US 3742480 A
An electric alarm device for detecting removal or displacement of objects comprises a lamp of the thermostatic intermittent flashing type connected in series with a semi-conductor switch which is biased to its non-conducting position by a circuit including a wire conductor which when detached or broken removes the bias on the switch and causes the switch to conduct. A second switch arranged to be connected in series with an alarm actuating coil is biased to its off or non-conducting condition when there is no current flowing through the circuit of the first switch and is turned on or triggered when the lamp is energized and thereby produces intermittent energization of the alarm actuating coil and effects intermittent operation of the alarm. The device including the lamp is encapsulated in a rigid synthetic plastic block by a method which affords protection of the lamp from breakage due to pressure during curing of the plastic.
Claims available in
Description (OCR text may contain errors)
United States Patent 1 Hoecker 11] 3,742,480 June 26,1973
1 1 ALARM DEVICE FOR DETECTING REMOVAL OF OR TAMPERING WITII- APPLIANCES OR OTHER ARTICLES  Inventor: August C. Iloecker, Broomfield,
-  Assignee: Dean Nicholson, Pittsburgh, Pa.
NOV. 4, I971  Appl. No.: 195,692
 References Cited UNITED STATES PATENTS 3,463,936 8/1969 Adem 340/331 Almassy 340/331 Primary Examiner.lohn W. Caldwell Assistant Examiner-William M. Wannisky- Attorney-McGrew and Edwards 571 ABSTRACT An electric alarm device for detecting removal or displacement of objects comprises a lamp of the thermostatic intermittent flashing type connected in series with a semi-conductor switch which is biased to its nonconducting position by a circuit including a wire conductor which when detached or broken removes the bias on the switch and causes the switch to conduct A second switch arranged to be connected in series with an alarm actuating coil is biased to its off or nonconducting condition when there is no current flowing through the circuit of the first switch and is turned on or triggered when the lamp is energized and thereby produces intermittent energization of the alarm actuating coil and effects intermittent operation of the alarm. The device including the lamp is encapsulated in a rigid synthetic plastic block by a method which affords protection of the lamp from breakage due to pressure during curing of the plastic.
6 Claims, 4 Drawing Figures pliances or other apparatus. These alarms have for the most part been satisfactory for their intended uses, however, they have not proved fully adaptable for use in all applications. It is, for example, desirable to provide a small, easily concealed alarm device for a wide range of applications. Accordingly, it is an object of the present invention to provide an alarm device of improved construction and operating characteristics for detecting the displacement of or tampering with selected objects.
It is another object of this. invention to provide a small and compact alarm device including an improved arrangement for facilitating its use inconcealed positions in automobiles and other locations,
It is another object of this invention to provide an im- -.proved method for making a compact encapsulated alarm device utilizing an electric lamp.
vBriefly, in carrying out the objects of this invention .in one embodiment thereof, an alarm device is provided which includes a small electric lamp of the thermostaticintermittent type connected "in series with a transistor whichis biased to its nonconducting position by a circuit including a wire employed as a sensing element. A second transistor is employed as a switch arranged to be connected in series with a relay coil or other actuating device and, which is biased normally to its off position; this second transistor is triggered by the passage of current through the lamp circuit. Intermittent actuation of the alarm device results from intermittent energization of the lamp and consequent intermittent removal of the bias on the second switch. The lamp and circuit components'are encapsulated, and, in order to prevent breakage of the lamp, the glass bulb is first coated with a compressible silicone rubber and thereafter the entire device encapsulated in a suitable synthetic plastic potting compound.
The features of novelty which characterize this invention, together with further objects and advantages thereof, are pointed out with particularity in the claims annexed to and forming a part of this application, the invention itself, however, will best be understood by reference to the following description taken in connection with the accompanying drawing in which;
FIG. I is a perspective view of an alarm unit embody- ,ing the invention and indicating diagrammatically its connections for alarm purposes;
FIG. 2 is a perspective view of the mounting board and circuit components of the unit of FIG. 1;
FIG. 3 is a sectional view through a broken away portion of the unit of FIG. 1; and
FIG. 4 is a schematic diagram of the circuit connections of the components illustrated in FIG. 2, illustrated as connected to actuate an automobile horn.
