Precision pyrotechnic display system and method having increased safety and timing accuracy

REFERENCE TO EARLIER PATENT APPLICATION

This patent application claims the benefit of (1) pending prior U.S. Provisional Patent Application Ser. No. 60/079,853, filed Mar. 30, 1998 by Paul McKinley for ELECTRONIC PYROTECHNIC IGNITOR OFFERING PRECISE TIMING AND INCREASED SAFETY, and (2) pending prior U.S. Provisional Patent Application Ser. No. 60/095,805, filed Aug. 7, 1998 by Paul R. McKinley et al. for PRECISION PYROTECHNIC DISPLAY SYSTEM HAVING INCREASED SAFETY AND TIMING ACCURACY.

The two aforementioned documents are hereby incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to the control of the launch and burst of pyrotechnic projectiles in a pyrotechnic display. More particularly, the invention relates to the use of electronic components for the purpose of improving the accuracy of the timing of both the launch and the burst of the pyrotechnic projectiles. The invention further relates to the use of electronic components for the purpose of increasing the safety of both the pyrotechnic operator and the viewing audience.

BACKGROUND OF THE INVENTION

The professional fireworks industry has employed black powder-based pyrotechnic ignition systems for many years. These systems typically use a black powder fuse—cotton string or cord impregnated with black powder—to ignite a “lift” charge, which propels the projectile high into the air. The ignition of the lift charge also ignites a second black powder fuse, which provides a time delay to allow the projectile to reach a desired height above the ground. After the time delay of the fuse, the “break” charge is ignited, causing the particular visual or auditory effect of the pyrotechnic projectile.

Although black powder-based ignition systems are relatively easy to use, the fundamental limitations of the black powder fuse prevent the industry from achieving the timing accuracy and repeatability necessary for precisely choreographed pyrotechnic displays. This is because the burn rate—and hence the delay time—for a black powder fuse can vary considerably depending on the fabrication of the fuse, the particular materials used in the construction of the fuse, and on other parameters such as the temperature of the fuse at the time of ignition. U.S. Pat. No. 5,627,338 by Poor et al. teaches that the typical accuracy of the time delay of a black powder fuse is on the order of +/−16%. Controlling the delay time for a black powder fuse to better than +/−1% is extremely difficult; and even if this accuracy could be reliably achieved, it would still contribute to a total variability of 100 milliseconds for a 5-second fuse. That is, a +/−1% variation would cause a 5-second fuse to vary by +/−0.05 seconds, or a total variability of 100 milliseconds. Tests with pyrotechnic audiences have shown that most people can detect timing differences as small as 20 milliseconds, and half the people can detect timing differences as small as 10 milliseconds. Thus, in order to achieve precisely choreographed displays for certain types of pyrotechnic shells, particularly shells with a short burst time, the variability of the fuse's time delay must be held to better than 10 milliseconds, and preferably to about 1 millisecond. A variability of 1 millisecond represents an additional factor of 100, or +/−0.01% accuracy for a 5-second fuse. Achieving such accuracy is impossible with black powder fuses.

In addition, the inherent limitations of the black powder fuse also provide a source of potential failures that present real risk to both the display operators and the proximate audience. Pyrotechnic shells can be manufactured with the lift and break charges protected relatively well from external sources of accidental ignition by the use of protective layers around the charges. However, the use of a black powder fuse for the lift charge necessitates the exposure of the black powder to the external environment of the shell. Consequently the shell becomes much more sensitive to false ignition by burning materials from nearby pyrotechnic shells, resulting in unintentional “crossfire”. If the lift charge of a shell is ignited but the time delay fuse to the break charge burns too slowly, a “hangfire” occurs, in which the shell explodes as it returns to the ground, often near the display operator or in the audience. Even more dangerous, if a hangfire explodes after the shell hits the ground, both the explosion and the falling shell itself present significant risks to the operator and audience. If a fuse fails to ignite the lift charge, but the fuse continues to burn and ignites the break charge while the shell is still on the ground, a “mortar burst” can occur, and the ignition products of the break can potentially ignite the break charges of all the adjacent shells of the display. A break charge being ignited on the ground can result in serious injury to the operating personnel as well as the destruction of the entire display.

