I have seen a few examples of wiring a red LED directly from the RPI GPIO pins, however, I need to wire a GREEN LED and am having trouble calculating the resistor needed. I believe that a green LED uses 3.3 volts and at 20ma, so if I use the 5V power on pin 1 would I end up with 5V - 3.3V = 1.7.
1.7 V = 20 mA × R
1.7 V / 20 mA = R
and when we solve that we get:
1.7 V / 20 mA = 1.7 V / 0.020 A = 85Ω ?