Arduino Duemilanove auto Power Supply select

Hi there!

Quick neebie question:
Can I connect both USB and an external power supply to the duemilanove board at the same time ?
The docs say, power supply is selected automatically...but i'm not sure what that exactly means...

Just don't want to fry any chips :-/
EDIT: I'm using high load motors powered by the Vin PIN. Could this damage my computer via the usb connection ? (if i do something wrong)


maybe my question was a bit unclear...

I don't want to use both power supplies at the same time.
I need an external power for the motors.
I just wanted to know, if i should unplug the external power, while connecting usb, for uploading the code.


Yes you can plug both in quite safely. The board will select the external power supply for power if plugged in. If not it will use the USB.

And if you have only USB power applied then any external loads like your motors that use Vin pin for power will not draw any current from the USB port. So you will be able to download new code using just USB power but not power your external motors. Keep in mind that the external power port uses a series polarity protection diode that limits the total external current draw from Vin to around 1 amp for the board and any external loads you are powering.


thanks a lot!
all this plugging in and out drove me crazy :smiley: