Apparatus and method for synchronizing visual/audible alarm units in an alarm system

The invention relates generally to an alarm system for providing visual and/or audio warnings and, more particularly, to an apparatus and a concomitant method for synchronizing a plurality of visual and/or audio alarm units.

BACKGROUND OF THE DISCLOSURE

This invention relates to circuits for electronic alarm systems such as are used to provide visual and audio warning in electronic fire alarm devices and other emergency warning devices and, more particularly, to a control circuit which enables the system to provide both a visual and an audio alarm signal, including a silence feature, while using only one signal wire loop.

Strobe lights and/or audio horns are used to provide warning of potential hazards or to draw attention to an event or activity. An important field of use for these signaling devices is in electronic fire alarm systems. Strobe alarm circuits typically include a flashtube and a trigger circuit for initiating firing of the flashtube, with energy for the flash typically supplied from a capacitor connected in shunt with the flashtube. In some known systems, the flash occurs when the voltage across the flash unit (i.e., the flashtube and associated trigger circuit) exceeds the threshold voltage required to actuate the trigger circuit, and in others the flash is triggered by a timing circuit. After the flashtube is triggered, it becomes conductive and rapidly discharges the stored energy from the shunt capacitor until the voltage across the flashtube has decreased to a value at which the flashtube is extinguished and becomes non-conductive.

In a typical alarm system, a loop of several flash units is connected to a fire alarm control panel which includes a power supply for supplying power to all flash units in the loop when an alarm condition is present. Each unit typically fires independently of the others at a rate determined by its respective charging and triggering circuits. Underwriters Laboratories specifications require the flash rate of such visual signaling devices to be between 20 and 120 flashes per minute.

In addition to having a strobe alarm as described above, it may also be desirable to have an audio alarm signal to provide an additional means for alerting persons who may be in danger. In such systems, a “silence” feature is often available whereby, after a period of time has elapsed from the initial alarm, the audio signal may be silenced either automatically or manually. Heretofore, in a system where alarm units having both a visual alarm signal and an audio alarm signal have been implemented, two control loops, one for video and one for audio, have been required between the fire alarm control panel and the series of alarm units.

In a system as described above, the supply voltage may be 12 volts or 20-31 volts, and may be either D.C. supplied by a battery or a full-wave rectified voltage. Underwriters Laboratories specifications require that operation of the device must continue when the supply voltage drops to as much as 80% of nominal value and also when it rises to 110% of nominal value. However, when the voltage source is at 80% of nominal value, the strobe may lose some intensity which could prove crucial during a fire emergency.

Thus, it is desirable to provide a control circuit which will enable an alarm system to provide both audio and visual synchronized alarm signals using only a single control signal wire loop between the alarm units, while allowing for the capability of silencing the audio alarm.

It is also desirable to provide the ability to lower the flash frequency when a low input voltage is detected, thereby ensuring a proper flash brightness.

It is also desirable to provide an alarm interface circuit which will enable an existing alarm system to sound a Code 3 alarm whether or not the existing alarm system is already equipped with Code 3 capability.

It is also desirable to provide a circuit having these properties and which will also work with: (a) both D.C. and full-wave rectified supplies; (b) all fire alarm control panels; and (c) mixed alarm units (i.e., 110 candela and 15 candela with and without audio signals).

It is also desirable to provide a method of reducing the number of synchronization pulses transmitted to the alarm units, thereby increasing the reliability of the overall alarm system.

SUMMARY OF THE INVENTION

In accordance with the present invention, an alarm system is provided which includes a control circuit that allows multiple audio/visual alarm circuits, connected together by a single two-wire control loop, to be synchronously activated when an alarm condition is present. The control circuit also allows for other alarm control functions, such as the deactivation of the audio alarm, to be carried out using only the single control loop. The control circuit is able to provide these functions by interrupting power to the alarm units for approximately 10 to 30 milliseconds at a time. Preferably, each alarm unit is equipped with a microcontroller which is programmed to interpret the brief power interrupt, or “drop out”, as either a synchronization signal or a function control signal, depending on the timing of the drop out. The microcontroller can also be programmed to interpret different sequences of drop outs as control signals for other functions such as reactivation of the audio alarm.

The alarm unit is capable of detecting a low input voltage. When the detected voltage drops below a predetermined threshold, the alarm unit will lower the frequency of the visual alarm signal, preferably a strobe, to ensure that the strobe flashtube receives enough energy to flash at an adequate brightness.

The alarm unit is also capable of functioning independently of any synchronization signal from the control circuit. In the event a synchronization signal is not received, an internal timer will cause the flashtube to flash at a predetermined rate.

Furthermore, the synchronization signal can be implemented as a reference or reset signal from which the alarm units derive a reference time to begin activation of the alarm units. Thus, when an alarm unit receives a reference synchronization signal, the alarm unit will use that reference synchronization signal as a reference point in time to trigger a series of flashes and/or audio tones.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:

FIG. 1

is a block diagram of a conventional prior art alarm system which provides for both visual and audio alarm signals;

FIG. 2

is a block diagram of one embodiment of an alarm system of the present invention;

FIG. 3

is a circuit diagram of one embodiment of an alarm unit employed in the present invention;

FIG. 4

illustrates the software routine of the main program of the microcontroller of the alarm unit shown in

FIG. 3

;

FIGS. 4A and 4B

illustrate the software routine of Control Program No. 1;

FIGS. 4C

,

4

D and

4

E illustrate the software routine of Control Program No. 2;

FIG. 5

is a circuit diagram of one embodiment of the interface control circuit of the present invention;

FIG. 6

illustrates the software routine of the microcontroller of the interface control circuit shown in

FIG. 5

; and

FIGS. 7A and 7B

are diagrams showing the relationship between the system sync signal and the audio alarm signal of one embodiment of the present invention;

FIG. 8

is a circuit diagram of another embodiment of an alarm unit employed in the present invention;

FIG. 9

illustrates a flowchart of a method for synchronizing a plurality of alarm units while reducing the number of synchronization pulses that are transmitted to the alarm units;

FIG. 10

illustrates a flowchart of an alternate embodiment of a software routine of the main program of the microcontroller of the alarm unit as shown in FIG.

3

and

FIG. 8

;

FIG. 11

,

FIG. 11A

, and

FIG. 11B

illustrates a flowchart of Control Program No. 1 of FIG.

10

.

FIG. 12

,

FIG. 12A

, and

FIG. 12B

, and

FIG. 12C

illustrates a flowchart of Control Program No. 2 of FIG.

10

.

FIG. 13

,

FIG. 13A

, and

FIG. 13B

illustrates a flowchart of an alternate embodiment of a software routine of the microcontroller of the interface control circuit as shown in

FIG. 5

;

FIG. 14

illustrates a flowchart of Control Program No. 3 of

FIG. 10

;

FIG. 15

is a diagram showing the relationship between the system sync signal and the audio alarm signal of one embodiment of the present invention; and

FIG. 16

is a circuit diagram of another embodiment of an alarm unit employed in the present invention.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.

DETAILED DESCRIPTION

In the conventional prior art alarm system shown in

FIG. 1

, which provides for both visual and audio alarm signals, multiple alarm units

4

,

8

and

12

, numbered

1

through N, are connected by two common loops

16

,

18

having the usual end of the line resistors

20

,

22

, respectively. The alarm units have both audio and visual signaling capabilities. The first control loop

16

handles visual control signals being output from the fire alarm control panel

24

to the alarm units, and the second control loop

18

handles audio control signals being output from the fire alarm control panel

24

to the alarm units.

FIG. 2

is a block diagram of an embodiment of the alarm system of the present invention. By contrast to

FIG. 1

, multiple alarm circuits

5

,

9

and

11

, numbered

1

to N, are connected in a single control loop

40

with the usual end of the line resistor

42

. In accordance with the invention, all units are caused to flash and sound synchronously using an interface control circuit

44

and the single control loop

40

. The interface control circuit

44

is connected to the fire alarm control panel

25

via a primary input loop

46

and a secondary input loop

48

. The alarm control panel

25

and the interface control circuit

44

can either be two separate devices or built into one unit.

The interface control circuit

44

provides the capability of silencing the audio alarms by outputting a signal to the alarm circuits

1

through N on the common loop

40

when a “silence” control signal is received from the fire alarm control panel

25

via the secondary input loop

48

. According to the present invention, a single power interruption or “drop out”, of approximately 10 to 30 msec in duration, is used as the synchronization, or “sync” pulse to keep the alarm units in sync with one another. A “silence” control signal is communicated to each of the alarm circuits by a second “drop out” in very close proximity to the sync pulse. As will be discussed in greater detail hereinbelow, it is possible to use the “drop outs” to signal any one of a number of functions to the alarm units, “silence” being just one.

Alternatively, the “sync” pulse can be implemented as a reference or reset signal (e.g., a pulse) from which the alarm units derive a reference time to begin activation of the alarm units. Namely, when an alarm unit receives a reference sync pulse, the alarm unit will use that reference sync pulse as a reference point in time to trigger a series of flashes and/or audio tones. Thus, the reference pulse does not directly activate the alarm unit, but only serves as a reference time signal for the alarm unit, as discussed in detail below.

There are an infinite number of possible audio sounds and signaling schemes which may be employed in an alarm system. Actual or simulated bells, horns, chimes and slow whoops, as well as prerecorded voice messages, can all be used as audio alarm signals. One audio signaling scheme gaining popularity is the evacuation signal found in NFPA 72 from the National Fire Protection Association. The signal is also known as Code 3. A Code 3 signal consists of three half-second horn blasts separated by half-second intervals of silence followed by one and one-half seconds of silence. Some alarm systems currently in use are equipped with Code 3 capability. For such systems, the present invention may be implemented using the secondary input loop

48

to transmit a Code 3 signal from the existing fire alarm control panel

25

to the interface control circuit

44

which will, in turn, send out a Code 3 signal to the alarm units. If the fire alarm system is one which is not equipped with Code 3 capability, the interface control circuit

44

can provide the signal itself. For purposes of illustration, but not limitation, the Code 3 signal will be discussed hereinbelow as the signaling scheme of the present invention.

Turning now to the visual alarm, for purposes of illustration, the strobe flashrate discussed herein is approximately 1.02 Hz under normal conditions. As will be explained in detail later, at an input voltage below the product specifications, the flashrate may be lowered to 0.5 Hz. Underwriters Laboratories permits a flashrate as low as 0.33 Hz.

FIG. 3

is a circuit diagram of one embodiment of each of the alarm units

5

,

9

and

11

. The unit depicted is a microprocessor-controlled audio/visual alarm unit which serves to demonstrate the full range of features available in the present invention. One skilled in the art will appreciate that an alarm unit with only visual or only audio capabilities may also be integrated into the system where desired. Each unit is energized from a D.C. power source embodied in the control panel

25

. Metal Oxide Varistor RV

1

is connected across the D.C. input to protect against transients on the input. A voltage regulator circuit provides the necessary voltage level to power the microcontroller U

1

. Resistors R

6

and R

17

are connected in series between the cathode of diode D

3

and the base electrode of transistor Q

2

, and also to the cathode of Zener diode D

6

which provides 5.00 volts ±5% volts to the microcontroller U

1

across terminals V

dd

and V

ss

. A capacitor C

3

connected across the V

dd

and V

ss

terminals of U

1

acts as a filter and will hold the voltage across U

1

during the power drop outs which are used in the system as control signals.

