I'm playing with an MCU board (like Arudino) to read the state of several switches in my home (i.e. magnetic switches). The wires between the sensor and the board are quite long: 15+ meters in a star topology.
I would isolate the inputs from the MCU, using opto-couplers. To provide the voltage needed to turn on the diode I'm going to use an isolated DCDC converter.
Question: do I need to use a different DCDC for each input? Or may I live with only one? In this case I will end up with all sensors that share the same power supply rail.
I.e.: one side of the switch goes to +12V (shared across ALL switches) while the other sides go to the anodes of the opto-couplers.
It's not an industrial design: I'm fine if it works without false detections due to the environmental noises.
To be more clear. Two ways: