233 replies to this topic

[MFX]

You could use a semiconductor output stage instead of a relay, they tend to be more reliable and safe. High current switching tends to knacker relays.

I have had a fault condition with Mosfets whereby when overloaded but NOT by a dead short they can fail short circuit giving you a nasty surprise in future (With a dead short they tended to blow open circuit). Relays can of course weld or stick short as well, So I wouldn't say that either was safer than the other. Only real solution is to test your system without pyro (I use a test load of a lamp board) after each gig and before the next one.

Martin.

Hi what type of connectors do some firing systems use? What are channels to on a firing system? I am making a firing system in school for my GCSE electronics main project and am a bit confused has to what i need i know mostly what i need but need to fill bits in . What type of cables do the slave boxes use and do the slave boxes use there own power supply? Thanks for any help.

Basicly use good quality robust connectors. For multicore systems I would avoid D type connectors, anything designed for military use is probably OK, if on a budget then centronics printer connections can take a decent amount of current. Bear in mind the enviroment most of these systems could be used in, Rain, Mud and you can't always rely on crew being carefull with your connectors. As for field boxes I use mini Pyroclips http://www.pyromagicinc.com/mpc.html , I've had problems with speaker terminals with the plastic tabs snaping particulary in cold conditions.

Martin.

[Karl]

Hi what type of connectors do some firing systems use? What are channels to on a firing system? I am making a firing system in school for my GCSE electronics main project and am a bit confused has to what i need i know mostly what i need but need to fill bits in . What type of cables do the slave boxes use and do the slave boxes use there own power supply? Thanks for any help.

Were in the same boat here mate! Im building a Model Rocket launch controler with a built in continuity test and relay, it run's off two 9.6v 2100mAh batteries and has a voltage changer between 9.6v & 18v. This is for my personal GCSE project.

I take it your gonna' be using E-Matches? You can use my PCB design if you wish. PM me for details.

My controler uses 'Locking Chassis, Plug 3-Way' and the 3way plugs for the handheld part, to the relay box and 2way's from the relay box to the launchpad. Im using 3 CoreCable from the handheld unit to the relay box then 2Core from the relay to the launchpad. I got everything from Maplins for about ?50. I doubt your schools Tech dept wont fund you for this project, they actually have a very low budget. I am using 16A Car Relays btw.

Edited by Karl, 04 January 2006 - 03:52 AM.

[mlepyro]

I have had a fault condition with Mosfets whereby when overloaded but NOT by a dead short they can fail short circuit giving you a nasty surprise in future (With a dead short they tended to blow open circuit). Relays can of course weld or stick short as well, So I wouldn't say that either was safer than the other. Only real solution is to test your system without pyro (I use a test load of a lamp board) after each gig and before the next one.

Martin.

I'd personally stay away from relay outputs.

If you do go the solid state route...

You work to getting around this in 2 ways...
1) current limit the system below the working peak of the output circuits
2) detect for faulty output circuits in a pre-show or power on test.

Relays are more expensive, mechanical, have the ability to stick and can be interferred with by strong magnetic fields.

Hi what type of connectors do some firing systems use? What are channels to on a firing system? I am making a firing system in school for my GCSE electronics main project and am a bit confused has to what i need i know mostly what i need but need to fill bits in . What type of cables do the slave boxes use and do the slave boxes use there own power supply? Thanks for any help.

This depends on the setup and what your trying to achieve. Pyrodigital, Pyrodigit, Elisy, Firebywire use XLR connectors for power and data... Pyromate, Fireone use centronics and network RJ45 connectors. In terms of the outputs you can use cheap speaker connectors, expensive speaker connectors, pyroclips or if you want the best - Schutzinger... what you need to consider is make it easy to replace and use cheap... or buy expensive and hope it lasts.

Although I've no idea how our firing systems exactly work, I am responsible for purchasing so can help people here source parts. We are quite open to the design of systems and encourage others to build there own. We have supplied our digital technology to some companies on a board level - this means they get the board and documentation for the wiring up of it and enclose it in there own casing/connector setup. Also when companies buy our systems we freely give the part numbers, suppliers bits to make up the firing modules so you can make your own additional ones and save money if you wish.

Mat

[The_Djinn]

hell, didnt know you knew how to type on the forum Mat !

