Patent Publication Number: US-6992579-B2

Title: Burglar alarm system having reduced wiring

Description:
FIELD OF THE INVENTION 
   Normal hard-wired burglar alarm systems for domestic and commercial applications include a number of event sensors situated around a space to be monitored, each in communication with a central controller. Some installations have a central controller communicating with a number of remote control panels or keypads—one at each main entry to the premises. Such alarm systems also employ a siren sounder/bell box, usually attached in a prominent out-of-reach position at the front of the premises. For example, some such boxes employ a flashing strobe light and are mounted beneath the eaves at the front of a house. 
   Ordinarily, a cable having six or more internal conductors extends between the central controller and the siren sounder/bell box, and between the central controller and each remote control panel/keypad. One pair of conductors provides electrical power to the bell box or keypad, another pair of conductors provides a tamper circuit and the other pair of conductors is for signal transmission. 
   OBJECTS OF THE INVENTION 
   It is an object of the present invention to reduce the required number of conductors between an alarm central controller and a bell box and/or a remote control panel. 
   DISCLOSURE OF THE INVENTION 
   There is disclosed herein an alarm system comprising:
         an alarm controller,   a remote input/output device,   a cable extending from the alarm controller to the remote input/output device, the cable comprising two conductors providing power to the remote input/output device, and   a signal processor at the controller monitoring and processing voltage and current fluctuations in the conductors and controlling functions of the alarm system.       

   Preferably be alarm system further comprises a mixer at the remote input/output device operative to affect current and voltage at the two conductors. 
   Preferably the signal processor monitors for predefined voltage and current levels at the two conductors. 
   Preferably the mixer applies predefined voltage and current levels at the two conductors. 
   DEFINITION 
   As used herein, the phrase “remote input/output device” is intended to encompass entry panels such as keypads, or other input devices such as card readers, iris scanners or fingerprint scanners for example, as well as visible/audible devices such as a flashing light, strobe light, siren sounder, or bell box. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred form of the present invention will now be describe by way of example with reference to the accompanying drawings, wherein: 
       FIG. 1  is a schematic diagram of a conventional prior art control panel communicating via six wires with a remote keypad, 
       FIG. 2  is a schematic diagram of a control panel communicating via two wires with a remote keypad, 
       FIG. 3  is a schematic circuit diagram showing circuitry in the control panel&#39;s signal processor and the remote keypad, 
       FIG. 4  is a schematic detailed circuit diagram of the remote keypad, and 
       FIG. 5  is a schematic detailed circuit diagram of the control panel. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In  FIG. 1  of the accompanying drawing there is depicted schematically a prior art conventional burglar alarm control panel  10  connected by a six-wire conductor  11  to a remote keypad  12 . Two of these wires are for DC supply, two wires are for the data transmission and two wires are for tamper indication. As the remote keypad  12  can be quite some distance from the control panel  10 , wiring can be expensive. Furthermore, it is necessary that the installation technician carefully connect the colour-coded wires to the correct terminals at both the control panel and remote keypad. 
   On the other hand, the arrangement depicted schematically in  FIG. 2  requires only a two-conductor cable  11  between the control panel  10  and remote keypad  12 . It is comparatively inexpensive and simple to install the system of  FIG. 2  because the two-conductor cable can be installed at either polarity and there is no need to mess around with wires of different colour. This reduces installation errors. Furthermore, the two-conductor unit will perform all of the tasks of the six-wire conventional unit, by use of a signal processor and a mixer. 
   There is a mixer circuit  13  at the remote keypad  12  and a signal processor  14  at the control panel  10 . The voltage and current in the two-conductor line  11  varies to indicate particular signals. The differing levels of voltage/current will be assigned to activate the functions for the control system or the remote unit through the signal processor and mixer. The processor  14  and mixer  13  both work to transmit and receive signals via the two-conductor cable. A reading of line voltage and/or current at the pre-assigned levels will result in correct functioning of the system. The signal processor is ordinarily to be built-in to the main control panel  10 . The mixer will ordinarily be built-in or installed at the remote unit. 
   Different output signals from the control system through the signal processor will change the voltage and/or current in the two-conductor cable to different levels. As the mixer in the remote control unit at the other end of line receives different voltage or current levels, the mixer will inform the remote unit what to do. 
   Different output signals from the remote unit through the mixer will also change the current or voltage in the two-conductor cable to different levels. At the other end of the cable, the signal processor receives different current and voltage levels in the line and thereby informs the control system to function accordingly. 
   Current Level Activation from Mixer 
   Once the mixer  13  receives a high-level signal from the keypad  12  by activating any key on the keypad, the transistor Q 2  works and draws high current by which the total current of the remote keypad is increased. This increasing current will turn the transistor Q 9  off, then there is a high-level voltage at R 84  sent to the SIGNAL port  33 # of the CPU at the control panel. 
   Voltage Level Activation from Control Panel Signal Processor 
   After the signal processor of the control panel receives an alarm signal from the alarm hold signal port  37 # of the CPU at the control panel, it creates a high-level voltage to the transistor Q 2 R. The voltage level of the two conductors  11  drops to a level whereupon Zener diode ZD 2  stops and the transistor Q 3  switches off to light up LED 1  and the buzzer beeps. 
   Current Level Activation from Two Conductor&#39;s 
   If the two-conductor cable is cut, there will be no current drawn by the remote keypad. There will also be much less current passing through R 87  and R 88  and the transistor Q 10  will switch off. As a result, there will be higher voltage at port  26 # at the CPU of the control panel, thus indicating tampering. 
   The bridges D 1 , D 2 , D 3  and D 4  make for a two-conductor cable having no polarity. 
   The transistor Q 1 R is for voltage level changing and protection against short-circuiting of the two conductors. 
   It should be appreciated that modifications and alterations obvious to those of skilled in the art are not to be considered as beyond the scope of the present invention. For example, although the drawings and above description relate to the association between a remote keypad and the central processor, the invention is equally applicable to a remote bell box or siren sounder and its association with the central processor.