Abstract:
An anti-theft alarm system includes a switch-detecting portion including a first switch and a second switch, a controller, a button for enabling the alarm system. If the portable computer is moved without deactivation of the alarm system, the second switch opens, causing a change of a voltage at the first switch which is detected by the controller, the controller thereby sends an alarm control signal to an audio system of the portable computer, and the audio system produces an audible sound for a theft deterrence effect.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    Reference is made to a copending U.S. Patent Application entitled “ANTI-THEFT ALARM SYSTEM FOR PORTABLE COMPUTER,” assigned to the same assignee as that of the present invention. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an alarm system, and particularly to an anti-theft alarm system for a portable computer. 
       DESCRIPTION OF RELATED ART 
       [0003]    Portable computers, as opposed to desktop computers, provide benefits to their users in direct proportion to their small size. Technology has expanded to allow small laptops and notebooks and even smaller palm-sized or hand-held portable computers. The benefits of small size allow portable computers to be carried from place to place with a minimum of effort while taking up very little room in backpacks or briefcases. 
         [0004]    As portable computers are made smaller and lighter, they are also made easier to conceal. The fact that these computers are easy to transport and conceal leads to an increase in the amount of theft of such systems. Portable computers are generally stolen by people who may see one lying unattended and simply pick it up and place it in their briefcase. 
         [0005]    What is needed, therefore, is an anti-theft alarm system for a portable computer which can provide a sounding of an alarm upon unauthorized movement of the portable computer. 
       SUMMARY OF THE INVENTION 
       [0006]    An anti-theft alarm system for a portable computer is provided. In a preferred embodiment, the anti-theft alarm system includes a controller, a button for enabling the alarm system, and a switch-detecting portion including a first switch and a second switch. When the controller outputs an enable signal to the first switch, the alarm system is active and protecting the portable computer from theft. If the portable computer is moved without deactivation of the alarm system, the second switch opens, causing a change of a voltage at the first switch which is detected by the controller, the controller thereby sends an alarm control signal to an audio system of the portable computer, and the audio system produces an audible sound for a theft deterrence effect. 
         [0007]    Other advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic diagram of an anti-theft alarm system for a portable computer, in accordance with a preferred embodiment of the present invention; 
           [0009]      FIG. 2  is a schematic diagram of an audio system of  FIG. 1 , in accordance with a preferred embodiment of the present invention; 
           [0010]      FIG. 3  is a schematic diagram of a switch-detecting portion of  FIG. 1 , in accordance with a preferred embodiment of the present invention; and 
           [0011]      FIG. 4  is a schematic diagram of two switches mounted in the portable computer of  FIG. 1 , in accordance with a preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]      FIG. 1  shows an anti-theft alarm system for a portable computer, in accordance with a preferred embodiment of the present invention. The anti-theft alarm system includes a keyboard controller (KBC)  10 , an enable/disable button  20 , a switch-detecting portion  30 , and a memory  40 , an audio system  50 , a light emitting diode (LED) indicator  60 , an input/output controller hub (ICH)  70 , a memory controller hub (MCH)  80 , a central processing unit (CPU)  90 . 
         [0013]    The button  20  is connected to a general purpose wake up pin of the KBC  10 , for delivering an alarm system enable or disable signal to the KBC  10 . The button  20  can be a key of a keyboard of the portable computer suitably configured and programmed. The switch-detecting portion  30  is provided for detecting unauthorized movement of the portable computer away from a supporting surface. The switch-detecting portion  30  is connected to the KBC  10  and when unauthorized movement of the portable computer is detected, the switch-detecting portion  30  will send an alarm signal to the KBC  10 . The memory  40  is used to store data processed by the KBC  10 , e.g. a user password to be input to the portable computer for enabling and/or disabling the alarm system. The indicator  60  is connected to a general-purpose input/output pin of the KBC  10 , for indicating whether the alarm system is enabled or not. When the alarm system is disabled, the indicator  60  is unlit. When the alarm system is enabled, the indicator  60  is lit. While the alarm system is enabled, if unauthorized movement is detected, the indicator  60  blinks. The KBC  10  is connected to the CPU  90  via the ICH  70  and the MCH  80 . The audio system  50  is also connected to the CPU  90  via the ICH  70  and the MCH  80 . 
