Question about current capacity

Hello,

I have a simple question. I need to control several LEDs, one 1W LED (350mA) and a servo. As far as I know this will use over 490mA (without the servo) which is probably too much for the Arduino Duemilanove which I use.
My idea was to use transistors, but where should I get the power from? Arduino has a 5V output with only a stabilizer between the output and the adapter input. My question is: how much current can the stabilizer handle?
It would be nice if I could use that port to control the powerled and servo, otherwise I have to modify my adapter. Other tips are welcome as well :wink:

Thanks in advance!

that is probably too much current for the Arduino board. You can use an external power supply just for the LED circuit (use common ground with the Arduino board) and use transistor/MOSFET to drive the output.

how much current can the stabilizer handle?

It can handle 1A but that's not the limit. You are limited by the amount of heat you can dissipate. This in turn depends on the voltage you are putting in. The bigger this is the more power you have to burn to get it down to 5V and the more heat you have to get rid of.
See:-

http://www.thebox.myzen.co.uk/Tutorial/Power.html

and there is a discussion of this problem at:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html

Many thanks, now I know for sure it is not possible without damaging Arduino :smiley: I have found another adapter of 12V so I will use that to power the LEDs. The servo on the 5V with a transistor should work on the Arduino I guess.
Thanks!

The servo on the 5V with a transistor should work on the Arduino I guess.

It will work as far as the current is concerned but sometimes servos put out interference that can disrupt or reset the arduino, so if there is a choice then have the servo on a separate supply or apply a bit of decoupling to the servo.:-

http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

The servo on the 5V with a transistor should work on the Arduino I guess.

It will work as far as the current is concerned but

I may have missed something, but some servo's draw quite a lot of current (much more than 0.5A). How did you figure out that it is okay to drive from the Arduino?

(I agree with separating the power to the servo or isolating it to avoid noise problems.)

GB

How did you figure out that it is okay to drive from the Arduino?

Well we had talked about current ratings and the op had done some calculations, enough to show him that the LEDs were not OK and he proposed to just drive the servo. Given that I assumed that he was happy with the current rating. While some servo motors can take many amps those are not the ones likely to be used by a beginner.