A reset circuit for the microcontroller U

1

includes a diode D

1

and a capacitor C

6

connected in series with the emitter electrode of transistor Q

2

and in parallel with a resistor R

18

, and a resistor R

1

connected in parallel with diode D

1

. The junction between diode D

1

and capacitor C

6

is connected to the “MCLR” terminal

4

of microcontroller U

1

. Oscillations at a frequency of 4 MHz are applied to terminals OSC

1

and OSC

2

of the microcontroller by a clock circuit consisting of a resonator Y

1

and a pair of capacitors C

1

and C

2

connected between the negative side of the voltage source and the first and second oscillator inputs, respectively.

Resistors R

7

and R

15

and capacitor C

8

provide a means at microcontroller input terminal

12

for detecting gaps or drop outs in input power which indicate the presence of either a full wave rectified (FWR) input voltage or a sync or control pulse from the interface module

44

.

In the alarm circuit of

FIG. 3

, the flash circuit portion utilizes an opto-oscillator for D.C.-to-D.C. conversion of the input voltage to a voltage sufficient to fire the flashtube. In the opto-oscillator, a capacitor C

4

connected in parallel with the flashtube DS

1

is incrementally charged, through a diode D

2

and a resistor R

5

, from an inductor L

2

, which is cyclically connected and disconnected across the D.C. supply. At the beginning of a connect/disconnect cycle, the light emitting diode (LED) and transistor of an optocoupler U

2

are both off and switch Q

4

is on, completing a connection between inductor L

2

and the D.C. power source. As the current flow through L

2

increases with time, the LED of U

2

energizes and turns on the optically coupled transistor of U

2

which in turn shuts off switch Q

4

, thereby disconnecting L

2

from the D.C. source. During the off period of switch Q

4

, energy stored in inductor L

2

is transferred through diode D

2

and resistor R

5

to capacitor C

4

. Capacitor C

7

and resistor R

13

are connected in series between diode D

2

and the base of the transistor of optocoupler U

2

. When inductor L

2

has discharged its stored energy into capacitor C

4

, the LED of U

2

ceases to emit light and the transistor of U

2

turns off. This in turn causes Q

4

to turn on, thereby beginning the connect/disconnect cycle again.

The on and off switching of Q

4

, and, therefore, the rate at which the increments of energy are transferred from inductor L

1

to capacitor C

1

, is determined by the switching characteristics of optocoupler U

2

, the values of resistors R

10

, R

11

, R

12

, the value of inductor L

2

and the voltage of the D.C. source, and may be designed to cycle at a frequency in the range from about 3000 Hz to 30,000 Hz. The repetitive opening and closing of switch Q

4

eventually charges capacitor C

4

to the point at which the voltage across it attains a threshold value required to fire the flashtube DS

1

. Overcharging of capacitor C

4

is prevented by a resistor R

14

and Zener diodes D

4

and D

7

connected in series between the base electrode of the optocoupler transistor and the positive electrode of storage capacitor C

4

. The values of these components are chosen so that when the voltage across capacitor C

4

attains the firing threshold voltage of the flashtube DS

1

, a positive potential is applied to the base electrode of the optocoupler transistor and turns on the transistor which, in turn, turns off switch Q

4

and disconnects inductor L

2

from across the D.C. source.

In addition to the opto-oscillator, the flash circuit includes a circuit for triggering flashtube DS

1

. The trigger circuit includes a resistor R

4

connected in series to the combination of a switch Q

3

, which in this embodiment is an SCR, connected in parallel with the series combination of a capacitor C

5

and the primary winding of an autotransformer T

1

. The secondary winding of the autotransformer T

1

is connected to the trigger band of the flashtube DS

1

. When switch Q

3

is turned on, capacitor C

4

discharges through the primary winding of transformer T

1

and induces a high voltage in the secondary winding which, if the voltage on capacitor C

4

equals the threshold firing of the tube, causes the flashtube DS

1

to conduct and quickly discharge capacitor C

4

. Q

3

is turned on from microcontroller output pin

1

and through a voltage divider composed of resistors R

8

and R

9

.

The alarm unit depicted in

FIG. 3

also includes an audio alarm circuit, comprised of resistor R

2

, transistor switch Q

1

, diode D

14

, inductor L

1

and piezoelectric element

50

connected as shown. In the alarm unit shown, both the audio and visual alarm signals are controlled by the microcontroller U

1

, the audio signal being operated via output terminal

17

and the visual signal being triggered via output terminal

1

. However, one skilled in the art will appreciate that a timer circuit means, such as disclosed in the commonly-owned U.S. patent application Ser. No. 08/133,519 (U.S. Pat. No. 5,400,009, issued on Mar. 21, 1995), which is hereby incorporated by reference, can be employed to cause the strobe to flash independently of the microcontroller in the event of a malfunction which causes a failure of the microcontroller U

3

in control unit

44

to send a sync signal.

By way of example, the circuit shown in

FIG. 3

, when using a 24 volt D.C. power source, may use the following parameters to obtain the above-described switching cycle:

ELEMENT

VALUE OR NUMBER

C1, C2

CAP., 33 pF,

C3

CAP., 68 μF, 6 V

C4

CAP., 68 μF, 250 V

C5

CAP., 047 μF, 400 V

C6

CAP., .47 μF

C7

CAP., 33pF, 250 V

C8

CAP., .01 μF

D1

DIODE 1N914

D2, D14

DIODE HER106

D3

DIODE 1N4007

D4, D7

DIODE 1N5273B

D5

DIODE 1N4007

D6

DIODE 1N4626

DS1

FLASHTUBE

L1

INDUCTOR, 47 mH

L2

INDUCTOR, 2.2 mH

Q1

TRANSISTOR, ZTX455

Q2

TRANSISTOR, 2N5550

Q3

SCR, EC103D

Q4

TRANSISTOR, IRF710

R1

RES., 39K

R2

RES., 560

R4

RES., 220K

R5

RES., 180, {fraction ({fraction (1/2)})} W

R6

RES., 4.7K

R7

RES., 10K, 1%

R8

RES., 1K

R9

RES., 10K, 1%

R10

RES., 1K

R11

RES., 1M

R12

RES., 5.36 OHMS, 1%

R13

RES., 100K

R14

RES., 33K

R15

RES., 2.21K, 1%

R16

RES., 10K

R17

RES., 330, {fraction ({fraction (1/2)})} W

R18

RES., 10K

T1

TRIGGER TRANSFORMER

U1

MICROCONTROLLER, PIC16C54

U2

OPTOCOUPLER, 4N35

Y1

CERAMIC RES., 4 MHZ

As mentioned above, the microcontroller U

1

of the alarm unit is responsible for activating and deactivating the audio horn alarm in a desired sequence, detecting FWR or D.C. voltage and adapting the visual strobe alarm to a low input voltage by lowering the flashrate. The flowcharts of FIGS.

4

and

4

A-

4

E illustrate the software routines of the microcontroller of the alarm unit shown in FIG.

3

.

FIG. 8

is a circuit diagram of another embodiment of each of the alarm units

5

,

9

and

11

. In brief, the alarm unit of

FIG. 8

includes an inrush-limiting circuit. Inrush is a condition that may occur upon initial power-on, where a higher than average current is present in the alarm unit when power is applied to the power terminals for the first time to start alarm notification. Inrush can cause a momentary overload in the power supply and may cause the overcurrent protection in the panel to activate which can prevent the alarm units from operating. The overload may also damage relay contacts located in the panel which switch the loop to an alarm condition. Thus,

FIG. 8

illustrates one embodiment of an alarm unit that contains an in-rush limiting circuit. The alarm unit of

FIG. 8

is described in U.S. Pat. No. 5,673,030, issued on Sep. 30, 1997, which is hereby incorporated by reference.

Returning to

FIG. 8

, the unit depicted is a microprocessor-controlled audible/visual alarm unit which serves to demonstrate the full range of features available in the present invention. One skilled in the art will appreciate that the invention is also applicable to an alarm unit having only visual, i.e. strobe, capabilities or only audible, i.e., horn capabilities. The unit is energized by a D.C. power source connected to power terminals

2

(Vin) and

4

(GND). A metal oxide Varistor RV

1

is connected across the D.C. input to protect against transients on the input. A voltage regulator circuit provides the necessary voltage level to power the microcontroller U

1

. Resistors R

1

and R

17

are connected in series between the cathode of a diode D

1

and the base electrode of a transistor Q

2

, and also to the cathode of a Zener diode Z

1

which provides a 5.60 volts +5% reference. The collector of Q

2

is connected to the common node of R

1

and R

17

. Transistor Q

2

provides 5 volts to microcontroller U

1

across terminals V

dd

and V

ss

. A capacitor C

3

connected across the V

dd

and V

ss

terminals of U

1

acts as a filter and will hold the voltage across U

1

during the power drop outs which are used in the system as control signals.

A reset circuit for the microcontroller U

1

includes a resistor R

24

and a Zener diode Z

2

connected in series between the terminals V

dd

and V

ss

of microcontroller U

1

, a switch Q

5

with its emitter electrode connected to the V

dd

terminal, a resistor R

25

connected between the collector electrode of the switch Q

5

and GND, and a resistor R

23

connected between the base electrode of the switch Q

5

and the anode of the diode Z

2

. The junction between the switch Q

5

and the resistor R

25

is connected to the “MCLR” terminal

4

of the microcontroller U

1

.

Oscillations at a frequency of 4 MHz are applied to the terminals OSC

1

and OSC

2

of the microcontroller by a clock circuit consisting of a resonator Y

1

and a pair of capacitors C

1

and C

2

connected between GND and the first and second oscillator inputs, respectively.

Resistors R

19

and R

20

and a capacitor C

8

provide a means at a microcontroller input terminal

9

for detecting gaps or drop outs in input power which indicate the presence of either a full wave rectified (FWR) input voltage or a sync or control pulse.

In the alarm circuit of

FIG. 8

, the flash circuit portion utilizes an opto-coupler U

2

to control the D.C.-to-D.C. conversion of the input voltage to a voltage sufficient to fire the flashtube. In the opto-oscillator circuit, capacitor C

4

connected in parallel with the flashtube DS

1

is incrementally charged, through a diode D

5

and a resistor R

5

, from an inductor L

1

, which is cyclically connected and disconnected across the D.C. supply. At the beginning of a connect/disconnect cycle, the light emitting diode (LED) and transistor of the optocoupler U

2

are both off and the switch Q

4

is on, completing a connection between the inductor L

1

and the D.C. power source. As the current flow through L

1

increases with time, the LED of U

2

energizes and turns on the optically coupled transistor of U

2

which, in turn, shuts off the switch Q

4

, thereby disconnecting L

1

from the D.C. source. During the off period of the switch Q

4

, energy stored in the inductor L

1

is transferred through a diode D

5

and a resistor R

5

to the series-connected capacitor C

4

. The capacitor C

7

and the resistor R

13

are connected in series between the diode D

5

and the base of the transistor of the optocoupler U

2

. When the inductor L

1

has discharged its stored energy into the capacitor C

4

, the LED of U

2

ceases to emit light and the transistor of U

2

turns off. This, in turn, causes Q

4

to turn on, thereby beginning the connect/disconnect cycle again.