         [0014]    As shown in  FIG. 2 , the audio system  50  is an existing system of the portable computer. The audio system  50  includes an AC 97  codec  51 , an audio amplifier  52 , a speaker  53 , and transistors  54 ,  55 . The KBC  10  provides an alarm-controlling signal PCBEEP to the audio system  50  when the KBC  10  receives the alarm signal. The codec  51  is connected to the ICH  70  via an AC-link interface. Collectors of the transistors  54 ,  55  are connected to an earphone input HP-IN of the audio amplifier  52 . Emitters of the transistors  54 ,  55  are connected to ground. A base of the transistor  54  is used for receiving an earphone interface input HP-IN#. A base of the transistor  55  is used for receiving an earphone bypass input BYPASS-HP-IN from the KBC  10 . The speaker  53  sounds an alarm only if the earphone input HP-IN of the audio amplifier  52  is at a low level. 
         [0015]    As shown in  FIG. 3 , the switch-detecting portion  30  includes a diode D 1 , metallic oxide semiconductor field effect transistors (MOSFETs)  31 ,  32 , mechanical switches  33 ,  34 , and resistors  35 ,  36 ,  37 ,  38 ,  39 . Gates of both of the MOSFETs  31 ,  32  are connected to the KBC  10  via the diode D 1 , and a 3.3V-voltage input V 1  via the resistor  35 . A source of the MOSFET  31  is connected to the voltage input V 1  via the resistor  36 , ground via the resistor  37 , and the KBC  10 . The switch  33  is connected between the drain of the MOSFET  31  and ground. A source of the MOSFET  32  is connected to the voltage input V 1  via the resistor  38 , ground via the resistor  39 , and the KBC  10 . The switch  34  is connected between the drain of the MOSFET  32  and ground. When a cathode of the diode D 1  receives a high-level disable signal from the KBC  10 , voltages at the sources of the MOSFETs  31 ,  32  remain constant despite changes in open-close states of the mechanical switches  33 ,  34 . When the cathode of the diode D 1  receives a low-level enable signal from the KBC  10 , and the mechanical switches  33 ,  34  switch from closed to open, the MOSFETs  31 , 32  switch from on to off, and voltages at the sources of the MOSFETs  31 ,  32  change. The changes are sent as alarm signals to the KBC  10 . The diode D 1  serves to avoid leakage when the voltage input V 1  is not provided and the high-level disable signal is provided. 
         [0016]    As shown in  FIG. 4 , the mechanical switches  33 ,  34  are respectively mounted in cushions  35 ,  36  of the portable computer  100  and deformable via an outside force. For example, when the portable computer  100  is placed on a supporting surface (not shown), the mechanical switches  33 ,  34  are depressed, that is, closed. When the portable computer  100  is moved away from the supporting surface, the mechanical switches  33 ,  34  release, that is, open. 
         [0017]    When the alarm system enabling signal is input to the KBC  10  by pressing the button  20 , an operating system, e.g. Windows or Linux, stores a status of a system volume control, a basic input/output system (BIOS) maximizes the system volume, and the KBC  10  outputs a mute-disabling signal MUTE-IN to the audio amplifier  52  for disabling a possible mute status of the audio system  50 . Then the KBC  10  sets an alarm system enable flag in a register of the KBC  10 , and the KBC  10  outputs the low-level enable signal to the switch-detecting portion  30 , enabling the switch-detecting portion  30  to detect unauthorized movement of the portable computer. 
         [0018]    Once the portable computer is moved away from the supporting surface, the first switch  33  and the second switch  34  are open. The switch-detecting portion  30  thereby provides the alarm signals to the KBC  10 . Then the KBC  10  outputs the alarm control signal PCBEEP to the codec  51 , which converts the alarm control signal PCBEEP to an analog audio signal. Meanwhile the CPU  90  calls an audio driver. The audio amplifier  52  amplifies the analog audio signal and causes the speaker  53  to output with maximum system volume. The KBC  10  also provides a high-level earphone bypass input BYPASS-HP-IN to the base of the transistor  55  in order to make the earphone input HP-IN of the audio amplifier  52  at a low level. Therefore even if an earphone is plugged in to the portable computer at a time of unauthorized movement, the earphone interface input HP-IN# is at a low level, and the speaker  53  can still sound an alarm. 
         [0019]    To disable the alarm system, the button  20  is pressed again. The alarm system disable signal is input to the KBC  10 . A dialogue box asking for a password pops up on a display of the computer. When a correct password is input, the alarm system enable flag in the register of the KBC  10  is cleared. Then the KBC  10  outputs the high-level enable signal to the switch-detecting portion  30 , disabling the switch-detecting portion  30  and the computer resuming a normal state. 
         [0020]    In addition, the MOSFETs  31 ,  32  may alternatively be replaced with other suitable electrical switches such as bipolar junction transistors. For the portable computer  100  generally having four cushions, the number of the mechanical switches can be one, three, or four, and the number of corresponding MOSFET can be one, three, or four. 
         [0021]    It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments.