I’ve spent some time thinking about how I’m going to build the overall wiring harness for the entire suit. The I2C buss is just that – a buss, which means everything hangs off it in parallel. That also means that I can tap the bus anywhere and hang a sub-buss off it – it’s still parallel.
The actual tapping part, however, is a kinda tenuous connection between two IDC headers, as shown here. The taps are big and relatively fragile. I expect that I’ll lash them with rubber bands to keep them from separating. Nevertheless, to me these taps feel like one of the most fragile aspects of the harness assembly. The last thing I need is to spend months building this thing and have some idiotic junction like this fail on me and cause problems in use.
Given that I made a design decision to opt for longer sub-busses and fewer buss-taps. I ended up with four large buss sections – legs, arms, a serpentine chest buss for the 5×4 array, and spine + head. This goes together with only three cross-taps. I calculate that the longest cable run here (to the LED at the end of the serpentine chest buss) is about 8.75 feet.
Tonight I’m going to build a 1/4-scale buss using real ribbon cable and IDC connectors for the junctions. This way I will be able to test the cable folds and make sure I get the pin-one orientation right everywhere. I’m not going to socket the thing for every LED – just the ones at the extremities. I will be able to hook it up to the Arduino and test that the extremity LEDs work on all busses. Seems worth it to sacrifice some of these IDC connectors to have some peace-of-mind that when I build the full-size busses everything will go smoothly.