user11556: I recently picked up an Uno clone and noticed that if pin 12 is set to an output and I run the Blink sketch on it, the built in led (supposedly connected to pin 13) blinks. It's not as bright as it is when I run it on pin 13, but nonetheless it blinks. If I run it on any other pin, nothing happens, which is the behavior I expected with pin 12.
Is this a common issue with arduino boards, the microcontrollers, etc. or did I get a bad board?
Overall the board visibly appears to have solid construction and appears as the one on the site that I linked to.
Lastly as a side note, I'm currently living in India and won't have a problem going back to their factory for a replacement, if it is a bad board. They include a 6 month warranty.
int ledPin = 12;
int delayPeriod = 100;

void setup()
{
  pinMode(ledPin, OUTPUT);
}

void loop()
{
  digitalWrite(ledPin, HIGH);
  delay(delayPeriod);
  digitalWrite(ledPin,LOW);
  delay(delayPeriod);
  delayPeriod = delayPeriod + 100;
}


user10794: See Have I bricked my Arduino Uno? Problems with uploading to board
As I state on that page, if pin 13 is set to input the LED may turn on due to being driven by an op-amp. A nearby pin turning on may be enough to cause that effect. Try adding:
 pinMode(13, OUTPUT);
 digitalWrite (13, LOW);

See if that changes the behaviour.

11556: <p>I recently picked up an <a href="http://www.avmicrotech.com/shop/product.php?id_product=123" rel="nofollow">Uno clone</a> and noticed that if pin 12 is set to an output and I run the Blink sketch on it, the built in led (supposedly connected to pin 13) blinks. It's not as bright as it is when I run it on pin 13, but nonetheless it blinks. If I run it on any other pin, nothing happens, which is the behavior I expected with pin 12.</p>

<p>Is this a common issue with arduino boards, the microcontrollers, etc. or did I get a bad board?</p>

<p>Overall the board visibly appears to have solid construction and appears as the one on the site that I linked to.</p>

<p>Lastly as a side note, I'm currently living in India and won't have a problem going back to their factory for a replacement, if it is a bad board. They include a 6 month warranty.</p>

<pre><code>int ledPin = 12;
int delayPeriod = 100;

void setup()
{
  pinMode(ledPin, OUTPUT);
}

void loop()
{
  digitalWrite(ledPin, HIGH);
  delay(delayPeriod);
  digitalWrite(ledPin,LOW);
  delay(delayPeriod);
  delayPeriod = delayPeriod + 100;
}
</code></pre>
 10794: <p>See <a href="https://arduino.stackexchange.com/questions/13292/have-i-bricked-my-arduino-uno-problems-with-uploading-to-board">Have I bricked my Arduino Uno? Problems with uploading to board</a></p>

<p>As I state on that page, if pin 13 is set to input the LED may turn on due to being driven by an op-amp. A nearby pin turning on may be enough to cause that effect. Try adding:</p>

<pre><code> pinMode(13, OUTPUT);
 digitalWrite (13, LOW);
</code></pre>

<p>See if that changes the behaviour.</p>
