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Thread: Teensy 4.1 Ethernet Kit w/POE Module

  1. #1

    Teensy 4.1 Ethernet Kit w/POE Module

    Hi
    I'm wondering about the feasibility and hookup method for using a POE module such as this https://www.adafruit.com/product/3848 with the Teensy 4.1 and ethernet kit to power up the teensy.
    The module's pins are meant to be connected to ethernet pins 4,5,7 and 8 but I can see the PJRC ethernet kit's capacitor is tied between 2,5 and 8. Would it still be needed?
    I would actually prefer to use a panel mount ethercon connector anyway. Can someone please advise me on the best way to hook this up?
    TIA

  2. #2
    Senior Member PaulStoffregen's Avatar
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    It can not work with the Cetus J1B1211CCD Magjack we use on the Ethernet Kit.

    A different Magjack meant for PoE is needed. Most of them are incompatible with PoE because they include the 75 ohm common mode termination resistors without capacitors in series, and without access to those other pins to extract the power. Here is one which looks promising...

    https://www.digikey.com/product-deta...2/535-14168-ND

  3. #3
    Quote Originally Posted by PaulStoffregen View Post
    It can not work with the Cetus J1B1211CCD Magjack we use on the Ethernet Kit.

    A different Magjack meant for PoE is needed. Most of them are incompatible with PoE because they include the 75 ohm common mode termination resistors without capacitors in series, and without access to those other pins to extract the power. Here is one which looks promising...

    https://www.digikey.com/product-deta...2/535-14168-ND
    Hmm, Ok. Other than the pin access it's over my head. Can you recommend an ethercon-style of panel mount connector that would be appropriate? Or at least what specs to look for? And would it need other components in the way the J1B1211CCD does?
    If there is a better way to PoE the teensy 4.1 please let me know.

  4. #4
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    Or just use a separate PoE extractor - something like this https://www.amazon.co.uk/Ethernet-In.../dp/B0044LFO70
    (not that I know if that particular one is any good or not, the reviews are rather mixed, but its inexpensive)

  5. #5
    Quote Originally Posted by MarkT View Post
    Or just use a separate PoE extractor - something like this https://www.amazon.co.uk/Ethernet-In.../dp/B0044LFO70
    (not that I know if that particular one is any good or not, the reviews are rather mixed, but its inexpensive)
    Thanks MarkT, but that's not a panel-mount connector. I find it difficult to build sleek, enclosed devices out of already enclosed devices. I would rather use compact daughter-boards, MCU's etc and achieve a tidy result for the customer. I think I just need a PoE compatible panel connector(d-style or ethercon style) that complies with the teensy. The capacitor in the kit throws me off on what to look for.

  6. #6
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by bLackburst View Post
    If there is a better way to PoE the teensy 4.1 please let me know.
    This really depends on what you consider "better". The easiest way would be to use a PoE splitter that's designed to extract the power and pass the signal on to a regular non-PoE ethernet port, and give you the power safely converted. While these are bulky and add extra cables, they're cheap and readily available.

    But if "better" means all integrated onto a small PCB rather than another product with extra cabling, then I'm afraid quite a bit of design work is needed.


    Or at least what specs to look for?
    Generally a magjack that is designed for PoE.

    But even then, that can have many different forms. The main thing all PoE compatible magjacks have in common is access to either RJ45 pins 4+5 and 7+8 (the unused pins), or the center taps of pins 1+2 and 3+6 (the pins used for 10/100 speed), or both. The Cetus J1B1211CCD part we use now does not bring any of the RJ45 signals out.

    PoE magjacks also must not have a DC path through 75 ohm resistors. Some add 22nF capacitors in series with those 75 ohm resistors. Others omit the resistors completely, and it's up to you to add them if you want the better signal quality that common mode termination brings. Still others seem to have 2 or the 4 resistors.

    Once you get DC coupled access to 2 or all 4 twisted pairs, you also need diodes to couple the DC to the input of that switching power supply. Some PoE magjacks have diodes built in, others have a minimalist design where you need to provide the diodes.


    And would it need other components in the way the J1B1211CCD does?
    Yes. I've not seen any magjacks that have absolutely all the needed parts built in.

    The reality is this gets into designing your own PoE splitter, which means a pretty deep dive into lots of PoE circuitry details.

  7. #7
    That's great info Paul, thanks heaps.

  8. #8
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    I am not a hardware guy (and these days how much of a software guy I still am is open to question) but it occurred to me that the olimex POE board is open source, and might provide a good source of inspiration for someone who wanted to design a POE solution for the teensy 4.1. I would like see such a creature, for a project I am working on. The information is here:
    https://github.com/OLIMEX/ESP32-POE/...aster/HARDWARE

    Note that the boards are available on Digikey for $22.70 in single quantities, so the parts are probably not pricey. It is even claimed to have 3000V galvanic insulation.

  9. #9
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    I just wanted to update my reply because I made a mistake. The board I indicted does NOT have galvanic isolation. I misunderstood a press release. If you want the 3000V galvanic isolation, you must get the ESP32-POE-ISO board, which is a bit more expensive than the one I have. So I had to buy a USB isolator gadget .. which has yet to arrive.

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