Lighting an external led

Hi every one, I use Arduino UNO. I've been trying to do blinking projects,using two leds, the first one is within the Arduino, the second one is a led with a resistor 22o ohm. my problem is that the first led is working fine, even if I've changed the delay time. but the other one(with the resistor) never light at all! I've checked the led using multi-meter and it's working fine. what do you think guys?

Forgive me if this is too obvious... have you tried the LED "the other way around"? Besides being light emitting, they ARE also diodes, and thus only "work" one "way around".

If not that, I'm not sure what you are asking. Does it not work when plugged in in place of the one that does work?? You mention "external"... do you mean that the LED on the board blinks, but yours won't?

Try plugging yours... WITH the resistor, never skip the resistor, "across" your power supply. I.e. one leg to the 3V3 or 5v your Arduino is running on, other leg to "Ground". Should work. Until it is working thus, the Arduino won't be able to make it work.

Or maybe you just have it connected to the wrong pin. Or you forgot to connect the other end to ground.

We can’t see what you have and how you’ve connected it together…so it could be anything.


Hi, Welcome to the forum.

Please read the first post in any forum entitled how to use this forum.,148850.0.html then look down to item #7 about how to post your code. It will be formatted in a scrolling window that makes it easier to read.

How have you got your LED and 220R resistor connected?

Tom... :)

You always need a resistor with an LED so your experiments without are wrong and will damage the Arduino and LED. Have you set the pin to be an output with a pinMode call?

Thanks guys for replying.. Ok, #1 the problem is that I can easily control the LED, but mine is always not working, neither blinking or light for a long time. I'm sure that I using it in the right way the negative(short one) goes to the ground, and the other one with the resistor.

I've just figured out that I'm the problem! I was connecting the resistor to the wrong pin. I'm sorry guys>