From: "Dave VanHorn"
References: <firstname.lastname@example.org> <email@example.com>
Subject: Re: Computer Controlled Pyrotechnic Firing Panel
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NNTP-Posting-Date: Wed, 04 Sep 2002 00:28:10 CDT
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Date: Wed, 04 Sep 2002 05:28:10 GMT
The main thing that I would caution you on, is that you design in a
dual-redundant safety mechanism that absolutely prevents ignition until it
is explicitly bypassed.
I've done some ignition controls for rocketry (not model rockets) and maybe
I go a bit overboard, but then agian, I've never had a problem.
The general approach that I use is that there has to be two different
mechanisms to prevent ignition, that require manual intervention. For
example, my launch controller uses a key switch (a real one, not a PC
cabinet thing) and two momentary buttons. I have to turn the key to apply
any power at all to the system. The two pushbuttons must be depressed at
the same time to effect a launch.. When the key is turned, a loud piezo
siren sounds at the remote head, located at the pad.
When saftied, there is no source of current to the remote head, and the
ignitor is shorted out at the remote head, preventing any current that gets
past the first safety from firing the ignitor.
If you handle the lockouts properly, then the worst the PC can do is fire
the wrong devices at the wrong time. That's maybe expensive and embarrasing,
but not fatal.
What I'd imagine in your application is a number of remote heads, each with
it's own local safties, then a master safety that requires that all local
safties be off before it can be turned off. You would activate each head as
you leave the field, in a planned "escape route".
The touchy part is verifying a good ignition circuit.
That can't be done any other way than putting current through the ignitors.
The trick of course is to make absolutely sure that there is no possible way
to get anywhere near the firing current, even with a fault in the circuit.
From what I've seen, crewing a couple of shows, you might have 10-100+
ignitors in the system, and this certainly gets complicated.