Self-powered sensor for use in closed-loop security system

Abstract

A self-powered sensor for a closed-loop security system includes a self-powered sensor network which provides a switch-actuating signal upon the detection of a physical condition. An electronic switch, which is in a normally closed position, is connected between the positive and negative poles of a closed-loop security system and opens the loop upon receipt of the switch-actuating signal thereby triggering an alarm. The self-powered sensor network may include a voltage doubler for converting the AC output of a transducer to a DC voltage of an amplitude sufficient to open the switch. When the switch is opened, voltage from the closed-loop security system becomes available to power a visible or audible alarm identifying the sensor that opened the loop.

What is claimed is: 
     
       1. A self-powered sensor for a closed-loop security system, comprising: (a) self-powered sensor network means for providing a switch actuating signal upon the detection of a physical condition wherein said self-powered sensor network means comprises transducer means, said transducer means having a pair of plates separated by a piezoelectric element and having a transient alternating current output, and voltage doubling circuit means responsive to the output of said transducer means, said pair of plates forming a charge storage element of said voltage doubling circuit means, for approximately doubling the peak voltage output of said transducer means to provide said switch actuating signal for a predetermined period of time; and   (b) electronic switch means, said electronic switch means having a semiconductor junction forming a diode included in said voltage doubling circuit means, said electronic switch means being in a normally closed position thereby allowing current in said closed-loop security system to flow therethrough, for opening said closed-loop security system in response to said switch actuating signal.   
     
     
       2. The self-powered sensor of claim 1 wherein said electronic switch means comprises a JFET transistor. 
     
     
       3. The self-powered sensor of claim 1 wherein said electronic switch means comprises a depletion-mode MOSFET transistor. 
     
     
       4. The self-powered sensor of claim 1, further including shunt resistor means connected across said plates for providing a high pass filter for said transducer means. 
     
     
       5. The self-powered sensor of claim 1, further including alarm means associated with said sensor and coupled to said closed-loop security system wherein voltage made available by the opening of said closed loop security system is used to provide power for said alarm means. 
     
     
       6. The sensor of claim 5 wherein said alarm means comprises light-emitting diode means connected in parallel with said electronic switch means. 
     
     
       7. The sensor of claim 5 wherein said self-powered sensor network means includes piezoelectric transducer means and said alarm means comprises an oscillator coupled between said piezoelectric transducer means and a pole of said closed-loop security system for activating said piezoelectric tranducer means so as to cause an audible sound. 
     
     
       8. The sensor of claim 2 wherein said closed-loop security system comprises a positive lead connected to a drain electrode of said JFET transistor and a negative lead connected to a source electrode of said JFET transistor and a voltage threshold detector connected between said positive and negative leads thereby forming a closed loop, said closed loop being powered by a current source. 
     
     
       9. The sensor of claim 1 wherein said self-powered sensor network means comprises a time delay means for maintaining said electronic switch means in an open position for a predetermined period of time after said switch means has been opened by said switch actuating signal. .Iadd. 
     
     
       10.  A self-powered sensor network for a closed loop security system, comprising: (a) self-powered sensor means for providing an electrical signal upon the detection of a physical condition;   (b) timing network means responsive to said electrical signal for generating a switch-actuating signal, said switch-actuating signal having a predetermined time period; and   (c) electronic switch means coupled to said timing network means, said switch means being in a normally closed position thereby allowing current in said closed loop security system to flow therethrough, and responsive to said switch-actuating signal so as to be open during said predetermined time period. .Iaddend. .Iadd.11. The self-powered sensor network of claim 10 wherein said self-powered sensor means comprises transducer means for generating a transient AC signal, and wherein said timing network means includes rectifying means for converting said transient AC signal to a DC signal. .Iaddend. .Iadd.12. The self-powered sensor network of claim 11 wherein said timing network means includes an RC timing circuit. .Iaddend. .Iadd.13. The self-powered sensor network of claim 12 wherein said electronic switch means comprises a JFET transistor. .Iaddend. .Iadd.14. The self-powered sensor network of claim 12 wherein said electronic switch   
     
     
        means comprises a depletion mode MOSFET transistor. .Iaddend. .Iadd.15. The self-powered sensor network of claim 10 further including alarm means associated with said closed loop security system wherein voltage made available by the opening of said closed loop security system is used to provide power for said alarm means. .Iaddend. .Iadd.16. The self-powered sensor network of claim 15 wherein said closed loop security system includes a current source connected in series with a plurality of said electronic switch means and a voltage threshold detector connected in parallel with said current source, said voltage threshold detector having an output coupled to said alarm means. .Iaddend.