Go Down

Topic: Powering 4 LEDs with single output (Read 788 times) previous topic - next topic

zzzajda

At first, sorry for my Engrish.
I would want to know:
Can single arduino digital output power 4 LEDs?
(Each LED: U= 3.2 V, I = 20 mA.)

Which resistor should I use?

Is 9V battery enough to power this for a reasonable time?

Picture:


Thank you very much!



fungus

#1
Jan 13, 2013, 10:09 pm Last Edit: Jan 13, 2013, 10:11 pm by fungus Reason: 1

At first, sorry for my Engrish.
I would want to know:
Can single arduino digital output power 4 LEDs?
(Each LED: U= 3.2 V, I = 20 mA.)


No. Each pin can only provide 40mA. Trying to draw more than that can damage your Arduino.

If you want to switch more you use a transistor (or use multiple Arduino pins).



Is 9V battery enough to power this for a reasonable time?


What do you mean by "reasonable"?

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

zzzajda

I tought that transistor is used to reduce voltage...
Reasonable time is about one hour.

Grumpy_Mike

Quote
I tought that transistor is used to reduce voltage...

No you are thinking of a resistor not a transistor, and even then a resistor limits current not reduces voltage.

Quote
Reasonable time is about one hour.

You must have deep pockets but you might just be able to run it for an hour. Normally these batteries are considered as rubbish.

zzzajda

Which battery would be better?
And what should I use to reduce voltage?

LarryD

You can purchase very bright LEDS at low current. You may be able to get away with 10mA per LED and drive them from the Arduino.
The way you have it in your schematic isn't the same as how you have it wired up!

fungus


I tought that transistor is used to reduce voltage...
Reasonable time is about one hour.


It should run for an hour, yes...but 9V batteries are very bad value for money (charge vs. price). Make sure it's rechargeable!
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

zzzajda

OK, but how should I reduce voltage from 5V to 3,2V?

fungus


Which battery would be better?
And what should I use to reduce voltage?


There's a lot of options depending on your exact needs.
9V is the easiest option (although it can get expensive).

6xAA is best for powering an Arduino Uno, or 6xAAA of you need small.

You can also use 3xAA plus a voltage booster to get 5V.

If you need long life...the Arduino Uno is very wasteful. Over half the power goes into the other chips on the board. Something like this will last MUCH longer on batteries and it can run off 3xAA: http://evilmadscience.com/productsmenu/tinykitlist/180
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

fungus


OK, but how should I reduce voltage from 5V to 3,2V?


Might as well use resistors.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

LarryD

Quote
http://evilmadscience.com/productsmenu/tinykitlist/180

Thanks fungus!

I like that, it looks like the 328 is soldered.
The way you have it in your schematic isn't the same as how you have it wired up!

Grumpy_Mike


OK, but how should I reduce voltage from 5V to 3,2V?

You do not reduce the voltage.
You use a resistor to limit the current through the LED.
See:-
http://www.thebox.myzen.co.uk/Tutorial/LEDs.html

zzzajda



R = U / I
R = 5V - 3.2V / 0.02A (Each led is 3.2V and takes 20mA)
R = 90 Ohm --> Is 100 Ohm resistor before each LED right?
Will it work, or will I damage my Arduino?

fungus

#13
Jan 14, 2013, 01:06 pm Last Edit: Jan 14, 2013, 01:08 pm by fungus Reason: 1

R = U / I
R = 5V - 3.2V / 0.02A (Each led is 3.2V and takes 20mA)
R = 90 Ohm --> Is 100 Ohm resistor before each LED right?
Will it work, or will I damage my Arduino?


No...that calculation is for a 1.8V LED. The voltage isn't 5.0-3.2, it's 3.2.

R = 3.2V / 0.02A (Each led is 3.2V and takes 20mA)

R = 160 Ohm, minimum.

nb. That resistor value is the minimum. In practice you should use something a little bit higher than that in case one of your LEDs is only 3.1V (the datasheet will tell you the tolerances).

Your circuit doesn't need a resistor on the GND wire. Apart from that it's fine.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

fungus


Quote
http://evilmadscience.com/productsmenu/tinykitlist/180

Thanks fungus!

I like that, it looks like the 328 is soldered.



Sockets are cheap ...
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Go Up