JPH04242892A - Robbery preventing device - Google Patents

Abstract

PURPOSE:To prevent the generation of malfunction due to temporary defective contact on the connecting position of a tag code by preventing the ON of the 3rd switching element when the pulse width of an output voltage from the 1st switching element is shorter than the time constant of a time constant circuit. CONSTITUTION:The collector voltage of a transistor(TR) 7 to be a tag code detecting circuit connected by a tag code 6 is impressed to a node between a diode 14 and a resistor 15. When a commodity to which a robbery preventing device is attached passes the vicinity of the entrance/exist of a shop, TRs 3, 4 to be the 1st and 2nd switching elements are conducted over pulse width longer than the time constant of the time constant circuit 13 and a buzzer 1 is continuously driven to inform the generation of illegal action. When the pulse width of the collector voltage of the TR 7 is shorter than the time constant of the circuit 13 even if the temporary detective contact of the tag code 6 is generated, a TR 12 to be the 3rd switching element is held at an OFF state and the buzzer 1 is not functioned.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-theft device that is attached to items on display in a store to protect the items from shoplifting.

0002

2. Description of the Related Art When using this type of device, a signal of a specific frequency f is radiated near the entrance and exit of a store, and the anti-theft device includes a buzzer 1, a battery 2, and a transistor as shown in FIG. 3, 4, a receiving circuit 5, etc. are built-in.

This anti-theft device is attached to a product with a conductive tag code 6, and has a built-in transistor 7 that detects when the tag code 6 is illegally removed.

[0004] The specific method for attaching the tag code 6 to a product is as described in Japanese Patent Laid-Open No. 2-14398, by joining with a snap, pressing the tag onto an electrode with a pressing member, or using a spring electrode. It is attached to the product by clipping.

In the example shown in FIG. 2, the snap joint 8
An anti-theft device is attached to the product by a and 8b, and a transistor 7 detects conduction between the snap joint 8a and the snap joint 8b. When the snap joint 8a and the snap joint 8b are electrically connected through the tag cord 6, the collector potential of the transistor 7 is at the "L" level.

The parallel resonant frequency of the coil 9 and capacitor 10 of the receiving circuit 5 is set to a specific frequency f, and when a product to which this anti-theft device is attached is taken out of the store, the product near the entrance of the store During the period when the signal of the specific frequency f radiated to the coil 9 is linked to the coil 9, the output voltage level of the receiving circuit 5 rises, and during that period, the transistor 4 turns on the base current of the transistor 3. Power is supplied to the buzzer 1 from the battery 2 via the transistor 3.

When the signal of the specific frequency f no longer interlinks with the coil 9, the output voltage of the receiving circuit 5 decreases and the transistor 4 turns off.However, in the past, the collector voltage of the transistor 3 was changed through the feedback resistor 11. is applied to the base of transistor 4, transistor 4 is kept on, and buzzer 1 continues to sound.

If an attempt is made to remove the anti-theft device attached to the product and take it out of the store, and the tag cord 6 is cut or the snap joints 8a and 8b are illegally removed, the transistor 7 The collector potential of is inverted to "H" level, and during that period, transistor 4 turns on the base current of transistor 3, and power is supplied from battery 2 to buzzer 1 via transistor 3.

[0009]

[Problem to be solved by the invention] In such a configuration,
If a temporary contact failure occurs at the connection point of the tag code 6 while a product with an anti-theft device is displayed in a store, this will simply cause the transistor 4 to remain in the on state. Then, a problem occurs in which the buzzer 1 continues to sound and an alarm continues to occur.

An object of the present invention is to provide an anti-theft device that can prevent malfunctions due to temporary poor contact at the connection point of the tag code 6.

[0011]

[Means for Solving the Problems] The theft prevention device of the present invention is an antitheft device in which a tag body is connected to an object to be protected using a conductive tag cord, and includes an alarm means for generating an alarm, and an alarm means for generating an alarm. the first in series between the power supplies driving the
A second switching element is connected to the control terminal of the first switching element, and the second switching element is turned on while the receiving circuit is receiving the signal. At the same time, a third switching element for bypass is connected in parallel with the second switching element, and the control terminal of the third switching element is connected to the alarm means of the first switching element. and the output voltage of a tag code detection circuit that detects that the conduction state between two points connected by the tag cord is turned off, and the control terminal of the third switching element. The feature is that a time constant circuit is connected to the .

