RGB LEDs

[badbean]

Hey Guys,

So I'm putting together a Pork Barrel and on the new boards there is an LED that pulses with the rate of the LFO, which is awesome.  There is also a spot on the board for a regular "I'm On" LED.  I was thinking that it would be awesome to use a RGB LED so that it always glowed blue, but pulsed to purple or yellow with the rate of the effect.  This is what I'm thinking. I'll probably use an LED with a common cathode.  I'd put the blue leg in the positive side of the "On" LED, and the red leg in the positive side of the "pulse" led, leave the green leg out, and then which ground to I tie to? and do I need to put another 4.7k resistor in addition to the one in the board before it goes to a negative terminal since I'm having two currents into one LED?

[mjg]

If you have a look at the data sheet for the LED, it should tell you if the red and blue have different voltage and current requirements... in which case you would need a different resistor value for each '+' leg.

The RGB ones that I've used definitely have a different voltage drop on the red part. 

What I would try would be to connect the common ground pin to any ground (doesn't matter where - ground is ground, no matter where it is on the board), and then put a resistor between the red LED leg and the '+' for pulse, and a different resistor between the blue LED leg and the '+' power indicator.  If there are already current limiting resistors on the board, they may be all you need if they are on the '+' side of the LED. 

Try it out on a breadboard first if you're not sure, so you don't have to unsolder lots of stuff (and if you blow an LED, you can try again easily!)