Headset circuit

Hello to all.
Somebody knows what is the circuit of an android headset.
Some of them have 2 keys to slow down or increase the sound of android.
I want to know what exactly is the circuit of that.
Very thank you.

Have you tried using Google?

I found this & may it will help you to create headset circuit.

https://source.android.com/devices/accessories/headset/specification.html

So much thank you .