Fireworks Launch Box blows LED indicator status lights

Wolframore

Joined Jan 21, 2019
1,796
I've figured it out what he's doing with a single strand of 30ga is making his e-match.... this is a poor idea. Copper is not the correct material you want to use Ni-Chrome or resistance wire because you need higher resistance. This is why you can't light them off with 48V let alone 12V. I make my own also for model rocket launches and I aim for 0.5 - 1 Ohm and will fire off 3V... it's almost immediate on 9V.

Using a super light gauge (36-40ga) nichrome wire - doped with blackpowder to increase flame... you would be able to use 12V and much safer conditions.

40ga nichrome at 1/4" would give you about 1 Ohm resistance. It would burn quickly at 12V drawing almost 12A from a car battery and suitable wires.

Definition of squibs: In the North American film industry, the term squib is often used to refer variously to: electric matches and detonators (used as initiators to trigger larger pyrotechnics).

Per NASA: https://ntrs.nasa.gov/search.jsp?R=19620007196
Squibs.- The basic component in any pyrotechnic device is the squib, initiator, or detonator. A squib in its.simplest forms is shown
in figure 2. It consists of two electrical leads which are separated by a plug of insulating material, a small bridge wire or electrical resistance
heater, and a bead of heat-sensitive chemical composition in which the bridge wire is embedded. Application of an electric potential across
the lead wires causes the bridge to heat up, and this in turn causes the chemical composition to react, liberating chemical energy in the form of heat.

squib.jpg
 
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djsfantasi

Joined Apr 11, 2010
6,820
I've figured it out what he's doing with a single strand of 30ga is making his e-match.... this is a poor idea. Copper is not the correct material you want to use Ni-Chrome or resistance wire because you need higher resistance. This is why you can't light them off with 48V let alone 12V.

Using a super light gauge nichrome wire - they are usually doped with balckpowder to increase flame... you would be able to use 12V and much safer conditions.
That makes sense! In the past, I have used a short (1”) piece of wire from a sacrificial toaster at 12VDC.

I’ve seen 1/8W 1Ω resistors used as igniters for model rocketry. Maybe they would work here.
 

dendad

Joined Feb 20, 2016
3,602
You do need a current limiting resistor for LEDs. This is a common error, folks think of LEDs as low voltage lamps. They are current operated devices with a fairly constant voltage drop across them, Running without a resistor is a good way to kill them.

AND DO NOT USE THE MAINS!!!!!!!!!

How many comments against that do you need before you take heed? Of course, using the mains will work, but it is very dangerous and quite foolish. When someone gets killed, I can guarantee the insurance company will not pay, and you will most likely have a free state sponsored holiday given to you. I know if my kids were killed by your badly designed setup, I'd be really upset with you.

PLEASE do not use the mains!

An isolation transformer at least is needed. Making your system run at lower voltage is best too.

I am often amazed at people who come onto this forum asking for advice and ignore most of it because they want to do it their way, even tho' it may not work or is just plain dangerous.
 
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ebeowulf17

Joined Aug 12, 2014
3,274
You do need a current limiting resistor for LEDs. This is a common error, folks think of LEDs as low voltage lamps. They are current operated devices with a fairly constant voltage drop across them, Running without a resistor is a good way to kill them.

AND DO NOT USE THE MAINS!!!!!!!!!

How many comments against that do you need before you take heed? Of course, using the mains will work, but it is very dangerous and quite foolish. When someone gets killed, I can guarantee the insurance company will not pay, and you will most likely have a free state sponsored holiday given to you. I know if my kids were killed by your badly designed setup, I'd be really upset with you.

PLEASE do not use the mains!

An isolation transformer at least is needed. Making your system run at lower voltage is best too.

I am often amazed at people who come onto this forum asking for advice and ignore most of it because they want to do it their way, even thio it may not work or is just plain dangerous.
+1 on everything @dendad said!
 

