Emergency Radio Warning System
United States Patent 3864674
A radio warning system includes emergency condition sensors for actuating respective radio transmitters which are modulated by identification generators to produce identification signals which contain one or more frequencies selected from groups of four frequencies in accordance with selected identifying binary coded decimal digits. A transmitted identification signal is detected by a radio receiver in a mobile unit or central dispatch location to operate a memory and a decimal display unit to indicate the existence and location of the emergency condition until reset by an operator. The transmitters are deactuated by a timing circuit after a predetermined period. Delay circuitry prevents operation of the memory and decimal display unit until the identification signal has been received for a predetermined continuous duration.
US Patent References:
Selective calling system
Durkee et al. - May 1962 - 3035250
Time delay circuit for briefly holding a selective call transmitter energized
Ruthenberg - February 1967 - 3304501
EMERGENCY WARNING AND IDENTIFICATION APPARATUS FOR TWO-WAY RADIO COMMUNICATION SYSTEM
Buehrle, Jr. - May 1971 - 3581208
CODED SIGNAL COMMUNICATION SYSTEM
Fraunfelder - December 1971 - 3629837
EMERGENCY REPORTING DIGITAL COMMUNICATIONS SYSTEM
McMurray - September 1972 - 3694579
Selective calling system
Durkee et al. - May 1962 - 3035250
Time delay circuit for briefly holding a selective call transmitter energized
Ruthenberg - February 1967 - 3304501
EMERGENCY WARNING AND IDENTIFICATION APPARATUS FOR TWO-WAY RADIO COMMUNICATION SYSTEM
Buehrle, Jr. - May 1971 - 3581208
CODED SIGNAL COMMUNICATION SYSTEM
Fraunfelder - December 1971 - 3629837
EMERGENCY REPORTING DIGITAL COMMUNICATIONS SYSTEM
McMurray - September 1972 - 3694579
Inventors:
Worsham, Robert (Opa Locka, FL)
Martin, Stephen J. (Miami, FL)
Martin, Stephen J. (Miami, FL)
Application Number:
05/315856
Publication Date:
02/04/1975
Filing Date:
12/18/1972
View Patent Images:
Export Citation:
Assignee:
Criminalistics, Inc. (Opa Locka, FL)
Primary Class:
Other Classes:
375/242, 340/539.180, 340/539.100, 340/825.750
International Classes:
G08B25/01; H04B7/00; H04Q11/02
Field of Search:
325/64,18 340/224,171,171PF,171R
US Patent References:
| 3713125 | ALARM SYSTEM UTILIZING A DIGITAL RADIO LINK | January 1973 | Miller |
Primary Examiner:
Yusko, Donald J.
Attorney, Agent or Firm:
O'brien, Anthony A.
Claims:
What is claimed is
1. An emergency radio warning system comprising:
2. A system as defined in claim 1 wherein said receiving and detecting means includes
3. An emergency radio warning system comprising:
4. A system as defined in claim 3 which includes:
5. A system as defined in claim 3 wherein:
6. An emergency radio warning system comprising
7. An emergency radio warning system comprising
8. A system as defined in claim 7 wherein the timing means for disabling the receiving and detecting means and for enabling the displaying means includes:
9. A sensing and transmitting system for generating a radio signal modulated by identification signals for identifying the location of an emergency condition comprising:
10. A system as defined in claim 9 which includes:
11. A sensing and transmitting system for generating a radio signal modulated by identification signals for identifying the location of an emergency condition, comprising:
12. A receiving and displaying system which senses and displays an identifying decimal digit from a radio signal which is modulated by an identification signal containing one or more frequencies selected from a group of four frequencies in accordance with a binary coded decimal digit which corresponds to the identifying decimal digit to indicate the location of an emergency condition, comprising
13. A system as defined in claim 12 wherein the timing means for disabling the receiving and detecting means and for enabling the displaying means includes:
14. A system as defined in claim 12 which includes:
15. A system as defined in claim 12 wherein each of the four filter means includes:
16. A system as defined in claim 12 wherein each of the four filter means includes a tuning fork filter.
1. An emergency radio warning system comprising:
2. A system as defined in claim 1 wherein said receiving and detecting means includes
3. An emergency radio warning system comprising:
4. A system as defined in claim 3 which includes:
5. A system as defined in claim 3 wherein:
6. An emergency radio warning system comprising
7. An emergency radio warning system comprising
8. A system as defined in claim 7 wherein the timing means for disabling the receiving and detecting means and for enabling the displaying means includes:
9. A sensing and transmitting system for generating a radio signal modulated by identification signals for identifying the location of an emergency condition comprising:
10. A system as defined in claim 9 which includes:
11. A sensing and transmitting system for generating a radio signal modulated by identification signals for identifying the location of an emergency condition, comprising:
12. A receiving and displaying system which senses and displays an identifying decimal digit from a radio signal which is modulated by an identification signal containing one or more frequencies selected from a group of four frequencies in accordance with a binary coded decimal digit which corresponds to the identifying decimal digit to indicate the location of an emergency condition, comprising
13. A system as defined in claim 12 wherein the timing means for disabling the receiving and detecting means and for enabling the displaying means includes:
14. A system as defined in claim 12 which includes:
15. A system as defined in claim 12 wherein each of the four filter means includes:
16. A system as defined in claim 12 wherein each of the four filter means includes a tuning fork filter.
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to emergency warning systems which are used to detect and warn appropriate authorities or personnel of emergency conditions such as crime, fire, pollution, or failure of critical equipment. This invention particularly concerns a remote emergency warning system which utilizes radio signals to indicate the existence and location of an emergency condition.
2. Description of the Prior Art
Present warning systems for alerting law enforcement personnel or police of a crime involve the use of a telephone system to call and alert the police department. The police department then contacts the nearest patrol car through the use of a radio communication system by a dispatcher. This procedure involves much time, with 5 to 10 minutes being typical in some cases, from the moment the emergency occurs to the moment that help is dispatched. Certain systems that automatically call the police department are being banned in many municipalities due to the fact that they tend to jam telephone switchboards and cause confusion. Further, the automatic calling systems are not under the direct control of the law enforcement agency, but represent systems and devices installed by individuals or companies using very unreliable alarm systems, prone to false alarms.
In addition to the warning systems using the telephone system, there are a number of prior art warning systems which utilize radio waves. Examples of prior art warning or communication systems which utilize radio signals are described in U.S. Pat. No. 3,581,208, No. 3,618,067, and No. 3,629,837. The prior art radio warning systems generally have one or more deficiencies, such as being subject to noise and interfering signals, being complex and expensive, interfering with other use of the frequency channels, etc.