Good to see you online

Will catch up with you some time and need to order a few bits and bobs.

Mark

[mlepyro]

Mark,

Yeah I was kinda lurking for a few years!

Good to see you here too...

How's the FireLite running?

Mat

[MFX]

You work to getting around this in 2 ways...
1) current limit the system below the working peak of the output circuits
2) detect for faulty output circuits in a pre-show or power on test.

Or instread of limiting the current, limit the On time of the Mosfet, E.G the N channel power MOSFET, RFD14N05L is quoted as 14A 50V However you can't have Both 14A AND 50V Going through it at the same time. At 24V the Max current is around 1.8 Amp and at 48V it's Just over 1 Amp, however limit the On time to 1ms and those currents rise to 8 Amps and around 4.5 Amps. The fault I had was NOT on a system that I built, but one that I maintain, it uses these Mosfets and the current is limited to around 4 Amps (Usefull if you sometimes want to fire igniters in Parallel), however if someone accidently shorts an output, and the firer holds the firing button for too long the Mosfet can fail short circuit. A rare occurance, and easily detected and repaired. Systems I build use a combination of current limiting, Max on time for the mosfet, and output stage checking, depending on the budget/requirement of the user.

[Andrew]

Or instread of limiting the current, limit the On time of the Mosfet, E.G the N channel power MOSFET, RFD14N05L is quoted as 14A 50V However you can't have Both 14A AND 50V Going through it at the same time.

That's not strictly true, it's a good guide for a beginner; as by assuming that the MOSFET is dissipating all the potential (even when in it's on state), you are over rating the device, this means you will never fry it.

When in the off state, the MOSFET will drop all the voltage, but the leakage current is that low that the power dissipated in the device is pico-watts (P=IV and all that). But in its on state, the MOSFET?s resistance is of the order of a couple of ohms. This in tern means that the voltage dropped over the transistor will not be the open circuit voltage, in a typical e-match system the transistor will drop about 1/10th of the potential, meaning that the device will dissipate 10 times less power that you would have expected.

The dynamic nature of this problem lends itself to a lot of unseen problems

[MFX]

1) current limit the system below the working peak of the output circuits

This needs some thought as well, although not really aplicable to rockets as you will generally be firing a single igniter, but if firing fireworks and you require series igniters then a simple fixed resistor will reduce the number of igniters that you can fire. On some desks I've seen high wattage bulbs used, when cold they have a very low resistance (around 0.2 ohms) so if you have a high circuit resistance due to using series igniters and maybe lots of bell wire, the current through the bulb stays relatively low, it doesn't heat up much, so it's resistance stays low allowing adequate current to fire the igniters. However a dead short in the system causes a large current in the bulb which quickly heats it up and increases it's resistance thus limiting the current and hopefully protecting the desk! You can also measure the voltage across the bulb and if it goes too high for too long, switch off the output stage of the desk.

Martin.

[ChesterPFX]

Ha ha, have just finnished my new 36 cue firing panel. Photos and description to follow.......

[pyrotrev]

One other thing you need to consider with MOSFETs is the possibility of static/overvoltage damage. With the large runs of wire that can be out on a large show, even a relatively distant lightning strike could develop enough potential to kill unprotected devices. Worth investing in a bit of EMI protection or MOSFETs with on-chip protecion I think!

[ChesterPFX]

Here is a bit about my new system

[brightonben]

Has anyone tried customising DMX technology for firing systems? I'm looking into it at the moment, seems perfect for computer controlled firing with up to 512 control channels. Can't find any DMX receivers with lots of MOSFETs on though, would it be easy to make?

[pyrotechnist]

Hi all again sorry for long long delay but thnxfor all your help i got an A in electronics with my firing system . Hope yours all goes well thnx ones again.

[adamw]

Hehe excellent, you get to build a firing system for the project and get an A! Cool

[Arthur Brown]

Beware of DMX it is not a robust protocol and has no error checking. Most people who use dmx for its intended (theatre) purpose have stories if whole systems twitching if there is a dmx fault, That could be a catastrophe if you wanted one thing to fire and something else went. Also the owners and originators of dmx (USITT) specifically state thatit is UNsuitable for critical applications, specifically fireworks or pyro.