Electronic system for activating a mechanical fire siren

An electronic device designed to activate a municipal mechanical fire siren upon the receipt of fire from any one of a plurality of inputs, where said fire siren is used to alert fire personnel of an emergency. In addition, through the use of a built in 24 hour clock, the device can operate the siren at noon each day, as a means of automatic testing. The gain time of the siren cycle and the number of cycles per alarm can be preset by the user.

BACKGROUND OF INVENTION 
1. Field of Invention 
The present invention is an electronic device used to activate a municipal 
mechanical fire siren upon the receipt of a signal of fire from any one of 
a plurality of inputs. Its placement would be in a fire station to alert 
firefighters when they have an alarm by sounding the fire siren. 
2. Description of Prior Art 
When volunteer fire departments in small towns across the country receive a 
call for help, the primary method used to call firefighters to the station 
is by the use of a large fire siren, usually mounted on or in close 
proximity to the firehouse. It is powerful enough to be heard all through 
the surrounding area, and the firefighters, upon hearing the siren, are 
expected to repair with all possible haste to the scene of the fire. If 
the siren is not activated when an alarm of fire has been reported to the 
fire station, then the firefighters are not immediately notified of the 
alarm, and response time is delayed, possibly causing unnecessary loss of 
life and property. 
Most municipal fire sirens today are radio-activated; that is, a central 
command center receives all telephone calls for help and when one is 
received, they transmit radio tones of a specific frequency to the fire 
department needed to respond to the call. At the fire station called, 
there is a radio receiver that upon receipt of these specific tones, close 
a dry contact switch for a few seconds. A siren activation system in use 
at that firehouse can utilize this switch closure to start its process of 
turning on and turning off the fire siren to produce the wailing effect 
that is so familiar. After a predetermined length of time, the siren 
activator shuts down until the next alarm is received. In some cases, a 
fire department may have their fire siren sound for one cycle at noon each 
day, as a daily test. 
In the past, the method used for turning the siren on and off upon receipt 
of an alarm was handled by a series of small 120 Volt AC motors. These 
motors would have cam plates attached to them that would turn with its 
corresponding motor. A microswitch riding on the edge of the cam would 
open and close with the contours of the cam. The current to the fire siren 
was controlled by the opening and closing of this microswitch via several 
step-up relays, as most siren motors operate around 220-440 Volts in 
3-phase form. After a predetermined amount of cycles of the cam, another 
microswitch would usually shut down the entire system. If the department 
wanted their siren to cycle once at noon each day as a daily test of the 
siren, then a separate AC clock/timer had to be purchased to keep track of 
time. This clock/timer would be preset to trip a microswitch at noon each 
day and an entirely different series of cams and microswitches would be 
needed to sound the siren for one cycle at noon and shut down afterward. 
An example of this older type of mechanical timer is discussed in U.S. 
Pat. No. 3,728,707 (Herrnreiter). 
There are many problems associated with the use of a system of AC motors, 
cams, and microswitches: 
1. The entire system operates at a minimum voltage of 120 volts AC 
(excluding the siren motor itself). If there was to be an AC power 
failure, nothing short of an emergency generator would be able to keep the 
system operational. Without AC power, a reported alarm could go unnoticed 
by firefighters as the siren would not be operational. 
2. By using AC motors, microswitches, cams, and the like, it is observed 
that there are many moving parts that can be subject to wear and tear, as 
well as frequent breakdown. 
3. Any indicator lights used with the system also use AC voltage. These 
lamps tend to become very warm after awhile and in some cases, have been 
known to start a fire, thereby causing a fire in the fire station. 
4. The noon clock, also dependent on AC power, will lose track of time 
during a power failure and may activate the noon test at any time during 
the day after AC power is restored, until it is manually reset by 
personnel. There are some timers on the market today that use a spring or 
a backup battery to keep track of time during a power failure, but their 
usefulness only spans over a few hours and only function to support the 
clock- nothing else. 
5. If the department wanted to add additional features to their siren 
activation system (i.e. noon timer, heat detectors to monitor for fire in 
the station, etc.) they had to seek out additional components and add them 
to the existing system. This would more often than not result in several 
different circuit panels, fuse boxes, and additional wiring to be added to 
an already cluttered system. 
6. AC powered components can be susceptible to power surges and 
interference by lightning and electrical storms. These can quite often 
lead to false activation of AC powered siren activation systems. 
