Abstract:
The present invention comprises a simplified control/hook-up circuit for intrusion detection devices that reduces the overall number of wires and attendant connections necessary between the control panel box and the terminals of the detector. This simplified design operates as efficiently as present intrusion device designs, while decreasing device hook-up time for field technicians and providing less opportunity for user error.

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention pertains to improved intrusion detectors, more particularly to improved circuit designs for intrusion detectors, and most particularly to simplified circuit designs for intrusion detectors. 
   2. Description of the Related Art 
   Current intrusion or motion detectors, such as passive infrared detectors, have seven terminals that are for use in connection via a maximum of six wires to the control panel box. In general two terminals are used to power the device (the power and ground terminals), two terminals are used for a tamper switch (to assure the integrity of the case of the detector during the time the alarm is not in use), and a choice of two of three terminals are used for the alarm function of the device when an intrusion is detected (a normally closed (NC), normally open (NO) and common (C) type circuit). In this configuration, two wires are normally required to be connected to the power terminals, two wires are normally required to be connected to the tamper terminals, and two wires are normally required to be connected to the alarm terminals. 
   While, in operation, this control circuit configuration operates efficiently, it becomes cumbersome for field technicians to attach this large number of wires within the device. It also increases the opportunity to connect wires in an incorrect configuration, thereby rendering the device inoperable. Finally, in a manufacturing environment, it is costly to manufacture a product with this number of connections to a control panel box. 
   Therefore, it is desired to provide a simplified circuit design for intrusion detection devices that reduces the number of connections required for the devices to operate correctly. 
   SUMMARY OF THE INVENTION 
   The present invention comprises a simplified control/hook-up circuit for intrusion detection devices that reduces the overall number of wires and attendant connections necessary between the control panel box and the terminals of the detector. This simplified design operates as efficiently present intrusion device designs, while decreasing device hook-up time for field technicians and providing less opportunity for user error. 
   Accordingly, it is an object of this invention to provide a simplified control/hook-up circuit for intrusion detection devices. 
   It is a further object of this invention to provide a simplified two wire control/hook-up circuit for intrusion detection devices to: allow the tamper switch within the intrusion detection device to be functional or indicate if the hook-up circuit is open; allow functioning of alarm status to the control panel box or show shorting of the hook-up circuit; allow easy optoelectronic coupling of tamper or firing status to the existing control panel box terminals; and allow pre-wiring the control panel box and intrusion device to effect two wire hook-up in the field. 
   This invention accomplishes these objectives and other needs related to simplified control circuits for intrusion detection devices by providing a simplified control circuit for an intrusion detection device. The intrusion detection device includes an intrusion detection alarm comprising a normally closed terminal, a normally open terminal, and a common terminal. The device further includes a power terminal and a ground terminal. Optionally, the device includes a tamper switch made up of a two terminal circuit. 
   The simplified circuit comprises the ground terminal connected to the common terminal. A direct current supply is included that provides sufficient power for the device in both a standby state and an active state. A positive terminal of the direct current supply is connected via a first return line to the power terminal. A negative terminal of the direct current supply is connected via a second return line to the normally open terminal. A first resistor is placed between the normally open terminal and the normally closed terminal and a second resistor is connected in the second return line so that current passes through the first and second resistor when the intrusion detection alarm is in the standby state. The circuit also includes a zener diode, having a peak reverse voltage, and an LED placed in parallel with the second resistor. 
   The resistances of the first and second resistors, the voltage of the direct current supply, and the peak reverse voltage of the zener diode are all selected, in conjunction with the power requirements of the intrusion detection device, to operate in the following manner. When the device is in the standby state (no intrusion has been detected), the voltage drop across the second resistor is insufficient for the zener diode to reach its peak reverse voltage. However, when the device is in the active state (an intrusion has been detected), removal of the first resistor from the circuit reduces the voltage drop across the intrusion detection alarm and increases the voltage drop across the second resistor to allow the peak reverse voltage of the zener diode to be exceeded. This added voltage allows the zener diode to conduct, activating the LED. 