A number of alternatives have been proposed to eliminate black powder fuses or to improve their reliability. The most notable of these involves the use of electrically operated ignition devices, commonly called “electric matches” or “e-matches”. The construction and ignition of various forms of e-matches are described in U.S. Pat. No. 5,544,585 by Duguet, U.S. Pat. No. 5,123,355 by Hans et al., U.S. Pat. No. 4,409,898 by Blix et al., U.S. Pat. No. 4,354,432 by Cannavo' et al., U.S. Pat. No. 4,335,653 by Bratt et al., U.S. Pat. No. 4,267,567 by Nygaard et al., and U.S. Pat. No. 4,144,814 by Haas et al.

The use of an e-match to replace the black powder fuse for igniting a lift charge has the advantage that the exposed electrical wires are not susceptible to false ignition by sparks or other ignition by-products. Such use of the e-match reduces the likelihood of crossfires, but does nothing to improve the timing of the break since a black powder delay fuse would still be required to ignite the break charge. On the other hand, U.S. Pat. No. 5,627,338 by Poor et al., U.S. Pat. No. 5,623,117 by Lewis, U.S. Pat. No. 5,499,579 by Lewis, U.S. Pat. No. 5,335,598 by Lewis et al., U.S. Pat. No. 4,363,272 by Simmons, U.S. Pat. No. 4,239,005 by Simmons, and U.S. Pat. No. 4,068,592 by Beuchat describe methods to delay the firing action of an e-match based on electrical or pyrotechnic delays, but none of these methods are suitable to achieving the high accuracy required for choreographed displays. A method of using an e-match is described by Poor et al. in U.S. Pat. No. 5,627,338, but even this technique is limited to about 25 milliseconds variability, which is still a factor of 25 worse than the desired 1 millisecond variability previously discussed.

A number of problems or faults can occur during the setup of a choreographed pyrotechnic display. The pyrotechnic operator cannot easily detect many of these problems. If e-matches are used to replace the black powder fuses, new problems unique to e-matches are possible. For example, if e-matches are used to ignite the black powder lift charges, the electrical connections to the e-matches may be faulty. A common practice by the industry is to connect multiple e-matches to the same ignition source to allow multiple shells to be fired at the same time. Such multiple connections are done either in parallel or in series. If multiple e-matches are wired in parallel to a single electrical ignition source, the possibility exists that some e-matches will not be connected properly. On the other hand, if multiple e-matches are wired in series, the possibility exists that the electrical ignition source will be insufficient to ignite all of the e-matches.

If e-matches are used to ignite both the lift and break charges, additional problems may develop. For example, either or both of the e-matches may have broken wires. Furthermore, since an energy source is required to fire both e-matches (and the source for the break match must travel with the projectile), the possibility exists that either energy source may be insufficient to ignite its corresponding e-match. If, for example, the lift energy source is sufficient to ignite the lift charge, but the break energy source is not sufficient to ignite the break charge, a dangerous hangfire can result, with significant risk to the pyrotechnic operator and the audience.

Accordingly, a definite need exists for a method and system for launching and detonating pyrotechnic displays, which is capable of accuracy on the order of 1 millisecond, particularly for conventional shells that use black powder for the lift charge. A need also exists for increasing the safety for both the pyrotechnic operator and the viewing audience for conventional black powder shells. A need also exists for increasing the safety for pyrotechnic shells that use e-matches to ignite the charges. The present invention satisfies these requirements and additionally provides further related advantages.

OBJECTS AND SUMMARY OF THE INVENTION

In a broad sense, the present invention describes a method and system for controlling the launch and burst of pyrotechnic projectiles in a pyrotechnic display. More particularly, the present invention describes a method and system for increasing the safety and improving the accuracy of ignition timing for pyrotechnic displays.

An object of the present invention is to provide a system capable of achieving ignition timing accuracy to better than 1 millisecond for pyrotechnic displays. A further object of the present invention is to achieve such accuracy in ignition timing for pyrotechnic displays that use conventional black powder for the lift charge. An additional object of the present invention is to achieve such accuracy in ignition timing for pyrotechnic displays that use means other than black powder, such as pneumatic power, for launching the pyrotechnic projectile.

A further object of the present invention is to provide the capability to use standard pyrotechnic projectiles with black powder fuses for some, but not all, of the pyrotechnic display. Thus pyrotechnic operators can mix pyrotechnic shells utilizing the present invention with more conventional pyrotechnic shells in order to achieve the most cost-effective pyrotechnic display possible.

A further object of the present invention is to increase the safety of the pyrotechnic display for both the pyrotechnic operator and the viewing audience. A further object of the present invention is to reduce the potential of misfires and crossfires (i.e., the ignition of a projectile by the ignition products of nearby shells) by eliminating the traditional black powder fuse. A further object of the present invention is to reduce the potential of hangfires (i.e., shells that explode after returning to the ground).