Today, most fire departments in the country have assigned radio receivers 
or pagers to their personnel. This affords them the opportunity to page 
firefighters when there is an alarm in addition to activating the siren. 
The radio page consists of a voice announcement made by a dispatcher 
actually describing the type of alarm and its location. In most instances, 
this dispatcher is the person that answers the phone when there is a call 
for assistance. Approximately 97% of all fire calls to most small fire 
departments are received from the public via telephone and processed 
through a dispatcher. The remaining 3% of alarms reported occur usually 
under one or more of the following methods: 1.) The fire department may 
employ the use of heat detectors in the building. These are connected to 
the siren activation system either directly or through a commercially 
available fire alarm system installed to protect the premises only. If a 
fire is detected within the building, this would automatically activate 
the fire siren, thus alerting fire personnel. 2.) A manual pull station 
(fire call box) is attached to the outside of the building so that 
passers-by may turn in an alarm to the fire department directly, if 
necessary. This pull station is also directly connected to the siren 
activation system. 3.) In some cases, a department may monitor a remote 
location within its fire protection district for fire. Some examples of 
remote locations may include a school, church, or government office. 
Should a fire be detected at any of these locations, a signal can be 
transmitted to the fire station (usually over a telephone cable or some 
similar method) to automatically activate the fire siren. In the example 
of remote location monitoring, there needs to be some sort of fire alarm 
system in operation at the location to be monitored. There are many 
examples of fire detection and warning systems in the prior art, specific 
examples include U.S. Pat. Nos. 4,086,573 (Sasaki); 4,092,642 (Green et 
al); 4,357,602 (Lemelson); 4,491,830 (Miyabe); 4,550,311 (Galloway et al); 
4,673,920 (Ferguson et al). In each of these examples, the systems being 
described are responsible for monitoring for an outbreak of fire. Upon 
detecting such a situation, it will then alert occupants of the building, 
provide emergency assistance in the form of visual and audio alerts, 
sprinkler activation and the like, and provide means to notify emergency 
personnel. The siren activation system being discussed in this application 
would actually receive the signal for assistance from the fire alarm 
systems described in the prior art. In essence, the siren activation 
system would provide a second level of notification of fire, but would in 
actuality be the first level of notification to fire personnel. 
If an alarm of fire is reported to the fire department using any of the 
three methods listed above, the siren is activated without the 
intervention of a dispatcher. Since the dispatcher (who could technically 
be located many miles away from the fire station) did not activate the 
alarm for the department, he is unaware that there is an alarm in progress 
and therefore does not page firefighters as to the location of the fire. 
The firefighters upon hearing the siren, would have to "figure out" where 
the fire is once they reach the station. With the older AC mechanical 
siren activation systems described earlier, should the siren fail to 
operate for an automatically activated alarm, then no one would know that 
there was a fire or similar emergency in progress. 
SUMMARY OF INVENTION 
The present invention improves on all existing and prior art by addressing 
the following: 
1. All control circuitry responsible for operating the fire siren is in the 
form of CMOS integrated circuits. This allows for compact design and the 
ability for system operation at 12 volts DC or less. 
2. Since CMOS IC's are being used in the system, current flow is in the 
milliampere range and the risk of fire caused by overheated components is 
greatly reduced if not eliminated altogether. 
3. Since CMOS ICs now take the place of AC motors and microswitches, it is 
observed that the liability of using a majority of moving parts in the 
system has been reduced. This allows for less frequent breakdowns due to 
the wearing out of contacts, motors, and the like. 
4. A sealed, rechargeable battery can be added to the system in order to 
keep it operational should an AC power failure occur. In the event of such 
a power failure, the battery would be able to sustain system operation for 
over 72 hours. If a larger battery is used, then the backup power time 
will extend even longer. 
5. Three normally open contact pairs are included in the system. Shunting 
any of the pairs together will cause the system to activate. In addition, 
there are another five pairs of contacts, each activated by applying 18-24 
volts DC across each pair. These can be used to activate the system from a 
remote location. This is useful when monitoring other buildings (such as a 
school or government office) for fire. 
6. Time delay circuitry has been incorporated into the system on each input 
so that the siren is not immediately activated upon closure of any one of 
the contact pairs. This delay is used to suppress possible false 
activations that may be caused by electrical circuit noise or lightning 
storms. 
