CAN-FD cable



  • This week, I received the Duet3HC boards.
    The boards can be daisy chained to each other. As cables are not included in the box,
    I tried to get information on the required CAN_FD cables. I am planning to connect
    3 expansion boards to the duet 3.

    What are the requirements for the CAN-FD cables?
    Can a normal network cable be used?

    Thank you in advance.

    Harald Witmer



  • Use ADSL cables.
    Preferably high speed ones so they are shielded



  • @ahwitmer said in CAN-FD cable:

    Can a normal network cable be used?

    If by "normal network" you mean an ethernet cable, no. Those have RJ45 connections. The Duet CAN connectors are RJ11, which is common on voice telephone cabling.

    Preferred cables will be marketed with terms like "High Speed" or "ADSL" or both. This indicates a shielded cable. I used these: https://www.amazon.com/gp/product/B011SS7LYU/

    While you get those cables... It is not in spec... but... I have run expansions on plain/flat telephone wire



  • @Danal said in CAN-FD cable:

    Preferred cables will be marketed with terms like "High Speed" or "ADSL" or both. This indicates a shielded cable. I used these: https://www.amazon.com/gp/product/B011SS7LYU/

    Which is very visibly not at all a shielded cable. There is no point in it being - the connector has no shield, the system it is intended for use in has no shield... If a foil is presented inside there unterminated, it's at best useless, probably harmful..

    Cabling required should be nothing more than a common two pair cable and 6P4C connectors.



  • Agreed on shield. At the same time, these cables marketed as "high speed" are typically twisted pair. Which might be marginally better than 'flat' silver phone cable. Maybe.

    Having said all above... CAN is designed to be very tolerant of a poor physical layer, and I'd expect two pieces of barbed wire to run it over a 1/2 meter length like is in our printers. As long as the little skritchy points don't touch. 🙂



  • Twisted pair on longer runs will help with noise immunity since it's a "balanced" bus. Just remember that the cables need to be "straight through" and not crossover. Most flat telephone cables are crossover.



  • When I started testing prototype expansion boards, @dc42's recommendation was to use high speed ADSL2 cables. Kenable do a nice range from about 200mm up to many metres



  • @gtj0 said in CAN-FD cable:

    Most flat telephone cables are crossover.

    Burned a couple of hours last night helping someone on the Jubilee discord because of this.

    The symptoms can be VERY misleading... because, with two boards, and therefore two crossed over cables, the second board will work as long as it is chained, and that same board will fail when attached alone. Sheesh.


  • administrators

    @deckingman said in CAN-FD cable:

    When I started testing prototype expansion boards, @dc42's recommendation was to use high speed ADSL2 cables. Kenable do a nice range from about 200mm up to many metres

    Exactly so. A single twisted pair using the centre 2 pins is sufficient. Cables sold as "high speed ADSL" are good for this, they are normally two twisted pairs. One uses the centre 2 pins, the other uses the next 2 pins out.

    For UK users, Kenable sells them at prices starting from under £1.



  • @Danal said in CAN-FD cable:

    @gtj0 said in CAN-FD cable:

    Most flat telephone cables are crossover.

    Burned a couple of hours last night helping someone on the Jubilee discord because of this.

    The symptoms can be VERY misleading... because, with two boards, and therefore two crossed over cables, the second board will work as long as it is chained, and that same board will fail when attached alone. Sheesh.

    HAHAHAHAHA!
    Oh...sorry. 🙂



  • Thank you all for the explanations!


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