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Termination Resistors on the PCB

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  • Termination Resistors on the PCB

    Hello :-)

    I want to design a board that gathering data by microphone sensor, communicate by CAN bus communication and transfer the data to the PC.
    (In the future I plan to add it to system that communicate by CAN bus)

    My current problem is, that I need to add termination resistors to the bus, but, as I understand, those resistors should be external to the board.
    How can I design the board, in such way the termination resistors will be locate on the board, and in the future I will be possible to remove the resistors from the board and connect them to the main CANbus system?

    I am new on the designing, so please go easy on me 😅

    Edit:
    Something like that will work?
    Click image for larger version

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    If it will work, there isn't problem to connect the routes in 90 degrees?
    Last edited by Doron Raz; 08-28-2022, 06:53 AM.

  • #2
    "those resistors should be external to the board."
    Maybe I would reformulate a little bit: "The termination may be on the cable or in a node, but if nodes may be removed from the bus the termination must be carefully placed so that it is not removed from the bus". So if it can be removed you may need to use a plug with termination or something like that.

    I have not designed many CAN boards, but we usually place termination on the board and you can provide an option to connect it or disconnect it e.g. you can use jumpers.

    Comment


    • #3
      CANbus is also very resilient - 1, 2, or 3x 120ohms and it will work.
      If there are a known amount of devices on the bus (or known parts) you can place the terminators on the board without problems.
      Optionally use jumpers like robertferanec mentioned or DIP switches.

      By the way, a gentle tap with a screwdriver to a resistor makes it disappear . Unfortunately it is a one time action.

      Comment


      • #4

        Originally posted by robertferanec View Post
        "those resistors should be external to the board."
        Maybe I would reformulate a little bit: "The termination may be on the cable or in a node, but if nodes may be removed from the bus the termination must be carefully placed so that it is not removed from the bus". So if it can be removed you may need to use a plug with termination or something like that.

        I have not designed many CAN boards, but we usually place termination on the board and you can provide an option to connect it or disconnect it e.g. you can use jumpers.

        Thank you!
        I will place them on the board with jumpers.

        Originally posted by qdrives View Post
        CANbus is also very resilient - 1, 2, or 3x 120ohms and it will work.
        If there are a known amount of devices on the bus (or known parts) you can place the terminators on the board without problems.
        Optionally use jumpers like robertferanec mentioned or DIP switches.

        By the way, a gentle tap with a screwdriver to a resistor makes it disappear . Unfortunately it is a one time action.
        Why does it matter if I know the number of devices?
        I think jumpers will work better for me than DIP switch.
        Thank you.

        Comment


        • #5
          a) If you know the number of devices + layout / order, you can place fixed termination on those boards at the ends of the bus.
          If this data is unknown then either you:
          b) do not add termination and have it all external, or you
          c) have something like jumper, dipswitches, etc. to have the ability to control termination.

          Solution A is the cheapest with regards to total cost, including the external terminator.

          Comment

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