SUMMARY OF THE INVENTION
An object of the present invention is a new and improved radio warning system utilizing identification modulation signals for readily identifying the location of an emergency condition.
A further object of the invention is a new and improved sensing and transmitting system for generating a radio signal modulated by identification signals for warning and identifying the location of an emergency condition.
A still further object of the invention is a new and improved receiving and displaying system for sensing an identification modulated radio signal and for indicating the location of an emergency condition.
In accordance with these and other objects, an embodiment of the invention includes an emergency condition sensor operating a radio transmitter modulated by an indentification signal generator which produces one or more frequencies selected from a group of four frequencies in accordance with an identifying binary coded decimal digit. A radio receiver detects the indentification signal and operates a decimal display in accordance with the frequencies in the indentification signal to indicate the location of the emergency condition.
Further, a sensing and transmitting system includes facilities for terminating the operation of the transmitter after a predetermined period.
A receiving and display system for a radio warning signal containing selected frequencies in accordance with an identifying binary coded decimal digit includes facilities for detecting the binary coded decimal digit and operating a decimal display to indicate the decimal digit. Further, the receiving and display system includes a memory for operating the decimal display after the radio warning signal has been terminated. Still further, the receiving and display system has delay facilities for preventing operation of the decimal display until the identifying signal has been received for a predetermined continuous duration.
Other objects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram illustrating the utilization of a radio warning system in accordance with the invention;
FIG. 2 is a block diagram of a sensing and transmitting system for producing radio signals modulated by one or more frequencies selected from a group of four frequencies in accordance with an identifying binary coded decimal digit;
FIG. 3 is a block diagram of a receiving and displaying system for detecting the signals from the system of FIG. 2 and displaying the indentifying decimal digit;
FIG. 4 is a detailed circuit diagram of arming and timing circuits in the system shown in FIG. 2;
FIG. 5 is a detailed circuit diagram showing an identification generator for producing identifying modulation signals in the system shown in FIG. 2;
FIG. 6 is a detailed diagram of a circuit for detecting an identification signal in the receiving and displaying system shown in FIG. 3;
FIG. 7 is a detailed diagram of a memory, driving and displaying circuits in the receiving and displaying system shown in FIG. 3;
FIG. 8 shows a timing circuit for delaying the operation of the displaying circuit of FIGS. 3 and 7 and for terminating the operation of a radio receiver of FIG. 3; and
FIG. 9 illustrates the allocation of identification numbers for different uses in a radio warning system.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As is illustrated in FIG. 1, a sensing and transmitting unit 10 produces a radio signal in response to an emergency condition. The radio signal produced by the unit 10 is modulated by one or more frequencies which are selected from groups of four frequencies in accordance with a binary coded decimal (BCD) number which identifies the location and/or nature of the emergency condition. Receiving and detecting units 11--11 are located in a central dispatch station 12, a vehicle 13 and/or a helicopter 14. The receivers 11--11 may share antennas and radio frequency amplifying and detecting functions with the normal transceiver units used for communication by using directional couplers and other appropriate circuitry. Each of the receivers 11--11 detect the indentification frequencies and operate respective decimal displays 15--15 to show the decimal number and thus indicate the location of the emergency condition.
Referring next to FIG. 2 there is shown a block diagram of transmitting circuitry in the unit 10 which is actuated by the operation of a sensor 17. The sensor 17 may be any electronic device which can be used to detect a condition. For example, the sensor 17 may be a switch device operated by (1) a teller in a bank, (2) the breaking of a window, (3) excessive heat, (4) pollution or (5) failure of critical equipment. An arming circuit 18 is triggered and latched by the operation of the sensor 17 to initiate operation of a radio frequency (RF) transmitter 19 and a BCD identification signal generator 20 to transmit radio warning signals from an antenna 21. The BCD generator 20 applies the identification signal to the audio or modulation input of the transmitter 19. A timing circuit 22 is also activated by the arming circuit 18 to disable the arming circuit 18 and terminate operation of the RF transmitter 19 and BCD generator 20 after a predetermined period of operation. The period is selected to avoid unduly interfering with other use of the RF frequency channel. The arming circuit 18 remains latched and disabled until reset by an operator, such as a police officer, momentarily opening a switch 23 to interrupt current from a battery 24 which is charged by a charger 25. A lamp 26 indicates that the arming circuit 18 has been actuated and latched. A lamp 27 indicates that the RF transmitter 19 and BCD generator 20 are operating. The arming circuit 18 and the timing circuit 22 are more fully described hereinafter under the heading "Arming Circuit and Transmitter Timing Circuit". The BCD generator 20 is more fully described hereinafter under the heading "BCD Generator". The RF transmitter 19 may be any suitable commercially available radio transmitter which can operate at a selected radio frequency under the appropriate government regulations. A frequency modulated transmitter is preferred, but a suitable amplitude modulated transmitter may also be employed. It is contemplated that the identification signals from the BCD generator 20 contain frequencies in the audio range, however, frequencies not within the audio range may be used where a suitable RF transmitter is employed.
A block diagram of circuitry for receiving, detecting and displaying a warning signal generated by the transmitting circuitry of FIG. 2 is shown in FIG. 3. The radio warning signal is received by an RF receiver 32 from an antenna 31. The RF receiver 32 may be any radio receiver, or channel in a multichannel receiver, which is tuned to the radio frequency transmitted by the warning transmitters 19 of FIG. 2. The receiver 32 detects the indentification signal and applies it to the input of a BCD frequency detector 33. The BCD detector 33 produces an output corresponding to a first binary coded decimal digit in the indentification signal after the identification signal has been received for a predetermined continuous duration. The first binary coded decimal digit is applied to a memory circuit 34 and a driving circuit 35 which operates a decimal display 36. If the indentification signal contains a second binary coded decimal digit, a detector 33a, a memory circuit 34a, a driving circuit 35a, and a decimal display 36a are employed to detect and display the second digit. A timing circuit 37 senses the presence of an identification number in the memories 34 and 34a to disable the receiver 32 and to enable the driving circuits 35 and 35a and the displays 36 and 36a after a predetermined delay. Also, an audio alarm 38 is actuated by the timing circuit 37 after the predetermined delay. The duration of delay by the timing circuit 37 insures that the identification signal is detected and applied to the memories 34 and 34a prior to disablement of the receiver 32 and operation of the displays 36 and 36a. The displays 36 and 36a and the audio alarm 38 remain activated until current from a battery 39 is momentarily interrupted by the opening of a manual reset switch 40. The BCD detector 33 is more fully described hereinafter under the heading "BCD Detector". The memory circuit 34, driving circuit 35 and display 36 are more fully described hereinafter under the heading "Memory, Driver, and Display" . The timing circuit 37 is more fully described hereinafter under the heading "Receiver Timing Circuit".
ARMING AND TIMING CIRCUITS
The arming circuit 18 is shown in detail in FIG. 4. The operation of the sensor 17 by an emergency condition applies a triggering signal to a voltage divider consisting of resistors 42 and 43 and thus to a control electrode of a silicon controlled rectifier (SCR) 44. The SCR is connected in series with a resistor 45 and the battery 24 so that a voltage is produced across the resistor 45 when the SCR 44 is triggered into conduction. The voltage on the resistor 45 is applied by a resistor 47 to the base of a transistor 48 to render the transistor 48 conductive. The transistor 48 is connected in series with the battery 24 and a coil 49 of a relay 50. When the coil 49 is energized by conduction of the transistor 48, contacts 51 of the relay 50 are closed to apply an energizing voltage from the battery 24 to a terminal 53 which energizes the RF transmitter 19, BCD generator 20 and lamp 27 of FIG. 2. Also, the voltage across the resistor 45 is applied by a resistor 54 to a base of a transistor 55 connected in series with the battery 24 and the lamp 26 to render the transistor 55 conductive and energize the lamp 26. The SCR 44 and the lamp 26 remain activated until the arming circuit is manually reset by the momentary opening of the reset switch 23 which interrupts the current from the battery 24.
The timing circuit 22 is also energized by the voltage produced across the resistor 45. Current through a variable resistor 57 charges a capacitor 58 to trigger a unijunction transistor 59 connected in series with a resistor 60 across the resistor 45 after a predetermined delay. When the unijunction 59 is triggered, the increase in voltage across the resistor 60 produces a pulse through a capacitor 62 connected to a control electrode of a SCR 63. The SCR 63, when triggered by the pulse through capacitor 62, connects the base of the transistor 48 to a reverse bias potential or ground to render the transistor 48 non-conductive. This deenergizes the relay 50 to terminate operation of the RF transmitter 19, the BCD generator 20 and the lamp 27 of FIG. 2. A diode 64 connected across the coil 49 provides a bypass for induced current when transistor 48 is rendered non-conductive. The values of the capacitor 58 and the variable resistor 57 are selected to produce the predetermined period of operation of the transmitter 19 and BCD generator 20. The SCR 63 is delatched when the reset switch 23 is opened.
BCD GENERATOR
Referring to FIG. 5 there is shown a circuit diagram of a single digit BCD generator 20 which is energized by the application of a voltage to terminal 53 by the arming circuit 18 of FIG. 4. Inverter amplifiers 66-69 with positive feedback through respective filters 71-74 and resistors 76-79 operate as individual oscillators producing frequencies F1, F2, F3, and F4. As shown the inverter amplifiers 66-69 may be a Quad NAND gate package 80, energized by the application of the voltage to terminal 53, with the inputs of each gate connected together. The RCA CD 4011AE has been found to work well in this circuit. The filters 71-74 are preferably a narrow bandwidth type, such as miniature piezoelectric coupled tuning fork filters for audio signalling, series EMR-S manufactured by the MURATA Corporation of America. High Frequency decoupling capacitors 81-84 prevent the oscillators from producing higher than audio frequencies. Capacitors 86-89 couple the outputs of the amplifiers 66-69 to a terminal 70 connected to the audio input of the RF transmitter of FIG. 2.
The oscillators are selectively disabled to produce only one or more of the frequencies F1, F2, F3, and F4 in accordance with a selected binary coded decimal digit which identifies the transmitter and the location of the emergency condition. The BCD generator shown in FIG. 5 generates an identification signal which contains simultaneously generated frequencies in accordance with a single binary coded decimal digit. If an identification signal is to include two or more binary coded decimal digits, additional oscillator circuits substantially similar to that of FIG. 5 are added. The additional circuits would produce additional groups of frequencies which are different from the group of frequencies F1-F4 but simultaneously generated with frequencies F1-F4. For example, 100 indentifying decimal digits 00 through 99 may be provided by using two groups of four frequencies F1-F4 and F5-F8.
BCD DETECTOR
FIG. 6 shows in detail the BCD detector circuit 33 of the circuit shown in FIG. 3. The audio output of the RF receiver 32 is applied in parallel to filters 91-94. The filters 91-94 are selected to pass the respective frequencies F1-F4. The filters 91-94, like the filters 71-74 of FIG. 5, are preferable narrow bandpass type filters, such as miniature piezoelectric coupled tuning fork filters, to prevent erroneous operation by noise and voice signals. The outputs of the filters 91-94 are amplified by the amplifiers 96-99 which are biased linearly by respective resistors 101-104. Like the amplifiers 66-69 of FIG. 5, the amplifiers 96-99 may be a Quad NAND gate package 100 with the inputs of each gate connected together.
The outputs of the amplifiers 96-99 are applied to respective voltage rectifying and doubling circuits including capacitors 106-109, diodes 111-114 and 116-119, capacitors 121-124 and resistors 126-129. During negative half cycles of the identifying signals from the amplifiers 96-99, the respective capacitors 106-109 are charged by current through the diodes 111-114. During positive half cycles of the identifying signals, the diodes 116-119 conduct to transfer the charges on the respective capacitor 106-109 to the capacitors 121-124 and produce output voltages on terminals 131-134 which are about double the maximum amplitudes of the respective identifying signals. The resistors 126-129 provide loads for the diodes 116-119. The capacitors 121-124 are relatively large D.C. filtering capacitors while the capacitors 106-109 are relatively small coupling capacitors. This produces a delay in the voltage on the terminals 131-134 reaching maximum amplitudes. This delay is selected, taking into consideration the bandpass of the filters 71-74, to prevent the operation of the memory circuit 34 of FIG. 3 until the one or more of signals F1-F4 have been present for a predetermined continuous duration to prevent spurious noise signals or voice signals from erroneously actuating the memory circuit 34. The selection of the values of the components in the rectifying and doubling circuits is made to produce the predetermined delay taking into consideration the different frequencies of operation.
The BCD detector circuit of FIG. 6 will only detect one binary coded decimal digit. Additional circuits substantially similar to FIG. 6 are used to sense additional digits in an indentification signal. For example, one additional circuit which senses frequencies F5, F6, F7, and F8 would provide for the detection of 100 decimal numbers 00 through 99.
MEMORY, DRIVER AND DISPLAY
Referring to FIG. 7 there is shown in detail the memory circuit 34, display driving circuit 35, and the decimal display 36. The outputs of the BCD detector 33 on terminals 131-134 are applied by respective diodes 136-139 to control electrodes of SCR's 141-144. If a sufficiently large signal is present on any of the terminals 131-134, the respective SCR is triggered to produce a voltage across a respective resistor 146-149. The SCR's 141-144 remain activated to retain the binary coded decimal digit until the circuit is reset by interruption of voltage on a terminal 150. The voltage or voltages across the resistors 146-149 are applied to terminals 151-154 of the display driving circuit 35 which operates the decimal display 36. The driving circuit 35 is selected to produce appropriate energizing voltages for the particular decimal display in response to a binary coded decimal digit input. For example, the display 36 may be a seven element type, such as RCA model DR 2000. RCA CD 2500E may be used to drive the RCA display. A switch 155 is provided for testing the display 36.
As previously explained, the driving circuit 35 and display 36 are prevented by the timing circuit 37 (FIG. 3) from operating for a predetermined duration after the memory 33 has received a binary digit. Diodes 156-159 are connected to the resistors 146-149 in an OR gate arrangement to apply a signal to terminal 160 when any of the SCR's 141-144 are actuated. This operates the timing circuit 37 (FIG. 3) which, after the predetermined duration, applies an operating voltage to a terminal 177. A transistor 181 connected between the terminal 177 and the power inputs of the driving circuit 35 and the display 36 is controlled by a zener diode 182 and bias resistor 183 to provide a regulated voltage to the driving circuit 35 and the display 36.
RECEIVER TIMING CIRCUIT
Referring to FIG. 8 there is shown the timing circuit 37 for disabling the RF receiver 32 of FIG. 2 and enabling the driving circuit 35 and display 36. When a binary digit has been received by the memory 34, a voltage on the terminal 160 is applied to a series connected resistor 161 and capacitor 162. When the capacitor 162 has sufficiently charged, a unijunction transistor 163 is operated to produce a voltage across a resistor 165. A capacitor 167 connected to the resistor 165 applies a pulse to a control electrode of an SCR 166 which is connected in series with the battery 39 and a coil 168 of a relay 169. Before the coil 168 is energized, a contact arm 171 engages a contact 172 to apply voltage from the battery 39 to a terminal 178 and filtering capacitor 179. The terminal 178 supplies voltage to the RF receiver 32. After the coil 168 has been energized by the conduction of SCR 166, the contact arm 171 disengages the contact 172 and engages a contact 173 to apply a voltage from the battery 39 to the terminal 177 and the audible alarm 38. Thus, the RF receiver 32 is disabled and the driving circuit 35 and display 36 are enabled. The delay of the timing circuit 37 is selected to be greater than any difference in the delays of any two of the outputs of the BCD detector 33 so that the display 36 will indicate the correct identification digit. The alarm 38 and the display 36 remain activated until the reset switch 40 is manually opened to interrupt the current to the SCR 166 and the SCR's 141-144 (FIG. 7) in the memory 33.
OPERATION
In operation of the radio warning system, sensing and transmitting units 10 (FIG. 1) are placed in locations where it is desired to monitor or sense a condition which may require immediate attention. When such a condition occurs, the respective sensing and transmitting unit 10 transmits a radio signal modulated by one or more frequencies selected from one or more groups of four frequencies in accordance with one or more identifying binary coded decimal digits. One or more receiving units 11--11 in the central dispatch station 12, automobile 13 and helicopter 14 receive the radio warning signal and display the identification decimal digit or digits on displays 15--15 and operate audible alarms 38 (FIGS. 3 and 8). The appropriate authority, such as a police officer, may immediately respond and take the appropriate action to overcome or meet the emergency condition.
It is contemplated that the system of the invention be under the control of an appropriate governmental agency, such as the police. The locations to be monitored can thus be selected and limited to readily cover the areas of greatest need within the capabilities of the available personnel. Also the quality of the sensing and transmitting units may be readily controlled and maintained to produce a high standard of service.
The identifying modulation signals for one binary coded digit are produced by the oscillator amplifiers 66-69 shown in FIG. 5. To select the frequencies in accordance with the identifying binary coded decimal digit, the oscillating circuits are selectively disabled by open circuiting the inputs or outputs of selected amplifiers 66-69 or eliminating or disconnecting selected filters 71-41, resistors 76-79 or capacitors 86-89. Thus, the modulation signal contains one or more simultaneously generated frequencies selected from the group of frequencies F1-F4. For additional identifying decimal digits, additional oscillator circuits may be added to supply additional groups of four frequencies. The use of identification frequencies selected in accordance with indentifying binary coded decimal digits allows the use of inexpensive conventional binary coded decimal circuits.
TABLE I ______________________________________ Binary Inverted Coded Binary Coded Decimal Decimal Decimal Inverted Digit Digit Frequencies Digit Frequencies ______________________________________ 0 0000 None 1111 F1, F2, F3, F4 1 0001 F1 1110 F2, F3, F4 2 0010 F2 1101 F1, F3, F4 3 0011 F1, F2 1100 F3, F4 4 0100 F3 1011 F1, F2, F4 5 0101 F3, F1 1010 F2, F4 6 0110 F3, F2 1001 F1, F4 7 0111 F3, F2, F1 1000 F4 8 1000 F4 0111 F3, F2, F1 9 1001 F4, F1 0110 F3, F2 ______________________________________ In TABLE I, there are illustrated two schemes for selecting frequencies F1, F2, F3, and F4 in accordance with a binary coded decimal digit. The third column lists a selection of frequencies made in accordance with binary coded decimal digits listed in the second column which correspond to the respective decimal digits in the first column. The fourth column is the inverse of the second column while the fifth column illustrates a selection of frequencies in accordance with the inverted binary coded decimal digits. Other conventional binary coding schemes and frequency selection may be used so long as they are readily employable with available decimal circuitry.
One of the advantages of the invention is the large number of identifying numbers which are available for a relatively few modulation frequencies. Four frequencies provide 10 identifying digits, eight frequencies provide 100 identifying digits, 12 frequencies provide 1,000 identifying digits, etc. This allows flexibility in the employment of a radio warning system with a minimum use of a radio frequency channel.
In FIG. 9 there is illustrated an allocation of the identifying numbers for a variety of uses. The numbers may be allocated for use in (1) sensing crime, such as burglary, robbery, etc.; (2) sensing a fire or fire alarm; (3) sensing other matters concerning public health and safety, such as air or water pollution, etc.; (4) sensing an emergency distress, such as a need for service on a highway; and (5) sensing industrial equipment failure. The allocation of the identifying numbers and use of the system may be under the control of a local governmental organization, such as a police department, thus enabling optimum usage of the system.
