I was wondering if anyone had any ideas on how I might be able to do this, i want an mp3 file that plays a tone to start a timer on the arduino, So that when the file starts playing a tone would play for a second or so and the arduino would be monitoring a pin and when it got this tone it would start a timing rotuine, would an op amp that was runing through the one of the audio channels do this? or a transistor? or would a certain frequency on a pin be sufficient, i don't have an oscilloscope to test that out. maybe just a transistor would do the trick, as the sound piece is part of a sound sculpture so there will only be one file for the person to play and the headphones won't be playing anything until someone hits play. any ideas would greatly be appreciated.
Depending on how accurate you want to be, that is not to trigger on things that are not your tone probably the best would be to use a UM3763 tone detector chip. This would give you a logic output when it detected the tone. This would be much better than trying to measure the frequency in software.
A thread I started earlier in the week might give you some ideas: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1227913947/1#1