Tonyr1084

Joined Sep 24, 2015
5,079
I use my gut on what would work and what not to use. I do extensive testing to ensure my system works and is safe. Is there a better, safer way? Undoubtedly.
The problem with the empirical method is that you judge the reasoning based on the outcome. What I mean is that when you observe a response, even repeatedly, you assume it's safe and reliable. It may be; it might not be. The problem comes when that one set of circumstances happen and suddenly you're faced with either a total failure of the system OR a sudden energetic release of all fireworks at one moment. The thing about "Gut Feelings" is that sometimes our guts get a little sick ( ill ) and can give us the runs. In the case of pyrotechnics, you can end up sending a lot of people running.

I was at a fireworks show three years ago when a mishap occurred. The fireworks were fuse launched. A hot ember fell on an unprotected fuse and ignited a cascading fire-off of all the fireworks. The crowd was thrilled at the "Finale" in the middle of the show. Trouble is that there was no "Finale" at the end. A large portion of fireworks were discharged uncontrollably. The show had been running for decades without incident. This goes to show that even under tight control, a tiger can sometimes get out of the cage. This is why we're concerned about your methodology and approach to this task. Unexplained or unexpected failure is a big issue when dealing with fireworks. Another great concern of ours is your use of 120 volts. On AAC 120 volts mains is a prohibited topic. Yet, we realize that mains are often needed to run our projects. We allow use of a transformer or other power supply to drop the voltage to our project voltage level and go from there. We even allow for switching mains voltage (when I say "We" I don't mean "Me included" I mean AAC) as a part of a project. But what concerns many of us (us common folk here on AAC) is the use of mains to fire off your display. So be cautious if you continue down that path. Like you, we've all (probably all of us) have been hit with mains voltage at one point in our hobby or career. I've been hit several times. Mains can be dangerous, and just because "Empirically" I haven't died yet - doesn't mean I'm safe. Nor does not having experienced a catastrophic failure of your system yet mean your system is safe. That's why we are employing you to take a different approach.

If I were to design a system I think I'd use some kind of gate or MOSFET to detect and indicate continuity between the firing circuitry. The LED can be controlled by a low voltage of 5 volts with a small resistor to give you plenty of indication a circuit is "LIVE", then when you fire off your cannon you do so with a much lower voltage, say 12 volts, and potentially more reliable than your current method.

Under the premises of 120 volts - what happens when someone comes in contact with a live line by accident? Like I've said, I've survived many accidental brushes with mains, but historically, many have not.

I used to fly model rockets. My squibs (electric matches) were professionally made and designed to work on two AA batteries. No continuity circuitry, just the match, battery and switch. If the rocket didn't launch then you knew there was a problem. In fact, many years ago I built a timer box with a sonic alert to give me a 20 second countdown. That gave me time to set the timer and run out to the field to recover the rocket. The kids LOVED catching their rockets when they came back down.

Anyway, please rethink your approach. There ARE better ways to do this. And be cautious with mains circuitry. You don't have to touch both lines to get bit. Damp grass and 120 volts mains can be just as lethal as touching mains and neutral (or ground, which is what wet grass is).
 

Tonyr1084

Joined Sep 24, 2015
5,079
Here's just one easy way to accomplish testing whether you have continuity through the squib (electronic match): 12 volts is supplied to both the LED and to the squib. If the squib is present and properly connected you will see a voltage on Q1's gate. That will turn the MOSFET on and the LED will light. When you press S1 (FIRE) button you will bypass R1 and cause the squib to ignite. If no squib is present then Q1 will remain off and the LED will not light.

The LED is a standard red LED with a typical forward voltage (Vf) of about 2.2 volts. Subtracting that from the 12 volts leaves you 9.8 volts. Divide that by the 1KΩ resistor (R2) and you see just about 10 mA current through the LED. That should be plenty bright at night. You may even want to go with a higher resistance for a dimmer LED. However, with the possibility of setting this display up during lighter hours, you may want to stick with the 10 mA current through the LED. If you use a different color LED you'll need to do the calculations. In fact, it's probably a good idea to do the calculations anyway, based on the LED you use. Don't just take the 2.2 Vf as a given value. ALL LED's have different Vf's.

