RGB and Current Limiting Resistors

My rgb leds arrived… I am going to begin multiplexing tonight and using the shift registers tomorrow.

But first I had to work out what current limiting resistor I would need. Using the datasheet for my LEDs I needed to know the led Current rating and the voltage drop (use a datasheet for your own Leds, as they will have different values to mine)

As I am using a standard Arduino the supply voltage from the D I/O pins is 5volts.  Now I can work out what resistor I need for each.  Here is my post-it note diagram:

Resistance =  Supply Voltage – voltage drop over the  Led current rating.

If you don’t feel like doing the calculation- here is a current limiting resistor calculator.

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