RGB Led

Maybe this is a dumb question but, is it possible to make the led show any other color than red, blue or green? I had the crazy idea I would be able to combine them but when I light blue+red (using the same voltage and current) I don't get purple, red just overwrite blue. Is that the normal behavior of these babies?

That's normal behavior; the red element is typically much brighter than the green and blue and will drown them out.

You need to connect the three colors to separate PWM pins on the arduino and use analogWrite() if you want to get a good mix of colors. Don't be surprised if it takes a while getting that color mixing right either.

Chagrin:
That's normal behavior; the red element is typically much brighter than the green and blue and will drown them out.

You need to connect the three colors to separate PWM pins on the arduino and use analogWrite() if you want to get a good mix of colors. Don't be surprised if it takes a while getting that color mixing right either.

Thank you Chagrin,
I was planning to multiplex them in a 595 cascade, but according what you mentioned if I want them showing non primary colors that would be impossible, right?

EDIT: I'm now reading about this chip: TLC5940
Does it also work as multiplexer?

Chagrin:
That's normal behavior; the red element is typically much brighter than the green and blue and will drown them out.

No, no, no.

The red LED has a lower voltage drop than the blue and green. The OP is effectively shorting out his power supply through the red LED and causing the voltage to drop below the point where the blue and green LEDs will light. If the power supply could supply the current, he would fry his LED.

Voltage is constant across circuits connected in parallel, and different colour LEDs have different forward bias voltage drops.

Yes, Socrat is correct if you're trying to drive all of the LED elements with the same voltage. You have to make sure you're limiting the current through each color to (typically) 20ma (or .02A):

Typical forward voltage (Vf) for each led color:
Red: 2.2V
Green: 3.5V
Blue: 3.5V

Subtract the Vf from your supply voltage, then use Ohm's law to calculate the correct resistor to limit it to 20ma. Example for the red when using 5V supply:

5V - 2.2Vf = 2.8V.
Ohm's law: V / I = R. So 2.6V / .02A = 130ohm resistor

BUT AGAIN, the red element tends to be more intense than the blue or green. If you light up all three colors with their 20ma limit the light will look reddish; it takes a bit of tweaking to get good color combinations.

BUT AGAIN, the red element tends to be more intense than the blue or green.

It depends on the LED. I have some where the red is the least intense.

You need to diffuse the light from the LED to make them mix better.

I noticed same with mine: the clear "glass" means the 3 colours are visible as 3 separate leds... I found "some" measure of success by scrunching up some tracing paper as a sort of "lamp shade" , but still by no means a single colour mix.

Try fine sand paper on the LED to make it mat.

Another favourite solution is to drill a 5mm hole in a ping-pong (table tennis) ball and insert the led into that.

Another favourite solution is to drill a 5mm hole in a ping-pong (table tennis) ball and insert the led into that.

But the wires make it difficult to serve.

You can also dip the led into solvent.

PaulRB:
Another favourite solution is to drill a 5mm hole in a ping-pong (table tennis) ball and insert the led into that.

Here is one I made earlier:-

Don’t you just like having to download images.
This is a great feature in the new forum look.
NOT!

Mike, it almost looks a bit naughty for some reason.
Not sure why.

It is a colour snap game from:-