Will this work - fireworks ignitor schematics

[newtothis]

Hello everybody,

This is an update (25 jan.) I found my answer elsewhere, but I will post it here for other interested parties.
Thanks to all that tried to help me.
schematic is appended - I try to remember to post a Picture of the reallife model, when I get the missing components and make it - maybe even a youtube demonstration.

I errorneously thought that the max output of a AA battery was 2A, but it turns out that you can Draw much more (20A has been reported!)- offcourse you need to ensure the battery doesn't overheat - this is not a problem with this design as it only are used for 2 sec and the Draw is only increased to 3A.

My math on the capacitor wasn't wrong so I have removed the capacitor - unfortunately this Means that the ignitor cannot be expanded to fire more fireworks simultaneously as planned - so far the only answer is a larger power supply. or strip a disposable camera (http://www.instructables.com/id/Not-your-ordinary-electronic-detonatorWith-Altoid/) - I'm not sure this Works solely by the large capacitor - or because the wires are very thin.

I decreased the nichrome lenght from 10cm to 5cm (1/3feet - 1/6feet) this lowered the resistance with 5ohm (I have seen fuses pierced with wire into the BP core, where the total length is less than an 1/3 inch decreasing resistance to 0,5Ohm this could be used to increase simultaneously capacity - but not something I'm going to consider as it seems brittle and prone to errors.)

purpose of the schematics (is attached)
The ignitor needs a LED diode that light up (D1) when power is ON (s2). I use 2 seriel AA as a power source.
The voltage will be stepped up (T1 - step up module/chip up to 7VV).
The system is armed with second switch (S1).
R3 and R4 represents 2* 90ft wires connecting (total of 2ohms)to a nichrome wire (R2~5hm).
so a system that is ON and armed can heat up the nichrome wire and ignite the fuse when S1 is pressed (2 seconds should be enough)

so total resistance is around 7ohms (there is a slight increase of the nichromewire as temp increases)
Voltage is 7VV
Amps needed is 1A across the nichrome wire.

(Nichrome Data)
http://hotwirefoamcutterinfo.com/_NiChromeData.html

[IanB]

Please don't try and do this.

Not only might you cause harm to yourself and others, you might also find yourself on the wrong side of the law if anyone does get injured.

Leave fireworks to the professionals, or light home fireworks by hand with a match--it is much safer that way.

[newtothis]

Thank you for taking your time to answer.

And while I can appreciate your concern  I would prefer we skipped the morale lecture as you have gotten the wrong idea of the purpose of this detonator.
but for your ease of mind this is a fuse ignitor not a detonater despite its name. and it is most certainly not going to be used for homemade fireworks - or other illegal fireworks

but thanks the same

[Andy Watson]

Look up "electric match" and in particular look at the rocketry websites. Somewhere on this site is all the information you need to use them.

http://aeroconsystems.com/

[apelly]

Where do you attach the cell phone?

[AG6QR]

A transformer won't step up a DC voltage.

You have no current-limiting resistor on your LEDs D1 or D2, so they will burn out when voltage is applied to them (but voltage won't be applied to D2 because the transistor won't turn on).

Your capacitor is apparently expecting a DC voltage out of the transformer, which it won't see.

The primary and secondary sides of the transformer are not connected, except through the transistor.  The transistor's emitter and collector are connected to the primary side, and the base is connected to the secondary side, but there is no other connection to establish a common reference voltage between the two sides.  With no return path, current can't flow through the base.

[Nerull]

Hello everybody,

I'm looking to make a fireworks detonator, but I'm really new to diy Electronics. I have made some research into basic Electronics and come up with this detonator schematic.(I have forgotten to add resistors in front of the diodes to regulate current)
I don't care for a bulky power source so it thought about Stepping up the voltage of a normal battery and using a capacitor. but my math seems to be screwed up because my capacitor needs to be ~6 fahrads - an insanely high amount.

purpose of the schematics (is attached)
The detonator needs a LED diode that light up (D1) when power is ON (s1). I want to utilise a 9V as a power source.
The voltage will be stepped up (T1) (got a step up module that can go up to 34V).
The higher voltage will charge an electrolytic capacitor (C1).
The system is armed with second switch (S2).
When the capacitor is charged voltage will drop at the base of PNP transistor (Q1) and FLow will allow LED diode (D2) to light up. but only if S2 is ON.
R1 and R2 represents wires connecting (total of 2ohms)to a nichrome wire (R3~9hm).
so a system that is ON and armed can heat up R3 when S3 is pressed for min. 2 sec before capacitor is discharged.

so total resistance is around 11-12ohms (there is a slight increase of the nichromewire as temp increases)
Voltage is 34V
Amps needed is 1A across the nichrome wire.

