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### Topic: 250mA from an Arduino Pin (Read 1 time)previous topic - next topic

#### Grumpy_Mike

##### Oct 18, 2009, 05:45 pm
Well I have done some tests and found that I can get over 250mA from an output pin of an Arduino.

Of course this will / has damaged my Arduino but it is still actually working. I did this to to investigate what sort of currents are being drawn by connecting an LED direct without a resistor. This followed some recent discussions on this forum.

I have added an LED page to my Tutorials:-
http://www.thebox.myzen.co.uk/Tutorial/LEDs.html

#### ahdavidson

#1
##### Oct 18, 2009, 06:56 pm
Grumpy Mike,

You seem very far from grumpy in your generous sharing of extensive knowledge.

Your site has lots of good explanatory info on it -- an RSS feed for newly added items would be great, in case one misses a thread here about it.

Thanks lots for all of it.

.andy
.andy

#### pekkaa

#2
##### Oct 19, 2009, 09:36 pm
That made me realize that I should probably use a resistor with an opto-isolator as well, right? Somehow I missed that before, even I knew that I should use resistors with LEDs and the other half an opto-isolator is a LED.

For some reason the circuit and Arduino Nano still seem to work after few months, but I don't want to push my luck any futher.

I checked the opto's (sharp pc817) datasheet. I am not sure if I got the terms right, but the parameters I used to calculate the resistor value was the typical forward voltage 1.2V @ 20mA (max rating for the forward current is 50mA). That led to resistor value (5V-1.2V)/0.02A = 190ohm. 220ohm is closest I have. Does that sound reasonable?

Btw, this might be a silly question but here it comes anyhow: It doesn't matter which side (anode or cathode) of the LED the resistor is, does it?

#### Boots

#3
##### Oct 19, 2009, 11:58 pm
Like Andy Davidson said, thanks for all the info you share on here.  I've learned lots from your posts alone!

#### Boots

#4
##### Oct 19, 2009, 11:59 pm
oh and this is the best quote imo

"Does my Arduino still work after this? Yes it does! Have I permanently damaged it? You bet I have!"

lol

#### Grumpy_Mike

#5
##### Oct 21, 2009, 12:29 amLast Edit: Oct 21, 2009, 12:31 am by Grumpy_Mike Reason: 1
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It doesn't matter which side (anode or cathode) of the LED the resistor is, does it?

No problem the electrons don't care what they see first.

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= 190ohm. 220ohm is closest I have. Does that sound reasonable?

Yes it does, spot on.

However, have you not got a 180R resistor, that is a standard value? Anyway it doesn't matter.

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