CA1106933A - Body capacitance intrusion alarm apparatus - Google Patents
Body capacitance intrusion alarm apparatusInfo
- Publication number
- CA1106933A CA1106933A CA302,638A CA302638A CA1106933A CA 1106933 A CA1106933 A CA 1106933A CA 302638 A CA302638 A CA 302638A CA 1106933 A CA1106933 A CA 1106933A
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- CA
- Canada
- Prior art keywords
- alarm
- oscillator
- battery
- signalling
- transistor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
BATTERY-OPERATED
BODY CAPACITANCE INTRUSION
ALARM APPARATUS
ABSTRACT OF THE DISCLOSURE
An intrusion alarm having an oscillator which is turned off by the body capacitance of a would-be intruder operates in the frequency range of 17-65 MHz. At this frequency, reliable discrimination between body capacitance and stray capacitance is possibly and therefore sensitivity is increased while false alarms are reduced. Battery life is increased by providing a high resistance load in the stand-by mode to reduce battery drain to 500 microamperes or less. Latching and non-latching embodiments are disclosed.
BODY CAPACITANCE INTRUSION
ALARM APPARATUS
ABSTRACT OF THE DISCLOSURE
An intrusion alarm having an oscillator which is turned off by the body capacitance of a would-be intruder operates in the frequency range of 17-65 MHz. At this frequency, reliable discrimination between body capacitance and stray capacitance is possibly and therefore sensitivity is increased while false alarms are reduced. Battery life is increased by providing a high resistance load in the stand-by mode to reduce battery drain to 500 microamperes or less. Latching and non-latching embodiments are disclosed.
Description
BATTERY-OPERATED
BODY CAPACITANCE INTRUSION
ALARM APPARATUS
~BACKGROUND OF THE INVENTION
Various alarm devices have been proposed heretofore llwhich produce an audible or other alarm signal when a person ¦itouches the outside doorknob of a door leading into the premises ~to be protected.
Examples of such prior proposals in which the alarm apparatus is A. C. powered are disclosed in my U. S. patent .
, .
.
4,011,554, "Popular Electronics" magazine, Feb. 1969, pp. 92-93, U. S. patent 3,508,239 to John V. Fontaine, and U. S. patent 3,465,325 to Goldfarb et al.
Examples of such prior proposals in which the alarm '~apparatus is battery powered are disclosed in U. S. patent 3,623,063 to John V. Fontaine, and in "101 Electronic Projects For Under $15", a Davis Publication, 1975 edition, pp. 56-67.
The previous battery powered intrusion alarms had two principal disadvantages: short battery life, and frequent false alarms Icaused by an inability to reliably discriminate between the capacitance of a person's body and various stray capacitances.
, ~
SUMMARY OF THE INVENTION
I have discovered that the successful, reliable perform-ance of a battery-operated intrusion alarm apparatus having an Ioscillator which is turned off by the body capacitance of a I Iwould-be intruder depends critically upon the oscillator fre-'quency. The critical operative range, from about 17 MHz. up to about 65 MHz., is much higher than the frequency of operation of llprevious battery powered alarms of this general type. Within lthis critical oscillator frequency range the alarm apparatus is sufficiently sensitive to respond to a person's touching or closely approaching the sensor of the apparatus. This would include touching the doorknob with a key or other metal object ;or with a heavy rubber or fabric glove. Also, it can discrim-inate dependably between the body capacitance of a person and ~stray capacitances, thereby preventing false alarms.
$~
,` ~
Another critical advantage of my alarm apparatus is that the standby current or current drain when the apparatus is in its normal, non-alarm condition is less than 500 microamperes, thereby prolonging the life of the battery.
~ My alarm apparatus has a fail-safe mode of operation which causes the oscillator to turn off and signal an apparent alarm condition continuously when the battery voltage drops below a certain value. This continuous apparent alarm condition tells llthe user that the battery is dying and should be replaced 'limmediately.
,l A principal object of this invention is to provide a novel and improved battery-operated intrusion alarm apparatus.
Another object of this invention is to provide such an ,~lalarm apparatus having a front end oscillator operating in what 1i I have determined is a critical frequency range between approxi-lmately 17 MHz. and 65 MHz. A sensor i5 connected in the feed-back circuit of the oscillator. The oscillator will be turned off to trigger an alarm by the body capacitance of a would-be in-~Itruder who touches or closely approaches the sensor. However, jlin this frequency range the oscillator will not be turned offby ambient stray capacitances usually encountered.
Another object of this invention is to provide a novel and improved battery-operated intrusion alarm apparatus having ~an extremely low current drain which prolongs the life of the 1l battery.
