My son and I are building a lamp based on Arduino Uno (he put me in charge of hardware) and he wants it to be able to flash based on music input from his phone. I found schematics to add a DC bias to the input to account for the AC nature of the music but he would like to know when the plug is inserted in the jack. We procured a 5 pin 3.5mm jack similar to http://www.switchcraft.com/Drawings/35rasmt4bhntrx_cd.pdf but I can figure out how to interface either pins 4 or 5 to the Arduino so to detect insertion. I Googled for this information but could find such application.
Any and all assistance extremely appreciated!