The on and off switching of Q

4

and, therefore, the rate at which the increments of energy are transferred from the inductor L

1

to the capacitor C

4

, is determined by the switching characteristics of the optocoupler U

2

, the values of the resistors R

10

, R

1

and R

12

, the value of the inductor L

1

and the voltage of the D.C. source, and may be designed to cycle at a frequency in the range from about 3000 Hz to 30,000 Hz. The repetitive opening and closing of the switch Q

4

eventually charges the capacitor C

4

to the point at which the voltage across it attains a threshold value required to fire the flashtube DS

1

. Overcharging of capacitor C

4

is prevented by resistors R

14

and R

3

connected in series between the GND terminal

4

and the positive electrode of the capacitor C

4

. The values of these resistors are chosen to feed a portion of the voltage across the capacitor C

4

back to the microcontroller U

1

. By checking for a relative high or low level after a trigger signal, the microcontroller U

1

can determine if the flashtube DS

1

fired. If the flashtube DS

1

did not fire, the opto-oscillator circuit is shut down by way of opto-coupler U

2

to prevent overcharging of the capacitor C

4

. This regulation of the capacitor's C

4

voltage occurs in all modes of operation including D.C., FWR, Sync and non-Sync. The microcontroller implementation is less costly than a Zener diode implementation and provides greater performance by eliminating Zener tolerance issues.

In addition to the opto-oscillator circuit, the flash circuit includes a circuit for triggering the flashtube DS

1

. The trigger circuit includes a resistor R

4

connected in series to the combination of a switch Q

3

, which in this embodiment is an SCR (or a TRIAC), connected in parallel with the series combination of a capacitor C

5

and the primary winding of an autotransformer T

1

. The secondary winding of the autotransformer T

1

is connected to the trigger band of the flashtube DS

1

. When the switch Q

3

is turned on, the capacitor C

5

pulses the primary winding of the transformer T

1

and induces a high voltage in the secondary winding which, if the voltage on the capacitor C

4

equals the threshold firing voltage of the flashtube, causes the flashtube DSi to conduct and quickly discharge the capacitor C

4

. Q

3

is turned on from a microcontroller output pin

1

and through a voltage divider composed of the resistors R

8

and R

9

.

Optimally, the alarm unit depicted in

FIG. 8

may also include an audio alarm circuit comprised, for example, of a resistor R

2

, a switch Q

1

, a diode D

4

, an autotransformer T

2

and a piezoelectric element

50

connected as shown. The autotransformer T

2

provides a voltage boost to the piezoelectric element

50

so that the audible alarm has more volume. The jumper selector JP

1

is connected to the cathode of a diode D

2

, the autotransformer T

2

and the resistors R

21

and R

22

to provide a means for adjusting the alarm volume. A “HIGH” volume setting connects T

2

directly to D

2

. A “MEDIUM” volume setting connects T

2

to D

2

with the parallel combination of R

21

and R

22

. Finally, the “LOW” volume setting connects D

2

to T

2

with R

21

. In the alarm unit shown, both the audible and visual alarm signals are controlled by the microcontroller U

1

, the audible signal being operated via an output terminal

17

and the visual signal being triggered via the output terminal

1

. However, one skilled in the art will appreciate that a software timer means can be employed to cause the strobe to flash, e.g., in the event of a malfunction which causes a failure of the microcontroller U

1

in the control unit

44

to send a sync signal.

In contrast to prior art implementations, the resistance of R

5

may be reduced to a minimum value, e.g. 27 ohms, in the present invention. This value is sufficient to prevent the flashtube DS

1

from exhibiting an afterglow effect due to current drawn from the power source after a flash occurs, but only minimally limits inrush. By using the smaller resistance R

5

, the operation of the circuit is made more efficient. In accordance with the invention, an inrush limiting resistance, e.g. resistor R

27

, is included in the circuit along with a switch Q

6

. The resistance of R

27

is substantially larger than the resistance of R

5

, e.g. 390 ohms, so that its inrush-limiting capabilities are superior to those of the prior art. The resistor R

27

and the switch Q

6

, to which the R

27

is connected in parallel, are connected between the negative terminal of the capacitor C

4

and the GND terminal

4

. The resistor R

26

is connected between the base electrode of the switch Q

6

and the microcontroller pin

19

and serves to limit current from the pin

19

to the switch Q

6

.

In accordance with the invention, the switch Q

6

is open for a period of time after power is applied to the power terminals

2

(V

in

) and

4

(GND). The period of time should be sufficient to minimize inrush, e.g., 100 milliseconds. After this period, the switch Q

6

is turned on by the microcontroller U

1

and remains on as long as power stays on. As a result, current ceases to flow through R

27

, leaving the minimal resistance R

5

in the current path between L

1

and GND terminal

4

. In addition, at regular intervals, the software of the microcontroller U

1

will refresh this function to be certain that the switch Q

6

remains on thereafter. One skilled in the art would appreciate that the resistor R

27

could be replaced with an equivalent resistance branch or network and the microcontroller could be replaced with a simple timer providing the desired off-period of the switch Q

6

.

By way of example, the circuit shown in

FIG. 8

, when using a 24 volt D.C. power source and producing a strobe with 15/75 candela brightness, may use the following parameters to obtain the above-described switching cycle:

ELEMENT

VALUE OR NUMBER

C1, C2

CAP., 33 pF, 50 V

C3

CAP., 68 μF, 6.3 V

C4

CAP., 47 μF, 250 V

C5

CAP., .047 μF, 400 V

C7

CAP., 33 pF, 250 V

C8

CAP., 1 μF, 100V

D1, D2

DIODE 1N4004

D4, D5

DIODE HER106

L1

INDUCTOR, 5.05 mH

Q1

TRANSISTOR, ZTX455

Q2, Q6

TRANSISTOR, 2N5550

Q3

SCR, EC103D

Q4

TRANSISTOR, IRF710

Q5

TRANSISTOR, 2N2907

R1

RES., 4.7K, ¼ W

R2

RES., 560, ¼ W

R4

RES., 220K, ¼ W

R5

RES., 27K, ½ W

R8, R10,

RES., 1K, ¼ W

R26

R9, R16,

RES., 10K, ¼ W

R18, R23

R11, R14

RES., 1M, ¼ W

R12

RES., 4.75, ¼ W

R13

RES., 100K, ¼ W

R17

RES., 330, ½ W

R19

RES., 10K, ¼ W

R20

RES., 2.21K, ¼ W

R21

RES., 680, ½ W

R22

RES., 270, ½ W

R24

6.8K, ¼ W

R25

39K, ¼ W

R27

390, ½ W

RV1

VARISTOR, 68 V

T1, DS1

FLASHTUBE/TRIGGER COIL

ASS'Y

T2

TRANSFORMER

U1

MICROCONTROLLER, PIC16C54

U2

OPTOCOUPLER, 4N35

Y1

CERAMIC RES., 4 MHZ

Z1

ZENER DIODE, IN4626

Z2

ZENER DIODE, IN4620

It should be noted that several differences exist between the alarm units of FIG.

3

and FIG.

8

. First, the components R

14

, D

4

and D

7

in

FIG. 3

are replaced with two resistors R

3

and R

14

and a software function in

FIG. 8

to effect the protection against overcharging of the storage capacitor C

4

. Namely, the microcontroller upon detection of a high post trigger voltage will disable the opto-oscillator to prevent overcharging of the storage capacitor C

4

. Second, the alarm unit of

FIG. 8

provides a jumper selector JP

1

for selecting the volume of the audio horn.

The microcontroller U

1

of the alarm unit is responsible for the operation of the audible and visual capabilities of the alarm units, e.g., activating and deactivating the audio alarm in a desired sequence, detecting FWR or D.C. voltage, and adapting the visual strobe alarm to a low input voltage by lowering the flashrate. The flowcharts below illustrate the software routines or methods of the microcontroller of the alarm units shown in FIG.

3

and FIG.

8

. It should be noted that since the hardware implementations of FIG.

3

and

FIG. 8

vary slightly, relevant portions of the software routines or methods below can be omitted depending on the hardware implementations.

FIG. 4

depicts the Main Program of the alarm unit microcontroller. This portion is responsible for the horn alarm and is executed at the desired frequency for the horn, here approximately 3,500 Hz.

The program begins and is initialized at blocks

402

and

406

. At block

410

, an inquiry is made as to whether the horn is currently being muted, as will be the case if the Code 3 signal is in one of the half-second or one and one-half second silence periods or if the “SILENCE” feature has been activated. If the “MUTE” function is not activated, the microcontroller U

1

will turn on the horn at block

414

by sending out a high signal from microcontroller terminal

17

to turn on switch Q

1

. In the preferred embodiment of the present invention, the horn is programmed to have a varying frequency, here between 3,200 and 3,800 Hz, to better simulate an actual horn, and will ramp up and down between the set minimum and maximum frequencies. In this embodiment, the “HORN ON DELAY” time, at block

418

is constant and is chosen to be approximately 0.120 msec. The varying of the horn frequency is accomplished by ramping the “HORN OFF DELAY” time up and down. Following the “HORN ON DELAY”, the horn is turned off at block

422

by turning off switch Q

1

.

At block

426

, Control Program No. 1 is run. Control Program No. 1 is responsible for detection and interpretation of the voltage drop outs, which serve as sync or control pulses (hereinafter “sync/control pulses”) to the units, and is represented in flow-chart form in

FIGS. 4A and 4B

.

FIGS. 4A and 4B

will be discussed in detail hereinbelow following the discussion of FIG.

4

.

After leaving Control Program No. 1, the main program, at block

638

, will begin the “HORN OFF DELAY”. As mentioned above, the “HORN OFF DELAY” time will be varied to better simulate an actual horn sound. At block

642

, the program will check to see whether the delay is currently being ramped up or down, and, in either of block

646

or

650

, will continue the ramping in the current direction on every other Main Program cycle. At either block

654

or

658

, the program will loop back to block

410

to determine if the “MUTE” function has been activated if neither the minimum nor maximum specified horn frequency has been reached, in this example 3,200 and 3,800 Hz, respectively. If the minimum or maximum frequency has been reached, the ramp direction will be changed at block

662

or

666

, after which the program will run Control Program No. 2, depicted in

FIGS. 4C

,

4

D and

4

E.

Turning now to

FIGS. 4A and 4B

, following the start of Control Program No. 1 the software looks for an input voltage drop out as indicated at block

430

. Detection of a drop out indicates either a sync/control pulse or a FWR input voltage. Detection of the leading edge of a drop out initiates a counter “DOsize”. If the drop out is present, “DOsize” is incremented at block

431

. If no drop out is present, the counter is reset to zero at block

432

. Drop outs are detected at microcontroller input terminal

9

.

Next, at block

434

, the program checks to see if this is the beginning of a drop out by inquiring as to whether “DOsize=1.” If so, the program at block

438

increments a counter, “DOnmbr”, which keeps track of the number of dropouts. At block

442

, the program checks for the presence of a sync/control pulse using the “DOsize” counter. If the drop out is wide enough, a sync/control pulse is present.

One skilled in the art will appreciate that multiple pulses can be used as control signals for the system. According to the present invention, in any such scheme, the first pulse will indicate the beginning of a new sync cycle. By way of example, here, the presence of a second pulse immediately following the first sync pulse will activate the “SILENCE” feature throughout the system and turn off any audio alarm which may be sounding. The presence of a pulse in the first and third pulse positions will deactivate the “SILENCE” feature causing the horns to sound when activated.

