Help with alternating LED flasher.

Discussion in 'General Electronics Chat' started by reno12469, Jan 23, 2009.

  1. reno12469

    Thread Starter Active Member

    Jan 17, 2009
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    Hi,
    I want to build an alternating LED flasher that uses 2 sets of 48 blue LEDs that operates at 3.2VDC to 3.8VDC and the current is 20ma. This will be in a car. So it has the 14V. I was thinking of using a 555 and a 4017 but can the 555 handle the current? Each one will generate a 20ms pulse at a frequency of about 0.5Hz.
     
    Last edited: Jan 23, 2009
  2. Wendy

    Moderator

    Mar 24, 2008
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    This is disturbing. I more or less answered all these questions and more with your last thread...

    http://forum.allaboutcircuits.com/showthread.php?t=18182

    So what was wrong with the work I did there, given it was exactly what you are requesting again? You'll need to pin the LED Vf a bit more, it matters. I assume you still want to use the ones you pointed at there, with the 3.8 Vf.

    BTW, alternating blue lights is still illegal, but that didn't stop me from diagraming the answers here...

    http://forum.allaboutcircuits.com/showpost.php?p=113209&postcount=18
     
    Last edited: Jan 23, 2009
  3. reno12469

    Thread Starter Active Member

    Jan 17, 2009
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    I want to have them so they are more stable when going back and forth.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    And why won't they be stable? They are exactly what you asked for, designed to specification! OK, since you seem to know something I don't I'm done here. Good luck.

    I put a lot of work in this, not that it matters since this kind of stuff is transferable, but I doubt you're going to get that kind of help again, especially how you take it for granted.
     
  5. reno12469

    Thread Starter Active Member

    Jan 17, 2009
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    its not your design. its just that ive seen some 555 with leds and one side tends to be off and they flash kinda wierd
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    If you're talking the 555 Hysteretic Oscillator that has been covered, along with reasons the flash isn't symmetrical. The 555 will do exactly what you want, as I drew it, but you want to make assumptions feel free. All the 4017 will do in this case is add complexity, unless you're wanting to go whole hog and do the double flash emergency vehicles use.

    Believe it or not, I know something about this subject. Feel free to check my blog out, the link is on the corner of this post. I think I've built a few more than you in my 30 or so years doing this stuff.

    Again, you want a second opinion, and a second design, it might pass someone will step up to the plate. Maybe you'll thank them this time.
     
  7. reno12469

    Thread Starter Active Member

    Jan 17, 2009
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    Ok, sorry about that. I've just seen so much of the 555 and 4017 combined to do it. i know you know a lot more than i do.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    What the 4017 will do is create patterns in the flash, things like double flashes, and more. I'm in the process of writing an article else where where I'll try to explain it. It is still a work in progress. You're not the first person to ask about this.

    BTW, Circuit #2 in the previous thread is probably what you want to build, assuming you give me the benefit of the doubt. If you want X16 on the ropes you'll need a bigger transistor, a power model, for Q1 and Q3. Also, add a 0.1µF capacitor on pin 5 to ground.

    [​IMG]
     
  9. reno12469

    Thread Starter Active Member

    Jan 17, 2009
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    K, Thank you very much.
     
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