Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 9 of 9

Thread: 2 ethernet ports

  1. #1

    2 ethernet ports

    Hello,

    For my project I'd like to have 2 ethernet ports, one will be used as a plain ethernet connection and the other will be a "pass through" so I can daisy chain my devices.

    For now, I'm relying on a single ethernet port per teensy and some ethernet switches.

    Any idea if this is achievable? And how?

    Best regards,

    Xavier

  2. #2
    Senior Member+ Theremingenieur's Avatar
    Join Date
    Feb 2014
    Location
    Colmar, France
    Posts
    2,586
    Ethernet is not a bus topology, but a star topology. Thus, there is no pass through possible. Switches/Hubs/Concentrators are the way to go. If you wanted to daisy chain your devices, every single Teensy in the chain would have to act as a mini-switch to analyze incoming traffic and re-route most packets to the second port which would "eat up" or waste much CPU time and resources.

  3. #3
    Senior Member
    Join Date
    Apr 2013
    Posts
    1,936
    If using the SPI ethernet modules like the W5500 it would certainly be possible to use different chip selects and manually pass the data onwards but would be complicated and you would be needing to manually bridge the all the data you needed within the hardware limits of the boards you used. A better solution might be a three port hub or possibly a two port tap device with a single SPI connection that meant the network worked as a network rather than a chain of individual networks. Unsure if such devices actually exist.

    Another option is to look to some of the serial interfaces/buses that can reach ranges similar to ethernet, potentially over the same twisted pair cables. https://en.wikipedia.org/wiki/RS-485 or possibly CAN.

  4. #4
    Thanks for your feedback, you confirmed my feelings.

    I really need RJ45, other interfaces/buses are a no go.

    Do you know where to find the smallest switch that I could integrate on my design?

    Regards

  5. #5
    Senior Member
    Join Date
    Apr 2013
    Posts
    1,936
    For what it's worth you can run anything you like across and RJ 45 plug as long you do not exceed the voltage or current capabilities, but equally have said very bad things about engineers in the past who have used incompatible signal types coming out of RJ45 jacks so going for ethernet is certainly not a wrong choice. Looking for device advice this may be more something to look at Raspberry pi/embedded computing forumns as more commonly dealt with in that space.

    If you do make a chain of switches do watch time to live (TTL) if you find some nodes cannot reach other nodes https://en.wikipedia.org/wiki/Time_to_live

  6. #6
    Well thanks, but teensy is the right choice of hardware here.
    I already have dozens of v1 in production. I must use ethernet because of the protocol I use.
    But I already consume most of the teensy cpu so having it acting also like a switch is not possible.
    I'll look more for other solutions.

    Thanks

  7. #7
    Senior Member+ Theremingenieur's Avatar
    Join Date
    Feb 2014
    Location
    Colmar, France
    Posts
    2,586
    To work around the potential TTL problem, I'd not daisy chain the Teensys, bit connect them all to one single central switch.

  8. #8
    That's what I do for now with my v1 design.
    But in this configuration, I have a dozen of 30 meters ethernet cables, but if I could daisy chain the teensy it would drop the length of RJ45 cable needed.

  9. #9
    Senior Member
    Join Date
    Dec 2016
    Location
    Montreal, Canada
    Posts
    3,464
    and if one teensy fails? you have a chain reaction...
    you cant parallel line the lines...
    you could probably find pocket sized 2-way split adaptors that fit in palm of your hand to split a single cable, but they need to be powered and the cost of getting a few of them arnt worth it, especially when u can get cheap chinese hubs that do the same for a fraction of the cost

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •