Antitheft system with digitally coded signal
First Claim
1. A security system for detecting the removal of an article from a premises to be protected, the protected premises including at least one exit through which the article may be removed from the protected premises, said security system comprising in combination:
- (A) a transmitter for transmitting at least one signal in the vicinity of said exit, said signal being transmitted as an electromagnetic radio wave of a predetermined frequency and being transmitted as a plurality of serially coded bits, said serially coded bits being transmitted by said transmitter during a corresponding plurality of successive code bit intervals;
(B) receiver means carried by said article, said receiver means including;
i. a receiver for detecting the presence of said signal, said receiver including a filter for passing signals of said predetermined frequency, said receiver being adapted to receive said serially coded bits when said article is brought into the vicinity of said exit;
ii. processing means for storing a pattern of code bits and being coupled to said receiver for comparing the serially coded bits received by said receiver with the stored code bits to determine whether they match one another, said processing means providing an output signal when said serially coded bits match the stored code bits;
iii. clocking means for providing clock signals to said processing means to distinguish the plurality of successive code bit intervals; and
iv. alarm means electrically coupled to said processing means and responsive to said output signal for creating an alarm to assist in the recovery of the removed article; and
(C) a power supply carried by said article and electrically coupled to said receiver means for supplying electrical power thereto.
3 Assignments
0 Petitions
Accused Products
Abstract
A transmitter emits a pulsed radio signal and a digitally encoded radio signal near each exit of a protected premises. Monitored articles carry a receiver having a first circuit for receiving the pulsed signal, a power source, and a power switch for coupling the power source to a second circuit on detection of the pulsed signal. The second circuit receives the digitally encoded signal as multiple, serially-transmitted code bits. It also contains a clock for generating timing signals synchronized by the pulsed signal in order to distinguish a plurality of code bit intervals. A processor, an associated memory, and an address counter compare the digitally encoded signal with a stored bit pattern. On receiving an improper code bit, the processor causes the power switch to decouple the power source from the second circuit to conserve power. If the received signal matches the stored bit pattern, power is maintained to the second circuit. Alarm circuitry is triggered by overflow from the address counter. The address counter is reset each time the pulsed signal is received and thus produces no overflow, but when the article is removed from the protected premises, the address counter is allowed to overflow, triggering the alarm circuit.
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Citations
6 Claims
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1. A security system for detecting the removal of an article from a premises to be protected, the protected premises including at least one exit through which the article may be removed from the protected premises, said security system comprising in combination:
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(A) a transmitter for transmitting at least one signal in the vicinity of said exit, said signal being transmitted as an electromagnetic radio wave of a predetermined frequency and being transmitted as a plurality of serially coded bits, said serially coded bits being transmitted by said transmitter during a corresponding plurality of successive code bit intervals; (B) receiver means carried by said article, said receiver means including; i. a receiver for detecting the presence of said signal, said receiver including a filter for passing signals of said predetermined frequency, said receiver being adapted to receive said serially coded bits when said article is brought into the vicinity of said exit; ii. processing means for storing a pattern of code bits and being coupled to said receiver for comparing the serially coded bits received by said receiver with the stored code bits to determine whether they match one another, said processing means providing an output signal when said serially coded bits match the stored code bits; iii. clocking means for providing clock signals to said processing means to distinguish the plurality of successive code bit intervals; and iv. alarm means electrically coupled to said processing means and responsive to said output signal for creating an alarm to assist in the recovery of the removed article; and (C) a power supply carried by said article and electrically coupled to said receiver means for supplying electrical power thereto. - View Dependent Claims (2, 3, 4, 5)
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6. A security system for detecting the removal of an article from a premises to be protected, the protected premises including at least one exit through which the article may be removed from the protected premises, said security system comprising in combination:
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(A) a transmitter for transmitting at least one radio signal of a predetermined frequency in the vicinity of said exit; and (B) a receiver carried by said article for detecting the presence of said radio signal and including a filter for passing signals of said predetermined frequency; and (C) a power supply carried by said article and electrically coupled to said receiver for supplying electrical power thereto; (D) said filter of said receiver including; i. a first current programmable operational amplifier having an inverting input terminal and an output terminal and including a first feedback resistor of a first magnitude coupled therebetween; ii. a second current programmable operational amplifier having an inverting input terminal coupled to the output of said first operational amplifier, said second operations amplifier having an output terminal; and iii. A second feedback resistor coupled between the output terminal of said second operational amplifier and the inverting input terminal of said first operational amplifier, the ratio of the magnitude of the first feedback resistor to the magnitude of the second feedback resistor being near unity to increase the selectivity of said filter; and iv. said first and second operational amplifiers are programmed to operate at substantially minimum current levels to minimize power drawn from said power supply and to minimize the bandwidth of the gain provided by each of said first and second operational amplifiers to increase the selectivity of said filter and to decrease the tendency of said filter to oscillate.
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Specification