Simple LED

To power an LED with a 9 volt, do you have to use a resistor? If not will it blow out the LED?

Yes, and Yes

mmpal78 said:

To power an LED with a 9 volt, do you have to use a resistor? If not will it blow out the LED?

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I usually use a 1K resistor, though you can usually use a lower value. It all depends on the values of your LED. I just use a 1K because it allows a large safety margin, and because most of my LEDs are salvaged out of old circuit boards, so I don't have the values.
Der Strom