7. As sirens vary in characteristics from model to model, the gain time 
(the amount of time it takes a siren to go from silence to its highest 
wail pitch) will vary as well. For that reason, the present invention has 
a user adjustable gain time setting that can be varied for the siren being 
controlled by the system. In addition, the number of cycles (defined as 
the start of the gain (ON) time of the siren to the start of the next gain 
time) that the siren will be activated for during an alarm can also be 
preset by the user. When the system is activated, it turns the siren on 
and off until the preset number of cycles is reached, at which point the 
system resets itself and waits for the next alarm condition to occur. 
8. A normally open (N.O.) dry contact switch has also been added to the 
system. This switch is designed to close upon system activation and hold 
for the duration of the alarm. This switch can be utilized by personnel to 
automatically activate electrical devices of their choosing upon the 
receipt of an alarm of fire. 
9. A digital clock has been integrated into the system so that if a noon 
test is desired, the department does not need to purchase an additional 
timer to add to the system. The noon test feature of the system is 
designed to sound one siren cycle automatically at 12:00 PM each day, 
where the gain time of that cycle can be preset by the user. 
10. Since the system is battery backed, it no longer is necessary to reset 
the clock after each power failure. That way, the possibility of a false 
noon test sounding after a power failure has also been eliminated. 
11. The system allows for the interconnection of a commercially available 
digital dialer unit, similar to those used in the burglar alarm industry 
for monitoring premises for holdups, or other criminal acts. That same 
dialer unit can be used with the present invention to alert fire personnel 
of alarms of fire should the fire siren be rendered inoperable by either 
an AC power failure or a mechanical defect. This reduces the possibility 
of fire personnel not being notified at the time of an alarm. The standby 
battery on the system will also power the dialer unit. This dialer unit 
would have the capability from the present invention to dial a monitoring 
service when an alarm is turned into the system and report which input 
source initiated the alarm. The monitoring service receiving the call from 
the dialer unit could then contact the dispatcher with the information so 
that he could page fire personnel and give them the exact location of the 
fire.

DETAILED DESCRIPTION OF THE INVENTION 
There are three primary circuits that make up the present invention. These 
are given in block diagram form in FIG. 1, 2, and 3. 
FIG. 1, "Siren Activation Circuit" 
This diagram shows input pairs 1 through 8 to the system that are each able 
to report the receipt of an alarm condition. These eight pairs are 
normally open (N.O.) contacts that merely need to be shunted together to 
activate the system. However, pairs 4 through 8 are closed by 
microminiature relays 9 through 13 that require a coil voltage potential 
of 18-24 volts DC to close its corresponding encapsulated switch. This has 
been done so that inputs 4 though 8 could be tripped by any device that is 
able to produce an 18-24 VDC external voltage source across the terminals 
of inputs 4 through 8. LED indicators 85 through 92 are connected between 
each input pair and Vdd so that when any pair is shunted together, the 
corresponding LED will illuminate. When an alarm condition is received on 
any one of input pairs 1 through 8, it passes through one of two MC14490 
bounce eliminator IC's 14 and 15, each able to handle four inputs. 
Capacitors 16 and 17 regulate the delay time of the debouncing IC's. 
Capacitor 16 is connected to IC 14 between the OSC IN and OSC OUT pins, 
while capacitor 17 is connected to IC 15 in a similar fashion. In this 
configuration, IC's 14 and 15 will delay the state of their inputs from 
changing the state of their outputs for approximately three seconds when a 
value of 3.3 uF for both capacitors 16 and 17 is used. With IC's 14 and 15 
in place as explained, an alarm condition received on any one of input 
pairs 1 through 8 must hold the selected pair in a shunted condition for a 
minimum of three seconds in order to allow the output of the appropriate 
debouncing IC (14 or 15) to go HIGH. The purpose for this delay is to 
prevent false signals that may appear on inputs 1 through 8 (i.e. those 
due to electrical noise) from activating the siren. Diodes are used to 
protect IC's 14 and 15 from damage that may occur at a delay time greater 
than two seconds. Each IC uses two diodes; one between OSC IN and Vdd and 
the other between OSC OUT and Vdd. The diodes are connected to allow 
current flow from the pins of the IC to Vdd only. Indicator LEDs 22 
through 29 are connected at each input to the system before IC's 14 and 15 
in order to display the status of each input pair 1 through 8 to the user. 
