233 replies to this topic

[pyrotechnist]

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

Lol yep but i have left it at school forgot to take it home since they packed all the projects away in boxes somewere .

Edited by pyrotechnist, 15 October 2006 - 12:19 PM.

[Ninjapoo]

hi all! before i start, i'd like to say im a complete amateur at pyros as well as firing systems...

i've had an idea that i could spend around ?60 for a wireless firing system that's completely secure... i can get them keyfob garage door controllers to set pyros off... but one thing i can think of already is some sort of a safety switch, how would i get one on it or improvise one that's reliable? i mean it uses the same technology as car remote alarms so it's pretty secure but it only takes a click of a button to set something off...

although i remember when i used to use my wireless home phone in the garage digging through some stuff my dad couldnt get in with that keyfob because it uses the same frequency i guess if i got myself a radio jammer that would work but that's too much hassle for me...

any help guys?

[karlfoxman]

Mobile phones work around 900 and 1800mhz, most keyfobs use 433mhz I think. Im not too keen on the idea of wireless systems unless they are very seure, you could use some sort of key switch and a firing button that is enclosed or has a cover. Try these:

KEYSWITHES

MISSILE TYPE COVER

The 10Amp switch to use the cover with is this:

10AMP SWITCH

Hope this helps.

Edited by karlfoxman, 14 September 2006 - 06:38 AM.

[Andrew]

Mobile phones work around 900 and 1800mhz, most keyfobs use 433mhz I think. Im not too keen on the idea of wireless systems unless they are very seure, you could use some sort of key switch and a firing button that is enclosed or has a cover. Try these:

KEYSWITHES

MISSILE TYPE COVER

The 10Amp switch to use the cover with is this:

10AMP SWITCH

Hope this helps.

I agree with Karlfoxman. Wireless in a very crude form is bloody dangerous. Wireless systems, unless you know exactly what you are doing should be avoided, whether it be your own proprietary protocol or using COTS sub-systems. There is also the licensing problem. If you use an unlicensed band there will be a lot of interference and crosstalk, none if your very lucky. If you use a licensed band you will need to pay out, and several people will be laughing all the way to the bank. If you used a licensed band and you do not get a licence, your looking at big fines and possible imprisonment depending on how dangerous you are with it. There is also the data rate problem. Using COTS transmitters that use the unlicensed band can only transmit up to about 10kbps in normal conditions. Given your system would probably have no error correction which is very dangerous indeed, correct operation could be severely hit. One of your ques could be set by your next door neighbour?s garage door for example. The limited bandwidth means that if done properly, (error correction, security, and so on) you would be able to fire two ques a second tops, enough for fun, but not a display. Interference and crosstalk rejection could cause the system to be unusable for periods of time, an annoying thought. There are many driving factor for wireless systems, and many considerations to make, safety being of primary concern means that a lot of redundancy need to be built in.

One the components front, avoid maplin, they are in the most part a rip off. Unless you live near a store and need something ?today?. Try some of these.

Rapid: Smaller catalogue, low prices
Farnell: V.large catalogue, mid prices
RS: Massive catalogue, expensive

[BrightStar]

Hi guys, I have to disagree slightly here. Reliable, digital RF coms are now cheaper than ever if you look around. I do however agree that you should never improvise a radio firing system. PMR radios, phones, intercoms, door openers, RC car servos etc could incredibly dangerous.

I'm planning a wireless system around RF Solutions transceiver modules:

RF Solutions Ltd Smart Radio Transceiver Module

Their OTS modules will run on a '1 - 1' or '1 - many' network model, include error correction and are very reasonably priced. The planned modular digital solution will probably be: Laptop running custom software -> MAX232 based level converter -> RF solutions transceivers x2 (wireless bridge at 38,400 Baud) -> PIC chip with built in USART and multiple outputs -> MOSFET power transistor array with test / continuity feedback and safety features. I'm hoping to publish the construction details on this forum as it develops.

My PIC chip ICD development kit has just arrived from Hong Kong ( 1/2 of the price of the American one BTW ) and I can't wait to try it out

One doubt I have is whether to just go with TCP/IP over 10-baseT Ethernet and Wi-Fi instead of serial as it would allow longer wireless ranges, enhanced security, simple distributed and redundant wiring via off the shelf hubs and cables and enough bandwidth for the biggest show. A slower RS485 (2 wire half-duplex) or RS442 (4-wire full-duplex) system might be easier to water-proof and ruggedise though.

Edited by BrightStar, 14 September 2006 - 10:37 PM.

[Andrew]

Ninjapoo,
?60 for a secure system that you can make easily is not posible. To buy wireless systems that are any good you're looking at at least a couple of hundred. To make one you're looking at at least ?60 in componants but then hundreds of hours of time, and thats if you know exactly what you are doing. It's just not worth risking your life when for a couple of quid you can have a perfectly safe wired system.


