The L LED Keeps Itself On

Question

I am using a Arduino Uno 3 for line follower robot. However when I power the Arduino Uno, the L led is turned on and is never turned off. After a bit of searching I found out that the L LED is connected to pin 13. So I set the pin 13 to low but still the led is on. Is there a problem with the arduino? Or there's something that I am unaware about? (Amongst a lot of other things that I don't know.)

You need to tell us more about your line follower robot. Specifically, where to find the schematic and code. The way you worded your question is similar to asking: "Where is the headlight switch in my car?" — st2000, Jun 16 '16 at 12:08
same problem here please cousld any one help!! i used arduino uno its L led is not turning off it used to turn of but now no it is not it stays on .and blink code works but i am trying to make balancing robot but no it doesnt work i started uploading code for it this morning then after 3 hours i dont know how it worked for about 30 mins i was tuning the pid values while that 30 mins also the led was on though.but after that 30 mins i am trying but it is not working.Please help! — Coder Manish, Aug 03 '20 at 11:40

score 7 · Accepted Answer · answered Jun 16 '16 at 14:16

This is a “feature” introduced in the revision 3 of the Uno board. Up to Rev 2, the “L” LED was connected to pin 13, through a 1 kΩ resistor. On Rev 3, the same LED+resistor combination is driven by pin 13 through an op-amp. Thus, when pin 13 is in high impedance mode (i.e. INPUT mode, the default mode when the program starts), the input of the op-amp is floating. The voltage at this input (and thus at the output) is not controlled and depends only on the parasitic conductances and on leakage currents.

If you want to turn the LED off, you not only need to write LOW to it, you also (and most importantly) should set the pin to OUTPUT.

score 2 · Answer 2 · answered Jun 16 '16 at 12:27

2

Its possible its the Power LED you are looking at - that will always be on.

Simplest test is to load up the Blink Example that's included in the Arduino IDE - and the LED should blink once a second. That will show you if your Pin13 LED is working ok.

answered Jun 16 '16 at 12:27

Ozmo

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The power LED is the green one, and the L led is the yellow one. I am looking at the yellow one – Redwanul Sourav Jun 16 '16 at 15:07

score 2 · Answer 3 · answered May 29 '19 at 08:53

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Now first check IC on your arduino UNO. if it is atmega328p, set the board to arduino nano in the software and set the processor th atmega328p. that makes it work. :)

answered May 29 '19 at 08:53

K'Robotics

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score 1 · Answer 4 · answered Oct 12 '20 at 05:17

I guess the arduino is burnt cus it happens with me in the same way. The usb port of my PC is writing device not recognize, and the atmega328p on the arduino temperature is getting high. To save my time I bought another new one I think that should help.

score 0 · Answer 5 · answered Jun 16 '16 at 12:13

An LED lights up when in forward bias. That is, when the voltage on the anode is greater then that on the cathode. If the anode is connected to an Arduino GPIO pin (and the cathode is connected to ground and an appropriate limiting resistor is used), the LED will light up when the pin has positive voltage. This is when it is set to 1 in the code. If the cathode is connected to an Arduino GPIO pin (and the anode is connected to positive voltage and an appropriate limiting resistor is used), the LED will light up when the pin has zero voltage. This is when it is set to 0 in the code.

The L LED Keeps Itself On

5 Answers5