Referring now to the drawing, the alarm actuating device illustrated in FIG. 1 comprises a body of rigid molded synthetic plastic material which has within it an embedded or encapsulated electronic circuit assembly having ground terminals 11 and 12 extending laterally from the body l0. These terminals also constitute attaching lugs for securing the body 10 in a selected position near the apparatus, device or object to be protected by the alarm. Electric lead wires 13, 14 and 15 extend from the device 10 and are of sufficient length to facilitate the connection of the device to the power supply and alarm actuator and to utilize the lead 13 for location through or around the object to be protected. For purposes of illustration, the diagrammatic circuit connection has been indicated, and it is assumed that the device 10 is attachedto an automobile in a suitably concealed position and that the lugs'll and 12 are attached to the ground or common connection provided by the frame member of the automobile. The lead 13 is connected to the ground, as indicated by a bolt 16 connected to a frame member 17 of the automobile which constitutes the ground. The lead 13 has been indicated as passing through a device 18 which may, for example, be a stereo tape deck mounted in the automobile. The lead 14 is connected directly to the battery of the automobile, indicated at 20, and the lead 15 is connected to the battery through the coil of a relay 2] which is the horn relay of the automobile, normallyconnected across the battery 20 by pressing the horn button.
The lead 13 is arranged so that if the device 18 is removedfrom its normal position the lead will be broken or broken loose from its connection to ground at 16. The opening of the circuit in this manner effects actuation of the alarm device 10 and energizes the relay 2] to actuate the horn of the vehicle. For greatest reliability in detecting the displacement or removal of an object such as the tape deck 18, the wire 13 is located so that there is minimum likelihood of detection of its presence and the detecting device 10 is similarly located in a concealed position. The alarm is sounded intermittently upon operation of the device of this invention and in a manner described in detail below.
The circuit assembly or chassis of the device 10, as illustrated in FIG. 2, comprises an insulated mounting plate or base 22, on whichthe lugs 11 and 12 are mounted, these .lugs being connected together by a suitable conductor such as a printed circuit connection. The components of the circuit include an electric lamp 23 of the thermostatic intermittent flashing type, and as illustrated the lamp includes the usual attaching base 25 and a glass bulb 24 and a stem 25 extending from the base and carrying two conductors 26 and 27 and a bimetal strip 28. The filament of the lamp, indicated at 30, is connected between the upper end of the conductor 26 and the upper end of the bimetal thermostat 28. At normal temperatures, thebimetal strip 28 engages the upper end of the conductor 27 when the filament 30 is not energized so that the filament 30 is connected between the two conductors. The heat of the filament upon energizationcauses the bimetal element 28 to made through printed circuit conductors (not shown)- by soldered connections on the bottom side of the plate 22.
When the circuit assembly, illustrated in FIG. 2, has been completed, it is encapsulated in the block 10. This encapsulation is effected by first covering the lamp bulb 23 and also other possibly breakable components, such as the diode 33, with a compressible insulating material. This covering may be accomplishedby enclosing the lamp and diode, for example, with a compressible synthetic plastic material wrapped about these components. Preferably the lamp bulb and any other components which may be subject to damage upon compression are coated with a compressible silicone rubber, the coating being accomplished by brushing or dipping the parts in a liquid silicone material which is then allowed to cure. The entire assembly is positioned in a mold with the lugs 11 and 12 and the leads 13, 14 and 15 protruding therefrom. The mold is then filled with a suitable synthetic resin potting compound, such as a polyester resin or an epoxy resin, a
suitable catalyst or setting agent being added. After the compressible layer 38 prevents injury to the bulb regardless of the length of time required for full curing of the plastic body, and the encapsulated alarm devices may be made in production with minimum likelihood of breakage. 1
The manner in which the circuit components illustrated in FIG. 2 are connected to provide the alarm device of this invention is indicated in FIG. 4, wherein the components and circuit of the device are shown to the left of a broken line 39 and the battery and horn circuit of an automobile to the right. The lamp 23 is connected in series with the transistor 31 between the high side of the battery or other source and ground or the common negative line. The transistor 31 is biased to its off or nonconducting condition by the resistors 34 and 35, the base of the transistor being connected to the junction of these resistors. The lead wire 13 which constitutes the alarm sensor is connected to the other end of the resistor 34 and when in use is connected to the ground as indicated to complete the bias circuit. The emitter of the transistor 31 is connected through the resistance 36 to ground and the transistor 32 is connected across the resistance 36, its base being connected to the junction of the resistance 36 and the emitter lead of the transistor 31 and the emitter of the transistor 32 being connected to ground. When no current is flowing through the transistor 31 and the lamp 23, the transistor 32 is biased to its off or nonconducting position. The lead 15 is connected to the collector of the transistor 32 and the diode 33 is connected across the transistor 32 between-ground and the collector. Thus, when the lead 15 is connected in series with the coil of the relay 21, indicated at 40, the relay will be actuated whenever the transistor 32 is rendered conducting and upon opening of the transistor 32 by restoration of its original bias, the reverse potential or inductive kick is dissipated through the diode 33. Energization of the coil 40 closes the relay to connect a horn actuating coil 41 or other suitable alarm across the battery 20 to actuate the alarm.
