Firing System : Help Needed

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sambo
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Firing System : Help Needed

Post by sambo »

Firstly, apologies for being somewhat quiet, it is for good reason, but I hope to catch up with all the posts soon.

I shot my show this year using my wireless fireworks system which you know I bought last year. I was actually very pleased with it but I want to take it to the next level. A fully fledged system is understandably expensive but my intention is to write my own web based scripting software and to put together my own system using Arduinos. I have 2 arduinos ( which cost me about £6 in total ) and 2 RF communication boards which have a distance of up to 1.8Km ( which also cost about £6 ). So the concept is to get a test system together to see how this pans out. If this works I could make remote firing modules for around £10 each including their batteries.

I'm ok with the digital side of things, the IO stuff and the coding but I'm stuck on the ematch circuitry - what the firing currents and voltages should be and similarly what the testing voltages and currents should be. Does anybody know where I should begin with that ?

If I'm successful I'll release this design in the tutorials section for all to benefit.

Sam.
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Lloyd
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Re: Firing System : Help Needed

Post by Lloyd »

Sambo,

First, before you write any scripting software, take a peek at ShowSim by Passfire (Kyle Kepley) at http://www.showsim.com . We've scripted multi-million dollar shows with it and it not only scripts well and intuitively, but simulates so realistically, you can submit the vids to clients for approval. The simulator allows full 3D animation with camera movement.

It's wildly flexible, allowing you to make your own effects when those in the 'stock' library don't match what you have (although that library is replete with available commercial goods). And it's inexpensive, even in the Pro versions, while dirt-cheap in the "Lite" version.

Now... where to start. Look up the "guaranteed no-fire current" and "guaranteed all-fire" current for the matches you intend to use (and I'd suggest for several brands, including 'professional' matches like MJG).

Regardless of applied voltage to your firing drivers, the current through the match during continuity testing should be 25% or less of the guaranteed no-fire value, and when firing, the current should be about 150% (minimum) of the guaranteed all-fire current.

I, personally, would not work with a firing system that had less that 24VDC available for the firing circuit, because many of my shows have had LONG runs of shooting wire -- and that wire is of a small gauge, in order to be inexpensive; thus, having a fairly high resistance per 1000' compared to heavier wires. A higher voltage also gives you the comfort of knowing that a marginal splice (say, tarnished wire, or 'loose') will arc-over and heal during firing.

LLoyd
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Boophoenix
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Re: Firing System : Help Needed

Post by Boophoenix »

I've glanced around a little for curiosity sake and there are some home built options out there you might find a couple of useful things from if you haven't got your all planned out yet. If I find some free time I'll try to relocated a few if you'd like?

Sounds like a fun project.
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Re: Firing System : Help Needed

Post by Tyvole »

I had a very casual look at doing this myself, on a very small scale, for garden shows. I have to confess I never actually got around to doing it.. However, here's a few things I picked up during my reading about similar attempts by others:
Be wary of using electro-mechanical relays, because they can potentially be actuated by an inadvertent knock or drop.
Consider carefully whether your switching should pull up to fire or down to ground. Personally, I would tend towards the former... an accidental ground seems the more likely scenario to me. I toyed with the idea of bi-polar switching on the output, where anything other than a simultaneous one rail up/other rail down would result in a no-fire situation.
If you write your own Arduino code, don't forget to de-bounce the switching inputs... ;-)
Make sure that the firing supply itself has a low enough internal resistance to deliver maybe twice the total required current without significantly dropping the firing voltage available at the match, especially if using many parallel matches.
Think about multiple possible failure modes and at least try to engineer the system to be fail-safe. For example things like MOSFETs are pretty tough, but they can and do sometimes go short-circuit. Something like that could have 'unwelcome' consequences.

I tied my head in knots when I tried to design such a system - have fun! :-)
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sambo
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Re: Firing System : Help Needed

Post by sambo »

Well I must say a big thank you to both Lloyd and Tyvole and Brad, whatever you find I'm sure will be helpful. I have some ideas on moving this forwards. At present I plan to :
Use 2 arduinos communicating via XBee ( 2mile range ) one will parse the script and send the cues to the controller module. That master controller module will send subsequent queues to the individual slave modules via a meshed network again using XBees connected to Arduinos. Those Arduinos will then be able to relay the status of each queue via a polling protocol and feed this back to the top of the heirachy, they will also obviously fire the queues and I'm thinking based on Lloyds' suggestion I will need 2 x 12V lead acid batteries for this or else I had another idea of using Lithium Polymer batteries with large capacitors ( but that is probably more expensive and over complicated ).

The coding and protocol side of things doesn't phase me but sadly the circuitry dose and that's a learning curve. I'm off to go and make some tests. As for the scripting software, Lloyd - Kyle's software looks perfect and really a bargain for what it appears to do so you've saved me a year or more of work there !

Sam.
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Re: Firing System : Help Needed

Post by sambo »

For the firing circuit I'd just like to check my workings with the more experienced amongst you.
I'm making the following assumptions which may or may not be correct :

1. El cheapo nasty 26 AWG gauge shooting wire @ 0.106 ohms per meter ( that is what I have but it may not be recommended ? )

2. A resistance per match of 2 ohms

3. A firing current of 1 amp

4. That the maximum fireable load on one cue will be 5 eMatches on a length of 200 foot ( 60m in total or a distance of 30m from cue to match allowing for both cores of wire ) - wired in series :

= ( 5 x 2ohms ) + (0.106ohms x 60 )
= 10 + 6.36
= 16.36 ohms

so, using ohms law the voltage required to fire this cue in series :

= 1A x 16.36 ohms
= 16.36V

for completeness, in parallel, this would be :

= ( 1A x 5 ) x Rt

where,

Rt = (0.106ohms x 60 ) + (2ohms / 5)
Rt = 6.76

thus V = 6.76 x 5 = 33.8V ( so it aint gonna fire ! )
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Lloyd
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Re: Firing System : Help Needed

Post by Lloyd »

1. El cheapo nasty 26 AWG gauge shooting wire @ 0.106 ohms per meter ( that is what I have but it may not be recommended ? )

#25 AWG is 0.106 ohms/meter. #26 is 0.134 ohms

2. A resistance per match of 2 ohms

A little high for good-quality domestic matches, but about right for Chinese goods.

3. A firing current of 1 amp

Ok... That, too sounds a bit high, but I don't know the all-fire current for your matches.

4. That the maximum fireable load on one cue will be 5 eMatches on a length of 200 foot ( 60m in total or a distance of 30m from cue to match allowing for both cores of wire ) - wired in series :

= ( 5 x 2ohms ) + (0.106ohms x 60 ) ; =10 + (0.134 * 60) == 8.04
= 10 + 6.36 ; =...
= 16.36 ohms ; = 18.04 ohms

so, using ohms law the voltage required to fire this cue in series :

= 1A x 16.36 ohms
= 16.36V ; 18.04V

for completeness, in parallel, this would be :

= ( 1A x 5 ) x Rt

where,

Rt = (0.106ohms x 60 ) + (2ohms / 5)
Rt = 6.76

thus V = 6.76 x 5 = 33.8V ( so it aint gonna fire ! ) ; Yep... even at the lower calculated resistance.


So... you move the firing module MUCH closer to the matches, and trigger it remotely with a very low current from the firing panel. That's the way almost all professional systems do it. If they don't, they use high-voltage Capacitive-Discharge circuits to do the long-distance firing.

LLoyd
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sambo
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Re: Firing System : Help Needed

Post by sambo »

ok, thanks again Lloyd, I'm picking this up slowly, I have a test circuit working which will allow me to test for eMatch continuity / short. Looking at this again, there is a significant cost saving to be had from using 12V relays! I'm leaning towards that option... that would just about fire 4 eMatches 10m away from the relay module using el cheapo 26 AWG wire. If my all-fire current is less than 1A then all the better but as they are unbranded imports ( I know ) I'd have to determine this by trial and error. Or of course, buy branded matches !
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Re: Firing System : Help Needed

Post by Lloyd »

I meant to ask (on that second part), "Why would you put matches in parallel?"