The software needed to perform these functions is illustrated in the flowchart of

FIG. 4A

following block

442

. If a sync/control pulse is detected, the program at block

446

determines whether it is a sync pulse by checking the how much time has elapsed since the last pulse. If “SYtimer” indicates that it has been more than 0.5 seconds, then the pulse is the first of the cycle. If less than 0.1 seconds has elapsed, then the pulse is determined at block

450

to be in the second position and the “SILENCE” and “MUTE” features are activated at block

454

. In this example, since only three pulse positions are being used, if “SYtimer” is any other value, then the pulse is determined at block

458

to be in the third position and the “SILENCE” feature is deactivated at block

462

.

If the pulse is a sync pulse, block

466

sets several functions. “MODE” is set to “sync”, “CODE 3” is turned on, “MUTE” is turned on, “SYtimer” is reset to zero, “FLASH” is turned on, and the horn frequency is returned to its starting position.

At block

470

, the program checks to see if the “SKIP” function is off. The “SKIP” function and “SKflash” variable are used to cut the flashrate in half when the input voltage falls below an acceptable level, in this example 20 V. When the “SKIP” function is activated, the variable “SKflash” will toggle between on and off once each flash cycle causing every other flash to be skipped. This is seen in the flowchart at block

474

where if “SKIP” is not off, the program checks to see whether “SKflash” is on, which it will be every other cycle. On the other hand, if “SKIP” is off at block

470

, the program jumps to block

478

and flashes the strobe by delaying 20 msec, turning on SCR Q

3

and delaying another 5 msec. If “SKflash” is on at block

474

, block

478

will be skipped and the strobe will not be flashed.

The next section of the program, beginning at block

482

in

FIG. 4B

, checks to see whether the capacitor C

4

is being charged high enough to sufficiently flash the flashtube DS

1

. At block

482

, a variable “AFcount” is incremented. “AFcount” is used to count the number of cycles of Control Program No. 1 which corresponds to the audio frequency of the audio alarm signal.

At block

484

, inquiry is made as to the status of a control variable “SoscSD”, which is indicative of the “oscillator shut down” function. “SoscSD” being on indicates that the opto-oscillator is shut down. If “SoscSD” is off, the program continues with box

486

which sets a lookup table pointer based on “AFcount”, i.e., based upon how many audio signal cycles have elapsed. The lookup table value, “LTvalue”, is a predetermined minimum desirable number of cycle counts for the opto-oscillator and is used to determine whether capacitor C

4

, which provides the energy to flash flashtube DS

1

, is charging too quickly. First, however, at block

488

, the program determines whether Vin is FWR or D.C. Depending on which one it is, the program will determine “LTvalue” using either a FWR lookup table at block

490

or a D.C. lookup table at block

492

.

Next, at block

494

, “LTvalue” is compared to the number of connect/disconnect cycles of the opto-oscillator responsible for charging C

4

. This is done by using the real time clock counter at microcontroller input pin RTCC and resistor R

16

to keep count of the number of times the opto-oscillator has cycled. If the count is greater than “LTvalue”, then the oscillator is turned off at block

496

by turning on “SoscSD” and turning off “Sosc”.

At block

502

, a variable “Vcount” is incremented. “Vcount” is used to determine whether the alarm unit is receiving a proper input voltage. Its significance will be discussed in greater detail shortly hereinbelow.

Returning briefly to block

484

, if “SoscSD” is not off, that is, if the “oscillator shut down” function is on, then the program jumps to block

504

and will not increment “Vcount”. As will be seen hereinbelow, once “SoscSD” is turned on, it will not be turned off again until Control Program No. 2 is executed. As discussed above with respect to the Alarm Unit Main Program, Control Program No. 2 is executed only at the top and bottom of the horn sweep cycles. The number of times this occurs can be controlled by the size of the step of the horn frequency increase or decrease. In the example under discussion, this will happen 120 times each second, one second being the approximate period between flashes. Therefore, the highest value which Vcount can attain between flashes is 120. This is also true when the “SKIP” function is activated and the flash period becomes two seconds, i.e., Control Program No. 2 is executed 240 times between flashes, since blocks

498

and

500

allow “Vcount” to be incremented only if either the “SKIP” function is off or both the “SKIP” function is on and the horn frequency is sweeping up.

Returning to block

494

, if RTCC has not exceeded “LTvalue”, the program jumps to block

504

and “Vcount” will not be incremented. At block

504

, the program checks to see if the “oscillator shut down” function is on. If not, the oscillator is turned on at block

506

and the control program is exited. If “SoscSD” is on, the control program is exited without turning on “Sosc”.

Now, turning to

FIGS. 4C

,

4

D and

4

E, which represents the flowchart for Control Program No. 2, the program checks at block

530

to see if the “FLASH” function has been activated. If not, at block

578

, SCR Q

3

of the alarm unit is turned off via pin

1

of the microcontroller and the next several program functions relating to determination of the input voltage are passed over.

If the “FLASH” function is on, the program, at blocks

538

,

542

and

546

, checks to see whether the number of drop outs, represented by the variable “DOnmbr”, indicates that a FWR input voltage is being used, and the variable “Vin” is set to the appropriate input voltage type, either FWR or D.C.

The next function carried out by the microcontroller software relates to the feature discussed briefly above whereby the alarm unit will compensate for a below-nominal input voltage by lowering the flash frequency. More particularly, when the input voltage is determined to be below 20 volts, the flash frequency will be cut in half to approximately 0.5 Hz, or one flash every two seconds. Determination of the input voltage is accomplished using the variable “Vcount” which, as previously discussed, under certain circumstances is incremented in Control Program No. 1 when the opto-oscillator has not been shut down and the real time clock counter as represented by variable “RTCC” has exceeded “LTvalue”.

Before performing this function, however, the program at block

548

checks to see if “SKflash” is off. If not, then the voltage check is passed over and the program proceeds to block

562

. If, on the other hand, the current flash is not being skipped, then at block

550

“Vcount” is compared to a predetermined constant, “Vref”.

As discussed above, “Vcount” will never be incremented higher than 120 within the time period between flashes, and, if the input voltage is over 20 volts, “Vcount” should be incremented all the way to 120 during each flash cycle. If the input voltage is below 20 volts, “Vcount” should be zero. In the embodiment under discussion, the value of “Vref” is chosen to be 30 which will smooth the switch between flashrates.

If, at block

550

, “Vcount” exceeds “Vref”, the input voltage is determined to be at least 20 V and the “SKIP” function is deactivated at block

554

. If “Vcount” is less than “Vref”, the input voltage is determined to be less than 20 V and the “SKIP” function is turned on at block

558

. After the comparison, “Vcount” is reset to zero and the “FLASH” function is turned off at block

562

.

Next, at block

566

, the program determines whether the “SKIP” function is on. If so, “SKflash” is toggled at block

570

. If not, “SKflash” is turned off at block

574

. At block

578

(All FIG.

4

D), the program again checks whether the “SKIP” function is on. If not, the program resets “RTCC” and “AFcount” to zero and turns off “SoscSD” at block

586

. If “SKIP” is on, then block

582

ensures that block

586

will be executed only if the horn frequency is currently being swept upward.

The software continues at block

588

which determines whether the “SILENCE” function is off and the “CODE 3” function is on. If not, the program skips the next function, which is maintenance of the Code 3 horn signal, and goes directly to block

618

. If the conditions are met at block

588

, the time since the last sync pulse, represented as “SYtimer”, is checked at block

592

. If it is equal to 0.5 seconds, then the variable “C

3

count”, which keeps track of the sync pulses in each Code 3 signal cycle, is decremented at block

596

.

The relationship among “C

3

count”, the sync pulses and the audio Code 3 horn signal is shown in

FIGS. 7A and 7B

. Each sync pulse triggers one-half second of silence followed by a one-half second horn blast, except when “C

3

count”=1. During that sync cycle, the horn blast is muted.

After decreasing “C

3

count”, the program checks at block

600

to see if “C

3

count” is zero. If not, block

604

, which sets “C

3

count” to 4, is skipped. Next, block

608

checks to see if “C

3

count” is greater than 1. If so, the “MUTE” function is turned off at block

612

. If not, block

612

is skipped and the program moves to the next task.

At block

618

(All FIG.

4

E), the program checks which mode the system is currently in, auto or sync. If it is in sync mode, “SYtimer” is increased at block

622

. Block

626

compares “SYtimer” to the predetermined maximum time, “SYlimit”, at which the system should be allowed to continue in the sync mode. If “SYtimer” is not less than “SYlimit”, then there is a problem with the sync pulses and the mode is switched to auto at block

630

. If not, the mode is left at sync and Control Program No. 2 is exited at block

634

.

If the system is in auto mode, that is, the alarm units are operating independently of one another, “FRtimer”, a variable which keeps track of the time since the last flash when in the auto mode, is decremented at block

638

and “C

3

count” is set to its initial value, “C

3

ini”. At block

642

, if “FRtimer” is not down to zero, Control Program No. 2 is exited. If “FRtimer” is zero, it is set to its initial value, “FRini”, at block

646

, and the “FLASH” function is turned on. Then, block

650

checks to see if the “SKIP” function is off. If not, block

654

checks to see if “Skflash” is on. If “SKflash” is on then control program No. 2 is exited. If not, the program flashes the strobe at block

658

by turning on SCR Q

3

. Returning to block

650

, if the “SKIP” function is off, the program jumps to block

658

which flashes the strobe and exits.

Turning now to the interface control circuit

44

of the invention, the preferred embodiment is shown in

FIG. 5

connected across a D.C. voltage source which supplies a voltage Vin. The input voltage enters the interface via the primary loop

46

and normally passes through single pole single throw relay K

1

and out of the interface to the system control loop

40

. The D.C. voltage source is typically housed in the fire alarm control panel

25

and V

in

is nominally 24 volts. As discussed above, this voltage may have a wide range of values and the present invention can compensate for unexpected drops in voltage below what is necessary to operate the system at the flash rate of 1.02 Hz noted above.

The supply voltage V

in

is also applied through a diode D

8

, which typically has a voltage drop of 0.7 volts, to a regulator circuit which includes resistors R

23

and R

24

, a transistor Q

5

and Zener diode D

11

connected as shown, with values chosen so as to provide a regulated 5.00 volts ±5% volts to the V

dd

input of microcontroller U

3

. Resistor R

23

is between the cathode of diode D

8

at one end and both the resistor R

24

and the collector of transistor Q

5

at the other end. The other end of R

24

is connected to the base of transistor Q

5

. A capacitor C

12

connected across the V

dd

and V

ss

terminals of U

3

acts as a filter.

Resistors R

26

and R

27

, capacitor C

11

and diode D

10

comprise a reset circuit for microcontroller U

3

. Resistor R

27

is connected at one end to the emitter of transistor Q

5

, the cathode of diode D

10

and resistor R

26

, and at the other end to the “MCLR” terminal

4

of microcontroller U

3

, the positive terminal of capacitor C

11

and the anode of diode D

10

. The other end of resistor R

26

is connected to the negative terminal of capacitor C

11

. Resistor R

28

is connected between the emitter of transistor Q

5

at one end and terminal

6

of microcontroller U

3

and optocoupler U

4

at the other end, to provide a control input to microcontroller U

3

for any one or more desired functions.

Oscillations at a frequency of 4 MHz are applied to terminals OSC

1

and OSC

2

of the microcontroller by a clock circuit consisting of a resonator Y

2

and a pair of capacitors C

9

and C

10

connected between the first and second oscillator inputs, respectively.

In the preferred embodiment, the secondary loop

48

is used as an input for control signals. In the example under discussion, the control signals relate to the “SILENCE” feature which turns off the audio alarm in each of the alarm units while allowing the visual alarm to continue. The secondary loop

48

may also be used to provide an audio alarm control signal from the fire alarm control panel to the multiple alarm units. The latter function is implemented where the fire alarm system is already equipped with the capability to provide a desired alarm sequence, Code 3 in the preferred embodiment, and provides the necessary control signals to the system. In the case where the system does not have Code 3 capabilities, the interface unit can be programmed to provide the Code 3 control signals to the alarm units as will be described hereinbelow.

The secondary input loop

48

of the interface control circuit is connected across a D.C. source. An input from the control panel will be in the form of a power interrupt, or “drop out”, which is detected by the microcontroller U

3

at pin

6

. Normally, voltage is applied at the secondary loop across the series connection of diode D

13

, resistor R

29

and optocoupler U

4

. The LED of U

4

turns on the transistor of U

4

thereby causing current to flow through R

28

and a low voltage at pin

6

of microcontroller U

3

. Interruption of the D.C. source will turn off the transistor of U

4

and pull pin

6

of U

3

to V

dd

or 5 V.

The direct connection from the primary loop input

46

to the control loop output

40

may be interrupted by activating the relay K

1

which is accomplished by turning on switch Q

6

. Switch Q

6

is turned on by an output of microcontroller U

3

which is applied to the gate of switch Q

6

via a voltage divider including a resistor R

21

connected from output pin

1

of microcontroller U

3

to the gate, and a resistor R

22

connected from the gate electrode to the negative side of the power source.

When Q

6

is closed, the potential at the output emitter of switch Q

7

, which preferably comprises a Darlington pair, is pulled to that of the negative side of the power source, causing Q

7

to conduct. The voltage applied to the base electrode of one transistor of the Darlington pair Q

7

is regulated by a resistor R

25

and a Zener diode D

9

in a series connection between the cathode of diode D

12

and the end of the coil of relay K

1

that is connected to switch Q

6

. When Q

7

conducts, current flows through the coil of relay K

1

and switches the relay from its normal position to the other contact. Actuation of the relay causes an interruption of the D.C. voltage normally supplied to the controlled alarm units.

The power drop outs can be used for any one of a number of control functions, “silence” being the example provided. Under the scheme discussed above, commands based on the position of sync/control pulses are sent to each alarm unit simultaneously. A more flexible alternative to pulse position coding is pulse train binary coding. One skilled in the art will appreciate that with a pulse train of, for example, eight pulse positions, several positions in the train can be assigned to the task of addressing commands to individual alarm units. One can envision circumstances where this would be advantageous, such as where one seeks to deactivate alarms on a particular floor while allowing the alarms to continue on others.

The interface control circuit

44

is capable of operating in three different modes. Which one of the three modes it will operate in depends on the capabilities of the existing system. The interface control circuit will operate in mode 1 in a system which is not equipped with Code 3 or silence capabilities. For mode 1 operation, the interface control circuit is installed with the primary loop, and the Code 3 signaling is performed by the interface control circuit as described earlier, not the fire alarm control panel. In mode 1, a silence feature is not available.

Mode 2 is used where the existing system has a silence feature, but not a Code 3 capability. In that case, the interface control circuit is installed with both a primary and secondary input loop, the secondary input loop being available for a silence signal from the control panel. As in mode 1, Code 3 is performed by the interface control circuit.

Finally, mode 3 is available for systems which already have Code 3 and silence function capabilities. Here, the interface control circuit is installed with both a primary and secondary input loop. The Code 3 control signal originates in the control panel as does the silence control signal.

By way of example, the interface control circuit under discussion and shown in

FIG. 5

, when energized from a 24 volt D.C. power source, may use the following parameters:

ELEMENT

VALUE OR NUMBER

C9, C10

CAP., 33 pF

C11

CAP., .47 μF

C12

CAP., 15 μF , 16 V

D8

DIODE, 1N4007

D9

DIODE, 1N5236, 7.5 V

D10

DIODE, 1N914

D11

DIODE, 1N4626

D12

DIODE, 1N4007

D13

DIODE, 1N4007

K1

RELAY, SPST

Q5

TRANSISTOR, 2N5550

Q6

TRANSISTOR, 1RF710

Q7

TRANSISTORS, T1P122

R21

RES., 220

R22

RES., 100K

R23

RES., 330

R24

RES., 4.7K

R25

RES., 4.7K, ½ W

R26

RES., 10K

R27

RES., 39K

R28

RES., 10K

R29

RES., 2.7K, ½ W

U3

MICROCONTROLLER; PIC16C54

U4

OPTOCOUPLER, 4N35

Y2

CERAMIC RES., 4 MHZ

The microcontroller U

3

of the interface control circuit of

FIG. 5

is responsible for closing switch Q

6

and thus transmitting power drop outs which will be interpreted by the alarm units as described earlier.

FIG. 6

illustrates the software routine of the microcontroller U

3

. At blocks

702

and

706

, the program begins and is initialized. At block

710

, mode 1 is assumed and the sync period limit is set to 0.98 seconds. Block

714

is an inquiry as to whether the secondary loop is present in the alarm system. If so, at block

718

, the mode is set to mode 2. At blocks

722

and

726

, a drop out of 30 msec duration which acts as the sync pulse is sent on the output control loop. Where the system is operating in either mode 2 or 3, the program inquires at block

730

as to whether there has been an interrupt in power of more than one second to the secondary loop, which would indicate a silence signal from the control panel. If so, at block

734

a second “drop out” is sent to the alarm units almost immediately. Although not shown in

FIG. 6

, one skilled in the art will appreciate that the silence feature can be similarly deactivated by another input of significant duration to the secondary loop after which a dropout in the third pulse position, for example, is sent to the interface control circuit.

Next, at block

738

, the program looks for an input indicative of Code 3 from the control panel on the secondary loop. If one is detected, block

742

sets the mode number to 3, sets the sync period limit to 1.10 seconds and sets the sync counter to the limit, 1.10 seconds. This slight increase in the sync period ensures proper Code 3 operation when Code 3 signals are originating from the control panel

25

rather than the interface control circuit

44

. If the Code 3 input is not detected, the sync counter is incremented at block

746

. Next, at block

750

, the program looks at whether the sync counter has reached the set limit. If so, the program clears the sync counter at block

754

and loops back to block

722

, thereby sending a drop out. If the limit has not been reached, the program loops back to block

738

.

FIG. 9

illustrates a flowchart of a method

900

for synchronizing a plurality of alarm units while reducing the number of synchronization pulses that are transmitted to the alarm units, thereby increasing the reliability of the overall alarm system. More specifically, the synchronization method as discussed above in

FIGS. 4A-4E

effects synchronization of all the alarm units by employing an interface control circuit to send synchronization pulses to the alarm units. Upon receipt of each synchronization pulse, the alarm units will flash in synchronization.

Although the above synchronization method is effective, the reliability of the overall alarm system can be increased if the number of transmitted synchronization pulses (transmission rate) is reduced. Namely, since the interface control circuit employs a relay that is activated for each synchronization pulse, the reliability of the interface control circuit can be increased if the duty cycle of the relay is reduced.

Returning to

FIG. 9

, method

900

starts in step

905

and proceeds to step

910

where a reference synchronization signal is sent to the alarm units from the interface control circuit. This reference synchronization signal is used by each alarm unit in step

920

to set or synchronize its local counter (or a clock). Each alarm unit will then activate itself (flash and/or sound horn) in accordance with the local counter. In other words, the reference synchronization signal does not directly cause the alarm units to activate, but instead provides an accurate time reference from which each alarm unit will generate one or more flashes, thereby reducing the total number of transmitted reference synchronization signals.

Method

900

then ends in step

935

. Method

900

is further described in detail below in

FIGS. 10-14

.

FIG. 10

illustrates a flowchart of an alternate embodiment of a software routine or method of the microcontroller of the alarm units as shown in FIG.

3

and FIG.

8

. More specifically, method

1000

starts in step

1005

and proceeds to step

1010

where initialization is performed, e.g., one or more registers and variables are initialized.

In step

1015

, method

1000

generates a delay, preferably 100 milliseconds (msec.). Namely, a delay is generated at the alarm unit during which time the switch Q

6

is off and the resistors R

5

and R

27

limit the inrush condition as shown in FIG.

8

.

In step

1020

, zero-inrush control (ZIctrl) is turned “ON”. More specifically, the switch Q

6

is turned on, thereby redirecting the current through Q

6

and around the resistor R

27

as shown in FIG.

8

.

In step

1025

, method

1000

queries whether the horn is currently being muted (represented by the variable or flag “MUTE”), as in the case if the Code 3 signal is in one of the half-second or one and one-half second silence periods, or if the “SILENCE” feature has been activated. If the query is affirmatively answered, then method

1000

proceeds to step

1035

. If the query is negatively answered, then method

1000

proceeds to step

1030

, where the microcontroller U

1

of the alarm unit will turn on the horn (turn on switch) by sending out a high signal from the microcontroller to turn on switch Q

1

as shown in

FIGS. 3 and 8

.

In step

1035

, method

1000

generates a “Horn On Delay”. Namely, as discussed above, the horn is programmed to have a varying frequency, e.g., between 3,200 and 3,800 Hz, for simulating an actual horn. Thus, the “Horn On Delay”, e.g., 120 msec., can be selectively set to control the frequency of the horn. However, in the preferred embodiment, the “Horn On Delay” is held as a constant, whereas the “Horn Off Delay” is varied as discussed below.

In step

1040

, method

1000

turns off the horn (turn off switch). More specifically, the horn is turned off by turning off switch Q

1

as shown in

FIGS. 3 and 8

.

In step

1045

, method

1000

executes Control Program No. 1. In brief, Control Program No. 1 is responsible for the detection and interpretation of the voltage drop outs, which serve as reference synchronization or control pulses or signals (hereinafter “sync/control pulses”) to the alarm units, and is described in detail below in FIG.

11

. Additionally, Control Program No. 1 is also responsible for the detection of proper charging of the capacitor C

4

that provides the charge to flash the flashtube DS

1

.

In step

1050

, method

1000

generates a variable “Horn Off Delay”. As discussed above, the “HORN OFF DELAY” time is varied to better simulate an actual horn sound. Namely, a counter value is varied.

In step

1055

, method

1000

queries whether the horn frequency is ramping up or ramping down. If the horn frequency is ramping down, method

1000

proceeds to step

1060

, where the horn frequency is decreased to the next step, e.g., three (3) micro seconds (μsec.). If the horn frequency is ramping up, method

1000

proceeds to step

1065

, where the horn frequency is increased to the next step, e.g., three (3) microseconds (μsec.).

However, since horn frequency is changed every other cycle, method

1000

incorporates two queries

1056

and

1057

, which inquire whether the horn frequency should be decreased or increased in the present cycle respectively. If the query is affirmatively answered, then method

1000

will either decrease or increase horn frequency in steps

1060

and

1065

respectively. If the query is negatively answered, then method

1000

proceeds to step

1073

where Control Program No. 3 is executed as discussed below in FIG.

14

.

In step

1070

, method

1000

queries whether the horn frequency has reached the minimum horn frequency. If the query is negatively answered, then method

1000

proceeds to step

1025

, where the loop of method

1000

is repeated. If the query is positively answered, then method

1000

proceeds to step

1080

, where the variable “Horn Off Delay” is toggled to sweep up for the next cycle. Namely, the horn frequency has been decreased to a predefined point, e.g., 3,200 Hz and will be ramped up on the next cycle.

