Please help me with LED lights

Discussion in 'The Projects Forum' started by luisfsds, Oct 15, 2008.

  1. luisfsds

    Thread Starter New Member

    Oct 15, 2008
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    Hi
    I am planning to produce a sort of computer shelving unit which will be decorated with LED lights, preferably blue. I am think of having about a maximum of 15 blue LED's which will be shun through acrylic, which will be connected to the USB port ( supplies 5volts DC). I am realy stuck on which are the best LED's suited for my project and what else i need like resistors and watt resistors. Please help. Some explanations would also be useful as I am a bit new to electronics. :D

    Luis
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    If you select one LED at a time, your USB port may be ok. If you want all 15 on bright, you will need more power. I would limit the current from a USB port to 50 mills.
     
  4. luisfsds

    Thread Starter New Member

    Oct 15, 2008
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    hey thx for your guys adive it realy helped. Seeing as you guys say that the usb power is a bit too low how would i exactly plug it into the computer power supply which i think is 12volts?
     
  5. luisfsds

    Thread Starter New Member

    Oct 15, 2008
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    oh sorry i forgot to mention when i did the caluclation thing with the site it said i should get a resistor with a 1/8 power rating and all the ones i have seen have a 0,6 watt power rating, what does that actually mean and will it make a difference?:confused:
     
  6. bertus

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    Apr 5, 2008
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  7. luisfsds

    Thread Starter New Member

    Oct 15, 2008
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    WOW!!!:p You guys are fast haha thx so much helped loads. hopefully i will later on post a picture when i finish thx a bunch
     
  8. karthik_dm

    Member

    Oct 16, 2008
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    since USB can allow the maximum output of 500mA current, your circuit should not draw more than that. for 5volts I suggest u to use 680ohms to 1kilo-ohms resistor. a 1/4Watt is enough. connect 15 LEDs each with a resistor and connect to power supply. it is wise to take (5v)power supply from the SMPS of PC not from the USB.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    How did you arrive at those numbers?
    A typical blue LED might have a rating of 3.4v to 3.8v @ 20mA.
    Rlimit = (Vsupply - VfLED) / DesiredCurrent, so with the above numbers,
    Rlimit = (5V - 3.4V) / 20mA = 1.6/0.02 = 80 Ohms, and
    Rlimit = (5V - 3.8V) / 20mA = 1.2/0.02 = 60 Ohms.
    Since Power in Watts = Voltage x Current, 1.6 x 0.02 = .032. A 1/10 Watt resistor would be more than enough.
    I do agree with your last assertion.
     
  10. ellluses

    New Member

    Oct 21, 2008
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    I am a beginner in electronics so this question may sound dumb. What is the simplest circuit I can create in a remote transmitter to activate a 5 or 10 watt bulb?
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    You hyjacked this thread. Make your own thread.

    A transmitter does not activate a light bulb. A receiver with a high current output circuit does. A transmitter and receiver are neeeded. It is simple for a couple of mm but you forgot to say the distance you need.
     
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