Building LED strip from RGB LED Pirahna

Discussion in 'The Projects Forum' started by aquarius, Oct 16, 2009.

  1. aquarius

    Thread Starter Active Member

    Mar 14, 2009
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    I need to build LED strip by using 20 RGB LED Piranha.
    This strip I'm going to connect to LED controller.
    Controller has 12VDC output with many color changing options.
    Please help with circuit.
    Thank you.
     
    Last edited: Oct 17, 2009
  2. Wendy

    Moderator

    Mar 24, 2008
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    We're going to need a lot more info I think. What is a Piranha? Do you have a LED controller, or are you asking how to build one?
     
  3. aquarius

    Thread Starter Active Member

    Mar 14, 2009
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    Yes, I have a LED controller and need a circuit to build 20 LED RGB strip.
    Please see attachment about LED RGB Piranha.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    It is good that you bought the common anode version; that will be much easier to deal with.

    You need to supply more information about the controller.

    Is the output 12v when the LEDs are supposed to be on, and 0v when they are supposed to be off?

    What will you be using for a power supply? 12v? Will you also have 5v available?
     
  5. aquarius

    Thread Starter Active Member

    Mar 14, 2009
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    Controller takes 12VDC from the power supply and has Vcc, R, G, B outputs. Controller is able to perform different color changing modes ( flashing, dimming, fixed colors, etc).
    Do you need more information?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, the information you have provided about the controller is far too general. More specific information is needed, as per my previous post.

    If you have a datasheet for the controller, please provide it, or provide a link to it, or the specifications of the controller.
     
  7. aquarius

    Thread Starter Active Member

    Mar 14, 2009
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    My friend gave it to me. As far as I know the controller can drive up to 252 LEDs. That's all I know about controller. Sorry.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Does the controller have a manufacturer and part number on it?

    Does your friend have instructions and/or schematic for it?

    If not, you will have to figure out how it works, and draw up a schematic for it.
     
  9. aquarius

    Thread Starter Active Member

    Mar 14, 2009
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    When I measure output voltage between Vcc and R or G or B it shows max 14V and min 0 V.
     
  10. aquarius

    Thread Starter Active Member

    Mar 14, 2009
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    This controller is from broken light bulb. There are some digits on the PCB, but it doesn't say anything about manufacturer.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    OK, so try connecting up just one RBG LED like this:

    [​IMG]

    The common cathode of the RGB LED is connected directly to Vcc.

    Each of the R,G,B leads needs a 430 Ohm resistor on it.

    I derived this current limiting resistance value by using the values in the datasheet for Vf (Forward Voltage), and the voltages that you are measuring:
    Rlimit >= (Vsupply - LED_Vf) / Desired_Current
    Rlimit >= (14v - 3.4v) / 25mA
    Rlimit >= 10.6v / 0.025 Amperes
    Rlimit >= 424 Ohms. 430 Ohms is the closest standard E24 value of resistance that is greater or equal to 424.
    Table of standard resistance values is here: http://www.logwell.com/tech/components/resistor_values.html
     
  12. aquarius

    Thread Starter Active Member

    Mar 14, 2009
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    Thank you for your effort. I've forgot to mention that I've connected that way only ONE RGB LED to the controller and it works great. I need to build a circuit for 20 LEDs, which will work from the same controller.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    OK, so you will need sixty 430 Ohm resistors for your twenty RGB LEDs.

    Each cathode lead (R, G, and B) on each LED will need a resistor.
    Don't try to "share" resistors between LEDs, or they will be very dim.

    Get yourself some stripboard or perfboard and wire it up.

    Try to be neat.
     
  14. aquarius

    Thread Starter Active Member

    Mar 14, 2009
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    You mean that I have to connect all 20 LEDs in parallel?
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Yes.

    If you had individual red, green, and blue LEDs, you could connect perhaps three in series strings with one current limiting resistor per string.

    However, you have RGB LEDs, that have a single common anode. You cannot connect them in series.
     
  16. aquarius

    Thread Starter Active Member

    Mar 14, 2009
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    Thank you again.
     
  17. SgtWookie

    Expert

    Jul 17, 2007
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    You're welcome. If you find yourself "stuck", post again. If you get it working, why not post photos here, or make a video and post it on YouTube or someplace and post a link to it.
     
  18. Wendy

    Moderator

    Mar 24, 2008
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  19. SgtWookie

    Expert

    Jul 17, 2007
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    Bill,
    That's all great info, but unfortunately with his current project he can't really use anything more than the formula for the current limiting resistors that I've already posted.

    His RGB LEDs have 4 pins; a common anode and one each for Red, Green, and Blue.

    There is just no way for him to use these RGB LEDs in series, nor to cut down on the number of resistors that are required - unless he wants to risk thermal runaway and subsequent melt-down.
     
  20. Wendy

    Moderator

    Mar 24, 2008
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    I suspect the current regulator info could be handy, which covers sinks as well as sources.

    His LEDs are not going to drop the same amount of voltage for each, which means one size for all resistors isn't really that appropriate. I've been pretty busy at work, but I also have the impression he may want to make it variable, though I could be off on that assesment. I've been meaning to redraw the standard transistor model I have using a LM317 as a voltage reference.

    [​IMG]
     
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