The BMS I had in mind consisted of a cell module screwed directly to the poles.

To make it smart I had to use a microcontroller.

The best choice was to use an ATTiny Microcontroller ATTiny84A powered directly from the cell.

For the control unit I immediately had in mind to use the Arduino Mega board, a very popular board, with widespread online support.

But how to manage the dialogue between Mega and the various ATTiny's?

Among the various possibilities I chose to use an I2c network, because from the programming point of view it was the simplest and safest way, thanks to the libraries available online.

But the first question was: how can I connect devices that have different power supplies (which absolutely must remain separate) communicate on the same bus?

Fortunately, a suitable component came to my aid: Adum1250, a bidirectional digital isolator.

So I bought the various components, networked them together in a breadboard, addressed them and started reading and writing bytes between Arduino Mega and  Attiny's.

The result was satisfactory and from this test I was able to say:

"IT CAN BE DONE !!!"