I have a few questions:
1 - Is there any errors in the schematics beside I havent added resistors?
2 - The base of the transistor needs to be grounded - not sure how this is done in a portable box - just continue wire to the negative terminal?
3 - How many Fahrads does my capacitor needs to be to sustain a 2 second burst? please feel free to explain the math as 6Fahrads seems excessive.
4 - I Also have a 1V-5V step up module what can make this Work with 5V?
5 - finally do a capacitor store a larger charge at a higher voltage - or have I misunderstood how fahrads Works.
6 - Anything else I have forgotten?


Thank you very much for any help

(Nichrome Data)
http://hotwirefoamcutterinfo.com/_NiChromeData.html

http://www.pratt-hobbies.com/proddetail.asp?prod=GO-12

Simple is best for these sorts of things, don't overcomplicate it. EMatches are much lower current and much more reliable than nichrome ignitors but are not as cheap and can be easily set off accidentally if you do any sort of continuity check without properly designing it to handle them.

You will never get a 9v battery to last more than a few uses. They die rapidly in this kind of application. They are commonly used for onboard electronics activated pyro charges in high power rockets and many people refuse to use them for more than one flight.

[Evil Lurker]

You don't need all that fancy stuff. Just use three or four 9v batteries in series, a push button switch, and size your nichrome wire accordingly for the proper amount of resistance to regulate the current flowing though it.

[AG6QR]

light home fireworks by hand with a match--it is much safer that way.

I don't think so.  Granted, using a bodged-up electrical ignition system has opportunities for danger, but a match isn't safe, either. 

A properly designed electrical system, used properly, is safer than a match, because it allows you to ignite the fireworks with nobody nearby.  Fuses have unpredictable delays, and if a person is required to be near the fuse to light it, there's no guarantee he'll be able to get away before it goes off.  One of the characteristics of a properly designed electrical system, used properly, is that there is an interlock to prevent the accidental application of power while a human is near the launch pad.

I believe the only reason fuses are commonly used on cheap fireworks is because fuses are a lot cheaper than electrical ignition.

There is a lot of similarity between fireworks and toy model rockets.  The model rocketry safety code requires electrical ignition, because it's safer that way.  What would make fireworks be the opposite?

http://www.nar.org/safety-information/model-rocket-safety-code/

Fireworks are very dangerous.  They're illegal to use without a license in many jurisdictions, and they cause many injuries, including amputated digits, hearing loss, and burns.  I'd recommend staying away from them entirely.  But if someone won't follow that advice, at least follow all local laws and regulations.

[IanB]

A properly designed electrical system, used properly, is safer than a match, because it allows you to ignite the fireworks with nobody nearby.  Fuses have unpredictable delays, and if a person is required to be near the fuse to light it, there's no guarantee he'll be able to get away before it goes off.  One of the characteristics of a properly designed electrical system, used properly, is that there is an interlock to prevent the accidental application of power while a human is near the launch pad.

This is what I was driving at. Nothing about the top post in this thread gives any suggestion of a properly designed system or consideration of interlocks. The danger inherent in a remote firing system if not properly designed is the possibility of ignition occurring with somebody nearby who is not expecting it.

If you light with a match you can:
(a) tell others to keep away
(b) ensure the site is clear before proceeding
(c) observe proper safety precautions on your own behalf
(d) avoid unintended ignition

I think a match is safer than a bodged up and badly designed remote firing system.

[Mechatrommer]

Where do you attach the cell phone?

i think i got the idea. please dont troll such an idea, people start speculating here.

I think a match is safer than a bodged up and badly designed remote firing system.

agree. i think a well designed remote firing with warning siren etc thereof is much safer than both. i've seen body parts in pieces try to match up a bodged up and badly calculated (or not even calculated) fuse length and firework's firepower. BOOM.