Further objects and advantages of this invention will be apparent from the following detailed description of two presently-preferred embodiments thereof, which are shown in the ~accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a perspective view showing the present alarm apparatus suspended from the inside doorknob on a door;
Figure 2 is a schematic electrical circuit diagram of la non-latching embodiment of the present alarm apparatus; and Figure 3 is a schematic electrical circuit diagram of a latching embodiment of the present alarm apparatus; and - I Figure 4 is a schematic electrical circuit diagram of the alarm signalling device H in either Figure 2 or Figure 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Before explaining the disclosed embodiments of the llpresent invention in detail, it is to be understood that the iiinvention is not limited in its application to the details of the llparticular arrangements shown, since the invention is capable of ¦l~other embodiments. Also, the terminology used herein is for the ¦Ipurpose of description and not of limitation.
¦¦ Referring first to Figure 1, the present alarm appara-tus has a small housing 10 with a chain 11 of electrically con-ilductive metal by which it is suspended from an electrically Iconductive metal doorknob 12 on the inside of a door 13 of wood or other suitable electrically non-conductive material. Enclosed within the housing 10 are all of the components of the electrical circuit shown in Figure 2 ( or the circuit shown in Figure 3) ~except the sensor K, which includes the chain 11, the inside Idoorknob 12, and the doorknob (not shown)on the outside of the ~door.
It is to be understood that instead of the doorknobs and chain, the sensor for the present alarm might have a floor ` ~ ' mat or any other suitable arrangement electrically coupled to the present alarm circuit to introduce more capacitance or electrical grounding into the alarm circuit to trigger the alarm.
Referring to Figure 2, the circuit shown there has Ithree principal stages: an RF oscillator, an RF detector and DC amplifier, and a DC power amplifier.
The RF oscillator includes a transistor Ql whose col-lector is connected to the positive terminal of a battery 14 ~through an inductance Ll. The emitter of Ql is connected to the Illnegative terminal of battery 14 through a load resistor R3 and a manual on-off switch 15. A feedback capacitor C3 is connected across the collector and emitter of Ql A bias resistor Rl is connected between the positive battery terminal and the base of I~Ql Another bias resistor R2 is connected between the base of I!Ql and the negative battery terminal. A bypass capacitor C1 is ~connected across the battery terminals via switch 15, and another jlbypass capacitor C2 is connected across resistor R2.
¦~ The sensor K is directly connected conductively to the ~collector of Ql ~l The feedback capacitor C3 is selected or factory-adjusted to provide a 90-degree phase shift between the collector and emitter of Ql normally (i.e., in the absence of a person's touching or closely approaching the outside doorknob which is Ijpart of the sensor K).
In the presently preferred embodiment of this oscil-lator the circuit elements have the following identity and values:
, , P~ 3 ` ~I Ql Type 2N 4401 Cl047 microfarad il ¦l C2047 microfarad I! Rl 87,000 ohms 5 I R2 22,000 ohms R3 2,000 ohms Ll1.2 microhenries C35-75 picofarads !l Using the well-known equation for resonance, in this Icircuit the resonant frequency~ 1/2~ ~ C3. When C3 is at its lower limit of 5 picofarads the oscillator frequency is sub-stantially 65 MegaHertz. When C3 is at its upper limit of 75 ¦picoferads the oscillator frequenc~ is substantially 17 MHz.
Within this critical frequency range from substan-~ 15 tially 17 MHz. to 65 Mhz. the oscillator will turn off when a I person touches or closely approaches the outside doorknob. The person's body capacitance of approximately 100 picofarads connects the sensor K to neutral potential and prevents the feedhack capacitor C3 from continuing to provide the 90 degree phase shift required for oscillations to be maintained. At an oscillator frequency of at least substantially 17 MegaUertz or higher the ¦ normal body capacitance of a human being is seen by the oscillator ¦as a high enough impedance that it can be distinguished from ~ -llambient stray capacitance at the sensor K or stray circuit 1ll capacitance within housing 10.
i The sensitivity of the oscillator to a person's touching or closely approaching the outside doorknob or any other part of the sensor K increases as the oscillator frequency is ,~ I
: , .
-,~increased. However, at oscillator frequencies substantially above 65 ~H~. the apparatus would be so sensitive that the oscillator might be turned off by a person who is a foot or more away from the sensor, and sometimes by stray capacitances. At frequencies substantially below 17 MHz. the oscillator is not able to discriminate reliably between a person's body capacitance ~`and stray capacitances, resulting in annoying frequent false alarms which made impractical the previously proposed alarms ~which operated at such lower frequencies.
The detector-amplifier stage of the Figure 2 circuit includes a coupling capacitor C4 connected directly to the ,collector of Ql and a resistor R4 connected between capacitor ,C4 and a point A in the circuit. A first rectifier Dl has its ~cathode connected to point A and its anode connected through ~Iswitch 15 to the negative terminal of battery 14. A second rectifier D2 has its anode connected to point A and its cathode connected to the base of a transistor Q2. The emitter of Q2 is connected to the negative battery terminal through switch 15.
ilThe collector of Q2 is connected through a load resistor R5 to Ithe positive battery terminal.
