Electronic firing system - for fireworks

[patrickredmon]

Hi guys,
Firstly let me say that I have my licence for fireworks, so this is all above board.
I am trying to avoid paying for a professional firing system, as they are really expensive. I don't have the too much experience in building circuits, and I thought it would be a lot easier than it is ending up. I hope someone here may shed some light on how to go from here.
Basically I want to end up with something that looks roughly like this.

There needs to be: a test circuit carrying 20mA, and that lights all the LEDs for stations with fireworks attached (ie electronic ignighter - therefore no firework = no circuit). A kill switch, to if the key is not on, nothing works. And there will be several stations (how many will depend on cost. I can always upgrade later).
The problem I am having is no matter which way I go, I always end up shorting the two circuits. So the test function works OK, but when I go to fire one station, they all fire because of the short.
How do I get around this?? I have tried a relay to seperate the circuits with a relay, but it didn;t work. I might need a relay for each station??
Is there a way to set it up so that there is a transistor which passes 20mA, but when the station fire button is triggered, it allows 1Amp??? I don't reaaly know.

If anyone can help, I'd really appreciate it. The guy at the local electronic store is more interested in telling me I should use a laptop system, but I am struggling to build this, let alone something that full on!!!
Any ideas???

 

[mramos1]

Can you post the schematic of what you have? That will help everyone help you.

 

[spuffock]

It seems that you only need 2 leds in series and a suitable resistor, say, 470 ohms for a 12v system, also in series, with each firing line. This will limit the current to under 20mA, and the firing key simply shorts out the leds and resistor.
Of course, if you want to run the whole lot via a mile of cheap twin flex, it gets a bit harder to do........

 

[eblc1388]

I am offering the following circuit for your consideration.

Assumptions:

a) the firework ignitor don't care about current direction
b) it does not goes off with 15mA current

The key switch reverse the battery polarity between unarm/armed position. When the switch is in unarmed position, the green LED will lights up if there is an ignitor connected and the associate cabling has good continuity. If the connection is bad, the LED goes off. This gives you a continuous indication that the circuit is good.

In this unarm position, pushing the PB has no effect and will not trigger the ignitor because the signal is blocked by the two 1N5404 diodes.

When its time to put the circuit in action, the key switch is selected to "armed". This reversed the battery polarity and now the green LEDs go off and red LEDs turn ON. If the PB is pressed, the ignitor will fire. I like this scheme than the simple firing line scheme because all green LEDs switch to RED meaning circuit is now "HOT".

I have designed in extra safety features to cater for component failure so do not modify the circuit by using only one component or combine the two resistors into one. I can add extra safety measure to cater for reversed 12V battery connection if you so wish.

If you have other questions, please ask.

 

[patrickredmon]

eblc1388, I don't care what anyone says, you deserve the title "Electronics God"!!! That is so basic, but I it seems it will do everything perfectly!!! I am truely speechless....

Thank you so much!!!


BTW - both assumptions are correct. Polarity is no issue, and properly functioning ignighter will not fire with 15 - 20mA.

 

[eblc1388]

There are still problem(s) with the previous circuit which you are not aware. I will give a slightly "improved" design, which allow future extensions like short circuit detection and current limiting.

What is the DC resistance of an ignitor, measured by a Digital Multimeter? If it is too low, extra electronics for short circuit detection will be difficult.

Do you know if the "professional" console deal with the problem of short circuit effectively?

There is, however, a simple solution. While the console is in "unarmed" mode, one can use a DVM with mV range and measures the voltage across the terminals. A good circuit would give some millivolts and be consistant with the rest of the circuits. A very low reading would requires furthur investigation for possible short circuit.

Edited: Resistor added to cater for external short circuit condition as per Nigel's suggestion.

 

[Nigel Goodwin]

Do you know if the "professional" console deal with the problem of short circuit effectively?

How about just adding a low value resistor in series with the PB switch, limiting the current to 1A? - if there's a dead short, and you press the button, it's likely to weld the PB contacts together, a series resistor will prevent it.

 

[eblc1388]

How about just adding a low value resistor in series with the PB switch, limiting the current to 1A? - if there's a dead short, and you press the button, it's likely to weld the PB contacts together, a series resistor will prevent it.

Good suggestion. A single 10 ohm resistor placed between key switch and "armed" rail will take care of this.

Above schematic updated to include Nigel's improvement.