After a predetermined period of operation, the transmission of a radio warning signal is terminated by the operation of the unijunction transistor 59 (FIG. 4) which fires the SCR 63 to render the transistor 48 non-conductive and open the relay 50 to disrupt power to the transmitter 19 and BCD generator 20. This prevents the transmitting unit from unduly interfering with other use of the radio frequency channel. The period of operation may be selected by adjusting the variable resistor 57. Typically, the period may be selected from the range of 10 to 100 seconds, but periods outside this range may be readily used.
Once the sensor 17 (FIGS. 2 and 4) has triggered and latched the arming circuit 18, the lamps 26 and 27 are energized. The lamp 27 remains energized only during the operation of the transmitter 19 and BCD generator 20. The lamp 26 remains energized until the arming circuit 18 is delatched by manually opening the reset switch 23.
The radio frequency warning signal is received by the RF receiver 32 (FIG. 3) which detects and produces the identifying signal. The receiving and displaying system may be readily employed with conventional radio communication equipment used by commercial establishments or governmental authorities, such as the police. The radio receiver 32 and the antenna 31 may be part of their normal communication equipment.
The frequencies in the identification signal are sensed by the filters 91-94 (FIG. 6) and applied to rectifying and doubling circuits. The use of narrow bandpass filters helps prevent interference from noise and spurious signals or ordinary communication in the operation of the warning system. Also, the delays caused by the capacitors 106-109 and 121-124, diodes 111-114 and 116-119, and resistors 126-129 in the rectifying and doubling circuits insure that the identification signals have been present for a predetermined continuous duration and help prevent interference from erroneously operating the SCR's 141-144 (FIG. 7) in the memory 34 or 34a. A range of delays from 1/2 to 1 second is acceptable but durations of delays outside that range may produce equally acceptable results.
Once a binary digit or digits have been received by the memories 34 and 34a, the timing circuit 37 (FIG. 8) is operated after a predetermined delay to disable the RF receiver 32 and to enable the driving circuits 35 and 35a, the displays 36 and 36a and the alarm 38. The delay of the timing circuit 37 allows for differences in the delays of the rectifying and doubling circuits of the BCD detector 33 to insure that all the binary digits of the binary coded decimal digit or digits have been received by the memories 34 and 34a. After the operation of the timing circuit 37, the identifying decimal digit or digits remain displayed on the displays 34 and 34a and the alarm 38 remains actuated until an operator resets the timing circuit 36 by momentarily opening the switch 40.
Inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
1. Field of the Invention
The present invention relates to emergency warning systems which are used to detect and warn appropriate authorities or personnel of emergency conditions such as crime, fire, pollution, or failure of critical equipment. This invention particularly concerns a remote emergency warning system which utilizes radio signals to indicate the existence and location of an emergency condition.
2. Description of the Prior Art
Present warning systems for alerting law enforcement personnel or police of a crime involve the use of a telephone system to call and alert the police department. The police department then contacts the nearest patrol car through the use of a radio communication system by a dispatcher. This procedure involves much time, with 5 to 10 minutes being typical in some cases, from the moment the emergency occurs to the moment that help is dispatched. Certain systems that automatically call the police department are being banned in many municipalities due to the fact that they tend to jam telephone switchboards and cause confusion. Further, the automatic calling systems are not under the direct control of the law enforcement agency, but represent systems and devices installed by individuals or companies using very unreliable alarm systems, prone to false alarms.
In addition to the warning systems using the telephone system, there are a number of prior art warning systems which utilize radio waves. Examples of prior art warning or communication systems which utilize radio signals are described in U.S. Pat. No. 3,581,208, No. 3,618,067, and No. 3,629,837. The prior art radio warning systems generally have one or more deficiencies, such as being subject to noise and interfering signals, being complex and expensive, interfering with other use of the frequency channels, etc.
SUMMARY OF THE INVENTION
An object of the present invention is a new and improved radio warning system utilizing identification modulation signals for readily identifying the location of an emergency condition.
A further object of the invention is a new and improved sensing and transmitting system for generating a radio signal modulated by identification signals for warning and identifying the location of an emergency condition.
A still further object of the invention is a new and improved receiving and displaying system for sensing an identification modulated radio signal and for indicating the location of an emergency condition.
In accordance with these and other objects, an embodiment of the invention includes an emergency condition sensor operating a radio transmitter modulated by an indentification signal generator which produces one or more frequencies selected from a group of four frequencies in accordance with an identifying binary coded decimal digit. A radio receiver detects the indentification signal and operates a decimal display in accordance with the frequencies in the indentification signal to indicate the location of the emergency condition.
Further, a sensing and transmitting system includes facilities for terminating the operation of the transmitter after a predetermined period.
A receiving and display system for a radio warning signal containing selected frequencies in accordance with an identifying binary coded decimal digit includes facilities for detecting the binary coded decimal digit and operating a decimal display to indicate the decimal digit. Further, the receiving and display system includes a memory for operating the decimal display after the radio warning signal has been terminated. Still further, the receiving and display system has delay facilities for preventing operation of the decimal display until the identifying signal has been received for a predetermined continuous duration.
Other objects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram illustrating the utilization of a radio warning system in accordance with the invention;
FIG. 2 is a block diagram of a sensing and transmitting system for producing radio signals modulated by one or more frequencies selected from a group of four frequencies in accordance with an identifying binary coded decimal digit;
FIG. 3 is a block diagram of a receiving and displaying system for detecting the signals from the system of FIG. 2 and displaying the indentifying decimal digit;
FIG. 4 is a detailed circuit diagram of arming and timing circuits in the system shown in FIG. 2;
FIG. 5 is a detailed circuit diagram showing an identification generator for producing identifying modulation signals in the system shown in FIG. 2;
FIG. 6 is a detailed diagram of a circuit for detecting an identification signal in the receiving and displaying system shown in FIG. 3;
FIG. 7 is a detailed diagram of a memory, driving and displaying circuits in the receiving and displaying system shown in FIG. 3;
FIG. 8 shows a timing circuit for delaying the operation of the displaying circuit of FIGS. 3 and 7 and for terminating the operation of a radio receiver of FIG. 3; and
FIG. 9 illustrates the allocation of identification numbers for different uses in a radio warning system.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As is illustrated in FIG. 1, a sensing and transmitting unit 10 produces a radio signal in response to an emergency condition. The radio signal produced by the unit 10 is modulated by one or more frequencies which are selected from groups of four frequencies in accordance with a binary coded decimal (BCD) number which identifies the location and/or nature of the emergency condition. Receiving and detecting units 11--11 are located in a central dispatch station 12, a vehicle 13 and/or a helicopter 14. The receivers 11--11 may share antennas and radio frequency amplifying and detecting functions with the normal transceiver units used for communication by using directional couplers and other appropriate circuitry. Each of the receivers 11--11 detect the indentification frequencies and operate respective decimal displays 15--15 to show the decimal number and thus indicate the location of the emergency condition.
