233 replies to this topic

[pyrotechnist]

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.

[RegimentalPyro]

I am also making a firing system this year, having taken a Bob Dylan like decision to "go electric".

I've decided to use RJ45 connectors and CAT5e cable out to the firing site [ie: Standard computer network cables]. This is because

• Cat 5 and RJ45 is cheap and easily available [?35 for 300 metres of 8 core]
• This gives me 7 "cues" per cable [8 cores, 1 for a common ground, 7 left]
• I can easily unplug "fired" cables and plug in unfired ones on-the-fly if I want more channels.
• I already had the RJ45-ends and the crimper.

Once out at the firing site, small distribution boxes take the RJ45 lead as input and output 7 pairs of cues

The firing box itself has a key switch for added security with positions for
Safe[Off], Test circuit, Armed[On]. The safe position isolates the battery at both poles for added security [4 pole rotary keyswitch]

The e-matches we are using will be one of two types
The first is the traditional 36swg NiChrome wire dipped in BP-Slurry. The second is one of my own design Featuring low power [0.25w] resistors which pop the instant you run 12v through them. These are also dipped in Slurry and then inserted into a two inch section of quickmatch. The Quickmatch is then slipped over the visco of the fuse I'm trying to light. This has the advantage of being legal as we shouldn't have to re-fuse the cakes for electric [dig out the visco, put in the e-match] but will also add a slight delay on the firing for said cake. We are using it for the background "filler" stuff. Any time critical stuff will be fired by the traditional e-match.

[phildunford]

Not sure RJ45 would be the best choice of connector. These are a bit low current and not very resistant to the ingress of moisture.

I tend to use standard 'D-type' connectors. These seem happy up to a couple of amps are relativly cheap and easy to terminate. you can also get them up to 50 way. I tend to use 25 way.

If you want a really high reliability system you would have to go for (very expensive) military spec connectors.

I have a basic 25 way box based on this sort of technology, but if I were designing something new I would probably go fro a microprocessor based 'head unit' that would live in the firing area and have short cables to the match heads and control this from a computer via a network or RS232 cable. This way the longest cable would not have to be multi way. - Alot more complicated though! - project for the winter evenings maybe...

[Arthur Brown]

Reliablity in arduous conditions is most important. You dont want any "fail to fire - cause unknown" or you have to deal with the UXB problem -- it might go off sometime.
Proper ematches have a certain no-fire current and a certain fire current typically 20mA and 500mA (varies according to manufacturer) so that circuit continuity can be checked prior to firing.

[Flashy]

You could easily control 8 channels from a parralell port from your laptop or PC. Of course you would need to use relays as the paralell port only puts out around 3V with 350mA, well thats what mine puts out. If you wanted more channels than this then you could use 4 74374 Chips to control upto 32 Relays.

Edited by Flashy, 11 July 2004 - 03:50 PM.

[pyrotechnist]

Hmm nice but how do you do the test switch do you have to send very low current throu the circuit? If so what do you need a variable transformer or variable risistor? I am after having 3 channels with 32 cues per slave box. With a key switch with power, arm and seperate button for test i will have two LED's per cue switch one for failer and one for ok. This is going to use PIC chips to control certain things and other stuff i program PIC chips in school just basic ones upto now I am not to good yet with them. Is a Bt one core cable good for the firing wire the one that goes from the slave boxes terminals tothe e-matches? Does the slave box use its own power supply to? Thanks like to see picys of your firing controlers . When i am done next year i will show mine.

EDIT: Does the amount of pins needed in a D-type connector depend on the amount of wires coming out of the slave box?

Edited by pyrotechnist, 11 July 2004 - 04:49 PM.

[RegimentalPyro]

The resistors I'm using for my ematches are rated at 0.25W which means they pop at 200mA[ish] with 12V. They cost about ?0.01 - ?0.04p each depending on amount ordered.

The LED's on my test circuit draw 8.5mA and have an integral current limiting resistor so no risk of firing the ematch whilst in test mode. They are product code CJ63 on maplin.

NB: I have a circuit diagram available for anybody that PM's me nicely!

[alany]

You mean like this:

http://www.vk2zay.ne...box-circuit.jpg

(modified URL as the original image has been replaced with a more recent one)

Edited by alany, 30 January 2005 - 04:31 AM.

[RegimentalPyro]

Very Similar! Except mine is not wuite so neatly presented [handrawn and scanned!]. It does however detail the switching of the unit between armed, test, and safe, along with the double isolation of the battery in safe mode.

[pyrotechnist]

I am going for hard project of making a system for firing it with slave boxes.

It is going to bee hard lol.

Do slave boxes use there own power supply? Or slats?

How many cues you having RegimentalPyro?

I am buying from maplin and rs and my electronics class has lots of electronic stuff to.

Does the D-type Connector which is for the slave boxes have to have the same amount of pins for how many wires are coming out of the slave box?

[alany]

The easiest way is to use a 25 way straight-through with shield data cable, it will give you 26 pieces of wire (counting the shield/shell too) or 25 cues using the shield as a return.

More fancy is passive multiplexing with diodes which lets you get 150+ cues over 26 pieces of copper.

Then you can go nuts and put intellegence in the remote ends and have basically unlimited cues depending on how you implement it.

You could have five 5 cue boxes driven off the one 25 way lead with suitable breakouts, say using D9s on the slaves rather than D25s. Really depends on what your requirements are.

Spring-loaded speaker terminals are great for the rails, although some prefer binding posts for mechanical reasons.

[pyrotechnist]

Thansk what are breakouts? I am not to up at electronics yet but am ok with it still learning so you are saying if you have like 25 wires coming out of your slave box you would need a 25 pin D-type connector? What are channels . Are the like the switches going to each slave box like channel 01 goes to slave box 01? Thanks.

[adamw]

No the slave boxes SHOULD NOT have their own power. This is very dangerous. IE: if there is a short in the box, and someone plugs an igniter in (connected to a shell etc) and it fires...

Safety is always NO1 when thinking about firing electrically. The main control should oh course have a ON / OFF switch as well as a keyswitch. You need to isolate power to the circuit when it is not needed.

[pyrotechnist]

So am i getting it right here. The on or off is going to the mains which is the batteries or battery and then that power is stoped by the key switch then the keyswitch is tunred on and it then lets the power go throu the hole circuit? Am i right? That is not including the test. I am having a seperate test which is going to be a button big green one lol.

What are channels?

[Richard H]

A channel is the same as a cue. E.g. an 8 channel firing system can fire 8 e-matches separately.