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Thread: First Saber wiring and resistors question

  1. #1

    Default First Saber wiring and resistors question

    Hello all. I am currently building my first saber (Blue) using an econo board from an Obi-wan "force action" saber from around 2008-9. I plan on using this RGB LED from a French site: http://www.selectronic.fr/star-led-a...mmune-120.html and this AV switch: http://www.selectronic.fr/poussoirs-...tenu-vert.html , all powered by 4 AAA batteries and wired like so:

    Wiring Schematic.jpg

    Normally 4 AAAs should be enough, but I can't seem to determine what resistors to buy. Using Ohm's Law as explained on this post:http://forums.thecustomsabershop.com...e-to-Ohm-s-Law, I already worked out that I need a total of 6.9 Ω and 1W. Could someone help me please?

  2. #2

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    You'd need a resistor of at least 6.9 ohms and at least 1 watt, assuming your math is correct. Which, if you followed the Ohms Law formulas, it should be.

    You can always go larger, but not smaller.
    When you do things right, people won't be sure you've done anything at all.

  3. #3

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    If using 4AA batteries that is 6v Some of the boards can take it some cannot. If the saber had 4 AA to start with you should be safe, if it had 3AA or 3AAA you will need to add a 5v regulator.

  4. #4

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    Awesome, thanks! This would be for the RGB LED, and the AV switch's LED ring would require a different resistor, right? Thing is, I can't find the current it needs to be run at on the webpage, the only specs for the led itself are that it requires 12V DC to run. Given that 4 AAA batteries give out 6V, I can't figure out if I don't actually need a resistor for that LED or if I'm making a mistake. I checked the custom saber shop page for practically the same switch (Latching 16mm AV with green LED ring (long) ), but the specs there are different, stating that the LED "has a forward voltage of 3.3V and runs at 20mA". I'm a bit confused, as I don't see any other difference between the French website's and the Custom Saber Shop's switch.

  5. #5

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    Each LED die should have its own resistor. The voltage drop of an LED is based on its color. Wattage is just volts x amps. So if you know the voltage drop and the wattage, you can figure out the current draw of the LED.

    If you have an RGB LED and an AV switch with LED, you should have 4 resistors.
    When you do things right, people won't be sure you've done anything at all.

  6. #6

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    Voltage drop is listed on the sheet you linked.

  7. #7

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    Oh that makes sense. Current = Wattage / Voltage. But if I need 4 resistors as you say, where on the circuit would they go? I'd have thought I only needed one before each led. In any case thank you both for your help so far!

  8. #8

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    Quote Originally Posted by RCPlaneguy View Post
    Oh that makes sense. Current = Wattage / Voltage. But if I need 4 resistors as you say, where on the circuit would they go? I'd have thought I only needed one before each led. In any case thank you both for your help so far!
    Yes 1 resistor on the positive feed between the PNP and the Die. You have to wire the main LEDs in parallel not series. If trying to mix a specific color you will need lots of different resistance value resistors and experiment to get the color you are going for. If you simply use the max value of each you will get white. Max blue and red will give you a pinkish white, blue and green will give you a tealish white, didn't try the red/green...now that I think about it.

  9. #9

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    Quote Originally Posted by RCPlaneguy View Post
    Oh that makes sense. Current = Wattage / Voltage. But if I need 4 resistors as you say, where on the circuit would they go? I'd have thought I only needed one before each led. In any case thank you both for your help so far!
    Just translated the website with the LED. I am not sure this LED will work for this conversion. The LED star you purchased is a Common Annode (+) not a Common Cathode (-). The wiring diagram may have to change. For the main LED, in theory you could put the resistors on the negative leads between the battery and the LED.

  10. #10

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    Alright. I understand, I'll re-think the circuit. But is it fine if I only use one color of the three in the main LED?

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