0012

According to this configuration, when the pulse width of the output voltage of the first switching element is shorter than the time constant of the time constant circuit, the third switching element is not turned on. Therefore, in this case, the first switching element is conductive only while the second switching element is on, and the conductive state is not maintained.

When the pulse width of the output voltage of the first switching element is longer than the time constant of the time constant circuit, the third switching element is turned on. In this case, even if the second switching element is turned off, the first switching element is maintained in a conductive state via the third switching element, so the alarm means continues to be driven by the power supply and an alarm is generated. Continue to do so.

[0014]

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. Components having the same functions as those in FIG. 2 showing the conventional example will be described with the same reference numerals.

As shown in FIG. 1, the anti-theft device of the present invention includes a transistor 12 in place of the resistor 11 shown in FIG.
A time constant circuit 13 and the like are provided. A first battery is connected in series between the buzzer 1 as an alarm means and the battery 2 as a power source.
A transistor 3 as a switching element is interposed,
A transistor 4 as a second switching element is connected to the base, which is a control terminal, of the transistor 3, and the output of a receiving circuit 5 is connected between the base and emitter of the transistor 4. The collector and emitter of transistor 12 as a switching element of transistor 3 are connected in parallel, and the collector voltage of transistor 3 is applied to the base as a control terminal of transistor 12 via diode 14 and resistor 15. A time constant circuit 13 composed of a resistor 17 and a capacitor 18 is connected between the reference potential 16 and the reference potential 16 .

Further, at the connection point between the diode 14 and the resistor 15, a transistor 7 is connected as a tag code detection circuit for detecting that the conduction state between the two points connected by the tag code 6 is turned off. Collector voltage is applied.

With this configuration, when a product with an anti-theft device is taken out of the store, the transistor 4 is activated over a pulse width longer than the time constant of the time constant circuit 13 when it passes near the entrance. In addition, transistor 3 becomes conductive, the base potential of transistor 12 rises sufficiently and becomes conductive, transistor 3 is kept on even if transistor 4 is turned off, and buzzer 1 continues to sound to notify the occurrence of fraudulent activity. be able to.

On the other hand, when a temporary contact failure of the tag code 6 occurs at the snap joint 8a or the snap joint 8b, the "H" level width of the pulse generated at the collector of the transistor 7 becomes shorter than the time constant. If the time constant of the circuit 11 is shorter than the time constant of the circuit 11, the base potential of the transistor 12 does not rise sufficiently due to the action of the time constant circuit 13 to the extent that the transistor 12 becomes conductive, so the transistor 12 is maintained in an off state. be done.

Therefore, in this case, transistor 3
is maintained in the off state, thereby avoiding malfunctions such as buzzer 1 continuing to sound.

[0020]

As described above, according to the present invention, the third switching element for bypass is connected in parallel to the second switching element that switches the first switching element that is interposed in series between the alarm means and the power source. A switching element is connected to the control terminal of the third switching element, and the voltage on the alarm means side of the first switching element is in an OFF state between two points connected by the tag cord. Since the output voltage of the tag code detection circuit that detects the occurrence of a change is applied and a time constant circuit is connected to the control terminal of the third switching element, the pulse width of the output voltage of the tag code detection circuit is equal to the time constant circuit. In the case of a pulse width shorter than the constant, the third switching element is not turned on, making it possible to avoid malfunctions in which alarms continue to occur.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the theft prevention device of the present invention.

FIG. 2 is a configuration diagram of a conventional anti-theft device.

[Explanation of symbols]

1 Buzzer [alarm means] 2 Battery [power supply] 3 Transistor [first switching element] 4 Transistor [second switching element] 5 Receiving circuit 6 Tag code 7 Transistor [tag code detection circuit] 8
a, 8b Snap joint 12 Transistor [third switching element] 13 Time constant circuit

Claims (1)

[Claims] Claim 1: In an anti-theft device in which a tag body is connected to an item to be protected by a conductive tag cord, a first anti-theft device is connected in series between an alarm means for generating an alarm and a power source for driving the alarm means. A second switching element is connected to the control terminal of the first switching element, and the second switching element is turned on while the receiving circuit is receiving the signal. At the same time, a third switching element for bypass is connected in parallel with the second switching element, and the control terminal of the third switching element is connected to the alarm means of the first switching element. and the output voltage of a tag code detection circuit that detects that the conduction state between two points connected by the tag cord is turned off, and the control terminal of the third switching element. An anti-theft device that has a time constant circuit connected to it.