A further object of the present invention is to provide the capability of reporting to the pyrotechnic operator the existence of faults within the system and to indicate which shells will not have their lift charge ignited because of the presence of these faults.

A further object of the present invention is to provide the capability to use multiple shells on the same ignition output and to provide the capability of reporting to the pyrotechnic operator the existence of faults in any of the individual shells.

While the present invention is presently intended primarily for use in improved pyrotechnic displays, the invention's advantages of increased safety and timing accuracy may be applied to other fields as well, such as construction and explosive demolition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

shows a mortar with a pyrotechnic shell that contains an ignitor module of the present invention.

FIG. 2

shows a block diagram of a complete pyrotechnic display system illustrating one embodiment of the present invention.

FIG. 3

shows the block diagram of an ignitor module of a preferred embodiment of the present invention.

FIG. 4

shows the block diagram of one embodiment of the interface module of the present invention.

FIG. 5

shows a flow chart for the system logic including the communications between the interface module and the ignitor module in one embodiment of the present invention.

FIG. 6

shows the detailed schematic of the ignitor module for one embodiment of the present invention.

FIG. 7

shows details of bi-directional communications, over a single pair of wires, between the ignitor and the interface module.

FIG. 8

shows the detailed schematic of the ignitor module for a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention involves a system and method for controlling the launch and burst of pyrotechnic projectiles in a pyrotechnic, or “fireworks,” display.

Pyrotechnic Projectile

FIG. 1

shows a typical pyrotechnic projectile

1

placed in mortar

2

. Projectile

1

utilizes load cord

3

to allow the pyrotechnic operator to easily place the projectile into mortar

2

. Embedded inside projectile

1

is ignitor

4

which is connected to the lift electric match (e-match)

5

and to the break e-match

6

. Wires

7

connect ignitor

4

to the pyrotechnic control system. Lift e-match

5

is embedded in lift charge

8

, which is typically made of black powder. Lift charge

8

, when ignited, provides the force to propel projectile

1

high into the air. Break e-match

6

is embedded in break charge

9

, which is also typically made of black powder. Break charge

9

, when ignited by break e-match

6

, causes projectile

1

to burst and provide the visual or auditory effect desired. Projectile

1

may contain additional pyrotechnic materials, such as stars

10

, which enhance the visual or auditory effect of the projectile.

Control System

FIG. 2

shows a block diagram of the control system. Control panel

11

is a manual control board which would be used by the pyrotechnic operator. Control panel

11

includes a key switch

12

for enabling the firing of the pyrotechnic shells. Use of key

13

allows the operator to remove the key to prevent accidental firing of the shells. The front panel of control panel

11

includes indicators

14

, typically incandescent lamps or light emitting diodes (“LED's”), which provide information on the status of the individual channels, or “cues.” The term “cue” has come into popular usage because of the interest in synchronizing the burst of the pyrotechnic projectiles with music. Although

FIG. 2

shows five cues on the front panel, in practice the control panel

11

will typically have many more cues, possibly as many as

20

to

40

. Control panel

11

also includes switches

15

that allow individual cues to be enabled for ignition at a particular time. The pyrotechnic operator will select one or more cues for ignition, observe the status of the cues, and then press firing button

16

, which initiates the ignition of the launch of the pyrotechnic shells for the enabled cue(s). After the firing of the previously-selected cue(s), the operator will select the next cue and again press the Firing Button

16

in order to initiate the launch of the shell or shells for that cue. By sequencing through the cues, the operator is able to use control panel

11

and firing button

16

to control the entire pyrotechnic display.

In

FIG. 2

, cable

17

connects control panel

11

to interface module

20

. Interface module

20

contains electronics that receive firing signals from control panel

11

and generates the necessary control voltages to fire the ignitors

4

in the pyrotechnic shells (FIG.

1

). These control voltages are passed through cable

21

to a distribution panel

22

. Interface module

20

includes additional display indicators

23

and

24

which provide information to the pyrotechnic operator of the status of each of the cues. Since interface module

20

is located closer to the pyrotechnic shells than control panel

11

, the display indicators

23

and

24

are used primarily during set up of the pyrotechnic display in order to verify that the system is wired properly. Interface module

20

also includes key switch

25

and key

26

to ensure that no power is applied to any ignitor

4

while people are loading the shells into the mortars. Interface module

20

is powered by battery

27

through cable

28

.

