It depends on the load resistance, which we don't know - the 8.2 ohm resistor will limit the maximum current (into a short) to around 1.5 amps.

How about showing us his figures?, although it's probably rare to hear of an electrician who knows ohms law

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The resistors are just used to limit the current through the LED, they wouldnt affect the safety of the device. I'd say you would be safe using a 1kohm resistor in place of the 2 470ohm.

Well it was more of an opinion really. I just think it would look cooler if you used the 2 switch setup like in the previous schematics.

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Jeff Zimmerman
To the optimist, the glass is half full.
To the pessimist, the glass is half empty.
To the engineer, the glass is twice as big as it needs to be.

 

Jeff, do you think Jaycar part RR0572 would do instead of the 2 470 resistors??
In Australia all electricians learn ohms law at TAFE (I am certain). This guy is pretty switched on. I asked him how I would test a wire to see if it would carry 3 amps. He said R=V/I so (if I'm reading his writing correctly), I would need to use a 36W resistor. But he said something about putting 5 20W's together instead. Maybe 4. Can't read the writing. I have no idea!!
Let me just go through the basics, and see if I understand it all. Sorry for my lack of knowledge here!!
As resistance goes up, current goes down. Hence the 10W resistor. It will drop the current below 3 Amps. Does this depend on something 'drawing' current?? There won't really be anything drawing current. As soon as 1 Amp flows through the ingightor, the circuit will be broken (as the ignightor fires).
The 2 470 Ohm (or 1 1K ohm) resistors are to protect the LEDs from excess current. They should drop the current to about 11 mA. Is that right?
I have put a 3 Amp fuse in the circuit. Now, I think the jey switch is rated at 3 Amps, so I guess I should drop the fuse to 2.5 Amps, so that the key switch won't blow first! But how do I know that there will not be more than that many amps normally, hence blowing the fuse all the time?? Because of the 10W fuse?
If the resistance of the ignighters varies between 1.8 and 2.2 ohms, this will be the equivalent of having a resistor there. If I have a 20M cable to get some distance between me and the fireworks, that will add to the resistance too. Will this be much? I guess it will depend on the cable used?
This is a lot more difficult than I thought!! I am beginning to think I might be better off just to spend the $2500 and buy a professional setup! But I want to avoid it if I can!
Thanks for your help guys!!

 

On a similar subject, I am trying to build around a 16 channel sequencer for firing fireworks, but it’s proving a little more difficult than just a straight firing system. I’ve been looking into using the basic components of a light sequencer and then somehow increasing the current to fire the igniters. I could have up to 10 igniters in series so need a good high current to blow them all.

It needs to be a stand alone box running with an internal 12v lead acid battery.

When a trigger voltage of 24v is sent from the main firing system, the sequencer needs to start its sequence with position 1 firing imeadiatly then a time delay to position 2 and so on firing each igniter in turn with a specific, but adjustable time delay. For example 1 to 16 channels will fire in turn having a 0.25 second gap in between each shot, or one of about 6 other selectable time delays.

It then also needs an output after channel 16 with the same time delay so several sequencers can be joined together.

Any help will be much apprieciated!

 

It won't work with ignitors in series. Ask yourself a question. If you have 10 one amp fuses in series and you connect them to a 12V supply. How many fuse(s) will blow? Why?

The variable timing for individual channel is not easy to do with one shot, logic gates and counters but will be a trivial task using a microcontroller.

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L.Chung

 

I'm sorry I obviously wasn't clear... The time delay in between each shot will be exactly the same for that sequence, say 0.25 of a second and all 16 will fire with that delay. But I want to add something maybe a variable resistor so I can alter this time delay to say 0.5 of a second next time I set up the sequencer.

As for the igniters in series this is the only way we use multiple igniters, this is to ensure we can check the continuity in the circuit before firing. It is common practice to wire igniters in this way. Professional igniters are very different than simple fuses as they do not blow completely.

Hope this helps. Thanks again.