   In a preferred embodiment of the invention, the circuit includes an on/off switch placed between the negative terminal and the power supply. A third resistor, one to limit current, and a second LED are placed in series with the direct current power supply so that when the switch is in the on position, power is supplied to the power terminal and the LED is activated. When the switch is in the off position, the LED comprises an inactive state and no power is supplied to the power terminal. 
   In a most preferred embodiment of the invention, the tamper switch terminals of the intrusion alarm are placed between the negative terminal and the power terminal. The circuit also includes: a series circuit comprising a third LED; a second zener diode having a second peak reverse voltage; and a fourth resistor in parallel with the intrusion detector and its first resistor. This series circuit is in parallel with the intrusion detector and its first resistor. In this configuration, when the tamper switch to the tamper switch terminal is broken/opened or the circuit is broken, the voltage across the second zener diode increases and exceeds the second peak reverse voltage, and, in turn, allows the second zener diode to conduct and operate (turn on) the third LED. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and, together with the description, serve to explain the principles of the invention. 
       FIG. 1  shows an embodiment of the simplified circuit of the present invention that reduces the required connections of the circuit by 2. 
       FIG. 2  shows an embodiment of the control panel box of the present invention. 
       FIG. 3  shows an embodiment of the simplified circuit of the present invention that reduces the required connections of the circuit by 4. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The invention, as embodied herein, comprises a simplified circuit for an intrusion detection device that reduces the overall connections required between the intrusion device terminals and the terminals of the control panel box. 
   This simplified circuit permits power wires, alarm wires, and tamper wires to be combined into a single pair of wires form many types of direct current intrusion detectors. The circuit permits visible confirmation of alarm status and/or tamper status of an intrusion detection device. 
   In general, the invention uses changes of resistance with attendant voltage change across resistors attached to the direct current power source resulting from alarm or tamper status changes in order to allow zener diodes to conduct and associated LED&#39;s to illuminate. Functioning of an LED is coupled with an optoelectronic circuit to the appropriate terminals of the control panel box to indicate an alarm or tamper/cut wires. 
   Referring to  FIG. 1 , the device comprises an intrusion detection alarm  100  comprising normally open  102 , normally closed  104 , and common  106  terminals. To power the device, a power terminal  108  and ground terminal  110  are also included. An optional tamper switch  112 , comprising a two terminal circuit may also be included. The improved circuit includes connecting the ground terminal to the common terminal. A direct current supply  114  having a first voltage sufficient to power the control circuit in standby and active states, is also included. In most configurations, the first voltage will be greater than the amount of power required to operate the device terminals described above. The direct current supply  114  also has positive  116  and negative  118  terminals. 
   The power terminal  108  is connected by a first return line  120  to the positive terminal  116  and the normally open terminal  102  is connected by a second return line  122  to the negative terminal  118 . A first resistor  124 , having a first resistance, is placed between the normally open terminal  102  and the normally closed terminal  104 . A second resistor  126 , having a second resistance, is placed within the second return line  122  so that current passes through the first  124  and second  126  resistors when the intrusion detection alarm  100  is in the standby state (the device is powered, but no intrusion has been detected). 
   A zener diode  128 , having a peak reverse voltage, and an LED  130  are placed in series across the second resistor  126 . In this configuration, when the device is in the standby state, a voltage drop across resistor  126  comprise insufficient voltage for the zener diode  128  to reach or exceed peak reverse voltage. Therefore, the zener diode  128  does not conduct and LED  130  is not illuminated/activated. When the device is in the active state (the device is powered and an intrusion has been detected), the first resistor  124  is removed from the circuit. This reduces the voltage drop across the intrusion detection alarm  100  and increases the voltage drop across the second resistor  126  to a voltage that will allow the peak reverse voltage to be exceeded. This allows the zener diode  128  to conduct and LED  130  to illuminate. 
