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Hot!CAN BUS with RJ45?

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amctech
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2019/05/14 23:13:37 (permalink)
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CAN BUS with RJ45?

Does anybody has any experience with CAN BUS using not DB9 connectors, but RJ45 or similar?
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    GreenDragonSA
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    Re: CAN BUS with RJ45? 2019/05/15 00:20:57 (permalink)
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    What would you like to know?
     
    We used DB9, SIL and RJ11
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    amctech
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    Re: CAN BUS with RJ45? 2019/05/15 00:26:13 (permalink)
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    Thank you for answer GreenDragonSA, 
    Did you put there 120 Ohm resistors in RJ11? And if yes, where exactly: on a board or inside a cable?
    The second question: how many nodes were there (using RJ11)?
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    GreenDragonSA
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    Re: CAN BUS with RJ45? 2019/05/15 00:36:34 (permalink)
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    We placed the terminating resistor on the PCB with a toggle switch to terminate the two ends of the bus.
    (Not fun when they are debugging on site one person decides to terminate all the units :D)
     
    5 Units was the largest that I have seen that one of our client used. 
     
    Just make sure that the CAN lines are on the same twisted pair wire with a nice screen connection.
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    amctech
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    Re: CAN BUS with RJ45? 2019/05/15 00:39:52 (permalink)
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    Thank you GreenDragonSA, 
    You really helped us.
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    GreenDragonSA
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    Re: CAN BUS with RJ45? 2019/05/15 00:40:44 (permalink)
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    But if you got 2 ports you can also create a terminating plug (Old coaxial cable terminator) to go into the 1st and last units plug that is located in the connector. Smile: Smile
     
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    amctech
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    Re: CAN BUS with RJ45? 2019/05/15 00:45:18 (permalink)
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    We do have two plugs on each board. 
    Good idea.
    Thank you.
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    du00000001
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    Re: CAN BUS with RJ45? 2019/05/15 10:25:32 (permalink)
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    With CAN, the wiring doesn't matter much: any twisted-pair cable with 100..120 Ohms impedance will do, and the connector ... choose one. (Sub-D certainly has an impedance differing significantly from 120 Ohms.)
     
    In the automotive world, "some" 2 pins on "some" connector are used. At least they are usually adjacent.
     
    I've had up to 30 units connected with "mini-Centronics" connectors - this was working as well. So do not bother about the connectors - just keep eventual stubs shorter than 50 cm.
    Termination is easiest implemented on the PCBs. (I just wouldn't recommend to fiddle with resistors and RJ connectors.)

    PEBKAC / EBKAC / POBCAK / PICNIC (eventually see en.wikipedia.org)
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    NorthGuy
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    Re: CAN BUS with RJ45? 2019/05/15 16:28:56 (permalink)
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    Xantrex (now Shneider Electric) uses RJ45 for their solar products. They use 3 wires for ground and 3 wires for power (15V if I remember correctly). One twisted pair is used for signal. Each device has 2 RJ45 sockets, so you can connect everything into a chain. They have cute little terminators with resistors in them, which you plug at the end of the chain. Works Ok.
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    johannespfister
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    Re: CAN BUS with RJ45? 2021/02/23 08:33:56 (permalink)
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    Yes i know i am very late for an answer but i want to post it anyway since this thread is the second search result for "CAN RJ45" on Google (at least for me).
     
    We use CAN and RJ45 and it has many advantages over DSUB. I don't think there is a better cable for CAN. The 100Ω differential resistance of RJ45 is close enough to the 120Ω required by CAN, RJ45 is cheap and easy to handle.

    Some things to note when using RJ45 for CAN :
    • Check online what pinouts are used by other people and use that which you think most other people are using. It makes it a lot simpler when you combine 2 systems and the pinning is identical. Use Pin 1 for CAN-HIGH and Pin 2 for CAN-LOW and Pin 3 for CAN-GND. 
    • Use RJ45 double connectors (one part with 2 RJ45 sockets). The CAN-Bus can be daisy-chained and the stubs are extremely short (around 3mm). It does not need to be that short but why not?
    • The terminator can be 100Ω or 120Ω, it does not really matter. We used both without ever having problems, even when having 50 nodes connected. We place one on each node and a DIP-switch to enable it. In our case, the rest of the DIP-switch is used for the node address. This method is easier and cheaper than a plugable terminator.
    • In theory the Power should not be delivered in the same cable. However, we use the same RJ45 cable for CAN signal and Power (Pin 3 and 7 is GND, Pin 4,5 and 8 is +12V) to connect nodes which control 12V DC-Motors (brushed) and never had any problems with it.
     
    #10
    du00000001
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    Re: CAN BUS with RJ45? 2021/02/23 10:41:39 (permalink)
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    johannespfister
    <...snipped...>
    • The terminator can be 100Ω or 120Ω, it does not really matter. We used both without ever having problems, even when having 50 nodes connected. We place one on each node and a DIP-switch to enable it. In our case, the rest of the DIP-switch is used for the node address. This method is easier and cheaper than a plugable terminator.
    • In theory the Power should not be delivered in the same cable. However, we use the same RJ45 cable for CAN signal and Power (Pin 3 and 7 is GND, Pin 4,5 and 8 is +12V) to connect nodes which control 12V DC-Motors (brushed) and never had any problems with it.

     
    Just to add a bit more of information:
    • The termination resistor should match thre line impedance. Not sure which impedance the cables usually used for RJ-45 have, but match it. (If it's 110 Ω, 100 Ω and 120 Ω are expected to deliver similar results. Not ideal, but close enough.)
    • Ever heard of DeviceNet? This is a CAN implementation that transfers power over the same cable. (I have to admit that this power is meant to only power the transceiver section as DeviceNet defines isolated transceivers.) They even had their own cable designed.
      The difference of the DeviceNet cable to "some" RJ-45-capable cable: DeviceNet defines one shield for the data wire pair, another one for the power pair. (This cable has 2 twisted pairs with different wire cross sections.)
    So while the 100/120 Ω termination should not be an issue, transferring power over the same cable might work better or worse - depending on whether your cable has shielding "per pair" (and properly attached) or not. (And how much conducted emissions your device produces.) But it is not completely impossible.

    PEBKAC / EBKAC / POBCAK / PICNIC (eventually see en.wikipedia.org)
    #11
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