After debouncing, all eight outputs of IC 14 and 15 are fed into the `B` 
inputs of one-shot IC's 30 through 33 whose `A` inputs are all connected 
to ground. The `B` input of each one-shot circuit is also connected HIGH 
via 1 K.OMEGA. resistors in order to hold the `B` input level HIGH when 
the circuit is idle. The active-low RESET input of each one-shot is 
connected HIGH to disable the reset function. Each one-shot IC (30 through 
33) contains two individual one shot circuits. The purpose of the one-shot 
circuit for each output of IC's 14 and 15 is to guarantee that should any 
input pair 1 through 8 become seized (i.e. did not reset after previously 
initiating an alarm condition), it will not prohibit the system from 
detecting an alarm condition on any of the remaining inputs. The one-shot 
circuits of IC's 30 through 33 are designed to have short output pulse 
lengths so the Q of each circuit will not be able to remain at a HIGH 
level for an extended period of time. This is done by connecting a 100 
K.OMEGA. resistor 93 and a 0.01 uF capacitor 94 to the timing input of 
each one-shot. The other side of resistor 93 is connected HIGH, while the 
other side of capacitor 94 is grounded. All eight outputs of one-shots 30 
through 33 are connected in parallel to plug 29 that allows for the 
interconnection of a commercially available digital dialer unit, if 
desired by the user. 
The eight separate outputs from one-shots 30 through 33 are next fed into 
an 8-input OR gate 34 so that only one output is needed to activate the 
rest of the system. The output of OR gate 34 is then inverted by inverter 
71 and directed into the SET input of NOR latch 35. A HIGH output from OR 
gate 34 will drive the NOR latch 35 output LOW where it will remain until 
it is reset. The Q output of NOR latch 35 output is then directed to two 
different functions: 1. it is used to drive the base of NPN transistor 36 
via a 2.2 K.OMEGA., 1/4W resistor 72. The collector of transistor 36 is 
connected HIGH and the emitter is connected to the coil of relay 37 whose 
encapsulated switch is used as a normally open accessory switch. A switch 
119 is used in between the Q output of NOR latch 35 and resistor 72 so 
that when open, will prohibit the system from closing the accessory switch 
during an alarm condition; 2. The Q output of NOR latch 35 output is then 
inverted by inverter gate 38. The common point of linear set switch 39, 
which allows the user to direct one of ten circuits to a common point, is 
then input to OR gate 40 along with the output from inverter gate 38. The 
resulting output from OR gate 40 is then used as the RESET input for CMOS 
decade counter 41. Positions 1 through 10 of set switch 39 are connected 
to outputs 0 through 9 of counter 41 respectively. The ENABLE input to 
counter 41 is grounded, and the CLOCK input is fed by a 1 Hz square wave 
being generated by counter 54 in the clock circuit (FIG. 2). In this 
scenario, the gain time of the siren, in seconds, can be directly set by 
the user by selecting the desired setting on set switch 39. When the Q 
output of NOR latch 35 is HIGH, the output of inverter gate 38 goes LOW. 
Provided that the common point of set switch 39 is also LOW, the output of 
OR gate 40 will provide a LOW on the RESET for counter 41. This will cause 
counter 41 to begin incrementing. When the Q1 output of counter 41 is 
HIGH, it will provide a CLOCK pulse to D-latch 42, whose SET input is 
grounded and D input is connected to its own NOT-Q output. When D-latch 42 
receives a HIGH on its clock input from counter 41, it allows its Q output 
to go HIGH. This output is then directed to the input of AND gate 73 along 
with the Q output from latch 35. The output of AND gate 73 is used as the 
clock input for the cycles-per-alarm decade counter 43, whose ENABLE input 
is grounded. The output of AND gate 73 is also connected to the input of 
OR gate 74 along with the Q output from D-latch 75. The output from OR 
gate 74 is used to drive the base of NPN transistor 44 via a 2.2 K.OMEGA., 
1/4W resistor 76. The collector of transistor 44 is connected HIGH and 
emitter the is connected to the coil of relay 45 whose encapsulated switch 
is used to start the siren. A switch 120 is used between the output of OR 
gate 74 and resistor 76 so that when open, will prohibit the system from 
activating the fire siren during an alarm condition. When a HIGH pulse is 
received on the clock input to counter 43, it increments one step. A 
second set switch 46, being the same type as set switch 39, has its 
positions 1 through 10 connected to output stages 0 through 9 of counter 
43, respectively. The common point of set switch 46 is connected to the 
RESET inputs of counter 43, D-latch 42, and NOR latch 35. 