To the right of point A in Figure 2 the circuit is entirely DC.
' Resistor R4 provides a load for the oscillator and l~provides an impedance match between the oscillator stage and the detector-amplifier stage.
The load resistor R5 for Q2 has a high enough resist-ance (at least 47,000 ohms) to hold the current to a satisfactorily low level for long battery life.
;
?~ 3 3 While the oscillator is oscillating a small DC voltage ~appears at point A, due to the rectifying action of Dl, and this is sufficient to turn on Q2. When Q2 conducts, the voltage from llits collector to ground is about 0.7 volts in the preferred em-llbodiments of this circuit. Because this voltage (at point B) isheld at this level, the Darlington combination Q3-Q4 of the power ~amplifier stage is normally maintained in a cutoff condition.
Point B (at the collector of Q2) is connected to point C (at the i~base of Q3) through a resistor R6. The collector of Q3 is con-¦nected to the collector of Q4 at point D. The emitter of Q3is connected to the base of Q4. The emitter of Q4 is connected to the negative battery terminal through switch 15. Point D is connected through an electrically operated alarm signalling jldevice H to the positive battery terminal.
i 15 j~ With the Darlington combination Q3-Q4 of the D. C.
power amplifier stage cut off as long as the oscillator is l oscillating, the leakage current through the alarm signalling ¦ device H is extremely low, virtually zero.
¦I Preferably, the overall current gain from point A to 20¦¦ point D is at least 125,000.
In the embodiment of the invention having the oscillator circuit elements already identified, the values and ~identities of the circuit elements in the RF detector and DC
llamplifier stage and the DC power amplifier stage of the circuit 'are as follows:
C4 .01 microfarads R4 560 ohms Dl & D2 type IN 4148 .
~, R5 47,000 ohms R6 1,000 ohms Q2' Q3 & Q4 type 2N 4401 battery 14 four series-connected 1.5 volt I' "c" cells 5 ¦1 In the operation of this circuit, the signalling device H sounds an alarm when the Darlington combination Q3-Q4 is turned on. This happens as a result of cessation of oscilla-tions in the oscillator when a person touches or closely Ilapproaches the sensor K. Normally, i.e., while the oscillator l~is oscillating, the current drain through the signalling device H is extremely low and as a consequence the battery iife is exceptionally long.
The circuit functions in a fail-safe manner in that l~when the battery begins to die and its voltage drops, the oscil-llator will be turned off and the signalling device H will be ¦ turned on. (The battery voltage will still be high enough to loperate the signalling device H.) Typically the signalling device ¦
¦at first will produce intermittent short bursts of sound and Igradually it stays on continuously. This tells the user (after Idetermining that a would-be intruder has not triggered the alarm) ~that the battery is dying and should be replaced.
In one practical embodiment, the actual voltage of the four series-connected 1.5 volt "c" cells, when fresh, is jl6.1 volts and the current drain (in the absence of an alarm condi-1li tion) is 470 microamperes. After a period of use, the bat-tery voltage drops to 5.5 volts and the current drain is 400 ~microamperes. Later, the battery voltage is down to 5.0 volts ~, , _g_ , ' ~
and at this voltage the current drain is 370 microamperes. ~.~hen ' the battery voltage is down to 4.9 volts the current drain is 310 microamperes.
The apparatus continues: to function properly for alarm signalling purposes until the battery voltage is down to 4.6 volts, at which point the current drain is 280 microamperes.
At this cutoff point of 4.6 volts battery voltage, the detector is disabled and the alarm signalling device H comes on and stays lon, at first intermittently and later continuously, even when a l'person is not touching or close to the sensor K. This continuous apparent alarm condition persists until the battery voltage drops to about 3.0 volts, and its continuity tells the user that the 'Ibattery needs replacement.
'l In practice, conventional lead-zinc batteries can be 11 expected to last eight months before requiring replacement in the present alarm apparatus. The useful life of alkaline bat-teries in the present alarm apparatus is two years or more.
Such long battery life is achieved by keeping the current drain ~at a very low value, preferably under 500 microamperes. In the Ipresent alarm apparatus this is achieved by using transistors ~having a high Beta (current amplification), at least 150. In the Figure 2 circuit, Ql' Q2'Q3 and Q4 all have this high Beta characteristic.
, It is to be understood that all of the circuit com-1,1 i~ponents, including the battery 14 and switch 15, are electrically insulated from the casing 10.
Figure 3 shows a modified circuit of the "latching"
type, in which the alarm signalling device H, once it turns on, ~will remain on until the user deliberately turns it off.
