Now that everything is setup, at least as basis for testing, there is the need to take the sonars around the room, while keeping them connected to the main board.
When I didn’t think of chaining and other complex wiring, I was leaning toward using a standard stereo cable, with positive, negative (the shield) and the signal (for the AN signal). But now that I need almost all the 7 pins of the sonar I need more connections: the 2 options I had in mind were the standard 8 wires Ethernet cable, or the serial cable.
At the end I’ve chosen the RJ45 because the ethernet cable can be easily bought everywhere and there is no need to solder it.
I also wanted, since we are just in a exploratory phase, the possibility to easily remove the sonars from the socket. So at the end I bought a protoboard, some RJ45 sockets and the 8 pin stackable headers used in arduino shields. I cut the board to size, bent the RJ45 socket’s pins so that they fit inside the standard protoboard spacing, and finally soldered everything and connected all the pins together with single core cable.
Since I need 4 sonars, I had to make 8 of these breakout boards: 4 to attach the sonars, and 4 to connect to the breadboard. It took a while to prepare them: the longest part was cutting them to the right size and drilling the hole for the plastic plugs for the RJ45 sockets. But at the end it was a very instructive experience and good training for soldering.