Similarly, in step

1075

, method

1000

queries whether the horn frequency has reached the maximum horn frequency. If the query is negatively answered, then method

1000

proceeds to step

1025

, where the loop of method

1000

is repeated. If the query is positively answered, then method

1000

proceeds to step

1085

, where the variable “Horn Off Delay” is toggled to sweep down for the next cycle. Namely, the horn frequency has been increased to a predefined point, e.g., 3,800 Hz and will be ramped down on the next cycle.

In step

1090

, method

1000

executes Control Program No. 2. In brief, Control Program No. 2 is responsible for the detection of low input voltage. Namely, if the input voltage falls below a preferred level, the flash rate of the flashtube can be reduced to maintain optimal brightness.

Additionally, Control Program No. 2 is also responsible for the maintenance of various counters. First, these counters are used to detect the absence of a reference synchronization pulse. Failure to receive a reference synchronization pulse within a predefined time limit will cause the alarm unit to enter into automatic mode, where the activation of the flashtube and/or the horn are locally controlled without the need of reference synchronization pulses. Second, these counters are also used to implement the Code 3 pattern as discussed below.

FIGS. 11

,

11

A and

11

B illustrates a flowchart of Control Program No. 1 (step

1045

) of FIG.

10

. Namely,

FIGS. 11

,

11

A and

11

B illustrates a method

1100

for detecting and interpreting voltage dropouts.

More specifically, method

1100

starts in step

1105

and proceeds to step

1110

, where method

1100

queries whether a voltage drop-out is present. If the query is affirmatively answered, then method

1100

proceeds to step

1115

, where a counter “DOsize” is incremented. Namely, method

1100

is checking the input voltage which is typically set at 24 volts. Detection of the leading edge of a drop out initiates a counter “DOsize”, such that a voltage drop-out greater than five (5) msec. constitutes the presence of a voltage drop-out. If the query is negatively answered, then method

1100

proceeds to step

1107

, where the counter “DOsize” is set to zero “0”. Namely, no voltage drop-out is detected so that the counter “DOsize” is reset to zero for the next cycle.

In step

1111

, method

1100

queries whether “DOsize” is equal to one (“1”). If the query is affirmatively answered, then method

1100

proceeds to step

1120

, where a counter “DOnmbr” is incremented. Namely, the counter “DOnmbr” keeps track of the number of drop outs. If the query is negatively answered, then method

1100

proceeds to step

1125

.

In step

1125

, method

1100

queries whether a reference synchronization pulse is present. Namely, method

1100

is determining if the drop out is sufficiently wide to constitute a sync/control pulse. If the query is affirmatively answered, then method

1100

proceeds to step

1127

. If the query is negatively answered, then method

1100

proceeds to step

1160

.

In step

1127

, method

1100

queries whether the detected sync/control pulse is greater than 0.5 seconds, e.g., relative to a previously received sync/control pulse. Namely, the time of detecting the sync/control pulse is stored in the counter “Sytimer” and this stored value is compared to the threshold value of 0.5 seconds. It should be noted that the “SYtimer” can be reset for every strobe flash or for every reception of the sync/control pulse.

Namely, method

1100

is determining if the present sync/control pulse is a first or a second pulse. According to the present invention, the first pulse indicates the beginning of a new synchronization cycle or sync cycle. By way of example, the presence of a second pulse immediately following the first sync pulse activates the “SILENCE” feature throughout the alarm system and turns off any audio alarm which may be sounding. Namely, if the present sync/control pulse is a first pulse then it is a reference synchronization pulse. If the present sync/control pulse is a second pulse, then it is a control pulse for the “SILENCE” feature. Thus, if the query in step

1127

is affirmatively answered, then method

1100

determines that the present sync/control pulse is a reference synchronization pulse and proceeds to step

1130

. If the query in step

1127

is negatively answered, then method

1100

proceeds to step

1135

.

In step

1135

, method

1100

queries whether the detected sync/control pulse is between a range of 0.05 to 0.15 second relative to a previously received sync/control pulse. If the query is affirmatively answered, then method

1100

proceeds to step

1140

, where the “SILENCE” feature is turned “On”. If the query is negatively answered, then method

1100

proceeds to step

1160

.

In step

1130

, method

1100

sets several functions or variables. First, the operational mode of the alarm unit is set to “SYNC” mode, where the operation of the alarm unit will be controlled by sync/control pulses. Second, if the alarm unit has Code 3 capability, then the Code 3 pattern is activated. Third, “MUTE” is turned “ON”, i.e., upon reception of a reference synchronization pulse, a period of silence is provided, e.g., the start of a Code 3 pattern. Fourth, the counter “SYtimer” is reset to zero (0). Fifth, a flash control bit, “Flash” is set to “ON”. Sixth, the counter “C

3

count” is initialized to 5. Seventh, a silence control bit, “Silence” is set to “OFF”. Finally, the HORN SWEEP is also reset to its starting position, e.g., 3600 Hz.

In step

1137

, method

1100

queries whether the variable, “Sfault”, is set to “Yes”. Namely, “Sfault” is set to “Yes” when a strobe fault, e.g., a high post trigger voltage, is detected by the microcontroller of the alarm unit. If the query is affirmatively answered, then method

1100

proceeds to step

1147

. If the query is negatively answered, then method

1100

proceeds to step

1145

.

In step

1145

, method

1100

queries whether the function, “SKIP”, is set to “Off”. Namely, the function “SKIP” allows the alarm unit to selectively skip one cycle of flash, i.e., altering the flash rate of the alarm unit. In the present invention, skipping a flash is optionally provided when it is determined that the input voltage is below an acceptable level. Such low input voltage may affect the brightness of the flashes produced by the flashtube. As such, it is desirable to reduce the flash rate, e.g., from one flash per second to one flash per two seconds, when a low input voltage condition, e.g., below 20 V, is detected, thereby ensuring that each flash meets a minimum criterion as to brightness. If the query is affirmatively answered, then method

1100

proceeds to step

1147

. If the query is negatively answered, then method

1100

proceeds to step

1150

.

In step

1150

, method

1100

queries whether the variable or bit, “SKflash”, is set to “On”. This variable is used to record the current state as to whether a flash should be skipped. Namely, when the “SKIP” function is activated, the variable “SKflash” is toggled between “On” and “Off” once each flash cycle causing every other flash to be skipped. Thus, if the query is affirmatively answered, then method

1100

proceeds to step

1160

. If the query is negatively answered, then method

1100

proceeds to step

1147

.

In step

1147

, method

1100

sets several functions or variables. First, “Sosc” is set to “Off”, where “Sosc” is employed to control the opto-oscillator. By turning off the opto-oscillator, power is further conserved for the flash cycle. Second, “Zlctrl” is optionally set to “Off”. Third, a 20 msec. delay is generated. This 20 msec. delay when combined with approximately 5 msec. of time that is used to detect the sync/control pulse, forms the width of a sync/control pulse. At the end of the total 25 msec. of elapsed time, SCR is set to “On”, thereby turning on SCR Q

3

to trigger a flash. Finally, another delay of 5 msec is provided for the SCR to complete its function, i.e., causing the discharge of a capacitor to provide the necessary energy to generate a flash in the flashtube.

In step

1155

, method

1100

queries whether the variable, “SoscSD”, is set to “On”. The variable “SoscSD” allows the control of the opto-oscillator to be set by a variable or flag. Namely, variable “SoscSD” is indicative of the “oscillator shut down” function, where “SoscSD=On” indicates that the opto-oscillator is shut down. There are certain situations where it is desirable to turn on or off the opto-oscillator as discussed below. Thus, if the query is affirmatively answered, then method

1100

proceeds to step

1160

. Namely, the opto-oscillator is left off for the present moment. However, if the query is negatively answered, then method

1100

proceeds to step

1157

, where “Sosc” is set to “On”.

In step

1160

, method

1100

increments the variable or counter “AFcount”. “AFcount” is used to count the number of cycles of Control Program No. 1 which corresponds to the audio frequency of the audio alarm signal.

In step

1165

, method

1100

queries whether the variable, “SoscSD”, is set to “Off”. If the query is affirmatively answered, then method

1100

proceeds to step

1167

, where a pointer is set in accordance with the value in “AFcount”, i.e., based upon how many audio signal cycles have elapsed. However, if the query is negatively answered, then method

1100

proceeds to step

1193

.

In step

1170

, method

1100

queries whether the input voltage V

in

is FWR or D.C. If the input voltage is FWR, then method

1100

proceeds to step

1175

, where a lookup table value, “LTvalue” is selected from an FWR lookup table. However, if the input voltage is D.C., then method

1100

proceeds to step

1177

, where a lookup table value, “LTvalue” is selected from a D.C. lookup table. The lookup table value, “LTvalue”, is a predetermined minimum desirable number of cycle counts for the opto-oscillator and is used to determine whether the capacitor C

4

, which provides the energy to flash flashtube DS

1

, is charging too quickly.

In step

1180

, method

1100

queries whether the variable RTCC is greater than the retrieved “LTvalue”. RTCC is implemented as a real time clock counter by the microcontroller to track the number of times the opto-oscillator has cycled. Namely, “LTvalue” is compared to the number of connect/disconnect cycles of the opto-oscillator responsible for charging C

4

. If RTCC is greater than “LTvalue”, then the opto-oscillator is turned off at step

1185

by turning on “SoscSD” and turning off “Sosc”. In other words, the charging of capacitor C

4

is sufficient such that the opto-oscillator can be turned off. This allows the alarm unit to precisely control the amount of energy stored in the capacitor C

4

, thereby allowing the alarm unit to maintain a substantially uniform brightness level for each flash.

In step

1187

, method

1100

queries whether the function, “SKIP”, is set to “Off”. If the query is affirmatively answered, then method

1100

proceeds to step

1192

, where the variable “Vcount” is incremented. “Vcount” is used to determine whether the alarm unit is receiving a proper input voltage. If the query is negatively answered, then method

1100

proceeds to step

1190

.

In step

1190

, method

1100

queries whether the horn frequency is ramping up. If the query is affirmatively answered, then method

1100

proceeds to step

1192

, where the variable “Vcount” is incremented. If the query is negatively answered, then method

1100

proceeds to step

1193

.

In step

1193

, method

1100

queries whether the variable, “Sfault”, is set to “Yes”. Namely, method

1100

is determining if a strobe fault has occurred. If the query is affirmatively answered, then method

1100

proceeds to step

1194

, where the variable “SoscSD” is set to “On”. If the query is negatively answered, then method

1100

proceeds to step

1195

.

In step

1195

, method

1100

queries whether the variable, “SoscSD”, is set to “On”. If the query is affirmatively answered, then method

1100

proceeds to step

1198

, where Control Program No. 1 ends and returns to method

1000

of FIG.

10

. If the query is negatively answered, then method

1100

proceeds to step

1196

, where “Sosc” is set to “On”. It should be noted that once “SoscSD” is turned on, it will not be turned off until Control Program No. 2 is executed.

As discussed above, Control Program No. 2 is executed only at the top and bottom of the horn sweep cycles. The number of times this occurs is controlled by the size of the step of the horn frequency increase or decrease. In one embodiment, Control Program No. 2 is executed 120 times each second, one second being the approximate period between flashes. Therefore, the highest value which “Vcount” can attain between flashes is 120. This is also true when the “SKIP” function is activated and the flash period becomes two seconds, i.e., Control Program No. 2 is executed 240 times between flashes, since “Vcount” is allowed to be incremented only if either the “SKIP” function is off in step

1187

or both the “SKIP” function is on and the horn frequency is sweeping up in step

1190

.