You cannot do an effective continuity test, and it demands huge currents.

Your series circuit will fire at 24V.

I have heard that the Chinese matches are not reliable in series, because no two of them show the same resistance. That would be a problem.

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Boophoenix
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Re: Firing System : Help Needed

Post by Boophoenix »

Lloyd left out the backyard version of Showsim in his mentions of Kyles software. It's certainly worth a try to see what ya think of it. If I recall Kyle set the structure of it up as a one tme purchase and you own it. However when updates happen to get those past a year you have to buy again. Which isn't a bad deal compared to other softwares. I had Finale pro which I purchased the year they restructured and canceled the pro product. If they thought this little of their customers I thought very little of their software and deleted it.

Sambo, I'm not sure what Ken's stance is on posting links to other communities so I'll PM you a link that may have a little useful info. If Ken doesn't mind I'll post it openly. Sorry I've been slow it's been a little busy around here getting back from the trip to 4F and have two memorial services coming up.
sambo
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Re: Firing System : Help Needed

Post by sambo »

Thanks Brad that all helps and I'll take a look at the backyard vesion.

Lloyd I was just really working up different circuits to see what I had in terms of flexibility but I wouldn't be connecting in parallel in usual circumstances ( or even ever )

I'm thinking currently that a set of N-type MOSFET is the way to go for firing the cues, it will be cheaper for one thing and allow the full 24V range.
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Re: Firing System : Help Needed

Post by Lloyd »

"I'm thinking currently that a set of N-type MOSFET is the way to go for firing the cues, it will be cheaper for one thing and allow the full 24V range."
-----------------
Yep, and if you get "SmartFET" type transistors, you'll have automatic over-temp and over-current protection, built-in. Helps when you inadvertently get a dead-short on a line.

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sambo
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Re: Firing System : Help Needed

Post by sambo »

you are such a legend Lloyd - the amount and lengths you go to help others is just unparalleled, the greatest honour I could ever have would be to pay it back to you someday. There is a lot that can be learned from your kindness.

Sam.
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Re: Firing System : Help Needed

Post by sambo »

hmm, I must say, I can't seem to see that the smartFET transistors are easy to find, I have just found a bag of IRZF44Ns in my cupboard though.... but I like the concept ?
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Boophoenix
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Re: Firing System : Help Needed

Post by Boophoenix »

Sambo, Lloyd has always said he learns a lot from us too. Even a lowly newbie like myself as we see things differently I guess. I always wondered that a little, but a little while back he had been fighting a problem with a project and I brought up a possible way to solve it. The first time it was discounted quickly the second or third time it finally hit him like a ton of bricks how to do it. So I was a little proud of myself for being a little helpful in return for a change.

I'll also add I've seen the look in his eye when he's Corupting a new soul into smelling the smoke. He does enjoy helping others along with sharing and helping out.

It fascinates me how helpful some of the people in pyro are with each other and it does span the whole art all the ways rom builders to shooters.
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Lloyd
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Re: Firing System : Help Needed

Post by Lloyd »

Sambo,
Here's an Infinion 2-channel high-side N switch employing SmartFET technology. Mouser sells these.

http://www.farnell.com/datasheets/1932161.pdf

$1.75 each onesies, for two channels. $1.41 for 10-20pc So 20 firing cues for $14.10 worth of drivers. And they're _almost_ indestructible, if you keep the applied voltage at or below 24V. They're automotive parts, so pretty much anyone who makes FETs should make similar drivers with similar specs.

These are good for 5A _actual_load_ at EACH output, and at 24VDC applied.

Lloyd

PS... T.I. and STtechnologies sell similar devices, and although I don't have the numbers, I'll bet IR does, too.
L
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sambo
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Re: Firing System : Help Needed

Post by sambo »

Brad, you've hit the nail on the head there. What I really value is the level playing field we are all on, drawn together by our common interest. We are all just human beings ( pyro ones nonetheless ) and our world is "flat" ( to borrow the term from Friedman's book ). I'm writing on a forum, hosted by remarkably generous goodwill, surrounded by kindness and passionate people who go out of their way to help each other, I only wish the "real" world was the same... Now I've gone too far and melodramatic I know but for some reason I can't help it.