Distribution panel

22

includes connectors

29

, which allow the operator to hook up wires

7

(

FIGS. 1 and 2

) to connect the ignitors

4

to the control system.

Control panel

11

is assumed to be built in accordance with pyrotechnic industry standards for manual control boards. Specifically, any current applied to cable

17

for the purpose of measuring electrical continuity in a lift e-match

5

would be less than 50 milliamperes. Any current applied to cable

17

for the purpose of igniting lift e-match

5

would be greater than 250 milliamperes.

FIG. 2

also shows an optional computer system

31

that would be used in a second preferred embodiment. Computer system

31

includes keyboard

32

and monitor

33

, which is connected to interface module

20

by cable

34

. Computer system

31

would be used for automatically sequencing the firing of the projectiles in response to a computer program in coordination with other effects such as music. Manual control panel

11

would not be used if computer system

31

were controlling the pyrotechnic display.

In a third preferred embodiment (not shown), interface module

20

and distribution panel

22

are combined into a single package. This embodiment eliminates the need for cable

21

and provides a more compact assembly.

Ignitor

FIG. 3

shows a block diagram of ignitor

4

, which would be used for all three embodiments discussed above (i.e., a system utilizing manual control panel

11

; a system utilizing computer system

31

in place of manual control panel

11

; and a system combining interface module

20

and distribution panel

22

into a single package).

FIG. 3

also shows lift e-match

5

and break e-match

6

. Wires

7

connect ignitor

4

to the remainder of the pyrotechnic control system. Ignitor

4

contains four functional blocks, i.e., transient protector

40

, polarity detector

41

, energy storage element

42

, and control and timing circuitry

43

.

The purpose of transient protector

40

is to prevent electrostatic discharges or other transient high-voltage events from passing on to the remainder of ignitor

4

and possibly damaging ignitor

4

or accidentally firing either lift e-match

5

or break e-match

6

.

Polarity detector

41

ensures that voltages are of the proper polarity and currents flow to the ignitor circuitry regardless of the polarity of wires

7

. Referring back to

FIG. 2

, polarity detector

41

allows the operator to connect a pair of wires

7

to the corresponding pair of connectors

29

without regard to polarity. The use of polarity detector

41

thus simplifies the wiring task for the pyrotechnic operator and, more importantly, reduces the possibility of wiring errors.

The third functional block for ignitor

4

is energy storage element

42

, which preferably comprises a capacitor. Recalling that ignitor

4

is embedded in pyrotechnic projectile

1

, when the projectile is launched by the ignition of lift charge

8

, wires

7

will be broken. Thus, ignitor

4

will be electrically separated from the distribution panel

22

and any source of energy, such as battery

27

. Therefore, in order to ignite the break e-match

6

, a source of energy must travel with projectile

1

. Although energy storage element

42

could be a battery, the use of a capacitor is preferred for several reasons. First, a capacitor can weigh less than a battery. Second, a battery tends to be more expensive than a capacitor. Third, the capacitor is preferred for environmental reasons. Fourth, and most important, the use of a capacitor ensures that there is no source of ignition energy for either of the e-matches

5

,

6

unless the pyrotechnic operator has intentionally provided the energy from battery

27

by use of key switch

25

. The use of a capacitor for energy storage element

42

thus reduces the possibility of accidental ignition of the projectile

1

and increases the safety of the total system.

The fourth and final functional block for ignitor

4

is the control and timing circuitry

43

, which is a microprocessor-based electronic circuit that is responsible for the ignition of the lift e-match

5

and break e-match

6

. The control and timing circuitry

43

includes embedded software, or “firmware”, which receives information from interface module

20

concerning the desired time for ignition and returns information back to interface module

20

regarding the status of ignitor

4

. As is discussed in greater detail below, the firmware includes both safety and timing features. These features preferably include verification of the following: (1) both lift e-match

5

and break e-match

6

are connected properly; (2) no ignition takes place unless both lift e-match

5

and break e-match

6

are verified electrically; (3) no ignition takes place unless sufficient energy is stored in energy storage element

42

to ensure proper ignition; (4) after the lift e-match

5

is ignited, launch is verified by loss of input power from wires

7

; (5) break e-match

6

is not ignited unless launch has been verified; (6) no ignition of break e-match

6

will occur after a maximum time delay (to prevent hangfires); and (7) the timing of ignition of break e-match

6

occurs within 1 millisecond after the programmed delay following ignition of lift e-match

5

(i.e., the shell bursts within 1 millisecond of its intended time).

