I choose the asynchronous serial bus.

First of all I make sure all the components I need to make the schematic.

I draw the schematic with all the components.

Go to Eagle and make the schematic with the right components.

Autorouter option and save the PNG image file.

Prepare the fabmods for milling.

Write down the O starting point.

Pick and solder the components.

I made two of the same boards. but then I realize I put the wrong FTDI pin header and also I had some cuts so I had to repeat and redesign the board.

Now all the components and traces where perfect.

Check if the connection between the programmer and the ATtiny board is ok.

Open arduino IDE software and burn the bootlader. We do so because I do not have a resaonator. The internal clock has to be 8MH.

Copy Neils code and change the node 1. And the same with the second board with node 2.

Connect all the components or network and open the serial monitor.

Write 1 or 2 and see the diference.