[ELI5] How do P3 audio input knows when you put a P2 earbud in it?

Question

When I put a P2 earbud in my smartphone it know it is P2, because it says I don’t have a mic.

How does it work when it’s touching one of the audio channels and the mic input?

In: 3

Answer 1

(just a guess) your cellphone has 4 pins matching the P3. The cellphone will try to read whatever is at the position of the mic pin.

When you use a P2 it will try to read the signal to detect if it is a “odd” signal or not. If it is “odd” then it know it is a P2.

More technically, I’m pretty sure the mic pin use part of the ground pin. This mean, if you use a P2 the microphone will be the ground pin. And the ground pin is basically the perfect silence. So if your cellphone detect the microphone to be pure silence (what I called “odd signal”) it know it is a P2.