[tautech]

Where do you attach the cell phone?

A neighbour every year at guy fawkes used to fill a bag with a oxy plant mix with a short length of fuse wire and a LONG lead to a car battery.

BOOM

Last one they did, I was driving 2 Kms away and nearly shit my pants. 
Their 70 Yr old mum always watched, but that was the last one they did as it upset a few neighbours even though we live in a rural area. 
Good rural fun. 

[newtothis]

Hi and thank you for the responses,


>> Andy Watson: Thank you, this ignitor is actually based on those schematics - but they usually use 12V leadbatteries or a bunch of serial connected AAs, which is what I try to avoid. So I realise this makes a simple job more complicated -  but I also learn more

>> AG6QR: I might have put in the wrong symbol - but it is there to indicate and increase in DC, but I plan to use a DC-DC step up module so DC voltage will be Applied and flow established. I'm aware of the lacking resistors, but thank you for pointing it out.
Thank you for the friendly warning.
Shouldnt a PNP transistor allow flow when the base voltage becomes 0, allowing the 9V to light up the diode? If it isnt so would you care to propose a correction?

>> Nerull: Thank you I know this overly complicated and as such a Little silly - but that was makes it interesting , I will consider switch the powersource to 4AAs - and this setup is actually made (by 1A) so it should also be able to use Ematches - but I'm unsure if they are regulated in my country so it is initially going to be nichrome wire.

>> evil Lurker: yes offcourse - but I would like to make this design for the added learning.

>> IanB: I think you are a Little hard on my system, I am afterall here to remedy any errors. safety was actually my first concern - Would'nt you consider 3 seperate switched and connecting of the wires interlock mechanismes - this is a clone of the standard pyrotechnician detonator - except I have the voltage boost/capacitor insert. I don't ever think any Ematches or the like are supposed to be connected to a turned ON and armed detonator before added to the fuse, so untill assembly they are inert, I'm not going to assemble and arm the detonator before I'm ready to detonate atleast, so even If I really screwed up I will be nowhere near at detonation (And I'm going to test the system before use offcourse..) - I don't think there are any additional benefits to the match, but if you have seen any flaws in the system please point them out.

Anyhow thank you taking your time to respond, but I really would appreciate if anyone could provide the answers to the toppost, and of we could limit safety advice to practical application for the project.

I realise that the use of the Word detonator instead of ignitor may have caused people to get the wrong idea - but English is my second language so I didn't think so much about it at the time

[Psi]

Model rocket igniters should do what you want.

[MattSR]

A neighbour every year at guy fawkes used to fill a bag with a oxy plant mix with a short length of fuse wire and a LONG lead to a car battery.

What on earth is an oxy plant mix?

[tautech]

A neighbour every year at guy fawkes used to fill a bag with a oxy plant mix with a short length of fuse wire and a LONG lead to a car battery.

What on earth is an oxy plant mix?

Not wanting to give too much away  for fear of somebody damaging themselves or property.
Gas welding set.
That's all I should say. 

[apelly]

I have experienced oxy acetylene employed this way. To say it is impressive is to employ humorous understatement!

[max_torque]

For what it's worth, i think a remote electrical system is "safer" than a match, with the assumption it's done right!


What i'd want to see as a minimum:

1) A single mechanical "KEY" is used to "SAFE" the system.  Only one key should exist, and needs to be physically tied to the person who is installing the ignitor/trigger in the pyro device.  That way, no one can fire the system by mistake when that person is close to the pyro.

2)  When the system is "SAFE" the output terminals are actively, and mechanically "CLAMPED at low impedance" together to prevent any potential difference between them

3) Firing should require two inputs; ARM & FIRE, at least one of which should be a physically difficult to move switch, such as a mechanically interlocked toggle switch.  That way, the device is unlikely to fire in the event of being dropped, stood on, etc!

4) Any "wiring check" low output current, should be carefully considered, and only connected when the system is ARMED.


5) The user needs to carefully consider the correct operational steps and stages to ensure safe useage, for example, trigger wires should be conected to the firing device first, so that they are forced to zero potential before being connected to the pyro trigger, and the pyro trigger should be connected to the firing device wires BEFORE being inserted in the test rocket etc (so accidental fires only set off the trigger, and NOT the rocket!)


