Bed egress alarm circuit

Abstract

A condition responsive circuit for generating an output signal upon the opening of a switch. An FET draws nominal current when the switch is closed. When the switch is opened the FET conducts to generate an output. The output may include an audio alarm, an oscillator and a transmitter to generate an alarm at a distant location, or a visual indicator.

What is claimed is: 
     
       1. A condition responsive circuit for signalling the departure of a patient from a bed or the like by generating an output signal upon the opening of a switch, comprising: a switch being normally closed by the weight of a patient in a bed;   an FET having source, drain and gate electrodes, said gate electrode connected to said switch for normally drawing only a nominal current and for continuously biasing said gate electrode to render said FET non-conductive;   a normally off output means coupled to said at least one of .Iadd.said .Iaddend.source and drain electrodes for generating an output signal when said FET is rendered conductive;   the opening of said switch to remove the continuous bias from said gate electrode;   delay means coupled to said switch and said gate electrode for maintaining a bias at said gate electrode to prevent said FET from being rendered conductive for a predetermined time interval after the opening of said switch; and   said output means including an SCR, an SCR switch, and a signal means, all connected in series;   said SCR being rendered conductive by said FET being rendered conductive to thereby generate an output signal from said signal means, and said SCR being thereafter rendered non-conductive only by operating said SCR switch.   
     
     
       2. A condition responsive circuit for signalling the departure of a patient from a bed or the like by generating an output signal upon the opening of a switch, comprising: a switch being normally closed by the weight of a patient in a bed;   an FET having source, drain and gate electrodes, said gate electrode connected to said switch for normally drawing only a nominal current and for continuously biasing said gate electrode to render said FET non-conductive;   a normally off output means coupled to at least one of said source and drain electrodes for generating an output signal when said FET is rendered conductive;   the opening of said switch to remove the continuous bias from said gate electrode; and   delay means coupled to said switch and said gate electrode for maintaining a bias at said gate electrode to prevent said FET from being rendered conductive for a predetermined time interval after the opening of said switch.   
     
     
       3. The circuit of claim .[.1.]. .Iadd.2 .Iaddend.and further including: second switch means connected in series with said normally closed switch for testing the operation of said circuit by removing said continuous bias from the FET gate.   
     
     
       4. The circuit of claim .[.1.]. .Iadd.2 .Iaddend.wherein said output means includes a normally non-conductive electronic switch rendered conductive when said FET is rendered conductive. 
     
     
       5. The circuit of claim 4 wherein said output means further includes an oscillator coupled in series to said electronic switch, said oscillator being energized when said FET and said electronic switch are rendered conductive. 
     
     
       6. The circuit of claim 4 wherein said output means further includes a normally off transmitter which is turned on by said FET and said electronic switch being rendered conductive, the frequency of the transmitter being modulated by said oscillator. 
     
     
       7. The circuit of claim 4 wherein said electronic switch is an SCR. 
     
     
       8. The circuit of claim 7 and including third switch means in series with said SCR for rendering said SCR non-conductive after said SCR is rendered conductive by said FET being rendered conductive. 
     
     
       9. The circuit of claim .[.1.]. .Iadd.2 .Iaddend.wherein said switch is pressure sensitive. 
     
     
       10. The circuit of claim .[.1.]. .Iadd.2 .Iaddend.wherein said output means includes an audio alarm.