Referring next to FIG. 2 there is shown a block diagram of transmitting circuitry in the unit 10 which is actuated by the operation of a sensor 17. The sensor 17 may be any electronic device which can be used to detect a condition. For example, the sensor 17 may be a switch device operated by (1) a teller in a bank, (2) the breaking of a window, (3) excessive heat, (4) pollution or (5) failure of critical equipment. An arming circuit 18 is triggered and latched by the operation of the sensor 17 to initiate operation of a radio frequency (RF) transmitter 19 and a BCD identification signal generator 20 to transmit radio warning signals from an antenna 21. The BCD generator 20 applies the identification signal to the audio or modulation input of the transmitter 19. A timing circuit 22 is also activated by the arming circuit 18 to disable the arming circuit 18 and terminate operation of the RF transmitter 19 and BCD generator 20 after a predetermined period of operation. The period is selected to avoid unduly interfering with other use of the RF frequency channel. The arming circuit 18 remains latched and disabled until reset by an operator, such as a police officer, momentarily opening a switch 23 to interrupt current from a battery 24 which is charged by a charger 25. A lamp 26 indicates that the arming circuit 18 has been actuated and latched. A lamp 27 indicates that the RF transmitter 19 and BCD generator 20 are operating. The arming circuit 18 and the timing circuit 22 are more fully described hereinafter under the heading "Arming Circuit and Transmitter Timing Circuit". The BCD generator 20 is more fully described hereinafter under the heading "BCD Generator". The RF transmitter 19 may be any suitable commercially available radio transmitter which can operate at a selected radio frequency under the appropriate government regulations. A frequency modulated transmitter is preferred, but a suitable amplitude modulated transmitter may also be employed. It is contemplated that the identification signals from the BCD generator 20 contain frequencies in the audio range, however, frequencies not within the audio range may be used where a suitable RF transmitter is employed.
A block diagram of circuitry for receiving, detecting and displaying a warning signal generated by the transmitting circuitry of FIG. 2 is shown in FIG. 3. The radio warning signal is received by an RF receiver 32 from an antenna 31. The RF receiver 32 may be any radio receiver, or channel in a multichannel receiver, which is tuned to the radio frequency transmitted by the warning transmitters 19 of FIG. 2. The receiver 32 detects the indentification signal and applies it to the input of a BCD frequency detector 33. The BCD detector 33 produces an output corresponding to a first binary coded decimal digit in the indentification signal after the identification signal has been received for a predetermined continuous duration. The first binary coded decimal digit is applied to a memory circuit 34 and a driving circuit 35 which operates a decimal display 36. If the indentification signal contains a second binary coded decimal digit, a detector 33a, a memory circuit 34a, a driving circuit 35a, and a decimal display 36a are employed to detect and display the second digit. A timing circuit 37 senses the presence of an identification number in the memories 34 and 34a to disable the receiver 32 and to enable the driving circuits 35 and 35a and the displays 36 and 36a after a predetermined delay. Also, an audio alarm 38 is actuated by the timing circuit 37 after the predetermined delay. The duration of delay by the timing circuit 37 insures that the identification signal is detected and applied to the memories 34 and 34a prior to disablement of the receiver 32 and operation of the displays 36 and 36a. The displays 36 and 36a and the audio alarm 38 remain activated until current from a battery 39 is momentarily interrupted by the opening of a manual reset switch 40. The BCD detector 33 is more fully described hereinafter under the heading "BCD Detector". The memory circuit 34, driving circuit 35 and display 36 are more fully described hereinafter under the heading "Memory, Driver, and Display" . The timing circuit 37 is more fully described hereinafter under the heading "Receiver Timing Circuit".
ARMING AND TIMING CIRCUITS
The arming circuit 18 is shown in detail in FIG. 4. The operation of the sensor 17 by an emergency condition applies a triggering signal to a voltage divider consisting of resistors 42 and 43 and thus to a control electrode of a silicon controlled rectifier (SCR) 44. The SCR is connected in series with a resistor 45 and the battery 24 so that a voltage is produced across the resistor 45 when the SCR 44 is triggered into conduction. The voltage on the resistor 45 is applied by a resistor 47 to the base of a transistor 48 to render the transistor 48 conductive. The transistor 48 is connected in series with the battery 24 and a coil 49 of a relay 50. When the coil 49 is energized by conduction of the transistor 48, contacts 51 of the relay 50 are closed to apply an energizing voltage from the battery 24 to a terminal 53 which energizes the RF transmitter 19, BCD generator 20 and lamp 27 of FIG. 2. Also, the voltage across the resistor 45 is applied by a resistor 54 to a base of a transistor 55 connected in series with the battery 24 and the lamp 26 to render the transistor 55 conductive and energize the lamp 26. The SCR 44 and the lamp 26 remain activated until the arming circuit is manually reset by the momentary opening of the reset switch 23 which interrupts the current from the battery 24.
The timing circuit 22 is also energized by the voltage produced across the resistor 45. Current through a variable resistor 57 charges a capacitor 58 to trigger a unijunction transistor 59 connected in series with a resistor 60 across the resistor 45 after a predetermined delay. When the unijunction 59 is triggered, the increase in voltage across the resistor 60 produces a pulse through a capacitor 62 connected to a control electrode of a SCR 63. The SCR 63, when triggered by the pulse through capacitor 62, connects the base of the transistor 48 to a reverse bias potential or ground to render the transistor 48 non-conductive. This deenergizes the relay 50 to terminate operation of the RF transmitter 19, the BCD generator 20 and the lamp 27 of FIG. 2. A diode 64 connected across the coil 49 provides a bypass for induced current when transistor 48 is rendered non-conductive. The values of the capacitor 58 and the variable resistor 57 are selected to produce the predetermined period of operation of the transmitter 19 and BCD generator 20. The SCR 63 is delatched when the reset switch 23 is opened.
