How to correctly interface Audio In and Out (line out or headphone) with Arduino

[DaAwesomeP]

Ok, so I re-wired up the circuit and the Arduino gave a reading of 509 and 510. I tested the circuit with the multimeter and it now gives off 2.5v DC. Thank you!

I tried the DTMF library to no avail. The Goertzel algorithm library, when set to 697hz lit up the LED when almost any number was pressed. At least now I'm getting a reading. Should I start a new forum page for helping me with the library?

To understand the touch-tone system (it is almost like an LED matrix), look at the table here: https://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling#Keypad

[Grumpy_Mike]

Glad it is working.
However the Goertzel algorithm is only good for one specific tone, here you want to detect up to eight. If it fires with any key then perhaps the threshold is set too low.
There are special chips you can get to decode DTFM I think you might be better off using one of them. or use a full FFT.

[DaAwesomeP]

Thanks for all your work! I know I had a lot of problems.

Once last thing: Do you know of any FFTs that would be good for this project?
I found this one: http://wiki.openmusiclabs.com/wiki/ArduinoFFT

[Grumpy_Mike]

Do you know of any FFTs that would be good for this project?

Sorry, while I have used FFTs on other machines I haven't used the ones on the Arduino.