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Thread: Some Electronics Help

  1. #1

    Default Some Electronics Help

    So, I've only ever built one saber before, and it was a super basic setup. Turned out well enough, I suppose, but now I'm kicking things up a notch.

    Working on the initial stages of a birthday gift for my fiancee. She's only recently taken any interest in this silly hobby (thank you, TFA!), and I thought it was a good time to give the grand old gift of her very own lightsaber. She's fairly set on purple.

    Now, I come to realize that purple LEDs don't exist (duh). No problem. I'm planning on using a Tri-Cree, Royal Blue-Red-Blue. I've done some research, and I've learned that you need to wire them parallel in terms of the resistors. Now, I'm gonna be honest: I have no clue what that means. Would someone mind explaining to a total electronics dolt what it means to wire them parallel, and maybe explain how to do it? Thanks a ton (sorry if I missed a thread that explains this).

  2. #2


    + to + and - to -. You'll need to buy several resistor values of resistors to dial it in. Check out the videos.

    The wiring will depend of what sound card you will use.

  3. #3


    I don't intend to use a soundcard; shoulda mentioned that this was a stunt saber. Will that actually have much effect on this?

  4. #4


    Parallel wiring means you attach a resistor to each LED die (either the + or the - pad, doesn't matter). Then you connect all the (+) together and connect all the (-) together. Then you hook the combined (+) and (-) to the battery and switch.

    Series is the other method of wiring (not particularly useful for color mixing). In series, you connect the (+) of one LED to the (-) of the next LED, making a chain of them. You hook up the unconnected (+) and (-) on the ends of the chain to the battery and switch.
    We all have to start somewhere. The journey is all the more impressive by our humble beginnings. for the lazy man's resistor calculator! for getting resistor values the right way!

  5. #5


    Just on the switch you use, wiring the LEDs would be the same if using resistors. For my purple saber using the hasbro/mosfets wiring I wired the rB and Red die. I had to resistor both slightly down from their max brightness to get the color I wanted. Using a 3.7v I used somewhere around a 1ohm on the rB and a 3 ohm on the red. I had several for testing and swapped them in and out using alligator clips until it was where I wanted it.

  6. #6


    Okay, so at present I'm planning to use a 3.9 ohm 5w resistor for the red and a 2.7 ohm 10w for royal blue and blue each. Does that sound about right, or am I doing something wrong?

    Edit: Also, would I just use a single 2.7 ohm 10w resistor for both rB and B? Sorry I'm so hopeless with these things.

  7. #7


    What battery setup? The wattage sounds fairly high. I did not exceed 2 watts on initially a 4.5v (3 AAA) setup. The 5w and 10w resistors wont hurt anything but they are large. You will want to get several different resistor values to mix to the desired color. I assume you are planning either a 3 or 4 AA/AAA setup or a 3.7 since a 7.4v in this case would be a waist of electricity.

    Running the math for a Red Cree 2.65 fv on a 3.7v input the 3.9 ohm gives 270 mA and only needs a minimum 1/2 W resistor. I would get several resistors ranging from 1.5 ohm to 3.9 ohm in a 1W rating.
    For the Blue the 2.7 ohm would only drive the LED at 111mA and would only need to be 1/8W. To be honest I don't think a Cree would even light at that low of current if it did it would be very dim. On a 3.7v battery the blues are safe on anything above a .5 ohm I would get several that range from .5 ohm to 1.5 ohm also in a 1/2W or 1W rating since you are not trying to fit a sound card and such into the hilt.
    Last edited by FenixFire; 06-07-2016 at 07:18 AM.

  8. #8


    Yeah, I was planing a 4AAA battery setup because of cost effectiveness. Will those resistors work for that, or should I change the battery setup?

    Thank you, by the way. All of this has been incredibly helpful, even if I'm too mathematically dense to make sense of much of it.

    Edit: When you say "several resistors ranging..." do you mean for just one die?
    Last edited by GarrHyde; 06-07-2016 at 02:05 PM.

  9. #9


    Personally that's a lot of wasted voltage being converted to heat by the resistors and not a lot of storage capacity. Basically if all 3 die on with a max of 1200 mAh battery you would have about 25 minutes of run time. If set on AAA try and find a 3 battery holder (Flashlights) or change to AA size for more capacity and use a 4 AA holder and a dummy AA insert. That way you are only supplying 4.5v so less wasted voltage for a slightly more efficient circuit. I initially did a 3AAA setup on my first build. Using only 2 dice and a Hasbro sound card I was getting between 20-30 minutes of run time depending on battery make. Within a month I had switched it over to a 3.7v cell.

    With those numbers that will run all 3 LEDs at full brightness probably resulting in a pinkish purple, you will definitely want to get some higher ohm resistors for each to dial in the color you want. I am still getting 3W for the wattage rating though, so no need for the monstrous 10W. If you don't want to do the math in your head here is a simple calculator that shows the actual value as well as the nearest commonly available resistor value.
    Last edited by FenixFire; 06-07-2016 at 02:30 PM.

  10. #10


    Ok, first check out the YouTube videos on color mixing LEDs and you will get an idea of what you will be doing. Basically you will need to test multiple resistors one at a time starting with the lowers recommended and working your way up in resistance until all 2 or 3 dice are resistor end enough to produce the hue of purple you are going for.


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