It should be appreciated that, with respect to the timing delay between activation of lift e-match

5

and break e-match

6

, this timing delay can either be (1) pre-programmed into the embedded software, or “firmware”, of the ignitor's control and timing circuitry

43

, or (2) programmed into ignitor

4

at the time of use by the control system, e.g., by computer system

31

.

Interface Module

As shown in

FIG. 4

, the block diagram of interface module

20

includes six functional blocks.

Front panel

50

of interface module

20

includes fault indicators

23

and ready indicators

24

that show the status of each of the system cues. Fault indicators

23

and ready indicators

24

can be made from incandescent lamps, light emitting diodes (LED's), or other suitable visible devices. Front panel

50

also includes key switch

25

and key

26

which can be used by the pyrotechnic operator to enable or disable ignition of the pyrotechnic shells. By putting key switch

25

into the “Safe” position and removing key

26

, the pyrotechnic operator can ensure that no ignition is possible while pyrotechnic projectiles

1

are being installed in mortars

2

.

The second functional block of interface module

20

is input current detector

51

, whose purpose is to detect if any electrical current is being drawn from cable

17

(

FIG. 2

) for any cue. Furthermore, input current detector

51

determines if the current is less than 50 milliamps (corresponding to a continuity test) or is greater than 250 milliamps (corresponding to a Fire command).

The third functional block for interface module

20

is output control switch

52

, whose purpose is to communicate if any ignitors

4

are connected to the particular cue. Such communication is bi-directional in nature. Output control switch

52

is further responsible for providing continuity current (less than 50 milliamps) and firing current (greater than 250 milliamps) if standard lift e-matches

5

are directly connected to the cue.

The fourth functional block for interface module

20

is controller

53

, a microprocessor-based circuit that supervises the entire operation of interface module

20

. Controller

53

receives input information from input current detector

51

and generates output signals for output control switch

52

. Controller

53

also receives status information from ignitors

4

and communicates that status information back to the control panel

11

through input current detector

51

. Controller

53

further reads the state of key switch

25

and displays status information on front panel display

50

. Additional details of the communication between interface module

20

and other parts of the pyrotechnic control system are discussed below.

If the pyrotechnic display is being controlled by computer system

31

, rather than control panel

11

, communications between controller

53

and computer system

31

are handled by I/O module

54

.

The final functional block of interface module

20

is power converter

55

, which draws power from battery

27

and provides regulated voltages for the remaining functional blocks of interface module

20

.

System Logic Flow

FIG. 5

shows the system logic flow diagram, including interaction between interface module

20

and ignitors

4

. The use of microprocessors in both interface module

20

and in each ignitor

4

allows diagnostics to be performed in multiple locations and further provides for a high level of communication between different microprocessors. Furthermore, each microprocessor is capable of performing tests to verify that commands are consistent with operating conditions. For example, the microprocessor in each ignitor

4

is able to determine if all conditions necessary for a successful launch and burst of the pyrotechnic projectile are being satisfied and is further able to communicate that information back to interface module

20

.

Upon power-up, interface module

20

executes a series of self-tests to confirm that all operating parameters, including input and output ports, are functioning properly. If so, interface module then examines its individual output ports to determine if any ignitors

4

are connected. If an ignitor(s)

4

is found, interface module

20

applies a current-limited voltage to ignitor(s)

4

and requests status information. Should interface module

20

not receive a “valid ignitor” response on any port for which it previously detected the presence of an ignitor

4

, it will disable, and signal a “fault” condition for, that particular port. Should interface module

20

detect multiple ignitors

4

on a given port, it will instruct all ignitors

4

on that port to generate a random number within a certain range as an identification (ID) number. It will then poll the port, sequentially stepping through subsets of the designated range, to ascertain the individual ID of each ignitor

4

. Should more than one ignitor

4

return an ID within any one range subset, interface module

20

will instruct all ignitors

4

within that subset to re-generate a new random number ID within the range of that subset. Interface module

20

will then re-evaluate the ignitors

4

utilizing a higher resolution. This process will repeat until each ignitor

4

is assigned a unique ID number. All further communications between interface module

20

and each ignitor

4

utilize this ID to ensure unique ignitor communications.