 

[Nigel Goodwin]

How about just adding a low value resistor in series with the PB switch, limiting the current to 1A? - if there's a dead short, and you press the button, it's likely to weld the PB contacts together, a series resistor will prevent it.

Good suggestion. A single 10 ohm resistor placed between key switch and "armed" rail will take care of this.

Don't forget, this needs to be a high wattage wirewound type!.

EDIT: Sudden extra thought! - how about using a charged electrolytic to fire the ignitor (obviously depending on the power it requires), this would obviate the need for big wirewound resistors. You could have a far higher value resistor charging the capacitor.

 

[eblc1388]

EDIT: Sudden extra thought! - how about using a charged electrolytic to fire the ignitor (obviously depending on the power it requires), this would obviate the need for big wirewound resistors. You could have a far higher value resistor charging the capacitor.

The high current from the cap discharge could weld the contact also.

 

[Nigel Goodwin]

EDIT: Sudden extra thought! - how about using a charged electrolytic to fire the ignitor (obviously depending on the power it requires), this would obviate the need for big wirewound resistors. You could have a far higher value resistor charging the capacitor.

The high current from the cap discharge could weld the contact also.

No, you still have the 10 ohm, but it can be a small one now - as the current isn't sustained if you hold the button down.

 

[patrickredmon]

Wow guys - thanks for your input.
I am fast approaching the limit of my understanding on this...
The resistance is between 1.8 and 2.2 ohms (depending on wire length). I believe that 12V is the usual voltage.
I believe there is an inbuilt short test. Before connecting any ignighter you simply switch it onto test mode. I any LED's light up, you have a short. That's how the pro system does it. I would assume this is the same. Would this rule out the need for short circuit detection?? I have never seen a multimeter built into a firing system
DVM = digital voltometer?? Sorry - not sure if I understand.
Not sure if I am on the right track here, but would the idea of an electrolytic take some time to charge?? This might be a pain. If it's the only way, I'll take it though!
BTW, when the firework fires, the circuit is broken. The ignighters are basically a fuse, with black powder on them so when the current is sufficient, it goes bang. This usually takes a fraction of a second, so I don't think heating will be an issue.
I also plan to break the wiring sections into groups of 10 for ease of spacing, but also to limit heating. Does this sound fair???
Can someone give me part numbers for the components. I want to make sure I get the right stuff!!!

Once again guys, thanks for your help!! It is amazing!!

 

[eblc1388]

The resistance is between 1.8 and 2.2 ohms (depending on wire length). I believe that 12V is the usual voltage.
I believe there is an inbuilt short test. Before connecting any ignighter you simply switch it onto test mode. I any LED's light up, you have a short. That's how the pro system does it. I would assume this is the same. Would this rule out the need for short circuit detection?? I have never seen a multimeter built into a firing system

No. I was advising to use a handheld DVM(digital voltmeter), setting to the mV range to measure across each connection at the console. This can be done circuit by circuit during connection or all at once after all the circuits are connected. With current of 15mA to 20mA flowing in the circuit via the green LED and resistors, a healthy circuit(good ignitor and no cable shorts) will develope about 30 to 40mV across the terminals, which shows up clearly on the meter display. A meter reading of under 20mV would indicate something not quite right and furthur investigation is required. Once you have confirmed there is no shorts, that's it. The meter can be removed.

This does not cater for the possibility that one of the circuits goes into short-circuit after connection to the console and before actual firing. But usually, a open-circuited situation(which is monitored by the green LED) is many times more likely to happen than a short circuit.

I also plan to break the wiring sections into groups of 10 for ease of spacing, but also to limit heating. Does this sound fair???

I agree that there is no possible heating problem. The 10 ohm resistor is there to protect against short circuit. It will barely heat up. The other components like LEDs and resistors generate very little heat to cause any concern.

Can someone give me part numbers for the components. I want to make sure I get the right stuff!!!

You need to fill in the "country" information in your profile or tell us which component shops you have access to.

 

[patrickredmon]

I'm in Australia. The supplier I know is www.jaycar.com.au

 

[eblc1388]

I have checked the Jaycar cataloge and can recommend the following items:

SL2610 Red LED 5mm
SL2612 Green LED 5mm
RR0564 470R 1/2W resistor (pack of eight)
RR3351 8.2 Ohm 10W resistor (instead of 10 ohm in schematic)
SZ2025 Fuse Holder
SF2107 Ceramic 5x20mm fuse 2.5A
ST0570 Toggle switch (for main power ON/OFF)
SP0716 Push Button

No suitable keyswitch was found. The circuit requires a SPDT types but all Jaycar's stock is SPST or DPST. Current rating required is about 2 to 3A, 12V. You have to try other venders or ask in forum.

