon it generates initiating signals to a microprocessor controller. When the microprocessor controller receives the initiating signals, it outputs both a switching signal and a pre-programmed dialing signal. A switching means responsive to the switching signal returns the telephone line briefly to an on-hook condition to reestablish dial tone and isolates the alarm system from the telephone line during the rerouting process. Upon reestablishing dial tone, a telephone communication dialer means responsive to the dialing signal, dials the telephone number of the desired central monitoring station. Once the dialing is complete, the alarm system is reconnected to the telephone line for data transfer to the central monitoring station. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments of the present invention are described below with reference to the drawings, in which like items are identified by the same reference designation, wherein: 
     FIG. 1A shows a simplified block diagram indicating the major components of an alarm system incorporating therein the alarm report rerouting system of the present invention; 
     FIGS. 1-7 collectively shows a detailed circuit schematic diagram of various components of the present invention; and 
     FIGS. 8A-8C collectively shows a flowchart illustrating operation of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1A depicts the placement and connection of the alarm report call rerouter in a subscriber&#39;s home alarm system. The TIP and the RING of the telephone company are connected respectively to the TIPIN and the RINGIN of the call rerouter  2 . The call rerouter  2  is then connected to the alarm system  4  by the loop pair TIPALARM and RINGALARM. The call rerouter  2  is also connected to the alarm system  4  by the loop pair TIPHAND and RINGHAND which corresponds to event detection on the handset  6  lines  8 ,  10 . 
     In FIG. 1, reference label TIPIN designates the tip (more positive conductor) of the local loop conductor pair as it enters the subscriber&#39;s home from the telephone company. The local loop current passes through a small resistor (R 5 B, 68 OHM in the preferred embodiment). The local loop current level can be measured from the voltage drop across R 5 B. Resistors R 3 B and R 4 B form a voltage divider network that attenuates the TIPOUT voltage signal by a fixed ratio. Thus the voltage delivered to the inverting input of Comparator U 4 B will be {fraction (1/11)} th  of the original voltage. Resistors R 6 B and R 7 B form a voltage divider network with an identical ratio of attenuation. This network attenuates the TIPIN voltage signal, less 0.7V (volt) due to the presence of diode D 2 B. This attenuated signal is applied to the noninverting input of Comparator U 4 B. The purpose of the twin dividers is to bring the common mode of the two signals being compared down into the common mode range of comparator U 4 B. Zener diodes Z 3 B and Z 4 B protect the inputs of the comparator U 4 B from exceeding the absolute maximum rating of the device in the event that high voltage transients appear on the local loop conductor pair. Resistor R 8 B is a pull-up resistor to hold the open-drain output of the comparator U 4 B high to produce a logic high state, typically designated as a digital “1”. Capacitor C 1 B prevents RF oscillation due to any coupling between comparator U 4 B inputs and its output that might occur in the associated printed-circuit layout. 
     Given that the comparator U 4 B will change logic state when the voltage present on the inverting input equals the voltage on the non-inverting input, and that the TIPIN signal is always disadvantaged by 0.7V due to the presence of D 2 B, the TIPIN signal must always be 0.7V more positive than TIPOUT at the point of comparator logic state transition. For the component values given in the preferred embodiment, this corresponds to a loop current of approximately 10 mA (milliampere). Given that typical local loop currents for the off-hook state range from 20 mA-120 mA, and are typically less than 6 mA in the on-hook state, the above circuit can reliably discern between the on-hook and off-hook line conditions, producing a logic high output when loop current is present and logic low output (typically digital “0”) when the line is on-hook. It is this circuit that allows pulse-dialing detection capability as well as on-hook/off hook discrimination in the preferred embodiment of the invention. 
