My arduino powered firework sequencer. 2018 version!

[DaJMasta]

For 2019 i've moved from mechanical relays to Darlington arrays, more integration onto single PCB. Lesson learned, put as much work into the PCB to avoid as much manual wiring as possible.

Also going to use pre-fabbed boxes probably from Hammond mfg. Constructing lasercut boxes is a lot of work.

Less setup when you have time constraints and other factors certainly sounds like a good move.  Maybe some combination of the two could work for boxes?  Something like using a prefab enclosure with a laser cut face for connectors/switches/what have you?  Maybe not required if the prefab boxes can meet those requirements, though.

[Yansi]

it's obvious most people here dont know electric matches are a virtual shortcircuit and need a MINIMUM 0f half an amp to fire - usually atleast double that to be sure it will go.

they arent like airbag triggers - they cant be fired by static.

Airbags can't be fired by ESD either. Even 9V battery is struggling to fire one.

Electric matches have a "no fire" and "all fire" spec on current.  Any current below "no fire" will not cause them to fire.  Currents above "all fire" are "guaranteed" to fire the e-match.  Some e-matches have surprisingly low "no fire" specs.

Why are you quoting me? I am not the one spreading bullshit that ESD can fire an airbag.

[texaspyro]

Why are you quoting me? I am not the one spreading bullshit that ESD can fire an airbag.

I quoted a post about electric match firing current...  your part of that post came along for the ride.

Oh, and ESD can fire ANY pyrotechnic device, including airbags.   It might not fire the pyrogen, but ESD has its ways of causing havoc.  Any person involved in pyrotechnics that forgets this fact will eventually be reminded of it in a rather spectacular manner. 

[usagi]

so my design currently uses port expanders driving darlington arrays.

i'm thinking i can get better integration with high power shift registers like tpic6b595...

[texaspyro]

My rocket launch controller uses 2 MOSFETS (rated at 1000 amps) for each channel.   There is a high side FET and a low side FET.   The ignitor connects between the two.  Both FETs have to turn on for current to flow.  The gate drive signals to the FETS are generated by transformer / capacitor coupled AC signals that have to be around 30 kHz to get through.  No static "stuck at"  or transient condition can turn on both FETs and cause a firing condition.  The drive waveforms for the high and low FETs are generated by two different mechanisms.  Both FETs are continuously monitored for unexpected turn-on.  Any faults sound an alarm and shut down the system.

[Dubbie]

That’s an interesting idea re. The AC gate signal.

[Yansi]

so my design currently uses port expanders driving darlington arrays.

i'm thinking i can get better integration with high power shift registers like tpic6b595...

Very substandard solution.  You will get a pretty firework on a shorted channel too. But not from the business end, but from your transistor array.

Any output should be short circuit protected, and preferably shorted at the driver side when inactive.

Any fault on any output shall never cause any other output to misfire. Neither may excessive current draw from a channel cause the supply voltage to droop to cause further damage or circuit mis-behavior.

Think about it. Solutions may get complicated pretty fast. Hence why the professional firing devices are not simple arduino toys!

[texaspyro]

Any fault on any output shall never cause any other output to misfire. Neither may excessive current draw from a channel cause the supply voltage to droop to cause further damage or circuit mis-behavior.

Number 1,2,3... rules in my launch controller design is: no single component failure can cause a launch condition.  Hence the AC coupled, dual FET switches.  All the components in the firing circuits (particularly the continuity / monitoring parts) are through hole... SMT parts are much more likely to fail short-circuit and shorts tend to cause excessive current to flow.   Critical resistors are use two in series so a shorted one will still limit currents to a safe level,  Although the output FETS can handle 1000 amps, the output current is limited by a 2.4 ohm, 20 watt resistor... that limits the max current to around 20 amps per channel.   Timers limit the output pulse to a max of 3 seconds.

[Yansi]

Any fault on any output shall never cause any other output to misfire. Neither may excessive current draw from a channel cause the supply voltage to droop to cause further damage or circuit mis-behavior.

Number 1,2,3... rules in my launch controller design is: no single component failure can cause a launch condition.  Hence the AC coupled, dual FET switches.  All the components in the firing circuits (particularly the continuity / monitoring parts) are through hole... SMT parts are much more likely to fail short-circuit and shorts tend to cause excessive current to flow.   Critical resistors are use two in series so a shorted one will still limit currents to a safe level,  Although the output FETS can handle 1000 amps, the output current is limited by a 2.4 ohm, 20 watt resistor... that limits the max current to around 20 amps per channel.   Timers limit the output pulse to a max of 3 seconds.