The drawing below demonstrates what I consider a far safer system than using 120 VAC. There will be other issues to negate, such as wire gauge and run lengths, but they are minor in comparison to the system you're currently using.

01 ROCKET FIRE.png
 

Tonyr1084

Joined Sep 24, 2015
5,079
Looking at my drawing, I think there should be an "ARM" switch between the power source and the squib. That way you don't accidentally set off the firework when you're connecting it. Also, care should be taken to make sure whatever method you're using to connect to the squib (alligator clips is common among model rocketeers) make sure they are not touching, shorting together. This will give you a false indication of a good circuit.
 

ebeowulf17

Joined Aug 12, 2014
3,274
Here's just one easy way to accomplish testing whether you have continuity through the squib (electronic match): 12 volts is supplied to both the LED and to the squib. If the squib is present and properly connected you will see a voltage on Q1's gate. That will turn the MOSFET on and the LED will light. When you press S1 (FIRE) button you will bypass R1 and cause the squib to ignite. If no squib is present then Q1 will remain off and the LED will not light.

The LED is a standard red LED with a typical forward voltage (Vf) of about 2.2 volts. Subtracting that from the 12 volts leaves you 9.8 volts. Divide that by the 1KΩ resistor (R2) and you see just about 10 mA current through the LED. That should be plenty bright at night. You may even want to go with a higher resistance for a dimmer LED. However, with the possibility of setting this display up during lighter hours, you may want to stick with the 10 mA current through the LED. If you use a different color LED you'll need to do the calculations. In fact, it's probably a good idea to do the calculations anyway, based on the LED you use. Don't just take the 2.2 Vf as a given value. ALL LED's have different Vf's.

The drawing below demonstrates what I consider a far safer system than using 120 VAC. There will be other issues to negate, such as wire gauge and run lengths, but they are minor in comparison to the system you're currently using.

View attachment 178622
Seems like most fire control descriptions include secondary safety measures, like a lockable switch that prevents launches from any device.

I like your circuit overall, so maybe in this case there could be a keyed master switch which interrupts the ground path of all the launch switches? That way, safety and continuity checks could be done with power and LEDs available for all launch circuits, but nothing would fire unless the master switch was closed.
 

Tonyr1084

Joined Sep 24, 2015
5,079
I actually had in mind an "OFF" switch between the squib and battery.

I've heard a horror story about a solid rocket motor that was accidentally set off in the factory. This wasn't a model rocket motor it was full scale. The story goes (true or not) that when hooking up the ignitor they tie both leads together and tie them to ground. Static electricity is what set it off and ended up firing off the motor in-house. Whether that's true or not - it merits consideration when hooking up squibs to fireworks. Like I said earlier, you never know when that one set of circumstances is going to let the tiger out of the cage. Blocking all sources of DC may be a safety measure. Using an "OFF" switch probably should be done via a SPDT switch configured so that when it's "OFF" the squib is grounded and not left floating. After all, multiple lines could accidentally touch and set off the display. This brings to mind the possible need of a fuse as well. All things that should be considered carefully.
 

MisterBill2

Joined Jan 23, 2018
7,028
Here is a simple alternative scheme, but you will need an isolation transformer for it to function correctly. For checking the connection have a neon light such as a NE2 device in series with a 47,000 ohm resistor, wired across both switch poles. If both bulbs illuminate the circuit has continuity, if neither lights it is open, and if only one lights it is grounded some place. The benefit is a constant indication with very limited power, and not needing any additional battery power. Cheap, easy, safe, and simple. Just what you need..
 

Tonyr1084

Joined Sep 24, 2015
5,079
The Aerotech or the CTI incident?
Was a long time ago when I heard it. I couldn't answer your question.

@MisterBill2 Sorry, I don't see a schematic.