   In a preferred embodiment of the invention, a switch  132 , having on and off positions, is placed between the positive terminal  116  and the power terminal  108 . A third resistor  134  that is current limiting and a second LED  136  are placed in series across the direct current power supply  114  so that when the switch  132  is in the on position, power is supplied to the power terminal  108  and second the LED  136  is activated. When the switch  132  is in the off position, the second LED  136  is not activated because no power is supplied to the power terminal  108 . 
   While the values associated with the components mentioned above may be selected depending upon the power requirements of the intrusion detection device, the following are exemplary values for an intrusion detection device needing from about 9.5 volts to about 14.5 volts in order to operate. The direct current power supply  114  provides approximately 18 volts. As noted above, this voltage level is higher than the device needs to operate. The first resistor  124  comprises a resistance of approximately 47 ohms and the second resistor  126  comprises a resistance of approximately 487 ohms. The zener diode  128  comprises a peak reverse voltage of approximately 6.2 volts in order to conduct. In operation, during the standby state, these values would produce a voltage drop across the first  124  and second  126  resistors of about 7.5 volts. The remaining voltage drop of 10.5 volts would occur across the intrusion detection alarm  100  (falling within the required operating range of the device). The voltage drop across the second resistor  126  would be about 6.7 volts. Because the resistance of the LED  130 , would provide greater than a 0.5 voltage drop, the zener diode  128  does not conduct (due to the required peak reverse voltage of 6.2 volts). 
   However, when the intrusion detection alarm  100  is in the active state, this removes the first resistor  124  from the circuit. The voltage drop across the intrusion detection alarm  100  is reduced to about 9.6 volts and the voltage drop across the second resistor  126  increases to about 8 volts. This increase in voltage is sufficient for the zener diode  128  to conduct and the associated LED  130  to illuminate. 
   Regarding the switch  132 , to operate with the exemplary values described above, the third resistor  134  comprises a current limiting resistance of approximately 5.11 K ohms and the second LED  136 . 
   Referring to  FIGS. 2 and 3 , LED  130 , as an indicator of an intrusion, is coupled with an optoelectronic circuit  242  to the control panel box  244 . A photodiode  246  is used to switch on a transistor  248 . When photons illuminate the photodiode  246 , a bias is provided to the base  253  of the transistor  248 . This allows the transistor  248  to conduct. In most common devices, the transistor  248  comprises a NPN silicon transistor. The collector  250  of the transistor  248  is connected to any Z terminal  252  of the control panel box  244 . An emitter  254  is connected to terminal  256 . An end-of-line resistor  258  is connected across the circuit at the terminals  252 ,  256  in accordance with control panel box  244  manufacturer&#39;s instructions. Similar circuits and connection means may be used to couple third LED  364 , as an indicator of tamper, to the control panel box  244 . 
   The invention may also include a tamper switch  360 , comprising a two terminal circuit  112  between the positive terminal  116  and the power terminal  108 . Therefore, if the case of the device is removed or the wires to the intrusion detector are cut, this part of the circuit becomes open. Without the present invention, two additional wire connections would be necessary for the tamper switch to operate. Further circuitry for proper tamper switch operation include a series circuit  362  comprised of a third LED  364 , a second zener diode  366  having a second peak reverse voltage, and a fourth resistor  368  across the first and second return lines. When the tamper switch  360  circuit is broken, the voltage increases across the second zener diode  366  increases to exceed the peak reverse voltage and allow the zerner diode to conduct the third LED  364  to illuminate. 
   Exemplary values for the circuit elements shown in  FIG. 3  are as follows. The fourth resistor  368  comprises a resistance of approximately 220 ohms. The second peak reverse voltage comprises approximately 12 volts and the LED  364  comprises a voltage of approximately 2.1 volts. 
   The invention also includes a method of reducing the number of connections required between a circuit controller and associated terminals within an intrusion detection device as described above. 
   What is described are specific examples of many possible variations on the same invention and are not intended in a limiting sense. The claimed invention can be practiced using other variations not specifically described above.