Changing LED colours

mongrol

Hi,

I've just received my kit (yay!) and will be start commencing my build this weekend. I'd like to perhaps change the chase light LED's from green/orange to blue/red. I believe I need to change the resistor values. Anyone know off the top of their head what value would be needed? From some brief googling it looks like I need the following info;

Voltage: 5v

LED Vf: should be supplied with LED.

LEF reference current: should be supplied with LED.

From the above I can use an interwebbed LED calculator to get my required resistor value.

Do I have that right?

cj55

Yes, it's easy:
The resistor (R) and the LED are connected in series. This means the current (I) of the LED (data sheet) will also flow through the resistor (R).
The supply 5V divide up in the known voltage of the LED (data sheet) and the rest will be on the resistor (R).
So: Resistor voltage (U) = 5V - LED voltage
Then Ohm's law: R = U / I

But you probably want to experiment with the resistor value, because especially blue LEDs are often much to bright!
Values from experience: normal LEDs (red, green, yellow): 220 Ohm. Bright LEDs (blue, white): 1K-10K Ohm

mongrol

Excellent thanks. So from that if I find a blue LED is too bright I increase it's resistence.

julian

another thing to note is that you are not restricted to use resistor networks for the LEDs.
normally the five 220 ohm resistor networks drive the LEDs.
you can also leave out the networks and use the spots marked "R_LED" on the PCB to use normal resistors.
just don't use both

mongrol

Thanks Julian. I've reconsidered in light of the new case being green so I'll be sticking with green/red to maintain the watermelon illusion. My kit didn't have any 220 Ohm networks in it so I'll pop along to our local leccy store and pick some up (or single ones if they they lack combs).