     Reference label TIPHAND from FIG. 2 designates the tip (more positive conductor) of the handset  6  conductor pair  8 , 10 . The handset  6  conductor pair  8 , 10  emerges from the alarm system  4  and continues on to connect to the subscriber&#39;s telephones. Reference label RINGHAND designates the ring (more negative conductor) of the handset  6  conductor pair  8 , 10 . Diodes D 6  and D 7  are arranged such that the junction of their cathodes will be at a voltage equal (less a 0.7V diode drop) to the more positive of these two signals. This allows normal operation of the circuit even in the case where improper wiring at the alarm system  4  has resulted in the reversal of electrical polarity in the handset  6  conductor pair  8 , 10 . Resistors R 5  and R 6  form a voltage divider network that attenuates the resulting signal by a fixed ratio. Thus the instantaneous voltage delivered to the inverting input of Comparator U 4 A will be ½ of the original signal level for original voltages in the range of approximately 0V-10V. When the input to the divider network exceeds 10V, Zener diode Z 3  begins a clamping action that holds the voltage of the inverting input of the comparator substantially constant at the rated Zener voltage (4.7V in the preferred embodiment). Diode D 3  and resistor R 7  are used to establish a reference voltage of approximately 0.5V, which develops on the anode of D 3  and is supplied to the non-inverting input of the comparator U 4 A. Resistor R 8  is a pull-up resistor to hold the open-drain output of the comparator U 4 B high to produce the logic high state “1”. 
     Given that the comparator U 4 A will change logic state when the voltage present on the inverting input equals the voltage on the non-inverting input, this corresponds to a line voltage of 1V. Thus, this circuit is useful for discriminating between normal operating line voltages (where even in the worst case line voltages never fall below 1V) and the case in which handset tip and ring conductors have been galvanically isolated from the local loop (in which case 0V develops on the inverting input of the comparator U 4 A). Such galvanic isolation occurs when a typical alarm system  4  activates, so that household telephones will not disrupt the report call process. Thus this circuit can signal the activation of the alarm system  4 , giving a logic high output “1” during alarm system  4  activation, and logic low output “0” while in normal operation. 
     FIG. 3 depicts a battery charger and power supply circuit of the present invention. Reference labels TIPIN and RINGIN designate the tip and ring, respectively, of the local loop conductor pair directly as it enters the subscriber&#39;s home from the telephone company. The conductor pair enters bridge rectifier B 1 B, which protects the battery charging circuitry against accidental tip-ring reversal. The positive tap of the bridge rectifier  12  supplies the input to the series voltage regulator formed by Q 1 B, resistor R 1 B, and Zener diode Z 1 B. This regulator holds the output at the voltage rating of the Zener diode Z 1 B (30V in the preferred embodiment). The high voltage rating of Q 1 B (300V in the preferred embodiment) protects the components of the battery charging system from ring signal voltages and transients on the local loop conductor pair. The output voltage of the serial regulator supplies the current source formed by U 2 B and resistor R 2 B. This current source supplies a substantially constant current (in the preferred embodiment, approx. 5.5 mA) used to charge battery B 2 B and supply standby current to the quiescent circuitry. Battery charging current is typically 3.5 mA in the preferred embodiment, with the balance of current going toward quiescent consumption. Diode D 1 B protects against battery B 2 B discharge through the charging system in the event the telephone line connection is removed and the battery remains installed. Zener diode Z 2 B prevents the charging system from producing excessive voltage output in the event the battery B 2 B is removed and the telephone line connection remains (output will be clamped at 15V in the preferred embodiment). Regulator U 1 B supplies a constant voltage (5V in the preferred embodiment) independent of the fluctuations in battery voltage associated with charging and discharging. 
     FIG. 4 depicts the dialing circuitry. As the tone generator IC chip U 2  in FIG. 4 is a commercial device, it will not be described in detail here. External components have been included as per the manufacturer&#39;s application notes. A bus of four conductors interconnects four output pins of the microcontroller U 1  in FIG. 7 with four tone selection input pins (R 1 -R 4 ) of the tone generator IC chip U 2  in FIG.  4 . Each permutation of this four bit binary word represents a unique DTMF tone to be generated. Transistor Q 3  and resistor R 9  interface the output of the tone generator to the telephone line. Diode D 4  protects Q 3  as well as the TO output of U 2  from negative-going transients on the tip conductor of the local loop pair. Resistor R 10  draws sufficient current to keep the phone line in the off-hook condition. 
