Originally Posted by
Darth Nater
Two resistors. One for Blue, one for Red. The red will require a larger resistor to tone it down since it will overpower the blue. They say "no certainty" because the values will differ depending on the led and power source. The following by no means will translate directly to your build, but can serve as a half a$$ed explanation.
I have one saber that uses a cheapo Obi-wan soundboard running off a 6volt power source (4AAA). Well, actually I just switched this out to a 7.4 lithium ion setup but no matter, that board has to be setup entirely different and likely runs around 5V anyway. Regardless, for my setup using a Dealextreme cheapo RGB from China, I have it parallel with a 1watt/4.7ohm resistor on the red and I think a 1watt/1ohm resistor on the blue. I got on mouser.com and bought like 2 each of various little 1 watt resistors and played around with it til I got the shade I wanted. They are like 17-50 cents each so no bank breaker. Could have used a potentiometer but couldn't find one that was 1 watt and while tedious, this seemed easier to me. And aside from when I built the saber, I'm never involved with this kind of thing.
Your setup would be much different with a NB board sending out more juice to the LED that my setup is with the $20 toy saber soundcard is, and depending on what LED you used, that would change as well. For the little setup I have on this saber it comes out a decent purple.
My other purple is out of a 7.4 source through a PC board and an LEDEngin RBGA. The PC of course regulates the current and it doesn't need a resistor for this, but for one reason or another, I have it wired in series and it comes out perfect. I would have thought the red would overpower without being resistored back, but it doesnt in this case.
Aside from my rambling, the short answer was 1 resistor for the blue die and one for the red. The red will need to be resistored more(larger resistor) since red will suck current and overpower blue. This prevents the pinkish. The larger the resistor on red, the closer to a purply blue it will get. The smaller the resistor on red, the more pinkish it will get. When the batteries get low, it will get a lot closer to pink as the red will suck up the power.
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