In 9th class, I made a interphone, where was one 10 meters long wire and one 1.5 meters long wire. In the head of whole wires is one speaker, and the wires is connected to the interphone main unit with audio plugs. Speaking can be performed between two speakers, and when you're speaking into a speaker, you aren't allowed to listen to from it. At the same time, speaking is performed as one-way. The direction can be changed by holding the changing key down.

The interphone on the top.

Some wood bars, which the interphone is built with.

The shorter speaker wire that can be connected to the interphone main unit.

The audioplug to be connected to the side of the interphone main unit.