current limit of arduino?

This info is probably on the website, but I couldn't find it.

How much current can the Arduino give when running off USB? I would like to power a servo, using the arduino board. The servo runs at 5volts, 180ma. How much can the Arduinos built in voltage regulator handle?

thanks chad


the regulator gives 500ma, but basic operations like USB, the LED and the Atmega take about 100. Your servo should be fine.


Thanks for the info. Is there a FAQ or tutorial that talks about power?

not really, but you can look up the datasheets to determine how much current is consumed if there is something in particular ou're curious about.

Hi, I had a question along these lines. I don't know a ton, but I've searched around on these forums.

I'm trying to run a relay off of the arduino board. The relay coils will work when I simply hook up the 5V power from the Arduino, but the individual pins seem to not have enough current to get the coils going. The individual pin(s) will try to energize the coils, and I can feel the relay's magnet start to move, but it isn't enough. I saw above you mentioned that there should be about 400ma left over, which is more than enough for my relay. I've tried using the diagram here but my circuit isn't working. I'm not entirely sure what the K1 box is; indicating the 16 and 1 pins; also it seems like the diode is short circuiting that anyway. I'm sorry if these questions are totally elementary, but I figured I might as well ask. Thanks so much for reading



K1 is the relay coil… welcome to the arcane world of schematic diagrams :slight_smile: (it’s ok: when I fist saw a resistor in a schematic I thought it was a printing error.)

Individual Arduino pins can sink or source a maximum of 40 milliamps each, so unless it’s a tiny relay you need the diagram above. it works, have a look at your circuit and see where it doesn’t match the diagram.


PS: the diode is there to clamp bad voltages generated by the relay; it only shorts current going in the opposite direction of the power supply, so it is OK.

Thank you so much. The arduino board is pretty nifty, i must say. have a good one, chris