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I trying to detect if a "dominant" state on the CAN bus is set from a specific CAN node. For this I place a "bridge" between the node and the bus.

I don't want to forward each frame with a microcontroller, rather I would like to have a possibility to determine the direction on the bit level regardless of frame structure/bit rate.

Two possible solutions I came up with so far:

  1. Clearly this blocks the bus, but would there be a way to prevent this from happening? Enter image description here

  2. Buffer each bit with a microcontroller before forwarding to any side of the bridge. With this solution I would shift all bits +1 and would also need to determine the bit rate.

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I've done this on single-ended signals by placing a small resistor in series with the data line. Use a differential scope probe or differential amplifier across the resistor to determine the direction of current flow.

For a differential signal this is more complex, although I suppose you could get away with only watching CANH or CANL instead of both bits.

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