Just a couple of days ago Pete Hand sent me the source code to his ACME test stand. He didn't have to do that ! Ned Gorski mailed me, out of the goodness of his heart, his copy of pyrocolor harmony which I read and sent back ( that's serious trust ) and I find myself talking to people all the time and exchanging ideas and sending out samples of gifts and this and that, I've had ( sort of still have ) many hobbies but this one is unique.

Anyhow, Lloyd, I've ordered a good bunch of those chips from Mouser, a little stung by the minimum order quantity but nevermind and have requested a catalogue. I can't seem to get a print catalogue for Farnell, maybe I am so out of date they don't make them anymore.

In the next couple of weeks I hope to have a good dev board up and running and will let you know how I get on.

If my "other" plans ( without being too taciturn ) pan out then my next 'donation' will be to this forum.

Sam.
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Lloyd
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Re: Firing System : Help Needed

Post by Lloyd »

Anyhow, Lloyd, I've ordered a good bunch of those chips from Mouser, a little stung by the minimum order quantity but nevermind and have requested a catalogue. I can't seem to get a print catalogue for Farnell, maybe I am so out of date they don't make them anymore.
---------------------

??? The minimum quantity is ONE, with 1665 in stock for the BTS5020-1EKA. For the BTS5020-2EKA, it's about double that cost, but still available in minimums of 1.


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Pyro-Gear
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Re: Firing System : Help Needed

Post by Pyro-Gear »

Sam when we had to close OB Alex set up a firing company with another guy, now I know that the firing system was scratch built by the two of them and from what I understand it was a 64 cue setup using fast acting relays running 24 volts, the micro-processor was an industrial unit, I have yet to find out what the make was, all I know is the thing is bullet proof and any repairs can be made in the field as all the relays are plug in, one thing I remember is it runs on lead acid battery power that can be charged from the van on sight should they go down.
The guy who built it is a member of the forum, I will try to get hold of him and see if he can let us have some more information, one other thing was I remember some tests he made using 24 volt lorry bulbs to simulate a firing sequence it was fascinating to say the least.
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Lloyd
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Re: Firing System : Help Needed

Post by Lloyd »

Ken,
I recommend against using mechanical relays. Especially where the firing modules are close to guns, but even in more distant setups, relays are subject to false triggering by mechanical shock. (blast force from guns) They exhibit other less-than-desirable properties, also.

Many of the less-expensive Chinese wireless firing systems are extremely prone to mechanical shock false-firing.

Big, robust relays with long contact throws are typically quite expensive, and physically large. Small 'sensitive' relays are not only sensitive to electrical triggering, but also sensitive to even minor mechanical shock.

Smart-FET-based output switches not only are less expensive than mechanical relays (even the small pcb types), but they are infinitely more-reliable. They self-protect against over-heating and over-current, they never experience "contact welding", and their 'contacts' never get corroded so as to fail to make.

That's just my take on it.

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Re: Firing System : Help Needed

Post by Pyro-Gear »

I need to get more information Lloyd, the relays are no way near to any mechanical shock that could be encountered.
So far all I know is the system has been in use for over 3 years with no issues if and when I can get more information I will let you all know.
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Lloyd
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Re: Firing System : Help Needed

Post by Lloyd »

Ask if he's ever drop-tested it for false firing.

Relay-based panels will seldom withstand a 1-foot drop (on at least one axis) without falsely triggering a cue.

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Boophoenix
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Re: Firing System : Help Needed

Post by Boophoenix »

One more thing to think about Sambo if you'll use it fairly often is maybe Lipo batteries. They can be much smaller than lead acid. However they require a little more care with charging it seems from all the bad stories ya hear these days.

