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Firing Sequential Ignitors with Just One Switch?

Discussion in 'Electronic Basics' started by Ike, Sep 27, 2005.

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  1. Ike

    Ike Guest

    Hello...

    I'm working with the electrically-fired nichrome rocket ignitors for a
    rocketry project.

    Is there a way to wire a number of ignitors to a single switch so that
    each time you close the switch it activates the next ignitor in the
    chain, burning it up, and somehow making the next ignitor ready for
    electrical activation? This would allow, for example, 10 rockets to be
    fired in succession by pressing the button 10 times.

    I DON'T want to push the button once and fire all 10 electric matches!

    If there isn't a way to do this, I will continue with my plan to use a
    PIC microprocessor, but that means relays and/or transistors and more
    cost if I wanted to control more than 5 or 10 ignitors.

    Thank you in advance!
     
  2. Tom Biasi

    Tom Biasi Guest

    The easiest way is with a rotary switch.
    Electronic step circuits are possible but you would need to examine all
    failure modes for safety reasons.
    You would have 10 "hot" rockets on the pad.
    Fly safely,
    Tom
     
  3. Ike

    Ike Guest

    Hi Tim...

    I'm really looking for a way to chain any number of ignitors, not just
    10. One button is pressed, and the first ignitor in the chain is lit
    and blown off the chain (electrically speaking), then the button is
    pressed and the next ignitor in the chain is lit, and so on.

    Thanks!
     
  4. Here's a thought that occurred to me - it's probably a bad idea, but I'd
    like to have it shot down professionally.

    Construct a number of independant counters - each initialized with the
    sequence number of the igniter, and set to actually ignite when and only
    when the counter reaches zero.

    Connect all your counters to a shared bus, and make it so that pushing the
    button signals all counters simultaneously to 'count down one step'. Thus,
    evey time you press the button, another counter will reach zero, and that
    counter will then ignite its rocket.

    You can, in this setup, even configure several counters to fire
    simultaneously, simply by setting them to the same sequence number.

    You could even then have a completely automatic launching sequence, simply
    by replacing your button with a 555 or similar.

    As everything is nice and modular, you could start out with modules that
    use a four-bit counter (which will allow for a max of 15 distinct launch
    events), and later add wider ones if necessary, while the narrower ones
    still retain their usefulness.

    Each counter module would need a counter, a way to pre-set the value, and
    perhaps a small display to display the current remaining count just so you
    can check things are as they should be.

    Let the shooting-down begin!
    Best wishes,

    // Christian Brunschen
     
  5. Here's a thought that occurred to me - it's probably a bad idea, but I'd
    Sounds a nice idea, I'd say.
    And don't forget a main switch, perhaps a keyswitch, for the ignition
    circuit only so you can set the counters without running the risk of
    igniting anything by writing a 0 in one of them. ;)

    **** Stephan ****
     
  6. ehsjr

    ehsjr Guest

    Good idea - but you don't need a counter for each igniter.
    Use a decade counter - like a 4017 - and each press of the
    switch will increment the count by 1. One chip will count
    from 0 to 9 with an individual output for each count. He
    can add as many counters as he needs to count from 1 to N,
    with each chip controlling 9 igniters.
    The pushbutton will need a debounce circuit - cross connected
    nand's can do that. I don't know what current the igniters
    need, but I expect he'll need a transistor on each output to
    fire them.

    A sample 4017 circuit is shown here:
    http://ourworld.compuserve.com/homepages/Bill_Bowden/page5.htm#shift.gif
    Look for 18 stage LED sequencer.

    Personally, I would use the rotary switch approach to select
    the rocket, and a pushbutton to fire it. He could add as many
    rotary switches as needed to select N rockets. That way, it
    takes two operations to fire a rocket - 1) select the rocket to
    be fired and 2) push the button. Seems safer that way.

    Ed
     
  7. mike

    mike Guest

    This sounds like a trip to the emergency room just waiting to happen.

    You really, REALLY, need to know EXACTLY which ignitor will fire when
    you push the button. Don't skimp on the status readouts if you
    do it with a PIC. AVOID hairbrained lashed together logic.
    All it takes is one missed switch bounce to fire the wrong rocket.

    The easiest and safest might be a row of 10 pushbuttons. If you need more,
    bank switch the ten buttons with a rotary switch.
    mike...I hate emergency rooms...