FIGS. 12

,

12

A,

12

B, and

12

C illustrates a flowchart of Control Program No. 2 (step

1090

) of FIG.

10

. Namely,

FIGS. 12

,

12

A,

12

B, and

12

C illustrates a method

1200

for detecting low input voltage and for maintaining a plurality of counters that are used to detect the absence of a reference synchronization pulse and to implement the Code 3 pattern.

More specifically, method

1200

starts in step

1202

and proceeds to step

1205

, where method

1200

queries whether the function “FLASH” is set to “On”. If the query is affirmatively answered, then method

1200

proceeds to step

1210

. If the query is negatively answered, then method

1200

proceeds to step

1207

, where the SCR is turned off. Namely, the SCR Q

3

of the alarm unit is turned off.

In step

1210

, method

1200

queries whether the counter “DOnmbr” is greater than the FWR frequency, e.g., 120 Hz. If the query is affirmatively answered, then method

1200

proceeds to step

1212

, where the V

in

is interpreted to be FWR. If the query is negatively answered, then method

1200

proceeds to step

1215

, where the V

in

is interpreted to be D.C.

In step

1217

, method

1200

queries whether the variable “SKflash” is set to “Off”. If the query is affirmatively answered, then method

1200

proceeds to step

1220

. If the query is negatively answered, then method

1200

proceeds to step

1227

.

In step

1220

, method

1200

queries whether the counter “Vcount” is greater than the reference value “V

ref

”. If the query is affirmatively answered, then method

1200

proceeds to step

1225

, where the “SKIP” function is turned “Off”, indicative of a normal input voltage level. If the query is negatively answered, then method

1200

proceeds to step

1222

, where the “SKIP” function is turned “On”, indicative of an abnormal input voltage level. Namely, the above steps

1217

-

1225

are executed to detect a below-nominal input voltage. More particularly, if the input voltage is determined to be below a predefined level, e.g., 20 volts, the flash frequency is reduced in half to approximately 0.5 Hz, or one flash every two seconds. Determination of a below-nominal input voltage is accomplished by using the variable “Vcount” which, as previously discussed, is incremented in Control Program No. 1 when the opto-oscillator has been shut down and the real time clock counter, as represented by register “RTCC” has exceeded “LTvalue”.

As discussed above, “Vcount” will never be incremented higher than 120 within the time period between flashes, and, if the input voltage is over 20 volts, “Vcount” should be incremented all the way to 120 during each flash cycle. If the input voltage is below 20 volts, “Vcount” should be zero. In the embodiment under discussion, the value of “Vref” is chosen to be 30 which will smooth the switch between flashrates.

In step

1227

, method

1220

resets “Vcount” to zero and the “FLASH” function is turned “off”.

In step

1230

, method

1200

queries whether the variable “SKflash” is set to “Off”. If the query is affirmatively answered, then method

1200

proceeds to step

1232

. If the query is negatively answered, then method

1200

proceeds to step

1240

.

In step

1232

, method

1200

queries whether the variable “Vcap” is set to “Hi” or “Low”. Vcap is represented by terminal

10

of U

1

in FIG.

8

. If “Vcap” is “Hi”, then method

1200

proceeds to step

1235

. If “Vcap” is “Low”, then method

1200

proceeds to step

1237

, where the variable “Sfault” is set to “No”. Namely, Vcap is a measure of the voltage of the storage capacitor C

4

at a particular time. In step

1232

, method

1200

presumes that a flash has just occurred. As such, at this point in time, Vcap under normal condition should reflect a low voltage, whereas a Vcap with a high voltage indicates that a fault has occurred.

In step

1235

, method

1200

sets several functions or variables. First, “Sfault” is set to “Yes”, since it is presumed that a fault has occurred where Vcap is “High” after a flash. Second, the function “SKIP” is set to “Off”, which allows the alarm unit to stimulate a flash as frequently as possible, in light of the detected fault condition. Third, “Sosc” is turned “Off” to avoid an overcharging condition, since it has been detected that Vcap is still “High” after a flash. Finally, the counter “Vcount” is set equal to “Vref” +1, thereby ensuring that the SKIP function will remain off.

In step

1240

, method

1200

queries whether the function, “SKIP”, is set to “On”. If the query is affirmatively answered, then method

1200

proceeds to step

1242

, where the variable “SKflash” is toggled. If the query is negatively answered, then method

1200

proceeds to step

1245

, where the variable “SKflash” is set to “Off”.

In step

1247

, method

1200

queries whether the function, “SKIP”, is set to “On”. If the query is affirmatively answered, then method

1200

proceeds to step

1250

. If the query is negatively answered, then method

1200

proceeds to step

1252

.

In step

1250

, method

1200

queries whether the audio frequency is sweeping “up”. If the query is affirmatively answered, then method

1200

proceeds to step

1252

. If the query is negatively answered, then method

1200

proceeds to step

1255

.

In step

1252

, method

1200

resets “RTCC” and “AFcount” to zero and turns off “SoscSD”.

In step

1255

, method

1200

queries whether the function “SILENCE” is set to “Off” and the function “Code 3” is set to “On”. If the query is affirmatively answered, then method

1200

proceeds to step

1257

. Namely, the Code 3 horn signal pattern has been previously selected and method

1200

will now maintain the predefined audio pattern. If the query is negatively answered, then method

1200

proceeds to step

1272

.

In step

1257

, method

1200

queries whether “Sytimer” is equal to 0.5 second. If the query is affirmatively answered, then method

1200

decrements a counter “C

3

count” in step

1260

. The counter “C

3

count” is employed to produce the Code 3 audio pattern. If the query is negatively answered, then method

1200

proceeds to step

1272

.

In step

1262

, method

1200

queries whether the counter “C

3

count” is equal to zero (0). Namely, method

1200

is checking whether the end of the Code 3 pattern has been reached. If the query is affirmatively answered, then method

1200

resets the counter “C

3

count” to a value of four (4) in step

1265

. If the query is negatively answered, then method

1200

proceeds to step

1267

.

In step

1267

, method

1200

queries whether the counter “C

3

count” is greater than one (1). If the query is affirmatively answered, then method

1200

sets the function “MUTE” to “Off” in step

1270

in preparation to sound the horn. If the query is negatively answered, then method

1200

proceeds to step

1272

.

The relationship between the counter “C

3

count”, the sync pulses and the audio Code 3 horn signal is shown in FIG.

15

. Each reference synchronization pulse triggers a set of three (3) one-half second of silence followed by a one-half second horn blast, and one (1) one and one-half second of silence.

In step

1272

, method

1200

increments “Sytimer”, which tracks the elapsed time from strobe flash to strobe flash. Since Control Program No. 2 is executed at the end of a sweep up or sweep down cycle, each increment of “Sytimer” represents a particular time duration, e.g., 0.0083 second.

In step

1275

, method

1200

queries whether the “Mode” is set to “Sync” and the counter “C

3

count” is set to “One” (1). If the query is affirmatively answered, then method

1200

proceeds to step

1277

. If the query is negatively answered, then method

1200

proceeds to step

1282

.

In step

1277

, method

1200

queries whether “SYtimer” is less than “SYlimit”. If the query is affirmatively answered, then method

1200

proceeds to step

1299

. If the query is negatively answered, then method

1200

proceeds to step

1280

, where “Mode” is set to “Auto”. Namely, method

1200

compares “SYtimer” to a predetermined maximum time, “Sylimit”, in which case, method

1200

expects a sync pulse to arrive relative to the previous strobe flash. “Sylimit” can be set equal to 1.1 seconds in one embodiment. As such, if “SYtimer” is not less than “SYlimit”, then there is a problem with the sync pulses and the operating mode of the alarm unit is switched to “Auto”.

In step

1282

, method

1200

queries whether “SYtimer” is equal to “SYflash”. “SYflash” is a preset value that indicates a time in which the alarm unit should flash, e.g., once every second after the reception of a reference synchronization pulse. It should be understood that “SYflash” can be modified to a different time duration in accordance with a particular application. If the query in step

1282

is affirmatively answered, then method

1200

proceeds to step

1285

where “SYtimer” is reset to Zero (0) and “Flash” is set “On”. Namely, it is time to trigger a flash. If the query is negatively answered, then method

1200

proceeds to step

1299

. Namely, insufficient time has elapsed to trigger a flash.

In step

1287

, method

1200

queries whether “Sfault” is set to “Yes”. If the query is affirmatively answered, then method

1200

proceeds to step

1290

where SCR is turned “On”. Namely, a fault has been previously detected. As such, method

1200

will turn SCR “On” as soon as possible regardless of other functions such as “SKIP”. If the query is negatively answered, then method

1200

proceeds to step

1292

.

In step

1292

, method

1200

queries whether the function, “SKIP”, is set to “Off”. If the query is affirmatively answered, then method

1200

proceeds to step

1297

where SCR is turned “On”. If the query is negatively answered, then method

1200

proceeds to step

1295

.

In step

1295

, method

1200

queries whether the variable or bit, “SKflash”, is set to “On”. If the query is affirmatively answered, then method

1200

proceeds to step

1299

. If the query is negatively answered, then method

1200

proceeds to step

1297

where SCR is turned “On”. In step

1299

, method

1200

ends and returns to method

1000

to step

1025

.

FIG. 14

illustrates a flowchart of Control Program No. 3 (step

1073

) of FIG.

10

. Namely,

FIG. 14

illustrates a method

1400

for detecting the selection of the Code 3 audio pattern or a continuous tone audio pattern in the alarm unit, e.g., as shown in

FIG. 16

below, by means of a jumper setting.

More specifically, method

1400

starts in step

1405

and proceeds to step

1410

, where method

1400

sets “Code 3” equal to “Off”.

In step

1415

, method

1400

queries whether the function “Mode” is set to “Sync”. If the query is affirmatively answered, then method

1400

proceeds to step

1425

, where “Code 3” is set to “On”. Namely, in one embodiment, it is optionally presumed that a Code 3 audio pattern is desired if the alarm units are operated under synchronization mode. If the query is negatively answered, then method

1400

proceeds to step

1420

.

In step

1420

, method

1400

checks the tone select input jumper on the alarm unit to determine the selected audio pattern. If a continuous tone is selected with the jumper, method

1400

simply proceeds to step

1430

, since “Code 3” was previously set to “Off” in step

1410

. If a Code 3 tone is selected with the jumper, method

1400

proceeds to step

1425

, where “Code 3” is set to “On”.

In step

1430

, method

1400

queries whether the “Code 3” is set to “Off”. If the query is affirmatively answered, then method

1400

proceeds to step

1435

, where the function “MUTE” is set to “Off”. If the query is negatively answered, then method

1400

proceeds to step

1440

.

In step

1440

, method

1400

queries whether the “SYtimer” is equal to “SYflash”−1. If the query is affirmatively answered, then method

1400

proceeds to step

1445

, where the function “Zictrl” is set to “Off”. If the query is negatively answered, then method

1400

proceeds to step

1450

.

In step

1450

, method

1400

queries whether the “SYtimer” is equal to the value “One” (1). If the query is affirmatively answered, then method

1400

proceeds to step

1455

, where the function “Zictrl” is set to “On”. If the query is negatively answered, then method

1400

ends in step

1470

.