Woke up this morning with this silly project on my mind. I modified my schematic as follows: I've added a main power switch and a MASTER ARM switch. There's also two more LED's. A yellow LED indicating power is applied, a red LED to indicate the MASTER ARM switch is armed and I've changed the originally red LED to green indicating a READY condition. I've also added a capacitor, 4700 µF to give the match a hell of a kick when the fire button is pressed. That will reduce the likelihood of a misfire due to a tired battery. It may even prolong battery life.

[edit] Maybe S3 should be 10 amps. Regardless, the descriptions of the switches are arbitrary as long as they are double throw. Any set of switches that will handle the task should be fine. {end edit}

01 ROCKET FIRE.png
 
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Ylli

Joined Nov 13, 2015
978
Make S1 a key switch - one where the key is removable only when the switch is off. The key should be in the operators pocket when he is out near the fireworks. Now add a Schottky diode between the common of S2 (anode) and the common of S1 (cathode) so that when the POWER switch is shut off, it discharges C1. As it is, if the 'ARM' is left on and 'Power' is switched off, C1 might hold enough energy to set off the squib.

But considering what the TS is using as an igniter, R3 may need to be lower and/or C1 may need to be larger.
 

djsfantasi

Joined Apr 11, 2010
6,820
The only question remaining is if the TS will consider our replies? It seems that he knows that 120VAC works and since no one has been electrocuted, why change it?

His previous solution had no safety precautions, he used no protocol other than flip a switch, he believes mixing low voltage with high voltage is ok, and his status circuit works... one time.

He hasn’t replied in some time. I think we lost one to the Dark Side :(
 

Tonyr1084

Joined Sep 24, 2015
5,079
@Ylli discharging C1 was one of my concerns. Using the 100Ω resistor allows the cap to charge rapidly without the high inrush of current. When either switch (S1 or S2) is in the off position they are grounded, thus draining the cap as fast as it charged. Should either switch ground fail, current will still flow back through either (or both) of the LED(s) and again, discharge the cap.

The key switch is a good recommendation. The circuit I drew is somewhat similar to one I did so many years ago when my children and I were flying model rockets. We used a couple AA batteries to fire the squib and rocket motor. Even a simple two-battery system worked well enough to launch rockets. Of course, the wire was only about 10 feet long, so you were fairly close to the launch pad when firing. So I built a timer into my launch system. That way I could go down range and recover the rocket without having to sprint across a 100 yard field.
 

Tonyr1084

Joined Sep 24, 2015
5,079
I think we lost one to the Dark Side :(
I've been thinking the same thing. Nevertheless, I've endeavored to pursue the diagram because now I'm thinking of rebuilding a system and taking the grandchildren out for a Sunday Rocket Ride (launch). After all, what are Grandpa's for? The park is big enough to fly A size rockets. I just hope our TS hasn't discovered his system WAS flawed and "Empirically" he's discovered he's not so safe after all.
 

Tonyr1084

Joined Sep 24, 2015
5,079
Hey @amtrakusa are you still with us? Have we discouraged you? If we've discouraged you I hope it's from using 120 VAC. The diagram I did shows how simple (or complicated) a launch (detonation) system can be. OH WAIT! I HOPE YOU'RE NOT PLANNING ON BLOWING SOMETHING UP. GEEZ, I'D HATE TO BE A PART OF THAT.
 

djsfantasi

Joined Apr 11, 2010
6,820
Kinda off topic, but since this is used multiple times, I got to thinking...

A pair of Bluetooth modules are used. A microprocessor at the control station a) checks for the status of each pyrotechnic device (provided by the firing station), enables/disables a given P-device and sends an unique code from the control station to the firing station.

A class 1 module lets you be ~1,000 feet away; a class 2 module lets you be ~+30 feet away. Class 2 is safer.

Safety is enhanced by the requirement that a unique code is required before a P-device will fire. The code can be very long since only the two Microcontrollers need it. The longer the code, the less likely a random string can trigger the pyrotechnic.

The firing station can check for continuity of each device without firing it. It can communicate back to the control station that it is present, it is ready, the pyrotechnic device is ready, acknowledge firing commands, wait for an acknowledgement of its acknowledgement, fire the pyrotechnic AND acknowledge firing.
 
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