Pyrodigi,
there are a few things that you must consider when designing your firing system. The most important feature, which is something that many people overlook when designing their own systems, is that there has to be a way to stop the show in the event of an accident. I know that PyroDigital uses a "dead-man's handle" approach where you have to press a button continuously (some people call this "the pickle" for the show to fire. If you let go of the button, the firing modules stop initiating their e-matches (though the script continues to run). This feature means that if, for example, a rack of mortars fell over (for whatever reason) you could prevent them firing even after the script was started.
Another important feature is the ability to test the connections from the firing modules to their e-matches. This allows the pyrotechnician to diagnose any connection problems, find bad e-matches etc. The test current has to be kept to a very low level to be safe - yet another consideration you have to make in your design. You will also want to design the firing module portion such that it can safely initiate multiple e-matches at once and also in quick succession. Many people make the mistake of using a small 9V battery thinking it will be sufficient. While it will fire several e-matches at once, it probably won't have the capacity to fire multiple shots in quick-succession (unless you use some kind of capacitive discharge (CD) circuitry for each output). If you do use a CD based system, you will also need to provide a means to remove the charge from the circuits to put them back into a safe mode.
Finally, it is best to have a firing module which will shunt (i.e. short-out) the e-matches for safety during display setup. The shunt is removed when the display setup is complete. On some systems the two modes are called "shunted" and "armed".
Oh yes, one other thing, you will want to make sure your system can fire at a suffcient rate such that exciting effects are possible. You will want at least 16 firings per second, but many systems are capable of more than that (up to 100). If you use SMPTE time code, I think the resolution is 30 frames per second - so that would give you up to 30 firings per second.
Good luck with your project!
Paul. |