LED Flasher circuit needed

Discussion in 'General Electronics Chat' started by BigTom, Jan 16, 2009.

  1. BigTom

    Thread Starter New Member

    Sep 21, 2006
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    I'm not sure if this was ever covered on this forum so I want to apologize if it has. I would like a simple schematic of an LED flasher that flashes two LEDs alternately. I would like it to have them double flash like you see on construction vehicles. It would also be nice to be able to vary the flash rate via a pot.

    Thanks for all your help in the past.
     
  2. Wendy

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    Mar 24, 2008
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  3. BigTom

    Thread Starter New Member

    Sep 21, 2006
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    Correct me if I'm wrong but these circuits don't alternate two LEDs with a double flash. It looks like they just flash a group of LEDs with a quick double flash and then a pause and then a quick double flash. I'm looking for LED #1 to double flash then LED #2 to double flash then LED #1 to double flash, etc. This type of flash is used on most every road crew truck that I've seen lately. I have a model railroad layout with construction vehicles that I want to put the flashing LEDs on. I already have the Velleman #102 LED flasher that I use in quite a few places but these kits only flash the LED alternately, no double flash.
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    The attached will give you the pattern you are talking about.
    Flash-left>pause>flash-left>pause>flash-right>pause>flash-right>...
    You will need to add a 555 astable for the clock input and resistor/transistors to drive the LEDs.

    Ken
     
  5. Wendy

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    The difference between one LED and groups of LEDs is none.
     
  6. Wendy

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    Don't see it, I see an every other light pattern, <left><pause><right><pause><left><pause><right>. The Q7 needs to be Q8, as it will reset before it pauses.
     
  7. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Yup! Wrong schematic and I was wrong about the reset pin. :( I think..and if you will verify... this one will work.

    Ken
     
  8. Wendy

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    Basically looks OK. I'd eliminate R3 and R4, and use this schematic for the 555 oscillator...

    [​IMG]

    Just eliminate the LED's and resistors, use 100KΩ variable pot and 10µF, or maybe 100µF if you want so really slow action. The range is quite wide, it will adjust up so fast you can't see the LED's blink with either capacitor.
     
  9. Wendy

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    The two groups in all my revisions do alternate, it occured to me what you were saying. However you want something a bit simplier from what I can see. I'm redrawing KMofetts schematic...

    [​IMG]

    Generally it is a terrible idea to use a CMOS chip to drive LEDs. However, I have a extremely similar one I've used for 20 years without any problems, just limit the current to 10ma.


    Since it keeps coming up one way or another, I've drawn up an automotive version, which is much closer to the base circuit I made over 20 years ago. The LM317 current regulator will compensate nicely for a cars power supply fluctuations. 3 LEDs per chain is the max (2 LEDs for blue), although you can have fewer LEDs in the chain with no other changes.

    [​IMG]
     
    Last edited: Jan 18, 2009
  10. italo

    New Member

    Nov 20, 2005
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    To me looks like two lm555 one is free running at x frequency the other reset the first at y freqency. Changing the rate is a snap.
     
  11. Wendy

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    Huh? Which drawing are you referring to? All the drawings I've seen are astable, and adjustable?

    Not being arguementative, just trying to understand what you're saying.
     
  12. Søren

    Senior Member

    Sep 2, 2006
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    Hi,

    It has been covered a few times before, but here's a circuit that's tried and tested (in actual use on several EV's around the globe).


    [​IMG]

    I do have the project with PCB layout and all - tell me if that would help (preferably by email).
     
  13. BigTom

    Thread Starter New Member

    Sep 21, 2006
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    Thanks to all. I'm going to experiment tonight to see what works best. I like the idea of a variable flash rate so I'll give that a try too. These flashers are for on my commercial model railroad exhibit in Strasburg, PA, the Choo Choo Barn.
     
  14. critiera119

    Active Member

    Nov 21, 2008
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    Can 1n5 diodes be used instead of the 1n4148s?

     
  15. Søren

    Senior Member

    Sep 2, 2006
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    1N5 what?
    It's like saying 1N4 about 1N4148 - The "extra digits" are needed to discriminate any given diode from its "siblings".
     
  16. Wendy

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    Maybe a germanium? Just joking. Older parts had really low numbers.
     
  17. Søren

    Senior Member

    Sep 2, 2006
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    Yeah, OA91 is fresh in my memory (well perhaps "fresh" is not totally accurate) and I seem to recall something like 61 or 64 as the number (from back when our telephone numbers were 6 digits :p).
     
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