~ The oscillator stage and the RF detector - DC
`amplifier stage are the same as in Figure 2 and need not be described again.
The final stage of the Figure 3 circuit is termed a "switch" stage, having a silicon controlled rectifier SCRl with its gate electrode connected to point B through a rectifier D3.
The positive battery terminal is connected through the alarm signalling device H to the anode of SCRl. The cathode of SCR
l~is connected through a normally-closed, push-button switch 16 land switch 15 to the negative battery terminal.
As long as the oscillator is oscillating, the output ~f Q2 will hold the gate of SCRl almost at ground potential and ~SCRl will be off. ~hen the oscillator stops oscillating, as l,described, this cutoff bias no longer appears on the gate of SCRl and the latter turns on, passing sufficient current through the alarm signalling device H to cause the latter to sound the alarm.
¦ Even if the oscillator resumes oscillating,SCRl will llremain on until the user depresses the push button of switch 16 l~to open this switch. As soon as this push button is released and switch 16 re-closes the circuit will be restored to its normal operating condition with the signalling device H turned off and the oscillator oscillating.
In the presently-preferred embodiment of Figure 3, the circuit elements which are the same as those in Figure 2 'have the same values and are the same type as in the Figure 2 .
circuit. In addition, SCRl is a Hudson 106 Dl silicon con-trolled rectifier.
The performance characteristics of the Figure 3 alarm circuit are essentially similar to those of the Figure 2 circuit ~already described. The current drain preferably is less than lil500 microamperes, both transistors Ql and Q2 have a high Beta, and the oscillator frequency is between substantially 17 and 65 ~I~Hz. All of the circuit components in Figure 3, including the ; llbattery 14 and both switches 15 and 16, are electrically in-sulated from the casing 10.
~i The alarm signalling device H in Figures 2 and 3 is ¦¦shown in detail in Figure 4.
It includes an NE 555 integrated circuit 17 of known ¦design which generates clock pulses, a transistor Q5 for amplify-ing these pulses and an 8-ohm speaker 18 of conventional design ¦for broadcasting these amplified pulses audibly. The pulse ~repetition rate preferably is about 1,000 Hz. as determined by the values of resistors R7 and R8 and capacitor C5. A load resistor Rg is connected between the output terminal of clock pulse generator 17 and the base of Q5.
ll In one practical embodiment, Q5 is a 2N4401 transistor l (the same as transistors Ql' Q2' Q3 and Q4), resistor R7 is 1,000 ohms, resistor R8 is 7,250 ohms, resistor Rg is 47 ohms, and capacitor C5 is 0.047 microfarad (the same as capacitor C2).
I have determined that the alarm signalling device of IFigure 4, when connected in the Figure 2 circuit or the Figure 3 ,Icircuit with its terminals X and Y as shown, enables the circuit to operate as described, both for normal alarm signalling and also for signalling that the battery is dying and needs replace-ment. In contrast, a conventional 6-volt or 3-volt buzzer would not work in this fashion when connected in this Figure 2 circuit or the Figure 3 circuit between the terminals X and Y.
It will be understood that in both the non-latching `embodiment (Figure 2) and the latching embodiment (Figure 3) 'various changes may be made in the circuitry. For example, in the~
iRF detector - DC amplifier stage the transistor Q2 might be ~changed to a PNP transistor, in which case rectifier D2 would be reversed and a large resistor would be connected between the base and emitter of Q2 to provide the complement of the NPN arrange-ment shown.
' , i, ~ -13-
BODY CAPACITANCE INTRUSION
ALARM APPARATUS
~BACKGROUND OF THE INVENTION
Various alarm devices have been proposed heretofore llwhich produce an audible or other alarm signal when a person ¦itouches the outside doorknob of a door leading into the premises ~to be protected.
Examples of such prior proposals in which the alarm apparatus is A. C. powered are disclosed in my U. S. patent .
, .
.
4,011,554, "Popular Electronics" magazine, Feb. 1969, pp. 92-93, U. S. patent 3,508,239 to John V. Fontaine, and U. S. patent 3,465,325 to Goldfarb et al.
Examples of such prior proposals in which the alarm '~apparatus is battery powered are disclosed in U. S. patent 3,623,063 to John V. Fontaine, and in "101 Electronic Projects For Under $15", a Davis Publication, 1975 edition, pp. 56-67.
The previous battery powered intrusion alarms had two principal disadvantages: short battery life, and frequent false alarms Icaused by an inability to reliably discriminate between the capacitance of a person's body and various stray capacitances.
