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Disaster Led confesses true colour

Discussion in 'Modding' started by Garbach, 18 Dec 2003.

  1. Shogun

    Shogun Banned

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    I have noticed when i overvolt leds they quickly go bright red and then give out a light which is invisible to see to the human eye. This is often reffered to as a nuked led. :lol:
     
  2. death_star

    death_star New Member

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    Opps, my bad, delete if u want.
     
  3. star882

    star882 New Member

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    Blue LEDs and white LEDs are similar in construction (in fact, most white LEDs are blue LEDs with a phosphor), so such a change is more likely.
     
  4. Pygo

    Pygo Rick Relixed

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    interesting.. I thoight that was posted before though...

    and hope you don't mind my asking.. why does Shogun's name say banned/suspended under it??? is he really??? I hope I am not offending anyone in any way by asking that.
     
  5. Neuffy

    Neuffy New Member

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    hehe....
    I've taken to overvolting leds as a hobby....
    At 12V, green leds just die. no colors, nothing.
    At 5V, they survive...did a 1/2 hour test, and it kept going.
    At 7V, they glow for a second, die, and then burst into life again as a weird orange. Then smoke and burnt center. Very, very bad smell :(

    Anyway, it's a cheap little thing...but not for 4 euros...I bought mine (550, - 300 blue, 50 red, green, white, 100 UV) from ebay...http://www.stores.ebay.com/chiwingledproductshop Free shipping, took 4 days to Canada. worked out to about $0.17CND/led.
     
  6. johnwilliams474

    johnwilliams474 Banned

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    lol i was doing some mods the ther day and at my house i have a couple of outlets that look like the 120volt outlet people are use to seeing but i have 240volts going through them fot bigger tools
    i told my freind to plug my new dremel it ant i turned it on and throud sparks and then it died
     
  7. David_Fitzy

    David_Fitzy I modded a keyboard once....

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    I always thought you needed a current limiting resistor on any LED otherwise you'll short out your supply, it being a diode and all :confused: and http://lsdiodes.home.comcast.net/circuitry.htm only confuses me more

    EDIT: Ok I've just played around with a simulation package (v. powerful Crocodile Clips) and I see you don't need a resistor now :duh: and I think I understand why not.

    Just so long as nobody finds out that I'm a electronics degree student :worried: :blush: (Well Robotics student really I haven't touched on any electronics theory for a year and a half now :( )
     
    Last edited: 12 Jan 2004
  8. Pygo

    Pygo Rick Relixed

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    I duno about shorting out the supply... But burning out the led maybe (with power fluctuations.)
    I would conult Zapwizard on his never ending wisdom of electronics...
    Or search the forums first so he doens't get mad about having to repeat himself... :lol: I saw him stating stuff about leds before.. don't remember which forum though... I think there were a few...
     
  9. Blue Raven

    Blue Raven New Member

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    You must always use a resistor on led's. This is because led's, like all diodes have a constant voltage drop. This means that a 1.7 volt led will try and keep the voltage across it to 1.7 volts. Led’s also have a current rating in milliamps. If you go too much above the current, the led will overheat and damage it's self. You cannot regulate the voltage for a led because unlike a resistor, led's have a negative resistance coefficient (I think that's what it is called, correct me if I’m wrong). This means that as the voltage goes up, the resistance of the led goes down to try and keep the voltage the same. Because of this, even a small variation is the voltage supply or if the led is slightly out of specification, the led will draw too much current and overheat. The reason for the resistor is that you can regulate the current going through the led and the led will settle on whatever voltage it likes (the voltage that the led is rated for). Sometimes you see led's without a resistor in keychain lights and other small lights. This is because coin cells can only supply a few milliamps and therefore limit the current without a resistor. Also some led's have the resistor built in, but this is quite rare.

    edit: (sorry if I am not verry clear, if people cannot understand this, I'l try to explain it better)
     
  10. David_Fitzy

    David_Fitzy I modded a keyboard once....

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    Well before I saw this thread I was of the opinion that LEDs where current driven and had negligable resitance so connecting them up directly would draw far too much current as Any Voltage/Zero Resistance = Infinite Current

    Ok, so in the case of my keyboard I used 3 Ultra bright BLue LED's in parallel in series with a Resistor and It's obvious why for this (PS/2 has limited current)

    Code:
                 ,-----(>|)-----.
         Res     |     LEDs     |
    5V--[===]----|-----(>|)-----|-------Gnd
                 |              |
                 '-----(>|)-----'
    LED's where 5V 30mA
    PS/2 current limit is 100mA max
    status LEDs (Caps, Num Scroll) took 25mA total (measured)

    So 100-25=75mA spare

    Res = 5V/75mA = 66 Ohm

    Each LED runs on 22mA

    (don't quote me I can't actually remember presisely :confused: )

    [​IMG]
     
    Last edited: 13 Jan 2004
  11. lamcdonald

    lamcdonald New Member

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    I was testing a 3-digit display out of an old AT case the other day. The segments were supposed to be RED. However I connected the 5V to the switch input instead of the supply pins :duh: And they went ORANGE for a few seconds and then died. But there were still some segments which hadn't been cooked, so I decided to kill the whole thing and connected it to 12V. The remaining segments went very bright WHITE for a few seconds and then died. :eeek:

    I've also managed to get blue light out of a green LED by connecting 150V DC through it. :hehe: But that was a spark, not the actual LED part making the light.
     
  12. Pygo

    Pygo Rick Relixed

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    No ****ing ****, eh? :lol: I gues it would do that. hmmmm... I wonder.. I should try somethin like that for fun next time I'm board.
     

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