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Led project

Discussion in 'LEDs and Optoelectronics' started by jerryb, Mar 1, 2014.

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  1. jerryb

    jerryb

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    Feb 18, 2014
    Hi, trying to help a friend with a small lighting project, she wants a few leds in a display she has got to make for a course, they need to be very bright and need to be on for a long time without creating a lot of heat. They must also not be to directional. Any ideas out there, thanks.
     
  2. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    What do you mean directional. LEDs are certainly that, they are not like a light bulb.
    Adam
     
  3. jerryb

    jerryb

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    Feb 18, 2014
    That's what my friend is trying to achieve, they have to look like fire flies and will be wrapped in gauze so cannot get hot hence the leds, but must try to give an all round glow. Not sure that makes sense but that is what is needed.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If you get a regular white LED and scuff them up with some fine sandpaper so they look frosted you may find you get a look something like you want. Another option is to look for so-called "straw-hat" LEDs.
     
  5. jerryb

    jerryb

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    Feb 18, 2014
    Ah, that looks a bit more like it, thanks. Better to wire in series or not?
     
  6. shumifan50

    shumifan50

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    Jan 16, 2014
    Series is more efficient, but if one fails the string is dead, much like cheap Christmas tree lights. Or if it fails, shorting, it could blow all the other ones.
    Parallel is less efficient, but one failing will not affect the rest.
    As LEDs are fairly reliable, series is probably the best option, depending on what 'few' means. if 'few' means lots, you could wire several series strings and then wire the strings in parallel - google LED arrays.
     
  7. jerryb

    jerryb

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    Feb 18, 2014
    OK, got some straw hats and they do the job. Now got a new request to rig a flickering led to mains. Found a lot of fake candle leds but they are all battery and I need to wire them to mains as they will not be easily accessed to change a battery, Is this possible or do I need to go a different way? Again thanks for any help.
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Use a wall wart type Ac adaptor with e.g. 3V output voltage. You can use this directly in place of a 3V Lithium battery or 2AA batteries. For other voltages use the equivalent wall wart.

    You will find simple looking circuit using a capacitor, resistor and possibly some diodes that claim to allow use of LEDs on mains voltage. While these circuits will work, I do not recommend using them if you don't have the necessary experience.

    An AC adapter is much safer!
     
  9. jerryb

    jerryb

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    Feb 18, 2014
    OK, so I've got the straw hats and I need to wire them in singles and threes. I've attached the specs for the adapter and the leds, how do I work out the resistor for the singles as it looks like the threes will be ok?
     

    Attached Files:

  10. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
  11. cjdelphi

    cjdelphi

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    Oct 26, 2011
    it outputs 12vac

    how did you plan on making them flicker?
     
  12. shumifan50

    shumifan50

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    Jan 16, 2014
    You are asking for help without describing EXACTLY what you are trying to do;

    1. How many LEDs
    2. How do you want them arranged, in groups, singly. Could groups be put on a PCB(veroboard).
    3. How fast/slow do you want them to flicker, if at all.


    You have to, at least. answer these questions to get a coherent answer.

    You could also consider buying a string of LED(or even incandescent) Christmas lights and just remove the decorative plastic around the LEDs. These are available in flicker and non-flicker versions. They are designed to be put in trees, be on for extended periods and therefore would pose no fire risk.
     
  13. jerryb

    jerryb

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    Feb 18, 2014
    Thanks Harald, I've got some reading to do now.
     
  14. jerryb

    jerryb

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    Feb 18, 2014
    Update, the reason I'm trying to do this is a friend has asked me to help with a Fairy display at a local tourist attraction. There are five display cases that have single and multiple lights in them. Only a few have to flicker to look like candles and they are only in one case, the rest are to represent fireflies caught in lanterns. It's spread out so I thought using xmas lights would be impractical as they would need a major rewire anyway. We've had it running well once but the leds didn't look very good in daylight so we have decided to try brighter ones. Hope this makes things a bit clearer.
     
  15. jerryb

    jerryb

    68
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    Feb 18, 2014
  16. jerryb

    jerryb

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    Feb 18, 2014
    OK, got some blue and green flashing LEDs and using the resistor thingy I used a 470 ohm resistor and they worked really well hooked up to a 12V ac transformer. connected them to a different 12V transformer and they light up but don't flash. What am I missing? First transformer is an old scalextric, input 240V-50 Hz, output 12V-11VA. The new transformer is input 230-240 Vac 50Hz 150 VA, output, 12Vac 150VA. The bulb is forward Voltage 3.0 V max current 30mA. I did try them on the old transformer and they flashed.
     
  17. kpatz

    kpatz

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    Feb 24, 2014
    Do the wall warts put out DC or AC? You'll need DC for LEDs, especially the ones with built-in flashers.

    Also, how are you wiring them? Series may or may not work for flashing LEDs, depending on how the flasher IC handles varying voltage/current loads.
     
  18. jerryb

    jerryb

    68
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    Feb 18, 2014
    Wiring in parallel, just figured out that the adapter that works is DC, bum, now I have to source some cheap AC to DC adapters. How would I work out the amps needed for say five LEDs in parallel
     
  19. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Look at the data sheet for the LEDs and that should give you a good indication for what current they draw. Doesn't the flashing LED have a built in resistor? Flashing LEDs used to draw a large current when they start up I don't know if they are better now. What will the resistor in series do I don't know, probably won't start up properly.
    Adam
     
  20. jerryb

    jerryb

    68
    2
    Feb 18, 2014
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