, ~
SUMMARY OF THE INVENTION
I have discovered that the successful, reliable perform-ance of a battery-operated intrusion alarm apparatus having an Ioscillator which is turned off by the body capacitance of a I Iwould-be intruder depends critically upon the oscillator fre-'quency. The critical operative range, from about 17 MHz. up to about 65 MHz., is much higher than the frequency of operation of llprevious battery powered alarms of this general type. Within lthis critical oscillator frequency range the alarm apparatus is sufficiently sensitive to respond to a person's touching or closely approaching the sensor of the apparatus. This would include touching the doorknob with a key or other metal object ;or with a heavy rubber or fabric glove. Also, it can discrim-inate dependably between the body capacitance of a person and ~stray capacitances, thereby preventing false alarms.
$~
,` ~
Another critical advantage of my alarm apparatus is that the standby current or current drain when the apparatus is in its normal, non-alarm condition is less than 500 microamperes, thereby prolonging the life of the battery.
~ My alarm apparatus has a fail-safe mode of operation which causes the oscillator to turn off and signal an apparent alarm condition continuously when the battery voltage drops below a certain value. This continuous apparent alarm condition tells llthe user that the battery is dying and should be replaced 'limmediately.
,l A principal object of this invention is to provide a novel and improved battery-operated intrusion alarm apparatus.
Another object of this invention is to provide such an ,~lalarm apparatus having a front end oscillator operating in what 1i I have determined is a critical frequency range between approxi-lmately 17 MHz. and 65 MHz. A sensor i5 connected in the feed-back circuit of the oscillator. The oscillator will be turned off to trigger an alarm by the body capacitance of a would-be in-~Itruder who touches or closely approaches the sensor. However, jlin this frequency range the oscillator will not be turned offby ambient stray capacitances usually encountered.
Another object of this invention is to provide a novel and improved battery-operated intrusion alarm apparatus having ~an extremely low current drain which prolongs the life of the 1l battery.
Further objects and advantages of this invention will be apparent from the following detailed description of two presently-preferred embodiments thereof, which are shown in the ~accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a perspective view showing the present alarm apparatus suspended from the inside doorknob on a door;
Figure 2 is a schematic electrical circuit diagram of la non-latching embodiment of the present alarm apparatus; and Figure 3 is a schematic electrical circuit diagram of a latching embodiment of the present alarm apparatus; and - I Figure 4 is a schematic electrical circuit diagram of the alarm signalling device H in either Figure 2 or Figure 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Before explaining the disclosed embodiments of the llpresent invention in detail, it is to be understood that the iiinvention is not limited in its application to the details of the llparticular arrangements shown, since the invention is capable of ¦l~other embodiments. Also, the terminology used herein is for the ¦Ipurpose of description and not of limitation.
¦¦ Referring first to Figure 1, the present alarm appara-tus has a small housing 10 with a chain 11 of electrically con-ilductive metal by which it is suspended from an electrically Iconductive metal doorknob 12 on the inside of a door 13 of wood or other suitable electrically non-conductive material. Enclosed within the housing 10 are all of the components of the electrical circuit shown in Figure 2 ( or the circuit shown in Figure 3) ~except the sensor K, which includes the chain 11, the inside Idoorknob 12, and the doorknob (not shown)on the outside of the ~door.
It is to be understood that instead of the doorknobs and chain, the sensor for the present alarm might have a floor ` ~ ' mat or any other suitable arrangement electrically coupled to the present alarm circuit to introduce more capacitance or electrical grounding into the alarm circuit to trigger the alarm.
Referring to Figure 2, the circuit shown there has Ithree principal stages: an RF oscillator, an RF detector and DC amplifier, and a DC power amplifier.
The RF oscillator includes a transistor Ql whose col-lector is connected to the positive terminal of a battery 14 ~through an inductance Ll. The emitter of Ql is connected to the Illnegative terminal of battery 14 through a load resistor R3 and a manual on-off switch 15. A feedback capacitor C3 is connected across the collector and emitter of Ql A bias resistor Rl is connected between the positive battery terminal and the base of I~Ql Another bias resistor R2 is connected between the base of I!Ql and the negative battery terminal. A bypass capacitor C1 is ~connected across the battery terminals via switch 15, and another jlbypass capacitor C2 is connected across resistor R2.
¦~ The sensor K is directly connected conductively to the ~collector of Ql ~l The feedback capacitor C3 is selected or factory-adjusted to provide a 90-degree phase shift between the collector and emitter of Ql normally (i.e., in the absence of a person's touching or closely approaching the outside doorknob which is Ijpart of the sensor K).
In the presently preferred embodiment of this oscil-lator the circuit elements have the following identity and values:
, , P~ 3 ` ~I Ql Type 2N 4401 Cl047 microfarad il ¦l C2047 microfarad I! Rl 87,000 ohms 5 I R2 22,000 ohms R3 2,000 ohms Ll1.2 microhenries C35-75 picofarads !l Using the well-known equation for resonance, in this Icircuit the resonant frequency~ 1/2~ ~ C3. When C3 is at its lower limit of 5 picofarads the oscillator frequency is sub-stantially 65 MegaHertz. When C3 is at its upper limit of 75 ¦picoferads the oscillator frequenc~ is substantially 17 MHz.