(text in bold) Not true, at all. Anything to back your statement?

Also your solution seems irrational in both design and economical point of view. Strongly, very, very strongly doubt your 1kA rating anyway.

Could be probably done much differently but still safely.

[texaspyro]

Any fault on any output shall never cause any other output to misfire. Neither may excessive current draw from a channel cause the supply voltage to droop to cause further damage or circuit mis-behavior.

Number 1,2,3... rules in my launch controller design is: no single component failure can cause a launch condition.  Hence the AC coupled, dual FET switches.  All the components in the firing circuits (particularly the continuity / monitoring parts) are through hole... SMT parts are much more likely to fail short-circuit and shorts tend to cause excessive current to flow.   Critical resistors are use two in series so a shorted one will still limit currents to a safe level,  Although the output FETS can handle 1000 amps, the output current is limited by a 2.4 ohm, 20 watt resistor... that limits the max current to around 20 amps per channel.   Timers limit the output pulse to a max of 3 seconds.

(text in bold) Not true, at all. Anything to back your statement?

Also your solution seems irrational in both design and economical point of view. Strongly, very, very strongly doubt your 1kA rating anyway.

Could be probably done much differently but still safely.

Yes, I have info on failure mechanisms of SMD resistors but am not a liberty to comment further.   One thing I can mention is the small spacing between pads that can short during faults that cause solder to melt.

The design was based upon over 40 years of experience with pyrotechnic systems and observed, real-world faults that caused unintentional firings.  It may appear to be over engineered, but every feature was designed in with special attention to how to prevent those things from happening.  Cost was at the very bottom (well, actually totally missing) from the list of requirements.   Have you ever designed safety-of-life critical systems?

As far as being able to handle 1000 amps... it can for a couple of seconds.  Tested with 4S16P A123 LiFePO4 battery.  Actually around 2/3 of the power at that level gets absorbed into the wiring and the 2.4 ohm current limiting resistors on the standard firing boards limits the current to around 20A per channel.  If you are doing a large cluster you can spread the igniter wiring across multiple channels or short/reduce the current limiting resistor.   Applying two much current (or ramping the current too quickly) across an igniter can pop the bridgewire without lighting the pyrogen.

[floobydust]

For 2019 i've moved from mechanical relays to Darlington arrays, more integration onto single PCB....

I'm not liking using a multi-channel Darlington array because a shorted channel can affect other channels, in FMEA you consider adjacent pins to short on a single IC as if the die has failed. A ULN200x would not withstand a short-circuit or over-current. I haven't seen the whole circuit though. if there is current-limiting and you only fire one channel at a time.

Vishay MEPIC resistor igniters smaller 0603 sized part is All Fire >0.8A. Another is AEC-Q200 qualified for airbags.
They are around 2-10 plus cable resistance.

[usagi]

igniter profile. 9.32A @ 12V for 200 microseconds to fire.

manually tested ~100 igniters, all fire was 0.55A @ 12v. igniters are ~1.17ohm.

extremely consistent and reliable, i have been using them for many shows for many years now. igniter wires are 27awg.

uC uses completely separate power source from the igniter power source.

cues are only toggled for a few milliseconds, as thats all that is needed to fire them. there is a master safe/arm switch, darlingtons choose the cue and an ssr controls igniter power. only one channel is fired at a time.

[usagi]

so my design currently uses port expanders driving darlington arrays.

i'm thinking i can get better integration with high power shift registers like tpic6b595...

Very substandard solution.  You will get a pretty firework on a shorted channel too. But not from the business end, but from your transistor array.

Any output should be short circuit protected, and preferably shorted at the driver side when inactive.

Any fault on any output shall never cause any other output to misfire. Neither may excessive current draw from a channel cause the supply voltage to droop to cause further damage or circuit mis-behavior.

Think about it. Solutions may get complicated pretty fast. Hence why the professional firing devices are not simple arduino toys!

so here is a video showing the inside of a cobra system. insides are shown around the 2:00 mark



another video, around 2:20



not that different from my current design.