I think i found a use for the several MCP2515 CAN modules i have from eBay, as the subject line says.
i can have a central monitoring and control arduino (likely a Mega2560, my favorite Arduino ), with a 7" Nextion i have had for a while.
then build some Arduino CAN sensor modules for things like tank levels, various temperatures (like for winter camping), room temperature (to control the furnace), battery volt level, and some other status info. like a sensor to detect when AC power is connected, or power fails. could be as simple as a relay on each leg of the incoming 240Vac (120 -L1 + 120 -L2, 50A RV power cord).
i can also control some items like the furnace (act as a thermostat, using a relay), battery charger (if volts drops to X volts, then solar isn't taking care of the load... and disconnect after the volts reaches Y level).
i found a useful library and CAN reference from: Arduino CAN Tutorial - Interfacing MCP2515 CAN BUS Module with Arduino
i will likely base my system on that library, and build from there. Seeed Studio makes a CAN dev board with an ATmega32u3 MCU (https://www.digikey.com/en/products/detail/seeed-technology-co-ltd/102991321/11201147) that i can use for the remote nodes, unless custom nodes are needed.
but the intent here is to develop a system where the master control unit supplies power for all the sensors, via the use of CAT5e cables for CAN + power (5V). one pair for CAN, and 3 pairs for sensor power, though this may be abandoned if i end up with a lot of nodes. not much current on 3 pairs of 22AWG...
still may use CAT5e cable for the twisted pair, somehow. maybe just higher power nodes will have their own power source, derived from the RV 12V power, with DC-to-DC step-down converters, and heavy power filtering. but the intent is to reduce the number of signal wires around the camper.
say each tank level sensor set (digital) has 5 wires (4 levels + common), or only 2 wires if i dare go analog with a resistor ladder setup (not crazy about the idea). but multiply the wires by 3 tanks, and that is too many wires to run back to a single arduino monitor. so, CAN would involve running a network of a twisted pair wire, and a power wire for high-power nodes. hence my plan to use CAN, and some arduinos.
just posting to see what others thought about my idea. keep in mind, my 5th wheel camper is currently gutted for renovation, so running some CAN bus wiring will be easier, as well as hiding some Arduinos.
most of the custom nodes will be derived from a bare-bones ATmega328PU, and will likely be on copper-pad perf-board as they will each be unique enough to not have the same exact circuit, and i don't think a shield system will work for me. mostly because in transit, things will loosen over time, and a custom circuit can be potted in resin for better vibration resistance, and once a node works, it won't need to be changed in design, and can be potted.