Multi Frequency

Hi everyone,
I am working with a metal detector that sends a signal to an ear piece. We are trying to manipulate the detector so that we control a light instead of sound to an earpiece. The detector is a PI and multi frequency. Is there anyone here that knows how to program off of the output (multi frequency)? It is not reading the correct values with a simple program made to read 1 frequency value.

Thanks

I suggest that you post the program that you have and describe the problem. What does it do ? What should it do ?

A diagram of how the detector is connected to the Arduino would also be helpful.