Dimming LEDs

Discussion in 'The Projects Forum' started by dickbillz3, May 27, 2007.

  1. dickbillz3

    Thread Starter New Member

    May 27, 2007
    2
    0
    I bought a submersible tube of 25 blue LEDs for my fish tank. I would like to have the ability to dim them. The light plugs into a standard wall socket. I was thinking maybe a potentiometer could do this (cheaply) or a dimmer switch for a light in the house (more expensive). Attached is a pic of the light tube.

    I don't know a whole lot about electrical type projects, but I'm good with a solder gun, and live near a RadioShack. So if anyone can help out I would greatly appreciate it.

    Thanks,
    Dick
     
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  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    You can learn how to do this by searching for "PWM" or "pulse width modulation." ;) The dimmers won't work very well (potentiameter) or at all (wall dimmer) for LEDs.
     
  3. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    Since it's all sealed up cracking it open would be a waste. What is the voltage supplied to it? I assume current regulation is done inside the water proof housing which may make it difficult to do if it's more than just resistors.
     
  4. dickbillz3

    Thread Starter New Member

    May 27, 2007
    2
    0
    I will do a search on PWM, thanks!

    You are correct, cracking it open would be a waste. Without knowing resistor values or how current regulation is setup, will make this a slightly more difficult project than I thought.


    I guess I could try emailing the manufacturer and see if they could shed some light on how it's all setup.

    Thanks for the info!!!!

    This is a great forum!! I love tinkering with electricity and this place will help greatly!!!
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Yep. The AAC forum is "Tinker Central" for all your tinkering needs.

    If you need a bit of introduction to theory on a level that makes electronics fairly accessible, visit the tutorial section of the AAC website at www.allaboutcircuits.com.

    hgmjr
     
  6. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
  7. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    Why resort to PWM? Why not using a potentiometer conected as a variable resistor, in order to control current. Althought LED brightnes is not proportional to the voltage across a resistor-LED network (or across a LED), it is proportional to the current biasing it (with some logaritmic tendency). You can confirm by reading Kingbright or Nichia datasheets.

    Also, with a 555 timer you can make a pulse width modulator, but you have to use pin 5 (if I am not mistaken).
     
  8. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    yes you can use a 555 timer as your pwm as what cumesoftware has suggested but use pin 3 (output) to control a power transistor or a power mosfet.

    moz
     
  9. Ribid

    New Member

    Sep 28, 2007
    1
    0
    I recently used a 555 to control LED brightness for lighting a metal sculpture. I put a slow sine wave into pin 5 (control voltage) of the 555 to get a gradual brightening and dimming. It worked great, but I was only able to get 20-80% duty cycle swing. Anyone know what the ultimate limit is for duty cycle control via pin 5?
    Thanks,
    Paul
     
  10. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    The cheapest way to design this tube would be to put all LEDs in series (the Xmas tree effect, if one goes out they all do), with a single ballast resistor and a series diode/rectifier.

    Now, based on that assumption, a standard light dimmer should work. You could try one and see, shouldn't hurt anything regardless.
     
  11. jut

    Senior Member

    Aug 25, 2007
    224
    2
    Have you considered that these poor fish have to deal with super bright LED's in their face? :(
     
  12. arthur92710

    Active Member

    Jun 25, 2007
    307
    1
    where did you buy one? i want one for my fish tank too!!
    Petland does not have it were i live :(
     
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