Within this critical frequency range from substan-~ 15 tially 17 MHz. to 65 Mhz. the oscillator will turn off when a I person touches or closely approaches the outside doorknob. The person's body capacitance of approximately 100 picofarads connects the sensor K to neutral potential and prevents the feedhack capacitor C3 from continuing to provide the 90 degree phase shift required for oscillations to be maintained. At an oscillator frequency of at least substantially 17 MegaUertz or higher the ¦ normal body capacitance of a human being is seen by the oscillator ¦as a high enough impedance that it can be distinguished from ~ -llambient stray capacitance at the sensor K or stray circuit 1ll capacitance within housing 10.
i The sensitivity of the oscillator to a person's touching or closely approaching the outside doorknob or any other part of the sensor K increases as the oscillator frequency is ,~ I
: , .
-,~increased. However, at oscillator frequencies substantially above 65 ~H~. the apparatus would be so sensitive that the oscillator might be turned off by a person who is a foot or more away from the sensor, and sometimes by stray capacitances. At frequencies substantially below 17 MHz. the oscillator is not able to discriminate reliably between a person's body capacitance ~`and stray capacitances, resulting in annoying frequent false alarms which made impractical the previously proposed alarms ~which operated at such lower frequencies.
The detector-amplifier stage of the Figure 2 circuit includes a coupling capacitor C4 connected directly to the ,collector of Ql and a resistor R4 connected between capacitor ,C4 and a point A in the circuit. A first rectifier Dl has its ~cathode connected to point A and its anode connected through ~Iswitch 15 to the negative terminal of battery 14. A second rectifier D2 has its anode connected to point A and its cathode connected to the base of a transistor Q2. The emitter of Q2 is connected to the negative battery terminal through switch 15.
ilThe collector of Q2 is connected through a load resistor R5 to Ithe positive battery terminal.
To the right of point A in Figure 2 the circuit is entirely DC.
' Resistor R4 provides a load for the oscillator and l~provides an impedance match between the oscillator stage and the detector-amplifier stage.
The load resistor R5 for Q2 has a high enough resist-ance (at least 47,000 ohms) to hold the current to a satisfactorily low level for long battery life.
;
?~ 3 3 While the oscillator is oscillating a small DC voltage ~appears at point A, due to the rectifying action of Dl, and this is sufficient to turn on Q2. When Q2 conducts, the voltage from llits collector to ground is about 0.7 volts in the preferred em-llbodiments of this circuit. Because this voltage (at point B) isheld at this level, the Darlington combination Q3-Q4 of the power ~amplifier stage is normally maintained in a cutoff condition.
Point B (at the collector of Q2) is connected to point C (at the i~base of Q3) through a resistor R6. The collector of Q3 is con-¦nected to the collector of Q4 at point D. The emitter of Q3is connected to the base of Q4. The emitter of Q4 is connected to the negative battery terminal through switch 15. Point D is connected through an electrically operated alarm signalling jldevice H to the positive battery terminal.
i 15 j~ With the Darlington combination Q3-Q4 of the D. C.
power amplifier stage cut off as long as the oscillator is l oscillating, the leakage current through the alarm signalling ¦ device H is extremely low, virtually zero.
¦I Preferably, the overall current gain from point A to 20¦¦ point D is at least 125,000.
In the embodiment of the invention having the oscillator circuit elements already identified, the values and ~identities of the circuit elements in the RF detector and DC
llamplifier stage and the DC power amplifier stage of the circuit 'are as follows:
C4 .01 microfarads R4 560 ohms Dl & D2 type IN 4148 .
~, R5 47,000 ohms R6 1,000 ohms Q2' Q3 & Q4 type 2N 4401 battery 14 four series-connected 1.5 volt I' "c" cells 5 ¦1 In the operation of this circuit, the signalling device H sounds an alarm when the Darlington combination Q3-Q4 is turned on. This happens as a result of cessation of oscilla-tions in the oscillator when a person touches or closely Ilapproaches the sensor K. Normally, i.e., while the oscillator l~is oscillating, the current drain through the signalling device H is extremely low and as a consequence the battery iife is exceptionally long.
The circuit functions in a fail-safe manner in that l~when the battery begins to die and its voltage drops, the oscil-llator will be turned off and the signalling device H will be ¦ turned on. (The battery voltage will still be high enough to loperate the signalling device H.) Typically the signalling device ¦
¦at first will produce intermittent short bursts of sound and Igradually it stays on continuously. This tells the user (after Idetermining that a would-be intruder has not triggered the alarm) ~that the battery is dying and should be replaced.
