1. Can you split the extender lines, so as to connect 2 extenders, in parallel? It appears that you use I2C as your communication protocol, but I didn’t see a means of addressing, so we can’t tell for sure. This isn’t as crucial, but would be nice.
I’ve never thought about it, but now you asked it, I think it’s fine to connect two expansion boards in parallel. It’s simple shift register cascading, so no I2C communication. Keep in mind that this means the two expansion boards will always be synchronized — always outputs the same.
2. How far can you chain extenders? By modifying the firmware we can have many extenders, and in another question it was stated that an extender could be about 50ft from the base station, but can another extender be another 50ft? This element is crucial for us, as we cannot run long lines to solenoids.
This is a commonly asked questions. Frankly I haven’t done careful study about it. The issue is that because the extension cable carries straightforward logic signals, it’s prone to interference if you run it over a very long distance. The software does refresh every second, so if the signal gets interfered at one moment it shouldn’t persist. So it’s probably fine to chain several expansion boards over 50 ft each.