Quick Newbie Question Regarding Resistors

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johnnyr
 
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Quick Newbie Question Regarding Resistors

Post by johnnyr »

Hello all,

I purchased the Arduino Starter pack, and already have a question! In the first tutorial, we connect up an LED to Pin 13 and GND, and upload a sketch to blink it. However, we do NOT use an Resistor! In all future tutorials when connecting an LED, we DO use a resistor. Why is this? why do we not need one for the first tutorial? I'm confused =)

Thanks!

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mitpatterson
 
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Re: Quick Newbie Question Regarding Resistors

Post by mitpatterson »

There is a LED soldered on the board already to pin 13, along with the needed resistor so connecting to pin 13 doesn't need a resistor

johnnyr
 
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Re: Quick Newbie Question Regarding Resistors

Post by johnnyr »

mitpatterson wrote:There is a LED soldered on the board already to pin 13, along with the needed resistor so connecting to pin 13 doesn't need a resistor
Ah ok! that makes sense. Thank you!

adafruit
 
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Re: Quick Newbie Question Regarding Resistors

Post by adafruit »

mitpatterson wrote:There is a LED soldered on the board already to pin 13, along with the needed resistor so connecting to pin 13 doesn't need a resistor
this is not correct at all. the photo is for using the NG only. please do not tell beginners incorrect information - thanks!

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mitpatterson
 
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Re: Quick Newbie Question Regarding Resistors

Post by mitpatterson »

mi copa(sp) so really the answer is you don't need a LED or resistor for that turooiral :D but if ii'm not mistaken(and i just tested this) you should be able to hook a LED up with up to pin 13 with out a resistor(other than the ones on the board) I just tested it and the led still works.

adafruit
 
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Re: Quick Newbie Question Regarding Resistors

Post by adafruit »

it is not good for the microcontroller. for more information about LED please read our LED tutorial

http://www.ladyada.net/learn/arduino/LEDs.html

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richms
 
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Re: Quick Newbie Question Regarding Resistors

Post by richms »

The arduino will limit the current to the point that the LED doesnt get killed, but its still a huge overcurrent for the LED and not advisable to connect without a resistor. There have been many "improvements" on other *duinos etc to do with the pin 13 situation so IMO its the last pin that should be used for projects except for using the onboard LED when it is present.

parkham
 
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Re: Quick Newbie Question Regarding Resistors

Post by parkham »

adafruit wrote:
mitpatterson wrote:There is a LED soldered on the board already to pin 13, along with the needed resistor so connecting to pin 13 doesn't need a resistor
this is not correct at all. the photo is for using the NG only. please do not tell beginners incorrect information - thanks!
I just checked and I think the confusion lies in the fact that most Arduino boards do indeed have a pull up resistor and LED attached to pin 13. The Uno does not have such a resistor (as you mentioned).

From http://www.arduino.cc/en/Tutorial/DigitalPins

NOTE: Digital pin 13 is harder to use as a digital input than the other digital pins because it has an LED and resistor attached to it that's soldered to the board on most boards. If you enable its internal 20k pull-up resistor, it will hang at around 1.7 V instead of the expected 5V because the onboard LED and series resistor pull the voltage level down, meaning it always returns LOW. If you must use pin 13 as a digital input, use an external pull down resistor.

and as a reference side note here: http://www.arduino.cc/en/Tutorial/Blink

If you've got experience with electronics, you may notice that the LED doesn't have a resistor in series with it. This is because the amount of current coming out of the output pin of the Arduino is low enough that it won't damage the LED. This simplifies the circuit for beginners to delete the resistor. In general practice, though, it's a good idea to add a resistor in series with the LED.

Just trying to help. Thanks.

adafruit
 
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Re: Quick Newbie Question Regarding Resistors

Post by adafruit »

you are misreading this information, please follow our LED tutorial
MOST arduinos DO NOT have any inline resistor, ONLY the NG which is rare to find these days as its many years old.

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mitpatterson
 
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Re: Quick Newbie Question Regarding Resistors

Post by mitpatterson »

Now i'm not trying to start a flame war here or a fight, but adafruit, i know its not inline, but as parkham pointed out that the voltage is low enoguht due to the resistor and lED already in place. and now unless the ardunio uno refernce designs are wrong(unlikley) then there is one, see the attached screen capture from the shematic:
resistor.JPG
resistor.JPG (51.02 KiB) Viewed 3948 times
That will always have some pull down effect on the pin

adafruit
 
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Re: Quick Newbie Question Regarding Resistors

Post by adafruit »

we're not going to explain the details on this since it not relevant, but perhaps someone else will be able to or would like to. if you are wiring up LEDs, please follow our LED tutorial and use a resistor.

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