RGB LED circuit

[mattko]

Hello!

I'm trying to build an LED board made from RGB LED's. LED's will be arranged in four letters - name of my group. I already bought a lot of through hole RGB LED's from eBay (not diffused- I think it would be better to use diffused, but it's good for now) and 28cm x 40cm perfboard. I will solder all LED's on the perfboard and control them with a small arduino or attiny. I want that the letters fade in different colors. Arduino would control 3 MOSFETS to control the PWM of an individual color.

If I connect them all in parallel (about 15-20 LED's per letter x 4 = 80 LED's per color), but that is not too good.

Probably the best option is to connect 3 LED's (or maybe a few more) in parallel and then a current limiting resistor in series.

Ideal for me would be to use 12V power source, but I can get other voltages also.

What soulution do you think is the best one?

[klr5205]

Your question is kind of vague... careful or people will accuse you of asking us to design the whole thing for you.

That being said, you can connect several LEDs in series until the forward voltage starts to approach the supply voltage. For example, if the forward voltage of the green leds was 3.4V (and Vcc = 12v) , you could not have more than 3 in series because a 4th one would make the total forward voltage greater than your 12V supply.

Also, you cannot directly parallel LEDs of different colors (i.e. they cannot share a single current limiting resistor). The reason is that the LED with the lowest forward voltage (usually red) will steal current from the other colors.