When the user-preset value of counter 41 is reached, a HIGH output from set 
switch 39 will be input to OR gate 40. This will result in a HIGH output 
which will reset counter 41 back to zero. This will cause the common point 
of set switch 39 to go LOW and thereby cause the RESET of counter 41 to 
also go LOW, and begin counting again. When the first count stage is 
reached, a HIGH pulse will be sent once again to the CLOCK input of 
D-latch 42. This time, since the Q of the D-latch 42 is already HIGH, this 
next input pulse will drive Q LOW, thus shutting off the siren. When the 
user-preset value of counter 41 is reached, a HIGH output from set switch 
39 will be input to OR gate 40. This will result in a HIGH output which 
will reset counter 41 back to zero. This will cause the common point of 
set switch 39 to go LOW and thereby cause the RESET of counter 41 to also 
go LOW, and begin counting again. When the first count stage is reached, a 
HIGH pulse will be sent once again to the CLOCK input of D-latch 42. When 
a HIGH appears on the counting stage output of counter 43 that is 
currently connected to the common point of set switch 46, via user input, 
it will reset counter 43, D-latch 42, and NOR latch 35. When NOR latch 35 
is reset, it's Q will go LOW, which in turn will turn off transistor 36 
and cause the output of inverter gate 38 to go HIGH. The will result in a 
HIGH input to OR gate 40, which will respond by applying a HIGH to the 
RESET input of counter 41. This will disable all ability for the circuit 
to count until the next time a HIGH input is received by NOR latch 35 via 
OR gate 34. If a HIGH did not yet appear on the common point of set switch 
46, then the entire counting process of counter 41 would have started 
again. It should now be realized that every other counting cycle of 
counter 41 will increment counter 43 and turn on the siren. This is how 
the wailing effect of the siren is produced. 
FIG. 2, "Clock Circuit" 
At the heart of the clock circuit is a 3.5759 MHz quartz crystal oscillator 
47, which is made to oscillate by connecting variable capacitor 49 with a 
range of 5-36 pF between one lead of oscillator 47 and ground and 
connecting a 33 pF fixed value capacitor 50 between the other lead of 
oscillator 47 and ground. One lead of oscillator 47 is connected to the 
OSC IN pin of a MM5369 frequency divider IC 52. The other lead of 
oscillator 47 is connected to a 2.2 K .OMEGA. resistor 51. The other lead 
of resistor 51 is connected to the OSC OUT pin of IC 52. A 20 M .OMEGA. 
resistor 48 is connected across the OSC IN and OSC OUT pins of IC 52. 
Connected in this fashion, when power is applied, the resulting output of 
IC 52 is a 60 Hz square wave. This square wave is then applied to the 
CLOCK input of a CMOS decade counter 53 whose ENABLE and RESET inputs are 
both grounded, thus allowing it to count whenever a clock signal is 
applied on its CLOCK input. In this configuration, the CARRY output of 
counter 53 will go HIGH once for every ten clock pulses on the input from 
IC 52. This resulting output is then considered one-tenth the value of the 
input, or 6 Hz. This 6 Hz output is then connected to; 1) one side of a 
normally open push button switch 62 and; 2.) the CLOCK input of another 
decade counter 54, whose ENABLE is grounded, and RESET is connected its 
own Q6 output. In this configuration, the Q5 output of counter 54 will go 
HIGH once for every six clock pulses on the input from counter 53. This 
resulting output is one-sixth the value of the input (one pulse every 
second), or 1 Hz. This 1 Hz output is sent to different parts of the 
circuit as follows: 
1. It is applied to the CLOCK input of a CMOS decade counter 55, whose 
ENABLE and RESET inputs are both grounded, thus allowing it to count 
whenever a clock signal is applied on its CLOCK input. In this 
configuration, the CARRY output of counter 55 will go HIGH once for every 
ten clock pulses on the input from counter 54. This resulting output is 
then considered one-tenth the value of the input, or 1 pulse every 10 
seconds. The output of counter 55 is then connected to the CLOCK input of 
another decade counter 56, whose ENABLE is grounded, and RESET is 
connected to its own Q6 output. In this configuration, the Q5 output of 
counter 56 will go HIGH once for every six clock pulses on the input from 
counter 55. This resulting output is one-sixth the value of the input, or 
1 pulse per minute. The output of counter 56 is connected to the `A1` 
terminal of a double-pole, double-throw switch 61, whose common terminal 
