Abstract:
A warning device having a sensing signal transmitting unit which includes a sensing element which operates when, for example, a door under observation is opened, and a receiving unit which produces a warning in response to the transmitted signal.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to a warning device. More particularly, it relates to a warning device comprising one or more sensing signal transmitting units and a single receiving unit electrically connected therewith wherein a sensor connected with the transmitting unit generates a sensing signal when, for example, a door under observation is opened, and the signal is transmitted to the receiving unit to provide a warning. 
     In particular, the warning device of the present invention comprises at least one sensing signal transmitting unit and a single receiving unit. 
     The transmitting unit includes a sensor which provides a sensing signal of a predetermined low frequency when, for example, a door under observation is opened. The transmitting unit further includes a low frequency oscillation portion which provides a low frequency signal in response to the sensing signal. The portion may be, for example, a resonance element. The low frequency signal is then frequency-multiplied and modulated to a high frequency signal by a modulation portion. A high frequency oscillation portion transmits the high frequency signal through a transmitting antenna. 
     The receiving unit in turn includes a receiving antenna to receive the high frequency signal from the transmitting unit, a frequency modulation portion which amplifies selectively the high frequency signal to an intermediate frequency signal, an intermediate frequency amplifying circuit which amplifies the signal, a detection circuit which detects a signal having the same frequency as that of the resonance frequency of the low frequency oscillation portion in the transmitting unit, a low frequency amplifying portion which receives the signal of the resonance frequency through a coupling condensor, a selection circuit which selects the output of the low frequency amplifying portion by, for example, the same resonance element as that in the transmitting unit, a low frequency amplifying circuit which amplifies the output signal of the selection circuit, a voltage doubler rectifying circuit which rectifies the output signal of the low frequency amplifying circuit to a direct current, and a driving circuit for warning which operates in response to a d.c. voltage resulting from the direct current. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The other features and the objects of the present invention will be apparent from the following description of preferred embodiments thereof in connection with the drawings attached hereto: in which, 
     FIG. 1 shows a block diagram of a sensing signal transmitting unit of the warning device of the invention; 
     FIG. 2 shows a block diagram of a receiving unit of the warning device of the invention; 
     FIG. 3 shows an embodiment of a circuit arrangement of the transmitting unit of FIG. 1; 
     FIG. 4 shows an embodiment of a circuit arrangement of the receiving unit of FIG. 2; and 
     FIG. 5 shows a further embodiment of a circuit arrangement of a receiving unit of the warning device of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     First referring to FIG. 1 which illustrates a block diagram of the sensing signal transmitting unit, the unit comprises a sensing portion 1, a low frequency oscillation portion 2, a high frequency oscillation portion and modulation portion 3, and a transmitting antenna ANT 1 . 
     FIG. 3 shows an embodiment of a circuit arrangement of the transmitting unit of FIG. 1, in which the sensing portion 1 has a sensor S 1 . When the sensor closes, the whole unit turns on, and a d.c. voltage is applied to an input terminal of a tuning fork filter FIL through resistors R 2  and R 4 , thereby causing a slight oscillation of the filter. The oscillation frequency of the filter is then amplified by an amplifying portion which comprises a transistor Tr 2  and resistors R 6 , R 7  and R 8 , and is positively fed back to the base of a transistor Tr 1  through a resistor R 5  and a condensor C 10 . The fed back signal is further amplified in an amplifying portion which comprises the transistor Tr 1  and resistors R 1 , R 2  and R 3 . The amplified signal enters again the filter. With the repetition of the above operations, the output of the transistor Tr 2  increases. 
     The output of the transistor Tr 2  is given to the base of a transistor Tr 3  to produce a modulated signal. The signal is multiplied and modulated to a high frequency signal in a multiplying and modulation portion. A high frequency oscillation portion, including transistors Tr 3  and Tr 4 , transmits the high frequency signal through the transmitting antenna ANT 1 . Diodes D 1  and D 2  are for bias stabilization. C 2  and C 3  are coupling condensors, and L 1  and L 2  are for stabilization of the circuit configurations involved. 