I have a couple of the tiny Lipo car jumper packs and one I really really like Microstart XP-10. It fairly impressive what it'll do with such a small foot print.
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Re: Firing System : Help Needed

Post by sambo »

Ken, any information you have would be hugely appreciated. Once this system is running I will publish it here for all to see or use as they see fit. Lloyd is right ( of course ;-) ) though, I initially looked at relays, thinking this would be more straightforward and in terms of wiring they are as you can just buy them on a board but as Lloyd says those SmartFET MOSFETS are completely the way to go, the price will probably even work out less per Cue. They should be arriving in the next day or two and then I can start prototyping. For some reason on the U.K. Site my MOC was 10 units ( I kept getting a warning saying we have updated your basket for you as the MOC is 10 units ) - but I'll need that many if this works anyway.

Brad, I'm thinking carefully about what you are saying with the Lithium Polymer Batteries, I'm really caught knowing what to do with that one. From what I can remember from the datasheet ( I would need to look again ) these IC transistors don't need a common ground, so it maybe that I don't need to decide immediately.
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Re: Firing System : Help Needed

Post by Boophoenix »

I'm not sure if it is important in your design or not, but I do know that Cobra runs a common ground per each strip of 6 cues. What I am not sure of if each strip caries a common ground though. That information is from the designer himself.

I should probably note I do believe it's a reversed polarity ground in my thinking since all US items prior to the Chinese market taking over red was always positive in automotive and most other DC products here when I use to tinker with things like that when I was younger. Where Cobra's positive is the black terminal. Although that's not really important for ematches unless you're trying to share the ground.
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Re: Firing System : Help Needed

Post by sambo »

Right, i've been swearing A LOT. I put this down, went back to it, then did some more swearing. FFSake...

I thought my soldering was reasonable, so hey, a bit of surface mount technology, yeah i can handle that, my SmartFET MosFets arrived as did my adapter boards but f%ck me soldering this was a bloody nightmare ! After burning a few boards and a few chips I have one I've soldered on to it's adapter. Then I went back to the datasheet to start laying out the pins and working with the IC. Then I read that Vs ( Voltage Supply ) doesn't have a pin, it just says "cooling tab". What the f%ck is a cooling tab, is this the silver shit I see on the underneath. I mean, now I've mounted it have I got to get it off the board again to get to the shiny bit underneath and do some kind of soldering for my supply to it ?????. Ahhhhhhhhhhhhhh

How does anybody ever do any soldering with surface mount technology ICs ?? I'm not going to be able to do this a hundred times for all my cues. Do i need some kind of amazing soldering iron and a big f%ck off magnifying glass. Ahhhhhhhhhhhhhhhhhhhh

cooling tab ? Que ?

Ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhh !
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Lloyd
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Re: Firing System : Help Needed

Post by Lloyd »

Man, Sambo! SORRY! That was MY fault. I should have recommended to you a 'trick' when you don't have reflow or IR soldering equipment.

You solder a strand of copper foil the width of the Vss tab to it first, sticking out one or both ends. Then you solder-down the pins, and solder directly to the foil (or solder the foil down to your board) for VSS. (urk! Shoulda mentioned that)

You may have to cut your own to fit the chip from copper burglar tape for glass windows.

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sambo
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Re: Firing System : Help Needed

Post by sambo »

no, definitely NOT your fault Lloyd. You have just opened up my eyes to an entirely different league of electronics, I never would have considered surface mount chips before but I've been frantically watching as many tutorials as I can and I think I have it, quite the eye opener I have to say ! I have some copper foil tape on order, I'm looking forward to giving this a go again, I reckon I can get this one nailed but I'll let you know.
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Re: Firing System : Help Needed

Post by sambo »

I have 2 bits of this working now. I have an eMatch sensing circuit using 2 op-amps that also detects a short and after burning a heartbreaking number of chips I have the SmartFet MosFet circuit working to fire. Lloyd, do you mind me asking - were you thinking of using the on-board diagnostics of those chips to detect a short, for example, in some super clever way. At the moment I have the firing circuit entirely separate from the test circuit and think this might be cleaner. I'm also thinking I should try and find a chip that doesn't have Vss on the cooling tab underneath the IC but rather on one of the pins as I think this will vastly improve the ease of my board design. What do you think ?

