Mac Maverics (Macbook Retina Pro) - strange behavior, UNO R3


I have very strange behavior with my original UNO R3 (no clone). When I plug it to the Macbook and try to load the sketch I got success message only the first time I do it. When trying to reload the sketch only combination of reseting, pluging and unpluging helps.

Is that normal?

What is more strange, when I use PIN 13 led for test I got short 2 blinks every 5 seconds no matter what pattern of blinking I set in the sketch. Such blinking does not occur when UNO is pluged to the external power supply.

Again, should it be like that?

It looks like something strange is heppening with the USB communication...

Can anyone help?

I thought that the problem is with USB driver, but R3 version does not use FTDI driver (it uses ATmega16U2 USB to serial converter) and no drivers for Mac I could find.

Best regards,

Ok, to know if a reset has occurred on the Arduino Uno, you can view an LED next to the "TX" and "RX" LED's. It has a label in the silkscreen that looks like an "L" next to it.

If you press the reset button and then release it, you should see the LED flash. That would be normal. If it does not flash, then maybe the switch is broken.

One thing I think we need to clear up is when you say, "Such blinking does not occur when UNO is pluged to the external power supply" do you mean no blinking or do you mean it correctly blinks per your program instruction.

And one more thing, go to the Tools menu and select "Board". Verify that you've selected "Arduino UNO". It is the default selection, but it is always good to make sure that is set up correctly.

Also, try using a different computer or USB port to make sure there are no hardware issues going on (if that is possible).

Oh, also too, make sure you save your program before you compile and upload it. If you do not save your program, it will compile and upload the previous unsaved program. At least, that is how it has been working on my machine.


Yes, I've checked ports and board type. Everything looks ok. here. Strange blinking occurs without pressing reset button.

I have tried switching USB ports, using hubs etc. with no success.

Once there is external power supply (not via USB) the LED blinks as programmed. Strange blinking patterns occurs only when UNO is USB powered from the computer :(.

Best regards,