Even with something like this, you are still open to other people's signals messing up your fun, and life if you happen to be anywhere near a device when it is set off. This device still uses the lower UHF unlicensed bands. Which is very crowded compared to higher ones. What data comes out is the data transmitted by every device on that frequency and shift keying in range. There is a likely chance that even if the traffic does not set off the que, you still cannot because the traffic is saturating your system. There is no built in collision avoidance protocol, devices on these frequencies are often dumb, so even if your system has intelligent drivers you still have to accept other peoples traffic. To use such a ?simple? device you need to devise a really rugged protocol that does the collision detection, EDAC, authentication and command processing. That?s why I said you really need to know what you are doing. A PIC is certainly capable, but programming all this from scratch is a bit of a mission. Again, you really need to know what you are doing; it?s not something for the novice, or even someone with an A-level in electronics. You simply do not learn enough at this level to make the system safe enough; safer, but not safe in the sense that it can not possibly go wrong. Redundancy is something you do not even hear about until deep in a degree. And although it is not essential; if a display does not fire it?s not bad, it?s just not good, so it is good to improve reliability. As opposed to satellite design, where redundancy saves billions of pounds, because in space everything that can go wrong, does, here it only saves disappointment (and perhaps some money). One major temptation is to just devise a code that is received to fire a certain que, problem is that might be the code for next door?s garage! How long does a code need to be to make it safe? Anyone?s guess is as good as the next persons. And then you have the inevitable bit errors. You cannot simply choose two digital codes with one bit difference to assign two different ques. You?re asking for trouble. Other considerations you may need to make is the BER for the system. EDAC systems can get confused so it is nice to know what sort of BER to expect. And thus the level of correction/rejection you need. Using the 12 bit encoder/decoder chips is not too good an idea either. These are in wide spread use and again when safety is an issue, 4096 combinations in a simple system is not worth chancing.

If you wanted a simple safety system to build in safety redundancy you could always have a single cable going to all the boxes that applies an active low or high signal (does not really matter), which tells the box it can fire any commands. Only switch it on when you are a safe distance away. The wireless then commands the que firings. You still have less cable all over the place and absolute safety. One wire is a small trade off in my opinion when you have potentially lethal devices on the other end. Remember were not talking sparklers, you could fire a cat 4 display safely with the capable range of the device you linked to. You really do not need any more range for fireworks.

Using stripped down PCMCIA WiFi adapters is the way forward I think, or even USB devices as the interface is more simple, but the drivers you need to write are more complicated. All the hard work is already done. Including WEP/WPA encryption that makes the system as safe as houses. Automatic collision detection, channel selection, the list of benefits is almost endless. The job as a whole is a lot more complicated. But in my opinion, the work involved in making a system out of ?simple? devices that is as safe as the 802.11 protocol, is more than learning about the PCMCIA interface and then developing drivers for the chosen device. Also, you can buy these adapters for much less than the rf devices that rfsolutions sell.

Brightstar, a safe system can be made, but certainly not as safe as a 802 based system, it sounds very interesting and I?m certainly looking forward to hearing about your system, and all the little bits that make it work. Sometimes simpler is more interesting to hear about. Good luck and if you have any specific questions just ask. I?m sure there is someone around that can answer it.

[Ninjapoo]

thanks for the advise guys...
that rules that out then just to show you what i meant, it was on rfsolutions too. i remember my dad getting one from their website when he ordered it from my computer.
link here

so going back to what i really want to do... i mean im clever enough to know how to wire a simple box with speaker ports for a firing system but i have no idea what to do when it comes to the chips you guys talk about... i know you're probably thinking this kid's a complete idiot and will blow himself up but no i'm not stupid enough to do something before asking... i've learnt from the stupid people's mistakes and from some of the people i know that are registered stage pyrotechnitians and stuff...

i'd rather look like a complete idiot that knows nothing on a forum than blowing myself up... (but i dont have the balls to wire something up that burns or goes bang anyway) just only been blowing small modelling light bulbs to see if i've wired my box up properly. but that's nothing special, just a rocker switch in series to a key switch for safety and to arm it... but basically do you guys have any pictures or plans for a SIMPLE firing system i can learn from? i can learn from your simplier designs and get hands on experience on how to get the firing system safe before i learn the harder stuff like the actual pyros.

thanks for the time guys

[Ninjapoo]

im also thinking about using cat5 cable for convenience... but i'm finding it hard to find the actual plug socket part for the cat5 network cable to plug into the actual firing unit.

if you could find me somewhere that i can get hold of some of those sockets that'll be awesome!

cheers guys

[BrightStar]

Hi Andrew, agreed - sometimes simpler is more interesting to hear about

Just for fun, here's my scruffy non-digital firing box, constucted many years ago as a student:



I originally built this to fire Le Maitre pyro cartridges on stage for college plays, having realised that it would be cheaper than hiring the kit to do so. It requires three actions for safety to fire - keyswitch arm, channel select and fire. I've recently used it for shell testing and SFX tests.

