Electrically fired displays bring a few more interesting facts into the equation. By firing each device electrically, you have complete
control over exactly when each will fire, as opposed to a handfired display in which delays in the quickmatch or fusing can cause unwanted gaps
in your show. In an electrically fired display, each device is rigged with an electric match.
Electric Matches
Electric matches use the concept of the lightbulb. They consist of a tiny bridgewire which is coated with a pyrotechnic composition
(which has a low ignition temperature). When a certain amount of electric current passes through the bridgewire, it heats up, quickly
passing the ignition temperature of the pyrotechnic coating. The flame which the pyrotechnic coating produces ignites the device in
question. In most cases, the e-match is stuck into a piece of quickmatch leading into a finale chain or directly into the lift charge of a
shell. The electric matches ignite fairly instantaneously due to the large amount of current that most pyrotechnic firing systems (see below)
put out. The "instantaneous" nature of electric matches allows for very precise firing of shells and related devices.
Firing Systems
Firing systems come in different sizes and with different capabilities. Being electrically inclined, I use firing systems which I
designed and built at all of my shows. Firing systems typically operate off of 24 volts, but can range anywhere from 9 volts to 200
volts. The number of shots you can shoot from each system can vary as well.
My 400 Shot System
My 400 shot firing system is the one that I most commonly use at all of my electrically fired shows. It utilizes a simple analog circuit
with a built in continuity check. There are 200 seperate copper contacts on the firing panel. When ever a contact is touched by the stylus
(similar to a pen), that cue will fire. For the 400 shots, there are 8 seperate slave modules, each of which has the capability to fire 50
shots. I have two kinds of slave modules; the box kind (seen in the pictures below) and the strip kind (not shown). The box is self explanitory,
and the strips simply consist of a cable with connectors at every 10.5"'s along the cable (used for shooting shows with mortar lines). Most firing
systems similar to the one I just described have one of two disadvantages. They either use 5 of the conductors in the firing cable as a ground
(which will eliminate 5 cues from each slave for a total of 40 less cues), or they will have a ground terminal on each slave in which you will have
to run ground wire back to the firing system from each slave (wastes alot of time and wire). So I designed my system to eliminate both of those
problems. It uses a ground terminal on each slave, however, attached to each firing cable is a ground wire which has a bananna plug on one end.
This bananna plug connects into a small ground junction box at the main firing box. This allows me to utilize all 50 conductors for actual shots in
each firing cable without wasting a bunch of wire each time. The ground junction box that I mentioned has two seperate rows with four terminals in
each row. The top row corresponds to shots 1-200 (slaves 1-4) and the bottom corresponds to shots 201-400 (slaves 5-8). With the flip of a switch
on the firing panel, the contacts go from being able to fire shots 1 through 200 to being able to fire 201 through 400. This way, only half
the space is used on the firing panel that would otherwise be needed for 400 shots (reverse polarity protection diodes prevent any sneak circuits
from occuring in this type of system). The built in continuity system sends a very low current through each electric match and beeps for each one
if you have a good connection. My system is powered by 24 volts. Here are some pictures for better understanding (Some are a little blurry since
they are screen captures off of a video):
Main firing panel
Closeup of the control switches
One of my slave boxes wired to a couple 3" mortar racks
Closeup of one of my slave boxes. Each of the stereo connectors corresponds to a cue #. The large 50 conductor connector in the middle is
the interface to the firing cable which will lead back to the firing panel.