One option of the mechanical KEY is to use something like a dual 4mm bananna plug socket, where the pins must be fully inserted to reach down and push open the output terminal zero ohm clamp etc.  In all cases, consideration must be given to static charges and provide them a route to earth away from the pyro trigger outputs.

(Generally, with restive triggering systems, static charges will not contain enough energy to fire the device, as it must physically heat up a metal coil of wire to ignition temp)

[AG6QR]

>> AG6QR: I might have put in the wrong symbol - but it is there to indicate and increase in DC, but I plan to use a DC-DC step up module so DC voltage will be Applied and flow established. I'm aware of the lacking resistors, but thank you for pointing it out.
Thank you for the friendly warning.
Shouldnt a PNP transistor allow flow when the base voltage becomes 0, allowing the 9V to light up the diode? If it isnt so would you care to propose a correction?

OK, if I assume that device you've denoted with a transformer symbol isn't a transformer, but is instead some sort of packaged DC-DC converter, the transistor still won't do what you want it to do.  Assuming the DC-DC converter is isolated, there's no connection from the primary side to the secondary side.  Electricity flows in a circuit, meaning it's got to have a path all the way around, but the only connection from the primary side to secondary side is through the base of the transistor.

If the DC-DC converter is wired with a common ground, that is, the primary ground is connected to the secondary ground inside the converter somewhere, then the base of the transistor will always be at ground voltage, and the transistor will always be on.  Except that there's nothing to limit current through the base, so the transistor will burn out from overcurrent as soon as S1 is first closed.

If the DC-DC converter is wired with a common  + rail instead of a common ground, then the base may become far more negative than either the emitter or collector, in addition to the problem with no current limit.

This is a minor point, but generally, NPN transistors work a little better than PNP.  Don't be afraid to use PNP when there's a reason to do so, but when a circuit can be equally well constructed using NPN or PNP, it's usually best to use NPN.  It probably doesn't matter so much in this situation, though.

For the reasons why NPN is generally preferred, see  http://www.madsci.org/posts/archives/2003-05/1051807147.Ph.r.html


Oh, and on a completely unrelated subject, pay attention to max_torque's good advice regarding interlock systems.  Being safe involves both a safe design, and a safe protocol for usage.

[tautech]

I have experienced oxy acetylene employed this way. To say it is impressive is to employ humorous understatement!

Shhhhh
Those are the words I was trying not to reveal. 

[Nerull]

You need to be very careful when using transistors/mosfets or even relays (Which can weld their contacts together) to switch current in a system like this. You have to consider the possibly of failure, and what happens if it fails and what you can do to reduce the risk. There has been more than one instance of launch systems at rocketry clubs failing closed and firing ignitors as soon as they are hooked up, and people needing to jump out of the way as their rocket launches on its own accord. You don't want that to happen with a firework. An interlock that can completely disconnect the battery from the circuit is a start. Things like loud buzzers on the output to provide an audible alert of live leads are good too.

[zapta]

Where do you attach the cell phone?

A manual switch on the body belt should do.

[MFX]

I'm not going to go all nanny state on you and say don't build a firing system but I would say you need to learn a lot more before you can do it safely. Start simple, in most cases there is simply no need for DC-DC converters, capacitor discharge units are only used when you have a large number of igniters to fire at once, unless of course you're intending to make your own "e matches" from resistors? BTW I have recently designed a completely self testing high side/low side firing system output stage, there would need to be a minimum of three catastrophic failures in the electronics (one of those being a fusable resistor going short circuit which is  pretty much unheard of).

[MFX]

1) A single mechanical "KEY" is used to "SAFE" the system.  Only one key should exist, and needs to be physically tied to the person who is installing the ignitor/trigger in the pyro device.  That way, no one can fire the system by mistake when that person is close to the pyro.

Just to add I use captive key switches where the key can only be removed in the safe position. Test current (I use 5 to 10mA) should be provided by a fusible resistor at a minimum and tests should be treated as if you were live firing, no people on site.

[zapta]

BTW I have recently designed a completely self testing high side/low side firing system output stage, there would need to be a minimum of three catastrophic failures in the electronics (one of those being a fusable resistor going short circuit which is  pretty much unheard of).

This is what they always say.

Be careful.