It should be noted that optional steps

1440

-

1455

provide dynamic control of the inrush limiting circuit as shown in FIG.

8

. As such, steps

1440

-

1455

can be omitted if the inrush limiting circuit is left “On” after initialization as shown in step

1020

.

FIGS. 13

,

13

A, and

13

B illustrates a flowchart of an alternate embodiment of a software routine or method of the microcontroller of the interface control circuit as shown in FIG.

5

. More specifically, method

1300

starts in step

1302

and proceeds to step

1305

where initialization is performed, e.g., one or more registers and variables are initialized, e.g., “SYNC” is set equal to “0”, “SYcount” is set equal to “0” and “mAUD” is set equal to “1”.

In step

1307

, method

1300

employs a delay where for a short period of time, e.g., 980 msec., the interface control circuit will not generate any reference signal.

In step

1310

, method

1300

sets the variable “mAUDpr” (e.g., a single bit) equal to “mAUD”, where “mAUD” represents a memorized setting of the audible input terminal (secondary loop

48

) on the interface control circuit and “mAUDpr” represents a previous “mAUD” setting. The audible input terminal is employed to indicate to the interface control circuit whether the “SILENCE” feature is activated for a loop of alarm units. If a voltage is present at the audible input terminal (e.g., AUD=1 or ON), then the “SILENCE” feature is not activated. If a voltage is absent or reversed at the audible input terminal (e.g., AUD=0 or OFF), then the “SILENCE” feature is activated.

In step

1312

, method

1300

queries by actually scanning the audible input terminal to determine whether the “SILENCE” feature is activated (ON or OFF). If the “SILENCE” feature is activated, then method

1300

stores that setting in step

1315

by setting “mAUD” equal to Off. If the “SILENCE” feature is not activated, then method

1300

stores that setting in step

1317

by setting “mAUD” equal to On.

In step

1320

, method

1300

sets the variable SYNC equal to “0”, clearing SYNC(1) and SYNC(2).

In step

1322

, method

1300

queries whether “mAUD” equals to OFF and “mAUDpr” equals to ON, i.e., whether a transition occurred. If the query is affirmatively answered then “SYNC(2)” is set equal to “ON” in step

1325

. “SYNC(2)=ON” represents that a second pulse will be sent after a first pulse by the interface control circuit to effect the “SILENCE” feature. As discussed above, when a second pulse is sent at approximately 0.1 second from a first pulse, the alarm unit will interpret the second pulse as a command to implement the “SILENCE” feature. If the query at step

1322

is negatively answered, then method

1300

proceeds to step

1327

.

In step

1327

, method

1300

queries whether “mAUD” equals to ON and “mAUDpr” equals to OFF, i.e., again whether a transition occurred. If the query is affirmatively answered then “SYNC(1)” is set equal to “ON” in step

1330

. “SYNC(1)=ON” represents that a first pulse will be sent by the interface control circuit. If the query at step

1327

is negatively answered then method

1300

proceeds to step

1332

.

In step

1332

, method

1300

increments a counter, “SYcount” by one. More specifically, the “Sycount” counter is used to count the number of predefined “cycles” that must occur prior to the transmission of a reference synchronization pulse. Each cycle can be perceived as representing the execution of method

1300

through one loop. In the present invention, if each cycle represents one second, then a reference synchronization pulse is sent after every four cycles or every four seconds. However, it should be understood that the predefined number of cycles can be adjusted in accordance with a particular implementation. For example, if the oscillator employed on the alarm unit is very precise, then the predefined number of cycles can be increased to further decrease the number of transmitted synchronization pulses, whereas if the oscillator employed on the alarm unit is not very precise, then the predefined number of cycles can be decreased to ensure synchronization.

In step

1335

, method

1300

queries whether “Sycount” is greater than a value of four (4). If the query is affirmatively answered then method

1300

resets the “Sycount” counter back to zero in step

1337

. Namely, a four second cycle is completed and the counter is reset to zero to start another four second cycle. If the query is negatively answered then method

1300

proceeds to step

1355

.

In step

1340

, method

1300

queries whether “mAUD” is equal to “OFF”. If the query is affirmatively answered , then “SYNC(2)” is set equal to “ON” in step

1342

. If the query at step

1340

is negatively answered, then method

1300

proceeds to step

1345

.

In step

1345

, method

1300

queries whether “mAUD” equals to “ON”. If the query is affirmatively answered then “SYNC(1)” is set equal to “ON” in step

1347

. If the query at step

1345

is negatively answered, then method

1300

proceeds to step

1350

. It should be noted that steps

1340

and

1345

allow the interface control circuit to check at the beginning of each four second cycle whether the “SILENCE” feature is activated. In contrast, the above steps

1322

and

1327

allow the alarm panel to have the option of activating the “SILENCE” feature during the four second cycle, without having to wait for the four second cycle to be completed.

In step

1350

, method

1300

queries whether “SYNC(2)” equals to “ON”. If the query is affirmatively answered then “SYNC(1)” is set equal to “ON” in step

1352

. Namely, in order to generate the second pulse (represented by having “SYNC(2)” equals to “ON”) of a “double pulse”, it is necessary to first generate the first pulse (represented by having “SYNC(1)” equals to “ON”). If the query at step

1350

is negatively answered, then method

1300

proceeds to step

1355

.

In step

1355

, method

1300

queries whether “SYNC(1)” equals to “ON”. If the query is affirmatively answered, then method

1300

resets the “Sycount” counter back to zero in step

1357

. Namely, step

1355

allows the interface control circuit to quickly respond to state transition of mAUD, e.g., in steps

1322

and

1327

. For example, if the “SILENCE” feature is deactivated and a Code 3 audio pattern is desired immediately, then it is necessary to reset the “Sycount” counter back to zero in step

1357

, so that the Code 3 audio pattern can start as soon as possible, i.e., within the next loop of method

1300

, e.g., approximately one second. If the query at step

1350

is negatively answered, then method

1300

proceeds to step

1360

.

In step

1355

, method

1300

queries whether “SYNC(1)” equals to “ON”. If the query is affirmatively answered, then method

1300

generates a reference synchronization pulse of a particular duration (typically between 10-30 msec.), e.g., a 25 msec. pulse in step

1365

. If the query at step

1355

is negatively answered, then method

1300

proceeds to step

1362

where a delay is generated, e.g., a delay of 25 msec.

In step

1367

, method

1300

generates a second delay, e.g., a delay of 75 msec. This delay is selected such that the time between the two pulses of a double pulse is 100 msec (25 msec. for the reference synchronization pulse and 75 msec. for the delay). It should be understood that the spacing of 100 msec. can be adjusted in accordance with a particular implementation.

In step

1370

, method

1300

queries whether “SYNC(2)” equals to “ON”. If the query is affirmatively answered, then method

1300

generates a second pulse of a particular duration (typically between 10-30 msec.), e.g., a 25 msec. pulse in step

1375

. If the query at step

1370

is negatively answered, then method

1300

proceeds to step

1372

where a delay is generated, e.g., a delay of 25 msec.

In step

1377

, method

1300

generates a third delay, e.g., a delay of 855 msec. This delay is selected such that the time for executing the loop of method

1300

is approximately one second (0.10 msec.+0.25 msec.+0.75 msec.+0.25 msec.+0.855 msec.=0.990 msec.). In turn, method

1300

returns to step

1310

where the loop of method

1300

is repeated.

FIG. 16

illustrates a circuit diagram of another embodiment of an alarm unit

1600

employed in the present invention. Namely, alarm unit

1600

shows a “Tone Select Input” jumper J

3

. The setting of this jumper can be detected in the above Control Program No. 3 as shown in

FIG. 14

, and is used to determine if a Code 3 horn or a continuous horn is to be generated.

More specifically, resistor R

26

pulls pin

8

of microcontroller U

1

“High” when jumper J

3

is removed indicating the continuous horn setting. When jumper J

3

is installed, pin

8

is forced “Low” indicating Code 3 horn setting.

FIG. 16

also shows another method of providing the “MED” volume level. The entire winding of transformer T

2

is connected to the cathode of diode D

2

. The additional inductance reduces the volume level from “HI” to “MED”. This method eliminates the need for a second resistor (R

22

) as shown in FIG.

8

. The balance of

FIG. 16

is essentially the same as FIG.

8

.

By way of example, the circuit shown in

FIG. 16

may use the following parameters to obtain the above-described switching cycle:

ELEMENT

VALUE OR NUMBER

T1, DS1

FLASHTUBE, TRIGGER COIL

ASSEMBLY

C1, C2

CAP 33 pF 5% 50 V

C3

CAP 68 uF 10% 6.3 V

C4

CAP 33 uf 10% 250 V

C5

CAP .047 uF 5% 400 V

C7

CAP 33 pF 5% 200 V

C8

CAP .10 uF 20% 100 V

D1, D2

DIODE, 1N4004

D4, D5

DIODE, HER105/UF4005

J1

CONN, MALE 2P

J2

HDR, R/A 4P

J3

HDR, R/A 2P

L1

IND ASY, 9.40 mH

Q1

TRANSISTOR, 2TX455

Q2

TRANSISTOR, 2N5551

Q3

TRIAC, LOGIC L401E5

Q4

TRANSISTOR, IRF710

Q5

TRANSISTOR, 2N2907

Q6

TRANSISTOR, MPSA27

R2

RES ¼ W 560 OHMS 5%

R3

RES ¼ W 12.1K OHMS 1%

R4

RES ¼ W 220K OHMS 5%

R5

RES ½ W 27 OHMS 5%

R8, R10

RES ¼ W 1.0K OHMS 5%

R1, R9, R16, R23, R26, R27

RES 1/4 W 10K OHMS 5%

R11, R14

RES 1/4 W 1M OHM 5%

R12

RES 1/4 W 9.31 OHMS 1%

R13

RES ¼ W 100K OHMS 5%

R17

RES ½ W 330 OHMS 5%

R19

RES 1/4 W 10K OHMS 1%

R20

RES 1/4 W 2.21K OHMS 1%

R21

RES 1/2 W 680 OHMS 5%

R24

RES 1/4 W 6.8K OHMS 5%

R25

RES ¼ W 39K OHMS 5%

R28

RES ½ W 220 OHMS 5%

RV1

VARISTOR, 40VAC/56VDC

T2

TRANSFORMER

U1

MICROCONTROLLER, PIC16C54

U2

OPTO-COUPLER, 4N35

W1, W2, W3, W4

JMPR, WIRE

Y1

CERA RESN, 4.00 Mhz

Z1

ZNR DIODE, 1N4626 5% .4W

Z2

ZNR DIODE, 1N4619 3.0V 5%

Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.

Number	Name	Date
4952906	Buyak et al.	Aug 1990
5341069	Kosich et al.	Aug 1994
5400009	Kosich et al.	Mar 1995
5559492	Stewart et al.	Sep 1996
5598139	Karim et al.	Jan 1997
5659287	Donati et al.	Aug 1997
5850178	Ha et al.	Dec 1998
5982275	Kosich	Nov 1999

	Number	Date	Country
Parent	08/807063	Feb 1997	US
Child	09/074328		US

	Number	Date	Country
Parent	09/074328	May 1998	US
Child	09/153105		US

Apparatus and method for synchronizing visual/audible alarm units in an alarm system

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Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

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Abstract

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Parent Case Info

US Referenced Citations (8)

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Continuation in Parts (1)