When the device illustrated in FIG. 1 is connected as shown in FIG. 4, the transistor.3l remains in its nonconducting condition until such time as the wire 13 may be broken or pulled from its ground or common connection. When this happens, the transistor 31 is rendered conducting and current flows through the lamp 23 heating the filament 30 and causing current to flow through the resistance 36 to render the transistor 32 conducting; this energizes the coil 40 and closes the relay switch 21 to energize the alarm coil 41. As soon as the temperature of the bimetallic strip 28 in the lamp 23 reaches a predetermined value the strip moves away from the lamp conductor 27 and opens the filament circuit, thereby stopping the flow of current through the lamp and through the resistance 36, so that the negative bias of the transistor 32 is restored and the coil 40 deenergized. Thereupon the reverse current is dissipated through the diode 33. As soon as the lamp cools, the bimetal strip 28 moves back into contact with the conductor 27 and the actuation of the alarm is repeated. The intermittent energization of the alarm will continue until the lead 13 is again connected to ground or until-the battery. is disconnected. The circuit thus operates to provide an intermittent alarm signal whenever the wire 33 is broken or detached from ground.
For purposes of illustration, and not by way of limitation, an alarm device embodying the above-described invention was built and tested and found fully effective for use'as an automobile accessory protection alarm. The device as constructed included the circuit as illustrated in FIG. 4 to the left of the line 39, and the com ponents employed were the following:
Resistance 34-33 ohms Resistance 35-] ,000 ohms Resistance 36-10 ohms Transistor 31 was a 2N5225 transistorMotorola Transistor 32 was a 2N5294 transistorSolitron Diode 33 was a lN4002Motorola The lamp was a General Electric No. 257 thermo static flashing lamp The circuit as provided was operated on the l2-volt battery of an automobile The horn relay coil of the automobile was connected between the positive terminal of the battery and through the lead 15 to the transistor 32. The device was encapsulated using as the compressible covering 38 a silicone rubber sold by General Electric Company under the designation GE-RTVIOS Silicone Rubber.
It will be understood that, if desired, instead of employing NPN transistors as the transistors 31 and 32, PNP transistors may be employed; in this case the circuit is connected with the negative terminal of the battery or other source connected to the lead 14 and ground connected to the positive side of the battery. Also, the connections of the diode 33 are reversed, whereupon the circuit employing PNP transistors oper ates in the same manner as the circuit as illustrated in the drawing.
In the illustration of the circuit in FIG. 4, a conven tional automobile horn button 42 has been illustrated which, upon closure, energizes the-coil 40 by connecting it across the battery 20. No modification of this circuitry is required in order to utilize the coil 40 in the manner illustrated for providing an alarm indication upon opening of the circuit between the resistance 34 and the ground. For purposes of illustration, the connection between the resistance 34 and ground has been indicated as an extended length of wire 13 which is broken when the protected apparatus or other item is removed; however, for different applications, other suitable connecting elements may be provided for opening the circuit between resistance 34 and ground upon tampering or displacement of the article to be protected by the alarm.
I claim: 1. As an article of manufacture, an alarm actuating device comprising, an electric lamp of the thermostatic intermittent flashing type, means including a first switch for connecting said lamp across a power source, means for biasing'said first switch to its open condition, a second switch, means for connecting said second switch across said power source, means for biasing said second switch to its open condition, and i means for utilizing current flowing through said lamp and first switch for triggering said second switch to its closed condition, whereby when said biasing means for said first switch is disabledto render said first switch conducting said second switch will conduct and the current passing therethrough may be utilized to'actuate an alarm, the current through said second switch flowing intermittently with the intermittent operation of said lamp and the resulting intermittent biasing of said second switch. 2. An alarm actuating device as set forth in claim 1 wherein said means for biasing said first switch includes an extended conductor constituting a sensor for engagement with an object, the displacement of which is to be detected.
3. An alarm actuating device as set forth in claim 1 wherein said first and second switches are transistors, and including a diode connected across said second switch for by-passing current flowing in a reverse direction through said connecting means from said second switch. r
4. An alarm actuating device as set forth in claim 1, said lamp having a covering of compressible synthetic plastic material, and said device being embedded in a block of rigid plastic material.
5. An alarm actuating device as set forth in claim 4, said covering being a coating of a compressible silicone rubber.
means including a relay coil for connecting said second switch across said power source,
means for utilizing current flowing through said lamp and said first switch for triggering said second switch to its conducting condition whereby disabling of said biasing means for said first switch renders said first switch conducting and energizes said lamp to effect intermittent energization of said lamp and of said relay coil, and
means effective upon energization of said relay coil for actuating said alarm.