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Topic: Arduino Leonardo , Run 3-4 5mm Leds w/resistor on one pin? Maybe 60mA? (Read 642 times) previous topic - next topic

Left4Dead

May 29, 2019, 05:24 pm Last Edit: May 29, 2019, 05:26 pm by Left4Dead Reason: pictures
I am building a certain movie prop. (something related to time travel) I currently have arduino uno r3 running this and it works, over night even. 4 pins blinking in sequence with 3 5mm Leds attached to EACH PIN with one 220ohm resistor! Works. I notice the Arduio uno specs state only 20mA per pin. Again it ran overnight just fine.

My question is since the forward current of the 5mm leds is 20mA each and I am running 3 in parallel(60mA) would the Arduino Leonardo - handle this better since it's specs are higher for the current draw needed?




Here is a video of it working

Link to video


larryd

It's not reasonable to link to a video which requires us to sign up for or download an app. :(


Resistors look like they are 680Ω.

Too contorted to follow your wiring.


Show us a 'good' schematic of your circuit.
Give links to components.
Posting images: 
https://forum.arduino.cc/index.php?topic=519037.0


Each output pin can can safely handle 20mA, period.



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DVDdoug

The datasheet for the ATmega chip says 40mA "absolute maximum" per pin and 200mA total.

That does NOT mean it's going to instantly fry at 41mA.    But if you exceed 40mA and it does die, you know who to blame, right?  ;)

If this for a critical application or if you are going into production, I'd advise against exceeding the specs.   But for a hobby project it's probably going to work if you "push it" a little, and if you kill it you just have to buy another one.   How bad are you going to feel that happens?   If you were going into production, I'd ask "how much is a failure going to cost?"     There's nothing wrong with taking a risk as long as you understand the risks.

Quote
...with one 220ohm resistor!

... since the forward current of the 5mm leds is 20mA each and I am running 3 in parallel(60mA)
Assuming about 2V across the LED and 3V across the resistor, that's about 14mA per LED.   








Grumpy_Mike

Quote
would the Arduino Leonardo - handle this better since it's specs are higher for the current draw needed?
Where do you get the idea that the Leonardo can handle more current per pin than the Uno?

Quote
Again it ran overnight just fine
Which means nothing. A marginal over stressing of a parameter does not lead to instant failure. To see the effect you have to test a system over many months and test a few hundred of them. Then you can do the statistics on your results to see how destructive your over stressing has been. Best to simply stick to what the data sheet tells you is safe.  

ChrisTenone

Cool video. Your flux capacitor looks great already!

Quote
…My question is since the forward current of the 5mm leds is 20mA each and I am running 3 in parallel(60mA) would the Arduino Leonardo - handle this better …
No. As the others have said, 60 mA is too much for an avr (the chip in all the 8 bit Arduinos such as the uno, nano, mini, leonardo, micro, etc.) pin. There isn't a common microcontroller that can handle that for very long. But you can trigger 3 transistors in parallel that way, and have each transistor drive an LED. In fact you should be able to drive all three LEDs with a single transistor.

Google 'transistor led arduino'.
What, I need to say something else too?

TomGeorge

Hi,

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?


A picture is worth a thousand words.


Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

Left4Dead

The datasheet for the ATmega chip says 40mA "absolute maximum" per pin and 200mA total.

That does NOT mean it's going to instantly fry at 41mA.    But if you exceed 40mA and it does die, you know who to blame, right?  ;)

If this for a critical application or if you are going into production, I'd advise against exceeding the specs.   But for a hobby project it's probably going to work if you "push it" a little, and if you kill it you just have to buy another one.   How bad are you going to feel that happens?   If you were going into production, I'd ask "how much is a failure going to cost?"     There's nothing wrong with taking a risk as long as you understand the risks.
Assuming about 2V across the LED and 3V across the resistor, that's about 14mA per LED.   


Super fair answer, thanks.  Just a hobby, let it run all day yesterday and last night hooked to pc, still going.








wolframore

How did you come up with 20 mA each?  Did you measure it, calculate it or assume?

I don't see the two red stripes on those resistors needed for 220 Ohm ... I really don't see parallel wiring either... but again the pictures are low res and not very clear.

We can do the math for you and you might be fine with what you have there... a lot of LED's look fine at 5-10 mA... You can do 3 LED's per pin at 7mA all day and all night...

There are a few issues with the way you're using the LED's with reliability and long term issues but again might not be a concern for you.

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