Sam.
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Lloyd
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Re: Firing System : Help Needed

Post by Lloyd »

Sam,
No... I wasn't thinking of any subterfuge with the drivers. They automatically protect against short and overheating, but don't provide any sort of direct external signals to show what they're thinking.

HOWEVER, if you can monitor the voltage across one (and do it rapidly enough) when one was shorted to ground (through a firing line), you'd see a brief period of LOW voltage across it, followed by the full 'applied' voltage, when the FET turned off. Given a quick enough processor, these could be the cues you need to identify a short.

Unfortunately, that only works during firing! (urk!)

SmartFETS similar in operating characteristics to those are available in TO-220 packages, as well. Perhaps, given your circumstances, those would be easier to work with.

Lloyd
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Re: Firing System : Help Needed

Post by sambo »

thank you again, I'll keep the 2 circuits as they are then. I'm on a steep learning curve here. I've downloaded Eagle to have a bash at designing a layout then i'm thinking of getting the board prototyped and then basically I need to man up and get this soldering cracked. I'm going to try doing this through some 0.3mm vias under the board. I had a look at a lot of other chips but there really isnt anything i can find as good; ifineon seem to be the "leaders" in this area, or at least they have the best chips. I was hoping anyone would just be able to follow the plans and replicate as they wish. I guess they still could but would have to sub the MosFets.
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Re: Firing System : Help Needed

Post by richardh08 »

I'm following this thread with great interest. Unfortunately, I don't have anything of value to add, as my experience of practical electronics came to an end many years ago, back in the day when DIL packaging was the new, smart way to go.

The sophistication of electronic components seems to have moved on a bit since then!
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Re: Firing System : Help Needed

Post by sambo »

Richard, this is a lot of fun ! Grab yourself an Arduino or a Raspberry Pi and someone with your skills would be zooming past me !

Lloyd, would you mind taking a look at this datasheet for me if you get chance :

http://www.infineon.com/dgdl/Infineon-B ... 8f7b2c724d

This looks like it would fit the bill nicely, with VBat on pins 6 & 12, but I don't know what the "heat slug" is, do I need to do anything with that ? It looks like I'd get 2 channels per component nicely too.

thanks,

Sam.
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Lloyd
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Re: Firing System : Help Needed

Post by Lloyd »

Sambo,
That chip looks a treat. It does what you want, even provides some diagnostic info (if you desire to read it), and has a Vbb PIN, instead of only inputting Vbb on the "heat slug". That's just another term for 'heat sink contact'.

Now... I temper this with some trepidation -- but you should STILL solder some sort of copper land or strip to the 'heat slug' if you plan prolonged ON cycles. But, if you plan very short initiation pulses, it shouldn't be necessary.

That chip is designed for continuous loads up to the 'nominal' drain current, and would overheat without heat-sinking, if you did that. But for 100ms (or so) pulses - and infrequently - I see no need to heat-sink the chip, at all. It will do it's normal SmartFET thing, and just shut down if it gets too hot. But I doubt it would ever heat enough to cause that -- with short firing pulses.

Nice find!

LLoyd
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Re: Firing System : Help Needed

Post by sambo »

Excellent ! Thanks Lloyd.
I've just started to learn Eagle CAD, another learning curve...
Few days and I should be able to post up my circuitry so far.
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Re: Firing System : Help Needed

Post by sambo »

I have my main circuit design for the test circuit as follows. I'm not sure if my Op-Amp configuration to detect the short / connection is a good way of doing things but it's all I could really come up with. There are 3 LEDs ( "no connection", "short" and "good to fire" ).

I've attached a link to a screen dump. I have the IO circuit working and I'm just working up the polling code and will then wire in the Smart Fet MosFets. All criticisms widely welcomed !

http://www.pyrobin.com/files/CircuitTester.png
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Re: Firing System : Help Needed

Post by Lloyd »

Sam,
I'm sorry, but I have not a clue as to what that circuit accomplishes by itself. I think the match goes between those two breaks in the trace between R10 and R11 (although there are no 'terminal dots' or nomenclature to say it does). And I see no means for actually firing a match, so I don't know how the 'other' circuitry might affect what you're attempting.

