Thank you for the tutorial. I learned a lot!
The first thing I learned is that the "lf" in my LED sticker stands for Forward Current.
Would you know what the "Uf" stands for?
...
I got a bit confused when we got to the actual formula part of your tutorial.
I see the +5V output and I see that we want to calculate R_LIMIT for 20mA.
I don't see how you jumped from the +5V above the R_LIMIT to the 3.0V in the R_LIMIT calculation rather than using 5V.
In your calculation 3.0V / 20mA = 150 Ohms. 3/20 = 0.15 so I assume that somehow 20mA gets converted to 0.02 in our calculation. We take 20 and divide it by 1000 as we're working with milliamps?
Why didn't we do 5.0V / 20mA to give us 250 Ohms as we have 5 volts coming out of the Arduino?
I therefore have a (red) wire going from the 5V of the Arduino to the (longer) Anode wire of my LED; a (black) wire going from the (shorter) Cathode wire of the LED to one end of the 150-270 Ohm resistor and another (black) wire going from the other end of the resistor to the GND pin of the Arduino.
My LEDs, except for the RGB ones, only have 2 pins. Where would I attach the wire going from the LED to the digital or analog output pin on the Arduino?