BCD GENERATOR
Referring to FIG. 5 there is shown a circuit diagram of a single digit BCD generator 20 which is energized by the application of a voltage to terminal 53 by the arming circuit 18 of FIG. 4. Inverter amplifiers 66-69 with positive feedback through respective filters 71-74 and resistors 76-79 operate as individual oscillators producing frequencies F1, F2, F3, and F4. As shown the inverter amplifiers 66-69 may be a Quad NAND gate package 80, energized by the application of the voltage to terminal 53, with the inputs of each gate connected together. The RCA CD 4011AE has been found to work well in this circuit. The filters 71-74 are preferably a narrow bandwidth type, such as miniature piezoelectric coupled tuning fork filters for audio signalling, series EMR-S manufactured by the MURATA Corporation of America. High Frequency decoupling capacitors 81-84 prevent the oscillators from producing higher than audio frequencies. Capacitors 86-89 couple the outputs of the amplifiers 66-69 to a terminal 70 connected to the audio input of the RF transmitter of FIG. 2.
The oscillators are selectively disabled to produce only one or more of the frequencies F1, F2, F3, and F4 in accordance with a selected binary coded decimal digit which identifies the transmitter and the location of the emergency condition. The BCD generator shown in FIG. 5 generates an identification signal which contains simultaneously generated frequencies in accordance with a single binary coded decimal digit. If an identification signal is to include two or more binary coded decimal digits, additional oscillator circuits substantially similar to that of FIG. 5 are added. The additional circuits would produce additional groups of frequencies which are different from the group of frequencies F1-F4 but simultaneously generated with frequencies F1-F4. For example, 100 indentifying decimal digits 00 through 99 may be provided by using two groups of four frequencies F1-F4 and F5-F8.
BCD DETECTOR
FIG. 6 shows in detail the BCD detector circuit 33 of the circuit shown in FIG. 3. The audio output of the RF receiver 32 is applied in parallel to filters 91-94. The filters 91-94 are selected to pass the respective frequencies F1-F4. The filters 91-94, like the filters 71-74 of FIG. 5, are preferable narrow bandpass type filters, such as miniature piezoelectric coupled tuning fork filters, to prevent erroneous operation by noise and voice signals. The outputs of the filters 91-94 are amplified by the amplifiers 96-99 which are biased linearly by respective resistors 101-104. Like the amplifiers 66-69 of FIG. 5, the amplifiers 96-99 may be a Quad NAND gate package 100 with the inputs of each gate connected together.
The outputs of the amplifiers 96-99 are applied to respective voltage rectifying and doubling circuits including capacitors 106-109, diodes 111-114 and 116-119, capacitors 121-124 and resistors 126-129. During negative half cycles of the identifying signals from the amplifiers 96-99, the respective capacitors 106-109 are charged by current through the diodes 111-114. During positive half cycles of the identifying signals, the diodes 116-119 conduct to transfer the charges on the respective capacitor 106-109 to the capacitors 121-124 and produce output voltages on terminals 131-134 which are about double the maximum amplitudes of the respective identifying signals. The resistors 126-129 provide loads for the diodes 116-119. The capacitors 121-124 are relatively large D.C. filtering capacitors while the capacitors 106-109 are relatively small coupling capacitors. This produces a delay in the voltage on the terminals 131-134 reaching maximum amplitudes. This delay is selected, taking into consideration the bandpass of the filters 71-74, to prevent the operation of the memory circuit 34 of FIG. 3 until the one or more of signals F1-F4 have been present for a predetermined continuous duration to prevent spurious noise signals or voice signals from erroneously actuating the memory circuit 34. The selection of the values of the components in the rectifying and doubling circuits is made to produce the predetermined delay taking into consideration the different frequencies of operation.
The BCD detector circuit of FIG. 6 will only detect one binary coded decimal digit. Additional circuits substantially similar to FIG. 6 are used to sense additional digits in an indentification signal. For example, one additional circuit which senses frequencies F5, F6, F7, and F8 would provide for the detection of 100 decimal numbers 00 through 99.
MEMORY, DRIVER AND DISPLAY
Referring to FIG. 7 there is shown in detail the memory circuit 34, display driving circuit 35, and the decimal display 36. The outputs of the BCD detector 33 on terminals 131-134 are applied by respective diodes 136-139 to control electrodes of SCR's 141-144. If a sufficiently large signal is present on any of the terminals 131-134, the respective SCR is triggered to produce a voltage across a respective resistor 146-149. The SCR's 141-144 remain activated to retain the binary coded decimal digit until the circuit is reset by interruption of voltage on a terminal 150. The voltage or voltages across the resistors 146-149 are applied to terminals 151-154 of the display driving circuit 35 which operates the decimal display 36. The driving circuit 35 is selected to produce appropriate energizing voltages for the particular decimal display in response to a binary coded decimal digit input. For example, the display 36 may be a seven element type, such as RCA model DR 2000. RCA CD 2500E may be used to drive the RCA display. A switch 155 is provided for testing the display 36.
As previously explained, the driving circuit 35 and display 36 are prevented by the timing circuit 37 (FIG. 3) from operating for a predetermined duration after the memory 33 has received a binary digit. Diodes 156-159 are connected to the resistors 146-149 in an OR gate arrangement to apply a signal to terminal 160 when any of the SCR's 141-144 are actuated. This operates the timing circuit 37 (FIG. 3) which, after the predetermined duration, applies an operating voltage to a terminal 177. A transistor 181 connected between the terminal 177 and the power inputs of the driving circuit 35 and the display 36 is controlled by a zener diode 182 and bias resistor 183 to provide a regulated voltage to the driving circuit 35 and the display 36.
RECEIVER TIMING CIRCUIT
Referring to FIG. 8 there is shown the timing circuit 37 for disabling the RF receiver 32 of FIG. 2 and enabling the driving circuit 35 and display 36. When a binary digit has been received by the memory 34, a voltage on the terminal 160 is applied to a series connected resistor 161 and capacitor 162. When the capacitor 162 has sufficiently charged, a unijunction transistor 163 is operated to produce a voltage across a resistor 165. A capacitor 167 connected to the resistor 165 applies a pulse to a control electrode of an SCR 166 which is connected in series with the battery 39 and a coil 168 of a relay 169. Before the coil 168 is energized, a contact arm 171 engages a contact 172 to apply voltage from the battery 39 to a terminal 178 and filtering capacitor 179. The terminal 178 supplies voltage to the RF receiver 32. After the coil 168 has been energized by the conduction of SCR 166, the contact arm 171 disengages the contact 172 and engages a contact 173 to apply a voltage from the battery 39 to the terminal 177 and the audible alarm 38. Thus, the RF receiver 32 is disabled and the driving circuit 35 and display 36 are enabled. The delay of the timing circuit 37 is selected to be greater than any difference in the delays of any two of the outputs of the BCD detector 33 so that the display 36 will indicate the correct identification digit. The alarm 38 and the display 36 remain activated until the reset switch 40 is manually opened to interrupt the current to the SCR 166 and the SCR's 141-144 (FIG. 7) in the memory 33.
