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[on:]

The board appears to be working fine, except that the Tx indicator LED remains lit after any sort of transmission.

E.g. this scenario:
 1. plug Arduino into USB - the 'L' LED and Tx and Rx lights flash briefly (seems normal)
 2. after this, no LEDs are lit
 3. upload a sketch - all LEDs flash as expected while uploading...
 4. now the Tx LED remains lit indefinitely

Step 3 above can be anything that causes transmission - e.g. opening the port in Matlab to use the Arduino, and then closing it properly and deleting the serial object in Matlab, after which the Tx LED remains lit. Or using the serial monitor in the Arduino app.

Is this a problem? Does it mean it's constantly trying to transmit? It doesn't seem to be an issue with how I'm using the Arduino board (i.e. one can still open a connection to the board fine (e.g. in Matlab) while its in the Tx-lit state)

Any ideas? Cheers

[Reply #1 on:]

On my Uno, I've noticed that if you have a Serial.begin() statement in your code and then attempt to output to serial with Serial.print(), then the TX light will stay solidly lit until you load the serial monitor in the IDE.  I'm pretty sure this is normal behaviour.

Troy