32bit microcontrollers + transistors help

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drmarvin2k5
 
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Joined: Mon Jul 01, 2013 11:52 pm

32bit microcontrollers + transistors help

Post by drmarvin2k5 »

Hello experts

I don't know too much about DIY electronics, but I would like to try building the following, and I would love some help to know if my thoughts are possible.

Raspi controlled fireworks ignition system

I already have a raspi. I need something to fire 150-200 separate fireworks. I know the raspi has an I2C system to communicate with a microcontrollers. I have looked into using something with a matrix (and judging a 32bit one should be able to have a 256 output matrix), this may be the way.
The next issue would be how to get the amperage to the igniters. As far as I have read, they take 6-9A from a 12V battery. I think that transistors could be used as a switch for each output. Since a matrix is used by activating pairs of outputs, are there transistors that activate only when 2 inputs are active?
If that is not possible, I would think that many 32bit MC's could be used with I2C, but I'd rather do it with 1 instead of 8.

Any input would be appreciated before I start trying to do this to help celebrate Canada Day next year. I'm getting a little tired of being right in the firing zone. :)

Thanks in advance

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westfw
 
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Re: 32bit microcontrollers + transistors help

Post by westfw »

Electrical ignition of fireworks is ... complicated, once you take into account all the safety features that you ought to be thinking about. You should probably start by looking at some the commercial systems that are available. For one thing, you have to be really careful about how things behave during power transients, or physical shocks. I've heard that mechanical relays are avoided, because they can make contact if you drop a box, for instance. Also, you typically want some sort of continuity check before firing, which means you need a way for the same matrix to limit current to well below the firing current.
[igniters] take 6-9A from a 12V battery.
REALLY strongly dependent on what you're using for igniters. Most US display use "electric matches" with an "all fire current" of about 1A, and a "no fire current" of much less. 6-9A sounds like a model rocket igniter. Which may have advantages and disadvantages. (one disadvantage is that eMatches are FAST, making possible the sort of choreographed-to-music displays that you see shot professionally.)

Here are a couple of manufacturers that I've heard mentioned in professional circles:
http://www.fireone.com/system_features.htm
http://www.pyromate.com/

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brucef
 
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Re: 32bit microcontrollers + transistors help

Post by brucef »

I would tend to trust westfw on, well, anything he cares to offer an opinion on.

As an academic exercise, though, I think what you're looking for isn't a 32bit microcontroller but rather a microcontroller with 32 bits of digital output. For example there's the Arduino Mega, which is an 8bit mcu with over 50 digital I/O lines. Alternately, you could use shift registers, like 4 74HC595's, to get your 16 row and 16 column signals out directly from the Raspberry Pi.

Then, connect the rows to a set of high-side mosfet drives to switch the 12V part and the columns to NPN transistors gating the connection to ground.

That doesn't provide for continuity testing, and I have no idea what other safety issues might be involved. I've seen home-built electronic firework launches before and nobody got hurt, but I guess there's always a first time.

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