OPERATION
In operation of the radio warning system, sensing and transmitting units 10 (FIG. 1) are placed in locations where it is desired to monitor or sense a condition which may require immediate attention. When such a condition occurs, the respective sensing and transmitting unit 10 transmits a radio signal modulated by one or more frequencies selected from one or more groups of four frequencies in accordance with one or more identifying binary coded decimal digits. One or more receiving units 11--11 in the central dispatch station 12, automobile 13 and helicopter 14 receive the radio warning signal and display the identification decimal digit or digits on displays 15--15 and operate audible alarms 38 (FIGS. 3 and 8). The appropriate authority, such as a police officer, may immediately respond and take the appropriate action to overcome or meet the emergency condition.
It is contemplated that the system of the invention be under the control of an appropriate governmental agency, such as the police. The locations to be monitored can thus be selected and limited to readily cover the areas of greatest need within the capabilities of the available personnel. Also the quality of the sensing and transmitting units may be readily controlled and maintained to produce a high standard of service.
The identifying modulation signals for one binary coded digit are produced by the oscillator amplifiers 66-69 shown in FIG. 5. To select the frequencies in accordance with the identifying binary coded decimal digit, the oscillating circuits are selectively disabled by open circuiting the inputs or outputs of selected amplifiers 66-69 or eliminating or disconnecting selected filters 71-41, resistors 76-79 or capacitors 86-89. Thus, the modulation signal contains one or more simultaneously generated frequencies selected from the group of frequencies F1-F4. For additional identifying decimal digits, additional oscillator circuits may be added to supply additional groups of four frequencies. The use of identification frequencies selected in accordance with indentifying binary coded decimal digits allows the use of inexpensive conventional binary coded decimal circuits.
TABLE I ______________________________________ Binary Inverted Coded Binary Coded Decimal Decimal Decimal Inverted Digit Digit Frequencies Digit Frequencies ______________________________________ 0 0000 None 1111 F1, F2, F3, F4 1 0001 F1 1110 F2, F3, F4 2 0010 F2 1101 F1, F3, F4 3 0011 F1, F2 1100 F3, F4 4 0100 F3 1011 F1, F2, F4 5 0101 F3, F1 1010 F2, F4 6 0110 F3, F2 1001 F1, F4 7 0111 F3, F2, F1 1000 F4 8 1000 F4 0111 F3, F2, F1 9 1001 F4, F1 0110 F3, F2 ______________________________________ In TABLE I, there are illustrated two schemes for selecting frequencies F1, F2, F3, and F4 in accordance with a binary coded decimal digit. The third column lists a selection of frequencies made in accordance with binary coded decimal digits listed in the second column which correspond to the respective decimal digits in the first column. The fourth column is the inverse of the second column while the fifth column illustrates a selection of frequencies in accordance with the inverted binary coded decimal digits. Other conventional binary coding schemes and frequency selection may be used so long as they are readily employable with available decimal circuitry.
One of the advantages of the invention is the large number of identifying numbers which are available for a relatively few modulation frequencies. Four frequencies provide 10 identifying digits, eight frequencies provide 100 identifying digits, 12 frequencies provide 1,000 identifying digits, etc. This allows flexibility in the employment of a radio warning system with a minimum use of a radio frequency channel.
In FIG. 9 there is illustrated an allocation of the identifying numbers for a variety of uses. The numbers may be allocated for use in (1) sensing crime, such as burglary, robbery, etc.; (2) sensing a fire or fire alarm; (3) sensing other matters concerning public health and safety, such as air or water pollution, etc.; (4) sensing an emergency distress, such as a need for service on a highway; and (5) sensing industrial equipment failure. The allocation of the identifying numbers and use of the system may be under the control of a local governmental organization, such as a police department, thus enabling optimum usage of the system.
After a predetermined period of operation, the transmission of a radio warning signal is terminated by the operation of the unijunction transistor 59 (FIG. 4) which fires the SCR 63 to render the transistor 48 non-conductive and open the relay 50 to disrupt power to the transmitter 19 and BCD generator 20. This prevents the transmitting unit from unduly interfering with other use of the radio frequency channel. The period of operation may be selected by adjusting the variable resistor 57. Typically, the period may be selected from the range of 10 to 100 seconds, but periods outside this range may be readily used.
Once the sensor 17 (FIGS. 2 and 4) has triggered and latched the arming circuit 18, the lamps 26 and 27 are energized. The lamp 27 remains energized only during the operation of the transmitter 19 and BCD generator 20. The lamp 26 remains energized until the arming circuit 18 is delatched by manually opening the reset switch 23.
The radio frequency warning signal is received by the RF receiver 32 (FIG. 3) which detects and produces the identifying signal. The receiving and displaying system may be readily employed with conventional radio communication equipment used by commercial establishments or governmental authorities, such as the police. The radio receiver 32 and the antenna 31 may be part of their normal communication equipment.
The frequencies in the identification signal are sensed by the filters 91-94 (FIG. 6) and applied to rectifying and doubling circuits. The use of narrow bandpass filters helps prevent interference from noise and spurious signals or ordinary communication in the operation of the warning system. Also, the delays caused by the capacitors 106-109 and 121-124, diodes 111-114 and 116-119, and resistors 126-129 in the rectifying and doubling circuits insure that the identification signals have been present for a predetermined continuous duration and help prevent interference from erroneously operating the SCR's 141-144 (FIG. 7) in the memory 34 or 34a. A range of delays from 1/2 to 1 second is acceptable but durations of delays outside that range may produce equally acceptable results.
Once a binary digit or digits have been received by the memories 34 and 34a, the timing circuit 37 (FIG. 8) is operated after a predetermined delay to disable the RF receiver 32 and to enable the driving circuits 35 and 35a, the displays 36 and 36a and the alarm 38. The delay of the timing circuit 37 allows for differences in the delays of the rectifying and doubling circuits of the BCD detector 33 to insure that all the binary digits of the binary coded decimal digit or digits have been received by the memories 34 and 34a. After the operation of the timing circuit 37, the identifying decimal digit or digits remain displayed on the displays 34 and 34a and the alarm 38 remains actuated until an operator resets the timing circuit 36 by momentarily opening the switch 40.
Inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.