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Author Topic: Complete newbie - completely thick - LED not lighting!  (Read 905 times)
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Hello everyone,

I just purchased an Arduino Uno after reading a bunch about it. Very excited about being a part of this.

I am, however, struggling with the first step! The orange LED on the board lights and flashes. When I upload to it, the TX/RX LEDs flash too so I have connectivity. When I stick an LED in gnd and 13... nothing happens with the LED. The LEDs are clearly rubbish, but I didn't really know that when I picked them up. They don't have an obvious longer/shorter leg either. I have tried a few of them (pack of 10) and still nothing. Could it really be that all the LEDs are dead? Could there be something wrong with the pins on the board? Could they be the "wrong kind" of LED as they have no longer/shorter leg?

Quite unbelievably inept at this. Sorry!
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For what it's worth - I tried the potentiometer tutorial and could see the numbers change in the serial monitoring bit, so the board seems fine. Could there be something wrong with just those pins?

Thanks smiley
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LED's are polarised. They need to be connected the right way round to work.  Plugging one into GND & pin 13 is not a good idea on an arduino made in the last 5 years (including the Uno). There is no current limiting resister in circuit. Its completely unnecessary any way, any arduino made in the last 5 years (The Uno)  will have one on board, already wired and working. Its usually labelled 'L'. The tutorial you've found is out of date and doing it today can damage the Arduino.  You may have already damaged the output on Pin 13.
« Last Edit: October 28, 2012, 11:05:11 am by pluggy » Logged


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Good to know. Thank you very much.
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LED's are polarised. They need to be connected the right way round to work.  Plugging one into GND & pin 13 is not a good idea on an arduino made in the last 5 years (including the Uno). There is no current limiting resister in circuit. Its completely unnecessary any way, any arduino made in the last 5 years (The Uno)  will have one on board, already wired and working. Its usually labelled 'L'. The tutorial you've found is out of date and doing it today can damage the Arduino.  You may have already damaged the output on Pin 13.

Further delving, I realise now what I did wrong. Though I won't do it again, I was curious as to why even if you shouldn't do it (and believe me I won't do it again based on your advice) why it was working on a couple of the tutorials and not for me.

Thanks for your help (and more importantly, the warning!)
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The old tutorials should have been updated or removed years ago.  I've been around Arduninos a while, but I never owned one I didn't make myself that didn't have a built in LED on pin 13.
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The tutorial on this site has you connecting the longer leg of the LED to a resistor, but as you say, not really necessary anyway. To be honest, the breadboard I bought doesn't correlate with the tutorials (only one ... power bit? where the tutorials all have two) and I got impatient. An unfortunate trait of mine... I'll buy a new breadboard tomorrow and make a start on more of the tuts.
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It doesn't matter which you connect the resistor to, it will work on either, the LED still needs it's longer leg (the Anode) to the positive end of the circuit however. 
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The tutorial on this site has you connecting the longer leg of the LED to a resistor, but as you say, not really necessary anyway.
No.  A resistor is ABSOLUTELY necessary, unless you want to buy new ATmega328 chips every so often.
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The tutorial on this site has you connecting the longer leg of the LED to a resistor, but as you say, not really necessary anyway.
No.  A resistor is ABSOLUTELY necessary, unless you want to buy new ATmega328 chips every so often.

I meant the exercise in its entirely, not the resistor smiley
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Okay... Just checking... smiley
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Okay... Just checking... smiley

I would appreciate it if you would continue to do so; I have no idea what I'm doing smiley-wink Ha. Thank you very much.
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