     FIG. 2 illustrates a block diagram of the receiving unit. The unit comprises a receiving antenna ANT 2 , an FM end portion 7 including a high frequency amplifying portion 4, a local oscillation portion 5 and a mixing portion 6, an intermediate frequency amplifying portion 8, a detection circuit 9, an amplifying portion 10, a selection circuit 11, an amplifying portion 12, a rectifying portion 13, a driving portion 14, and a warning portion 15. 
     As shown in FIG. 4, the signal from the transmitting unit is received by the receiving antenna ANT 2 , and then by the FM front end portion 7. The FM portion 7 amplifies the signal selectively to an intermediate frequency signal. The signal is then selectively amplified by an intermediate frequency amplifying portion 8, and enters a detection circuit 9 which includes diodes D 3  and D 4 . 
     The thus detected signal is a signal of the same frequency as the resonance frequency of the filter FIL, and enters a low frequency amplifying portion 10 which comprises an amplifying circuit IC 1  and resistors R 16 , R 17  and R 18 , through a coupling condensor C 6 , thus providing an input signal to a tuning fork filter FIL 1  in the selection circuit 11. 
     The filter FIL 1  has the same resonance frequency as that of the filter FIL in the transmitting unit so as to oscillate at that frequency only, to thereby select the desired signal. 
     The selected signal is amplified in a low frequency amplifying portion 12 which comprises an amplifying circuit IC 2 , resistors R 21 , R 22  and R 23 , and then is converted into a direct current in a voltage doubling rectifying circuit 13 which comprises diodes D 5  and D 6 , and condensors C 11  and C 12 . Switch contact Sx is provided to selectively disable the receiving unit by shorting the rectified selected d.c. voltage signal to ground. The thus produced d.c. voltage produces a gate voltage of an SCR V 2 , thereby causing the SCR to conduction. Upon the conduct of the SCR V 2 , a relay R1 1  is activated to close its contacts, thereby causing a buzzer BZ to generate a warning. 
     According to the present invention, as is apparent, even when the sensor is restored to its original position, the warning continues on account of the operation of the SCR. The warning stops by the pushing a reset switch S 2  after restoring the sensing portion to its original state. Furthermore, according to the present invention, a self-restoring warning device is obtainable by the use of a transistor circuit arrangement including a timer means arranged so as to operate the reset switch S 2 . 
     According to the present invention, there is further provided a warning device which is so designed as not to generate a warning signal needlessly. The warning device further comprises, in addition to the sensing signal transmitting unit as is above stated, at least one portable transmitting unit and at least one modified receiving unit. The portable unit has the same construction as that of the transmitting unit previously described except with regard to the sensor S. The portable unit has a hand-operated switch in place of the sensor. The modified receiving unit, (as illustrated in FIG. 5), further includes, in addition to the construction previously described, a tuning fork filter FIL 2 , a low frequency amplifying portion 12a including an amplifying circuit IC 3  and resistors R 28 , R 29  and R 30 , and a rectfying circuit 13a, with the filter FIL 2  tuned to the same resonance frequency as that of the portable transmitting unit filter and connected with the filter FIL 1  in parallel and having a resonance frequency ratio of 2:1. The second relay R1 2  is arranged to operate the switch contact Sx when activated by transistor V 3 . The warning device, comprising the sensing signal transmitting unit, the portable transmitting unit and the modified receiving unit, is used when a needless warning should be avoided. That is, the portable unit is turned on by a carrier when he opens a door to disable the warning unit. Each of a plurality of carriers may have each portable unit. 
     As has been set forth above, since the warning device of the present invention operates through electric waves, there is no need of connecting the units with each other by wires. Also, the sensing signal transmitting units may be provided at any desired number of places to be observed since the units can have the same tuning fork filter oscillating at a single frequency so as to operate the single receiving unit. The warning device of the invention has a further advantage in that any type of sensing element can be used, that is, either a contacting type or non-contacting type. Furthermore, the device has an excellent selectivity for signals since it has a resonance element, and is thus capable of avoiding erroneous operation. 
     According to the modified device of the invention, the warning operation is effected by electric waves, and if necessary, the device can be made inoperative by a similar operation. If desired, the device can be connected to remote buzzers, etc, by telephone circuits.