`C1` is connected to the ENABLE input of a BCD counter 57 which indicates 
minutes. The CLOCK and RESET inputs of counter 57 are both grounded. When 
switch 61 is in the A-C shunt position, it allows counter 57 to count in 
BCD form whenever a HIGH level is present on its ENABLE input. The `A` and 
`D` outputs of counter 57 are ANDed together by AND gate 101, the output 
of which is connected to the ENABLE input of another BCD counter 58, which 
indicates tens of minutes. The CLOCK input of counter 58 is grounded. The 
`B` and `C` outputs of counter 58 are ANDed together by AND gate 102, the 
output of which is connected to the RESET input of counter 58. The `A` and 
`C` outputs of counter 58 are ANDed together by AND gate 103, the output 
of which is connected to the ENABLE input of BCD counter 59, which 
indicates hours. The CLOCK input of counter 59 is grounded. The `A` and 
`D` outputs of counter 59 are ANDed together by AND gate 104, the output 
of which is connected to the ENABLE input of BCD counter 60, which 
indicates tens of hours. The CLOCK input of counter 60 is grounded. The 
`B` output of counter 60 and the `C` output of counter 59 are ANDed 
together by AND gate 105, the output of which is connected to the RESET 
inputs of counters 59 and 60. In this fashion, a 24-hour clock has been 
constructed that will keep time from 00:00:00 to 23:59:59 before resetting 
back to midnight, or 00:00:00. 
2. It is also applied to the CLOCK inputs of counters 41 (Siren Activation 
Circuit), and 116 (Noon Test Circuit). 
Push button switch 62, which has one pole connected to the output of 
counter 53 as explained previously, has its other pole connected in 
parallel to a 1 K.OMEGA., 1/4W resistor 63 which has its other side 
grounded, and terminal `B1` of switch 61. To set the clock, switch 61 
should be first placed in the B-C shunt position. This action will disable 
the ability for counters 57, 58, 59, and 60 to advance. Resistor 63 
prevents the circuit to drift as the B-C shunt position of switch 61 would 
theoretically leave an open circuit. In this configuration, depressing and 
holding switch 62 will allow the output of counter 53 to be directly 
applied to the input of counter 57. This will allow the user to rapidly 
advance the time stored in counters 57 through 60. To return to the normal 
time keeping mode, switch 61 should be placed back into the A-C shunt 
position. 
To display the time of day to the user, BCD-to-seven segment decoder/driver 
IC's are used to convert the output of counters 57 to 60 to seven segment 
numerals that are displayed on LCD 64. Only the minutes, tens of minutes, 
hours, and tens of hours are displayed to the user. Therefore, only four 
BCD-to-seven segment decoder/driver IC's are needed. Driver 65 is 
connected to counter 57 as follows: The A output of counter 57 is 
connected to the A input of driver 65. The B output of counter 57 is 
connected to the B input of driver 65. The C output of counter 57 is 
connected to the C input of driver 65. The D output of counter 57 is 
connected to the D input of driver 65. The outputs of driver 65 make up 
the segments a through g of the seven-segment digit of the LCD display 
that corresponds to the minutes of the clock (the extreme right-hand side 
digit of the LCD display). Driver 66 is connected to counter 58 in the 
exact same manner as driver 65 is connected to counter 57. The outputs of 
driver 66 make up the segments a through g of the seven-segment digit of 
the LCD display that corresponds to the tens of minutes of the clock (the 
second from the extreme right-hand side digit of the LCD display). Driver 
67 is connected to counter 59 in the exact same manner as driver 65 is 
connected to counter 57. The outputs of driver 67 make up the segments a 
through g of the seven-segment digit of the LCD display that corresponds 
to the hours of the clock (the second from the extreme left-hand side 
digit of the LCD display). Driver 68 is connected to counter 60 in the 
exact same manner as driver 65 is connected to counter 57. The outputs of 
driver 68 make up the segments a through g of the seven-segment digit of 
the LCD display that corresponds to the tens of hours of the clock (the 
extreme left-hand side digit of the LCD display). In order to allow the 
LCD numerals to appear on the display 64, the backplane input of drivers 
65 through 68 are each connected to the 60 Hz output of IC 52 via two 
inverting buffers 69 and 70. The purpose of inverters 69 and 70 is to 
allow connection of LCD drivers 65 through 68 without overloading the 
output of IC 52. 
