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January 21, 2014
about 7 years ago
Thanks. So I need to first find the current I want and then find the forward voltage in the datasheet graph. Then I can calculate the resistor value. Since the resistor on the LED board is known to be 100 ohm, I will have to find which current and voltage pair that give a 100 ohm resistor. Correct?
3 mA give approximately 2.7 V forward voltage according to my interpretation of the diagram. This give (3-2.7) V / 3 mA = 100 ohm resistor.
So this means that when the battery (actually the AVR output pins) are at 3V, the LEDs get 3 mA given this LED datasheet and the 100 ohm resistor.
One of the comments for the white LEDs say "You can definitely run these without a LilyPad. But note that the forward voltage on these white LEDs is 3.3V, so your power supply will need to be higher than that."
How does the ProtoSnap - LilyTwinkle work with a 3V coin cell battery if the LEDs require more than 3.3V power supply?