Resistor value?

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1

Hi,

I have a quick question about what resistor to use. I'm just starting to learn Arduino and electronics in general and am getting ready to go through Beginning Arduino. The first project calls for a 5mm LED light, and the one I have is 2v and 20mA. This equates to the resistor needing a value of 150 ohms. The book says not to use a resistor with fewer ohms (i.e 100), which I understand. My question is how much over that amount can the resistor be? I have some 330 ohm resistors. Is this acceptable or do I really need to get some 150s?

Thanks!

2

higher is fine but your LED's will be dimmer

3

(5V - 2V)/0.02A = 150 ohm.
Or,
(5V-2V)/150ohm = 20mA.

Higher resistor, lower current. Change in brightness may or may not be noticable.

Two 330 ohm resistors in connected in parallel may also be used.

Requivalent = R1R2/(R1+R2) >> 330330/(330+330) = 165 ohm.

3V/165 ohm = 18mA.