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### Topic: Bright LED's (Read 1 time)previous topic - next topic

#### Terri

##### Nov 02, 2008, 09:21 pm
Hi im having trouble with something which i thought would be simple, but its doesn't seem to be.

i compiled  the blinking test and is it communicating with my arduino.  so i know it is working. however i wanted to switch the current LED with a brighter LED (product code - N20BY Blue LED), i read on some forums that i needed a resistor otherwise it will fuse out, so with that i put the new LED through a breadboard.  so the current circuit is

connected through the breadboard via wires
GRD--> to LED --> to 1kohm resistor -->back to 13pin

but im having difficulty with making the Bright LED turn on

i was trying to mimic this tutorial
http://www.ladyada.net/learn/arduino/lesson3.html

can anyone advise. thanks

#### madworm

#1
##### Nov 02, 2008, 10:34 pm
The led is either reversed or 1k is too much. It's got a forward voltage of 3.6V (link), so 1k limits the current to 1.4mA. The led is rated for 30mA max.

R = (supply voltage - forward voltage) / desired current

So I'd test for polarity and later switch to a different resistor to allow for some more current. A value of 100 should give about 14mA.
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#### Terri

#2
##### Nov 02, 2008, 10:59 pm
sorry im very new to all of this, but does that mean, i could actually use the LED without a resistor?

thanks

#### madworm

#3
##### Nov 02, 2008, 11:35 pmLast Edit: Nov 02, 2008, 11:37 pm by madworm Reason: 1
Please don't !

The current grows exponentially once you  pass the on-voltage (link). So either you precisely hit the right spot on the VI curve, or you create SMOKE. LEDs need a current limiting "device", the simplest being a resistor.

• Upload doesn't work? Do a loop-back test.
• There's absolutely NO excuse for not having an ISP!
• Your AVR needs a brain surgery? Use the online FUSE calculator.
My projects: RGB LED matrix, RGB LED ring, various ATtiny gadgets...
• Microsoft is not the answer. It is the question, and the answer is NO!

#### Terri

#4
##### Nov 02, 2008, 11:48 pm
thats fine, i'll just go out and buy one. thanks for the advice

#### gnu_linux

#5
##### Nov 03, 2008, 12:10 amLast Edit: Nov 03, 2008, 12:23 am by gnu_linux Reason: 1
Doesn't Pin 13 already have a built-in current limiting resistor on it for LEDs?

The rest of the digital pins do not so you will need the appropriate resistors for them but I believe Digital Pin 13 already has a resistor

Please correct me if I'm wrong

#### madworm

#6
##### Nov 03, 2008, 12:26 am
There is a 1k resistor at pin13, but it only limits the current of the on-board led.
• Upload doesn't work? Do a loop-back test.
• There's absolutely NO excuse for not having an ISP!
• Your AVR needs a brain surgery? Use the online FUSE calculator.
My projects: RGB LED matrix, RGB LED ring, various ATtiny gadgets...
• Microsoft is not the answer. It is the question, and the answer is NO!

#### Terri

#7
##### Nov 03, 2008, 02:24 am
the new LED that i brought didn't want to work in the PIN13 hence i felt i had to the use the bread board, and it worked somehow. so no worries there

#### robotkid249

#8
##### Nov 03, 2008, 02:45 am
Obviously it seems to be that the positive and negative are switched around.

#### Grumpy_Mike

#9
##### Nov 07, 2008, 01:06 pm
Quote
I believe Digital Pin 13 already has a resistor

It depends on what sort of Arduino you have. I have seen one on the Arduino mini schematics.

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