Help with adding an LED indicator to my fireworks ignightor

I find it hard to believe the resistor becomes a short. I would have expected it becomes open. In any event, why not use nichrome wire as an igniter?

I would have expected it to open too, but having done this several times, every one of them is just shorted, not open (at least according to my DMM). I played with the nichrome wire, but found it more difficult to work with and the only advantage was it was slightly faster to burn. I know most fireworks guys that don't use professional ematches use nichrome, but I'm sticking with resistors at this point.

I will say that most of the firing panels that fireworks DIY'ers do are based on nichrome ematches and I'll probably have to go in that direction if/when I want to take my fireworks shooting to the next level.

Having thought about this question a bit more, I realize that the circuit as I described it (with a momentary pushbutton) won't have current running through it until the button is pushed, so adding in the LED won't be as straight forward as I thought. I guess I should probably stick with no indicators for this year and build a proper firing panel next year.

The problem I see with the present design is you need a "current sense" scheme, and these generally increase the resistance in the circuit. That is, you would not want your test circuit to make it less likely the fuse gets popped. If your fuse popped open, lots of circuits come to mind. Since it pops in a short, I have to wonder how low of resistance is this short. I just don't think I can come up with anything reliable.

If you popped surface mount resistors, I bet they would open up. However, nichrome seems like the better solution.

I know some crappy tantalum surface mount caps catch fire if presented with overvoltage. ;-)

I would also expect that the resistor would open instead of shorting. In fact, I suspect you're misreading the DMM. Try putting it in series with a test light to verify it's really shorted.

I recall from my teenage days using model rocket igniters for most large improvised explosives. At least when cannon fuse wasn't handy. I'm honestly surprised I survived with all my body parts intact...

Chris

Here's the simplest design I can think of.

Let's say your igniter (and associated wire leads) varies between 10 ohms (not on fire) and 1 ohm (on fire).

Put a fixed resistance of, say, 1 ohm in series with your igniter. Then put a small 12v indicator bulb in parallel with the igniter.

When your igniter is not on fire yet, your bulb will be bright. When your igniter is on fire, your bulb will be either very dim or completely off.

LED with resistor can be substituted for bulb, but why bother?

I'm going to assume open circuit when that resistor blows..

How about...

Put (LED with series R) across fuse..It won't light until the fuse burns. This is the burnt fuse indicator. Also... Put (LED with series R) across switch. This is the fuse connected indicator..

Initially, there will be one LED lit. Fuse is ready to go. After firing, one LED will go out and then the burnt fuse LED will light. After switch return, both LED's will be lit. D from BC

Reminds me of the day I used a 4017 to blow firecrackers sequentially :) D from BC

It might be useful to put a snubber diode across the LED in the event there is an inductive kick. Long wires and pulses...you get the idea.

I was reading about something similar today:-

regards, IanM

Unfortunately that seems to lead to a dead link, but you can find "Big Clive" on 'rec.arts.theatre.stagecraft'.

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John B

Ahh.. I think that's an example of "it's easier to add a cheap part than to do the analysis"

My gut feeling is that an LED in series with a resistor can handle the brief spike induced into 100ft of 18ga wire at the current once used. But I could be wrong.. D from BC

Nice! Here's the drawing of your idea for the op, and a sort of "truth table".

+--[470R]--[LED1]---+ | _ | +12 ---+-------o o---------+--------+ | | [470R] | | [10R] [LED2] | | | Gnd -----------------------+--------+

LED1 | LED2 | Button | Indication ------|--------------------- On | Off | Not Pressed | System Ready ------|--------------------- Off | Off | Pressed | Firing Initiated ------|------|--------------- Off | On | Pressed | Fuse burned, button pressed ------|------|--------------- On | On | Not Pressed | Fuse burned, button not pressed ------ ------ -------------

Wow - thanks! I've got some good ideas to try out. Have a great (and safe) July 4th!

Yes - use actual squibs:

And maybe lurk in rec.pyrotechnics for awhile.

Good Luck! Rich

LEDs are sensitive to reverse bias. Most have a 5V limit.

"John B" wrote in news:46829886$0$22489$ snipped-for-privacy@master.news.zetnet.net:

try rec.model.rocketry,they use an electrical launch system,make their own igniters for their model rockets.

what you want is a continuity tester.

--
Jim Yanik
jyanik
at
kua.net

Is that reverse blocking up to 5V? After 5V, the LED breaks down and conducts. Like a zener I suppose.. But wouldn't a series resistor limit reverse breakdown mode energy at the LED? Or is there more going on like a solid state chemical reaction that damages the LED (not from heat)? D from BC

I hope it's only fireworks.. :( D from BC

Probably - Independence Day is coming, but Canada doesn't seem to have an equivalent, so you probably don't understand.

Cheers! Rich