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  • I expect RS485 devices to use specific communication protocols, which frequently have some addressing feature. So one bus suffices, if EV charger and energy meter are set to different addresses. The Arduino will play the role of the EV charger for the energy meter, and vice versa. The MITM attack works then on the protocol level, not the electrical level. Commented Jun 28, 2024 at 5:44
  • That's really helpful. I know that power meter is addressable, not sure about the charger. So basically I need to use MAX 3157 to read needed registers from power meter and store it in Arduino's memory as a float (adding 20A in the meantime). Then charger needs to speak with Arduino (via another MAX 3157 or using addressing) and ask for these registers thinking it speaks with power meter, correct? Commented Jun 28, 2024 at 6:50
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    RS-485-based protocols are typically single master: the master queries a slave, and the slave responds only when it has been addressed. If you add an Arduino that can behave as a master, then you will risk collisions on the bus. Collision detection and mitigation can be implemented, but I doubt the charger does that. Commented Jun 28, 2024 at 7:01
  • @EdgarBonet I stand corrected respective the single bus. Thanks! Commented Jun 28, 2024 at 7:58
  • @thebusybee: If the charger sends its requests on a predictable timing, maybe the Arduino could manage to send its own requests in-between the ones from the charger, and your scheme could still work. Commented Jun 28, 2024 at 8:39