model rocket launch controller help

Discussion in 'The Projects Forum' started by CastleBravo, Apr 6, 2014.

  1. CastleBravo

    Thread Starter New Member

    Apr 6, 2014
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    Hey everyone. I am new to this site and relatively new to circuit design. Surprise! I am having a few problems. I am trying to design and build a rocket launch controller but I am having a little trouble getting it to work right. Any help and advice that y'all can give would be really appreciated. This is what I have so far with a description of what I want to have happening if you want to help. Thanks in advance.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Your red power LED is backwards.

    None of your yellow LEDs will ever light, since they have no ∆V across their leads.

    Whenever the individual fire switches is thrown (required to light the yellow LED?), the rocket will fire.

    Do you want both the green and yellow to light at the same time, or do you want a green to switch to yellow when it's armed?
     
  3. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    How does the +bty DC get to the ARM switch line.?

    E
     
  4. wayneh

    Expert

    Sep 9, 2010
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    That points out another problem: You don't want to drive the firing current through the red LED, even of it's oriented properly.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    150 Ohms is way too low for the LED current limiters.

    What gauge wiring were you planning on using?

    It takes several amperes of current to fire an igniter. You'll need to use heavy gauge wire.
     
  6. wayneh

    Expert

    Sep 9, 2010
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    The power-on indicator LED circuit must go from battery to ground. Otherwise it will not light if no current is flowing through the igniters. Not good to have the power indicator show "off" when it is in fact hot.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    The ignitors must have a direct connection to the battery when the launch button is pressed. This is lacking. They require quite a bit of current to work.
     
  8. CastleBravo

    Thread Starter New Member

    Apr 6, 2014
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    So I need to increase the resistors for the LEDs to 1000 Ohms, flip the red LED around so it is pointed the correct way and move it parallel to the line leading to the arm and fire switches. @wayneh, I would like the green LED to light for the continuity check, it doesn't matter if it stayed lit or switched to the yellow LED when the rocket is selected I just want to be able to see which rockets have good igniters, and which ones I have selected for firing.

    Thanks again everyone for the help.
     
  9. CastleBravo

    Thread Starter New Member

    Apr 6, 2014
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    Ok, so this is attempt number 2 after tweaking and testing it on a simulator. I work for a program through the BSA for underprivileged youth. We don't really have a whole lot of spare cash to spend so I just want to make sure that it will work before I build it. Thanks again for all the help.
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Looks workable, a green will dim slightly when a SW is selected as green & yellow are now in series. Might lower LED resistors to about 450 Ω
     
  11. wayneh

    Expert

    Sep 9, 2010
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    That's looking a lot better!

    About the only quibble I have is that, once selected so that the green and yellow LED both light, the presence or absence of the igniter is no longer under test. That's OK, but I think you meant for the lights to remain on only IF the igniter was still in the circuit? I think you can still attain this with a minor rewire.
     
  12. CastleBravo

    Thread Starter New Member

    Apr 6, 2014
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    That is the idea, Any suggestions on how to do the rewire to make that work? Instead of having the yellow LED connected to a wire going straight to the battery have it go through the wire leading to the rockets maybe?
     
  13. wayneh

    Expert

    Sep 9, 2010
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    Supply power thru the limiting resistor to one pole of the switch. Connect the LEDs identically in parallel, both on top of the igniter. Let one side of the switch choose between the green and the yellow. The other pole of the switch carries full power.
     
  14. CastleBravo

    Thread Starter New Member

    Apr 6, 2014
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    Like this?
     
  15. wayneh

    Expert

    Sep 9, 2010
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    That will work, although the green LED will dim when the yellow comes on.

    What I meant is to place the green LED where that horizontal line is now, the one just above the yellow LED. After the switch, not before it. So the green will turn off completely when it switches to yellow instead.

    Either is fine though. Just depends what you prefer.
     
  16. CastleBravo

    Thread Starter New Member

    Apr 6, 2014
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    OK, thanks a lot for your help, my scouts and I really appreciate it.
     
  17. wayneh

    Expert

    Sep 9, 2010
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    A few last things. The battery might be asked to supply 6-9A if all 6 rockets are selected. Are you sure it's up to that? It'd be unfortunate to have anything less than blast-off when you hit the button. Been there.

    And the "launch" switch should be rated for all that current also, so that the contacts stand up over time.

    Consider a 10A fuse at the battery (with spares in the box), to protect against shorts in system.

    Now I want to go launch something! Love that whoosh sound they make.
     
  18. Wendy

    Moderator

    Mar 24, 2008
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    Why do you want to have the ready light on when the ignitor is activated? As a warning? Somehow it seems off, but you may have meant it to be that way.

    A SLA battery (commonly used in UPSs) would have more than enough juice.
     
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