I'm trying to figure out the feasibility of setting up some type of differential bus communication for up to 400 devices outdoors. The main constraints are mainly power consumption, complexity, wire count, and whether something like this is electrically possible (with reasonable bus capacitance/speed/pullups).
The other constraint is that each node should be able to connect ad-hoc in an arbitrary position on the bus. Termination resistors are possible if needed. For example:
+----+ +----+ +----+ +----+
| +-----+ +----+ +--------+ |
| 5 | | 0 | | 1 | | 4 |
+-+--+ +-+--+ +----+ +----+
| |
| +-+--+ +----+
| | | | |
+--------+ 2 +----+ 3 |
+----+ +----+
The distance covered between the farthest nodes shouldn't be more than 15 meters. I'm assuming the bus capacitance will be quite large with 255+ nodes. Does it make sense to include a bus repeater in each node? Would this use unnecessarily high power or significantly slow down communications? High speed communication isn't super necessary, for instance 9600 baud would do the trick.
The microcontroller that I'm using is reasonably fast, but has a single USART and limited free IO pins. So I don't think it would make sense to use something like RS422 and pass through data. I'm thinking that RS485 half-duplex would make the most sense, paired with a custom protocol based on Modbus. For this application, it seems much simpler to implement in software than CAN, plus making >8bit addressing possible. Does this make sense, or is it unfeasible?