But... IF you're intending to fire a match with an open-drain FET AND the match goes between R10 and R11, where's the ground for the match? It can't be fired through the 56K of R11...

More! I need MORE!

Lloyd
"Pyro for Fun and Profit for More Than Sixty Years"
sambo
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Re: Firing System : Help Needed

Post by sambo »

Sorry Lloyd !!!!!!!!!!!

just getting to grips with Eagle is proving an entire challenge in itself. It's taking me a long time to find the components I need and work out how to connect them etc.

You're right the match is fired between R10 + R11, i've just found a renumbering script so i've tidied up the resistor numbering. At the moment the bit that is connected is only the test circuit - so there is no firing circuitry connected yet, that will come via an IC2 bus IO extender which will feed into the FETs so there will be ( when i've connected it and I'm sorry as it's so incomplete ) a connecting point into the gap between R10 + R11 for the FET.

I might just put some header pins there for now and work out exactly what kind of pcb connection to place later. I've also, bravely, gone through and swapped out all the chips for SOICs.

is it still completely unclear ? I'll work hard to try and get the whole thing wired up in Eagle.
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Re: Firing System : Help Needed

Post by sambo »

Also, I'm not sure if I have my nomenclature correct on the resistor values as 5K6 is supposed to indicate 5.6Kohms. I haven't, yet, worked out how to 'switch' out the test circuit completely to allow me to fire the match without sending a huge pulse of current through the test side, unless I do this using standard MosFets to isolate it whilst the firing pulse is sent.
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Re: Firing System : Help Needed

Post by sambo »

This is how I was envisaging isolating the test circuit from the firing circuit. I'm using another automotive power transistor to sink x1-2 to ground. The match is connected between x1-1 and x1-2.

The input to the SmartFet comes from mcp23s17 ( IC3 ) which is driven using the IC2 bus from the Arduino. When this goes high the match will be pulsed at VBatt.

Am I getting any closer ? Got a headache now so will look again tomorrow. This stuff is almost as addictive as pyro ( almost )

Sam.

http://www.pyrobin.com/files/CircuitTester_1.png
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Re: Firing System : Help Needed

Post by Lloyd »

Sambo,
DON'T 'isolate it'. An open-drain FET provides almost infinite resistance when off.

Instead, reference your testing (all modes) directly to ground. Then you can 'insert' your firing pulse directly to the + side of the match, without having to jury-rig something that re-grounds the match just before firing. Doing that would require a 'mirrored' p-channel FET on the ground side (or an open source N-channel). You don't need the expense or the complication of the circuit.

Lloyd
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sambo
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Re: Firing System : Help Needed

Post by sambo »

Lloyd,

I cannot tell you how much I appreciate your help. All of my electronics knowledge is that which I acquired working for a nuclear power station after leaving school. I was due to go on to study Electrical and Electronic engineering but my best friend died of leukaemia after a long and deeply moving battle. He had always thought he'd get through it and wanted to pay it back by doing medicine. When he died, I quit and decided to do it for him. I have no regrets on that front but this sort of stuff has always wanted to be in my blood. Unfortunately all that was just over 20yrs ago so I'm seriously rusty / naive.

I think I am guilty of trying to over-engineer a solution to fit with what I've already done without thinking it all through, thank you for the wave of clarity !!!! I can do what you suggest, back to the drawing board !

thanks
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Re: Firing System : Help Needed

Post by sambo »

Here's my second attempt.

I've referenced to ground Lloyd, it makes total sense to me now ! I need to redirect the Group B (inputs) pins on IC3 via an NAND gate, so that for each eMatch line, the voltage comparator is NOT high and the short detecting comparator is NOT high as these 2 conditions are required for a good line. IC3 will then send back to the Arduino the result which would indicate a match ready-to-fire or a fault. The Group A (outputs) pins will trigger the Fets which are applied directly over the matches - again the instruction being sent by the Arduino when the system fires.

I also haven't fully wired in the chips or the power lines / clock line from the Arduino / reset line etc.

