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Thread: Ethernet PCB Devolopment Teensy 4.1

  1. #1
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    Ethernet PCB Devolopment Teensy 4.1

    Hi there,

    I designed a PCB-Board to transfer informations from a USB-Scanner via MQTT to a Server. At first glance, this is not a complex task.
    But: I gradually realized that Ethernet is not as trivial as I thought it was.
    As a basis for my PCB design I used the Ethernet module available on the PJRC site:
    https://www.pjrc.com/store/ethernet_kit.html
    Unfortunately, my design is not working and I just can't find the problem. Hopefully there are people here on the forum who are pro's in the subject and can help me! Regarding to my PCB-Design: I know that I should not have placed a ground area under the RJ45 jack. Furthermore I know that it is very suboptimal that the VCC line runs directly underneath the RJ45 jack.
    I have attached the PBC design, the schematic and the datasheet of the used RJ45 jack (Sorry, its in german).

    I am very happy about help! Thanks a lot in advance!

    Chris
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  2. #2
    Senior Member PaulStoffregen's Avatar
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    Which ethernet magjack did you solder to your PCB?

    Design looks correct for Cetus J1B12111CCD or Link-PP LPJ4012AHNL (the 2 possible parts used on the ethernet kit - PJRC has used both of these parts over the last 2 years - the PCB we ship today has both parts numbers printed).

    But your message has a datasheet for Weidmüller M100_T1D_32E4N, which has different pinout.

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  3. #3
    Senior Member PaulStoffregen's Avatar
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    Ethernet magjacks have many different pinouts. There is no official or de-facto standard.

    During Teensy 4.1 development, we used UDE RB1-125BAG1A, which has a completely different pinout from Cetus and Weidmüller.

    https://oshpark.com/shared_projects/5epewE3O

    But the UDE part was unavailable when Teensy 4.1 started shipping, so the PCB was redesigned for the Cetus part.

  4. #4
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    Oh wow...that's not fair! I've spent hours for finding the problem and you are solving the problem in minutes.
    Thanks a lot Paul! So my fault was the pin-mapping.
    One more questing: In our case T+ of the magjack has to be connected to T+ of the Teensy-Board? Because in UART its Tx to RX.

  5. #5
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    Hello again, I have another question:
    In your old version with UDE magjack you've implemented 4 capacitors. What are these for? And why did you reduce the capacitor number in the newer version?

  6. #6
    Senior Member PaulStoffregen's Avatar
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    The old PCB has 3 capacitors and 1 resistor. But it's really 2 pairs of parts in parallel.

    The ones joining the grounds were completely unnecessary.

    The other pair became just a single 0.1uF in the final version. But early on, it wasn't known (at least to me) whether a single capacitor would be good enough, or if a large cap and small higher frequency one would be needed.


    And FWIW, I did spend several minutes following the wires on your PCB and coming back again and again to the conclusion it really ought to work. Wasn't until I closed the windows with copies of the images and a copy of the ethernet kit's PCB that I saw the datasheet with a different part number.

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