 

Thanks for the clarification as it was mentioned in previous postings that they became open-circuited after firing. So I guess they still has a ohm or so after firing in order for a string of ignitors to work.

In that case you have to turn off any firing channel after firing and this would make it even more difficult to implement using discrete components.

Off my head one can have different clocking rate selectable using data multiplexer gates. Then connects two 4017 counters together to get the required 16 outputs with logic gates. When this counter chain overflowed then it select another clock rate and moves on to the next 16-output counter arrangement and so on.

As said earlier, a microcontroller or an I/O card connects to a personal PC printer port or serial port would be a much more flexible and easier solution.

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L.Chung

 

You dont have to turn of the firing channel after it has fired, as long as it is easily reset. If it stays on at least it will be sure to fire.

Yes I have seen several circuits using the 4017 chip. But would it be able to handle/output around 1amp?

The I/O card idea is another thing I’ve been thinking about, but computer programming isn't one of my best subjects! I have also been looking into a programmable relay box which has about 100 relays in the box, this would be perfect but... relays are a big no no for this type of thing and shouldn’t be used with fireworks in damp fields, and the relay mechanism isn’t the best solution when working with high currents. What else would I be able to use?

 

If you don't turn off individual channel after firing, there will be a current drain of one amp or more flowing. Is that right? The current adds up quickly with additional channels.

No. One would need buffering in form of transistor or relay.

Let's hear from other users of the forum.

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L.Chung

 

Hi Mikebang.
I'm interested to hear that your pro ignightors do not fully blow!! The ones I use do - if they light, there is no more circuit. Otherwise it would be silly to have LEDs showing which fireworks have been detonated, as all the LEDs would stay alight!
I have found a great fireworks forum, which also has topics on DIY. I'm not sure if I can post about other forums on here - if someone clarifies I will post a link.

 

No problem with me!, at least not for such a specific subject.

Moderator.

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Thanks Nigel
www.pyrouniverse.com

Some of you guys should drop in and have a look. There seem to be a lot of people who are fairly good at this electronics stuff. Better than I am. They definately have the tricks of the trade stuff!

BTW I am looking at modifying the circuit so instead of having individual PB switches, I will have two 6 position selector-switches. That will allow for 36 channels, while still using the 12 core wire. A very clever trick!! I've considered using two 10 position switches, and 25 core cable (100 shots), but cannot find the cable. Makes the wiring a little more tricky, but brings the cost down!!!

 

The igniters I use come from China, when they have fired the LED's in the circuit fade, obviously they haven't blown all the way. When you apply more current they will eventually fade to virtually nothing but there is still a small connection. I think you'll find that most pro ignters behave like this as the only way you should connect igniters is in series so you can perform your test on the whole circuit.

 

Hi,

Came across this topic by chance, but its one I find quite interesting. I'd be interested in taking this a step further and having a microprocessor in the firing unit (in fact the idea being to have a number of firing hubs, with a central controller. Moving a lot of the intelligence into the hub).

From the microprocessor we would need to be able to arm the hub, and detect the continuity of each channel (so it could be reported back to the central station), and obviously fire the channel. I would be looking to be able to switch 12v @ 1A for each channel, but would rather stay with solid state devices than relays.

My initial thoughts on the continuity side would be to have one of the input pins of the processor connected after the current limiting resistor, that way it should read 1 when open circuit, and 0 when connected to a live fuse.

What I would like a hint on would be the best way to fire the pyro. The transistor circuits I am familiar with switch the load from the ground side, but I would have thought thats not good to have live wires around pyros until your ready to fire.

As far as the communications goes it would be a 2 way protocol with error checking etc. I'm not concerned with that at the moment as I find the firmware side of things easy to sort out.

Regards

Ben

 

eblc1388
I was wondering if you could add a short detection to the circuit you gave to patrickredmon. I would like to make it easier to find shorts than having to meter everthing out and hope it stays when I hook it to the circuit.
Thanks eejjr