In one practical embodiment, the actual voltage of the four series-connected 1.5 volt "c" cells, when fresh, is jl6.1 volts and the current drain (in the absence of an alarm condi-1li tion) is 470 microamperes. After a period of use, the bat-tery voltage drops to 5.5 volts and the current drain is 400 ~microamperes. Later, the battery voltage is down to 5.0 volts ~, , _g_ , ' ~
and at this voltage the current drain is 370 microamperes. ~.~hen ' the battery voltage is down to 4.9 volts the current drain is 310 microamperes.
The apparatus continues: to function properly for alarm signalling purposes until the battery voltage is down to 4.6 volts, at which point the current drain is 280 microamperes.
At this cutoff point of 4.6 volts battery voltage, the detector is disabled and the alarm signalling device H comes on and stays lon, at first intermittently and later continuously, even when a l'person is not touching or close to the sensor K. This continuous apparent alarm condition persists until the battery voltage drops to about 3.0 volts, and its continuity tells the user that the 'Ibattery needs replacement.
'l In practice, conventional lead-zinc batteries can be 11 expected to last eight months before requiring replacement in the present alarm apparatus. The useful life of alkaline bat-teries in the present alarm apparatus is two years or more.
Such long battery life is achieved by keeping the current drain ~at a very low value, preferably under 500 microamperes. In the Ipresent alarm apparatus this is achieved by using transistors ~having a high Beta (current amplification), at least 150. In the Figure 2 circuit, Ql' Q2'Q3 and Q4 all have this high Beta characteristic.
, It is to be understood that all of the circuit com-1,1 i~ponents, including the battery 14 and switch 15, are electrically insulated from the casing 10.
Figure 3 shows a modified circuit of the "latching"
type, in which the alarm signalling device H, once it turns on, ~will remain on until the user deliberately turns it off.
~ The oscillator stage and the RF detector - DC
`amplifier stage are the same as in Figure 2 and need not be described again.
The final stage of the Figure 3 circuit is termed a "switch" stage, having a silicon controlled rectifier SCRl with its gate electrode connected to point B through a rectifier D3.
The positive battery terminal is connected through the alarm signalling device H to the anode of SCRl. The cathode of SCR
l~is connected through a normally-closed, push-button switch 16 land switch 15 to the negative battery terminal.
As long as the oscillator is oscillating, the output ~f Q2 will hold the gate of SCRl almost at ground potential and ~SCRl will be off. ~hen the oscillator stops oscillating, as l,described, this cutoff bias no longer appears on the gate of SCRl and the latter turns on, passing sufficient current through the alarm signalling device H to cause the latter to sound the alarm.
¦ Even if the oscillator resumes oscillating,SCRl will llremain on until the user depresses the push button of switch 16 l~to open this switch. As soon as this push button is released and switch 16 re-closes the circuit will be restored to its normal operating condition with the signalling device H turned off and the oscillator oscillating.
In the presently-preferred embodiment of Figure 3, the circuit elements which are the same as those in Figure 2 'have the same values and are the same type as in the Figure 2 .
circuit. In addition, SCRl is a Hudson 106 Dl silicon con-trolled rectifier.
The performance characteristics of the Figure 3 alarm circuit are essentially similar to those of the Figure 2 circuit ~already described. The current drain preferably is less than lil500 microamperes, both transistors Ql and Q2 have a high Beta, and the oscillator frequency is between substantially 17 and 65 ~I~Hz. All of the circuit components in Figure 3, including the ; llbattery 14 and both switches 15 and 16, are electrically in-sulated from the casing 10.
~i The alarm signalling device H in Figures 2 and 3 is ¦¦shown in detail in Figure 4.
It includes an NE 555 integrated circuit 17 of known ¦design which generates clock pulses, a transistor Q5 for amplify-ing these pulses and an 8-ohm speaker 18 of conventional design ¦for broadcasting these amplified pulses audibly. The pulse ~repetition rate preferably is about 1,000 Hz. as determined by the values of resistors R7 and R8 and capacitor C5. A load resistor Rg is connected between the output terminal of clock pulse generator 17 and the base of Q5.
ll In one practical embodiment, Q5 is a 2N4401 transistor l (the same as transistors Ql' Q2' Q3 and Q4), resistor R7 is 1,000 ohms, resistor R8 is 7,250 ohms, resistor Rg is 47 ohms, and capacitor C5 is 0.047 microfarad (the same as capacitor C2).
I have determined that the alarm signalling device of IFigure 4, when connected in the Figure 2 circuit or the Figure 3 ,Icircuit with its terminals X and Y as shown, enables the circuit to operate as described, both for normal alarm signalling and also for signalling that the battery is dying and needs replace-ment. In contrast, a conventional 6-volt or 3-volt buzzer would not work in this fashion when connected in this Figure 2 circuit or the Figure 3 circuit between the terminals X and Y.