In one embodiment of the present invention, the operating frequency of ignitor

4

is controlled by a resistor and capacitor combination. Since resistors and capacitors are generally not of high accuracy, the resulting frequency will vary from one ignitor

4

to another. Since the time delay-of ignitor

4

is generated by counting cycles of its operating frequency, the time delay will depend directly on the value of the resistor and capacitor. In order to improve the accuracy of the time delay, interface module

20

next sends a timing calibration sequence to each ignitor

4

. This sequence includes an accurately controlled pulse, 400 milliseconds in the preferred embodiment, which is measured by each ignitor

4

. The ignitor

4

counts cycles of its operating frequency during the controlled pulse and reports the number of counts back to interface module

20

. This process allows interface module

20

to indirectly measure the operating frequency of each ignitor

4

and to verify that the frequency is within acceptable limits. If the operating frequency of any ignitor

4

is outside the acceptable limits, interface module

20

will disable the respective output port and signal a “fault” condition. Assuming that the calibration sequence produces measurements within the acceptable limits, ignitor

4

will then use the results of the measurement of the controlled pulse to compensate for the inaccuracy of the operating frequency and to modify the pre-programmed time delay to improve the overall accuracy of the system. Then, as long as the operating frequency of the ignitor

4

remains constant, the time delay will be accurate. Experiments have shown that time delays of up to 5 seconds, accurate to better than 1 millisecond, can be obtained even if the operating frequency of the ignitor

4

is only accurate to + or − 20%.

In a second embodiment of the ignitor

4

, the operating frequency is determined by a more accurate crystal rather than a resistor and capacitor. As a result, the calibration process is not necessary in order to produce accurate time delays. However, the calibration process can still be used in order to verify the proper operation of ignitor

4

and to verify that the oscillator frequency of ignitor

4

is consistent with the crystal.

Having completed the evaluation of all ignitors

4

connected to the output ports, the interface module

20

then enables all output ports not previously disabled, turns on the respective “Ready” lights

24

on front panel

50

and provides a closed circuit at input current detector

51

that can be detected from control panel

11

as “continuity”. This provides the pyrotechnic operator with remote indication (at control panel

11

) of the status of all ports of interface module

20

.

Interface module

20

next enters a program loop whereby it continuously looks for the receipt of a valid “fire” command at input current detector

51

. Upon receipt of a “fire” command, interface module

20

confirms that the respective output port has not been disabled through failure of any previous test and validation sequence.

If the output port has not been disabled, interface module

20

issues an “arm” command to all ignitors

4

attached to the respective port and waits for confirmation from all ignitors

4

attached to that port that they have received a proper “arm” command and have entered the armed state. If any failure occurs in an ignitor

4

, interface module

20

will disable the respective port and indicate a “fault” on front panel

50

.

For all armed ports, the interface module

20

next issues a “fire” command. Upon receipt of a “fire” command, each ignitor

4

evaluates the “fire” command to ensure that it meets all protocol requirements. If the “fire” command does not meet protocol requirements, the ignitor

4

will return a “fault” command and immediately disable itself. If the “fire” command does meet protocol requirements, the ignitor

4

will fire lift e-match

5

and immediately check to see if the data/power cable has been disconnected, an expected result of the shell having lifted and broken the cable. Should the ignitor

4

detect that it is still connected to the interface module

20

, it will assume that the lift charge failed to ignite, return a “fault” command to interface module

20

and immediately disable itself. If the ignitor

4

does detect a successful disconnect, it will enter its timing sequence until it reaches the programmed delay, upon which it will fire its break e-match

6

match, thereby igniting the pyrotechnic break charge and causing the shell to appear in the sky.

After the break e-match

6

ignites the break charge, the entire ignitor

4

will be destroyed. However, in case the ignition did not occur, ignitor

4

will wait a short period of time and then apply high current loads to the ignitor's microprocessor output ports in order to discharge energy storage element

42

. In this manner, the source of energy to ignite break e-match

6

will be eliminated and the possibility of a late ignition of the break charge, termed a “hangfire”, will be greatly reduced.

As an additional safeguard, the interface module

20

monitors the current flow through all ports which have been issued a “fire” command. If it detects any ignitors

4

still connected, it will disable that port and signal a “fault” condition on front panel

50

in order to notify the pyrotechnic operator that a particular mortar still holds a live pyrotechnic projectile

1

.

Detailed Circuit of One Form of Ignitor

FIG. 6

shows the detailed circuit schematic for ignitor

4

for one embodiment of the present invention. Capacitor C

1

provides protection from electrostatic discharges or any other voltage transients that may occur on the input wires at connector J

1

. Diode pairs D

1

and D

2

are configured as a full wave rectifier and ensure that the voltage that appears at the cathode of D

2

is always positive. The use of diode pairs D

1

and D

2

allows the pyrotechnic operator to connect the two wires for ignitor

4

without regard to polarity. Resistor R

1

limits the current into capacitors C

5

and C

6

, which are isolated from each other by dual diode D

3

. When an input voltage of nominally 12 volts appears on the input wires at connector J

1

, the C

5

and C

6

capacitors begin to charge up. Capacitor C

5

provides energy storage for the break e-match

6

, which would be connected to ignitor

4

at connector J

2

. Thus capacitor C

5

is energy storage element

42

previously discussed and shown in FIG.

