Sending Data through Headphone jack in Android phones
android, headphones
Solution
Here is a HackADay article dealing with this issue. http://hackaday.com/2010/02/01/android-audio-serial-connection/ It offers working code which was quite a bit simpler than I thought it would be.
Although, like others have suggested, including this very similar SO post, you might have an easier time using the USB port.
Problem
I'm currently dealing with a new project and I have to send data through headphone jack with specific voltage, then i can work on that voltage. so here i need to program the specific voltage depends on my data. is it possible that i can access the output voltage of headphones in android and then create a application to control that voltage?