user6761: I am following Jeremy Blum's tutorial for Holiday Lights: http://www.jeremyblum.com/2011/12/25/tutorial-14-for-arduino-holiday-lights-and-sounds
I am just trying to set up the circuit for one of the audio channels. I believe I followed the breadboard schematic. However, when I connect the Arduino the power, but without any audio input, the LED lights up. I would've thought that would not be the case.
Can someone help me correct my understanding here? Thanks.
Image of my breadboard: http://postimg.org/image/ibqfvezqp/ 

user6761: Per Jeremy Blum:

If the input doesn’t have a audio input plugged in, then it’s said to be “floating” and you >can’t really count on the circuit to do what you would expect. The audio input connection >introduces a known voltage (0 when no sound is playing) connection between the positive op->amp input and GND that we then amplify. Try connecting the input to GND and you should see >the LED turn off.

Source: http://www.jeremyblum.com/2011/12/25/tutorial-14-for-arduino-holiday-lights-and-sounds/comment-page-2/#comment-1373392 

6761: <p>I am following Jeremy Blum's tutorial for Holiday Lights: <a href="http://www.jeremyblum.com/2011/12/25/tutorial-14-for-arduino-holiday-lights-and-sounds" rel="nofollow">http://www.jeremyblum.com/2011/12/25/tutorial-14-for-arduino-holiday-lights-and-sounds</a></p>

<p>I am just trying to set up the circuit for one of the audio channels. I believe I followed the breadboard schematic. However, when I connect the Arduino the power, but without any audio input, the LED lights up. I would've thought that would not be the case.</p>

<p>Can someone help me correct my understanding here? Thanks.</p>

<p>Image of my breadboard: <a href="http://postimg.org/image/ibqfvezqp/" rel="nofollow">http://postimg.org/image/ibqfvezqp/</a> </p>
 6761: <p>Per Jeremy Blum:</p>

<blockquote>
  <p>If the input doesn’t have a audio input plugged in, then it’s said to be “floating” and you >can’t really count on the circuit to do what you would expect. The audio input connection >introduces a known voltage (0 when no sound is playing) connection between the positive op->amp input and GND that we then amplify. Try connecting the input to GND and you should see >the LED turn off.</p>
</blockquote>

<p>Source: <a href="http://www.jeremyblum.com/2011/12/25/tutorial-14-for-arduino-holiday-lights-and-sounds/comment-page-2/#comment-1373392" rel="nofollow">http://www.jeremyblum.com/2011/12/25/tutorial-14-for-arduino-holiday-lights-and-sounds/comment-page-2/#comment-1373392</a> </p>