3

. Capacitor C

6

provides energy storage for lift e-match

5

, which is connected to ignitor

4

at J

3

. The use of capacitor C

6

ensures that sufficient peak current will be available to ignite lift e-match

5

even though resistor R

1

and any additional wire resistance in the input wires would otherwise limit the current available. Darlington transistor Q

2

provides an electronic switch to connect break e-match

5

to capacitor CS. Resistor R

2

connects output pin

8

of microprocessor U

1

to the base of transistor Q

2

. Thus resistor R

2

allows microprocessor U

1

to ignite the break e-match

5

by applying a five-volt signal to output pin

8

and turning on transistor Q

2

. Resistor R

4

ensures that transistor Q

2

will not be accidentally turned on when the output pin

8

of microprocessor U

1

is initially open-circuited during the power-on initialization of microprocessor U

1

. Transistor Q

3

provides an electronic switch to connect lift e-match

5

to capacitor C

6

. Resistor R

3

connects the base of transistor Q

3

to output pin

7

of microprocessor U

1

. Thus microprocessor U

1

can fire the lift e-match

5

by applying a five-volt signal to pin

7

. Resistor R

5

ensures that transistor Q

3

will not be accidentally turned on when output pin

9

of microprocessor U

1

is initially open-circuited during the power-on initialization of microprocessor U

1

. Resistors R

7

and R

12

provide a resistor divider to monitor the voltage on the collector of transistor Q

2

. If capacitor C

5

is charged, the voltage at the collector of transistor Q

2

will be approximately 10 volts if break e-match

6

is connected properly. If break e-match

6

is broken or if the wires to break e-match

6

are disconnected, the voltage at the collector of transistor Q

2

will be approximately zero volts. Thus, the use of resistors R

7

and R

12

allows microprocessor U

1

to determine if the break e-match

6

is operational by monitoring the voltage at input pin

9

. In a similar manner, resistors R

8

and R

13

allow microprocessor U

1

to determine the status of lift e-match

5

by monitoring the voltage on pin

6

of microprocessor U

1

.

Voltage regulator U

2

provides a constant five-volt output at pin

3

. Capacitor C

4

provides a small amount of energy storage to ensure that when the break e-match

6

is ignited, the sudden load on capacitor C

5

does not disturb the power source for microprocessor U

1

. Voltage regulator U

2

is necessary because the operating frequency of the particular type of microprocessor, a PIC16C505, varies as the voltage at pin

1

of microprocessor U

1

changes. Thus, voltage regulator U

2

ensures that the operating frequency remains constant and that the accuracy of the time delay is maintained even if the voltage on capacitor C

5

varies. Resistor R

14

and capacitor C

3

are the components that determine the operating frequency of microprocessor U

1

. As previously discussed, the accuracy of the time delay is improved by the timing calibration process.

The connection of pin

3

of microprocessor U

1

to ground allows microprocessor U

1

to rapidly discharge capacitor C

5

by trying to drive pin 3 to 5 volts. The high current at the output port pin

3

will cause the supply current at pin

1

to increase. This in turn will cause a higher load current for the voltage regulator U

2

and will discharge capacitor C

5

.

Resistors R

1

and R

6

form a resistor divider that allows microprocessor U

1

to sense a successful launch of the pyrotechnic projectile

1

. As long as power is applied to ignitor

4

through connector J

1

, the voltage at pin

11

of microprocessor U

1

will be five volts. However, when the lift charge is ignited and the shell is launched, wires

7

will break. At this point, the voltage at pin

11

of microprocessor U

1

will drop to zero volts, and can be detected by microprocessor U

1

.

Communication Between Ignitor and Interface Module

Transistor Q

1

and resistor R

15

provide a means of communication from ignitor

4

to interface module

20

. Capacitor C

2

and resistors R

9

and R

10

provide a means of communication from interface module

20

to ignitor

4

. The operation of this method of bi-directional communication over a single pair of wires, that also supply power, is best understood by looking at FIG.