    --
    Wanted, Serial cable for Dell Axim X5 PDA.
    Return address is VALID but some sites block emails
    with links. Delete this sig when replying.
    FS 500MHz Tek DSOscilloscope TDS540 Make Offer
    Bunch of stuff For Sale and Wanted at the link below.
    MAKE THE OBVIOUS CHANGES TO THE LINK
    ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/
     
  8. I don't know what your budget is, but a basic PLC - like the pico from
    A-B - can do that along with inputs from safety observers with kill
    switches. It has the dry relay contacts to provide the power handling,
    too. And a nifty little LCD display you can program to show the
    countdown.....

    I'd guess less than $100 for the PLC and a handful of pushbuttons. I
    think a pico has 12 dry relay contacts. You'd have to chain them
    together to get more....

    For a low-tech alternative, see the nail-and-wire pegboards the
    fireworks guys use. Basically, a bunch of 12 penny nails with wires;
    you hit each one in turn to fire the next sequence of fireworks.
     
  9. Bob Monsen

    Bob Monsen Guest

    One way to do this safely would be for each rocket to physically close a
    switch as it goes, making the next one hot. Perhaps a little pin/string
    arrangement might work? A nonconductive pin holds two contacts apart. Once
    the pin is pulled, the contacts close, and the next one is ready.
    There are a few issues to work out here (like not launching two rockets
    when you only wanted to do one), but it is probably simple to do, and
    practically free.
     
  10. Jasen Betts

    Jasen Betts Guest


    If you can get hold of an old rotary selector from an old electromechanical
    phone exchange that'd do the trick... (with the one I had you could switch
    50 ignitors sequentially) electromech is two generations ago so they may
    be rare even in the best stocked surplus outlets, the one I had needed
    48V to fire the solenoid but was easily dissasembled (all bolts, no rivets)
    and could have been re-wound for 12 or 6V operation with only hand tools
    and a bench vice...



    if you go with the microcontroller you can matrix the output
    so that 10 output devices (relays/transistors etc) can control 25 igniters,
    do 5 rows and 5 columns with a diode in series with each ignitor.

    you could also use a decade counter (two for a matrix) instead of the
    microcontroller that may save you a few bucks.

    a ULN2003 driver chip may be cheaper than 8 transistors, (but not in the
    catalogue I have here)

    hmm, if you want cheap driver hardware dissasemmble an old 24-pin dot matrix
    printer :) 24 pin drivers and 4 drivers each for the two motors...



    Another possibility would be using some contacts that close when the rocket
    departs so that the next ignitor is connected to the circuit, you'd need to
    set your button up to send only a short pulse so you don't get accidental
    multiple launches.

    +V -----------------------+ +--------------->
    |nc |
    || __o |
    +---||------o-~~ |
    | || com o---+---/\/\/\--+ to ignitors
    | no |
    | |
    0V -----+---------------------------------+--->


    the optimum component values depend on the specifications of the ignitors.

    Bye.
    Jasen
     
  11. quietguy

    quietguy Guest

    It seems to me that there is a time to buggerise around,and a time to go safe
    and simple - I reckon firing rockets should be safe, simple, and with minimum
    error risks

    Another poster suggested a rotary switch to select the rocket, and a pb switch
    to fire - sounds like the best safe and simple way to go safely

    David
     
  12. BobG

    BobG Guest

    Seems like timed charges get used in these building demolitions. They
    really dont want one of the charges to hang and stop the process once
    started, so I believe there are standard procedures and protocols that
    are proven effective in this area, I just don't know if a demo expert
    would tell us, because then he'd have to whack us.
     
  13. John Fields

    John Fields Guest

    ---
    I'd go with a pushbutton for each rocket and a separate momentary
    spring-loaded "ARM" toggle switch under a switchguard to enable the
    array of pushbuttons:


    ARM
    +V>--O---> |
    |
    O---> |
    | |
    | O---[IGNITER 1]---+
    | |
    | |
    O---> | |
    | | |
    | O---[IGNITER 2]---+
    | |
    . |
    . |
    . |
    | |
    O---> | |
    | |
    O---[IGNITER n]---+
    |
    RETURN>----------------------------+
     
  14. BobG

    BobG Guest

    JF:
    I'd go with a pushbutton for each rocket and a separate momentary
    spring-loaded "ARM" toggle switch under a switchguard to enable the
    array of pushbuttons:
    ============================
    Elegant
     
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