Arduino Uno Board R2

Dear Forum,
I don’t know what is going on with my original Arduino Uno R2 board :frowning:
I have downloaded the “blink” app which is toggeling PIN13 perfectly fine as long as it is connected via USB to my PC.
Once I have connected an external 12V power supply to the board, the green power supply LED is ON but the builtin LED on PIN 13 is not blinking anymore…

Am I missing something? Isn’t it possible to run a sketch on the board without the USB connection to the PC?

Thanks for your support

where are you connecting the twelve volts? VIN? Power Jack?

The external power supply is connected to the power jack

That is very strange. If it is running on USB, does it stop running if you plug in the power without unplugging the USB?

I have put in the blink to check whether the board is actually running or not.
Basically digitalWrite(13, !digitalRead(13)) and everything is running fine.

I have connected the USB and the 12V power jack
When disconnecting the USB it is still running
When reconnecting USB and disconnecting 12power jack, it is still running

Disconnecting USB and 12V … of course it stops running :slight_smile:
When reconnecting the 12V power jack only, Green power LED comes on, but no blinking
It does not even start when reconnecting the USB at this point.

I really have to download the sketch again … and then it is running again …

Hmm that is very weird! I have never seen that. Maybe you should try it on a different Arduino? If you have one.

Still very weird. I’m thinking it might be a bootloader problem. Have you ever written a new bootloader to this board? Perhaps burning a fresh bootloader would fix it.

Yep… with my Arduino Uno R3 board everything is working as expected.
It seems like the program I am running on the Arduino (using FastLED) is much faster up an running than on the R2 board (connected to USB).

I will try your idea with the bootloader too

The UNO R2 uses Atmega8U2 for the USB interface, right?
Maybe it holds the reset line for some reason?
Can you compare with a DMM the state of the reset pin when blink is working and when it isn’t?