I am currently attempting to control the Arduino Uno's Tx and Rx LEDs.

These are connected to digital pins 0 and 1 respectively, which are AFAIK, PD4 and PD5.

They are held at +5V, so I assumed that they would switch on when PD4,5 were driven low, however this has not proven to be the case.

I would be immensely grateful if anybody could offer a solution.

The schematic I referred to is here: http://arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf


I have literally just noticed that the Tx and Rx LEDs are controlled by a second microcontroller!

Thought I was writing for the 328, happens that they're controlled by a 16U2 on the board.

Teaches me not to read all the small print.

  • \$\begingroup\$ p.s., I did succeed in controlling them by soldering wires from digital pins 12 and 13 to cathodes of the two LEDs. \$\endgroup\$ – Mitchell Oct 17 '13 at 14:47

There should be a built-in LED controlled by the ATMega328

This is shown at top-centre of your circuit diagram, near U5B

On the top of the physical board it appears to be near the Tx and RX LEDs and is marked "L"

LED: 13. There is a built-in LED connected to digital pin 13. When the pin is HIGH value, the LED is on, when the pin is LOW, it's off.


The Duemilanove also has a LED on header-pin 13 - I think this is an Arduino tradition.


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