Having an external power source while maintaining a serial link

I'm using an UNO, and have certain amperage requirements. So it has been suggested that I need to plug in an external power supply. I just want to ask if anyone knows if I can plug in an external power supply into an UNO while it's connected to the USB? Will that fry it? I need the serial communication link to do diagnostics.

If not, then how would you suggest that I proceed to get such diagnostic info?

Thanks,

Adrian

Yes. You can.

If Vin/2 is > 3.3V, the external power source will be used. Note that Vin is after the reverse polarity protection diode. Thus the Source coming in thru the barrel jack connector needs to be ~0.7V + 6.6V, or >=7.3V. http://www.dipmicro.com/store/DCA-07510 or http://www.dipmicro.com/store/DCA-0910 for example.

adrian_h: I'm using an UNO, and have certain amperage requirements. So it has been suggested that I need to plug in an external power supply. I just want to ask if anyone knows if I can plug in an external power supply into an UNO while it's connected to the USB? Will that fry it? I need the serial communication link to do diagnostics.

If not, then how would you suggest that I proceed to get such diagnostic info?

Thanks,

Adrian

Keep in mind that using external DC input connector on your Arduino board may not give you all that much more 5V pin current capacity then the USB power does (USB limit = 500ma) as it is a function of the power dissipation of the on-board +5vdc regulator (heat limited). Do you know how much total +5vdc board current you need to supply for your external circuitry?

Lefty

CrossRoads:
If Vin/2 is > 3.3V, the external power source will be used.
Note that Vin is after the reverse polarity protection diode.
Thus the Source coming in thru the barrel jack connector needs to be ~0.7V + 6.6V, or >=7.3V.
Switching DC Wall Power Adapter 7.5V / 1A - dipmicro electronics
or
Switching DC Wall Power Adapter 9V / 1A - dipmicro electronics
for example.

That’s great to know. Thanks.

Now, does it matter that I plug them each in, in a particular order? Or can I just keep the barrel jack plugged in and just unplug and replug in the USB in whenever?

retrolefty: Keep in mind that using external DC input connector on your Arduino board may not give you all that much more 5V pin current capacity then the USB power does (USB limit = 500ma) as it is a function of the power dissipation of the on-board +5vdc regulator (heat limited). Do you know how much total +5vdc board current you need to supply for your external circuitry?

Lefty

Ahhh, good to know. I was under the impression that it was limited to 100mA. Now that I read the specs again I see that it can go up to 500mA for a USB2 high power device. So I assume that the Arduino UNO is reporting itself as such then?

Perhaps. There is a 500mA resettable fuse on board for USB current.

Barrel jack has no such fuse - but the reverse polarity protection diode, when it was wired in series leading to the 5V regulator, was only rated for one amp. So it sort of acted like a fuse.

Also keep in mind that plugging in the USB usually causes a reset to occur.