7

. Interface module

20

contains components Dx, Rx and Swx. Dx is a diode that provides the source of power (12 volts) for ignitor

4

through wire

7

a

. Wire

7

b

provides a ground return path to complete the power connection. Switch Swx, under control of the microprocessor in interface module

20

, momentarily closes, causing the voltage at the cathode of diode Dx to become 20 volts. The quiescent value of the voltage at point B is nominally zero volts. When switch Swx closes, the 8-volt increase in the voltage on wire

7

a

is coupled by capacitor C

2

, through resistor R

9

, to point B. Thus, the voltage at point B will increase by 8 volts whenever switch Swx is closed, and will return to zero when switch Swx is opened. Resistor R

9

ensures that any over-voltage at point B, which is connected to an input pin of microprocessor U

1

of

FIG. 6

, does not adversely affect microprocessor U

1

. Resistor R

9

further ensures that if the voltage at B becomes less than zero, microprocessor U

1

is not adversely affected. Note that resistor R

1

, in conjunction with capacitor C

5

, reduces the switch current at switch Swx and further reduces any voltage change on capacitor C

5

due to the low-pass filter nature of the circuit. Thus, pulses in the range of 1 microsecond to 100 milliseconds can be easily sent from interface module

20

to ignitor

4

with the particular component values chosen for the circuit. Communication in the reverse direction (from ignitor

4

to interface module

20

) is accomplished with components transistor Q

1

, resistor R

15

and resistor Rx. The voltage at point A is normally five volts and transistor Q

1

is off. At that point, the current in wire

7

a

supplies the operating current for ignitor

4

, which is a relatively small and constant value. As a result, Vx, the voltage across resistor Rx, is also a relatively small and constant value. When the voltage on point A is pulsed to zero volts, additional current flows through transistor Q

1

, causing the voltage across resistor Rx to increase. This increased current may be smaller than, or even much higher than, the nominal operating current for ignitor

4

. By monitoring voltage Vx, the microprocessor in interface module

20

can receive information from ignitor

4

by using pulses at point A in the range of 1 microsecond to 100 milliseconds. Note that diode D

3

prevents any current in transistor Q

1

from being drawn from capacitor C

5

. Thus bi-directional pulsed communication can be accomplished with a pair of wires which are also supplying power. Not shown in

FIG. 7

are the two diode pairs D

1

and D

2

in

FIG. 6

which form the full wave rectifier and allow wires

7

a

and

7

b

to be connected in reverse to ignitor

4

. Diodes D

1

and D

2

do not adversely affect the bi-directional communication method.

Detailed Circuit of Alternative Form of Ignitor

FIG. 8

shows the detailed schematic of ignitor

4

in a second embodiment of the present invention. This version of ignitor

4

is quite similar to the embodiment of

FIG. 6

in a number of ways. The similarities include the input protection, full wave rectifier, energy storage, voltage regulation, and lift e-match

5

and break e-match 6 drivers.

The schematic of

FIG. 8

differs from that of

FIG. 6

in the following ways. First, there is no provision for bi-directional communication between ignitor

4

and interface module

20

. Second, ignitor

4

uses a different firing protocol from interface module

20

. This protocol, used by the Fire One Computerized Fireworks Shooting System from Pyrotechnics Management, Inc., State College, Pa., provides 12 volts for testing continuity (that is, presence of either an ignitor

4

or a lift e-match

5

) and 24 volts for firing the ignitor

4

or lift e-match

5

. Resistors R

13

and R

14

form a resistor divider to detect the 24-volt firing signal. Resistors R

4

and R

5

form a second resistor divider that detects a successful launch by removal of the input voltage. Diode D

9

and resistor R

15

provide clamping to ensure that the input pin that detects power loss (microprocessor U

1

pin

11

) does not become damaged when the input voltage increases to 24 volts to signal the fire command. Q

3

is a crystal that provides increased accuracy over the resistor-capacitor oscillator of the

FIG. 6

circuit. Capacitors C

1

and C

2

are required by the internal crystal oscillator of microprocessor U

1

. Resistors R

2

and R

3

provide a resistor divider that is used to measure the voltage on capacitor C

4

, the energy storage element

42

. Upon receipt of a fire command, microprocessor U

1

checks that the voltage on capacitor C

4

is sufficient to provide enough energy to ignite break e-match

6

before igniting lift e-match

5

. The schematic of

FIG. 8

thus represents an ignitor

4

that provides increased safety and timing accuracy but does not use extensive communication capability. Thus

FIG. 8

describes an ignitor that appears more like a conventional electric match but with increased safety and timing accuracy.