I'm building an audio amplifier (prototype) with display and MCU (Arduino Nano), see photo below (not finished ;-) ).
On the display I want to show some VU-meters of the input but there are different implementations how to do this.
Some claim that you can connect the audio input directly to the pins of Arduino which I have tried but doesn't seems to work. Other claim it is not a good idea to do it that way because there is no circuit seperation or claim that it is impossible because the signal is AC and is too weak (like I just discover, just a few millivolts and Arduino can't measure that).
So I found a few solutions to amplify the signal with use of decoupling and a voltage divider. The voltage divider pull out 2.5V at maximum at a input voltage of 5. The arduino is able to measure this.
The solutions I found are a little different so the question is, which one should I use? Why are they different? Which one is the best to use to show a VU-meter?
1. Arduino Audio Input http://duino4projects.com/audio-input-to-arduino/
3. DTMF detection library http://forum.arduino.cc/index.php?topic=121540.0