A good investment for a beginner is the 100m reel of bell wire shown in the pic, about ?7.50 from Maplin. The total loop resistance of this reel is about 15 ohms, so with a 24v panel (like this one) you can reliably ignite a 1 amp match at 300ft range.

For a mains powered panel, there is no need to oversize the transformer - you can at least double the rated current output for a few seconds - enough time to fire a cue or two. 2 - 3 amps output will be fine. I do recommend 24v as a minimum though as it gives you the flexibility to use thinner, cheaper firing wire.

BTW - I have no intention at all to write 802.11g drivers for the digital system - I'll be using either the built in PIC serial comms functions with the RF Solutions kit, or the light weight IP stack from Microchip with OTS wireless hubs in bridging mode... My time is much better spent working on the fireworks

EDIT - Ninjaguy, Rule 1 of electric firing - Keep it simple and test, test and test again. Rule 2 - Take the batteries out and unplug from all power while rigging, whether wireless, wired, digital or whatever. Rule 3 - Trust your instincts - if you're not certain it's safe, it's probably not...

Edited by BrightStar, 18 September 2006 - 11:01 PM.

[Ninjapoo]

thanks brightstar. im not going to touch the pyros yet... im going to test it with either LEDs to blow that up or mini light bulbs to see if it'll work with say 10metres away or something... i like to move slowly up the difficulty level here... i have no intention to setting anything off at the moment... i just want to get enough knowledge about the firing system before i touch anything that burns/flares/goes bang

just a quick question... would it be practical for me to use a single pp3 battery to power the firing system to fire off any pyros?
because i've used 1 single pp3 battery on my previous one only to see if i can wire things properly. and it worked, but i was wandering if it would be sufficient to take it to 10-20metres as 9v is pretty low compared to what you pros use.

i chose 9v before just because it'll be convenient for me to change the battery if i wanted and i didnt like the idea with playing with higher voltages.

thanks again

[BrightStar]

Hi ninja, a single PP3 will probably work with a short cable run but I wouldn't recommend it. Two in series for 18v, (use ni-cads for high current), would be better. A small 12v lead acid gel battery (look on ebay or visit Maplin) would also be a good starting point.

You need to consider the resistance of your circuit, which will be the internal resistance of the battery (about 0.7 ohms for a rechargeable PP3, 1.7 ohms for an alkaline PP3, 0.05 ohms for a lead acid cell) + the cable resistance (0.15 ohms per metre for the bell wire above) + the match resistance (assume about 2.5 ohms). Then make sure your circuit will deliver at least 1.5 amps by dividing the battery voltage by this resistance to find the current.

I'm reminded here of an accident in the UK a few years back with Navy cadets at an open day. Two teams had to complete a mini field gun race, place a thunderflash (electrically fired for safety) in the barrel and fire it to win. One of the cadets was badly injured on loading the thunderflash when it went off. The cause? Their 'firing system' was just a 6v lantern battery and bare wires. Somebody slipped and that's all it took...

Do PM me though with your circuit ideas - I'm happy to help!

Edited by BrightStar, 19 September 2006 - 06:59 AM.

[Ninjapoo]

thanks again for the advise brightstar.
i'll pm you my circuit ideas and i have to say using bare wires is kinda silly when you use it to electrically fire anything...

i've been so busy lately and literally rushed off my feet so i think at the moment i only have a drawing on a bit of paper for the circuit lol i'll draw it on the computer asap thanks again brightstar

[Ninjapoo]

edit:

ignore this post... just made a complete fool outta myself

Edited by Ninjapoo, 04 October 2006 - 10:18 PM.

[fishy1]

I was just thinking, as I don't have much knowledge of electrical firing systems, instead on needing two wires for each cue going from your e-match to your firing box, could you not have one wire (+) going to one terminal of the e-match and connected to your firing box, and the other terminals of all the e-matches connected together and to a piece of thicker wire connecting all of them up and going to 0V.

This system has several advantages that I can see:

Lower cost as 1 thick wire costs less than 10 thin wires
Lower total resistance of the wire
Less wire needed so less bulk and easier to set up

Disadvantages

E-matches would need to be fairly close (say 10m) or else you'd have a bother making multiple connections to the thick wire.

Is this system used already? Have I just thought of an old idea? It seems pretty good to me, but maybe I've overlooked something? You could still fire cues individually.

I'll put up a diagram later to illustrate my idea.

[karlfoxman]

For anyonw with the money I recomend one of THESE I have used it twice and both times it has been outstanding, nice and easy to use, very very strong in its Peli case. Fires e-matches quicker than you can blink at 200+ meters of cable. Im very proud of it and what it can do! We do have a manual firing system and im thinking of making a sequencer from scratch using my knowlage of electrontics and my fathers knowlage of the software side of things! Superb and sexy piece of kit!!