Please go to Jaycar's website and check the part number, size and the quantity required to build your console. You also need to find suitable connection terminals.

 

[patrickredmon]

A few queries regarding components:
Would it be any different to use ZD0100 as the LED's (just to keep it a little cheaper)??
I can't find a SPDT 12V switch anywhere. I think I may swap the key switch with the toggle switch. That way you need to key in to test or fire. Can I use the jaycar part SM1030 (SPST)??

Do you agree I should use 2 lead acid batteries (12V)?

EDIT: Would OZS2604 from http://www.ozgear.com.au/electronicparts/Switches_Relays_Fuses2.htm work?? All the key switched seem to be 250VAC.

Or this: http://www.rsaustralia.com/cgi-bin/...o=0332537&prmstocknum=0332537&prodoid=1881276

 

[eblc1388]

A few queries regarding components:
Would it be any different to use ZD0100 as the LED's (just to keep it a little cheaper)??

No problem. The one I suggested is chosen for ease of mounting. To use ZD0100 LED, you also need to buy some cheap plastic clips(HP1100 from jaycar) to mount it.

I can't find a SPDT 12V switch anywhere. I think I may swap the key switch with the toggle switch. That way you need to key in to test or fire. Can I use the jaycar part SM1030 (SPST)??

You need the security of keyswitch in your application.

The RS one only rated at 125mA so is not suitable.

The OZS2501 or OZS2600 from OZgear.com fit the the purpose. The main consideration is current rating and not voltage rating at 12V usage.

One keyswitch allows key removal in either position while the other allows removal in one position only. The key is trapped in the other position. Personally I would choose this one.

Do you agree I should use 2 lead acid batteries (12V)?

There is no need for two 12V lead acid batteries. What is your reason to use two?

 

[patrickredmon]

I thought that one wouldn't give the required current. I have only discussed it with the guy from the electronics store. Maybe he was trying to sell me extra. Do you think it is unnecessary.

What rating wire do I need?? I have been looking at ribbon type as it is the only stuff I can find with more than 10 cores. I will nee something like that so I can run out ignighters in groups of 10.

Also, I think I will use spring connectors like in "100-in-one" kits as my connectors. Jaycar don't sell them. Dick Smith do (www.dse.com.au). There is no issue using these is there???

Thanks again for your help!!

 

[eblc1388]

I thought that one wouldn't give the required current. I have only discussed it with the guy from the electronics store. Maybe he was trying to sell me extra. Do you think it is unnecessary.

A single 12V GEL type battery would give out over 50 Amps for a short period of time and so one amp is of no consequence. You only need one 12V battery.

What rating wire do I need?? I have been looking at ribbon type as it is the only stuff I can find with more than 10 cores. I will nee something like that so I can run out ignighters in groups of 10.
Also, I think I will use spring connectors like in "100-in-one" kits as my connectors. Jaycar don't sell them. Dick Smith do (www.dse.com.au). There is no issue using these is there???

This is where I can't advise you much more as I know nothing about how these professional guys work and their code of practice. The answer depends largely on whether you are getting paid commerically for firing firework or you are just building one to fire them in your back garden.

For the former you have to look physically at how these guys wire up their ignitors and what knid of wires to be used. This is more commonly known as the "trick of the trade". There is some pyrotechnics forums that you can get help from too. Follow their practices and when you are good at it, you can then make changes to suit your own if necessary.

Ribbon cable may be too thin to pass good current for a long distance, expensive and difficult to join together, unless you are using them in a one off situation. Looks for multi-core cable in the cable stores.

 

[patrickredmon]

CAT. NO. ZD0100
LED 3mm RED 15mcd

Emmitted colour: red
Lens colour: difused
Wave length: 700
nm: 90
Pd W: 45nW
If mA: 15
If mA (peak): 50
Min: 1.5
Vf (V) Typ: 2.0
Max: 2.8
IV Min: 3.0
MCD Typ: 5.0
Viewing Angle: 40

Are you sure this is OK?? It says peak current is 50mA.
Am I reading this incorrectly. Sorry for my ignorance!