FIG. 3, "Noon Test Circuit" 
The Noon Test Circuit, which is responsible for controlling the activation 
of a single siren cycle each day at 12:00 PM, is actually a cross between 
the two circuits already discussed in FIGS. 1 & 2. Specific outputs from 
the clock circuit are combined in such a manner that when 11:59:59 is 
present on the clock, a HIGH signal lasting a period of one second will be 
generated. This is accomplished as follows: 
1.) the `C` and the `D` output of counter 59 are NORed together by NOR gate 
106; 2.) the `B` output of counter 59 and ground are NORed together by NOR 
gate 107; 3.) the outputs of NOR gates 106 and 107 are ANDed together by 
AND gate 108; 4.) the `A` output of counter 60 and the output of AND gate 
108 are ANDed together by AND gate 109; 5.) the output of AND gate 101, 
the Q9 output of counter 55, the output of AND gate 103, and the output of 
AND gate 109 are all ANDed together by a four-input AND gate 110; 6.) the 
output of AND gate 110, the `A` output of counter 59, the Q5 output of 
counter 56, and Vdd (constant HIGH input), are all ANDed together by 
four-input AND gate 111. The output of AND gate 111 is sent to the `A2` 
terminal of switch 61, whose common terminal `C2` is connected to the SET 
input of NOR latch 113, whose ENABLE input is connected HIGH (to Vdd). The 
common point of linear set switch 114, which allows the user to direct one 
of ten circuits to a common point, is input to the RESET inputs of NOR 
latch 113 and D-latch 75, whose SET input is grounded and D input is 
connected to its own NOT Q output. Positions 1 through 10 of switch 114 
are connected to outputs 0 through 9 of CMOS decade counter 116 
respectively. The ENABLE input of counter 116 is grounded, while the CLOCK 
input is fed by the output of counter 54. The Q1 output of counter 116 is 
also connected to the CLOCK input of D-latch 75. The Q output of NOR latch 
113 is inverted by inverter gate 117, the output of which is fed to the 
RESET input of counter 116. 
When 11:59:59 appears on the BCD outputs of the clock circuit, it will 
cause the output of AND gate 111 to go HIGH. With switch 61 is in the A-C 
shunt position, the HIGH output of AND gate 111 will cause NOR latch 113 
to set. The resulting HIGH appearing on the Q output of latch 113 will 
cause the output of inverter gate 117 to go LOW. This will allow counter 
116 to begin incrementing. When the Q1 output of counter 116 is HIGH, it 
will provide a clock pulse to D-latch 75. This will cause the Q output of 
D-latch 75 to go HIGH. This output is then ORed together with the output 
of AND gate 73 by OR gate 74, whose output indirectly will cause the siren 
to sound, as discussed in FIG. 2, Part 1. When the user-preset value of 
counter 116 is reached, a HIGH output from the common point of switch 114 
will be sent to the RESET inputs of D-latch 75 and NOR latch 113, thus 
shutting down the siren after one cycle. It should be seen that the 
purpose of switch 114 is to set the gain time of the noon test siren, 
similar to the method used for the gain time of the siren during an alarm 
condition. A switch 115 is placed in series between the output of AND gate 
111 and switch 61, so that if opened, it will prohibit the system from 
sounding the siren for a noon test. The main purpose of switch 61 is to 
allow the user to set the time of the system clock. The second pole has 
been added to this same switch to prevent an accidental false noon test 
from occurring should the user, during the course of setting the clock, 
happen to advance the time to 11:59 at the precise time that the Q9 output 
of counter 55 and the Q5 output of counter 56 are both HIGH. A 1 K .OMEGA. 
resistor 118 has been connected between the SET input of NOR latch 113 and 
ground to prevent an accidental noon test activation while moving either 
switch 61 or switch 115 to another position.