     FIG. 5 depicts the switching elements, relays RE 1  and RE 2 . Relay RE 1  is used to return the line on-hook briefly to then re-establish dial tone when local loop current is re-established. Relay RE 2  galvanically isolates the tip conductor of the local loop conductor pair of the incoming phone line from the alarm system. This interrupts the dialing process of the alarm system and allows the invention to dial another number without the dialing activity of the alarm system interfering with the process. The switching action of relay RE 1  occurs when the logic state of the microcontroller U 1  output pin RB 5  swings from logic low “0” to the logic high state “1”. This causes base current to flow in transistor Q 1  through current limiting resistors R 1  and R 3 . The establishment of base current causes Q 1  to turn on, allowing current to flow through the coil  12  for energizing the relay RE 1 . Zener diode Z 1  protects the microcontroller U 1  output pin from voltage transients associated with coil deenergization. Diode D 1  is an anti-kickback diode designed to clamp the collector voltage of Q 1  to the supply rail during de-energization to prevent destructive high-voltage spiking from coil  12  that would otherwise occur. Back-to-back Zener diodes Z 7  and Z 8  are designed to limit the transient spikes on the local loop caused by the switching action of the relay RE 1 . The diodes Z 7  and Z 8  are wired across the normally closed contacts of the relay RE 1 , and, when these contacts open, allow loop current to decay slowly, thus avoiding the generation of high-voltage spikes on the line. Relay RE 2  has identical drive components and topologies, and functions likewise, with Z 9  and Z 10  serving to limit transient spikes. 
     The diode D 5  blocks DC current flow in the reverse direction, thus alerting the user to improper wiring of the system (tip-ring inversion), as household telephones will be rendered inoperative as long as this condition persists. Capacitor C 10  and resistor R 14  allow AC to bypass diode D 5 , allowing the ring signal to be substantially unaffected by the presence of this blocking diode D 5 . 
     Integrated circuit U 3  shown in FIG. 6 serves to detect DTMF tones. Operation of the circuit will not be described in detail here, as it is a commercial device and external components have been included as per the manufacturer&#39;s application notes, with the exception of Zener diode Z 6 , which has been included to protect the detector from excessive voltage imposed by the ring signal. The tip of the local loop conductor pair is capacitively coupled to the detector, and DV pin (Data Valid) output is routed to the input RA 4  of microcontroller U 1 . This output will be logic high whenever any one of the sixteen valid DTMF tones is present on the phone line. 
     Integrated circuit U 1  shown in FIG. 7 serves as the microcontroller of the device. It is this component where the software is stored and executed. Operation of the circuit will not be described in detail here, as it is a commercial device and external components have been included as per the manufacturer&#39;s application notes. Transistor Q 4  allows the microcontroller U 1  to have the ability to remove power from the peripheral IC chips (U 2  and U 3 ). Logic low on the RB 3  output of U 1  turns on the  5 V rail to integrated circuits U 1 B, U 2 , and U 3 , and a logic high removes power. This feature allows standby power to the device to be very low (2 mA in the preferred embodiment). The jumpers J 7  and J 8  are used to select any one of four  11  digit pre-programmed telephone numbers to be dialed by the microcontroller U 1 . These jumpers control the logic state of two input pins of the microcontroller U 1 , with each penetration of this 2-bit binary word corresponding to a unique telephone number to be dialed. FIGS. 8A,  8 B, and  8 C show a flowchart for programming of microcontroller U 1 . 
     Although various embodiments of the invention have been shown and described, they are not meant to be limiting. Those of skill in the art may recognize certain modifications to these embodiments, which modifications are meant to be covered by the spirit and scope of the appended claims.