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Need some help with a simple circuit

Discussion in 'General Electronics Discussion' started by bwoogie, Jun 6, 2012.

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  1. bwoogie

    bwoogie

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    Jun 5, 2012
    I've never made my own circuit before, but I have followed other schematics and built small boards so I'm not completely lost, but have a very limited understanding of how electronics actually work.

    With the 4th of july coming up I'm building a fireworks igniter. Simple enough. An On/Off switch and LED, 8 push buttons each with an LED and 8 terminals. Connected to the terminals are nicrome wires for the ignition.

    I'm able to ignite the wire but was having problems with the LED's not lighting up. So I rewired one of the push buttons and it was working until i wired up the second push button now neither of them work. So here is my schematic.. Will this work? I might just have a loose wire somewhere.

    [​IMG]
     

    Attached Files:

  2. john monks

    john monks

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    Mar 9, 2012
    The circuit looks workable. I don't know where the problem is but the LED's are probably getting an inductive kick after the fuse wire burns open wiping them out. You might try use incondescent bulbs instead.
     
  3. davenn

    davenn Moderator

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    Sep 5, 2009
    Hi Bwoogie
    welcome to the forums

    The LED's will never light as it stands as they never get any current
    When the push button switch is closed the current takes the lowest path of resistance which is via the terminals to the right, through the nicrome wire and second set of terminals to the negative rail

    therefore the LED in that circuit wont get any current.

    cheers
    Dave
     
  4. bwoogie

    bwoogie

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    Jun 5, 2012

    Ok, to test that I unplugged the wire from terminal 1 and the LED did light up! Like I said I know next to nothing about electronics. I figured the current will just flow through anywhere it was allowed.

    So, what do i need to change in order to fix this?
     
  5. bwoogie

    bwoogie

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    Jun 5, 2012
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Given your current findings it appears that the load the ignitor places on the battery is so large the voltage drops below the LED voltage.

    A bigger battery is one solution.
     
  7. bwoogie

    bwoogie

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    Jun 5, 2012
    i have 12 volts running through it (8 AA batteries)
     
  8. CocaCola

    CocaCola

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    Apr 7, 2012
    Even if that was the case they should get their full compliment of current immediately after the electronic match burns and breaks that alternate path... That is assuming the loops on the far right of the diagram represent the matches, see attached slightly modified (4 e-matches depicted) as to what I believe is a better representation of the circuit?
     

    Attached Files:

  9. bwoogie

    bwoogie

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    Jun 5, 2012
    Correct.

    Also, do i have my resistors in the correct place? http://en.wikipedia.org/wiki/LED_circuit show's on the cathode while I have mine on the anode.
     
  10. davenn

    davenn Moderator

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    Sep 5, 2009
    they are not electronic matches
    they are pieces of nicrome wire, they will just get hot without fusing


    Dave
     
  11. davenn

    davenn Moderator

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    Sep 5, 2009
    yes the resistor location is ok

    in fact I prefer that way rather than the wiki way

    D
     
  12. CocaCola

    CocaCola

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    Apr 7, 2012
    And if that is the case there could very well be an issue...

    But, you can easily reverse the logic by simply moving the switch location...

    Light on in standby and light off when igniting...
     

    Attached Files:

    Last edited: Jun 6, 2012
  13. davenn

    davenn Moderator

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    Sep 5, 2009
    yup :) hence my original post .... the LED's will never see any current

    dang been watching the transit of Venus across the sun today
    its been a bit of a trying exercise with sun at times, cloudy and some times rain

    but managed to get some pics ... will put in the other off topic part of the forum later


    Dave
     
  14. CocaCola

    CocaCola

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    Apr 7, 2012
    edited my previous post in regards to reversing the logic by simply moving the switch...
     
  15. bwoogie

    bwoogie

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    Jun 5, 2012
    I like that idea. I will try it out when i get a chance.
     
  16. bwoogie

    bwoogie

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    Jun 5, 2012
    Ok! It works! Thanks for your help guys!
     
  17. CocaCola

    CocaCola

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    Apr 7, 2012
    Glad to hear it works, you can still get it to work the other way if you want, my suggestion of reversing the logic was just trying to keep it as simple as possible and still get a visual indicator...
     
  18. bwoogie

    bwoogie

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    Jun 5, 2012
    and here is a video of it working. it's daylight out so its kinda hard to see the LEDs but trust me they're working! :)

     
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