GB2117949A

GB2117949A - Alarm

Info

Publication number: GB2117949A
Application number: GB08209088A
Authority: GB
Inventors: Der Post Jan Rupert Van; Jonathan Charles Martin Savill
Original assignee: VISIONCREST Ltd
Current assignee: VISIONCREST Ltd
Priority date: 1982-03-27
Filing date: 1982-03-27
Publication date: 1983-10-19

Abstract

An alarm designed as a self- contained box 10 to be inserted into an article to be protected includes two trembler switches 20 arranged at right angles to each other each being sensitive to movement along two perpendicular axis so that the combination responds to movement in any direction. A trigger stage connected to the trembler switches energises a buzzer 18 in the event of the box being dislodged. <IMAGE>

Description

SPECIFICATION Alarm The present invention relates to an alarm for the protection of a portable article.

There often arises a need when carrying personal property such as suitcases, camera cases, handbags etc. to leave such items unattended. It has been proposed in the past to incorporate an alarm within a brief case, but the previous proposal consisted of an expensive builtin alarm which in most cases, would be impracticable on account of the cost.

According to a first aspect of the present invention, there is provided an alarm for the protection of a portable article which comprises a housing containing an internal power supply, a trembler switch, a trigger circuit an an alarm device the trigger circuit serving to energise the alarm device in response to actuation of the trembler switch, the alarm being in the form of a self-contained unit which, in use, is inserted into the article to be protected.

Thus, in the first aspect of the invention, there is provided a self contained housing which may be placed within any portable article to sound an alarm in the event of that article being dislodged.

Preferably, the trembler switch is sensitive to movement along any of three mutually orthogonal axes.

According to a second aspect of the invention, there is provided an alarm which comprises a power supply battery, a trembler switch, an alarm device and a trigger stage for energising the alarm device in response to actuation of the trembler switch, wherein the trembler switch is sensitive to movement along any of three mutually orthogonal axes.

Preferably, the trembler switch is formed of two or more pairs of contacts each sensitive to movement along a respective one of the three axes.

Conveniently, the pairs of contacts constituting the switch may comprise a stationary contact secured to the housing of the alarm and a movable contact in the form of an inertial mass suspended on a spring.

If the spring is in the form of a helical spring and the inertial mass is situated ate the centre of a circle constituting the stationary contact, then one pair of contacts may be sensitive to movement along mutually perpendicular axes normal to the axis of the helical spring.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which; Figure 1 is an exploded perspective view of an alarm in accordance with the invention, and Figure 2 is a circuit diagram of the alarm shown in Figure 1.

The alarm in the drawings comprises a box generally designated 10 provided with a lid 12.

The box 10 has a compartment 14 which is intended to receive a battery. A printed circuit board 1 6 is received within the box, the circuit boård 16 supporting a buzzer 18 and two trembler switches 20 arranged at right angles to each other. Each of the trembler switches 20 comprises a stationary contact in the form of a cylindricai tube 22 and a movable contact in the form an inertial mass 24 suspended on a spring 28 and supported on an upstanding peg 28.

Movement in the direction of the length of the box 10 would not cause the first of the two trembler switches to respond, being parallel to the axis of the spring, but the second trembler switch would respond. Conversely, movement in the direction of the width of the box actuates the first of the trembler switches but not the second.

Because of the cylindrical construction of the stationary contacts, both of the trembler switches respond to movement in the direction of the height of the box.

Consequently, the trembler switches are sensitive to movement in any direction and contact would always be made in the event of the alarm being moved.

The alarm is provided with a key operated switch 30 which is arranged in the lead connecting the battery in the compartment 14 to the circuitry generally designated 32 and shown only schematically in Figure 1.

It will be noteri that the lid 12 of the box 10 has holes 34 and 36 which align with the buzzer 1 8 and the key operated switch, respectively.

