A lot of designers have the luxury of creating things that aren’t supposed to explode. That’s usually easy. The trick is designing things that are supposed to explode and then making absolutely sure they explode at the right time (and only the right time). [JonBush] recently did a beautiful build of an Arduino-based fireworks controller. Seriously, it looks like a movie prop from a summer blockbuster where [Bruce Willis] is trying to decide what wire to cut.
[Jon] used a mega 2560 because he wanted to do the I/O directly from the device. His code only takes about 8K of the total program storage, so with some I/O expansion (like shift registers) a smaller chip would do the job. The device can control up to 8 sets of fireworks, uses a physical arm key, and has a handheld remote. It is even smart enough to sense igniter failures.
The front panel is a work of art and includes a seven-segment display made from Neopixel LEDs. The whole thing is in a waterproof case and uses optical isolation in several key areas.
Fireworks are dangerous, so we might have designed in some more electronic safety features. For example, the power switch only interrupts the ground. It might be safer to disconnect both battery legs when off which would make it hard for a short to accidentally power the device. On commercial devices that explode, you’d probably see dual inputs so that a stuck switch causes a failure (that is, arming or firing requires one switch contact on and another off). The same for outputs. Driving the firing relays on both sides makes it harder for a stuck output to fire accidentally. Still, using a box like this is probably safer than a lit punk, so for this application, it is probably safe enough.
We’ve seen a lot of fireworks controllers in the past, but few of them have looked this good physically. We expect to see a copy of this in some movie next summer.
He should have incorporated some sort of frame behinde the display panel so the lights do not blend in to parts that should not be lit e.g. the “dis” part of “disarmed” when it is actually armed. This sure looks worse in the video than in reality.
But hey – well done anyway!
As owner of Chinese radio relay box I can tell at least two ways how this can fail. First is igniter antenna loop. Without closing resistor in the igniter end, misfire will come. It is only matter of time when igniter wires are rightly apart to tune into something with little too sensitive igniter.
Second way to fail with relay box is that something blows near it and relays close from the shock. This can easily tested. connect igniters, arm and kick the box.
So please remember safety tie when operating fireworks firing devices.
I’d have put something into the remote relay box, like another little Arduino to control the relays so you’re not running a number of CAT5 cables out. Just have one cable or something lighter weight carry a communication signal and power, then isolate that from the relays which have the battery. At a minimum. :)
The best source for the ignition wire is single strands from within electric fence wire or strip. Much cheaper to buy.
When you buy commercially made igniters in volume, you can’t simply beat the price. Get a few friends that will want some and you’ll have enough for a minimum order straight from the manufacturer.
This is how could get them at less then the equiv. of 25c/piece with a 500 piece order.
Medium resistant, lacquer coated pill, with 30cm leads, with the short leads they light up even from a single AA cell.
Nichrome wire is awesome for electric starters. Old toasters are an endless supply.
For pyro initiators, you should drive only the high side. That way, things are always grounded unless they are being deliberately fired. This takes care of the antenna loop issue. And having an arm switch that does not interrupt the power side is just unforgivable.
Also, in this day and age, there is no excuse not to go solid state. MOSFETs can’t accidentally trigger with a good hard (physical) kick.
They can however, suffer shoot-through from both overvoltage and/or overcurrent.
Also, while the MOSFETs themseves will resist mechanical shock (quite sure that Randall Munroe’s “What if” could prove that wrong :D ), that doesn’t have to be true for the rest of the box.
Safest way is to never energize the firing circuit until people are clear, since there is no reason to have the juice on when there are people still nearby.
Overvoltage and overcurrent are both highly unlikely in a battery powered circuit without substantial inductance in the current path. If you have cause to worry, you can get high side MOSFET drivers with integrated protection (frex IR’s AUIPS6041 chips). And I agree that you should keep igniter power turned completely off until you are ready to fire.