It will be understood that in both the non-latching `embodiment (Figure 2) and the latching embodiment (Figure 3) 'various changes may be made in the circuitry. For example, in the~
iRF detector - DC amplifier stage the transistor Q2 might be ~changed to a PNP transistor, in which case rectifier D2 would be reversed and a large resistor would be connected between the base and emitter of Q2 to provide the complement of the NPN arrange-ment shown.
' , i, ~ -13-
Claims (8)
1. In a battery-operated intrusion alarm apparatus having:
a battery;
an oscillator energized by said battery to normally produce oscillations;
a sensor operatively coupled to said oscillator to stop said oscillations in response to the body capacitance of a person touching or in close proximity to the sensor;
and means operatively coupled to said oscillator for signalling an alarm when it stops oscillating;
the improvement which comprises means for causing said oscillator to oscillate at a predetermined frequency within the range from substantially 17 MegaHertz to 65 MegaHertz.
a battery;
an oscillator energized by said battery to normally produce oscillations;
a sensor operatively coupled to said oscillator to stop said oscillations in response to the body capacitance of a person touching or in close proximity to the sensor;
and means operatively coupled to said oscillator for signalling an alarm when it stops oscillating;
the improvement which comprises means for causing said oscillator to oscillate at a predetermined frequency within the range from substantially 17 MegaHertz to 65 MegaHertz.
2. An alarm apparatus according to claim 1, and further comprising means for limiting the current drain on the battery to less than substantially 500 microamperes while said oscillator is oscillating.
3. An alarm apparatus according to claim 2, wherein said oscillator is operative to stop oscillating and thereby operate said alarm signalling means when the voltage of said battery drops below a predetermined value.
4. An alarm apparatus according to claim 1, wherein:
said oscillator includes a transistor having a Beta of at least 150;
and further comprising:
an RF detector and DC amplifier having a transistor with a Beta of at least 150 coupling said oscillator to said means for signalling an alarm.
said oscillator includes a transistor having a Beta of at least 150;
and further comprising:
an RF detector and DC amplifier having a transistor with a Beta of at least 150 coupling said oscillator to said means for signalling an alarm.
5. An alarm apparatus according to claim 4, and further comprising:
a DC power amplifier coupling said RF detector and DC amplifier to said means for signalling an alarm, said power amplifier including a Darlington pair of two transistors each having a Beta of at least 150.
a DC power amplifier coupling said RF detector and DC amplifier to said means for signalling an alarm, said power amplifier including a Darlington pair of two transistors each having a Beta of at least 150.
6. An alarm apparatus according to claim 4, and further comprising:
an SCR and a manually operated switch connected in series with said means for signalling an alarm across said battery, whereby to maintain said last-mentioned means energized, after the SCR is turned on, until said switch is opened;
and a rectifier connecting the output of said RF detector and DC amplifier to the gate of said SCR.
an SCR and a manually operated switch connected in series with said means for signalling an alarm across said battery, whereby to maintain said last-mentioned means energized, after the SCR is turned on, until said switch is opened;
and a rectifier connecting the output of said RF detector and DC amplifier to the gate of said SCR.
7. An alarm signaling apparatus according to claim 5 wherein:
said alarm signalling device is connected between the positive battery terminal and said Darlington pair and com-prises:
a clock pulse generator;
a transistor coupled to the output of said pulse generator to amplify its pulses;
and a speaker operatively connected to said last-mentioned transistor for audibly broadcasting the amplified pulses.
said alarm signalling device is connected between the positive battery terminal and said Darlington pair and com-prises:
a clock pulse generator;
a transistor coupled to the output of said pulse generator to amplify its pulses;
and a speaker operatively connected to said last-mentioned transistor for audibly broadcasting the amplified pulses.
8. An alarm signalling apparatus according to claim 6 wherein:
said alarm signalling device is connected between the positive battery terminal and said SCR and comprises:
a clock pulse generator;
a transistor coupled to the output of said pulse generator to amplify its pulses;
and a speaker operatively connected to said last-mentioned transistor for audibly broadcasting the amplified pulses.
said alarm signalling device is connected between the positive battery terminal and said SCR and comprises:
a clock pulse generator;
a transistor coupled to the output of said pulse generator to amplify its pulses;
and a speaker operatively connected to said last-mentioned transistor for audibly broadcasting the amplified pulses.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US79288777A | 1977-05-02 | 1977-05-02 | |
| US792,887 | 1977-05-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1106933A true CA1106933A (en) | 1981-08-11 |
Family
ID=25158365
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA302,638A Expired CA1106933A (en) | 1977-05-02 | 1978-05-04 | Body capacitance intrusion alarm apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1106933A (en) |
-
1978
- 1978-05-04 CA CA302,638A patent/CA1106933A/en not_active Expired
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| MKEX | Expiry |