Referring now to Figure 2, the circuit comprises a Darlington transistor 40 the switching path of which is connected in series with the buzzer. The base of the Darlington transistor 40 is connected to the output of an integrated circuit timer 42 by way of an RC circuit formed of a resistor 44 and a capacitor 46. The timer 42 may conveniently be a CMOS 555 timer connected as a monostable multivibrator with the resistor 48 and the capacitor 50 determining the timing duration. A further RC circuit comprising the resistor 52 and a capacitor 54 is connected to the reset input of the timer 42 and acts to reset the circuit automatically when power is initially switched on. The two trembler switches 20 are connected to the trigger input of the timer and to a pull up resistor 56.A diode 58 is provided to ensure that the capacitor 54 is rapidly discharged on switch-off so that the alarm should not be switched on in the event of the power being switched on and off rapidly.

In operation, when the key operated switch 30 is actuated to supply power to the circuit, the circuit is rapidly reset by the RC circuit 52, 54 and the output of the timer will be low, that is to say at the negative potential. With both the base and the emitter of the Darlington transistor 40 at the negative potential, the latter transistor is switched off and the buzzer 1 8 remains inactive.

If either of the switches 20 should close, the high input to the trigger electrode of the timer 42 will briefly go low to trigger the monostable multivibrator. The multivibrator will switch to a high state for a period determined by the values of the RC circuit 48, 50. When the output of the timer 42 initially goes high, the capacitor 46 commences to charge and until it is charged maintains the base of the Darlington stage at a low level. However, as the charge on the capacitor 46 builds up the potential at the base of the Darlington transistor 40 reaches a sufficient level to switch on the Darlington transistor 40 and energise the buzzer 1 8. Consequently, the buzzer 1 8 will not sound immediately after one of the trembler switches 20 has been activated but a short delay is allowed.This delay is sufficient to enable a user to switch off the power supply by inserting the key into the key operated lock and opening the switch 30. After the opening of the switch 30 the capacitor 54 is rapidly discharged through the diode 58.

If it is not desired to have a period for enabling the key operated switch to be switched off, it is possible to dispense with the capacitor 46. In the absence of the latter capacitor 46 in parallel with the base emitter junction of the output transistor, it no longer becomes necessary to employ a Darlington output stage and instead an ordinary NPN transistor such as a BC107 may be employed.

The following component values have been found suitable and are given below by way of non-limiting example: Resistor 56 1 5 Kohm Resistor 48, 52 10 Mohm Resistor 44 22 Kohm Capacitor 50, 54 10 ,uF Capacitor (Ref) 0.1 ssF Capacitor 46 1000,uF Diode 58 IN 4148 IC 42 CMOS 555 Transistor 40 BC 517

Claims

1. An alarm for the protection of a portable article which comprises a housing containing an internal power supply, a trembler switch, a trigger circuit and an alarm device, the trigger circuit serving to energise the alarm device in response to actuation of the trembler switch, the alarm being in the form of a self contained unit which, in use, is inserted into the article to be protected.

2. An alarm as claimed in Claim 1, in which the trembler switch is sensitive to movement along any of three mutually orthogonal axis.

3. An alarm which comprises a power supply battery, a trembler switch, an alarm device and a trigger stage for energising the alarm device in response to actuation of the trembler switch, wherein the trembler switch is sensitive to movement along any of three mutually orthogonal axis.

4. An alarm as claimed in any preceding claim, wherein the trembler switch is formed of two or more pairs of contacts each sensitive to movement along, at least, a respective one of the three orthogonal axes.

5. An alarm as claimed in Claim 4, in which the pairs of contacts constituting the switch comprise a stationary contact secured to the housing of the alarm and a movable contact in the form of an inertial mass suspended on a spring.

6. An alarm as claimed in Claim 5, in which the spring is in the form of a helical spring and the inertial mass is situated at the centre of a circle constituting the stationary contact, whereby the pair of contacts is sensitive to movement along two mutually perpendicular axis mormal to the axis of the helical spring.

7. An alarm as claimed in any preceding claim, wherein the trigger stage comprises a timer for energising the alarm device for a predetermined length of time following actuation of a trembler switch.

8. An alarm as claimed in Claim 7, in which a delay circuit is included between the output of the timer and the alarm device to delay the energising of the alarm device for a predetermined time following the actuation of the trembler switch.

9. An alarm constructed, arranged and adapted to operate substantially as here and before described with reference to and as illustrated in the accompanying drawings.