The concept here is an 8 channel board, which I aim to get the pcbs made and i will solder them up. As many 8 channel boards can be chained together as necessary ( or at least up to 8 per Arduino ) - each Arduino + n[firing board(s)] will be configured as slaves in a mesh network with XBee and one of those XBees being a sentinel module which will transmit over another wireless connectionl back to the main controlling Arduino.

What do you think Lloyd, I'm sorry the circuit is so big and busy. Let me know if I need to explain more or label things better ?

http://www.pyrobin.com/files/CircuitTester_2.png
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Re: Firing System : Help Needed

Post by sambo »

meant to also say, the DIP switches set the address of the IO expander on the IC2 bus.
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Re: Firing System : Help Needed

Post by Lloyd »

Well, the 'open' detectors look like they monitor for anything greater than 50% of VSS, so they appear that they would work OK.

I'm not sure about the short-circuit detectors, because I don't know what the minimum threshold input voltage of an LM324 actually is. It could be that you might have to set up a (very high-ratio) resistor ladder as a reference to those, too, rather than just using ground as your reference.

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Re: Firing System : Help Needed

Post by Lloyd »

PS...
I might add that IF ground is to be your detection level for a short, you might have to add a negative supply to run the LM324s... something more than the input threshold voltage, so that the op-amp is working in its acceptable input range.

THAT would be a pain; so the other option is that R/R ladder I mentioned, to get the voltage up... but then I don't know what the LED-current drop across your matches will be... so again, don't have much of a clue if it will sense what you want.

I think that's something that needs to be bread-boarded and tested before it's actually built.

Lloyd
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Re: Firing System : Help Needed

Post by sambo »

I'll look at the short testing circuitry again - it works on my breadboard, but I need it to be robust so that it doesn't fail in the field. If I had 200 foot of shooting wire, the resistance across that might not trigger the op amp in the event of a short so I need to remodel that.

I have a further trick up my sleeve, I hope you are going to like... I'll post this up in the next couple of days. However, I was intending on using a 24 volt powerpack for shooting but powering the test circuitry and ICs off the Arduino direct. I'm worried that passing a pulse at this higher voltage into the circuit will upset the op-amps as they would receive a pulse greater than their Vcc of 5v into one of their input lines. Do you think this is bad Lloyd, my instincts are telling me this is not good for the op-amps.

Sam.
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Re: Firing System : Help Needed

Post by Lloyd »

Sam,
They have 'specs' for that (haven't looked). But in general, if you're inputting something that might exceed the max allowable input voltage, you 'clamp' it with a zener, or use a resistor ladder to reduce the voltage.

Lloyd
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Re: Firing System : Help Needed

Post by Lloyd »

Sam,
I just looked. The LM324 honors a common-mode voltage down to ground (surprising!), but the input high value is limited to VSS. So you'll have to limit it, somehow.

Lloyd
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Re: Firing System : Help Needed

Post by sambo »

Hi Lloyd,

I've modularised my test circuit - i'll then poll each line individually and feed the output from the test circuit back up to the Arduino. It's a lot cleaner, I hope to show you the drawings later on.

I've looked at Zener diodes - I hadn't realised just how versatile they are. The problem I can't fathom in my head is that if I apply a 1amp 24 volt pulse across those match lines then current is likely to flow up into my +5V rail which would blow the Arduino, but also into 2 of the pins of one of the op-amps, so I'd need to limit this voltage across all 3 lines. At the moment, without having read enough to exactly work out how to do it yet, this seems tricky. Do you think I should persevere along those lines or just physically disconnect the test circuitry ( I mean by a power transistor or a SmartFet ) at the point at which the match is fired? I could have a fire signal coming off one of the arduino pins which when set to high ( this would be a pre-requesite for the Smart Fets to trigger via an AND gate ) would disconnect the 5v rail and the test circuitry.

I could mitigate some of this by powering the board off the same battery being used to fire the pulse but I had liked the idea of essentially being able to use ANY ( within a set of given parameters ) battery hooked up to the Fets to fire the matches, separeate to the board power. I'd still then have the problem of limiting the voltage across the op-amp pins.

think I might need to beg for more help, I'm ok with the digital side of things but my analogue electronics is lacking :-(

Sam
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